Mineral Resources of the Little 

Owyhee River Wilderness Study 

Area, Owyhee County, Idaho

U.S. GEOLOGICAL SURVEY BULLETIN 1719-C

Chapter C

Mineral Resources of the Little Owyhee 

River Wilderness Study Area, 

Owyhee County, Idaho

By JAY A. ACH and HARLEY D. KING 

U.S. Geological Survey

ALAN R. BUEHLER and DONALD O. CAPSTICK 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1719-C

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

OWYHEE RIVER REGION, IDAHO AND NEVADA
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1986

For sale by the

Books and Open-File Reports Section

U.S. Geological Survey

Federal Center, Box 25425

Denver, CO 80225

Library of Congress Cataloging-in-Publication Data

Mineral resources of the Little Owyhee River Wilderness 

study area, Owyhee County, Idaho

U.S. Geological Survey Bulletin 1719-C

Bibliography

Supt. of Docs. No.: I 19.3:1719-C

1. Mines and mineral resources Idaho Little

Owyhee River Wilderness. 2. Geology Idaho Little

Owyhee River Wilderness. 3. Little Owyhee River

Wilderness (Idaho) I. Ach, Jay A. II. Series.

QE75.B9 No. B1719-C 557.3 s 86-600161

[TN24.I2] [553'.09796'21]
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 of 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 Little 

Owyhee River Wilderness Study Area (ID-016-48C), Owyhee County, Idaho.

CONTENTS

Summary Cl

Abstract 1

Character and setting 1

Identified resources 1

Mineral resource potential 1 

Introduction 1

Area description 1

Previous and present investigations 3

Acknowledgments 3 

Appraisal of identified resources 3

History and production 3

Mineral deposits 3 

Assessment of mineral resource potential 5

Geology 5

Geochemical studies 5 

Conclusions 6 

References cited 7 

Appendix 1. Definition of levels of mineral resource potential and certainty of assessment 9

FIGURES

1. Index map showing location of the Little Owyhee River Wilderness Study Area, Owyhee County, Idaho C2

2. Map showing mineral resource potential and geology of the Little Owyhee River Wilderness Study Area, 

Owyhee County, Idaho 4

3. Major elements of mineral resource potential/certainty classification 9

TABLE

1. Mines, prospects, and mineralized areas in and adjacent to the Little Owyhee River Wilderness Study 

Area CIO

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

OWYHEE RIVER REGION, IDAHO AND NEVADA

Mineral Resources of the Little Owyhee River 

Wilderness Study Area, Owyhee County, Idaho

By Jay A. Ach and Harley D. King 

U.S. Geological Survey

Alan R. Buehler and Donald O. Capstick 

U.S. Bureau of Mines

SUMMARY 

Abstract

The Little Owyhee River Wilderness Study Area 

(ID-016-48C) encompasses 8,460 acres in the extreme 

southwest corner of Idaho along the canyon of the 

Little Owyhee River. Throughout this report, 

"wilderness study area" and "study area" refer to the 

8,460 acres on which mineral surveys were 

completed. Fieldwork for this report was carried out 

between 1983 and 1985. No mines, prospects, or 

mining claims were located inside the study area, and 

no mineral resources were identified. The wilderness 

study area has a low mineral resource potential for 

silver, gold, and mercury. There is also a low mineral 

resource potential for the nonmetallic commodities 

diatomite and zeolites.

Character and Setting

The Little Owyhee River Wildernesss Study Area 

is located 8 mi northeast of the southwest corner of 

Idaho (fig. 1). The terrain consists of a flat to gently 

rolling plateau deeply incised by the spectacular 

canyon cut by the Little Owyhee River to depths of 

800 ft. The surface of the plateau is defined by the 

thin flows of the Banbury Basalt of late Miocene age. 

Beneath surficial flows, additional basalt flows are 

interbedded with lacustrine sediments. The Banbury 

Basalt and lacustrine sediments overlie the Swisher 

Mountain Tuff, a rhyolitic ash-flow tuff of middle 

Miocene age. The Swisher Mountain Tuff is the oldest 

unit exposed in the study area. (See Ekren and others, 

1981, 1984.)

Identified Resources

No known mines, prospects, or mining claims are 

located within the study area, but parts of the study

area are included in petroleum and natural gas leases 

or lease applications. There are no identified mineral 

or energy resources within the study area.

