United States Gold Terranes Part I

U.S. GEOLOGICAL SURVEY BULLETIN 1857-B
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Chapter B

United States Gold Terranes Part I

Geographic Distribution of Gold Mining Regions and 

Types of Deposits in the United States

By EDWIN W. TOOKER

Patterns of Gold Mineralization in Nevada and Utah

By WILLIAM C BAG BY

Gold-Silver Deposits Associated with the 

Trans-Challis Fault System, Idaho

ByTHOR H. KIILSGAARD, FREDERICKS. FISHER, 

and EARL H. BENNETT

Geologic Setting and Potential Exploration Guides 

for Gold Deposits, Black Hills, South Dakota

By JACK A. REDDEN and GREGORY McN. FRENCH

U.S. GEOLOGICAL SURVEY BULLETIN 1857

GEOLOGY AND RESOURCES OF GOLD IN THE UNITED STATES

DANIEL R. SHAWE and ROGER P. ASHLEY, Scientific Editors 

LM.H. CARTER, Technical Editor
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: 1989

For sale by the

Books and Open-File Reports Section

U.S. Geological Survey

Federal Center

Box 25425

Denver, CO 80225

Library of Congress Cataloging-in-Publication Data

United States gold terranes Part I.

p. cm. (Geology and resources of gold in the United States ; ch. B) 

(U.S. Geological survey bulletin ; 1857-B)

Includes bibliographies.

Contents: Geographic distribution of gold mining regions and types of 

deposits in the United States / by Edwin W. looker Patterns of gold 

mineralization in Nevada and Utah / by William C. Bagby Gold-silver 

deposits associated with the trans-Challis fault system, Idaho / by Thor H. 

Kiilsgaard, Frederick S. Fisher, and Earl H. Bennett Geologic setting and 

potential exploration guides for gold deposits, Black Hills, South Dakota / by 

Jack A. Redden and Gregory McN. French.

1. Gold mines and mining United States. 2. Gold deposits United States. 

I. Series. II. Series: U.S. Geological Survey bulletin ; 1857-B. 

QE75.B9 no. 1857-B 

[TN423.A5] 

557.3 s dc19

[553.4' 1 '0973] 89-600031

CIP
CONTENTS

Geographic distribution of gold mining regions and types of 

deposits in the United States

Abstract Bl

Introduction Bl

Pattern of growth of known geographic distribution of gold in the

United States B4

Geologic basis for the geographic distribution of gold B6 

Geographic distribution of gold deposit types B7 

References cited B9

Patterns of gold mineralization in Nevada and Utah

Abstract fill

Introduction Bll

Terranes of Nevada and Utah 812

Patterns of gold-producing districts in Nevada and Utah B13

Discussion BIT

References cited B20

Gold-silver deposits associated with the trans-Challis fault 

system, Idaho

Abstract B22 

Introduction B22 

Trans-Challis fault system B23

Age of faulting B23

Mineralized localities associated with the trans-Challis fault system B24 

Southwest part B25 

Boise basin B25

History and production B25 

Lode deposits B27

Tenor of ore B29 

Mineralogy B29 

Molybdenum-copper deposits B30 

Banner mine B30 

Central part B31

Stanley district B31

History and production B31

Contents III
Lode deposits B31 

Gold-bearing resources B31 

Custer graben B31

Yankee Fork district B32

History and production B32 

Character of the lode deposits B32 

Mineralogy and geochemistry B33 

Wall-rock alteration B33 

Age of mineralization B33 

Ore controls and resources B33 

Loon Creek district B33

Loon Creek placers B34 

Lost Packer mine B34 

Other mines and prospects B34 

Yellowjacket district B34

Yellowjacket mine B35 

Northeast part B35

Mackinaw (Leesburg) district B36 

History and production B36 

Geologic setting B37 

Characteristics of the deposits B37 

Mineral Hill district B38

History and production B38 

Geologic setting B38 

Characteristics of the ore deposits B39 

Indian Creek district B39

History and production B39 

Geologic setting B39 

Dahlonega (Gibbonsville) district B40 

History and production B40 

Geologic setting B41 

Characteristics of the deposits B41 

Molybdenum-copper deposits B41 

Discussion B42 

References cited B43 

Appendix 1989 update B44

Geologic setting and potential exploration guides for gold 

deposits, Black Hills, South Dakota

Abstract B45 

Introduction B46 

Precambrian rocks B46

Archean rocks B46

Proterozoic rocks B47

Structure and metamorphism B51 

Phanerozoic rocks B56

IV Contents
Paleozoic and Mesozoic rocks B56 

Cenozoic rocks B56

Tertiary igneous rocks B56

White River group B56 

Types of gold deposits B56

Proterozoic deposits B57

Homestake-type B57

Gold-quartz veins B58

Fault-controlled deposits B58

Placer deposits B59 

Phanerozoic deposits B59

Replacement deposits in lower Paleozoic rocks B59

Disseminated and vein deposits in Tertiary igneous rocks B60

Placer deposits B61

Potential deposits and exploration guides B61 

Homestake-type deposits B62 

Gold-quartz veins B64 

Fault-controlled deposits B64 

Placer deposits in Proterozoic rocks B64 

Replacement deposits in lower Paleozoic rocks B64 

Disseminated and vein deposits in Tertiary igneous rocks B71 

Conclusions B72 

References cited B72

FIGURES

Bl-14. Maps showing:

Bl. The known geographic distribution of some major gold deposits in

the conterminous United States B2 

B2. The known geographic distribution of some major gold deposits in

Alaska B5

B3. Geologic terranes of Nevada and Utah B13 

B4. Distribution of gold-producing districts in Nevada and

Utah B14 

B5. Distribution of gold-producing districts in Nevada and Utah with

more than 1,000 oz of gold BIS 

B6. Distribution of gold districts in Nevada and Utah with more than

1,000 oz of gold, showing mineral belts and structure B16 

B7. Outline of upper Eocene and lower Oligocene igneous rocks and

locations of Nevada and Utah gold districts of similar age B17 

B8. Outline of upper Oligocene and lower Miocene igneous rocks and

locations of Nevada and Utah gold districts of similar age B18 

B9. Outline of middle and upper Miocene igneous rocks and locations

of Nevada and Utah gold districts of similar age B19

Contents
BIO. Location of the Chain's 1° x 2° quadrangle and the trans-Challis

mineralized area, Idaho B22 

Bll. The trans-Challis fault system and location of associated gold-silver

deposits B24 

B12. Boise Basin, Idaho, showing locations of gold-silver veins, faults of

the trans-Challis fault system, and stocks of Tertiary

age B26 

B13. Generalized geology of Precambrian rocks in the

Black Hills, South Dakota B48 

B14. Generalized geology of Early Proterozoic rocks in part of the central

Black Hills showing early and late fold axes B55 

B15. Structure contour map of the Precambrian-Cambrian contact, LeadDeadwood dome, Black Hills B66 

B16. Isopach map of the lower sandstone-conglomerate unit of the Deadwood

Formation, Lead-Deadwood dome, Black Hills B68 

B17. Structure contour and isopach map, lower Deadwood Formation, Bald 

Mountain area, Black Hills B70

TABLES

Bl. Gold production from Boise County (principally Boise Basin), Idaho,

1863-1982 B27 

B2. Gold-silver production from Boise County (principally from Boise Basin),

Idaho, 1941-1982 B28 

B3. Production from the Mackinaw (Leesburg), Indian Creek, and Dahlonega

(Gibbonsville) districts, Idaho B36 

B4. Tentative correlation of Precambrian rock unit protoliths in various parts of

the Black Hills, South Dakota B52

VI Contents
GEOLOGY AND RESOURCES OF GOLD IN THE UNITED STATES

United States Gold Terranes Part I

Geographic Distribution of Gold Mining Regions and Types of 

Deposits in the United States

By Edwin W. looker

Abstract

Early settlement and westward expansion of the 

geographic borders of the United States commonly were 

accompanied by a search for gold, as chronicled by the 

discovery dates of the classic western mining districts. This 

search still continues in known gold-producing regions as 

well as in other areas now known to contain the geologic 

environments favorable to gold occurrence. The geographic 

distribution of gold is related fundamentally to the geologic 

structures and lithologies of discrete parts of craton or 

accreted crustal terranes. Numerous gold-producing areas 

occur in the outer craton platform and shelf, generally in 

favorable Precambrian and Phanerozoic host rocks along or 

overlying basement suture zones, whereas gold deposits are 

rare in the mid-continent craton platform. Gold also occurs 

locally along accretionary fault contacts or zones in favorable 

host rocks in the accreted terranes, generally at an angle to 

the basement zones in the cratonal terranes. Several types of 

primary or byproduct gold occurrences, such as quartz 

lodes, polymetallic veins and replacements, skarns, porphyries, bonanza deposits, disseminated types, massive 

sulfide deposits, iron-formation deposits, and placers are 

equally distributed between the outer craton and the 

accreted terranes of the Appalachian and Rocky Mountain 

Cordillera. The most economically minabletype at present in 

the eastern and western cord ill eran regions is the disseminated deposit. Commonly production and reserves of 

disseminated deposits have surpassed those of the other 

types that may have been mined previously in a terrane. 

Several types of gold deposits may occur within large 

complex mining districts, such as Bingham, Utah.

INTRODUCTION

Knowledge of the geographic distribution of gold 

deposits in the United States has grown as the nation 

expanded westward. Beginning with the first settlers 

along the Atlantic Coast as early as 1607, the quest for 

gold was one of the incentives that led inexorably to the 

westward exploration and settlement of the continent. In 

the West, gold had been recovered from placers by the 

Spanish and Mexicans as early as 1775 (Clark, 1970), but 

exploration for it there remained localized until the 

arrival of Americans in the mid-nineteenth century. 

Interest in gold was motivated first by the intrinsic value 

and mystique of the metal itself, and was quickened by 

the apparent ease of its early discovery and recognition in 

a variety of deposits, some originally developed for 

metals other than gold.

The geographic distribution of gold-bearing 

regions, in part at least, may be correlated with geologic 

terranes.1 The range of types of gold deposits and their 

locations in terranes of the conterminous United States 

have been compiled by Tooker and Vercoutere (1986), 

and those in Alaska by Berg and others (1964). These 

data are summarized in figures Bl and B2.

Manuscript approved for publication December 9, 1988.

*A terrane is here considered to be a geographic region having 

a singular geologic history that differs from that in adjoining regions 

and is separated from its neighbor terrane by major faults, fault zones, 

or other geologic discontinuities.

United States Gold Terranes B1
Pa

/ ^fllli* /? '^^illllill . ;....- i-^v£& i- ;f ^^^^^ii/i

iii| .- ' fcissr v

UCPp

DEPOSIT LOCATION

x^, ^a? /4 ll% JriJ* yffliT i Cp

Arizona

1. Ajo

2. Blsbee

3. Globe-Miami

4. Jerome

5. Waters Sunset

6. Lost Basin-Gold Basin 

California

Colorado

1. Central City

2. Cripple Creek

3. Silverton

4. Summitville

5. Telluride

6. Leadville 

Idaho

1. Grass Valley

2. McLaughlin

3. Mesquite

4. Mother Lode

5. San Juan Ridge

6. Mammonton

7. Sonora

1. DeLaroar

2. Orogrande 

South Dakota

1. Homestake (Lead) 

Montana

1. Butte

2. Helena

3. Montana Tunnel

4. Zortman-Landusky

Nevada

1. Carlin

2. Cornstock

3. Ely

4. Goldfield

5. Jerritt Canyon

6. Round Mountain

7. Tonopah

8. Battle Mountain

9. Rawhide 

New Mexico

Ss

>

I

4

i

Ape ,' 

:V -. # 

1. Central

2. Orogrande

3. Ortiz 

Utah

1. Bingham

2. Mercur

3. Tintic

Washington 

1. Wenatchee

Wyoming

1. Dixie Springs

CPs

B2 Geology and Resources of Gold in the United States
Ss /

/

AAa

\

Pp

 (§

/

f-

^§)

\

Cp

Aps ...- '

CPs

Alabama^

Arbacoochee 

Maine

Bald Mountain 

Michigan

1. Ropes 

North Carolina

1. Gold Hill

2. Kings Mountains

3. Reed planation 

South Carolina

1. Haile

2. Ridgeway 

Tennessee

1. Ducktown 

Virginia

1. Whitehall

GULF OF MEXICO 200

1

400

1

KILOMETERS

United States Gold Terranes B3
Figure B1 (on preceding pages). Known geographic 

distribution of some major gold deposits in the conterminous 

United States (in fine stipple). The larger gold districts are 

numbered and named on the map as well as discussed in 

the text. The patterned areas, outlined by light dashed lines, 

contain additional smaller gold mining districts and areas of 

known resources. Generalized geologic terranes (after Beck 

and others, 1980), outlined by heavy solid, dash (including 

ticked-dash), or dot boundaries, are identified as follows: 

Cratonal terranes Ws, Wyoming shield; Ss, Superior shield; 

Tp, Trans-Hudson platform; Pp, Penokean platform; UCPp, 

Uinta-Central Plains platform; CPp, Colorado Plateau platform; Cp, craton platform, undivided; Cps, Cordilleran 

platform shelf; Aps, Appalachian platform shield. Accreted 

terranes Aa, Atlantic, composite; AAa, Atlantic Avalon; Pa, 

Pacific, composite. Overlapped (covered) areas CPs, 

Coastal Plain sedimentary rocks; Cv, Cenozoic volcanics; Cs, 

Cenozoic sedimentary rocks. Circled numbers and heavy 

dash-dot lines indicate basement fault or lineament zones: 1, 

Lewis and Clark; 2, Trans-Challis; 3, Uinta-Central Plains; 4, 

Precambrian shear (Colorado mineral belt); 5, New Mexico 

mineral belt; 6, Walker Lane belt; 7, San Andreas; 8, Nemaha 

Ridge; 9, Midcontinent rift; 10, Northeast Missouri-St. Genevieve; 11, Mississippi embayment; 12, Thirty-eighth parallel; 

13, Avalon accretion zone. Coarse stippled areas are sites of 

major batholiths. Western edge of the craton is shown by a 

light-weight dash-dot line extending through Washington, 

Idaho, Nevada, and southern California. Circled dots indicate 

districts that have produced more than 3 million oz (93.3 t 

(metric tons)) of gold; squared dots are districts whose 

production and announced reserves exceed 3 million oz 

(93.3 t) of gold. Data from Tooker and Vercoutere (1986).

PATTERN OF GROWTH OF KNOWN 

GEOGRAPHIC DISTRIBUTION OF GOLD 

IN THE UNITED STATES

Knowledge of the geographic distribution of gold 

deposits has developed gradually and continues to 

broaden, the cumulative result of the chance discoveries 

of placers and the "rushes" to explore the new areas, the 

subsequent diligent search for the source lodes, and a 

variety of technologic and economic factors that have 

spurred exploration for lower grade deposits. These 

factors include new mining and extraction techniques, 

periodic urgent national need for gold, and legislation to 

deregulate the price of gold. Although the broad pattern 

of gold distribution in the United States largely had been 

established by the early 1900's, new areas containing 

gold-bearing deposits are still being identified.

A chronology of dates of discovery (and in some 

cases rediscovery) of gold districts parallels the territorial 

expansion of the United States. Spurred by earlier 

Spanish successes at exploiting precious metal resources 

in the New World, the English settlers of early 1600's 

began to look for gold. A "feverish hunt" in Virginia by 

Capt. John Smith's group (Rabbitt, 1979) proved unsuccessful, and the necessity to survive the harsh climate in

New England slowed the pace of exploration in that 

region, but the search continued in coastal areas. The 

French and English governments vied for control of the 

lands and potential resources west of the Appalachians 

during the territorial wars that preceded the American 

Revolution. Following the Revolutionary War, individual 

States created geological surveys that gradually began 

systematic investigations of the lands and their resources. 

Placer gold was reported in Virginia in about 1782, 

followed by the discovery of additional placers and their 

source lodes in several of the southeastern States. 

Notable examples (located on fig. Bl) include:

Reed plantation, North Carolina 

Gold Hill, North Carolina 

Haile, South Carolina 

Arabacoochee, Alabama 

Kings Mountain, North Carolina 

Whitehall, Virginia 

Ducktown, Tennessee

1799

1824

1827

1830

1834

1836

1850

Production from these and other small districts in the 

region was sufficient to establish a branch of the U.S. 

mint in Dahlonega, Ga., in 1838 (Rabbitt, 1980). The 

southeastern States remained an important source of 

domestic production until 1859. Spanish explorers 

searching for silver discovered and worked placer deposits in southern Arizona and southern California as 

early as 1775 (Moore, 1969; Clark, 1970), but American 

entry to develop the gold resources of the western region 

was delayed until after 1848.

The lure of the western territories led President 

Thomas Jefferson to send the Lewis and Clark expedition 

in 1805 to survey the resources of the lands comprising 

the Louisiana Purchase. Lewis and Clark's report encouraged further exploration of western territories. However, 

it was the chance discovery of easily mined placer gold in 

the Sierra Nevada foothills in 1848 that launched the 

massive gold rush in California and shifted the focus of 

attention of gold-seekers to the West. The search soon 

broadened throughout the Cordilleran region and led to 

the discovery of many placer and vein lode mining 

districts. Subsequently, the pace of search increased with 

discovery close to the turn of the century of a new type of 

deposit, the celebrated epithermal bonanzas in the 

volcanic terranes of Nevada and Colorado. The wide 

geographic distribution of high-grade deposits recognized during this period is illustrated by the dates of 

discovery in the following districts (fig. Bl):

B4 Geology and Resources of Gold in the United States
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a Fin ii re B2 Known nRonranhifi riistrihution of some maior lode and nlaner no

200 400 KILOMETERS 

1 . 1

H Hfinnsits in Alaska fin finp st nnle^ Mi 

09 

<n

named on the map, are noted in the text, and areas enclosed by dashes contain additional smaller gold mining distric

in Alaska; generalized geologic terrane and structural framework elements include: Cratonal terrane NAM, North A

shaded); accreted terrane Pa, Pacific, composite. Circled numbers identify basement fault or lineament zones 

2, Chugach-St. Bias; 3, Denali; 4, Tintina; 5, Kaltag; 6, Bruin Bay. Circled dots locate districts that have produced more 

tons) of gold. Data from Berg and others (1964).
Mother Lode, California.............................. 1849

Grass Valley, California............................... 1850

Comstock Lode, Nevada and

Central City, Colorado............................. 1859

Bingham Canyon, Utah................................ 1860

Helena and Butte, Montana........................ 1864

Summitville and Silverton, Colorado ......... 1872

Lead (Homestake), South Dakota............. 1875

Cripple Creek, Colorado.............................. 1892

Tonopah, Nevada.......................................... 1900

Goldfield, Nevada......................................... 1902

The geographic range of the search for gold was 

enlarged in 1853 by the Gadsden Purchase of the 

southwestern United States and in 1867 by the purchase 

of Alaska. The search also was intensified by the 

economic and political demands of the American Civil 

War (1861-1865). Completion of the transcontinental 

railroad in 1869 stimulated further exploration and 

discovery by providing much-needed access to mining 

camps in the mountainous regions of the West.

Gold was discovered in Alaska as early as 1848, but 

the first mining in southeastern Alaska began in 1869. 

The Juneau lode was discovered in 1880, and Nome 

placer production began in 1897. The Klondike discovery 

and subsequent rush of 1896 in neighboring Canada also 

broadened the geographic focus of gold exploration 

along the extensive river systems in Alaska.

The development of new mining technology also 

had an impact on the discovery of new gold-bearing 

regions or extensions in known regions. Placers, which 

had been the chief sources of gold until 1873, were 

gradually displaced by lode production, even though brief 

periods of resurgence in placer mining occurred as large 

dredges began to operate in California (1896) and at 

Fairbanks, Alaska (around 1900). Technology for the 

recovery of dispersed low-grade, fine-grained gold from 

porphyry copper deposits in the early 1900's resulted in 

byproduct production of gold in a number of wellestablished base- and precious-metal mining districts in 

the West and Southwest, such as these:

Mining district Original 

mining began

Mining of

porphyry

deposits began

Bingham, Utah 1860

Globe-Miami, Arizona 1874

Central, New Mexico 1804

Ely, Nevada 1873

Ajo, Arizona 1750

Butte, Montana 1864

1904

1904

1906

1908

1917

1955

By 1945, more than 50 percent of U.S. gold production 

was derived from deposits of this type. Most mining 

devoted exclusively to gold production ceased during 

World War II and production fell drastically. Acceleration in the production of base metals from porphyry 

copper deposits during the war, however, resulted in 

continued although low production of gold (Stowe, 

1975).

In the early 1960's, very fine grained, low-grade, 

bulk-minable, epithermal gold disseminated in sedimentary and volcanic rocks was recognized at Carlin, 

Cortez, and Round Mountain, Nev. These discoveries, 

together with the earlier recognized disseminated 

deposits at Getchell and Gold Acres, Nev., led to an 

awareness of the significance of this gold deposit type. As 

a result, the western and subsequently the Appalachian 

cordilleran regions were reopened to a renewed search 

for gold in previously mined areas as well as in new 

geographic areas that contained the geologic and 

economic characteristics of disseminated (bulk minable) 

type deposits (Tooker, 1985). The broad geographic 

distribution of disseminated gold ores in some old as well 

as new mining areas is shown by the following examples:

Waters Sunset, Arizona

McLaughlin, California

Mesquite, California

Summitville, Colorado

DeLamar, Idaho

Orogrande, Idaho

Bald Mountain, Maine

Ropes, Michigan

Montana Tunnels, Montana

Zortman-Landusky, Montana

Carlin, Nevada

Round Mountain, Nevada

Jerritt Canyon, Nevada

Ely, Nevada

Orogrande, New Mexico

Ortiz, New Mexico

Haile, South Carolina

Ridgeway, South Carolina

Lead, South Dakota

Mercur, Utah

Bingham, Utah

Discovery of Barney's Canyon

Petroleum Company, 1986).

Early

production

began

none

1862 (mercury)

none

1870

1863

1857

none

1880

none

1884

1900

1906

none

1867

1905

1828

1827

none

1877

1870

1960

reported, but mining had

Mining of

disseminated

deposits

began

1984

1986 (gold)

1986

1986

1977

198?

1986

1985

1987

1980

1965

1977

1971

1987

1981

1981

1986

1986

1986

1981

H987

not begun (British

GEOLOGIC BASIS FOR THE 

GEOGRAPHIC DISTRIBUTION OF GOLD

Although gold occurs in at least 40 States (Tooker 

and Johnson, 1980) and in more than 1,000 mining 

districts, major United States production and significant

B6 Geology and Resources of Gold In the United States
reserves are located in relatively few restricted geographic regions (Tooker and Vercoutere, 1986). The 

geographic distribution of gold (figs. Bl and B2) seems 

to be closely related to specific parts of the continental 

framework composed of a craton and peripherally 

accreted host rock terranes. Distribution of gold districts 

in these terranes differs, and generally gold is abundant 

in only parts of a terrane (Tooker, 1979).

Favorable host regions for the occurrence of gold, 

shown in figures Bl and B2, contain concentrations of 

deposits that are the sites for major U.S. production 

(from Tooker and Vercoutere, 1986). Deposits in the 

accreted terranes, which were attached to the craton 

during Phanerozoic time, occur as clusters along 

recognized accretionary structures or in favorable lithologic units. Those deposits that formed locally in 

favorable Precambrian and Phanerozoic units on the 

craton commonly seem to be grouped geographically in 

the outer craton platform and shelf along persistent 

Precambrian basement suture zones rather than along 

the structures or rock units in the overlying Phanerozoic 

cover rocks. Cratonal terrane districts are clustered 

mainly along the outer edges of the western platform and 

shelf. Few gold districts are known in the central part of 

the craton. The shield areas (Ss and Ws, fig. Bl) are not 

major U.S. gold-producing regions, whereas in Canada 

the Archean Superior shield hosts most of the productive 

deposits (Boyle, 1979; Cameron, 1988). The Wyoming 

shield has some districts characterized by small lode and 

disseminated gold deposits, and a potentially large (Dixie 

Springs) placer district, whose source lode is as yet poorly 

identified. Most of the Precambrian gold deposits in the 

United States are hosted in Proterozoic platform terranes, close to the shield-platform boundaries (Ropes, 

Midi., and Homestake, S. Dak.). Potential byproduct 

gold also is known in the Duluth Gabbro in northeast 

Minnesota, and in metamorphosed sedimentary rocks 

such as the Crandon-type massive sulfide deposits in 

north-central Wisconsin. Important sources of gold in the 

Rocky Mountain region occur in Precambrian and Phanerozoic rocks composing the craton platform and shelf 

terranes. These regions appear to be aligned along 

northeast-trending zones that may intersect and cross the 

exposed structural fabric of the Phanerozoic cover rocks. 

Some evidence suggests that major controls for this 

pattern of distribution are basement shear zone structures, such as those in the mineral belt in central 

Colorado, Trans-Challis in southwestern Montana, the 

Uinta-Cortez trend in north-central Utah, and probably 

the New Mexico mineral belt. In contrast, the central 

craton platform of the midcontinent region and the 

Colorado Plateau region lack igneous intrusions and the 

structural deformation that characterize the outer craton 

platform and shelf regions of the Rocky Mountain and 

Appalachian cordillera.

The gold-producing regions in the accreted terranes are closely aligned with Phanerozoic structural 

features such as Sierra foothills and Klamath belts in 

California, Southeast Alaska, and Atlantic Avalon and 

Arabacoochee belts in the Appalachian terranes (figs. Bl 

and B2). This relation is well shown in the eastern U.S. 

(Ma and Aa) and Alaskan (Pa) accreted terranes, and is 

also repeated in the accreted terranes in western 

Washington, Oregon, and California.

The geographic distribution of gold districts in 

north-central Nevada seems not exclusively related to the 

geologic features of the host accreted terranes. Here 

rocks of oceanic origin have been obducted onto continental crust of the craton shelf. The resulting distribution and magnitude of gold deposition may reflect 

contributions from both terranes.

GEOGRAPHIC DISTRIBUTION OF GOLD 

DEPOSIT TYPES

Assessment of the geographic distribution of types 

of gold deposits is made difficult because no generally 

accepted genetic classification of them exists, and gold 

deposits in a single mining district may consist of more 

than one type. A number of gold classifications emphasize features such as temperature-pressure (depth) of 

formation (Lindgren, 1933), host rocks and structures 

(Boyle, 1979), or a combination of genetic and descriptive features (Ashley, in press). Furthermore, some 

types of gold deposits are more amenable to one system 

of classification than to another, and commonly types 

overlap, even within a single deposit. A tentative descriptive classification of types is shown in the following 

tabulation, based mostly on the compilation of gold data 

by Tooker and Vercoutere (1986).

General classification of types of primary and byproduct 

gold deposits:

1. Skam. Irregular replacement of fractured carbonate rock adjacent to granitic intrusives (contact metamorphism) to form gold-bearing calcsilicate mineralized rock; gold may be a primary 

product or a byproduct of base metals.

2. Dispersed (porphyry). Large-volume, low-grade, 

vein and disseminated sulfides in sheeted zone or 

stockwork of an associated subvolcanic porphyry; 

gold may be a primary product or a byproduct of 

base metal sulfides.

3. Pofymetallic vein and replacement. Sulfide-rich 

fissure and replacement deposit in sedimentary or 

igneous host; gold may be a primary product or a 

byproduct of base and other precious metals.

United States Gold Terranes B7
4. Quartz lode. Vein and shear zone deposit generally in regionally metamorphosed sedimentary 

and igneous rocks and composed primarily of gold 

with quartz-pyrite gangue; a lode may contain 

minor base metal sulfides.

5. Disseminated sediment- and volcanic-hosted. 

Large-volume, low-grade, bulk-minable, generally 

epithermal deposit of primary gold, which may or 

may not be associated with intrusive rocks. The 

disseminated type also has been applied to bulkminable parts of quartz lode, stockwork, bonanza, 

and other types.

6. Bonanza. Exceptionally rich ore shoot of primary 

and oxidized epithermal gold generally in a volcanic 

host, but also as an enriched quartz lode, replacement, stockwork, or breccia pipe.

7. Massive sulfide. Irregular peneconformable concentration of sulfide minerals in volcanic, metavolcanic, and metasedimentary rocks of mobile 

belts or accreted terranes; gold occurs mostly as a 

byproduct of base metals.

8. Iron-formation. Local concentration of primary 

gold in stratabound stringers and fracture fillings of 

"banded" (layered) marine metasedimentary and 

volcaniclastic rocks that contain more than 15 

percent iron, abundant chert, and fine-grained 

quartz segregations.

9. Placer. Eluvial, alluvial, and colluvial modern and 

fossil local accumulation of free gold, the result of 

surface erosion of other types of deposits (types 

1-8) and mechanical concentration of gold by 

stream or wave action.

10. Saprolite. Secondary enriched deposit of gold in 

place, localized in decomposed soft clay-rich igneous or metamorphic rocks by chemical weathering. 

This classification is similar to the classification 

adopted by Shawe (1988) for grouping ore deposits in the 

various chapters of this Bulletin series. That classification 

consists of gold deposits in metamorphic rocks (including 

some quartz lodes and massive sulfide deposits), mesozonal gold deposits (including polymetallic replacements 

and veins, porphyry copper systems, and intermediate 

level gold-quartz veins), epizonal gold deposits (including bonanza-type and disseminated gold deposits), and 

placer gold deposits. In Shawe's classification, skarn 

deposits are considered part of porphyry copper systems, 

iron-formation deposits are grouped under deposits in 

metamorphic rocks, and saprolite deposits are not 

considered.

Tooker and Vercoutere (1986) arbitrarily placed a 

deposit in a class on the basis of the main ore type 

produced; they also indicated associated types where 

present. In some cases, the literature did not provide 

sufficient information for them to distinguish between a 

quartz vein (lode), which contained only minor base

metal sulfides, and a polymetallic vein, in which the base 

metal value generally exceeded that of gold. This fact 

may account for the significant variation in the proportions of lode and polymetallic veins in the craton and 

accreted terranes shown in the following table.

Types of gold occurrence Cratonal Accreted 

(percent) (percent)

Skarn, bonanza, iron-formation, and

massive sulfide.................................... 5 6

Porphyry.................................................. 5 small

Polymetallic veins and replacement... 50 25

Quartz lode............................................ 6-10 30

Disseminated.......................................... 5-10 14

Placer...................................................... 20 25

Analysis of the geographic distribution of deposit 

types in this classification indicates that non-vein types 

are distributed nearly equally in cratonal and accreted 

terranes. However, the Tooker and Vercoutere (1986) 

data suggest that certain types are characteristic of, but 

not confined to, specific geographic regions. Massive 

sulfide and saprolitic deposits predominate in Appalachian accreted terranes; iron-formation deposits are 

concentrated in South Dakota, polymetallic vein and 

replacement deposits predominate in the Colorado Front 

Range, quartz lodes and placers are most abundant in the 

Sierra foothills of California (placers are also abundant 

in Alaska), and disseminated gold deposits are most 

numerous in Nevada.

Most geographic regions, and even individual 

districts, contain a mix of deposit types. The table on page 

B9 illustrates some of the diversity to be expected.

However, as these generalizations suggest, the 

"disseminated" category in particular may include parts 

of virtually all lode deposit types (for example, Sierra 

foothills Mother Lode), carbonate-hosted (Carlin), 

arkosic-hosted (Wenatchee), volcanic-hosted (Round 

Mountain), and bonanza (Goldfield) types. Their common thread is that most are considered to be of epithermal origin and are bulk-minable; the Mother Lode is 

mesothermal, and moreover, in places (Bingham, for 

example) gold seems to have been introduced in several 

stages of the ore-forming process. At Bingham the 

copper-gold-molybdenum stage was an early hightemperature dispersed (porphyry) system in which the 

gold was deposited from a saline solution as fine-grained 

particles in veinlets and permeable altered zones in 

fractured wall rock (Roedder, 1971). Skarn coppergold-silver deposits in the limestone beds adjacent to the 

porphyry intrusives were formed at the same time as the 

dispersed ores (Cameron and Garmoe, 1987). Locally 

rich concentrations of gold in peripheral base-metalsilver veins and replacement deposits are coarser grained 

and were deposited from lower-temperature, low-salinity

B8 Geology and Resources of Gold in the United States
Geographic areas 

and typical districts Prominent types of deposits

Western Washington

(Wenatchee). 

Sierra foothills, California

(Mother Lode). 

Central Nevada

(Carlin). 

Western Montana

(Butte, Montana Tunnels). 

Central Utah

(Bingham, Tintic). 

Western Arizona-Southwest

California (Mesquite). 

South-central Arizona

(Jerome). 

Southwest Oregon.

Colorado Front Range

(Central City). 

Western South Dakota

(Homestake). 

South Carolina

(Haile). 

Southeast Alaska

(Juneau).

Disseminated, and polymetallic veins. 

Placer, quartz lode (and disseminated).

Disseminated, bonanza, polymetallic

vein and replacement. 

Polymetallic vein, porphyry (disseminated).

Porphyry, quartz lode, polymetallic vein 

and replacement, skarn, disseminated. 

Disseminated.

Massive sulfide, polymetallic vein and

replacement. 

Quartz lode, polymetallic vein and

replacement, placer. 

Polymetallic vein and replacement, placer.

Iron-formation, quartz lode, disseminated. 

Disseminated, massive sulfide, placer. 

Quartz lode, placer.

fluids (Rubright and Hart, 1968; Bowman and others, 

1987). The gold that originated in these early stages 

apparently was the source of placer gold in Bingham 

Canyon (Boutwell, 1905). Just north of the Bingham 

porphyry intrusives, along a prominent north-northeasttrending fault, altered carbonate sedimentary rocks 

contain epithermal low-temperature fine-grained disseminated gold (British Petroleum Co., 1986) that is 

presumed to be derived from the hydrothermal system 

active at Bingham.

The timing of deposition stages is not fully known 

at present, neither at Bingham nor elsewhere. Most of 

the deposits in the major terranes are post accretionary, 

but some deposits such as the massive sulfide bodies 

were formed early. Much recycling or remobilization and 

concentration of gold in the cratonal terranes is suspected, but is not as yet well documented.

Manuscript received by scientific editors February 1988

REFERENCES CITED

Ashley, R.P., in press, Gold and silver, in Gluskoter, H.J., Rice, 

D.D., and Taylor, R.B., eds., Economic geology, U.S.: 

Geological Society of America, Geology of North 

America, v. P-2.

Beck, M., Cox, A., and Jones, D., 1980, Mesozoic and Cenozoic

microplate tectonics of western North America: Geology,

v. 8, no. 9, p. 545-546. 

Berg, H.C., Eberlein, G.D., and MacKevett, E.M., Jr., 1964,

Gold in metallic and nonmetallic mineral resources, in

Mineral and water resources in Alaska: Committee Print

88th Congress, 2d session, Committee of Interior and

Insular Affairs, United States Senate, p. 104-108. 

Boutwell, J.M., 1905, Economic geology of the Bingham mining

district, Utah: U.S. Geological Survey Professional Paper

38, 413 p. 

Bowman, J.R., Parry, W.T., Kropp, W.P., and Kruer, S.A., 1987,

Chemical and isotopic evolution of hydrothermal

solutions at Bingham, Utah: Economic Geology, v. 82,

no. 2, p. 395-428. 

Boyle, R.W., 1979, The geochemistry of gold and its deposits:

Geological Survey of Canada Bulletin 280, 584 p. 

British Petroleum Company, 1986, Financial and operating

information: British Petroleum Company, London,

p. 112-114. 

Cameron, D.E., and Garmoe, W.J., 1987, Geology of skarn and

high-grade gold in the Carr Fork mine, Utah: Economic

Geology, v. 82, no. 5, p. 1319-1333. 

Cameron, E.M., 1988, Archean gold Relation to granulite

formation and redox zoning in the crust: Geology, v. 16,

no. 2, p. 109-112. 

Clark, W.B., 1970, Gold districts of California: California

Division of Mines and Geology Bulletin 193, 186 p.

United States Gold Terranes B9
Lindgren, Waldemar, 1933, Mineral deposits: New York, 

McGraw-Hill Book Co., p. 203-212.

Moore, R.T., 1969, Gold, in Hilpert, L.S., Mineral and water 

resources of Arizona: U.S. Senate Committee on Interior 

and Insular Affairs, Committee Print, 90th Congress, 2d 

Session, p. 156-167.

Rabbitt, M.C., 1979, Minerals, lands, and geology for the 

common defense and general welfare; Volume 1, Before 

1879: Washington, D.C., U.S. Government Printing 

Office, 331 p.

___ 1980, Minerals, lands, and geology for the common 

defense and general welfare; Volume 2, 1879-1904: 

Washington, D.C., U.S. Government Printing Office, 

405 p.

