Silver-rich 

Disseminated Sulfides 

From a Tungsten-bearing 

Quartz Lode 

Big Creek District 

Central Idaho 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 594-C 

Silver-rich 

Disseminated Sulfides 

From a Tungsten-bearing 

Quartz Lode 

Big Creek District 

Central Idaho 

By B. F. LEONARD, CYNTHIA W. MEAD, and NANCY CONKLIN 

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 594-C 

Study of a low-grade tungsten deposit 

whose associated suljide minerals, 

extracted as waste, are rich in 

silver and contain some gold 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1968 
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary 

GEOLOGICAL SURVEY 

William T. Pecora, Director 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price 35 cents (paper cover) 
CONTENTS 

Page Abstract __________________________________________ _ C1 Mineralogy and paragenetic sequence-Continued Introduction ______________________________________ _ 1 Alteration products ____________________________ _ 

Location and operation _____________________________ _ 4 Paragenetic sequence ___________________________ _ 

Geology __________________________________________ _ 4 Geologic thermometry __________________________ _ 

Ore deposit _______________________________________ _ 5 Classification and origin of hypogene mineralization ____ _ 

Mineralogy and paragenetic sequence ________________ _ 6 Oxidation and enrichment ___ ------------------------

Typical ore ___________________________________ _ 6 Economic considerations ____________________________ _ 

Gangue indicated by mill products _______________ _ 7 Acknowledgments ___________________ .:. ______________ _ 

Tungsten minerals _______ , ______________________ _ 8 References ________________________________________ _ 

Sulfides and related minerals ____________________ _ 8 

ILLUSTRATIONS 

[Plates follow page C24f -

PLATE 1. Drawing and X-ray micrographs of acanthite and copper sulfides on galena. 

2. Drawing and X-ray micrographs of electrum in pyrite. 

3. Photomicrograph of electrum in pyrite. 

Page 

C15 

16 

18 

19 

20 

21 

23 

23 

4. Photomicrographs of native silver and inverted Ag-Fe-S mineral in pyrite. Page 

F~GURE 1. Index map of parts of Big Creek and Yellow Pine districts, Idaho_________________________________________ C4 

TABLES 

Page 

TABLE 1. Assays of concentrates and tailings, McRae Tungsten Corp. milL___________________________________________ C2 

2. Semiquantitative spectrographic analyses of concentrates and tailings, McRae Tungsten Corp. milL___________ 3 

3. Semiquantitative spectrograptic analyses of handpicked mineral fractions of sulfide concentrates, McRae Tungsten Corp. milL_________________________________________________________________________________ 3 

4. Approximate mineralogic composition of sulfide fraction of sulfide concentrates, McRae Tungsten Corp. milL___ 4 

5. Minerals of the New Snowbird deposit _____________ --------------··------------------- ----------------- 7 

6. Chemical analysis of tailings, McRae Tungsten Corp. milL__________________________________________ _ _ _ _ _ 8 

7. -D1str16ution -of ore-mineral inclusions in discrete grains of the sulfide-sulfosalt-native-element suite____________ 17 

8. Metal concentration (recoverable basis) in crude ore, New Snowbird tungsten deposit and San Manuel copper 

deposit_______________________________________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 22 

III 

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

SILVER-RICH DISSEMINATED SULFIDES FROM A TUNGSTEN-BEARING 

QUARTZ LODE, BIG CREEK DISTRICT, CENTRAL IDAHO 

By B. F. LEONARD, CYNTHIA W. MEAD, and NANCY CoNKLIN 

ABSTRACT 

Sulfide colliCentratels :removed as wa1ste :from the milling of 

l<mr-~grade tun~ten ore at the New Snowbird deposit rontain 

roughly 100-300 troy ounces of ,silver per ton, 2-4 ounces <Yf gold, 

and a few percent each of copper, leald, and zinc . .S'parsely di,sseminated sullfides make up only about 0.1 weight if*"rcent of the 

tunglsten ore, and not more tJhan 1 ton oif sulfide concentrates 

wrus accumulated annually during the :short Ufe of the mine. 

The total metal eontent per ton of ore is eompa:rable to tlhat of 

'some 'PO!rrfuyry 'Copper deposits. At the New Snowbird, tungsten 

proxies for 'copper, and the precious metals and base metaLs a•re 

potential coproductJs. The isize o:f the disseminated sulfidetungtsten depoisit is unknown, 'but itls o~urren!ce a!s a xenotihermaiJ. 

replacement witlhin a very ·la·rge 'Sili'cified zone coextensive wi:th 

a!major Tertiary dike swarm 'su~gestJs tlhat the New Snowbi1rd 

abd similiar deposits are potentially valuable, though extr,emely 

low grade, sources of precious meta'ls. 

This report defineis the mineralogy orf one deposit by microscopic, electron prdbe, X~ray, spectrochemi•cal, and ·C'hemical 

analyse'S. Huelbnerite, sC'heeUte, and a little stolzite a'r,e the main 

tllllglsten minerals. Pyrite, chalcopyrite, 'Sphalerite, ,galena, 

d~genite, and acanthite are the principal sulfides. Elemental 

g~ld is present as gold-rich electrum included in pyrite. Elem~ntal silver is present in native silver, electrum, argentopyrite ( ?) , acanthite, argentian tetrahedrite, silver sulfosalts, hessite, argentian digenite, cera:f!gyrite, anld perhaps otiher minerals. 

Deposition oif the complex mineral assemiblage within the quartz 

'lode :began witJh huebnerite and ·scheelite. Pyrite with abundant 

heterogenoous ore-mineral inclusions was then dumped. IncLu-

'sion~rich base-metal sulfides and tetJrahedrite followed in weakly 

ordered sequence, telescoped upon miaTgyrite( ?) , acantJhite, and 

late rim~forming copper sulfides. '.Dhe inferred tempertature range 

for hypogene sulfide mineralization extends from 491°0 or less 

(pyrite-pyrrhotite-arsenopyrite assemblage) to 177°C or less 

( acantJhite formed 'below ~he argentite-acantJhite inversion 

t~mperature) . Olay mineral's and oxidation products a~re sparse. 

The extent Olf 1supergene sulfide enrichment i1s indeterminate 

hut proba'blly 1sligtht, tJhough an unknown quantity of supergene 

a'lteration 1products may have 'been eroded. 

INTRODUCTION 

Sulfide concentrates accmnulated as a waste product 

during the beneficiation of low-grade huebneritescheelite ore from the New Snowbird deposit contain 

110'---316 troy ounces of silver per ton, 2.7-4.1 ounces of 

gold, and a few percent each of copper, lead, and zinc. 

The sulfides were very sparsely disseminated in the 

tungsten ore, and the accumulation of "pyrite concentrate" known to contain base metals and silver was 

roughly 1 ton per year, an amount regarded by the operator as too small to be worth marketing. Nevertheless, 

milling of the tungsten ore carried out an experiment 

in concentration that nature apparently failed to perform on a large scale in this district, where bonanzas 

have not been found. Sulfide concentrates from the New 

Snowbird mill thus provide the first large sample of a 

disseminated sulfide deposit from the district, revealing 

its mineralogy and 1netal content in a way that conventional sampling and a~ssaying could not have done and 

suggesting that the extensive, sparsely sulfide-bearing 

silicified zones of the district may merit attention as 

potential sources of disseminated metals in bodies reminiscent of the porphyry copper deposits of the Western 

States. 

This report deals mainly with the mineralogy of the 

sulfide concentrates. The deposit from which they came 

was, economically, a tungsten ore body in which the 

value of the other metals probably did not exceed 30-80 

cents per ton of crude ore. The sulfide-bearing 1naterial 

itself was not ore ; the sulfides were remo-ved merely 

because a price penalty is imposed for sulfur in tungsten 

concentrates. Other tungsten deposits of similar type 

occur in the neighborhood, but this deposit alone has 

been worked, and no low-grade sulfide deposits have 

been exploited except. the Yellow Pine and Meadow 

Creek (fig. 1) .

1 The intensity of sulfide mineralization 

1 The Yellow Pine mine became the Nation's leading producer of 

tungsten in 1942-44, when it yielded more than 800,000 units of WOa. 

Though the ratios of the dollar value of tungsten, antimony, and gold 

in the ore were approximately 2: 2: 1 during the productive life of the 

mine (1938-52), the ore came from a low-grade pyrlte-arsenopyrltestibnlte-quartz lode that contained a large shoot of scheelite ore. Thus, 

sulfides predominated over scheelite in the ore body as a whole. The 

Meadow Creek mine produced antimony and gold only, but some scheelite 

was present in the deposit. Silver was recovered from both deposits, the 

weight ratio of Ag: Au being 8.2: 1 at the Yellow Pine mine and 3.4: 1 

at Meadow Creek. For details, see Cooper (1951) and U.S. Bureau of 

Mines (1938-52). 

C1 
C2 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

at the latter deposits was at least one order of magnitude 

greater than that inferred for the New Snowbird. Thus 

there is no local standard against which to compare the 

New Snowbird sulfide assemblage. 

Fine grain size and sparse dissemination of 'the New 

Snowbird sulfides hamper one's study of the deposit in 

the field and limit the usefulness of any collection of 

ore samples numbering less than hundreds. Concentration of the sulfides during beneficiation has largely 

overcome these drawbacks, probably with little loss of 

natural detail except in the relation of ore minerals to 

matrix. Many pyrite g:vains in the concentrates are 

euhedral, other sulfide grains are delicately rimmed with 

soft minerals, and the dust that might be expected from 

overgrinding is sparse. These features suggest that 

many sulfide grains simply popped out of the quartz 

matrix during crushing and wet grinding, with little 

attendant destruction of the ore-mineral fabric and 

without development of polymorphic inversions in 

temperature-sensitive members of the sulfide suite. 

Interesting as the mineral assemblage has proved to 

be, its study might be viewed merely as a prerequisite 

for understanding the chemical composition of the 

sulfide concentrates, reported in tables 1 and 2. The 

data in ta)ble 3, analyses of handpicked mineral fractions, represent an unsuccessful shortcut toward that 

understanding. They illustrate the futility of handpicking apparently homogeneous grains that are complex 

fine-grained aggregates. These annotated tables will not 

be discussed in detail, but their interpretation should 

become plain as the mineralogic study develops. Table 4 

shows reasonable agreement between observed and calculated minerals in the most fully analyzed sample of 

the sulfide concentrates. Table 5 lists the minerals of 

the deposit. The heavy sprinkling of question marks, 

either printed or implied there, refers to minerals that 

make up less than 0.5 volume percent of the deposit. 

Perusing the ;five tables before reading the text will be 

b.elpful. 

Elemental gold in the sulfide concentrates is present 

mostly as gold-rich electrum included in pyrite. A little 

pure native gold may also be included in pyrite, but 

this is an inference based on the rich golden color of 

the particles. The evidence from fabric studies indicates 

that the electrum (and native gold, if actually present) 

is hypogene. If the deposit contains electrum or native 

gold outside pyrite, we did not find evidence of it in 

this study. Elemental silver is, in contrast, distributed 

among many minerals: native silver, electrum, argentopyrite ( ? ) , acanthite, argentian tetrahedrite, argentian digentite, hessite, inadequately identified silver 

sulfosalts, cerargyrite, and perhaps other minerals: 

Acanthite is the most abundant of these. The Ag : Au 

TABLE 1.-Assays of concentrates and tailings, McRae Tungsten 

Corp. mill 

[Parts per million, ppm; parts per billion, ppb] 

2 3 4 5 

Field No ______________________ SN/56/7b SN/64/1 SN/64/2 SN/56/7a SN/64/3 

----------------------------

Lab. No _______________________ D113983 D115110 D115111 D113982 Dl00632 

--------------------------------

Ag ___________ troy oz per ton __ Au ______________________ do ___ _ 

Cu ___________ weight percent__ Pb ______________________ do ___ _ 

Zn ______________________ do ___ _ 

316.1 

3. 57 4. 2 3.40 

3. 2 

142. 62 4. 07 1. 21 2.14 

1.14 

109.89 0. 94 2. 73 . 02 1. 24 .10 1. 81 . 74 1. 40 <.1 

w ______________________ do ___ _ 3 1 . 5 . 7 4 45 As ______________________ do ___ _ . 36 . 41 . 37 . 0090 Mn _____________________ do ___ _ 3.3 3.2 3.3 4.0 P20o-- ____ - _____________ do ___ _ <. 01 ---------- ---------- .12 Total S _________________ do ___ _ 44.3 ---------- ---------- <.1 

Br____________________________ (5) (5) 

CL____________________________ (5) (5) 

Se ______________________ ppm__ <. 5 20 Te ______________________ do____ 15 45 Hg ______________________ ppb __ 1,300 1,200 

(5) 

(5) 

15 

20 1, 000 

. 5 90 

180 

I 0.47 

<.02 

2.01 

2.01 

20 

2.2 

20 

.05 

.02 

.02 

(5) 

(5) 

<.5 

10 

20 

1 Ag determined by atomic absorption by J.D. Mensik and Claude Huffman is 14 ppm, equivalent to 0.41 oz per ton. 2 Semiquantitative spectrographic analysis by Harriet Neiman. a Semiquantitative spectrographic analysis by Nancy Conklin. 4 Equivalent to 57 percent WOa. Residues from analysis contained some huebnerite 

and scheelite. s Not detected. Less than 0.0005 percent or 5 ppm. 

1. Sulfide concentrate collected August 1956 while mill was operating. . . 2. Sulfide concentrate collected September 1964. Represents upper, more oxidized part of small pile of concentrates remaining at southwest corner of mill fl?or after mill was dismantled. Screened to remove contaminants-pebbles, twigs, 

spruce needles. 3. Sulfide concentrate collected September 1964. Represents lower, less oxidized part of the residual pile sampled by 2, above. Screened to rem?ve t!ash. . 4. Huebnerite-scheelite concentrate collected August 1956 while mill was operatmg. 5. Tailings collected September 1964. Represents upper 8 in. of tailings, sampled on 25-ft centers, over entire tailings pile whose diameter was lOQ-150 ft. Screened 

to remove trash. 

Ag and Au determined by fire assay by W. D. Goss and 0. M. Parker (Nos. 1, 4); 

by 0. M. Parker (Nos. 2, 3, 5). As and Cu determined colorimetrically by Ardith Bartel and W. D. Goss (Nos. 

1, 4); by W. D. Goss (Nos. 2, 3). Pb and Zn determined voltimetrically by W. D. Goss and L. F. Rader (Nos. 1, 4); determined by atomic absorption by Claude Huffman, Jr. (Nos. 2, 3): W determined colorimetrically by L. F. Rader (Nos. 2, 3); by G. H. Van Sickle (No.4). Mn and P 20 5 determined volumetrically by W. D. Goss and L. F. Rader (No.4; P 20 5 in No.1); by Christel Parker (No.5) by methods descri~ed by Peck (1964). S determined gravimetrically by L. F. Rader (Nos. 1, 4); by Chnstel Parker (No.5) 

by methods described by Peck (1964). Brand Cl sought by X-ray fluorescence spectroscopy by Polly J. Dunton. Se determined nephelometrically by G. T. Burrow. Te determined by J. B. McHugh by method of Lakin and Thompson (1963). 

Hg determined by vapor absorption by W. W. Janes and J. H. McCarthy. 

ratio of the sulfide concentrates ranges from 35 : 1 to 

88 : 1. This high Ag: Au ratio relates the New Snowbird deposit to the epithermal silver-gold class of Nolan 

(1933, p. 624-625) and Ferguson (1929, p. 134-141), 

but the assortment of mineralogic, fabric, and structural 

features that denotes an epithermal origin for the Nevada deposits is not found at the New Snowbird, which 

is better classed as a xenothermal deposit. 

Polished sections of concentrates and crude ore were 

made in cold-setting plastic mounts cured at room temperature without detectable exothermic reaction. Surfaces were given an adequate polish of low relief by 

intermediate-speed low-pressure hand-lapping with 

diamond abrasives on Pelion. Low relief is essential for 

the detection of native gold and silver in pyrite, and a 

relatively scratch-free surface is helpful for the positive 

identification of acanthite by optical means. Low temperature for curing, grinding, and polishing is a nee-
SILVER-RICH DISSEMINATE·D SULFIDES, CENTRAL IDAHO 03 

TABLE 2.-Semiquantitative spectrographic analyses of concen- trates and tailings, McRae Tungsten Corp. mill 

[Analyses 1-4 by Nancy Conklin; analysis5 by Harriet Neiman. M, major; 0, looked for but not detected; ___ , not looked for. Other results are reported in weight 

percent to the nearest number in the series 1, 0.7, 0.5, 0.3, 0.2, 0.15, 0.1, and so forth; these numbers represent approximate midpoints of group data on a geometric scale. The assigned group for semiquantitative results will include the quantita- tive value about 30 percent of the time] 

3 4 

Field No ____________ SN/56/7b SN/64/1 SN/64/2 SN/56/7a 

Lab. No ____________ D113983 D115110 Dl15111 D113982 

SL __________________ 0.5 0. 7 0. 7 5. AL ______ -- __ - ___ ---- . 2 . 3 .3 2 . 

