.Mineral Resource Potential and Geology of 

I he Challis National Forest, Idaho 

U.S. GEOLOGICAL SURVEY BULLETIN 1873 

Mineral Resource Potential and Geology of 

the Challis National Forest, Idaho 

By RONALD G. WORL, ANNA BURACK WILSON, 

COLE L. SMITH, and M. DEAN KLEINKOPF 

U.S. Geological Survey 

with a section on Salable Minerals 

By ROBERT C. SYKES 

U.S. Forest Service 

U.S. GEOLOGICAL SURVEY BULLETIN 1873 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade, product, industry, 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 

Mineral resource potential and geology of the Challis National Forest, Idaho 

(U.S. Geological Survey bulletin; 1873) 

Bibliography: p. 

Supt. of Docs. no.: I 19.3:1873 

1. Mines and mineral resources-Idaho-Challis National Forest. 

2. Geology-Idaho-Challis National Forest. I. Worl, Ronald G. 

II. Series. 

QE75.B9 no. 1873 557.3 s [553'.09796] 88-607946 

[TN24.12] 
CONTENTS 

Summary 1 

Character and geologic setting 1 

Mineral resources 2 

Resource potential-locatable and leasable minerals 2 

Resource potential-salable minerals 7 

Introduction 7 

Geology 11 

Geologic framework 15 

Precambrian rocks and structures 20 

Paleozoic rocks and structures 21 

Quartzite terrane 21 

Carbonate terrane 21 

Black-shale terrane 22 

Flysch terrane 23 

Mesozoic rocks and structures 23 

Tertiary rocks and structures 24 

Quaternary rocks and structures 25 

Geochemistry 25 

Geochemical surveys 25 

NURE programs 26 

U.S. Geological Survey programs 26 

Geochemical signatures 27 

Geophysics 27 

Mineral resources-locatable minerals 28 

Mining and exploration history 28 

Metals 29 

Industrial minerals 36 

Resource potential-locatable minerals 37 

Fluorspar veins (A) 37 

Polymetallic veins in black-shale terrane (B) 39 

Polymetallic veins in quartzite terrane (C) 41 

Polymetallic veins in carbonate terrane (D) 43 

Polymetallic veins in tertiary extrusive terrane (E) 45 

Precious-metal veins (F) 48 

Base-metal veins (G) SO 

Vein uranium deposits (H) SO 

Tungsten stockwork and vein deposits (I) 53 

Stockwork molybdenum deposits (J) 56 

High-level, rhyolite-hosted, precious-metal deposits (K) 58 

Polymetallic skarn deposits (L) 60 

Irregular replacements of base and precious metals (M) 62 

Fluorspar breccia manto deposits (N) 64 

Sediment-hosted, jasperoid-associated, precious-metal deposits (0) 66 

Precious-metal deposits in volcanic tuffs (P) 68 

Stratabound syngenetic deposits of precious and base metals (Q) 70 

Contents Ill 
Stratiform vanadium deposits (R) 73 

Gold placer deposits (S) 73 

Radioactive black-sand placer deposits (T) 76 

Other commodities 78 

~anganese 78 

Semiprecious gemstones 78 

Limestone 79 

Iron 79 

Graphite in metamorphic rocks 79 

Pegmatite minerals 79 

~ercury 79 

Zeolites 79 

Barite 79 

Uranium in sedimentary rocks 80 

Cobalt 80 

Alunite 80 

Silver 80 

Gold 80 

Areas of unknown resource potential 80 

Area Ul-Lone Cedar Creek 80 

Area U2-Iron Bog and Leadbelt Creeks 8_0 

Area U3-Hamilton Creek-Burma Road 82 

Area U4-Sheep ~ountain 82 

Area US-North Creek 82 

Area U6-~ahogany Creek 82 

Area U7-Porphyry Peak 82 

Area US -Squaw Creek 82 

~ineral resources-leasable minerals 82 

Resource potential-leasable minerals 83 

Geothermal resources (V) 83 

~ineral resources-salable minerals 84 

Resource potential-salable minerals 84 

Sand and gravel 84 

Dimension stone 85 

Riprap 85 

Recommendations for future studies of mineral resource potential 85 

Selected references 86 

Appendix 1. Definitions of levels of mineral resource potential and certainty of 

assessment 98 

Appendix 2. Size classification of deposit types 101 

PLATES 

[Plates are in pocket] 

1. Geologic terrane map of the Challis National Forest and adjacent areas, Idaho. 

2. Aeromagnetic map of the Challis National Forest and adjacent areas, Idaho. 

3. ~ineral resource potential map for locatable lode commodities in the Challis 

National Forest and adjacent areas, Idaho. 

IV Contents 
4. Mineral resource potential map for locatable placer deposits and leasable and 

salable commodities in the Challis National Forest and adjacent areas, Idaho. 

FIGURES 

1. Map showing resource potential for locatable lode minerals, Challis 

National Forest, Idaho 3 

2. Map showing resource potential for locatable placer deposits and leasable 

(geothermal) commodities, Challis National Forest, Idaho 4 

3. Map showing resource potential for salable minerals, Challis National 

Forest, Idaho 5 

4. Index map showing location of the Challis National Forest and principal 

mining districts within or partially within the Forest 10 

5. Map showing location of type mine localities for mineral deposit types and 

boundaries of geochemical surveys that cover parts of the Challis National 

Forest 12 

6. Map showing major structural elements within or close to the Challis 

National Forest 17 

7-12. Schematic diagrams of: 

7. Deposit types in black-shale terrane 30 

8. Deposit types in Idaho batholith terrane 31 

9. Stockwork molybdenum and tungsten vein deposits 32 

10. Deposit types in volcanic terrane 33 

11. Deposit types in carbonate terrane 34 

12. Deposit types in quartzite terrane 35 

13-32. Mineral resource potential maps of the Challis National Forest and 

adjacent areas, Idaho, for: 

13. Fluorspar veins (A) 38 

14. Polymetallic veins in black-shale terrane (B) 40 

15. Polymetallic veins in quartzite terrane (C) 42 

16. Polymetallic veins in carbonate terrane (D) 44 

17. Polymetallic veins in Tertiary extrusive terrane (E) 46 

18. Precious-metal veins (F) 49 

19. Base-metal veins (G) 51 

20. Vein uranium deposits (H) 52 

21. Tungsten stockwork and vein deposits (I) 54 

22. Stockwork molybdenum deposits (J) 57 

23. High-level, rhyolite-hosted, precious-metal deposits (K) 59 

24. Polymetallic skarn deposits (L) 61 

25. Irregular replacements of base and precious metals (M) 63 

26. Fluorspar breccia manto deposits (N) 65 

27. Sediment -hosted, jasperoid-associated, precious-metal 

deposits (0) 67 

28. Precious-metal deposits in volcanic tuffs (P) 69 

29. Stratabound syngenetic deposits of precious and 

base metals (0) 71 

30. Stratiform vanadium deposits (R) 74 

31. Gold placer deposits (S) 75 

Contents V 
32. Radioactive black-sand placer deposits (T) 77 

33. Map showing areas of unknown resource potential in the Challis 

National Forest and adjacent areas, Idaho. 81 

TABLES 

1. Summary of areas of high and moderate mineral resource potential 2 

2. Mineral-materials transactions 1983-1986 7 

3. Type mine localities for mineral deposit types 8 

4. Description of areas of mineral resource potential for locatable and leasable 

resources in the Challis National Forest, Idaho 13 

5. Geochemical studies that cover parts of the Challis National Forest, 

Idaho 15 

6. Sources of analytical data, Challis National Forest, Idaho 16 

7. Geochemical signatures of mineral deposit types at type mine localities 18 

8. Size classification of deposit types 101 

VI Contents 
Mineral Resource Potential and Geology of the 

Challis National Forest, Idaho 

By Ronald G. Worl, Anna Burack Wilson, 

Cole L. Smith, and M. Dean Kleinkopf 

U.S. Geological Survey 

With a section on Salable Minerals 

By Robert C. Sykes 

U.S. Forest Service 

Summary 

This assessment of the mineral resource potential of the 

Challis National Forest, Idaho, was made to assist the U.S. 

Forest Service in fulfilling requirements of Title 36, Chapter 2, 

part 219.22, Code of Federal Regulations, and to supply 

resource information and interpretations so that the mineral 

resources of this Forest can be considered with other 

resources in land use planning. Geologic, geochemical, and 

geophysical data were compiled at 1 :250,000 scale, and all 

available published information on mineral deposits and 

occurrences, as of June 1987, was used in assessing the 

mineral resource potential of the Forest. 

The mineral resource potential of some of the wilderness study areas in the Forest has already been assessed by 

the U.S. Geological Survey and the U.S. Bureau of Mines; 

published studies cover the Frank Church-River of No 

Return Wilderness and additions, the Sawtooth National 

Recreation Area, the Boulder-Pioneer Wilderness Study 

Area, and the White Cloud-Boulder Roadless Area. The U.S. 

Geological Survey recently completed a mineral resource 

evaluation of the Challis 1 ox 2° quadrangle. 

The Challis National Forest is endowed with a wealth of 

mineral resources, and mining and exploration activity has 

played a central role in the settlement and economic devei?Pment of this area. Major deposits of silver, gold, lead, ztnc, 

copper, tungsten, and molybdenum have been exploited, 

and there has been some production of fluorspar, uranium, 

and rare-earth minerals. Active exploration programs by 

industry are designed to seek new deposits of base and 

Manuscript approved for publication September 30, 1988. 

precious metals, rare-earth elements, and other mineral 

resources. Commercially important mineral production in the 

future seems assured. 

Character and Geologic Setting 

The Challis National Forest and administrated lands 

cover 4,338 mi2 of mountainous terrain in an area about 140 

mi long in a northwest direction and 75 mi wide. The Forest 

consists of four major tracts; the northeastern and central 

tracts are separated from each of the others, and the 

northwestern and southwestern tracts are connected only by 

a narrow strip. The northeastern tract is along the west slope 

of the Lemhi Range; the central tract is in the higher parts of 

the Pahsimeroi Mountains and the Lost River Range; the 

northwestern tract covers the Boulder Mountains, northern 

Sawtooth Range, Stanley Basin, and the extensive Salmon 

River Mountains; and the southwestern tract covers the White 

Knob Mountains, Copper Basin, and the eastern part of the 

Pioneer Mountains. Elevations range from about 6,000 ft 

above sea level near Howe on the edge of the Snake River 

Plain to 12,662 ft on Borah Peak, which is the highest point in 

the State of Idaho. 

Rocks exposed in the Forest range from nearly 2 billion 

year old Precambrian gneisses to modern alluvial gravel~. 

Five major rock-forming and structural events occurred In 

this part of Idaho: (1) Depqsition of sedimentary rock~ ~long 

the margin of a major land mass from about 2,000 mtllto~ .to 

260 million years ago; (2) compressional structural acttvtty 

within the sedimentary pile after 260 million and prior to 70 

million years ago; (3) emplacement of the Idaho batholith 

plutonic rocks from about 110 million to 70 million years ~~o; 

(4) extensional tectonic activity that started about 70 mtllton 

Summary 
(4) extensional tectonic activity that started about 70 million 

years ago and continued to Holocene (Recent) time; and (5) 

volcanism that produced the Challis volcanic field from about 

51 million to 37 million years ago. Glaciation and erosion 

during the past 2 million years sculpted the landscape to its 

present form. 

The oldest recorded geologic event was the deposition, 

beginning about 2 billion years ago, of a thick sequence of 

Precambrian marine sedimentary quartzite, argillaceous 

quartzite, local limestone and sandstone, and minor interbedded volcanic rocks. These rocks were deformed, metamorphosed, and intruded by plutonic rocks 1.4--1.2 billion 

years ago. From about 570 million to 240 million years ago 

(the Paleozoic Era), the area was part of a geosyncline along 

the west edge of a major land mass. The types of 

sedimentary rocks deposited at this time ranged from 

dominantly limestone in the east, through clastic rocks, to 

dominantly deep water black-shale sequences in the west. 

Facies changes across short distances of time-equivalent 

rocks characterize the Paleozoic rocks in this area. During 

Mesozoic time, 240-66 million years ago, thrust faulting of 

the Paleozoic rocks resulted in juxtaposition of rock units that 

were originally many miles apart. This faulting, combined 

with the depositional facies changes, has resulted in a very 

complex Paleozoic rock terrane. Most of the Paleozoic rocks 

exposed in the Forest are part of imbricated structural plates 

and were moved along thrust faults from the places where 

they were formed. 

During mid- to Late Cretaceous time, 110-70 million 

years ago, granitic to tonalitic intrusive activity formed the 

Idaho batholith and related bodies. Emplacement of the 

batholith engulfed, deformed, and metamorphosed the 

Paleozoic sedimentary host rocks. Extensive volcanism from 

several centers and calderas produced the volcanic and 

volcaniclastic rocks of the Challis volcanic field during the 

period from about 51 million to 37 million years ago. Most of 

the area of the Forest was covered by volcanic rocks by the 

end of this period. Numerous intrusive bodies, which range in 

size from the large Sawtooth batholith (about 20 x 12 mi) to 

small dikes, also were emplaced during this period. 

Formation of regional northeast-trending high-angle faults 

occurred from the end of the Mesozoic, about 65 million 

years ago, to late Tertiary time. Block faulting along north and 

northwest trends, which started sometime in the mid-Tertiary 

and continued to the Holocene, produced the Basin and 

Range topography characteristic of this area. Glaciers 

sculpted some of the higher mountains from about 1.5 million 

years ago to Holocene time, and erosion by fluvial and masswasting processes produced the steep-sided mountain 

stream valleys. Debris from the mountain streams formed the 

large mountain-front alluvial fans present in much of the 

Forest. 

Mineral Resources 

The first major prospecting and mining in the Forest 

took place during the 1860's and 1870's when most of the 

known gold placer and lode deposits were discovered. 

Production of gold from d posits in and near the Forest has 

been nearly continuous un il the present. Lead-silver-copperzinc ores were discovered uring the gold rush of the 1860's, 

and the rich secondary d posits of the oxidized zone were 

mined during the 1880's. ining of primary ores has been 

nearly continuous since th turn of the century; the Clayton 

Silver mine recorded the I rgest production. Tungsten was 

produced sporadically fro mines in and near the Forest 

from about 1911, with major production, mainly from the lma 

mine, from 1936 into the late 1950's. Extensive exploration for 

molybdenum during the 1960's resulted in several discoveries and the development of the Thompson Creek mine 

which is still in production. Of the 2,516,191 acres within the 

Challis National Forest proper, about 1,800,000 acres are 

available for location of mining claims and mineral materials 

development. The remaining 787,789 acres are legislative 

and administrative withdrawals closed to the location of 

mining claims and mineral-materials development. 

Resource Potential-Locatable and Leasable Minerals 

The assessment of mineral resource potential in this 

report is summarized in table 1, which gives the total size of 

areas of high, moderate, or unknown resource potential for 

locatable lode, locatable placer, leasable, and salable commodities. Figure 1 shows areas of high, moderate, and 

unknown resource potential for locatable lode minerals; 

figure 2 shows areas of high and moderate resource potential 

for locatable placer minerals and high to moderate potential 

for leasable commodities; figure 3 shows areas of high 

resource potential for salable commodities. 

Table 1. Summary of areas of high and moderate mineral resource potential 

[Leaders ( ---) indicate no areas present or no value calculated) 

Type of resource Area of resource potential (in square miles) 

High Moderate Total 

Locatable lode •••••••••••• 1002 1037 

Locatable placer •••••••••• 298 200 

Leasable •••••••••••••••••• 1930 

Salable ••••••••••••••••••• 132 132 

Unknown ••••••••••••••••••• 851 

2 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
CJ) 

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EXPLANATION 

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MINERAL RESOURCE POTENTIAL 

HIGH 

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Figure 1. Map showing resource potential for locatable lode minerals, Challis National Forest, Idaho. 
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EXPLANATION 

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LOCATABLE PLACER 

MINERAL RESOURCE POTENTIAL 

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HIGH 

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Figure 2. Map showing resource potential for locatable placer deposits and leasable (geothermal) commodities, Challis National Forest, Idaho. 

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115°30' 115°00' 112°45' 

45°00'r---------------r-------,-----------------------~---------r-----,------------~;:----~ 114°00' 113°00' 

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EXPLANATION 

SALABLE MINERAL 

RESOURCE POTENTIAL 

HIGH 

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Figure 3. Map showing resource potential for salable minerals, Challis National Forest, Idaho. 
Most metals and industrial minerals are included in the 

category of locatable commodities by the General Mining 

Law of 1872. The principal types of deposits considered in 

the assessment of mineral potential for locatable commodities in the Challis National Forest are listed below, and 

the metals found in each type of deposit and the principal 

areas of resource potential are briefly summarized. Letter 

symbols shown in the list below are used throughout this 

report to designate particular types of deposits. 

A Fluorspar veins; formed from low-temperature hydrothermal solutions, commonly related to hot spring systems 

along regional high-angle faults. Areas of high resource 

potential are in the trans-Challis fault system at Meyers 

Cove and near Stanley. 

B Polymetallic veins in black-shale terrane; related to 

igneous intrusions emplaced during the interval 1 OG-40 

million years ago; principally valuable for silver, lead, and 

zinc, but also contain some gold, tin, antimony, and 

copper. Most of the black-shale belt, as exposed in the 

Star Hope Creek and Summit Creek areas and in a broad 

band extending from Galena Summit northward and 

northeastward to Mill Creek just west of Challis, has 

moderate to high resource potential. 

C Polymetallic veins in quartzite terrane; formed by fissure 

filling and replacement from hydrothermal solutions of 

unknown origin; contain mainly lead and silver with some 

zinc and gold. Areas of moderate to high resource 

potential are in the southern part of the Lemhi Range. 

D Polymetallic veins in carbonate terrane; formed by fissure 

filling and replacement of limestone along fractures; 

generally associated with igneous intrusions; contain 

mainly lead and silver with some gold and zinc. Areas of 

high resource potential are in the central Lemhi Range, in 

the White Knob Mountains, and at Leadbelt Creek. 

E Polymetallic veins in Tertiary extrusive terrane; complex 

deposits within large areas of alteration; formed from 

hydrothermal systems driven by the heat from intrusive 

bodies; principally valuable for silver, lead, and zinc, but 

also contain copper, gold, tin, and bismuth. Areas of 

moderate to high resource potential are in the Sheep 

Mountain-Bowery Peak, Lehman Creek, and Iron Bog 

Creek areas, all in the southwestern portion of the Forest. 

F Precious-metal veins; formed from hydrothermal solutions along fractures of the northeast-trending transChallis fault system; contain mainly gold and silver with 

some lead, zinc, and copper. Principal areas of high 

resource potential include a broad zone extending from 

Stanley northeast through the Yankee Fork mining district and two small zones in the Meyers Cove area. 

G Base-metal veins; related to igneous intrusions (Idaho 

batholith) emplaced about 80 million years ago; valuable 

mainly for zinc and lead, but also contain copper, gold, 

and silver. Areas of moderate to high resource potential 

are in parts of the Idaho batholith in the northwestern 

portion of the Forest. 

H Vein uranium deposits; formed from hydrothermal solutions associated with igneous intrusions. Data are 

adequate for assessment only in that portion of the Forest 

within the Challis 1 ox 2° quadrangle. A small area of high 

resource potential is in the Stanley area. 

Tungsten stockwork and vein deposits; developed in 

shear zones and close to igneous intrusive bodies of 

Cretaceous and Tertiary age; valuable mainly for tungsten, but also contain antimony, gold, silver, and 

molybdenum. Areas of high resource potential are in the 

northern Lemhi Range and the northwesternmost part of 

the Forest. 

J Stockwork molybdenum deposits; formed in the upper 

parts of granite bodies; valuable mainly for molybdenum, 

but also contain copper, silver, gold, tungsten, and 

antimony. Areas of high resource potential are in the 

northern Lemhi Range, White Cloud Peaks, and Thompson Creek area. 

K High-level, rhyolite-hosted, precious-metal deposits; 

disseminations and stockworks of gold and silver formed 

in structurally favorable parts of rhyolite intrusive bodies 

that were emplaced at or near the surface. Data are 

adequate for assessment only in that part of the Forest 

within the Challis 1 ox 2° quadrangle. Area of high 

resource potential extends as a broad band along the 

northeast-trending trans-Challis fault system from Cape 

Horn to Meyers Cove in the north-central part of the 

Forest. 

L Polymetallic skarn deposits; formed at the contacts 

between intrusive igneous rocks and chemically reactive 

host rocks; valuable mainly for tungsten and copper, but 

also contain zinc, lead, silver, gold, bismuth, iron, and 

molybdenum. Principal areas of high resource potential 

include several small areas in the northwestern part of the 

Forest, part of the black-shale belt extending north and 

northeastward from Galena Summit to Mill Creek just 

west of Challis, and the eastern part of the White Knob 

Mountains. 

M Irregular replacements of base and precious metals; 

formed by hydrothermal solutions moving along and 

outward from high-angle faults and reacting with limestone and dolostone; contain silver, lead, and zinc with 

some copper and gold. Principal areas of high resource 

potential are in the Bayhorse mining district west of 

Challis. 

N Fluorspar breccia manto deposits; formed by hydrothermal solutions reacting with limestone and dolostone in 

stratiform breccia zones; fluorspar is main commodity, 

but barite, gold, silver, lead, and zinc are also present. 

Area of high resource potential is on Keystone Mountain 

west of Challis. 

0 Sediment-hosted, jasperoid-associated, precious-metal 

deposits; formed where solutions replaced receptive host 

rocks with massive silica Uasperoid); contain gold and 

silver with trace amounts of arsenic, antimony, mercury, 

and thallium. Areas of moderate resource potential are 

mainly in Paleozoic carbonate rocks in the south-central 

part of the Forest. 

P Precious-metal deposits in volcanic tuffs; stratabound 

disseminations and veinlets formed during the late 

stages of deposition of the host rocks; contain mainly 

gold and silver. Areas of high resource potential are in the 

Yankee Fork area and in the northwest corner of the 

Forest. 

6 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
Q Stratabound syngenetic deposits of precious and base 

metals; formed from geothermal brines in restricted depositional environments during the Paleozoic Era; valuable 

mainly for barite, zinc, lead, silver, or gold with some 

vanadium and molybdenum. Areas of moderate to high 

resource potential are in the black-shale belt in the 

Summit Creek area and in a broad band extending 

northeast from Galena Summit to Mill Creek just west of 

Challis. 

R Stratiform vanadium deposits; formed from geothermal 

brines in restricted depositional environments during the 

Paleozoic Era; principally valuable for vanadium. Areas of 

moderate to high resource potential are in the blackshale belt in the Summit Creek area and in a broad band 

extending northeast from Galena Summit to Mill Creek 

just west of Challis. 

S Gold placer deposits; deposited by streams that 

traversed and eroded gold-bearing bedrock. Areas of 

moderate to high resource potential are in Yankee Fork 

drainage, in Stanley Basin, and along several streams 

that drain into the Middle Fork of the Salmon River. 

T Radioactive black-sand placer deposits; deposited by 

streams carrying weathered material from the Idaho 

batholith terrane; contain varying amounts of heavy 

minerals with thorium oxide, rare-earth oxides, and niobate and tantalate pentoxides. Areas of moderate 

resource potential are in the western part of the northwestern portion of the Forest where rocks of the Idaho 

batholith crop out. 

U Areas of unknown resource potential; indications of 

mineralization, but no definitive data for resource assessment. Eight areas located in the northeastern, central, 

and southwestern parts of the Forest, all outside the 

Challis 1 ox 2° quadrangle, in areas with sparse data. 

V. Geothermal resources; manifested by natural hot waters 

and steam. Area of moderate to high resource potential 

is in the western part of the Forest. 

Resource Potential-Salable Minerals 

Present production of salable mineral materials on the 

Forest meets current U.S. Forest Service needs. Local needs, 

principally for sand and gravel, are met from alluvial deposits 

on private and Bureau of Land Management lands in the Lost 

River Valley and Pahsimeroi Valley and from patented placer 

mining claims in the Yankee Fork drainage. 

Sand and gravel that is suitable for construction 

purposes is available in certain areas of the Forest; the major 

source areas are the Yankee Fork drainage and the Cape 

Horn area. The Lost River and Lemhi Ranges have little to no 

potential for the development of sand and gravel deposits. 

Sand and gravel are in Pleistocene and Holocene fluvial 

deposits. 

Sources of dimension stone that is suitable for 

construction purposes are located in the Summit Creek, 

Squaw Creek, Bayhorse Creek, and Mill Creek areas of the 

Forest. Riprap that is adequate for construction purposes is 

available in most areas of the Forest except for the Lost River 

Range and southern Lemhi Range. Deposits of riprap are 

mostly colluvial deposits of Tertiary volcanic rocks of the 

Challis Volcanic Group and some fluvial deposits that contain 

rocks of the Cretaceous Idaho batholith and Tertiary Sawtooth batholith. 

Areas of high potential for salable minerals are shown 

on figure 3. Table 2 shows the average use per year 

calculated over a 4-year period of the Forest's mineralmaterials transactions from 1983 to 1986. 

INTRODUCTION 

This report presents an assessment of the mineral 

resource potential of the Challis National Forest, Idaho 

(usually referred to as the Forest in this report), based on 

information available as of June 1987. The Challis 

National Forest and administrated lands contain 4,338 

Table 2. Mineral-materials transactions 1983-1986 

[Leaders(---) indicate no data or no value calculated] 

Commodity Permits 

(per year) 

Sand and gravel •••••••• 

Dimension stone •••••••• 

(building stone). 

Riprap ••••••••••••••••• 

0.25 

.75 

3.50 

.75 

.75 

Tons Value (in dollars) 

mined Sold Free Used by U.S. 

Forest Service 

98.00 75.00 

288.00 280.00 

11,630.00 2,908.00 

25.00 41.00 

.25 25.00 

64.00 66.00 

63.00 44.00 

1,974.00 995.00 

Introduction 7 
Table 3. Type mine localities for mineral deposit types 

[Numbers refer to reference numbers in Mitchell and others (1981b, 1986), Hustedde and others (1981), 

and Strowd and others (1981)] 

A. Fluorspar veins: 

A Meyers Cove deposits; Nos. 139-164, Challis 1° x 2° quadrangle. 

B. Polymetallic veins in black-shale terrane: 

B Livingston mine; No. 1170, Challis 1° x 2° quadrangle. 

C. Polymetallic veins in quartzite terrane: 

C Wilbert mine; No. 150, Idaho Falls 1° x 2° quadrangle. 

D. Polymetallic veins in carbonate terrane: 

D Windy Peak area; Nos. 215-224, Dubois 1° x 2° quadrangle. 

E. Polymetallic veins in Tertiary extrusive terrane: 

E Hornsilver mine; No. 112, Idaho Falls 1° x 2° quadrangle. 

F. Precious-metal veins: 

F Lucky Boy mine; No. 403, Challis 1° x 2° quadrangle. 

G. Base-metal veins: 

G Sea Foam mine; No. 205, Challis 1° x 2° quadrangle. 

H. Vein uranium deposits: 

H Lightning mines; Nos. 945 and 946, Challis 1° x 2° quadrangle. 

I. Tungsten stockwork and vein deposits: 

1 Ima mine; No. 328, Dubois 1° x 2° quadrangle. 

J. Stockwork molybdenum deposits: 

Ja Thompson Creek; No. 1123, Challis 1° x 2° quadrangle. 

Jb Walton-White Mountain; No. 536, Hailey 1° x 2° quadrangle. 

K. High-level, rhyolite-hosted, precious-metal deposits: 

K Golden Sunbeam mine; No. 346, Challis 1° x 2° quadrangle. 

L. Polymetallic skarn deposits: 

La Empire mine; No. 13, Idaho Falls 1° x 2° quadrangle. 

Lb Springfield mine; No. 778, Challis 1° x 2° quadrangle. 

M. Irregular replacements of base and precious metals: 

M Clayton Silver mine; No. 1103, Challis 1° x 2° quadrangle. 

N. Fluorspar breccia manto deposits: 

N Keystone Mountain deposits; Nos. 1063-1076, Challis 1° x 2° 

quadrangle. 

O. Sediment-hosted, jasperoid-associated, precious-metal deposits: 

None. 

P. Precious-metal deposits in volcanic tuffs: 

Pa Sunnyside mine; No. 66, Challis 1° x 2° quadrangle. 

Pb Dewey mine; No. 47, Challis 1° x 2° quadrangle. 

Q. Stratabound syngenetic deposits of precious and base metals: 

Qa Hoodoo mine; No. 1160, Challis 1° x 2° quadrangle. 

Qb Phi Kappa mine; No. 563, Hailey 1° x 2° quadrangle. 

R. Statiform vanadium deposits: 

None, see Fisher and May (1983). 

s. Gold placer deposits: 

None. 

T. Radioactive black-sand placer deposits: 

None. 

me (2,776,668 acres) of mountainous terrain, much of 

which has difficult access (fig. 4). Central Idaho is 

sparsely populated, and Stanley, Challis, and Mackay are 

the closest towns to the Forest. Material in this report is 

provided to assist the U.S. Forest Service in fulfilling the 

requirements of the Code of Federal Regulations (CFR 

219.22) to supply information and interpretations so that 

the mineral resources of this area can be considered 

along with other kinds of resources in land use planning. 

Mineral resource information is given in terms of 

mineral deposit types and their geologic settings. Deposit 

types are based on geologic characteristics of known and 

inferred deposits within or close to the Forest. Most 

deposit types are represented by type mine localities 

(fig. 5, table 3). A letter designation (A, B, and so on) for 

various deposit types is used in the text, tables, figures, 

and plates. Areas of resource potential for each deposit 

type are summarized in table 4. The geologic setting is 

discussed in terms of geologic terranes and major 

structural features. Geologic terrane for this report is 

defined as a particular rock type or assemblage and the 

area in which it crops out. Definitions of terms used in 

the assessment of mineral resource potential are provided in Appendix 1. 

8 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
The first step in assessing the mineral resource 

potential was compilation of data at a scale of 1:250,000. 

The geologic map (pl. 1) was compiled by Anna Wilson, 

U.S. Geological Survey (USGS), and Victoria Mitchell, 

Idaho Geological Survey, using the best available geologic mapping at any scale. This map is a simplified 

geologic map in which the units have been combined in 

such a way as to best illustrate the various geologic 

terranes. The purpose is to emphasize the geologic 

features that are important to the mineral resource 

assessment. 

The USGS recently completed a detailed 

CUSMAP (Conterminous United States Mineral 

Assessment Program) study of the mineral resources of 

the Challis 1° x 2° quadrangle which includes much of the 

northwestern part of the Challis National Forest. 

Preliminary results of that study were published in Mcintyre (1985) and Fisher and Johnson (1987). These results 

provided the data base for the resource analysis of that 

part of the Forest within the Challis 1 o x 2° quadrangle. 

The geology, mineral resource data, and mineral deposit 

models from the CUSMAP study were recast into the 

format of this study with few changes. The rest of the 

Forest by comparison, except for local exceptions, does 

not have as complete a data base in quantity or quality. In 

fact, some areas are almost totally lacking in data needed 

for a resource assessment. This has resulted in the 

assignment of lower levels of certainty to areas of 

potential in that part of the Forest outside the Challis 

1 o x 2° quadrangle. 

Published data from nine geochemical surveys 

were used as an aid in the assessment of mineral resource 

potential of the Challis National Forest (tables 5, 6). No 

single geochemical survey covered the entire area of the 

Forest (fig. 5). Geochemical signatures for individual 

mineral deposit types were determined from published 

results of the geochemical surveys that covered the area 

of a type mine locality for that deposit type (tables 3, 7; 

fig. 5; pl. 3). In areas where a type mine locality was 

within the boundaries of more than one geochemical 

survey, only data from the survey most useful for 

resource assessment were used to determine the geochemical signature of the type deposit. 

Several USGS resource assessment programs 

included parts of the Challis National Forest (table 5), 

and all of the Challis National Forest was covered by 

samples collected and analyzed by various laboratories 

under the National Uranium Resource Evaluation 

(NURE) program. NURE data were used to determine 

geochemical signatures where USGS data were unavailable. Where available, published threshold values were 

used to determine the geochemical signatures reported 

here. If threshold values were not published, they were 

determined from raw data at two standard deviations 

from the population mean, assuming that the element 

distribution was lognormal. Sampling density of the 

surveys, within the Forest boundaries, ranged from about 

2.6 samples per 1 me in the Boulder-Pioneer Wilderness 

Study Area (Simons, 1981) to less than 0.03 samples per 

1 m? in the Dubois NURE project (LaDelfe, 1980). 

The geophysical data available for use in the mineral resource assessment studies of the Challis National 

Forest are regional aeromagnetic and gravity data. 

Additional information about the mineral resources and 

the geologic terranes of the Forest might be obtained 

from a more in depth analysis of the gravity and magnetic 

data. 

Aeromagnetic data are presented on plate 2. These 

data were compiled from a variety of magnetic surveys 

that were flown for mineral resource evaluation during 

the past 17 years (see index map, pl. 2). The surveys were 

flown at line spacings that ranged from 0.5 to 5 mi, either 

at a constant barometric elevation or a constant altitude 

above terrain. These variable datums have been normalized, and the resultant magnetic map is a composite 

of these surveys with the digital data reduced by computer techniques to a uniform datum of 1,000 ft above 

terrain. In addition to the aeromagnetic data (pl. 2), a 

regional gravity map (A.E. McCafferty and Viki Bankey, 

written commun., 1987) was compiled for the mineral 

resource assessment. 

