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' v/ 



The Branner Geological Library 



I 




I 




%<^ ^C- /Jt^*-**^^*^ 






THE NATURE OF 
ORE DEPOSITS 



BY 



DR. RICHARD BECK 

Professor of Geology and Economic Geologjr 
Freiberg Mining Academy 



Translated and Revised 
by 

WALTER HARVEY WEED, E.M. 

Geologist, United States Geological Survey; Fellow Geological Society of America; 

Member Institution of Mining Engineers (England) ; Member American 

Institute of Mining Engineers; Member Institute of Mining 

and Metallurgy; Member of the Washington 

Academy of Science, etc., etc. 



WITH 272 FIGURES AND A MAP 






FIRST EDITION 
IN TWO VOLUMES 

VOL. I 



NEW YORK AND LONDON 
THE ENGINEERING AND MINING JOURNAL 

1905 



Copyright, 1005. 
by 

TbM EnGIKKSBINO and MllONO JoUBNAfc 



2426:i2 



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TRANSLATOR'S PREFACE. 



In presenting an English edition of Professor Beckys *Lehre von den 
Erzlagerstatten/ for which he has generously given his consent, a few 
words of explanation are necessary. I was originally asked by the publishers 
to practically rewrite the book from an American standpoint, giving greater 
prominence to American ore deposits. This was abandoned because it in- 
volved serious abridgement of the descriptions of important foreign locali- 
ties, descriptions which make the work especially valuable to American en- 
gineers and geologists. I have, however, in most instances^ consulted the 
original authorities, and written many new descriptions of American ore de- 
posits, especially where, by reason of personal study or of recent detailed 
scientific investigation made since Professor Beckys book was issued, such 
a course seemed advisable. For such additions and changes I alone am re- 
sponsible. 

A slight abridgment of the historical matter will also be noted. In the 
rendering of technical terms the word ^formation* has been used only ex- 
ceptionally, as it is not in accordance with current American usage in treoir 
ing on ore deposits on account of its use in general geology. Flache, 
Stehende, etc., have been dropped in the translation. Lode and vein have 
been discriminated, as done by Emmons. The arrangement has not 
been altered, although it is recognized that it is not so convenient for refer- 
ence as it would be to group the descriptions under the name of the predom- 
inant metal. The table of contents and index will, however, fully answer 
the requirements of those who only seek special information about a particu- 
lar metal. 

I am under deep obligation to Mr. Robert Stein, of the Bureau of Statis- 
tics, for his help in the translation, and to Mr. S. F. Emmons for his criti- 
cism and revision of a number of descriptions. The prefaces are given in 
the original German, that the charm and spirit of Professor Beck's text 
may be retained. 

Walteb Harvey Weed. 
Washington, D. C, July 26, 1905. 



iii 



AUS DEM VORWORT ZUR ERSTEN AUFLAGE 



Ak die Vortrage iiber Lagerstattenlehre an der Eoniglichen Berg- 
akademie zu Freiberg mir iibertragen worden waren^ wurde ich gar bald 
inne, wie sehr Lehrer sowohl wie Sehiiler dieser Wissenschaft ein dem 
bentigen Stande derselben entsprechendes Lehrbuch in deutscher Sprache 
▼ermissen. Hieraus entsprang der Plan, selbst jene LUcke anszufiilleny 
nnd alle Studien nnd Reisen, alle Niederachriften, Ausziige nnd Er- 
kundigungen wnrden fortan mit diesem Ziele yor Augen ansgefohrt. Zug- 
leich bot die umfassende^ von A. W. Stelzner so griindlich dnrehgearbeitete 
Hnd naeh seinem Tode stark vermehrte und von neuem durchgesehene Liager- 
fyiattensammlung der Bergakademie eine vortreffliche Grundlage, auf der 
allmahlich das Werk auf gebaut werden konnte. 

Durch viele Beisen und Grubenbef ahrungen versuchte der Verfaaser Ton 
alien zu beschreibenden Lagerstattentypen eigene Ansehauung zu gewinnen. 
Ddnkbar war er A6h hierbei der steten Anregung und Forderung bewusst, 
die der Wobnsitz und die amtliehe Thatigkeit in der alien Bergstadt^ der 
ununterbroehene Verkehr mit befreundeten CoUegen aus den wissenschaf i- 
lichen Nachbargebieten und die vielen Beriihrungen mit erfahrenen Mannern 
der Praxis gewahren mussten. Auch die engen Verbindungen mit auslan- 
dischen Bergrevieren durch alte Freiberger Bergingenieure, die kommen 
und gehen und selten mit leeren Handen kommen, waren einer solchen 
Arbeit hochst forderlich. Ebenso dankbar wurde die Schulung im praktis- 
chen geologisehen Arbeiten empfunden, die der Verfasser als die Frucht 
einer zwolf jahrigen Dienstzeit an der Kgl. saehsischen geologisehen Lande- 
sanstalt imter dem von ihm hoch verehrten Herm Geheimen Bergrath Prof. 
Dr. H. Credner in das neue Amt mitbringen durfte. 

Seit B. V. Cotta's Lagerstattenlehre erschien, ist der zu bewalti- 
gende Stoff ganz riesenhaft angeschwollen. Man denke nur allein an 
die seither zugewachsene, damals nur erst in ihren Anfangen vorhandene, 
jetzt so iiberaus grossartige und werthvoUe amerikanische Litteratur auf 
diesem Qebiete. Eine TJnzahl von , Veroffentlichungen musste eingesehen 
und verarbeitet, ihr Inhalt mit den Belegstiicken der Sammlung verglichen 
werden. Wer den TJmfang der Lagerstattenlitteratur nur einigermassen 
kennt, wird es entschuldigen und erklarlich finden, wenn dies und jenes 
trotz alien guten Willens vergessen werden konnte. Fiir alle freundlichen 
Belehrungen, die kiinftige Verbesserungen ermoglichen, besonders auch fur 
Uebersendung von Publicationen werde ich stets dankbar sein. Eine Ltick- 

iv 



AU8 DEM VORWORT ZUR ER8TEN AUFLAOE. v 

enhaftigkeit wird man namentlich bei den statistischen Notizen finden, did 
in diesem Werbe den Zwedc haben, eine VarflteUtmg ton der Qrosse der 
Erzlagerstatten iind daneben auch von deren okonomischer Bedeutung zu 
erleichtem. 

Zu grossem Danke yerpflichtet bin ich Allen, die mich durch. Beant- 
wortung von Fragen, durch Sendungen von Litteratur und Belegstucken, 
durch UeberlasBung von Notizen und Skizzen in so uneigenniitziger Weise 
unterstiiizt haben, ganz besonders auch meinem Collegen, Herrn Professor 
Uhlichy der mir den Abschnitt iiber ^e markscheiderische Ausrichtung von 
Verwerfungen lieferte, Herm Bergingenieur H. Oehmichen, der mir bie der 
Ausarbeitung des Abschnittes liber die Siebenbiirgischen und Banater Lager- 
statten behiilflich war, und Herm Privatdocent Bauinspector Hoyer in Han- 
nover flir eine Ausarbeitung iiber die Eisenerze der (legend von Ilsede und 
Salzgittcr. Dem Herm Verleger endlich verdanke ich das opferwilligste 
Entgegenkommen bei der Ausstattung des Buches. 

So wunsche ich denn dieser Arbeit eine nachsichtige Beuriheilung und 
g^be sie hinaus mit einem hoffnungsreichen 

Gliickauf 1 

Freiberg, im Juxu 1900. 

DB. BICHABD BECK 



VORWORT ZUR ZWEITEN AUFLAGE. 



Dass es schon nach drei Jahren moglich und nothwendig war^ eine zweite 
Auflage dieses Werkes hinaus zu senden^ die zugleich mit einer f ranzosischen 
Uebersetzung (im Verlag von B^ranger, Paris) erscheint, hat den Verfasser 
mit Freude erf iillt. Er war sieh aber auch der grossen Verantwortlichkeit 
bewusst, die ihm hierbei auferlegt war, und ist emstlieh bestrebt gewesen, 
den Inhalt eines Buches, das vielfach als Lehrbuch dient, einer kritisehen 
Nachpriif ung zu unterwerfen. Auch bemiihte er sich moglichsv alle seit der 
ersten Auflage erschienenen wichtigeren Veroffentlichungen auf dem weiten 
Oebiete der Erzlagerstattenforsehung zu beriicksiehtigen. 

Die Anordnung des Stoffes musste mehrf ach in Folge besserer Erkennt- 
niss der genetisehen Vorgange abgeandert werden. Auch stilistisch wurde 
an vielen Stellen naehgefeilt. Mehrere Abbildungen wurden verbessert oder 
durch andere ersctzt. Eine grosse Zahl neuer Beispiele in zum Theil 
ausfiihrlicherer Schilderung kamen hinzu. 

Inzwisehen vermochte der Verfasser seine Reisen zu eigenen Studien fort- 
zusetzen und in dem Werke zu verwerthen. Er sah die wichtigsten Erzre- 
viere auf Elba und in Toskana und schloss die monographische Bearbeitung 
mehrerer sachsiseher Lagerstatten ab. Endlieh konnte er viele seither 
eingegangene, reiche und interessante Zusendungen von Belegstlicken aus 
auswartigen Grubendistricten, die er grossten Theils alten Freibergem ver- 
dankt, in der zweiten Auflage beriicksiehtigen. 

Die Litteratur ist seit 1900 wieder gewaltig angesehwollen. Mit grosser 
Freude gedenkt hierbei der Verfasser auch einer Anzahl von Veroffentli- 
chungen seiner ehemaligen Schiller. Die Publicationen, die ihm in dankens- 
werther Weise von Seiten der Fachgenossen zugingen, waren so zahlreich 
und vielfach so inhaltsreich, dass die Zeit kaum hinreichte, um dies weit- 
Bchichtige Material zu bewaltigen. 

Um den Umfang des Buches trotz der starken Erweiterung seines In- 
haltes nicht zu vergrossem, musste theilweise kleiner Druck in Anwendung 
kommen. 

Aufrichtigen Dank stattet der Verfasser alien denen ab, die ihn durch 
erganzende Mittheilimgen und durch Angabe einer Anzahl von Irrthiimem 
innerhalb der ersten Auflage zu unterstiitzen die Giite hatten. 

Freiberg, im Mai 1903. 

DR RICHARD BECK. 



VI 



TABLE OF CONTENTS 

Introduction. 

PAOB 

Definition of an Ore and of an Ore Deposit 1 

Most Imi>ortant Treatises on Ore Deposits 2 

Classification of Ore Deposits 4 

I. Primary Ore Deposits 4 

II. Secondary Deposits 4 

Table of the Most Important Ore Minerals 5 

Table of Units in which Metallic Contents of Ores are Most Commonly Expressed. 10 

Section I. 

Magmatic Segregations. 

(A) Segregations of Native Metals in Eruptive Rocks 12 

1. S^regation of Native Iron in Basalts 12 

2. S^regations of Nickel Iron in Olivine Rock and Serpentine of Awarua in 

New Zealand 14 

3. Segregations of Platinum in Olivine Rocks 14 

4. Gold as a Primary Constituent of Eruptive Rocks 15 

(B) Segregations of Metallic Oxides in Eruptive Rocks 16 

Table of the Imfmrtant Iron Ores 16 

1. Segrt^tions of Magnetic Iron Ore in Quartz-free Orthoclase Porphyries 

and Syenites 17 

(a) The Vysokaya Gora 17 

(6) The Goroblagadot Iron Deposit 18 

(c) Kiirunavaara and Luossavaara 20 

2. Segregations of Titaniferous Magnetite in Gabbro 21 

(o) The TabeiTK near Jonkoping 21 

(6) The Titslniferous Magnetites of the Adirondacks 22 

(c) Deposit of Routivare in Norbotten, Sweden. 24 

3. Segregations of Titaniferous Magnetite Iron Ore in Nepheline Syenites 25 

4. Segregations of Titanic Iron Ore in Gabbro Rocks 26 

The Titanic Iron Ore Deposits of Ekersundsoggendal 26 

5. Segregations of Chrome Iron Ore in Olivine Rock and Serpentines 27 

(a) The Chrome Deposits of Hestmando and Other Localities in Norway . . 29 

(6) The Chromite Ore Deposit of Kraubath in Upper Styria 30 

6. Tin-Stone as a Primary Segregation in Granitic Rocks 30 

The Etta Knob Tin Deposit of the Black Hills, Dakota 31 

(C) Segregations of Sulphiaic and Arsenical Ores 31 

1. Deposits of Nickel and Copper Ores in Connection with Gabbro Rocks or 

Diabases and their Metamorphic Derivatives 33 

(a) The Norwegian Nickel Ore Deposit* 33 

(6) The Nickel Ore Deposits of Varallo. Italy 39 

(c) The Nickel Ore Deposits of Sudbury, in Canada 39 

(d) Deposits of Nickeliferous Pyrrhotite at Schweidrich near Schluckenau, in 
Northeastern Bohemia, and at Sohland, in Saxony 42 

(e) Arsenious Nickel Ores in the Serpentine of Malaga, Spain 43 

2. Copper Deposits in the Serpentines of Italy 45 

The Monte Catini Copper Deposit 45 

3. The Copper Ores of Ookiep, in Little Namaqualand 48 

Section II. 

Bedded Ore Deposits, 

General Features of Bedded Deposits 49 

1 Flexures 55 

^. Displacements. (Thrust Faults.) 56 



• • 



Vll 



viu CONTENTS. 



PAOB 

Distribution of Ore within an Ore Bed 57 

Structure of Bedded Ore Deposits 57 

Mineral Ck>ntents of Stratified Deposits 58 

Classification of Sedimentary Ore Deposits 58 

I. Sedimentary Iron Ore Depoeiis 60 

(A) Sedimenta^ Iron Ores of the Crystalline Schists 60 

(a) Crystalline Schists with Disseminated Iron Ores 60 

Specular Hematite Schists 60 

Itabirite 60 

The Iron Ore Field of Naeverhaucen 61 

(b) Compact Iron Beds of the Crystalline Schists 61 

(a) The Carbonate Iron Ore Beds of the Crystalline Schists 61 

1. The Iron Ore Deposits of Huttenberg, in Carinthia 62 

2. Gyalar in Transylvania (Hungary) 65 

(fi) Beds of Magnetite and Hematite 65 

1. The Iron Ore Beds of the Archean Rocks of Sweden 65 

I. Norberg 67 

II. Persberg 68 

III. Duinemora 69 

IV. Grangesberg 71 

V. The Iron Ore Deposits in the Province of Norbotten, Gcllivare and 

Svappavara 74 

2. The Iron Ore Deposit* of the Arendal Rc^on in Norway 75 

3. The Iron Ore Deposits of Krivoi-Rog, in Southern Russia 75 

4. Iron Deposits of Spain (El Pedroso) and the Bukowina 76 

5. Archean (Laurentian) Magnetic Iron Deposits of North America .... 76 

6. Pre-Cambrian (Algonkian) Iron Ore Deposits of North America 77 

Marc^uette Iron Ore District in the State of Michigan 77 

7.^ African Iron Ore Deposits in Crystalline Schists 80 

M Origin of the Iron Ore Deposits of Crystalline Schists 81 

CB) Iron Ores as Original Intercalations in Normal Sediments 82 

(a) Silurian Iron Ores 82 

1. The Iron Ore Deposits in the Lower Silurian of Central Bohemia. ... 82 

2. The Lower Silurian Iron Ores of the Thiiringerwald and Vicinity 84 

3. The Clinton Hematite Ores 85 

(5) Ironstone Deposits of the Carboniferous Rocks 87 

1. The Iron Ores of the Ruhr Coal Basin 87 

I. A Spathic Iron Ore Measure 87 

II. Clay Ironstone Measures 88 

III. Spnerosiderites ' 88 

2. Carbonaceous Iron Ores of Upper Silesia and Saxony 88 

3. Carbonaceous Iron Ores of Great Britain 89 

(c) The Iron Ore Formations of the Northern Alps (probably Permian) 90 

The Erzberjg near Eisenerz 91 

(d) Permian Spnerosiderites 93 

(c) Sedimentanr Ironstones of Jurassic Age 93 

1. Liassic Iron Ores 93 

2. Iron Ores of the Dodger Formation of the Jiu^ 94 

Oolitic Iron Ores (Mmettes) of Luxemberg and Lorraine 94 

3. The Iron Ores of the Dogger Formation of Wurtembei^, Upper Silesia • 
and Switzeriand 97 

F) The Eocene Iron Oolites of Kessenberg and Sonthofen, Bavaria 98 

r) Bog Iron Ores and Lake Ores 98 

Character and Mode of Deposition of Bog and of Lacustrine Iron Ores. . . 99 

Chemical Analyses of Lacustrine and Bog Ores 99 

General Remarks on the Origin of Lake and Bog Ores 101 

(h) Recent Iron Ores of Marine Origin 103 

II, Sedimentanf Deposits of Manganese Ore 104 

(A) Within the Crystalline Schists 104 

1. Man^pnese Ore Deposits of Langban, Sweden 104 

2. The Manganese Deposits of Southern Bukowina, Austria 106 

3. The Maogaiiese-Zinc Deposits of New Jersey 107 



8 



CONTENTS. ix 

rxoB 

4. Manganese Ore Deposits in Minas Geraesi Brasil 108 

(fi) Manganese Ores in Normal Sediments 109 

(a) Man^nese Ore Deposits in the Carboniferous 109 

(b) Mesozoic Manganese Deposits of Chile. 110 

(c) The Eocene Oolitic Man^yuiese Ores of Transcaucasia 1 10 

id) Recently Formed Deposits of Manganese Ore Ill 

Section III. 

Epigenetie Deposits, 

I. Mineral Veins 112 

(A ) General Description of Mineral Veins 112 

(0) Definition of the Term 'Mineral Vein' 112 

(b) Dimensional Relations of Mineral Veins 115 

(c) The Termination of a Vein 119 

(d) Length and Vertical Extent of Veins 121 

(e) Structural Relations of Veins to Country Rock 125 

(/) Relations of Veins to Each Other 130 

(a) Structural Relations of True Veins to Each Other 132 

(fc) Displacements 138 

(«) Displacement Produced by Vertical Movement 139 

I. General Properties of Simple Faults 139 

II. Filling of Fault Fissures 140 

III. Fault Veins 145 

IV. Condition of Fault Walls 147 

V. Torsional or Turning Movement during Displacement 151 

VI. The Surface Evidence of Displacements 152 

VII. Different Kinds of Simple Displacement 153 

VIII. Special Types of Displacements 156 

IX. Simple Displacements 157 

X. On the Location of Faulted Parts of Veins 157 

XI. EHsplaoements Due to Horizontal Movement 161 

ft) Fissure Formation 161 

(tt) Entokinetic Fissures 163 

I. Contraction Fissures 163 

1. Cooling Fissures 163 

II. Desiccation Fissures 166 

2. Dilation Fissures 168 

(jS) Exokinetic Fissures 168 

I. Fissures of Collapse and of Expansion 168 

II. Fissures Due to Folding 168 

III. Compression Fissures 170 

[k) Time Required for Fissure Formation 173 

[1) The FiUing of Vein Fissures 174 

(m) Structure of the Vein Filling 176 

1. Massive Filling 177 

2. Banded or Crusted Filling 177 

(n) Paragenetic Occurrence of Vein-forming Minerals 189 

, (o) Vein Formations and Vein IVpes 191 

Summary — ^The Different Classes of Mineral Veins and their Varieties 193 

(a) Veins Consisting Mainly of Oxidic Ores 193 

I. Veins of Iron and Manganese Ores 193 

II. Tin Veins 193 

^ (6) Deposits Characterized by Metallic Sulphides 193 

III. Copper-bearing Veins 193 

IV. Silver-Uad Veins 194 

V. Veins Carrying Rich Silver Ores 194 

VI. Gold Veins 194 

- * VII Veins of Antimonial Ores 194 

- : VIII. Veins of the Cobalt, Nickel and Bismuth Ores 195 

iX. Lodes of Mercurial Ores , , , 195 



i: 



9 



g 



CONTENTS. 

PAGE 

(B) DeBcriptions of Vems of Each T^ 195 

(a) Veins Consisting Mainl^r of Oxidic Ores 195 

(a) Iron and Manganese Veins 195 

1. Veins of Spathic Iron Ore 195 

2. Veins of Red Hematite 197 

3. Veins of Manganese Ores 198 

05) Veins of the Tin Ore Class 200 

4. Tin Veins. . . ; 200 

I. General Remarks 200 

II. The Tin Deposits of Altenbei^, Zinnwald and Graupen 202 

III. ITie Deposits of Geyer and Ehrenfriedersdorf 208 

IV. The Tin Deposits of Cornwall 211 

V. Tin Districts Outside of Europe 213 

VI. Veins Showing Transitions between Normal Tin Deposits and 
OtherClasses 217 

VII. Tungsten Deposits 218 

) Deposits Formed B^ssentially of Sulphide Ores 219 

7) Copper Veins 219 

6. Veins of Copper Ores Carrying Tourmaline, including also Veins 
Characteristic of the Tin Ore Types. (Tourmaline-bearing Copper 

Formations.) 219 

6. Cupriferous Quartz Veins 220 

Australian Deposits 222 

African Veins 222 

Japan 223 

Butte, Montana 223 

7. Spathic Copper Veins (Gangue of Various Carbonates with Quartz, 

Barite, and sometimes Fluorspar) 226 

8. Zeolitic Copper Veins with Native Copper 230 

Disseminatea Grains with Amygdules m the Mclaphyre Lava Sheets. 232 

In the Conglomerates 232 

Filling of True Fissures 232 

(0) Silver-Lead Veins 235 

9. The Pyritic Lead Deposits 235 

10. Vems of Spathic Lead Ore 243 

The Clausthal Veins 247 

11. Barytic Lead Veins.' 258 

(e) High-mde or Noble (Edle) Silver Veins 261 

12. High-grade Silver Quartz Veins 262 

13. Rich Silver-Calcite Veins (Rich Calcspar Formation) 272 

14. Rich Silver-Copper Veins 279 

15. Veins of Rich Silver-Cobalt Ores 282 

(fi Gold Veins 292 

Gold Quartz Veins (the Gold Quartz Formation) 292 

Silver-Gold Veins 293 

Fluoritic Gold Quartz Veins 293 

16. Gold Quartz Veins 293 

I. Pyritic Gold Quartz Veins 297 

II. Cupriferous Gold Quartz Veins 304 

III. Antimonial Gold Quartz Veins 307 

IV. The Arsenical Gold Quartz Veins 308 

V. The Cobaltiferous Gold Quartz Veins 310 

17. The Silver-Gold Veins 311 

18. The Fluoritic Gold-Tellurium Veins 332 

(if) Antimony Veins 335 

19. Antimony Quartz Veins 335 

(Sf) Cobalt-Nickel and Bismuth Veins 339 

20. Cobalt-Nicked Veins with Carbonate gangue 340 

21. Quartz-Cobfdt Veins (Quartz-Cobalt-Btsmuth Deposits) 342 

22. Veins of Hydrosilicate Nickel Ores 347 

Quicksilver Veins 350 

(C) General Description of Mineral Veins 361 



CONTENTS. xi 

PAOB 

Differences in Vein Contents at Different Depths 861 

Changes in Character of Primary Vein Filling with Depth 861 

Secondary Alteration of the Minerals in Veins 868 

Superficial Alteration of Ore Deposits (Gossan Formation) 868 

I. New Substances Developed in the Zone of Oxidation 867 

II. New Substances Developed by the Chlorine, Bromine and Iodine 
Comi>ounds of the Seepage Water 878 

III. New Compoimds FormM by Combination with Phosphoric Acid. . 876 

IV. New Minerals Formed by the Liberation of Silicic Acid 876 

V. Removal of Dissolved Substances 877 

The Zone of Enrichment b^ Rich Secondaiy Sulphides 878 

Formation of Chalcopynte and Bomite 881 

The Distribution of Ore within the Veins 882 

Influence of the Coimtry Rock on the Richness of Lodes 884 

Influence of Vein Intersections on Ore Content 891 

Influence of Conversinj; or Diverging Stringers on the Ore Content of Veins. . 891 
Influence of the Folding of a Stratified Country Rock on the Richness of 

Veins 892 

Cause of the Influence of Country Rock on the Distribution of Ore 892 

The Action of Vein-Forming Solutions ufmn the Wall Rock 895 

Scricitization 897 

Kaolinization 400 

Propylitization 401 

Silicification 402 

Alteration of Limestone into Ore-bearing Pyroxene-Epidote Rocks 402 

Alteration of the Country Rock into Greisen or Zwitter 408 

Tourmalinization and Topazization 404 

Metasomatic Replacement of Countrv Rock by Ore 405 

Alteration of the Hangine-Wall Rodt 406 

Geolo^c Age of Mineral Veins 407 

Association of Certain lypes of Veins with Particular Eruptive Rocks. . 410 

A Review of the Various Theories of the Origin of Mineral Veins 411 

(a) Congeneration Theory 411 

lb) Descension Theory. 411 

(c) Lateral Secretion Theory 413 

(d) The Ascension Theories 420 

1. The Igneous Injection Theory 421 

2. The Sublimation Theory 421 

8. The Hydrothermal Theory 424 

II. Epigenetic Ore Deposits in Stratified Rocks (Exclusive of Veins) 432 

(A) Epigenetic Ore Deposits 433 

(a) In the Cr^talline Whists 433 

(a) Epigenetic Deposits of Oxides and Sulphides 433 

1 . The Ore Deposits of Schwarzenbeii, Saxony 433 

2. The Orebodies in the Crystalline Schists of the Riesengebirge 438 

3. The Ore Deposits of Pitkaranta in Finland 440 

4. Kallmora Silver Mine at Norberg, in Sweden 442 

5. The Deposit of Schneeberg, near Sterzing 443 

6. The Copper-bearing Sjanf^eli Schists 445 

09) Epigenetic Deposits of Sulphidic Ores 445 

I. Zinz-Blende Deposits 445 

1 . The Zinc- Blende Deposits of Ammeberg, in Sweden 44 

2. The Zinc-Blende Deposit of Langfallsgrufva, near Rafvala, Sweden . • . 448 
U. The Pyrrhotite and Pyrite Deposits of the Silberberg, at Bodenmais. . . 450 

III. Silver-Lead Deposits 452 

The Ore Deposits of Broken Hill, New South Wales 452 

IV. Copper Deposits and Iron Pyrite Deposits 457 

1. Copper Deposits of Schmollnitz, Upper Hungary 457 

2. Bedded Copper Deposits of Graslitz, in Bohemia 457 

3. The Pyrite Deposits of Chessy and Sain-Bel (Rhone) 458 

4. The Copper Deposit of Falun, Sweden 459 

5. The Pynte Beds of Norway 462 



xii CONTENTS. 

rAoa 

6. The ]^te Beds of Ducktown, in TenneaBee 465 

V. Ck)balt Fahlbanda 466 

1. The Cobalt Fahlbands of Skuterud and Snanim, in Norway 466 

2. The Cobalt Deposits of Dashkessen, in the Caucasus 469 

VI. Bedded Gold Deposits in the Cmtailine Schists 471 

1. The Gold Deposits of the Appalachian States 471 

2. The Homestidce, South Dakota, Gold Deposits 472 

3. Other Examples of this IVpe 474 

4. The Gold Deposits of Zell, m the Ziller Valley, Austria 475 

5. Gold-bearing Quartz-Dionte Gneiss of Mashonaland 476 

6. The Auriferous Gneisses of Madagascar 477 

(b) Epigenetic Ore Deposits Formed Essentially by Impregnation within Non- 

Crystalline Strata 477 

(o) I^te Deposits 477 

1. The Rammelsberg Pyrite Deposit near Goslar 477 

2. The pyrite and Barite Deposit of Megffen, on the River Lenne 480 

3. FVrite Beds in the Paleozoic Rocks of the Austrian Alps 482 

4. line IVrite Deposits of Huelva, in Southern Spain and Portugal 483 

6. The Mount Lyell Gold-Silver Copper Deposit 486 

6. The Copper Deposits of Iron Mountain, California 486 

7. Mesozoic and Cenozoic IVrite Beds 488 

08) Permian and Younger Beaded Deposits of Copper 488 

1. The Copper Shale of the Zeehstem Fonnation 488 

The Orijrin of the Copper Shale and Similar Formations 495 

2. Copper Ores of the Permian Red Beds (Rothliegende) of Northeastern 

Bohemia 497 

3. The Copper Deposits in the Permian Formation of Russia 497 

4. Copper Ores in the Permian of Texas and Nova Scotia 498 

5. The Copper Deposits of Corocoro, in Bolivia 499 

6. Copper Ores in the Bunter (Triassic) Sandstone Formation of Saint 
Avoid and Wallerfangen 500 

7. Copper-bearing Triassic Sandstones in New Mexico 502 

8. Copper-bearing Sandstones of the Copper Basin, Arizona 502 

9 Copper Ores in the Cretaceous of Angola 503 

10. Tne Bedded Copper Deposits of Boleo, Lower California, Mexico 503 

(c) Lead Deposits 504 

1. Tlie Nodular Ores of Commem, in the Rhine Province 504 

2. Lead Ores of the Triassic Sandstone at Freyhung, in the Oberpfalx of 

Bavaria 508 

(d) Silver Deposits 509 

The Silver Sandstones of Utah 509 

(e) Stratified Gold Deposits of Paleozoic Formations 509 

1. The Gold-bearing Conglomerates of the Witwatersrand, South Africa . . . 509 

Genesis of the Gold-bearing Conglomerates of the Witwatersrand 516 

Hypotheses and Theories 517, 518 

2. The (Conglomerates of the Taricwa Goldfield in West Africa 519 

(J) Antimony Deposits 519 

1. Antimony Deposits of Westphalia, Prussia 519 

2. The Antimony Deposit of Bruck 520 

3. The Bedded Antimony Deposits of Sidi-R^heiss, in Algeria 521 

Conclusions upon Epigenetic Ore Deposits 521 

(B) Epig«ietic Ore Stocks 527 

(a) Epigenetic Stocks of Iron and Manganese Ores. 527 

1. The Iron Ores of the District of Sbingerode, in the Harz 527 

2. The Iron Ore Deposits oi the Iberg, near Grund, in the Harz 529 

8. The Iron Deposits in the Devonian Rocks of the Southern Ural, Russia. . 530 

4. The Red Hematite Ore Deposits in the Limestones of England 531 

5. The Iron Ore Deposits in the Zechstein Dolomite of the Region of Schmal- 

kalden 532 

6. The Iron Ore Deposits of Amberg 532 

7. The Iron Ore Deposits in the Lower Cretaceous at Bilbao 533 

8. The Man«inese Deposits of Nassau, the Wetzlar Diirtrict, in Hesse and 

on theUunsruck 535 



i 



CONTENTS. jSa 

PAOB 

9. The Manganese Depoaitei of Las Cabesse^, in the Fmioh Fjrranees 537 

(&) Epigenetic Tin Ore Stocks 538 

1. Tinstone in a Lower Liassic Limestone of the Oampi|^, Italy 538 

2. Tungsten Ores in Crystalline Limestone in Connecticut 538 

3. Tungsten Ores in a Cambrian Dolomite 530 

(c) Epigenetic Ore Stocks of Copper Ore 539 

T^e Copper Deposits of Bisbee, Arizona. 539 

(d) Epigenetic Stocics of Silver, Lead and Zinc Ore 540 

1. The Ore Deposits of Laurium, Greece i 641 

2. The Silver-Lead Ore Deposits of Eureka, in Nevada. 544 

3. The Lead and Zinc Ore Deposits of Monteponi 545 

4. The Zinc and Lead Deposits of the Mississippi Valley 546 

5. The Zinc Deposits of Iserlohn, Prussia 550 

6. The Ore Deposits near Aachen (Aix la Chapelle), PnisBia 551 

7. The Oxidized Zinc Deposits of Picos de Europa, Spain 555 

8. Lead Deposits in the Carboniferous Limestone, England 555 

9. The Silver-Lead Deposits of Leadville, Colorado 557 

10. The Silver-Lead Ore Deposits of Aspen District, Colorado 559 

11. Ore Deposits in Triassic (Muschelkaik) Limestones of Upper Silesia. . . 559 

12. The Zinc Deposits of Wiesloch, near Heidelbeiv, Baden 564 

13. The Lead and Zinc Deposits of Raibl, in Carintma, Austria 565 

14. The Lead Deposits of Bleiberg, in Carinthia. 569 

15. The Silver- and Gold-bearing Lead Deposits of Mapimi, Durango, 

IVlexico 572 

16. The Silver-Lead Mines of Santa Eulalia, Chihuahua, Mexico 573 

17. The Sierra Mojada Silver Mines, Mexico 7 574 

(e) Epigenetic Stocks of Gold Ore 575 

1 . Silver-Gold Ores in Calcareous Strata of the Cambrian of the Black Hills, 

South Dakota 575 

2. The Gold Deposits in Dolomite at Pilgrim's Rest in the Transvaal, Africa .. 576 

3. Gold Ores ot Bannock, Montana 578 

(/) Epigenetic Stocks of Antimony Ores 578 

The Antimony Deposits of Kostainik, in Servia 578 

Antimony Deposits in Italy 581 

Antimony Deposits of the United States 581 

(O Contact-Metamorphic Ore Deposits '. 582 

1. The Ore Deposits in the Contact Area of the Granite of Berggiesshubel, 

in Saxonjr 583 

2. The Magnetic Iron Ore Deposits of Schmiedeberg in the Riesengebiii^, 

Germany 586 

3. The Iron Ore Deposits of the Schwarzen and Gelben Krux, Germany. . . . 587 

4. The Contact Ore-Deposits of the Banat, Hungry 587 

5. The Contact Deposits of the Christiania Region 594 

6- The Ore Deposits of Traversella and Brosso, Italy 595 

7. The Iron Ore Deposits of the Island of Elba 596 

8. The Iron Ore Deposits of the Gora Magnitnaia. . . 598 

9. The Copper Deposits of MiednorudiansJc, near Nizhnyi Tagilsk 599 

10. The Copper Ore Deposits of Gumeshevalc 600 

11. The Copper and Lead Ore Deposits in the Campiglia Marittima, Italy . . . 601 

12. The Silver-Lead Deposits of Sala, in Sweden 603 

13. Gold-bearinff Contact Metamorphic Deposits in Montana 605 

14. Examples of Contact Deposits Outside of Europe 606 

(D) Ore-filled Cavities in Rocks 607 

1. Nodular Iron Ore 607 

Detrital Deposits. 

A) Older Detrital Deposits 611 

Detrital Deposits of Iron Ore 611 

Detrital Deposits of Limonite in the Cretaceous Formation 611 

(a) In the Lower Cretaceous 61 1 

The Iron Ore of Salzgitter and of Domten, North of Goslar 611 



xiv CONTENTS. 

PAOI 

(b) In the Upper Cretaceous 612 

1. The Iron Ores of Ilsede 612 

2. Tertiary Alluvial Deposits of Magnetite and Red Hematite of the Banat, 

Hungary 614 

n. Ancient Deposits of Crold-bearing Gravels 614 

1. The Gold-bearing Cambrian Conglomerates of the Black Hills in Dakota . 614 

2. Gold-b€»rin^ Detrital Deposits of the Carboniferous Fonnations 615 

3. Gold Deposits of the Mesozoic Formations 616 

III. Old Gravel Deposits with Copper and Lead Ores 616 

The Copper and Lead Deposits of Cap Garonne, near Toulon 616 

(B) Recent DepoeUs of Placer Gravel {Seifen) 617 

General Characters 617 

Different Kinds of Gravel 623 

(a) Magnetic Iron Ore Gravels 623 

lb) Lateritic Decomposition Products Rich in Iron Ore 625 

(c) Tinstone Gravels 625 

1. The Tinstone Gravels of the Erzgebirge and the Neighboring Mountains. 625 

2. The Tinstone Gravels of Cornwall 627 

3. The Tin-bearing Gravels of Australia 629 

4. The Residual /m Deposit of Mount Bbchoff 630 

5. The Tin-bearing Gravels of Banka and Billiton. Malay Archipelago . . 632 

6. The Tin-bearing Gravels of the Malay Peninsula and of Other Parts 

of Asia 633 

7. Tin-bearing .Gravels of Mexico , 634 

8. Tin-bearing Gravels of South Africa 635 

(d) The Gold Gravels 635 

1. The Gold Gravels of the North American Continent 635 

2. The Gold-bearing Gravels of Califomia 635 

(a) Alluvial and Pleistocene Auriferous Gravels 636 

(6) The Late Tertiary Auriferous Gravels (Bench Gravels) 636 

(c) The Tertiary Gold Gravels 637 

3. The Gold Placers of the Yukon and Other Districts in Alaska 638 

4. The Gold Gravels of the Cape Nome District 640 

5. Gold Gravel Areas in South America 641 

6. The Gold Placers in the Ural 644 

7. The Gold Placers of Siberia 645 

8. Gold Placers in India 647 

9. Gold Placers of Australia 647 

10. African Gold Placers 650 

11. Gold Placers of Europe 650 

12. Theories to Explain tne Distribution of Gold in Placers and the Forma- 

tion of Large Nuggets 651 

^ (c) Platinum Placers 656 

1. Platinum Placers in the Ural 656 

2. Occurrences of Platiniferous Gravels Elsewhere 658 

(/) The Copper Placers of the Philippines and in Argentina 660 

General Advice to the Prospector. 

Association of Ore Deposits with Certain Rocks 661 

Special Indications of Ore Deposits 663 

^ llie Taking of Samples for Scientific Purposes 668 

Index 671 









.% • 



• •• • 

• • • < 



INTRODUCTION. •••• / 



• • 



DEFINITION OP AN ORE AND OP AN ORB DEPOSlt/.>*/'. 



• •• 
• • •• 



In a mineralogical sense an ore is a metalliferous mineral or a mix1tujpt*» • 

* * * • 
of such minerals. Praeticallv, however, this definition of an ore must bfe 2** 

qualified by the statement that only those minerals and mixtures of minerals 
are ores jrom which metals or metallic compounds tnay be produced on a 
commercial scale and at a profit. 

Two examples of equal mineralogie or petrographic value may differ 
materially: a basalt carrying enough magnetite to influence the mag- 
netic needle, but yet containing less than 10 per cent of iron, is far 
from being an iron ore. On the contrary, a vein with a silver content of 
only 0.5 per cent is an ore deposit, since with this content it is commer- 
cially valuable. In the case of a gold deposit the amount sufficient to dis- 
tinguish a gold ore from barren rock may be even less, for in California 
and Dakota gold ores with only from 4 to G grains per ton^ of gold are 
exploited. Hence it is the economic point of view that must always be 
borne in mind, the profit of working being subject to variation in the 
course of time. Wliile nickel and cobalt were formerlv nicknames for 

ftr 

materials which were thrown upon mine dumps as useless, and were con- 
sidered as a mere nuisance in silver mining, today the compounds of these 
metals and the associated minerals are in great demand as ores. 

To a certain degree a mineralized material may be an ore in one locality 
and yet not be an ore in another place, the cost of reduction depending on 
the proximity to linos of traffic and cheap freights. 

The science of ore deposits is, in other words, the study and considera- 
tion of the deposition, distribution and origin of rock bodies containing 
ores in such quantities that they may be extracted profitably by mining op- 
erations. 

The science of ore deposits is a branch of geology which can only be under- 
stood and practiced by those who have some knowledge of that science, par- 
ticularly of petrography, and of course, also, a knowledge of mineralogy and 
chemist rv. 

*The ton as used in this work is the metric ton of 2,205 !b. 



>•• 



2 THE NATUBSr'jOi'B-'ORB DEPOSITS. 



• •. 



The Most Important T&sk^isES on Ore Deposits^ and the List of 

Journals in W^j^'b O^e Deposits Are Described or Discussed. 

• • *•• 

Bemhard vonjCbtl^* *Die Lehre von den Erzli^erstatten. ' Two parts: First 




1879. .•(Trrfqsiated into French by M. Kuss.) Out of print and in inany respects 

*Ji. FVichs and L. De Launay. 'Traits des Gftes Mindraux et M^tallif^res. ' Vol- 
/i^^to*r and II. Paris, 1893. Large encyclopedic handbook. 
*• *\\L, De Launay. 'Formation des Gttes Mdtallif ^res. ' Paris, 1893. Encycloptedia 
*• Stientifique des Aide M^moires. Small manual. 
* J. A. Phillips and H. Louis. 'A Treatise on Ore Deposits.' Second edition. 
London, 1896. 

J. F. Kemp. 'The Ore Deposits of the United States and Canada.' Third edition. 
New York and London, 1900. 

Branner, J. C. 'Syllabus of Economic Geology.' Stanford University, California. 

B. Lotti. ' I Depositi de i Minerali Metalli.' Milan, 1903. 

Posepnv, Van Hise, E3mmons,Weed, Le Conte, Lindgren. * Genesis of Ore Deposits.' 
Am. Inst. Min. Eng. New York, 1900. 

Rickard, Weed and others. 'Ore Deposits — a Discussion,' New York, 1903. 

The Engineering and Mining Journal^ New York City. 

Zeitechrift fur Praktische Geologie. Eklited by M. Krahman. Berlin. 

ZeiUchrift fur das Berg-, Hiitten- und Salinen -Wesen im Preussichen Staate. 
Published by the Minister for Commerce and Industry, Berlin. 

Oesterreichieche Zeitsrhrift fiir Berg- und Huttenwesen. Vienna. 

Jahrbuch der k. k. dsterreichischen Bergakademien. Vienna. 

Jahrbuch fur das Bei]E;- und Huttenwesen im KOnigreiche Sachsen, Freiberg. 

Bera- und Huttenmdnnische Zeitung, Published by G. Kfthler (Clausthal) and 
F. Kolbeck (Freiberg). Leipzig. 

Mining Journal. Ix>ndon. 

Transactions of the Institution of Mining Engineers. Newcastle, England. 

Transactions of the American Institute of Mining Engineers. New York. 

Annates des Mines, Paris. 

Geologiska FOreningens i Stockholm F6rhandlingar. Stockholm. 

Bergj'oumal. St. Petersburg. (In Russian.) 

Revista minera periodico cientifico ^ industrial. Madrid. 

Among general textbooks* of geology which devote special attention to ore deposits 
we may mention: H. Credner, 'Elemente der Geologie,' ninth edition, Leipzig, 
1903; M. Neumayr, 'Erdgeschichte,' second edition, Leipzig, 1900. 

Many essays on ore deposits are also scattered througn periodicals dealing with 

5eneral geologv, especially Zeitschrift der Deutschen geologiscnen Gescllschaft, Berlin ; 
oumal of Geology, Chicago University, Chicago, Illinois; .4 mmran Journal of Science, 
New Haven, Connecticut; American Geologist, Minneapolis, Minnesota; N cues Jahr- 
buch fur Mineralogie, Geologie and Palieontologie, Stuttgart; and Tschermak's Miner- 
alog u. Petrograpliische, Mittheilungun, Vienna. 

The statistical data on the different mining districts of the world are best summar- 
ized in the following works, which appear every year: ' The Mineral Industr\',' pub- 
lished by The Enmneering and Mining Journal', New York and London; 'Mineral 
Resources,' published by the U. S. Geological Survey, Washington, D. C. 

Classification of Ore Deposits. 

A historical sketch of the different attempts at a classification of ore 
deposits has been given by J. F. Kemp^ to which little need be added. 

* J. F. Kemp. 'The Classification of Ore Deposits.' A review and a proposed 
scheme based on origin. Contributions from the geological department of Columbia 
College, No. 5. New York. 



INTRODUCTION. , 8 

The practical miner even nowadays names and clasgifies his deposits 
according to their form and appearance, and this was the method used by 
the first scientific writers. Waldauf von Waldtenstein^ (1824), and B. 
von Cotta* (1869), subsequently Lottner-Serlo* (1869). 

G. Kohler* (1884) and lately H. Hofer» (1897) based their groupings 
solely on fonn. J. D. Whitney* (1864), J. Grimm^ (1869), J. S. New- 
berry (1880), and J. A. Phillips' (1884), laid stress on the mode of origin. 
A. von Groddeck* (1879) on the other hdud, introduced a mainly genetic 
system, and advocated this principle again in his essay of 1886^®. 

Genetic principles were followed by H. S. Munroe, J. F. Kemp^*, P. 
Posepny", G. Giirich" and W. H. Weed". 

A. W. Stelzner's system, used in his lectures, briefly stated in the pro- 
gram of the Freiberg Mining Academy and employed by him in arranging 
the collection of ore deposits in that institution, is also purely genetic. 
Finally, J. H. L. Vogt, among the more recent writers, furnished many 
important data for a scientific classification in this field, especially in his 
essay of 1894*". The classification of W. H. Weed follows a logical sequence 
from magmatic segregations to placer gravels, and utilizes the results of 
modem petrologic research and chemistry to a greater extent than preceding 
schemes. It entirely abandons form as a factor of importance and is thus 
purely genetic Following Stelzner^s system in many ways we have in the 
present work used the following classification : 

* J. Waldauf von Waldenstein : 'Die besonderen Lagerstatten der niitzbaren 
Mineralien.' Volumes I and II. Vienna, 1824. 

'B. vonCotta: 'Lehrevonden Erzlagerstatten. ' Volumes I and II. Freiberg, 
1859. 

' E. H. Lottner and A. Serlo : 'Leitfaden xur Bergbaukunde.' Volumes II and 
III. Berlin, 1869-1872. 

*G. K6hler: 'Lehrbuch der Bergbaukunde.' Leipzig, 1884. 

•H. HMer: ZeiL f. Prak. Geol., 1897. 

•J. D. Whitney: 'The Metallic Wealth of the United States.' Philadel- 
phia, 1854. 

'J. Grimm: 'Die Lagerstatten der nutzbaren Mineralien.' Prague, 1869. 

■ J. A. Phillips: 'A Treatise on Ore Deposits.' First edition. London, 1884. 

• A. von Groddeck : * Die Lehre von den Lagerstatten der Erze. * Leipzig, 1869. 

*® 'Bemerkungen zur Classification der Erzlagerstatten. ' B. u. H. Z., 1885,p.217. 

" J. F. Kemp: *The Ore Deposits of the United States.' New York, 1893. 

"F. Posepny: 'Die Genesis der Erzlagerstatten. ' Jahrb. d. k.k. osterr. Berga- 
kademien. Vienna, 1895. 

" G. Gurich: 'Ueber die Eintheilung der Erzlagerstatten. ' Schlessche Ges.f. 
vaterl. Kultur. Breslau, 1899. 

** * Classification of Ore Deposits — a IVoposal and a Discussion.* The Engineering 
and Mining Journal, P'eb., 1903. Also * Ore Deposits— a Discussion.' 

"J. H. L. Vogt: 'Beitrage zur genetischen Classification.' 1894, p. 381. 



4 THE NATURE OF ORE DEPOSITS. 

CLASSIFICATION OP ORB DEPOSITS. 

(compare with tablb or oontentb or this work.) 

I. Primary Ore Deposits. 

A. Syngexetic; formed simultaneously with the country rock. 

1. Magmatic segregations; for example, magnetic iron ores in orthoclase 
porphyries. 

2. Sedimentary ores; in part approximately in the same condition as at 
the time of their deposition, for example, bog iron ores; in part altered 
by metamorphic processes, as, for example, the magnetic iron ores of the 
cr}^stalline schists. 

B. Epioenetic deposits : formed later than the countn' rock. 

1. Veins; fillings of fissures, together with kindred formations, for 
example, tin. veins, in which filling of the fissures was accompanied by 
replacement of the wall rock. 

2. Epigenetic ore deposits other than veins, 

(a) Epigenetic deposits, formed essentially by an impregnation of non- 
calcareous rocks, the deposits being generally in distinct beds. 

(b) Epigenetic stocks; formed essentially by a metasomatic replace- 
ment of calcareous rock, mostly in the form of stocksS pockets, or 
stringers ; for example, the cadmium deposits in the ^fuschelkalk. 

(c) Contact metamorphic ore deposits; ore-beds and stocks formed 
through contact metamorphism caused by Plutonic intrusive masses; for 
example, contact metamorphic magnetic iron ores. 

(d) Ore-bearing cavity fillings; deposits formed essentially by a simple 
filling of pre-existing cavities mostly in the form of stocks or stringers ; for 
example, pisolitic iron ores. 

II. Secondary Deposits. 

Those formed by the destruction and transposition of primary deposits : 

1. Residual deposits formed essentially by chemical alteration of 
primary deposits. 

2. Placer deposits formed essentially by mechanical degradation of 
primary deposits or placers. 

' i.e., irregular masses, with or without definite boundaries. 



INTRODUCTION. 



TABLE OP THE MOST IMPORTANT ORB MINERALS. 



/-\ 


Cryst. 
System. 


Chemical 


Percentage of 


Ores. 


Composition. 


Gold. 


Other Metals. 


Gold 
Gold 


isom. 
orth. 

14 
M 

mono. 


Au, mostly (Au, Ag) 
(Ag, Au) Te, 
Au,Sb,Pb,oTe.Si5 
(Ag, Au),Te 
AuAffTe. 


• ••••••« ■ 

35 

5.9—7.6 
3.3—25.6 

26.5—40.6 

39.5— 


0.16— 39 Ag 


lO^nncrite 


NaflTvacite 


57.2—60.5 Pb 


fsJ o •••••••••••• 

Petzite 


40.8—59.6 Ag 

2.24— 11.3 Ag 

3.1 Ag 


Svlvanite 


Calaverite 


tri. (Au, Ag) Te, 



The following minerals are sometimes auriferous: pyrite, arsenopyrite, chalco- 
pyrite, stibnite. zinc-blende. 



w 



Silver. 



isom. 



Argentite 

Bromyrite 

Chlorargyrite 

Embolite 

Dyskrasite orth. 

lodyrite hex. 

Polybasite mono. 

Proustite ! hex. 

Pyrargyrite (dark ruby 

silver) 

Silver, native 



Stepfianite. . . 
Stromeverite. 



hex. 



isom. 



orth. 
rh. 



AgBr 

Ag CI 

Ag (CI. Br) 

Ag,Sb (?) 

Ag«i 

SbS, (.\g,Cu), 

As S, Ag3 

3 Ag^, Sb A 
Ag 



5 AgjS, Sb.A 
Cu^+AgaS 



68.4 
53.1 



Silver. 

87.1 

57.4 

75.2 

61—69.8 i 

63.9—94.1 

45.9 

64—72 

65.5 

59.8 
90—100 



3— lOCu 



Often holding 
Sb, As, Hg, 
Co, Fe, Cu 
and Au 



31.2Cu 



The minerals given in this table include only those of economic importance in 
mining and smelting or those which are particularly characteristic of certain deposits. 
The chemical formulas are chiefly taken from ' Tabellarischen Nebersicht der 
Mineralien' of P. Groth, 4th edition, 1898; revised in this edition to accord with Dana's 
Mineralogy.' The metallic percentages are from F. Kolbeck's new revision of Platt- 
ner's 'Blowpipe Analysis/ Leipzig, 1897. 



6 



THE NATURE OP ORE DEPOSITS. 



The following minerals often hold silver: tetrahedrite, galena, sine blende, pyrite, 
chalcopyrite, chalcocite: 





Cryst. 
System. 


Chemical 
Composition. 


Contents in 
Percentages of 


Ores. 


Silver: 


Other Metals. 


Platinum. 
Platinum, native 


isom. 


Pt 


70—90 


Nearly always 
holds Fe, Cu, 
Rh, Ir, Pd 
and Os 



Iridium, osmiridium, etc., also contain platinum. 



Mercury. 



Cinnabar 

Mercury, native 



hex. 



HgS 
Hg 



Mercury. 
86.2 



Mercurial tetrahedrite also contains 1.56 — 1.73% quicksilver. 



Lead. 



Anglesite. . . . 

Boulangerite. 

Boumonite . . 

Cerussite 

Galena 

Jamesonite . . 

Mimetite .... 
i^Phosgenite . . 
.' Pyromorphite. 

Wulf enite .... 
- Croicite 



orth. 



tt 



orth. 

M 

isom. 

orth. 

hex. 

tetr. 

hex. 

tetr. 
mono. 



PbSO^ 


68.3 


2PbS+SbA 


53.9—59.5 


2PbS+Cuj^+SbA 


42.3 


PbCO, 


77.6 


PbS 


86.6 


2PbS+Sb,S, 


50.6 


SPbaAsjOg + PbCl, 


69.5 


PbCla+PbCO, 


73.8 


SPbjPjOs + PbCl, 


76.2 


Pb Mo O4 


55.8 


Pb Cr 0, 


64.6 



Lead. 



Copper. 



Atacamite 

Azurite 

Boumonite 

Bomite 

Brochantite 

Chalcopyrite (copper 
pyrite) . .^^^j,^._^^^ 



orth. 
mono, 
orth. 
isom. 
orth. 

tetr. 



Cu Cl„ 3CuO, 3 Kfi 
3CuO,2CO,+aq. 
2PbS + Cu2S + Sb^, 
X Cuj, S + y Cu S + 2 FeS 
4CuO,SO,+ 3aq. 

Cu.S-f Fe^, 



Copper. 

52.7—59.4 

55.2 

13.0 

43—63.4 

56.1 

34.5 



42.3 Pb 



INTRODUCTION. 



Ores. 



Copper. 

Chalcocite (cop'r glance) 

Chrvsocolla 

CovelHte 

Cuprite 

Enargite 

Famatinite 



Tetrahedrite 



Copper, native 
Malachite . . . . 
Tennantite . . . 



Cpyst. 

System. 




hex. 
isom. 
orth. 



isom. 

isom. 
mono, 
bom. 



Chemical 
Composition. 



CUj^ 

Si O, Cu. 2 H,0 

CuS 



Cnfi 



As S^ Cu 

Sb S^ Cu 

f As^S/Cu,, Fe„ Zn), \ 
Sb^S^Cu,, Ag„ Fe, . 

Zn), 



Contents in 
Percentages of 




79.8 
33.9 
66.4 
88.7 
48.2 
43.2 

13—43 



CO, [Cu.OH], 
As^SyCCu,) (Fe, Zn), 



Pyrite and pyrrhotite are also cupriferous. 



57.4 
47.7—51.6 



Other Metals. 



0—31 Ag 
0.5— 17.2 Hg 



Nickel. 
Annabenrite 


mono, 
isom. 


Chloanthite 


Garnierite 


Gersdorffite 


isom. 

M 

hex. 
amor. 


Linnseite 


Niccolite 


Genthite 


Ullmannite 



Ni, As, Og + 8 aq. 

Ni As, 

Si O, (Ni, Mg) H, + aq. 

(Xi Fe) As S 

[(Ni, Co, Fe)SJ,(Ni, Co) 

NiAs 

Si3 0,0 Ni, H, 

Ni Sb S 



Pyrite and pyrrhotite are also nickeliferous. 



Cobalt. 



Asbolite .... 
Erythrite. . . 
Glaukodot . . , 
Cobalt ite. . . 
Linnseite. . . . 
Skutterudite. 
Smaltite .... 




Mn 0„ Co O, Cu O, H,0 
Co, As^Og + 8 aq. 

(Fe, Co) (As. S), 

rCo, Fe) As S 

[(Ni, Co, Fe)S,] (Ni, Co) 

Co A S3 

(Co, Fe. Ni) (As S), 



Nickel. 
29.2 




28.2 
3 33 


Contains Co. 


30—35.1 




14.6—42.6 
43.6 


11— 40.7 Co. 


39.1 




27.6 





Cobalt. 

19.4 

29.5 
4.5—24.8 

35.5 
11—40.7 

20.8 
8.2—23 



14.6—42.6 Ni 



8 



THE NATURE OF ORE DEPOSITS. 



The following minerals also contain cobalt: pyrrhotite, white nickel pyrite,gray 
nickel pyrite, arsenopyrite, danaite, cobalt-areenic-pyrite. 



Iron Ores. 
Chamosite 




Hematite (red, specular 
iron) 

Ilmenite (menacconite) . 



Limonite. 
Magnetite 
Titanite. . 
Siderite . , 



hex. 



ortho. 
isom. 

u 

hex. 



Chemical 
Composition. 



Percentage of 



Iron. 



Other Metals. 



Fe O, Mg O, Al, ()„ 
Si 0„ H,0 



Fe^Oa 



33—47 



70 



Fe Ti O., + X Fe, O. 

X = 0—5 " 20.6—68 

2 Fe, O3 + 3 H2O 59.9 

Fe O + FcjOj 72.4 

[(Fe Ti) O,] ,Fe 

Fe CO, 48.2 

Mixed with other substances forms: 

Argillaceous spharosiderite = iron carbonated clay. 

Blackband = iron carbonate + coal. 

(Pisolitic ore bohnerz, minette)= oolitic limonite with clay and quartz 

Seerze = limonite, earthy; often oolitic. 

Iron Sulphides. I 

Arsenopyrite orth. 

Chalcopyrite tetr. 

Pyrrhotite hex. 

Marcasite 

Pyrite 



Chromium Ores. 
Chromite 



orth. 
isom. 



isom. 



tetr. 



Manganese Ores. 

Braunite 

Asbolite 

Hausmannite I tetr. 

Manganite ' orth. 

Polianite [ orth. 

Psilomelane i amor. 

I 

I 
I 

Pyrolusite ' orth. 



Rhodochrosite 
Rhodonite. . . . 



Wad. 



hex. 
trie. 



not 
cryst. 



FeS^ + Fe As, 




34.3 


Cu,S + FeA 




30.5 


Fe„S„+, 




60— Gl.() 


FeS, 




46.6 


FeS, 




46.(> 
Chromium 


(Fe, Mg, Cr) O 4- 




40—60 


(Cr„ Al,, Fe,) O3 




usually 
40—53 






Manganese 


Mn^Oj 




60.6 


Mn O2, Co 0, Cu 0. 


Ufi 


c. 19 


Mn30, 




72.1 


MnPa + aq 




62.5 


MnO, 




63.2 


Combined with M 


n 0.„ 




Mn 0, Ba 0, K,() and 


49.2—62.9 



15— 25rc() 



H/). 

MnO, 

Mn C O3 

[Si 03].^Mn2Commonly also 
[Si0j2(MnFeCaMg)2 

Predominant: Mn O, 
MnO and H^O 



63.2 

47.8 

42 



INTRODUCTION. 



Zinc. 



Calamine. . . 
H vdrozincite 
Smithsonite . 
Willemite . . . 
Wurtzite. ... 
Sphalerite — 



Zincite. 



Bismuth. 



Bismutite 

Eulytite 

Bismuth, native 

Bismuthinite (bismuth 

glance) 

Bismite (Bismuth ochre) 

Tin. 

Cassiterite (tinstone). . . 
Stannite (tin pyrite) . . . 

Tungsten. 



Cryst. 
System. 



Scheelite . . 
Wolframite 
Hubneritc. . 



Molybdenum. 



Molybdenite 

Antimony. 

Stibnite (antimonite) 

Cervantite 

Stibiconite 

Valentinite 



Arsenic. 



Arsenic, native. 
Arsenopjmte. . 

Orpiment 

LOllingite 

Realgar 



orth. 

amor. 

hex. 

M 

orth. 
isom. 

hex. 



isom. 
liex. 

isom. 
isom. 



tetr. 
isom. 



tetr. 
mono. 



hex. 



orth. 
crj'st. 



orth. 



Chemical 
Composition. 



Si O, [Zn OH], 
Coj^ [Zn OH], 
ZnCO, 
Si O^Zn, 

ZnS 
ZnS 

ZnO 



CO3 [Bi O] Bi (OH), 

[Si O J 3 Bi, 
Bi 



BijS, 
Bi,0, 



SnO, 



Sn S, Cu, Fe 



CaWO, 
WO,(Mn, Fe) 
Mn WO4 



MoS, 



Sb^, 
Sb 0,Sb 
H'Sb,0 



2^5 



Sb,0, 



hex. As (Sb, Ni, Fe, Mn, S) 
orth. Fe As S 

As^3 

Fe Asj 
mono. lAs^S, 



Percentage of 



Zinc. Other Metals. 



53.7 
57.1 
52.0 
58.1 
to 67 
67 

80.2 

Bismuth 

87.1 

83.8 

95—99.9 

81.2 
89.6 

Tin. 

78.0 
24.1—31.6 

Tungsten. 

63.9 

57.9—60.3 

60.7 

Molybde'm 

59.0 

Antimony 

71.7 
79.2 
74.6 
83.5 

Arsenic 

90—100 

46 

61.0 

72.8 

70.1 



The colored 
species u 
to 8% Fe 



23.6—29.8 Cu 



10 THE NATURE OF ORE DEPOSITS. 

TABLB OP UNITS IN WHICH METALLIC CONTENTS OP ORES 
ARE MOST COMMONLY EXPRESSED. 

Ia this work the metric ton of 2,205 pounds is used, unless otherwise stated. 

100 kg. « 1 centner — 1 quintal. 

Gebmany. 

The contents are mostly given in percentages. In Saxony for silver ores 
''pound parts" are still in use. 1 pound part=0.01 per cent or 100 grams 
per 1,000 kilograms. 

The contents of gold ores are given in grams (g) per metric ton (t) of 
1,000 kilograms. For statements of production the metric ton is used: 
1 ton= 1^000 kilograms. 

England. 

1 long ton -2,240 lb. - 1 ,016 kg. 
1 short ton -2.000 lb. -907.2 kg. 
1 pound avoirdupois Gb.) — 453.6 g. 
1 lb. — 16 ounces (oz.) 
1 ounce (os.) — 28.3 g. 

The contents of gold and silver ores are entered by means of 

1 oimce troy (oz.) — 31.1 g 

1 pennyweight (dwt.) — 1-20 oz. — 1.5 gram. 
1 gndn (gm.) — 1-24 dwt. —0.06 ^am. 
1 grain troy — 1 grain avoirdupois. 

United States. 

Like England, except that the short ton is almost exclusively used, 1 
ton 2,000 pounds=907.2 kilograms. 

1 kilogram (kg.) —2.20462 pounds avoirdupois. 
1 flask mercury —76.5 pounds avoir. —34.7 kg. 

Gold contents in dollars : 



1 dollar ($) - 100 cents (cts.). 

1 o«. troy - S20.6718 1 - $1.2929 1 



Idwt. -SI .0386 ( f^--„ij 

Igr^ -$0.04306 f ^^'6°^^- 

Igram -$0.6646 J -0.04157 



►for silver. 



In Many States of South America. 
Contents in marcos per cajon: 

1 marco — 230 grams = 7.398 troy ounces. 
1 cajon — 64 quintals. 
1 quintal— 46 kg. 

Russia. 
Gold contents are given in zolotniks per 100 poods or 10 berkowitz: 

1 berkowitz - 10 poods - 163.8 kg. 
Ipood - 16.379 kg. 

Izolotnik - 4.265 g. 

1 dole - 0.044 g. 



SECTION I. 

MAQMATIC SBORBOATIONS. 

It is known that all eruptive rocks, especially those with but little silica, 
in rising from the unknown depths of the earth's interior to higher regions 
of the crust or to the surface, bring with them metals and metallic com- 
pounds, mostly, it is true, in very small amount. Magnetite and titanic 
iron ore, also pyrite, magnetic pyrite and chromite, are found in the form of 
small grains and crystals, scattered rather uniformly through many such 
eruptive rocks, in which the nature, microscopic intergrowth and relation 
to other constituents show conclusively that these small ore particles are 
primary constituents of the rock. It is true, as a rule, that such examples 
do not form true ore deposits, since the amount of these primary ores con- 
tained in such rocks is too small to pay for mining. • However, weathering 
and erosion occasionally lead to a concentration on the eari;h's surface of 
these uniformly disseminated metallic minerals, as will be explained in the 
section on placers. 

In some cases a concentration of the ores either into stock-like masses or 
into bands (schlieren) has taken place in the rock either before or during 
its solidification from the molten condition; these magmatic segregations 
or secretions, being of primary origin, will be considered first in this work. 

Although concentrated in compact masses, the ore of these magmatic de- 
posits is exactly the same as that which occurs in sparsely scattered particles 
through, the enclosing rock, in which the ore minerals are accessory constitu- 
ents. This, as will be shown in specific cases, is proven by the conditions of 
microscopic structure and intergrowth. This particular fact is the most im- 
portant argument for the truly primary nature of such deposits, and enables 
one to discriminate between magmatic segregations and those accumulations 
of ore that have been formed through secondary processes in an eruptive 
mass. 

The exact physico-chemical processes involved in the segregation of defi- 
nite components of the magma into distinct portions of different composi- 
tion, the so-called process of magmatic differentiation, is not as yet under- 
stood, although this problem has, in recent decades, occupied the attention 
of many investigators.^ 

' A verv comprehensive presentation of these relations was given bv J. P. Iddings: 
*The Origin of Igneous Uorks.' Phil. Soc. of Washington, Bi/U. XII, pp. 89-214, 



12 THE NATURE OF ORE DEPOSITS. 

As regards this particular theory of the origin of ore deposits, the work 
of J. H. L. Vogt is most important. The process had long been recognized 
in examples of lean ore; notably the remarkable *'mixed lodes^^ described by 
H. Biicking and others, where, in an eruptive dike, the more basic material 
of the magma has become concentrated in the two borders in sharply defined 
zones, making three parallel lodes or dikes side by side. Attention has also 
been devoted for a good while to the more basic, and often more highly 
iron-bearing marginal facies of eruptive stocks and large massives. In this 
segregation, processes of diffusion seem to have played a leading part. Teall, 
Lagorio and Brogger long ago noted the experiments of Soret (1879-1881), 
who, upon an unequal heating of different parts of saline solutions, obtained 
a different distribution of the salts, the solutions becoming more concen- 
trated in the colder part than in the warmer. This is a consequence of 
the principle subsequently developed by van t'Hoff that the osmotic pres- 
sure inci*eases in proportion to the absolute temperature. No doubt, how- 
ever, other causes not yet known co-operate in producing this result. 

Following J. H. L. Vogt, we will use the following grouping of ore de- 
posits formed by magmatic differentiation according to the character of the 
ores predominant in each case: 

A. Segregations of native metals. 

B. Segregations of oxidic ores. 

C. Segregations of sulphide and arsenical ores. 

(A) Segregations of Native Metals in Eruptive Rocks. 
1. Segregation of Native Iron in Basalts. 

The famous occurrence of native iron in the porphyritic feldspar basalt 
of Ovifak on Disko Island on the west coast of Greenland^ is of great scien- 
tific, but of no economic importance. 

Since the time of Captain Ross's visit it had been known that the Esqui- 
maux worked up natural native iron into tools, but the place whence they 
obtained the raw material was not known. Finally A. E. Nordenskiold, in 
August, 1870, discovered the most important place to be Blaafjeld, on the 

1892. Also in other publications. Compare also J. II. li. Vo^: 'Formation of 
Ore Deposits Through Processes of Differentiation in Basic Eruptive Magma.' 
Zeit. f, Prak. GeoL^ 1893, p. 4, etc. The researches of J. Morozewitz are also of the 
irreatest importance in this connection. 'Exper. Untersuch. uberdie Bild. d. Min. im 
Magma.' Tschemiak's Min. Mitth., 1899, Vol. XVIII, pp. 1-240. 

* G. Nauckhoff: 'On the Occurrence of Native Iron in the Basalt Lode at Ovifak.' 
Tsehermak : Min. Mitth., 1874, pp. 109-136. J. K. V. Steenstrup : *On the Iron 
of Greenland.' Zeit. d. Deutch. Geol. Gesell. 1876, pp. 225-233, and in the Med- 
delelser fra Oronland IV. Copenhagen, 1882. A. E. TSmebohm : 'On the Iron 
JJearing Rocks of 0^^fak and Assuk.' .\ppendix to K. Svenska Vet. Ak. Ilandl.f Vol. 
V, No. 10, Stockholm, 1878, also contains further papers. 



MA OMA TIC SEGREGA TI0N8. 13 

south side of Disko Island. In 1871 a special expedition, with G. Nauek- 
hoff as geologist, undertook a detailed investigation of the locality, and 
carried to Europe not only several very large blocks of iron found l3ring loose 
on the shore, but also abundant material still enclosed in the rock. It is 
now generally believed that the basalt of Ovifak is not a dike, but forms a 
sheetlike flow such as is common in the Tertiary coal-bearing formation of 
that region. This basalt porphyry encloses, according to A. E. Tornebohm, 
masses of a doleritic rock belonging to an earlier period of formation, hold- 
ing inclusions of a highly graphitic anorthite rock. This dolerite consists 
of labradorite, augite, olivine, titanic iron ore, magnetite and a glassy 
groundmass. Furthermore, it contains native iron (Schreibersite), usually 
near the boundary with the anorthite inclusions, also troilite, magnetic py- 
rite, graphite and a silicate, for the most part greatly altered and resembling 
hisingerite. The metallic iron appears in flakes, grains, globular masses 
and large lumps. On etching, it shows the Widmanstatten figures and con- 
tains nickel and cobalt, according to a new analysis by A. Iwanoflf^ 

Fe 02.91 

Ni 2.66 

Co 0.69 

Cu 0.19 

C 3.29 

S 0.26 

100.00 



The rust-like decomposition crust of the ore consists essentially of basic 
hydroxides, basic oxychlorides and basic sulphates of iron. Many observera 
have noted, as shown in the illustration of thin sections of the rock given 
in Tornebohm's report, that in the smaller nests of iron the metal apparently 
must have been segregated after the other constituents. Nauckhoff and 
Tornebohm demonstrated that the iron probably occurred in the form of 
phosphor-nickel iron (Schreibersite) in breccia-like fissure fillings in the 
midst of the basalt, and Tornebohm inferred from this, and from the above 
mentioned microstructure of the iron-bearing dolerite, that the iron of 
Disko must have been formed secondarily from solutions. This inference, 
however, may be questioned, especially in view of the above-mentioned large 
blocks. The breccia in fact may be due to a basalt zone, broken up by dis- 
locations after the iron had been segregated. From the chemical pbint of view 
Tornebohm's theory has recently been strongly supported by C. Winkler*, 

'C.Winkler: *Zur Ziisammensetzung: des Eisens von Ovifak,' etc. Kongl. Vetensk 
Ak. Fork, 1901, No. 7, Stockholm, p. 495. 

'C. Winkler: 'On the Possibility of the Immipration of Metals into Eruptive 
Rocks throueh the Agencv of Carbon Dioxide.' Ber, d. Math.-Phya.^KL d. Kgl. 5. 
Ak, d. W. Leipzig, 1900, p. 9. 



14 THE NATURE OF ORE DEPOSITS. 

who has called attention to the freely fluid compounds which, according 
to recent investigations, carbon dioxide forms with nickel-iron on 
even moderate heating, and which decompose again, with separation 
of the native metals. Such heating might take place for a considerable 
time at the contact of such gases with an eruptive body still undergoing 
congelation. The author himself, it is true, raises the difficult question a«j 
to the origin of such iron carbon compounds which must have been formed 
in a cooler zone. The geologic conditions of these and other closely related 
occurrences indicate that the original seat of the native metals was in thp 
eruptive hearths themselves. 

E. J. V. Steenstrup subsequently found in basalts, at several other points 
of Disko, inclusions of native iron, graphite and nickeliferous magnetic 
pyrite, which renders it very likely that the iron and nickel content was an 
original constituent of those basaltic magmas, and the masses are not of 
cosmic origin, as Nordenskiold had originally conjectured. 

2. Segregations of Nickel Iron in Olivine Rock and Serpentine of Awarua 

in New Zealand. 

A very interesting occurrence of nickel iron, awaruite, discovered on the 
west coast of the south island of New Zealand, by W. Skey, in 1885, has 
been described by 6. H. F. Ulrich^ This region consists of gneisses, mica 
schists and chloritic schists, which are broken through by vast stocks of an 
olivine rock of the composition of saxonite (olivine + enstatite), in part 
transformed to serpentine. In the river valleys, descending from the moun- 
tains formed of serpentine and saxonite, the nickel iron was found in loose 
grains, and it was intended to wash it from the gravel. Subsequently it 
was also found in small particles intergrown with the eruptive rocks just 
named. The composition of awaruite, according to Skey, is as follows : 

Ni 67.63 

Co 0.70 

Fe 31.02 

8 0.22 

SiC 0.43 

100.00 

3. Segregations of Platinum in Olivine Rocks. 

It had long been suspected that the platinum of the Ural placer gravels 
(see later) must have its original source in the serpentines and olivine 
rocks found in the region drained by the upper courses of the platinum-car- 
rying rirers. This inference became a certainty when an olivine gabbro 

' G. H. F. ITlrich: 'On the Discovery, Mode of Occurrence, and Distribution of 
the Nickel Iron Alloy, Awaniite, on the West Coast of the South Island of New Zea- 
land. ' Quart, Joum. Geol. Soc. London, 1890, Vol. XL VI, pp. 619-633. 



MAQMATIC SEQREOATIONS. 16 

with grains of intergrown platinum was discovered on the Krestovozdri- 
schensky property, in the western Ural, and later, in the eastern part of the 
mountains in the Goroblagodatsk district, nests of chromite with platinum 
were found in an olivine rock^ 

Extensive experiments with crushed samples of olivine rock and olivine 
gabbro from the vicinity of Mount Soloviov, near Nizhni Tagilsk, have 
shown a slight platinum content in these rocks.* 

The platinum of the Ural contains 5 to 13% of iron, besides some iridium, 
rhodium, palladium, osmium and copper. (See platinum gravels.) 

St. Meunier* calls attention to the very irregular and often branched 
forms of the grains of iron-platinum in the olivine rocks of the Ural, and 
compares it with the peculiar structure of the small nests of native iron in 
the dolerite of Ovifak and the iron grains in meteoric magnesian silicate 
rocks. By experiment he obtained similar structures by using gases to re- 
duce the respective metals from a heap of granules of such silicates. A jet 
of platinum chloride, hydrogen and some ferrous chloride passing through 
the heap at red heat produced iron platinum in quite analogous develop- 
ment These observations are important. The conclusion he draws from 
them, however, that the rocks in question are products of primitive congela- 
tion, after the manner of meteorites, is not borne out by the conditions under 
which the platinum-bearing eruptive rocks actually occur. 

The platinum contents of the olivine rocks of the Ural have, with few 
exceptions, been found much too low to give to these primary platinum de- 
posits an economic significance; only the residual and alluvial placers pay 
for the working. 

4. Oold as a Primary Constituent of Eruptive Rocks. 

Though it may be difficult in an individual case to decide whether the 
particles of native gold found in eruptive rock are primary and really due 
to segregations or have been introduced by secondary processes, yet a series 
of occurrences seems to indicate the probability of the former alternative. 
Most of the observations relate to granites and other acid eruptive rocks. 

G. P. Merrill* describes primary free gold occurring as an inclusion of 

' A. Inoatranzeff: 'Primary Site of Platinum in the Ural.'*" Mitth. an d. Ges. d. 
Naturf, in St. Petersburg. ISfov. 7, 1892. (Reviewed by R. Helmhacker. Z, f. pr. 
G., 1893, p. 87.) 

' Oral communication of Mining Engineer Hamilton of Nizhni Tagilsk to R. Beck 
when on a visit to Mount Soloviov in 1897. 

'St. Meunier: 'Study of the Matrix of the Platinum of the Ural,' etc. Compte 
Rendu du VII. Conqr. O'eol. Intern,, 1898, p. 157. 

* G. P. Merrill: 'Occurrence of Free Gold in Granite.' Am, Jour. Sci„ 1896, 1, p. 309. 
H. Schultze: 'Gold Mining,' in H. Kunz's 'Chile. ' 1890, p. 78. W. MOricke: 'The Gold, 
Silver, and Copper Ore Deposits of Chile.' Freiburg, 1898, Vol. I, p. 16. 



16 



THE NATURE OF ORE DEPOSITS. 



feldspar and quartz in a granite from Sonora, Mexico, as ^'a product of cool- 
ing and crystallization from the original magma." H. Schultze demon- 
strated the primary nature of gold in many granites of the coast Cordillera 
of Chile; W. Moricke proved the same for glassy and crystalline quartz 
trachytes of that country; W. P. Blake added examples from Arizona; 
Forbes^ examples from Bolivia. It also seems that the primary nature of the 
gold in the granites in the Ekaterinburg region in the Ural, as, for ex- 
ample, on Lake Shartash, has been satisfactorily demonstrated. These oc- 
currences are, however, only of economic importance because payable placer 
gravels may develop from them. 

On the other hand, the primary content of free gold in diorites or am- 
phibolitized diabases, so often referred* to in different publications, seems 
of very doubtful authenticity. The occurrences of this kind examined by 
us, for example, from Mashonaland, rather suggest the assumption of a 
secondary immigration of gold. The reader will find further statements 
on this subject on a subsequent page. 

In connection with this it may be mentioned that according to E. Dain- 
tree* gold-bearing pyrites are found widely distributed in the diorites 
which occur in the Upper Silurian or Devonian of New South Wales, Vic- 
toria and Queensland. The primary nature of these pyrites is not, how- 
ever, evident from the accompanying plates of thin sections. 

A remarkable ease is that mentioned by K. Schmeisser*, of gold in a 
basalt from Bichmond river in New Zealand, which is said to assay as high 
as 18 grams per ton. This may be a local occurrence and due to highly 
auriferous sands gathered from gravels which were broken through by the 
basalt. 

(B) Segregations op Metallic Oxides in Eruptive Rocks. 

Table of the Important Iron Ores. 



Ore. 



Magnetite FeO, Fe, O, 

Hematite (Specular ore) Fe- O,. . 
Siderite (Spathic iron ore) Fe CO, 

Limonite. 2Fea O3.3H2O 

IVrite, FeS, 



Fe. 


HjO. 


CO,. 

1 

• * . . • 


72.4 





70.0 






48.27 




37.92 


59.89 


14.4 


1 


46.7 







s. 



53.3 



* R. Daintree: 'Occurrence of Gold in Australia.' 
1878, Vol. XXXIV, p. 431. 

' K. Schmeisser: 'Australasien/ p. 92. 



Quart, J (mm. Geol. Soc., 



M AQUATIC SEGREGATIONS. 17 

1. Segregations of Magnetic Iron Ore in 'Quartz-free Orthoclase Porphyries 

and Syenites, 

This group ineludeij the best studied and authenticated magmatic de- 
posits known^ especially the famous deposits of the UraP and of Lapland^ 
which we will describe in detail. 

(a) The Vysokaya Gora. 

The famous iron ore deposit of Vysokaya Gora (High Mountain) lie« 
directly west of Nizhni Tagilsk, the most important mining locality of the 
central Ural. It is merely one link in a chain of similar magnetite deposits 
of these mountains, which are all associated with a series of syenite and 
accompanying porphjTitic rocks covering an area about 70 kilometers long 
and 15 kilometers broad, and striking north-south. The main mass of the 
Vysokaya intrusion consists of augite-syenite, which in many instances al- 
ternates with hands of a quartz-free orthoclase porphyry. The latter rocks 
consist of orthoclase feldspar and a little plagioclase; it is only here and 
there that augite (or uralite) and biotite take part in their composition. 
Besides the accessory ingredients (titanite, zircon and apatite), magnetite 
is also found in small granules or rounded crystals, which may constitute 
as much as 20% of the entire rock mass, until finally whole lumps of this 
mineral make their appearance, thus gradually effecting the transition to 
true orebodies and forming an irregular stock. At times, as, for example, 
in the fragments of a breccia due to later disturbance, the result of igneous 
energy, the orthoclase porphyry is amygdaloidal and shows primary mag- 
netite concentrated around vesicular cavities now filled with calcite (Hog- 
bom). According to Tschernyschew, there is a connection between the dis- 
locations and the epidote-zoisite-gamet rocks of the Vysokaya, which, be- 
sides these minerals, contain also zeolites, chlorite, quartz and calcspar. 
According to Hogbom their structure shows them to be metamorphosed 
porphyries and syenites, since they still show feldspar lathes arranged in 
a fluidal structure. These eruptive masses are intruded in Devonian lime- 
stones, the rocks being well exposed in the open-cuts made in mining. Great- 
ly decomposed interbedded tuffs odcuT with these limestones, especially in 
the eastern part of the mountain. The sedimentary strata are faulted, hring- 
ing the eruptive rocks and orebodies in contact with the tuffs and epidote- 
gamet rock masses along the fault plane. 

* II. Muller: 'ITebcr den Macnetbers: Gora Blaprodat.' Berg v. ffutfen Zeii., 1866. 
p. 54. P. J^r^m^ew: 'Les minemis de fer dans les districts miniers de la chatne de 
rOural.' Joum. d Mines, 1S59, II.. p. 313. Th. Tschemvschew: 'Guidebook of the 
Excursions of the VII. International Geolopioal Confrreas. 1897.' Vol. IX. A. H. 
HOpbom : 'Om de \nd avenit bererarter bundna jemmalmema i Ostra Ural.' GeoL 
Faren, i Stockholm Fftrh.' Vol. XX, part 4, 1898. 



18 THE NATURE OF ORE DEPOSITS. 

The magnetic iron ore of Vysokaya is remarkable for its great purity. 
The ore has averaged 65 per cent during the past ten years. A large part 
of the ore that is mined has the composition of martite.^ The ore is low 
in phosphoric acid compared with the analogous deposits at LeSiashaya 
pituated farther northeast, near Nizhni Tagilsk. The Vysokaya iron ores 
at times contain scattered grains of copper pyrite. To the southeast of this 
mountain of magnetic iron ore is the famous copper mine of M^dnorudiansk. 
The characteristic analysis of the ore of the Vysokaya given below is from 
the oflBcial report of the company operating the mines : 

F:b^v;::::::::::::::::l6:7?)F«««p— * 

Mn,0, 1.30 

Cu 0.06 

S Trace 

P 0.03 

SiO, 2.85 

AljO, 1.80 

CaO 0.99 

MgO 0.98 

100. 12 per cent. 

The iron industry of Nizhni Tagilsk was founded about 1725 during the 
reign of Peter the Great. The mines supply half a dozen furnaces in 
the Ural district with ore, the average annual production during the past 
decade being a little over 100,000 tons. 

(b) The Goroblagodat Iron Deposit.* 

This famous mountain of magnetic iron ore, whose name means blessed 
mountain/' is an isolated peak rising to a height of 156 meters above the 
Kushva plain. The deposit supplies extensive reduction works, and is 
worked by vast open-cuts which run around the south side of the summit, 
and in terraces far down the west slope. A high pillar of rock has been 
left at the summit which is crowned by a chapel. (See Fig. 1.) The view 
from this point includes the range of the Ural, which here is not very high, 
to the west, while eastward the Tura and Tagil rivers are seen traversing 
the gently undulating west Siberian lowlands. 

At Blagodat the same conditions seen at Vysokaya are exactly repeated, 
except that the arrangement of the orebodies proper is somewhat dif- 
ferent. Here they have the form of streaks arranged in benches, one above 
the other, as shown in Pig. 1. This figure also exhibits the two main 
faults of the deposit. The transition between ore and normal eruptive rock 
is gradual and not sharp as represented in the figure. 

> G. Lebedew: 'Lehrbuch der Mineralgi' (Russian), St. Petersburg, 1900, p. 126. 
' Literature the same as under Vysokaya Gora. 



MAOMATIC SEOREOATIONS. 19 

In contrast with the Vyeokaya oree, the magoetite contains mnch pyroz^ia 
and its chloritic decompoaition products, ae well as spinel, so that the per- 
centage of iron is considerably lower, being on an average only 55%, On 
the other hand the quality is excellent because of the very small percentage 
of phosphorus and pyrite. 

Mining began at Blagodat the early part of the last century, and the out- 
put reached 16,000 tons as early as 1770. From 1813 to 1898, 2,730,000 




Fig. 1 — SectiOD of Qoroblagodat after Th TgohemyHchew, 
p, orthoclase porphyry, m, magnetic iron ore, e, epidote-gamet rock. 

tons of ore were taken from this mountain. In 1898 the production was 
66,000 tuns. 

A characteristic analysis of the ore according to D. J. Mendelejeff is 
given below : 

SiO, 9.40 percent. 

AlA 7.18 

Mn,0, 0.20 

F$;. -. ; ; ; : : ; ; : : : : : : : : li :U 1 ^« ^^^^ p*' "°*- - 

Cab 6.00 

MgO 1.62 

8 0.05 

80, 0.12 

PA 0.33 

Cu 0.01 

MoUture.... 0.20 

The amount of ore exposed and ready for extraction in 1890 was esti- 
mated to be 15,000,000 tons. The ore is treated in the furnaces of Kuahva. 
Barancha and Vcrhneturyo, the pig iron being shipped to Nizhni Turinsk 
and Perm. The chapel on the summit is dedicated to the memory of Vogul 
Stephen Chumpin, who revealed to the Russians the wealth of the mountain, 
and for doing so was burned alive by his tribe on the summit. 

A third iron deposit in the southern Ural, 60 to 70 kilometers south of 
Verhne Uralsk, called Oora Magnitmaya, or Ataeh, seems to be connected 
with porphyritic and syenitic masses, but detailed geologic investigations 
have not yet been made. The ores contain 67 to 68% of iron and are almost 
free from phosphorus and sulphur. 

■ 'Iron Furnace Industry of the Ural in 1S99. ' II, p. 174. (In Ruanan.) 



20 THE NATURE OF ORE DEPOSITS. 

The iron (i(*])08it8 of Kiinmavaara and I^uoKsavaura in I^ipland are of 
the l-ral ty])o just denerihed*. They have been recently investigated in de- 
tail and actively developed. 

(c) Kiirunavaara and Luossavaara. 

Tht»8e two great dejwsits are r?ituated in the Swedish province of Norr- 
bottom, in about 67^ 50 north latitude. The ortv form great stocks, re- 
minding one of strata by the manner in which they outcrop within a vast 
mass of quartz- fnv orthoclase pori)hyry. Tliis rock is bounded on the east 
by grayv/acke slate, ebiy shito and eonglonierates, overlain by quartzitic sand- 
stones, while on the west it abuts against strongly metamorphosed conglom- 
erate s. 

The ore stock of Kiirunavaara forms a barren mountain ridge, the out- 
crop extending for ly^ miles, while magnetic observations prove its con- 
tinuation northward to the sliore of Lake Jjuossajarvi, and out as far as an 
island, so that the entire length must be m^arly thrcK? miles. Through- 
out its entire extent the deposit dij)s uniformly eastward at from 45* to 80*, 
as determined by drilling. The thieknrss of the ore sheet is between 34 and 
160 m. (Ill and 500 feet) and averages 70 m. (2'M) fwt). Tlie total amount 
of ore available for extraction is estimated by Iljalmar Lundbohm to be 
at least 215,000,000 tons. This ore is not everywhere of the sjime quality. 
The author just named distinguishes five ty])es with many intervening 
transitions: (1) Magnetic iron ore, poor in phosphorus; (2) the same, 
mixed with hematite; (3) pliosj)horus-l)earing magnetic iron ore, with a 
little apatite; (4) highly pbosphoritic magnetic iron ore, with apatite, in 
numerous pockets, stringers and stratiform bodies; (5) highly phosphoritic 
magnetic iron ore with minutely divided apatite. In more than 60% of 
the samples from the very numerous prosj)ects the iron exceeded 67%, while 
the phosphorus varied Ix'tween 0.05 to ()%. 

The ore mountain of T^uossavaara liis north of Lake Luossajarvi, and 
forms a broad stratiform stock about % of a mile long by about 180 feet 
broad, dipping steeply east within the same porj)hyry mass. This deposit 
is estimated to contain at least 4,700,000 tons of ore carrying 67 to 70.5% 
iron and a very low phosphorus content. These oecurrenoes will become 
of great importance upon the completion of the railway which will extend 
from the Tjapland iron ore region across to the Ofoten Fjord, on tlie west 
coast of Norway. 

* K. A. Fredholm: 'Hook» and Ores in Luossavaara and Kiirunavaara.' Crol, 
F&rtn, Fdrh., 1891. Vol. XIII. p. 26fi. Hj. Lundhohni: 'Kiinmavaara and Luossa- 
vaara Iron Ore Field.' Geol. Surv. of Sweden, series C, No. 175, 189S, with 3 plates 
and 1 map. « 



MA GMA TIC SEOREGA TI0N8. 21 

2. ISegregatiom of Titaniferous Magnetite^ in Gabbro. 

The most important examples of this class are the deposits of Taberg 
and Houtivarc in Sweden, Valimaki in Finland and the Adirondacks in 
Xew York. Kemp has published a review of all known deposits of this 
class-. 

The genesis of these segregation deposits has been discussed by Vogt*. He 
has attacked the problem by a study of numerous analyses of rocks and 
ores which have been platted in tables giving a graphic representation of 
the relations of the different elements. One of these tables, reproduced in 
Fig. 2, shows how, in the transition stages from normal rock to segregated 
ore, the amount of FejOj and TiOj increases as the silica, lime and alumina 
decrease. The magnesia increases, attains a maximum in the middle 
transition forms, and afterwards decreases. Vogt infers from these rela- 
tions that the renl 8olv(»nt of the ores must be an alumina-lime-sodium- 
silicate, and that this silicate plays the same part as the mother liquor of 
saline solutions. A part of the silica is, however, supposed to have taken 
part in the differentiation as a silicate of magnesia and iron. Petrographic 
investigations confirm these conclusions. Kemp has recently reviewed the 
evidence and presented his conclusions*. 

(a) The Taberg Near Jonkoping. 

The iron deposit of Taberg" in Smaland, southwest of Lake Wetter, near 
Jonkoping, in Sweden, is a belt or streak of ore-rich rock forming a 
part of a mass of olivine gabbro (olivine hyperite or Tornebohm). This 
basic rock has by reason of its greater resistance been left during the degra- 
dation of the region as a residual mountain. The iron ore forming this 
mountain consists of titaniferous magnetite and olivine, with subordinate 
admixtures of biotite and plagioclase. Transitions may, however, be ob- 
served, showing all gradations between the magnet ite-olivenite occupying 
the center of the igneous stock, to the ordinary olivine-gabbro, poor in 
magnetite, forming the border of the intrusive mass. The stock is intruded 

* J. F. Kemp: ' Titaniferous Iron Ores of the Adirondacks. ' 19th .t nn. Rept. U. S. 
Geol. Sur\'., Ill, 1S99, p. 3S7. 

'J. F. Kemp: *A Brief Ueview of the Titaniferous Magnetites/ School of Mines 
Quarterly, 1899, July, pp. 323-356. Nov., pp. 56-6.5. 

* J. H. L. Vogt : * Further Researches upon the Segregation of Titaniferous Iron 
Ores in Gabbro.' Zeit. /. Prak. Geol., 1900-1901. 

* The Engineering and Mining Journal, November 28, 1903. 

* A. Sjogren: 'On the Occurrence of the Iron Ore of Taberg in Smaland.' GeoL 
Foren. Forh:, 1876 and 1877, p. 42, with older literature. Ibid., 1882-1883, p. 264. 
A. E. T6mebohm: 'On Taberg in Smaland,' etc. Ibid., 1880-1881, p. 610, plates 25 
and 26. J. H. L. Vogt: 'Formation of Ore Deposits bv Differentiation,* etc. Zeit. 
/. Prak, GeoL, 1893, p. 8. 



22 



THE NATURE OF ORE DEPOSITS. 



in a complex of gneisses and gneiss granites, and is accompanied by horn- 
blende schists, probably patches of dynamo-metamorphosed gabbro. 

The Taberg ore is characterized by the presence of 0.12 to 0.40% of van- 
adic acid; in fact^ the element vanadium was first discovered by Seffstrom 




tig. 2. — Diagram showing Normal Differentiation. (Vogt.) 

in 1830 in the crude iron of Taberg. The high percentage of titanium 
greatly lowers the value of the Taberg ore ; moreover, the iron content, even 
at the richest spots, is low, not exceeding 32 per cent. 



(b) The Titaniferous Magnetites of the Adirondacks. 

Among the North American representatives of this type of deposit the 
Adirondack iron deposits are the best known, and have been carefully 



MAGMATIC SEGREGATIONS. 23 

studied and described by Professor Kemp.^ The mines of the Adirondack 
region are in Essex county, New York, southwest of Lake Champlain. 

The older gneisses and crystalline limestone of this region contain many 
intrusive masses of gabbro and closely related rocks which have been altered 
by regional metamorphism to schistose rocks. 

These rocks include both anorthosites (coarse-grained rocks of almost 
pure lahradorite) and the dark-colored gabbros and norites in which the 
ferromagnesian silicates predominate. These extreme types are both con- 
nected with masses of titaniferous magnetite and menaccanite, the former 
at Newcomb, Wilmington and North Hudson, the latter at Crown Point, 
Elizabethtown, etc. The minerals of the normal gabbro occur disseminated 
through these ores, and all transitions occur from gabbro to ore. 

The petrographic features as described by Kemp correspond closely to 
those of Valimaki, Finland. The following analysis by Hillebrand, of the 
typical ore from Oak hill, represents the normal composition of this class 
of ores: 

Fe 38.98 Al^O, 7.03 

Fe,0, 30.34 CaO 3.59 

FeO 22.81 MgO 6.92 

TiO, 6.21 P,0, 0.14 

SiO, 21.42 S 0.04 

The iron deposits of the Mesabi range, Minnesota', Port Henry and Lake 
Champlain*, New York; Iron Hill, Cumberland, Rhode Island*, and those 
of various gabbro areas of Quebec** and Ontario®, all belong to this class. 

The magnetite and chromite deposits of the Zwartkoppies range and else- 
where in the Transvaal, Africa, occur in norites forming the contact facies 
of a red granite. They are regarded as magmatic segregations by Molen- 
graar. 

Similar occurrences, though of less extent, have been found at several 
points in Sweden ; for example, in the gabbro of Langhult in Smaland and 
of Ransberg in Vestergotland. 

* J. F. Kemp: 'The Titaniferous Iron Ores of the Adirondacks. ' 19th Ann. Rept. 
U. S. Geol. Survey, Part III, 1899, p. 383. 

* N. H. and H. V. Winchell: 'The Iron Ores of Minnesota.' Geol. Surv. of Minn., 
1891. 

* Kemp in Trans. Am. Inst. Min. Eng., Vol. XXVII, pp. 146-203, 1898. 

* M. E. Wadsworth: *A Microscopic Studv of the Iron Ore Peridotite of Ironmino 
Hill.' Bull, Mus. Comp. Zool. Harvard College, Vol. VII, 1881, p. 183. 

' F. D. Adams: 'On the Igneous Origin of Certain Ores,' Montreal, 1894. Proc. 
Gen. Min. Assoc, of the Province of Quebec, Jan. 12, 1894. 

* E. J. Chapman: 'On Some Iron Ores of Central Ontario.' Trans, Royal Soc. 
Canada, 1885. p. 9. 

''Geol. Aufnahme der Sud-Afrikanischen Republik.' Jahresber, for the year 
1898. Pretoria, 1900, p. 14. 'G6ol. de la R^p. Sud-Africaine,' 1901, pp. 48 and 52. 



24 TEE NATURE OF ORE DEPOSITS. 

(c) Dq>osit of Routivare in Xorrbotten, Sweden*. 

This great deposit occurs in a gabbro (gabbro diorite) which has been 
subjected to strong regional metamorpbism. The deposit forms a band 
1,600 meters long by as much as 300 meters broad^ consisting of titanif erous 
magnetite, menacconite, spinel, olivine, a pyroxene and some magnetic 
pyrite. The ore differs from that of other similar deposits, as it contains 
a large amount of spinel. It contains between 48 and 52% of iron and be- 
tween 11 and 13% of titanic acid. Other magmatic deposits of similar 
ores rich in spinel occur in Norway and have been described by Vogt*. From 
his study of these ores in thin section under the microscope he has reached 
the important conclusion that the iron magnesian silicate has been the first 
to separate out of the magma, followed by the titaniferous magnetite. 
If the ores also contain p}Tite and spinel the order of crystallization 
is: Pyrite, spinel, titaniferous magnetite, an exception to the usual 
order observable in eruption rocks, in which magnetite is the first mineral 
to separate out. 

Between Sordavala and Pitkaranta, on the northeast shore of Lake 
Ladoga, near the village of Yalimaki, a rock-complex consisting of phyllite, 
quartzitic schist, nodular and hornblende schist, together with mica schist 
carrying andalusite and staurolite, is penetrated by a coarse-grained diorite 
which is apparently an altered gabbro. 

According to Blankett' this gabbro diorite forms a stock, having a north- 
south direction, cutting the schists and enclosing metamorphosed portions 
of them. The rock consists of plagioclase, hornblende (at times with augite 
core) with some epidote, apatite, magnetite, muscovite and hematite. Within 
this intrusive mass at some distance from its contact with the schists there 
are basic streaks of a rock very rich in hornblende, diallage, bronzitc, olivine 
and titaniferous magnetic iron ore, with subordinate amounts of green 
spinel, pyrite, magnetic pyrite, copper pyrite, mica and apatite. These dark 
streaks as a rule contain 15 to 30% of iron, while richer portions run as 
high as 40%. One specimen contained 63.40% of ferric oxide and 2.90% 
of titanic acid. All possible transitions from poor to rich ore may be found 
within these very extensive segregation streaks, whose distribution is usually 
quite regular. The iron ore is crushed and the magnetite extracted 
by magnetic separators, the concentrate being briquetted and smelted at 

* W. Peterson: 'On the Iron Ore Field of Routivare in Norrbotten Lane.' Geol, 
Foren. Fork., Vol. XV, 1893, p. 45, with map. H. Sjftgren: 'Additional Notes on 
Routivare Iron Ore.' Ibid., p. 140. 