Fe __ ---------------- M M M M Mg ______________ ---- .015 .007 . 007 .05 Ca __________________ .2 7 .5 M 

Na __________________ 0 0 0 0 

K------------------- 0 0 0 0 TL __________________ 1 1 .1 .3 

p- ------------------ 0 0 0 0 Mn _________________ .3 .2 . 3 7 . 

Ag __________________ 2. 5 .3 .005 

A:s_- ---------------- 7 .5 .5 0 

Au __ ---------------- .02 .05 .005 0 

Ba __ ---------------- . 005 . 01 .01 .07 Be __________________ 0 0 0 .0002 

Bi_ __________________ . 007 .003 .002 0 Cd __________________ . 05 .02 .02 0 Ce __________________ 0 0 0 .07 Co __________________ . 002 . 0015 .0015 .0015 Cr __________________ 0 . 001 .001 .007 

Cu__________________ 5. 2. 2. .15 

Ga __________________ ------------ ------------ ------------ ------------ In_______________________________ 0 0 ___________ _ La __________________ o o o .05 

Mo__________________ <.003 <.01 <.01 <.003 

Nb _________________ _ NL ________________ _ 

Fib ______________ ---- Sb _________________ _ Sc __________________ _ 

Sn _________________ _ Sr __________________ _ v __________________ _ w __________________ _ 

y __________________ _ 

Yb _________________ _ Zn _________________ _ Zr __________________ _ 

.005 

. 0015 

5. 

.3 

0 

0 

.002 

0 

1. 

0 

0 

5. 

0 

0 

.0015 

2. 

.07 

0 

. 005 0 

3. 

0 

0 

1.5 

0 

0 

. 001 1.5 

.07 

0 

. 005 0 

2. 

0 

0 

1.5 

0 

.07 

.001> 

1. 

0 

.01 

0 

.3 

. 015 M 

. 015 

.002 

0 

. 03 

SN/64/3 

D100632 

0. 001 0 

0 

. 03 

.0002 

0 

0 

0 

0 

0 

0 

0 

. 0003 

. 01 

.0007 

.003 

0 

. 01 0 

0 

0 

.005 

. 001 

.2 

0 

0 

o· 

. 005 

l No~E.-Mi~or elements looked fo_r, but found to be below the limits of spectrogfaphtc detectwn: B, Ge, Hf, Hg, L1, Pd, Pt, Re, Ta, Te, Th, Tl, U. 

1. Sulfide concentrate collected August 1956 while mill was operating. 2. Sulfide concentrate collected September 1964. Represents upper, more oxidized part of small pile of concentrates remaining at southwest corner of mill floor after mill was dismantled. Screened to remove contaminants-pebbles, twigs, spruce needles. 3. Sulfide concentrate collected September 1964. Represents lower, less oxidized part of the residual pile sampled by 2, above. Screened to remove trash. 4. Huebnerite-scheelite concentrate collected August 1956 while mill was operating. 5. Tailings collected September 1964. Represents upper 8 in. of tailings, sampled on 25-ft centers, over entire tailings pile whose diameter was 10Q-150 ft. Screened to remove trash. 

essary precaution against artifically inducing phase 

transformations in certain sulfides. 

Samples used for electron-probe analysis were coated 

with a thin film of eva ported carbon to make the sample 

surface electrically conducting. This procedure is particularly important when analyzing disaggregated 

grains mounted in a nonconducting plastic. For some 

minerals, the carbon coating enhances the visual contrast between different phases, but for others it obscures 

the contrast and makes the recognition of a desired grain 

quite difficult. By confining the electron probe work 

to qualitative and semiquantitative analysis, we were 

able to obtain information on a large number of phases. 

TABLE 3 .-Semiquantitative spectrographic analyses of handpicked 

mineral fractions of sulfide concentrates, McRae Tungsten 

Corp. mill 

[Nancy Conklin, analyst. M, major; 0, looked for but not detected; ____ ,not looked for. Other results are reported in weight percent to the nearest number in the series 1, 0.7, 0.5, 0.3, 0.2, 0.15, 0.1, and so forth; these numbers represent approxi- mate midpoints of group data on a geometric scale. The assigned group for semi- quantitative results will include the quantitative value about 30 percent of the time] 

2 3 4 

Field No _____________ SN/56/7b.1 SN/56/7b.2 SN/56/7b.3 SN/56/7b.4 

------ Lab. No _____________ D113984 D113985 D113986 D113987 

Si _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ________ _ 

AL____________ 0. 5 0. 2 <O. 007 0. 1 

Fe____________ M M 10 M 

Mg____________ .005 . 005 .0015 .005 

Ca____________ . 07 . 05 . 07 . 05 

Na __________ _ 

K ------------ Ti ___ ----- ____ _ p ____________ _ 

Mn __________ _ 

Agl ___________ _ As ___________ _ 

Au ___________ _ Ba ___________ _ Bi ____________ _ 

0 

0 

. 05 

0 

. 03 

. 10 

1. 

. 005 

. 005 

0 

0 

0 

. 07 

0 

. 0015 

. 24 

.7 

. 005 

. 003 

. 003 

Cd_ _ _ _ _ _ _ _ _ _ _ _ o . 01 

Co____________ . 002 . 0015 

Cu_ _ _ _ _ _ _ _ _ _ _ _ . 3 M 

Ga _________________ ~ _____________ _ 

Mo____________ <. 003 <· 003 

Nb ___________ _ Ni ___________ _ Pb ___________ _ Sb ___________ _ Sn ___________ _ 

w ------------- Zn ___________ _ 

0 

. 001 

. 15 

0 

0 

. 15 

.3 

1 Quantitative spectrographic analysis. 

. 002 

. 001 

1.5 

. 02 

0 

.2 

1.5 

---------- ---------- 0 0 . 01 . 05 

0 0 

2. . 5 

2.4 >3.8 

0 0 

<. 005 . 005 . 0015 . 01 . 03 . 15 

>.46 .5 

0 0 

>4.6 M 

0 0 

<. 0015 <. 0015 

0 . 002 . 0007 . 0007 

M M 

5 . . 3 

0 . 002 

. 1 . 07 

M M 

NOTE.-Minor elements looked for, but found to be below the limits of spectrographic detection: B, Be, Ce, Cr, Ge, Hf, Hg, La, Li, Pd, Pt, Re, Sc, Sr, Ta, Te, 

Th, Tl, U, V, Y, Yb, Zr. Not looked for: In. 

1. "Pyrite." Contaminated by inclusions of arsenopyrite, etc. 2. "Chalcopyrite." Contaminated by inclusions and by locked grains, especially 

pyrite. 3. "Sphalerite." Contaminated by inclusions and by foreign grains, especially 

argentian tetrahedrite. 4. "Tetrahedrite." Mainly acanthite-rimmed grains of chalcopyrite, copper sulfides, galena, and sphalerite. 

However, doing this largely qualitative work required 

some sacrifice of analytical sensitivity. The electron 

probe should not be considered an instrument which 

can detect hundredths of a percent or less of an element 

but rather an instrument which can detect major elements present in areas of micron size. To obtain maximum sensitivity, which varies with the sample being 

studied, one must have both a good set of standards 

and an electron probe set up specifically for the elements 

of interest. Qualitative analysis has neither of these requirements. In this study, we shall consider that the cutoff point for elements reported as "not detected" is about 

1 percent. 
C4 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

TABLE 4.-Approximate mineralogic composition of sulfide fraction 

of sulfide concentrates, McRae Tungsten Corp. mill 1 

Pyrite _________________ ---------- Arsenopyrite _____________________ } Chalcopyrite _____________________ Digenite 6 ________________________ 

Sphalerite ________________________ Galena ___________________________ Acanthite ________________________ 

'.rotaL _____________________ 

Volume 

percent 

(mode)2 

76.5 

10.1 

2.8 

6.1 

2.8 

1.7 

100.0 

Weight percent 

Calculated Calculated Calculated 

from mode from chem- from chemical ical 

analysis 3 analysis 4 

77.8 76.66 77.73 

.84 .84 

8. 6 13.86 12.20 

2.4 1. 07 1. 62 

5.1 3.44 3.46 

3.8 2.80 2. 81 

2. 3 1. 33 1.34 

100.0 100.00 100.00 

I Sample SN /56/7b. Sulfide fraction makes up 97.8 volume percent of the sulfide concentrate. Remainder is huebnerite and gangue. 

2 Number of points counted (179) is too small, owing to coarse "jumps" on the 

available counter. Only the major minerals are listed. 3 Assumptions: AllAg isinacanthite; all As is in arsenopyrite; 80percent of total Cu 

is in chalcopyrite, 20 percent in digenite; total Fe, not determined in the analysis, is adequate to satisfy total S in pyrite after other sulfides have been calculated. 4 Assumptions: Same as (3), except 70 percent of total Cu is in chalcopyrite, 30 

percent in digenite. 5 Blaubleibender covellite is seen more often, but digenite probably has the greater bulk. 

Qualitative analyses were made by comparing the 

spectrometer traces of unknown minerals with the traces 

produced by reference minerals, and by displaying the 

X-ray pulses on an oscilloscope screen on which one can 

see the distribution of elements of interest in areas 

whose size ranges from a maxilnum of about 360 microns 

square down to a minimum of about 1 micron diameter 

(pis. 1, 2). Semiquantitative analyses were made for selected elements, such as silver in tetrahedrite. The limiting size of grains suitabie for semiquantitative analysis 

is 1-3 microns. All analyses were carried out with an 

accelerating voltage of 25 kilovolts and a specimen current of approximately 0.01 microampere. 

Cynthia Mead carried out the electron microprobe 

analyses of the ore minerals. Nancy Conklin made most 

of the semiquantitative spectrographic analyses. Mrs. 

Conklin's analyses first indicated the remarkable concentration of precious metals in the sulfide concentrates 

and led to the present chemical and mineralogic study. 

X-ray diffraction data not credited to Fred A. Hildebrand, Shirley K. Mosburg, or T. Botinelly are those 

of Leonard, who is responsible for the study as a whole. 

LOCATION AND OPERATION 

The New Snowbird deposit is 4.75 miles northwest of 

Big Creek settlement, Valley County, Idaho, and 1.2 

miles northeast of Elk Summit, in the northwest corner 

of the central ninth of the Big Creek 15-minute quadrangle. (See fig. 1.) The deposit is reached from Big 

Creek settlement either by the Warren road and Fawn 

Meadow cutoff or by the Smith Creek road, routes best 

traveled by four-wheel-drive vehicle. The deposit is on 

the Tungsten claim of the Snowbird group of seven unpatented mining claims, Big Creek mining district. 

The McRae Tungsten Corp. mined the deposit from 

115" 30' 

~p LOCATION 

0 5 10 MILES 

FIGURE 1.-Index map of parts of Big Creek and Yellow Pine 

districts, Idaho. 

1954 to 1957, producing high-grade and low-grade huebnerite-scheelite concentrates whose value exceeded $90,-

000. Ore was crushed to 1-inch size, ground to -20 mesh 

(0.833 mm), classified hydraulically, and separated by 

tabling supplemented by froth flotation. Sulfides were 

floated from the huebnerite-scheelite concentrate. The 

operation was abandoned when removal of the subsidy 

for domestic tungsten concentrates caused the price to 

be halved. 

GEOLOGY 

-The New Snowbird deposit is near the north end of 

a major system of silicified zones, near the heart of the 

Idaho batholith. In the Big Creek area, the silicified 

zones accompany the Profile-Smith Creek dike swarm. 

(See Shenon and Ross, 1936, fig. 3; Leonard, 1965, p. 

B24.) Within the swarm, elongate lenticular relics of 

granitic rock, locally silicified, alternate with dikes and 

small stocks of Miocene ( ? ) granite porphyry and related rock. The silicified zones at this latitude are in my-
SILVER-RICH DISSEMINATED SULFIDES, CENTRAL IDAHO C5 

lonitized, sheared, and brecciated felsic granodiorite, 

alaskite, and aplite of the batholith. Slab'by inclusions 

of metasedimentary rock are sparse and considerably 

argillized. The whole system of silicified zones is more 

than 18 miles long and a few hundred feet to several 

thousand feet wide. It forms a composite, sheared, 

crackled, and block-faulted unit in which lenticular 

quartz veins, groups of contiguous veins, and sporadic 

stockworks alternate with bodies of host rock that contain little or no introduced quartz. Individual quartz 

bodies range from veinlets a fraction of an inch wide 

and a few inches long to lodes and masses several hundred feet wide and 1nore than a thousand feet long. 

Groups of quartz bodies of various shapes and dimenstons constitute the silicified zones of the area. The 

q~artz concentrations are partly fissure fillings and 

stockworks but mostly replacement bodies showing 

evidence of repeated deformation and reintroduction 

of quartz. 

The quartz-rich intensely silicified zone at the New 

Snowbird mine is a southward-tapering mass that is 

shielded from the flanking dikes by a n31rrow envelope 

of partly silicified granitic rock. In most places the 

quartz-rich zone is little more than 100 feet wide. Five 

hundred feet south of the southernmost workings, the 

zpne narrows to 2 feet and ends abruptly against the 

granite envelope, which pinches out between dikes less 

·than 200 feet f31rther south. This quartz-rich zone is 

the most conspicuous of several subparallel zones, 15-

150 feet wide and smne hundreds of feet long, each isolated fr01n its neighbor by one or more dikes. North 

of the mine, the continuity of the complex of dikes and 

silicified zones is disrupted by the concealed Elk Creek-

~iddle Fork Smith Creek fault. 

The western (hanging-wall) dike at ~the mine is a 

brown-weathering gray-green quartz-bearing latite. Its 

outci"op width is 90 feet. Phenocrysts of hornblende and 

plagioclase are abundant; those of biotite, K-feldspar, 

and magnetite are sparse ; those of quaPtz, apatite, and 

zircon are very sparse and small. The groundmass is 

mainly turbid alkali feldspar accompanied by some 

chlorite, sparse quartz and biotite, and sporadic apatite. 

At the south end of the silicified zone, the western dike 

is almost devoid of 1nafic minerals. The eastern dike is 

pale greenish-gray rhyol:iote, weathering pink. It is 15 

feet wide. Phenocrysts-quartz, sanidine (dominant), 

sodic plagioclase, and biotite (mostly altered to chlorite 

and leucoxene )-are rather abundant. The equant, embayed phenocrysts of high-temperature quartz are 

mantled by spherulitic aggregates of alkali feldspar. 

Except for a little apatite, zircon, and limonitized pyrite, the minerals of the granular groundmass are the 

same as the phenocryst minerals. The feldspars are tur- 1 . 

I 270-675 0-6S-2 

bid and locally flecked with a little calcite and micaceous stuff. The composition, fabric, and extent of 

alteration of these dikes vary slightly from specimen 

to specimen, but in general the dikes look fresh and 

are representative of the two principal varieties found 

in this and other dike swarms of the region. 

The age relations between the local dikes and the silicified zone are indeterminate. At the Red Bluffs deposit 

nearby, angular inclusions of sheared, schistose, silicified but unmetallized alaskite gneiss are present in a 

rhyolite dike. Shearing and granulation occurred after 

silicification of the granoblastic gneiss but before 

emplacement of the unsheared, unaltered dike. It is 

reasonable to suppose that a similar sequence of events 

took place at the New Snowbird. How metallization 

relates t!() these events is debrutable. At both deposits, 

undeformed hue!bnerite crystals are studded throughout nonschistose, unsheared but locally crackled quartz 

that replaces older sheared silicified gneiss. Inclusions 

of this younger quartz (which represents several generations geometrically, if not genetically) have not been 

found in dikes of the region. This relation suggeslts 

that the dikes are older than some relatively coarse, 

unsheared quartz, but the ·two might be roughly contemporaneous. A few scheelite specks were found in a 

thin hanging-wall dike at the New Snowbird (R. J. 

McRae, oral commun., 1956), but whether these were 

inclusions, accessory grains, or replacements was indeterminate. Disseminated pyrite is common in many 

dikes of the region; it seems generally ·to be a primary 

accessory mineral, but its origin in some dikes is debatable. We believe that the weight of evidence favors the 

introduction of sqme quartz, all the local tungsten minerals, and at leagt some sulfides ·a:flter the emplacement 

of dikes that cut older silicified zones. Metallization is 

not predike, but it might be either contemporaneous or 

younger. If the dikes are older than the ore, then a local 

flattening of the regionally prevailing vertical dip of 

the western dike at the New Snowbird may have provided a structural trap for the ascending ore solutions; 

but, as the foregoing account indicates, the dike itself 

is not everywhere the hanging wall of the ore body. 

