Mineral Resources of the

Quigg West Wilderness Study Area,

Granite County, Montana

U.S. GEOLOGICAL SURVEY BULLETIN 1724-D

MONTANA

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CHAPTER D

Mineral Resources of the

Quigg West Wilderness Study Area,

Granite County, Montana

By R.G. TYSDAL and W.F. HANNA 

U.S. Geological Survey

D.O. CAPSTICK 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1724

MINERAL RESOURCES OF WILDERNESS STUDY AREASSOUTHWESTERN MONTANA
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

UNITED STATES GOVERNMENT PRINTING OFFICE: 1988

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

Tysdal, Russell G.

Mineral resources of the Quigg West Wilderness Study Area, Granite 

County, Montana.

(Mineral resources of wilderness study areas southwestern Montana ; 

ch. D) (U.S. Geological Survey bulletin ; 1724-D)

Bibliography: p.

Supt. of Docs, no.: I 19.3:1724-0

1. Mines and mineral resources Montana-Quigg West 

Wilderness. 2. Quigg West Wilderness (Mont.) I. Hanna, William F., 

1938- . II. Capstick, Donald O. III. Title. IV. Series. V. Series: U.S. 

Geological Survey bulletin ; 1724-D.

QE75.B no. 1724-D [TN24.M9] 557.3 s 88-600210

[553'.09786'88]
STUDIES RELATED TO WILDERNESS 

Bureau of Land Management Wilderness Study Areas

The Federal Land Policy and Management Act (Public Law 94-979, October 21, 

1976) requires the U.S. Geological Survey and the U.S. Bureau of Mines to conduct mineral 

surveys on certain areas to determine the mineral values, if any, that may be present. Results 

must be made available to the public and be submitted to the President and the Congress. 

This report presents the results of a mineral survey of the Quigg West Wilderness Study 

Area (MT-074-155), Granite County, Montana.

CONTENTS

Summary Dl

Abstract Dl

Location, geologic setting, and resources Dl 

Introduction D3

Investigations by the U.S. Bureau of Mines D3 

Investigations by the U.S. Geological Survey D3 

Acknowledgments D6 

Appraisal of identified resources D6

Mining and mineral exploration history D6 

Prospects and mineralized areas D6 

Appraisal of mineral resources D6 

Assessment of potential for undiscovered resources D7 

Geology D7

Geologic setting D7

Description of rock units D7 

Geochemistry D9

Analytical methods D9

Results of study D9 

Geophysics D12

Methods D12

Gravity anomaly interpretation D12

Magnetic anomaly interpretation D14 

Mineral resources D16

Gold and molybdenum D16

Copper and silver D20

Sapphires in placer deposits D21

Barite D22

Energy resources D22 

References cited D23 

Appendix D27

FIGURES

1-6. Maps showing:

1. Location of the Quigg West Wilderness Study Area, Granite County , 

western Montana D2

2. Mineral resource potential, geology, and sample localities, Quigg West 

Wilderness Study Area D4

3. Regional features of the Butte 1° x 2° topographic quadrangle, 

Montana D7

4. Geology of region surrounding Quigg West Wilderness Study 

Area D8

5. Complete Bouguer gravity anomalies and generalized geology in the 

vicinity of the Quigg West Wilderness Study Area D15

6. Aeromagnetic anomalies and generalized geology in the vicinity of the 

Quigg West Wilderness Study Area D16

Contents
TABLES

1-3. Semiquantitative spectrographic and chemical analyses; Quigg West 

Wilderness Study Area, Granite County, Montana:

1. Rock samples D10

2. Stream-sediment samples D13

3. Heavy-mineral concentrate samples D14

VI Contents
MINERAL RESOURCES OF WILDERNESS STUDY AREAS-SOUTHWESTERN MONTANA

Mineral Resources of the

Quigg West Wilderness Study Area,

Granite County, Montana

By R.G. Tysdal anc/W.F. Hanna 

U.S. Geological Survey

D.O. Capstick

U.S. Bureau of Mines

SUMMARY

Abstract

A mineral resource survey of the 520-acre Quigg West 

Wilderness Study Area (MT-074-155) was made in 1986-87 

at the request of the U.S. Bureau of Land Management. The 

study area, in central-western Montana, about 16 miles (mi) 

west of Philipsburg, was evaluated for its mineral resources 

(known) and mineral resource potential (undiscovered). No 

identified (known) resources exist in the wilderness study 

area and no producing mines exist in or adjacent to it. 

However, high-grade gold values, as much as 1.24 troy 

ounces gold per ton, were obtained from one prospect in the 

southern part of the study area. About 20 claims have been 

located in the vicinity since the late 1800's, but none are 

currently active.

The southern part of the wilderness study area has a 

moderate resource potential for gold and molybdenum in 

quartz veins related to granitic intrusive rocks; the remainder 

of the area has a low potential for deposits of this type. The 

northwestern part of the wilderness study area has a 

moderate resource potential for copper and silver in 

sandstone-hosted strata-bound deposits; the remainder of 

the study area has a low resource potential for sandstonehosted copper and silver. Two small areas of gravels in 

terrace deposits are present in the southern part of the 

wilderness study area and have a low resource potential for 

placer gold and placer sapphires. The entire area is rated as 

having a low resource potential for gold and molybdenum 

within the interior part of a porphyry molybdenum system; 

silver-copper-gold within the peripheral part of a porphyry 

molybdenum system; gold in alluvial deposits of present-day

streams; barite in veins; uranium; and geothermal resources. 

The entire area is rated as having no potential for oil and gas.

Location, Geologic Setting, and Resources

The Quigg West study area is in the Northern Rocky 

Mountains and lies in an unnamed range immediately west 

of the John Long Mountains (fig. 1). The 520-acre study area 

is on the northeast side of Rock Creek, which flows across 

the structural grain of the rocks of the region, and the study 

area ranges from about 4,700 to 6,900 feet (ft) in elevation. 

The area is near Philipsburg, Montana, from which a paved, 

then gravel, road provides access to the valley of Rock 

Creek.

The study area consists mainly of strata of the Middle 

Proterozoic Belt Supergroup, a sequence of sedimentary 

rocks that were laid down about 900-1,600 million years 

(m.y.) ago (see geologic time chart in Appendix). Only the 

Mount Shields Formation of the Missoula Group of the Belt 

rocks is exposed in the study area. Mountain-building forces 

deformed the sedimentary strata prior to about 82 m.y. ago, 

and resulted in the development of westward-dipping thrust 

faults that separate repeated (stacked) sequences of strata. 

Granitic rocks intruded the strata after they were thrustfaulted and are exposed about 1 mi east of the study area, 

about 3 mi west of it, and may lie concealed in the subsurface 

immediately west of the study area.

Field and laboratory studies were conducted to assess 

the identified resources and mineral resource potential of the 

study area. Geologic mapping was conducted to supplement 

that done previously in the general area to aid in the 

determination of possible controls of mineralization. A geochemical study was made, based on spectrographic and 

chemical analysis of stream sediments and rock samples

Quigg West Wilderness Study Area 01
114'00' 113°30'

46°30' -

APPROXIMATE 

BOUNDARY OF 

QUIGG WEST 

WILDERNESS 

STUDY AREA 

(MT-074-155)

46°00'

Figure 1. Index map showing location of the Quigg West Wilderness Study Area, Granite County , Montana.

collected by the U.S. Geological Survey (USGS). The U.S. 

Bureau of Mines (USBM) examined the one prospect found 

and searched for other mineral occurrences.

No production has been recorded from the wilderness 

study area, although as many as 20 claims may have been 

located in or near the area since the late 1800's; no claims

02 Mineral Resources of Wilderness Study Areas Southwestern Montana
were active at the time of this study. Production of lode and 

placer gold has been documented or reported from mines 

3-7 mi from the wilderness study area.

The one prospect in the wilderness study area is in an 

area rated as having moderate resource potential for gold 

and molybdenum in quartz veins related to granitic intrusive 

rocks (fig. 2). The prospect workings straddle the southern 

boundary of the study area and explore a narrow, 

discontinuous quartz vein. High-grade gold values, as much 

as 1.24 oz/ton, were obtained at the prospect. Drilling would 

be required to determine if resources are present.

Geochemical data show anomalous values for copper 

in Capron Creek in the northwestern part of the study area, 

but no mineralized rock was found that could be the source 

of the copper. The source rocks could lie outside the area, or 

possibly lie concealed beneath talus, alluvium, and colluvium 

of the wilderness study area. The northwestern part of the 

study area is rated as having a moderate resource potential 

for strata-bound, sandstone-hosted copper, and for silver 

that commonly accompanies copper in this type of deposit.

Two small areas of terrace gravels, remnant deposits of 

former streams, occur in the southern part of the study area 

and have a low resource potential for placer gold and placer 

sapphires. The study area also was evaluated for several 

other types of deposits that exist within the general region. 

The entire area is rated as having a low resource potential for 

gold and molybdenum deposited in the interior part of a 

porphyry molybdenum system; silver-copper-gold minerals 

formed in the peripheral part of a porphyry molybdenum 

system; gold in alluvial deposits of present-day streams; 

barite in veins; uranium; and geothermal resources. The 

entire area is rated as having no potential for oil and gas.

INTRODUCTION

The USGS and the USBM studied the 520-acre 

Quigg West Wilderness Study Area (MT-074-155) at 

the request of the U.S. Bureau of Land Management 

(BLM). In this report the studied area is called the 

"wilderness study area" or simply the "study area." The 

study area is located in the Rocky Mountains of centralwestern Montana, in Granite County, about 16 mi west of 

Philipsburg (fig. 1). It is accessible from a road that is 

adjacent to Rock Creek, which flows past the southern 

edge of the study area. The wilderness study area ranges 

from about 4,700 to 6,900 ft in elevation.

This report presents an evaluation of the mineral 

endowment (identified resources and mineral resource 

potential) of the study area and is the product of several 

separate studies by the USBM and the USGS. Identified 

resources are classified according to the system of the 

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

(1980), which is shown in the Appendix of this report. 

Identified resources are studied by the USBM. Mineral 

resource potential is the likelihood of occurrence of 

undiscovered concentrations of metals and nonmetals, of

industrial rocks and minerals, and of undiscovered 

energy sources (uranium, oil, gas, oil shale, and geothermal sources). It was evaluated using the system of 

Goudarzi (1984), which is shown in the Appendix of the 

present report. Classification is according to type of 

deposit, level of potential, and level of certainty. The 

mineral resource potential for undiscovered resources is 

studied by the USGS. In this report, the term "deposit," 

unmodified, carries no connotation of economic value.

Investigations by the 

U.S. Bureau of Mines

Work by the USBM entailed prefield, field, and 

report preparation phases during 1986-87. Prefield 

studies included library research and perusal of Granite 

County, BLM, and Forest Service mining and mineral 

lease records, and a search of USBM production records. 

In August and September 1986, the area was searched by 

ground and air for all prospects and claims indicated by 

the prefield study to be within the wilderness study area 

and vicinity. In addition, searches were made for 

evidence of mining-related activity that may not have 

been recorded. Workings at the one prospect found were 

sampled and mapped, and reconnaissance placer samples 

were taken of alluvium at the mouths of Capron Creek 

and Sheep Gulch (fig. 2), which drain the wilderness 

study area. Results of these studies are presented in 

Capstick (1987) and are summarized in the present 

report.