*Vo^,: Zeii. f. Prak. Ceol., 1900. pp. 233-242. Kolderup: 'Petrog Beschreibung 
Lofatena,' etc. Bergena Mus. Aarbog,\ll, 1898, pp. 1-54. 

» Blankett: 'Ore Field of Valimaki, etc' Geol, Fdren, % Stockholm Fork., 1896, 
p. 201 , with map. 



M AQUATIC SEGREOATIONS. 26 

Widlits on the opposite side of the lake. TJie miiies produced some 7,764 
tons of ore fit for smelting in 1896. 

In other cases the magnetite is not only accompanied by spinel, but also 
by corundum and sillimanite, as in the norites of Westchester county de- 
scribed by G. H. Williams.^ 

3. Segregations of Titaniferous Magnetite Iron Ore in Nepheline-Syenites. 

The iron deposits of Alno, near the east coast of Sweden, in the Gulf of 
Bothnia, are described by A. G. Hogbom^ as basic segregations of nepheline- 
syenite. The nephcline-syenite of that locality shows an extraordinary num- 
ber of varieties, and is closely associated with remarkable masses of crystal- 
line limestone which, according to Hogbom, are possible primary segrega- 
tions from the extremely basic magma. The surrounding rocks are gneisses 
which have been altered by contact metamorphism. The basic streaks of 
the nepheline-syenite are distinguished by large amounts of titano-mag- 
netite, abundant apatite, many silicates of iron and magnesium, as well as 
the absence of feldspar and, ordinarily, also of titanitc, nepheline and can- 
crinite. Some portions are so rich in titano-magnetite as to be workable. 
Such an ore from the Tryg mine had, according to A. Tamm, the fol- 
lowing composition : 

SiO, 3.10 

TiO. 12.14 

AljOa Trace. 

FeO 8.95 

Fe,03 64.38 

MnO. 1.15 

CaO 2.30 

MgC) 8.00 

S 0.07 

P^Oj Trace. 

Total 100.09 

An occurrence in Brazil, which possibly may be much younger in age, 
is most naturally mentioned here. According to 0. A. Derby' and E. 
Hussak,* the magnetic deposits of the Jacupiranga and Ipanema mines in 
the province of Sao Paulo are segregations in granular pyroxenic rocks. The 
deposits of magnetite-pyroxenite (jacupirangite) with 60 to 70% of mag- 
netite are, moreover, closely connected by transition forms with nepheline 

^ G. H. Williams: 'The Iron Ore and Emerv in the Cortlandt Norites.' Am. 
Jour. Sn\, Ser. Ill, Vol. XXXITI, 1887, p. 194.* 

'A. G. Ilftgbom: 'On the Nepheline-Svenite Area of the Island of Aln6.' Geol. 
Fdren. Fork., Vol. XVTI, 1895, pp. 100-214. 

' O. A. Derby: 'On Nepheline Rocks in Brazil.* Quart. Journ. Geol. Soc., 1891, 
Vol. XLVII, p. 251. 

* E. Huasak : 'On Brazilite,' etc. Neuea Jahrhuch f. Min., 1892, Vol. II. 



86 THE NATURE OF ORE DEPOSITS. 

Tocke. The iron-bearing streaks also contain, besidee magnetite and pyror- 
eoe, nepheline, perofskite and apatite, as well as brazilite, a tantalo- 
niobate. 

4. Segregations of Titanic Iron Ore in Qahhro- Bocks. 
Segregations of titanic iron ore in gabbro are less numerous than the 
magnetites just described. Snch occurrences have been described in great de- 
tail by J. H. L. Yogt* and Kolderup, from whose description the following 
abstract is given : 

The Titanic Iron Ore Deposits of Ekeraundsoggendal. 

In Bouthem Norway, in the Ekcrsund-Soggendal district, the crystalline 
schists are broken tiiiough by a norite intrusion forming a mass 1,200 
square kilometers in extent. The eruptive rock shows a great variety of de- 
velopment with all possible transitions between pure labradorite and norltes 
rich in hyperathcne, apatite and enstatite-granite or bronaito-granite. 




Fig. 3.— Section tliroutsli the Blaafjeld. (VoRt.) 
1, labradorite; np, dikea of norite-pegniBitite: t, titanic iron or«. 

The labradorite contains veins and nostg of pure titanic iron ore up to 
masses of 11 meters in thickm'ss and 50 meters in length, as at BlaafjeM. 
illustrated in Fig. 3 after Vogt. The boundary between the ore and 
the labradorite is sometimes sharp, sometimes the reverse. Furthermore, 
the labradorite is traversed by dikes of a norite very rich in titanic iron 
ore. The rock of these menacconite-norite lodes consists of a granular crj's- 
tallinc aggregate of titanic iron ore, hypersthono ami some labradorite. It 
contains as Bceessories, chrome-spinel, iroh pyrite and verv scanty apatite. 
The large lode (Storganpen) about 3 kilometers long ami 30 to 70 kilo- 
meters wide, which is represented in Fig. 4. contains on an average 40% 
of titanic iron ore, and in some of its dark bands parallel to the selvage 
even "JO to 80 per cent. 



Aho. 'Oin (lannclse af jemmnim forrkomster. ' ChriBtiania. 1892. Also 
Hildunevoii ErztncprftAllen. ' Zeil, j. Prak. Ceol.. 1S06, p. 6. Kolderup; 'The 
Labrador rocks of West Norwny. Bergen's -Vug. Aarbog, 1896. No. 5, pp. 158-181. 



MAOMATIC 3E0BE0ATI0N8. 



27 



5. Segregations of Chrome Iron Ore in Olivine Roch and Serpentinet. 

It hae been koown for a long time that all large deposits of chrome iron 
ore' are associated with serpentiDe. It might be readily imagined that all 
these ores were segregated during the eerpentinization of olivine rocks. In- ' 
deed, it is probable that a part of the chromite masses enclosed in serpeo- 
tines was formed during this process of rock alteration, since it is known 
that certain original ingredients common in olivine rocks, especially chrome 
diopside and chrome spinel, or picotite, contain chromine in considerable 
amount. Just as magnetite is segregated during the alteration of iroo- 




Fig. 4. — ProBle through the Storg&ng. (Vogt.) 
1, laboradorite; in, Umcnite-norite with dark streaks very rich in on. 



bearing silicates, as, for example, of olivine into serpentine, so in the de- 
composition of chrome diopside, and other chromine containing silicates, 
chrome iron ore may be formed. However, this origin, as already noted, 
holds true for only a part of these orts, not for all. On the contrary, the 
discovery of segregations of chromium ores in entirely fresh olivine rocks 
proves that in the main the chrome iron ore represents a segregation in the 
original magnia. This has been shown very convincingly by Vogt*. 

The most important chrome iron mines, arranged according to their ap- 
proximate figures of production, are scattered over the earth at the follow- 
ing places: In Asia Minor' ( Harmand jyk, Brussa, vicinity of Smyrna); 
in the Ural (district of Ekaterinburg and Nizhni Tagilsk) ; in California; 
in North Carolina (.\phe and Clay counties) ; in Pennsylvania and Mary- 
land; in New Caledonia (Tiobaghi Mountains at Mount Dore) ; in New 
Zealand; in Greece (Burdaly and Thessaly on Skyros) ; in Styria (Krau- 

' Accordinc to Vopt tlip total anniiBl production of chrome iron ore for the entire 
world is onlv 20,000 ton*'. Tt is used for chrome steel, dvein(c, et<'. (The TJ. S. imports 
tor 1902 amounted to 20,000 tons;the world's production to 30.000 f«ns.—W. H,W.) 

>J. H. I,. Vopt: 'Zur nasBificstion der Erivorkommen,' ZHf. I. Prak. Gfol.. 
1894, p. 384. 

'K.E. Weiss: 'LaKerstAttenim West. AnatoIien,'Zn"(,/.Pnit. Geo/., 1901, p. ZM. 



28 



THE NATURE OF ORE DEPOSITS. 



bath) ; in Bosnia (Dubostica) ; and in Norway (island of Ucstmando^ vi- 
cinity of Roros). Within the German Empire the inconsiderable occurrences 
of Silberg and Grochau in Silesia are the only ones known. 




Fig. 5. — Section of a segregation band of chromitiferous olivine rock in the 

saxonite of Varnasfjeld. (Vogt.) 

Length of lode 40 to 50 meters; thickness 0.1-0.8 meters . 



^T^ 



■B*^ 







• B t t ^-IP^^^ • • ■ t 



> . . .; ,• .;,; •, ', /• • • '..,.. • • • 



Fig. 6.— Profile of a si^grcgation band (streak) of pure chromite and cliromitiferoua 
olivine rock in saxonite; streaks rich in enstatite with nests of chromite seen 
below. Ramberg on Uestmando. (Vogt.) 

Streak lode, 5 to 7 meters long; 0.5 to 0.8 meters thick. 

Under this heading we will merely mention a few instances that have 
been accurately investigated. 



^AOMATIC SEORKGATIONS. 29 

From a genetic jioiiit of view ilifiiktily the most interesting are the Nor- 
wegian oecurreniH* studied l)y \'ogt', 

(a) The Chrome DepopiU uf Hestiuando and Other Localities in Norway. 

The island of Heetinando lies in northern Norway under the Polar Circle. 
Here the gneisx rock is intruded by at least a dozen small stocks 
of olivine rock, at nio«t, O.U mile in diameter. Tliey consist of olivine, en- 
statite, chrome-spinel and chromite. Sometimes they also contain a color- 
leas or greenish actinolite, various mica-like minerals and as secondary 




Fig. 7.— cliromilKerous olivine rock of Kamberg. (Eiiiarfjed HO timcB.) 
o, olivine; ch, chromite. 

formations magnesite and talc. According to the usual petrographic classi- 
fication the rock would have to be called a saxonite. It varies from enstatite- 
poor to enstatitc-rich rocks, bo that the extreme types might be designated 
as cnstatite-bearing dunite and cnstatito rock. Within these olivine rocks 
the chrome iron ore forms streak-like, that is to eay, ill-defined bands and 
Itunps, or lode-liko zones consisting of many such lumps as shown in Fig. 
6 and 6, after Vopt. On the boundaries of such segregations, where the 
chromite masses are shown to be connected by transitions with the normal 
olivine rock, the microscope reveals the chromite as shown in Fig. 7, with 
well developed erv'stalline forms defined against the olivine. The segrega- 
tion of ore must undoubtedly have taken place before the crystallization 
of the olivine. 

From observations upon about 40 chromite deposits in olivine rock or 

' J. H. L. VofTt: Zfit. f. Prak. Geol., 189-1. p. 3S,a. 



30 THE NATURE OF ORE DEPOSITS. 

serpentine in Norway, Vogt infers that the size of the ore occurrences is 
about proportional to the magnitude of the respective eruptive stocks; 
thus the largest orebodies are found at Feragen and Bodhammer, near 
Horos, where they have been traced to a depth of about 50 meters, being at 
the same time within the largest serpentine fields.^ 

(b) The Chromite Ore Deposit of Krcmbath in Upper Styria, 

These conditions also obtain at the well known Kraubath' deposits whoee 
genesis has been recently studied and explained. 

The chromite ores of Kraubath, according to F. Ryba, are associated with 
an olivine rock, forming the remnant of an intrusive mass that rests un- 
confomiably on hornblende gneiss. The rock consists mainly of olivine 
and chromite, and hence must be called dunite. At some points, however, 
owing to the occurrence of bronzite, it passes over into chromite-harzburgite, 
which also contains some chrome diopside. As secondary alteration prod- 
ucts serpentine masses occur with magnetite and a little brown hematite. 

On the right bank of the Mur in the Sommergraben, where the chrome 
mining industry was carried on, the dunite or the chrome-harzburgite is so 
little serpentinized that it shows perfectly the character of the olivine rock 
even to the naked eye. The chromite is scattered through it irregularly, 
for the most part in octahedrons with more or less rounded edges; more 
rarely these crystals are crowded closer together, or the chrome iron ore 
occurs in irregular compact segregations or nests, which have been the ob- 
jects of much prospect work and long-continued but unsuccessful mining. 

The occurrence of the chromite in perfectly fresh olivine, rock is also 
good proof of the magmatic segregation of the ore, the thin sections show- 
ing distinctly that the olivine must have been crystallized out later than 
the larger chromite grains, which look as if they were broken. 

G. Tin-Stone as a Primary Segregation in Granitic Rocks, 

Besides the occurrences of tin-stone as a constant ingredient of greisen 
(granite without feldspar) which is a rock of secondary origin, this ore is 
also a primary component of many granites, as, for example, the tourmaline- 
granite of Eibenstock of the Greifenstein and of Altenberg in the Erzge- 

* Compare A. Helland: *0m Kromjernsten i Serpentine/ Vidensk. Selk. Fork,, 1873. 

' A. Miller von Hauenfels: 'Bericht iiber die geopn^. Erforschung der Umgebung 
von St. Michael u. Kraubath, V. Jahresber. die peogn. mont. V. f. Obersteiermark, 
pp. 53-76. Also ' Nutzbaren Min.,' etc. B. u. H. Jahrb. der k. k. Bergakademie, 
1864, Vol. XIII, pp. 214-217. H. H6fer: 'Anal, mehrerer Magnesia ges. der Ober'k,' 
Jahrb. d. k. k. geol. R. A., 1866, pp. 443-446. A. Kahl: 'Der Chrombergbau von 
Kraubath,' Berg u. Hutten Jahrb , 1869, Vol. XVII. pp. 266-281. H. Wieser: 'Olivin 
fels von Kraubath,' Tschermak's Min. Mitth,, 1872, p. 79. F. Ryba: 'Beitragzur 
Genesis der Chromeisenerzlagerstatten bei Kraubath/ ZeiU /. Prok, OeoL, 1900, pp. 
337-341. 



MAOMATIC SEOREOATIONS. 31 

birge. However, these examples have as yet no economic importance, except 
in so far as the small original granules of these granites, upon the decay 
of the mother rock, concentrate in and enrich the residual gravels whose 
chief tin content is, however, derived mainly from the greisen zones. There 
are no occurrences of primary tin-stone in a granitic rock which is rich 
enough to mine. A supposed example of this kind which proved an eco- 
nomic failure is found in South Dakota. 

The Etta Knob Tin Deposit of the Black mils, Dakota. 

Etta Knob, situated in about the middle of the Black Hills, consists, ac- 
cording to Blake*, of gametiferous mica schist, with intervening quartzitic 
beds, broken through by a granite stock whose nearly circular outcrop meas- 
ures 30 to 60 meters in diameter. By prospecting it was ascertained that 
this stock is an upright pillar-shaped mass with a pronounced concentric 
structure. Next to the country rock there is a sharply defined peripheral 
zone of. dark mica rock with large plates of muscovite, which are workable. 

Next inward follows a band of compact quartz, with irregular bunches 
of compact albite and orthoclase, as well as enormous crystals (up to 12 
meters in length!) of spodumene, which lie in the midst of a fine-grained, 
scaly mass consisting essentially of mica and albite. In this complex mass 
the cassiterite is interspersed in granules or imperfectly developed crystals, 
the ore forming about 2.6% of the aggregate. The association of a lithion- 
pyroxene with tin-stone is also reported from several localities in Maine 
(E. Richards). Besides the minerals named, the tin-stone of Etta Knob 
is also accompanied by the following; Apatite, triphyline, tantalitc, colum- 
bite, arsenical pyrite and copper glance. Besides tin ore spodumene has 
also been mined. 

The Etta Knob rock is a pegmatite which cannot be assumed to have orig- 
inated as a segregation of the normal granite, but shows, on the contrary, 
evidence that water had a decided part in its formation. 

'" (C) Seoreoations of Sulphidic and Arsenical Ores. 

The sporadic occurrence of small particles of pyrite in volcanic and plu- 
tonic rocks is well known. Iron pyrite in particular is one of the most 
widely distributed accessory constituents of many eruptive rocks, especially 
in diabase, diorite and syenite. It appears in entirely fresh undecomposed 
rocks of this kind under such conditions of microscopic association with 

» W. P. Blake: 'Tin Ore Deposits of the Black Hills,' Trans. Am. Inst. Min. Eng., 
1885, Vol. XIII, p. 691. W. O. Crosby: 'Geology of the Black Hills/ etc., Proc. 
Boiton Society Nat. Hist., Vol. XXIII. 



32 THE NATURE OF ORE DEPOSITS. 

the other constituents that there can be no doubt as to its primary nature. 
At times the iron pyrite is replaced by copper pyrite. Thus, the tourmaline- 
granite of Predazzo, the diabases of the eastern Harz and even the younger 
lavas of the Alban Mountains at Cai>o di Bove carry granules of copper 
pyrite. Variegated copper ore is known from the tourmaline-granite of 
Kittlisvand in the Norwegian district of Nummedalen. Various sulphidic 
copper ores also occur disseminated through the syenite of the Plauen area 
near Dresden, more especially in the dark streaks rich in augite and horn- 
blende, in which native copper, copper pyrite and copper glance often occur, 
besides other secondary products. Pyrrhotite is often found interspersed 
in gabbros; it is also observed sometimes in basalts, as at the Landberg, 
near Tharandt, and on the west coast of Greenland, on Disko, etc. Since, 
moreover, small crystals of copper pyrite, and, according to J. Scheerer, 
also another mineral of the same chemical composition, but rhombic form, 
become segregated before our eyes in smelting operations upon a slow 
cooling of a siliceous slag, it appears that the magmatic segregation of large 
bunches, stockiS, primary stringers or streaks in the midst of eruptive rocks 
is a priori both possible and probable. According to L. De Launay^ certain 
solvents existing under pressure in the magma, such as liquid carbonic 
acid, alkaline chlorides, fluorides or sulphates, perhaps also water vapor, 
have taken part in the concentration of such ores from the magma. It is 
true, however, that the evidence that the deposits of this class are direct 
segregations from a molten magma, is not as clear and conclusive as it is 
in the examples of the groups already noted. For many occurrences which 
are regarded by various authors as direct segregations from eruptive rocks, 
it will probably be necessary to allow at least a secondary concentration of 
the ores in the aqueous way, with a partial local transfer of material and 
an impregnation of the country rock, etc. The great mobility of the sul- 
phide ores, as known from our observation upon them in veins, renders it 
exceedingly difficult to obtain a clear insight into this matter, especially as 
a special and detailed microscopic study of the problem has not been made. 
For these reasons there is grave doubt about the true genesis of such de- 
posits. This is true particularly of the first of the deposits described in 
this chapter, as magmatic deposits. Recent microscopic study has indeed 
proved the Sudbury Canada deposits to be metasomatic replacements. There 
is, therefore, not a single example of magmatic copper deposits known in 
North America. 

* Ann. d. Mines, 18Q7, Vol. XII, p. 119 et aeq. 



MAGMATIC SEOREOATIONS. 83 

1. Deposits of Nickel and Copper Ores in Connection with Oabbro Rocks or 

Diabases and Their Metamorphic Derivatives. 

The deposits of this class, consisting of nickel-bearing pyrrhotite, chalco- 
pyrite and iron pyrite found in Xorway, Canada and some other countries, 
have in recent years attracted general attention, particularly as a result of 
the work of J. H. L. Vogt*. A brief description of the Norwegian and 
Swedish occurrences studied by this author is given first, although from 
an economic point of view they are far inferior to those of Canada. 

(a) The Norwegian Nickel Ore Deposits. 

Norway contains, according to Vogt, some 40 intrusive masses of gabbro 
which are distributed uniformly over the country. These rocks are char- 
acterized by the presence of nickel ore, whose genetic connection with the 
gabbro was first described by Th. Kyerulf and T. and J. Dahll. These rock 
masses, nearly all of which have been strongly altered by regional meta- 
morphism, were, in most cases, formerly regarded as cr}'stalline schists of 
the same age as the gneisses about them, and the theories concerning the ore 
deposits were based on this supposition. It is necessary, therefore, to note 
the decisive observations which convinced the Norwegian investigators of 
the eruptive nature of this gabbro. The facts are as follows : 

1. The boundary between these gabbros and the gneisses or the Cambro- 
Silurian regional-metamorphic schists is in places very sharply defined. 

2. The other rock strata are often truncated and stop at the boundaries 
of the gabbro. 

3. Blocks of schist occur enclosed in. the gabbro. 

4. Marginal facies, such as orbicular norites, have sometimes been ob- 
served. 

5. Finally, younger dikes of normal and of pegmatitic gabbro occurring 
in the gabbro itself bear witness as "subsequent intrusions" and prove the 
eruptive nature of all these rocks. Their present petrographic character is, 
it is true, very unlike the prototype, being commonly that of an amphibolite 
or garnet amphibolite. 

Where the original character of these gabbros has not been entirely 
obliterated by regional metamorphism it is seen that they were at first either 
olivine gabbros with ophitic structure or true granular-crystalline norites. 
The ores show a preference for the latter rocks which may or may not carry 
olivine and show transitions to olivine gabbros. 

* J. H. L. Vopi; : 'Nickel forekomst^r op nickel producktion, ' GeoL Fdren. Fdrh, 1892. 
pp. 315-338. Also 'Bildung von Erzlaperstatten dureh DifFerentiationsprocesse in 
basischen Eniptivmagmata, ' II, Nickelsulfiderze. Zeit. f. Prak, Geol,, 1893, pp. 125- 
143,257-284. 



34 THE NATURE OF ORE DEPOSITS. 

The ores connected with the norites consiBt of : 

(1) Magnetic pyrite with 2 to 5%, rarely as high as 10%, of nickel and 
some cobalt; (2) iron pyrite with some nickel and cobalt; (3) copper 
pyrite with up to 0.5% nickel and cobalt; (4) titanic iron ore. 




Fig. 8. — Sketch-niap of the Erteli mineral region. (Vogt.) 
I, I'O'i'tA'line schists; on, olivine noritc and other v&rieties o( norite; g, granite; 




(■'iff. 9. — Skelcli-iiiBp of the Meinkjar iiiimiig field. (Voct.) 
S< g"^y g'leias; rg, red gneiss; li, Iiornblende schist; n, norite; m, orebodies. 

The magnetic pyrite always greatly predom i nates ; the iron pyrite Bome- 
timt'S appears to have been tiegregatcd earlier tlian tlie magnetic pyrite, 



MAGMATIG SEGREGATIONS. 35 

since it is embodied in the latter in the form of cubic crystals. Only in 
very rare cases do we also find iron-Dickei pyrite and some other nickel anl- 
phides proper. 

mimmiTTTnl^ j|:^r;;Vrh'?^P^nTTTTTTD»trt7TnotTl 
ProfUI 

'e of Meinkjjir. (Compare 



All the ores mentioned are also present in very small amount in fine 
particles disseminated through the norntal norite, while in the deposits 
proper they form com])a(-t ore maBsos up to 120 or even 200 meters (393- 
65(i ft.) in diameter. These masses have a very irregular shape and are evi- 
dently associated with the contact between the gabbroe and the country 




Pig. 12. — Section of a pyr 
Erteli mine No. 1. (Vofit.) 
norite; )t, gneiss ;m. pyrite mi 
Height of section, 5 meters. 



Fig. 13. — Section of a part of a norite contact 
in tlie Meinkj^ir field. (Voet.) Explanation 
the Eiame as in Fig. 12. Height of section, 



rock. At times they arc also found about the borders of enclosed blocks of 
country rock. 

Both these facts are clearly illustratcil in Figuro 8 (after Vogt), which 
shows the distribution of the ore masses in the Erteli mining field in the 



36 THE NATURE OF ORE DEPOSITS. 

district of Bingerike, northweet of Drammen. The norite maasiTe of that 
locality has a longitudinal diameter of about 600 meters. Not less in- 
Btructive arc the figures y-11 of the Meinkjar mine field (after Vogt). 

In some places the pyrite inasi* passes very gradually into norites poor io 
pyrite, and finally into almost normal non-pyritiferous norites. In such 
transition rocks the pyrite often appears in the form of a very irregular 
venation in the midst of the mass of silicates. Furthennore, the pyrite, as 
pointed out hy Vogti forms real stringers and lodes which branch away 
from the orebodics proper, either into the norite or into the country rock, 
and may also enclose fragments of both. The detailed profile (from 
Vogt) of the Erteli mine No. 1, in Figure 12, shows these relations very 
ditttinctly. 




Fig. 14. — Nickel ore of Varallo under the niicroHcoiKt, with fifty-fold enlargemeni, 

d, Uiallage; p, plagioclasc (with cros,'^ nicols); m, mngiiclic' p}'nte. 

A second profile of the sniijc kind from Vogt, from the Itleinkjar mine in 
Banile, northwest of the island of Kragero, Figure i;t, shows how the pyrite 
has penetrated the neighboring gneiss parallel to tjie stratification so that 
we here find perfectly isolated patches of are and fahlband-like impregna- 
tions of larger rock bodies. 

According to Vogt the pyrite is a direct differentiation product of the 
noritic magma, a fractional part of the magma whose melting point is some- 
what lower than that of the silicates which compose the normal rock. The 
pyrrhotite of the original magma, with the other metallic constituentB, is 
supposed to have been concentrated in about the same way as in metallurgi' 
ca] furnaces, the copper and lead separate from the slag. The silicates are 



MAOMATIC SEGREGATIONS. 37 

supposed to have formed after this metallic Begregation, aod the pyritc, 
which was still fluid, filled the spaces between the crystals of silicate 
minerals aod was itself congealed upon further lowering of temperature. 

There are serious objections, however, to the theor}' that these ore masses 
in their present state are simple magmatic segregations. First of all the 
penetration of molten sulphides so far into the cooler country rock, as 
appears from Figures II and 13, Is very difficult to explain in accordance 
with the laws of physics. Still more serious doubts are suggested by the 
condition of the ore-bearing rock bodies, as revealed hy microscopic 
examination. 

Cases occur, indeed, in which evidently corroded remnants of the normal 
silicates of the gabbros lie embedded in the mass of the ore as if they were 




Fig. 15. — Ore-bearing norite from Solum Schurf, northwest of Erteli. (Enlarged 50 
times.) e, eiiatatite; p, plagiodoae; h, hornblende; g, gurnet; m, magnetic pyrite. 

earlier segregations which bad been once more half melted down. In 
Figure 14 we give such an occurrence from Varallo, to be mentioned later 
on, and we admit that similar ones may be found in IJorway, as in fact 
appears from Vogt's description. The corrosion of the plagioclase and 
diallage which we here observe, however, probably is due to solution by 
water, and this hypothesis is supported by the observation that in most 
cases the ore deposits are found in those parts of the gabbros that have been 
subjected to very strong regional metamorphism, and that in such cases the 
segregation of ore is shown to have taken plaop simultaneously with, or sub- 
sequent to, the regional metamorphism. The gabbro and norite patches 
against which the ores rest directly, or with which they are intersperpcd. 



38 THE NATURE OF ORE DEPOSITS. 

have slmoet always been more or less completely transformed into am- 
phibolitee and gametiferous amphibolites. Figures 15 and 16 ehoir this 
process not quite terminated. 

Here we still have remnants of enstatite or diaUage. In Figure 15, how- 
ever, the ores prove to be yonnger than the two products of this later trans- 
formation, the green hornblende and the garnet. In Figure 16 the ore ap- 
pears to have been segregated simultaneously with the garnets, and pene- 
trates the older diallage only along fissures. We believe, therefore, that the 
real and economically important concentration of ike svlphides in the 
gabbro rocks took place only during the period of regional metamorphism 
and thai it was effected by aqueous solution. What was the original 




R(f. 16. — Ore-bearinK gabbro from Erteli-l'riistcliaug. (Enlarged 50 times.) 
d, diallogc; p. plapoclase ; a, apatite; h, horublenrte; lieh, chloritiied lionibleiide; 
g, garnet; in, niagiielic pyrite, 

form and distribution of the metallic compounds in question in these 
eruptive rocks; whether they were very finely and uniformly disseminated 
pyrite partich's, or chemical components of the hisilicates, cannot at 
present be decided. This will require a much more thorough petrographie 
investigation than any yet made. 

The production of Norway attained its ma.ximum in 187C, with 42,500 
tons of ore containing 3C0 tons of nickel, the favorable conditions at that 
time permitting the smelting of ores with only 0.0 to IJtfo nickel. Accord- 
ing to Vogt, 330,000 tons of nickel ore were produced between 1850 and 
1893. 

Analogous deposits occur in the neighboring kingdom of Sweden. The 
best known is Klefva in Smaland, whose nickel ores, by the way, show a 



MAOMATIC SEOREOATIONS. 39 

very small content in platinum^ iridium, and rhodium.* To this class belong 
also Kusa in Dalarne, and Ruda in Ostergotland. 

(b) The Nickel Ore Deposits of Varallo, Italy. 

A second European occurrence of such deposits exists at Varallo^ in Pied- 
mont in the valley of Sesia. The gneisses and mica schists of the Monte Rosa 
area are traversed by an intrusive mass of norite about 20 kilometers long 
and 4 kilometers broad. The rock is an ordinary norite showing transitions 
to gabbro and to an olivine norite, but it has been largely altered by regional 
metamorphism into a hornblende rock like those of Norway. Large masses 
of magnetite found at the gneiss-gabbro contact in the Cevia and Sella 
Bassa mines were found to contain 4 to 5% of nickel and cobalt, and to 
hold pyrite and copper pyrite. The amount of nickel (including cobalt) in 
the ores formerly smelted in the Sesia* and Scopello furnaces was 1.2 to 
1.5%. The cobalt content is somewhat higher than in Norway, the ratio be- 
ing 100 Ni : 50 Co : 40-50 Cu. The mines were worked from the end of the 
sixties to the end of the seventies. The Sesia mine belonged to the Saxon 
Blue Color Works. 

From a genetic point of view what has been said of Norway is also true of 
Varallo. Compare also Figure 14. 

s (c) The Nickel Ore Deposits of Sudbury in Canada. 

The Canadian nickel deposits are the most important deposits known of 
this kind. They have been described by numerous authors, but most of the 
papers deal with general and not the structural or genetic conditions'. 

The town of Sudbury is in northern Ontario on the line of the Canadian 
Pacific Railway, in the midst of an area formed ma/inly of Huronian schists, 

^ B. Santesson : 'Nikkdmalm fyndigheten vid Klefva.' Geol. Foren Fork., Vol. 
IX, 107, 1887, pp. 66-73. 

'A. W. Stelzner: 'Referat eines Vortrages,' Bera u. Hiitten Zeit., 1877, p. 87. 
M. Badoreaux: 'M^moire sur la metallurgie du Nickel.' Ann. d. Mines, 1877, 
M^moires, Vol. XII, p. 237. J. H. L. Vogt : 'Varallo in Piedmont, ' Zfi7. /. Prak, Geol, 
1893, p. 257. 

*T. G. Bonnev: 'Notes on a part of Huronian series of Sudburv,' etc., Quart. 
Janrn. Geol. Soc, 1888, pp. 32-44. W. H. Merritt: 'The Minerals of Ontario.* 




Bell : 'The Nickel and Copper Deposits of the Sudburv district. ' Bull. Geol. Soc. Am., 
1891, Vol. II, pp. 125-137. Also 'Report on the Sudburv mining district.' Geol. 
Sun-ey of Canada, 1891. H. B. v. Foullon: 'Ueber einipe Nickelerzvorkommen. ' 
Jahrb. d. k. k. peol. Reichsanst, Vienna, 1892. J. H. L. Voirt: 'BildunR von Erzlaper- 
statten,' etc. Zeit. /. Prak. Geol, 1893, pp. 128, 257. G. R. Mickle: 'The relation 
between Pyrrhotite. Gan^e.and the accompanying Rocks of the Sudburv District. * 
Rudbunj Journal, 1894. F. A. Adams: 'On the i|E:neou8 origin of certain ore deposits.' 
Min. Assoc. Prov. of Quebec, Jan., 1894. F. L. Walker: Quart. Joum. Geol. Soc.. 
Vol. LIII, No. 209, 1897, pp. 40-65. A. P. Coleman : Report, Bureau of Mines, Ontario, 
1903, pp. 235-303. Also 1904, pp 192-224. 



40 THE NATURE OF ORE DEPOSITS. 

extending from the north shore of Lake Huron northeast to Lake Mistas- 
sini. According to Coleman, the nickel deposits are confined to the outer, 
basic edges and offshoots of a mass of igneous rock. A nearly continuous 
band of this rock, about 2 miles wide, forms a rude ellipse 36 miles long 
and 8 miles across, enclosing an area of tuffs, sandstones and slates of Cam- 
brian or Upper Huronian age. Outside of this ellipse the rocks are of 
Laurentian or Lower Huronian age, a part of the so-called basal complex. 
The igneous rock presents a well defined gradation from norite (now 
largely altered to diorite) on its outer edge, to the quartz syenite and granite 
of the inner border. The norite (a hypersthene gabbro) contains scattered 
grains of bluish quartz and black mica. The ore deposits are of two types, 
(1) those "crowded into bay-like indentations in the adjacent rocks," (2) 
those "strung out along tlie narrow offshoots of the norite like sausages on 
a string, but with a long piece of string between them." The deposits are 
prevailingly lenticular, pinching out in both directions, and conforming to 
the general strike of the schists. The orebodies are much larger than those 
of the Scandinavian peninsula. 

The Sudbury ores consist mainly of a mixture of pyrrhotite and chal- 
copyrite intimately associated with more or less country rock. The nickel 
occurs in the pyrrhotite, varying in amount from 2 to 5.5%, ordinarily 4 to 
4.6%. The nickel occurs in the pyrrhotite as pentlandite (Fe-f-Ni)S. The 
copper pyrite is free from nickel. Occasionally polydymite (with 43% Ni) 
and millerite (64% Ni) occur in the ore, and at times patches of titani- 
ferous magnetite have been observed. From the residue of weathered ores 
T. L. Sperry* isolated the interesting mineral sperrylit^?, a platinum 
arsenide, with traces of rhodium, palladium, and antimony. Furthermore, 
the Canadian matte, like that of Klefva and Ringerike-, shows a small 
amount of platinum (0.25 to 0.60 oz. per ton) and palladium, as well as 
traces of iridium and osmium. Associated with the sperrylite some tinstone 
is found. Some ores contain small quantities of gold. The sperrylite 
occurs with the chalcopyrite in the unaltered sulphide ore. 

According to A. McCharles* it has been found that the richest ores occur 
in the smaller offshoots of gabbro-diorite, and that the larger massives, with 
few exceptions, yield no workable ores at all. The gold, platinum, and the 
other accessory metals are contained not in the magnetic pyrite, but in the 
copper pyrite. 

In their structure and in their relation to the countrv rock the Canadian 
deposits present a great similarity to those of Xorway and Piedmont. The 

» Am. Jour. Sci.. Vol. XXXVII, 1S99. 

' Voirt : ' Phitinireljah in \on\'o«?i.schen Xicki^lerz. ' Zt'i't. /. Prnk. GeoL, pp. 258-260, 

' *Th«^ Minornl ludustn-/ Vol. VII. 1899, ]>. .524. 



MAOMATW SEGREGATIONS. 



4X 



Sudbury ores, moreover, contain peculiar breccias in which eharp- 
edged or rounded nxik fragments lie imbedded in a paste consisting 
essentially of magnetic pyrite and some copper pyrite. The iragroents con- 
sist of gabbro in highly varying stages of regional metamorphosis. Besides 
those which consist of a micro-breccia of minute diallage and plagioclasc 
splinters, there are others which have been completely amphibolitized, or 
also show a distinct scbiBtose structure. All are, moreover, more or less 




I'lR. IT.^Polifihed ore Specimen from Murray mine nearSudhmy. 
Two-thirda natural size. Guhhro fragments more or less transformed into horn- 
blende schist in the midst of tbe ore mixture, which appears uniformly light colored. 

impregnated with ore. Figure 17 shows an instance of such an occurrence, 
genetically interesting, from the Murray mine. Such specimens prove 
that the segregation of the magnetic pyrite and copper pyrite in their pres- 
ent condition took- place dttrinij or after the dyttamo-metamorphosis of the 
gabbro rucks of that locality, and nut by means of a magtnalic differentia- 
(ion. This baa been confirmed by the very careful detailed work of C. W. 
Dickson, who says that the evidence points to the secondary formation of 
the Sudbury orebodies as replacements along crushed and faulted zones'. 



1WI3, 



■ The Ore Deposits of .'iiidhiirj-. Cftr 



I. fn»il. Min. En^-, February, 



42 THE NATURE OF ORE DEPOSITS. 

The ore deposits of the Sudbury district are occasionally traversed by 
younger dikes of an olivine diabase^ in which analysis has demon- 
strated the presence of NiO (0.027%) and CoO (0.00595)) which was 
probably taken up secondarily (Walker). 

The first deposit worked at Sudbury, the Copper Cliflf mine, at first 
produced only copper, as indicated by the name. Later, toward the end of 
the eighties, the presence of a workable amount of nickel was found in the 
associated magnetic pyrite. This discovery in what had been waste ore at 
once caused the establishment of a very active nickel-ore mining industry. 
In the Sudbury district in 1903, a total of 220,937 tons of ore carrying 
3.16% nickel were smelted, of which the greater portion came from the 
Creighton mine. 

In the United States, the Lancaster Gap mine in Pennsylvania is, accord- 
ing to Kemp, the most important nickel deposit in the country. It seems 
to belong to the group just treated, being also situated at the boundary 
between a hornblende rock and crystalline schists. 

Similar nickel ore deposits occur in other basic eruptive rocks altered by 
dynamo-metamorphism, especially in diabases. 

(d) Deposits of Nickeliferous Pyrrhotite at Schweidrich near Schluckenau, 
in northeastern Bohemia, and at Sohland, in Saxony. 

At Schweidrich the Lusatian granitite is traversed by a great west-north- 
west dike of a coarse-grained diabase, fine-grained at the borders, whose 
normal rock carries some primary hornblende and biotite besides the 
ordinary constituents. Near the northern wall of the dike this diabase is 
altered to a rock consisting mainly of secondary uralitic green hornblende, 
but at the same time more or less impregnated with nickeliferous magnetic 
pyrite and some iron pyrite. Under the microscope the se^egation of the 
ores in many cases is distinctly seen to be younger than the formation of 
this secondary hornblende. The adjoining rock, a somewhat decomposed 
granite, is also impregnated with the same ores to a distance of more than 
one meter. Patches of compact ore occurring more rarely in the diabase 
contained, according to von FouUon^, 7.8% nickel, 2.90% copper, 49.90% 
iron. No mining is going on there at present. At Aeusserst-Mittel- 
Sohland, north of Schluckenau, on the boundary betweim Saxony and 
Bohemia, the digging of a well in 1900 led to the discovery of an entirely 
analogous but much richer deposit. A dike 10 m. (33 ft.) thick of protero- 
base* rich in biotite traverses the Lusatian granite in a west-northwest 

' H. B. v. Foullon : 'Ueber oini^e Nickplerzvorkommen.' Jahrh. k. k. geol. 
Reichanst, Vienna, 1892, p. 302. Compare O. Herrmann in 'Geol. Maps of Saxony,' 
1897. Hintcrhermdorf-Daubitz sheet, p. 19. 

' A diabase rich in hornblende. 




M AQUATIC SEGREGATIONS. 43 

direction. Along the northern border, this rock has been found to be ore- 
bearing to a distance of about 700 ni. (2,296 ft.) The ores consist of 
nickeiiferous pyrrhotite, some copper pyrite and a little iron pyrite, form- 
ing either a mere impregnation, extending outward as much as half a 
meter into the granite, or as in the Herbergs Fund shaft, a compact ore up 
to 2.5 meters in thickness, dipping north at 75**, like the dike walls, and 
traceable for 20 meters along the strike, and yielding specimen ores with 
an average content of 5% of nickel and about 2% oi copper. In the pro- 
terobase the sulphides are the last materials to crystallize, as in many 
cases fragments of pyroxene and of primary hornblende, which evidently 
have undergone corrosion, are surrounded by the pyritesL On the other 
hand, the pyrites are often seen in the midst of serpentinized pyroxenes, 
with a band of ore running parallel to their contour at a little distance from 
the edge. Very often, also, tlie pyrite is found in the form of thin lamellae 
wedged in between foliations of biotite. 

In the hanging wall of the ore of the Fund shaft there are found in the 
proterobase very remarkable portions, quite rich in spinel and corimdum. 
The rock also carries inclusions of sillimanite. 

Immediately below the gossan of the deposit, which sometimes extends 
down as far as 10 meters, there has been found, as a secondary fissure filling, 
a rich blackish copper ore consisting essentially of copper glance. Recent 
investigations by R. Beck show that the ore was formed at the same time 
as the uraltic hornblende and the ore is regarded as a deposit from thermal 
waters rising as an aftermath of the diabase e^uption^ 

The nickel deposits of Horbach in the Black Forest, concerning which 
but little scientific information is available, possibly should be included 
here, as also the nickel ore of the Hilfe Oottes mine, near Nanzenbach, in 
the Weyerheck, 4 miles (7 km.) northeast of Dillenburg in Nassau^, w^liere 
irregular stocklike masses of iron pyrite, copper pyrite, and nickel arsenide 
are associated with a greatly altered rock of the diabase group. 

(e) Arsenious Nickel Ores in the Serpentine of Malaga, Spain. 

While the widely distributed scxjondary nickel ores found in serpentines 
are treated under another h(»a(ling, the Malaga deposits of arsenical nickel 
are most naturally ineliuliKl here. 

In the Archean strata to the west of that town there are serpentine rocks 
which have resulted from the alteration of an olivine pyroxene rock, and 
from olivine norite, as well a,s from olivine rock (dunites) proper. 

* Zeit. f. Prak. Genl., Feb.. 1904. The Engineering and Mining Journal, 1904, 
Vol. LXXVII, p. 363. 

' H. T.aspevreH: 'T)jis Vorkonimt'ii,' etc. Verhandl, d. Xaturh. Ver zu Bonn. 
1893, Vol. 50, Piute IV, and Ft. 11. p. 451. 



44 



THE MATURE OF ORE DEPOSITS. 



According to F. Gilman' thu upper portions of these serpeDtinee were 
found to contain secondary nickel ores of the pimelite and gamierite type, 
with 1 to 20% of nickel. At greater depth nickel arsenide (nlccolite) 
made its appearance In the following maimer : 

1. Fine chromite grains are cemented by niccolite (see Figures 18 
and 19) ; the bronze mosaic ore exists in nests and veins in fresh serpentine, 
and contains 6 to 20% of nickel. 

2. Crystals of a dark greenish brown augite up to 1 centimeter long are 
cemented by niccolite and chrome iron. 




Hr. IK. --(.'hrotiiite (dark) with iiiiTolite Fie. 19— AiiKilecrj-slaU{bri5lit)cemented 
(bright) from Primere mine; with linht bynirrolite(dark);withincidniitsndiilso 

from above. (F^nlurf^ed 27 times.) traimTnitted light. (Enlarged 10 times.) 



3. Masses of uimltcrud noritt.' soinotinu'S as large as an ostrich egg occur 
in the Ber|>entiDe, which besides its main ingredients (plagioclase and 
rhombic pyroxene) also contains interspersed granules of niccolite and 
chromite and chronic iron ore. Sometimes the niccolite forms a regular 
groundmass iilx)ut the silicad' crystals; more rarely it has been secreted, to- 
gether with chromite, in streaks and bands. 

At times iron pyrite and coppi-r pyrite are found in the ores. The above 
named author considers tjie niccolite (Xi As) as a product of magmatic dif- 
ferentiation. The e.taniple sufifrestfi that fresher rocks with arsenide nickel 
ore also may he expected, as other garnierite deposits arc worked to a greater 
depth. 



MAGMATIG SEGREGATIONS, 45 

2. The Copper Ore Deposits in the Serpentines of Italy. 

According to B. Lotti* the serpentines of Tuscany and Liguria almost all 
contain some copper sulphide, some of the serpentine masses containing 
deposits known for many centuries. According to Lotti three rock types are 
recognized in the strongly serpentinized rocks of this region: altered 
Iherzoliths (olivine rock proper), decomposed olivine gabbros, and trans- 
fonned olivine diabases (called by others melaphyres). These rocks form 
lenticular or stocklike intrusions in Eocene strata, occurring usually in an 
orderly sequence in which the former Iherzolith is below, and the diabase on 
top. It is probable that there were two intrusions, first one of Iherzolith, 
next a second whose magma congealed in the form of gabbro at the bottom, 
and as diabase at the top. In the middle member of this series, the gabbro. 
the following ores are found : pyrite, copper pyrite, bornite, copper glance, 
rarely also blende and galena, all in finely disseminated particles. At some 
points, however, these ores also occur as globular masses or large lumps, 
about which the decomposition of the country rock is apt to be particularly 
pronounced. Authors are at present fairly well agreed that the finely dis- 
tributed ores are original segregations of the magma. On the other hand, 
in regard to the spherical masses and lumps the views are as yet wide apart. 
As described later the character and occurrence of such ore masses indicate 
their origin by secondary concentration of the sulphidic ores into such 
masses. Exact proof seems as yet impracticable. The best authority on 
these formations, B. Lotti, now regards them as original segregations. As a 
special example for this type of deposits we will select the famous locality 
of Monte Catini. 

The Monte Ca/tini Copper Deposit. 

Between the Maremna Marshes and the Apennines in Tuscany there ex- 
tends a hilly country whose numerous wooded summits of eruptive rock over- 
top the gently sloping areas of Tertiary marls. The mine of Caporciano, near 
Monte Catini, situated on one of these hills, is said to have been founded by 
the ancient Etruscans, and in fact the ancient Etruscan town of Felathri, 
now the walled town of Volterra, lies near the mine. The ignegus rocks are 
intruded in the Tertiary strata in the form of a great lens or laccolith. 
Above the Eocene marls and limestones, which form the floor of the 
intrusion, is a strongly serpentinized olivine gabbro forming the base of the 
eruptive series. This occurs as a stock, which in cross-section is three- 
armed, and enveloped by the olivine diabases (melaphyres) of Monte Massi. 
and in part appears intercalated between the diabase and the sedimentary 

* B. Lotti: 'T>a cren^se des pisements cnprin^res des depots ophiolitiques tertiaires 
d ritali^/ Mem. Geol. Soc. Belgium, Vol. Ill, 1899. 



46 



TEE NATURE OF ORE DEPOSITS. 



Etrata. A longitudiDal layer of diabase dividee the gabbro into two ap- 
proximately parallel parts known ae the filnne rosso and the filone bianco, 
both wedging out downward at the point whore the underlying aedimentary 
rocks begin (Figure 20). ■ The serpentine stock is bounded on both sides by 
Blickensidee and its central portion is, moreover, exceedingly fiseured and 
crushed to a fine breccia, probably as a result of the increase of volume on 
serpentinization. Certain parts of the stock resemble a breccia whose frag- 
ments are in part scrpentinized olivine gabbro, in part decomposed olivine 
diabase (Fig. 31 and 33)'. In this breccia are also found concretionary 
secretions of quartz and chalcedony. 




1 prolile throuRh the deposit of Monte Catiiii frojn south-southwest 
to nortli-iiortheast, (Fucha and De I.auuay.) 
8, day elates and calcareous marls of the Eocene; d,olinne diabase; sp. serpentine, 
;, conglomerate, tlie black parts represenlin): ore; k, younjier marls and limestones. 



The ores form bodies of irregular shape and varying size, which are quite 
irregularly distributed in the serpentine, or occur at its contact with the 
above mentioned breccia; some of them are quite isolated (Figure 21); 
others are connected by ore stringers (Figure 23). The isolated ones attain 
a diameter of several meters, while occasional compact masses of copper 

'G. vom Rath: 'Ein Besurh der Kupfergnibe Monte Catini,' etc. Zeit. d. D 
Gfol.. 186.';, pp. 277-310. E. Ueyer; 'Ails Toscana.' Vicuna, 1884. R. Lotti: 'I^ 
miniem cnprifera di Montecatini. ' Boll. Com. Geol.. XV, 1884. A. Schneider: 
'I:aminierHdi Montecatini.' .Append. Riv. Mineraria del ISSfl. B. I.otti : 'Con- 
sidcraiioni sintetiche auUa oroerafiH e siilla geologia delta Catena Metallifera in Toscana,' 
Boll. Com. Geol., Vol. XXIII, 1892. 



MAOMATIC SEGREGATIONS. 



47 



pyrite have been met, having a volume of 6 to 10 cubic meters. Tbe 
majority are rounded bodies coated with a brilliantly polished serpentine- 
like crust. This crust often shows cracks and streaks which record a 
movement in the soft country rock. Such streaks lead often to other orfr 
bodies. 
In the main, these ore boulders or lumps consist of copper pyrite. Fre- 




48 THE NATURE OF ORE DEPOSITS. 

quently, but not always, they show a concentric structure, with a core of 
copper pyritc surrounded by a shell of bornite, often covered by an outer 
crust of pyrite or of copper glance and native copper. Jkloreover, the ser- 
pentine which surrounds the rounded ore masses contains so much ore in a 
finely divided condition that it is worked. The ores of Monte Catini are 
classed as rich ores when the copper content is as high bls 7%; sls lean 
ores when it is but 1.25 to 1.50%. The irregular distribution of the ore 
masses, and their irregular form, together with the absence of continuous 
lodes or beds, has rendered mining very diflScult; nevertheless, it had its 
periods of great prosperity. Some 400 meters east of the main stock and at 
a depth of 150 to 200 meters there is a second bed running east-southeast, 
the so-called Demetrio lode, with copper pyrite, bomite and copper glance. 

According to G. vom Eath the orebodies of Monte Catini were formed 
by a concentration of the metallic sulphides of the original rock during 
their serpentinization. E. Reyer considers the deposit as a lode that subse- 
quently had been strongly dislocated. B. Lotti, as already stated, considers 
the lumps of ore as original segregations. The mining industry of Monte 
Catini, abandoned during the Middle Ages, was resumed in the 15th cen- 
tury, again interrupted, and once more resumed in 1828. It attained its 
maximum of 3,000 tons of ore in 1860. 

Similar, though less important copper ore deposits associated with ser- 
pentine are known on the island of Corsica (Ponte Alle Ix?cchia), in 
ServiaV, in Greece (Epidauros) and in Northern Norway (Hatfjelddal), and 
in Cuba^. 

The deposit of Cava Grande on the Temperino lode, in the Campiglia 
Marittima, which by some is placed in this category, will, in the present 
work, be treated under contact ore deposits. 

3. Th^ Copper Ores of OoJciep in Little Namaqualand. 

According to A. Schenk', the copper ore deposits of Ookiep, formerly 
considered as lodes, are magmatic segregations in a rock consisting almost 
entirely of plagioclase with but little biotite, hornblende and augite, form- 
ing stocklike intrusion in gneiss. The ores contain bornite, chalcopyrite, 
some copper glance, pyrrhotite and molybdenite. The mines have yielded 
as high as 30,000 tons of ore a year, with an average content of 27.5% 
copper. 

* R. Beck and W. Baron v. Fircks: 'Die Kupfererzlagerstatten von Rebelj und 
Wis in Sen-ia. ' Znt. f. Prak. OeoL, 1901 . p. 321. 

' W. H. Weed: Engineering and Afining Journal, Feb. 3, 1905. 

' Engineering and Mining Journal, Feb. 10, 1905. See also Zeit. d. D. 0. G., 1902, 
Vol. Lin,pt. 4,p.64. 




SECTION II. 

BEDDED ORE DEPOSITS. 

Ore deposits of direct sedimentary origin, together with deposits of 
similar form resulting from impregnation and metasomatic replacement of 
sedimentary beds, are grouped together as bedded ore deposits. 

General P'eaturks of Bedded Deposits. 

According to the generally accepted definition of B. von Cotta^, 
•^Accumulations of ore, which lie parallel to the stratification or foliation 
of the rock enclosing them, consequently forming one or more subordinate 
layers between any stratified or foliated (schistose) rock, are called ore 
beds." We may further distinguish between interhedded deposits which 
are overlain by other strata and surficial deposits when there are no over- 
lying beds, as, for example, a bog iron ore bed. If the stratified deposits 
are syngenetic, as has been assumed, the further tacit supposition follows 
that the ore beds and ore strata were deposited but little later than the 
underlying rock and but little earlier than their overlying bed. In the case 
of the metasomatic ore beds and impregnated layers this assumption refers 
only to the original layer, whose substance was subsequently displaced by 
ore or whose interspaces were subsequently filled by ore ; they are then not 
true beds but bedded veins. 

Like any other stratum of sedimentary rock, an ore bed may contain and 
be recognized by certain fossils (diagnostic fossils) which are usually 
mineralized. Thus, a characteristic fossil of the Oolitic iron ore beds of the 
Brown Jura is an ammonite {Harpoceras Murchisona-e) ; and for the 
Eocene iron ore measures of upper Bavaria it is a sea urchin (Conoclypeus 
Conoideus). 

Sometimes it is very difficult to distinguish the true stratified beds from 
bedded veins (see later on). The stratified beds are distinguished from 

*B. von Cotta: 'Die Lefire von den Erzlaperstatten. ' Freiberg, 1859, Vol. I, 
p. 86. Prime's translation, New York, 1870, p. 17. 



50 THE NATURE OF ORE DEPOSITS. 

\be stzatiform or bedded lodes mainly by negative marks; their boundaries 
abore and below are for the moet part not so sharp. They never cause dis- 
placements and never cat acrosi* another bed or a lode. They never form 
veinlike offshoots entering into the adjacent rocks, and do not enclose 
fragments of the country rock. In folded r^ons the beds follow all the 
windings of the surrounding strata. 

Formerly ore beds when tilted at a high angle were considered as lodes, 
even in mining legislation, because mining such a deposit is like that of a 
lode. 

The definition given for stratiform deposits involves, furthermore, a con- 
siderable extension of the deposit in length and breadth, combined with a 
relatively small thickness. The known exceptions to this law, such as the 
so-called ore 'pods' (Erzlineale) of the Norwegian p>Tite deposits (see 
description) are, in point of fact, examples which are not true beds or are 
at least of doubtful genesis ; as for instaDce, at the l^Iug mine, near Roros, 
in Norway, there is a low-dipping bed of phyllite and pyrite, which was 
found to be ten times longer than it was wide, the length coinciding with 
the dip. 

It is customary in many places to apply the name 'seams' to those 
stratified ores which have a great horizontal distribution with a small aud 
nearly constant thickness. The name 'lenticular^ Ix^ls (lager) has been 
given to those which have a relatively small horizontal distribution with a 
relatively great thickness, and which may show great variation in thickness. 
As typical examples of these two extremes we may mention the copper shale 
measure of the German Zechstein formation, which maintains its thickness 
of 0.5 meter over about 4 square miles, though it does not ever}'where pay ; 
and the Norwegian pyrite VkmIs, whose thickness varies between and 26 
meters and which have slight areal extent. Some writers call the older de- 
posits beds (lager), the younger ones seams (flotze). In any case the 
distinction is not a sharp one. 

The thickness of bedded deposits is never very great ; the extreme thick- 
ness of the big iron ore lens of the Sjustjcmberg, near Grangesberg, in 
Sweden, amounting to 90 meters, probably represents tlie greatest thick- 
ness known, and this really includes some intervening strata which are 
either barren or poor in ore. 

Where the thickness of the orebody decreases until it disappears the ore 
bed is said to wedge out (as at a in Figure 23), or it may merely become 
much constricted with a narrow band of ore still remaining (at b), which 
iricreases in thickness some distance away, forming another orebody. This 
is termed "enlargement." After wedging out, a clay-filled or even entirely 



BEDDED ORE DEPOSITS. 



51 



empty joint fissure sometimes indicates the horizon, and the miner most 
carefuil; follow this fifisore if be wishes to find farther orebodieB. 

Freqaentif this alternate wedging out and thickening cuts up a deposit 
into series of lenticular beds belonging to a common horizon, which may be 
termed a chain* (lagenng) (Figure 24). The German term is also 
applied to a succession of beds which belong not exactly but at least approxi- 
mately to the same horizon. An example of this is found in the series of 
'minette' beds or tneasores of the Uoselle region occurring in the Harpo- 
ceras Murchisottae formation; also tbe doable series of magnetic iron ore 
deposits at Gellirare. 

A bed which has a comparatiTelj great thickness, bat wedges oat rapidly 
in all directions, is called a lens (>ec Figure 35). As examples we may 
mention many magnetic iron ore lenses in the crystalline schists. The flat, 
disc-shaped spbcrofiderittt concretions in clay slates of the Carhoniferous or 




of the Jurassic are miniature lenses, which are also called "buttons' in 
some localities. Similar t-pheroidal formations constitute the 'muggoln' of 
the Austrian miners. 

If the Itins has an irregular outline it passes, according to its dimensions, 
into a bonch, pocket, or stock ( Fig. 20 ) . These irregular forms of deposit 
are less common in the stratified iliposits, propter, than in the uH'ta.'u>matic 
orebodies, such as mass** of spathic ironstone, while in still other cases 
they are the result of orographic pressuri'. One may further subdivide such 
deposits into flat and upright stocks, according as their longitudinal axis is 
horizontal or vertical. 

Very fri-quc-ntlv a stratified orebody contains barren or at least poor 
unworkable layers, intercalated parallel to the stratification. These are 
called 'partings' (zwischonmittcl), or 'stone-band' (bergemittel) , as, for 
example, the partings nf gray gni-iss in the inm orebodies of Sweden. 

' i. e., the leneB are tbe links of a chain of umbodiei.' 



Si 



THE NATURE OF ORE DEPOSITS. 



In certain cases a bed of ore docs not terminate b}' simple wedging ont, 
but by the intervention of thin bands of barren rock, which increase in 
number or thickness. In other cases there is simply a gradual increase in 
the barren constituests of the normal ore. In the latter case the bed is 
said to become impoverished. This is particularly frequent in metasomatic 
replacements and impregnations. Thus the pyrite and blende deposits near 
Schwarzenberg in the Erzgebirge paea very gradually along the strike into 
barren amphibole-gamet rocks. 

The part of an orebody intersected by the earth's surface is called the 
outcrop. A distinction is made between a true or exposed outcrop and a 
blind or covered outcrop. In the latter case the ore bed ia concealed by 
unconformable debris or deposits of alluvial strata. 

To both the miner and the mining geologist the form of the outcrop of 
a bed is of much importance, since it indicates the direction for further 
exploitation. 




Fig. 25. — An ore lens. 



Fig, 2S.— .\n ore stock. 



The shape and extent of tlie outcrop dopi'nds on (1) the inclination of the 
bed, and (2) on the relief of the ground. A practiced eye will be able, from 
the form of the outcrop shown on an accurate geologic map, to infer with 
certainty the direction and angle of dip, and conversely, those factors will 
have to be known in order to plot a bed correctly on a map. According to 
K. Keilback', the following typical cases occur. 

1, Horizontal strata form lenticular outcrops running parallel with the 
contour lines of a good map. A horizontal bed outcropping on the slope of 
a mountain shows in a gorge as a crescent-shaped outcrop or bifurcated 
figure, in which one branch is seen on one side and the other branch on the 
opposite side of a valley. In a valley whose slopes are furrowed by lateral 
guUeys a horizontal bed will form a sinuous outcrop (Fig. 27-29). 

' K. Keilhack: 'Lehrbuch der praktischen Geologie.' Stuttpirt, 1896, p. 210, 



BEDDED OEE DEPOSITS. 63 

2. Vertical beds give, under all circumstances, straight outcrops which 
nm, undenating, over mountain and valley, and at the same time represent 
the direction of strike (Fig. 30). 

3. A more complicated form is assumed by an outcrop of inclined strata. 
In this case it is first to be noted that in general the boundary line or out- 




Fig. 27-29.— BebaWor of the otitcropa of horizontal strata iii diverse ty pea of topognphy^. . 

crop of the bed rans parallel to the contour lines only when the strike of 
the bed agrees with the direction of the contour. 

On the contrary, if the inclined lines of the outcrop run at right angles to 
a valley they form in it an acute angle; the water flows into this V when 
the dip of the bed is down the valley and steeper than the elope of its bot< 
torn; in all other cases it flows out of the A (Fig. 31 and 33). If out- 




Fig. 30. — Course of the outcrop of a vertical bed in irr^ular topc^aphy. 



crops of inclined strata run across a mountain ridge, they form arches which 
open toward the foot of the mountain when the dip runs in that direction 
and is steeper than that of the slope. In the opposite case the arches open 



THE NATURE OF ORE DEPOSITS. 




Hg. 31-32.— Outcrop of differenUy ixudined beds in a voUey. (K. Kulhack.) 




Tig. 33-34.^-Outcropfl of dtfTerently inclined beds on a ridf;e. (K. Keilhack.) 



BEDDED ORE DEPOSITS. 



55 



toward the siunmit of the mountain or even form closed figures. (Fig. 33 
and 34.) 

In searching for ore beds, or for any other kind of beds, one should, in 
prospecting by tunneling, boring, or by sinking shafts, run as nearly 
as possible at right angles to the general strike of the stratified rocks of the 
region. If the beds form an isolated exposure, the first thing to 
be done is to obtain an exact section of the local series of strata to 
which it belongs, identifying individual beds by means of characteristic 
fossils or locating certain prominent strata by their particular lithological 
character, as the case may be. This section afterward often will be of 
the greatest practical use when the miner encounters dislocations in work- 
ing the bed. 

Disturbances or dislocations of strata show: 

(1) In a bending and folding of the beds without interruption of their 
continuity. 

(2) In a breaking and disruption of tlie strata, by flexure, pressure, 
thrusts, etc., accompanied by the formation of fissures or cracks. If dis- 
placements occur along these fissuree we speak of them as faults. 

1. Flexures. 

In describing the various forms produced by folding we may begin with 
the closed syncline (Fig. 35). In this case the bed forms a 'canoe' or 
bowl, dipping downward from all sides to the bottom of the basin (center or 
axis of syncline). The structure is concentric and the outcrops form circles 




F'\^. 35. — Plan of a Closed Syutline. 

or ellipses. Thus, the Mansfeld copper shale, aside from small deviations, 
forms a trough 4 k. (2.4 miles) wide and open only toward the southeast. 
• The opposite of a basin or closed trough whose concavity is directed 
downward is the dome or closed saddle. The two forms are contrasted as 
synclines (trough) and anticlines (saddle). Wlien the axis of a syncline or 



. 66 THE NATURE OF ORE DEPOSITS. 

anticline has a certain Ittngtb and itt cut oB at both ende bj erosion or dislo- 
cation, open synclinea and open anticlines result. (Fig. 36.) 

Every open form of thie kind coneiBts of two limbs or flanks connected at 
the axis of the syncline or the axis of the anticline. The strike of the 
strata in these cases is not quaquaversal — i, e., encircling — but rectilinear. 

The axis of a fold may be horizontal or be inclined toward the horizon ; 
in the latter case its inclination is called its pitch. 

The transition from one limb of a fold to another is ordinarily effected 
by a gradual curve (op«i fold), more rarely by an abrupt, sharp angle 
(closed fold) or by a repeated plaiting of minor plications. In large syn- 
dines, lesser flexures may produce subsidiary synclines and anticlines. All 
these phenomena are well exhibited in the main bed of the Carboniferous 
spathic ironstone measures of Westphalia, and the anthracite coal beds of 
Pennsylvania. 




Fig 36. — (Jpen syiicline and open anticline, together fomiins a flat fold. 

Both in anticlinal and synclinal folds a strong horizontal thrust may 
cause a complete inversion of the strata. Examples may be found in the 
inverted, that is to say, reversed, succession of strata shown in the Lower 
Silurian iron ore deposits of the Steinach valley in the Franconian forest, 
and the inverted pyrit« beds of Rammelsberg. 

Anticlines whose upper parts have been removed by erosion and denuda- 
tion arc called aerial arches. 

An anticline and a sjTicline that have been brought close together hy 
horizontal thrust form a recumbent fold with a middle limb and two side 
limbs. 

2. Displacements. (Thrust Faults.) 

Sometimes the limbs of an overturned fold have been subjected to such 
intense thnist or squeezing that they have finally yielded and been torn 



BEDDED ORE DEPOSITS. 67 

apart along a gliding plane. The discussion of such thrusts^ or fold faults^ 
is reserved for the general discussion of faulting, which, for various rea- 
sons, is not treated in this place, but later in connection with mineral veins. 



DiSTmBUTiON OP Obe Within an Ore Bed. 

When stratified deposits consist not of solid ore, but of ore mixed with 
barren, non-metallic minerals in one stratum, the distribution of the ore 
is an important factor. The determination of the distribution of the ore is 
especially important in those stratified deposits formed by impregnation, 
because in such cases its occurrence is apt to be very irregular, as for in- 
stance, in the gold-bearing conglomerates of South Africa. The particles of 
ore interspersed in the barren matrix may be of dust-like fineness, as 
in the Mansfeld copper shale; they may form small nodules, as in the 
galena-bearing variegated sandstones of Commem, or finally they may form 
larger concretions, as in many spherosiderite deposits. 

If the rock in which the ore occurs in very fine particles or granules is a 
crystalline schist, it is customary to call the deposit in question a fahlband. 
The word was first ujsed for the schist zones of Kongsberg, in Norway, con- 
taining iron pyrite, copper pyrite, magnetic pyrite, etc., in very fine par- 
ticles, and though the beds are not sufficiently rich to be workable them- 
selves, they are important because they enrich the silver veins which cut 
through them. German miners call these zones fahlbands because in the 
outcrop where the pyrites have been decomposed, the rock is gray. Typical 
fahlbands are found in the glance-cobalt deposits of Skuterud. 

Structure of Bedded Ore Deposits. 

Like all stratified formations, bedded ore deposits quite frequently appear 
to be built up of different strata, as for example, with many iron ore 
deposits. If the stratum consists of layers of different mineralogic com- 
position the true bedded deposits fail to show a symmetrical disposition of 
duplicate bands, in cross-section. This is an essential mark by which to 
distinguish them from the true veins which they often closely resemble. As 
a rule the true bedded depa^its also lack druse cavities (vugs) extending 
parallel to the stratification. On the other hand, certain bedded ore 
deposits possess a feature lacking in lodes: they carry fossils or pebbles of 
true fluviatile or littoral origin. 

Mineral Contents of Stratified Deposits. 
The only ore deposits thus far positively demonstrated to be of actual 



M THE SATIRE OP ORE DEPOSITS. 

wtAimaHuj origin {mi kan on a large icale; are tfaoee of iron and 
gancKy tfae ores ajfTimH to be of thi§ nature being described under the 
name of tfae metaL An inip>rtant feature of ore beds is the 
presence of a matrix of certain non-metallic minerals which are oitirely 
ifT almost wboUjr lacking in veins, riz.: green hornblende, light green 
fpjToxene, pitftazite and garnet. Tfae primary ore otmtent of a bed i^ aa 
a rule, apt to be mocfa more constant than in a Ton, and hence in 
optomed ftrata the raloe u not apt to change with increaang depth. The 
caie may be different with epigenetic ore beds; for example, the beds of 
Megg^n on the \jiiine C'oni»i.«t in one part of barite. in another part of iron 
pyrite. An exception is also found in beds of metasomatic origin, sncfa as 
the Schwarzenberg beds, wfaicfa in one place may be dcTeloped as copper, in 
anotfaer as a blende deposit. 

As regards the differences in mineral content by reason of snpo^cial 
alteration at and beneath the outcrop^ the same results occur with strata as 
with vein outcropci, as will be shown later. Both hare a gossan wiiose 
secondary minerals depend entirely on the primary contents. A bed of 
iron pyrite carries a go«<(an of brown hematite; a bed of galena forms a 
gossan with much cemssite, etc. 



Classification op Sedimextabt Ore Deposits. 

The primary ore deposits of this gronp may be divided into two classes : 

(a) Thr>se in which the ore befl and its enclosing strata have undergone little 
or no f'hango since their deposition (purely sedimentary deposits), and 

(b) ihfmi in which both ore and eountr}* rock have passed through a recrys- 
tallization or muui other important structural transformation (metamorphic 
ore depoHits.). Typical f»xainples of the first group are the lacustrine iron 
ores and hiohI of the Oolitic iron ores; for the second group the Archean iron 
oni*. In many cases, however, it is not possible to draw a sharp boundary 
bf.'tween them ; in general, the older the deposit the more likely it is to be 
metarnorphowd. \h'i\vv tho primary ore deposits of this kind will be arranged 
by gwlogic age, progressing from the older to the younger, and subdividing 
all into different groups according to the respectively predominant metal?. 

We include in sedimentary ore deposits those stratiform masses which 
contain the ores finely distributed, in the form of dust, granules, scales, or 
nodules, provided the assumption is justified that this ore content intor- 
Hperwd in particles was deposited simultaneously with the barren con- 
stituents. Here, too, a suhserpient motamorphisra has often occurred, as 
for example, in the specular iron schists. It will he difficult in individual 



BEDDED ORE DEPOSITS. 69 

casee to diatinguish sedimentary ores whoce finely disseminated metallic 
particles are of simultaneous origin, from those strata whose ores are the 
result of a secondary impregnation. The Mansfield copper shale, for 
example, is placed by various authors now in one group, now in the other. 
The discriminatior bccomra even more difficult when such secondarily im- 
pregnated sedimontt as the cobalt fahlbands of Modum have undergone a 
subsequent metamorphism which has effaced the original cliaracter of the 

Id a rigorously consistent classification we should have to add to the two 
categories just discussed, acconling to G. Gurich*, a third category, a 




Fig. 37. — Lena of spherosiderite from the clay elate of Bocksberg, split longitudinally. 
(Une-fourth natural size.) 



diagenetifi group of stratified ore deposits, namely, those deposits in 
which the concentration of the ore took place in the muddy sediment of a 
water-laid deposit before it was hardont'd into rock, as for example, in the 
alate clays with kidneys of spherosideritf, A good instance of this process 
is^seen in the clay ironstone lenses up to 1.5 feet across in size in the l^ower 
Coal measures of western Pennsylvania. The concretions in the roofing 
slate of Bocksberg, Gormany, show an outer layer impregnated with pyrite 
crystals, whose arrangeiimnt, as will appear by reference to Fig. 37, shows the 
stratification of the clay i-latc displaced by the spherosiderite. In the 

■ •Siti.-Ber. d. Schles, Ges, f. vaterl. Kultur ' February, 1S99. 



60 THE NATURE OF ORE DEPOSITS. 

center is seen a network of quartz stringers. However, for the sake of sim- 
plicity we include this small group with the ore deposits regarded as normal 
sediments. We will now proceed to the special classification and sketch- 
ing of the most important groups, laying special stress on certain examples. 



1. SEDIMENTARY IRON ORE DEPOSITS. 
(A) Sedimentary Iron Ores of the Crystalline Schists. 

(a) Crystalline Schists with Disseminated Iron Ores. 

Magnetite and hematite occur as accessory constituents disseminated 
through portions of crystalline schists of almost all known areas. At times, 
however, they form the principal constituent of quartzites, mica schists, 
and similar rocks, and thus attain importance as ore deposits. The follow- 
ing occurrences illustrate this class: 



Specular Hematite Schists, 

Specular hematite schists are granular schistose mixtures of micaceous 
hematite and quartz. They are known to occur fit several localities in 
Germany S viz.: Soonwald and Marmarosch (Cotta), in many parts of Nor- 
way, and particularly in the ancient schistose rocks of BraziP. In. the latter 
country at Itabira and Antonio Pereira they form a great series of strata 
intercalated between clay slates and itacolumites. They also occur in South 
Carolina'. In both countries they are associated with gold deposits. 

Itahirite. 

Ttabirite is a granular schistose mixture of quartz with hematite and 
magnetite, which occurs at Itabira, Villarica, and other localities in Brazil, 
associated with specular hematite schists. It also occurs at Suttonr in 
Canada, included in metamorphosed Silurian strata. In Brazil this rock 
also contains gold, and llussak* considers itabirite as the matrix of the 
waterworn specimens of cinnabar found in the alluvial ^Cascalho* of 

» Noggerath, in Karsten's Archiv., Vol. XVI, 1S42, p. 515. 

' V. Eschwege: 'Beitrage zur Gebirgskunde lirasiliens.' lierlin, 1832. 

' Lieber: Rep. Geol. Surv. S. Car., 1856. 

*Hussak: Zeit. f. Prak. GeoL, 1897, p. 65. 



BEDDED ORE DEPOSITS. 61 

Tripuhy. The same rock occurs in South Carolina associated with mica 
schist, itacolumite and talcose schist rich in magnetite grains, the so- 
called catawbirites. Here, too, gold deposits are known in this group. 
These examples are economically of less importance than certain Nor- 
wegian deposits of which a fuller description is given. 

The Iron Ore Field of Naeverhaugen. 

This district, situated on the west coast of Norway, 24 miles (40 kms.) 
east-northeast of the town of Bodo, is, according to A. W. Stelzner^ and J 
H. L. Vogt^, a region of metamorphosed Paleozoic rocks consisting of 
gametiferous mica schists, quartz schists, amphi])ole schists, mica gneisses, 
pyroxene gneisses, epidote schists, and granular crystalline limestones. In 
certain layers both the mica and the quartz-schists carry numerous inter- 
spersed flakes of specular hematite, with subordinate granules of magnetite. 
Thin, highly ferriferous layers alternate with barren layers These finely 
banded layers of ore attain a thickness of 16 to 22 ft. (5 to 7 m.), sometimes 
25 to 30 ft. (8 to 9 m.) ; greater thicknesses, up to 50 fi (16 m.), occur, 
but are due to folding. The foliated schists contain, moreover, layers of 
rich ore sometimes 0.3 feet to 0.6 ft. (10 to 20 cm.) rarely a foot thick, in 
which the amount of iron, ordinarily about 50%, may rise to 58%, with 
a phosphoric acid content of 0.2 to 0.4%. The barren layers of the banded 
ores consist of quartz, with some hornblende, pyroxene, epidote, and garnet. 
Accordingly these ores approach the Swedish Striberg type. 

These occurrences form a transition from the deposits of disseminated 
ore to the beds of the compact iron ore in the crystalline schists. This last 
named class includes a variety of ores. Those of spathic ore will be de- 
scribed first, then those of magnetite and iron glance: 

Compact Iron Ore Beds of the Crystalline Schists. 

The Carbonate Iron Ore Beds of the Crystalline Schists. 

Owing to the ready solubility of iron car])onate where it is associated 
with limestone or dolomite, and the frequent migration of material, the 
original sedimentary character of all the deposits of this class has been 
greatly obscured by secondary metasomatic processes. This is particularly 
true of the most important example, described below. 

* A. W. Stelzner: 'Das Eisenerzfeld von Naeverhaiicten. ' Berlin, 1891. 

' J. H. L. Vogt : 'Salten og Ranen. ' Christiania, 1891. Cited in Zeit. f. Prak. Geol,, 
1894, p. 30. 



62 THE NATURE OF ORE DEPOSITS. 

1. The Iron Ore Deposits of Huttenberg, in Carinthia^. 

In the eastern Alps crystalline schists and granites make up the central 
east to west range of the system. To the north and south the rocks of other 
ages occur as steep-dipping and often dislocated strata lying against this 
zone ; first a low area of essentially Paleozoic rocks, then the Mesozoic lime- 
stone of the steep and high ranges of the Alps. The spathic ironstone beds 
of Huttenberg, northeast of Klagenfurt, belong to the central zone. The 
beds and the associated granular crystalline limestones form a series of 
strata which extend from the vicinity of Friedsach on the Olsabach ranges, 
across Huttenberg and Lolling, and farther across Wolfsberg into the 
Lavant valley. The limestone in which the several beds of these series are 
intercalated is itself interstratified between mica schists and gneisses. 

At the Erzberg, near Huttenberg, which in popular parlance is called the 
"main iron root" (Haupteisenwurze) of the country, as shown by a section 
(Fig. 38, after Seeland), the lower member of the crystalline schist series 
is the same gneiss that contains the well known mineral deposits of the 
Sualpe. Its strata dip southwest. It is followed by mica schist with ore- 
bearing limestone intercalations, as well as with intervening layers of tour- 
maline rock (probably a pegmatite rich in tourmaline), eclogite, and 
amphibolite. These are finally followed by phyllites. 

The main limestone bed at P]rzbcrg has a length along the sti^ike of more 
than one and one-third miles (2,400 m.), and a thickness of 1,312 feet to 
2,296 feet (400 to 700 m.). LeHi^es of gneiss and mica schist, together with 
small quartz streaks are intercalated in it, and it often carries muscovite, 
passing into calcareous-mica schists. Disseminated grains of pyrite, arseno- 
pyrite, and rarely chrome-mica and realgar, occur here and there. Some- 
times the limestone is ankeritic (that is to say, it contains much iron 
carbonate). 

The spathic ironstones, which when undccomposed are called white ores 
on account of their light gray color, contain considerable manganese 
which, when weathering begins, shows on the surface as a violet sheen (blue 
ores) and eventually forms a large amount of wad and pyrolusite. These 
manganese minerals form a gray coating called mold (schimmel) over ore 
fragments. The orebodies have been largely transformed into limonite, and 
as this alteration is accompanied (despite the absorption of oxygen and 
water) by a loss of volume amounting to one-fifth of the original mass, the 

* F. Mumchsdorfer: 'Greolorisches Vorkommen am Huttenberger Erzberg.' 
Jahrb. d. k. k. geol. Reichsanst, 1856. F. Seeland: *Der Huttenberger Erzberg und 
seine nachste Umgebung.' With plates I-IV. Jahrb. d. k. k. geol. Reichsanst., 
Vol. XXVI, 1876, pp. 49-112. A. Brunlechner : 'Die Form der Eisenerzlagerstatten 
in Huttenberg.' (Karnthen.) Zeit, /. Prak. Geol, 1893, pp. 301-306. 



BEDDED ORE DEPOSITS. 



limonite has a spoogy structure. Their cavitiee often contain hematite 
stalactites, and sometimes pseudomorphs of gothite after blende. 



'■^ 



X 



According to F. Seoland the spatliic ironstone of Hiittenberg contains in 
fresher samples : 



64 



THE NATURE OF ORE DEPOSITS. 



Iron 41 .28 to 44.33 per cent 

or Ferrous oxide 47.62 to 56. 11 

Manganese oxide up to 5 . 02 ** 

Lime 0.79 to 1.33 

Magnesia 3.05 to 4.35 

Carbonicacid 32.79 to 37.70 

Silicic acid up to 2.47 

Water 0.43 to 2.47 

The different orebodies retain a partly lenticular form, but as a whole 
they form a rather irregular system of deposits since they overlie one 
another variously, both in the direction of the strike and in the direction of 
the thickness, or are connected by spurs. Divisions of beds recur rapidly 
in one and the same orebody. On a small scale, too, the outlines of the 
lenses next to the limestone wind about in a most irregular way, and sack- 
shaped s-purs 6 to 10 feet long occasionally project into the underlying or 




Fig. 39. — Cross-section through a part of the Hiittenberg field. (Bruiilechner.) 

The shaded patches are ore. 



overlying limestone. At the end the masses either wedge out or break up 
into several wedges or strings. All this is shown in the section. Figure 39. 
Sometimes the ore encloses also boulders of slate or limestone. 

In isolated cases distinctly lode-shaped ore masses were also observed; in 
the Seeland shaft a schistose, well stratified limonite was traversed by a 
vein of younger limonite. 

In the Gliicklager the conditions of stratification seem to clearly indi- 
cate that the ore has been formed by a progressive replacement of the lime- 
stone. In a mass of brown ankerite [ankerite=(Ca, Fe) CO3] obtuse- 
angled fragments of crystalline limestone, with an etched appearance, are 
found entirely isolated. 



BEDDED ORE DEPOSITS. 65 

According to Brunlecliner there has been a partial transposition of the 
ore, as follows: The surface water seeping downward absorbed the car- 
bonic acid which had been liberated by a superficial alteration of the 
siderite into brown hematite. Charged with this solvent the water was now 
able to decompose the ironspar below the zone of oxidation. The redeposi- 
tion of the ferric carbonate taken up by these waters had to occur where the 
water flowed away from the siderite mass and encountered Ca CO,, that is 
to say, at the margins of the lenses, at the contact with the lime, through 
the replacement of the limestone and the exchange of the iron carbonate 
with the calcium carbonate. Hence it occurs that the ores of such sacklike 
offshoots are particularly pure. Similar replacements seem to have occurred 
very soon after the first layers of the limestone were deposited. However, 
that the iron carbonate has in tlie main been directly deposited as a sedi- 
ment, is shown by the distinct stratification of many orebodies as well as 
by the manner of the connection with the series of which it forms but a 
member. 

The Hiittenberg deposits were known to the ancient Romans. In the 
seventies of the last century an average of 146,000 tons of ore per year were 
produced, averaging 68.8%. In the nineties the annual output was, 
in round numbers, 100,000 tons of spathic ironstone and limonite, the out- 
put for 1898 being 7,244.1. tons of spathic ironstone, and 58,558.8 tons of 
limonite. 

2. Gyalar in Transylvania (Hungar\^). 

An analogous iron ore deposit exists in Transylvania, in the mountainous 
country south of the Maroe-, near Vajda-Hunyad. Crystalline limestones 
extend for miles through mica schist rocks and hold vast intercalations of 
spathic ironstone, which, however, in the levels thus far worked has in al- 
most every case been altered into limonite. In the nineties there were pro- 
duced near Vajda-Hunyad annually about 180,000 tons of brown hematite, 
with a content of 52 to 56% of iron.^ 

(b) Beds of Magxktite akd Hematite. 
1. The Iron Ore Beds of the Archean Bocks of Sweden. 

Sweden is very rich in iron deposits, the total iron ore production of 1903 
being 3,677,841 tons. Tlioro are in tlie main two great areas containing 

' F. Bevsrhlaff: *I)as Moiitanwesen auf der Milleniumausstellung.' Zeit. f.Prak, 
OeoL, 1890, p. 465. 



66 TEE NATURE OF ORB DEPOSITS. 

these underground treasures. One lies in central Sweden on both sides of 
the 60th degree of latitude; it is the long famous Jembaraland, with the 
well-known mines of Persberg, Taberg-Nordmark, Striberg, Grangesberg, 
Norberg and Dannemora. The other field lies far to the north, immediately 
north of the Polar Circle; it consists of the much discussed fields of Gelli- 
vara and those of Luossavaara and Kiirunavaara and Svappavare in the 
province of Norrbotten, described previously. With the exception of the 
last named, all the deposits belong to the crystalline schists whose classi- 
fication must, for that reason, be briefly described in order to define the 
geologic position of the occurrences. 

According to A. E. Tomebohm* the primitive rocks of Sweden are classi- 
fied as> follows : 



Upper division . . 



Lower division. 



' Granites ; in part also gneisses (Vermland) . 
Phyllitic schists*, dark h^Uefiintas' at bottom, with a diorite (Grji," 

thyttan) sheet. 
Porphyroid and halleflintas. 

Fine-grained, scaly gneisses (the so-called grauulites or eurites). 
Banded gneissoid graniilites.^ 

Red and gray granites and granitic gneisses. 

Banded gneisses as well as cordierite gneisses (eastern Sweden) 

and epidote gneisses (western Sweden). 
Iron gneisses (with finely interspersed magnetite). 



Iron ores and crystalline limestones — the two almost always found to- 
gether — occur but rarely in central Sweden in the lower series of gneisses, 
but are very abundant in the upper, in the group composed of granulites, 
porphyroids and halleflintas. Both magnetite and hematite ores occur ; the 
former are closely associated with either limestone or with a rock consist- 
ing essentially of pyroxene and hornblende, often carrying garnet and epi- 
dote, rock called sham by Swedish authors. The hematite ores, on the 
contrary, are usually directly interbanded with the granular gneisses. 

In the description of examples from the mining fields it is advisable to 
begin with Norberg, because it contains a great variety of ore types crowded 

*T6rnebohm: 'Ofverblick ofver Mellesta Sveriges ITrformation. ' GeoL Foren, 
F&rh., Vol. VI, part 12. 

* Phyllite is a semi-crystalline somewhat metamorphosed clay slate containing 
sericite, ottrelite, ilmanite and garnet. 

' Halleflinta, an exceedingly compact hornstone-like rock formed of microscopic 
particles of feldspar and quartz with scales of mica and chlorite. Porphyroid is a 
fibrous schistose siliceous micaceous rock with scattered porphyritic crj'stals of 
feldspar and quartz. 

* Graniilite, a schistose rock (German and Ensjlish usage), with peculiar granular 
structiire resulting from cnishing and re-cr\'stallization. Not a granite as understood 
in French. Composed of feldspar, garnet, etc. 



BEDDED ORE DEPOSITS. 67 

into a small space. Among the many others we select Persberg^ Danne- 
mora and Orangesberg. 



I. Norberg. 

'^orberg Bergslag/^ in Westmanland, ccmtains several hundred iron 
mines distributed over a narrow zone 12 miles (20 k.) long and 2 miles 
(3k.) wide. All these mines lie in a zone of fine-grained^ scaly micaceous 
gneisses (granulites of Swedish authors) and of halleflintas^ bounded on 
both sides by granite and gneiss^ and containing intercalations of mica 
schist as well as of crystalline limestone and dolomite. Three kinds of ore 
occur there: (1) Red hematite ores, consisting of crystalline hematite with 
numerous exceedingly thin quartzite lamellae, often crumpled and hand- 
somely folded by rock pressure, to which is given the name dry ores, t. e., 
needing a flux; (2) finely crystalline magnetic iron ore intermingled with 
a gamet-pyroxene-skam ; they need no fiux and hence are called self-fluxing 
ores; (3) magnetic iron ores, mostly highly manganiferous (at Klackberg 
up to 7% of MUjOg) in lenses in the midst of the dolomite and limestone, 
and hence highly calcareous, being called fluxing ores because as a rule they 
are added to others to make a smelting mixture. 

The dry quartzose hematite ores which occur under precisely similar 
conditions at Striberg^ in the Orebro area, and hence are called by Swedish 
authors "iron ores of the Striberg type," are, in the main, confined to tne 
lower geologic horizon of the ore zone. Above them come the ores 
associated with pyroxene skam, and in the uppermost horizon the cal- 
careous fluxing ores of the dolomite intercalations predominate'^. The iron 
contents of the ore vary between 43 and 60%, with a phosphorus content 
of only 0.004 to 0.035%. During the years 1891 to 1895 the average an- 
nual output was 172,516 tons of iron ore*. 

Sometimes the magnetic iron ores associated with limestone contain an 
admixture of pyrite, and hence have to be roasted before being put in the 
furnace, as for example at Klackgrufva. In some mines the pyrite is ac- 
companied by such an abundance of other sulphide ores, especially galena 

* Birjifcr Santeeson: * Beskrifnincr till Karta Ofver Berggrunden af Orebro Lan 
n. Devigti^areGnifvef alien.' Stockholm, 1889. 

'A. E. Tflmebohm: * Om la<?erfftljden inom Norberprs malmfallt med karta.' 
Geol. F6renF6rh., Vol. IT, 1874-75. p. 329. Also see G. A. Granstrftm: ' Nagra 
underr^ttelser om KTufvorna och grufdriftn inom Xorbergs berslas:.' Jem-Kontorets 
Annaler, 1876, p. 1. 

' T6rnebohm : * Geolo'^iska 5fversiHskarta ofver Mellersta Rvericres Berslag 
Blad. 1 med Beskrif nine:/ 1880. Nordedstrftm's * Katalog Mellersta Sveriges Grufut- 
stallning/ Stockholm, 1897. 



68 THE HATURE OP ORE DEPOSITS. 

and chalcopyrite, as to pay for their workJDg. (See further account under 
Epigenetic Ore Beds.) 

II. Pereberg*. 
The iron ore mines of Persberg, which according to legend were worked 
as early as 1390, lie in Vermland on the peuinsula projecting into the 
Yngen Lake, in a low, hilly country. Although the pro<luction has de- 
clined, the annual airerage from 1891 to 1895 was 31,884 tone of ore, in 
which the iron content was 63 to 60% in the better ores. Magnetite (svart- 
malra) ie the only ore produced. The beet grades contain only slight ad- 
mixtures of pyroxene in their fine crystalline mass. The poorer grades en- 
close also garnet and talc. The phosphorus content amounts on an aver- 



SlorgruPv* 




age only to 0.002, at most 0.013%. The manganese content varies between 
0.20 to 0.35%,. 

The surrounding rock also consists here of a so-called granulite, an ex- 
ceedingly fine-grained gneiss wliich in many cases passes into dense look- 
' ing halloflinta-like rocks and adjoins extensive granite areas. The ore- 
- lodies form lenses or often vt'ry irregular and wholly shapeless masses, im- 
oedded in the garnet and epidote-salite skarn. The skam occurs either 
aa an independent intercalation in the granulite gneiss or at the boundary 
of several largo beds of crystalline limestone and dolomite, inserted in the 
granulitcs. 

The association of these strata is apparent from the accompanying pro- 
file through the Storgrufva (Figure 40). The sknrn. together with the ore 
beds, takes part in all the numerous foldings of the country rork. Tlie skam 

' A. E. Turnebohm: ' Karta ofver nerejrniiiden inoni Filip^ladt Herslu!;,' 1874. 
The same author: ' Oeoffnoatisk RpskrifriiiiE iifver Persberirets nnifvef.ilt.e/ 1876. 
Walfr, Peterssoii: 'HflgbergH faltet vid I'ersberg,' ]897. Xordenatrom's ' Katalf^.' 



BEDDED ORE DEPOSITS. 69 

beds in the Hogsberg field are especially strongly folded and crumpled. 
Walfr. Petersson states that he ascertained that at the flexure points of the 
arches, t. e,, anticlinal folds, the largest orebodies are to be found. A 
special kind of skam, consisting mainly of talc, prevails in the area of the 
Alabama mine. Sometimes the skarn shows a bedlike stratification of alter- 
nating layers of garnet and pyroxene, but this is mostly confined to its 
barren portions. The ore beds are either sharply defined or pass gradually 
into the skam by transitions containing more and more of its mineral con- 
stituents. On the other hand, pyroxene-bearing bands may at times be seen 
occurring in the granulite and thus effecting a transition to the skarn. In 
some parts of the mine magnetic iron ore is filled with stringers of calcspar. 
In many places so-called skblar are seen to run through the ore beds. By 
a skol the Swedes understand a zone of slipping or movement, mostly verti- 
cal, and generally nearly parallel to the strike, its filling consisting of 
crushed rock, mostly altered and either chloritic or serpentinized. They 
may be several meters in thickness, and in mining sometimes tfause the 
loosening of large portions of the walls. 

III. Dannemora^. 

The famous Dannemora mine lies near the railway line from Upsala 
to Gefle, in a low, hilly country, on the shore of the reed-bordered Grufva 
lake. Directly east of the mines are the furnaces of Osterby, where the 
choice Dannemora steel is obtained from the ore of this mining field. The 
mines are mentioned as early as 1481, although the real industry began 
only in 1532. From 1891 to 1895 the average annual output was 55,440 
tons* of iron ore, and 390 tons of zinc-blende. 

The Dannemora ore is a very dense magnetic iron ore, with 20 to 65% 
of iron, averaging 50%, the percentage of iron depending upon the amount 
of the intermingled actinolite (a variety rich in manganese called danne- 
morite) as well as on the calcspar. 

The geologic conditions are as follows: A broad mass of granite, the 
Upsala granite, partly gneissoid, occurs intruded in a very thick series 
of bands of halleflinta, fine-grained gneisi. (granulite, eurite of Swedish 
authors) and cr^'stalline limestones, carrying: considerable manganese. The 
halleflinta of the Dannemora has for a long time attracted the attention of 
geologists. It consists of eruptive rocks, in part clearly recognizable as 
quartz porhpyr}% m part of strongly altered porphyry tuffs, which may al- 
ternate with the limestone in layers, sometimes as thin as a sheet of paper: 
thus distinctly showing their sedimentary origin. The orebodies occur in 

* A, E. Tc^rnehohni: * Oeolopisk Atlas ofver Dannemora Grufvor vid Beskrifning.' 
Stockholm, 1878. 



70 



TBE NATURE OF ORE DEPOSITS. 



three main bands, whidi are found intercalated in the limeetone, or between 
it and the halleflinta. Theae ore belts strike north-northeast for a distance 
of over a mile (2 km.) and dip northwest at 75 to 80°. 

The largest of the ore lenses, situated in the middle field, has been ex- 
posed by a vast open-cut, whose almost vertical walls descend to a depth 
of 475 feet (145 m,). (See Fig, 41.) The present workings are all 
underground, below the floor of this gigantic open-cut This orebody has 
a thickness of 98 feet (30 m ) and has been produced by the convergence 
of three closely adjoining parallel lenses 

At the boundary between the limestone and the ore masseB, which are 
often distinctly stratified, a layer of skaru is often developed; this is an 



WW 



Fig. 41.— Cross-section through Storrymninpen at Dannemora. 
h, lialleflirila; k, limeBtone; e, iron ore; Tagebau-opeii-cut, 



amphibole ealite rock, frequently garnetiferous, and with streaks of mag- 
netite. At many points in the field dikes of fel site- porphyry and diorite 
cut across the beds. 

A pL-euliar feature of tho Dannt'mora field is seen in the Svafvel 
mine in the southern field. At this place the ore bods and accompanying 
rocks are obliquely traversed in strike hy a broad iodclikc zone of impreg- 
nation extending from the Kiirface to a depth of about 213 feet (G5 m.). 
This often contains good-sized masses of pyrife and zinc-blende, with ac- 
cessory galena, magnetic pyrite, copper pyrite and arscoopyrite. A similar 
impregnation with secondary sulphide ores, but following the strike of the 
strata, is observed at a depth of about 754 feet (230 m.). The Danne- 
mora south field formerly produced up to 2.000 tons of blende per year. 

Finally mention may be made of the remarkable occurrence of asphalt 



BEDDED ORE DEPOSITS. 71 

■ 

in small calcspar veins traversing the iron ore beds^ asjdialt pellets being 
enclosed by calcite skalenohedrons. 

IV. Grangesberg^. 

Grangesberg is at present the largest iron ore district of central Sweden, 
The geologic mode of occurrence is as follows : The field is about 3 miles 
(5 km.) long and 0.6 mile (1 km.) wide, lying in the granulitc zone of 
the primitive rocks, whose prevailing type is a fine-grained scaly biotite 
gneiss. The principal ore beds occur in the lower strata, in which there is 
intercalated at Grangesberg a vast bed of a coarse, fibrous, reddish granite 
gneiss. All the schists strike north-northeast and dip steeply east-southeast. 
The district is divided into four parts, the Lomberg field at the south, the 
Ormberg and Kisberg field at the west, the Export field at the east and the 
NorrarHammer field at the north. The first two contain a very great 
number of small beds of hematite carrying an admixture of magnetite and 
a phosphorus content of 0.02-0.8%. These ores are in part associated with 
the pyroxene skarn, in part intergrown with calcspar. 

The conditions are totally different in the Export field. In the first 
place, we are here dealing with far greater deposits. They consist in the 
main of two great lenticular masses. In the southernmost mass the great- 
est thickness in the Bredsjo mine is 212 feet (65 m.), from there north- 
ward it has for a great distance a thickness of 100 to 130 feet (30 to 40 m.), 
until finally the lens wedges out abruptly. This, however, includes a num- 
ber of intervening beds 10 to 13 feet (3 to 4 m.) thick, as well as inter- 
calated pegmatite masses. The orebody proper consists exclusively of fine- 
grained crystalline magnetite, with 60 to 62% of iron and 0.7 to 1.2% phos- 
phorus. Quartz, feldspar, fluorspar and actinolite are accessory constitu- 
ents. The great northern ore lens of Sjustjemsberg, whose exposures form 
the Bergsbogrufva, attains a length of 1,312 feet (400 m.) along the strike, 
and a thickness of 295 feet (90 m.). The upper part consists of magne- 
tite, which, however, contains so much apatite that the phosphorus content 
may rise to 2.8% ; moreover, layers of almost pure apatite rock up to 0.06 to 
0.1 feet (2 to 3 cm.) in thickness are not infrequently intercalated in the 
ore. The lower half of the lens, on the other hand, consists of hematite ore 
with 0-5 to 2% of phosphorus. At times large octahedrons of magnetite 
are found sparsely scattered through the fine-grained crystalline hematite. 
The Bergsbo lens also carries some intervening beds of granulite, which 
may attain a thickness of 8 meters. From their course it is seen that the 
entire ore mass must be regarded as a complex of several closely crowded 
lenses. Furtherpiore, the ore is frequently traversed by vast intrusive stocks 

*N. Hedberg: *The Grangesberg Iron Mines in 1898.' Falun, 1898. 



72 THE NATURE OF ORE DEPOSITS. 

and dikes of pegmatite. This rock, poor in mica, contains apatite, beryl, 
and^ curiously enough^ asphalt in kidney-shaped or drop-shaped pieces in 
the midst of druse-like portions, also as inclusions in feldspar and quartz. 
Where the larger pegmatite dikes traverse the hematite ore they have trans- 
formed it into magnetite, sometimes for a distance of 6.5 feet (2m.) from 
the contact. It is also affirmed that the iron ores in the vicinity of the peg- 
matite have a higher phosphorus content, up to 2.8%. 