Thus the genetic c01mection of dikes and ore is as uncertain here as in many other districts. 

ORE DEPOSIT 

Tungsten ore was mined from a somewhat irregular, 

crudely tabular lode striking N. 25° E. and dipping 

70° W. The footwall of the ore body was partly silicified 

granitic rock. Locally a selvage of similar material, 

roughly 5 feet thick, made the hanging wall; locally 

the hanging wall was the quartz-bearing latite dike. The 

ore body was 150-170 feet long and generally 4--7 feet 
C6 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

thick. It consisted of a northern, higher grade segment 

and a southern, lower grade segment; possibly these 

reflect a crude shoot structure that rakes nearly vertically. Within the segments, scheelite and huebnerite 

were irregularly distribut~d, but details of this smallscale variation are not known. The ore body was cut by 

minor faults of north or north-northeast strike and 

seemingly slight displacement. The relation between the 

main body (McRae vein) and an East' vein was not 

determined during exploration of the deposit. Regardless of the possible identity of the veins, they 1nay belong to adjacent blocks separated by a north (?)-striking 

normal fault. 

The tungsten ore was of low grade. Only a small 

part of the explored body contained ore averaging more 

than 1 percent W03 (Defense Minerals Exploration 

Admin. field team, unpub. data). Ore mined in 1956, 

the last year of 1najor operation, averaged 0.65 weight 

percent W03 (U.S. Bur. Mines, 1956, p. 389). 

The quantity of disseminated sulfides in the ore was 

not of interest to the operator and 'vas never determined. From published and unpublished production 

data we estimate that it was roughly 0.075-0.2 weight 

percent. The value 0.1 weight percent is a usable approximation. Probably the sulfides were more widely 

distributed than the tungsten minerals within the silicified zone, for this is a usual pattern in the district. However, the details for the New Snowbird deposit are 

unknown. 

MINERALOGY AND PARAGENETIC SEQUENCE 

The 1ninerals of the deposit are divisible into four 

suites : gangue, tungsten minerals, sulfides and related 

minerals, and alteration products. This listing represents, with minor exceptions, the order of deposition 

of the suites. A description of representative ore precedes the discussion of the suites and their complex 

relations. 

TYPICAL ORE 

Typical tungsten ore consists of massive milky quartz 

with sporadic subhedral prisms of huebnerite, small 

patches of scheelite, and very sparse specks of sulfides. 

The quartz is fine to medium grained, greasy in luster, 

and devoid of vugs except where the sulfide specks have 

weathered from it. The dark-brown huebnerite crystals 

are mostly less than 1 em long. Scheelite, looking flesh 

colored against the quartz, appears in ultraviolet light 

as brilliant bluish-white patches a few millimeters long, 

as trains of minute specks, and as threadlike discontinuous veinlets. Irregular joints are slightly iron 

stained and locally coated with specks and dendrites of 

black manganese oxides. Some specimens show small 

areas of buff clay minerals. With a hand lens, a few additional constituents can be seen : muscovite as small 

flakes and patches; blue-green copper ( ? ) minerals as 

granules surrounding specks of limonite and cuprite ( ? ) ; pyrite, chalcopyrite, and sooty sulfides as 

minute specks; jarosite(?) as a few small patches. The 

sulfides are so sparse that one seldom sees more than a 

few specks in a fist-size piece of ore. 

Thin sections add little to know ledge of the ore's mineralogy, but they do reveal its remarkable fabric. 

Three kinds of quartz are present: 

1. Medium grained (1-3 mm, locally coarser) anhedral 

to subhedral, mottled at average extinction for a given 

"individual," turbid from an abundance of fluid inclusions, locally twinned, rarely zoned; most abundant 

and oldest. 

2. Variably grained, inclusion-poor, as narrow replacement veinlets cutting quartz 1 and one another, the 

individuals always in optical continuity with their 

host grains; least abundant and seemingly of intermediate age. 

3. Fine grained ( 0.02-0.1 mm, locally much finer), 

anhedral or rarely subhedral, inclusion-poor, as replacement and dilation veinlets in quartz 1 and 2, and 

perhaps in small part as narrow granulation zones in 

quartz 1; common, seemingly youngest, rarely containing a trace of K-feldspar. 

H uebnerite, subhedral to euhedral, locally showing 

darker cores, is mostly confined to medium-grained 

quartz. Scheelite, anhedral to subhedral, is mostly disseminated through fine-grained quartz or present as thin 

veinlets collinear with those of fine quartz. Some scheelite veinlets cut across fine quartz veinlets, and some 

corurser soheelite is found in medium-grained quartz. 

Scheelite locally replaces huebnerite, rimming and veining the host and forming a cleavage-controlled lattice 

within it. Some of this "scheelite" may be stolzite, but 

the distinction cannot be made optically on these finegrained products. Rarely, huebnerite contains small 

round inclusions of scheelite. Sulfides-identifiable in 

thin section only as pyrite cubes and black granules, 

each rimmed by limonite-seem not to show a preference 

among the quartz vrurieties, though the larger pyrite 

crystals are oonfined to ~the coarser qua.rtz. 
SILVER-RICH DISSEMINATED SULFIDES, CENTRAL IDAHO C7 

Limonite locally replaces a little scheelite, huebnerite, 

and clay minerals, as well as sulfides. 

Chlorite, nontronite(?), K-feldspar, malachite(?), 

and another blue-green secondary mineral (possibly a 

copper phosphate or arsenate) ar£' very sparingly 

present. 

Fluorite was not found in thin sections, but a colorless 

variety is present in tungsten concentrates and in the 

heavy-mineral fraction of tailings. Pale-green and 

purple fluorite are sparse in the mill products. 

GANGUE INDICATED BY MILL PRODUCTS 

The tailings pile provides a sample of gangue unequaled for displaying the contents of a silicified z;one 

of the New Snowbird type. Bec.ause the ore was of relatively low grade, the tailings are a large proportion of 

the material1nilled and consequently are rather closely 

representative of the whole ore body. Our study of the 

tailings is only semiquantitative (table 5, ool. 1). It 

TABLE 5.-Minerals of the New Snowbird deposit 

[Arrangement within suites is alphabetical. Minerals forming >1 percent of each 

suite are starred] 

Apatite 

!Biotite 

'1Calcite 

Chlorite 1 

Gangue 

Clay minerals 1 

Epidote 

*Fluorite 

Hornblende 

K-feldspar 

*Muscovite 

Plagioclase 

*Quartz 

Unidentified minerals 

Tungsten minerals 

*Huebnerite 

*Scheelite 

Stolzite 

Others? 1 

Sulfides and related minerals 

*Acanthite 

Aramayoi te ( ?) 

Arsenopyrite 

B la ublei bender covelli te 

.Bornite 

Chalcocite 

*Chalcopyrite 

Covellite 

Diaphorite(?) 

1 Alteration products. 

*Digenite 

*Galena 

Gold 

Hessite 

ldaite(?) 

Ilmenite(?) 

Marcasite 

Miargyrite(?) 

Polybasite(?) 

*Pyrite 

Pyrrhotite 

Silberkies(?) group 

Silver 

*Sphalerite 

Tetrahedrite 

Unidentified minerals 2 

Alteration products 

Anglesite(?) 

Bianchite(?~ 

Cerargyrite 

Cerussite 

Chlorite 

*Clay minerals 

Cuprite(?) 

*Goethite 

Jarosite group 

Malachite(?) 

Psilomelane 

Pyrolusite 

Tenorite 

Tungsten alteration products 

Unidentified minerals a 

2 Principal ones are soft white mineral and green-orange unknown. 3 Possibly hydrated sulfates and arsenates. 

shows that the body was 1nore complex than one would 

infer from field study and examination of a modest 

number of thin sections, but the difference is slight. It 

lies mainly in the presence of accessory phosphates 

(apatite and perhaps others) and a few accidental minerals probably derived from small horses of wallrock. 

Barite, tourmaline, and topaz-minerals that might be 

expected in a tungsten deposit within a quartz lode-are 

absent.· A few of the constituents are discussed below. 

Accidental constituents.-Biotite, muscovite, quartz, 

K-feldspar, sodic plagioclase, and accessory apatite and 

zircon are components of sheared granoblastic alaskite 

gneiss th31t occurs as relics within the New Snowbird 

and nearby silicified zones. Small bodies of gneiss, intimately associated with ore, may have been mined and 

milled here, and part of the mineral assemblage noted 

in table 5 may thus be extraneous t.o the quartz veins. 

However, most of the qua,rtz, muscovite, and apatite and 

some of the I{-feldspar probably belong to the suite of 

vein minerals proper. 

K-feldspar, which is slightly less than 1 percent of 

the tailings, was investigated on the supposition that it 

might be adularia. It is not. Both !{-feldspar from the 

tailings and K-feldspar from a granite gneiss inclusion 

at the neighboring Red Bluffs deposit are intermediate 

mioroclines, but their X-ray-diffraction powder patterns 

are not identical : the New Snowbird microcline has a 

triclinicity of 0.4; the Red Bluffs microcline has a triclinicity of 0.1. The triclinicity would be zero for monoclinic feldspar, such as orthoclase, and unity for a most 

highly triclinic microcline. These measurements of 

degree of symmetry, based on the method of Goldsmith 

and Laves (1954, p. 3-5), suggest that K-feldspa.r of the 

New Snowbird deposit may originally have been xenocrystic, and that it has been partly recrystallized by the 

veinforming solutions, becoming more nearly monoclinic and thus more like the adularian K-feldspars 

found in many veins. A study of other minerals that 

may have been reworked, such as hornblende, is beyond 

the scope of this report. 

Apatite.-This is a oommon fluorapatite, but its 

sharply euhedral habit and abundance exceeding that 

common to alaskite gneiss of the area strongly suggest 

that it was brought in or a:t least concentrated by the 

quartz-depositing ore fluids. 

The presence of at least one additional phosphate as 

a rare primary ( ? ) accessory is suspected from optical 

data. However, the impossibility of handpicking the 
08 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

minute grains for X-ray or chemical confirmation 

leaves the species in doubt. 

Clay minerals are discussed subsequently as alteration 

products. 

A chemical analysis of the tailings (table 6) confirms 

the results of the mineralogic stu die.:;. The gangue of the 

ore body wa;s chemically as well as mineralogically 

simple, consisting mainly of quartz with a little muscovite, fluorite, K-feldspar, clay 1ninerals, phosphates, 

and accidental constituents. In more densely settled 

parts of the country, mill tailings of this sort have been 

marketed for use as roofing granules, poultry grit, and 

concrete aggregate. 

TUNGSTEN MINERALS 

The chief tungsten mineral of the deposit is huebnerite, ranging in color from dark red through dark reddish brown and very dark brown to brownish black. 

Most of the huebnerite contains about 86 mole percent 

Mn W04 • In the laboratory, it is recoverable at 0.5 amp 

on a F1rantz 1nagnetic separator. Other and less 

abundant InagneJtic fractions, recoverable at 0.2-0.9 

amp, range in composition from about 84 to 88 mole 

percent Mn W04 • Successive magnetic fractions differ 

little in appearance, presumably because the color of individual grains depends more on their thickness than 

on their chemical composition. The estimates of composition were made on representative -150 and + 200 

mesh fractions by X-ray powder diffraction according 

to the peak difference method of Sasaki (1959, p. 386-

388, 391), to which he ascribed an accuracy of +6 mole 

percent. 

TABLE 6.-Chem1'cal analysis of tailings, McRae Tungsten Corp. 

mill 

[Christel L. Parker, analyst. Field No. SN-64--3, Lab. No. D 100632. Tailings collected 

Septewber 1964. Represents upper 8 in. of tailings, sampled on 25-ft centers, over entire tailings pile whose diameter was 100-150 ft. Screened to remove trash. 

For semiquantitative spectrographic analysis, see table 2] 

Con8tituent 

Si02-------------------------------

Al20a------------------------------

Fe20a------------------------------ Fe0 ______________________________ _ ~gO _____________________________ _ CaO ______________________________ _ 

~a20 _____________________________ _ ]{20 ______________________________ _ 

H20 + ---- _- _---------------------- H20- ____________________________ _ 

Ti02------------------------------

P20s------------------------------

~no _____________________________ _ C02-- ____________________________ _ Cl _______________________________ _ F ________________________________ _ s ________________________________ _ 

Weight 

percent 

90.49 

4. 03 

. 95 

. 16 

. 13 

. 54 

. 24 

1. 97 

. 56 

. 12 

. 08 

. 02 

. 07 

. 01 

. 01 

. 34 

. 02 

SubtotaL____________________ 99. 7 4 

Less 0 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . 14 

TotaL _______________________ 99. 60 

Scheelite is roughly half as abundant as huebnerite 

in the mill concentrates. Its low molybdenum content, 

indicated by bluish-white fluorescence in short-wave 

ultraviolet light, is borne out by spectrographic analysis 

(table 2, No. 4) . The difficulty of getting pure fractions 

of huebnerite and scheelite by the usual laboratory separation techniques makes detailed chemical or spectrochemical analysis of these minerals infeasible at present. 

Stolzite, tetra.gonal Ph W04 , is sparingly present. It 

is buff to pale brown, fine gra.ined to exceedingly fine 

grained, and virtually indistinguishable from slightly 

brownish scheelite. It is identifiable, even in scheeliterich mixtures, by its principal reflections in X-ray powder diffractograms : 3.24, 100; 2.72, 28; 2.02, 28; 1.776, 

12; 1.653, 24 (dis in angstroms, I is relative intensity; 

for comparative data, see Berry and Thompson, 1962, 

p. 228) . Because these reflections are close to those of 

wulfenite, PbMo04 , one X-rayed scheelite-stolzite mixture was qualitatively analyzed by X-ray fluorescence by 

J. S. Wahlberg, who found Ph and W to be major constituents and Mo to be absent; Ca was not sought (J. S. 

Wahlberg, oral commun., 1966) . Stolzite, rather than 

wulfenite, is therefore present in the mixture. Stolzite 

is rela.tively abundant in the clay-size fraction separated 

by ultrasonic cleaning of tungsten concentrates and tailings, though some stolzite is also present in cleaned sandsize concentrates. Stolzite accounts for all or most of 

the Ph in tungsten· concentrates and tailings (ta.ble 1, 

Nos. 4 and 5) , both of which contain little S. Since Ph 

is disproportionately higher in the tailings, it seems 

that a fair part of the tungsten lost in the tailings was 

in extremely fine grained stolzite. 

Other tungsten minerals ma.y be sparingly present as 

clay-size altera;tion products mixed with true clays. (See 

section on "Alteration Products.'') 

SULFIDES AND RELATED MINERALS 

The sulfides, sulfosalts, and native metals are a complex suite, genetically divisible into three groups or 

stages: (1) ea,rly sulfides-pyrite and its included ore 

minerals; (2) intermediate sulfides and sulfosalts with 

inclusions of native silver-minerals that, excepting 

relatives of the ruby silver minerals, do not almost exclusively form crusts-and (3) late sulfides that form 

conspicuous crusts. For descriptive purposes, this threefold division is unmanageable, owing to the occurrence 

of some species in several stages. Therefore, we shall 

describe the main minerals in order of abundance (table 

4) and their associates in alphabetical order. ·we ha.ve 

tried to present enough information on ea.ch species to 

support our interpretation of the fabric of the whole 

assemblage and to permit other workers to construct 

alternative schemes if they wish. 
SILVER-RICH DISSEMINATED SULFIDES, CENTRAL IDAHO C9 

The chemical composition of smne less common minerals is shown by formulas taken from Hey (1955), unless another source is cited. Optical properties are listed 

only for species whose identification here is doubtful. 

The term "discrete grains" denotes grains that do not 

occur as inclusions. Such grains ma.y, however, be locked 

or composite. 

Pyrite, the most abundant sulfide in the deposit, is 

almost a microcosm of the sulfide assemblage. It contains as inclusions nearly all the sulfides and sulfosalts 

that subsequently crystallized as discrete grains, as well 

as eight or nine species not found elsewhere in the 

assemblage. These included minerals are listed in table 

7 and individually described elsewhere in this section. 

Some pyrite grains show no inclusions, and some contain only arsenopyrite, pyrrhotite, or chalcopyrite, but 

many of them contain a mixed assemblage of several 

sulfides with or without native gold, native silver, and 

gangue minerals (pis. 2, 3, 4A). Pyrite contains, in the 

form of mineral inclusions, all the elemental gold, a 

substantial part of the elemental silver, and much of 

the elemental arsenic found in the sulfide concentrates. 

