Mineral Resources of the

Henry's Lake Wilderness Study Area,

Fremont County, Idaho

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Chapter D

Mineral Resources of the

Henry's Lake Wilderness Study Area,

Fremont County, Idaho

By R.G. TYSDAL and D.M. KULIK 

U.S. Geological Survey

T.J. PETERS

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1718-D

MINERAL RESOURCES OF WILDERNESS STUDY AREAS SOUTHEASTERN IDAHO
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

UNITED STATES GOVERNMENT PRINTING OFFICE: 1988

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Books and Open-File Reports Section

U.S. Geological Survey

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Any use of trade names in this report is for descriptive purposes only and does 

not imply endorsement by the U.S. Geological Survey and U.S. Bureau of 

Mines.

Library of Congress Cataloging-in-Publication Data

Tysdal, Russel G.

Mineral resources of the Henry's Lake wilderness study area, Fremont 

County, Idaho.

(U.S. Geological Survey bulletin ; 1718) (Mineral resources of wilderness 

study areas southeastern Idaho ; ch. D) 

Bibliography: p. 

Supt. of Docs, no.: I 19.3:1718-0

1. Mines and mineral resources Idaho Henrys Lake Wilderness.

2. Henry's Lake Wilderness (Idaho) I. Kulik, D. M. II. Peters, T. 

J. III. Title. IV. Series. V. Series: Mineral resources of wilderness study 

areas southeastern Idaho ; ch. D.

QE75.B9 no. 1718-D 510s [553'.09796'56] 88-600296 

UN24.I2]
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 Henry's Lake Wilderness Study 

Area (ID-035-077), Fremont County, Idaho.

CONTENTS

Summary Dl

Abstract Dl

Character and setting Dl

Mineral resource potential Dl

Introduction D3

Investigations by the U.S. Bureau of Mines D3 

Investigations by the U.S. Geological Survey D3 

Acknowledgments D3 

Appraisal of identified resources D4

Mining and mineral exploration history D4 

Claim and prospect areas D6 

Identified resources D6

Assessment of potential for undiscovered resources D6 

Geology D6

Geologic setting D6 

Description of rock units D7 

Geochemistry D9

Analytical methods D9 

Results of study D9 

Geophysics D9

Mineral and energy resources DIG 

Talc DIG

Other mineral resources D14 

Geothermal energy D14 

Oil and gas D15 

References cited D15 

Appendix D23

FIGURES

1-5. Maps showing:

1. Location of Henry's Lake Wilderness Study Area, Fremont County, 

Idaho D2

2. Geology, mineral resource potential, sample localities, and prospects in 

the Henry's Lake Wilderness Study Area D4

3. Generalized geology of Henrys Lake region D8

4. Complete Bouguer gravity anomalies and generalized geology in the 

vicinity of the Henry's Lake Wilderness Study Area D12

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

Henry's Lake Wilderness Study Area D13

TABLE

1. Analyses of rock samples, Henry's Lake Wilderness Study Area Dll

Contents

MINERAL RESOURCES OF WILDERNESS STUDY AREAS-SOUTHEASTERN IDAHO

Mineral Resources of the

Henry's Lake Wilderness Study Area,

Fremont County, Idaho

By R.G. Tysdal and DM. Kulik 

U.S. Geological Survey

T.J. Peters

U.S. Bureau of Mines

SUMMARY 

Abstract

A mineral resource survey of the 350-acre Henry's Lake 

Wilderness Study Area (ID-035-077) was made in 1986-87. 

The wilderness study area is in the southern part of the 

Madison Range, Fremont County, Idaho, and is about 17 mi 

(miles) north of the hamlet of Island Park. No identified 

resources (known) or currently active claims exist within or 

adjacent to the wilderness study area. There is potential for 

several types of undiscovered mineral resources within the 

study area. The southwestern part of the wilderness study 

area, along the Madison Range fault, is rated as having a 

moderate energy resource potential for geothermal water; 

the remainder of the study area has a low potential for 

resources of this commodity. A small outcrop of marble in the 

southernmost part of the study area has a low mineral 

resource potential for talc; for talc in marble possibly 

concealed beneath the study area the mineral resource 

potential is rated as unknown. The study area has a low 

mineral resource potential for iron in hematite-mineralized 

amphibolite gneiss, and for gold, silver, and uranium. The 

area has no mineral resource potential for phosphate, 

because the host strata have been eroded; and no resource 

potential for oil and gas.

Character and Setting

The Henry's Lake Wilderness Study Area is in the 

southern part of the Madison Range of the Rocky Mountains, 

in Fremont County, Idaho (fig. 1). It is between 6,600 and

Publication approved by the Director, U.S. Geological Survey 

June 10, 1988.

7,600 ft (feet) in elevation on the south-facing slope of the 

range, which rises steeply from the north side of the 

sedimentary basin that contains Henrys Lake. The study area 

is about 17 mi north of Island Park, Idaho, 13 mi west of West 

Yellowstone, Montana, and is directly north of Idaho State 

Highway 87.

The study area largely consists of Precambrian-age 

rocks (see geologic time chart in Appendix) that were 

metamorphosed about 2,750 m.y. (million years) ago. In the 

northeast corner of the study area, the metamorphic rocks 

are overlain by sandstone strata of Cambrian age, and in the 

southern part by unconsolidated sediments of Holocene age. 

Mountain-building forces deformed this part of the Rocky 

Mountains during the Laramide orogeny, approximately 

60-80 m.y. ago. Rocks of the general region were folded and 

faulted. The range itself began to emerge as a discrete 

mountain mass a few million years later, when the Madison 

Range fault developed along the west and southwest flank of 

the range. Displacement on this fault served to separate the 

rising Madison Range from the downdropped sedimentary 

and volcanic rocks that lie beneath the basin which contains 

Henrys Lake. The wilderness study area is in the Intermountain Seismic Belt, a zone of pronounced earthquake activity, 

and is adjacent to a region that historically has been the most 

seismically active in the Rocky Mountains.

Mineral Resource Potential

Field and laboratory studies were conducted to assess 

the mineral resource potential of the study area. Limited 

geologic mapping was undertaken to supplement that done 

previously; existing geophysical data were adequate for the 

region of the wilderness study area. A geochemical study 

was undertaken and was based mainly on spectrographic

Henry's Lake Wilderness Study Area D1
45° 00

44°30'

'/ " RANGE X '' APPROXIMATE BOUNDARY 

OF HENRY'S LAKE

WILDERNESS STUDY AREA i

(ID-035-077) j

Upper ffecf y~~

/ fiock Lake

i /

_^ iDAficT"" "- '

CENTENNIAL / MOUNTAINS 

i \ i / i i i \ » / i i r

Is J and Park 

Reservoir

Figure 1. Index map showing location of Henry's Lake Wilderness Study Area, Fremont County, Idaho.

D2 Mineral Resources of Wilderness Study Areas Southeastern Idaho
and chemical analysis of rocks but also was based on 

stream-sediment and heavy-mineral concentrate samples 

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

(U.S. Bureau of Mines) examined and sampled prospects 

and mineral occurrences.