Ten rock (lode) and three alluvial (placer) samples 

were collected. The rock samples were analyzed for gold 

and silver by fire assay; some were analyzed for copper, 

lead, zinc, or molybdenum by other methods. The 

samples were also analyzed for 24 elements by the 

induction-coupled plasma (ICP) method.

Alluvial samples were concentrated in the field by 

hand-panning and further concentrated on a laboratorysize Wilfley1 table. The concentrates were then examined 

for gold and other heavy-metal content.

Sample analytical results are on file at U.S. Bureau 

of Mines, Western Field Operations Center, E. 360 Third 

Ave., Spokane, WA 99202.

Investigations by the 

U.S. Geological Survey

During the summers of 1986-87, stream-sediment 

and rock samples were collected from the area and 

analyzed chemically and spectrographically. These data

:Trade and company names are used for descriptive purposes 

only and do not imply endorsement by the U.S. Bureau of Mines.

Quigg West Wilderness Study Area D3
117°39' 117°37'

! 1 , \ "" '/ s- '' * \ - * ' -'_ - "

, 1')%,}%:^

A^PROXIIVf ATE ^BOUND^RY^OP

^GUIC^ V^sV

^ STUDY AREA.x ^ :^

Figure 2 (above and facing page). Map showing mineral resource potential, geology, and sample localities, Quigg West 

Wilderness Study Area, Granite County, Montana.

D4 Mineral Resources of Wilderness Study Areas Southwestern Montana
EXPLANATION OF MINERAL RESOURCE POTENTIAL 

Geologic terrane having moderate resource potential 

For gold and molybdenum in quartz veins related to granitic intrusive rocks

For sandstone-hosted strata-bound copper and silver; pattern shows the part of the terrane that is concealed by

terrace gravels

L/B,C Geologic terrane having low resource potential 

For the entire area, except as shown above:

Gold and molybdenum in quartz veins related to granitic intrusive rocks; sandstone-hosted strata-bound copper and silver 

For the entire area: 

Gold and molybdenum in interior part of porphyry molybdenum system; silver, copper, and gold in peripheral

part of porphyry molybdenum system; placer gold in gravels of presently active streams; barite in veins 

Uranium; geothermal resources; placer gold in terrace gravels; placer sapphires in terrace gravels 

N/D Geologic terrane having no resource potential 

For the entire area:

Oil and gas 

Levels of certainty

B Available information suggests level of resource

C Available information gives good indication of level of mineral resource potential 

D Available information clearly defines level of mineral resource potential

CORRELATION OF MAP UNITS

;

|

1

APPROXIM

, ' '}

/

/

ATE MEAN

DECLINATION, 1975

] % 1 MILE 

1 1

CONTOUR INTERVAL 40 FEET

Base from U S. Geological Survey 

Alder Gulch, Cornish Gulch, 

and Quigg Peak, 1975, 

Stoney Creek, 1974

Geology from Wallace and others (1986), 

C A. Wallace, and unpublished data

Qa

Oaf

Qls

Qo

Unconformity

> Holocene

QUATERNARY

TERTIARY

CRETACEOUS

MIDDLE 

PROTEROZOIC

- Contact Approximate location

 Fault U, upthrown side; D, downthrown side. Dotted where concealed

il5 

35

1P

Thrust fault Sawteeth on upper plate; queried where uncertain;dotted 

where concealed

Strike and dip of beds

Sample locality Stream sediment, heavy-mineral concentrate, or 

terrace gravel

Sample locality Rock

Prospect Showing caved adits, trench, and pit

Caved adit

Trench

Pit

Qa 

Qls 

Oaf 

Qo

Tg 

TKi

LIST OF MAP UNITS

Alluvium (Holocene)

Landslide (Holocene)

Alluvial fan (Quaternary)

Glacial outwash (Quaternary)

Terrace deposits (Tertiary)

Dacite dike (Tertiary or Late Cretaceous)

Mount Shields Formation (Middle Proterozoic)

Upper member

Middle member

Lower member

Quigg West Wilderness Study Area D5
were supplemented by analyses of stream sediment, 

heavy-mineral concentrates of stream sediments, and 

rock samples collected from the vicinity of the study area 

by Campbell and others (1982a). No new geophysical 

measurements were made because adequate data had 

been collected recently for the region of the Butte 1° x 2° 

quadrangle, in which the study area lies. Geologic 

mapping was undertaken to supplement that previously 

conducted within the study area by Wallace and others 

(1986) and C.A. Wallace (unpublished data).

Acknowledgments

Jim Sheldon, geologist, Butte BLM District Office, 

provided author Capstick with pertinent mineral and 

mining information. John R. Benham, Alan R. Buehler, 

Martin D. Conyac, Phillip R. Moyle, and Thomas J. 

Peters, U.S. Bureau of Mines, assisted with the USBM 

field investigation. Authors Tysdal and Hanna thank 

C.A. Wallace and J.E. Elliott, both of the USGS, for 

providing manuscripts that were in review and for other 

unpublished data as well. Discussions of the regional 

geology and mineral resources of the region were most 

useful.

APPRAISAL OF IDENTIFIED RESOURCES

By D.O. Capstick 

U.S. Bureau of Mines

Mining and Mineral Exploration History

There has been no recorded production from the 

Quigg West Wilderness Study Area.

The Bagdad mine, 3 mi to the west, possibly 

produced some gold in the late 1890's. Exploration was 

underway, and mine workings were being rehabilitated in 

1987. Remains of milling facilities and numerous 

workings indicate that gold was produced from the 

Crescent mine, 4.5 mi to the southwest. The Silver King 

mine, 7 mi to the southeast, has had production valued at 

about $2 million in gold and silver during the last two 

decades; no production is currently (1986) being 

reported.

Placer gold is reported (Lyden, 1948; Wallace and 

others, 1981) to have been mined nearby from Holocene 

gravels in Rock Creek and some of its tributaries.

Deposits or occurrences of placer gold, titanium, 

corundum, and sapphires, and lode gold, zinc, silver, 

copper, tungsten, molybdenum, antimony, fluorspar,

manganese, rare earths, uranium, vermiculite, and 

pumice have been prospected or mined 3-15 mi from the 

study area in the same or similar rock formations.

Mining claim notices give only vague descriptions 

for claims in or near the wilderness study area. 

Consequently, the actual number of claims is estimated 

at 5-20; the earliest recorded dates are from the late 

1800's, and none are current. Several unorganized 

mining districts that may have enclosed all or a part of the 

study area were identified, but descriptions were inexact. 

The unorganized Rock Creek mining district, 

encompassing much of the main Rock Creek drainage, is 

the only name in current use.

Prospects and Mineralized Areas

Four workings were found at a prospect that 

straddles the south boundary of the wilderness study 

area. They consist of two caved adits, estimated from the 

size of the dumps to have been 50 ft and 250 ft long, a 

40-ft trench, and a small pit (fig. 2). They expose or were 

driven into an apparent fault zone containing a goldbearing, 7-inch-thick quartz vein. The workings and the 

one accessible vein exposure suggest that the mineralized 

fault zone, containing the narrow, discontinuous quartz 

vein, extends about 700 ft and is steeply dipping. Ten 

samples assayed from 0.004 to 1.244 oz gold/ton, nil to 

0.45 oz silver/ton, and nil to 0.02 percent molybdenum; 

one of the samples also contained 0.39 percent copper 

(Capstick, 1987).

Alluvial samples, taken near the mouths of Capron 

Creek and Sheep Gulch which drain the study area (fig. 

2), showed no placer gold or other significant heavy 

minerals; 30 acres of perched Tertiary-age gravel in the 

southeast part of the study area is drained by Sheep 

Gulch.

Appraisal of Mineral Resources

No mineral resources were identified in the 

wilderness study area. Although samples taken from 

mineral-rich stockpiles at the only prospect have good 

gold values, caving and sloughing precluded extensive 

sampling of in-place material, and field evidence 

indicates that the mineralized zone is too narrow and 

discontinuous to constitute resources. Drilling would be 

required to determine if the mineralized zone increases 

in size and persistence with depth, thereby delineating 

possible resources.

The Tertiary-age gravel terranes in the study area's 

southeast corner are similar to gravel occurrences 

elsewhere in the vicinity, some of which contain placer 

gold. One reconnaissance pan sample from the mouth of 

Sheep Gulch, which drains the gravel, showed no placer 

gold.

D6 Mineral Resources of Wilderness Study Areas Southwestern Montana
ASSESSMENT OF POTENTIAL FOR 

UNDISCOVERED RESOURCES

By R.G. Tysdal and W.F. Hanna 

U.S. Geological Survey

Geology

Geologic Setting

The Quigg West Wilderness Study Area is in an 

unnamed range of mountains directly west of the John 

Long Mountains (fig. 1). It is underlain by strata of the 

Belt Supergroup of Middle Proterozoic age, of which 

only quartzite and minor argillite of the Mount Shields 

Formation crop out. The total thickness of the formation 

in this part of Montana is 13,000-15,000 ft (C.A. Wallace, written commun., 1987). Dacite of Cretaceous or 

Tertiary age forms two dike-like intrusive bodies in and 

directly adjacent to the study area. Unconsolidated 

deposits of late Tertiary and Quaternary age occur locally 

within the study area.

Strata of the general region form part of the 

Sapphire thrust plate, an eastward-convex part of the 

overthrust belt of western Montana (Ruppel and others, 

1981). The western part of the Sapphire plate consists of 

a terrane of stacked thrust sheets, and the eastern part 

consists of a frontal zone of anastamosing imbricated 

thrust faults (Lidke and others, 1987; Wallace and 

others, in press) (see fig. 3). In a preliminary 

interpretation of the structural framework of the region, 

Wallace (in Ruppel and others, 1981) used the name 

Rock Creek subplate for the general region of the 

wilderness study area. The new terminology reflects 

substantial revision of the boundaries of the Sapphire 

plate and its internal subdivision.

The following descriptive and interpretative 

material is from Wallace and others (in press). Individual 

sheets in the thrust sheet terrane are composed of 

distinct lithologic sequences bounded by decollements, 

which are generally parallel to bedding. The thickness of 

thrust sheets ranges from about 5,000 to 15,000 ft. The 

stacked thrust sheets end in imbricate thrust faults that 

form the leading edge of the Sapphire plate. The plate 

was emplaced during regional compression, in three 

main phases: (1) emplacement of thrust sheets at the 

same time as the frontal parts of the sheets were being 

imbricated in the frontal zone; (2) folding of the thrust 

sheets; and (3) displacement along zones of younger 

imbricate thrust faults. The entire sequence was later cut 

by steeply dipping faults. Granitic stocks and batholiths 

intruded the Sapphire plate, mostly after emplacement of 

the plate.

Figure 3. Map showing structural setting of region 

surrounding the Quigg West Wilderness Study Area, 

Montana. Thrust sheet terrane and imbricate frontal zone 

are described in text. Intrusive rocks are shown by shaded 

pattern. Map area shown is that of Butte, Montana, 1°x2° 

topographic quadrangle.

