~ 

DEPAH.TMENT OF THE INTERIOR 

·. ·FRANKLIN K. LANE, Secretary 

UNITED STATES GEOL.OG-ICAL SURVEY 

GEORGE OTIS SMITH, Director 

Professional Paper 104 

THE GENESIS OF TI-lE ORES AT 

TONOPAH, NEYADA 

.. •' 

...... 

BY 

EDSON S. BASTIN 

AND 

FRANCIS B. LANEY 

[In cooperation with the Bureau of Mines] 

WASHI'NGTON 

GOVERNMENT PRINTING OFFICE. 

1918 

4397 

)/. t/ ~~ .. /0 . 

CONTENTS. 

·Page .. 

lritroduction..................................... 7 

The Tonopah district. . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

Stratigraphy: ......................... ·........... 8 

Relations of ores to inclosing rocks. . . . . . . . . . . . . . . . . 9 

Diversity in mineralization....................... 10 

Hypogene mineralization. . . . . . . . . . . . . . . . . . . . . . . . 10 

Hypogene ore textures ....................... ; 10 

Larger textural features. . . . . . . . . . . . . . . . . . 10 

Hypogene (?) veinlets and "breccias" of 

pyrargyrite ........................... . 

:Minute textural features ........ · ......... . 

Alpha hypogene minerals ................... . 

General relations ....................... . 

Sphalerite ............................. . 

9alena ............. : ..............•..... 

Chalcopyrite ............................ . 

Pyrite ................................. ·.· 

Arsenopyrite ........................... . 

Arsenical pyrargyrite ................... . 

Argyrodite (?) ........ ; ................. . 

Polybasite .............................. . 

Stephanite (?) ........................... . 

Electrum .............................. . 

Selenium .............................. . 

Argentite ................... ; ..........• 

Quartz ................................ . 

Carbonates .............................. . 

Carbonate-sulphide aggregates ........... . 

Wolframite ............................ . 

Beta hypogene minerals ..................... . 

General features ......................... . 

Polybasite ............................. . 

Argentite ............................... . 

Undetermined mineral, probably a leadbearing silver sulphide ............... . 

Chalcopyrite ............................ . 

Carbo:Q.ate-sulphide aggregates ........... . 

Electrum .............................. . 

Summary of evidence of hypogene replace:. 

ment ....... : . ..... · ...................... . 

Sequence in depositio-n among "hypogene 

minerals ................ ~ .......... " ...... . 

Nature of deep mirie waters ................ · ..... . 

Supergene mineralization ....................... . 

General character ........................... . 

Depth of oxidation .......................... . 

Oxidation at several periods .... .' ............ . 

11 

12 

13 

13 

13 

14 

14 

14 

14 

14 

16 

16 

16 

17 

17 

18 

18 

18 

18 

19 

19 

19 

20 

21 

21 

23 

23 

24 

24 

25, 

26 

30 

30 

31 

31 

. ·· ..... ' 

Supergene miheralization-Con:tinued. 

Ground water .............................. . 

Residual products of oxidation and deposits in 

open spaces by supergene solutions ......... . 

:Minerals noted ......................... . 

Gold ................................... . 

Silver ................................... . 

Pyrite .................................. . 

·Chalcopyrite ............................ . 

Argentite ......... ;.: ...... : ..... .' ....... . 

Polybasite .................. · ............. . 

Pyrargyrite ............................. . 

Silver haloids ............................ . 

Quar~z ... : ...........................•... :. 

Hyalme s1lica .......................... . 

Oxides of iron and manganese ............ . 

Calcite .................................. . 

Mixed ·carbonates ........ : ............... . 

Malachite ............... · ............ : ... . 

Calamine ............................ ; ... . 

KaOlinite .............. · ................. . 

Dahllite ................................ . 

Barite .................... · ............... . 

Gypsum ............................... . 

Epsomite ............................ : ... . 

Supergene replacement deposits ............ · ...... . 

Replacement of chalcopyrite by bornite (?), 

covellite, and argentite .................... ; 

Replacement of sphalerite and galena by covellite or argentite or a mixture of these minerals ............. · .............•........... 

~ative silver ................................ . 

Relation between . supergene mineralization 

and fracturing ...... ~ ...................... . 

Summary of evidence of supergene origin of 

certain ore minerals ..........•............. 

Nature of solutions producing supergene miner-

. alization .......................... · ........ . 

~obable persistence of ores in depth ............. . 

Oxidation banding in wall rocks .................. . 

Analyses of ore, bullion, etc ...................... . 

Identification of metallic minerals in polished 

sections ................................ · ...... . 

Summary of more important conclusions .......... . 

References ............. ;.' ........•............... 

Index .... , ...................................... . 

s· 

Page. 

33 

33 

·33 

33 

34 

34 

35 

35 

35 

36 

36 

37 

37 

37 

37 

37 

37. 

37 

38 

38 

38 

38 

39 

39 

39 

40 

40 

41 

42 

43 

44 

45 

46 

46 

47 

47 

49 
ILLUSTRATIONS. 

PLATE I. A, Banded hypogene ore from Belmont 

vein; B, Banded hypogene ore from 

Murray vein, Tonopah Extension mine. 

II. A, B, Supposed hypogene veinlets of pyrargyrite, Tonopah Extension mine; C, 

Breccia of quartz and sericitized wall 

rock· partly replaced by pyrargyrite, 

Tonopah Extension mine ............ . 

III. A, Hypogene ( ?) intergrowth of quartz and . 

pyrargyrite, Last Chance mine; B, Irregular veinlet of sphalerite and argen- · 

tite traversing quartz, West End vein, 

West En4 mine ...... , .................. . 

IV. A, Irregularintergrowthofpolybasitewith 

quartz and pyrite, West End :vein, West 

End mine; --B, Polybasite with bladelike outlines inclosed by pyrargyrite,. 

Tonopah E.xtension mine . : . ......... . 

V. A, Electrum irregularly intergrown with 

sphalerite and quartz, MacDonald vein, 

North Star mine; B, Electrum showing 

crystal outlines associated with quartz 

and su~phid~s, Murray vein, Tonopah 

ExtensiOn mme ... ~ .................. . 

VI. A, Radiating intergrowths of quartz a:pd 

ferruginous rhodochrosite, Belmont . 

. vein, Tonopah Belmont mine; B, Irregular fine aggregates of carbonate, 

argentite, and chalcopyrite intergrown 

with ore materials in larger grains, 

_Favorite vein, Tonopah Belmont mine. 

VII. A, Transition from areas that are wholly· 

galena _into areas that are mainly galen.a 

with some carbon~te and argeptite, 

and finally into areas that are mainly 

carbonate with ·~ubordinate metallic 

minerals,.· Favorite vein, Tonopah 

Belmont mine; B, Replacement of 

galena by polybasite, Favorite vein, 

Tonopah Belmont mine ............... · 

VIII. A, Sphalerite traversed by ;minute veinlets of chalcopyrite and polybasite, 

Belmont vein, Tonopah Belmont mine; 

B, Galena bordered by an undetermined replacement mineral, probably 

a lead-bearing silver sulphide, Favorite 

vein, Tonopah Belmon~ mine ......... . 

IX. A, Partial replacement of galena by a fine 

aggregate of a light-colored carbonate, 

argentite and some chalcopyrite, Favorite vein, Tonopah Belmont mine; B, Peripheral replacement of galena by argentite and electrum, Murray vein; Tonopah Extension mine ................. . 

4 

Page. 

10 

11 

12 

13 

16 

17 

20 

I 

21 

24 

PLATE X. A, Photomicrograph showing tuffaceous 

character of Fraction dacite breccia, West End mine; B, Ferruginous 

Galcite coating highly oxidized ore, 

West End vein just below Fraction daPage. 

cite breccia, West End mine ......... ·. 25 

XI. A, Branching deposit of argentite, probably supergene, on fracture in quartzose 

hypogene ore, MacDonald vein, North 

Star mine; B, Lichen-shaped deposits 

of argentite, probably supergene, on 

wall <?f fracture in hypogene ore, Mur-

. ray vein, Tonopah Extension mine . . . 34 

XII. A, Polybasite, probably supergene, partly 

fillingfracturesin white, opaque quartz, 

MacDonald vein; Montana Tonopah 

mine; B, Branching deposits of pyrargyrite and polybasite, probably supergene, on walls of fracture in white 

. quar~z, Montana Tonopah mine....... 35 

XIII. A, Association of silver and argentite, sug-

. gesting replacement of the sulphide by 

the native metal, Shaft vein, Tonopah 

Belmont mine; B, Oxidation bandingin 

M~zpah _trachyte from walls of Valley 

VIew vein .............. ·............... 40 

XIV. ·A, Oxidation banding in Mizpah·trachyte 

adjacent to Valley View vein; B, Oxidation bandi11g in fine, even-grained felsite near North Star shaft.............. 41 

XV. A, B, Photomicrographs of contact. between oxidized and unoxidized portions 

of specimen shown in Plate XIV, A... 44 

XVI. A, B, Liesegang rings of ferrous and ferric 

h?'dro~i~es developed in agar agar by 

diffUSIOn ...... '-. . . . . . . . . . . . . . . . . . . . . 45 

FIGURE 1. Concentric arrangement of sulphides 

around angular fragment of wall rock, 

Belmont vein....................... 11 

2. Crustification in small veinlet traversing. 

wall rock, Belmont vein....... . . . . . . 11 

3. Typical association of alpha hypogene 

ore minerals, Favorite vein, Tonopah 

Belmont mine~...................... 13 

4. Sphalerite with rounded outlines sur- · 

rounded by galena, Favorite vein, 

Tonopah Belmont mine ............ ,. 14 

5. Irregular intergrowth of pyrargyrite, 

with quartz, sphalerite, pyrite, and 

polybasite, Fraction vein, Jim Butler 

mine·............................... 15 

6. Replacement of galena by polybasite, 

Favorite vein, Tonopah Belmont mine 1l1 

7. Replacement of galena and sphalerite 

by polybasite and chalcopyrite, Belmont vein, Tonopah Belmont Il!ine. . 20 
ILLUSTRATIONS •.. 

FIGURE 8. Small galena areas in fine carbonate sulphide aggregates, partly replaced Ly 

polybasite, Favorite vein, Tonopah 

Belmont mine...................... 20 

9. Replacement of galena by argentite, 

Belmont vein, Tonopa~ Belmont 

mine............................... 21 

10. Sphalerite with rounded outlmes and 

quartz with crystal outlines in a matrix mainly argentite, Favorite vein, 

.Tonopah Belmont mine ...... ~.·...... 22 

11. Replacement of polybasite by argentite 

and some chalcopyrite, Favorite vein, 

.Tonopah Belmont mine .. :........ . . . 23 

12. Replacement borders of tmdetermined 

mineral, probably a lead-bearing silver mineral, around galena, Shaft 

vein, Tonopah Belmont mine....... 24 

13. Galena areas 'in chalcopyrite partly 

replaced by an undeterii).ined m~neral, probably a lead-bearing si~ver 

mineral, West End vein, Jim Butler 

mine................................ 25 

14. Partial replacement of galena by an undetermined mineral, probably a leadbearing silver sulphide which in turn 

is replaced by argentite and· chalcopyrite, West End vein, Jim Butler 

mine............................... 25 

FIGURE 15. Section through portion of West End 

mine shawing structural relations of 

th~ Fraction dacite breccia to the 

West End vein and to the :Mizpah 

trachyte ......................... :. 

16. Sketch of contact betweenFractiori dacite breccia and West End vein ..... . 

17. Replacement rim of probable bornite 

bordering chalcopyrite, Shaft vein, 

ronopah Belmont mine ............. . 

18. Peripheral replacement of chalcopyrite 

by probable bornite which in turn is 

partly replaced by argentite and covellite, Shaft vein, Tonopah Belmont 

mine .............................. . 

19. Replacement of galena and sphalerite 

by covellite, Shaft vein,. Tonopah 

Belmont mine ...................... . 

20. Peripheral replacement of sphalerite by 

covellite and argentite, Shaft vein, 

Tonopah Belmont mine ...... · ....... . 

21. Association of argentite and native silver, Shaft vein, Tonopah Belmont 

mine ............................ .- .. 

22. Plan of part of North Star mine workings, showing relations between supergene enrichment and fault fractures ........ · ..................... . 

5 

Page. 

31 

32 

39 

39 

40 

40 

41 

THE GENESIS OF THE .ORES AT TONOP"AH, NEVADA .. 

By EnsoN S. BASTIN ··and FRANCIS B. LANEY. 

INTRODUCTION. Forthe structural observations and the dis-

. In the spring of 1915, while engaged in a cussion of the·mine waters the senior author is 

study of silver emichment for the United responsible; for the detailed mineralogic and 

States Geological Survey, Mr. Bastin spent a inicroscopic 'studies both authors are remonth at Tonopah, Nev., in studying the ores· sponsible. They are ·indebted to Mr. Chase 

and their mode of occurrence. At. about the Palmer, of the United States Geological Sursame time Mr. Laney was directed by the vey, for careful analyses of samples· of the 

United States Bureau of Mines to make collec- mine waters and for chemical and mineralogic 

.. tions of Tonopah ores and to study their studies, and to Messrs. F. L. Ransome and 

·mineralogy in connection with the researches Adolph Knopf, also_ of the .Survey,·for valuable 

~f that Bureau on their metallurgic treatment~ criticisms and suggestions. ~ 

To avoid duplication of effort and to secure the The mine operators and others in Tonopah 

added fruitfulness which should follow the con- gave generously of their time and their knowleentration of more than one mind on a scientific edge and contributed many choice specimens 

problem, it :was decided to ccmbine these efforts in furtherance· of the work. To them the. 

in so far as the two fields of research overlapped. writers' sincere thanks are offered. 

The paper accordingly presents the results of 

informal cooperation between the Geological 

Survey and the Bureau o~ Mines. 

The investigation . was intended to supplement the impqrtant work of Spurr 1 and 

Burgess. 2 t>y applying to the ores methods of 

microscopic study which were not in general use 

by economic geologists at the time their reports 

were prepared, but which, in other districts, 

have proved of 111aterial assistance in the interpretation of ore genesis. 

THE TONOPAH DISTRICT. 

The Tonopah mining district is too well 

known to require an extended description. 

From the discovery of its ores in 1900, its output h~s increased year by year until in 1915 

its production of silver was exceeded in the 

United States only by that of Butte. Its 

metal output since 1904 is shown in the following t·able, compiled by V. C. Heikes,3 of the 

Geological Survey: 

Gold, silver, copper, and lead produced in .To~opah district, Nev., 1904-:-1916. 

Number Total Year. of pro~ Ore. Gold. Silver. Copper. Lead. 

ducers. value. 

Short tons. Fine ounces: Pounds. Pound.~. 

1904. ········ .............. · .... 10 22, 703 $386, 526 2, 119, 942 ............. ............ $1,594,893 

1905 ......................... 12 91,651 1, 206, 345 5, 369,439 -········- ·········· 4,449,486 

1906 ......................... 9 106,491 1, 304,677 5,697, 928 ............ ·········· 5, 122, 289 

1907 ......................... 10 214, 608 1, 183, 628 5,370, 891 5, 939 195, 508 4, 739, 966 

1908 ......................... 13 273, 176 1, 624,491 7,172,396 -········· .......... 5,425, 861 

1909 ......................... 9 278, 743 1,400, 361 7,872,967 1, 784 1,488 5,494, 600 

1910 ......................... 18 365, 139 2,303, 702 10,422,869 942 6,902 7,932,475 

1911 ......................... 19 404, 375 2,366,495 10,868,268 ·········· ........... 8, 12G,677 

1912 .......................... 17 479,421 2,223, 878 10, 144, 987 14 700 8,463,079 

1913 ......................... 32 574, 542 2,613, 843 11,563,437 1, 150 9,001 9,598, 733 

1914 ......................... 23 531, 278 2,648, 833 11,388,452 2,284 924 8,946, 987 

1915 ......................... 22 516, 337 2, 228. 983 10,171,374 ·········· ·········· 7, 385,870 

1916 .......................... 21 455, 140 1,941,441 8,734, 726 ·········· ·········· 7,688,891 

·········· 4,313, 604 1 23,433,203 106,397,676 12, 113 214, 523 84,969,807 

I Spu~r, J. E., Geology or tho Tonopah mining district, Nev.: U. S. Geol. Survey Prof. Paper 42, 1905; Geology and oro deposits at Tonopah, Nev.: F~con. Geology, vol. 10, pp. 713-769, 1915. 2 Burgess, J. A., The geology or the pr~ducing part or the Tonopah mining district: Econ. Geology, vol. 4, pp. 681-712, 1909. a Heikes, V. C., U. S. Gool. Survey Minora~ Resources, 1914, pt. 1, p. 702, 1915; idem, 1915, pt. 1, p. 647, 1916. . 

7 
8 GENESIS OF THE ORES AT TONOPAH, NEV. 

The copp·er -and lead c_ame ·from properties 

closely adjoining the district. · During the 

years represented in the table dividends were 

paid amounting to $21",000,000. 

The average 'ratio· of the gold to the silver 

in ·ounces recovered during this period was 

about 1: 98. 

The ·total average· recovery ·value per ton of 

the ore produced in 1913 was $16.71, in 1914 

$16.84, and in .1915. $14.30. M9st of. the ore 

-mined is treated by cyanidation, .with or without concentration; It is stated that in certain 

plants ore assaying as low as $8 a ton can 

under certain circumstances be profitably 

treated. 

STRATiGRAP}lY. 

-It w·as not the -~vriters·; ·purpose in visiting 

Tonopah to review the work of Sptirr and· of 

Burgess on the age and mutual relations of 

the rock formations of the district; nor would 

this have been possible in the short . time 

available for field work, ·as. ·will be- ··readily 

appreciated by anyone familiar with the remarkable co:rpplexity of the geology. The 

divergent views of Spurr and Burgess have 

been summarized with unusual ·clearness by 

Augustus Locke .. 1 Locke's own views ·are so 

nearly in harmony with those of Burgess that 

it appears unnecessary to present them separately. The following brief summary of the 

major stratigraphic features of the district will 

assist in understanding the data on the. genesis of the ores .presented in this paper. 

The Tonopah district is underlain by a thick 

series of rocks that are products of volcanic 

activity and are believed to be of Tertiary 

age.· Broadly classified, these rocks ·consist of 

a lower series, mostly rhyolitic, which is over-

· lain by two andesites, distinguished as 

"earlier" (now term~d Mizpah· trachyte by 

Spurr) and· "later (now termed Midway) 

andesite." The "later andesite" is overlain 

Geologic formations at Tonopah, Nev. 

Origin and relative age according to Approximate s~ratigraphic Origin· and relative age according to 

. . . Spurr. · successwn. . . Burgess. _ 

11. Intru.sive as volcanic necks. Brougher dacite and Oddie 9. Surface flows and the conduits through 

rhyqlite. which the lavas rose. . 

10. Surface flow. Basalt. 8. Surface flow. 

Sb. Intrusive .. · Tonopah rhyolite of Spurr in 

northern part of area. 6b. Surface flows. 

9. :Lake deposits of volcanic mater~al. Siebert tuff. 7. Lake deposits of v()lcanic material. 

Sa. Intrusive, surface flows and tuffs. Tonopah southern rhyolite part of 

of 

area. Spurr in I . 

6a. "Surface flows of rhyolites, and 

7. Tuffs and mud flows .. Fraction dacite breccia. breccias. " Not separately considered. 

6. Volcanic necks and possibly some sur- Heller dacite. face flows. 

5. Surface flow. Midway andesite 

andesite." or "later 5. Surface flow .. 

lb. Surface flow. I Mizpah trachyte or ''earlier 

andesite." · 

'4. Surface flows. 

4. Intrusive sheet. West Erid rhyolite or "upper 

rhyolite." 3. Surface flows. 

3. Intrusive sheet· with -many inclusions. Montana breccia. - Not specifically mentioned hut evidently 

classed as surface volcanic rocks. (See 

la. Basal phase of Mizpah trachyte flow . Glassy trachyte. Burgess, J. _A., op. cit., p. 682.) 

.. Sand grass ''calcitic'' 2. Flat-lying intrusive. or 2. Surface flow·. andesite. 

Sc. Intrusive with "autobrecciati~d;·~·· ..... Lower rhyolite. 1. Complex of t_uffs, breccias, and flows. 

1 The geology of the· Tonopah mining district: Am. Inst. Min. Eng. Tians., vol. 43, pp. 157-166,1912. 
1.:· 

RELATIONS OF ORES TO !~CLOSING ROCKS. '9 

by rhyolite; lacustrine tuffs,. and thin flows of Spurr bases his classification. Locke 2 says.: 

basalt. In spite of complicated faulting most "There is no mineralogical distincti.qn whatof the volcanic forrilations are rather flat- ever to be made between. many veins wliich, 

lying. The ·middle column of the table on according to the hypothesis [Spurr's], shol)id 

page 8 shows the formations that have been belong to different periods." · T;he writers' 

re~ognized, arranged in ·the normal order of observations tend to indicate at least the 

superposition. I~ the left-hand column is appro:xlmate ·correctness of. Locke's st~tegiven Spurr's latest interpretation of· their ment.' The principal productive veins of the 

origin and age relations, an,d in the right- region show notable similarity in the minerals 

hand column Burgess's interpretation. The present and in the mutual relations of these 

numbers indicate the relative ages under the minerals. The ore of t~e Belmont vein, for 

two interpre.tations; formations that are :re- example, which Spurr classes as a first-period 

garded as contemporaneous are given the same vein, is practically identical in mineral ·com-

.number but-differentiated by 'letter, as Sa, Sb. position with that of the .MacNamara and -

The two interpretations differ materially, lllOSt Fraction veins, which he classes as secondof the rocks which Spurr regards as flat-lying period veins. Mineralogic differences between 

'intrusive rocks being interpreted by Burgess ~eins of supposed different ages are commonly 

as flows poured out upon ancient surfaces. no greater than may be observed in different 

The decision between these two interpre- parts of one continuous vein. In most of the 

tations must be left to future students of "first-period" veins there is little evidence of 

Tonopah geology'. Successful refutation of fracturing of the ore and filling of the fracthe detailed work of Spurr and his associates tures by later ore except that resulting from 

must be founded o'n observations comparable downward enrichment. Upon the sole basis 

with theirs in detail and comprehensiveness. . of the mineral composition and texture of the 

RELATIONS OF ORES TO INCLOSING ROCKS. 

'fho bulk of the metal production of . the 

district ~1as come fro1n ore bodies lying wholly 

within the Mizpah tr~chyte (''earlier. andesite"). Within recent years, however, as the 

result of deeper development and l.mdergrouncl eA.~loration of new territory, an increasing percentage of the output has c9me 

from ore bodies bounded on one or both sides 

by other formations. Many of· th,e veins, for 

example, whose upper portions are wholly in 

the Mizpah trachyte have at greater depth 

o one or both walls of West End rhyolite. Spurr 1 

believes that the productive veins are of several ages· and classifies them as first-period 

and second-period veins, the latter with four 

subclasses. He recognizes also third-period 

veins, which are not productive. The veins of 

· the first p~riod he believes are older than the 

· Montana breccia and West End rhyolite; those 

of ·the second period ·are younger than these 

formations; and both sets are older than the 

"cap rock" or Midway andesite. 

The writers.hadlittle. opportunity to study 

in the field the structural evidence on which 

t Spurr, J. E., Geology and ore deposits at Tonopah, Nev.: Econ. 

Geology, vol. 10, pp. 751-760, 1915. 

primary ore there would be little reason for 

the impartial geologic observer. to regard· the .. 

principal productive veins as of more than 

one age; · Mineralogic similarity eari not, 

however, be taken as proof of.contemporaneity, 

for in a region where there has been recurrent 

volcanic ac.tivity it is possible if not probable 

that similar mineralization might take place 

. at more than· one period. Structural observations must furnish the final test. 

· In the descriptions here give:t;t the ores of the 

principal productive veins are described as a 

unit but without implication of preciso 

equality in age. The wolframite of the ·Belmont vein is an exception, for it is shown 

by textural relations to be somewha~ later 

than the silver ore with which it is associated. 

As emphasized by Spurr 3 the ores of Tonopah are in the main replacemen·t deposits 

along sheetlike zones of fracturing._ They are 

therefore typical replacement veins. Every 

gradation may be traced from heavy sulphide 

ore into slightly replaced wall rock. Oreceme:Qted ·breccias, true crustification, comb 

struct~e, and other features charac'teristic of 

· 2 Locke, Augustus, Tbe geology of the Tonopah mining district: Am. 

Inst. Min. Eng. Trans., vol. 43, p. IG4, 1912. · 

s Spurr, J. E., Geology of the Tonopah mining distnct, Nev.: U.S. 

Geol. Survey Prof. Paper 42, p. 84, 1905. 
10 GENESIS OF THE ORES AT .TONOPAH, NEV. 

the filling of open spaces are rare or developed 

only on a small.scale. Banding somewhat re-· 

sembling true· crusti:fication, which is locally. 

c·onspicuous, is possibly to be explained by diffusion 1 during replacement. 

Most of the. veins dip .steeply, but some, like 

the West End and MacNamara, are _only inoder;;. 

ately inclined. 

DIVERSITY IN MINERALIZATION. 

Whatever may be the differences in· age 

among the veins of Tonopah, it is certai:r;1 at 

least· that most of the ores represent the net 

result of _several successive geologic processes. 

A study of their t'exture and mineralogy makes 

it possible to group the ore minerals according 

to. their relative ages and to reach. conclusions 

in regard to the nature of the processes responsible 'for the deposition of. each group. 

The solutions that deposited the great bulk 

of the minerals of the Tonopah ores were, it is 

believed, exudations from cooling, buried 

bodies of igneous rock or magma. In expressing this view the writers accept the opinion of 

Spurr for the Tonopah district and align their 

conclusions with the trend of opinion among 

American geologists in regard to the genesis of 

the majority of precious-metal lode deposits. 

The ·ac.cl,lmuiation of independent evidence of 

such an _origin would have involved skuctural 

and strati'graphic studies for which the writers 

had little opportunity. Such mineralization 

is commonly termed primary, but the writers 

prefer to use. the term hypogene, proposed by 

Ransome. 2 . Solutions coming from great 

deptl;ls withi.n the earth and having a general 

upward_ flo_w will therefore be termed hypogene 

solutions and the work they accomplished hypogene mineralization. 