Information on mines, prospects, and resources 

came mainly from the Idaho Geological Survey Mines 

and Prospects Map Series for the Challis, Dubois, Hailey, 

and Idaho Falls 1 ox 2° quadrangles. These publications 

contain resource information from all available sources, 

including the USGS Mineral Resource Data System 

(MRDS) and the U.S. Bureau of Mines Mineral Inventory Lands System (MILS). 

All available information was assembled and 

analyzed according to procedures outlined by Shawe 

(1981) and Taylor and Steven (1983). Mineral resource 

potential information is portrayed on plates 3 and 4 and 

on figures 1-3 and 13-33 .. 

Known mineral deposits and their geologic settings 

were examined by R.G. Worland A.B. Wilson during the 

summer of 1986. Field work was not undertaken to fill 

gaps in knowledge or to reconcile differences in interpretations. The resource analysis is based upon the 

geologic interpretations by the authors at the time of 

writing. Significant new data in the future may lead to 

new interpretations that could affect the mineral 

resource assessment. Many geologists with the USGS, 

U.S. Bureau of Mines, U.S. Forest Service, U.S. Bureau 

ofLand Management, and Idaho Geological Survey were 

consulted, and their help is gratefully acknowledged. 

This study is based primarily on information from 

published literature, including theses and dissertations, 

and unpublished material from studies in progress. 

Introduction 9 
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Specific references have been kept to a minim urn to 

avoid excessive interference with continuity of the text. 

References are given where needed to indicate the 

source of information or to give proper credit for studies, 

Q) ideas, or concepts. The reference list indicates the 

£ available literature that provided background infor- c 

:E mation; not all of the references are cited in the text. -~ The assessment of mineral resource potential, ~ which is at a scale of 1:250,000, is meant to show areas (ij 

t: where mineral deposits of a certain type may occur. 

c [ Although these assessments are not site specific, infor- "(U 0 E c mation provided in the report should be useful in site- ::l 

0 :s specific examinations. Characteristics of each mineral c ~ c -~ 

0 deposit type are given and information is provided to Q) _g en ·-s en Q) 

ns c .E E t5 indicate what mineral deposit types could be expected in c X ·g_ ::l Q) ns 0 ·;:: 

...., each of the geologic terranes present in the Forest. I- en ::c Cl (j) 

:0 Knowledge of the type of geologic terrane and the C\1 M -.::1" 1.0 c.o Q) 

C\1 C\1 C\1 C\1 C\1 c presence or absence of the assessment criteria for each ·c: 

(i) .E mineral deposit type will be useful for site-specific > (ij evaluations. a: a. ~ "0 ~ ·u Q) 

0 Q) Q) c ~ 0 Q) t:: c ·g_ () ~ 0 ·::;: ~ (i) Q) "0 GEOLOGY Q) 

~ Cl Q) c "0 E () ::l ns <( :..::i ....J ~ m 1ii 

~ The Challis National Forest includes the western """ CX) m 0 C\i 0 C\1 LL. 

part of the Lemhi Range, the Lost River Range, the (ij 

~ 

Q) en c White Knob Mountains, Copper Basin, the eastern part Q) c 0 

~ c ·u; -~ of the Pioneer Mountains, the Pahsimeroi Mountains, ·g_ ns () ~ aJ z the White Cloud Peaks, Stanley Basin, the northern part (i) 0 en (i) ~ "0 LL. E a. (ij of the Sawtooth Range, and parts of the extensive Salmon :; 1ii (ij .9 a. .c 0 ns 0 () River Mountains (fig. 4). The major drainages include cc w ~ <( () Q) 

C\1 M -.::1" 1.0 c.o £ the Salmon, Big Lost, and Little Lost Rivers. Rocks that - host the mineral deposits range in age from Precambrian T"" 0 

c to Holocene . c . Q -~ (ij «i The basic framework for discussion of mineral c ~ () 

::l cc .Q resources in this report is the geologic terrane as defined 0 0 Q) 

~ LL. c Q) by rock assemblages (pl. 1). Superimposed on the Q) 0 ~ c >- en -~ (i) Q) Q) c 0 geologic terranes are regional structures that influenced ~ c ~ :0 .c 0 

.rg c >- .c ns ns the location of some of the mineral deposits (fig. 6). An 0 ns en a.. en >- a: cc a. 

ns understanding of the nature and distribution of geologic 

""" CX) m 0 E terranes and structures is necessary for an assessment of X 

Q) mineral resources. The important terranes in the Forest c "0 

~ c .E are Precambrian (Proterozoic) rocks, Paleozoic car- "(ij 

::l Q) E ~ bonates, Paleozoic quartzites, Paleozoic flysch assem- 0 Q) Q) 

~ c ::l ~ Q) c blage, Paleozoic black shales, Cretaceous batholithic and ns E 0 Q) ns a: ~ Q) 

<D a: ns 0 a. plutonic rocks, Tertiary extrusive volcanic rocks, Tertiary ~ 0 Q) "0 o:; LL. a. 

.Q c > Q) c c intrusive rocks, and post-Challis cover rocks. The ::l ~ ns CD 0 ·u <D .c Q) .c .9 .e >- I- (!) en en important structural features include the northeastcij "0 

I- trending trans-Challis fault system and parallel high- C\1 M -.::1" c () 1.0 c.o ns 

a: Q) angle fault systems to the south (fig. 6), north- to > I- .8 northwest-trending high-angle fault systems, extensive en 

Ci ~ thrust fault plates in Paleozoic rocks, and caldera and 

C!J ~ collapse features associated with the Challis Volcanic z CD...: 

... en z :::J Q) Group. Only parts of the individual terranes contain or C) .... 

~ ·- 0 U..LL. have potential for mineral deposits. The occurrence of 

Geology 11 
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114000' 113°00' 

CHALLIS'. .. ~URE PROJECT BOUNDARY~F CHALLIS NATIONAL FOREST 

)Pb~Pa j _ __ l_.) 

IDAHO PRIMITIVE AREA 

(USGS) 

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• Arco 

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Figure 5. Map showing location of type mine localities for mineral deposit types [identified by crossed-hammers symbol and letter (identified in table 3)] and boundaries 

of geochemical surveys that cover ~arts of the Challis National Fore~t. 
Table 4. Description of areas of mineral resource potential for locatable and leasable resources in the Challis 

National Forest, Idaho 

[Commodities listed in order of relative importance; level of potential/level of certainty explained in Appendix 1. Leaders (---), not 

applicable] 

Map Resource Potential/ Commodities Size, type of deposit 

area potential certainty (by-products) 

Al High H/D Fluorspar (Au) Medium, fluorspar veins. 

A2 High H/D Fluorspar Medium, fluorspar veins. 

A3 Moderate M/D Fluorspar (Au, Sb) Small, fluorspar veins. 

A4 Moderate M/D Fluorspar (Au) Small, fluorspar veins. 

A5 Moderate M/D Fluorspar Small, fluorspar veins. 

Bl High H/D Ag,Pb,Zn (Au,Sn,Sb,Cu) Medium, polymetallic veins. 

B2 Moderate M/D --do---- Do. 

B3 High H/B Ag,Pb,Zn (Au,Cu) Do. 

B4 Moderate M/B --do---- Do. 

Cl High H/B Ag,Pb Small, fissure veins. 

C2 Moderate M/B Ag,Pb (Au) Do. 

Dl High H/C Ag,Pb (Cu,Zn,Au) Medium, replacement veins. 

D2 High H/C Pb,Zn,Ag (Cu,Au) Do. 

D3 Moderate M/B Ag,Pb (Cu,Zn,Au) Small, replacement veins. 

D4 Moderate M/B Pb,Zn,Ag (Cu,Au) Do. 

DS High H/B Ag,Pb,Zn (Au,Cu) Medium, replacement veins. 

El Moderate M/B Ag,Pb,Zn (Au,Bi,Sn) Small, polymetallic veins. 

E2 Moderate M/B Ag,Pb (Zn,Au) Do. 

E3 Moderate M/C Ag,Au (Zn,Pb,Sn,Mo) Do. 

Fl High H/D Au,Ag (Pb,Cu,Zn) Small, lenticular pods. 

F2 Moderate M/D --do---- Do. 

Gl High H/D Zn,Pb,Cu (Ag,Au) Medium, pods and veins. 

G2 Moderate M/D --do---- Do. 

HI High H/D U (Au,Ag) Small, stringers in faults. 

H2 Moderate M/D --do---- Do. 

Il High H/C W (Sb,Au,Ag) Medium, veins and replacements. 

12 High H/C W (Mo,Pb,Zn) Medium, veins and stockworks. 

13 Moderate M/B --do---- Small, veins and stockworks. 

14 Moderate M/C W,Mo (Ph, Zn) Small, veins and replacements. 

Jl High H/D Mo,W (Ag,Cu) Large, stockworks. 

J2 High H/D --do---- Do. 

J3 High H/B Mo,W (Pb,Zn) Medium, stockworks. 

J4 Moderate M/D Mo(?) Do. 

JS Moderate M/C Mo(?) Medium, veins and stockworks. 

Kl High H/C Au,Ag Large, stockworks and disseminations. 

K2 Moderate M/C --do---- Do. 

Geology 13 
Table 4. Description of areas of mineral resource potential for locatable and leasabe resources in the Challis 

National Forest, Idaho-Continued 

[Commodities listed in order of relative importance; level of potential/level of certainty explained in Appendix 1. Leaders ( ---), not 

applicable] 

Map Resource 

area potential 

Ll High 

L2 Moderate 

L3 Moderate 

L4 Moderate 

L5 Moderate 

L6 High 

L7 Moderate 

LB High 

L9 Moderate 

Ml High 

M2 Moderate 

M3 Moderate 

Nl High 

N2 Moderate 

01 Moderate 

PI High 

P2 Moderate 

P3 Moderate 

Ql High 

Q2 Moderate 

Q3 Moderate 

Rl High 

R2 Moderate 

R3 Moderate 

Sl High 

S2 Moderate 

Tl Moderate 

T2 Moderate 

Ul 

U2 

U3 

U4 

us 

U6 

U7 

us 

v 

Unknown 

Unknown 

Unknown 

Unknown 

Unknown 

Unknown 

Unknown 

Unknown 

High 

Moderate 

Potential/ 

certainty 

H/C 

M/C 

M/C 

M/B 

M/D 

H/D 

M/D 

H/D 

M/B 

H/D 

M/B 

M/B 

H/D 

M/D 

M/B 

H/C 

M/C 

M/C 

H/D 

M/D 

M/B 

H/D 

M/C 

M/B 

H/D 

M/D 

M/D 

M/B 

H/C 

M/C 

Commodities 

(by-products) 

Cu (Pb,Zn,Ag,Au) 

--do----

W (Mo) 

Cu (Pb,Zn,W) 

W,Zn,Cu,Pb,Ag 

--do----

W 

w 

Pb, Zn,Ag, Fe 

Ag,Pb,Zn 

Ag,Pb,Zn (Cu,Au) 

Ag,Pb,Zn (Au) 

Fluorspar (Ag,Au,Pb,Zn) 

--do----

Au,Ag 

Au,Ag 

--do----

--do----

Zn,Pb,Ag,Au 

--do----

--do----

V (Zn,Pb,Ag,Ba) 

--do----

--do----

Au 

--do----

Th,REE,Nb,Ta,U,Au 

--do----

Size, type of deposit 

Large, contact skarn. 

Do. 

Small, skarn lenses. 

Medium, contact skarn. 

Do. 

Do. 

Small, skarn lenses. 

Medium, contact skarn. 

Medium, contact skarn. 

Large, irregular replacements. 

Medium, irregular replacements. 

Do. 

Large, mantos and replacements. 

Do. 

Medium, disseminations. 

Medium, blankets. 

Do. 

Medium, disseminations. 

Medium, syngenetic stratiform. 

Do. 

Do. 

Medium, syngenetic stratiform. 

Do. 

Do. 

Medium to large, placers. 

Do. 

Medium, placers. 

Do. 

Base- and precious-metal veins, replacements, and 

disseminations. 

Base- and precious-metal veins, skarns, and replacements. 

Veins, skarns, replacements, and jasperoid-associated deposits. 

Veins, skarns, replacements, disseminations, and jasperoidassociated deposits. 

Base- and precious-metal vein and stockwork deposits. 

Vein and stockwork deposits associated with ring fractures. 

Base- and precious-metal stockworks and disseminations. 

Base- and precious-metal veins and replacements. 

Hot- and warm-water springs. 

Steam. 

14 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
Table 5. Geochemical studies that cover parts of the Challis National Forest, Idaho 

Study Percent 1 Collect2 Analyze3 Reference 

Challis CUSMAP •••••••• 59 

project (CHUS). 

Challis NURE.......... 59 

project (CHNU). 

Eastern part of....... 7 

the Sawtooth 

Recreation Area 

(SNR). 

Idaho Primitive Area •• 15 

(IP). 

Dubois NURE project ••• 20 

(DUNU). 

Idaho Falls NURE •••••• 15 

project (IFNU). 

Boulder-Pioneer Wilder- 4 

ness Study Area (BPW). 

Hailey NURE project •••• 5 

(HANU). 

White Cloud-Boulder •••• (.5 

Roadless Area 

(WCBRA). 

USGS 

SLR 

USGS 

USGS 

LANL 

SRL 

USGS 

SRL 

USGS 

USGS Fisher and Johnson (1987); 

Adrian and others (1985); 

Callahan and others (1981a, 

b); McDanal and others, 

(1984); Hopkins and others 

(1985). 

SLR Thayer and Cook (1980). 

USGS Tschanz and others (1974); 

Tschanz and Frischnecht 

(1986); Kiilsgaard and Van 

Nay (1984). 

USGS Cater and others (1973). 

LANL LaDelfe (1980). 

ORGDP Grimes (1982c, d). 

USGS Simons (1981). 

ORGDP Grimes (1982a, b). 

USGS Fisher, May, and others 

(1983). 

1Percent of the Challis National Forest covered by the study. 

2organization that collected geochemical samples: USGS, U.S. Geological 

Survey; LANL, Los Alamos National Laboratory; SRL, Savannah River Laboratory; 

ORGDP, Oak Ridge Gaseous Diffusion Plant. 

3organization that analyzed geochemical samples. 

the mineral deposits in a terrane may also depend upon 

other factors such as the presence of a specific 

sedimentary bed, high-angle regional faults, thrust faults, 

or juxtaposition of two terranes, such as igneous rocks 

that intrude carbonate rocks. 

Geologic Framework 

The oldest rocks in the Challis National Forest 

were deposited in deep basins along the margin of a 

major landmass starting about 1, 700 million years ago 

during the Early Proterozoic Era. The deposits were 

primarily sedimentary in origin but included some 

volcanic material. The earliest sequence of rocks was 

deformed, metamorphosed, and intruded by plutonic 

rocks 1,400-1,200 million years ago. Deposition in the 

basins continued to about 900 million years ago at which 

time the area was uplifted to form a highland along the 

northwest-trending Lemhi arch (fig. 6). The seas invaded 

the region again about 550 million years ago, and the 

region remained submerged through most of the Paleozoic to about 260 million years ago. During the early 

Paleozoic, sediments were deposited in a miogeosynclinal basin west of the Lemhi arch and on the shallowly 

submerged cratonic shelf to the east. Intermittent uplift, 

from Late Devonian through Early Mississippian time, of 

the Antler highlands to the west of the area shed clastic 

material to the Copper Basin depositional trough to the 

east. In Late Mississippian time, the Copper Basin 

highlands began to rise, and shelf carbonates were 

deposited to the east while deeper water sediments were 

Geology 15 
Table 6. Sources of analytical data, Challis National Forest, Idaho 

Laboratory! 

Savannah River ••• 

Laboratory. 

Los Alamos ••••••• 

Scientific 

Laboratory. 

U.S. Geological •• 

Survey. 

Elements analyzed 

U, Th, Hf, Ce, Fe, 

Mn, Na, Sc, Ti, V, 

Al, Dy, Eu, La, Sm, 

Yb, Lu, Br, Cl, F. 

Ag, Co, Cu, Ni, Zn, 

Mo, Cr, Y, Be, Sr, 

Mg, Pb, Sn, Ba. 

Nb, W, P 

K, Li 

u 

Ag, As, Bi, Cd, Cu, 

Nb, Ni, Pb, Se, Sn, 

W, Zr. 

Bi, Li 

Al, Au, Ba, Ce, Cl, 

Co, Cr, Cs, Dy, Eu, 

Fe, Hf, K, Lu, Mg, 

Mn, Na, Rb, Sb, Sc, 

Sm, Sr, Ta, Tb, Th, 

Ti, V, Yb, Zn. 

Fe, Mg, Ca, Ti, Mn, 

Ag, As, Au, B, Ba, 

Be, Bi, Cd, Co, Cr, 

Cu, La, Mo, Nb, Ni, 

Pb, Sb, Sc, Sn, Sr, 

V, W, Y, Zn, Zr, Th. 

Analytical Reference 

method2 

NAA Cook and Fay (1982). 

AA 

Color 

Flame 

DNC LaDelfe (1980). 

XRF 

ESpec 

NAA Nunes and Weaver (1977). 

ESpec O'Leary and Meyer (1986). 

10nly those laboratories providing data used in the resource assessment 

are listed. 

2 Several analytical methods were used: NAA, neutron activation analysis; 

AA, atomic absorption; Color, colorimetric analysis; Flame, flame emission; 

XRF, X-ray fluorescence; DNC, delayed neutron counting; ESpec, emission 

spectrography. 

deposited to the west. The entire region was emergent by 

Late Permian time. Changing depositional patterns 

throughout the Paleozoic resulted in the complex interfingering and facies changes that characterize the Paleozoic units in this area. 

During Mesozoic time, extensive thrust faulting of 

the Paleozoic rocks resulted in foreshortened sections 

and juxtaposition of time-equivalent rocks that had been 

deposited in different depositional environments. Most 

of the Paleozoic formations exposed in the Forest are 

allochthonous and occur in imbricated structural plates 

that are stacked younger over older. Many of the 

individual formations, especially in the flysch and blackshale terranes, are tectono-stratigraphic units in the 

sense that neither the base nor the top is exposed because 

of faulting. Different formation names have been applied 

to units that are essentially coeval but are in different 

structural plates. 

The complex of plutons known as the Idaho batholith and satellite bodies of similar composition were 

emplaced from about 110 million to 70 million years ago, 

that is, in mid- to Late Cretaceous time. Late-stage 

pegmatites and quartz veins accompanied most of the 

intrusive events. The batholithic intrusions engulfed and 

metamorphosed large blocks of sedimentary rocks. 

Extensive areas of sedimentary rocks surrounding the 

plutons also were contact metamorphosed. 

High-angle faulting, mainly along northeast trends, 

began at the end of Mesozoic time and helped localize 

extensive Eocene volcanism. Volcanism that produced 

the Challis Volcanic Group began about 51 million years 

16 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
C) 

CD 

0 

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ca 

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115°30' 115°00' 114°00' 113°00' 112°45' 

45~0'r-----------~-.------------------------------~~-------------,~----------~~----~ 

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y 

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ANTLER HIGHLANDS 

(LOCATION UNCERTAIN) 

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---- ZONE OF MAJOR 

HIGH-ANGLE FAULTS 

0 5 10 15 20 25 MILES 

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Ketchum 

"""'\ MONTANA 

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IDAHO \ 

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~ 30' ~----------------~------------------------------------L-----------------------------------~L_ ______ j 

Figure 6. Map showing major structural elements within or close to the Challis National Forest. 
Table 7. Geochemical signatures of mineral deposit types at type mine localities 

[Leaders (- -) indicate no data] 

Deposit type 

A. Fluorspar veins 

B. Polymetallic veins 

in black-shale 

terrane. 

C. Polymetallic veins 

in quartzite 

terrane. 

Type mine locality 

(shown on pl. 3) 

Meyers Cove (A) 

Livingston mine (B) 

Wilbert mine (C) 

Geochem 

survey I 

CHUS 

SNR 

IFNU 

Sample 

media2 

cons 

ss 

r 

ss 

ss 

Signature3 

Sn, Ag, Au, Pb. 

Ag, Be, Mo. 

Hg, Sn , W, Bi , 

As, Sb, Cu, 

Cd, Zn, Pb, 

Au, Ag. 

Mo, Sn, As, 

Sb, Cd, Zn, 

Ph, Au, Ag. 

Ph. 

D. Polymetallic veins 

in carbonate 

terrane. 

Windy Peak area (D) DUNU no samples Unknown. 

E. 

F. 

G. 

H. 

I. 

J. 

K. 

Polymetallic veins 

in Tertiary 

extrusive terrane. 

Precious-metal veins 

Base-metal veins 

Vein uranium 

deposits. 

Tungsten stockwork 

and vein deposits. 

Stockwork molybdenum 

deposits. 

High-level, rhyolite-hosted, 

precious-metal 

deposits. 

Hornsilver mine (E) 

Lucky Boy mine (F) 

Sea Foam mine (G) 

Lightning mines (H) 

Ima mine (I) 

Thompson Creek (Ja) 

Walton-White 

Mountain (Jb). 

Golden Sunbeam 

mine (K). 

IFNU 

CHUS 

CHUS 

CHUS 

DUNU 

CHUS 

BPW 

CHUS 

ss 

cons 

ss 

cons 

ss 

cons 

ss 

ss 

cons 

ss 

ss 

cons 

ss 

18 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 

Ag, Cu. 

Ag, Au, Sn, 

Ba, Bi, Cu, 

Mo, Ph. 

Ag. 

Ag, Bi, Cu, 

Ph, Sn, Au, 

B, Mo, W, Th. 

P b , Ag, B , Cu • 

Th, Mo, Ph, Sn. 

None. 

Cu, Ph, Sb, W. 

Bi, Cu, Mo, 

Ph, W, B, 

Sn, Th. 

Mo, W, Ag, 

Bi, Cu. 

Cu, Ph, Mo, 

Ag, Zn. 

Ag, Cu, Pb, 

Au, As, Ba, 

Sn, w. 

Ag, Be, Mo, 

Cu, Pb, Zn. 
Table 7. Geochemical signatures of mineral deposit types at type mine localities-Continued 

[Leaders(--) indicate no data] 

Deposit type Type mine locality 

(shown on pl. 3) 

L. Polymetallic skarn Empire mine (La) 

deposits. 

Springfield mine 

(Lb). 

M. Irregular replace- Clayton Silver mine 

ments of base (M). 

and precious 

metals. 

N. Fluorspar breccia Keystone Mountain 

manto deposits. deposits (N). 

o. Sediment-hosted, None. 

jasperoid-associated, preciousmetal deposits. 

P. Precious-metal Sunnyside mine (Pa) 

deposits in 

volcanic tuffs. 

Dewey mine (Pb) 

Q. Stratabound syn- Hoodoo mine (Qa} 

genetic deposits 

of precious and 

base metals. 

Phi Kappa mine (Qb) 

R. Stratiform vanadium None. 

deposits. 

s. Gold placer deposits None. 

T. Radioactive black- None. 

sand placer 

deposits. 

Geochem Sample 

surveyl media2 

IFNU ss 

IP ss 

CRUS cons 

ss 

CRUS cons 

ss 

IP ss 

r 

IP ss 

r 

SNR ss 

r 

BPW ss 

Signature3 

Cu. 

Zn, Mn, Cu, 

Mo, Be, As. 

Ag, B, Cu, 

Pb, Zn, Ba, 

Bi, Mo, Cd, 

Sn, w. 

Ag, B, Pb, Zn, 

As, Cu. 

Ag, B, Be, Pb, 

Bi, Cd, Cu, 

Mo, Sb, zn. 

B, Ag, Ph. 

Mo, Cu, As. 

As, Mo, Ag. 

As. 

As, Mo, Ag. 

Sb, Cd, Zn, 

Pb, Ag, Mo., 

Au. 

Hg, Zn, Pb 

Sn, Bi, Sb, 

Cu, Ag. 

Pb, Mo, Zn, B. 

1cHUS, USGS Challis 1° x 2° quadrangle CUSMAP project; SNR, Eastern part of thE 

Sawtooth National Recreation Area, Idaho; IFNU, Idaho Falls 1° x 2° quadrangle NURE 

project; DUNU, Dubois 1° x 2° quadrangle NURE project; BPW, Boulder-Pioneer 

Wilderness Study Area, Idaho; IP, Idaho Primitive Area, Idaho. 

2sample media: cons, panned heavy-mineral fraction of stream-sediment sample; 

ss, stream-sediment sample; r, rock sample. 

3Elements with anomalous concentrations in one or more samples from sites near 

the type mine locality. 

Geology 19 
ago with effusive eruptions of intermediate-composition 

lavas. At about 49 million years ago volcanism changed to 

explosive eruptions of rhyodacite ash-flow tuff with 

attendant development of cauldron complexes. Volcanism ceased about 37 million years ago (Fisher and 

Johnson, 1987). Numerous intrusive bodies, including 

the Casto pluton and the Sawtooth batholith, were 

formed concurrently with the Challis volcanism. Block 

faulting mainly along north to northwest trends 

throughout the Tertiary and Quaternary is reflected by 

present topography. The present landscape of the Forest 

was created by glaciers that sculpted some of the higher 

mountains and by high-gradient streams that transported 

and, in the valleys, deposited the detritus. The degree of 

maturity of the landscape varies from young along some 

of the mountain fronts where large alluvial fans are 

forming to a more mature appearing landscape over 

some of the Idaho batholith terrane. 

Several metallogenic episodes during the geologic 

history of the Forest produced the metal deposits that are 

available today. Metals were deposited syngenetically 

with volcanic and sedimentary rocks during Early Proterozoic time. Later in Proterozoic time some of the 

metals were remobilized by tectonism and plutonism into 

vein deposits. During most of Paleozoic time deposition 

of metal-enriched sediments in deep, restricted marine 

basins formed in parts of the flysch and black-shale 

terranes. Some of the metals in these units were locally 

remobilized during at least two later episodes, the 

emplacement of the Idaho batholith and the emplacement of Tertiary plutons. There may have been other 

periods of remobilization that are now indistinguishable 

from those related to the main periods of plutonism. 

More metals, including a suite of elements characteristic 

of felsic igneous rocks and pegmatites, were introduced 

at the same time as the emplacement of the Idaho 

batholith during the Late Cretaceous. The metals were 

concentrated as disseminations, in pegmatitites, in 

contact skarn deposits, or in vein and replacement 

deposits through related hydrothermal systems. The 

Tertiary also was a time of introduction and remobilization of metals. Metals introduced during Tertiary time 

include those characteristically found in terranes of 

extensional tectonics. Most of the metals introduced or 

remobilized at this time were concentrated in hydrothermal systems. These systems developed commonly during 

the late stages of volcanic and intrusive activity and were 

centered on deep-seated high-angle faults and other 

fractures such as those in caldera structures. Hydrothermal systems were very widespread during the Tertiary 

and affected all rock types, even at considerable distances 

from known volcanic centers. The processes of erosion 

and transportation during the past million years have 

extracted the heavier metals and minerals from country 

rock and lode mineral deposits and concentrated them in 

placer deposits. 

The description that follows is based upon geologic 

terranes. The formations that compose a particular terrane will be discussed briefly along with the geologic 

settings of any mineral resources that may occur in that 

terrane. 

Precambrian Rocks and Structures 

Precambrian rocks in the Challis National Forest 

include the Early Proterozoic gneiss complex of Wildhorse Creek and a thick sequence of Middle Proterozoic 

metaquartzites and argillaceous metaquartzites. Several 

map units are represented in the metaquartzite sequence 

including, from oldest to youngest, the Middle Proterozoic Y ellowjacket Formation, the Hoodoo Quartzite, 

formations of the Lemhi Group (Inyo Creek, West Fork, 

Big Creek, Apple Creek, Gunsight), and the Swauger 

and Lawson Creek Formations. The gneiss complex of 

Wildhorse Creek, with an age of about 2,000 million 

years (Dover, 1981, p. 25), may be the oldest rocks in the 

Forest. The gneiss complex is mainly quartzo-feldspathic 

and quartzitic gneiss and some calc-silicate zones and a 

distinct marble unit. The marble is locally metasomatized 

to tactite that contains economic to subeconomic 

amounts of tungsten (Cook, 1956, p. 12). 

The Yellowjacket Formation is mainly dark-gray 

argillaceous metaquartzite and includes some intervals of 

calcareous strata, siltite, and volcanic and subvolcanic 

material. The Hoodoo Quartzite is chiefly massive, very 

light colored, fine- to medium-grained quartzite that may 

be a facies of the Yellowjacket Formation. Parts of the 

Yellowjacket Formation and the Hoodoo Quartzite, 

mainly calcareous and metavolcanic strata, are hosts for 

gold, silver, cobalt, and base-metal deposits just north of 

the Forest. These metals were probably originally 

deposited syngenetically with the enclosing sediments 

from seafloor springs or volcanic activity. Later metamorphic, tectonic, and plutonic activity remobilized the 

metals into the present deposits. The other Precambrian 

units are mainly fine-grained micaceous quartzites, argillaceous metaquartzites, and siltstones with locally abundant feldspar and hematite and calcareous cement. The 

Big Creek, Apple Creek, and Gunsight Formations host 

the tungsten and base-metal stockwork veins associated 

with the Tertiary intrusive in the Blue Wing district (Ima 

mine) (fig. 4). These deposits are fracture-fillings 

deposited from hydrothermal solutions. The metals were 

probably introduced with the intrusive body rather than 

remobilized from the country rock. Generally the Proterozoic quartzites, other than the Yellowjacket Forma20 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
tion and Hoodoo Quartzite, do not host significant 

deposits. Quartz veins where present in the quartzites are 

generally thin and contain only trace amounts of base and 

precious metals, in sharp contrast to the large and 

metal-rich quartz veins that occur in nearby Paleozoic 

carbonate terrane. Numerous prospects explore hematitic quartz veins and secondary copper occurrences, but 

no production has been recorded. The secondary copper 

occurrences are in or associated with the locally pyritic 

Apple Creek Formation and may represent metal 

leached from the green siltite and fine-grained quartzite 

of that formation (E.T. Ruppel, Montana Bureau of 

Mines and Geology, written commun., 1987). 

Paleozoic Rocks and Structures 

Paleozoic sedimentary rocks in the Forest, which 

range in age from Late Cambrian to Early Permian, were 

deposited in a major geosyncline along the western edge 

of a craton. Numerous lithologic types are represented 

that attest to deposition in several marine-shelf and 

geosynclinal environments. There are four major Paleozoic geologic terranes in the Forest, each represented by 

a dominant rock assemblage-quartzite, carbonate, 

flysch, or black shale. The quartzite terrane is mainly in 

the Lemhi and Lost River Ranges, the carbonate terrane 

is in the Lemhi and Lost River Ranges and the White 

Knob and eastern Salmon River Mountains, the flysch 

terrane is in the eastern Pioneer Mountains, and the 

black-shale terrane is in the Boulder-Pioneer Mountains. 

Evidence of tectonic activity in the Paleozoic is in 

the depositional record; individual structures developed 

at that time were probably reactivated or obscured by 

major tectonic activity in the Mesozoic (Dover, 1980, 

p. 371). The important structures for ore control in the 

Paleozoic rocks are post-Paleozoic in age. Major Paleozoic structural elements indicated by the depositional 

record include the Lemhi arch, Antler highlands, and 

Copper Basin highlands (fig. 6). Although the northwesttrending Lemhi arch was emergent only until the Middle 

Devonian, it continued to influence depositional patterns 

through the late Paleozoic even after submergence (Ruppel, 1986, p. 119). The Copper Basin Formation is 

composed of detritus shed from a highland west of the 

region during the Mississippian. The highland probably 

developed during the Antler orogeny (Dover, 1980, p. 

371 ). The Copper Basin highlands arose in Middle 

Pennsylvanian time and influenced depositional patterns 

for the remainder of Paleozoic time by separating deepwater deposition to the west from deposition on a 

carbonate bank to the east (Skipp and Hall, 1980, p. 387). 

Quartzite Terrane 

The quartzite terrane includes a few formations, 

principally Cambrian and Ordovician in age, that are 

dominantly composed of quartzite. The Late Proterozoic(?) and Lower Cambrian Wilbert Formation and the 

Lower Ordovician Summerhouse Formation are exposed 

in the southern part of the Lemhi Range and in small 

areas of the Lost River Range. These units thin and pinch 

out to the north. They were apparently deposited in 

near-shore environments on the edge of the emergent 

Lemhi arch. The Wilbert and Summerhouse Formations 

are dominantly pink, maroon, and white quartzites that 

contain interbedded sandstone, shale, conglomerate, and 

sandy dolostone. Portions of the quartzite have been 

altered to carbonate. Differential weathering of the 

carbonate alteration areas has resulted in a mottled rock 

with an abundance of irregular cavities. Carbonate 

alteration is associated with the economically significant 

polymetallic vein deposits in fractured quartzite in the 

southern Lemhi Range. Metals in the vein deposits were 

introduced by hydrothermal solutions from an unknown 

source. The massive, cliff-forming Middle Ordovician 

Kinnikinic Quartzite, which was the first unit to be 

deposited across the Lemhi arch following its submergence, is extensively exposed in the Forest. In most 

places, the Kinnikinic unconformably overlies Proterozoic rocks. Numerous prospects for base and precious 

metals are in Kinnikinic rocks, but no significant deposits 

have been found and there is no recorded production. 