Roedder, Edwin, 1971, Fluid inclusion studies of the porphyrytype ore deposits at Bingham, Utah, Butte, Montana, 

and Climax, Colorado: Economic Geology, v. 66, no. 1, 

p. 78-118.

Rubright, R.D., and Hart, O.J., 1968, Non-porphyry ores of the 

Bingham District, Utah, in Ridge, J.D., ed., Ore deposits 

of the United States 1933-1967 (Graton-Sales Volume): 

American Institute of Mining, Metallurgical, and 

Petroleum Engineers, v. 1, p. 886-907.

Shawe, D.R., 1988, Introduction The case for gold, in Shawe, 

D.R., Ashley, R.P., and Carter, L.M.H., eds., Geology 

and resources of gold in the United States: U.S. 

Geological Survey Bulletin 1857-A, p. A1-A8.

Stowe, C.H., 1975, Utah mineral industry statistics through 

1973: Utah Geological and Mineral Survey Bulletin 106, 

121 p.

Tooker, E.W., 1979, Metal provinces and plate tectonics in the 

conterminous United States, in Ridge, J.D., ed., Papers 

on mineral deposits of western North America: Nevada 

Bureau of Mines and Geology Report 33, p. 33-38.

___ 1985, Geologic characteristics of sediment- and 

volcanic-hosted disseminated gold deposits Search for 

an occurrence model: U.S. Geological Survey Bulletin 

1646, 150 p.

Tooker, E.W., and Johnson, M.G., 1980, Preliminary map of 

gold provinces in the conterminous United States: U.S. 

Geological Survey Open-File Report 79-576-S, scale 

1:5,000,000.

Tooker, E.W., and Vercoutere, T.L., 1986, Gold in the conterminous United States, Prospective of 1986 Preliminary 

map of selected geographic economic and geologic 

attributes of production (> 10,000 oz) gold districts: U.S. 

Geological Survey Open-File Report 86-209, 32 p.

B10 Geology and Resources of Gold in the United States
Patterns of Gold Mineralization in Nevada and Utah

By William C. Bagby

Abstract

The distribution of gold-producing districts in Nevada 

and Utah is controlled by a combination of interacting 

regional geologic features. Spatial associations between 

gold-producing districts and aeromagnetic anomalies, 

certain types of tectono-stratigraphic terranes, plutonic and 

volcanic rocks of certain chemical affinities, and regional 

tectonic, stratigraphic, and structural features have provided 

a context for research and exploration for gold. Maps 

showing the distribution of mining districts that have 

produced at least 10 ounces of gold give the appearance of 

scatter diagrams; however, gold-producing districts are twice 

as abundant in accreted terranes as they are in cratonal 

terranes. Reasonably distinct patterns appear on maps 

drawn to show major districts that have produced more than 

1,000 ounces of gold. These patterns reinforce the association of gold with accreted terranes but also indicate a 

preferred localization of the districts in accreted terranes 

along northwesterly lineaments. Major districts that occur in 

cratonal terranes form east-trending patterns. Both the 

northwest and east trends of major gold-producing districts 

also contain intrusive and volcanic rocks, major faults and 

folds, and, in some cases, coincide with aeromagnetic 

anomalies. Although ages of gold mineralization are mixed in 

the pattern analysis, certain conclusions may be drawn 

regarding the genetic significance of the patterns. The 

conclusions are (1) that districts that produce gold are twice 

as likely to occur in accreted terranes as in cratonal terranes 

and (2) that deep-seated regional structures are major 

controls of the locations of these districts. The deep-seated 

structures are also the loci of magmatic and fault activity.

INTRODUCTION

The distribution of gold-producing districts in 

Nevada and Utah apparently is controlled by a combination of interacting regional geologic features. Several 

investigators have examined the spatial distribution of 

gold and other types of ore deposits within the framework of known regional geologic features in an attempt 

to understand and to define metallogenic controls in 

Utah and Nevada. For example, Ferguson (1929) 

recognized two metallogenic provinces in Nevada:

(1) a western province that contains mostly gold, silver, 

mercury, and antimony, and (2) an eastern province that 

is dominated by base metal deposits with peripheral 

precious metal ore bodies. Roberts (1966) expanded on 

Ferguson's metallogenic provinces and identified a series 

of 11 mineral belts in Nevada that are defined by 

alignments of ore deposits along structural trends. Jerome and Cook (1967) discussed the spatial distribution 

of mineral deposits and their regional tectonic, sedimentary, and igneous host environments in the Western 

United States. Silberman and others (1976) noted the 

similarity of ages among Tertiary volcanic rocks, precious 

metal deposits, and regional structural trends in Nevada 

and proposed a genetic association. Shawe and Stewart 

(1976), Shawe (1977), Stewart and others (1977), and 

Shawe and others (1978) interpreted the distribution 

patterns of precious and base metal deposits in Nevada 

and Utah in terms of aeromagnetic patterns, the ages and 

distribution of intrusive rocks, and regional structural 

trends, including the possible influence of plate interactions along the western margin of North America.

These examples represent a classical approach to 

the problem of explaining the distribution of ore deposits. Recently, the occurrence of mineral deposits 

related to tectono-stratigraphic terranes has been considered. For example, Albers (1983) and Tooker (1983) 

suggested that a genetic association is possible between 

tectono-stratigraphic terranes and ore deposits. Tooker 

(1983) showed that cobalt, chrome, and platinum group 

metals predominate in accreted terranes, and that gold 

and copper occur abundantly in both accreted terranes 

and over cratonic basement in the northwestern United 

States. On the other hand, lead, zinc, tin, and tungsten 

are predominantly concentrated in or along the margins 

of the craton. Likewise, Albers (1983) noted that some 

types of ore deposits are restricted to certain accreted 

terranes throughout the Western United States.

The success of applying the terrane concept to the 

location of ore deposits in general suggests that the 

concept should be considered as a factor in explaining the 

distribution patterns of gold-producing districts in 

Nevada and Utah. These patterns are examined herein

United States Gold Terranes B11
and interpreted in light of the temporal and spatial 

relations between gold districts and the associated 

structural, magnetic, and igneous trends noted by earlier 

workers.

TERRANES OF NEVADA AND UTAH

The Nevada-Utah region contains a diverse 

assemblage of geologic terranes. For example, the areas 

of central and western Nevada are composed of a collage 

of tectono-stratigraphic terranes accreted to, and in part, 

overlying cratonic basement which underlies eastern 

Nevada (Silberling and others, 1984). In contrast, Utah 

contains no accreted terranes, but instead consists of a 

complex of older cratonic basement terranes, different 

parts of which may have experienced different geologic 

histories.

The definition of a geologic terrane, as used in this 

report, is one that was proposed by the Penrose 

Conference on microplate tectonics: "a fault-bounded 

geologic entity characterized by a distinctive stratigraphic 

sequence and/or a structural history differing markedly 

from those of adjoining neighbors" (Beck and others, 

1980, p. 454). This definition is most commonly used with 

reference to accreted terranes, those that are interpreted 

to have formed in a different geographic location from 

that in which they now occur. Thus, oceanic terranes may 

be accreted to a craton by either collision or transform 

tectonics. This definition may also extend to areas that 

may or may not have moved but that have experienced 

unique geologic histories: such terranes may be identified 

as cratonal terranes because they formed over cratonic 

basement and have not moved from their original site. 

Also, the definition is broadened to include basement 

terranes of distinctive rock units that, owing to highgrade metamorphism, cannot strictly be interpreted as 

stratigraphic sequences.

The distribution of accreted and cratonal terranes 

in Nevada and Utah (Silberling and others, 1984; Hilpert, 

1964) is shown in figure B3. Allochthonous terranes 

underlie the central and western parts of Nevada and 

include the Paleozoic Roberts Mountains allochthon 

(Poole and others, 1977); the middle to upper Paleozoic 

Golconda allochthon (Silberling and Roberts, 1962), and 

the upper Paleozoic to lower Mesozoic Sonomia terrane 

(Speed, 1977; 1979). The latter of these three major 

terranes is a composite of several island arc and ocean 

floor terranes, including: (1) the upper Paleozoic to 

Middle Triassic Black Rock terrane (Ketner and Wardlaw, 1981), (2) the lower Mesozoic Jackson terrane 

(Russell, 1984), (3) the lower Mesozoic Jungo terrane 

(Silberling and others, 1984), and (4) the lower Mesozoic 

Walker Lake terrane which is divided into the Paradise 

and Pine Nut subterranes (Silberling and others, 1984). 

The separate terranes that together compose Sonomia

are delineated in figure B3. Cenozoic rocks cover large 

parts of the accreted terranes in western and northern 

Nevada. A boundary that is generally used to define the 

easternmost extent of outcrops of lower Paleozoic 

oceanic siliceous assemblage rocks (the Roberts 

Mountains allochthon) in Nevada separates accreted 

oceanic and island arc terranes to the west from cratonal 

terranes to the east (fig. B3).

The lower Paleozoic Roberts Mountains allochthon is the oldest accreted terrane in Nevada, and as 

such, is farthest inboard and overlaps both Paleozoic 

miogeoclinal sedimentary rocks and Precambrian crystalline basement. The approximate amount of overlap is 

shown in figure B3 by the location of isograds marking 

initial strontium isotope ratios of 0.7060 and 0.7080 in 

Mesozoic and Tertiary intrusives. The 0.7060 strontium 

isotope line is commonly accepted as the western edge of 

Precambrian crystalline basement in Nevada (Kistler and 

Peterman, 1978; Kistler, 1983). Farmer and DePaolo 

(1983), however, have suggested that the 0.7080 line, 

which is based also on Nd isotope systematics, is a better 

location for that boundary. The amount of overlap of the 

cratonic block by the Roberts Mountains allochthon is 

approximately 100-200 km east of the 0.7060 line or 50 

km east of the 0.7080 line. Thus, Precambrian crystalline 

basement may underlie a significant portion of both the 

Roberts Mountains allochthon and the younger, overlying middle to upper Paleozoic Golconda allochthon.

Eastern Nevada and all of Utah are underlain by 

cratonal terranes of continental origin (fig. B3). These 

include the Rocky Mountains, Colorado Plateaus, and 

miogeoclinal shelf terranes. The miogeoclinal terrane is 

further subdivided into the Sevier erogenic belt and its 

hinterland, the Mesozoic metamorphic belt. These terranes overlap due to superimposed deformation events. 

For example, the Mesozoic metamorphic belt affected 

parts of the area overlain by the Roberts Mountains 

allochthon. Likewise, younger Laramide deformation 

associated with the formation of the Rocky Mountains 

overlapped part of the Sevier orogenic belt in northeastern Utah. Despite these superimposed events, cratonal terranes are herein defined by the dominant type of 

deformation style, or lack thereof, in order to simplify the 

terrane picture.

Miogeoclinal sediments were deposited in shallow 

epicontinental basins and on the continental shelf in 

eastern Nevada and western Utah. During the Late 

Jurassic to Late Cretaceous, the eastern half of the 

sedimentary pile was folded as well as thrusted during the 

Sevier orogeny (Armstrong, 1968), whereas the western 

hinterland of the Sevier orogenic belt (Misch and Hazzard, 1962; Armstrong, 1968; Snoke, 1980) was metamorphosed but not strongly deformed. On this basis, 

these areas are separated into two different cratonal

B12 Geology and Resources of Gold in the United States
114° 112°

IOOMILES 

IOOKILOMETERS

Figure B3. Geologic terranes of Nevada and Utah. Cratonal terranes (various dash and dash-dot outlines): 

Colorado Plateaus (CP), Rocky Mountains, Precambrian 

basement (p-C), and miogeoclinal terrane, divided into the 

Mesozoic metamorphic and Sevier orogenic belts (Hilpert, 

1964; Armstrong, 1968; and looker, 1983). Accreted terranes (dashed outlines): Roberts Mountains allochthon (RM); 

Golconda allochthon (GO); and the terranes that compose

subterranes, even though their geologic histories are 

similar. Clastic debris shed to the east off the Sevier 

highlands formed a sedimentary pile on a lower Phanerozoic basement that has not been strongly deformed, 

the Colorado Plateaus terrane. This terrane acted as an 

undisturbed block during Laramide (Late Cretaceous to 

early Tertiary) deformation that resulted in Precambrian 

basement uplifts and the formation of the Rocky 

Mountains terrane.

The southeastern corner of Nevada, south of the 

Colorado Plateaus terrane, is dominated by Early and 

Middle Proterozoic rocks (Stewart, 1980). Paleozoic or 

Mesozoic sedimentary rocks that may have covered the 

area have been eroded. Mesozoic and Cenozoic igneous

Sonomia: Jungo (JO), Black Rock (BRK), Jackson (JN), 

Walker Lake-Paradise (WPD), Walker Lake-Pine Nut (WPN) 

(Silberling and others, 1984). Cenozoic cover (solid outline; 

CZ) is postaccretionary; patterned areas indicate Mesozoic 

intrusions. The 0.7060 and 0.7080 initial strontium isotopic 

lines (dotted) are from Kistler and Peterman (1978) and 

Farmer and DePaolo (1983), respectively.

rocks intrude the Precambrian. This area is considered 

herein as Precambrian basement terrane.

PATTERNS OF GOLD-PRODUCING 

DISTRICTS IN NEVADA AND UTAH

Gold-producing districts in Nevada and Utah 

(Bonham, 1976; Bergendahl, 1964) are shown in figure 

B4 together with accreted and cratonal terranes and 

strontium isotope isograds. The types and sizes of goldproducing districts are not discriminated. For example, 

predominantly gold producing districts (for example, 

Carlin, Jerritt Canyon) are included with predominantly

United States Gold Terranes B13
base metal producing districts (for example, Bingham 

Canyon, Ely) that have produced more than 10 ounces of 

gold. For some of these base metal districts, the current 

and the future gold production may actually be more 

important economically than base metal production.

The distribution of gold-producing districts shown 

in figure B4 gives the impression of a scatter diagram that 

indicates no correlation between either accreted or cratonal terranes and the locations of gold-producing districts. However, gold-producing districts are about twice 

as abundant in accreted terranes (about 170) as they are 

in cratonal terranes (about 70), the two regions being 

of roughly comparable area. Gold-producing districts 

located in cratonal terranes are limited predominantly to 

the miogeoclinal terrane with a sparse scattering of 

deposits in the other cratonal terranes. Although areas of 

postaccretionary Cenozoic cover in western and northern Nevada contain notable precious metal deposits

such as Comstock and Jarbidge, gold-producing districts 

are sparse in this cover compared to occurrences in the 

accretionary and cratonal terranes.

In order to clarify the distribution of goldproducing districts in terms of substantial production, I 

have defined "important" districts as those that have 

produced, or have reserves of, more than 1,000 oz of gold 

and plotted them in figure B5. This distribution shows 

that a higher proportion (again, about 2:1) of deposits of 

this size occur in the accreted terranes, especially along 

northwest-trending lineaments, and it enhances the 

perception that gold is more abundant in accreted terranes than it is in cratonal terranes. The northwesterly 

trends are easier to discern in figure B6 where the 

important gold districts are plotted together with 

different regional structural trends. Important gold 

districts in cratonal terranes seem to define (1) broad 

east-trending patterns that cut across the north- to

120

0 100 KILOMETERS 

110°

100 MILES

Figure B4. The distribution of gold-producing districts in Nevada and Utah (Bergendahl, 1964; Bonham, 1976). Accreted 

terranes (shaded) occur west of the eastern limit of Paleozoic oceanic siliceous assemblage outcrops, and cratonal terranes are 

east of that boundary. Major geologic boundaries as in figure B3.

B14 Geology and Resources of Gold in the United States
IOOMILES

100 KILOMETERS

r

/

1

f

P ,

i | i J !

Figure B5. The distribution of gold-producing districts in Nevada and Utah that either have produced or have reserves of 

more than 1,000 oz of gold (Bergendahl, 1964; Bonham, 1976). Geologic boundaries and terrane patterns from figure B4.

northeast-striking geologic fabric of the Sevier erogenic 

belt and (2) a north-trending belt of deposits along the 

boundary of the Rocky Mountain and Sevier terranes in 

northern Utah.

The east-trending patterns of gold-producing districts in cratonal terranes in Utah and eastern Nevada 

coincide with prominent belts of Tertiary calc-alkalic 

intrusions. These east-trending belts of ore deposits 

associated with intrusive and volcanic rocks in Utah have 

been termed the Park City-Bingham, Tintic-Deep 

Creek, and Marysvale-Pioche belts (Butler and others, 

1920; Morris and Levering, 1961; Hilpert and Roberts, 

1964; Tooker, 1971). These belts also have strong positive aeromagnetic signatures that are possibly related to 

concealed, near-surface intrusive rocks (Shawe and 

Stewart, 1976; Stewart and others, 1977).

Comparison of the distribution of significant goldproducing districts in Nevada and Utah with igneous

rocks of comparable age also suggests a close genetic 

relationship between gold deposits and igneous rocks. 

Silberman and others (1976) illustrated the close spatial 

association of the following deposits with igneous rocks 

of comparable age:

Tuscarora, Battle Mountain, 

Bullion, Cortez, Bingham, 

Park City

Tintic district and Round Mountain

Pyramid, Wonder, Tonopah, 

Goldfield, Gold Mountain

Comstock, Rawhide, Camp 

Douglas, Silver Dyke, Manhattan, 

Divide, Seven Troughs, 

Ten Mile, Adelaide, Midas, 

Jarbidge, Buckhorn, Marysvale, 

Deer Trail

Talapoosa, Monitor, Aurora, Bodie, 

Gilbert, Bull Frog, Silver Peak

early Oligocene igneous rocks 

(fig. B7)

late Oligocene (fig. B8) 

I early Miocene (fig. B8)

 middle Miocene (fig. B9)

late Miocene (fig. B9)

United States Gold Terranes B15
120° 118

IOOMILES

IOOKILOMETERS

Figure B6. Distribution of gold districts in Nevada and Utah that either have produced or have reserves of more than 

1,000 oz of gold (fig. B3), together with various mineral belts and named structural trends. East-trending mineral belts: 

Marysvale-Pioche (P), Tintic-Deep Creek (T), and Park City-Bingham (B), from Stewart and others (1977). The locations of the 

Cortez-Uinta axis (C-U axis) and the Wasatch fault are from Tooker (1983). Mineral belts in Nevada are from Roberts (1966). 

Other geologic boundaries as in figure B4.

Another important spatial association is that the 

Park City-Bingham zone lies along the flanks of the 

Cortez-Uinta axis. In the Rocky Mountains and miogeoclinal terranes in Utah, episodic uplift has occurred along 

this axis beginning in the Precambrian and extending 

through the Paleozoic. Roberts (1966) and Tooker 

(1971, 1983) proposed that the Cortez-Uinta axis 

extends west of the Rocky Mountains uplift as a basement structural zone beneath the Sevier erogenic belt 

terrane. Such a deep, through-going structural zone of 

Precambrian age could serve to localize Tertiary intrusive rocks.

There is a diffuse northerly alignment of very small 

gold-producing districts in Utah, north of the Park CityBingham mineral belt. The alignment extends away from 

the north flank of the Cortez-Uinta axis, suggesting

that some other regional geologic feature is responsible 

for the formation of deposits along this trend. Three 

important gold districts are isolated in the southern part 

of the Colorado Plateaus terrane. These are spatially 

associated with intrusions, suggesting some temporal and 

thus, probably, a genetic association. Two districts lie in 

the eastern part of the Rocky Mountain cratonal terrane 

in Utah. These are presumably related to Laramide 

deformation. The Precambrian basement terrane in 

southeastern Nevada hosts three known important goldproducing districts. Each of these is located along 

contacts between Precambrian and either Mesozoic or 

Tertiary intrusive rocks.

Gold-producing districts in the accreted terranes of 

Nevada have a more scattered distribution than do those 

in the cratonal terranes of Utah and eastern Nevada.

B16 Geology and Resources of Gold in the United States
0

h0

50

50 100

100 I50MILES 

». )

I50KILOMETERS

Figure B7. General outline of upper Eocene and lower Oligocene igneous rocks in Nevada and Utah and locations of 

gold-producing districts that have early Oligocene ages. Modified from Silberman and others (1976).

Despite this scatter, a preferred alignment of some 

districts nevertheless exists along northwest-striking 

mineral belts (fig. B6). These belts have been identified 

and discussed by Roberts (1966), Shawe and Stewart 

(1976), and Silberman and others (1976). Although 

Roberts (1966) attributed these belts to older structural 

zones beneath allochthonous terranes, recent work 

indicates that these belts crosscut the northerly fabric of 

the accreted terranes and are thus younger, probably of 

Mesozoic age (R.J. Madrid, oral commun., 1984). If this 

is true, it is still possible that older, buried structures 

guided later deformation by serving as zones of 

weakness, at least in areas where deformation affected 

thin-skinned, allochthonous terranes.

Consideration of the distribution of gold districts in 

light of the terrane concept in Nevada and Utah must 

take into account that the deposits shown on the map are

not all the same age. Thus the distribution appears 

scattered, and some gold belts are poorly defined 

because of the scatter. The well-defined east-west gold 

belts that cross the Utah-Nevada border are all of 

Tertiary age. In contrast, mixing of deposit ages in 

Nevada results in more diffuse patterns.

DISCUSSION

The significant patterns that emerge from the 

distribution of gold-producing districts in Nevada and 

Utah are that (1) deposits that have produced at least 10 

ounces of gold are broadly scattered, with the majority of 

the districts occurring in accreted terranes of Nevada, 

(2) gold districts are sparse in the postaccretionary 

Cenozoic cover of western and northern Nevada and in

United States Gold Terranes B17
T0M0PAH 

-:':- :.£.' : :' ' "' "" .: ' '.

octiUDFtgt.0

0 50 100 I50MILES *-i H '

0 50 100 I50KILOMETERS

Figure B8. General outline of upper Oligocene and lower Miocene igneous rocks in Nevada and Utah and locations of 

gold-producing districts that have ages of mineralization within the same time frame. Solid triangle, district of late Oligocene 

age; solid circle, early Miocene. Modified from Silberman and others (1976).

the cratonal Colorado Plateaus terrane of Utah, and 

(3) gold-producing districts with greater than 1,000 oz of 

contained or produced gold occur predominantly in 

accreted terranes, coincide in position and in age with 

particular igneous rock assemblages, and are spatially 

associated with major structural trends.

Albers (1983) noted that gold districts throughout 

the Western United States seem to be preferentially 

associated with accreted terranes of oceanic affinity. This 

is borne out by the gold distribution patterns for Nevada 

and Utah and suggests that accreted oceanic terranes in 

Nevada may have served not only as a host environment 

for gold, but also as the source for gold and associated 

metals (such as arsenic, antimony, mercury) in these 

districts. For example, Keays and Scott (1976) suggested 

that pillow basalts are possible source rocks for gold 

because gold is concentrated in easily leachable mineralogical sites on pillow margins. In addition, black 

shales also may be source rocks due to possible enrichment of gold in the shales during diagenesis (Boyle, 

1979). Thus, it is permissive to consider the presence of 

high contents of easily leachable gold in oceanic terranes 

as an explanation for the number of gold districts that 

occur in these accreted terranes. However, other 

geologic factors may be as important if not more so. For 

example, Shawe and Stewart (1976) noted a close spatial 

association of precious metal deposits with Cretaceous 

and Tertiary intrusions in Nevada, and Silberman and 

others (1976) noted both a spatial and temporal association between some precious metal districts and 

intrusive rocks. Thus, the intrusions in accreted terranes 

may have acted as more than heat engines to drive 

circulating hydrothermal systems; they may also have 

served as sources of gold. This is a viable alternative,

B18 Geology and Resources of Gold in the United States
120

 iiiiiiii

COMSTOCK

TALAPOOSA

RA B MANHATTAN 

CAMP DOUGLAS. SILVER DYKE

GILBERT 

DIVIDE

110'

MARYSVALE 

DEER TRAIL

1 1__ 

0h0

 1 

50i

i i 

50 100

100 150 MILES i i

150 KILOMETERS

Figure B9. General outline of middle and upper Miocene igneous rocks in Nevada and Utah and locations of 

gold-producing districts that have ages of mineralization within the same time frame. Medium screen, intermediate volcanic 

rocks; light screen, basalt, silicic tuff, and rhyolite; cross lined, mostly silicic tuff. Solid square, district corresponding to 

middle Miocene age rocks; solid circle, late Miocene. Modified from Silberman and others (1976).

because Farmer and DePaolo (1983) showed that 

intrusions west of the 0.7080 strontium isotope isograd 

(in the accreted oceanic terrane province) contain a 

major mantle component, whereas the intrusions east of 

the line show a major crustal component. Thus, gold in 

the upper mantle could have been concentrated by 

partial melting and introduced into the upper crust of 

accreted terranes by intrusive activity.

Although the postaccretionary Cenozoic cover of 

western and northern Nevada contains notable precious 

metal deposits (for example, Jarbidge and Comstock), 

the lack of numerous gold-producing districts in that 

terrane compared to accretionary terranes invites speculation as to what may exist beneath that cover. Based on 

the observation that most gold-producing districts of 

Nevada occur in exposed accreted terranes, major gold 

deposits possibly occur in accreted terranes that likely

underlie the Cenozoic volcanic cover. In fact, since 

most of the Cenozoic cover is volcanic, it is entirely 

possible that the magmas responsible for the volcanism 

also were responsible for either generating mineral 

leaching-transporting-depositing hydrothermal systems, 

or providing gold, or both. The cratonal Colorado 

Plateaus terrane, like this Cenozoic-covered area of 

Nevada, contains few important gold districts. Those that 

are exposed are either associated with the MarysvalePioche mineral and intrusive belt (fig. B6) or are spatially 

associated with isolated intrusions. Note, however, that 

the Precambrian terrane in southeastern Nevada and 

northwestern Arizona contains several important gold 

districts (Theodore and others, 1982). Thus, the absence 

of numerous gold districts in the Colorado Plateaus 

terrane of Utah may simply reflect younger sedimentary 

cover over gold-bearing Precambrian terrane.

United States Gold Terranes B19
The association of gold districts with igneous 

provinces and (or) structural trends in both accreted and 

cratonal terranes suggests that deep-seated structures 

may be the ultimate control on the alignments of gold 

districts. These structures most likely served as conduits 

not only for intrusive activity but also for hydrothermal 

circulation. As discussed previously for accreted terranes, the gold in these mineral belts may be either 

leached from the sedimentary pile or introduced by 

intrusive activity. At this point it is virtually impossible to 

determine the relative importance of these possible gold 

sources.

In summary, the distribution of gold-producing 

districts in Nevada and Utah seems to be controlled by 

deep-seated regional structures. That these structures 

cut across both cratonal and accreted terranes suggests 

that the structures, and not the terranes, are the most 

important regional controls on the distribution of goldproducing districts. This interpretation suggests several 

lines of research that need to be followed on a detailed, 

district-by-district basis within the different mineral belts. 

For example, Shawe and Stewart (1976) discussed the en 

echelon faults in the Pioche and Manhattan mineral belts 

and their orientation relative to those belts. However, we 

don't have a clear idea as to the nature of these faults at 

depth; for that reason, seismic and other geophysical 

studies oriented perpendicular to the different belts 

would be most illuminating. In addition, it would be 

important to compare the geochemistry and ages of 

mineralization in the different belts in hopes of identifying a mantle source for gold west of the 0.7080 

strontium isotope line and a crystalline basement source 

for gold east of that line, for those districts that can 

unequivocally be related to igneous activity. If these data 

are collected by detailed geologic mapping and integrated over the length of the mineral belts, answers 

should begin to appear regarding the origin of gold and 

associated metals in these deposits, and distribution 

patterns of the important gold-producing districts in 

Nevada and Utah should become clearer.

Manuscript received by scientific editors December 1984

REFERENCES CITED

Albers, J.P., 1983, Distribution of mineral deposits in

accreted terranes and cratonal rocks of western United

States: Canadian Journal of Earth Sciences, v. 20, no. 6,

p. 1019-1029. 

Armstrong, R.L., 1968, Sevier erogenic belt in Nevada and

Utah: Geological Society of America Bulletin, v. 79,

no. 4, p. 429-458. 

Beck, Myrl, Cox, Allan, and Jones, D.L., 1980, Mesozoic and

Cenozoic microplate tectonics of western North

America: Geology, v. 8, p. 454-456. 

Bergendahl, M.H., 1964, Gold, in Mineral and water resources

of Utah: Report of the U.S. Geological Survey in

cooperation with Utah Geological and Mineralogical 

Survey and the Utah Water and Power Board, p. 83-89.

Bonham, H.F., Jr., 1976, Gold producing districts of Nevada: 

Nevada Bureau of Mines and Geology Map 32.

Boyle, R.W., 1979, The geochemistry of gold and its deposits 

(together with a chapter on geochemical prospecting for 

the element): Geological Survey of Canada Bulletin 280, 

584 p.

Butler, B.S., Loughlin, G.F., Heikes, V.C., and others, 1920, 

The ore deposits of Utah: U.S. Geological Survey 

Professional Paper 111, 672 p.

Farmer, G.L., and DePaolo, D.J., 1983, Origin of Mesozoic and 

Tertiary granite in the western United States and 

implications for pre-Mesozoic crustal structure, 1 Nd 

and Sr isotopic studies in the geocline of the northern 

Great Basin: Journal of Geophysical Research, v. 88, 

no. B4, p. 3379-3401.

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

Economic Geology, v. 24, no. 3, p. 115-148.

Hilpert, L.S., and others, 1964, Geology, in Mineral and water 

resources of Utah: Report of the U.S. Geological Survey 

in cooperation with Utah Geological and Mineralogical 

Survey and the Utah Water and Power Board, p. 17-37.

Hilpert, L.S., and Roberts, R.J., 1964, Economic geology, in 

Mineral and water resources of Utah: Report of the U.S. 

Geological Survey in cooperation with Utah Geological 

and Mineralogical Survey and the Utah Water and Power 

Board, p. 28-34.

Jerome, S.E., and Cook, D.R., 1967, Relation of some metal 

mining districts in the western United States to regional 

tectonic environments and igneous activity: Nevada 

Bureau of Mines and Geology Bulletin 69, 35 p.

Keays, R.R., and Scott, R.B., 1976, Precious metals in oceanridge basalts Implications for basalts as source rocks for 

gold mineralization: Economic Geology, v. 71, no. 4, 

p. 705-720.

Ketner, K.B., and Wardlaw, B.R., 1981, Permian and Triassic 

rocks near Quinn River Crossing, Humboldt County, 

Nevada: Geology, v. 9, no. 3, p. 123-126.

Kistler, R.W., 1983, Isotope geochemistry of plutons in the 

northern Great Basin, in The role of heat in the 

development of energy and mineral resources in the 

northern Basin and Range province: Geothermal 

Resources Council Special Report 13, 384 p.

Kistler, R.W., and Peterman, Z.E., 1978, Reconstruction of 

crustal blocks of California on the basis of initial strontium isotopic compositions of Mesozoic granitic rocks: 

U.S. Geological Survey Professional Paper 1071, 17 p.

Misch, Peter, and Hazzard, J.C., 1962, Stratigraphy and 

metamorphism of late Precambrian rocks in central 

northeastern Nevada and adjacent Utah: American 

Association of Petroleum Geologists Bulletin, v. 46, 

no. 3, p. 289-343.

Morris, H.T., and Lovering, T.S., 1961, Stratigraphy of the east 

Tintic Mountains, Utah: U.S. Geological Survey Professional Paper 361, 145 p.

Poole, F.G., Sandberg, C.A., and Boucot, A.J., 1977, Silurian 

and Devonian paleogeography of the western United 

States, in Stewart, J.H., Stevens, C.H., and Fritsche, A.E.,

B20 Geology and Resources of Gold in the United States
eds., Paleozoic paleogeography of the western United 

States, Pacific Coast Paleogeography Symposium 1: 

Society of Economic Paleontologists and Mineralogists, 

p. 39-65.

Roberts, R.J., 1966, Metallogenic provinces and mineral belts 

in Nevada: Nevada Bureau of Mines and Geology 

Report 13, Part A, p. 47-72.

Russell, B.J., 1984, Mesozoic geology of the Jackson 

Mountains, northwestern Nevada: Geological Society of 

America Bulletin, v. 95, p. 313-323.

Shawe, D.R., 1977, Continent-margin tectonics and ore 

deposits, western United States: Society of Mining 

Engineers of A.I.M.E. Transactions, v. 262, p. 185-190.

Shawe, D.R., Poole, F.G., and Heyl, A.V., 1978, Geologic 

framework of the Cordilleran region traversed by field 

excursion C-l in eastern Nevada and western Utah: 

Nevada Bureau of Mines and Geology Report 32, p. 2-9.

Shawe, D.R., and Stewart, J.H., 1976, Ore deposits as related to 

tectonics and magmatism, Nevada and Utah: Society of 

Mining Engineers of A.I.M.E. Transactions, v. 260, 

p. 225-232.

Silberling, N.J., Jones, D.L., Blake, M.C., Jr., and Howell, D.G., 

1984, Lithotectonic terrane maps of the North American 

Cordillera, Part C Lithotectonic terrane map of the 

western conterminous United States, in Silberling, N.J., 

and Jones, D.L., eds., Lithotectonic terrane maps of the 

North American Cordillera: U.S. Geological Survey 

Open-File Report 84-523, p. C1-C43, scale 1:250,000.

Silberling, N.J., and Roberts, RJ., 1962, Pre-Tertiary stratigraphy and structure of northwestern Nevada: 

Geological Society of America Special Paper 72, 58 p.

Silberman, M.L., McKee, E.H., and Stewart, J.H., 1976, 

Igneous activity, tectonics, and hydrothermal mineralization in the Great Basin during Cenozoic time: 

Society of Mining Engineers of A.I.M.E. Transactions, 

v. 260, p. 253-261.

Snoke, A.W., 1980, Transition from infrastructure to suprastructure in the northern Ruby Mountains, Nevada, in 

Crittenden, M.D., Jr., Coney, P.J., and Davis, G.H., eds., 

Cordilleran metamorphic core complexes: Geological 

Society of America Memoir 153, 490 p.

Speed, R.C., 1977, Island-arc and other paleogeographic terranes of Late Paleozoic age in the western Great Basin, 

in Stewart, J.H., Stevens, C.H., and Fritsche, A.E., eds., 

Paleozoic paleogeography of the western United States, 

Pacific Coast Paleogeography Symposium 1: Society of 

Economic Paleontologists and Mineralogists, p. 349-362.

___ 1979, Collided Paleozoic microplate in the western 

United States: Journal of Geology, v. 87, 

p. 279-292.

Stewart, J.H., 1980, Geology of Nevada: Nevada Bureau of 

Mines and Geology Special Publication 4, 136 p.

Stewart, J.H., Moore, W.J., and Zietz, Isidore, 1977, East-west 

patterns of Cenozoic igneous rocks, aeromagnetic 

anomalies, and mineral deposits, Nevada and Utah: 

Geological Society of America Bulletin, v. 88, p. 67-77.

Theodore, T.G., Blair, W.N., and Nash, J.T., 1982, Preliminary 

report on the geology and gold mineralization of the 

Gold Basin-Lost Basin mining districts, Mohave county, 

Arizona, with a section on K-Ar chronology of mineralization and igneous activity by E.H. McKee and 

implications of the compositions of lode and placer gold 

by J.C. Antweiler and W.L. Campbell: U.S. Geological 

Survey Open-File Report 82-1052.

Tooker, E.W., 1971, Regional structural controls of ore 

deposits, Bingham mining district, Utah, U.S.A., in 

International association on the genesis of ore deposits, 

Tokyo-Kyoto meetings, papers and proceedings: Society 

of Mining Geologists of Japan Special Issue 3, p. 76-81.

___1983, Correlation of metal occurrence and terrane 

attributes in the northwestern conterminous United 

States: Canadian Journal of Earth Sciences, v. 20, no. 6, 

p. 1030-1039.

United States Gold Terranes B21
Gold-Silver Deposits Associated with the 

Trans-Challis Fault System, Idaho

ByThor H. Kiilsgaard, Frederick S. Fisher, andEar\ H. Bennett1

Abstract

Many gold-silver deposits in central Idaho, including 

those of the productive Boise Basin, are located near or along 

northeast-trending faults of the trans-Challis fault system. 

