Mineral Resources of the Orejana Canyon 

Wilderness Study Area, 

Harney County, Oregon

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Chapter B

Mineral Resources of the Orejana Canyon 

Wilderness Study Area, 

Harney County, Oregon

By JAMES E. CONRAD, HARLEY D. KING, 

MARK E. GETTINGS, MICHAEL F. DIGGLES, 

and DON L. SAWATZKY 

U.S. Geological Survey

DAVID A. BENJAMIN 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1738

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

SOUTH-CENTRAL 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

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Library of Congress Cataloging-in-Publication Data

Mineral resources of the Orejana Canyon Wilderness Study 

Area, Hamey County, Oregon.

(U.S. Geological Survey Bulletin ; 1738)) (Mineral 

resources of wilderness study areas south-central 

Oregon ; ch. B)

Supt. of Docs. no. : I 19.3:1738-6

Bibliography: p.

1. Mines and mineral resources Oregon Orejana 

Canyon Wilderness. 2. Orejana Canyon Wilderness (Or.) 

I. Conrad, James E. II. Series. III. Series: U.S. Geological 

Survey bulletin ; 1738-B.

QE75.B9 no. 1738-B 

[TN 24.07]

557.3 s 

[553'.09795'95]

88-600194
STUDIES RELATED TO WILDERNESS

Bureau of Land Management Wilderness Study Area

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 part of the Orejana Canyon Wilderness Study Area (OR-001-078), Harney County, Oregon.

CONTENTS

Summary Bl

Abstract 1

Character and setting 1

Identified resources 1

Mineral resource potential 1 

Introduction 3

Area description 3

Previous and present investigations 3

Acknowledgments 5 

Appraisal of identified resources 5

Mines and prospects, mining claims, and leases 5

Reserves and identified resources 5

Recommendations for further study 6 

Assessment of mineral resource potential 6

Geology 6

Geochemical studies 6

Geophysical studies 7

Mineral and energy resource potential 8 

References cited 8 

Appendixes

Definition of levels of mineral resource potential and certainty of assessment 12

Resource/reserve classification 13

Geologic time scale 14

FIGURES

1. Index map showing location of the Orejana Canyon Wilderness Study Area, Harney County, 

Oregon B2

2. Map showing mineral resource potential and generalized geology of the Orejana Canyon Wilderness Study Area, Harney County, Oregon 4

Contents

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: SOUTH-CENTRAL OREGON

Mineral Resources of the Orejana Canyon 

Wilderness Study Area, Harney County, Oregon

By James E. Conrad, Harley D. King, Mark E. Gettings, Michael F. Diggles, and

Don L. Sawatzky

U.S. Geological Survey

David A. Benjamin 

U.S. Bureau of Mines

SUMMARY 

Abstract

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

approximately 14,800 acres of the Orejana Canyon Wilderness Study Area (OR-001-078) was evaluated for identified 

mineral resources (known) and mineral resource potential 

(undiscovered). In this report, the area studied is referred to 

as the "wilderness study area" or simply "the study area;" any 

reference to the Orejana Canyon Wilderness Study Area refers only to that part of the wilderness study area for which 

a mineral survey was requested by the U.S. Bureau of Land 

Management. The study area is located in south-central 

Oregon, 35 mi north of Plush, Oreg. Geologic studies, 

geochemical sampling, and an inventory of mines and prospects indicate low resource potential for gold and silver along 

the west boundary of the study area and low resource potential for tin in the northwestern part of the study area. The 

entire study area has low potential for oil and gas resources. 

There is no geothermal energy or energy mineral resource 

potential in the study area. The study area contains no 

identified resources.