Strata of the wilderness study area and the adjacent 

region are part of one thrust sheet within the thrust sheet 

terrane. The thrust faults shown on figure 2 are some of 

the younger imbricate faults within the sheet. Outcrops 

of the Mount Shields Formation are part of this sheet, 

but regional data of Ruppel and others (1981), Wallace 

and others (1986), and unpublished data of Wallace 

indicate that other thrust sheets lie beneath the study 

area and that they contain Belt strata of the Snowslip 

Formation of the Missoula Group and Helena (or the 

equivalent Wallace) Formation, respectively.

The study area lies 1 mi west of the Miners Gulch 

stock and 3 mi east of the Big Spring Creek stock (fig. 4); 

both stocks truncate the thrust faults of the region. The 

Miners Gulch stock has yielded a potassium-argon age of 

about 81 m.y. (Wallace and others, in press). The Big 

Spring Creek stock has not been dated radiometrically, 

but it is considered to be about 73 m.y. old (C.A. 

Wallace, oral commun., 1987), because the stock is a 

zoned intrusive much like the Sapphire batholith (12 mi 

to the south) that has been dated at 73 m.y. (Wallace and 

others, 1982). Zoning of the Sapphire batholith shows an 

outer rim composed of hornblende-biotite granodiorite 

and monzogranite, and a small inner core composed of 

muscovite-biotite granodiorite and monzogranite (Wallace and others, 1982,1984); the Big Spring Creek stock 

shows the same compositional zonation (C.A. Wallace, 

oral commun., 1987).

Description of Rock Units

Rock units within or near the Quigg West 

Wilderness Study Area are described next, with letter 

symbols as shown on figure 2.

Quigg West Wilderness Study Area D7
46° 

30'

113 0 45'

46° 

15'

APPROXIMATE 

SQUNDARY^QF

QTu

<> Yms 

i:;:::j; YfaM .^

EXPLANATION

Quaternary and Tertiary unconsolidated sedimentary rocks

Tertiary volcanic rocks of andesitic, latitic, and rhyolitic composition

Tertiary and Cretaceous gabbro and diorite (TKgb); Cretaceous 

granodiorite (Kgdm), granodiorite and .monzogranite (Kgdb)

Middle Proterozoic Belt Supergroup Mount Shields Formation (Yms); 

quartzitc, siltite, argillitc, and limestone of Belt Supergroup, undivided (Ybu)

Contact

Normal fault Dotted where concealed; ball and bar on downthrown side

^ Thrust fault Sawteeth on upper plate

Figure 4. Generalized geologic map of region that contains the study area. Geology generalized from Wallace 

and others (1986).

Mount Shields Formation (Middle Proterozoic) of to 100 ft thick. Quartzite is pink, flaggy, fine- to mediumthe Missoula group of the Belt Supergroup. Three. grained arkose and quartzite. Argillite sequences are

informal members.

Lower member (YmSj). Alternating quartzite 

and argillite in sequences that each range from about 50

composed of rhymthically interbedded red argillite and 

buff to pink siltite. Ripples, mud cracks, and fluid-escape 

structures are common in argillite sequences, crossbeds

D8 Mineral Resources of Wilderness Study Areas Southwestern Montana
are common in quartzite sequences. Regional thickness 

of the unit is 3,000-3,500 ft. This unit does not crop out 

in wilderness study area, but is shown on the geologic 

map of figure 2. The description is from C.A. Wallace 

(written commun., 1987).

Middle member (Yms2 ). Gray, buff, and pale 

reddish brown fine- to medium-grained, and locally 

coarse-grained quartzite and arkosic quartzite. Beds are 

commonly 1-3 ft thick and graded; the upper part is fine 

grained and capped by layer or thin unit of argillite. 

Ripped-up clasts of argillite are present locally in the 

basal part of the overlying bed. Locally contains trough 

crossbeds, as much as 3 ft across. Forms blocky outcrops. 

Data of C.A. Wallace (written commun., 1987) indicates 

regional thickness of the unit is about 7,000 ft.

Upper member (Yms3 ). Tan, brown, and 

maroon arkosic siltite and fine-grained quartzite, and 

minor interbedded gray-green argillite. Crossbeds and 

oscillatory ripple marks are present locally. Beds 

generally are less than 3 ft thick, but some are several feet 

thick. Regional thickness of the unit is about 3,500 ft 

(C.A. Wallace, written commun., 1987).

Dacite dike of Late Cretaceous or Tertiary age 

(TKi). Medium-gray, poorly exposed biotite dacite that 

forms dike-like intrusive bodies along a fault zone. Its age 

is inferred from data and interpretations of Loen and 

others (in press).

Terrace deposits of Tertiary age (Tg). Unconsolidated deposits of clay, silt, sand, gravel, cobbles, and 

boulders that form a veneer on some ridge crests. 

Cobbles and boulders are mainly composed of maroon, 

well-rounded, fine- to coarse-grained quartzite. Deposits 

are isolated remnants of terrace gravels that probably 

were laid down by an ancestral stream.

Glacial outwash deposits of Quaternary age (Qo). 

Unconsolidated rock materials transported in streams 

that were active during time when glaciers existed in the 

general area.

Alluvial fan of Quaternary age (Qaf). Fan-shaped 

alluvial deposits of unconsolidated clay, silt, sand, gravel, 

and boulders. Clasts are angular to well rounded.

Landslide deposits ofHolocene age (Qls). Unconsolidated deposits of silt, sand, and gravel that have 

moved downslope as the result of water saturation and 

the influence of gravity.

Alluvium of Holocene age (Qa). Unconsolidated 

clay, silt, sand, gravel, and boulders of present-day 

streams and flood plains of the streams. Larger clasts 

tend to be rounded or well rounded.

Geochemistry

Geochemical data for use in this study were 

obtained from stream-sediments (11 samples), heavymineral concentrates (4 samples), and rocks (19

samples) collected during the summers of 1986-87, and 

from the regional sample data set of Campbell and others 

(1982a, b). Geochemical data used for the mineral 

deposit models largely came from Loen and others (in 

press), J.E. Elliott (unpublished data) and Campbell and 

others (1982a).

Analytical Methods

Stream-sediment samples collected during this 

study and that of Campbell and others (1982a) were 

obtained from active and intermittent streams. At each 

site a composite sample of fine detritus was collected 

from several places within the stream bed and later 

air-dried and sieved for analysis. Heavy-mineral 

concentrates of stream sediments, and the sample of 

Tertiary gravel, were panned from coarser detritus 

believed to represent a fairly high-energy depositional 

environment.

Rock samples were collected (1) to identify and 

evaluate places where obvious mineralized or hydrothermally altered rock exist within the wilderness study 

area, and (2) to determine background abundances of 

elements to help evaluate the stream-sediment samples. 

The samples were taken as representative composites of 

chips from outcrops, except for three samples collected 

from float (indicated in table I).7

All samples were analyzed for 31 elements using a 

six-step, direct-current arc, optical-emission, spectrographic method (Grimes and Marranzino, 1968). 

Stream-sediment samples were sieved through an 80- 

mesh (177-micrometer) screen, and a split of the portion 

passing through the sieve was analyzed. A split of each 

crushed and ground rock sample, and a small split of 

each heavy-mineral concentrate sample, also were 

analyzed by this method. Atomic-absorption analyses for 

gold were made on the remainder of each concentrate 

sample, and on each rock sample, using the method of 

Thompson and others (1968). Splits of the rock samples 

also were analyzed for antimony, arsenic, bismuth, 

cadmium, and zinc using the partial extraction, atomicabsorption method of Viets and others (1984), in which 

the readily soluble portions of these elements are 

dissolved and analyzed.

Results of Study

Anomalous geochemical data are briefly described 

in this section. The characteristics of the anomalies and 

their implications are discussed more fully in the section 

of this report entitled "Mineral Resources."

Anomalous concentrations of gold, silver, 

molybdenum, arsenic, and barium (table 1, fig. 2) were 

found in rocks from the southeastern part of the 

wilderness study area in the valley of Sheep Gulch. The

Quigg West Wilderness Study Area D9
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D10 Mineral Resources of Wilderness Study Areas Southwestern Montana
Locality 

No. 

(fig. 2)

1R

3R

4R 

5R

6R 

7R 

8R

9R

10R

11R

12R

13R

14R

15R

16R

17R

18R

19R

Spectrographic analyses, in parts per million

Cu 

(5)

50

50 

L

N 

150

5 

7 

5

L

L

L

L

N

5

5

30

L

10

L

La 

(20) 

(50)

L

20

N

L

20 

20 

L

L

L

N

L

N

30

30

30

20

20

L

Mo 

(5)

70

70

N

N

N 

N 

N

N

N

N

N

N

N

5

N

N

N

N

Nb 

(20)

N

N

N 

N

N 

N 

N

N

L

N

N

N

L

L

L

N

L

L

Ni 

(5)

30

7 

5

15

7 

5 

7

7

7

7

N

L

30

15

7

5

7

30

Pb 

(10)

L

30

N

N

30 

20

N

N

L

10

N

L

15

10

15

10

10

10

Sb 

(100)

N

N

N

N 

N

N

N

N

N

N

N

N

N

N

N

N

Sc 

(5)

5

5

N

5

L

L 

L 

L

L

L

15

N

L

7

7

5

L

5

7

Sn 

(10) 

(20)

N

N

N

N 

N

N

N

N

N

N

N

N

N

N

N

N

Sr 

(100)

N

150

N

N

300 

300

N

5000

N

N

N

5000

L

N

N

N

N

N

V 

(10)

50

70 

30

30

30 

20 

15

30

30

50

15

10

50

50

50

20

10

50

W 

(50)

N

N

N

N

N 

N

N

N

N

N

N

N

N

N

N

N

N

Y 

(10)

15

20 

10

30 

15

N 

15

15

20

20

20

N

30

15

20

15

20

20

Zn 

(200)

N

N

N

N 

N

N

N

N

N

N

N

N

N

N

N

N

Zr 

(10)

50

200 

150

20 

50

150 

150 

30

150

70

200

50

N

300

200

700

200

150

200

Th 

(200)

N

N 

N

N

N 

N 

N

N

N

N

N

N

 

 

N

 

N

N

As 

(10) , 

( 5 ) "

300

490 

6

L 

10

N

N

N

L

130

11

9

 

 

 

 

 

 

Chemic

Bi

9

L

N

N 

N

3

N

L

L

L

N

N

N

N

N

N

Cd 

(0.

0.2

L

.1

.1

N

N

.1

.4

L

.5

.3

.3

.2

.2

.3

.5

' Limit of determination applies only to sample localities 3R, 4R, 11-13R. 

Limit of determination applies only to sample localities 14R-19R.

CO 

CO

I

Q.

 <
area, here called the Sheep Gulch anomaly, contains 

mineralized quartz veins and hydrothermally altered 

country rock and is the site of a prospect. One streamsediment sample from locality 4S from within this 

anomaly yielded a low value (0.1 ppm) for gold (table 2). 

