Gold-Bearing Skarns 

U.S. GEOLOGICAL SURVEY BULLETIN 1930 
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Gold-Bearing Skarns 

By TED G. THEODORE, GRETA J. ORRIS, 

JANE M. HAMMARSTROM, and JAMES D. BLISS 

U.S. GEOLOGICAL SURVEY BULLETIN 1930 
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade, product, or firm names in this publication 

is for descriptive purposes only and does not imply 

endorsement by the U.S. Government 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1991 

For sale by the 

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Library of Congress Cataloging-in-Publication Data 

Gold-bearing skarns I by Ted G. Theodore ... [et al.} 

p. em.- (U.S. Geological Survey bulletin : 1930) 

Includes bibliographical references. 

Supt. of Docs. no.: I 19.3: 1930 

1. Skarn. 2. Gold ores. I. Theodore, Ted. G. II. Series. 

QE75.89 no. 1930 

[QE475.A2} 

557.3 s-dc20 90-3885 

[553.4'1} CIP 
CONTENTS 

Abstract 1 

Introduction 1 

Acknowledgments 1 

Data 2 

Geology 6 

General deposit definition 6 

Associated deposits 7 

Tectonostratigraphic setting and paleodepths 10 

Age range 11 

Host and associated rocks 11 

Ore minerals 13 

Gangue mineralogy 14 

W allrock alteration 17 

Structural setting 18 

Dimensions of ore in typical deposits 18 

Dimensions of alteration or distinctive haloes 18 

Effect of weathering 18 

Effect of metamorphism 19 

Geochemical signatures 19 

Isotopic signatures 20 

Fluid inclusions 20 

Geophysical signatures 21 

Ore controls/exploration guides 21 

Grades and tonnages of gold-bearing skarns 21 

References cited 23 

Bibliography of additional gold-bearing skarn references 32 

FIGURES 

1. Graphs showing distributions of tonnage for Au-bearing skarn deposits 2 

2. Graphs showing distributions of gold grade for Au-bearing skarn deposits 3 

3. Graphs showing gold skarn classification schemes based on metal ratios 4 

4. Schematic cross sections of Au-skarn deposits in north-central Nevada 8 

5. Map showing distribution of Au-skarn districts and geological provinces in the 

cordillera of western North America 10 

6. Map showing worldwide distribution of major Au-bearing skarn deposits and 

fold belts 12 

7. Graphs showing chemical compositions of igneous rocks associated with major 

types of mineralized skarn 13 

8. Photomicrographs showing textural relations of gold and electrum in selected 

Au-skarn deposits 14 

9. Photomicrographs showing complexly zoned garnets from oxidized skarn, 

Surprise Mine, Nevada 16 

10. Ternary diagrams showing ranges of garnet compositions for representative 

samples from five Au-bearing skarn systems in north-central Nevada 16 

11. Ternary diagrams showing ranges of pyroxene compositions for representative 

samples from three Au-bearing skarn systems in north-central Nevada 17 

12. Photomicrograph showing massive garnet partly replaced by pyrrhotite and 

chalcopyrite 18 

13. Graphs showing distributions of silver grade for Au-bearing skarns 22 

14. Graphs showing gold grade compared with copper grade and silver grade 23 

Contents Ill 
IV Contents 

TABLES 

1. Abbreviations used in tables 38 

2. Gold-bearing skarns in which gold and silver are major commodities 

exploited 40 

3. Gold-bearing skarns in which gold and silver are byproduct commodities 46 

4. Gold-bearing skarn deposits and deposits purported to be gold-bearing skarns 

for which grade and tonnage data are unavailable 54 

5. Mineral abundances for gold-bearing skarns 59 

6. Analytical data for some igneous rocks associated with gold-bearing skarn 

deposits in north-central Nevada 59 · 

7. Representative data for minerals in gold skarns from north-central Nevada 60 

8. Chemical signatures of nontronite clay layers associated with gold-bearing 

skarns 61 
Gold-Bearing Skarns 

By Ted G. Theodore, Greta j. Orris, jane M. Hammarstrom, and james D. Bliss 

Abstract 

In recent years, a significant proportion of the mining 

industry's interest has been centered on discovery of gold 

deposits; this includes discovery of additional deposits where 

gold occurs in skarn, such as at Fortitude, Nevada, and at Red 

Dome, Australia. Under the classification of Au-bearing skarns, 

we have modeled these and similar gold-rich deposits that 

have a gold grade of at least 1 g/t and exhibit distinctive skarn 

mineralogy. Two subtypes, Au-skarns and byproduct Au-skarns, 

can be recognized on the basis of gold, silver, and base-metal 

grades, although many other geologic factors apparently are 

still undistinguishable largely because of a lack of detailed 

studies of the Au-skarns. Median grades and tonnage for 40 

Au-skarn deposits are 8.6 g/t Au, 5.0 g/t Ag, and 213,000 t. 

Median grades and tonnage for 50 byproduct Au-skarn deposits 

are 3.7 g/t Au, 37 g/t Ag, and 330,000 t. Gold-bearing skarns 

are generally calcic exoskarns associated with intense retrograde hydrosilicate alteration. These skarns may contain economic amounts of numerous other commodities (Cu, Fe, Pb, 

Zn, As, Bi, W, Sb, Co, Cd, and S) as well as gold and silver. 

Most Au-bearing skarns are found in Paleozoic and Cenozoic 

orogenic-belt and island-arc settings and are associated with 

felsic to intermediate intrusive rocks of Paleozoic to Tertiary 

age. Native gold, electrum, pyrite, pyrrhotite, chalcopyrite, 

arsenopyrite, sphalerite, galena, bismuth minerals, and magnetite or hematite are the most common opaque minerals. 

Gangue minerals typically include garnet (andradite-grossular), 

pyroxene (diopside-hedenbergite), wollastonite, chlorite, epidote, quartz, actinolite-tremolite, and (or) calcite. 

INTRODUCTION 

Gold exploration efforts of the mining industry in 

the last few years have centered on discovery of skarn 

deposits, such as Battle Mountain Gold Company's Fortitude 

deposit in Nevada, and Elders Resources' Red Dome deposit 

in Queensland, Australia, as well as on discovery of 

disseminated, carbonate-hosted, or Carlin-type deposits. 

Carbonate-hosted gold deposits are generally much larger 

deposits than skarns but are of much lower grade. Bagby 

and others (1987) report median tonnage and grade values 

Manuscript approved for publication, January 11, 1990. 

of 5.1 million tonnes and 2.5 g/t Au, respectively, for 35 

Carlin-type deposits. Median tonnage and grade values for 

the 90 skarn deposits we report in this study are 0.279 

million tonnes and 5.7 g/t Au, respectively. Some major 

gold skarns, such as the Lower Fortitude deposi4 Nevada 

(5.1 million tonne, 10.45 g/t Au), and the deposit at Bau, 

Malaysia (2.4 million tonnes), however, contain more gold 

than many of the large, disseminated-type deposits and are 

thus extremely attractive as exploration targets. The geologic 

characteristics of gold-bearing skarn deposits have only 

recently been addressed (Meinert, 1988a,b, 1989). This paper 

presents descriptive and grade-tonnage information obtained 

from more than 90 deposits that have been referred to in the 

literature as "Au-bearing skarns," "Au-rich skarn," or "Auskarn," in a format somewhat similar to models in Cox and 

Singer (1986) but as modified by P.B. Barton (written 

commun., 1986). These and many other deposits, generally 

referred to as gold skarns in the literature, are occasionally 

further differentiated into contact, or proximal, skarns and 

distal skarns (Sillitoe, 1983, 1987; Bonham, 1985). Special 

attention has been given to the mineral chemistry of gangue 

skarn minerals as they have previously proved useful in 

distinguishing skarn types. 

This paper consists of a geologic description of Aubearing skarns, presented in a form modified from that 

established previously for Cu-, Zn-Pb-, and Fe-skarn 

descriptive models (Cox and Singer, 1986) to allow rapid 

comparison and contrast; grade-tonnage distributions of Aubearing skarns; and a combination references-bibliography 

section. 

Acknowledgments 

We thank the following people who contributed to 

this paper: William C. Bagby, Donald A. Singer, Greg E. 

McKelvey, W. David Menzie, Dan L. Mosier, Robert C. 

Pearson, James E. Elliott, and James J. Rytuba of the U.S. 

Geological Survey; David W. Blake, R.G. Benson, Kirk W. 

Schmidt, and Patrick R. Wotruba of Battle Mountain Gold 

Company; Edward I. Bloomstein of Santa Fe Pacific Mining, 

Inc.; Gail M. Jones of Western Geologic Resources, San 

Rafael, Calif.; Bruce A. Kuyper of Echo Bay Mining Co.; 

JeffS. Loen and John Childs of Lupine Minerals; N. Eric 

Pier of Pegasus Gold Corporation; Larry Hillesland of West 

Introduction 
Gold; Fess Foster, Golden Sunlight Mines, Inc.; Sharon E. 

Lewis, Montana Bureau of Mines and Geology; Nolan 

Smith, Philipsburg, Montana, and Robert G. Russel, Coeur 

d'Alene, Idaho. 

DATA 

In our examination of the geologic literature for over 

300 skarns, we determined that about 65 percent of those 

reported detectable gold in amounts ranging from a trace to 

approximately 157 grams per tonne (g/t). Data are compiled 

for approximately 125 skarn deposits, and the deposit 

tonnage and gold grade distributions of 90 of those with a 

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gold grade of 1 g/t or higher are compiled in tables 1-4 and 

are shown in figures 1 and 2. Grade and tonnage values 

(tables 2 and 3) are reported in metric units: grams per 

tonne (g/t) and millions of tonnes (Mt), respectively. Most 

of the production data in the references cited is reported in 

terms of troy ounces (1 troy ounce= 31.103 g) and short 

tons (1 short ton = 1.102 t) and was converted to the 

appropriate metric equivalent for this report. In many older 

publications, only ore tonnages and dollar amounts of gold 

produced are cited. Where possible, we estimated gold grades 

from these dollar amounts using the appropriate prevailing 

gold price. For example, the price of gold was fixed at 

$20.67 per troy ounce from 1834 to 1934, except during the 

Civil War and during suspensions of specie payment in 

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MILLIONS OF TONNES, IN LOG UNITS 

Figure 1. Distributions of tonnage for Au-bearing skarn deposits. A, Tonnage histogram for 90 Au- and byproduct Au-skarn deposits. 

8, Tonnage model, same data set. C, Tonnage model for 39 Au-skarns. 0, Tonnage model for 59 byproduct Au-skarns. 

2 Gold-Bearing Skarns 
1837 and 1857 (see discussion in Shawe, 1988). 

All gold-bearing skarns can, as a first approximation, 

be treated as deposits in one of two subtypes that have 

different gold, silver, and base-metal grade distributions: 

(1) skarns in which gold is the primary commodity and (2) 

skarns in which gold had been or is being recovered as a 

byproduct However, in some already mined out deposits 

wherein gold was recovered as a byproduct, changes in 

metal prices to those prevailing during the late 1980's would 

result in gold assuming the role of primary commodity 

because of sufficient gold grade. A set of criteria has been 

established to determine whether a deposit should be 

classified as an Au-bearing skarn: 

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1. The deposit must have an average gold grade of 

at least 1 g/t. 

2. The mineral assemblage(s) of the deposit must 

include mineralogy that indicates that a skarn environment 

was genetically associated with introduction of gold Meinert 

(1988a) emphasized that a critical mineralogic feature of 

Au-bearing skarn is the presence of pyroxene and garnet. 

However, as we discuss below, introduction of most gold in 

such deposits does not necessarily occur during prograde 

pyroxene- and garnet-stages of skarn development 

Among skarns that meet these two criteria, some 

were mined primarily for their precious-metal content, 

whereas others were either mined primarily for their base0 

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GOLD GRADE, IN LOG UNITS OF GRAMS PER TONNE 

Figure 2. Distributions of gold grade for Au-bearing skarn deposits. A, Gold grade histogram for 90 Au- and byproduct Au-skarn 

deposits. B, Gold grade model, same data set. C, Gold grade model for 39 Au-skarns. D, Gold grade model for 59 byproduct 

Au-skarns. 

Data 3 
and ferrous-metal content or were mined for precious metals 

but contained very large amounts of base and ferrous metals. 

The presence of some gold in Cu-, Fe-, and W-skarn was 

characterized appropriately by Lindgren (1933): "Gold is 

present in traces in almost all sulphide deposits of the 

pyrometasomatic type, and a few ounces of silver to the ton 

is likewise not unusual***." Skarn deposits with byproduct 

gold that average at least 1 g/t and with base-metal grades 

less than the lowest tenth percentile of a grade model of 

copper (0.7 percent Cu) in Cu skarns (Jones and Menzie, 

1986), of zinc (2.7 percent Zn) or lead (0.87 percent Pb) in 

a Zn-Pb skarn model (Mosier, 1986), or of iron (36 percent 

Fe) in Fe skarns (Mosier and Menzie, 1986) are included in 

an Au-skarn data subset (table 2). Skarn deposits with greater 

than 1 g/t gold and higher base- and ferrous-metal grades 

that fit existing models of base- and ferrous-metal skarndeposit types are assigned to a byproduct Au-skarn data 

subset (table 3). Orris and others (1987) presented these 

criteria for classification of Au-bearing skarns along with a 

preliminary compilation of deposits. Much of the information 

in that report has been updated and revised because of 

subsequent availability of newly released data, and a number 

of deposits have been added. The geologic characteristics 

of many deposits in our byproduct Au-skarn subset are as 

important from the viewpoint of a gold explorationist in the 

late 1980's as are the characteristics of the Au-skarn subset. 

Many of the byproduct Au-skarn deposits exploited at their 

respective grades of gold greater than 1 g/t before 1950 

(table 3) undoubtedly would have been evaluated only for 

their precious-metal content if first discovered in the late 

1980's. Admittedly, the classification scheme above is for 

drilled out deposits currently in production or for deposits 

that have been mined out, and the classification scheme 

strictly cannot be used to classify precious-metalmineralized, unexploited skarns (Ettlinger and Ray, 1989). 

Nonetheless, the classification schem~ provides a data base 

of precious-metal-mineralized skarns to which data from 

unexploited skarns may be compared. Studies by Myers 

and Meinert (1988), G.L. Myers (written commun., 1988), 

and Ettlinger and Ray (1989) have shown that metal ratios 

in metallized skarns may be used to discriminate effectively 

among types of Au-bearing skarn. Myers and Meinert (1988) 

suggested that true copper skarns have Au/Cu ratios (where 

gold grade is in grams per tonne and copper grade is in 

weight percent) less than about 3. On the one hand, all 20 

skarns classed as Au-skarns, as we defined above, for which 

gold and copper grades are available, show Au/Cu ratios 

greater than 3 (table 2). On the other hand, 22 of 50 

byproduct Au-skarns have Au/Cu ratios greater than 3 (table 

3). Therefore, adoption of the classification scheme of Myers 

and Meinert (1988) based on that ratio would result in the 

addition of the 22 deposits to our Au~skarn data set (table 

2). These 22 deposits, however, fit existing models for basemetal skarns. Within gold-bearing skarn, deposits of our 

Au ... skarn subset cluster in a domain showing elevated overall 

4 Gold-Bearing Skarns 

abundances of gold and an increased Au/Cu ratio relative to 

most deposits in the byproduct Au-skarn subset for which 

data are available (tables 2, 3; fig. 3A). Ettlinger and Ray 

(1989, fig. 51) defined fields for gold (silver), copper, iron, 

and silver-poor gold-rich skarns based on Cu/Ag and Cu/ 

Au ratios. Of the 20 deposits in our Au-skarn subset (table 

2) that report grade values for Au, Ag, and Cu, 16 plot 

within the gold (silver) field (fig. 3B). The Surprise deposit, 

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EXPLANATION 

o Byproduct Au-skarn 

• Au-skarn 

11 '1o 1oo 10oo 1o:ooo 1oo.ooo 

Cu (WEIGHT PERCENT)/ Au (WEIGHT PERCENT) 

Figure 3 .. Gold skarn classification schemes based on metal 

ratios. A, Gold-copper ratios compared with contained gold 

(average grade multiplied by tonnage) for 20 Au- and for 47 

byproduct Au-skarn deposits for which copper grades are 

available. B, Copper/silver ratios compared with copper/gold 

ratios for the same data set. Fields for gold (silver), copper, iron, 

and silver-rich skarns are from Ettlinger and Ray (1989). 
which we included as an Au-skarn rather than a byproduct 

skarn, plots on the boundary of the copper skarn field. 

Although the Surprise deposit is copper-rich and has an 

average grade of 0.85 percent Cu (above the 0. 7 percent Cu 

grade for the lowest tenth percentile grade for copper in the 

copper skarn model of Jones and Menzie, 1986), we included 

it in table 2 because it is presently being mined for gold 

alone. The 42 deposits in our byproduct subset (table 3) for 

which grade data are available for all three elements are 

scattered about the central region of figure 3B; nearly half of 

the deposits cluster in and near the copper skarn field. 

Interestingly, the one iron skarn in our byproduct subset, 

Larap, plots in the gold (silver) region of figure 3B, at a much 

lower Cu/ Au ratio than that defmed for iron skarn. Four of 

the seven Zn-Pb byproduct gold skarns plot outside of any 

of the fields defmed by Ettlinger and Ray due to their low 

Cu/Ag ratio; one deposit plots within the gold (silver) field 

and two plot within the copper skarn field. 

All three methods for classifying gold-bearing skarn 

deposits (this study, Myers and Meinert's Au/Cu ratio, and 

Ettlinger and Ray's Cu/Ag vs. Cu/Au ratio) converge on 

the conclusion that most deposits that can be mined primarily 

for their gold content have log Cu/Au ratios less than about 

3 to 3.5 and have a slightly lower Cu/Ag ratio than copperrich skarns. By restricting our byproduct Au-skarn data (table 

3) to those known skarn systems wherein gold concentrations 

are greater than or equal to 1 g/t, we provide composited 

cumulative-distribution relations only for the Au-enriched 

part of Cu, Pb-Zn, and Fe skarns as defined by Jones and 

Menzie (1986), Mosier (1986), Mosier and Menzie (1986), 

and Meinert (1988a, b). According to our definitions, Aubearing skarn may include both Au-rich and Ag-rich variants 

of skarn as employed in the terminology of Ray and others 

(1986a). An example of geologic linkage between Au-skarn 

deposits and byproduct Au-skarn deposits is present at 

Copper Canyon, Nevada (Wotruba and others, 1986; 1987a, 

b; Myers and Meinert, 1988). At Copper Canyon, the West 

ore body is an Au-bearing Co-skarn that formed adjacent to 

a 38 Ma granodiorite (Theodore and Blake, 1978). However, 

its gold grade (approximately 0.7 g/t) is less than the 1 g/t 

cutoff that we use in this report for deposits to be included 

in our byproduct Au-skarn subset (table 3). Nonetheless, at 

Copper Canyon the Fortitude Au-skarn (table 2) formed in 

the same stratigraphic sequence of rocks as the West ore 

body, but at a much greater distance from the granodiorite 

(Wotruba and others, 1986; 1987a, b). 

Deposits for which some geologic or grade-tonnage 

data are available are listed in tables 2 through 4. Grades, 

tonnages, and some geologic data available for 40 Au-skarns 

are listed in table 2; most of these skarns were (or are 

being) exploited primarily for their precious-metal content. 

Byproduct Au-skarns that can be classified under other skarn 

types, including Cu, Zn-Pb, and Fe skarns, and that have 

grade-tonnage and some geologic data are included in table 

3. Deposits that have been described as "gold skarns" in the 

literature and for which complete grade-tonnage data are 

not available but are suspected to have average gold grades 

greater than or equal to 1 g/t are described in table 4. 

Although Schrader (1947) from his studies in the 1920's, 

cited production in the 1880's of extremely high grade gold 

(622 g/t for 272 t) from gossaniferous skarn at the Mottini 

Mine, IXL Mining District, Nevada (table 4), subsequent 

geochemical studies have failed to confmn the occurrence 

there of such concentrations of gold (Vanderburg, 1940; 

David A. John, written common., 1989). 

The Cable Mine in the Southern Flint Creek Range, 

Montana, has long been recognized as a gold skarn. Knopf 

(1933) classified the Cable Mine, along with deposits in the 

Hedley district of British Columbia, as a pyrometasomatic 

gold deposit. The production history of the Cable Mine 

(table 4) provides a good example of the difficulties of 

assigning reliable tonnage or grade values to long-lived 

deposits. The mine was discovered in 1866, and Emmons 

(1907) reported that 9,000 tons of ore produced $172,000, 

mostly in gold, in 1867. Emmons and Calkins (1913) report 

$400,000 from production up to 1872, including $30,000 

from one ton of ore, a single gold nugget valued at $375, 

and more than $2,000,000 in gold produced from 1877 to 

1891. They also described average tailings from upper levels 

and partly oxidized ore of $2.97 per ton in gold, 0.15 ounces 

per ton in silver, and 3.06 percent copper. Earll (1972) 

noted that 90 percent of the production from the district took 

place prior to 1900, and reported district production, 

including placer, of $3,535,820 from 165,127 oz of gold 

and 134,904 oz of silver. The Cable area and nearby veincontrolled and oxidized ores at the Southern Cross, Gold 

Coin, and Pyrenees deposits are currently under exploration 

(Nolan Smith, oral common., 1989) as a joint venture by 

Magellan Resources and Chevron Resources Company. 

Paired grade-tonnage values are available for 90 ore 

bodies in 89 skarn systems mineralized to gold 

concentrations equal to or greater than 1 g/t. At Tillicum, 

British Columbia, two entries (table 2) are included in the 

statistical calculations: estimated reserves of 2 million tonnes 

at 6.9 g/t Au in the East Ridge zone of the deposit and 

proven reserves of 0.05 million tonnes at 35 g/t Au in the 

Heino-Maney zone of the deposit (Ettlinger and Ray, 1989). 

The deposit tonnage estimate consists of any known 

production plus reserves (proven, estimated, or drillingindicated) at a given point in time; the grade is an estimated 

average grade for the total tonnage. For some deposits, 

tonnage and grade are based on known production only. 

These values probably are representative of the entire ore 

bodies for many of those small deposits mined during the 

late 1800's and early 1900's. It should be noted that most 

of the production for over one-half of the skarns was 

concluded prior to 1950, and we cannot be sure that many 

of those deposits of base-metal skarn did not have a gold 

content that would be significant under today's (1989) 

economics. Values of tonnage and ore grades qualified as 

Data 5 
"greater than" in tables 2 and 3 were used in statistical 

calculations and graphs of data described below. This results 

in two tonnage values, one gold grade value, and two silver 

grade values being substituted by an unqualified numerical 

value. Values qualified as "less than" were not considered 

further in either statistical calculations or graphs of data. 