Character and Setting

The Orejana Canyon Wilderness Study Area lies on 

the east side of the northernmost part of Warner Valley 

about 35 mi north of Plush, Oreg. (fig. 1). Most of the 

study area is situated on a plateau at an elevation of about 

5,000 ft, with gentle topography of low, rolling hills and 

isolated ridges. Along the west side of the study area, 

however, Orejana Rim forms a steep west-facing escarpment about 500 ft high at the edge of Warner Valley, and 

the steep and narrow Orejana Canyon cuts the plateau in 

the southern and eastern parts of the study area. The climate is semiarid and vegetation consists of sagebrush, 

desert bunchgrass, and many varieties of wildflowers.

Publication authorized by the Director, U.S. Geological Survey, May 24, 1988.

The study area is underlain by a sequence of basaltic 

to andesitic lava flows and interbedded tuffaceous sedimentary rocks that are capped by a rhyolite welded tuff of 

Miocene age (see appendixes for geologic time chart). 

Faulting related to regional basin and range extension has 

cut these rocks; the largest of these faults produced the 

uplift along Orejana Rim. Other minor faults in the study 

area have displacements of less than 50 ft.

Identified Resources

No metallic or nonmetallic resources were identified 

within the Orejana Canyon Wilderness Study Area. Investigation into potential resources of diatomite, zeolite, and 

perlite postulated in a 1985 U.S. Bureau of Land Management study indicated the presence of only minor zeolite, 

perlite of poor quality, and no diatomite. However, three 

samples taken of tuffaceous rock units were slightly 

anomalous in gold, silver, arsenic, lead, antimony, and 

bismuth. These samples may indicate the presence of lowgrade gold and silver mineralization in the area.

Examination of the literature and U.S. Bureau of Land 

Management and Hamey County records contained no 

evidence of claim or lease activity in the study area. Field 

examinations also yielded no evidence of mining or claim 

staking within or adjacent to the area.

Mineral Resource Potential

Geologic, geochemical, and geophysical studies 

give only slight indications of significant mineralization in 

the study area. Small, scattered geochemical anomalies, including gold, silver, arsenic, and antimony in rock samples 

suggest there has been some hydrothermal activity in the 

area. On this basis, there is low resource potential for gold 

and silver along the north-south fault paralleling the 

Orejana Rim escarpment. Anomalous concentrations of tin 

found in heavy-mineral concentrates from stream sediments

Mineral Resources of the Orejana Canyon Wilderness Study Area, Harney County, Oregon B1
120°00' 119°45' 119°30'

43°00' 

42°45' 

42°30' 

42°15' 

OREJANA CANYON 

WILDERNESS STUDY AREA

(OR-001-078)

Figure 1. Index map showing location of the Orejana Canyon Wilderness Study Area, Harney County, Oregon. 

B2 Mineral Resources of Wilderness Study Areas: South-Central Oregon
and one rock sample north of the study area suggest low 

resource potential for tin at the northwest corner of the 

study area.

The dominantly volcanic rocks exposed in the study 

area are unlikely to have significant hydrocarbon source 

beds, but carbonaceous source beds may underlie the study 

area at depth. The study area has a low potential for oil and 

gas resources. There is no geothermal energy or energy 

mineral resource potential in the study area.

Introduction

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

of Land Management and is the result of a cooperative 

effort by the U.S. Geological Survey and the U.S. Bureau 

of Mines. An introduction to the wilderness review 

process, mineral survey methods, and agency 

responsibilities was provided by Beikman and others 

(1983). The U.S. Bureau of Mines 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, claims, and 

mineralized areas. Identified resources are classified 

according to a system that is a modification of that 

described by McKelvey (1972) and U.S. Bureau of Mines 

and U.S. Geological Survey (1980). U.S. Geological 

Survey studies 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, 

presence of geochemical and geophysical anomalies, and 

applicable ore-deposit models. Goudarzi (1984) discussed 

mineral assessment methodology and terminology as they 

apply to these surveys. See appendixes for the definition of 

levels of mineral resource potential and certainty of 

assessment and for the resource/reserve classification.