A heavy-mineral concentrate sample from locality 8S, 

about 1 mi southeast of the study area (table 3, fig. 2), 

yielded a value of 3.94 ppm gold. This sample is from 

Windlass Gulch and could represent gold concentrated 

from rocks of the Sheep Gulch anomaly of the wilderness 

study area, from terrace gravels that cap the anomaly 

area, or from rocks from an extensive area of terrain 

outside the study area.

The stream-sediment samples from localities 2S 

and 3S show anomalous values for copper in Capron 

Creek (table 2, fig. 2). These anomalies could represent 

strata-bound copper- and silver-sulfide deposits in the 

drainage area because the stream drains strata that are 

potential host rocks for such mineral deposits. The 

stream-sediment samples have the geochemical characteristics that Harrison and others (1986) showed are 

useful in defining areas of potential for strata-bound 

copper- and silver-sulfide deposits: they contain 

anomalous amounts of copper, with or without silver or 

lead; none, however, contain anomalous amounts of 

bismuth, molybdenum, antimony, or zinc.

Barium in stream-sediment samples from the 

general region of the wilderness study area commonly 

shows values as high as 1,500-2,000 ppm, as revealed by 

our geochemical data and that of Campbell and others 

(1982a). The high value (greater than 10,000 ppm) of 

barium in the sample from locality 10S (table 3) likely 

represents barium derived from barite float that was 

found at locality 13R directly north of the wilderness 

study area. No sulfide elements were detected in either 

the concentrate sample or the barite float.

Geophysics

Methods

The Quigg West Wilderness Study Area and 

surrounding region are covered by regional gravity and 

aeromagnetic surveys having sufficient resolution to 

define anomalies of one or more square miles in areal 

extent. Gravity data are in the form of a terrain-corrected 

Bouguer gravity anomaly map (Hassemer and Hanna, 

1982; Hassemer, 1984) and are based largely on about 50 

observation points within or adjacent to the map area 

shown on figure 5 (Hassemer and Lidke, 1986). Aeromagnetic data are in the form of an anomaly map (U.S. 

Geological Survey, 1984) contoured from measurements 

made along flight lines in an east-west direction, spaced 1 

mi apart, at a barometric elevation of 9,000 ft, and are 

based on 13 flight lines within or adjacent to the map area 

of figure 6.

Gravity Anomaly Interpretation

The gravity anomaly map (fig. 5) shows that the 

Quigg West Wilderness Study Area is flanked by two 

elongate lows one shown in the eastern half of figure 5 

and the other in the western half separated by a broad 

high. The study area is located on a locally flattened part 

of the eastern flank of the western gravity low. The 

eastern (2-minima) gravity low, which has a northerly 

trend, is mainly associated with low-density Tertiary and 

Quaternary unconsolidated deposits. However, the 

gravity minimum within the northern part of the low is 

unexpectedly associated with part of the Cretaceous 

Miners Gulch stock, which is composed principally of 

hornblende-biotite granodiorite that has somewhat 

higher density than hornblende-poor granodiorite. The 

western gravity low, which trends northwest, is unexpectedly associated with Middle Proterozoic sedimentary 

rocks of the Belt Supergroup and with part of the 

Cretaceous Big Spring Creek stock, which is composed 

principally of monzogranite. The intervening high is 

associated with the western two-thirds of the Miners 

Gulch stock and the adjacent terrane of Belt Supergroup 

strata, which includes the wilderness study area.

The eastern low, when considered in relation to 

mapped geology and inferred average densities based on 

measurements made in nearby areas, suggests several 

possibilities, which are as follows. (1) The Miners Gulch 

stock is laccolithic in part; the eastern third of the 

mapped exposures are composed only of a very thin layer 

of granodiorite that extends over lower density Belt 

strata. (2) The stock may be cut at depth by a westwarddipping thrust fault of the Sapphire thrust plate; much of 

the eastern part of the stock is thinner in the subsurface 

than the western part. (3) Field studies of Loen and 

others (in press) show that this part of the stock is 

intruded by a younger, low (or lower) density leucocratic 

porphyritic granodiorite, is pervasively altered, and is 

associated with anomalous concentrations of molybdenum. Neither possibility (1) nor (2) is supported by 

field evidence. The lower density intrusive body, and the 

associated pervasive silicification, is the most likely cause 

of this gravity low. The western gravity low also may be 

due to an altered, low-density intrusive body at depth. 

Although the southwestern flank of this low might be 

explained in part by an eastward decrease in density of 

the zoned Big Spring Creek stock as granodiorite 

becomes monzogranite, it is unlikely that the central part 

and northeastern flank of the low are due to lateral 

changes in density of Belt strata.

A clue to the cause of the western gravity low, and 

the unexplained part of the eastern low, lies in a region 

about 5 mi south of the area of figure 5, where the 

eastern and western gravity lows converge. The resulting 

broad low marks their convergence and clearly is

D12 Mineral Resources of Wilderness Study Areas Southwestern Montana
(Q 

IQ

I

Table 2. Semiquantitative spectrographic and chemical analyses of stream-sediment samples, Quigg West Wildernes

Montana

[Values are reported in the six-step classification, at midpoints 1,1.5, 2, 3,5, 7,10, and so forth; L, detected but less lhan limit of determin

detected at limit of determination; , not determined; values in parts per million except Fe, Mg, Ca, and Ti. Analytical work for the samp

(USGS), D.E. Detra(lS, 4S) and B.M. Adrian and O. Erlich (2S, 3S); chemical (USGS), D.L. Fey and P.L. Hageman (1S, 4S), and P.L Ha

(2S, 3S). Sample data for localities 6S-11S are from Campbell and others, 1982a, b]

Spectrographic analyses

Locality 

No. 

(fig. 2)

IS

2S

3S

4S

6S

7S

8S

9S

10S

US

Sample 

No.

86MTz66

86MTz31

86MTz30

86MTz57

ALD1223S

ALD1225S

COG3249S

QUI3203S

QUI3201S

QUI2399S

Latitude 

deg-min-sec

46-24-05

46-23-35

46-23-22

46-22-53

46-24-06

46-24-05

46-21-48

46-22-35

46-22-52

46-23-23

Longitude In percent

deg-min-sec Fe ^ 

(0.05) (0.02)

113-38-04 1.

113-37-46 2

113-37-47 2

113-37-51 1.

113-36-13 2

113-36-09 3

113-37-17 1.

113-38-35 3

113-38-59 1

113-39-22 1

5 2

.7

.7

5 1.5

.5

.7

5 .5

1

.3

.5

Ca 

(0.05)

1

.5

.3

1

.7

.7

.5

1

1.5

.7

Ti 

(0.002)

0.7

.1

.1

.5

.15

.2

.2

.2

.15

.15

Mn Ag As Au 

(10) (0.5) (200) (10)

500 N N N

500 N N N

700 0.5 N N

500 N N N

500 N N N

1000 N N N

300 N N N

1000 N N N

500 N N N

100 N N N

B 

(10)

500

50

100

70

100

200

150

200

100

100

In parts per mill

Ba Be 

(20) (1)

500 2

1500 7

1000 3

500 2

500 7

1000 7

500 3

1000 7

2000 7

1500 2

Bi 

(10) 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

Locality 

No. 

(fig. 2)

IS 

2S 

3S 

4S 

6S

7S

8S

9S

10S

11S

Spectrographic analyse

Mo Nb 

(5) (20)

N N 

N N 

N N 

N N 

N L

N L

N L

N L

N N

N L

Ni Pb 

(5) (10)

15 10 

20 10 

20 70 

15 10 

10 20

20 30

10 20

30 20

10 20

10 20

Sb Sc Sn 

(100) (5) (10)

N 10 N 

N 15 N 

N 10 50

N 7 N 

N 7 N

N 10 N

N 5 N

N 7 N

N 5 N

N 5 N

s, in parts

Sr V 

(100) (10)

100 70 

L 50 

L 50 

100 50 

L 30

L 70

N 50

N 50

N 30

N 30

per million

W 

,(50) 

^20)

N 

N 

N 

N 

N

N

N

N

N

N

Y 

(100)

70 

100 

50 

30 

70

70

30

50

50

30

Zn Zr Th As 

(200) (10) (100) (10) 

!(

N 200 N 17 

N 100 10 

N 200 10 

N 100 N 15 

300 150 N

N 200 N 

N 300 N 

N 200 N

N 200 N 

N 300 N

Chemical analyses

Bi 

(2)

L 

1 

N 

L 

L

L

1

1

7

8

Cd

,(o.D ,

2 (0.02) 2 (

0.7 

.4 

.3 

.4 

.04

L

.19

.2

.3

L

, in p

Sb 

(2) 

0.1)

L 

2 

2

L 

L 

2 

N 

N 

N 

(D analytical procedure 

D>

*Limit of determination applies only to sample localities IS and 4S .

2 Limit of determination applies only to sample localities 6S-11S; a few values are below these limits due to use of a larg
Table 3. Semiquantitative spectrographic and chemical analyses of heavy-mineral concentrate 

samples, Quigg West Wilderness Study Area, Granite County, Montana

[Values are reported in the size-step classification, at midpoints 1, 1.5, 2, 3, 5, 7, 10, and so forth; L, detected but less 

than limit of determination shown in parentheses; N, not detected at limit of determination; values in parts per million 

except Fe, Mg, Ca, and Ti. Analytical work for the sample localities shown: spectrographic (USGS), D.E. Detra (5S); 

chemical (USGS), P.L. Hageman (5S). Sample data for localities 8S-10S are from Campbell and others, 1982a, b]

Locality 

No. Sample 

(fig. 2) No.

5S 86MTz53 

8S COG3293P 

9S QUI3202P 

10S QUI3200P

Analyses, in percent

Latitude Longitude Spectrographic

deg-min-sec deg-min-sec pe ^ £a ^ 

(0.1) (0.05) (0.1) (0.005)

46-23-00 113-38-13 2 0.7 0.2 1 

46-21-48 113-37-17 3 .3 .15 0.7 

46-22-35 113-38-35 1.5 1 .15 .5 

46-22-52 113-38-59 1.5 .3 .15 .5

Analyses, in parts per million

Spectrographic

Mn Ag As Au B 

(20) (1) (200) (10) (20)

700 N N N 70 

150 N N N 300 

300 N N N 150 

20 L N N 100

No.

Analyses, in parts per million

Spectrographic

(fig. 2) Ba gg Bi cd Co Cr Cu La Mo Nb Ni pb

(10) (1) (10) (20) (10) (10) (10) (50) (5) (50) (10) (20)

H20) ^100)

5S

8S

9S

10S

700

5,000

1.IJOO

>10,000

L N N N 10

2 N N N 70

5 N N L 20

3 N N L 20

500 N

10 50

L 50

L 50

N

N

N

N

N

L

L

L

N L

10 150

20 20

10 L

No.