Some of the deposits are hosted in granitic rocks of the Idaho 

batholith of Late Cretaceous age, but many are along or 

partially within Tertiary dikes. Other deposits are in Tertiary 

plutonic rocks, or in dikes that cut Tertiary plutonic rocks. In 

the northeast part of the Challis 1°x2° quadrangle, several 

gold-silver deposits of the trans-Challis fault system are 

related to bodies of Tertiary rhyolite, whereas others are in 

Precambrian sedimentary rocks, in Paleozoic and Precambrian roof pendants in the Idaho batholith, and in pyroclastics and lavas of the Challis Volcanics. The northeasttrending belt of regional faults, Tertiary intrusive rocks, and 

mineral deposits extends at least 270 kilometers across 

Idaho and probably into Montana. The extent and linearity of 

the northeast-trending fault system, the grabens and 

cauldrons aligned along the faults, the igneous rocks of 

Tertiary age that have been intruded along the fault system, 

many of them also aligned along the faults, and postintrusive 

adjustment along the faults indicate a major zone of rifting 

and crustal extension that has guided emplacement of the 

mineral deposits.

INTRODUCTION

A broad system of northeast-trending, subparallel, 

high-angle faults, aligned grabens and eruptive centers, 

and roughly aligned intrusive rocks of Tertiary age 

extends across the Challis 1° x 2° quadrangle (Fisher and 

others, 1983). This broad structural system, identified as 

the trans-Challis fault system (Bennett, 1984; Kiilsgaard 

and Lewis, 1985, p. 20-42), has been traced from the 

vicinity of Idaho City in the Boise Basin northeastward to 

beyond Leesburg, a distance of at least 270 km (fig. BIO), 

and has exerted structural control on the location of

80 KILOMETERS

^daho Geological Survey, University of Idaho, Moscow, Idaho. 

B22 Geology and Resources of Gold in the United States

Figure B10. Location of the Challis 1° x 2° quadrangle and 

the trans-Challis mineralized area, Idaho.

gold-silver deposits in the area. The system is aligned 

with and appears to be a continuation of the Great Falls 

lineament, projected by O'Neill and Lopez (1985) 

northeast from Idaho across Montana.
TRANS-CHALLIS FAULT SYSTEM

Faults of the trans-Challis fault system have been 

mapped in the Boise Basin (fig. Bll; Kiilsgaard, unpub. 

mapping, 1985). The faults are particularly evident along 

Mores, Elk, Grimes, Big Muddy, Little Muddy, and West 

Fork Clear Creeks, and across Wild Goat Creek and 

Rattlesnake Creek (Pioneerville, Placerville, Idaho City, 

and Warm Springs Point 7V2-minute quadrangles). A 

northeast-trending shear zone described by Ballard 

(1924) as being half a mile or more wide near the Gold 

Hill mine in the Boise Basin (fig. Bll) is the westernmost 

known fault of the system. That fault defines the western 

edge of the most intensively mineralized part of the Boise 

Basin mineralized area. Southwest of Idaho City, several 

faults of the system pass beneath an embayment of basalt 

of the Snake River Group of Pleistocene age. Northeasttrending faults in the vicinity of Idaho City are mentioned 

by Lindgren (1898) and Anderson (1947).

The northeast-trending faults are well exposed 

about 30 km west of Stanley in the upper reaches of 

Warm Springs, Eightmile, and Cat Creeks (Fisher and 

others, 1983). Some fault zones in this area are more 

than 500 m wide, and the sheared and pulverized granitic 

rocks of the Idaho batholith within the zones are so 

altered that their original composition is difficult to 

determine (Luthy, 1981). Tertiary granite and dioritic 

rock, in part elongate along the fault system and in part 

fault bounded, are exposed in the faulted area, as are 

swarms of Tertiary dikes that are elongate along the 

system. Locally, the Tertiary plutonic rocks are offset in 

a left-lateral sense along the faults. Many of the dikes 

also have been offset by post-dike fault movement.

A gap in the fault system appears northeast of 

Casto (fig. Bll). Adjacent to and southeast of the gap are 

the Custer graben and the Twin Peaks caldera, which are 

considered to be part of the fault complex, although not 

aligned within it. The Van Horn Peak cauldron complex 

(Fisher and others, 1983) also occupies part of the gap. 

Within the gap and in the Custer graben and the Panther 

Creek graben are numerous quartz porphyry and rhyolite 

dikes, pods, irregular plugs, and domes, many of which 

are linear and coincident with the trans-Challis fault 

system. The rhyolites were emplaced at high levels in the 

crust, and several vented to the surface. Most of the plugs 

and domes are small (less than 2.5 km2 ); however, one 

complex rhyolitic stock is exposed over about 129 km2 

(Hardyman and Fisher, 1985). The rhyolites range in age 

from 48 to 39 Ma (Fisher and others, 1983) and can be 

shown locally to have been emplaced along preexisting 

faults of the trans-Challis fault system. In places the 

rhyolites have been offset by younger faulting.

The Panther Creek graben, similar to the Custer 

graben, is bounded on the southeast side by faults of 

great displacement (Mclntyre and others, 1982), which

continue on to the northeast, where Bunning and Burnet 

(1981) have identified the zone as the Panther Creek 

fault. The fault is aligned with a broad set of northeasttrending faults that are exposed west of Stanley. Other 

northeast-trending faults are exposed near Shoup and 

Gibbonsville (fig. Bll).

Three major northwest-trending faults, Sawtooth, 

Bear River-Montezuma, and Deer Park, terminate 

against the trans-Challis fault system (Kiilsgaard and 

Lewis, 1985). The northwest-trending faults do not 

appear to have been truncated and displaced by the 

trans-Challis faults, as no evidence of them has been 

found northwest of that system. Instead, the trans-Challis 

faults appear to be older and the northwest-trending 

faults simply terminated at intersections with the older 

faults. In the eastern part of the Challis quadrangle, many 

north-trending faults also appear to terminate against the 

trans-Challis fault system (Fisher and others, 1983), 

further evidence of the controlling effect of the system.

Age of Faulting

Field evidence indicates that movement along the 

trans-Challis fault system may have been recurrent from 

Precambrian to Holocene time. According to Lopez 

(1981), the Panther Creek fault offsets the contact 

between the Early and Middle Proterozoic Yellowjacket 

Formation and 1,370 Ma plutonic rock southwest of 

Leesburg. At the contact locality, the Panther Creek fault 

is defined, in part, by tight isoclinal folds in the Yellowjacket Formation; truncation of the folds by the 1,370 Ma 

plutonic rocks indicates Precambrian movement along 

the fault (O'Neill and Lopez, 1985). Hughes (1983) 

described northeast-trending transverse faults in the 

vicinity of Blackbird and noted how movement along 

these faults imposed damming effects on turbidity 

currents that deposited sediments of the Proterozoic 

Yellowjacket Formation. The northeast transverse faults 

fit in the trans-Challis fault system. Faults of the system 

clearly displace granitic rocks of the Idaho batholith of 

Late Cretaceous age and have guided emplacement of 

Eocene plutonic rocks and rhyolites and younger dikes. 

Subsequent movement along the faults has displaced the 

Eocene rocks. Stream terraces that contain glacial erratics of probable Pleistocene age have been displaced by 

Holocene faults. A dense concentration of recent 

earthquake epicenters (Breckenridge and others, 1984) 

in the area north and northwest of Stanley is indicative of 

continuing movement along the trans-Challis fault 

system.

United States Gold Terranes B23
115°

EXPLANAT

MINES AND PROSPECTS

ILLINOIS

GAMBRINUS

WASHINGTON

50 OWL CREEK

51 BIG LEAD

52 BRITTANic

53 KENTUCK (GOLD HILL)

54 CLIPPER BULLION

55 GRUNTER

56 MONOLITH

57 SAGE CREEK

58 ULYSSES

59 Km IE BURTON

60 GOLDEN REWARD

61 RED STAR

62 BIG FOUR

63 TWIN BROTHERS

64 LAMOREAUX

65 CORN BEEF

66 ANDERSON

67 ADM&R

68 CLARA MORRIS

FAULT, BAR ON THE 

DOWNTHROW) SIDE 	GOLD HILL

8 MINERAL HILL

9 MISSOURI

10 COMBACK

11 GOLDEN AGE

12 CUMO

13 MAMMOTH

14 GOLDEN CHARIOT

15 GOLDEN CYCLE

16 SLOPER

17 BANNER

18 LITTLE FALLS

19 MILLER MTN.

20 IDAHO BIRTHDAY

21 BRONCO (MOUNTAIN GIRL)

22 IRON CROWN

23 GOLDEN DAY

24 BUCKSKIN

25 VALLEY VIEW

26 RED MTN.

27 MORRiSON

28 LUCKY BOY

29 GENERAL CUSTER

30 CHARLES DICKENS

31 GOLDEN SUNBEAM

32 MONTANA

33 McFADDEN

34 LOST PACKER

35 PARKER MTN.

36 WILLIAMS

37 SINGHEISER

38 RABBIT FOOT

39 MEYERS COVE

40 YELLOWJACKET

41 U. P.

42 GOLD RIDGE

43 GOLD DUST

44 GOLD FLINT

45 ITALIAN

46 HAIDEE

47 BEAVER CREEK

48 SHOO FLY

49 BOBCAT GULCH

MINING DISTRICTS

(Ross, 1936) 

A STANLEY 

B YANKEE FORK 

C LOON CREEK 

D YELLOWJACKET 

E MACKINAW (LEESBURG) 

F MINERAL HILL 

G INDIAN CREEK 

H DAHLONEGA (GIBBONSVILLE)

Figure B11. The trans-Challis fault system and location of associated gold-silver deposits.

MINERALIZED LOCALITIES ASSOCIATED 

WITH THE TRANS-CHALLIS FAULT 

SYSTEM

Many mineral deposits in central Idaho show a 

spatial relation to the trans-Challis fault system (figBll),

and they appear to be genetically related to structures of 

the system and to Tertiary rocks that have been intruded 

along it (Kiilsgaard and Bennett, 1985). The deposits 

form a belt that consists, for the most part, of gold-silver 

deposits, in many of which silver output has exceeded 

that of gold but in which gold has been the principal

B24 Geology and Resources of Gold in the United States
metal in terms of value. Byproduct metals produced 

include lead, zinc, and copper. Several molybdenumcopper deposits in the faulted area have been explored, 

but none have been brought into production. Fluorspar 

has been mined from deposits in the Panther Creek 

graben and uranium from deposits at the southwest end 

of the Custer graben. Productive gold-silver deposits and 

some prospects along the fault system are shown in figure 

Bll. They include mines in the vicinity of Gibbonsville 

and Leesburg in the northeast part, deposits in the 

Panther Creek graben, the Twin Peaks caldera, and the 

Yankee Fork mining district in the central part, and those 

in the Boise Basin and nearby localities in the southwest 

part. Of these mineralized localities, the Boise Basin has 

been, by far, the largest gold producer.

Southwest Part

Boise Basin

More gold has been produced from the Boise Basin 

than any other mining locality in Idaho. The basin, a 

physiographic feature, is in the southwest part of the 

trans-Challis fault system (fig. Bll). Within the basin are 

the Pioneerville, Centerville, Quartzburg, Mores Creek, 

and Gambrinus mining districts (Ross, 1936). (For 

purposes of this report the Grimes Pass and Summit Flat 

mining districts also are included even though parts of 

these latter districts are topographically north of the 

basin.)

Boise Basin is underlain by granitic rocks of the 

Idaho batholith of Late Cretaceous age. Intrusive into 

these granitic rocks are northeast-trending Tertiary 

stocks (fig. B12) and dikes, the emplacement of which 

has been guided by faults of the trans-Challis system. 

Depiction of the distribution of dikes on figures Bll and 

B12 is precluded by the small scales of the maps. Near 

Idaho City the Payette Formation of Miocene age is 

more than 200 meters thick; basalt is intercalated in the 

Payette. Northwest and southwest of Placerville, similar 

basalt, identified as the Weiser Basalt of the Columbia 

River Basalt Group (Kiilsgaard and Lewis, 1985), rests 

unconformably on an eroded surface of Idaho batholith. 

Two patterns of gold-bearing quartz veins, one trending 

northeast and the other northwest, crop out in the basin. 

Erosion of the veins has formed placer deposits that have 

yielded about 75 percent of the gold produced from the 

basin.

History and Production

Placer gold was discovered near the present site of 

Centerville (fig. B12) in 1862 and lode deposits were 

discovered soon thereafter. The Gold Hill lode deposit 

(fig. Bll), discovered in 1863, was worked almost 

continuously until 1938 (Anderson, 1947). In 1867 and 

1868 at least 10 stamp mills in Boise Basin were treating

free-milling oxidized gold ore, but after a period of 

activity and considerable production many of these were 

dismantled, in part because ore bodies were exhausted 

but also because deeper sulfide ores could not be treated 

by the stamp-amalgamation process (Jones, 1916). Aside 

from the Gold Hill mine, most lode mining in Boise 

Basin has been sporadic. A spurt of mining activity in the 

1920's resulted in the discovery of at least one significant 

gold producer, the Comeback mine, and in the expanded 

output of others; but mining was curtailed in 1931 by a 

forest fire that destroyed the surface plants of several 

mines in the northwest part of the basin. Lode mining 

since World War II has consisted of small-scale sporadic 

efforts at several mines and prospects, but no significant 

production of gold. No mines were being worked in 1988, 

and most mine workings were caved or otherwise 

inaccessible.

More placer gold was produced from the Boise 

Basin in the 9 years following discovery (Lindgren, 1898) 

than during any other similar length of time. Placer 

mining led directly to lode discoveries, with some rich 

placers being mined up to the vein outcrop, as at the 

Illinois vein, north of Idaho City, where rich placer gold 

was sluiced from surface material at the vein outcrop 

(Lindgren, 1898). No rich placers have been found 

upstream from presently known vein outcrops. Early-day 

placer mining was by sluicing, although hydraulic mining 

was employed on higher bench gravels. The largest 

deposit to be mined by hydraulic jets is about 1 km north 

of Idaho City, where auriferous gravel was reported by 

Ballard (1924) to have an average depth of 60 feet, a 

value per cubic yard of $0.0979, at a gold price of $20.67 

per troy oz, and a ratio of gold to silver in bullion of about 

8:1. According to Ballard (1924) gold dredging started 

near Placerville in 1898. Early-day dredgable placer 

ground was richer in gold than was placer gravel dredged 

in later years. Placer gravel near Placerville, dredged 

from 1905 to 1909, is reported to have averaged 30 feet 

in depth and $0.30 per cubic yard (gold at a price of 

$20.67/oz) (U.S. Geological Survey, 1909). Dredged 

gravel along Mores and Grimes Creeks in the 1940's 

ranged in value from $0.11 to $0.22/yd3 (U.S. Bureau of 

Mines, 1942-1948), with gold at a price of $35.00/oz. 

Bullion obtained from dredging in the 1940's had an 

average gold-silver ratio of 4.3:1. Dredging in the basin 

terminated in 1951.

The total amount of gold produced from the Boise 

Basin is a subject of dispute because of incomplete 

early-day records, because of the difficulty of separating 

gold produced from Boise Basin from that produced at 

other localities in Boise County, and because some of the 

gold that was mined was not reported. Lindgren (1898) 

used U.S. Mint reports and other sources of data to 

prepare gold production statistics for the years 1863- 

1896. Jones (1916) updated production statistics from

United States Gold Terranes B25
116 e OO' 115M5'

44° 

00'

43« 

45'

SUNSET PEAK

EXPLANATION

l-H-4-1

Granite 

Diorite complex

Fault

Vein showing strike 

Number keyed to list 

MINES AND PROSPECTS

1. Mountain Chief

2. Belshazzar

3. Crown Point

4. Newburg

5. Silver Star

6. Mayflower

7. Blue Rock

8. Silver Hill

9. Bold Hill

10. Last Chance

11. Coin Bond

12. Hartford

13. Black Bear

14. Sold Dollar

15. Silver Bell

16. Saunders

17. Mineral Hill

18. Buckskin

19. Grandview

20. Missouri

21. J.S.

22. Oro

S3. Mountain Queen

24. Silver Bern

25. Mieslng Link

26. Bruser

27. Golden Age

28. Smuggler

29. St. Clair

30. Comebeck

31. Clear Creek

32. Coon Dog

33. Independence

34. Grimes Homestake

35. Mohawk

36. Enterprise

37. Overlook

38. K.C.

39. Bray Eagle

40. Branson

41. Black Jack

42. McKinley

43. K.M.

44. Big Gulch

45. Bert Day

46. Boomer

47. Blue Bird

48. Mud Springs

49. Mattle

50. Twin Sister

51. Summit

52. Big Ben

53. Cash Register

54. Antimony Lode

55. Blaine

56. Illinois

57. Lucky Boy

58. Mascot

59. Eureka

60. Texida

61. Cleveland

62. Orphan

63. Accident

64. Gambrinus

65. Boulder

66. MacCarthy

67. Forest King

68. Subrosa

69. Washington

70. Elkhorn

71. Hayfork

72. Red Lode

73. Smiths

74. Mammoth

75. Sloper

76. Golden Cycle

77. Solden Chariot

78. Edna

79. Little Falls

80. Hole in the Wall

81. CUMO

B2. Forrex

83. Morning Mist

Figure B12. Boise Basin, Idaho, showing locations of gold-silver veins (identified by mines and prospects) with respect to 

faults of the trans-Challis fault system and to stocks of Tertiary age (modified in part from Anderson, 1947).

1863 to 1914, and Anderson (1947) further updated gold 

production statistics.

Table Bl, based on production statistics from 

Anderson (1947) for the years 1863-1940 and U.S. 

Bureau of Mines data for subsequent years, updates gold

production in Boise County (principally Boise Basin) to 

1982. Gold-silver production from 1941 to 1982 is shown 

in table B2. The accumulated output of 2,818,596 oz of 

gold makes Boise Basin the largest gold producer in 

Idaho.

B26 Geology and Resources of Gold in the United States
Table B1. Gold production from Boise County (principally Boise Basin), Idaho, 1863-1982

[Production statistics 1863-1940 from Anderson (1947); other statistics from U.S. Bureau of Mines Minerals Yearbooks 

(1932-1983) and unpublished data. Annual production figures from 1953 to 1980 commonly available only as combined 

lode and placer (see table B2) and are summarized in this table as total gold. From 1911 to 1970, 98 percent of the gold 

produced in Boise County came from deposits in Boise Basin. A similar percentage probably holds for gold produced in 

Boise County from 1863 to 1910. Value is based on the price of gold at the time of production; for the period 1968-1980, 

value is based on the average annual price of gold; data from U.S. Bureau of Mines (1924-31; 1932-83). Leaders ( ), no 

production or no data available]

Year

Lode gold

Troy 

ounces Value

Placer gold 

Troy 

ounces Value

Total gold

Troy 

ounces Value

Boise County

1863- 70

1871- 80

1881- 90

1891-1900

151,414

133,166

106,737

93,143

$ 3,130,000

2,752,780

2,206,452

1,925,444

1,362,724

247,307

87,330

62,096

$28,170,000

5,112,306

1,805,279

1,283,630

1,514,138

308,473

194,067

155,239

$31,300,000

7,865,086

4,011,731

3,209,074

484,460 $10,014,676 1,759,457 $36,371,215 2,171,917 $46,385,891

Boise Basin

1901-

1911-

1921-

1931-

1941-

1951-

10

20

30

40

50

55

46,351

84,033

64,463

54,079

6,421

305

$ 958,155

1,737,122

1,332,571

1,732,584

224,735

10,675

67,673

120,629

14,094

109,580

72,539

4,929

$1,398,932

2,493,625

291,350

3,783,530

2,538,865

172,515

114,024

204,662

78,557

163,659

78,960

5,711

$ 2,357,087

4,230,747

1,623,921

5,516,114

2,763,600

199,885

255,652 $ 5,995,842 389,444 $10,678,817 645,096 $16,674,659

TOTAL 

Boise County

1956- 60

1961- 70

1971- 80

1981- 82

16

513

$560

18,653

185

19

$6,475

665

512

932

139

$17,920

33,940

35,600

529 $ 19,213 204 $7,140 1,583 87,460 

740,641 $16,029,731 2,149,105 $47,057,172 2,818,596 $63,148,010

Almost as much silver as gold was produced from 

Boise County, from 1863 to 1914 (Jones, 1916). If 

gold-silver production from 1942 to 1980 (table B2) is 

indicative, the amount of silver mined from Boise Basin 

lode deposits exceeds the amount of gold.

Lode Deposits

Two groups of veins in the Boise Basin have been 

described by Anderson (1947). Veins of one group are

found only in rock of the Idaho batholith, they generally 

strike west and northwest, they are chiefly quartz with a 

scanty content of sulfide minerals, and they show feeble 

wall-rock alteration. These veins are chiefly north of 

Idaho City (fig. B12), were productive only to shallow 

depths, and produced gold valued at perhaps less than 

$2,000,000; but they probably contributed most of the 

placer gold mined from Mores Creek and some of its 

tributaries. The veins formed at shallow depths and were

United States Gold Terranes B27
Table B2. Gold-silver production from Boise County (principally from Boise Basin), Idaho, 1941-1982

[Data from U.S. Bureau of Mines (1924-31; 1932-83). Leaders (- -), no production or no data available. Gold values 

1968-1980 based on the average annual price of gold]

Year

Lode

Troy

ounces

gold

Value

Placer gold

Troy

ounces Value

Total

Troy

ounces

gold

Value

Silver

Troy

Lode

ounces

Placer

Boise Basin

1941

1942

1943

1944

1945

1946

1947

1948

1949

1950

1951

1952

1953

1954

1955

2,302

1,597

370

361

329

198

260

694

106

204

84

57

164

 ~

$80,570

55,895

12,950

12,635

11,515

6,930

9,100

24,290

3,710

7,140

2,940

1,995

5,740

 

20,758

13,112

35

65

1,635

7,706

7,864

11,733

4,789

4,842

4,926

3

$726,530

458,920

1,225

2,275

57,225

269,710

275,240

410,655

167,615

169,470

172,410

105

23,060

14,709

405

426

1,964

7,904

8,124

12,427

4,895

5,046

5,010

60

326

164

151

$807,100

514,815

14,175

14,910

68,740

276,640

284,340

434,945

171,325

176,610

175,350

2,100

11,410

5,740

5,285

34,484

33,795

5,573

6,819

1,644

1,734

116

1,991

3,107

1,033

73

771

268

2,392

957

5,504

3,250

10

17

391

1,750

1,453

2,528

1,243

1,212

1,306

 ~

Boise County

1956

1957

1958

1959

1960

1961

1962

1963

1964

1965

1966

1967

1968

1969

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

Total 

16

113

13

21

162

81

123

7,255

560

3,955

455

735

5,670

3,362

4,476

$254,623

185

19

77,672

6,475

665

$2,718,520

15

93

175

28

201

132

79

13

21

175

162

146

81

123

80

28

3

28

86,254 $3

525

3,255

6,125

980

7,035

4,620

2,765

455

735

6,125

5,670

5,732

3,362

4,476

12,779

4,746

923

17,152

,050,945

5

1,174

3,529

1,294

14

757

1,734

513

761

1,155

55

848

89

335

107,020

41

2

18,707

B28 Geology and Resources of Gold in the United States
considered by Anderson (1947) to be of questionable 

early Tertiary age. The second group, the Miocene veins 

of Anderson (1947), are in or near porphyry dikes and 

stocks of Tertiary age, and they generally strike northeast 

more or less parallel to dikes and faults in a mineralized 

belt that trends northeast across the basin. They are 

characterized by distinctive sulfide mineral assemblages, 

and widespread and conspicuous wall-rock alteration 

effects. These veins have produced most of the lode gold 

mined in the area.

Quartz is the principal gangue mineral in the veins, 

and three stages of quartz were described by Anderson 

(1947), the last two in breccias of earlier quartz. The 

youngest and most abundant quartz is rather coarsely 

crystalline and somewhat drusy, and it commonly shows 

comb structure. Locally, it contains grains of native gold 

and auriferous pyrite and is considered the most important guide to ore.

Veins of the northeast-trending mineralized belt 

probably are genetically related to dikes (Ballard, 1924). 

The principal veins extend along northeast-trending 

shears; they may parallel dikes, be within dikes, or may 

crosscut dikes at acute angles. Some mineralized shears 

are in the hydrothermally altered granitic country rock, 

but some of the more productive ore bodies occurred at 

the intersections of mineralized shears and dikes. 

According to Ballard (1924) the Gold Hill vein, the most 

productive vein in the basin, is in a northeast-trending 

shear zone half a mile or more wide that cuts across 

numerous rhyolite dikes. Near the surface, the productive segments of the vein cut granitic rock of the 

Idaho batholith and dacite- and rhyolite-porphyry dikes. 

At depth most of the ore came from shear zones oblique 

to the Gold Hill vein, at intersections of the shear zones 

and rhyolite dikes. The shear zones in hydrothermally 

altered granitic rock were gouge-filled, tight, and 

impermeable. At intersections with the brittle rhyolite 

dikes, the shears resolved into counties^ seams and 

fractures which were more permeable to mineralizing 

solutions than was the impermeable clay-enriched 

granitic country rock. Mineralized quartz veins along the 

shears rarely extended more than a meter or so away 

from the shattered dikes.

Veins in the Boise Basin vary in size, but most of 

them are small. They range from a few centimeters to 

2 m in thickness and are as much as a few hundred 

meters in length. The largest vein, the Gold Hill, had a 

developed length of about 1,070 m and a maximum width 

of about 2 m. On the 400 level, where the bottom of the 

productive part of the Gold Hill vein was reached, the 

stope length of the vein had decreased to 305 m 

(Anderson, 1947). Gold Hill ore shoots at dike-fault 

intersections were from 1 to 12 m wide, and had stope 

lengths of more than 30 m and vertical dimensions 

ranging from 30 to 245 m. The ore shoots persisted to the

1100 level, but ore of minable grade was not found on 

the 1250 level, and the mine was closed. The Mountain 

Chief, Belshazzar, Mayflower, and Golden Age mines, all 

in the northeast-trending belt, were developed extensively and mined to about 120 m below the surface. Other 

lodes in the basin were mined to shallower depths.

Tenor of Ore

The grade of ore in Boise Basin lode mines was 

richer in oxidized parts of the veins than in the underlying 

sulfide zone. Early-day ore at the Gold Hill mine 

averaged about 1.0 oz Au/ton (Lindgren, 1898), but 

230,100 tons of ore produced from deeper levels of the 

mine, from 1911 to 1923, had an average grade of 0.41 oz 

Au/ton (Ballard, 1924). A total of 30,256 tons of ore 

produced in 1930-1931 had an average grade of 0.379 oz 

Au/ton (Minerals Yearbooks of the U.S. Bureau of 

Mines). The average grade of Gold Hill ore appears to 

have been comparable to that of other mines, which 

apparently ranged from 0.2 to 0.5 oz Au/ton. The grade 

of ore in all the mines was irregular, and small pockets 

and stringers of rich ore commonly were interspersed in 

large volumes of low-grade material.

Mineralogy

Complex mineral suites from Boise Basin lode 

deposits were described by Anderson (1947), Ballard 

(1924), and Ross (1937). According to Ballard, auriferous pyrite is the predominant sulfide in the lode 

deposits. The gold is disseminated as minute particles 

and in varied quantities in the pyrite. At the Belshazzar 

mine, pyrite in vein quartz consistently assayed 0.50 oz 

Au/ton or more, whereas pyrite elsewhere along the vein 

assayed 0.10-0.20 oz Au/ton (Ballard, 1924). Ross 

(1937) described a sample of pyrite taken from a seam on 

the 100 level of the Gold Hill mine, away from the sloped 

area, as containing 0.205 oz Au/ton and 4.33 oz Ag/ton. 

Arsenopyrite also occurs in small amounts in various 

lode deposits, and a sample of it taken 76 m below the 

surface at the Mountain Chief mine assayed 0.55 oz 

Au/ton.

In oxidized parts of veins, gold particles were 

coarser in size than was gold recovered from underlying 

sulfide zones. Nuggets found in placers near vein 

outcrops also were far larger than particles of gold found 

in veins. The larger sizes suggest mobilization and 

accretion of gold during the process of oxidation and 

supergene enrichment (Lesure, 1971; J.C. Antweiler, 

oral commun., 1984). Ballard (1924) recognized this fact, 

and he described gold-bearing iron oxide sludge that

United States Gold Terranes B29
collected on the wall of a crosscut at the Gold Hill mine. 

Two samples of the iron-oxide sludge assayed 0.12 oz 

Au/ton. A sample of similar material that collected on 

mine timbers in the Belshazzar mine assayed 0.10 oz 

Au/ton. Ross (1927) also described supergene-enriched 

gold ore bodies in Tertiary lavas of central Idaho.

Galena, sphalerite, chalcopyrite, and tetrahedrite 

are common minerals in the lode deposits, particularly 

those in the northern part of the basin, in the area north 

of Pioneerville (fig. B12). However, these minerals do 

not occur in sufficient quantity to be mined solely for 

their base metal content.

According to Ballard (1924) the gold of Boise 

Basin invariably was associated with bismuth. At Gold 

Hill, where ore shoots formed at the intersections of 

faults and rhyolite dikes, the highest content of gold was 

found with bismuth minerals. Several bismuth minerals 

were found in veins in the vicinity of Quartzburg 

(fig. B12), including bismuthinite, beegerite, cosalite, 

lillianite, galenobismutite, and tetradymite (Ballard, 

1924; Ross, 1937). Anderson (1947) recognized native 

bismuth in the Gold Hill mine and matildite at the nearby 

Mayflower mine. All three authors called attention to the 

association of native gold and bismuth minerals. Silverbearing minerals identified in vein deposits include 

miargyrite, pyrargyite, tetrahedrite, argentite, andorite, 

electrum, and native silver (Anderson, 1947); they were 

most abundant in the northern part of the basin. The 

volume of silver produced from mines in that locality was 

14 times that of gold. Stibnite occurs in a few of the veins 

but in minor amounts.

Molybdenum-copper Deposits

Although gold and silver generally have been the 

metals sought in Boise Basin, principal mineral exploration in the area in the late 1970's and early 1980's was 

directed at two molybdenum-copper deposits, in the 

northeast-trending belt of veins (fig. B12). At the CUMO 

deposit, extensive diamond drilling by the AMAX Corp. 

and other companies indicated that Tertiary rhyolite 

porphyry dikes and contiguous Cretaceous biotite 

granodiorite contain veinlets and disseminations of 

molybdenite and chalcopyrite. The deposit is cut by a 

post-mineral rhyolite dike. DJ. Baker (oral commun., 

1985) estimated the CUMO deposit to contain 1 billion 

tons of material, the average grade of which is 0.10 

percent MoS2 . A swarm of rhyolite dikes crop out in the 

vicinity of the CUMO deposit and continue on to the 

northeast. The Little Falls molybdenum deposit is in the 

dike swarm, about 5.5 km northeast of the CUMO 

deposit. Veinlets of molybdenite cut rhyolite dikes at the 

Little Falls deposit, and also occur in contiguous 

Cretaceous biotite granodiorite of the Idaho batholith. 

Fission-track dating of zircon from a rhyolite dike at the 

deposit gave an age of 29.3± 1.7 Ma (P.A.M. Andriessen,

written commun., 1982). Molybdenite veinlets that 

cut the rhyolite dike, therefore, are younger. Abella 

Resources drilled the deposit extensively in 1978-1981. 

About 2,500 m of core from the Abella drill holes gave a 

weighted average grade of 0.05 percent MoS2 .

Banner Mine

The Banner mine and nearby prospects are in 

Boise County, Idaho, about 30 km northeast of Idaho 

City. Veins at the Banner mine were discovered in 1866, 

and during the height of production, from 1878 to 

1906, the mine produced more than 3,000,000 oz of silver 

(M.G. Hansen, unpub. data, 1935). Bullion from the 

mine had a gold:silver ratio, in dollar value, of 0.4:1 

(Anderson and Rasor, 1934). Mining activity at the 

Banner mine declined in 1906, and little ore has been 

produced since then.

The Banner mine area is underlain by biotite 

granodiorite of the Idaho batholith. Cutting the granodiorite are a number of rhyolite dikes of Tertiary age 

that follow northeast-trending shear zones of the transChallis fault system. Twelve en echelon veins crop out in 

the vicinity of the Banner mine. The veins follow the 

northeast-striking faults and dikes, although at least one 

vein is known to crosscut a rhyolite porphyry dike. A 

rhyolite dike cuts what is probably the northeast 

extension of the Crown Point vein, and a mafic dike along 

the vein system is younger than the mineralized veins 

(Anderson and Rasor, 1934). The veins are of fissurefilling origin and range in width from a few centimeters to 

a meter or so; ore values vary widely. The Banner vein, a 

principal producer, ranged from 1.5 to 3 cm in width on 

the lowest drift level, which was 160 m below the outcrop, 

whereas the Crown Point vein averaged about 1 m in 

width, was characterized by erratic ore values, and was 

not mined below the 450 level (Anderson and Rasor, 

1934).

Principal silver-ore minerals, according to 

Anderson and Rasor (1934), were pyrargyrite and owyheeite, with lesser proustite, miargyrite, and tetrahedrite. 

Additional silver-bearing minerals in oxidized parts of 

the Banner veins include argentite, stephanite, native 

silver, polybasite, and cerargyrite (Shannon, 1926). 

Galena, sphalerite, and chalcopyrite occurred in the veins 

but not in sufficient quantities to be minable by 

themselves. On the lowest level of the Banner mine, the 

ore minerals formed faint narrow parallel bands in 

quartz, which was drusy and showed comb structure. 

Some ore minerals were brecciated by recurrent 

movement along the fissures during mineralization 

(Anderson and Rasor, 1934).

Attitudes and dike associations of the Banner veins 

are similar to those of the Boise Basin. The character of 

the ore minerals and accompanying quartz and the 

nature of the veins suggest they are epithermal.

B30 Geology and Resources of Gold in the United States
Central Part 

Stanley District

History and Production

Placer gold was discovered in the Stanley district in 

1863, and most placer mining activity was in the 1870's 

and 80's, with a resumption of placer mining during the 

1930's. The total amount of gold produced from placers 

in the district is unknown. Placer gold mined prior to 

1900, calculated from reported dollar values, amounted 

to about 20,800 oz, whereas reported production since 

1900 totaled 6,716 oz (Fisher, 1987, tables 10 and 11). A 

number of small lode mines and prospects are known, of 

which the Valley Creek, Buckskin, and Bronco 

(Mountain Girl) mines (fig. Bll) are the only gold-silver 

producers of record. These three mines, worked 

intermittently from 1904 to 1942, yielded 5,284 tons of 

ore from which was recovered 1,583 oz gold, 33,949 oz 

silver, 2,053 Ibs copper and 73,050 Ibs lead (Van Noy and 

others, 1986, table 20).

Lode Deposits

Gold-silver lode deposits in the Stanley district are 

chiefly small discontinuous quartz veins and mineralized 

shears that cut granodiorite of the Idaho batholith. The 

Iron Crown, Golden Day, and Bronco (Mountain Girl) 

deposits, and many small prospects, are within or at the 

southwest end of the Custer graben (fig. Bll). The larger 

Valley Creek and Buckskin deposits lie near a main 

strand of the trans-Challis fault system (fig. Bll). The 

Valley Creek and Buckskin mines also are along a belt of 

northeast-trending Tertiary dikes that range from latite 

to more commonly rhyolite in composition. At the two 

mineralized deposits, granodiorite country rock of the 

Idaho batholith is intensely altered and brecciated. The 

Valley Creek deposit consists of near-vertical mineralized shears and quartz veins that range from 0.3 to 

1.4 m in thickness in a fracture zone that trends N. 

70°-85° E., has a maximum observed thickness of about 

18 m, and may be traced on the surface for more than 600 

m. The deposit has been explored by 630 m of adits and 

drifts on eight different levels and by surface workings 

that include a large open pit. No free gold or sulfide 

minerals were seen in the oxidized surface material.

Four quartz veins crop out at the Buckskin mine, 

which is 2 km southwest of the Valley Creek mine. The 

veins are 0.3-1 m thick, vuggy, and iron stained, but they 

also contain pyrite, which in places makes up as much as 

20 percent of the vein material. Galena occurs sparingly 

in the veins. Tertiary dikes are exposed near the veins in 

the altered granodiorite country rock. Three adits at 

the Buckskin deposit explore a shear zone that strikes

N. 80° E., is as much as 1.5 m wide, and contains stringers 

and lenses of quartz, some of which are enriched in 

pyrite. Samples of the mineralized zone and dumps 

averaged 0.04 oz Au/ton and 2.6 oz Ag/ton; however, a 

sample of pyrite-rich vein quartz contained 0.583 oz 

Au/ton and 6.38 oz Ag/ton, which suggests that the 

precious metals are associated with the pyrite (Van Noy 

and others, 1986).

The Bronco (Mountain Girl) mine workings 

explore a northeast-trending brecciated quartz vein that 

averages about 0.5 m in thickness. No sulfide minerals 

were seen in the vein by Choate (1962), although a 

composite sample chipped across the vein by him 

contained 0.41 oz Au/ton and 2.46 oz Ag/ton. Twentytwo tons of ore shipped from the mine contained 17 oz 

gold and 83 oz silver (Van Noy and others, 1986). Small 

shipments of gold-silver ore also have been made from 

narrow, northeast-striking quartz veins at the Golden 

Day mine.