Iron skarn dominates the mineralized skarns worldwide, 

comprising approximately one-third of the deposits; however, 

gold contents for most of these skarns were reported in the 

literature as "trace," "minor," or "detectable." Only two 

deposits of iron skarn with grade and tonnage figures 

reported average gold grades exceeding 1 g/t (table 3), and 

11 deposits reported grades lower than 1 g/t as deposit 

averages or in selected parts of a compositionally zoned 

skarn body. In a comprehensive data compilation for Alaskan 

skarns, Newberry (1986) classified 109 deposits as Fe-Auskarns. He reported typical grades for these deposits of 40 

percent Fe, 1 percent Cu, 0.1 oz Au per ton (3.4 g/t), 10 oz 

Ag per ton (343 g/t), and 50 ppm Co. 

Several additional deposits have been described as 

gold skarns in one or more publications listed in the 

bibliography but were not included in the above tables for 

the following reasons: inadequate description of the deposit; 

inaccessibility to the publication; description(s) of the deposit 

showed the deposit to be inappropriately classified as a 

gold-bearing skarn according to the classification scheme 

we have adopted; or the gold grade was less than 1 g/t. 

These deposits include: Tennant Creek, Australia; LanduskyZortman, Montana; Ertsberg, Indonesia; Andacollo, Chile; 

Equity (Sam Goosly), British Columbia; Salsigne, France; 

Pamlico, Nevada; Red Cloud, Nevada; Island Copper, British 

Columbia; and others. Ertsberg has an average gold grade 

below 1 g/t. Wedekind (1988) and Wedekind and others 

(1988) did not include garnet or pyroxene as part of the 

composite mineral assemblages of the deposits at Tennant 

Creek. Andacollo has been cited under other deposit types, 

and a detailed geologic description of the area is not 

available. Inappropriate or alternate classification of deposits 

and (or) lack of detailed geologic data have excluded the 

other deposits. Some deposits with grade and tonnage data 

reported were placed in table 4 because the tonnage and 

grade information conflicted with other known data and we 

were unable to resolve the conflict; an example of this 

situation is Mt. Biggenden, Australia. Although the Mt. 

Biggenden magnetite-bismuth-gold skarn is classified as an 

Au-skarn by Meinert (1988a) and assigned a size of 500,000 

tons and a gold grade of 15 g/t, we have not included it 

with either our Au-skarn or byproduct Au-skarn subtypes 

primarily because of our uncertainty about the gold grade 

and tonnage of mined ore. For example, total gold production 

to 1969 from Mt. Biggenden is more than 7,000 oz, of 

which 5,751 oz was produced before 1901 (Clarke, 1969). 

The corresponding tonnage of ore mined is not reported. As 

of 1917, Dunstan (1917) calculated magnetite ore reserves 

as 500,000 tons, which apparently includes only "a few 

6 Gold-Bearing Skarns 

grains of gold per ton" (Clarke, 1969), because all of the 

"actinolite rock" that contained most of the gold and bismuth 

had been already mined out by that time. If 500,000 tons is 

a correct tonnage for the gold ore, then 14,500 oz of total 

gold production is required for an average grade of 1 g/t, 

and over 200,000 oz of production would be needed for a 

grade of 15 g/t. If the grade of 15 g/t is correct, 7,000 oz of 

gold could have been produced from about 16,000 tons of 

ore. 

Pegasus Gold Corporation's Beal Gold deposit in 

the Siberia Mining District near Butte, Montana, described 

as a 9.2-million-tonne, low-grade (1.509 g/t Au), bulk 

minable precious-metal reserve (Hastings and Harrold, 

1989), has some characteristics of skarn (N. Eric Pier, oral 

common., 1989), but shows no extensive calcsilicate 

exoskarn gangue mineral assemblage at the present levels 

of exposure. Precious metals and sulfides (pyrrhotite, pyrite, 

chalcopyrite, trace arsenopyrite and molybdenite) are 

disseminated in metaconglomerate, quartzite, diopside 

hornfels, and potassium feldspar hornfels and also are present 

in veins with chlorite, quartz, adularia, and carbonate 

minerals. Gold is present as free gold and in association 

with Pb- and Bi-tellurides. 

GEOLOGY 

General Deposit Definition 

Smirnov (1976) suggested that classification of 

skarns be based upon the composition of the original 

protolith of the skarn: calcareous, magnesian, or silicate. 

However, we follow the nongenetic definition of skarn 

proposed by Einaudi and others (1981): "replacement of 

carbonate [or other sedimentary or igneous rocks] by CaFe-Mg-Mn silicates [resulting from] (1) metamorphic 

recrystallization of silica-carbonate rocks, (2) local exchange 

of components between unlike lithologies during high-grade 

regional or contact metamorphism, (3) local exchange at 

high temperatures of components between magmas and 

carbonate rocks, and ( 4) large-scale transfer of components 

over a broad temperature range between hydrothermal fluids 

***and predominantly carbonate rocks." Most Au-bearing 

skarns owe their genesis to processes largely involving the 

fourth process. Thus we follow an overall classification of 

skarns based upon their sought-for metal content (see also 

Shimazaki, 1981, and Zharikov, 1970). 

As recognized by Meinert (1988a), many deposits 

referred to as Au-skarns in the literature have been classified, 

or could be classified, under skarn deposit models such as 

Cu- and Fe-skams by their dominant base- or ferrous-metal 

contents. For these deposits, gold production may be 

considered a byproduct of base- or ferrous-metal mining. 

Furthermore, Au-bearing skarn deposits commonly may be 

gradational into skarn that contains no gold but does contain 
significant other metal(s), including the Ag-rich skarns as 

defined by Ray and others (1986a), sediment-hosted 

disseminated Au-Ag deposits (also known as carbonatehosted and Carlin-type), porphyry Cu or Cu-Mo deposits, 

or polymetallic replacement deposits (exemplified by the 

McCoy megasystem in Nevada), as well as other deposit 

types related to felsic to intermediate plutonic emplacement 

or volcanic activity. The Cove deposit, McCoy Mining 

District, Nevada, has been classified recently as a distal 

disseminated Ag-Au deposit according to a scheme proposed 

by Dennis P. Cox (written commun., 1989). Polymetallic 

veins are one of the other deposit types that may be present 

on the fringes of Au-bearing skarn deposits. Therefore, we 

have chosen to use the term "Au-bearing" skarn as most 

aptly describing such skarn deposits and related 

mineralization commonly distal to the immediate contact 

zone. Other commodities produced by Au-bearing skarns 

include silver, copper, zinc, iron, lead, arsenic, bismuth, 

tungsten, and tin as principal or byproduct commodities 

and cobalt, cadmium, and sulfur as byproducts. 

In addition, we have provisionally restricted our 

working model of this deposit type to those Au-bearing 

skarns that have more than 1 g/t gold. This figure is based 

largely on cutoff grades that were reported as low as 1 g/t 

for many Au-bearing skarn operations in production in 1988 

that required milling of their ore to a very fine grain size for 

efficient gold recovery. Some Au-skarn operations, such as 

McCoy, Nevada, that utilize heap-leach extraction 

procedures for their ores, have cutoff grades as low as 0.3 

g/t for oxidized ore (Bruce A. Kuyper, oral commun., 1987), 

but the average deposit grade is greater than 1 g/t. Deposits 

with average gold grades below 1 g/t and without other 

economic mineralization are rarely reported in a quantitative 

manner in the literature and thus result in an artificially 

truncated data set. In an attempt to limit the influence of 

this reporting problem when comparing Au-bearing subsets, 

we have limited all our data to those with gold concentrations 

greater than 1 g/t or reasonably inferred by cited reporters 

to be greater than 1 g/t. 

Gold-bearing skarns are generally calcic exoskarns 

with gold associated with intense retrograde hydrosilicate 

alteration, although Au-bearing magnesian skarns are known 

and in some areas are dominant. Some economically 

significant Au-bearing skarns (Hedley, British Columbia, 

and Suian, South Korea), however, are partly in endoskarn 

(Barr, 1980; see also Lee, 1951; Lee, 1981). Reported 

pyrrhotite, chalcopyrite, and "augite" enclosed in quartz 

monzonite at the Golden Curry deposit, Montana, may be 

endoskarn (Knopf, 1913; Pardee and Schrader, 1933). 

Significant concentrations of gold-bearing endoskarn also 

are present at the Nambija, Ecuador, Au-skarn· deposit (table 

4). In some districts, our data set includes deposits that are 

significantly distant from igneous contacts at current levels 

of erosion but still exhibit high-temperature, prograde 

mineral assemblages composed of garnet and (or) pyroxene. 

Gold-bearing skarns show diverse geometric relations to 

genetically associated intrusive rocks and nearby 

premetallization structures (fig. 4). 

As presently constituted (tables 2, 3), our compilation 

includes some deposits that were previously considered as 

Cu, Fe, or Zn-Pb skarns in the classification schemes of 

Einaudi and others (1981) and Meinert (1988a). In some 

cases when establishing deposit size or grade, we have 

included other styles of genetically related, generally latestage mineralization adjacent or continuous to known skarn 

mineralization under the size estimate and description of 

the Au-bearing skarn deposit when demarcation between 

the mineralization styles would be arbitrary. 

Associated Deposits 

Deposit types most commonly associated with Aubearing skarn include Cu, Fe, Zn-Pb, and porphyry Cu 

skarn-related deposits. Other deposit types include porphyry 

Cu-Mo or Cu-Au deposits, porphyry Cu deposits, carbonatehosted Au-Ag (see Sillitoe, 1983), polymetallic replacement 

and polymetallic veins, distal disseminated Ag-Au deposits 

(Dennis P. Cox, written commun., 1989), W skarns, Sn 

skarns and greisens, Au placers, and other deposits related 

to felsic and intermediate intrusions (Cox and Singer, 1986), 

including stockwork molybdenum systems such as at Red 

Dome, Australia, and Buckingham, Nevada. The Carissa 

and the Surprise Cu-Au-Ag skarn deposits are on the 

northern fringes of the Late Cretaceous (86 Ma) 

Buckingham, Nevada, stockwork molybdenum system, and 

they appear to be related genetically to emplacement of 

potassic-altered monzogranite porphyry (Schmidt and others, 

1988; Theodore and others, 1989). Other examples of 

deposits associated with Au-skarn include skarn 

mineralization at Katanga, Peru, which becomes porphyry 

Cu-Mo mineralization at depth, and the deposit at Bau, 

Indonesia, that includes a large component of sedimenthosted gold mineralization as well as that hosted by skarn. 

Other areas that probably document transition from a skarn 

environment into mostly sediment-hosted systems are silver 

and gold mineralization at the McCoy-Cove mineralized 

system in north-central Nevada, gold mineralization in the 

general area of the Broadway, Montana, Au-skarn deposit 

(Sahinen, 1939), and mostly gold at the Kavak-tau area in 

Kirghiziya, U.S.S.R. (Dolzhenko, 1974). Near the Broadway 

deposit and other nearby Au-skarn-related occurrences, Aubearing jasperoid mantles epidote-rich endoskam that formed 

at the contact of Cretaceous quartz monzonite and Cambrian 

limestone (Sahinen, 1939). At Kavaktau, most of the gold 

mineralization is apparently associated with "secondary 

silicates," probably jasperoids in North American 

terminology, that are present in marble and silicate-carbonate 

rock beyond the outer limit of well-developed skarn 

assemblages. Placer gold deposits are found associated with 

Associated Deposits 7 
copper and gold deposits of the Battle Mountain Mining 

District, Nevada, of the Helena, Bannack, and Cable Mining 

Districts, Montana, and in the Zeballos area, Vancouver 

Island, British Columbia. Gradational changes from Aubearing skarn mineralization to another deposit type (Myers 

and Meinert, 1988), relatively small areas of gold enrichment 

within or peripheral to base- or ferrous-metal skarn 

mineralization, the presence of minerals that can be 

attributed to weak or distal development of skarn in deposit 

types not in a contact-metamorphic aureole, and continuous 

gold mineralization through multiple deposit types related 

to a single intrusion or series of events are common to Aubearing skarn environments. In many gold-enriched skarn 

deposits of British Columbia, Ettlinger and Ray (1988) noted 

multiple types of gold mineralization within single deposits. 

For example, at the Discovery deposit at Banks Island, gold 

is present in skarn with massive pyrrhotite that replaces 

marble, as well as in brecciated quartz-pyrite veins that 

cross-cut skarn and marble. Ettlinger and Ray suggested 

that skarn and quartz-pyrite mineralization may be 

genetically linked. Similarly, high-grade gold mineralization 

(Parnell gold shoot) overprints earlier formed copper-gold 

skarn at Carr Fork in the Bingham district, Utah (Cameron 

and Garmoe, 1987). 

WEST 

METERS 

1650 

1600 

1550 

1500 

1450 

1400 

A 

Triassic Agusta 

Formation 

(clastic facies) 

Tertiary monzogranite and tonalite 

0 

Further studies are needed to address the problem of 

whether all of the gold, or some of the gold in a few deposits, 

represented a much later epithermal overprint on an earlier 

skarn system or was deposited as a continuum near the fmal 

stages of the skarn process along structures that permitted 

extensive development of retrograde assemblages. 

In a number of mining districts that contain gold 

skarn deposits, ore deposits are zoned from a core area 

(sometimes, but not always, a porphyry copper or other 

stock) of Cu±Au and Ag mineralization, to an intermediate 

zone of Au-skarn or other types of gold mineralization, to 

an outermost area of dominantly Zn+Pb+Ag±Au 

mineralization. Blake and others (1984) demonstrated such 

a zonation about the middle Tertiary altered granodiorite 

stock of Copper Canyon in the Battle Mountain Mining 

District, Nevada, where the Tomboy-Minnie and Fortitude 

gold skarn deposits lie between an area of Cu+Au+Ag and 

Pb+Zn+Ag mineralization. El-Shatoury and Whelan (1970) 

described a zonal arrangement of ore deposits in the Gold 

Hill Mining District, Utah, from a central zone of 

W+MO+Cu, through Cu, Cu+Au, Cu+Pb+As and Pb+Zn+Au 

mineralization. The Alvarado, Cane Spring, and Bonnemort 

skarn deposits all lie within the Cu+Au wne in the Gold 

Hill Mining District. In the Elkhorn Mining District, 

100 METERS 

EXPlANATION 

Skarn 

Contact 

Triassic Agusta 

Formation 

(carbonate facies) 

EAST 

METERS 

1650 

1550 

1500 

1450 

1400 

Figure 4. Schematic cross sections of Au-skarn deposits in north-central Nevada. A, McCoy Mine, modified from Lane 

(1987). B, fortitude Mine, modified from Myers (1988). C, Surprise Mine, modified from Schmidt and others (1988). 

8 Gold-Bearing Skarns 
Montana (Klepper and others, 1957), the distribution of 

deposits around the eastern edge of the stock of the Black 

Butte area suggests that the Klondyke and Dolcoath gold 

skarn deposits, and possibly the Golden Curry deposit to 

the west, represent a gold-rich zone interior to a zone of 

Pb+ Ag mineralization. 

SOUTH 

METERS 

800 

600 

Permian and Pennsylvanian Havallah Sequence 

Permian and Pennsylvanian 

Antler Peak Limestone 

400 

200 

NORTHWEST 

METERS 

140 

120 

100 

80 

60 

40 

20 

c 

Pennsylvanian 

Battle Formation 

(middle unit) 

Cambrian Harmony Formation 

0 

Cambrian 

Harmony 

Formation 

EXPlANATION 

11111111111111·111 Skarn 

Contact 

300 METERS 

Fault-Dashed where approximate. 

Arrows show relative movement 

EXPlANATION 

Skarn 

Contact 

Pennsylvanian 

Battle Formation 

(lower unit) 

NORTH 

METERS 

800 

600 

400 

200 

SOUTHEAST 

METERS 

140 

120 

100 

80 

60 

40 

20 

o~------------------------------------------------------------------------------------~0 

0 50 METERS 

Figure 4. Continued. 

Associated Deposits 9 
Tectonostratigraphic Setting and Paleodepths 

In North America, Au-bearing skarn is present most 

commonly in Mesozoic and Cenozoic orogenic-belt and 

island-arc settings (fig. 5); a few Au-bearing skarns have 

been found in rifted craton. The regional distribution of Aubearing skarns may have been confined partly by 

emplacement of Au-enriched magmato-hydrothermal 

systems possibly controlled by long-active rifts intersecting 

the craton's edge in the continental-margin environment of 

western North America (Roberts, 1966). Such magmatism 

may be related to onset of regional-scale extensional 

tectonism in the northern Great Basin. 

Ettlinger and Ray (1989) examined the distribution 

of 126 precious-metal-enriched skarns in British Columbia 

in terms of tectonic belt and tectonic terrane. They found 

that gold- and silver-bearing skarns are present throughout 

the four westernmost, mobile tectonic belts in British 

Columbia, but are absent from the easternmost, stable 

Foreland belt. Of the 14 terranes in which precious-metalenriched skarns are present, Ettlinger and Ray (1989) showed 

that most occurrences and most producing deposits are in 

the Wrangellia and Quesnellia terranes. Most of the gold 

produced from skarns in British Columbia comes from 

deposits in the Quesnellia tectonic terrane, which includes 

the world-class gold skarn deposit at Hedley and the 

Greenwood Mining District. A recently announced gold 

skarn occurrence in northern Washington, the Buckhorn 

Mountain deposit (table 4 ), lies within the southern extension 

of the Quesnellia terrane into the United States (Silberling 

and others, 1987). A similar analysis of the terrane 

distribution for the 106 Fe-Au-skarn occurrences (34 

producers) reported by Newberry (1986) reveals 54 

occurrences (24 producers) in the Alexander terrane, 

followed by 26 occurrences ( 6 producers, including the large 

Nabesna deposit) in Wrangellia, and 15 occurrences (2 

producers) in the Peninsula terrane. Less than 5 occurrences 

in each are reported for the Tracy Arm, Chulitna, Dillinger, 

Mystic, and Nixon Fork terranes. 

Island-arc volcanic sequences, clastic sediments, and 

comagmatic calc-alkaline intrusions are common features 

of the terranes that host the largest proportions of known 

Au-skarn deposits in British Columbia and in Alaska 

(Ettlinger and Ray, 1989; Monger and Berg, 1987; Jones 

and others, 1987). In the conterminous United States, the 

important gold skarn districts of north-central Nevada lie in 

the Roberts terrane (Silberling and others, 1987), in a 

geographic position analogous to Quesnellia to the north, 

just west of ancestral North America proper. However, the 

Figure 5. Distribution of Au-skarn districts and geological 

provinces in the cordi II era of western North America. Modified 

from Monger and others (1972). 

10 Gold-Bearing Skarns 

1\t 

I 

\ 

3T 114° 

0 250 KILOMETERS 

EXPlANATION 

Au-skarn districts: 

1 Banks Island/Discovery 9 

2 Zeballos 10 

3 Texada Island 11 

4 Vancouver 12 

5 Hedley 13 

6 Dividend-Lakeview 14 

7 Tillicum Mountain 15 

8 Greenwood 16 

.............., Thrust fault-Sawteeth on upper plate 

I 

I 

Ophir/Elliston 

Elkhorn 

Silver Star 

Bannack 

Battle Mountain 

McCoy 

White Pine 

Gold Hill 
gold skarn districts of southwestern Montana, and Utah occur 

to the east of the accreted terrane boundary. 

Some of the most productive Au-skarn systems in 

western North America apparently formed in relatively 

shallow seated geologic environments, probably at 1.5-3.0 

km below their respective paleosurfaces. Other Au-bearing 

skarn systems formed as much as 5 km below their 

paleosurfaces. At the Mottini Mine in the IXL Mining 

District, Nevada (table 4; also see Schrader (1947) and 

Vanderburg (1940)), gossaniferous Pb-Zn-Cu skarn with 

some gold is associated with emplacement of a 28-Ma, 

zoned granodiorite that is cogenetic with a tilted caldera 

(David A. John, oral commun., 1989). The Au-bearing PbZn-Cu skarn apparently developed approximately 5 km 

below the 28-Ma paleo surface on the basis of removal of 

the present-day tilts in the rocks of the caldera. The 38- to 

39-Ma Au-skams at McCoy, Fortitude, Tomboy-Minnie, 

and Labrador, all in Nevada, regionally are clustered not 

far from the 34-Ma erosion surface upon which the 34-Ma 

Oligocene Caetano Tuff was deposited. This relation 

suggests that those four Au-skarn systems must have formed 

in a relatively shallow geologic environment-a conclusion 

confirmed by study of fluid-inclusion relations in the Auskarn deposits (see below). Much less abundant are Tertiary 

Au-bearing skarns in cratonic environments (Bright 

Diamond and Iron Clad, Colorado, see Irving, 1905; Irving 

and Cross, 1907). 

In the Soviet Union, most reported data on Aubearing skarns seem to indicate development in geologic 

environments deeper than those in western North America. 

As such, they have been classified as medium-depth deposits 

according to the scheme of Bodaevskaya and Rozhkov 

(1977). Furthermore, according to them, Au-bearing skarns 

are associated with deformed Paleozoic early-eugeoclinalstage batholiths of granite-granodiorite composition or with 

minor Paleozoic late-eugeoclinal stage gabbro-plagiogranite 

or gabbro-syenite intrusive complexes. In Australia, most 

known Au-bearing skarns are in the Paleozoic Tasman 

geoclinal belt, and some of the most significant deposits 

(Red Dome) are associated with late Paleozoic stocks. 

Worldwide distribution of some important Au-bearing skams 

relative to major fold belts is shown in figure 6. 

Age Range 

Gold-bearing skarns are generally Mesozoic or 

Tertiary in the cordillera of western North America, probably 

middle Tertiary in the rifted cratonic regions (Bright 

Diamond, Iron Clad, Colorado), and probably middle 

Tertiary in West Sarawak, Malaysia (Bau), according to 

Wolfenden (1965). Several significant systems of early 

Paleozoic age are also known in the Soviet Union, and a 

significant Au-bearing skarn in Australia (Red Dome) is 

late Paleowic in age. The base-metal-dominated deposits at 

Falun and Garpenberg Oda, in Sweden, are present in 

Proterowic rocks (table 3). 

Host and Associated Rocks 

Gold-bearing skarn may be hosted by a wide variety 

of sedimentary and igneous rocks, including limestone, 

dolomite, shale, conglomerate, rhyolitic to andesitic tuff, 

and granitoids; however, a premetamorphic calcareous 

component is commonly present. Meinert (1988b) further 

noted that the overwhelming bulk of the Au-skarns are 

present in clastic or volcaniclastic-rich sequences. Pearson 

and others (1989) showed that gold-bearing skams in the 

Dillon, Montana, 1 o x 2° quadrangle have the same gangue 

minerals and same kinds of associated plutons as tungsten 

skams in the area but that the tungsten skams are mostly 

hosted by the Mississippian and Pennsylvanian Amsden 

Formation whereas gold-bearing skarns in the Bannack and 

Silver Star Mining Districts are in Mississippian Mission 

Canyon Limestone. 