After the hypogene mineralization the slow 

removal of the covering of, volcanic rocks by 

erosion exposed the upper parts of many of the 

veins to the action of the air and of waters of 

surface origin. By.the combined attack of these 

agents upon the upper parts, of the hypogene 

1 R. E. Liesegang (Geologische Di.ffusionen, Dresden, 1913) has shown 

that certain phases of banded structure may be produced by rhythmic 

precipitation during the diffusion of a solution into some medium with 

which it reacts chemically, or by simultaneotis diffusion of two mutually 

interaetmg solutions into an inert medium. It is lughly probable that 

some of the banding observed in ores formed by replacement has developed in this way. · 

2 Ransome, F. L., Copper deposits near Superior, Ariz.: U. S. Geol. 

Survey Bull. 540, p. 152, 1914. 

ore bodies, sliver _and other metals· were dissolved. These metals were carried downward 

in solution and eventually redeposited, com~ 

monly in fractures or vugs in the hypogene 

ores. These. are the· processes commonly referred to as "oxidation"· and "enrichment," 

but they will be referred to collectively in this 

paper as supergene mineralization.3 

Although . supergene · mineralization ·has 

played an interesting part in the genesis of 

certain of the Tonopah ores, it appears to have 

been quantitatively much less important than 

the hypogene mineralization. Most of the ore 

bodies in which. i.t was most prominent are 

worked out, and the principal dependence of 

the mines to-day is upon ores that, the writers· 

believe, are almost wholly ·of hypogene origin. · 

HYPOGENE MINERALIZATION. 

The hypogene ores will be considered first, 

because they· are at present the principal 

economic resource of the camp and are the 

parent type froin which ~he supergene ores 

were derived. 

HYPOGENE ORE TEXTURES. 

The ores of Tonopah occur in veins that 

were formed mainly by replacement 4 of the 

country rocks along zones of closely _spaced 

fracturing. Ore deposition in open spaces was 

an accompanying but minor process. In 

places, conspicuous slip planes, accompanied 

by much gouge, limit or ·traverse the ore 

bodies,. but commonly the ore bodies are without definite walls on one or on both sides. 

LARGER TEXTURAL FEATURES. 

The observations :here recorded on the c 

larger textural features of the· hypogene ores 

were mainly incidental to the n1icroscopic 

studies. A complete study of the larger vein 

textures was not attempted. 

Banding in the_ ores was particularly conspicuous in parts of the Murray veins and 

·commonly presents the appearance shown in 

a Idem, p. 153. "The suggestion is offered that minerals deposited by 

generally dO\'.'llWard-moving and initially temperate solutions may be 

termed supergene minerals." 

4 The term "replacement," as used by most economic geologists, sig· 

nifies the removal of material by solution and the immediate deposition 

of different material in its place-either the removal of rock minerals 

and the deposition of ore minerals or the removal of one ore mineral 

and the deposition of another. 
A. BANDED HYPOGENE ORE. 

Enlarged 1 ~ diameters. The light-gray areas are mainly a fine intergrowth oi ferruginous rhodochrosite and quartz; 

the dark-gray to black areas are mainly quartz carrying hypogene sulphides in numerous very minute grains. 

The radial structure of some of the rhodochrosite-quartz intergrowths at right angles to the banding is dimly shown. Belmont vein, 1,000-foot level. 

B. BANDED HYPOGENE ORE. 

Murray vein, Tonopah Extension mine, just below 950-foot level. One-half natural size. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 104 PLATE II 

A. B. 

A, B. SUPPOSED HYPOGENE VEINLETS OF PYRARGYRITE. 

The veinlets pass from areas of partly altered wall rock (a) into quartz areas (b) and become less well defined in 

the quartz. Tonopah Extension mine, exact location uncertain. Natural size. 

C. BRECCIA OF QUARTZ AND SERICITIZED WALL ROCK PARTLY REPLACED BY PYRARGYRITE 

(BLACK). 

Photomicrograph of polished surface of ore. Tonopah Extension mine, exact location uncertain. Enlarged 25 

diameters. 
HYPOGENE MINERALIZATION·. 11 

Plate I, A. Most of the lighter areas are a 

microscopic intergrowth of rhodochrosite and 

quart.z; the darker areas are quartz carrying 

sulphides in a ·very fine st~te ~f division. 

Plate I, B, shows a similar structure in ore of 

identical appearance from the Belmont vein .. 

In many places in both veins the banding is 

concentric around fragments .of wall rock 

(probably silicified rhyolite), one of :which,· 

partly replaced by quartz, is shown below the 

FIGURE 1.-Rudely concentric arrangement of sulphides around angular 

fmgment of wall rock. One-half natural size. Belmont vein, 1,_000-

foot level. Sketched by K S. Bastin. 

center of Plate I, B. The demarcation of the 

light and dark bands is in place·s sliarp but 

elsewhere vague. The bands n1ay be a nlillimeter or less in width and confined to those 

parts of .the matrix imn1ediately bordering the 

fragments, or they Iiuty be fairly .wide, as 

shown in Plate I. Scattered grains of pyrite 

are abundant in the rhyolite fragments but are 

absent froin the ore surrounding them: The 

fragmen~s are commonly angular, but some 

show evidences of gradual replacement by the 

:fino quartz-rhodochrosite intergrowth. Tha 

arrangement of tho black sulphide-rich portions around a wall-rock fragment in ·the 

Belmont vein is sketched in figure 1. 

Tho concentric arrangement of many of the 

bands. around angular fragments of wall rock 

favors their interpretation as true crustifica-: 

tion. As banding of somewhat similar appearance may be developed in ores that have 

been formed solely by replacement, in the absence of any but very minute openings, it is 

difficult to exclude tho possibility that.some· of 

the banding in the Tonopah ores niay .have 

originated during the replactlment of a matrix 

of crushed rock in which larger fragments of 

wall rock wei·e embedded. Undoubted crusti-

:fication is locally observed in narrow veinlets 

traversing the wall rocks, as sketched Ill 

figure 2. 

HptOGENE ( ~) VEINLETS AND ''BRECCIAS'' OF 

PYRARG YRITE. 

A number of specimens of rich ore obtain6d. 

through·the co~tesy of Mr. John G. Kirchen 

show veinlets, mainly of pyrargyrite; traversing quartz. and partly silicified wall rock. · 

These specimens came from the TonopahExtension mine, but their exact location in 

the mine is uncertain.- The · appearance of 

sawed faces is shown in Plate II, .A fl,nd B. 

As shown particularly well in Plate II, B, these 

veinlets pass from areas of only partly silicified 

wall rock (a) into areas of quartz (b) that apparently represent completely silicified wall rock. 

Upon entering the quartz. the v,einlets become 

somewhat less well defined. Thin sections 

across the contact between· the partly silicified 

and completely silicified wall rock show u11:der 

the microscope that the veinlets continue with 

little change of form from . the partly ·altered 

rock into the quartz and that they were 

formed· after the silicification that developed 

the quartz areas. The veinlets are planes of 

minor fracturing, along which pyrargyrite has 

.been. deposited along minute fractures partly 

filled with fragments of quartz and altered 

wall rock (mainly sericite. ·and pyrite).· ·Some 

pyrargyrite has replac~d the sericitized fraglnents and some ·has filled small quart~~lin~d 

vugs. · In places some ·pyrite is so intergrown 

with pyrargyrite as to suggest that both we1:e 

depo.sited f:Lt the same time. · Pyrargyrite . is 

FIGURE 2.-Crustificationinsmall veinlct traversing wall rock. Natural 

size. a, Sulphides; b, quartz; c, center of veinlet. Belmont vein, 

1,000-foot lev~!. Sketched by E. S. Bastiil. · · 

not · confuled to the. veinlets~ but occurs· .also 

as sinall patche.s of irregUlar outline scattered 

through and evidently replacing the partly 

altered hordering rock. 

Areas showing pyrargyrite · veinlets .of the 

type just q.escribed or s'J.lowing minute quantities of pyrargyrite replacing altered rock are 

closely associated with areas as much as 2 

inches across of what appears to be a breccia 

of pyrargyrite fragments In a gray siliceous 
12 GENESIS OF THE ·oRES AT TONOPAH, NEV. 

matrix. The pyrargyrite fragments are at 

·most 1 centimeter across. When viewed in 

detail under the microscope the pyrargyrite 

areas are seen to have irregular outlines, as 

shown in- Plate II, 0, and to be in the ·maiti 

formed by the replacement of a brecc1aof quartz 

and sericitized wall rock. The fragmental 

appearance is due to the faqt that certain'fragments in this breccia. which were evidently 

more susceptible to replacement than the 

matrix and other fragments have been. alm,ost 

completely replaced by the pyrargyrite. 

· Reliable criteria for determining whether 

these pyrargyrite veinlets and breccias were 

deposited qy hypogene or by supergene solutions seem. to be lacking. They may represent 

an early step in the extensive rephtcement ·of 

wall rock by an . association of quart.z and 

pyrargyrite of the type shown in Plate III, A, 

which may ·be very. uniform in char-acter 

througlt several cubic incl1es and . is regarded 

by the writers as probably. hypogene .. Fur., 

thermore, most deposits of py.rargyite and 

other silver minerals in late fractures in the 

Tonopah ores can be cleanly stripped from 

·the walls of sucli fractures, and the walls 

· appear to have undergone no replacement. 

· · Such deposits are interpreted as supergene 

· and are quite. different from the pyrargyrite 

deposits described in the present section. The 

writers are inclined to believe, therefore, that 

tliese unusual p:frargyrite veinlets and breccia-like deposits are hypogene, though recognizing that the evidence is not ~onclusive. 

MINUTE TEXTURAL FEATURES. 

The 1nicroscopic study of the ores reveals 

minute textural relations, not otherwise recognizable, that are of great importance in interpreting their gene~is. It. shows ;repeatedly 

and with especial clearnes~ that the primary 

or hypogene mineralization was not a simple, 

brief event but was a process of considerable 

duration accomplished by solutions whose 

composition was not at all times the same. 

.Ore minerals· deposited early in the hypogene 

.mineralization were partly or wholly dissolved. 

at a later stage in the _process, and. other ore 

minerals more ~table in the presence of ~he 

changed solutions were deposited in their· 

place. 

Some of the general.features of the hypogene 

mineralization· and the· principles which they 

exemplify niay first be considered. The· Tonopah pres are in the main formed by the replacement of igneous. rocks; these rocks are aggregates of many miner'al species, some of whicp 

are more susceptible to replacement-, under a 

given set of conditions,. than others. The 

effects of the first of the hypogene solutions, 

. the adv.all:ce· wave of mineralization, were the 

replacement of certain of the wall-rock minerals 

by other nonmetallic minerals .and by pyrite, 

alterations commonly included under .the term 

"hydrother~al· alteration." These changes 

are now shown in the wall . rock bordering the 

. veins and probably were accomplished in the 

main vein zones themselves, where they have 

since been obliterated by further ohanges.· 

They have been. carefully studied by Spurr.1 · 

In the Mizpah trachyte, the predominant wall 

-rook of many of the veins, the first alterations 

commonly consisted in th'e. selective replacement 

of certaih minerals by calcite, siderite, chlorite, 

sericite, and pyrite; later there was progressive 

destruction of chlorite and caloite and to some 

extent of pyrite, accompanie.~ by an increase. 

in the amount of siderite and sericite and the 

development of quartz and adularia; finally 

the pyrite was completely redissolved and the 

rock conv~rted into an aggregate of quartz 

and silica. These ohanges, · while broadly a 

part of the mineralization process, preceded 

th~ introdU<:~tion of the valuable metals, for, 

according to Spurr, 2 ·the· pyritized wall rocks 

cai';ry only negligible amounts of gold and 

silver. The present paper is concerned with 

the succeeding changes, which involved the 

further replacement of the altered rocks and 

t;he development of the typical ore minerals. 

Mainly _for convenience in description and 

without attributing· any p~rticular significance 

to s~ch a classification, the writers· have divided 

the hypogene ore' minerals into two classes~ 

.alpha hypogene and beta-hypogene. . 

The · . alpha hyppgene minerals are those 

which are· formed by the direct hypogene· replacement. of .wall-rock :Qlinerals or their corrirrion hydrothermal alteration products, such as 

sericite· and quartz, or which are not demon-

. 1 Spurr, J. E., Geology of the Tonopah minin~: d~trict, Nev.: U. S. 

Gcol. Survey Prof. Paper 42, pp. 207-252, 1905. 

2 Idem, p. 207. . 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 104 PLATE III 

A. HYPOGENE ) INTERGROWTII OF QUARTZ (DARK) A,ND PYRARGYRITE (LIGHT). 

Photomicrograph of polished surface of ore from vein· between 400 and 500 foot levels, Last Chance mine. These 

minerals are believed to be contemporary results of rock replacement. 

B. IRREGULAR VEINLET OF SPHALERITE (SMOOTH LIGHT GRAY) AND ARGENTITE (ROUGH 

LIGIIT GRAY), BORDERED BY QUARTZ (DARK GRAY), WITH SCATTERED IRREGULAR AREAS 

OF SPHALERITE. 

The sphalerite-argentite veinlet is believed to mark a line of easy replacement in the ori~;inal rock. All the minerals are interpreted as alpha hypogene. Photomicrograph of polished surface of ore n·om stope 600 C, West End 

vein, West End mine. 
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 104 PLATE IV 

1mm 

A. IRREGULAR INTERGROWTH OF POL YBASITE (pol), PROBABLY ALPHA HYPOGENE, WITH 

QUARTZ (q) AND PYRITE (py). 

Photomicrograph of polished surface of ore just above 500-foot level. West End vein, West End mine. 

B. POLYBASITE (LIGHT GRAY) WITH BLADELIKE OUTLINES, INCLOSED BY PYRARGYRITE 

(WHITE). 

The dark gray is quartz. The po1ybasite has been made visible by brief treatment with mercuric chloride solution. 

Photonncrograph of polished surface of ore, Tonopah Extension mine, exac.t location uncertain. 
.HY~OGENE MINERA!--IZA~ION:. 13 

strably otherwise. The beta hjpogen~ ~nerals are formed by the replacem1mt of earlier 

hypogene metallic ore minerals.· Replacement 

of the host rock may go on until it is practi-

·cally complete, after which !urther replace~_ent 

must involve tho destruction of' earlier ore min-

·erals. ·Tho beta hypogene minerals. ~re. obviously younger than those particular alpha hypo-

,geno nunorals wluch they replace, but they are 

not necessarily. younger than an 

.alpha hypogene minerals. On the 

-contrary, there is .much evidence 

that direct replacement of the host 

.rock by ore minerals at one place 

was coincident with replacement 

-of oro minerals by other ore min.:. 

.-erals at another place. For this 

Carbonates were noted in ~U these veins, 

b11:t their. composition co~only differs f~om 

point to point even within a l?ingle vein, as 

exphtined in the paragraph on carbonates. 

SPHALERITE. 

Sphalerite, which is one of the. commonest 

sulphides of the ores, was noted only as .. an 

alpha hypogene mineral. Crystal faces on 

reason "beta" the are preferred tern1s ''alpha'' to terms that and.~~~~~~~~~~ 

·carry a time significance, such as. 

·"early" and "late." 

ALPHA HYPOGENE MINERALS. 

GENERAL RELATIONS. 

Tho individual grains of the 

.minerals that are believed to be 

alpha hypogene interlock irregu1arly in a fashion indicative of 

mutual interference during growth 

and produce ore textures somewhat comparable to the granular 

texture$ of certain igneous. rocks. 

'Typical examples of these textures 

lmm. 

are shown in :figlires 3 to 5 and in FrGURE a.-Typical association of alpha hypogene ore minerals. A few small areas of 

'Plates V, A, and VI, B. Such tex _ argentite (arg) may be later replacement deposits, but the other minerals are believed to be essentially contemporaneous. q, Quartz; gal, galena; chal, chalcopyrite; sph, 

tures are indicative of general COn- sphalerite; carb, carbonate; arq, argentite. Camera Iucida drawing from polished 

'tempora;nei ty of the nlinerals pres- surface o~ ore from Favorite vein, Tonopah Belmont mine. Depth uncertain. 

·ent, although certain n1inor aee differences sphalerite. were noted only in a few places 

probably exist, such as are shown by the order where the mineral was in contact with galena 

·Of crystallization usually recognizable among . or chalcopyrite.. Commonly it forms rounded. 

tho components of a massive igneous rock. areas, -wluch are surrounded (~ee fig. 4) by 

The minerals named below appear to have one· or more of the minerals galena, argent~te, 

·been formed by alpha hypogene crystalljzation __ ·or chalcopyrite .. Such rounded outlines might 

innoarlyall thoveinsstudied-Behnont,Favor- suggest that· the sphalerite has been parely 

.ito, Shaft, MacDonald, North Star footwall vein, r~placed. by the minerals that surround it, but 

Last Chance, West. End, Extension combined there are no other indications that· sphalerite 

vein on 770-foot level, Egypti~n, Extension has been replaced to more than a very minor 

.lower contact vein, McNamara, and Murray: extent during the entire process of mineraliza-· 

Sphalerite.. Argyrodite (?). tion. Locally, as shown in Plate III, B, tl:le 

·Galena. Polybasite. sphalerite has very irregular outlines. This 

·Cha_lcopyrite. ~!~~~=: . plat~ also illustrates a less common mode of 

Pyrite. occurrence of sphalerite, as small, irregular .Arsenopyrite (noted only in Quartz. b 

the La.st Chance vein). C;ubonates. veinlets that appear to have been formed y 

:Pyrargyrite. replacement of the host. rock along. minut.e 

•. 
14 GENESIS OF THE ORES AT TONOPAH, NEV. 

fractures. The boundaries between sphalerite 

and quartz are generally very irregular· (see 

fig. 5) and suggest complete contemporaneity 

of deposition. In a few· places sphalerite is 

traversed by minute r~placement veinlets of 

chalcopyrite and polybasite, as is shown m 

Plate VIII,. A, and figure 7. 

In. general the maximum deposition . or. 

sphalerite and quartz appears.to have occurred 

early in the hypogene mineralization, and the 

maximum deposition of galena, chalcopyrite, 

pyrargyrite, and argentite was slightly later, 

as is shown by their m.a.trical position. The 

two periods overlapped, however, and locally 

sphalerite and quartz are later than the other. 

FIGURE 4.-Sphalerite (sph) with rounded outlines surrounded by 

· galena (gal). A few small areas of argentite (arg). q, Quartz. Camera 

Iucida drawing from polished Stl!face of ore from Favorite vein, Tonopah Belmont mine. Depth uncertain. 

minerals. Jn most of the ores s'phalerite is not 

identifiable without the aid of the ~icroscope. 

GALENA. 

Galena, which is also one of the commonest 

sulphides of the ·ores, was noted only as an. 

alpha hypogene mineral. It almost invariably 

conforms to the crystal outlines of bordering 

quartz areas, as shown in figure 3, and in many 

places it forms the matrix of areas of sphalerite 

of rounded outline, as shown in figure 4. Its 

contacts with alpha hypogene . chalcopyrite 

and argentite are commonly irregular or 

smoothly curving. Galena has been replaced 

by beta hypogene minerals to a greater extent 

than any other sulphide. 

CHALCOPYRITE. 

Alpha hypogene chalcopyrite is nearly as 

abundant as sphalerite or galena~· It also 

supergene mineral, and it is not always possible 

to determine to which class. ft. given occurrence 

belongs. Chalcopyrite in relations like those 

shown in figure 3 is interpreted as alpha 

hypogene. The mineral commonly conforms 

to the crystal outlilles of quartz and locally 

embeds sphalerite of rounded or crystal outline. Its boundaries against galena and alpha 

hypogene argentite are commonly irregular or 

rounding. Alpha hypogene chalcopyrite has 

locally been replaced by beta hypogene minerals 

and by supergene minerals. 

PYRITE .. 

Pyrite is in general less abundant in the 

ores than chalcopjrite, but tends to form 

larger grai~s .. It was the first sulphide to 

form in the process of ·mineralization by replacement, and in slightly mineralized rock 

it is the only one present. (See Pl. XV, B.) 

Its deposition appears to_ have continued 

throughout. the hypogene· mineralization, for 

in many phtces it conforms ·to the crystalline 

outlines of quartz and has irregular boundaries 

next to chalcopyrite. 

Pyrite ·appears to hav·e· formed loc8Jly as a 

late deposit in open fractures but was nowhere 

noted as having replaced other metallic ore 

minerals. · ARSENOPYRITE. 

A mineral that is nearly white in the polished 

sections and only slightly softer than pyrite, 

though it takes a sm.oother polish, is probably 

arsenopyrite. The outlines ·of the orystal indicate orthorhombic crystallization. Stellar 

trillings, such as are common in arsenopyrite, 

were noted. Though the niineral is fairly 

abundant in an ore specimen from a depth of 

about ·500 feet in the Last Chance vein, it was 

not noted in any other specimens. It is irregularly intercrystallized with sphalerite, galena, 

and quartz, and except for its presence the ore 

in which it is found presents no unusual features. 

ARSENICAL PYRARG1."RITE. 

Arsenical pyrargyrite, though rare compared 

with the sulphides of the base metals, is present 

in all the veins studied and is locally very abundant .. Spurr 1 appears to have ~egarded it as 

invariably supergene. Some of the pyrargyrite almost certainly is of supergene deposition, 

1 Spurr, J. E., Geology. of the Tonopah mining district, Nev.: U. B. 

occurs as a beta hypogene and probably as a Geol. survey Prof. Paper 42, pp. 94-95.1905. 
HYPOGENE MINERALIZATION. 15 

as will be shown later, but most of it appears to 

be. hypogene. 

"'There ·particularly abundant its chief associates are quartz, polybasite, and probably argyrodite, but in places, as· shown in figure 5, it 

is irregularly intercrystallized with the comInon sulphides, sphalerite, pyrite, chalcopyrite, etc. V einlets of pyrargyri te that may be 

alpha ·hypogene are· described on page 11 and 

illustrated in Plate II. More irregular intergrowths with quartz of the. type shown in_ 

Plate III, A, were n_oted in ores from the Last 

Chance and Fraction veins and the To_nopah 

Extension mine. A texture of this sort might 

be explained through the deposition of pyrargyri te in the open spaces of a porous 1nass of finely crystalline quartz, 

but it is more probably the result of 

simultaneous replacement of a rock 

by quartz and pyrargyrite, for analogous textural relations exist elsewhere between quartz and the commoner sulphides or n1ixtures of the 

coininoner sulphides with pyrargyrite, as shown in figure 5. In ores 

· like those shown in Plate III, A, 

and figure 5 the quartz posse~sed 

greater power of assuming crystal 

outlines than the other ore minerals. 

The microscopic intergrowths of 

pressures they are unstable in hot solutions of 

alkaline sulphides. He suggests that whenever these minerals are found in apparently 

primary occurrences their precipitation has 

. resulted from the mingling of ascending alkaline 

sulphide solutions with descending acid -solu~ 

tions. It appears to the writers inherently 

improb~ble that oxidation could be furnishing 

any significant amount of acid water ·at a time 

when hot mineralizing solutions were .,still 

ascending. Unless it is assumed that n1ineral 

deposits from hypogene solutions are nowhere 

being formed at the present day it must be 

supposed that certain hot springs .(not all or 

even the-majority) are the surface expression 

quartz and pyrargyrite may consti- 1 mm. 

tute several cubic inches of material . · . . . · . . . . FIGURE 5.-Irregular mtergrowth of pyrargynte (pyrg) With quartz (q), sphalente (sph), 

whlCh, VIewed Wl th the una1 ded eye, pyrite (pyr), and polyhasite (pol). Camera Iucida drawing frorp. polished surface of ore 

appears to be pure pyrargyri te. from Fraction vein, Jim Butler miae, between 600 and 700 foot levels. 

A few small crystals of pyrargyrite occur: in ·of mineralization in progress below them . 

. vugs, and the angles of some of these have been Mineral deposits being formed at or near the 

Ineasured by Eakle. 1 surface . in regions 'of hot-spring activity are 

A large number of samples of pyrargyrite characteristically rich in gangue and poor in 

heated in closed tubes before the blowpipe car- metallic minerals; moreover, the metallic 

ried arsenic, and in some samples arsenic ap- minerals are confined to certain species, such 

peared to be as abundant as antimony. as _stibnite and cinnabar, and rarely, so far 

Pyrargyrite was not noted as replacing other as the· writers are aware, include the comore minerals (beta hypogene). mon sulphides galena, sphalerite, and chalLouis 0: Ravicz 2 in a recent paper expresses copyrite, which are the pre~o~inant sulphides 

the view th~t the sulphosalts of silver, such as at Tonopah and are. locally intergrown conpyrargyrite and polybasite, can not be formed temporaneously with the sulpho -:salts of 

by precipitation from solutions containing silver. ·The composition of ores· known to be 

alkaline sulphides through decrease of pressure formed at the surface appears therefore to be 

or tmnperu.ture alone, be-cause under ordinary not the most favorable for the ·development 

tEakle,A.S.,ThemlneralsofTonopah,Nev.: CaliforniaUn.iv.Dept. through oxidation of large amounts of acid 

Geology Bull., voi. 7, P· 9, 19l2. solutions, even if the upflow of ascending hot 2 Experiments in the enrichment ofsilvcrores: Econ. Geology, vol.10, 

p. a7s, 1915. wate:rS did not inhibit extensive· -oxidation. 
l6 GENESIS _QF. THE qR.E~ _AT_..TONOPAH, NEV •. 

Furthermore, the mine~alogy of the ·Tonopah 

Ores· is !lOt that. of the shallowest ""types of ore 

deposits.. Mmmg ha·s shown that the hypogen~ 

ores rari.ge.: through ·a vertical interval of 1 ,5.00 

foot without notable change in mineral: composition, and. it seems probabl~ that' they were 

originally deposited. at several times this depth~ 

at ho:d.zons' '·'where effective :mingling with 

acid supergEm~ solutions probably could not 

occur~ if Ransome 1 has correctly" interpreted 

· the., fo~ation of alunite· ·at th~; · ne_ighbormg 

cani·p of Goldfield as·; the result .. of a ·-fu.ingling 

of descendilig acid' sohitl.oiis with the . ascel).di}ig _soluti~ris, the ap~~:ll~ce.of alunite at T~:mop~h 

may·:be taken as additional evidence that 'such 

intermmgllrlg did;nbt' t~ke place there. ..~ · · 

made caref..P. ·qu~itative te~ts for germanium 

in a s.aniple · of the m:1xture ·which carried the 

unkno~ mineral and definitely determined· 

that': thiS element was present. It is therefore · pro_bable that the mineral :argyrn.dite is 

present:· in these ores, although the possibility 

that. the germanium may be in some other 

mineral combinattion can no"t be excluded·. 

In the two localitie~· in.which argyrodite has 

been identified, it is. also associated with other 

silver mineral~. Near Freib~rg, Saxony, it i~ 

associated With pyrargyrite, polybasite, stephanite, and common sulphides of the base 

rri.etais.2 in Bollvia it is associated with poly-

~-asite and stephanite. 