Carbonate Terrane 

The carbonate terrane includes many formations, 

and limestone and dolostone are the dominant rock types 

in the eastern half of the Forest. The carbonate units 

differ from the east to the west sides of a major northnortheast -trending structural element called the Salmon 

River lineament (Hobbs, 1985, p. 67) (fig. 6). Rocks on 

the east side of the lineament are part of the predominantly carbonate facies Paleozoic strata that are 

extensively exposed in southeastern Idaho and southwestern Montana. These rocks are Ordovician to Permian in age and are composed of sediments deposited on 

the continental shelf. The carbonate units include the 

Saturday Mountain Formation (Middle and Upper 

Ordovician and locally Lower Silurian), Fish Haven 

Dolostone (Upper Ordovician and Lower Silurian), 

Laketown Dolostone (Middle and Upper Silurian), 

Roberts Mountains Fm:mation (Upper Silurian and 

Lower Devonian), Beartooth Butte Formation (Lower 

Devonian), Jefferson Formation (Middle and Upper 

Devonian), Grand View Dolostone (Upper Devonian), 

Three Forks Formation (Upper Devonian), Middle 

Canyon Formation (Lower and Upper Mississippian), 

Geology 21 
Scott Peak Formation (Upper Mississippian), South 

Creek Formation (Upper Mississippian), Surrett Canyon 

Formation (Upper Mississippian), White Knob Limestone (Upper Mississippian), Arco Hills Formation 

(Upper Mississippian), Bluebird Mountain Formation 

(Upper Mississippian and locally Lower Pennsylvanian), 

and Snaky Canyon Formation (Upper Mississippian to 

Lower Permian). The lower part of this sequence 

(Ordovician through Devonian) is mainly dolostone and 

limestone, silty limestone, quartzite, sandstone, and siltstone. The middle part of the sequence (Mississippian) is 

mainly massive limestone that is locally fossiliferous, 

bioclastic, or cherty. The upper part of the sequence 

(Pennsylvanian to Early Permian) is interbedded 

limestone, dolostone, sandstone, siltstone, and mudstone. Significant mineral deposits occur in carbonate 

rocks of this sequence at several locations. The White 

Knob Limestone is host rock for skarn and polymetallic 

vein deposits in the Alder Creek district (fig. 4) where all 

deposits are close to the Mackay stock. In the Spring 

Mountain district (fig. 4) in the central part of the Lemhi 

Range, replacement and polymetallic vein deposits occur 

in limestone and dolostone of the Saturday Mountain 

Formation. The mines on Leadbelt Creek, Lava Creek 

district (fig. 4), are in limestone of the carbonate bank 

sequence where deposits are polymetallic veins and 

replacements. The few deposits in the Lost River Range 

are in carbonate terrane. Most are small, except for those 

in the Lone Cedar Creek area, which are shown as an 

area of unknown potential on plate 3. 

Carbonate units exposed west of the Salmon River 

lineament include the Upper Cambrian or Lower Ordovician Bayhorse Dolomite, Middle Ordovician Ella 

Dolomite, and Middle and Upper Ordovician Saturday 

Mountain Formation. The Saturday Mountain Formation, which is the only unit exposed on both sides of the 

Salmon River lineament, is of significantly different 

facies and thickness on the western side of the lineament 

than on the eastern side. This western sequence of rocks 

is mainly sandy and silty dolostone and limestone, and 

shale, quartzite, and some argillite. A major distinction 

between the western and eastern carbonate sequences is 

the presence of an under lying thick sequence of black 

shales and other carbonaceous beds beneath the western 

sequence. These black shales and other carbonaceous 

beds have been proposed as the source of some of the 

metals for the extensive mineral deposits in the carbonate 

rocks (Hobbs, 1985). The Bayhorse Dolomite hosts lead, 

zinc, silver, and fluorspar vein and replacement deposits 

in the Bay horse district (fig. 4) and at Keystone Mountain 

just to the east. Within the Bayhorse district extensive 

lead, silver, and zinc replacement deposits along Kinnikinic Creek, including those of the Clayton Silver mine, 

are in the Ella Dolomite. Lead-silver replacement bodies 

and vein and replacements in shear zones along Squaw 

and Sullivan Creeks, to the south of the Bay horse district, 

are in the Saturday Mountain Formation. The western 

sequence of carbonate rocks is in a structurally complex 

area that contains numerous intrusive bodies; both the 

complex structure and the intrusions influenced the 

remobilization of metals from the sedimentary rocks into 

vein and replacement deposits. 

Mineral deposits in the carbonate terrane are 

dominantly silver, lead, and zinc, and some copper, iron, 

and fluorspar. There is no apparent lithologic preference 

in terms of which carbonate unit is most likely to host ore 

deposits. The important factors for formation of the vein 

and replacement deposits seem to be carbonate rock in 

contact with or in close proximity to felsic igneous 

intrusive rocks in areas of deep-seated high-angle faults. 

Carbonate rocks in other terranes are also prime host 

rocks. In all three of the other Paleozoic geologic terranes represented, many of the deposits are in thin 

interbeds of carbonate rock. 

Black-Shale Terrane 

This terrane is in a belt of highly mineralized, 

black, siliceous-facies, clastic sedimentary rocks of Late 

Cambrian to Permian age that are exposed in the westcentral part of the Forest from the Summit Creek area, 

Alto district, northward through the Bayhorse district 

just west of Challis (fig. 4). Map units include, from 

youngest to oldest, the Lower Permian Grand Prize 

Formation, Lower Permian to Middle Pennsylvanian 

Wood River Formation, Devonian Milligen Formation, 

Middle Silurian Trail Creek Formation, Middle Silurian 

to Lower Ordovician Phi Kappa Formation, Ordovician(?) Ramshorn Slate, Paleozoic(?) Salmon River 

assemblage, and several unnamed units of probable 

Silurian to Devonian age. The units are allochthonous 

and occur in imbricated structural plates separated by 

thrust faults. Rocks of the black-shale terrane are 

predominantly black, fine-grained argillite, siltite, limy 

sandstone, siltstone, shale, fine-grained quartzite, and 

micritic limestone. Deposition was in relatively deep 

basins and restricted basins west of the cratonic shelf 

where the rocks of the carbonate terrane were deposited. 

Syngenetic metal deposits may form locally in these 

depositional environments, and carbonaceous lithologies 

deposited in them are commonly metal enriched. Rocks 

of the black-shale terrane contain stratiform deposits of 

barite, zinc, and vanadium, and vein, skarn, and replacement deposits of silver, lead, zinc, antimony, arsenic, 

barite, gold, molybdenum, tin, tungsten, and vanadium. 

The source for many of the metals in the vein, skarn, and 

replacement deposits was probably the more carbonacous units of the rock sequence. The metals were 

remobilized out of the sedimentary rocks by heat and 

hydrothermal convection cells related to igneous intrusive activity (Hall, 1985). 

22 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
Flysch Terrane 

A flysch terrane is represented by the Copper 

Basin and McGowan Creek Formations of Mississippian 

age (Skipp and Hall, 1980, p. 391). The lower parts of 

both formations were deposited in deep and narrow 

marine foreland basins. Clastic material and turbidites 

were derived from eroding highlands to the west, the 

Antler highlands (fig. 6), and carbonate turbidites were 

derived from the developing carbonate bank to the east. 

Rocks in the lower parts of the Copper Basin and 

McGowan Creek Formations are poorly fossiliferous, 

fine-grained, thinly bedded argillite, mudstone, siltstone, 

and limestone turbidites. The upper part of the Copper 

Basin Formation is mainly siliceous pebble conglomerate, quartzite, and sandstone deposited in marginalmarine to shallow-marine environments. The upper part 

of the McGowan Creek Formation is calcareous siltstone 

interbedded with silty micritic limestone deposited in a 

deep-marine starved basin. The Copper Basin and 

McGowan Creek Formations are treated as black-shale 

terrane for resource analysis. Deposits in the lower parts 

of the formations include polymetallic veins and replacements in the Lava Creek, Copper Basin, and Alto 

districts and possible syngenetic stratiform deposits in the 

Alto district (fig. 4). Polymetallic vein deposits in the 

Lone Cedar Creek area of the Lost River Range may be 

within or composed of metals remobilized from the 

McGowan Creek Formation. Geochemical studies 

(Erdman and others, 1988) suggest that parts of the 

McGowan Creek Formation in the Timbered Dome 

area, Lava Creek district, are metal enriched. 

Mesozoic Rocks and Structures 

Mesozoic time was one of major igneous plutonic 

activity and major low-angle thrust faulting. Sedimentary 

or volcanic rocks were not deposited in this area during 

the Mesozoic. The Idaho batholith, a very extensive mass 

of relatively homogeneous igneous rock that underlies 

much of the western part of the Forest, was emplaced 

during the Late Cretaceous to earliest Tertiary. In detail 

this mass is composed of several plutonic phases that 

range in composition from granite to tonalite and have 

gradational borders. Ages of the various phases range 

from 97 million to 64 million years (Kiilsgaard and Lewis, 

1985, p. 37). The various phases are peraluminous and 

show a calc-alkaline alkali-enrichment trend. Magmas 

that formed rocks of the batholith were probably 

generated by partial melting along a major subduction 

zone at a continental margin. Rocks in the eastern part of 

the batholith probably formed as a result of partial 

melting of metamorphic rocks in the lower crust, whereas 

those in the western part formed as a result of partial 

melting in or above a subducting slab of oceanic lithosphere (Lewis and others, 1987). Along its eastern 

border, which is the area covered by the Forest, the 

batholith intruded Paleozoic sedimentary rocks. Sedimentary rocks in the contact area and the numerous 

inclusions in the batholith were metamorphosed to hornfels and calc-hornfels. Satellite plutonic bodies of 

compositions similar to those of the batholith intruded 

the sedimentary rocks tens of miles east of the main 

batholith. 

Cretaceous plutonic rocks are associated with 

several different types of mineral deposits, many of which 

are genetically related to the plutonic rocks. Deposit 

types include disseminations in the host rock, polymetallic skarns, pegmatites, stockworks, and hydrothermal 

veins. At the present time the most economically important deposits are the stockwork molybdenum deposits, 

such as those at Thompson Creek (Ja, pl. 3) and Little 

Boulder Creek, Boulder Creek district (fig. 4). Numerous polymetallic tactite (skarn) deposits along the 

eastern border of the batholith and in inclusions in the 

batholith contain mainly tungsten with some zinc and 

lead, such as at the Springfield (Lb, pl. 3) and Tungsten 

Jim mines, Bayhorse district (fig. 4). Pegmatites of the 

batholith have been prospected for a variety of minerals, 

but there has been no recorded production within the 

Forest. Base- and precious-metal veins in the batholith, 

such as those at the Lost Packer, Loon Creek district (fig. 

4), Sea Foam (G, pl. 3), and numerous other mines and 

prospects, may relate to the formation of the batholith. 

Many other vein deposits, primarily precious-metal 

types, and alteration zones are related to emplacement of 

Tertiary stocks and hypabyssal bodies. Weathering and 

erosion of the batholithic rocks concentrated heavy 

minerals, such as columbite-tantalite, ilmenite, monazite, 

euxinite-polycrase, allanite, zircon, and numerous others, 

into radioactive black-sand deposits. The most extensive 

of these deposits are located west of the Forest. 

Sometime after deposition of Early Permian 

sediments and prior to deposition of the conglomerate at 

the base of the Challis Volcanic Group, large masses of 

rocks were thrust eastward and northeastward. Faulting 

began no later than 100 million years ago and terminated 

70-75 million years ago (Ruppel and Lopez, 1984, p. 33). 

The resultant complex of thrust faults juxtaposed marine 

rocks of deep-water, transitional, and miogeosynclinal 

facies. Several thrust plates in the region are composed of 

imbricated thrust complexes; within the Forest these 

plates include, from west to east, the Milligan-Wood 

River-Grand Prize thrust complex; Devonian, Silurian, 

and Ordovician rocks undivided; Copper Basin plate; 

White Knob plate; Grouse plate; Lost River-Arco Hills 

plate; and Hawley Creek plate (Skipp, 1987, p. 220). All 

rocks from Archean (Precambrian) through Lower Permian were involved in the thrust faulting (fig. 6). Most, if 

Geology 23 
not all, of the thrust sheets are cut by rocks of the 

Cretaceous Idaho batholith and related intrusive bodies. 

Following thrusting, but prior to volcanism, the thrust 

plates were broadly folded. Tectonic models for this 

thrust belt have included overthrusting, gravitational 

sliding or spreading, and underthrusting or continental 

subduction. 

Much of the area of the thrust faults has not been 

mapped in detail, and as these studies are completed in 

the future the distribution and mechanisms of formation 

will become better known. Whatever the exact mechanism, the present configuration of thrust plates had a 

pronounced effect on the localization of the Tertiary 

mineral deposits. Hall (1985, p. 127) noted that the 

vein-type lead-silver-zinc deposits in the black-shale terrane lie directly under regional thrust faults, especially 

where the faults are domed. In the Lemhi Range, Ruppel 

(1978, p. 18) has shown that the emplacement of Tertiary 

intrusive rocks and related mineral deposits was to a 

large extent controlled by structural features associated 

with a regional thrust system. 

Tertiary Rocks and Structures 

The Tertiary was a time of large-scale volcanism 

and extensional tectonics, in contrast to the Mesozoic, 

which was a time of batholith formation and large-scale 

compressional tectonics. The change was not abrupt as 

there is some overlap in ages of all the above activities. 

Many of the important rock terranes-volcanic rocks, 

plutonic and hypabyssal rocks, epiclastic sediments, and 

tuffaceous rocks-formed in Tertiary time, as did the 

major high-angle faults of northeast, northwest, and 

locally north trend. High-angle faults also formed in the 

Mesozoic, but these are tear faults related to the 

thrusting and, where found, are confined to the Paleozoic 

rocks of a particular thrust plate. The trans-Challis fault 

system (fig. 6), which is a series of northeast-trending 

high-angle faults and related structures (Fisher and 

Johnson, 1987) that extend discontinously across Idaho 

and Montana, is the most important Tertiary structure. 

Subparallel fault systems occur to the south; the most 

prominent is the series of dikes and faults that extend 

southwestward from just north of Mackay (fig. 6). 

Northwest- to north-trending deep-seated high-angle 

faults also developed during the Tertiary; the most 

prominent are the range-bounding faults along the 

Lemhi and Lost River Ranges. Movement along the 

northwest- to north-trending structures during Tertiary 

to Holocene times created the Basin and Range topography of the southeastern part of the Forest. In general, 

the northeast-trending systems are thought to be older 

than the northwest -trending systems. 

In that portion of the Forest within the Challis 

quadrangle many features associated with Challis volcanism, intrusive activity, and related mineralization are 

localized along the trans-Challis fault system (Fisher and 

Johnson, 1987). Southeast of the trans-Challis fault 

system, the major northwest-trending faults may have 

been just as important in localizing plutonism and mineralization; one example is the northwest-trending 

system that extends from the Lava Creek district northwest through the Pioneer Mountains. The Challis 

volcanic rock terrane includes volcanic rocks and volcaniclastic sediments deposited within and outside of 

large calderas, on the sides of stratovolcanoes, and in the 

vicinity of numerous smaller vents. This terrane also 

includes a great variety of hypabyssal bodies. Within the 

Challis quadrangle the volcanics are a suite of calcalkaline, peraluminous rocks deposited between 51 

million and 45 million years ago (Fisher and Johnson, 

1987). These compositional and age constraints may or 

may not fit the Challis Volcanic Group in the rest of the 

area covered by the study (pl. 1). 

Plutonic and related hypabyssal rocks of Eocene 

age, which are part of a diorite-granite bimodal group, 

constitute the Tertiary plutonic rock terrane. Dacite and 

rhyodacite dike swarms are associated with diorite plutons, and rhyolite dikes are associated with granite plutons (Fisher and Johnson, 1987). Rocks in the plutonic 

terrane have equivalents in rocks of the volcanic terrane. 

The diorite and granite complexes occur near each other. 

Granite bodies (for example, the Casto batholith, Sawtooth batholith, Pioneer Mountain stock, and Mackay 

stock) are generally larger than the diorite bodies and 

also form most of the spectacular peaks in this region. 

The diorite complexes were emplaced 50-45 million 

years ago, and the epizonal granites were emplaced 

45-42 million years ago (Bennett and Knowles, 1985, 

p. 82). Eocene granites are distinguished by a coarse 

granitoid texture and a characteristic pink color that is 

caused by an abundance of perthitic potassium feldspar. 

They also contain miarolitic cavities and have uranium, 

thorium, and potassium-40 contents two to three times 

higher than granitic rocks of the Idaho batholith (Fisher 

and Johnson, 1987). Eocene plutonic rocks in this area 

are of the type that forms in zones of intercontinental 

rifting or extensional tectonics (Bennett and Knowles, 

1985, p. 82). 

Large areas of the Eocene volcanic and plutonic 

rock terranes are hydrothermally altered, including the 

areas around all known mineral deposits. Altered rocks 

should be treated separately for the purposes of mineral 

resource appraisal, but in most areas mapping is not 

adequate to do so. During the late stages of volcanic and 

plutonic activity, meteoric water was set into convective 

motion by heat generated from shallow intrusive bodies. 

Convective cells developed best in permeable volcanic 

rocks but were present in all rock types. Several cells have 

been documented in the Challis quadrangle by Criss and 

24 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
others (1984), and many more cells that were active, as 

indicated by altered zones, have not been studied. The 

degree of alteration varies considerably from the 

presence of zeolites along fractures in otherwise 

unaltered rocks, through rocks that show an increase in 

calcite, chlorite, and epidote, to rocks that have been 

completely replaced by variable amounts of sericite, clay 

minerals, secondary silica, arsenopyrite, and pyrite. 

Altered rocks associated with mineral deposits are 

commonly highly silicified, bleached, and stained with 

iron oxides. 

Mineral deposits that formed during the Tertiary 

are all genetically related. They contain the same group 

of elements with variable degrees of concentration; some 

of the elements were remobilized from previous concentrations, mainly in the black-shale sequences, and some 

were introduced from other sources. All the deposits 

have a tie to the major geologic events of the perioddeep-seated extensional faulting along northeast and 

north to northwest trends, volcanism, emplacement of 

plutonic and hypabyssal bodies, and generation of hydrothermal cells. Many of the mineral deposit types discussed in this report were formed in the Tertiary. The 

fluorspar veins, fluorspar breccia manto deposits, polymetallic veins in Tertiary extrusive terrane, preciousmetal veins, high-level rhyolite-hosted precious-metal 

deposits, precious-metal deposits in volcanic tuffs, and 

sediment-hosted jasperoid-associated precious-metal deposits all formed at this time. Many, if not all, of the 

polymetallic veins in quartzite terrane, polymetallic veins 

in carbonate terrane, and irregular replacements of base 

and precious metals also formed in the Tertiary. Some of 

the polymetallic veins in black-shale terrane, tungsten 

stockwork and vein deposits, stockwork molybdenum 

deposits, and polymetallic skarn deposits formed in the 

Tertiary; the rest formed in the Cretaceous during 

emplacement of the Idaho batholith. During volcanism 

and plutonism the metals were concentrated in several 

environments. Some metals were deposited in stockworks in the late stages of crystallization of the igneous 

rocks; other metals were moved into the hydrothermal 

systems along with volatiles and were deposited in veins 

and replacement bodies. The exact character of the 

deposits that were formed depended upon the host rock 

and configuration, distance from intrusive bodies, and 

nature of the fracture systems. 

Quaternary Rocks and Structures 

Pleistocene and Holocene alpine glacial till and 

glaciofluvial sand and gravel record glaciation that 

affected the central parts of the high ranges. The 

increased weathering and fluvial transport associated 

with the glaciation choked all but the larger streams with 

debris, much of which remains today. Rock glaciers and 

talus slopes, which are still forming today, are characteristic of the higher mountain slopes. The erosional 

base level of many areas in the Forest changed several 

times during Pleistocene and Holocene time as 

evidenced by the numerous terraces along many of the 

valleys, especially in the southeastern part of the Forest, 

and by the multiple pediment surfaces in some of the 

larger valleys. The large alluvial fans and Holocene fault 

scarps along some of the range fronts and recent seismic 

activity attest to the continuing tectonic activity and uplift 

in this area. 

In the western part of the Forest are remnants of a 

high-level erosional surface called the "Idaho peneplain" 

which exposed Idaho batholith rocks. Soil horizons were 

developed on this decomposed surface prior to glaciation. The soil and eluvium on this surface were enriched 

in heavy minerals. Increased fluvial activity during 

glaciation concentrated heavy minerals into alluvial 

deposits nearby. Also during glaciation streams eroded 

areas of lode-gold deposits and concentrated the detrital 

gold into placer deposits, locally at some distance from 

the source. Subsequent erosion following the lowering of 

erosional base levels has resulted in reworking of some of 

the older placer deposits in terrace gravels into Holocene 

alluvial deposits farther downstream. 

Aspects of Quaternary erosion other than placer 

deposits also have to be considered in mineral evaluations. Pediment surfaces and many of the terraces along 

the streams are cut in bedrock. Commonly there is a 

relatively thin veneer of gravel on these surfaces that may 

mask mineral deposits or geologic features diagnostic of 

mineral deposits at depth. 

GEOCHEMISTRY 

Geochemical Surveys 

Two government organizations have conducted 

regional geochemical surveys of the areas within the 

boundaries of the Challis National Forest, the Department of Energy (DOE) and the USGS (fig. 5). 

The NURE program was a program of the DOE to 

acquire and compile geologic and other information with 

which to assess uranium resources at a scale of 1:250,000 

and to determine areas favorable for the occurrence of 

uranium in the United States. The hydrogeochemical and 

stream-sediment: reconnaissance (HSSR) program of 

NURE provided for the collection of water and sediment 

samples located on the 1 ox 2° National Topographic 

Map Series quadrangle grid across the conterminous 

United States and Alaska and for the analysis of these 

Geochemistry 25 
samples for uranium as well as for a number of additional 

elements (Information Systems Program, 1985). Both 

the sample collection and analysis were contracted to 

commercial laboratories. 

The USGS programs in the Chaliis National Forest 

were designed either for resource assessment of areas 

being considered for wilderness status or for resource 

assessment of the Challis 1° x 2° quadrangle. The USGS 

was responsible for both the collection and analysis of 

samples. USGS sampling and analytical techniques have 

evolved over a period of years, and analytical results of 

earlier studies are not directly comparable with those of 

later studies. 

Table 5 lists geochemical surveys that cover parts 

of the Challis National Forest, the area of the National 

Forest covered by the survey, the group that collected the 

samples, and the group that analyzed the samples. Table 

6 indicates laboratories and their analytical methods for 

the geochemical data used in the mineral resource 

assessment of the Challis National Forest. In most 

surveys, not all samples were analyzed by all the listed 

methods. 

NURE Programs 

(1) Hailey NURE program; samples were collected by Savannah River Laboratory and were analyzed 

by Oak Ridge Gaseous Diffusion Plant. Analyses for 

soils, dry-wash sediments, and waters were reported 

(Cook and Fay, 1982). Although sediments from streams 

with flowing water might have been collected, analytical 

results are not available. The minus-100-mesh fraction of 

soils and dry-wash sediments was analyzed by an ioncoupled plasma (ICP) analytical technique. The minus100-mesh fraction of sediments is a useful sample 

medium in areas that produce good hydromorphic 

anomalies. Even in arid regions where hydromorphic 

anomalies are not well developed, this size fraction is 

adequate, provided the analytical technique is precise 

and has relatively low limits of determination. ICP is a 

precise analytical method, but the limit of determination 

for some elements such as Ag is high (2 ppm) and several 

elements of interest in resource evaluation, including As, 

Sb, Bi, Cd, and W, were not analyzed. Sample density of 

the survey was adequate but not uniform. Most samples 

were collected near roads, and thus those areas with few 

or no roads have few or no sample sites. 

(2) Idaho Falls NURE program; like the Hailey 

NURE program, samples were collected by Savannah 

River Laboratory and were analyzed by Oak Ridge 

Gaseous Diffusion Plant. This sampling and analytical 

program shares the same strengths and weaknesses as 

the Hailey NURE program. For general resource assessment, the sample density was adequate within the 

boundaries of the Challis National Forest. 

(3) Dubois NURE program; water and streamsediment samples in this program were collected and 

analyzed by Los Alamos Scientific Laboratory. The 

minus-100-mesh fraction of stream sediments was 

analyzed for an extensive suite of elements that includes 

As, Sb, Bi, Cd, and W. Precision of the analyses was 

typically better than 25 percent if the element concentration was an order of magnitude above its detection 

limit. Although some elements, such as Ag (limit of 

detection 5 ppm), had limits of detection that are too high 

to be useful for a thorough resource evaluation, many 

elements had limits of detection that were within an 

order of magnitude of their average crustal abundance. 

Unfortunately, few samples were collected within the 

boundaries of the Challis National Forest, and this area 

has the lowest sample density of any of the study areas 

(0.01 samples per 1 mi2). 

U.S. Geological Survey Programs 

(1) Challis CUSMAP project; samples in this 

project were collected and analyzed by the USGS. This 

study was chosen instead of the Challis NURE program 

to determine geochemical signatures of type mine 

localities, because the USGS study was designed for 

resource assessment of a broad range of commodities, 

not just uranium. The USGS Challis CUSMAP geochemical group is a composite of five separate studies, 

many with different sampling and analytical techniques. 

Samples collected specifically for the Challis CUSMAP 

project were collected only in areas not previously 

sampled by projects in the Sawtooth Primitive Area, 

Idaho Primitive Area, Sawtooth National Recreation 

Area, or Ten Mile West Roadless Area. Three of these 

studies (eastern part of the Sawtooth National Recreation Area, Idaho Primitive Area, and Challi 

CUSMAP) included portions of the Challis National 

Forest. These three studies will be discussed separately. 

Idaho Primitive Area.-Rocks collected from 

mineralized and unmineralized areas and sediments 

collected from both flowing and intermittent streams 

(mesh size not specified) were analyzed by semiquantitative emission spectrography. During the time period of 

this study, analytical techniques were modified and limits 

of detection for some elements changed for samples 

analyzed at the beginning of the study and those analyzed 

toward the completion of the study. The element suite 

analyzed for this study is more restricted than other 

studies in the Challis CUSMAP project. The semiquantitative emission spectrographic analytical method is not 

precise (plus or minus one reporting interval at the 83 

percent confidence level and plus or minus two intervals 

at the 95 percent confidence level), but it does allow 

quick processing of samples. The sample density is high 

and the samples are evenly distributed compared to the 

Challis NURE study in this same area. 

26 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
Eastern part of the Sawtooth National Recreation 

Area.-Rocks, soils, and stream sediments (minus-SOmesh size fraction) were collected and analyzed by semiquantitative emission spectrography, by atomicJtbsorption, and by colorimetric analytical techniques. The 

sampling density is high -4,654 samples were collected 

in the eastern part of the Sawtooth National Recreation 

Area. The elements analyzed include those commonly 

used in resource evaluation. The limit of detection or the 

precision of the analysis, or both, were improved by 

analyzing Au, Ag, Sb, Cu, Pb, and Zn by either atomic 

absorption or color spectrophotometry. The lack of 

precision in the semiquantitative emission spectrographic 

analytical technique is at least partially overcome by the 

high sample density in this area. 

Challis CUSMAP project.-Rocks, soils, stream 

sediments (minus-200-mesh size fraction) from both dry 

and flowing streams and the- heavy-mineral ofraction of 

the stream sediments were analyzed by semiquantitative 

emission spectrography (Adrian and others, 1985; Hopkins and others, 1985). Sample density is about one 

sample per 2 mi2

• This is the only study in which the 

heavy-mineral fraction of stream sediments was collected 

and analyzed. Compared to the less dense silicates and 

oxides, heavy minerals tend to have higher concentrations of some elements of interest in resource 

evaluation. Many of these elements reside in the mineral 

matrix rather than in surface coatings, and the heavymineral fraction tends to have a good contrast between 

anomalous and background samples regardless of 

climate. 

(2) Boulder-Pioneer Wilderness Study Area; 

samples in this study were collected and analyzed by the 

USGS. This study covers a southwestern part of the 

Challis National Forest and overlaps portions of both the 

Hailey and Idaho Falls NURE program studies. Rock, 

soils, and stream se-diments were collected and analyzed 

by atomic absorption, neutron-activation, and semiquantitative emission spectrography. Sample density in this -

study was high, about 2.6 samples per 1 mi2

• For the 

reasons previously given, this study was used to determine the geochemical signatures of the type mine 

localities within the boundaries of this study rather than 

using either the Hailey or Idaho Falls NURE studies. 

Geochemical Signatures 

The geochemical signatures for each deposit type, 

as listed in table 7, were defined by examining the -

analytical results of samples collected near the type mine 

localities (fig. 5, table 3) and determining which elements 

had unusually high concentrations in those samples. 

Because of different limits of detection/determination, 

elements analyzed, sample media, sampling density, and 

analytical prectston among the various geochemical 

surveys, the geochemical signatures given in table 7 

should be used for resource assessment only within the 

boundaries of the survey that contains the type mine 

locality. Many of the mineral deposit types described in 

this report have theoretical geochemical signatures that 

are based on similar mineral deposits that occur outside 

of the Challis National Forest. These "ideal" geochemical signatures are modified from geochemical signatures 

associated with deposit models in Cox and Singer (1986). 

Because of different sampling and analytical methods, 

these "ideal" geochemical signatures usually will not 

match the observed geochem·ical signatures reported in 

table 7. A discussion of the geochemical signatures for 

each type is included in the deposit type descriptions in 

the "Resource potential-locatable minerals" section of 

this report. 

GEOPHYSICS 

The aeromagnetic map as superimposed on the 

geologic map (pl. 2) illustrates the correlation of 

magnetic patterns with various types of mineral deposits 

and provides information applicable to prospecting for 

buried geologic structures and igneous intrusions that 

might have associated mineral deposits. The gravity maps 

are reconnaissance in nature, but provide valuable 

insights for prospecting, such as information about 

regional structures and distribution of low-density 

igneous intrusions typical of the felsic granitic rocks of 

this region (Mabey and Webring, 1985). 

- Several of the mineral deposit types discussed in 

this report commonly are spatially related to granitic 

intrusions and fault or shear zones. Within the Forest 

prominent positive magnetic anomalies are often 

associated with the exposed Tertiary granitic intrusions. 

In some cases the correlations are not exact, which 

indicates that the intrusion is not uniformly magnetic. 

Configuration of some individual anomalies may indicate 

the presence of concealed Tertiary intrusions or more 

extensive subsurface development of the exposed plutons. The widespread Cretaceous biotite-granodiorite 

rocks of the Idaho batholith are less magnetic and 

generally show low magnetic gradients and exhibit no 

distinctive expressions that could be used to pinpoint 

their contacts. Diorites of Cretaceous age are sparse, but 

where present they exhibit high-amplitude positive 

anomalies. Thus, in areas where distinctive positive 

anomalies occur over Cretaceous granitic terrane, buried 

dioritic or Tertiary intrusions may be present. 

Fault zones and shear zones may exhibit linear 

magnetic trends, typically as patterns of contours parallel 

to the zones. A series of northeasterly linear magnetic 

Geophysics 27 
trends correlates with the trans-Challis fault system as 

defined by Fisher (1985). The sources of these trends are 

interpreted as faults that cut or offset the rhyolite, which 

results in the juxtaposition of rocks with different 

magnetic properties. Some of the faults inferred from the 

magnetic data have not been recognized in exposures and 

apparently do not cut the ground surface. 

The regional gravity map (A.E. McCafferty and 

Viki Bankey, written commun., 1987) exhibits patterns 

that can be attributed largely to the low-density granitic 

intrusions of Cretaceous to Tertiary age. Mabey and 

Webring (1985) made physical property measurements 

of rocks in the study of the Challis 1 o x 2° quadrangle and 

reported the following average specific gravity values: 

Precambrian crystalline rocks, 2.7 g/cm2 ; sedimentary 

rocks, 2.6 g!cm2

; Cretaceous Idaho batholith, 2.58 g!cm2; 

major intrusions of Tertiary granite, 2.56 g/cm2

; Tertiary 

diorite intrusions, 2.7 g!cm2

; and Tertiary Challis 

Volcanic Group, about 2.5 g!cm2 • 

MINERAL RESOURCESLOCATABLE MINERALS 

Locatable minerals include all minerals subject to 

exploration, development, and production under the 

Federal General Mining Law of 1872. Most metals and 

industrial minerals are included in this group and are 

considered in this section. 

Mining and Exploration History 

The area covered by the Challis National Forest 

has experienced a long history of mining and mineral 

exploration. See Ross (1963a) and Wells (1983) for 

excellent discussions of the history of mining in this area. 