Pyrite is partly replaced by several of the intermediate 

and youngest sulfides. Pyrite has not been found as inelusion~ in any other mineral unless it is an obvious relic, 

~s in some grains of chalcopyrite and goethite. Thus it 

seems to have formed first among the sulfides. Its age 

relations with the tungsten minerals are seldom determinable, though pyrite is the sulfide most often found 

in contact with these minerals. In one place, an irregular 

pyrite grain partly replaces the margin of a zoned 

huebnerite crystal; in another, pyrite envelopes quartz 

gangue that contains euhedral scheelite; in most places 

pyrite is molded on euhedral scheelite. 

Semiquantitative microprobe analysis of the pyrite 

shows only the major elements Fe and S. If other elements are present in the pyrite lattice, they are below 

the limits of detection. Presumably the Co and Ni reported in nearly the same low concentration in spectrographic analyses of sulfide concentrates (table 2, 

Nos. 1, 2, 3) and of the handpicked pyrite fraction 

(table 3, No. 1) is accommodated in the pyrite lattice, 

or in pyrite plus chalcopyrite (table 3, No. 2). Alternatively, the Co and Ni might be concentrated in 

minute stray inclusions of minerals such as cobaltian 

loelljngite and skutterudite, which could easily go undetected among the arsenopyrite inclusions in pyrite. 

However, we have looked for these optically and by 

microprobe hut have not found them. 

Chalcopyrite is the most abundant base-metal sulfide 

in the concentrates (table 4) . Most of it is present 

as discrete grains, badly pitted in polished section, containing sporadic inclusions of sphalerite and galena. 

Small chalcopyrite blebs are common in pyrite, very 

abundant in most sphalerite, and sparse in galena and 

tetrahedrite. Chalcopyrite is molded on some scheelite 

grains and partly replaces others, but the two minerals 

are seldom seen in contact. Stubby veinlets of chalcopyrite penetrate pyrite. Rarely, chalcopyrite almost 

wholly replaces pyrite, leaving relics of chalcopyrite, 

arsenopyrite, and marcasite. The contacts of chalcopyrite with other base-metal sulfides and sulfosalts are 

discussed in the section on "Paragenetic Sequence." 

The discrete grains of chalcopyrite show a slightly 

anomalous rose tint, suggesting that the mineral might 

represent the cubic, high-temperature form recently 

described by Bud'ko and Kulagov (1963) and by Genkin 

and others (1966). To check this possibility, powder 

was drilled from three homogeneous grains and X-rayed 

by T. Botinelly. Powder photographs of samples from 

two grains showed the diagnostic 024 reflection of the 

common tetragonal form; the third photograph was 

unusable because the powder sample was too small. 

Thus both X-ray diffraction and electron microprobe 

analysis (see below) point to ordinary chalcopyrite as 

the form present here. 

Semiquantitative electron microprobe analysis shows 

Cu, Fe, and S as major constitutents of the discrete 

chalcopyrite grains. No concentration of Ag or Au 

within the chalcopyrite lattice was detectable. Relict 

chalcopyrite blebs in pyrite are, under the ore microscope, slightly greener than chalcopyrite that was introduced as veinlets and replacement bodies, but we 

were unable to make a microprobe comparison of the 

two varieties. 

Sphalerite is the second most abundant base-metal 

sulfide. Most of it is present as discrete grains, and 

most of these contain abundant inclusions of chalcopyrite-so many, indeed, that the uncorrected modal 

value of sphalerite (table 4) becomes too high for the 

quantity of Zn determined chemically. Acanthite (inverted from argentite), galena, and native silver are 

very sparingly present as inclusions. A few sphalerite 

grains contain no inclusions. A little chalcopyritebearing sphalerite occurs as small round inclusions in 

pyrite, chalcopyrite, galena, and tetrahedrite. 

Semiquantitative microprobe analysis of several 

sphalerite grains shows major Zn and S, and minor but 

appreciable amounts of Fe. Silver, Cu, Mn, and Sb are 

undetectable. Cadmium, if present, is distinctly minor. 

This relation differs from one previously inferred from 

semiquantitative spectrographic analyses of sulfide 

concentrates and hand-picked fractions (table 2, Nos. 

1, 2, 3 ; table 3, Nos. 3, 4) . Those analyses show a Cd -Zn 

ratio of 0.01-0.013 in the concentrates and a similar 

or perhaps higher ratio in the hand-picked mixtures. 
ClO SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

Either the microprobe analysis o:f sphalerite grains :for 

Cd was relatively insensitive, or some discrete but still 

unfound Cd mineral is present in the concentrates, or 

Cd is bound to some element other than Zn. The first 

possibility seems most likely. 

Microprobe analysis o:f inclusion-free sphalerite 

grains shows roughly the same Fe content in them as 

in the host o:f the chalcopyrite-rich grains. This relation suggests that low-temperature, Fe-poor sphalerite 

is either sparse or absent from the assemblage. 

Galena makes up several percent o:f the sulfide concentrates (table 4). Most o:f it is present as discrete 

grains, commonly rimmed by later sulfides (pl. 1A). 

A little is present as round inclusions in pyrite, 

sphalerite, chalcopyrite, and tetrahedrite, and as ra,re 

replacement veinlets in pyrite. Discrete grains o:f galena 

infrequently contain sparse round inclusions o:f sphalerite, chalcopyrite, and tetrahedrite, and 1ninute subhedral inclusions o:f acanthite ( ? ) , aramayoite ( ? ) , 

native silver (rare), and unidentifiable sulfosalts (?). 

Semiquantitative mieroprobe analysis of several galena 

grains yields only the major elements Ph and S, and 

confirms the optical identification o:f galena inclusions 

in other sulfides. 

Digenite, cubic Cul.SS (Djurle, 1958) or Cu9 _a:S5 

(Morimoto and ICullerud, 1963), seems to be the most 

abundant copper sulfide in the concentrates, though it 

is less conspicuous and less :frequent than the covellites. 

Much o:f the digenite occurs as discrete, equant grains, 

commonly rin1med by still younger sulfides, but some 

digenite replaces pyrite, sphalerite, galena, and acanthite. Digenite does not form crusts on older sulfides, 

but it may be encrusted by younger ones. (See section 

on "Paragenetic Sequence.") Either bornite or idaite(?) 

is very sparingly present as an extremely fine grained 

intergrowth with digenite, generally near the borders 

o:f the digenite grains, but bornite and idaite(?) have 

not been :found together within the digenite host. 

Rarely, a bit o:f chalcocite is intergrown with digenite. 

Semiquantitative electron microprobe analysis o:f several digenite grains shows Cu and S to be major eleInents in all grains, Fe minor in some grains, and Te 

slightly above background in one grain. Silver is sparingly present in some grains. Gold, Bi, Sn, Zn, and 

probably Se too, are absent. Possibly Fe is due to bornite 

as extremely fine intergrowths, though the analyzed 

digenite grains looked homogeneous at very high 

1nagnification. 

Acanthite, monoclinic Ag2S, is the most abundant 

silver 1nineral in the sulfide concentrates. Typically it 

occurs as ragged replacement rims on galena (pl. 1A). 

These rims range in width :from about 2 microns to more 

than 0.1 mm. Many rims are about 20 microns wide. A 

:few rims engulf all but a minute central speck o:f galena. 

Acanthite less com1nonly :fonns rims on sphalerite, 

where acanthite replaces sphalerite preferentially, 

thereby inheriting the chalcopyrite inclusions o:f the 

sphalerite host. Acanthite rims on discrete grains o:f 

chalcopyrite are rare. Some acanthite is present as discrete, homogeneous grains, perhaps representing complete replacmnent o:f galena. A little acanthite occurs 

as collo:form aggregates interlaminated with an unidentified weakly reflecting 1nineral. A trace o:f acanthite 

probably occurs as rare inclusions in pyrite, sphalerite, 

galena, and tetrahedrite, thongh the identification o:f 

the included phase is positive in sphalerite only. 

In all its :fonns, the acanthite is an aggregate o:f very 

small grains, commonly subhedral. An acicular or 

thornlike habit is shown by some acanthite crystals that 

penetrate galena. This habit is diagnostic :for the monoclinic, low-temperature Ag2S polymorph, acanthite. 

The cross section o:f one acanthite inclusion in sphalerite 

resembles that o:f a slightly distorted octahedron 

bounded on two sides by sphalerite, on the third side 

by chalcopyrite, and on the :fourth by a sphalerite cleavage pit. This acanthite is indistinctly twinned. Both 

crystal habit and twinning strongly suggest that this 

acanthite is pseudomorphous after argentite, the cubic, 

higher temperature modification o:f Ag2S, for which 

Kracek (1946) reported 177.8°+0.7°0 as the temperature o:f the reversible transformation in the presence o:f 

sulfur. A single acanthite inclusion in tetrahedrite shows 

cleavage that looks cubic, suggesting that this acanthite 

likewise inverted :from argentite. Many other acanthite 

areas have been examined for evidence o:f the high-tolow inversion, but without success, possibly because of 

the extremely fine grain o:f the mineral, or possibly because all acanthite except the grains included in sphalerite and tetrahedrite developed below the inversion 

temperature as primary acanthite. The genetic and 

economic implications o:f this problem are discussed 

subsequently. 

Rarely, acanthite that rims galena contains minute 

bright needles o:f native silver. Acanthite partly altered 

to cerargyrite is accompanied by pips of native silver. 

A few grains of acanthite are coated with a thin skin 

o:f a hydrated ( ? ) iron arsenate. The relations o:f acanthite and copper sulfides are discussed in the section on 

"Paragenetic Sequence." 

The optical identification o:f New Snowbird acanthite 

was confil'llled by semiquantitative electron microprobe 

analysis of several discrete grains and rims. Analysis 

showed Ag major, S major (concentration approximately equal to that in galena, or ""13 percent), and Cu 

barely detectable (perhaps 1 percent as a maximum). 

Quantitatively, the Ag and S content o:f the acanthite 
SILVER-RICH DISSEMINATED SULFIDES, CENTRAL IDAHO Cll 

is identical with that of an inverted acanthite, USNM 

R-7560 from Batopilas, Mexico, whose X-ray powder 

photograph is that of monoclinic Ag2S (Leonard, from 

a film prepared by Shirley K. Mosburg). 

Aramayoite( ?), 6[Ag(Bi,Sb) 8 2], forms minute euhedral inclusions-some lathlike, some diamondshaped-in galena. The mineral seems to be rare. In air it 

looks somewhat darker than galena; its estimated re~ 

flectivity is about 30 percent; its reflection-pleochroism 

is distinct, from pale gray ( j_ length of laths) to lighter; 

yellowish gray (II length) ; its anisotropism is strong; 

internal reflection is not detectable. In oil the mineral 

looks n1uch darker than galena, its reflection-pleochroism is slightly increased, and a faint orange internal 

reflection is visible. These properties are appropriate 

for several sulfosalts, among which ara1nayoite is suggested to account for the Bi and Sb found spectrographically in some acanthite-coated galena (the 

handpicked but impure "tetrahedrite concentrate" of 

table 3, No. 4). The aramayoite ( ? ) inclusions were 

found too late to be checked by microprobe.2 

Arsenopyrite is confined to pyrite, in which it occurs 

sparingly as euhedral to subhedral inclusions, singly 

or clustered, in roughly 8 percent of the grains. These 

inclusions, seldom detectable at X < 340, are best seen 

"tith an oil-immersion objective. Optical identification 

1f the mineral was confirmed by semiquantitative 

!p_icroprobe analysis. 

' Bornite. See digenite. 1 Chalcocite is rare and extremely fine grained. Bits 

of it are present as partial rims and replacements of 

chalcopyrite and galena. A trace of chalcocite occurs 

in mixtures with one or all of the following: Acanthite ( ? ) , covellite and blaubleibender covellite, digenite, and the pinkish-gray unknown. 

Oovellite and blaubleibender covellite 3 are widespread and conspicuous but quantitatively negligible, 

forming peripheral patches or complete rims on other 

sulfides, or cutting the sulfides as replacement veinlets. 

The rims and veinlets are narrow, and the individuals 

that make them up are for the most part very fine 

grained. The covellite and blaubleibender covellite occur singly or together, with or without chalcocite and 

digenite. Both "coveUites" seem to be young but not 

necessarily supergene. Blaubleibender covellite, the 

1nuch more abundant of the two, generally encases covellite, though in places the minerals are randomly in2 Microprobe analysis subsequently showed Ag, Cu, S, Sb present, Bi 

absent. Thus the mineral is not aramayoite. This note was added in 

page proof. 3 Blaubleibender covellite, a distinct species of copper sulfide (Mob, 

1964), looks like covellite in polished sections viewed with a single 

nicol and a dry objective. However, the minerals behave differently 

when viewed in oil: covellite shows a striking color change to purplish 

red; blaubleibender covellite ("covellite that remains blue") merely 

looks darker and shows more richly the strong blue reflectionpleochroism that was visible in air. 

tergrown. Covellite and blaubleibender covellite are 

seen most often on sphalerite, chaloopyrite, galena, and 

acanthite, though they have also been seen as rims on 

or veinlets in scheelite, pyrite, tetrahedrite, cerargyrite( ?), and gangue minerals. The ragged·-and embayed inner edges of the covellite and blaubleibender 

covellite rims indicate at least partial replacement of 

the host minerals, not merely deposition on them. 

Diaphorite ( ? ) , 8 [ Ag3Pb2Sb3S8], is suspected as 

elongate inclusions in a small aggregate of miargyrite ( ? ) that also contains an inclusion of native silver. 

The aggregate has a smooth contact against chalcopyrite. In air, the diaphorite ( ? ) looks white, is distinctly 

anisotropic, and shows no internal reflection; its polishing hardness is less than that of miargyrite ( ? ) ; its 

reflectivity for one position in orange light is equal to 

that of chalcopyrite, for the other position slightly 

greater. In oil, the diaphorite ( ? ) shows distinct reflection-pleochroism from white to gray-white with a yellowish tint, is anisotropic, and lacks internal reflection; its reflectivity for one position in orange light is 

slightly less than that of chalcopyrite, for the other position equal. If the 1niargyrite ( ? ) is correctly identified, the white inclusions are very likely diaphorite, 

for few minerals softer than miargyrite have the optical 

properties listed here. 

Gold is mostly and perhaps entirely electrum, the natural variety of Au-Ag alloy. Gold is confined to pyrite, 

in which it occurs mainly as circular grains 5 microns in 

diameter (pl. 3). A few reach 12 microns. The largest 

grain-elongate, with cuspate sides-is 17 X 67 microns. 

A grain of this size is conspicuous at medium power 

( X 130), owing to Hs extreme brightness. With practice, 

an observer C'an spot even the 5-micron grains at that 

magnification. A unique grain shaped like a triskelion 

occurs at the contact of pyrite and included arsenopyrite, 

penetrating the latter. All other gold grains are isolated 

within pyrite, which may or may not contain other inclusions, such as arsenopyrite, pyrrhotite, sphalerite, 

silver minerals, and quartz (pls. 2, 3). The frequency of 

gold grains is two to six per polished section containing 

several hundred pyrite grains. We have never observed 

more than one gold grain in a single pyrite crystal, 

possibly because many pyrite crystals have been fragmented but more likely because the gold, unlike silver, 

seems to have been readily collectable. One might expect 

to find among goethite pseudomorphs after pyrite a 

grain or two containing gold, or an isolated gold flake, 

but we have not found any. 

All gold grains checked by semiquantitative microprobe analysis are gold-rich electrum (pl. 2). However, 

the variable color of the gold, ranging from pale golden 

yellow to rich golden yellow, indiorutes a range of com-
C12 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

position that may extend nearly to pure gold. There is 

no correlation between the color of the gold and the 

abundance of native silver inclusions visible in the 

pyrite host. Elemental gold as a minor element within 

~the crystal lattice of sulfides was not detected by 

microprobe. 

Clark's (1960, p. 1375, 1379-1381, 1645-1647) experiInental observations on the solid solubility of gold in 

arsenopyrite and in As-rich As-S fluid ~at and above 

660°C are intriguing. In the New Snowbird sulfide concentra,tes, we found native gold in contact with arsenopyrite in just one place. (See preceding description of 

gold.) Here and in arsenopyrite-bearing pyrite grains 

that contain blebs of native gold not in contact with 

arsenopyrite, the quantity of gold is roughly 20 areal 

percent that of the arsenopyrite-considerably more 

than Clark observed as a product of solid diffusion in 

short experimental runs at 'and above 660°C. However, 

the quantity of arsenopyrite lost mechanically or con-

. cealed below the surf,ace of our polished sections is unknown. Moreover, it is conceivable that, under natural 

conditions, time or other variables might compensat.e for 

lower temperature, effecting enough diffusion of gold 

into and out of arsenopyrite to give the quantitative 

relations we observed. Nevertheless, the total amount of 

As in the sulfide concentrates ( 0.36-0.41 weight percent) 

seems much too low to make Clark's ~attractive hypothesis of gold diffusion directly applicable to the New 

Snowbird deposit. 