The Iron Crown mine consists of three adits on 

different levels, all of which explore a Tertiary dike of 

rhyolite porphyry. Quartz-pyrite veinlets in the rhyolite 

porphyry contain free gold as irregular-shaped blebs and 

as wire gold intimately intergrown with pyrite (Choate, 

1962).

Gold-bearing Resources

Eleven placer deposits in the Stanley district have 

been estimated to contain about 26.8 million yd3 of gravel 

in which the average gold content ranges from a trace to 

605 mg/yd3 (Van Noy and others, 1986, table 37). Veins 

in the district are estimated to contain from 295,000 to 

410,000 tons, with average grades ranging from 0.06 to 

0.25 oz Au/ton and 1.8 to 4.12 oz Ag/ton (Van Noy and 

others, 1986). Substantial volumes of placer and lode 

material in the district are probably of minable grade, but 

future mining of the resources will be hampered by the 

fact that they are within the Sawtooth National 

Recreation Area, which is withdrawn from mineral entry 

under the 1872 mining laws, subject to valid existing 

rights, and where restrictive regulations are enforced to 

guard against impairment of the scenic features of the 

area.

Custer Graben

The Custer graben, in the central part of the 

trans-Challis fault system, is northeast of the town of 

Stanley, Idaho (fig. Bll). The graben is an Eocene 

volcanotectonic structure that subsided partly in 

response to the eruption of latitic ash-flow tuffs and 

partly owing to crustal extension (Mclntyre and Johnson, 

1985). It has little or no present-day physiographic 

expression. Northeast-trending normal faults are the 

most common structures within the graben. Most of

United States Gold Terranes B31
these faults have dip-slip displacements of several tens to 

several hundreds of meters. Some have strike-slip 

displacements of several hundreds of meters to 2 km.

Two principal groups of rocks underlie the graben: 

siltite, argillite, quartzite, and limestone of the Permian 

Grand Prize Formation, and granitic rocks of the Late 

Cretaceous Idaho batholith. Volcanic rocks in and 

adjacent to the graben include andesitic lavas and pyroclastics erupted about 50 Ma, just prior to graben 

subsidence, and quartz latite to rhyolite ash-flow tuffs, 

lavas, and pyroclastics deposited during graben subsidence about 48 to 47 Ma. Locally, several hundred 

meters of lake sediments were deposited on lower parts 

of the graben floor.

Several types of Tertiary intrusive rocks are present 

in or near the graben. Andesitic dikes and plugs are 

found near vent areas of the andesite lavas. A small 

granodiorite-quartz monzonite stock is exposed near the 

south-central edge of the graben. Numerous dikes, 

domes, and irregular masses of rhyolite are present 

throughout the graben. Several of the domes vented to 

the surface, and many were probably emplaced at very 

shallow depths (Hardyman and Fisher, 1985). Ore 

deposits are genetically related to both the granodioritequartz monzonite stock and to several rhyolite intrusions.

Numerous gold mines and prospects are scattered 

near and within the central part of the trans-Challis 

fault system. However, within the Challis quadrangle 

(fig. Bll), except for the Yankee Fork mining district, 

only two lode mines (the Yellowjacket mine, in the 

Yellowjacket mining district, and the Lost Packer mine, 

in the Loon Creek mining district) and one placer area 

(Loon Creek placers, in the Loon Creek mining district) 

have produced more than a few thousand ounces of gold 

each. Individual production from all the other mines has 

been small, and at a maximum has ranged from a few 

tens to a few hundreds of ounces.

Yankee Fork District

History and Production

Placer gold was discovered in the Yankee Fork 

district near the mouth of Jordan Creek in the early 

1870's. The first lode discovery was at the Charles 

Dickens property in 1875, and by 1877 most of the lodes 

in the district were located. The ores were very rich, 

ranging from $350 to several thousand dollars in silvergold values per ton (Anderson, 1949). The district was 

most productive during the 1880's and 1890's, whereas by 

1905 many mines had shut down. The Golden Sunbeam 

mine produced ore from 1907 to 1911; the Montana 

mine was reopened and in production from 1914 to 1917, 

and the Lucky Boy mine was a notable producer from 

1933 to 1942. Activity at most properties in the district, 

however, has waxed and waned with only minor production recorded from the lode mines since the turn of 

the century. Placer deposits were worked intermittently, 

and from the 1930's to 1960, dredging was conducted at 

various times on the Yankee Fork of the Salmon River 

and on Jordan Creek. Total production from the placer 

deposits is unknown. Umpleby (1913a) estimated the 

value of placer production to be about $50,000 prior to 

the date of his report. U.S. Bureau of Mines unpublished 

records list total placer production since 1901 at 

38,272 oz gold and 22,299 oz silver. The bulk of the 

placer production between 1940 and 1962 came from 

dredging on the Yankee Fork of the Salmon River and on 

Jordan Creek, and it totaled 29,356 oz gold and 21,037 oz 

silver. Production values (mostly at $20.67/oz of gold, 

and various prevailing silver prices) from the major lode 

mines are: General Custer ($8,000,000), Lucky Boy 

($2,200,000), Charles Dickens ($600,000), Golden 

Sunbeam ($400,000), Montana ($350,000), McFadden 

($200,000), and Morrison ($100,000) (Anderson, 1949). 

Most of these values were produced prior to 1901, as 

total lode production from the district between 1901 and 

1982, according to unpublished U.S. Bureau of Mines 

records, amounted to only 41,650 oz gold and 433,269 oz 

silver.

Character of the Lode Deposits

Nearly all the lode production from the district has 

come from epithermal silver-gold veins. Veins in the 

northwestern part of the district are hosted in silicic tuff 

and intrusive rhyolite, whereas those in the southeastern 

part of the district are in andesite. All the rocks are of 

Eocene age. The veins formed at shallow depths and ore 

occurred along the veins in rich bonanza shoots. Silver 

was much more abundant than gold, and in some 

deposits the ratio of silver to gold was 80 or 90:1. Only 

ore from the upper workings of the Montana mine and 

from the Golden Sunbeam produced higher ratios of 

gold to silver. With the exception of the Charles Dickens 

mine, base metals are not abundant in the district, and 

only a few mines have recorded minor production of 

byproduct lead and copper. In the Charles Dickens the 

base metals were present in chalcopyrite, covellite, 

galena, and sphalerite; the 1983 operators of the property 

reported that the highest gold values were associated 

with chalcopyrite.

Northeast- and northwest-trending faults and 

fractures controlled location of the ore deposits, and 

mineralization was most intense in two areas, one in the 

Golden Sunbeam-Estes Mountain area and the other in 

the Charles Dickens-General Custer-Lucky Boy area. 

Rocks around these two mineralized areas are characteristically depleted in 18O (Criss and others, 1985). The 

deposits occur as simple fracture-filling veins, filled breccia veins, shear zones, and stockworks. Some veins are an 

aggregate of small fracture zones, whereas others are

B32 Geology and Resources of Gold in the United States
simple structures with well-defined walls. The exposed 

strike length of the veins ranges from a few hundred 

meters to as much as 1,000 m. The average width of the 

veins is about 1 m, but they range from a few centimeters 

to a maximum of 5-6 m wide. Productive parts of the 

veins decrease rapidly with depth, and in most mines the 

veins are barren below 150-200 m.

Since 1975 exploration activity has focused on 

large-tonnage, lower grade gold-silver deposits associated with high-level rhyolite intrusions and also broad 

areas of pervasively altered rock adjacent to some of the 

major veins (Hardyman and Fisher, 1985; Mclntyre and 

Johnson, 1985). The principal exploration targets have 

been at the Golden Sunbeam and General Custer mines. 

Rocks that host the deposits are extensively shattered and 

intensely altered to clay minerals and quartz. They 

contain disseminated gold and silver. Gold values are in 

the range of 0.02 to 0.03 oz/ton.

Mineralogy and Geochemistry

Cryptocrystalline to fine-grained, laminar, vuggy, 

drusy, white to dark-gray quartz is the main gangue 

mineral in the veins. Lesser amounts of chalcedony, 

calcite, barite, and adularia also are present. Pyrite is 

ubiquitous; however, it commonly has been oxidized. The 

other metallic minerals, fine grained and in most cases 

sparse, include chalcopyrite, sphalerite, tetrahedrite, 

galena, arsenopyrite, enargite, stephanite, miargyrite, 

pyrargyrite, argentite, electrum, and gold (Anderson, 

1949). Anderson (1949) also reported gold and silver 

selenides; however, the presence of these minerals 

cannot be confirmed by the present authors. In the 

low-grade disseminated deposits, the ore is essentially 

indistinguishable (except by assay) from the barren 

altered country rock. These rocks are bleached and 

silicified, and clay minerals are common in them. Finegrained disseminated pyrite is sparse, and other metallic 

minerals are rare.

Stream sediments from the district are enriched in 

gold, silver, copper, and molybdenum (Callahan and 

others, 1981; Mclntyre and Johnson, 1985). Arsenic, 

molybdenum, beryllium, zirconium, and barium are 

commonly enriched in the altered rocks near the ore 

bodies, and these elements may provide useful prospecting guides (Hardyman and Fisher, 1985).

Wall-rock Alteration

Hydrothermally altered rocks are common in the 

Yankee Fork district. Alteration was most intense in the 

Golden Sunbeam-Estes Mountain area, Charles 

Dickens-General Custer-Lucky Boy area, and in the 

Red Mountain area, where altered zones range from 

several hundred to a thousand meters in width and 

length. Propylitized rocks are widespread, and silicification and argillization were more intense near the 

central controlling fractures and faults. Oxidation of the 

ubiquitous pyrite has stained and bleached many areas to 

shades of red, orange, and yellow. 18O/16O ratios are 

lowest in the intensely altered and mineralized zones, and 

the zones of 18O depletion extend well beyond the areas 

of visibly altered rocks (Criss and others, 1985).

Age of Mineralization

Ages of ore formation are not well known. Zircon 

from hydrothermally altered rhyolite at the Golden 

Sunbeam mine yielded a fission-track age of 45.8±2.3 

Ma (P.A.M. Andriessen, written commun., 1982), and 

sericite from the General Custer vein yielded K-Ar ages 

ranging from 48.4 to 44.0 Ma. These ages suggest that 

mineralization was associated with hydrothermal events 

that occurred after the main graben subsidence had been 

completed (Mclntyre and Johnson, 1985).

Ore Controls and Resources

Structures are the principal ore controls in the 

district. Most of the richer lodes are on northeast- or 

northwest-trending faults or fracture systems. Richer ore 

shoots are commonly found near intersections of the 

main veins with cross faults. Lodes nearer the surface 

tend to be richer than those at depth. Most veins are 

barren at depths of more than about 200 m front the 

surface. Finally, undulations in strike and dip of the veins 

appear to have enhanced ore deposition in some lodes 

(Anderson, 1949). In some mines richer ore is associated 

with base metals if they are present; however, in most 

mines the youngest quartz commonly contains the 

highest values.

Undoubtedly a few high-grade pockets of bonanza 

ore are still present in the district, but they are likely to be 

small and to constitute no significant resource. Likewise 

small amounts (a few hundred to perhaps a maximum of 

1,000 oz) of gold and silver may be produced from 

placers, mainly along Jordan Creek and the Yankee Fork 

of the Salmon River. The greatest resources in the 

district are most likely contained in the lower grade 

disseminated deposits associated with the high-level rhyolite domes (for example, the Golden Sunbeam and Red 

Mountain areas) and with the areas of extensive fracturing that hosted widespread alteration and mineralization (such as the extensive altered zone adjacent to 

the General Custer vein). Resources from these zones 

will be low grade (about 0.02 to 0.03 oz Au/ton). Millions 

of tons of this low-grade material may be present in the 

district.

Loon Creek District

The Loon Creek district (fig. Bll) is west of the 

Custer graben and at the extreme northeast end of the

United States Gold Terranes B33
Knapp Creek graben. The only significant gold production has come from the Lost Packer lode mine and 

the Loon Creek placers. The few other lode mines in the 

district have had little development and essentially no 

production. Rocks underlying the district consist of the 

Idaho batholith of Late Cretaceous age, metamorphosed 

Precambrian and Paleozoic sedimentary rocks (roof 

pendants in the Idaho batholith), dacitic and granitic 

stocks of Eocene age, and extrusive lavas and pyroclastic 

rocks of the Eocene Challis Volcanics (Fisher and others, 

1983).

Loon Creek Placers

The Loon Creek placers were discovered in 1869 

and reached their greatest development and production 

during the next 10 years (Ross, 1934). There has been 

little activity since 1880 and only minor production. The 

placers extend about 7 km northeast from the abandoned 

townsite of Casto (fig. Bll). They average about 300 m in 

width and comprise the flood plain and higher terraces 

along Loon Creek. The gravel is as much as 10 m thick 

but more commonly is about 5 m thick. The gold was 

generally coarse, and nuggets weighing more than 1 oz 

were not uncommon (Umpleby, 1913c). Gold produced 

from the placers was estimated by Umpleby (1913c) to 

be valued at between $500,000 and $2,000,000.

Lost Packer Mine

The Lost Packer mine was discovered in 1902, and 

most development and mine production was between 

then and 1927. Umpleby (1913c) estimated the total 

production to 1911 to be valued at $500,000, with gold 

accounting for $350,000 and copper $150,000. Ross 

(1934) reported an additional $100,000 in metal values 

that were produced between 1911 and 1927. Unpublished records of the U.S. Bureau of Mines show that the 

mine produced 19,791 oz gold, 48,451 oz silver, 

1,797,786 Ibs copper, and 8,038 Ibs lead between 1903 

and 1937. There has been essentially no production of 

ore since 1937.

The Lost Packer lode is in quartzose, micaceous, 

and calcareous metasedimentary rocks of Precambrian 

or possibly Paleozoic age. Mica schist and dark micaceous quartzite are common. These rocks have been 

intruded by Cretaceous rocks related to the Idaho batholith and by Tertiary dacite, dacite porphyry, and granophyre dikes. The ore appears to be younger than the 

Cretaceous aplite dikes and older than the Tertiary 

granophyres.

The Packer vein extends along the Packer fault, 

which strikes N. 10° E., dips steeply northwest, and 

exhibits left-lateral displacement of only a few meters. 

The vein is a narrow structure formed chiefly by fissure 

filling; it consists mostly of quartz and is generally sparse

in sulfides. Ore was produced from three major shoots 

along the vein the north, south, and main shoots. These 

shoots had vertical dimensions of about 50-100 m, and 

ranged from about 1 to 2 m in thickness.

Gangue minerals include abundant quartz and 

siderite, smaller amounts of pyrite and pyrrhotite, and 

minor amounts of calcite and barite. Ore minerals are 

chalcopyrite, tetrahedrite, bornite, native copper, and 

gold. The high-grade ore consisted mostly of goldbearing massive chalcopyrite, which according to 

Umpleby (1913c) ran about $80-$90 per ton in gold, 

silver, and copper values. The chalcopyrite commonly 

assayed IVi to 3 oz Au/ton, and quartz from some ore 

shoots was equally rich in gold (Umpleby, 1913c). Jennings (1906) estimated that the high-grade ore averaged 

15 percent Cu and contained 2-20 oz Au/ton and only 

minor amounts of silver.

Exploration of the property has continued sporadically; high-grade chalcopyrite-gold ore was discovered in 

1983 and was being evaluated in 1984. Small high-grade 

shoots may be present, but large reserves of high-grade 

ore are unlikely. An unknown tonnage of lower grade 

material is present.

Other Mines and Prospects

Many other gold mines and prospects occur within 

and adjacent to the central part of the trans-Challis 

mineral belt within the Challis quadrangle (fig. Bll). 

Most of these deposits are small veins or placers with no 

recorded production and very low future potential. 

However, some of these occurrences, notably the Singheiser, Rabbit Foot, and Parker Mountain deposits, have 

produced a few hundred ounces each and may offer 

targets for large-tonnage, low-grade type operations. All 

three of these occurrences are associated with high-level 

rhyolite intrusions (Hardyman and Fisher, 1985) and 

have similarities to the disseminated deposit at the 

Golden Sunbeam mine in the Yankee Fork district. 

Numerous other rhyolite intrusions occur along the 

central part of the trans-Challis fault system (Fisher and 

others, 1983), and several are known to be mineralized 

(Hardyman and Fisher, 1985). A sum total of probably 

millions of tons of low-grade (0.01-0.02 oz Au/ton) 

resources may be associated with the high-level rhyolites.

Yellow/jacket District

The Yellowjacket mine (fig. Bll) is just north of 

the northwestern edge of the Panther Creek graben, an 

asymmetric volcanotectonic structure that subsided 

partly owing to regional rifting and partly owing to 

magma withdrawal associated with the eruption of rhyolite tuffs (Fisher and others, 1983). It is similar to the 

Custer graben. The Panther Creek graben is a tilted

B34 Geology and Resources of Gold in the United States
block whose bounding faults on the southeast side have 

displacements of about 4,000 m, whereas northwest-side 

bounding faults have maximum displacements of a few 

tens to a few hundreds of meters (Mclntyre and Johnson, 

1985; Fisher and others, 1983).

Total production from the Yellowjacket district is 

unknown because prior to 1893 no records were kept. 

Umpleby (1913b) estimated total gold production to 

1910 to be valued at about $450,000. Between 1902 and 

1949, the district produced 3,855 oz gold, 5,608 oz silver, 

20,792 Ibs copper, and 17,175 Ibs lead. The biggest 

producer of precious metals, by far, was the Yellowjacket 

mine, which accounted for 3,003 oz gold and 3,397 oz 

silver (Anderson, 1953). The Yellowjacket lode was 

discovered in 1868 and was extensively developed in the 

1880's and 1890's. By 1900, however, mining activity had 

slowed, and since then development and production have 

been sporadic. Placer mining in the district has not been 

extensive, but production from placers is unknown and 

probably minor (Anderson, 1953).

The district is underlain by argillaceous and 

calcareous quartzite of the Yellowjacket Formation and 

by the Hoodoo Quartzite, both formations of Early and 

Middle Proterozoic age. A wide variety of igneous rocks 

has intruded the Precambrian metasedimentary rocks. 

Stocks, dikes, and irregular plugs of gabbro, diabase, 

olivine gabbro, diorite, lamprophyre, granite porphyry, 

and granophyre have been emplaced at various (but 

uncertain) times from the Precambrian to the Tertiary 

(Anderson, 1953; Fisher and others, 1983).

The Precambrian sedimentary rocks in the district 

have been repeatedly deformed since Early Proterozoic 

time. They are complexly folded and fractured. Most 

of the mineralized fractures in the district strike about 

N. 60° E. or N. 15°-20° W. Dips of the northeast set range 

from 35° to 80° NW., and those of the northwest set dip 

steeply to the southwest (Anderson, 1953). Major 

regional faults mostly of northeast trend and less 

commonly of northwest trend also cross the district. 

Dip-slip movement on these faults has been as much as 

1,000 m.

The deposits are mainly fracture-filling veins with 

minor replacement. Gold is the most important metal 

followed by silver, copper, and lead. Base metals are 

sporadic in their occurrence, and the veins may be 

classed as gold-base metals, silver-copper, and silver-lead 

deposits. Most of the individual veins are narrow (a few 

centimeters to a meter wide) and are not persistent along 

strike. Lodes generally contain numerous veins, and the 

entire zone may be several tens of meters wide and 

hundreds of meters long. In places the mineralized rock 

has a stockwork character. Gangue minerals include 

quartz, calcite, siderite, barite, and pyrite, of which 

quartz is by far the most abundant. Ore minerals include

chalcopyrite, sphalerite, tetrahedrite, galena, and gold. 

Secondary minerals are chalcocite, covellite, cuprite, 

malachite, azurite, and native copper. The gold is very 

fine grained and is most commonly associated with the 

quartz (Anderson, 1953).

Yellowjacket Mine

The Yellowjacket mine consists of more than 

2,000 m of underground workings on four main and 

several intermediate levels. The mine is in quartzitic and 

calcareous units of the Yellowjacket Formation. The lode 

is along a wide (100-150 m) zone of fractured rock about 

400 m in length that trends N. 70° E. and dips steeply to 

the northwest. Innumerable northeast- and northweststriking veins and stringers separated by altered rock are 

present in the fractured zone. The ore was erratically 

distributed in the zone with individual ore shoots being 

100 m long by 10-15 m wide and 40-50 m deep (Ross, 

1934). The ore was extensively oxidized, was free-milling, 

and originally contained minor amounts of chalcopyrite 

and pyrite. The average gold content was 0.387 oz 

Au/ton. Base metals were more common in deeper levels 

of the mine.

According to Ross (1934), structural relationships 

of the veins may indicate the existence of undiscovered 

gold-bearing base-metal ores at depth. The greatest 

potential for the district, however, probably lies in the 

altered stockworks and fracture zones that may contain 

large tonnages of low-grade gold ore amenable to heap 

leaching. Some exploration of these possibilities was 

being conducted in the district in 1984.

Northeast Part

The northeast part of the trans-Challis fault system 

in Idaho has been heavily mineralized. There are four 

main types of deposits: (1) stratiform or mobilized stratiform copper-cobalt deposits that are Precambrian in 

age, (2) thorium and rare-earth deposits that are possibly 

Precambrian, (3) molybdenum-copper porphyry and 

stockwork deposits of Tertiary age, and (4) epithermal 

gold-silver deposits that are Tertiary and are directly 

related to the trans-Challis fault system. The gold-silver 

deposits are in the Mackinaw (Leesburg), Mineral Hill, 

Indian Creek, and the Dahlonega (Gibbonsville) 

districts. A brief description is also given of some 

molybdenum-copper deposits.

Production figures for the districts are incomplete; 

what is known is shown in table B3.

The gold lode deposits have several characteristics 

in common. All the mines are in vein deposits that have 

a simple mineralogy. The gangue mineral is quartz, and 

the economic minerals are free gold and auriferous 

pyrite. Pyrite is the common sulfide, and most mines

United States Gold Terranes B35
Table B3. Production from the Mackinaw (Leesburg), Indian Creek, and Dahlonega (Gibbonsville) districts, Idaho

[Data from U.S. Bureau of Mines (1924-31; 1932-83). Leaders ( ), no production or no data available. No recorded production after 1955. Lode 

no. and placer no. indicate number of such properties active in specified year]

Lode

(no.)

Placer

(no.)

Gold

(dollar

value)

Gold

(oz)

Silver

(oz)

Copper Lead Lode

(Ib) (Ib) (no.)

Dahlonega (Gibbonsville) district

1910

1911

1912

1913

1914

1915

1916

1917

1918

1919

1920

1921

1922

1923

1924

1925

1926

1927

1928

1929

1930

1931

1932

1933

1934

1935

1936

1937

1938

1939

1940

1941

1942

1943

1944

1945

1946

1947

1948

1949

1950

1951

1952

1953

1954

1955

 

4

9

10

13

5

16

9

8

6

9

2

1

1

1

8

4

9

4

4

13

11

8

14

13

9

1

3

3

1

1

2

1

11,868

9,628

11,796

4,863

410

1,028

551

492

185

1,264

1,239

1,365

715

959

3,004

4,440

3

1,338

3,441

104

43

8

9

2

__

108

421

97

36

369

640

450

160

608

464

492

96

367

311

343

120

232

10

8

_

1,340 12,044

_

_

_

3,095 267 1

4,875 6,351 2

3,500 4,162 2

795 2

2,663 -- 1

1,785 610 2

408 870 1

346 234 2

1,133 1,200 1

550 1,600 1

1

300

Placer Gold Silver Copper Lode Placer

(no.) (oz) (oz) (Ib) (no.) (no.)

Indian Creek district Mackinaw

1 830 7 2 13

1 29 -- 1 12

48 34 4 73

238 34 50 2 22

851 816 6,935 1 17

35 13 124 1 22

60 34 194 3 23

32 9 3 17

221 14 248 3 18

412 38 1,500 1 16

6 1 9

I

2

1

4

4

4

3

 1 3

1

2

I

I

Gold

(dollar

value)

(Leesburg)

3,966

857

2,132

2,765

2,384

2,192

2,448

1,893

3,530

3,317

2,725

1,817

2,247

1,944

1,972

Gold

(oz)

Silver

(oz)

district

4,083

334

651

310

262

200

295

305

1,240

1,221

73

1

10

2

39

13

14

9

14

1

1

7

29

12

27

15

8

15

17

13

20

10

7

8

7

14

20

2,025

1,550

12

13

280

240

204

128

14

17

59

5

11

24

1

contain sparse sphalerite, galena, and chalcopyrite. Many 

of the veins are in northeast-trending shears or fissures 

that are believed to be part of the trans-Challis fault 

system. Most of the gold production has been from 

placers, and the largest lode producer, the Gold Hill 

mine in the Mackinaw (Leesburg) district, accounts for 

only a little more than 43,000 oz. None of the lode 

deposits extend to any great depth.

Mackinaw (Leesburg) District

The Mackinaw (Leesburg) district, approximately 

20 km northwest of Salmon, Idaho, is the oldest mining 

district in Lemhi County.

History and Production

Placer gold was discovered near Leesburg (fig. 

Bll) on July 6, 1866, and by August a full-fledged gold

B36 Geology and Resources of Gold in the United States

rush was underway. By 1867,130 houses had been built 

or were under construction, and the new settlement of 

Leesburg had a population of about 2,000. The town 

would serve as the jumping-off point for exploration in 

rugged central Idaho in the coming years. The initial gold 

rush was over by 1895.

All mining work in the district was placer until 

1870. The first lode claim, the Shoo Fly (fig. Bll), was 

located in 1870. In 1880 the Gold Flint was staked, and in 

1892 the Italian mine claims were located. Large placers 

have been worked near Leesburg since the initial 

discovery in the district. The use of sluice boxes and 

shakers to mine placers in the late 1800's gave way to 

hydraulicking in the 1920's and to dredges in the 1930's 

and 40's. Major production in 1940-41 came from a 

dry-land dredge, which recovered more than 1,000 oz of 

gold and 95 oz of silver each year. The jump in gold 

production shown in table B3 was due to this operation.
Interest in placers has been continuous. In 1981, 

the Napias Mining Co. began a large placer operation at 

Leesburg using power shovels and a washing plant. The 

operation was still active in 1984.

The major lode producer in the district has been 

the Italian mine, so named because three Italians discovered the property. These men operated the mine until 

1902 when it was purchased for $20,000 by the Van Horn 

Co. of Fremont, Nebr. In 1903, the mine produced 

$60,000 in bullion. The mine was sold in 1908 to the 

Leesburg Mining Co., which installed a hoist, started 

shaft sinking, and discovered gold ore in the shaft. A 

30-stamp mill was built in 1910, and a 700-horsepower 

hydroelectric power plant was installed 11 km west of the 

mine. The new facilities apparently did little to increase 

production. The mine operated for 3 months in 1921, had 

minor production in 1922, and has been inactive ever 

since. Total production from 1902 through 1935 was 

722 oz of gold and 194 oz of silver (U.S. Bureau of 

Mines, unpub. data).

The Haidee mine is 2.4 km north of the Italian 

mine. In 1903, a New York firm started driving a 900 m 

adit on the property. Ore was discovered, but the adit 

never reached the target vein owing to caving problems, 

and the project was abandoned. The Gold Flint mine, 

about 2.4 km north of Leesburg (fig. Bll) had about 

300 m of drifts along a northeast-striking mineralized 

fault, according to Umpleby (1913b), but it has been 

inactive since 1913. The Gold Dust mine had a 10-stamp 

mill that operated for a total of 90 days (Umpleby, 

1913b). Further work was done in 1921, but there was no 

production. The Gold Ridge mine on the same mineralized fault as the Gold Flint and Gold Dust mines 

(Umpleby, 1913b) was developed by 300 m of workings; 

a 10-stamp mill and a 50-ton cyanide plant, built in 1907, 

operated intermittently for 2 years. Production in 1907 

was 9 oz of gold and 10 oz of silver from 75 tons of ore. 

The mine closed in 1907 and has been inactive since. The 

Shoo Fly lode produced about $75,000 in gold within 

several years of discovery, mostly from boulders of vein 

material that were mined below the outcrop (Umpleby, 

1913b). Mine production since then has been sporadic. 

The property was not developed further until 1932. In 

1934,775 tons of ore were treated by amalgamation, and 

some production also was recorded in 1935. The mine 

accounted for all lode production for the Leesburg 

district in 1936 and 1938. Production from the Shoo Fly 

mine, from 1932 through 1941, was 666 oz of gold and 

19 oz of silver from 1,792 tons of ore. Operations at the 

mine ceased in 1941.

Umpleby (1913b) noted that the Mackinaw (Leesburg) district had produced about $5 million in gold and 

silver from placers and $250,000 in lodes by 1913. 

Two-thirds of the recorded lode production came from

the Italian mine and the rest from the Shoo Fly mine. 

Metal production for the Mackinaw (Leesburg) district, 

from 1910 to 1955, is shown in table B3.

Geologic Setting

The geology of the Mackinaw (Leesburg) district 

has been described by Umpleby (1913b), Shockey 

(1957), Bennett (1977), Lopez (1981), Hillisland (1981), 

and Jordan (1984). Major rock units include the Yellowjacket Formation, the Hoodoo Quartzite, and several 

varieties of augen gneiss and related rocks that are all 

Precambrian in age. Tertiary dikes exposed north of 

Leesburg are probably related to a buried Tertiary 

plutonic complex that hosts, in part, the Bobcat Gulch 

porphyry molybdenum-copper deposit (fig. Bll). However, Evans and Zartman (1981b) have dated zircons in 

other igneous rocks in the district as Ordovician (493 

Ma), suggesting that the plutonic history of the area is 

complex. Cretaceous rocks of the Idaho batholith 

probably also are present but are not as prevalent as 

noted in the early literature. Miocene lake-bed deposits 

composed of volcaniclastic sediments and patches of 

Challis Volcanics are exposed north of Leesburg and 

southwest of North Fork (fig. Bll).

Perhaps the most important structural element in 

the district is the Panther Creek fault (Bunning and 

Burnet, 1981), a major structure in the trans-Challis fault 

system that probably has been active since the Precambrian. The Gold Dust, Gold Reef, and Gold Flint 

mines are on a parallel structure very close to this fault.

Characteristics of the Deposits

Umpleby (1913b) noted five types of veins in the 

Leesburg district. Quartz veins accompanied by quartz 

stockworks in granite are the first type. Characteristic of 

this type is the Italian mine and the nearby Haidee mine. 

The Italian mine is in a fracture zone that extends more 

than 1,600 m in a north-south direction and dips 45° W. 

A second type of deposit is replacement veins along fault 

planes, characterized by the Gold Dust, Gold Reef, and 

Gold Flint mines. In these mines, Precambrian metasedimentary rocks are faulted against augen gneiss. All 

three mines are in the same structural zone which, as 

noted, is close to and parallels the Panther Creek fault 

(fig. Bll). Umpleby (1913b) noted that these three 

mines were higher in silver content than other lodes in 

the district and were probably the source of the placer 

gold near Leesburg, as that gold contained more silver 

than other placers in the district. Lenses in schist and 

granite, a third type of mineralized rock, are believed to 

be another source of the placer gold. The Shoo Fly mine 

exploited a lode deposit of this type. A vein in contact 

with a monzonite dike in the Italian mine is a fourth type 

that was thought by Umpleby (1913b) to postdate the

United States Gold Terranes B37
stockwork mineralization. The last type of vein is 

replacements along shear zones, as found in the western 

part of the district.

Quartz is the primary gangue mineral of the lodes, 

with some calcite stringers; auriferous pyrite and free 

gold are the economic minerals; and there is usually 

sparse galena and sphalerite. The monzonite-related vein 

in the Italian mine is anomalous in that it contains 

considerable chalcopyrite and sphalerite.

Mineral Hill District

The Mineral Hill mining district is approximately 

34 km west of North Fork, near the former town of 

Shoup. The district contains three gold mines that have 

been significant gold producers: the Kentuck (Gold Hill), 

Grunter, and Clipper Bullion, as well as numerous 

prospects.

History and Production

The following history and production data are, for 

the most part, modified and paraphrased from a study by 

E.T. Tuchek, A.B. McMahan, and L.Y. Marks (unpub. 

report for the U.S. Bureau of Mines, 1973). The Kentuck 

mine (later known as Gold Hill mine) was opened in 

1882 and the Grunter mine in 1891. The first production 

from the Kentuck mine was in 1882. For 2 years ore was 

processed using a single-stamp mill, two arrastre beds, 

and direct amalgamation. In 1884, a 10-stamp mill was 

installed. Production of gold reached a value of $7,200 a 

month in 1889. The stamp and amalgamation processes 

were used to treat about 46,000 tons of ore, with a gold 

recovery rate of 40 percent, until 1893 when the mine 

closed. Production was only minor until 1931, when the 

mine was sold and subsequently incorporated as Gold 

Hill Mines. A 100-ton/day flotation plant was erected in 

1935 and operated for several years. The property has 

been idle since 1949.

The Grunter mine was in production shortly after 

discovery in 1882. Bell (1904, p. 104) gave the following 

discussion of one of the early mining ventures on the 

property:

The Grunter mine, situated a mile east of the 

Kentuck on the same vein, is a fine example of one of the 

most flattering gold enterprises in the state that was 

butchered by a would-be mining capitalist who, through 

blundering misconception of the enterprise he was 

undertaking, started in to put up a first-class ten-stamp 

concentrating mill for a half interest in the property and 

wound up by furnishing a five-stamp mill with a hogtrough mortar and an overshot wheel that was just about 

as effective as a good-sized coffee mill and never gave 

the property half a chance to show its merits.

Ore was processed in a stamp mill using direct 

amalgamation until 1935, when the mill was destroyed by 

fire. In 1938, the property was purchased by Gold 

Producers, Inc., and a 50-ton/day mill was moved to the 

mine from the Twin Brothers mine near Gibbonsville. 

The following year, a 100-ton/day flotation plant was 

erected. Operations at the mine terminated in 1948.

Underground workings in the two mines consist of 

36 adits with crosscuts and slopes, one glory hole, one 

underground shaft, and numerous prospect pits and 

trenches. More than 3,000 m of workings are reported in 

the area. The vein in the Kentuck was worked downdip 

for about 200 m.

The Gold Hill mine, consisting of 10 patented and 

41 unpatented claims, and the Grunter mine, consisting 

of 5 unpatented claims, were acquired by Nevcal 

Resources, Ltd., in 1984.

According to U.S. Bureau of Mines unpublished 

data, production from the two mines is:

Period

1882-1900

1901-1913

1932-1949

Crude ore 

(tons)

50,000

67

150,281

Gold 

(oz)

25,000

87

18,127

Silver 

(oz)

_ i

15

13,614

Copper 

(Ib)

...

...

4,712

Lead 

(Ib)

...

...

95,418

1Leaders ( ), no production, or no data available.

The Clipper Bullion mine is 1.6 km southeast of the 

Grunter mine (fig. Bll). Ten mining claims were located 

in 1887, and gold was mined through 1932. Silver was 

recovered from 1902 through 1932, the last year of 

operation. Total production, according to Bureau of 

Mines records and estimates from Umpleby (1913b), was 

3,893 oz of gold, 209 oz of silver, and 279 Ibs of lead. 

Mine workings consist of four adits and numerous 

prospect pits and trenches. According to Umpleby 

(1913b) there were 820 m of mine workings, but only 

about 200 m of workings were open in 1972.

Another property with minor production was the 

Monolith mine, which in 1947 and 1948 produced 6,247 

tons of ore that yielded 1,659 oz of gold and 657 oz of 

silver. Only 1 ton of high-grade ore was mined in 1948 

before the mine closed.

The Big Lead mine (fig. Bll) produced 144 oz of 

gold and 8 oz of silver from 322 tons of ore in the period 

1904-1923. The mine is developed by about 460 m of 

adits.

Geologic Setting

The country rock that hosts producing mines in the 

Mineral Hill district is augen gneiss that underlies much 

of the area around Shoup. The augen gneiss intrudes the 

Yellowjacket Formation of Early and Middle Proterozoic

B38 Geology and Resources of Gold in the United States
age and amphibolite that itself also intrudes the Yellowjacket elsewhere in the area. Younger granite of the 

Idaho batholith and Tertiary porphyry dikes ranging in 

composition from andesite to rhyolite cut the gneiss. 

Umpleby (1913b) noted that in the Kentuck mine, a 

granite porphyry dike crosscuts the augen gneiss but is in 

turn cut by veins. The producing mines are all in shear 

zones that trend N. 10°-70° E. and dip 40°-90° SE. These 

shear zones are believed to be part of the trans-Challis 

fault system.