Several commodities have been sought and exploited and 

many others have been sought, but because of geologic 

conditions, logistics, or economics, have not been fully 

exploited. The cycle of mineral exploration and appraisal 

never ends, and deposits and occurrences known for 

many years become resources due to increased knowledge, technological advances, or changes in supply and 

demand. Exploration and development have come in 

spurts with emphasis at various times on ores of gold, 

silver-lead-zinc, copper-lead-zinc, tungsten, molybdenum, uranium, fluorspar, radioactive minerals, and 

rare-earth minerals. Some of these commodities sustained a sizable industry that lasted many years; others 

were short lived in interest and production. Commodities 

such as iron, barite, cobalt, mercury, sulfur, antimony, 

manganese, and arsenic are recorded as present but have 

had essentially no production. Lands of the Forest have 

also been evaluated for many other commodities of 

which there is no record. 

This part of Idaho was first explored in the 1860's 

by groups of gold seekers. By 1869 all the known placers 

and most of the lode deposits had been discovered 

(Weissenborn, 1964, p. 14). Gold has been mined intermittently from lode deposits since the 1860's. Production 

of gold from placer deposits was mainly prior to 1900 

with a revival of placer operations during the 1930's and 

the operation of the Yankee Fork dredge in the 1940's 

and 1950's. The latest exploration activity in the Forest 

has been for gold in large low-grade lode deposits. 

During the "gold rush" in the 1860's rich silverlead ores were noted in several areas. Mining of these 

ores began in the early 1880's at many locations within 

the Forest. Smelters were constructed at Bayhorse 

(fig. 4), Nicholia to the east of the Forest, and Wood 

River (Ketchum) to the west of the Forest. The erection 

of smelters in these districts spurred exploration activity, 

and small operations from most of the known mineralized areas in the area shipped ore to one of these 

smelters during the 1880's. Stamp mills were constructed 

at many of the sites. There was a sharp decline in 

production around 1890 when the rich secondary 

deposits being mined were exhausted, and the smelters 

were closed, the last at Clayton in the Bayhorse district 

(fig. 4) in 1902. Mining of the silver, lead, zinc, and 

copper in and near the Forest, however, has continued 

almost uninterrupted since the turn of the century: For 

example, the Wilbert mine in the Dome district from 

1906 to 1918 and 1924 to 1931; the Empire mine in the 

Alder Creek district intermittently from 1901 into the 

1960's; mines at Leadbelt Creek in the Lava Creek 

district in 1908, 1910, 1913, and the mid 1920's; the Last 

Chance mine in the Lava Creek district in 1943; mines in 

the Bayhorse district nearly continously with a major 

period from 1920 to 1923; the Lost Packer mine in the 

Loon Creek district from 1904 to 1916; the Livingston 

mine in the Boulder Creek district from 1920 to 1930; the 

Clayton Silver mine in the Bayhorse district in nearly 

continuous operation from the mid 1920's to 1986; and 

numerous small operations. 

Mines within or near the Forest have been major 

past producers of tungsten. Tungsten minerals were 

known in this part of Idaho from the time of the active 

gold and silver mining in the late 1800's mainly because 

tungsten minerals came as unwanted by-products in the 

extraction of the precious metals. There was sporadic 

production of tungsten from the Ima mine in the Blue 

Wing district from 1911 to 1935 and continuous 

production from 1936 to the late 1950's. The Ima mine 

was a major domestic producer and is second in total 

tungsten production in Idaho only to the Yellow Pine 

mine which is located just northwest of the Forest. The 

major period of tungsten production was 1942-1944. 

Another period of major tungsten activity in this part of 

Idaho was 1950-1956; several new discoveries were 

28 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
made, and the deposits at Wild Horse Creek in the Alto 

district and at Thompson Creek in the Bayhorse district 

were worked at this time. This period of activity was in 

response to Federal Government stockpile purchases, 

which ceased in 1956. 

Molybdenite, the major molybdenum mineral, has 

been known in numerous occurrences in the Forest since 

early in this century. Little interest was shown in the 

commercial extraction of molybdenite until extensive 

exploration during the 1960's discovered or delineated 

several major stockwork molybdenite deposits within or 

close to the Forest. The Thompson Creek deposit was 

brought into production in 1983. Molybdenum exploration is currently at a standstill because of worldwide 

oversupply and low prices. 

Extensive exploration projects sought uranium in 

this area in the 1950's and again in the 1970's. The 

Stanley area produced uranium ore from vein and 

bedded deposits in 1959 and 1960. Uranium was also one 

of the commodities recovered from placer mining of 

radioactive black sands in the late 1950's. Most of this 

placer mining was west of the Forest in Bear Valley, 

although there was extensive exploration throughout the 

region. The other commodities produced from the blacksand deposits include niobium-tantalum oxides, thorium, 

rare-earth minerals, and titanium oxides. The placer 

mining was in response to Federal Government stockpiling orders. 

Almost all the known fluorspar deposits in Idaho 

are in or close to the Forest. The first commercial 

production of fluorspar was in 1951-1953 from the 

Meyers Cove deposits in the Gravel district, which were 

discovered in 1941 and worked intermittently from 1954 

to 1972. A small amount of fluorspar was mined from the 

Keystone Mountain area in the Bayhorse district during 

1947-1953 and from the Stanley district in the late 

1940's. Extensive exploration in the 1960's and 1970's 

delineated large stratabound fluorspar deposits in the 

Bayhorse district, but there has been no production from 

these deposits. 

A variety of commodities have been mined in the 

Forest in the past. Much of the mining activity came in 

spurts, usually in response to a national demand. Major 

wars fueled some of the demand, but some came in 

response to modern technological needs that require 

"space-age" elements, such as the rare-earth elements. 

This trend will probably continue in the future; as a new 

need arises, the known occurrences will be reexamined 

and new sources will be sought. 

Metals 

The Challis National Forest has many types of 

mineral deposits that contain base, precious, and ferrous 

metals in several geologic terranes (figs. 7-12). The 

deposits formed during many metallogenic events 

including Precambrian sedimentation and later plutonism, Paleozoic sedimentation, Cretaceous igneoushydrothermal activity centered on the formation of the 

Idaho batholith, Tertiary igneous-hydrothermal activity 

related to formation of the Challis volcanic field, and 

Pleistocene to Holocene weathering and erosion. 

Precambrian submarine exhalative metal concentrations of cobalt, bismuth, arsenic, nickel, copper, silver, 

gold, and iron formed during deposition of the.'( ellowjacket Formation. These metals ~~re remobilized. by 

intrusive activity about 1,800 milhon years ago mto 

deposits such as those at the Blackbird mine located just 

north of the Forest and at small and low-grade occurrences within the Forest. 

Stratabound concentrations of metals that formed 

during deposition of the Paleozoic black-shale seque~ces 

include silver, barium, copper, molybdenum, vanadmm, 

lead, zinc, nickel, and others. Some of these metals, 

namely vanadium, molybdenum, nickel, and zinc, have 

relatively high solubilities in sea water (Desborough and 

Poole, 1983, p. 99) and may have been concentrated 

directly from sea water by bacteriogenic activity. Other 

possible concentrating mechanisms inclu~e depositi~n 

from heated basin brines or from submarme exhalative 

solutions. The metal concentrations took the form of 

massive sulfide lenses, stringers and disseminations of 

sulfide minerals, and probably entrapment of metals i.n 

nonsulfide minerals. Known stratabound syngenetic 

deposits of precious and base metals (Q) (fig. 7~ include 

the stratiform zinc deposits at the Hoodoo mme (Qa, 

fig. 5) and the Livingston mine (Boulder Creek district, 

fig. 4). Numerous other deposits are tho~ght to be 

stratiform in part. In parts of the Salmon River assemblage vanadium occurs in concentrations greater than 1 

percent in stratabound vanadium deposits (R) (fig. 7) 

that may be commercial in the future. In addition to the 

stratabound deposits that may be present, the carbonaceous sedimentary rocks (black shales) held an enormous reservoir of metals that could have been mobilized 

and concentrated by igneous-hydrothermal systems 

active in the Cretaceous and Tertiary (examples are 

deposits of type B, fig. 7). 

Igneous-hydrothermal systems related to the 

emplacement of the Cretaceous Idaho batholith and the 

Tertiary Challis volcanic field developed mos.t of the 

deposit types present in the Fares~. :he bat~ohth event 

and the volcanic event were distinctly different as 

reflected in the characteristics of metallogenesis and the 

associated deposit types. Some deposit types were 

formed exclusively during emplacement of the Cretaceous batholith, whereas other types formed exclusively 

during the Tertiary plutonism and volcanism;.a few other 

types formed during both events. There 1~ a strong 

genetic relationship among all the depostts formed 

Mineral Resources- Locatable Minerals 29 
EXPlANATION 

Tertiary intrusive rock 

Cretaceous intrusive rock 

Precambrian rock 

Carbonate rock 

Quartzite 

~ Black shale J 

----- Regional fault 

--~---Thrust fault-Arrow shows direction of displacement 

t t t Thrust fault-Sawteeth on upper plate 

Possible location of mineral deposit type B-Mineral deposit types (designated by letters) 

are listed in tables 3 and 4 

Figure 7. Schematic diagram of deposit types in black-shale terrane. 

during the Tertiary igneous-hydrothermal events. The 

main differences among deposit types formed during the 

Tertiary events are in details of structural and lithologic 

setting. The same may be true, although less obviously so, 

for the deposits formed during the Cretaceous event. 

Pegmatites and veins that formed from the latestage fluids of the developing Cretaceous batholith 

concentrated a characteristic suite of metals including 

niobium, thorium, tin, tungsten, lithium, rare-earth 

elements, beryllium, and uranium. Some of the vein 

uranium deposits (H) (fig. 8), such as those at the 

Lightning No. 2 mine (H, fig. 5), might be related to 

pegmatitic rocks of the Idaho batholith. Known 

commercial metal deposits in pegmatites are located 

outside the Forest to the southwest. The metal and 

mineral concentrations in the late-stage crystallization 

products of the Idaho batholith, including pegmatites, 

were the source of the minerals in the radioactive blacksand placer deposits formed in Pleistocene to Holocene 

times. 

30 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
EXPlANATION 

)( )( )( lx )( )( )( )( )( )( 

~ 0 0 

0 0 

-~L 

--r I 

r- ,..- ....,._ - --

Quaternary deposits 

Tertiary intrusive rock 

Cretaceous intrusive rock 

Pegmatite 

Carbonate rock 

Black shale 

:====~Fault 

------

~ 

Thrust fault-Arrow shows direction of displacement 

+ + + Thrust fault-Sawteeth on upper plate 

mmmmmmm~mm B Possible location of mineral deposit type 8-Mineral deposit types (designated by letters) 

are listed in tables 3 and 4 

Figure 8. Schematic diagram of deposit types in Idaho batholith terrane. 

Some of the Cretaceous plutons (probably satellite 

bodies of the Idaho batholith) contain stockwork 

molybdenum deposits (J) (figs. 7, 8, 9) with associated 

copper and silver, such as at the Thompson Creek mine 

(J a, fig. 5). The stockworks are located in the upper parts 

of the intrusive body or in the surrounding country rocks 

and are generally associated with tungsten and basemetal skarn and vein deposits. Some stockwork molybdenum deposits (J) (figs. 8, 9) formed in and along 

Tertiary hypabyssal bodies. Examples are the WaltonWhite Mountain prospect (Jb, fig. 5) and the Ima mine 

(1, fig. 5). These deposits are a combination of disseminations in the intrusive rocks and stockworks and subparallel veins in the intrusive rocks and surrounding, 

Mineral Resources- Locatable Minerals 31 
EXPLANATION XV 7 )( "' 

<x " > L. < (' )( Tertiary or Cretaceous intrusive rock 

I I 

_l Carbonate rock 

-

gtj Quartzite 

----Fault 

mmmmmmmmmi I Possible location of mineral deposit type 1-Mineral deposit types 

(designated by letters) are listed in tables 3 and 4 

Figure 9. Schematic diagram of stockwork molybdenum and tungsten vein deposits. 

intensely altered country rocks. Tungsten veins formed 

directly above the molybdenum stockworks at the Ima 

mine. 

Polymetallic skarn deposits (L) (figs. 7, 8, 10, 11) 

formed where Cretaceous or Tertiary magmas intruded 

favorable country rocks, such as limestone and dolostone, and altered them to silicate minerals. Polymetallic 

skarn deposits associated with Cretaceous intrusive rocks 

are generally enriched in tungsten but also contain lead 

and zinc. Many such deposits, like those at the Springfield 

mine (Lb, fig. 5), are within carbonate inclusions in 

batholithic rocks (fig. 8). Other such deposits are around 

the satellite bodies of the Idaho batholith, especially 

bodies that contain the stockwork molybdenum deposits, 

such as at the Tungsten Jim mine (Bayhorse district, 

fig. 4). Polymetallic skarn deposits formed along Tertiary 

plutonic bodies and along smaller felsic dikes, dike 

swarms, and irregular-shaped bodies. Examples of skarn 

deposits along a plutonic body are the deposits at the 

Empire mine (La, fig. 5). Examples of skarn deposits 

along hypabyssal bodies (fig. 10) are some of the deposits 

in the Star Hope (Copper Basin district, fig. 4) and 

Windy Peak areas (Spring Mountain district, fig. 4 ). 

Polymetallic skarn deposits are mainly copper, lead, zinc, 

and silver occurrences but include some tungsten and 

uon. 