(fig. 2)

5S

8S

9S

10S

Sb

(200)

N

N

N

N

Analyses, in parts

Spectrographic

Sc Sn Sr V W

(10) (20) (200) (10) (100) 

HSO)

L N 200 100 N

L N N 70 N

10 N N 70 N

10 N N 50 N

per million

Y Zn

(20) (500)

50 N

30 N

70 N

70 N

Zr

(20)

300

2000

500

700

Th

(200)

N

N

N

N

Chemical

Au

(0.05)

N

3.94

L

L

Limit of determination applies only to sample locality 5S.

associated with low-density silicic volcanic rocks 

principally rhyolite and latite shown on the regional 

geologic map of figure 4. The northward and northwestward divergence of the eastern and western lows, 

respectively, from the terrane of volcanic rocks is sharply 

defined by a two-pronged occurrence of discontinuous 

patches of these extrusives. Volcanic rocks extend into 

the southern part of the eastern low, as shown on figure 

5, but end about 1 mi south of the western low of the 

figure. By extrapolation of these lows northward and 

northwestward from these limits of exposed rocks, we 

tentatively infer that in the map area of figure 5 both 

gravity lows are underlain by concealed, low-density, 

intrusive rocks similar in composition to the volcanic 

rocks. Thus, the western gravity low is inferred to be 

caused by a combination of these concealed intrusives

and adjacent monzogranite; the eastern gravity low is 

inferred to be caused by a combination of the hidden 

intrusives and low-density basin fill. The wilderness study 

area itself is located on a locally flattened part of the 

eastern flank of the western gravity low, suggesting that 

Belt Supergroup strata underlying the study area abut, or 

are very close to, the inferred concealed intrusive rocks to 

the west.

Magnetic Anomaly Interpretation

The aeromagnetic anomaly map (fig. 6) shows four 

notable features: (1) part of a magnetic high in the 

northeast corner of the map; (2) part of a magnetic high 

in the northwest corner of the map; (3) a conspicuous 

magnetic high in the eastern half of the map, here termed

D14 Mineral Resources of Wilderness Study Areas Southwestern Montana
46° 

30'

113M5

46° 

20'

4 MILES

EXPLANATION

Gravity contours Contour interval, 2 milligals; dots show location of 

measurement station; L, area of gravity minimum within region of gravity 

low

Quaternary and Tertiary unconsolidated sedimentary rocks

Tertiary volcanic rocks of andesitic, latitic, and rhyolitic compostition

Tertiary and Cretaceous gabbro and diorite (northwesternmost part of

map) and Cretaceous granitic rocks of stocks 

Middle Proterozoic quartzite, siltite, argillite, and limestone of Belt

Supergroup, undivided 

Contact

Figure 5. Terrain-corrected Bouguer gravity anomaly map and generalized geology in the vicinity 

of the Quigg West Wilderness Study Area, Montana.

"the eastern magnetic high;" and (4) an irregular 

magnetic high in the western half of the map, here 

termed "the western magnetic high." The wilderness 

study area is situated at the southwestern extremity of the 

eastern magnetic high. The high in the northeastern 

corner is a blunt nose that represents the southwestern 

subsurface extent of granodiorite of the Henderson 

Creek stock, which crops out about 4 mi east of the map 

area of figure 6. The high in the northwestern corner is 

associated with discontinuous exposures of gabbro, 

microgabbro, and diorite, and probably coincides with 

subsurface bodies of these compositions. This high 

indicates that the mafic igneous rocks extend 

continuously beneath Belt strata in a zone from the map 

area to the southern margin of the the Welcome Creek 

stock, which is exposed 3 mi north of the area of figure 6.

The highest part of the conspicuous eastern 

magnetic high, which covers the western two-thirds of the 

Miners Gulch stock, clearly is associated with strongly 

magnetic granodiorite of this part of the stock. The major

indentation of the contour lines over much of the eastern 

third of the stock indicates the existence of less strongly 

magnetic rocks. One explanation for this occurrence of 

weakly magnetized material is that it represents a less 

magnetic phase of granodiorite. Another explanation, 

based on observations made 50 mi to the east (Hanna, 

1969), is that the granodiorite is both hydrothermally 

altered and intruded at depth by material of felsic 

composition. As stated in the discussion of gravity 

anomalies, field work in this area (Loen and others, in 

press) has delineated a porphyritic granodiorite body that 

is younger than the main phase of the Miners Gulch stock 

and has an associated zone of alteration.

The western magnetic high is associated with the 

Big Spring Creek stock. The irregular magnetic high 

appears to be related to partly exposed, but mostly 

buried, hornblende-biotite granodiorite that C.A. Wallace (oral commun., 1987) found to rim the large 

exposure of monzogranite on the western and southern 

margins of the stock. This partial rimming of monzoQuigg West Wilderness Study Area D15
46° 

30 f

113M5 1

113°15 f

46° 

20'

.-500

EXPLANATION

Magnetic contours Contour interval, 10 gammas; hachures indicate

closed areas of lower magnetic intensity; H, area of magnetic high 

 Flight path of airborne survey

Quaternary and Tertiary unconsolidated sedimentary rocks

Tertiary volcanic rocks of andesitic, latitic, and rhyolitic compostition

Tertiary and Cretaceous gabbro and diorite (northwesternmost part of

map) and Cretaceous granitic rocks of stocks 

Middle Proterozoic quartzite, siltite, argillite, and limestone of Belt

Supergroup, undivided

Contact

Figure 6.

Wilderness

Aeromagnetic anomalies and generalized geology in the vicinity of the Quigg West 

Study Area.

granite by granodiorite is mirrored on a much grander 

scale in the strongly zoned 600-mi2 Sapphire batholith 

(Wallace and others, 1982) 12 mi to the south, where 

strongly magnetic granodiorite and monzogranite completely encircle weakly magnetic granodiorite and monzogranite. Two peaks of high amplitude and short 

wavelength on the western magnetic high of the Big 

Spring Creek stock (fig. 6) suggest that minor amounts of 

gabbro may occur with the granodiorite in the 

subsurface.

Relative to the eastern magnetic high, Belt Supergroup strata beneath the wilderness study area lie about 

1 mi west of the granodiorite in the subsurface of the 

Miners Gulch stock. The region extending west from the 

study area, to the western magnetic high, is underlain by 

weakly magnetic to nonmagnetic rocks; such rocks could 

be Belt strata, or granitic intrusive rocks, such as those 

inferred from the gravity anomaly data.

Mineral Resources

Gold and Molybdenum

Two deposit models are used in an evaluation of 

the mineral resource potential for lode gold in the 

wilderness study area; gold in placers also is assessed. (1) 

In the section entitled "Gold associated with granitic 

intrusive rocks," characteristics of mineralized quartz 

veins in granitic and country rocks adjacent to the Miners 

Gulch stock are described and compared with those of 

the wilderness study area. The two areas have similar 

geologic settings. (2) A bipartite model of a stockwork 

porphyry molybdenum system also is compared with 

mineralized rocks of the wilderness study area, (a) In the 

section entitled "Gold in interior part of porphyry 

molybdenum deposit model," gold-bearing quartz veins 

within the Miners Gulch stock are described. The veins 

are part of a mineralized area that has several characD16 Mineral Resources of Wilderness Study Areas Southwestern Montana
teristics in common with a low-fluorine porphyry molybdenum deposit (Loen and others, in press), (b) In the 

section entitled "Gold in peripheral zone of porphyry 

molybdenum deposit model," silver-copper-gold mineralization that appears to be 2-3 mi distant from granitic 

rocks (Waisman, 1985) is described.

Gold associated with granitic intrusive rocks. The 

model used for gold associated with an igneous intrusive 

is based on rocks in Jimmy Lee Gulch, located about 3 mi 

east-southeast of the wilderness study area (fig. 1). The 

intrusive at Jimmy Lee Gulch (labeled Kgdm on figure 4) 

lies about 3 mi southeast of the southeast corner of the 

Miners Gulch stock. The following characteristics of the 

model are from data of J.E. Elliott (written commun., 

1987), and geophysical data from the present report. (1) 

Gold and associated elements occur in quartz veins, 

commonly about 1 ft thick, which are (2) in shear zones, 

breccia zones, or small faults that cut both the granite 

and the adjacent country rock of the Belt Supergroup. (3) 

The veins are spatially, and presumably genetically, 

related to an intrusive, a porphyritic quartz monzonite 

(classification system of the International Union of 

Geological Scientists, Streckeisen, 1973) that contains 

more potassium feldspar and less quartz than the biotitehornblende granodiorite of the Miners Gulch stock. The 

Jimmy Lee Gulch intrusive is compositionally distinct 

from the Miners Gulch stock. (4) The Jimmy Lee Gulch 

intrusive is small and lacks significant density contrast 

with the surrounding rocks; hence, it is not discernible at 

the scale and contour interval of the gravity map (fig. 5). 

(5) The intrusive lies about 3 mi from the Miners Gulch 

stock and (6) lies outside the closely spaced magnetic 

contour lines that define the steep gradient, and nearly 

vertical contact, at the southeast margin of the stock (fig. 

6). The quartz monzonite intrusive does not display the 

magnetic properties of the Miners Gulch stock. (7) 

Mineralized veins are chiefly in the country rock, and (8) 

contain anomalous amounts of several elements. The 

range of values are shown in parentheses, as follows, 

where L = less than limit of detection and N = no 

detection (the limits of detection for each element are 

shown in table 1): gold (low to 16 ppm), silver (not 

detected to 2 ppm), molybdenum (not detected to 50 

ppm), arsenic (not detected to 450 ppm), and barium 

(150 to greater than 5,000 ppm). The highest values were 

obtained from samples of dump materials. (9) The veins 

and adjacent rock show argillic alteration and silicification. (10) Barite is a common gangue mineral in the 

gold-bearing quartz veins.

The mineralized area of the Sheep Gulch anomaly 

of the wilderness study area (fig. 2) has many features in 

common with those of the Jimmy Lee Gulch area, as 

shown by the following point by point comparison. (1) 

The suite of anomalous elements in the Sheep Gulch 

anomaly is like that at Jimmy Lee Gulch, except that the

Sheep Gulch suite includes bismuth and copper in 

addition to gold, molybdenum, arsenic, and barium. 