The three prospect pits in and immediately adjacent to 

the northeastern part of the wilderness study area occur in 

hematite-mineralized amphibolitic gneiss. A talc prospect lies 

about 1/4 mi east of the study area. The entire wilderness 

study area is rated as having a low mineral resource potential 

for gold, silver, uranium, and iron in amphibolitic gneiss; and 

no resource potential for phosphate in the Phosphoria 

Formation, or for oil and gas. In the southeasternmost part of 

the wilderness study area, talc in marble is rated as having a 

low mineral resource potential. Marble also may occur 

beneath the surface of the study area and possibly could 

contain talc, but the potential for such an occurrence of talc is 

unknown. The southwestern part of the wilderness study 

area is rated as having a moderate potential for geothermal 

water, along the Madison Range fault, but the remainder of 

the area has a low potential for this resource.

INTRODUCTION

The USGS (U.S. Geological Survey) and the 

USBM (U.S. Bureau of Mines) studied the 350-acre 

Henry's Lake Wilderness Study Area (ID-035-077) at 

the request of the BLM (U.S. Bureau of Land 

Management). The study area is located in the southern 

part of the Madison Range in Fremont County, Idaho 

(fig. 1). It is directly north of Idaho State Highway 87, 

about 13 mi (miles) west of West Yellowstone, Mont. 

The wilderness study area ranges from about 6,600 to 

7,600 ft in elevation and is on a south-facing slope of the 

Madison Range.

This report presents an evaluation of the mineral 

resource 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 U.S. Geological 

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

report. Identified resources are studied and evaluated by 

the USBM. Mineral resource potential is the likelihood 

of occurrence of undiscovered metals and nonmetals, 

industrial rocks and minerals, and of undiscovered 

energy sources (coal, oil, gas, oil shale, and geothermal 

sources). It is classified according to the system of 

Goudarzi (1984) and is shown in the Appendix of this 

report. Classification is according to type of deposit, level 

of potential, and level of certainty. The mineral resource 

potential for undiscovered resources is studied and

evaluated by the USGS. In this report, the term 

"deposit," unmodified, carries no connotation of 

economic value.

Investigations by the 

U.S. Bureau of Mines

The USBM part of the wilderness study included 

pre-field, field, and report preparation phases. Pre-field 

preparation included a library search of pertinent 

geological and mining literature and examination of 

BLM master title plats to search out actively held mineral 

properties and property owners. Field work, in June 

1987, included examination of a talc prospect east of the 

study area, and examination of an area of iron oxide 

mineralized gneiss in the northeast corner of the study 

area. A total of 16 rock and 2 alluvial samples were taken 

by the USBM, and prepared for analysis at WFOC 

(Western Field Operations Center), Spokane, Wash. 

Rock samples were analyzed for 25 elements by a 

commercial laboratory and alluvial samples were 

analyzed at WFOC's placer laboratory; Peters and 

Winters (1988) reported the results of these analyses. 

Complete assay data are available from Western Field 

Operations Center, U.S. Bureau of Mines, E. 360 Third 

Ave., Spokane, WA 99202.

Investigations by the 

U.S. Geological Survey

During the summers of 1986-87, stream-sediment 

and heavy-mineral concentrate samples were collected 

from the area and analyzed chemically and spectrographically. Rock samples were collected and analyzed 

chemically to aid in the interpretation of the streamsediment and concentrate data. No new geophysical data 

were obtained. Geologic mapping was conducted within 

the area to supplement previously conducted mapping of 

Witkind (1972a, b).

Acknowledgments

The authors thank R.L. Weeks, Geologist, Cyprus 

Industrial Minerals Company, Englewood, Colo., and 

John Childs, Consulting Geologist, Bozeman, Mont., for 

helpful information on the Tick Heaven talc claims, and 

talc deposits of the region. Mr. and Mrs. E.L. Machamer,

Henry's Lake Wilderness Study Area D3
111°22'30

APPROXIMATE BOUNDARY 

OF HENRY'S LAKE 

WILDERNESS STUDY AREA 

(ID-035-077)

44° 

39'

Base from U.S. Geological Survey 

Targhee Pass and Targhee Peak, 1964

Geology modified from Witkind |1972a)

Figure 2. Geologic map showing areas of mineral resource potential and prospects in the Henry's Lake Wilderness Study 

Area.

and Stanley Goode, granted access to the study area 

across their properties.

For the one stream-sediment sample reported 

herein, the spectroscopic analyst was R.T. Hopkins and 

the chemical analyst was J.D. Sharkey. For the one 

heavy-mineral concentrate sample, the spectrographic 

analysts were B.M. Adrian and O. Erlich; the chemical 

analysts were P.L. Hageman, R.H. Hill, and T.A. Roemer. All analysts are members of the USGS.

APPRAISAL OF IDENTIFIED RESOURCES

By T.J. Peters

U.S. Bureau of Mines

Mining and Mineral Exploration History

Two prospect areas occur in the Henry's Lake 

Wilderness Study Area and vicinity (fig. 2). The name

D4 Mineral Resources of Wilderness Study Areas Southeastern Idaho
EXPLANATION OF MINERAL RESOURCE POTENTIAL

Geologic terrane having moderate resource potential for 

geothermal energy, at certainty level B

Geologic terrane having low resource potential for talc, at certainty level C

Geologic terrane having low resource potential for geothermal 

energy, iron in amphibolite, gold, and silver, at certainty 

level C Applies to entire wilderness study area, except as 

noted above

Geologic terrane having low resource potential for uranium, at 

certainty level B Applies to entire wilderness study area

Geologic terrane having no resource potential for phosphate 

and oil and gas, at certainty level D Applies to entire 

wilderness study area

Geologic terrane having unknown mineral resource potential 

for talc in concealed marble, at certainty level A Applies 

to entire wilderness study area, except as noted above

L/B

N/D

U/A

t

_l 

<

TENTI

U

0.

LU

o

F RESOUF

0 

£

LU

_J

U/Xta

U.:NiKfii$WN

POTENTIAL

:; J: . . . . ........... ...:

H/B

HIGH POTENTIAL

;;M/Bi^:O.;!-:.;;:;

: : MODERATE 'HS 

,: -X ;pOTENTIAI. : :M

!:V^jC;iW:; ii:|:

; : LOW 1 j: -: -

POTENTIAL ; ; : ;

H/C

HIGH POTENTIAL

M/C

MODERATE 

POTENTIAL

JL/C i^iiii

;:;;' ;: :;;:ilLpw-;;.:;:;;: ;i:;|': '

;:.:x|. POTENTIAL :>|;

H/D

HIGH POTENTIAL

M/D

MODERATE 

POTENTIAL

L/D

LOW

POTENTIAL

N/D :;;:S;?s>ssHi;^ ::xSS:;S-;' N0: : " :y ---: ;

I:;:;:;:;::: POTENTIAL

B C

LEVEL OF CERTAINTY

LEVELS OF RESOURCE 

POTENTIAL LEVELS OF CERTAINTY

H High mineral resource potential 

M Moderate mineral resource

potential

L Low mineral resource potential 

U Unknown mineral resource

potential

A Available data not adequate 

B Data indicate geologic environment and 

suggest level of resource potential 

C Data indicate geologic environment, give 

good indication of level of resource 

potential, but do not establish activity 

of resource-form ing processes

D Data clearly define geologic environment 

and level of resource potential and 

indicate activity of resource - forming 

processes in all or part of the area

Diagram showing relationships between levels of mineral resource 

potential and levels of certainty. Shading shows levels that apply to 

this study area

N No known mineral resource 

potential

CORRELATION OF MAP UNITS

Holocene \ QUATERNARY 

I CAMBRIAN

Ags

Qa

U 

U

Oaf Qls

nconformity

Cm

Cf

nconformity

Am Aa Aq } Relative age ""i 

not implied > ARCHEAN

A

X

LIST OF MAP UNITS

Qa

Oaf

Qls

Cm

Cf

Ags

Am

Aa

Aq

Alluvium (Holocene) 

Alluvial fan (Holocene) 

Landslide f Holocene) 

Meagher Limestone (Cambrian) 

Flathead Sandstone (Cambrian) 

Gneiss and schist (Archcan) 

Marble (Archean) 

Amphibolite (Archean) 

Metaquartzite (Archean)

EXPLANATION 

Contact Approximately located

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

downthrown side

Strike and dip of beds

Strike and dip of beds of foliation

Sample locality

Stream sediment and heavy-mineral

concentrate 

Rock

Prospect pit

Henry's Lake Wilderness Study Area D5
and history of the prospect area of iron oxide enriched 

amphibole gneiss at the northeast corner of the study 

area are unknown. The pits, discovered during field 

work, appear to be tens of years old; no claim markers or 

other indications of recent activity were observed.

