Mineral Resources of the

Fifteen Mile Creek, Oregon Canyon,

Twelve Mile Creek, and Willow Creek

Wilderness Study Areas,

Malheur and Harney Counties, Oregon

U.S. GEOLOGICAL SURVEY BULLETIN 1742-B

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Chapter B

Mineral Resources of the

Fifteen Mile Creek, Oregon Canyon,

Twelve Mile Creek, and Willow Creek

Wilderness Study Areas,

Malheur and Harney Counties, Oregon

SyJOCELYN A. PETERSON, JAMES J. RYTUBA, 

DONALD PLOUFF, THOMAS L. VERCOUTERE, 

ROBERT L. TURNER, and DON L. SAWATZKY 

U.S. Geological Survey

ANDREW M. LESZCYKOWSKI, THOMAS J. PETERS, 

STEVEN W. SCHMAUCH, and RICHARD A. WINTERS 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1742

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

TROUT CREEK MOUNTAINS REGION, OREGON
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Any use of trade names and trademarks 

in this publication is for descriptive 

purposes only and does not constitute 

endorsement by the U.S. Geological Survey

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1988

For sale by the

Books and Open-File Reports Section

U.S. Geological Survey

Federal Center, Box 25425

Denver, CO 80225

Library of Congress Cataloging-in-Publication Data

Mineral resources of the Fifteen Mile Creek, Oregon 

Canyon, Twelve Mile Creek, and Willow Creek 

Wilderness Study Areas, Malheur and Harney Counties, 

Oregon.

(Mineral resources of wilderness study areas Trout 

Creek Mountains Region, Oregon ; ch. B) (U.S. 

Geological Survey bulletin ; 1742-B)

Bibliography: p.

Supt. of Docs, no.: I 19.3:1742-8

1. Mines and mineral resources Oregon Fifteen Mile 

Creek Wilderness. 2. Mines and mineral resources 

Oregon Oregon Canyon Wilderness. 3. Mines and mineral 

resources Oregon Twelve Mile Creek Wilderness. 

4. Mines and mineral resources Oregon Willow Creek 

Wilderness. 5. Fifteen Mile Creek Wilderness (Or.) 

6. Oregon Canyon Wilderness (Or.) 7. Twelve Mile Creek 

Wilderness (Or.) 8. Willow Creek Wilderness (Or.) 

I. Peterson, Jocelyn A. II. Series. III. Series: 

U.S. Geological Survey bulletin : 1742-B. 

QE75.B9 no. 1742-B 557.3s 88-600315 

[TN24.07] [553'.09795'97]
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 parts of the Fifteen Mile Creek 

(OR-003-156), Oregon Canyon (OR-003-157), Twelve Mile Creek (OR-003-162), and 

Willow Creek (OR-003-152) Wilderness Study Areas, Malheur and Harney Counties, 

Oregon.
FIGURES

1. Index map showing location of Fifteen Mile Creek, Oregon Canyon, Twelve Mile 

Creek, and Willow Creek Wilderness Study Areas, Malheur and Harney Counties, 

Oregon B2

2. Map showing generalized geology and mineral resource potential of Fifteen Mile 

Creek Wilderness Study Area, Malheur County, Oregon B4

3. Map showing generalized geology and mineral resource potential of Oregon Canyon 

Wilderness Study Area, Malheur County, Oregon B6

4. Map showing generalized geology and mineral resource potential of Twelve Mile 

Creek Wilderness Study Area, Malheur County, Oregon B8

5. Map showing generalized geology and mineral resource potential of Willow Creek 

Wilderness Study Area, Harney and Malheur Counties, Oregon B9

6. Bouguer gravity map for area including Fifteen Mile Creek, Oregon Canyon, 

Twelve Mile Creek, and Willow Creek Wilderness Study Areas, Malheur and 

Harney Counties, Oregon B15

IV Contents
CONTENTS

Summary Bl

Abstract Bl 

Character and setting B2

Identified resources and mineral resource potential of the Fifteen Mile Creek Wilderness Study Area B3 

Identified resources and mineral resource potential of the Oregon Canyon Wilderness

Study Area B3

Identified resources and mineral resource potential of the Twelve Mile Creek Wilderness Study Area B3 

Identified resources and mineral resource potential of the Willow Creek Wilderness

Study Area B3 

Introduction B3

Character and setting B5 

Previous investigations B5 

Present study B7 

Acknowledgments B7

Appraisal of identified resources of the Fifteen Mile Creek Wilderness Study Area B7 

Mining and exploration history B7 

Results of investigation B7

Appraisal of identified resources of the Oregon Canyon Wilderness Study Area BIO 

Appraisal of identified resources of the Twelve Mile Creek Wilderness Study Area BIO 

Appraisal of identified resources of the Willow Creek Wilderness Study Area BIO 

Mining and mineral exploration history BIO 

Methods of investigation BIO 

Results of investigation Bll 

Assessment of mineral resource potential Bll 

Geology Bll 

Geochemistry B12 

Geophysics B13

General discussion of mineral and energy resources B14 

Mercury, uranium, and lithium B14 

Epithermal vein deposits B16 

Rare-earth elements and zirconium B17 

Tin B17

Industrial minerals B17 

Geothermal energy B17 

Oil and gas B18 

Mineral and energy resources of the Fifteen Mile Creek Wilderness Study

Area B18

Mineral and energy resources of the Oregon Canyon Wilderness Study Area B18 

Mineral and energy resources of the Twelve Mile Creek Wilderness Study

Area B18

Mineral and energy resources of the Willow Creek Wilderness Study Area B18 

References cited B19 

Appendixes

Definition of levels of mineral resource potential and certainty of

assessment B22 

Resource/reserve classification B23 

Geologic time chart B24

Contents

Mineral Resources of the

Fifteen Mile Creek, Oregon Canyon,

Twelve Mile Creek, and Willow Creek

Wilderness Study Areas,

Malheur and Harney Counties, Oregon

By Jocelyn A. Peterson, James J. Rytuba, Donald Plouff, 

Thomas L. Vercoutere, Robert L. Turner and Don L. Sawatzky 

U.S. Geological Survey

Andrew M. Leszcykowski, Thomas J. Peters, 

Steven W. Schmauch, and Richard A. Winters 

U.S. Bureau of Mines

SUMMARY 

Abstract

The parts of the Fifteen Mile Creek (OR-003-156), Oregon Canyon (OR-003-157), Twelve Mile Creek 

(OR-003-162), and Willow Creek (OR-003-152) Wilderness 

Study Areas for which mineral surveys were requested by the 

U.S. Bureau of Land Management encompass 51,290, 

42,900, 25,340, and 26,130 acres, respectively, in southeastern Oregon. Throughout this report, reference to those specific areas, or to the "study areas" refers only to those parts 

of the wilderness study areas for which mineral surveys were 

requested. Field work was carried out during the summer of 

1986 by the U.S. Bureau of Mines and the U.S. Geological 

Survey to appraise the identified (known) resources and assess the mineral resource potential (undiscovered) of the 

study areas.

The four contiguous study areas lie near mineralized 

calderas to the south; however, none of the study areas have 

any identified resources. The southern part of the Fifteen 

Mile Creek study area has low potential and the southern part 

of the Oregon Canyon study area has moderate and low 

potential for mercury and uranium resources near ring fractures around a caldera. In the Oregon Canyon study area, the

Manuscript approved for publication July 22, 1988.

tuff of Oregon Canyon and the caldera rim have low potential 

for gold and silver resources in epithermal veins. The southern parts of the Fifteen Mile Creek, Oregon Canyon, and 

Willow Creek and the northwestern part of the Oregon 

Canyon study areas have low potential for antimony, bismuth, mercury, silver, molybdenum, and zinc resources in 

epithermal deposits. Tin geochemical anomalies in the 

southeastern part of the Oregon Canyon, the southwest corner of the Fifteen Mile Creek, and the southeast corner of the 

Willow Creek study areas suggest a terrane having low potential for tin resources of unknown origin, possibly related to 

the basaltic rocks in those parts of the three study areas. All 

four study areas have low potential for zeolite resources 

because of their volcanic terrane. The northernmost part of 

the Twelve Mile Creek and the northwest tip of the Fifteen 

Mile Creek study areas have low potential for pumice as 

scattered fragments in tuff. The four areas have a low potential for geothermal energy resources because of their proximity to warm-water wells and springs nearby. There are no oil 

and gas leases in the areas, and all areas have low potential 

for resources of oil and gas. The tuff of Trout Creek Mountains, exposed in all the study areas, has a low potential for 

resources of light rare-earth elements and zirconium in local 

accumulations of aenigmatite, a sodium-iron-titanium mineral. This same rock unit is locally attractive enough for use 

a decorative building stone; therefore, this unit has low potential for decorative stone resources. Sand and gravel accumulations are present locally in all the study areas, but 

material of similar quality is available closer to potential 

markets.

Fifteen Mile Creek, Oregon Canyon, Twelve Mile Creek, and Willow Creek Wilderness Study Areas, Oregon B1
Character and Setting

The Fifteen Mile Creek (OR-003-156), Oregon Canyon (OR-003-157), Twelve Mile Creek (OR-003-162), 

and Willow Creek (OR-003-152) Wilderness Study Areas 

are located in southeastern Oregon between 7 and 35 mi 

northwest of McDermitt, Nev. (fig. 1). The regional topography is characterized by plateaus and mountainous terrain

dissected by deep canyons. The study areas lie between the 

Whitehorse caldera and two calderas (Long Ridge and 

Washburn) of the McDermitt caldera complex (fig. 1; 

Rytuba and McKee, 1984), which are sources of the tuffs 

found within the study areas. Rocks of the study areas 

consist mostly of welded to nonwelded rhyolitic ash-flow 

tuffs and mafic to felsic flows.