Silver is present at Sheep Gulch, but not in anomalous 

amounts as it is at Jimmy Lee Gulch. Anomalous 

elements common to both areas have a similar range of 

values (table 1). Three of the four rock samples (1R-4R, 

table 1) analyzed from the Sheep Gulch anomaly yielded 

gold, with values ranging from 0.15 to 0.65 ppm; gold was 

found in one stream-sediment sample (4S, table 2) and 

was detected (but was not measurable) in a concentrate 

sample (9S, table 3). USBM assays of samples from the 

one prospect (IP) (fig. 2) in the area yielded gold 

quantities ranging from 0.004 to 1.244 oz/ton. (2) 

Mineralized quartz veins at Sheep Gulch are in small 

fault zones, as they are at Jimmy Lee Gulch. (3) No 

granitic intrusive rocks are exposed within or 

immediately adjacent to the study area, as they are in the 

model area. But (4) on the basis of gravity data, it is 

reasonable to infer that granitic rocks may lie concealed 

near or beneath the Sheep Gulch anomaly. The study 

area lies along the eastern part of the western gravity low 

(fig. 5). As discussed previously, the terrane of Belt 

Supergroup strata immediately west of the study area 

may have been intruded by hidden silicic rocks of low 

density and weak magnetization; or, less likely, by 

moderately dense, weakly magnetic, monzogranite in a 

concealed eastward extension of the Big Spring Creek 

stock. (5) The Sheep Gulch anomaly lies about 2 mi from 

the margin of the Miners Gulch stock, similar to the 3-mi 

distance of the intrusive at Jimmy Lee Gulch. (6) The 

magnetic map (fig. 5) shows that the Sheep Gulch 

anomaly is not underlain by biotite-hornblende granodiorite of the stock. Closely spaced magnetic contours 

indicate that the southwest margin of the stock is nearly 

vertical, the same as at the southeast margin near Jimmy 

Lee Gulch. (7) The mineralized quartz veins are in 

country rock, in contrast to their presence in both granitic 

and country rocks at Jimmy Lee Gulch. (9) The 

alteration zone of the Sheep Gulch area is of the argillic 

to sericitic stage. In contrast to the model area, the zone 

of alteration extends well beyond individual quartz veins, 

affecting country rock over thousands of square feet. This 

contrast may indicate that the north-south fault (fig. 2) of 

the wilderness study area provided a much better conduit 

for mineralizing fluids than did the small faults of Jimmy 

Lee Gulch.

Resource potential. The mineral resource 

potential for gold and associated molybdenum in quartz 

veins (and adjacent country rock) deposited under the 

conditions of the granitic intrusive rocks model in the 

area of the Sheep Gulch anomaly in the southern part of 

the study area is rated as moderate, with a certainty level 

of C: the available information gives a good indication of 

the level of mineral resource potential. The mineral 

resource potential for gold and associated molybdenum

Quigg West Wilderness Study Area D17
in quartz veins in the remainder of the wilderness study 

area is rated as low, with a certainty level of C.

Gold in interior part of porphyry molybdenum 

deposit model. The mineralized area of the granodiorite 

plug that intrudes the Miners Gulch stock has the 

following characteristics, summarized from Loen and 

others (in press) for an area associated with a porphyritic 

granodiorite plug in the central part of the eastern third 

of the stock (fig. 4). Most of the characteristics are typical 

of low-fluorine, or calc-alkaline, stockwork porphyry 

molybdenum systems (Westra and Keith, 1981; Theodore, 1982, 1986). (1) The mineralized area is centered 

about a porphyritic granodiorite plug that is about 0.5 mi 

in diameter, nearly cylindrical in plan view, and probably 

is steep sided. (2) Granodiorite of the plug lacks mafic 

minerals, in contrast to that of the hornblende-biotite 

granodiorite of the Miners Gulch stock. (3) The 

mineralized rock occurs in a stockwork of veins and 

fractures in the plug and surrounding rocks, and 

probably represents multiple stages of intrusion, 

fracturing, and mineralization. (4) A zone of pervasive 

propylitic, argillic, and sericitic alteration characterizes 

the plug, adjacent rocks, and related dikes of porphyritic 

granodiorite and dacite that locally cut the plug and 

adjacent rocks. (5) Anomalous concentrations of molybdenum are present in the hydrothermally altered plug 

and adjacent rocks, stockwork veins, and dikes that cut 

the plug and adjacent altered rocks. The geochemical 

signature also includes anomalous amounts of antimony, 

gold, arsenic, tungsten, and barium. Antimony, arsenic, 

and the highest gold values each define semicircular 

halos at a radius of about 1.5 mi from the center of the 

plug. The highest barium values are concentrated within 

the molybdenum anomaly.

In addition to the preceding data that generally are 

typical of low-fluorine porphyry molybdenum systems, 

(6) the area of the porphyritic granodiorite plug is 

marked by a pronounced westward indentation in the 

bold, positive magnetic anomaly pattern of the Miners 

Gulch stock (fig. 6), reflecting (a) the absence of 

magnetic minerals from the granodiorite plug and (b) 

hydrothermal alteration of the magnetic minerals in the 

older granodiorite of this part of the stock. (7) The 

north-trending eastern gravity low overlies the eastern 

third of the Miners Gulch stock (fig. 5), reflecting (a) the 

slightly less dense rocks of the plug; (b) the hydrothermally altered rocks of the stock; and perhaps (c) other, 

concealed, felsic igneous rocks as well.

In the wilderness study area, the Sheep Gulch 

anomaly has several characteristics (items 1-4 that 

follow) that are the same or similar to those of the 

mineralized area in and adjacent to the granodiorite plug 

of the Miners Gulch stock. None of these four 

characteristics is considered definitive for determining if 

minerals of the study area are related to porphyry

molybdenum mineralization. Items 5 and 6 that follow, 

however, suggest that the Sheep Gulch anomaly does not 

represent mineralized rock of a porphyry molybdenum 

system. (1) The Sheep Gulch anomaly contains a suite of 

elements similar to that present in the area of the 

granodiorite plug that intruded the Miners Gulch stock 

and in about the same range of values (table 1). 

Tungsten, however, was not detected in the samples from 

the Sheep Gulch anomaly, but it is present in the area of 

the plug. Anomalous values of molybdenum in goldbearing quartz veins are similar to those reported by 

Loen and others (in press) from the area of the Miners 

Gulch stock. But molybdenum also is known to occur in 

quartz veins in the general region, where no porphyry 

molybdenum deposits are known to exist, as shown by the 

data of Loen and others (in press, and unpub. data) and 

by Campbell and others (1982a, and unpub. data). (2) 

The quartz veins east of the plug are in granodiorite of 

the Miners Gulch stock, but in quartzite of the Belt 

Supergroup at Sheep Gulch. Both the granodiorite of the 

stock and the quartzite are country rock and are 

independent of a porphyry molybdenum system. (3) The 

Sheep Gulch anomaly also differs from that of the 

mineralized halo of the granodiorite plug in that gold is 

present in strata of the Belt Supergroup as well as in the 

quartz veins. This is not a definitive criterion for or 

against a plug existing beneath the wilderness study area 

because a halo of mineralized sedimentary rock at one 

time could have existed over the granodiorite plug of the 

Miners Gulch stock, as well as lateral to it as is presently 

true. (4) Alteration in the vein systems in the two areas 

east of the plug is sericitic, and occurs mainly in veins and 

for a few feet into adjacent country rock. This alteration 

contrasts with the widespread alteration of country rock 

at the Sheep Gulch anomaly where, as noted earlier, a 

large fault may have served as a conduit for mineralizing 

fluids.

Features that characterize the exposed, pervasively 

altered zone of the probable low-fluorine porphyry 

molybdenum system in the east-central part of the 

Miners Gulch stock are not found in the wilderness study 

area. (5) No granodiorite plug is exposed in or near the 

wilderness study area, and (6) gravity data indicate that a 

plug is not likely to be concealed beneath the study area. 

The area of the granodiorite plug in the Miners Gulch 

stock is coincident with the gravity minimum of the 

eastern gravity low (fig. 5), indicating a mass of lowdensity altered rock (both exposed and concealed). The 

pattern of the western gravity low is permissive of altered 

rocks beneath the Sheep Gulch anomaly, but the study 

area lies about 3 mi east of the gravity minimum of the 

western gravity low. Hence, mineralized rocks that 

constitute the Sheep Gulch anomaly probably were not 

formed within a porphyry molybdenum system.

D18 Mineral Resources of Wilderness Study Areas Southwestern Montana
Resource potential. The mineral resource 

potential for gold and molybdenum deposited in the 

interior part of a porphyry molybdenum system in the 

Quigg West Wilderness Study Area is rated as low, with 

a certainty level of C.

Gold in peripheral zone of porphyry molybdenum 

deposit model. This part of the model is based on data 

of Waisman (1985) and regional mineral resource 

studies of J.E. Elliott (written and oral communs., 1987, 

and unpub. data). Elliott's studies indicate that the John 

Long Mountains several miles east of the study area (fig. 

1) contain mines, prospects, and mineral occurrences 

characterized by quartz veins, or vein systems, that are 

laterally extensive and generally concordant to bedding of 

the country rocks. The deposits probably are associated 

with the peripheral zones of porphyry molybdenum 

systems. The deposits are distal to exposed granitic 

intrusives, or to inferred (concealed) granitic intrusives, 

and provide the characteristics for the distal features of 

the porphyry molybdenum model.

The silver-copper-gold veins of the John Long 

Mountains have been important mainly as silver 

producers but also have yielded gold and copper and 

minor amounts of lead and zinc. They also typically 

contain anomalous concentrations of antimony, arsenic, 

bismuth, barium and, locally tungsten, molybdenum, and 

tin. The most important mine of this type is the Black 

Pine, located about 12 mi northeast of the study area (fig. 

1), which produces silver-copper-lead-zinc ore. Since 

1974, about 1 million tons of ore have been mined 

(Waisman, 1985). Another important deposit of this type 

is the Silver King mine, located about 7 mi southeast of 

the study area. This mine produced approximately 2,650 

tons of gold-silver ore during 1976-80 (J.E. Elliott, 

unpub. data). The principal ore minerals are tetrahedrite, chalcopyrite, sphalerite, and galena. These occur in 

a gangue of quartz that contains abundant pyrite and 

minor huebnerite, a manganese-tungsten mineral (Waisman, 1985; Volin and others, 1952; Emmons and 

Calkins, 1913; and J.E. Elliott, written commun., 1987).

The following features of these mineral deposits 

serve as criteria that characterize mineralized rock in 

distal vein deposits of the porphyry molybdenum model. 

The data are from Waisman (1985), Campbell and 

others (1982a), and J.E. Elliott (unpub. data). (1) The 

deposits are in the peripheral zone of a known or 

suspected porphyry molybdenum system, and (2) are 2-3 

mi distant from granitic intrusive rocks. (3) The deposits 

are in a favorable structural environment, which at the 

Black Pine mine is fractured rock related to a major 

thrust fault. (4) The deposits are hosted by a thick, brittle 

sequence of rocks, which in the John Long Mountains are 

strata of the Belt Supergroup. (5) Anomalous 

concentrations of tin, tungsten, and (or) molybdenum are 

present in rock, stream-sediment, and (or) concentrate

samples, indicating the existence of a porphyry 

molybdenum system. Mineralized quartz veins like those 

of the Black Pine mine yield anomalous concentrations of 

the following suite of elements: silver, copper, gold, 

bismuth, arsenic, antimony, barium, lead, zinc, and (or) 

tungsten.

Resource potential. The mineral resource 

potential for silver, copper, and gold in quartz veins 

formed in the peripheral zone of a porphyry 

molybdenum system within the wilderness study area is 

rated as low, with a certainty level of C. The wilderness 

study area lacks several elements that are present in 

anomalous concentrations in the element suite indicative 

of the peripheral part of a porphyry molybdenum system. 

Further, silver values reported from mineral deposits of 

this type are several times higher than those observed in 

rocks of the wilderness study area.

Gold in placer deposits . Strata in which gold 

placer deposits may exist in the wilderness study area 

include some of the same types of deposits as those found 

in the extensively placer-mined Miners Gulch area 3-6 

mi to the east. The Miners Gulch placer deposits, 

recently studied by Loen and others (in press), are 

described briefly and used as a comparative model for 

deposits in the wilderness study area.