The Tick Heaven group of eight talc claims extends 

northeast across the north half of sec. 34, T. 16 N., R. 43 

E. (fig. 2), covering an area about 1,200 ft wide by 6,000 

ft long. The claims encompass outcrops of Archean 

dolomitic marble east of the boundary of the study area. 

The claims were acquired by Cyprus Minerals Company 

on July 7, 1985 (R.L. Weeks, oral commun., 1987).

There are no oil and gas leases in the wilderness 

study area.

Claim and Prospect Areas

An area of iron oxide mineralized Precambrian 

gneiss occurs unconformably beneath the Cambrian Flathead Sandstone within down-dropped fault blocks. Iron 

oxide minerals (primarily hematite) form veinlets within, 

and coatings on, the gneiss. Workings consist of three 

shallow pits (fig. 2); the north and south pit are within 

Archean gneiss, and the west pit appears to be underlain 

by Flathead Sandstone. Four samples of the iron oxide 

mineralized gneiss averaged 17.08 percent Fe (iron) 

(Peters and Winters, 1988); five background samples of 

unmineralized gneiss and schist averaged 6.84 percent 

Fe. Base metals (copper, lead, and zinc), ferro-alloys, and 

major elements are depleted in the mineralized gneiss. 

The possible origin of the iron mineralization is discussed 

in Peters and Winters (1988, appendixes C-E).

The Tick Heaven talc claim group covers an 

Archean dolomitic marble unit. Dark-bluish-gray talc 

schist was seen only as pebble and cobble float between 

elevations of 7,000 and 7,200 ft along the northwest 

contact of the dolomitic marble. A select grab sample 

analyzed by X-ray diffraction contained talc 

(approximately 75 percent), lesser calcite, and minor 

dolomite and tremolite (Peters and Winters, 1988).

Identified Resources

No resources of iron, talc, marble, or other lode or 

placer commodities were identified. The iron occurrence 

is too low in grade, small in size, and remote from 

markets to be classified as an identified resource. The 

known extent of the Tick Heaven talc occurrence is 

limited to a small area of talc schist float outside the 

wilderness study area, and cannot be classified as an 

identified resource. The term "marble" as used in this 

report, refers to dolomite that has been recrystallized by 

metamorphism into medium- or coarse-grained metadolomite. It lacks attractive textures and patterns 

commonly associated with decorative marble, and cannot 

be classified as an identified resource. Sand and gravel 

occur in alluvial fans in the southern part of the 

wilderness study area but are not classified as identified 

resources because more accessible deposits have been 

quarried for local use in other parts of the region, as 

shown on the map of Mitchell and others (1981), and 

extensive deposits exist outside the wilderness study area, 

as shown on the construction materials map of Witkind 

(1972f).

ASSESSMENT OF POTENTIAL FOR 

UNDISCOVERED RESOURCES

By R.G. Tysdal and D.M. Kulik 

U.S. Geological Survey

Geology

Geologic Setting

The Henry's Lake Wilderness Study Area is 

located at the south end of the Madison Range and is 

composed of Archean metamorphic rocks that are 

overlain locally by Cambrian strata and Holocene unconsolidated deposits. The Archean rocks are contiguous 

with those farther north in the Madison Range, in 

Montana, which were metamorphosed to upper amphibolite grade or granulite grade (Erslev, 1983) about 2,750 

m.y. (million years) ago (James and Hedge, 1980). The 

wilderness study area apparently is south of the 

southwestern Montana region that underwent a second, 

milder thermal event, dated at 1,600 m.y. by Giletti 

(1966, 1971).

Rocks of the Henrys Lake area, including those in 

the southern part of the Madison Range and the eastern 

end of the Centennial Mountains (fig. 1), were mapped in 

detail and published in a folio of six maps by Witkind 

(1972a-f). A geologic map of the region (fig. 3), 

generalized from Witkind (1972a), shows that Archean 

metamorphic rocks are overlain by Paleozoic strata that 

aggregate as much as 4,200 ft thick and are chiefly 

limestone and dolomite. An incomplete Mesozoic 

sequence in the eastern part of the Centennial Mountains 

totals about 2,200 ft (Witkind, 1982). In comparison, a 

nearly complete Mesozoic sequence in the central part of 

the Madison Range, about 25 mi north of the wilderness 

study area, is more than 10,000 ft thick and is composed

D6 Mineral Resources of Wilderness Study Areas Southeastern Idaho
chiefly of clastic strata (Tysdal and Simons, 1985); a 

similar thickness of Mesozoic strata may have overlain 

the Archean and Paleozoic rocks of the wilderness study 

area.

Eocene(?) mafic volcanic rocks as much as 2,000 ft 

thick overlie Archean and Phanerozoic rocks of the 

eastern part of the Centennial Mountains south of 

Henrys Lake (Witkind, 1972a, 1982). A sequence of late 

Pliocene and Quaternary volcanic rocks, produced by 

volcanism in and near Yellowstone National Park (Christiansen and Blank, 1972; Hamilton, 1965) covers 

extensive areas south of Henrys Lake (Hamilton, 1965; 

Witkind, 1972a, 1982), and to the east in the Park (U.S. 

Geological Survey, 1972). These young volcanic rocks 

tend to be thinner, and are preserved in less extensive 

areas, north of the wilderness study area (Witkind, 

1972a; Tysdal and Simons, 1985). The Henrys Lake basin 

is believed to contain a fill of about 3,500 ft of Cenozoic 

sedimentary and volcanic rocks (Peterson and Witkind, 

1975).

The region was deformed during the Late 

Cretaceous-early Tertiary Laramide orogeny, and rocks 

of the area were faulted and folded. A Laramide-style 

thrust formed along what is now the western flank of the 

Madison Range, and displaced metamorphic rocks 

eastward onto Phanerozoic strata (Tysdal, 1986). The 

rocks of the southern part of the Madison Range are 

interpreted to be part of the terrane that was thrusted 

(Tysdal, 1986; Witkind, 1969). The Madison Range fault, 

a Cenozoic basin-and-range normal fault (Pardee, 1950), 

formed later and severed the leading edge of the thrust 

plate. Part of the thrust plate was downdropped beneath 

what is now the Madison Valley, along the western side 

of the Madison Range, and the Henrys Lake basin along 

the southern to southwestern part of the range. The two 

normal faults at the northeast corner of the wilderness 

study area are considered to be down-to-the-basin faults 

related to the Madison Range fault.