Mineral Resource Potential

The Little Owyhee River Wilderness Study Area 

does not lie within any established mining district.

The northeastern part of the wilderness study 

area has low mineral resource potential for both 

epithermal silver-gold and epithermal mercury 

deposits. This is indicated by weak geochemical 

anomalies in rock samples from within the study area 

and the presence of small areas of altered rock and 

additional geochemical anomalies immediately outside 

the study area.

Some geochemical evidence of the presence of 

tin was gathered to the west of the study area, 

although the geologic environment is not favorable for 

a tin resource in that area. However, no geochemical 

evidence of tin was found within the study area and 

the wilderness study area is considered to have no 

mineral resource potential for tin.

The mineral resource potential for the 

nonmetallic commodities diatomite and zeolites is also 

considered low in the wilderness study area. Evidence 

of the occurrence of these minerals exists 1-1.5 mi 

outside the study area in sedimentary rocks, but little 

evidence of their existence within the study area was 

found.

INTRODUCTION 

Area Description

The Little Owyhee River Wilderness Study Area 

(ID-016-48C) consists of 8,460 acres recommended 

suitable for wilderness consideration out of 24,677 

acres originally considered. The study area is located 

8 mi northeast of the southwestern corner of Idaho

Cl
42°30' 117°00' 116°45' 116°30'

42°15' -

42°00

SQUAW 

MEADOWS

LITTLE OWYHEE RIVER

WILDERNESS STUDY AREA

(ID-016-48C)

- MALHEUR CO A" _ _ ___ _<L__ __ IDAHO 

HUMBOLDTCO ~l / NEVADA

OWYHEE CO 

ELKO CO

Figure 1. Index map showing location of the Little Owyhee River Wilderness Study Area, 

Owyhee County, Idaho.

C2
(fig. 1) and includes a part of the Owyhee Plateau, a 

flat to gently rolling plateau with an average elevation 

of about 5,200 ft within the study area . The Owyhee 

Plateau is deeply incised by the spectacular and 

precipitous canyons of the various branches of the 

Owyhee River system. The part of the plateau 

included in this wilderness study area surrounds the 

canyon cut by the Little Owyhee River, immediately 

upstream of that river's junction with the South Fork 

of the Owyhee River. Within the wilderness study 

area, the canyon of the Little Owyhee River reaches 

depths of 800 ft below the surrounding countryside. 

The climate is arid to semiarid, with an average of less 

than ten inches of precipitation a year. The 

vegetation is sparse, consisting of sagebrush, various 

range grasses, and the odd juniper tree.

Access to the study area is by approximately 41 

mi of graded dirt and gravel roads that lead west from 

Idaho State Highway 51 through the Duck Valley Indian 

Reservation to the 45 Ranch (fig. 1). From the ranch, 

the study area can be reached by the dirt road that 

bounds the area on the east.

Previous and Present Investigations

Geologic mapping and studies by Ekren and 

others (1981, 1984) provided the basis for the mapping 

for this study. Additional information on the general 

regional geology is contained in Walker and Repenning 

(1966), Kittleman and others (1967), Hope and Coats 

(1976). and Bonnichsen and Breckenridge (1982). 

Previous reconnaissance studies of the geology and the 

energy and mineral resources of wilderness study areas 

in the region were carried out by Mathews and 

Blackburn (1983a, b). The uranium resource potential 

for the region was evaluated as part of the National 

Uranium Resource Evaluation (NURE) program (Berry 

and others, 1982; Geodata, 1980).

The U.S. Geological Survey carried out field 

investigations in the study area during the summers of 

1984 and 1985. The work included field checking of 

existing geologic maps, new mapping where necessary, 

and geochemical sampling. Rock samples were 

collected from areas of observed alteration and from 

each lithologic unit in order to obtain information 

about trace-element signatures associated with 

potentially mineralized areas and to provide traceelement background data.