Area Description

The Orejana Canyon Wilderness Study Area is located 

in south-central Oregon at the north end of Warner Valley 

(fig. 1). Mineral surveys were requested on 14,800 acres of 

the wilderness study area by the U.S. Bureau of Land 

Management. This region is typified by extensive basaltic 

to andesitic lava flows of Miocene age and interbedded 

sedimentary rocks that have been cut by numerous faults 

into a series of broken, flat-topped mountain blocks and 

intervening alluviated valleys. Most of the study area is 

situated on a plateau at an elevation of about 5,000 ft, with 

gentle topography of low, rolling hills and isolated ridges 

uplifted along minor faults. Along the west side of the 

study area, Orejana Rim forms a steep west-facing escarpment about 500 ft high at the edge of Warner Valley, and 

the steep and narrow Orejana Canyon cuts the plateau in 

the southern and eastern parts of the study area. The climate is semiarid and vegetation consists of sagebrush, 

desert bunchgrass, and many varieties of wildflowers.

The study area is located about 35 mi north of the town 

of Plush, Oreg., and about 5 mi north of the Hart Mountain 

National Antelope Refuge (fig. 1). The study area is 

bounded on three sides by dirt roads and jeep trails that can 

be reached by roads leading north from Plush or from the 

Hart Mountain National Antelope Refuge. An unimproved 

jeep trail along the west boundary provides access from 

Warner Valley below Orejana Rim. Access to the southern 

and eastern parts of the study area is by maintained dirt 

roads along the boundaries. Other maintained dirt roads 

from the north provide access to the northern part of the 

study area.

Previous and Present Investigations

The study area is included in regional geologic maps at 

scales of 1:250,000 (Walker and Repenning, 1965) and 

1:500,000 (Walker, 1977). Other regional geologic studies 

in southeastern Oregon include those by Lawrence (1976), 

McKee and others (1983), and Carlson and Hart (1987). A 

regional aeromagnetic survey conducted by the U.S. Geological Survey (1972) includes the study area. Information 

relevant to the study area from this geophysical survey is 

included in this report.

The U.S. Geological Survey conducted field investigations in the study area in the summer of 1986. The work 

included geologic mapping, geochemical sampling, and 

geophysical studies. Geochemical samples were collected 

from stream drainages to obtain information about mineral 

suites and trace-element signatures associated with mineralizing systems.

The U.S. Bureau of Mines investigation was conducted 

by personnel of the Western Field Operations Center 

(WFOC), Spokane, Wash., and consisted of literature 

search, field work, and report preparation that spanned the 

years 1985 through 1987. The literature search included an 

examination of the Harney County mining claim and mineral lease records. U.S. Bureau of Mines, State of Oregon, 

and U.S. Bureau of Land Management mineral property 

files also were examined and pertinent data compiled. 

Field studies included a search for evidence of mining 

activity and mineralized sites within the area studied.

Much of the field work consisted of examination of 

tuff and rhyolite beds for presence of diatomite, zeolite, and 

perlite, which a previous study conducted by the U.S. 

Bureau of Land Management (1985) suggested was present 

in the study area. Sixteen rock samples were taken during 

the course of study, 11 from rhyolite flows and 5 from tuffaceous beds.

Nine samples were analyzed for 18 metallic elements 

using atomic-absorption spectroscopy (Benjamin, 1987). 

All tuffaceous samples were examined for diatomite using

Mineral Resources of the Orejana Canyon Wilderness Study Area, Harney County, Oregon B3
119°30' 119°25'

42°55'

42°50

Tr

APPROXIMATE BOUNDARY

OF

OREJANA CANYON 

WILDERNESS 

STUDY AREA

(OR-001-078) 

\

L/B O,G (entire study area)

Tr

1 2 MILES 

I_____ j

Figure 2. Mineral resource potential and generalized geology of the Orejana Canyon Wilderness Study Area, Harney 

County, Oregon.