Characteristics of the Ore Deposits

The Grunter and Kentuck (Gold Hill) mines are in 

a large northeast-trending shear zone that is exposed for 

900 m along strike and 300 m down dip in the mine 

workings. Three primary shears contain major veins in 

the zone. Numerous fractures and minor shears cross the 

three major shears. Three more major shears contain 

veins called the Tramway, Hennessey, and Clipper 

Bullion in the Clipper Bullion mine. The Tramway 

strikes N. 70° E., dips 80° S., and averages 1 m in width; 

the Hennessey strikes N. 20° E., dips 85° E., and is 0.5 m 

wide; and the Clipper Bullion (the most productive) 

strikes N. 42° E., dips 65°-85° SE., and is about 1 m wide. 

The main vein in the Big Lead mine also strikes N. 65° E. 

and dips 80° S.; it ranges from a few centimeters to about 

1 m in width.

The mineralogy of the veins in the mines is simple. 

Quartz is the dominant gangue mineral, and free gold, 

auriferous pyrite, and pyrite are the minerals of economic interest. Other minerals present in minor amounts 

at the Grunter and Gold Hill (Kentuck) mines include 

sparse galena, sphalerite, and arsenopyrite (Umpleby, 

1913b). Tuchek and others (1973) reported minor 

tungsten minerals in one shear zone. The vein at the 

Clipper Bullion contains some barite in the gangue, and 

magnetite occurs in the Big Lead mine. Alteration is 

similar in all of the mines; the augen gneiss is silicified for 

several meters away from the veins, and pyrite is 

disseminated in the wall rock. Rocks along the shear 

zones are highly altered and iron stained. Oxidation has 

been relatively minor, and its effect extends to a depth of 

about 10 m in the glory hole of the mine.

Indian Creek District

The Indian Creek district is approximately 16 km 

west of North Fork and 11 km east of Shoup (fig. Bll). 

The topography is rugged, with elevations ranging from 

1,067 m to more than 2,134 m.

Two veins the Ulysses and the Kittie Burtonwere mined. These deposits are considered to be epithermal veins associated with the trans-Challis fault system, 

but the dip of the veins is flat whereas other veins in the 

zone generally dip steeply.

History and Production

Umpleby (1913b) noted that the first claims in the 

district were located in 1895, but that little further work 

took place until the Kittie Burton Gold Mining Co. 

acquired the Kittie Burton and Ulysses properties in 

December 1901. The late development of the area was a 

result of difficult access and transportation to the mine 

site. Wells (1983, p. 78) described some of the early 

history:

In spite of such obstacles [transportation], a 

15-stamp mill which commenced production in 1902 

was enlarged to 30 stamps the next year. This operation 

processed enough low-grade ($10) ore to yield a 

monthly profit of 3 percent on a large capital investment 

through 1904. That September, afire destroyed the plant 

and set Ulysses back seriously. At the time of the fire, 

Ulysses had Idaho's largest active gold mine.

After the 1904 fire, an improved 15-stamp mill was 

built. By 1907, free-milling ore was mined out, and 

production slowed as primary sulfide ore was reached. 

Lessees operated the mine in 1908, and shipments 

resumed in 1909 when a concentrator was added to the 

mill. A 900-m Leschen aerial tram connected the Kittie 

Burton mine to the mill, and another tram delivered ore 

from the Ulysses. In 1910 the mine was the largest gold 

producer in Lemhi County. It held the record again in 

1914, but production declined drastically in 1915, and the 

property was idled in 1917. The Buchanan Mining and 

Leasing Co. repaired the mill and tramline in 1919, went 

into production in 1920, and produced considerable gold 

and silver in 1921 and 1922. Minor production, tailings 

processing, and cleanup carried the mine through 1928 

when it closed again. In 1932 the Indian Creek Leasing 

Company reopened the mine, built a small tramline, and 

refurbished the mill. The company operated until 1937 

when the operation shut down. The American-Idaho 

Gold Corp. operated the property in 1940, treating 900 

tons of ore in a 50-ton flotation mill. All operations 

ceased in 1943, and there has not been any recorded 

activity since.

The Sage Creek Lumber Co. operated the Sage 

Creek mine (fig. Bll) in 1950, and produced 75 oz gold 

and 9 oz silver. The Sage Creek veins are similar to the 

Kittie Burton and Ulysses veins according to Umpleby 

(1913b).

Production from the district is shown in table B3. 

Umpleby (1913b) noted that early production was valued 

at a little less than $600,000.

Geologic Setting

Country rock in the area is metamorphosed Early 

and Middle Proterozoic Yellowjacket Formation

United States Gold Terranes B39
intruded by augen gneiss and amphibolite, all Precambrian in age. Umpleby (1913b) described granite 

porphyry dikes that intrude the older units.

The Ulysses vein is a tabular body, varying in width 

to as much as 3.5 m, striking east-west, and dipping 

10°-25° S. Because of the flat attitude of the vein, it could 

be mined by stripping the overburden. The vein does not 

extend more than 46 m deep. The Kittie Burton vein 

strikes N. 20°-30° W. and dips 40° SW. in the upper 30 m, 

but it is almost flat below this depth. It has a maximum 

thickness of 30 m in the flat part of the vein that was 

called the "Big Stope" (Umpleby, 1913b).

The mineralogy of both veins is similar. Quartz is 

the primary gangue in silicified wall rock, and economic 

minerals include free gold and auriferous pyrite. Some 

chalcopyrite and pyrrhotite are also present in the ore.

Dahlonega (Gibbonsville) District

The Dahlonega mining district is near Gibbonsville. Mines in the district produced gold from placers 

and lodes. Major lode production came from the American Development, Mining, and Reduction (ADM&R) 

Co. mines near Gibbonsville. The Twin Brothers, Clara 

Morris, and Big Four mines also have been productive.

History and Production

The early history of the district was described by 

Umpleby (1913b, p. 128) as follows:

Placers were discovered on Anderson Creek in 

1877, and although not very productive, their presence 

led to the location of gold-bearing veins in September of 

that year. During the fall, one arrastre was built, and the 

next year two more added. By this means of treatment 

$20 to $30 per ton was saved. Early in 1881 most of the 

producing mines were sold to an English company, 

which later went into liquidation and sold the properties 

to Adelbert Ames, of New York who operated them for a 

number of years. After changing hands several times, 

the American Development, Mining, and Reduction 

Company purchased the principal group from the Northfork Reduction Company and in 1895 erected a 30- 

stamp mill with accessory cyanide and chlorination 

plants. This company operated until March 20, 1898, 

when it also became insolvent, the receiver and others 

operating the property intermittently until July 1906, 

when the American Development, Mining, and 

Reduction Co. resumed control.

The closure in 1898 was due to a change in tenor 

and grade of the ore. The oxidized ore had been mined 

out, and gold was in sulfides at depth. Lincoln (1912, p. 

49) observed, "A series of tests that I made showed that 

there is no free gold in the deeper ores and that in order 

to obtain an extraction of 90 percent by cyanidation, it

will be necessary to slime them." The ADM&R 

operation suffered a setback in the fall of 1907 when the 

principal reduction plant burned.

A 20-stamp mill and 20-ton cyanidation plant were 

built in 1908 by the ADM&R Co. to replace the older 

mill that had burned. Production from these mines from 

1901 to 1917 was 4,481 oz of gold and 755 oz of silver 

(U.S. Bureau of Mines, unpub. data).

The district saw little activity until 1930 when 

Rescue Gold Mines reopened the ADM&R mines. In 

1933 tailings were shipped by a lessee from these mines 

and from the Twin Brothers mine. Smelting ore was 

shipped from the Lamoreaux, Clara Morris, and Golden 

Reward mines, and ore was treated from the Big Four 

and Golden Reward mines by amalgamation and 

concentration. In 1934, the largest producer was the 

lease operation at Rescue Gold Mine (ADM&R), 

although Gibbonsville Premier Gold Mines, Ltd., processed 50 tons of gold ore from the Big Four mine in a new 

10-stamp mill. A 50-ton/day flotation-concentration 

plant was built by Gold Producers, Inc., in 1935 at the 

Twin Brothers mine, to process ore from the Twin 

Brothers mine and to custom mill for other mines in the 

district. Premier was active at Gibbonsville, and the Clara 

Morris mine was an important producer in 1935 and 

1936.

The Golden Reward and Twin Brothers mines 

were operated in 1937. The 50-ton/day mill at the Twin 

Brothers mine was moved to the Grunter mine near 

Shoup the same year. From 1902 to 1938, the Twin 

Brothers mine yielded 1,449 oz of gold and 1,052 oz of 

silver (U.S. Bureau of Mines, unpub. data). The loss of 

the Twin Brothers mill slowed lode production from 

Gibbonsville mines considerably. Gibbonsville Premier, 

owner of the Twin Brothers and Big Four mines, 

operated with small crews until 1942 when the mines 

were shut down. This marked the end of precious-metal 

lode mining in the district, although the area was prospected heavily for uranium in the middle 1950's.

Placer mining has continued on and off throughout 

the productive history of the district. In 1937, placer gold 

production was increased substantially by North Fork 

Placers. Placer deposits in the district, which accounted 

for most of the district's production, yielded 520 oz of 

gold in 1939. A dramatic production increase, from 959 

oz of gold in 1940 to 3,004 oz in 1941 (table B3), was due 

to a bucket line dredge and two floating dredges. In 1942 

a dredging operation by Smith Brothers and Courtis, 

Inc., recovered 2,466 oz of gold and 203 oz of silver, 

and the Idaho-Warren Dredging Company recovered 

1,900 oz of gold and 123 oz of silver. All lode and placer 

mines were shut down in 1942 by War Production Board 

Order L-208. Placer mining resumed in 1946, but ceased 

again in 1948.

B40 Geology and Resources of Gold in the United States
Geologic Setting

Mines in the Dahlonega district are hosted by the 

Yellowjacket Formation, which may be the equivalent of 

the Precambrian Prichard Formation of the Belt Supergroup (Ruppel, 1975). These rocks are intruded by 

augen gneiss near Shoup; zircons from the gneiss were 

dated by Evans and Zartman (1981a) at 1,370 Ma. A 

detailed description of the Yellowjacket Formation in 

this area was given by Lopez (1981).

A large north-trending dike in the vicinity of Gibbonsville was described by Lincoln (1912) and Umpleby 

(1913b). It appears to be a Tertiary diorite, probably 

similar to Tertiary diorite that is common in the Challis 

quadrangle.

The trans-Challis fault system crosses the area, as 

do northwest-trending Basin-Range structures of eastern 

Idaho. As shown on the Dillon 1°X2° geologic map 

(Ruppel and others, 1983), closely spaced north-south 

Tertiary faults also transect the area (Ruppel, 1981). 

According to Bacon (1905) and Umpleby (1913b), these 

faults offset veins in the mines. In spite of the complex 

faulting, the veins in the district trend east-west and 

contain a simple mineralogy of quartz, auriferous pyrite, 

pyrite, and free gold. The mineralogy is typical of epithermal veins associated with the trans-Challis fault 

system.

Characteristics of the Deposits

The best description of veins at the ADM&R 

mines was given by Umpleby (1913b, p. 132):

Six or seven veins have been encountered in the 

mine [ADM&R], all of them striking east and west, and all 

except the Eckhart dipping 50-85° N. These veins are 

thin, tabular bodies and present a marked variation in 

the thickness from place to place, both along the strike 

and dip. The larger ones average perhaps 12 inches in 

width. The better ore occurs in shoots, which pitch east 

at about the angle of the inclosing rock. As a rule, the 

ores are higher grade where the inclosing rock is black 

slate, and comparatively lean where it is quartzite or 

diorite.

The outcrops of the veins usually have little or no 

topographic expression. Heavy iron and some manganese stains are everywhere present in them, and in 

places a short distance below the surface, the vein 

material is in an earthy mass of manganiferous hematite. 

The upper 10 to 50 feet is much poorer than the next 100 

feet or so, and at 150 to 200 feet primary ore is reached.

The primary ore consists of pyrite, with a few 

crystals of chalcopyrite, in a silica gangue rarely 

including a little calcite. The pyrite appears as cubes, as 

fine-grained disseminations, and as patches. In its 

broader distribution, the ore occurs in shoots which vary 

in length from 25 to 300 feet, and within the shoots pyrite

has a rather even general distribution, although in detail 

such as is seen in the hand specimen, a bunchy 

arrangement is pronounced.

Umpleby (1913b) also noted that oxidation in a few 

places extends to depths below 50 m but is less in many 

other places.

Molybdenum-copper Deposits

The northeast end of the trans-Challis fault system 

in Idaho contains several molybdenum or molybdenumcopper occurrences that are probably related to the fault 

system and associated Tertiary igneous intrusive rock. 

Most of the mineral deposits were discovered within the 

period 1965-1985.

Molybdenum is mentioned as a resource in Lemhi 

County, Idaho, in several State Mine Inspector reports, 

dating to the early 1920's, but the first mention of 

molybdenum in the part of the county under discussion is 

in an unpublished report of 1931 by the Owl Mining 

Company to the State Mine Inspector. Among several 

mining claims listed as being located west of Shoup 

(fig. Bll) was one called the Molybdenum lode. Little is 

known about these claims. They are probably related to 

the plutonic suite of Painted Rocks of Tertiary age 

mapped north of Shoup (Lund and others, 1983).

The best known molybdenum-copper deposit is the 

Bobcat Gulch porphyry system (fig. Bll), which is about 

30 km north of Salmon and was explored by Cominco 

American, Inc. Bunning and Burnet (1981) described the 

deposit, noting that mineralization was related to two 

intrusive centers in which the sequence of intrusion was 

quartz diorite-granodiorite-quartz latite. The quartz 

latite is the most heavily mineralized, although the granodiorite also is mineralized and altered locally. Molybdenite but no chalcopyrite is present in quartz veinlets 

cutting rhyolite porphyry dikes, and molybdenite-pyrite 

but no chalcopyrite is present in the quartz diorite 

porphyry. Molybdenite and chalcopyrite are present in 

quartz latite and granodiorite porphyry, which suggests 

that the minerals have been introduced during separate 

mineralizing events. One of the latite dikes was dated at 

48.5 Ma (whole rock 40Ar/39Ar), and biotite from the 

dike was dated at 49.1 Ma (K-Ar method) (Bunning and 

Burnet, 1981). Clusters of the quartz latite dikes are 

exposed at the deposit, and quartz veins in these dikes 

contain molybdenum. The dikes and plutons trend 

northwest, although the deposit is on line with the 

Panther Creek fault. Bunning and Burnet (1981) noted 

that northwest structures in the area probably predate 

Eocene intrusion.

Bennett (1977) reported anomalous molybdenum 

in soil and stream-sediment samples from a locality 

northwest of Leesburg (fig. Bll). In 1979, the Anaconda

United States Gold Terranes B41
Copper Co. followed up on this study (Hillisland, 1981) 

and examined (without locating molybdenum ore) a 

1,672,000 m2 part of the area where soil samples contain 

concentrations of 10 ppm or greater Mo. Numerous 

quartz veins but no igneous rocks crop out in the area. 

More work will be necessary to determine the source of 

the molybdenum anomaly.

Molybdenite and ferrimolybdite occur in a deposit 

of quartz veinlets that cut augen gneiss in the Spring 

Creek area, north of Shoup (fig. Bll) and near the 

Idaho-Montana border. According to King (1964), 

samples of the mineralized material contained 0.12 to 

1.27 percent Mo. The deposit was drilled by Brenda 

Mining Company during the period 1978-1980 and two 

adits were driven, but no further work is known to have 

been done at the property.

DISCUSSION

The trans-Challis fault system consists of 

northeast-trending subparallel, high-angle faults, aligned 

grabens, and roughly aligned intrusive rocks of Tertiary 

age. It extends at least 270 km across central Idaho and 

appears to be a broad zone of crustal extension within 

which faulting has been active since Precambrian time. 

Evidence gleaned from a literature review and from our 

field work indicates that most, if not all, of the gold-silver 

deposits within the system or adjacent to it are genetically 

related to the faults and to various intrusive rocks of 

Tertiary age, the emplacement of which has been guided 

by the faults. Throughout the faulted area, mineralized 

veins extend along the northeast-trending faults, 

although locally veins strike in other directions, following 

fractures established by fault movement within the 

system. Many veins follow along the walls of dikes, 

particularly rhyolite dikes, but some veins cut the dikes 

and clearly are younger. Other dikes cut the veins, which 

suggests a close vein-dike relationship. Potassium-argon 

ages of biotite and hornblende from Tertiary plutonic 

rocks along the fault system range from about 45 to 48 

Ma. Younger dikes cut the plutonic rocks, and 

mineralized veins in the dikes therefore are known to be 

even younger. To date, we have been unable to satisfactorily establish the age of gold-silver mineralization. 

The fact that it was of Tertiary age, however, is proven by 

field relationships and documented by available radiometric ages. Zircon from hydrothermally altered intrusive rhyolite at the Golden Sunbeam mine yielded a 

fission-track age of about 46 Ma, and sericite from the 

General Custer vein yielded K-Ar ages of about 44- 

48 Ma. A fission-track age of zircon from a rhyolite dike 

at the Little Falls molybdenum deposit is about 29 Ma. 

Veinlets of molybdenite cut a rhyolite dike at the Little 

Falls deposit and gold-silver veins at the Golden 

Sunbeam mine cut altered rhyolite. Sericite from the

General Custer vein could be the same age as the vein, 

but if it originated from the andesitic host rock it could be 

older.

Hydrothermal alteration of the wall rock adjacent 

to veins is common along the trans-Challis fault system. 

Moderately argillized and sericitized rock extends to 

several meters away from vein walls in Boise Basin, but 

intensely propylitized zones range from hundreds to 

thousands of meters in length and width in the Yankee 

Fork district. Silicification and argillization were more 

intense near faults and mineralized veins within the 

propylitized zones than elsewhere. Tertiary plutonic 

rocks and hypabyssal rocks both are altered near 

mineralized deposits. Tertiary hydrothermal alteration 

was extensive in the central part of Idaho and appears to 

have been directly related to Tertiary plutonism. Criss 

and Taylor (1983) called attention to widespread hydrothermal alteration around Tertiary plutonic bodies, and 

field evidence suggests that even more intensive alteration occurred in shattered and permeable rocks along 

fault zones. The widespread alteration that took place 

where veins are absent in the Yankee Fork district, and 

the fact that gold-silver veins in the Boise Basin tend to 

pinch out in intensely altered and impermeable rocks, 

suggest that alteration preceded or was contemporaneous with development of ore shoots in veins. 

Extensive fracturing along the trans-Challis fault system, 

however, provided access for hydrothermal solutions 

associated with Tertiary plutonism, which carried mineral components that formed the mineral deposits.

Gold-silver veins along the trans-Challis fault 

system are epithermal in type, as indicated by the 

mineralogy of the deposits. The principal ore mineral in 

most of the gold deposits is auriferous pyrite or native 

gold, whereas complex suites of silver sulfides with 

accompanying minor amounts of base metals are more 

common in others. Quartz is the common gangue 

mineral, mostly cryptocrystalline to fine grained and 

banded with fine-grained sulfides. Drusy and combtextured quartz also is common. The youngest quartz in 

brecciated vein-quartz sequences is more abundant than 

older quartz and tends to be more auriferous. Other 

gangue minerals in the veins, including adularia, also 

typify epithermal deposits. The ore shoots appear to have 

been richer near the surface and did not extend to great 

depths. Most ore shoots have been mined within 200 m of 

the surface. The presence of extensive placer deposits 

downstream from known lode deposits indicates that 

large portions of the epithermal ore shoots have been 

removed by erosion. Some areas, however, appear to 

have a good potential for large-tonnage, low-grade goldsilver deposits.

Manuscript received by scientific editors January 1985

B42 Geology and Resources of Gold in the United States
REFERENCES CITED

Anderson, A.L., 1947, Geology and ore deposits of the Boise 

Basin, Idaho: U.S. Geological Survey Bulletin 944-C, 

319 p.

___ 1949, Silver-gold deposits of the Yankee Fork district, 

Custer County, Idaho: Idaho Bureau of Mines and 

Geology Pamphlet 83, 37 p.

___ 1953, Gold-copper-lead deposits of the Yellowjacket 

district, Lemhi County, Idaho: Idaho Bureau of Mines 

and Geology Pamphlet 94, 41 p.

Anderson, A.L., and Rasor, A.C., 1934, Silver mineralization in 

the Banner district, Boise County, Idaho: Economic 

Geology, v. 29, no. 4, p. 371-387.

Bacon, H.C., 1905, A complicated fault system: The Engineering and Mining Journal, February 16, 1905, 

p. 324.

Ballard, S.M., 1924, Geology and gold resources of the Boise 

Basin, Boise county, Idaho: Idaho Bureau of Mines and 

Geology Bulletin 9, 103 p.

Bell, R.B., 1904, Report of mining districts of Idaho: Report of 

the State Mine Inspector for the year 1903, p. 104.

Bennett, E.H., 1977, Reconnaissance geology and geochemistry 

of the Blackbird Mountain-Panther Creek region, Lemhi 

County, Idaho: Idaho Bureau of Mines and Geology 

Pamphlet 167, 108 p.

___ 1984, The trans-Challis fault zone, a major crustal 

discontinuity in central Idaho: Geological Society of 

America Abstracts with Programs, v. 16, no. 6, p. 442.

Breckenridge, R.M., Sprenke, K.F., and Stryhas, B.A., 1984, 

List of Idaho earthquakes 1872-1983: Idaho Bureau of 

Mines and Geology Technical Report 84-1, 41 p.

Bunning, B.B., and Burnet, F.W., 1981, Copper-molybdenum 

mineralization in the Bobcat Gulch porphyry system, 

Lemhi County, Idaho: paper presented at the 87th 

Annual Northwest Mining Association Convention, 

Spokane, Washington, lip.

Callahan, I.E., Cooley, E.F., and Neuerburg, G.J., 1981, 

Selected Mo and W assays from stream-sediment 

samples and panned heavy-mineral concentrates, Challis 

Idaho 2° topographic quadrangle: U.S. Geological Survey 

Open-File Report 81-1344, 12 p.

Choate, R., 1962, Geology and ore deposits of the Stanley area: 

Idaho Bureau of Mines and Geology Pamphlet 126, 

121 p.

Criss, R.E., Champion, D.E., and Mclntyre, D.H., 1985, 

Oxygen isotope, aeromagnetic, and gravity anomalies 

associated with hydrothermally altered zones in the 

Yankee Fork mining district, Custer County, Idaho: 

Economic Geology, v. 80, no. 5, p. 1277-1296.

Criss, R.E., and Taylor, H.P., Jr., 1983, An 18O/16O and D/H 

study of Tertiary hydrothermal systems in the southern 

half of the Idaho batholith: Geological Society of 

America Bulletin, v. 94, no. 5, p. 640-663.

Evans, K.V., and Zartman, R.E., 1981a, U-Th-Pb zircon geochronology of Proterozoic Y granitic intrusions in the 

Salmon area, east-central Idaho: Geological Society of 

America Abstracts with Programs, v. 13, no. 4, p. 195.

___1981b, Evidence from U-Th-Pb zircon ages for 

Cambrian-Ordovician plutonism in east-central Idaho: 

Geological Society of America Abstracts with Programs, 

v. 13, no. 4, p. 195.

Fisher, F.S., 1987, Mineral resources, in Mineral resource 

potential and geology of the Challis I°x20 quadrangle, 

Idaho: U.S. Geological Survey Open-File Report 

87-480, 51 p.

Fisher, F.S., Mclntyre, D.H., and Johnson, K.M., 1983, 

Geologic map of the Challis 1° x 2° quadrangle, Idaho: 

U.S. Geological Survey Open-File Report 83-523.

Hardyman, R.F., and Fisher, F.S., 1985, Rhyolite intrusions and 

associated mineral deposits in the Challis volcanic field, 

Challis quadrangle: U.S. Geological Survey Bulletin 

1658, p. 167-179.

Hillisland, L.L., 1981, The geology, mineralization, and geochemistry of the Pine Creek area, Lemhi County, Idaho: 

Corvallis, Oreg., Oregon State University M.S. thesis, 

197 p.

Hughes, G.J., Jr., 1983, Basinal setting of the Idaho cobalt belt, 

Blackbird mining district, Lemhi County, Idaho: Proceedings of the Denver Regional Exploration Geologists 

Society Symposium; Genesis of Rocky Mountain ore 

deposits; Changes with time and tectonics, p. 21-27.

Jennings, E.P., 1906, The Lost Packer copper-gold lode: 

Canadian Mining Institute Journal, v. 9, p. 54-57.

Jones, E.L., Jr., 1916, Lode mining in the Quartzburg and 

Grimes Pass porphyry belt, Boise Basin, Idaho: U.S. 

Geological Survey Bulletin 640, p. 83-111.

Jordan, D.C., 1984, The geology and geochemistry of the 

south-central portion of the Ulysses Mountain quadrangle, Lemhi County, Idaho: Moscow, Idaho, University 

of Idaho M.S. thesis, 149 p.

Kiilsgaard, T.H., and Bennett, E.H., 1985, Mineral deposits in 

the southern part of the Atlanta lobe of the Idaho 

batholith and their genetic relation to Tertiary intrusive 

rocks and faults: U.S. Geological Survey Bulletin 1658, 

p. 153-166.

Kiilsgaard, T.H., and Lewis, R.S., 1985, Plutonic rocks of 

Cretaceous age and faults in the Atlanta lobe of the 

Idaho batholith, Challis quadrangle: U.S. Geological 

Survey Bulletin 1658, p. 29-42.

King, R.U., 1964, Molybdenum, in Idaho Bureau of Mines and 

Geology Special Report 1: p. 133-138.

Lesure, F.G., 1971, Residual enrichment and supergene 

transport of gold, Calhoun mine, Lumpkin County, 

Georgia: Economic Geology, v. 66, p. 178-186.

Lincoln, F.C., 1912, Gold deposits of Gibbonsville, Idaho: 

Mining and Scientific Press, July 13, 1912, p. 47-49.

Lindgren, Waldemar, 1898, The mining districts of the Idaho 

Basin and the Boise Ridge, Idaho: 18th Annual Report 

of the U.S. Geological Survey, Pt. 3, p. 617-719.

Lopez, D.A., 1981, Stratigraphy of the Yellowjacket Formation 

of east-central Idaho: U.S. Geological Survey Open-File 

Report 81-1088, 219 p.

Lund, K., Rehn, W.M., and Benham, J.R., 1983, Mineral 

resource potential map of the Blue Joint wilderness study 

area, Ravalli County, Montana, and the Blue Joint

United States Gold Terranes B43
Roadless area, Lemhi County, Idaho: U.S. Geological 

Survey Miscellaneous Field Studies Map MF-1557-A, 

scale 1:50,000.

Luthy, S.T., 1981, The petrology of Cretaceous and Tertiary 

intrusive rocks of the Red Mountain-Bull Trout Point 

area, Boise, Custer, and Valley Counties, Idaho: Missoula, Mont., University of Montana M.A. thesis, 109 p.

Mclntyre, D.H., Ekren, E.B., and Hardyman, R.F., 1982, 

Stratigraphic and structural framework of the Chain's 

volcanics in the eastern half of the Challis I°x20 

quadrangle, Idaho, in Bonnichsen, Bill, and Brechenridge, R.M., eds., Cenozoic geology of Idaho: Idaho 

Bureau of Mines and Geology Bulletin 26, 725 p.

Mclntyre, D.H., and Johnson, K.M., 1985, Epithermal goldsilver mineralization related to volcanic subsidence in the 

Custer graben, Custer County, Idaho: U.S. Geological 

Survey Bulletin 1658, p. 109-116.

O'Neill, J.M., and Lopez, D.A., 1985, Character and regional 

significance of Great Falls tectonic zone, east-central 

Idaho and west-central Montana: American Association 

of Petroleum Geologists Bulletin, v. 69, p. 437-447.

Ross, C.P., 1927, Ore deposits in Tertiary lavas in the Salmon 

River Mountains, Idaho: Idaho Bureau of Mines and 

Geology Pamphlet 25, 21 p.

___ 1934, Geology and ore deposits of the Casto 

quadrangle, Idaho: U.S. Geological Survey Bulletin 854, 

135 p.

___ 1936, Mining districts of the State of Idaho: Idaho 

Bureau of Mines and Geology Map, scale 1:500,000. 

1937, Some lode deposits in the northwestern part of

the Boise Basin, Idaho: U.S. Geological Survey Bulletin 

846-D, p. 239-276.

Ruppel, E.T., 1975, Precambrian Y sedimentary rocks in eastcentral Idaho: U.S. Geological Survey Professional Paper 

889-A, 23 p.

___ 1981, Cenozoic block uplifts in southwest Montana and 

east-central Idaho: U.S. Geological Survey Professional 

Paper 1224, 24 p.

Ruppel, E.T., O'Neill, J.M., and Lopez, D.A., 1983, Preliminary 

geologic map of the Dillon 1° x 2°quadrangle, Montana: 

U.S. Geological Survey Open-File Report 83-168, scale 

1:250,000.

Shannon, E.V., 1926, The minerals of Idaho: United States 

National Museum Bulletin 131, 483 p.

Shockey, P.N., 1957, Reconnaissance geology of the Leesburg 

quadrangle, Lemhi County, Idaho: Idaho Bureau of 

Mines and Geology Pamphlet 113, 42 p.

Umpleby, J.B., 1913a, Some ore deposits in northwestern 

Custer County, Idaho: U.S. Geological Survey Bulletin 

539, 104 p.

___ 1913b, Geology and ore deposits of Lemhi County, 

Idaho: U.S. Geological Survey Bulletin 528, 182 p.

___ 1913c, A preliminary account of the ore deposits of the 

Loon Creek district: U.S. Geological Survey Bulletin 530, 

p. 66-74.

U.S. Bureau of Mines, 1924-31, Mineral Resources of the 

United States, Idaho chapter.

___ 1932-83, Minerals Yearbook, Idaho chapter. [Yearly 

volume, pages vary.]

U.S. Geological Survey, 1905-23, Mineral Resources of the 

United States, Idaho chapter. [Yearly volume, pages 

vary.]

Van Noy, R.M., Ridenour, James, Zilka, N.T., Federspiel, F.E., 

Evans, R.K., Tuchek, E.T., and McMahan, A.B., 1986, 

Economic appraisal of the eastern part of the Sawtooth 

National Recreation Area, Idaho, in Mineral resources 

of the eastern part of the Sawtooth National Recreation 

Area, Custer and Blaine Counties, Idaho: U.S. Geological Survey Bulletin 1545, p. 231-472.

Wells, M.W., 1983, Gold camps and silver cities, 2nd edition: 

Idaho Bureau of Mines and Geology Bulletin 22, 165 p.

APPENDIX-1989 UPDATE

Terrane of the trans-Challis fault system, from the 

Boise Basin to Gibbonsville, underwent intensive mineral 

exploration in 1989, and in immediately prior years.

In the northeast part, Meridian Gold Co. and 

Canyon Resources announced, in 1988, the discovery of 

the Beartrack deposit northeast of Leesburg. The deposit 

is in the area of the Gold Dust, Gold Flint, and Gold 

Ridge mines (fig. Bll), and is the largest gold discovery 

ever made in Idaho. It is reported to contain 2.6 million 

oz of gold. Plans are to mine the deposit by open-pit 

methods and to process the ore by the heap-leach 

technique. In the vicinity of the nearby Haidee mine, 

major exploration by B.P. Minerals and American

Gold Resources was underway in 1989. Tenneco 

Minerals drilled the Ulysses and Kittie Burton mines in 

1986 and further exploration at the mines was planned by 

Noranda Co. for 1989. About 6,000 tons of ore was 

minetf from the Yellowjacket mine in 1988 and intensive 

exploration for bulk-minable precious metal ore was 

planned for the mine in 1989. Renewed exploratory 

interest in the northeast part of the trans-Challis terrane 

was reflected by the 5,358 mining claims staked in Lemhi 

County in 1988.

In the central part, gold mining was resumed at the 

Valley View mine (fig Bll) in 1986. At the Golden 

Sunbeam mine, Geodome Resources Ltd. was investigating, in 1989, a deposit reported to contain 3.3 million 

tons of near-surface material that averaged 0.077 oz 

Au/ton.

B44 Geology and Resources of Gold in the United States
Geologic Setting and Potential Exploration Guides for 

Gold Deposits, Black Hills, South Dakota

By Jack A. Redden1 and Gregory McN. French2

Abstract

The core of the Black Hills is underlain by Early Proterozoic metasedimentary rocks deposited unconformably 

on Archean basement. Most of the core is dominated by 

deep-water marine turbidite deposits and minor tholeiitic 

volcanic rocks (Early Proterozoic, «2.0-1.8 Ga), although 

shallow-water marine shelf quartzite is abundant along the 

eastern margin. In contrast, the Nemo area in the northeastern part of the core differs from the remainder of the 

Black Hills because it is characterized by mostly marine 

fanglomerate, and minor quartzite, arkose, carbonate rocks, 

and fluvial deposits of Early Proterozoic age («2.4-2.1 Ga) 

which were deposited in a long-lived rift basin. Late Archean 

(>2.5 Ga) and Early Proterozoic («2.4-2.2 Ga) ironformations in the Nemo area are typically oxide fades, but 

Early Proterozoic («2.0-1.8 Ga) gold-bearing iron-formation 

units are predominantly carbonate-silicate facies and may be 

associated with volcaniclastic rocks or tuffaceous metasedimentary rocks.

Early Proterozoic metasedimentary rocks in the central 

Black Hills were folded (F.,) along east-northeast axes and 

strongly refolded (F2) along north-northwest axes and regionally metamorphosed. The 1.7 Ga Harney Peak Granite and 

associated pegmatite bodies in the southern Black Hills were 

emplaced in a major dome which modified earlier structures. 

Phanerozoic rocks which covered the area were uplifted, 

along with the basement, to form the present Black Hills 

during Laramide time.

Gold deposits in Proterozoic rocks include (1) stratabound syngenetic Homestake-type; (2) gold-quartz veins; 

(3) fault-controlled deposits; and (4) fossil placers. Of these, 

the Homestake-type is by far the most productive, and is 

believed to have formed during the deposition of carbonatesilicate-sulfide-facies iron-formation by hot springs in small, 

shallow, probably fault-bounded basins. The deposits have 

been modified subsequently to a minor degree by deformation and regional metamorphism.

Geological Survey and South Dakota School of Mines 

and Technology, 501 E. St. Joseph St., Rapid City, SD 57701-3995.

3Atlas Precious Metals, Inc., Box 251, Eureka, NV 89316.

Phanerozoic gold deposit types include (1) replacement deposits in lower Paleozoic rocks, (2) disseminated and 

vein deposits in Tertiary igneous rocks in the northern Black 

Hills, and (3) placer deposits in Cambrian, Tertiary, and 

Holocene strata.

Of all the various types of deposits, the Homestaketype, the Tertiary replacement deposits in Paleozoic rocks, 

and the vein and disseminated deposits in Tertiary igneous 

rocks have much gold resource potential. Lenses and units 

of iron-formation similar to that at the Homestake mine are 

abundant in the Rochford and Keystone districts where small 

gold deposits were mined in the past. Iron-formation units in 

the Rochford district are apparently younger (1.88 vs. 

»2.0 Ga) than the Homestake Formation, however. Absolute 

ages of iron-formation units in the Keystone district are 

unknown, but most gold deposits are unlike the Homestaketype: in the Keystone district they are localized in faultcontrolled breccia that cuts iron-formation and other rock 

types. Gold may have been remobilized, at least in part, from 

iron-formation.

Replacement deposits in Phanerozoic rocks are limited 

to areas of Tertiary igneous rocks in the Lead-Deadwood 

dome and are largely in the basal part of the Cambrian 

Deadwood Formation. Structure contours on the Proterozoic 

unconformity indicate that the Lead-Deadwood dome was 

formed by emplacement of Tertiary sills and dikes in the 

basement and in Paleozoic strata; minor structural highs 

represent paleotopographic hills underlain by Proterozoic 

quartzite, predominantly the Ellison Formation. Isopachs on 

the lower sandstone-conglomerate part of the Deadwood 

suggest a strong control of thickness by paleotopography; 

gold deposits are concentrated in areas where the basal 

Deadwood is anomalously thin. A combination of lithologic 

and alteration changes, along with fracturing related to both 

paleotopographic highs and emplacement of Tertiary rocks, 

is believed to have been important in localizing the gold 

deposits.

The basal part of the Deadwood Formation is derived 

largely from the locally underlying Proterozoic rocks; heavymineral suites suggest only minor transport of detrital grains 

from west to east. The Deadwood is therefore a good 

geochemical indicator of the underlying rocks and should be

United States Gold Terranes B45
a significant indicator of underlying or nearby gold deposits 

in Proterozoic rocks.