The U.S. Bureau of Mines conducted a library 

search for information on mines and prospects within 

the study area. These data were supplemented by 

information from Owyhee County, U.S. Bureau of Land 

Management, and U.S. Bureau of Mines records. Field 

studies by U.S. Bureau of Mines personnel were carried 

out in 1984 (Buehler and Capstick, 1985). One hundred 

thirty-nine rock samples and 20 stream-sediment 

samples were collected from areas of possible 

mineralization within and immediately outside the 

study area. Samples were analyzed by fire-assay, 

atomic-absorption, and inductively coupled argonplasma spectrophotometric methods. Selected rock 

samples of lacustrine and tuffaceous sediments were 

analyzed by X-ray diffraction for zeolites or examined 

microscopically and ignition-tested for diatomite. 

Complete analytical data are on file at the U.S.

Bureau of Mines, Western Field Operations Center, 

Spokane, Washington 99202.

Acknowledgments

The staff of the Boise District Office of the U.S. 

Bureau of Land Management provided logistical 

support, information, and the use of the fine U.S. 

Bureau of Land Management camp at Mud Flat. Ben 

Glanville, owner of the 45 Ranch, and Sonny and Judy 

Smith, caretakers of the 45 Ranch, graciously provided 

information, access, and many courtesies.

APPRAISAL OF IDENTIFIED RESOURCES

By Alan R. Buehler and Donald O. Capstick. U.S. 

Bureau of Mines

History and Production

The Little Owyhee River Wilderness Study Area 

is not within a mining district and there are no mines 

or prospects within or near the area. Minor, 

unrecorded production of jasper, chalcedony, and 

common opal suitable for lapidary purposes or as 

specimens has occurred. The only known production 

near the wilderness study area is of several hundred 

pounds of this material produced from the Lu Lew 

prospect (P.M. Gabby, unpub. data), a rock collectors' 

locality located approximately 0.4 mi west of the 45 

Ranch (fig. 2)(see table 1).

Mineral Deposits

No diatomite or zeolites were found in the 

wilderness study area. However, nearby areas show 

evidence of zeolitic alteration or diatomite 

deposition. These occur within the lacustrine 

sediments beneath and interbedded with the Banbury 

Basalt flows and the tuffaceous horizons lying beneath 

the flows. At one location 1 3/4 mi south-southwest of 

the southwest corner of the study area (locality A, fig. 

2), a 100-ft-thick section of zeolitic ash beds averaged 

42 percent clinoptilolite (a zeolite mineral) (Table 1). 

Development of the zeolite minerals here would be 

nearly impossible because of the 200-300 ft of 

sediment and basalt overburden at this locality. At 

another location 1.3 mi west of the northern end of the 

study area (locality B, fig. 2), an exposure of lacustrine 

sediments contains diatomite, although much of it is of 

unsuitable quality (Table 1).

Stream-sediment samples from the Little 

Owyhee River show only minor, very fine placer gold, 

typical of the Owyhee River region (highest value 

$0.03/yd3 , average value $0.016/ydJ; calculated with 

gold at $400.00/oz).

Sand and gravel deposits suitable for 

construction use occur in the wilderness study area, 

but larger, more accessible deposits are widely 

available outside the study area.

C3
APPROXIMATE BOUNDARY

OF

LITTLE OWYHEE RIVER 

WILDERNESS STUDY AREA

- ^Si

Tb |Y

1 MILE

EXPLANATION

.Area of low mineral resource 

potential with some evidence 

of resource-forming processes. 

See appendix 1 and figure 3 for 

definition of levels of mineral 

resource potential and certainty 

of assessment.

COMMODITIES 

Au Gold 

Ag Silver 

Hg Mercury

CORRELATION OF MAP UNITS

^ Quaternary

Tertiary

GEOLOGIC MAP UNITS

Qls Quaternary landslide deposits

Tb Tertiary Banbury Basalt

Ts Tertiary lacustrine and fluviatile sediments

Tt Tertiary Swisher Mountain Tuff

MAP SYMBOLS

 - - - Contact-Dashed where approximately 

located or uncertain

I Fault-Bar and ball on downthrown side; 

dashed where approximately 

located or uncertain

 Mineralized area-Letters refer to table 1 

X Prospect

Figure 2. Map showing mineral resource potential and geology of the Little Owyhee 

River Wilderness Study Area, Owyhee County, Idaho.

