Mineral Resources of the

Prospect Mountain Wilderness Study

Carbon County, Wyoming

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Chapter E

Mineral Resources of the

Prospect Mountain Wilderness Study Area,

Carbon County, Wyoming

By EDWARD A. DU BRAY, VI Kl BAN KEY, and 

RANDALL H. HILL 

U.S. Geological Survey

GEORGE S. RYAN 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1 757

MINERAL RESOURCES OF WILDERNESS STUDY AREASSOUTHERN WYOMING
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L Peck, Director

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Library of Congress Cataloging-in-Publication Data

Mineral resources of the Prospect Mountain wilderness study area, Carbon 

County, Wyoming.

(Mineral resources of wilderness study areas southern Wyoming ; ch. E) 

(U.S. Geological Survey bulletin ; 1757) 

Bibliography: p. 

Supt. of Docs, no.: I 19.3:1757-E

1. Mines and mineral resources Wyoming Prospect Mountain Wilderness.

2. Prospect Mountain Wilderness (Wyo.) I. du Bray, E. A. II. Series. 

III. Series: U.S. Geological Survey bulletin ; 1757. 

QE75.B9 no. 1757-E 557.3 S [553'.09787'86] 88-607941 

[TN24.W8]
STUDIES RELATED TO WILDERNESS

Bureau of Land Management Wilderness Study Areas

The Federal Land Policy and Management Act (Public Law 94-579, 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 Prospect 

Mountain Wilderness Study Area (WY-030-303), Carbon County, Wyoming.

CONTENTS

Abstract El 

Summary El

Character and setting El

Identified mineral resources El

Mineral resource potential E2 

Introduction E2

Investigations by the U.S. Bureau of Mines E3

Investigations by the U.S. Geological Survey E4 

Appraisal of identified resources E4 

Assessment of potential for undiscovered resources E4

Geology E4

Geochemistry E5

Geophysics E6

Mineral and energy resources E8 

References cited E8 

Appendix E9

FIGURES

1. Index map showing location of the Prospect Mountain Wilderness Study 

Area E2

2. Map showing mineral resource potential and generalized geology for the Prospect 

Mountain Wilderness Study Area E3

3. Residual aeromagnetic anomaly map of the Prospect Mountain Wilderness Study 

Area and vicinity E6

4. Uranium equivalent (eU) values for the Prospect Mountain Wilderness Study 

Area and vicinity E6

5. Thorium equivalent (eTh) values for the Prospect Mountain Wilderness Study 

Area and vicinity E7

6. Potassium (K) values for the Prospect Mountain Wilderness Study Area and 

vicinity E7

Contents V

MINERAL RESOURCES OF WILDERNESS STUDY AREAS-SOUTHERN WYOMING

Mineral Resources of the

Prospect Mountain Wilderness Study Area,

Carbon County, Wyoming

By Edward A. du Bray, Viki Bankey, and

Randall H. Hill

U.S. Geological Survey

George S. Ryan 

U.S. Bureau of Mines

ABSTRACT

The Prospect Mountain Wilderness Study Area (WY030-303), located about 20 miles east-southeast of Encampment, Wyoming, contains 1,145 acres whose 

mineral endowment was jointly studied by the U.S. 

Bureau of Mines and the U.S. Geological Survey in 1987. 

There are no identified resources in the study area. 

Resource potential for undiscovered metallic commodities and for industrial minerals is low. The study 

area has no potential for undiscovered energy resources, including oil and gas, coal, geothermal resources, 

and uranium.

SUMMARY

Character and Setting

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

(U.S. Bureau of Mines) studied the mineral resource 

potential of 1,145 acres in the Prospect Mountain Wilderness Study Area (WY-030-303), Carbon County, Wyo.,

Manuscript approved for publication January 11,1989.

at the request of the BLM (U.S. Bureau of Land Management). In this report, the area studied is referred to as 

the "wilderness study area" or the "study area." Field 

studies of the study area were conducted during the 

summer of 1987 by USBM geologists and by USGS 

geologists, geochemists, and geophysicists.