117°45'

42°00'

\ APPROXIMATE BOUNDARY 

\ OF 

\ TWELVE MILE CREEK 

WILDERNESS STUDY AREA 

i (OR-003-162)

FIFTEEN MILE CREEK 

WILDERNESS STUDY AREA CANYON 

WILDERNESS 

STUDY AREA

APPROXIMATE 

BOUNDARY 0 ;c 

OF g lr ' 

WILLOW CREEK 

WILDERNESS 

STUDY AREA g 

(OR-003-152) <i<

area Aurora 

deposit

OREGON___ 

NEVADA McDe

MALHEUR CO 

HUMBOLDT CO

Figure 1. Index map showing location of Fifteen Mile Creek, Oregon Canyon, Twelve Mile Creek, and Willow Creek Wilderness Study Areas, Malheur and Harney Counties, Oregon.

B2 Mineral Resources of Wilderness Study Areas: Trout Creek Mountains Region, Oregon
Identified Resources and 

Mineral Resource Potential of the 

Fifteen Mile Creek Wilderness Study Area

No identified mineral resources are present in the Fifteen Mile Creek study area. Sand and gravel accumulations 

along creeks are not considered to be resources because 

material of similar quality is available closer to prospective 

markets. Four prospect pits (fig. 2) in the southeast corner 

of the area are the only known mining claims or prospects. 

The Opalite mining district (fig. 1) in the McDermitt 

caldera complex is south of the study area; however, the 

geologic environment of the district does not extend into 

the study area. The southern part of the study area has low 

potential for mercury and uranium resources associated 

with the caldera complex (fig. 2). The entire study area has 

low potential for zeolite resources in the volcanic rocks. 

The southern part of the study area has low potential for 

antimony, bismuth, mercury, silver, molybdenum, and zinc 

resources in epithermal deposits. Geochemical anomalies 

for tin in the southwest corner of the area suggest low 

potential for tin resources of unknown origin possibly in 

the basaltic rocks. The northwest tip of the study area has 

low mineral resource potential for pumice. The tuff of 

Trout Creek Mountains has low resource potential for 

decorative building stone and for rare-earth elements and 

zirconium. The entire area has low potential for geothermal energy resources. There are no oil and gas leases in 

the study area, and the area has low potential for resources 

of these commodities.

Identified Resources and 

Mineral Resource Potential of the 

Oregon Canyon Wilderness Study Area

No mineral resources were identified in the Oregon 

Canyon Wilderness Study Area. The study area contains 

no mining districts, although the Opalite mining district, 

within the McDermitt caldera complex, is adjacent to the 

south. There are 8 inactive claims, recorded in 1914, in the 

southeastern part of the study area and 110 current claims 

in the eastern part. Concentrations of metallic minerals in 

the study area are small and of low grade. Occurrences of 

nonmetallic commodities are too low grade, small, and far 

from foreseeable markets to be mined. Sand and gravel 

along creek beds are not classified as identified resources 

because equally suitable material is available closer to 

prospective markets. Rocks adjacent to and near to the 

caldera rim, in the southern part of the study area, have 

moderate and low potential, respectively, for both mercury 

and uranium resources (fig. 3). This caldera rim area and 

the tuff of Oregon Canyon have low potential for gold and 

silver resources in epithermal veins. The southern and

northwestern parts of the Oregon Canyon study area have 

low resource potential for antimony, bismuth, mercury, 

silver, molybdenum, and zinc in epithermal deposits. Tin 

geochemical anomalies in the southeastern part of the study 

area suggest a low resource potential for tin in deposits of 

an unknown type possibly related to basaltic rocks. The 

entire study area has low potential for zeolite resources. 

The area has low resource potential for both geothermal 

energy and oil and gas. The tuff of Trout Creek Mountains 

has low resource potential for decorative building stone and 

for rare-earth elements and zirconium.

Identified Resources and 

Mineral Resource Potential of the 

Twelve Mile Creek Wilderness Study Area

There are no identified mineral resources in the study 

area. Sand and gravel along creek beds do not constitute 

resources because suitable material is readily available 

closer to prospective markets. There is low potential for 

zeolite resources throughout the study area in the volcanic 

rocks, and the northernmost part of the area has low potential for pumice resources (fig. 4). The resource potential 

for oil and gas and for geothermal energy is low. The tuff 

of Trout Creek Mountains has low resource potential for 

decorative building stone and for rare-earth elements and 

zirconium.

Identified Resources and 

Mineral Resource Potential of the 

Willow Creek Wilderness Study Area

Identified mineral resources, mining activity, and oil 

and gas leasing are not present in the study area; however, 

evidence for fault-zone-related epithermal mineralization is 

present at two localities. Minor amounts of sand and gravel 

along narrow creek beds are too small and remote from 

markets to constitute resources. The southern part of the 

area has low mineral resource potential for antimony, bismuth, mercury, silver, molybdenum, and zinc in epithermal 

deposits (fig. 5). The southeast corner has geochemical 

anomalies that suggest low resource potential for tin in 

deposits of an undetermined kind possibly in basaltic rocks. 

The entire area has low potential for zeolite resources. The 

entire area has low potential for both geothermal energy 

and oil and gas. The tuff of Trout Creek Mountains has 

low resource potential for decorative building stone and for 

rare-earth elements and zirconium.

INTRODUCTION

This mineral survey was requested by the U.S. Bureau 

of Land Management (BLM) and is a joint effort by the

Fifteen Mile Creek, Oregon Canyon, Twelve Mile Creek, and Willow Creek Wilderness Study Areas, Oregon B3
118°07'30"

L/B Zeo (entire study area) 

L/C Geo. O,G (entire study area)

APPROXIMATE BOUNDARY

OF

FIFTEEN MILE CREEK

WILDERNESS STUDY AREA

(OR-003-156)

L/B REE, Zr, Sto

units labeled Ttt)

L/B Sb, Bi. Hg 

Ac, Mo, Zn

Figure 2. Generalized geology and mineral resource potential of Fifteen Mile Creek Wilderness Study Area, Malheur County, 

Oregon.

B4 Mineral Resources of Wilderness Study Areas: Trout Creek Mountains Region, Oregon
U.S. Geological Survey (USGS) and the U.S. Bureau of 

Mines (USBM). An introduction to the wilderness review 

process, mineral survey methods, and agency responsibilities was provided by Beikman and others (1983). The 

USBM evaluates identified resources at individual mines 

and known mineralized areas by collecting data on current 

and past mining activities and through field examination of 

mines, prospects, and mineralized areas. Identified resources are classified according to the system that is a 

modification of that described by McKelvey (1972) and 

U.S. Bureau of Mines and U.S. Geological Survey (1980). 

Studies by the USGS are designed to provide a reasonable 

scientific basis for assessing the potential for undiscovered 

mineral resources by determining geologic units and structures, possible environments of mineral deposition, presEXPLANATION

Geologic terrane having low mineral resource potential (L) for

Sb, Bi, Hg, Ag, Mo. and Zn in epithermal vein deposits 

Geologic terrane having low mineral resource potential (L) for

Sn 

Geologic terrane having low mineral resource potential (L) for

Hg and U in caldera-related deposits 

Geologic terrane having low mineral resource potential (L) for

Zeo, Geo, Pum, and O,G 

Geologic terrane having low mineral resource potential (L) for

REE, Zr, and Sto

Levels of certainty of assessment

Data only suggest level of potential

Data give good indication of level of potential

Commodities

Ag

Bi

Geo

Hg

Mo

0,0

Pum

REE

Silver

Bismuth

Geo thermal

Mercury

Molybdenum

Oil and gas

Pumice

Rare-earth elements

Sb

Sn

Sto

U

Zeo

Zn

Zr

Antimony

Tin

Decorative building stone

Uranium

Zeolite minerals

Zinc

Zirconium

Description of map units

Qal Alluvium (Quaternary)

Ttw Tuff of Whitehorse Creek (Tertiary)

Ttl Tuff of Long Ridge (Tertiary)

T tt Tuff of Trout Creek Mountains (Tertiary)

Tf Basaltic andesite, andesite, and rhyolite flows (Tertiary)

 Contact Dashed where approximately located

 - Fault Dashed where approximately located

X Prospects

Figure 2. Continued.

ence of geochemical and geophysical anomalies, and applicable ore-deposit models. Mineral assessment methodology and terminology as they apply to these surveys were 

discussed by Goudarzi (1984). See appendixes for the 

definition of levels of mineral resource potential and certainty of assessment and for the classification of identified 

resources/reserve classification.

Character and Setting

The Fifteen Mile Creek (OR-003-156), Oregon Canyon (OR-003-157), Twelve Mile Creek (OR-003-162), 

and Willow Creek (OR-003-152) Wilderness Study Areas 

are located in southeastern Oregon between 7 and 35 mi 

northwest of McDermitt, Nev. (fig. 1). They cover 51,290, 

42,900, 25,340, and 26,130 acres, respectively. The areas 

lie in the northwestern part of the Basin and Range physiographic province in a region characterized by north-trending horst-graben structures, calderas, and thick volcanic 

sequences of Tertiary age (see geologic time chart in appendixes). Steep topography is common; elevations range 

from 7,949 ft in the Oregon Canyon Mountains to about 

4,700 ft in the northwestern parts of the Twelve Mile Creek 

and Willow Creek study areas. The study areas are accessible by numerous graded dirt roads branching off of U.S. 

Highway 95 to the east and Nevada Highway 140 to the 

south. Dirt roads separate each of these four contiguous 

areas, but some interior parts of the areas are difficult to 

reach. The climate is semiarid with moderately warm to 

hot summers and cold winters; most precipitation falls 

during the winter.

Vegetation in the study areas belongs to the sagebrush 

steppe community of the Great Basin Floristic Province. A 

sagebrush steppe, sometimes referred to as the sagebrushgrass vegetation type, consists of a series of generally 

treeless, shrub-dominated communities. The dominant 

shrub in the study areas consists of big sagebrush (Artemisia tridentata), and the dominant grass is bluebunch 

wheatgrass (Agropyron spicatum). Idaho fesque (Festuca 

idahoensis) becomes the dominant grass in drier situations. 