POLYBASITE. Although. the -writers .. are .. not· inclined to 

regard. the mingling of superge~e.with hypogene The mode of o·ccurrence of polybasite is very 

solutions as the. cause of the prec;ipitation ·of similar· to that of pyrargyrite, with which it is 

the hypogene sulphosalts of silver at Tonopah, commonly associated. It occurs not only as an 

these minerals are ~1 the main. the_ latest of ~he. alpha hypogene but also: as a beta hypogene 

hypogene minerals·, and i_t_ is qu.ite probable ·and a supergene deposit. In its alpha hypogene 

that· ~t the._time~~t~ey were deposited the occurrence it may be irregularly mtergrown 

hypogene s<?lutions had become_ somewhat with pyrargyrite an.d the comm9ner sulphides, 

depleted in alkalies, through sericitization of as shown in figure 5, or may be a component 

the wall rocks, and in sulphur, through pre- of veinlets of the type illustrated in Plate II,· 

· cipitation of the early hypogene sulphides. .A and B. In a few deposits of the type shown 

'A~GJ:RODITE ( n. 

. In intergrowths of qu~rtz and. pyrargyrite, 

such. as those shown in Plate III, .A, small 

. amounts o(poiybasite occur' and also a metallic mineral that could not be. certainly ident~.:. 

fied .. This mineral, which is irregularly intergrown with the pyrargyrite a.nd polybasite 

· and is plainly contemporaneous with them, is 

recognizable only upon. microscopic study of 

in Plate IV, .A, the polybasite, probably hypogene, is intimately intercrystallized with quartz 

·and· pyrite . 

In one specimen from the Tonopah Extensioi). 

mine polybasite inclosed by pyrargyrite showed 

the blade-like forms illustrated in Plate IV, B. 

These· blades are presumably cross sections of · 

po~ybasite crystals. · · 

STEPHANITE ( n. 

polished spe'cimens. On freshly pollshed sur- Th_e presence of stephanite in the Tonopah 

faces it is distinguishable from the pyrargy- ores has not ·been proved. .Numerous tests 

rite, though not easily, by its slightly pinkish I were made on crystals that from general ap.-

tint. It is brittle and near pyrargyrite in pearance might be either stephanite or polyhardri.ess, but has a black streak a:bout like basite, to "determine whether they contained 

that of ·polybasite. It is not tarnished by copper. Upon dissolving in n~tric acid and 

silver nitra.te or·· mercuric chloride solutions n~utralizing with ammonia the blue C<?lor of the 

that tarnish pyrargyrite and polybasite brown. copper-ammonium salt was obtai?-ed in every 

The min·eral was found in too small amounts test. This "\yas not due to admixed chalcopy~ 

to be isolated .for analysis, hut its ·physical rite, for no precipitate of ferri~. hydroxide 

properties ·appeared to agree with those ·of the formed. All these crystals were therefore iden~ 

mine:ral argyrodite (Ag8GeS6 or_.Ag6GeS5 ), in tified as polybasite. Spurr 3 and Eakle 4 also 

which the element germanium was first discovered. Chase Palmer, of this Survey, has 

1 R~om~t.~F. L., The geology and ore deposits of Goldfield, Nev.: 

U.S. Geol. Survey Prof. Paper 66, pp. 193-195, 1909. 

2 See Hintze, Carl, Handbuch der Mineralogie, Band 1, Abt. 1, pp. 

1193-1197, 1904, for full references to the litcrattire. 

a Spurr, J. E.; Geology of the Tonopah oin.ing district, Nev.: U.S. 

Geol. Survey Prof. Paper 42, p: 9S,.1905. ' · · ··. 

• Eakle, A. S., op. cit., p. 9. · 
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 104 PLATE V 

'. 

I 0.3mm I 

A. ELECTRUM (STIPPLED) IRREGULARLY INTERGROWN WITH SPHALERITE AND QUARTZ. 

The argentite (arg) shown in this photograph was probably formed by the replacement (beta hypogene) of galena (gal), 

all the other minerals, including the electrum, are believed to be alpha hypogene. Photomicrograph of 

polished surface of ore from 1,050-foot level, Macdonald vein, North Star mine. sph, Sphalerite; q, quartz. 

B. ELECTRUM SHOWING CRYSTAL OUTLINES ASSOCIATED WITH QUARTZ AND SULPHIDES. 

The argentite was very probably formed bythe replacementof galena, but all the other minerals are believed to be 

alpha hypogene. Photomicrograph of polished SUl'face of ore from 1,260-foot level, Murray vein, Tonopah 

Extension mine. chal, Chalcopyrite; sph, sphalerite; arg, argentite; elec, electrum; q, quartz. 
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 104 PLATE VI 

,"Jmm I 

A . RADIATING INTERGnOWTHS OF QUARTZ (WIDTE) AND FERRUGINOUS RHODOCHROSITE 

(GRAY) WITH SMALL PATCHES OF FINELY DIVIDED SULPIDDES (BLACK). 

Photomicrograph (ordinary light) of thin section of ore from 1,000-foot level, Belmont vein, Tonopah-Belmont mine. 

B . IRREGULAR FINE AGGREGATES OF CARBONATE, ARGENTITE, AND CHALCOPYRITE (chal) 

INTERGROWN WITH ORE MINERALS IN LARGER GRAINS. 

Photomicrograph of polished surface of ore from Favorite vein, Tonopah-Belmont mine. sph, Sphalerite; q, quartz. 
HYPOGENE MINERALIZATION. 17 

were unable to identify· any of the -"brittle 

silver'·' as stephanite. · 

ELECTRUM. 

· Assays 1 to 4 ~bove were commuclc~ted by 

Mr. A. E. Lowe, superintendent at the North 

Star mine. Sample 2 is said ,to have ~hown no 

free ~old~ even on panning; presumably the . 

A. pale-yellow mineral that is sectile .and is gold was In very minute grains, which were not 

not tar.J?.ished by IICl, HN,03

, or (NH4

)

2

S is rec- freed from the sulphides in the· crushing pre-

. ognizable under the m.icroscope in a large num.:.. pru;atory to panning·.· Microscopic examination 

ber of the ores. l t QCCUrs in grains SO fine that by the writers. of"' of<{ ··said to be from the lot 

its Inechanical separation from the other, ore represen~ed in assay 4 revealed the presence 

mi:nerals is extremely difficult; Ore fr01n the of the hght-yellow sectile mineral in unusual 

West End vein between the 400 and 500 foot abundance and in unusually large· grains (as 

levels that was known from microscopic study much a~ 0.36_ milli_meter in diameter). A part 

to carry this ~nineral was very finely crushed of the s~lver In th1s ore occurs in pyrargyrite, · 

and carefuJ].y panned. After the heavy pan- polybas1te, and argentite, aU of which were 

nings were treated with hot dilute nitric acid to iden~ifi.ed microscopically. Assay 5 was made 

dissolve the sulphides, null?-erous heavy minute by the Bureau of Mines on a small sample colblack particles, visible under a hand l~ns, re-. lected by the. writers and shown by ~icroscopic 

mained. Upon further treatment with hot con- st~dy to be unusually rich· in the light-yellow 

centrated nitric acid these particles acquired ~.1neral. Pyrargyrite, arge-ntite, and polybathe yellow color characteristic of gold. Similar site were also recognized microscopically in this. 

blackening of the mi:q_eral upon treatment with sample. . 

dilute acid w.as also noted by Hillebrand. Sev- In most of ~he .m;.ess the electrum grains con- · 

eral specimens shown by microscopic. study to form to the characteristic ro·unded b~undaries 

be rich in the light-yellow mineral·assayed ex-. of sphalerite and to crystal boundaries of 

ceptionally high in gold. This mineral is be- quartz, sh_aring the m~trical position o{galena, 

lieved to be electrum, possibly carrying some chalcopyrite, and argentite. (See Pl. V, A.) 

seleniutn, as discussed below. This conclu- In places it develop~ crystal faces. (See Pl. V, 

sion accords with the ·studies of Hillebrand B.) . The argentite shown in Plate V, B, is beon ores collected by Sp~rr, which showe.d that lieved to 1lave been formed, at least in part, by 

at least some of the gold in the ores was heavily the replacement of galena; for reasons-discussed 

alloyed with-silver. . · in the section on.argentite (p: 18). It is possible 

A number of .assays of Tonopah ores excep- that the electrum in this sectiono also replaces 

tionally rich in gold· are given below. How galena, but more· probably it crystallized conmuch of the silver in these ores was alloyed tempora~eous!y with the galena whose place is 

with gold is unknown, for sulphides·and sulpho...: now occupied by· argentite. Exceptionally the 

salts of silver were present in all the sa:QJ.ples. electrum is intercrystallized irregularly with 

Assays of some Tonopah o1·es. 

[Ounces per ton.] 

Gold. Silver. 

1. North Star mine footwall vein, 

1,250-foot level; grab sample 

from 250 tons .......... _....... . 47. 96 

2. ~ame lo~ality as No. 1; picked 

p1ece of nch ore ....... _........ 367.22 

3. ~ame local~ty as No. 1; · two 

p1eces ........................ _ _ 79.60 

4. Same vein as No. 1, stope above 

1,130-foot level. . .. . . . . . . . . . . . . . 10. 72 

5. West End vein in stope·522 be- . tween 500 and 600 foot levels; 

small piece of rich ore. . . . . . . . . . 23. 50 

19. 35 

185.15 

36.20 

681.90 

1;483.00 

sphalerite or bordered by it on all sides in the 

plane .of the section. In a number of ores it 

was observed as a minor component of the· 

carbonate-s11lphide aggregates. (See p. is and 

Pls. VI, B, an'cl VII, A.) 

SELENIUl\I. 

Small. amoutits of selenium have long been 

known to be present in the ores of Tonopah and 

in the derived concentrates and bullion. The 

.largest amount recorded is 2.56 per cent, in an 

analysis by W. F. Hillebrand of panp.ings from 

heavy sulphide ore (analysis 2, p. 46). The 

p1ineral combination in. which it occurs is not 

yet definitely determined, but there is co~id~ 
18 'GENESIS OF THE ORES AT TONOPAH, NEV. 

erable ground for believing that it is associated· with the gold and silver· in electrum ... 

Mr. Palmer defini~ely:determined the ·presence of 

selenium in pannings consisting n1ainly of elec.., 

trum, from ore obtained in the West End mine; 

unfortunately the quantity· of material available was very small. It is possible that selenium 

produced the blackening in the electrum upon 

treatment with dilute nitric· acid, noted .above. 

ARGENTITE. 

The extent to which argentite occurs as an 

· alpha hypogene mineraJ is somewhat uncertain. 

In a few places it is associated with sphalerite 

in the irregular fashion shown· in Plate III, B, 

and in such places it appears to be alpha hypogene. Small areas of argentite bordered on all 

sides, in the plane of t.he section, by sphalerite, 

as shown in figure 4, also appear to be alpha 

hypogene. Argentite is also an abundant component of the fine carbonate-s~phide intergrowths described below; and in some of these 

it ·probably dire·ctly replaces the host rock 

and is therefore alpha hypogene. 

One of the commonest modes of occurrence of 

argentite is shown in figure 10 and Plate V, B. 

In the specimens illustrated its position is interstitial with respect to quartz with. crystal outlines and· entirely 'similar to that conlm.only 

assumed by galena. (See fig. 4.) As -a rul~ it 

·is possible to prove that' this argentite is at least 

in part 'formed by' the replacement of galena, 

but some of it may directly replace the host 

rock. 

Argentite Is also abundant as a supergene 

mineral. 

·QUARTZ. 

Quartz is the most abundant gangue mineral 

of the ores and is universally present. Most of 

it appears to have been formed by direct replacement of the host rock. In a few places it 

appears to have been replaced by the carbonate-sulphide aggregates described bel~w, 

but replacement of quartz has occur.red only 

to a yery minor extent in this district. 

Thin coatings of . quartz, locally folin.d on 

the walls of certain ·open fractures, are believed to be in part supergene and in part very 

late hypogene dep.osits. · 

CARBONATES. 

The pale-pink n1aterial so abundant in 

many of the Tonopah ores has commonly been 

ermed rhodonite, on accouri.t of its apparent 

ha:rdness, the fact that it effervesced with acid 

being ~ttributed to admixed carbonates. 

Microscopic study shows, however, that it is a 

very fine intergrowth of quartz and a carbonate, and that no rhodonite is present. 

An analysis by W. F. Hillebrand 1 of sulphide ore from depths of 460 to 512 feet in the 

Montana Tonopah mine showed. that0 four elements were combined ·as carbonates in the 

following proportions: Calcium 2.7, magnesium 0.9, iron 1.14, and manganese 1.32. 

·Qualitative tests py the writers on pink carbonate from ·the 906-foot level on the Murray 

vein showed the presence of calcium, magnesium, manganese, and a very srriall amount 

of iron. Carbonate of similar appearance 

from the 1 ,260-foot level on the same vein carried a much larger proportion of iron. The 

fine state of division of the carbonate in the 

ores makes it difficult to determine whether 

several hypogene carbonates are present in 

varying proportions or a single carbonate of 

varying composition. 

Much· of the carbonate is present in the fine · 

intergrowths with sulphides, which are described in the nex_t section, but radiating 

intergrowths with quartz of the type shown in 

Plate VI, A, are common, especially in banded 

ores 'li]ie those shown in Plate I. 

In some veins, ·such as the Murray, intergrowths of quartz and pink carbonate are very 

abundant an·d give a pink cast to much of 

the ore; in other veins, such as ·the West End · 

and Favorite, hypogene carbonates are usually 

visible only with the aid of the microscope. 

Carbonates also occur as supergene deposits. 

CARBONATE-SULPHIDE AGGREGATES. 

Microscopic aggregates of light-colored carbonates with one or more of the minerals 

chalcopyrite, galena, argentite,. and polybasite are common in many of the ores and are 

shown in Plate VI, B. Usually only one of the 

silver minerals is present. In general, all the 

minerals of these aggregates conform to the 

crystal outlines of quartz and to the rounded 

outlines of-sphalerite. The fine aggregates are, 

as a rule, sharply demarked from the borooring coarser material, but exceptionally there 

are gradual transitions from fine aggregates 

in which carbonates predominate to coarser 

intergrowths in which sulphide's predominate. 

1 Spurr, J. E., Geology of the Tonopah mrnrng distrrct, Nev.: U.S. 

Geol. Survey Prof. Paper 42, p. 89, 1905. . 
HYPOGENE MINERALIZATION. 19 

Such a transition from areas consisting mainly 

of carbonate ~ith small amounts of galena and 

argentite to areas consisting of mainly galena 1 

and argentite with scattered patches of carbonate is shown in Plate VII, .A. Transitions 

into areas consisting mainly of chalcopyrite 

were noted in other speci;mens. The!;)e transitions, as well as the matrical position of the 

carbonate-sulphide aggregates, indicate that· 

they were deposited for the most part contemporaneously with the larger areas of 

galena and chalcopyrite. As-already stated, a 

few grains of electrum occur in some of these 

aggregates. 

WOLFRAMITE. 

The tungstate of iron and. manganese has 

been noted at a number of localities in the 

mines at Tonopah. The Writers are not completely informed as to all its occurrences,' but 

it was noted by ·them. in the Belmont vei.ti 

and in a small vein in the Valley View mine. 

In the· Valley View_ mine, on 'th~ 300-foot 

level, quartz and wolframite form a small 

vein as much as 4 in64es wide, lying well within 

the footwall of 'the Valley View vein. Its 

relations to the silver veins are not shown. 

BETA HYPOGENE MINERALS· .. 

GENERAL FEATURES. 

Certain minerals and mineral aggregates of 

the Tonopah ores are formed by the replace.:. 

ment of earlier ore minerals rather than by 

direct replacement of the wall rock or of the 

products of its hydrothermal alteration. The 

criteria by which those deposits that repiace_ 

ear lie~ ore minerals may be·. recognized in 

these ores are here briefly summarized. Some 

of_ the deposits are believed to- be hypogene· 

and others supergene, and the criteria for 

distinguishing between them are discussed on 

pages 24 a~d 42.' . 

The textural relation of the replacing minerals of greatest diagnostic value is ·their 

FIGURE 6.-Replacem:ent of galena (gal) by polybasite (pol) along its 

contacts with other minerals (as at A and A'), along contacts between 

two differently oriented galena crystals (aS at B), and along galena 

cleavages ·(as at C). Rims of an earlier replacement product Hke. 

those shown in figure 14 are invariably present between polybasjte 

and galena but ate too narrow to be shown on this scale. q, Quartz; 

carb, carbonate; chal, chalcopyrite; sph, sphalerite. Camera Iucida 

drawing from polished surface of ore from Favorite vein, TonopahBelmont mine. Depth uncertain. 

In the Belmont vein as exposed on the 1,000-

foot level of the Tonopah Belmont mine, in 

south crosscut 1044, wolframite is very abundant and its relation to the silver ore is ·well 

exhibited. · The silver ore at this locality 

consists 1nainly of quartz_ and an intergrowth 

of quartz and ferruginous rhodochrosite of the 

sort described on page 18, through ·which 

aggregates of very . :fi~1ely divided sulphides 

are distributed. Fractures traversing ·this ore 

are partly or completely filled with crystalline 

quartz, with which wolframite is so intimately 

intergrown as to leave no· .doubt that the 

quartz and wolframite are ·strictly contemporaneous. Wolframite is also intercrystallized 

with quartz that lines vugs in quartzose parts 

of the ore. 

So far as the writers are aware wolframite 

has nowhere been established as a mineral of 

supergene deposition. The wolframite at 

Tonopah is believed to have been deposited 

fron1 ascending silica bearing waters after the 

deposition of most of the silver ores and after 

these ores had undergo~e some fracturing. 

localization at places that were obviously 

channels of easy access for mineralizing solutions. Situations particularly favorable. for th<t 

repla.cement_of hyPogene· ore minerals by other 

ore minerals are the following: 

1. Contacts between hypogene minerals of 

. different species, at least one of which was 

replaceable under the then existing conditions. 

In such situations the replacing minerals 
20 GENESIS OF THE ORES AT TONOPAH, NEV. 

commonly form narrow replacement bands; as 

shown at A and A' in figure 6 ·and in Pl~te 

VIII, B. 

2. Contacts between two crystals of· the 

same' replaceable mineral. The replacing 

mineral along such contacts commonly takes 

the form of narrow bands expanding here and 

there into lenticular areas, as is weil shown at 

Bin figure 6 and A in Plate VII, B. 

FIGURE 7.-Replacement "of galena (gal) and sphalerite (sph) by polybasite (pol) and chalcopyrite (cllal). In sphalerite the replacement· 

Yeinlets are commonly irregular, but in galena many of them follow 

cleavage directions. Locally the replacement has followed the contacts between galena and other minerals. q, Quartz.· Camera·lucida 

·drawing from polished··surface of ore from_ Belmont vein, 1,200-foot 

level of Tonopah Belinont mine. · · 

3. Narrow . wedges of replaceable n1ineral 

between cohverging contacts with other miuei·als· or between intersecting fractures. These 

are particularly vulnerable to replacement, as 

is well illustrated at A in figure 9. 

4. Cleavage planes in replaceable minerals 

o:r<obscure fractures following cleavages. Replacement of galena along cleavages is shown 

at 0 in figure.6 and in figure 7. 

5. :Minute irregular fractures. Replacement 

~long irregular fractures in sphalerite is shown 

in figure 7 and in Plate VIII, A.. · 

oughly "soaked" with the replacing solutions 

that replacement ·proceeded with great facility, 

without. much regard to the. earlier textural 

features of the. ore. Instances of replacement 

of this sort will be cited in_the detailed descriptions. In some places the resulting textures 

can be identified as due to replacement only 

by local gradations into undoubted replacement deposits along mineral contacts and fractures or by close textural and mineralogic resemblance to such deposits. . · 

The minerals believed to have been formed 

by hypogene replacement of earlier hypogene 

ore minerals are polybasite, argentite, an undetermined mineral that is probably a lead-sliver 

sulphide, chalcopyri~e, electrum, and a· finegrained carbonate-sulphide aggregate. 

PO.LYBASITE. 

Polybasite is very common in- the ·ores of. 

Tonopah, replacing galena and, very rarely, 

sphalerite. The situations at which replacement may occur are well shown in figures 6, 7, 

· and 8. Along the contacts between galena 

~ 

~:~~~~ ~-

'if 

car· 

0.1 mm. 

FIGURE 8.-Small areas of galena (gal) in the fihe carbonate-sulphide. 

aggregates partly replaced by polybasite (1>0l). The first product of 

the replacement, possibly a lead-bearing silver mineral, formil narrow 

rims (black in the drawing) between the galena and the polybasite. 

car, Carbonate. ·Camera Iucida drawing from polished surface of ore 

from Favorite vein, Tonopah Delmont-mine. Depth uncertain. - . 

The replaoement of alpha hypogene minerals 

appears not to liave been· confined to situations 

of. obvious vulnerability but in many. places 

se~~s to have proceeded irregularly through crystals the replaci:p.g mineral commonly· apthe ore.· Borne deposits so formed represent ·pears in the polished sections as minute threads 

~erely advanced stages of a· process which (as at A, Plate VII, B), which enlarge to lenses 

began by replacement along mineral contacts_ at intervals (as at B, fig. 6). 

or fractures, but in reference to ot4ers it seems Very rarely polybasite occurs alone or with 

necessary to conclude that the ore was so thor- c~_alcopyrite as minute replacement veinlets i? 
U.S. GEOLOGICAL SunVEY PROFESSIONAL PAPER 104 PLATE VII 

gaL 

• arg . , 

0.3mm 

A. TRANSITION FROM AREAS WHOLLY GALENA (gal) INTO AREAS (A) THAT ARE MAINLY 

GALENA WITH SOME CARBONATE (ROUGH DARK GRAY) AND ARGENTITE (arg), AND FINALLY 

INTO AREAS (B) THAT ARE MAINLY CARBONATE WITH SOME ARGENTITE, GALENA, CHALCOPYRITE, AND ELECTRUM, NAMED IN THE ORDER OF ABUNDANCE. 

Photomicrograph of polished swface of ore from 1,000-foot level, Favorite vein, Tonopah-Belmont mine. q, Quartz. 

I I 

B. REPLACEMENT OF GALENA (gal) BY POLYBASITE (pol). 

Between these two minerals occur narrow bands of an unidentified transition mineral (not visible in the picture), and · the very narrow light-colored bands (as at A) that mark the initiation of the replacement process alo~ the contacts 

between galena crystals consist of this mineral. Photomicrograph of polished surface of ore from Yavorite vein, 

Tonopah-Belmont mine, depth uncertain. 
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 104 PLATE Vlll 

sph 

L lmm 

A. SPHALERITE (sph)TRAVERSED BY MINUTE VEINLETS OF CHALCOPYRITE AND POLYBASITE. 

Some of the veinlets in sphalerite are continuous with areas of the same minerals replacing galena (gal); this feature 

does not show in this picture but is illustrated by fiaure 7, di·awn from the same specimen. The veinlets are in the main formed by replacement, thou"'h possib"iy in small part fracture fillings. Photomicrograph of 

polished surface of ore from hanging-wall branch of Belmont vein, 1,200-foot level, Tonopah-Belmont mine. 

q, Quartz. 

B. GALENA (gal) BORDERED BY AN UNDETERMINED REPLACEMENT MINERAL, PROBABLY A 

LEAD-BEARI G SILVER SULPHIDE. 

In a few places, as .at A and A1, the replacement process has proceeded further, with the development of argentite. Photomicrograph of polished surface of ore from Favorite vein, Tonopah-Belmont mine, depth not known. 

q, Quartz; py, pyrite; sph, sphalerite. 
. HYPOGENE MINERALIZATION. 21 

sphaleritQ, as is shown in Plate VIII, A. These 

veinlets are commonly irregular in the sphaler-

'ite, but upon entering neighboring galena 

grains they conform to the cleavage I)lanes of 

the gal~na. 'These features _are shown in figure 7, a drawing, on:a larger scale, from a portiqn of' the specimen shown in Plate VIII, A. 

In places· even minute areas of galena in the 

carbonate-sulphide aggregates (f?ee p. -18) have 

been partly replaced by polybasite, as is shown 

in figure 8. 

Between galena and the polybasite which has 

replaced it, but not between sphalerite and 

polybasite, there is invariably a narrow band 

of· a third mineral which is evid~ntly a temporary transition . product in the replacing process. This ··ap.pears to be 

the sanie mineral that ·js developed 

between gnlena n.nd arg-entite. It is 

considered 1nore fully below. 

ARG ~N:TITE. 

Although argentite occurs as a supergene deposit on the walls of open 

fractures, it has been formed priricipally by the replacement. of galena. 

For reasons cited on ·page 24 most 

such roplacemen t deposits are believed 

to be hypogene, although. in gen~ral 

UNDETERMINED MINERAL, PROBABLY A LEAD-· 

BEARING SILVER SULPHIDE. 

Betw-een galena and argentite or polybasite. 

that has replaeed it there is invariably a band 

of a replacement mineral representing an 

intermediate .. step· in the alteration. These 

transition bands, which are of varying width, 

are particularly well sho':Vll in figure 12 bu.t 

also appear in figures 8 and .14 and Plate 

VIII, B. . Other illustrations o~ such replacement deposits do not show these bands be-. 

cause they are too narrow to appear on the 

scale· used. They are not formed between 

galena and chalcopyrite that replaces it or at 

appearance they are similar to others 0.2.mm. 

that are probably supergene. Typical FIGURE 9.-Repiacement of galena (gal) by argentite (arg) at A. q, Quartz; sph, 

replacement of galena by argen ti to is sphalerite. Camera .lueidadrowingfrom polished surface of ore from Belmont vein, 

shown in figures g and 10 and . in 1,200-foot level of Tonopah Belmont mine. · 

Plates VIII, B, and IX, B. Relations like the contacts of silver minerals With any other 

those shown in figure 101 in which argentite sulphide sav:e galena. 

embeds quartz and sphalerite, are particu- Here and there the replacement has prolarly common, and are in many places demon-· ceeded no further than the formation of the 

strably the result of replacement of galena by undetermined mineral, as is shown in figure 13. 

argentite. Areas in which argentite without :Most of the . replacement. borders shown in 

galena embeds quartz and sphalerite ·may be Plate VIII, B,· consist of the undetermined· 

traced continuously into others like that mineral, but in a few places, as at A and A', 

shown in figure 10, in which both sulphides argentite has formed as the final product. 

are present,. the argentite replacing the galena, The transition ·mineral is indistinguishable 

in p~rt peripherally, with the invariable from ·galena on freshly polished surfaces, but 

development between argentite and galena upon treatment with hydrogen peroxide the 

of narrow bands of an intermediate repla~e..: galena is tarnished brown while the transition 

ment product. In a few places argentite; mineral is unaffected. Its hardness, tested 

alone or with chalcopyrite, replaces polybasite ·by drawing a needle across the contact of 

(probably alpha hypogene), as is shown in galena and the transition mineral under a 

figure 11. low power of the microscope, appeal'S to be 
22 GENESIS OF THE ORES AT TONOPAH, NEV. 

about the same as that of galen~. The triangular depressions. developed in the galena in the 

grinding process continue-into the unidentified 

mineral, as shown in figures 12 and 14.· These 

depressions are due to the tearing out of small 

· inverted pyramids of the minerals between 

three intersecting cleavage planes, and their 

continuity from galena into the other mineral 

shows that the latter possesses a cleavage 

identical with and ·continuous with that of 

lmm. 

product between galena and argeriti_te it may 

be suspected of being a double sulphide of 

lead and silver or a solid· solution of galena 

and argentite with physical properties like 

those of galena. 