Encampment, Wyo., about 20 mi (miles) westnorthwest of the Prospect Mountain Wilderness Study 

Area, is the nearest sizable town (fig. 1). The study area 

is accessible on its west side from graded unpaved 

roads that intersect Wyoming State Route 230. The 

study area is located on the gently sloping western flank 

of the Medicine Bow Mountains. Elevations in the study 

area range between 7,400 and 8,400 ft (feet). The study 

area is underlain by Middle Proterozoic (see geologic 

time chart in Appendix) gabbro, granite, and hornblende 

gneiss. Hornblende gneiss occurs throughout the 

southern part of the study area, whereas gabbro and 

granite occur in the northern part. Pegmatite dikes intrude all other rocks.

Identified Mineral Resources

There are neither mining districts nor any records of 

production from ore deposits in the study area. (In this

Prospect Mountain Wilderness Study Area E1
APPROXIMATE BOUNDARY 

OF PROSPECT MOUNTAIN 

WILDERNESS STUDY AREA 

(WY-030-303)

Rgure 1. Index map showing location of the Prospect Mountain Wilderness Study Area, Carbon County, Wyo. Dashed lines are selected 

unpaved roads.

report, the term "deposit," unmodified, does not connote 

economic value.) No mineral resources were identified 

by the USBM in the Prospect Mountain Wilderness Study 

Area. Three samples collected by USBM geologists at a 

prospect pit and caved adit on the northern boundary of 

the study area contained minor amounts of gold, silver, 

and copper and lower concentrations of other elements 

in a limited area; assay results from a pegmatite sample 

Indicate the occurrence of a minor amount of silver. The 

study area is underlain by crystalline rocks, which do not 

host hydrocarbon accumulations; there are no oil and 

gas leases in the study area. No sand and gravel 

deposits occur in the study area.

propriate to undiscovered resources of these commodities. The absence of uranium-anomalous values in 

the geochemical database and the failure of the 

aeroradiometric survey to identify anomalous uranium 

concentrations indicate no potential for uranium 

deposits in the study area. The absence of geothermal 

phenomena and the old age of the rocks in the study 

area indicate that there is no potential for geothermal 

energy resources. Accordingly, the study area has no 

potential for energy resources (fig. 2).

Available geologic, geochemical, and geophysical 

data indicate low potential for undiscovered industrial 

mineral resources in the study area (fig. 2).

Mineral Resource Potential

The geologic environment in the Prospect Mountain 

Wilderness Study Area is favorable for the occurrence 

of certain types of metallic mineral deposits, but the insignificant quantity of mineralized rock, lack of major 

geochemical anomalies not attributable to differences in 

lithology, and absence of favorable geophysical characteristics indicate that mineral resource potential in the 

study area is low for all metals (fig. 2).

Energy resources, including oil and gas, coal, 

uranium, and geothermal resources, are unknown in the 

study area. The crystalline rocks that underlie the study 

area are neither source nor reservoir rocks for oil, gas, 

or coal, nor is the structural setting of the study area apINTRODUCTION

The Prospect Mountain Wilderness Study Area is 

about 20 mi east-southeast of Encampment, Wyo., the 

nearest sizable town (fig. 1). The study area, a gently rolling, dissected upland covered by grasses and sage, is on the 

sloping western flank of the Medicine Bow Mountains and 

is accessible on its west side from graded unpaved roads 

that intersect Wyoming State Route 230. Travel in the study 

area is by way of a few rough jeep roads and on foot. Valleys and the highest north-facing slopes support stands of 

aspen and fir trees. The North Platte River flows north in 

a 1,000-ft-deep canyon just east of the study area.

This report presents an evaluation of the mineral endowment (identified resources and mineral resource

E2 Mineral Resources of Wilderness Study Areas-Southern Wyoming
106«27' 106«26'

41 e 07'

41«06'

APPROXIMATE BOUNDARY

OF THE PROSPECT MOUNTAIN

WILDERNESS STUDY AREA

EXPLANATION OF MINERAL

RESOURCE POTENTIAL

L/C Geologic terrane having low mineral resource 

potential, with certainty level C, for all 

metals and industrial minerals

N/D Geologic terrane having no resource potential, with certainty level D, for coal, oil 

and gas, geothermal resources, and 

uranium

Levels of Certainty

C Data indicate geologic environment and 

resource potential, but do not establish 

activity of resource-forming 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

EXPLANATION OF GEOLOGY

[All units are Proterozoic in age] 

E?pg Pegmatite

Egr 

Bhg

Gabbro

Granite

Hornblende gneiss

Contact

Strike and dip of foliation

Strike of vertical foliation

WYOMING

Area of map

Rgure 2. Map showing mineral resource potential and generalized geology for the Prospect Mountain Wilderness Study Area, Carbon County, 

Wyo.