Stream banks in the study areas support characteristic riparian vegetation, including typical trees of the Great Basin: 

aspen (Populus tremuloides), juniper (Juniperus spp.), 

cottonwood (Populus fremontii), and oak (Quercus spp.). 

Rush- (Juncus spp.-) dominated meadows and seeps represent a common wetland vegetation community found in the 

study areas.

Previous Investigations

The geology of the Opalite mining district was first 

described by Yates (1942). The district includes the Opalite and Bretz mercury deposits and the Aurora uranium 

deposit, all located about 1.5 mi south of the Oregon

Fifteen Mile Creek, Oregon Canyon, Twelve Mile Creek, and Willow Creek Wilderness Study Areas, Oregon B5
118°00' 117°52'30"

___ L/ J I /-"H

L NJ

L/B Zeo (entire study area) 

L/C Geo, O,G (entire study area)

APPROXIMATE BOUNDARY

OF

OREGON CANYON

WILDERNESS STUDY AREA

(OR-003-157)

L/B Au, Ag (all units labled Tto)

L/B Sb, Bi

Hg, Ag, 

Mo, Zn

L/B REE, Zr, Sto

(all units labeled

L/B Sb, Bi, Hg, Ag, Mo, Zn

EXPLANATION

Geologic terrane having moderate mineral resource potential (M) for 

Hg and U and low mineral resource potential (L) for Au and Ag

B Geo logic terrane having low mineral resource potential (L) for Hg and U 

Geologic terrane having low mineral resource potential (L) for Sb,

Bi, Hg, Ag, Mo, and Zn in epithermal vein deposits 

Geologic terrane having low mineral resource potential (L) for Sn

Geologic terrane having low mineral resource potential (L) for Ag and

' Au in epithermal veins I -I-- I Geologic terrane having low mineral resource potential (L) for REE,

I I Zr, and Sto

n Geologic terrane having low mineral resource potential (L) for Zeo, Geo, and O,G

Levels of certainty of assessment

B Data only suggest level of potentialC Data give good indication of level of potential

Description of map units

Qal Alluvium (Quaternary)Ttl Tuff of Long Ridge (Tertiary)

Tr Rhyolitic plugs and dikes (Tertiary)

Ttt Tuff of Trout Creek Mountains (Tertiary)Tf Basaltic andesite, andesite, and rhyolite flows (Tertiary)

Tto Tuff of Oregon Canyon (Tertiary)

Tfl Basalt flows (Tertiary)

Contact

Fault Dashed where 

approximately located; dotted 

where concealed

Commodities

Au Gold

Ag Silver

Bi Bismuth

Geo Geothermal

Hg MercuryMo Molybdenum O.G Oil and gas

REE Rare-earth elementsSb Antimony

Sn Tin

Sto Decorative building

	stone

U UraniumZeo Zeolite minerals

Zn Zinc

Zr Zirconium

Figure 3. Generalized geology and mineral resource potential of Oregon Canyon Wilderness Study Area, Malheur County, Oregon.
Canyon study area. Reconnaissance geologic maps of the 

Adel and Jordan Valley 1° by 2° quadrangles, which include the study areas, were published by Walker and 

Repcnning (1965, 1966). Initial detailed mapping within 

the McDermitt caldera complex was provided by Greene 

(1972, 1976); revised and more detailed geologic mapping 

and interpretations of the McDermitt caldera complex were 

presented by Rytuba (1976), Rytuba and Conrad (1981), 

and Rytuba and McKee (1984). Several quadrangles covering the study areas have been mapped at a scale of 

1:24,000 (Rytuba and others, 1983a, b, c, d; Rytuba and 

Curtis, 1983; Peterson and Tegtmeyer, 1987; JJ. Rytuba 

and others, unpub. mapping, 1980). Rytuba and Glanzman 

(1979) and Glanzman and Rytuba (1979) investigated 

mineral deposits associated with the McDermitt caldera 

complex, and Rytuba and others (1981) presented a detailed geologic history of the Whitehorse caldera and discussed associated mineral deposits.

Present Study

The USBM searched published literature, Harney and 

Malheur County mining claim records, USBM Mineral 

Industry Location System records, and BLM mining and 

mineral lease records. Information from USBM, Oregon 

Department of Geology and Mineral Industries (DOGAMI), and other production records was also used. Fieldwork carried out in 1986 included a search for mines, 

prospects, mining claims, and mineralized areas within and 

adjacent to the study areas. Samples were taken of potentially mineralized rocks for geochemical assay and of alluvial material primarily for placer analysis to detect free 

gold and other valuable heavy minerals. Analytical data 

are on file at the U.S. Bureau of Mines, Western Field 

Operations Center, E. 360 Third Ave., Spokane, WA 

99202.

The USGS mapped the geology of the quadrangles that 

include the study areas from about 1980 to 1987 (see previous section) and in 1986 collected rock and stream-sediment samples for geochemical analysis. Gravity data were 

collected to augment previously published information; 

aeromagnetic and radiometric interpretations are based on 

published regional data.

Acknowledgments

Personnel from the Oregon Canyon, Stoddard, and 

Whitehorse Ranches kindly allowed us passage across their 

lands to gain access to parts of the study areas and provided 

indispensable information and directions. J.J. Gray of 

DOGAMI provided helpful advice and information on the 

study areas. George Brown and Mark Hosket of the BLM,

Burns, Oreg., provided logistical and land status information. The BLM mineral staff in Vale, Oreg., particularly 

William Holsheimer and Wylmoth Jones, provided helpful 

information about access to the areas and about mineral 

deposits of the region. C.S. Harwood and S.L. Jones assisted with the field work by the U.S. Geological Survey.

APPRAISAL OF IDENTIFIED RESOURCES OF 

THE FIFTEEN MILE CREEK 

WILDERNESS STUDY AREA

By Andrew M. Leszcykowski 

U.S. Bureau of Mines

Mining and Exploration History

A search of Malheur County, State, and Federal mining records revealed no mines, claims, or mineral leases 

within the study area. Four prospect pits, which appear to 

be relatively old, were found near the junction of Minehole 

and Whitehorse Creeks (fig. 2) during a search of the area 

(Leszcykowski, 1987). The study area lies immediately 

north of the Opalite mining district (Benson, 1956), where 

five mercury mines are located. The Ruja, Cordero, and 

McDermitt mines lie about 15 mi southeast of the study 

area, and the Opalite and Bretz mines are about 5 mi southsoutheast.

Results of Investigation

No mineral resources were identified during this study. 

None of the four rock samples collected from the prospect 

pits near the confluence of Minehole and Whitehorse 

Creeks contain anomalous elemental concentrations. Of 

the nine alluvial samples collected, one from just outside 

the northwest boundary of the area contained a small flake 

of gold; the others had none. No samples have indications 

of metal concentrations, but four samples contain minor 

amounts of moonstone (the potassium feldspar adularia). 

However, the moonstones are too small to be considered 

gem quality, and the source of the alluvial moonstone was 

not found. Sand and gravel accumulations in the lower 

canyons of the Fifteen Mile, Doolittle, Whitehorse, and 

Cottonwood Creeks have no local markets because road 

metal and gravel for road base are available closer to areas 

of probable use. There are no oil or gas leases within the 

study area. All of the mines in the nearby Opalite mining 

district are located in the McDermitt caldera complex, 

which does not extend into the study area.

Fifteen Mile Creek, Oregon Canyon, Twelve Mile Creek, and Willow Creek Wilderness Study Areas, Oregon B7
APPROXIMATE BOUNDARY

OF

TWELVE MILE CREEK

WILDERNESS STUDY AREA

(OR-003-162)

LB Pum

Tf Tf

L/B REE. Zr. Sto 

(all units labeled Ttt)

L/B Zeo (entire study a 

L/C Geo, O.G (entire study area)

EXPLANATION

I I Geologic terrene having low mineral resource

1 potential (L) for Geo, O,G, Zeo, and Pum

I Ttt I Geologic terrene having low mineral resource

 potential (L) for REE, Zr, and Sto

Levels of certainty of assessment

B Data only suggest level of potential 

C Data give good indication of level of 

potential

Commodities

Geo Geothermal Slo Decorative building stone

O,G Oil and gas Zeo Zeolite minerals

Pum Pumice Zr Zirconium

REE Rare-earth elements

Description of map units

Qal Alluvium (Quaternary)

Ttl Tuff of Long Ridge (Tertiary)

Ttt Tuff of Trout Creek Mountains (Tertiary)

Tf Basaltic andesite and andesite flows (Tertiary)

 Contact Dashed where approximately located

 Fault Dashed where approximately located; 

dotted where concealed

___________________I

3 MILES

Figure 4. Generalized geology and mineral resource potential of Twelve Mile Creek Wilderness Study Area, 

Malheur County, Oregon.