Chase Palmer, ·of this Survey, has studied 

experimentally the action of dilute s6lu tions 

of silver salts on galena from Joplin, Mo., for. 

the purpose of throwing some light on the 

character of the transition mineral observed in 

the Tonopah ores. In his :first experiment galena, carefully picked to 

obtain as pure material as possible, 

was finely pulverized and treated in. 

a flask with a solution of silver sulphate (about N/40) to which had 

been added a slightly acid. solution 

of sodium acetate to keep ill 'solution 

any lead that might be dissolved. 

The flask was heated in a water bath 

for two weeks, a stream of purified 

carbon dioxide passing continuously 

through it to. prevent oxidation by 

air. 'At. the end of the experiment. 

no metallic silver could be detected· 

by microscopic examination of the 

solid residue, but it was found that 

small amounts of lead had been dissolved and some silver removed from 

. the ~olu tion. 

FIGURE 10.-Areas of sphalerite (sph) with rounded outlines and of quartz (q) with 

crystal outlines in a· matdx consisting mainly of argentite (arg). These relations appear to have resulted from the replacement of galena (gal, alpha hypogene)· by 

argentite (probably beta hypogene) in ore whose original appearance was like that 

shown In figure 4. Numerous remnants of galena remain, and between these and 

the argentite narrow rims of an intermediate replacement product (too narrow to show 

on this scale) are invariably present. pyr, Pyrite. Came,ra Iucida drawing from 

polished surface of ore from Favorite vein, Tonopah Belmont mine. .Depth uncertain. 

For a more detailed study of the 

reaction between galena and a soluble 

silver. salt, Mr. Palmer chose the orga~ic salt silver-benzol sulphonate, 

which, though· resembling the sulphate in containing the 803 radicle, 

is much more soluble and yields a 

soluble lead salt by reaction with 

galena. The results are stated by . 

Mr. Palmer 1 as follows: 

galena. The undetermined mineral is therefore probably, like galena, isometric; 

The mineral is readily distinguished from 

argentite by its lighter color and the fact that 

it is brittle rather than sectile. It is present 

in too small amounts and is too intimately 

associated with other minerals to be separated 

for analysis. From the properties already 

described )t is believed to be an isometric· 

mineral with perfeet . cubical ·cleavage,. in 

hardness,- color, and· lus.ter very similar to 

galena. From its position as a transition 

The galena, obtained from the Joplin district, Mo., was 

carefully picked. It was reduced to grains that were 

collected on a sieve with 40 meshes to the inch. Particles 

of galena were selected from these small fragments. The 

mineral thus chosen was ground to pass through.a 200-

mesh sieve. · 

Analysis of the powdered galena. 

Lead ...... _ . . 86. 56 

Sulphur. . . . . 13. 39 

Iron ..... _ . . Trace. 

99.95 

Required for PbS . 

. Lead.... .. .. . 86. 60 

Sulphur ..... 13. 40 

100.00 

1 Manuscript re1>9rt, May 16, 1916. 
HYPOGENE MINERALIZATION. 23 

For the experiment, 0.5145 gram of the powdered galena 

was digested in a solution of silver-benzol sulphonate containing 2.075 grams, slightly acidified with benzol suiphonic acid. The volume of the solution was about 250 

cubic centimeters. The minera! was digested in this soluti~n five days on the steam bath. The solution was then· 

filtered. No trace· of sulphate was found in the filtered 

solution, an indication that the sulphur of the galena had 

not been oxidized. 

After the removal of the excess of silver from the solution, it was found that 0.11379 gram of lead had been dissolved. This represents 22.18 ·per cent of the galena used 

in the experiment. The· residue was found to contain 

13.38 per cent of sulphur-that is, all the sulphur present 

in the galena used-and from· the residue was obtained 

0.11242 gram of silver, representing 21.85 per cent of the 

weigh~ of the galena. 

and 

21.85+107.9=·0.2025 silver. 

22.18+207 0.=1071 _lead. 

0.2025+0.1071=1.89. 

The rea.ction between galena and silve~-ben~ol sulphonate may therefore be written 

PbS+2(C6H5S03Ag)=Ag2S+(C6H5S03)2Pb. 

The normal reaction occurring between galena and a soluble si.lver salt may therefore be regarded as strictly metathetical. · 

Mr. Palmer's experimental ·results are in 

agreement with the microscopic evidence in 

indicating that argentite is one of the stable 

products of the reaction of a soluble silver salt 

upon galena. The nature of the intermediate 

replacement product revealed by the microscope between galeri.a and argentite· still remains in <;Ioubt; it may be a solid solution of 

galena and argentite or a double sulphide of 

lead and silver. Nissen and Hoyt 1 from a 

of galena, either alone or in association wi..th 

argentite. Where gal~na has been replaced by 

a mixture of argentite .and chalcopyrite, tran-

.sition rims of the pq_ssible lead-silver sulphide 

are invariably present between argentite and 

galena but n<_)t between· ·chalc9pyrite' ·and 

g~ena, ~ feature ~hich is shown in figure 14. 

Replacement of polybasite by an association 

of chalcopyrite and argentite is shown in 

figure 11. . In a very few places .chalcopyrite 

was noted with polybasite in replacement vein-

,; ? 1_ ·' 7 

·o.3mm 

. FIGURE 11.-Replacemerit ·or polybasite (pol), probably alpha hypogene, by argentite (arg) and some chalcopyrite (chal). q, Quartz. 

Camera Iucida drawing from polished surface of ore from Favorite 

vein, 1,000-foot level of Tonopah Belmont mine. 

lets trave~ing sphalerite, as is shown in Plate 

VIII, A, and figure 7. 

CARBO~ATE-SULPHIDE AGGREGATES. 

study of a series of melts of galena and.silver Fine aggregates of light-colored carbonate· 

sulphide conclude that "the limit of solid solu- with argentite or polybasite and locally chaltion at atmospheric temperatures is below 0.2 copyrite, identical in character with those deper cent Ag~S." The apparent homogeneity s.cribed above· as probably representing alpha 

of the transition mineral and the extreme sharp-· ·hypogene crystallization, replace galena in a 

ness of th~ boundaries between it and both .number of the ores. Such replacement is 

galena and argentite seem to favor its interpre- clearly shown in Plate IX, A. Carbonatetation as a double sulphide of lead and silver. sulphide aggregates replacing galena occur in 

· Although galena is the mineral most com- the same ·specimen with aggregates of identical 

monly replaced by argentite, a f.ew instances character that apparently have · directly reo£ the replacement of polybasite by argentite placed the host rock. ' 

or an association of argentite and chalcopyrite Proofs that·the aggregates replace gal~na are 

wer~ noted, as ~hown in figure 11. found (1) in the ininutely irregular character 

of their contact with galena; (2) in the presence 

of small "ou~liers" of galena in the carbonate 

areas that have the same crystall-ographic orientation as the larger galena areas near by, of 

which th~y were evidently once a part; (3) in 

the complete t~ansition of carbonate-polybasite 

CHALCOPYRITE. 

The copper-iron sulphide chalcopyrite has· 

been formed rather commonly by replacement 

t Nissen, A. E., and Hoyt, S. L., On theoccurrenceofsilverinargentiferous galena ores:·Econ. Geology, vol. 10, p. 179, 1915. · 
24 GENESIS OF THE .ORES AT TONOPAH] NEV. 

areas into areas of polybasite that clearly replace tact with galena. Such replacement presents 

galena, in the general fashiop. shown in figure 6; some analogies to the replacement of galena. 

and (4) ~n-the minor irregularity of the contacts by the carbonate-sulphide aggregates shown 

between quartz and the carbonate-sulphide in Plate IX, A, though in the electrum-

. aggregates contrasted with the smoothness of bearing deposit only 'two replacing min.erals are 

those between quartz and galena (a contrast involved. Electrum is, indeed, a component 

well shown at A and B in Pl. IX, A.), iD;diGating of a few such carbonate-sulphide aggregates. 

: •1' • ~ '; : .• 

SUMMARY OF EVIDENCE OF HYPQGENE REPLACEMENT. 

The conclusion that the replacement of one ore mineral by another 

in the Tonopah <?res occurred mainly 

during the hypogene mineralization 

is perhaps the most important contributio~ of this paper. It is there-· 

fore desirable to ·summarize briefly 

the grounds upon which this conclusion rests. 

1. The minerals that are described 

as form~d by hypogene replacement 

of other ore minerals- include no 

species that are not al~o found as 

undoubted alpha hypogene min- · 

·erals-that is, ·directly replacing, the 

host rock. The occlirrence of electrum of identical appearance intergrown irregularly with sphalerite 

(alpha hypogene) and also peripherally replacing galena (beta hypogene) is particularlysignificant. 

2 .. The fine carbonate-sulphide 

aggregates that replace galena (Pl. 

IX, A) are identical in mineral composition and in texture with others 

(Pls. VI, B, and VII, A) that directly 

FIGURE 12.-Replacement borders of an undetermined mineral, probably a lead-bearing 

silver mineral, around galena (gal). The i.mdetermincd mineral is in turn replaced 

locally by argentite (arg). The triangular pits developed in the. grinding of the ore 

surface are common to the galena and the bordering replacement rims. The surface 

was tarnished with hydrogen peroxide to differentiate galena from the undetermined mineral. q, Quartz; ·sph, sphalerite. Camera Iucida drawing from polished surface of ore from Shaft vein, 1,000-foot level of Tonopah Belmont mine. replace the host rock and that are 

.irregularly intergrown with coarser and. undoubtedly hypogene sulphides. 

that not galena alone but also. small amount~ 

of quartz have been replaced by the aggregate. 

ELECTRuM. 

Most of the electrum of the Tonopah ores 

·appears to ·replace rock minerals (alpha 

hypogene) directly, as shown in Plate V, A 

and B ,· some of it is clearly formed by the 

replacement .of galena. In Plate IX, B., is 

shown.· peripheral replaceriie.nt·:~f. galena by an 

aS!iJOCiation. of electruffi arid ~rgentite. . While 

argentite and e lectrum -are'··sharply segregated 

iii different parts of the replacement border, 

the galena boundary shows no jog· in passing 

from the contact with . argeri.tit'e. irito the. con3.· Continuous areas of certain minerals and 

mineral aggregates were noted which appeared 

at one point · to replace the host rock and at 

another point to replace earlier ore :minerals. 

This was notably true of the carbonate-sulphide aggregates. 

4. The presence of electrum peripherally 

replacing galena is highly suggestive of hypogene origin, for it is well known that gol.d 

and silver tend to- part company in the processes involved in supergene enrichment because, of . their great difference in solubility 

under conditions of oxidation. If. the elec-, 

t.rum is ·hypogene the ·argentite which accom-
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 104 PLATE IX 

A. PARTIAL REPLACEMENT OF GALENA (gal) BY A FINE AGGREGATE OF A LIGHT-COLORED 

CARBONATE, ARGENTITE, AND SOME CHALCOPYRITE. 

There has also been a slight replacement of the quartz (compare the ragged boundary of the quartz (q) at A with 

the smooth boundary at B). Photomicrograph of polished surface of ore from Favorite vern, Tonopah-Belmont 

mine, depth uncertain. 

B. PERIPHERAL REPLACEMENT OF GALENA (gal) BY AN ASSOCIATION OF ARGENTITE (arg) AND 

ELECTRUM (STIPPLED). . 

Note the smoothness of the galena border in passing from contact with argentite to contact with electrum. There has also been replacement of the type shown in figure 6 along the contact between two galena crystals of differe~t orieJ?-tat10ns. Photomicrograph of polished surface of ore from 1,250-foot level, Murray vein, Tonopah 

Extens10n mrne. q, Quartz. 
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 104 PLATE X 

A. PHOTOMICROGRAP~ SHOWI G TUFFACEOUS CHARACTER OF FRACTION DACITE BRECCIA. 

Near station 1447 on 300-foot level of West End mine. 

B. FERRUGINOUS CALCITE COATING HIGHLY OXIDIZED ORE JUST BELOW FRACTION DACITE 

BRECCIA. 

From stope 484 not far above 400-foot level, West End vein, West End mine. Two-thirds natural size. 
'· " 

HYPOGENE MINERALIZATION. '25 

panics it in the peripheral replacement of 

galena (see Pl. IX, B) is also hypogene. ~ 

5. Replacement of the type behoved t~ be 

hypogene is as conspicuous in unoxidized ore 

from some of the deepest workings (for example, in ore from the 1250-foot level of the 

Murray vein, Pl. IX, B J. and ·from the . 1200-

foot level of the Belmont vein, figs. 7 and 9) 

.as in ores near the !:lurface. This argument 

is believed to have weight in spite .of the great 

depth to which oxidation locally extends. 

6. The prevalence of the . supposed hypogene replacement minerals does nqt appear to 

be closely dependent upon the degree. of 

fracturing, as it l)resumably . would if ·the 

replacement had been accomplished by supergene solutions. The 1nicroscope shows that 

replacement has .been very extensive in ores 

which· exhibit little fracturing and no. deposition of supergene minerals along the fmv 

fractures that are present. 

SEQUENCE IN DEPOSITION AMONG HYPOGENE 

MINERALS. 

The alpha and beta hypogene n1inerals, 

which, to simplify the· discussion, have been 

separately described, are believed to have been· 

O.Jmm. 

FIGURE 13.-:-Galcna (gal) area in chalcopyrite (chal) partly r!)placcd. 

by an tmdctermined mineral, probably a lead-bearing silver mineral· 

Camera Iucida drawing from polished surface of ore from West End 

vein, between 700 and .800 foot levels of Jiin Butler mine. 

deposited during a single period of nlinei·alization, in the course .of which the com position of 

the n1ineralizing solutions gradually changed. 

In the early stages of the process ore minerals 

were deposited mainly through replacement of 

the host Tock; later~ when less of the host rock' 

rmnained near the vein fractures and when .the 

character of· the n1ineralizing solutions had 

changed, certain of the ore n1inerals, notably 

galep.a, were themselves replaced· by other ore 

minerals. -

·· 'The microscopic relations of the hypogene 

minerals show that in. general quartz and spht).lerite werts deposited. most abundantly early in 

the mineralization; ga1ena, chalco.pyrite;. pyrargyrite, polybasite, argentite, electrun1, and 

carbonates of calcium, magnesium, iron, and 

manganese formed most abundantly a little 

FIGURE 14.-Partial replacement of galena (gal) by an .. unidentified 

mineral, probably a Iead~bearing silver sulphide (x); 'this ii~· tu;.n is 

replaeed by an association of argentite (arg) and chalcopyrite (~hal). 

In the left-hand figure the unidentified miner!J.l forms only a narrow 

band between galena and argentite and is not present between' galena 

and chalcopyrite .. q, Quartz. Camera Iucida dra\\iogsfrompolished 

surface of ore from y,r.est End ve~1, betwee~ 700 ~d 800 f~t level~- of 

Jim Butler mine. 

later in the proce~s. Still later galena. and to 

son1e extent sphalerite, q11:artz, and. polybasite 

became unstable and were replaced by one or 

more of the minerals. argentite,. chalcopyrite, 

carbonates, and electrum, :whose- depo'sition 

appears to have· persisted nearly to the end ·of 

the hypogen~ mineralization. 

Hypogene replacement of the type here described ha~ i1ot beeil widely recognized by students of ore deposits, because methods of microscopic study necessary to their perception have 

been developed only withii1 recent y~ars. The 

studies of Rogers 1 and Ray2 on the ~opper 

ores of Butte, Mont., indicate that hypogene 

replacement has probably been a· widespread 

process in that distr~ct, although the progress 

of the mineralization appears .to have been 

punctuated by periods of fracturing to a greater 

extent than at Tonopah. 

It appears certain that considerable changes 

in physico-chemical equilibriu.rU, due to variations either in. pressure or tern perature or .in 

the com position of the mineralizing solutions, 

have occurred during the formation of nearly 

J Rogers, A. F., Upward secondary sulphide enrichment and chalcocite formation at Butte, Mont.: Econ. Geology, vol. 8, pp. 781-794,-1913 . 

. 2 Ray, J. C., Pamgenesis of tho ore minerals in the Butt,e district, 

Mont.:.Econ. Geology, vol. 9, pp. 463-481,1914. · ·. · 
26 GENESIS OF THE ORES AT TONOPAH, NEV. 

all ore deposits. In ores· that are mainly fissure 

fillings· tliese changes may be recorded by the 

presence of a suite of minerals in vug$ and the 

medial portions of the veins different from those 

next the walls, or by crusti:fication in which the 

laye~ formed last are mineralogically different 

from those formed first. In ores formed 

mainly by replacement such -features as those 

observed at Tonopah may· riot be present if the 

earlier minerals are s.table in the presence of the 

later solutions. The writers are _inclined to 

believe, however, that careful study .of other 

. ores' will show that replaceiru3nt o£ earlier ore 

minerals by later ones during hypogene mineralization is not uncommon ... 

Although silver minerals and possibly gold 

were .deposited in greatest ·abundance in the 

later stages of the hypogene mineralization at 

Tonopah, the writers prefer not to refer to the 

process as ''upward enrichment," reserving that 

· terin for the rare occurrences in whiGh the enriching metals can be shown to have been 

leached from deeper-lYing ore by ascending 

solutioas that were not at the start highly 

metalliferous. The deeper ores of Tonopah 

show no evidences of notable solution of any 

minerals except quartz. In the restricted 

sense indicated the term may find an application in dis.cussions of certain western deposits 

in which ·thermal waters are now ascending 

along veins. The senior writer' has now in. 

hand the study of a nUm.ber of such deposits. 

drill holes and small fractures in the face of a 

crosscut and was depositing a sludgy mass of 

hydrous oxides of iron (ocher-yeliO'\·Y) and oxides of manganese (black). The water as tested 

in the mine was not acid to methyl red solution 

and did not appear to be alkaline to phenolphthalein. Field tests with standard potassium permanganate solution showed that practically all the iron was in the ferrous condition. 

Two gallons of this water was collected and was 

analyzed by Chase Palmer, of the Geological 

Survey, with the .tesults shown on page 29 . 

A sample of water from the Mizpah mine, 

collected by Spurr, was analyzed by R. C. 

Wells, of the Geological Survey, in 1910; -the 

results are also recorded in the table. This 

water flowed from a drill hole which started 

·from the 1,500-foot level of the Mizpah shaft 

and penetrated. 816 feet below that level. Its· 

temperature at the-point of issuance was about 

106° F. 

The analyses are stated ill the table in terms 

of radicles (or the roots of substances), such as 

Na, Ca, 8041 and C08, which experience has 

shown to represent basal units of chemical interchange .. This method of statement rather 

than a statement in terms of oxides is particularly appropriate to water analyses, for it indicates the pomts at which, according to the conceptions of the physical chemist the dissociation 

of the molecules of dissolved substances occurs. 

Most substances in water solution are not completely· dissociated, the degree of dissociation 

:NATURE OF DEEP MINE WATERS. differing for different substances and varying 

Warm waters have been encoutered in a with temperature, ·pre.ssure, the concentration 

number of the deeper mine workings at Tono- of the solution, etc. In general the more dipah, particularly ill the western part of the lute the solution the greater the proportion of 

camp. The questions arise: Are these waters ionization. · 

now: depositing ores~ If not, what.relation, if From the mere statement of the analysis in 

any, do they bear to the solutions that did parts per million of the various radicles it is 

deposit the ores~ impossible to obtaffi: a clear insight into the 

Water from the-Halifax mine, 1,400-footlevel, quality of the water, because each radicle has 

about 380 feet east of the shaft, flo"ring as a a different combining weight. It is convenient, 

·small stream from a fracture in .slightly min- ·therefore, to divide the total weight of each 

eralized Mizpah trachyte, had when collected· a ra~icle present by the combining weight of that 

temperature of 106~ F. (41 ° C.)~ This water radicle, to obtain figures representing the reactw~s not acid·· toward methyl red solution and ing values of the radicles. The values so obwas not alkaline toward phenolphthalein. It tained are given in the columns headed "Rewas colorless, clear, and tasteless. acting value by weight" and may be halanced 

; --·Water from---·-the-·Tonopah Belmont. mine, directly one against another by simple addition 

· 1,500-foot level, about 100feetnorthof the Bel- or subtraction. The 2.205 reacting value of 

niont vein:, 'h~d as· it issued from the rock a tern-. SO, in the Belmont water, for example, may be 

perature of 9'9° F. (37° C.). It flowed from balanced agains_t 3.472 reacting value of Na, 
HYPOGENE MINERALIZATION. 27 

leaving 1.267 (3.4 72 ~ 2.205) reacting value of 

N a to be balanced against other radicles. 

Even this mode of statement is not fully satisfact.ory wh~n it is desired to compare the 

qualities of several waters, for the re_acting values obtained vary with the concentration of the 

solution. If the Belmont w~ter, for example, 

were diluted ·with an equal volume of pure 

water the reacting value of each radicle would 

be halved. It will be readliy understood also 

that where dilute solutions act through considerable periods of time two waters carrying like 

COD$tituents in' like proportions but differing in 

· concentration will in general produce similar 

chemical effects but at different· rates. Although the concentration of the solution must 

therefore be duly considered, it is convenient in 

comparing waters to eliminate this factor.· This 

resll;lt may be accomplished by rating the total 

value of all the radicles as 100 and proportioning the value for each rt;1dicle to this total; this 

~as been done in the columns headed ''React-

~g value by per cent." 

The method of statement and ~nterpretation 

of water analyses here outlined is essentially 

that developed by Herman Stabler ·

1 and Chase 

Palmer,2 of the United States Geological. 

Survey. 

The factors.which in general exert the greatest· influence on the potency of natural waters 

as geologic agents are the hydr·ogen ion and the 

hydroxyl ion. Hydrogen ions give acidity and 

hydroxyl tons alkalinity (or basicity); to the 

physical chemist, indeed, (' hydrion" is the true 

acid and "hydroxion" the true base. Acid and 

alkaline waters are, at least so far as ore d~pbsition is concerned, the niost potent of natural 

solutions. Hydrogen ions may result from the 

ionization of free acid present in the water, as 

they possibly have in the acid water from the 

West End mine, Tonopah, describ.ed on page 43. 

. (See analysis, p. 29.) Hydroxyl ions may .re-

_sult from the ion1zation of hydroxides present 

in the water,. as in a deep water from the Comstock lode recently analyzed for the senior author by Mr. Palmer. Hydrogen ions may also 

be liberated less directly by the hydrolysis of. 

various salts and the ~onization of the resulting 

1 Stabler, Herman, The mineral analysis of water for industrial pur-

·poses and its interpretation by the engineer: Eng. News, vol. 60, p. 356, 

1908; The industrial application of water analyses: U.S. Geol. Survey 

Water-Supply Paper 274, pp. 1Q5-181, ~911. 

ll Palmer, Chase, The geochemical interpretation of water analyses: 

U.S. ~eol. Survey Bull. 479, 1911 .. 

acids; the acidity of copper sulphate m aq"Q.eous 

solution is attributable to· this action. Simi~ 

larly, hydroxyl· ions may be liberated by the 

hydrolysis of various salts and the ionization of 

the resulting hydroxides; to this action is at-

'trioutable the alkalinity of a solution of sodium 

carbonate. 

The geologic importance ·of · the presence of 

so-called free acid or free hydroxides in natural 

·waters is self-evident. The ge.ologic importance of the formation of hydrogen or hydroxyl 

by hydrolysis and ionization of salts might on 

first thought be questioned, for the proportion 

of a salt dissociated at one time is in most cases 

very small. As soon, however, as the small 

amounts of hydrogen or hydroxyl formed are 

neutralized, other hydrogen or hydroxyl ions 

are at once liberated, and by such progressive 

action a large part of a salt present in solution 

may eventually be involved in a reaction. A 

solution of copper sulphate carrying at any one 

time only a small proportion of hydrogen ions 

may, for example, react with calcium carbo-· 

nate until a large part 'of the copper. is converted into copper. carbonate. 

The amount of so-called free. acid or free 

alkali present can be computed from the water 

analysis. At the present stage in the study of 

water analyses the extent to which hydrogen 

or hydroxyl ions :will be formed through hydrolysis and ionization of salts must be inferred 

from a consideration of the relative. strength of 

the acids and bases that compose the salts, on 

the principle that salts of strong acids and 

weak bases yi~ld an excess· of hydrogen ions 

giving acidity, salts of strong bases and weak 

acids yield. an excess of hydroxyl ions giving 

alkalinity, an4 salts of strong bases and strong 

acids do not hydrolyze perceptibly, and give 

merely neutrality or salinity in the restricted 

sense of the term. . 

The considerations outlined above and the 

need of redu.cing so far as practicable the multiplicity of terms in ~ost water analyses make 

it desirable to gro:up the basic radicles in the 

general order of the relative strength of their 

hydroxides and the acid radicles in the general 

order of the relative strength of their acids or 

combinations with hydrogen. In the analyses 

in the accompanying. table (p. 29) they are 

grouped as (1) strong base or alkali radicles~ 

(2) weaker base or alkali-earth radicles; (3) 

· w~akest base or metal radicles, (4). strong ·acid 

. -
,. 

28 GENESIS OF THE ORES AT TONOPAH, _NEV. 

radicles, and (5) weak acid radicles. As the 

strength of an· acid or base is, according·to the 

ionic conception, a direct measure of the degree 

of ionization 1 such a grouping is a logical preliminary in any attempt to estimate the prob-_ 

able ionization in the solution. By balancing 

group totals of basic radicles against group 

totals of acid radicles in accordance with th.e 

. well-established chemical principle of satisfying the strong. acids and bases before the weak, 

an insight may be obtained into the quality of 

the water: In some waters individuals within 

the groups must also be considered. By apply-

.ing this method of study it is generally possible 

to determine from·the analysis with a fair degree of probability not only whether the water 

is acid,_ alkaline, or neutral, but also what constituents have conveyed these qualities to the 

water. Such computations should be supplemented in the field and. in the laboratory by 

testing the water with indicators. In the present studies methyl- red, methyl orange, and 

phenolphthalein were used in the field. 