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 by the USBM. Mineral resource potential 

is the likelihood of occurrence of undiscovered concentrations of metals and nonmetals, of unappraised industrial 

rocks and minerals, and of undiscovered energy resources 

(coal, oil, gas, oil shale, and geothermal resources). It is 

classified according to the system of Goudarzi (1984),

which is shown in the Appendix of this report. The potential for undiscovered resources is studied by the USGS.

Investigations by the U.S. Bureau of 

Mines

USBM geologists reviewed mining, mineral lease, and 

mining claim information and other published material related to mineral resources and mining activities in and near

Prospect Mountain Wilderness Study Area E3
the Prospect Mountain Wilderness Study Area. Mining 

claim and master title plat information was reviewed in the 

BLM State Office in Cheyenne, Wyo., and the County 

Courthouse in Rawlins, Wyo. Two USBM geologists conducted a 2-day field examination in the study area and 

vicinity. The abundances of 32 elements in four rock 

samples collected in or near the study area were determined by inductively coupled plasma-atomic emission 

spectrometry; gold and silver abundances were determined by fire-assay. All analyses were performed by the 

Chemex Labs, Incorporated, facilities in Sparks, Nev., and 

selected results are shown in Ryan (1988, p. 8). Complete 

analytical data are available for inspection at the U.S. 

Bureau of Mines, Intermountain Field Operations Center, 

Building 20, Denver Federal Center, Denver, Colo.

Investigations by the U.S. Geological 

Survey

The assessment of the mineral resource potential of 

the Prospect Mountain Wilderness Study Area is based on 

data from many sources. Among these are geologic studies 

of the Sierra Madre and the Medicine Bow Mountains 

(Houston, 1961; Houston and others, 1978; du Bray, this 

report), geochemical studies by the USBM (Ryan, 1988) 

and the USGS (R.H. Hill, unpub. data, 1987); and interpretations of geophysical data, including aeromagnetic and 

aeroradiometric data (Viki Bankey, this report), Landsat 

Thematic Mapper data (Alta Walker, written commun., 

1988), and telluric survey data (D.H. Hoover, written commun., 1988).

APPRAISAL OF IDENTIFIED 

RESOURCES

By George S. Ryan 

U.S. Bureau of Mines

No recent mining activity was noted in the wilderness 

study area, although mining claim notices on file with the 

BLM indicate recent claims were located in and near the 

study area. One unreadable claim notice was found posted 

on a tree within the study area, but no claim posts nor signs 

of recent excavations, drill holes, or other exploration activities were found.

No mineral resources were identified in the wilderness 

study area. The walls and dump material of a prospect pit 

and caved adit on the northwestern side of Prospect Mountain are stained with copper carbonate and manganese 

oxide. Sample assays indicate the presence of small

amounts of copper, gold, and silver and minor, but 

anomalous, amounts of other elements (Ryan, 1988, p. 8). 

A small shear zone exposed in the pit is covered with talus 

on the surface and could not be traced; mineralized rock 

appeared to be restricted to the pit and the adit driven 

along the shear. A sample collected from a 25-ft-wide pegmatite dike exposed on the ridge south of Prospect Mountain Peak assayed 0.006 oz/st (ounces/short ton) silver 

(approximately 1,000 times below ore grade). Only quartz, 

feldspar, and magnetite could be identified in hand 

samples of the pegmatite.

No oil or gas has been produced from the study area, 

nor has any exploratory drilling been conducted; there are 

no oil or gas leases or lease applications for areas within 2 

mi of the wilderness study area. The soil cover is very thin, 

and no sand and gravel deposits exist in the study area.

ASSESSMENT OF POTENTIAL FOR 

UNDISCOVERED RESOURCES

By Edward A. du Bray, Viki Bankey, and

Randall H. Hill

U.S. Geological Survey

Geology

A small-scale geologic map of the Medicine Bow 

Mountains (Houston and others, 1978) was used to compile a preliminary large-scale map of the study area. Outcrops were examined for signs of mineralized rock. 

Samples of all rock units were collected for petrographic 

studies.