B4 Mineral Resources of Wilderness Study Areas: South-Central Oregon
Ag 

Au 

Sn 

O,G

[ 1

1

2

Qa

Tr

Tb

EXPLANATION

Area having low resource potential for specified 

commodity (L); data only suggest level of potential (B)

Commodities

Silver

Gold

Tin

Oil and gas

Deposit types

Epithermal or hot-spring gold-silver lowgrade bulk-mineable 

Rhyolite-hosted tin

Correlation of map units

^-Quaternary _J

-Tertiary

- Cenozoic

Description of map units

Alluvium, colluvium, and talus (Holocene or 

Pleistocene) Mostly stream sand and 

gravel, fanglomerate, and aeolian and lacustrine sediments

Rhyolite (Miocene) Rhyolite welded tuff. 

Contains phenocrysts of quartz, sanidine, 

and plagioclase in a eutaxitic groundmass of 

devitrified glass shards. Abundant lithophysae in the lower two-thirds of the flow, 

commonly weathering out to give the rock a 

"swiss cheese" appearance

Basalt flows and tuffaceous sedimentary rocks 

(Miocene) Includes basalt flows and flow 

breccia, air-fall tuff, and associated sedimentary rocks

Contact

Normal fault Bar and ball on downthrown

side; dashed where approximately located 

Dirt road or jeep trail

Figure 2. Continued.

a petrographic microscope; the same samples were also 

tested at WFOC for zeolite content by the ion exchange 

capability method (Helfferich, 1964). Three zeolite 

samples were sent to the Cominco Exploration Research 

Laboratory (Vancouver, B.C.) for further testing. Additionally, eight rhyolite samples were examined petrographically for perlite.

Further information concerning analytical and other 

testing methodology, detection limits, and results is available in Benjamin (1987) and at the U.S. Bureau of Mines, 

Western Field Operations Center, E. 360 Third Ave., 

Spokane, WA 99202.

Acknowledgments

U.S. Geological Survey authors were assisted in the 

field by Gerilyn Andrews and Steve Smith. The U.S. 

Bureau of Mines author was assisted in the field by Terry 

Neumann and Spencee Willett of WFOC. Appreciation is 

also extended to Douglas Troutman (Lakeview, Oreg., U.S. 

Bureau of Land Management) for information about road 

conditions and mineral activity in and around the area 

studied.

APPRAISAL OF IDENTIFIED RESOURCES

By David A. Benjamin 

U.S. Bureau of Mines

Mines and Prospects, Mining Claims, and 

Leases

Examination of the historical literature and county and 

U.S. Bureau of Land Management records indicates that no 

claim or lease activity has ever taken place in the study area 

or within a mile of the study area. Furthermore, field 

investigation failed to identify any evidence of exploration 

or mining activities.

Reserves and Identified Resources

No reserves or resources of either metallic or nonmetallic commodities were identified in the Orejana Canyon 

Wilderness Study Area. A study by the Bureau of Land 

Management (1985) suggests the existence of diatomite, 

zeolite, and perlite; however, the present study did not 

confirm the presence of any diatomite and only confirmed 

very minor amounts of zeolite. Perlite textures were poorly 

developed in some lava flows, and the material did not 

approach commercial quality.

Assay results indicate that three tuff samples are 

slightly anomalous in gold, silver, arsenic, lead, antimony, 

and bismuth. This could be an indicator of low-grade gold 

mineralization.

Mineral Resources of the Orejana Canyon Wilderness Study Area, Harney County, Oregon B5
Recommendations for Further Study

No further work is recommended on diatomite, zeolite, 

and perlite. The gold-silver-antimony-lead-bismuth-arsenic 

anomaly indicated by the three slightly anomalous samples 

may warrant additional geologic mapping and sampling.

ASSESSMENT OF MINERAL RESOURCE 

POTENTIAL

By James E. Conrad, Harley D. King, Mark E. Ceilings, 

Michael F. Diggles, and Don L. Sawalzky 

U.S. Geological Survey

Geology

The Orejana Canyon Wilderness Study Area is in a 

transitional zone between the Basin and Range and Columbia Plateaus physiogeographic provinces. Extensive flood 

basalts and associated interbedded air-fall tuffs and sedimentary rocks of Miocene age underlie most of the region. 