Emplacement of the Idaho batholith and related 

bodies generated hydrothermal vein deposits. Most of 

the base-metal veins (G) (fig. 8) probably formed during 

the Cretaceous intrusive-hydrothermal activity. Deposits 

in the Sea Foam mine (G, fig. 5) are good examples of 

this type. Many of the tungsten vein deposits that occur 

along north-trending fractures in Idaho batholith rocks 

32 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
EXPLANATION 

)( )( )( 

)( )( )( )( 

)( )( )(_ 

"' " ., v v < .,. r 

') L,.. " < 

I I I 

Quaternary deposits 

Tertiary intrusive rock 

Cretaceous intrusive rock 

Precambrian rock 

Volcanic rock 

Carbonate rock 

Black shale 

--==-.....----=-Fault 

------ Regional fault 

~~~;:~::~?.;;~=~~~~~=~~~~~~. E Possible location of mineral deposit type E-Mineral deposit types (designated by letters) are 

listed in tables 3 and 4 

Figure 10. Schematic diagram of deposit types in volcanic terrane. 

may also have been formed during this event, but some 

were probably formed during the Tertiary igneoushydrothermal event. Polymetallic veins in black-shale 

terrane (B) (figs. 7, 8) developed within the contact 

metamorphic zones of both Cretaceous and Tertiary 

intrusive bodies. The Cretaceous and Tertiary deposits 

are indistinguishable, at least with the present state of 

knowledge, because most of the metals in these polymetallic veins were probably remobilized from the carbonaceous units. 

Tertiary igneous-hydrothermal activity and attendant metallization took place in an environment of 

structural extension that was characterized by deepseated high-angle fractures and rift structures. Deposits 

Mineral Resources- Locatable Minerals 33 
EXPlANATION 

Tertiary intrusive rock 

Precambrian rock 

Volcanic rock 

Carbonate rock 

,........____ 

t;.._ ...__ "\ Black shale 

-::=:=- -==....:::= Fault 

----- Regional fault 

-~=;;;....- Thrust fault-Arrow shows direction of displacement 

+ + + Thrust fault-Sawteeth on upper plate 

;\~~;~f,i..~~~;~\~~~\~~ A Possible location of mineral deposit type A-Mineral deposit types (designated by letters) are 

listed in tables 3 and 4 

Figure 11. Schematic diagram of deposit types found in carbonate terrane. 

formed in these geologic environments generally show 

some enrichment in fluorine, barium, potassium, silica, 

gold, silver, antimony, beryllium, iron, lithium, manganese, molybdenum, lead, strontium, tin, tellurium, 

uranium, vanadium, and zinc. The mineralogy, metal 

content, and physical form of an individual deposit 

depended upon the relative control of igneous rock 

composition, regional and local structures, depth below 

ground level, distance from intrusive rocks, composition 

and permeability of host rock, extent of development of 

hydrothermal system, and availability of metals. 

The high-level, rhyolite-hosted, precious-metal 

deposits (K) (fig. 10) and the precious-metal deposits in 

volcanic tuffs (P) (fig. 10) represent late-stage and hydrothermal deposition of metals within the igneous rocks. 

The Tertiary stockwork molybdenum deposits (J) are 

similar but formed at a lower level in the crust and, in 

fact, may underlie some of the high-level, rhyolite-hosted, 

34 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
EXPlANATION 

X X X 7 

,... x ; x ~ Tertiary or Cretaceous rock ..l. X X 

Precambrian rock 

Carbonate rock 

••••• 0 •• 0 Quartzite 

~-Fault 

----- Regional fault 

-==---Thrust fault-Arrow shows direction of displacement 

t~~~:1.:.:~}~~~~~~~~~~ C Possible location of mineral deposit type C-Mineral deposit types (designated by letters) are 

listed in tables 3 and 4 

Figure 12. Schematic diagram of deposit types in quartzite terrane. 

precious-metal deposits (K). An example of the highlevel, rhyolite-hosted, precious-metal deposits is the 

Golden Sunbeam mine (K, fig. 5); an example of the 

precious-metal deposits in volcanic tuffs is the Sunnyside 

mine (Pa, fig. 5). Polymetallic vein deposits in carbonate 

terrane (D) (fig. 11), quartzite terrane (C) (fig. 12), 

black-shale terrane (B) (fig. 7), and Tertiary extrusive 

terrane (E) (fig. 10) are essentially the same in contained 

metals and mineralogy, although the types of deposit 

differ slightly in form. All polymetallic vein deposits 

formed in open fractures and breccia zones from hydrothermal solutions. Examples include the Windy Peak 

area (D, fig. 5) for carbonate terrane, the Wilbert mine 

(C, fig. 5) for quartzite terrane, the Livingston mine (B, 

fig. 5) for black-shale terrane, and the Hornsilver mine 

(E, fig. 5) for Tertiary extrusive rocks. Replacement of 

Mineral Resources- Locatable Minerals 35 
chemical1y receptive rocks accompanied all the polymetallic vein deposits. Polymetallic veins developed anywhere fractures and solution traps were available within 

an igneous hydrothermal system. The metals were in part 

remobilized from the country rock and in part introduced 

with the magmatic fluids. Some of the polymetallic veins 

are a considerable distance from major intrusive bodies 

(figs. 10, 12), whereas other veins are next to and within 

intrusive bodies (figs. 7, 8). The precious-metal veins (F) 

(figs. 8, 10, 11 ), fluorspar veins (A) (figs. 8, 10), and 

fluorspar breccia manto deposits (N) (fig. 11) are 

associated directly with rift systems and deep-seated 

extensional fault systems such as the trans-Challis 

(fig. 6). These deposits formed from low- to moderatetemperature hydrothermal systems and may be a 

considerable distance from any known, related intrusive 

activity (figs. 8, 10, 11 ). 

Metal-bearing solutions that coursed along major 

high-angle fault systems in carbonate rock selectively 

formed irregular replacements of base and precious 

metals (M) (figs. 10, 11, 12) in carbonate rock. The 

replacement bodies are most common in breccia zones 

or beneath an impervious cap to the solutions. The 

irregular replacements of base and precious metals (M) 

are similar in metal content to the polymetallic veins in 

black-shale terrane, which suggests that the metals were 

mobilized from the underlying black shales. The Clayton 

Silver mine (M, fig 5) is an example of this type of 

deposit. The age and source of the solutions are unknown 

as there is no obvious igneous relationship. 

Large areas of jasperoid associated with sedimenthosted, jasperoid-associated, precious-metal deposits 

(0) (fig. 11) were formed by solutions that replaced the 

enclosing rock with silica. Most of the known jasperoids 

in the Forest are in limestone and along or close to major 

fault systems and probably formed during mid- to late 

Tertiary time. The solutions may have been metal bearing, in which case there may be large low-grade gold 

deposits within or closely associated with some of the 

jasperoids. Jasperoids can be seen at Lehman Butte and 

Bartlett Point north of Mackay. 

Certain minerals, including some heavy minerals, 

are resistant to chemical weathering and collect as a 

weathering residue in soils and eluvium. The heavy 

minerals are further concentrated because they tend to 

lag behind during fluvial erosion or to be deposited first 

when stream currents become inadequate to carry the 

sediment load. The resistance to weathering and lag 

effect were important factors in formation of the gold 

placer deposits (S) (fig. 10) and radioactive black-sand 

placer deposits (T) (fig. 8). The source of the gold was 

lode deposits, and the source of the radioactive black 

sands was rocks of the Idaho batholith. Weathering and 

fluvial action formed these deposits in Pleistocene to 

Holocene time. 

Industrial Minerals 

Fluorspar in veins (A) (figs. 8, 10) and in breccia 

manto deposits (N) (fig. 11) formed in and near deepseated extensional faults of the trans-Challis fault system 

during the Tertiary igneous-hydrothermal event. Precious metals, base metals, and barite are associated with 

these deposits. Barite also formed in hydrothermal veins, 

stringers, and pods that may represent an outer zone of 

polymetallic veins in carbonate terrane. Examples occur 

in the Lone Cedar and Saw Mill Canyon areas of the 

west -central Lost River Range (shown as an area of 

unknown potential on plate 3). Higher concentrations of 

barite formed during deposition of the black-shale 

sequences. Syngenetic, bedded barite deposits in the 

black-shale sequences have been exploited south of the 

Forest boundary near Hailey, Idaho. 

High-purity limestone and dolostone in the carbonate bank sequence and the White Knob Limestone 

formed in a shallow-water marine environment by precipitation of calcium carbonate from sea water and by 

accumulation of organisms rich in calcium carbonate. 

Lime rock in the Forest has not been exploited, but some 

of the beds may be of metallurgical or chemical grade. 

Pegmatites are coarse-grained, dikelike or 

irregular-shaped masses of igneous rock that represent 

crystallization of the late-stage magmas and solutions of 

a developing batholith or pluton. Small pegmatites are 

common in association with the Idaho batholith. In 

addition to a distinctive suite of metals, pegmatites may 

also contain potentially commercial amounts of feldspar, 

quartz, and mica. Some of the pegmatites in the Forest 

have been prospected, but there is no recorded production. Many of the characteristic "pink" granites of 

Tertiary age in this part of Idaho contain abundant 

miarolitic cavities, which are small crystal-lined cavities 

that may contain semiprecious gemstones, such as smoky 

quartz, microcline, topaz, and beryl (aquamarine). 

Carbonaceous sedimentary rocks, such as those in 

the black-shale terrane, are converted to graphitic schist 

upon medium-grade metamorphism. Graphitic schists 

are common along the eastern edge of, and as inclusions 

in, the Idaho batholith. An example of this type of 

occurrence is at the Gem State mine at the north end of 

Elk Mountain in the Stanley district (fig. 4). 

Hydrothermal cells generated from the heat of 

intrusive magmas are often very large, and the solutions 

have a slight to pronounced effect upon the rocks 

through which they circulate. In addition to depositing 

36 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
metals in various forms and concentrations, the solutions 

produce economic concentrations of industrial minerals 

by alteration of the country rocks at some locations. Two 

industrial mineral commodities that form in this manner 

are alunite and the zeolite group of minerals; both 

commodities occur in the Forest, but neither has been 

exploited. Alunite [KAh(S04 )2(0H)6] forms as a product of the highest degree of alteration from strongly 

acidic fluids that interact with volcanic host rocks. The 

alteration effects on volcanic rocks in the outer margins 

of hydrothermal cells and from diagenetic reactions with 

meteoric water are commonly subtle and not readily 

apparent. Zeolite minerals (hydrous aluminosilicates) 

are common alteration products in these environments. 

Alteration products also include pods and veinlets of 

chalcedony (including agate), jasper, and opal; all these 

minerals are of interest as semiprecious gem stones. 

RESOURCE POTENTIALLOCATABLE MINERALS 

The Challis National Forest was evaluated for 20 

deposit types (pl. 3, table 4). Table 4 is shown in the text 

and reproduced in part on plates 3 and 4 as an aid in 

following discussions of each deposit type. In this section 

the characteristics of known and inferred deposit types 

are summarized and specific areas of high, moderate, 

and unknown potential are reviewed. Definitions of the 

terminology that is used, specifically the meaning of the 

several levels of resource potential, are in Appendix 1. 

Size classifications for each deposit type are listed in 

Appendix 2. 

Specific areas having high, moderate, or unknown 

mineral resource potential are given a letter-number 

designation. As an example, all areas that have a resource 

potential for stockwork molybdenum deposits, are shown 

with the letter J and a number following the letter, such 

as J1, J2, J3, and so on. Each letter-number combination 

(J2, for example) indicates an area with a specific 

resource potential/level of certainty for a restricted set of 

commodities that occur in a certain size and type of 

deposit. Areas can have different potential/certainty 

levels, for example J2 (HID), J3 (H/C), J4 (MID), and 

so on. Areas can have the same potential/certainty levels, 

such as J1 (HID) and J2 (HID), but different potential commodities or deposit size. All areas of a single 

letter-number combination, such as J2, have the same 

potential/certainty levels for the same set of commodities 

and same deposit size. 

On plates 3 and 4 and figures 13-32, areas of high 

potential are shown in red, and areas. of moderate 

potential are shown in pink. Areas of unknown potential 

are shown by black diagonal lines (fig. 33). 

Fluorspar Veins (A) 

Commodities, By-products, and Trace Metals 

Fluorspar and gold; antimony is a potential byproduct. 

Host Rocks 

Deposits are in plutonic and volcanic rocks. In the 

Stanley district (fig. 4) deposits are in granodiorite and 

porphyritic granodiorite of the Idaho batholith. In the 

Meyers Cove area, Gravel Range district (fig. 4), deposits 

are in a thick section of welded ash-flow tuffs of Eocene 

age (Fisher, Mcintyre, and Johnson, 1983). Other deposits are in Tertiary granitic and dioritic rocks. 

Structural Control 

Deposits are within the trans-Challis fault system 

and localized along northeast- and northwest-trending 

high-angle faults and shears. 

Age 

Tertiary, probably Oligocene. 

Deposit Description 

Deposits are discontinous fissure and breccia 

fillings along northeast- and northwest-trending zones. 

Individual veins range from a few inches to more than 12 

ft wide and 10 ft to several hundred feet long. Composite 

veins and groups may cover much larger areas. The veins 

are banded, vuggy, crustiform, and drusy and are 

suggestive of near-surface deposition. Fluorite, chalcedony, and quartz are the dominant minerals with some 

calcite, barite, stibnite, and base-metal sulfides. In the 

Stanley area fluorite is a common component of quartzpyrite-gold veins. Small felsic and mafic dikes occur 

within and adjacent to many of the deposits. The type 

locality for this model is the Meyers Cove area (A, 

fig. 13), Gravel district (fig. 4). 

Geochemical Signature 

The Meyers Cove type locality was sampled by the 

USGS Challis CUSMAP project (fig. 5). Both the heavymineral fraction of the stream sediments and the stream 

sediments contained anomalous concentrations of some 

metals. Stream sediments contained anomalous concentrations of Ag, Be, Mo, and the heavy minerals contained 

Resource Potential- Locatable Minerals 37 
w 

(X) 

3: 

:;-

CD 

~ 

::0 

CD 

0 

0 

~ n 

CD 

"'C 

0 

ct 

3. 

!: 

II) 

:I 

c. 

C) 

CD 

0 

0 

(Q 

'< 

2. 

r+ 

;:r 

CD 

(') 

;:r 

~ u;· 

z 

II) 

r+ o· 

:I 

!!!. 

"T1 

0 

; 

-~ 

a: 

I» 

;:r 

115°30' 115°00' 113°00' 112°45' 

45°00'~--------------~-------r-----------------------.~--------~-----,------------~;:----~ 114°00' 

& 

\t; 

\%. \ 

~ ~_.....--..., MONTANA 

~ \ 

) 

.... 

IDAHO \ \,,J' 

fen 

w 

0: 

0 

LL 

.....J 

<1: 

z 0 44°00' EXPLANATION LL 0 0 i= 

<1: 

z 

RESOURCE POTENTIAL 

- HIGH 

D MODERATE 

~ A TYPE MINE LOCALITY 

0 5 10 15 20 25 MILES 

~~--,% ~ 

~:mch= ro 

""\ 

43°30' ~----------------~------------------------~------------~--------------------------------~--~------~ 

Figure 13. Mineral resource potential map for fluorspar veins (A) in the Challis National Forest and adjacent areas, Idaho. Areas (A 1, A2, and so forth) of mineral resource 

potential are described in table 4. 
anomalous concentrations of Sn, Ag, Au, and Pb (table 

7). A geochemical signature commonly associated with 

fluorspar deposits of this type is Sb, Fe, As, Au, Ag, Hg, 

W, Pb, and Zn. 

Geophysical Signature 

The deposits have no geophysical expression, but 

some major faults show as linear zones of sharp magnetic 

gradient. 

Assessment Criteria 

1. Presence of high-angle faults or fractures. 

2. Proximity to major tensional faults of the 

trans-Challis fault system. 

3. Evidence of fluorspar mineralization. 

4. Proximity to Tertiary hypabyssal intrusions. 

Assessment 

Fluorspar occurrences of this type are mostly 

confined to structures related to the trans-Challis fault 

system. They are part of a northeast-trending zone of 

fluorite occurrences, which extends from northwestern 

Nevada through Idaho into Montana. Two areas in the 

Forest, the Stanley fluorspar district ( Al) and the Meyers 

Cove fluorspar district (A2), are assigned a high potential 

(HID) for fluorspar vein deposits. In both areas fluorspar 

is in major deep-seated fracture systems of sufficient size 

to host exploitable deposits. Three other areas (A3, A4, 

AS) are assigned moderate potential (MID). In these 

areas fluorite occurs mainly as a gangue mineral in other 

vein systems or as fluorspar veins in ·small isolated 

structures. In the Bay horse area (A3) the fluorspar 

potential is mainly in manto bodies discussed elsewhere. 

The areas of resource potential for fluorspar veins (A) 

are shown on plate 3 and figure 13 and summarized in 

table 4. 

Economic Significance 

Fluorspar districts in Idaho and elsewhere in the 

Western United States are mostly inactive. Nearly all the 

fluorspar consumed in the United States comes from 

much larger foreign sources. Development of fluorspar 

properties in Idaho would require an increased demand 

and higher prices for fluorspar. 

Polymetallic Veins in Black-Shale 

Terrane (B) 

Commodities, By-products, and Trace Metals 

Silver, lead, and zinc; gold, tin, antimony, and 

copper are potential by-products. Tellurium and 

selenium are present in some deposits. 

Host Rocks 

The host rocks are mainly black argillite or carbonaceous micritic limestone and also include siltstone, 

shale, fine-grained quartzite, and gray limestone. Veins 

are mostly in contact metamorphic zones close to felsic 

intrusive bodies where the country rocks have been 

altered to hornfels, tremolite-bearing limestone, calchornfels, and locally skarn. 

Structural Control 

The deposits are in high-angle faults and flat to 

steep-dipping sheared zones beneath major thrust faults 

or near regional unconformities. 

Stratigraphic Control 

Host rocks are the Salmon River assemblage of 

Late Cambrian, Late Devonian, and Late Mississippian 

age, the Ramshorn Slate of Ordovician(?) age, the lower 

part of the Copper Basin Formation of Mississipian age, 

and unassigned Ordovician, Silurian, and Devonian 

argillaceous rocks. Known deposits are all within about 

3.5 mi of felsic intrusive bodies. 

Age 

Probably ranges from Cretaceous to Eocene. 

Deposit Description 

Small discontinous veins, lenses, and pods with 

strike length as much as 900ft and width as much as 15 

ft. Ore is mostly massive, fine- to coarse-grained sulfides 

but also includes disseminated sulfides in a quartz and 

(or) siderite or calcite gangue and in altered, sheared 

carbonaceous host rock. Weathering of the deposits 

forms noticeable to inconspicuous gossans, some of 

which were mined in the past for lead-silver and gold. 

The type locality for this model is the Livingston mine (B, 

pl. 3, fig. 14), Boulder Creek district (fig. 4). 

Resource Potential- Locatable Minerals 39 
~ 

0 

!.:: 

:;· 

CD 

!. 

::0 

CD 

(I) 

0 

~ (") 

CD 

"tl 

0 

... 

CD 

a 

!: 

Q) 

::s 

a. 

C> 

CD 

0 

0 

co 

'< 

2. 

... 

::s" 

CD 

("') 

::s" 

~ c;;· 

z 

a s· 

::s 

!. 

., 

0 

; 

(I) 

~ ... 

a: 

Q) 

::s" 

0 

115°30' 115°00' 

45°00' 

440QQ' EXPLANATION 

RESOURCE POTENTIAL 

- HIGH 

D MODERATE 

84 

o/6\ 

~ 8 TYPE MINE LOCALITY 

114°00' 

~ Bs:DARV OF CHALLIS NATIONAL FOREST 

Ketchum 

0 5 10 15 20 25 MILES 

\ 

113°00' 112°45' 

~ /"""'-, MONTANA 

~b.~ \ 

e,.. ' ) 

..... 

IDAHO \ 

\,, (' 

\) 

..... 

CJ) 

w 

cr: 

0 

u.. 

_J 

<( 

z u.. 0 0 i= 

<( 

z 

CJ) 

:::::i 

_J 

<( 

:X: 

u 

~~ ~ 

Figure 14. Mineral resource potential map for polymetallic veins in black-shale terrane (B) in the Challis National Forest and adjacent areas, Idaho. Areas (81, 82, and 

so forth) of mineral resource potential are described in table 4. 
Geochemical Signature 

The Livingston mine type locality is within the 

eastern part of the Sawtooth National Recreation Area 

(fig. 5). Rock and stream-sediment samples are characterized by several elements in anomalous concentrations 

(table 7). Both rocks and stream sediments were 

anomalous in Sn, As, Sb, Cd, Zn, Pb, Au, and Ag. Rock 

samples were also anomalous in Hg, W, Bi, and Cu. 

Stream sediments were also anomalous in Mo. A 

geochemical signature commonly associated with polymetallic veins, regardless of terrane, is Zn, Cu, Pb, As, 

Au, Ag, Mn, Ba, Sb, and Bi. 

Geophysical Signature 

The deposits themselves have no direct geophysical 

expression, but some intrusives and major structures 

exhibit prominent anomalies and steep gradient zones in 

the magnetic and gravity anomaly data. Magnetic data 

suggest the presence of larger intrusive bodies in the 

subsurface beneath the outcrops of small plutons and 

hypabyssal bodies in the Bayhorse district (fig. 4) (B1, 

B2) and the Summit Creek area (Alto district, fig. 4) 

(B3). Likewise in the Star Hope (Copper Basin district, 

fig. 4) (B3) and Leadbelt (Lava Creek district, fig. 4) 

(B3) areas, magnetic data suggest buried intrusives in the 

vicinity. 

Assessment Criteria 

1. Black-shale terrane with carbonceous beds, 

micritic limestone, and black argillite. 

2. Proximity (within 4 mi) to a granitic pluton. 

3. Locally anomalous concentrations of Pb and 

Zn. 

Assessment 

A large part of the exposed black-shale terrane is 

favorable for polymetallic vein deposits. Two areas (B1) 

are assigned high potential (HID) because of the 

presence of all three criteria, plus the presence of known 

deposits. Three areas (B3) are assigned a high level of 

potential but with low certainty (H/B) because of a lack 

of geochemical and stratigraphic knowledge. Much of the 

remainder of the black-shale terrane [areas B2 (MID) 

and B4 (M/B)] is assigned moderate potential. Special 

attention is directed to area B4 by Fisher and others 

(1987) because of extensive areas of anomalous silver 

shown by stream -sediment samples. This is an area 

where volcanic cover is thin and discontinuous and 

windows of Paleozoic rocks are present. The areas of 

resource potential for polymetallic veins in black-shale 

terrane (B) are shown on plate 3 and figure 14 and 

summarized in table 4. 

Economic Significance 

Base metals and silver are supplied primarily from 

large-tonnage domestic and foreign mines. A major 

increase in demand or much higher prices for these 

commodities would be needed to support operation of 

small mines. The possible production of antimony, 

gold, and tin as by-products would enhance a mining 

operation. 

Polymetallic Veins in Quartzite 

Terrane (C) 

Commodities, By-products, and Trace Metals 

Silver and lead; gold and zinc are potential byproducts. 

Host Rocks 

Host rocks are quartzite, dolomitic quartzite, and 

sandy dolostone. The rock sections also include some 

shaly limestone and black shale. The mineralized zones 

are mostly in dolomitic members and in carbonatealtered quartzite (Umpleby, 1912). In the southern 

Lemhi Range the host units are in the Wilbert and 

Summerhouse Formations. Alteration consists of formation of jasperoid in the dolostone and carbonate replacement of the quartzites, with a halo of manganese and iron 

oxides. It is not known if the silicification and carbonate 

alteration involved introduction of silica and carbonate 

with the mineralizing solutions or local redistribution by 

hydrothermal solutions. 

Structural Control 

Structures important to ore deposition are northto northwest-trending high-angle faults. Alteration patterns and mineralized zones are centered on these 

structures. Local fracture zones associated with northtrending folds and thrust faults were favorable for ore 

deposition. 

Stratigraphic Control 

The major mineralized zones are along bedding of 

dolomitic members of the quartzites, along carbonatized 

quartzites, or along highly fractured zones in quartzite. 

Age 

No older than Tertiary as mineralization cuts dike 

rocks thought to be Tertiary (Ross, 1933, p. 5). 

Resource Potential- Locatable Minerals 41 
115°30' 115°00' 113°00' 112°45' 

~ 45°00'~---------------r------~~~::~~~::~~::~::~~~--------~-----r------------~~~--~~ 114000' 

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RESOURCE POTENTIAL 

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0 5 10 15 20 25 MILES 

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43°30'L_ ______________ L_ ____________________ ~---------L----------------------------~--~----~ 

Figure 15. Mineral resource potential map for polymetallic veins in quartzite terrane (C) in the Challis National Forest and adjacent areas, Idaho. Areas (C1, C2) of 

mineral resource potential are described in table 4. 
Deposit Description 

Three types of ores are recognized in the Wilbert 

mine (C, pl. 3, fig. 15), Dome district (fig. 4), that are 

typical of this deposit type (Umpleby, 1917). The higher 

grade ore (20-35 percent lead) is composed of thin 

lenses and stringers of galena partially altered to anglesite. The second type, which is lower grade (12-20 percent 

lead), consists of disseminated grains of galena and has a 

salt-and-pepper appearance. The third type consists of 

galena as a fissure filling and breccia cement. The 

primary ore mineral is galena with minor amounts of 

sphalerite. Gangue is sparse and consists mainly of 

carbonate minerals, jasperoid, and wall-rock fragments, 

with minor vein quartz, barite, and smithsonite. Pyrite is 

disseminated through altered wall rocks. The oxidized 

portions contain anglesite, cerussite, lead oxides, and 

locally malachite, azurite, and wulfenite, in addition to 

iron and manganese oxides. These ores are characterized 

by their fine-grained nature, by the individual grains of 

galena which are generally less than 2 mm in diameter, 

and by the lack of gangue minerals. They have no close 

spatial association with igneous bodies. 

Geochemical Character 

The Wilbert mine type locality is within the Idaho 

Falls NURE study boundary (fig. 5). Stream sediments 

nearest the mine were anomalous in Pb (table 7). Few 

samples were collected near the type locality, and the 

anomalous element suite is based on only one sample. A 

geochemical signature commonly associated with polymetallic veins regardless of terrane is Zn, Cu, Pb, As, Au, 

Ag, Mn, Ba, Sb, and Bi. 

Geophysical Character 

Some of the regional high-angle faults may be 

detectable by magnetic or gravity methods. 

Assessment Criteria 

1. Evidence of base- or precious-metal mineralization. 

2. Presence of deep-seated high-angle faults. 

3. Presence of quartzite terrane with dolomitic 

units. 

4. Carbonate alteration of quartzites along and 

extending away from faults. 

Assessment 

Portions of the southwestern part of the Lemhi 

Range (C2) have a moderate potential for this type of 

deposit. A small area (C1) in the vicinity of the Wilbert 

mine is assigned a high potential. The areas of resource 

potential (C1, C2) are cut by several high-angle fault 

systems, carbonate-altered quartzites occur along some 

of the fault systems, the quartzite sequence contains 

dolomitic units, and there has been production from 

several mines. Because there is no supporting geochemistry or detailed field mapping, a low certainty level is 

given to the high (H/B) and moderate potential (M/B) 

assignments. The expected orebodies are similar in size 

and grade to those exploited in the Wilbert mine. Consideration must also be given to potential gold deposits in 

this area, perhaps in zones of intense silicification. The 

areas of resource potential for polymetallic veins in 

quartzite terrane (C) are shown on plate 3 and figure 15 

and summarized in table 4. 

Economic Significance 

Lead and silver are supplied primarily from largetonnage domestic and foreign mines. A major change in 

demand or increase in price for these commodities would 

be needed to support operation of small mines. Production of gold as a by-product would certainly enhance 

the possibility of development. 

Polymetallic Veins in Carbonate 

Terrane (D) 

Commodities, By-products, and Trace Metals 

Lead and silver; trace to by-product amounts of 

zinc, gold, and copper. 

Host Rocks 

Known host rocks are white to blue, massive to 

thick-bedded limestone of the Saturday Mountain Formation, the White Knob Limestone, and the carbonate bank 

sequence. The host rocks are generally not altered, and 

contact metamorphism is limited to a narrow zone of 

calcite and some calc-silicate minerals along some of the 

veins. 

Structural Control 

The deposits are within or closely related to highangle faults. In the central part of the Lemhi Range, 

Spring Mountain district (fig. 4 ), the faults trend just east 

of north and dip steeply west. Locally felsic dikes occupy 

faults of the same general trend. In Leadbelt Creek area 

of the Lava Creek district (fig. 4) the faults and dikes 

trend northwest. 

Resource Potential- Locatable Minerals 43 
~ 

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115°30' 115°00' 

45°00' 

44°00' r EXPLANATION 

RESOURCE POTENTIAL 

HIGH 

-

D MODERATE 

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0 5 10 15 20 25 MILES 

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er 

IDAHO 

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z 

Figure 16. Mineral resource potential map for polymetallic veins in carbonate terrane (D) in the Challis National Forest and adjacent areas, Idaho. Areas (D1, 02, and 

so forth) of mineral resource potential are described in table 4. 
Age 

Cretaceous to Eocene. 

Deposit Description 

The deposits are mainly replacements along 

fractures and bedding planes of limestone. The ore 

minerals, argentiferous galena, pyrite, chalcopyrite, and 

sphalerite occur as disseminations, clots, and lenses; 

gangue is not abundant and is largely quartz and some 

calcite. Many of the deposits were worked only in the 

oxide zones where iron and manganese oxides, cerussite, 

and cerargyrite are common. The individual orebodies 

are generally tabular and range greatly in size, with none 

larger than a few thousand tons. The type locality for this 

model is in the Windy Peak area (D, fig. 16), Spring 

Mountain district (fig. 4). 

Geochemical Signature 

The Windy Peak area type locality is within the 

Dubois NURE study boundary. No samples were 

collected near the type locality, and thus no geochemical 

signature can be identified with the type locality. A 

geochemical signature commonly associated with polymetallic veins, regardless of terrane, is Zn, Cu, Pb, As, 

Au, Ag, Mn, Ba, Sb, and Bi. 

Geophysical Signature 

Deposits of this type may be detectable by detailed 

electrical methods. In the Windy Peak area the strongly 

oriented, linear magnetic gradient zones suggest 

northeast-trending structural zones that may have 

influenced the distribution of mineralization. 

Assessment Criteria 

1. Presence of carbonate terrane. 

2. Presence of high-angle faults or fractures. 

3. Indication of base- or precious-metal mineralization. 

4. Hypabyssal igneous bodies; also along highangle faults. 

Assessment 

The area (D1) around the mines in the vicinity of 

Windy Peak, Spring Mountain district (fig. 4), in the 

central part of the Lemhi Range, is assigned a high 

potential (H/C). This is the western part of a major 

mining district. A larger area (D3) surrounding D 1 is 

assigned a moderate potential, but with a low level of 

certainty (M/B) because of a lack of information. The 

eastern part (D2) of the Alder Creek district (fig. 4) in 

the White Knob Mountains is assigned a high potential 

(H/C). Much of the lead and zinc production from this 

district was from veins in limestone. A small area of 

limestone (D4) in the western part of the Alder Creek 

district (fig. 4) is assigned a moderate potential with a low 

level of certainty (M/B). The vicinity of the Leadbelt 

mine (D5) in the Lava Creek district (fig. 4) is assigned a 

high potential with low certainty (H/B) for polymetallic 

veins in limestone. This area is along a major thrust fault, 

and mineralization occurs in the overlying limestone and 

in the underlying rocks of the black-shale terrane. 

Hidden orebodies of this type are difficult to 

detect, and there are probably others similar in size and 

grade to those already mined in all of these districts. The 

areas of resource potential for polymetallic veins in 

carbonate rock terrane (D) are shown on plate 3 and 

figure 16 and summarized in table 4. 

Economic Significance 

Lead and silver are supplied primarily from largetonnage domestic and foreign mines. A major change in 

demand or increase in price for these commodities would 

be needed to support operation of small mines. 

Production of gold as a by-product would certainly 

enhance the possibility of development. 

Polymetallic Veins in Tertiary Extrusive 

Terrane (E) 

Commodities, By-products, and Trace Metals 

Silver, lead and zinc; trace to by-product amounts 

of copper, gold, tin or bismuth. 

Host Rocks 

Host rocks are highly altered volcanic rocks 

including flow rock, pyroclastics, and hypabyssal intrusive 

rocks. Rocks in the vicinity of the orebodies are silicified 

(chalcedony), sericitized, pyritized, and locally altered to 

alunite. The rocks in general are bleached light gray and 

have abundant cubes of weathered pyrite. Sericitization 

extends farthest (tens of feet) from the lodes; on the 

outer edges sericitization is shown by partial replacement 

of feldspars by sericite. Near the lodes the original 

texture of the wall rocks is completely obliterated. 

Structural Control 

The deposits are associated with major northwesttrending high-angle faults, especially near the intersection with northeast -trending high-angle faults. The 

Resource Potential- Locatable Minerals 45 
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115°30' 115°00' 

45°00' 

44°00' I EXPLANATION 

RESOURCE POTENTIAL 

D MODERATE 

~E TYPE MINE LOCALITY 

0 5 10 15 20 25 MILES 

\ ~"<:. \!Jt, \'tJ 

?--

• Ketchum 

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114°00' 

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43°30' --......J 

Figure 17. Mineral resource potential map for polymetallic veins in Tertiary extrusive terrane (E) in the Challis National Forest and adjacent areas, Idaho. Areas (E1, E2, 

E3) of mineral resource potential are described in table 4. 
deposits are mostly in minor fissures and fracture zones 

that trend north and west; a few deposits are in minor 

fractures parallel to the major trends of northwest or 

northeast. Intersections of fissure and fracture zones 

contain the larger and higher grade orebodies. 

Age 

Tertiary. 

Deposit Description 

These deposits are characterized by an unusual 

mineral assemblage resulting from several stages of 

mineralization. At the Hornsilver mine (E, fig. 17), Lava 

Creek district, just south of the Forest, the ore minerals 

are grouped into early and late assemblages (Anderson, 

1947b, p. 459). The early assemblage includes chalcedony, sericite, galena, sphalerite, pyrite, marcasite, and 

wurtzite. These minerals occur as fillings and replacements along fissures and complexly fractured rock. The 

ore minerals form small shoots and scattered masses 

along the fissures or breccia zones and are disseminated 

in the altered wall rock. The ore zones are very irregular 

and range from stringers to fillings and replacements in 

breccia zones that are several feet wide. The fissures and 

breccia fillings generally do not have distinct boundaries 

with the altered country rock. The late assemblage 

includes quartz, barite, pyrite, stannite, tetrahedrite, 

famatinite (Cu3SbS4 ), enargite, klaprothite [shown to be 

a mixture of emplectite (CuBiSz) and wittichenite 

(Cu3BiS3)], chalcopyrite, and aikinite (PbCuBiS3). The 

late-assemblage minerals are superimposed on the earlyassemblage minerals in previously unfilled openings and 

along fractures. Because the various stages of mineralization were not entirely overlapping, there are individual 

lodes rich in certain metals such as zinc, copper, iron, 

lead-zinc, tin-bismuth, silver, gold, and tungsten. The 

deposits in volcanic rocks are zoned with a base-metalrich core surrounded by a precious-metal-rich rim. 

Geochemical Signature 

The Hornsilver mine type locality is within the 

Idaho Falls NURE study boundary (fig. 5). Streamsediment samples were anomalous in Ag and Cu (table 

7). Few samples were collected near the type locality. A 

geochemical signature commonly associated with polymetallic veins regardless of terrane is Zn, Cu, Pb, As, Au, 

Ag, Mn, Ba, Sb, and Bi. 

Geophysical Signature 

Detailed magnetic and electrical methods may be 

useful in delineating major structures and extensions 

beneath and in altered volcanic rocks. In the Sheep 

Mountain-Bowery Peak area in the White CloudBoulder Road less Area (fig. 5) the magnetic data suggest 

that the outcrops of dikes and hypabyssal bodies may be 

underlain by a large intrusive body at depth. Magnetic 

data in the vicinity of Iron Bog Creek, north of the Lava 

Creek district (fig. 4 ), are complex and show linear trends 

and high gradients associated with rocks of the Challis 

Volcanic Group. It is uncertain whether the positive 

anomaly is related to an intrusive at depth beneath the 

volcanic rocks. 

Assessment Criteria 

1. Regional high-angle faults. 

2 Rocks of the Challis Volcanic Group. 

3. Zones of alteration including sericitization and 

silicification. 

4. Evidence of precious- or base-metal mineralization. 

5. Presence of felsic hypabyssal bodies. 

Assessment 

The type locality for this deposit model is in the 

Champagne Creek area (E, fig. 17), Lava Creek district 

(fig. 4), just south of the southwestern part of the Forest. 

In the Lava Creek district polymetallic vein deposits 

occur in rocks of the Challis Volcanic Group and in 

underlying Paleozoic sedimentary rocks. Deposits in the 

sedimentary rocks were described as polymetallic veins in 

black-shale and carbonate terranes, and they are similar 

to those located in Leadbelt and Iron Bog Creeks just 

north of the Lava Creek district (fig. 4). An area (E3) 

around Sheep Mountain-Bowery Peak as described by 

Fisher, May, and others (1983) is assigned a moderate 

potential (M/C) for this type of deposit. Two areas of 

moderate potential but low certainty (M/B) are shown 

for this deposit type. The first area (E1 ), which is along 

the eastern side of Iron Bog Creek, contains numerous 

hypabyssal bodies and altered volcanic rocks. A prospect 

along the east side of Iron Bog Creek is not accessible, 

but the dump contains about equal amounts of 

sedimentary and altered volcanic rocks. The second area 

(E2) is along Lehman Creek, northwest of the Mackay 

Reservoir, where there is extensive silicification along a 

northwest-trending fault zone. Both areas are given low 

certainty because the alteration types and patterns in the 

volcanic rocks and the geochemistry are unknown. The 

areas of resource potential for polymetallic veins in 

Tertiary extrusive terrane (E) are shown on plate 3 and 

figure 17 and summarized in table 4. 

Economic Significance 

Lead and silver are supplied primarily from largetonnage domestic and foreign mines. A major change in 

Resource Potential- Locatable Minerals 47 
demand or increase in price for these commodities would 

be needed to support operation of small mines. 

Production of gold as a by-product would certainly 

enhance the possibility of development. 

Precious-Metal Veins (F) 

Commodities, By-products, and Trace Metals 

Gold and silver; lead, copper, and zinc are potential 

by-products. 

Host Rocks 

Veins are mainly in Cretaceous and Tertiary 

igneous rocks that have been moderately to intensely 

hydrothermally altered. Propylitized and sericitized rocks 

are widespread. Close to the veins the rocks have been 

silicified and argillized. 

Structural Control 

Most of the veins are in the trans-Challis fault 

system and along northeast- or northwest-trending highangle fractures. Ore is in fissures and breccia fillings. Ore 