Green-orange unknown.-This mineral seems to be a 

new species. CharacJteristically it encrusts and replaces 

late copper sulfides and is locally encrusted by the 

pinkish-gray unknown. Where fresh, the unknown mineral is a peculiar greenish orange, optically anisotropic, 

and ra,ther soft. In a dry clim·ate it tarnishes slowly, 

becoming orange-pink and then dull pink after a few 

weeks. Because the color of the freshly polished mineral 

resembles that of an unripe orange, we refer to this 

mineral as green -orange unknown. It is essentially a 

Cu-Fe(?) sulfide. We hope to obtain enough quantitative data to describe this species in a subsequent report. 

Hessite, Ag2Te, was positively identified in one particle only, a broken crystal of pyrite penetrated by stubby 

veinlets of hessite. Microprobe analysis showed Ag and 

Te to be major contituents. Gold and other expectable 

telluride-forming elements were not detected. The electron probe spectrometer trace of this hessite is identical 

to thrut of 'a reference sample of hessite (RTO 267) previously identified by Leonard from an X-ray powder 

diffraction photograph taken by T. Botinelly. 

I daite ( ? ) , Cu5FeS6 (Frensel, 1959), may be present 

as a trace in some grains of digenite, with which it 

forms an extremely fine grained and intimate intergrowth. The idaite( ?) is soft, relatively bright, pinkish 

orange, seemingly anisotropic, and perhaps platy. As 

the individuals are barely resolvable in oil at X 1600 

and the aggregates present too small a target for the 

electron beam of the microprobe, the identification of 

this mineral is dubious. 

Ilmenite ( ? ) .-This mineral was identified by Fred A. 

Hildebrand in X-ray powder photographs that he took 

of iron oxide-m,anganese oxide coatings of huebnerite 

grains. We have not found ilmenite in the polished section made from these coatings. The Ti content of all 

samples of concentrates is low, but its higher value in 

the tungsten concentrates (table 2, No.4) lends support 

to the notion that a Ti mineral might be present in them. 

Marcasite is sparse. It is confined to pyrite, within 

which it characteristically forms a delicate grating of 

prismatic crystals interspersed with small voids. A few 

pyrite grains contain isolated ~arcasite euhedra, or 

clusters of arsenopyrite and marcasite. Isolated marcasite euhedra ·are seldom distinguishable from arsenopyrite. A few grains consist of stripes of marcasite 

alternating with slightly wider stripes of chalcopyrite, 

the later enclosing arsenopyrite crystals and irregular 

pyrite relics. Evidently chalcopyrite selectively replaced 

pyrite here. Grains of this sort strongly suggest that at 

least some, and perhaps all, marcasite is early in this 

assemblage. Optical identification of marcasite in nets 

and isolated euhedral inclusions was confirmed by semiquantitative microprobe analysis, which showed. Fe and 

S as major elements, and As, Co, and Sb to be absent. 

The voids between marcasite prisms in the characteristic pseudomorphs occupy about 20-30 percent of the 

area and thus indicate direct conversion of pyrite to 

marcasi1te, rather than volume-for-volume replacement 

of pyrite by marcasite. Theoretically, the marcasite unit 

cell has a volume that is 51 percent of the pyrite unit 

cell; therefore, direct conversion of pyrite to marcasite 

should produce voids. In area, this change corresponds 

to a reduction of 18-49 percent, averaging 35 percent, 

which agrees fairly well with the observed void area of 

20-30 percent. 

M iargyrite ( ? ) , 8 [ AgSbS2 ], is rare. It occurs as a very 

fine grained aggregate of stubby prisms in smooth contact with chalcopyrite, and as a rim, a few microns wide, 

consisting of stubby prisms on subhedral grains of argentian tetrahedrite. (See also diaphorite, p. Cll.) In 

air, the miragyrite( ?) is slightly greenish gray white, 

has a reflectivity very close to that of tetrahedrite, shows 

distinct reflection-pleochroism in weakly tinted pale 

grays, is distinctly anisotropic, and lacks internal reflection. In oil, reflection-pleochroism is distinct, from 

yellowish gray or brownish gray to green gray to blue 

gray; anisotropism is distinct; and a faint internal re-
SILVER-RICH DISSEMINATED SULFIDES, CENTRAL IDAHO C13 

flection in red or orange is visible in places. The optical 

properties and occurrence are appropriate for lniargyrite, but the identification is only tentative. 

Pinkish-gray wnknown.-An unidentified soft, anisotropic, moderately bright pinkish-gray or brownishgray mineral is the youngest member of the rim-forming suite. (See "Paragenetic Sequence.") The rims of 

the unknown are so narrow and the individuals so fine 

that even the qualitative optical properties are difficult 

to determine. They do not seem much like those of the 

Cu-Ag-S minerals stromeyerite, jalpaite, and mckinstryite. (The last is natural ,B-Cu0 , 8Ag1, 2S, recently 

described by Skinner and others, 1966.) We did not find 

large enough areas of the unknown to analyze by 

microprobe. 

Polyb(usite (?), 16[Ag16Sb2S11], is very rare. It forms 

an irregular replacement rim, 4 microns wide, on one 

grain of galena. The rim is an aggregate of irregular 

grains accompanied by one small area of a similar but 

yellower mineral; both sulfosalts ( ? ) are irregularly 

replaced by a partial rim of acanthite. In air, polybasite ( ? ) looks slightly bluish gray and darker than galena; it looks slightly darker, considerably greener gray, 

and smoother than ·acanthite. In oil, polyhasite ( ? ) appears darker-distinctly darker than the bright position of acanthite. In air, reflection-pleochroism is rather 

strong, slightly yellowish gray or slightly greenish 

gray to bluish gray. In oil, the effects are similar but the 

yellowish gray position now has a pinkish tint. Anisotropism is strong in both media. In air, purplish-red 

internal reflection is faint and local; in oil,· a suggestion 

of it is detectable with a single nicol, and with nearly 

crossed nicols it is red to purplish red but neither strong 

:ror pervasive. Polishing hardness is less than that of 

galena, greater than that of acanthite. Though the optical properties of the polybasite(?) are very similar to 

those listed above for miargyrite ( ? ) , the habit is not. 

Whatever these minerals are, they are almost certainly 

different species. 

Pyrrhotite is present as sporadic droplike inclusions 

in about 5 percent of the pyrite grains. The frequency 

of pyrrhotite in such grains seldom exceeds one bleb 

per pyrite grain. The inclusions range in diameter from 

less than 4 microns to about 80 microns. A few are 

dumbbell shaped, and some of the larger grains contain 

a single minute bleb of chalcopyrite. Pyrrhotite has not 

been found as discrete grains, or as inclusions in any 

other mineral except chalcopyrite, where it was observed as a minute bleb in one chalcopyrite inclusion in 

pyrite. The optical identification of pyrrhotite was confirmed by semiquantitative microprobe analysis of several grains, none of which contained Ag, Co, Cu, or Ni. 

8'l~lberkies group of Ag-Fe sulfides. Some member of 

this group, most likely argentopyrite (AgFe3S5 ; Ram270-675 0-68-3 

dohr, 1960, p. 588), is suspected in the form of extremely 

rare inclusions in pyrite. We have found only two or 

three such inclusions in successive mounts containing 

several hundred pyrite grains apiece. The inclusions are 

round or elliptical, 2-4 microns across, generally unique 

in the pyrite host, and commonly accompanied by a grain 

or two of pyrrhotite, chalcopyrite, arsenopyrite, or soft 

white mineral. The suspected Silberkies mineral is 

softer than pyrite but harder than pyrrhotite, nearly 

as bright as pyrite, and distinctly anisotropic. It is 

paler, yellower, and brighter than pyrrhotite, slightly 

brighter and less y·ellow than chalcopyrite. In air, the 

mineral shows distinct reflection-pleochroism from very 

pale yellow to brownish or grayish yellow; in oil, pale 

grayish yellow to pale gray. The optical properties are 

1nost like those of argentopyrite as reported by Ramdohr. However, the mmnbers of the group are difficult 

to distinguish from one another, if indeed they are all 

valid species, and from several commoner sulfides. 

Though the New Snowbird argentopyrite ( ? ) can be 

recognized under the ore microscope without much difficulty, it is indistinguishable from pyrrhotite and chalcopyrite in the carbon-coated speci1nens viewed through 

the optical microscope of the electron microanalyzer. 

All grains hopefully analyzed as argentopyrite ( ? ) 

proved to be pyrrhotite or chalcopyrite. We think this 

result demonstrates the rarity of argentopyrite ( ? ) and 

the impossibility of recognizing it under the carbon 

coating, not its absence. 

The presence of one pyrite cube containing a peculiar 

intergrowth supports the notion that some mineral of 

the Silberkies group is or was part of the local assemblage. This pyrite, appearing as a pitted square 0.14 mm 

on an edge, contains a central square that is 77 microns 

across. The central square resembl.es a pegboard in which 

the board's rectangular system of holes corresponds to 

minute, nearly equant grains of a soft gray 1nineral, 

somewhat darker than pyrite (pl. 4B). A few "holes" 

are randomly occupied by minute pips of native silver, 

and a few by pyrrhotite ( ? ) . A few areas between the 

"holes" are argentopyrite(?). The largest gray grains 

are 4 microns across ; the smallest are less than a tenth 

of that size. In oil, the la.rgest gray grains show distinct 

reflection-pleochroism from slightly greenish gray to 

slightly bluish gray. If these grains represent some mineral identified elsewhere in the New Snowbird mineral 

assemblage, their properties agree best with those of 

acanthite; and if the gray mineral is now acanthite, its 

equant habit suggests that it was formerly argentite. 

The geometric relations and the minerals present, to the 

extent that one can guess at their identity, suggest that 

some high-temperature cubic(?) Ag-Fe-S precursor occurred within this pyrite cube; on cooling, this precur-
014 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

sor broke down, exsolving argentite and pyrite accompanied by a little native silver and pyrrhotite; the 

argentite later inverted to acanthite. The barely visible 

argentopyrite( n grains might represent a low-temperature polymorph of the cubic (?) Ag-Fe-S precursor, 

or they might be an exsolution product thereof. 

Silver as the native metal is widespread but not 

abundant. Most of it occurs in pyrite as clusters and 

strings of minute round or oval blebs (pl. 4A) or very 

rarely as elongate patches having one edge straight 

and the other jagged. The blebs are generally less than 

2 microns in diameter, evidently diminishing to irresolvable specks. A train or cluster commonly consists 

of one to five of the larger blebs accompanied by a host 

of smaller blebs and black specks. Occasionally a single 

grain of native gold is present, dwarfing the silver blebs 

with its relatively large diameter of 5 microns. Because 

the silver blebs are a brilliant yellowish white against 

the enclosing pyrite, one may see their flash or wink 

with a medium-power objective, provided the section 

has just been polished. Even in a dry climate the silver 

blebs tarnish in a day or two, taking on the appearance 

of pits locally surrounded by slightly tarnished areas 

of pyrite host. Only 1 pyrite grain among 50-150 contains recognizable blebs of silver when scanned at high 

magnification ( X 336), but other pyrite grains that show 

clouds of "dust" are suspected of eontaining submicroscopic silver particles. 

A little native silver also occurs as discrete grains, as 

s1nall equant inclusions in sphalerite and galena, as 

slivers in acanthite and the green-orange unknown, and 

as specks in colloform goethite encrusting chalcopyrite. 

Of these minor occurrences, silver in sphalerite is the 

lP.ast rare. 

Semiquantitative microprobe analyses show Ag as 

the only element detectable in the native silver inclusions in pyrite and sphalerite. 

Jacobsen ( 1965, p. 12) recently described the occurrence of droplets of native silver in bornite and chalcopyrite from the disseminated copper sulfide deposit 

. at Mangula, Southern Rhodesia. 

Soft W 1hite 1nineral.-Minute grains and patches of 

an unidentified soft white mineral, commonly accompanied by galena, are present in 8 pereent of the pyrite 

grains. The unidentified mineral is bright, white, optically anisotropic, and very soft, having a polishing 

hardness much less than that of pyrite and slightly 

greater that of native silver. In oil, the mineral looks 

gray against pyrite and shows reflection-pleochroism 

from gray or slightly bluish gray to yellowish gray or 

slightly brownish gray; some grains are faintly mottled. 

Thus the unidentified mineral resembles not only the Pb 

sulfosalts and their relatives, but also hessite and 

matildite (AgBiS2). However, the Te content of the 

sulfide concentrates (table 1, Nos. 1, 2, 3) seems too 

low to account for all the anisotropic white inclusions 

as hessite, and the lack of Bi in the hand-picked 

"pyrite" concentrate (table 3, No. 1) eliminates matildite from further consideration. Grains of the unidentified mineral large enough for satisfactory microprobe 

analysis have not beeen found. 

Tetrahedrite, ideally 8[CuaSbSa] or 2[Cu12Sb4Sla], 

is rather sparse, probably making up less than 0.5 percent of the sulfide concentrates. It is 1the argentian variety, freibergite, and is rich in elemental silver. Most of 

the tetrahedrite is present as discrete grains, some of 

which contain small inclusions of acanthite (inverted 

from argentite?), ehalcopyrite, galena, and sphalerite, 

generally as a 1nixed assemblage. A few of these grains 

are partly rimmed by 1niargyrite ( ? ) , with or without 

an outer partial rim of acanthite. A little tetrahedrite 

occurs as small round inclusions in pyrite and galena. 

Optical identification of the tetrahedrite as an argentian v~riety, based on its yellowish tint, was confirmed 

by se1niquantitative microprobe analysis of several 

grains. Copper, S, and Sb are major constituents; Ag 

is always present; Fe, Zn, and either Pb or As are 

minor elements; Hg is absent. An approximate quantitative d~termination of Ag indicates that 12-15 percent 

is present in seven grains and about 8 percent in another grain. Smne Ag is definHely present in the tetrahedrite inclusions in pyrite. Attempts to determine As 

versus Ph by means of the {3 peak were unsuccessful; 

the peak was irresolvable, owing to the low concentra.-

tion of one or both elements. 

Tramp i~on-stray pieces of partly oxidized steel 

from mining and milling equipment--is an a:bundant 

accessory component of the tungsten concentrates. Obviously malleable and magnetic particles are not likely 

to be mistaken for minerals, but dust-size particles are 

sometimes found in the nominally nonmagnetic fractions of these concentrates and in the insoluble residues 

from incompletely digested samples thereof. Though 

tramp iron was not seen in polished sections of sulfide 

concentrates, its presence there or in steel-ground nonflotation samples might lead the unwary into thinking 

the samples contained a high proportion of native silver 

grains. Steel and na:tive silver are bright, yellowish 

white, optically isotropic, and free of scratches in a 

well-polished section. Tests for magnetism and scratching hardness easily distinguish •these substances if the 

particles are sufficiently large. If they are minute, a 

measurement of microindentation hardness will quickly 

tell them apart., as the Vickers hardness at 100-gram 

load is about 60 for native silver and about 490-575 at 
SILVER-RICH DISSEMINATED SULFIDES, CENTRAL IDAHO 015 

50-grrun load for several kinds of steel from 1the New 

Snowbird mill. 

ALTERATION PRODUCTS 

Alteration products make up less than 1 percent of 

the ore that was mined. The number of these products 

(table 5) is quite disproportionate to their volume, yet 

the very presence of oxidized 1ninerals affects one's inter:pret:ation of economic features of the deposit, such 

as expectable extent of supergene enrichment. Presumably the oxides, sulfates, arsenates ( ? ) , and halides of 

the alteration suite are mainly supergene and the clay 

minerals mainly hypogene, but many of the alteration 

products are so fine grained and intermixed that evidence of their origin is not to be had. Clay minerals 

are mentioned first in the following notes, then goethite, 

then other members of the suite in alphabetical order. 

Olay ~minerals are very sparingly present. The claysize fraction recovered by ultrasonic cleaning is considera;bly less than 1 weight percent of the tailings and 

less than 0.01 weight percent of the tungsten concenh·ates. No clay-size fraction was recovered from the 

sulfide concentrates. Argillic minerals in the mill prodnets and in specimens of crude ore are chlorite, illite, 

kaolinite, montmorillonite ( ? ) , muscovite (sericite), 

Ilontronite, and palygorskite ( ~) . I\:aolinite is the most 

abundant of 'these, and illite next. Some chlorite of clay 

size is intimately mixed with kaolinite in patches in the 

ore; coarser chlorite is a direct alteration product of 

biotite. Artificial1nixtures of clay-size material always 

contain additional components-especially jarosites 

and tungsten 1ninerals-that make more refined studies 

of the clays virtually impossible. 