In general, compositionally expanded I-type 

(Chappell and White, 1974) felsic and intermediate plutons, 

dikes, sills, or stocks that may or may not be porphyritic are 

associated with Au-bearing skarn. Some deposits (for 

example, Tumco, California) may be associated with weakly 

to strongly peraluminous calcic granite (Smith and Graubard, 

1987). In north-central Nevada, Au-skarns (Fortitude, 

McCoy, Northeast Extension, Surprise, Carissa, Labrador) 

are associated with monzogranite stocks (table 5), whereas 

in British Columbia many Au-bearing skams (Tillicum 

Mountain, Oka) are associated with diorite to gabbro stocks 

(see Ray and others, 1987a, b). In addition, Keith and Swan 

(1987) have shown that an area in north-central Nevada with 

plutons that have reduced ferric:ferrous ratios (less than 

0.85) correlates in part with the regional distribution of Aubearing sediment-hosted and porphyry deposits. According 

to them, such reduced ratios may reflect minor assimilation 

of reduced crust during magma genesis. Leveille and others 

(1988) showed that most Au-associated plutons have low 

oxidation state and (or) high alkalinity when plotted in terms 

of an alkalinity index (~O+Na 0-0.57 Si02

) and ratio of 

Fe20 3 to FeO. Meinert (1983) presented mean compositions 

for igneous rocks associated with different types of 

mineralized skarn and noted that the most distinctive 

chemical trends are for parameters that reflect magmatic 

oxidation state and degree of differentiation, notably 

ferric:ferrous ratios and alkali contents. The mean igneous 

rock composition associated with Au-bearing skams (J.M. 

Hammarstrom, unpub. data, 1989) and with other types of 

mineralized skams (Meinert, 1983) is shown in figure 7. 

Gold-bearing skams appear to be associated with slightly 

less siliceous rocks than other skarn types, and in terms of 

alumina, total alkalis, and calcium they are most similar to 

granitoids associated with iron and copper skams (fig. 7). 

Host and Associated Rocks 11 
..... 

~ 

C') 

0 

c:: 

c., 

ttl 

~ :;· 

CIQ 

Vl 

& 

... 

:J 

Cll 

80° 

40" 

00 

40° 

160° 120° 

PACIFIC OCEAN 

EXPlANATION 

D Shield areas 

Paleozoic fold belts 

Mesozoic/Cenozoic 

fold belts 

80° 40° 

ATLANTIC 

OCEAN 

00 

t) 

Figure 6. Worldwide distribution of major Au-bearing skarn deposits (solid dots) and fold belts. 

40° 80° 

INDIAN 

OCEAN 

120° 

~\J 

It&.."' 

160° 

PACIFIC OCEAN 

\[} .~ JJ 
1-

z 

w 

() 

a: 

w 

a_ 

1-

I 

~ w 

~ 

~ 

M 

0 

N 

<( 

1-

z 

w 

() 

a: 

w 

a_ 

1-

I 

~ 

w 

~ 

~ 

u.i 

g 

X 

0 

0 

N 

(\1 

z 

" 0 

N 

~ 

22 

20 

18 

16 

14 

12 

40 

18 

12 

6 

0 

50 

2 

1.6 

1.2 

0.8 

0.4 

0 

0 

EXPLANATION 

A • Hedley • • • "' Nevada ''·· . • Other 

• ••. I • 

• • • . ... ... • ...... ... .... .. . ...••• t .... ... 

• •• ... • ... • • ... 

50 60 70 80 

Si02, IN WEIGHT PERCENT 

I • I I I I I ' I ' I f I 

B I I I I I I ' • I (/) (/) (/) (/) (/) 

c c c c c I I ~ ~ ~ ~ ~ ..X: ..X: ..X: ..X: ..X: I • I (/) (/) (/) (/) (/) 

I :::1 Q) :::1 ..Q 

<{ lJ._ 3': I 0 a... I I I I I I I c: 

+ I N I I 

EXPLANATION I I • • • (/) ' ... ' I c 

I I ~ (/) 

• AI203 • c 

4 I I ..X: ~ I I t (/) 

..X: 

• K20+Na20 I l 0 (/) 

I I I I I ~ c 

.a. CaO I I I l (f) 

I I I I I I I I I t 

60 70 80 

Si02, IN WEIGHT PERCENT 

c 

• Sn sk<un 

Cu skarn I •• • W skarn' Zn-Pb skarn 

• Au skarn 

• Fe skarn 

0.2 0.4 0.6 0.8 

Fe 20 3 /Fe0 

Figure 7. Chemical compositions of igneous rocks associated 

with major types of mineralized skarn. A, Al 2

0 3 versusSi02 , in 

weight percent, for unaltered igneous rocks associated with Aubearing skarn deposits in the Hedley district, British Columbia 

(Ray and others, 1987a), in the Battle Mountain and McCoy 

districts, Nevada (this study), and in other districts. B, Mean 

compositions for igneous rocks associated with major skarn 

classes, in terms of weight percents. Squares, Al2

0 3

; filled 

circles, K2

0+Na20; triangles, CaO. Data for Au-skarn, this 

study; data for other skarns, from Meinert (1983). C, Mean 

compositions for igneous rocks associated with major skarn 

classes in terms of alkali and oxidation ratios. Same data sources 

as in B. 

Our preliminary compilation also suggests that the intrusions 

associated with Au-bearing skams appear to be more reduced 

than intrusions associated with copper and (or) iron skarns, 

also noted by Keith and Swan (1987), and are less evolved 

than those associated with tin skarn mineralization. These 

associations do not necessarily imply that all gold in skarn 

originates in the nearby genetically associated pluton . 

In southwestern Montana, a number of gold-bearing 

skarn districts lie at the periphery of the Cretaceous Boulder 

batholith and appear to be associated with satellite bodies 

and with sodic series rocks of the batholith rather than with 

main series rocks, as defmed by Tilling (1973) on the basis 

of rock chemistry. 

Ore Minerals 

Ore minerals typically found in Au-bearing skarn 

include native gold, electrum, pyrite, chalcopyrite, pyrrhotite, 

arsenopyrite, sphalerite, galena, bismuth minerals (especially 

bismuthinite and native bismuth), magnetite or hematite, 

tellurides (commonly those of Au, Ag, Ni, and Pb), 

tetrahedrite, tetradymite, bornite, marcasite, loellingite, 

stibnite, and W- and Mo-bearing minerals. Mineral 

abundances for ore and gangue assemblages (table 5) were 

compiled for our Au-skarn data (table 2) and for our 

byproduct Au-skarn data (table 3), along with the minerals 

reported by Newberry (1986) for 106 Alaskan Fe-Au-skarn 

deposits. This compilation is based on the assemblages 

reported in tables 2 and 3 from the references cited therein. 

We emphasize that these data are not modal and are probably 

incomplete, so the actual percentages of various minerals 

reported are not significant. However, the relative abundance 

of a given mineral, the frequency of occurrence of some 

unusual minerals, and apparent differences in mineralogy 

between deposits mined primarily for gold and those where 

gold is recovered as a byproduct may be significant in 

characterizing gold skarn deposits. 

Meinert ( 1988a, b) stated that the most abundant 

sulfide minerals in gold skams are arsenopyrite, pyrrhotite, 

and marcasite and also noted the common occurrence of 

bismuth and telluride minerals. R.G. Russell (written 

commun., 1989) reported pyrrhotite as the principal sulfide 

mineral in gold exoskam, with lesser amounts of arsenopyrite 

and traces of chalcopyrite, but noted that the major gold 

skarn deposits in the Hedley district, on which much of his 

model is based, are unusually arsenic-rich. Our compilation 

(table 5) suggests a different conclusion. Chalcopyrite is 

the most common sulfide mineral reported; it is reported 

from 85 percent or more of the deposits in all three data 

sets. For the Au-skarn data set, the next most common ore 

minerals reported (in decreasing order of occurrence) are 

pyrite, pyrrhotite, gold (or electrum), arsenopyrite, sphalerite, 

magnetite, galena, tellurides, bismuth (or bismuthinite), 

hematite (or specularite), molybdenite, hedleyite, and 

Ore Minerals 13 
scheelite. For the byproduct Au-skarn data set, following 

chalcopyrite, the sequence is pyrite, magnetite, pyrrhotite, 

sphalerite, gold (or electrum), galena, hematite (specularite), 

molybdenite, arsenopyrite, scheelite, tellurides and 

bismuthinite. None of the byproduct Au-skarn deposits report 

hedleyite. 

As might be expected, magnetite is the most 

commonly reported ore mineral in the Alaskan Fe-Au-skarn 

data set, galena is uncommon, and no bismuth minerals, 

tellurides, free gold or electrum, or scheelite are reported. 

In many of the deposits that report no free gold or electrum, 

gold is present as auriferous pyrite, gold tellurides, and 

auriferous jasperoid, and in some cases the mineralogic 

residence of gold in the system is not identified. In some 

deposits, silver occurs in Bi-bearing galena. Some free gold 

and native bismuth occur in galena, all as probable latestage reaction products from breakdown of cosalite (ideally 

Pb2Bi2S5

) or galenobismutite (ideally PbBi2

S4

) near the 

northern, distal edge of the Fortitude Au-skarn deposit (T.G. 

Theodore, unpub. data, 1989). These samples show 

prominent myrmekitic or eutectoid-type intergrowths 

between native bismuth and galena. Some domains of mostly 

intergrown native bismuth and galena at the Fortitude deposit 

include small anhedral blebs of gold. Other phases present 

in very minor amounts include bismuthinite, tellurobismutite, 

and possibly schirmerite (ideally 3(Ag2,Pb)S•2 Bi2

S3). 

In addition, many other minerals have been reported 

for skarns studied in detail, including scorodite, wittichenite, 

sperrylite, and malayaite. Textural relations of electrum in 

massive pyrrhotite and in association with native bismuth 

and galena in clinopyroxene at the Fortitude, Nevada, 

deposit; gold in late-stage quartz-potassium feldspar-garnet 

assemblages that cut Jurassic granodiorite at the Nambija, 

Ecuador, Au-skarn deposit; gold in iron oxide(s) that replace 

pyrite and (or) pyrrhotite at the Surprise, Nevada, deposit; 

and gold in pyrite at the McCoy, Nevada, deposit are shown 

in figure 8. 

Gangue Mineralogy 

Typical composite assemblages in Au-bearing skarn 

include garnet (andradite-grossular), pyroxenes (diopsidehedenbergite), wollastonite, chlorite, epidote-clinozoisitezoisite, scapolite, quartz, actinolite-tremolite, prehnite, 

potassium feldspar, plagioclase, calcite and serpentine as 

gangue. Additionally, various micas, ilvaite, vesuvianite, 

talc, sphene, fluorite, apatite, and abundant clays have been 

reported from several deposits (tables 2, 3). 

Garnet and epidote, its typical retrograde alteration 

product, are the most commonly reported minerals in goldbearing skarns (table 5), followed by pyroxene, amphibole, 

and chlorite. Of the 39 deposits in our gold skarn subset, 5 

(13 percent) report boron minerals in the gangue assemblage, 

including axinite and ludwigite. No boron minerals are 

14 Gold-Bearing Skarns 

reported in the byproduct Au-skarn subset or in Newberry's 

(1986) Alaskan Fe-Au-skarn compilation Many deposits 

include both garnet and pyroxene, but others report only 

one mineral or the other or are zoned from proximal garnetrich to distal pyroxene-rich assemblages. Pyroxene tends to 

be dominant in unoxidized, pyrrhotite-rich, more distal 

skarns, such as the Fortitude deposit, Nevada (Myers and 

Meinert, 1988). Massive hedenbergite skarn formed in the 

Black pit of the Broadway Mine in the Silver Star Mining 

District, Montana, distal to mineralized jasperoid at the 

granodiorite contact (Larry Hillesland, oral commun., 1989). 

Gamet is the characteristic prograde silicate mineral 

of many calcic Au-bearing skams (rocks are commonly 

massive garnetite); garnet is later than and replaces pyroxene. 

Mineral chemistry studies show that garnets are andraditegrossular solid solutions (mostly A~0 to Ad1

oJ with less than 

5 mole percent pyralspite components. Both isotropic and 

anisotropic varieties are common (fig. 9). Multiple 

generations of garnet are present in some deposits (for 

example, Fortitude, Surprise, and McCoy, Nevada). In some 

deposits from north-central Nevada, early garnet is colorless, 

anisotropic, zoned toward more Fe-rich rim compositions, 

A 0 

I 

20 MICROMETERS 

I 

Figure 8. Textural relations of gold and electru min selected Auskarn deposits. Au, gold; E, electrum; Q, quartz. A, Electrum in 

massive pyrrhotite (po} from the Lower Fortitude, Nevada, Auskarn deposit. Plane-polarized light. 8, Electrum associated 

with native bismuth (B) and galena (G) hosted by clinopyroxene 

(cpx} from the Lower Fortitude, Nevada, Au-skarn deposit. 

Backscattered electron micrograph. C, Gold in quartz associated with a quartz-garnet (ga}-potassium feldspar assemblage 

that alters granodiorite at the Nambija, Ecuador, Au-skarn 

deposit. Plane-polarized, reflected light. 0, Gold in pyrite (py} 

associated with quartz from the McCoy, Nevada, Au-skarn 

deposit. Backscattered electron micrograph. f, Electrum (Au6

Ag4

} 

in limonite (L} from the 5,595-ft bench, Surprise, Nevada, Auskarn deposit. Plane polarized, reflected light; reflectivity differences due to variations in content of silica. 
and poikilitically encloses relict diopsidic pyroxene. Late 

garnet pods and veins are inclusion-free, are less altered 

than early garnets, and have distinctly yellow (in thin 

section), isotropic, andradite cores and colorless, anisotropic 

rims that have oscillatory zoning with respect to AI and Fe. 

Contents of 0.4 to 3 weight percent Ti02 are common for 

early garnet, whereas late garnet is nearly Ti-free. Gamet 

compositions for representative samples of some Au-bearing 

skams from north-central Nevada (fig. 10) fall within the 

compositional fields outlined for garnets from copper and 

magnetite skarns and are distinct from garnets associated 

with tungsten, tin, zinc, and molybdenum skarns, primarily 

due to more oxidized, less manganiferous compositions. 

Ettlinger and Ray (1989) reached similar conclusions for 

garnet compositions in precious-metal-enriched skarns from 

British Columbia. 

B 

c 0 

0 

I 

Figure 8. Continued. 

10 MICROMETERS 

I 

0.24 MILLIMETER 

Meinert (1988a) suggested that garnets associated 

with gold skarns may be more aluminous than those 

associated with many other skarn types. Bin and Barton 

(1988) inferred from a study of mineralized skarns in China 

that andradite components in andradite-grossular garnets of 

calcic skarn will decrease gradually in the following order 

of associated metals: W-Zn-Cu, Fe-Cu, W-Bi-Cu-Mo, Fe, 

Sn-Mo-Bi-W, Cu-Zn, Sn, Pb-Zn, W. Compositions as 

aluminous as Gr60 to Gr70 are observed for some zones in 

garnets from the McCoy and Surprise deposits; however, 

nearly pure andradites are present within the same domains 

at a thin-section scale. Myers and Meinert (1988) have shown 

that garnet in the distal Fortitude Au-skarn has compositions 

(Ad90-too cores; A~~ rims) that contrast with garnets in 

the West orebody Cu-Au-Ag skarn (Ad a- ~, which is 

proximal to altered granodiorite of Copper Canyon 

D 

E 

0 

0 

I 

20 MICROMETERS 

20 MICROMETERS 

I 

Gangue Mineralogy 1 5 
(Theodore and Blake, 1978). Brooks and others (1989) 

reported garnet compositions of Ad1

S-too for the McCoy 

deposit, Nevada, which includes the range of compositions 

encountered in our study of selected samples (fig. 10). 

Reported hand-specimen colors for garnets from Auskarns vary from buff to yellow to yellow-green to red to 

brown. Different colors can be used to distinguish among 

different generations and different compositions within some 

deposits, however, correlations of a particular color with a 

particular range of composition are highly variable. Einaudi 

A 0 2 MILLIMETERS 

B 0 2 MILLIMETERS 

Figure 9. Photomicrographs showing complexly zoned garnets 

(ga) from oxidized skarn, Surprise Mine, Nevada. A, Planepolarized light; note growth zone in garnet rim. 8, Crossed 

nicols; garnet has isotropic, andradite core (C) and sectortwinned, anisotropic, oscillatorily zoned rim (R). 

16 Gold-Bearing Skarns 

(1982) noted that garnets in skarns associated with porphyry 

copper deposits are commonly reddish brown proximal to 

the stock and greenish distal to the stock. Meinert (1988a) 

found yellowish-tan to brown garnet in skarn formed in 

limestone and reddish-brown garnet in skarn formed in 

dolostone in moderately gold-bearing porphyry-Cu skarn in 

the Whitehorse Mining District, Canada. Torrey and others 

(1986) reported brown and green garnet (A~ to Ad1

oo> with 

pyroxene (Hd10 to Hd15) in early-metasomatic stage skarn at 

Red Dome, Australia, red-brown garnet (Ad40 to Ad~ with 

pyroxene (Hd5 to H~ ) in late-metasomatic wollastonitegarnet endo-exoskarn associated with rhyolite porphyry, and 

pale-green garnet (Ad50 to Ad100) with minor pink garnet 

(Ad60 to Ad8J associated with early retrograde alteration and 

the minerals vesuvianite, epidote, quartz, fluorite, calcite, 

chlorite, sphene, orthoclase, magnetite, and hematite. At 

Red Dome, most of the primary copper-gold-silver ore is in 

wollastonite-garnet skarn. Red, brown, yellow, and green 

garnets, all more iron-rich than Ad90, formed in limestone at 

Carr Fork, Utah (Atkinson and Einaudi, 1978). Callow 

10 

Grossular 

Pyrope +almandine 

+Spessartine 

Buffalo Valley Mine 

MCCoy Mine 

Fortitude Mine 

Surprise Mine 

....... Carissa Mine 

50 

. 

• 

n = 91 

n = 27 

Andradite 

Figure 10. Ternary diagrams showing ranges of garnet compositions for representative samples from five Au-bearing skarn 

systems in north-central Nevada. n, number of samples. 
(1967) presented an andradite analysis for brown garnet in 

garnet-clinozoisite skarn at the Thanksgiving Mine in the 

Philippines. Late, coarse, zoned andradite (Ad8s to Ad1oc) is 

reported as the latest skarn mineral in some Au-bearing 

skarn from the Altai-Sayan region (Vakhrushev, 1972). The 

wider range of compositions reported for more recent 

(1980's) studies reflects data acquired by electron 

microprobe, wherein compositional data for different grains 

and different zones within a grain can be obtained, whereas 

much of the earlier data represents wet chemical analysis of 

a garnet separate. 

Many recent studies have examined garnet zoning 

patterns and protolith effects on garnet composition for goldmineralized skarn systems (for example, Beddoe-Stephens 

and others, 1987; Hammarstrom in Theodore and others, 

1989; Ettlinger and Ray, 1989; Brooks and others, 1989). 

These studies show that (1) garnets commonly remain stable 

throughout extensive retrograde alteration processes, (2) 

Ti02 contents of a few weight percent are typical of many 

garnets, especially those formed from impure carbonates or 

noncarbonates, and (3) although the normal zoning trends 

(core to rim increases in andradite content) typical of copper 

and base-metal skarn garnets are observed, aluminous zones 

and aluminous rims may be a feature peculiar to goldmineralized systems. Ettlinger and Ray (1989) suggest that 

the deposition of Al-rich zones in both garnets and 

pyroxenes (see below) in precious-metal-enriched skarns 

reflects changes in availability or solubility of aluminum in 

the system. Alternatively, fluctuations in ferric ironaluminum availability in the system could reflect changes 

in sulfidation state (J. Remley, oral commun., 1989); that 

is, ore minerals (predominantly iron sulfides) could 

effectively deplete the iron available at silicate-hydrothermal 

Johannsenite 

Diopside 50 Hedenbergite 

Figure 11. Ranges of pyroxene compositions for representative 

samples from three Au-bearing skarn systems in north-central 

Nevada. 

fluid interfaces, resulting in growth of relatively aluminous 

zones. 

Pyroxene in Au-bearing skarns is typically a 

diopside-hedenbergite solid solution having low manganese 

contents. V akhrushev (1972) described diopside (pure to 

Hd20) as the characteristic pyroxene of the Altai-Sayan gold 

skarns. Pyroxene in garnet skarn at the middle Tertiary 

McCoy deposit is diopside-rich (Hd10 to HdSO' <3 percent 

johannsenite ). Pyroxene coexisting with massive pyrrhotite, 

other sulfides, and late garnet at the Fortitude deposit is 

more iron-rich (Hd40 to Hd60) whereas pyroxene in pale-green 

gametite skarn from the 5,770-ft bench of the Buffalo Valley 

Mine is nearly pure hedenbergite (Hd80 to H~) (table 7; fig. 

11). Skarn mineral assemblages in the gold-enriched part of 

the Mam property, Yukon, contain iron-rich pyroxene (Hd40 

to Hd8J (Brown and Nesbitt, 1987). Brooks and others 

(1989) noted the presence of narrow aluminous zones in 

pyroxenes from the McCoy deposit. Ettlinger and Ray (1989) 

recognized similar zones in pyroxenes in precious-metalenriched skarns from British Columbia and suggested that 

(1) the presence of high Al2

0 3+ Ti02 (>1.25 weight percent) 

in skarn pyroxene may be an indication of precious-metal 

potential, and (2) the presence of very iron rich (>26.0 

weight percent FeO) or very iron poor (<3.5 weight percent 

FeO) pyroxenes may indicate a low precious-metal potential 

for a given skarn. 

Amphibole typically replaces pyroxene as 

pseudomorphs in Au-skarns and is present with sulfides; 

reported compositions include actinolite, tremolite, ferrotremolite, and hornblende. Representative amphibole 

compositions for some Nevada gold skarns are given in 

table 6, along with data for other minerals. In sulfidized 

skarn at the Fortitude deposit, ferro-actinolite (low fluorine, as 

much as 1 percent MnO, 2 percent Al20 3

) is intergrown with 

or replaces pyroxene; pyroxene is present adjacent to massive 

garnet that is replaced partly by pyrrhotite and chalcopyrite 

(fig. 12). Actinolite is present with epidote and chlorite in 

sulfidized retrograde skarn at the Northeast Extension Mine, 

and in pyrite in garnet skarn at the Carissa Mine. 