B8 Mineral Resources of Wilderness Study Areas: Trout Creek Mountains Region, Oregon
L. B REE. Zr. Sto 

(all units labeled APPROXIMATE BOUNDARY

OF

WILLOW CREEK

WILDERNESS STUDY AREA

(OR-003-152)

L/BZeo

(entire study area) 

L C Geo, O.G 

(entire study area)

1. B Sb. Bi. Hii. 

As. Mo. Zn

L. B Sn

4 MI

EXPLANATION

Commodities

Ag

Bi

Geo

Hg

Mo

0,G

REE

Silver

Bismuth

Geo thermal

Mercury

Molybdenum

Oil and gas

Rare-earth elements

Sb

Sn

Sto

Zeo

Zn

Zr

Antimony

Tin

Decorative building stone

Zeolite minerals

Zinc

Zirconium

Geologic terrane having low mineral

resource potential (L) for Sb, Bi, Hg,

Ag, Mo, and Zn 

Geologic terrane having low mineral

resource potential (L) for Sn 

Geologic terrane having low mineral

resource potential (L) for Zeo, Geo, and

0,G 

Geologic terrane having low mineral

resource potential (L) for REE, Zr, and

Sto

Description of map units

Levels of certainty of assessment

Ttl Tuff of Long Ridge (Tertiary)

B Data only suggest level of potential Ttt Tuff of Trout Creek Mountains (Tertiary) 

C Data give good indication of level of Tf Basaltic andesite, andesite, and rhyolitic flows 

potential (Tertiary)

 Contact

 Fault Dashed where approximately located

' Sample locality noted in text

Figure 5. Generalized geology and mineral resource potential of Willow Creek Wilderness Study Area, Harney 

and Malheur Counties, Oregon

Fifteen Mile Creek, Oregon Canyon, Twelve Mile Creek, and Willow Creek Wilderness Study Areas, Oregon B9
APPRAISAL OF IDENTIFIED RESOURCES OF 

THE OREGON CANYON 

WILDERNESS STUDY AREA

By Richard A. Winters 

U.S. Bureau of Mines

There are no identified resources in the Oregon Canyon Wilderness Study Area. There were 8 inactive claims 

recorded in 1914 that are present in the southeastern part of 

the study area, and 110 current claims are in the eastern 

part. No mines or mineralized structures were observed 

during the field studies. The study area contains no mining 

districts, but the Opalite mining district located within the 

McDermitt caldera complex is immediately to the south. 

This district has produced mercury and also has been 

explored for uranium and lithium.

Metal concentrations in samples collected in the study 

area are too low to classify as identified resources. Nonmetallic identified commodities, such as building stone and 

sand and gravel, do not constitute identified resources in 

the study area as they are small, of low quality, and far 

from prospective markets.

APPRAISAL OF IDENTIFIED RESOURCES OF 

THE TWELVE MILE CREEK 

WILDERNESS STUDY AREA

By Steven W. Schmauch 

U.S. Bureau of Mines

There are no identified resources in the Twelve Mile 

Creek Wilderness Study Area (Schmauch, 1987). No 

mineralized fracture systems, visibly altered rocks, or intensely silicified areas, like those in the Opalite mining 

district, were seen during traverses across the study area, 

and no significant accumulations of unwelded ash-flow 

tuffs or tuffaceous sedimentary rocks were observed.

There are no mining claims in or adjacent to the study 

area, and there is no recorded past or current mining activity. Analyses of alluvial samples collected in the main 

drainages indicate slightly anomalous concentrations of 

molybdenum, lead, and arsenic in the southeastern part of 

the study area but not in sufficient concentrations to identify resources.

APPRAISAL OF IDENTIFIED RESOURCES OF 

THE WILLOW CREEK 

WILDERNESS STUDY AREA

By Thomas J. Peters 

U.S. Bureau of Mines

Mining and Mineral Exploration History

A search of BLM and Hamey and Malheur County 

records uncovered no evidence of mining claim locations or 

of leases for minerals, gas, or oil. No evidence of mining 

or prospecting was seen during traverses of the study area. 

Most mining and prospecting in the region has been confined to the McDermitt caldera complex, southeast of the 

study area, which contains several important mercury, 

uranium, and lithium deposits (Rytuba and Glanzman, 

1979). The Whitehorse caldera, northwest of the study 

area, hosts diatomite deposits and an epithermal uranium, 

mercury, and precious-metal prospect at Flagstaff Butte, 8 

mi west-northwest of the study area.

There is no history of mining in the Willow Creek 

study area. Gray and others (1983, appendix B) reported 

that more than half of the 30 stream-sediment samples they 

collected from the study area contain anomalous beryllium, 

mercury, lead, tin, and uranium. Bukofski and others 

(1984, appendix K) collected 30 panned-concentrate 

samples from the study area and reported anomalous copper, fluorine, molybdenum, silver, tin, and tungsten. A 

draft environmental impact statement (U.S. Bureau of Land 

Management, 1985, p. 283) indicates moderate or low 

favorability for beryllium, silver, mercury, and geothermal 

resources, as well as possible gold, lithium, and pumice 

resources.

Methods of Investigation

The USBM collected 57 rock and 40 alluvial samples 

to evaluate the possibility of identified resources in areas 

where Gray and others (1983) or Bukofski and others 

(1984) indicated geochemical anomalies and in areas where 

the U.S. Bureau of Land Management (1985) suggested 

mineral resources. The rock samples were collected from 

volcanic units, especially from the porous tuff of Trout 

Creek Mountains, which is capped by the impermeable tuff 

of Long Ridge and was considered a prospective host rock 

for submicroscopic beryllium (bertranditc) mineralization. 

All samples were tested for radioactivity and fluorescence. 

Rock samples were dried, pulverized, and analyzed for 27 

elements by neutron-activation analysis. Alluvial samples 

were concentrated on a Wilfley table to extract gold and 

other heavy minerals, and a split of each concentrate was 

analyzed for 18 elements by inductively coupled plasma 

methods.

BIO Mineral Resources of Wilderness Study Areas: Trout Creek Mountains Region, Oregon
Results of Investigation

There are no identified mineral resources in the Willow Creek Wilderness Study Area. Although concentrations were too low to delineate identified resources, sampling by the USBM detected slightly elevated concentrations of several elements at two sites. One sample, from an 

area of hematitic alteration along a poorly exposed fault 

near the northeast corner of the study area (fig. 5, No. 1), 

contains twice the expected normal (background) concentrations of arsenic, antimony, and cesium. Arsenic and 

antimony are common indicators of gold mineralization; 

however, no significant levels of gold were detected. The 

other sample, taken from a silicified zone between two 

faults in the southern part of the study area (fig. 5, No. 2) 

contains slightly more than twice the background concentrations of uranium, cesium, and the rare-earth elements 

lanthanum, scandium, thorium, and ytterbium. Rare-earth 

elements are currently of interest for high-technology applications; however, sample concentrations are too low to be 

of economic interest. Cesium, found at both sites, is 

commonly an indicator for beryllium mineralization; however, beryllium at both sites did not exceed the background 

concentration.

ASSESSMENT OF MINERAL RESOURCE 

POTENTIAL

By Jocelyn A. Peterson, James J. Rytuba, 

Donald Plouff, Thomas L. Vercoutere, 

Robert L. Turner, and Don L. Sawatzky 

U.S. Geological Survey

Geology

The Fifteen Mile Creek, Oregon Canyon, Tw61ve Mile 

Creek, and Willow Creek Wilderness Study Areas are in 

the northern part of the Basin and Range physiographic 

province, a region characterized by northeast-trending, 

uplifted ranges, and intervening basins and calderas. The 

four contiguous study areas are located mostly on the uplifted plateaus of the Oregon Canyon and Trout Creek 

Mountains (fig. 1). They are bounded by the Quinn River 

Valley on the east, the McDermitt caldera complex on the 

south, and the Whitehorse caldera on the northwest. The 

Oregon Canyon and Trout Creek Mountains are capped by 

Miocene rhyolitic ash-flow tuffs erupted from the McDermitt caldera complex and the Pueblo and Whitehorse 

calderas to the south, west, and northwest, respectively. 

Underlying the tuffs is a thick sequence of basalt, basaltic 

andesite, andesite, and rhyolite flows. This entire sequence 

dips 3° to 5° north-northwest to northwest.

The oldest rocks exposed in the study areas are porphyritic basalt flows that contain large plagioclase phenocrysts. Flows average 20 ft thick, have vesicular tops, and 

typically form prominent ledges. Air-fall tuffs and flow 

breccias are present locally. These basalt flows may be 

correlated with the Steens Basalt (Mankinen and others, 

1987).

The tuff of Oregon Canyon overlies these flows (fig. 

3). It erupted 16.1 million years ago from the Washburn 

caldera, the oldest in the McDermitt caldera complex. The 

tuff is chemically zoned from peralkaline rhyolite at the 

base through low-silica rhyolite in the middle to dacite at 

the top. The lower peralkaline part of the unit is white to 

bluish white, porphyritic, densely welded tuff that is granophyrically crystallized. Phenocrysts make up as much as 

10 percent of the rock and consist of sanidine (5 percent), 

quartz (4 percent), and sodium amphibole (1 percent). The 

peralkaline tuff grades upward into brown, porphyritic, 

low-silica rhyolitic tuff that, in turn, grades into dacitic tuff 

near the top of the unit. This dacitic tuff is less welded and 

is characterized by reddish-brown pumice and ash.

A flow sequence above the tuff of Oregon Canyon 

(figs. 2-5) is dominated by andesite and basaltic andesite 

flows. These flows are locally interstratified with andesitic 

to basaltic tuffs and flow breccias. Rhyolite flows are 

found locally in the uppermost and middle parts of this 

volcanic sequence in the southern and eastern parts of the 

Oregon Canyon and Trout Creek Mountains. The basaltic 

andesite and andesite flows are generally aphyric, but two 

flows near the base of the sequence have abundant large 

plagioclase phenocrysts. Around the margin of the Washburn caldera (fig. 1), porphyritic rhyolite flows and breccias 

make up the base of these flows. They form a very thick 

sequence within the Washbum caldera but thin abruptly to 

the north.

The tuff of Trout Creek Mountains overlies the andesite and basaltic andesite flows. It erupted 15.8 million 

years ago from the Pueblo caldera adjacent to Steens and 

Pueblo Mountains about 25 mi west of the study areas. 

This ash-flow tuff is a single cooling unit composed of 

porphyritic peralkaline rhyolite with phenocrysts of potassium feldspar (26 percent), quartz (1 percent), and aenigmatite (1 to 5 percent). The basal part of the unit consists 

of bedded air-fall and base-surge deposits in which phenocrysts predominate over the ash components. These deposits grade upward into a basal black vitrophyre as thick as 6 

ft. The remainder of the tuff is densely welded and granophyrically crystallized. The unit has a distinctive bluegreen color, which strongly contrasts with the enclosed 

chatoyant potassium-feldspar phenocrysts. The tuff, which 

has an average thickness of about 220 ft, has local columnar jointing, and forms prominent cliffs along canyon 

walls.