The Prospect Mountain Wilderness Study Area is in 

the Colorado Plateaus physiographic province (Bickford 

and others, 1986) and is adjacent to the south end of the 

Archean Wyoming craton (Hills and Houston, 1979) along 

the Cheyenne belt. The study area is underlain by 

Proterozoic gabbro, granite, and hornblende gneiss, which 

is locally intruded by pegmatite dikes. The Cheyenne belt 

is an inferred suture zone at the southern edge of the North 

American craton along which lithospheric material was accreted during Proterozoic time. The hornblende gneiss and 

to a lesser extent the granite and gabbro are foliated; their 

deformation is probably related to the compressional 

suturing event associated with accretion of the Colorado 

province to the Wyoming craton.

Granite pegmatite dikes are especially abundant in the 

hornblende gneiss. The dikes are unzoned and are principally composed of coarse-grained quartz and feldspar 

but also contain minor amounts of biotite, muscovite, garE4 Mineral Resources of Wilderness Study Areas - Southern Wyoming
net, and opaque oxides. They have sharp contacts and are 

approximately conformable with their host rocks.

Gabbro crops out in the northwest and northeast 

corners of the study area. The gabbro is fine to medium 

grained and weakly foliated and has a seriate texture. Unzoned, albite-twinned plagioclase occurs interstitially and 

forms anhedral grains (0.02-0.16 in. long) that compose 

about 55 percent of the gabbro. Subhedral hypersthene and 

augite grains (0.02-0.1 in. long) are approximately equally 

abundant and account for about 40 percent of the rock. 

About 5 percent interstitial, anhedral opaque oxides are 

also present. Chlorite occurs as narrow alteration rims on 

the pyroxene crystals.

Granite crops out in a northwest-trending zone that 

crosses the northern part of the study area. The coarsegrained granite, characterized by a weakly developed 

gneissic foliation, is composed of potassium feldspar, 

quartz, plagioclase, biotite, and hornblende and has a 

seriate texture. Abundant potassium feldspar forms 

gridiron-twinned, anhedral grains (0.2-0.4 in. long) that 

impart a vague porphyritic texture to the granite. Quartz is 

characterized by undulose extinction and occurs as anhedral grains (0.08-0.16 in. in diameter). Biotite and 

hornblende are about equally abundant and compose 5-10 

percent of the granite. Subhedral, light-brown to darkgreen biotite laths are 0.02-0.06 in. long, and anhedral, 

light-tan to dark-green hornblende aggregates are 0.02-0.1 

in. in diameter. Accessory epidote in granular clusters 

0.004-0.02 in. in diameter compose 1-2 percent of the rock. 

Trace amounts of apatite were also identified.

The hornblende gneiss is a plagioclase-amphibole 

rock, with quartz and epidote as accessory minerals, whose 

distribution is widespread throughout southern Wyoming. 

The gneiss is characterized by great textural and 

mineralogic variation. The gneiss in the study area consists 

of alternating bands of amphibole-rich gneiss and felsic 

gneiss, the amphibole-rich variety being predominant.

Geochemistry

In September of 1987, a reconnaissance geochemical 

survey was conducted to aid evaluation of the mineral 

resource potential of the study area. Rocks, stream sediments, and heavy-mineral concentrates derived from 

stream sediment were selected as the sample media for 

evaluation.

Five minus-60-mesh stream-sediment samples collected from alluvium of active streams and five corresponding heavy-mineral concentrates panned from stream 

sediment were selected as primary sample media. The sediments are presumed to represent a composite of the rock 

and soil exposed in the drainage basin upstream from the

sample site. Chemical analysis of such stream-sediment 

samples provides data useful in identifying those basins 

that contain unusually high concentrations of elements that 

maybe related to mineral occurrences. In addition, studies 

have shown that heavy-mineral panned concentrates 

derived from stream sediment are useful in evaluating aridsemiarid environments or areas of rugged topography, 

where mechanical erosion predominates over chemical 

erosion (Bugrov and Shalaby, 1975; Overstreet and Marsh, 

1981). Heavy-mirieral-concentrate samples provide information about the chemistry of a limited number of minerals 

present in rock material eroded from the drainage basin 

upstream from each sample site. Preparation of heavymineral concentrates from stream sediment results in a 

concentration of mineral assemblages that may contain 

ore-forming and ore-related minerals. The selective concentration of these minerals permits analytic determination of some elements that are not easily detected in bulk 

stream-sediment samples.