Goethite is the principal oxidation product of the 

ore. Most of it has formed from pyrite, but some has 

formed from chalcopyri1te and some from huebnerite. 

The quantity of goethite in samples of sulfide concenh·ates ranges frmn less than 1 to about 5 percent. The 

distribution of goethite within the ore body itself seems 

to have been errrutic. Since goethite is among the youngest minerals in the assemblage and apparently belongs 

to a single generation, we suppose it to be wholly supergene. Goethite occurs as replacement veinlets and nets 

rn pyrite and huebnerite; as rims of variable thickness 

on pyrite and chalcopyrite; as discrete grains representing patchy, cellular, zoned boxwork, or colloform 

aggregates; and rarely as perfect pseudomorphs after 

arsenopyrite-bearing pyrite cubes, the diamond shape 

of the former arsenopyrite inclusions being preserved 

as well as the cubic shape of the host. 

Bianchite(?), 8[(Zn, Fe)S04 .6H2 0], or a similar 

sulfate is suspeotecl in trace amounts. Semiquantitative 

1nicroprobe analysis of a gray grain whose reflectivity 

is distinctly less than 15 percent shows Fe, Zn, and S 

to oo rna jor elements, Cu minor, Ag trace or absent, Cd 

and Mn absent, 0 not detectable with the detectors then 

available. 

0 erargyrite.-At least one member of this group 

occurs very sparingly as a partial replacement of acanthite, of acanthite plus an unidentified ruby silver mineral, or of 1the pinkish-gray unknown. The cerargyrite 

and accompanying acanthite contain minute bright 

specks, presumably of native silver. The low concentration of Br and Cl in sulfide concentrates and tailings 

(table 1, nos. 1, 2, 3, 5) confirms the results of mineragraphic study: cerargyrite is not a major source of elen1e111tal silver in the New Snowbird ore. 

Cerussite seems to be very sparse. Difficult to identify 

optically, this gray mineral, which fluoresces white 

under the electron beam, was suspected of being a tungstate. An uncorrected determination by electron microprobe, using galena as a standard, gave 78.2 weight 

percent Ph. Eighteen common elements, including As, 

Bi, Cl, S, Sb, and W, were looked for but not found. 

Carbon and oxygen could not be determined with the 

analyzing crystals and -detectors available when our 

work was done. Nevertheless, the determined Pb content 

and absence of the elements noted, in conjunction with 

white fluorescence, adequately identify this mineral as 

cerussite. Anglesite ( ? ) may be intergrown with several 

cerussite grains that were found after the microprobe 

study. 

Jarosite or natroj arosite, or more likely both minerals, 

are found in clay-size mixed fractions removed ultrasonrcally from tungsten concentrates and tailings. The 

yellow eolor of clay from the tailings is probably due 

to one or both of these complex hydrated Fe-bearing 

sulfates mixed with tungsten alteration products. 

Plumbojarosite is present in one sample. 

The presence of additional hydrated sulfates and one 

or more arsenates is indicated by fragmental data from 

optical, X-ray diffraction, and electron microprobe 

studies. These sparse minerals have not yet been 

identified. 

Psilomelane and pyrolusite are rather sparse but common alteration products of huebnerite, which they vein 

and encase. The manganese oxides are usually accompanied by goethite. Their age relations a.re indeterminate. The iron and manganese oxides were isolated by 

Fred A. Hildebrand and identified by him by X-ray 

powder photography. We did not analyze these minerals 

by microprobe. 

Secondary tungsten minerals of clay size are present, 

but their identification in X-ray powder diffrructograms 

of mixtures is so unsatisfactory, owing to coincident 

reflections, that we prefer not to attach names to our 
C16 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

guesses. Stolzite was positively identified (see "Tungsten Minerals"), but there is no way of telling whether 

the extremely fine grained variety is an alteration 

product or a primary mineral. 

Tenorite, 4[Cu0], is very spa.rse. It occurs as an 

extremely fine grained platy ( ? ) , twinned ( ? ) aggregate 

in crusts with goethite and unidentified oxidation 

products. 

PARAGENETIC SEQUENCE 

A generalized paragenetic sequence for the deposit is: 

gangu~primary tungsten minerals~pyrite and its 

inclusions~ intermediate sulfides and sulfosalts~rimforming sulfides and oxidation products. 

Arrows are used to indicate sequence from left to 

right in this and subsequent schemes. Read the arrows 

as "followed by or replaced by." These schematic representations of paragenetic sequence are useful so long as 

the reader bears in mind that the relations are necessarily generalized, and that the position inferred for 

eaeh species reflects more nearly the end of crystallization of the species than its beginning. If two varieties 

of a mineral are present, such as sphalerite, only the 

dominant variety is shown in the sequence. If the substance is polymorphic, such as Ag2S in the acanthiteargentite pair, the observable species is shown in the 

sequence-acanthite, in this example. Position within 

a sequence has been determined from ( 1) crosscutting 

and encrusting relations, (2) distribution of inclusions, 

and ( 3) absence of discrete grains of a species. Fabric 

features that seem especially significant for age· relations 

are noted below; details are given in the descriptions 

of individual species. 

In searching out and presenting evidence for sequential relations, we hope we have not arrived at a degree 

of orderliness that was lacking in nature. Evidence for 

the paragenetic position of some minerals is hard to 

find; nevertheless, it exists. Perhaps it can be found 

here only because the natural a;ssemblage has been concentrated roughly a thousandfold by milling. The point 

is this: we may find order where other workers, dealing 

with similar but 1nechanically unconcentrated assemblages, would not. For all but the late and dearly 

ordered rim-forming sulfides, other workers might see 

our sequence as their dumped assemblage. 

The gross relations of huebnerite to quartz in this 

deposit suggest that huebnerite generally replaces the 

host but locally is intergrown with and indented by 

euhedral milky quartz. The random orientation of disseminated euhedral huebnerite in quartz of several generations is difficult to explain by any process except 

replacement, perhaps attended by local recrystallization 

of quartz. The coarser scheelite of the deposit shows 

similar relations to quartz; the finer scheelite forms 

replacement veinlets in it. · 

The veining and replacement of huebnerite by 

scheelite indicates that some scheelite is younger than 

huebnerite. However, a few huebnerite prisms contain 

small round inclusions of scheelite. This suggests either 

partial Contemporaneity of the tungsten minerals, 

scheelite then continuing to form after huebnerite 

finished crystallizing, or the existence of two distinct 

generations of scheelite-one euhedral, coarser, and 

older ( ? ) and one finer, crosscutting, and definitely 

younger than huebnerite. 

The relations between pyrite and tungsten minerals 

suggest that pyrite is younger than huebnerite, and 

either younger than or roughly contemporaneous with 

scheelite. The .scarcity of intergrowths of pyrite and 

tungsten 1ninerals indicates either that pyrite preferentially replaced quartz, or that it replaced whatever 

was available in a vein system that contained 100-300 

times as much quartz as tungsten minera18. 

It is convenient now to discuss the sulfides as if they 

were a unit set apart from the tungsten minerals. There 

is no field or laboratory evidence that such a clivision. existed within the deposit, either spatially or 

temporally. 

The paragenetic sequence for the principal sulfides is: 

pyrite~sphalerite~chalcopyrite~ (galena) ~tetrahedrite~acanthite ~ ( digenite) 

The positions of galena and digenite are uncertain. 

Galena locally replaces pyrite, probably replaces sphalerite, is of indeterminate age relative to chalcopyrite, 

and is rimmed separately by tetrahedrite or by digenite, 

as well as by acanthite. Digenite also replaces sulfides 

that precede and follow galena. It is dealt with in the 

discussion of rim-forming sulfides. 

Smooth, slightly curved or straight contacts prevail 

among sphalerite, chalcopyrite, and galena, though 

chalcopyrite locally veins sphalerite. The three sulfides 

locally replace pyrite; but here too the evidence of age 

difference, though it exists, is slight. Moreover, all members of the sequence from pyrite through acanthite contain inclusions (table 7, part A). Commonly these are 

inclusions of one another, pyrite presenting a notable 

exception. Arsenopyrite, native gold, marcasite, pyrrhotite, Silberkies ( ? ) minerals, and the soft white mineral 

occur only as inclusions in pyrite. Pyrite itself is not 

included in later sulfides except as an obvious replacement relic. These relations point to pyrite and its inclusions as the first-formed members of the sulfide 

assemblage. 

The distribution of inclusions of the principal metallic minerals among all the intermediate sulfides and 

sulfosalts of the weakly ordered sequence is brought 

out in table 7, part B, which shows the inclusion data 

rearranged horizontally and vertically according to the 
SILVER-RICH DISSEMINATED SULFIDES, CENTRAL IDAHO C17 

TABLE 7.-Distribution of ore-mineral inclusions in discrete grains of the suljide-sulfosalt-native-element suite 1 

A. HOST MINERALS (COLUMN HEADINGS) LEFT TO RIGHT IN PARAGENETIC SEQUENCE; INCLUSIONS (COLUMN CONTENTS) TOP TO BOTTOM 

IN ALPHABETICAL ORDER 

Pyrite Sphalerite Chalcopyrite Galena Tetrahedrite Miargyrite(?) Acanthite Silver 

------- ------

acanthite(?) acanthite acanthite(?) acanthite(?) 

arsenopyrite 

chalcopyrite chalcopyrite chaloopyrite chalcopyrite 

galena galena galena galena 

gold 

marcasite 

pyrrhotite 

Silberkies 

group 

silver silver silver silver silver 

sphalerite sphalerite sphalerite sphalerite 

tetrahedrite tetrahedrite 

1midentified unidentified diaphorite (?) 

minerals 2 minerals 3 

I 

I 

,(3. HOST MINERALS LEFT TO RIGHT IN PARAGENETIC SEQUENCE; INCLUSIONS TOP TO BOTTOM IN SAME SEQUENCE AS HOST MINERALS 

i Pyrite Sphalerite Chalcopyrite I 

Galena Tetrahedrite Acanthite Silver 

T 

sphalerite sphalerite sphalerite sphalerite 

chalcopyrite chalcopyrite chalcopyrite chalcopyrite 

galena galena galena galena 

tetrahedrite tetrahedrite 

acanthite(?) acanthite acanthite(?) acanthite(?) 

silver silver silver 

1 Table does not consider minerals "included" by obvious replacement rims. ! 2 Mainly soft white mineral. 

I 

fnferred paragenetic sequence of the host minerals. The 

unique inclusions in pyrite, the rarely occurring miargyrite ( ~) , and the traces of unidentified sulfosalts in 

galena and acanthite have been omitted. Eliminating 

~he minor inclusions heightens the impression that the 

intermediate sulfides and sulfosalts (sphalerite through 

tetrahedrite) are, like inclusion-rich pyrite, a dumped 

assemblage. The rearrangement also calls attention to 

the absence of some expectable inclusions, especially to 

the absence of tetrahedrite, acanthite, and native silver 

from chalcopyrite. We attribute this apparent absence 

to the poor polishing quality of chalcopyrite : the chalcopyrit~ host is so badly pitted that only the much more 

abundant sphalerite and galena have been retained as 

detectable inclusions. Finally, the change from an earlier, inclusion-rich sulfide-sulfosa1t assemblage to a 

later, inclusion-poor one is plainly indicated. 

The late, rim-forming sulfides present abundant and 

clear-cut evidence of sequential deposition. Acanthite, 

the most abundant rim-former, is a convenient starter 

for the sequence, which in comprehensive form is: 

acanthite~ ( digenite )~blaubleibender covellite~ 

green-orange unknown~pinkish-gray unknown 

, ( ~cerargyrite) I 

I This comprehensive scheme is inferred from two sets ?f partial schemes, the first involving mainly acanthite, 

silver 

3 Includes mineral tentatively identified as aramayoite. 

the second digenite. Except where otherwise shown, the 

following sequences are directly observable: 

1. acanthite~hlaubleibender covellite~greenorange unknown (common) 

acanthite~digenite (rare) 

acanthite~green -orange unknown (rare) 

acanthite~pinkish-gray unknown (less rare) 

galena~(black crust; pitn~green-orange unknown~pinkish-gray unknown~cerargyrite 

(rare) 

2. digeni~blaubleibender covellite 

digenite~green-orange unknown 

(common) 

(common) 

~ 

digeni~blaubleibender corvellite~greenorange unknown (inferred) 

Locally, acanthite is deposited on blaubleibender covellite, but the usual sequence is that shown in scheme 1, 

line 1. In some places, blaubleibender covellite and the 

green-orange unknown are intimately mixed rather than 

sequentially related, and the pinkish-gray unknown 

may be sparingly present in the mixture. In all associations, blaubleibender covellite may be accompanied by 

a very little covellite, and a little bornite may accompany digenite. Rarely, digenite and blaubleibender 

covellite form alternating thin crusts on earlier sulfides. 

Among minerals that almost surely resulted from 
C18 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

oxidation, cerargyrite alone can be linked to the assemblage of late sulfides. 

GEOLOGIC THERMOMETRY 

Recent experimental work on sulfide systems provides 

some clues to the approximate temperatures prevailing 

during sulfide mineralization. The presence of arsenopyrite fixes an upper limit at 702°C, for arsenopyrite is 

not stable above that temperature (Clark, 1960, p. 1642). 

Pyrite and arsenopyrite existing together, and presmnably formed in the presence of vapor, indicate that 

at least one member of the pair crystallized below 

491 o ± 12°C (Clark, 1960, p. 1642). Pressure affects the 

equilibrium only slightly. Therefore, 491° ± 12°C is the 

probable upper limit for the formation of most and 

perhaps all pyrite in the deposit, though some arsenopyrite-free pyrite might have formed above that 

temperature. The minute size of the arsenopyrite grains 

precludes a determination of their temperature-sensitive 

S-As ratio by Morimoto and Clark's (1961) method of 

X-ray diffraction, and the difficulty of recognizing 

arsenopyrite under the microscope of the electron microanalyzer has made direct determination of the ratio 

infeasible. 

Pyrrhotite included within pyrite can be used as another 1neans of estimating the temperature of formation 

of the pyrite-pyrrhotite-arsenopyrite part of th-e assemblage. Pyrrhotite is not stable with pyrite and arsenopyrite above 491 °+12°C, but it is stable with them at 

and below that temperature (Clark, 1960, p.1376). Thus 

if all three minerals formed in equilibrium and in the 

presence of vapor, 491 °±12°C is the maximum temperature for their crystallization. 

We hoped to make a closer estimate of the temperature 

of formation of New Snowbird pyrrhotite by applying 

the pyrite-hexagonal pyrrhotite equilibrium relations 

determined by Arnold (1962). To do this, one must 

know both the composition of the pyrrhotite and its 

structural form, whether hexagonal or monoclinic. (See, 

for example, Kullerud and others, 1963.) Attempts to 

determine these properties of New Snowbird pyrrhotite 

were disappointing, owing to the very small size 

of the inclusions. Electron microprobe analysis of 

three pyrrhotite inclusions in separate pyrite grains 

gave Fe and S in weight percent as follows: 58.1 

and 40.9, 62.5 and 41.9, 53.9 and 34. These are equivalent to 44.9, 46.2, and47.6 atom percent Fe, or to Fe0 •82S, 

Feo.s6S, and Feo.91S. The host pyrite, assumed to be 

stoichiometric FeS2 , served as an analytical standard. 

Total Fe plus S in the pyrrhotite is 99 weight percent 

for the first grain but far from it for the others. The 

individual variations a,re presumably due to imprecise 

analysis of the minute inclusions, not to actual variation 

in composition; thus even the mean value of --46 atom 

percent Fe provides only. a rough estimate of the composition of this pyrrhotite. If the pyrrhotite were hexagonal, existed in equilibrium with pyrite, remained unchanged in equilibrium composition during its history, 

and were relatively free of substituted minor elements, 

its temperature of formation estimated from the diagraln of Arnold (1962, p. 73) would be --550°0. Because of the uncertainty in composition, this estimated 

temperature merely points toward some high value not 

exceeding the maximum of 491 °+12°C inferred from 

the phase relations detennined by Clark ( 1960). 

The structural form of this pyrrhotite also remains 

uncertain because the grains are too small to be sampled 

for X-ray powder diffraction analysis. However, etching with chromic acid (Arnold, 1966, p. 1221) provided 

an indirect approaeh to establishing the structural form. 

Pure samples of this pyrrhotite being unobtainable, 

etching had to be done on bulk samples of pyrite concentrates in which the position of pyrrhotite inclusions 

had been carefully determined before etching. Twentyminute immersion of a polished section in a saturated 

solution of Cr03 produced a strong etch on 12 pyrrhotite 

inclusions out of 17 and a slight or moderate etch on 4. 