The northernmost mining field, Norra-Hammargrufva, yields a mag- 
netic iron ore exceedingly rich in apatite, and holding 6 to 8% of phos- 
phorus. The immediate country rock is a hornblende gneiss with layers 
rich in mica. This particular occurrence at Grangesberg shows very great 
petrographic similarity to the Gellivare ores. The ores of Norra-Hammar- 
grufva are characterized by pegmatitic pegregations with large individuals 
of titanite, with hornblende and asphalt, sometimes also with scheelite and 
zeolitic minerals. 

Nowhere in the Swedish iron ore fields are there more distinct indica- 
tions of the genetic conditions of these ore masses than just here at Granges- 
berg. When we see how, for example, in the Mor mine an alternation of 
extremely thin layers of normal granulitc and magnetite-bearing rock is re- 
peated a thousand times, there can be no doubt that the magnetite and hema- 
tite were crystallized out simultaneously with the ingredients of the country 
rock. This is confirmed by microscopic investigation. In the rock of the 
Mor mine just mentioned the magnetite is clearly of the same age, and is 
syngenetic with the quartz, orthoclase, plagioclase and mica, of which the 
striped granulite of that mine is chiefly composed. It occurs partly in 
grains and partly in concentric layers about other minerals; also as inclu- 
sions in the midst of quartz and feldspar, while conversely it may enclose 
the minerals named. The same is true of the apatite-rich ores of the Bergs- 
bo lens. Here, too, oft-repeated alternations of ore and rock and the micro- 
scopic conditions of mutual intcrgrowth show a simultaneous crystalliza- 
tion of ore- and rock-forming minerals. In the apatite-rich ores of Norra- 
Hamrti^rgrufva the microscopic sections suggest, it is true, a certain suc- 
cession in the segregation of the several ingredients, which is absent in the 
examples above mentioned. The apatite of the latter mine is always free 
from inclusions, and this, together with the abundant brown titanite, 
seems in each' case to have been the earliest formed mineral in the various 
layers of ore. Next in age follows the hornblende, then the infrequent 
quartz and finally the fluorspar. The magnetite existed before the horn- 
blende onlv in small individuals, for onlv in this form is it found enclosed 
in the hornblendo. Subsequently it filled the gaps between the hornblendes 
in the form of larger grains and aggregates. 



BEDDED ORE DEPOSITS. 7S 

The question as to the form in wliieh the iron compounds were preseiU 
in the rock before they were altered by regional metamorphism cannot be 
definitely answered. Their present mineralogic nature, however, was cer- 
tainly imparted to them simultaneously with the general alteration of the 
rock. The mineral wealth ol Grangesberg seems d^tined to last for many 
years. Inasmuch as on Vestra Ormberg an orcbody has been followed to 
a depth of 984 feet, it is fair to assume that the others also extend far down. 

The total production from Grangesberg (629,802 tons) in 1897 exceeded 
that of Nor berg, and by a small amount that of the Gellivare field of north- 
em Sweden, which in 1897 produced only 623,110 tons. This great de- 
velopment has, however, taken place only in recent time; though the ore 
beds of Grangesberg have been known since the beginning of the 17th cen- 
tury, they have been worked but little. The very largest deposits were 
practically untouched because the high j)hosphoru8 content of the ores ren- 
dered them unsuitable for furnace tri'atment. It is onlsr since the inven- 
tion of the Thomas basic Bessemer process that the revolution took place 
here, and all at once production increased tremendously. The many com- 
panies which formerly operated small mines are now consolidated into 
four large companies. By far the larger part of the phosphoric ores is at 
present shipped from the port of Oxelosund, in eastern Sweden. The bulk 
of it goes via Stettin and Rotterdam to upper Silesia and Westphalia. 

In the following table we give some typical analyses of different varieties 
of iron ores from central Sweden taken from four localities: 

I. Pyroxene-hearinp magnetic iron ore of the Storpnifva at Pereherg. (Average 
sample taken by W. Petersson.) 

II. Qiiartzose hematite ore from Striberg (Karrgnifva). (C. J. SamstrSm, analyst.) 

III. Apatite-bearing hematite ore j From Grangesberg, Bergsbd mine, 

IV. Apatite-hearing magnetic iron ore. . . ( after N. Hedherg. 

I. II. III. IV. 

Magnetic oxide 26.78 14.81 79.04 

Ferric oxide 55.24. 47.32 73.50 9.13 

Ferrous oxide 23 .80 ... . 

Iron 57.18 52 52 62.18 63.63 

Manganese oxide 0.21 0.19 0.04 0.10 

Lime 5.17 0.95 5.09 3.61 

Magnesia 1.85 0.40 0.82 2.72 

Alumina 2.38 35 0.^3 1 .78 

Silica 10.45 23.80 1.62 2.00 

Phosphoric arid 0.007 0.034 3.53 2.42 

Phosphoni.s 0.0033 0.015 1 .54 1 .00 

Carbon dioxide 0.51 

Sulphur 0.02 0.020 Trace. 0.013 

Copper Trace 

99.637 99.844 100.04 100.813 



74 THE NATURE OF ORE DEPOSITS. 

V, The Iron Ore Deposits in the Province of Norrbotten, Gellivare and 

Svappavara. 

The famous ore mountain of Gellivare/ 80 kilometers north of the Polar 
Circle^ in Swedish Lapland^ province of Norrbotten, .which is now connected 
by a railway line of 132 miles (220 k.) with the port of LuM, and is to be 
connected in the near future by the Ofoten railway with the Norwegian 
coast, is the largest iron ore deposit of Scandinavia. About one-twentieth 
of the slopes of the mountain, in all about 65 hectares, are occu- 
pied by the outcrops of the iron orebodies, arranged in two series. The 
prevailing country rock, in which the beds are intercalated, is a coarse- 
grained, reddish gneiss, which is seen outcropping especially on the slope 
of the ^alkomann' peak. Farther south it becomes more fine-grained, and 
contains a good deal of hornblende. It is always garnetiferous. Toward 
the west it passes over into halleflinta*. At the Capitan and Frederika 
grants, and thence to the Tingfall peak, it is banded, owing to the develop- 
ment of layers especially rich in hornblende, and in such case shows in- 
tense folding. The gneisses and ore are often broken through by granite, 
as at Valkomman and Kungsryggen. 

The series of ore lenses take part in all the changes of strike of the granite, 
even the finer plications. 

The ore consists of magnetite and hematite, and is usually rich in apatite, 
sometimes even passing over into apatite rock proper. Out of 41 samples 
26 showed an iron content of 70 to 74.3% ; 13 a content of 60 to 70% ; 2 a 
content of 50 to 60%. The phosphorus content varies from 0.05 to 1.5%. 
The sulphur content is quite insignificant. The manganese content is only 
about 0.15%, and titanic acid 0.45 to 1.9%. 

The outcrop of the orebodies is in part concealed by glacial drift. 

Gellivare has been officially known as a mineral deposit since 1704. It was 
only in 1797 that Hermelein, to whom the development of Lapland is so 
largely due, established an industry of note in this locality. Transportation 
was effected solely in winter by means of reindeer. The KoskuU and Capitan 
mines were then the largest. In 1837 that first mining period attained its 
greatest annual production, with 540 tons. After 1870 the work was almost 
entirely al)andoned, but of late years there has been a remarkable develop- 
ment, as noted previously. 

* 'Berattelije om Malnifynclip:hetcr inom Gellivare och Jukkaajarvi Socknar,' etc. 
afgiven af Chefen fdr Sverip:es Geol. Uridersokninpj, 1S77. Contaias the work of D. 
Hummel, O. Gumaelius, (). Trv.s(^n and C. A. Dellwik. Wedding: ' Die ELsenerzvor- 
kommen bei Gcllivara,' etc. Preuss. Z. f. B., II. u. S. Wesen, Vol. XLVI, 1898, pp. 
69-78. For further literature consult Fork. Geol. Foren., Stockholm.. 

' The \orwe«cian halleflintas are exceedingly compact homstone-like rocks produced 
by metamorphism from fine sediment. (Geikie.) 



BEDDED ORE DEPOSITS. 76 

dvappavara lies between the rivers Tomio and Kalis, 43 kilometers south- 
east of Luossavaara, already described. The deposits are intercalated 
between mica schists and fine-grained quartzites. They were discovered as 
early as 1654 and were worked at that early date, but became important 
only in recent time. The ore resembles that of Gellivare — ^but that it has 
a higher sulphur content, which is a disadvantage. Copper ore deposits 
are also known in the same locality. 

2. The Iron Ore Deposits of the Arendal Region in Norway. 

In southern Norway there are iron ore deposits, formerly extensively 
worked, which appear to be related to those of Persberg, although Th, 
Kjerulf and Telleff Dahl,* in accordance with the state of knowledge at that 
time, were inclined to regard them as lode-like occurrences. The deposits 
are near the coast and form an ore zone about 15 miles (25 km.) long. The 
most important mines lay along the Langsev Vand (Langsev and Vas 
mines) at Naskillen and on the Hellesund on Lango and Gamo. The coun- 
try rock is biotite gneiss with intercalations of mica schist, quartzite, horn- 
blende schist and crystalline limestone. The ore consists of magnetite, 
with some intermingled garnet and augite, the deposits being enveloped in 
a mantle of skam composed of garnet, light green augite, together with 
some epidote and calcite. The various ore masses are irregularly lenticular 
in shape, and attain a thickness of 6.5 to 65 ft. (2 to 20 m.), with a length 
along the strike of 300 to 650 feet (90 to 200 m.). While the boundary be- 
tween garnet skam and country rock is very sharply defined, stringers of 
ore frequently penetrate the skam, the ore occurring also in smaller lenses 
by itself in the surrounding gneiss. The fragments of the country rock de- 
scribed by Kjerulf and Dahl in these deposits may indicate local disturb- 
ances. The ore beds themselves and the pegmatite veins by which they are 
traversed are rich in various minerals, including some rare species. 

3. The Iron Ore Deposits of Krivoi-Bog , in Southern Russia. 

These ore depositi^i-, ordinarily grouped as those of the Saxagan basin, lie 
on the Inguletz, a western tributary with north-south course entering into 
tne Dnieper river above Cherson. They are of exceedingly grwit importance 
to Russia, because they lie close to the Donetz coal basin extending east of 

* Th. Kjenilf and Tellef Dalil. 'Ucber das Vorkommen der Eisenerze bei Arendal,' 
Neues Jahrb. /. Min., 1862, p. 557. 

'See reviews of the works of Kontkiewitsch, Piatnitzkv, Domherr, Monkowskv, 
Karpinsky, and others: Zeif. /. Prnk. Geol., 1896, p. 271 ; 1897, np. 182, 186, 278, 374; 
1898, p. 139 (Macco). See also, L. Strippelmann : Sud-Russlanas Mapneteisenstein u. 
Eisenglanzlaperstatten in don Oouvcrnements Jokaterinoslaw u. Cherson,' 1873. 
J. Cordeweener: 'Geologic de Krivoi-Hog et de Kertsch.' Paris, 1902. 



76 THE NATURE OF ORE DEPOSITS. 

the Dnieper. The ores occur in a strongly folded crystalline schist striking 
north-fiouth, whose geologic age is as yet uncertain. In its upper part this 
rock consists of carbonaceous slate with but few layers of ore; next below 
come the ore-bearing quartzite schists, underlaid by clay slate, actinolite 
schist, quartz chlorite schist, talc schists, arkose and itacolumite-like mica 
schists, and finally by gneiss (probably dynamo-metamorphic granites) and 
true granites. The ore-bearing strata form a long-extended fold, and show 
a close minor plication by which quartzite beds have, according to Macco, 
changed into a succession of quartzite nodules, like conglomerate cobbles 
in a clay slate. In the double row of deposits extending parallel to the 
Saxagan river the two most important orebodies are those near Krivoi- 
Bog; the lower one about 98 feet (30 m.) and the uppermost about 262 feet 
(80 m.) thick. The ores consist of magnetite, for the most part altered 
to red hematite, with 45 to 70% of iron and 0.01 to 0.02% PjOq. The very 
irregular ore masses lie in a finely banded yellowish white, red or brown 
ferruginous quartz schist whose crystalline quartz grains enclose numerous 
magnetite particles. In 1894 the production of Krivoi-Rog had already 
risen to 880,000 tons, and by 1900 to about 2,700,000 tons. According to 
J. Cordeweneer there are about 73,000,000 tons of ore yet available. 

4. Iron Deposits of Spain (El Pedroso) and the Bvkowina. 

Spain, also, possesses important iron ore deposits in crystalline schists, 
which recently have been worked on a large scale. At El Pedroso,* on the 
south slope of the Sierra Morena, famous for its mines, there is in the 
mining field of Juanteniente, northeast of Seville, a hematite deposit 4 to 5 
meters thick, interbedded with upturned mica schist; it has been followed 
over 600 meters. Near Navalazaro another magnetite deposit 19 to 26 ft. (6 
to 8 meters) thick, containing some granite and pistazite, has been disclosed 
in the midst of the gneiss. Further discoveries have been made lately in this 
region by means of magnetic prospecting. 

A brief mention should be made of the magnetic iron ore deposits in the 
mica schist area of southern Bukowina (Rusaja mine and others)*. 

5. Arch can {Laurentmn) Magnetic Iron Deposits of North America. 

Deposits of magnetic iron are found in various places in North America 
in Archean gneisses and crystalline limestones. The most important are 

* F. R5mer: Teber die Eisenerzlagerstatten von El Pedroso in der Provinz 
Sevilla.' Z. d. D. G. G., 1875, pp. 63-G9. 

' B. V. Cotta: 'Lehre voni den T.agerstatten der Erze,' II, p. 260. B. Walther: 
Jahrb, d. k. k. jjeol. Reichsanst., 1876, pp. 391, 415. 



BEDDED ORE DEPOSITS. 77 

found in the hills of southeastern New York and northern New Jersey 
(Tilly Foster mines, Forest of Dean mine), and in western North Carolina 
(Cranberry).* 

6. Pre-Cambrian {AlgonJdan) Iron Ore Deposits of North America. 

Marquette Iron Ore District in the State of Michigan. 

Deposits belonging only in part to the class of syngenetic stratified de- 
posits, probably more properly to the metasomatic formations, are those 
of the Marquette district, in the State of Michigan, which have recently 
been the subject of painstaking study. According to Van Hise and Bayley* 
the geologic conditions there are as follows: 

This district is about 29 miles (65 km.) long and 1.2 to 3 miles (2 to 5 
km.) wide, extending along the south shore of Lake Superior between Mar- 




« 9"' « 

Fig. 42. — Profile thiougli the area south of Negauiiee. (Van Hise.) 

sp, gneiss; ^. eranite; q, quartzite; s, clay slate; e, iron-bearing Negaunee strata; 
d, (Horite and diabase. 

quette and Michigamme. The oldest bedrock consists of Archean mica 
schists, hornblende schists, gneisses, granite gneisses and intrusive granite 
masses. Above these, as shown in profile (Fig. 42) come the unconform- 
able Algonkian (Huronian) formations, the lower and the upper Mar- 
quette. The first consists of quartzites, dolomites, schists and the iron-ore- 
bearing Negaunee strata; the latter of quartzites, schists, graywackes and 
conglomerates, in part marked by strong regional metamorphism as well 
as basic eruptive sheets 

The iron-bearing Negaunee formation, 984 to 1,476 feet (300 to 450 m.) 
thick, is in its lower level, where it is found unchanged, mainly formed 
of finely b^d'ed sideritic slate, consisting of alternating lamellae of spathic 
iron ore and quartz, and containing about 30 to 40% of ferrous oxide. 
These slates, however, are very commonly altered in the lower levels by 
metasomatic processes into grunerite-magnetite slate. These are composed 

*J. Kemp: 'Ore Deposits of the United States/ 1900, p. 166. H. B. Nitze: 
'Iron Ores of North Carolina/ N. Car. Geol. Surv., Bu/Z. 1, 1893. Arthur Keith: 
Cranberry folio, Geologic Atlas of the U. S., folio No. 59. Washington, 1903. 

'Van Hise and Bavlev: 'The Marquette Iron-Bearing District of Michigan.' 
With Atlas. Washington, 1897, U. S. Geol. Survey, Monograph XXVIII. J. E. 
Jopling: 'The Marquette Range, its discovery, development and resources.* Trans, 
Amer. Inst. Min. Eng., Vol. XXVII, 1898, pp. 541-555. 



rs TEE NATURE OF ORE DEPOSITS. 

of thin layers of quartz, magnetite and gninerite, the almoet pure ferric 
eilicate in the form of hornblende. In many cases they also carry a garnet 
of secondary origin. These metasomatic proceeses are suppoeed, by the 
above-named authors, to be connected with the intrusion of the diabase 
characteristic of the entire Negannee group. These diabases have been 
intruded in vast stocks and penetrate through the ore-bearing strata in 
numerous dikes. 

Subsequent alkaline solutions are supposed to have passed through the 
sideritic slates and occasioned the exchange of the iron carbonate with alka- 
line silicates. At the higher levels, on the contrary, the sideritic- slates 
by recry stall ization under the influence of atmospheric seepage water, enter- 
ing the de^r strata with its charge of oxygen, have been formed into hand- 




ZflZ 



Fig. 43. — Diain-Bm showinic the occurrenre of the iron ores of the Marquette diHtnH 
(Van Hise.) 
B, schist; i, Jnsper schist; q, qunrtzite; d, diabase and diorite; z, decomposed 
diabase and diorite; e, orebodics. 

somely banded hematite-Umonite-quartzites. Ifl these, strata of specular 
ore and hematite are seen to alternate with bands of ferruginous quartz or 
jasper, which in many areas have been subjected to great pressure and 
curiously folded or often comminuted into a breccia. Crystalline hem- 
atite has at the same time penetrated into the cracks between the indi- 
vidual jasper fragments. From the chemical mobility of the iron com- 
pounds of the Negaunee strata the authors infer the origin of the orebodies 
forming the actual object of the mining industry. These orebodies consist 
partly of distinctly granular-crystalline to dense hematite mi.xed with mag- 
netite (hard ores) partly of red hematite, with transitions into brown 
hematite (soft ores). 

Though the orebodies in general are associated with a definite strati- 
graphic horizon, yet their position in detail, as appears by investigation, 
is dependent on structural conditions. The ore masses arc always 
found in synelines of folded, impermeable rocks, or in troughs formed of 
such strata, or in basins formed by impermeable chlorilic and talcose erup- 
tive rocks, as shown in the accompanying section (Fig. 43). Tliest- solid 
ore masses, therefore, cannot have been formed by direct sedimentation, al- 



BEDDED ORE DEPOSITS. 79 

though they may have originated genetically from the undoubtedly sedi- 
mentary sideritic slates. Accordingly they are supposed to be rather en- 
richment formations deposited by iron-beering water penetrating down- 
ward, which received their charge from the upper strata greatly disinte- 
grated by the folding process. 

They would thus constitute an excellent example of ore deposits which 
have to be explained by the aid of the descension theory (see later). The 
greatest objection to this theory is its failure to show how the silicic acid 
was removed from the quartzose rock masses in order to leave the spaces 
free for the invading iron ore, thus finally forming compact orebodies. 
The authors of the monograph ascribe this action to alkaline compounds 
derived from the diabasic rocks. 

Other deposits similar in character and genesis occur in the Menominee 
district, on the boundary between Michigan and Wisconsin, as well as of 
Penokee-Gogebic district in the latter State, and the Vermilion and Mesabi 
districts north of Lake Superior in Minnesota*. 

In 1903 the annual production of all the iron ore fields in the vicinity of 
Lake Superior was 26,573,271 long tons. The composition of the ores is 
shown by the following analyses, the material being dried at 100° C. \ 

Marquette Mesabi 

Range. Menominee. Gogebic. Vermilion. Range. 

(Bamum)(Appleton) (Anvil) (Chandler) (Adams) 

Iron 65.30 63.30 62.74 

Silicic acid 3.49 4.61 4.09 

Phosphorus !. 0.075 0.018 0.055 

Manganese 0.36 0.27 0.82 

Alumina 1.79 1.30 1.10 

Lime 0.33 0.5? 0.47 

Afagnesia 0.26 0.47 0.11 

Sulphur 0.026 0.019 0.018 

The subject of the origin of the Lake Superior iron ores has been in- 
vestigated by a number of geologists during a long term of years. Prof. R. 
D. Irving at first adopted the theory that the ores were due to the replace- 
ment of the limestone, but he afterwards abandoned it, considering that the 
original rock must have been an iron carbonate and not a carbonate of lime. 
For the ores of the Vermilion Range of Minnesota, N. H. and H. V. Win- 
chell propounded the explanation that they were due to direct precipitation 
from the waters of a hot primordial ocean. Alternating conditions pro- 
duced from these waters alternating precipitations of iron and silica, form- 
ing the characteristic banded ores. 

* H. V. Winchell : * The Lake Superior Iron Ore Region/ InM. of Mining Engineers 
(Eng.), 1897. Irving and Van Hise: Monograph XIX, U. S. Geol. Survey, 1892. 



64.70 


64.18 


4.26 


2.80 


0.036 


0.035 


0.13 


0.40 


1.37 


0.80 


0.33 


0.21 


0.10 


0,10 


Trace. 


0.007 



80 THE NATURE OF ORE DEPOSITS. 

It was held by J. D. Whitney as early as 1854 that the iron-bearing rocks 
df the Lake Superior region were volcanic rocks, erupted in practically their 
present condition, and this view was held by subsequent geologists. To 
this supposed volcanic rock the name jaspillite was given. In their mono- 
graph on the Penokee-Gogebic iron range, Irving nd Van Hise came to 
the conclusion that the iron was originally precipitated as carbonate or 
oxide, and that the accompanying chert was simultaneously precipitated. It 
is supposed that the atmosphere was more highly charged with carbonic 
oxide than at present, and that the general temperature of the earth's 
crust was somewhat higher. J. E. Spurr* studied in 1893 the iron ores 
of the Mesabi Range in Minnesota and found the rocks substantially like 
those of the Penokee-Gogebic Range. However, the iron carbonate, which, 
according to the researches of Irving and Van Hise was the oldest type that 
could be found, and was therefore held to represent nearly the condition 
of the original rock, was found on the Mc9al)i to be in nearly all cases of 
undoubtedly secondary origin and to have been formed by the carboniza- 
tion of iron oxides. It was found, moreover, that all of the constituents of 
the rocks, including the iron carbonate and oxides and the silica, could be 
shown to have been derived from an original green ferrous silicate which 
Spurr classed as glauconite, although the analysis showed very little potash. 
This explanation of the origin of the Mesabi ores has been accepted gen- 
erally. Recently the work of Ijeith on the Mesabi Range^ confirms Spurr's 
observations concerning the nature of the original mineral, its manner of 
formation and the manner in which iron carbonates and oxides are derived 
from it. On account of the scarcity or lack of potash, the writer objects 
to the name glauconite for the original ferrous silicate and coins a new 
name, greenalite. Spurr'*, however, after a review of the evidence, is 
still in favor of retaining the name glauconite for the Mesabi mineral, al- 
thougti acknowledging, as before, that it constitutes a somewhat unusual 
variety. 

7. African Iron Ore Deposits in Crystallin-c Schists, 

Among these the best known are the numerous iron ore deposits which 
France possesses in Algiers. The most important of them have hitherto 
been those of Mokta-El-Hadid (or Ain Mokra) in the Department of Con- 
Btantine, at the foot of the south slope of the Coast Range, between Cape 
de Fer and Bone, near Lake Fezzara. 

The ores consist of magnetite and red iron ore, and occur interbedded 
with limestones, forming part of a -series of garnetiferous-mica schists, in- 

* Bull. Minn. Oeol. Surv., No. 10, 'TVie Mesabi Iron-Bearing Rocks.' 
» Monogravh XLIII, U. S. Geol. Surv. 

• Amer, Geologist, June, 1902. 



BEDDED ORE DEPOSITS. 81 

tercalated in crystalline gneisses. The main ore deposit has a thickness 
of 40 meters (131 ft.). The production in some years rose to 430,000 tons* 
(1874). Other important occurrences have recently been exploited. 

Mention may also be made of the red hematite intercalated in the quartz- 
ite of the crystalline schists in the German possession of Togo at Banyeri, 
Kabu and Basari.^ 

(c) Origin of the Iron Ore Deposits of Crystalline Schists. 

To the remarkable works of Hj. Sjogren and J. H. L. Vogt^, on which 
the following remarks are in the main based, we owe some deeper insight 
into the genesis of the iron ores of the crystalline schists. It cannot be said, 
however, that the question of their genesis has as yet been conclusively 
answered. 

The theory of a direct sedimentary origin of the magnetite and hema- 
tite ore deposits is sustained, according to Vogt, by the following facts: 

1. Their complete conformity with the country rock. 

2. Their very pronounced- stratification. 

3. Their association with definite stratigraphic horizons. 

4. Their frequent association with limestone. 

5. The occurrence of chemically similar formations in younger non- 
metamorphic formations. 

Sjogren is inclined to regard the older Swedish iron ore deposits as lacus- 
trine or terrestrial, at most as littoral, which he supposes to have been se- 
gregated from very dilute iron solutions in the manner of bog ores and 
lake ores (see p. 101), that is, with the aid of vegetable material. In point 
of fact this hypothesis is supported by the occurrence in many deposits of 
substances probably of vegetable origin, such as petroleum, asphalt, bitumen 
and anthracite. The stock-like or lenticular form of manv old iron ore 
deposits is also readily explained if we imagine that they were deposited on 
a somewhat uneven surface under lacustrine conditions. On the other hand, 
it must be remarked that we know also of younger genuine marine iron 
ore deposits even containing mineralized ammonites and sea urchins, such 
as those of the Brown Jura and the Eocene. While this^ is true in the in- 
dividual cases, it must be assumed that the iron ores were primarily de- 
posited at the bottom of some body of water from highly dilute solutions. 
The formation of such solutions is to be explained by the decomposition of 
the finely interspersed iron ores and ferrous silicates contained in so many 

* E. Fuchs and L. de Laiinay: 'Tnui6 des Cites Min^raiix,' 1S03. 1, p. 721. 

' Ft. Hupfeld : 'Die Eiaenindustric in Tofco. * Mitth. a. d. dcutschen Schiitz^ijebietcn, 
Vol. XII, 1899, part 4. pp. 175-193. 

* Hj. Si5jrren: *Om de svenska jernmalnilar'Tons jrcncsis.' Ccrl. Foren i. Stock- 
holm, F6rh. 13, 1891, p. 373. J. H. L. Vogt: * Salten och Kanen,' Christiania, 1891. 



82 THE NATURE OF ORE DEPOSITS. 

older rocks^ througb the agency of terrestrial water charged with carbonic 
acid, sulphuric acid or organic acids. (On this mode of precipitation of 
iron^ see p. 102). The decomposition undoubtedly must have originally 
taken place in many cases in the form of iron carbonate. This was in most 
cases at once further oxidized into ferric hydrate. Only with an abundance 
of reducing organic substances could the carbonate remain as such; in 
most cases ferric hydrate was at once formed. The silicic acid in the quartz- 
ose iron ores may in* part be derived from alkaline iron solutions. From 
such a solution the silicic acid is precipitated simultaneously with the se- 
gregation of ferric hydrate. The hematite ores are in general rich in silicic 
acid, while the magnetic iron ores are poor in that respect. The latter often 
carry sprinklings of sulphur ores. These facts point to reducing processes in 
the formation of magnetic iron ores, by which the iron was probably pre- 
cipitated from carbonate solutions as carbonate, or from humic acid solu- 
tions at first as iron crenate, while during the formation of the hematite 
ores rich in silicic acid these reductions did not take place. 

The phosphoric acid content is derived originally from the apatite of 
th : rocks. Phosphoric acid is accumulated by plants ; when they decay it 
passes into solution as ammonium phosphate. During the sedimentation 
of the iron ores the phosphoric acid was also precipitated as iron or lime 
phosphate. 

Manganese is precipitated from solutions in the same way as iron, but 
since the iron is more rapidly oxidized, the manganese is precipitated later 
jWhen the solution contains less carbonic acid. In this way we may explain 
the fact that manganese ores are ordinarily found above the iron ores and 
associated with limy ores, often connected with limestone and dolomite. 

It was only by means of regional metamorphism, more particularly the 
factors which are probably most active in that process, pressure, moisture 
and heat, that the final alteration of the iron carbonate and ferric hydrate 
into magnetite and hematite was effected. Not only the ore beds, but also 
the country rock, undergo a complete recrystallization in this process (see 
remarks on p. 71 on Grangesberg). 

(B) Iron Ores as Original Intercalations In Normal Sediments* 

(a) SiLUBiAK Iron Ores. 
1. The Iron Ore Deposits in the Lower Silurian of Central Bohemia.^ 
The Bohemian iron ores are intercalated in Lower Silurian strata (Bar- 

*M. V. Lipoid: 'Die Eisensteiiilager der ailuriscben Grauwackenformation in 
BOhmen.' Jahrb. d. k. k. eeol. Reichsanst., Vol. XIII, 1863, pp. 339-448. With 
40 Fig. Jos. Vala and R. Helmhacker: 'Das Eisenateinvorkommen in der GeRend 
von Prag und Beraun.' Prage, 1873. C. Feistmantel: 'Die Eisensteine in der 



BEDDED ORE DEPOSITS. 83 

randoms stage D) made up in the main of quartzites^ associated with slateSi 
graywackes^ conglomerates^ diabases^ amygdaloids and diabase tnffs. 

The ores occur within these stages at different horizons : 

The lowest horizon, D^, consisting of conglomerates, graywackes, gray- 
wacke slates, diabase tuffs and tuff slates^ contains the iron ore deposits 
of the S&rka, Svdrov, Libecov and Chynava. Two vast beds of diabase tuffs 
and tuffaceous slate, separated and overlain by gritty slate, ore here the ore- 
bearing rock proper. This bed here consists of oolitic red hematite up to 5 
meters in thickness, but is elsewhere a poor blackish gray oolitic chamosite 
(a water-bearing aluminous iron silicate with slight magnesia content). 
These chamosite beds attain a thickness of up to 20 meters. The several ore 
beds in the tuff slates form extended lenses or short beds which either wedge 
out or pass along the strike into tuff slate poor in iron. 

An overlying horizon, D^, consisting essentially of an alternation of 
graywacke slates and quartzites, encloses the ores of Jinocan, Nucic, Chru&- 
tenic and Vraz. 

The most important is the ore bed of Nucic west of Prague. 

The Nucic ore possesses a pronounced oolitic structure. It consists of 
a groundmass of light brownish gray spathic iron ore, or more frequently 
of dark gray chamosite, in which the ooliths are interspersed as concentric- 
shelled ellipsoids of chamosite. The size of these small concretions ordi- 
narily varies between 1 and 2 millimeters in diameter. A very firm and 
brittle ore called sklenenka (glass ore) also occurring there is especially 
rich in ironspar and calcspar, which completely impregnate the groundmass 
of chamosite. 

Owing to the high percentage of phosphorus, most of the ores are treated 
by the Thomas process. 

The bed attains its greatest thickness of 16 in. at Nucic itself; the length 
in the strike has been ascertained to be 15 kilometers. It shows distinct 
stratification. Overlying and underlying it are graywacke slates, farther 
on also is quartzite with lower Silurian fossils. The ore bed itself has fur- 
nished some fossils, among them Trinud&us Omaius Barr., Asaphus No- 
bilis Barr., Orthis Macrostoma Barr. At times the bed has been influenced 
and bleached by decomposing solutions. In the outcrop to a depth of 6 to 
12 m. (19 to 38 ft.) the ore has been transformed into brown hematite. 

The Nucic beds especially, which are either flat or but gently inclined, 
are cut obliquely by numerous faults. At the present time the greatest out- 
put is from the open cuts and imderground workings of the two companies 

Etaj;e D des b6hmischen Silurgebirgies. ' Abh. d. k. B6hm. Ges. d. Wiss. VI, Vol. 
VlII, 1875 and 1876. Also, * Ueber die Lagerunffsverhaltnisae der Eisensteine, ' etc. 
Sittungfber, d. k. Bohm. Ges. d. Wiss., 1878, pp. 120-132. 



84 THE NATURE OF ORE DEPOSITS. 

operating the Nucic minee. The Zdic mines are the only others of im- 
portance. In 1898 Bohemia produced a total of 633,183.7 tons of iron 
ore. In 1899 the Prager Eisenindustrie at Nucic produced 396,734 tons ; 
the AtontangesellBchaft 344,718 tons of ore, with an average iron content 
of 37.25%. 

2. The Lmi-tr Silurian Iron Ores of the ThUringerwald and Vicinity, 

Oolitic iron ores eimilar to those of Bohemia' occur in the lowest horizon 
of the lower Silurian in the Thiiringerwald and the Frankenwald, as well 
as in the Vogtland. In recent years the deposit at Schmiudcfeld (Sachsen- 
Meiningen) near Grafenthal in Thiiringia has become eepeciaUj im- 
portant. 

The petrographic character of the Schmiedefeld iron ore has been studied 
by H. Loretz. According to this author it consists of thuringite and chamo- 
site. The thuringite ie a compact olive-greea mineral with a finely foliated 




Fij;. 44. — Thin section through a chainositc oolite from Schmiedefeld. (Enlar)^ 
fifty times.) 

crystalline texture, which on weathering often becomes oolitic. Its average 
chemical composition as given by Lorttz is as follows: 

SiO, 22 . 61 per cent. 

.\l,0, 16.80 

Fe,0, 15.43 

FeO 33.10 

M(?0 ■ 1 . 20 

ll,0 10.60 

Total 00.74 

' C. W. von Gumbel: ' FiclitelKebirce, ' 1879, pp. 235, 236, 420-428. Th. Liebe: 
'Ueberek'ht uber den Schichtenbau Osttburingens, Abh. ?,. geol. Spezialk. v. Preusacn. 
Vol. V, part 4, 1SS4. H. Loretz: 'Ziir Kenntniss der untersilurischen Eisensteine 
im Thflniiger Walde. ' Jahrb. d. k. preuss. Landeaanst, 1884, pp. 120-1 47. 



BEDDED ORE DEPOSITS. 85 

The tiinringite often forms email thin layers or oolitic granules in an 
ordinary soft clay slate, in which case it is called thuringite elate. The 
chamosite, which is far more abuodant than the thuringite, coDsistB of a 
dark gray compact aggregate of small concentric pellets, of about the size 
of millet, lying close together and cemented by siderite. 

We give the figure of a thin section through a typical chamosite oolite 
of Schmiedefeld. (Figure 44.) 

The chemical composition of typical chamosite ore from Schmiedefeld 
(W. Bottcher) is given under (a), while column (b) shows the calculated 
theoretical composition of true chamosite, as calculated by H. Loretz: 

M (h) 

SiO. 1«.63% SiO 20% 

AlA S-IS M/*:. 1.1 

Fe-O:, 3.73 Fe.O, 6 

FeO 45.13 FeO 42 

MrO 1.68 H,() 10 



CaO n.ftt 

P,Oj 0.44 Total 100 



TiO,. . 
H,0. . 



, 13.00 



Total 100.00 

The structural conditions as outlined by Lorotz are as follows: The 
Cambrian rocks, near Schmiedefeld. arc overlaid by quartzite similar to 




-(Iross-sertioci tliroUKh the main bed at Srhmipdcfeld. 
s, clay slitte; e, iron ore; h, dump. 

the phycod slates and by Griffel slates, these beds forming transition strata 
between Cambrian and lower Silurian beds. These are overlaid by iron- 
stone beds, followed by typical lower Silurian slates. The main iron ore 
bed is sometimes as much as 18 meters (.5!) ft.) thick and is now worked in 
the Ma.xhiitte at I'nterwellcnborn. Its position is shown in the cross-sec- 
tion (Fig. 45) kindly furnished by tlie mine manager. 

The production at Schmiedefeld for 1899 was 140,000 tons of iron ore. 



86. THE NATURE OF ORE DEPOSITS. 

A similar deposit of chamosite ore and thuringite slate occurs northwest 
of Hof in the valley of the Saale, and in inverted beds in the Steinach Val- 
ley of the Franconian forest. The thuringite rocks of Leuchtholz, near 
Hirchberg, contain numerous casts of orthis, (Gumbel.) 

The following examples are, because of their structure, classed in the 
same category as the lower Silurian iron ores of central Europe. 

3. The Clinton Hematite Ores. 

The Clinton* iron ore received its name from the town of Clinton, near 
Utica, New York, where it was extensively mined. The ore is an al- 
most constant accompaniment of the Clinton series of the Upper Si- 
lurian throughout its exposure in New York, Pennsylvania, Wisconsin, 
Virginia, Kentucky, Tennessee and Alabama. The ore forms one or more 
beds, interbedded with clay slates, sandstones and impure limestones, which 
are overlain by the Niagara slate and underlain by the Medina sandstone. 
The ore beds vary greatly in thickness and position. At Clinton three beds 
are known, the uppermost, 4 to 6 ft. thick, not being workable. The middle 
. bed, 2 ft. thick, is the only one now worked. At Birmingham, Alabama, the 
ore is rich in fossil remains and occurs in several beds which may reach a 
total thickness of 9 meters (29.5 ft.). 

The Clinton ore is often oolitic, and in that case is then called flaxseed 
ore. In this ore, from which the calcareous cement has often been leached 
out, the grains consist of concentric shells of iron oxide and some amorphous 
silica, about a nucleal grain of quartz. 

Some of the deposits often consist of an aggregate of countless frag- 
ments of various calcareous marine organisms, such as bryozoa, corals, cri- 
noids, brachiopods, etc. (fossil ore) all more or less replaced by iron oxide, 
and cemented by carbonate of lime. The soft ores are mostly red in color, of 
earthy appearance and loose texture. The hard ore is a highly ferru- 
ginous limestone. The hard ore has been found to average between 
35 and 40% of iron with 0.5% to 1% of phosphorus, and is seldom 
a bessemer ore^. According to C. H. Smyth and others, these hematite beds 
are original deposits in an inland sea that received the drainage of an ex- 
tensive area of crystalline rocks. The ferruginous and somewhat siliceous 
waters of this shallow body of water deposited the iron about nucleal grains 
of sand and replaced the calcium carbonate of the fossil fragments before 
the sediment forming the overlying strata was deposited. The alternative ex- 
planation of these red hematite beds by a subsequent replacement of beds of 

' C. H. Smyth, Jr: 'On the Clinton Iron Ore.' Am. Jour. i?ci., June, 1892, p. 
487. Zeit. /. Prak. Geol., 1894, p. 304. 

' W. B. Phillips: 'Iron Making in Alabama,' 1898, Alabama Geol. Survey. 



BEDDED ORE DEPOSITS. 87 

limestone by iron-bearing seepage waters seems to us to have been complete- 
ly disproved by Smyth. 

The oolitic hematites of Belle Island^ near Newfoundland, seem to belong 
to the Clinton group. They form two beds intercalated in slates and sand- 
stones, one 3 m. (9.8 ft.) and the other 1.8 m. (5.9 ft.) thick, the ore frac- 
turing in remarkably regular parallelopipeds. 

The precipitation of amorphous silica and the formation of iron oolite 
is a very common phenomenon, as has been proved by Ch. Bleicher^s* in- 
vestigations upon samples of the most diverse origin. 

(b) Ironstone Deposits of the Cabboniferous Rocks. 

Wherever the carboniferous rocks contain coal seams, there are almost 
always beds of iron ore of more or less economic importance. One of the 
most carefully investigated European examples is the following : 

1. The Iron Ores of the Ruhr Coal Basin, 

The iron ores of the Ruhr coal basin' are associated with the lowest and 
leanest coal measure of that locality. Baumler distinguishes the following 
occurrence : 

I. A Spathic Iron Ore Measure. 

This bed, which is 0.24 m. (0.7 ft.) to 0.48 m. (1.5 ft.), more rarely 1.4 
m. (4.6 ft.) thick, has been traced for a distance of several miles, and has 
here and there been worked. It is not, however, a single bed throughout, 
but consists of thin lenticular beds as much as 1 km. (0.6 mile) in ex- 
tent, with intervening barren layers. This ore is a yellowish gray granular 
crystalline spathic ironstone ore without lamination or cleavage structure 
and carrying 45.66% of iron (65.3% when roasted) with some carbonace- 
ous material. Underlying the iron ore measures there is usually a layer of 
coal (Kohlenpacken) varying up to 30 cm. (1 ft.) thick, while a foot above 
the barren overlying rock often contains a layer of spherosiderite concre- 
tions. The spathic iron oro horizon lies 80 to 100 m. (260 to 328 ft.) below 
the Mausegatt, the leading bed of the lean measures. Of course the ore bed 

* Ch. Bleicher: 'Sur la structure mikroscopique du mineral de fer de Lorraine.' 
Compte Rendu, 114, p. 590. 

'R.Peters: 'Der Spatheisenstein der westfalisrhen Steinkohlenformation.' Z. 
d. V. Deutsch. Insj. I. 1857, p. 155. Haumlcr: 'T'eber das Vorkommen der Eisen- 
steine im Westfalischen Steinkolengebirfce. Z. f. B. H.- u. S.-Weseri im preuss. St., 
1868, Vol. XVTT, p. 426. W. Runge: 'Das Ruhr-Steinkohlenbecken.' Berlin. 1892, 
pp. 70-73. 



88 TEE NATURE OF ORE DEPOSITS. 

participates in all the flexures and faults to which the entire formation has 
been subjected. 

II. Clay Ironstone Measures. 

These ores accompany the coal beds, especially in the lowest measures, 
lying either above or below or forming partings, which may replace 
the coal seam altogether. This clay ironstone is very rich in carbon, and 
contains as high as 39% of iron (up to 60% roasted). In the fifties and 
sixties large quantities of this black band ore were produced. About four- 
teen different layers, varying up to a meter in thickness, have yielded work- 
able ores in the past. The ores are sometimes so rich in phosphorus that 
they are used for the production of superphosphates. 

III. Spherosiderites. 

Sphcrosiderite concretions containing up to 45% of iron are not infre- 
quently found in the clay slates an-d coal seams of the lower measures, 
and sometimes unite and form extensive beds of clay iron ore. 

The production of iron ores in the Ruhr coal district reached, according 
to Baumler, 167,609 tons in 1890. 

2. Ccurhonaceous Iron Ores of Upper Silesia and Saxony. 

Workable ore beds also occur in the coal basin of upper Silesia.^ Spher- 
osiderites within the clay slates are especially common, and in rare cases, as 
in the upper coal bed of the Saara measure, and at Czernitz, bituminous 
iron ores (black band ores) have also been developed. The spherosiderites 
form large lenticular and nodular masses, which may extend along the strike 
for a few meters. Fig. 46 illustrates this occurrence. 

The largest production in the sixties took place at Antonienhutte, Frie- 
dcnshiitte and Ruda, at Zalenze, Janow, Orzesze, Dubensko and Ornonto- 
witz. 

At many points, as at Zalenze, it has been noted that the spherosiderites 
occur especially above the flat depressions in the coal measures. 

In 1900 upper Silesia produced 7,147 tons of carbonaceous iron ore. In 
the Zwickau area district^ of Saxony spherosiderites and carbonaceous iron 
ore were for a while produced along with the coal. 

Deposits of the first named ore were mined from especial pits in the region 

* F. Romer: 'Geologic von Oberschlesien. ' 1870. Appendix bv W. Runge, p. 
533. 

* H. Mietzsch: 'Erlauterungen zu Section Zwickau der geol. Spez.-K./ 1877. d. 11. 



BEDDED ORE DEPOSITS. 



89 



of the Kusskohlen measures and also from the Segen Gottes measures (lower 
reef) within the clay slates. Carbonaceous iron ore, found, for example, 
in the lower part of the measure at the Bahnhof shaft at Zwickau, formed 
a stratum 0.2 m. (0.6 ft.) in thickness, containing veins of zincblende, but 
possessing little extent. 

At the coal mines of Kastner & Co., in the Reinsdorff, near Zwickau, a 
spathic iron ore deposit up to 0.8 m. (2.6 ft.) thick has recently* been dis- 
covered under the earthy coal measures. The spherosiderite found between 
the third and fourth measures of the Hilfe Gottes shaft, near Zwickau, 
contained the rare mineral whewellite, besides zincblende and iron pyrite in 
its fissures. 




Fig. 46. — Section through the carbonaceous clay slate at Janow. (F. Rdmer.) 

8, sand; t, clay slate; e, spherosiderite lenses; k, coal pockets and carbonized sigil- 
laria trunks. 



Spathic iron ore and brown hematite are also found in the Carboniferous 
formations of the eastern Austrian Alps, as at Turrach, southwest of Murau, 
where 5,327.3 tons of brown hematite were produced in 1898. 



3. Carbonaceous Iron Ores of Great Britain. 

Great Britain is rich in deposits of this kind. In southern Wales' most 
of the ironstones are found in the lower divisions of the productive coal 
measures. Many of the nunierous blackband beds of that region seem to 
be continuous throughout the entire district, as, for example, the Three-quar- 
ter Balls measure. The main production in Wales comes from Ebbw Vale, 

* Jahrb. f. B. u. H. in Sachsen, 1899, p. 141. 

» Phillips-Louis. ' Ore Deposits. ' 1896, pp. 285. 323. 



90 THE NATURE OF ORE DEPOSITS. 

Blaenafon^ Pontypool^ Abercam and Dowlais. The ore contains 21 to 38% 
of iron. The production of South Wales in 1880 was 170,000 tons. Import- 
ant deposits of blackband ironstone also occur in Scotland. The iron ore 
measures of that country occur, according to H. Louis, in both the upper and 
the lower Carboniferous formations. The upper Carboniferous contains 
seven beds of this ore, one of which reaches a thickness of 0.9 m. (2.9 ft.). 
The lower Carboniferous holds three iron ore beds 0.3 m. thick. These 
blackband ores contain such an abundance of carbonaceous matter that 
they burn in the roasting furnaces without the addition of fuel, the residue 
containing 50 to 70% of iron. Besides these blackband ores, clay ironstone 
occurs at Bauton, Denny and elsewhere. In 1881 Scotland produced 1,402,- 
700 tons of blackband ore and 1,192,675 tons of clay ironstone. In 1894, 
however, the total output had dropped to 631,304 tons. 

(c) The Iron Ore Formations of the Northern Alps (Probably 

Permian). 

Iron ore deposits occur in the so-called graywacke* zone, which lies be- 
tween the central range of crystalline rocks and the limestone peaks of the 
Tyrolean Alps on the north, the Salzkammergut of Styria and Austria. Re- 
cently, through the labors of M. Vacek, the geologic age and structure of 
the rocks of this complicated region have been determined, and the true 
stratigraphic position of these iron ores, hitherto in dispute, has been clearly 
established. In the area between Enns and Mur the iron ores consist of 
spathic ironstones and brown hematites with associated slaty, conglomeratic 
and breccia-like rocks, especially limestone breccias with a sericitic cement, 
whose fragments are derived from the upper Silurian. Ordinarily the iron 
ores form the lowest beds, resting unconformably on lower Devonian lime- 
stone, as at Eisenerz, or sometimes on still older gneisses. The slates and 
breccias, which are well developed at Admont, but are quite subordinate in 
the Eisenerz measures, are often unconformably overlain by lower Triassic 
Werfener slates. The exact age of the formation is still unknown, but is 
either Permian or between that and upper Devonian. 

A continuous series of such iron ore deposits is always found on the im- 
conformitv at the base of the lower Triassic formation, from Schwatz and 
Pillersee in Tyrol, across Dienten, Flachau and Werfen in Salzburg, Liet- 
zen. Admont in the Eadmer, Eisenerz, at Feistereck, on the Veitsch and Neu- 

* " Graywacke is an old name of loose signification, but chiefly applied to metamor- 
phosed shaly sandstones that yield a tough irregularly breaking rock different from 
slate on the one hand and from quartzite on the other." — J. F. Kemp, ' Handbook of 
Rocks/ pp. 140. 



BEDDED ORE DEPOSITS. 91 

berg in Styria as far as Keichenau in lower Austria. The strata unques- 
tionably attain their greatest development at Erzberg^ near Eisenerz. 

The Erzberg Near Eisenerz. 

Eisenerz* lies on the northwest side of the Prebichel Pass, which connects 
the valley leading to the Enns near Hieflau with the valley discharging into 
the Mur at Leoben. The district is in a depression of the high mountain 
range lying between the lower Tauem on the west and the Hochschwab on 
the east. 

The Erzberg itself is an almost isolated cone 1,537 m. (5,131 ft.) high, 
whose summit affords a magnificent panorama. The upper part of the cone 
is formed of an enormous thickening of an iron ore bed, which, according 
to M. Vacek, rests unconformably on lower Devonian limestone, carrying 
Bronieus palifer Beyr, etc. This unconformity is well exposed in the lime- 
stone cliffs, which show the underlying rock projecting into the ore de- 
posit. The accompanying cross-section after M. Vacek (Fig. 47) gives 
a clear representation of the structural conditions. It shows that the lower 
Devonian Sauberg limestones underlying the ore beds rest unconformably on 
the so-called granular graywackes of Eisenerz, rocks which, according to 
Vacek, are really gneisses. In the northeastern part of the Erzberg, in the 
Sobberhaggen, the ore lies immediately above this graywacke-like gneiss. It 
should be noted that in the eastern part of the district, near the Barbara 
chapel, the Erzberg ore deposit is unconformably overlain by the Werfener 
slates which dip north. These slates ordinarily begin with a breccia forma- 
tion, seen in the Peter Tunner adit. In the western part of the Erzberg, 
however, through which the profile is drawn, these lower Triassic Werfener 
strata have been removed by denudation, and the ores outcrop. 

According to F. v. Hauers the ore bed is sometimes as much as 125 m. 
(410 ft.) in thickness. A part of the deposit shows, however, a large pro- 
portion of ankerite, and all transitions from siderite and ankerite to or- 
dinary limestone, and in several cases the deposits consist entirely of "Roh- 
wande," as the ankerite ore is called. 

The ore averages 40% of iron. The spathic iron ore is not entirely free 

* F. Ritter von Ferro: Innerberper Hauptffewerkschaft. Tunners mont. Jahrb., 
Vol. Ill, 1845, p. 197. A. von Schouppe: 'Erzberp bei Eisenerz.' Jahrb. d k. k. 

feol. Reichsanst. 1854, p. 396. A. Miller von Hauenfels: 'Die steiermarkischen 
(er^baue,' in 'Ein treues Bild des Herzo^h, Steiermark,' Vienna, 1859, p. 16. 



D. Stur: 'Vorkonimen obersilur. Petrefacten am Erzberp.' Jahrb. d. k. k. geol. 
Reichsanst., 1865, p. 267. F. von Hauer: 'Geolopie dor 6sterr. Monarchie. ' 1875, 
p. 223. M. Vacek : 'Ueber den geolojdschen Bau der Centralalpen zwischen Enns und 
Mur.* Verh. d. k. k. geol. Reichsanst., 1886, p. 71. Also 'Skizze eines geologischen 
Profiles durch den steierischen Erzberg.' Jahrb. d. k. k. geol. Reichsanst., 1900, Vol. 
L., p. 23. (The foregoing represent the most important publications about Eisenerz.) 



THE NATURE OE ORE DEPOSITS. 




BEDDED ORE DEPOSITS. 93 

from sulphides, as p}Tite and chalcopyrite occur in scattered grains, and 
rarely it holds small streaks of cinnabar. The phosphorus content hardly 
reaches 0.01%. 

The mining industry of Eisenerz began in Roman time. Documents 
extending back to the year 712 A. D. are said to have been formerly in ex- 
istence. At any rate Tacitus and other classic writers mention "Noric iron." 
The mining is carried on both by open cuts rising in terraces along the slope, 
and by underground work. 

The production in 1898 was as follows : 

Innerberger Gewerkschaft, near Eisenerz, 923,454.2 tons of spathic iron 
ore; Vordernberger Gewerkschaft (Oesterreichische Alpine- Montangesell- 
schaft), 75,038 tons; Veitsch mine, 152.5 tons; Olimie mine, near Win- 
disch-Landsberg, 965 tons. 

(d) Permian Spherosidebites. 

Clay ironstone concretions occur in the Acanthodes slates of the Lebach 
formation of the lower Rothliegende at Saarbrucken. These ellipsoidal con- 
cretions often enclose organic remains, such as Archegosaurus and Walchia, 
They are called "Knopfstrich." 

At Goldlauter, near Suhl, in Thuringia, the dark clay slates of the Roth- 
liegende carry nodular concretions consisting of alternate shells of 
slaty brown spar, arsenopyrite and pyrite, and often containing a central 
core of copper pyrite, gray copper and native silver.^ 

(e) Sedimentary Ironstones of Jurassic Age. 

1. Liassic Iron Ores. 

Germany possesses true ironstone measures in many of the Jurassic forma- 
tions^. The Lias, for example, contains four beds of finely oolitic, usually 
porous limonite, with an aggregate thickness at Bundheim, near Harzburg, 
of 4 m. (13.1 ft.) (zone of Amm. Buchlandi), The output of the Fried- 
erike mine at that place averaged 44% of iron. The ironstone measures of 
Willershausen, Calefehl and Ohlorsliausen in Hanover also belong to the 
Lias (zone of Amm, Jamesrmi and .4mm. Ibex). 

The Middle Lias of England also contains iron ores mined in the Cleve- 
land district. The principal bed extends over an area of 350 square miles, 

* B. von Cotta: 'p:rzlafierstatten/ II, 1861, p. 72. 

* J. Haniel: 'Ueber das Auftreten und die Vcrbroitung des Eisensteins in den 
Jura-Ablac:erunRen Deutachlands.' Z. d. Deutsch. geol. Ges., Vol. XXVI, 1874, 
pp. 69-118. 



94 THE NATURE OF ORE DEPOSITS. 

and is workable for one-fifth of this area^. The ores average 30% of iron 
and 1.5% of phosphoric acid. 

2. Iron Ores of the Dogger Formation of the Jura. 

The most widely distributed iron ore beds of Jurassic age are those of 
the Dogger formation. The Minette ore beds belong to this fonnation. 

Oolitic Iron Ores (Minettes) of Luxemberg and Lorraine*. 

The Minette beds belong to the lower Dogger formation, which is char- 
acterized by the fossils Harpoceras Murchisonae and Harpoceras Opalinum. 
The accompanying profile (Fig. 48), after W. Branco, gives the detailed 
classification of the various beds of the Minette horizon. 

The J^Iinette measures occur mainly throughout the frontier region be- 
tween Luxemberg, German Lorraine and French Lorraine, in a strip of 100 
km. (60 miles) long, 18 km. (10.8 miles) wide, west of the Moselle, the 
portion belonging to Germany being 60 km. (36 miles) long and 12 km. 
(7.2 miles) wide. 

The most important mines of Luxemberg are at Beles, Esch and Riim- 
lingen; of Lorraine (German) Ottingen, Tillots, Neufchef, Hayingen, 
Moyeuvre, Rosslingen, Maringen, Vaux, Chabonniere, Varraines, Nov^ant 
and Arry; in France, Longwy and Briey. This plateau-like area is tra- 
versed by long cliffs running north and south, which show at the foot a 
gently sloping area of Liassic beds, and at the summit an abrupt slope cut in 
oolitic limestone (Dogger). At the boundary between the gentle slope and 
the steep escarpment the outcrops of the Minette measures are usually 
found. In Luxemberg, the valley of the Alzette divides the formation into 
two flat basins. The different beds do not always extend uniformly through- 
out both basins, but show the distribution indicated in the diagram (Fig. 
49, after Van Werveke), which also applies to other areas. 

> J. D. Kendall: 'The Iron Oree of Great Britain/ 1893. Cited by Phillips-Louis, 
'Ore Deposits,' p. 44. 

* E. Giesler: 'Das oolithische Eisensteinvorkommen in Deutsch-Lothrinpen.' 
Z. f. B. H. u. S.-Wesen im preuss. St. Vol. XXIII, 1875, pp. 9-41. W. Branco: 'Der 
untere Dogger Deiitsch-Lothringens. ' Strassburg, 1879. Van Werveke: 'Erlau- 
teningen zur geologischen Uebersirhtslcarte des westlichen Deutsch-Lothringen. ' 
Strassburg, 1887, pp. 83-99. L. Hoffmann: Stahl u. Eisen, 1896, Nos. 23 and 24. 



» pp. 
Schr5dter: Zeit. /. Prak. GeoL, 1897, p. 296. W. Kohlmannj^ 'Die Minettefor- 

aer Fentsch.' Stahl u. Eisen, July, 

1898, p. 363. ' Uebersichts-karte der Eisenerzfelder des westlichen Deutsch-Loth- 



mation nSrdlich der Fentsch.' Stahl u. Eisen, July, 1898. Zeit, /. Prak. Geol., 



ringen.' 3d edition, Strassburg, 1899. F. Greven: 'DasVorkom. der Oolith Eisenerz 
im siidlirhen Deutsch-Lothringen,' Stahl u. Eisen, 1898, No. 1. H. Ansel: 'Die 
Oolith. Eisenerzform. Deutsch-Lothringens.* Zeit. f. Prak. Geol., 1901, pp. 81-94. L. 
von Wcrv'eke: 'Ueber die Zusammensetzung und Entstchung der Minetten.' lie- 
viewed Zeit, f. Prak. Geol, 1901, pp. 396-403. 



BEDDED ORE DEPOSITS. 95 

In German Lorraine the following strata are distinguiBhed from below 
upward : 

The black bed, the moat extensive, but bo Biliceous that it is only mined 




for a flux for the calcareous orfcs; 1.2 to 3.9 in. (-1 ft. to 13 ft.) thick. 

The brown bed, whouc ore is also silifuoiis, id separated from the preced- 
ing by a marly parting to 4 m. (0 to 13.1 ft.) thick. 



96 



TEE NATURE OF ORE DEPOSITS. 



The gray bed, whose nearly uniform thickness of 5 to 6 m. (16.4 ft. 
to 19.6* ft.) and excellent quality make it the most important, is accom- 
panied by a yellow bed and carries as fossils Oryphaera ferruginea, Amm. 
radians, etc. 

The red limy bed, the most valuable of the Luxemberg beds, has a 
maximum thickness of 8 m. (26.2 ft.), though seldom workable in German 
Lorraine; its lower layers contain Amm, Murchisonae and Pholadomya 
reticulata. 

The red sandy bed, the thickest of all, being sometimes 13 m. (42 ft.) 
through ; but it contains a great deal of quartz in sandy grains. 

The following table, by H. Ansel, gives a summary of tlie average chem- 
ical composition of the different beds, only the technically important ele- 
ments being given : 



Bed. Fe C^O SiO^ Al^Oa 

Black 30 6 24.5 10 

Brown 34.3 8.6 16.6 6.5 

Gray 39 8.0 7.5 6 

Yellow 36 12.3 8.5 3 

Red (limy) 40 9.5 7.5 5 

Red (siliceous) 31 5.3 33.6 4.2 



1.4 



1.7 
1.3 
1.8 
1.6 



MgO 

1.5 
2 

1.6 
1.4 
1.2 
9.5 



Wesdickir FUigtl 



Mitdingett Obtthnm. 



I Osdicher FUigel 




scKroiuwM Lagtr 



^UMUb der L&nge 1 : 25000. d«r B3ho 1 1 0000 
Fig. 49. — Diagram showing the development of the Miuette measures. (Van Werveke.) 



The Minettes of Lorraine consist of oolitic grains, mostly less than 0.25 
millimeter in diameter, and consist essentially of ferric hydrate. The grains 
have a smooth surface and are bound together by a cement that is usually 
calcareous, but is rarely clayey or siliceous from the presence of interspersed 
quartz grains. In thin section under the microscope tlie oolites show very 
distinct concentric shells about one or sometimes two cores. In raro 
cases organic remains are found to have served as a nucleus, consisting of 
fragments of echinoderms, segments of crinoid stems or small gastropods. 
On the other hand, the grains sometimes contain scales of an indeter- 



BEDDED ORE DEPOSITS. 97 

minate green iron silicate, and the presence of a microscopically fine 
siliceous skeleton enclosed in the limonite oolites indicates a former greater 
abundance of the iron silicates. More frequently . scales are found of a 
chamosite-like mineral in the cementing material. In some beds iron spar 
is present in considerable amount, constituting as much as 60% of the ore 
of the lowest bed. Pyrite is also occasionally present, particularly in the 
black bed ores. In some Minettes the green mineral of the cement and 
the limonite of the oolites are both replaced by magnetite. Xot infrequent- 
ly the ores contain calcspar casts of large fossils, and sometimes carbonized 
wood remains. 

The beds of the ore-carrying Dogger formation are inclined gently west- 
ward. The structural feature of the greatest importance to the mining in- 
dustry is the faulting, and there are numerous displacements along north- 
east fissures such as the fault of Deutsch-Oth, with a throw of 120 m. 
(393 ft.) and the fault of Gorze-Metz, known for a distance of 85 km. 
(51 miles). 

A valuable summary of our present knowledge concerning the genesis 
of the Minettes is given by L. van Werveke (1901). According to him 
most authors agree that the oolitic iron ores of Ix)rraine were deposited on 
the bottom of a shallow coastal sea. "The iron was brought from the land 
to the sea by brooks and rivers, and was precipitated in very diverse forms 
as silicate (looking like glauconite), also as carbonate, sulphide and ses- 
quioxide in the upper strata, possibly also as ferric hydrate." (L. Van 
Werveke.) The cement in part is a mechanical sediment. 

Another theory less generally accepted is advanced by Villain. Accord- 
ing to him, the iron-bearing solutions were carried directly to the sea by 
thennal springs issuing from fissures in the ocean's bed. For the deposits 
of German Lorraine at any rate the agency of such "failles hourricieres" 
(feeding faults) seems to be untenable. A metasomatic origin of the Min- 
ettes seems to be altogether out of the question. 

The production of Minette ores in the French department of Meurthe-et- 
Moselle was 2,630,311 tons in 1890. In German Lorraine 5,955,351 
tens of iron ore were produced in 1899. The stock of ore still available is 
very large, being estimated at two thousand million tons in the German 
areas. 

3. The Iron Ores of the Dogger Formation of Wurtemburg, Upper Silesia 

and Switzerland. 

The iron ore measures of Wurtemburg belong to the Jura (zone of Amm. 
Murchisonae), e^^pecially in the region of Wasseralfingen and Aalen. 



98 THE NATURE OF ORE DEPOSITS. 

The sedimentary sequence at that locality is, according to Schuler/ as 
follows : 

Sandstones, sandy slates and clay sandstones overlying the measure; 
upper ironstone bed 1.1 m. (3.6 ft.) ; sandstones and sandy slates 10 m. 
(32.8 ft) ; lower ironstone bed, 1.6 m. (5.2 ft) ; so-called stalhstein and 
sandy hard limestone .02 m. (4-5 in.) ; sandstones and clay sandstones un- 
derlying the above. 

The ores of Waseeralfingen and Aalen are oolitic red and brown hema- 
tites, containing about 40% of iron. They not infrequently enclose fos- 
sils, especially Amm. Mvrchisonae, Avicula elegans and laevigata, Venvlites 
aalensis, Pecten demissus. The production at the present day is inconsid- 
erable. 

The Dogger formation of upper Silesia also encloses iron ore in a zone 
characterized by fossils of Ammonites parkinsoni, according to F. Romer*. 
At Bodzanowitz, Wichrow and Stemalitz, southeast of Landsberg, a sandy 
upper bed and a purer lower bed of spherosidcrite have long been mined 
for the Malapane furnaces. Similar occurrences are mined in Poland at 
Kostrzyn and Przystayn, as well as at Stara Kuznica. 

In the iron mines of the Kleine Windgalle, in the canton of Uri (Switz- 
erland) oolitic iron ores belonging to the Dogger arc seen altered by dyna- 
mo-metamorphism ; the hematite concretions have been pressed into flat 
lenses tfnd iron silicates and magnetite crystals have been formed*. 

(f ) The Eocene Iron Oolites of Kessenbero and Sonthofen, Bavaria. 

In the Nummulitic sandstone* of Kressenberg and Sonthofen in upper 
Bavaria three groups of oolitic limonite beds are intercalated, which have 
been steeply upraised along with the other strata and dislocated by many 
faults. The local miner gives the name lodes (gange) to these measures, 
the principal one of which attains a thickness of two meters. Besides glau- 
conite, the ore contains numerous quartz grains, and thus gradually passes 
^ into an iron sandstone. The most abundant fossil of the measure is Con- 
oclypeus conoideus Ag., whose shell is entirely filled with oolitic brown 
hematite. 

(g) Bog Iron Ores and Lake Ores. 

This class of the iron ore deposits is of especial interest because the beds 

* J. Haniel : ' Ueber diis Auftreten und die Verbreitung ties Eisensteins in den 
Jura-Ablagerungen Deutsclilands. ' Z. d. Deutsch. geol. Ges., Vol. XXVI, 1874, p. 97. 

' F. Romer: 'Geologie von Oberechlesien,' 1870, p. 210. 

' A. Heim: 'Mechanismus der Gebirgsbildung,' Vol. I, p. 62, Vol. II, p. 98. 

*C. W. Giimbel: *Geogn. Beschr. dos bayerischen Alpengebirges,' 1861, p. 647. 
O. M. Ueis: *Zur Geologie der Eisenoolithe mhrenden Eocanschichten am Kressen- 
berge in Bayeru.' Geogn, Jahresh,, Munich, 1897. 



BEDDED ORE DEPOSITS. 99 

are now formings and the process of ore formation is taking place, as it 
were, before our eyes ; so that we may obtain important ihf ormation bearing 
upon the genesis of the older formations. In addition to this geologic im- 
portance, they have recently acquired an economic value, since it is now 
possible toUmelt these high phosphorus ores, and at the same time to re- 
cover the phosphoric acid in them, and return it to Nature as the fertilizer 
known in Europe as Thomas meal. 

Character and Mode of Deposition of Bog amd of Lacustrine Iran Ores} 

Bog iron ore, also called swamp ore, meadow ore and bog ore, is yel- 
lowish, brownish or blackish brown limonite, with resinous luster on fresh 
fractures, always highly porous and cavernous, often slag-like and hard, 
sometimes ochrous, loose, earthy and mingled with many other substances. 
The ores contain hydrated iron silicate (a gelatinizing basic iron-silicate), 
also iron phosphates, crenates, ulmates and humates. The ores contain 
between 20 and 60% of FejOg. The phosphoric acid content rises as high as 
10%. There is also a mechanical admixture of sand grains and clayey parti- 
cles. 

Chemical Analyses of Lacustrine and Bog Ores^. 

I. II. III. IV. 

Ironoxide 62.92 67.461 .|,^ 62.57 

Manganese oxide 4.13 3.19J °^'^^ 5.58 

SUica 8.12 7.00 9.20 12.64 

Phosphoric arid 3.44 0.67 10.99 0.48 

Sulphuric acid 3.07 0.07 

Alumina 4.60 0.41 3.58 

Lime 0.90 1.37 

Magnesia 0.19 

Water 18.40 17.00 28.80 13.53 



101.66 99.29 100.50 99.82 

I. Bog ore from Schleswig (Pfaflf). 

II. From Auer near Moritzburg in Saxony (Bischof). 

III. From Leipzig (Erdmaun). 

IV. Average of thirty analyses of Swedish lake ores (Svanberg). 

Deposits of bog iron ore are found where surface water stagnates in the 
shallow depressions of flat lands, especially in the vicinity of sluggish streams 
whose waters are colored brown by dissolved humous acids or humic salts, 

» F. Senft: 'Die Torf und Liraonitbildungen/ etc. Leipzig, 1862. F. M. Stapff: 
Ueber die Entstehung der Seeerze.' Z. d. Deutsch. geol. Ges., Vol. XVIII, 1866, 
pp. 86-173. A. W. Cronquiat: 'Om sjomalmyfyndigheten,' etc. Geol. For. Fork. 
No. 65, Vol. V, 1880, p. 402. Hj. Sj5gren: 'Oni de svenska jemmalmens genesis.' 
Geol. For. Fork. Vol. XIII, 1891, p. 373. II. Klebs: 'Dm Sumpferz.' Vortrag, 
Kdnigsberg, 1896. 

' F. Zirkel. ' Petrographie. ' III, p. 574. 



tr-^ 



100 THE NATURE OF ORE DEPOSITS. 

and in the moor and meadow bottoms of the lowlands of northern Europe^ 
Asia and North America. The Saxon and Prussian parts of lower Lusatia, 
Brandenburg, Mecklenburg, Pomerania, Prussia, Masuria, Poland, Euro- 
pean Russia, Holland, Finland and Sweden are rich in bog iron ores. In 
North America the Three River district, Province of Quebec,' contains a 
typical deposit, in which mining was begun as early as 1730. Sometimes 
ores of this kind are also found on high plateaus of the mountains of central 
Germany. 

These deposits rarely attain a thickness of over a meter. For the most part 
they show no stratification. Often they form isolated lumps, cakes or slabs, 
which exert an unfavorable influence on the immediately overlying field or 
meadow land, because they shut off water and air from the deeper layers 
of soil and hence are disliked by the farmers. 

These iron ores have been worked since the earliest period known ; hence 
Linn^ called them Tophus Tubalcaini, because Tubal Cain, the first iron 
worker, is supposed to have manufactured iron out of them. 

The Lake ores (Sjomalmer of the Swedes) are somewhat different in 
quality and quite different in their deposition. They are found at the bot- 
tom of innumerable lakes in the Swedish Province of Sm&land, Ostergotland, 
Dalame, Herje&dalen, Jamtland and Norrland ; in Finland, European Rus- 
sia and in Canada. They are mostly found on a sandy bottom at a dis- 
tance of about ten meters from the shore and up to a depth of about 10 m. 
(32.8 ft.). The deposits are usually thin, rarely reaching 0.5 m. (1.6 ft.) 
in thickness, but as they may be obtained by simple dredging, they are 
worked even if but 10 cm. to 15 cm. (4 to 6 inches) thick. The supply is 
renewed in about fifteen to thirty years. "Estque thesaurus hie perennis 
et inexhaustus'^ (this is a perpetual and inexhaustible treasure), says 
Swedenborg of these lake ores of his home. The ore in the lakes does not 
form a continuous sheet, but occurs in round or elongated patches, whose 
direction and arrangement is evidently determined by the currents due to 
streams entering the lakes, since the ore beds are in shallows covered by 
an abundant growth of water plants, while the currents supply sand and 
mud. Lake ores sometimes occur in rivers, as, for example, in the channels 
connecting Swedish lakes, but the deposits only occur in quiet water found 
on the convex side of curves and not in the rapid current. Thus we have 
an example, showing how streaks or linear masses of ore of fairly uniform 
character may be formed with and as part of a series of sediments. 

The formation of these lake ores is accomplished in several stages, each 
characterized by different material. In the first stage the iron oxide settling 
on the bottom, at first as a light ochrous mud, gradually hardens into crusts, 
having the luster, color and hardness of true ore. This mud has a black- 



BEDDED ORE DEPOSITS. , 101 

ish gray, brownish or greenish color, and is filled with vegetal d6bris. Ex- 
posed to the air, it dries to a gray or yellow powder. It is rich in g;elatinoii6 
silica and contains numerous algae. On hardening, the masses of jmud 
form either compact lumps (rusor), small or large discs and balls, .pr eise 
they encrust roots, portions of trunks and branches of plants and anlma^ 
remains, such as beetles and worm tubes, Phryganid quivers and the like 
All of these deposits consist partly of hard, brown resinous-lustrous and 
partly loose, yellowish or brownish ochrous ore. In the spherical masses 
concentric shells of hard and loose ore alternate, often about a nucleal grain 
of sand or a vegetal remnant. The Swedish miners class the ores accord- 
ing to size and shape of these concretions as krutmalm (powder ore), aert- 
malm (pea ore), bonmalm (bean ore), penningmalm (penny ore) and 
skraggmalm (fragment ore). The fresh and soft unhardened ores often 
. contain the phosphoric acid in the form of earthy vivianite, a blue iron ore, 
which may be greatly concentrated at certain spots. A good deal of man- 
ganese ore, probably in the form of wad, is also frequently mixed with the 
pulverulent lake ores of Sweden. 

General Remarks on the Origin of Lake and Boo Ores. 

It is certain that the deposition of all these ores took place from very 
dilute iron solutions, belonging to either the groundwater or that of lakes 
and rivers. The origin of the iron is apparent, for almost all rocks contain 
iron compounds, which, under certain circumstances, are soluble. If rare 
metals are present in Ihe ores, one must look for older primary deposits 
of sulphide ores, whose decomposition furnished the material for such solu- 
tions. Thus in the Lake ores of Sweden there are found traces of copper, 
nickel, cobalt and zinc, which unquestionably are derived from decomposed 
pyrites of older deposits, which are abundant in the vicinity. Thus a bog 
ore from the Tertiary trough between Grochau and Briesnitz, which lies 
southwest of the nickel ore deposit of Frankenstein in Silesia, was found to 
contain : 

Nickel 3.5% 

Cobalt 1.3 

Copper 0.1 

Next follows the question, What was the nature of the solutions? The 
following are the chief solvents: 

1. Sulphuric acid formed by the decomposition of iron-bearing sulphides. 

2. Carbonic acid supplied by the air and by decaying organisms, and to 
some extent by the living animals. This enables it to attack various sili- 
cates. 



_ • 






102 . vj^e'natvre of ore deposits. 



>• • 



••. 



3. Orgaiiic'^dids also play a part. These are, moreover, transfonned into 
carbonic? aieij*by oxidation, when vegetable masses decompose. In the pres- 
encfi-.of Sfetxaying vegetable matter, deprived of an adequate oxygen supply, 
Afbn jfesquioxide is reduced to ferrous oxide, which forms soluble double 

•*./sjCl^, with humous acids and ammonium. 

*• • • 

: • The precipitation of iron from these dilute solutions may take place in 
various ways. 

In solutions of iron sulphate, the mere addition of ammonium humate, 
which is always present in the brown waters of peaty areas, eflfects a pre- 
cipitation of iron oxide and later on of ferric hydrate. 

From carbonated solutions the iron is precipitated as ferric hydrate by 
the escape of carbonic acid into the air, or by its absorption by plant cells. 
The deposition of iron carbonate is only possible when the air is excluded 
or in the presence of organic matter, which seems to harmonize with the 
known facts concerning spherosiderite and blackband ores. 

From humates and other organic compounds the ferric hydrate is pre- 
cipitated by the oxidation of the humous acids and their decomposition 
into carbonic acid and water. Here, too, the plant cell accelerates this 
process by furnishing oxygen. Lastly, by the mingling of iron humates 
and sulphates, the sulphuric acid, which kept the iron sesquioxide in so- 
lution, unites with ammonium, and iron is precipitated as hydroxide or as 
ferric humate. 

In this action, the life processes of plants take a part, entirely inde- 
pendent of any products of plant decay. According to Ehrenberg, the algae, 
especially the so-called iron algae, OalioneUa ferruginea, Ehrenb., are active 
ore precipitants, coating their cell walls with ferric hydrate and opaline 
silica. This alga is abundant on the sea bottoms. According to the recent 
works of Molisch and Winogradsky, these and most other supposed alga^ 
are ciliated bacteria of different kinds, especially Leptoihrix ochracea} 

The silica of these ores may originally have been held in solution as alka- 
line silicates, which are supposed to be decomposed by carbonic acid. This 
silica is precipitated simultaneously with the ferric hydrate. The phos- 
phoric acid was certainly present as ammonium phosphate and is precipi- 
tated at first as iron phosphate and as calcium phosphate in calcareous ores. 

The further speculations which these processes suggest as to the genesis 
of the older stratified iron ore beds are given on page 81. 

We saw that in the case of lake ores the deposition took place quite slow- 
ly. This process is more rapid where the drainage from the gossan (which 
see) of a large pyrite deposit is carried into a lake basin, or into the sea, or 

*Weed: 'Geological Work of Plants,' Am. Geo/., June, 1894. Walther: 'Einleitung 
in die Geologie.' Jena, 1893-4, p. 655. 



BEDDED ORE DEPOSITS. 103 

where mining operations produce an inflow of great quantities of iron-bear- 
ing mine waters. Thus the bottom of Lake Tisken, near Falun, is covered 
with a layer of ocher-mud several meters thick that has been furnished by 
the neighboring pyrite stock. The bed of the Rio Tinto carries ocher-mud 
and diatoms derived from the waters of the copper mines as far as Palos 
in Huelva Bay. That this was the case even before mining began at that 
locality is proved by the deposit of iron ore on the Mesa de los Pinos and 
the Cerro de las Vacas (see Figure 50). These limonite deposits were 
formed in a bog which was afterwards dissected by the river. The iron- 
stones contain plant remains of the same character as the present flora. Slabs 
of this ore were used by the Romans for tombstones.* 

The deposition of iron ore is also rapid in places where iron-bearing min- 
eral waters come to the surface in swampy hollows. An interesting case is 



817 

SodrTUA IfteidtUPlmft 







Fig. 50. — Profile through a part of the Rio Tinto ore field. (A. PhillipB.) 
8, clay slate; p, porphyry; k, copper ore bed; e, Pleistocene iron ores. 

the extensive mineral marsh in the Soos near Franzensbad, described by 0. 
Bieber.' The marshy beds of that locality are strongly impregnated by the 
waters of mineral springs^ carrying sodium sulphate^ magnesium sulphate^ 
iron sulphate and other salts^ and are overlain in many cases by whole beds 
of bog iron ore^ blue iron ore and iron ocher. East of the sour spring called 
Polterer or Kaiserquelle, for example, we find the following section : 

(1) Mineral bog 3 to 5 meters; (2) bog iron ore 0.3 m. ; (3) blue iron ore 
(vivianite) 0.5; (4) iron ocher 0.3 to 0.5 meters. 

The occasional occurrence of pyrite and marcasite in the mineral moor 
is noted later on. 

(h) Recent Iron Ores of Marine Origin. 

Aside from the deposits of iron ocher above mentioned, which must be 
forming at present in Huelva Bay, and perhaps to a less extent on some 
other portions of the coast, we do not know of any really recent iron ores 
found on the sea bottom. However, deep sea investigations have proved the 
very wide distribution of a highly ferruginous sediment, the glauconite 

' H. Louis: 'Ore Deposits.' Second edition. 1896, p. 41. 
' O. Bieber: 'Das mineralmoor der Soos/ Marburg, 1887, p. 29. 



104 



THE NATURE OF ORE DEPOSITS. 



ooze.^ It is probable that certain older iron ore deposits may be sediments 
of this kind altered by subsequent metamorphosism and modified perhaps 
by a subsequent concentration of the iron compounds. 

According to J. Walther* the S. S. Tuscarora found oflE the coast of Cali- 
fornia, at a depth of 180 to 730 meters, black sands consisting almost en- 
tirely of dark green glauconite grains 0.6 millimeter in size. Glauconite 
sand of such purity is rare, while glauconitic sediments have been shown by 
the Challenger and other expeditions to be very widely distributed at depths 
of 690 to 5,395 ft. Phosphate concretions also occur associated with 
the glauconite. The amount of lime may reach 56%, and increases with 
the distance from the land. These masses of green mud contain an insolu- 
ble residue of 44% or more, consisting of siliceous shells and portions of 
skeletons of organisms, as well as of granules of quartz and very diverse 
rock silicates. Towards the middle of the ocean basin these formations are 
wanting. 

The following analyses of recent glauconite sediments are taken from 
the work, 'The Voyage of H. M. S. Challenger; Report on the Deep-Sea 
Deposits,^ p. 387: 



.2 

3 

GQ 






164 B 410 
164 B 410 
164 B 
164 B 
185 B 



SiO, 



56.62 

50.85 

410 51.80 

410|55.17 

155.27.74 



A1,0, 



12.54 
8.92 
8.67 
8.12 

13.02 



Fe, O, 



15.63 
24.40 
24.21 
21.59 
39.93 



FeO 



1.18 
1.66 
1.54 
1.95 
1.76 



MnO 



Trace 
Trace 
Trace 
Trace 
Trace 



CaO 



MgO 



K,0 



1.69 
1.26 
1.27 
1.34 
1.19 



Na,0 



2.49 
3.13 
3.04 
2.83 
4.62 



2.52 
4.21 



0.90 
0.25 



3.86 0.25 



3.36 
0.95 



0.27 
0.62 



H,0 



6.84 
5.55 
5.68 
5.76 
10.85 



Total. 



100.41 
100.23 
100.32 
100.39 
100.68 



11. SEDIMENTARY DEPOSITS OF MANGANESE ORB. 

A. Within the Crystalline Schists. 

1. Manganese Ore Deposits of Ldngban, Sweden,* 

This mining district lies north of Philipstad, in Vermland, between 
Lake liangban on the east and Hytt Lake on the west. The deposits arc as- 
sociated with a band of dolomite, 4 km. (2.6 miles), with north-south 
course and west dip. This dolomite is intercalated in granulite,* that is, 

* The manganiferous ironstone concretions of the deep sea are spoken of later. 
See Gumbel 'Ueber die Natur und Bildungsweise des Glaukonits.' Sitz derK, Ak. 
Munich, 1886. 

* J. Walther: 'Einleitung in die Geologie.' Jena, 1893-4, pp. 880-882. 
» Zcit. /. Prak. Geo!., 1899, pt. I. 

*Tftmebohni: 'Ofverblick ofvcr Berpbyggnaden inom Filipstads Rergslag,' 1S77. 
Nordenstrom's Katalog, p. 38. 



BEDDED ORE DEPOSITS. 105 

a fine-grained biotite gneiss poor in mica^ forming an island-like mass in a 
great area of granite. Dioritic rocks occur on the east. 

There are six main deposits, besides many small ones of very irregular 
shape and having an approximately lineal distribution. The deposits are 
ordinarily considerably enlarged near their base and thus approach close to 
one another. They do not consist of workable ore throughout, but some- 
times wedge out and are replaced by dolomite or a pyroxene skarn con- 
taining scattered streaks of ore. 

The L&ngban dolomite contains about 20% of magnesia and is of granu- 
lar-crystalline structure. While it is white when fresh and unaltered, it 
usually turns brown upon exposure to the air, owing to the decomposition of 
finely interspersed manganese minerals. The ores are divided into iron ores 
and manganese ores. The former consist mainly of specular hematite and, to 
a smaller extent, of magnetic iron ores. The manganese ores are mainly 
braunite and hausmannite in dolomitic matrix. Furthermore, a great num- 
ber of other manganese minerals appear as rock constituents, the common- 
est being rhodonite, tephroite, schefferite (a lime-manganese-pyroxene with 
8 to 10% of MnO), and richterite (a soda hornblende with 8 to 11% MnO). 
Not infrequently large bunches of rose quartz and of red, ferruginous 
quartz are found, the latter material being formerly cut up into cups, paper 
weights, etc. Certain crush zones or shear zones (skolar), traversing the 
beds, are frequently coated with manganophyllite (a reddish magnesia 
mica, with up to 20% MnO). 

According to H. Tiberg^ the strata are arranged in the following manner 
from above downward. (See Fig. 51, which shows too gentle a dip. The 
numbers below correspond to those in the figure.) 

1. Dolomite with lenticular layers of fine-grained gneiss, mostly poor in 
mica. 

2. Thin layer of homblende-pyroxene-garnet skarn. 

3. Magnetic iron ore with melanite (up to 2 meters). 

4. Iron ore with nests of ferruginous quartz (up to about 20 meters). 

5. Hausmannite in dolomite (to 3 meters). 

6. Braimite and hausmannite (up to 20 meters). 

7. Thin layer of skarn (schefferite, richterite, tephroite and rhodonite). 

8. Footwall dolomite with streaks and layers of fine-grained gneiss. 
The most important layer is the manganese deposit, mainly braunite, 

forming the lower part of the iron bed of the Kollegii mine, a bed which 
reaches a thickness of 40 m. (131 ft.) and has been followed for a distance 
of 65 m. (213 ft.) along the strike. The braunite was not recognized until 

^ Wermlandska Bugmannaforen, 1901. Lately Tiherp a«mbe8 the origin of the 
deposit to replacement and not sedimentation. 



106 



TEE NATURE OF ORE DEPOSITS. 



187S, the hatumaimite somewhat earlier. The braunite ore contains as high 
as ib% of manganese, the hausmannlte ore up to 47%. The manganese' 
ore is naually sorted into three grades, with 40, 30 and 20% of manganese. 
The two last named are concentrated to a 54 to 56% product. Most of 
tiie ores are used in the production of bessemer steel, as well as in the glass 
industry. 




Similar deposits, also associated with dolomite, are found at Fajsberg 
near Nordmarken, at Jakobsberg and in the Sjfi mine in the Oerebro district 
It may here be remarked that to the north of L&ngban, in the Stora Getberg 
mine, lead, zinc and copper ores occur in the same dolomite intercalation. 
At L&ngban itself these ores occur only in subordinate amounts. A remark- 
able feature of this mine is the association of native lead* with hausmannite 
in fissures in the dolomite. The mao^nese ore produced in Sweden in 189t> 
was 2,056 tons. 



2. The Manganese Deposits of Southern Bukowina. A%tstTia.' 

The manganese mines of Oborarschitza and Arschitza-Anna occur high 
up on the slopes of the Eisenthal, 4 km, (2.4 miles) from Jakobeny. The 

' Ijrelst'^m in B. II. ff. Z.. 1S16, p. 26. 

' B. V. Colta: ' Einlacerunaen im GlimmerarhWerdersudl. Bukowina, 'fl. u. //. Z., 
1855. No. 39, p. 319. B. Walter: 'Die Er/laeereUtten derBudl Bukowina,' Jahrb. 
d. k. k. geol. KeichssDat., Vienna, 1876, pp. 372-382. 



BEDDED ORE DEPOSITS. 107 

ore deposit is 40 m. (133 feet) thick, being enclosed in mica schists that 
are either horizontal or dip northeast at 30°. Directly beneath is a bed of 
siliceous schist 6 to 20 m. (19 to 65 ft.) thick, lying upon a hornblende- 
bearing mica schist. Above the ore is a much decomposed brownish yellow 
hornblende schist. The ore deposit consists of a mixture of pyrolusite, some 
hausmannite, brown hematite and quartz. The whole is locally called 
Schwarzeisenstein (black ironstone). This mass shows distinct bedding, 
even when decomposed, and in places its primary composition is disclosed, 
especially at another mine, the Oitza, near the Transylvania boundary. The 
deposit is in such cases seen to be built up of beds 0.1 to 2 m. thick of man- 
ganese silicate (rhodonite), of grayish green to flesh color, and with inter- 
spersed portions of rose-colored manganese-spar and quartz, and layers of a 
yellowish green mica hornblende schist. The transformation of the rhodonite 
into the more highly oxidized manganese ores and into quartz is traceable 
step by step through every gradation, the alteration starting along cracks 
and fissures. The Jiomblende schist when decomposed furnishes the inter- 
mingled brown hematite. 

The mines belonging to the Greek Oriental Church yielded 2,063 tons of 
manganese ore in 1898. 

3. The Manganese-Zinc Deposits of New Jersey} 

Although there is considerable doubt as to the sedimentary origin of this 
deposit, we include in this section the remarkable ore deposits of Franklin 
Furnace and Sterling hill in New Jersey, deposits whose exact genesis is still 
imcertain. It is possible that they do not belong in this group, but to that 
of contact metamorphic formations. 

These deposits occur in a zone of white cr^'stalline limestone, lying upon 
gneiss and regarded as a metamorphosed Cambrian rock, since it becomes 
dense away from the deposit, where, according to Nason, it contains Cam- 
brian fossils. If this is correct, the gneiss is probably an altered granite. 
This hypothesis is further supported by the presence of intrusive masses and 
veins of a pegmatitic granite, traversing the limestone and carrying augite, 
hornblende, allanite, zirkon and orangite (Groth). The limestone is ex- 
ceedingly rich in Mn CO3 (16.57%) as shown by the brown color of the 
surface of the weathered rock owing to the formation of MnOj. In the lime- 
stone at its contact with the gneiss, layers of magnetic ore occur, which were 
formerly worked. At a somewhat higher liorizon, however, this marble con- 

' H. Credncr: 'Franklinit und Rothzinkerz im kn'stallinen Kalkstein,' B, u, H. Z., 
1866, p. 29. F. L. Nason: Geol. Survey, New Jersey, ISOO, XIV; and 'Franklinite 
Deposits of Mine Hill,' Trans. Am. Inst. Min. Eng., February, 1894. P. Groth: 
'Zinkerzlacerstiitten von New Jersev,' Zeit. f. Prak. Geol., 1894, p. 230. J. F. Kemp: 
'Ore Deposits of U. S./ 1900, p. 251. Also Bull. 210, U. S. Geol. Survey, 1903. 



i08 



THE NATURE OF ORE DEPOSITS. 



tains two stratiform orebodies, composed of black crystals of franklinite 
lZnFeMn)0,(Fe,Mii,)0„ zincite (ZnO with up to 8% MnO), wille- 
mite and calcite. One of the beds outcrops on Mine hill, near Franklin Fur- 
nace; the other on Sterling hill, near Ogdenburg. Between the two hills 
the valley shows no outcrops. The Franklin Furnace deposit, 12 m. (39 ft. 
thick), has been the most carefully investigated. As shown by the accom- 
panying section (Fig. 52, after P. Groth), it forms a syncline followed to 
the southeast by a strongly compressed anticline. After the folding the 
strata were cut obliquely aeroea by a later dike of diabase. 




Fig. 62.— Profile through the ore bed of Franklin Furnace. (P. Groth.) 
g, gneiss; k, crystaliine limestone; e, ore bed; q, croas-cut. 

Besides the minerals already mentioned, jeffersonite (a zinc manganese 
pyroxene), hornblende, tcphroite, troostite, fluorite and chloanthite occur 
in the mine. Near the granite intrusions there are certain other minerals 
not found elsewhere, namely, garnet, rhodonite, cleiophane (colorless zinc- 
blende) and axinite. 



4. Manganese Ore Deposits in Minas Oeraes, Brazil. 

These deposits of manganite and pyrolusite occur as beds up to 2 m. 
thick, traceable for over 2 km. (1.2 miles) along the strike. The beds occur 
intercalated in crvritntlinc schists in the region, between the railway sta- 
tionK nf Queluz and .Miguel Bumier of the Brazilian Central railway. 



BEDDED ORE DEPOSITS. 109 

According to Lisboa^ the steeply upraised strata at Miguel Bumier show 
the following succession : 

1. Mica schist. 

2. White limestone with 1.5% manganese content (over 10 meters). 

3. Impure earthy iron and manganese ore (24 meters). 

4. Pure manganese ore, mostly hard (over 3 meters). 

5. Itabirite (quart-schist rich in specular hematite). 

6. Gray limestone with 1.5% manganese, 11% iron, 13.8% SiOj. 

7. Overlying mica schists. 

The production reached 100,000 tons in 1900. The ores contain between 
45 and 55% of manganese, and very little silica (up to 1.3%) and phos- 
phorus (up to 0.07%). They are shipped from Rio de Janeiro to North 
America. 

Similar deposits are exploited, according to J. C. Branner,* in the Pedras 
Pretas mine, 26 kilometers west of Nazareth in the State of Bahia. 

B. Manganese Ores in Normal Sediments. 
(a) Manganese Ore Deposits tn the Carboniferous. 

The ores obtained from the Kaiser Franz mine near Elbingerode, in the 
Harz, occur, according to W. Holzberger and C. Zerrenner,' as pocket-shaped 
intercalations a meter or so thick in the siliceous shales of the Culm.* The 
ore consists of psilomelane in dense and botryoidal masses, some pyrolusite 
and coatings of wad, with rhodonite, rhodochrosite and quartz present as 
accessories. The ore formerly worked contained on an average 60 to 63% 
of manganese peroxide, sometimes rising to 67%. Zerrenner considers 
these maganese ores as later material separated out of the siliceous shales, 
a theory which needs further investigation The bed-like deposits of rho- 
donite and manganspar near Lautenthal in the Harz, mentioned by Klock- 
mann,' are found also in the siliceous shales of the Culm formation. 

The manganese ore deposits of Alosno, north of Huelva, in Spain, which 
contain pyrolusite and psilomelane, are also said to belong to the lower Car- 
boniferous (Culm). 

Beds of psilomelane, pyrolusite and brown hematite, as well as those of 
arsenious black oxide of copper and malachite, are found in the horizontal 

* R. Ribeiro Lisboa: Jomal do Commerdo, June, 1898, and March, 1899. Review 
Zeit. f. Prak. GeoL, 1899, p. 256. H. K. Scott: 'Manganese ores of Brazil,' Jour. 
Iron and Steel Inst., London, 1900, No. 1. 

* Trans. -\m. Inst., Min. Eng., 1900 (Meeting September, 1899). 

* W. Holzberger: 'Neiies Vorkommen von Manganerzen bei Elbingerode am 
Harze, ' B. u. H. Z., 1859, p. 383. C. Zerrenner: ' Die Manganerz-Bergbaue in Deutsch- 
land, Frankreich und Spanien.' Freiberg, 1861, p. 103. 

* The Culm is the basal formation of the Carboniferous of E^astern Europe. 
^ B.u. H. d. Oberharzes, p. 65. 



110 THE NATURE OP ORE DEPOSITS. 

upper Carboniferous (lower Nubian) sandstones of Wadi Nasb and Wadi 
Chalig of Mount Sinai.* 

(b) Mesozoic Manganese Deposits of Chile. 

The extensive manganese deposits in the districts of Coquimbo and 
Carrizal^ in Chile, worked by the Chilean Manganese Mining Company, 
have received but little study as yet. According to H. Louis^ they occur in- 
terbedded with Jurassic and Cretaceous sandstones, clay slates, limestones 
and gypsum that rest on eruptive rocks. The ores consist of manganese 
oxides, peroxides and silicates in a gangue of silica, calc and heavy spar, 
the ores averaging about 50% manganese and having very little phosphorus. 
Chile produces some 30,000 tons of manganese ore annually. 

(c) The Eocene Oolitic Mangamese Ores of Transcaucasia, 

The principal manganese deposit of Transcaucasia lies near Tschiatura 
on the Kwirila river in the province of Kutais, 42 kilometers from Kwirila 
railway station on the Tiflis-Poti line. The ores form a nearly horizon- 
tal bed in the Eocene, underlain by limestones and marls of the Turonian, 
which, in their turn, are underlain by granite below Tschinopoli. The 
Eocene series begins with a red or greenish sand 0.4 to 4 meters thick, con- 
taining teeth of Lamina elegans. Above this follows the manganese ore bed, 
averaging 2 meters and reaching 5 meters thick. The bed is composed 
of 5 to 12 layers of hard oolitic pyrolusite, with a cement of pulverulent ore. 
It outcrops underneath the bluffs of the low plateaus into which the Tertiary 
has been dissected by the Kwirila river and its tributaries. The overlying 
strata are sandstones and limestones of later Tertiary epochs. The ore bed 
can be traced 120 kilometers, so that the bed will last a long time. 

The average amount of manganese in the ores, as determined by F. Drake, 
is 40 to 45%, while within certain areas it rises to 50%. When dressed 
for shipment, the ore averages 51 to 52%, reaching as much as 61%. The 
ore averages 0.16% of phosphorus and not over 8% of silica. 

According to the same authority, a complete analysis of concentrates ex- 
ported from Tschiatura gave: 

MnOj 86.25% Na»04-K,0 0.22% 

Mn,0, 0.47 " Si O2 3.8r) " 

FcjOa O.Gl " COj 0.63 " 

CuO O.Ol" S 0.23" 

NiO 0.30" P2O»(P = 0.14) 0.32" 

AljOj 1 .74 " Hfi 1 .85 " 

Qg^ Q 1 . 73 " 

Mgo. . . !!!!!!!!!.!!!!!...... 0.20 " Total 99.95% 

Ba 1 .54 " Mn 54.90 " 

*M. Blankenhom: 'Neues zur Geol. u. Paleon. Aegypten",' Zeit. f. Prak. GeoL, 
1899, p. 392. 

* 'Ore Deposits,' 1896, p. 878. 



BEDDED ORE DEPOSITS. Ill 

The brittle nature of the ore is a serious detriment in shipping. 

The deposit was discovered in 1848 by the geologist Abieh, and has been 
worked since 1879. In 1897 it produced 231,868 tons. The total produc- 
tion has already reached one and one-half million tons. The deposits of 
Samtredie and Novo-Senaki are similar. 

European Russia, also, contains manganese ore deposits in the Eocene 
formation,, at Nicopolis on the lower Dnieper. The manganese ore bed is 
O.o to 3 meters thick, and where worked it contains as high as Z0% of man- 
ganese. The production in 1894 was about 58,000 tons.* 

(d) Recently Formed Deposits of M^r-ganese Ore. 

Ihe discovery that manganese-iron concretions of irregular flat forms are 
of frequent occurrence on the sea bottom at depths of 1,800 to 3,000 meters 
is of much genetic importance. In the region of the Gulf Stream the Alba- 
tross party found the sea bottom covered with them. Amoog them were 
pieces 2 to 15 centimeters thick and 10 kilograms in weight, the lower 
side of which often consists of tough, blue clay. 