Four fresh and unaltered rock samples were collected 

from outcrops to provide chemical and mineralogic information for rocks exposed near stream-sediment sample 

sites. In addition, one mine-dump sample was collected to 

provide information concerning the composition of 

mineralized rock present in the study area. The actual areal 

extent of the influence of each rock type on the chemistry 

of individual stream-sediment and panned-concentrate 

samples is indeterminate, though the sampling program 

was designed to provide general information concerning 

the geochemical nature of the exposed lithologies.

The dry stream-sediment samples were sieved through 

60-mesh stainless-steel sieves. The minus-60-mesh 

material was retained for analysis and pulverized with 

ceramic plates to at least minus-100 mesh prior to analysis. 

To produce the heavy-mineral concentrate, bulk stream 

sediment was first sieved through a 10-mesh screen. Approximately 25-30 pounds of the minus-10-mesh sediment 

was panned to remove most of the quartz, feldspar, organic 

material, and clay- sized material. These samples were then 

air dried, passed through a 30-mesh sieve, and separated 

into light and heavy fractions by means of bromoform 

(heavy liquid, specific gravity 2.86). The light fraction was 

discarded. The material of specific gravity greater than 2.86 

was separated into three fractions (highly magnetic, weakly magnetic, and nonmagnetic) by means of a modified 

Frantz Isodynamic Magnetic Separator. The nonmagnetic 

fraction was hand ground and retained for emission 

spectrographic analysis. Rock samples were crushed and 

pulverized to at least minus-100 mesh with ceramic plates 

prior to analysis. Rock, stream-sediment, and nonmagnetic 

portions of the heavy-mineral concentrates were analyzed 

for 35 elements by means of a semiquantitative, direct-current arc emission spectrographic method (Grimes and

Prospect Mountain Wilderness Study Area E5
106° 29' 106° 25' 106° 25'

Figure 3. Residual aeromagnetic anomaly map of the Prospect 

Mountain Wilderness Study Area and vicinity, Carbon County, Wyo. 

Heavy line is approximate boundary of wilderness study area. 

Contour interval 25 nanoteslas; hachures indicate area of closed low.

Rgure 4. Uranium equivalent (ell) values for the Prospect Mountain 

Wilderness Study Area and vicinity, Carbon County, Wyo. Heavy line 

is approximate boundary of wilderness study area. Contour interval 

0.5 parts per million; hachures indicate area of closed low.

Marranzino, 1968); abundances of palladium and platinum 

in the concentrates were also determined by this method.

Threshold values, defined as the upper limit of normal 

background values, were determined for each element by 

inspection of frequency-distribution histograms for all 

sample media. The composite mine-dump rock sample was 

not included in construction of the histograms. Concentrations of elements greater than the threshold values are considered anomalous and worthy of consideration as possible 

indicators of mineralized rock.

The primary criterion for delineating an area as 

anomalous is the presence of multi-element geochemical 

anomalies clustered within a restricted geographic region. 

Follow-up studies should, however, include isolated 

anomalous sample localities with geographically extensive, 

geochemically anomalous areas because the scale of sampling conducted for this study is so small that moderatesized deposits could be indicated by single sample sites, or 

not be apparent at all. In addition, this study is a surface 

study and may not reflect the presence of mineralized rock 

at depth.

A very weakly anomalous area is present in the 

northwestern part of the study area, where the drainage 

basin contains granite in contact with gabbro. The 

anomalous heavy-mineral concentrate contains 150 ppm 

(parts per million) copper, 150 ppm chromium, 50 ppm gallium, and 70 ppm nickel. These concentrations may reflect 

the presence of dense minerals (such as chromite) that are 

characteristic accessory phases in mafic and ultramafic 

rocks, such as those exposed in the drainage basin represented by this sample. The abundance of these minerals in 

this area may be somewhat enhanced in the border phase 

of the gabbro exposed at its contact with granite due to 

segregation layering and accumulation of dense minerals 

at the margins of mafic and ultramafic intrusive bodies in 

many places.