Disseminated gold deposits in Tertiary igneous rocks 

are localized in breccias and fractured stockworks. Alteration 

mineral assemblages, including argillic, sericitic, and potassic types, locally may be accompanied by quartz, fluorite, 

and barite. Pyrite is the most common sulfide but sparse 

amounts of arsenopyrite, pyrrhotite, and magnetite are 

locally present. Limited salinity and temperature data on fluid 

inclusions plus isotope data suggest that dominantly magmatic fluids were involved in the disseminated mineralizations, although the source of the metals and relationship of 

the fluids to specific igneous rock types are not known. Areas 

of extended igneous activity seem to have been favored for 

mineralization, but such areas require detailed mapping and 

exploration to outline mineralized deposits.

INTRODUCTION

The Black Hills area has produced gold for more 

than 100 years, much of it being derived from the worldclass Homestake gold deposit, which is in Proterozoic 

rocks exposed in the small Lead-Deadwood dome at the 

northern end of the core of the Black Hills uplift 

(fig. B13). Smaller gold deposits in Paleozoic rocks and in 

Tertiary intrusive rocks also occur throughout the LeadDeadwood dome. Outside this dome area, small lode 

deposits in Proterozoic rocks of the main uplift have had 

sparse production. Gold has also been produced from 

placer deposits in basal Cambrian rocks, in Tertiary 

gravel deposits, and in Quaternary gravels, as well as 

from the lode deposits. The richest placers, however, also 

were in the Lead-Deadwood area and derived their gold 

from both lode and older placers. The Lead-Deadwood 

area is clearly the major focus for gold production and 

exploration in the Black Hills.

This overview of the geologic setting of the 

different gold-deposit types in the northern Black Hills 

presents new data on relationships between the Phanerozoic gold deposits and depositional environments of 

Phanerozoic host rocks. We also interpret some Proterozoic structural features, correlations of lithologic 

units, and depositional environments, such that the new 

data and interpretations may be of use in exploration for 

new deposits. Work in progress by S.W. Caddey and 

others and a paper by Norton (1989) describe the 

geology of the Homestake deposit and Tertiary mineralization in the Bald Mountain area, respectively, and 

provide more details of gold mineralization in these 

major deposits.

Gold was discovered along French Creek in the 

southern Black Hills in 1874 by members of General 

George A. Glister's expedition. Much richer gold placers 

were discovered in the Lead area in 1875, and the first 

lode claims were located shortly thereafter on what 

ultimately became part of the Homestake deposit. By

1877, gold deposits in the basal Cambrian strata near 

Tertiary intrusive rocks were recognized in the LeadDeadwood area. These deposits, Tertiary in age, 

included not only gold but also silver, lead, zinc, and 

tungsten, although the value of these latter metals was 

insignificant relative to that of gold. In the late 1880's 

dozens of mines were in operation in the LeadDeadwood area.

Production of gold from the Homestake deposit to 

1988 totals more than 36 million troy oz, which far 

surpasses that from the other Black Hills deposits. The 

deposits of Tertiary age (as summarized by Norton, 

1974) produced approximately 2.7 million oz excluding 

placer gold. Production from other deposits in the main 

Black Hills uplift is about 200,000 oz. Another 150,000 

oz of gold was produced from unidentified sources 

(Norton, 1974).

PRECAMBRIAN ROCKS

The Black Hills consist of two areas of largely 

granitic rocks surrounded by a terrane of metamorphic 

rocks, all of Precambrian age. The metamorphic terrane 

is dominated by metamorphosed equivalents of Early 

Proterozoic deep-water turbidite deposits, but it includes 

also significant amounts of metamorphosed shale, black 

shale, shelf quartzite, and greenstone, and lesser 

amounts of other rock types. The oldest Early Proterozoic rocks, near Nemo, were deposited in a shallow 

marine rift environment and are dominated by coarse 

clastic sediments that also include some fluvial deposits. 

Small metamorphosed intrusive bodies of gabbro of 

several ages are relatively widespread. In the southern 

Black Hills the Harney Peak Granite and associated 

pegmatite deposits (^1.7 Ga) represent the youngest 

known Precambrian rocks. In the following sections, 

sedimentary protoliths will be used in the description of 

the metamorphic rock units wherever these protoliths are 

clearly recognizable.

Archean Rocks

Late Archean rocks (unit Wos; fig. B13) intruded 

by «2.5 Ga granite (unit Wgr) (Ratte, 1986) are present 

in the center of a small dome at Bear Mountain along the 

west side of the Precambrian core and in the Little Elk 

Creek area (Zartman and Stern, 1967) north of Nemo 

(fig. B13). At Bear Mountain the country rock consists of 

quartzose biotite-feldspar schist probably derived from 

graywackes, whereas at Little Elk Creek it consists of 

schist and feldspathic gneiss derived from marine arkose, 

quartzite, and conglomerate. Adjacent thin taconite 

lenses at Little Elk Creek are also probably Late 

Archean. Schist in the isolated Tinton area (fig. B13) 

does not resemble most of the Proterozoic rocks in the

B46 Geology and Resources of Gold in the United States
central Black Hills and is shown as Late Archean(?) 

although it may be Early Proterozoic.

Proterozoic Rocks

The oldest Early Proterozoic metasedimentary 

rocks (unit Xcq) in the Black Hills are in the Nemo area 

and have been described by Redden (1981). The lowmetamorphic-grade protoliths consist largely of marine 

fanglomerate, quartzite, and an overlying oxide-facies 

banded iron-formation. A tongue of pyritiferous fluvial 

conglomerate, grit, and quartzite within the unit contains 

anomalous concentrations of uranium and small 

amounts of placer gold. The fanglomerate and associated 

rocks contain clasts of older, presumably Archean oxidefacies taconite. These coarse clastic sedimentary rocks 

almost certainly were deposited in a rift environment. A 

gabbroic, gravity-differentiated layered sill (unit Xlg) that 

intrudes unit Xcq is 2.17±0.1 Ga (U-Th-Pb zircon date, 

Z.E. Peterman, written commun., 1986). Thus unit Xcq 

was deposited between 2.5 and 2.17 Ga, the age interval 

of the Little Elk Granite. Because the fanglomerate 

contains clasts of taconite that have been refolded prior 

to formation of the clasts, and clasts of other rocks 

similar to those exposed in the Little Elk Creek area, it is 

inferred to have been deposited unconformably on the 

Archean units Wes and Wgr (table B4).

These oldest Early Proterozoic rocks were folded 

and faulted, and an angular unconformity developed 

above listric fault blocks which were then covered by 

marine fanglomerate, quartzite, and arkose of the Estes 

Formation (unit Xqc) in the Nemo area. Younger 

shallow-water carbonate deposits (unit Xd) containing 

clastic terrigenous debris overlie the Estes Formation 

and are in turn apparently conformably overlain by 

amygdule-bearing pillow basalt (unit Xb) about 6 km 

northwest of Nemo. The Nemo section, including units 

Xcq, Xlg, Xqc, Xd, and Xb, constitutes a typical shallowwater rift-related sequence.

An inferred fault separates the rocks of the Nemo 

section from those of the central Black Hills basin. The 

fault is bordered on the west by an unnamed magnetiterich carbonate-silicate facies iron-formation that is 

believed to be the lateral equivalent of the oxide-facies 

Benchmark Iron-formation (included in unit Xcq) in the 

Nemo area. The Benchmark Iron-formation is the 

youngest unit exposed below the angular unconformity at 

the base of the Estes Formation. The unnamed ironformation is unconformably overlapped by shallow-water 

shelf quartzite, arkose, silty shale, and local conglomerate which Bayley (1972a, 1972b) named the Buck 

Mountain Quartzite. The Buck Mountain Quartzite 

(Xqc) is therefore considered to be equivalent to the 

Estes Formation, and it is believed to underlie a large, 

but poorly known area of high-grade metamorphic rocks

in the southeastern Black Hills that consists largely of 

quartzite and sillimanite schists. A gabbroic sill which 

intrudes unit Xd has been dated at «1.97 Ga (Z.E. 

Peterman, written commun., 1986). If the inferred correlations are correct, this age would represent the 

minimum age of the Xqc unit shown on figure B13.

At Bear Mountain the unit that is probably 

equivalent to these Estes-age metasedimentary rocks 

consists largely of quartzite and arkose (unit Xqc) which 

unconformably overlie the Archean rocks and fine upwards into a thin carbonate and shale section (unit Xd). 

These rocks are metamorphosed to various types of 

schists and marbles.

The shallow-water shelf quartzite (unit Xqc) is 

overlain by deeper water deposits of the basin in which 

the Black Hills Proterozoic rocks were deposited. 

Amygdule-free tholeiitic basalt (unit Xb) forms northnorthwest-trending, narrow greenstone fold- and faultbounded belts along the eastern part of the central Black 

Hills. Individual flows interfinger with black shale (unit 

Xsc) to the west, suggesting that the main center of 

basaltic volcanism was to the northeast. The basalt belts 

are characterized by interflow units of pyritic graphitic 

shale and local lenses of massive chert and carbonatesilicate-facies iron-formation. No age determinations 

have been possible on the basalt, but it is younger than 

unit Xqc.

In the southwestern and east-central parts of the 

central Black Hills basin, the sedimentary section is 

dominated by deep-water turbidite deposits (unit Xgw) 

characterized by proximal and medial graywacke fans. 

Proximal graywacke fan deposits are metamorphosed to 

quartzose schists, whereas more distal deposits contain 

various metamorphic minerals such as garnet, staurolite, 

or sillimanite depending on metamorphic grade. 

Although the detailed delineation and correlation of 

these fans are not everywhere clear, at least three 

separate units of graywacke are separated by shale (unit 

Xbs) and a heterogeneous unit consisting of conglomerate, debris flows, quartzite, shale, basalt, gabbroic sills, 

and lenses of massive chert and carbonate-silicate-facies 

iron-formation (unit Xcg). The shale is dominantly 

garnet phyllite or schist whereas the heterogeneous unit 

consists of a variety of metamorphic rocks, including 

recrystallized chert and cummingtonite-grunerite rock 

derived from the carbonate-silicate-facies iron-formation 

(larger units shown as Xif). Some of the conglomerate in 

unit Xcg is in part derived from the shelf quartzite (unit 

Xqc) to the east. In the Keystone area and west of 

Rockerville, unit Xcg is associated with tholeiitic pillow 

basalt (unit Xby), and basaltic fragments occur within 

debris flows. Thus, a volcanic center was located in the 

area west of or near Rockerville. Characteristic lithologies of unit Xcg ultimately pinch out in a general 

westerly direction where the heterogeneous unit

United States Gold Terrenes B47
B48 Geology and Resources of Gold in the United States
c

Ia 

S 

i

W

a 2.

a00 Figure B13. Generalized geology of Precambrian rocks in the Black Hills, South Dakota. Explanation on following page.
DESCRIPTION OF MAP UNITS. FIGURE B13 

(For correlation of map units see table B4)

TPz

^

Tertiary igneous rocks Shown only

intruding Precambrian rocks 

Phanerozoic rocks

EARLY PROTEROZOIC ROCKS

Harney Peak Granite Coarse-grained 

to pegmatitic muscovite granite 

and pegmatite

Phyllite and slate: mica schist in 

Lead area Includes the Grizzly 

Formation (Dodge. 1942). Swede 

Gulch Formation (Bayley. 1972c). 

part of the Oreville Formation 

(Ratte and Wayland. 1969), and a 

large area of rocks in the core 

of the Black Hills

Biotite schist, calc-silicate gneiss, 

and amphibolite Includes Crow 

Formation (Redden. 1963) southwest 

of Custer

Metagabbro: sills and dikes of

amphibolite or greenstone At 

least two separate ages ( 1. 944 Ma 

and 1. BBS Ma) known

Phyllite and biotite schist Contains 

minor chert and amphibole-bearing 

rocks; locally intruded by thin 

sills of metagabbro. Includes 

Poverty Gulch Slate. Nahant Schist, 

and Irish Gulch Slate in the 

Rochford area (Bayley. 1972c) and 

Northwestern and Flag Rock 

Formations in Lead area (Hosted 

and Wright. 1923)

Muscovite schist and phyllite Includes 

part of the Oreville Formation: 

equivalent to Xpb unit in Rochford 

and Lead areas

Quartzite. metagraywacke. and siliceous 

schist Includes Ellison Formation 

in the Lead area (Hosted and Wright. 

1923). Moonshine Gulch Quartzite 

north of Rochford (Bayley. 1972c). 

and siliceous graywacke west of 

Rochford. Possibly equivalent to 

part of Xgw and Xcg units in central 

Black Hills

Biotite schist or phyllite Thin-bedded 

and commonly garnet-rich schist: 

largely parts of the Oreville 

Formation (Ratte and Wayland. 1969. 

Ratte. 1986). but includes units 

east of the Grand Junction fault in 

the Berne quadrangle (Redden. 1968)

Conglomeratic biotite schist and

phyllite Also siliceous biotite 

phyllite. garnetiferous schist, 

quartzite. and carbonate-silicatefacies iron-formation

Metabasalt near Rockerville Includes 

metabasalt in Rochford. Lead, and 

Rockerville areas. Believed to be 

younger than Xb unit but locally 

may be equivalent in age

Metagraywacke; siliceous mica schist 

and impure quartzite at repeated 

stratigraphic intervals Includes 

part of Roubaix Formation (Bayley, 

1972b). Mayo and Bugtown Formations 

(Redden. 196B). and members of the 

Oreville Formation as well as unnamed 

units in the central Black Hills

Metabasalt; amphibolite. greenstone.

and actinolite schist Included are 

Hay Creek Greenstone (Bayley. 1972c) 

and part of the Vanderlehr Formation 

(Redden. 1966)

Iron-formation Iron-formation.

ferruginous chert, and minor mica 

schist: included are Homestake 

Formation (Hosted and Wright. 1923). 

Rochford Formation and Montana Mine 

Formation (Bayley. 1972c), and ironformation in the Keystone area and 

in minor areas throughout the 

Proterozoic core of the Black Hills

Siliceous biotite phyllite. calcareous 

biotite phyllite. and schist 

Includes the Poorman Formation 

(Hosted and Wright. 1923) and the 

Reausaw Slate (Bayley. 1972b). 

which intertongues with metabasalt 

(Xb)

Dolomitic marble and schist: marble.

phyllite. and calcareous phyllite 

Includes the Roberts Draw Formation 

in the Nemo area (Redden. 1961) and 

part of the Vanderlehr Formation at 

Bear Mountain

Metaquartzite and metaconglomerate: 

conglomeratic, siliceous schist, 

feldspathic schist, and minor 

marble In the Nemo area, map unit 

includes taconite conglomerate and 

is equivalent to the Estes Formation 

(Redden. 1981): in the eastern and 

southeastern part of the Black Hills, 

includes the Buck Mountain Quartzite 

(Redden. 1981) and Gingrass Draw 

Slate (Bayley. 1972b) and the 

extensive quartzite southeast of the 

Harney Peak Granite; in the Bear 

Mountain area, includes lower part 

of the Vanderlehr Formation (Redden. 

1968; Ratte. 1986)

UNCONFORMITY

Layered metagabbro Gravity-differentiated 

Blue Draw Metagrabbro sill (Redden. 

1981)

Metaconglomerate and quartzite:

conglomerate and feldspathic schist, 

biotite schist, taconite. and 

phyllite Includes the Boxelder 

Creek Formation and Benchmark Ironformation (Redden. 1981)

UNCONFORMITY

LATE ARCHEAN ROCKS 

Granite and gneissic granite Includes

the Little Elk Granite and granite

of Bear Mountain 

Older metasedimentary rocks; dominantly

quartz-feldspar-biotite schist 

Includes Nemo Iron-Formation (Redden.

1981); schist in Tinton area is

Archean (?)

Contact Dashed where approximately 

__ located 

"Fault Dashed where approximately

located 

Garnet Metamorphic isograd (shown in inset)

B50 Geology and Resources of Gold in the United States
gradually changes to graywacke and loses its identity as a 

mappable unit. The uppermost turbidite deposits of unit 

Xgw also pinch out to the west more or less at the 

longitude of Mystic, thus indicating that the deep part of 

the basin lay to the east.

A distinctive laminated, mica-rich, typically 

magnetite- and ilmenite-bearing phyllite-schist (unit 

Xms), believed to be derived from reworked and altered 

tuff, is widespread in the west-central part of the uplift. 

To the east it is overlain by the uppermost turbidite 

tongue of unit Xgw, but farther east and also to the north 

it is diluted by turbidite deposits and loses its distinctive 

characteristics. Similarly, in the Rochford district the tuff 

unit probably is generally equivalent to a sequence of 

heterogeneous rocks characterized locally by tholeiitic 

pillow basalt, volcaniclastic rocks, biotite-rich impure 

tuffaceous rocks, and carbonate-silicate-facies ironformation (unit Xpb). Bayley (1972c) divided these rocks 

in the Rochford district into five separate formations 

(table B4). He included four of these formations 

(including two carbonate-silicate-facies iron-formations) 

in the Flag Rock Group, which he believed was equivalent to the Flag Rock Formation at Lead (Hosted and 

Wright, 1923; Noble and Harder, 1948). Although additional mapping suggests that these subdivisions may not 

all be tenable, the general rock types are shown extending 

toward the Lead area from Rochford in figure B13. In 

the immediate Rochford area these rocks contain minor 

coarse angular volcaniclastic material indicative of a 

localized volcanic center. Alkalic ash-fall tuff that is 

interbedded with carbonate facies iron-formation at the 

Montana mine 4 km north-northwest of Rochford is 

dated at 1.88±0.03 Ga (U-Th-Pb zircon date, Z.E. 

Peterman, written commun., 1985). The uppermost part 

of the turbidite section in the central Black Hills is 

believed to be of this general age.

Below these volcanic-related rocks of the Rochford 

area is a unit of shallow-water quartzite which Bayley 

(1972a, 1972c) considered to be equivalent to the Ellison 

Formation in the Lead area. Weissenborn (1987), 

however, indicated that this quartzite is also probably 

equivalent to quartzose graywacke northwest of Rochford that Bayley considered to be part of the younger 

Swede Gulch Formation. Lateral facies changes in the 

quartzite in the Rochford area indicate that depositional 

conditions changed from deeper water west of Rochford 

to shallower water to the east and in the Lead area. 

Tuffaceous sedimentary rock within the Ellison Formation is 1.97 ±0.01 Ga (U-Th-Pb zircon date, Z.E. 

Peterman, written commun., 1986); therefore the most 

likely age of the lower part of the turbidite section in the 

southeastern central Black Hills is 5SS'2.0 Ga. The two 

available ages in the Rochford and Lead areas (1.88 and 

1.97 Ga) suggest that either an unconformity or a tectonic break must exist within the turbidite section.

Although this break has not been identified for certain, 

the most likely location for an unconformity is below the 

heterogeneous unit Xcg in the central Black Hills. 

Volcanic rocks within the heterogeneous debris flow unit 

(unit Xcg) near Storm Hill west of Rockerville would 

therefore be approximately equivalent in age to the 

younger tuff in the Rochford area.

The youngest Precambrian metasedimentary unit 

consists of a thick, monotonous sequence of graphitic 

slate and phyllite (unit Xps) derived from shale that 

underlies much of the northwestern part of the central 

Black Hills in the area west and north of Mystic. The unit 

has several different formation names depending on the 

geographic area studied (Bayley, 1972b, 1972c; Hosted 

and Wright, 1923).

Small metagabbro bodies (Xgb) intrude all of the 

Proterozoic rock units except unit Xps. Most of the 

bodies consist of either greenstone or amphibolite and 

are too small to show in figure B13. The metagabbro 

bodies are probably the same ages as associated volcanic 

rocks and therefore range in age from about 1.87 to 

1.97 Ga.

The Harney Peak Granite in the southern Black 

Hills is the youngest Proterozoic rock and is approximately 1.7 Ga (Rb-Sr whole rock date, Riley, 1970; 

U-Th-Pb monazite and zircon dates, Z.E. Peterman, 

written commun., 1986). Thousands of small pegmatite 

and granitic bodies in the country rock surround the main 

granitic area shown in figure B13. The granite has been 

petrographically and chemically described most recently 

by Redden and others (1982).

Structure and Metamorphism

The structure of the Proterozoic rocks is extremely 

complex and not everywhere fully understood. Major 

structures of representative areas are described in the 

following section, but no attempt is made to synthesize all 

structural events.

In the Nemo area Redden (1981) noted that folding preceded listric faulting and the deposition of the 

Estes-type rocks (unit Xqc) unconformably above the 

oldest Early Proterozoic rocks (unit Xcq). The unconformity between units Xqc and Xcq trends easterly and 

dips relatively steeply to the north-northwest. Both units 

Xqc and Xcq are overturned to the southeast. Folds in 

unit Xcq plunge about 70° to the north-northwest and are 

essentially coaxial with younger folds which affect all rock 

units. These younger folds have a well-developed axial 

plane foliation that trends about N. 30° W. and is nearly 

vertical. Conglomerate clasts are flattened and rotated 

into this foliation plane; their longest axes plunge steeply 

northwest.

Major faults in the Nemo area include northnorthwest-trending listric faults that developed

United States Gold Terrenes B51
Table B4. Tentative correlation of Precambrian rock unit protoliths in various parts of the Black Hills

[Abbreviations used:; FM, formation; QTZ, quartzite; BIF, banded iron-formation; MBR, member; lithologic symbols from figure B13]

Bear Mountain 

(formation names 

from Ratte, 1986, 

and Redden, 1968)

Rochford 

(formation names 

from Bayley, 1972c)

Lead

(formation names 

from Hosted and 

Wright, 1923)

Central Black Hills 

(formation names 

from Redden, 1963; 

Ratte and Wayland,

1969; Bayley, 1972b)

Nemo

(formation names 

as redefined by 

Redden, 1981)

Shale (Xps) part 

of OREVILLE FM

Graywacke (Xgw)

MAYO FM SW of

Custer.

Not present E of

Bear Mt.

CROW FM (Xc) 

tuffaceous rocks

Graywacke (Xgw) 

BUGTOWN FM and 

ZIMMER RIDGE MBR, 

OREVILLE FM

SWEDE GULCH FM 

(Xps) shale 

Gabbroic sills 

(Xgb)

GRIZZLY FM (Xps) 

shale

HARNEY PEAK GRANITE 

(Xh) 1.715+3 Ma

Shale (Xps)

Gabbroic sills 

(Xgb)

Graywacke (Xgw) 

BUGTOWN FM and 

part of OREVILLE FM

Altered tuffs 

(Xms) Part of 

OREVILLE FM

Black shale and 

distal graywacke 

(Xbs) Part of 

OREVILLE FM

POVERTY GULCH SLATE 

(Xpb) shale and 

chert ROCHFORD FM 

(Xif)

carbonate-silicate 

BIF

NAHANT SCHIST and 

RAPID CREEK 

GREENSTONE (Xby) 

basalt and black 

shale

MONTANA MINE FM 

(Xif) carbonatesilicate BIF 1,884 

^29 Ma

IRISH GULCH FM 

(Xpb) shale and tuff

FLAG ROCK FM 

(Xpb, Xby) shale, 

basalt, chert

MOONSHINE GULCH 

QUARTZITE (Xqg) 

sandstone changing 

to graywacke toward 

southwest

NORTHWESTERN FM 

(Xpb) shale 

ELLISON FM (Xqg) 

sandstone and 

siltstone shelf 

facies 

1,974+8 Ma

Altered tuffs 

(Xms) Part of 

OREVILLE FM 

Gabbroic sills 

(Xgb) 1,883 Ma

Graywacke (Xgw) 

Part of OREVILLE FM 

Black shale and 

distal graywacke 

(Xbs) Part of 

OREVILLE FM 

Graywacke (Xgw) 

Part of OREVILLE FM

Debris flow 

conglomerate to 

east; sandstone, 

carbonate-silicate 

BIF and basalt near 

Rockerville (Xcg, 

Xby)

Gabbroic sills at 

Bogus Jim Creek 

(Xgb) 1,944^15 Ma

B52 Geology and Resources of Gold in the United States
Table B4. Tentative correlation of Precambrian rock unit protoliths in various parts of the Black Hills Continued

Bear Mountain 

(formation names 

from Ratte, 1986, 

and Redden, 1968)

Rochford 

(formation names 

from Bayley, 1972c)

Lead

(formation names 

from Hosted and 

Wright, 1923)

Central Black Hills

(formation names 

from Redden, 1963; 

Ratte and Wayland, 

1969; Bayley, I972b)

Nemo

(formation names

as redefined by

Redden, 1981)

UNCONFORMITY OR 

FAULT

CONCEALED

HOMESTAKE FM (Xif) 

carbonate-silicate 

BIF

POORMAN FM (Xsc) 

black shale and 

possible basalt

CONCEALED

 FAULT 

UPPER PART, 

VANDERLEHR FM 

Basaltic 

volcaniclastic 

rocks (Xb), black 

shale with 

carbonate-silicate 

BIF (Xsc)

LOWER PART, 

VANDERLEHR FM 

Dolomite and shale 

(Xd)

LOWER PART, 

VANDERLEHR FM 

Sandstone, arkose, 

conglomerate -(Xqc)

LOCAL UNCONFORMITY

Graywacke 

(unnamed) (Xgw)

HAY CREEK 

GREENSTONE (Xb) 

pillowed basalt 

and lenses of 

carbonate-silicate 

BIF

REAUSAW SLATE (Xsc) 

black shale

 FAULT 

Amygdular pillow 

basalt (Xb)

BUCK MOUNTAIN QTZ and 

GINGRASS DRAW SLATE 

(Xqc) sandstone and 

siltstone shelf 

facies

ROBERTS DRAW FM (Xd) 

dolomite and siltstone

ESTES FORMATION (Xqc) 

fanglomerate, BIF 

conglomeratic 

sandstone, arkose and 

dolomite

 UNCONFORMITY UNCONFORMITY 

Carbonate-silicate 

BIF (Xif)

 FAULT 

 UNCONFORMITY 

BLUE DRAW METAGABBRO 

Gabbroic sills (Xlg) 

2,170+110 Ma

BENCHMARK IRON-FM 

(Xcq) oxide-facies BIF

BOXELDER CREEK FM 

(Xcq) BIF 

conglomerate, 

fanglomerate, 

quartzite, lithic 

arenite

Granite, pegmatite 

(Wgr) ca 2,500 Ma 

Siltstone and 

graywacke (Wos)

 UNCONFORMITY -

LITTLE ELK GRANITE 

(Wgr) 2,549+_ll Ma 

Arkose, conglomerate, 

quartzite, oxide 

BIF (NEMO IRON-FM) 

(Wos)

United States Gold Terranes B53
contemporaneously with the deposition of the Estes-type 

rocks (unit Xqc). These faults developed sequentially 

from west to east (Redden, 1981). The largest known 

fault has a displacement of approximately 10 km, and its 

dip is inferred to flatten parallel to bedding at depth. 

Right-lateral shear which may have been contemporaneous with the younger folding produced offsets 

subparallel to the dominant foliation and reactivated 

segments of the older listric faults.

In the central Black Hills and especially in the area 

south of Mystic, stratigraphic repetition and graded 

bedding in the turbidite deposits indicate that early folds 

had northeast trends (fig. B14). Bedding attitudes strike 

predominantly northeast or northwest and dip vertically 

or steeply south. Outcrop patterns indicate that the early 

folds have been strongly refolded along north-northwest 

trends, with the result that the plunges of the early folds 

reverse abruptly over the axes of later folds. The dominance of south-plunging minor folds over wide areas 

indicates that early folds were isoclinally overturned to 

the north. In addition a third set of younger, right-lateral 

isoclinal folds (not shown on fig. B14) trends more 

northwesterly than the second set and probably was 

formed by a right-lateral shear couple. A similar 

structural pattern is evident in the Rochford area where 

an anchor-shaped map pattern (fig. B13) suggests that 

early east-trending folds were refolded along northnorthwest axes. Small closed, "eyed" folds are evident on 

the south end of the Rochford structure (Bayley, 1972c; 

McMillan, 1977). Continuation of the Rochford structure to the north below Paleozoic rocks and into the 

Lead-Deadwood dome would suggest that the major 

south-plunging folds in the Homestake mine (Noble and 

others, 1949) are actually secondary to the original fold 

pattern.

Along the eastern side of the central Black Hills 

from south of Nemo to near Rockerville, early folds, if 

they existed, appear to have been completely warped into 

north-northwesterly trends. However, in the Keystone 

area ample evidence exists of the warping of earlier 

east(?)-trending folds along northwesterly trends. For 

example, unit Xcg is a doubly plunging anticline refolded 

into a southeast-plunging synform in an arcuate exposure 

extending 1-3 km west-northwest of Keystone (fig. B13).

In the southern Black Hills, these two major earlier 

fold trends are modified by a domal structure around the 

Harney Peak Granite. Adjacent to the granite on the 

north half of the dome, folds plunge gently to the north or 

northeast, but on the south side of the dome virtually all 

folds plunge to the south or southwest. Small, nappe-like 

folds having northeast trends are common on the 

northwest side of the dome in the Hill City area (Ratte" 

and Wayland, 1969; fig. B13). These may be early folds, 

or later folds reoriented by emplacement of the granite.

A smaller dome at Bear Mountain is believed to have 

been superposed on earlier structures and to be cored by 

an unexposed granite contemporaneous with the Harney 

Peak Granite.

Faults in the central Black Hills trend dominantly 

north-northwest, although earlier faults having original 

northeast trends have been recognized locally (figs. B13, 

B14). The earlier faults are subparallel to stratigraphic 

contacts, are folded, and probably originated as thrust 

faults during the earliest folding. The Grand Junction 

fault (Redden, 1968), which passes through Custer, dips 

generally to the west and has an unknown amount of 

displacement. The fault was deformed by the emplacement of the Harney Peak Granite and therefore is older 

than the granite, but breccias and local quartz veins 

suggest that movement along the fault probably followed 

closely in time with the regional metamorphism. 

Deflection of the fault around the Bear Mountain area 

supports the belief that the Bear Mountain dome is cored 

at depth by granite of age similar to that of the Harney 

Peak Granite. North of Harney Peak the largest faults 

are a left-lateral fault that passes through Keystone and a 

right-lateral fault that passes through Silver City. The 

apparent horizontal displacement along the fault at Silver 

City is several kilometers, but the fault probably also has 

a considerable vertical component of movement. Other 

faults shown in figure B13 are largely northwest trending 

and apparently have right-lateral displacement, or they 

follow contacts, making their relative displacements 

difficult to assess.

The Precambrian rocks have been metamorphosed 

to various degrees, as shown by the isograds in figure B13 

(inset map). The distribution of the garnet isograd in the 

pelitic rocks indicates a low-grade metamorphic trough 

trending northwesterly across the north-central Black 

Hills. The garnet isograd along the northeast part of this 

trough passes through the Homestake mine. Staurolite at 

Deadwood and Galena, and the presence of inclusions 

of pegmatite in Tertiary laccoliths northeast of Deadwood, suggest a Harney Peak-like granite beneath the 

Paleozoic rocks to account for the increased metamorphic grade to the northeast. The garnet isograd also 

deflects around the Rochford area, where it appears to 

follow the superposed north-northwesterly structural 

trend.

Near the Harney Peak Granite the isograds are 

compressed and the low-sillimanite isograd coincides 

more or less with the north contact of the granite. Small 

areas of high-sillimanite grade rocks (second sillimanite 

isograd, not shown on fig. B13) are known adjacent to the 

south side of the granite north of Custer and in unit Xq or 

Xcq to the southeast. Near the granite, lower-pressure 

minerals andalusite and cordierite in aluminous schist 

coexist with staurolite-bearing assemblages, indicating

B54 Geology and Resources of Gold in the United States
R.4 E. R.5 E. EXPLANATION 

| ftps;; | Phyllite/slate 

Hlyll Upper metagraywacke 

[xms | Mica-chlorite phyllite/schist 

t »Xb^ Metabasalt 

||xcjwm| || Middle metagraywacke 

E:kbsx:| Biotite phyllite/schist 

^Xawl^ Lower metagraywacke

Siliceous biotite phyllite

Contact Arrow points to younger unit

Fault Dashed where approximately located

Approximate axial trace of early (Fl) anticlineArrow indicates generalized plunge direction

Approximate axial trace of early (Fl) syncline 

Arrow indicates generalized plunge direction

Approximate axial trace of late (F2) antiform

Approximate axial trace of late (F2) synform

5 KILOMETERS

I 

3 MILES

Figure B14. Generalized geology of Early Proterozoic rocks in part of the central Black Hills showing early and late fold axes.

pressures of about 3.5 kb at the time of crystallization of 

the granite (Redden and others, 1982). These and other 

relationships indicate the superposition of thermal metamorphism associated with the granite upon the earlier 

regional metamorphism.

In summary, the structural patterns of the central 

Black Hills indicate that early east-northeast-trending 

folds (FJ were overprinted by widespread northnorthwest-trending folds (F2). F2 folding was accompanied by a general low-grade metamorphism which 

increased in intensity to the south and developed axialplane foliation. F1 and F2 folding affected the Nemo area

rocks where the oldest Early Proterozoic rocks (unit 

Xcq) were deformed prior to F1 folding in the central 

Black Hills. Most of the north-northwest-trending faults 

in the central Black Hills may have developed during the 

late stages of F2 folding, but earlier thrust faulting was 

presumably associated with F1 structures. Emplacement 

of the Harney Peak Granite caused major and minor 

domes which modified F1 and F2 structures, and produced a large relatively low-pressure metamorphic 

aureole in the southern Black Hills. Numerous other 

post-F2 structural features in local areas will not be 

discussed in this brief summary.

United States Gold Terranes B55
PHANEROZOIC ROCKS

Paleozoic and Mesozoic Rocks

Paleozoic rocks are not subdivided in figure B13, 

and only those containing gold deposits are discussed 

here. The oldest Paleozoic rock unit is the Upper Cambrian Deadwood Formation, which unconformably overlies the Precambrian metamorphic rocks. The Deadwood 

in the northern Black Hills ranges in thickness from 

about 115 m near Galena (Shapiro and Gries, 1970) to 

about 150 m west of Lead; it is generally divided 

informally into lower, middle, and upper parts. The lower 

part consists dominantly of sandstone, which locally 

overlies lenses of basal conglomerate. The sandstone is 

as much as 35 m thick; the conglomerate rarely exceeds 

12 m in thickness. Carbonate rocks are present locally in 

the upper part of the sandstone. The middle part of the 

Deadwood, about 50 m thick, consists largely of shale 

and fossiliferous glauconitic limestone pebble conglomerate. The upper part consists of flaggy sandstone, 

siltstone, pebble conglomerate, and massive red sandstone. The red sandstone is most abundant at the upper 

contact and contains tubular structures which may be the 

borings of a large worm. The regional variations of the 

Deadwood have been described in considerable detail by 

Kulik (1965), who attributed the various lithologic differences to repeated transgressions and regressions of 

the Cambrian sea. One of the important features, 

discussed in more detail in a later section on the gold 

deposits, is that the lower part of the Deadwood was 

deposited over a surface of considerable relief which 

markedly influenced the lithology of the lowermost units.

The only other Paleozoic unit containing gold 

deposits is the Mississippian Pahasapa Limestone. Gold 

deposits are sparse in this thick-bedded unit, which is 

about 170 m thick. The upper part of the Pahasapa is 

locally cavernous because of a karst surface that 

developed prior to deposition of overlying Pennsylvanian 

rocks. Three relatively thin lower Paleozoic formations 

aggregating about 50 m in thickness separate the Pahasapa from the Deadwood. These include the Ordovician 

Winnipeg and Whitewood Formations and the Englewood Formation of Devonian and Mississippian age. 

Above the Pahasapa Limestone is a nearly continuous 

Paleozoic and Mesozoic section that lacks known gold 

deposits.

Cenozoic Rocks

Tertiary Igneous Rocks

Tertiary igneous rocks intrude the Paleozoic and 

Precambrian rocks in a relatively narrow belt which

crosses the northern Black Hills in a west-northwesterly 

direction (Redden, 1975; Lisenbee, 1981). These 

intrusive rocks are especially abundant in the LeadDeadwood dome, where they are genetically related to 

Tertiary gold deposits (Norton, 1989), but they are 

scattered throughout a west-northwest-trending belt 

across the entire Black Hills (Lisenbee, 1981).