In a finely divided condition manganic hydrates in combination with fer- 
ric hydrates are, according to J. Walther*, among the most widely dis- 
tributed substances in marine sediments; all the rocks, shells, calcareous 
alga? and limestone fragments covering the sea bottom at Millport, Scot- 
land, at a depth of 90 meters, show thin, black coatings of manganese com- 
pounds. The Challenger observed similar manganese coatings on ptero- 
pod and globigerina shells obtained from depths of 2,560 to 2,743 meters, 
and the drcdgings corroborate previous observations showing the great dis- 
tribution of the manganese concretions previously noted in the deep sea 
deposits of the Indian and Pacific oceans and in the vicinity of volcanic is- 
lands in the Atlantic Ocean'*. 

* A. Macco: 'Reisebericht/ Zei7. /. Prak, GeoL, 1898, p. 203. F. Drake: 'The Man- 
ganese Ore Industry of the Caucasus,' Trans, Am. Inst. Min. Eng., Vol. XXVIII, 1899, 
pp. 191-208. 

' * Einleitung in die Geologie,' Jena, 1893-4, p. 700. 

• Gumbel: *Ueber die Manganknollen in Stillen Ocean.' Sitz. derK. Ak., Munich, 
1878. Murray-Ir\'ine: 'On the Manganese Oxides and Nodules in Marine Deposits,' 
Trans. Roy. Soc. Edinburgh, 1894, Vol. XXXVUI, 






SECTION III. 

EPIQENETIC DEPOSITS, 

1. MINERAL VEINS. 
A. General Description of Mineral Veins. 

(a) Definition of tue Tekai *Mineual Vein/ 

The material filling a fissure in the earth's crust is called a vein; if the 
material is igneous the vein is called a dike^ if not, it is a true vein; i1 
the material contains minerals of economic importance it is a mineral vein 
More briefly, veins are fissure fillings; mineral veins are those containing; 
ores. Their general form resembles that of ore-beds, since they are more o • 
less irregular sheets wedging out in two directions, and showing great varia- 
tions in thickness and great departures from rectilinear strike and dip. 
The enclosing rock is called country or country rock and the rock walls 
of the fissure are vein walls. The outer surface of these slab-shaped forma- 
tions are often called selvages, but this term is only appropriate for the 
layer or sheet of clayey material, often soft and unctuous, which frequently 
lies between the body of the vein and the country rock.* It is also known 
as gouge or fluccan. 

As veins exhibit a great diversity in character, the definition of the term 
given above is not sufficient and needs amplification. According to Lind- 
gren* a fissure vein is a mineral mass tabular in form as a whole, though 
often irregular in detail, filling or accompanying a fracture or set of frac- 
tures in the enclosing rock. This mineral mass has been formed later than 
both the country rock and the fracture, either through the filling of open 
spaces along the fracture or through chemical alteration of the adjoining 
rock. Many veins are not single fissure fillings, but zones of rock with nu- 
merous parallel, very narrow fissure fillings or stringers. Such lines of 
stringers practically form a lode, being, strictly speaking, composed of very 
small veins. According to Emmons,* "the term vein should be confined as 
far as possible to a single mineralized fissure, or the orebody formed along a 
single fissure, while the term lode is applied to an assemblage of ore-bearing 

* W. Lindgren: 'Metasomatio Processes in Fissure- Veins'; 'Genesis of Ore Deposits/ 
1902, p. 500. 

» Text of Folio 39, U. S. Gcol. Survey, 1899. 



EPIGENETIV DEPOSITS. 



113 



fissures so closely spaced that the ore that has been formed along and be- 
tween them may in places be considered to form a single orebody. The 
principal fissures making iip a lode are nearly parallel, but there are 
aisc smaller cross fissures connecting them, through which the interme- 
diate countrj' (granite) becomes impregnated with ore until it may constitute 
vein material. A Iixle may be only ten feet wide, or it may be a hundred 
OT more; and within it are included zones of more or lesa altered country 
rock, sometimes carrying enough values to pay for mining; in others too 
barren to pay, when they are generally called horses. When there is an 
assemblage of veins too widely spaced to be included in a single lode, and 




Fir. 53.— Simple vein (KrieRand Frieden 
Stehender of the Himmelfahrt, near 
Freiberg), 

q, quartz; b, lino-blende; g, gray gnnsa. 



i 


^/KaI 


-§ 


' ^ 


¥^i - 


3 



Rg. 54. — Compound vein, 
b, lead glance; q, quarti; i, blocks 
of deconpowd gneiaa; 1, clay selvage; 
g, gray gneiss. 



yet to a certain extent eoordinatcd into one eystem, they may be designated 
as a vein system." The various stringers of such lodes may, indeed, have a 
transverse course. Farts of the country rock, either in groat blocks or little 
bits, by lucans of such tranaverse and parallel stringers, may be entirely de- 
tached from connection with the country rock. B. von Cotta' has given the 
name compound veins to such lodes. They consist essentially of country 
rock traversed by ore stringers, tlius differing from the simple fiKsuro veins 
which, according to the general definition, are formed by the filling of a 
single fissure. This distinction was accepted by A. von Groddeck and is 
now much used. Compound veins or lodes often lack a sharp wall, at least 
' ' Ueber den. Bog. Ganjcthonschiefer von (lauathal, ' B. u. H. Z., 1SC4, p. 303. 



114 THE N ATI' HE OF ORE DEPOSITS. 

on one side, and it ia then left to the judgment of the obserrer to locate 
the hoimdary iK'tweon the lode and the eountry rock. 

The two figures, 5;) and 54, reprewnt these two types of lodea. 

A part of a lode or compound vein is shown in Fig. 55, reproduced from 
a photograph.* 

A good example of a Bo-called lode not enibraeed in any of the above defi- 
nitions, hut, on the contrary, representing a gront, oft^-n very thick, zone of 
veins and lodes, is the famous mother-lode in California, containing numer- 




FIb. -W.— Part <)f n laiie or compomid vein (of the Traupott Spat of the Gesegnete 
Bei^inauirs lIofTiiuiif! .Miiip, iipur Obcr^runa) showing sray suciss traversed by 
nnmjw stringptv of galena iiiiil iwiue quorti. 

0U8 gold quartz veins. Which one of tlie nHiiierou8 parallel fissures of this 
zone are to be regarded as its bounding surfaces is a matter of arbitrary judg- 
ment and is of eeouoniic rather than of guologic interest 

Compound veins are common at Freilicrg, Clausthnl in the Uarz and at 
Kremnitz'in Hungary, 

The term "lilling' may sornelinu^ ho misusinl in this connection. Cer- 
tain veins, especially gold veins, arc nothing less than zones of rock, tra- 
versed by innumerable practically barren fissures, from which they have 
been impregnated with gold-bearing pyrites or other ores to a workable 
' Rickard: Trans, .ini. Iiwt. Miu. EnR., Vol, XXVI, p. 216. 



EPIOENETIC DEPOSITS. 115 

degree. Such zones of disintegrated and impregnated rocks, called lodes 
by miners, usually coincide with lines of displacement. Finally, the defini- 
tion of a filled fissure is unsuitable when the barren fissure, almost devoid 
of minerals, has been a conduit for solutions penetrating a zone of country 
rock on both sides and entirely replacing the rock by new-formed ores and 
other minerals, as seen in many galena deposits in limestone. The author 
(R. B.) does not entirely agree with S. F. Emmons,^ who attributes an im- 
portant role in tlie formation of many veins to metasomatic processes, as 
such processes are regarded by him as always subordinate phenomena in 
vein formation. 

(b) Dimensional Relations op Mineral Veins. 

"The width of the filled fissure, measured at right angles from wall to 
wall, is called the thickness. The rock in which the fissure has been opened 
is called the country rock. If the vein is not vertical the rock above is called 
the hanging-wall rock and that below the footwall rock. The horizontal di- 
rection of the vein is called the strike, that which comes nearest to the ver- 
tical is called its dip. If the body of the vein has undulations these may, 
by several observations, be plotted and reduced to a plane corresponding 
to the average attitude of the vein, on which the strike and dip is called the 
average or principal strike and the principal dip of the lode.'* (Von Cotta.) 

The strike of a lode was usually determined in European mines by means 
of a miner's compass divided into twice twelve hours. The dip is ordinarily 
on a graduated circle connected with the compass. This form of compass is, 
however, not used outside of Europe, and even there is being more and more 
displaced, even among miners, by one with a graduation into twice 180**, 
and in most scientific monographs we find the strike of veins given in de- 
grees, as has long been done in general geology. 

The old division of veins into different categories, according to their 
strike and dip, long in use in the Erzgebirge of the Harz and other Ger- 
man mountains, is still used in Europe. The diagram (Fig. 56, page 116) 
gives the designations of this kind based on the strike. 

According to this scheme, 'low' strike veins are those situated at the be- 
ginning of a division ; 'high' strike veins are those situated near the end of 
it. A morgengang striking 4 hours is thus a 'low,' while one striking 5 
liours is a Miigh' lode. As to the veins striking almost centrally, 3, 6, 9 and 
12 hours, they are said to strike in the alternating hours (Wechselstunden). 

It is to be noted that in the German mines, in giving a name to a newly 
discovered vein, its insertion in one of the above named divisions was made 

* 'Structural Relations of Ore Deposits.' Trans. Am. Inst. Min. Eng., February,! 888. 



116 



THE NATURE OF ORE DEPOSITS. 



according to the observed magnetic strike, not the true strike, that is to say, 
without regard to the declination of the magnetic needle at the time. Fur- 
thermore, on the plats the name once given was retained, although greater 
development work might show that the portion of the vein first worked had 
a somewhat different strike from that of the vein as a whole. Thus it may 
happen that a vein mentioned on official plats and in diagrams as high-strike 
Spatgang really belongs to the group of Flache Gauge. Such contradictions 
have also arisen from the fact that when, at a much later time, a survey of 
the mine is made^ the declination may have changed materially from that 



¥" 



h.^ 









he. w- 



jl. 



.r9 



6^ / 

''1 



Jui 4 



lu3. 






'fiS^ 



e 



/■ 



/ G 



0.71,6 






3. ^ 



Ju9. 



S 
hIZ 



Fig. 56. — Division of veins according to their strike. 



officially entered on older maps, and thus the observed strike may no longer 
agree with the older observations. Hence it is now the custom to plot the 
lodes with reduced strike, that is to say, referred to the true meridian. 

In the Austrian mines the terminology is somewhat different. A com- 
pass divided into 24 hours is there generally used, and lodes striking be- 
tween 21 and 3, or 9 and 15 hours, are called midnight lodes; those between 
3 and 9, or 15 and 21, are called morning lodes. 

The divisions according to the difference in dip are shown in the dia- 
gram (Fig. 57, page 117) : 

Most of the veins belong to groups between 90 and 75*^ or 75 and 45** ; 
the other two divisions occur much more rarely. German terms rechtsin- 



EPIQENETIC DEPOSITS. 



117 



nig (right- wise) and windersinnig (contrary- wise) are not used in 
America and only have a local significance. In the Freiberg area, for ex- 
ample, most of the lodes dip west, and hence those members of the network 
of lodes that by way of exception dip east are said to dip contrary-wise. In 
another area the reverse may occur. 

If a lode suddenly changes its dip it is said to 'get out of the hour^; to re- 
turn to the old direction a short distance farther on it is said to 'strike or 
throw a hook.' The vein 'straightens up' if a prevailing low dip suddenly 
changes to a high dip ; it 'flattens out' if the reverse takes place. 



90' 



7SO 



W 







e 



../5^ 



Z^'-fcTv^^^''^^^^^ 



Fig. 57. — Division of veins according to their dip. 



The thickness often shows great and frequent changes. It may be re- 
duced to nothing, when the lode is said to pinch out (at "a," Fig. 58) ; to 
'open up' periiaps a short distance farther on (at "b," Fig. 58). 

In the great majority of veins the thickness varies between 0.5 to 1 meter. 
Ik the Freiberg area the greatest thickness shown by the barytic lead veins 
is 6 meters, while the others ordinarily vary between 0.15 to 0.5 
meters. In exceptional cases lodes may be 50 meters and more thick, as, for 
example, the famous Comstock lode in Nevada and Veta Madre of Guana- 
juato,* Mexico. In such cases we are always dealing with combined lodes, 
iiia«lc up cf closely spaced parallel lodes, or broad zones of impregnated rock. 

Veins of slight thickness are called stringers, veinlets, etc. 

A vein showing frequent pinching out and widening up, repeated at short 
intervals, is called a lenticular vein (Playfair) (Fig. 59). When the lenses 
are approximately perpendicular, it may be defined as a series of pyrite 

*Carl Henrich: 'Mines of Guanajuato, Mexico/ Mining Magcmine, 1904, Vol. X, 
pp. 63-75, 101-108. 



118 THE NATURE OF ORE DEPOSITS. 

Btocka. Such l^ticular lodes, according to K. Schmeisser, are quite fre- 
quent, for example, in the region of Coolgardie, in veetem Australia, in the 
auriferous quartz lodes, especially the Gdjudina lode group. 

By leaves' the Austrian miner means 'fissures,' sometimes no thicker than 
a sheet of paper, which though barren themselves are Bometimes accom- 



n or 'opens up' (b). (A, vod 

panied by a zone of country rock impregnated with ore. At the RathauE- 
berg, near Gastein, a whole system of such leaves exists in the gneiss or 
mica schist, between which the country rock proves to be impregnated with 
native j?old and auriferous sulphides. The name leaves is also given to 
the fissures connected with the ores in the dolomite of Baibl. 




Viz. 5U. — I, ei> titular lodes. 

Somewhat eimilar fissures, called Zwitterbander, i. &, narrow fissures, are 
often no thicker than a knife-blade, filled with quartz, topaz, lepidolite, 
fluorspar and a little tin ore, from which the country rook, granite or «chist 
has been 'impregnated,' as it is expressed by the Saxon inini;n-, with tin- 
stone and its accompaniments, on both sides to a dlBtancc of 1 to 10 centi- 
meters from the fissure. 



EPIOENETW DEPOSITS. 119 

Terticala' are similar to the leaves' just noted, Tlie term is ueed in the 
Black Hills of Dakota for barren fissures that have been chatmels for min- 
eralizing solutions forming ores in favorable strata. 

(c) The Termination op a Vein. 

The vein 'wedges out' if its sides graduall) converge and finally join 
(Fig GO) Often, however, a joint plane, at least, t-ontmues on through 
tlie rock often shoumg as a mere dim of cla^ In case tho \e\n splits up 
into narrow stnngers it is said to 'fray out' (Fig 61) As an example 
onL m„j mention the branching sub-dmsion of the tin veins of Sau- 




Fig. 61. — A vein dividing below. 



Iicrj:, near Ehrenfriedersdorf in the Erzgebirge, a short distance before they 
renc-li the surface. Very often veins subdivide when they pass from a firm 
into a more brittle rock. Thus the Freiberg veins very frequently divide 
on passing out of the gneiss, whose toughness favors the development of a 
uniform single vein into the quartz porphyry dikes which pass through the 
gneiss. Figure 62 shows the behavior of the Gottlob Morgengang, at the 
David Richt shaft near FreilxTg, where it passes through such a porphyry 
dike. The vein retains its full thickness up to the porphyry, but on en- 
tering it becomes scattered into numerous more or less parallel stringers. 
Immediately after leaving the quartz porphyry it resumes its previous con- 
dition. It is to be noted, however, that this division into stringers does not 
take place in all cases where the porphyries in the Freiberg area are tm- 



120 



TIIK NATURE OF ORE DEPOSITS. 



versed by ore lodus. If the vein strikes the porpliyry at a blunt angle it may 
pass through it smoothly and without materiel impoverishment 

A similarly instructive example described by T. A. Bickard* occurs in 
the silver veins of the Enterprise mine of Colorado. These divide and grow 
barren in the limestone, but cut cleanly and with a fine body of rich ore 
through the sandstones that alternate with the limestone. Similarly, in 
the tourmaline bearing qnartzose elvans (quartz porphyry) of Cornwall, 




Fig. 62. — Scattering of the Gottlob Uorgeiigang in the David Richt Bhaft near Freiberg. 
8.8™y gneiss; p, quartz porphyry; m, ore lode. 

the reins, according to W. J. Henwood", ordinarily divide into countletw 
stringere, which re-unitc when the vein passes into a softer rock richer in 
feldspar. Similar conditions are observed in the veins of the Spitzenberg 
near Silberberg in Silesia, where the vein passes from the gneiss into the 
overlying graywackes. 

A very gradual fading and 'dying out' of veins does not occur in truo 
vein fissures, but only in veinlike ore-bearing streaks in eruptive rooks, as 
in the case of ilraenite streaks in the norite of Ekersund in Norway (see 
p. 34). 

Conversely several individual vein-stringers may converge and unite or 
'gather' into a larger vi-in. This will be more fully discussed in the sec- 
tion or vein intcrseeliona (p. i;!2). 

A cross stringer or diagonal is one which connects, at on acute or obtuse 
angle, two parallel or diverging veins (Fig. C3), aa. for example, a stringer 
between the Biirgstadter main vein and the Kranicher vein on the upper 
Harz. A erescentic stringer, on the contrary, runs out from the main vein 
at an acute angle, to rcfum to it again at an acute angle some distance 
away (Fig. (54). The English-speaking miner calls the block between two 
such branch lodes a horse, and the outer vein about it, on a corresponding 

' Tmng. Am. Inst. Min. EnE-, 1897, Vol. XXVI, p. 197. 

* Tratu, Roy. Gcol. Soc, romwali, 1843, pp. 2X0-2M, 



EPIGENETIC DEPOSITS. 



131 



analog)-, a rider. Typical branching lodes are found, ior example, at the 
Bockwieser main lode on the upper Haiz. Side stringers or companions 
(t'ig. Gi) are small Btringcrs parallel to the main lode, but not converging 
toward it, aa, for instance, in the Xeu Hoffnung Flachen on Himmelfahrt 
near Freiberg. Feeders and droppers are small veins or stringers falling 
into the hanging-wall (t. e., intersecting vertically), or running out and 
down from the footwall of a vein. 

A total cutting off of a lode can be caused only by younger veins or faults 
or by eruptive masses or dikes. 

'«' (d) Lenoth and Vertical Extent of Veins. 
In speaking of veins, we distinguish between the length along the strike, 
that is, the longitudinal extension of the vein, and its depth or downward 
extension on the dip. Veins vary greatly in both length and depth. In dis- 
tricts where there are several varieties of mineral veins with different con- 
tents, the varieties sometimes differ also in longitudinal extension. Thus 
in the Freiberg area the bnrj-tic lead veins show the greatest length; the 
length of the Halsbriicker Spates with its aBsociated stringers being 8.4 kilo- 
meters (5,0 miles). One of the pyrite-blende lead veins, the Kirschbaum 
Stehendc, and its southward continuation, the Hohn Birke Stehende, shows 




Fig. 63. — Two veins converKinfj east- 
ward, and connected by a diagonal 

stringer. 



Fig. 64.— A mineral vein with an arched 
stringer and two side stringers. 



a length of 7 kilometers {4.2 miles). The veins of the rich lead forma- 
tion were in most cases traced only 1 kilometer (0.6 mile), but three veins, 
Johnannes St., Neugliickstcm and the Neue Hohe Birke St., near Bescheert 
Gluek, have a length of over 2 km. {1.2 miles). Finally the longest rich- 
silver-quartz-lodes were only traced 1.5 kilometers. Much longer veins 
occur in the Harz mountains. Thus, the Rosenhofer, Kosenbiischer and 
Schulthaler lodes form the filling of a compound lode fissure 16.3 km. (9.84 



122 TEH nature of ORE DEPOSITS. 

miles) long (von Groddeck), and the Gegenthal-Wittenberger series attains 
a length of 18 km. (10.8 miles). The mineralized zone or gold belt of 
California, known as the Mother lode, does not conform to the definition 
given of either a vein or lode, being rather a system of veins. Its length is 
estimated at about 67 miles (112 kilometers). 

The question "How far do veins extend downward?" is a most important 
one. Most veins continue downward below the lowest mine workings of the 
region, or, as the miner' says, "to the eternal depths." Very often the old«r 
reports on mineral veins stated that this or that lode came to an end at a 
certain depth. More often, however, the vein ceased to pay and was aban- 
doned. In many cases various difficulties of mining, or finance, prevented the . 
exploration work necessary for its development, and in many instances subse- 
quent workings have led to the rediscovery of apparently lost lodes at con- 
siderably greater depth. Thus, in the earlier descriptions of the Bescheert- 
Gliick lodes l)etween Freiberg and Brand they are said to be 'sod runners' 
confined to the upper strata. This, however, has been disproved by the later 
workings at that locality. Modern technical appliances have sometimes en- 
abled lodes to be followed down to very great depths without disclosing any 
notable change in the character of the fissure fillings. Thus, the develop- 
ment of the Adalbert lode at Pribram has reached a depth of 3,640 feet 
(1,110 meters), or 564 m. (1,850 ft.) below sea-level. The lodes of the 
upper Harz have been followed to a depth of over 850 m. (2,788 ft.). In 
Freiberg, the Wurnerian doctrine long prevailed that mineral veins are sur- 
face phenomena of the earth's crust. It was von Beust who exposed the 
falsity of this theory. He urgently recommended deep mining on a large 
scale, so that the Tiefe Rothschonbreger shaft, planned as early as 1838 by 
von Herder, was put down and the veins worked to a depth of over 650 m. 
(2,132 ft). Veins have been followed to great depths in many other dis- 
tricts, for example, the gold veins of the Bendigo gold field in Victoria 
are mined to a depth of 1,210 m. (4,000 ft.). In general the empiric rule is 
that veins with a great horizontal extent continue to great depth, while those 
which extend for only a short distance along the surface do not go far 
downward. 

It must be remembered, of course, that the greatest depths reached in 
mining operations are exceedingly small when compared with the radius of 
the earth, and even with the latest mechanical improvements the depths to 
which mines may be worked will still be relatively small. There is, how- 
ever, a theoretical interest in the question to what depth ore lodes may pos- 
sibly extend. 

A discussion of his observations on rock metamorphism and of the 
known conditions of the geothermic gradation, as gathered from thermal 



EPIGENETIC DEPOSITS. 123 

springs, led A. Heim^ to assume that water-filled open fissures may extend 
to a depth of 3,000 to 4,000 meters without being instantly closed by the 
tremendous side pressure in the earth's crust. liecently C. E. Van Hise* 
has been engaged on a theoretical investigation as to what depth fissure 
formation is possible. In his opinion the zone of the plastic condition of 
the rocks (zone of flowage) begins at 10,000 to 12,000 m. (32,810 to 39,372 
ft.), because from there downward the weight of the superincumbent mass 
is too great to allow even the hardest rocks to retain their form. The fis- 
sure formation from there downward is replaced by flowage due to a dis- 
placement of the small particles, which is not infrequently combined with 
solution and recrystallization of mineral substance (granulation and re- 
crystallization). 

According to the same author it must not be supposed that at a particular 
depth, even above that zone, the water in a fissure will be transforrtied into 
steam. True, if we assume a geothermic gradation of 30 m. (98 ft.) the 
critical temperature of water, 3G4° C, would prevail at a depth of not more 
than 10,920 m. (35,810 ft.), but this is true only if we disregard the pres- 
sure of the column of water. In reality this hydrostatic pressure is at any 
given depth in a fissure abundantly sufficient to retain the water in liquid 
form. 

Many mineral veins terminate upward and do not show on the surface; 
that is to say, do not outcrop. This is illustrated by numerous well-de- 
scribed examples, although it must be remembered that errors in this re- 
spect are readily committed because the uppermost part of the ore lode may 
have been disfigured beyond recognition by atmospheric influences. Such 
a limitation in upward extension is found in the so-called cobalt ridges 
(Riicken) of Riechelsdorf in Hesse (von Leonhard). In the Freiberg area 
most of the lodes of the Himmelsfiirst mine show no outcrop, not even that 
of the Sill>erfund Stehende, which in depth attains large dimensions. At the 
Rogen Gottes shaft and the Moritz shaft, according to E. W. Neubert,* the 
projection of this lode was several times passed through without the vein 
being encountered. Similar reports are made in regard to the Neu Gliick 
Stehende of the Alte Hoffnung Gottes mine. Finally a very remarkable 
condition is reported by T. A. Rickard* at the Enterprise mine, Colorado. 
The numerous silver-gold veins cut through gently inclined beds of Car- 
boniferous rocks, but could only be followed upward from the floor of the 

» 'Mechanismus,' etc., Vol. II, 1878, p. 107. 

' Trnn.9. Am. Inst. Min. Eng., February, 1900, pp. 7, 9, 11. Reprinted with papers 
by Posepnv, Emmons, Lindgren, AVeed, Vf>gt, Kemp, Rickard, etc., in 'Genesis of Ore 
Deposits,'* 1902. 

•' Freiherger Jahrhurh, 1881 , p. 51. 

* The Enterprise Mine/ Trans. Am. Inst. Min. Eng., Vol. XXVI, 1896, p. 975. 



124 THE NATCim OF ORE DEPOSITS. 

Group tuimel to the horizon formed by a bed of shale (Kig. (i5). Before 
reaching this horizon the veins became much poorer and were no longer 
workable; but along the contact or bedding plane there are flat and very rich 
orebodiea whose composition ia similar to that of the lodea. According to 
Bickard's explanation the somewliat plastic shales, offering resistance ti) 
the opening of lissurea, were not cut by the veins, and tiie solutions rising 
through the open fisaures were dammed back by the shales and spread out 
along this horizon. The carbonaeeoua material of this shale led to the pre- 
cipitation of the metallic campounds contained by the stagnant Bolutions, 
thus giving rise to bedded ore masses. 

A vein may also fray out upward before reaching tlie surface, only its 
Ematlcr branches outcropping, as was the eafc in the famous silver-tin veins 
of the quartz-trachyte Cerro de Potosi in Bolivia {A. W. Stelzner). At Nag- 




Fig. 05.— The teraiinatiou ot mineral vcius at the top of the Enterprise mine. (Hickard.) 
shale; d, younger overlying 'rock; e, ore-beds in 



yag, too, many fissures fail to reach the surface (J. Grimm). The outcrop 
of a vein is not always distinctly recognizable at the earth's surface. If the 
predominant ganguc is a hard material, resisting weathering, a vein may 
project as a rocky crest or a low wall, as Is so often the case with gold-quartz 
lodes, wliieh for that reason are called reefs anil hdifes. On the contrary, 
a vein may be marked along the surface by a trench-like depression if the 
vein filling consists of carbonates and easily decomposed ores. (See also 
description of popcan formation Iwlow.) 

The outcrop of a lode, like that of a hed, may bo exposed or covered, that 
is to say, concealed by younger deposits. Pleistocene alluvium is particu- 
larly apt to form such mantles over lode outcrops, but igneous intrusions 



El'lGENETlC DEPOSITS. 125 

may also do ho, as is seen at El Oro, Mexico, where andeEitic lavas conceal 
the outcrops. 

'"' (e) Structobal Belatioxs of Veins to Counthy Rock. 

The most comnion tjpe of vein is that which cuts across the stratifica- 
tion of the country rock and is, therefore, called a cross vein (Fig. 66). 
Ulien the lodes have the same strike and dip as the country rock, they are 
commonly called bedded veins (Fig. 67), The type is very common among 
gold quartz veins, which usually show numerous lenticular swellings of the 
vein quartz. 

It is often difficult to distinguish these bedded veins from true strata. 
The principal features by which doubtful cases of such veins can be recog- 
nized are, 1st, the occurrence of local cut-offs of the stratification; 2d, the 
presence of small transverse stringers ; and, 3d, the prcBcnce In the district 
of genuine fissure lodes of similar or identical composition. The true vein 




Fig. 67. — A bedded or stratum vein. 
At u, a local cut-oR; at t, e. small 
side stringer. 

nature may also be proved by the presence of fragments of country rock in 
the midst of the vein filling. 

A special form of bedded vein is known as a saddle reef. The best 
examples are those of the Bendigo goldfield of Victoria, whicli have been 
described by Dunn,' Rickard,* Pittmann, Samuels,' Schmcisser and 
Vogelsang.* As they are a new type they warrant a somewhat detailed de- 
scription. 



Bendigo Gold Fields,' Published by the Victoria Mines 
Trans. Amer. Inst. Min. Eng,, Vol. 



' Dunn: 'Report on 
Department, Melbourne. 

' Ilickard, T. A. ; 'The Bendign Gnld Field. 
XX, ISSl.p. 49<). 

'Samueln: 'Origjnnf theBendlgoSaddlc Reefs.' Zeil.}.Prak.Oeol.,lS94,p.95. 

' K. Schmeisaer and K. Voeelsang: 'Die Goldfelder Australiena.' Berlin, 
1897, p. 64. 



126 



THE NATURE OF ORE DEPOSITS. 



The Silsrian Bhales and sandstones of Bendigo have been sharply folded 
into anticlines and synclines and the strata at the flexure points have slipped 
upon one another in such a way as to form cavities in the arches and 
troughs. (Fig. 68.) 

The reefs are arch-like masses of quartz filling the cavities of anticlines 
and the bowl or trough-shaped synclines (inverted saddles). The quartz 
contaiiiH both free gold and finely distributed auriferous sulphides, and 
sometimes encloses angular fragments of country rock. These fragments, 
end the presence of short transverse stringers running from the quartz bed 
into the underlying layers, prove the deposits to be true veins (Fig. 69). Sev- 



HtW GHUU LIht 









¥ip. IVt.— Ideul section through the Beiidi^ goldfield. (T. A. Uickard.J 



eral groups of saddle-veins may follow one another at greater or less dis- 
tances. They arc often quite large, the anticline of the Xct Chum mine 
being exposed for a distance of 23 km. (14 miles) and to a depth of 975 
m. (3,200 ft.) Besides these saddle reefs, ordinary quartz veins of sim- 
ilar mincralogic composition also occur in the district. 

Similar anticlinal deposits have been described by E. E. Faribault from 
Nova Scotia (see iindcr Stratified fiold Ore Deposits), 

The famous deposit of Broken Hill in the Barrier range. New South 
Wales, is, according to E, F. Pittman and J. B. Jaquct,' regarded as a 
great anticlinal deposit, as indicated in the detailed description which is 
given later. 



EPIGENETIC DEPOSITS. 



127 



Quartz segregatione, on a very small scale, often occur in cl^ sUte^ 
phyllitcs and mica schists, in which the foliations have been forced apert by 
folding. Sometimes these quartz lenticules contain gold. 

Bedded veins are most frequent in platy or shaly or foliated rocks in which 
the bedding planes are marked by very distinct joints and are not apt to 
occur in heavy bedded, more brittle rocks. 

Bedded veins are simulated when the beds along the walls of a quartz- 







Fig. 69. — Section through the saddle reef of the New Chum Consolidated 
Mine, Bendigo, Victoria, (T. A. liickwd.J 
A, sandstone; B, shaly saudatone, with quartz strings; C, lode quartz ynth gold 
and eulpludes. 



filled fault are bent so that the layers lying against the vein wall are paral- 
lel to it, as figured further on. 

Gash veins are commonly understood to be those formed in joints and 
cross fissures in limestone, which have been widened by the solvent action 
of circulating water and filled by galena, zinc-blende and other ores. A 
characteristic feature of this variety of vein is the very short length and 
depth in strike and dip, and the association with certain calcareous beds. 



138 



J- 



THE NATUHK OF ORE DEPOSITS. 



and absence in intercalated slates. Figure 70, after Whitney, illostrates 
their mode of occurrence; the form is especially common in the Carbon- 
iferouB limestones of southwestern Missouri. They might, perhaps, be fitly 
called solution deposits, due to leaching out along velnk'ts (Auslauguug 
triinier), that is, fissures enlarged by solution and filled witli ore. They 
belong to the group of irregular cavity fillings, not to true veins. 

The pipe veins, as certain tubes of ore have been called which traverse 




zi - - - 



V — T 



Fig. 70.— Gaah veinB, after Whitney, 
k, Jimestone with Btringera of lead glanre; s, slate. 



the stratification of limestone obliquely, are of similar class and origin; 
they present a strong contrast to the cavity fillings ealJed flats, wliieh are 
parallel to the bedding. A more extended application of this term seems 
to us inappropriate, an opinion already expressed by R. W, Raymond', 

Columnar deposits are occasionally formed by the stretching and squeez- 
ing out of beds between more resistant strata. Thus the ore chimneys of 
Raposos in Brazil are not true veins, but masses of quartzite impregnated 
with auriferous pyrite and arsenopyrite.' Chambered vein is the name 
given by G, F. Becker to a type of deposit common in the quicksilver de- 
posits of California. Fig. 71 shows the difference between an onlinary and 
a chambered vein. la this type the vein proper is connected with very irreg- 
ular, large stock-like orebodles extending from the vein into an insoluble 
country rock. Their origin is supposed to be due to a condition of varying 
cohesion of the country rock, the weaker parts of which, when subjected to 
torsional forces, became broken and crushed. Chambered veins are, how- 
ever, very different from cavities dissolve<l in limestones, whicli are con- 
nected with vein fissures in a similar manner. 

' 'WhaJ is a pipe vein?' Tnrnt. Am. Inst. Min. Ene;., Vol. VI, 1S79. p. 30.1. 
'G. Berj;: 'Goldlageretatten von Itaposos.' Zeit.f. Pnk. Oeol.. 1002, p. HI. 



El'lGENETlC DEPOSITS. 



129 



Contact veins occur at the boundary between sedimentary and igneouB 
rocks. Underground water, circulating mainly along joints, and to Bome ex- 
tent in pre-existing quartz veins, is checked when it encounters intrusive 
eruptive masses, because the igneous rocks are less permeable. The flowage 
thus checked may spread out laterally along the contact plane, because it is 
the path of least resistance, and in doing so the waters may deposit such sub- 
stances as they held in solution. In other cases the cooling of eruptive 
rocks may have formed contraction fissures subsequently filled by ores. 

A typical example of such a contact lode is seen in the Haile gold mine 
in South Carolina, described by H. Credner* and illustrated in Fig. 72. 

According to J. H. L. Vogt° well developed contact lodes (with copper 
ore in quartz) accompany granite dikes which traverse quartzite slate at the 
Moberg mine in Thelemarken. 

Fine examples occur in Idaho, in which quartz veins overlie or underlie 
dikes of porphyry or basic rocks.' In some cases faults form contact veins. 
A good example of this variety of contact vein is seen in the Johannes mine, 
near Schwarzenberg, described' by Charpentier.* An ordinary hematite 
vein 2 to 17 meters thick has been opened to a depth of 200 meters. Near 
the outcrop the vein follows the contact plane between granite and mica 
schist, but in depth it passes into the granite. Its origin through general 




orogentc causes is shown by its great length; it extends 7 kilometers nortii- 
ward (to Lauter) and passes through alternations of gneiss and mica schist 

The well-known contact lode of the old Haiis Baden mine, near Baden- 
weiler, is also a fault fissure. It traverses granite and the Bunter sandstone 

' Zeil. }. d. gf». Natvr, 1370, Vol. XXXV, p. 20. 

'J. H. L. Vogt: 'Zur Classification der Erzvorkommen. ' 
1S9S, p. 140. 

•W. Lindgren: 
p. 701. 

' Charpentier: 'Minenflogische Geographic von SachHen,' 1778, p. 248. 



Zeil. f. Prak. Gtol., 
'The Mining Districts of the Idaho Basin.' Washington, 1898, 



130 



THE NATURE OF ORE DEPOSITS. 



and cootains qnaitz, barite, fiuonpar, galena, copper pyrite and copper 
glance (Q. Leonhard). At this place the Bunter sandstone, the normal 
stratified rock, is younger than the eruptiTe rock. The term contact vein 
should properly be restricted to onl; those which coincide vith a real erup- 
tive contact. 

(f ) RBLA.TI0N8 OF YbINS TO EaCB OtHEB. 
Several veins vith approximately identical strike are called parallel lodea, 
as, for example, the gold quartz lodes of the Sierra Nevada in California, 
which run parallel to the longitudinal axis of the range; and the fifteen 
lead veins of SvenniDgdal in Norway, which run at right angles to the strike 
of the strata. 



I] 


Pilllilii|i|l!il 






! li 



Rg. 72,— Contact veins of Ilaile Rold mine, South Carolina. (H. Credner.) 
a, quartz Bchist b quartz; c, quartz schist with auriferous pyrite; d, diorite 
vein; e, brown hematite contact lodes. 



V. Radiating veins is a term applied to a cluster of veins diverging approxi- 
mately from one point. The arrangement of the veins of the upper Harz 
might serve as an example. (See map sketch Fig. 166.) Typical radiating 
veins exist in the Ccrro de Fotosi, Bolivia, tin deposits. Systems of paral- 
lel lodes are called series. 

The orientation of the vein series of Saxony has been studied in detail.' 
The special geologic maps of that kingdom show them as generalized by H. 
Miiller. As may be seen by the map of the Freiberg veins, accompanying 
this work, two main directions may be distinguished in the strike of the 
Freiberg lodes : 1. A aeries with a few deviations between north-south and 
northeast Though this series does not coincide exactly vrith the main 
northeast strike of the Erzgebirge, it is very close to it, and hence is called 
the Erzgebirge series. S. A series striking between northwest and west- 

' F. C. V. Beusti 'GanfEkarte uher den inneren Theil des Freiber^er BcrRrevieres 
nebst ErlSuterungen. ' Leipzig, 1842. Also 'Ueber die Erigangiuge im sachsischen 
" ' ' 'a ihnr Bedehung lu den daaigen ^rphyridgen.' Fraberg, 1856. 



EPIOENETIC DEPOSITS. 131 

northwest is called the Harz system, because it coincides with the main 
strike of the Harz. Upon close examination of the special map it appears 
that the several vein formations distinguished in Saxony (see later) favor 
one of these directions. The pyrite-blende-lead veins, which predominate at 
Freiberg itself, as well as the rich silver quartz veins developed at a distance 
from the town near Braunsdorf and Oross-Yoigtsberg, also have a course 
parallel to the Erzgebirge ; the lead barite veins and many barren lodes run 
with the axis of the Harz mountains, while the galena and the spathic lead 
veins have numerous representations in both series, especially in the areas 
called Bescheert Oliick and Himmelsf iirst, near Brand. 

The Harz (Hercynian) direction is also followed by a majority of the 
iron ore and cobalt lodes of the upper Erzgebirge, especially in the Schwarz- 
enberg and Schneeberg areas. The formation of all these more or less par- 
allel ranges is evidently connected with the main uplift and folding of the 
Erzgebirge, which occurred in Permian and late Carboniferous time. In 
fact, post-Cretaceous mountain-building forces have formed entirely differ- 
ent systems of fissures at other localities, as is so plainly seen in the directions 
of the two systems of barren fissures so numerous in the so-called Saxon- 
Switzerland fissures, which, as a whole, form two series similar in orienta- 
tion to those already noted. The same rule holds true in many other min- 
ing areas; thus an exact plotting of the prevailing strike of the veins of a 
district may lead to important inferences as regards the general structure 
and vice versa. In the Freiberg area, which we have used as an illustration, 
local orogenic processes, as well as general ones, have evidently been active 
in forming the network of veins. It should be particularly noted that the 
gneisses of the Freiberg area form a dome whose summit is traversed by the 
veins. 

When in a certain area the veins strike irregularly in all directions the 
network of lodes is called a stochwork} Thus innumerable tin lodes occur 
in the granite at Altenberg in the Erzgebirge, and with the intervening coun- 
try rock which is impregnated with ore, form what is called the ^^Alten- 
berger Stockwerk.*' Similar stockworks also occur at several other localities 
in the Erzgebirge. In Cornwall a tangle of tin veins has penetrated the 
rock so generally, and at the same time has impregnated it with tin ore 
so abundantly, that large masses of rock have been mined out as ore, and 
vast chambers mined out at different levels. Mention may also be made of 
the Geyer stockwork, whose workings, like those of the Altenberger Zwit- 
terstock, collapsed, forming a great basin. 

^ This German term, adopted in both French and English literature, applies to a 
mass of frranitic rock traversed bv a network of small veins, interlacing; with one another 
and traversing the rock in all directions, but the ore also impregnates the interlacing 
rock. (Louis.) 



132 THE NATURE OP ORE DEPOSITS. 

Many vein aggregates resembling stockworks are also found in the gold 
ore district of Ttansylvania; for example, at Offenbanya, where trachyte 
breccia in the Kreisova stock is penetrated by innumerable gold- and silver- 
bearing veins. 

(g) Structural Relations op Two Veins to Each Other. 

Double Veins. When a fissure vein has been reopened and a new fis- 
sure formed, usually along one wall, but sometimes through the middle 
portion of the vein, and this fracture is filled by the deposition of material 
which may be unlike that of the primary vein, the result is a double 
vein, which may be composed of different layers or bands. Thus, for 
example, several of the veins at Himmelsfiirst, near Brand, in the 
Erzgebirge, consist of a band^of galena or brown spar ore, and a harder 
layer, which must be classed as a pyritic blendic lead vein. A similar con- 
dition is observed at the Christian Stehende at Himmelfahrt, near Frei- 
berg. A specially instructive example of double lode is the famous 
Halsbriicker Spat near Freiberg. It consists of a soft band, com- 
posed chiefly of thin layers of barite, containing a slightly argentiferous 
galena, while a hard band consists of ferruginous quartz with highly ar* 
gentiferous galena and rich silver ores. These two divisions of the vein 
diverge northwestward and are worked as separate veins — the soft stringer 
as the Drei Prinzen Spat, the hard as the Ludwig Spat (H. Miiller). 

If two approximately parallel veins are, as a whole, separate and only 
occasionally combine into a double lode, one lode (a) is said to drag against 
the other (b) (Fig. 73). If after their meeting they remain permanently 
connected, they are combined or are said to have joined. 
A If two veins cross, either in the strike or dip, the veins intersect. Inter- 
sections are further subdivided into: 

1. Bectangular intersections (Fig. 74) when the strikes of the two lodes 
are at right angles. 

2. Convergent intersections (Fig. 75) when the veins cross at an acute 
angle. 

3. A dip intersection occurs (Fig. 76) when the veins are parallel in the 
strike, but intersect in dip. 

As the lode cutting across another must necessarily always be the younger, 
the relations of two lodes to each other is used to determine their relative age. 

For this purpose, it is, of course, necessary that the filling of the two 
veins shall be of different nature, or at any rate that one of them shall show 
distinct layers or crusts, in order that one may see whether the layers of 
the one pass through the mass of the other. Fig. 77 shows a simple vein 
crossing between an older stringer (a) with a younger barite stringer (b). 



EPIOENETIC DEPOSITS. 



Id very rare cases two intersecting fisBuree have been filled at the same 
time. If both veins show a banded structure or cruetification, the hiyers of 




t'ig. 73. — One vein (a) drags against another (b). 



one vein pass uninterruptedly into those of the other. An excellent ex- 
ample ie shown in Fig. 78 recorded by K. A. Kiilm.* It r^»r 




Fig. 75. — A convergent interaectioD. 

sents a crosging of the Karl and the Ludwig veins in the now abandoned 
Habacht Fundgrube near Freiberg (Bescheert Gliick). "The two lodes, 
' 'Handbuch der Geognoeie,' Freibei^, 1836, Vol. 11, p. 604. 



134 THE NATURE OF ORE DEPOSITS. 

each of an average thicknees of 10 to 15 cm. (4 to 6 in.), join in such a way 
that the outermoet crust of quartz (q) and the second of roee spar (r) pass 
irithout interruption from the one into the other, while the third, a mix- 




Fig. 76. — An intersection 



ture of rose spar, argentiferous black zinc-blende and argentiferous galena 
(b), encloBCB within the space formed by the two lodes a druse-like cavity 
18 to 23 cm. (7 to 9 in.) long." This druse is lined with quartz crystals. 




A similar description is given by K. t)almer' of the crossing of the flat 
dipping veins with the horizontal tin veins at Zinnwald in the Erzgebirge. 
In this case, too, there is no intersection, but a coalescence of the vein fill- 
ings as well as of the greisen zones on both sides. 

I 'Eridut. I. S. AltenbuTg-Zinnwald,' p. 36. 



EPWENETIC DEPOSITS. 



135 



A deflection of a vein occurs when one vein drags against another for 
some distance and then cuts through and along it (compare, on this point, 
Figs. 79 and 80) . 

It sometimes happens that the approaching vein breaks up into stringers, 
only a few of the stringers passing through the other lode and uniting on 
the other side again to form the lode with its former thickness. This break- 
ing up may take place on one side only, while on the other the lode may at 
first appear mearly as a single, feeble stringer, as in the example (Fig. 81) 
from Aodreasberg. In this case the deflection is produced not by an ore 




Fig. 78. — V«n crossing with umultaneous filling. (Kuhn.) 
K> gray gneiss; q, quarti; r, rose spar; b, roseaparwith nnc-blende andgalena. 
In the center a quarti druse. 

vein, but by a fault (geschiebe) fissure filled with cniabed country rock and "; 
traversed by many slip planes. * 

Sometimes a vein splits into stringers as it approaches another, and at 
that point stops, as shown in the example (Fig. 83) described by von Weiss- 
enbach. 

The deflection of younger veins against older ones before the older vein 
is actually reached is due to numerous shear planes or joints approximately 
parallel to the older fissure and closely spaced, but which may be so fine 
that they are barely recognizable. The force producing the later vein would 
be relitn'ed or entirely changed in direction along the shear planes, as well 
as by the older fissure, since the new fissure would follow the line of least re- 
sistance in the rock. 

Fault fissures filled by attrition breccia and mashed country rock also 
cause rein deflections. Thus the so-called Buscheln (rotten lodes) cause 
deflection of miuerel veins even more frequently than other veins do. By 



I as TIIK NATtRE OP ORE DEPOSITS. 

RnM^a Um H«n onaer Ainpwtea flj^enu of pcnOel doaelj 
mrertbnHi bah ^OMa Clkd vHh teu^ittUAj en»fae4 and 




M(t. HI. Dedprtion nf Ml Andn-iwh^rB vein BimiiMt< «n oHer vein with a Mattering 
Into rtrlnBcni on one wide only. (ZImmermann.) 

try mrk, tlio to-cancd vein ilatc, Oangthonschiefer, and sometimes with 



EPIGENETIC DEPOSITS. 137 

solid fragments of graywacke. The constrnction of thcee Rnacheln is eotne- 
times disclosed by mining operations. One, for example, the Faulenischel, 
near ClauBthal, was cut by a drift from the Kaiser Wilhelm, shaft II, In- 
numerable folds and crinkles were found within it, as veil as many well 
marked slip or gliding fissures.* Similar conditions prevail in the 'Let* 
tenkluft' (clay fissure) at Pribram, which is also a reverse fault, against 
which many of the veins are deflected, also in the 'Bar Flache' of the Him- 
melfurst mine, near Brand, a zone of barren crushed and altered material 
which cuts off a great many veios. It will be observed that this feature 
differs from the cutting off of a vein by a later fault. The mineral vein 
splits up or ends against the vein of crushed rock. 




Fig. 82. — Complete splitting up into etrinpera of the Frisch Giuck Stehende on ap- 
proachiDg: the Peter Slehende in tlie HofFnung Oottes mine. (Ground plan, after 
von Weiasenbsch.) 



The deflection of dikes of eruptive rock by fissures is of very frequent oc- 
currence. Fig. 83 represents the ground plan of a porphyrite dike cutting 
quartzitic slate, at DovigfoBS, near Aamot, in Norway. The dike is deflected 
several times by small quartz stringers. This dike is itself a branch of a 
larger dike, and it is clear that the course of the walls of this larger dike is 
also influenced by the quartz stringers. 

The discussion of deflection naturally suggests and leads up to the sab- 
ject of dUplacements, a feature which is most appropriately treated here, 

' G. Kfihier: 'Beitrafce x. Kenntnisa d. ErdbewegungcD und StAnugen der Lager- 
atitten,' B. u. H. Z. 1897, p. 317. 



138 TEE NATURE OF ORE DEPOSITS. 

Bince numy mineral veins are formed by tlie filling of faolt, tliat is, displace- 
nunt fimires. 

(h) D18FU.CEIIENT8.* 

By faulting we mean a change in the relative position of one block com- 
pared with the other, along a plane separating them. Such dislocatioDs fall 
into two main grot^: 1, faults or displacements produced by vertical 




Fig. 83. — Dike of sugit« porphynte u 

q, quftrtrite alate; Q, quartz strmgers p augite porphyrite, finely crystaUioe 
along the Belvage. 



movemeots; 2, faults produced by honzoDtal movements. The second 
group is the least frequent and least important. There is a possibility of 

' A very full list of publicationH aliout the faulting of veina \% p\'en by F. T. Free- 
land, ' Fflult Hules,' Jrantaetionit American Institute Uining Engineere, Vol. SXI, 
1892, p. 491. The more important publications include: J. C. 1.. Schmidt: 'Theorie 
der Verachiebung alterer Gange.' Frankfort, 1810. C. Zimmermann: 'Die Wieder- 
aiisrichtung verworfencr Gange,' etc. Leipsig, 182S. R. von Carnal: 'Die Sprunge 
im Steinkohlengehirge. ' Karsten's Arthiv n. F. 1S32, IX. H. HOfer: 'Die 
Auwichtung von Verwerfungen. ■ Out. Z. f. B. u. H., XXIX, 1881, and XXXIV, 
1886. G. Kehter: 'Die StCningen der Gange, Fl6t£e und Lager.' I^ipiig, 18S6. 
E. de Margerie and A. Heim: 'Die Dislocationen der Erdrinde.' Zurich, 1888. 



EPIQENETIC DEPOSITS. 139 

combination of the two kinds of movement, and hence cases may uriee 
which may not fit into these two classes. 

<a) Displacement Produced hy Vertical Hovementa. 

This title implies movement along a vertical line. In most cases, how- 
ever, the movement is not exacti; vertical, but oblique. This kind of dia- 
placement can be subdivided into two classes: (a) DiBpIacements pnre 
and simple; (b) flesures. The first is caused by a fracture acccmipanied 
by a relative shifting of the two parts (Fig. 84} ; the latter la merely a bald- 
ing or sharp flexure of a part of a layer or plate of rock (Fig. 86). If the 





Fig. 84.— Simple fault (aection.) 



Fig. 85.— flazure (section). 



flexure is so sharp that rupture occurs, the flexure thea becomes a trott 

fault, accompanied by a drag of the ends of the strata on both sides 
(Fig. 86). 

I, Oeneral Properties of Simple Faalta. 

A few definitioDB are needed as a preface to a discusBion of faults. The 
distance between the faulted ends measured along the plane is the displace- 
ment or shift (/ in Fig. 87). The distance along a horizontal plane be- 
tween the ends of the faulted vein is called the heave {w in Fig. 87). The 
vertical distance betwe^i two displaced portions of a vein or bed is called 
throw or vertical downthrow (s in Fig. 87). It should also be remembered 
that the width of the fault fissure must be considered ae a factor in discussing 
the heave of faults. 



140 



THE NATURE OF ORE DEPOSITS. 



The horizontal projection of the fault plane is usually a straight line 
(Fig. 88) ; sometimes it shows curves^ which are merely variations of the 




Fig. 86. — Section of a fault becoming a flexure. 

general strike. In rare cases closed curves have even been observed 
(Margerie and Heim). 




Pig. 87. — A displacement in profile. 

f, displacement or shift; s, vertical 
displacement or throw; w, heave or hori- 
zontal displacement. 



Fig. 88. — ^A faulting shown in ground plan. 

g, displaced vein dipping northwest; 
V, fault fissure dipping north. 



11. Filling of Fault Fissures. v 

A fault is but rarely a gaping fissure. It is usually filled either by more 
or less comminuted and ground up fragments of rock from both the walls. 



■J 



EPIOENETIC DEPOSITS. 141 

or by mineral material subsequently introduced, which may include ore. 
Very frequently both rock rubbish and mineral deposits are present, espe- 
cially in faults occupied by mineral veins. 

We will first describe in some detail the mechanical fillings which are 
common in both barren and in ore-bearing fissures. This filling may con- 
sist of irregular, mostly angular blocks and fragments, sometimes sub- 
angular or even rounded. The material is often held together by a paste or 
cement of firmly compressed, finely triturated particles, or it may even be 
cemented together by a mineral deposit. Such friction breccias, as this kind 
of material is called, are sometimes quite thick. In the great Feldbiss 
fault of the Aachen coal basin, the breccia attains a maximum thick- 
ness of 12 m. (40 ft.). The mineral veins of Freiberg very frequently con- 
sist of a breccia of gneiss, with scattered stringers of ore. Such a structure 
is especially frequent in compound veins or lodes. At Freiberg, the spaces 
between the rounded blocks of gneiss are often filled by pebbles of greatly 
decomposed gneiss with ore veinlets between. The fragments of rock are 
often flat, and the slabs lie parallel to the walls. If these fragments ex- 
hibit the banding of the gneiss, it is generally seen that the direction of 
banding docs not agree in the different blocks, and differs from that of the 
solid country rock. Similar conditions were described and figured by G. A. 
von Weissenbach at the Machtigen Gang of the Onade Oottes and Neujahrs 
Maasen mines at Johanngeorgenstadt, a vein occurring in altered schist 
(Fig. 89). As he graphically describes it, the schist "appears jammed to 
the side or somewhat displaced, one part over the other, in the same way 
that the fibres of wooden props in mines are seen to be jammed by the pres- 
sure of the rocks above and squeeze out in a plane at right angles to the 
axis of the timber.*' 

Sometimes well-rounded fragments of the country rock lie scattered 
through a finely crushed mass, and by movement within the mass during 
faulting, and by contact with harder grains or with sharp projections of the 
fissure walls, they have been scratched and scarred exactly like the striated 
bouldef s of the ground moraines of a glacier. Such striated surfaces are 
especially well developed in the veins of the Himmelfiirst mine near Brand. 
On the Bar Flache, distinctly scratched specimens of country rock were 
found. In the Daniel Flache, ground-up specimens of this kind occurred 
in the midst of a clayey mass 0.5 to 2 m. thick, formed by fragments of 
ore and gangue, and older vein* fillings. 

Figure 90 represents a fault cobble showing distinct friction striae from 
the Neugliick Spat drift. No. 15, below adit. The cobbles lie either in the 
vein clay or among the pebbles of crushed gneiss, both along the walls and 

* E. W. Neubert in Freiberger Jahrbuch, 1881, p. 63. 



142 



THE NATURE OF ORE DEPOSITS. 



in the center of the lode. Such friction gravels when compacted and in> 
dniated form a conglomerate vein. In such cases the pebbles are some- 
timefl packed close together, as on the Peter Stehende of Christhescheerimg 
nine, near Freiherg. Sometimes thejr are incrasted over with mineral de- 




fig. 89. — Section of a mineral vein near Johaungeorg^iiBtadt. (Von Weissenbach.) 
Shows flat scliist blocks parallel to the lode surface, with planes of schistoBity 
running in various directions. 

posits, as on the Eduard Spat of Himmelsfnrst, where crystals of stephanite 
coat pebhles of mica schist. Q. A. von Weissenbach' described such vein 




conglomerates under the term 'Kugelgestein' (ball rock) and very aptly 
compared the process of their formation by friction movement between the 
fissure walls to that observed in grinding>mills. 

* ' Abbildungen merkw. Gang veihAltnisHe. ' 1836, p. 18. 



EPIOENETIC DEPOSITS. 



143 



Such conditiona are fairlj conunon in the tin veins in quartz porphyry, 
at Altenberg in the Erzgebirge. The vein filling consists of hard balls 
of porphyry imbedded in a clayey mass compoeed of completely altered 
and ground-up porphyry. Similar formations are known in the 
Elias vein near Joachimsthal, and from Uie tin veins of Cornwall (Collins). 
S. F. Emmons* also mentions similar cases, but ascribes the rounding as 
often due to decomposition resulting from the action of mineral solutions 
acting upon fragments that had previously been angular. In Fig. 
91, we give a picture, after Q. A. von Weissenbach, of such a drag or con- 
glomerate vein 10 centimeters (0.33 ft.) thick, which lies along the hang- 
ing wall of a vein at Luxbach near Annaberg. 




Fig. Bl. — A conglomerate veia along the hanging wall o( the Neu UaverhoSt Gluck 
vtau, near Anuabe^. 

This attrition gravel of veins must not be confounded with those real 
gravels derived from overlying sedimentary strata, and which, in some 
cases, have fallen into open fissures, as shown later. 

In connection with these vein gravels,' mention should also be made of 
the rare occurrence of rock fragments that have been twisted off cylindrically 
in fault fissures. The Freiberg mining school museum contains such a 
piece 16 cm. (0.5 ft.) long, as thick as an arm, and resembling the branch 
of a tree. It consists of a hard, brittle greisen from Altenberg, which, be- 
sides having two rounded faces of cross fractures, is completely covered with 

' 'Structural Relations of Ore Depoaita. ' Trans. Am. Inst. Min. EnR., 1888, p. Ifl. 

'This paraeraph in the German original desrribeH diatinptions not used in America. 
The finer particles, ronsigtinR of fracmenta of the size of a hazelnut, and mostly quite 
soft aa a result of advanced decampoaition, constitute the Becondary layer (auwchram, 
liiinicBV The scMralled (luhre are still finer, forming a clayw gravel. Lastly we have 
the vein claya, whii-h are very common, and represent the finest product of rock com- 
minution. 



144 rUE NATURE OF ORE DEPOSITS. 

slip striae runniiig obliquely aronnd it. These gliding surfacee (Fig. 92) 
are even at one point involute, that is to say, tvo of them follow at a little 
distance, one over the other, in such way that the slip planes intersect at 
acute angles. Such peculiar specimens are formed when an upright frag- 
ment of rock is dragged l>etwccn the two walls of the fault fissure in a direc- 
tion parallel to the longer axis of the fragment, while at the same time it is 
moved about or revolved about this axis. 




Ytg. 92. — Drawn-out rylirider of graaen fragmeut from a fault-cleft at Altenberg. 



The vein clays are soft, pasty or tough, plastic clays, frequently mixed 
with larger grains, and often colored black by carbonaceous material. In 
the blackish vein clay of Verespatak and Maidnnpock, the i^o-oalled 'Glamm,' 
the coloring, according to E. Tietzc,' is due to copper oxide. Posepny's* 
Tiew that the Hungarian 'Glanini' has been washed into the fissures from 
the surface seems improbable, and it appears more likely that this material 
is the result of trituration and decomposition, and was either formed in 
the lode fissure itself or forced into it from greater depth, as will be ex- 
plained later on. 

' E. TietKe: Jahjh. A. k. fc. Geol. ReicliHarurt. IR70, p. 321. 
» F. Posepny; Idem. 1867, p. 101, and 1870, p. 273. 



EPIQENETIC DEPOSITS. 146 

Sometimes such a vein clay shows a distinct slaty or schistose structure, 
due to strong pressure. Such material separates along these cleavage planes 
into scales which are often as smooth as glass or are covered with parallel 
friction striae. Such vein clay slates from lodes of the upper Harz, de- 
scribed in detail by A. von Groddeck/ are mechanically altered Culm clay 
slates, which have undergone, especially the variegated varieties, a chem- 
ical transformation, as noted later. 

The finer pebbles (ausschram) and the clays are often confined to a nar- 
row zone along the wall, in which case they form the clay selvage or gouge. 
Such a clay selvage is ordinarily welcome to the miner because it facilitates 
the loosening of the true vein filling from waste material, while the work is 
more di£5cult when the lode is "coalesced with the country rock^ by crystal- 
line crusts, as the (German miner puts it, or **frozen hard to the country,'* 
as the American miner picturesquely expresses it. 

These friction products are workable when they are impregnated with 
finely disseminated ores, which are mostly of secondary (t. e., later) origin. 
In the Erzgebirge such vein clays are colored yellowish, reddish or brown- 
ish by metallic compounds, being known as gilben (mountain yellows) or 
braunen (browns). At Freiberg, in the Thurmhof vein, a yellow vein clay 
with 0.062% of silver was formerly mined, while in the Friedrich vein the 
yellow vein clay held scattered particles of wire silver and grains of earthy 
silver glance, so that the clay contained 1.6 to 1.9% silver. In the Anna- 
berg area, according to H. Miiller,* these vein-clays often contained a consid- 
erable amount of silver, so that they paid to vrork in the Himmlisch Heer. 
Black clays containing as much as 6% in silver were also extracted there. 
[At Butte, Montana, the fault clays often contain ore particles and the fill- 
ing sometimes consists of balls of pyritic ore, bomite, glance or enargite. 
quartz and altered granite, so that the entire mass is workable. The blade 
clays often contain as high as 8% copper, but are not mined alone.] Mention 
must also be made of the fine crystals of native gold in clay of the 
Famcomb Hill veins of Summit county, Colorado, described by Rickard. 

The description of the mechanical material filling fault fissures and 
the impregnations just mentioned naturally precedes an account of the fault 
fissures which form mineral veins. 

III. Fault Veins. 

Mineral veins are often true faults. In the Freiberg area it is seldom 
that this can be shown by a comparison of the rock of the two walls, be- 

' A. von Groddeck: Z. d. D. g. G., 1866, Vol. XVIII, p. 603 and 1869; Vol. XXI, 
p. 499, and Jahrb, d. k. preuss. geol. Landesanst. , 1885, pp. 1-52. 

' 'Die Erzg&nge dee Annaberger Revieres.' Leipzig, 1894, p. 96. 



146 



THE NATURE OF ORE DEPOSITS. 



cause tbe rock is of very nnif onn nature, but it is frequently demonstrable 
when the fault Teins cut fhrougli older veins. 

A good example in which the faolting can be shown by the rocks is sem 
in the Htmmelefiirst mine near Brand, where the Benjamin Stehende cuts 
throng and displaces bands of muscovite gneiss and mica schist intercalated 
in btotite gneiss; the fanlt-vein ig itself dlBplaced by another mineral vein, 
the Neugliick Spat <E. W. Neubert, MSS.). 

The lodes of the npper Harz are, as is well knovm, fault veins in which 
the dislocation is very clearly shown by the different beds of the Devonian 
and Culm (carboniferoua) formations. At Bockswiese and Lautenthal the 
veins have a Devonian footwall, while the hanging wall is formed of rocks 



gZJft 




Fig. 93.— The Benjamin fault vein of Himmelsfttrst. (Ground plun.) 
B, Benjamin Stehender; N, Neugluck Spat; g, biotite gneiss; m, muscovite f;neiss; 
gl, muscovite ecbist, 

belonging to the Culm. The throw, according to A. von Groddeck,* is 200 
meters. Fig. 94 (after E. Msier') shows a cross-section of the displace- 
ments of Paleozoic strata produced by the main Bockwieser (Pisthaler vein 
and the Ortinlindener vein). 

Good examples of silver veins filling fault fissures displacing Carbonif- 
erouB strata occur at the Enterprise mine, Colorado, and have been de- 
scribed by T. A, Bickard.* 

Even where the uniformity of country rock prevents a direct recognition 
of displacement along mineral veins^ the dislocation may often be inferred 

' 'Lehre,' etc. 1879, p. 229. 

' ' Beitnuje zur Geo!, dea Bookwieeer Ganggebietes.' JHea. Ber. d. Natorf. G, ru 
PreiberK, 1900, Vol. X, p. 2. 

• T. A. Rirkard: "The Enterprise Mine,' Tram. Am. Inat. Min. Eng., 1896, Vol. 
XXVI, pp. 906-980. 



EPIGENETIC DEPOSITS. 



147 



from other obserTations. Thus the local videningB of veins have been ex- 
plained eiacc De la Beebe's* time as the result of dielocation of the vein 
walls and duo to their projccti<His and irregularities. The accompanying 
Fig. !>5 illustrates this shifting of irregular walls, which must nccesRarily 
produce priamatio or lenticular cavities. Le Neve Foster* uses the same 
theory to explain the peculiar pipe veins in some Cornwall mines, and Th. 




Fig. 04.'-<.-nKis-section of displacements gf Paleozoic strata. {E. Maier.} 
Kjenilf has endeavored to explain the genesis of the Norwegian 'rulers' 
(erzlineale) in the same way. 

^ IV. Condition of Fault Walls. 

The sliding motion of one side of a fault over the other, and the conse- 



• 'Respurdies in Theoretical Geology," 1834, Chap. 10, and 'Ileport ■ 
of Cornwall," 1839, p. 317. 

' Trans. Roy. Geol. Soc. Vol. IX, 1876. 

' 'Geologic von Norwegen,' Trans, by Gurlt. 18S0, p. 294, 



a Geology 



148 



THE NATURE OF ORE DEPOSITS. 



quent rubbing of the walls, produces emooth and eTenl; polished faces. 
Such polished surfaces are called slickeuBidea and sometimes show tml; 
mirrOT-like surfaces, if the material itself has a metallic luster, as, for ex- 
amine, the magnificent mirrors of pyrite found in the Confesionario mice 
(Huelva) or of galena of Incurtosi (Igleeias, Sardinia). Similar examples 
may bave led the Aztecs to make their remarkable pyrite mirrors. In other 
cases, numerous parallel scratches are seen on such polished surfaces, either 
as delicate striae or relatively deep furrows. An example of this kind from 
the Lade des Bundes lode at Hinunelaftirst, near Brand, in which the stria- 
tions are cut in galena, is shown in Fig. 96. Wherever these features occur 
they indicate that the &iilt desure was not an open one during the moTB- 




Fig. 95. — An explanation of local vdn-wideiiing from a fault. 



ment The direction of the striations on the vein wall is supposed to rep- 
resent the direction in which motion has taken place, but one must not a»- 
sume that they are always parallel to the dip of the fault fissure. This ia 
by no means the case, as has been shown by H. Hofer. This view (at one 
time generally prevalent) arose from the Schmidt^Zimmermann fault rule, 
according to which the rocks in the hanging-wall of the displacement fis- 
sure slid down parallel to their former position. This rule does indeed hold 
for many cases, hut it is by no means universally valid. 

Fault striations often form an acute angle with the line of dip; indeed, 
cases occur where they are almost perpendicular to the dip. Such a condi- 
tion, for example, has been described by H. Hijfer from the ironstone mine, 
near Ober-Zeiring, near Judonburg,.in Styria, and from the Hodritsch lode 
area near Schemnitz in Hungary. In the faolt fissures of the npper Hars 



EPIQENETIC DEPOSITS. 149 

region the fault slipe or gliding planes show horizontal striae, as has been 
known since Fr. Ad. Somer'e time. Finally, very fine instances of hori- 
zontal friction striations several meters long have been observed by the pres- 
ent author in the main great fault in the sandstone of Lnsatia. 

The direction of fault striae is not always the same over the entire wall 
of the same fault fissure. 

Numerous deviations occur and several systems of lines and furrows may 
even cross, and in one cluster of many parallel faults the striae may have 
various directions on different surfaces. 

The striations are not always straight. The slipping may have taken 
place in rapidly varying directions, and in such cases the striae may form 
curiously winding curves, as in the specimen exhibited before the Natiiral- 
ists' meeting at Vienna in 1892 by Ed. Suess. 




In this case the intricately tangled scratch lines showing on a polished 
fault plane surface of black calcareous slate, from Radotin in Moravia, were 
evidently caused by minute but hard projecting points of the opposite wall 
of the fault fissure. This is borne out by the complete agreement of the 
various scratch figures (reproduced in Fig. 97 from a self-printed plate, 
vrith the kind permission of the discoverer, J. J. John, and the first describer, 
Ed. Suess). Suess very appropriately styled the specimen a nitural earth- 
quake autograph, for it may readily be imagined that its formation was 
due to an earthquake tremor. 

In other cases it is probable that the curved scratches were produced by 
hard grains and fragments present in the fissure filling itself, and not by a 
projection of the opposite walla. Intersecting striations can also be pr> 



ISO 



THE NATURE OF ORE DEPOSITS. 



doced by a change of position of the rock fragment, while it was pushed 
along in the fissnre. 

The reader is cautioned not to assume that the length of the striation 
represents the extent of the movement. On the contrary, the length of such 
a scratch represents in most cases the combined length of the scratched sui^ 
face and that of the dislocation (moTement). It is only in rare cases that 
Huch a scratch can be supposed to be caused by a single hard grain, that is 




Pig. 97. — Earthquake aiitoErjph, (jliding surface with intricately tnneled strine c 
limestone from liadotin. (A piiiit from the stone itself.) 



to say, geometrically speaking, by a single point over which the surface was 
drawn. 

All these considerations show that these "handwritings on the wall" 
(Rickard) cannot always be deciphered as easily as might seem at first sight. 
At any rate, a test made by II. Hofcr seeuis to apply to many cases. If, 
in passing the hand over an extensive gliding plane, you receive the impres- 
sion of perfect smoothness, your hand has been moving in the direction in 
which the opposite rocks moved ; if you feel any roughness the hand is mov- 
ing opposite to the rock movement. The reason is that the gliding planes 



EPIQENETIC DEPOSITS. 



161 



have the same relief on a small scsle as the glacier-polished snrfacea of rocks, 
ae ie shown in the following diagram (Fig. 98). In this diagram, grotind- 
up material has been indicated as filling the fault fissure. Such material 
may, however, be practically absent. 

When a fault passes transversely through thinly bedded rocks the edges 
of the strata are often bent downward (or upward) in the direction of the 
movement. In some veins the walls of the open fissure may have been coated 
with mineral crusts which remain intact on one wall, while along the other 
the mineral crusts were broken by later fracturing and the ends of the beds 
bent around {Fig. 99). 




V. Torsional or Taming Hovement During DispUicemmt. 

A consideration of slip surfaces or planes, whose striation is not always 
coincident with the dip, shows that the Schmidt-Zimmermann rule has many 
exceptions. In these exceptional cases the dislocation sometimes may be 
inferred from observations of a different kind. 

H. Hofer has properly revived an observation communicated long ago 
by J. F. W. von Charpentier.' In the Himmelsfiirst mine, near Freiberg, 
at the junction of a Morgengang with the Schneider vein, 120 feet below 
the deep level of that locality, the two veins intersect without change of 

* 'Beobacbtungen uber die Lagerat&tten der Erse.' Ldpng, 1799| P- 103. 



158 TSS NATURE OF ORE DEPOSITS. 

either strike or dip. On tiie contrary, 240 feet lower, the course of the 
Stebende veiD changes at its junction with the Morgan vein, and a ao- 
called dragging of both lodefi could be noticed. This is alao obeerved at a 
depth of 360 feet, except that there the union of the two lodes is maintained 
for a greater distance than in the first instance. Thus the ends of the 
faulted vein on opposite eidea of the fault approach each other in depth, and 
actually meet 120 feet below the drift This proves that the displacement 
is not parallel, but due to a twisting (torsional) movement. Similar ex- 
amples have been recently found in various places. In the Freiberg area a 
tarn or twist of this kind is shown in the diBplacemeot of the Peter 
Stebende of the Alta Hoffnong Gottee mine. This vein is dislocated by the 
Flache fissure, dipping 70° east In the upper part, the two sections thus 
formed (the northern of which is entered on the maps as Eini^eit Morgen- 




Tig. 99. — Section of a fissure with sharply cut footwaU, while the hanging wall shows 

the strata bent. 

a, older ore-bearing stringer; b, younger friction breccia. 

gang) are rather far apart. The distance between them along the Flache 
fissure is 13 meters; in the counter drift, only 11 meters; in the seventh, 
only 5 ; in the ninth, 0. Thus if we could see a considerable extent of the 
atriations and alickensidcs of the fault-wall, they would represent segments 
of a circle. 

Among more recent examples may be mentioned the great displacement 
called MiiDstergewand Feldbiss, near Aachen, which, according to Hofer, is 
connected with a distinct twist. [Also at Butte, Montana, the great Ana- 
conda vein is displaced several hundred feet vertically by a fault showing a 
torsional movement.] 

VI. 7%e Surface Evidence of Ditplacementt. 
A fault does not usually show as a cliff or wall mi the earth's surface. ^ 
That it does so at first is evident, and scarps are formed by fissures due 



EPIGENETIC DEPOSITS. 153 

to the sinking of the earth's surface as a result of ooal mining, but such 
superficial scarps though sharply accentuated at first are very quickly 
leveled by the rainfall. In the first stage of this leveling process trench- 
like depressions are often formed as the rainwater washes away the loose 
material filling the displacement fissure, and a secondary subsidence there- 
upon occurs near the surface, as shown in Fig. 100 and 101. Such a 
section is often shown by faults resulting from coal mining, provided the 
fissures have a favorable dip. 

Fault scarps do sometimes form natural features, especially in dry 
countries where erosion makes but slow progress, as, for example, the dis- 
placement scarps of the Colorado plateaus described by Powell. In most 
cases, however, all traces of the fault scarp are quickly effaced and merely 
indirect topographic indications are presented ; such as the course of brooks 
that have followed a fissure, or a line of springs along the displacement. If, 
on the contrary, the fissure is filled with loose, permeable material it may 
gather the ground-water from afar, become completely saturated in its lower 
portion, and give rise to dangerous outbreaks of water in mines. Though a 
displacement may not be indicated topographically, yet in most cases it 
can be detected by the interrupted or diverted course oi the rock outcrops. 

VII. Diffetent Kinds of Simple Displacement. 

If we include displacements of sheets and beds with those of veins, we 
may distinguish the following cases based on the relation of the down- 
thrown block to the strike : 

1. Strike faults, or longitudinal displacements in which the course or 
strike of the fault coincides with the strike of the strata or of the lode 
(Fig. 101 and 103). Two cases are possible, (a) normal faults dipping 
toward the down-thrown block (Fig. 102), (b) reverse or overlap faults 
in which the opposite is true (Fig. 103). Strike faults of tilted beds are 
recognized on the earth's surface by repetitions of the outcrops of the dif- 
ferent beds, often with omission of several members, as shown in Fig. 104. 

2. Cross faults striking at or near a right angle with that of the displaced 
blocks (Fig. 106 and 106). 

3. Acute angled or diagonal faults, in which the course of the fault forms 
an acute angle with the strike of the displaced block. (Fig. 107 and 108.) 

Furthermore, displacements may be classified in accordance with the rela- 
tive direction of displacement of the thrown block. According to this we 
have three cases : 

1. Normal or gravity faults are ordinary dislocations in which the hang- 
ing wall block has slipped down along an inclined fault plane ; according to 



154 



THE NATURE OF ORE DEPOSITS. 



the Schmidt-Zimmermann rule this takes place in the direction of the dip 
and the two displaced blocks maintain a parallel position. As shown on 
p. 151, this rule has many exceptions. In plan the faulted beds occupy more 
space horizontally than they did before dislocation, i, e., an area greater 
by the amount of the horizontal throw than its original area (extension dis- 



•^i^pcasaRj^iJSjEi?^ 




Fig. 100. — Recent displacement fissure 
unchanged by rain-water. 




FSg. 101. — ^The same with a block 
dropped down. 



placement of Margerie and Heim). Most faults belong to this first group. 
(Fig. 109.) 

2. Vertical faults. In these the eflfect is the same whichever side is down- 
thrown (Kg. 110). 




iMiiiHitittitiHmtiiimjiiiiiBB 



.' N 



Fig. 102. — Model of a normal strike 

fault. 



Fig. 103. — Model of a reverse or over- 
lap displacement. 



3. Overthrusts or reverse or overlap faults, when the hanging wall block 
has been shoved upon the block that lies beneath the fault plane. As 
this is accompanied by a compression of the beds, so that they occupy a small- 
er space than before, this might, following Margerie and Heim, be called a 
compression displacement. (Fig. 111.) 



EPIGENETIC DEPOSITS. 



Very fine examples of OTerthroBte are found near Johanneeburg in the 
TrauBvaal, where the beds of gold-bearing conglomerate are dislocated by 





-7 tf~ 

Fig. 104.— Section of a strike fault. 



i-i_JA:j 



Fig. 10.').— Model of a cross fault. Fig. 106.— Plan of a cross fault 





nil 


M& 


'iliS 

111' 


, 


I 

IT 


4 
l>l> 


1 


1 


Ml 
. ■■ II 

■1 


: 

1 

1 
1 



Fig. 107. — Model of diagonal fault. 



Fig. 108. — Plan of a diagonal fault. 



several overlap faults. (Fig. 112.) This example also proves that over- 
thrusts, though common in strongly folded mountain ranges, can and do 
occur in regions of open and comparatively slight folding. 



166 THE NATURE OF ORE DEPOSITS. 

OverthniBts may also occur along vein fiBBuree, as, for example, in the 
ore-bearing lode of the Qute Hoflnimg mine, near Werlaa on the Rhine, and 
in the Schwebende of the upper Erzebirge in Saxony. 




Fig. 109. — Normal displacement. 
(Section.) 

VIII. Special Types of DispJacem&tts. 

Many diaplacemente are the result not of a single fault with down-throw 
or orerthruBt, but of a serieB of parallel fault fieaures with succesBive dis- 
placernente in the same direction. Groups of such faults, all in the same 
- direction, are termed step faulU or distributed faults. A good example is 
the great trunk fault, known as the "Rother Ochse," which traverses the 




Fig. 111.— Overthrust fault. 



northeast flank of the Permian coaf baein in the Planen baein near Dres- 
den. At Zechiedge, R. Hausee calculated the total throw of the many in- 
dividual faults ae 350 m. (1,148 ft.). Many partial faults have produced 
a complete chopping up of the main coal seam, since the brittle coal breaks 



EPIOENETIC DEPOSITS. 



167 



into slabs and blocks that can readily turn about in the rather soft coontry 
rock. 

The coal miners of Germany deeignate the thin blocks or slabs dropped 
down by step faults, or lying between two parallel faults, ae graben (moat). 
Good examples of this character of displacement occur in the Mansfeld 
copper shales. In the vicinity of the veins such dislocations are naturally 
quite rare. 

A block that has remained stationary between faults is called a horat 
(upthnist), or if narrow and long, it is called a Btppenhorst. 




Rg. 112.~ReveT8e<l faulting of the gold-beuing con)^ment« meaauna of tbs 
May Consolidated mine near Johatmcebuig. (Schiatiaaer.) (Section.) 



IX. Simple Displacements. 

Displacements that are perfectly apparent occur when a vein of con- 
siderable thickness passes diagonally throu^ another, as illnstiated in 
Fig. 113. 



X. On the Location of Faulted Parts of Veins. 

1. Before assuming that a displacement exists when a vein is lost in a 
mine working, its possible deflection must be considered, viz. : Whether 
the lode has not merely changed its direction and followed an older fissure. 
This supposition would be proven true if stringers occurred in the filling of 
the supposed fault fissure. These stringers would then have to be followed 
by an exploratory drift in order to locate the extension of the deflected 
lode beyiHid the transverse fissure. 



158 TEE NATURE OF ORE DEPOSITS. 

2. If the veia is not deflected, but is actoall; displaced by a yovn^r £&• 
Bure, the first thing to do is to look in the fault filling for fragments broken 
off from the dislocated vein. If such fragments are entirely wanting on 
ono side of the vein, while on the other they occur In a cluster, or fan, or 
are strung out along the fault forming a fan or string, a drift should be 
driven along the fault in this second direction (Fig. 114). It should also 
be noted that in a faulted bed the bending or change of dip next the fault 
may indicate the direction of the movement. It points in the direction the 
sheet has been moved. {See Fig. 99.) 

3. If fault striations are found on the fault wall their character and di- 
rection will often enable one to correctly infer the direction in which the 
missing part of the lode has been moved. By passing a hand over the elick- 




enaides one may ascertain whether there exists a diSerence in the rough- 
ness, as set forth on page 150. The opposite wall has been moved in the 
direction in which the wall feels smoother. 

4. If in a lode the hanging wall strata differ from those of the footwalL 
it may be assumed that the displaced portion of the lode has been moved 
downward. If the faulted vein has unlike rocks on opposite sides (contact 
vein) the drift should be driven across the fault to determine the nature 
of the rock at that point. If the hanging wall country is found across the 
fault the throw is normal and the displaced block has moved down. This 
rule is even more important in stratified deposits, and for this purpose a 
carefully made section of the overlying and underlying beds should first he 
made. 

5. If the faulting is in a district whore several other faults occur, which 
have been accurately located and their characteristics known, the new case 



EPIQENETW DEPOSITS. 



159 



should be treated aa analogous to those already known, for ordinarily in 
the eame vein district the faults all shoT movement in the same direction. 
This, according to H, Hofer, is especially true for the lateral diBplacements 
along many faults, which may be alike over an entire vein area; thuA ac- 
cording to H. Hofer, in the ore district of Littai in Carnicia they are left- 
sided; at the vestem Harz thc^y are right-sided. At Chaiiarcillo, accord- 
ing to Moesta, they are left-sided. 

6. When special indications of this kind are lacking it is necessary to 
attempt a graphical solution of the problem by means of a diagram based on 
geometrical principles. For such cases the Schraidt-Zimmermann rule is 
used, a rule which in practice is found to be true in the majority of cases. 
The procedure is as follows ; 




Fig. 114.^Fragments of the cut-off lode in the clayey fiUing of a dbplapement 
fissure as guide in tracing the lode. 



First constmct the projection of the line of intersection of the vein and 
the fault fissure. An example will show how this is done in a simple case : 

Two intersecting veins, A S and B S, meet at S on the floor of a drift. 
The vein A S dips at the angle T„ the lode B S at the angle t^ v, being 
larger than Tj (see Fig. 115), From point S measure any equal distance 
along each lode, S C and S D, and erect perpendiculars at points C and D. 
At the point S draw on S C the angle 90° — 7,. At point S draw on S D 
the angle 90" — Tj. Through the intersections E and F of these lines with 
the perpendiculars at C and D draw parallels to the corresponding vein, 
namely, through E parallel to A S, and through P parallel to B S. The 
two parallels intersect at the point 0, which connected with S represents 
the line of intersection of the two lodes. 



160 THE NATURE OF ORE DEPOSITS. 

The line of intersection in the case of normal displacement is situated 
within the obtuse angle ; in the case of left-handed or reverse displacement 
it is within the acute angle^ and is always closer to the vein having the 
higher dip. 

Having constructed the projection of the line of intersection, the follow- 
ing general rule is followed in order to find the missing vein : 

The displaced lode is to be sought beyond the fault within the ohiuse 
angle between the line of intersection and the fault. 




J 



Fig. 1 15. — Coustructiou of the liue of iutersectioiu (Explauatiou iu the text.) 



In Figv 116, for example, a lode has been cut off at B by the fault Wj. 
KKi is the line of intersection between the two. The direction of the ar- 
rows indicates the direction in which the fault block must be sought follow- 
ing along the fault. 

For the better understanding of the rule we reproduce a portion of the 
plan map of the Himmelsfiirst mine, near Brand (Fig. 117), showing the 
actual recovery of the Silberfund vein which was faulted by the Neugliick 
vein at I. The dotted line indicates the projection of the intersection, which 
was drawn from the known intersection on the Halbvierzehnten level through 
the points II and III, intersections known in the higher drifts and pro- 
jected on the map. The Neugliick vein was followed along its hanging wall, 
according to the rule, in the direction of the arrows a-d, and the Silber- 
fund Stehende was actually recovered a short distance away. At point II 
the situation was more complicated because the vein was first faulted by a 



EPIOENETIC DEPOSITS. 



161 



parallel fissure of the Neugliick Spat, and then once more by the latter itself. 
Hence at point II it waa necessary to apply the rule twice in succession. 

• 

XI. Displacements Due to Horizontal Movement 

It has already been shown that in true faulting lateral movement is an 
occasional but a subordinate feature. We now take up a small group 
of faults in which a transverse horizontal displacement is the predominant 
feature. They are termed simple shifts (Verschiebungen), and the steep 
dipping fault planes along which horizontal movement takes place msff be 
called slip planes (Blatter leaves). 







/ 
/ 






r 




-y 

• 




Vi 




/ 




V 






/ 

• 


\ 


• 






/ 


^^^ 








/ 


j§^ 








m 


\v 







Fig. 116. — Diagram to illustrate the rule for tracing displacements. 

G. Eohler has described shifts of this kind from several lodes in the Harz, 
such as the Samsoner lode at St. Andreasberg (Fig. 118) and the Altenseg- 
ener main lode. They are still commoner in stratified deposits^ as, for ex- 
ample, in the Rammelsberg ore deposit. 

In the recovery of faulted and shifted veins, rules 1 to 6, given for or- 
dinary faults, apply in a slightly changed form. 



(i) Fissure Formation. 

Fissures are planes of disruption ; hence dicission spaces (from discindere, 
to tear apart) must be discriminated from the cavities formed by the leach- 
ing action of water on readily soluble rocks, called dissolution spaces by F. 
Posepny. Fissures sometimes show clear proof of strain and shear (or a 
tearing apart) in the distorted fossils found in the country rock immedi- 
ately adjoining. Such phenomena have been described by Harkness from 
the vicinity of Cork, and their significance discussed by Daubrfe. 



162 THE NATURE OF ORE DEPOSITS. 

In Bome casoa the fissnreB are formed by forces originating in the rup- 
tured rock itaelf ; in such casee the fractures are usually confined to this 
particular rock mass, occasionally passing outside for a fev yards. This trpe 




of fracture, called evlokineU'c fissure (A. W. Stclzner), falls into two sub- 
groups. In the first, the fractures are contraction fissurt's due to a diminu- 
tion of volume of the rock mass as a consequence of cooling or drjing (cool- 
ing fieeurcs and dtying fissures). The second t^'pc originates through an 



SPIOENETW DEPOSITS. 



m 



increaee of volume in consequence of the absorption of water or some other 
chemical procesa as in se^atiiu^tion (dilation Eesures of A. W. Stelz- 
ner). To a much wider extent fissures result from general mountain build- 
ing forces, and may then be called, following Stelzner, exokinetic fissures. 
Manj fissures cannot be readily classed in any of these groups because tiiey 
are due to complex causes. 

A. Daubree* calls all disruption fissures lithoclases, and makes a further 
distinction between simple joints (diaclases), that is to say, fissures without 
demonstrable displacement, and paraclases, that is, fissures with displace- 
ment 




The classification adopted and the nature of the formation of fiBanzes will 
be rendered clearer by a number of examples: 



a- Eatoklnetlc Fissures. 

I. CONiaACTION FiBSCBES. Y 
1. Cooling Fissures. 
It is well known that eruptive masses after cooling and Bolidifyisg fnnn 
a molten condition are commonly traversed by numerous contraction cracks, 
which are often quite regular in occurrence, producing the characteristic 
columnar, laminated or spherical structures, while in other cases the frac- 
tures occur without any recognizable order. 

Mineral veins resulting from the filling of such cooling (contraction) 
fissures are represented by the flat tin veins in the Zinnvald granite dome 
. Eur Exper. Oeologie.' Germui tranaUtion by Qurit. 



\ 



164 TEE NATURE OF ORE DEPOSITS. 

of the Erzgebirge. That granite masses are traversed by spherical contrac- 
tion fi9sure8 due to coolings which often conform approximately to the 
gently rounded surfaces of the hills, is a well-known fact In quarry- 
ing out slabs for sidewalks from the granite quarries of Bautzen these fis- 
sures are often of great practical importance,^ because along them even the 
fresh, unaltered, unfissured rock may be readily wedged into slabs. At Zinn- 
wald such fissures were apparently filled with the gangues and ores of the 
tin formation, especially quartz, lithia-mica, tin-stone and wolframite, at a 
time when the cooling had not yet been completed. As shown in the 
cross-section. Fig. 119, these veins have the form of a pile of inverted sau- 
oers, the superimposed veins being near together. Eleven of them are being 
worked in the granite itself. A few very low grade ones were also found 
in the Teplitz quartz porphyry, into which the flat granite dome has pene- 
trated from below.* 

A case in direct contrast to this example of fissure formation is found 
near by in the mines of Altenberg, where a granite stock is traversed by in- 
numerable small fissures utterly irregular in course, from which the rock 
has been enriched with tin ore. These fissures, together with their impreg- 
nation zone, form, as a whole, the so-called Zwitterstock (tin ore stock). 
Most of them are probably simply fissures of cooling. 

On. the other hand, it is difficult to decide whether the network of lodes 
in the propylites of Hungar}' is or is not due to fissures of cooling, though 
the fact that the veins of that region also occur in the adjoining Eocene 
sandstone is against the cooling theory. The mineral veins of Nagyag, 
however, are not fissures of contraction, according to B. von Jnkey. 

If an eruptive dike is fractured on cooling by a succession of transverse 
fissures occurring close together they form a so-called ladder vein (Leiter- 
gang). A well-known example of this is found in the Waverly mine at 
Victoria, Australia, where a dike of decomposed diorite is traversed by 
numerous stringers of gold-bearing quartz. Some of them are forked, and 
most of these stringers stop at the selvage, though a few continue a short 
distance into the adjacent slate' (Fig. 120). 

In the same way, according to Th. Scheerer, a granite dike cutting 
through mica schists at the Nasmark mine at Thelemarken, Norway, is itself 
cut by numerous transverse stringers of quartz containing copper ores, and 
accompanied, according to J. H. L. Vogt,* by zones of greisen. 

' O. Herrmann: * Steinbruch 's Industrie und Steinbnich's geologie.' Berlin, 1899, 
p. 112. 

' K. Dalmer: 'Erlauterungen zu Sect. Altenberg-Zinnwald der geol. Spe6ial-karte 
von Sachsen. 

■ As a result of the cooliuje; of the highly heated contact zone. 
* Zeit /. Prak. Geol. 1895, p. 149. 



EFIOSyETIC DEPOSITS. 




166 TEE NATURE OF OSE DEPOSITS. 

laical ladder lodes are also seen in the gold-bearing quartz stringers 
of the dikee of fine-grained granite catting schistoee rocks at Berezovsk, 
near Ekaterinburg in the central Ural.^ A part of the plan of the working 
of the nines of that locality (given in Fig. 121) ehowe the many short side 
drifts mn after the gold stringers, all starting from main levels driven 
along the body of the dike (Polo). This plan gives a clear idea of the ar- 
rangement of these cooling (contraction) fisanres, which but rarely extend 
into the country rock (Fig. 121). Exactly the same phenomenon is found 
daewheie in the Ural in the diorite and serpentioe dikes of Pyechminak.* 




n. Desiccation Fissures. 

That fisenree may be formed by the drying of sedimentary roeks is veil 
known, but it is difficult to prove in individual cases that veins have this 
manner of origin. The small fissures in the spherosiderite nodules of the 

' 1S« Golddiatricte von Bereaow u. Hiu am Ural,' Arehiv /. Prak. Oeol., U, 189S, 
p. 499. 

' F. Pcsepny: 'Geneeifl,' etc., p. 102. 



EFIOEKETIC DEPOSITS. 




168 THE NATURE OF ORE DEPOSITS. 

Carboniferous formation^ for example, those ooeurring at Zwickau^ which 
often carry zinc-blende and galena, are undoubtedly a result of contraction 
due to drying. 

2. DibUion Fissures. 

The best examples of these are the numerous fissures and slip planes 
which are so often found traversing stocks of serpentine. In such cases 
the cause of the increase in volume was the absorption of water in the ser- 
pentinization of the olivine rock. Such fissures have often received deposits 
of gamierite and other secondary iron and nickel ores, as in New Cale- 
donia and at Frankenstein in Silesia. 

P. Exokinetic Fissures. 

I. Fissures of Collapse and of Expansion. 

Collapse fissures (Einsturz spalten) are due to the caving in of the strata 
overlying a cavity formed by the leaching out of rock salt, gypsum or lime- 
stone. Instances of mineral deposits capable of such interpretation are 
not known. In a broader sense, tliis class of fissures includes those in great 
blocks of the earth's crust dropped down by the removal of great masses of 
material by volcanic eruptions, a feature not infrequently found on the con- 
cave side of mountain ranges. Certain ore-bearing lodes foimd in the 
eruptive districts of the Carpathian arch may be of this origin. 

Expansion (tension) fissures are formed in beds overlying olivine rocks, 
which swell up on serpcntinization, or above anhydrite lenses, that alter 
into gypsum. This may be the origin of some garnierite stringers, which 
are said to continue from the serpentine into the country rock. 

Expansion fissures arc more common in stratified rocks forced up into 
great arches by lateral pressure. The vein system of a mineralized tract 
may be explained in this way, as for example, that of Freiberg, which, as a 
whole, is situated over the summit of a great dome of gneiss. The fissures 
produced by folding may be summarized in a very general way, as follows : 

II. Fissures Due to Folding. 

Fissures develop, especially in the more brittle strata of a rock series, 
when the rocks are pressed together into folds, anticlines and sjuclines. 
Thus this class of fissures, like the folding itself, is due to the progressive 
cooling and contraction of the deeper zones of the earth's crust. They may 
be subdivided into strike, intersecting (at acute angles) and cross fissures, 



EPIOENETIC DEPOSITS. 169 

according as their course conforms to, let, the etrike of the folded beds ; 3d, 
crosses the beds at an acute angle; or, 3d, crosses the fold at a right angle. 
It is probable that many mineral veins, owe their origin to such rock flex- 
ures^ 

Strike fiasares are almost alff8ye''faults, generally overi^rust faults. A. 
Ton Groddeck' mentioiiB mineral veins in the Rhenish schists as examples 
of strike faults along folds. Such fissures are certainly not so frequent 
among veins as those crossing the folds at either an acute angle or a right 
angle. 

The formation of these fissures is the result of an unequal distribu- 
tion of pressure during the folding process. The intensity of a thrust 
acting vertically or obliquely against a fold may undergo a uniform diminu- 
tion at slight intervals; for example, vhen an unusually resistant rock is 




Fig. 122. — Model exhibiting the origia of fissures acroaa folds. 

encountered, or when pre-existing folds and fissures effect a deviation. In 
such cases a fissure forms between the more compressed and less compressed 
areas, as may be observed by an examination of the sketch-plan shown above 
{Fig. 122). 

Foliation fissures are also produced by folding. If a pile of paper sheets 
be pressed together from the sides, some sheets will spread over each other; 
in the same way the layers of schistose rocks when pressed will fold up. The 
cavities thus formed have the shape of flat lenses, are generally curved irreg- 
ularly, and may be filled with quartz containing ores, especially aurifer- 
ous pyrite. Such foliation fissures are common among the gold-bearing 
quartz veins of the crystalline schists of the Appalac^iian region and Nora 
Scotia. 

< ' LagersUtten der Erie,' 1879, p. 316. 



170 THE NATURE OF ORE DEPOSITS. 

This daSB iuclades aUo the remarkable saddle lodes of Australia, de- 
scribed in detail previoosly. 

III. Compression Fissures. 

Some rock masBes are unable to form folds when subjected to pressure. 
The hard and brittle eruptive rocks especially arc not able to yield by fold- 
ing, and in consequence are crushed and split. The cracks thus formed are 
appropriately called fissures of compression. 

Oar conception of this process is largely based on the beautiful ezperi- 
m^its of A. Daubrfe.' 

In these experiments, cubes of brittle rocks are by simple pressure brokeo 




Ftg. 123. — Artificial compression fissures in a prism. (A. Daubr^e.) 



into irregular prismatic pieces arranged at right angles to the plane of 
pressure. In this case the direction of the fissure is parallel to the direc- 
tion of pressure. In nature, however, the masses subjected to pressure are 
more or less plastic. Daubree endeavored to approximate this condition 
in his experiments by using prisms consisting of a mixture of gypsum, wax 
and resin. The result was the formation of principal fissures, oblique 
(46°) to the direction of pressure, along which movement had taken place. 
These cracks were accompanied by a great number of lesser fissures on 
each side and running either parallel or at right angles to the main fissure 

* A. Daubr^: 'Etudes Synthetiquea de Geologis Experimentale, ' 1S79, p. 23.5, 



EPIQENETIC DEPOSITS. 



171 



(see Fig. 123). This cluster of fissures resembles in miniature the net- 
work of veins seen at Freiberg or that of the Cornwall tin district. As 
the mineral districts just named show clear evidences of lateral pressure, it 
is apparent that ihe plan of the veins of such an area is very properly com- 
parable with the fissures on the surface of Daubr^e's prisms. 

Daubree also experimented with artificial models made of alternate layers 
of different materials, the whole subjected to a pressure acting parallel to 
the stratification. In this way he obtained fissures running obliquely to 
the direction of pressure, accompanied by displacements when there was a 
chance for lateral displacement. The formation of fissures in this experi- 
ment was always preceded by a folding of the layers. 

These experiments proved that the forces producing systems of parallel 




g. 124. — Formation of regular fissure systems through toraon. (A. Daubr^.) 



fissures, whether mere fissures of disruption or of displacement, did not 
necessarily act in the direction of the fissures. The direction of the force 
can only be inferred from the arrangement of all the fissure systems of a 
region. In the case of a system of paired fissures the diagonal seems to 
usually indicate the true direction. It is assumed, of course, that all the 
fissures taken into consideration are approximately simultaneous in origin, 
which, of course, is only in part true of the fissures at Freiberg and in Corn- 
wall. 

It also appears that a fissure and a displacement along this fissure may 
be produced by one and the same force. 