Wallrock Alteration 

Metasomatic, anhydrous calcic (or magnesian) skarn 

assemblages in Au-bearing skarn are typically superposed 

on preceding contact-metamorphic assemblages and followed 

paragenetically in most deposits by hydrous assemblages 

with abundant sulfide(s) and (or) magnetite. Some deposits 

(Bau, Malaysia) show lateral gradation and subsequent 

replacement by jasperoid (Wolfenden, 1965; W.C. Bagby, 

oral commun., 1987). Calcic Au-bearing skarns typically 

are zoned from marble, wollastonite, diopside-hedenbergite, 

and finally grossular-andradite with or without retrograde 

tremolite-actinolite-epidote-chlorite assemblages. Watanabe 

(1943) reported in his study of the Suian Mining District, 

Wallrock Alteration 17 
North Korea, that magnesian Au-bearing skarn may show 

dolomite followed by marble bearing kotoite [M~(B0 ] 

and ludwigite [(Mg,Fe2+)2Fe3+BOs]; a narrow fluoborite 

[Mg3

(B03)(F,OH)3]-bearing reaction zone marking the 

contact between skarn and marble; a marked concentration 

of native gold, bismuth, chalcopyrite, pyrrhotite, and cubanite 

just inside the reaction zone; diopside; clinohumite; and, 

finally, diopside partly replaced by phlogopite-all zones 

developed across 25-35 em. At the Surprise, Nevada, gold 

skarn, limonite, fine-grained quartz, copper oxide(s), and 

calcite occur interstitial to massive garnet; garnet is crosscut 

and replaced by veins of limonite and chlorite (Schmidt and 

others, 1988). In this deposit, gold is present as electrum in 

limonite (fig. 8) associated with quartz, calcite, and 

secondary copper minerals. The only sulfides remaining in 

extensively oxidized high-grade ore currently (1989) exposed 

at the Surprise Mine are pyrite remnants in limonite and 

tiny blebs of various sulfides encapsulated in late, euhedral 

quartz crystals. The Buffalo Valley, Nevada, gold skarn 

shows widespread development of nontronite throughout 

much of the exposed ore. 

Structural Setting 

Gold-bearing skarn may occur in the immediate 

vicinity of, or relatively distal from, weakly mineralized 

intrusive rocks, commonly where wallrocks are extensively 

brecciated or faulted (fig. 4). On a local scale, gold-enriched 

dikes and small plutons astride hinge regions of broad 

anticlinal arches seem to have been an important structural 

control (Madrid, 1987). The Bau Mining District, Malaysia, 

lies along the axis of a major anticline flanked by synclinal 

basins (Wolfenden, 1965). 

0 0.2 MILLIMETER 

Figure 12. Photomicrograph showing massive garnet (ga), partly 

replaced by pyrrhotite (po) and chalcopyrite (cp) and separated 

from a pod of actinolite (act) grains by pyrrhotite; Fortitude 

Mine, Nevada. 

18 Gold-Bearing Skarns 

Dimensions of Ore in Typical Deposits 

Overall dimensions of ore in Au-bearing skarn are 

highly variable; dimensions possibly increase with distance 

from the genetically associated intrusive rock and as grade 

decreases. Geologic configuration of such deposits is largely 

a function of respective geometries of mineralizing magma 

and premineralization structures, favorable replacement 

sequences, and impermeable barriers to fluid flow, if present. 

However, eventual configuration of economic dimensions 

of deposits results from cut-off grades that are influenced 

highly by factors such as pre-mining topography (R.G. 

Russell, written commun., 1989). 

Dimensions of Alteration or Distinctive Haloes 

Alteration haloes that surround Au-bearing skarn are 

highly variable in size, from very restricted to as much as 

several kilometers from inferred loci of mineralizing systems. 

In some systems, the overall size of the alteration zone has 

been enhanced by the presence of premineralization 

structures that channeled fluid flow. Nonetheless, in a largely 

carbonate terrane, the Au-bearing skarns are almost always 

found within the outer limit of conversion of carbonate 

sequences to marble. 

Effect of Weathering 

The economic limits of some deposits are entirely 

within the oxide zone. In fact, gold grade is commonly 

higher in the oxide zone than in the equivalent sulfide zone. 

The oxide zone in some deposits includes coarsely crystalline 

vivianite along fractures in areas showing limited overall 

amounts of iron oxide development and limited amounts of 

subjacent iron sulfide(s) (R.G. Benson, written commun., 

1988). At the McCoy, Nevada, Au-skarn, samples from the 

5,080-ft bench show some extremely small, micrometersized crystals of greenockite (CdS) concentrated at interfaces 

between chalcopyrite and chalcocite. In this deposit, some 

chalcocite also appears to be associated paragenetically with 

a silver-selenide mineral, possibly Ag2(S, Se). Nontronite 

layers are commonly interbedded with some garnet skarn 

and locally concentrated along fractures in some deposits. 

At Browns Creek, Australia, gold-bearing nontronite was 

the major target of mining activity inasmuch as it typically 

contained greater than 10 g/t gold (Creelman and others, 

1988). The term "nontronite" is used as a field term for 

iron-rich, yellow-green montmorillonite that swells upon 

treatment with ethylene glycol; a Mossbauer spectrometic 

study of one such clay from skarn in the Harmony Formation 

near the Surprise Mine shows that nearly all of the iron 

present in the sample is ferric iron. Thus, nontronite is the 

main component of the clay layer there. Clay layers include 
quartz and calcite and may include relict skarn silicates 

(pyroxene, garnet, and epidote). Oxidized karst-collapse 

breccia developed in marble as a result of marble reacting 

with acidic ground water at Red Dome (Torrey and others, 

1986). At this deposit, acidic ground water probably resulted 

from breakdown of sulfides in the surrounding pyritic halo 

of the Au-skarn. 

Effect of Metamorphism 

Gold-bearing skarn systems could undergo regional 

metamorphism to yield gneiss-hosted Au deposits with a 

resultant loss of most contact-metasomatic features. The 

Tumco deposit, California, which has been metamorphosed 

to amphibolite grade and is provisionally included by us 

with Au-bearing skarn (Smith and Graubard, 1987; Tosdal 

and Smith, 1987), may be an example of such a process. 

However, some relatively extensive tin-tungsten-base-metal 

skarns in Alaska show readily recognizable prograde and 

retrograde contact-metasomatic assemblages through a 

superposed greenschist dynamothermal event (Newberry and 

others, 1986). In these Sn skarns, strain is confined largely 

to 1-m-wide wnes at the margins of skarn where calc-silicate 

porphyroclastic mylonite is present. Skarn away from the 

contact shows some kinked chalcopyrite-bornite exsolution 

lamellae, but no cleavage or foliation. The Falun deposit in 

Sweden is hosted by Proterowic granite, amphibolite, and 

quartz porphyry (Grip, 1978). Greenstone-hosted Au-AgW-As deposits in the Southern Cross greenstone belt of 

western Australia may represent Archean analogues of 

Phanerozoic gold skarn deposits (Mueller, 1988). 

Geochemical Signatures 

Geochemical signatures for Au-bearing skarn include 

anomalous gold primarily in an environment of retrogradealtered, sulfidized skarn. The associated pyrite in some Auskarn deposits is reported to contain 0.1 to 250 ppm Au 

(Vakhrushev, 1972). At Bau, Malaysia, anomalous antimony 

(in stibnite) and arsenic (in scorodite) are present with gold 

in wollastonite-bearing skarn assemblages and in colloformbanded quartz and jasperoid, all distal to quartz- and calciteflooded, calc-silicate gold ore (Wolfenden, 1965; W.C. 

Bagby, oral commun., 1987). In other Au-bearing skarn 

systems, quartz-calcite veins contain anomalous gold. In 

addition, gold mineralization and highly anomalous 

concentrations of gold in some skarn systems (Akshiryak 

Range, U.S.S.R.) are found mostly in fme-grained, gray to 

light-gray, highly silicified sequences of rock in carbonate 

beyond the outer limit of established skarn (Dolzhenko, 

1974). Many Au-bearing skarns in British Columbia contain 

elevated abundances of arsenic, bismuth, and tellurium (Ray 

and others, 1987b; Ettlinger and Ray, 1989). The bismuth 

minerals reported from some Au-skarns include native 

bismuth,.bismuthinite, wittichenite, hedleyite, maldonite, and 

Bi-bearing galena (Meinert, 1988b). Theodore and others 

(1989) report major-element and trace-element data for 

garnet skams associated with gold mineralization at Copper 

Basin, Nevada, including low-grade, oxidized ore from the 

Surprise Mine (29 ppb Au, 6 ppm Ag, <10 ppm Bi, 57 ppm 

As, 4 ppm Sb, 3 ppm Co, 25 ppm Cu). Finally, surface 

expression of some Au-skarn systems (Red Dome, Australia; 

Surprise, Nevada) includes relatively abundant, fracturecontrolled secondary copper minerals (Torrey and others, 

1986; Schimdt and others, 1988). 

The Au/Ag ratio in rock apparently increases laterally 

outward (away from the center of the associated intrusion) 

in some productive copper-bearing calcic skarn systems 

toward ore (Fortitude, Nevada) that is approximately 0.6 

km from the exposed, genetically associated intrusion. The 

Fortitude Au-skarn is close to a relatively sharp boundary 

between marble and sulfidized calc-silicates (Blake and 

others, 1984; Theodore and others, 1986; Wotruba and 

others, 1987a, b; Myers and Meinert, 1988). In other Auskarn systems that are predominantly wned vertically close 

to the related intrusive rocks (Red Dome, Australia}, much 

of the gold ore is near the original intrusion-wallrock contact 

and interior to massive magnetite developed at the calcsilicate-marble interface (Torrey and others, 1986). 

Surrounding rocks in many systems typically show high 

local thresholds for many associated base and ferrous metals 

and, for some deposits, arsenic, bismuth, selenium, and 

tellurium values in particular may be relatively high both 

within and peripheral to the Au-bearing skarn (Ray and 

others, 1987b). 

Zonation of gold in Au- and Pb-Zn-bearing skarn 

(Ban Ban, Australia; Thanksgiving, Philippines; TomboyMinnie, Nevada) seems to show inconsistent patterns. At 

Ban Ban, gold in unreported trace abundances may coincide 

with known distribution of silver, which varies directly with 

lead and zinc concentrations that are, in tum, constrained 

tightly to the central part of associated garnet skarn (Ashley, 

1980). At Thanksgiving, irregularly distributed sphaleritepyrite pods that replace andradite skarn show higher gold 

contents than pyrite-magnetite replacement pods (Callow, 

1967). At Tomboy-Minnie, local metal zoning of the gold 

orebodies shows high concentrations of gold (more than 

0.05 troy oz/ton or more than 1. 7 g/t}; these high 

concentrations of gold show increased abundances of zinc 

and silver (more than 500 ppm and more than 0.1 troy oz/ 

ton, or more than 3.4 g/t respectively) on the granodiorite 

side of the gold orebody. Such metal-zoning relations 

constitute a local reversal of the district-wide wning from 

Cu+Au+Ag, through Au+Ag, to finally Pb+Zn+Ag 

(Theodore and others, 1986). 

Zonation of gold in some Fe-skam systems that 

contain byproduct gold (Benson Lake, British Columbia) 

seems to be related directly to the abundance of sulfide 

Geochemical Signatures 19 
associated with magnetite (Eastwood, 1965). At the Merry 

Widow pit of the Benson Lake cluster of magnetite skarns, 

concentrates of chalcopyrite were reported to contain as 

much as 1 oz gold per ton of chalcopyrite. 

Significant concentrations of gold have been 

reported, although specifics are unavailable, in many of the 

Paleozoic W skarns in the Soviet Union (table 4). Gold is 

an associated minor metal in approximately one-half of the 

W-skarn deposits in the Ural Mountains, U.S.S.R. 

(Rabchevsky, 1988). These skarns are reported to be 

associated with Devonian- to Permian-age granitoid bodies 

(Rabchevksy, 1988). In addition, selected samples of 

Mesozoic W skarns from Alaska are reported to contain as 

much as 30 ppm gold (R.J. Newberry, oral commun., 1987; 

Newberry and others, 1987). Tin skarns in China and 

Australia have reported significant Au or Au-enriched areas 

(see Stormont and Ge Jiou, table 4). 

At a more detailed level, nontronite layers from some 

Au-bearing, calcic skarn deposits show significant 

concentrations of silver and copper and variable, but 

enhanced levels of other trace elements, such as tin (table 

8). Spectral analyses of garnets from four Au-bearing skarn 

deposits in the Altai-Sayan study (Vakhrushev, 1972) show 

trace-element signatures distinct from those of garnets from 

Fe skarns: copper and zinc (tens to hundreds of parts per 

million), molybdenum, scandium, gallium, and tin (10 to 50 

ppm each) are present in all the garnets from Au-skarn; 

some garnets carry several hundred parts per million arsenic, 

as much as 30 ppm lead, and similar concentrations of silver 

as well. In contrast, garnets from Fe skarns have titanium, 

chromium, vanadium, nickel, cobalt, and germanium as a 

characteristic trace-element suite and lack the elements 

associated with Au-skarn garnets or show inconsistent 

distributions of them. 

The single report of platinum associated with gold 

skarn that we found is in northern Sumatra, where Bowles 

and others (1985) described a reference to 8 ppm Pt and 4 

ppm Au in wollastonite-garnet skarn; however, they point 

out that some confusion exists over the precise locality of 

the occurrence. 

Isotopic Signatures 

Isotopic data are not available for a great number of 

Au-bearing skarns. However, the range in o34S values for 

sulfides is clustered tightly in one examined system: +2.7 

to +4.7 permil for the Tomboy-Minnie deposit (Theodore 

and others, 1986). Such values suggest a magmatic source, 

and minimal contribution from heavy, crustal sulfur that 

was highly homogenized. An associated Cu skarn adjacent 

to the intrusion, the West orebody, shows more scattered 

values of o34S, +1.1 to +5.1, in sulfides there, possibly 

reflecting disequilibria resulting from passage of retrograde 

fluids. Derivation of the associated altered granodiorite 

20 Gold-Bearing Skarns 

apparently was primarily from crustal components, to judge 

from initial neodymium isotopic compositions (Farmer and 

DePaolo, 1984). 

Fluid Inclusions 

Boiling, high-salinity fluids are associated with the 

early, prograde paragenetic stages of many Au-bearing skarn 

systems. The fluid-inclusion signature of skarn probably is 

most easily inferred from fluid inclusions trapped in quartz 

in the associated intrusive rocks if optical limitations 

preclude study of fluid inclusions in garnet or pyroxene. 

For example, possible involvement of high-salinity fluids 

some time during the generation of Au-bearing skarn may 

be implied by occurrence of halite-bearing fluid inclusions 

in quartz phenocrysts of a genetically associated granitoid. 

In some deposits (Tomboy-Minnie, Nevada), early fluids 

associated with diopside-quartz assemblages were 

dominantly CaC12 -brines and were boiling at temperatures 

higher than 500 OC. Fluids then were progressively enriched 

in sodium and potassium over time, and during hydrosilicate 

stages, temperatures ranged from 320 to 500 °C at the time 

actinolite formed, and from 220 to 320 OC at the time chlorite 

became dominant in the assemblages (Theodore and others, 

1986). Much of the gold is paragenetically late, deposited 

from NaCl-rich brines at temperatures less than 300 °C. 

However, genetic association of highly saline brines with 

skarn does not guarantee presence of a metal-bearing deposit 

somewhere in the environment of the skarn. Some Tertiary 

garnet-pyroxene skarn in the northern Battle Mountain 

Mining District shows fluid-inclusion signatures highly 

suggestive of many porphyry copper systems, yet the skarn 

is barren of any associated metal deposits (Theodore and 

Hammarstrom, 1989). At the Fortitude, Nevada, deposit, 

initial fluid-inclusion studies indicate that the Au-skarn was 

formed by fluids ranging from 300 to 450 oc and with 

salinities much less than 26 weight percent NaCl equivalent 

(Myers and Meinert, 1988). At Red Dome, Australia, coppergold-silver ores apparently were deposited during a 

retrograde stage attendant with the circulation of relatively 

low-salinity (less than 10 weight percent NaCl equivalent), 

possibly meteoric-dominant fluids at temperatures in excess 

of 350-380 °C (Torrey and others, 1986; Ewers and Sun, 

1988). In other skarn systems, gold also was deposited 

mostly during low-temperature stages: Alae-Sayan, U.S.S.R. 

(250-150 °C), Central Tadzhikistan, U.S.S.R. (350-250 OC), 

Sayakskig, U.S.S.R. (greater than 250-225 °C), and 

Kochulak, U.S.S.R. (270-240 °C; 190-170 °C) (table 4). 

Deposition of most gold close to the calc-silicate-marble 

interface, as reported in many Au-bearing skarns (Myers 

and Meinert, 1988), may reflect a combination of protracted 

solubility of gold in bisulfide complexes and build-up of 

HC03

- in the fringe environment of evolving skarn 

(Gumenyuk and Glyuk, 1983), thereby decreasing the 
solubility of gold owing to a change in pH (Henley, 1984). 

Gold solubility relations at 250 °C, a temperature considered 

by many to approximate thermal conditions in most Aubearing skarns during paragenetic stage(s) of gold deposition, 

culminate at oxygen activity-pH conditions compatible with 

pyrite stability (Romberger, 1988). As Romberger (1988) 

further noted, if most gold is transported as a bisulfide 

complex, gold deposition may be accomplished by any 

chemical reaction or physicochemical process that decreases 

chemical activity of sulfur components dissolved in aqueous 

fluids circulating through skarn, including deposition of 

sulfide minerals and loss of sulfur components because of 

boiling. 

Geophysical Signatures 

Well-developed, local magnetic highs result from 

increased abundance of pyrrhotite and (or) magnetite in some 

Au-skarn systems (see Wotruba and others, 1987a, b). 

However, other Au-skarn systems are associated mostly with 

pyrite in their unoxidized parts (McCoy) and show no 

distinctive magnetic signatures (Bruce A. Kuyper, oral 

commun., 1987). 

Ore Controls/Exploration Guides 

In established mining districts zoned from mostly 

proximal copper-dominant deposits to distal precious-metaldominant and base-metal-dominant veins, all stratigraphic 

sequences favorable for development of skarn in the zone 

of precious-metal deposits should be considered as 

permissive hosts for development of Au-bearing skarn. 

Polymetallic veins and polymetallic replacement deposits 

showing geochemical signatures and sulfide mineral 

assemblages similar to those at many Au-bearing skarns 

(for example, the Fe-As-Zn-Cu-Bi-Au- and Sb-bearing ores 

at the Matsuo Mine, Japan; Matsukuma, 1962) may be highlevel or lateral reflections of Au-bearing skarn. Other guides 

include: reported gold in base- and ferrous-metal skarn 

systems; gold placers in regions permissive for the formation 

of skarn (R.G. Russell, written commun., 1989), especially 

if the placer gold is intergrown with bismuth minerals, 

including bismuth oxides or bismuth tellurides (Theodore 

and others, 1987; Theodore and others, 1989). Anomalous 

values of bismuth, tellurium, arsenic, selenium, and cobalt 

are useful geochemical signatures for some gold-bearing 

skarns (tables 2, 3; Brooks and Meinert, 1989). 

Metal ratios in jasperoids, which commonly occur 

in or on the fringes of gold skarn systems, may also provide 

useful geochemical signatures for exploration. Faults cutting 

skarns and intersecting structures are important pathways 

along which retrograde assemblages and associated ores are 

concentrated. R.G. Russell (written commun., 1989) 

distinguishes between barren, early, high-temperature contact 

skarn formed adjacent to intrusive rocks and mineralized, 

fracture-enhanced exoskarn developed in Au-skarn systems. 

Although pyroxene (hedenbergite )- and pyrrhotiterich distal skarns host gold mineralization in some deposits, 

such as the Fortitude, garnet-pyroxene (diopsidic) and 

chalcopyrite or pyrite-rich proximal skarns are the locus of 

gold mineralization at other deposits, such as McCoy. Further 

studies on Au-bearing skarn deposits may reveal relatively 

reduced (Fortitude) and oxidized (McCoy) types of goldbearing skarn, such as have been recognized for tungsten 

skarns (Einaudi and others, 1981). 

GRADES AND TONNAGES OF 

GOLD-BEARING SKARNS 

Graphs of grades and tonnages of 40 Au-skarns from 

table 2 and 50 byproduct Au-skarns from table 3 are shown 

in figures 1, 2, and 13. Gold grade must be 1 g/t or higher 

to be included, as described above. Median tonnage for the 

Au-skarn subtype is about 213,000 tonnes (fig. lC), and 

median tonnage for the byproduct Au-skarn subtype is about 

330,000 tonnes (fig. 1D). For the Au-skarn subtype there is 

a strong negative correlation between gold grade and tonnage 

(linear correlation coefficient = -0.69); this relation is slightly 

weaker for the byproduct Au-skarn subtype (linear 

correlation coefficient= -0.54). The Au-skarn subtype has a 

median gold grade of about 8.6 g/t and a median silver 

grade of about 5.0 g/t (figs. 2C and 13A). The determination 

of median silver grade for the Au-skarn subtype is based 

upon values of silver grade available for 29 of 40 deposits 

(table 2). Meinert (1988a) tabulated Au, Ag and Cu grades 

for various types of skams. The fourteen deposits he 

classified as gold skarns all have gold grades greater than 1 

g/t Au and largely overlap our data set. Median gold grade 

for Meinert's gold skarn set is 6.5 g/t; median silver grade 

for the nine deposits that report silver is 9 g/t. For the 

byproduct Au-skarn subtype, the medians are 3. 7 g/t gold 

and approximately 34 g/t silver. Nearly 90 percent of the 

byproduct Au-skarns report silver (table 3). Silver content 

appears to have a strong correlation with base-metal content. 

As a comparison, the median gold grade for 14 porphyry 

copper-related Cu skarns, as reported by Meinert (1988a), 

is approximately 0.3 g/t and the median silver grade is 

approximately 8 g/t (note that these values are higher than 

those reported by Singer, 1986) for gold in porphyry copperrelated skarns. 

We found wide variations in gold grade distributions. 

In fact, values of gold grade reported during various stages 

of exploration and development of many deposits typically 

show significant adjustments, usually in a descendent 

manner. Furthermore, tests of the gold grade distribution 

for Au-skarns indicate that the addition of approximately 

40 deposits with grades less than 3.7 g/t would be required 

Grades and Tonnages of Gold-Bearing Skarns 21 
to change the median to a value approximately the same as 

that of the byproduct Au-skarn subtype. 