The intrusive rocks are largely porphyritic, and 

they consist of phonolite, monzonite, quartz monzonite, 

latite, and trachytic rhyolite of a subvolcanic-volcanic 

association. Rocks that tend to be undersaturated are 

concentrated in the northwest part of the main belt of 

intrusives, whereas oversaturated rocks are most common in the southeast part. In the Bear Lodge Mountains 

in Wyoming, the igneous rocks are predominantly alkalic, 

include carbonatite, and are host to large reserves of 

rare-earth elements (Staatz, 1983). Radiometric ages of 

all the different intrusive rocks range from approximately 

40 to 60 Ma (summarized in Shapiro, 1971; also see 

Redden and others, 1983).

White River Group

Small deposits of Oligocene gravel are relatively 

widespread over the central Black Hills uplift and they 

document the Laramide uplift and subsequent early 

Cenozoic erosion of the Black Hills (Darton and Paige, 

1925). The deposits are largely locally derived gravel, but 

their persistence as remnants at elevations in valleys not 

far above the present drainage floor indicates that much 

of the Black Hills was eroded before the Oligocene to a 

relief not much different from that at present. For 

example, Darton and Paige (1925) recognized remnants 

of White River deposits along Whitewood Creek within 

the town of Lead. The White River deposits, not shown 

on figure B13, are nonetheless of some importance 

because they contain placer gold derived from older 

deposits; moreover, they were themselves reworked 

locally to form the gold-bearing Quaternary gravel which 

led to the discovery of the lode deposits of the Black 

Hills.

TYPES OF GOLD DEPOSITS

The main types of gold deposits in the Black Hills 

have been recognized for a long time, but recent work 

on the Precambrian and Phanerozoic rocks permits 

better understanding of the age, setting, and formation of 

the deposits. Both Proterozoic and Phanerozoic deposits 

are recognized; these in turn are subdivided into various 

genetic types. Proterozoic deposits consist of 

(1) Homestake-type stratabound deposits, somewhat 

remobilized syngenetic gold associated with carbonatesilicate-sulfide-facies iron-formation; (2) gold-quartz

B56 Geology and Resources of Gold in the United States
veins such as worked by the Holy Terror mine at 

Keystone; (3) fault-controlled deposits such as that of the 

Bullion mine at Keystone; and (4) fossil placers. Phanerozoic deposits consist of (1) replacement deposits in 

lower Paleozoic rocks and disseminated and vein 

deposits in Tertiary igneous rocks such as those at 

Richmond Hill west of Lead and the Gilt Edge mine at 

Galena; and (2) placer deposits in Cambrian, Oligocene, 

and Quaternary rocks. Two or possibly more factors were 

involved in the formation of some of the deposits.

Proterozoic Deposits

Homestake-type

Work is in progress on the world-class Homestake 

deposit (S.W. Caddey and others, written commun., 

1988); only salient features are mentioned here. Deposits 

smaller than Homestake, but of apparently similar 

character, are widespread in the Black Hills and are 

described in a general way.

The major characteristic of the Homestake deposit 

is its stratabound nature within a carbonate-silicatesulfide-facies banded iron-formation (Homestake Formation). Quartz veins within the iron-formation are 

abundant but essentially lack gold. Gold may be enriched 

in the wall rock along the veins. Sulfide mineralogy of the 

gold-bearing rocks typically consists of pyrrhotite, pyrite, 

and arsenopyrite. Free gold is observable only in the 

richest ore. Chlorite is the most abundant alteration 

mineral and tends to be associated with richer ore. The 

host rock consists of either recrystallized chert beds and 

sideroplesite-rich schist below the garnet isograd or chert 

and cummingtonite-garnet-biotite-rich rock above the 

garnet isograd. Chert beds are commonly only a few 

centimeters thick and both lensoid and ribbonlike.

Within the Homestake deposit, the major structures are north-northwest-striking, southeast-plunging, 

overturned isoclinal folds. These extremely tight folds are 

modified by later cross folds, resulting in an exceedingly 

complex structure. Individual ore bodies are elongate, 

highly irregular podlike masses localized in apparently 

tectonically thickened parts of the Homestake Formation. The ore bodies also generally plunge to the 

southeast through distances exceeding several thousand 

meters, but they do not coincide with the major fold 

noses.

Noble (1950) discounted the idea of Precambrianage mineralization because of the existence of Tertiary 

gold-bearing veins within the mine, and because he 

believed that forces related to the intrusion of Tertiary 

magmas caused some of the cross folding in the mine, 

and the cross folding, in turn, was thought to have 

localized the ore. Lead-isotope data obtained by Rye and 

others (1974) on galena from the mine suggested a

s=»2.5 Ga source age for lead in the Homestake Formation if a 1.6 Ga age for its metamorphism is assumed. The 

1.97 Ga U-Th-Pb zircon age of metasedimentary rock 

cited on p. B51 was obtained on a tuffaceous sample from 

the Ellison Formation but only a few meters from the 

Homestake Formation. Hence this seems to be a more 

likely age for the host rock and the age of the gold 

mineralization. Also more recent Pb isotope models 

would make the 2.5 Ga date closer to 2.0 Ga (E.H. 

DeWitt, written commun., 1987), and therefore the age 

of mineralization almost certainly was Proterozoic. A 

Proterozoic age also is consistent with that of other gold 

deposits in rocks of Proterozoic age in the central Black 

Hills in areas which show no evidence of possible 

Tertiary mineralization.

Stable isotope investigations by Rye and Shelton 

(1983) revealed distinct differences in the sulfur, carbon, 

and oxygen isotope ratios in the formations overlying and 

underlying the Homestake Formation. They also showed 

that all the economically recoverable gold within a 

mineralized horizon is in rock with a 634S range of + 4.0 

to + 9.0 permil and that 13C and 18O are depleted in the 

gold-rich areas. Their evidence indicates that sulfide 

minerals were produced in a system dominated by lowtemperature bacteriogenic processes and that the 

mineralization took place in a submarine hot spring 

system that vented along fracture systems.

Sulfur, carbon, and probably gold have been remobilized to some extent in the mine by regional metamorphism and formation of quartz veins (Rye and Rye, 

1974; Wolfgram, 1977); Norton (1974) suggested that 

the coincidence of the garnet isograd with the Homestake mine may have been important in remobilization of 

the gold into ore bodies. This remobilization has not been 

documented, however, and migration distance of gold 

seems to have been limited to a few meters.

The model of submarine hot spring deposition in a 

localized tectonic basin agrees with data elsewhere in the 

Black Hills that show a generally consistent association of 

tuffaceous sediment (reflecting volcanism) interbedded 

with carbonate-silicate-facies banded iron-formation. 

Thin-sections of iron-formation from the Rochford area 

(iron-formation similar to that of the Homestake mine) 

show graphite-rich layers in an anastomosing orientation 

subparallel to bedding: these layers in this orientation 

may reflect biologic activity associated with hot springs. 

Elsewhere in the Black Hills massive chert lenses 

commonly are associated with carbonate-silicate-facies 

iron-formation and basaltic flows, but such are not 

known within the Homestake Formation. Massive chert 

lenses locally present in the turbidite units are believed to 

represent somewhat lower temperature thermal spring 

deposits that formed during compaction dewatering of 

the turbidite section. The thin carbonate-silicate-facies

United States Gold Terranes B57
iron-formation units commonly associated with massive 

chert in the turbidite section ordinarily have a low sulfide 

mineral content and are essentially barren of gold.

Iron-formation very similar to the Homestake 

Formation is relatively abundant in the Rochford and 

Keystone areas where a number of small mines, 

including the Standby, Montana, King of the West, 

Bullion, and Keystone, have been developed in ironformation. Carbonate-silicate facies predominates in 

these areas; amounts of sulfide-facies iron-formation are 

relatively small. The low sulfur content (paucity of sulfide 

minerals) may be a factor in explaining why no major 

mines have been discovered in these areas.

Studies of the gold content of Homestake-type 

iron-formation in the Blue Lead Mountain area north of 

the Keystone gold belt (Raymond, 1981; Raymond and 

others, 1975) and in areas to the north near Nemo 

(Fantone, 1983) confirm that gold is considerably 

enriched within the iron-formation and chert-rich rocks 

relative to other rock types. Fantone (1983) showed that 

the enrichments are considerably less than those noted in 

similar rocks in Australia and South Africa but 

comparable to those in greenstone belts in Canada. He 

also noted that the best minor element correlation with 

gold was arsenic, but even that correlation was not 

strong.

Gold-Quartz Veins

The gold-quartz vein type is essentially limited to 

the southern Black Hills, where all known deposits are 

small. The Holy Terror mine at Keystone opened one of 

the richest veins, which has been described (Connolly, 

1929; Allsman, 1940) as a massive white quartz vein with 

minor arsenopyrite and pyrite and abundant free gold. In 

some specimens, muscovite is common along the contact 

with wall rock. The vein was less than a meter thick at the 

surface but thickened to several meters at depth where 

the grade reportedly was considerably lower than near 

the surface. Other gold-quartz veins relatively near the 

Harney Peak Granite, such as that of the St. Elmo mine, 

are generally no longer accessible but are described as 

having relatively coarse-grained quartz and virtually no 

or only very small amounts of pyrite and arsenopyrite. 

Several quartz veins in the area west of Custer are 

reported to contain gold-bearing tetradymite (Allsman, 

1940), but this telluride mineral has never been confirmed (W.R. Roberts, South Dakota School of Mines 

and Technology, written commun., 1986). Other small 

mines on gold-quartz veins in the southern Black Hills 

located farther away from the granite in areas of lower 

metamorphic grade are also generally not accessible, but 

ore samples indicate that the veins typically contain gray 

quartz and minor sulfide minerals. Graphite is relatively 

common, although not abundant, and some of the veins

are bounded by tourmaline-rich wall rock. Some descriptions indicate that the adjacent schist wall rock was 

brecciated and gold mineralized. Virtually all the goldquartz veins are within metamorphosed graywacke, 

except for a few small mines and prospects southwest of 

Custer in small quartz veins cutting metagabbro bodies. 

Northwest of Hill City, exploration workings in veins are 

all confined to a thin unit of graywacke which lies 

structurally below the unit of micaceous phyllite (unit 

Xms, fig. B13) and above slightly pyritiferous graphitic 

slate and phyllite (unit Xps). These adjacent slates and 

phyllite rocks have no known mines, although they 

underlie large areas of the central Black Hills.

That gold-quartz veins are concentrated in graywacke wall rocks in preference to other rocks suggests 

that the more competent graywacke was favorable for 

migration of the gold-bearing solutions either because of 

fracturing or because of original permeability. Local 

faulting or hydrofracturing may have been instrumental 

in localizing the veins, as many descriptions cite evidence 

of movement and minor brecciation. The source of the 

mineralizing fluids is not known; the fluids could have 

been of metamorphic origin. Some veins in the southern 

Black Hills are cut by granites or pegmatites, indicating 

an age older than that of the granite but possibly contemporaneous with or younger than the early regional 

metamorphism.

Fault-controlled Deposits

Fault-controlled epigenetic gold deposits differ 

from the gold-quartz vein type in that they have diverse 

wall rocks, occur in rocks of diverse metamorphic grade, 

and are localized along known faults and breccia zones; 

however, the two types of deposits may have formed in a 

somewhat similar manner. The largest deposits of the 

fault-controlled type include the Keystone and Bullion 

mines in the Keystone district and other smaller, neighboring deposits localized along a major fault and 

subsidiary breccia zones (Connolly, 1925,1929; Allsman, 

1940). Recent detailed mineralogic and geologic studies 

of these deposits are not available, but examination of the 

available exposures indicates that gold is concentrated in 

breccia zones which have had repeated movement. 

Complexly folded chert-cummingtonite iron-formation 

generally borders or is cut by the mineralized zones, 

although the enclosing rock may be metagabbro or 

metabasalt and schist. All the rocks are crossed by the 

breccia zones which are impregnated with graphite, sericite, and chlorite, and cut by small quartz-carbonate 

veins. Pyrite and arsenopyrite are concentrated in the 

breccia and gouge. Although gold generally is in 

mineralized breccia and gouge, Connolly (1929) indicated that most of the gold in the Columbia mine

B58 Geology and Resources of Gold in the United States
came from a gray quartz vein which developed prior to 

the gouge. In most of the deposits pyrrhotite and minor 

arsenopyrite as well as minor amounts of gold are also 

concentrated in the iron-formation away from the breccia 

zones; pyrrhotite appears to be lacking within the breccia. 

Therefore sulfur appears to have been introduced along 

with the quartz-carbonate veins in the breccia zones. 

Because the most productive mines all have ironformation closely associated with the breccia zones, gold 

may have been remobilized from the iron-formation and 

concentrated in the breccia.

At small gold mines localized along faults, northwest of Hill City and west of Custer, iron-formation is not 

exposed along the faults; instead, the wall rocks are 

metagraywacke or metamorphosed shale. Therefore, 

iron-formation may not be a requirement for the 

concentration of gold. On the other hand, all the faultrelated deposits lacking iron-formation in the immediate 

vicinity are very small; this fact suggests the importance 

of associated iron-formation rock for the formation of 

larger deposits.

Most of the faults, and thus the age of gold 

mineralization, postdate regional metamorphism. The 

Grand Junction mine west of Custer is along a major 

fault, but the fault appears to have been deformed by 

domes associated with the Harney Peak Granite 

(Redden, 1968) and as such might seem to be an 

exception. However, local exposures of the fault have 

minor breccia zones, suggestive of repeated movement. 

The north-northwest-trending fault passing through 

Silver City (fig. B13) apparently localized deposits that 

contain gold and silver-sulfosalt minerals (Larson, 1971). 

Because these deposits are in an area of low metamorphic grade, the fault-controlled mineralization may 

have caused a broad regional zonation of antimony and 

silver at lower metamorphic grades; deposition of gold 

took place only at higher metamorphic grades.

Kulp and others (1956), in contrast, obtained a 

much younger (400 Ma) model lead date for galena from 

the Spokane lead-zinc mine southeast of Keystone. They 

commented that the age indicated Tertiary mineralization. The lead-zinc vein follows a fault zone which 

cuts granite/pegmatite, and the age of the galena clearly 

indicates that the mineralization was not Precambrian 

but probably Laramide. Obviously, additional isotope 

work is needed on the fault-related deposits to better 

establish the ages and depositional conditions.

Placer Deposits

Proterozoic placer gold is limited to the Nemo 

area, where it is present in individual beds of pyritic, 

uraniferous, fluvial conglomerate (Redden, 1980, 1981; 

Kim, 1979) of unit Xcq. The conglomerate is interbedded 

with coarse-grained quartzite and grit, and generally

individual beds are only a few meters thick. The total 

thickness of conglomerate may be several tens of meters 

within a total section of 50-150 m. Individual conglomerate beds intertongue laterally with the associated 

quartzite in a fashion typical of a braided stream 

environment.

Although the rocks are metamorphosed, detrital 

gold particles have been identified, along with detrital 

chromite, zircon, and numerous other heavy minerals. 

Much of the pyrite is euhedral, and original titaniferous 

minerals have altered to sieve aggregates of euhedral 

rutile, quartz, and pyrite thereby indicating the introduction of sulfur. Gold is generally concentrated in zones 

of increased radioactivity which correspond to either the 

base or the upper part of an individual conglomerate bed. 

The gold content is subeconomic, and short channel 

samples, up to a meter in length, contain a maximum of 

only 2 to 3 ppm Au. Most samples contain less than 

1 ppm Au. The only known former mine in the conglomerate is the Lucky Strike, located about 6 km 

northwest of Nemo, which reportedly had an 80-m-deep 

shaft and several drifts. Although a mill was built on the 

property, no production records are available.

Phanerozoic Deposits

Replacement Deposits in Lower Paleozoic Rocks

These deposits are restricted to the area of Tertiary 

igneous activity in the northern Black Hills. They are 

especially concentrated in the area around the LeadDeadwood dome, and dozens of mines were developed in 

them around the turn of the century. Norton (1989) has 

described the history, production, and geology of the 

major producing area of the Bald Mountain district and 

the dominant features of the replacement deposits in the 

lower Paleozoic rocks. Hence only salient features of this 

type of deposit are repeated here. Because the replacement deposits are transitional to the disseminated and 

vein deposits in Tertiary igneous rocks, the origin of the 

deposits is discussed later with that of the disseminated 

and vein deposits.

The replacement deposits produced principally 

gold, but some mines also produced silver, lead, zinc, and 

tungsten. Emmons (1926) and Connolly (1927) recognized that gold and associated metals are distributed in a 

classical zonal pattern with the tungsten ore centered 

near the Homestake mine at Lead and the silver-lead ore 

concentrated on the periphery of the mineralized region. 

The deposits are largely in the basal part of the 

Deadwood Formation and are lateral replacements of 

dolomite or dolomitic quartzite beds extending outward 

from nearly vertical fractures that cut the basal 

sandstone (commonly silicified to a quartzite) or basal

United States Gold Terranes B59
conglomerate. Localized breccia along the fractures also 

contained some ore in open-space filling, but this ore was 

minor. Because lateral replacement from the fractures 

was limited, density of fractures was important in 

localizing the largest deposits that could be mined. In 

some parts of the area, fractures extended upward from 

the basal Deadwood, and similar carbonate rock below 

the uppermost sandstone-quartzite part of the Deadwood was mineralized. Rarely an intermediate zone near 

the middle of the formation was mineralized. In the 

extreme northwest part of the region near Ragged Top 

Mountain, mineralization extended upward into the 

Pahasapa Limestone.

Disseminated and Vein Deposits in Tertiary 

Igneous Rocks

Disseminated and vein deposits in Tertiary igneous 

rocks include those in intrusive bodies that cut the 

Proterozoic rocks exposed in and adjacent to the LeadDeadwood dome, and also those in intrusives in the lower 

Paleozoic rocks of the northern Black Hills. Typical 

examples of such deposits are the Richmond Hill deposit 

located in the northwestern part of the Lead-Deadwood 

dome and the Gilt Edge deposit located about 3 km west 

of Galena. Considerable drilling has been done on these 

deposits in recent years, so that the geologic relationships 

are becoming much better known (Duex and others, 

1987; MacLeod, 1986). Mineralization at the Richmond 

Hill deposit was localized in a Tertiary breccia pipe and 

adjacent fractured Tertiary igneous rocks and Proterozoic metamorphic rocks. The deposit is largely 

oxidized, but Duex and others (1987) noted that gold 

mineralization was richest in areas of most intense argillie alteration. Pyrite and marcasite are the dominant 

sulfides in unoxidized ore. Quartz-barite and quartzkaolinite veinlets are locally present.

At the Gilt Edge deposit MacLeod (1986) recognized that argillic, sericitic, and potassic alteration took 

place in brecciated trachyte porphyry, which hosts a gold 

deposit that is characterized, at least in part, by small 

quartz-pyrite veins.

Although the Golden Reward property in the Bald 

Mountain area described by Norton (1989) is dominantly 

a sedimentary rock-hosted replacement deposit, recent 

extensive exploration (Emanuel and Walsh, 1987) 

indicates that much of the low-grade gold mineralization 

occurred in igneous breccia bodies and smaller vein 

stockworks in Tertiary igneous bodies which pervasively 

intrude the Deadwood Formation. Low-grade mineralization also was not limited to the basal Deadwood but 

extended throughout the lower half of the formation. 

Emanuel and Walsh (1987) also recognized an early 

stage of silicification accompanied by gold-silver mineralization and arsenic-bearing sulfides, which was

followed by another mineralization stage characterized 

by gold-silver-bearing pyrite. In addition, argillic and 

propylitic alteration types and local fluoritized rock were 

recognized. Barite, pyrrhotite, and magnetite are sparsely 

present and tellurium minerals have been noted. Silver: 

gold ratios of the low-grade ore average about 4:1 in 

contrast to somewhat lower ratios for the high-grade ore 

previously produced.

Norton (1989) suggested that Tertiary igneous 

rocks have served as a heat source to generate hydrothermal fluids which obtained their metals and gangue 

constituents from the underlying rocks. Thus he envisaged gold coming from a Proterozoic source, possibly 

the ore in the Homestake Formation or other auriferous 

iron-formation, which is believed to underlie the Golden 

Reward property (Emanuel and Walsh, 1987). Deposits 

were therefore related to hydrothermal convection cells 

tied to the Tertiary igneous rocks. His model is 

reasonably consistent with the isotope data of Rye and 

others (1974) and is the favored model of Emanuel and 

Walsh (1987).

Recent work by Paterson and Uzunlar (1987) on 

fluid inclusions in quartz and fluorite from eight different 

Tertiary deposits in the northern Black Hills indicates 

that some inclusions have high salinities (20 to 60 wt. 

percent equivalent NaCl) and filling temperatures in the 

range of 150-450 °C. Paterson and Uzunlar (1987) also 

determined 618 O values for quartz and biotite from 

Tertiary veins and also for some of the Tertiary igneous 

rocks associated with the gold deposits. These data, 

combined with previous 6D values of Rye and Rye 

(1974), suggest that the ore-forming fluids were 

dominated by magmatic water, although Paterson and 

Uzunlar (1987) noted that the isotopic compositions 

possibly could result from the interactions of small 

amounts of meteoric water and larger volumes of 

Tertiary igneous rock or from the mixing of magmatic 

and meteoric water. Because Paterson and Uzunlar were 

also able to sample Tertiary-age veins within Proterozoic 

rocks at depths as great as 7,200 feet in the Homestake 

mine, it seems that their evidence for magmatic water is 

strong. Their fluid-inclusion work positively correlates 

the higher salinities and temperatures with greater 

inferred depths of deposition of the different sampled 

deposits; and only the shallower deposits, in contrast, are 

characterized by lower salinities and temperatures, 

suggesting possible involvement of meteoric water.

Tertiary igneous rocks are obviously required to 

form both the replacement deposits in sedimentary rocks 

and the disseminated and vein deposits in Tertiary 

igneous rocks. If the precious metals came directly from 

the igneous rocks, relating the mineralization to a 

particular rock type or types would be extremely 

important. At present such information is not available,

B60 Geology and Resources of Gold In the United States
although Emaniiel and Walsh (1987) suggested that at 

the Golden Reward an aegerine-nepheline-bearing 

trachy-syenite is genetically related to the hydrothermal 

solutions. If on the other hand hydrothermal solutions 

from the igneous rocks or from heated meteoric waters 

scavenged the metals from the country rocks, target areas 

for new deposits would include all areas of Tertiary 

igneous bodies.

If the characteristics of the different Tertiary 

deposits are considered, it is apparent that ground 

preparation was especially important for the formation of 

disseminated and vein deposits in Tertiary igneous rocks. 

Favorably prepared ground includes intrusion breccias, 

brecciated or fractured intrusion margins, faults, and 

shear zones. Formation of replacement deposits in the 

lower Paleozoic rocks also has relied on faults, fractures, 

aquitards, and the existence of favorable carbonate rocks 

for replacement. Knowledge of the abundance and 

nature of fractures in the lower Paleozoic rocks and of 

the depositional environment of the basal Deadwood 

Formation is therefore important for the discovery of 

new deposits.

Placer Deposits

Placer deposits in the basal conglomerate of the 

Deadwood in the vicinity of the Homestake mine were 

described in considerable detail by Devereux (1882) and 

Irving and Emmons (1904), who examined the deposits 

while they were being mined. Irving and Emmons (1904) 

recognized that a paleohill above the outcrop of the 

Homestake discovery controlled the distribution of goldbearing conglomerate in the Deadwood, and they 

recognized that the conglomerate pinched out against the 

hill. Because Tertiary replacement deposits involving 

silicification, pyritization, and the introduction of additional gold were superimposed upon the placer deposits, 

the placer origin of the gold in the conglomerate was not 

always evident. In fact, Noble (1950) believed most of the 

gold was of Tertiary age, but his view was undoubtedly 

influenced by the belief that the Homestake ores were 

emplaced during the Tertiary. Arguments for and against 

the placer origin have been noted by Norton (1974), and 

more recent work by French (1985) and examinations by 

Homestake personnel (Gordon Nelson, oral commun., 

1986) document that the placer gold developed in 

response to preexisting drainages and the advance of the 

Cambrian sea. Inadequate exposures of remnants of the 

basal Deadwood exist to document in detail the ancient 

topography of the outcrop of the Homestake deposit and 

the adjacent Ellison Formation. However, the available 

present outcrops suggest, as indicated by Irving (Irving 

and Emmons, 1904), that a topographic high which shed 

placer gold into conglomerate of the basal Deadwood 

was developed over resistant outcrops of the chert-rich

Homestake Formation and quartz-rich Ellison Formation. Irving did not believe the conglomerate in the basal 

Deadwood was fluvial, or if it had been, it certainly was 

reworked by the advancing Cambrian sea.

Other placer deposits in the Deadwood Formation 

in the Rockerville area have been mined, and similar 

deposits were partly reworked and provided gold for 

gravels in nearby Quaternary deposits. Detrital gold has 

been recognized in sandstone of the basal Deadwood in 

the Nemo area; this gold presumably was derived from 

fluvial placers in the Proterozoic rocks, especially unit 

Xcq (fig. B13). Tuysuz (1986) also noted placer gold in 

heavy-mineral concentrates from basal conglomerate of 

the Deadwood in several samples obtained north of lat 

44° N.

Tertiary placers were mined on a small scale south 

of Rockerville near the settlement of Hayward and also 

in the Lead-Deadwood area. The Tertiary Hayward 

placer gold deposits lie very close to the Oligocene and 

Miocene erosion surface, and their source is likely placer 

gold in the Deadwood as well as in the Proterozoic rocks 

to the west. Tertiary placers are also known southwest of 

Custer (Redden, 1963).

Holocene placers are relatively widespread 

through the drainages of the Black Hills. The LeadDeadwood area placers were by far the richest, producing about 200,000 oz of gold (Norton, 1974). Placers 

were also relatively rich in the Tinton area west of Lead. 

Over most of the central Black Hills, Holocene placers 

are relatively low grade; they thus suggest lack of a major 

exposed lode deposit.

POTENTIAL DEPOSITS AND 

EXPLORATION GUIDES

The existence of the Homestake mine in the 

northern Black Hills, which has produced approximately 

36 million oz of gold from about 130 million tons of ore, 

is an obvious incentive to seek a similar deposit. In 

addition, the size and grade of some of the Tertiary 

deposits (see Norton, 1989) are worthy targets under 

present high gold prices. Because of the extensive 

prospecting in the past and the continued exploration by 

mining companies, any rich gold deposit to be found will 

probably be a concealed one, as Norton (1974) concluded. Hence costly exploration for concealed targets 

that might or might not be extensions of existing deposits 

will be benefited by a knowledge of the genetic factors 

that formed the deposits, and by additional geologic 

information on the setting of the known deposits.

Norton (1974) outlined possible approaches and 

favorable areas in the search for new gold deposits in the

United States Gold Terranes B61
Black Hills. Here, we discuss new geologic data that bear 

on gold mineralization and that may prove useful in 

exploration. Because the Phanerozoic placer deposits 

now known are small, they will not be discussed except as 

an indicator of a possible Proterozoic deposit.

Homestake-type Deposits

The present commonly favored model of the 

formation of the Homestake deposit incorporates submarine hot springs, probably a localized basin bounded 

by syndepositional faults, and volcanic-related tuffaceous 

rocks. These attributes of the model rule out most of the 

Proterozoic rocks in the Black Hills and restrict the 

search either to areas of carbonate-silicate-facies ironformation or relatively quiet-water depositional environments such as shale basins associated with volcanic 

activity. Iron-formation is rather widely distributed as 

shown in figure B13. We believe, however, that the 

richest concentrations of gold are associated only with 

iron-formation that has significant concentrations of 

sulfide minerals, and therefore most of the carbonatesilicate iron-formation horizons are probably not 

particularly favorable. Another possible guide (as 

suggested by Norton, 1974) is the garnet isograd, inasmuch as mobilization of gold may have been influenced 

by the release of volatile components (H2O, CO2) from 

metamorphic reactions at or near the garnet isograd. If 

the obviously fault controlled deposits in the Keystone 

area are excluded, it is true that the known deposits in 

iron-formation are approximately on the garnet isograd. 

Recent research involving metamorphosed interbedded 

impure carbonate rocks, shales, and pure carbonate 

rocks (Ferry, 1987; Nabelek and others, 1984) suggests 

that highly channelized fluid flow results from metamorphic reactions (especially decarbonation reactions). 

Thus, the impure sideroplesite-bearing (at low metamorphic grade) Homestake Formation might act as a 

major conduit for fluid movement which can concentrate 

gold into an ore body. If so, the general intersection of 

the garnet isograd and iron-formation units indicates 

favorable areas. At present, however, no proof exists that 

such migrations of gold at the garnet isograd are possible.

In the Homestake mine area, the continuity of the 

Homestake Formation is relatively well known and the 

unit is obviously a target examined and sampled by many 

geologists. Past mining and exploration have been based 

partly on the concept that major folds in the mine area 

represent the major structures of the region. As indicated 

in an earlier section, the regional structural interpretation favored here suggests that major folds in the 

mine are most likely F2 folds superposed on nearly 

east trending Fx folds. If this interpretation is correct, the 

Homestake Formation may be repeated to the north

below Paleozoic rocks on the overturned limb of a larger 

anticline. Also, this model suggests that the plunge of the 

superposed F2 folds should decrease at depth in the mine 

as it crosses the east-trending axis of an Fj syncline to the 

south. A model of the mine workings prepared by 

Homestake geologists suggests some flattening of plunge 

in the deepest mine workings, but the data are not 

conclusive. Also, no intermediate-scale folds having 

easterly trends have been recognized within the extensive 

mine workings, although Roland Reed (University of 

Idaho, oral commun., 1984) has recognized early smallscale, east-trending structures within the mine which he 

believed might be F1 structures. Although early large 

east-trending structures exist farther to the south in the 

Hill City area (fig. B14) and in the Rochford area (fig. 

B13), one cannot unequivocally assume that they are 

present in the Lead area. Therefore exploration for a 

continuation of the Homestake Formation based entirely 

on the assumption of such Fj folds would be risky unless 

additional confirming evidence becomes available. 

Furthermore, there would be no assurance that conditions for gold deposition would necessarily be the same 

as those that obtained at the Homestake deposit.

In the remainder of the Black Hills, the potential 

for Homestake-type deposits would appear to be limited 

to areas such as the Keystone or Rochford districts where 

considerable sulfide minerals are present in the ironformation. In the Keystone district, late mobilization of 

gold into breccia along faults apparently played a 

significant role in formation of ore. The district has been 

relatively well explored by earlier mine workings, and 

although the area has moderate reserves (Allsman, 

1940), there are no indications that a major deposit is 

concealed in the immediate Keystone area. Thick ironformations north of Keystone (Norton, 1976) contain 

relatively low gold concentrations (Raymond and others, 

1975).

Pillow lavas, coarse volcanic debris, and units of 

massive chert extensively interbedded with ironformation (Norton, 1976) indicate that a volcanic center 

existed a few kilometers west of Rockerville in an area 

around Storm Hill. Younger metagabbro dikes intrude 

the section, and in combination with colluvium from 

massive chert and quartzite, they tend to conceal most of 

the iron-formation. No mines are known in the area, 

although numerous prospect pits exist. To our knowledge 

no exploratory drilling has taken place near this volcanic 

center. The nearby placer deposits at Rockerville 

produced at least 20,000 oz of gold, presumably largely 

from basal Deadwood placers, but Norton (1974) did not 

consider the Storm Hill area as a likely source of the 

gold, probably because the area lacks mines. Recent 

work on the heavy minerals in the basal Deadwood by 

Tuysuz (1986), and mapping of the basal Cambrian 

unconformity in many areas by Redden, show that

B62 Geology and Resources of Gold in the United States
although local relief on the unconformity is as much as 

60 m, the lithology and heavy-mineral content of the 

basal Deadwood are strongly controlled by the immediately underlying Proterozoic rocks. Where the basal 

Deadwood contains heavy minerals which are not representative of the underlying rocks, the suite is characteristic of the Proterozoic rocks a few kilometers to the 

west. In other words, beach transport in general occurred 

from west to east. Hence, we believe that gold in the 

placer deposits at Rockerville was most likely derived 

from the Storm Hill area to the west. The quantity of 

placer gold recovered would not indicate a major 

exposed ore body, but it could well indicate partially 

exposed or large low-grade deposits.

The Rochford area with its extensive exposures of 

iron-formation (Bayley, 1972c), some containing productive gold mines, is an obvious favorable area because 

of the presence of iron-formation similar to that at the 

Homestake mine. Furthermore, the area had a similar 

structural and metamorphic history and was a center of 

volcanic activity. In addition, arsenopyrite and pyrrhotite 

from four mines in iron-formations from the Rochford 

area have 634S values similar to those in the Homestake 

Formation (Rye and Rye, 1974, p. 300-301). One 

unfavorable criterion is that none of the Rochford ironformations are, according to Bayley's (1972c) stratigraphy, time equivalent to the Homestake Formation. 

The stratigraphic sequence of Bayley that indicates a lack 

of correlation is corroborated by the 1.97 ±0.01 Ga 

U-Th-Pb zircon age of the Ellison Formation (and by 

inference the underlying Homestake Formation) versus 

the 1.88±0.03 Ga U-Th-Pb zircon age of iron-formation 

(Montana Mine Formation) at the Montana mine in the 

Rochford area.

Although the evidence is strong for assuming that 

the iron-formations described by Bayley (1972c) are 

younger than the Homestake Formation, the assumption 

is uncertain because (1) the structure is extremely 

complex, (2) there are relatively rapid facies changes in 

the Rochford area (death, 1986; Weissenborn, 1987), 

(3) outcrop is extremely sparse north of Rochford near 

the Paleozoic unconformity and hence geologic interpretations tenuous, and (4) reliable relict structures that 

can be used to indicate stratigraphic sequence are 

generally lacking. Hence the lithologic correlations and 

locally the extensions of certain units shown in figure B13 

may be in error. If thrust faulting accompanied the early 

Fj deformation, as seems likely, it is possible that some 

apparently conformable contacts are faults which repeat 

or juxtapose units and have been refolded by the F2 

deformation. Thus, we suggest that the correlations 

indicated by Bayley (1972a,c), which are approximately 

accepted in this report, should not be considered as 

irrefutable.

Regardless of the precise correlations of the ironformation units in the Rochford area, we emphasize that 

they, like the Homestake Formation, are closely associated with tuffaceous volcanic material and probably 

formed by hot spring discharge onto the sea floor. The 

Rochford area iron-formation units also commonly are 

sulfide bearing and have produced gold. Thus, they 

clearly have the potential to host a significant gold 

deposit.

Iron-formation in the Rochford area mapped by 

Bayley (1972c) locally has been remapped in more detail, 

and its distribution interpreted differently from Bayley's 

map (Atkinson, 1976; McMillan, 1977; Cleath, 1986; 

Weissenborn, 1987). Only the more continuous of the 

iron-formation units are shown in figure B13, where they 

are included within unit Xpb. Recent mapping by Weissenborn (1987) along the west side of the Rochford 

district in the Nahant area and additional reconnaissance 

work to the west by Redden indicate that the Xpb unit 

is distributed as shown in figure B13. Although not 

shown in figure B13, one and possibly two thin units of 

low-metamorphic-grade carbonate-sflicate-facies ironformation are present within the Xpb unit which rims the 

Xqg unit west of Nahant. The low-metamorphic-grade 

iron-formation units may very well be the lateral 

equivalents of either the Rochford or Montana Mine 

Formations of Bayley (1972c). These low-metamorphicgrade iron-formation units are poorly exposed, especially 

near the Paleozoic rocks. The area merits more detailed 

investigation and prospecting.

The presence of carbonate-silicate-facies ironformation in the Rochford area (as in other areas) should 

not be construed as evidence for a concealed gold 

deposit. In all known areas where ore-grade material has 

been developed, sulfide-rich rocks accompany the anomalous gold concentrations. Therefore, special efforts 

should be made to identify sulfide-rich facies and also to 

examine what appear to be thick depositional parts of 

iron-formation (rather than structurally thickened 

sections). Such depositionally thick sections are likely in 

local fault-controlled basins and should be especially 

favorable areas for thermal spring deposition. Geochemical indicators of such basins and the particular 

spring systems which are most favorable for gold 

deposition would have to be determined in existing mines 

such as Homestake. Possibly these data are already 

collected but for obvious proprietary reasons are not 

published.

In the northeastern part of the Black Hills Precambrian rocks, an unnamed carbonate-silicate ironformation separates unit Xqc from a fault to the east; the 

unnamed unit can be traced for approximately 25 km 

before it disappears below the Paleozoic rocks. This 

iron-formation is here tentatively correlated with the 

oldest Early Proterozoic rocks of unit Xcq in the Nemo

United States Gold Terrenes B63
area (table B4). Bayley (1972a, 1972b) considered this 

subunit, which he included in the lower part of the Buck 

Mountain Quartzite, to be equivalent to the Homestake 

Formation. He based this correlation on the equivalency 

of the Buck Mountain Quartzite and the Ellison 

Formation. The correlation which we favor, shown in 

table B4, indicates that the Buck Mountain Quartzite is 

older than the Ellison Formation and therefore the 

iron-formation is probably not equivalent to the Homestake Formation. The iron-formation also has considerable magnetite and stilpnomelane and is locally transitional to the oxide facies. In the relatively few exposures 

of the iron-formation, the sulfide mineral content is low 

or lacking completely. Thus, this iron-formation does not 

appear to have been favorable for gold mineralization. 