·The details of the method of balancing the 

radicles are set forth below: · 

A. Balancing of strong acids. 

1. Strong acid radicles should be balanced first against 

~trong base or alkali radicles. Salts derived from strong 

acids and strong bases do not hydrolyze appreciably in 

water solution and so impart neither alkalinity nor acidity· 

but merely Salinity to the solutio·n. · 

2. Remaining strong acid radicles should be balanced 

against alkali-earth radicles. Most salts of the aikali 

earths and strong acids do not ·hydrolyze appreciably in 

water solutions and so impart only salinity to the solution. 

3. Remaining strong acid radicles should be balanced 

against the metallic radicles, the term metallic being here 

used in the restricted sense, exclusive of the alkali metals 

and metallic earths. Most of the salts of the metallic 

elements and strong acids hydrolyze to a considerable 

degree in water solution. The resulting strong acids 

ionize to a much greater extentthan the weak hydroxides 

that .are also formed, giving an excess of hydrogen ions 

over hydroxyl ions and rendering the solution acid. Ferric and copper sulphates in water solutions furnish excellent examples of acidity produced in this way: Waters 

rich in ferric sulphate will vigorously attack iron pipes in 

mines, even though sufficient iron is already present in 

solution to balance all the sulphate :radicles. 2 The degree 

1 Walker, James, IntroductiOn to physical chemistry, p. 313, 1913 . 

. 2 Jones, L. J. '\V., Ferric sulphate' in mine waters, and its action on 

metals: Colorad:> Sci. Soc. Proc.; vol. 6, pp. 46-55, 1897. · 

of acidity imparted by such salts varies greatly, according 

to the relative strengths of the acids and bases concerned, 

so that each association must be individually considered. 

4. Remaining strong acid radicles should be considered 

as in balance with hydrogen radicles-that is, as free 

strong acid. · 

B. Ba.lancing of weak acids. 

5. Weak acid radicles should be balanced first against 

alkali radicles if any remain after satisfying the strong 

acids.. Most salts of the alkalies and weak acids hydro-

. lyze to a notable degree in water solution. The resulting 

alkaJ.i.ne hydroxides ionize to a much greater degree than 

the weak acids also formed, giving ari ~xcess of hydroxyl 

·over hydrogen ions and imparting alkalinity to the solution. · 

· 6. Remaining weak acid radicles should be balanced 

against remaining alkaline-earth radicles. Salts of the 

alkaline earths and weak acids hydrolyze to some extent 

in water solutions, yielding hydroxyl ions in excess of 

hydrogen ions and imparting alkalinity to the water.· 

7 ~ Remaining weak acid radicles should be balanced 

against remaining metallic radicles (exclusive of the alkali 

or alkali-earth metals). The acids and hydroxides resulting from the hydrolysis of these salts are both weak; 

their ionization being slight, its· effect is not likely to be 

pronounced in the direction of either acidity or· alkalinity. . 

· 8. Remaining weak acid radicles should be considered 

as in balance with hydrogen radicles-that is, as free weak 

acid. · · 

In practice there are always analytical. 

errors that require adjustment in calculations 

of this sort. If the basic radicles are in excess the reacting values of all of them may be reduced proportionately until their total exactly 

equals that of the reacting values of the acid 

radicles. If the acid radicles are in excess arid 

the water is· not acid to indicators 'there has 

probab1y been an error in their determination, 

arid. the reacting values of all .of them may be 

reduced proportionately until their total exactly equals that of the reacting values of the 

basic radicles. If the water is acid to indicators, a notable exces·s of acid over basic radicles is usually interpreted as indicating .the 

presence of free acid; a slight excess is not 

significant, as the observed acidity may be· 

due to hydrolysis and ionization of salts of' 

strong ·acids and weak bases. If it is known 

that the analytical error ·probably lies in the. 

determination· of certain radicles it may be 

desirable to apply the correction to those radi--

cles only .. 
HYPOGENE MINERALIZATION. 29 

Analyses ofrMne waters from Tonopah, Nev. 

Radicles. 

Na ....................... 

K ......................... 

Total alkali radicles. 

Ca ........................ 

Mg ........................ 

Total alkali earth 

Belmont, 1.500-foot level; · tem- perature, 99° F.; Chase Palmer, 

analyst. 

Parts 

m88~n. 

80 

5 

········ 

20 

4.4 

Reacting 

value by weight. 

3.472 

.128 

............ 

1. 000 

. 362 

Reacting 

value hy 

per cent.a 

31.4 

1.2 

32.6 

9. 1 

3.3 

radicles ....................•........ 12.4 

Mizpah, 2,31frfoot dril! hole; 'temperature, near 106° F.; R. C. 

Wells, analyst. 

. Parts 

m&~~n. 

148. 8 

3.4 

.......... 

68.8 

6.3 

Reacting 

value hy weight. 

6.'473 

. 087 

........... 

3. 433. 

. 518 

Reacting 

value by percent.b 

30. 2 

.4 

30. 6 

16.0 

2.4 

18.6 

West End, 5~foot level; acid; 

Chase Palmer, analyst. 

Parts 

mEu~n. 

135 

12 

··'······· 

249 

10 

Reacting 

value hy ~vcight. 

5.859 

. 307 

. ........... 

12.450 

. 822 

Reacting 

value by pe'rcent.c 

12. 7 

. 7 

13.4 

27. 1 

1.8 

28.9 

Fe (ferrous)............... 3 . 107 L 0 . 7 . 025 . 1 7 . 252 . 5 

Al........... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 . 077 . 4 · 3 . 332 . 7 

Mn (bivalvent)......... .... ~ 12 . 436 4. 0 ....................... -·.. 75 2. 720 5. 9 

Zn........................ . . . . . . . .. . . . . . . . . . . . . . . . . . . . Trace ............................................. . (TI:) ......................................•.... · ..................... -.- .......... -........ . • • • • . • • . • (.6) 

Total metal radicles. . . . . . . . . . . . . . . . . . . 5. 0 ............ -.-.... . . 5 . . . . . . ... . . . . . . . . . . . 7. 1 

(Deficitofbasicradicles).. ........ .......... ......... ......... .......... (.3) .......................... . I=== I 

so, ...................... 106 2.205 20.2 

CL ........... _............ 35 . 987 9. 0 

327.2 6.806 31. 7 1,019 21.195 46.0 

35. 6 1. 004 4. 7 65 1. 833 4.0 

Br a'nd I ................................ -.... --. -... -- None. ----·-···· ............... (e) ........... ·····-·· N03 ••••••••••••••••••••••••••••••••••••••••••••••••• Trace. ................. .. .............. None. ·········· ........ 

Total strong acid 

radicles ............................ . 29. 2 ............. -... ~. 36. 4 ... : .. -. . -.. - - - -... 50.0 

I==;:= I 

C03 • • • • • • • • • • • • • • • • • • • • • 36 1. 199 10. 9 10. 6 . 353 1. 6 . 

Aso .... _ .......................... ~ ........ " ..... -.--.- .. -.--.- · ·. ------ ·- · · · ·- ·- · · · 

None. 

Trace. 

HC0 None. 3 ••••••••••••••••••••• '51 .836 7.6 157.2 2.578 12.0. 

Total weak acid 

radicles .....................•.•..... 18.5 13. 6 

SiO? . _..... . . . . . . . . . . . . . . . 15 .. ·. . . . . . . . . . . . . . • . . 64. 8 . . . . . . . . . . . . . . . . . . 15 ................. . (Deficit of acid radicles)... . . . . . . . . . . . . . . . . . . -(2. 3) .......... · ................... ~ ........................ . 

Total solids......... 367. 4 . . . . . . . . . . . . . . . . . . . 824. 1 ............... ·... 1, 590 ................. . 

. . . . . . - . . 10. 732 ' 97. 71. . . . . . . . . 21. 3541· 99. 7 . . . . . . . . . 45. 770 99. 4 ........ (f 11. 010) (100. ~) .. -.- .. :. (g 21. 482) (100. 0) .... -.... '(g 46. 056) (100. 0) 

' . a Tho reacting values of the basic radicles in th.is analysis exceed those of the acid radicles but the discrepancy is within the permissible limit or experimental error. · · b In this analysis the reacting values of the acid radicles exceed those of the basic radicles by a very slight margin, well within the permissible limits of experimental error. . ' . c This water was fotmd by testing in the field to be notably acid toward methyl red. The slight excess of acid radicles in the analysis is within 

the permissible limits of experimental error and is not therefore a certain indication of the presence of free acid. It is uncertain whether the ucidi ty toward methyl red is due to free acid or to the hydrolysis and ionization of the small amounts of iron and aluminum salts· present (ferrous and 

aluminum sulphates in aqueous solutions are both acid to methyl orange). . d At tho time ofanalysis.this water had deposited no-sediment but on subsequent exposure to the air for several weeks all ofthe manganese deposited. e Bromine and iodine i r present are in minimal amounts. ·· f '.rwico tho total reacting value of basic radicles. g Twice the total reacting values of acid radicles. 

I:r;:tStead of distributing the error among all 

the acid or basic· radicles it is in most analyses 

only necessary to distribute it ·among the 

group totals, as has been done for the .first two · 

analyses in the table. The results of the 

application of these methods to the two deep 

mine waters shown in the table are given 

in the following paragraphs: · 

Thermal water from Belmont mine, 1,500-foot level: 

Alkali radicles balanced by strong acid radicles 58. 4 

Alkali ra9-icles balanced by weak acid radicles. . 6. 8 

Alkali-earth radicles balanced by weak acid 

radicles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24. 8 

Metal radicles balanced by weak acid.radicles. . . 10. 0 

10().0 

The above statement shows . that this water 

should be alkaline because of the presence of 
GENESIS OF· THE ORES AT TONOPAH, NEV • 

alkali and alkali-earth carbonates which by 

hydrolysis and ionization give an excess of 

hydroxyl . over . hydrogen ions. Tests with 

phenolphthalein .at. the time of analysis gave 

an. alkaline reaction. As noted on page 26, 

th~ water at the time of ~ollecting did not 

appear to be alkaline toward phenolphthalein, 

but the test was made underground, and a 

faint pink coloration may have escaped detection. It is hardly probable that there was any 

appreciable absorption of alkali from the glass 

of the bottle in which the sample was shipped. 

The water may be described as essentially 

a sodium and calcium sulphate and carbonate 

water which is somewhat alkaline arid carries 

considerable manganese. In view of the absence of manganese in the Mizpah water it is 

not improbable that the Belmont water acquired 

its manganese content from manganiferous ores 

with which· it came into contact. 

Thermal water from Mizpah mine: · . 

Alkali radicles balanced by strong acid radicies 61. 2 

Alkali earth radicles balanced by strong acid 

radicles ................ , .. :. . . . . . . . . . . . . . 11. 6 

Alkali earth radicl~s balanced by weak acid 

radicles .. ~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25. 6 

Metal radicles balanced by weak acid radicles.. 1. 6 

100.0 

This is also essentially a sodium and calcium . sulphate and carbonate water but has 

more than twice the concentration of the 

Belmont water and carries .·proportionately 

much· more silica. No field tests with indicators are recorded by Spurr, but from the 

analysis this :water would appear to possess 

only the very faint ·alkalinity attributable to 

al~ali-earth bicarbonates. Unlik~ the Belmont 

water it carries no manganese. The presence 

of traces of nitrate in the Mizpah water is 

of interest in view of the known accumulation of nitrogen gas in the tops of certain 

stopes and raises at Tonopah. 

Although both these waters are hot and the 

Mizpah water is 'clearly ascending from a 

· considerable . depth, there is not~ing in their 

composition to indicate whether . they' come 

from an igneous ·source, or are surfa~e waters 

that descended, became heated in some man-

. ner, and ro13e again toward the surface, or 

represent mixtures of waters from several 

sources. 

No indications of the deposition of sulphides 

from these waters' were found in the mines. As, 

. according to the analyses, the waters contain no 

sulphur beyond that present in the sulphate 

radicle, there was probably no deposition of 

sulphides from them merely through a decrease 

in their pressure and temperature during their 

ascent. The deposition of sulphides and of certain native metal~ from sulphate solutions of 

this general character through reaction with 

earlier sulphides appears, however, to be possible. Su~h reactions may be metathetical, or 

they may involve reduction by the sulphides of 

certain metallic salts in the water. Iron and 

'manganese, the only metallic components· except aluminum sufficiently abundant to be determined iri- the water analyses would probably. 

not be susceptible of such precipitation. The 

iron and manganese in these waterS as they 

issued -from the rock were already in a reduced 

condition incompatible with furtlier reduction. 

As these metals stand at the end of the Schuermann series, 1 they are not likely to displace 

metathetically other metals from· their combinations with sulphur.- Certain other metals, 

however, notably silver, might if present ~e 

precipitated. . . 

It may ·be concluded that these waters, if 

forming ore at all, are depositing sulphides or 

nativ·e metals only in ·small amounts by interaction with earlier sulphides. 

It appears idle to spe<mlate upon the possible 

relationship between these wa,ters and the solu~ 

tions that deposited the hypogene ores, either as 

regards origin or composition. They differ 

from those solutions at least in the absence of 

sulphides,. for as the rocks that were replaced 

by the hypogene ores contained no minerals 

capabie of reducing sulphates to sulphides, it is 

necessary to assume the presence of sulphides 

in 'the ore-depositing solutions. 

SUPERGENE MINERALfZATION. 

GENERAL CHARACTER. 

Many of the hypogene ores have been extensively modified through the action of .the air. and 

of waters o~ surface origin descending through 

the lodes. The extent and degree of such 

action· are dependent on the. readiness with 

which the agents of alteration can gain access 

to the primary ores and are therefore intimately related to the nature an'd degree of frac1 Schuermann, Ernst, Ueber die Verwandtschaft der Schwermetalle 

zum Schwefel: Liebig's Annalen, vol. 249, p. 326, 1888. 
SUPERGENE :MINERALIZATION •.. 31 

.. turing of the ores and wall.rocks and the nature We$t of the fault plane proper the ore is much 

of the ground-water circulation. The complex shattered and is considerably more -oxidized 

history of the superficial alterations at Tono- than the less.shattered ore farther west. Slight 

pah, involving two or more periods of oxidation oxidation near fractures was noted in ore of the 

subsequent to the primary mineralization, Belmont vein on the 1,500-foot level of the 

makes it unusually difficult to classify the alter- Tonopah Belmont mine. In the workings on 

ation products in close accordance With the the Murray vein slight oxidation was noted on 

physioal and che1nical conditions under which the 1,170-foot level but not on the. 1,260-foot · 

· they were fonned. In· the descriptions that or deepest level. 

s. 

LEGEND 

1!%~&!1 Frac;tion dacite brecc1a 

.. Midway andesite 

~ M izpa ~ trachyte 

__ Leanore 

~Ore 

0 50 100 200 FEET 

~--~--~--------~ 

FIGURE 15.-Section.through portion of West End mine showing structural relations of the Fraction dacite breccia to the West End vP-in and 

. to the Mizpah trachyte. · 

follow they have been grouped according to 

their mode of occurrence as (1) residual products of oxidation and deposits in open spaces 

and (2) supergene replacement deposits. 

PEPTH OF OXIDATION. 

General oxidation is characteristic only of the 

upper portions of the few veins that crop out. 

In the upper portions of the veins that do not 

crop out and in the deeper portions of the outcropping ·veins· oxidation is local only. Such 

local oxidation was noted in some of the deep~ 

est workings near cross fractures that intersect 

the veins. It is well shown, for example, on the 

770-foot level of the Tonopah Extension 1i1ine, 

the deepest level reached by the workings connected with the main shaft, where fractured ore 

and wall rock just above the Rainbow fault 

are much more oxidized than those at a distance fron1 the fault. On the 600-foot level of 

tllis mine the Extension north vein is cut· and 

offset by the Rainbow fault; for over 100 feet 

OXIDATION AT SEVERAL PERIODS. 

At a· number of loc.alities in Tonopah there 

is evidence of oxidation ·connected no~ with 

the present surface but with ancient land 

surfaces now deeply buried. The most striking evidence of this sort ~s found at several 

points near the 300 and 400 foot levels of the 

West End mine, where the ore of the West 

End vein is capped for short spaces by the 

Fraction dacite breccia. In the vicinity of 

the West End mine· the Fraction dacite 

breccia is the surface rock; its base appears 

to have a general southwesterly dip of about 

30° and truncates the ~1idway andesite, the 

Mizpah trachyte·, · and in a few places the· 

West End vein. · The general structural relations are shown in figure 15. 

The dacite breccia is, at least in large part, 

a volcanic tuff, which, like the other volcanic 

rocka of the region, is believed by Spurr to ·be 

of Tertiary age. Its tuffaceous ·nature is 

'suggested by its appearance to the unaided 
32 GENESIS OF THE ORES .AT TON<?~AH, NEV. 

eye but is especially evident under the m,icroscope, as shown in Plate X, A (p.· 25). The 

specimen studied microscopically. and figured 

in· this illustration .was obtained near station 

1447 on the 300-foot level of the West End 

mine. It contains .rock fragments irregularly 

angular in form and of various sizes and 

kinds; most of ·them are so much altered that 

their original character can not be determined; some show plagioclase phenocrysts in a 

:finely granular ground mass. In addition, 

there are numerous 'fragments of quartz and 

feldspar ph~nocrysts,. as· shown in the illustration. rhe feldspar crystals are mostly andesine. A few of the feldspar. crystals are perfect, but most of them are mere fragments, and 

many are very angular and irregular in form. 

Son1e are much fractured, not along cleavage 

IS inches 

FIGURE 16.-Sketch of a portion of the contact between the Fraction 

-dacite breccia and the West End vein in stope 309, West End mine. 

a, Unoxid.ized bre9cia; b, breccia oxidized near fracture; c, highly 

oxidized ore. 

planes but very irregularly; the fractures do nut 

extend into the inclosing matrix. One feldspar 

crystal may be much fractured and another 

very close to i.t may be. unfractured, indicating 

that the fracturing:took place before the crys-

·tals became embedded in their present matrix. 

Under high magnification (240 ·diameters) the 

matrix still appears fragmental and the frag-_ 

ments show diversity·of size and shape. The 

smallest fragments are isotropic mid are possibly volcanic glass. The alterations include 

partial calcitization of the plagioclase, some 

secondary enlargement of quartz fragments; 

· and the .develop~ent of chlorite in certain 

rock fragments. 

That the breccia is younger than the ore 

of the West End vein is·shown by the presence 

of .a, number of fragments o{ ore and pyritized 

wall rock in the breccia.riear its contacts with 

the vern. 

Where the relations are not complicated by 

faulting .the. breccia appears to have been deposited directly upon the ore; in places it 

shows an obscure stratification parallel to the 

contact. Oxidation of the breccia near its 

contact with the vein '{s not general, but is 

usually confined to the vicinity of fractures, as 

shqwn in. figure 16. Breccia in immediate 

contact with the vein may be wholly free from 

·oxides of iron. The ore underlying the breccia, 

on the other hand, is as highly oxidized as 

. much of the ore found at -the present surface 

and ca.rries iron oxides in mammillary and 

botryoidal forms.. Some · of the quartzose 

. ore next to the con tact is porou~ from partial 

·solution of its constituents·. 

The high degree of oxidation in the ore, the 

unoxidized condition of much· of the breccia in 

contact with the ore, and the local inclusion of 

oxidized fragments of ore· in unoxidized breccia indicate that much of the oxidation of this 

ore took place before the deposition of the 

breccia. 

Other· evidence leading to the same conclusion consists in the· presence of coatings of 

calcite, barite,· crystalline ·quartz, and, rarely, 

pyrite on .the hydrous iron. oxides of the ore 

just below the breccia cmitact. -(See Pl. X,. B.). 

In ore .fron1 stope 484, not far above the 4:00-

foot level of the West End mine, a coating of 

crystals. of a carbonate of iron and calciun1 is 

deposited <;>n hydrous iron oxides. Some barite 

. is intergrown with t?e carbonate. bn top of 

the carbonate occur well-formed crystals of 

clear quartz. Locally, quartz has replaced 

the exterior of scalenohedral crystals of calci~e 

which Fest on iron oxide. Ore fron1 stope 400A 

shows thin coatii1gs · of pyrite oi1 hydrous 

oxides of .iron. These· associatio-ns, except 

that of quartz, constitute mineral Inisalliances, for' the minerals of the coatings are 

not normally formed during the oxidation of 

a sulphide ore. Their prese~lCe is, therefore,· 

indicative of a change. in the physical and 

chemical co·:p.ditions surrounding. this ore. 

The structural relations described on page 31 

indicate that this change was brought about 

by the burial of an ancient, probably Tertiary 

gossan under a great thickness of volCanic 
SUPERGENE MINERALIZATION. 33 

tuffs, inducing a return from· surficial . to 

deeper-sea ted conditions. 

Spurr 1 calls attention to the probability of 

a still earlier period of denudation· and oxidation between the deposition of the Mizpah 

trachyte and that of the Midway andesite. 

l-Ie says: "Most likely the earlier andesite 

[Mizpah. trachyte] was deeply eroded and the 

veins were exposed befqre the later andesite 

[Midway andesite] was poured out." The 

contact between these two formations is in 

most exposures a fault contact, SO· that conclusive evidence of oxidation . during this 

period could not be obtained. 

Fron1 the evi.dence above set forth it may be 

concluded that although a part of the oxidation, even in those veins which do not crop· 

out, is certainly recent, some is to be correlated with ancient, probably Tertiary land 

surfaces. As downward enrichment has- been 

an acconlpaniment of the recent o~idation, it 

is logical to suppose that it was also an accompaniment of the ancient oxidation, and 

that there have, therefore, been several periods 

of downward enrichment. 

GRO:UND WATER. 

The common text-book diagram in which the 

water table is shown as a; subdued counterpart 

. of the land surface is. applicable in a general 

way to regions, such as the Mississippi Valley, 

characterized _by moderate humidity and fiatlying strata through which lateral circuJat~on of 

ground water is easy, but it does not at all express the relations at Tonopah. In the Tono- · 

pah mines the active ground-water circulation 

is practically confined to. zones of fracturirig; 

copious flows are limited to a few such zones and 

usually to their more open parts. Other fract:ures have, for considerable periods at least, and 

to great depths, been sufficie~tly: free fron1 

water to permit extensive oxidation through 

the ~gency of the atmosphere. These relations· 

were emphasized by Spurr, 2 who says: 

No general body of ground water has been encountered, 

although the rocks are extremely fractured; yet along certain steeply inclined fract.t~re zones wat'er is found sometimes quite near the surface and occasionally in considerable quantity. This water is cool, is sufficiently nonmineral to be fair drinking water, and is undoubtedly the 

storage of precipitation. 

1 Spurr, J. E.,_ Geology of the Tonopah mining district, Nov.: U. S. 

Geol. Survey Prof. Paper 42, p. 35, 1905. 

• Idem, p. 107. 

2601°-18-3 

Spurr cites much eviden<?e found in the 

sinking of shafts and driving of drifts illustratmg the ·localization of the ground water in 

fractures·. Observations from later mining experience, reported to the writers are wholly 

similar in their import and need not be enumerated here. 

RESIDUAL PRODUCTS OF OXIDATION AND ·DE-· 

POSITS IN OPEN SPACES BY SUPERGENE 

SOLUTIONS. 

MINERALS NOTED. 

The minerals listed below were noted either 

as residual untransported products of oxidation 

or as deposits in open spaces at·. a very late 

stage in the mineralization. As. pointed out on 

page 42, certain· of them, notably ·the sulphides~ were formed as a rule at greater depths 

than others, but the fact that there have been 

several. periods of oxidation n1akes it impracticable to define closely the cbndit!orrs of formation of each mineral. 

Native .elements: 

Gold. 

Silver. 

Sulphides: 

Pyrite. 

Chalcopyl-ite. 

Argentite. 

. Sulpho-salts: 

Polybasite. " 

Pyrargyrite. 

Haloids: 

Cerargyrite. 

Embolite. 

Iodobromite(?). 

Iodyrite. 

Oxides: 

Quartz. 

Hyaline silica. 

Oxides-Continu·ed. 

Hydrous oxides of !ron. 

Oxides of manganese. · 

Carbonates: 

Calcite. 

Mixed carbonates. 

Malachite. 

Silicates: 

Calamine. 

Kaolin'.' 

Phosphate: 

Dahllite. 

Sulphates: 

· Barite. . 

Gypsum. 

GOLD. 

Grains of bright-yellow gold large enough to 

he seen with the unaided eye are commonly 

confined to. the much oxidized ores of the few 

veins that crop out. Such gold was abundant 

~t a depth of about 100 feet in the Valley View 

v·ein, above and below a fault that displaces the 

vein. In specimens examined by the writers 

from the 500-foot level on this vein it forms 

minute flakes on oxidized surfaces, on which 

iodyrite and ·iodobromite were also deposited: 

. Gold in association with iodobromite was also. 

:_noted in abundance as golden-yellow grains 

: q.1 to 0.2 millimeter in diameter in the pan-

/' 
34 GENESIS OF THE ORES AT .TONOPAH, NEV •. 

nings from soft oxidized ore from the Sou_th vein 

of the Desert Queen mine. about 112 feet above 

the 600-foot level. . Fractures in this ore are 

. heavily coated with oxides of manganese. 

The gold of the. oxidized ores is commonly i~ 

larger gr~tins than the hypogene electrum and, 

to judge from its yellow color, is of much greater 

purity. It is probably of supergene origin. 

SILVER. 

Silver occurs here and there in certain highly 

or moderately oxidized ores and in a. very few 

places is fairly abundMlt. Argentite is in 

many places closely associated with it. 

teristic copper-blue to the solution.· .. Acidification with :Q.ydrochloric. acid. yields ~o precipita-te, showing that, contrary to the prevailing 

opinion among the miners, the blue material 

does not contain silver haloids. In this nlaterial are embedded flakes- of silver and some 

grains of argentite, but crushing and panning 

may be necessary before they become visible_. 

, Local shearing since J;he. silver \vas deposited 

has compacted. the blue-green kaolin-like nlaterial into a talclike nHtss and :drawn out the 

silyer flakes into a very thin natural foil. Sue~ 

shearing must be very recent. 

Tapering, fanglike forms of silver were noted 

in ores fr01n the Beln1ont, Shaft, and West End 

veins and c01nmonly. rise abruptly fron1 a base 

of argentite or 1110re rarely of polybasit~; ·in 

some ores n1inu,te 1nasses of argentite are attached to their sides . or tips· .. Rarely· the 

"teeth'' are attached to a base of quartz or of 

barite. It is believed that the silver ".teeth" 

In the Tonopah Belmont mine native silver 

is present locally in the Belmont and Shaft 

v:e1ns. In the Belmont it was found from the 

900-foot level, shortly below the "cap rock," 

down to thel,400-foot level, though n1ost a bundan t in the riches~ parts of the. vein near the 

1.,100 and ·1,166 foot levels; in the Shaft vein . have resulted fron1.the reduction of silver cOin- it was noted in ore from depths as far down as 

the L400-foot level. Silver was observed by pounds in place. 