The effect on one grain was indeterminate because of an 

obscuring water droplet. As Arnold ( 1966) found that 

treatment for 1 hour etched monoclinic pyrrhotite but 

did not affect the hexagonal pyrrhotite intergrown with 

it, we conclude that the New Snowbird pyrrhotite is 

homogeneous and probably monoclinic. (The use of an 

aggregate of grains containing many foreign elements 

introduces some uncertainty in interpreting the results, 

but perhaps not much.) This inference of monoclinic 

form is consistent with the average but equally uncertain composition of the pyrrhotite, Feo.s6S, which is 

close to the narrow range of composition-Feo.s7S to 

Feo.ssS-shown by the monoclinic pyrrhotites investigated by Kullerud and others (1963) and by Desborough and Carpenter (1965, p. 1436). 

Because the New Snowbird pyrrhotite is most likely 

monoclinic, it is at present unsuitable for direct use as 

a geologic thermometer, as there seems to be no way of 

distinguishing a monoclinic pyrrhotite that has always 

been monoclinic from one that underwent a hexagonalto-monoclinic transformation during cooling. If the 

New Snowbird pyrrhotite actually did undergo a hexagonal-to-monoclinic transformation on cooling, its 

equilibrium temperature estimated from the pyritehexagonal pyrrhotite solvus of Arnold (1962) would 

be --490°C. This value differs from the earlier cited 

550°C in the same proportion as the restricted composition of monoclinic pyrrhotite differs from the uncertain 

average composition of New Snowbird pyrrhotite. The 
SILVER-RICH DISSEMINATED SULFIDES, CENTRAL IDAHO C19 

close agreement between this estimated formation temperature of ,-,490°C and Clark's (1960) maximum 

stability temperature of 491° ± 12°C for the pyritearsenopyrite-pyrrhotite assemblage may not be fortuitous. Nevertheless, some indeterminate temperature below ,-,500°C is the best we can infer for crystallization 

of the pyrrhotite inclusions. 

Acanthite included in argentian tetrahedrite must 

qriginally have crystallized above 178°C if our interpretation of cubic cleavage as indicative of preexisting 

argentite is correct, if native silver was absent (it has 

not been found within the tetrahedrite), and if the system was "condensed" (Kracek, 1946; Skinner, 1966, 

p. 21). The inversion temperature is lowered only to 

176°C in the presence of free silver. Therefore, the 

tJetrahedrite host itself must have begun to form above 

approximately 177°C. 

Acanthite in acicular form, rimming tetrahedrite, 

*ust have formed at or below about 177°C. The apparent correlation between the assemblage of included 

~ulfides in pyrite and the paragenetic sequence of disdrete-grained minerals, extending through native silver, 

suggests that at least some late-formed acanthite is hypogene, but we know of no criteria for distinguishing 

between it and supergene acanthite. 

.I Digenite, bornite(?), and chalcocite in this assemI:Hage cannot be used as geologic thermometers because 

their polymorphs cannot be determined in these ext.femely small grains. Covellite is stable through a wide 

temperature range (l{ullerud, 1965). Because it replaces 

acanthite here, it must have formed below 177°C. 

Blaubleibender covellite is commonly a supergene min-

~ral (Frenzel, 1959, p. 157), but according to Skinner's 

~1966, p. 4) interpretation of Moh's (1964) work, it has 

no true stability field ; it occurs metastably ( ~) with 

covellite below 157°C (Moh, 1964) and might thus be 

either hypogene or supergene in the New Snowbird 

assemblage. 

The probable range in crystallization temperature for 

hypogene sulfides in the deposit is thus from something 

less than 491 o to less than 177°C, a range generally 

regarded as hypothermal to epithermal. Even if much 

qf the acanthite is supergene, which we doubt, more than 

9f5 percent of the sulfide-sulfosalt-native element assemWage formed above 177°C. 

CLASSIFICATION AND ORIGIN OF HYPOGENE 

MINERALIZATION 

We regard the New Snowbird deposit as xenothermal. The characteristics of this class are well summarized by Buddington ( 1935), who introduced the 

ttrm, and by Park and MacDiarmid ( 1964), who prov~de additional data. and examples. The dominant feature of xenothermal deposits is a misfit assemblage of 

minerals occurring together and including typically 

high-temperature minerals and typically low-temperature ones. Buddington interpreted such assemblages as 

having formed at high temperature and shallow or 

Inoderate depth. Regardless of origin, deposits that have 

this misfit composite assemblage are aptly termed 

xenothermal. 

Most features of the New Snowbird deposit are 

markedly similar to those listed by Park and MacDiarmid ( 1964, esp. p. 346-34 7, 350) for the xenothermal 

class, but other features are different. The similarities 

are: complex mineralogy; fine grain size; dumping, 

or simultaneous precipitation of minerals that are not 

ordinarily found together (pyrite with its varied inclusions) ; a recognizable sequence of deposition similar to that usually found in mesothermal base-metal 

vein deposits (the sequence of sulfides occurring as 

discrete grains), followed by minerals usually formed 

at lower temperature (silver sulfosalts, acanthite, blaubleibender covellite, and their associates) :_the telescoping of Spurr (1923, p. 292-308), which would 

embrace the whole New Snowbird assemblage; wide 

range of temperature indicated by certain geologic 

thermometers (pyrite-arsenopyrite formed at some 

temperature below 491° ± 12°C, but perhaps not much 

below; acanthite at or below 177°C); gangue minerals 

including quartz, feldspar, and apatite; a range of argillic and other alteration products; occurrence in a region of hypabyssal intrusives and associated volcanic 

rocks; repeated penetration of the lode by vein material (multiple generations of quartz). 

The principal differences are: occurrence of the ore 

minerals in massive replacement quartz (many xenothermal deposits are in fissure veins) ; lack of a pattern of hypogene zoning in nearby ore deposits of the 

district (the deposits are too poorly known to eliminate the possibility of zoning) ; lack of evidence that the 

New Snowbird and bro3Jdly similar deposits of the district were deposited at slight depth or have a restricted 

vertical range. 

The vertical range of mineralization at the New 

Snowbird is unknown. Ore was mined only above the 

haulage level, and exploration at greater depth was 

precluded by the fall of the price of tungsten ooncentrates. 

Classifying the deposit is easier than determining 

its origin. Except for the complexity of the local mineral assembl'age and the evident dumping and telescoping, the evolution of the assemblage seems consistent 

with that of the common ore minerals considered 

by Holland ( 1965) in his thermochemical treatment of ore genesis. The hypogene New Snowbird 
C20 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

assemblage 1nay have formed as temperature fell 

and the fugacity of S2 and 02 decreased in a 

hydrous; mildly :alkaline; C02-poor, Si02-rich system. (See Holland, 1965, figs. 37, 27, 17, 5, 8 and table 

2.) The stages or groups of ore minerals that we 

have recognized are merely convenient terms for 

grouping minerals according to their fabric. These 

groups are not separated by episodes of deformation 

or distinguished by radical change in the mineral 

assemblage, and there is no need to invoke polyascendent solutions to explain the groups. Rate of change 

in pressure, temperature, and fugacity-factors now 

beyond assessing in· detail-may account for the 

dumped assemblage included in pyrite, and for the 

weak evidence of depositional order among sphalerite, 

chalcopyrite, and galena. The process of metallization, 

though complex, seems to represent a single, uninterrupted episode. 

As an alternative hypothesis of origin, hypogene 

mineralization might represent two principal stages: 

earlier, high-temperature tungsten mineralization and 

later, medium- to low-temperature sulfide-precious 

1netal mineralization. Schneider-Scherbina ( 1962) 

postulated this sort of superposition for the tin-silver 

deposits of Bolivia, for which other geologists have inferred a xenothermal or telethermal origin. SchneiderScherbina related the earlier, generally high-temperature gold-tungsten-tin stages to deep-seated Mesozoic 

intrustives and the later, lower temperature stage to 

shallow Tertiary magmatic activity. Though a complete 

picture of vein mineralization in central Idaho is not 

at hand, several features suggest that Schneider-Scherbina's hypothesis is not directly applicable to the New 

Snowbird and broadly similar deposits of the Big Creek 

and Yellow Pine quadrangles. An episode of intense, 

deep-seated, but linearly localized metamorphism, yielding granoblastic microcline-bearing alaskite gneiss from 

the alaskitic facies of the Idaho batholith, occurred 

after consolidation of the batholith, whose age is commonly regarded as Cretaceous. No lode deposits of tungsten referable to this episode of metamorphism have 

been found during mapping of this 430-square-mile 

area, and none were documented by earlier workers. 

The linear granoblastic zone containing theN ew Snowbird deposit was silicified and then sheared before Tertiary dikes of the Profile-Smith Creek swarm were emplaced, for a dike at the Red Bluffs deposit locally carries small inclusions of sheared but barren replacement 

quartz. Tungsten minerals at these two deposits are 

confined to relatively coarser, not extensively sheared 

quartz that replaces parts of the zone of earlier silicification and evidently postdates (or perhaps is roughly 

contemporaneous with) the Tertiary dikes. Elemental 

silver is not restricted to relatively late minerals, such 

as acanthite and most of the native silver; it also occurs in pyrite as minute inclusions of native silver, electrum, inverted acanthite ( ~), Silberkies ( ~) minerals, 

argentian tetrahedrite, and argentian digenite. Some of 

the pyrite is arsenopyrite-pyrrhotite bearing, and 

pyrite with its inclusions seems to represent the initial 

wave of sulfide-precious metal mineralization. The 

fabric of the whole assemblage strongly suggests initial 

dumping of the precious-metal-bearing constituents 

and telescoping of the remaining members. Moreover, 

the widespread association of typically low-temperature 

1nineral assemblages with tungsten minerals, locally accompanied by molybdenite and tin minerals, in the 

eastern part of the Soviet Union, in Japan, in the Cordillera of the Americas, in Western Europe, in the 

Erzgebirge, and elsewhere, suggests a genetic unity that 

has seldom been demonstrable as an effect of discrete 

superposed episodes of mineralization. Therefore, an 

interpretation of the New Snowbird deposit as a xenothermal one resulting from a complex but essentially single episode of tungsten-sulfide-precious metal mineralization seems more reasonable at present. 

OXIDATION AND ENRICHMENT 

Some oxidation of primary ore is indicated by the 

presence of small quantities of goethite, much smaller 

quantities of pyrolusite, psilomelane, jarositic minerals, 

other sulfates, and tungsten alteration products, and 

traces of minerals such as tenorite and cerargyrite 

(table 5) . The lack of a gossan, the scarcity or ·absence 

of sulfates of Cu, Pb, and Zn, and the very low concentration of Br and Cl suggest either that oxidation 

has been very slight or that part of a preexisting oxidized zone of unknown metal content has been eroded. 

The latter possibility is more reasonable because even 

in this glaciated region highly oxidized base-metal 

sulfide veins are present within 3 miles of the New 

Snowbird; the cupriferous scheelite-pyrrhotite deposit 

at the Springfield mine (U.S. Geol. Survey, 1964, p. 

A4), 26 miles distant, shows much oxidation to goethite 

and melanterite; and the mercury-bearing stibnite deposit at the B and B mine is, in places, partly altered 

to antimony ocher (Leonard, 1965). Among these examples, only the oxidation of the Springfield protore is 

approximately datable: it is post-Idaho batholith and 

pre-Wisconsin, for large boulders of the former gossan 

are scattered throughout fresh glacial d~bris for 4,000 

feet downvalley from the outcropping primary sulfide 

body. If hypogene mineralization at the New Snowbird 

were as old as early Tertiary (which seems unlikely), 

the interval of planation and development of grus on 

Idaho batholith rocks, preceding deposition of the 
SILVER-RICH DISSEMINATED SULFIDES, CENTRAL IDAHO C21 

<Jhallis Volcanics, would be a likely time for oxidation 

~f the New Snowbird ore body. The Idaho batholith 

is generally regarded as mid -Cretaceous; the Challis 

Volcanics, mainly Oligocene, range in age from 

Eocene(?) to Miocene(?). Thus the interval of preChallis weathering of batholithic rocks is roughly 

limited between Late Cretaceous and perhaps Oligocene 

time. However, the age of hypogene mineralization at 

the New Snowbird's neighbor, the Red Bluffs tungsten 

deposit, is somewhat younger than, or perhaps roughly 

contemporaneous with, the enclosing swarm of Tertiary 

dikes. Dikes petrographically identical with those of 

the swarm cut the Challis Volcanics and are thus presumably Oligocene at the oldest. Ross ( 1934, p. 67; 

Shenon and Ross, 1936, p. 12, 19) thought that dikes 

qutting the Challis and dikes of the major swarms out-

¥de the Challis were Miocene, and they are generally 

fegarded as approximately mid-Tertiary. If dikes of 

tlhe Profile-Smith Creek swarm are Miocene, oxidation 

df the New Snowbird ore must have occurred between 

Miocene and Wisconsin time, an interval about which 

little is known in this area, where upper Tertiary deposits have not been recognized and lower Pleistocene 

deposits are sparse. The possibility of any but minor 

~xidation during Recent time is too slight to consider. 

I Oxidation of the ore is a fact, though the extent and 

ciate are unknown. Was oxidation accompanied by apIjreciable supergene sulfide enrichment? The only evidence now available is mineralogic; it is equivocal, but 

it bears directly on the attractiv.eness of disseminated 

~ulfide deposits as targets for exploration. The coatings 

f covellite, blaubleibender covellite, digenite, unidentied copper minerals, miargyrite ( ? ) , and acanthite are 

te, but their supergene origin is by no 1neans assured. 

igenite is usually regarded as hypog·ene, but the rest 

1re thought to be supergene in many deposits, hypogene 

in others. (See, for example, Bateman, 1950, p. 285-287; 

Mcl{instry, 1948, p. 150-155; Moh, 1964; Ramdohr, 

1960, p. 431-434, 441, 613, 629-630.) Part of the New 

Snowbird acanthite seems to be hypogene; all of it might 

be. The origin of the rim-forming copper sulfides is 

utterly enigmatic. Investigating the disseminated sulfides by probing at various depths offers the only solut~on to the problem. 

: If there is no bonanza here, are other bonanzas nevertheless present but undiscovered in the region? The 

possibility exists, but the likelihood seems slight. Most 

df the region is well exposed, and probably all of it 

has been searched for bonanzas lv; two generations of 

competent prospectors and company scouts. Conceivably some downfaulted block of oxidized or sulfideenriched ore may be concealed beneath glacial debris 

dnd alluvium in valleys athwart the major silicified 

zones. Other blocks might be thinly mantled by glacial 

debris and colluvium on north slopes. Doubtless some 

hypogene deposits, such as the recently found B and B 

anti1nony deposit (Leonard, 1965), have been so concealed. But until there is evidence that supergene alteration of a sparsely disseminated sulfide body has actually 

yielded rich ore somewhere in this region, the notion of 

bonanzas, concealed or otherwise, deserves no encouragement. 

ECONOMIC CONSIDERATIONS 

We have tri·ed to show what the disseminated sulfide 

assemblage from one deposit is, what and where its 

metal values are, and what kind of deposit yielded this 

material. The sulfides with their contained metals are 

efficiently recoverable by the simple, conventional techniques already used by the McRae Tungsten Corp. The 

grade of the crude ore is not precisely known, but a fair 

approximation of it shows that the metal content of 

the sulfides alone, divorced from the associated tungsten 

minerals, is not economic at prices prevailing in 1965. 

Nevertheless, deposits of this sort, provided they are 

sufficiently large, are a metal source of considerable 

potential value. The development of such a resource 

depends on many factors, of which geologic occurrence 

is only one, but the interplay of demand, price, scientific knowledge, technologic skill, and initiative that 

have in a few generations led to the exploitation of remarkably low-grade deposits of copper, iron, and uranium should stimulate us to look closely at resources 

that are not at the moment commercially attractive. 

Three factors bearing on the immediate problem 

deserve comment. These are : local geology, difficulties 

of sampling disseminated d·eposits, and relation to 

porphyry copper deposits. 

Our mineralogic study is a byproduct of regional 

geologic mapping of the Yellow Pine and Big Greek 

quadrangles. Maps in preparation show the general 

distribution of Inajor silicified zones in the first quadrangle and thei~ coextension with the Profile-Smith 

Creek dike swarm in the second. These zones are very 

large. Commonly though not uniformly 'they contain 

sparsely disseminated sulfides. Local concentrations of 

base and precious metals are present, with or without 

mercury, antimony, and tungsten minerals. Many of 

these concentrations have been prospected; a few have 

been mined. The number of showings of gold-bearing 

base-metal sulfides grerutly exceeds all others. It is geologically reasonable to suppose that some of these, as 

well as some unexploited tungsten deposits, may be accompanied by disseminated precious-metal-bearing sulfides similar to those of the New Snowbird deposit. 