Because most of the unit is concealed by colluvium from 

adjacent quartzite, however, the possible presence of 

sulfide-rich lenses cannot be ruled out.

Lenses of carbonate-silicate-facies iron-formation 

are relatively abundant as interflow units in the greenstone (unit Xb, fig. B13) overlying the Buck Mountain 

Quartzite to the west as shown by Bayley (1972b). 

Although these lenses of iron-formation have been 

prospected extensively, no gold deposits, even small ones, 

have been located. The gold content of the ironformation is anomalously high compared to other rock 

types (Fantone, 1983) but apparently conditions were not 

favorable for economic concentrations of gold. The 

present evidence does not indicate that an environment 

of iron-formation within basalt is favorable for a 

Homestake-type deposit in the Black Hills.

Gold-Quartz Veins

As a group, the gold-quartz veins do not appear to 

be favorable for discovery of a major deposit. Intense 

surface exploration during the early days of mining in the 

Black Hills has virtually eliminated the possibility that 

any deposits as rich as the Holy Terror mine or possibly 

the Clover Leaf mine are exposed at the surface. If 

formation of the deposits were connected to regional 

metamorphism, as some evidence indicates, areas of low 

metamorphic grade (fig. B13) apparently are unfavorable for these deposits. Also, graywacke and possibly 

metagabbro (amphibolite) wall rocks are more favorable 

than any of the shaly rocks. Because fracturing appears to 

have been an important ore control, possibly some areas 

above the garnet isograd in crossfolded and fractured 

competent strata might contain enough small veins to 

define a large-tonnage, low-grade deposit.

Fault-Controlled Deposits

Exploration potential for this type of deposit is 

obviously enhanced where faults cut favorable country

rocks, namely iron-formation. Most of the small deposits 

recognized to the present (1988) are near relatively large 

faults; seemingly this was a criterion for their formation. 

However, relatively little is known about the origin of 

these deposits; some of them may not be Proterozoic in 

age (DeWitt and others, 1986, p. 76; Norton, 1974, p. 13). 

Additional work is needed in order to develop criteria 

that might facilitate discovery of new deposits. If known 

deposits are representative of this class, however, 

significant new deposits will be minimal.

Placer Deposits in Proterozoic Rocks

Although the fossil deposits of the Nemo area have 

a number of similarities to the Witwatersrand, South 

Africa, and Jacobina, Brazil deposits, the low gold 

content, complex structure, and relative thinness of the 

auriferous conglomerate are believed to be unfavorable 

for the discovery of a minable deposit. The fluvial 

conglomerate of unit Xcq is concealed to the east by 

Paleozoic rocks, and exploration based on the possibility 

that richer gold deposits might exist in extensions of the 

unit beneath the cover would be extremely expensive. 

Furthermore, because the conglomerate was deposited 

in a braided stream environment, the gravel is unlikely to 

have extensive lateral continuity nor should gold grade 

necessarily increase to the east based on present 

knowledge.

Replacement Deposits in Lower 

Paleozoic Rocks

Evaluation of the potential for replacement 

deposits in the lower Paleozoic section would be 

enhanced if the following were known: (1) source(s) of 

the mineralizing fluids and metals; (2) local depositional 

environment of the basal Deadwood Formation; and 

(3) reasons for the development of fractures or other 

ground preparation structures which could serve as channelways or depositional loci for the hydrothermal solutions. In our earlier description of the Tertiary gold 

deposits, relatively strong evidence was cited that the 

mineralizing fluids were probably magmatically derived, 

although the possible involvement of heated meteoric 

water in the stratigraphically higher deposits cannot be 

entirely ruled out. Clearly, gold is associated with 

Tertiary igneous centers, but whether or not one 

particular type of igneous rock developed the magmatic 

fluids that carried gold is not certain. The source of the 

precious and other metals is less clear inasmuch as they 

could have been magmatically derived with the fluid, or 

they could have been obtained by reaction of magmatic 

fluids with wall rocks. Isotope data of Rye and others

B64 Geology and Resources of Gold in the United States
(1974) suggest that lead in galena from Tertiary veinlets 

in Proterozoic rocks could have been derived from the 

wall rocks. Their isotope data for Tertiary veins in 

Paleozoic rocks also are compatible with the idea that 

some of the lead in galena was derived from the enclosing 

wall rocks. For the precious metals, the only evidence 

relative to source is Devereux's (1882) statements that 

placer gold in the Deadwood Formation was locally 

removed or exhibited solution pitting adjacent to Tertiary 

intrusive bodies. However, within the Homestake mine 

no evidence supports any depletion of gold where Proterozoic ore bodies are cut by Tertiary igneous rocks 

(Gordon Nelson, Mine geologist, Homestake Mining 

Company, oral commun., 1985). Because the Tertiary 

gold deposits contain a diverse assemblage of elements 

(for example, tungsten, molybdenum, gold, silver, lead, 

zinc, and fluorine), we believe that the precious metals, 

like the hot fluids, were derived from the Tertiary 

magmas.

Replacement deposits could have formed in the 

lower part of the Deadwood Formation only where 

metal-bearing fluids were available, where suitable rock 

types were available for replacement, and where local or 

regional structures were present to help prepare the 

ground or produce gradients for fluid movement. 

Ground preparation is exemplified in the Bald Mountain 

area, where two moderate-sized faults produced a grabenlike structure which was then extensively intruded by 

igneous sills and dikes. Deposition of the basal Deadwood was clearly controlled by existing topography 

during Late Cambrian time.

Detailed structure contour maps of the basal 

Deadwood unconformity and isopach maps of the basal 

sandstone-conglomerate unit of the Deadwood for the 

entire Lead-Deadwood dome (figs. B15, B16) and on a 

larger scale for the Bald Mountain area (fig. B17) have 

been constructed by French (1985) from drill hole data, 

mine shaft maps, and surface exposures. A striking 

feature of figures B16 and B17 is a major thinning of the 

basal Deadwood in the general area of Bald Mountain. 

This anomalously thin basal part of the Deadwood 

overlies resistant quartzites of the Ellison Formation. In 

the Nemo area and along the eastern side of the Black 

Hills, Redden (1987) and Daly (1981) documented that 

buried hills as much as 65 m in relief are preserved above 

quartzite units in the Proterozoic rocks, whereas paleotopographic lows or surfaces of little relief are generally 

underlain by phyllite. A clearly defined hill, or thinning of 

the basal Deadwood above the Ellison Formation, in the 

vicinity of the Homestake mine, is not apparent in figure 

B15 due in part to the scale. Irving (living and Emmons, 

1904, p. 100), however, cited the absence of the basal 

conglomerate above the Homestake deposit outcrop as 

clear indication that a paleohigh existed above the ore

body and associated Ellison quartzites. Figure B15 also 

shows a small topographic low above the incompetent 

rocks of the Poorman Formation north of Lead.

Because the structure contours on the base of the 

Deadwood Formation may be elevated due to Tertiary 

intrusive bodies in the underlying Proterozoic rocks (as is 

true for the major structure of the Lead-Deadwood 

dome), the structure contours can be used only in 

conjunction with isopach maps of the basal Deadwood. 

For example, figure B15 reveals a small structural high 

about 3 km west of Galena. The high is due to the 

igneous distension of the basement rocks and emplacement of igneous rocks below the Deadwood. There is no 

corresponding thinning of the basal Deadwood above the 

high (fig. B16).

The isopach map of the basal sandstone of the 

Deadwood for the entire dome (fig. B16) indicates in a 

general way that thin parts of the basal Deadwood tend to 

overlie paleotopographic highs developed on quartzite 

units, especially the Ellison Formation. This relationship 

is best shown in the Bald Mountain area where detailed 

control is available (fig. B17). Clearly the thickness of the 

basal Deadwood is related to paleotopographic highs 

underlain by quartzite, much like the pinchouts of sandy 

units above granite knobs in southeast Missouri (Ohle 

and Brown, 1954). Although precise control is lacking 

owing to recent erosion that has removed the basal 

contact, the structure contours and isopachs apparently 

indicate not only the large-scale northwest-trending 

Lead-Deadwood dome, but also the north-trending 

smaller high centered over the Golden Reward mines. 

The Golden Reward mines are all located near the apex 

of the dome. To the west in the area of the Tornado shaft 

(fig. B17), the ore shoots are along a subsidiary structural 

high. As a generalization, based on the distribution of' 

underground workings, ore shoots are absent in basins 

where the basal Deadwood is thick. Several possible 

factors could have caused this distribution. Areas immediately adjacent to highs are likely to have experienced 

more fracturing and hence are better channelways. Also, 

local up-dip movement of solutions may have been 

 increased near paleotopographic highs. Thicker sandstone (quartzite) sections in the basins are likely to have 

experienced less fracturing than those adjacent to highs. 

Two other important factors are the dolomitic character 

of the lower quartzite unit and local thinness or possible 

absence of the quartzite unit above topographic highs. 

Proterozoic rocks may be directly overlain by dolomitic 

rocks. Thus, rocks favorable for replacement by the 

ore-bearing solutions were controlled by paleotopography. The increased dolomite content of the carbonate 

could have resulted during sedimentation, but as pointed 

out by Norton (1989), it may have resulted instead

United States Gold Terranes B65
103«52'30'

i!L___ ___L 

T.4 N. '

EXPLANATION

Tertiary igneous rocks 

Shown only in arees below 

Phanerozoic rocke

Contact Approximately located: 

hachures identify 

Phanerozoic boundary

Pnansrozoic rocks Includes 

Paleozoic rocks and Tertiary igneoue eille end dikee

Fault Dashed where

approximately located: 

symbol on downthrown side I

Structure contour on 

Precambrian-Cambrian 

contact Dashed where 

eroded, queried where 

uncertain. Contour 

interval 100 ft above 

5000 ft. 200 ft bslow 

5000 ft

Control point Data from 

drill holes or mine 

workings

Figure B15. Structure contour map of the Precambrian-Cambrian contact, Lead-Deadwood dome, Black Hills. Map from 

area from MacLeod (1986).

B66 Geology and Resources of Gold in the United States
French (1985); Precambrian geology from Noble and Harder (1948) and Bayley (1972a). Structure contours in the Gilt Edge

United States Gold Terranes B67
103 52'30

 

___ /

 -t ,

ED

Tertiary ignaous rocks 

Shown only in areae below 

Phanerozoic rocks

Phanerozoic rocks Includes 

Paleozoic rocks and Tertiary igneous sille and dikee

Grizzly Formation

Flag Rock Formation

Northwestern Formation

Ellieon Formation 

|xnp [

Homesteks end 

Poorman Formations

Contact Approximately located: 

hachures identify 

Phenerozoic boundary

Fault Dashed where

approximately located; 

symbol on downthrown eids

Isopach on the lower

sendetons-conglomerate unit 

of .the Deadwood Formation 

Qusried where eroded or 

distant from control dste; 

isopach interval 20 ft

Control point Dats from 

drill hoIBS or mine 

workings

I- i

R.2 E

I_ _ _ _ _ _ _I _ _ _

. lfi.3 E. I

.2000 METERS

Englewood

2000 4000 6000 FEET

Figure B16. Isopach map of the lower sandstone-conglomerate unit of the Deadwood Formation, Lead-Deadwood dome,

B68 Geology and Resources of Gold in the United States
_____I____±

Black Hills. Map from French (1985); Precambrian geology from Noble and Harder (1948) and from Bayley (1972a).

United States Gold Terranes B69
1000 0 1000 2000 FEET

SOLOBV f&tAoo MINES

Structure contoure Drawn on the base of the Deadwood 

Formation (Precambrlan-Cambrlan contact): dashed whare 

contact ie eroded: fault displacements ana removed to 

accentuate original relief; contour interval 100 feet

Isopachs on bassl sandstone of the Deadwood Formation 

Dashed where unit is removed by erosion: isopach 

interval 10 feet

Mine workings (After Shaplro end Gries. 1970)

Figure B17. Structure contour and isopach map, lower Deadwood Formation, Bald Mountain area, Black Hills.

from alteration during solution movement. Small local 

structures that created structural highs in the sedimentary rocks are believed to have been important in ore 

localization, and the emplacement of Tertiary sills at the 

Cambrian unconformity probably localized fractures.

We suggest, based on the previous descriptions and 

conclusions, that a thorough knowledge of the topography of the Cambrian-Proterozoic surface is of considerable importance in exploration for new replacement 

deposits in the lower Paleozoic rocks and especially in the 

lower Deadwood. Our work elsewhere in the Black Hills 

to the present (1988) indicates that the basal Deadwood 

sandstone generally is thicker than average only immediately adjacent to areas where the underlying basement 

rocks consist of quartzite. The basal Deadwood is thin or 

absent above paleotopographic highs developed locally 

on the quartzite. The basal Deadwood in areas on or 

adjacent to ancient topographic highs seems to have been 

especially favorable for gold deposition, but mineralizing 

solutions would have been available only close to Tertiary 

intrusions. In areas that contain no quartzite in the 

Proterozoic, the basal Deadwood sandstone generally is 

thin and its grains are poorly rounded. On the other 

hand, basal sandstone derived from quartzite is thicker 

and the grains are well rounded. The thick accumulations 

of well-rounded quartz grains resulted from the partial

B70 Geology and Resources of Gold in the United States
disintegration of quartzite as a consequence of tropical 

weathering preceding advance of the Cambrian sea 

(Redden, 1987).

Where quartzite in the Proterozoic extends in the 

subsurface away from the Lead-Deadwood dome, there 

may be increased potential for replacement deposits. 

Increased potential would also seem possible in Paleozoic rocks above the probable subsurface extension of 

quartzite south of the Bald Mountain area toward Rochford. Some Tertiary sills intrude and dome Paleozoic 

rocks as far south as Custer Peak (fig. B13), but the 

basement rocks do not appear to be greatly uplifted or 

distended. The approximate axis of the main Black Hills 

dome extends south-southeast of Bald Mountain toward 

Rochford, although structure contours on the base of the 

Deadwood are not accurate enough to show details. 

Thus, one cannot rule out the possibility that Tertiary 

igneous rocks, whose presence could be indicated by 

detailed structure contours, may occur as far south as the 

north end of the Rochford district.

The Proterozoic quartzite in the Ellison Formation, although unrelated intrinsically to the Tertiary 

replacement deposits in the lower Deadwood, directly 

overlies the Homestake Formation. Thus recognition of 

paleohighs as a result of examination of the lower 

Deadwood lithologies also may indicate possible extensions of the Homestake Formation in the subsurface. 

Further, the distribution of detrital gold in the basal 

Deadwood is an obvious geochemical guide to possible 

gold deposits in Proterozoic rocks, no matter what their 

origin.

Disseminated and Vein Deposits in 

Tertiary Igneous Rocks

The characteristics of these deposits, as discussed 

earlier, indicate a continuum between them and the 

replacement deposits in the lower Paleozoic rocks. The 

disseminated and vein deposits in Tertiary igneous rocks 

are discussed separately here because the recent 

discovery of several such low-grade deposits, suitable for 

development by open-cut/heap-leach methods, indicates 

considerable gold reserve potential. Although data are 

not yet available to indicate whether or not certain 

Tertiary igneous rocks are more favorable than others, as 

previously indicated, some generalizations can be made. 

Earlier lack of success in discovering minable replacement deposits associated with laccolithic intrusions in 

Paleozoic rocks on the periphery of the Black Hills 

suggests that such intrusive bodies are unfavorable as 

guides to gold deposits. On the other hand, in a general 

way areas characterized by considerable intrusion of the 

basement rocks or by multiple intrusions in the lower 

Paleozoic section probably are favorable. The structure

contours on figure B15 show greatest closure approximately above the largest mass of Tertiary igneous rocks 

in the Black Hills, known locally as the Cutting stock. 

Evidently the Tertiary intrusions were principally 

responsible for formation of the dome, as documented by 

Noble and others (1949). Noble (1952) presented firm 

evidence in the three-dimensional exposures of the 

Homestake mine that emplacement of the igneous rocks 

produced distension of enclosing Proterozoic rocks and 

overlying Phanerozoic rocks approximately equivalent to 

the quantity of magma emplaced. If the entire LeadDeadwood dome resulted from this emplacement, 

approximately 10 km3 of igneous rock is required to be 

emplaced within the Precambrian rocks (fig. B15). A 

considerable volume of igneous rock was emplaced also 

in the lower Paleozoic section, but the igneous rock has 

been largely removed by erosion above the central part of 

the dome. The quantity of igneous rock intruded in the 

Paleozoic section is not known, but based on the extent of 

sills and dikes in areas such as the Golden Reward, an 

estimate of at least 20-30 percent of the volume present 

in the basement dome seems reasonable. The quite 

extensive introduction of magma in the basement rocks 

readily could provide either fluids and precious metals 

derived from crystallization of the magma under lowpressure conditions, or adequate heat for thermal 

leaching by meteoric ground-water fluids of metals from 

wall rocks or igneous rocks.

Ground preparation that resulted from emplacement of breccia pipes or dikes, and fracturing adjacent to 

igneous intrusions or along later faults, probably were 

prerequisites for mineralization (Emanuel and Walsh, 

1987). Some igneous sills may have acted as aquacludes 

and may have trapped fluids, which were then able to 

precipitate low-grade gold in underlying sedimentary or 

igneous rocks. Faulting, fracturing, and jointing, on both 

a regional scale and a local scale, also were important as 

ground preparation for both lode and sediment-hosted 

mineralization. Small-scale faulting commonly was 

associated with emplacement of sills and dikes, and 

earlier igneous bodies emplaced at higher stratigraphic 

levels as well as the enclosing sedimentary rocks were 

displaced by sill and dike intrusion. At present there are 

no specific guides to predict faults or fracture patterns. A 

roughly radial fracture pattern might be expected around 

the slightly elongated (N. 30° W.) Lead-Deadwood dome 

(fig. B15). Slaughter (1968) suggested that a regional 

poorly developed radial fracture pattern in fact existed, 

but later work by Shapiro and Gries (1970) and by Rueb 

(1984) did not substantiate such a pattern. The lack of 

clear-cut fracture patterns around the Tertiary LeadDeadwood dome probably is related to preexisting 

divergent fracture patterns that resulted from the Laramide uplift of the Black Hills. Most of the mapped faults 

and many lenticular igneous bodies trend subparallel to

United States Gold Terranes B71
the dominant N. 30° W. schistosity of the Proterozoic 

rocks. The available data on existing deposits suggest that 

diverse local features of igneous emplacement and 

fracturing were more important controls on ore deposition than were the regional fractures. Probably areas of 

continued igneous intrusion and accompanying fracturing and faulting are most likely to contain disseminated gold deposits which have commercial potential. 

Because of the complexity of the relationships, detailed 

maps, though generally not available, are a clear 

necessity to indicate favorable targets. We cannot 

overemphasize the need for detailed mapping that not 

only shows the distribution of intrusive rocks but also 

recognizes the different petrologic and alteration 

characteristics of the rocks.

CONCLUSIONS

Proterozoic strata of the Black Hills record a 

relatively detailed history of development of an apparently small intracontinental basin, although not all stratigraphic relationships have been completely resolved. 

The basin had a complicated history that began with 

rifting in Early Proterozoic time (s«2.4-2.1 Ga) and 

progressed through marine deep-water turbidite deposition and accompanying volcanism later in the Early 

Proterozoic («**2.0-1.8 Ga). Most of the volcanic rocks 

are tholeiitic basalts; only a minor amount of relatively 

young («1.9 Ga) alkalic tuff is known. The strong 

association of gold and carbonate-silicate-facies ironformation in the Black Hills is well known. We note that 

this facies is commonly associated with tuffaceous or 

volcaniclastic rocks, and on the basis of. the gold 

association with the Homestake Formation, we suggest 

that gold was probably deposited by submarine hot 

springs. Submarine hot springs were also responsible for 

local lenticular deposits of chert and iron-formation, 

apparently less enriched in gold, in the turbidite section.

The potential for the discovery of significant gold 

deposits is limited largely to Homestake-type stratiform 

deposits, or to deposits associated with Tertiary igneous 

rocks. Correlation and extension of the Homestake 

Formation outside of the Lead-Deadwood dome have 

not yet been possible. Available age data and stratigraphic sequences suggest that at least some of the 

iron-formation units in the Rochford areas are 

considerably younger than the Homestake Formation. 

Recent work indicates that rapid lateral facies changes 

occur in the Rochford district; these must be fully 

understood in order to assess the potential for 

Homestake-type deposits. Because the Rochford district 

is near an Early Proterozoic volcanic center, and because 

the Early Proterozoic depositional environment deepened from Lead toward Rochford and to the area west of

Rochford, stratiform deposits that may have formed 

could be of a nature somewhat different from that of the 

Homestake deposit.

An apparent continuum exists between the 

Tertiary replacement deposits in lower Paleozoic rocks 

and the disseminated and vein deposits in the Tertiary 

igneous rocks. Areas of intensive Tertiary igneous 

activity characterized by brecciation, fracturing, and 

faulting are favorable for low-grade gold deposits, both in 

the igneous rocks and in adjacent sedimentary rocks. 

Knowledge of paleotopography of the basal Deadwood 

unconformity may be important in recognizing areas of 

favorable rock types, or areas of porosity features 

favorable for mineralization, because the character of the 

basal Cambrian rocks is directly related to the paleotopography. Paleotopography is also related to the 

underlying Proterozoic rocks, and it can be used as a 

general guide to basement rock types.

Additional work is needed to establish whether or 

not gold is genetically related to specific Tertiary igneous 

rock types, and to establish the ultimate source of the 

gold. Hence, detailed geologic mapping and exploratory 

drilling in the Tertiary igneous rocks are critical for the 

discovery of new deposits.

Manuscript received by scientific editors January 1987

REFERENCES CITED

Allsman, P.T., 1940, Reconnaissance of gold-mining districts in 

the Black Hills, South Dakota: U.S. Bureau of Mines 

Bulletin 427, 146 p.

Atkinson, R.D., 1976, Geology of the Pony Gulch area near 

Mystic, South Dakota: Rapid City, S. Dak., South Dakota 

School of Mines and Technology M.S. thesis, 51 p.

Bayley, R.W., 1972a, Geologic field compilation map of the 

northern Black Hills, South Dakota: U.S. Geological 

Survey Open-File Report 72-29, scale 1:48,000.

___ 19725, Preliminary geologic map of the Nemo district, 

Black Hills, South Dakota: U.S. Geological Survey 

Miscellaneous Geologic Investigations Map 1-712, scale 

1:24,000.

___ 1972c, A preliminary report on the geology and gold 

deposits of the Rochford district, Black Hills, South 

Dakota: U.S. Geological Survey Bulletin 1332-A, 24 p.

Cleath, R.A., 1986, Geology of the Precambrian rocks in the 

Silver Creek area, near Rochford, Black Hills, South 

Dakota: Rapid City, S. Dak., South Dakota School of 

Mines and Technology M.S. thesis, 130 p.

Connolly, J.P., 1925, Geology and mineralogy of the Keystone 

district: Black Hills Engineer, v. 13, p. 11-18.

___ 1927, The Tertiary mineralization of the northern Black 

Hills: South Dakota School of Mines and Technology 

Bulletin 15, 130 p.

___ 1929, Gold deposits of the Keystone district: Black Hills 

Engineer, v. 17, p. 12-20.

B72 Geology and Resources of Gold in the United States
Daly, W.E., 1981, Basement control of the deposition of the 

Cambrian Deadwood Formation in the eastern Black 

Hills, South Dakota: Rapid City, S. Dak., South Dakota 

School of Mines and Technology M.S. thesis, 89 p.

Darton, N.H., and Paige, Sidney, 1925, Central Black Hills, 

South Dakota: U.S. Geological Survey Geologic Atlas of 

the United States, Folio 219, 34 p.

Devereux, W.B., 1882, The occurrence of gold in the Potsdam 

Formation, Black Hills, Dakota: American Institute of 

Mining Engineers Transactions, v. 10, p. 465-475.

DeWitt, Ed, Redden, J.A., Wilson, A.B., and Buscher, David, 

1986, Mineral resource potential and geology of the 

Black Hills National Forest, South Dakota and 

Wyoming: U.S. Geological Survey Bulletin 1580, 135 p.

Dodge, T.A., 1942, Amphibolites of the Lead area, northern 

Black Hills, South Dakota: Geological Society of 

America Bulletin, v. 53, p. 561-583.

Duex, T.A., Smith, T.J., McConnell, P.A., Osmundson, T.M., 

Petersen, M.A., and Stanley, T.M., 1987, Geology of the 

Richmond Hill gold deposit, in Proceedings of the third 

western regional conference on precious metals, coal and 

environment: Black Hills section, Society of Mining 

Engineers, p. 67-71.

Emaniiel, K.M., and Walsh, J.F., 1987, Alkalic intrusive rocks 

and gold mineralization at the Golden Reward, 

Lawrence County, South Dakota, in Proceedings of the 

third western regional conference on precious metals, 

coal and the environment: Black Hills section, Society of 

Mining Engineers, p. 23-61.

Emmons, W.H., 1926, Relations of metalliferous lode systems 

to igneous intrusives: American Institute of Mining and 

Metallurgical Engineering Transactions, v. 74, p. 29-70.

Fantone, Kenneth, 1983, Geochemistry and petrology of the 

carbonate iron formations and ferruginous cherts of the 

northeastern Black Hills, South Dakota: Rapid City, 

S. Dak., South Dakota School of Mines and Technology 

M.S. thesis, 107 p.

Ferry, J.M., 1987, Metamorphic hydrology at 13-km depth and 

400-550°C: American Mineralogist, v. 72, p. 39-58.

French, G.McN., 1985, Relationships of lithology and ore 

deposits in the lower Cambrian Deadwood Formation 

and Precambrian basement in the Lead-Deadwood dome 

area, Black Hills, South Dakota: Rapid City, S. Dak., 

South Dakota School of Mines and Technology M.S. 

thesis, 69 p.

Hosted, J.O., and Wright, L.B., 1923, Geology of the Homestake ore bodies and the Lead area of South Dakota: 

Engineering and Mining Journal, v. 115, p. 793-799, 

836-843.

living, J.D., and Emmons, S.F., 1904, Mining geology, Part 2 of 

living, J.D., Emmons, S.F., and Jaggar, T.A., Jr., 

Economic resources of the northern Black Hills: U.S. 

Geological Survey Professional Paper 26, p. 43-222.

Kim, J.D., 1979, Mineralogy and trace elements of the uraniferous conglomerates, Nemo district, Black Hills, South 

Dakota: Rapid City, S. Dak., South Dakota School of 

Mines and Technology Ph. D. thesis, 113 p.

Kulik, J.W., 1965, Stratigraphy of the Deadwood Formation, 

Black Hills, South Dakota and Wyoming: Rapid City, 

S. Dak., South Dakota School of Mines and Technology 

M.S. thesis, 263 p.

Kulp, J.L., Eckelmann, W.R., Gast, P.W., and Miller, D.S., 

1956, Age of the Black Hills (South Dakota) gold 

mineralization: Geological Society of America Bulletin, 

v. 67, p. 1557-1558.

Larson, J.L., 1971, The sulfosalt mineralogy of the Silver City 

mining district, central Black Hills, South Dakota: Rapid 

City, S. Dak., South Dakota School of Mines and 

Technology M.S. thesis, 41 p.

Lisenbee, A.L., 1981, Studies of the Tertiary intrusions of the 

northern Black Hills Uplift, South Dakota and Wyoming: 

a historical review, in Rich, FJ., ed., Geology of the 

Black Hills, South Dakota and Wyoming: American 

Geological Institute, p. 106-125.

MacLeod, R.J., 1986, The geology of the Gilt Edge area, 

northern Black Hills of South Dakota: Rapid City, 

S. Dak., South Dakota School of Mines and Technology 

M.S. thesis, 146 p.

McMillan, R.C., 1977, Geology of the Lookout Mill area along 

Castle Creek, Black Hills, Pennington County, South 

Dakota: Rapid City, S. Dak., South Dakota School of 

Mines and Technology M.S. thesis, 55 p.

Nabelek, P.I., Labotka, T.C., O'Neil, J.R., and Papike, J.J., 

1984, Contrasting fluid/rock interactions between the 

Notch Peak granitic intrusion and argillites and limestones in western Utah Evidence from stable isotopes 

and phase assemblages: Contributions to Mineralogy and 

Petrology, v. 86, p. 25-34.

Noble, J.A., 1950, Ore mineralization in the Homestake gold 

mine, Lead, South Dakota: Geological Society of 

America Bulletin, v. 61, p. 221-252.

___ 1952, Evaluation of criteria for the forcible intrusion of 

magma: Journal of Geology, v. 60, p. 34-57.

Noble, J.A., and Harder, J.O., 1948, Stratigraphy and metamorphism in a part of the northern Black Hills and the 

Homestake mine, Lead, South Dakota: Geological 

Society of America Bulletin, v. 59, p. 941-975.

Noble, J.A., Harder, J.O., and Slaughter, A.L., 1949, Structure 

of a part of the northern Black Hills and the Homestake 

mine, Lead, South Dakota: Geological Society of 

America Bulletin, v. 60, p. 321-352.

Norton, J.J., 1974, Gold in the Black Hills, South Dakota, and 

how new deposits might be found: U.S. Geological 

Survey Circular 699, 22 p.

___1976, Field compilation map of the geology of the 

Keystone area, Black Hills, South Dakota: U.S. 

Geological Survey Open-File Report 76-297, scale 

1:20,000.

___1989, Bald Mountain gold mining region, northern 

Black Hills, South Dakota, in Shawe, D.R., Ashley, R.P., 

and Carter, L.M.H., eds., Geology and resources of gold 

in the United States: U.S. Geological Survey Bulletin 

1857-C, p. C1-C12.

Ohle, E.L., and Brown, J.S., 1954, Geologic problems in the 

southeast Missouri Lead District: Geological Society of 

America Bulletin, v. 65, p. 201-222.

United States Gold Terrenes B73
Paterson, C.J., and Uzunlar, Nuri, 1987, Epithermal Au-Ag 

deposits in the northern Black Hills A variety of oreforming fluids, in Proceedings of the third western 

regional conference on precious metals, coal and 

environment: Black Hills section, Society of Mining 

Engineers, p. 83-89.

Ratte", J.C., 1986, Geologic map of the Medicine Mountain 

Quadrangle, Pennington County, South Dakota: U.S. 

Geological Survey Miscellaneous Investigations Series 

Map 1-1654, scale 1:24,000.

Ratt<*, J.C., and Wayland, R.G., 1969, Geology of the Hill City 

Quadrangle, South Dakota A preliminary report: U.S. 

Geological Survey Bulletin 1271-B, 14 p.

Raymond, W.H., 1981, Geochemical data from Precambrian 

meta-iron-formation and related rocks of the Keystone 

area, South Dakota: U.S. Geological Survey Open-File 

Report 81-772, 16 p.

Raymond, W.H., King, R.U., and Norton, JJ., 1975, Anomalous concentrations of several metals in iron-formation of 

the Blue Lead Mountain area, Pennington County, South 

Dakota: U.S. Geological Survey Circular 707, 14 p.

Redden, J.A., 1963, Geology and pegmatites of the Fourmile 

quadrangle, Black Hills, South Dakota: U.S. Geological 

Survey Professional Paper 297-D, p. 199-291.

___ 1968, Geology of the Berne quadrangle, Black Hills, 

South Dakota: U.S. Geological Survey Professional 

Paper 297-F, p. 343-408.

___ 1975, Tertiary igneous rocks, in U.S. Congress, Senate 

Committee on Interior and Insular Affairs, Mineral and 

Water Resources of South Dakota: 94th Congress, 1st 

Session, p. 45-47.

___ 1980, Geology and uranium resources in Precambrian 

conglomerates of the Nemo area, Black Hills, South 

Dakota: U.S. Department of Energy Open-File Report 

GJBX-127(80), 147 p.; available from U.S. Geological 

Survey, Book and Open-File Services Section, Federal 

Center, Box 25425, Denver, CO 80225.

___ 1981, Summary of the geology of the Nemo area, in 

Rich, F.J., ed., Geology of the Black Hills, South Dakota 

and Wyoming, Geological Society of America 

Guidebook, Rocky Mountain Section, Annual Meeting, 

Rapid City, S. Dak., 1981: Falls Church, Va., American 

Geological Institute, p. 193-210. 

1987, Early Proterozoic and Precambrian-Cambrian

unconformities of the Nemo area, Black Hills, South 

Dakota, in Beuss, S.S., ed., Centennial Field Guide, v. 2: 

Rocky Mountain Section, Geological Society of America, 

p. 219-226.

Redden, J.A., Norton, J.J., and McLaughlin, RJ., 1982, 

Geology of the Harney Peak Granite, Black Hills, South 

Dakota: U.S. Geological Survey Open-File Report 

82-481, 18 p.

Redden, J.A., Obradovich, J.D., Naeser, C.W., Zartman, R.E., 

and Norton, J.J., 1983, Early Tertiary age of pitchstone in 

the northern Black Hills, South Dakota: Science, v. 220, 

p. 1153-1154.

Riley, G.H., 1970, Isotopic discrepancies in zoned pegmatites, 

Black Hills, South Dakota: Geochimica et Cosmochimica 

Acta, v. 34, p. 713-725.

Rueb, R.A., 1984, Lineament analysis of the Black Hills, South 

Dakota and Wyoming: Rapid City, S. Dak., South 

Dakota School of Mines and Technology M.S. thesis, 

89 p.

Rye, D.M., Doe, B.R., and Delevaux, M.H., 1974, Homestake 

gold mine, South Dakota; [Part] 2, Lead isotopes, 

mineralization ages, and source of lead in ores of 

the northern Black Hills: Economic Geology, v. 69, 

p. 293-317.

Rye, D.M., and Rye, R.O., 1974, Homestake gold mine, South 

Dakota; [Part] 1, Stable isotope studies: Economic 

Geology, v. 69, p. 293-317.

Rye, D.M., and Shelton, K.L., 1983, A stable isotope study of 

the Homestake gold mine An example of a lower 

Proterozoic submarine hydrothermal vent system: 

Geological Association of Canada, Mineralogical 

Association of Canada, Canadian Geophysical Union 

Annual Meeting 1983, Program with Abstracts, p. A60.

Shapiro, L.H., 1971, Structural geology of the Black Hills 

region and implications for the origin of the uplifts of the 

Middle Rocky Mountain province: Minneapolis, Minn., 

University of Minnesota Ph. D. thesis, 213 p.

Shapiro, L.H., and Gries, J.P., 1970, Ore deposits in rocks of 

Paleozoic and Tertiary age of the northern Black Hills, 

South Dakota: U.S. Geological Survey Open-File Report 

70-300, 235 p.

Slaughter, A.L., 1968, The Homestake mine, in Ore deposits of 

the United States, 1933-1967 (Graton-Sales Volume), 

Volume 2: American Institute of Mining, Metallurgical, 

and Petroleum Engineers, p. 1436-1459.

Staatz, M.H., 1983, Geology and description of thorium and 

rare-earth deposits in the southern Bear Lodge 

Mountains, northeastern Wyoming: U.S. Geological 

Survey Professional Paper 1049-D, 52 p.

Tuysuz, Necati, 1986, Heavy mineral distribution in the basal 

Deadwood Formation A possible geochemical tool for 

Precambrian mineralization in the northern Black Hills, 

South Dakota: Rapid City, S. Dak., South Dakota School 

of Mines and Technology M.S. thesis, 122 p.

Weissenborn, P.R., 1987, The Precambrian geology of the 

western portion of the Rochford gold-mining district, 

Black Hills, South Dakota: Rapid City, S. Dak., South 

Dakota School of Mines and Technology M.S. thesis, 

143 p.

Wolfgram, Diane, 1977, Wall rock alteration and the location 

of gold in the Homestake mine, Lead, South Dakota: 

Berkeley, Calif., University of California, Berkeley, 

Ph. D. dissertation, 139 p.

Zartman, R.E., and Stern, T.W., 1967, Isotopic age and 

geologic relationships of the Little Elk Granite, northern 

Black Hills, South Dakota, in Geological Survey research 

1967: U.S. Geological Survey Professional Paper 575-D, 

p. D157-D163.

B74 Geology and Resources of Gold in the United States &U.S. GOVERNMENT PRINTING OFFICE: 1989-673-047/8611|1
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