C4
ASSESSMENT OF MINERAL RESOURCE POTENTIAL

By Jay A. Ach and Harley D. King, U.S. Geological 

Survey

Geology

Pre-Miocene basement rocks are not exposed 

within or near the Little Owyhee River Wilderness 

Study Area, but may consist of Cretaceous granites 

overlain by mixed volcanic rocks of Eocene and 

Oligocene age. The oldest unit exposed in the study 

area is the middle Miocene Swisher Mountain Tuff. It 

is overlain by the late Miocene Banbury Basalt and 

associated interbedded sediments.

Cretaceous granitic plutons of the Idaho 

Batholith, which intrude metasedimentary rocks of 

pre-Cretaceous age, crop out on South Mountain and in 

the Owyhee Mountains, 35 mi north and 45 mi northnortheast, respectively, of the study area. These 

outcrops of basement rocks are the closest to the 

study area; however, similar basement rocks may 

extend beneath the area (Ekren and others, 1984). In 

the Owyhee Mountains, locally preserved Eocene 

intermediate lavas and quartz latite tuffs, and 

Oligocene olivine basalt and andesite of restricted 

extent overlie the Cretaceous granites. The regional 

extent of all of these lavas is conjectural, and they 

may or may not overlie basement rocks within the 

study area.

The oldest unit exposed in the wilderness study 

area is the middle Miocene Swisher Mountain Tuff (fig. 

2), with reported potassium-argon ages of 14.2 ± 0.4 

m.y. (Armstrong and others, 1980), and 13.1 ± 0.2 m.y. 

and 13.8 ± 0.4 m.y. (Neill, 1975). Ekren and others 

(1984) assumed an age of 13.85 m.y. The tuff is a 

flow-foliated compound cooling unit of rhyolitic ashflow tuff of calc-alkalic (Ekren and others, 1984) or 

possibly peralkaline (J.J. Rytuba, oral comm., 1985) 

chemistry. The unit ranges in color from light grey to 

light purple- or pink-grey. Phenocrysts total 

approximately 15 percent and include plagioclase (62 

percent of total), alkali feldspar (15 percent), 

pigeonite (20 percent), and opaque oxides (3 percent) 

(Ekren and others, 1984). An upper vitrophyre is well 

developed in the study area; additional vi trophy res 

within the unit are found at other locales. The 

maximum exposed thickness of the Swisher Mountain 

Tuff in the study area is about 650 ft, but the base is 

not exposed. Ekren and others (1984) consider Juniper 

Mountain, 12 mi to the north of the study area (fig. 1), 

to be the eruptive center for the Swisher Mountain 

Tuff, the second oldest of five tuffs erupted from this 

center over a time span of at least two million years. 

These eruptions did not produce a caldera or other 

eruption-related subsidence features.

Late Miocene basalt flows and interbedded 

sediments overlie the Swisher Mountain Tuff. The 

basalt was assigned to the Banbury Basalt by Ekren and 

others (1984), which gives potassium-argon ages of 8.0 

to 10.5 m.y. (Armstrong and others, 1975). These 

numerous, thin flows (generally less than 50 ft thick) 

are olivine tholeiites (Ekren and others, 1984) and 

contain small quantities of small phenocrysts (less than

2 mm) of plagioclase and olivine in a very fine-grained 

matrix of intergranular to ophitic 

texture. Small vesicles, less than 4 mm in diameter, 

are common, some of which are partially filled with 

secondary silica or zeolites. At least some of these 

flows are of local derivation, and were erupted from 

45 Hill and Spring Butte, inferred vents (figs. 1, 2).

The white-to-buff sediments beneath and 

interbedded with the basalt flows are of lacustrine and 

fluviatile origin. The part of the sediments beneath 

the basalts contains some beds of tuffaceous 

material. The sediments are generally composed of 

fairly well-bedded clay- to coarse sand-sized material, 

with lenses of gravel and rare cobbles occasionally 

found in the fluvial deposits. The combined thickness 

of the sediments and the Banbury Basalt varies from 

300 to 600 ft within the study area.

Quaternary deposits consist of alluvium in the 

canyon bottoms, talus on canyon slopes, and fairly 

large landslide and slump deposits at some locations 

along the canyon sides.

Geochemical Studies

A reconnaissance geochemical study was made 

based on analysis and evaluation of stream sediments, 

the non-magnetic fraction of heavy-mineral 

concentrates from stream sediments, and rock 

samples. The stream-sediment and concentrate 

samples contain material derived from major rock 

units of the drainage basin. Sampled drainage basins 

range in area from less than one to several square 

miles.