Probably not more than one of the gold-bearing basemetal showings has been carefully examined with an 
C22 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

eye to the occurrence of extremely low-grade gold or 

silver. Yet the old prospectors' dictum (C. P. Ross, oral 

commun., 1953) that "* * * any quartz vein in the Big 

Gr'eek country will run a dollar a t;on [combined gold 

and silver?], old price * * * ." indicates that very small 

amounts of gold and silver are present and perhaps 

widespread in the silicified zones, though the assay 

value may have been exaggerated by the early 

prospectors. 

Pyrite is sparsely disseminated in some porphyry 

dikes between the New Snowbird and Red Bluffs deposits and occurs elsewhere in dikes and batholithic 

rocks of the major silicified zones. Scheelite is present in 

a very few dikes. The metal content of these rocks may 

be worth investigating because of their involvement 

with the silicified zones. 

Sampling a disseminated deposit such as the New 

Snowbird is difficul1t, especially if the metals sought are 

bound to fine-grained, brittle pyrite. For example, conventional sampling techniques used in underground 

exploration of a disseminated pyritic gold deposit 

near Yell ow Pine yielded an occasional high 'assay 

value for precious metals but many virtual blanks. 

More reliable sampling results might be obtained by 

collecting fewer and larger samples-say 100 pounds-, 

carefully separating the sulfide fraction by froth flotation in a pilot cell, splitting the concentrate for microscopic study and assay, and assaying the concentrate 

and tailing separately. 

The sulfide-bearing part of ·the New Snowbird deposit has several cha!'lacteristics required by Parsons' 

(1957, p. 8-12) definition of porphyry copper deposits. 

These are low average metal content, spatial if not 

genetic association with intrusive porphyry, presence 

of products of oxidation and sulfide enrichment, and 

occurrence of protore. H. remains to be determined 

whether the other requirements of convenient mining 

shape and large size, uniformity of metal distribution, 

and limitation by assay value of metals are satisfied. 

Table 8 shows considerable similarity in the total 

metal content of New Snowbird ore and ore from the 

San Manuel porphyry copper deposit. Data for the 

New Snowbird are only approximate. Nevertheless, 

the correspondence in magnitude is enough to show that 

in grade, as well as in some other features, the New 

Snowbird might be viewed as a sort of porphyry tungsten deposit. San Manuel is used for comparison because :the mine was developed rather recently, data on 

recoverable precious-metal content of the ore are conveniently •available, and the mine ranks low among 

porphyry coppers that yield precious metals. For San 

Manuel ore, the value of metals listed in table 8 is $5.20 

per •ton at September 1965 prices. This is about 10 times 

the value of metals in the New Snowbird ore, if tungsten is excluded. The per-ton dollar value of the tungsten 

ore when sold was, of course, about 10 times the 1965 

value of San Manuel ore. But more important resource~ 

wise than the dollar value of the San Manuel 

ore is the mine's annual production of about 187,000 

·troy ounces of silver and 12,600 ounces of gold during 

the period represented in table 8 (data from Creasey, 

1965, p. 30). San Manuel is generally one of the 25 top 

silver producers of the country, as well as one of the 20 

top gold producers, though the ore averages only 0.8 

ppm (parts per million) Ag and 0.05 ppm Au per ton, 

equivalent to 0.023 and 0.0015 troy ounces, respectively. 

The precious-metal content of the New Snowbird ore 

is higher (table 8) . Again, this ernphasizes a potential 

resource value, not a currently assessable dollar value. 

TABLE 8.-Metal concentration (recoverable basis) in crude ore, 

New Snowbird tungsten deposit and San Manuel copper deposit 

[Values in ppm] 

New Snowbird t 

Ag_________________ 7. 5 

Au_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . 1 

Cu_________________ 27 

Pb_________________ 27 

Zn_________________ 22 

San Manuel2 

0. 8 

. 05 

5,780 

w----------------- 4, 420 - - - - - --- - - - - Mo ________________ ------------ 47 

TotaL _______ _ 4,504 5,828 

t Data for elements except W estimated from 

approximately known recovery of pyrite concen- trate and from weighted assays that include one low-Ag assay not made by U.S. Geological Survey. 

Data for W based on known recovery of """' 82 

percent. 2 Data based on 1956-59 production from San 

Manuel deposit (Creasey, 1965, p. 30), recalculated 

by Leonard. 

The extraction of gold and silver from deposits 

whose base-metal content is very low could be temporarily advantageous to the mineral economy because it 

would not simultaneously stimulate a large production 

of copper, lead, and zinc-metals whose supply is normally more nearly adequate. (See Kiilsgaard, 1964; 

Merrill and others, 1965.) At least one of the disseminated sulfide deposits in silicified zones of the Big 

Creek-Yellow Pine area has this favorable ratio of 

precious metals to base metals. 

Careful examination of the poten'tial resources of the 

silicified zones of the region seems warranted. The exploration and development of such resources, if the 

time is ever ·ripe for i•t, will be costly, difficult, and time 

consuming, presumably in some measure as the expected value of the metal content relates to that of the 

porphyry coppers. The problem is great, but so is the 

challenge. 
SILVER-RICH DISSEMINATED SULFIDES, CENTRAL IDAHO C23 

ACKNOWLEDGMENTS 

We could not have made this study without the aslsist:ance of many people. Robert McRae, president of 

McRae Tungsten Corp., provided aecom!noda.tions at 

the mine and supplied information on the deposit and 

on extraction of the ore. Paul Desautels, U.S. National 

Museum, provided a large surte of 1nineral specimens 

for c01nparison. Brian Skinner, formerly of the U.S. 

Geological Survey, provided polished sections of jalpaite, mckinstryite, and stron1eyerite. Detailed geologic 

mapping by the U.S. Geological Survey Defense Minerals Exploration field team was used to supplement 

Leonard's fieldwork. Indispensable analytical work 

1

was done by Survey colleagues whose contributions are 

noted in the tables of analyses and in the text. Many 

of the mineral separa:tions were carried out by William 

Brennan, George Fairer, Paul Mayrose, and Lee Shropshire. W. N. Sharp took photomicrographs used to locate grains for electron probe analysis. E. P. l{rier took 

the photmnierogra phs that illustrate this report. Professor J. 0. Kalliokoski, Princeton University, called 

our attention to the paper by Genkin and others 

(1966). H. R. Cornwall, R. P. Fischer, S. W. Hobbs, 

R. L. Parker, Ray E. Wilcox, and a seminar at the 

University of Minnesota improved this report by disrussian and comment. 

. REFERENCES 

Arnold, R. G., 1962, Equilibrium relations between pyrrhotite 

and pyrite from 325° to 743°C: Econ. Geology, v. 57, p. 

72-90. 

' 1966, Mixtures of hexagonal and monoclinic pyrrhotite 

nd the measurement of the metal content of pyrrhotite by 

-ray diffraction: Am. Mineralogist, v. 51, p. 1221-1227. 

~ateman, A. M., 1950, Economic mineral deposits: 2d ed., New 

I York, John Wiley & Sons, 916 p. 

Berry, L. G., and Thompson, R. M., 1962, X-ray powder data for 

ore minerals-the Peacock atlas : Geol. Soc. America Mem. 

85, 281p. 

Buddington, A. F., 1935, High-temperature mineral associations 

at shallow to moderate depths: Econ. Geology, v. 30, p. 

205-222. 

Bud'ko, I. A., and Kulagov, E. A., 1963, Natural cubic chalcopyrite: Acad. Sci. USSR Doklady, Earth Sci. Sections [translation], v. 152, p. 135-137. 

plark, L. A., 1960, The Fe-As-S system-Phase relations and applications: Econ. Geology, v. 55, p. 1345-1381; 1631-1652. I 

Cooper, J. R., 1951, Geology of the tungsten, antimony, and gold 

deposits near Stibnite, Idaho: U.S. Geol. Survey Bull. 969-

F, p. 151-197. 

Creasey, S. C., 1965, Geology of the San Manuel area, Pinal 

1 County, Arizona: U.S. Geol. Survey Prof. Paper 471, 64 p. 

Desborough, G. A., and Carpenter, R. H., 1965, Phase relations 

of pyrrhotite: Econ. Geology, v. 60, p. 1431-1450. 

Djurle, Seved, 1958, An X-ray study on the system Cu-S: Acta 

Chern. Scand., v. 12, p. 1415-1426. 

Ferguson, H. G., 1929, The mining districts of Nevada: Econ. 

Geology, v. 24, p. 115-148. 

Frenzel, Gerhard, 1959, Idait und "blaubleibender Covellin": 

Neues Jahrb. Mineralogie, Abh., v. 93, p. 87-132. 

Genkin, A. D., Filimonova, A. A., Shadlun, T. N., Soboleva, S. 

V., and Troneva, N. V., 1966, 0 kubicheskom kubanite i kubicheskom khal'kopirite [Cubic cubanite and cubic chalcopyrite]: Geologiya Rudnykh Mestorozhdenii, v. 8, p. 41-54. 

Goldsmith, J. R., and Laves, Fritz, 1954, The microcline-sanidine stability relations: Geochim. et Cosmochim. Acta, v. 

5, p.1-19. 

Hey, M. H., 1955, An index of mineral species and varieties 

arranged chemically: 2d ed., London, British Museum 

(Natural History), 728 p. 

Holland, H. D., 1965, Some applications llf thermochemical data 

to problems of ore deposits, II, Mineral assemblages and the 

composition of ore-forming fluids: Econ. Geology, v. 60, p. 

1101-1166. 

Jacobsen, W., 1965, Untersuchungen iiber den SUbergehalt der 

Kupfererze von Manglila, Siidrhodesien: Neues Jahrb. 

Mineralogie Abh., v. 104, p. 1-28. 

Kiilsgaard, T. H., 1964, Silver: Mining Cong. Jour., v. 50, p. 

60-64. 

Kracek, F. C., 1946, Phase relations- in the system sulfur-silver 

and the transitions in silver sulfide: Am. Geophys. Union 

Trans., v. 27, p. 364-374. 

Kullerud, G., 1965, Covellite stability relations in the Cu-S 

system: Freiberger Forschungshefte C 186, p. 145-160. 

Kullerud, G., Doe, B. R., Buseck, P. R., and Troften, P. F., 1963, 

Heating experiments on monoclinic pyrrh<Ytites: Carnegie 

Inst. Washington Year Book 62, p. 210-213. 

Lakin, H. W., and Thompson, C. E., 1963, Tellurium-a new 

sensitive test: Science, v. 141, no. 3575, p. 42-43. 

Leonard, B. F., 1965, Mercury-bearing antimony deposit between 

Big Creek and Yellow Pine, central Idaho, in Geological 

Survey research 1965: U.S. Geol. Survey Prof. Paper 525-B, 

p. B23-B28. 

McKinstry, H. E., 1948, Mining geology: New York, PrenticeHall, 680 p. 

Merrill, C. W., McKnight, E. T., Kiilsgaard, T. H., and Ryan, 

J. P., 1965, Silver-facts, estimates, and projections: U.S. 

Bur. Mines Inf. Circ. 8257, 22 p. 

Moh, G. H., 1964, Blaubleibender covellite : Carnegie Inst. Washington Year Book 63, p. 208-209. 

Morimoto, Nobuo, and Clark, L. A., 1961, Arsenopyrite crystalchemical relations: Am. Mineralogist, v. 46, p. 1448-1469. 

Morimoto, N., and Kullerud, G., 1963, Polymorphism in digenite: 

Am. Mineralogist, v. 48, p.110-123. 

Nolan, T. B., 1933, Epithermal precious-m£>tal deposits, in Ore 

deposits of the Western S1tates (Lindgren volume): New 

York, Am. Inst. Mining Metall. Engineers, p. 623-640. 

Park, C. F., Jr., and MacDiarmid, R. A., 1964, Ore deposits: San 

Francisco, W. H. Freeman & Co., 47G p, 

Parsons, A. B., 1957, The porphyry coppers in 1956: New York, 

Am. Inst. Mining, Metall., and Petroleum Engineers, 270 p. 

Peck, L. C., 1964, Systematic analysis of silicates: U.S. Geol. 

Survey Bull. 1170, 89 p. 

Ramdohr, Paul, 1960, Die Erzmineralien und ihre Verwachsungen: 3d ed., Berlin, Akademie-Verlag, 1089 p. 

Ross, C. P., 1934, Geology and ore deposits of the Casto quadrangle, Idaho: U.S. Geol. Survey Bull. 854, 135 p. 

Sasaki, Akira, 1959, Variation of unit cell parameters in 

wolframite series: Mineralog. Jour., v. 2, p. 375-396. 
C24 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

Schneider-Scherbina, Alexander, 1962, Uber metallogenetische 

Epochen Boliviens und den hybriden Charakter der sogenannten Zinn-Silber-Formation: Geol. Jahrb., v. 81, p. 157-

170 [19641. 

Shenon, P. J., and Ross. C. P., 1936, Geology and ore deposits 

near Edwardsburg and Thunder Mountain, Idaho : Idaho 

Bur. Mines and Geology Pamph. 44, 45 p. 

Skinner, B. J., 1966, The system Cu-Ag-S : Econ. Geology, v. 61, 

p.l-26. 

Skinner, B. J., Jambor, J. L., and Ross, Malcolm, 1966, Mckinstryite, a new copper-silver sulfide: Econ. Geology, v. 61, 

p. 1383-1389. 

Spurr, J. E., 1923, The ore magmas, v. l: New York, McGrawHill Book Co., 430 p. 

U.S. Bureau of Mines, 1938--1952, 1956, Minerals Yearbook 

[annual volumes for the years indicated]. 

U.S. Geological Survey, 1964, Geological Survey research 1964: 

U.S. Geol. Survey Prof. Paper 501-A, 367 p. 
PLATES 1-4 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 594-G PLATE 1 

A 

B c D 

ACANTHITE AND COPPER SULFIDES ON GALENA 

A.-Galena (white) rimmed by acanthite (light gray) and then by unidentified copper minerals (medium gray). Grain mounted 

in plastic (black). Drawn from a photomicrograph of a polished section. Dashed square represents area scanned by electron 

beam in B, C, D. 

B.-X-ray scanning micrograph (photograph of X-ray pulses displayed on oscilloscope screen). Emitted PbLa radiation. 

C.-X-ray micrograph, AgLa. 

D.-X-ray micrograph, CuKa. 

Sparsely distributed bright specks in B, C, and D are due to background radiation recorded during long exposure, not to 

characteristic X-rays emitted by element present in trace amount. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 594- C PLATE 2 

A 

B c D 

ELECTRUM IN PYRITE 

A.-Gold-rich electrum (white) in pyrite (dark gray) that is slightly pitted (black patches). Other inclusions are mainly quartz 

(l ight gray). Grain mounted in plastic (white background). Drawn from a photomicrograph of a polished section. Dashed 

square represents area scanned by electron beam in B, C, D . 

B.- X-ray micrograph, AuLa radiation. 

C.-X-ray micrograph, AgLa. 

D.-X-ray micrograph, FeKa. 

Sparsely distributed bright specks in B, C, and D are due to background radiation recorded during long exposure, not to 

characteristic X-rays emitted by element present in trace amount. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 594-C PLATE 3 

ELECTRUM IN PYRITE 

Photomicrograph of gold-rich electrum (white) in 

pyrite (light gray). Elongate blacl{ grain at lower 

right is sphalerite with adjoining gray grains of a 

Silberkies ( ? ) mineral (upper left) and pyrrhotite 

(lower left). Gray grains left of center are soft 

white mineral. Black "inclusions" at left and bottom 

are pits. Euhedral arsenopyrite inclusions, easily 

seen in the original, are invisible in the photogmph 

because their polishing hardness and reflectivity 

match those of the pyrite host. Black background 

is pla•stic mounting medium. Oil immersion. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 594- C PLATE 4 

SILVER AND INVERTED AG-FE-S MINERAL IN PYRITE 

A.-Photomicrograph of blebs of native silver (white) in pitted subhedral 

pyrite (light gray). Bits of galena (low relief) and pyrite are 

attached to upper and right edges of the pyrite cube. Embedding 

medium is plastic (black). Dry objec<tdve. 

B.-Photomicrograph of "pegboard" of minute inclusions in slightly 

corroded pyrite (light gray). Inclusions are mainly acanthite (medium gray) after argentlite. Bright specks northeast and west of 

crosshairs are native silver (white). Inclusions of pyrrhotite(?) 

and argentopyrite( ?) cannot be distinguished in photograph. Inclusions are inJterpreted as inversion products of a high-temperature 

cubic(?) Ag-Fe-S precursor, Oil immersion. 

U.S. GOVERNMENT PRINTING OFFICE: 1968 0-27<>-675