Porphyritic rhyolite plugs and dikes cut all units older

Fifteen Mile Creek, Oregon Canyon, Twelve Mile Creek, and Willow Creek Wilderness Study Areas, Oregon B11
than the tuff of Long Ridge. These intrusions, near the 

eastern margin of the Oregon Canyon study area (fig. 3), 

contain phenocrysts of quartz (5.5 percent), sanidine (5.5 

percent), biotite (1 percent), and pyroxene (less than 1 

percent) in a cryptocrystalline groundmass of quartz and 

feldspar.

Overlying the tuff of Trout Creek Mountains is the tuff 

of Long Ridge, which caps the plateaus within the study 

areas (figs. 2-5) and extends farther south, west, and north. 

This ash-flow tuff was erupted about 15.6 million years ago 

from the Long Ridge caldera, the youngest in the McDermitt caldera complex. The tuff is complexly chemically 

zoned, ranges from peralkaline rhyolite in the lower part to 

low-silica rhyolite in the upper part, and has an average 

thickness of about 350 ft. The peralkaline rhyolite is 

aphyric, whereas the low-silica rhyolite is porphyritic. The 

base of the unit is a brick-red unwelded tuff that grades 

upward into a black basal vitrophyre as thick as 6 ft. 

Above the vitrophyre is the aphyric part of the tuff, which 

is greenish gray, densely welded, and granophyrically crystallized. Brown porphyritic tuff is interstratified with the 

middle and upper parts of the aphyric tuff and makes up the 

upper part of the unit. Nonwelded black pumiceous tuff is 

present locally in the uppermost part of the unit.

The youngest ash-flow tuff is the tuff of Whitehorse 

Creek, which was erupted from the Whitehorse caldera 

about 15 million years ago and is present only in the northwest tip of the Fifteen Mile Creek study area (fig. 2). It is 

a peralkaline rhyolite tuff that consists of two main cooling 

units separated by bedded air-fall tuffs and capped by 

welded tuff. The lower unit is nonwelded, light gray, and 

pumiceous. The lower part of the upper unit is a nonwelded gray pumiceous tuff that grades upward into a darkgray to black tuff. Above the upper cooling unit is welded 

tuff that contains sanidine phenocrysts (as much as 5 percent). This tuff of Whitehorse Creek forms prominent redbrown cliffs along canyon walls and has an average thickness of about 125 ft.

Quaternary alluvium is present in canyons and along 

the margins of the mountain ranges. The alluvium consists 

of coarse, poorly sorted, locally derived material.

The buried margin of the Washburn caldera transects 

the southeastern part of the Oregon Canyon study area. 

The caldera boundary is defined by the lack of outcrops of 

the tuff of Oregon Canyon, which has been displaced 

downward within the caldera and covered by caldera-fill 

rhyolite flows and flow breccias. Part of this caldera 

margin was reactivated along a northeast-trending fault 

during collapse of the younger Long Ridge caldera. Rhyolite dikes having similar trends have been emplaced along 

the projected caldera margin but are too small to map at 

this scale.

The north wall of the Long Ridge caldera is well 

developed as a topographic feature within the southern part

of the Oregon Canyon study area. The structural margin of 

the caldera lies south of the study area, but several arcuate 

normal faults subparallel to the main zone of structural 

collapse transect the southwestern part of the study area. 

These faults have displacements as large as 1,500 ft, but 

usually 840 ft or less, which are generally down toward the 

caldera. Near the border of the Long Ridge caldera, volcanic units dip as much as 15° inward toward the caldera. 

One arcuate normal fault that has a displacement of 

about 1,500 ft, adjacent to and within the southernmost part 

of the Oregon Canyon study area, has accommodated much 

of the collapse of the Long Ridge caldera. South of this 

fault, the volcanic units dip as much as 30° inward toward 

the caldera. Hydrothermal alteration occurred along the 

fault zone and spread out laterally into the volcanic rocks 

north and south of the zone. The alteration formed from 

the same hydrothermal system that formed the Bretz mercury and Aurora uranium deposits 1.5 mi to the southeast

(fig. 1).

In the southwestern part of the Oregon Canyon study 

area, six arcuate normal faults subparallel to the structural 

margin of the Long Ridge caldera displace the volcanic 

sequence downward to the south about 900 ft. All the 

faults except one displace fault blocks down toward the 

caldera. One fault displaces rocks downward away from 

the caldera, creating a graben having a maximum width of 

0.3 mi and a strike length of 2.5 mi. Hydrothermal alteration occurred along each of these faults but was most intense along those nearest the main structural margin of the 

Long Ridge caldera. Alteration extended laterally into 

volcanic rocks adjacent to the faults.

A few normal faults that strike northeast, north, and 

north-northwest and have displacements as large as 320 ft 

transect the study areas. They displace all of the stratigraphic units and are probably related to Basin-and-Range 

extension.

Geochemistry

A reconnaissance geochemical survey was conducted 

in the Fifteen Mile Creek, Oregon Canyon, Twelve Mile 

Creek, and Willow Creek Wilderness Study Areas in the 

summer of 1986. Samples of stream sediments from 191 

sites, and heavy-mineral concentrates derived from them, 

and 16 rock samples were analyzed for this study. Stream 

sediments represent a composite of rock and soil eroded 

upstream from the sample site. Heavy-mineral concentrates represent the heavy minerals present in rocks exposed 

in the drainage basin and permit the determination of some 

elements that are not easily detected in stream sediments. 

These concentrates may include minerals related to any 

mineralization that might have occurred in the area of the 

drainage basin.

B12 Mineral Resources of Wilderness Study Areas: Trout Creek Mountains Region, Oregon
The stream-sediment samples were collected from 

active alluvium in the stream channels. Each one is a 

composite from several localities along a channel length of 

approximately 50 ft and was sieved through an 80-mesh 

screen and pulverized to a fine powder for analysis. 

Heavy-mineral-concentrate samples were sieved through a 

10-mesh screen and then panned to remove most of the 

quartz, feldspar, clay-sized material, and organic matter. 

These raw concentrate samples were further concentrated 

by using a heavy liquid and a magnetic separator to produce nonmagnetic heavy-mineral-concentrate samples 

(hereafter called concentrates). The concentrates were 

ground to a fine powder for analysis.

Rocks were collected from mineralized and unmineralized outcrops and from stream float. Samples that appeared 

fresh and unaltered were collected to provide information 

about geochemical background levels. Altered or mineralized samples were collected to determine the suite of elements associated with alteration or mineralization. The 

rocks were crushed and pulverized to a fine powder for 

analysis.

The concentrate, stream-sediment, and rock samples 

were analyzed for 31 elements by direct-current arc 

semiquatitative emission spectrography (Grimes and Marranzino, 1968; Crock and others, 1987). The rocks and 

stream sediments were also analyzed for the following 

elements: arsenic, bismuth, cadmium, antimony, and zinc 

by inductively coupled plasma emission spectrography 

(Crock and others, 1987); gold by atomic absorption 

(Thompson and others, 1968); and mercury by atomic 

absorption (Koirtyohann and Khalil, 1976). The anomalous levels for each element are defined as at least twice the 

average concentrations of the element in the rock types 

found in the study areas. Analytical data and a description 

of the sampling and analytical techniques were provided by 

J.L. Jones (written commun., 1987).

Some of the concentrates contain anomalous levels of 

silver (2 to 150 parts per million, or ppm), bismuth (20 to 

greater than 2,000 ppm), antimony (200 to 2,000 ppm), 

lead (1,500 to 20,000 ppm), and tin (2,000 ppm and 

greater). The silver, bismuth, and antimony anomaly patterns suggest that a broad zone of epithermally mineralized 

rock crosses the southern part of the study areas. Anomalous amounts of tin (2,000 ppm and greater) are present 

across the southeastern part of the Oregon Canyon study 

area and along the boundary between the Fifteen Mile 

Creek and Willow Creek study areas. There are no corresponding anomalies in the stream sediments. Low-grade 

mineralization probably occurred during or shortly after 

extrusion of the volcanic rocks.

The stream-sediment data indicate several anomalous 

zones. Analytical results indicate that the southeastern part 

of the combined study areas has anomalous bismuth (2 to 

3 ppm), arsenic (10 to 12 ppm), and mercury (0.15 to 0.3

ppm), that the southwestern part has anomalous bismuth (2 

to 7 ppm), and that the central to west-central part has 

anomalous arsenic (10 to 17 ppm), molybdenum (5 to 7 

ppm), and zinc (200 to 300 ppm). In the southeast anomalous zone, no sites contain both anomalous bismuth and 

anomalous arsenic. This area is at and near the ring fracture zone of the Long Ridge caldera where the rocks are 

both tuffs and flows (figs. 2-5). The southwest anomalous 

zone is underlain primarily by basaltic andesite and andesite flows (figs. 2, 5). A central to west-central anomalous zone has eight sites having both anomalous molybdenum and arsenic. Rocks in this zone are welded ash-flow 

tuff and andesite, basaltic andesite, and rhyolite flows (figs. 

2,3).

Of the 16 rock samples collected, only 4 have anomalies for a single element. One sample from the southeast 

zone has 0.38 ppm mercury, two from the central area have 

2,000 ppm barium, and one from the central area has 200 

ppm copper.

Most of the anomalies described above are single-element, low-level anomalies and are difficult to ascribe to 

specific mineral deposit types or ore-forming processes.

Geophysics

Geophysical evaluation of the mineral resources of the 

Fifteen Mile Creek, Oregon Canyon, Twelve Mile Creek, 

and Willow Creek Wilderness Study Areas is based on 

interpretations of aerial gamma-ray, gravity, aeromagnetic, 

and remote-sensing surveys.