As already described, skarns that contain byproduct 

gold show no statisticaily significant differences in tonnage 

distributions from Au-skarns exploited almost exclusively 

for their precious-metal content (figs. 1, 2). This relation is 

primarily a reflection of the highly variable exploitability of 

many polymetallic skarn systems under a wide range of 

economic circumstances. Tonnages of deposits that comprise 

the Au-skarn subtype vary widely, from approximately 9 

tonnes to 15 million tonnes (table 2), primarily because of a 

combination of both differing economic circumstances and 

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SILVER GRADE, IN LOG UNITS OF GRAMS PER TONNE 

Figure 13. Distributions of silver grade for Au-bearing skarns. A, 

Silver grade model for 29 Au-skarn deposits. 8, Silver grade model 

for 44 byproduct Au-skarn deposits. 

22 Gold-Bearing Skarns 

advances in metaiiurgical techniques over the many years 

these types of deposits have been mined. However, there is 

a marked difference in cumulative distributions for gold 

and silver grades of Au-skarn and byproduct Au-skarn as 

defmed previously: Au-skarns have a median gold grade of 

8.6 g/t and byproduct Au-skarns have a median grade of 3.7 

g/t Median silver in Au-skarns is 5 g/t as compared to 37 

g/t in byproduct Au-skarns (fig. 13). Both gold (greater 

than 1 g/t) and silver grade populations as currently reported 

are significantly different between the Au-skarn and 

byproduct Au-skarn subtypes. Median silver grades were 

determined from silver data available for 29 of 40 deposits 

included in the Au-skarn subset, and for 44 of 50 deposits 

included in the byproduct Au-skarn subset. It should also be 

noted that in element-versus-element plots for byproduct 

Au-skarn and Au-skarn subtypes, byproduct Au-skarns (or 

Au-rich Cu-skarn deposits in the terminology of many 

others), for instance, plot in a cluster spatiaiiy separate from 

most Au-skarns and tend to represent the Cu-rich part of 

the domain with gradational and overlapping relations with 

other skarns; these types of relations hold for many other 

elements (fig. 14A). However, as shown by the graph of 

these data (fig. 14A), strengths of association of gold grade 

for copper grade in the two subsets of Au-bearing skarn 

seem to show extremely weak correlations between gold 

grade and copper grade; correlation coefficients for the two 

subsets of types of Au-bearing skarn are less than 0.2. Gold 

and copper grades are available only for 20 of 40 Au-skarn 

deposits (table 2), which may in part be an indication of an 

underreporting of copper contents for some deposits because 

of its economic insignificance during the time many of those 

deposits were being mined. Nonetheless, very significant 

gold grades can occur in some very Cu-rich skarns. Many 

Au-skarn deposits show a strong spatial association between 

gold and copper within the deposits themselves. A plot of 

gold grades versus silver grades for both subsets of Aubearing skarn shows that most Au-skarns have silver grades 

lower than byproduct Au-skarns (fig. 14B). Gold grades 

compared with silver grades for the Au-skarns have a 

correlation coefficient of approximately +0.4, and for the 

byproduct Au-skarns a correlation coefficient of 

approximately +0.2. One important exploration implication 

is that economicaiiy viable Au-bearing skarn deposits may 

be associated with Cu, Pb-Zn, Fe, or W skarn, and although 

the median gold grade of these byproduct Au-skarns is lower, 

the highest grades are similar to those of the Au-skarn 

subtype. Perhaps the only types of metal-bearing skarn that 

might be excluded from consideration as permissive for the 

occurrence of significant concentrations of gold and silver 

are tin-skarn and lithophile-element (beryllium, fluorine, 

tungsten, molybdenum, tin, and zinc) skarn associated with 

two-mica granite. Significant gold or silver mineralization 

is not known in classic Sn-skarn regions in Cornwall 

(Hosking, 1964) or Malaysia (Hosking, 1977, 1979). 

However, some Au- and Bi-bearing skarns (Stormant) are 
known in the Moina Mining District, Tasmania, Australia, 

which is largely known for its Sn-W skarn and greisen 

deposits (Collins and Williams, 1986). Lithophile-element 

skarn is associated with numerous Late Cretaceous, 

peraluminous, two-mica granitoids across a broad region in 

the eastern Great Basin of the United States (Barton, 1987; 

Barton and others, 1988). Significant concentrations of 

gold have not been reported from this lithophile-elementskarn environment. However, silver is present in many of 

these lithophile-element skams in apparently genetically 

1. 5 .-------.---,..---.----r--~-....---~--r----T---. 

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GOLD GRADE, IN LOG UNITS OF GRAMS PER TONNE 

Figure 14. Gold grade compared with copper grade and silver 

grade. A, Gold grade compared with copper grade for Au-skarns 

and byproduct Au-skarns; 8, Gold grade compared with silver 

grade for Au-skarns and byproduct Au-skarns. 

associated silver-base-metal, quartz-carbonate veins (Barton, 

1987). 

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BIBLIOGRAPHY OF ADDITIONAL 

GOLD-BEARING SKARN REFERENCES 

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TABLES 1-8 
Table 1. Abbreviations used in tables 

Term Abbreviation Term Abbreviation Term Abbreviation 

Mineral name 

actinolite act forsterite fo prehnite preh 

amphibole am ph galena gal pyrite py 

andradite an garnet gar pyrolusite pyr 

ankerite ank goethite goe pyroxene px 

apatite ap grossular gros pyrrhotite po 

argentite arg hedenbergite bed quartz qtz 

arsenopyrite apy hedleyite hedl realgar real 

azurite azur hematite hem sea polite scap 

biotite biot hessite hes scheelite sch 

bismu thinite bism hornblende hom scorodite scor 

bornite bor jasper jas sericite ser 

calcite cal K-feldspar k-spar serpentine serp 

carbonate minerals carbs leucopyrite leucopy siderite sid 

cerargyrite erg limonite lim spadaite spa 

cerussite cer loellingite loel specularite spec 

chalcocite cc ludwigite lud sphalerite sph 

chalcopyrite cpy magnesite mags spinel spin 

chlorite chl magnetite mag stibnite stib 

chrysocolla chr malachite mal stilpnomelane stilp 

clinopyroxene clinopx maldonite mald telluride(s) tell 

clinozoisite clinoz marcasite marc tenorite ten 

covellite cov molybdenite moly tetradymite tetd 

cubanite cub muscovite muse tetrahedrite tet 

cummingtonite cum native bismuth Bi tourmaline tour 

cuprite cup native copper Cu tremolite trem 

diopside diop native gold hi vermiculite ver 

dolomite dol native silver Ag vesuvianite ves 

electrum elec nontronite non white mica wm 

enargite enar orpiment orp wolframite wolf 

epidote ep oxide(s) ox wollastonite wol 

feldspar feld phlogopite phlg zoisite zoi 

fluorite fl plagioclase plag 

Rock type 

agglomerate agglom hornfels hfs sandstone sst 

andesite and limestone Is sedimentary sed 

argillite argl manganiferous mang sediments seds 

calcareous calc marble mar shale sh 

carbonaceous carb monzonite monz siltstone sltst 

conglomerate congl mudstone mdst skarn skn 

dolostone do los porphyry porph slate sl 

greenstone grnst quartzite qtzite volcanic rocks voles 

38 Gold-Bearing Skarns 
Table 1. Abbreviations used in tables-Continued 

Term Abbreviation Term Abbreviation Term Abbreviation 

Age 

Tertiary Tert. Carboniferous Car b. Proterozoic Prot. 

Miocene Mio. Pennsylvanian Penn. Early E. 

Eocene Eo c. Mississippian Miss. Middle M. 

Mesozoic Mes. Devonian Dev. Late L. 

Cretaceous Cret. Silurian Sil. early e. 

Jurassic Jur. Ordovician Or d. middle m. 

Triassic Tri. Cambrian Cam b. late 1. 

Paleozoic Pal. Precambrian Prec. Upper u. 

Permian Perm. 

Other 

average avg million M sequence seq 

Formation Fm. million years Ma short ton (2000 lb) st 

gram g tonne(s) (metric tons) trace tr 

Group Gp. 

Country Country code Country Country code 

Afghanistan AFGH Philippines PLPN 

Australia, New South Wales AUNS Papua New Guinea PPNG 

Australia, Queensland AUQL South-West Africa (Namibia) SAFR 

Australia, Tasmania AUfS Spain SPAN 

China CHNA Sweden SWDN 

Colombia CLBA Thailand 1lll.D 

Canada, British Columbia CNBC United States, Alaska USAK 

Canada, Quebec CNQU United States, California USCA 

Canada, Yukon Territory CNYf United States, Colorado usco 

Ecuador ECDR United States, Idaho USID 

Indonesia INDS United States, Montana USMf 

Japan JPAN United States, Nevada USNV 

Mexico MXCO Soviet Union USSR 

Malaysia MYLA United States, Utah usur 

Nicaragua NCRG United States, Washington USWA 

North Korea NKOR Federal Republic of Germany WGER 

Peru PERU 

Table 1 39 
Table 2. Gold-bearing skarns in which gold and silver are major commodities exploited 

[p, metal present in unquantified amount; other abbreviations listed in table 1] 

Name Location Host lithology Formation age/ Igneous rocks Age Ore minerals Gangue 

(mining district) name minerals 

Bau MYLA mar, sh L. Jur./Bau Ls. acid porph stocks & Mio. Au, apy, py, sph, chi, diop, ep, gar, 

dikes stib, real, orp, wol, ves, qtz, cal, 

scor rare plag, ap, preh 

Beano CNBC Is, and tuff Tri.-Jur./ diorite-rhyolite Jur. po, cpy, apy, act, qtz, cal, chi, 

(Zeballos) Quatsino Fm. porph sill mag, hedl clinopx, Cl-amph 

Bonanza voles. 

Broadway USMT Is Miss./Mission Boulder batholith, Cret. auriferous jas, jas, lim, ep, gar, cal, 

(Victoria) (Silver Star) Canyon Ls. Rader Creek pluton, cup, mal, py, serp hed, chi, 

qtz monz argentiferous non, diop 

lead ore, py, po, 

cpy 

Brown's AUNS Is & mdst in tuff Ord./ Carcoar Granite Dev. Au, apy, cpy, py, act, diop, ep, gar, 

Creek Angullong Tuff diorite po, ten, tet, bor wol, ves, trem, 

clinoz, phlg, sid, 

clay, chl 

Buffalo USNV chert, argl, Is Penn.-Perm./ granodiorite Tert. py (Au?), hem, qtz, lim, px, cal, ep, 

Valley (Battle Havallah seq. porph Au, cpy, Ag, gar, non 

Mountain) mal, chr 

Canty CNBC Is, sltst, limy L. Tri./ Hedley intrusions, E. Jur. Au, apy, py, cpy, clinopx, cal, gar, ep, 

(Hedley) argl, tuff Nicola Gp. qtz diorite sills po qtz, scap, k-spar, 

albite 

Discovery CNBC mar Pal.(?) Coast plutonic Cret.(?) py, po, cpy, mag, gar, px, chi, qtz, cal, 

(Banks Island) complex apy, sph am ph 

Dividend- CNBC Is, grnst, qtzite, Perm.-Tri./ Kobau Nelson/Osoyoos Cret. mag, cpy, py, po, qtz, cal, ep, gar, chi, 

Lakeview and flows & tuffs Gp. or batholith, qtz apy, Au, Bi, Ch-amph, act, 

Perm/Anarchist Gp. diorite-granodiorite marc, hedl sphene, clay, minor 

diop 

Esmeralda USMT Is, and, grano- Pal., Cret. granodiorite, and Cret. Au, cpy, mal, jas gar, ep 

(Ophir) diorite, mar 

Excelsior USMT Is Miss./ Bannack stock auriferous py, gar, cal, ep, qtz 

(Bannack) Madison Ls. granodiorite Au in goe, Ag, 

bor, tetd, spec, 

hem 

Fortitude USNV calc seds Antler Sequence granodiorite stock Tert. po, cpy, apy, clinopx(hed), 

(Lower (Battle elec, bism, Bi, gar( an), act, chi, 

Fortitude) Mountain) tell, marc, gal, preh, ep, qt 

mag, sph 

French CNBC Is boulder congl, L. Tri./ Hedley intrusions, E. Jur. po, cpy, py, bor, clinopx, gar, ep, qtz, 

(Oregon) (Hedley) limy argl, tuff Nicola Gp. porph qtz diorite, apy, Cu, sch cal, axinite, wol, 

sills clinoz, biot, 

trem-act, k-spar 

Golden USMT Is, qtz monz Cam b./ Boulder batholith, Cret. po, bism, tetd, gar, diop, cal, ep 

Curry (Elkhorn) Wolsey Fm. qtz monz cpy, mag 

40 Gold-Bearing Skarns 
Ore control Tonnage Au (g/t) Ag (g/t) Base metals Comments References (millions of tonnes) 

contact zone, fractures, 2.4 7.2 0.1 Area includes skn, vein, and replacement 1, 2, 3, 4 

permeable lithology mineralization in irregular pods and lenses 

along joints and fractures; contains 0.002% 

Sb 

0.000021 157 67 0.16% Cu Contains Au, Ag, Cu,Bi, Te, Co; 5, 6, 7 

Au-poor iron skams nearby; similar setting 

for nearby Hiller property (potential Au skn 

based on assays > 1 g Au/t) 

contact zone between 0.0272 37.6 p CupPbp Ore concentrated in jasper zone along 8, 9 

qtz granodiorite-Is contact; px-gar skn locally 

1st-tuff contact, 0.39 8.7 10 0.44% Cu Contains As, Sb 10 

fractures 

intense qtz-py 1.81 1.71 Skn assemblages are rare in pit but more 11, 12, 13 

silicification in (0.0027 13.88 17.6 Cup) common at depth; produced approx 9,200 

fractured skn near oz Au during fiscal1988; geologic gold 

porph resetves, 110,900 oz in 1988 (1924-51 

production: 1,380 oz Ag from 0.0024 Mt, 

0.80% Cu from 542 t of ore, 1937-39); 

Horizon Gold Inc./Chevron Resources 

Cahill Creek fault zone, 0.0015 10.8 p Size based on 1939 and 1941 production; 5, 7, 14, 15 16 

lithology mineralization probably hosted by upthrown, 

fault-bounded sediments within the fault 

zone; contains Au, W, As, Co, Ag; Mascot 

Gold Mines Ltd. 

fracture zone at 0.038 17.1 p p Probable resetves indicated by drilling; Au 7 

granodiorite-mar in skn and in qtz-py veins; additional 

contact resetves (0.0955 Mt of ore at 16.21 g!t) for 

a massive sulfide vein (Tel zone) that cuts 

mar and metapelite; Trader Resources 

Corp. 

contact zone, structure 0.1113 4.5 0.79 0.06% Cu Gar-ep skn replaces voles and mar; contains 5, 7, 17, 18, 19 

Pb p As, Co, Bi, Te 

Znp 

contact zone between 0.00000907 20.5 6.8 Skn explored by 120-m-long adit; surface 20 

granodiorite and Is cuts contain Is, and, jas-all of which 

probably contain Au 

contact zone between 0.000599 27 74.1 Cup Production reported for 1902, 1917-19; 21, 22 

granodiorite and Is 385 t contained 3.2% Cu; estimate 0.0058 

Mt produced 36.5 g Cult before 1914 

favorable lithology 5.1 10.45 27.8 0.2% Cu Porph Cu skn, polymetallic veins; Battle 23, 24, 25, 26 

Mountain Gold Co. 

hinge zone of anticline 0.068 19.9 2.6 0.03% Cu 8700 t of unmined ore reported to contain 5, 7, 14, 27 

as much as 85 g!t Ag and 2% Cu; contains 

W, As, Mo, Bi, Co, Sb 

contact zone 0.089 8.3 4 0.33% Cu; Production data for 1904-51. Four types 28,29 

Fe p of ore present: mag veins, jasperoid lodes, 

massive mag-po, and massive po-cpy in px 

gangue 

Table 2 41 
Table 2. Gold-bearing skarns in which gold and silver are major commodities exploited-Continued 

Name Location Host lithology Formation age/ Igneous rocks Age Ore minerals Gangue 

(mining district) name minerals 

Golden USMT ls Miss./ Bannack stock Tert. Au, Ag, tet, erg, qtz, gar, py, cal, ep, 

Leaf (Bannack) Madison Ls. granodiorite cpy, bor, mal, chi, sid, ves 

gal, cer, sph, 

mag 

Good CNBC tuff, argl, Is L. Tri./ Hedley intrusions, E. Jur. apy, py, cpy, po, clinopx, gar, cal, 

Hope 1 (Hedley) Nicola Gp. qtz diorite Bi, moly, hedl wol, ep, biot, qtz 

Hardcash USMT Is Camb./Park Sh. Boulder Cret. bism, tetd, cpy gar, ep, diop, cal 

(Dolcoath) (Elkhorn) batholith 

Labrador USNV calc sh, calc sst, U. Camb./ granodiorite Tert. Au, py, po, lim gar, ep, chi, cal, qtz 

(Battle arkose, calc Harmony Fm. porph 

Mountain) congl M. Penn./ 

Battle Fm. 

La Luz NCRG Is, limy sh, Mine Series granodiorite Tert. Au, cpy, py, hem ep 

(Siunna) agglom, tuff 

Lebedskoe USSR Is, calc sh, dolos E. Pal. diorite Pal. Au, apy, sph, tet, gar (an, gros ), diop, 

(Kaurchak) Pb tell, mag, cpy, bed, trem, ep, 

hem, py, cc, po, clinoz, wol, act 

gal, sph, ten, bor 

Marshall CNBC Is, siliceous sltst, L. Tri./ microdiorite L. Tri. cpy, py, po, sph, chl, gar, diop, 

(Greenwood) argl, congl Brooklyn Gp. granodiorite Au, minor mag, amph, ep 

hem, gal, marc 

Mascot CNBC sltst, ls, congl, L. Tri./ Hedley intrusions, E. Jur. apy, po, cpy, px, gar, wol, biot, 

Fraction (Hedley) tuff Nicola Gp. porph qtz diorite, mag, bor, mald, k-spar, cap, cal, qtz, 

(Hedley Fm.) gabbro, sills & dikes hedl preh, ap, axinite 

McCoy USNV ls, dolos, qtzite Tri./ Augusta Brown stock Tert. Au, py, cpy, cc, gar, px, ep, cal, qtz, 

(McCoy) Mountain Fm. granodiorite (39.7 Ma) cov, sph, gal, po, chl, amph, ves, feld 

Tri./Cane Spring hem, mag 

Fm. 

Midas USUT ls Manning qtz monz Tert. py, apy, Cu wol, diop, gar, ves 

(Gold Hill) Canyon Sh. & sulfides 

Oquirrh Fm. 

Molly B CNBC tuff, argl, ls Jur./ Coast Range Cret.(?) py, po, cpy, moly, gar, ep, px, qtz 

Haselton Gp. batholith sch 

Mt. USNV sh, ls, calc sh Camb./ Secret Seligman and Cret. Au, sch, moly, gar, qtz, ep, cal 

Hamilton (White Pine) Canyon Sh. Monte Cristo cpy, py, apy, sph, 

stocks, granodiorite gal, bor, tetd, py, 

hem 

Navachab SAFR turbidites, L. Prec. 2 mica granite Cam b. 

clastics 

Nickel CNBC Is, limy argl, L. Tri./ Hedley intrusions, E. Jur. Au, elec, apy, gar, clinopx, cal, 

Plate (Hedley) qtzite, tuffs, sltst, Nicola Gp. qtz diorite, gabbro, (180 Ma) cpy, py, po, tetd, axinite, scap, ap, 

congl (Hedley Fm.) sills & dikes sph, marc, gal, clinoz, ep, biot, 

moly, mag, trem-act, qtz, preh, 

titanite, hedl, wol 

tell, cobaltite, 

ecythrite, 

platinum, Bi, 

maldonite, 

gersdorffite, Cu, 

pyrargyrite 

Northeast USNV calc congl M. Penn./ granodiorite stock M. Tert. po, cpy, py, Au act, ep, sphene, 

Extension (Battle Battle Fm. k-spar, chi 

Mountain) 

Pagaran INDS Is, and voles Perm./ Muara Sipongi L. Jur. Ag, Au, cpy, bor, gar, wol, diop, qtz, 

Siayu (Muara Silungkang Fm. intrusions, tetd, tell, apy, preh, chi, cal 

Sipongi area) granodiorite, diorite sph, gersdorffite 

42 Gold-Bearing Skarns 
Ore control Tonnage Au (g/t) Ag (g/t) Base metals Comments References (millions of tonnes) 

contact zone between 0.0875 10.8 34.1 <0.01% Production figures for 1909-41; Cu, Pb, 21,22 

granodiorite and ls Cu; Zn production for lower tonnages of ore; 

Trace Zn oxidized to 100-m depth 

0.06% Pb 

fault cutting skn 0.0114 15.6 10.5 Same stratigraphic horizon as French mine 5, 7, 14, 15, 16 

replaced bed 0.003 8.52 4.13 0.20% Cu 28,29 

0.006% Pb 

northeast- & 0.907 1.3 3.7 Minable reserves. Ore associated with 30 

northwest-striking oxidized py along faults cutting gar skn; 

faults Battle Mountain Gold Co. 

fault/hanging wall 15 4.1 1.2 0.44% Cu 31, 32, 33 

andesite 

0.12 4 Estimated tonnage and grade (ref. 37). Au 1, 34, 35, 36, 

in py, 0.8 to 30 ppm; Au in cpy, 13.6 ppb; 37,38 

low quantity of sulfide in deposit (few 

percent) 

crest isoclinal fold at 0.00019 77.3 92.8 0.24% Cu; Described as Au-enriched Cu skn 5, 7, 17, 39 

contact of ls with 0.29% Zn; 

underlying siliceous 1.19% Pb 

sltst 

skn-mar contact 0.6186 11.2 2.76 0.14% Cu Forms part of same deposit as Nickel Plate; 7, 14, 15, 16, 

As-Au skn; Mascot Gold Mines Ltd./Corona 40,41 

Corp. 

contact between ls and 13.2 1.5 30 0.08% Cu Distal disseminated Cove Ag-Au deposit 42, 43, 44, 45, 

stock, endoskarn, nearby with 16.4 Mt of 2.6 g Au/t and 111 g 46, 47 

shears, bedding planes, Aglt; Echo Bay Minerals Co. 

faults 

bedding 0.0006 25 p Production estimated for 1902 data; 48 

estimate 86 t higher grade ore pre-1897; 

lower grade production reported for 1904 

0.00029 2.36 4.5 0.13% Cu 7,49 

contact zone between 7 1.7 17.1 Cup Au associated mostly with intense 50 

granodiorite and calc Wp retrograde alteration of gar-py skn; 

sh; retrograde Mop sulfide-bearing qtz veins overprint skn; 

alteration Westmont Mining Inc. 