All 39 stream-sediment samples, 24 heavymineral-concentrate samples, and 16 rock samples 

were analyzed for 31 elements by six-step 

semiquantitative emission-spectrographic methods 

(Myers and others, 1961; Grimes and Marranzino, 

1968), with additional analyses by atomic-absorption 

spectroscopy and inductively coupled argon plasmaatomic emission spectroscopy (ICAP-AES). These 

analyses identify drainages with anomalously high 

concentrations of metallic and metal-related 

elements. Anomalous values were determined by 

inspection of histograms and noting enrichment 

relative to crustal abundances.

Stream-sediment samples and heavy-mineralconcentrate samples show no geochemical anomalies 

within the wilderness study area; however, heavymineral concentrates from some drainages of 45 Hill, 

1.5 mi west of the wilderness study area, show 

anomalously high concentrations of tin (3 samples, 500 

to 1,000 ppm). Microscopic examination of those 

concentrates revealed the presence of cassiterite, the 

primary tin ore. Tin mineralization is most commonly 

associated with granites, although epithermal vein 

deposits of cassiterite are mined from silicic volcanic 

rocks in Bolivia and Mexico. The veins there occur in 

rhyodacite-to-rhyolite stocks, plugs, and breccia pipes 

interpreted to represent volcanic vents (Hutchinson, 

1983). There are no recorded instances of tin deposits 

associated with basalt, however, and the drainages 

near the wilderness study area that have anomalously 

high tin values are entirely underlain by basalt. The 

likelihood that these anomalies are related to a tin

C5
resource is therefore very remote.

Widely scattered tin anomalies in heavy-mineral 

concentrates are relatively common elsewhere in the 

Owyhee Plateau (H.D. King, unpub. data). Peralkaline 

rhyolites are commonly enriched in lithophile 

elements, including tin (MacDonald and Bailey, 1973). 

The Swisher Mountain Tuff and other peralkaline 

rhyolitic tuffs occurring in the region are probably the 

source of the tin detected regionally; however, the 

source of the tin detected in the 45 Hill drainages is 

unknown.

Rock samples within and immediately outside the 

wilderness study area just west of the 45 Ranch show 

weak-to-moderate geochemical anomalies for arsenic 

(As) (6 and 17 ppm), antimony (Sb) (12 and 17 ppm), 

molybdenum (Mo) (5, 7, and 15 ppm), and possibly 

mercury (Hg) (0.07 and 0.19 ppm) . These samples are 

all from the tuffaceous sediments overlying the 

Swisher Mountain Tuff. Two samples of sediments of 

the same unit from outside the study area (near the Lu 

Lew prospect and 0.2 mi south-southeast of the 

prospect area) are of locally brightly stained rock that 

has been very locally brecciated, silicified, and cut by 

thin goethite veins. These two samples produced the 

strongest geochemical anomalies, with one containing 

anomalous quantities of As, Sb, Mo. and Hg and the 

other containing anomalous As and Mo only. This rock 

occurs in only two small outcrops that seem to lie on 

the local north-northwest fault trend, suggesting that 

the alteration was fault-controlled. Such visibly 

altered rock is not found within the study area, 

although the three samples with slightly anomalously 

high values (Sb in one, Mo in another, and Hg in the 

third) indicate that some alteration or mineralization 

may have occurred. The locus of mineralization 

probably lies outside the wilderness study area in the 

visibly altered rocks to the east.

Anomalously high values for As, Sb, Mo, and Hg 

are often associated with epithermal mercury 

mineralization (Rytuba and Glanzman, 1979) or 

epithermal silver-gold mineralization of the low-sulfur 

type (Bonham, 1984; Bonham and Tingley. 1984), both 

of which occur within silicic volcanic or related host 

rocks. Important mineral deposits of these two 

different types are usually associated with the 

complex structures found in volcanic eruptive 

centers. These structures include strongly persistent 

fracture systems, especially caldera-related ring 

fractures and grabens, and volcanic domes and plugs in 

complexly faulted areas (Berger, 1982). Although 

minor faults of limited offset are present in the study 

area, such complex structures are absent, and the 

study area is several miles removed from Juniper 

Mountain, the postulated eruptive center for the 

Swisher Mountain Tuff. Even though the overall 

geologic environment of the study area is permissive 

for epithermal silver-gold and epithermal mercury 

deposits, it is not a highly favorable environment 

because of the study area's distance from the Juniper 

Mountain eruptive center and the corresponding 

absence "of complex structures in the area.