Radiometric data were compiled by Geodata International, Inc., (1980a, b) for the National Uranium Resource 

Evaluation (NURE) program of the U.S. Department of 

Energy. The coverage consists of 11 east-west flightlines 

spaced at 3-mi intervals and 2 north-south flightlines. 

Right altitudes ranged from 200 to 700 ft above the 

ground. Recordings were made of gamma-ray flux from 

radioactive isotopes of uranium, thorium, and potassium. 

Additional radiometric data (nine east-west lines) were 

collected near the south edge of the Fifteen Mile Creek and 

Oregon Canyon study areas at a spacing of 0.33 mi and a 

flight altitude of 400 to 600 ft above the ground (U.S. 

Geological Survey, 1982). Radiometric profiles in the 

region show abrupt changes of radioactive count rates over 

contacts between the principal rock units. Count rates 

generally were low over andesite and basalt, low to moderate over sedimentary rocks, and moderate to high over 

rhyolite. Although a radiometric high exceeding 10 ppm 

equivalent uranium occurs 1 mi southwest of the southeast 

corner of the Oregon Canyon study area, no intense anomalies indicating high concentrations of thorium or uranium 

were recorded along flightlines within the study areas.

Fifteen Mile Creek, Oregon Canyon, Twelve Mile Creek, and Willow Creek Wilderness Study Areas, Oregon B13
High concentrations of radioelements in the study areas are 

not precluded, however, because, assuming a 45-degree 

cone of detectability at 400 ft, the flightline spacing of 3 mi 

only samples radioactivity for about 5 percent of the 

ground surface.

The U.S. Geological Survey established 114 gravity 

stations in and within 3 mi of the borders of the study areas 

in 1986 (Plouff, 1987). These data supplement that collected previously from a set of stations located mostly 

south of the study areas (Plouff, 1977). A gravity map 

prepared from these data shows a complex pattern of 

anomalies (fig. 6). The most conspicuous anomaly is a 

north-trending gravity low, having an amplitude of about 8 

milligals (mGal) and extending about 8 by 20 mi, which is 

centered along the border between the Fifteen Mile Creek 

and Oregon Canyon study areas. A smaller but more intense gravity low, having an amplitude of about 11 mGal, 

and extending about 6 by 8 mi, is centered about 3 mi 

northwest of the Willow Creek study area. This gravity 

low reflects the contrast in densities between tuffaceous 

sedimentary rocks that fill the Whitehorse caldera (Rytuba 

and McKee, 1984) and the surrounding denser volcanic and 

basement rocks. Gravity-anomaly values increase northwestward by about 25 mGal in 8 mi, away from the conspicuous gravity low and through the Twelve Mile Creek 

area. This gravity gradient seems to be part of a fairly 

continuous band, having a gravity relief of at least 10 

mGal, which bends and continues southeastward and southward for about 50 mi along the east and south edges of the 

McDermitt caldera complex (Rytuba, 1976). Plouff (1985) 

suggested that this and similar gravity gradients may overlie edges of underlying Cenozoic batholiths whose upper, 

silicic parts have lower densities than surrounding basement rocks.

A conspicuous gravity high that extends southward for 

about 20 mi covers most of the Willow Creek study area 

(fig. 6). The south edge of the gravity high overlies extensive outcrops of pre-Cenozoic plutonic rocks (Stewart and 

Carlson, 1978), and, therefore, the gravity high probably 

reflects a wedge of pre-Cenozoic basement rocks that is 

concealed at shallow depth beneath less-dense Cenozoic 

rocks that surround it. A gravity high that extends about 5 

mi into the southeast corner of the Oregon Canyon study 

area seems to reflect the northern end of a wall of older 

rocks that extends for about 35 mi along the arcuate east 

edge of the central part of the McDermitt caldera complex. 

A gravity low extending southeastward then southward 

outside the east edge of the Oregon Canyon study area joins 

a major gravity low in Quinn River Valley, which Rytuba 

and McKee (1984) interpreted as a reflection of an underlying caldera.

A regional aeromagnetic survey was flown over the 

study area at a constant barometric elevation of 9,000 ft 

above sea level and with an east-west flightline spacing of

2 mi (U.S. Geological Survey, 1972). An intense, northtrending magnetic high overlies normally magnetized andesite flows in the southwestern part of the Willow Creek 

study area. Another intense magnetic high, centered near 

the southwest corner of the Fifteen Mile Creek study area, 

mostly overlies rhyolitic ash-flow tuffs, which have low 

magnetization elsewhere in the study areas.

A magnetic low that closely matches the shape and 

location of the gravity low over the Whitehorse caldera 

west of the study areas indicates that the intracaldera sedimentary rocks are nonmagnetic compared to surrounding 

volcanic rocks. A magnetic low also superimposes the 

gravity low east of the Oregon Canyon study area. A 

magnetic low similarly reflects possible sedimentary rocks 

beneath the gravity low along the boundary between the 

Fifteen Mile Creek and Oregon Canyon study areas. 

However, the deepest part of the magnetic low, which 

occurs over the southern part of the gravity low, indicates 

that the sedimentary rocks within, or rocks beneath, the 

northern part of the magnetic low apparently have weak to 

moderate magnetization. Alternatively, the southern part of 

the magnetic low may overlie reversely magnetized volcanic rocks or may incorporate reversely magnetized tuff. 

Several intense magnetic lows south and southwest of the 

study areas overlie reversely magnetized flows of Steens 

Basalt (Mankinen and others, 1987).

Photogeologic interpretations of linear features on 

l:800,000-scale Landsat multispectral scanner images that 

cover southeastern Oregon were used to prepare trendconcentration maps that show two prominent linear trends 

in the study areas. A large region centered near the wilderness study areas has linear features that trend between 

about N. 35° W. and N. 15° E., which most likely reflect 

trends of Basin-and-Range faulting. A second, prominent, 

west-to-northwest set of linear features trends N. 45° to 95° 

W. and includes some of the faults related to caldera structures.

General Discussion of Mineral and 

Energy Resources

Mercury, Uranium, and Lithium

Mercury, uranium, and lithium deposits of Miocene 

age are associated with hydrothermal activity related to the 

McDermitt caldera complex. These deposits are found 

mostly within caldera-fill areas that do not extend in the 

study areas, but they may also be present in and near structures along the caldera rim. Such structures are present in 

the southern part of the Oregon Canyon study area. Mercury deposits occur as veins in volcanic rocks and in opalized (silicified) lake-bed sediments in the McDermitt 

caldera complex directly south of the study areas (Rytuba 

and Glanzman, 1979). The main ore minerals, cinnabar

B14 Mineral Resources of Wilderness Study Areas: Trout Creek Mountains Region, Oregon
(HgS) and corderoite (Hg^Cy, in the volcanic rocks at 

the Cordero mine (about 10 mi southeast of the Oregon 

Canyon study area) are closely associated with ring fractures of the calderas. At the McDermitt (about 10 mi

southeast of the Oregon Canyon Study area), Opalite, and 

Bretz mines, locations of ore minerals are controlled by 

favorable beds in sediments. In the mineralized areas, 

rhyolitic rocks have been silicified and basaltic rocks have

118" 15' 118*00' 117* US'

42° IS'

42" 00' -

Figure 6. Bouguer gravity map for area including Fifteen Mile Creek (FM), Oregon Canyon (OC), Twelve Mile Creek 0"M), and 

Willow Creek (WC) Wilderness Study Areas, Malheur and Harney Counties, Oregon; bold lines indicate approximate boundaries of study areas. Contour interval 2 milligals; hachures indicate closed gravity lows. Squares indicate locations of gravity 

stations; W, gravity low associated with Whitehorse caldera; M, McDermitt, Nev.

Fifteen Mile Creek, Oregon Canyon, Twelve Mile Creek, and Willow Creek Wilderness Study Areas, Oregon B15
been argillized. Unaltered rhyolites and caldera-fill sediments contain high concentrations of mercury (0.25-0.65 

ppm) for several miles from the mercury deposits and, thus, 

may also have been affected by the mineralization. Mercury accumulations in the sedimentary rocks within the 

calderas are accompanied by widespread zeolite minerals 

and by local potassium feldspar and other silicate minerals 

near the ore deposits. The zeolites, however, may be diagenetic (Wallace and Roper, 1981). These sedimentary 

rocks do not extend into the study areas.

Some of the high concentrations of uranium occur in 

mercury deposits, but others are in rhyolitic domes emplaced along ring fractures and intrusions along the western 

margins of the calderas (Rytuba and Glanzman, 1979). 

Similar rhyolite domes occur along the north margins of the 

calderas (Rytuba and Glanzman, 1979) adjacent to and 

within the Oregon Canyon and near the Fifteen Mile Creek 

study areas. Some uranium concentrations also occur along 

flow-boundary zones (Wallace and Roper, 1981). At the 

Aurora deposit about 1 mi south of the Oregon Canyon 

study area, uraninite and coffinite are commonly localized 

in the upper parts of altered vesicular flows and in breccia 

layers, primarily within volcanic rocks of intermediate 

composition (Roper and Wallace, 1981). Rocks adjacent to 

the uranium concentrations have been altered to clay minerals, zeolites, and pyrite. The uranium minerals may have 

been derived from hydrothermal fluids genetically related 

to the host volcanic rocks, and mineralization in the adjacent sediments may be syngenetic at least in part (Roper 

and Wallace, 1981). Background uranium concentrations 

in unaltered volcanic rocks are as high as 20 ppm (Rytuba 

and Glanzman, 1979).

Both the uranium and mercury mineralization may be 

related to the same hydrothermal system, with the mercury 

concentrating near the surface and the uranium concentrating deeper or with the uranium forming at the last stages of 

hydrothermal activity (Rytuba and Glanzman, 1979; Roper 

and Wallace, 1981). Geochemically anomalous arsenic, 

molybdenum, and antimony are also present in the mercury- and uranium-enriched areas south of the study areas.