9.75 2.5 Purported to be a skn deposit; Erongo 51, 52 

Mining and Exploration Co. Pty. Ltd. 

contact zone 2.986 13.96 1.39 0.03% Cu Forms part of same deposit as Mascot 1, 7, 14, 53, 

Fraction; As-Au skn; Mascot Gold Mines 54, 55, 56, 57, 

Ltd./ Corona Corp. 58 

favorable lithology 1.4 2.9 5.1 0.11% Cu Porph Cu skns, polymetallic veins; Battle 59 

Mountain Gold Co. 

contact zone regional 0.113 5.6 2.5 0.2% Cu Production for 1936-39; numerous 3, 60, 61 

faults Au-Ag-Cu skarns in this area of West 

Sumatra; N. V. Mijnbouw Maatschappij 

Moeara Sipongi 

Table 2 43 
Table 2. Gold-bearing skarns in which gold and silver are major commodities exploited-Continued 

Name Location Host lithology Formation age/ Igneous rocks Age Ore minerals Gangue 

(mining district) name minerals 

Red Dome AUQL sst, chert, Sil.-Dev./ qtz feldspar Carb.- Au, bor, mag, gar, wol, clinopx 

(Mungana) (Chillagoe) andesite, lithic Chillagoe Fm. porph dikes & sills Perm. sph, Pb & Ag 

congl, Is tells, cc, 

wittichenite, cpy, 

moly 

Rokuromi JPAN biot schist, Is Carb./ qtz diorite, Mes. po,apy gar, ep, others 

Utakai Fm. granodiorite 

Second CNBC basalts, tuffs L. Jur./ Nelson batholith py, po, cpy, mag, gar, ep, qtz, amph, 

Relief Rossland Gp. diorite porph dike moly clinopx, biot, carb 

(Elise Fm.) 

Sheahen- AUNS sltst, sh, sl, Ord./ granodiorite Dev.(?) Au, po, maid, py, px, hom, bio, ep, 

Grants mostly calc Malongulli Fm. apy, cpy, sph, trem, preh, cal, qtz, 

Au-Bi-sulfide chi 

Silverado CNBC metavolc, Is granodiorite Jur.-Tert. sph, cpy, po, mag px, gar, ep, qtz, cal 

Suian NKOR schist, qtzite, sl, Suian granite stock Mes.(?) Au, apy, cpy, gal, gar, diop, phlg, act, 

dolos, Is py, po, sph, lud, chi, talc, trem, 

bism, tetd, loel, wol 

moly, borate 

minerals 

Surprise USNV calc sh, calc sst U. Camb./ Cret.(?) elec, py, cpy, gar, diop, chi, cal, 

(Battle Harmony Fm. mal, lim, hem, qtz, amph, ap, 

Mountain) sph k-spar, non 

Tillicum CNBC tuffaceous seds, E. Jur./ qtz monz E. Jur.(?) Ag, Au, gal, po, act, gar, feld, trem, 

(Heino- (Till cum calc slst, argl Rossland Gp. sph, clinoz, py, apy, cpy, 

Money, Mountain) marc, biot, qtz, cal, 

East k-spar tetd, elec 

Ridge) 

Tomboy- USNV calc congl M. Penn./ granodiorite Tert. Au, cpy, gal, py, act, chi, ep, trem, 

Minnie (Battle Battle Fm. porph po,sph,apy clays, muse 

Mountain) 

TulMi NKOR schist, qtzite, sl, Suian granite stock Au, apy, cpy, gal, gar, diop, phlg, act, 

Chung dolos, Is py, po, sph, lud, talc, trem, wol, 

bism, tetd, loel chi 

1. Boyle, 1979 16. Ray and others, 1988 32. Plecash and others, 1963 

2 Wolfenden, 1965 17. Ettlinger and Ray, 1988 33. R.H. Sillitoe, oral common., 1987 

3. Bowles, 1984 18. Cockfield, 1935 34. Vakhrushev, 1972 

4. W.C. Bagby, written common., 1987 19. McKechnie, 1964 35. Ivankin and Rabinovich, 1972 

5. British Columbia Ministcy of Energy, 20. McCleman, 1976 36. Vakhrushev and Tsimbalist, 1967 

Mines and Petroleum Resources, 1981 21. Geach, 1972 37. E.L. Bloomstein, written common., 1987 

6. Stevenson, 1950 22. Winchell, 1914 38.1Veritonov, 1966 

7. Ettlinger and Ray, 1989 23. Argall, 1986 39. Canada Department of Energy, Mines 

8. Gilbert, 1935 24. Wotruba and others, 1987a and Resources, 1986 

9. Sahioen, 1939 25. Wotruba and others, 1987b 40. Dolmage and Brown, 1945 

10. Taylor, 1983 26. Myers and Meinert, 1988 41. Billingsley and Home, 1941 

11. Coffey and others, 1988 27. Canada Department of Energy, Mines 42. Kuyper, 1987 

12 Horizon Gold Shares, Inc., 1988 annual report and Resources, 1980 43. Tingley and Smith, 1982 

13. Roberts and Arnold, 1965 28. Roby and others, 1960 44. Schrader, 1934 

14. Ray and others, 1987a 29. Klepper and others, 1957 45. Kral, 1947 

15. Ray and others, 1986b 30. Schmidt and others, 1988 46.L'lne, 1987 

31. Sillitoe, 1983 47. Emmons and Coyle, 1988 

44 Gold-Bearing Skarns 
Tonnage Ore control (millions of tonnes) 

intrusive contact 

dike contact, fault 

contact 

multistage contact 

metasomatism of 

reactive bed 

faults 

contact zone 

favorable beds, faults 

contact zone, 

permeable lithology 

contact zone 

48. Nolan, 1935 

49. Hanson, 1935 

50. Dennis and others, 1989 

51. Mining Magazine, 1987 

52. Mining Activity Digest, 1987 

53. Lee, 1951 

52. Barr, 1980 

55. Northern Miner, 1986 

56. Northern Miner, 1987 

57. Northern Miner, 1989a 

58. Northern Miner, 1989b 

59. Wotruba and others, 1986 

60. Bowles and others, 1985 

13.8 

0.081 

0.206 

1.52 

0.00013 

0.53 

1.53 

0.05 

2 

3.54 

0.4 

61. Beddoe-Stephens and others, 1987 

62. Torrey and others, 1986 

63. Murray, 1986 

Au (g/t) Ag (g/t) Base metals Comments References 

2.3 5.25 0.46% Cu; Deposit includes mineralization in breccia 62,63 

1% Zn and qtz vein stockwork; associated with Cu 

and Zn-Pb skns; Murray reports a Zn grade 

of 1.8%; Elders Resources Ltd. 

8 2 Fe (mag) skams; adjacent to Kamaishi 64 

15.1 4.16 0.0098% Production data for 1900-48; anomalous 7 

Cu· ' As, Bi; skn overprints voles and porph 

0.0005% Pb; diorite; skn cut by later qtz veins, sulfides 

0.0002% Zn 

4.53 Tonnage and grade composited from 65,66 

recorded production and drill-proven 

geologic resetve 

42.8 79.2 0.07% Cu Skn cut by faults 7, 67, 68, 69 

Znp 

13 4.9 Cu skns; worked from ancient times; grade 11, 70,71 

and (or) tonnage may be underestimated 

2.77 23.1 0.85% Cu Mineable resetves; associated with Late 30 

Cret. porph Cu skns and polymetallic veins; 

Battle Mountain Gold Co. 

35 p Zn p; Pb p Proven resetves (ref. 7) for the 7, 72, 73, 74, 

6.9 p Zn p; Pb p Heino-Maney zone, and estimated resetves 75, 76, 77 

for the East Ridge deposit (0.34-Mt core of 

deposit grades 10.3 g!t Au); two phases of 

metal deposition-Au, apy, ±sph, qtz, calc 

silicates followed by Ag-gal, apy, sph; 

Esperanza Exploration Ltd. 

3.1 9.6 0.03% Cu; Associated with Mid.-Tert. porph Cu skns 31, 78 

Znp; and polymetallic veins; Battle Mountain 

Pb p Gold Co. 

12 70, 71 

64. Grant, 1950 

65. Stevens, 1975 

66. R. Overton, written commun., 1987 

67. Muller and others, 1981 

68. Carson, 1969 

69. Carson, 1973 

70. GalL'lgher, 1963 

71. Watanabe, 1943 

72. Ray and others 1985 

73. Ray and others, 1986a 

74. McClintock and Roberts, 1984 

75. Roberts and McClintock, 1984a 

76. Roberts and McClintock, 1984b 

77. Mining Journa~ 1989 

78. Blake and others, 1984 

Table 2 45 
Table 3. Gold-bearing skarns in which gold and silver are byproduct commodities 

[p, metal present in unquantified amount; other abbreviations listed in table 1] 

Location Host Formation age/ Associated Ore Gangue Name igneous Age (mining district) lithology name rocks minerals minerals 

Fe skarns with byproduct gold 

Larap PLPN calc seds Eoc.(?)/ diorite, grano- Mio. mag, hem, py, gar, px, ep, 

including Is, calc Universal Fm. diorite, syenite po, moly, cpy, amph, cal, chi, 

sh, arkose stocks, dikes bor, gal, sph, ap, k-spar, scap 

cobaltite albite 

Nabesna USAK ls, dolos, marl, Tri./ monzodiorite 104-114 py, mag, cpy, Au, gar, wol, ves, ep, 

mafic voles Chitistone Ls. stock Ma po, gal, sph, apy, act, hom, chl, 

stib scap, ap, serp, 

qtz 

Cu skarns with byproduct gold 

Apex CNBC Is, voles Tri./Kunga Fm. San Christoval E. Jur. py, cpy, mag qtz, cal, gar, ep 

(Queen or Kamutsen Fm. batholith -qtz 

Charlotte) diorite 

Bailey Day USNV calc sst U. Camb./ Tert. (?) py(Au), cpy, mal, ep, k-spar, 

(Battle Harmony Fm. chr, azur, ten, sphene, gar, chi, 

Mountain) hem, lim, Au, biot 

Ag 

Benson Lake CNBC ls, voles U. Tri. & L. Jur./ · Benson Lake Jur. cpy, mag, bor, gar, ep, cal, chi 

(Vancouver) Vancouver Series stock py, po, apy 

Quatsino Ls. & qta diorite 

Karmutsen voles. 

Blue Bell USMT qtz monz Cret. qtz monz Cret. mal, azur, Au, gar, ep, qtz, scap 

(Elliston) moly, py 

Bluestone USNV Is Tri. granodiorite Jur. cpy, py ep, gar, minor 

(Yerington) diop 

Carissa USNV sh, calc sh, Is U. Camb./ granodiorite- Tert. or Cu carbs, Fe ox, ep, diop, gar, 

(Battle Harmony Fm. monzogranite Cret. py, cpy, po, sch qtz, cal, chl, clays 

Mountain) 

Coast Copper CNBC Is, and voles U. Tri. & L. Jur./ diorite-gabbro cpy, bor, mag 

(Vancouver) Vancouver Series 

Quatsino Ls. & 

Karmutsen voles. 

Concepcion MXCO Is, sltst granodiorite stock Mes. Eoc. cpy, py, mag, an, chi, diop, ep, 

del Oro hem, enar, tet, px, plag, ves, zoi, 

ga~ sph, po, ten, scap, act, ilvaite 

bism, cosalite, 

wittichenite 

Copper Queen CNBC Is, mar Tri./ diorite porph Mes. (?) bor, cpy, Ag, tet, gar, px, ep, cal 

(Texada Marble Bay Ls .. moly, sch 

Island) 

Cornell CNBC ls, mar Tri./ gabbroic Mes. (?) cpy, ~or, po, cal, gar, diop, ep, 

(Texada Marble Bay Ls. suite-diorite mag, marc, Ag, serp 

Island) porph py, moly, tet, sch 

Crevice Creek USAK ls, argl, chert, U.Tri./ granodiorite Jur. (?) py, cpy, mag ep, gar 

(McNeil) metavolcs Kamishak Fm. stock of Pilot 

Jur.{falkeetna Fm. Knob 

Cyclone USMT Is Pal. porphyritic Cret. mal, Au gar, qtz, ver 

(Ophir) granite 

Empire USID dolomitic ls Miss. granite, porph cpy, py, po, gar, px 

(Alder Creek) dikes secondary Cu 

minerals 

46 Gold-Bearing Skarns 
Tonnage Base metals Ore control (millions of Au (g/t) Ag (g/t) and Fe Comments References 

tonnes) 

Fe skarns with byproduct gold 

fractures, sediment >18 1.37 6.2 0.12% Cu Deposit grades into Cu-Mo porph at lower 1, 2, 3, 4, 

contact with 43% Fe levels ; 0.08% Mo, 0.02% Ni, 0.03% Co; 

unconformably Pim Bessemaer 

overlying voles 

contact zone 0.08 25 p Fep Main Au ores are py veins along fractures; 6, 7 

minor Au in mag and po bodies; no Fe 

production; Nabesna Mining Corp. 

Cu skarns with byproduct gold 

0.000099 58.1 17 0.70% Cu Based on 1945 production; note that 8, 9, 10 

Ettlinger and Ray (1989) report reserves 

of 163,000 t for Ag-Cu Alpine (Apex 

Star) skn of 34% Fe, 0.90% Cu, 24.6 g!t 

Ag, no Au reported 

favorable bed, structure 0.0023 19.2 38.9 1.2% Cu Additional Au-ore tonnages discovered in 11 

1980's at this deposit; associated with Cu 

and Au skns, polymetallic veins 

Is-and contact 1.26 1.98 4 1.6% Cu Coast Copper Co., Ltd. 8, 9, 12, 13 

0.0000045 6.9 186 1.62% Cu Gar apparently veins qtz monz 14 

0.378 2.86 3.34 2.08% Cu Associated with a porph Cu deposit 15, 16, 17 

favorable bed 0.0091 17.1 73.7 2.96% Cu Associated porph Cu deposit; Battle 11, 18 

Mountain Gold Co. 

lst-and contact 2.99 2.31 >2.1 1.56% Cu Adjacent to Benson Lake mine; Quatisino 19 

33.3% Fe Copper-Gold Mines Limited and Empire 

Development 

contact zone 15 1.7 2% Cu Fe p In Zactecas; endoskam present 1, 2, 20, 21 

PbpZnp 

contact zone 0.0041 11.5 87 4.4% Cu Based on 1903-17 production; reported 9, 22,23,24 

Mo, W 

contact zone 0.0407 11.6 53.9 3.4% Cu Based on 1897-19 production; Vanada 9, 22, 23, 24 

Mining Co., Ltd. (1943) 

0.000011 4.5 514 17.5% Cu Ep-gar skn bodies in Is adjacent to stock; 5, 25, 26 

mag zones; magnetic anomalies around 

stock 

contact zone 0.000028 10.96 110 9.7 Based on 1942-61 production; Ag grade 14 

from 23 t; Cu grade from 22 t 

contact zone 0.694 1.65 53.89 3.64% Cu 27 

Table 3 47 
Table 3. Gold-bearing skarns in which gold and silver are byproduct commodities--Continued 

Location Host Formation age/ Associated Ore Gangue Name igneous Age (mining district) lithology name rocks minerals minerals 

Cu skarns with byproduct gold-Continued 

Esashi JPAN Is Carb./Shiba & qtz porph, Cret. cpy, py, bism, Bi, diop, ep, gar, 

(Akagane) Yonezato Fms. granodiorite sch, cub tour, amph, bed 

Gold Bug USMT Is Miss. granodiorite Tert. auriferous py, qtz, cal, gar, goe, 

(Bannack) Au, auriferous ep, mal 

tetd 

ll'mensk USSR diorite(?) gar, px 

(ul'ma) 

Jumbo USAK mar L. Pal./ granodiorite E. Cret. Au, cpy, sph, diop, gar, wol, 

(Jumbo) Wales Gp. stock moly, hem, py, ep, act, hom, 

po, spec chl, scap, plag, 

qtz 

Katanga PERU Is, sh Cret./equivalent of qtz dioritie, Tert. cpy, py, bor, gar, trem 

Ferrobamba & qtz monz chal, chr, mal, 

Tintaya Ls. brochantite, 

mag, Au, Ag 

Klondyke USMT dol Dev./Jefferson Fm. Boulder Cret. tetd, py, cpy, lim, diop(?), gar, 

(Elkhorn) batholith mal trem, cal, chl 

near Black 

Butte 

stock-gabbro 

diorite 

Lily CNBC gmst, Is L. Tri./ Jedway stock L. Cret. mag, po, cpy, py, gar, act, chl, cal 

Karmutsen Fm. sph 

E. Jur./Kunga Fm. 

Little Billie CNBC Is, mar Tri./ felsic Mes. (?) cpy, bor, Ag, Au, cal, diop, gar, ep, 

(Vananda) (Texada Marble Bay Ls. granodiorite, py, po, sph, mag, act, wol, amph, 

Island) qtz monz moly, sch, marc, ves, qtz 

gal, tell 

Lucky Mike CNBC gmst, Is, L. Tri./ acidic dikes, Jur. (?) py, po, cpy, sch gar, px, ep, cal 

(Last Chance) breccia, agglom Nicola Gp. granite-diorite 

Marble Bay CNBC Is, mar Tri./Marble Bay Ls. diorite Mes. (?) cpy, bor, po, ep, gar, cal, diop, 

(Texada mag, marc, Ag, wol?, trem, qtz 

Island) Au, py, sph, 

moly, tet 

Morning CNBC Is, basalt L. Tri./ Collision Bay L. Cret.- mag, py, cpy, po, gar, px, qtz 

(Ikeda) Karmutsen Fm. diorite stock, E. Tert. apy, bor 

Kunga Fm. Carpenter 

qtz monz 

stock 

Mother Lode CNBC sharps tone L. Tri./ Wallace Creek L. Jur. cpy, py, hem, ep, gar, cal, qtz, 

(Greenwood) congl, Is Brooklyn Gp. granodiorite mag, Au act, trem, chl 

Natalevskoe USSR Is, calc sh, dolos Pal. diorite, Pal. cpy, bor, apy, py, an-gros, diop, 

syenite, aplite po, bism, sph, trem, wol, 

mag, moly, cc, ep-clinoz, fo, 

Au, gal, elec, Bi, phg, serp, ves, 

cub, Pb tell, Ni scap, spin, fl, 

selenide, tet, ten, chondrodite, 

Ag clinohumite, 

preh, ap, chl, 

sphene 

48 Gold-Bearing Skarns 
Ore control 

granodiorite-Is contact; 

ore generally exterior 

to gar skn 

contact zone 

contact, fissures 

fractures, bedding 

planes 

granodiorite-mar 

contact 

faults, intrusive 

contacts 

faults 

steep fracture-skn 

intersection 

Tonnage 

(millions of 

tonnes) 

3.796 

0.0021 

0.1 

0.1115 

2 

0.0006 

0.0134 

0.0637 

0.000024 

0.199 

0.000029 

4.24 

0.48 

Base metals Au (g/t) Ag (g/t) and Fe Comments 

Cu skarns with byproduct gold-Continued 

1.1 10.1 0.8% Cu 

23.7% Fe 

31.7 70.3 0.76% Cu 

0.31% Pb 

1 5% Cu 

1.97 24.5 4.1% Cu 

Fep 

6.1 46.5 3.5% Cu 

Fep 

30.3 17.4 1.04% Cu 

1.58% Pb 

3.82 64.3 4.28% Cu 

5.7 18.8 1.3% Cu 

Fep 

2.58 178 3.65% Cu 

3.31% Pb 

7.75 63.4 3.4% Cu 

Fep 

30 25.8 2.49% Cu 

Zn p Fe p 

1.27 5 0.82 

5 11 1.6% Cu 

Deposit has 5 ore bodies, largely skn but 

some disseminated veins; 5.9%pyrite, 

reported Bi 

Tonnage and grade figures represent 

1922-41 production; originally staked 

as Dakota claim 

Estimated tonnage and grade (ref. 31); in 

northeastern Altai Mountains; Au-Cu 

mineralization in skn may predate 

associated diorite 

Production data for 1907-44; estimated 

0.28 Mt ore resetves of 45% Fe, 0.73% 

Cu 

In Chillioroya region; Mitsui Mining and 

Smelting Co.(?) 

Based on 1915-57 production. Cu grade 

for 375 tore; Pb grade for 16.3 tore; 

similar to nearby Hardcash deposit 

Veinlike masses in altered and sheared gmst 

Deposit size based on production; reported 

Mo; Texada Mines Ltd. 

Deposit size based on production; Ideal 

Basic Industries, Inc. 

Production from Cu claims; ore in dikelike 

sulfide bodies along faults and contacts 

Includes Sunset property; Gold Mines 

Resources, Ltd. 