The Henrys Lake region is in the Intermountain 

Seismic Belt, a zone of pronounced earthquake activity 

extending north from Arizona through Utah, eastern 

Idaho, western Wyoming, and western Montana (Smith 

and Sbar, 1974). The Hebgen Lake area, north of the 

wilderness study area (fig. 1), and Yellowstone National 

Park have been the most seismically active areas in the 

Rocky Mountains in historic time, experiencing the 7.1 

magnitude 1959 Hebgen Lake earthquake as well as 

seven other earthquakes of greater than 6 magnitude 

(Trimble and Smith, 1975; Smith and Braile, 1984). The 

epicenter of the 1959 Hebgen Lake earthquake lies

about 10 mi north of the Henry's Lake Wilderness Study 

Area.

Description of Rock Units

Rock units within and adjacent to the Henry's Lake 

Wilderness Study Area are described below, with letter 

symbols as shown in figure 2. Descriptions of the rock 

units are from Witkind (1972a), supplemented with data 

obtained during the present investigation. No relative age 

is implied by the order of the Archean rock units.

Archean gneiss and schist (Ags). Chiefly light- to 

dark-gray, foliated, fine- to coarse-grained biotitequartz-feldspar gneiss and schist. Within the wilderness 

study area and west of the drainage that contains sample 

locality IS, the unit is biotite-staurolite-feldspar schist; 

the staurolite typically forms knots, but in some places it 

occurs as crystals as much as 2 in. long. Staurolite is 

absent east of this drainage and the rocks generally are 

biotite-quartz-feldspar gneiss, and in a few places 

hornblende-feldspar-quartz gneiss. Thin units of amphibolitic gneiss, garnet-amphibolite, and quartz-feldspar 

pegmatite are present locally east of the drainage.

Archean marble (Am). Light-brown to light-gray, 

thin- to thick-bedded, medium- to coarse-crystalline metadolomite (marble). Bedding is defined by thin seams of 

quartz.

Archean amphibolite (Aa). Dark-gray, strongly 

foliated, fine- to coarse-grained rock that is banded due 

to alternating laminae of hornblende and quartzplagioclase.

Archean metaquartzite (Aq). White, light-gray, 

and green foliated thin- to thick-bedded, medium- to 

coarse-grained micaceous metaquartzite; contains minor 

accessory minerals.

Cambrian Flathead Sandstone (C-f). Tan to 

brown, thin- to thick-bedded, fine- to coarse-grained 

sandstone. The strata commonly are crossbedded, and 

locally are cemented by hematite. Witkind (1972a) noted 

that the unit locally contains 5-10 ft of glauconitic shaly 

siltstone beds in the uppermost part; he tentatively 

assigned these strata to the Wolsey Shale, a unit that is 

otherwise absent from the general area. No shaly strata 

were observed in the wilderness study area. The unit 

ranges from 20 to 200 ft thick but is about 50 ft thick in 

the wilderness study area.

Cambrian Meagher Limestone (C-m).-Gray thinbedded limestone that contains abundant light-brown 

and pale-red siltstone mottles. The unit locally contains 

intraformational limestone conglomerate. It is about 550 

ft thick.

Holocene alluvial fan (Qaf). Fan- or cone-shaped 

deposits of unconsolidated silt, sand, gravel, and cobbles.

Henry's Lake Wilderness Study Area D7
111«30* 

44°45'

44«30 f

APPROXIMATE BOUNDARY OF 

HENRY'S LAKE WILDERNESS 

STUDY AREA (ID-035-077)

CENTENNIAL^

012 MILES

D8 Mineral Resources off Wilderness Study Areas Southeastern Idaho
Qu

QTv

TV

Mzr

Ps

Rzr

Ag-5

EXPLANATION

Quaternary unconsolidatcd sedimentary rocks

Quaternary and Tertiary volcanic rocks of rhyolitic composition

Eocene(?) volcanic rocks of trachyitic and basaltic composition 

Mesozoic rocks, chiefly clastic strata

Permian Phosphoria Formation, chiefly sandstone and cherty 

sandstone

Paleozoic rocks, chiefly limestone and dolomite 

Archean gneiss and schist

Contact

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

side

Figure 3 (above and facing page). Generalized geologic 

map of Henrys Lake region ; geology from Witkind (1972a). 

(Note The name "Shedhorn Sandstone" has been applied 

in the Madison Range (to the north) to rocks here indicated 

as the Phosphoria Formation.

Holocene alluvium (Qa). Unconsolidated 

deposits of fluvial silt, sand, and gravel in area marginal 

to Henrys Lake.

Holocene landslide deposits (Qls). Unconsolidated water-saturated deposits of soil, sand, and 

other rock materials that have slid under the influence of 

gravity.

Geochemistry

Geochemical data for use in this study were 

obtained from stream-sediment and heavy-mineral 

concentrate samples, and rock samples collected during 

the summer of 1986.

Analytical Methods

The one stream-sediment sample collected during 

this study was obtained from an intermittent stream. A 

composite sample of fine detritus was collected from 

several places within the stream bed and later air dried 

and sieved for analysis. The heavy-mineral concentrate of 

stream sediment was panned from coarser detritus 

believed to represent a relatively high-energy 

depositional environment.

Rock samples were collected (1) to identify and 

evaluate places where obvious mineralized or altered 

rock exist within the wilderness study area, and (2) to 

determine background abundances of elements to help 

evaluate the stream-sediment and heavy-mineral 

concentrate samples. The samples were taken as 

representative composites of chips from outcrops.

All samples were analyzed for 31 elements using a 

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

stream-sediment sample was sieved through an 80-mesh 

(177 micron) 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 the heavymineral 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, atomic-absorption 

method of Viets and others (1984), in which the readily 

soluble portion of these elements is dissolved and 

analyzed.

Results of Study

Semiquantitative spectrographic analyses of the 

stream-sediment sample (locality IS, fig. 2) yielded 

elevated values of manganese (7,000 ppm (parts per 

million)), chrome (100 ppm), nickel (20 ppm), and 

vanadium (50 ppm). The heavy-mineral concentrate 

sample, from the same locality, yielded anomalous 

amounts of the same elements, as follows: manganese 

(1,000 ppm), chrome (100 ppm), nickel (50 ppm), and 

vanadium (70 ppm). No silver was detected in the 

spectrographic analyses of either sample, and no gold 

was detected in either sample although it was analyzed 

for by both spectrographic and chemical methods. These 

samples are from a stream that drains the staurolite 

schist terrane, and rock sample 5R (table 1) of the schist 

shows similar values for the same elements. An exception 

is manganese, which could readily be concentrated by 

stream processes. The values determined are not unusual 

for staurolite schist; hence, the four elements are not 

considered anomalous.

None of the rock samples showed values for silver 

or gold. Small amounts of copper, lead, and zinc were 

found in the metamorphic-rock samples (table 1, sample 

localities 1R, 2R, 4R, 5R). A value of 70 ppm for zinc was 

detected at locality 4R, but the sample is not considered 

anomalous. None of the geochemical data are believed to 

indicate significant mineralization.

Geophysics

Gravity and magnetic studies were undertaken as 

part of the mineral resource assessment of the Henry's 

Lake Wilderness Study Area. Data from the studies 

provide information on the subsurface distribution of 

density and magnetization and can be used to infer

Henry's Lake Wilderness Study Area D9
geological structure and rock composition. The gravity 

and magnetic data are of a reconnaissance nature and are 

adequate only to define regional (large scale) features. A 

study of linear structural, topographic, and other patterns 

on Landsat multispectral scanner images of southern 

Idaho revealed no features within the wilderness study 

area (D.L. Sawatzky, written commun., 1988).