Geophysics

A detailed aeromagnetic survey of the wilderness 

study area and vicinity was flown in 1979 (as part of the NaE6 Mineral Resources of Wilderness Study Areas - Southern Wyoming
tional Uranium Resource Evaluation) by a fixed-wing 

aircraft at a nominal ground clearance of 400 ft. Flight 

traverses were oriented north-south and spaced 0.25 mi 

apart; these specifications provide 60 percent coverage of 

surface sources and 100 percent coverage of sources buried 

below 200 ft depth. After correction for diurnal effects and 

tie-line discrepancies, the International Geomagnetic 

Reference Field was removed. The resulting residual magnetic data were compiled and contoured bylhe contractor 

(Bendix Field Engineering Corporation, 1983) to produce 

a regional aeromagnetic map. The map is useful in geologic 

interpretations of the region that contains the study area; 

a subset of the data was used to aid interpretation of the 

geology in the study area.

Aeromagnetic data (fig. 3) may be useful in delineating concealed intrusive rocks that could be associated with 

mineral deposits. Two magnetic highs, in the southern and 

northeastern parts of the study area, respectively, may indicate the presence of intrusions. The northeastern anomaly is probably caused by the gabbro outcrop that is part of

a Proterozoic mafic complex north of the study area. This 

mafic complex is characterized by many high-amplitude, 

high-frequency positive magnetic anomalies (fig. 3). The 

southern anomaly is associated with hornblende gneiss that 

is continuous across the study area and extends well beyond 

the anomaly. A magnetic high lies in the center of a much 

broader magnetic low that separates it from other positive 

magnetic features. Mapped geology does not suggest a 

source for the magnetic low (such as a less magnetic 

granite). The broad low is probably too large to be the 

result of alteration around a body inferred to be the source 

of the imbedded magnetic high.

Aerial gamma-ray spectroscopy is a radiometric technique that provides an estimate of the near-surface (depth 

0-20 in.) concentrations of uranium (U), thorium (Th), and 

potassium (K) and is used in exploration for uranium 

deposits. The occurrence of radioactive quartz-pebble 

conglomerate in the Medicine Bow Mountains and Sierra 

Madre necessitated a detailed aeroradiometric survey in 

this region to determine the extent and abundance of

106° 29' 106° 25' 106° 29' 27'

Figure 5. Thorium equivalent (eTh) values for the Prospect Mountain 

Wilderness Study Area and vicinity, Carbon County, Wyo. Heavy line 

is approximate boundary of wilderness study area. Contour interval 

1.5 parts per million; hachures indicate area of closed low.

RgureS. Potassium (K) values for the Prospect Mountain 

Wilderness Study Area and vicinity, Carbon County, Wyo. Heavy line 

is approximate boundary of wilderness study area. Contour interval 

0.5 percent; hachures indicate area of closed low.

Prospect Mountain Wilderness Study Area E7
uranium. Aeroradiometric data for the study area were obtained from traverses flown in 1979 by contractors working 

for the U.S. Department of Energy as part of the National 

Uranium Resource Evaluation (Bendix Field Engineering 

Corporation, 1983). The traverses are along north-south 

lines spaced 0.25 mi apart and have a nominal ground 

clearance of 400 ft. These specifications are sufficient to 

achieve 60-percent ground coverage (figs. 4-6). The U and 

Th values are "equivalent" values (eU and eTh) to account 

for possible disequilibrium in the decay series for those elements.

Generally, silicic rocks are more radioactive than 

mafic rocks. This holds true in the study area, where the 

granitic rocks are associated with increased levels of 

uranium (U), thorium (Th), and potassium (K). Values 

range from 1.0 to 2.0 ppm eU, 4.5 to 7.5 ppm eTh, and 1.0 

to 3.0 percent K. Apart from the slightly increased concentration found where granitic rocks occur, the radio-element values are at or below background levels.

Landsat Thematic Mapper data can be used to identify indications of mineralized or altered rock exposed at 

the Earth's surface. Data for seven spectral bands, 

analyzed individually, as composites, and as ratios, do not 

indicate the presence of mineralized or altered rock in the 

study area (Alta Walker, written commun., 1988).

Telluric surveying is a method whereby the electrical 

resistivity of rock present at various depths below the 

ground surface can be determined. The method can be 

used to explore for changes in resistivity that may indicate 

altered or mineralized rock. Resistivity variation along two 

traverses in the study area is within the range expected as 

a function of lithologic variation; the method does not indicate the presence of unusually altered or mineralized 

rock.

Mineral and Energy Resources

Mineral resource potential for all metals in the study 

area is low. The geologic setting of the study area is 

favorable for various types of metalliferous deposits (including deposits of platinum-group elements associated 

with mafic and ultramafic rocks and pegmatite-hosted 

deposits), but supporting evidence and additional features 

indicative of favorablity for the occurence of deposits in the 

study area are absent. Mineralized rock identified at the 

surface during field work is of very limited extent. 