Other experiments convinced A. Daubree that under certain circumstances 
a torsion of a part of the solid crust of the earth would lead to a develop- 



172 THE NATURE OF ORE DEPOSITS. 

ment of perfectly regular fissure systems, especially for blocks of horizontal 
strata^ such as plateaux and block mountains formed ol level beds. By 
means of a wrench (Fig. 124) Daubree twisted a rectangular plate of mir- 
ror glass on which a coating of paper had been glued. He obtained two sys- 
tems of cracks running obliquely to the plane of torsion, one crack being 
often terminated against another. A consideration of the combined effect 
of the two forces, lateral thrust and gravity, shows that such torsional 
stresses and resulting fissures must often occur in nature. The fact that 
many of the cracks formed in the glass terminate one against the other is 
noteworthy, as it shows that a fissure dislocating another need not necessar- 
ily be younger than the dislocated fissure. It is only by a careful study of 
the fissure filling that the relative ages of the fissures can be determined. 

These experiments of A. Daubree have been repeated by 6. F. Becker,^ 
and' the importance of their application to the theory of vein formation has 
been confirmed. The slickensides frequently found on fissure surfaces, even 
in veins with no apparent faulting, and the spiral bending and twisting of 
many vein walls, indicate that the fissures originate through torsion. 
Daubrte also, it may be observed, noted the spiral form of the cracks made 
in his glass plate. 

Fissure systems still more closely resembling those in nature are obtained 
when provision is made for the asymmetrical and one-sided distribution of 
pressure and resistance in place of the symmetrical arrangement of Dau- 
brte^s experiment. 

Lossen^ ascertained this by accident. Cracks were formed in a pane of 
glass by the sudden opening out of a window sash caught below. These 
were mostly diagonal fractures, dipping in part in different directions, to- 
gether with other curved and transverse cracks. The entire group of fissures 
bore a striking similarity to parts of the lode system of the upper Harz. 
Another variety of displacement that is manifestly a consequence of torsion 
forms the faults with opposing throw, failles a charni^re (hinge faults), as 
they are graphically called by the French and Belgian miners. In this case 
each part of the faulted block has been elevated at one end of the fissure 
and depressed at the other end, while in the middle there is a neutral center 
or point of revolution (Fig. 125). 

That the formation of fissures depends not only on the arrangement of 
the forces, but also to a certain degree on the greater or less brittleness and 
toughness of the country rock is manifest from the conditions already de- 
scribed (page 119). 

* G. F. Becker: 'Torsional Theory of Joints,' Trans. Amer. Inst. Min. Eng., 1894, 
Vol. XXIV, p. 130. 

' K. A. Lossen : 'Feber ein diirch Ziifall in einer Fensterscheibe enst.,'etc. Jahrb. 
d. k. preuss Geol. Landesanst, 18S6J p. 336. 



EPIOENETIC DEPOSITS. - 173 

(k) . Time Required foe Fissure Formation. 

Well authenticated instances are known of the formation of vast fissures 
by a single shock during a violent earthquake. Thus according to B. Koto^ 
a fault fissure was formed during a destructive earthquake in central Japan 
on October 20> 1891. The fissure showed both vertical and lateral shifting 
of the walls^ and extended in a straight line across mountains and valleys 
for a distance of 64 k. (38.4 miles). At Midori the throw was 6 m. (19.6 
ft.) and the horizontal shifting 1 m. to 4 m. (3.3 ft. to 13.1 ft.). This 
fissure did not gap. On the other hand^ great open fissures were caused by 
the great earthquake in Calabria in 1783 at Monte Sanf Angelo. 

Mining operations have exposed open cavities in true vein fissures in 
the Freiberg mines, as in the Churprinze mine, where druses were often en- 
countered that were so large that a man might crawl into them. 




Fig. 125. — Model of a hiuge fault. 

• 

Ver}' broad veins are, however, not necessarily due to the filling of wide 
and open fissures. Observations upon veins show that, on the contrary, 
most large veins are due to an oft-repeated reopening of the fissures, so that 
only a small fissure space need remain open at a time. This successive frac- 
turing has formed fissures not always exactly parallel to their predecessors, 
and not infrequently traversing them obliquely, as is proved by the fre- 
quent diagonal stringers of later age found in lodes. As an example, we 
may cite a rich silver quartz vein, the Traugott Spat, near Freiberg. This 
vein shows many irregular stringers of secondary quartz and ruby silver, 
cutting an older vein filling, consisting essentially of argentiferous blende, 
with some pyrite (Fig. 126). These younger quartz stringers are plainly 
distinguishable from the old vein filling on the selvage wall, whose character- 
istic comb structure proves it to have been formed before the blende mass. 

The younger fissures will sometimes follow the wall or selvage of the old 
vein for a long distance and then cut directly across the vein. This condi- 
tion results in the formation of cross stringers, which pass immediately 
into parallel stringers along the wall. The specimen shown in Fig. 127 is 

^ 'On the Cause of the Great Earthquake in Central Japan, 1891/ Tokio, 1893. 



174 



THE NATURE OF ORE DEPOSITS. 



taken from the Eomet Stehendc on the Himmelsfiirst mine, near Freiberg. 
(Fig, 127.) The croas vein of the specimen conEists of white calc- 
Bpar, with some pyrite, while the mass of the vein cat by it coneiets of 
reddiBh rhodochrosite with zinc-blende and pyrite. 




Fig. 126,— View of the vdn of the Tranprtt Spat (rich quarti tormation). From 
nature; an example of a vein reopened many times in succession. (Composite vein.) 
gn, decomposed Kneiss: q, vein filling, conaiating eeaentially of quarti; e, ore, munly 
■rgentifeniUB blende, with some copper pyrite, bb well as g^ena. 



Clay Bclvagee and false walls are often formed by movements taking place 
after the vein has been formed, and, as shown by Emmons,' they may lead 
the miner aatray or prevent his discovering pay shoots. Drifts are often 

■ S. F, Emmons: 'Origin of Fiaaure Veins,' Proe, Colo. 8d. Soc, 1887, p. 200. 



EPIOENETIC DEPOSITS. 



175 



nm along such planes of easy breaking, because tbey are thought to be the 
true wall of the entire lode, and because, moreover, it greatly facilitates 
the loosening of rock and ore. In such a case when a cross drift is finally 
run through the clayey or altered and rotten country rock, inside the false 
wall, a second layer or stringer may be encountered lying parallel to the 
one hitherto worked, and which is perhaps much richer. The selvage ap- 
parently defining the wall is merely a plane due to reopening of the lode. 

(I) .The Fillikq or Vein Pissdees. 

As already pointed out, it is seldom that vein fiesnres are filled with ore 
alone. Most often the vein filling is made up of ore and gangue {i. «., non- 




Fig. 127. — Vlev of the Komet Stehende (Carbocispathic lead fonnation) with « 

croai stringer. 

gn, gnBiM; m, mangaiuptU'; b, brown Bpor; p, pyrite, blende uid galena. 

metallic minerals), together with fragments of the country rock showing va- 
rious conditions of comminution, trituration and decomposition. In com- 
pound lodes this filling is the rule, and in many cases these masses of altered 
country or veinstuff form the main mass of the vein AH'"^ 



176 THE NATURE OF ORE DEPOSITS. 

The uiottt widely distributed gaugue niinerals are quartz and the car- 
bonates (calespar, brownspar, dolomite, magnesite, manganese-spar^ man- 
gan-calcspar) also barite and fluorspar. The less common constituents are 
zeolites^ gypsum, orthoclase, lithia-mica and chlorite. It is usually as- 
sumed that certain particular species of non-metallic minerals do not occur 
in veins, and the presence of these minerals in an ore deposit is considered 
as a proof that the deposit is not a mineral vein. Such assumptions must, 
however, be used with caution, for it has been repeatedly found that various 
minerals supposedly absent in veins have subsequently been found in them. 
This is true, for example, of actinolite, which, according to W. Moricke,^ 
occurs together with tremolite, quartz and calcspar as the matrix of the 
gold-bearing copper veins of La Higuera in Chile, and, according to W. 
Lindgren,* in the auriferous copper veins of Rossland, in British Columbia. 
Oamet, which was formerly supposed to be foreign to lodes, has now been 
shown to exist in veinlike orebodies.* G. F. Becker mentioned it many years 
ago as a constituent of certain gold-quartz veins of the Appalachians.^ 

(m) Structure of the Vein Filling. 

It is evident that the development of one or more of the minerals of a 
vein in a peculiar form, as, for example, the coarsely foliated development of 
calcspar, the sheaves of fibrous pyrolusite, etc., will influence the structure 
of the lode as a whole, particularly if one of the minerals predominates. As 
a rule, however, several gangue and ore minerals are present in the vein 
filling, and the structure of the aggregate is the result of the mixture and 
intergrowth of all these minerals. The intergrowth and relation of the vein 
minerals to each other (paragenesis) has been studied very closely mega- 
scopically, t. e., so far as recognizable with the naked eye, ever since the time 
of G. A. von Weissenbach.* Very little, however, is as yet known of the 
microscopic structure of ores, although the result of such studies may throw 
much light on the question of ore genesis and deposition, and offers a wide 
field for future investigation. Up to the present time such studies have been 
confined almost entirely to the ores of gold-quartz lodes. This subject will 
be referred to later. 

While veins show a great variety of structures, the following types 
of vein structures may be distinguished: 

>W. MOricke: 'Die Gold, Silber und KupfererdagereUttcn in Chile/ Freiberg, 
1897, p. 27. 

• Trans, Am. Inst. Min. Eng., February, 1900, p. 33. 

■R. Beck: 'Beitrdge zur Kenntniss von Brokenhill,' Zeit, f. Prak. GeoL, 1899, 
pp. 65-71. 

* 16th Ann, Rep. United States Geo!. Survey, Vol. Ill, p. 274. 

•G. A. von Weissenbach: 'Abbildungen merkwurdiger Gangverhaltnisse aus 
demsachs. Erzgebirge,' Leipzig, 1836, p. 27. 



EPIQENETIC DEPOSITS. 177 

1. MoBgive Filling. 

A massive filling is especially connnon in 'simple' veins, and the gaogue 
and ore minerals usually show a compact massive development. Man; 
gold quartz veins are of this type, the vein consisting of a unifonn and 
compact mass of quartz containing disseminated grains of gold-bearing 
' pyrite and particles of free gold (disBeminated vein structure) . Many pyrite- 
blcnde-lead veins show thiB structure, an older fissure being filled with com- 




, Piff. 128. — View of the Rudolf Stehende (pyritous lead ore formation) with domi- 
nant mssMve structure. (From nature.) 
I gr, decomposed gray gnNw; q, quarti; b, argentiferous galena; a, pyrite. 



pact ore. Fig. 138 represents the Budolf Stehende on the Himmelsfahrt 
mine near Freiberg, in which the vein is mainly compact galena. 

Examples of a purely massive structure are seen in the small lodes of 
compact bornJte ore encased in gneiss at Hvidesoe (Hvideseid), Norway. 

8. Banded or Crusted Filling. 

This filling in which the different constituents are arranged in more 
or less sharply defined layers or crusts is a common feature of veins. It ie 



178 THE XATCBE OF OBE DEPOSITS. 

wiuA'ij unlike ihe -^tniciare prfnski'.inz in mioeralized igneous dikes, and ia 
n^ilv iJstiBguishtd from the etratiiied nmcture of EHimentaiy depositB. 

Wh'.'ii th« erosts are xert thin ther commonlr occur in great namber, as, 
for example, io maoT of the l«ad-I>arite \clas in the Erzg^iige. A trpicd 
e'xamiil'; i- *hown in Fig. 12'J representing a specimen from the Friedricb 
vein of Memmendorf in the Erzgebirge. The delicate cmeta consist le- 
fpef/tively of <)en«e harite. fluorspar, zinc-blende an'l galena. 

When the mineralfl forming a croEt are crystalline and the cirstals are 
elongated and arranged at right angles to the layer so that the ends of the 




crystals project into the next following crust or into a free dnise space, it 
is known as 'comli structure,' a rarietr of crustification confined to min- 
eral lodes. Thia structure ia shown by the primary quartz layers of the 
Traugott vein in Fig. 126, and it is common in veins of the rich silrer 
quartz class. The ore breccia of the HimmeUfiirst mine (Fig, 133) shows 
this structure, quartz crystals projecting into a dark band of blende. 

Occasionally there is a regular and smmetncal development of Qie 
crusted structure with a regular soccessiOD of mineralogically diSezent 



EPIGENETW DEPOSITS. ITO 

cTxiBta, countiDg from the vein wall to its middle, the succession following 
a definite order. This symmetric crust-structure is very common in lead- 
barite veine of the Freiberg district, and is also observable in many 
tin veins of the Erzgebirge. The symmetric succession may be repeated 
several times, as shown in the filling of the Drei Frinzen vein of the Ghnr- 
prinz (Fig. 130). In this we may distinguish the following crystalline 
layers stated in order from the selvages toward the middle: 




(a) Brown blende; (b) white quartz; (c) asparagus green flnorepar; 
(d) an exceedingly delicate band of brown blende; (e) dirty, flesh-red, 
curved, scaly barite; (f) a narrow band of radiated pyrite; (g) barite like 
e; (h) fluorspar like c; (!) baud of marcasite like f ; (k) white calcspar; 
(1) light wine-yellow calcspar occasionally forming small dmsee in the 
middle. The lode traverses gneiss. 

The Qomber of layers and of the different minerals and the regularity and 
symmetry of this specimen are very ezceptionaL A crust may form at first 



180 THE NATURE OF ORE DEPOSITS. 

only on one wall of s lode and afterward simultaneonBly on both or vict 
versa. Such alteration may even be caused by chemical reaction of pre- 
ezJeting crusts on the circnlating solutions. If a vein is fractured and the 
old fissure reopened by a crack that does not exactly follow the middle 
of the vein, the crusts subsequently formed are not symmetrically disposed 
with those of earlier origin. An example of this is shown in Fig. 131 




(after G. A. von Weissenbach), representing the JiIliDg of the Frischgliisk 
Tein at Klein-Voigtsberg. 

In this illustration we see that, progresBing aucccssively from right to 
left, new openings and new double crusts have been formed, which could 
not conform to thoee of the oldest part of the lode. On the other hand, 
in lodes formed by rising water and at preat depths below the surface, it 
is inconceivable that such unsymmetrical deposition could be dependent 
on the inclination of the lode unless it is assumed that the water did not fill 



EPIGENETIC DEPOSITS. 



181 



the fissure, bat followed its foot-wall. Such vein fissures muBt have been 
completely filled with water, and it is only in the zone above the water 
level that such partial and unilateral fissure filling is conceivable, as point- 
ed out by F. Posepny.' 

That the form of the crusts is dependent on the fonn of the cavity walls 

' is beet exhibited by the crusts which rest directly upon the country rock. 
We may distinguish : (a) flat crustified vein filling; (b) concentric crusted 

' vein filling. The former predominates in vein fissures with approximately 
rectilinear walls. The latter k found on projections of the fissure walls, and 




fig. 132.— Concentric crusU of the Drei Prinun Spat (a baiitlo lead vdn). 
(From natuie.) 



' is even more beautifully exhibited by the coatings about included fragments 

. bf country rock, or of fractured older vein filling of the fissure. Finally, 

this structure may be developed by the filling of the spherical spaces left in 

: the partly filled fissure, as is very often the case with ore deposits filling 

cavities in limestones and dolomites. 

A tine example of concentric crusted structure along the selvage of a 
vein is shown in Fig. 133, representing a specimen from the Drei Priozen 
Spat of the Churprinz mine near Freiberg. 

In this specimen masses of galena arc surrounded by exceedingly thin 
shells or layers of bante and crusts of fluorspar. The kidney-shaped layers 
' F. Poeepny: 'Geneus,' p. 78. 



182 THE NATURE OF ORE DEPOSITS. 

of barite soperimpoeed a hundredfold in some Freiberg lodes were joetl; 
compared by C. F. Nanmann with the formation of trsTertine or hot spring 



The gradual encnutatioD of rock fragments originally lying loose within 
the vein fissure may sometimes he traced step by step. At first there is 
only a scanty coating of minerals, so that the fragments are not as yet firm- 
ly cemented to each other. Such is the condition of the very imperfect 
quartz breccias of some tin ore lodes of Zinnwald, cemented by a rec^it de- 
posit of quartz, scheelite and fluorspar; of the mica schist fragments loosely 
conented by barite in the Eduard Spat of the Himmelsfiirst mine. More 




y\^ 133.— Breccia structure in the Lade dra Bundea Flache at Himmetefuirt n 
Freiberg. (From nature.) 



commonly there is complete cementation of brecciatcd material, hut with- 
ont cruBtification. Such simple lode breccias are rather common in all 
large lode areas, as at Freiberg in the upper Harz, and at Pribram. The 
cement, of couise, varies with the character of the lode. Thus, for example, 
at Pribram dark schist fragments are often found cemented by zinc-blende, 
brown spar and quartz. Id other eases, the breccia consists of fragments 
of an older lode filling and not of country rock. This is well shown in 
the ore from the Lade des Bundcs Flache (drift No. 8, 1884) shown in 
Fig. 133. 

In this case sharply angular platy fragments of decomposed gneiss and 
oi an older cnistified vein filling of quarte, blende and galena are imbedded 



EPWENETIC DEPOSITS. 183 

in a drusy cement of brownspar. The brittle galena is completely com- 
minuted. 

If the different ore and gangue minerals form crusts about the frag^ 
ments, ring ores or cockade ores are formed. In the Freiberg area sucli 
"Spharengesteine" {spherical rocks), as they used to be called, are well 
knovn in the Peter Stehende of the Alte Hoffnung Qottes mine and in 
the Helmrich Spat of the Gesegnete Bergmanne Hoffnung mine. But 
nowhere are they so magnificently developed as in the upper Harz, espe- 
cially in the "Ring und Silberschnur," near Zellerfeld. The specimea repre- 
sented in Fig. 13^ was taken from this mine. 




The specimen shows fragments of qnartzitic sandBbme and dark colored 
slate sunounded by galena, zinc-blende and quartz. If the succession of 
the different crusts of the ring ores be examined, it is found that the layers 
show the same order of succession as those on the walls of the stringers and 
veins. This is seen at a glance in a comparison of Fig. 135 and 136 (after 
A. von Groddeck).' 

Sometimes the first crust formed on the fragments is so sharply defined 
from the later ones that it appears to constitute the true nucleus or rock 

' A. voirGtoddeck: 'ErslagenUtten,' p. 64. 



184 



THE NATURE OF ORE DEPOSITS, 



fragment. Thus, according to Fhillipe-Lonie,* the main vein of Huelgeet 
in BrittaDy consists of what appear to be qnartz pebbles cemented b; blende, 
pyrite, quartz and lead glance. In reality these pebbles are fragments of 
slate surrounded by concentric sheila of quartz resembling fibrous chaloe- 
dony. In fact, this radial structure is very conunon in the individual crusta 
formed about rock fragments, especially the qoartz crusts, forming the so- 
called cockade ores. In such cases the crust may resemble stellate quartz. 
The encrusted balls of such ring ores axe sometimes isolated, and there 
is no contact between the original rock fragments, and hence A. von Weis- 




Figa. 136 and 136. — Specimsns of vein fillina from the Bflrgmaniutroflt mine. 

(A. Ton Groddeck.) 

N, oountry rock; a, quaiii; b, load ^laxiat; c, nac-blende; e, calcspar. 



senbach' and Seich have inferred that fragments onginally in contact were 
forced apart by the ciystallizing force of the minerals subsequently segre- 
gated, just as fragments of the Alte Uann in the Sauberg, near Ehren- 
friedersdrof, according to C. F. Reich, were driven apart by the crusts of 
freezing seepage water. While the process in itself is physically quite con- 
ceivable, it must be remembered that in some cases the only reason why 

• 'Ore Deposits,' p. 88. 

■ G. A. von Wdssenboch : 'Abbildungea mericw. OongvarfaaKnisse,' 1836, p. 22. 

'F.Posepny; 'Geneeis,' p. 89. 




EPIOENETIC DEPOSITS. 185 

points of contact are not found is that the observers cannot compare a 
sufficient number of parallel sections.^ 

Ring ores are often of very recent formation^ and there are even cases 
where their formation takes place before our eyes. Posepny mentions the 
quicksilver deposit of Sulphur Bank, California, where fragments of ba- 
salt, sandstone and slate are coated with concentric layers of cinnabar by 
the hot spring water. If the concentric crusts occur as coatings on the 
walls of cavities, their form depends on the shape of the little cavity. This 
is also well shown in the cross-sections of agate amygdaloids. The crusts 
may in such cases either line all parts of the wall uniformly, or the layers 
may only be found at the bottom, or finally the two cases may be combined. 
Very good examples of such cavity fillings are found in the zinc lead de- 
posits of Raibl (see further on), where fibrous i}lend is found, to be made 
up of thin layers of dense zinc-blende and galena. 

Druses occur in lodes as well as in chambers. These druses or vugs are 
characterized by an inner coat or crust studded with crystals projecting 
into an open space. I They are not always the residual spaces of an im- 
perfectly filled fissure, but may be formed by a secondary leaching out of 
older crusts or by the solution of fragments of the country rock. Such 
crystal formations are even possible in stratified deposits; for example, 
druses formed by the leaching out of plates of anhydrite and the subsequent 
deposition of calcspar in gypsum deposits. As a rule, however, druses are 
characteristic of cavity filling. 

These vugs are sometimes quite large. In the Freiberg lodes they are 
sometimes large enough to admit a man's head. They are usually situated in 
the middle of the lode (see p. 173). 

The minerals forming the druse walls show the successive deposition of 
the various ore and gangue minerals even better than the material filling 
the body of the vein, the crusts sometimes showing several generations 
of each ore. One should, however, be cautious in drawing conclusions from 
such observations, since the minerals found in these vugs are often formed 
at a much later time than those which constitute the real vein filling. In 
fact, this deposition in vugs is in some veins known to be taking place at 
the present day. Undoubtedly, in many instances, the deposition of druse 
minerals took place under physical and chemical conditions different from 
those prevailing when the true vein filling was formed, and at a later time, 
when this section of vein had been raised above the level of ground water, 
as a result of extensive superficial denudation of the country. 

While we have every reason to believe that the open vein fissures were, at 
some depth below ground-water level, entirely filled with mineral solutions, 

* F. Posepny: 'Genesis,' p. 88. 



186 



THE NATURE OF ORE DEPOSITS. 



this may not always have been the case with the residual open parts of 
those fissures loft uDfillcd until the stage of druse formation. That this 
is true is shown by the not infrequent occurrence of later minerals deposit- 
ed on the upper side of the large crystals of vugs and druses. This is com- 
mon at Freiberg; thus the large quartz crj-stals of the Drei Cruder vein 
at Obergruna are coated on one side only with brown-spar and other car- 




e side with brawn spar. 



bonates (see Fig. 137) ; similarly the quartz crystals of the Selig Trost 
Flache lode of Himmelfahrt mine near Freiberg are coated with ankerite 
and pyrite on one side only. ) These conditions show that descending solu- 
tions seeped through the druse spaces, so that only the downward facing 
surfaces received new secretions, as may be seen with ice crusts along the 
eaves of houses in the winter. 

The new mineral secretions formed in open cavities (i. e., containing 
only gases or air) producL> stalactites at points where the amount of water is 
snfiTicient to overcome adhesion and drop downward by gravity. Such 
stalactitic deposits arc most common in ore deposits forming irregular 
filling of cavities' ; particularly in zinc-lead deposits in dolomites and lime- 
stones. At Saibl stalactitic tubes of galena occur that are as much as tffl 



EPIGENETIC DEPOSITS. 18Y 

centimeters in length; they consist of a number of delicate^ concentric 
crusts of this mineral^ combined sometimes with crusts of zinc-blende and 
pyrite. The center is often a cavity through which one could blow. These 
stalactites of galena were^ it is true, no longer pendent from the cavity 
roof^ but had fallen and been embodied in a later deposit of dolomite spar. 
Since the succession of the several crusts is not the same in all^ it is prob- 
able that they fell at different times. 

The fibrous blende of the zinc deposits of Raibl is also in part a stalac- 
tite formation, occurring as hemispherical stalactites and reniform and 
botryoided masses formed on the cavity roof. It consists of very fine con- 
centric scales of blende and galena, as well as of pyrite. This fibrous blende 
is most beautifully developed in the Schmalgraf mine near Moresnet. 
Pig. 138 shows a cross-section of fibrous blende from that locality. 

At Wiesloch in Baden long stalactites of calamine and galena were 
formerly found which resembled in form and occurrence the calcspar stal- 
actites of caves. Similar examples occur in the calamine mine of Cata- 
vera in Spain. The Freiberg collection contains a specimen from that lo- 
cality that is a fine, slender, snow-white zincspar stalactite 0.25 meters 
in length, not counting the missing point. 

Stalactite formations are also known to occur in the vugs of veins. They 
are most common in deposits of manganese and iron, especially psilomelane 
and limonite. As examples we may mention the stalactite groups of 
psilomelane in the spathic iron ore lode of the Luise mine at Horhausen 
(see Fig. 139), and those from the iron ore lodes of the Schwarzenberg 
region in the Erzgebirge. Stalactites of brown hematite are found in the 
veins of the Siegen country and in those of Aue in the Erzebirge. Stalac- 
tites of pyrite were found at Freiberg in the Johannes vein of Himmels- 
f iirst, and some of pyrite in the Lade des Bundes Flache of the same lo- 
cality. We ourselves possess a group of marcasite stalactites collected by 
H. Muller from the workings in the Drei Priifzen vein of the Churprinz 
mine near Freiberg (above the sixth drift of the Friedrich gallery on the 
west, about 230 meters below the surface). As lode fissures at such a depth 
are far below ground-water level, these stalactites could only have been 
formed withdn an empty or gas-filled cavity, which renders their explanation 
very diflScidt. 

The most remarkable occurrence of this kind is, without doubt, the stal- 
actites described by F. Posepny* from the Matyas Kiraly mine at Vere- 
spatak in Hungary (illustrated in Fig. 140). They are completely studded 
externally with small quartz crystals, while internal layers of calcspar al- 
ternate with layers of rhodonite; in the middle line angular gold wires run 

* F. Posepny: 'Genesis/ p. 95, ! 



188 



THE NATURE OF ORE DEPOSITS. 



down which eometimee project at the lowor gentl; rounded ends of these 
Btalactit«fi. 

Mention must also be made here of the stalactites of crystalline qnartz 
{or chalcedony) 7 centimeters long, from a druse cavity in the cobalt ore 
lode of Scheneeberg, described by H. Mullet.' 

Stalactites of ore minerals, as well as unilaterally encrusted crj-stals, 
tnuet be regarded aa records of a descending movement of solutions along 
vein fissures, as suggested by A. Schmidt' for the stalactites of Wiesloch, 




F[g. 138.^CrosB-flection through » 
stalactite of fibrous blende from 
Moreanet. (From n&ture, two-thirds 
natural size.) 
b, lead Klaiire: p, pyrite; z, tinc- 

bl«nde; outer crutt limonite. 



Fig. 130. — Psilomelane stolactitea from 
the T.uise mine near Horhausen. 
(From nature.) 



Of conrse, one may adopt the alternative explanation suggested by F. Pose- 
pny,' namely, that, with sufficient jiressure, uprising solutions may also be 
preesed through the roof of cavities when the floor and side walls are not 
permeable. This mode of origin, however, is undoubtedly of very rare oc- 
carreuce. The above mentioned occurrence in the Churprinz may be an 
instan'^ of it. 



' H. Mullen 'T^eber eine merkwilrdige Druse auf ei 
Kfinge.' Z. d. d. g. G.. 1850, p. 14. 

' A. Schmiilt: 'Die Zinkerzlanerxtattcn von Wiealoch ii 
' F. Poaepny: 'Genesis,' p. 93. 



lem SchneeberRpr Kobalt- 
Boden,' 1881, p. 94. 



EPIGENETIC DEPOSITS, 



189 



In cunclusioa we may mentioD, in dlecuesisg lode structures, that in some 
lodes soft clayey masses of crushed material contain nodular concretions 
of or&') and of gangue minerals. Examples are seen in the nodules of 
natiTe copper in a vein of the Vesuvio mine near Salinas, east of Mejil- 
lones in Chile ; of zinc-blende, in the llalhada mine near Albergia Velha 
. in Portugal ; siliceous concretions in vein clay of the Gott mit TJns vein 
of the Himmelsfiirst mine near Freiberg. Such formations could de- 
velop only in a medium whose particles could readily be driven asunder by 
the force of crystallization. 

(n) Pabaqbnbtic Occurrence of Vein-Forming Mimerala. 

By paragenesis of minerals August Breithaupt' understood "the more 
or less definite manner of their association," at the same time "laying par- 




Fig, HO. — Cross-section through s stalactite of VerespatAk. (Posepny.) 
g, gold; p, caldte; r, rhodonite; q, quartz; d, druse. 



ticular stress on the relative age of the materials where a succession may he 
recognized." 

Examples of such associations, given by Breithaupt, may be mentioned 
here. Copper pyrite will always he found where bismuthinite is present. 
Id like manner pyrrhotite and copper pyrite, bornite, chalcopyrite 
and p)Tite are always found associated. There is an especially intimate 
connection, as a rule, between fluorspar, topaz, molybdenite, wolframite 
and tinstone; of the common manganese and iron ores; galena and zinc- 
blende; cobalt and bismuth ores. Such associations have always been of prac- 
tical importance to the miner and prospector in unexplored regions. The 
finding of certain minerals, either of ore or gangue, warns the prospector 

' 'Die Par«geaesiB der Mineralieu,' Freibetg, 1849. 



190 THE NATURE OF ORE DEPOSITS. 

to keep a keen lookout for the associated valuable mineral. If in a quartz 
vein you find pyrite, arsenopjrrite and antimonite, the search for gold in 
the outcrop, as a rule, will not be in vain. 

Quite as important as this association of the minerals is the manner of 
their intergrowth or succession, and the investigation of these features may 
throw much light on the genesis of the ore deposit in question. The definite 
succession of the various chemical crusts, the superposition of the 
druse minerals in a definite order betrays, in many cases, a progressive 
change in the chemical constitution of the solutions that circulated in the 
fissure, and possibly a change of the conditions of pressure and heat in the 
mineral springs supplying the material for the vein. It is true that the 
application of these hints to particular cases is as yet impossible. The 
recent important work of J. Vater and others on the influence of the ac- 
companying solutions is merely the beginning of the exact studies which 
must be made before anv definite conclusions can be reached on this sub- 
ject. Sometimes the succession of minerals appears quite capricious. Thus, 
as mentioned by A. Brcithaupt, in the beautiful druses of the barytic lead 
veins, the younger calcspar always rests on barito, never on pyrite. "It 
occasionally arches away over the pyrite as if it were trying to keep out of 
its way.'' In like manner, in the Bescheert Gliick mine near Freiberg, the 
later formed ruby silver of the druses occurs only on white silver ore, not 
on galena. 

A definite succession of minerals recurs with special regularity in the 
tin lodes of Saxony. The quartz and lithia mica form the basal layer, fol- 
lowed by topaz, cassiterite and wolframite, and finally by fluorspar and 
scheelite, together with uranium-mica (chalcolite). 

In many cases the succession of the minerals is inversely as their relative 
solubility. "In many fissures and cavities the walls are covered with quartz 
druses followed by crusts of calcspar. The quartz being far less soluble in 
water, was of necessity deposited first." (Tschermak^) 

Conclusions regarding the succession of minerals may often be drawn 
from the nature of pseudomorphism. The significance of this feature is 
very forcibly emphasized by C. F. Naumann.^ "These residual monu- 
ments of former mineral bodies, now completely or almost completely van- 
ished, give us a deep insight into the various processes of formation and 
reformation, destruction and annihilation that takes place successively in 
the course of time within the lode spaces, and which prove not only a 
very long duration of the lode forming process, but also a frequent change 
in conditions and a perplexing variation in the efiiciency of each cause.'* 

' G. Tschermak: 'Lehrbuch der Mineralogie, ' 1894, p. 271. 

'C. F. Naumann: 'Lehrbuch der Qeognoeie/ Leipzig, 1866, Vol. Ill, p. 575. 



EPIOENETIC DEPOSITS. 191 

Sometimes almost all the mineral contents of a lode is affected by pseudo- 
morphism. Thus the silver-cobalt lodes of Schneeberg originally had a 
gangue of calcspar and barite, which is at present almost always trans- 
formed into hornstone, common quartz, chalcedony and amethyst. In 
tlie silver-gold ore lodes of De Lamar/ Idaho, and the gold-silver veins 
of the Drumhummon mine, Montana, the original calcite and barite of tho 
gangue has been replaced by quartz, and at the former the country rock 
and rhyolite have been partly silicified. This Replacement of calcite by 
quartz is now actually taking place in the veins forming at Boulder Hot 
Spring, Montana.* 

Neither the work of A. Breithaupt nor the earlier work of W. J. Hen- 
wood' on the mineral succession observed in definite vein types has led to 
the discovery of any laws of general application, and the same is true of 
the more recent studies of F. Sandberger* and others. At most the con- 
clusions apply to limited areas only. The influence of local conditions, 
the number of substances dissolved, and consequently the multitude of con- 
sequent reactions of the substances among themselves and with the con- 
stituents of the country rock, make the phenomena exceedingly compli- 
cated. 

(o) Vein Formations and Vein Types. 

All the distinctive features of a vein, those of paragenesis and mineral 
succession, geological conditions, prevailing structure, the nature of its 
country rock, its age, etc., give to it a distinctive character and a particular 
type will always recur where lodes have been formed under similar condi- 
tions. This fact has been used by different authors in various attempts to 
group the confusing multitude of mineral veins into a number of types, a 
group to which additions are constantly made. Various attempts have 
been made to classify veins according to their physiognomy, with the great- 
est possible scientific precision. G. A. Werner, and after him S. A. W. 
von Herder, J. C. Freieslehen and A. Breithaupt, distinguished *forma- 
tions*; A. von Groddeck and J. H. L. Vogt distinguished *types.' These 
attempts, however, have been but partly successful, owing to the difficulty 
of assignment resulting from the transitional or composite features in the 
physiognomy of the veins. Moreover, the same vein may change its char- 
acter in strike or dip. In studying such changes in dip a rigorous discrim- 
ination must, of course, be made between those differences that existed 

" W. Lindgren: 20th Ann. Rep. United States Geol. Survey, part III, 1900, p. 164 

' W. H. Weed : 22d .4 nn. Rep. United States Geol. Survey, 1902. 

" Trans. Roy. Geol. Soc., Cornwall, Vol. V, 1843, p. 214. 

* 'Untersuchungen uber ErzgSnge,' Wiesbaden, 1882, 1, p. 96. 



192 THE NATURE OF ORE DEPOSITS. 

from the beginning and those that were subsequently added^ that is to say^ 
between the primary and the secondary differences in the physiognomy of 
the lode according to depths as will be discussed in detail further on. It 
may also happen that two characteristic mineral associations may occur 
in one and the same fissure, but in separate groups, as, for example, in f 
some lodes of the Himmelsf iirst mine near Brand, where one stringer be- 
longs to the pyritic-blcndic lead type of deposit, while the other 
belongs to the spathic lead class; or in Tuscany, where the north part of 
the Boccheggiano vein is a typical quartzose copper ore, while at the south 
it must be classed as a pyrite-blende lead deposit. 

In classifying a vein by its mineral contents the main point to remem- 
ber is (as emphasized by A. Breithaupt) to base one's judgment not on one 
specimen or on a few specimens in a collection, but to determine the gen- 
eral character of the vein from the examination of very many samples " 
belonging, if possible, to the most diverse parts of the vein, and, so far as 
may be done, uniting the data found in many separate lodes of an area into 
a general picture after inspection of the occurrence in situ. In old mining 
regions, as at Freiberg, in the Harz, in Cornwall, etc., where scientific 
observations have been made and recorded for a long time, the grouping of - 
the various vein formations has, after many vicissitudes, at last been fixed 
in a scientifically satisfactory manner, after discarding the sub-classes 
formerly used. 

The fundamental idea and definition of "lode formation" is due to 
G. A. Werner, who expressed himself on this point as follows :* "I give the 
name lode formation' to all lodes of one and the same origin, whether they 
occur close together in one region or far apart in different countries." . 
Werner distinguished eleven mineral formations or *niederlagen' for 
Saxony alone; Von Herder limited the number for the Freiberg area to 
five; Freiesleben by establishing subdivisions raised the number to fifty; 
Breithaupt took twenty for his standard, while von Groddeck established 
a great multitude of converging types which often can be distinguished only 
by emphasizing the local mode of occurrence, the nature of the country 
rock, etc. 

A complete summary of the older literature on vein formations is found 
in the valuable treatise by G. A. von Weissenbach* 'on lode formations.' 

In the following pages a summary is given of the most important mineral 
veins of the world. In this summary the arrangement followed is a modi- 
fication of the one adopted by A. W. Stelzner for the collection of ores from 
the Freiberg deposits, a system which closely follows the old Freiberg classi- 

* G. A. Werner: 'Neue theorie von der Entstehung der Gftnge/ 1791, p. 5. 
> Cotto's 'Gangstudien/ 1847. Vol. I, p. 1 et aeq. 



4*^ 




EPIOENETIC DEPOSITS. 193 

ficafion^ which has met with acceptance by many students of ore deposits. 
The classification of gold deposits and some other details are innovations 
made by the author. 

Following this summary of the leading features of each class and its sub- 
divisions^ a brief characterization of each group or formation will be given. 
This will be followed by a brief description of selected examples. For 
this purpose preference will be given to the deposits of producing mining 
regions^ to those recently opened and to those deposits which even though 
no longer worked are world-famous and have been ^carefully and scien- 
tifically studied. In the brief descriptions given^ it is impossible in some 
instances to treat certain types of veins separately and independent of their 
connection with the general geologic conditions of the mineral area^ and 
it is therefore necessary in such cases to give^ in a few lines^ a geologic 
sketch of the whole region. 

y 

SUMMARY. ^ 

The Different Classes of Mineral Veins and Their Varieties. 

A. Veins Consisting Mainly of Oxidic Ores. 
I. Veins of Iron and Manganese Ores. 

1. Veins of spathic iron ore (spathic iron ore formation). 

2. Veins of red hematite (red hematite formation). 

3. Veins of manganese ores (manganese ore formation). 

II. Tin Veins. 

4. Tin veins (tin ore deposits). 

B. Deposits Characterized by Metallic Sulphides. 

a 

III. Copper-Bearing Veins. 

5. Veins with copper ores in a gangue characteristic of tin deposits 
(tourmaline-bearing copper formation). 

6. Quartz veins containing copper ores (quartzose copper formation). 

7. Veins containing copper ores in a gangue of carbonates and quartz^ 
together with barite and sometimes fluorspar as gangue (spathic copper 
formation). 



194 THE NATURE OF ORE DEPOSITS. 

8. Veins of native copper with carbonates and zeolite (zeolitic copper 
ore formation). 

IV. Silver-Lead Veins. 

9. Veins of predominant quartz with argentiferous galena^ zinc-blende, 
pjrrite and arsenopyrite (pyritic lead ore formation). 

10. Veins of calcite and other carbonates with argentiferous galena, zinc- 
blende and rich-silver ores (spathic lead formation). 

11. Veins of barite and fluorspar, with galena^ zinc-blende and rich- 
silver ores (barytic lead formation). 

V. Veins Carrying Rich Silver Ores-. 

12. Veins of quartz with rich-silver ores (silver-quartz formation). 

13. Veins of calcspar with rich-silver ores (silver-calcspar formation). 

14. Veins with both copper ores and rich-silver ores (rich silver-copper 
ore formation). 

15. Veins with silver^ cobalt, nickel, bismuth, and uranium ores (rich 
silver-cobalt ore formation). 

VI. Gold Veins. 

16. Veins with predominant quartz gangue containing gold ores (gold 
quartz formation). 

(a) Gold quartz veins with predominant pyrite (pyritic gold quartz 

formation). 

(b) Gold quartz veins with copper ores (cupriferous gold quartz 

formation). 

(c) Gold quartz veins with stibnite (antimonial gold quartz forma- 

tion). 

(d) Gold quartz veins with arsenopyrite (arsenical gold quartz 

formation). 

(e) Gold quartz veins with cobalt ores (cobalt gold quartz forma- 

tion). 

17. Veins of quartz and carbonates with gold and silver ores (silver-gold 
ore formation). 

18. Veins of quartz and fluorspar with gold ores (fluoritic gold forma- 
tion). 

VII. Veins of Antimonial Ores. 

19. Veins of predominant quartz with antimony ores (antimonial forma- 
tion). 



EPIOENETIC DEPOSITS, v 195 

VIII. Veins of the Cobalt, Nickel and Bismuth Ores. 

20. Veins of nickel and cobalt ores in a carbonate gangue (carbonspar 
cobalt ore formation). 

21. Veins of quartz with cobalt, nickel and bismuth ores (quartzose 
cobalt formation). 

22. Veins of hydrated nickel-magnesia silicates (hydrosilicate nickel 
formation). 

IX. Lodes of Mercurial Ores. 

23. Quartz-calcite quicksilver formation. 



B. DESCRIPTIONS OF VEINS OF EACH TYPE. 

{-) Veins Consisting Mainly of Oxidic Ores. 

(d) Iron axd Maxoaxese Veixs. 
1. Veins of Spathic Iron Ore. 

The veins consist essentially of siderite with quartz or calcspar, and 
subordinate pyrite, copper pyrite, etc., and barite. The alteraticm of 
the upper part of the veins into brown hematite liberates the manganese 
originally present as carbonate, and this is frequently segregated in the 
form of pyrolusite, manganite, psilomelane and wad. 

An important example of this type, now of but little economic impor- 
tance, is the Stahlberg near Miisen, where a lode 12 to 27 meters thick has 
been worked since 1313.* The vein occurs in lower Devonian clay and 
graywacke slate. It is cut oflF to the southeast by a fault, while northwest it' 
splits into three main branches, which also subdivide, and have been fol- 
lowed to a distance of 145 meters. It dips east 80°, and consists of almost 
pure, or but slightly quartzose, compact spathic iron ore, whose high man- 
ganese content renders it desirable for the manufacture of steel. There 
are but slight admixtures of copper pyrite, pyrite, gray copper and galena. 
The walls are not sharp, and the country rock is penetrated by fine string- 
ers of spathic iron ore. 

In 1901 the mines of this type in the Siegen country yielded 854,008 
tons of iron ore. The Siegen I district produced 641,170 tons and the Siegen 
II district 212,838 tons. 

* A. von Nopgerath : 'Die Grube Stahlberg bei Musen,' Z. f. d. B. H. u. S. im 
preuas. St., 1863, Vol. XI, p. 63. Th. Hundt, G Gerlach, F. Roth, and W. Schmidt: 
'^Beschreibung der Bergreviere Siegen I und II, Burbach und Musen.' Bonn, 1887, 
p. 137. 



196 THE NATURE OF ORE DEPOSITS. 

Similar conditions prevail in the vein of spathic iron ore of the Luise 
mine, near Horhausen, described by Hilt,* as well as in the lodes worked 
by the Krupp Company, in the Georg and Harxborg mines near that place. 
Pyrolusite, gothite, rhodochrosite, copper pyrite, sphalerite, galena, 
boulangerite and gray copper ore occur alongside of the spathic iron ore. 
In the Luise mine an intrusion of basalt has transformed the spathic iron 
ore at that place into magnetite. 

A lode which has become famous for its rare minerals is the siderite 
lode of the Friedrich and Eisengarten mines of the Hamm district.^ This 
vein traverses lower Devonian rocks. Besides siderite it also contains nests 
and stringers of sulphidic ores, mainly galena and chalcopyrite, also zinc- 
blende, pyrite and bomite. In the siderite ore of the hanging-wall split 
of the vein, a great nest of ore was struck in 1884, consisting of filiform 
niccolite, hauchecornite (a nickel bismuth sulphide) and kallilite (bismuth 
antimony nickel glance). 

Analogous veins occur in the green Paleozoic sericitic and chloritic schists 
of upper Hungary.' Now only spathic iron ore is obtained, especially at Kot- 
terbach in the Zips. The two most important lodes striking west-northwest 
and dipping steeply south are the Drozdziakow lode and the Grobe lode. 
The former is at points 25 to 30 meters (82-98 ft.) thick, and is usually 
split up into two stringers from 2 to 6 m. (6.5 to 19.6 ft.) thick. The lower 
one carries much gray copper ore and copper pyrite in bunches or in parallel 
layers in the spathic iron ore, whereas otherwise the structure is purely mas- 
sive. The coarse-grained crusts of the Grobe vein consist of siderite and 
barite together with some quartz and jcalcite and much copper pyrite and 
mercurial tetrahedrite. Sometimes the barite entirely displaces the siderite 
of the veins and in isolated cases specularite occurs in lenticular 
patches. In the ferruginous gossan, cinnabar and native quicksilver are 
found, besides malachite, azurite and native copper. These peculiarities 
serve to indicate that the veins are closely related to the spathic copper 
deposits (q. v.). 

No veins of this type are now worked in the United States, though a 
6 to 8 ft. vein in gneiss at Roxbury, Conn., was formerly mined. It consists 
of crystalline siderite with a little quartz and a variety of metallic sul- 
phides. The type is a transition to the sideritic silver lead deposits, such 

" Hilt : 'Die EisensteinlafferRtAtte der Grube Louise bei Horhausen,' etc., Z. f. d. 
B. H., u. S. im preuss. St., Vol. XHI, 1865, p. 13. 

* Wolff: ' Beachreibung des Berpreviera Hamm a. d. Sieg.' Bonn, 1885. C. 
Leybold: 'Geopn. Beschreibunp der Eisenerzpniben Wingerehardt, Friedrich, Eisen- 

gtrten,' etc. Jahrb. d. k. preuss. peol. Landesanst., 1882, pp. 3-47. R. Scheibe: 'Ueber 
auchecomit, ein Nickel wismuthisulfid,' Jahrb, d. k. preuss. geol. Landesanst., 1891, 
p. 91 et seq. 

' Faller: 'Rcisenotezen,' etc. Jahrb. d. k. k. montan.Lehranst., 1867, p. 132. 



EPIOENETIG DEPOSITS. 197 

as those of Coeur d'Alene, where as a gangue the siderite is worthless. 
Similar ores occur in the Slocan district^ B. C.^ and Wood river^ Oregon. 



2. Veins of Red Hematite. 

These veins consist of dense^ earthy and fibrous red hematite, together 
with quartz, jasper, ferruginous quartz and more rarely caxbonspars, barite 
and manganese ores. 

This class of veins is common in the Saxon Erzgebirge in the contact 
area about the great granite stocks in the vicinity of Schwarzenberg.^ Some 
of the veins occur on the contact plane between crystalline schist and 
granite, others are in granite itself. The Rothenberger vein is the most 
important. Besides the minerals mentioned above, copper ores occasionally 
occur. A notable feature is the frequent occurrence of pseudomorphs 
of quartz, limonite and red hematite after calcspar, more rarely after barite 
anhydrite and fluorspar, or of mere impressions of crystals of the last men- 
tioned minerals. These show that the original vein filling has undergone 
great changes. The vein structure is either massive or brecciated. These 
veins are 10 or even 20 meters (33 — 66 ft.) thick, and cut thorough the bar- 
ren "quartz-brockenfels" veins and stocks of the region. Among the miners 
of that locality the expressions 'red,' 'hlacV or 'brown' stringer were former- 
ly current. This fact indicates the frequent change in the development of 
these lodes in which red hematite, manganese ores, brown hematite or iron 
ocher prevailed by turns. 

In the Harz, especially in the region of Zorge, a somewhat different type 
occurs, consisting of veins of red and brown hematite in diabase. The 
ores were certainly formed as a consequence of lateral secretion, and the 
veins become barren when they pass from the diabase to silicious schist 
or gra3rwacke.* Their origin is disclosed by the fact that red hematite 
also fills the interspaces between the decomposition boulders of the 
diabase. * 

Many lodes of brown hematite undoubtedly originally contained red 
hematite, while in others it is impossible to tell whether the original ore 
was red hematite or spathic iron ore, as, for example, in the veins of Berg- 
zabern, in Rhenish Bavaria, which cut Triassic sandstone.* Small stringers 
of brown hematite are a common phenomenon in all sandstone areas 

'A. Breithaupt: 'Para^neeis/ 1849, p. 195. H. V. Oppe: 'Die Zinn- und 
Eisenerz^nge der Eibenstocker Granitpartie und Umgebung/ Cotta's Gangstudienf II, 
1854, p. 133. 

'Von Groddeck: 'Erzlajaferetatten,' 1879, p. 153. 

» B. v. Cotta: 'Erzlageretatten.' 11, p. 170. 



198 



THE NATURE OF ORE DEPOSITS. 



of the world, but while deposits of specular hematite are abundant in 
America, no true veins of the type are now known to be worked. 

3. Veins of Manganese Ores. 

Manganese ores, especially pyrolusito, psilomelane, braunite, manganite, 
polianite, more rarely hausmannitc and wad, accompanied in most cases 
by oxide iron ores, are associated with quartz, barite and calcspar as 
gangues. 

There are numerous deposits of this kind in Saxony in the vicinity of 
Schneeherg, Aue and Schwarzenberg, which are found in part in granite, 
in part in contact metamorphic schists. 

In the vicinity of Langenberg, not far from Schwarzenberg, the veins are 
found to be directly connected near the outcrop, with very peculiar strati- 
form deposits of an efflorescent iron-manganese ore. These deposits either 
fill flat basin-shaped depressions, overlaying the prevailing mica schist cut 




Fig. 141.— Profile from Gottes Gcsrhick to Schwarzbach. (H. Muller.) 

gl and ge, mica schist; ks, pyrite bed; k, bed of dolomitic limestone; em, efflores- 
cent iron manganese ore ana quart z-brockonfels; e, veins of the iron manganese 
formation; co, veins of the silver-col)alt ore formation. 



by the veins, or thoy form stocks in the midst of the schist. These stocks 
seem to be the result of lateral impregnation and mctasomatic replacement 
of certain beds of the country rock ( Fig. 141 ). These deposits are intimate- 
ly connected with great veins of iron and manganese ores which often swell 
into stocks called ^cjuarzhrockenfels' because of thoir brecciated structure. 
Cobaltiferous manganese deposits of this type occurring near the outcrop 
of cobalt veins cutting mica schists in the mines near Graul (Fig. 141) 
enclose rich and sometimes large fragments of siliceous bismuth ochre. 
These mines during the last decade showed a considerable output of bis- 
muth and cobalt ores; in 1898 they produced 2,726 tons of those ores. A 
more detailed description of these efflorescent manganese ore deposits is 
given by H. Muller* and R. Beck.^ 

' * Die Erzgange des Annaberger Revieres,' Leipzig, 1894, p. 104. (Erlaut d. geol. 
Spezialk.) 

' 'Erzlager von Schwarzenberg,' part T, Freiberger Jahrbuch, f. d. B. u. H., 1902, 
p. 64. 



EPIOENETIC DEPOSITS. 199 

The manganese veins of Ilfeld in the Harz mountains occur^ according to 
0. Schilling,^ in a hornblende porphyrite mass which is occasionally, as at 
Moncheberg, completely penetrated by their stringers. The veins are for 
the most part only a few centimeters thick and usually grow poor at 12 
meters; only in exceptional cases have they been followed down as far as 
60 meters. Their filling consists of manganite, pyrolusite, varvicite, 
braunite, hausmannite, psilomelane and wad, besides barite, calcspar, brown- 
spar and manganspar. Their manner of occurrence shows that their origin 
is due to lateral secretion. 

In the Thuringer Wald there are deposits of this class at Rumpelsberg 
and the Mittelberg near Elgersberg in veins in porphyry. Other veins 
which occur in porphyry in Thuringia possess a brecciated structure, and 
according to H. Credner,' the manganese ores are practically free from 
gangue. At the present time they are still worked at Arlesberg (Morgen- 
stem mine).. 

In the Oerenstocker district other veins occur partly in por- 
phyry, partly in melaphyre, and at Friedrichsrode a melaphyre conglom- 
erate forms the country rock of such fissure fillings. At Friedrichsrode 
fissure veins traverse a melaphyre, the ores occurring in remarkably well 
defined bands and crusts 1 to 3 centimeters thick, parallel to the vein 
walls.* The manganese minerals alternate with layers of calcspar, and 
barite is usually intergrown with them. 

Manganese veins occur in granite near Wittichen in the Black Forest, 
west-southwest of Santander in northern Spain.* 

The manganese lodes of the Veitsch in Styria are quite diflFerent. The 
headwater valleys of the Veitsch, especially the Kaskogerl and Friedelkogel, 
consist, according to M. Vacek,* of Silurian limestones traversed by strike 
fissures filled with manganese ores. According to analyses by C. von John 
the latter consists solely of rhodochrosite. These deposits were formeriy re- 
garded as beds. Mention may here be made of the lodes at Romaneche in 
France, to be referred to later. (See under 'Primary Differences in 
Depth.') 

Although manganese minerals are common constituents of mineral veins, 
workable deposits of this type are rare. This is probably because an ore 
carrying less than 40% is not ordinarily marketable. The world^s pro- 
duction comes mainly from concentration due to weathering. 

* Geo!. Spezialkarte, 'Norhausen Blatt,' 1870, p. 9. 

» H. Credner: 'Geol. Verb. d. Thur. Waldes und d. Harzes,' 1843, p. 130. 
' Cited by Breithaupt, 'Paragenesis,' p. 195. 

* Zeit. f. Prak. GeoL, 1897, p. 90. 

*M. Vacek : 'TJeber die peol. Verb, des Flusspebietes der unteren Mfirz,' Verh. 
d. k. k. peol. Reichsanst., 1886, p. 459. C. v. John. Jahrb, d. k. k., Reichsanst., 
1886. p. 344. 



200 TBE NATURE OF ORE DEPOSITS, 

(fii Veins of the Tta Ore CUss. 

4. Tin Veins. 

I. General Bemarhs. 

The most important ore-miDeralB of tin depoeits are csHiterite, wolf- 
ramite (tungsten), native biemuth, areenopyrite and loUingite,' molybdenite 
and acheelite; more rarely stannite, bismuthinite, specular hematite, iron 
spar, chalcopyrite and other copper ores, magnetite, stolzite (lead tung- 
Btate), as well as the secondary minerals Bcorodite, pharmacoaiderite and 
bismuth ochre. In the gangue, quartz and lithia-mica are most common. 




Fig. 142. — Thin sectiuu of a greiseii from Oanka, enlarged fitty timea. 
quartz; g, mica, w' ' ' " 
(Zml. /. Prak. GeoL, April, 



q, quartz; g, mica, with dark aureoles around «rcona; t, topaz; z, tinstotif 
■ ' " ' Gto! ' " 



Orthoclase, gilbertite, topaz and its fibrous variety, pycnite, flnorspar, apa- 
tite and tourmaline are also frequent Beryl, herderite PO.Ca [Be(OH,F)] 
and triplite PO, (Fe,Mn) [(Fe,Mn)] are rarer. Tin veins occur associated 
with granites that carry lithia-bearing mica and caesiterite among 
their normal ingredients; sometimes their silicates also contain some tin. 
A few deposits are found associated with acid eruptive rocks, rhyo- 
litee and trachytes. The lodes cut through the eruptive masses, as 
well as the other country rocks, the rocks showing a peculiar and charac- 
teristic alteration adjacent to the veins. By this alteration the feldspars 
' Fe As,. Probably also leucopyrite, Pe, As^. 



EPIGENETIC DEPOSITS. 201 

have been destroyed and in their place quartz^ lithia mica^ topaz and tin- 
stone, and often tourmaline also have been deposited. This altered rock 
is called greisen when derived from granite, the alteration product of the 
other rocks having no special name, being simply called tin ore. The 
accompanying figure (142) represents a thin section of a typical greisen 
of a coarse-crystalline variety. 

The structure of the original rock, as, for example, the porphyritic struc- 
ture of many granites, is often exhibited in the structure of the greisen. 
The large masses of feldspar formed, in such cases, the main points of at- 
tack by the invading tin compound, as proved by the fine pseudomorphs 
of tin ore after orthoclase which have been obtained from the Botallack mine 
in Cornwall. 

The bands cf greisen and tin ore, though mostly no thicker than a finger 
or a hand's breadth, and rarely as much as a meter thick, are often the real 
object of mining operations because of their great abundance and bulk de- 
spite their great poverty, while the true veins or fissure filling, being for 
the most part narrow, rarely pay for working. However, in some cases 
the true fissure filling is one to three meters wide, consisting in such cases 
of quartz, having a massive structure or only showing a S3rmmetric band- 
ing when considerable lithia-mica is present. 

Cassiterite or tinstone, the most important ore of the formation, occurs 
crystallized in several types: (1) In more or less perfectly developed 
twinned crystals and crystalline grains, as, for example, in Saxony and 
Bohemia; (2) in simple columnar crystals called *needle-tin,' in Cornwall; 
according to Becke, the hematite-like, so-called wood tin ore of Cornwall and 
Bolivia belongs to this group; (3) in compact masses suggesting brown 
hematite, in which form it is thus far known only from Bolivia. 

The probable mode of origin of the tin lodes is discussed further on in this 
work. 

Besides the strictly typical examples of this class, there are also transi- 
tions toward the tourmalinic copper type, the pyrite-blende-lead deposits 
and the rich silver ore formations (silver-quartz veins). 

Among the numerous occurrences found in nearly all parts of the globe, 
only the most important are selected as examples. 

The European mines are at present competing with diflBculty with the 
mines of the P^ast Indies and Australia. They are in part also actually 
exhausted. The most important are those of the Erzgebirge of Saxony and 
Bohemia, and the mines of Cornwall and Brittany. 

In the Erzgebirge the districts richest in tin are those of Altenberg, Zinn- 
wald and Graupen; further west, in the vicinity of Ehrenfriedersdorf and 
Geyer, Eibenstock, Johanngeorgenstadt and Flatten. The tin production 



202 THE NATURE OF ORE DEPOSITS. 

of the Erzgebirge reached its maximum before the fifteenth century, with 
about 250 tons a jear^ and since then has steadily declined. 



II. The Tin Deposits of Altenberg, Zinnwald and Oraupen.^ 

Between Dippoldiswalde and Teplitz the Erzgebirge is traversed oblique- 
ly by a north-south zone of fracturing along which vast eruptive masses 
have come up ; first, the long extended stock of Teplitz quartz porphyry run- 
ning north and south, spreading out from the feeding fissure of the erup- 
tion as a sheet covering both the gneiss, in which the fissure occurs, and 
also the adjacent Carboniferous and Permian strata. The second eruptive 
mass is granite porphyry occurring in several broad dikes, one of which 
forms the eastern boundary of the Teplitz porphyry stock for a great dis- 
tance. Finally, and latest in time, a number of granite stocks were formed, 
piercing the two preceding intrusive masses. At Altenberg a small granite 
stock of this kind pierces the granite porphyry. As the Teplitz porphyry 
eruptions belong to the period of the Bothliegende, the granite is of post- 
Permian age. A feldspar (nearest to albite), a dark lithia-bearing po- 
tassium-iron mica, with cassiterite and topaz as accessories, are its chief con- 
stituents. Both the granite and its enclosing rock are traversed by in- 
numerable small stringers of tin ore, each quite insignificant by itself and 
often hardly perceptible, but accompanied by adjoining zones of ore. Figure 
143 represents a piece of Altenberg granite with ore bands of this nature. 
In some of the fissures the filling consists of quartz and topaz. Many 
bands that are not thicker than a knife-blade are noticeable onlv by reason 
of their whitish color. In the rocks lying above the dome formed by the 
granite intrusion, these small veins are so closely crowded, and the country 
rock so strongly impregnated with ore, that is to say, transformed into tin- 
bearing greisen, that this 'stockwork' was formerly exploited on a large scale 
by extensive drifts. This Altenberg tin stock, so far as known from ex- 
posures thu» far made, continues only to a depth of about 230 meters (754 
ft.) below the summit of the granite dome. At a greater depth there are 
merely a few narrow impregnation fissures scattered through the otherwise 
normal granite, as shown in the accompanying section (Fig. 144). 

' Most important publications: G. A. von Weissenbach: 'Die Zinnerzlagerst§tten 
von Altenberg und Zinnwald,' 1823. Manuscript in Freibei^. H. Muller: 'Bildiing 
der Zinnstockwerke.' Berp u. Hittten. Zeit., 1865, pp. 178-180. E. Reyer: 
'Zinnendfuhrende Tiefeniptionen von Altenberg und Zinnwald.' Jahrh, d. k. k. 
geol. Reichsanst, 1878. H. Zinkcisen: 'Geopnostisch-mineralopnsche Bcschreibung 



der Geji^end Von Zinnwald und Altenberg,' 1888. Ms. in the Kgl. Ber^akademie. 
K. Dalnier: 'Sect. Altenberj^-Zinnwald der SpeciaUc. von Sachsen nebst Erlaut, 
1890 und Ueber den Altenberpj-Graupener Zinnerdistrict,' Zeit. f. Prak. GeoL, 1894, 
pp. 313-322.- See also publications of R. Beck in Zeit. f. Prak. Geol., 1896, pp. 
148-150, and general account by E. Reyer, 'Geologiedes Zinnes,' 1«81. 



EPIQENETW DEPOSITS. 803 

The casBiteritc content of the ores mined at Altenberg varieB between 0.1 
to 0.9%. The tin-stone granules are very small, mostly only 0.01 to 0.1 
millimeters in diameter, and, as a rule, are not visible to the naked eye. 
Between 1809 and 1887 the ore treated averaged O.Hfo Sn and 0.003% Bi. 
Only its great <juantity makes it possible to work this very low-grade 
rock. Altenberg was discovered in 1458 and at first, probably during 
the time when the loose granite debris covering the granite boss was washed, 
it gave a very rich yield, 5,000 to 6,000 centners of tin per year. The 
Zwitterstock Company was founded in 1546 and is still in existence. 




Fig. 143. — Granite of Altenberg with Zwitter bsads. (From natute.) 



After various small subsidences the workings completely collapsed in 
1620, forming the great basin seen to-day. From that time to the present 
day mining has been confined to the caved-in area. Real vein mining has 
l>een carried on in some of the larger tin ore veins, but only to a very sub- 
ordinate degree. In 18!)8 the production of Altenberg had declined to 14 
tons of tin, but it has risen again during the last four years. 

A diiferent ftate of affairs exists at Sachsisch Zinnwald and Bohmisch 
Ziunwald to the south of Altenberg, -where not only has tiu-bcarinp greisen 
been extracted, but a lively mining industry has been prosecuted upon the 



THE NATURE OF ORE DEPOSITS. 



trne fissure fiUisg of the tin lodee of this place. At present the lodes are 
TOTked maixd; for wolframite and lepidolite, and all the old dumps have 




been turned over several times for these formerly worthless minerals, which 
are now much in demand. 



■ BPIOENETW DEI OSITS. 206 

The mineB are exceedingly rich in wolframite, and about 1900 the de- 
mand for this mineral gave rise to a rejuvenation of the Zinnwald mine, 
vhich was discovered about the middle of the fifteenth century, had its cli- 




Fig. 145. — Section through the north port of the Zinnwftld granite stock. 
G, granite moetiv altered to greisen. Dark area on rif^ht ude Tepiitz quarts 
porphyry. 1—4, Michael seam; 5, day seam; 6, upper seam; 7, organ seam; 8, middle 
seam; G, upper pyritic seam; 10, lower pyritir seain; 11, lean seam. 

max of proBperity about the middle of the sixteenth century, but of late 
yeare was merely able to maintain a modest existence. In 1899 Sacbsiecb 
Zinnwald produced 50 tons of wolframite. 




Fig. 14S. — Ideal section of a so-called tiiuitone seam in granite at Zinnwald. 
G, granite; gr,greise&; q, quartz; l,1epidolite; i, tinstone; w, wolframite; f.fluor- 
■par; sch, scbeeltte. 



At Zinnwald only the summit of a granite dome intruded in the Tepiitz 
porphyry is seen exposed, the surface of the dome dipping gently in all 



206 TBE NATURE OF ORE DEPOSITS. 

directions under the porphyry. Cloae to the contact the granite some- 
times assumes a coarse-grained development, otherwise it is medium- 
grained. As shon'n by the profile (Fig. 119), the upper portion of this 
dome contains a number of parallel veins which may be compared 
to flat inverted bowls; because of their horizontal or gently dipping posi- 
tion these are called seams or beds (fiotze). The tcIds are not exactly 
parallel to the contact plane between the granite and the porphyry, as 
the dip is somewhat lower, and the veins therefore occasionally pass into 
the adjoining porphyry, where, however, they grow poor (see Fig. 145). 




Sometimes two such veins converge into a single one. They usually con- 
sist of quartz with a selvage zone of lepidolite, on each side, as shown in 
Fig. 146. Only rarely is the quartz replaced by orthoclase. Along the 
middle of the vein, druse cavities arc abundant and are lined with quartz 
crystals sometimes 30 cm. long and 17 cm. thick. Some of these projecting 
crystals are built up of quartz 'caps' consisting of several layers, between 
which minute mica scales have produced planes of parting. Crushed quartz 
crystals are often found, whose fragmnnts are again encrusted by quartz, 
a phenomena indicating a continued growth for considerable periods. The 
cassiteritc, also, is not all of one generation, since broken crystals occur 
whose fracture surfaces are studded with Bmaller individuals. Ordinarily 
the cassiterite and wolframite are most abundant at the selvage, or between 



- EPIOENETIC DEPOSITS. 207 

the mica bands and the quartz^ but they also occur in irregular transverse 
rows of granules and stringers^ which rarely attain a thickness of two centi- 
meters. Sometimes the wolframite may occupy almost the entire fissure, 
as shown in the latest great mining developments. Among the commoner 
oree^ scheelite (timgstate of lime) is the yoimgest^ and is found by prefer- 
ence in the quartz druses^ often cementinr; quartz fragments^ and often 
accompanied by fluorspar. The less abundant minerals of the lodes include 
topaz (as pycnite)^ black tourmaline^ apatite^ uranium mica^ zeunerite 
(CuUjAsjOij + 8 HjO) , specular hematite^ spathic iron ore, stolzite (lead 
tungstate) ; finally, copper pyrite, gray copper, arsenopyrite, tin pyrite, 
galena and zinc-blende. The thickness of the bed-like veins varies be- 
tween 15 and 70 centimeters, but may also reach 1.5 and 2 meters 
(4.9 to 6.5 ft.) ; about twelve of them have become economically important. 
Some steep-dipping tin veins are also known in the locality. Both 
horizontal and vertical veins are accompanied by bands of greisen on each 
side. Extensive drifts, especially in the Eeichstroster Weitung, have devel- 
oped some very large masses of greisen within the Zinnwald granite, 
which cannot be referred to any recognizable impregnation fissures. Prob- 
ably they owe their origin to an immense number of minute fissures like 
those of th€ Altenberg stockworks. Younger veins of barytic ores also 
occur. The adjoining quartz porphyry also contains numerous narrow 
bands of ore traversed by narrow veins of a fine-grained aplite-granite 
(alaskite), representing later phases of the normal granite of the stock* 
The impregnation with tinstone occurred', therefore, before the last phase 
of the eruptive activity in that region. The accompanying representation 
of a platy fragment of quartz porphyry from the Hoffnung Gottes Erb- 
stoUn at Zinnwald bhows the manner in which the rock is traversed by a 
great number of parallel bands of tin ore succeeding one another at short 
intervals (Fig. 147). 

The tin veins formerly worked contained 0.2 to 0.8% of tin, and about 
1 to 2% of tungsten, while the greisen, which was picked out and treated 
in the stamp mill, gave 0.2 to 0.5% tin, and was very low in tungsten. In 
1898 Sachsisch Zinnwald produced 50.5 tons of tungsten, 116.8 tons of 
lepidolite and only 1.2 tons of limestone. 

In the Graupen^ region on the south slope of the eastern Erzgebirge 
tin ore has been produced since the end of the twelfth century, at first from 
the gravel in the extensive alluvial fan at the mouth of the Graupen valley 

'Important publications: Th. Schiller and P. Lewald : 'Das Zinnerzvorkommen 
zu Graupen,' etc., in H. Hallwich. Geschichte von Graupen. Praf^ue, 1868. 
R. Beck: ' Erlauteningen zu Section Mfickenthurmchen der geol. Spezialkarte von 
Sachsen. ' Leipzig, 1903. A monograph on the Graupen district by the same 
author is in preparation. 



208 THE NATURE OF ORE DEPOSITS. 

near the present town of Mariaschein. The ores at Steinknochen and at 
the Miickenberg, near Obergraupen, as well as at the Knotel further down 
the mountains, were developed next, and for some time mining was 
also carried on in a number of impregnation fissures at the Preisselberg 
Klosenberg and at the Zwicken basin. An insignificant mining industry 
still continues in the Martinistolln. 

The tin ores of Qraupen are genetically connected with a granite mass 
and with granite dikes which cut through both the gneiss and in part also 
the porphyry rocks of that region. A characteristic feature of the Qraupen 
tin lodes is the large amount of orthoclase ( micro-pert hite) and of 
fluorspar in the lode filling. Where quartz and lithia-mica predominate, the 
rock alongside of the veins is altered to a zone of tin ore rich in topaz. 

The Schellerhauer granite stock,^ west of Altenberg, is also associated 
with tin veins, and further northwest, at Pobel at the Sadisdorf basin, 
veins of copper-tin ore were formerly worked, which pass into a granite stock 
in depth. 

In the SeifPen mine, on the other hand, impregnation fissures in gneiss 
with tinstone and copper ores were worked. No granite was encountered, 
although it may be presumed to exist at a greater depth.' 

III. The Deposits of Oeyer and Ehrenfriedersdorf, 

In the western Erzgebirge, near the town of Qeyer, a zone of mica schist 
is broken through by three small granite masses. This rock, which is rich 
in topaz, is accompanied by tin veins at Greifenstein, Zinnberg and (Jeyers- 
berg. The most important mines of former days were those of Geyersberg, 
which have formed a basin on the surface by their collapse. A characteristic 
feature of the granite of Geyersberg is the 'stockscheider,' a very coarse, 
crystalline 'giant granite* developed in the porphyry of the stock near its 
contact with the mica schist. It forms a granite dome or boss, for the most 
part concealed, but with the apex showing in outcrop as the Weisse Erden- 
zeche near Aue, where it is decomposed and used as a porcelain clay. This 
Geyersberg stock, 240 meters wide, whose upper surface dips at 50 to 60 
degrees in all directions beneath the schists, is traversed near its top by in- 
numerable tin-bearing fissures varying up to five centimeters thick, striking 
northeast to east and dipping northwest at 70 to 80*. They are grouped in 
19 series, and together with the greisen zones on both sides, which attain 
10 centimeters across, are called 'streams,' and are exploited by drifts. 
These lodes contain quartz, topaz, mica and tinstone; also fluorspar, tour- 

* F. Schalch: 'Erldut. Zu Section Dippoldiswalde Frauenstein,' 1887, p. 17. 

'J. F. W. V. Charpentier : 'Mineralog. Geopjaphie,' 1778, p. 133. H. Muller: 
'Die Erzgange des Freiberger Bergrevieres. ' 1901, pp. 130-138. 



EPIOENETIC DEPOSITS. 209 

maline^ geyerite and arsenopyrite rich in arsenic; more rarely wolframite, 
native bismuth^ molybdenite and triplite, as well as apatite. 

The conditions at the Qeyer mines are shown in two figures. One of 
them (Fig. 148), taken from the work of Charpentier^, cited below, 
takes us back to the times of fire-mining. It gives a good view of 
a series of lodes, showing distinctly how several parallel vein stringers are 
accompanied on both sides by impregnation zones, which fade away in a 
cloudy, blurred fashion toward the brighter, normal granite. The second 
(Fig. 149) is a photograph of a sample from the lode. The broader 
stringer is about one centimeter thick, and besides the predominant 
quartz, it carries along the middle a line of dark-looking tinstone and mica. 
The granite in the vicinity of the two stringers has, with the exception of 
a small remnant at the left edge, been altered to gray greisen. 

Mining began at Qeyersberg in 1315. In 1803 the works caved in, form- 
ing a great hollow. A quarry in this basin now affords excellent ex- 
posures of the vein structure. 

Until lately the tin veins northeast of Q^yer near Ehrenfriedersdorf 
were also worked. At the Sauberge these lodes axe united into an entire 
series, the so-called ^rissen' traversing the mica schist, which have long 
been famous for their fine crystals of tinstone and apatite. They also carry 
colorless tourmaline, anatase, arsenopyrite, chlorite, fluorite, molybdenite, 
scheelite, wolframite, gilbertite, herderite and barite. They intersect rich 
barytic silver veins, and at the meeting the two ores are said to blend ; they 
also traverse older dikes of mica diorite. Granite has not been found here, 
but may possibly exist at no great depth. 

Tin veins were also formerly worked at numerous places in the peri- 
pheral parts and within the contact area of the Eibenstock granite massive, 
for example, at Aue, Sosa, Burkhardtsgriin near Schneeberg, at Auers- 
berg near Eibenstock, at Gottesberg, at Schneckenstein near Auerbach, at 
Johanngeorgenstadt, and at Flatten. At Hengstererben near Flatten the 
Sanct Mauritius mine was opened again in recent time, toward the end of 
the seventies. The Eibenstock granite carries tinstone microliths among 
its primary ingredients, as all the granites associated with tin ore de- 
posits (Altenberg, Schellerhau, Banka) probably do. Furthermore, accord- 
ing to Stelzner* and others, the silicates composing this granite also 
contain some tin, namely, the dark lithia-iron mica, 0.32% ; the orthoclase, 
0.019%; the plagioclase (albite), 0.074% SnO,. This granite is more- 

* J. F. W. V. Charpentier: 'Mineralos;. Geofrraphie der Chureachs. Lande.* 1778. 
A. W. Stelzner: 'Die Granite von Geyer und Ehrenfriedersdorf, sowie die Zinnerz- 
lagerstatten. ' Freiberg, 1865. 

' A. W. Stelzner: 'Entstehung der Freiberger Gange.' Zeit. f. Prak, Geol., 1896, 
p. 394. 



210 THE NATURE OF ORE DEPOSITS. 

orer rich in tourmaline ss well as in topaz, a feature typical of the granites 
associated with tin ores. The adjoining schists metamorphoBed into andalu- 




Fig. 148. — Tin veinlets of the Geyer stockwork, (Charpcntier.) 

site-mica rock, etc., have often been impregnated along minute fissures by 
tourmaline associated with tinstone. Such tinstone-bearing tourmaline 
schists were formerly worked at Auersberg. The well-known topaz rock 



BPWBNETIC DEPOSITS. 211 

of the Sctmeckenstein, near Auerbach, represeiits a breccia of Euch tinstime- 
bearing tourmaline Bchist, whose cement coneieta of quartz and topaz. 

The Eibenatock granite area is connected geologically with that of 
Carlsbad of Bohemia; here, too, at Schlaggenwalde, the contact zone be- 
tween granite and gneisB contains tin veins closely resembling those of 
Ehrenfriederedorf and Geyer. As early as the fourteenth century an active 
mining industry flourished there, its center being the town of Schoenfeld.* 




Ftg. 149. — Two tin ore veinlets from the Gvyer Btookwork. 



The tin production of Bohemia in the sixteenth century, When it reached 
its climax, is eatiinated to have been 500 to 800 tons per year (H. Louis). 
At present it is hardly worth mentioning. 

IV. Tlie Tin DepodU of Cornwall 
The tin depoeits of the peninsula of Cornwall are of far greater impor- 
tance than those of the Erzgebirge. In this region the elates, which are 

'K. StemberRer: 'Die ararischen BerpbBUuntemehmungen im bOhm. Ert- 
gebirge in Oesterr.' Z. t. B. u. H. 1857., p. 63. 



212 THE NATURE OF ORE DEPOSITS. 

mostly of Devonian age, are traversed by five large and several small stocks 
of tourmaline-bearing granite. Both the slates^ locally called Jdllas, and 
the granite are cut by numerous dikes, some as much as 120 m. (393 ft.) 
thick, of quartz porphyry, also tourmaline-boaring, called elvans. These 
dikes also traverse carboniferous rocks (Culm). The granite intrusions, 
whose contact generally dips gently below the slates, have caused con- 
siderable contact metamorphism, transforming the slates into green, pur- 
ple and violet homfels and similar rocks. All these rocks are traversed 
by lodes of copper and tin ores,^ which show a great tendency to 
break up into stringers, and often pass into an exceedingly fine network 
of veins. These are especially numerous near the granitic masses. Their 
strike is mostly between east and east northeast; their dip is ordinarily 
20 to 50^ north. The thickness may rise to 1.5 meters, but is mostly much 
less. The principal gangue is quartz, with associated orthoclase, tourma- 
line, chlorite, lithia-mica and some fluorspar. The tin veins contain caa- 
siterite, stannite, copper pyrite, tungsten, blende, arsenopyrite, native bis- 
muth and other rarer minerals; the copper lodes proper also contain gray 
copper, tennantite, cuprite, native copper, malachite, azurite, pyrite, 
arsenopyrite and blende. A remarkable feature is the change in the 
nature of the ore in many lodes when they pass from the slate into the 
granite, the pure copper becoming tin deposits.' This is especially well 
shown in the longitudinal section (Fig. 150) of the Dolcoath mine, and 
the cross-section of the same lode (Fig. 151) gives a striking illus- 
tration of the stringer formation of those lodes. Some lodes are filled by 
a breccia enclosing many fragments of the country rock ; but the vein fill- 
ing is generally massive, in some cases showing a symmetric banded struc- 
ture. The veins are accompanied by zones of impregnation, some of them 
very wide, which are also worked for tin, and have furnished the main bulk 
of the ores turned into the furnace. 

While the vein fissure itself is often only a few centimeters thick, the 
lode' as worked is several meters in thickness, and is formed of granite al- 
tered to greisen.' The so-called Carbonas of St. Tves is worked for tin 
ore to which its high content of tourmaline imparts a dark color. This 
greisen rock forms very irregular deposits connected by a transverse fissure 
with one of the main lodes of that locality. These deposits consist mainly 
of feldspar, quartz, tourmaline and cassiterite, associated sometimes with 

* W. J. Henwood: 'On the Metalliferous Deposits of Cornwall.' Trans. Roy. Geol. 
Soc. of Cornwall, Vol. V, 1843. H. T. De la Bfiche: Rep. on geology of Cornwall and 
Devon, 1839. C. liC Neve Foster has published many papers on this district since 
1875 in Trans. Royal Geol. Soc, Cornwall. 

» C. Le Neve Foster: Mining, 1883, p. 452. 

" C. Le Neve Foster: 'On the Great Flat Lode South of Redruth,' etc. Quori. 
Jaum, Geol. Soc. 1878, Vol. XXXIV, p. 640. 



EPIQENETIG DEPOSITS. 213 

fiuorspar^ lithia-mica, copper pyrite and iron pyrite.^ In the slate, also, 
the altered rock of the zones of impregnation is rich in cassiterite and is 
mined, being called capeL This dark-colored rock consists mainly of quartz 
and tourmaline, with short quartz stringers interpolated, and is traversed 
by small stringers of tinstone and chlorite. These capels accompany the 
cassiterite veins ('leaders'). 

The most important tin vein in Cornwall is the Dolcoath lode, already 
mentioned, which for a length of 2.25 miles is worked in the Cam Brea, 
Tincroft, Cook's Kitchen and Dolcoath mines. The last named mine at 
present furnishes one-third of the production of Cornwall. 

The richness of Cornwall in tin ore was known to the ancients and gave 
to Great Britain the name of Cassiterides. The greatest annual production 
of tin ore was 16,769 tons in 1871. It had declined to 12,880 tons in 1894, 
and is annually diminishing, being but 4,700 tons in 1901. Copper min- 
ing, proper, only began in 1700. In 1838 the yearly production was 
146,000 tons, but in 1894 it was only 3,370 tons. Copper-tin ore deposits, 
quite analogous to those of Cornwall, are also found in the adjoining 
county of Deyonshire. 

In France, tin deposits of similar nature occur in Brittany ; for example, 
at Pyriae, west of the mouth of the Loire, and at Villeder in the depart- 
ment of Morbihan, but are at present of no economic importance. 

The tin veins of Montebras are worked mainly for amblygonite.* 

Among the occurrences of the Iberian peninsula we may mention those 
of Santo Tome, south of Salamanca, and at Cartagena in Spain, as well 
as those of Bamalhoso near Amarante in Portugal, province of Beira. Some 
of the Spanish lodes are particularly rich in wolframite. In 1900 Spain 
produced about 1,968 tons of wolframite. 

V. Tin Districts Outside of Europe. 

Among the tin deposits of other countries, the first and most important 
are those of Banka and Billiton and those of the Malay peninsula. 

The lodes of Banka and Billiton,' the so-called "tin islands,*' occur in 
granite or older schists. Besides quartz and cassiterite, they nearly, all con- 
tain magnetite, some also tourmaline, and some tungsten, or else pyrite, 
and spathic iron ore, so that their mineralogic character presents consid- 
erable variety. The remarkable occurrence of true magnetite veins in that 

* W. J. Henwood, op. cit., 21. 

» J. H. L. Vogt: Trans. Am. Inst. Min. Eng., 1901, p. 11. 

'Th. Posewitz: 'Das Zinnerzvorkomnien und die Zinnerzgewinnung in Bangka,' 
1886. R. D. M. Verbeek: 'Geologische Beschrijvninjj; van Banska en Billiton.* 
1897. R. Beck: Zeit. /. Prak, Geo Z., 1898, part 4, gives many references. 



Itt. 



814 THE NATURE OF ORE DEPOSITS. 

locality is also noteworthy. The lumps of tinstone weighing more than 
1,000 kilograms found in the eastern part of Billiton seem to have been 
derived from the upper portion of the tin lodes. Alongside of the lodes 




the granite has here and there been transformed into greiscn, rich in tin- 
stone and topaz. (For geological occurrence and description see chapter 
on tin placers.) 



EPIGENETIC DEPOSITS. 



215 



On the Malay peninsula special mention must be made of the deposits of 
Malacca on the west aide and of Kuantan* on the east side. However, 
by far the greater part of the supply of Malacca tin is obtained from placer 
gravels. 

Siam and China are also to be mentioned as Asiatic tin producers, and 
in Japan the Taniyama mine in the Province of Satauma is located on a 
tin lode {see 'Copper in Japan'). 



1 K. 




Fig. 151. — Cross-section through the veins of the Dolcoath mine. 
G, granite; K, Killas or altered slate; E, Elvan (qiurts porphjrry) dikes. (Figuiea 
give feet.) 



In recent decades the Australian tin veins have attained great impor- 
tance, especially those in the New England district of New South Wales, 
and at Mt. Bischoff in Tasmania. As the ore from the latter locali^ 
comes mainly from residual gravels, we will discuss the Mt. Bischoff lodes 
in describing the tin placer deposits. Two other tin districts have recently 
heen opened in Tasmania ; the first is in the Blue Tier mountains in the 
northeast part of the island, where, aa at Altenberg, the ore is obtained 
from tin-bearing greiscn zones in the granite, holding from 0,375 to 1% 

'Tin Deposits of 



216 THE NATURE OF ORE DEPOSITS. 

of tinstone.^ The other area lies at Mt. Heemskirk near the west coast,- 
where quartz-tourmaline veins traverse a tourmaline-granite and the ad- 
joining Silurian sandstones and slates. Along these veins the country rock 
has been hardened and impregnated with tourmaline and tinstone, exactly 
like that of Auersberg in Saxony. 

In the United States, tin deposits are known in South Dakota, South 
Carolina (near Gaffney), and Texas. The first has already been described. 
The Gaffney deposit occurs in pegmatite dikes in sedimentary rocks changed 
to crystalline schists. The tin belt is 35 miles long, extending northward 
to Lincolnton, N. C. Similar deposits occur on Irish creek, near Roanoke, 
Virginia. The Texas deposits, as yet of no economic importance, are in 
the Franklin mountains, near El Paso. The veins are in a mass of in- 
trusive granite that breaks through and uplifts Paleozoic limestones. The 
fissures are filled by quartz carrying cassiterite and wolframite and have 
greisen-like walls.* 

As an African tin ore occurrence, we may mention that described by A. 
F. Molengraaff from Swazieland in the Transvaal.* An old schist is here 
broken through by granite masses surrounded by contact zones. Within 
the latter and in the granite itself, the occurrence of pegmatite veins has 
been noted, which at Embabaan, in the region of the Ryan tin works, 
have been found to contain corundum and tinstone. The pegmatite veins 
are 10 to 40 centimeters thick, consisting of quartz, with a lesser amount 
of feldspar, and carrying tinstone next to the walls in crystals which pro- 
ject toward the center of the lode. 

Tin veins were discovered in 1903 in Seward peninsula, the most west- 
erly portion of Alaska. The ores occur in wide dikes of rather fine-grained 
granite impregnated with fluorite.* 

The youngest tin veins geologically are probably those of Mexico, which 
are associated with rhyolites and rhyolite tuffs. According to J. G. Aguil- 
era,* besides cassiterite, they contain also specular hematite, topaz, some- 
times tungsten, native bismuth and durangite (Na[AlF]As04), but are 
without tourmaline. The most important deposits are near Aguascalientes, 
Durango, Guanajuato, San Luis Potosi and Zacatecas. 

" W. H. Twdvetree: Trans, of the Austr. Assoc, for Adv. of Sc. Hobart, 1902, 
rcf. Zeii, f. Prak. Qeol,, 1902, p. 276. I 

*G. A. Waller: ' On the Tin Ore Deposits of Mt. Heemskirk.' Rep, to Secretary 
for Bfines. A. 2236. Hobart, 1902. 

»W. H. Weed: * The El Paso, Texas, Tin Deposits.' BuU. 178, U. S. Geol. Survey, 
1901. Also Bull, 213, pp. 99-102, 1903. 

*A. F. Molengraaflf: Ann, Rep. of State Geol. of S. Afr. Republic, 1897. 'The 
Mmeral Industry,' Vol. XII, 1903, p. 332. 

•A. J. Collier: BuU, 225, U. S. Geol. Survey, 1904. p. 221. See also Bull, 229. 
* Mexican Volume Trans, Am. Inst. Min. Eng., 1903, p. 325. 



EPIOENETIC DEPOSITS. 217 

« 

VI. Veins Showing Transitions Between Normal Tin Deposits and Other 

Classes. 

Examples of transitions from the purely tin-bearing deposits to copper 
deposits have been repeatedly mentioned, especially those of Cornwall. But 
there also exist transitions to the class of pyrite-blende-galena deposits. A. 
W. Stelzner and ScherteP were able to prove that the black zinc-blende of 
the Freiberg veins, in which a tin content had long been known, often en- 
closes microliths of tinstone, and we know from older reports that tin ore 
was obtained even from Ramnielsberg, and near Rosine* at Freiberg, in the 
gossan of the pyritic-zinciferous lead veins, so that the miners spoke of 
a tin gossan over silver-lead ore-lodes. 

There is one^ example of the transition type between tin deposits and 
deposits of silver ores, upon which we have ample data, a type which is 
numerously represented on the high plateau of Bolivia between the 15th 
and 21st degrees south latitude. According to A. W. Stelzner,* this type 
includes the veins of the Cerro de Potosi (discovered in 1545), Ouro Col- 
quiri, Poopo, Tasna, Milluni, Chorolque [highest mine on the earth, 5,309 
m. (17,416 ft.) above the sea]. The gangue consists of quartz, with va- 
rious carbonate spars and barite. The ore consists of sulphides and sul- 
phates of iron, lead, zinc, copper, silver, tin, bismuth and antimony, but 
also includes tinstone. Silver and tin ores are so intimately mingled and 
intergrown that they cannot be separated by hand picking, and it is only 
after roasting and amalgamation that the tin can be obtained from the 
residue. 

Besides cassiterite, the tin ores include stannite (tin pyrite), to- 
gether with wolframite and, in places, tourmaline (chorolque) and fluor- 
spar (cloquirri) also. An interesting fact is the presence of the two ger- 
manium-containing ores, argyrodite and franckeite.* In the upper work- 
ings the lodes were especially rich in tin, and it was only at greater 
depth that the tin ores were found rich in silver and lead. The cassiterite 
occurs especially in the form of wood tin and as hematite-like masses. In 
the Freiberg collection there is a lump of almost pure tin ore* from that 
locality, weighing 93 kilograms. A secondary concentration of the tin 
content seems to have taken place in the outcrop. The silver occurring in 
the form of native silver and silver chloride and found in the astonishingly 

* A. W. St«lzTier and A. Schertel: 'Ueber den Zinnirehalt der schwarzen Zink- 
blende von Freiberg. ' J. f . d. B. u. H. im K. Sachsen, 1886. 

'J. F. W. V. Charpentier: 'Mineral. Geographie der Chursachs.' 1778, p. 101. 

" A. W. Stelzner: 'Die Silber-Zinnerzlafferetatten Bolivia.' Z. d. D. G. G. 1897, 
part 1. M. Frochot: 'L'^tain en Bolivie.' Ann. d. Mines 90, XIX, pp. 186-222. 

♦A. W. Stelzner: 'Ueber Franckeit, ein neues Erz aus Bolivien,' N. Jahrh. f. 
Min., 1893, Vol. II, p. 114. 



218 THE NATURE OF ORE DEPOSITS. 

rich gossan^ continued for centuriee to maintain the reputation of Bolivia 
as the foremost silver-producing country of the globe. These Bolivian 
lodes are not associated with granite intrusions, but are, for the most part« 
connected with intrusive mtfsses of dacite and rhyolite. 

The tin exported from Bolivia in 1902 aggregated 16,779 tons, the 
product coming mainly from the departments of Potosi and Orouro. In 
the latter district the Huanuni mine alone produces every year 3,000 tons 
of tin ore. 



VII. Tungsten Deposits. 

In connection with the group of tin veins, we may here mention certain 
veins of tungsten, which, though devoid of tin, yet in their associations 
show altogether the same features as the tin lodes. 

Thus Bodenbender^ described veins in the southern part of the Sierra 
de Cordova in Argentina, which occur in granite and gneiss, and consist 
of quartz with wolframite, molybdenite, pyritc, chalcopyrite, covellite, lim- 
onite, apatite, mica, etc. 

Tungsten veins are also known at several different points in North 
America, those occurring at Osceola, in the granite area of the Snake Moun- 
tains in Nevada,' containing besides wolframite a good deal of hiib- 
nerite. 

In Portugal, veins of tungsten are exploited in the mines of Covelha 
(Castello Blanco), etc. 

Another end product, or extreme example, of the type of deposit under 
discussion, which has been called the tin ^formation,' is represented by the 
pure fluorspar lodes, which, according to J. Valentin, are also worked in 
Argentina at San Roque in the province of Cordova.' The lode materials 
are fluorspar and quartz, with an occasional addition of red feldspar 
and a silverv white mica. Similar veins occur in Southern Illinois. Ac- 
cording to Bain they are true fissure veins filled with fluorspar, calcite and 
scanty amounts of lead and zinc sulphides. The veins are 12 to 20 feet wide 
and cut Carboniferous limestones. 

On the contrary, the fluorspar lodes of the Saxon Vogtland are more 
naturally classified with the copper deposits (which see), although they 
have some quite characteristic features, which they share in common 
with the tin veins. 

* Bodenbender : * Die Wolfram-Minen der Sierra von Cordoba. ' Zeit, /. Prak. 
Geol, 1894, p. 409. 

»U. S. Geol. Survey, 'Mineral Resources for 189^-1900,' pp. 300-304. 

*J. Valentin: 'Ueber dAs Flusspathvorkommen von La Roque,* etc. Zeit, f. 
Prak, Geol, 1896, p. 104. 



EPIOENETIC DEPOSITS. 219 

(b) DEPOSITS FORMED ESSENTIALLY OP SULPHIDE ORES. 

(7) Copper Veins. 

5. Veins of Copper Ores Carrying Tourmaline ; Includino Also Veins 

Characteristic of the Tin Ore Types. 

{TourmaHne-bearing Copper Formations.) 

In discussing the characters of certain formations^ mention was made 
of transition forms between the true tin veins and those of copper de- 
positS; which were observed in many of the Cornwall and Saxon Erzgebirge 
veins, in which both tinstone and copper ores occur. Under the present 
head, however, we wish to include distinctively cupriferous veins, free from 
tin ore, which nevertheless contain, in both the ores and gangues, several 
minerals usually characteristic of tin lodes, veins which, like the tin de- 
posits, are connected with granitic eruptions. This type, as J. H. L. Vogt 
correctly remarks,^ represents, therefore, an extreme terminal member of 
the class of tin-copper veins already noted several times. For this rea- 
son this subdivision of the group of copper deposits has been placed im» 
mediately after the tin veins, heading the very important group of sul- 
phide veins although it is not economically important enough to entitle 
it to that place when compared with the other types of copper veins, which 
are not only far more widely distributed, but are of very great economic im- 
portance. 

The ores of this class of veins consist of chalcopyrite, bomite and cop- 
per glance, with accessory hematite, molybdenite, galena, zinc-blende, tetra- 
hedrite, arsenic, bismuth and uranium ores and native gold, the gangue 
consisting of quartz, muscovite, calcspar, dolomite, siderite, fluorspar and 
tourmaline, as well as beryl and apatite. 

As is the case with the tin lodes, the granite on both sides of these veins 
is strongly altered. The feldspar of the rock is destroyed and formed into 
quartz, mica and calcite. When altered to a typical greisen, it contains 
topaz and lepidolite. 

This class of veins is especially represented in the Thelemark region in 
southern Norway, where it has been described by Th. Scheerer, T. Dahll, 
P. Herter and J. H. L. Vogt.* The lodes there outcrop either in granite, 
as at Klovereid, or in slate, near a granite massive as at the Aamdal cop- 
per works, or they form ladder* veins within the c^anite dikes that cut 

* 'Zur Classification der Erzvorkommen, ' Zeit, /. Prak, Geot., 1895, p. 149. 

' Th. Scheerer: 'Beitraee zur Kenntniss Norweg. Mineralien^ Berg u. Hutten Zeit,, 
1845, p. 849 and 'Ueber die Kupfererz-Gan^ormation Thelemark ens/ Bergu. IliUten 
ZeiL, 186^, p. 157. Th. Dahll: *0m Thelemarkens Geolopi/ 1860. P. Herter: 
'Ueber die Erzfuhning der Thelemarkischen Schiefer:' Z. d. D. G. G., 1871, p. 377, 
J. H. L. Vogt. op. at. 



220 THE NATURE OF ORE DEPOSITS. 

quartzitic slate at the Nasmark mine^ or as contact lodes along the borders 
of a granite dike^ as in the Moberg mine. Bedded veins occurring between 
the planes of stratification of the slates have also been observed at the 
Aamdal copper works. On the contrary, the Svartdal lodes, in which the 
copper ores are associated with gold and tourmaline, are in a quartz-mica- 
diorite, not in granite, and this rock has, like the granite, been changed 
along the lodes into a greisen-like rock. 

The Svartdal lodes show a close resemblance to the gold-bearing copper 
deposits described by A. von Groddeck, A. M. Stelzner and W. Moricke^ 
in Chile, as at Bemolinos and Ojancos in the province of Atacama, at Tam- 
aya and La Higuera in the province of Coquimbo, and at Las Condes in 
the province of Santiago. The Chilean veins contain quartz and tourmaline, 
forming the matrix of the gold-bearing copper ores; the latter also con- 
tains some free gold, and rarely molybdenite and scheelite. They are usu- 
ally associated with acid or moderately acid eruptive rocks, which in some 
instances have undergone tourmalinization along the lodes. The copper 
production of Chile in 1903 amounted to 31,330 tons, which, however, in- 
cludes the product of other types of deposits. 

6. Cupriferous Quartz Veins. 

Chalcopyrite, chalcocite, bornite, enargite and tetrahedrite occur in veins 
with quartz filling. Pyrite often occurs in the chalcopyrite. 

The most instructive European example of this type is probably the Kup- 
ferberg district in Silesia, of which we have a detailed description by Web- 
sky.* The veins outcrop in a hornblende schist and other crystalline schists, 
which form a zone between the Paleozoic grits of Landshut and a granite 
massif, and are traversed by dikes of porphyry. The vein filling consists 
of quartz and homstone; the ores occur in bunches and pockets, and con- 
sist of copper glance, bornite, chalcopyrite, pyrite, pyrrhotite and zinc- 
blende, and in druses, of tetrahedrite. In rare cases a flesh-red feldspar is 
also said to be a constituent, and, finally, in some cases, cobalt and nickel 
ores. For the most part the deposits are true fissure veins with a good 
deal of enclosed country rock. Krusch divides the deposits into three 
classes, viz.: (1) Older veins, with quartz, calcite, gypsum, fluorite, chal- 

' A. V. Groddeck: 'T^eber Turmalin enthaJtende Kupfererze von Tamaya.* Zeit. 
d. D. G. G., 1887. A. W. Stelzner: *Ueber die Turmalin-fuhninp der Kupfererzgange 
in Chile.' Zeit.f. Prak. Geol, 1897, p. 41. W. MOricke: 'Die Gold,- Silber, und 
Kupfererlagerstatten in Chile. ' 1897. 

'Webskv: 'Ueber die geo^ost. Verb. d. Erzlageratatten von Kupferberg und 
Rudelstadtin Schlesien.' Z. d. Deutsch. geol. Ges., Vol. V., 1853, pp. 373-438. P. 
Krusch: ' Die Classification der Erzlagerstatten von Kupferberg in Schlesien.* Zeit.f. 
Prak. GeoL, 1901, pp. 226-229. 