The gravity map (fig. 4) is from Peterson and 

Witkind (1975), who conducted a study of the Henrys 

Lake region shown in figure 1. Complete Bouguer gravity 

values were computed using an assumed average density 

of 2.67 g/cm3 (grams per cubic centimeter). Terrain 

corrections were made for a distance of 103 mi from each 

station by a method described by Plouff (1977). The 

Henrys Lake basin coincides with a gravity low that 

narrows northwestward (fig. 4), decreasing in amplitude 

across a gravity saddle (3 mi northwest of the study area), 

which Peterson and Witkind (1975) interpreted as 

reflecting a bedrock high. Gravity data from files 

maintained by the U.S. Department of Defense (not 

shown in fig. 4) indicate that the saddle is part of a 

regional high gravity trend that extends at least 10 mi to 

the northeast and 50 mi to the southwest beyond the area 

shown in figure 4.

Peterson and Witkind (1975) interpreted the 

Henrys Lake basin to be bounded by at least three major 

faults. They believed the east-west-trending gravity 

gradient immediately south of Henrys Lake to be 

associated with the Centennial fault (fig. 4); the steep 

gradient immediately west of Henrys Lake to be 

associated with a north-trending fault concealed beneath 

unconsolidated sediments and volcanic rock; and the 

steep southwest-dipping gradient (bracketed between 

points A and B in fig. 4) on the northeast side of the 

Henrys Lake basin to be associated with the Madison 

Range fault. Their gravity model across the gradient 

between points A and B indicates the Madison Range 

fault has a steep dip to the southwest. The wilderness 

study area lies northwest of the bracketed area, where the 

gradient broadens and the gravity values increase to the 

northeast over the core of the Madison Range. Peterson 

and Witkind (1975) believed this broad gradient over the 

range to reflect an increase in density of the crystalline 

rocks toward the core of the range, rather than 

displacement on the Madison Range fault, but their 

geologic map (Peterson and Witkind, 1975, figs. 1 and 2) 

and that of Witkind (1972a) show the fault as continuous 

along the range front. The broader gradient may reflect 

diminishing displacement on the Madison Range fault 

and thinning of the low density Cenozoic rocks of the 

basin over the bedrock high in the valley north of Henrys 

Lake. The increased gravity values over the core of the 

range reflect a northeastward continuation of the 

subsurface bedrock high beneath the exposed Archean 

rocks of the Madison Range itself, similar to a parallel

gravity high associated with the southern part of the 

Blacktail-Snowcrest uplift about 65 mi to the west (Kulik 

and others, 1982).

The aeromagnetic anomaly map (fig. 5) is an 

enlargement of part of the residual intensity magnetic 

anomaly map of the Ashton I°x2° topographic 

quadrangle (scale 1:250,000) (U.S. Department of 

Energy, 1982), in which the study area lies. The map was 

compiled from data collected along east-west flight lines 

spaced at 3-5 mi intervals at 400 ft above the ground 

surface. Magnetic data primarily reflect differences in the 

composition of the Archean crystalline rocks. The 

wilderness study area lies within a regional low magnetic 

anomaly that extends another 25 mi to the northeast and 

is associated with Archean biotite-quartz-feldspar gneiss 

and schist, marble, and metaquartzite of the southern 

part of the Madison Range (fig. 5). The high anomaly 

southwest of Henrys Lake is part of a magnetic high ridge 

that extends to the west-southwest beyond the area of 

figure 5, and the high probably reflects a change in 

composition of the metamorphic rocks in the basement. 

Volcanic rocks at the surface do not appear to have a 

characteristic magnetic signature. The low culmination 

of the magnetic anomaly over Henrys Lake may be 

augmented by the dipole effect the high-low anomaly 

pair relationship commonly seen in magnetic data.

The geophysical data suggest the location of faults 

and compositional differences in rocks or the subsurface 

but do not directly indicate the existence or location of 

mineral resources.

Mineral and Energy Resources

Talc

Talc deposits occur locally in marble of Archean 

metamorphic rocks in southwestern Montana, and the 

marble-bearing metamorphic rocks of the Henry's Lake 

Wilderness Study Area were examined for talc because 

they are a contiguous part of the same metamorphic 

terrane. In a discussion of the Montana talc deposits, 

Berg (1979) stated that all the known talc deposits of 

economic importance occur in the Precambrian marble. 

He further stated that most of the talc deposits formed by 

reaction of the Archean marble with siliceous fluids, an 

event that Garihan (1973) suggested may have occurred 

during the retrograde metamorphic episode 1,600 m.y. 

ago. An exception to this origin are three talc 

occurrences associated with mafic dikes that cut an 

extensive area of dolomitic marble in the Henrys Lake 

Mountains west of Henrys Lake (Berg, 1979, p. 58; 

Sonderegger and others, 1982), about 10 mi west of the 

wilderness study area. The only other talc described in 

the Henrys Lake Mountains was a minor occurrence 

adjacent to a small body of metagranodiorite (Berg, 

1979).

D10 Mineral Resources of Wilderness Study Areas Southeastern Idaho
Table 1. Semiquantitative spectrographic and chemical analyses of rock samples, in and near Henry's Lake Wilderness Study Area, Fremont County, Idaho

[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 than limit of determination shown in parentheses; N, not detected at 

limit of determination. R.T. Hopkins, spectrographic analyst, USGS; T.A. Roemer, chemical analyst, USGS]

Spectrographic analyses

In percent

Locality Sample

No. No.

(fig. 2)

1R 86MTz35

2R 86MTz39

3R 86MTz40

4R 86MTz41

5R 86MTz42

Latitude

deg-min-sec

44-37-56

44-38-15

44-38-1244-38-10

44-38-16

Longitude

deg-min-sec

111-22-41

111-22-36

111-22-42

111-22-43

111-22-52

Rock type

Quartz vein

Oxidized hornblende gneissHematite sandstone

Biotite gneiss

Staurolite schist

Spectrographic analyses, in

(0ET ST(D

$a(D5(0(0

f?

a

Locality

No.

(fig. 2)

1R

2R

3R

4R

5R

Mo

(5)

N

N

N

N

N

Nb

(20)

N

N

N

N

L

Ni Pb

(5) (10)

30 15

5 10

7 N

50 30

100 30

Sb Sc Sn Sr

(100) (5) (10) (100)

N 5 N N

N N N N

N N N N

N 7 N L

N 20 N 100

Fe

(0.05)

2

10

1

3

5

parts

V

(10)

30

1015

70

150

Mg

(0.02)

0.5

.07

.03

1

2

Ca Ti Mn Ag As Au

(0.05) (0.002) (10) (0.5) (200) (10)

0.7 0.15 300 N N N

.3 .002 150 N N N

L .2 L N N N

.3 .3 300 N N N

.7 .5 300 N N N

per million Chemical

W

(50)

N

N

N

N

N

Y Zn Zr Th As

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

15 N 100 N N

10 N N N N

L N 300 N N

15 N 150 N L

15 L 100 N N

In parts per million

B Ba Be

(10) (20) (1)

20 1000 2

10 70 L

50 L N

L 500 L

L 500 1

analyses, in

Bi Cd

(D (0.1)

N 0.1N .1N N

N .1

1 .1

Bi Cd Co Cr

(10) (20) (5) (10)

N N 10 150

N N N L

N N N 70

N N 15 150

N N 30 500

parts per million

Sb Zn Au

(2) (5) (0.05)