is richest close to the premineralland surface, and values 

diminish with dept~ (Fisher and others, 1987). 

Lithologic Control 

The orebodies are commonly within, along side, or 

near dikes and stocks of Eocene age. 

Age 

Tertiary, probably Eocene. 

Deposit Description 

Deposits are small lenticular pods or lenses more 

than 100 ft across and 3 ft or more thick. Quartz, the 

dominant gangue mineral, ranges from cryptocrystalline 

to coarsely crystalline and is sometimes comb structured. 

Most of the precious metals are in electrum. Native gold, 

native silver, auriferous pyrite, and several silver-bearing 

sulfide minerals are also present. Other gangue minerals 

are fine-grained base-metal sulfides, calcite, adularia, 

siderite, barite, pyrite, pyrrhotite, and arsenopyrite. The 

deposits are massive fissure fillings, breccias, and 

aggregates of veinlets. Ore minerals occur in clusters, 

thin layers, lenses, and disseminations in vein material 

and altered wall rock. The type mine locality for this 

model is at the Lucky Boy mine (F, fig. 18), Yankee Fork 

district (fig. 4). 

Geochemical Signature 

The Lucky Boy mine type locality is within the 

geochemical survey for the USGS Challis CUSMAP 

project (fig. 5). Samples of both the heavy-mineral 

fraction of the stream sediments and stream sediments 

have anomalous concentrations of Ag. The heavy 

minerals also contain anomalous concentrations of Au, 

Sn, Ba, Bi, Cu, Mo, and Pb (table 7). A geochemical 

signature commonly associated with precious-metal veins 

regardless of terrane is Au, As, Sb, Hg, Ag, Pb, Zn, Cu, 

W, Bi, Te, and Tl. 

Geophysical Signature 

The deposits themselves have no geophysical 

expression, but the ore-controlling faults might be 

detected by detailed magnetic surveys. Regional 

magnetic data shows the northeast-trending structures of 

the trans-Challis fault system. The Lucky Boy mine (F, 

fig. 18) occurs at the intersection of strong east-west and 

northeast linear magnetic trends. Delineation of other 

similar intersections may be a useful exploration tool. 

Assessment Criteria 

1. Evidence of precious-metal mineralization. 

2. Presence of planar high-angle faults or fractures. 

3. Presence of Tertiary felsic hypabyssal intrusive 

rocks, including dikes, stocks, and plugs. 

4. Presence of open-space filling materials m 

faults, and fractures. 

5. Proximity to trans-Challis fault system. 

Assessment 

Deposits of this type seem to be confined mainly to 

the trans-Challis fault system, but there may be some 

potential for deposits of this type along parallel fault 

systems. The potential is for precious metals within the 

vein systems and for broad zones of dissemination in 

altered rock. One large area (F1) of high potential (HID) 

extends from Stanley northeast through the Yankee Fork 

district (fig. 4). Two small areas (F1) of high potential 

(HID) are shown in the Meyer's Cove area, Gravel 

Range district (fig. 4 ). Four small areas (F2) of moderate 

48 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
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RESOURCE POTENTIAL 

- HIGH 

D MODERATE 

I ~F TYPE MINE LOCALITY 

I 0 5 10 15 20 25 MILES I I I I I I 

4JOJ0' 

Figure 18. Mineral resource potential map for precious-metal veins (F) in the Challis National Forest and adjacent areas, Idaho. Areas (F1, F2) of mineral resource 

potential are described in table 4. 
potential (MID) are shown within the trans-Challis fault 

system. The areas of resource potential for preciousmetal veins are shown on plate 3 and figure 18 and 

summarized in table 4. 

Economic Significance 

The important gold production in the Western 

United States, and much of the World, is from largetonnage, low-grade deposits and not from smaller, higher 

grade deposits of this type. This trend will probably 

continue into the future. However, as long as the price 

remains high, smaller operations on deposits of this type 

could be viable. 

Base-Metal Veins (G) 

Commodities, By-products, and Trace Metals 

Zinc, lead, copper, silver, and gold. 

Host Rocks 

The veins are in granitic rocks of the Idaho batholith and in metasedimentary roof pendants. One deposit 

is in a phyllitic member of the Yellowjacket Formation. 

Hydrothermally altered rock displays argillic and sericitic 

alteration of the feldspars with some silicification near 

the veins. 

Structural Control 

The deposits are along high-angle shear zones and 

fractures, but not those of a regional trend. 

Age 

Cretaceous, probably the same age as and related 

to the Idaho batholith. 

Deposit Description 

The deposits are mainly small pods and lenses 1 ft 

or so thick and tens of feet long. A few are as much as 300 

ft long and 5 ft wide and extend 700 ft downdip. Ore 

minerals are chiefly galena, sphalerite, and chalcopyrite 

in a gangue of quartz, siderite, calcite, pyrite, pyrrhotite, 

and arsenopyrite. The ore is in layers, pods, stringers, and 

disseminations in the vein material. Precious metals are 

locally abundant. Vein contacts with the wall rocks are 

sharp everywhere. The Sea Foam mine (G, fig. 19), Sea 

Foam district, is the type locality of this model. 

Geochemical Signature 

The Sea Foam type mine locality is within the 

boundaries of the geochemical survey conducted specifically for the USGS Challis CUSMAP project (fig. 5). 

Samples of both the heavy-mineral fraction of the stream 

sediments and stream sediments have anomalous concentrations of Ag, Pb, B, and Cu. The heavy-mineral 

fraction also contains anomalous amounts of Bi, Sn, Au, 

Mo, W, and Th. A geochemical signature commonly 

associated with base-metal veins is Zn, Cu, Pb, As, Au, 

Ag, Mn, Ba, Sb, and Bi. 

Geophysical Signature 

High-angle shear zones and fractures, where 

mineralized, can be mapped with detailed magnetic and 

electrical surveys. 

Assessment Criteria 

1. Evidence of base and precious metals. 

2. Presence of high-angle planar fractures or 

faults. 

3. Quartz is the principal gangue mineral. 

4. Proximity to granitic rocks of the Idaho batholith. 

Assessment 

Deposits of this type are largely confined to the 

Idaho batholith or close proximity to it. Known deposits 

are small and with few exceptions have not been 

significant producers. Two areas (G1) of high potential 

(HID) and two areas (G2) of moderate potential (MID) 

are defined. The areas of resource potential for basemetal veins (G) are shown on plate 3 and figure 19 and 

summarized in table 4. 

Economic Significance 

Base metals are supplied primarily from foreign 

sources. A major change in the supply and demand of 

these commodities would be needed to support operation of small base-metal mines. 

Vein Uranium Deposits (H) 

Commodities, By-products, and Trace Metals 

Uranium; trace amounts of gold, silver, antimony, 

lead, zinc, and molybdenum. 

50 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
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Figure 19. Mineral resource potential map for base-metal veins (G) in the Challis National Forest and adjacent areas, Idaho. Areas (G1, G2) of mineral resource potential 

are described in table 4. 
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Figure 20. Mineral resource potential map for vein uranium deposits (H) in the Challis National Forest and adjacent areas, Idaho. Areas (H1, H2) of mineral resource 

potential are described in table 4. 
Host Rocks 

Known deposits are in the granitic rocks of the 

Cretaceous Idaho batholith, Tertiary granite, dolomitic 

marble, graphitic argillite, and quartzite. 

Structural Control 

The deposits are in or along fracture zones. 

lithologic Control 

The deposits in the Stanley area are commonly at 

the intersection of aplitic or pegmatitic dikes and steeply 

dipping fractures. 

Age 

Unknown, probably Tertiary, although those near 

Stanley could be related to pegmatites of the Cretaceous 

Idaho batholith. 

Deposit Description 

Most of the occurrences consist of secondary 

uranium minerals with or without quartz along fault 

systems. The occurrence at the Sullivan uranium prospect on the Middle Fork of the Salmon River, in the 

north-central part of the Forest, includes sugary quartz, 

fluorite, arsenopyrite or pyrrhotite, thorite(?), chalcopyrite, azurite, and malachite. The deposits in the Stanley 

area are pitchblende stringers with or without quartz. 

Uraninite (mostly as pitchblende), uranophane, metaautunite, and rare coffinite and brannerite are the 

uranium minerals. Gangue is quartz and chalcedony with 

minor amounts of pyrite, chalcopyrite, stibnite, galena, 

sphalerite, molybdenite, gold, and silver. A variety of 

secondary uranium minerals also occur in these deposits. 

The Lightning mines (H, fig. 20), Stanley district (fig. 4 ), 

are the type locality for this model. 

Geochemical Signature 

The Lightning mines type locality is within the 

boundaries of the geochemical survey conducted 

specifically for the USGS Challis CUSMAP project 

(fig. 5). No elements were anomalous in the stream 

sediments, but the elements Th, Mo, Pb, and Sn were 

anomalous in the heavy-mineral fraction of the stream 

sediments (table 7). A geochemical signature commonly 

associated with uranium mineralization in epithermal 

veins is U, Hg, As, Sb, F, Mo, and W. This common 

signature does not appear to be reflected by the signature 

of the heavy minerals collected near the type mine 

locality. 

Geophysical Signature 

No significant magnetic signature. Gamma-ray 

spectrometer surveys may be applicable for exploration. 

Assessment Criteria 

1. Evidence of uranium mineralization. 

2. Presence of steeply dipping fractures and 

joints. 

3. Presence of aplite or pegmatite dikes in 

medium- to coarse-grained granites (for 

Stanley-type deposits). 

Assessment 

Assessment for this model type is only for that 

portion of the Forest within the Challis 1 ox 2° quadrangle. Data are inadequate for assessment of the 

remainder of the Forest. The type of uranium vein 

deposit with resource potential is that found in the 

Stanley area. One area (Hl) around the Stanley deposits 

is assigned a high potential (HID), and another area (H2) 

to the north is assigned a moderate potential (MID). The 

other types of uranium vein deposits are thought to have 

low resource potential in the Challis National Forest. The 

areas of resource potential for vein uranium deposits (H) 

are shown on plate 3 and figure 20 and summarized in 

table 4. 

Economic Significance 

The uranium industry in the United States is 

currently nearly inactive and may remain in this condition 

in the near future. It would take a major increase in the 

demand for uranium for small mines to become 

competitive. 

Tungsten Stockwork and 

Vein Deposits (I) 

Commodities, By-products, and Trace Metals 

Tungsten; antimony, gold, silver, or molybdenum 

are potential by-products. 

Resource Potential- Locatable Minerals 53 
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Figure 21. Mineral resource potential map for tungsten stockwork and vein deposits (I) in the Challis National Forest and adjacent areas, Idaho. Areas (11-14) of mineral 

resource potential are described in table 4. 
Host Rocks 

Host rocks are mainly altered granitic plutonic 

rocks and sedimentary and metasedimentary rocks 

including quartzitic and carbonate-rich rocks. Wall rock 

is strongly brecciated, silicified, and sericitized. The plutonic rock is bleached and vuggy, and the feldspars have 

been altered to clay. 

Structural Control 

These deposits are localized along major highangle faults, most of which trend north to northwest. 

Many of these faults have strong shear components. 

Deposits are best developed at the junctions of faults and 

their eastward-branching splays. 

Lithologic Control 

The vein deposits of the Ima mine, Blue Wing 

district (fig. 4), which is the major tungsten producer in 

the Forest, are above and genetically related to a felsic 

intrusive body. There are several skarn-type tungsten 

deposits, described elsewhere, in the Forest that are 

associated with similar intrusive bodies. 

Age 

Cretaceous and Tertiary. 

Deposit Description 

The deposits are fissure-filled quartz veins and 

veinlets that form a stockwork pattern in broad areas of 

shearing. In addition to quartz, the veins contain variable 

amounts of fluorite, arsenopyrite, calcite, rhodochrosite, 

sericite, vein feldspar, pyrite, sphalerite, chalcopyrite, 

tetrahedrite, galena, and cinnabar. Ore minerals are 

wolframite (including ferberite and huebnerite ), some 

scheelite, stibnite, gold, and silver. Manganese oxides are 

ubiquitous. The ore minerals occur in the veins and 

stockworks, as replacement of carbonate minerals in the 

vicinity of calcareous rocks, and as a coating on the 

manganese oxides. Some of the deposits are related to 

stockwork molybdenum deposits in porphyritic plutons. 

The Ima mine (I, fig. 21), Blue Wing district (fig. 4), is 

the type locality for this deposit model. 

Geochemical Signature 

The Ima mine type locality is within the Dubois 

NURE study boundary (fig. 5). A stream sediment 

collected from the alluvium in the valley adjacent to the 

Ima mine had anomalous concentrations of Cu, Pb, Sb, 

and W (table 7). This signature is based on only one 

sample and may reflect contamination from mine dump 

material. A geochemical signature commonly associated 

with tungsten veins is W, Mo, Sn, Bi, As, Cu, Pb, Zn, Be, 

and F. 

Geophysical Signature 

The deposits themselves have no geophysical 

expression, but the major shear zones and related 

intrusive bodies show on regional magnetic and gravity 

surveys. 

Assessment Criteria 

1. North-trending major shear-fault zones. 

2. Secondary silica enrichment. 

3. Evidence of tungsten mineralization. 

4. Proximity to plutonic rock. 

Assessment 

Vein tungsten deposits are part of a group of 

tungsten deposits in south-central Idaho that extend from 

the Craters of the Moon northwestward through the 

Challis National Forest (Cook, 1956). Tungsten vein and 

skarn deposits, described under skarn deposits, are 

genetically related. Many of the vein and skarn deposits 

are confined to rocks of the Idaho batholith and related 

stocks, whereas others are associated with Tertiary plutons. The potential for tungsten vein and skarn deposits is 

difficult to assess in view of the present state of 

knowledge. There are numerous tungsten occurrences, 

some of which have had production, and tungsten 

geochemical anomalies are common, especially in rocks 

of the Idaho batholith. Much of the area of the Idaho 

batholith has potential for small tungsten deposits mainly 

where major north-trending high-angle faults cut 

carbonate inclusions. Mapping detail is not sufficient to 

delineate individual locations. One area (Il) of high 

potential (H/C) is shown along the northwest border of 

the Forest. A small area (I2) of high potential (H/C) is in 

the vicinity of the Ima mine. A larger area (I3) of 

moderate potential (M/B) is drawn to include a set of 

northeast-trending structures in the vicinity of the Ima 

mine. Several areas (I4) of moderate potential (M/C) 

generally correspond to areas of potential for stockwo.rk 

molybdenum deposits. The areas of resource potential 

for tungsten stockwork and vein deposits (I) are shown 

on plate 3 and figure 21 and summarized in table 4. 

Economic Significance 

Tungsten is a strategic and critical metal; the 

United States is almost entirely dependent upon foreign 

Resource Potential- Locatable Minerals 55 
sources for supplies. Although known foreign deposits 

are very large, smaller isolated, domestic tungsten 

deposits may be in critical demand in times of national 

emergency. 

Stockwork Molybd~num Deposits (J) 

Commodities, By-products, and Trace Metals 

Molybdenum; copper, silver, or gold are potential 

by-products. 

Host Rocks 

The deposits are in or associated with gramtic 

plutons that range from quartz diorite to granite and 

hypabyssal bodies of rhyolite. The deposits may be 

entirely within the intrusive rock, entirely within the 

adjacent metamorphosed country rock, or within both. 

The ore is in pods of intensely silicified and pyritized rock 

surrounded by envelopes of potassic, argillic, and propylitic altered rocks. 

Structural Control 

Stockwork veins may be controlled by joint 

patterns within the pluton or by bedding, joints, or faults 

outside the pluton. Some of the deposits associated with 

hypabyssal rhyolite bodies are aligned along major highangle fault systems as are the hypabyssal bodies. 

Lithologic Control 

These deposits are all associated with low-fluorine 

1-type compositionally zoned or expanded granitic magmatism, which is characterized by subduction-related 

plutons with low fluorine concentrations, high ratios of 

strontium to rubidium, and low niobium concentrations 

as compared to average granites. 

Age 

Cretaceous and Tertiary. 

Deposit Description 

The deposits consist of stockworks of quartz veins 

and veinlets containing molybdenite and pyrite and 

locally chalcopyrite, galena, scheelite, arsenopyrite, stibnite, pyrrhotite, biotite, muscovite, gold, and silver. 

Molybdenite occurs with the quartz stockworks as 

rosettes, flakes, fracture fillings, intercalations with 

secondary mica, and selvages, and as disseminations in 

tactite. The Cretaceous orebodies are arched or domed, 

elongate tabular in shape, and associated with plutons. 

The best known Cretaceous orebody is at Thompson 

Creek (Ja, fig. 22), Bayhorse district (fig. 4). The Tertiary 

deposits are elongate oval in shape and generally within 

hypabyssal bodies. The better known Tertiary deposits 

are located a few miles south of the Challis National 

Forest at the Little Falls and CUMO Prospects. The 

Thompson Creek mine (Ja, fig. 22) is the type locality for 

Cretaceous stockwork molybdenum, and the WaltonWhite Mountain prospect (Jb, fig. 22) in the Alto district 

(fig. 4) is the type locality for Tertiary stockwork 

molybdenum. 

Geochemical Signature 

The Thompson Creek type locality is within the 

boundaries of a geochemical survey conducted specifically for the USGS Challis CUSMAP project (fig. 5). 

Samples of both the heavy-mineral fraction of the stream 

sediments and the stream sediments had anomalous 

concentrations of W, Mo, Bi, and Cu. The stream 

sediments were also anomalous in Ag, and the heavy 

minerals were also anomalous in Pb, Sn, B, and Th (table 

7). The Walton-White Mountain type locality is within 

the boundary of the Boulder-Pioneer Wilderness Study 

Area (fig. 5). Stream-sediment samples from this area 

had anomalous concentrations of Cu, Pb, Mo, Ag, and 

Zn. A geochemical signature commonly associated with 

low-fluorine porphyry molybdenum deposits is W, Mo, 

Cu, Au, Ag, Pb, Zn, and F (less than 1,000 ppm). 

Geophysical Signature 

The known Cretaceous deposits at Thompson 

Creek (Ja, fig. 22) and in the Boulder Creek district (fig. 

4) are on the flanks of positive magnetic anomalies that 

probably indicate buried granitic plutons. The Tertiary 

intrusive at the Walton-White Mountain prospect (Jb, 

fig. 22) is also on the flank of a large positive magnetic 

anomaly. However, the Tertiary intrusive at the lma 

mine, Blue Wing district (fig. 4), exhibits only low 

magnetic gradients, possibly due to insufficient resolution of the ~urvey. 

Assessme~t Criteria 

1. Proximity to granitic plutons or hypabyssal 

bodies, especially differentiated or expanded, 

low-fluorine, 1-type granitic plutons or multiple plutons. 

2. Extensive hydrothermal alteration in and 

around the deposit. 

56 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
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Figure 22. Mineral resource potential map for stockwork molybdenum deposits (J) in the Challis National Forest and adjacent areas, Idaho. Areas (J1, J2, and so forth) 

of mineral resource potential are described in table 4. 
3. Presence of molybdenite in veins and veinlet 

stockworks and as disseminated flakes. 

4. Local anomalous molybdenum concentrations. 

Assessment 

A late Mesozoic-Tertiary magmatic arc extending 

from southeast California to southeast Alaska contains 

many economically significant molybdenum stockwork 

deposits. This broad arc extends through the Challis 

National Forest. In addition to numerous small deposits 

and occurrences associated with Tertiary granitoid 

stocks, there are two large, well-known, molybdenum 

stockwork deposits and numerous prospects associated 

with Cretaceous granitoid stocks in the Forest. Two areas 

(J1, J2) of high potential and certainty level of D (HID) 

are indicated. Area J1 is in the vicinity of the Thompson 

Creek molybdenum deposit (Ja, fig. 22), and area J2 

contains the molybdenum deposit at Little Boulder 

Creek in the Boulder Creek district (fig. 4 ). One area 

(J3) of high potential with a certainty level of B (H/B) is 

drawn around the vicinity of the Ima tungsten mine in the 

Blue Wing district (fig. 4). The intrusive below the 

tungsten veins contains stockwork molybdenum, but the 

extent of mineralization and alteration is unknown. 

Several areas of moderate potential are shown; those 

marked J4 (MID) are for Cretaceous deposits, and those 

marked J5 (M/C) are for Tertiary deposits. The areas of 

resource potential for stockwork molybdenum deposits 

(J) are shown on plate 3 and figure 22 and summarized in 

table 4. 

Economic Significance 

One of the large Cretaceous stockwork molybdenum deposits, Thompson Creek, is presently (July 

1988) being mined. Molybdenum is a commodity needed 

by technologically advanced societies, and although there 

is currently an overabundance of supply in the world, 

many of the deposits discussed here will probably be 

exploited in the future. 

High-Level, Rhyolite-Hosted, 

Precious-Metal Deposits (K) 

Commodities, By-products, and Trace Metals 

Gold and silver. 

Host Rocks 

The deposits are in high-level rhyolite intrusives 

and the surrounding, altered country rock. The term 

"high-level" implies uncertainty as to how close these 

intrusives came to the surface-some breached it, others 

did not (Fisher and Johnson, 1987, p. 163). Where 

mineralized, the rhyolites are bleached, iron stained, and 

silicified. Sanidine and quartz are the most abundant 

phenocryst minerals. 

Lithologic Control 

The intrusive rocks are massive to flow-laminated, 

porphyritic to aphyric, alkali rhyolites that were intruded 

as domes or dikes. 

Structural Control 

The rhyolite bodies are along or near bounding 

faults of major volcanotectonic features, mainly within 

the trans-Challis fault system. The individual mineralized 

zones are on fracture systems and shattered zones that 

reflect the major structural trends. 

Age 

Tertiary, Eocene or younger. 

Deposit Description 

Deposits are quartz-veinlet stockwork zones and 

disseminations in altered rock, in places associated with 

major quartz veins. Ore minerals are electrum, native 

gold, and native silver, with a gangue of secondary silica, 

clay minerals, and pyrite, and minor amounts of zircon, 

apatite, fluorite, and amethystine quartz. The orebodies 

are irregular in shape but generally elongate and narrow 

downward into fault systems. Mineralized rock occurs 

mainly in the rhyolites but also in the country rock. The 

type locality for this model is the Golden Sunbeam mine 

(K, fig. 23), Yankee Fork district (fig. 4). 

Geochemical Signature 

The Golden Sunbeam mine type locality is within 

the boundary of a geochemical survey conducted 

specifically for the USGS Challis CUSMAP project 

(fig. 5). Samples of both the heavy-mineral fraction of the 

stream sediments and the stream sediments had 

anomalous concentrations of Ag, Cu, and Pb. The stream 

sediments were also anomalous in Be, Mo, and Zn, and 

the heavy minerals were also anomalous in Au, As, Ba, 

Sn, and W (table 7). A geochemical signature commonly 

associated with precious-metal veins is Au, As, Sb, Hg, 

Ag, Pb, Zn, Cu, W, Bi, Te, and Tl. 

58 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
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Figure 23. Mineral resource potential map for high-level, rhyolite-hosted, precious-metal deposits (K) in the Challis National Forest and adjacent areas, Idaho. Areas 

(K1, K2) of mineral resource potential are described in table 4. 
Geophysical Signature 

The deposits themselves have no geophysical 

expression, but some major faults show on regional 

magnetic and gravity surveys. The magnetic data exhibit 

regional northeast trends and intersections with northwest and east trends in the areas of mineral resource 

potential (K1, K2). 

Assessment Criteria 

1. Evidence of precicus-metal mineralization. 

2. In or associated with high-level rhyolite bodies. 

3. In or near bounding faults or major volcanotectonic features. 

4. Presence of anomalous concentrations of secondary and remobilized silica. 

5. Within the trans-Challis fault system, especially in the north-central parts of the Forest. 

Assessment 

Assessment for this model type is only for that 

portion of the Forest within the Challis 1 o x 2° quadrangle. Data are not adequate for an assessment of the 

remainder of the Forest. Much of the area of Challis 

Volcanic Group in the trans-Challis fault zone has 

moderate or high potential for discovery of deposits of 

this type. High potential (H/C) is shown as area K1, and 

moderate potential (M/C) is shown as area K2. The areas 

of resource potential for high-level, rhyolite-hosted, 

precious-metal deposits (K) are shown on plate 3 and 

figure 23 and summarized on table 4. 

Economic Significance 

Precious metals are currently in demand, and 

throughout the Western United States they are being 

economically extracted from large low-grade deposits. 

This mining trend and demand will probably continue 

into the future. 

Polymetallic Skarn Deposits (L) 

Commodities, By-products, and Trace Metals 

Tungsten, copper, zinc, lead, and silver; trace 

amounts of gold and bismuth. 

Host Rocks 

Host rocks are carbonate-bearing rocks, mainly 

clean to impure limestone, carbonaceous micritic 

limestone, or limey sandstone, in contact with intrusive 

rocks. Carbonate rocks in the contact zone are altered to 

Fe-Mg-Mn-silicate mineral assemblages that may 

include: diopside-hedenbergite, grossularite-andradite, 

wollastonite, idocrase, calcite, epidote, chlorite, and 

quartz. 

Lithologic Control 

The deposits occur where receptive carbonate 

strata were replaced by silicate and ore minerals within, 

next to, or close to a felsic intrusive body. 

Structural Control 

The contact between the intrusive body and the 

carbonate host rock, local bedding planes, faults, and 

breccia zones controlled location of the orebodies. At the 

Empire mine Alder Creek district (fig. 4) the oreforming solutions apparently penetrated the skarn rock 

along preexisting fractures (Ross, 1930, p. 16). 

Age 

Same as that of the related intrusive body; variable, 

from Cretaceous to Miocene. 

Deposit Description 

This classification includes several types of skarn 

(tactite) deposits of different ages and igneous rock 

associations that could be further subdivided if data were 

adequate. These deposits vary from irregular- to podshaped to tabular to pipelike bodies, in which the ore may 

be coarse to fine grained. Ore deposits in skarn are 

massive replacements, disseminations, podiform bodies, 

stringers, or fracture fillings. In some deposits, such as at 

the Empire mine, part of the ore occurs as replacement 

of altered intrusive rock. Associated polymetallic veins 

are common. Deposits range in size from small pods to 

bodies as much as 1,000 ft long. Ore minerals include 

scheelite, sphalerite, molybdenite, chalcopyrite, galena, 

tetrahedrite, and bornite; gangue minerals include pyrite, 

pyrrhotite, arsenopyrite, specularite, calcite, fluorite, 

magnetite, and quartz, in addition to the silicate skarn 

minerals. At the Empire mine the principal commodity 

produced from skarn deposits was copper, with minor 

lead, zinc, silver, and gold. Skarns in the northwestern 

part of the Forest have produced mainly tungsten. In the 

Windy Peak area, Spring Mountain district (fig. 4), some 

skarns are magnetite and hematite rich. A large variety of 

minerals may occur in the weathered zone of skarns, 

including azurite, malachite, brochantite, calamine, chalcanthite, chrysocolla, native copper, copper pitch, covellite, cuprite, gypsum, hematite, limonite, kaolinite, opal, 

60 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
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mineral resource potential are described in table 4. 
pyrolusite, smithsonite, and tenorite. The type locality for 

base-metal skarns associated with Tertiary intrusive 

bodies is the Empire mine (La, fig. 24) Alder Creek 

district (fig. 4) and that for tungsten skarns is the 

Springfield mine (Lb, fig. 24) just south of the Yellow 

Pine district (fig. 4). 

Geochemical Signature 

The Empire mine type locality is within the 

boundary of the Idaho Falls NURE study area (fig. 5). 

Few samples were collected near the type mine locality, 

but one stream-sediment sample collected near the type 

locality had anomalous Cu (table 7). The Springfield 

mine type locality is within the boundary of the Idaho 

Primitive Area (fig. 5). Stream-sediment samples collected near the type locality had anomalous concentrations of Zn, Mn, Cu, Mo, Be, and As (table 7). A 

geochemical signature commonly associated with polymetallic skarn deposits is Zn, Pb, Mn, Cu, Co, Au, Ag, 

As, W, Sn, F, and Be. 

Geophysical Signature 

Magnetic anomalies indicate intrusive bodies in 

Paleozoic rocks in several areas, namely the Alto district, 

Bayhorse district, Star Hope area of the Copper Basin 

district, and Windy Peak area of the Spring Mountain 

district (fig. 4). The magnetic data suggest that the 

Mackay stock in the White Knob Mountains is more 

extensive to the west in the subsurface in Paleozoic 

carbonate rocks than is shown by its surface exposure. 

The individual bodies would probably have local electrical and magnetic expression, depending upon the 

mineralogy and composition of the host rock. 

Assessment Criteria 

1. Intrusive contact with sedimentary or metasedimentary carbonate-bearing strata. 

2. Skarn mineral assemblage. 

3. Geochemical anomalies including W, Zn, Cu, 

Pb, or Mo. 

Assessment 

The Forest has numerous intrusive bodies in 

contact with carbonate strata, many of which have skarn 

mineral assemblages in their border zones. Although 

only a few of the numerous prospects have produced ore, 

there is potential for significant deposits of this type. A 

large area (L7) underlain by the Idaho batholith is 

assigned moderate potential (MID) for tungsten skarn 

deposits in calcareous roof pendants. Several small areas 

(L8) of high potential (HID) are drawn around Tertiary 

intrusive bodies in the northwestern part of the Forest. 

Areas L5 and L6 are moderate (MID) and high (HID) 

potential areas, respectively, in the black-shale belt. The 

black-shale belt contains possible ore-receptive (host) 

carbonate beds, source beds for metals, and numerous 

felsic intrusive bodies. Areas marked L4 have moderate 

potential (M/B) for contact skarn deposits at depth. Area 

L3 (M/C) is a special case that represents the Wildhorse 

tungsten deposits which are in small, isolated tactite 

lenses in a gneissic intrusive. The areas (Ll) around the 

Empire mine (La, fig. 24) and Copper Basin mine, Alder 

Creek district (fig. 4 ), are assigned a high potential 

(H/C). A larger area in the White Knob Mountains (L2) 

is assigned moderate potential (M/C). The Windy Peak 

area (L9), Spring Mountain district (fig. 4), is assigned a 

moderate potential (M/B) with low certainty level 

because of the lack of information on deposit types. The 

areas of resource potential for polymetallic skarn 

deposits (L) are shown on plate 3 and figure 24 and 

summarized in table 4. 

Economic Significance 

See discussions under tungsten stockwork and vein 

deposits (I) and base-metal veins (G). 

Irregular Replacements of Base and 

Precious Metals (M) 

Commodities, By-products, and Trace Metals 

Silver, lead, and zinc; copper and gold are byproducts. 

Host Rocks 

The ores occur in selectively replaced carbonate 

strata of the Bayhorse Dolomite, Ella Dolomite, and 

Saturday Mountain Formation. The host rocks are all 

calcareous or dolomitic and contain various amounts of 

impurities such as sand or silt. There was local dolomitization in the vicinity of orebodies but no pervasive 

hydrothermal alteration. 

Lithologic Control 

Impervious shale zones and siltstones trapped 

ascending ore-forming solutions in the underlying carbonate strata. 

62 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
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115°30' 115°00' 113°00' 112°45' 

45°00'~-------------.------ r-------------------~~;------- -----,~----------~~----~ 114°00' 

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RESOURCE POTENTIAL 

- HIGH 

D MODERATE 

~M TYPE MINE LOCALITY 

I 0 5 10 15 20 25 MILES I I I I I I 

43°30' 

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z 

Figure 25. Mineral resource potential map for irregular replacements of base and precious metals (M) in the Challis National Forest and adjacent areas, Idaho. Areas 

(M1, M2, M3) of mineral resource potential are described in table 4. 
Structural Control 

Steep faults, shear zones, and brecciated zones 

served as channels for ore-forming solutions. Thrust 

faults in some areas placed impervious strata over the 

receptive carbonate beds. Anticlinal folds formed large 

solution traps below the impervious strata. 

Age 

Deposits in the Bayhorse district (fig. 4) are 

thought to be of Late Cretaceous age and related to the 

Idaho batholith (Fisher and Johnson, 1987). Potential 

deposits in other areas could be Cretaceous or Tertiary. 

Deposit Description 

Deposits are elongated lenses or ovoid pipelike 

bodies that follow the bedding of the host rock but are 

generally very irregular and discontinous. Ore occurs as 

numerous veinlets, disseminations, breccia fillings, and 

massive or discontinous replacements. Primary ore 

minerals are galena, tetrahedrite, sphalerite, and minor 

chalcopyrite, which have been locally oxidized to cerussite, anglesite, cerargyrite, and smithsonite. Gangue is 

quartz, barite, calcite, fluorite, and pyrite. Grade ranges 

from a few percent lead and zinc and a few ounces per 

ton of silver to 30-40 percent lead and 40-60 ounces per 

ton of silver. The type locality for this model is the 

Clayton Silver mine (M, fig. 25), Bay horse district (fig. 4 ). 

Geochemical Signature 

The Clayton Silver mine type locality is within the 

boundary of a geochemical survey conducted specifically 

for the USGS Challis CUSMAP project (fig. 5). Samples 

of both the heavy-mineral fraction of the stream 

sediments and the stream sediments had anomalous 

concentrations of B, Ag, Cu, Zn, and Pb. The stream 

sediments were also anomalous in As, and the heavy 

minerals were also anomalous in Ba, Bi, Mo, Cd, Sn, and 

W (table 7). A geochemical signature commonly 

associated with polymetallic replacement deposits is Cu, 

Zn, Pb, Mn, Ag, Au, As, Sb, Bi, and Ba. 

Geophysical Signature 

None known, but local detailed electrical surveys 

might detect individual orebodies. 

Assessment Criteria 

1. Presence of carbonate strata, especially in the 

Bayhorse Dolomite, Ella Dolomite, or Saturday Mountain Formation. 

2. Steep north-trending faults. 

3. Evidence of base- and precious-metal mineralization. 

Assessment 

Three areas (M1) classified as high potential 

(HID) are in the vicinity of known deposits in the 

Bayhorse Mining district (fig. 4). The Windy Peak area 

(M2) of the Spring Mountain district (fig. 4) and Leadbelt Creek area (M3) of the Lava Creek district (fig. 4) 

are assigned moderate potential (M/B). In both areas 

carbonate beds are cut by mineralized high-angle faults. 

In the Windy Peak area the possible deposits may be at 

depth below a cap of quartzite. The areas of resource 

potential for irregular replacements of base and precious 

metals (M) are shown on plate 3 and figure 25 and 

summarized in table 4. 

Economic Significance 

This type of deposit in the past has been a major 

producer in the Challis National Forest, primarily from 

the Clayton Silver mine, which was not operational in 

1986. Considerable reserves would be needed to support 

a new mining venture. 

Fluorspar Breccia Manto Deposits (N) 

Commodities, By-products, and Trace Metals 

Fluorspar; base and precious metals are potential 

by-products.37 

Stratigraphic Control 

All known occurrences are in the upper few 

hundred feet of the Bayhorse Dolomite below a cap of 

Ramshorn Slate. The dolostone and the slate have been 

silicified in the vicinity of the ore deposits. Because of an 

unconformable contact between the Bayhorse Dolomite 

and the overlying Ramshorn Slate, different parts of the 

dolostone are mineralized. 

Structural Control 

Associated fluorspar veins are in high-angle 

regional faults that probably served as channels for the 

ore solutions. All the known deposits are on the crest and 

flanks of a major north-trending anticline. 

64 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
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- HIGH 

D MODERATE 

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I 0 5 10 15 20 25 MILES I I I I I I 

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Figure 26. Mineral resource potential map for fluorspar breccia manto deposits (N) in the Challis National Forest and adjacent areas, Idaho. Areas (N1, N2) of mineral 

resource potential are described in table 4. 
Age 

Tertiary, probably same as fluorspar veins; associated sulfides may be Cretaceous. 

Deposit Description 

Deposits are stratabound, stratiform to irregular 

breccia fillings and replacements in the Bayhorse 

Dolomite. The deposits roughly parallel the unconformable contact between Bayhorse Dolomite and Ramshorn 

Slate. The tabular bodies range from less than 1 ft to 

15-20 ft thick and as much as 3,000 ft long in the planar 

dimension. Fluorite, quartz, chalcedony, sandy dolomite, 

calcite, and minor barite and sulfide minerals make up 

the deposits. Type locality for this deposit model is the 

fluorspar deposits on Keystone Mountain (N, fig. 26), 

Bayhorse district (fig. 4). 

Geochemical Signature 

The Keystone Mountain deposits type locality is 

within the boundary of a geochemical survey conducted 

specifically for the USGS Challis CUSMAP project 

(fig. 5). Samples of both the heavy-mineral fraction of 

the stream sediments and the stream sediments had 

anomalous concentrations of B, Ag, and Pb. The heavy 

minerals were also anomalous in Bi, Be, Cd, Cu, Mo, Sb, 

and Zn (table 7). A geochemical signature commonly 

associated with fluorite gangue is Sb, Fe, As, Au, Ag, Hg, 

W, Pb, and Zn. 

Geophysical Signature 

The deposits themselves have no geophysical 

expression, but some major controlling faults show in the 

regional magnetic anomaly data. 

Assessment Criteria 

1. Presence of carbonate rocks. 

2. Breccia horizons. 

3. Deep-seated high-angle faults. 

4. Proximity to Tertiary intrusive rocks. 

5. Evidence of fluorspar in country rock, faults, 

or breccias. 

Assessment 

This is a type of deposit that is dependent upon 

several factors for development: brecciated and permeable zones in carbonate rock below a solution trap, 

deep-seated high-angle faults, and hypabyssal felsic 

intrusive rock of the correct composition and magmatic 

evolution. These factors could occur in conjunction with 

any receptive carbonate host. Assessment criteria are 

satisfied only in one area (Nl) that contains known 

deposits. This area is assigned high resource potential 

(H/D) for fluorspar breccia manto deposits. Three small 

nearby areas (N2) are assigned moderate potential 

(MID). The areas of resource potential for fluorspar 

breccia manto deposits (N) are shown on plate 3 and 

figure 26 and summarized in table 4. 

Economic Significance 

See discussion under Fluorspar Veins (A). 

Sediment-Hosted, Jasperoid-Associated, 

Precious-Metal Deposits (0) 

Commodities, By-products, and Trace Metals 

Gold and silver; trace amounts of arsenic, antimony, mercury, and thallium. 

Host Rocks 