EPIOENETIC DEPOSITS. 221 

copyrite and some galena, together with chloritized country rock. (2) 
Younger, pure quartz veins, with disseminated chalcopyrite. (3) Ore beds 
like those of Schwarzenberg, with a floor of actinolite, prase and chlorite, 
much pyrite and accessory pyrrhotite, chalcopyrite and bomite, with liev- 
rite and magnetite (Einigkeit vein). 

A similar deposit described by A. von Groddeck^ occurs at Bheinbreiten- 
bach on the Rhine, in the Devonian graywacke area. 

In the kingdom of Saxony this class of copper veins is found in the 
Schneeberg mining district, particularly at the old mines of Konig David 
and Sanct Michaelis near Oberschlema.' 

Many of the veins of the Massa Marittima district of Tuscany belong 
to this quartz-copper vein type, as shown by Lotti'; as, for example, the 
Boccheggiano vein, while others, viz., the Fenice Massetana, Capanne Vec- 
chie, Serrabottini, Sud and Guardione veins also carry blende and galena, 
and thus form transitions to the pyrite-blende-lead veins. 

These deposits also show great variety of form, for besides the true veins 
just mentioned, irregular stock-like bodies occur, as a result of the replace- 
ment of lime rocks along the bedding planes separating dissimilar strata 
or along faults. Thus, at the plane of separation between the dolomitic 
Hhaetic limestones and the alternating beds of shale and limestone of the 
Eocene, there are ore deposits, as, for example, the iron and calamine de- 
posits of Carbonais (Valdaspra), the copper, lead and calamine deposits 
of Rocchette and Serrabottini-Nord, as well as those of the Speziala, and 
the copper and iron ore deposits of Cagnano-Pighetti. The lead ore de- 
posits of Montieri and Gerfalco are associated with Liassic limestones. 

The veins occupy fault lines, along which the country rock has been 
much altered. This alteration has produced either silicification with the 
deposition of copper and iron pyrite and in part a segregation of epidote 
or else a complete metamorphism into a pyroxene-epidote rock. In some 
cases (Guardione) this alteration and replacement extends much farther 
into the hanging-wall than into the footwall. All the veins are of post- 
Eocene age. 

The vein worked at Boccheggiano, an important mining town, northeast 
of Massa Marittima, is worthy of special mention. The course of the vein 
is north-northeast, the dip 40 to 50"* northeast. The vein has a thickness 
of 30 m. to 33 m. (98 ft. to 114 ft.) and is mined for 1,200 m. across the 
Merse valley, being worked on both sides of the stream. It occupies a fault 

» A. V. Groddeck: 'Erzlageretatten,' 1879, p. 202. 

'H. Muller: 'Die Erzdistrict von Schneeberg im Erzgebirge.' 1860. Cotta's 
Gangst, III, p. 70. 

' B. Lotti : ' Descrizione Geologico-Mineraria dei Dintomi di Massa Marittima.' 
Rome, 1893. (Gives other references.) 



222- TEE NATURE OF ORE DEPOSITS. 

Dvjih micaceous shales of Permian age beneath^ and the Eocene lime- 
stones and clay shales above. Segregations of epidote occur along cross 
fissures as far as 50 meters from the vein. The ore consists of quartz^ con- 
taining pyrite and copper pyrite, with scanty amounts of marcasite^ bis- 
muthinite and hematite. The workable ore occurs in three column-shaped 
shoots pitching northward. The rich ores show^ in part, a massive and, 
in part, a banded structure. Large pyrite cubes occur sparsely interspersed 
through the ore. In places the vein filling consists of a mineralized slate 
breccia. The ore contains 3 to 11% of copper, with various other metals, 
including 0.04% of tin. The gangue is chiefly quartz. 

A spring tapped at the lowest part of the shaft, with a temperature of 
40.6 "* C, is at present greatly interfering with the work. 

Some of the more important occurrences of other continents should also 
be noted : 

Among these is the copper vein of the Chudak mine in the Altai, 6-7 m. 
thick, outcropping in the quartz porphyry.^ 

Splendid examples of this type of vein occur in diabase at the Siinik 
mine, near Kata, south of Schuska, in the Transcaucasia.' 

Australian Deposits. 

Many of the copper veins of Australia are quartz-pyrite veins. The 
Burra-Burra mines of South Australia, since their discovery in 1845, in 
the space of 29.5 years, have yielded 234,648 tons of copper ore, with an 
average content of 22% copper, corresponding to 61,622 tons of copper. 
Work ceased in 1877, as the two main lodes were worked out. The vein 
lies on a contact between ^serpentinous' limestone' and steeply upturned, 
thinly bedded limestones. Subsequently the lodes of Wallaroo, in porphy- 
rite and Moonta,* also in porphyrite, were discovered, which are also ex- 
ceedingly large (30 feet) and average 12% copper. The two together pro- 
duced in 1897 about 5,100 tons of copper. 

The Great Cobar copper mines in New South Wales, which recently re- 
gained their former importance, work quartz veins in the Silurian slates. 
The main ledge is in its upper level, 25 to 45 feet wide and composed of 
nearly solid sulphides. The total copper production of Australasia in 1902 

was 29,098 tons. 

African Veins. 

The most noteworthy African examples are the veins in metamorphic 

* B. von Cotta: ' Kupfergnibe Tschudack im Altai.* Berg u. Hutten Zeit., Vol. 
XXIX, 1870, No. 7, p. 29. 

' K. Ermisch: 'Die Kupfererze der Sunikgruben', Zeii, /. Prak. GeoL, 1902, p. 88. 
» J. D. Woods: 'The Province of South Australia.' 1894, p. 258. 
« Phillips-Louis: 'Ore Deposits.' 1896, pp. 691-693. 



EPIOENETIC DEPOSITS. 223 

Devonian slate and granite in Little Namaqualand and Demaraland and 
on the west coast of South Africa, from which in 1898 the production was 
2,438 tons of copper. This class also includes the veins of the Albert silver 
mine, 50 miles northeast of Pretoria in the Transvaal. These veins out- 
crop in an area of reddish porphyritic granite traversed by dikes of olivine 
diabase. The primary vein consists of quartz with bomite, chalcopyrite, 
silver-bearing tetrahedrite and some hematite (Freiberg collection). 

Japan. 

The most productive copper veins of Japan, those of Ashio, belong to this 
group. These lie near Nikko, so famous for its shrines and temples (prov- 
ince of Shimodzuke). According to Yamada (statement in a letter) the 
Paleozoic (pre-Carboniferous) sandstones, clay slates and hornstones of 
that locality are traversed by a stock of rhyolite. This rhyolite, which 
grades at times into dacite, has altered the sedimentary rocks along the 
contact and encloses many fragments of them. In the rhyolite, but not 
in the contact rocks, there are numerous northeast or west-northwest 
to east- west veins dipping steeply north or south. These veins con- 
sist mainly of copper pyrite, pyrite, arsenopyrite and quartz. Their 
walls are usually sharply defined, but sometimes only on one side. Be- 
sides the typical copper veins, there are also pyrite-blendic lead veins at 
Ashio, though these are much rarer. The production of the Ashio mines 
in 1902 was 6,762 tons of copper. The total Japanese production in 1903 
was 31,360 tons of copper.^ 

Butte, Montana.* 

The prodigious production of the veins of this kind at Butte City, Mon- 
tana, in recent years, has surpassed that of any other district of the world. 

The Butte district is situated in southwestern Montana, in the central 
part of the Rocky Mountain region. The city, which is built about and 
over the mines, is the largest settlement of the State, while the neighbor- 

* Sketch of the Mininer Indiistrv of J<)pan. Published by the Bureau of Mines of 
Japan for the Louisiana Purchase Exposition, 1903. 

' W. H. Weed: 'Ore Deposits at Butte, Montana/ BvU. 213, IT. S. Geo! Survey, 
1903, p. 170. S. F. Emmons: 'Xot«s on the GeoloffV of Butte, Montana.' Trans. 
Amer. InaL Min. Eng., Vol. XVI, 1887. p. 49. Jss. Doiiplas: 'The Copper Resources 
of the UTTited States.' Trans. Amer. Inst. Min. Eni?.. Vol. XIX. 1891, p. 693. 
R. Vogelsang: 'Ueber den KuDfprberj?bau in Nordamerika.' Z. f. d. B. H. u. S. 
im preuss. St., 1891. Vol. XXXIX, p. 248. C. A. Herinp: 'Die KupfererzlajrerstAtten 
der Erde.' Idem, 1897, pp. 19-22. S. F. Emmons : 'Economic Geolo^ of the Butte 
District.' Geol. Atlas of the U. S.. Butte, Montana, folio, 1897. W. H. Weed: 'The 
Secondary Enrichment of Ore Deposits.' Bull Geol. Soc. Am., Vol. XI. pp. 179-206, 
1899-1900. R. C. Brown: 'The Ore Deposits of Butte City.' Trans. Am. Inst 
Min. Eng., Vol. XXIV, 1895, p. 666. 



224 TEE NATURE OF ORE DEPOSITS. 

ing city of Anaconda, 20 miles distant, is a dependent. The rocks of the 
ore-bearing area are all igneous, the district forming part of an extensive 
region of Tertiary igneous activity. The prevailing rock, and the one in 
which all the veins occur, is a dark basic granite, technically known as quartz- 
monzonite, which is a part of a great mass of granitic rock. This rock is 
cut by dikes and irregular intrusions of the Bluebird granite, a white aplite^ 
composed of quartz and feldspar, with a little mica. In the copper-bearing 
area the Modoc porphyry appears in lenticular dikes, traversing both va- 
rieties of granite in very irregular fissures. It is a light-colored rock, car- 
rying large and distinct crystals of feldspar and quartz in a dense ground- 
mass, and is technically designated rhyolite-porphyry or quartz-porphyry. * 
After the intrusion of the Modoc porphyry, extensive fracturing occurred, 
with vein formation, the veins cutting the porphyry in many instances. 
After the formation of these earlier veins they were fractured, and silver 
veins formed, followed by renewed volcanic activity, resulting in the in- 
trusion and eruption of rhyolite, forming dikes cutting across the veins, 
and in extensive extrusive masses covering the silver veins to the west. The 
veins of the district, both copper and silver veins, belong to four distinct 
systems. The oldest lodes have a general east-west course, the Parrot, 
Anaconda and Syndicate lodes being examples. Another set of veins has 
a northwest-southeast course, and has displaced the earlier veins. A still 
later set has an east-northeast course and has displaced both the earlier 
systems of veins. These veins, in the eastern part of the area, are cut and 
displaced by a great northeast fault which carries no endogenous ore, the 
material mined having been broken off from earlier deposits and included in 
the fault d6bris. 

The silver veins surround the copper lodes on the north, west and south- 
west. TJieir course and geologic relations are very similar to those of the 
copper veins, but their structure and mineralogic character are different. 
The silver veins contain sulphide of silver, blende, pyrite and a little galena, 
and commonly contain no copper, save near the border of the copper area, 
where, though occasional bunches of copper ore occur, it consists of chal- 
copyrite, and, more rarely still, tetrahedrite, minerals which occur rarely 
and very sparingly in the copper lodes. The gangue consists of quartz, with 
rhodonite and rhodochrosite, and shows marked banding and crustifica- 
tion, in strong contrast to the structure of the copper veins. 

Several of the copper veins were, as is well known, at first worked as 
silver veins. The upper portion of the veins consisted of quartz somewhat 
stained by iron, but not like the great iron gossan caps of other regions. 

* Called 'jn^nulite' by some writers — a name applied by German geolo^sts to a 
variety of schist, but by French petrographers to aplite. 



EPIOENETIC DEPOSITS. 225 

This extends to a variable distance below the surface^ 200 to 400 feet in 
some instances^ where it is replaced by partly oxidized and decomposed 
copper ores that form the upper limit of the remarkable glance, enargite 
and bomite orebodies of the district. Carbonates and oxides are rare. 

The copper minerals occur in quartz-pyrite veins of remarkable width 
and extent The Anaconda ledge is sometimes 100 feet wide, and will 
average half that width, as will also the Syndicate lode. 

Character of the Ores. — The copper ores average 55% silica and 16% 
iron. About 15% of the tonnage mined is first-class ore, averaging 12% 
copper; the remaining 85% carries 4.8% copper, and is treated in con- 
centrating mills, the resulting product containing but 15 to 20% of silica, 
while the copper is increased to 18%. 

The ores contain gold to the extent of about 2.25 cents to each pound of 
copper, with 0.0375 ounce of silver. Native gold has been found upon 
crystallized glance, and native silver is common in bornite and glance in 
some mines. It is estimated that the total production of copper ore has 
been about 31,000,000 tons, averaging 5% copper. The amount of arsenic 
(and antimony) present is very large, it being estimated that over 32,000 lb. 
a year pass off in smelter fumes. Tellurium is present in very small quan- 
tity in the ores, amounting to 2.375 ounces, or 0.008%, in the crude copper 
from the converters. 

In general, it may be stated that the original mineral-bearing solutions 
were in all probability hot and ascended through fractures in the granite. 
The copper deposits are almost entirely replacement deposits. There 
is a marked association of faulting of the veins with bodies of rich 
ore, and these faulted areas are wet, so that the miners say: "A dry 
and tight vein is barren; a wet and crushed one is rich.'^ There is also 
a distinct genetic relation between ore and country rock, as a result of 
the deposition of the ore by metasomatic replacement. Thus the Anaconda 
ledge is low grade where it crosses either the Bluebird granite or the 
Modoc porphyry, a feature explainable by the lack of easily replaceable, 
dark-colored, ferromagnesian minerals in those rocks.* 

In 1903 Montana produced 272,555,854 lb. of copper. The Anaconda 
mine alone yielded between 1879-1897 about 470,000 tons of copper. 

Cupriferous quartz veins also occur in the Virgilina district along the 
border between Virginia and North Carolina, but the annual production 
does not exceed 3,000 tons. The copper occurs as glance and chalcopyrite, 
more rarely as bomite, in bunches and stringers sparingly distributed 
through the massive quariz filling of the veins. In the Blue Wing mine the 

' W. H. Weed: 'Inruenre of Country Rock/ etc., Trans. Amer. Inst. Min. Enir., 
Vol. XXXI, p. 634, 1901. Also Amer. Geol., Vol. XXX, p. 170, 1902. 



/ 



226 THE NATURE OF ORE DEPOSITS. 

vein filling is calcite and the ore bomite. These veins are traceable for 
several miles by well defined outcrops. They cut soft micaceous schists 
formed by the metamorphism of pre-Cambrian andesites and volcanic tuffs.^ 

The type of copper quartz veins just described is connected by various 
gradations with the pyrite blende bearing lead deposits. Several veins 
in the Freiberg area, proper, belong to such a transitional type. The quartz 
gangue contains copper pyrite, bomite, copper glance and gray copper, 
and in the upper portions oxidized ores, Galena, zinc-blende, arseno- 
pyrite and pyrite occur in lesser amoimts. As examples the (Jottlob Spat, 
Franzer Spat and Heinricher Spat at Morgenstem may be mentioned. This 
was also the character of the now abandoned veins of Junge Hohe Birke 
and Alte Mordgrube, at least of certain parts of the veins, as, for example, 
the steep-dipping layers of the Alte Mordgrube. 

Veins of intermediate type also occur at Hohenstein* in Saxony. They 
consist of pyrite, arsenop}Tite, chalcopyrite and tetrahedrite, in quartz, brown 
spar and calcite, with some marcasite, galena, zinc-blende and boumonite. 
These veins are remarkable for their gold content. They are typical cop- 
per veins in certain parts of the lode. The two copper minerals named 
above are carriers of the silver and gold content, the gray copper containing 
about 0.01% of gold. The Lampertus mine is still in operation. 

Similar transitional types are found in other countries; for example, 
some of the lodes of Sado and Ikuno in the province of Tashima, in Japan, 
are, according to Yamada, of this nature. 

As an appendix to this last group, we may mention the remarkable man- 
ganiferuus copper lodes, forming a transition of purely manganese veins, 
found in the vicinity of Muleye in lower California. Their mineralogy 
has been studied by P. Krusch.* They outcrop in Tertiary trachytic tuffs 
about 110 kilometers north-northwest of the town. In the undecomposed 
state they carry a manganiferous and cobaltiferous copper glance with 
gangue of chalcedony with associated gypsum. Farther east there are also 
found true maganese lodes, with quartz and gypsum as matrix and a psi- 
lomelane containing 0.38 to 1.2% copper. 

7. Spathic Copper Veins (Gangue op Various Carbonates with 

Quartz, Barite and Sometimes Fluorspar) . 

The gangue of these veins includes some quartz, but often consists chiefly, 
and sometimes entirely, of various carbonates, particularly iron spar, as well 

* W. H. Weed: 'Types of Copper Deposits in Southern Unit^ States.' Trans. 
Am. Inst. Min. Eng., 1900. 

* H. Mullen 'Ueber die Erzgange von Hohenstein,' 1879, in Erlaut. zu Sect. 
Hohenstein., p. 28 et seq. 

* P. Krusch : 'Ueber manganhaltige Kupfererzgange. ' Zeit. /. Prak. Geol, 1899, p. 83 



BPlOENEfIC DEPOSITS. 221 

as calcspar and dolomite. Barite is very common and is at times accom- 
panied by fluorspar. The ore minerals are chalcopyrite, bomite, glance^ tetra- 
hedrite and pyrite. Cobalt and nickel ores and various other ores also occur 
as accessory minerals. 

The lodes of Kamsdorf, near Saalfeld, in Thiiringia, have been studied 
and described by F. Beyschlag.^ The veins fill fault fissures in the zecK- 
stein (Permian limestone) formation, and they also continue downward 
as barren siderite-barite veins, into the strongly folded and tilted Culm 
slates underlying the zechstein formation. In these lodes, barite is the 
chief vein mineral, carbonates appearing but scantily, and quartz only show- 
ing where the fissure is within the Culm. Among the ores an argentiferous 
gray copper and a non-silver-bearing copper pyrite, together with secondary 
copper ores, are most common; cobalt and nickel ores are accessory con- 
stituents, especially smaltite (cobalt pyrite) and niccolite (NiAs). The 
ores often enclose fragments of the country rock. The structure is bot& 
massive and brecciated, and it is only where the lodes descend into the 
Culm that a symmetric banding of the lode is seen. The veins are richest 
between the dislocated parts of the bed of Kupfershiefer faulted by the 
veins. In the upper strata as well as in the Culm the lodes are barren of 
ore. Near the veins certain beds of the lower and middle zechstein, especially 
limestone and dolomite strata, are replaced for varying distances by spathic 
iron ore. The veins are now worked for these masses of spathic iron ore, 
or the secondary brown hematite derived from them. The orebodies at times 
contain impregnations of copper ore. The diagrammatic section (Fig. 153) 
is a composite made from several of Beyschlag's profiles. The total product 
of the Kamsdorf mines for 1898 was 24,760 tons of spathic iron ore and 
17,929 tons of brown hematite. 

Near Ceilsdorf and Oelsnitz, in the Vogtland of Saxony, similar veins 
cut Devonian rocks, not the zechstein. Analogous veins were worked at the 
beginning of the 19th century, at the mines of Deichselberg. The mines 
of Sanct Burkhard and Heilige Dreifaltigkeit (Holy Trinity) were for- 
merly important. Some of the lodes, it is true, are worked mainly for spathic 
iron ore; in fact, transitions to the non-copper-bearing spathic iron ore 
lodes may be very frequently observed in this class of copper veins. 

Some of the copper veins of Vogtland vary in character, containing 
a large amount of fluorspar, being, in fact, worked only for this mineral 
to-day. The Auf der Kunst vein, which is in places over 25 meters thick, 
is a typical example of this kind. It lies between Schonbrunn and Planz- 
schwitz in the Saxon Vogtland and belongs to the Heilige Dreifaltigkeit 

* F. Beyschlag: 'Die Erilaflcerstatten von Kamsdorf inThuringen.' Jahrb. d. k. 
preuss. geol. Landesanst., 1888 i p. 329. 



228 THE NATURE OF ORE DEPOSITS. 

mine just noted. According to E. Weise,' this vein occupiee a fault fissure 
dipping steeply eaBt-northeast and striking north 25° west, cutting Devon- 
ian states, diabase breccias and diabases. The footwall streak carries brown 
hematite (altered spathic iron ore) and copper ores. Above this lies a thick 
streak of quartz, carrying fluorspar, brown hematite and subordinate cop- 
per ores. The middle band, 2 to 8 meters thick, is fonned of white and 




Fig. 152a — Ideal croHB-aectioa through a mineral vein at Kamsdorf. (F. Iteysohlag.) 
O* upper Mchate n slates d dolom te; ek.ferriterouslimestoneisp.hrown hematite 
and spattuc iron ore, Ub, lower sechstein limeBtone; of, upper bed; uf. lower slate bed 
{copper slate bed) ; mf, mother bed; w, techstein conglomerate; c, Culm schist. 



green fluorspar. In the uppermost layer lenticular bodies of copper ore 
with barite and violet fluorspar occasionally occur imbedded in the barite. 
A similar vein is worked at the Briider Einigkeit mine at Biisenbrunn, 
near Oelanitz. 

'E. W«se: 'Eri&ut zu Section PlaUfln-OelBnitz' der geol. Spezialk. v. Sachsen, 



EPIGENETIC DEPOSITS. 229 

It may be well to point out that this somewhat aberrant development of 
the spathic copper deposits agrees in many respects with that of the tour- 
maline-copper veins^ and thus approaches the tin deposits in character^ a re- 
lationship which does not obtain in the case of the typical examples 
of Kamsdorf. As a matter of fact^ tin ore was obtained between 1511 and 
1533 from the Vogtland region, where these fluorspar-bearing lodes occur, 
and even from the Sanct Burkhard and Heilige Dreifaltigkeit, now re- 
ferred to as copper mines. 

The numerous barytic copper veins of the Rhine valley are of purely 
scientific interest. They occur in the Black Forest, the Odenwald and 
at Spessart. These deposits are, according to K. von Kraatz-Koschlau,* 
partly of pre-Triassic age, in part of Tertiary age. They strike northwest, 
rarely east-west. Their filling consists of barite of two generations, fluor- 
spar, homstone, chalcedony, quartz, copper pyrite and pyrite, as well as 
oxidized copper ores. 

Among the copper deposits in the Alps this class is represented by a vein, 
2 to 3 meters thick, outcropping in the Silurian clay slate of Mitterberg 
near Werfen in the Salzburg district. The vein filling consists of quartz, 
siderite, ankerite, copper pyrite and iron pyrite. F. M. Stapff* points out 
the fact that in tiiis lode both copper pyrite and spathic iron tend to 
form lenticular masses in the quartz, and these ore shoots are at times in- 
clined at an oblique angle to the walls. Sometimes the ores contain inter- 
grown leaves of hematite. 

A quartzose variation of this type of vein appears among the copper veins 
recently described and graphically represented by C. Dferler,* veins which cut 
the Silurian clay slates in the vicinity of Kitzbiihel in the Tyrol. They 
were formerly worked at Eohrerbiihel and Sinwell, and even to-day some 
mines are still worked at Schattberg, in the Kupferplatte and on the Kelch- 
alpe. The fissures, which attain a width up to 4 m. (13.1 ft.), are filled with 
quartz, some ankerite, fragments of slate and copper pyrite, and at times 
contain also pyrite, gray copper ore, niccolite, chloanthite (NiAsg), zinc- 
blende and galena. The chalcopyrite occurs in scattered grains, small 
streaks, and as occasional large masses of compact ore within the vein 
filling. 

A typical development of this form of lode is found at Altgebirg and Her- 
rengrimd, north of Neuschl, in northern Hungary. Quartz, barite, siderite, 
brown spar, copper pyrite and gray copper form the fissure filling of the 

* K. V. Kraatz-Koschlau : Ahh. d. Hess. Landesanst, 1R97, Vol. Ill, part 2, p. 55. 

' F. M. Stapff: 'Geoi^iost. Notizen uber einige alpine Kupfererzlagerst&tten. ' 
Berg u. Hutten. Zeit., 1835 p. 6. 

' 'Bilder von den Kupferkies-LagerstStten bei Kitzbuhel.' Vienna, 1890. Pub- 
lished by J. Graf. Falkenhayn. 



230 THE NATURE OF ORE DEPOSITS. 

Pfeifer vein, which traverses the mica schist, while the Kugler vein miis 
parallel to the stratification of the Triassic greywacke schist.^ Similar lodes 
at Kotterbach, Szlovinka and Gollnitz in the Gomor-Zips schist area con- 
tain, besides the minerals mentioned, also some cinnabar.' 

In the Swiss Alps the lodes of Miirtschenalp, in the canton of Glarus,* 
described by G. Troger and E. Stohr, outcrop in the Semf conglomerate 
rock. They are probably of Permian age, and contain besides the copper 
ores (mainly bomite) also some pyrite, gray copper, hematite and molyb- 
denite, the matrix being finely crystalline dolomite. 

This type of vein also occurs in the Japanese copper districts. In the 
northern and central part of the main island there are five examples, viz. : 
Osaru-zawa, in the province of Rikutschu, Arakawa and Ani in the province 
of Ugo, Kusakura in the province of Etachigo, and Ogoya in the province of 
Kaga. According to a letter from Mr. Yamada, the strata of the Twiiary 
formation are there everywhere traversed by rhyolites and partly by propy- 
litized andesites. The veins occur in the eruptive rocks. They consist of 
copper and iron pyrite, with lesser amounts of specularite and lead, zinc and 
silver ores in a gangue of quartz, calcspar, rhodochrosite and barite. In the 
Kusakura mine the specularite content increases considerably in depth. 
Similar veins occur in Paleozoic beds at Yoshioka in the province of Bitshu, 
and at Sassagatani and Dogamaru, in the province of Iwami, district of 
Chugoku. They are said to be connected with the granite and diorite in- 
trusions of that locality. 



8. Zeolitio Copper Veins v^ith Native Copper. 

This t3rpe of copper vein is quite uncommon, but, with the mineralogically 
similar amygdaloid beds and copper-bearing conglomerates, forms the 
enormously productive deposits of the Lake Superior region. The veins, 
formerly tlie exclusive source of copper, are no longer worked. Native 
copper and some native silver occur, accompanied by calcspar, laumontite^ 
prehnite, apophyllite, natrolite, datolite, dcsmine, quartz, fluorspar, epidote 
and chlorite. 

A brief description of the entire copper ore district of Lake Superior 
is given because these veins form a genetically connected whole with the 
other copper deposits of the locality. 

* B. V. Cotta: Erzlagerstatten. II, p. 304. 

'G. Faller: 'Reisenotizen' in Berg- u. H.-Jahrb, d. k. k. Bergak, 1867, Vol. 
XVII, p. 132. 

' G. Trftper: ' Ueber den Kupfer- und Silberbergbau an der Mtirtschenalp. * Bery u. 
^. Z., 1860, p. 305. £.St6hr: 'Die Kupfererze an der Mtirtschenalp.' Zurich, 1805. 



EPIQENETW DEPOSITS. 231 

The copper region of Lake Superior* lies on a long penineula projecting 
into lake Superior and terminating in Keweenaw Point, the copper belt 
heing 130 miles long and 6 miles wide. The eastern side of the peninsula 
is formed of Cambrian (Potsdam) sandstone, the west side of vast 
sheets of melaphyre (Irving's diabase) and melaphyie-amygdaloid, 
with intercalated beds of conglomerate. The age of the melaphyres, 
which in part bear all the characters of old lava streams, has been 
much disputed. According to M, E. Wadsworth the copper-bearing strata 




fig. Ifi2a.— The Quiacy (amygdaloid) lode. (T. A. Rickaid.) 



rest on the Cambrian sandstones; according to B. D. Irving and T. C. 
Chamberlin this overplacement is merely apparent, in consequence of an 
over-thmst along a plane of dislocation, which in certain portions can 
be identified with certainty. The amygdaloidal structure of the eruptive 
sheets has been especially developed in the parts near the surface, while 

'The foUowine list cofflprisee the most important publicationH upon this district: 
Herm. Credner: ^cechreibune einiger charskteriHtiscner Vorkommen dee gedief^nen 
Kupfera auf Keweenaw Point, etc. N. Jahrb. f. Min., 1S89, pp. 1-14. R. Pumpelly; 
'The Paragenesis and Derivation of Copper and Its Associates on Lake Superior.' 
Amer. Joutti. Sc.. 1S71 (3), pp. 1,18 et tea. and 'Geo!. Surv. of Michipin,' Vol. I, pt. 
II. 'Copper Hearing Rockb, 1873. 'The Metaaomatic Development of the Copper- 
Bearing Rocks of Lake Superior,' Proc. Amer. Acad, of Arts and Sc, Vol. XlII, 
1877-78, p. 253. E. Wadsworth: 'Notes on theGcolocvofthelron and Copper Districts 
of Lake Superior.' Cambridge, I8S1. R. D. Irving: 'The Copper-Bearing Rocks of Lake 
Superior.' Washington. Monograph. V, 3. Geol. Surv., 1883. T. C. Chamberlin: 
'The Copper-Bearing Series of Lake Superior. 'Cambridge, 1883. T. A. Kiekard: 'Copper 
Mines of Lake Superior,' The Bngirteering and Mining Journal, 1904, Vol. LXXVIIT, 
So. 15e(**7? 



232 THE NATURE OF ORE DEPOSITS. 

the deeper parts show a diabasic stmctxure. On Keweenaw penin- 
stila^ the largest and most famous mine is the Calumet & Hecla, one of 
whose vertical shafts is 4,920 feet deep ; the Portage, Osceola, Quincy, Cen- 
tral mines, where the largest masses of native copper were found, and the 
Copper Falls and Cliff mines are well-known producers. The copper area 
extends along the south shore of the lake southwestward, where the Min- 
esota mine, in the vicinity of Ontonagon, is especially noteworthy. In this 
direction the copper-bearing series may be fo)'owed into Wisconsin, but 
no workable deposits are known. On Isle Boyale, near the Canadian shore, 
deposits of similar character were worked. 

Following H. Credner, three different kinds of deposits may be distin- 
guished within the copper-bearing rock group : 

Disseminated Grains and Amygdules in the Melaphyre Lava Sheets. 

Such copper-bearing lavas, called amygdaloids and ^ash beds,* are worked 
in the Quincy, Franklin, Osceola, Atlantic, Huron and Copper Falls mines. 
At times the vesicular cavities of the amygdaloids are exclusively filled with 
native copper, sometimes accompanied by native silver, calcspar, quartz, 
chlorite, laumontite, prehnite, analcite, epidote, datolite, hematite, etc. 
The two native metals often occur intergrown into one lump, and hence 
cannot have been congealed from the molten condition as a magmatic seg- 
regation, for in that case they would have formed an alloy. On the con- 
trary, like the constituents of the accompanying zeolites, they seem to have 
been leached out of the melaphyre itself, in which they may have existed 
at one time in fine particles of sulphides, subsequently concentrated by sec- 
ondary process in the existing cavities. 

In the Conglomerates. 

The conglomerates, according to Wadsworth, are characteristic littoral 
formations. Their pebbles consist of quartz porphyry and melaphyre, and 
are often quite decomposed and disintegrated, and this material has been re- 
placed and impregnated with copper. The interspaces between the pebbles 
are largely filled by native copper, with the same associated minerals as in 
the amygdaloid. Such conglomerates are worked at the Calumet & Hecla 
mine. 

Filling of True Fissures. 

The thickness of these veins is usually 1 to 3 m. (3.3 to 10 ft.), but some- 
times rises to 10 m. (33 ft.) The more decomposed and porous the country 



EPIQENETIC DEPOSITS. 



233 



tock, the richer the ore ; the fiseures accordingly cany their beet orebodies 
at the points where they traverse the amygdaloids. The greet thickneaees 
given for some veins include the adjacent country rock, which, when 
strongly impregnated with copper, has been counted as included in the vein 
proper; occasionally vein stringers group themselves into stock-like aggre- 
gates. The fissure filling consists of quartz, calcspar, prehnite, laumontite, 
apopbyllite, natrolite, stilbite, as well as epidote, chlorite and finorepar, 
native copper and some native silver. Fragments of the decomposed coun- 
try rock are always found in the fissures. The sketch by Credner (Fig. 153) 
gives a typical cross-section of such a vein. The native copper forms jagged 
and stout branched lumps, sometimes of astonishingly stoat dimenstODS and 




Fig. 153. — Croea-section through Cliff lod«. (H. Credner.) 
m, amygdaloid; c, calcite; I, laumontite; k, copper; q and p, quarti and prehnite 
with copper; e, epidot«; a, apophyllite. 



weighing several thousand kilograms. Mining is now confined to the con- 
^:;lomerate and amygdaloid beds. 

Genetically these deposits are best explicable by the assumption of a lateral 
secretion of the copper orea, which were originally finely distributed in the 
melaphyres. The only enigma is, why the re-secretion and concentration 
took the form of native copper. According to Pumpelly, and, later. Van 
Hise, the copper is reduced from solution by magnetite and iron oxide. 

The copper mines of Lake Superior for a long time took the lead in the 
copper production of the world. The Calumet & Hecla alone yielded 
565,000 tons of copper in 1867-1897, all the other works on Lake Superior 
from 1845-1897 about 440,000 tons. The mines have been carried to aston- 
iehing depths ; Ked Jacket shaft of Caltunet & Hecla has attained 1,460 m. 
(4,920 ft.). At the present day the "Lake Mines" occupy the second place 
in the world's production, being surpassed only by the mines in Montana. 



234 



THE NATURE OF ORE DEPOSITS. 



In 1903 the total production of the works on Lake Superior was 192,400,577 
pounds of copper, of which Calumet & HecU alone produced 76,630,145 
ponnds, or about 6 per cent^ of the world's entire supply of copper. 

Copper-bearing amygdaloid melaphyres also occur in the district of 
Dschida in the Trans-Baikal, carrying native copper associated with opal, 
chalcedony, caicite, epidote and prehnite. 

Native copper accompanied by native silver occurs' in diabase porphyries 
in the Mercedes mine, near Algodones, Chile. The eruptive rock shows 
propylitic alteration, and holds small amygdules of caicite, an undetermined 
green decomposition product, native copper and cuprite. Miiricke cites 







Fig. I53o.— The Franklin, Jr. (conglomerate) lode. (T, A. Rickari.) 

the Queensland deposits described by Daintree as analogous in character. 
The latter contain native copper and copper sulphides, with malachite, cai- 
cite and prehnite in amygdaloidal dolorites. Native copper is also found 
with zeolites in basalt in the Faroe Islands. 

An interesting occurrence of native copper in feldspathic segregations of 
the gabbro of Pari, in Tuscany, is described by Lotti.' 

The deposits at Zwickau, Saxony, seem to be genetically analogous, 
though not of economic importance, native copper occurring in quartz 
porphyry and porphyry tuff. These rocks form intercalations in the middle 
Kothliegende close to an underlying sheet of melaphyre. The copper is 

■W. Mnrieke: 'Die Gold. Silver und EupferlsRerBtatten in Chile.' Freiberg, 
Bftden, 1898, p. 33. 

' B. Lotti: Z«(. /. Pro*. GtoL, I8fl9, p. 3M. 



EPIOENETIC DEPOSITS. 235 

found in thin sheets (rarely as much as 3 m. thick^ up to 0.5 m. long and 
G.15 m. broad) which usually fill short fissures^ that rapidly wedge out on 
both sides; more rarely it is found in larger fissures which may be con- 
nected with fault planes. On both sides of the fissures, in zones 0.5 to 2 cm. 
wide, the dirty violet colored rock is leached and altered to yellowish white. 
This is supposedly due to reducing solutions. Spherical reduction spots 
are also found in the midst of the unfissured porphyry mass, and in the 
center of these spots native copper was also found at times in grains. Be- 
tides the native copper, A. Weisbach^ discovered domeykite (mohawkite) 
(CujAs) in the quartz porphyry. Especially rich masses of copper ore 
were found in sinking several coal mine shafts, showing a rather wide hori- 
zontal distribution and a close genetic relation to the above mentioned 
intrusive sheets, intercalated in the *Rothliegende.'* 

(8) Silver-Lead Veins. 

The veins of this type are characterized by silver-bearing galena and 
sphalerite, with high-grade silver ores in subordinate amount. Accordingly 
as the gangue is predominantly quartz, or carbonates, or barite, S. A. W. von 
Herder," in treating the veins of the Freiberg district alone, established 
three subdivisions, which he called formations and which are in the main 
quite sharply defined^ and are as follows : 

9. The pyritic lead quartz formation. 

10. The rich (high-grade) lead formation, also called brown spar formar 
tion or Brander formation, with carbonates. 

11. The barytic lead formation, also called heavy spar formation or Hals- 
briick formation, with barite as the principal matrix. 

These Freiberg vein-types have been found to exist with but little varia- 
tion in the mineral districts of all parts of the globe, so that they are really 
cf universal application. In using the terms originally chosen for the veins 
of Saxony, it is found that the term high-grade lead formation or brown 
spar formation proves to be too restricted, and it is changed to "carbon 
spar lead formation" (t. e,, carbonate gangue). The following detailed de- 
scriptions fully indicate the character of the various divisions. 

9. The Pyritic Lead Deposits. 

In the pyritic lead veins, quartz, galena, sphalerite, pyrite, arsenopyrite 
and chalcopyrite are most abundant. As accessory constituents of the 

*A. Weisbach: 'Arsen Kupfer von Zwickan.' Neues Jahrbuch /. JIf in., 1873, 
p. 64. H. Mietzsch: 'Erlaut z. S. Zwickau/ 1877, p. 36. 

» A. V. Gutbier: Brief comment in Neues Jahrbuch f, Min,, 1843, pp. 460-461. 

•S. A. W. von Herder : 'Der tiefe Meissner Erbstolln/ 1838, p. 17. 



236 THE NATURE OF ORE DEPOSITS. 

gangne, we have homstone^ jasper^ ferruginous quartz, calcspar, siderite, 
more rarely brown spar and chlorite. As rarities^ and occurring, as a rule, 
only in the vicinity of intersecting veins of a different nature, fluorspar, 
barite, nacrite, tetrahedrite and its argentiferous variety, silver glance, 
native silver, black silver ore, arsenical sulphide of silver and other high- 
grade silver ores are found. Witherite and smithsonite, too, are among 
the very rare occurrences in this formation. 

The most important of these minerals to the miner is galena. In the 
Freiberg area it contains 0.1 to 0.2% of silver; elsewhere the percentage 
of silver is somewhat higher, but rarely more than 0.5%. Pyrite and arseno- 
pyrite as a rule are very poor in silver, containing for the most i)art only 
0.005 to 0.02% of it, rarely as high as .05%. The Freiberg sphalerite, 
always blackish, contains up to 0.03% silver and usually some tin, as noted 
by A. W. Stelzner and A. SeherteP, owing to mechanically intergrown tin- 
stone microliths. 

The vein filling has a prevailingly massive structure, in which the ore 
minerals occur either commingled or in separate compact masses. More 
rarely the ingredients are arranged in bands. 

One of the most important occurrences of this formation is found at Frei- 
berg. 

This mining field is a part of a gently undulating plateau, dissected by 
the moderately deep valleys of the Mulde and its tributaries. This plateau 
forms the gentle basal slope of the Erzgebirge, which rises to the northwest, 
while to the southeast a rather steep scarp forms the descent into northern 
Bohemia. The region of Freiberg, 400 to 450 m. (1,312 to 1,476 ft.) above 
tide, lies on the northwest side of the range, which trends southwest-north- 
east. This part of the range has a relatively much greater altitude than 
that lying to the southeast of the chain, which along the scarp just men- 
tioned has been downthrown along a fault zone, commonly called the 
Bohemian thermal fissure. Biotite gneisses, with some subordinate inter- 
calations of mica schist, form the countrv rock of the veins. These rocks at 
Freiberg are only approximately parallel in strike to the trend of the moun- 
tains, as they form a great dome or anticlinal uplift, the center of which 
coincides approximately with that of the city. The summit of this dome of 
Freiberg gneiss is cut by the ore-bearing fissures. 

A great stock of granite breaks up through this dome, not in the center, 
but to the east of it, at Bobritsch-Naundorf. The eruptive dikes occurring 
in the field consist of mica diorite, a fine-grained mica syenite and quartz 
porphyry. These rocks, especially the last named, are all cut by the min- 

* A. W. Stelzner and A. Schertel: 'TTeber den Zinngehalt und uber die chemische 
Zusanimensetzung der Schwarzen Zinkblende von Freiberg,' Freiberg, 1886. 



EPIOENETIC DEPOSITS. 237 

eral veins. The porphyry dike of Muldener Hiitton plays an especially 
prominent role in the mines. It may be traced with slight interruptions 
to a distance of about 20 km. (12 miles) from Frauenstein as far as the 
Nonnenwald^ with strike north-northwest and thickness not exceeding 10 
m. (33 ft.). The quartz porphyries cut through the high-grade silver 
quartz veins, but are themselves cut by the pyritic, barytic and rarely 
also by the high-grade lead lodes. The unfavorable influence of the quartz 
porphyry on the development of the vein fissures of the pyritic lead veins 
})as already been referred to. 

The mineral veins of the Freiberg district belong for the most part to this 
class of pyritic lead deposits; to a lesser extent to the high-grade silver 
and to the barytic lead types. In the northern, western and southeastern 
part of the district high-grade silver quartz veins are also found. As shown 
by their relation to the above mentioned eruptive dikes, these types of lodes 
are not of the same age. The high-grade silver quartz veins are the oldest; 
the barytic lead formation is the youngest. They also show some diflference 
in strike. In general the Freiberg veins strike in two principal directions : 
(1) North-south to northeast, mostly north-northeast; these are the lodes 
of the pyritic and of part of the high-grade lead formation, as well as most 
of the representatives of the high-grade silver quartz formation; (2) north- 
west to west-northwest ; to this group belong the barytic and another part 
of the high-grade lead ore lodes, as well as many barren lodes. The lodes 
of the first group are for the most part called ^stehende' (strike south- 
southwest to north-northeast), in part also ^flache' (strike north-north- 
west to south-southeast) and ^morgengange* (strike west-southwest to east- 
northeast) ; those of the second group are called ^Spatgange' (west-north- 
west to east-southeast), in part also ^flache* (north-northwest to south- 
southeast. (See page 121.) 

The lead veins belonging to the category just mentioned are at the pres- 
ent time worked in the Himmelfahrt mine, owned by the State and situated 
close to the city, also in the Himmelfiirst mine, also owned by the State, 
situated at Erbisdorf, near Brand, and, until recently, other veins were also 
worked in the Mord mine division of the Vereinigt Feld mine, near Brand, 
and in Junge Hohe Birke, between Freiberg and Brand, and still earlier 
in a very large number of other smaller mines. The veins for the most part 
have a thickness of only 0.1 to 0.8 m. (0.3 to 2.6 ft.), rarely over 2 m. 
(6.5 ft.). On the map of the Freiberg veins, accompanying the present 
work, the names of the most important representatives of this formation 
are given. Some of them have been found workable to considerable hori- 
zontal and vertical distances; for example, Kirschbaum or Hohe Birke 
Stehende to a distance of about 7 km. (4.2 miles) and a depth of 650 m. 



JB88 THE NATURE OF ORE DEPOSITS. 

(2,134 ft) and the Selig Trost Stehende to a distance of 2.2 Ian. (1.3 
miles) and a depth of more than 500 m. (1,640 ft.). ' 

The pyritic lead veins were probably the first to be discovered in the Frei- 
berg field, their gossan being very rich in secondary silver ores and especially 
in native silver. This discovery must have taken place about 1162 to 1170* 
and was followed by an immigration of miners from Ooslar and other points 
of lower Saxony, who built the "Sachsstadt,^^ the oldest part of Freiberg, 
which under that name was founded by Margrave Otto den Reichen, of 
Meissen, being subsequently fortified and further developed. In 1218 Frei- 
berg is named for the first time in a document. The first mines mentioned 
in the documents, the Gottesgabe, Schone Maria and Heiliger Gregorius, 
were probably located on the "HauptstoUngang'^ (main adit lode). After 
many vicissitudes, the silver mining industry of Freiberg attained a great 
period of prosperity between 1795 and 1870, during which time the produc- 
tion reached 45,000,000 to 60,000,000 oz. of silver a year. Somewhat 
earlier, on Easter, 1766, the Royal Mining Academy of Freiberg had been 
opened, and in 1776 the Royal Mining School. Despite great improve- 
ment in methods, the mining industry of Freiberg has, by reason of the 
depreciation of silver, ceased to be remunerative, and although the ore pro- 
duction and the output of silver and lead are still very considerable, and 
the works employ a large number of people, the Government has decided 
to gradually close down the mines. In 1901 the ore production in the 
Freiberg mining district was as follows: 11,563 tons silver ores, 6,195 tons 
arsenious, iron and copper pyrite, 28 tons of zinc-blende, 409 tons of barite. 
The output of silver was 17,573 kg., that of lead 2,090 tons. For every 
square meter of lode surface worked, there were produced 0.3 kg. silver and 
87.73 kg. lead. 

From the beginning of mining up to the year 1896, according to H. 
MQlIer, the total production was 5,242,957 kg. silver, worth about $227,- 
000,000.* 

Pyritic lead veins also occur elsewhere in Saxony, especially at 
Schneeberg and Annaberg. At Schneeberg, particularly at Kuttengrund 

* H. Ermisch: 'Das Sachsische Bergrecht/ Leipzig, 1887, p. xvi. 

* The following is a list of some of the more important publications upon the Freibere 
veins: J. F. W. von Charpentier: 'Mineralog. Geographie der chursachsischen Lande," 
1778. H. MuUer: 'Die Erzlagerstatten nftrdlich und nordwestlich von Freiberg,' 
Cotta's 'Gangstudien, ' 1847, Vol. I, pp. 101-305. W. Vogelsang: ' Die Erzlagerat&tten 
sfidlich und sadOstlich bei Freiberg. ' Cotta's 'Gangstudien, ' 1848, Vol. II, pp. 19-133. 
H. Muller and B. R. FOrater: 'Gangstudien aus dem Freiberger Revier.' With two 
plates. Freiberg, 1869. H. Muller: 'Die Freiberger Erzlagerstatten in Freiberg's 

Berg und Huttenwesen, ' 1883, pp. 28-84. 'Gangkarte der Freiberger Bergrevier.' H. 
Muller: 'Ueber die Erzgange des Freiberger Bergre\'ieres. ' A monograph accompany- 
ing the special geologic niap of Saxony, 1901. (A comprehensive work, in course of 
publication.) 



EPIOENETIC DEPOSITS. 239 

near Lossnitz, a peculiar variety of this type of deposit occurs^ in which 
galena is subordinate to arsenical pyrite. The lodes produced 118 tons of 
arsenopyrite in 1898. At Annaberg this class exists in an aberrant formy 
sinoe the deposits contain a predominance of copper ores^ and cassiterite 
appears. Similar transitions to the copper formations were mentioned 
previously. 

In this place one should also mention the many parallel veins which, 
according to E. Haber^, traverse the Devonian shales of Ramsbeck, in the 
mining district of Brilon in Westphalia, the veins in the clay slate south- 
east of Trier in the Bischofsheim mine and those of the Aggerthal north 
of Siegburg, in the Rhenish Schiefergebirge. 

Other veins which are not quite typical, since they differ from the 
examples just noted by the constant presence of siderite in the vein filling, 
are found in the mining district of Diez and Wiesbaden, on the lower Lahn, 
in Nassau.^ Transitions Vfo the class of carbonate-bearing lead deposits are 
also found there. Wenckenbach* divided the lead lodes of Nassau into 
seven reefs, of which the veins at Ems and Holzappel are the most im- 
portant. 

The vein system of Ems comprises all the veins occurring between Dem- 
bach and Braubach. The most important are the Mercur vein at Ems and 
the Friedrichssegen at Oberlahnstein. It would be more accurate to desig- 
nate these veins as a vein-group, since, in spite of their close association, . 
they differ in strike and dip. They all occur cutting Lower Devonian clay 
felate, impure sandstone and quartzite belonging to the Upper Coblenz 
formation, whose beds strike northwest. The strike of the lodes lies between 
north-northwest and east-west. The predominant gangue mineral is a firm 
massive quartz, often cementing fragments of slate, while calcspar and 
brown spar occur sparingly. In the upper part of the veins siderite has 
altered to brown hematite, but in depth siderite is always present. The ores 
consist of argentiferous galena, with sphalerite, together with copper and 
iron pyrite. In the oxidized zone of the vein, white, green and brown lead 
ores occur frequently, together with occasional plumbo-rcsinite, native silver 
and copper, cuprite, chalcocite, azurite, malachite, lead sulphate and 
cuprous anglesite; at greater depths, gray copper, cobalt pyrite, nickel- 
arsenic-glance and boumonite, with other antimonial lead ores, are present. 
The structure of the veins is partly massive, partly banded. The thick- 

' E. Haber : 'Der Blei-und Zinkbergbau bei Ramsbeck/ Z. f. d. B. H. S. u. S. im 
preuss. St., 1894, Vol. XLII, p. 77. 

* Oberbergamtliche Beschreibung 'der Bergreviere Wiesbaden und Dies,' Bonn, 
1893, pp. 91-116. 

' Wenckenbach : 'Beschr. der im Herzogthum Nassau, eto., aufaetzenden £rz- 
gange.' Wiesbaden, 1861. 



240 THE NATURE OF ORE DEPOSITS. 

ness may be as much as 10 m. (33 ft.)^ and^ in an exceptional case in the 
Friedrichssegen mine^ as high as 20 m. (65 ft.) 

As early as 1158^ Emperor Frederick I. (Barbarossa) conferred on Arch- 
bishop Hillin of Treves the right to mine silver near Ems. Subsequently 
the Ems mining industry is said to have been flourishing in the 14th and 
15th centuries. New enterprises began in 1743. Since 1791 the mines 
of Ems have been uninterruptedly in the possession of a company now 
called Emser Blei- und Silberwerk zu Ems, and have been continuously 
worked to the present time. The largest production of lead ores in the 
mining district of Diez^ to which the Ems lodes belong, was reached in 
1878-1880, with 22,539 to 24,611 tons per year. 

The great Holzappel lode may be traced, according to Bauer,^ from 
Holzappel on the Lahn, across the Obemhof, to the west of Singhofeny 
across Dahlheim, Ehrenthal, Werku and Norath as far as Peterswalde, a 
distance of '50 km. (30 miles). In recent years the ore shoots in this lode 
at the Gute Hoflfnimg mine, near Werlau, described by L. Souheur,* have 
attracted much attention. Here the clay slates, sandy slates and seii- 
cite schists belonging to the lower Coblenz stage of the lower Devonian 
ere traversed by a main lode with a parallel hanging- wall vein 10 m. (33 ft.) 
from it, both veins striking east-northeast, with a dip of from 50 to 90** 
southeast. The thickness is from 0.3 to 4 m., averaging 1 m. The fissure 
filling consists of quartz, sphalerite, galena and chalcopyrite, with frag- 
ments of country rock, and subordinate amoimts of siderite and pyrite. 
The lode cuts the strata at an acute angle. The adjoining schists, as well 
as a parallel diabase dike in the overlying strata, are partly sericitized and 
are then called *white rock^ (weisses (Jebirge). The lode is dislocated on 
its dip by flat dipping overthrust faults (so-called Deckelkliifte). Mention 
may also be made here of a similar vein at the Altgliick mine, near Uck- 
crath, not far from Sieg. 

The structural relations of similar pyritic lead veins to eruptive dikes 
traversing Silurian shale is especially noteworthy in the Katzbach region of 
lower Silesia, and at Eisenberg, near Altenberg. According to Bosenberg- 
Lipinsky,* the veins accompany steep dipping dikes of olivine ker- 
santite (olivine-mica-diorite) in such way that the kersantite either 
forms the middle of the lodes or is confined to one side. Dike-like intru- 
sions of quartz porphyry also occur, and run at times parallel and close 

* Bauer: 'Die Silber, Blei und Kupfererzganpje von Holzappel an der Lahn, 
Wellmich und Werlau am Rhein.' Karsten's Arckw f. Berpb., etc., Vol. XV, 1841 ! 

' L. Souheur: 'Die Laperstatte der Zink, Blei und Kupfererzgrube Gute Hoff- 
nung bei Werlau am Rhein,' Jahrb. d. k. preuss. geol. Landesanst, 1892, p. 96. 

• V. Roaenberg-Lipinsky: 'Beitrage zur Kenntniss des Altenberger Erzbergbaues/ 
Jahrb, d. k. preuss. geol. Landesanst, 1894, pp. 161-182. With list of previous works 
on the district. 



EPIGENETIC DEPOSITS. 241 

to the ore-baring fissures. The fissure filling of the mineralized veins 
consists of clay, fragments of shale and olivine kersantite, arsenious- 
copper pyrite (arsen-kupfer-schwefelkies), galena, tetrahedrite and 
rarely of zinc-blende, antimonite, boulangerite, epiboulangerite and bour- 
nonite, as well as quartz. Of the ores just named, arsenopyrite is by 
far the most abundant, constituting about 40 to 50% of the ore. The cop- 
per pyrite is gold-bearing. This gold content and the richness in arseno- 
pyrite, as well as the presence of gray copper, establishes a close relation- 
ship between these lodes and those of Hohenstein in Saxony, whose more 
highly copper-bearing variety was described previously. The Altenberg 
mining industry, which is said to have been flourishing in the thirteenth 
century, was forgotten for a long time and again resumed lately. 

As a typical example in Austria, the old and famous lodes of Kut- 
tenberg* in Bohemia may be noted. The region consists of gneisses, in 
part overlain by Cretaceous strata. The gneiss is traversed by a great 
number of veins which may be grouped into 18 series, with uniform north- 
south strike and steep dip east or west. The filling is of quartz, homstone, 
fragments of the country rock, calcite, ankerite, pyrite, zinc-blende, argen- 
tiferous galena and arsenopyrite, with rare native silver, zincite, boulanger- 
ite, proustite, siderite, cronstedtite and lillite. The district is 6.5 km. 
(3.9 m.) long and 4.5 km. (2.7 m.) broad. The mining industry dates back 
to the beginning of the thirteenth century, flourished in the fourteenth 
century, and its revival was recently attempted. 

The lodes in the pre-Cambrian clay slate at Mies,* Bohemia, which are 
distinguished by uncommonly large druse cavities, form a transition to the 
barytic lead deposits by reason of the presence of a little barite. 

Among Hungarian deposits, the Schemnitz lodes belong to or are closely 
related to the pyritic lead veins. As they are, however, rich in gold and 
silver, they will be included in that class of veins instead of the one 
treated here. 

In Spain veins of pjrritic lead ores are of considerable importance, espe- 
cially at Linares in the province of Jaen, in the eastern part of the Sierra 
Morena; at L'Horcajo in the province of Ciudad Real, and at Castuera in 
the District of Badajoz. 

The mining field of Linares is, according to Caron,* about 12 km. 
(7.2 m.) long and 9 km. (5.4 m.) broad, lying north of the town on an arid 
plateau and rocky hilly country south of the Sierra Morena proper. The 

' F. Katzer: 'Der Kuttenberger Erzdistrict, ' Oesterr. Z. f. B, u, H., 1896, p. 247 
et seq. 

' F Posepny: 'Der Bergbaudistrict von Mies,' Vienna. 1874. 

* Caron: 'Bericht iiber eine Instruktionsreise nach Spanien im Jahre 1878.' Z, f. 
d. B H. u. S. im preuss. St., 1880, Vol. XXVIII, p. 119. 



^42 THE NATURE OF ORE DEPOSITS. 

whole rcgioir consists of granite, which on the south and west is overlain by 
clays, sandstones and conglomerates of uncertain age while at the 
north it adjoins the Silurian shales, forming the high mountains. The 
veins are in the granite, only few of them continuing into the shales. 
Their strike is in the main northeast and their dip is quite steep. In 
general they are relatively thick, reaching eight meters in La Cruz lode. 
The veins are often quite long, exceeding 1 km., while the Alamillos lode is 
6 km. (3.6 m.), and La Cruz and Arrayanes veins 4 km. (2.4 m.) long. 
The veins are exceedingly rich, as gangue and country rock form but a 
small amount of the fissure filling. The total thickness of a lode is often 
filled with the galena, not very rich in silver it is true, but mingled with 
very little blende and a small amount of pyrite. The gangue is mostly 
quartz, with small amounts of calcspar, dolomite, barite and siderite. Cop- 
per ores occurred in the outcrop. The average silver content of the ores 
is stated to be 180 gm. (5.3 oz.) silver per ton. The Arrayanes mine, be- 
longing to the State, and La Fortuna, belonging to an English Company, 
are the principal mines. The ancient Phoenicians, Carthaginians and 
Romans had mines in this region. The old shafts situated north of Linares, 
on the Cerro de Val de Infierno, are called to this day "Pozos de Anibal" 
(HannibaFs wells). The most brilliant period of recent mining in that 
district was about 1889, when the production of lead in the province of 
Jaen rose to 188,325 tons. 

Deposits of this class also occur in France. A great vein which occurs 
in the Silurian shale of Pontp6an, in the vicinity of Rennes, and the lodes 
of Huelgoat and PouUaouen (Finistire) in granite and in the adjoining 
Paleozoic shales are the most noteworthy. The two last named localities 
were formerly the most important lead mines of France, but they are now 
abandoned.^ 

The main vein of La Touche mine, in the neighborhood of Rennes,* 
is of considerable geologic interest and deserves a brief description. The 
lode occurs in granite and has been traced for about two km. (1.2 m.) ; 
some of its orebodies have been opened up to a depth of more than 100 m. 
Its strike is north-south, its dip 70** east. It is a very characteristic double 
vein. In all parts of its known extent a gray breccia-like quartz, barren 
of ore and 5-10 meters thick, forms the lower and larger streak of the vein. 
In the hanging-wall of this, but only about certain ore-shoots, the true ore- 
bearing branch vein is developed. The ore consists of argentiferous galena, 
argentiferous zinc-blende and pyrite with quartz, chalcedony and horn- 

* Fuchs and De Launay: 'Gftes Mineraux/ 11, p. 498-509. 

' According to a brief communication of W. Frhr. von Fircks, and specimens in 
the Freiberg museum. 



EPIOENETIC DEPOSITS. 248 

stone as gangue minerals. The structure is either banded or brecciated. A 
peculiarly mottled ore, occurring in the vein, consists of sharp angled 
splinters of the quartzose lower stringer, which are coated with several 
layers of chalcedony and cemented by zinc-blende and. homstone. Parts 
of the country rock are not infrequently found enclosed. The granite in 
the hanging-wall is decomposed to a distance of 1.5 meters and impreg- 
nated with finely divided ore; in the immediate vicinity of the lode itself, 
the granite has frequently been altered into a clay. Away from the 
ore-shoots, the upper streak of the vein narrows from a thickness of 1-2 
meters down to a thin homstone layer. 

Examples of this class, very rich in silver, occur, according to Vogt, in 
Svenningdalen district of northern Norway.* 

In the United States examples of this class occur at Bingham,* Utah, 
the veins consisting of quartz and galena, together with pyrite, chalco- 
pyrite and blende, with a gossan which was rich in silver. This class also 
includes the veins of the Clear Creek district in Colorado. 

10. Veins of Spathic Lead Ore. 

In this class the gangue consists essentially of the carbonates, calcspar, 
brownspar, rhodochrosite, siderite and quartz. The ore minerals are ar- 
gentiferous galena, argentiferous sphalerite, and, less often, P3nrite, mar- 
casite, tetrahedrite, both with and without silver, together with high-grade 
silver ores, especially ruby silver and argentite. The structure is usually 
imperfect and but seldom well banded. The ore minerals frequently 
occur sprinkled through the gangue. 

In the Freiberg district proper, this class of veins is especially developed 
in the Himmelsfiirst and Bescheert Gliick mines near Brand (see page 
245), where they exist as high-grade lead ores or the brownspar forma- 
tion. The high-grade ^noble* veins of that locality are, according to H. 
Miiller,' distinguished by their composition, consisting of brownspar and 
rhodochrosite, galena, sphalerite, argentiferous and ordinary tetrahedrite, 
antimony-silver blende, silver glance and native silver. The sub- 
ordinate minerals are quartz, homstone, calcspar, siderite, pyrite, 
arsenopyrite and copper pyrite, stephanite and polybasite; nickeliferous 
pyrrhotite, native arsenic, pitchblende (Uranpecherz), etc., are rarely ob- 
served. 

* J. H. L. Vog:t: 'Sfindre Hel^reland,' Norges Geol. UnderaOg., No. 29, Christiania, 
1900, and Zeit. /. Prak. GeoL, 1902, pp. 1-8. 

» J. M. Boutwell: ' Ore Deposits of Bingham, Utah,' Bull. 213, U. S. Geol. Survey, 
1902, pp. 105-122, also 'Economic Geology of the Bingham District, Utah,' by Bout- 
well, Keith and Emmons, Professional paper No. 38, U. S. Geol. Survey, 1905. 

' 'Litteraturangaben/ p. 249. 



244 



THE NATURE OF ORE DEPOSITS. 



The galena contaiue between 0.4 and 0.6%, and in some cases as hi{^ 
as 2% silver. A very characteristic feature ie the so-called glazed bl^ide, 
a dork zinc-blende with microscopic inclusions of silv^ glance (Qlasen) 
and possibly other high-grade silver ores, having a silver cootcut of ae 




;, gray decomposed ^eiss; gi, gneisa impregnated with pyrit« and ropper pyrite; 
aleapar and browiuipar; m, rhodoehroBite ; e, argentiferous blende ana some gray 



high as 1.5%. Even the pyrit« in this formation often contains as high 
as 0.2% silver. When a banded structure is developed in these lodes, zinc- 
blende and galena, together with rhodochrosite and brownspar, are usually 
found concentrated immediately along the selvages, while in the middle 



EPIGENETIC DEPOSITS. 8tf 

calcBpar, and at times quartz predominates. Fig. 1S4 shows the manner 
of development of these veins, whose thickness usually amounts to 0.08-0.76 
meters, rarely over 1.5 meters. 

The reproduction of a thin section. Fig. 155, gives an idea of the man- 
ner of microscopic intergrowth between the gangue and ore minerals. 

Most of tlie lodes of this kind, including the most important examples in 
tlie Freiberg district, have a low strike (11.4 to 12.4 hours) (see page 130), 
with flat dip of 40 to 60* west. According to H. Uiiller, another important 
parallel reef follows the main direction Dorth-northeaat to northeast and 




Fig. 156.— Thin section of ore of the Silberfund St. auf HimmebfQnt. 
(Magnified 50 diametera.) 
Shows the inner core of zinc-blende (b), with argentite and gray copper (a), i 
calcite and browDspar (c), as weU as quarts (d). 



dips steeply 70 to 90' southeast or northwest, as illustrated by the Dorothea 
and the Silberfund veins of the Himmelafiirst mine, the Neugliickstem, 
and the Johannes and David veins of Bescheert Gliick. A peculiar 
development is shown by the Habacht stringers in the Bescheert Qliick and 
£inigkeit mines. They strike northeast and dip northwest at no more 
than 15° to 40'. They are narrow veins, consisting mainly of rhodochrodta 
and quartz, argentiferous gray copper and argentiferous galena. In the 
aggregate 350 of these high-grade lead lodes are known. They have 
been opened up over a distance of 600-1,000 m. (1,968-3,880 ft), 
while s few like the Neue Eohe Birke Stehende are worked for a distance 



*46 TBE SATVBE OF ORE DEPOSITS. 

<A 2 km. (1.2 miles.) A somewfaat abnonna] diancter ia shown by tiieTem 
of tbe Gate Oottes mine st Sdurfenberg near lieiasen, discovered in 1225 
and worked anew from 1867 to 1898. According to H. Zinkei4en, tbe vein 




fig. 166. — Qeneral sketch of the lode ayatem of the Upper Hars. 
- I, Devonian; 2, culm; 3, ochre Rranite; 4, wchstein foot-hills; 5. Jura-Trias and 
1-ower Cretaceous; 6, Upper Cretaceous and younger formations of the foot-hiUe; 7 
veiiis;8, Ruscheln. 

fissures occur in the granite-eyenit* massive of Meissen. They contain 
quartz, hrownspar, rhodochrosite, celestite an<i galena, with an avera^ 
silver content of about O.SO to 0.30%, and a yellow bltaide almost as rich 



EPIGENETIO DEPOSITS. 247 

in silver, together with gray copper having as high as S% silver.* The veins 
also include great masses of vein clay and granitic friction debris. The 
accessory constituents include strontianite, barite, gypsum, pyrite, copper 
pyrite, very rarely also glass ore (earthy argentite), ruby silver and native 
silver. 

The stringers and veins form a zone of 2 km. (1.2 m.) long, and 600 m. 
(1,968 ft.) wide, and striking northeast. The thickness of the veins, about 
50 of which are known, varies from a few centimeters in the small string- 
ers to 2 meters in the Heinrich Morgengang. All the veins show a pro- 
pensity to fray out in stringers, and to take an irregular course. They are 
often dislocated by transverse faults, and by the so-called "Schwebenden,'* 
which are horizontal, or nearly horizontal, narrow clay fissures or move- 
ment planes, only rarely carrying ore. The filling of the veins and stringers 
is usually massive. Quartz and brownspar, intimately mingled, contain 
the ores in scattered particles. More rarely the metallic minerals are found 
in compact, coarsely crystalline bodies of nearly pure ote, which in such 
cases are crossed in ell directions by veins of homstone. A banded struc- 
ture occasionally appears, ordinarily with streaks of blende along the two 
selvages and with a central often breccia-like part, consisting essentially 
of brownspar and rhodochrosite. 



The Clausthal Veins. 

In the Harz, the famous lodes of the Clausthal area are, for the most 
part, closely related to the carbonspar-lead formation. According to F. 
Klockmann,' the Clausthal district (see general map Fig. 156) com- 
prises an area 18 km. (10.8 mi.) long and 8 km. (4.8 mi.) broad, part of 
the North German plateau in the region of Clausthal, Grund, Wildemann, 
Bockswiese and Schulenberg. This plateau, whose elevation is 550-600 m. 
(1,804-1,968 ft.) above sea level, rising in the Schalke to a height of 764 m. 
(2,506 ft.) forms a part of the northwestern upper Harz range, which drops 
down northward and westward with steep scarps to the foot-hills. To the 
southeast the plateau is bounded by the Bruchberg range, to the north by 
the mountain wall of the Bocksberg and the Kahleberg. The entire area 
is formed of the nucleal rocks of the Harz ; that is, of Devonian and Lower 
Carboniferous beds, especially the Culm, whose lower division consists of 
clay shales and silicious shales, while the upper division is mainly gray- 

* H. Zinkeisen: ' TJeber die ErzRanfre von Gute Gottes zu Scharfenberg. ' Frei- 
berger Jahrb., 1890, pp. 40-64. Gives also the older literature of H. Miiller. 

' F. Klockmann: 'Die Erzlagerstatten des Oberharzes im Werke Berg und Hiit- 
tenwesen des Oberharzes,' 1895, pp. 43-65. -. .. . 



248 THE NATURE OF ORE DEPOSITS. 

wacke. Lying unconformably upon the upraised edges of these Paleozoic 
rocks, close to the west edge of the mountains, are the strata of the Zeehstein 
formation. The Devonian and Cuhn strata have been squeezed together 
into northeast folds with associated overturns and overthrusts, with many 
true fault fissures. Overthrust zones also occur as the so-called Ruscheln, 
lode-like formations, filled with strongly folded or crushed and mashed 
country rock, called Gangthonschiefer (vein clay slate). In the vicinity 
of Clausthal, the well-known Faule Ruschel, with nearly east-west strike, 
crosses the main Burgstadt series and the so-called Charlotte lode. Many 
veins are true fault fissures, as shown by A. von Groddeck,* and, still earlier, 
by Schmidt. Other fault lodes at Bockswiese displace the Devonian by 
about 200 m. (656 ft.), as determined by the dislocation of the Culm 
beds (Fig. 94). 

The vein system of Clausthal consists of several series of veins, often con- 
vergent and which frequently fray out. The following may be distinguished 
from north southward: 

• 

1. The Gegenthal- Wittenberg series. 

2. The Lautenthal-Hahnenkleer series. 

3. The Bockswieser-Festenburg-Schulenberg series. 

4. The Hiitschenthal-Spiegelthal series. 

5. The Haus Herzberg series. 

6. The Zellerf eld main series. 

7. The Burgst&dt series. 

8. The Rosenh5fer series. 

9. The Silbemaaler series. 
10. The Laubhiitte series. 

The length of each series along the strike is considerable. The Schulen- 
berg series has been traced for a distance of 10 km. (6 m.) ; the Gegen- 
thal-Wittenberg series is probably much larger. Without exception, they 
all have a strike of from southwest to west, and dip, almost without ex- 
ception, south at 70 to 80**. 

They consist wholly of compound lodes, mostly with a distinct footwall 
selvage, but passing into the hanging-wall country rock by a gradually di- 
minishing succession of stringers. They are, therefore, not solid fissure 
fillings, but zones of stringers or zones of sheeting which may be as much 
as 40 m. (131 ft.) across. A good idea of this stringer formation is afford- 
ed by Fig. 157, after Zirkler.* 

* A. V. Groddeck : 'Ueber die Erzfc&n^ des Oberharzes.* Zettschr. d. Deutsch ^eol, 
Ges.f 1866, pp. 693-776. Also, 'Geoenostischen Durchschnitten durch den Oberhars ' 
Z, f. d. B. H. u. S. im preuss. St., 1873, pp. 1-14. 

» Zirkler: 'Essener Gluckauf,' 1897, Vol. XXXIH, p. 73. 



EPIQENETIC DEPOSITS, 



249 



The Boeenhofer Beriea of veins scatters in passing into Qie Kuscbeln, 
while in the Zellerfeld and Burgstadter series some veins are deflected, while 
others pass through with unaltered course. 

As has been noted, all the veins are probably fault Sssnres, though this 
is hard to prove in the case of the lodes occurring in the monotonously simi- 
lar beds of the Culm. 

The vein filling consists of ore, gangue minerals and fragments of coun- 




^ ore-canying; t, barren vriuB. The dark places have been worked 01 



try rock. The predominant ore is argentiferous (0.0 — 0.3%) galena, with 
associated zinc-blende, which predominates at Lautenthal, with subordinate 
copper pjrite, pyrite and mareasite, and rarely tetrahedrite and boumonite. 
AinoDg the matrices, quartz and calcspar are predominant, except in the 
Silbemaaler and Rosenhiifer vein series, which are rich in barite; siderite, 
pearl spar and strontianite also occur. The rock fragments consist of hard 
Randy slate in angular fragments or of crushed clay slate. The inclusions 
often far exceed the ore in bulk. In many cases we find an irregularly 



260 THE NATURE OF ORE DEPOSITS. 

massive lode structure, and not infrequently 'ring ore' is developed, espe- 
cially in the lodes of the Bing and Silberschnur mine at Zellerfeld (see 
Rg. 135-137). 

According to A. Lengemann, the silver-lead mining industry began in 
the Clausthal district about 1220, was abandoned in 1350, but resumed in 
1526. In this second period it was at first concentrated aroimd the newly 
founded mining town of Zellerfeld. Clausthal did not obtain a mining 
grant until 1554. The greater part of the mining population of the upper 
Harz came from the upper Erzgebirge in the 16th century. In 1811 the 
mining academy of Clausthal was founded, a one-year course for prospective 
miners having been introduced in the Clausthal lyceum as early as 1775. 

The mines on the Clausthal plateau (Clausthal, Lautenthal and Grund) 
produced, in 1898, 196,985 tons of crude ore. 

The lodes oi Neudorf-Harzgerode, in the eastern Harz of Anhalt, de- 
part even further than those of Clausthal from the typical high-grade 
(noble) lead deposits.^ At Neudorf-Harzgerode the plateau of upper Silu- 
rian slate is traversed by several vein systems very nearly parallel to 
one another, among which the Dillenberg lode, with the mines of Pfaf- 
fenberg and Mcisenberg, is the most important. This double vein consists 
of a true lead vein and another of spathic iron ore. The two are either 
directly in contact or are separated only by a narrow layer of rock. The ore 
vein, which is often split up into stringers, consists of siderite, quartz, calc- 
spar, fluorspar, galena, zinc-blende, gray copper, pyrite, copper pyrite, bour- 
nonite, sometimes with the addition of hubnerite, scheelite and wolframite. 
The silver lead ores of the Neudorf mine contained, towards the end of the 
seventies, on an average 40% lead and 0.061% silver. The spathic iron ore 
appears now above, now below, and may attain a thickness up to 4 m. 
(13 ft.). An abundance of fluorspar and the occasional presence of other 
minerals, characteristic of tin deposits, distinguishes the Neudorf lodes 
from the normal type of 'rich' lead veins. 

A good Austrian example of this type occurs at Pribram, in Central 
Bohemia. 

The Pribram lode area proper lies in a mountainous region 600-550 m. 
(1,640-1,804 ft.) above sea level. The prevailing rock is a quartzitic grit 
(greywacke), which, though it has not yet yielded any fossils, is probably 
Cambrian. In some beds it becomes conglomeratic; in the vicinity qt the 
Lill shaft intercalations of oolitic limestone occur, as indicated by blocks 

* Heinr. Credner: 'Uebersicht der ficeogn. Verb. Thurinpens und des Harzes,' 
1843, p. 123. Kegel: 'Beitrap zur Kenntniss der Neudorf-Harzgeroder Gange,' 
Berg. u. Hutten Zeii., 1877, pp. 397-400. C. Bldmeke: 'TTeber die Erzlageretatten d. 
Harzes/ Vienna, 1885, p. 85. H. Fischer: 'Gutachtenuber die Anhaltinischen Blei- 
und Silberwerke/ 1804. 



EPIOENETIC DEPOSITS. 



scattered thereabouts. The strata fonn a trough, as indicated m the sec- 
tion after J. Schmid, Fig. 158 To the southeast below this trough, clay 




slates, probably of Cambrian age, are traversed bj granite and altered by 
contact metamorphism. The homfels immediately adjoining the contact 



MS 



TBE NATURE OF ORE DEPOSITS. 



fa crossed in all directions by fine-grained granite apophyses. The exact 
relation between the grits and the shales does not appear to have been 
quite made out. In the section an uncomformity between these two rocks 



ADALBERT 






PROKOPSCHACHT. | 


[PHT 


n 


i 


A 






'™w^ 


Br" 


« 


^ «7aaff 

1. to. „ 


.ziijj^M 


mw 


i[ 


pSVS ,^^^. 


III 


t^OE^\\\\ 


vfflQ 


ss 


».......„,Ay\\ 

33..... Aji 








M.,.. \\\v 




4r..-.....i\.U| 
w........Y.\i| 




s 


1 


.._...M 






\ 






„, \V{|fdf^ 


KAl 





Pig. 169, — Section through Ad&lbert and Prokop thaftB. (J. Schmid.) 



EPIOENETIC DEPOSITS. 253 

is assumed. At the northwest edge of the greywacke. trough the stratifi- 
cation has been interrupted by a fault, dipping steeply northwest, and filled 
with a clayey mass or with highly decomposed material, folded in a most 
complicated manner, the so-called Lettenkluft (clay fault), most probably 
an overthrust f ault, along which the greywacke beds abut sharply against a 
second slate zone. The minute folding of the adjoining slate is indi- 
cated in the section. Quartzitic grajrwackes recur further northwest. 

Where the ore veins occur, at Bohutin and Birkenberg, the trough of 
(Cambrian grits is traversed by numerous greenstone dikes, often swelling 
into stock-like forms 1 to 30 m. (3 to 98 ft) thick. The rocks are mostly 
diabases, rarely diorites. These dikes of igneous rocks are followed by 
the lodes, the mineral veins either clinging to the selvages or running 
through the middle of the dike and parallel to its contact. The section. 
Fig. 159, based on surveys by J. Schmid, as well as the ground plan 
in Fig. 160, by the same author, gives a clear representation of this 
close connection between the veins and the greenstone dikes. Besides the 
eruptive masses thus far named, a quartz diorite mass encountered in the 
mining operations west of the Stephan shaft at Bohutin is noteworthy be- 
cause the mineral veins in passing from the sandy slate into this quartz 
diorite lose the lead and silver ores and carry antimony ores instead. This 
eruptive stock is surrounded by a contact zone. 

The most important and richest of the Pribram lodes occur in a narrow 
belt, 4 km. (2.4 miles) long, running southwest and northeast along the 
Lettenkluft (clay fissure). Where the lodes, issuing from the grit, run 
into the clay fissure, and up against the greatly folded clay slate, they 
contract decidedly and become almost barren, or they split up into several 
insignificant stringers, which are often found to be deflected eastward. 
Some of them indeed have been followed bevond the ^av fissure' into the 
slates, but there they turned out to be much poorer than in the grit, and as 
a rule carried only spathic iron ore, brownspar and calcspar, as well as 
some blende. In the granite area, mineral veins are also known, both iron- 
and lead-bearing ones, as, for example, at Milin and Vrancice, but they 
are not of economic importance. 

Within the graywacke, the veins have, as a rule, the following character : 
Down to a remarkable depth, usually 60 m. (196 ft.) in the Segen Gottes 
shaft southwest of Pribram, in the Liegend lode, and in the Nordwest 
lode even to 270 m. (885 ft.), the ore is altered to a gossan, consisting of 
broMm iron ore, cerussite, pyromorphite, malachite, native silver and sec- 
ondary silica as chalcedony. At greater depths the veins assume the 
character of su\phide lead veins, mostly of the character of the spathic lead 
formation. The veins, according to J. Schmid, consist, in the richer por- 



THE NATVRS Of OHM DEPOSITS. 




EPIQENETIC DEPOSITS, 



265 



tione, mainly of compact argentiferous galena, zinc-blende, eiderite, qnartz 
and calcBpar, in the barren portions of only iron spar and calcspar 

The silver content of the galena varies between 0.1 and 0.7%, and it was 
not possible to ascertain whether there was a decrease in the content with 
increaee in depth. The zinc-blende is generally, though but feebly, argen- 
tiferous (0.04 — 0.06%). Higher percentages are rare. Besides the minerals 
just named, fragments of the country rock also occur frequently in the 
midst of the vein filling. The structure of the latter is sometimes massiTe, 
banded or with stringers of ore. The illustration of the lode in 




Fig. 161 .—The Adalbert mniQ veto at Pribram. (J. Zadraiil, reproduced by J. Schmid.) 
G,graywacke; D.diorite;q,quaTtE;c,calGspar;g, galena; b, lioc-blende. 



Fig. 161, taken from the official report on Pribram, shows the Adalbert main 
lode, and illustrates a type which is of common occurrence there. 

In the Anna mine and elsewhere, eepecially in the deep workings, an- 
other kind of lode filling often occurs, called there Diirrerz (dry ore) ; 
approaching the character of the high-grade quartz formation of the Frei- 
berg area. A matrix rich in quartz, but poor in carbonates, carries, besides 
silver-bearing galena, ruby silver ore, native silver, stephanite, gray copper 
ore and stihnite, mostly in diseeminat«d grains. 

The filling of the fissure often consists of several bands quite sharply 
divided from one another, a galena band, one or two bands of dry ore and 



266 THE NATURE OF ORE DEPOSITS. 

a younger one of calcspar. The diy ores steadily increase in amount with 
increasing depth. 

The thickness of the Pribram veins varies^ according to J. Schmid^ 
from nothing up to 8 m. (26 ft.). The most important veins are the main 
Adalbert vein^ the Abendseitsfallende (westward dipping) Liegend vein, 
the northwest vein, the Adalbert Liegend vein, the Fundgruben vein, the 
Eusebi vein and the Widersinnige (contrary) vein. 

The silver mining industry of Pribram is stated to date back to 843. 
In recent time the production has vastly increased. In 1898 it amounted 
to 263,979 tons of crude ore. From this were obtained 20,882 tons of pure 
ore, with 38,599 kilograms of silver and 4,826.1 tons lead. The ore de- 
livered at the furnace contained on an average 0.185% silver and 23.10% 
lead. The work has been carried to extraordinary depths, in the Adalbert' 
shaft to 1,099 m. (3,606 feet).^ 

Another undoubted example of this type of deposit occurs in the Aus- 
trian Alps, at Metnitz and Zweinitz, in Carinthia.* 

The silver lead deposits of Mazarr6n, in the Spanish province of Murcia, 
which were mined by the ancient Romans, have become notorious by their 
dangerous eruptions of carbon dioxide. The basal rocks consist of mica- 
ceous and talcose slates, passing into argillaceous, chloritic and amphibole 
schists, and of crystalline limestones. These are covered by Tertiary strata, 
which are cut by rhyolite stocks. The north-south mineral veins which 
cut these stocks at the Cabeza de San Cristobal are thus proved to be of very 
recent age. As the veins pass into the slate they quickly wedge out. One 
vein, Las Laguenas, clings close to the contact between the two rocks. The 
vein filling consists of disintegrated rhyolite, silver-bearing galena, blende, 
pyrite and siderite. At a depth of 400 to 500 meters the veins become 
impoverished. The horizontal length is also small, but the veins sometimes 
reach a thickness of 16 meters (52 feet). 

The outbursts of carbon dioxide always take place when slate is struck, 
and are accompanied by large outflows of warm water at 35' C. (95* F.) 
The rapid diffusion of the gas and the hurling of rock fragments by these 

* The most important publications inchide: W. Vogelsang: 'Die Pribramer Ers- 
niederlage. ' Cotta's Ganpstudien, I, 1850, pp. 305-329. John Grimm: ' Die Erznieder- 
lage von Pribram/ 1855; and several later essays by the same author. Babanek: *Zur 
Kenntniss der Pribramer Erz^ance.' Oeaterr. Z. i. B. u. H., 1878. J. Schmid: 'Bilder 
von den Erzlanrerst^tten zu Pribram.' I\iblishea by the Imperial Royal Ministry of 
A^rulture, 1887, with atlas. Contains a biblioeraphy of the subject. F. Poeepny: 
'Beitrag zur Kenntn'ss der montanTeolog. Verhaltnisse von Pribram. ' Archiv f. Frak.' 
Geol., II, Freiberg, 1895, pp. 609-745. 

* R. Canaval : ' Die Blende und Bleielanz fuhrenden Gange bei Metnitz und Zweinits 
in Kamthen.' Carinthia, II, No. 4, 1899. D. F. Villasante v Gomez: 'La industria de 
Mazarr6n,' 1892. 'Sur les filons de Mazarr6n,' Revista Min., No. 1393-1396, 1902. 
D. F. Iznardi u. a. Revista Min., 1902, No. 1873. 



EPIOENETIC DEPOSITS. 257 

outbursts caused repeated accidents. An eruption of gas in the Triumfo 
mine at a depth of 440 m. (1,443 ft.) produced 200 cubic meters of debris 
and filled the levels with the gas^ 

As an American example of the carbonspar lead ore formation we will 
mention the Enterprise mine at Rico, in southwestern Colorado. Accord- 
ing to T. A. Rickard,* the gently dipping Lower Carboniferous slates, lime- 
stones, and sandstones of this locality are traversed by two systems of veins. 
One set has a northeast course and very steep dip; the other strikes north- 
south, and has a low dip. The fissures of the former are ore-bearing; those 
of tlie latter are of importance only as 'cross veins^ enriching the others, 
being themselves merely lean quartz veins, much too poor to pay for working. 
The ore-veins cannot be followed up beyond a definite horizon, the so-called 
'contact.' This contact is between high fissured limestone, overlain by 
solid but warped shales. Within the 'contact zone' lateral infiltration 
from the tops of the veins has produced rich deposits of banded ore. Fol- 
lowed downward the mineral veins continue, but their character changes. 
At 30 to 45 m. (98 to 147 ft.) below the 'contact zone' the ore and rhodo- 
chrosite disappear and the veins below this depth contain only barren quartz 
and crushed country rock. All the veins are fault filbures, with but slight 
throw and a thickness rarely exceeding a foot. (0.3 m.) Their physical 
development depends greatly on the nature of the country rock. In the 
sandstone the veins are formed by a single fissure; in the limestone the 
fracture splits up into a number of stringers. The filling consists of rho- 
dochrosite and quartz, with galena, zinc-blende, pyrite, copper pyrite, argen- 
tite and stephanite. They often show a remarkably well banded structure 
in which the quartz crusts show comb structure. At one point the veins 
change from their normal development, as silver veins with carbonate 
gangue, and occasionally carry native gold, besides native silver. Thus 
their example represents a transition of the carbonspathic lead ore forma- 
tion to the silver-gold ore formation. 

The ore of the Rico district was discovered as early as 1864, but it was 
only in 1881 that an active and remunerative mining industry began to 
develop, at the Enterprise, Rico and Aspen mines. 

This class also includes the silver-lead veins occurring in the quartzites 
of the Coeur J'Alene Mountains in Idaho, whose main gangue is siderite 
(see later). 

As an extreme member of the carbonspathic lead type of vein we have 
the two pure zinc-blende veins, with calcspar and some homstone as 
gangue, which occur in the granite at Merklin, southwest of Pilsen in 

' T. A. Rickard: 'The Enterprise Mine, Rico, Colorado,' Trans, of the Am. Inst. 
Min. Eng., XXVI, 1897, p. 906 et 9eq. 



268 THE NATURE OF ORE DEPOSITS. 

Bohemia. According to E. Biiger they strike northwest, and belong structu- 
rally to the lead vein system of Mies. The southwestern vein especially has 
been extensively mined, though work has recently been suspended. The lode 
matter contained many angular fragments of decomposed granite embedded 
in it, and also in places lenticular masses of impure graphite lying acroBS 
the strike. When the vein was narrow the mineral filling consisted of 
nothing but zinc-blende ; when of greater thickness the filling was calcspar, 
with blende, in which case the country rock also was found to be impr^- 
nated with blende. In the upper portions smithsonite and calamine were 
found. A very remarkable phenomenon is the fact that the zinc-blende 
veins on passing into the pre-Cambrain ( ?) clay slate ontJiin more and 
more galena, until this mineral finally predominates. Merklin was founded 
in 1842. The annual production sometimes amounted to 2,000 tons of 
zinc-blende ores, with a zinc content of about 52%. 

11. Barytic Lead Veins. 

In this class of veins the gangue consists of predominant barite with 
fluorspar and quartz* or jasper besides calcspar. These minerals are 
generally intergrown in a remarkably thin-banded structure. The barite 
especially occurs in finely crystalline crusts (calc-barite), the fluorspar in 
diverse tints, but mainly green and yellow. The ore minerals, which either 
form thin crusts or appear sprinkled through the gangue, consist of ar- 
gentiferous galena, often developed in large flakes, pyrite and marcasite, 
also zinc-blende, copper pyrite, gray copper and at times rich silver ores. 

In the Freiberg mining district (see page 238), the most prominent 
representatives of this formation are found in the region of nalsbriicke, 
where the Halsbriicke Spat and the Drei Prinzen Spat called for special men- 
tion. These lodes all strike northwest, and ordinarily dip steeply northeast. 
At Halsbriicke itself they traverse biotite gneiss; farther north they cut 
through mica schist and granulite. The main veins are distinguished by 
their thickness, usually 1 to 4 m. (3 to 13 ft.), at times up to G m. (19 ft.). 
They are the youngest of the Freiberg veins, often traversing and dislocating 
both the pyritic and the high-grade lead veins. On the Halsbriicke Spat, 
according to H. Miiller 'T)esides the normal, so-called soft band, carrying 
lead ore poor in silver, there is also a so-called hard band, consisting es- 
sentially of crystalline and jaspery quartz with thinly laminated barite, 
fluorspar, argentiferous tetrahedrite, galena, carrying 0.02-0.08% of silver, 
antimonial silver blende and arsenical silver blende, boumonite and copper 
P3rrite. The two main bands of the lode diverge toward the northwest in 
the mining field of Kurprinz Friedrich August ErbstoUn near Oross- 



BPIQENETIC DEPOSITS. 269 

schirma, and are there worked as separate veins, the soft one taider the name 
of Drei Prinzen Spat (see Fig. 130), the hard vein undet the name of 
Ludwig Spat." 

Aside from the main representatives just named, the barytie lead veins 
of the Freiberg area proper are not particularly rich. They show a peculiar 
behavior at points where they cross older veins, especially the P3rritic lead 
veins. At these crossings they carry rich silver ores, 'edler (Jeschicke,' 
including especially argentite, ruby silver, acanthite, polybadite, stephanite, 
native silver and tetrahedrite, ordinarily in a carbonate gangue. In rare 
cases the veins also carry nickel and cobalt ores. Such rich intersections 
were especially productive in the Himmelfahrt mine directly outside the 
town, especially at the crossing of the Neu Hoffnung Flache, the Ludwig 
Flache and Ludwig Spat, the Abraham Spat and the Friedrich Spat, with 
the pyritic lead lodes. One square meter of vein surface sometimes 
contained rich silver ores having a value of several thousand marks^ 

A very typical development of barytie lead ore was also observed in the 
Tobias Flache, Hilfe Gottes Morgengang and Friedrich Flache, at the 
Segen Gottes Erbstolln at Gersdorf, near Eosswein, in Saxony. In these 
lodes, the crustified or laminated structure was found to be developed in 
wonderful perfection. Magnificent druses of fluorspar were often found, 
those of dark wine-yellow color being found in all large collections. This 
mine, which had good orebodies as late as the fifties, is at present idle. 

Another Saxon district showing barytie lead veins is the zone 2-3 km. 
(1.2-1.8 miles) ^wide between Uie towns of Mittweida* and Oederar.. 
a distance of about 24 km. (14.4 miles). They are mostly Spat and 
Flache lodes (see page 132), which here have imited into a series. As late 
as the eighties mining continued in this region, being formerly quite exten- 
sive, on the right bank of the Zschopau, in the Alte Hoflfnung Erbstolln, 
near Schonborn. The vein series traverses a body of schists intercalated 
among the granulites (gneiss, mica schist, biotite gneiss, cordierite gneiss, 
amphibole schist, alum slate, clay slate and quartzite slate), to a small 
extent also granulite and granite. The main lode, the Clementine Spat, 
strikes on an average north 60^ west and dips northeast at 60-80\ Its 
thickness varies ordinarily between 1.5 and 2.6 m. (6-8 ft.), but in excep- 
tional cases rises to 7 m. (22 ft.), where side stringers unite with the main 
vein. Quartz, fluorspar, barite and calcspar, with galena, pyrite, copper 
pyrite and gray copper, besides fragments of the country rock, form the 
main filling of the vein, the structure being unusually massive, but some- 
times stratiform. The galena occurs in two varieties : coarse-foliated with 

' H. Muller: 'Die ErzlagerstAtten der Sectionen Mittweida, Frankenberj; und 
Schellenberg/ Leipzig, 1881, in ErlauL z. Sect. FraiJcenberg-Hainichen, pp. 84-120. 



260 THE NATURE OF ORE DEPOSITS. 

0.02-0.03% silver and fine-foliated (feinspeisig) with 0.05-0.10% silver. 
The high content of the latter is attributed to finely intermingled gray 
copper. The mining industry of Schonborn may be traced back to the 
twelfth century (Ermisch). In 1847 it was resumed, but has again been 
abandoned for a decade. 

This mineral zone also includes the veins of Hilfe (}ottes near Mem- 
mendorf, in the vicinity of Oederan, a typical specimen of which was 
shown in Fig. 129. 

There are also transitions from the barytic lead veins to the barren barite 
veins, which are worked at several points in the Erzgebirge of Saxony, for 
example, near Aue. 

As further German examples, we mention the lodes in the Miinsterthale. 
in the southern Black Forest, described by A. Schmidt*, especially the 
Shindler lode and the Teufelsgrund lode, as noted long ago by B. von 
Cotta*. Some lodes of the Kinzig valley, near Shapbach, also belong to 
this class. 

On the Iberian peninsula this barytic lead t3rpe is found in the lode dis- 
trict of Hien de la Encina, in the Sierra de Guadalajara, between Madrid 
and Zaragoza, in a high mountain country built up of mica schist and 
gneiss. The gangue consists of barite, quartz and siderite. Among the 
ores, silver glance and other high-grade silver ores predominate to such 
extent that the habit of the deposit approaches that of the high-grade silver 
ore lodes'. 

The same transitions to the high-grade silver ore formations are exhib- 
ited by the very rich bar}'tic lead veins in the mining region of Sarrabus, in 
the southwest part of the island of Sardinia*. The region is composed of 
Lower Silurian slates, abutting on the south against a granite mass, 
which has altered them by contact metamorphism. The lodes, which for 
the most part strike east and west, and traverse these schists, are for the 
most part developed as double veins. One may distinguish in them an older 
band, consisting of finely crystalline barite, some calcspar, quartz and 
coarsely foliated galena, poor in silver, associated with a little blende. The 
younger part of the lode forms a band of reddish, foliated barite, calcspar 
and fluorspar, with galena and blende both highly argentiferous, with 

' A. Srhmidt: 'Geologic des Muntserthales/ part II. 'Erzgange und Bergbau,' 
Heidelberg, ISSn. 

' B. V. Cotta: *ErzIagerstatten.' Vol. II, p. 177. 

> B. V. Cotta: 'Erzl»c:erstatten,' Vol. II, p. 443. Fuchs and De Laiinay: 'Traits des 
Gltes Min^raux,' Vol. II. p. 778. 

*Traver8o: *Giacimenti a mineral d'argento del Sarralnis,' .Inn. Mus. Civico, 
Genova, 1880-81, Vol. XVI, p. 403. De Castro: 'Desrriptione et carta gf^oloTica 
de la zona argentifera del Sarrabus,* 1890. Fuchs and De Launav: 'Trait^,' 1893, 
II, pp. 769-776. 



EPIQENETIG DEPOSITS. 261 

brightly glistening fracture surfaces, together with native silver, horn 
silver, argentite, stephanite, pyrargyrite and proustite. Pyrite^ marcasite^ 
arsenopyrite, copper pyrite, molybdenite, as well as cobalt and nickel ores, 
appear merely as accessories. The lodes were first mined in 1622, but an 
active industry has existed only since 1870, and yielded rich returns in the 
seventies. 

(«) HIgh-Qrade or Noble (Bdle) Silver Veins. 

The lead veins connect by gradual transitions with those of the high- 
grade silver veins, in which the rich silver minerals, which in the first- 
named class were oily occasionally present, decidedly predominate and 
impari; to the veins their distinguishing character. It is possible to intro- 
duce some order into the chaos of phenomena, if the deposits are grouped 
according to their natural mode of occurrences. If, however, one follows 
the method adopted for other groups of veins, basing the division solely 
on the predominant matrix, we should be obliged to separate veins that 
belong together. We will therefore adopt a combined method, even though 
it is not consistent. Two groups, both of which are characterized by rich 
silver ores, will be distinguished by the prevailing gangue. Two other 
groups we will distinguish by the abundant presence of ores of a certain 
other kind, laying less stress on the matrix, because it is not always uni- 
formly developed. 

On this basis we may distinguish : 

A. Veins with rich silver ores only, grouped as: 

1. Those with quartz as predominant matrix, the rich quartz 
formation : 

2. Those with calcspar as predominant matrix, the rich calcspar 
formation; 

B. Veins with silver ores and other characteristic ores, grouped as: 

1. Those in which many copper ores enter, with barite as the pre- 
dominant gangue mineral, but frequently also with quartz and earthy 
carbonates; the high-grade silver-copper veins, 

2. Those in which many cobalt ores, together with nickel-bismuth 
ores and uranium ores, are present, with quartz or carbonates form- 
ing the gangue ; the high-grade silver cobalt veins. 

Another group, the silver-gold veins, might have been added. It ap- 
peared, however, that the most prominent character of these veins is marked 
by the presence of gold, not silver, especially from an economic point of 
view. Hence, the silver-gold veins are not included here, but described 
with the gold veins proper. From what has been said it is apparent that 
the various types of rich silver veins admit of no sharp delimitation, 



262 THE NATURE OF ORE DEPOSITS. 

their frequent tranaitions to other very diverse types causing the distinction 
to become at times very faint. This will appear still more decidedly 
in the detailed presentation. In characterizing the different groups^ advan- 
tage may also be taken of their geologic age. 

12. High Grade Silver Quartz Veins. 

These veins consist of ordinary white or gray quartz or homstone^ fre- 
quently showing a brecciated structure^ with fragments of the country rock 
or of an older quartzose filling held together by later quartz. The ore 
minerals occur sprinkled through this matrix, in rather fine particles 
rarely united into bunches, nests, streaks or stringers. They are chiefly 
rich silver sulphides, such as silver glance^ ruby silver, native silver, etc., 
but include argentiferous arsenopyrite and iron pyrite, more rarely argentif- 
erous zinc-blende &nd galena. The mixture of ores ordinarily contains also 
a slight percentage of gold. Some departures from this prevailing char- 
acter and some rarer ingredients will be enumerated and discussed in the 
several examples that follow. 