North-south-trending basin and range faults have cut these 

rocks, producing the north-south-trending mountain blocks 

and intervening alluvium-filled valleys. The study area lies 

between the Brothers and Eugene-Denio northwest-trending fault zones, interpreted as boundary zones between 

basin and range extension to the south and unextended terrane of the Columbia Plateaus to the north (Lawrence, 

1976).

At least two periods of volcanism are recorded within 

the study area. The older period produced a sequence of 

nearly flat-lying basalt flows and interbedded tuffaceous 

sedimentary rocks. The base of this sequence is not exposed, but nearly 500 ft of section is present in the study 

area. The top of this sequence is marked by an erosional 

unconformity that dips about 5° to the south. A rhyolitic 

welded ash-flow tuff as much as 100 ft thick lies above the 

unconformity and forms a cap over the older volcanic and 

sedimentary rocks.

Rocks in the lower volcanic sequence consist of three 

separate basaltic to andesitic lava-flow units interbedded 

with air fall tuffs and tuffaceous sedimentary rocks. The 

lava-flow units are about 30 to 70 ft thick and are typically 

black, aphanitic, vesicular to nonvesicular and may be 

composed of one or several individual flows. Basaltic flow 

breccias are present in the middle part of this unit, consisting of basaltic blocks 0.5 to 20 in. across in a matrix of 

ropy basalt.

The upper volcanic unit consists of rhyolitic welded 

tuff that underlies the plateau and forms a near-vertical cliff 

as much as 100 ft high at the top of Orejana Rim and 

rimming Orejana Canyon. Widely spaced vertical joints in 

this unit are responsible for the unusual topography in the 

southwestern part of the study area beneath Orejana Rim, 

where hundreds of huge blocks as much as 50 ft across

have broken off and litter the slopes below the rim. The 

rhyolite tuff is as much as 100 ft thick, has a basal surge 

zone about 5 ft thick, and a basal vitrophere of black 

obsidian about 3 ft thick. The remaining part of the unit 

consists of a welded zone of vitric ash-flow tuff containing 

collapsed pumice fragments and phenocrysts of quartz, 

sanidine, and plagioclase. All but the upper part of this 

welded zone contains abundant lithophysae about 1 in. 

across, which in many places have weathered out to give 

the rock a "swiss cheese" appearance. This tuff probably 

correlates with tuffs exposed near Harney Basin, about 30 

mi to the north, which have been dated at about 8 Ma 

(Fiebelkorn and others, 1982).

Geochemical Studies

A reconnaissance geochemical survey was conducted 

in the Orejana Canyon Wilderness Study Area in the 

summer of 1986. Minus-80-mesh stream sediments, nonmagnetic heavy-mineral concentrates of stream sediments, 

and rocks were used as the sample media in this survey. 

Twenty-two minus-80-mesh stream-sediment, 22 nonmagnetic heavy-mineral-concentrate, and two rock samples 

were collected from 22 sites. The stream-sediment samples 

and the stream sediments from which the concentrates were 

derived were taken from the active alluvium in the stream 

channels.

Stream sediments were selected as a sample medium 

because they represent a composite of the rock and soil 

exposed upstream from the sample site. Nonmagnetic 

heavy-mineral-concentrate samples provide information 

about the chemistry of a limited number of minerals in rock 

material eroded from the drainage basin upstream from 

each sample site. Many of the minerals found in the 

nonmagnetic fraction of heavy-mineral concentrates may 

be ore-forming or ore-related, providing mineralization 

processes have been active in the area. The selective 

concentration of minerals permits determination of some 

elements that are not easily detected in bulk stream-sediment samples.

One of the rock samples appeared fresh and unaltered 

and was collected to provide information on geochemical 

background values. The other rock sample appeared altered and possibly mineralized; this was collected to determine the suite of elements associated with the observed 

alteration or mineralization.