The most common hosts for deposits of this type in 

the Western United States include carbonaceous limestone and dolostone, calcareous carbonaceous shale and 

siltstone, and bioclastic limestone. Host rocks are silicified, commonly enough to be termed jasperoids. 

Lithologic Control 

Intermediate to silicic plutonic or hypabyssal intrusive rocks are generally present in the immediate area, 

although their relationship to the precious-metal mineralization is unknown. Many of the deposits are in thinbedded carbonate and siltstone. 

Structural Control 

High-angle faults are present in all known deposits 

of this type and apparently served as conduits for the 

solutions that formed the jasperoids and the mineralized 

areas. 

Age 

Probably Cretaceous to middle Tertiary. 

66 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
115°30' 115°00' 113°00' 112°45' 

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Figure 27. Mineral resource potential map for sediment-hosted, jasperoid-associated, precious-metal deposits (0) in the Challis National Forest and adjacent areas, 

Idaho. Areas (01) of mineral resource potential are described in table 4. 
Deposit Description 

Bagby and Berger (1985, p. 169) recognized two 

subsets of sediment-hosted, disseminated precious-metal 

deposits: jasperoidal type and Carlin type. J asperoidaltype deposits are those in which the precious metals are 

hosted in highly siliceous rocks including jasperoids and 

associated quartz veins and silicified wall rocks; this type 

of deposit occurs mainly along fault zones. Carlin-type 

d~posits are. those in which the precious metals are evenly 

d1stnbuted m the host rocks which do not always appear 

to .be silicified, although jasperoids are generally present; 

this type of deposit occurs as a podlike body that extends 

several tens of meters away from a fault. There is a 

complete gradation between the two subtypes, and there 

are both gold- and silver-rich end members of each type. 

Veins of quartz, calcite, and barite are common 

especially with the jasperoidal type, and late calcite vein~ and veinlets are present in most deposits. Jasperoidal 

breccias and jasperoid veins generally occur near ore, 

even though they may not carry precious-metal values. 

I7rite is u~ually p~esent, and cinnabar, stibnite, arsenopynte, fluonte, bante, calcite, and various thallium and 

arsenic sulfides and sulfosalts may be present. Gold is 

typically submicroscopic (1-5 micrometers) and associated with pyrite, clay, silica, and organic matter. Organic 

matter is present in the primary ore of all known deposits 

as amorphous carbonaceous material, pyrobitumen, 

graphite, or kerogen. These are large-tonnage, low-grade 

deposits; median grade of 30 deposits in the Western 

United States is 0.088 oz (ounce) per ton, and most 

deposits contain 1-24 million tons of ore (Bagby and 

Berger, 1985, p. 197). 

Geochemical Signature 

The trace-element association of Au As Sb Hg ' ' ' ' and Tl is well known for deposits of this model type. The 

element association is important in defining target areas, 

not high values of individual elements. Other elements 

that may be present include W, Te, Se, Cd, and F. 

Geophysical Signature 

Several of the areas of jasperoid (pl. 1) show an 

association with deep negative magnetic anomalies of 

unknown origin. 

Assessment Criteria 

1. Presence of carbonaceous sedimentary rocks. 

2. Jasperoid, especially as breccia or veins. 

3. Presence of high-angle faults. 

4. Indications of hydrothermal activity. 

5. Presence of the geochemical suite, arsenic, 

antimony, mercury, and thallium in rock or soil 

samples. 

Assessment 

Assessment for this model type is based on criteria 

developed for deposits elsewhere in the Western United 

States. There are no known deposits of this type within 

the region, although several areas within and next to the 

Forest have geologic characteristics that meet all the 

criteria (Wilson and others, 1988a). Areas (01) shown 

on plate 3 and figure 27 have a moderate potential but 

with a low level of certainty (M!B) because of a lack of 

adequate geological and geochemical data. Jasperoid as 

used in this report indicates a rock composed predominantly of silica, mainly aphanitic to fine-grained quartz, 

formed by replacement of the enclosing rock (Lovering, 

1972). Jasperoids can form by several mechanisms, not 

all of which are related to hydrothermal mineralization. 

Detailed studies to determine the origin of the jasperoids 

in the Forest are in progress. The areas of resource 

potential for sediment-hosted, jasperoid-associated, 

precious-metal deposits (0) are shown on plate 3 and 

figure 27 and summarized in table 4. 

Economic Significance 

Large, low-grade, fine-grained "invisible-gold" 

deposits of this type are currently in production at several 

locations in the Western United States. Exploration 

activity for similar deposits is still active and will continue 

into the future. This activity will lead to an increased 

understanding of the jasperoids of the Forest and may 

delineate areas of potential not recognized today. 

Precious-Metal Deposits in 

Volcanic Tuffs (P) 

Commodities, By-products, and 

Trace Metals 

Gold and silver. 

Host Rocks 

Host rocks may be volcanic or epiclastic carbonaceous sediments. Volcanic host rock at the known 

deposit of this type is highly fractured, nonwelded porous 

rhyolite tuff characterized by abundant rounded pumice 

fragments that are only slightly flattened. Phenocryst 

content is 15-40 percent, with quartz composing 35-48 

68 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
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Figure 28. Mineral resource potential map for precious-metal deposits in volcanic tuffs (P) in the Challis National Forest and adjacent areas, Idaho. Areas (P1, P2, P3) 

of mineral resource potential are described in table 4. 
percent, sanidine 50-70 percent, and biotite 0-3 percent 

of the phenocrysts (Fisher and Johnson, 1987). Host 

rocks are fractured, oxidized, and stained with iron 

oxides, with extensive argillic alteration in the vicinity of 

the deposits. 

Deposits in epiclastic rocks are in black, carbonaceous mudflow breccia and carbonaceous volcanic 

sandstone. 

Lithologic Control 

The highest grade ores in volcanic rocks are 

concentrated beneath less permeable mudstones or clayrich strata. Those in epiclastic rocks are associated with 

brecciated carbonaceous material. 

Structural Control 

Deposits are associated with northeast- and 

northwest-trending high-angle fracture zones. 

Age 

Tertiary. 

Deposit Description 

The only known deposit in volcanic rock is at the 

Sunnyside mine (Pa, fig. 28) in the Thunder Mountain 

district, just northwest of the Forest. The ores are stratabound and blanketlike and composed of fine-grained 

gold, silver, and electrum, and sparse acanthite and 

naumannite (A~Se ), dispersed along fractures and 

cracks. Ore distribution is uneven throughout the host 

rocks. Gangue is drusy quartz, clay, jarosite, sericite, 

illite, and sparse pyrite and arsenopyrite. The known 

deposit in epiclastic rock is at the Dewey mine (Pb, fig. 

28) also located just northwest of the Forest. The deposit 

consists of fine-grained gold and silver in seams, cracks, 

and bedding-plane laminations distributed unevenly 

through the rock. Pyrite and clay minerals accompany the 

precious metals. 

Geochemical Signature 

The Sunnyside mine type locality is within the 

boundary of the Idaho Primitive Area (fig. 5). Both 

stream-sediment and rock samples collected near the 

type mine locality contained anomalous concentrations 

of As and Mo. Rock samples also had high concentrations of Ag, and stream-sediment samples had high 

concentrations of Cu (table 7). The Dewey mine type 

locality is within the boundary of the Idaho Primitive 

Area (fig. 5). Both stream-sediment and rock samples 

collected near the type mine locality contained anomalous concentrations of As. Rock samples also had high 

concentrations of Mo and Ag (table 7). A geochemical 

signature commonly associated with precious-metal 

veins, regardless of host rock, is Au, As, Sb, Hg, Ag, Pb, 

Zn, Cu, W, Bi, Te, and Tl. 

Geophysical Signature 

No recognizable magnetic signature. 

Assessment Criteria 

1. Evidence of precious-metal mineralization. 

2. Within volcanotectonic subsidence structures. 

3. Presence of nonwelded rhyolitic tuff and (or) 

epiclastic sedimentary rocks containing carbon 

trash. 

4. Proximity to high-angle faults. 

Assessment 

Although the only known deposits are located just 

northwest of the Forest, there is potential for this type of 

deposit within the Forest. Geologic conditions in that 

part of the Forest within the Challis 1 ox 2° quadrangle 

indicate four areas (P1) of high resource potential (H/C) 

and five areas (P2) of moderate resource potential (M/C) 

for deposits in volcanic rock and one area (P3) of 

moderate resource potential (M/C) for deposits in epiclastic rocks. The remainder of the Forest cannot be 

assessed for this model type because of the lack of 

adequate data. The areas of resource potential for 

precious-metal deposits in volcanic tuffs (P) are shown 

on plate 3 and figure 28 and summarized in table 4. 

Economic Significance 

The potential is for large low-grade deposits that 

could be worked by some of the new techniques 

developed for the large low-grade deposits now being 

worked in the Western United States. 

Stratabound Syngenetic Deposits of 

Precious and Base Metals (Q) 

Commodities, By-products, and Trace Metals 

Zinc, lead, silver, gold, and barite; trace amounts of 

vanadium and molybdenum. 

70 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
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I 0 5 10 15 20 25 MILES I I I I I I 

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Figure 29. Mineral resource potential map for stratabound syngenetic deposits of precious and base metals (0) in the Challis National Forest and adjacent areas, Idaho. 

Areas (01, 02, 03) of mineral resource potential are described in table 4. 
Host Rocks 

Black siliceous-facies carbonaceous argillite and 

fine- to medium-grained gray limestone or micritic carbonaceous limestone that were deposited in an euxinic 

environment. Alteration adjacent to known orebodies is 

not distinctive and, where present, was produced by 

contact metamorphism near Cretaceous and Tertiary 

plutonic bodies. 

Lithologic Control 

The deposits formed in restricted depositional 

basins in which metal-bearing geothermal brines 

accumulated. 

Age 

Mineralization IS the same age as the enclosing 

host rock. 

Deposit Description 

Deposits are composed of stratiform -bedded 

masses and lenses rich in sphalerite and galena with 

pyrite, pyrrhotite, barite, arsenopyrite, quartz, calcite, 

clay minerals, and tremolite. The orebodies can be 

several hundred feet in length. Associated stringers and 

disseminations of sulfide minerals may reflect feeder 

zones for the metal-bearing brines. Metals in these 

deposits have been remobilized where cut by plutonic 

and hypabyssal intrusive bodies and by hydrothermal 

solutions moving along faults and fractures. Two type 

localities are shown: the Hoodoo mine (Oa, fig. 29), 

Boulder Creek district (fig. 4), in the Salmon River 

assemblage, and the Phi Kappa mine (Ob, fig. 29), Alto 

district (fig. 4), in the Copper Basin Formation and 

undivided Ordovician and Silurian argillites. 

Geochemical Signature 

The Hoodoo mine type locality is within the eastern 

part of the Sawtooth Recreation Area (fig. 5). Both 

stream-sediment and rock samples collected near this 

type mine locality contained anomalous concentrations 

of Sb, Zn, Ph, and Ag. Rock samples also had high 

concentrations of Hg, Sn, Bi, and Cu, and streamsediment samples also had high concentrations of Cd, 

Mo, and Au (table 7). The Phi Kappa mine type locality 

is within the boundary of the Boulder-Pioneer Wilderness Study Area (fig. 5). Stream-sediment samples 

collected near this type locality contained anomalous 

concentrations of Pb, Mo, Zn, and B (table 7). A 

geochemical signature commonly associated with stratiform sulfide deposits is Cu, Pb, Zn, and Mn. Compared 

to the common geochemical signature, the type localities 

have higher concentrations of precious metals and 

elements such as Hg and Sb that are usually associated 

with precious-metal deposits. 

Geophysical Signature 

Detailed magnetic, electromagnetic, and gravity 

surveys have been used successfully in exploration for 

similar types of orebodies elsewhere. 

Assessment Criteria 

1. In black-shale terrane. 

2. Anomalous concentrations of zinc and (or) 

lead. 

3. Evidence for presence at time of deposition of 

a basin to localize metalliferous brines. 

Assessment 

Large areas in the Challis National Forest are 

underlain by units containing black shales. The units 

include the Ramshorn Slate, Trail Creek Formation, Phi 

Kappa Formation, Milligen Formation, Salmon River 

assemblage, and Wood River Formation. The lower part 

of the Copper Basin Formation and the McGowan Creek 

Formation also contain black shales. Stratiform zinc 

deposits are known in the Forest in at least two locations, 

the Hoodoo and Livingston mines in the Boulder Creek 

district (fig. 4), and are known in the same belt of rocks 

to the south in the Hailey area. In addition, many of the 

metal occurrences in the black shales are suspected to be 

stratiform deposits. The polymetallic veins in black-shale 

terrane may be remobilized ore from stratiform beds or 

may be feeders for the stratiform deposits. Two areas 

(01 ), mainly underlain by the Salmon River assemblage, 

are assigned high (H/D) resource potential. Several other 

areas (02 and 03) are assigned moderate (MID and 

M/B, respectively) potential. The known deposits are in 

the Salmon River assemblage and undivided Ordovician 

and Silurian argillites, and perhaps the lower part of the 

Copper Basin Formation. South of the Forest the Milligen and Wood River Formations contain stratiform baseand precious-metal deposits. An unknown potential is 

assigned to the black-shale units in the Copper Basin and 

McGowan Creek Formations. These units are mostly 

outside the black-shale belt but are of the right lithology 

and were formed in the correct deposition environments. 

The areas of resource potential for stratabound syngenetic deposits of precious and base metals (0) are 

shown on plate 3 and figure 29 and summarized in 

table 4. 

72 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
Economic Significance 

There is not sufficient knowledge about this type of 

deposit in the Forest to speculate on grades or tonnages, 

but grades could be high and tonnages could be as much 

as tens of millions of tons. See the discussions in the 

several sections on Polymetallic Vein Deposits (B, C, 

D, E). 

Stratiform Vanadium Deposits (R) 

Commodities, By-products, and Trace Metals 

Vanadium; zinc, lead, silver, or barite are potential 

by-products; trace amounts of molybdenum, nickel, 

chrome, selenium, and arsenic. 

Host Rocks 

Black shales; fine-grained siliceous mudstone, siltite, micritic limestone, chert, and dolomitic siltstone. 

Veinlets of chalcedony and opaline silica-filled fractures 

are common. 

Stratigraphic Control 

The known vanadium-rich horizons are in the 

Salmon River assemblage (Fisher and May, 1983) and 

the Glide Mountain plate of the Copper Basin Formation (Simons, 1981 ). Concentration of metals is thought 

to have occurred during deposition of organic-rich 

fine-grained marine clastic sediments in a euxinic 

environment. 

Age 

Mineralization is the same age as the host rock. 

Deposit Description 

Disseminated and bedded deposits in organic-rich 

horizons with pyrite, marcasite, sphalerite, chalcedony, 

vanadium, and molybdenite. Highly anomalous vanadiferous beds contain greater than 1 percent vanadium 

(Fisher and May, 1983). Weathered zones·have a distinct 

pink vanadium "bloom." 

Geochemical Signature 

Probably same as for stratabound syngenetic deposits of precious and base metals. 

Geophysical Signature 

None known, but detailed geophysical methods 

may be useful in delineating deposits of this type. 

Assessment Criteria 

1. Anomalous concentrations of vanadium in 

rock or stream-sediment samples. 

2. In black-shale terrane with organic-rich 

horizons. 

3. Evidence of synsedimentary structures that 

may have localized metalliferous brines. 

Assessment 

There are no known deposits of this type in the 

Challis National Forest, and although they do occur 

elsewhere in the Western United States, none have been 

mined. The area (R1) along the Slate Creek lineament in 

the Salmon River assemblage is assigned high potential 

(HID). Other areas (R2 and R3) underlain by black shale 

are assigned moderate potential (M/C and M/B, respectively). The areas of resource potential for stratiform 

vanadium deposits (R) are shown on plate 3 and figure 

30 and summarized in table 4. 

Economic Significance 

In the future this type of deposit may become an 

exploitable resource (millions of tons) for vanadium and 

associated metals. 

Gold Placer Deposits (S) 

Commodities, By-products, and Trace Metals 

Gold and silver; radioactive minerals, niobium, 

tantalum, and rare-earth elements are potential byproducts. 

Host Rocks 

Gold placers are in fluvial deposits consisting of 

sand, gravel, and boulders. Most clasts are less than 2 ft 

in diameter, and clay is common locally. These deposits 

are commonly in terraces a few to several hundred feet 

above the present stream. 

Resource Potential- Locatable Minerals 73 
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115°30' 115°00' 

45°00' 

44°00' EXPLANATION 

RESOURCE POTENTIAL 

- HIGH 

MODERATE 

0 5 10 15 20 25 MILES 

114°00' 

\ 

113°00' 112°45' 

~ /"-, MONTANA ~ \ ~b. e,.... 

IDAHO 

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z LL 0 0 f= 

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43°30' ~ 

Figure 30. Mineral resource potential map for stratiform vanadium deposits (R) in the Challis National Forest and adjacent areas, Idaho. Areas (R1, R2, R3) of mineral 

resource potential are described in table 4. 
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44°00' r- EXPLANATION 

I RESOURCE POTENTIAL 

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I D MODERATE 

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z 

Figure 31. Mineral resource potential map for gold placer deposits (S) in the Challis National Forest and adjacent areas, Idaho. Areas (S1, S2) of mineral resource 

potential are described in table 4. 
Lithologic Control 

The major placers are directly downstream from 

known lode precious-metal deposits. The highest concentrations of placer gold are in pay streaks just above 

bedrock. 

Age 

The alluvial deposits are Pleistocene to Holocene. 

Deposit Description 

Placer deposits formed in streams where turbulent 

and irregular flow patterns separated light from heavy 

components of bedload. Gold is not dispersed throughout but is concentrated in pay streaks that constitute only 

a small part of the gravels. Both free gold and electrum 

are present. Other heavy components associated with the 

gold placers are ilmenite, magnetite, euxenite, brannerite, zircon, monazite, cinnabar, stibnite, and garnet. Gold 

in these placer deposits ranges in size from grains a few 

millimeters in diameter to nuggets as much as 1 inch in 

diameter. The placers range in size from a few acres to 

several thousand acres and are a few feet to more than 

100 ft thick. Grades range from 0.09 to 0.005 oz per yd3 • 

Geochemical Signature 

Gold and silver, and black-sand minerals. 

Geophysical Signature 

Regional geophysical surveys are of little use, but 

local seismic surveys may be of use in defining gravel 

depths. Ground magnetometers could be used to detect 

magnetite and ilmenite that may be concentrated in the 

gold placers and could serve as a prospecting tool in 

search of shallowly buried placers. 

Assessment Criteria 

1. Evidence of precious-metal mineralization. 

2. Within 5 mi downstream from known 

precious-metal lode deposits. 

3. Presence of adequate amounts of alluvium. 

Assessment 

Placer deposits in the Forest have been worked 

intermittently since 1860. Major operations were prior to 

1900, in the 1930's, and most recently (the Yankee Fork 

dredge) in the late 1940's and 1950's. Substantial 

amounts of placer gold still remain in areas previously 

unmined and also in areas already mined because earlier 

operations were very inefficient. Large known resources 

exist in several areas (Fisher and others, 1987). Five 

areas (S1) are assigned high potential (HID) and three 

areas (S2) are assigned moderate potential (MID) for 

gold placer deposits of sufficient size (100-100,000 

ounces Au) to justify development. All areas are within 

the Challis 1 ox 2° quadrangle which is where most of the 

known major gold lode deposits are located. Areas 

outside the Challis quadrangle may have some potential 

for smaller placer deposits, especially in drainage basins 

that contain other types of deposits where gold is a 

by-product. The areas of resource potential for gold 

placer deposits are shown on plate 4 and figure 31 and 

summarized in table 4. 

Economic Significance 

Gold is a commodity that is always in demand, and 

placer deposits can commonly be worked with a 

minimum of overhead expenses. However, placer mining 

is an environmentally disruptive process and any mining 

operation must adhere to State and Federal regulations 

that govern all forms of placer mining. 

Radioactive Black-Sand Placer 

Deposits (T) 

Commodities, By-products, and Trace Metals 

Thorium dioxide, rare-earth oxides, niobate and 

tantalate pentoxides, U9

0s, ilmenite, zircon, garnet, and 

gold. 

Host Rocks 

Alluvium, consisting chiefly of clay, sand, pebbles, 

and a few boulders of granitic rock. Black-sand minerals 

are found throughout but are most abundant in lenses 

and beds of coarse sand and fine gravel in which the 

larger pebbles are generally less than 1 inch in diameter. 

Structural Control 

Streams that carry weathered material off of the 

Idaho batholith terrane formed these deposits where 

stream flow was blocked or impeded by faults, Pleistocene ice or moraines, landslides, or basalt flows. 

Age 

The richer deposits formed during the early Pleistocene when an abundance of pre-Pleistocene weathered 

76 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
::D 

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115°30' 115°00' 113°00' 112°45' 

45°00'~-------------,r-----~~----------------------~---------r-----,------------~~----~ 114000' 

44°00' 

43°30' 

EXPLANATION 

RESOURCE POTENTIAL 

D MODERATE 

0 5 10 15 20 25 MILES 

~~10 ~ 

• :etchum 

g· 

'"'I 

\ 

~,.....-, MONTANA 

~(J. \ 

~ ') 

..... 

IDAHO \ 

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I-

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UJ 

a: 

0 

lL 

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z lL 0 0 t= 

<! 

z 

Figure 32. Mineral resource potential map for radioactive black-sand placer deposits (T) in the Challis National Forest and adjacent areas, Idaho. Areas (T1, T2) of 

mineral resource potential are described in table 4. 
mantle was transported by accelerated glacial erosion. 

Later deposits contain lesser amounts of heavy minerals, 

except where such minerals are concentrated through 

winnowing by streams. 

Deposit Description 

Deposits are alluviual blankets that range considerably in size, shape, and thickness, and that contain 

lenses and beds rich in black-sand minerals. An 

exploitable deposit should contain at least 1 million yd3 of 

alluvium and a minimum of 0.5 lb per yd 3 of monazite or 

other radioactive minerals. The ore minerals include 

monazite, euxinite-polycrase, brannerite, samarskite, 

xenotime, fergusonite, uranophane, columbite, allanite, 

ilmenite, magnetite, zircon, garnet, and gold, of which 

ilmenite is by far the most abundant. These minerals 

occur in the black sands as individual crystals and are 

mostly minus-16-mesh in size, which means they are 

easily separated by various methods. Black-sand minerals 

are present in the alluvium in amounts ranging from less 

than 1 lb per yd3 to more than 30 lb per yd3

• 

Geochemical Signature 

The best indicator in a stream bed is black sand. 

Mineralogy of the black sand can be determined by a 

variety of methods including visual inspection, magnet, 

geiger counter or gamma-ray spectrometer, and chemical analyses. 

Geophysical Signature 

Detailed gravity, magnetic, seismic, and radiometric surveys can provide information on depth of alluvium 

and presence of radioactive minerals and can aid m 

delineating the course of enriched paleochannels. 

Assessment Criteria 

1. Large amount of alluvium, more than 10 

million yd3

• 

2. Contains monazite or radioactive minerals. 

3. Derived from Idaho batholith terrane that was 

extensively glaciated. 

4. In valley of low-gradient stream. 

Assessment 

The major known radioactive black-sand placer 

deposits are just west of the Forest. Within the Forest 

known deposits are at Williams Creek-Gold Creek 

southeast of Stanley and at Warm Springs Creek-Pigtail 

Creek (Meadows) northwest of Stanley. The vicinities 

(T1) of the known deposits are assigned a moderate 

(MID) potential. The Sawtooth Valley (T2) is assigned a 

moderate potential with low certainty (M!B) because 

much of the alluvium is overlain by glacial materials. The 

areas of resource potential for radioactive black-sand 

placer deposits (T) are shown on plate 4 and figure 32 

and summarized in table 4. 

Economic Significance 

Some of the commodities in these deposits, mainly 

niobium and tantalum, are of critical importance to the 

United States because of this Nation's total dependence 

upon foreign sources and lack of domestic reserves. At 

the present time, large low-grade foreign sources control 

the market. Rare-earth metals are also in demand. The 

major problem in extracting rare earths from these 

deposits is the presence of thorium in the monazite. 

Thorium is not in demand now, and the accumulation of 

this radioactive by-product from rare-earth extraction 

causes a major disposal problem. 

Other Commodities 

Several other mineral deposit types need to be 

mentioned, but because they are not yet commercially 

valuable, or because available information is not sufficient, they cannot be assessed in the same way as the 

major deposit types. 

Manganese 

Manganese minerals are common in small 

amounts in many mineral deposits in the Forest but are 

not present in sufficient quantity to be considered as a 

potential resource. Most of the manganese is present as 

oxides that are mainly a surface coating or as a mixture 

with iron oxides called wad. A few of the hydrothermal 

deposits have some rhodochrosite. 

Semiprecious Gemstones 

Opal occurs in small veins and veinlets in fractures 

in volcanic rock in several places in the Forest. The opals 

are brittle and not of gem quality. The "pink" granites of 

Tertiary age of Idaho, such as the Sawtooth batholith, 

have miarolitic cavities with crystals of smoky quartz, 

microcline, topaz, and beryl (aquamarine), along with 

fluorite, carpholite, bertrandite, helvite, and ilmenite. 

Smoky quartz and microcline are the most common 

minerals; the others are rare. The occurrences are widely 

scattered and the access is difficult; thus there is little 

78 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
likelihood of commercial production. Jasper, chalcedony, 

and agate (the variegated form of chalcedony) are found 

in many places in the Forest, but there has been little 

commercial production. 

Limestone 

Production of lime-bearing rock in the United 

States is greater in volume than that of any metallic 

mineral and is exceeded only by coal and sand and gravel 

(Savage, 1961, p.111). The value of lime-bearing rocks as 

a resource depends upon their chemical and physical 

characteristics and accessibility to markets. There is 

significant production of these rocks in other parts of 

Idaho, but within and close to the Forest there has been 

little production. Several carbonate units of Paleozoic 

age are exposed in the Forest. The lower Paleozoic units 

are generally very siliceous and dolomitic. Some of the 

upper Paleozoic units, mainly the Madison and White 

Knob Limestones, are widespread and relatively pure 

limestones. These upper Paleozoic units do contain chert 

layers and nodules and intercalated lenses of shale and 

sandstone which make parts of them commercially 

unusable. 

Iron 

Three areas within or close to the Forest have been 

prospected for iron resources. The contact metamorphic 

skarn deposits in the Alder Creek district near Mackay 

are locally rich in magnetite and hematite, as are the 

skarns just north of Windy Peak in the Lemhi Range. 

Deposits in both areas, although high grade in places, are 

probably not large enough to constitute major resources. 

Magnetite and hematite also occur as small, irregular 

replacement bodies in dolostone and limestone in the 

central and southern parts of the Lemhi Range. 

Graphite in Metamorphic Rocks 

Graphite is common in some metamorphic rocks in 

the Forest, especially in the Stanley area. The known 

occurrences are low grade, although they may contain 

large tonnages. The ready availability and low demand 

for graphite, plus logistics of mining the local occurrences, suggest that these mineral occurrences are not 

potential resources. 

Pegmatite Minerals 

Pegmatites are coarse-grained igneous dikes and 

irregular-shaped bodies that are common in some parts 

of the Forest. They are composed mainly of feldspar, 

quartz, and mica, but they locally contain minerals of 

commercial importance, including beryl, columbitetantalite, cassiterite, scheelite, spodumene, tourmaline, 

uranium minerals, and rare-earth minerals. Pegmatites 

elsewhere in the world have been a commercial source 

for these minerals, but there is no recorded production in 

the Forest. Although pegmatites are common in the 

Forest, most are simple pegmatites a few inches thick and 

a few feet long that do not contain mineable quantities of 

economic minerals. 

Mercury 

Mercury has been produced at several locations in 

the Yellow Pine district just north of the Forest, and one 

area of mercury resource potential lies on the northern 

boundary of Boise National Forest lands administered by 

Challis National Forest. Cinnabar occurs in jasperoid or 

chalcedonic quartz along high-angle faults that cut 

calcareous metasedimentary rocks. Cinnabar has been 

reported in float and placer deposits in the Stanley area 

(Choate, 1962) and in panned concentrate samples from 

the Lava Creek district (fig. 4) (Erdman and others, 

1988). 

Zeolites 

Minerals of the zeolite group (hydrated silicates of 

AI, Ca, Na, and K) have been identified in altered 

volcanic rocks of the Challis Group in the Twins Peaks 

area (Fisher and Johnson, 1987). The altered area is 8 mi 

long and three-quarters of a mile wide, but the zeolite 

resource potential is unevaluated. Similar altered volcanics are common in the Forest; some of these rocks may 

contain significant amounts of zeolite minerals. Identification of most zeolite minerals in the field is difficult, if 

not impossible. 

Barite 

Barite (BaS04 ) is a common mineral in many of 

the base- and precious-metal deposits in the Forest and 

composes 2-3 percent of the fluorspar ore from the 

Meyers Cove deposits. There are a few barite vein 

occurrences in the Forest, the most notable being the 

small veins in the Borah Peak area. More importantly, 

bedded barite occurs in the black-shale terrane. Deposits 

near Hailey have been mined, and there is a bedded 

barite occurrence at the Hoodoo mine in the Challis 

National Forest. Pan-concentrated samples from the 

black-shale terrane contain anomalous amounts of 

barite, which could come from either bedded deposits or 

barite gangue in the base- and precious-metal deposits. A 

large, and accessible, bedded barite deposit would be a 

significant resource. 

Resource Potential- Locatable Minerals 79 
Uranium in Sedimentary Rocks 

Several occurrences of uranium minerals in 

Tertiary sedimentary rocks are in and near the Forest. 

These are in the Basin Creek area, northeast of Stanley, 

and on the northeast side of the Pahsimeroi Valley, south 

of Ellis. The uranium occurs in channel-filling deposits of 

carbonaceous arkose and mudstone. There has been 

minor production from the deposits near Stanley. Other 

deposits similar to those near Stanley may exist, but none 

have been found, even though the region was extensively 

explored in the late 1950's and late 1970's. 

Cobalt 

Cobalt, along with copper, is mined at the 

Blackbird mine just north of the Forest and occurs at 

several other localities in the same area. The deposits are 

stratiform and are in the Middle Proterozoic Yellowjacket Formation. Appreciable amounts of bismuth, 

arsenic, nickel, iron, and gold are also present. The areas 

of resource potential for cobalt do not extend into the 

Forest. However, known cobalt occurrences are on the 

northeast side of the Lemhi Range at the Wells cobalt 

property. There is also some question as to how far the 

Y ellowjacket Formation extends to the south. If the 

Yellowjacket Formation is present at or near the surface 

along the northeastern edge of the Lemhi Range, there 

may be an unrecognized potential for cobalt deposits in 

this area. 

Alunite 

Vein and replacement alunite deposits are found in 

volcanic terranes throughout the world, and in the 

Western United States, they are most commonly associated with Tertiary volcanic rocks. The calderas and 

volcano-tectonic grabens of the Challis volcanic field are 

potentially favorable localities for alunite deposits, but 

this resource potential is unknown. 

Silver 

Calderas and grabens of the Challis volcanic field 

contain carbonaceous volcaniclastic rocks, most of which 

predate the precious-metal vein deposits and associated 

alteration. Permeable beds in sequences of alternating 

permeable and impermeable beds may have been 

receptive hosts for precious-metal solutions moving 

outward from the vein zones. These speculative deposits, 

which might contain silver, would be somewhat analogous to those at Creede, Colo. 

Gold 

Large-tonnage low-grade gold deposits of several 

types are currently being mined or evaluated in the 

Western United States. The types of deposits include 

epithermal sediment-hosted deposits, volcanic-hosted 

deposits, and deposits associated with flat faults and hot 

springs. Most of the important geologic parameters that 

define these deposits are present in the Forest: evidence 

of large-scale hydrothermal activity; major high-angle 

faults; major low-angle faults; carbonaceous, calcareous, 

and quartzitic sedimentary rocks; extensive areas of 

silicic volcanic rocks; hypabyssal intrusive bodies; and 

alteration assemblages generally associated with epithermal gold deposits. Areas of resource potential for these 

deposit types cannot be defined, but there is a moderate 

potential with low certainty that somewhere in the Forest 

conditions were right for the formation of a largetonnage low-grade precious-metal deposit. Localities of 

interest are the altered quartzites in the southern Lemhi 

Range, altered volcanic rocks north and south of Mackay, 

and altered carbonate rocks within the trans-Challis and 

parallel fault systems. 

Areas of Unknown Resource Potential 

Some areas within and close to the Forest have 

some suggestion of the presence of mineralization but 

lack definitive data to indicate the type or kind. These 

areas are assigned an unknown resource potential and 

are discussed separately in this section by area. Areas of 

unknown resource potential are shown on plate 3 and 

figure 33. 

Area U1-Lone Cedar Creek 

This area in the Lone Cedar Creek and Sawmill 

Canyon areas of the west -central part of the Lost River 

Range had some base- and precious-metal production in 

the past from hydrothermal vein-type deposits in 

carbonate rock. Hydrothermal barite stringers and felsic 

to intermediate dikes and pods are common along 

high-angle faults. The unknown resource potential is for 

base- and precious-metal veins, replacements, and disseminations at depth. 

Area U2-lron Bog and Leadbelt Creeks 

This area just north of the Lava Creek district 

(fig. 4) has a thin to moderate cover of Challis Group 

volcanic rocks overlying a black-shale terrane and is at 

the intersection of northwest- and northeast-trending 

zones of faults, dikes, and altered zones. A positive 

magnetic anomaly in the eastern part of the area suggests 

80 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
:c 

ell 

UJ 

0 

c 

.. 

() 

ell 

., 

0 

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b 

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ell 

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115°30' 115°00' 114000' 113°00' 112°45' 

45°00'r---------------.-------~----------------------~~--------~-----,------------~~~--~ 

44°00' 

43°30' 

EXPLANATION 

RESOURCE POTENTIAL 

~UNKNOWN 

0 5 10 15 20 25 MILES 

BOUNDARY OF CHALLIS NATIONAL FOREST 

\ 

~,.,...-,\MONTANA 

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.... 

IDAHO \ 

1\ (' 

'\) 

II)) 

w 

a:: 

0 

u.. 

-' 4: 

z u.. 0 

0 i= 

4: 

z 

Figure 33. Map showing areas of unknown resource potential in the Challis National Forest and adjacent areas, Idaho. Areas (U1, U2, and so forth) of unknown resource 

potential are described in the text. 
a buried intrusive. Known base- and precious-metal 

mineral occurrences are in Paleozoic rocks on both the 

northwest and southeast sides of the volcanic rocks. The 

unknown resource potential is for base- and preciousmetal veins, skarns, and replacements in the Paleozoic 

rocks at depth beneath the volcanic rocks. 

Area U3-Hamilton Creek-Burma Road 

This area just west of Mackay Reservoir has a 

moderate to thin cover of volcanic rocks over carbonate 

terrane. Altered and mineralized fault zones of northwest trend in the volcanic rocks contain some base and 

precious metals. The unknown resource potential is for 

veins, skarns, replacements, and jasperoid-associated 

deposits in the Paleozoic carbonate rocks at depth below 

the volcanic cover. 

Area U4-Sheep Mountain 

This area just south of the Alder Creek district 

(fig. 4) has a moderate to shallow cover of volcanic rocks 

over carbonate terrane. Altered zones and intrusive 

rocks in the volcanic piles and the aeromagnetic data 

suggest an intrusive at depth. The unknown resource 

potential is for veins, skarns, replacements, and 

jasperoid-associated deposits in the Paleozoic rocks at 

depth below the volcanic cover and for veins and 

disseminations in the altered volcanic rocks. 

Area US-North Creek 

This area is just west of the Wilbert mine (C1, fig. 

15) and on the edge of a broad positive aeromagnetic 

anomaly. The anomaly may reflect a buried intrusive 

body related to the mineralization in the Wilbert and 

other mines in the near vicinity. Much of area US is a 

pediment surface, and exposures are very sparse. The 

unknown resource potential is for base- and preciousmetal vein and stockwork deposits. 

Area US-Mahogany Creek 

This area in the Blue Wing district (fig. 4) is along 

a ring-fracture system that was thought by Ruppel (1978) 

to have controlled emplacement of the intrusive body and 

related mineralization at the Ima mine. The unknown 

resource potential is for vein and stockwork mineral 

deposits along or close to one of the ring fractures. 

Area U7-Porphyry Peak 

Porphyry Peak is an Eocene volcanic vent region 

northwest of Mackay with comagmatic intrusive phases. 

Rocks in much of the area are bleached and iron stained, 

and there are zones of intense silicification. The country 

rocks are highly fractured, and felsic dikes are abundant. 

Little is known of the geology, and no geochemical data 

are available. The unknown resource potential is for 

base- and precious-metal stockworks and disseminations 

in altered volcanic rocks. 

Area US-Squaw Creek 

This area is just west of the mineral deposits in the 

Windy Peak area, Spring Mountain district (fig. 4 ), and 