Placers in the Miners Gulch area overlie the 

eastern part of the Miners Gulch stock. They occur in 

alluvium, colluvium, lower terrace deposits, and upper 

terrace deposits (Loen and others, in press). The alluvial 

placers were the most widespread, the most intensely 

mined, and the most productive. They are restricted to 

active stream channels and contain rounded quartzite 

clasts recycled from the terrace gravels. Terrace deposits 

were not mined, although test pits had been dug into 

them in an apparent evaluation effort. Loen and others 

(in press) speculated that the terrace gravels were not 

mined because the grade of gold was too low, the clay 

content was too high, and (or) a water supply was not 

available. They sampled a trench cut into the terrace 

gravels but found only a "negligible amount of gold."

The wilderness study area does not contain 

deposits correlative with the lower terrace deposits of the 

Miners Gulch area. Colluvium in the study area is 

present in local patches but is only a veneer. Gold in 

these two types of deposits is not considered further.

Terrace deposits of the Quigg West Wilderness 

Study Area overlie parts of two ridges (fig. 2) and 

probably are remnants of stream-laid deposits. The 

gravels lie at about the same elevation as the "upper 

terrace" deposits of Loen and others (in press). One test 

pit (loc. 5S, fig. 2) was dug to sample the terrace gravels 

of the study area and the sample from it did not yield 

detectable amounts of gold.

Quigg West Wilderness Study Area D19
Alluvial deposits of active streams in the wilderness 

study area yielded measurable amounts of gold in only 

one stream-sediment sample (4S, table 2,0.10 ppm), and 

no concentrate samples, within or immediately adjacent 

to the wilderness study area. The sample from locality 4S 

(fig. 2) is from within the Sheep Gulch anomaly and was 

collected downslope from an area of mineralized quartz 

veins. The gold could have come from the veins, or from 

the terrace gravels that cap the ridges to the north and 

south, assuming the terrace gravels contain gold. Sheep 

Gulch contains only a minor amount of alluvial material 

deposited by the presently active stream.

About 1 mi southeast of the wilderness study area, 

in Windlass Gulch, a heavy-mineral concentrate sample 

from locality 8S (fig. 2) yielded a gold value of 3.94 ppm 

(table 3). The sample could reflect gold concentrated 

from one or more possible sources: (1) mineralized rock 

that is present in the Sheep Gulch anomaly in the 

wilderness study area; (2) the terrane east of Windlass 

Gulch; (3) terrace gravels that cap ridges adjacent to 

Windlass Gulch; or (4) veins within or adjacent to the 

Miners Gulch stock, part of which is drained by the 

stream in Windlass Gulch. The stream-sediment sample 

from locality 7S, 2 mi upstream from locality 8S and near 

the edge of the stock (fig. 2), did not have detectable gold 

at the detection limit of 10 ppm but was not analyzed by 

the more sensitive chemical method which has a 

detection limit of 0.07 ppm.

Resource potential. The mineral resource potential for gold in placer deposits of the terrace gravels in the 

wilderness study area is rated as low, with a certainty 

level of B. A higher level of certainty would require that 

additional pits be dug to sample the terrace gravels. The 

gravels lie at about the same elevation as those of the 

Miners Gulch area, which apparently lack significant 

concentrations of gold. The mineral resource potential 

for gold in placer deposits of presently active streams 

within the wilderness study area is rated as low, with a 

certainty level of C.

Copper and Silver

Strata-bound copper-silver deposits. Copper-silver 

sulfide minerals in strata-bound deposits occur in three 

types of rocks in the Belt Supergroup of western 

Montana: green argillite, carbonate (limestone and 

dolomite) beds, and sandstone (Harrison, 1972, 1974). 

The first two types are discussed only briefly, due to a 

lack of outcrops of the host-rock types within the 

wilderness study area.

In the argillite type, minerals occur in green argillite in sequences where red and green argillite beds are 

closely associated (Harrison, 1972, 1974; Harrison and 

Reynolds, 1979). No strata of this association were seen 

in the study area, although there is a slight possibility

that such strata could be present, but unobserved. The 

carbonate-hosted copper-silver sulfide minerals occur in 

carbonate strata of the Helena Formation (Harrison, 

1972, 1974) and in limestone to calcareous siltstone of 

the Middle Proterozoic Spokane Formation of the 

Ravalli Group of the Belt (Lange and Eby, 1981; Lange 

and Sherry, 1986; Lange and others, 1987). The Helena 

Formation crops out in the general region of the study 

area (in the southern part of the region shown on fig. 4), 

but no strata-bound copper-silver sulfide occurrences 

have been reported (Lidke and others, 1983; J.E. Elliott, 

oral commun., 1987); the Spokane Formation is not 

present near the study area.

In the sandstone-hosted strata-bound copper-silver 

sulfide deposits, ore minerals occur in fine- to mediumgrained beds of quartzite, which commonly are crossbedded (Clark, 1971; Harrison, 1974; Hayes and Einaudi, 

1987). Deposits of this type are known in prospects about 

20-25 mi southeast of the study area (J.E. Elliott, oral 

commun., 1987), and rocks in the wilderness study area 

are possible host strata for similar deposits.

In a resource appraisal of the Wallace I°x2° 

topographic quadrangle (northwest of Missoula), 

Montana and Idaho, Harrison and others (1986) 

presented several geochemical criteria that are useful in 

the assessment of potential for strata-bound coppersilver sulfide deposits. They found that stream-sediment 

samples in drainages near known strata-bound coppersilver sulfide occurrences show anomalous amounts of 

copper, with or without silver or lead. None, however, 

contains anomalous amounts of bismuth, molybdenum, 

antimony, or zinc. These criteria were utilized to aid in 

interpretation of the stream-sediment samples of the 

Quigg West Wilderness Study Area.

In the Quigg West Wilderness Study Area, streamsediment samples 2S and 3S from Capron Creek (fig. 2; 

table 2) contain anomalous amounts of copper (100 and 

1,000 ppm, respectively), and 3S shows silver and 

anomalous lead (70 ppm); bismith, molybdenum, 

antimony, and zinc were not detected in the spectrographic analyses of these samples. The two samples are from 

a sluggish stream, and some of the sampled material 

contained mud that gave off a hydrogen sulfide odor, thus 

indicating a reducing environment; such an environment 

might concentrate elements in greater amounts than 

would a nonreducing environment. However, the sample 

from locality IS, upstream from 2S and 3S, has the same 

characteristics but lacks the concentration of copper. 

Samples 2S and 3S, therefore, are considered anomalous 

and permissive for strata-bound copper-silver deposits. 

Possible sources for the copper are considered as follows.

1. The anomalous copper values could reflect 

source terrane north of the study area. The samples are 

from a drainage that is divided upstream from sample 

locality 3S (fig. 2). No sample was taken from the eastern

D20 Mineral Resources of Wilderness Study Areas Southwestern Montana
fork, which extends about 0.5 mi north of the study area 

boundary, because the drainage bottom was dry and 

covered by large blocks of talus. The western fork 

extends about 1.5 mi upstream (north) from sample 

locality 2S, which is near the northern edge of the study 

area, but a sample from locality IS (0.4 mi north of the 

boundary) did not show anomalous concentrations of 

copper or other elements. A source within the study area 

is possible.

2. Mineralized rock of the strata-bound variety 

typically occurs in layers that are commonly less than 25 

ft thick, in some places only 1-2 ft thick, yet much of the 

bedrock in the Capron Creek drainage is covered by talus 

or by alluvium, making a bedrock source for the copper 

difficult to find. No mineralized rocks were found in 

outcrops in the vicinity of the copper-bearing stream 

sediments, but three rock samples (11R-13R; fig. 2, table 

1) were collected from talus on the west side of the 

stream. The sample from locality 11R is hydrothermally 

altered quartzite that contained an anomalous amount of 

arsenic and minor amounts of zinc; the sample from 

locality 13R is barite (from the head of a talus cone) that 

contained no anomalous amounts of metallic elements 

other than barium; the sample from locality 12R shows a 

boxwork texture of quartz but no anomalous concentrations of elements were detected.

3. The only rock sample that contained an 

anomalous amount of copper (150 ppm) is from locality 

5R (fig. 2), from a thin zone of sheared, tan, mediumgrained quartzite. The locality is near a ridge crest, in the 

drainage of Sheep Gulch, but the shear zone may extend 

west into the Capron drainage as well. This sample could 

reflect mineralizing fluids associated with the Sheep 

Gulch anomaly, although stream-sediment (locality 4S, 

9S; table 2) and concentrate (locality 9S, table 3) samples 

from Sheep Gulch do not show higher values of copper. 

Rock samples 1R and 2R from the Sheep Gulch anomaly 

show values of 50 ppm for copper. Strata represented by 

rock samples from localities 16R and 17R, from the 

upper reaches of Sheep Gulch, strike at a high angle to 

the drainage, and thus represent strata that are drained 

by the stream; the samples yielded low amounts of 

copper.

4. Rock samples from 2 to 3 mi north-northwest 

to northwest of the wilderness study area contain 

anomalous values of silver (3.6-80 ppm), copper (19-470 

ppm), lead (26-960 ppm), zinc (7-160 ppm), cadmium 

(1.75-70), antimony (10-350 ppm), and barium 

(70-3000 ppm) (samples QUI0513R, 515R, 519R, 520R 

of Campbell and others, 1982a). One sample, 513R, 

contained anomalous amounts of zinc and antimony, 

elements that Harrison and others (1986) indicate are 

absent from stream-sediments in areas of strata-bound 

copper-silver mineralized rock. The samples are (1) from 

near a 2-mi-long stream segment that cuts middle

member of the Mount Shields Formation, (2) on strike 

with strata of the wilderness study area, and (3) probably 

from strata of a single thrust sheet (location of thrust 

fault locally is queried on fig. 2). In regard to the 

foregoing, a plausible proposition is that the correlative 

Mount Shields strata in the wilderness study area may 

contain strata-bound copper-silver mineralized rock. 

However, the sediment samples from the stream that 

drains the area of the four rock samples failed to reveal 

anomalous concentrations of any of the elements.

Resource potential. The mineral resource potential for copper and silver resources in strata-bound 

deposits of the sandstone type in the wilderness study 

area is rated as moderate in the northwestern part of the 

study area, with a certainty level of B. A higher level of 

certainty would require additional analyses of rock and 

stream-sediment samples collected from within and 

adjacent to the study area. In addition, because of limited 

exposures on the hillsides, a soil-sampling survey also 

would be useful to aid in determining the source of the 

copper in the stream-sediment samples. The mineral 

resource potential for copper and silver resources in the 

remainder of the study area is rated as low, with a 

certainty level C.