·the writers 41 ores fron1 the MacDonald vein on 

PYRITE. 

the 330-foot level of the North Star mine and Deposits of pyrite were noted in a few places 

from vertical dept,hs of 500 to 600 feet in the coating fractures in hypogel}e ores to depths of 

West End vein. · about 600 feet. At several localities it is interThe silver may occur in wires, flakes, or taper- ·groWn. wi_th barite, clear .crystals of which in 

ing, fanglike forms comn1only curling-at the tip. places con1pletely inclose small pyrite pyritoheThe silver wires are .found as a rule· in ri1att€d drons. Pyrite closely . associated with barite 

aggregates in small vugs or . open fractures, was noted in fracture.s in the MeN mnara vein. 

w:P.ere they may be attached to quartz or.barite not far above the 300-foot level '(344 raise) of 

crystals or to argentite. Ragged incrustations the. TQnopah Extension mine·; in the Murray. 

of silver on fractures and in small solution cavi-. ·vein on the 600-foot level (end of 603 north 

ties we·re noted in ore from the 1 ,400-footi level ·crosscut) of the same mine; and in the West 

on the' 'Belmont. vein, where they coat quartz . End vein on the SOO-foot level (502 drift) of the 

or hydrous oxides of iron. ·· West End mine. On the pyrite and barite loSmall, bright flakes of silver of irregular out- cally · ferruginous and manganiferou~. calcite, 

line on fractures in hypogene ore obtained ·be- ~rgentite, or- b_oth, have been deposited. In· 

.tween the 1,300 nnd 1,400 foot levels of the o'p.e. place intergrown pyrite and quartz are. 

Belmont :vein were not evenly dis~ributed over d'eposited on earlier, more coa~ely crystallized. 

t~e walls of the fractur.es but ·w~te d~posited quartz coating a fracture in hypogene ore. 

only where hypogene sulpJ:lides were abundant, In all the late pyrite deposited in fractures in. 

suggesting that. t_he sulph~des exerted an influ- the Tonopah ores . the predoiiunant crystal 

. ence in th~ silver precipitation. In some faces are· those of the pyritb4~s]ro;, whereas in 

~lightly oxidized ores of the Belmont vein the the pyrite of the u.p.doubt_e,~. hypogene ores and 

~ilver flakes t:tre associated with. a. soft claylike . in the pyrite developed hydrothermally in the 

material of 'blue-green color .. Close st1.1dy of wall rocks cube faces predominate. That this 

this n1aterial shows that it -is· probably kaplin :contrast in crystal ,form signifies different con-

_Qolored 'by an adsorb~d ~oluble _salt of copper. ditions Qf deposition can hardly be·questioned, 

When pulverized and t.l,'e~~e_<;l with cold ~qua. but sufficient data are ·not at hand to -warrant 

ammonia the .b~ue mate:ri~l impart~ the charac- conclusions as to its precis·e significanc~. 
U .. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 104 PLATE XI 

A. BRANCHING DEPOSIT OF ARGENTITE, PROBABLY SUPERGENE, ON WALL OF FRACTURE 

IN QUARTZOSE HYPOGENE ORE. 

Small amounts of finely crystalline chalcopyrite are associated with the argentite. Specimen from 1,130-foot level, 

Macdonald vein, North Star mine, in collection of A. E. Lowe, Tonopah. Natuml size. 

B . LICHEN-SHAPED DEPOSITS OF ARGENTITE, PROBABLY SUPERGENE, WITH A LITTLE POLYBASITE, 0 WALL OF FRACTURE IN HYPOGENE RHODOCHROSITE-RICH ORE. 

Not far below 950-foot level, Mun-ay vein, Tonopah Extension mine. Natural size. 
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 104 PLATE XII 

A. POLYBASITE, PROBABLY SUPERGENE, PARTLY FILLING FRACTURES IN WHITE, OPAQUE 

QUARTZ. 

In a few places finely crystalline chalcopyrite and in one place a little native silver are deposited on the polybasite. Macdonald vein, Montana-Tonopah mine. 

B. BRANCHING DEPOSITS OF PYRARGYRITE AND POLYBASITE, PROBABLY SUPERGENE, ON 

WALLS OF FRACTURE IN WHITE QUARTZ. 

Montana-Tonopah mine, exact location uncertain. About natural size. 
SUPERGENE l\HNERALIZATION. 35 

. . CHALCOPYRITE .. 

·Small amounts of very finely crystalline_Qhal..:. 

copyrite occur as late deposits alqng fractures 

in hypogene ore. In the Murray v-ein not far 

below the ·1,000-foot level (~03 $tope) of the 

Tonopah Extension n1ine, chalcoprri te, polybasite, b.arite, and argentite have been deposited 

on crystalline quartz that coats fractures in 

hY])Ogene ore. Th~ sulphides are locally on or 

in the barite; elsewhere barite crystals lie on the 

sulphides. A pai't .of the argentite in these 

fra,ctures is an alteration fron1 polybasite, for the 

exterior portions of flat hexagonal ·crystals of 

the typical polybasite for1n are no--\v sectile 

argentite. . · 

In the spechnen from the MacDoll,ald vein 

illustrated in Plate XII, A, finely crystalline 

chalcopyrite locally coats the polybasite · in 

· fractures only partly filled· by polybasite. In 

the Fraction Yein between the 600 and 700 foot 

levels of the Jin1 Butler 1nine argentite, locally. 

intergrovrn \\rith barite, coats fractures in hypo-

. gene ore; and on the argentite or intercrystallized with it are small- crystals of chalcopyrite. 

Ore frmn the West End vein between the 700 

and 800 foot levels shows intin1ate 1ni..xtures of 

argentite and chalcopyrite coating fractures in 

hypogene ore, also chalcopyrite, polybasite, and 

pyrargyrite in quartz-lined Vtigs. 

ARGENTiTE. 

dollar. In other1 ph~&~s argentite and carbonate are. intercryst·allized in a fashion suggesting 

contemporaneity .. In fracture~ in the West 

End vein-for example,. in. a specimen taken 

between· the 400 !tnd ~00 foot levels.of the West 

End mirie-~rgentite lias been deposited ·over 

SOp:le Cry,st~J~. qf __ f~r!uginous calcite; elsewhere 

on the' same :speci_in~n:•_the calcite coats the argentite, or the t\V.Q. arer:irregularly..intercrystallize.d. I.n. the Vraction vein between the 600 

and 700 foot levels· of the .Jim Butler mine the 

the wall of a small fracture· cuttii1g hypogene 

ore is coated with slightly ferruginous calcite; 

over this .in 'places. is- an· intimate mixture of 

calcite, argentite, and some barite, the argentite in part inclo~ed by the cal9ite or barite; and 

on this mix:ture pure argentite is locally deposited. In the West End vein, between the 

400 and 500 foot levels of the West End :r;nine; 

the Fraction vein, not far above the 700-foot 

level of. the Jim Butler mine; and the Murray 

vein in the 1 ,000:-fQQt level of the Tonopah Extension m.ine argentite was noted entirely inclosed by cl~ar barite. cryst~ls. · 

POLYBASITE. 

. Polybasite is common as a late deposit in 

fractures tra;versing hypogene ores;· in some 

places it is in~imately intergrown with pyrargyi:ite,- 3:nd in many others· it is closely associated with argentite. The first coati!lg on such 

Argentite is partic-qlarly comn10n as a late fractures is colDlil.only brystallin.e quartz, the 

deposit on the ·,valls of fractures cutting the polybasite being deposited on this qu·artz. 

hypogene ores. In one specimen frmn .the Jinl. In the Belmont vein on the 1,000-foot level 

Butler 1nine it ·partly fills fractures in clean of the Tonopah Belmorit mine, near so11th crosswhite quartz' in 1nuch the fashion that polyba- cut 1044, fractures cutting hypogene ore are 

site does in thespeciinenshowninPlateXII,A. lined with finely crystalline quartz, on which 

A bt·anching deposit of argentite on a fracture thin patches of polybasite and argentite are 

in quartzose ore of the MacDonald vein is shown deposited. . ·A particularly fine specimen s4ow-

. in Plate·:x;I,. A, and lichen-like deposits frow. the ii1g .· polybasite- deposited along "fractures in 

.Murray vein are shown i1i Plate XI, B. Tl;wse white quattz from the MacDonald vein is shown 

deposits lie directly on the hypogene ore; in in Plate XIl, ·A .. · In·on:e part of this specimen 

. other places a thin layer of crystalline quartz . a little native silver and in another part finely 

intervenes. . · · crystalline chalcopyrite were' deposited on the 

In many fractures ru:gentite is accompanied polybasite. 

by light-colored carbonates. : In. some places Polybasite in fractures· is locally associated 

the argQntite coats the carbonate, as in the with light-colored carb.o!}ates. In the Murray 

Fraction vein between the 600 and 700 foot vein not far above the' 1,100-foot level polyba-. 

levels of the Jim Butler mine (stope 4), where site in some places lies on calcite and. iii others is 

siderite on a fracture is coated with a thin de- . coated-·by calci.te, the ~wo minerals being essenposit of argentite _a~out the area. of a silver . tially contemporaneous. · · ~ 
36' GENESIS OF THE ORES AT TONOPAH, NEV. 

PYRARGYRITE. 

Late pyrargyrite that can be cleanly strippe~ 

from fractures· and vugs in hypogene ores was 

noted in several plac~s· ·but was much less abundant than the pyrargyrite described on pages 

14-15, which is believed to be hypogene. Such 

late pyrargyrite·is also less abundant in general 

than. late argentite and polybasite. . . 

Pyrargyrite with intergrown polybasite and 

chalcopyrite was noted coating quartz cr;y-stals 

lining vugs in. the West End vein between .the 

700 and 800 foot levels of .the Jim Butler mine. 

The sulphides c?uld be _clea-nly .. stripped from 

the·quar~z and were plainly de.po~ited at a la~er 

· period.· Branching forms of. late PJ!a;rgynte 

i_ntergr.own with some p.olybasite on the wall of· 

a fracture in white quartz in the Montana 

Tonopah mine are shown' in Plate XII, B. 

In .ore rich in rhodochrosite· fron: the West 

End vein between the 400 and 500 foot levels 

of the West End mine pyrargyrite and'polybasite form thin coatings on the walls of fractures, 

from which· they· ·can be. cleanly· stripped. 

Specimens showing identi~al relations were obtained from the Tonopah Extension office, but 

their ·origi~al location in the Extension wo~kings ·is unknown. 

SILV~R HALOIDS. 

but :nearly pure iodyrite is locnlly · abundant .. 

The colors of the silver haloids are in places 

deceptive, for much ~ranslucent pale-gray 

haloid appears to carry as much bromine as 

chlorine, and some pale-gray iod}rrite was 

noted. . . 

The mode of occurrence of these minerals 

presents a number of inte.rest~ng features. In 

orie specimen from the Tonopah Mining Co.'s 

upper workings (exact Jocality unknown) fractures in sulphide ore were coated with hydrous 

oxides of iron; on these was deposited a thin 

coating .. of malachite, which, in turn, was 

coated with calcite. Cerargyrite of dirtygray col~r, c'arrying son1e bromine, is locally 

intercrystallized 'Yith the malachite and. calcite. ln one place the cerargyrite is wholly 

inclosed in calcite, but a short dist~ce away it 

lies on unetched crystal faces of ·calCite. 

· ·A "sand" from porous oxidized ore fr_om the 

Mizpah ve:n between the 400 and 500 foot 

-levels carries yellowish iodyri te and a yellowishgreen haloid _without· cleavage, that appears,-

upon testing/ to contain much bromine and· 

less iodine and chlorine. The associated iodyrite is pale yellow, reacts .only for iodine, and 

shows the hexagonal form and basal cleavage 

characteristic of that mineral.· 

In othe;r specimens from the Tonopah Mining Co.'s upper workings (e~act locality lmSilver haloids were ·~oted only in the. v;eins known) iodyrite that was deposited on the surthat cro.p out. They we~e· rep6rted from ~ev- ·face of iron oxide coating quartz is in part pale 

eral part:; of the · Tonopa.h Belmont mine. yellow and in part ·dirty gray in color. Both 

Specim~ns said to co~tain them were found to varieties are hexagonal, have perfect basal 

.carry native. silver · and a ·_soft bl_ue-green cleavage and yellow streak, and react only for 

material,. probably kaolin, with adsorbed sol- iodine when tested in the closed tube. Some 

uble copper salts, but no silver haloids were crystals are gray iodyrite at the base and yellow 

found. According to Burgess, 1 who had un- above. In parts ·of one specimen a :first generausual opportunities for studying the occur- · tion of iodyrite crystals has been coated with 

renee of the silver haloids at Tonopah, the transparent colorless hyaliiie. silica, and on top 

most abundant of them is cerargyrite, al- of this a later generation of smaller iodyrite 

though . most of the samples teste~. by hi~ crystals has been deposited. A centimeter or 

showed traces oJ bromine. All the gray silver so away on the same surface, where hyaline 

haloids tested by the 'writers contained con- ·silica Is -not present, there is only one· set of 

sid~rable bromine, .but comparatively few iodyrite crystals, the later iodyrite ap~aring 

. specimens were available.. The_r~ ~re_ evi- to have enlarged the earlier crystals without 

dently aU gradations ~rom cerargyr1te 1~to the formmg new ones. Locally iodyrite crystals 

chlorob.romide emholite. Silver h~oids, carry;.. ~re entirely inclosed by the hyaline sili_ca, showing chlorine, bro~ine, . and iodi.ne and others 

earrying brom,ine and iodine, were also· noted. 

_The. pure bromide, bromyrite, ·was ~ot noted, 

1 Burgess, J. A:, The halogen salts of silver and associated minerals at 

Tono~, Nev.: Econ. Geology, vol. 6, p.l7, 1911. 

2 The silver haloids were mixed with a little pulverized galena and 

heated before the blowpipe in the closed tube in accordance with the 

method recommended by Brush and Penfield (Manual of determinat_ive 

mineralogy, p. 68, 1911). The lead chloride, bromide, a~d io.di~e fo~med 

are deposited at different heights in the tube and are easily dist~ngUJshed 

from ont' another. Their relative amounts can be roughly estimated. 
... 

SUPERGENE .MINE~a.pZAT~QN. 

at on~, place.· The n1aterial~·is ,dark dull gr1:1,y 

a;ild . fuiely cryst~lline, g~ves ~.a .. dark-brown 

streak,·.and is ·p·rob~bly ma~ganite. . . · 

'CALCITE; 

ing that the two minerals forineci contemporaneously. Another specimen from the same 

mine shows hyaline .silica deposited .on iodyrite and iodobromite deposited on top of .the 

silica; still ·anoth~r shows .both iodyrite and 

io9-obromite on silica that coats earlier .iody- Q~lcium c~rbonate ne·arly free from iron, 

-rite. The largest crystals of iodyrite seen were manganese, and magnesium is much less comin a Vug in oxidized ore, in a specimen from the mon than the mixed carbonates described 

Tonopah Milling Co.'s property, in the collec~ . belo.w and was noted in only a few places. 

tion of J. A. Uhland. They measured three-· Colorless calcite carrying a trace of manganese 

sixteenths of an inch across the hexagon. was noted in the Belmont vein on the 800-foot 

The relation of the silver haloids to the pho~·- level of the Tonopah Belmont mine as a crysphate dahllite is considered on page 38. talline ·coating on fractures traversing coarse 

QUAl'tTZ. hypogeil~ sulphide ore. In places this calcite 

is intergrown with crystals ·of polybasite, the 

Quartz is abundant as a coating on the wallS- two bemg apparently' contemporaneous .. Calof fractures· traversing hypogene .ores; It cite was also- noted coating malachite in ore 

commonly forms· continuous ·coatings from 1 fr~m the Ton~pah Mining Co.'s property. 

to 3 1nillimeters thick composed of minute col-:. · . 

orless, transparent hexagonal crystals. It is. · MIXED ·cARBONATES. · 

usually the frrst·coating on such fractures, and Qualitative tests on many qf the c~rbonate 

on it barite, carbonates, kaolin, polybasite,_ coatings on .fractures· in hypogene ore show 

· ar~entite,_pyrite, chalc~p~ite, and a few other . the pre~.:ience of two or m9re of the elem~nts 

mn1~rals are loca~y ?epos1ted. These quartz. iron, _manga1;1ese, calcium, and magnesium. 

· coatings are poss1bly late hypogene, as noted Many carbonates that are pure white in col<?r. 

on page 18. ·,_are notably ferruginous and turn brown on 

HYALINE SILICA. :·:heating. Manganese ill: ~any places ~ccomA number -of characteristic occurrences of. panies the iron, but its proportion appears less 

hyalllle .silica are· described in the sections on than in mos_t of the hypogene carbonates, for a 

silver haloids and dahllite. The mineral was ·pink color was nowhere noted. 

also no.ted. coating .psilomelane ~ the· Valley MALACHITE. 

Yiew vein on the 400-foot level. It is not confined to the veins but occurs abundantly at the 

"surface as thin coatings along jqints m the 

Midway andesite. 

OXIDES 01<' ll'tON AND MANGANESE .. 

The presence of rhodochrosite in the hypo:.. 

gfme ores has led to an abundance of hydrous 

oxides· of n1anganese in the produc.ts of their · 

oxidation. These are rarely pure, being mixed 

usually with hydrous oxides of iron. :·In the 

Behnont vein between the 1,300 and 1,400 foot 

levels there are masse's a foot or so across composed ahuost wholly of these oxides. Thin 

exterior, coatings of dark :reddish-brown pu1-

verulent oxides coat a porous framework of 

hnrd ~·ay metallic oxides that give an ocheryellow streak. On the 1,300-foot level on, the 

same vein a lens. of pulverulent. m_anganese 

oxide 10 inqhes wide and 2 feet long was noted 

Carbonates of copper are not at all common 

in t.he ores now visible at Tonopah. In a · 

specimen from the property of the Tonopah 

Mining Co. (exact location unknown) a fracture in the hypogene ore is coated with hydrous 

iron· oxides; ·on these locally malachite and 

gray cerargyrite· carrying some bromine have 

been deposited. Both these minerals are ·in 

places coated with transparent· colorless cal-

·cite. 

CALAMINE. 

Characteristic "sheafs" of the hydrous zinc 

silicate calamirie were noted ·in the West End 

vein between the 500 and 600 foot lev-els 

(stope 600 C) of the West End mine.· A fracture·in the sulphide ore was first coated wi.th a 

. thin layer of crystalline quartz; on this argentite and siderite were- deposited; oxidation . 

followed, converting part of the siderite to 

.• 
38 GENESIS OF THE ORES AT TO~?,fA;H;, .NEV~ 

hydrous i.r~Il: Qxjdes ·and rendering the argentite dull and .locally pulverulent; ap.d finally 

calamin~· was deposited qn the iron oxide. 

KAOLINITE. 

DAHLLITE. 

The; presence· of dahllite, the· ·calcium carbono-phosphate· (3 Ca3 (P0.) 2.Ca003 ), at To~o- · 

pah was fi:rSt recognized by Roger~ 2 in ore 

from the Mizpah mine. This ore also contained 

A white pulverulent infusible ~aterial that iodyrite, hyaline silica, quartz, and manganese 

reacts strongly for alumina but not for potas- dioxide. The dahllite formed small white tabusium 1 1s common in the vugs and· pores of lar crystals of hexagonal outline resembling 

many of the ores. Microscopic examinatioD: apatite in form but· effervescing· with warm 

shows that this material is an aggregate of nitric acid. · 

· minute, roughly spindle-shaped crystals . of The same mineral was observed by the 

quartz and anotl}.er mine_r_al':df :r;te~rly the same ~ite:rS in ore from the Valley View vein just 

index of refraction but- of very low double below the 400-foot level. It forms short 

refraction ... This second. mi_neral, ':Vhi?h . i~ hexagonal prisms 0.5 millimeter or less in 

probably kaolinite, is in to9 minute ?rains_ . diameter that effervesce slightly with cold 

permit the determinatioD; of its optical con- . nitric acid and react for phosphorus with ainstants. · monium molybdate. The dahllite ·crystals lie 

Kaolinite has been one of the latest minerals . upon·quartz crystals lining vi.tgs and also upon 

to form i~ the Tonopah ores. Locally it hydrous oxides of iron, and on the dahllite in 

occupies spaces formed by the solution of· turn silver haloids are deposited. All these 

hypogene quartz or carbon~tes; elsewhere it minerals are covered locally by clear, .colorless 

has been deposited on argentite, polybasite, · hyaline silica.. Of the silver haloids olive-green 

and .carbonates that .appear to be of. supergens iodobromite was first deposited,· and on this 

origin. In a specimen from a vertical dep~h of . and also on the ·dahllite is iodyrite. 

1,395 feet on. the Shaft vein (east_ stope 3) in In- another ore specimen from the Tonopah 

the Tonopah Belmont mine kaolinite has been Mining Co.'s workings (exact locality unknown) 

deposited subsequent to the formation of 'Y'ires dahllite· occurs both in and on hyali:ne silica 

of native .silver, which it locally coats. Its coating oxidized surfaces. 

presence was noted ·-in·· ores. fr01n. the. deepest It is apparent that the dahllite was deposited 

workings; it is cm;nmon in\il-lnoxidized ores; ·under the sanie conditionsas the silver haloids 

and where it occurs in oxidize'd·-ores.its develop- and hyaline silica. 

ment has preceded oxidation axcept where,· as 

shown by other evidences, there ha,s been a 

return fron1 oxidizing to deeper-seated· conditions. . 

Kaolinite is not confined to the ores but is 

common in the neighboring wall rocks. In 

the north crosscut on the 850-foot level of· the 

North Star mine, for example, it forms the 

matrix of ~ock fragments in a brecciated zone 

in the Mizpah.trachyte. 

Much of the ~aolinite occurring in the ores 

is not a purely residual product but is either a 

' precipitate from solution or has been intro-

. duced in suspension. This is. shown by its 

mode of occurrence in certain quartz-lined 

vugs, wh~re it'is heaped up lik~. sn~w on a fence 

top on the upper sides of _.the _quartz .crystals 

and is relatively scarce on .their. under sides. 

i Tho materi~l was tested for alum.na by moistening with cobalt 

. nitrate and-heating before blowpipe; for ~otassium by the flame coloration test. 

BARITE. 

. 'Q 

Barium sulphate is fairly abundant in wellformed crystals on fractures ~raversing hypogene ore; commonly the first coating is qu&rtz 

and the barite crystals lie on that. In many 

plac-es the barite was clearly deposited contemporaneously with one or more of· the minerals pyrite, argentite, and polybasite, ·grains 

of ·these sulphides being whclly inclosed by the 

barite. · I~ other places barite is the only coating on the fractures or bn the quartz lining the 

fractures." 

GYPSUM. 

Selenite crystals· are not uncommon in the 

oxidized ores, especially ip.· the veins that crop 

o:ut. Abundant selenite was observed in the 

2 Rogers, A. F., Dahllite (podolite) from Tonopah, Nev.: Am. Jour . 

Sci., 4th ser .• vQl. 33, pp. 475-482, 1912. 
. SUP~RGENE MINERALIZATION. . 39 

South vein of the Desert Queen mine on the 

700-foot level, where it occupies fractures .in 

oxidized ore. Pyrolusite is the most abundant 

oxidation· product there, and the selenite lies 

on the. pyrolusite, being clearly of later forma-· 

tion .. EPSOMITE. 

Crystals of hydrous magnesium sulphate 

were noted in the West ·End mine on the 

400-foot level (near raise 415 B), where ·they 

had be<3n deposited recently near cracks on 

the walls of the drift by the ·evaporation o{ 

water used in wetting down the stopes. The 

epsomite may have been an original constituent in the water supply or may have been acquired by the water through reaction with the 

waste in the stopes. 

SUPERGENE REPLACEMENT DEPOSITS. 

REPLACEMENT OF CHALCOPYRITE .·BY BORN-· 

ITE ( ~), COVELLITE, AND ARGE:RTITE. 

·The supposed bornite rims around ·chalcopyrite showed the 'purplish color usual in freshly 

polished ·bornite. ·The quantities being micro~ 

scopic, it was impossibJe to isolate any of. the 

minerals for B:nalysis. It is known that chalcopfrite immersed iri silver sulphate solution 

SOQn becomes coated with a tarnish resembling. 

·bornite, probably a sulphide of silver ·an'd iron, 

as Palmer 1 has shown. This mineral is of course 

0.1 mm. 

~II\_URE 18.-Peripheral replacement of chalcopyrite (chal) by probable 

bornite (b) which is in tum partly replaced by a fine intergrowth of 

aigep.tite and covellite (a-<'). q, Quartz; sph, sphalerite. Camera 

Iucida drawing from polished surface of ore from Shaft vein, 1,000-foot 

level of Tonopah Belmont mine. 

In the processes of mineralization thus far 

described chalcopyrite has replaced other minerals but has not itself been replaced. In other 

words, chalcopyrite has behaved as a stable· 

mineral under the conditions of supposed hy- · 

pogene mineralization. 

In an ore specimen from the Shaft ·vein on stable in contact with silver sulphate solution. 

·To determine whether the bornite-like· rims the 1,000-foot level of the Tonopah BQlmont. 

FIGURE 17.-Replaccment rim of probable bornite (b) bordering chalcopyrite (chal). q, Quartz; sph, sphalerite. Camera lucida drawing 

from polished surface of ore from Shaft vein; 1,000-foot level of Tonopah 

Belmont mine. 

mine, .examined under the microscope, chalcopyrite has been replaced by what is probably 

bornite and this in turn by eovellite, argeiltite, 

or an intergrowth of these two. minerals, as 

shown in figure.s 17 and 18. · 

were this mineral, they were treated with silver . 

sulphate solution. They tarnished in the same 

manner as known bornite from Virgilina, V a., 

and are believed to be boffii.te. · . The covellite 

shows the characteristic blue color .. There are 

gradations from· apparently ·pure covellite 

through fine intergrowths of covellite and 

supposed argentite in~o areas that are unquestionably pure sectile argentite. When the fine 

intergrowths were treated with silver nitrate 

solution the covellite ·became gray and indistinguishable in tint from th~ supposed argentite with which it was intergrown. As it is 

well kn<?wn that ·covellite changes to !1rgentite .. 

on treatment with silver nitrate, . the identification of both minerals appears reasonably 

certain.-

The close association of covellite- and .argentite is of interest in view of the known capacity 

of · c~vellite to form silver sulphide (Ag2S) 

when treated with silver n.itrate or silver sui-

. 1 Palmer, Chase, Bornite as silver precipitant: Washington Acad. Sci. 

Jour., vol. 5, pp. 351-354, 1915. · 

. I 
40 GENESIS OF THE ·oRES AT TONOPAH, NEV. 

phate solution.1 In 'this speCiine:ri the arg.en-' 

tite appears not to· be a replacement of the 

covellit.e but to be .contemporaneous with it.' 