N 15 N

N 10 N

N N NN 70 N

N 35 N

Cu La

(5) (20)

L 20

30 N

L N

30 L

30 L
111 0 30'

44°35'

 200

EXPLANATION

Gravity contours Contour interval 2 milligals; hachured contours enclose area of low gravity. Dots show location of 

measurement stations

Quaternary and Tertiary unconsolidated sedimentary rocks 

Quaternary and Tertiary volcanic rocks 

Mesozoic and Paleozoic sedimentary rocks 

Archean crystalline rocks

Contact

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

side

Figure 4. Complete Bouguer gravity anomaly map and generalized geology in the vicinity of the Henry's Lake Wilderness 

Study Area. Gradient between points A and B is discussed in text. Gravity stations from Peterson and Witkind (1975); geologic 

base generalized from Witkind (1972a)

D12 Mineral Resources of Wilderness Study Areas Southeastern Idaho
44°35'

EXPLANATION 

/c/yTSj Magnetic contours Contour interval 20 nanoteslas (gammas);

 400^ hachured contours indicate areas of low magnetic values 

 Flight path of airborne survey

Quaternary and Tertiary unconsolidated sedimentary rocks 

Quaternary and Tertiary volcanic rocks 

Mesozoic and Paleozoic sedimentary rocks 

Archean crystalline rocks

Contact

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

side

Figure 5. Aeromagnetic anomaly map and generalized geology in the vicinity of the Henry's Lake Wilderness Study Area. 

Magnetic data from U.S. Department of Energy (1982); geologic base generalized from Witkind (1972a).

Henry's Lake Wilderness Study Area D13
Talc was not found in the small outcrop of marble 

that lies in and adjacent to the southernmost part of the 

wilderness study area (fig. 2). No mafic dikes were 

observed to cut the marble and no granitic intrusive 

rocks, from which siliceous fluids might have originated 

and reacted with marble to form talc, were found in the 

vicinity by us or mapped by Witkind (1972a). However, 

traces of talc were found in the tabular body of marble 

that crops out about 0.25-0.75 mi east of the study area 

(fig. 2), where the USBM (this report, and Peters and 

Winters, 1988) found talc in float chips. The tabular 

marble body also contains small quartz knots and tremolite, a fibrous amphibole. The tabular marble unit is 

inclined to the west and part of it could lie concealed 

beneath the study area. Rocks exposed in the study area 

have been downdropped and displaced basinward along 

the two arcuate, north-trending normal faults shown in 

figure 2. If part of this tabular marble body is present 

beneath the study area, it likely was downdropped and 

would lie at a greater depth beneath the surface than 

would otherwise be the case.

Resource potential. The mineral resource 

potential for talc in marble exposed in the southeasternmost part of the study area is rated as low, with a 

certainty level of C. The mineral resource potential for 

talc in marble strata that could lie concealed beneath the 

study area is rated as unknown, with a certainty level 

of A.

Other Mineral Resources

No gold, silver, or significant concentrations of iron 

or other metals were found in the wilderness study area. 

Gold and associated silver occur locally in Archean 

metamorphic rocks in the adjacent region of 

southwestern Montana, but neither of these elements is 

known to be present in Archean rocks in or near the 

wilderness study area. No gold or silver was detected in 

the rock, stream-sediment, or concentrate samples 

analyzed. The one quartz vein that was sampled yielded 

only an elevated value for barium, but no other 

anomalous metal value (table 1, locality 1R). The 

resource potential for gold and silver is rated as low with 

a certainty level of C.

Iron in hematite of oxidized Archean amphibolite 

gneiss occurs in and adjacent to the northeast corner of 

the wilderness study area, but, as discussed in the USBM 

section of this report, the iron is not so significantly 

enriched as to constitute a resource. No hematite of 

oxidized Archean amphibolite was found in other parts 

of the study area. The mineral resource potential for iron 

in hematite of oxidized amphibolite gneiss in the entire 

wilderness study area is rated as low, with a certainty 

level of C.

Uranium potential of the Ashton I°x2° topographic 

quadrangle, in which the wilderness study area occurs, 

was evaluated during the NURE (National Uranium 

Resource Evaluation) program. No samples were 

collected from the study area, but samples collected from 

similar metamorphic rocks nearby do not show 

anomalous concentrations of uranium (Shannon, 1980, 

1982). As part of the NURE study, Suekawa and others 

(1982) concluded that the Archean metamorphic rocks 

within the Ashton quadrangle contain environments that 

are unfavorable for uranium deposits. The resource 

potential for uranium is rated as low, with a certainty 

level of B. Geochemical sampling within the wilderness 

study area would be necessary to have a higher level of 

certainty.

The major source of phosphate in the Western 

United States is the Permian Phosphoria Formation. 

Although phosphate resources exist in the Centennial 

Mountains a few miles southwest of the wilderness study 

area (fig. 1), phosphate-bearing strata have been eroded 

from the general vicinity of the study area (fig. 3). No 

resource potential for phosphate of the Phosphoria 

Formation exists within the Henry's Lake Wilderness 

Study Area. The rating is made with a certainty level 

ofD.

Geothermal Energy

No hot springs, or tufa deposits of former hot 

springs, occur within or adjacent to the wilderness study 

area. But the area lies just north of the eastern part of the 

Snake River Plain, a region of geologically young volcanic 

rocks that are suggestive of high heat flow (Brook and 

others, 1979; Smith and Shaw, 1979). Yellowstone 

National Park (about 9 mi east of the wilderness study 

area) lies at the northeast end of the Snake River Plain 

and contains abundant resources of geothermal energy; 

and a known geothermal resource area (KGRA) lies 

about 7 mi east of the study area, along the western 

border of the Park (Muffler, 1979). About 25 mi south of 

the wilderness study area, Muffler (1979) showed many 

KGRA's present in the vicinity of the Island Park 

Caldera. Although the Henry's Lake Wilderness Study 

Area and the immediately adjacent terrain do not contain 

the geologically young volcanic rocks, the close proximity 

of the Snake River Plain and Yellowstone National Park 

with their geothermal waters suggests that the wilderness 

study area must be considered favorable for geothermal 

resources.

Movement along the Madison Range fault possibly 

could provide a conduit for geothermal water to reach 

the ground surface. The wilderness study area lies in a 

region that, historically, is the most seismically active in 

the Rocky Mountains (Smith and Braile, 1984), and it is 

within seismic risk zone 3, defined on the Seismic Map of

D14 Mineral Resources of Wilderness Study Areas Southeastern Idaho
the United States (Algermissen, 1969) as an area in 

which major destructive earthquakes may occur. Some 

segments of the Madison Range fault underwent 

movement during the 1959 Hebgen Lake earthquake 

(U.S. Geological Survey, 1964), but the southeasttrending, southern extent of the fault north of Henrys 

Lake is concealed beneath alluvial deposits, as shown on 

the geologic map of Witkind (1972a). Peterson and 

Witkind (1975) stated that the trace of the fault is 

marked by a scarplet 10-30 ft high, indicating that the 

fault is active, but no ground breakage in or adjacent to 

the wilderness study area took place during the 1959 

Hebgen Lake earthquake (U.S. Geological Survey, 1964, 

pi. 5). Interpretative maps of Witkind (1972d, e) show 

that a zone along the concealed trace of the Madison 

Range fault, including the segment in the wilderness 

study area (fig. 2), could experience fault movement and 

ground breakage during an earthquake.