Sapphires in Placer Deposits

For about 100 years sapphires have been recovered 

from placer deposits about 6-8 mi south of the study area 

(Clabaugh, 1952; Ziehen, 1987). The placers are in 

alluvial deposits in an area underlain by Tertiary volcanic 

and sedimentary rocks (fig. 4), but no bedrock source has 

yet been found for the sapphires (J.E. Elliott, oral 

commun., 1987). (The bedrock sources for sapphires in 

central Montana, for example, are mafic dikes (Clabaugh, 1952) and, possibly, contact-metamorphic rocks 

in the roof zone of a granitic intrusive (Mertie and others, 

1951).) No sapphires are known to have been recovered 

from terrace deposits or deposits of active streams in the 

Miners Gulch area northeast of the wilderness study area 

(J.S. Loen, oral commun., 1987). However, Tertiary(?) 

gravel deposits similar to those of the Miners Gulch area 

have yielded sapphires in the area of the Sapphire 

batholith (12 mi south of the study area) (U.S. 

Geological Survey, 1980).

Terrace deposits overlie parts of two ridges in the 

southern part of the Quigg West Wilderness Study Area 

(fig. 2) and are the same deposits discussed in the section 

of this report entitled "gold in placer deposits." At one 

time the two areas of terrace deposits probably formed 

part of a single sheet of stream-laid gravels. The one 

sample collected from terrace gravels (locality 5S, fig. 2) 

did not contain sapphires and no sapphires are known to 

have been recovered from the terrace gravels or

Quigg West Wilderness Study Area D21
alluvium. No bedrock source for sapphires, such as mafic 

dikes or contact-metamorphosed rocks in the roof zone 

of an intrusive, occurs in or adjacent to the study area. 

Resource potential. The mineral resource potential for sapphires in the terrace gravels of the wilderness 

study area is rated as low, with a certainty level of B. A 

higher level of certainty would require digging additional 

test pits to sample the terrace gravels, and examining of 

the heavy mineral suite in deposits of the present 

streams. The absence of sapphires from the extensively 

mined and prospected placer deposits of the Miners 

Gulch area argues for a low resource potential in the 

Quigg West Wilderness Study Area.

Barite

White coarsely crystalline barite occurs in veins in 

the eastern part of the Miners Gulch stock (Loen and 

others, in press) and that occurrence serves as a deposit 

model for comparison. The barite veins of the stock are 

commonly less than 3 ft thick and occupy fault or breccia 

zones within the stock. Sulfide minerals were found in 

only one of the veins, but none of the veins has been 

mined for metallic minerals or for barite. The veins are 

widely distributed, and the map of Blaskowski and others 

(1983) shows that they also are widely separated.

The wilderness study area is close to the Miners 

Gulch stock and barite of the study area likely would 

have had the same origin as that reported by Loen and 

others (in press). Barite was found only in one place, 

however, in float of a talus cone in the northwestern 

corner of the study area. Barite of the talus was traced to 

the head of the talus cone, immediately outside the study 

area, but no bedrock source was found. A float sample 

from locality 13R (fig. 2) at the top of the talus cone was 

analyzed (table 1) and showed no anomalous concentration of metallic elements. Heavy-mineral concentrate 

sample 10S, about 1.5 mi downstream from the talus 

cone (fig. 2), shows a barite value of greater than 10,000 

ppm. The sample probably represents barite carried 

downstream from talus in the area of locality 13R.

Resource potential. The mineral resource 

potential for barite in veins in the wilderness study area is 

rated as low, with a certainty level of C. No barite veins 

were found in the wilderness study area, although the 

barite float of locality 13R probably came from a source 

immediately outside the study area. The sample, like 

most of those in the Miners Gulch area to the east, 

contained no anomalous concentration of metallic 

elements.

Energy Resources

Uranium. The uranium potential of the Butte 

1° X 2° topographic quadrangle (area shown on fig. 3), in 

which the wilderness study area occurs, was evaluated

during the National Uranium Resource Evaluation 

(NURE) program. No samples were collected from the 

study area, but sediment samples collected from streams 

that drain nearby strata of the same formations as occur 

in the study area do not show anomalous concentrations 

of uranium (Broxton, 1980). As part of the NURE study, 

Van Eeckhout (1980) and Sartoris and others (1982) 

concluded that the region of the study area lies west of 

the areas of the Butte quadrangle that are considered 

favorable for uranium deposits.

Intrusive rocks in the vicinity of the study area were 

specifically rated as unfavorable for uranium. A goldplacer deposit about 7 mi west of the study area, on the 

western side of the Big Spring Creek stock (fig. 4), 

reportedly contained grains of a uranium mineral (brannerite), but more than 100 analyzed samples of plutonic 

and Belt metasedimentary rocks from the placer area 

yielded no detectable uranium; radiometric traverses 

revealed no anomalous uranium concentrations (Sartoris 

and others, 1982, p. 27). On the east side of the Big 

Spring Creek stock, about 3 mi southwest of the study 

area, a uranium occurrence was found in Belt rocks 

adjacent to a hydrothermal quartz vein, but rock analyses 

and radiometric traverses in the area revealed no 

anomalous concentrations (Sartoris and others, 1982, p. 

27-28).

Resource potential. The resource potential for 

uranium in the study area is rated as low, with a certainty 

level of B. Geochemical sampling and radiometric 

surveying within the wilderness study area would be 

necessary to achieve a higher level of certainty.

Geothermal energy. No hot springs, or tufa 

deposits of former hot springs, occur within or adjacent 

to the wilderness study area, and, according to the studies 

of Robertson and others (1976), Muffler (1979), and 

Sonderegger and Bergantino (1981), no known geothermal resource area (KGRA) exists within the region. 

The study area is near two major igneous intrusives, and 

concealed intrusives could lie adjacent to (or under) it. 

Near-surface rocks of these intrusives have cooled and 

thus could not provide heat to ground water. Deeply 

buried parts of the intrusives possibly could retain heat, 

but water heated by contact with the rock would require 

a conduit, such as a fault zone, to reach shallow depths. 

Steep faults occur within and near the study area, but at 

present do not serve as conduits for hot water.

Resource potential. The wilderness study area is 

rated as having low potential for geothermal resources, 

with a certainty level of B. A higher level of certainty 

would require specific studies, such as heat-flow 

measurements, to better evaluate the potential for geothermal resources.

Oil and gas. The wilderness study area lies at the 

southern limit of an area rated by Perry and others 

(1983a) as having zero potential for petroleum resources.

D22 Mineral Resources of Wilderness Study Areas Southwestern Montana
The study area lies immediately west of a large tract of 

land assigned "a zero oil potential and, optimistically, a 

low to zero gas potential on the basis of the possibility of 

thermogenic gas in generally low-grade Precambrian 

metamorphic rocks . . ." (Perry and others, 1983b). 

Several geologic factors are unfavorable for the 

occurrence of petroleum resources in the study area. 

After strata of the Belt Supergroup in the study area 

were thrust into their present position, they were heated 

to the greenschist facies of metamorphism during burial 

and intrusion of igneous rocks. The Miners Gulch stock 

lies only 1 mi to the east of the study area and the Big 

Spring Creek stock 3 mi to the west. In addition, the 

study area may be adjacent to, or underlain by concealed 

granitic rocks, based on gravity data.

Resource potential. The wilderness study area is 

rated as having no resource potential for oil or gas, with 

a certainty level of D: available data clearly define the 

level of resource potential.

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Quigg West Wilderness Study Area D23
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Qulgg West Wilderness Study Area D25

APPENDIX
DEFINITION OF LEVELS OF MINERAL RESOURCE POTENTIAL 

AND CERTAINTY OF ASSESSMENT

Definitions of Mineral Resource Potential

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

U/A

UNKNOWN

POTENTIAL

H/B

HIGH POTENTIAL

M/B 

MODERATE POTENTIAL

L/B

LOW

POTENTIAL

H/C

HIGH POTENTIAL

M/C 

MODERATE POTENTIAL

L/C

LOW

POTENTIAL

H/D

HIGH POTENTIAL

M/D 

MODERATE POTENTIAL

L/D

LOW POTENTIAL

N/D

NO POTENTIAL

o

OL

LU

O

cc

LU

cc

u.

o

LU

B C 

LEVEL OF CERTAINTY

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, An 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.
RESOURCE/RESERVE CLASSIFICATION

ECONOMIC

MARGINALLY 

ECONOMIC

SUBECONOMIC

IDENTIFIED RESOURCES

Demonstrated

Measured Indicated

1

Reserves

' 

Marginal Reserves

Demonstrated 

Subeconomic Resources

Inferred

Inferred Reserves

Inferred 

Marginal Reserves

Inferred 

Subeconomic 

Resources

UNDISCOVERED RESOURCES

Probability Range

 (or) 

Hypothetical i Speculative

1 

I

1 

1

1

Major elements of mineral resource classification, excluding reserve base and inferred reserve base. Modified from 

U. S. Bureau of Mines and U. S. Geological Survey, 1980, Principles of a resource/reserve classification for 

minerals: U. S. Geological Survey Circular 831, p. 5.
GEOLOGIC TIME CHART 

Terms and boundary ages used in this report

EON

Phanerozoic

Proterozoic

Archean 

pre-Arc

ERA

Cenozoic

Mesozoic

Paleozoic

Late Proterozoic

Middle Proterozoic

Early Proterozoic

Late Archean

Middle Archean

Early Archean 

jhean2

PERIOD

Quaternary

Neogene 

Subperiod

Tertiary 

Paleogene 

Subperiod

Cretaceous

Jurassic

Triassic

Permian

Pennsylvanian 

Carboniferous

Periods 

Mississippian

Devonian

Silurian

Ordovician

Cambrian

 3800? -

EPOCH

Holocene

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Paleocene

Late 

early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Early

Late 

Middle 

Early

Late 

Early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Middle 

Early

 -

BOUNDARY AGE 

IN 

MILLION YEARS

-0.010

- 1.7

- 5

 JO

- 55

oo

- 96

1 JO

-A, 240

-~ 330

- "ten

- 410

- 500 

- ~ 570 1

- 900 

- 1600

£OUU

-3000 

- 3400

'Rocks older than 570m.y. also called Precambrian, a time term without specific rank. 

1 Informal time term without specific rank.

*U.S. GOVERNMENT PRINTING OFFICE: 1988-0-573-047/66086
Mineral Resources of 

Wilderness Study Areas 

Southwestern Montana

This volume was published as 

separate chapters A-D

U.S. GEOLOGICAL SURVEY BULLETIN 1724
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary

U. S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director
CONTENTS

[Letters designate the chapters]

(A) Mineral resources of the Ruby Mountains Wilderness Study Area, Madison 

County, Montana by R.G. Tysdal, O.K. Lee, J.H. Hassemer, W.F. Hanna, 

and S.W. Schmauch, with a section on Talc by R.B. Berg.

(B) Mineral resources of the Blacktail Mountains Wilderness Study Area,

Beaverhead County, Montana, By R.G. Tysdal, O.K. Lee, J.H. Hassemer, 

W.F. Hanna, and J.R. Benham.

(C) Mineral Resources of the Farlin Creek Wilderness Study Area, Beaverhead 

County, Montana, by R.C. Pearson, J.H. Hassemer, W.F. Hanna, 

D.B. Hoover, H.A. Pierce, and S.W. Schmauch.

(D) Mineral resources of the Quigg West Wilderness Study Area, Granite 

County, Montana, by R.G. Tysdal, W.F. Hanna, and D.O. Capstick.


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