contains numerous prospects, but is not mapped in 

detail. Quartzite and underlying carbonate beds are 

intruded by a Tertiary felsic pluton. Exposures are 

sparse. The unknown resource potential is for base- and 

precious-metal veins and replacement deposits in the 

carbonate rocks and precious-metal veins in the 

quartzites. 

MINERAL RESOURCESLEASABLE MINERALS 

Oil and gas, oil shale, potash, sodium, native 

asphalt, bitumen or bituminous rock, phosphate, and 

coal are leasable commodities or "mining act minerals." 

They were excluded from the General Mining Law of 

1872 by the Mineral Leasing Act of 1920 which set up 

laws requiring prospect permits and leases to control 

their exploration, development, and production. Geothermal energy was added to the list of leasable 

commodities by the Geothermal Steam Act of 1970. 

There is no recorded production of any of these 

commodities within the Forest and adjacent lands 

administered by the Forest. 

A thin coal (lignite?) seam is about 1 mi outside 

the Forest in the northwest part of the Lemhi Range. The 

seam has been prospected for uranium but is not large 

enough to mine for its coal. Graphitic material, assumed 

to be metamorphosed coal, crops out near Ketchum, 

nearly 10 mi outside the Forest boundary. This is in an 

area of contact and regional metamorphism, and any coal 

beds present are probably thermally altered to carbonaceous graphitic material. 

Oil and gas have not been identified within the 

Forest or nearby areas. Presence of hydrocarbons 

requires porous reservoir rocks; organic-rich source 

beds; stratigraphic, lithologic, or structural traps; and 

favorable thermal history. Whereas the first three criteria 

may be met several places in the eastern portion of the 

Forest, the thermal history has not been favorable for 

accumulation of hydrocarbons. Conodont studies indicate that the Color Alteration Index of the region is 

82 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
about 5, whereas the limit for oil is 2-3 and that for gas 

is 4-4.5. Mineral-resource potential for oil and gas 

resources in the Forest is low. 

Thermal springs in the Forest, especially in the 

western part, are used for recreation, irrigation, and 

space heating. There may be potential for greater exploitation of the springs as hot -water and steam resources. 

RESOURCE POTENTIALLEASABLE MINERALS 

Geothermal Resources (V) 

Commodities 

Hot water and steam. 

Host Rocks 

Thermal springs emerge from rocks of all ages 

(Precambrian to Holocene), especially in the vicinity of 

Cretaceous and Tertiary volcanic or plutonic rocks. 

Structural Control 

Geothermal springs generally occur along faults 

and fractures near igneous intrusive bodies. The 

intrusions themselves may have been emplaced along 

major fault zones. Springs not associated with igneous 

rocks are related to deep-seated high-angle fault zones. 

Age 

Holocene. The hot springs are heated by currently 

active hydrothermal systems. 

Deposit Description 

Thermal springs are most common in areas of high 

regional geothermal gradients or in the vicinity of young 

intrusions or magma bodies. They are abundant in the 

western part of the Forest where they are almost entirely 

related to large intrusive bodies. In the southern and 

eastern portions of the Forest they are less common and 

are hosted by Paleozoic rocks; these springs may be 

associated with intrusive bodies at depth. Surface-water 

temperature ranges from 28 oc (an arbitrary cut -off of 

what is considered to be thermal) to 88 oc (82-190 °F) 

(Waring, 1965; Ross, 1971; Breckenridge and others, 

1980). 

Geochemical Signature 

Geothermal waters in the Forest are alkaline with 

pH ranging from 7 to 9. They are very low in specific 

conductivity and thus low in dissolved solids considering 

their temperatures. Water from volcanic rocks has a 

slightly higher conductance than that from granitic rocks. 

Sodium and bicarbonate are common as are calcium and 

magnesium in areas underlain by carbonate rock. Sulfate 

and chloride are generally low, and silica is nearly the 

same as in nonthermal waters (Ross, 1971). 

Geophysical Signature 

Geophysical methods are not practical for exploration or assessment of thermal springs. The areas known 

to have geothermal springs are also known to be regions 

of high heat flow and locally high thermal gradients. 

Assessment Criteria 

1. Presence of naturally occurring warm or hot 

water. 

2. Proximity to areas of Eocene or younger volcanism or magmatism. 

3. Presence of regional high-angle faults. 

Assessment 

Thermal springs are located throughout the 

western part of the Forest. This area (V) has high 

potential (H/C) for small hot- and warm-water springs 

that could be used by homes and small businesses, 

including agriculture. This area (V) has moderate 

potential (M/C) for steam (pl. 4). To date, drilling and 

exploration have focused on hot water and not steam. 

Economic Significance 

As Idaho is deficient in conventional forms of fuel 

there is an incentive to develop steam-generated 

electricity as an alternative, inexpensive energy source. 

Steam resources have not been as thoroughly explored as 

hot water. In fact, exploration for hot-water sources has 

avoided areas with high steam potential. Increased 

exploitation in the future of small springs by private 

residences and small business entrepreneurs for hot 

water, space-heating, swimming pools, spas, greenhouses, and irrigation seems assured. 

Resource Potential- Leasable Minerals 83 
MINERAL RESOURCESSALABLE MINERALS 

By Robert C. Sykes 

U.S. Forest Service 

The General Mining Law of 1872 declared "all 

valuable mineral deposits in lands belonging to the 

United States ... to be free and open to exploration and 

purchase." It authorized placer and lode mining claims to 

be located on lands containing valuable minerals. This 

Act still forms the bulk of present-day mining law. In 

1892, lands chiefly valuable for building stone came 

under the purview of the mining law. The Mineral 

Materials Act of July 31, 1947, permitted the Secretary of 

Interior to sell sand, stone, gravel, and common clay 

through a contract of sale. The Multiple Surface Use Act 

of July 23, 1955, removed common varieties of sand, 

stone, gravel, pumice, pumicite, cinders, and clay from 

the category of locatable minerals and placed them under 

the Minerals Material Act as salable minerals. Several 

exceptions to the salable category are block pumice, 

perlite, and forms of dimension stone such as travertine, 

high-quality marble, and micaceous meta-quartzite 

("Oakley Stone"). Determination that a particular 

mineral is a salable mineral must be reviewed on a 

case-by-case basis in light of past legal decisions. To 

determine if the mineral material is salable or locatable, 

an evaluation of the mineral deposit must be done. For a 

mineral such as dimension stone to be locatable, it must 

exhibit a unique property that will give the mineral 

material a distinct and special value in the market place. 

Salable commodities generally have low unit value (value 

per ton); their exploitation is dependent on easy access to 

transportation, and generally they are used near the site 

of production. 

Sand and gravel, dimension stone, and riprap are 

the only salable mineral commodities located on the 

Forest. These commodities are only in certain areas. The 

potential for their development is low; deposits of sand 

and gravel and riprap are much more abundant and more 

accessible on private and Bureau of Land Management 

lands. These off-Forest deposits presently meet the needs 

of the local communities. 

Sand and gravel deposits are not abundant on the 

Forest. There are 22 sand and gravel pits on the Forest 

which are exploited mainly for road fill and resurfacing 

material. None of the sites is used on a regular basis. The 

Pleistocene and Holocene gravel deposits are composed 

mostly of Cretaceous granitic and Tertiary granitic and 

volcanic rock. The Yankee Fork drainage and Cape Horn 

area are the principal sources of sand and gravel for 

construction purposes. Major production is from alluvial 

deposits, but special needs for aggregate are met by 

crushing coarse alluvium and colluvial material. 

Dimension stone has been quarried from the Challis Volcanic Group and from talus slopes consisting ofthe 

Ramshorn Slate in Bayhorse Creek and the Kinnikinic 

Quartzite in Squaw Creek. A mineral materials deposit 

containing quartz monzonite boulders in Summit Creek 

has been mined, and the boulders from there have been 

used for landscaping and building facing. Other sites are 

in the Kane and Mill Creek drainages and in an area next 

to the Burma Road. 

Ten riprap sites are in the northern portion of the 

Forest, and seven sites are in the southern portion of the 

Forest. Most of the sites are talus slopes consisting of 

volcanic rock of Eocene age and quartzite of Ordovician 

age. Copper Basin, Cape Horn, Kane and Summit 

Creeks, and Bonanza-Yankee Fork areas contain the 

majority of the riprap sites. None of the riprap sites is 

used on a regular basis. 

RESOURCE POTENTIALSALABLE MINERALS 

Income from the sale of salable mineral commodities will vary according to accessibility, unit value, 

cost, and amount produced. Environmental factors, such 

as other resource disturbances due to bulk mining, and 

reclamation costs have not been considered in this 

assessment. 

The potential for the development of salablemineral material sites beyond those that already exist on 

the Challis National Forest is very low. This is due to the 

remoteness, inaccessibility, location, and lack of demand 

for these deposits on the Forest. Private and Bureau of 

Land Management lands contain mineral material 

deposits that are more readily available to meet the needs 

of other Federal and State agencies and the public. 

Sand and Gravel 

Sand and gravel for road construction, road 

resurfacing, and aggregate are available in the Forest in 

quantities adequate for most Forest Service needs. 

Almost all bedrock units disaggregate on weathering to 

form alluvial and colluvial deposits, some of which are 

suitable for construction. The majority of the talus 

material (colluvial) sites consist of welded tuff and (or) 

rhyolite, although one area consists of Ramshorn Slate. 

The talus material is crushed and used for road fill and 

resurfacing material. Most of the talus material that is 

used is not good surfacing material as it breaks down 

quickly. Generally the talus material is more readily used 

than sand and gravel (alluvial) deposits because talus is 

more widely distributed on the Forest. However, in areas 

84 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
where the alluvial sand and gravel deposits are present, 

they are exploited much more readily than the colluvial 

talus material. The distribution of colluvial talus and 

alluvial deposits is shown on plate 4. 

The distribution of all the alluvial and colluvial 

units on the Forest cannot be shown at 1:250,000 scale; 

only those alluvial units that are substantial and (or) 

contain existing mineral material sites are shown. The 

geologic map should not be used to inventory all sources 

of materials. 

Dimension Stone 

The majority of the dimension stone exploited on 

the Forest is the Ramshorn Slate of Ordovician(?) age 

and volcanic rock of Eocene age. These deposits are 

principally talus. In the Summit Creek . area, granitic 

boulders of the Tertiary Sawtooth batholith have been 

produced from alluvial deposits for use as dimension 

stone, as have Kinnikinic Quartzite boulders from talus 

slopes in the Squaw Creek area. Those areas of the 

Forest that have potential for dimension stone are shown 

on plate 4 (existing sites). There are several factors that 

must be considered when evaluating a potential area and 

the proposed use of the material: shape and size, 

aesthetic qualities, distance to market, strength and 

durability, and ease of quarrying and utilization. 

Riprap 

Riprap sites occur in most areas of the Forest 

where major access is readily available. A majority of the 

riprap sites occur in colluvium and talus consisting of 

volcanic rock, mostly welded tuff; some sites occur in 

granitic alluvium and Kinnikinic Quartzite. Riprap is 

produced from these sites intermittently by the U.S. 

Forest Service for use on Forest projects. Riprap areas 

are shown on plate 4. 

RECOMMENDATIONS FOR 

FUTURE STUDIES OF 

MINERAL RESOURCE POTENTIAL 

The Challis National Forest contains several 

geologic terranes, which are hosts to a variety of mineral 

resources that have been extensively mined and 

prospected. A few of the mineral deposits and occurrences have been studied in detail, and most have been 

examined in a reconnaissance manner. However, many of 

the geologic terranes in the Forest have not yet been 

studied in sufficient detail to assess mineral resource 

potential adequately. In addition, many of the geologic 

studies on the mineral deposits, although classic studies, 

were undertaken before modern geologic mapping and 

investigative techniques were developed. The U.S. 

Geological Survey CUSMAP project to study and 

evaluate the mineral resources of the Challis 1° x 2° 

quadrangle (Fisher and Johnson, 1987) is the type of 

study that provides the background data needed for 

resource assessment. Information from this project provides the foundation for detailed, sophisticated studies 

directed toward understanding the processes that form 

mineral deposits. Geologic knowledge in that portion of 

the Forest outside the Challis 1 ox 2° quadrangle needs to 

be brought to the same level of sophistication and 

reliability as that available in the Challis 1° x 2° quadrangle. The present disparity in the quality and quantity 

of data between the two areas is evident in the higher 

levels of confidence assigned to areas of resource potential within the Challis 1 o x 2° quadrangle. 

Geologic mapping detail varies greatly within the 

Forest; some parts have adequate coverage at 1:24,000 

scale, whereas other parts that are essentially unmapped 

are not adequately covered, even at 1:500,000 scale. 

Many of the known mineralized and altered areas need to 

be mapped in detail. Mineral exploration and assessment 

is a continuing process. As new concepts are formulated, 

new mineral deposit types recognized, and supply and 

demand fluctuates, various geologic terranes will be 

examined and reexamined many times. The importance 

of adequate geologic maps in this process cannot be 

overstated. 

The black-shale belt of central Idaho, much of 

which is in the Challis National Forest, is an enormous 

reservoir of metals. These metals were concentrated in 

certain stratigraphic beds at the time of deposition. 

Several major deposits, which are thought to have 

formed from material remobilized from the black shales, 

have been exploited in the belt (Hall, 1985). The potential for large sediment-hosted, stratabound deposits has 

not been thoroughly examined. Detailed studies to define 

the metal-bearing horizons and depositional environments of the black-shale units are needed. The lower 

parts of the Copper Basin and McGowan Creek Formations should be included, although they are not usually 

considered as parts of the black-shale belt. 

The importance of the trans-Challis fault system in 

localization of ore deposits was only recently recognized 

(Fisher and Johnson, 1987). Most of the major preciousmetal and fluorspar deposits are within this fault zone, 

commonly at the intersections with north- to northwesttrending structures. A similar, parallel fault system may 

extend through the Pioneer and White Knob Mountains. 

A detailed structural and lineament analysis as related to 

Recommendations for Future Studies of Mineral Resource Potential 85 
ore deposits is needed for the region. A study of that 

type, combined with regional geology and geochemical 

and geophysical data, may reveal other structural trends 

and intersections. 

Some of the larger orebodies that have been 

exploited to date were formed by irregular replacement 

of carbonate rock; the best examples are at the Clayton 

Silver mine. Extensive carbonate terrane in the eastern 

and southern parts of the Forest is cut by major faults 

and contains exposed and postulated buried intrusives. 

Occurrences of irregular-replacement-type orebodies 

are hard to predict, but detailed stratigraphic and rock 

geochemistry studies, detailed geophysical surveys, alteration studies, and structural studies would help define 

areas of potential. 

The Challis volcanic field is adequately described 

and studied within the Challis 1 ox 2° quadrangle, but 

little is known of these rocks outside the quadrangle. 

Possible volcanic-vent areas north and south of Mackay 

are of particular interest, because they may have been the 

source of mineralizing solutions. Petrologic and geochemical studies along with detailed mapping is needed 

in these areas. 

Sediment-hosted disseminated precious-metal 

deposits, which are common in Nevada, are not known to 

occur north of the Snake River Plain. However, geologic 

conditions in parts of the carbonate terrane in the Forest 

are favorable for this deposit type. Several areas of 

jasperoid in the Lemhi and Lost River Ranges, and 

especially in the White Knob Mountains, should be 

studied and sampled in detail and related to the regional 

geology and mineral occurrences. Some of the carbonate 

host rocks for the jasperoids are thought to be correlative 

with the Roberts Mountains Formation, which is a 

common host for deposits of this type in Nevada. 

Therefore, definitive stratigraphic studies need to 

accompany the examination of the jasperoids. 

Geochemical surveys adequate for mineral 

resource assessment are lacking in about 40 percent of 

the Challis National Forest, mostly in the Dubois and 

Idaho Falls 1 ox 2° quadrangles. Even in areas where 

geochemical coverage is adequate, data from different 

surveys cannot be easily integrated because of differences 

in sample media and analytical techniques. In order to 

get a consistent data set, some lands in and associated 

with the Forest would have to be resampled and sample 

splits, if available, from previous surveys would have to 

be reanalyzed. Rocks, stream sediments, and heavymineral (panned concentrate) fractions of stream 

sediments should be collected and the samples analyzed 

for elements such as tungsten, silver, arsenic, antimony, 

cadmium, copper, lead, zinc, gold, bismuth, and molybdenum. Semiquantitative emission spectrography should 

be used to analyze the heavy-mineral fraction of the 

stream sediments. An ICP instrument, which has better 

precision than the spark-source emission spectrograph, 

should be used to analyze the rocks and stream 

sediments. 

The entire Forest should be surveyed by modern 

aeromagnetic methods with flight-line spacings of 0.5 mi. 

Excellent surveys are available for part of the Forest, but 

several areas of resource potential and structural complexity lack adequate coverage. Aeromagnetic data are 

very useful for outlining structural elements and also for 

indicating the presence of buried plutons. 

Eight separate areas in the Lemhi Range, Lost 

River Range, and White Knob Mountains have unknown 

potential for mineral resources. Studies designed to 

develop the data base for each of the areas should be 

undertaken as a first priority. Detailed geologic mapping 

and limited geochemical surveys are needed in some 

areas, whereas geophysical, petrologic, isotopic, or stratigraphic studies in addition to mapping and geochemistry 

may be needed in other areas. 

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41, 36 p. 

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Wilbert mine, Butte County, Idaho: Economic Geology, 

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and Hom Silver Mines, Lava Creek District, Butte 

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custer County, Idaho: Idaho Bureau of Mines and 

Geology Pamphlet 83, 37 p. 

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86 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
___ 1954a, A preliminacy report on the fluorspar mineralization near Challis, Custer County, Idaho: Idaho Bureau 

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Pamphlet 98, 34 p. 

___ 1961, Geology and mineral resources of the Lemhi 

quadrangle, Lemhi County, Idaho: Idaho Bureau of 

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sheets. 

Anderson, A.L., and Wagner, W.R., 1946, A geological 

reconnaissance in the Little Wood River (Muldoon) 

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Anderson, R.A., 1948, Reconnaissance survey of the geology 

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Armstrong, R.L., 1975a, The geochronometcy of Idaho: 

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J.M., and Evenson, E.B., 1988, Glacial geology of the 

Stanley Basin, in Link, P.K., and Hackett, W.R., eds., 

Guidebook to the geology of Central and Southern 

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resources: U.S. Geological Survey Professional Paper 

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Bunning, B.B., and Burnet, F.W., 1981, Copper-molybdenum 

mineralization in the Bobcat Gulch porphycy system, 

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resources of the Blue Wing district, Lemhi County, 

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stream-sediments surveys for Mo-W-Results from the 

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resources of the Borah Peak study area, Custer County, 

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graptolite succession in the Trail Creek area, central 

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Weldin, R.D., Close, T.J., and Zilka, N.T., 1973, Mineral 

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Lemhi Range Study Area, Lemhi and Custer Counties, 

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Creek molybdenum deposit, Custer County, Idaho: Missoula, University of Montana, M.S. thesis, 100 p. 

Selected References 87 
Chambers, A.E., 1966, Geology and mineral resources of part 

of the Bayhorse Mining district, Custer County, Idaho: 

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area: Idaho Bureau of Mines and Geology Pamphlet 126, 

122 p. 

Churkin, Michael, Jr., 1963, Ordovician trilobites from graptolithic shale in central Idaho: Journal of Paleontology, 

v. 37, p. 421-428. 

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of fluorite from the Challis quadrangle, Idaho: Geological Society of America Abstracts with Programs, 

v. 17, no. 4, p. 214. 

Cook, E.E., 1956, Tungsten deposits of south-central Idaho: 

Idaho Bureau of Mines and Geology Pamphlet P-108, 

40 p. 

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[ abs.], in Proceedings of the International Meeting of 

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models: U.S. Geological Survey Bulletin 1693, 379 p. 

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Davis, J.E., Jr., 1983, Geology of the Darlington quadrangle, 

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Dover, J.H., 1980, Status of the Antler Orogeny in central 

Idaho-Clarifications and constraints from the Pioneer 

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___ 1981, Geology of the Boulder-Pioneer Wilderness 

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___ 1983, Geologic map and sections of the central Pioneer 

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Pioneer Mountains, central Idaho-Stratigraphic and 

structural revisions, and new data on graptolite faunas: 

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Pioneer Mountains region, Blaine, and Custer Counties, 

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scale 1:62,500. 

Drew, L.J., Bliss, J.D., Bowen, R.W., Bridges, N.J., Cox, D.P., 

DeYoung, J.H., Jr., Houghton, J.C., Ludington, S., 

Menzie, W.D., Page, N.J., Root, D.H., and Singer, D.A., 

1986, Quantitative estimation of undiscovered mineral 

resources--A case study of U.S. Forest Service Wilderness tracts in the Pacific Mountain System: Economic 

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EG&G GeoMetries, 1979, National Uranium Resource Evaluation aerial gamma-ray and magnetic survey, Hailey 

quadrangle, Idaho-Final Report: U.S. Department of 

Energy, Grand Junction Office, Open-File Report 

GJM-338, scale 1:250,000. 

___ 1982, National Uranium Resource Evaluation aerial 

gamma-ray and magnetic survey, Idaho Falls quadrangle, 

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Junction Office, Open-File Report GJM-320, scale 

1:250,000. 

Ekren, E.B., 1981, Van Hom Peak-A welded tuff vent in 

central Idaho: Montana Geological Society, Field 

Conference and Symposium Guidebook to Southwest 

Montana, p. 311-315. 

88 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
Ekren, E.B., 1985, Eocene cauldron-related volcanic events in 

the Challis Quadrangle, in Mcintyre, D.H., ed., 

Symposium on the geology and mineral deposits of the 

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___ 1930, Geology and ore deposits of the Seafoam, Alder 

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___ 1934a, Correlation and interpretation of Paleozoic 

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___ 1934b, Geology and ore deposits of the Casto 

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___ 1937, Geology and ore deposits of the Bayhorse 

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___ 1947, Geology of the Borah Peak quadrangle, Idaho: 

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___ 1961, Geology of the southern part of the Lemhi 

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___ 1962a, Stratified rocks in south-central Idaho: Idaho 

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___ 1978, Medicine Lodge thrust system, east-central Idaho 

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Selected References 93 
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Tietbohl, Douglass, 1986, Middle Proterozoic diamictite beds 

in the Lemhi Range, east-central Idaho, in Roberts, S.M., 

ed., Belt supergroup-A guide to Proterozoic rocks 

of western Montana and adjacent areas: Montana 

Bureau of Mines and Geology Special Publication 94, 

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deposits of the Seafoam mining district, Custer County, 

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96, 19 p. 

Tschanz, C.M., and Frischknecht, F.C., 1986, Geochemical and 

geophysical studies of selected parts of the eastern part of 

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Geological Survey Bulletin 1545-D, p. 211-230. 

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1545-A, p. 18-43. 

Tschanz, C.M., Kiilsgaard, T.H., Seeland, D.A., VanNoy, R.M., 

Ridenour, James, Zilka, N.T., Federspiel, F.E., Evans, 

R.K., Tuchek, E.T., and McMahan, A.B., 1974, Mineral 

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Geological Survey Open-File Report 74-1100, 2 v., 

648 p. 

Tuchek, E.T., and Ridenour, James, 1981, Economic appraisal 

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Umpleby, J.B., 1912, The lead-silver deposits of the Dome 

district, Idaho: U.S. Geological Survey Bulletin 540, 

p. 212-222. 

___ 1913a, Geology and ore deposits of Lemhi County, 

Idaho: U.S. Geological Survey Bulletin 528, 182 p. 

94 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
___ 1913b, Some ore deposits in Northwestern Custer 

County, Idaho: U.S. Geological Sutvey Bulletin 539, 

182 p. 

___ 1917, Geology and ore deposits of the Mackay region, 

Idaho: U.S. Geological Sutvey Professional Paper 97, 

scale 1:375,000, 129 p. 

Umpleby, J.B., and Livingston, D.C., 1920, A reconnaissance in 

south-central Idaho embracing the Thunder Mountain, 

Big Creek, Stanley Basin, Sheep Mountain, and Seafoam 

districts: University of Idaho Bulletin, v. 15, 22 p. 

Umpleby, J.B., Westgate, L.G., and Ross, C.P, 1930, Geology 

and ore deposits of the Wood River region, Idaho: U.S. 

Geological Sutvey Bulletin 814, 250 p. 

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Bureau of Mines Bulletin 675, 956 p. 

__ 1986, Mineral Inventory Location System (MILS): U.S. 

Bureau of Mines active computer file; data available 

from U.S. Bureau of Mines, Intermountain Field 

Operations Center, Building 20, Denver Federal Center, 

Denver, CO 80225. 

U.S. Bureau of Mines and U.S. Geological Sutvey, 1980, 

Principles of a resource/resetve classification for minerals: U.S. Geological Sutvey Circular 831, 5 p. 

U.S. Geological Sutvey, 1971a, Aeromagnetic map of the 

Challis, May, Lone Pine Peak, and Doublespring quadrangles, east-central Idaho: Open-File Report 71-291, 

scale 1:62,500. 

___ 1971b, Aeromagnetic map of the Patterson and Leadore quandrangles, east-central Idaho: Open-File Report 

71-293, scale 1:62,500. 

___ 1972, Aeromagnetic map of southeastern Idaho and 

part of southwestern Montana: Open-File Report 

72-388, scale 1:500,000. 

___ 1975, Aeromagnetic map of southwestern Montana 

and east-central Idaho: Open-File Report 75-655, scale 

1:250,000. 

___ 1978, Aeromagnetic map of Idaho: Geophysical Investigation Map GP-919, scale 1:500,000. 

___ 1979a, Aeromagnetic map of the Arco area, Idaho: 

Open-File Report 79-1445, scale 1:250,000. 

___ 1979b, Aeromagnetic map of the Pioneer area, Idaho: 

Open-File Report 79-1450, scale 1:62,500. 

___ 1981a, Aeromagnetic map of the Italian Peak area, 

Idaho and Montana: Open-File Report 81-1162, scale 

1:62,500. 

___ 1981b, Aeromagnetic map of the Jerry Peak area, 

Idaho: Open-File Report 81-933, scale 1:62,500. 

___ 1981c, Aeromagnetic map of the Ten Mile West area, 

Idaho: Open-File Report 81-930, scale 1:62,500. 

___ 1986, Mineral Resources Data System (MRDS, 

formerly Computer Resources Information Bank, 

CRIB): active computer file; data available from U.S. 

Geological Sutvey, Branch of Resource Analysis, 

Building 25, Denver Federal Center, Denver, CO 80225. 

U.S. Geological Sutvey and U.S. Bureau of Mines, 1981, 

Mineral resources of the Boulder-Pioneer Wilderness 

Study Area, Blaine and Custer Counties, Idaho: U.S. 

Geological Sutvey Bulletin 1497, 303 p. 

___ 1986, Mineral resources of the eastern part of the 

Sawtooth National Recreation Area, Idaho: U.S. 

Geological Sutvey Bulletin 1545, 472 p. 

VanNoy, 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: U.S. Geological 

Sutvey Bulletin 1545-E, p. 232-4 72. 

Volkman, R.G., 1972, Geology of the Mackay 3NE quadrangle, 

Custer, Blaine, and Butte Counties, Idaho: Milwaukee, 

University of Wisconsin, M.S. thesis, 122 p. 

Walker, E.H., 1964, Subsurface geology of the National 

Reactor Testing Station, Idaho: U.S. Geological Sutvey 

Bulletin 1133-E, 22 p. 

Waring, G.A. (revised by R.R. Blankenship and Ray Bentall), 

1965, Thermal springs of the United States and other 

countries of the world-A summary: U.S. Geological 

Sutvey Professional Paper 492, 31 p. 

Webring, M.W., 1981, MINC; a gridding program based on 

minimum cutvature: U.S. Geological Sutvey Open-File 

Report 81-1224, 43 p. 

Webring, M.W., and Mabey, D.R., 1981, Principal facts for 

gravity stations in the Challis, Idaho 1 ox 2° quadrangle: 

U.S. Geological Sutvey Open-File Report 81-651, 25 p. 

___ 1981, Principal facts for gravity stations in the Challis, 

Idaho 1 o x 2° quadrangle: U.S. Geological Sutvey OpenFile Report 81-652, 25 p. 

Weissenborn, A.B., 1964, The mineral industry in Idaho, in 

U.S. Geological Sutvey in collaboration with Idaho 

Bureau of Mines and Geology and Idaho Department of 

Reclamation, Mineral and water resources of Idaho; 

Committee report, Interior and Insular Affairs, 88th 

Congress, 2d Session: p. 13-22. 

Wells, M.W., 1983, Gold camps and silver cities in Idaho: Idaho 

Bureau of Mines and Geology Bulletin 22, 165 p. 

Wilson, A.B., Soulliere, S.J., Skipp, Betty, Worl, R.G., and 

Rhea, K.P., 1988a, Geology and geochemistry of jasperoid near Mackay, Idaho, in Link, P.K., and Hackett, 

W.R., eds., Guidebook to the geology of Central and 

Southern Idaho: Idaho Geological Sutvey Bulletin 27, 

p. 183-192. 

___ 1988b, Geology and geochemistry of jasperoid from 

Mackay, Idaho: Geological Society of America Abstracts 

with Programs, v. 20, no. 6, p. 474. 

Wust, S.L., 1986a, Tectonic development of the pioneer 

structural complex, central Idaho: Tucson, University of 

Arizona, Ph. D. thesis, 79 p. 

___ 1986b, Extensional deformation with northwest vergence, Pioneer core complex, central Idaho: Geology; 

v. 14, p. 712-714. 

___ 1987, Reply to comment on "Extensional deformation 

with northwest vergence, Pioneer core complex, central 

Idaho": Geology, v. 15, p. 284. 

Wust, S.L., and Link, P.K., 1987, Geology of the Pioneer 

Mountains core complex, south central, Idaho: Northwest Geology, v. 16, p. 85-94. 

Selected References 95 

APPENDIXES 1 AND 2 

DEFINITIONS OF LEVELS OF MINERAL RESOURCE 

POTENTIAL AND CERTAINTY OF ASSESSMENT 

AND 

SIZE CLASSIFICATION OF DEPOSIT TYPES 
APPENDIX 1. DEFINITIONS OF LEVELS OF MINERAL RESOURCE POTENTIAL AND CERTAINTY OF 

ASSESSMENT 

LOW mineral resource potential is assigned to areas where geologic, geochemical, and geophysical characteristics define a geologic environment in which the existence of resources is unlikely. This broad 

category embraces areas with dispersed but insignificantly mineralized rock as well as areas with few 

or no indications of having been mineralized. 

MODERATE mineral resource potential is assigned to areas where geologic, geochemical, and geophysical 

characteristics indicate a geologic environment favorable for resource occurrence, where interpretations 

of data indicate a reasonable likelihood of resource accumulation, and (or) where an application of 

mineral-deposit models indicates favorable ground for the specified type(s) of deposits. 

HIGH mineral resource potential is assigned to areas where geologic, geochemical, and geophysical characteristics indicate a geologic environment favorable for resource occurrence, where interpretations of 

data indicate a high degree of likelihood for resource accumulation, where data support mineral-deposit 

models indicating presence of resources, and where evidence indicates that mineral concentration has 

taken place. Assignment of high resource potential to an area requires some positive knowledge that 

mineral-forming processes have been active in at least part of the area. 

UNKNOWN mineral resource potential is assigned to areas where information is inadequate to assign low, 

moderate, or high levels of resource potential. 

NO mineral resource potential is a category reserved for a specific type of resource in a well-defined 

area. 

levels of Certainty 

t 

..J 

c( 

~ 

z 

w 

b 

a.. 

w 

u 

a: 

:::> 

0 

VJ 

w 

a: 

u. 

0 

..J 

w 

> w 

..J 

U/A 

UNKNOWN 

POTENTIAL 

A 

H/B 

HIGH POTENTIAL 

M/8 

MODERATE POTENTIAL 

L/B 

LOW 

POTENTIAL 

B 

LEVEL OF 

H/C 

HIGH POTENTIAL 

M/C 

MODERATE POTENTIAL 

LIC 

LOW 

POTENTIAL 

c 

CERTAINTY ..,.._ 

H/0 

HIGH POTENTIAL 

M/0 

MODERATE POTENTIAL 

LID 

LOW POTENTIAL 

N/0 

NO POTENTIAL 

D 

A. Available information is not adequate for determination of the level of mineral resource potential. 

B. Available information suggests the level of mineral resource potential. 

C. Available information gives a good indication of the level of mineral resource potential. 

D. Available information clearly defines the level of mineral resource potential. 

Abstracted with minor modifications from: 

Taylor, R. B., and Steven, T. A., 1983, Definition of mineral resource potential: Economic Geology, 

v. 78, no. 6, p. 1268-1270. 

Taylor, R. B., Stoneman, R. J., and Marsh, S. P., 1984, Ar. assessment of the mineral resource potential 

of the San Isabel National Forest, south-central Colorado: U.S. Geological Survey Bulletin 1638, p. 

40-42. 

Goudarzi, G. H., compiler, 1984, Guide to preparation of mineral survey reports on public lands: U.S. 

Geological Survey Open-File Report 84-0787, p. 7, 8. 

98 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
ECONOMIC 

MARGINALLY 

ECONOMIC 

SUBECONOMIC 

RESOURCE/RESERVE CLASSIFICATION 

IDENTIFIED RESOURCES UNDISCOVERED RESOURCES 

Demonstrated Probability Range 

Measured I Indicated 

Inferred (or) 

Hypothetical I Speculative 

I I 

Reserves Inferred Reserves 

~-+- ------ ~ + - Inferred Marginal Reserves Marginal Reserves 

~-+- ------r----- + - Demonstrated Inferred 

Subeconomic 

Subeconomic Resources Resources 

Major elements of mineral resource classification, excluding reserve base and inferred reserve base. Modified from McKelvey,1972, Mineral 

resource estimates and public policy: American Scientist, v.60, p.32-40, and U.S. Bureau of Mines and U.S. Geological Swvey, 1980, 

Principles of a resource/reserve classification for minerals: U.S. Geological Survey Circular 831, p.5. 

Definitions of Levels of Mineral Resource Potential and Certainty of Assessment 99 
GEOLOGIC TIME CHART 

Terms and boundary ages used in this report 

BOUNDARY AGE 

EON ERA PERIOD EPOCH IN 

MILLION YEARS 

Holocene 

Quaternary 0.010 

Pleistocene 

1.7 

Neogene Pliocene 

5 

Cenozoic Subperiod Miocene 

24 

Tertiary Oligocene 

Paleogene 38 

Eocene 

Subperiod 55 

Paleocene 

66 

Cretaceous 

Late 

Early 1- 96 

Late 138 

Mesozoic Jurassic Middle 

Early 

Late 205 

Triassic Middle 

Early 

Phanerozoic Late IV 240 

Permian F.1rly 290 

Late 

Pennsylvanian Middle 

Carboniferous Early 

Paleozoic Periods rv 330 

late Mississippian Early 360 

Late 

Devonian Middle 

Early 

410 

late 

Silurian Middle 

Early 

435 

Late 

Ordovician Middle 

Early 

500 

late 

Cambrian Middle 

Early N 570' 

Late Proterozoic 

900 

Proterozoic Middle Proterozoic 

1600 

Early Proterozoic 

2500 

Late Archean 

Archean Middle Archean 

3000 

3400 

Early Archean 

-------- -------38007- _._ __ --- pre -Archean 2 

4550-

'Rocks older than 570m.y. also called Precambrian, a time term without specific rank. 

2 Informal time term without specific rank. 

100 Mineral Resource Potential and Geology of the Challis National Forest, Idaho 
APPENDIX 2. SIZE CLASSIFICATION OF DEPOSIT TYPES 

Sizes of deposit types are discussed throughout the text. Table 8 lists the approximate tonnages of various sizes of deposit types 

(small, medium, large) for locatable commodities (A-T). 

Table 8. Size classification of deposit types 

[ <, less than; >, greater than] 

Type of deposit 

Small 

Size of deposit (short tons) 

Medium 

A. Fluorspar veins 

B. Polymetallic veins in 

black-shale terrane. 

C. Polymetallic veins in 

quartzite terrane. 

D. Polymetallic veins in 

carbonate terrane. 

E. Polymetallic veins in 

Tertiary extrusive 

F. 

G. 

H. 

I. 

terrane. 

Precious-metal veins 

Base-metal veins 

Vein uranium deposits 

Tungsten stockwork and 

(25,000 

<5,000 

<5,000 

(10,000 

(10,000 

(10,000 

<5,000 

<5,000 

J. 

vein deposits. 

Stockwork molybdenum 

deposits. 

<20,000 

<10,000,000 

K. 

L. 

M. 

N. 

o. 

P. 

Q. 

R. 

s. 

T. 

High-level, rhyolitehosted, precious-metal 

deposits. 

Polymetallic skarn 

deposits. 

Irregular replacements of 

base and precious 

metals. 

Fluorspar breccia manto 

deposits. 

Sediment-hosted, 

jasperoid-associated, 

precious-metal deposits. 

Precious-metal deposits 

in volcanic tuffs. 

Stratabound syngenetic 

deposits of precious 

and base metals. 

Stratiform vanadium 

deposits. 

Gold placer deposits 

Radioactive black-sand 

placer deposits. 

<100,000 

(25,000 

<20,000 

<25,000 

<1,000,000 

(100,000 

<500,000 

500,000 

<2~ ,000 

<25,000 

25,000-1,000,000 

5,000-100,000 

5,000-100,000 

10,000-250,000 

10,000-250,000 

10,000-250,000 

5,000-100,000 

5,000-100,000 

20,000-500,000 

10,000,000-100,000,000 

100,000-1,000,000 

25,000-1,000,000 

20,000-2,000,000 

25,000-2,000,000 

1,000,000-5,000,000 

100,000-5,000,000 

500,000-5,000,000 

500,000-5,000,000 

25,000-1,500,000 

25,000-1,500,000 

Large 

)1,000,000 

)100,000 

)100,000 

)250,000 

)250,000 

)250,000 

)100,000 

)100,000 

)500,000 

)100,000,000 

)1,000,000 

)1,000,000 

)2,000,000 

)2,000,000 

)5,000,000 

)5,000,000 

)5,000,000 

)5,000,000 

)1,500,000 

)1,500,000 

·t:I U.S. GOVERNMENT PRINTING OFFICE: 1989---673-047/86,063 REGION NO.8 Size Classification of Deposit Types 101