The resource potential for geothermal water along 

the Madison Range fault is rated as moderate, with a 

certainty level of B. A higher level of certainty would 

require specific studies, such as heat flow measurements 

and collection of data from existing wells, to better 

evaluate the potential for geothermal resources. For the 

remainder of the wilderness study area, the resource 

potential for geothermal water is rated as low, with a 

certainty level of C.

Oil and Gas

The energy resource potential for oil and gas in the 

wilderness study area is not considered favorable because 

of the thermal effects of the geologically young volcanic 

systems in the nearby Snake River Plain and Yellowstone 

National Park. Sandberg (1983, p. F4) stated that conodont alteration index values of 1.5 to 2 were obtained 

from (Paleozoic) strata at Targhee Peak, 3 mi north of 

the wilderness study area, which he stated indicated 

optimum maturation for oil and gas generation in the 

area. These strata overlie Archean metamorphic rocks 

and have been eroded from all but the crestal area of the 

southern part of the Madison Range, and eroded from 

the Henrys Lake Mountains west of Henrys Lake; hence, 

potential source rocks no longer exist in the wilderness 

study area. No resource potential exists for oil and gas in 

the wilderness study area, with a certainty level of D.

REFERENCES CITED

Algermissen, ST., 1969, Seismic risk studies in the United 

States: World Conference on Earthquake Engineering, 

4th, Santiago, Chile.

Berg, R.B., 1979, Talc and chlorite deposits in Montana: 

Montana Bureau of Mines and Geology Memoir 45,66 p.

Brook, CA., Mariner, R.H., Mabey, D.R., Swanson, J.R., 

Guffanti, Marianne, and Muffler, L.PJ., 1979, Hydrothermal convection systems with reservoir temperatures 

<90°, in Muffler, L.J.P., ed., Geothermal resources of 

the United States: U.S. Geological Survey Circular 790, 

p. 18-40.

Christensen, R.L., and Blank, H.R., Jr., 1972, Volcanic stratigraphy of the Quaternary rhyolite plateau in Yellowstone 

National Park: U.S. Geological Survey Professional 

Paper 729-B, 18 p.

Erslev, E A., 1983, Pre-Beltian geology of the southern Madison Range, southwestern Montana: Montana Bureau of 

Mines and Geology Memoir 55, 26 p.

Garihan, J.M., 1973, Origin and controlling factors of the talc 

deposits of steatite grade in the central Ruby Range, 

southwestern Montana [abs.]: Geological Society of 

America, Northeast Section Meeting, Abstracts with 

Programs, v. 5, p. 164.

Giletti, B.J., 1966, Isotopic ages from southwestern Montana: 

Journal of Geophysical Research, v. 71, p. 4029-4036.

___ 1971, Discordant isotopic ages and excess argon in 

biotites: Earth and Planetary Science Letters, v. 10, p. 

157-164.

Goudarzi, G.H., 1984, Guide to preparation of mineral survey 

reports on public lands: U.S. Geological Survey OpenFile Report 84-787, 30 p.

Grimes, D.J., and Marranzino, A.P., 1968, Direct-current arc 

and alternating-current spark emission spectrographic 

field methods for the semiquantitative analysis of 

geologic materials: U.S. Geological Survey Circular 591, 

6 p.

Hamilton, W.B., 1965, Geology and petrogenesis of the Island 

Park caldera of rhyolite and basalt, eastern Idaho: U.S. 

Geological Survey Professional Paper 504-C, 37 p.

James, H.L., and Hedge, C.E., 1980, Age of the basement rocks 

of southwestern Montana: Geological Society of America Bulletin, v. 91, p. 11-15.

Kulik, D.M., Perry, W.J., Jr., Skipp, Betty, 1982, A model for 

Rocky Mountain foreland and overthrust belt development geophysical and geological evidence for spatial 

overlap [abs.]: Geological Society of America Abstracts 

with Programs, v. 15, no. 5, p. 318.

Mitchell, V.E., Stroud, W.B., Hustedde, G.S., and Bennett, 

E.H., 1981, Mines and prospects of the Ashton 

quadrangle, Idaho: Idaho Bureau of Mines and Geology, 

Mines and Prospects Map Series, 4 p., map.

Muffler, L.P.J., editor, 1979, Assessment of geothermal 

resources of the United States: U.S. Geological Survey 

Circular 790, 163 p.

Pardee, J.T., 1950, Late Cenozoic block faulting in western 

Montana: Geological Society of America Bulletin, v. 61, 

p. 359-406.

Peters, T.J., and Winters, R.A., 1988, Mineral resources of the 

Henrys Lake Wilderness Study Area, Fremont County, 

Idaho: U.S. Bureau of Mines Open File Report MLA 

15-88, 20 p.

Peterson, D.L., and Witkind, I.J., 1975, Preliminary results of a 

gravity survey of the Henrys Lake quadrangle, Idaho and 

Montana: U.S. Geological Survey Journal of Research, v. 

3, p. 223-228.

Henry's Lake Wilderness Study Area D15
Plouff, Donald, 1977, Preliminary documentation for a FORTRAN program to compute gravity terrain corrections 

based on topography digitized on a geographic grid: U.S. 

Geological Survey Open-File Report 77-535, 45 p.

Sandberg, C.A., 1983, Petroleum potential of wilderness lands 

in Idaho, in Miller, B.M., ed., Petroleum potential in 

wilderness lands in the western United States: U.S. 

Geological Survey Circular 902, p. F1-F6.

Shannon, S.S., Jr., 1980, Uranium hydrogeochemical and 

stream sediment reconnaissance data release for the 

Ashton NTMS quadrangle, Idaho/Montana/Wyoming, 

including concentrations of forty-two additional 

elements: U.S. Department of Energy Open-File Report 

GJBX-146(80), 168 p.

___ 1982, Geochemical provenance of anomalous metal 

concentrations in stream sediments in the Ashton 

1:250,000 quadrangle, Idaho/Montana/Wyoming, in 

Reid, S.G., and Foote, D.J., eds., Geology of Yellowstone 

Park Area: Wyoming Geological Association 33rd 

Annual Field Conference Guidebook, p. 323-333.

Smith, R.B., and Sbar, M., 1974, Contemporary tectonics and 

seismicity of the western U.S. with emphasis on the 

Intermountain Seismic belt: Geological Society of America Bulletin, v. 85, p. 1205-1218.

Smith, R.L., and Braile, L.W., 1984, Crustal structure and 

evolution of an explosive silicic volcanic system at Yellowstone National Park, in Studies in Geophysics, 

Explosive Volcanism: Inception, evolution, and hazards: 

National Academy of Sciences/National Research 

Council, p. 96-109.

Smith, R.L., and Shaw, H.R., 1979, Igneous-related geothermal 

systems, in Muffler, L.P.J., ed., Assessment of geothermal resources of the United States 1978: U.S. 

Geological Survey Circular 790, p. 12-17.

Sonderegger, J.L., Berg, R.B., and Mannick, M.L., 1982, 

Geologic map of the northern part of the Upper and 

Lower Red Rock Lake quadrangles, Beaverhead and 

Madison Counties, Montana, in Sonderegger J.L., Schofield, J.D., Berg, R.B., and Mannick, M.L., The Upper 

Centennial Valley, Beaverhead and Madison Counties, 

Montana: Montana Bureau of Mines and Geology 

Memoir 50, 53 p.

Suekawa, H.S., Merrick, D., Clayton, J., and Rumba, S., 1982, 

National uranium resource evaluation, Ashton 

quadrangle, Idaho, Montana, and Wyoming: U.S. 