Estimated tonnage and grade (ref. 31); 3 

stage magnesian skn; numerous small 

podlike bodies of ore form at intersection of steeply dipping fractures; 

gold is relatively fine ( avg about 930); 

only a few percent sulfide in deposit 

References 

28 

29, 30 

31, 32, 33 

5, 6, 34, 35 

36,37 

38,39 

9, 10, 40 

22, 23 

9, 44 

22,23 

9, 10,42 

8, 9, 22, 43, 

44,45 

31, 46, 47, 

48, 49, 50 

Table 3 49 
Table 3. Gold-bearing skarns in which gold and silver are byproduct commodities-Continued 

Location Host Formation age/ Associated Ore Gangue Name igneous Age (mining district) lithology name rocks minerals minerals 

Co skarns with byproduct gold-Continued 

Old Sport CNBC Is, and voles L. Tri./ Coast Copper Jur. cpy, po, bor, cpy, cal, ep, gar, 

Quatsino Ls. Stock diorite/ py, mag, apy amph, diop, chi, 

gabbro qtz 

Pauline USAZ Is Cret. qtz latite Tert.- gal, cer, cpy, py, gar, qtz, ep 

(Helvetia- porph Cret. sph, moly, Au, 

Rosemont) Ag, spec 

Phoenix CNBC sharpstone L. Tri./ granodiorite Cret. po, cpy, py, hem, amph, ep, gar, 

(Greenwood) congl, Is, argl, Brooklyn Gp. of Nelson spec, minor mag, qtz, cal, chi 

tuff batholith Ag,Au 

Pioneer- USCA hfs, mar hom grano- Mes. py, cpy, bor, gar, ep, qtz, feld, 

Lilyama (ElDorado, diorite mag, hem, ves, cal 

CO) minor sch 

Rosita NCRC Is, mar Cret. diorite, monz Tert. cpy, py, po, mag, gar, ep 

bor, cc, mal, cup 

Seven Devils USID Is Tri./Martin Bridge Deep Creek Cret. cpy, bor, cc, mal, gar, ep, diop, 

district Ls. (?) stock-qtz azurite, chr, cov, bed, trem, act 

diorite sch-powellite 

Sinyuzhinskoe USSR Is, calc sh, dolos Pal. diorite Pal. Au, apy, Ni & gar(an-gros), 

Pb tells, ten, tet, diop-hed, wol 

moly, mag, bor, 

cc, cpy, py, gal, 

sph, po 

Vieja CLBA lbaque 130-150 cpy, gal, py, spec cal, ep, 

batholith Ma marmetite, qtz 

Yaguki JPAN sh, Is Perm. granodiorite Cret. cpy, po, cub, ep, gar(an), qtz, 

mag, W, Bi, px, preh, 

hem, bism, babingtonite, chi, 

cobaltite, sph, act, plag 

gal, moly 

Yreka CNBC limy tuffs, and L. Jur./ qtz-feldspar po, cpy, py, sph, 

Is Bonanza Gp. porph dikes & mag, spec 

sills 

Zackly USAK mar Tri. qtz Cret. cpy, born, py, gar (an), wol, px, 

monzodiorite Au, Cu, mal, clinopx 

lim, chalcedony 

Porphyry Co skarn related byproduct gold 

Carr Fork USUT Is L. Penn./ Bingham Tert. py, cpy, po, apy, gar, diop, qtz, 

Parnell ore (Bingham) Bingham Mine Fm., stock-qtz hem, mag, sid, clay 

body Parnell Is. monz porph tet-tennantite 

50 Gold-Bearing Skarns 
Ore control 

Is-vole contact 

Is-dike contacts 

congl-lst contact, faults 

faults 

Is, xenoliths in qtz 

diorite, fractures 

limy tuffs 

contact zone, faults 

faults, distance to 

stock, elevation 

Tonnage 

(millions of 

tonnes) 

2.658 

0.000136 

26.96 

0.004296 

3.45 

0.00071 

0.65 

0.45 

> 1.08 

0.495 

1.25 

0.8 

Base metals Au (g/t) Ag (g/t) and Fe Comments References 

Cu skarns with byproduct gold-Continued 

1.46 4.41 1.55% Cu Ls beds in voles; may be Cu-rich part of 8, 9, 22, 51 

20.6% Fe zoned system; nearby Merry Widow, 

Kingfisher, and Ravel deposits produced 

3.4 Mt iron ore; grab samples from Merry 

Widow assay as high as 19 g Au/t; Coast 

Copper Co. Ltd. (1968) 

8.57 28.6 2% Cu Although Is and qtz latite porph both 52, 53 

2%Pb silicated, bulk of sulfides is in skn; erratic 

py in porph 

1.12 7.12 0.85% Cu Includes Knob Hill and several other claims; 8, 9, 22, 44, 

Pb p mine was closed in 1978 and reclaimed; 45,54, 55 

Granby Co. 

1.57 16.5 2.3% Cu Bulk of sulfides associated spatially with 56,57 

mag; some syenite porph as dike 

1.17 15.8 3% Cu Gar-ep skn is deeply weathered; Rosita 1, 46, 58, 59 

Mines, Ltd. 

2.54 165 16.1% Cu Composited production from 1943-51 for 60,61 

10.0% Pb Arkansas-Decorah, South Peacock, and 

Helena mines; Pb grade for 131 t of ore; 

Pb-rich zones in some mines; W present. 

8 2.5% Cu Au in stage II py, 0.1 to 1.6 ppm; Au in cpy; 46, 47, 48, 

0.93 ppb; deposit has only small amount 49 

of sulfide (a few percent) 

0.9 35 1.7% Cu 62 

3.4 171 0.8% Cu Deposit is 1 km by 310 m and as much as 1 

70 m thick 

1.1 33.5 2.6% Cu Uke Resources, Ltd. 8 

>6 p 2.6% Cu Estimated reserves. Assays up to 6.6% Cu, 5 

4.4 g!t Au. Zoned 

Porphyry Cu skarn related byproduct gold 

8.7 4.2 1.02% Drill-indicated resource for Parnell gold 63, 64, 65 

shoot. Multistage mineralization: 

high-grade Au in py-qtz and py-clay 

overprint on Cu-Au-Ag skn. Avg 1.9 

g Au/t in gametized ls. Byproduct Au 

was produced 1979-81 at Carr Fork mine 

from estimated reserves of 61 Mt of ore 

of avg grade 1.89% Cu, 0.38% g Au/t, 

10.6 g Ag/t, and 0.027% Mo 

Table 3 51 
Table 3. Gold-bearing skarns in which gold and silver are byproduct commodities-Continued 

Name Location 

(mining district) 

Host 

lithology 

Formation age/ 

name 

Associated 

igneous 

rocks 

Age Ore 

minerals 

Gangue 

minerals 

Porphyry Cu skarn related byproduct gold-Continued 

Ok Tedi 

Chichibu 

El Sapo 

Falun 

Garpenberg 

Oda 

Maxfield 

SE 

Afghanistan 

PPNG 

JPAN 

CLBA 

SWDN 

SWDN 

USUT 

(Big 

Cottonwood) 

AFGH 

Thanksgiving PLPN 

(Baguio) 

Tsumo JPAN 

Woodlawn- USUT 

Kentuck)'-Utah (Big 

Cottonwood) 

1. Einaudi and others, 1981 

2. Philippine Bureau of Mines and 

Geosciences, 1986 

3. Bryner, 1969 

4. Frost, 1965 

5. Nokleberg and others, 1987 

6. Newberry, 1986 

7. Wayland, 1943 

Zn-Pb skarns with byproduct gold 

sl, sst, chert, Is Pal. qtz diorite 

lbaque 

batholith 

Is, qtzite Prot./Leptite Series granite, qtz 

porph dikes, 

amphibolite 

dolos, qtzite, Prot./Leptite Series granite 

mica, schist 

Is Miss./ diorite 

Gardison Ls. 

ls, minor congl, Mio./Zig-Zag Series diorite porph 

sst, sh, lithic 

tuff 

dolomitic mar 

ls 

Pal./Koseiso Fm. 

Miss./ 

Deseret Ls. 

diorite, 

granodiorite, 

granite 

Alta stock, 

granodiorite 

17. Harris and Einaud~ 1982 

18. Roberts and others, 1971 

19. Canada Department of Energy, Mines 

and Resources, 1984 

20. Buseck, 1966 

21. Bergeat, 1910 

22. Ettlinger and Ray, 1988 

23. Little and others, 1970 

8. British Columbia Ministry of Energy, 

Mines and Petroleum Resources, 1981 

24. McConnell, 1914 

25. Martin and Katz, 1912 

9. Ettlinger and Ray, 1989 26. Richter and Herreid, 1965 

10. Sutherland Brown, 1968 27. Koschman and Bergendahl, 1968 

11. Roberts and Arnold, 1965 28. Shoj~ 1978 

12. L1znicka, 1985 29. Geach, 1972 

13. Wilkins, 1971 30. Winchell, 1914 

14. McCleman, 1976 31. E.I. Bloomstein, written commun., 1987 

15. Knopf, 1918 32. Bulynnikov, 1948 

16. Einaud~ 1982 33. 'I'veritinov, 1966 

52 Gold-Bearing Skarns 

cpy, gal, py, po, 

sph, mag, marc 

act, cal, gar, px, 

trem, talc 

Mio. 7.9, cpy, sph, py, mag gar, clinopx, ep, 

8.2Ma act, cal, qtz 

130-150 cpy, gal, py, mag, gar, wol, 

Ma 

Prot. 

Prot. 

Tert. 

Cret. 

Tert. 

bor 

py, cpy, po, sph, 

gal, mag, Au, 

gahnite, 

weibullite 

sph, gal, py, po, 

cpy, Au 

py, gal, tet, sph, 

Cu-stained oxide 

minerals 

py, cpy, cc, rare 

Mo 

marmetite, qtz 

trem, talc, act, 

diop, qtz, biot, 

anthophyllite, 

chi, almandine, 

cummingtonite, 

ophicalcite, cordierite, 

andalusite 

trem, qtz, mica, 

talc, fl, tour, 

diop, gahnite 

cal, qtz, 

sepiolite, diop, 

ep, mica, wol, 

gar 

py, sph, apy, cpy, chl, gar, cal, qtz, 

gal, hem, mag, clinoz, ep, 

Au tell, Au act-trem, ves 

cpy, mag, 

malayaite 

qtz, clay, phlg, 

gar, trem, 

chondrodite, 

wol, hed 

mag, cpy, py, gal, trem, 

cer, arg, Au, sph calcsilicates 

34. Kennedy, 1953 

35. Herreid and others, 1978 

36. Sociedad Mineria y Petroles, 1969 

37. Frank Simon, written commun., 1987 

38. Roby and others, 1960 

39. Klepper and others, 1957 

40. British Columbia Minister of Mines 

Annual Report, 1981 

41. Cockfield, 1948 

42. Young and Uglow, 1926 

43. C.·mada Department of Energy, Mines and 

Resources, 1980 

45. Peatfield, 1978 

44. Church, 1986 

46. Boyle, 1979 

47. Vakhrushev, 1972 

48. Ivankin and Rabinovich, 1972 

49. Vakhrushev and Tsimbalist, 1967 
Tonnage 

Ore control (millions of 

tonnes) 

40 

0.5 

0.33 

lithology, contact zone 35 

structure, contact zone 9.6 

fissures 0.00486 

0.227 

contact, favorable beds 1.7 

& structures 

4.9 

contact 0.000368 

50.Bazheno~ 1968 

51. TRM Engineering Ltd., 1986 

52. Keith, 1974 , 1981 

53. Schrader, 1915 

54. Hedley, 1981 

55. Little, 1983 

56. Clark and Carlson, 1956 

57. Cox and others, 1948 

58. Bevan, 1973 

59. Plecash and others, 1963 

60. Cook, 1954 

61. C. Field, oral commun., 1989 

62. Jurada, 1982 

63. Cameron and Garmoe, 1987 

Base metals Au (g/t) Ag (g/t) and Fe Comments 

Porphyry Cu skarn related byproduct gold-Continued 

1.6 1.5% Cu 

Zn-Pb skarns with byproduct gold 

3.6 52 0.45% Cu Cu is restricted to gar-bearing skn; 12% 

6%Zn Pb p pyrite; Nitchitsu Mining Co., Ltd. 

Fe P 

11.5 79.8 5.1% Cu 

16.21% Pb 

3 18 1.06% Cu Associated with Fe skn; deposit is zoned 

4.1% Zn 

1.4% Pb 

1 86 0.3% Cu Deposit has well-developed zoning 

5.2% Zn 

3.6% Pb 

5.65 1774 19.7% Pb Average grades reported for 1902--40 

1.4% Cu production 

<5 >100 3%Zn Average composition reported from Pb-Zn 

9% Pb exploration of Cu-skam mineralization 

6.41 40.55 0.36% Cu Mined largely for Au-Ag; reported Cd; 

4.47% Zn Banquet Explorations, Ltd. 

1.36 50.9 0.68% Cu Two ore bodies: Tsumo, Maruyama 

2.43% Zn 

1.48 933 11.9% Pb 

2.64% Zn 

Pb-Ag-Zn production from bedded 

replacement fissure 

64. Tooker, 1989 

66. R.H. Sillitoe, oral commun., 1987 

67. Imai, 1978 

68. Grant, 1950 

69. DA. Singer, oral commun., 1988 

70. Grip, 1978 

71. James, 1979 

72. Calkins and Butler, 1943 

73. Bybochkin and Kats, 1972 

74. Callow, 1967 

75. Geological Sutvey of Japan, 1980 

References 

1, 66 

67,68 

62, 69 

70 

70 

71,72 

73 

2, 74 

67, 75 

71,72 

Table 3 53 
Table 4. Gold-bearing skarn deposits and deposits purported to be gold-bearing skarns for which grade and tonnage data are 

unavailable 

[Abbreviations listed in table 1] 

Mine name 

Akshiyryak Range 

Alae-Sayan 

Alvarado 

Ban Na Lorn 

Blue Grass 

Bright Diamond 

Buckhorn Mountain 

Bumblebee 

Cable 

Cadia 

Cane Springs 

Location 

(mining district) 

USSR (Kirghiziya) 

USSR 

USUT (Gold Hill) 

THLD 

USMT (Bannack) 

us co 

USWA 

USMT (Ophir) 

USMT (Cable) 

AUNS 

USUT (Gold Hill) 

54 Gold-Bearing Skarns 

Description 

280-Ma granite (K/Ar, biot) intrudes carbonate-siliceous 

sequence. Au mineralization is associated with skarnoid & 

secondary silicified rocks in mar & silicate-carbonate rocks 

gradationally farther out than skarn. Au is mainly in highly 

silicified rock that contains wol, locally ves, px. Dark-gray 

highly silicified rock contains po, py, Au (as 0.1-mm-wide 

flakes). 

Skn includes px, gar, amph, serp, and late qtz with Cu, Pb, 

Zn, As, Sb, Cd. Fluids: high Cl; Na/K=l.1 to 1.5:1. Early 

skarns formed at 480-890 oc. Au deposited at 250-150 oc. 

Cu-Au skn formed in Miss. Ochre Mountain Ls. near 

Tertiary Gold Hill qtz monz stock. Ore includes Au, py, 

cpy, gal, bor, cc, mag, mal, lim, chalcanthite, jarosite. 

Gangue consists of wol, diop, ap, gar, spa, zoi, ves, trem, 

serp, qtz. Nolan (1935) reports $120,000 in Au produced 

1892-1895.Channel sample assays range from tr to 5.8 g 

Au/t, tr to 387 g Aglt, tr to 1.9% Cu. Woodman Mining Co. 

Au, py, cpy associated with qtz deposition during or after 

retrograde skn formation. Although 3 skn types are recognized, Au mineralization is associated with relatively 

coarse grained gar-ep skn. Calcic skn is thought to be a 

metasomatically transformed tuff sequence. 

Gar-ep-cal skn veined by qtz as much as 5 m wide; veins not 

continuous. Ore along contact between granodiorite & Is 

mined from 40- by 7-m open cut. 

Ore in flat shoots about 3 m thick; Au localized in 

mag-py; porph dike as much as 10 m wide nearby. 

Described as a gold-bearing skn in Okanogan Co., 

Washington, that displays geological similarities to some 

major gold skn deposit in Nevada. Exploration in progress. 

Crown Resources Corp. and Gold Texas Resources Ltd. 

Gar skn showing superimposed faults. Explored by 30-mdeep shaft. Mal in qtz stringers in skn. 

Mineralized Is pendant of Camb. Hasmark dol, calc sh of 

Silver Hill Fm. in Eoc. Cable granodiorite stock. Primary 

ore: py, cpy, mag, po, Au, gal, sph, apy, tetd, marc. 

Oxidized ore: lim, hem, cc, bor, mal, azurite, Cu, Mn ox. 

Gangue minerals: gar, px, amph, wol, qtz, cal, dol, sid, 

mica, scap. Mag skn (Pomeroy mine) nearby. Most 

production pre-1900; total production for district, which 

includes Cable placer, estimated at 165,127 oz Au, 134,583 

oz Ag. Nearby structurally controlled vein mineralization 

and oxidized ores occur at Southern Cross, Gold Coin, and 

Pyrenees deposits; Magellan Resources-Chevron Resources 

Co. 

Au-bearing skn in area of Fe skn. 

Cu-Au skn formed in Miss. Ochre Mountain Ls. near Tert. 

Gold Hill qtz monz porph stock. Ore: Au, py, cpy, bor, cc, 

cov, moly, mal. Gangue: gar, wol, diop, ves, zoi, qtz, cal, 

spa. Produced $50,000 to $70,000 gold 1892-95; 42 t ore 

assayed at 36.6 g Au/t, 103 g Aglt, and 5.5% Cu in 1914; 

1,479 t ore produced 1931-35. Recent assays reported by 

El-Shatoury and Whelan (1970) range from tr to 21.2 g 

Au/t, tr to 6.8 g Aglt, and 0.12 to 1.03% Cu. 

Reference(s) 

Dolzhenko, 1974 

Indukaev, 1977 

Nolan, 1935; Wilson, 

1959; El-Shatoury and 

Whelan, 1970 

Pisutha-Armond and 

others, 1984 

Geach, 1972 

Irving, 1905; Irving and 

Cross, 1907 

Mining Journal, 1989 

McCleman, 1976; 

Mineral Resource 

Data System, 1989, 

record DC09691 

Earll, 1972; Emmons 

and Calkins, 1913; 

Emmons, 1907; 

Holmes, 1982; 

Meinert, 1988a; 

Holser, 1950 

McLeod, 1965 

Nolan, 1935; Wilson, 

1959; El-Shatoury and 

Whelan, 1970 
Table 4. Gold-bearing skarn deposits and deposits purported to be gold-bearing skarns for which grade and tonnage data are 

unavailable--Continued 

Mine name 

Carles (Salas, Asturias) 

Carr Fork 

Central Tadzhikistan 

Charmitan 

Chihuahua district 

Chihuahua 

Chillioroya area 

Chumbivilcas 

CulveiWell 

Dutro 

East Sayan Mtns. 

(Medrezhye and 

Konstan tinovskoe 

deposits) 

El Fenomeno 

First Chance 

Ge Jiou Yun Nan 

Geunteut area Sumatra 

Gissaro-Alay 

Glassford Creek 

Goldstrike 

Location 

(mining district) 

SPAN 

USUT (Bingham) 

USSR 

USSR 

MXCO 

PERU 

USNV (Pennsylvania) 

USMT (Blue Cloud) 

USSR (Siberia, middle 

Asia) 

MXCO 

USMT 

CHNA 

INDS 

USSR (central 

Tadzhikistan) 

AUQL 

USNV (Carlin) 

Description 

Apy-cpy-py-Au in qtz-veined skn; 5- to 100-14m-size Au 

associated with apy. 

Gar-diop-act-ep-wol skn associated with porph Cu 

mineralization. 

Au-Cu-As in px & gar-px skn associated with L. Miss.- E. 

Perm. granodiorite & qtz diorite rocks; overall trapping 

temperatures of fluid inclusions range from 450° to 7500C; 

Au ores deposited paragenetically late in two stages: early 

py-apy, late tet-cpy at 2500-350°C. 

Four ore-forming stages: Au-Bi-tell, py-apy, Au-sulfide 

polymetallic, qtz-cc. 

Au-Ag-Pb-Cu skn occurs at Is-diorite contact. Over 2,100 kg 

Au was produced 1928-49 from approx 60,000 tore, with 

grade ranging from 0.1 to > 100 g Au/t. 

Cu-Ag-Au ore occurs in small bodies of gar-mag skn at ls-qtz 

monz porph contact. Ore minerals include cpy, py, bor, cc, 

Au. Grades are reported as "few" g Au/t, about 5% Cu, 

< 100 g Aglt for 2-10 Mt ore. Katanga (table 2) is found 

in this area. 

Skn associated with mag replacement pods in Camb. Is. Ep 

replaces monz-diorite; some skn includes copper ox, py, 

cpy. Grab samples assay as much as 85 g Au/t. 

Free Au, cassiterite, Bi reported from hydrosilicate altered 

skn including qtz, jas, trem, opal. 

Au ores preferentially formed in calcic skn from Cl-S04-Ca 

Na-bearing fluids (Na/K=2:1 to 6:1; Cl/F=31:1) at 

220°-420°C; Cl > F in leachates from productive Au skn. 

Au, Cu are reported to occur in this W skn mined during 

WWI and 1937-44; possible additional ore exists. Sch, 

secondary Cu minerals, py, po, cpy, apy occur in gangue of 

gar, ves, axinite, dio, q tz, cal. Main ore body was 

fan-shaped tactite zone at contact of L. Pal. mar & 

Cret.-Tert. diorite. In northern Baja California. 

Au reportedly produced, together with W, from xenoliths of 

Dev. Jefferson Ls. in granodiorite. 

Sn-Au skn formed during Mes. contact metasomatism. 

Geunteut granodiorite (14.3 Ma) intrudes L. Jur. & E. Cret. 

Is of Woyla Gp. Mineralization includes cpy, py, bor, azur, 

mal. 

W-apy-Au-Cu skn containing p:x, gar, qtz, feld, amph, dol, 

wm. 

Gar-mag-ep-wol-hem-act skn in Is at granite contact; ore 

minerals include cpy, bor, po, hes, Bi, Au, secondary Cu 

minerals; 735 t Cu, 80 kg Au 725 kg Ag were produced 

1905-7. 

Au-bearing skn occurs at the No. 9 Pit & at Skarn Hill at the 

Goldstrike Mine (includes several types of ore bodies); 

skn formed in Dev. Is, informally named the Popovich Ls., 

beneath the Roberts Mountain thrust. At West No. 9 Pit, 

Au mineralization occurs in 160-Ma(?) granodiorite. Skn 

assemblages include gar, diop, act, chi, Au. American 

Barrick Resources, Inc. 

Reference(s) 

Rau-Figueroa and 

others, 1985 

Atkinson and Einaudi, 

1978; Reid, 1978 

Morozov, 1976; Morozov 

and others, 1974; 

Morozov and others, 

1973 

Proskuryakov and others, 

1979 

D.L. Mosier (oral 

commun., 1987) 

Mineral Resource Data 

System, 1981, record 

W002200; Frank 

Simon (written 

commun., 1960) 

Mineral Resource Data 

System, 1984, records 

M241646 and 

M032085 

Knopf, 1933 

Korobeynikov, 1976a, b, 

c; Korobeynikov and 

Chernyaev, 1976; 

Korobeynikov and 

Matsyushevskiy, 1973 

Salas, 1975; Fries and 

Schmitter, 1945; 

Leonard, 1989 

Pardee, 1918; Kaufmann, 

1963 

Sang and Ho, 1987 

Bowles, 1984 

Khasanov, 1982 

Murray, 1986 

R.J. Roberts (oral 

commun., 1989); 

Schafer and Buffa, 

1988 

Table 4 55 
Table 4. Gold-bearing skarn deposits and deposits purported to be gold-bearing skarns for which grade and tonnage data are 

unavailable-Continued 

Mine name 

Gould-Corry 

Hua Tong An Hui 

Huarca 

Hudson Group 

Iron Clad 

Kaliostrovskoe 

Kochulak Dalnagorsk 

region 

Kommunar district 

Kaznetskiy Alatau and 

Gornyi Altai 

La Gloria 

La Sonora 

Lucky Strike 

Many Peaks 

Marn (Mini Grid) 

Midas 

Midas (Berg Creek) 

Mottini 

Mount Biggenden 

Location 

(mining district) 

USMT (Red LionHidden Lake) 

CHNA 

PERU (Cuzco) 

USMT (Silver Star) 

us co 

USSR 

USSR 

USSR (Altai-Sayan) 

USSR 

MXCO 

MXCO 

AUNS 

AUQL 

CNYT 

USUT (Gold Hill) 

USAK 

USNV (IXL) 

AUQL 

56 Gold-Bearing Skarns 

Description 

Au reportedly produced from Au-Ag-Cu-W skn in Camb. ls 

intruded by Cret. granodiorite; gar, ep, goe, qtz present. 