Covellit.e alone peripherally replacing ·chalcopyrite was noted 'hi ore from the West End 

vein: a short distance above the 600-foot level 

(stope 6_00 C). Areas· of pyrite adjacent, to 

the.· chalcopyrite ha;ve not been replaced by 

covellite. · 

REPLACEMENT OF SPHALERIT-E AND GALENA 

BY COVELLITE 0~ ·ARGENTITE OR A MIXTURE 

OF THESE MINE~ALS. 

In other _parts o_f the specimen from the 

Shaft vein mentionedin the preceding section, 

covellite and mixtures of covellite and argentite 

were noted as formed by 'the replacement, 

mainly peripheral; of galena and 'sphalerite. 

0.1-mm. 

FIGURE 19.-Replacement of galena (gal) and sphalerite (sph) by covel-

. lite (c). q, Q.uartz. Camera Iucida drawirig of polished surface of ore 

from Shaf~ vein, 1,000-foot level of Tonopah Belmont mine. 

These replacen;wnt. deposits .are shown in figures 19 and 20. In the supposed hypogene 

replacement deposits lescribed on pages 19-25 

sphalerite was rarely attacked, being ~n general stable under _'hypogene conditions. 

In the specimen shown in figure 20 the width 

<;>f the replacement rim does not chang~ in pass-

. ing from parts that are wholly argentite to parts 

that are wholly covellite. This feature was 

also noted in replacement borders of argentite 

and electrum developed around galena, as ' 

shown in Plate IX, B. · In other parts of the 

same specimen galena _is replaced by argentite, but there is a transition band --of the unidentified galena-like mineral between the argentite and the galena. 

1 Anthon, E·. F.; Ueber die Anwendung der auf lla.ssem Wege darge-

. ste!!ten Schwefelmetalle bei'der chemischen Analyse: Jour. prakt. Chemic, · 

vol. 10, p. 3.53, 183i. Posnjak, Eugene, Determination of cupric and· 

cuprous sulphides in ini:~tures of one another: Am. Chern. Soc. Jour., 

vol. 3fi, pp. 24i5-24i9, 1914. 

NATivE SILVER. 

In the . sp~cimen from the Shaft vein in 

which. the replacement deposits described 

above· were noted small areas of native s]ver 

1 -. 

0.1 mm. 

.., .., , .. , : ~ 

. \., .. / 

,_ - "' -.... • J 

FIGURE 20.-Peripheral replacement of sphalerite (sph) by ail associati_on of covellite (c) and argentite (arg). q, Quartz. Camera Iucida 

drawing of polished surface of ore from Shaft vein, 1,000-foot level of 

Tonopah Belmont mine. 

are abundant. The silver-bearing parts of 

the specimen are commonly more or less porous 

and are apparently the most -altered parts of 

the ore. The silver is usually associated with 

argenite and may, at ·least in part, replace it-, 

as suggested by the relations shoWn. in Plate 

XIII, .A. In other parts of the same specimen; as shown in figure 21,. silver and argentite 

- -, ' I - ~· 1 '-

( r '- ? 

.... q \.J ("' 

< \ ./ _, 

I . .,_ \ I .._ S '- ' - I ~. 

0.2 mm. 

FIGURE 21.-Association of argentite (arg) and native silver (sil). Both 

minerals are probably a replaceDJ.ent of some hypogene sulphide. q, 

Quartz.. Camera Iucida drawing of polished surface of ore from Shaft 

vein, 1,000-foo~ level of Tonopah Belmont mine. 

are so irregularly intergrown as to suggest 

contemporaneity. 

As electrum is so common in the ores as a 

hypogene mineral, !t would appear theoreti-

-cally possible that native silver should occur 
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 104 PLATE XIII 

A. ASSOCIATION OF SILVER (sil) AND ARGENTITE (arg) SUGGESTING REPLACEMENT OF THE 

SULPHIDE BY THE NATIVE METAL. 

Photomicrograph of polished surfaee of ore from 1,000-foot level, Shaft vein, Tonopah-Belmont mine. The argentite 

boundaries have been outlined to render them more distinct. The knob of polished silver and argentite is 

surrounded by soft porous material which shows black in the photograph. 

B. OXIDATION BANDING IN MIZPAH TRACHYTE. 

From walls of Valley View vein. Natural size. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PA'PER 104 PLATE XIV 

A. OXIDATION BAND! GIN MIZPAH TRACHYTE ADJACENT TO VALLEY VIEW VEIN. 

About two-thirds natural size. Small crystals of pyrite are abundant in the unoxidized portion (A) but are absent 

from the banded portion of the vein. 

Near North Star shaft. Natural size. 
SUPERGENE MI:NERALIZATieN. 41 

also as a hypogene ore mineral. Close study 

of the ores, however, has failed t'o discover 

native silver in ·any situation where a supergene origin is not more probable than a hypogene origin. Furtherm~_re,. as gold was fairly 

abundant in the hypogene solutions, electrum 

would seem to be the more likely mineral to 

form. 

'RELATION BETWEEN SUPERGENE ENRICHMENT 

AND FRACTURING. 

Deposition in open spaces and metasomatic 

:re{flacement have both taken part in the super-

,gene mineralization, but the former method of 

.deposition has greatly predominated. Char~ 

·rite, argentite, etc. The value of the ore qecreased fron1 the fault eastward and ill the 100 

feet west_ of ·winze 1,050 fell to $3 or $4 a t.on. 

Low assays continued up to a northerly fault 

dipping 65° E. Just east of or above this fault 

high-grade ore averaging 0.3 ounce of gold and 

-30 ounces of silver to the ton was found for 

about 30 feet.· ·Examination of this ore showed 

argentite along fractures in thin layers that 

could be readily stripped off and that are prob~ 

· ably of supergene origin~ There is half an inch 

or so of gouge along this fault, but the vein 

is not greatly displaceci by it. 

In the Extension No. 1 workings <;>re tenor 

in the Extension North yein appears to have 

High-grade silver ore with 

· - Hif1,h-11,rade ore· lew;grade ore,ave~- &23to1124 perton'. age value 't3to'iJ4 · Argent.it.e on per ton fractures 

........ , 

';;i' '\ 

~~r:-:te) ~ 65° _,, :J ,_ ... -----

~ Vein broken up. 

Low-grsde ore,hi8h- est value 1!>7 per ton 

. pyrergyrita, argentite, etc., 

along fractures. Averageval- u e about $28 per ton · 

Not workable 

N 

o...__ __ 4,_o __ __.eo reet.. 1 . - . fiGURE 22.-Plan ofa portion of tho North Star ~ine workings, showing the relations betwe~n supergene enrichment and fault fractures. . . 

:acteristic deposits of argentite, pyrargyrite, 

polybasite, chalcopyr~te, pyrite, native silver, 

barite, and carbonates on fractures cutting 

the hypogene ores are described above. The 

-effect of such deposits on the average tenor of 

the ore in certain parts of a vein is in many 

places masked by the somewhat spor~dic distribution of the ·hypogene replacement. depos-. 

:~ts; nevertheless a distinct relationship between late fracturing and _ore tenor is recog:.. 

.nizable in a number of places. 

On the 1,050-foot level of the North Star 

:mine (see fig. 22) the MacDoliald vein west of 

the point where it was cut by the eastward-

-dipping North Star fault was not of exceptionul grade; just east of or above this fault 

occurred the richest silver o're the n1ine ha~ 

. produced,_ carrying an abundance of pyrargy~ 

been influ~nced by th~ degree of fracturing 

near the Rainbow fault,· which trends northnortheast· and is not itself- mineralized. The 

zone of n1a,ximun1 n1ovement along this_.fault is 

marked by 2 'feet of gouge dipping 50°-60° E. 

The North vein west of this gouge was little 

shattered, and its ore was not notably rich, 

but .for 120 feet east of the gouge the vein 

was intensely shattered without serious _.dis.., 

placement, was_ much oxidized, and was of high. 

grade. · . 

According .to Mr. J. H. Dynant, of the Tonopah Extension Co., the ore of the MeN mnara 

vein on the 400-foot le;vel wa$ notably richer 

close to the Rainbow fault than away from it 

.on either side. The fractured zone here is 

at least . 20 feet wide, and_ the ore is highly 

brecciated and oxidize~. 
42 GEN_ESIS OF THE ORES AT TONOPAH, NEV. 

In the Tonopah Extension and West· End, ment of the MacDonald vein above certain 

mines the inost per-Sistent and conspicuous inclined faults (see p. 41) by deposits of pyrar..; 

fractures traversing the veins strike N, l0°- gyrite and argentit~ on fractures is -concrete 

30° E. and are nearly vertical. Along most evidence that suchdeposition has taken place. 

of these fractures the displacement has been The thin coatings of crystalline quartz comslight, but some of. the larger .faults of similar monon fractures may be of diverse origin and 

trend and considerable displacement, such as age. Though clearly formed after the main 

the Rainbow fault, may. belong to this series. hypogene mineralizatio.n and after the ores 

Late deposits of argentite, polybasite, ·and had been fractured, some of this quartz was 

carbonates are common along these fractures,. probably deposited by ascending solutions, as· 

which appear to have been influential in guid- is shown by the presence of wolframite, an uning the enriching solutions. doubted. hypogene mineral, intergrown with 

Just above the 500-foot level of the West such quartz in parts of the Belmont vein. 

End n1ine in stope 505 the West End vein, Othe~ quartz co~tings are probably supergene, 

which strikes N. 80° W. and dips 35° N., is as for example those on oxidized ore below. the 

cut by a vertical fault striking N. 10° W. Fraction dacite ·breccia. Not all the late fracFor ·50 feet from the main fault the ore is tures 'are coated with quartz, but where q~artz 

traversed by a number of- parallel subsidiary is present it usually forms the first coating and 

fractures.- The ore of this 50~foot interval is the late silver minerals lie on the quartz, not 

said by Mr. J. W. Chandler. to have been intercrystallized with it. · 

notably richer than that on either side. Ex- Structural evidence of the supergene origin 

amination showed that. it carried argentite, of some of the argentite, polybasite, and pyrarchalcopyrite, barite, and· ferruginous calcite gyrite in the ores has been presented, but the 

on fractures. " supergene origin of all occurrences of these 

In the Tonopah Belmont mine no such regu- minerals in late fractures and of the pyrite, 

lar and extensive system of fractm:es travers- chalcopyrite, barite, and carbonates in places 

ing the ore was noted as in the western part of associated with them can not be said to have 

the camp, and it was reported that the few been proved. Some. of them may have been 

well-defined fractures that occur appear not to deposited by ascending solutions ·at a period 

have influence<il.greatly the tenor of the ore. distinctly later than the main hypogene minA probable exception to this statement is the 

Belmont fault, for some of the richest ore of the eralization, or by interaction between ascendmine has been found in the Beln;wnt vein for so·. ing and descending solutions. If 'they are hypfeet east of (above) this fault on the 1,100 and ogene they are probably later than the period 

1,166 foot levels, where the ore was much frac- of oxidation which preceded the deposition of. 

tured and oxidized. Irregular minor fractures the Fraction dacite breccia, for barite, calcite, 

are numerous in the. ores of this mine, anq it is and rarely pyrite ~oat highly oxidized ore just 

probable tha.t most of the ore was fairly per- below this breccia. (See p: 32.) The writers· 

meable to descending solutions. believe that the probabilities favor the sup~r:-

gene origin of all the minerals except wolframite 

SUMMARY OF EVIDENCE OF SUPERGENE ORIGIN and a part of the quartz, whichcoat·sharp-walled 

OF CERTAIN ORE MINERALS. fractures cutting t~e typical hypogen~ ores. · 

The supergene origin of the deep-yellow gold, 

silver haloids, hyaline silica, hydrous oxides of 

iron, oxides of manganese, malachite, calamine, 

dahll~te, gypsum, and epsomite in the Tonopah 

ores is not·. open to queston. 

The silver haloids are evidence of solution 

and redeposition of silver in· the oxidized zone, 

and it is certainly to be expected that some of 

the silver taken into solution would be redeposited at greater depths as the sulphide 

or sUlphosalts of silver~ The notable enrichNative silver appears to be absent from the 

deeper ores at Tonopah, even from those that 

carry argentite and sulphosalts· of silver in 

abundance. It was noted only in ores that 

were. somewhat. oxidized, were more or less 

porous through solution of certain constituents, 

or showed other evidences of alteration, such 

as the presence of kaolin ·cont'ainin.g adsorbed 

soluble salts of copper. In places, its relations 

suggest that it has been formed by the' alteration of argentite or polybasite. All the native 
SUPE:RGENE MINERALIZATION. 43 

silver at Tonopah is, therefore, believed to be 

supergene. 

The replacement of chalcopyrite by bornite, 

of bornite by covellite t.tnd argentite,_ of sphalerite by. coveilite and. argentite·, and. possibl;y 

of argentite by native silver, shown by a specimen from the Shaft vein, contrasts strongly with 

the r~placement characteristic of most of the 

Tonopah ores. Under the conditions of ~he 

more usual and supposedly hypogene replacement chalcopyrite is-stable (being itself a replacing mineral), arg¢ntite is never ~ccomp·anied by 

native silver bu.t · on the contrary is in places 

accompanied by. electrum, · and sphalerite is 

o~1ly rarely replaQed a:nd then not by co.vellite 

and argentite but by chalcopyrite. and polybasite. Obviously, these types of replacement 

occurred under physical and chemical conditions 

quite .different fron1 those under which n1ost of 

the ores were forn1ed. The loss of iron and the 

substi-tution of silver for copper involved in 

the replacen1ent of chalcopyrite by bornite and 

of bornite. by argentite,. as well as .the formation of native silver, are changes- in harmony 

with well-known chemical tendencies in supergene enrichment, and to this process the 

writers attribute ~hem. 

NATURE OF SOLUTIONS PRODUCING .SUPERGENE MINERALIZATIO~. 

Where. active oxidation of pyrite and chalcopyrite was in progrQss, acidity 1nust, at least 

locally and transiently, have been Imparted. to 

the waters l.n: contact w~ith the ore .. The abun~ 

dance of prin1ary C!1rbonates (of one or nwre 

of the. elen1ents calciu1n, n1agnesiu1n; iron, and 

n1anganese) in n1ost of the Tonopah ores, however, favors the neutralization of acidity early 

in tp.e descent ofthe solution. This·inferential 

conclusion appears to tally with th~ observeq 

facts, for, as shown in the d.etailed descriptions 

that precede, the argentite and polybasite in 

late fractures are in n1any places intergroWJi 

with or ev~n wholly inclosed in calcite or related. 

carbonates. Such n1ineral associations were 

evidently deposited by neutral or possibly alkaline and not by acid solutions .. If such deposits 

in fractures ~ave b3en correctly interpreted as 

supergene, it follows that the supergene solutions w.ere not acid at the places at which these 

1ninerals were deposited, whatever n1ay have 

been thejr .reaction earlier in their descent. 

Even the silver haloids were, locally at least, 

deposited by neutral solutions, as shown by 

their intercrystallizat.ion with malachite and 

calcite. _Barite is associated with supposedly 

S':!pergene argentite and polybasite in much the 

same manner as the carbonates. The nlineralogic evidence indicates therefore (l) . that the 

solutions .which produced supergene enrichment becan1e neutral early .in their do'\\TJ.1Ward 

journey; (2) that they carried carbonates and 

sulp~ates in abundance, with lesser an1ounts of 

halogens and phosphates; and (3) that they 

transported . silver, copper, iron, n1anganese; 

arsenic, antin1ony, and possibly other 1netals. 

In the hope of obtaining further evidence concerning the character of the solutions that produced the supergene ·~nrichment, a. sample of 

descending ·mine water was collected in the ~ 

West End mine and was anaJyzed . by Chase 

. Palmer. (See table ·on p. 29). This water 

flowed down thio·ugh the broken ore and waste 

filling of a large ·caved stope· bet,veen the 400 

.and 500 foot levels and issued in a s1nall stream 

at raise 524 on the 500-foot level. In the stope 

it is in contact with ore and with the air, and the 

conditions simulate those originally existing a 

short distance below the natural outcrop of the 

veins. The water as tested in. the 1nine was decidedly adid to. Inethyl Orange and had eaten 

holes where it dripped on corrugated iron at 

the foot of raise 524. 

The analysis shows .that this is essentially a 

sodium and· calcium sulphate water, carrying 

also manganese and chlorine radich~s in abund~ 

ance. Its concentration is nearly twice that 

of the Mizpah deep water and nearly five times 

that of the Belmont deep water. The general 

relations between its con1ponents, computed in 

accordance with the Palnier method, are as 

follows:. 

Alkali radicles balanc.ed by strong acid radicles. 0 0 0 26. 8 

Alkali earth radicles balanced by strong acid radicleso: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 57. 8 

Metallic radicles balanced· by strong acid radicleso 0 14. 2 

Fre~ s~rong acid (?)o .... 0: ..... 0 o ..... : .. ~.... ..... 1. 2 

100.0 

. The sligllt excess of strong acid radicles. in 

the analysis is within the permissible limits of 

experimental error, ·and it is therefore uncertain whether the qbserved acidity of the water 

toward ·methyl orange is due to the presence 

of free ·acid (S04 in balance with H) or to the 

hydrolysis and ionization of the small amounts 

. of salts of strong acids and weak bases present. 
A4 GENESIS··OF. THE ORES AT TONOPAH, NEV. 

fe~rous··and ~uminous .sulphate in iuiueous so- between. A sample··of this ~re assayed by the 

lution both giving acid reactions. The eptire Bureau of Mines showed 0.08 ·olince of gold 

.. ·absence of carbonate and bicarbo~ate radicles, and.3.90 ounces of silver to the ton. The hand 

in spite of the -fact that the .water has perco- specimen _shows very sli'ght. oxidation .. along· 

lated through carbonate-bearing ore, :ls ~ nat- fractures, and kaolin occurs as a late deposit 

ural· co'nsequence of the acidity of the wat~r, on· the quartz crystals· in-·some vugs .. · 

as a. result of ·which carbonates would be con- Ore from the 770-foot level of the Extension · 

verted into sulphates with liberation of carbon No. 1 workings is highly quartzose and carries 

dioxide. . sca~tered minute grains of pyrite and, rarely, 

It appears that this water may pr13sent soine . small dark-colored . aggregates of other suianalogy to the waters that. accomplished the phides. A polished surface of a piece com-

, sup~rgene enrichment in the early part of their paratively rich_ in dark sulphides shows galena, 

descent, before neutralization and before t~ey sphalerite, pyrite, chalcopyrite, anq polybasite. 

-. ·had _~cquired their full load of dissolv.ed mate- The polybasite is· peripherally repla·ced by an 

r~als. ;-·l~- is apparently not an analogue of the aggregate of argentite and cl?-alcopyrite. The 

sup13rgene solutions at. the stage when they de- hand specime~s show hydrous iron oxides along 

posited most. of th~ SUpergene ~ilve,r ntinerals, SOUle fractures and manganese oxides along 

for at that stage they appear to have beeifneu- others .. 

. tral and were depositing. also .carbonates. In contrast to the veins just mentioned, other 

PROBABLE. PERSISTENCE OF ORES IN DEPTH. veh'lS sh.ow strong mineralization on the deepest leveis·to which they have been developed. Ore 

The deepest deveJopments in the Tonopah ·from the Murray vein, for example, on the 

min~s have shown that in certain veins the 1,260-foot- level, is rich in sulphides and is 

·degree of mineralization ·gradually decreases equal iJ). grade to much of the ore higher up. 

with ii1creasing depth. ·The deep ores of such This ore .. is unoxidized. Microscopic study of 

veins carry more quartz and less sulphides than a pol~shed specimen shows the presence of 

the o~es higher ·up; microscopic study sho-\vs, galena, sphalerite, pyrite, and· chalcopyrite, in 

however, that the sulphides are the same species addition to quartz and a pink manganiferous 

as in the ores. above and 'that replacement carbonate. In -places the galena- has been 

deposits of the. type described as probably peripherally replaced by argentite and electhypogene are present, t4ough naturally not in rum, as shown in Plate IX, B. Some kaolin 

such abundance as in the ores-richer in sui- has been deposited in small vilgs:: 

·phides. The Belmont vein on the 1,500-foot The decrease in tenor with increasing depth 

.level of the .'.fonopah Belmont mine, the com- in the veins of the Tonopah Belmont mine is 

bined vein on the 770-foot level of the Exten-· . concomitant with the passage of the veins 

sion No. 1 workings, and the lTavorite vein on from the 'Mizpah trachyte _into the We'St End 

the 1 ,200-foot level of the Tonopah Behnont rhyolite and is doubtless dependent, at least in 

inine. afford good examples of such diminution part, upon the differing susceptibilities of the 

in value with depth. two rocks to fracturing and replacen1ent. .The 

The Belmont vein on: the 1 ,500-foot level mineralization, though varying in degree, was 

shows sulphid~s only in a few .places; much of continuous fron1 one. formation to the other. 

it is brecciated· wall rock traversed by veinlets. Although obviously 'all veins must tern1inate 

o_f white or dark-gray quartz, and no ore in ill deptp as well as laterally, the evidence from 

comn1ercial quantity has yet been found. Ore microscopic studies that many. of the silver minfrom a poii1t 40 feet east·of raise No. 2, when erals at Tonopah are hyp.ogene (primary) and 

examined microscopically, was 'seen to carr-y that they occur in ore from the deepest workings 

scattered grains and small aggregates of galena, offers substantial encouragement to deep minsphalerite, chalcopyrite·, pyrite, and polybasite ing. -In some veins change in wall rock was 

in a quartz gai1gue. The polybasite, at least probably a more important factor than mere 

in part, replaces galena, and there are narrow increase in .depth in causing the decreased ore 

transition rims of probable lead-silver sulphide tenor. · 
U S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 104 PLATE XV 

A. 

B. 

PHOTOMICROGRAPHS OF CONTACT BETWEE OXIDIZED AND UNOXIDIZED PORTIONS OF 

SPECIMEN SHOWN I PLATE XIV, A. 

A was taken in ordinary light and B in polarized lig-ht. In the unoxidized half, as shown at the left in A, small 

pyrite crystals abound; in the oxidized half the uon occms as finely divided oxide, though the spaces originally 

occupied by pyrite are still recognizable. B shows that the oxidation banding is in a general way independent 

of the original rock textme. It will be noted, however, that very little iron oxide has developed in the 

phenocrysts. 

• 
• 

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 104 PLATE XVI 

Agar a gar 

A B 

A . 

B. 

LIESEGANG RINGS OF FERROUS AND FERRIC HYDROXIDES DEVELOPED I AGAR AGAR BY 

DIFFUSION FROM OPPOSITE ENDS OF TUBES OF IRON SULPHATES AND SODIUM HYDROXIDE. 

A. After 17 days. A iB the first and B the second ring formed. 

B. After one month. Most of the rings were ferrous hydroxide, but in the late stages, when the iron solution 

had oxidized, rings of ferric hydroxide were developed at A. 
GENESIS OF THE ORES AT.TONO_PAH, NEV;. 45 

O~IDAT~ON BANDING IN WALL ROCKS. 

A feature of no economic importance but of 

some scientific interest is the regularly banded 

distribution of hydrous oxides of iron in certain 

of the wall rocks. This feature is especially 

well shown in· material from the dump of the 

Valley View shaft, and most of the specimens 

studied were fro1n that source. Similar banding was noted in place in the walls of the South 

vein, Desert Queen mine, at a .depth of about 

500 feet. · 

· The agents producing this banding evidently 

gained access to the wall rock through fractures and from then1 permeated. the rock. Polygonal blocks bcmnded by fractures show completely concentric structures such. as are illus...: 

trated in Plate XIII, .. B. 

T~e iron oxides appear to have be01Y derived 

fr01n the oxidation of pyrite, for in many specimens cores carrying abundn,nt disseminated 

grains of pyrite remain. · This is: true of the 

speci1nen illustrated in Plate XIV, A, the lightcolored, unba;nded portion carrying. abundant 

pyrite grains. Plate XV shows photomicrographs taken at the jU?ction of the oxidized 

and unoxidized areas. Plate XV, A, taken 

in ordinary light, shows the scattered crys-. 

tals of pyri to (black) in the unoxidized portio~ and irregular blotches of iron oxide, prob-· 

ably amorphous, in the oxidized portion. In 

tho oxidized portion are visible several voids 

co~responding in size and shape to the pyrite 

crystals and evidently representing their former 

presence. Plate Xy, B, gives tho appearance 

of tho· samo field in polarized light" and shows 

that the oxidation banding ·is independent of 

the original texture of the rock.. · 

Quartz v:einlets that traverse tho rock were 

at first believed to· be later tha~ the banding, 

but closer study leads to the conclusion that 

they were earli~r. In places they haNe had 

surprisingly little influence on the course of the 

oxidation bands. Near some very late fractures the iron oxides have been leached. 

A very interesting example of oxidation banding in fine-grained felsite from the vicinity of 

the North Star shaft is shown in Plate XIV, B. 

The senior writer w:as at· first inclined to interpret this as a "development" by oxidation 

processes of a banded distribution of pyrite or 

ferruginous carbonates produced during hydro-

. thermal metamorphism; microscopic study 

shows, however, that the position of the bands 

of iron oxide is· wholly.independen.t of the distribution of the pyrite from which it was plainly 

derived. 

It has -been suggested by A. C. Spencer that 

the banding is the result of alternate wetting 

and drying during many seasons. This ex-

~lanation has inuch to recommend it in a region 

hke Tonopah, where cyclonic storms are mainly 

confined to the winter months, the remainder of 

the year being rainless except for occasional 

showers. Furthermore, occasional dryip.g permitting access "of ·air would appear to be necessary fo~ the oxidation of the pyrite. 

The p9ssibility of the development of such 

oxidation banding by diffusion processes anal-. 

ogous to the formation of the so-called Liesegang rings has been pointed o:u t by Liesegang 1 

and unquestionably merits serious consideration, although the progress of such processes 

must necessarily have been modified by alternations of wet and dry p~riods. In this connection two experiments carried out by the 

writers :may be of interest. 

In the first experiment the central portion of 

a straight glass tube about half an inch in internal diameter ~as filled with a solution of 

agar agar in water. This was retained in place 

by a wad of cotton until it hardened. After 

the agar agar had set to a firm jelly. a soluti~~ 

of N /20 ferric ·sulphate was placed i~ one end 

. of the tube a1.1d a solution of N/16 sodium 

hydroxide in the other end; the ends were then · 

corked and sealed. After two days a faint. 

brown band of ferric hydroxide had developed 

at the point .marked A in Plate XVI, A. At 

the end of another two days the band A had 

not moved but was b~tter defined and a new 

band of ferrous hydroxide (green) had developed at the point marked B. By the successive formation of new bands shown from left · . ' t9 right in Plate XVI, A (from Fe2 (S04) 3 toward 

NaOH), the_ tube at the end of 17 days pre~ 

sen ted the appearance shown in the illustration. 