Department of Energy Open-File Report 

PGJ/F-074(82), 24 p.

Thompson, C.E., Nakagawa, H.M., and Van Sickle, G.H., 1968, 

Rapid analysis for gold in geologic materials, in 

Geological Survey Research 1968: U.S. Geological 

Survey Professional Paper 600-B, p. B130-B132.

Trimble, A., and Smith, R.B., 1975, Seismicity and 

contemporary tectonics of the Hebgen Lake Yellowstone Park region: Journal of Geophysical Research, v. 

80, p. 733-741.

Tysdal, R.G., 1986, Thrust faults and back thrusts in Madison 

Range of southwestern Montana: American Association 

of Petroleum Geologists Bulletin, v. 70, p. 360-376.

Tysdal, R.G., and Simons, F.S., 1985, Geologic map of the 

Madison Roadless Area, Gallatin and Madison Counties, 

Montana: U.S. Geological Survey Miscellaneous Field 

Studies Map MF-1605-B, scale 1:96,000.

U.S. Bureau of Mines and U.S. Geological Survey, 1980, 

Principles of resource/reserve classification for minerals: 

U.S. Geological Survey Circular 831, 5 p.

U.S. Department of Energy, 1982, Ashton quadrangle: residual 

intensity magnetic anomaly contour map: U.S. 

Department of Energy Open-File Report GJM-098(82), 

scale 1:250,000.

U.S. Geological Survey, 1964, The Hebgen Lake Montana 

earthquake of August 17, 1959: U.S. Geological Survey 

Professional Paper 435, 242 p.

____ 1972, Geologic map of Yellowstone National Park: U.S. 

Geological Survey Miscellaneous Geologic 

Investigations Map 1-711, scale 1:125,000.

Viets, J.G., Clark, J.R., and Campbell, W.L., 1984, A rapid 

partial leach and organic separation for the sensitive 

determination of Ag, Bi, Cd, Mo, Pb, Sb, and Zn in 

surface geologic materials by flame atomic absorption: 

Journal of Geochemical Exploration, v. 20, p. 355-366.

Witkind, I.J., 1969, Geology of the Tepee Creek quadrangle, 

Montana-Wyoming: U.S. Geological Survey Professional 

Paper 609, 101 p.

____ 1972a, Geologic map of the Henrys Lake quadrangle, 

Idaho and Montana: U.S. Geological Survey 

Miscellaneous Geologic Investigations Map I-781-A, 

scale 1:62,500.

____ 1972b, Generalized slope map of the Henrys Lake 

quadrangle, Idaho and Montana: U.S. Geological Survey 

Miscellaneous Geologic Investigations Map I-781-B, 

scale 1:62,500.

____ 1972c, Map showing seiche, rockslide, rockfall, and 

earthflow hazards in the Henrys Lake quadrangle, Idaho 

and Montana: U.S. Geological Survey Miscellaneous 

Geologic Investigations Map 1-781-C, scale 1:62,500.

___ 1972d, Map showing faults and ground-breakage 

hazards in the Henrys Lake quadrangle, Idaho and 

Montana: U.S. Geological Survey Miscellaneous 

Geologic Investigations Map I-781-D, scale 1:62,500.

____ 1972e, Earthquake hazard map of the Henrys Lake 

quadrangle, Idaho and Montana: U.S. Geological Survey 

Miscellaneous Geologic Investigations Map 1-781-E, 

scale 1:62,500.

____ 1972f, Map showing construction materials in the 

Henrys Lake quadrangle, Idaho and Montana: U.S. 

Geological Survey Miscellaneous Geologic 

Investigations Map I-781-F, scale 1:62,500.

____ 1982, Geologic map of the Centennial Mountains 

Wilderness Study Area and contiguous areas, Idaho and 

Montana: U.S. Geological Survey Miscellaneous Field 

Studies Map MF-1342-A, scale 1:50,000.

D16 Mineral Resources of Wilderness Study Areas Southeastern Idaho
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

UJ O 

cc

I

01

cc

UJ

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

Reserves

Marginal Reserves

1 

Demonstrated 

Subeconomic Resources

Inferred

Inferred Reserves

Inferred 

Marginal Reserves

Inferred 

Subeconomic 

Resources

UNDISCOVERED RESOURCES

Probability Range

 (or) 

Hypothetical i Speculative

I

1

1 

1

1

Major elements of mineral resource classification, excluding reserve base and inferred reserve base. Modified from McKelvey, 1972, Mineral 

resource estimates and public policy: American Scientist, v.60, p.32-40, and U.S. Bureau of Mines and U.S. Geological 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-Ar<

ERA

Cenozoic

Mesozoic

Paleozoic

Late Proterozoic

Middle Proterozoic

Early Proterozoic

Late Archean

Middle Archean

Early Archean 

:hean*

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

IB

- 55

_ CO

- 96

-A, 240 

- 290

-~ 330

- ^RO

- 410

- 4^S

- 500

U ~ 570 1

- 900

. icon

- 2500

-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:1908- 573-047/66099


SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS

Periodicals

Earthquakes & Volcanoes (issued bimonthly). 

Preliminary Determination of Epicenters (issued monthly).

Technical Books and Reports

Professional Papers are mainly comprehensive scientific reports of 

wide and lasting interest and importance to professional scientists and engineers. Included are reports on the results of resource studies and of 

topographic, hydrologic, and geologic investigations. They also include 

collections of related papers addressing different aspects of a single scientific topic.

Bulletins contain significant data and interpretations that are of lasting scientific interest but are generally more limited in scope or 

geographic coverage than Professional Papers. They include the results 

of resource studies and of geologic and topographic investigations; as well 

as collections of short papers related to a specific topic.

Water-Supply Papers are comprehensive reports that present significant interpretive results of hydrologic investigations of wide interest 

to professional geologists, hydrologists, and engineers. The series covers 

investigations in all phases of hydrology, including hydrogeology, 

availability of water, quality of water, and use of water.

Circulars present administrative information or important scientific 

information of wide popular interest in a format designed for distribution 

at no cost to the public. Information is usually of short-term interest.

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topographic bases in 71/2- or 15-minute quadrangle formats (scales mainly 1:24,000 or 1:62,500) showing bedrock, surficial, or engineering geology. Maps generally include brief texts; some maps include structure 

and columnar sections only.

Geophysical Investigations Maps are on topographic or planimetric 

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reflect subsurface structures that are of economic or geologic significance. 

Many maps include correlations with the geology.

Miscellaneous Investigations Series Maps are on planimetric or 

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present a wide variety of format and subject matter. The series also includes 71/2-minute quadrangle photogeologic maps on planimetric bases 

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Oil and Gas Investigations Charts show stratigraphic information 

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Miscellaneous Field Studies Maps are multicolor or black-andwhite maps on topographic or planimetric bases on quadrangle or irregular areas at various scales. Pre-1971 maps show bedrock geology 

in relation to specific mining or mineral-deposit problems; post-1971 

maps are primarily black-and-white maps on various subjects such as 

environmental studies or wilderness mineral investigations.

Hydrologic Investigations Atlases are multicolored or black-andwhite maps on topographic or planimetric bases presenting a wide range 

of geohydrologic data of both regular and irregular areas; principal scale 

is 1:24,000 and regional studies are at 1:250,000 scale or smaller.

Catalogs

Permanent catalogs, as well as some others, giving comprehensive listings of U.S. Geological Survey publications are available under 

the conditions indicated below from the U.S. Geological Survey, Books 

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