Cenozoic Cu-Mo-Au skn. 

Irregular patches of Cu-Ag-Au ore in gametite at contact of 

qtz monz porph with ls. Minerals include cpy, mag, minor 

bor & cc. Average grades of < 1 to 2 g Au/tare reported 

for 1-10 Mt of ore. 

Reference(s) 

Earll, 1972 

Sang and Ho, 1987 

Frank Simon (written 

commun., 1960) 

Gar-ep skn developed in Camb. ls near contact with Cret. qtz Sociedad Nacional de 

monz of Boulder batholith; average grade reportedly 32-42 Mineria y Petroleo 

g Au/t, 42-52 g Ag/t; serp, sid, cal, asbestos present. (Peru), 1969 

Ore in flat shoot; Au localized in mag-pyas replacement with Winchell, 1914; Sahinen, 

silicates of blue-gray ls. 1939 

Large blocks of ls engulfed totally by granitoid rock. 

Au-tell-tet stage formed at homogenization temperatures of 

240°-270°C and 170°-190°C, together with Ag, Pb, Cu tell 

at lower temperatures (130°-150°C). 

In 8 deposits, Au associated with py, po, cpy, mag primarily 

in qtz-act veined skn developed in Camb. sed-voles 

sequence as result of emplacement of L. Camb. px diorite 

& monz. 

Au-bearing skn formed at 280°-700°C from homogenization 

temperatures in qtz & gar. 

Irving, 1905; Irving and 

Cross, 1907 

Ivankin and Rabinovich, 

1972 

Genkin and others, 1983 

Lobanov, 1972 

Small Au-bearing W skn with Cu, Mo. Sch cpy, auriferous py, Pavlova, 1983 

apy, moly occur in E. Cret. ls adjacent to granite. Gangue 

minerals include gar, ep, tour. Reserves of W-Mo ore are 

estimated at 25,000 t. In State of Sonora. 

A small Au-Cu skn in Pal. ls associated with L. Cret.-E. Tert. Perez Segura, 1985; 

granite. Minerals include Cu-ox. In State of Sonora. Radelli, 1985; 

Leonard, 1989 

South of Bathurst, near Beuraga. 

Gar-mag-cal skn in shear zone with py, cpy; 8,650 t Cu, 130 

kg Au were produced from 1910-18. 

Assemblage elec (AuS0-40)-Bi-bism-hes associated with cub 

exsolution in cpy or as blebs in apy, all hosted by px 

(diop20-40)-act (trem25_85)-po skn; avg grade 1.4 g Au/t, 2.8 

g Ag/t. 

Ls beds in Manning Canyon Fm. altered to wol-gar-diop-ves 

skn near qtz monz; associated with oxidized and sulfidized 

Cu & Pb-Ag ore. Minor production (86 t, avg $56 Au per 

st produced before 1897). 

Cu-Au skn in Tri. Nizina Ls adjacent to Jur. granodiorite-qtz 

monzodiorite pluton. Ore: mag, py, cpy, Au. Gangue: ep, 

gar,qtz. Grab samples assay as high as 8 g Au/t, 10 g Ag/t, 

20%Cu. 

Au skn in U. Tri. sh, sst, sltst associated with 28-Ma 

granodiorite. Produced 272 t ore, avg $375 Au per st 

(est. 564 g Au/t, assuming a price of $20.67/troy oz); Ag, 

Cu, Pb, Ni present. Gangue of gar, cal, qtz, mag, spec, Fe 

and Mn ox. Ore consists of free Au, Ag & sulfides (py, gal, 

cpy). 

Gar-cal skn at granite contact; ore minerals include mag, 

bism, Bi, cpy, py, apy; 185 kg Au, about 235 t Bi produced 

1890-1901; 378,725 t magnetite produced from adjacent 

skn from 1967 to present. 

Perez Segura, 1985; 

Leonard, 1989 

Murray, 1986 

Brown and Nesbitt, 

1984, 1987 

Nolan, 1935; Thompson, 

1973 

Nokleberg and others, 

1987 

Schrader, 1947; D.A. 

John (oral commun., 

1989) 

Murray, 1986 
Table 4. Gold-bearing skarn deposits and deposits purported to be gold-bearing skarns for which grade and tonnage data are 

unavailable-Continued 

Mine name 

Nambija 

Natal Sumatra 

New Calumet 

New World district 

Nixon Fork-Medfra 

Novo Brdo 

Oka 

Olkhovskii West Siberia 

Primor'ye area 

Sara Alicia 

Location 

(mining district) 

ECDR 

INDS 

CNQU 

USMT 

USAK 

YUGO 

CNBC 

USSR 

USSR (Far East) 

MXCO 

Description 

Gar skn, including k-spar altered to chi, ep, cal; includes Au, 

sch, auriferous py, apy; related to emplacement of Jur. 

batholithic rocks; grade reportedly may be as high as 30 g 

Au/t; notable concentrations of Au at qtz-qtz boundaries 

and qtz-gar-k-spar flooded portions of endoskam. 

Skn has formed where L. Cret. Manunggal batholith (87 Ma) 

intrudes E. Cret. Soma Fm. & U. Jur., Lower Cret. Woyla 

Gp. sed rocks; both include meta-vols, Is, meta-ls members. 

Skn has formed at margins of batholith & in xenoliths of 

Is. Mineralization includes py, mag, Au, Ag, Cu-Pb-Zn 

minerals. 

Pb-Zn-Ag ores; Grenville province. Ore shoots, masses occur 

in Grenville biot gneiss near its contact with an overlying 

amphibolite. Minerals include sph, py, marc, po, gal, cpy, 

apy, Ca & Mg silicates. Production (1943-68): 3.74 Mst 

at 6% Zn, 1.7% Pb. Reserves (1968): 0.282 Mst at 4.51% 

Zn, 1.08% Pb, 2.34 oz Agist, 0.014 oz Au/st. Consolidated 

Professor Co. 

Cu-Pb-Au skn in Camb. Is & shaly Is associated with Tert. 

rhyodacite porph & other intrusions. Ore: Au, gal, sph, py, 

cpy, spec. Gangue: gar, ep, trem, ves, qtz, ank. Daisy mine 

produced 13 carloads of gold ore in 1888 that averaged 

$50 per ton (est. 83 g Au/t). Skn gangue reported at other 

mines, prospects in district. Crown Butte Mines, Inc. 

developing New World Project for Au, Cu in 1987. 

Group of Cu-Au skn deposits at contact (of Is) of Ord. 

Telsitna Fm. with L. Cret. monz pluton; in fractures, roof 

pendants. Ore: cpy, py, bor, Bi, lim, mal, Au. Gangue: diop, 

gar, ep, plag,qtz, ap, act. Produced 1.24 to 1.87 Mg Au, 

with Cu, Ag. Some deposits have grades as high as 113 

g Au/t, 1.5 to 2.0% Cu. 

Skn & replacement mineralization in Is along schist-Is & 

dacite-Is contacts; ore minerals include sph, gal, po, cpy, 

marc; main skn mineral is gar. Ore contains 1-5% Pb, 

1-8% Zn, about 100 g Aglt, 3-4 g Au/t. 

Au in sulfide pods along skn-mar contacts & in faults; 

associated with diorite sills & reported to be similar to 

Mascot deposit 50 km to southwest. Fairfield Minerals Ltd. 

has identified several areas of mineralization along 5-km 

soil geochemical anomaly through mapping, chip sampling, 

trenching. Future drilling is planned on basis of chip 

sample analyses with 0.24-1.12 oz Au/st. Contains Au, 

Ag, Cu, As, Zn. 

Ord. diabase, diorite porph, qtz porph, aplite dikes intrude 

M. Camb. carbonate & tuffaceous rocks. Au-bearing 

mineralization occurs in gar-px skn & in qtz-sulfide veins. 

Ore minerals include cpy, sph, gal, bism; Au, Ag tells. 

Alteration includes chloritization, sericitization, slight 

serpentinization. Deposit is considered to have formed at 

medium depth, moderate temperature. 

Sch-Au-py skn formed under relatively reducing conditions; 

some associated Au-wolf deposits; mafic granite intruded 

into Sikhole Alin folded belt; some apy, mica, po; bed, 

gros, ves, cum, ep, act, tour, stilp, bustamite; mag, cc 

assemblages in skn. 

Small Au-Cu skn in Jur.-Cret. Is(?) associated with L. 

Cret.-E. Tert. granitic intrusives. In State of Sonora. 

Reference(s) 

E. Salazar (written 

commun., 1987); 

Minera Nambija 

(written commun., 

1988) 

Bowles, 1984 

Boyle, 1982; Canada 

Department of 

Energy, Mines and 

Resources, 1980 

Lovering, 1929; Reed, 

1950; Elliott, 1979; 

Elliott (oral commun., 

1989); Lawson, 1988 

Nokleberg and others, 

1987; Newberry, 1986 

Jankovic, 1982 

Skillings' Mining Review, 

1987; Ettlinger and 

Ray, 1988, 1989 

Smimov and others, 

1981 

Stepanov, 1977, 1981; 

Stepanov and others, 

1976a, 1976b; 

Stepanov and 

Kucyakova, 1973; 

Makiyevskiy, 1978, 

1979; Efimova and 

others, 1982; Piskunov 

and Makiyevskiy, 1978 

Perez Segura, 1985; 

Leonard, 1989 

Table 4 57 
Table 4. Gold-bearing skarn deposits and deposits purported to be gold-bearing skarns for which grade and tonnage data are 

unavailable-Continued 

Mine name 

Sayakskiy region 

Shul Kou Shan 

Spring Hill 

Stormont 

Sylvester K 

Terrazas 

TP (claims) 

Union Amalgamated 

West Park 

USSR 

Location 

(mining district) 

CHNA 

USMT (Helena) 

AUTS 

CNBC 

MXCO 

CNBC 

USNV (Manhattan) 

USUT (Snake Creek) 

58 Gold-Bearing Skarns 

Description 

High-temperature zones of skn contain three assemblages: 

(1) Au1: gersdorffite (NiS XN~)-apy-cobaltite (>250° 

C); (2) Au2: Bi-cpy-po (250°C) with ep, act; (3) Au3: 

wittichenite (Cu3BiS3)-moly-bor-cpy (225°C). 

Pal. contact metasomatic deposit. Skn mined for Pb, Zn, Au. 

Gar-px skn developed in Miss. Madison Ls; skn altered to 

qtz-ank-cal-chl assemblage with Au-apy-po-py-cpy-gal inore; 

much of ore reported to be px-rich. 

A u-Bi skn in Moina district, area known primarily for Sn-W 

skn, veins, greisens. Deposit is in Ord. Gordon Ls., 

associated with Dev. granite. Had minor production 

1928-34. Reported Au values at Moina skn, 4.5 ppm. 

Lenticular bodies of Au-bearing skn concordant with 

enclosing rocks of Tri. Brooklyn Fm., associated with 

micro-diorite stocks, dikes of L. Jur. to E. Cret. age. 

Mineralization consists of massive py, mar, po, minor cpy 

in calcic exoskn. Deposit has lim-goe cap several meters 

thick. 

Au-bearing Cu skn along Is-diorite contact. Skn runs 2-3% 

Cu as cup, azur, mal, cpy, Cu. Associated Pb-Ag veins. In 

State of Chihuahua. 

As much as 15 g Au/t, 3.9% Co in chip samples from 

mag-calgar-amph skn in pre-Tri. gneiss, schist, mar of 

Yukon Gp. Skn zone is 15 by 200 m, controlled by two 

NW.-trending fracture zones. Four types of skn present. 

Sulfide-bearing skn veined by Au-bearing qtz; developed in 

Pal. marine sed & metamorphic rocks; possibly related to 

16-Ma caldera or Cret. intrusion. 

Skn formed along contact of Miss. Is with Tert. granodiorite 

Peak Stock); ore includes cpy, bor, mag; average grade 

production 1946-50: 3% Cu, 17.2 g Ag!t, 1.57 g Au/t. 

Reference(s) 

Fomichev and 

Kuznetsova, 1972 

Sang and Ho, 1987 

Pardee and Schrader, 

1933 

Green, 1975; Collins and 

Williams, 1986; Kwak 

and Askins, 1981 

Church, 1984; Canada 

Department of 

Energy, Mines and 

Resources, 1986 

Salas, 1975; Gonzalez, 

1956; Clark and 

Goodell, 1983; 

Leonard, 1989 

Ettlinger and Ray, 1988 

Shawe and others, 1986 

U.S. Bureau of Mines, 

Strategic Minerals 

Examination, 1950; 

Mineral Resource 

Data System, 1984, 

record D011978 
Table 5. Mineral abundances for gold-bearing skarns 

[Data are reported as a percentage of the number of deposits in the data set 

that report a given mineral present] 

Data set ----------- Au-skarn Byproduct Alaskan 

Au -skarn Fe-Au skarn 

Reference -------- This study, This study, Newberry, 

table 2 table 3 1986 

Number of 

deposits ---------- 39 47 

Ore minerals (in percent) 

Au/electnun------------- 6 2 

pyrite----------------- 7 2 

pyrrhotite--------------- 6 7 

chalcopyrite------------- 8 5 

arsenopyrite----------- 51 

magnetite------------------ 3 3 

hematite/specularite------- 20 

sphalerite------------------- 46 

galena--------------------- 28 

Bi or bismuthinite---------- 23 

hedleyite--------------- 13 

telluride minerals---------- 26 

molybdenite--------------- 18 

scheelite------------- 8 

36 

91 

51 

96 

17 

64 

28 

38 

34 

9 

0 

9 

23 

15 

Gangue minerals (in percent) 

garnet------------- 82 

pyroxene------------ 72 

epidote--------------- 72 

amphibole--------------- 46 

chlorite--------------- 46 

prehnite----------------- 13 

vesuvianite------------- 13 

wollastonite------------- 31 

scapolite----------- 8 

boron minerals---------- 13 

91 

60 

66 

45 

34 

2 

13 

21 

13 

0 

106 

0 

72 

42 

90 

6 

77 

25 

8 

1 

0 

0 

0 

11 

0 

78 

42 

70 

41 

28 

0 

8 

6 

9 

0 

Table 6. Analytical data for some igneous rocks associated with 

gold-bearing skarn deposits in north-central Nevada 

[n.d., not detected;-, no data] 

Analysis -------- 2 3 4 

Si~-------------- 64.0 70.5 66.2 63.6 

A1 fJ3 ------------ 15.1 14.5 15.1 16.5 

F~0:3 ---------------- 2.0 1.0 13.34 12.82 

FeO------------------ 3.1 .16 

MgO-------------- 3.5 1.5 2.5 2.5 

CaO--------------- 3.5 .95 4.1 6.8 

N~O -------------- 1.5 2.1 3.1 2.7 

K20 ------------- 4.3 6.1 2.9 2.3 

Ti~-------------- .51 .47 .50 .56 

P205 ------------- .16 0 .16 .21 

MnO--------------- .02 0 .03 .05 

Other2 ----------- 1.94 2.0 1.65 1.40 

Au (ppb )----------- n.d. 100 42.4 <1 

Cu (ppm)--------- 990 1,500 

K20/Na20 -------- 2.87 2.90 .94 .84 

F~0:3 ---------- .65 6.25 

1. Altered granodiorite sill at north edge of West ore body, a Cu-Au 

skarn deposit related to 38-Ma altered granodiorite of Copper 

Canyon. Fortitude Au-bearing skarn deposit lies just north of 

West ore body and is also probably genetically related to altered 

granodiorite of Copper Canyon. Analysis from Theodore and 

others (1973) (loc. 12, sample MB-40). 

2. Altered granodiorite of Copper Canyon. Analysis from Theodore and 

others (1973)(1oc. 9, sample MB-18). 

3. McCoy granodiorite stock, 5,300-ft bench McCoy Mine sample 

87JH013. XRF analysis by J. Taggart, A. Bartel, and D. Siems. 

Gold determined by INAA, G. Wandless, analysL 

4. Granodiorite dike at South shaft, Buffalo Valley Mine, sample 

87TT228. Same methods as 3. 

1Total iron as Fe203. 

20ther =H2o+, H20-, C~ for analyses 1, 2; =loss on 

ignition for analyses 3, 4. 

Tables S and 6 59 
Table 7. Representative data for minerals in gold skarns from north-central Nevada 

[Total iron as FeO for pyroxene, idocrase, amphibole; total iron as Fe10 3 for gameL Values are in weight percent. n.d., not detected] 

Analysis 2 3 4 5 6 7 8 9 10 

Mineral Pyroxene Garnet ldocrase Amphibole 

Si02 -------- 50.4 53.8 35.1 34.8 37.6 34.9 36.2 50.5 51.2 55.0 

Al20J .36 .65 6.35 .01 13.0 0 14.4 1.25 4.49 2.49 

FeO (F~OJ)- 18.2 3.40 23.4 32.5 13.8 31.7 3.40 27.1 12.4 8.12 

MgO ------- 6.99 16.49 .27 .29 .29 .29 2.71 6.34 15.4 18.7 

CaO ------- 23.2 25.6 34.4 33.0 35.8 33.5 34.6 11.4 12.6 13.0 

N~ ------ .11 .02 0 0 0 0 .01 .11 .33 .12 

K20 0 0 n.d. n.d. n.d. n.d. .01 .06 .29 .07 

Ti~ -------- .01 .02 .49 0 .48 0 3.67 .04 .10 .05 

MnO ------- .66 .20 .33 .23 .31 .30 .12 .92 .06 .28 

F ---------- n.d. n.d. n.d. n.d. n.d. n.d. .97 .01 .06 .09 

a ---------- n.d. n.d. n.d. n.d n.d. n.d. .61 .01 .18 0 

--- Total----- 99.8 100 100 101 101 101 95.3 97.7 96.9 97.9 

1. Fortitude deposit sample 85TT243; averafT of 7 grains in massive pyrrhotite ore. 2. McCoy dea,osit, samples 86TT134 and 86 137; average of 5 grains in massive oxidized garnet skarn. 

3. Fortitude eposit, diill core sample of garnet-bearing sulfidized skarn; colorless, anisotropic zone. 4. yell ow isotropic andradite zone in same armet grain as 3. 

5. Surtlcrise deposit, drill core sample of oxi 'zed garnet skarn; colorless, anisotropic rim of large, euhedral zoned grain. 

6. Ye ow isotropic andradite core in same grain as 5. 

7. McCoy de~sit, sample 87TT137; average of 3 grains in idocrase-rich pod in garnet skarn. 

8. Fortitude eposit, sample 85TTI43; ferro-actinolite in phcoxene-bearing sulfiruzed skarn. 

9. Northeast Extension deposit, sample 87TT2; actinolitic ornblende in epidote-amphibole-quartz-chlorite-sulfide skarn; no garnets 

10. or pr;;oxenes present. 

Actina ite in sample 87TT2. 

60 Gold-Bearing Skarns 
Table 8. Chemical signatures of nontronite clay layers associated with gold-bearing skarns 

[-,not detected; N.D., not detennined] 

Sample1 85JH115 85jH142 86TT135 88TT63 87jH004 

Method2 a b a b b b 

Weight percent 

Al ------------ 0.33 1.5 0.12 2.94 

Ca ----------- 1 .73 10 15 5.8 3.65 

Fe -------------- 10 8.2 10 7.3 5.3 12.7 

Mg --------- 1 .89 .5 7.7 .13 .29 

Na -------------- .02 .19 .02 

K ----------------- <.05 .37 <.05 <.05 

p ------------------ .01 .1 .1 .12 

Ti --------------- .1 .08 .1 .1 .01 .51 

Parts per million 

Mn ----------------- 100 660 1000 760 977 2150 

Ag ------------------ 2 30 7 8 <2 12 

As -------------- <10 20 40 30 

B ----------------- 10 10 

Ba ------------- 200 160 500 82 13 17 

Be -------------- <1 2 <1 3 

Bi ------------------- 10 <10 <10 <10 

Cd --------------- <2 50 2 5 <2 

Ce ------------ <4 7 <4 993 

Co ---------- 5 210 14 2 17 

Cr ------------ 50 46 70 44 9 1350 

Cu ------------- 200 320 20 3800 1 6050 

Ga -------- <4 8 <4 23 

La ------------- <2 4 7 636 

Li -------------- 7 7 9 23 

Ni ---------------- 15 12 12 5 553 

Pb ---------------- 20 100 11 6 326 

Sc --------------- 7 4 6 <2 20 

Sn ------------- <10 100 <10 20 

Sr ---------- 100 53 200 61 49 164 

v ------------- 100 71 100 40 23 53 

y -------------- 3 20 3 9 16 

Zn ----------- 500 550 200 400 240 564 

Zr --------------------- 50 200 

Hg3 ----------- 0.03 N.D. 0.08 N.D. N.D. 

Au3 --------- .07 N.D. 5.1 0.04 0.42 

Pd3 --------------- .001 N.D. . 001 N.D . N.D. 

Pt3 ---------------- <.010 N.D. <.010 N.D. N.D. 

Rh3 -------------------- <.001 N.D. <.001 N.D. N.D. 

w3 ---------------- 5.0 N.D. 5.0 N.D. N.D. 

1 Analyses were done on bulk samples of earthy, yellow-green clay layers in skams. X -ray diffraction studies show that all 

samples are mixtures of clay and significant amounts of quartz and calcite or pyroxene. All samples have characteristic 

smectite peaks at 14 angstrom that expand to about 17 angstrom with glycolation. Microprobe work on 85JH 115 confirms 

the Fe-rich nature of clay. Samples are from skams in the Harmony Formation (85lli115) and in the Battle Formation 

(85JH142) in Battle Mountain Mining District, the McCoy Mine (86TT135) in McCoy Mining District, the Buffalo Valley 

Mine (88TT63), and the Sutprise Mine (87JH004). 

2 Elements sought for but not detected at limit of methods a and b include Au, Mo, and W. (a) Six-step direct current arc 

semi-quantitative spectrographic analyses; analyses performed in U.S. Geological Survey exploration research laboratories by 

Betty Adrian and Olga Ehrlich; X-ray studies by Steve Autley and Ted Botinelly. (b) Quantitative inductively coupled plasma 

direct reader emission spectroscopy by M. Malcolm in U.S. Geological Survey analytical laboratories; X-ray work by Karen 

Gray. 

3 Trace analysis and chemical separation by C. Gent, R. O'Leary, B. Libby, N. Rait, and S. Wilson in U.S. Geological 

Survey analytical laboratories. 

Table 8 61 



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