Lithium concentrations in the clay mineral hectorite 

are present in tuffaceous sediments altered to zeolites and 

potassium feldspar in altered zones within the McDermitt 

caldera complex (Rytuba and Glanzman, 1979). The largest lithium concentrations are in altered zones near the 

north and west margins of the Long Ridge caldera. These 

altered zones extend within 5 mi south of the study areas, 

but they do not continue into them; therefore, the potential 

for lithium is not discussed in the sections below. Hectorite 

is not currently a source of extractable lithium (Ferrell, 

1985, p. 462, 463). Both anomalous lithium and uranium 

concentrations are less widespread than anomalous mercury.

Miocene mercury and uranium mineralization of hydrothermal origin also occurred on the east side of the 

Steens and Pueblo Mountains about 30 mi northwest of the 

study areas (Roback and others, 1987; Minor and others, 

1987; Williams and Compton, 1953). These deposits are in 

silicified and argillized rocks locally enclosed in a halo of 

limonitic and calcitic clays. The mercury, which occurs in 

veins and breccia bodies, is commonly accompanied by 

iron and copper sulfides and barite. Only some of these 

deposits are related to a caldera structure.

Epithermal Vein Deposits

Two mining districts near the study areas have precious-metal quartz veins and associated disseminated ore 

minerals that are thought to be genetically related to subsidence features similar to calderas. These are the National 

mining district in the Santa Rosa Mountains, about 35 mi 

southeast of the study areas (Vikre, 1985), and the Silver 

City and DeLamar mining districts in Idaho, about 90 mi 

northeast of the study areas (Piper and Laney, 1926; 

Pansze, 1975; Halsor, 1983). Quartz veins host gold- and 

silver-bearing sulfide and sulfosalt minerals in these districts, and ore mineral are also disseminated in the country 

rock in the Silver City district. Silicic alteration has characteristically occurred in these deposits, but in some places 

adularia, sericite, clay minerals, chlorite, and other minerals 

are also present. Precious-metal quartz veins in the National district occur in a thick volcanic and intrusive sequence along the west side of a shallow structural basin that 

resembles a partly collapsed caldera (Vikre, 1985). Ore 

occurs in rhyolitic rocks of the sequence. In addition to 

gold and silver in these veins, mercury, antimony, copper, 

lead, zinc, and arsenic are present in the upper part of the 

system. Veins and disseminated ore in the DeLamar deposit occur in a ring dome complex that has some features 

of a caldera system, and structural control localizes the ore 

deposits (Halsor, 1983). Rhyolitic lava flows and exogenous domes are the main host rocks in a bimodal suite 

of volcanic rocks. Supergene enrichment may have been 

important in the district (Piper and Laney, 1926). Small 

concentrations of antimony, arsenic, copper, lead, zinc, and 

selenium are also present. These deposits all formed about 

15 to 16 million years ago in middle Miocene. This is near 

the time of volcanic and hydrothermal activity in the 

McDermitt caldera complex (Rytuba and McKee, 1984).

Although no epithermal gold and silver ore bodies 

have been discovered in the McDermitt caldera complex, 

the geologic environment resembles those of mining districts described above. In the southwestern part of the 

Trout Creek Mountains about 15 mi southwest of the study 

areas, anomalous silver concentrations as high as 16 ppm 

(S.A. Minor, oral commun., 1987), in rock samples from 

the upper part of the tuff of Oregon Canyon, suggest the 

possible presence of epithermal veins. Geochemical data

B16 Mineral Resources of Wilderness Study Areas: Trout Creek Mountains Region, Oregon
from the Fifteen Mile Creek, Oregon Canyon, Twelve Mile 

Creek, and Willow Creek study areas also suggest that a 

broad region centered in the Fifteen Mile Creek study area 

may have been permeated by hydrothermal fluids enriched 

in antimony, bismuth, mercury, and silver and possibly in 

molybdenum and zinc. However, mineralized and altered 

areas that may have formed by such a hydrothermal system 

have not been identified, so the nature and extent of any 

such mineralization is unknown.

Rare-earth Elements and Zirconium

Base-surge deposits near the base of the tuff of Trout 

Creek Mountains are locally enriched in phenocrysts. 

Concentrations of phenocrysts such as aenigmatite, a sodium-iron-titanium silicate that is rich in rare-earth elements and zirconium (Conrad, 1984), may locally be high 

enough to constitute a resource for light rare-earth elements 

and zirconium.

Tin

Geochemical anomalies for tin in the southeastern and 

southwestern parts of the study areas may possibly have 

been derived from basaltic flows in the areas. Similar tin 

anomalies have been found in basalt in the Sheephead 

Mountains, Oreg. (D.R. Sherrod, oral commun., 1987), and 

tin from the four study areas may have had a similar origin. 

A deposit model for this type of anomaly has not yet been 

developed.

Industrial Minerals

Zeolite minerals are present in lakebed sedimentary 

rocks of the McDermitt caldera complex, either as hydrothermal alteration products associated with mercury mineralization (Glanzman and Rytuba, 1979) or as a result of diagenesis of the sediments (Wallace and Roper, 1981). The 

zeolite minerals include clinoptilolite, mordenite, erionite, 

and analcime (Glanzman and Rytuba, 1979). Zeolites also 

occur in caldera-fill rocks in the Whitehorse caldera directly north of the Willow Creek study area (Rytuba and 

others, 1981). These sedimentary environments do not 

extend into the study areas. Zeolite minerals commonly 

also occur in altered tuffaceous volcanic and sedimentary 

rocks; however, they were not seen in the tuffs in these 

study areas and, if present, are not likely to be abundant.

Pumice and perlite are commonly found in young 

volcanic terranes. Small perlite resources have been identified in Tertiary volcanic rocks in the S teens Mountain 

area about 30 mi west of the study areas (Minor and others, 

1987), where perlite is found in the glassy margin of a 

rhyolite dome. Pumice fragments have been found in the 

nonwelded parts of the tuff of Long Ridge north of the 

Twelve Mile Creek study area (Peterson and Tegtmeyer,

1987), but typically they are scattered throughout the ash 

matrix. Minor nonwelded tuff may extend into the extreme 

northern part of the study area, although it is unlikely that 

any large accumulations would be present. Pumice is also 

present in limited exposures of the lower part of the tuff of 

Whitehorse Creek in the Fifteen Mile Creek study area. 

Pumiceous nonwelded tuff was not seen in the other study 

areas.

Diatomite constitutes about the upper 100 ft of calderafill deposits from the Whitehorse caldera in a drill core 

taken from about 3 mi northwest of the Willow Creek study 

area (Rytuba and others, 1981). The diatomite contains 

interbedded volcanic ash and clay layers. Below the diatomite layer are unaltered tuffaceous sedimentary rocks and, 

lower down, altered beds that contain zeolites and potassium feldspar. Diatomite has also been reported from sedimentary rocks of the McDermitt caldera complex (Rytuba 

and Glanzman, 1979). The northwest corner of the Willow 

Creek study area is close to exposures of caldera-fill sediments that contain diatomite but is geologically different, 

so resources of this type are not expected in the study area.

Rocks suitable for use as building stone and crushed 

aggregate are readily available in all of the study areas, but 

there is no local market for large quantities of these commodities. Building stone for local use is plentiful outside 

the study areas. The tuff of Trout Creek Mountains is 

locally attractive enough to warrant transportation to more 

distant markets for use as dimension stone.

Sand and gravel in the creeks are not considered to be 

resources in these study areas, even where abundant 

enough to map, because similar material is available closer 

to markets.

Geothermal Energy

Warm-water springs and wells are found at scattered 

localities in southeastern Oregon. The Alvord Known 

Geothermal Resource Area lies about 25 mi northwest of 

the study areas, and smaller localities with warm-water 

wells are even closer (Oregon Department of Geology and 

Mineral Industries, 1982). Seven wells and springs about 

5 mi northwest of the Willow Creek study area have temperatures ranging from 68 to 127 °F. Five wells in two 

areas 5 mi northeast of the Twelve Mile Creek study area 

have temperatures ranging from 70 to 111 °F. Two warmwater springs, one about 5 mi east and the other 5 mi south 

of the Oregon Canyon study area, have temperatures of 126 

and 97 °F, respectively (Oregon Department of Geology 

and Mineral Industries, 1982). Waters in these temperature 

ranges could be used for local space heating but are unsuitable for power generation because of their low temperature 

and the small size of the springs. Although these warmwater wells and springs are nearby, they all occur in valleys 

and calderas. Because the study areas are within mountain

Fifteen Mile Creek, Oregon Canyon, Twelve Mile Creek, and Willow Creek Wilderness Study Areas, Oregon B17
ranges, they have only low potential for geothermal energy 

resources.

Oil and Gas

The resource potential for oil and gas for most of 

southeastern Oregon is low (Fouch, 1983). However, some 

areas may be underlain by nonmarine sedimentary rocks, 

and some of these may contain organic remains. If such 

rocks are present, heating or bacterial action could have 

converted any organic remains into oil or gas. The depth 

and structure of any such rocks below these study areas is 

not known.

Mineral and Energy Resources of the 

Fifteen Mile Creek Wilderness Study Area

There is low potential for mercury and uranium resources, certainty level C, in the southernmost part of the 

study area near the outer margin of the McDermitt caldera 

complex (fig 2). Most of the southern two-thirds of the 

area has low potential, certainty level B, for resources of 

antimony, bismuth, mercury, silver, molybdenum, and zinc 

in epithermal vein deposits, based primarily on geochemical information. The southwest corner of the area has low 

potential, certainty level B, for tin resources of unknown 

origin. The northwest tip of the study area, underlain by 

the tuff of Whitehorse Creek, may have scattered pumice 

and is therefore assigned low potential, certainty level B, 

for pumice resources. The entire study area has low potential for zeolite resources, certainty level B. The geothermal 

energy resource potential of the study area is low, certainty 

level C. The study area has low potential for oil and gas 

resources, certainty level C. Locally, parts of the tuff of 

Trout Creek Mountains have low potential for decorative 

building stone resources, certainty level B, although transportation to distant markets would be required. The tuff of 

Trout Creek Mountains also has a low mineral resource 

potential, certainty level B, for rare-earth elements and 

zirconium contained in phenocrysts. There is no potential 

for sand and gravel resources, certainty level D, beyond 

what is currently mapped.