Previous regional uranium surveys, which 

included aerial gamma-ray emission studies (Berry and 

others, 1982; Geodata, 1980), found no indications of 

uranium concentrations in the vicinity of the 

wilderness study area.

Conclusions

Geological and geochemical data indicate that 

the Little Owyhee River Wilderness Study Area has 

low resource potential for epithermal mercury deposits 

and epithermal silver-gold deposits with a C certainty 

level. The resource potential for zeolites and 

diatomite is also low with a C certainty level. The 

resource potential for petroleum and natural gas is 

unknown (certainty level A), but their occurrence 

within the study area is very unlikely. The resource 

potential for geothermal energy is low, with a C 

certainty level. See Appendix 1 and Figure 3 for 

definitions of levels of mineral resource potential and 

certainty.

The investigations by the U.S. Geological Survey 

and the U.S. Bureau of Mines indicate that there is low 

mineral resource potential for epithermal silver-gold 

and epithermal mercury in the area just west of the 45 

Ranch (fig. 2). A certainty level of C is assigned 

because the area of strongest alteration, denoted by 

the strongest geochemical anomalies and most visibly 

altered outcrops, lies outside the study area. This 

alteration may be fault-controlled; if so, local fault 

trends indicate that the trend of the inferred fault and 

the alteration involved do not intersect the study 

area. Geologic mapping indicates that the tuffaceous 

lacustrine sediments, the host rock for the alteration, 

are very thin (0 to 100 ft) in the area around the 

visibly altered zone. Therefore, the alteration (and 

any associated mineralized zone) must necessarily be 

of very limited vertical extent, assuming the 

alteration is indeed confined to the sediments. The 

only possible indication of this type of mineralization 

within the study area is the presence of slightly 

anomalous geochemical values in rock samples 

collected from within the indicated area of low 

potential (fig. 2).

Although traces of zeolites and diatomite occur 

in the sediments associated with the Banbury Basalt in 

the wilderness study area, and somewhat higher-grade 

accumulations are found within two miles of the study 

area, the resource potential of these two minerals is 

probably poor. A low resource potential with a 

certainty level of C is assigned because no evidence of 

deposits of suitable purity was found within or near the 

study area. Additionally, the traces of these minerals 

observed within the study area do not seem to be of 

great thickness or large lateral extent. Development 

of any deposit of either of these minerals, if they 

existed, would be nearly impossible because of the 100 

to 400 ft of basalt and sediment overburden that would 

need to be removed.

Sand and gravel deposits suitable for 

construction use occur in the wilderness study area. 

Because similar materials of equal or better quality 

are abundant closer to local markets, and the probable 

costs of mining exceed the present market value of 

these materials, their future development is highly 

unlikely.

Geologic data indicate a low probability for the 

occurrence of petroleum and natural gas in the 

Cenozoic rocks of the wilderness study area. Evidence 

for hydrocarbon potential is negligible; the volcanic 

rocks and lacustrine and fluviatile sedimentary strata 

immediately underlying the study area might include

C6
suitable reservoir rocks, but lack hydrocarbon source 

beds. The nature of the basement rocks is conjectural, 

however, and therefore the hydrocarbon resource 

potential is considered unknown, certainty level A.

Geothermal energy resource potential for the 

wilderness study area is low with a C certainty level. 

There is no evidence of geothermal activity in or near 

the study area. Previous regional geothermal surveys 

have not indicated any geothermal potential for the 

area (Muffler, 1979; Reed, 1983), but the absence of 

wells in the study area and surrounding region makes a 

survey of local groundwater temperatures impossible 

(see Bliss, 1983a, b, c). The existence of a geothermal 

resource is considered highly unlikely.

This assessment of mineral resource potential for 

the Little Owyhee River Wilderness Study Area was 

completed November, 1985.