The silver quartz veins of Freiberg in Saxony are first noted. According 
to H. Miiller*, the high-grade quartz veins are especially numerous to the 
north and west of the town, in the region of the upper gneiss (a micro- 
granular biotite gneiss), and of the mica schist. The veins are grouped in 
an important series in a belt about 9 km. (5.4 miles) wide that extends from 
the region of the lower Muld valley between Hohentanne and Zella, 
near Nossen, in a southwest direction, for a distance of 22 km. (13.2 miles) 
across Braunsdorf and Oberschona, to the region of Oederan. The veins 
strike mostly between north-northeast and east-northeast and dip north- 
west. Their thickness varies between 0.1 and 1 m. (0.3-3 ft.) Some of 
them have been opened up to a distance of 2,600 m. (8,528 ft.) and for a 
depth of 460 m. f 1,508 ft.) The general characterization given above 
applies with the following additions: Alongside of the principal quartzose 
matrix there are occasionally found subordinate amoimts of ankerite, 
calcite and rhodochrosite. Besides the ores already mentioned, there are 
also found both ordinary and silver-rich tetrahedrite, miargyrite, 
stephanite, polybasite, freieslebenite, xanthocone, hydrostilpnite (3 AgjS, 
SbaSg), alabandite, copper-pyrite, marcasite, capillary pyrite, stibnite, ber-* 
thierite, kermesite, bournonite, zinkenite, jamesonite, etc. Arsenopjrrite 
sometimes contains as much as 0.3% silver, iron pyrite up to 0.5 or 
even 1.2%, galena and zinc-blende usually still more. The zinc- 
blende is dark and "vitrified,** that is to say, coated with films of argentitc 



EPIOENETIC DEPOSITS. 263 

or intinuktely oveTgrown with graatiles of argentit^ giving it its hi^ siWer 
content. The pyritic and aotimoDial oree contain 0.5-8 g. per ton in gold. 
The ore minerals rarely form large compact bodies, being on the contrary 
for the most part in the form of fine dust-like particles Bcattered through 
the quaxtz. The ailvei minerftla occur nt&inly as emidl parasitic 
crystals in small druses. The exceedingly iLne distribution of the silver 
minerals in the qnartzoee matrix is eihihited in the reproduction of a thin 
section shown in Fig. 162, vhich is also of interest for the information it 
gives as regards the mode of treatment necessary for such ores. The lode 
structure is massive or breccia-like. 

The most important veins of this series, and the ones most l^pical of the 




FifE. 162, — Thin section of gray quorti of Freiberg Bilver quarts veins, with fine pM- 
ticlee of aiventite and other high-grade silver minerals. (Enlarged 50 timeaO 
(Outlines of quarti grains as shown in polarized light.) 

formation, but no longer worked, are the lodes of the so-called 'Schwarze 
Qebirge' (black rock) of Braunsdorf, a very irregular block of carbonaceous 
rock, resembling alum shale lying in the midst of the mica schist. Hence 
J. C. Freiesleben called the entire formation "the Braunsdorf formation." 
In the black rock, according to H. Miiller', the vast Neue Hoffnung Gottea 
Stehende vein, the main lode, from 300 m. (984 ft.) downward, becomes 
broken up into a series of smaller veins, such as the Verlorae HofEnung 
Stehende, the Felix Morgengang, Aaron Morgengang, Jupiter Morgen- 
gang, Zweifler Stehenden, Augustus Spat, etc. All these veins, from 5 cm. 

' H. M-Qller: 'Enlagenttatten nOrdlich und nordwestlich bei Freiberg,' in B. 
V. Cotta's 'Ganiwludieii,' Vol. I, p. 174. 



264 THE NATURE OF ORE DEPOSITS. 

to 2 m. (0.1-6.5 ft.) thick, break up again into innumerable stringers. 
This whole network of stringers extends from northeast to southwest 
through the black rock^ but only in rare cases does it send short branches 
into the adjoining mica schist. The most important ores of the Braunsdorf 
lodes were what was there called 'Weisserz' (white ore)^ that is to say, a 
highly argentiferous arsenopyrite, ruby silver, miargyrite, native silver, 
stibnite, kermesite and berthierite. Beside the predominant quartz matrix, 
rhodochrosite, brownspar and calcspar appeared as accessories, in rare 
cases also fluorspar, barite^ etc. 

Somewhat farther to the southeast are the old mines of Oberschona, on- 
of which, the Zenith, was in operation as late as 1879-1893. Here, too, the 
typical high-grade silver quartz veins were mined. 

The Braunsdorf lodes are similar to the Peter Stehende vein of the 
Christbescherung mine near Grossvoigtsberg, which is still mined. Men- 
tion should also be made of the veins of Emanuel Erbstolln near Nieder- 
Beinsberg, Bomanus Erbstolln and Vereinigt Feld near Siebenldin, the last 
of which is still mined in a small way. 

At the Gesegnete Bergmanns Hoflfnung mine near Obergruna, which has 
recently been abandoned, all the veins, but more especially the Helmrich 
Spat and the Traugott Spat (see Pig. 126), are examples showing a 
slight variation from the type of the high-grade silver quartz veins. The 
ores are especially rich in argentiferous blende (^vitrified' blende, that is, 
coated with films of vitreous or earthy argentite) and galena, with pyrite, 
and also argentiferous arsenopyrite, which as 'coarse ore' are associated, 
even in the richer leads, with the %igh-grade ores' constituting the silver 
ores proper. 

The lodes of the neighboring and still flourishing mine of Alte Hofibnng 
Qottes, near Klein- Voigtsberg, especially the rich main veins, the Peter 
Stehende and the Christliche Hilfe Stehende, are also not strictly rich 
silver quartz veins, but transition veins to the rich brownspar formation. 
Besides quartz, they carry much rhodochrosite, brownspar and calcspar, 
and besides the rich silver ores, much coarse matrix occurs. This mine is 
the only one of the veins of the Freiberg district proper which, thanks to 
its rich ore shoots, continues to pay working to the present day, despite the 
depreciation of silver. 

Somewhat farther off from Freiberg one finds the tjrpical rich quartz vein 
of the Friedrich August mine near Reichenau in the neighborhood of Fran- 
enstein, which was in operation as late as the middle of the seventies. This, 
and the Emanuel Erbstolln near Drehfeld, were the mines which revealed 
the fact, 80 important in determining the age of the veins, that the rich 
quartz lodes are traversed by the Permian quartz porphyries. 



EPIOBNETIC DEPOSITS. 266 

Eich silver quartz veins also occur in the granulite (gneiss) formation of 
Rosswein, especially in the fibrous-uralite gabbro of Oersdorf and 
Wolfsthal^ and again in the gneiss area near the Orossdorfhain and Hock- 
endorf near Tharandt (Unverhofft Gliick and Edle Krone mines), near 
Eeichstadt and Ammelsdorf, in the vicinity of Dippoldiswalde, at all of 
which mining has ceased. 

Eich silver quartz veins were also worked in former times in the neigh- 
boring regions of Bohemia, as at Nicklasberg and Klostergrab in the 
Bohemian Erzgebirge, at Adamstadt and Eudolstadt, northeast of Budweis. 

Among the veins of the Kinzig valley in the Black Forest, this type is 
represented by those of the Morgen series.^ 

Numerous examples of rich silver quartz veins occurring in countries 
outside of Europe differ from the original Erzgebirge type in being of much 
younger age. 

Where silver veins are associated with andesites and other Tertiary erup- 
tive masses, as at Pachuca and Eeal del Monte, and where the ores contain 
gold even in small amounts, it is difficult to draw a distinction between 
veins of this class and those of the rich silver-gold ore formation. 

Among the many known occurrences of this class those of Mexico prob- 
ably claim the first rank. Most of the silver veins of that country* belong 
by their mineral composition to this division of the system into which we 
have grouped ore deposits. With few exceptions the predominant matrix 
of the Mexican veins is a crj'stalline quartz, often violet-colored, ac- 
companied by subordinate quantities of calcite and rhodonite. In the zone 
of unaltered primary ores, they consist essentially of ruby silver ore, both 
proustite and pyrargyrite, accompanied at increasing depths by more and 
more gray copper, and finally also zinc-blende and pyrite, so that the rich- 
ness slowly decreases. As regards the alteration products, there has been 
developed, directly above the primary ore, first a zone with simple silver 
sulphides, which usually contained the richest bonanzas, above this a second 
zone rich in chlorine-, bromine- and iodine-compounds of silver, and finally 
the gossan with native silver predominating, but usually of moderate rich- 
ness (see gossan). These silver ore' lodes traverse very diverse rocks. 
The famous Veta Madre of Guanajuato,' Mexico,* is probably the richest 

* Vogelgesang : 'Geogrt.-bergm. Beschr. des Kinzigthaler Bergbaues/ Carlsnihe, 
1865, p. 9. 

' Fuchs and De Launay: 'Traits des Gftes Min^raux,' 1893, pp. 811-829. 

* Visited in 1903 by W. H. W., who supplies description. 

* 'Carta Minera de la Republica Mexicana por Antonio del Castillo/ 1893, Mexico. 
See also 'The Mineral Deposits of Mexico,' by Apuilera. Trantt. Am. Inst. Min. Eni?., 
Mexican Volume, 1903. C. Henrich: Mining Magazine^ New York, 1904, Vol. VI, 
No. 1, p. 83. 



266 TEE NATURE OF ORE DEPOSITS. 

gilver-gold vein of the entire worlds the production of the district^ mainly 
from this one vein, reaching the enormous total of nearly $1,000,000,000. 
I%e vein occupies a well defined fault on the west slopes of a range of steep 
and barren mountains, composed mainly of well bedded volcanic tuffs with 
a capping of dacitic rocks and intrusive dikes of rhyolite. The andesitic 
tuffs, called sandstones by all earlier writers, are of varying colors and 
textures, mostly well bedded, but showing conclusive evidence in both field 
relations and in thin section under the microscope, of their origin by ejec- 
tion, but in part sorted by water. These beds of andesitic tuffs rest upon 
micaceous schists and slaites, cut by a mass of intrusive diorite, which 
altered the shale about it. The Veta Madre cuts through these earlier rocks, 
and at the south end through the tuffs, but so far as known does not cut 
the outflows and dikes of dacitic lava. The vein varies from a few feet to 50 
feet across, widening in places to 120 feet. The ores occur in well defined 
shoots, the greatest — that of the Valenciana mine — ^being 1,400 feet long, 
40 to 60 feet thick, and workea to a depth of 2,100 feet on the dip, or 1,750 
feet vertical. The vein strikes northwest, and dips west with the mountain 
slopes at 46**. The vein filling between and alongside of the ore shoots 
consists of crushed and much altered countrv rock. The ore consists of 
quartz with orthoclase (var. valencianite) dusted and stained with minute 
specks of rich silver sulphide and rarely with pyrite. Galena is a rarity. 
The neighboring La Luz vein carries druses with remarkable cr}'stals of 
apophyllite. The ores have averaged about 50 oz. silver for 350 years, but 
the rich oxidized and secondary sulphide orebodies run much higher. The 
ore shoots occur at and just beyond the intersection of the hanging-wall 
veins, coming in from the west, or La Luz system. At such points the vein 
is enormously thickened and the bonanzas occur. Earlier writers locate the 
richest ores at the points where the vein is crossed by ravines, and it is 
possible that secondary enrichment may have been particularly active at 
such places. The vein has a generally obscure outcrop, but is to-day trace- 
able for seven miles by a very remarkable line of shafts and buildings. 

Mining began at Guanajuato in 1558, and has continued with some inter- 
ruptions ever since. Though in the last half century the production has 
come mainly from La Luz system, mining in the Veta Madre area has 
lately been very successful. 

The lodes of Zacatecas and Fresnillo traverse similar conglomeratic 
porphyry tuffs, clay slates and calcareous shales, alternating with quartz- 
ites. At Catorce the veins occur in hornblende porphyrites. As these 
h(»iiblende porphyrites are intruded in white Jurassic limestones with 
Perisphinctes plicatUis, the post-Jurassic age of the lodes is there estab- 
lished beyond doubt. We will dwell in somewhat greater detail on the 



EPIOENETIC DEPOSITS. 267 

famous lodes of Pachuca and Heal del Monte^ situated north-northeast of 
the capital, abstracting from the official account published by the Geologi- 
cal Institute of Mexico.^ 

The mining area of Pachuca lies about 150 kilometers north-northeast of 
the City of Mexico in the region of the Sierra of the same name. Embrac- 
ing an area of about 20 square kilometers, it is the largest and at the same 
time the oldest mining district of the entire republic. The Sierra de 
Pachuca, whose main strike is northeast-southwest, extends over a length of 
43 km. and attains its greatest height in the northeastern part in the sum- 
mit of the Cerro de las Navajas, 3,212 m. (10,536 ft.) The mountain range 
is traversed by numerous valleys, but only on the east slope are there any 
rivers that carry water throughout the year; they belong to the drainage 
area of the Bio del Amayac, a tributary of the Montezuma. According to 
Aguilera and Ordonez, the Sierra de Pachuca owes its origin to a period 
of violent eruption, which apparently occurred in the middle Tertiary as a 
sequel to great dislocations. The latter led to the upraising of non-fossil- 
iferous sediments, probably belonging to the Cretaceous. The products of 
those eruptions were, in the order of their age, andesites with their tuflfs 
and breccias, rhyolites and their glassy forms, and, as last member, basalts. 
Dacites, too, were observed. The andesites, for the most part pyroxene 
andesites, sometimes diabasic in character, possess by far the greatest ex- 
tent, and are of special interest, because they form the most widely dis- 
tributed country rock of the lodes. 

The latter may be divided into four groups, each of which embraces a 
main lode and several lateral veins. They comprise the Vizcaina, Cristo 
and Analcos lodes and of those of the Santa Gertrudis region. The strike 
of all these lodes is east-west^ the dip, at a high angle, mostly south. The 
thickness, both in the strike and in depth, is subject to great change. Thus 
the Vizcaina lode at some points attains a thickness of 8 m., while that of 
the other parts of the lode varies between 0.3 and 6 m. 

The matrix is, in the main, quartz, often developed as chalcedony ; more 
rarely calcite, rhodonite and rhodochrosite occur. This explains why the 
outcrop of the lodes may often be traced far across the ground in the form 
of white crests. The lode structure is for the most part markedly banded, 
and only in isolated cases has a breccia structure been observed. A remark- 
able feature is a wide zone of decomposition along the selvages. The 
country rock, which often appears strongly silicified, has been found to be 
abundantly impregnated with pyrite at all depths. Part of it is also 
propylitized. 

* J. G. Apuilera and E. Ordoflez : 'Mineral de Pachuca/ 1897. E. Ordonez v M. 
Range! : 'El Real del Monte/ 1899. 



268 THE NATURE OF ORE DEPOSITS. 

According to the richness of the ore, three zones are distinguished from 
above downward: 

1. MelaUa ooloraA t (podridot) (red ore, rotten). 

9 Mrinl,. »«nu Chl(u-lf1 i f** Mefalet de pinto (spotted ore). 

2. Mdofc* napw (black) J ^^,j i^^i^ ^ j;,^ (g„ ore). 

In the first zone, that of the "colored or rotten ore," which owes ita name 
to the prevailing iron and mangauese oxides, silver chloride, bromide 




Elg. 162a. — C^ross-sertioD of veins at Paehuca, Mexico. 

and native silver are fonnd, sometimes also native gold. This zone is con- 
siderably richer in gold than those which follow. 

In the second zone (3a), fine-grained galena, argentite, pyrite and more 
rarely chalcopyrite occur. 

The lowest zone (3b) contains galena, zinc-blende, pyrite, stephanite 
and polybasite. Some native copper, too, was observed. These ores, which 
are found but very rarely in definite crystalline forme, occur intimately 




Fig. 1626. — Pachuca croes-sectioD, continued. 



intergrown with quartz. The presence of zinc-blonde is unfavorable and 
indicates early impoverishment. Analysis has shown that the pyrito is 
always argentiferous, the percentage rising to 0.05%. The galena, too, is 
argentiferous, though not to the same degree, while the blende is almost 
always free from silver. Here, as in most of the silver lodes of Mexico, the 
occurrence of rich shoots, the bonanzas, is of the greatest importance in 
mining. It is not known that their occurrence is subject to any law, but 
they certainly begin only at a depth of 150 m. and seem on the whole to be 
normal in their course to the strike of the lodes. The size of these 



EPIOENETIC DEPOSITS. 269 

bonanzas varies greatly; the greatest^ encountered in the San Rafael mine^ 
has a length of 1,000 meters. 

Mining at Paehuca extends back to the time when the Aztecs obtained 
the ore by the aid of fire and stone implements. Inmiediately after the con-» 
quest of Mexico, the Spaniards began to exploit these rich mines^ and, down 
to the eighteenth century, the Spanish Crown possessed the exclusive right 
of mining. The most famous mine at the banning of that period was 
Xacal, which produced $7,000 worth of ore a day. After the war of 
independence the mines were sold to English companies (1824). After 28 
years, however, these companies, burdened with debt, ceased operations, 
and the work was resumed only later and after the completion of railways, 
with Mexican capital. The production thereupon increased considerably, 
the San Rafael y Annexas company obtaining in eight years a gross retun^ 
of $12,500,000. 

Exactly similar conditions are found at Real del Monte, situated some- 
what farther northeast of Paehuca. Mining operations were begun in 
1578 and were formerly exceedingly remunerative. The work is mainly 
on three lodes: the Veta Vizcaina, 2 to 16 m. (6.5 to 48 ft.) thick, striking 
west-northwest and dipping south, extending over from Paehuca and 
opened up to a depth of 400 m. (1,312 ft.) ; the Veta Santa Inez, 40 m. 
(131 ft.) thick; and the Veta Santa Brigida, as much as 10 m. (32.3 ft.) 
thick, the two latter, striking north-south and dipping more or less steeply 
west and east, intersect the first named lode. All these veins have lenticular 
enlargements at close intervals, these ore shoots proving to be very rich in 
ore. These lenticular bonanzas coincide with those portions of the lode in 
which the dip is especially steep, almost perpendicular. 

In the lower or deeper zones, to which working is now confined, at depths 
of 300 to 400 m. (984 to 1,312 ft.), the vein filling consists of quartz, often 
brecciated, and frequently associated with rhodonite and to a subordi- 
nate extent with calcite. The ores consist mainly of pyrite, copper 
pyrite, galena, in part argentiferous, and zinc-blende, together with 
argentite, polybasite and native silver. Druses studded with crystals of 
quartz, calcite, manganocalcite and rhodochrosite are common. In the 
upper part of the veins, on the contrary, the rich silver ores, especially ruby 
silver, exceed the pyritous ores in amount. The outcrop consists of a 
gossan rich in manganite, pyrolusite and wad. 

Very commonly the country rock. is pyritized or transformed into clayey 
masses, lamas,' or impregnated with pyrites. 

The lodes of Real del Monte, too, are Tertiary beyond a doubt. The 
volcanic activity began in this region in the middle Miocene coincident 
with a strong folding of the Mesozoic strata, the earliest eruptive being 



wo TB£ NATURE OF ORE DEPOSITS. 

pyrozene-andesite. Next followed flows and dikes of rhyoUte^ in whose 
train the ore-bringing thermal waters rose. The next and last act of the 
Tokanic period was an eruption of basalt^ during which the vein fissures 
were in many cases fractured and displaced. 

The period of greatest prosperity of Real del Monte was in the last 
two decades of the 17th century. From 1687-1697, La Trinidad mine 
alone is said to have yielded 40 million pesos. As late as 1759-1771, the 
mines of Real del Monte yielded to the principal owner at that time, Don 
P. R. de Terreros, $6,126,000. When mining became confined to the 
pyritous zone, the profit quickly decreased. 

Prom what has just been said, it is doubtful whether Guanajuato, Pa- 
chuca and Real del Monte, with the other Mexican lodes mentioned, should 
be included in the rich silver quartz formation, since the ores contain from 
20 to 30% of their value in gold, and have carbonates in the matrix. On 
the other hand, the association with rhyolites and andesites, the propylitiza- 
tion of the country rock, the participation of rhodonite as matrix, and the 
occasional gold content, establish a close similarity with Schemnitz. But 
for that matter, Schemnitz, too, as we shall see, does not represent a pure 
type, but constitutes a transitional form between the rich quartz and the 
silver-gold vein-types. 

Another example of this class of veins occurs at Tonopah, Nevada, a dis- 
trict that has astonished the world by the richness of its bonanza ores. Ac- 
cording to Spurr, the district is one of Tertiary volcanics, or sedimentary 
Tolcanic tuflFs. The oldest rock is hornblende andesite, and still later rhyolite 
and dacite rocks occur, and the whole is cut into a complex system of blocks 
by faulting. The important veins of the region occur only in the early 
andesite, but four periods of hot-spring action and vein-formation are 
recognizable. The veins are linked veins, branching and reuniting both 
laterally and vertically. They are typical replacement veins formed along 
zones of fracturing. The primary ore consists of argentite, polybasite, and 
small amounts of chalcopjrrite, galena blende and pyrite, in a gangue of 
quartz and orthoclase (valencianite). The rich ores occur in roughly de- 
fined shoots, with west-east pitch. These veins, though rich, are so cut 
by faults of different systems as to cause great trouble in working. The 
Mizpah vein, for example, is not only cut off east, west, and at the bottom 
by faults of great magnitude, but is broken up by minor fractures. The 
veins in the riiyolo-dacite rocks are characterized by a lack of persistence 
and definition. Bunches of high-grade ore sometimes occur in these usually 
barren veins, but only near andesite masses. The Goldfield veins, 23^ 
miles south of Tonopah, are similar, showing irregularly branching out- 
crops of pipes of jaspery quartz, the jackets about pay shoots of very rich 



EPIGENETIC DEPOSITS. 271 

gold ores. In the past two years the district has produced ores to the 
value of $2,000,000. 

A very rich development of the formation occurs at some points in Peru, 
in particular in the lodes. of Quespesisa mine near Castrovirreyna in the 
department of Huancavelica, exploited during the last decades. The 
matrix there, according to the material furnished to the Freiberg 
collection by Mr. E. Treptow, is mainly a milk-white to glassy quartz, 
of distinctly crystalline, often drusy development, often colored dark gray 
by minute ore inclusions. This is found in association with subordinate 
amounts of a homstone-like material composed mainly of chalcedony, only 
rarely of barite. The ores consist of pyrargyrite, polybasite and other rich 
silver ores, together with galena, fine-grained zinc-blende, a little chalcopy- 
nte and pyrite. The rich portions contained on an average 2% of silver. 
The country rock is a strongly decomposed augite andesite. 

The famous lodes of the Cerro de Pasco, in the Peruvian province of the 
same name, known from d'Achiardi's and Fuchs and De Launa3r's descrip- 
tions* may also be included with the rich silver quartz lodes, despite some 
aberrant features. At this place profitable silver mining has been carried 
on ever since the end of the thirties of the 17th century, despite the alti- 
tude, 4,352 m. (14,278 ft.), and the inhospitable climate. As late as 1879, 
179 mines were in operation. The veins are of post- Jurassic age. The un- 
altered ores found in the deeper workings consist of highly argentiferous 
gray copper associated with galena in a gangue of quartz. In the upper 
zones, much p}Tite and argentiferous copper pyrite are found, and at the 
very top, in the gossan, the rich secondary ores were found, which are here 
called pacos or cascajos, and contain an average content of 500 gm. silver 
per ton. The primary pre contains much copper and the district will soon 
be one of the great copper producers of the world. 

Among the numerous silver veins of North America, those of Austin, 
Nevada, which, according to S. F. Emmons*, occur in granite, and consist 
of a series of quartz stringers with pyrargyrite, proustite, polybasite, 
stephanite and tetrahedrite, and associated galena and* blende, fit remark- 
ably well into this category. Rhodochrosite and calcite occur together 
with the predominant quartz of the gangue. Some veins have been 
worked for stibnite. This occurrence is, therefore, completely analogous to 
the typical Braunsdorf or rich silver quartz lodes of the Freiberg area. 

As an appendix to the discussion of the rich silver-quartz veins, mention 
may be made of a rare example, decidedly unique in its composition: a 
rich silver vein with quartz and orthoclase as gangue. According to 

' Fuchs and De Launay: 'Traits.' II, pp. 829-832. 

' S. F. Emmons: 'Fortieth Parallel Survey/ Vol. Ill, p. 349. 



272 THE NATURE OF ORB DEPOSITS. 

W. Lindgren/ the Black Jack-Trade Dollar vein occurs in granite, and 
in the basalt and rhyolite which rest upon it, at Silver City in south- 
em Idaho. Where granite is the country rock, the vein filling contains 
orthoclase in addition to the more abundant quartz, and is often banded. 
The ores contain pyrite, copper pyrite and silver glance, enclosed in milk- 
white orthoclase, intergrown with quartz. This vein also contains druses 
lined with crystals of feldspar of the type called valencianite by Breithaupt, 
and first described from the Valenciana silver mine near Guanajuato in 
Mexico as noted in the description of that property. 

13. High Silver-Calcite Veins (Eich Calcspar Formation). 

Veins of this class consist mainly of calcite, sometimes colored dark by 
bituminous matter, together with quartz, fluorspar, zeolites and rarely 
axinite. Rich silver ores occur either finely disseminated through this 
gangue, or forming small pockets and short stringers. They comprise 
pyrargyrite, proustite, silver glance and native silver, more rarely dyscrasite 
(antimonial silver), arsenical silver, pyrostilpnite (fire blende), etc., 
usually associated with galena, zinc-blende, pyrrhotite, pyrite atid native 
arsenic. 

The veins are mostly thin and in large part scattered into stringers. The 
best known example of this class is seen in the veins at Sanct . Andreasberg 
in the Harz, the following summary being based largely on the account 
given by F. Klockmann. 

The Sanct Andreasberg^ region is underlain by the Wieder slates, 
belonging to the so-called Harz formation of the lower Devonian, which 
contains many limestone layers, and holds numerous intrusive sheets of 
diabase. A little north of the mining area the Brocken granite forms in- 
trusive bodies surrounded by contact zones of altered slates. The Andreas- 
berg veins lie south of the contact zone of the granitic intrusive masses. 

The veins are limited to a narrow wedge of rock, about 3 km. (1.8 miles) 
long and 1 km. (0.6 m.) wide on the east, but tapering westward. This 
block is bounded by two zones of faulting, viz.: the so-called Neuf anger 
Ruschel at the north and the Edelleuter Ruschel at the south, as shown in 
the following sketch. Fig. 163, after F. Klockmann. These faults 
or "Ruscheln*^ meet near the Sieber river; eastward the network of 

* W. LindjireTi: 'Orthoclase a Ganpcue Mineral.' Amei\Joum.of 8c, 1898, Vol. 
V, p. 418. Also in 20th Annual Rep., part III, Geol. Surv., Washingfton, 1900. 

'Heinr. Credner: 'Geocnost. Verhaltn. Thurineens und des Harzes.' 1843, 
Also, 'Geognost. Beschreibunp des Bergwerks-Distrikts von Set. Andreaa- 
b-rff.' Zeitschr, d. d. G. G., 1865. C. Blftmecke: 'Die ErzlafferetStten des 
Harzes.' Vienna, 1885, p. 48 et seq, F. Klockmann: Berg u. Huttenv>e9en dea 
Oberharzes. Stuttgart, 1895, pp. 50-57. 



EPIOENETIC DEPOSITS. 273 

veins extends geologically as far as the Oder valley. However, lodes of 
the same character also occur farther east, at Brannlage. 

These delimiting faults are as much as 60 m. (186.8 ft.) wide, and con- 
sist of highly altered, leached and crushed rock, with alternating layers of 
harder rock, less affected by crushing, and consisting of layers of slate 
traversed by innumerable slips and planes of pressure and of slight move- 
ment. 

The course of the northern fault corresponds approximately to the strike 
of the surrounding country rock, and may be conceived of as a system of 
overthrust planes, after the manner of the Clausthal lodes (see page 247). 
The Edelleuter Ruschel, on the other hand, cuts the strata at an acute angle, 
and the fault brings the slates against the diabase, the fault forming the 
boundary for some distance. This fracture is accompanied by two lesser 
converging faults, the Silberburger Ruschel and the Abendrother Euschel. 
The two main fault lodes dip south 60 to 70**. 

The Andreasberg veins are confined to the space between the main faults. 
Fissures do, indeed, occur beyond these limits, but they are of different 
character and filled with other ores and gangues. North of the Neuf anger 
Ruschel the veins contain a quartzose red hermatitc filling, while south of 
the Edelleuter Ruschel the veins contain chalcopyrite in a barite filling. 

Grouped according to their strike, the Andreasberg veins belong to two 
divisions. Those of the first group, for example the Fiinf Biicher Moses 
series, the Samson lode, etc., strike northwest transversely to the faults 
(Ruscheln), and dip steeply northeast. They terminate against the fault- 
fissures by wedging out and breaking up into stringers. The others run 
approximately parallel to the faults, that is to say, between east-west and 
west-northwest, and dip north at 60-80**. They are deflected by the veins 
of the first group. The Bergmannstrost and the Gnade Gottes lodes are 
examples of this. 

All the veins are in the main simple in structure, without stringers, and 
of but little thickness, usually between 1 cm. and ^ m. The filling con- 
sists mainly of compact, whitish calcspar (older calcspar generation), in 
which ores occur either as impregnations or in stringers and pockets and 
consist of galena, zinc-blende, native arsenic, proustite, dyscrasite, arsenical 
silver, native silver, rarely argentite. Here and there other minerals are 
seen, namely, antimony, and arsenious nickel (breithauptite and niccol- 
ite), cobalt pyrite, linnaeite, fluorspar and barite, as well as axinite as 
accessories. In numerous druses a second generation of the above named 
ores and gangues are found, particularly crystals of calcspar and ruby 
silver, in a great variety of forms with associated flreblende, antimony and 
numerous zeolites, such as apophyllite, analcite, harmotome, desmine^ 



THE NATUBS OF ORE DSPOSITS. 



ftilbite, natrolite and wmetimfli ilso ditolite. The distribotiMi td the < 
in veins is vei; irregular. 




The Asdreasberg veins were diecoTered in 1E21 by Joachimethal miners, 
vho opened the first mine, called Ssact Andreaakreuz am Beerberg. so 



BPIOSNSTIO DEPOSITS. ' 275 

diriBtened, it is aaidy beeanse two of the lodes intersected like beams of a 
Si Andrew^s cross. The newly founded town was called bj the name of 
the mine. The period of greatest prosperity was from 1565 to 1570. 
Though abandoned soon after that^ work was resumed in 1646 and is in 
progress to this day. 

A second typical representative of the rich calcspar formation is the 
group of reins at Kongsberg in southern Norway. 

Kongsberg^ lies in the southern part of the Numedal (southwest of 
Christiania)^ on both sides of the Laagen Ely. Most of tiie mines are 
situated about 6 km. (3.6 miles) west of the town^ in a highly mountainous 
region^ near the Jonsknut^ 908 m. (2^978 ft.) high. The veins occur in 
steeply tilted crystalline schists, biotite schists, chlorite, talcose, quartzite 
and homblendic schists as well as a gametiferous biotite gneiss. These 
rocks are intruded by plutonic rocks near the ore deposits, as, e. g,, an oli- 
vine gabbro near Yinor, uralite gabbro and Flasergabbro (gabbro altered by 
pressure), at the Jonsknut, and norite at Skollenberg. In the Armengrube 
and the Kongensgrube, a dike of augite porphyry, a few decimeters thickj 
is known, which is cut by the veins and is but slightly displaced. In cer- 
tain zones the foliated schists are impr^nated with pyrite, which imparts 
to the weathered rock a rusty brown, or yellowish brown color, appearing 
gray when compared with the color of the normal schists. This led the 
German miners who founded the Kongsberg mining industry to call such 
zones Tahlbander* (gray bands). 

Six bands of this sort are usually distinguished, whose aggregate thick- 
ness amounts to 300 m. (984 ft.) The pyrite is most abundant in the mica 
schist, less in the hornblende schist and is quite scanty in the gneiss. This 
impregnation with pyrite may be so abundant as to actually form compact 
layers of pyrite, as is seen in the pyrite pits of the Oberberg in the main 
fahlband of that locality. The distribution of the sulphides is always very 
irregular; the fahlbands may often enclose masses of rock entirely free 
from pyrite. The pyrite consists mainly of ordinary pyrite and magnetic 
pyrite, but includes copper pyrite, rarely cobalt glance (see the Modum 
occurrence). Fahlbands are also described as occurring in the gabbros. 

'Most important publications: Bobert: 'Ueber den KongsberRer Bergbau.' 
Karsten's Arcniv., vol. All, pp. 267-346, 1833. Report of Conunission of Jahre 1865. 
Th. Ktemlf u. Tell. Dahll: *^Ueber den Erwiistrict Konfrsberg.' Christiania, 1860. 
Th. Scneerer: 'Vorkommen des Sobers «u Kongsben;.' Berg u, Hutten, Zeit., 1866, 
p. 25. C. F. Andresen: 'Om Gangformationer ved Kongsben?.' 1868. O. Holland: 
*M4m. sur la g^^ologie de Kongsberg.' Ann, d. Mines, vol. VII, ser. XI., 1877, p. 301. 
Chr. A. Munster: 'Kongsberg ertsJistrikt. ' Christiania, 1894. P. Knisch. 'Das 
KongBbergerErsrevier.' Zei<. /. Profc. Oeo^, 1896, pp. 93-104. J. H. L. Vogt: 'Ueber 
die Bildung des ged. Sitt>ers, etc. und ein Versuch zur ErkUrung der Edelheit der 
Kongsberger GSnge an den Fahlbandkreuzen. ' Zeit /. Prak, GeoLf 1899, pp. 113-123 
and 177-181. 



276 THk NATURE OF OBE DEPOSITS. 

The pyrites of the fahlbands contain merely traces of silver. According 
to Chr. Munster, the pure pyrrhotite of a fahlbaad contained 0.0005^ 
silver, besides 0.2% nickel and copper, while the pure pyrite contained only 
0.0005% silver. 




Kg. 164.— Ground plan of the 310 fathom level of the .\rmeii r 

cna mine at Kongsbent. (From the official plana.) 
G1. mica schist; H, hornblende srhlst; Q, quartzite schist; Gn. gray biotite gne'iBS 
(dots indicate development as fahlbands) ; P, dike of auKite porphyry; A, drifts with 
lodea and orebodiea (the latter shaded) ; ((( rich, {( medium, ( poor ores. 



The Kongsberg veins are distinguished by their steep dip and their 
decided tendency to stringers. In various parts of the mine, several 
stringers, usually only 10 to 30 cm. thick, are worked simultaneoosly. This 



EPIOENETIC DEPOSITS. 



277. 



is shown in Fig. 164, representing a portioo of a mine map placed at our 
disposal by the administration of the mine. The longitudinal section. 
Fig. 165, also shows the same thing, and represents the distribution 
of the working drifts, not over a single compact lode, but over a series 
of stringers. The stringers may show local thickening, and in such eases 
may enclose druses of as much as 1.25 cubic meter in capacity. 

The prevailing strike of the lodoa is northwest. The main lodes are con- 




nected by a perfect network of diagonal and transverse stringers. All dip 
very steeply. 

The predominant gangue is calcspar with leaser amounts of fluorspar, 
quartz and anthracite. Barite, axinite, albile, adularia and zeolites are 
rarities. The calcspar is usually colored brown by bitumen or coal. The 
ores consist in the main of native silver and silver glance. The native 
silver occurs as wires and points forming mosslike patches, as well as in 
large lumps of odd shape, especially finr specimens of which may be seen in 
the collection of the Royal Museum of Mineralogy at Copenhagen, collected 



ST8 THE NATURE OF ORE DEPOSITS. 

in the old dajs of mining. As late as 1867 there was f onnd in the main lode 
of Kongens mine at a dq>th of 530 m. (1,738 ft) a lump wei^iing 500 
kilograms (1^10 lb.) ccmsisting of silver with silver glance. J. H. L. Vogt 
has shown that the native silver is almost always younger than the silver 
glance, which is often coalesced with it. Sprigs and mosslike aggregates 
of silver often encrust the silver glance. Vogt thinks there has been an 
alteration of the argentite into native silver. Alongside of the silver glance 
is also found some ruby silver ore (proustite). The proportion of silver 
glance to native silver is about as 1 : 15. The Kongsberg native silver is 
often alloyed with other metals, especially quicksilver (up to about 1%) 
and antimony (up to about 0.6%). Silver amalgam, acanthite, homsilver, 
and stephanite have also been found. These rich ores are often accompanied 
by pyrite, sphalerite, galena (with up to 0.05% Ag), pyrrhotite, copper py- 
rite, sometimes also arsenopyrite and cobalt ores, but pyrite is the only 
one found as a general constituent of the veins. 

The ore shoots of the silver veins are confined chiefly but not entirely to 
the fahlbands, t. e., where the veins traverse the pyritized gneiss. This 
local distribution of the ores is apparent from the longitudinal section of 
the vein series of the Kongens mine shown in Fig. 165. The output of 
silver in the fahlband zone is as a rule 0.2 to 4 kilograms to the square meter 
of lode surface, and is only exceptionally as much as 20 kg. (642 oz.) per 
square meter. At a little distance from the fahlbands, the veins are invari- 
ably barren. 

In addition to the silver veins, younger, barren calcspar veins are 
known at Kongsberg; also quartz veins with chalcopyrite and bomite, 
which sometimes carry electrum (silver and gold). Neither of these two 
varieties of lodes is of any economic importance. 

The Kongsberg lodes were discovered in 1623. The German names of 
the mines Gottes Hilfe, Armen Grube, Haus Sachben, together with 
Kongens (Konigs-) Grube, as well as the family names of many of the 
miners, recall the fact that Germans started this mining industry. In the 
Kongensgrube the work has now advanced to a vertical depth of 720 m. 
(2,260 ft.) The mines belongs to the Norwegian crown and continue to 
produce annually about 5,000 kilograms of silver. From 1623 to 1805 
they produced about 543,000 kilograms of fine silver. 

Very remarkable veins of this class characterized by rich silver-antimony 
ores occur east of Broken Hill in the Barrier Eange of New South Wales. 
A vein occurs in the crystalline schists of that region which, wherever it 
crosses amphibolite intercalations, carries rich silver ores, namely the 
otherwise rare ores dyscrasite ( Ag, Sb^ ), stromeyerite (CuAgS) and anti- 
monious silver chloride, besides gray copper, in a gangne of calcite and iron 



EPIOENETIC DEPOSITS. 279 

spar^ These ores occur in rich bunches ofisociated witb clayey material. 
Cobalt ores play a subordinate part. 

14. Rich Silvkb-Coppeb Veins. 

The veins of this class consist of rich silver and copper ores in a barite 
gangue^ carrying quartz in the deeper levels^ with associated zeolites and 
carbonates. The rich silver and copper ores are generally associated^ 
especially in the deeper levels, with rich gray copper and pyrite-blende ores, 
and cobalt and nickel ores as mere accessories'. The rich silver-copper 
veins occur most often in basic plagioclase-augite rocks, especially augite 
porphyries, or at any rate within sediments of Mesozoic age traversed by 
those rocks. This is especially true of the Chilean occurrences described by 
W. Moricke' at Tres Puntas, Cabeza de Vaca, Los Bordos, Chanarcillo, San 
Antonio, and Caracoles, all in the region of the Atacama desert, as well as 
those of Arqueros in the province of Coquimbo. 

Only a few of the best known examples can be described in detail. 

Chanarcillo* lies about 80 km. (48 miles) south of Copiapo, the most im- 
portant town of northern Chile. The prevailing rock is a gray-blue or dark 
gray limestone of Upper Jurassic age. This limestone is cut by numerous 
dikes and intrusive sheets of augite-porphyrite accompanied by contact 
zones rich in calcium-silicates. These rocks are themselves cut by numer- 
ous veins, mostly striking north-northeast. The best known veins are the 
Corrida colorada, Guias de la Descubridora (a network of stringers in the 
Lorete mine; Quia = guide-streak), Guias de Carvallo, Mercedes vein, the 
Candelaria vein, whose strike, by way of exception, is east-northeast. The 
Corrida colorada has been found to carry rich ore to a depth exceeding 600 
m. (1,968 ft.), and has been traced over a distance of 1,800 m. (5,904 ft.) 
horizontally, with a thickness of 10 m. (32.8 ft.) in the upper regions, only 1 
m. (3.2 ft.) in the lower. At the north it is cut off by a great fault The 
veins in the upper levels carry native silver, silver chloride, silver bromide 
and malachite, besides brownspar, calcspar and barite. These ores lie in 
a clayey gangue colored yellow by ferric hydrate; farther down they carry 

> G. Smith: Trans. Am. Inst. Min. Eng., Vol. XXVI, 1897, p. 69. 

' On account of the predominance of barite, it mi^ht seem natural to use the term 
*'rich barite formation," which would be very appropriate for many cases, especially 
in Chile, and would moreover be more consistent with preceding cate^ries, out the 
occurrences at Huanchaca and Huancavelica, thouirh closely related to the others, yet 
almost or entirely free from barite, would then have no place. Hence the above 
designation, first used by W. Moricke, was chosen. 

*W Moricke: 'Die Gold- Silber- und Kupfer erzla^erstitten von Chile.' Frei- 
berp. 1898, p. 27. 

^ Fr. Moesta: 'tleber das Vorkommen" der Chloi^; Brom- und Jodverbindungen 
des Silbers in der Natur.' Marburg, 1870, p. 15, 



280 THE NATURE OF ORE DEPOSITS. 

native silver,, argentite, polybasite, proustite and p}Targ}Tite; still deeper, 
increasing amounts of blende, galena, arsenopyrite and a little pyrite. In ^ 
crossing certain beds (porphyrite sheets), not only are the veins them- 
selves enriched but they have also impregnated these adjoining rocks with 
valuable ores. The enriched beds adjoining the vein are called mantos 
pintadores. The impregnation is especially strong in the hanging-wall of 
the lodes and in the upper levels. It is often associated with silicification. 
Such enrichment may also be observed at the points where the augite- 
porphyrite dikes (the so-called chorros) cross. 

The lodes of Chanarcillo were only discovered in 1832 by the Indian 
Juan Godoi, and soon became famous because of the fabulous wealth of 
their outcrop. The mines yielded a very large silver production until very 
recently. 

A similar reputation is enjoyed by the mining district of Caracoles 
(meaning "snails") in northern Chile, north of Antofagasta in the 
Atacama desert. Highly fossiliferous Upper Jurassic marls and lime- 
stones, whose fossil ammonites gave the name to the mine, are cut by 
intrusive masses of quartz porphyry and augite-porphyry. The silver veins 
are said to be much richer in these porphyries than in the limestone. The 
veins carry ores similar to those at Chanarcillo, in a matrix consisting es- 
sentially of barite and calcite. Argentite, proustite, pyrarg}'rite and highly 
argentiferous galena are common, while in the upper depths several kinds 
of silver chloride and bromides occur with native silver. 

The veins have only been known since 1870. According to an estimate 
by Domeyko they produced in the best years 120,000 kilograms of silver. 

Similar conditions prevail at Arqueros in the province of Coquimbo. 
Upper Jurassic limestones, broken through by porphyries, are traversed by 
barite veins rich in native silver, amalgam, silver chloride, stephanite, gray 
copper, cobalt pyrite and copper pyrite. 

In the adjoining republic of Bolivia, the copper-silver veins also contain 
lead. The veins of the region of Huanchaca in the province of Potosi are 
most interesting. Among the various mining fields of this region, Pula- 
cayo, Ubino and Asiento — the first named in particular — have become famous 
during the last few decades by a large production, and the mining opera- 
tions, begun by the Spanish conquerors at an early date, and afterward long 
abandoned, have recently been extensively resumed. 

The lodes of Pulcayo* occur in trachjrtic and andesitic rocks. The main 
lode, striking east-west and 1/3 m. thick, has been opened up to a distimce of 
1,100 m. (3,608 ft) in the strike, and to 500 m. (1,640 ft.) in the dip. In 

' A. Gmehling: 'Huanchaca. ' Oesterr. Zeitsch, f. B, u H., 1890, p. 281 . Fuchs and 
Pc Launay: "Traits/ Vol. Ill, 1893, p. 852. 



EPIOENETIC DEPOSITS. 281 

the upper depths it is said to have shown a great resemblance to the 
Chilean examples of the rich silver-copper formation, and, like them, to have 
been characterized by barite and rich silver minerals, together with gray 
copper. With increasing depth, quartz with a little calcite took the place 
of barite. Finally, in the lower workings, according to A. Gmehling, the 
proportion of barite to quartz was 0.5 : 21. At the same time the rich silver 
ores were replaced by a mixture of metallic minerals, which, according to the 
same author, consisted, as stated in the relative order of quantity, of zinc- 
blende, with 0.2% and more of silver, pyrite, copper pyrite with about 0.3% 
silver, and galena with an average of 0.6% silver, a mixture whose real 
value was derived from the presence of tetrahedrite with as much as 10% 
silver. This gray copper often occurred finely crystallized in druses associated 
with quartz. In rare instances radial aggregates of stibnite are observed. Men- 
tion should also be made of a small content of gold, tin and bismuth in 
the various ores, while large masses of white lithomarge, with inclusions of 
gray copper, also occur in the vein filling. 

In 1893 the Huanchaca mines produced 281,006,924 kilograms of sil- 
ver. In 1898 it was only 144,049,443 kilograms, 51,500 tons of ore being 
exported. 

The same type of lode is found in Peru, in the department of Huan- 
cavelica, for example, the mines of Morlupa and Julio Caesar, whose ores at 
some depth consist mainly of a mixture of gray copper, chalcopyrite and 
galena, in a gangue of quartz and carbonates. Sometimes, as in the case 
of the Caudalosa mine in the department of Vuitava, there is found a 
mixture of gray copper, red zinc-blende, famatinite (Cu8SbS4), antimony 
glance and realgar, with quartz and barite. 

The occurrence of famatinite associated with enargite (CU3ASS4) also 
characterizes many veins in the Argentine Republic. Such veins were 
described by A. W. Stelzner* at the Cerro de Famatina in the province de 
la Bioja. They occur in clay slate broken through by intrusions of dacite 
and andesite: Rich silver ores occur but very scantily and the ore deposit 
has the character of a copper formation. Besides enargite, which is 
decidedly the prevailing ore, the veins also carry famatinite, pyrite, copper 
pyrite and zinc-blende, with a little proustite, in a gangue composed of 
quartz, homstone and barite. The mines are now worked mainly for cop- 
per. The Mejicana, TJpulongos and Capillitas are the best known. 

In the Old World, this type of copper-silver vein, so widely prevalent in 
South America, presents conditions of a widely different nature. It is 
probably developed in the remarkable silver mines of Smeinogorsk or 

* A. W. Stelzner: 'BeitrSge zur Geologic der Argentin. Republ.' 1885. Vol. I, 
pp. 216, 232. 



282 THE NATURE OF ORE DEPOSITS. 

Schlangenberg (snake mountain) in the Altai Ifountaina of Siberia 
described by B. von Cotta*. 

The mines lie in a region of Paleozoic rodss^ traversed by porphyries and 
porphyrites. At Snake mountain^ there is a vast interbedded ore deposit 
which expands locally into the form of a stock in the midst of these 
strata. It is composed essentially of barite and some quarts^ and contains 
rich silver ores^ such as native silver^ silver chloride^ argentite^ pronstite, 
miargyrite and highly argentiferous gray copper^ as well as some native 
gold, together with copper ores, such as glance, copper pyrite and secondary 
copper ores, as well as galena, pyrite and zinc-blende. The f ootwall consists 
of a fossiliferous Devonian homstone, swarming with stringers of ore- 
bearing barite, and representing perhaps a silicified limestone. The hang- 
ing consists of clay slates of the same formation. The mass of the vein, 
which is still found here and there to be 20 m. (65.6 ft.) thick, and is 
said to be still thicker at the outcrop, may be divided into five streaks, 
defined by the richness of the ore ; the uppermost consisting of pure barite 
and containing but little silver; the second, a mixture of baryta carrying 
silver ores as very fine dust; the third, a mixture of ore-bearing barite and 
homstone; the fifth consisting of homstone traversed by ore-bearing barite 
veins; and, finally, the homstone of the f ootwall, which is devoid of ore. 
The deposit is traversed by porphyrite dikes, 1-3 m. thick. 

The mineral veins of Smeinogorsk, which were worked by the Tschudes 
in prehistoric tiroes, were rediscovered in 1742, and have since then been 
imperial crown land, being worked with varying success. 

15. Veins of Bich Silver-Cobalt Ores. 

In this type of vein, the gangue is not everywhere developed in the 
same way. In one variety, seen at Joachimsthal, Austria, it consists mainly 
of quartz, homstone, calcspar and dolomite; in the other, as at Annaberg, 
barite and fluorspar are added to the first named minerals. The ore 
minerals, on the contrary, are everywhere uniform in occurrence, consisting 
of cobalt, nickel and bismuth minerals, as well as uranium ores, which 
usually occur associated with the non-carbonate gangues that form an older 
part of the lode filling; also of rich silver ores, which are wont to repre- 
sent a younger generation. These veins belong to the older geologic 
formations. In the Erzgebirge they are found about the borders of granitic 

' B. von Cotta: 'Sohlan^enberg-Silbergnibe im Altai.' Berg u. Hutten Zeit., 
1869. No.28. Also/ Der Altai.' Leipzig, 1871, p. 192. C.Griwnak: ' Les juiaement* 
de min<^rais dans T Altai.' Joum. d. Min., 1873, Vol. II, No. 5, 6, pp. 172-265; 1875, 
Vol. II, No. 6, pp. 277-311. (In Russian.) G. Maver: ' I^ mines d'arjrent de 1' Altai.' 
CompU-rendu du Conseil de la Soc. Amat. Investig. d 'Altai, 1891-1893, p. 31. , 



EPIQENETIC DEPOSITS. 283 

iotmsiTe maeaea of late Paleozoic age, with which the; are genetically con- 
Dected. Th^ ore traversed bj Tertiary baaalta. Analogous Tcina tmaid- 
at other localities and of similar age ara of no economic importance as 
GtHupared to the Eizgebirge. 




For our first example of tnis formation we will select Joachimsthal, 
Bohemia, where at the present time mining operations are confined to veins 
of diis typei 

The Joachimsthal district lies on the higher eoiithem slope of the 
Erag^irge, sonthweat of its hi^eat elevation, the Keilberg, 1,238 m. high, 



284 



TEE NATURE OF ORE DEPOSITS. 



near the Sason boundary. The rocks are mica schists, with east-west to 
vestDOrthwest foliatioii aad north dip. In the vein area ^ely crystalline, 
slaty mica schists predominate, with intercalated layers of calcareous mica 
schists, crystalline limestones and coarse-fibered mica schista. (See Fig. 
166.) Toward the northeast and east gneisses occur, while toward the south- 
west the schist ends abruptly against granite, the northeast contact of the 
great Eibenstock-Karlsbad massive of tourmaline granite, which crosses 
the axis of the Erzgebirge. At its border a contact zone is developed, which, 
however, does not quite extend into the Joachimsthal mineral vein area. 
Numerous dikes of quartz porphyry, sometimes quite large and running 
northwest to north-northwest, traverse both the region northeast of the 




Fig. 167. — Section throuf^h the Werner shaft at JoBchimstahl. {F. Babenek.) 
gl, micaschiat; P, qu&rtt porphyry; B, basalt; Bt, basalt tuff (Putzeowacke) 



granite, and the mineral area. Dikes of basalt and phonolite, as well as 
boBscs of these rocks, were intruded in Tertiary time. The tremendous 
earthquake shockB that must have taken place during that period have left 
their record in wide fiBsures extending deep into the rocks, which must have 
remained open for long periods, since volcanic, phonolitic and basaltic ma- 
terial, together with stlicilied deciduous trees, that is to say, debris washed 
from above, were found in the Joachimsthal deep levels within the so-called 
wacke lodes in mica schist, particularly in the Barbara drift, at a depth of 
262 m. (859 ft.) (See Fig. 167.) This remarkable fact was mentioned as 
early as ln57 by ^^lathesius, the preacher miner and reformer o£ Joa- 
chimsthal. 
According to their strike, the silver-cobalt veins of JoacfaimstliAl, 



EPIGENETIC DEPOSITS. 285 

especially those close to the town on the northwest, fall into these two 
groups : 

(a) Morgengange, striking eastnortheast (7 hours) and dipping north 
at 60-80**; (b) Mitternachtgange, striking northnortheast to northnorth- 
west, for the most part, almost exactly north-south (11-1 hours) and dip- 
ping at times 45-85** west or east. 

Some of the lodes of the first group, for example, the Geyer and 
Mauritius veins, were very rich in the upper levels, but grew poorer 
in depth, so that they became of little importance in the modem mining 
period. On the contrary, some of the veins of the second group have in 
recent decades been worked by deeper drifts with success, particularly the 
Geistergang, which showed fine bodies of silver ore, especially in 1853 ; also 
the Rothe, Prokopi, Anna, Geschieber, Hildebrand, Junghauerzecher and 
the Evangelisten veins. 

The width of the veins varies between 15 and 60 cm. and only excep- 
tionally reaches 1-2 m. (3.28 to 6.56 ft.) Stringers are common. Some 
of the Mittemacht veins reach the surface not as true veins, but as narrow, 
barren cracks*. 

The filling is not the same in all the veins. Thus in the western 
Mitternachtgange it is for the most part a brittle clay, with quartz and 
hornstone; in the eastern veins it is mostly calcspar and dolomite, while 
both sets of veins occasionally show a brecciated structure. The ores in 
these gangues form stringers, branches and pockets that are very spotty. 
According to G. Laube, these ores may be divided into: 

1. Silver ores (native silver, argentite, polybasite, stephanite, tetrahe- 
drite, proustite, pyrargjTite, sternbexgite, argentopyrite, besides rittingerite, 
acanthi te and cerargyrite). 

2. Nickel ores (niccolite, chloanthite, millerite). 

3. Cobalt ores (smaltite, as well as bismuth-cobalt-pyrite and asbolate). 

4. Bismuth ores (native bismuth, as well as bismuth glance and bismuth 
ocher). 

5. Arsenic ores (native arsenic, arsenopyrite). 

6. Uranium ores (pitchblende). 

Galena, zinc-blende, pyrite, marcasite, copper pyrite and bomite only 
occur subordinately and occasionally. Among these ores, the cobalt and 
nickel ores appear to be on the whole the older, the silver ores the younger. 
From the numerous sections of the lode published by F. Babenek, we 
have chosen the one shown in Fig. 168^ which exhibits the characteristic 
distribution of ores and gangues. 

* Compare with W. P. Jennev: 'Mineral Crest,' Trans, Am. Inst. Min. Eng., Vol. 
XXXVII, p. 46; discuflsion. p. 1060. 



«86 TES NATURE OF ORB DSP0BIT8. 

'Sear the lode fiamres, tbe vtnmtrj rodi frequently hu been 
impregnated with extremely finely divided ore particles. This explaios 
the small percentage of inetals shown by F. Saodberger and A. Seifert to 
exist in Taiioos rocks of Jotchimsthal, especially copper, cobalt, nicbd 
and arsenic. In like manner the preaence of minnte granules of oranium 
pitchblende in & scapolite-mica-schiet of that locality, first discovered by 
F. Sandberger and conclusively confirmed by F. Babenek and A. Seifert, 




Tig. 168.— Crosa^ection of tbe Hildebrand lodcfl at Joachinuthal. (BsbBnek-KemveA.) 
Sch, schist; D, dolomite spar; C, calcite; Q, qturti; I., vdn-clay; R, pyraigyritc: 
V, [Ntchblende; A, argentiferous arsenic ore; P, pyrits. The van croBseB threeold 
lodes with quarti filling. 



by meam of large-scale ore concentration experiments, is most natnrally ex- 
plained by an infiltration from the lode fisBures. Their presence aa primaiy 
constitaents seems to be gainsaid by their very unequal distribntion in 
the rock. In the experiment just noted, the dressing of 6,358 kg, from a 
richer zone gave 226 kg. of concentrates with a content of 0.3% of 
uranic binoxide. 



EPIOENETIC DEPOSITS. 287 

The veins trayerse dikes of quartz porphyry, and in their tarn are cut 
across by dikes of basalt and the wacke veins. However, since these wackes 
sometimes contain some interspersed argentite (earthy silver glance) where 
they cross the ore veins it is inferred that at the time of the eruption of 
the younger volcanic rocks the vein formation had not yet been quite com- 
pleted. It may also be mentioned here that in 1864, according to Fr. 
Weselsky, a spring with a temperature of 23^ Beaumur (84'' F.) was 
tapped on the Oeschieber lode at a depth of 531 m. (1741 ft.) 

At the acute-angled lode crossings there has been an enrichment of the 
ore. The veins are richer in the porphyry and to the east in the limestone 
intercalation than in the schist. 

The Joachimstahl mining industry began, according to G. Laube, at the 
end of the 15th or in the early years of the 16th century. As early as 
1517 a mining settlement existed in the valley, and as early as 1518 the 
first ''Joachimsthaler^' were minted, this coin being now known as the 
thaler. In 1520 the settlement obtained the privilege of a free mining 
town. The total output for the first 44 years is put at 40 tons of gold, 
that is to say, over foiir million gulden, reckoning silver at the value pre- 
vailing at that time. After 1545 the industry suffered a great decline, but 
acquired new vigor when the cobalt and bismuth ores became valuable. In 
recent time the industry has languished because of the depreciation of 
silver. During the last decades, special attention has been paid to the 
extraction of uranium, for which a government factory has been set up at 
Joachinisthal. In 1898, 50.9 tons uranium ore was obtained^. 

Conditions similar to those of the Joachimsthal lodes were found to pre- 
vail on the Saxon side of the Erzgebirge in the silver-cobalt veins of the 
vicinity of Annaberg, described in the detailed monograph of H. Miiller*. 

In this vein area the rock consists mainly of gray gneiss (the ^i- 
micaceous principal gneiss" of the geologic map). The district forms the 
southwest part of the Annaberg-Marienberg gneiss dome. In this dome, 
at the southwest periphery of the area, at Buchholz, a granite stock is 
exposed, from which a tongue of fine-grained granite (porphyritic micro- 
granite) runs through the mineralized district northeastward in the form 
of a dike. Similar smaller dikes of this rock have been met with at 

^ Some of the more important publications upon Joachimstahl are: G. Laube: 
•Au8 der Verj^angenheit Joachimsthal?/ Pra^e, 1873. Also, 'Geolo^c des bohmischen 
Erzgd^irges/ Pr^e, 1876, p. 176-192. F. Babenek: ' Ucber die EnrfGhning der 
Joachimsthaler Gauge.' OesUrr, f. B. u. H., 1884, pp. 1,21,61. Abo, 'Die Uranhal- 
tigen Skapolith-Glimmerechicfer von Joachimsthal,' 188D, p. 343. Also, Geologic, 
bergm. Karte mit Profilen und Bildem von den Elrzgangen in Joachimsthal.' Pub- 
Ibhed by the Imperial Royal Ministry of A^culture, 1891. 

'H. Muller: 'Die Erzgange des Annaberger Bergrevieres. ' Geolog. Survey. 
Leipzig, 1894. 



288 THE NATURE OF ORE DEPOSITS. 

several points above ground and underground. At the northeast edge of 
the field, at Wiesenbad, in the valley of the Zschopau, the erosion of the 
river has laid bare an intrusive stock of granite, so that this rock may be 
presumed to be rather widely distributed in the deeper levels of the mining 
area. Furthermore, mining operations very frequently encounter narrow 
dikes of lamprophyre (fine-grained mica syenites and mica diorites), at 
times also basalt dikes. The latter are genetically connected with the sheet 
of leucite basalt, which resting on a substratum of fluviatile clays, gravels 
and sands of the Oligocene, forms the tomb-shaped Pohlbe^g immediately 
southeast of Annaberg. 

More than 300 veins traverse the rocks near the town and in the district 
about it. They may be divided according to age into two groups. Of the 
older, it may suffice to mention briefly the tin lodes of the former Alte 
Thiele Fundgrube near Buchholz and the pyrite blende lead veins, which, 
because of their unusual richness in copper-pyrite and other copper ores 
(see page 238), were worked in the Sanct Briccius, Heilige Dreifaltigkeit, 
Weinkeller, Rothe Pfiitze and Spanier mines on the east slope of the Pohl- 
berg and at several other points. The strike of these veins is usually about 
east-west. They have always proved to be younger than the lamprophyres, 
but older than the basalts. 

On the other hand, the younger group consists of the silver-cobalt veins, 
in which we are here especially interested, and of examples of the iron and 
manganese veins which are developed farther southwest, in the region of 
Scheibenberg. 

The silver-cobalt veins are the most important ore deposits of the Anna- 
berg field. Besides those of the Annaberg district itself, the only one 
which we will here consider, there arc others at Schmalzgrube and Stein- 
bach in the Pressnitz valley, at Johstadt, at Barenstein and Weipert, and 
at Oberwiesenthal, where they form a transition to the great Qottesgabe- 
Joachimsthal mining field, and a sixth area near Scheibenberg. In all these 
fields, mining is no longer carried on. 

The silver-cobalt veins occur in two principal series, whose directions in- 
tersect at nearly right angles. Most of them strike northnorthwest, a less 
number strike eastnortheast to east-west. Only a few have a diagonal 
strike of north-south to northnortheast. The northnorthwest veins belong 
exclusively to the silver-cobalt class ; the veins of other courses are in part 
of different characters and age. The veins of the northnorthwest series 
have usually a steep dip, those of the east-west series have a dip of hut 
45-60** in different directions. Most of the veins have been followed for a 
horizontal distance of 800 m. (2,624 ft.), some much farther, the Treue 
Freundschaft Stehende at least 2 km. (1.2 miles). On the other hand. 



EPIQENETIC DEPOSITS. 289 

mining operations on'fheee lodes have penetrated to no great depths the 
deepest^ about 400 m. (1^312 ft.), being in the Erstneugliick Flaehen and the 
Heynitz Flaehen. The thickness varies between 10 and 20 cm., in ex- 
ceptional cases amounting to 2 meters (6.5 feet). 

The vein filling consists mainly of barite, fluorspar, quartz and brown- 
spar with various cobalt, nickel and bismuth ores, especially chloanthite, 
smaltite, gersdorflSte, annabergite (nickel-ocher) and native bismuth, 
rarely bismuthinite, rich silver ores, especially pyrargyrite, proustite, ar- 
gentite, earthy silver glance, native silver, silver chloride, and finally 
pyrite. The subordinate gangue minerals include homstone, chalcedony, 
amethyst, calcspar, aragonite, kaolin, lithomarge, gypsum; among the ore3, 
copper pyrite, galena, zinc-blende, marcasite, gray copper, siderite, uranium 
pitchblende, uranochalcite, gummite, zippeite, native arsenic, with others 
of minor interest. 

An interesting feature of the vein is the occurrence in former times of 
great masses of silver chloride; for example, in the 16th century, in the 
Himmlisch Heer vein, masses of pure horn-silver were found as much as 
20 pounds in weight. 

The veins are frequently filled with fragments of country rock and the 
brittle inter-vein rock and attrition clays. Argentiferous vein clays have 
sometimes been mined. The prevailing structure of the vein filling is 
irregularly massive. 

According to H. Muller, the result of more than 200 observations showed 
as a rule a definite succession in the deposition of the minerals of these 
Annaberg silver-cobalt veins, which he summarized as follows : 

V. Decomposition products such as annabergite and cobalt efflorescence. 

IV. Bich silver ores and native arsenic. 

III. Calcspar and uranium pitchblende. 

II. Brownspar and cobalt-nickel-bismuth ores. 

I. Barite, fluorspar and quartz. 

I and II together always form the bulk of the filling. 

As already stated, the silver-cobalt veins cut through the tin-bearing and 
pyritic lead veins, as well as the dikes of microgranite and lamprophyre. 
The basic dykes are often accompanied by silver-cobalt veins. Thus the 
Heynitz Flache vein follows a lamprophyre dike 0.1-3 m. thick, for almost 
600 m. along its strike and to a depth of 340 m. It follows first one wall, 
then the other, and in places crosses the dike. On the other hand, both this 
and other examples of this type of vein are cut across by basalt. The 
basalts encountered in the mines not only form true dikes, but also occur 
as vertical chimneys or pipes of round cross-section. As rich silver ores 



aso 



THE NATURE OF ORE DEPOSITS. 



ocetsioittlly occtir interspersed in fissures in the midst of the baealt masB 
near vein crossings, as at Oberwiesentbal, it is inferred that chemical trans- 
positions of the metallic compounds took place even later on. 

The various relations of veins and eruptive dikes are illustrated by the 
accompanying Fig. 169. 

An important feature in the mining industry of Annaberg is the 
presence of the so-called "Schwebenden," that is to say, sheets of decom- 
posed rock ordinarily parallel to the foliation of the gneiss, but sometimes 
also transverse to it. These sheets are from 1 cm. to S meters thick, are 
ordinarily colored blackish by fine earthy, carbonaceous substances, and 
often contain finely inteispersed pyrite and sometimes copper pyrite. As 
indicated by their name, they are distinguished by a fiat dip. The "obere 
Schwebende," of the Markus Bohling Fundgrube at Scbreckenberg, dips in 




Vtg. 16S.— Ground plap ot a drift in the Neu Unverhofft Glack-At the Luxb&ch 
Annaberg. (H. MuUer.) 
gn, eneiss, micaceous; L, lamprophyre (fine-);rained mica eyeDJte); GO, lodes of 
the rich ailver-cobalt ore formation; B, basalt, with fragments of gneisB and 
lamprophyre on one side. 



, directions at 15-20°. Where the silver-cobalt veins cross these 
Sehwebenden, they often show an extensive enrichment, as appears by the 
mine section. Fig. I lO, According to U. Miiller, at least half the entire out- 
put of silver and cobalt is derived from ore bunches found at these cross- 
ings, especially in the Bauerin, Heilig Kreuz, Zehntaueend Hitter, Himm- 
liacb Hcer, Galilaischc Wirthschaft, Konig David and Markus Rbhling 
mines. Besides these, there are others at the intersections of various min- 
eral veins, and the junctions of various stringers are marked by the oc- 
currence of rich ores. 

The Annaberg veins are said to have been first opened for copper minin/ 
in the first half of the 15th century at the town of Geyersdorf, near the 
Pbblberg. On October 27, 1492, a prospector discovered rich silver veins at 
the Scbreckenberg, near Frohnau. By 1496 the "Neue Stadt am Schreck- 
enberge" was formed by the great infiux of foreigners. In 1497 the town 
received the name of Sanct Annaberg. In 1495 silver mines were 



BPI6BNBTIC DEPOSITS. 



291 



opened in the beech forest of the Schottenberg, which led in 1501 to the 
foundation of Sanct Kathaiinenberg iu Buchholz, subsequently abbreviated 
to Bucholz. According to H. MUller, during the greatest period of pros- 
perity of the Annaberg-Bucbholz mining industry, from 1496-1600, a total 
of approximately 1,352,900 marks of silver and 48,460 centners of copper 
were obtained, having a total value of about 24,300,000 marks ($6,000,000) 
in present coinage. The industry dechned from 1560 until towards the 
middle of the 17th century, when the utilization of the cobalt ores caused 
a gradual revival of mining activity. Cobalt mining was particularly active 
from 1701 to 1850, during which time 25,534 centners of cobalt ore were 




Fig. 170. — Longitudinal Section of the Heynitz FUche vtm, llarkua RAhling min 

Annaberg. (H. Mtiller.) 

B, Intruaive maaa of basalt; Schw., "Schwebende"; M, various Morgengftoge. 



produced. The silver produced as a by-product daring this time amounted 
to 26,945 kilograms. Since 1850 the mining industry has been at a low 
ebb. 

Silver-cobalt veins as well as simple cobalt veins occur also at Schneeberg 
proper, as described farther on. 

The same is true of the mining field of Johanngeorgenstadt. At the 
Fastenberg, the Eibenstock tourmaline granite is concealed by a corer of 
phyllite, which it has altered by contact metamorphism into spotted 
slate and andalusite-mica rock. These contact rocks are trav- 
ersed by many dikes of fine-grained granite. Numerous mineral veins 
form a dense network in this rock, some belonging to tlie tin-cobalt and 



292 THE NATURE OF ORE DEPOSITS. 

some to the silver-cobalt formation, as well as pure cobaltic veins, all 
showing but little uniformity in strike. The veins are cut off by a vast 
network of iron ore stringers, the so-called Faule (rotten lode). The filling 
of the silver-cobalt veins of this locality is similar to that at Annaberg. 
They are often rich in uranium pitchblende. 

Johanngeorgenstadt, the youngest mining town of the Erzgebirge, was 
founded as late as 1654 by the Protestants who were driven out of Bohemia, 
but mining began a few years earlier. It still continues, and produced in 
1901 nine tons of bismuth and uranium ores. 

The group of the silver-cobalt ore lodes also includes the deposits of 
Wittichen (Kinzig valley) and of Wolfach in the Black Forest, described 
by Vogelgesang* and F. Sandberger*. 



(0 Gold Veins.' 

The gold veins are exceedingly varied in their composition, but may be 
grouped according to the prevailing gangue into: (1) Gold quartz veins; 
(2) Quartz-calcite veins, which contain other carbonates and rarely barite 
also; (3). Quartz-fluorite veins. The gold quartz veins contain a variety 
of gold-bearing sulphides and other minerals besides free gold. The pre- 
dominance of a particular sulphide gives a special character to the par- 
ticular example and thus various sub-divisions of the group may be dis- 
tinguished. This diffSrentiation of separate vein-types may be of practical 
interest, because of a corresponding difference in metallurgical treatment. 
Of course, these sub-classes are connected by transitions. The most im- 
portant of them are the following: 

« 
Gold Quartz Veins (the Oold Quariz Formation). 

(a) Pyritic gold-quartz veins in which pyrite prevails or at any rate 
predominates as compared to the other sulphides. 

(B) Cupriferous-gold-quartz veins in which copper ore is prominent. 

(c) Antimonial gold-quartz veins in which stibnite is abundant. 

(d) Arsenical gold-quartz veins in which arsenopyrite is the predomi- 
nant sulphide. 

' Vogelgesang : 'Geogn.-bergm. Beschr. des Kinzigthaler Bergbaues. ' Carlsruhe, 
1865, p. 19. 

' F. Sandberger : Netiea Jahrh. f . Min., 1868, p. 385 ; also the volume for 1869, p. 290. 

• A general discussion of the occurrence of gold in veins is given by Fuchs and De 
Launay: 'Traits,' II, 1893, pp. 890-893. CG<5n6ralit<^s sur les filons d'or.') E. Cum- 
enge and F. Robellaz : 'L'or dans la nature. ' Paris, 1898. Ed. Suess : 'Die Zokunft 
deeGoldes.' 1877. 



EPIOENETIC DEPOSITS. 298 

(e) CobaltiferouB-gold-quartz veins in which smaltite holds the gold. 

Silver-Oold Veins. 

The second main group^ in which the gangue consists of quartz^ together 
with earthy carbonates and sometimes barite^ is also sharply defined by the 
fact that both gold and silver ores occur together^ and gold-bearing and 
silver-bearing tellurides also occur very often. 

Fltumtic Oold Quartz Veins. 

The prevalence of fluorspar intermixed with the quartz and the 
presence of tellurides marks this group. 

We will now give a detailed description of the different groups and cite 
examples of them. 

16. QoLD Quartz Veins. 

These are simple or compound lodes^ mostly of massive structure^ and 
with the particles of ore irregularly distributed, or more rarely showing a 
banded structure, the individual thin or thick-sheeted layers being in. such 
case divided by scales or films of ferric hydrate with free gold, or by talc, 
sericite, chlorite and other decomposition products. As shown by W. Lind- 
gren, a ribbon structure is often present, having been produced by secondary 
movements and the formation of cracks, parallel to the strike, in the vein 
mass. This is proven by the pressed and crushed pyrite particles lying 
along the plates, and also by the forking of the joints between the quartz 
bands. In lodes that are rich in sulphides, however, a primary banding 
also occurs occasionally, in which case the ores are strongly concentrated 
along special planes parallel to the selvage. 

The nature and habit of the quartz, the only essential gangue, varies 
greatly, and it is not possible to formulate any set of characteristics for the 
gold-bearing variety of this mineral, that may be applicable in all regions. 
In general it is a micro-crystalline, whitish, faintly translucent mass, ap- 
pearing opaque to the naked eye, tinted grayish by finely divided sulphidcb 
in the deeper parts of the veins, and yellowish or rusty colored from the 
oxidation of those sulphides in the upper portions. The luster varies from 
glassy to greasy. 

On examining a thin section of this with high powers of the microscope 
(see Fig. 171) the various individual grains show under polarized light a 
very irregular outline, which is but rarely formed even in part by crystal 
planes. Many specimens exhibit the marks of a strong secondary pressure, 
and the aggregations are often traversed by delicate, dark streaks represent- 



294 THE NATURE OF ORE DEPOSITS. 

ing slip or fracture planes, being minute fiasuree of displacement filled 
with extremely fine grains of cruahed quartz, and ordinarily impregnated 
and colored vith various ores or the products of their decomposition (see 
Fig. 171 c). Posepny', who described such minute shear planes in the 
quartz from the Tauem gold veins, explained these fissures as the result of 
a shrinkage of the mass in passing from an opal-like condition into a C17B- 
talline quartz, analogous to the process advocated by Fuchs and Breitbaupt^ 




Fig. 171.— Gold quani from Sheba n 
secondary ciiiahing; 



on a large scale to explain the soK^lled Quarzbrockenfels of the I 
It appears unlikely that this explanation will maintain itself. 

Individual crystals of the gold-quartz are usually rich in liquid iD- 
clusions. As the bubbles disappear in most cases on heaUng the sections to 
30° C, and reappear on subsequent cooling, it may be inferred that the 
liquid is carbonic acid. This, however, is not true in all cases. Fmn a 

' F. Posepnv : 'Goldhergbaue der Hohen Tauem,' Arekiv f. Prak. Geol., I, Prei 
berg, 1S80, p. JO. 

*A. Breithaupt: 'Parogeneeis,' 1849, p. 9. 



EPIOENETIC DEPOSITS. 295 

chemical analysis by 6. Steiger^ Lindgren^ for example, inferred that such 
liquid inclusions consisted of sulphates of calcium and alkalies, mixed with 
a small amount of chlorides. It is remarkable that the lines into which 
these inclusions are so often grouped sometimes pass through several ad- 
joining quartz individuals without regard to the contours. W. M. Courtis' 
tried to establish definite relations between the microscopic structure of the 
gold quartz and the gold content of the lodes concerned, but was unable 
to find any rule of practical value. 

Through the leadling out of the sulphides in the gossan, the gold quartz 
becomes porous. Such occurrences are sometimes erroneously designated 
as silicious sinter. 

True sinter is probably deposited by the silicious water of some gold-bear- 
ing veins or lode-like deposits, though deposited only in the uppermost 
regions. The pure white, porous and even foam-like silicious sinters, suggest- 
ing pumice stone, seen in the gold deposit of Mount Morgan in Queensland 
and at some other Australian localities, are occurrences of this sort, 
which may without hesitation be compared with the deposits of some 
geysers, an assumption which is confirmed by the amount of water shown 
to exist in them.* Opal, too, has been described from gold quartz lodes, 
for example, in California. Its presence in veins need not be considered 
surprising, since opal, accompanied by gold-bearing pyrite and stibnite, 
has been observed in process of deposition by the spring waters of Steam- 
boat Springs (see under ^Thermal theory') close below the surface of 
the earth, at the Monarch Geyser in the Yellowstone Park, and Boulder 
Hot Springs, Montana, and it is known that the thermal springs of Taupo 
in New Zealand produce a slightly auriferous silicious sinter. 

Sometimes chalcedony is observed, for example in the gold ore veins of 
Donnybrook* in Western Australia. Here the chalcedony-quartz aggregates 
formed at first were afterward leached out in such way that a loose gold- 
bearing quartz dust remained. 

For that matter, besides quartz, carbonates are not unknown in lodes of 
this group, as for example at Nevada City and in Grass Valley in Cali- 
fornia, and Idaho. However, they always play merely a subordinate part. 

The native gold of quartz lodes is usually interspersed in the quartz 
grains in exceedingly fine scales, dust-like particles or small crystals, or 

* W. Lindgren: 'Gold Quartz Veins of Nevada City,' etc., 17th Ann. Rep. V. S. 
Geol. Surv'e>'. 1896, p. 130. 

»W. M. Courtis: 'Gold Quartz.' Trans. Am. Inst. Min. Eng., Vol. XVIII, 
1800, p. 639. 

• Weed, Walter Harvev : * A Gold-bearing Hot Spring Deposit. ' Am. Joum, Set., 
3d Series, 1891, Vol. XLII, pp. 166-169 

*F. Beyschlag and P. Krusch: 'Die Goldgange von Donnybrook in W. A.,' Zeif, 
/. Prak. Geol, 1900, pp. 169-174. 



296 • THE NATURE OF ORE DEPOSITS. 

lies wedged in between the surfaces of the quartz grains. More rarely is it 
found as dendrites^ sheets^ tangles of wires or crystalline lumps. The 
latter may in exceptional cases^ as in that of a specimen from Monumental 
Mine^ Sierra County^ California^ attain a weight of 43.08 kilograms. (See 
discussion of gold nuggets under the head of placer gravels, farther on.) 
Such nuggets are always jagged in outline and usually coated with crystals 
of gold. A special form is exhibited by the aggregations of gold derived 
from the decomposition of tellurides. They form dark yellow moss-like or 
spongy crusts, which, because of their color, are popularly termed ^^mustaxd 
gold/' 

At times the gold is so exceedingly finely divided as to suggest that it is 
contained as a silicate in the quartz of some lodes. This assumption is 
unnecessary, since the fineness of the flakes may far exceed our ordinary 
visual power. J. A. Edman,^ using very strong magnifying powers, was 
able to detect, in quartz, particles of gold dust whose diameter was only 
from 1/40 to 1/480 of a millimeter. 

All the gold of this type of veins contains silver. The degree of fineness 
differs greatly. In California, for example, in the case of gold dust it is 
0.850 to 0.870, while in larger nuggets it is up to 0.950. 

The sulphides, which often occur in great abundance in the lodes, and 
are rarely entirely absent, are developed either in finely interspersed 
crystals and granules, or in compact aggregates. The most widely dis- 
tributed sulphide is iron pyrite, which is sometimes, but rarely, replaced by 
pyrrhotite. Associated with the pyrite there is also copper pyrite, galena, 
zinc-blende, arsenopyrite, stibnite, as well as molybdenite, all of which are 
apt to contain gold and silver. 

The lodes often enclose fragments of country rock, which in such cases 
are usually more or less strongly impregnated with gold, auriferous pyrite 
and other ore minerals, as is also the case with a zone of the adjoining 
country rock along the vein-walls. 

Gold quartz veins occur in all kinds of rocks, but are most frequent in 
crystalline schists. They most often occur in regions where the older 
schistose rocks are broken through by granitic, dioritic and diabasic rocks 
and are genetically connected with such intrusions as will be shown in de- 
scribing the various examples. 

The genetic connection of many gold quartz lodes with granitic intrusive 
masses has been brought into prominence by late researches. They cluster 
about the borders of the granite areas in Montana, and elsewhere, even the 
ancient veins of the Appalachian gold belt showing this association. It has 
been shown that some of these lodes show a close relationship to pegmatite 

* Cited by E. Cumenge, op. cit.y p. 40. 



EPIGENETIC DEPOSITS. 297 

veins. J. E. Spurr^ has shown that gold quartz veins contain a great num- 
ber, of such accessory minerals as are also characteristic of pegmatite veins, 
although the amoimt is trifling compared to the gangue proper, the quartz. 
Thus among the 62 mineral species enumerated by 6. F. Becker* from the 
gold veins of the southern Appalachians, there were, among others, 
tourmaline, cassiterite, apatite, orthoclase, albite, garnet and scheelite. In 
the Fortymile and Birch Creek districts of the Yukon, Spurr observed what 
he considered to be transitions from gold quartz lodes to aplites, that is to 
say, finely crystalline granites, poor in mica (alaskite), which often 
passed into pegmatites. These transitions take place very gradually by an 
increasing abundance of feldspar. This phenomenon only became intelli- 
gible after the work of W. 0. Crosby, M. L. Fuller, W. C. Brogger and 
others had afforded us a better understanding of the probable conditions 
under which pegmatites are segregated. These conditions must have been 
intermediate between those under which an acid eruptive rock congealed, 
and those under which an ordinary quartz vein was segregated. As the 
water and various gaseous compounds become more and more concentrated 
in a residual ^'mother liquor'' during the crystallization of the magmas, 
these residual solutions, charged with silicic acid, penetrate from the con- 
tact into fissures and deposit vein quartz, together with metallic and non- 
metallic compounds, which were previously uniformly distributed in the 
molten magma, but gradually retreated into this residual water. 

The reader should compare these deductions with what was previously 
said (page 14:\ on the processes of magmatic differentiation. , 

Independent of the above mentioned American authors, E. Hussak ex- 
pressed similar views in regard to the deposits at Passagem (see later). 

From this point of view, the genesis of such gold quartz veins is analo- 
gous in nature, though of very different material, to that of tin veins, whose 
genesis is discussed farther on. The statements just made also apply par- 
ticularly to the cuprous gold quartz veins characterized by the presence of 
tourmaline. 

T. Pyritic Oold Quartz Veins} 

A typical development of this class is found in the famous "gold belt*' of 

' J. E. Spurr: 'Creolopy of the Yukon Gold District, Alaska.' 18th Ann. Rep., 
IT. S. Geol. Surv., Ill, 1896-97, p. 298, et seq. 

' G. F. Becker: 'Goldfields of the Southern Appalachians.' 16th Ann, Rep., 
p. 274. 

•M. Laur: 'Du eisement et de 1 'exploitation de I'or en Calif omie.' Ann. d 
Mines, 1863, Ser. VII, Vol. III. J. D. Whitney: 'Geol. Surv. of California,' 1865, 
Vol. I. H. W. Turner : 'Notes on the Gold Ores of California.' Amer. Jovm. of 8c, 
1894. 
W. 
Geol. 




298 THE NATURE OF ORE DEPOSITS. 

California. This very extensiTe mineralized area lies on the west flank of 
the Sierra Nevada, sloping gently toward the great longitudinal yalleys of 
the Sacramento and the San Joaquin rivers. 

This great mountain range is essentially composed of slates of Carbon- 
iferous (Calaveras formation) and Jura-Triassic (Mariposa formaticMi) 
age^ which are everywhere broken through by granite rocks and altered by 
contact-metamorphism. Black slates with limestone intercalaticms and 
diabasic intruded masses, as well as sandstones, prevail in both the two 
formations. The beds appear overturned, probably in consequence of an 
overfold in an easterly direction, and a steep easterly dip prevails. The 
beds strike north, or toward the axis of the range, which runs northnorth- 
west. After some older folding and faulting, the principal uplift of the 
range began in late Tertiary time. 

The gold veins are in the main parallel with the older folds, that is, 
parallel to the axis of the range. The main so-called ^mother lode' is a 
zone of veins 70 miles long, 6i/^ miles wide, extending from Mariposa 
County (Mount Ophir) to beyond Placerville, and often following the con- 
tact zones of intrusive plutonic masses. It is, in fact, a collection of par« 
allel quartz veins, often interrupted, which either coincide in strike with 
the black clay slates of the Mariposa formation, or cross them at a very 
acute angle. The dip is usually east at 50 to 70% and follows in the main 
the dip of the slates. The thickness of the larger veins is often 10 m. (32.8 
ft) or more, but occasionally decreases to 1 m. (3.3 ft.) North of the 
Lawrence mine the mother lode breaks up into stringers, and finally re- 
solves itself into a tangled network of small, often highly auriferous quartz 
stringers, associated with a definite plate zone (seam diggings). Other 
important veins occur independently of the mother lode, in the contact 
zone between the Calaveras slates and the granite at Grizzly Flat, southeast 
of Placerville, others to the north at Grass Valley and Nevada City. Some 
of the lodes follow for some distance the contact between the slates and 
intercalations of altered diabase rocks. The veins are sometimes dliaplaced 
by cross faults, as observed by Laur. 

Outside of the real gold belt of the Sierra Nevada, California contains 
various other gold veins of less importance, for example in the Coast Range 
at San Diego. 

The workable ore occurs in pay shoots in true fissure veins, best developed 
in schists, and absent in serpentine. Very large outcrops of white quartz 
are low grade, lenticular, and pinch out. (Ransome.) 

quartz veinw. ' IH95, Bull, of the Geol. Soc. of Am.. Vol. VT. p. 221. Ihid. : 'The Gold- 
Quart z- Veins of Nevada Citv and GrrRs Valley Distr., Calif.' 17th Ann. Rept, U. 8. 
Geol. Sun.. 1896. pp. 13-202. B. Knochenhauer : 'Der Goldherpbau CaliloniienB ' 
^Leipzig, 1897. F. L. Ransome : Gold Belt,' folio, U. S. Geol. Sun-. 



EPIQENETIC DEPOSITS. 299 

In all these lodes^ the only gangue is quartz, which in the richer occur- 
rences tends to separate into thin layers (ribboned quartz), while in the 
poorer ones it is more massive. In this quartz the gold is usually inter- 
spersed as very fine, hardly perceptible particles, more rarely in larger 
aggregations. The fineness of this gold is as a rule 850-870. The gold is 
always accompanied by gold-bearing pyrite, occasionally also by zinc- 
blende, galena, copper pyrite, arsenopyrite and tellurides, rarely by pyrrh- 
otite, molybdenite, tctrahedrite, cinnabar and antimonial-lead ores. The 
concentrates contain 120-140 gm. (3i^ to 4 oz.) gold to the ton, rarely 
more. The average amount of gold in the total amount of ore extracted 
is assumed by B. Knochenhauer to be 15-20 gm. (0.4 to 0.6 oz.) per ton. In 
the gossan, which extends to a depth of 40 m. (131 ft.), rarely to 60 m. (196 
ft.), much higher values were found, 125-160 g. (3.7 to 4.7 oz.) per ton 
being not infrequent. 

Though the amount of gold gradually decreased below the gossan, yet in 
the undecomposed zone itself no decided impoverishment or even barrenness 
has yet been observed in the Califomian lodes. The shafts of Kennedy 
mine near Jackson City encountered workable gold ore even at 600 m. 
(1,968 ft.) to 655 m. (2,150 ft.) The distribution of the gold in the 
lodes, it is true, is not uniform. Ore shoots occur in overlapping lenses 
and ordinarily replace each other in such fashion that one wedges out down- 
ward, while a new one wedges in somewhat to the side. 

The origin of these lodes is thought by Lindgren, one of the best posted 
authorities, to be independent of the country rock, and hence the veins 
cannot have been formed by lateral secretion as that theory is understood 
in its narrower acceptation, but rather by rising thermal waters, charged 
with silica, various carbonates and carbonic acid. This hypothesis is fur- 
ther strengthened by a study of the alteration of the vein walls and the 
included material. This rock is altered with the formation of carbonates 
and partial sericitization. 

The auriferous wealth of California was discovered in 1848. The pro- 
duction continues to be considerable; in 1903 the total production was* 
$16,363,000, of which $1,475,749 was produced by dredges working in the 
river bottoms, while $872,812 was the result of hydraulic mining and 
$905,679 of drift mining. 

During the last 50 years, California produced gold to the value of 
$1,251,696,817, an annual average of $25,031,936. In 1898 the gold pro- 
duction was 22,418 kilograms, $15,906,478 ; for 1903 it is in round numbers 
$16,363,000, or including the $498,412 commercial value of silver alloyed 
with the gold, it is $16,861,412. 

Gold veins of this type are also found in various other parts of the United 



'« 



300 THE NATURE OF ORE DEPOSITS. 

States^ as in Idaho% Oregon^ Bouthem Alaska^^ the Yukon' gold district, 
and in part also in the southern Appalachians^. A special description of 
these areas, treated in a masterly way in the works cited below, would ex- 
ceed the limits of space of the present work. 

In South America an important mining district containing this kind of 
gold vein occurs at Callao, on the right bank of the Yuruari, south of the 
Orinoco delta, in the so-called Caratal district of Venezuela, The lodes of 
this region are remarkable in that the pyrite is subordinate in amount to 
the free gold, which is probably due to a specially deep secondary decom- 
position of the pyrites. The region exported from 1866 to 1886 the grand 
total of 55,862 kilograms of gold^. 

Pyritous gold quartz lodes are also worked in Dutch Ouiana (Surinam) 
and in British Ouiana. 

A grand development of the pyritous gold quartz formation is. witnessed 
in Australasia^ both on the continent and on the islands of New Zealand and 
Tasmania. Out of a great number of examples, we can only select a few. 

A large and rapidly rising gold production has recently drawn attention 
to the gold fields of West Australia, whose veins are mostly of the class 
under discussion. 

The gold field of that region, which covers an area greater than Germany, 
occurs in the arid tableland of Western Australia, and owing to its lack 
of water and wood, presents great difficulties to mining enterprises. The 
country consists of upturned clay slates, quartzites, mica schists, phyllites, 
talcose schists and chloritic schists, with many diorite and diabase dikes, 
which have often been transformed by pressure into schistose amphibolites. 
In the Coolgardie district, east-northeast of the port of Perth, at Kalgoorlie 
and elsewhere, these rocks are traversed by many zones of decomposition, 
mostly striking north-northwest or north-northeast and penetrated by 
numerous auriferous quartz stringers. Simple gold quartz lodes, often de- 
veloped as bedded or lenticular veins, sometimes traverse the country rock. 
While the stringer zones do not show at all on the surface, the simple quartz 
lodes, called ^reefs,' often form long and high qyartz crests, a prominent 

' Lindffren : 'Mining Distrirts of Idaho Basin, * 18th Ann. Rep. U. S. Geo!. Survey, 
1898. 'Blue Mts. of Oregon,' 22d Ann. Rep., 1902. 

' G. F. Becker: 'Recon. Gold Fields Southern Alaska,' 18th Ann. Rep. U. S. Geol. 
Survey, 1898, III, pp. 1-86. 

» J. E. Spurr: 'Geol. of Yukon Gold Dist., Alaska,' 18th Ann. Rep. U. S. Geol. 
Sun^ey, 1898, III, pp. 87-392. 

*G. F. Becker: 'Gold Fields of Southern Appalachians,' 16th Ann. Rep. U. 8. 
Geol. Survey, 1896, III. 

* C. Le Neve Foster : 'On the Caratal Goldfield. ' Quart. Joum. Geol. Soc., XXV, 
1869, p. 236. Fuchs and De Launay : 'Trait<5,' II, pp. 896-902. 

•K. Schmeisser: 'Die Goldfelder Australiens. ' Berlin, 1897. Wolff: 'Das 
Australische Gold, seine Lagerstatten und Associationen. ' Zettschr. d. d. 0. G., 1877. 



EPIOENETIC DEPOSITS. 301 

feature in the landscape. The gold is free in some veins, as in the Great 
Boulder main reef at Kalgoorlie, and also occurs in calaverite and other 
tellurides of various kinds, and is everywhere associated with pyrite. Be- 
sides this, some arsenopyrite, galena, copper pyrite and some rarer ores are 
mentioned. The telluride lodes, according to Pittman, accompany eruptive 
dikes of porphyries now altered to schists. They form perhaps a special 
type and should not be included in the gold-quartz veins. The amount of 
gold in thjB quartz lodes averages, according to K. Schmeisser^ 30-60 gm. 
per ton ($20-$40), and in the quartz stringers of the compound lodes and 
alteration zones 30-120 gm. ; in the rest of the filling of these shear zones it 
reaches at most 30 gm. per ton. In exceptional cases, some mines for a while 
recorded a gold content of the ore treated in their stamp batteries of 90-470 
grams per ton. The gold content decreases almost everywhere from the 
zone of oxidation downward. According to H. C. Hoover, at a depth of 
but 30 m. (98 ft.) it has declined to one-half, or even to one-fourth of the 
amount found at the top. 

The remarkable residual placer gold deposits of this rjegion, called ce- 
ments, are discussed under gold-bearing gravels. 

The gold production of West Australia in 1898 was 29,218 kilograms of 
fine gold. In 1902 it was 1,819,308 oz. or $82,454,344. 

Most of the gold veins of Victoria belong to the pyritic gold-quartz tjrpe, 
with transitions to the arsenical type, the most important districts being 
Ballarat, Beechworth, Bendigo (Sandhurst), Maryborough, Castlemaine, 
Ararat and Oippsland. The veins occur mostly in Silurian slates and in 
many cases are closely related to dioritic eruptive masses. We have already 
described the remarkable saddle lodes of Bendigo in the Sandhurst district. 
This district also contains the largest deep mines of Australia, One shaft 
on these gold quartz lodes has, according to Lindgren, reached, in 1904, a 
depth of 4,000 ft.^ Mention has already been made of the ladder* lodes of 
Waverley. 

In New South Wales', veins of this class occur in the Wyalong goldfield, 

and in Queensland at Charters Towers*. In the latter area the pyrite is in 

part replaced by auriferous pyrrhotite. This same colony also contains the 

' K. Schmeisser: 'Die Goldf elder Australiens. * Berlin, 1897. p. 43. A. Gmeh- 
linp : ' Beitrag zur Keimtniss der Westaustralischen Goldfelder./ Oeaterr. Z. f. B. u. H., 



1898, p. 161, and 'Ueber die Golderzlageretatten von Coolgardie,* Ebenda, 1897, p. 

upon the Coolgardie 
Goldfields.* Mining Journal, 1897, p. 819. P. Knisch: *Zeit f. Prak. Geol.,' 1901, 



_ — ^ ^^ J _ y , — ■ ^ — — _ — ^-^ — — — ^^ — , , J 

425. Sloet van Oidruitenborph : 'Technical observations upon the Coolgai 



pp. 211-217 

' 'Gold Vans of Victoria,' The Engineering and Mining Journal, March 9, 1905. 

' E. F. Pittman: 'On the Geol. Structure of the Wvalong Goldfields.' Records 
Geol. Su^^'ey, N. S. W., 1894, p. 107. 

* R. L. Jack : Report on the Geology and Mineral Resources of the District between 
Charters Towers Goldfields and the Coast, 1879. 



302 THE NATURE OF ORE DEPOSITS. 

Crocodile goldfield, 42 km. (25.2 miles) southwest of Roekhampton/ with 
the remarkable deposit of Mount Morgan^ which deserves a few remarks. 

Mount Morgan^ "the greatest gold deposit of the earth"^ rises 152 m. 
(498 ft.) above Linda (Mundic) Creek and 1^225 ft. above sea level. It 
is an obtusely conical hill, by far the greater part of which consisted of 
workable gold ore. Its summit has long been removed by open-cuts, and its 
deeper parts have been explored in all directions by drifts and stopes ex- 
tending even below the bottom of the valley. Down to a depth of 90 m. 
(295 ft.) the ore is very uniform, consisting of bluish-gray quartz, silicious 
red hematite, colored light red to bluish black, brown hematite and man- 
ganese iron ore, together with white, vesicular, often foam-like, silicious 
sinter, kaolin and ocherous earth. Below 90 m. (295 ft.) this gossan 
changes into a gold-bearing and pyrite-bearing quartzite. The average gold 
content decreased constantly downward, toward the end very slowly, from 
about 115 grams to 40 grams per ton. The production of this single mine 
in 1896 was some 95,000 tons of ore with 4,560 kilograms of gold. In the 
year ending May, 1902, 213,907 tons of ore were treated, yielding 147,628 
oz. of gold. 

The form of the deposit is stock-like, tapering downward, and it is trav- 
ersed by several dikes of dolerite, rhyolite and felsite which, according to 
T. A. Bickard, are genetically associated with the impregnation of the 
entire rock mass with gold-bearing quartz. On the other hand, the occur- 
rence of silicious sinter, which seemed to indicate a deposition of dissolved 
silicic acid near or on the earth's surface, induced R. L. Jack to interpret 
Mount Morgan as a geyser formation*. It seems premature to pronoimce 
in favor of either view, especially as the argument for the former does not 
seem to include a definite statement as to the petrographic character 
formerly possessed by the main rock mass of the mountain, which is now 
completely silicified and mineralized. 

This class also includes most of the veins of the African goldfields. We 
will mention but one example, the famous Sheba mines' near Eureka City 
in the Transvaal, whose ores created universal astonishment by their re- 
markable richness, up to 250 grams per ton, when the work was as yet con- 
fined to the gossan. These mines lie in the DeKaap goldfield between Del- 
agoa bay and the capital of the former Transvaal republic. 

' R. L. Jark : 'Reports of the Queensland Geoloe:. Survey,* 188^, and *Mt. Morean 
Gold Deposits/ 1892. T. A. Rickard: *The Mt. Morgan Mine.' Trans, Am. Inst. 
Min. Eng., XX, 1891, p. 133. K. Srhmeisser: op. cit., pp. 81-84. 

'W. H. Weed: 'A Gold-bearing Hot Spring Deposit.' Amer, Jour. Set., 3d 
series, Vol. XLII, pp. 166-169. 

•P. R. Krause: 'Kurze Schilderung der Grubenbezirke von Pilgrim's Rest.' 
Zeit. /. Prak. Geol, 1897, p. 22. 