~ands,onc~ formed did not shift appreciably. 

The agar agar appears to have exerted a reducing-influence on the ferric sulphate, so that 

:r:nost of the rings were of ferrous hydroxide 

instead of ferric hydroxide as was expected: · · 

· In a second experiment the agar agar was· 

placed in the lower part of a U tube; · sodi~m 

1 Liesegang, R. E., Geologische Difiusionen, pp. 106-116, 1913. 
46 GENESIS OF 'JHE ORES AT T'ONOPAFJ;; NEV. 

hydroxide was placed 'above. it in one arm and 

ferrous· hydroxide in ·the other. The appear-: 

ance at the end of one month is shown in Plate 

XVI, B. Most of the rings were green, but 

those last formed, at the point marked A, were 

brown, evidently because of oxidation of the 

iron-bearing solution by.the air. 

Rings were also produced in compacted filter 

paper under conditions similar to those of the. 

first· experiment. 

ANALYSES OF ORE, BULLION, ETC. 

The following analyses, published by Mr. A. 

·H. J<?nes a and inserted here with hi~ permission, have significanoo Ul indicating ~he presence of certau1 elements, notal:>ly selenium. 

whose p~esence is not apparent fron1 a min:eralogic exan1mation, and u1 showing that certau1 

others, such as nickel and ·cobalt, which are 

characteristic of some silver deposits, are probably absent. For comparison· the analysis by 

Hillebrand publishe9. in Spurr's report b is 

included. 

Analyses of Tonopah ores, concentrates,_ bullion, etc. 

1 2 . 3 4 5. 

----'------;-----------

Si02 ••••• __ ••• -... 72. 00 15. 18 . . . . . . . 5. 50 . ~"'- ... Al 20 3 ••• - ... _-- .. • • • 42 . ·. . . . . . . 0. 42 2. 00 

CaO................ 3.10 ·3. 70 . 80 .10 

MgO............... 2. 95 1. 49 ....... Trace. 

QaC03 ••••• ~ • • • • • • • • • • • • • • • • • • • • • • •••• ~ • 3. 60 

CO;:.-..... . . . . . . . . . . . . . . . . . 6. 34 ................... . Naul and KCL.... . . . . . . . . . • . . . . . . . . . . . l. 00 ..... . FeSO 4 • • • • • • • • • • • • • • • • • • • • • • • • • • •. • • • • • • • • 26 ..... . Fe.. . . . . . . . . . . .. . . 2. 10 9. 87 29. 80 ............ . Mn. . . . . . . . . . . . . . . l. 60 l. 36 1. 10 ......... · ... . Cu....... . . . . . . . . . . . l. 09 l. 32 . 60 , 2. 10 l. 02 

NiandCo ......... None.--------------- ............. . Pb. . . . . . . . . . . . . . . . 1. 50 6. 21 1. 30 2. 36 2. 41 

Zn ................. 3.00 5.84 .60 4.70_ .06 

Cd ................. None ... : ........... 1.00 ..... . As ......... · .. _..... 1.'race. . 19 .... · .... : . ......... . Sb .......... _ . . . . . . 10 . 92 ................... . Bi... . . . . . . . . . . . . . None. . _ ......................... . -8. . . . . . . . . . . .. .. . . 2. 60 Not det 31. 60 . . • . . . . . 17 

Se. . . . . . . . . . . . . . . . · . 20 2. 56 . . . . . . . l. 40 1. 80 

Te ................ Trace. 'None .......... .' ......... . 

Au................. .06 -82 } 1.60 74.23 93.23 

Ag ................. - . 4. 88 25. 92 . Undetermined . . . . c 4. 40 · .. . . . . . l. 58 d 1.15 · b1. 31 

Insoluble ......................... 30.60 ............ .. 

100. 00 81. 72 100. 00 100. 00 100. 00 

a ~y difference,_ mainly Na, K, and combined H20. 

b By difference. 

c Jones, A. H. (superintendent of mills. Tonopah Belmo:.J.t Development Co,), The Tonopah plant of the Belmont :Milling Co.: Am. Inst. 

Min. Eng. Trans., vol. 52, pp. 1731-1738, 1916. 

d Spurr, J. E., Geology of the Tonopah mining district, Nev.: U.· S. 

Geol. Survey Prof. Paper 42, p. 89, 1905. 

l. Analysis hy A. H. Jones of piece ·of rich silver ore 

·from Belmont mine; exact location in mine unkn.own. 

2. Analysis by W. F. Hillebrand, in the laboratory of 

the United States Geological Survey, of sulphides separated bycrushingand panning from sample of rich sulphide · 

ore from Montana vein at depths of 460 to 512 feet in Montana Tonopah mine. 

3. Partial analysis by A. H. Jones of concentrates from 

Belmont mill. 

4. Analysis by A. H. Jones of zinc box precipitate, Belmont mill. 

5. Analysis by A. H. Jones Of bullion, Beimont mill. 

. The cadmiUm. shown in analysis 4 very possibly represents a· concentration ·of cadmium· 

occurring as ·an impurity in the zinc used for 

precipitatio~. It is noteworthy that the ratio 

of gold to selenium is very nearly the sarne in 

both analyses 1 and 2. 

IDENTIFICATION OF METALLIC MINERALS IN 

POLISHED SECTIONS. 

Some of the. methods of identification of nlinerals in polished section that were used in. these 

studies may ·include a- few new points of possible service to other students of or~ ~eposits. 

Whenever possible_ small fragments of tlie 

mineral to be identified were chipped from the 

edges o'f the polished specimen with a stout 

needle or very sharp steel prod and tested 

be~ore the blowpipe or in a wet way. .. ' 

· Needles of .several sizes mounted in .the ends 

of wooden penholders were found very· useful 

as prods for_ testing the hardness, streak, sectility, etc., of min~rals. 

.-Most reagents for tarnishing the minerals can 

be convenien.tly applied on a strip of· blotting 

paper about half an inch wide and 3 inches long. 

One end of this strip is moistened with the 

reag~nt a~d is ru~bed lightly back and f~rth 

over. the polished surface of the mineral, ·the 

progress of the tarnishing being watclied under 

the low or moderate powers- of the microscope 

and checked at the desired stage by .simply rubbing with the dry end. of the biotti;ng paper. 

. Reactions aiding in the identification of certain minerals are the following: 

. The bright silvery luster of. galena in polished sections, its lead-gray streak, and the 

development of triangular pits due to . the· tearing out of inverted pyrarnids of galena between 

the three sets of cleavage planes during polishing (see, for example, Pl. VII, B.) have usually 

been considered sufficient to identify it. The 

~!iters· discovered, however, that another min-
SUMMARY-REFER.ENCES. 47. 

eral, probably a lead-silver sulphide, also pos-~ of the ore obtained in the past and of some 

sesses these characteristics. It w.as found that ore now remaining is unquestionably due in 

the twocouldbedifferentiatedbytreatmentwith. part to these processes. . 

ordin~ry commercial hych·ogen. peroxide (H20 2 ). 2. There is evidence not only of recent 

l'hisreagenttarnishesgalenabrownbutdoesnot oxidation of the ores but also of at least one 

affect ti1e supposed lead-silversulphide or any of· period of ancient oxidation, an~ supergene 

the other silver minerals with which galena is sulphide enrichment was ·probably an accomcomnlonly associated. It is therefore a reagent ·paniment of each of these periods. 

of great utility in studyirig the relations between -3. The rich silver or~s now being mined at 

galena and associated s~lver minerals. The tar- Tonopah are ~r~bably in th~ main of hypogene 

nishit produces on galena appears slowly, can be or pnmary opg1n. . 

quickly checked, and can be easily re1noved by 4. Mining has shown that in certain veins 

a little polishing with rouge on a bit of cotton. the primary .sulphides become less abundant 

The polished surfaces of.argentite usu~lly ap- with increasing depth, though the same species 

pear slightly "rougher" under the microscope are present; mere increase in depth tnay account 

thnn most of the other sulphides with which it for this change in some veins, for every vein· 

is associated except pyrite; this feature is w:ell .n1ust finally end in <;lepth as well as laterally; in 

shown in Plate III, B. Pricking with a fine ·many veins change in :wall rock has· been· at 

needle reveals its soft sectile char~cter. It is least a contributing factor. The veins develunaffected by hydrogen peroxide and silver ni- oped by other d.E}ep workings are heavily minertrate but is rapidly tarnished brown by satu'- alized and of high grade, and the geologic evirated n1ercuric chloride solution. deuce· is ·favorable to the persistence of rich 

Polybasite is brittle and gives a black streak. primary silver ores to depths considerably 

Its polished surfaces are ·unaffected by hych·o- greater than those yet attained in the mining · 

gen peroxide but are tarnished reddish brown operations. 

by silver nitrate solution and rapidly tarnished Although hot ascending waters· are encounbrown by satm·ated n1ercuric chloride solution. tered in a number of the deeper workings, 

Pyrargyrite is b1~ittle and gives a r!3d streak.· there. is little evidence that these waters are 

It is unaffected by hydrogen peroxide but is now depositing ores ... 

REFERENCES. 

tnrnished brown by· silver nitrate solution, 

tho,ugh much more slowly than polybasite. 

Short treatment with saturated mercuric chloride solution tarnishes it pale brownish yellow; The following list gives the nwre important 

potybasite by the same treatment is tarnished ~ublications on the Tonopah dist~ict: 

a pronounced brown. The polybasite shown in BuRGEss, J. A., The geology of the producing p::..i·t.of the 

Plate IV, B, has been differentiated from the Tonopah mining dish:ict: Econ .. .§t:)<;>logy, vol. 4, PP· 

681-712, 1909. 

pyrargyrite which incloses it by such treatment. --The halogen salts of silver and·associated minerals 

Before treatn1ent.the two minerals were hardly at Tonopah, Nev.: Econ. Geology, vol. 6, . .pp. 18-21, · 

distinguishable from each other: 1911. 

Silver nitrate is a useful reagent for tar.!lish- EAKLE, A. S., The minerals of Tonopah, Nev.': California 

ing chalcopyrite, which becomes reddish yellow, Univ. Dept. Geology Bull., vol. 7' PP· 1-20, 1912. 

LocKE, AuousTus, The geology of the Tonopah mining 

then deep amber, mid finally madder:-red; ar- district: Am. Inst. Min .. Eng. Trans., vol. 431 pp·. 

gentite, galena, and sphalerite are unaffected by . 157-166, 1912. 

the snme treatnlent. RoGERS, A. F., Dahllite (podolite) from Tonopah, Nev.: 

Am. Jour. Sci., 4th ser., vol. 33, pp. 475-:482, 1912. 

SUMMARY OF MORE IMPORTANT CONCLUSIONS. . . 

1. The hypogene or primary ores have been 

modified in places by oxidation and enrich,_ 

ment through the· agency of the air and· 

oxygenated solutions originating at. or near 

the surfnce. The high silver content· of n1uch 

SPURR, J. E., Geology of the Tonopah mining district, 

Nev.: U.S. Geol. Surv.ey Prof. Paper 42, 1905. 

--Report on the geology of the property of the Montana.Tonopah Mining Co., Tonopah, Nev., published 

· by the company, 1910. Abstract in Min: and Sci. 

Press, vol. 102~ pp. 56Q-562, 1911. . 

--Geology and ore deposits at Tonopah, Nev.: Econ. 

Geology., '\rol. 10, pp. 713-769, 1915. 

INDEX. 

Page. Page. 

Acids, balancing of, in analyses.................................. 28 Galena, aggregate of minerals replacinl!', plate showing............ 24 

Acknowledgments for aid....................................... 7 form and deposition of....................................... 14 

Alteration, hydrothermal, nature of... . . . . . ................. ·. . . . 12 identification of, in polished sections ......................... 46-47 

Analyses, water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 origin and replacement of .................................... 25-26 

water, correction of errors in ..... : ......................... 28,29-30 

method of stating. . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-27 

replacemcn• of, by argentite... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 

by carbonate-sulphide aggregates ................... : ..... 23-24 

Argontito, association of native silver with, plate showing........ 40 

deposits of, on fractures in hypogene ore, plates showing...... 34 

by chalcopyrite and argentite. . . . . . . . .. . .. . . . . . . . . . .. . .. · 23 

by covellite or argentite ............................ : . . . . . 40 

form and deposition of....................................... 18 by electrum ... :. . . . . . . .. . . . • . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

identification of, in polished sections......................... 47 bypolybasite ..... .' ............. ." ....................... 20-21 

intergrowths or,· with other orcs, plate showing............... 17· plate showing.... . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . .. . . . . 20 

occurronco and origin of ...................................... 35,42 solubility of, in solutions of silver salts .................... : .. 22-23 

roplacomont of born ito by ................................. 39-40,43 ttansition from areas of, to areas of carbonate, plate showing~. 20 

replacement of galena by .................................. 21, 23,40 transition replacement mineral from .......................... 21-23 

roplaccmont of poly basi to by................................. 21 plate showing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 

roplacomont of sphalerite by ................................. 40,43 

Argyrodito, probable occurrence of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 

irsonopyrite, probable occurrence of ...................... ,. . . . . . 14 

Banding of ores, features of ....................................... 10-11 

Germanium, occurrence of. ... :.................................. 16 

Gold, occurrence and origin of.. .................................. 33-Jll 

production of, from 1904 to 1916.............................. 7 

Gypsum, occurrence and origin of~ .......................... .' .... 38-39 

Banding of wall rock, cause of ............ · ......................... 45-46 

Barite, occurronco and origin of. ................................. 38,42 

Halifax mine, water from ....................................... : 26 

Hillebrand, W. F.,analysisby................................... 18 

Belmont vein, banded hypogene oro from, plate showing. . . . . . . . . 10 

tungsten in. . . . . . . . . . . . . . . . . . . . . . . . . . • • . . . . . . . . . . . . . . . . . . . . . . 19 

Hoyt, S. L., and Nissen, A. E., cited............................. 23 

Hydrogen ions, sources of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 

Bibliography of tho district....................................... 47 Hydroxy lions, sources of......................................... 27 

Bornite, roplaccmont of, by covcllite and argentite ........... 39-40,43 Hypogene, use of term........................................... 10 

replacement of chalcopyrite by ....................... .' ....... 39,43 Hypogene minerals, alpha, general relations of................... 13 

Breccias, pyrargyrite, ori~:,in of ................................... 11-12 alpha and beta, use of terms .................................. 12-13 

Bullion, analysis of............................................... 46 beta, general features of. ..................................... 19-20 

Bureau of Minos, cooperation with ......................... .'.... 7 Hypogene ore, plates showing ........... ~ .· ....................... 10, 11 

Burgess, J. A., cited ................ · ....... \"..................... 8 Iodobromite, occurre..'lCe of. ... ·................................... 37 

Calamine, occurronco and origin of ............................... 37-38 Iodyrite, occurrence and origin of. ................................. ·36-37 

Calcite, ferruginous, coating highly oxidized oro, plato showing... · 25 Iron, oxides of, banding with .... ,................................ 45· 

occurronco of.... . . . . . . • • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . 37 oxides of, occurrence oC: .......... : . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 

Carbonates, aggrogatos of, with sulphides ......................... 18-19 Jones, A. H., analyses by ..................... : ..... _............ 46 aggregates of, with sulphides, roplacomont of gal~na by... . . . . 23-24 

intergrowths of, with other orcs, plate showing .. :............ 17 

occurronco and composition of ........................ .' .... IS, 37,42 

transition to areas of, from areas of galona, plate showing... . . 20 

Corargyrito, occurrence and origin of............................. 36 

Chalcopyrite, form and deposition of............................ 14 

idontiftcntlon of, in polished sections. . . . . . . . . . . . . . . . . . . . . . . . . 47 

jntcrgrowths of, with other orcs, plate showing............... 17 

occurronco and origin of.......... . . . . . . . • . . . . . . . . . . . . . . . . . . . . 35, 43 

replacement of, by bornite ............... : ............•....... 39,43 

roplaccmont of galona by .............................. .._. . . . . . 23 

\'Oinlets of, traversing sphalerite, plate showing............... 21 

Concontrutos, analyses of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 

Cooperation with U.S. Bureau of Mines.......................... 7 

Copper, production of, from 190-1 to 1916.......................... 7 

Covelli to, replacement of bornit!} by ........................... 39-40, •a 

replacement of sphalerite and galena by ............. :........ 40 

Crustiftcation, occurrence of ............................... :..... . 11 

Kaolin,silver embedded in ...................................... . 

Kaolinite, occurrence and origin of .......... ~ ................... . 

Kirchen, John G., acknowledgment to .......................... . 

Knopf, .A,dolph, acknowledgment to ............................. . 

Last Chance mine, ore from, plate showing ...................... . 

Lead,production of, from 1904 to 1916 ........................... . 

Liesegang, R. E., explanation of banded structure by ........... . 

Liesegang rings in agar agar, plate showing ...................... . 

Locke, Augustus,cited .......................................... . 

Lowe, A .. E., acknowledgment to ..... : .......................... . 

~4 

38 

11 

7 

12 

7 

10 

45 

8,9 

17 

Malachite,occurronceof.......................................... 37 

Manganese, oxides of, occurrence of.. ..... · ..................... :.. 37 

Mineral, undetermined transition, nature and occurrence of. ...... 21-23 

Minerals, hypogene, sequence in deposition among ............... 25-21> 

id?~tifica~ion of, in polished sections ..................... : ... 46-47 

ongmof. ........................................... ·.......... 33 

Dahllitc, occurrence and origin of. ... _ ....... _ ... : _ ......... _.... 38 replacement of, conditions favoring ........................... 19-20 

Deposition of hypogene minerals, sequence in .... · ................ 25-26 supergene enrichment of.. .. ··~····························-·- 47 

Mineralization, classes of......................................... 10 

mcctrmn, crystal outlines or, associated with quartz and sui- supergene, conditions governing .............................. 30-31 

phldcs, plato showing................................. 16 nature of solutions producing ........................ · ..... 43-44 

form rmd tic position of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 summary of evidence of .................................. 42-43 

lntcrgrowth of, with sphalerite and quartz, plate showmg.... 16 Mizpah mine, water from, analysis of. ............................ 29,30 

probablo"occurronco or........................................ 17 water from, description of .................................... 26,30 

replacement of galena by.................................. . 24 Mizpah trachyte, ore bodies in................................... 9 

Enrichment, supcrgonc, relation of, to fracturing ................ 41-42 oxidation banding in, plates showing ...................... 40, 41,44 

upward, restriction of term ............................... ·.... 26 Montana Tonopah mine, ores from, plates showing .... :.......... 35 

F.psomitc, occurronco and origin of............................... 39 N" · A E d H t 8 L · d 

ExtousionNo.1mine,tenorofsilvcrorcin ...................... 41 Issen, · .,an oy' · .,Cite·······-~·-·················· 23 

North Star mine, ore from, assay of............................... 17 

Fraction dacite breccia, photomicrograph showing. . . . . . . . . . . . . . . 25 ore from, platesshowing ................................... 61,34,41 

Fracturing, relation of, to supergene enrichment .................. 41-42 tenor of. • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 

2601°-18-4 49 
50 INDEX. 

Page. 

Ores, analysis of ........................ ~ ..................... ·..... 46 

assays of. •........... ~ ......... -~............................. 17 

formed by replacement....................................... 9-10 

persistence of, in depth ....................................... 44, 47 

recovery value of. ....................... ~ .............. ~ . . . . . . 8 

relations of, to inclosing rocks .............. :. . . . . . . . . . . . . . . . . 9-10 

silver, hypogene origin of..................................... 47 

See also Minerals. 

Oxidation, depth of. ...... .- ..................... , ... , . . . . . . . . . . . . 31 

periods of. ................................................... 31-33 

Oxidation banding in fine-grained ·relsite, plate showing.......... 41 

in Mizpah trachyte, platesshowing~ ....................... 40,41,44 

Palmer, Chase, acknowledgment to............................... 7 

analyses by .................... ·. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 

determination of selenium by .... ·............................. 18 

experiments on the reaction between galena and silver salts by. 22-23 

interpretation of water analyses by ................ -.... ~ ...... 26-27 

test for germanium by........................................ 16 

Polybasite, deposition and replacement of. ....................... 2&-26 

deposits of, in fractures in quartz, plates.sbow~ng............. 35 

forin and deposition of....................................... 16 

identification of, in polished sections. . . . . . . . . . . . . . . . . . . . . . . . . 47 

int~rgrowth of, with quartz and pyrite, plate showing........ 18 

occurrence and origin or ...................................... 35, 42 

replacement of, by argentite .................................. 21,23 

·by chalcopyrite .......... ~ .......... : . ... ·. . • . . . . . . . . . . . . . 23 

replacement of galena by, plate showing ................. : ... ~- 20 

replacement of sulphides by .................................. 2o-21 

veinlets of, traversing sphalerite, plate showing............... 21 

with blade~ ike outlines inclosed by pyrargyrite, plate showing. 13 

Publications on the district ................•........... : .. ,....... 47 

Pyrargyrite ,arsenical, texture and deposition of .................. 14-16 

breccia partly replaced hy, pbte showing..................... 11 

deposits of, in fractnre in quartz, plate showing......... . . . . . 35 

identilication of, in polished sections......................... 47 

int"ergrowth of, with quartz, plate showing................... 12 

occurrence and origin of ............. ·.. . . . . . . . . . . • . . . . . . . . . . . 36, 4.2 

polybasite inclosed by, plate showing....................... . 13 

veinlets of, origin of. .... · ............... : . ................... 11-12 

supposed. hypogene veinlets of, plate sho,,ing... .. .. . . ... ... . 11 

Pynrgyri te hrecrias, origin of. ......... ~ .... ::: . ............ : . . . . 11-1~ 

Pyrite, form and deposition cL... .. .. .. .. .... .. . . . . .. . .. .. ... .. . 14 

occnrrencl! and origin of... . ........ . · .......... :......... . .. 34,42 

"Pyrolusite, occurrence of ..............•...................... :. . . ·39 

Quartz, deposition a~d replacement cf. ........................... 2&-26 

occurrence and origin of ................................... 1~, 37, 12 

·Radi.cles, gro·Jping of, in water analyses ....................... , .. 27-28 

use of, in water analyses ..•................ ~ .................. 26-:-27 

"Ransome, F. T •. , acknowledgment to ..... _ ................ , ...... · 7 

Ravicz, Louis G., on tho deposition uf snlphosalts of sih:or....... 15 

Reacting values, stateme'lt of. ..................... :............. 27 

.Jleplacement, conditions prod~1cing ........................ 19-20, 21.)-26 

hypogene, summary of evidence of. .........•.. · ............... 24-25 

supergene, summary or evidence of.. ......................... 42-43 

use of term ............................... :: ........ :......... 10 

Rbotlochrosite, intergrowth of, with quartz, plate showing....... 17 

occurrenc~ of. ...................•.•..•..• : • . . • . . . . . . . . . . . . . . . 36 

:Rhodonite,sbsenc~of.. .......•.•..•.• _. ••••• ~ •.•.•.. · •.......... ~. 18 

Page. 

Sections, polished, identification of minerals in ................... 46-47 

Selenium, occurrence of. ......................................... 17-18 

. Silica, h~aline, occurrence of. ...... ~ . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . · 37 

Silvrr, native, association of argentite "ith, plate showing........ 40 

native, replacement deposits of.. ............................. 40-41 

occurrence a:.d origin of .................................. 34.42-43 

production of, from 190-l to 1916 ••••.•.......••....•......•..• · 7 

salts of, reaction of, with galena .............................. 22-23 

sulphosalt3 of, deposition r.f. ................................. 15-16 

SHYer haloids, occPrrence and origin of ........................... 3f)-37 

Solutions, mineralizing, reaction of. ............................... 43-44 

Sphalerite, form !\nd deposition of.. .............................. 13-\4 

intergrowth of, with electrum, plato shO\\ing................. 16 

origin a"!ld replacement of. .••................... ~ ............ 2&-26 

replacoiiienfof, by covellite or argentite ...................... 40,43 

by polybasite ••....•..................................... 20-21 

t,raversed by veinlcts of chalcopyTite ·and polybasite; plate 

showing: ............................................ ·. 21 

Sphaleritrand argentite, veinlet of, plate showing................. 12 

Spurr, J. E., <Jited......... .... .. .... .... .. ........ . . . ... ... .. .. . 8,33 

classification of veins hy ............ ::... . . . . . . . . . . . . . . . . . . . . . 9-l!l 

Stabler, Herman, interpretation of wat11r analyses by •...•..• : .... 26-:-27 

Stephanite, presence of, not prO\'ed ............................... 16-:-17 

Stratigraphy of the district ....... :. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-6 

Sulphides, aggregation of, with carbonates ........................ 1S....19 

SupergenE~, use of term............ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

Supergene deposits, formation of ................................. 39-41 

Tonopah Belmont mine, orf! from, plates sho"ing ....... 1i, 2C, 21, 24,40 

ore from, tenor of... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 

oxidation in.................. . . . . . . . . . . . ."............. . . . . . . 31 

water from,.analysis of. ...................................... 29-30 

description or ............................................ 25,30 

'ronopah Extension mine, ore from, plates showing ...... 10, 11, 13, 16.34 

ore from, tenor of ............... ,· . . . . • . . . . . . . . . . . . . . . . . . . . . . 42 

oxidatio'l in.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 

Tun~ten, cccurrence of. .......................... : . . ·... . . . . . . . . . 19 

V!llley View mine, tnngston in................................... 19 

Valley View vein, <'xi:lation ba':lding in and near, plates showing .... :: ........................................... 40,41,44 

Veinlets, pyrargyrito, origin of. .................................. 11-12 

Veins, ages o! ........................ ·.... .. . .. . . .. . . . . . . . . . . . . . . . 9 

Wall rocks, oxidation handing in ... ,., .............. ".: .......... 45-46 

'Vater,·ground, occurrence of..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . · 33 

Waters, hot ascending, deposition by............................ 47 

· mine, acidity of. ............................................. 43-44 

nature of. ........... ·.: .............................. :. . . . 26-:-30 

Wells, H. C., a!lalysis by.................................... .. .. 29 

West End mine, ore from, plates showing ..................... 12, 13,25 

ore from, tenor of ..... :... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 

water from, analysis of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 

West End-rhyloito, ore todies in................................. 9 

West End voin, ore from, assay of.... . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 

oxidation on, period:; of. ...................................... 31-32 

\\"olframite,·age of............................................... 9 

occurrence and deposition oi....... .•.. .•.... .. .•. . . . .. •. .. . . . 19 

ADDITIONAL COPIES 

OF TIDS PUBLICATION MAY BE PROCURED FROM 

THE SuPERINTEN_DENT OF DOCUMENTS 

GOVERNMENT PRINTING OFFICE 

WASHINGTON, D. C. 

AT 

15 CENTS PER COPY