Anomalous concentrations in the geochemical data are 

probably a consequence of lithologies present in the 

sampled drainage basins and do not reflect the presence of 

mineralized rock. Geophysical data do not indicate the 

presence of mineral deposits; nor are geologic settings 

favorable for their occurrence. These findings suggest that

the mineral resource potential for all metals in the wilderness study area is low, with level-C certainty.

Energy resources, including oil and gas, coal, uranium, 

and geothennal resources are unknown in the study area. 

The crystalline rocks that underlie the study area are 

neither source nor reservoir rocks for oil, gas, or coal; nor 

is the structural setting of the study area appropriate to undiscovered resources of these commodities. The absence 

of uranium-anomalous values in the geochemical database 

and the failure of the aeroradiometric survey to identify 

anomalous uranium concentrations indicate no potential 

for uranium deposits in the study area. The absence of 

geothermal phenomena and the old age of the rocks in the 

study area indicate that there is no potential for geothermal energy resources. Accordingly, there is no potential 

(with certainty level D) for energy resources in the study 

area.

Available geologic, geochemical, and geophysical data 

indicate low potential (with certainty level C) for undiscovered industrial mineral resources in the study area.

REFERENCES CITED

Bendix Field Engineering Corporation, 1983, Aerial radiometric and 

magnetic survey, Sierra Madre Detail Area: U.S. Department of 

Energy Open-File Report GJBX-034(83), scale 1:62,500.

Bickford, M.E., Van Schmus, W.R., and Zietz, Isidore, 1986, Proterozoic 

history of the midcontinent region of North America: Geology, v. 

14, p. 492-496.

Bugrov, V.A., and Shalaby, I.M., 1975, Geochemical prospecting in the 

eastern desert of Egypt, in Elliott, I.L. and Fletcher, W.K., eds., 

Geochemical Exploration, 1974: Elsevier, p. 523-530.

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

public lands: U.S. Geological Survey Open-File Report 84-787,42

PGrimes, 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.

Hills, F.A., and Houston, R.S., 1979, Early Proterozoic tectonics of the 

central Rocky Mountains, North America: Contributions to Geology, v. 17, p. 89-109.

Houston, R.S., 1961, The Big Creek pegmatite area, Carbon County, 

Wyoming: Geological Survey of Wyoming Preliminary Report 1,11

PHouston, R.S., and others, 1978, A regional study of rocks of Precambrian 

age in that part of the Medicine Bow Mountains lying in 

southeastern Wyoming, with a chapter on The relationship between 

Precambrian and Laramide structure: Geological Society of Wyoming Memoir 1,167 p.

Overstreet, W.C., and Marsh, S.P., 1981, Some concepts and techniques 

in geochemical exploration, in Skinner, BJ., ed., Economic Geology, 75th Anniversary Volume: Economic Geology Publishing 

Company, p. 775-805.

Ryan, G.S., 1988, Mineral investigation of the Prospect Mountain Wilderness Study Area, Carbon County, Wyoming: U.S. Bureau of Mines 

Open File Report MLA 3-88,8 p.

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

resource/reserve classification for minerals: U.S. Geological Survey 

Circular 831,5 p.

E8 Mineral Resources of Wilderness Study Areas - Southern Wyoming
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/0

LOW POTENTIAL

N/D

NO POTENTIAL

t

LU

O 

V)

LU

oc

u. 

O

ui

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, AP 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

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- Art

ERA

Cenozoic

Mesozoic

Paleozoic

Late Proterozoic

Middle Proterozoic

Early Proterozoic

Late Archean

Middle Archean

Early Archean 

:hean 2

PERIOD

Quaternary

Tertiary

Neogene 

Subperiod

Paleogene 

Subperiod

Cretaceous

Jurassic

Triassic

Permian

Carboniferous 

Periods

Pennsylvanian

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

. £JC

- 96

one

-A/ 240

£.;Jv

-~ 330

- ^fiO

- 410

>- 435

- 500 

L~ 570 1

- 900 

- 1600

- 2500

-3000 

- 3400

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

2 Informal time term without specific rank.

 &U.S. GOVERNMENT PRINTING OFFICE 1989-673-047/86089


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