REFERENCES CITED

Armstrong, R.L., Harakal, J.E., and Neill, W.M., 1980, 

K-Ar dating of Snake River Plain (Idaho) volcanic 

rocks - new results: Isochron/West, no. 27, p. 5- 

10.

Armstrong, R.L., Leeman, W.P., and Malde, H.E., 

1975, K-Ar dating, Quaternary and Neogene 

volcanic rocks of the Snake River Plain, Idaho: 

American Journal of Science, v. 275, p. 225-251.

Berger, B.R., 1982, The geological attributes of AuAg-base metal epithermal deposits; in Erickson, 

R.L., ed., Characteristics of mineral deposit 

occurrences: U.S. Geological Survey Open-File 

Report 82-795, 248 p.

Berry, M.R., Castor, S.B., and Robins, J.W. (Bendix 

Field Engineering Corporation), 1982, National 

uranium resource evaluation, Jordan Valley 

quadrangle, Oregon and Idaho (contract no. DEAC07-76GJ01664): U.S. Department of Energy 

Open-File Report PGJ/F-132(82), 33 p.

Bliss, J.D., 1983a, Idaho - Basic data for thermal 

springs and wells as recorded in GEOTHERM; Part 

A: U.S. Geological Survey Open-File Report 83- 

431 A, 63 p.

___1983b, Nevada - Basic data for thermal springs 

and wells as recorded in GEOTHERM; Part A: 

U.S. Geological Survey Open-File Report 83-433A, 

101 p.

___1983c, Oregon - Basic data for thermal springs 

and wells as recorded in GEOTHERM: U.S. 

Geological Survey Open-File Report 83-435, 342

PBonham, H.F. Jr., 1984, Three major types of 

epithermal precious-metal deposits: Abstracts 

with programs, Geological Society of America 

annual meeting, vol. 16, no. 6, p. 449.

Bonham, H.F. Jr., and Tingley, J.V., 1984, Bulkminable gold deposits in Nevada: Abstracts with 

programs, Geological Society of America annual 

meeting, vol. 16, no. 6, p. 449.

Bonnichsen, W., and Breckenridge, R.M. eds., 1982, 

Cenozoic Geology of Idaho: Idaho Bureau of 

Mines and Geology Bulletin 26, 725 p.

Buehler, A.R., and Capstick, D.O., 1985, Mineral 

resources of the Little Owyhee River Wilderness 

Study Area (B.L.M. No. ID-16-48C), Owyhee

County, Idaho: U.S. Bureau of Mines Open File 

Report 77-85, 15 p.

Ekren, E.B., Mclntyre, D.H., and Bennett, E.H., 1984, 

High-temperature, large-volume, lavalike ashflow tuffs without calderas in southwestern 

Idaho: U.S. Geological Survey Professional Paper 

1272, 76 p.

Ekren, E.B., Mclntyre, D.H., Bennett, E.H., and Malde, 

H.E., 1981, Geologic map of Owyhee County, 

Idaho, west of 116, West Longitude: U.S. 

Geological Survey Miscellaneous Geologic 

Investigations Map 1-1256, scale 1:125,000.

Geodata International, Inc., 1980, Aerial radiometric 

and magnetic survey, national topographic map, 

Jordan Valley, Oregon/Idaho: prepared under 

Bendix Field Engineering Corp. subcontract no. 

79-336-S, U.S. Department of Energy Open-File 

Report GJBX-95(80), 201 p.

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emmission spectrographic field methods for the 

semiquantitative analysis of geologic materials: 

U.S. Geological Survey Circular 591, 6 p.

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Geological Survey Open-File Report 76-779, 6 pis.

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tectonic setting: New York, Wiley-Interscience, 

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APPENDIX 1. Definition of levels of mineral resource 

potential and certainty of assessment

Mineral resource potential is defined as the 

likelihood of the presence of mineral resources in a 

defined area; it is not a measure of the amount of 

resources or their profitability.

Mineral resources are concentrations of naturally 

occurring solid, liquid, or gaseous materials in such 

form and amount that economic extraction of a commodity from the concentration is currently or potentially feasible.

Low mineral resource potential is assigned to 

areas where geologic, geochemical, and geophysical 

characteristics indicate a geologic environment where 

the existence of resources is unlikely. This level of 

potential embraces areas of dispersed mineralized rock 

as well as areas having few or no indications of 

mineralization. Assignment of low potential requires 

specific positive knowledge; it is not used as a catchall 

for areas where adequate data are lacking.