Mineral and Energy Resources of the 

Oregon Canyon Wilderness Study Area

The study area has a moderate potential, certainty level 

B, and low potential, certainty level C, for both mercury 

and uranium deposits in the southern part of the area, respectively adjacent to and near to the ring fractures of the 

McDermitt caldera complex (fig. 3). The tuff of Oregon 

Canyon has low potential, certainty level B, for gold and 

silver resources in epithermal veins because of the proximity of the study area to the McDermitt caldera complex; the

southern part of the study area, adjacent to the caldera 

complex, also has a low potential for gold and silver resources in epithermal vein deposits, certainty level B. On 

the basis of geochemical anomalies, the southern and northwestern parts of the area have low potential, certainty level 

B, for antimony, bismuth, mercury, silver, molybdenum, 

and zinc in epithermal deposits. Geochemical anomalies 

indicate that the southeastern half of the area has low 

potential, certainty level B, for deposits containing tin resources of unknown origin. The entire study area has low 

potential for zeolite resources, certainty level B, because of 

the presence of favorable rock types, even though zeolites 

have not been seen. The study area has low resource 

potential for geothermal energy, certainty level C, and for 

oil and gas resources, certainty level C. Locally, the tuff of 

Trout Creek Mountains has low resource potential, certainty level B, for decorative building stone, although transportation to distant markets would be required. The tuff of 

Trout Creek Mountains also has a low mineral resource 

potential, certainty level B, for rare-earth elements and 

zirconium contained in phenocrysts. There is no potential 

for sand and gravel resources, certainty level D, beyond 

what is currently mapped.

Mineral and Energy Resources of the 

Twelve Mile Creek Wilderness Study Area

The entire study area has low potential, certainty level 

B, for zeolite resources because favorable rocks are present, 

even though zeolites have not been seen (fig. 4). Scattered 

pumice fragments are present north of the study area in 

nonwelded parts of the tuff of Long Ridge, and the northernmost part of the study area, where small amounts may 

also be present, has low resource potential, certainty level 

B, for pumice. The study area has low resource potential 

for geothermal energy, certainty level C, and for oil and 

gas, certainty level C. Locally, the tuff of Trout Creek 

Mountains has low potential, certainty level B, for decorative building stone resources, although transportation to 

distant markets would be required. The tuff of Trout 

Creek Mountains also has a low mineral resource potential, 

certainty level B, for rare-earth elements and zirconium 

contained in phenocrysts. There is no potential for sand 

and gravel resources, certainty level D, beyond what is currently mapped.

Mineral and Energy Resources of the 

Willow Creek Wilderness Study Area

The southern part of the area has low mineral resource 

potential, certainty level B, for antimony, bismuth, mercury, silver, molybdenum, and zinc in epithermal deposits 

(fig. 5). Geochemical anomalies for tin indicate that the 

southeast corner of the area has low potential, certainty

B18 Mineral Resources of Wilderness Study Areas: Trout Creek Mountains Region, Oregon
level B, for tin resources of an unknown type. The area has 

low potential for zeolite resources, certainty level B, because of the volcanic terrane. The geothermal resource 

potential of the study area is low, certainty level C. The 

study area has low potential for oil and gas resources, 

certainty level C. Locally, the tuff of Trout Creek Mountains has a low potential, certainty level B, for decorative 

building stone resources, although transportation to distant 

markets would be required. The tuff of Trout Creek 

Mountains also has a low mineral resource potential, certainty level B, for rare-earth elements and zirconium contained in phenocrysts. There is no potential for sand and 

gravel resources, certainty level D.

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Association of Petroleum Geologists Studies in Geology, no. 

13, p. 73-79.

Walker, G.W., and Repenning, C.A., 1965, Reconnaissance geologic map of the Adel quadrangle, Lake, Harney, and Malheur 

Counties, Oregon: U.S. Geological Survey Miscellaneous 

Geological Investigations Map 1-446, scale 1:250,000.

 1966, Reconnaissance geologic map of the west half of the 

Jordan Valley quadrangle, Malheur County, Oregon, U.S. 

Geological Survey Miscellaneous Geological Investigations 

Map 1-457, scale 1:250,000.

Williams, Howell, and Compton, R.R., 1953, Quicksilver deposits 

of S teens Mountain and Pueblo Mountains, southeast Oregon: 

U.S. Geological Survey Bulletin 995-B, p. 19-77.

Winters, R.A., and Peters, T.J., 1987, Mineral resources of the 

Oregon Canyon Wilderness Study Area, Malheur County, 

Oregon: U.S. Bureau of Mines Open-File Report MLA 38- 

87, 14 p.

Yates, R.G., 1942, Quicksilver deposits of the Opalite district, 

Malheur County, Oregon, and Humboldt County, Nevada: 

U.S. Geological Survey Bulletin 931-N, 319-348 p.

B20 Mineral Resources of Wilderness Study Areas: Trout Creek Mountains Region, Oregon
APPENDIXES
DEFINITION OF LEVELS OF MINERAL RESOURCE POTENTIAL 

AND CERTAINTY OF ASSESSMENT

LEVELS OF RESOURCE POTENTIAL

H 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.

M 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 reasonable likelihood for resource accumulation, and (or) where an application of mineral-deposit models 

indicates favorable ground for the specified type(s) of deposits.

L 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 permissive. This broad category embraces 

areas with dispersed but insignificantly mineralized rock, as well as areas with little or no indication of having 

been mineralized.

N NO mineral resource potential is a category reserved for a specific type of resource in a well-defined area.

U UNKNOWN mineral resource potential is assigned to areas where information is inadequate to assign a low, 

moderate, or high level of resource potential.

LEVELS OF CERTAINTY

A Available information is not adequate for determination of the level of mineral resource potential.

B Available information only 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.

hZ

LLJ

oQ_ 

LLJ 

(J

O to

LLJ

_

O

_]

LLJ

A

U/A

UNKNOWN POTENTIAL

B

H/B

HIGH POTENTIAL

M/B

MODERATE POTENTIAL

L/B

LOW POTENTIAL

C

H/C

HIGH POTENTIAL

M/C

MODERATE POTENTIAL

L/C

LOW POTENTIAL

D

H/D

HIGH POTENTIAL

M/D

MODERATE POTENTIAL

L/D

LOW POTENTIAL

N/D

NO POTENTIAL

LEVEL OF CERTAINTY

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. 1268-1 270.

Taylor, R.B., Stoneman, R.]., 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.

B22 Mineral Resources of Wilderness Study Areas: Trout Creek Mountains Region, Oregon
RESOURCE/RESERVE CLASSIFICATION

ECONOMIC

MARGINALLY 

ECONOMIC

SUBECONOMIC

IDENTIFIED RESOURCES

Demonstrated

Measured Indicated

I 

Reserves

I

I 

Marginal 

Reserves

Demonstrated 

Subeconomic 

Resources

Inferred

Inferred 

Reserves

Inferred 

Marginal 

Reserves

Inferred 

Subeconomic 

Resources

UNDISCOVERED RESOURCES

Probability Range

Hypothetical Speculative

I

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

Fifteen Mile Creek, Oregon Creek, Twelve Mile Creek, and Willow Creek Wilderness Study Areas, Oregon B23
GEOLOGIC TIME CHART

Terms and boundary ages used by the U.S. Geological Survey in this report

EON

Phanerozoic

Proterozoic

pre-Archean2

ERA

Cenozoic

Mesozoic

Paleozoic

Late Proterozoic

Middle Proterozoic

Early Proterozoic

Late Archean

Middle Archean

Early Archean

PERIOD

Ncogene

Subperiod

Tertiary

Jurassic

Triassic

Permian

Pennsylvanian 

Carboniferous

Mississippian

Devonian

Silurian

Ordovician

Cambrian

tior\r\?\

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

AGE ESTIMATES OF 

BOUNDARIES IN 

MILLION YEARS (Ma)

 0.010

 1.7

5

O A

T Q

 55

 66

96

1 DQ

 205

o A r\

290

r~33O

 360

 410

 435

JWW

J/ w

 1600 

 2500

JUVAJ

 3400

 ytccn 

'Rocks older than 570 Ma also called Precambrian, a time term without specific rank, 

informal time term without specific rank.

B24 Mineral Resources of Wilderness Study Areas: Trout Creek Mountains Region, Oregon
Mineral Resources of 

Wilderness Study Areas: 

Trout Creek Mountains Region, 

Oregon

This volume was published as separate chapters A and B

U.S. GEOLOGICAL SURVEY BULLETIN 1742
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director
CONTENTS

[Letters designate the separately published chapters]

(A) Mineral Resources of the Disaster Peak Wilderness Study Area, Harney and 

Malheur Counties, Oregon, and Humboldt County, Nevada, by Scott A. Minor, 

Robert L. Turner, Donald Plouff, and Andrew M. Leszcykowski.

(B) Mineral Resources of the Fifteen Mile Creek, Oregon Canyon, Twelve Mile 

Creek, and Willow Creek Wilderness Study Areas, Malheur and Harney 

Counties, Oregon, by Jocelyn A. Peterson, James J. Rytuba, Donald Plouff, 

Thomas L. Vercoutere, Robert L. Turner, Don L. Sawatzky, Andrew M. 

Leszcykowski, Thomas J. Peters, Steven W. Schmauch, and Richard A. Winters.


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