EPIOENETIC DEPOSITS. 303 

Mention may also be made of the gold deposits in Matabeleland and 
Mashonaland^ the ancient Semitic mining settlements of Zimbabwe^^ and^ 
lastly^ of the lodes exploited by the ancient Egyptians in the desert that 
lies between the Nile and the Bed Sea*. 

Asia^ in the Ural and the Amur country^ presents numerous deposits of 
this kind. Among the Ural deposits belonging to this class the veins of 
the areas east of the mountains proper, at Cheleabinsk, where the great 
Siberian railway begins, are worthy of mention. The rock of this locality, 
according to A. Karpinsky', is a highly dynamo-metamorphosed granite, in 
part a hornblende granite. This is traversed by numerous gold-bearing 
veins, some striking northeast, some northwest. The vein filling consists 
of completely decomposed country rock and of quartz. The latter usually 
forms solid vein stringers 0.2-0.7 m. (0.6-0.22 ft.) thick, exceptionally 
2 m. (6.6 ft.), or may also pervade the decayed granite in a network of 
veins. In the upper part of the vein the quartz contains free gold, but at a 
depth of 30-40 m. auriferous pyrite and arsenopyrite make their ap- 
pearance. The gold content varies as a rule between 2.0 and 10.4 grams 
per ton. However, enrichments with 30 grams per ton and above have been 
encountered. Some of the veins, like those of California, are built up very 
regularly out of quartz layers 2-5 cm. thick. These veins are especially 
notable because of their gold-bearing pyrites and the presence of ocher 
enclosing free gold. Such a lode, when its dip is very low, as in the Ivan- 
ovsky vein, which dips north-northwest at 15**, is at first often taken for 
a bed. 

Among the Siberian gold veins of this kind, we will merely mention that 
of Onon*, west-southwest of Nerchinsk in Transbaikalia. The lodes there 
are associated with aplites traversing Paleozoic schists. 

Of European gold quartz veins of this type, the Hohe Tauem veins 
of the eastern Alps are best known. The mines are still worked in 
Goldberg of Kauris and at the Rathhausberg, near Oastein". Gneisses and 
other crystalline schists of the central Alps are traversed by narrow quartz 
veins, usually so thin as to be called leaves.' These contain extremely fine 

' R. Rugg: 'Matabeleland, its Goldfields,' etc. London, 1891. Idem.: 'New 
map of Matabeleland, Mashona and Tati Goldfields,' London, 1891. A. G. Sawyer: 
'The Goldfieldrt of Mashonaland,' with 21 mapB and plates. London, 1894. Th. 
Bent: 'The Ruined Cities of Masjonaland/ London, 1896. C. Pieters: 'Im GMr 
lande des Alterthums.' Munich, 1902. 

' Ch. A. Alford: Reference in Zeit /. Prak. Oeol, 1902, p. 9. 

' 'Guide des excursions du VII Congres. Geolog. International/ 1897, V, p. 30. 
« E. D. Levat : 'L'Or en Siberie Orientale.' I, p. 64. 

*B. V. Cotta: 'Erzlagerstatten.' II, pp. 318-324. F. Posepny: 'Goldbergbauder 
Hohen Tauem. ' A rchiv f. Prak. Geol., I, 1880, p. 1 et sea. R. Canaval : 'Das Bei^au- 
Terrain in den Hohen Tauem.' Klagenfurt, 1896. With bibliography. P. Knisch: 
'Die Goldlagerstatten in den Hohen Tauem. ' Zeit. f. Prak, GeoL, 1897, p. 77 et aeq. 



304 THE NATURE OF ORE DEPOSITS. 

particles of free gold, with pyrite and a number of other sulphide ores, such 
as copper pyrite, arsenopyrite, galena, zinc-blende and stibnite, and very 
rarely molybdenite and various rich silver ores. Because of this highly 
varied mixture of ores, in which, however, pyrite greatly predominates, the 
veins are not so truly typical of the class as the Califomian or Australian 
gold quartz lodes. They form a transition from the pyritic-gold-quartz 
veins to the pyritous lead formation. A feature of special importance in 
these Tauern ^leaves' is the strong impregnation of the wall-rock with ore, 
which in some cases has led to the development of banded masses re- 
sembling beds, as at the Heinzenberg, near Zell, in Tyrol. The production 
of the Bathhausberg in 1898 was only 76.7 tons of gold-bearing concen- 
trates. 

A more typical development of the pyritic gold-quartz vein is seen in the 
Piedmont Alps, as for example at Brusson^. 

In Bohemia, mention must be made of Eule-Jilova*, between the valleys 
of the Sazava and the Libre. Besides pyrite and free gold, the ores also 
carry arsenopyrite. The mining industry of Eule is extremely ancient, 
dating back to the end of the 8th century. This place may have been the 
greatest producer of the former golden wealth of Bohemia. In 1898 the 
work at Jilova had almost entirely stopped and only 38 tons of gold ore 
were produced. On the contrary, the Borkowitz mines in the Kuttenberg 
district produced during the same year 2,288.4 tons of gold ore. Work has 
also been recently resumed on pyritous gold ore lodes at Mount Roudny, 
east of Wotitz. 

II. Cupriferous Oold-Quartz Veins. 

In this type, the quartz gangue contains not only free gold and auriferous 
pyrite, but also a good deal of copper pyrite and other copper ores. Tour- 
maline is very often a characteristic accompaniment. The lodes are gen- 
erally connected with acid eruptive rocks, especially granites. 

The best known example of this type of vein is found in the vicinity of 
Berezovsk (Berjosowsk)', near Ekaterinburg, on the east slope of the Ural 
mountains. 

Berezovsk lies in a low-rolling region, covered with pine and willow, and 

underlain by a muscovite granite schist and mica schists, strongly affected 

by d}Tiamo-metamorphism and deeply decomposed. These talcose, chlorite 

> C. Schmidt: 'Geol. Gutachten/ Berne, 1900. 

' F. Posepny : 'Goldvorkommen in Bdhmcn/ Archiv f. Prak. Geol., II, 1895, p. 79. 

' B. von Cotta : * Erzlapjerstatten, * II, pp. 554-550. F. Posepny : 'Golddistricte von 
Berezov iind Mias im Ural,' Archiv. f. Prak. Geol., II, pp. 409-598. A. Kaminskv : in 
'Guide des excursions du VII. ConRrfes Gdolog. Internal./ 1897, V, p. 42. With biblio- 
graphy. 



EPIGENETIC DEPOSITS. 305 

and clay schists^ all of which in the decomposed^ reddish-colored condition, 
are called 'krassik/ are traversed by numerons vertical dikes, 2-40 m. (6.6 
ft. to 131 ft.) thick, running north and south. The dike rock is a micro- 
granite called beresite, and this rock is also decomposed down to great 
depth. These dikes have been exposed by deep open-cuts and extensive gscl- 
leries and shafts. At right angles to the strike of these beresites, extending 
from wall to wall, and sometimes for short distances past the dike wall, 
there are numerous veinlets or stringers of gold-bearing quartz, which are 
seldom over a few cm. (3 inches) thick, but in exceptional cases as much 
as 1 m. (See Fig. 121.) 

Besides free gold, these quartz veins carry a. variety of sulphide ores and 
the products of their decomposition; according to B. von Cotta these sul- 
phides consist of pyrite, some aikinite (PbCuBiS,), gray copper, copper 
pyrite and compact galena, as well as red lead ore, melanochroite, vauque- 
linite, pyromorphite, vanadinite, cerussite, anglesite, limonite, and bismuth 
ocher. Very frequently the quartz also contains long needles of a gray- 
green tourmaline, running at right angles to the walls, as well as small 
crystals or radiating balls of pyrophyllite, and sometimes magnesite. A 
very remarkable phenomenon is the presence of pseudomorphs of a chrome- 
bearing tourmaline after pvrite, which are occasionally found in these gold 
quartz stringers, as illustrated by specimens in the collection of the Moscow 
University. 

Besides free gold, these veins also contain gold in the pyrite. According 
to A. Karpinsky, it varies between 2.5 and 30, locally even 250 g. per ton. 
The average may be assumed at about 13 g. per ton. 

The micro-granite dikes (aplite veins) carrying the gold quartz stringers 
may be genetically connected with the granite massive of Lake Shartash, 
which is not far away. The chips of this perfectly fresh rock knocked off 
in quarrying it for use in stairways and steps, door jambs, etc., are credibly 
stated to contain as much as 1 gm. (66 cents) of gold per ton. If thus the 
intrusive stock proper is auriferous, it need not be wondered at that the 
subsequent extrusions from the same magma hearth in the form of aplites 
also brought with them a gold content, which was concentrated in the 
quartz stringers. These quartz stringers must, it would seem, be accepted 
as having the same origin as pegmatite. See other statements on this 
subject on page 297. 

The gold veins of Berezovsk were discovered in 1745, and the mines are 
still being worked. 

The cupriferous-gold-quartz class of veins also includes most of the gold 
veins of Scandinavia. On Bommel Island, on the west coast of Norway, 
between Bergen and Stavanger, veins of this class have been described by 



306 THE NATURE OF ORE DEPOSITS. 

Th. Scheerer and afterward by H. Reusch/ and have been mined since 1884 
by an English company. The rocks consist mainly of a saussurite gabbro, 
broken through by quartz porphyr}' and dikes of a 4iorite altered by dyna- 
mo-metamorphism. The gold quartz veins occur in tliese rocks, especially 
in the quartz porphyry. Their thickness may amount to as much as 1 m., 
strike northeast, dip 25-45** southwest. The vein filling consists of quartz, 
some calcite and chlorite, with free gold, copper pyrite, pyrite, galena and 
at times tetradymite (bismuth telluride) and very rarely native silver. 
The gold content of the ore, according to H. Louis, varies between 7 and 
28 g. per ton. 

The gold-bearing tourmaliniferous copper veins in the Thelemark area of 
southern Norway have already been mentioned. The gold vdna 
of Eidsvold, too, 75 km. (45 miles) north of Christiania, should alao be 
mentioned here. 

In Sweden the cupriferous gold quartz veins are represented by the lodes 
of Adelfors in Sml^land, as well as by gold quartz stringers in the pyrite 
stock of Falun {q. v,). 

Very typical examples of the cupriferous gold quartz veins have been 
reported by W. Moricke^ in Chile. They represent an extreme variation of 
our group of the tourmaline-bearing copper formation. Besides quartz with 
tourmaline, they contain pyrite, free gold, copper pyrite and other copper 
ores. They are also apt to be associated with granites a^d other acid 
eruptive rocks. As examples may be mentioned the veins of Guanaco, An- 
dacollo and IjOs Sauces in Chile. 

In Australia also gold-quartz veins rich in copper ores seem to be rather 
common, especially in New South Wales, judging by the material in our 
collection. Whether they carry tourmaline or in other ways form a well 
characterized group, lias not yet been ascertained. 

On the Philippine Islands, according to oral statements by P. V. Voit, 
this class is represented by the veins of Mambulao and Paracale. A Trans- 
vaal example on the Malmani river is a vein in dolomite in the Marico 
District'. 

A unique type of gold vein occurs at Bossland, B. C, characterized by 
Lindgren* as biotitic gold copper veins. They are well marked fissure veins, 
contained in granular intrusive rocks, ranging from diorites to monzonites 
and even syenites. The ore minerals are pjrrrhotite, chalcopyrite and a lit- 
tle arsenopyrite, all holding gold, but usually not free, or amenable to amal- 

* H. Reiisch : 'Bommelften og IvarmSen, Cristiania/ 1888, p. 392. Fhillipe-Louii: 
Ore Deposits,' 1896, p. 519. 

' W Moricke: 'Die Gold-, Silber- und Kupfererzlagerstatten in Chile,' 1897. 

* G. A. F. Molonj^aafT: 'G^ol. de la Rep. Sud Africaine,' 1901, p. 40. 

* W. Lindgren : 'Metasomatic Processes,' Trans, Am. Inst. Min. Eng., 1900, p. 69. 



EPIGENETIC DEPOSITS. 807 

gamation. The chief gangue mineral is biotite, with a little quartz, ealcite, 
muscovite, amphibole, chlorite, tourmaline and garnet. The veins are 
replacement deposits along fissures, the hornblende of the rock altering to 
biotite, and the feldspar replaced by pyrrhotite and chalcopyrite. The 
process indicates dynamic metamorphism rather than ordinary vein-forming 
processes. 

III. Antimanial Oold-Quartz Veins. 

In place of pyrite this class contains stibnite as a characteristic com- 
panion of the free gold, the antimony glance itself being gold-bearing. As 
subordinate minerals of these veins p}Tite still continues to appear with 
arsenopyrite, rarely galena, blende and copper pyrite, and, together with 
quartz, there may be a slight amount of carbon spars. 

Good examples of the class are seen in the mineral district of KrdsnA- ' 
hora (or Schonberg) and Milesov (or Mileschau) in central Bohemia, south- 
west of Prague, described by F. Posepny*. An intrusive stock of granite 
intercalated between schists, is traversed by a few porphyry dikes and 
numerous ones of lamprophyre. Most of the veins accompany these dikes. 
Besides quartz as the principal gangue, they carry some ealcite, and as 
ore minerals, stibnite with a gold content of 100-133 g. ($66.00 to $87.88) 
per ton, arsenopvrite and pyrite, together with about 300-400 g. ($198- 
$264) per ton in native gold in scales and botryoidal aggregations in the 
quartz ; also antimony, ochre and pyrostibite. The stibnite often constitutes 
the larger part of the filling. Masses with a thickness of as much as 1 m. 
(3.28 ft.) are said to have been found. 

At Mileschau a thriving gold mining industry was carried on as early as 
the fourteenth ccnturv. Of late vears the mines have been worked for 
stibnite. Incidentally, however, in the production of 661.5 tons of anti- 
mony ore in 1898, 254.3 tons of gold quartz and 180.4 tons of gold-bearing 
pyritic concentrates were produced at Schonberg and Proutkowitz. 

Another typical example of this class occurs, according to B. von Cotta*, 
at Magurka, in Hungary, on the north slope of a granite range, 1,200-1,800 
m. high, separating the Comitat of Sohl from Liptau. The granite is there 
traversed by quartz veins varying from a few cm. (or inches) to 4 m. (13 
ft.) thick. The veins contain stibnite and free gold, together with balls of 
granite. The accessory minerals are galena, zinc-blende, pyrite, copper 
pyrite, brownspar and calcspar. Ordinarily the quartz occurs along the 
walls of the vein, while the stibnite is found in the middle of the vein. 

This class also includes the veins of the well-known district of Brand- 

* R. Helmhacker : 'Der Antimonbergbau Miles6 bei Krfen^ Hora.' 1874. P. 
PoBcpny : *Goldvorkommen, Bdhmens/ Archiv. /. Prak. GeoL, 1895, p. 165. 

' B. von Cotta: Berg u. Hutten. Zeit, 1861, p. 123. 



308 THE NATURE OP ORE DEPOSITS. 

holz, near GtoldkronachS in the Fichtelgebirge. At this place Cambrian 
8ericite schists are cut by quartz yeins, containing subordinate quantities 
of brownspar^ more rarely calcspar^ and occasionally barite, and carrying 
stibnite, gold- and silver-bearing pyrite and arsenopyrite and free gold, be- 
sides very small amounts of striated galena, brown blende, native antimony, 
antimony ocher, stiblite, heteromorphite and boumonite. The quartz is 
often thoroughly impregnated with minutely disseminated ores. The veins 
often wedge out and are for some distance replaced by a simple fissure, 
alongside of which the adjoining rock is silicified and impregnated -with 
arsenopyrite and iron pyrite. Mining, which dates back to the fourteenth 
century, was resumed after the transfer of the principality of Bayreuth to 
Prussia, about 1800, in part under the management of A. von Humboldt, 
but was again abandoned in 1861. 

Antimonial gold quartz veins occasionally occur in gold ore districts 
outside of Europe ; for example, at several points in Australia, in the Selati 
goldfield and in the Murchison range in the Transvaal. 

In the last-named mountains, hornblende schist and quartzite schist are 
traversed by a series, almost 36 miles long, of veins which generally follow 
the strike of the schists in the form of beds, and contain quartz with aurif- 
erous antimony glance, in part also with gold-bearing pyrite and copper 
pyrite. The Invicta, Free State and Gravelotte mines are operated on such 
veins. 

IV. The Arsenical OoldrQvartz Veins, 

In this class free gold is accompanied by arsenopyrite as the most promi- 
nent of the ore minerals in a gangue of quartz. 

Such veins have been worked since 1881 at Santa Cruz, in the state of 
Santa Barbara, Honduras'. The principal veins, 2 m. thick on an average, 
consist of quartz, gold-bearing arsenical pyrite and mere traces of galena. 
The ore contained 25-30 gm. per ton. 

Occurrences of similar kind are scattered all over North America, being 
mostly connected with the pyritous gold quartz veins by transitions. The 
veins in the Huronian schists at Marmora, Ontario", Canada, are typical 
examples. 

The peculiar arsenical gold ore deposits, regarded by many as beds, at 
Passagem in Brazil, are peculiar, as will be seen by a brief description, 
taken from E. Hussak. 

» C. W. Gumbel : 'Fichtelpfebirp:e,' 1879, pp. 386-393. F. v. Sandberger: 'Ueber 
die Erzlagerstatte von Goldkronach bei Bemeck,' Sitzber. d. math-.phys. CI. d. k 
bayer. Ak. d. W., 1894, Vol. XXIV, part II. 

' Fuchs and De Launay: 'Traits,' II, p. 942. 

■ R. P. Rothwell: 'The Gold Bearinj^ Mispickel veins of Marmora, Ontario, 
Canada/ Trans, of the Amer. Inst, of Min. Eng., 1881. 



EPIQENETIC DEPOSITS. 



309 



Paseagem* lies in the province of MinaB Geraee, 1 km. (4.2 milee) east of 
Ouro Preto. Next to Morro Velho it ie to-day tiie moat productive gold 
mine of Brazil, and has been worked since the end of the last century. 

According to Hussak, the most important deposit of the locality ia a 
bedded vein of quartz, carrying tourmaline and auriferous areeoopyrit^ 
with subordinate amounts of pyrit« and pyrrhotite in patches. It dips 
southeast at an angle of but IS-SO", and is entirely conformabk with the 
enclosing quartzite schist. The latter is part of a series of rocks made of 
hematite mica schist and of mica schists and itabirite*. 

The matrix ia here and there replaced by lenticular masses of sericite- 
quartzite schists. N'ear the underiying mica schist, which contains ataaro- 




Ttg. 172. Croea-eection through the quartz b«d of Paasagem. (M. P. Ferrand.) 
a, CAngt. (weathered cover); b, Hnbirite; c, crypto-crystalline echut; d, quart* 
vein and quartzites; e, contact quattzltea; f, mica schist. 

lite and cyanite, a selvage zone or streak of black graphitic schist occurs, 
and this material is also occasionally seen near the finely crystalline qoartz- 
amphibole-schist, that forms the hanging-wall (see Fig. 173). 

In this quartz vein, aggregations are very often found of a finely felted 
quartz-itourmaline rock, called carvoeira, in which andalusite also occurs 
at times. Other aggregations consist of garnet with biotite, pyrite and 
cyanite, as well as of a greenish oligoclase-albite. 

The gold occurs either in beautiful crystals or merely in jagged or scaly 
flakes, filling the interspaceB of the tourmaline rock, especially where the 
latter is rich in araenopyrite. The gold carries a considerable amount of 
'M. P. Ferrand: 'L'or a Minas Geraes,' Vol. II, pt. 1. Ouro Preto, 1894. E. 
Huseak* 'Der enldfflhrende kiesifn Quarzlagergang von Passagem, Zeil. f. Prak. 
Oeot., 1898, p. 345. 

* Itabirite is reKarded by eome ReoloKiats as a mantle of residual rand remented bv 
limonite depc«ite<rby surface water, and merely a result of weathering. See 'Harrison ■ 
Report on British Quiana Laterites.' — W. 



310 THE NATURE OF ORE DEPOSITS. 

bismuth, which apparently is present in the form of an alloy. The hi^j 
auriferous arsenopyrite-tourmaline aggregations also carry small crystalfl 
of monazite and xenotime. 

E. Hussak is inclined to consider the vein as of intrusive nature, and to 
regard it as an ultra-acid granite apophysis. In support of this view, he 
points to the presence of zircon, monazite, xenotim and albite, minerals that 
are characteristic of granite, and which occur as accessories in the quarts 
vein, and also to the presence of a large granite mass only 1 km. away. 
(Both Lindgren and Emmons maintain, however, that Hussak's facts 
prove it to be a normal fissure vein. See 'Genesis Ore Deposits,' p. 758.) 
The minerals tourmaline, andalusite, staurolite, cyanite, garnet, biotite, 
hercynite (iron spinel), which are also found in the vein, he regards ss 
contact minerals, resulting from thermal metamorphism of the quartzite 
schist. His interpretation of this remarkable deposit is akin to the views 
of North American investigators on the relationship of certain gold quartz 
veins with pegmatites, mentioned on page 297. In many respects the veins 
in diorite and granite of Meadow Lake, California, resemble the Brazilian 
deposits just described. According to Lindgren,* these veins contain a 
quartz and tourmaline gangue carrying pyrite, arsenopyrite, pyrrhotite, 
blende and copper, besides gold. 

Among the gold ore deposits in the Ural, the arsenical gold quartz 
formation includes the veins of Kotchkar*, repeatedly described in recent 
times, situated in the steppe immediately adjoining the cast slope of the 
mountains, in the Government of Orenburg. The region is underlain by 
sheared and decomposed granite. The vein filling consists of crushed and 
leached rock with cavernous quartz, particularly porous in the richer por- 
tions and carrying free gold, much arsenopyrite, somewhat smaller quan- 
tities of pyrite, and still more rarely manganite, copper pyrite, galena and 
stibnite. The arsenopjrrite also impregnates the adjoining granite, which 
contains from 2.5 to 375 gm. gold per ton. The ore averages .8 to 10 gm. 
^$5.20 to $6.60) per ton. In the Transvaal the bedded veins of Krouniraai, 
north of Krugersdorp, belong to this class*. 

V. The CohaUiferons Gold-Quartz Veins. 

This class has been established to include the unique deposits which 
differ decidedly from all the gold-bearing types of veins thus far treated, 

* Am. Jour. Set., Vol. XLVI, Sept., 1893. 

* N. Wyssotsky: 'Les Gisements d'Or du svstfeme de Kotchkar dans I'Ounl du 
Sud,' 'GuiSe des excursions du VII Conprfes G^ol. Intern./ 1897, St. Petersburg. 
H. B. C. Nitze and C. W. Purinjrton : 'The Kotchkar Gold Mines,' etc., TrauR. Amer. 
Inst. Min. Eng., Vol. XXVIII, 1899. p. 24. Chr. T. Nissen : 'Einiges aber das 
Goldvorkommen, ' etc., bei Kotschkar, Berg u. Hutten. Zeit., 1900, p. 121. 

» G. A. F. Molengraaflf: 'G^ol. de la Rep. Sud. Africaine,' 1901. p. 34. 



EPIGENETIC DEPOSITS. 811 

especially in the fact that the quartzy matrix is small in amount compared 
to the ores. The real carrier of the gold is in this case the cobalt mineral, 
smaltite. 

According to H. Oehmichen* and Dorffel, this imusnal occurrence of gold 
is found in the Middelburg district, northern Transvaal, along the Kruis 
river. The Lydenburg shales, part of the Cape formation, contain at this 
place intercalated eruptive sheets of aplite-like rocks and diabase, which 
are traversed by an east- west vein 2-3 cm. thick, dipping 60-70** south, 
whose chief and almost only filling is smaltite, the ore carrying 60-150 g. 
of gold per ton. The ore contains between 7 and 8% cobalt, with 0.5 to 1% 
of nickel. The aplite wall rock is sericitized and is also impregnated with 
ore. 

« A second and similar vein occurs 5 km. farther west and is also in 
diabase. This, the Laatste-Drift vein, has a gangue of auriferous quartz 
mixed with kaolin which holds smaltite and copper ores in bunches some- 
times containing molybdenite. Erythrite, limonite and scorodite are sec- 
ondary minerals found in the outcrop. The ores carry from 100-250 g. of 
gold per ton, of which only a very small part is native, while 90% of the 
gold is contained in the chalcopyrite. The smaltite contains almost no goljd. 
As the specimens from these veins that have thus far come into our 
hands differ so much from all other types of gold quartz veins we have 
thought it necessary to place these deposits in a group by themselves. They 
form a transition from the gold ore veins to the true cobalt veins, and, 
in fact, pure, non-auriferous cobalt veins are also known to occur along- 
side of the gold-bearing ores at this locality. 

17. The Silveb-Gold Veins. 

The veins of this class are of widespread distribution and include the 
greatest goM-pro<lucing deposits of the world*. The matrix of veins of 
this class is mostly quartz, but also includes lesser amounts of various car- 
bonates, especially calcspar and rhodochrosite, and rarely small amounts 
of barite. The ores contain gold in various forms, viz.: native gold, 
auriferous p3Tites and other sulphides, and very frequently various tellu- 
rides, especially nagyagite (the sulpho-telluride of lead, containing 
6-13% gold), sylvanite, a gold-silver telluride and silver telluride. 
On the other hand, various rich silver minerals occur, sUch as argentite, 

*H. Oehmichen: 'Goldhaltijre Kobaltgdnge in Transvaal,' Zett, /. Prak. GeoL, 
1899, pp. 271-274. 

'See 'Concentration des Metalleehaltes zu Erzlajrerstatten.' Zeit. f. Prak, GeoL, 
1898, p. 416. -^ . / 



312 TEE NATURE OF ORE DEPOSITS. 

stephanite, proustite, pyrargyrite, etc.^ together with argentiferous galena^ 
zinc-blende and more rarely copper pyrite, gray copper, native arsenic, 
boumonit^ stibnite, realgar and orpiment. 

All the examples of the various classes of veins thus far mentioned show 
a close geologic connection with Tertiary or late Mesozoic eruptive masses, 
especially andesites and trachytes, dacites and rhyolites. Their formation 
seems to be conceivable as an aftermath of the eruption of these magmas, 
eruptions whose only survival or lingering remnant of igneous activity is 
foimd in thermal springs and gas exhalations, genetically connected with 
the eruptions. 

The transformation of the above named eruptive rocks into propylite 
seems to have been a concomitant phenomenon of the origin of those veins. 

The silver-gold deposits of Transylvania have been carefully studied for 
a long time^ 

The deposits occur mainly in the mountain region rising from the flat 
Tertiary land north of the Maros and drained by the head waters of the 
Aranyos (that is to say, gold river), Szamos and Koros. The true nucleus 
of these "Transylvanian ore-mountains" consists of crystalline schists, 
which, however, are only seen outcropping in large areas in the northeast 
part of the region. Elsewhere they are covered and concealed by Permian, 
Triassic, Jurassic and Cretaceous strata, mainly limestones, and also by 
Tertiary beds. These rocks are cut and broken through by intrusive masses 
of andesites and dacites, trachytes and rhyolites, as well as basalts. The 
gold veins are connected with these igneous outbreaks, especially with 
stocks of the propylites just mentioned, which, as will be explained farther 
on, probably represent later andesites. The gold veins traverse both erup- 
tive masses and the adjoining Tertiary strata. 

Some of the gold deposits of Transylvania are especially characterized by 
an abundance of tellurides, especially at Nagyag, Oflfenbanya, Faczebanya 
and Fericiel. The telluride-bearing deposits of this country will be first 

* General works upon this District: Frh. F. von Richtofen: 'Studien aiis den 
ungarisoh-siebenbur^schen Traohytjjebirfcen/ Jahrb. d. k. k. geol. Reichsanst, Vienna. 
1860, pp. 1 53-277. B. von Cotta : ' Ueber Erzlajjeretatten Unpams und Siebenbiirgens, 
Gancstudien, IV, 1, 1862 (with E. v. Fellenberjr). F. von Hauer and G. Stache: 
'Geolopne Siebenburpens, ' 1863. F. Posepny: '*Zur Geolopie des siebenbflrgischen 
Erzpebirges,' Jahrh. d. k. k. geol. Reichsanst, 1688, 1, pp. 53-56. Ibid. 'Allgemeines 
Bila der Erzfuhning im siebenburgischen Bergbauaiptricte,' Jahrh, d. k. k. geol. 
Reichsanst, 1868, II, PP- 7-32. C. Doelter: 'Aus dem siebenburgischen Erzgebirge,' 
Jahrb. d. k. k. geol. Reirhsanst, 1874, 1. Ibid. 'Die Trachyte des siebenb. Erzgeb.' 
Tschermaks Mineral. Mittheil, 1874, pp. 13-30. Ibid. 'Ueber das Vorkommen von 
Propylit und Andesit in Siebenbiirgen.' same journal, II, 1880, p. 1. P. T. Weiss: 
'Der Berffbau in den sicbenburgischen Landcstheilen,' Also, Jahrh, d. k. ungar. geol. 
Landesanst., Vol. IX, part 6, 1891. Semper: 'Beitrage zur Kenntniss der Uold- 
lagerstatten des Siebenburgischen Erzgebirges,' A bhandl. d. k. preuss. geol. Landesanst. 
New series. Part 33, Berlin, 1900. L. Remenyik: 'Les Mines de M^taux de Hongrie 
i Texposition Universelle, ' Budapest, 1900. 



EPIOENETIC DEPOSITS. 818 

described and afterwards those without tellurides. We begin with Nagyag. 

The mining town of Nagydg^, in the Hunyadi Comitate lies in a narrow 
gorge in the midst of a magnificent mountain region, near Mount Hajto, 
1,047 m. (3,335 ft.) high. The surrounding heights all consist of ande- 
sitic and trachytic rocks, part of the eruptive chain of the Transylvanian 
Erzgebirge, which also contains various other mines of ancient and modern 
times, such as Coranda, Magura, Fiizesd, Boicza, Trestia, Porcura, Zrdaholz 
and Ruda* On the valley bottom, and in the deep mine workings, there are 
exposures of the sedimentary rocks, broken through by the eruptive masses. 
These stratified rocks consist of yellowish sandstones and conglomerates, as 
well as gray and reddish clays, all of Mediterranean age, and with highly dis- 
turbed stratification. Large detached blocks of these sediments are enclosed 
by the andesites in the mining area. At still greater depth, phyllite-lika 
schists are suspected to exist, being indicated by the inclusions of 
such phyllites in the andesites. The stratified rocks but very rarely, how- 
ever, form vein walls, the deposits being almost entirely in Tertiary erup- 
tive rocks. Two types of these eruptives outcrop at Nagydg. Their age is 
regarded as Miocene, since fragments of them are found in the Sarmatian 
(upper Miocelie) limestones of Vormaga. 

The neighboring eminence of Mount Calvary is formed of a quartz-free 
homblende-andesite. In the immediate vicinity of the veins, on the other 
hand, the prevailing rock is a quartz andesite or dacite with biotite and 
hornblende, as well as augite, in greatly varying quantity. The latest 
monograph on Nagydg, by B. von Inkey, following Szabo's nomenclature, 
designates both rock types as trachytes. 

The Nagydg dacite has been affected by three different kinds of altera- 
tion: (1) Nortnal weathering or decomposition on the surface, (2) by a 
propylitization or alteration into 'greenstone trachyte,* with formation of 
secondary chlorite and of carbonates from augite and hornblende, with 
accompanying introduction of gold-bearing pyrite, (3) by kaolinization. 
The two last named processes, certainly the kaolinization, seem to be 
genetically connected with the formation of the mineral veins. (See 
Thermal metamorphism.*) The propylitization is most intense and wide- 
spread in the middle and lower parts of the eruptive stock, a place that is 
also the site of the ore deposits. The kaolinization of the rocks is still more 

* Frhr. von Hincenau : 'Geol. berpmAnn. Skizze des Berpwerkes Nagyd^,' Jahrb. d. 
k. k. peol. Reichsanst., 1857, pp. 82-143. B. von Cotta : ' Ueber Erzlagerstatten Ungams 
und Siebenburpens. ' Gangstuaien, Vol. IV, part 1 , 1862. F. von Hauer and G. Stache : 
* Geol6gie.Siebenburgens, '1863. H. H5fer : '^Beitrage zur Kenntn. der Trachyte und der 
Erzneiderlage von Nagydg, ' Jahrb, d. k. k. geol. Reichsanst., 1886, p. 1. G. vom Rath : 
'V6r5spatak und Nagydg,' Sitzb. der niederrh. Ges. f. Natnr- und Heilk. in Bonn, 
March, 1876. and March, 1879. B. von Inkey: 'Nagydg und seine Erzlagerstatten,' 
Budapest, 1885. 



intimately connected with the 
Pig. 173. 



THE NATURE OF ORE DEPOSITS. 

as IB apparent from the 




Fig. 173.— Diagrammatic crosa-eection tlirougli the veina of Nagyig. {B. von Inkey.) 
p, phyllite; t, tertiary sediments of the Mediterranean stage; d, dacite; pr, prapy- 
)ite;g, vein atraiks; Ic, kaoliniEed dacite; v, superficial weathered cover. 

Another peculiarity of the Nagy&g district that needs mention ifl the 
presence of 'barren' vdns (Glauchgangue), a feature which is also known 
in cither Hungarian and Servian ore depoeits in propylitic rocks, as for 
example at Vonrapatak, where they are called 'glamm.' The 'barren' 




Fig. 174. — ^Horizontal plan of barren veins at II I.onfrin at the 75 fathom level at 
.NajO'ifi. (B. von Irikey.) 
g,, oldest barren veins ; r„ second barren vein, dark 20 cm. thick; g^ 3rouiig«Bt 
barren vein, light gray, 15 cm. thick. 

veins of Xagiag cut through the propylite and the blocks of Tertimry 
rocks enclosed by it. The fissures vary from mere cracks up to 10 <»- even 
20 m. in thickness. They are filled with a dark sandy or clayey maaa, con- 



EPIOENETIC DEPOSITS. 315 

taining angular or sub-angular fragments of the adjoining rock. These 
barren' veins cut one another and are thus shown to be of different ages* 
Fig. 174, after B. von Inkey, shows as many as three sets of these Glauch* 
gauge differing in age. The included fragments can often be shown to be 
torn from portions of the wall rock 10 m. (32.8) to even 20 m. (65.6 ft.) 
distant. This displacement appears to be even greater since bits of phyllite 
are not infrequently encountered, which seem to have been brought up from 
a greater depth. The T)arren' veins are explained in various ways. Some 
authors regard them as fault fissures, filled with friction breccias and the 
finer products of attrition. This view is, however, opposed by the fact that 
very many ^barren' veins show no dislocation whatever in the adjoining 
rock. F. Posepny for some time thought of an in-washing of the material 
from above. This is hardly conceivable, however, in view of the fineness 
and manifold ramification of the network of the *barren^ veins. H. Hofer 
and others supposed them to be decomposed and crushed dikes of eruptive 
rock, but this is not confirmed by the petrographic character of the finer ma- 
terial composing the filling. B. von Inkey, who seems to have devoted much 
attention to these phenomena, notes "that the debris material in the Glauch- 
gange breccia is evidently derived from the fissure walls, while the matrix, 
which is a mixture of fine sand with clay, was originally a watery 
mud, whose solid particles may be derived partly from the dust particles 
produced by the comminution of the adjoining rock, and in part represent 
triturated material of deeper rocks. The water which made mud of this 
dust is supposed' to be derived from the ground-water of the rocks of the 
Mediterranean stage. When afterward a mighty eruption fissured these 
strata and forced great wedges of a hard rock between them, the subter- 
ranean water circulation was altered, the passage of the ground-water was 
checked and dammed back, and large accumulations of water or even of 
thin liquid mud, were formed beneath the trachyte cover and between the 
eruptive wedges.'* He next imagines that the mass of the eruptive stock, 
through the yielding of its sedimentary base and its lateral supports, be- 
came fissured, and that thereupon those masses of mud were forced by high 
pressure from below into these collapse-fissures*. 

The mineral veins found within the stock of propylitized dacite, at 
NagyAg, form a tangled network of fissures showing great variety in thick- 
ness and direction. Most of the fissures, however, strike about north-south. 
Minute veinlets and veins i/^ m. thick fray out, gather into clusters or 
cross one another in the most diverse manner, though apparently all be- 
longing to the same period of formation. According to B. von Inkey, the 
veins are not contraction fissures, but are due to external orogenic causes. 

' B. von Inkey: A. a. O., p, 149. 



816 THE NATURE OP ORE DEPOSITS. 

Classified according to the nature of their ores^ Freiherr von Hingenau at 
an early date was able to distinguish three areas^ each characterized by its 
own peculiar distribution of the prevailing vein minerals, a conclusion con- 
firmed in general by H. Hofer and von Inkey. These three districts are 
the following: 

(a) The region of telluride-carbonate veins, with calcite, siderite, dolo- 
mite and rhodochrosite, some quartz and homstone with alabandite (Mn 
S), nagyagite and other tellurides of gold, also some tetrahedrite and pyrite; 
the latter, it is true, merely as an impregnation in the adjoining rock. 
This is in the southeast part of the district, mainly below Mount Szekeremb, 
extending as far as the Anastasia cleft. 

(b) The telluride quartz veins or rich quartz area whose veins carry 
gray, non-crystalline, often cellular quartz, with auriferous sylvanite, kren- 
'nerite, gray copper and rarely free gold. This area is in the northeast parts 
of the district and near Mount Hatjo. 

(c) The area of the sulphide ores, which pass into the two other 
classes by gradual transitions. It is marked by the prevalence of galena, 
zinc-blende and pyrite in a gangue of carbonates, in which argentiferous 
tetrahedrite occasionally appears. 

The subordinate minerals of the Nagyag veins inclade gypsum, which 
sometimes encloses flakes of native gold, native arsenic, boumonite, stib- 
nite, plumose jamesonite, realgar and orpiment, all of which occur mainly 
in the upper parts of the veins. 

An enrichment of the veins is generally found to occur when strings of 
P3rrite cross the fissures, and when the veins themselves form intersections, 
or when in contact with the ^barren* veins (Glauchgange), which in such 
cases they either traverse or follow as a network of stringers. When the 
ore-bearing veins ramify in a large mass of barren vein matter the result 
is a "Triimerstocke" (stringer stock), as it is called, such as the Philipp 
and the Adam stock. Neither a diminution of the gold content or a wedg- 
ing out in depth has thus far been observed at Nagyag. 

The Nagydg goldfield was the last of the Hungarian-Servian mineral 
districts of the region to be discovered, being found in 1745. Mining oper- 
ations began in 1748 and have continued in a flourishing condition ever 
since, the mines being in part the property of the crown and of the state 
treasury. It may be mentioned that it was in the Nagyig gold ores that 
the element tellurium was discoverofi in 1782 by Muller von Reichenstein. 

At Offenbanya*, which is situated in the valley of the Aranyos, on the 

* J. Grimm : 'Die Erzniederlapje und der Berpbau zu OffenbAnya in Siebenburgen, ' 
Jnhrh. d. k. k. Montan-Akademion, XVI, 1S67. F. Posepny: 'Ueber den inneren 
Ban der OfTenb^nyaer Bergbaugegeml,' Verh, d. k. k. geol. Reichsanst., 1875, IV, p. 70. 



EPIOENETIC DEPOSITS. 317 

north border of the Transylvanian Erzgebirge^ two classes of deposits are 
distinguished: (1) Contact aeposits^ occurring at the contact between 
intercalated beds of crystalline limestone in the garnetiferous mica schist 
and Tertiary dacites and hornblende andesites; (2) mineral veins. 

The contact deposits locally called lead stocks are formed of pyrite, zinc- 
blende^ arsenopyrite and galena imbedded in a calcareous matrix, and the 
deposit shows no connection with the gold veins. They were formerly mined 
by the state, but are now of no importance. 

The mineral veins occur in a stock of dacite. Where they pass 
into a mass of friction breccia, developed locally along the contact 
between the eruptive rock and the mica schists and limestones, most of the 
veins wedge out. They are of very small thickness, mostly only 5 to 25 mm., 
and can only be followed 130 m. in the strike. 

Some of them carry only native gold, some only telluridc ores, others 
carry both at the same time. The matrix consists of quartz and calcspar. 
The more quartz the fissures carry, the richer they are in tellurides (sylvan- 
ite and nagyagite). The subordinate accompaniments of the tellurides are 
pjrrite, zinc-blende, realgar, more rarely proustite, boumonite, tetrahedrite, 
marcasite and arsenopyrite. In druses, crystals of quartz, calcspar, barite, 
aragonite, albite and gypsum are found. In certain veins, free from tellu- 
rides, wulfenite, pyromorphite, as well as stibnite, were also found. 

Most of these fissures have a general east- west course. The vein wall-rock 
is thoroughly decomposed and impregnated with small crystals of aurifer- 
ous pyrite, so that zones of this altered rock, 6-8 m. (1G.4 ft. to 23.2 ft.) 
broad, are mined as gold ore, and where several fissures meet or come close 
together great masses of rock have been impregnated with gold, the deposit 
resembling the so-called gold quartz stock of Nagydg. 

Since mining has been resumed the work has been confined mainly to 
one such stock, the so-called Kreisova stock. This consists of a crushed or 
brecciated dacite in which the veins consist of drusy quartz with pyrite 
and silver ores, gray copper, copper pyrite and galena. The amount of 
silver and gold is stated to be very considerable. 

Verespatak occupies the first rank, among the telluride bearing districts, 
not so much because of its present production as because of its historic 
fame.^ 

* F. von Hauer: 'Der Goldber^bau von Vdrftspatak,' Jahrh, d. k. k. pjeol. Reich- 
sanst., 1851, IV, p. 64. J. Grimm: 'Einige Bem. fiber die geogn. und bergbaul. 
Verb, von V6r6spatak,' op cit., 1852, III, p. 54. F. Posepny: 'Einige Resultatc 
meiner bisberigen Stiidien uber Verespatak,' etc. VerhanaL d. k. k. geol. Reicb- 
sanst., 1867, p. 99, 1870, p. 95 and 1875, p. 97. G. vom Ratb: 'VdrOspatak und 
NagyjCg,' Sitzb. der niedeirbein. Ges. f. Natiir- und Heilkunde in Bonn, March, 1876. 
F. J. Kremnitzki: ' Beobacbtungen uber das Auftreten des Goldes im Verespataker 
Erzreviere,' F5ldtani K«zl6ny, 1888, pp. 517-520. Also the works noted on p. 331; 
particularly the work of Semper, pp. 125-172. 



318 THE NATURE OF ORE DEPOSITS. 

This place is situated in a deep valley about 10 km. (6 miles) northeast 
of Abrudbanya. B. von Cotta called it the Eldorado of Transylvania, and 
even to-day 172 small companies are busy in this region, and the waters 
from 5 reservoirs drive over 6,000 stamps. Back of the town and to the 
south of it lies the famous Csetatye, a bald, rocky ridge, completely 
honeycombed by mining works, which have been carried on from Boman 
times, A. D. 106-276, down to the present day. 

The Verespatak mineral area is an isolated mass consisting mainly of 
eruptive rocks lying in the midst of the monotonously uniform Carpathian 
sandstone (Cretaceous and Eocene). This mass consists of dacite, rhyolite, 
and rhyolite breccias, the latter often silicified. It forms the two mountain 
stocks of Kimick and Boi. The great Csetatye mentioned above consists 
in part of this dacite, which carries large dihexahedrons of quartz, in part 
of the silicified rhyolite breccia. Younger Tertiary sediments, namely con- 
glomerates, sandstones and tuffs with rhyolitic material in them, are also 
found there. 

A very remarkable feature of the district is the occurrence of the so- 
called 'glamm' veins, which form a network of fissures throughout the 
district. Their filling consists of a clayey mass containing rounded rock- 
fragments, including pieces of coal of considerable size, trachyte fragments 
and bits of mica schist and phyllite. These masses are impregnated with 
pyrite and limonite, and seem to have been pressed into the fissures with 
great force, apparently from below. Semper thinks them intrusions of 
volcanic mud. 

The ore-bearing veins occur partly in the eruptive masses and partly in 
the above mentioned sediments. In the Carpathian sandstone the veins 
contain practically only quartz with free gold. Elsewhere the quartz and 
free gold are accompanied by banded rhodonite, calcite, calcspar, rhodo- 
chrosite, gold-bearing pyrite, zinc-blende, as well as galena, gray copper and 
seldom adular spar. The gold occurs in crystals intergrown with rhodonite 
and quartz. In the heart of the Csetatye ridge the gold-bearing fissures 
form a stock of rich stringer veins, called Ejttnmza (petticoat), whose ex- 
traction has left great excavations. Similar stringer vein stocks were 
worked as early as Boman times. They commonly consist of eruptive brec- 
cia impregnated and cemented by gold-bearing pyrite and quartz. 

A similar deposit is found at Bucsum, about 10 km. southeast of Abmd- 
banya, in the mines of the Concordia company. 

The Vulkoy Korabia and Botes^, mining districts about 15 km. north of 
Zalathna, which are similar, were also known to the Bomans. The veins 
occur partly in the trachyte, partly in the Carpathian sandstone. Their 

^ Fuchs and de Launay: 'Traits,' II, p. 932. Semper, op. cit., pp. 178-181. 



SPIOSNETIC DEPOSITS. Sid 

filling consists mainly of quartz with fine sprinklings of free gold, besides 
gold-bearing pyrite, and a little ehalcopyrite, gray copper and galena. The 
gangue carries hessite. 

The largest gold mines that are being worked at the present time in Tran- 
sylvania are situated near the town of Brad, the Twelve Apostles* and Mus- 
zari mines, and at Boicza, all of which are located in the western part of the 
gold area. 

An extraordinary excitement was recently created by the great success 
of the Geisslinger Industrial Company in the Muszari mine near Brad', 
which in 1895 produced 732 kilograms of crude gold (gold-silver). The 
entire workings lie in a massive of andesitic and dacitic rocks. Two sys- 
tems of veins intersect at right angles with very rich orebodies at the 
crossings, as, for example, that between the Clara and Karpin veins, 
from which, in 1891, 53 kilograms of crude gold were taken. The vein 
filling at this place consisted of quartz, calcspar, pyrite and some light- 
colored zinc-blende. The Clara vein sends out several lateral stringers, 
which gather and ramify in the Clara stock. This stock, varying up to 
7 m. thick, is interspersed with druses containing quartz, pyrite and free 
gold. The ores in this ^'treasure chest of Muszari'' contained in places as 
much as 1,000 gm. per ton. This space, which is enclosed by an iron 
grating, yielded about 600 kg. of gold in 1% years. 

The other veins of this mine have a thickness of 2 cm. to 2 m., and 
carry a gangue of quartz and calcspar each in varying amount with gold- 
bearing pyrite, free gold, sphalerite, ehalcopyrite, marcasite, arsenopyrite 
and some galena. The latter does not seem to have a favorable effect on the 
gold contents. The amount of gold in the veins varies from 9 to 30 gm. 
per ton. 

The last Hungarian locality to be mentioned as illustrating this class of 
deposits is that of Boicza, near D6va, in the district of Brad, whose mines 
are of great importance*. The veins are found in a stock forming the 
Szvregyel mine, which is about 1 km. from the place itself. The core of 
this mountain is formed of a rock which is regarded by Primics as a mela^ 
phyre, whose age lies between lower Triassic and upper Jurassic. This 
makes it older than the Tithonian limestone which apparently overlies it in 
many places. According to other authors, the rock is much younger, belong- 
ing to the andesitic group. This older eruptive mass is broken through by a 
spreading stock of dacite, especially broad in the upper part of the moun- 

See Semper, op. cU.^ pp. 86-109. 

' According to a communication received from H. Oehmichen. 

■ Primics Gyftrgy • 'Die Geoloirie des Csetrfeer Erzrevieres' (Hungarian), Budapest, 
1896. L. Venator: 'Monogr. uber das Gold- und Silberbergwerk Rudolfi in Boicza/ 
Hermannstadt, 1900. 



320. THE NATURE OF ORE DEPOSITS. 

tain. This dacite encloses numerous fragments of the melaphyre and the 
Tithonian limestone along the contact zone. 

The gold veins occur chiefly along the contact between the two eruptive 
rocks^ but in part also within the melaphyre. They strike northwest and 
dip 75 to 85^ in two different directions. Two systems may be distin- 
guished, whose principal veins show a tendency to unite into a single vast 
fissure, the so-called stock, in the southeast part of the mineralized district 
The two main fissures, Schuhaida and its companion, the Kreuzschlager 
vein, show payable ore for a length of 800 m. (2,624 ft.) The veins 
are not thick, varying between and 1 m., the average being 0.35 m. 

According to L. Venator, the filling, which differs considerably from 
vein to vein, consists mainly of quartz, in which gold-silver, calcspar, 
barite, rhodonite, amethyst, pyrite, chalcopyrite, galena, sphalerite, 
argentite and proustite occur. In most cf the fissures, pyrite predominates 
over the other ore minerals, though in some veins galena and zinc-blende 
are the chief ores. The gold (which contains much silver) occurs in 
microscopic grains scattered through the ore and it is only in the very 
richest ore that it is visible to the naked eye. At times the gold is associated 
with pyrite, more rarely with zinc-blende. The vein junctions and inter- 
sections are here followed by distortion and not by ore shoots and enrich- 
ments, these being, however, sometimes found at some distance beyond the 
intersections. The ore ^stock^ is due to the meeting of many of the veins. 
It attains 40 m. in longitudinal and 30 m. in transverse diameter, at 
the 110 m. level. Its filling consists sometimes of fragments of melaphyre 
and dacite, cemented by an ore-bearing material, which at some points is 
very rich. 

As is known from various archeologic discoveries, mining operations 
were carried on at Boicza as early as Boman times. About the year 1444 
the work was resumed, but not until 1884 did modem mining begin. In 
1898, 212,43G kg. of fine gohl and 171,700 kg. of silver were produced. 

This brief summary of the Dacian gold districts has shown that less than 
half of them can be assigned to the typical silver-gold-veins, since the 
majority of them just described contain tellurides. All of them are, how- 
ever, of the same age, are genetically dependent on masses of Tertiary 
eruptive rocks of the andesite and trachyte families, and show so many 
other geologic characteristics common to all that they can not well be 
separated in the classification adopted. 

A second region containing similar deposits is that of Schemnitz^ (in 
Hungarian, Selmeczbanya) in the Erzgebirge of lower Hungary. 

* Beiidant : 'Voyage min^^ralopcique et g^lopique en Hongric,* Paris, 1822. Frhr. 
J. von Richthofen: 'Studien aiis den ungarischsiebenburigschen Trachytgebirgen,' 



EPIQENETIG DEPOSITS. 321 

This long-famed mining region, whose mining work probably dates back 
to the eighth century, and which, as the seat of an old mining academy, 
has always had keen intellectual men watching its development, is, geolog- 
ically, one of the best-studied mining areas of the globe. The older pioneer 
works of Esmark, Beudant and Pettko were followed by the more recent ones 
of von Richthofen, von Cotta, Lipoid, Szabo, Cezell, Cseh and H. Bockh, of 
which we are only able to cite some of the more important. According to 
the recent work of Bockh, the oldest formation in the vic.nity consists of 
Triassic slates which, along their contact with diorite, are altered to gneiss- 
like homstone and mica schists. The Trias also contains limestones and 
quartzite. After this come Eocene Nummulitic shales. The series of 
eruptions began between the time of the lower and upper Mediterranean 
stage. These eruptions were the cause of the vein and ore formation of the 
district. At first pyroxene andesite, then diorite and granodiorite (quartz 
diorite), next aplite, then biotite and amphibole-andesite aad finally rhyo- 
lite. Much later in the Pliocene period basalt eruptions occurred. The 
rhyolites are predominant and show very diverse modifications, besides 
forming obsidians, perlites and pumice stones. Furthermore, it happens 
that just in the region of the ore veins the various trachytic and andesitic 
rocks have experienced a very widespread hydatometamorphic alteration 
into propylites, locally called greenstones or greenstone-porphyries. The 
propylite is, however, no longer regarded as an independent rock of older 
age than the porphyries, as at one time maintained by F. von Richthofen. 
The rocks carry much pyrite and are silicified near the veins. Besides ande- 
site flows there are also tuflf-like accumulations, trachyte breccias and 
trachyte conglomerates, which sometimes enclose fragments of coal torn off 
from Tertiary strata broken through by the eruptive rocks. 

The lodes occur in exceedingly great numbers. The strike of most of 
them is between north-south and northeast and the dip is steep, more fre- 
quently southeast than northwest. The vein fissures traverse not only the 
trachytic and andesitic rocks, but in their southwest continuation they cut 
Miocene strata. They are for the most part of considerable thickness, 
usually being compound lodes without clearly defined walls. They enclof^e 
a good deal of material from the adjoining wall rock, which is decomposed 

Jahrb. d. k. k. p:eol. Reichsanst., Vol. XT, 1.S60, pn. 153-277. B. von Cotta: 'Ueber 
Erzlajuerstatten Unsams und Siebenbiirirens/ 1862, pp. 28-41. M. V. Lipoid: 'Der 
Berp:bau von Sohemnitz in rngarn.' ./a/jr6. d. k. k. jreol. Reichsanst., 1867, Vol. XVII, 
pp. 317-458; with bibliocrraphy. J. W. Judd : 'On the Ancient Volcano of Schemnitz,' 
Quart. Jmim. Geol. Soc, Aiiirust. 1876. 'Die Erzpanpe von Schemnitz und dessen 
UmKebuncT, ' official man, 1883, written by von J. Szab6, L. Cseh and G. Gezell. J. Szabo : 
'Geaohichte der Geolotrie von Schemnitz.' announcement, 1885. Idem: ' Monopraphie 
der T"^m«'ebnnfl: von Schemnitz. ' H. Bftokh : 'Ueber das Altenrverh der in Umg. von 
Selmeczb^nya vork Eniptivgesteine,' Foldtani Kdzlony, Vol. XXXI, 1901. 



322 



THE NATURE OF ORE DEPOSITS. 



into clay or is ailicified. The prevailing gangue consiete of quartz, ame- 
thjet and homstone; other minerals, iisuall; of later formation, include 
calcepar, brownapar, rhodochroeite, siderite, barite and gypsum. The 
most common ore minerals are argentiferous galena, zi^ob'.ende, cfaalco- 
pyrite and auriferous pyrite, vhich occur scattered through a gangue of 
quartz and jasper-like material, this ore being called zinopel. Besides the 
zinopel, there are found rich silver ores, sudi as native silver, argentite, 
stephanite, polybasite and pyrargyrite, at times also native gold. Barer 
occurrences arc, among others, stibnite, hiibnerite, tetrahedrite, mar- 
caaite, pyrrhotite, copper glance, cinnabar, fluorspar, diaspore and adular 
spar. 

Most of the veins occur (1) in the andesites and rhyolites and (S) in 
diorite. Among the lodes in the andesite rock we may mention the Gruner, 
Stefan, Johann, Spitaler and Biber veins, vhile of the second group, which 




Fig. 175. — Horizontal section of the Grunt 
shoots forming a continuous son 



ia developed at Hodritsch, west-northweat of Schemnitz, we may mention the 
AUerheiligen, Josefi, Schopfer and the BrennoratoUn lodes 

As representatives of the first group, the Gruner and the Spitaler veins 
may be characterized in a few words. 

The Griiner vein has been traced for a distance of 1 5 km. (0.9 mile). 
The course is northeast, the dip 70 to 80° southeast, and the thickness 
2-12 m. (6.5-39 ft.). The larger part of this great fissure ia uaually 
filled with much-crushed and pyritized rhyolite, which is traversed by 
stringers of ore forming compound veins. The ore ia characterized by 
the great predominance of the true silver ores over galena and blende. The 
most abundant ore mineral is stephanite with associated argentite, poly- 
basite and a little native silver, all of which, intergrown with pyrite crystals, 
occur in a grayish densely crystalline or drusy transparent quartz mixed 



EPIOENETIC DEPOSITS. 323 

with carbonates. The pay ore occurs in flat ore shoots or columns, whose 
horizontal extent is but 40 m. (131 ft.), but which extend downward much 
farther. These shoots have a flat pitch southwest as shown in the sketch 
(Fig. 175). Outside of the ore shoots the vein is much lower grade, though 
not barren. 

The Spitaler vein is the most important of the entire area. It has 
been traced for a distance of over 8 km. (4.8 miles) and may have a total 
length of over 12 km. (7.2 miles). The course is mainly north-northeast, 
the dip south-southeast at 32 to 70% being steeper with increasing depth. 
The vein is very thick, averaging 40-50 m. (131-164 ft), which, how- 
ever, does not mean that this is a single vein fissure. On the contrary, it 
is a lode formed of a system or cluster of veins consisting of single veins 
and stringers, very close together, but separated by layers of barren 
material. At points where the stringers converge, the lode attains a thick- 
ness of as much as 5 m. The gangue is principally quartz, with some 
rhodochrosite, calcite, brownspar and barite. The ore throughout the 
greater part of the lode consists of auriferous and argentiferous galena, 
blende, copper pyrite and pyrite, with a little free gold and rarely some 
cinnabar. In the southwestern region, the lode assumes quite a different 
character, rich auriferous silver ores being predominant. 

The lodes of the second group cut the diorite at Hodritsch. They contain 
rich silver ores in a gangue of quartz and carbonates. The adjoining rock 
is strongly impregnated with pyrites. 

The Schemnitz mines are the oldest in central Europe. According to 
some authors, the Quadi at "Vania,*' in this vicinity, had mines as early as 
the beginning of our era. About 745 the mines passed into the possession 
of the Slavs, who continued to work them. Their rights were left undis- 
turbed by the Magyars, who came into power at the beginning of the 10th 
century. The names of the mines, moreover, indicate that there were nu- 
merous immigrations of Germans, especially Saxons from Meissen. They 
infused hew life into the operations and the Germans monopolized the 
mines under Andrew II. Under Bela IV (1235-1270) the town was 
granted municipal and mining rights under the name of Schemnitz (Seb- 
nitz). The first chair of the Mining Academy was established in the year 
1763*. 

The Schemnitz lodes are similar to those of Kremnitz* (Kormoczbdnya), 
situated farther north. The latter also are associated with propylitized 

* 'Oedenkbuch zur hundertjahrigen Grundunji: der k. nng. Berg- und Forstakademie 
in Schemnitz,' 1871. 

' E. Windakirwioz: 'Gold- iind Rilherberirbau zu Kremnitz in Ungam,' Jahrb, 
d. k. k. geol. Reichsanst., 1866, Vol. XVI, p. 217. 



324 THE NATURE OF ORE DEPOSITS. 

trachytic rocks; The ores occur in wide lodes composed of stringers and 
not in a single fissure. The ores and vein stone are exactly like those of 
the Schemnitz lodes. 

A third Hungarian district distinguished hy silver-gold veins is found in 
the Wihorlet-Gutin mountains, along the boundary line between the Mar- 
maros, Szatmar and Ugocsa comitates. This moimtainous tract, which 
rises steeply to a height of 1,500 m. above the great Hungarian plains to 
the west, consists of trachytes, rhyolites and dacites in part of propylitic 
habit. In the Nagybdnya region, at Kreuzberg, 1 km. north of the town, 
at Veresviz (meaning red water) 3.5 km. northwest, at Felsobdnya on the 
east, and farther oflf at Turcz, Negy-Tdma, Visk, lUoba, Laposb&nya and 
Miszabdnya and at Borpatak and Kapnik, these rocks are traversed by lodes 
quite similar to those described at Schemnitz. For further details the 
reader is referred to G. Szellemy^s comprehensive work^ 

These silver-gold deposits of Transylvania and lower Hungary, which 
have been so briefly summarized or merely mentioned, all form a geologic 
unit. They are associated with vast eruptions of trachyte and andesite, 
which took place along the inner side of the mountains formed by the great 
Carpathian anticlinal uplift. Thus they are a final consequence of the 
shrinkage of the earth's crust. The molten matter rose along a basin 
formed by the one-sided nature of the mountain-folding, forming intrusive 
and extrusive masses. These eruptions were followed by the formation of 
fissures through which the metallic materials from the still hot masses of 
the interior could be conveyed in solution and deposited in the upper part 
of the earth's crust. Entirely similar phenomena occur in western North 
America. 

The Great Basin of Utah and Nevada, lying between the Sierra Nevada 
and the Eocky Mountains, was the theatre of tremendous volcanic activity 
in Tertiary time. Immense quantities of lava were poured out from the 
interior of the earth, forming lava flows many miles in length, or spreading 
out in great sheets and forming monotonous plains. Craters are recog- 
nizable at many points, the vents being surrounded by vast tracts of land 
covered with the ejecta of the volcanoes, either as loose lapilli and cinders 
or firmly cemented. Erosion and denudation have dissected these vol- 
canoes, exposing the cores as great ^stocks,' whose rocks mostly belong to 
the andesite family. These volcanic centers and their immediate environ? 
are the seat of numerous vein-like deposits of silver-gold ores. The greatest 
and most famous is the Comstock lode, situated in the Washoe district in 
Nevada. 

' Gevza Szcllemv: 'Die Erzlaporstritten von Na^ybdnya in Ungam,* Zeit, /. 
Prak. GcoL, 1894, pp. 265-271 , 449-157; 1895, pp. 17-25. 



EPIOENETIC DEPOSITS. 



325 



The Comstock Lode. — This famous deposit has been the object of care- 
ful and repeated examination by various scientific observers^. 

The geologic conditions may be generalized as follows: A huge stock, 
whose highest point forms Mount Davidson, consists of pyroxene andesite. 
whose upper part is of normal andesitic habit, and contains porphyritic 
crystals in a partly glassy groundmass. In depth this rock gradually as- 




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Fig. 176. — Outcrop of the Comstock lode, Nevadn, showing location of the 

mining claims. 

sumes a granular structure so that the crystalline rocks thus developed, 
which are badly changed by a secondary propylitic alteration, apparently 

* F. V. Richthofen: *The Comstock Lode,' San Francisco, 1S6G. Clarence King : 
'U. S. Geol. Explor. of the 40th Parallel,' Vol. Ill, Min. Ind., Washington. 1870. J. A. 
Church : *The Comstock Lode, its formation and historv,' Trans. Am. Inst. Min. Eng., 
New York, 1S79. G. F. Becker: 'Geol. of the Comstock Lode.' etc., V. S. Geol. 
Surv., Monogr. Ill, 1882. E. Lord : 'Comstock Mining and Miners,' U. S. Geol. 
Surv., Monogr. IV, 1883. A. Hague and J. P. Iddings: 'On the development of 
crystallization in the igneous rocks of Washoe/ Bull, U. S. Geol. Surv., No. 17, 1$85. 



326 



THE NATURE OF ORE DEPOSITS. 



differ so much from the andesite that they were formerly described as dia- 
base or granular diorite. Farther east pyroxene-andesite is intruded by a 
huge mass of mica-hornblende-andesite, formerly called porphyritic diorite. 
On the east flank of Mt. Davidson this rock has overflowed the pyroxene- 
andesite, and like it, passes downward into granular-crystalline varieties, 
the deep-seated facies hebxg formerly called mica diorite. This mica-hom- 



FropyltttatrUr 




Fyroacenandssit 



(DiorU Beckers) 



Fig. 177. — Cross-section througl\ the Comstock lode. (Becker.) 
g, lode body ; q, quartzose lode uiass; b, excavation in the bonanza. 



blende-andesitc has also undergone partial propylitization. The study of 
Becker s thin section by Hague and Iddings convinced them that the various 
Comstock rocks discriminated by older authors and assumed to be partly 
pre-Tertiary and partly Tertiary, may be referred to the two Tertiary ande- 
site magmas mentioned, which were possibly intruded at approximately the 
same time. Furthermore, in the mines of that locality a great number of 
younger dike^like or stock-like intrusive masses of mica-homblende-ande- 



EPIOENETIC DEPOSITS. 




328 TEE NATURE OF ORE DEPOSITS. 

site^ dacite and rhyolite (formerly called quartz porphyry) and of basalt 
have been met with. 

The Comstock lode has a north-northeast course^ and dips at 45 to 50** 
east-southeast The lode occurs approximately but not always exactly 
at the boundary between the altered pyroxene and the mica-hornblende an- 
desites just mentioned. It is a zone of faulting of greatly varying thick- 
ness. The upper part of the lode near the outcrop is exceedingly wide, but 
consists mainly of completely altered country rock, often decomposed into 
clay. In this, the main body of the lode, there is observed a hanging-wall 
vein and a foot-wall vein, the latter very large and of very irregular shape. 
In the cross-section, Fig. 177, taken from Becker's atlas, the orebodies are 
seen to be great lenses, dividing into two parts, and very irregular in outline. 

These lenses and ore shoots have in part a course transverse to that of 
the lode itself, and sometimes extend far beyond the lode wall. F. Posepny* 
has very wisely suggested that this may be due to cross fissures. 

These orebodies consist mainly of quartz. If we consider that the quartz 
orebodies and the decomposed rock form a unit, the entire lode has an 
average thickness of 60 to 100 m. (196 to 328 ft), and extends for a dis- 
tance of nearly 2 miles. The vein divides at each end into several 
branches ; including these its outcrop has been traced more than four miles 
(7 km.). 

The quartz ore shoots just mentioned usually carry considerable gold and 
silver, and are but rarely barren. The ores include stephanite, polybasite, 
argentite, native gold, some galena and sphalerite, all of which occur in 
minute particles distributed through the friable quartz. The ore minerals 
also occur concentrated into very rich bonanzas. But small amounts of 
calcspar, gypsum and zeolites are found mixed with the quartz. Near the 
outcrop the bonanzas were rich in Tiom silver* (silver chloride), as, for 
example, the one encountered in 1874, which was 360 m. (1,180 ft.) across. 
The bonanza ores averaged 0.001 to 0.5% of gold, and 0.05 to 1.78% silver. 
Notwithstanding the large dimensions and rich contents of the various 
bonanzas, it must not be forgotten that they formed but a very small part 
of the entire mass of the lode, amounting to only about 1 :600, according 
to Burthe. Nor do they show any definite rule or arrangement in the lode. 
At any rate this lode was, to quote Ed. Suess', "the greatest accumulation 
of precious metal that man ever laid hands on." From 1859 to 1889 the 
Comstock lode produced 4,820 tons of silver and 214 tons of gold, of a 

* F. Posepnv: 'Genesis der Erzlagerstatten,' Jdhrh, d. k. k. Asterr. Bergak. 1S95, 
p. 124. 

» E. Sucss; 'Die Zukunft des Silbers/ Vienna, 1892. 



EPIQENETIC DEPOSITS. 329 

total value of $340,000,000 (J. Vogt). In brief, the history of the lode 
is as follows: As early as 1856 gold gravels were discovered and washed 
near the lode. The lode itself was discovered in 1857 by the Grosh 
brothers. It was first worked, however, by others in 1859, for free gold 
only. The silver ore was not recognized for a while, but soon after its dis- 
covery it became the main object of mining. The towns of Virginia City 
and Gold Hill rose like magic on the flanks of the desert! Deeper and 
deeper the work penetrated until great diflBculty was encountered in keep- 
ing the mines dry. In 1878 the famous Sutro tunnel completed draining 
the mines to its level. With increasing depth, however, mining became 
more and more difficult, owing to the increasing heat, until in 1877, in the 
shaft of the Savage mine at a depth of about 900 m. (2,950 ft.), a spring 
with a temperature of 69.4** C. (157** F.) was tapped^ This put an end 
to any downward advance. 

The Veta Madre, of Guanajuato, Mexico, is very similar to the Comstock 
in its structure and ores, belonging to the same type. Its production has 
far exceeded that of the Comstock, but has been spread out over a period 
of 300 years. It is described on page 266 as a silver vein. 

A somewhat more pyritic example of the silver-gold formation, also asso- 
ciated with andesitic rocks, is represented by the Smuggler* vein, near 
Telluride, in the San Juan Mountains, in Colorado. While the Comstock 
Lode was characterized by rich bonanzas distributed in a capricious way, 
the Smuggler lode shows great uniformity and constancy of values, with 
some variation of ratio of gold and silver contents. 

The Smuggler lode fills a fault fissure in augite andesite and the under- 
lying andesite breccias. It has a thickness of 1 to 1.5 m. (3.2 to 4.9 ft.), 
sometimes up to 3 m., and is traceable a distance of 3 k. (2 miles). The 
vein filling consists of quartz, with a little calcite and barite. Quite uni- 
formly interspersed throughout the quartzose gangue one finds pyrite, 
chalcopyrite, galena and zinc-blende, together with rich silver ores, espe- 
cially pif>ustite and polybasite, as well as native gold. For a distance of 
three-fifths of a mile not one spot was found unremunerative. The ores 
average 0.04% of silver and 0.0016% of gold. From north to south the 
gold content gradually increases, while the silver content decreases until at 
its south end the Smuggler is a true gold vein. 

Silver-gold veins are also found in Custer County, Colorado, and have 

' J. A. Church: 'The heat of the Comstock mines/ Trans. Am. Inst, of Min. Eng., 
1879, p. 45. 

* J. A. Porter: 'Tlie Smuggler Union Mines, Telluride/ Trnn^. Am. Inst, of Min. 
Eng., 1806. Ch. Wells Purington : Preh'minan/ Rep. on the Mining Industries of the 
Telluride Quadrangle, Col., 18th Ann. Rep. U. S. Geol. Sur\'., II, pp. 751-84$. 



330 



THE NATURE OF ORE DEPOSITS. 



been described by Emmons and Crose*. The ores contain besides free gold 
and auriferous tellurides, various ricb silver ores, as well as sulphides of 
lead, zinc and iron. The gangue, however, differs from the deposits de- 
scribed in that barite predominates. These occurrences, too, are associated 
with recent volcanic eruptive centers. 

Of these deposits the Baeaick mine is the most interesting. The bedrock 
coniists of gneisses intruded by granites, as well as by dikes of syenite and 
peridotite. This rock complex is covered by younger eruptive rocks, lavas, 
breccias and tuffs. The eruptive series begins with andesites. Next follow 
in succession dioritee, dacites, rhyoUtes, younger andesites and trachytes. 
Finally, the andesitic agglcmierations of Mount Bassick were accumulated, 




Kig. 178, — Section through the Bassick shaft. (S. F. Emmonn.) 
^11, gcieisa; at, andeuite tuff; tr, trachyte; aa, andesite agglomerate; e, ore shoot. 

proFmbly in consequence of vast volcanic explosions which broke up the 
oldtT rocks. At some points there were subsequent eruptions of mica- 
dacitc and glassy basalt. (See Fig. 178.) 

A very remarkable ore deposit occurs in thin Bassick agglomerate. Its 
form is hardly veinlike, but, uiineralofrically and fn-netically, it belongs to 
this class of the system. The defio^iit fonris an upright stock of elliptical 
cross-section with diameters of 8 m. (25 ft.) and 30 m. (98 ft.) in the 
midst of andesite breccias. It has been followed to a depth of 1,200 ft. 
Not far from it a second deposit was found. In these 'pipes' the andesite 

' miitmunOroM: 'GeoloRv of Siivpr Cliff and the Boaita Hills, Colorado,' S. P. 
Emmons 'The .Miiiea of Custer County, Colorado,' 17th .Inn. Report U. S. Geolog. 
Surv..ll, ISH6, pp.26<MrO. /dem.: 'Ronit- Mines of RoaitaatidSilverCliff, Colorado,' 
Trans, of llie .^m. Iiuit. Min. Eng.. 1887, Vol. XXVI, p. 773. 



EPIOENETIC DEPOSITS. 331 

fragments, which vary from 1 cm. to a meter across, are surrounded by 
concentric layers of ore, varying between 1 cm. and 60 cm. in thickness. 
These encrusted fragments are impregnated with pyrite and are much more 
decomposed than those of the surrounding rock. The crusts of ore consist 
(from within outward) of (1) a blackish mixture of sulphides of zinc^ anti- 
mony and lead with 0.2% silver and 0.005 to 0.01% gold; (2) a brighter 
thin layer, richer in lead, varying up to 0.7% of silver and 0.35% of gold; 
(3) a layer of crystalline zinc-blende 5 to 50 millimeters thick with 0.2 to 
0.4% of silver and 0.5 to 0.16% of gold; sometimos also (4) a crust up to 
2 centimeters thick of silver-bearing and gold-bearing copper pyrite; (5) a 
thin layer of pyrite. The free interspaces are filled with kaolin, but some- 
times also contain quartz, gray copper, gold-telluride and silver-telluride, 
or secondary ores such as hydrosilicate of zinc and smithsonite. 

The ore shoot is not sharply divided from the surrounding barren 
breccias, but in the latter there are fissures intersecting in such way that 
the ore column lies between them. 

Emmons states that the vehicle for the metallic compounds was not 
vapor and gas which condensed on the fragments of the breccia, but solu- 
tions containing such gases, and he regards their rise as the last phase of 
the dying activity of this volcanic throat^ The John Jay mine near Jim- 
town, in Colorado, is worthy of mention in this place on account of the 
native tellurium found in masses weighing as much as 25 pounds. 

Examples of the present group are also found among the gold deposits 
of Australia. Only one of them will be briefly described here, namely, the 
Hauraki goldfield, on the Coromandel Peninsula^ on the north island 
of New Zealand, and reaching south as far as Waiorongomai. In this ex- 
tensive area the Paleozoic rocks, and in part also late Cretaceous and Ter- 
tiary strata, according to Park, are intruded or covered by andesites, 
dacites and trach3rtes, as well as by their tuffs and breccias*. At many 
places the andesitic rocks are found altered to propylites, which in turn are 
intruded by younger underlying andesites. Numerous q\iartz veins traverse 
both the andesites and the propylites, but are mainly developed as work- 
able gold lodes in the propylite only. Twelve groups of veins are distin- 
guished in the area, -among which the Thames group is richest and of the 
greatest scientific interest. 

It lies in a tract about 2.7 km. (1.6 miles) wide, north of Hape creek. 
The veins striking northeast are intersected by two very large displace- 

* Revised by S. F. Emmoas. 

' James Park : Papers and Reports relatinf? to Minerals and Mining, Wellington, 
1894, p. 52. K. Schmeisser: 'Australasien,' p. 92, also Zeit. f. Prak. Geol., 1899, 
p. 366 et •cj. 'The Hauraki Goldfield, New Zealand,' Waldemar Lindgren, Engineer^ 
ing and Mining Journal, Ffh. 2, 1905. 



332 THE NATURE OF ORE DEPOSITS. 

ments, the Moanatairi and Collarbone faults^ which divide the entire area 
into three terraces. 

The thickness of the veins varies greatly. The largest, the Waiotahi; 
averages 3.5 meters wide, but is sometimes as much as 13 meters across. 
The veins are nearly all accompanied by lateral spurs or stringers. The 
gangue consists mostly of brittle, sugar-like quartz. The gold in it is finely 
divided, sometimes appearing in the form of wire and plates, and contains 
30 to 40% of silver, giving it a whitish-yellow color. With it is found 
pyrite, and more rarely chalcop}Tite, galena, manganese ores, zinc-blende, 
stibnite and gothite. A quartz vein of the Tararu mine contains much 
rhodonite, with finely divided gold. The largest lodes are generally poorest, 
and none have been worked to any great depth. 

New Zealand in 1901 had a total production of 412,189 oz. of fine gold. 

Instances of the silver-gold ore formation have lately become known also 
in the Dutch Indies, to wit: veins characterized by a large amount of 
selenium at the Eedjang Lebong mine north-northeast of Benkoelen, in 
southern Sumatra, The lode, which is over 5 meters thick, and occurs in 
andesitic rocks, consists mainly of a dense-looking mass rich in silica. 

The gold and auriferous silver (electrum), the latter predominating, 
occur disseminated in minute particles, invisible even under the magnifiring 
glass. The composition of the crude bullion is as follows : 

Gold and silver 91 .52 per cent. 

Se 4.35 

Cu 1 .82 

Pb 1 . 65 

Zn 0.4S 

Fe 044 

90.96 

The average content of the 12,072 tons of ore produced up to 1900 waj? 
45 gm. of gold and 385 gm. of silver per ton^ 

A similar deposit is worked at Lebong Soelit 7 to 8 k. (4.2 to 4.8 miles) 
farther west. 

This type of vein is also represented in the Philippines*. 

18. The Fluoritic Gold-Tellurium Vein^. 

This group is closely related to the preceding, but is sharply character- 
ized by the appearance of tellurides of gold and silver in a gangue of fluor- 
ppar and quartz. The ore minerals consist mainly of native gold, tellurides 

' According: to S. J. Tniscott, cited in Zeit. f. Prnk. CeoL, 1902, p. 225. 

*F. W. Voit: 'Goldvorkommen auf den Philippinen/ Berg m. Hiiiten, Zeit., Vol. 
LVn, 1898, p. 251. 



EPIOENETIC DEPOSITS. 338 

end auriferoiifl pyrites ; to a slight degree of gray copper, galena, sphalerite, 
and stibnite. 

The beet known example is the goldfield of Cripple Creek', directly 
southwest of Pike's Peak, Colorado. 

According to Cross a somewhat circular area of 4 to 5 b. {2.4 to 3 miles) 
in diameter, occurring in the midst of a very extensive tract of porphyritic 
granite, is covered by volcanic breccias and tuffs, whose material consists 
mainly of trachv-phonolite frapments, but in part also of fragments of 
the granite carried up from deep-seated masses. These volcanic accumu- 
lations are broken through in places by stock-like masses of trachy-phonolite 
and phonolite. The last-mentioned rock is exceedingly rare in the United 
Stetes, being known only at one other place, viz., the Black Hills, So. Dakota. 




Fif;. )7(l. — Thin aection of a 'purple quartz' from Summit mine. Cripple Creek, 
f , fluorspar; n, quartz nith enclosed Suorspar crystaln (outlines drawn by polarised 
light); e, iron ocher with free gold. (Eolarged dity timea.) 

Finally the area is travcrecd by dikes of basic rocks, ncpheline and feldspar 
basalts, which for the most part strike northeast and northwest. 

These recent dikes are often accompanied along one wall by gold veins, 
while other veins also occur independently of the dikes, cutting not only the 
andesite, but also the underlying granite. The 'true fissure veins' are 
mete fissures, often an inch or less thick, and often entirely closed, but not 
only does this narrow fissure filling carry ore, but the strongly altered 
country rock on both sides is heavily impregnated with ore. These impreg- 

'Hini 



331 THE SATIRE OF ORE DEPOSITS. 

ution tteant eontaio gold tellnrides, principallT sTlmiite tnd caUmite, 
nrely petzite, in le« amoimt natiTe gold, as veil u anriferons jmites, 
vhile in depth the ores contain gray copper, galena, Ephalerite and stilMUte. 
The gangue is quartz and flnor^par intimatelr coalesced, as ebown in Fig. 
179. The qnartz is of a riolet or reddish color, as it is tbonragfalj per^ 
meated with fluorspar; it is locally called 'parple qoartz.' lite metaso- 
matic alteration of the country rock hm been ^ndied by W. Lindgren. The 
ininerals, vhich are especially common as replacements of the orthoclase 
of the granite, inclnde quartz, Saonpar, pyrile, sericite. as veil as Talen- 
cUnite- The distribation of the tellorides or other ore mioerals is Terr 
variable and oncertain. Very often ore shoots of very unequal aize amd 
shape are found in the same rein. 




Fif;. 180. — Columnar orebodiea in a 
Cripple Creek vein. (R. A. F. Penrose.) 



Ordinarily the ore shoots are approximately vertical columns varying 
from a few centimeters to several meters in thickness and up to 100 m. 
(328 ft.) long (sec Fig. 180). The ore shoots sotpetimes occur directly 
under the grass roots, while more often their summit? are only encountered 
in depth. In certain cases their location is at once seen to be dependent 
upon cross fissures, as shown in Fig. 181. These shoots sometimes yield 
very large amounts of gold, 

A unique ore shoot of the Portland mine is called the "Anna Lee Chim- 
ney." A volcanic vent in basaltic rock has been worked to a depth of about 
300 m. (984 ft.) This chimney, which is 4 to 9 m. across, is filled with 
rounded basalt fragments cemented by a ca lea reo- ferruginous material con- 
taining auriferous tollurides quite uniformly distributed. 

Mention must also be made of the columnar masses of gypsum encoun- 
tered in the breccias in the Deerhorn shaft. Eickard regards them an 



EPIOENETIC DEPOSITS. 336 

deposits of thermal waters^. They may represent products of oxidizing 
sulphides on country rock and calcite. 

The Cripple Creek district had long been known, but it was not until 
1890 that gold ore was found in large quantities on what was afterward 
the Gold King mine in Poverty Gulch. Production began in 1891. Ac- 
cording to Penrose it amounted to $5,543^967 from 1891 to 1894, in- 
clusive. In 1898 the production was $13,507,349. 

Deposits of gold with fluorspar also occur in Montana as described by 
Weed.* The Judith and Mocassin (Warm Springs) districts are situated 
in the Judith Mountains of Montana, which rise to a height of 6,386 ft. 
and extend over a distance of 29 km. (17 miles) between the arid grassy 
plains of the Yellowstone and those of the Missouri river. This mountain 
mass is an isolated uplift east of and independent of the Hocky Moun- 
tains. It consists of Paleozoic and Mesozoic limestones and shales, prin- 
cipally of Carboniferous age, domed by laccolitic intrusive masses. The gold 
deposits are found at the contact between limestones and syenite porphyries, 
which are regarded by the author as belonging to the trachyte group. The 
deposits consist of a contact breccia whose fragments are cemented by 
fluorspar, quartz, and a little calcite, with finely interspersed particles of 
tellurides, and the free gold formed by their alteration. The **purple 
quartz,'' an intimate mixture of fluorspar and quartz, recurs here. 

The characteristic feature of the group of deposits last discussed, 
namely, the intimate blending of quartz and fluorspar, has been used by 
Penrose as the basis for a theory of the origin of these deposits. He 
imagines a reaction of soluble or gaseous fluorides with the calcium car- 
bonate that resulted from the decomposition of calcareous silicates, or 
which is, as in the last example, supplied directly by the limestone. If the 
fluorine was introduced as hydro-fluoride of silicon, there might have been 
a simultaneous precipitation of fluorspar and quartz, such as we commonly 
have in the purple quartz. The original seat of the fluorine, as well as of 
the gold, Penrose imagines to have been heated rock masses found at great 
depths'. 

(if) Antimony Veins. 

19. Antimony Quartz Veins. 

This class of vein is closely allied to the antimonial gold quartz veins, 

and represents the extreme or gold-poor facies of the group. It is, how- 

'T. A. Rickard: 'The Cripple Creek Volcano.' Trans, Am. Inst. Min. Eng., 
February, 1900. 

' W. H. Weed and L. V. Pirsson: 'Geology and Mineral Resources of the Judith 
Mountains of Montana.' 18th Ann, Rep, U. S. Geolog. Survey, III, 1896-1897, pp. 
445-614. 

» See 'Telluride Veins of America,' Kemp, 'The Mineral Industry,' 1900. 



336 THE NATURE OF ORE DEPOSITS. 

ever, desirable, for practical reasons, to make a separate group of the 
deposits because they are worked for antimony, not for gold. Most of them 
carry but a very slight amount of gold, whose extraction is unprofitable by 
reason of existing metallurgic ditficulties. 

The prevailing gangue consists of quartz, with some calcspar. The ores 
con^in stibnite and its products of decomposition, namely, stiblite, anti- 
mony-ochre, valentinite and senarmontite, more rarely also antimony 
blende (pyrostibnite) and sometimes pyrite, bournonite, berthierite, galena; 
zinc-blende, steinmannite, zinckenite, and cinnabar ochre, rarely native 
gold. Ordinarily the stibnite is interspersed in the gangue, in rare cases 
it occurs in compact masses, forming almost all the vein filling, or it is 
concentrated into ore shoots, while the rest of the vein is lean. 

A description of examples will better explain the characteristics of this 
type. 

At Bohmsdorf and Wolfsgalgen, near Schleiz, the Paleozoic schists are 
traversed by veins of quartz carrying stibnite, with minor amounts of zinc- 
blende, plumose stibnite, pyrophyllite and ironspar. The veins have some- 
times been extensively mined, as at the Halber Mond mine at Bohmsdorf in 
the fifties of the 19th centurv. 

Among the antimony deposits of Bohemia special mention must be made 
of that of Pricov, near Selcan, 15 kilometers west of Wotitz, in central 
Bohemia. At that locality, according to A. Hofmann, a great number of 
kersantite dikes occurring in granite, are accompanied by veins of horn- 
stone rich in stibnite. The veins were worked for antimony alone for many 
years, but were abandoned in 1897. The ores held no free gold, and the 
stibnite contained only traces of that metal. For a depth of 18 m. (59 ft.) 
below the croppings, the stibnite was changed to antimony ochre (stibicon- 
ite). The largest vein, which has a thickness of as much as 20 meters, and 
forms the rocky crest of the Deschna mountain, does not contain stibnite 
throughout its entire mass. It is only where the homstone assumes a light 
gray color that it is foimd, w^hen examined under the microscope, to be com- 
pletely filled with innumerable handsopie crystals of ore, and also to carry 
larger segregations of it. Thus far only the Emil lode, 10 to 60 centi- 
meters thick, has been worked. 

Entirely similar, but less extensive, lodes are found at Punnau, near 
Marienbad. They occur in mica schist and amphibolite near the great 
granite massive of that locality^ 

In Hungary antimony ores are still extracted from the veins of the Rech- 
nitz Mountains, of the Eisenburger Comitat. Some of the veins have been 

* J. Srhwarz: 'Das Rmnaiicr Antinionberpwerk bei Michaelsberg in BChmen.' 
Oesterr, Z. /. B. u, II., 1881, pp. 595-608. 



EPI GENETIC DEPOSITS. 337 

followed for a distance of 3 km. (2 miles), cutting crystalline schists. Ac- 
cording to A. ScKmiut*, the veins are especially rich when the country rock 
is a chloritic or graphitic schist. The vein tilling consists of quartz, calc- 
spar and stibnite, with stibiconite and pyrite. The masses of antimony ore 
proper attain a thickness of 2 to 50 centimeters. The graphitic schists 
alongside of the lodes, for a distance of 3 to 4 meters from the vein walls, 
are so richly impregnated with stibnite, together with pyrite and cinnabar, 
tliat they also pay working. The pyrite of this ore contains about 0.0021% 
of gold. 

Other veins of stibnite, with a gangue of quartz and carbonates, with 
small amounts of jamesonite, berthierite, blende and auriferous pyrites, 
were worked between Aranyidka and Rosenau, in upper Hungary^. 

A noteworthy deposit of antimony occurs at Pereta, south Tuscany. 
According to Coquan(P and Toso* it consists of a mass of crushed white 
quartz, whose north end is intercalated in Eocene limy shales, while to the 
south it cuts Pliocene limestones. To the north of the outcrop exhala- 
tions of hydrogen sulphide (putizze) occur. The stibnite occurs in the 
(juartz in the form of stringers and pockets, occasionally of large size. Sul- 
phur occurs with it and in the northern part of the deposit considerable 
amounts have l)e('n extracted. In these workings the sulphur-bearing 
(juartz is occasionally sein to be coated with a crust of stibnite, which in 
turn is studded with small crystals and aggregates of sulphur. Eocene 
limestones, at the contact with the deposit, are traversed by quartz stringers 
and larg(*ly altered to gypsum or to alum rock. 

Stibnite associated with cinnabar is found at other places in Tuscany, 
notablv San M:irtino, in tl:e ]\Ionte Amiata district**. 

In recent years the veins of the northern part of the island of Corsica 
have become important producers. The veins occur in sericite schist, the 
gangue materials being quartz, calcite, blende with antimonite and more 
rarely pyrite, cinnabar and boiirnonite'*. 

In Portugal rich veins of stibnite worked until recently occur 40 km. 
(24 miles) east of Porto, in the Moinho da Igreja, and San Pedro da Cova, 
on the Rio Ferreira. They traverse Paleozoic schists. 

* A. Rrhmidt: 'Frhor eini*?"e Minerale der Umcrebunfj von Sclilainin^.* Grotli's 
Z. /. Krijst. u. Min., 1S98. Vol. XXIX, part 3, p. 104. 

' G. Faller: 'Reisenotizen.' Jahrh. d. k. k. Montanlcbranst., 1S67, p. 13?. 

*TT. Connnnd: 'Solfatares, A lu mitres, etc., de la Toscanc. ' Bull. Soc. Cool, de 
France, VI, 1829. 

♦ P. Toso: Riiyista del SeriK Min., 1809, p. 144. 

** "R. T.o^ti: 'Zinnober- und Antimonlagerstatten Toscanas.' Znt.f. Prak. Ocol., 
1901. pp. ^3-40. 

•M. yo^+ion: 'Etude sur les pttes min^^raux de la Corse.' Ann. drs Mi7irs, Vol. 
XII. 1897, pp. 231-296. 



338 THE XATUnE OF OUE DEPOSITS. 

The central plateau of France is very rich in antimony. According io 
Euchs and De Launay^ the most important lodes are found in various 
rocks, viz. : 

Mica schist in the worked-out mines of Xades in the Bourbonnais; in 
granite at Bresnay ; on the contact between granite and gneiss at Montignat 
(AUier) at Villerange, in the Culm graywackes, south of Saint- Y'rieux 
(Haute-Vienne). Great numbers occur in mica schist and amphibolc 
schist, at Freycenet, and elsewhere in the cantons of Puy-de-D6mc, Cantal, 
and Haute Loire, where they are still extensively mined for antimony ore. 
Quartz is tJie main gangue, accompanied at Malbose (Ardeche) by a little 
calcite and barite. 

The stibnite is accompanied by arsenopyrite, occurring in small quartz 
veinlets in Carljoniferous aplite dikes, forming veritable stock works at 
Montignat (Allier)-. 

Similar deposits are known in Australia, viz., on ^lacleay river. South 
Australia, on Donovan's creek and on the Ui)])er Yarra, near Sunburg, 
Victoria, and in the Hillgrove district. New South Wales. 

Mexico contains imjmrtant antimonial veins, traversing quartzites and 
limestones at La Sonora. Deposits in Asia Minor are described by K. E. 
Weiss^. 

Much discussion, especially upon the mineralogic associations, has been 
aroused by the sti])nite veins of Japan. According to K. Yamada"* they 
are especially al)undant on the island of Shikoku ; they are not thick, and 
occur mostly in schists and other Paleozoic rocks. Quartz is usually the 
only gangue, the stibnite being sometimes accompanied by pyrite. 

The largest and most famous antimony mine of Japan is that of Itshino- 
kawa on Shikoku, which furnishes large stil)nite crystals. 

The country rock is a sericite schist, which is imprcgnatofl with pyrite 
near the veins. Four east-west lodes are known, three of which dip about 
80° south, the other l)ut 25° in the same din^ction, this beinir the one con- 
taining the large crystnls up to 0.5 metcT lonir. Tlie gangue is qunrtz with 
a little calosj)ar; the vein filling is banded with druses containing the large 
crystals. With one exception, the Xakase mine, the anti?nony ores do not 
carry gold. The Itshinokawa district produced 700 tons of antimony sul- 
phide nnd S3.S tons of refined antimonv in 1807^. 

Great quantities of antimony ore have also been from time to time ox- 

' Fuclisnn'l Do Lauiiny: 'Traite dcs Cites Mim'niux.' Vol. IT. 1S03, pp. 103-100; 
with full l)i!)lio,L^rnpliy. 

* L. Do Launay: Compir-Tirvdu dii VIIT Oool. Conjrrtis Tntor., 1000. 

' K. E. Woiss: 'Laiiorstatton ini Wost. Anatolion,' Zcit j. Prnk. CcoL, 1001, part 7. 

* T-oltcr to the author. 

* 'Los Minos dos Japan,' Paris Exposn., 1000, p. 10. 



epigi:ni:tic dkvoslt.s. o^j 

ported from Borneo. Tlic oro comes from veins at Tanibusnn and Tagiii, 
in the Sarawak district, in the northern part of the island. They occur 
in limestone and slate and carrv stibnite, oxidized antimony ores, and as a 
rarity native antimony, in a (juartzose gangue. 

While in most cases the antimonv vi?ins may be recrarded as extreme 
members of the antimonial gold quartz veins, in which the gold content is 
nil, and vice versa, there are, on the other hand, examples of antimony 
veins which may be regarded as extreme developments of the class of rich 
silver veins. An example of this kind was mined until the sixties at Moben- 
dorf, Sixonv. seven miles northwest of Freiberg\ which Freiesleben has 
designated as the Mobendorf type. According to II. ^liiller-, these veins 
occur in gneiss, have a steep dip and but rarely exceed 5 cm. in thickness. 
Their filling consists of stibnite, with some berthierite, bournonite, striated 
kaolin, stein mannite (antimonial galena), zincite, kermesite, stibi- 
conite, pyrite, quartz and some brownspar. A few kilometers farther east- 
southeast at Briiunsdorf the same ores are found intimately associated with 
rich silver ores in the rich silver quartz veins. 

(d) Cobalt-Nickel and Bismuth Veins. 

Two classes of veins, quite different from each other, are included under 
this heading, viz.: 

A. Veins composed essentially of cobalt-nickel and bismuth sulphides. 

R. Veins consisting of nickel-magnesia hydrosilicates. The first group 
is itself subdivi(l(d into a class characterized by a gangue cojuposed mainly 
of a carbonspar gangue. with pure cobalt-nickel ores, and n second class 
characterized by a gangue of (piartz. and other siliceous minerals in which 
carbonates are subordinate, containing bismuth ores, besides cobalt-nickel 
ores. 

Accordingly tin* various groups may be <l<signated as follows: 

1. Co])alt-niekel deposits with carbonate gangue. 
"2. Quartzose cobalt-nickel-bismuth dejmsits. 
.1. Hydrosilicate nickel deposits. 

Further dilTcnnccs betwec^n these three groups will be given in the de- 
scription of various examples. 

^ J. C. Froioslohf'Ti: 'Masazin fur Orvktoirrapliie von Sarlisori.' 1. Api)endix, p. 77 
2. Appr-ndix, p. 17P. 

- H. Mullcr: 'Krzlaixorstatten bri Fmberc:/ rott.i's Oanirstudion. I, IS.V), p. 104. 



340 THE NATURE OF ORE DEPOSITS. 

20. Cobalt-Nickel Veins with Cahbonate Gangue. 

This type is most pronounced in the cobalt veins of Dobschau, Hungary, 
which represent an extreme facies of the spathic iron-ore veins. 

According to Voit/ chloritic-talcose and quartzose Paleozoic slates are 
intruded by a sheet of diorite, wliich follows the contact with a stock of 
gametiferous serpentine. The diorite is badly altered and shows transi- 
tions from a hornblende diorite to a hornblende granitite. The basic con- 
tact facies next to the clay slate has been altered to a chloritic schist rich 
in epidote. The cobalt veins on the south flank of the Langenbcrg, four 
miles south of Zemberg, cut the diorite close to its contact with the underly- 
ing chloritic schiiiits. Three lodes composed of veins with steep southerly 
dip are recognized, each one dividing into fanlike stringers alx)ve, while 
downward they disappear, or at any rate grow barren, at a depth of 180 io 
200 m. (590 to 655 ft.) The fissures are not over 3 m. (10 ft.) thick, and 
consist mainly of siderite, calcite, ankerite and some quartz. In the 
southern veins tourmaline needles also occur, usually in the quartz, more 
rarely in the siderite. Many fragments of decomposed country rock also 
occur in the vein. The ore minerals occur as in pockets, parallel layer?, 
and large compact bodies, irregularly scattered through the vein. The 
common ore is a compact, very finely crystalline mixture of smalt ite 
(cobalt pyrite) and Kainmelsbergite (XiAs..). The richer ores yield 8 to 
10% of cobalt and about 17% of nickel, others only 4% of cobalt, but hold 
22% of nickel. This ore is usually fissured, the fractures showing slickon- 
fiides, whose glassy surface is coated with earbonaetous material. Rich ore- 
bodies, consisting of tetrahedrite, sometimes occur in the upper parts of the 
vein. Chalcopyrite, borniU*,, arsenopyrite, lollingite (FeAso) and niccolite 
are rarelv observed. Seeondarv ores, ervthrine, malachite, etc., also occur. 

The cobalt veins broaden upwards into trumpet-shaped expansions of 
coarsely crystalline siderite as much as 100 feet thick, which are exposed by 
great open-cuts, at Langenberir, Binirarten and l\tassortern. These deposiis 
completely fill irregular depressions on the surface of the diorite, and are 
in turn overlain by Carboniferous sandstones, slates and limestones carrv- 

■ > * 

ing segments of crinoid stems and othcT fossils. These deposits set^ni to he 
eoniiected with the lodes, for the siderite contains scattered nests, or evr. 
distinct la vers in its lower lavers, of nickel ores, together with some tetrn- 
hedrite, chalcopyrite, arsenopyrite and brown hematite. The solution? 
rising in the ore-bearing fissures seem to have metasomatically replae<»d 
pnrt of the Carboniferous limestone overlying the diorite. 

' F. W. Voit: 'Oonrrnost. Scliild. d. T-npcrst.-Verh. von Dobschau in T'nrarn 
Jnhrh. d. k. k. pool. Rrichsanst., 1000, Vol. L, pnrt 4. 



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