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 chance for resource 

accumulation, and where an application of genetic and 

(or) occurrence models indicates favorable ground.

High mineral resource potential is assigned to 

areas where geologic, geochemical, and geophysical 

characteristics indicate a geologic environment 

favorable for resources, where interpretations of data 

indicate a high likelihood for resource accumulation, 

where data support occurrence and (or) genetic models 

indicating presence of resources, and where evidence 

indicates that mineral concentration has taken place. 

Assignment of high resource potential requires positive 

knowledge that resource-forming processes have been 

active in at least part of the area; it does not require 

that occurrences or deposits be identified.

Unknown mineral resource potential is assigned 

to areas where the level of knowledge is so inadequate 

that classification of the area as high, moderate, or

low would be misleading. The phrase "no mineral 

resource potential" applies only to a specific resource 

type in a well-defined area. This phrase is not used if 

there is the slightest possibility of resource 

occurrence; it is not appropriate as the summary 

rating for any area.

Expression of the certainty of the mineral 

resource assessment incorporates a consideration of (1) 

the adequacy of the geologic, geochemical, geophysical, and resource data base available at the time of 

the assessment, (2) the adequacy of the occurrence or 

the genetic model used as the basis for a specific 

evaluation, and (3) an evaluation of the likelihood that 

the expected mineral endowment of the area is, or 

could be, economically extractable.

Levels of certainty of assessment are denoted by 

letters, A-D (fig. 3).

A. The available data are not adequate to 

determine the level of mineral resource potential. 

Level A is used with an assignment of unknown mineral 

resource potential.

B. The available data are adequate to suggest 

the geologic environment and the level of mineral 

resource potential, but either evidence is insufficient 

to establish precisely the likelihood of resource occurrence, or occurrence and (or) genetic models are not 

known well enough for predictive resource assessment.

C. The available data give a good indication of 

the geologic environment and the level of mineral 

resource potential, but additional evidence is needed 

to establish precisely the likelihood of resource occurrence, the activity of resource-forming processes, or 

available occurrence and (or) genetic models are 

minimal for predictive applications.

D. The available data clearly define the geologic 

environment and the level of mineral resource 

potential, and indicate the activity of resourceforming processes. Key evidence to interpret the 

presence or absence of specified types of resources is 

available, and occurrence and (or) genetic models are 

adequate for predictive resource assessment.

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

MO POTENTIAL

LEVEL OF CERTAINTY

Figure 3. Major elements of mineral resource potential/certainty classification.

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oI 

o

Table 1 . Mines, prospects, and mineralized areas in and adjacent to the Little Owyhee River Wilderness S

Map No.

or name

(fig. 2) Location Summary Workings 

Lu Lew prospect

SE1/4 sec. 26,

T. 14 S.,

R. 5 W.

and

SW1/4 sec.

T. 14 S.,

R. 5 W.

25,

SE1/4 sec. 4, 

T. 16 S., 

R. 5 W.

SE1/4 sec. 20, 

T. 14 S., 

R. 5 W.

Upper surface of Swisher Mountain Tuff, 

containing "thunder eggs" (fist-sized, 

spherical to oblong aggregations of 

chalcedony). Overlain by lacustrine 

sediments.

Several small, shallow pits 

and a 20-ft-long bulldozer 

scrape. Several hundred 

pounds of thunder eggs and 

jasper suitable for lapidary 

purposes or as specimens were 

probably produced over the 

past several years.

One hundred ft of zeolitic ash beds and pebble 

conglomerate, overlain by 200-300 ft of 

lacustrine sediments and basalt.

Lacustrine sediments containing diatomite and 

volcanic ash beds. Overlain by basalt.

Thunder eg

the Swishe

overlying 

eggs occur

area and s

surface of 

indicating 

probably b

circulation

small amou

exposed. 

geochemica

arsenic (1

was detect

Ten sample

average of 

range of 3

analyzed f

and mercury

elements w

would be n

overburden

Twenty-fou

vertical f

were colle

diatomite; 

quality du

high cryst

dark color

properties

poorer. O

content; n

O) 

00-J

o .&.

CO

Ol

o 

ro