Rock samples were crushed and pulverized to less than 

80-mesh grain size prior to analysis. Stream-sediment 

samples were sieved using 80-mesh stainless-steel sieves 

and the minus-80-mesh fraction was used for analysis. The 

heavy-mineral concentrate was produced by panning minus-10-mesh stream sediment to remove most of the quartz, 

feldspar, organic material, and clay-sized material. Bromoform (specific gravity, 2.86) was then used to remove

B6 Mineral Resources of Wilderness Study Areas: South-Central Oregon
light mineral grains from the panned concentrate. The 

resultant heavy mineral concentrate was separated by use of 

an isodynamic magnetic separator into three fractions: a 

magnetic fraction, chiefly magnetite, an intermediately 

magnetic fraction consisting largely of mafic rock-forming 

minerals, and a nonmagnetic fraction, which is composed 

dominantly of light-colored rock-forming accessory minerals and primary and secondary ore-forming and ore-related 

minerals. Using a microsplitter, the nonmagnetic fraction 

was split into two fractions. One of these splits was used 

for analysis and the other for visual examination with a 

binocular microscope. In some instances, sample volume 

was too small to provide a split for visual examination. 

These samples were examined visually prior to grinding for 

analysis; archived reference material for these samples 

contain no material not ground to fine powder.

All samples were analyzed semiquantitatively for 31 

elements using direct-current arc-emission spectrography 

(Grimes and Marranzino, 1968). Rock and stream-sediment samples were also analyzed by atomic-absorption 

spectrometry for certain elements of special interest or 

which have high lower limits of determination by emission 

spectrography. Antimony, arsenic, bismuth, cadmium, and 

zinc were analyzed by the method of O'Leary and Viets 

(1986), gold by the method of Thompson and others 

(1968), and mercury by the method described in Crock and 

others (1987).

Anomalous values of tin (700-2,000 parts per million 

(ppm)) were found in five nonmagnetic heavy-mineralconcentrate samples collected in the north end of the 

sampled area, just north of the study area boundary. 

Microscopic examination of the concentrates revealed that 

the high tin values were due to the presence of several 

grains of wood tin (cassiterite) in the samples. These 

grains of wood tin possibly eroded from fractures in the 

rhyolitic ash-flow tuff that underlies those drainages north 

of the study area. One rock sample was collected from an 

altered zone in this area and contained slightly anomalous 

values of tin (10 ppm) and lead (50 ppm).

Slightly anomalous values of mercury (0.18-0.38 ppm) 

were found in four stream-sediment samples, three from the 

south end of the study area and one from about 1.7 mi north 

of the study area. The drainage area of the latter site is 

outside of the study area. The mercury detected in the 

samples may have moved upward along fractures in volcanic rocks within the drainage areas of the sample sites 

and have been adsorbed on mineral grains that were later 

eroded and incorporated into the stream sediment. These 

anomalous values apparently do not indicate significantly 

mineralized rock at the surface, but may reflect rock enriched in mercury or other metals, including gold, at some 

unknown depth. It is possible that the anomalous mercury 

values are not related to significantly mineralized rock. 

These slightly anomalous mercury values are not interpreted to be associated with anomalies of other elements 

discussed in this report.

Geophysical Studies

An aeromagnetic survey including the Orejana Canyon 

Wilderness Study Area was flown and compiled in 1973 

under U.S. Geological Survey contract (U.S. Geological 

Survey, 1972). Total-field magnetic data were collected in 

analog form along east-west flight lines spaced approximately 2 mi apart at a constant barometric altitude of 9,000 

ft. Corrections were applied to the data to compensate for 

regional and diurnal variations of the earth's magnetic field 

to yield a digital residual magnetic anomaly data set. An 

aeromagnetic map of the wilderness study area was prepared at a contour interval of 50 nanoteslas (nT) from the 

digitized analog data for comparison with geologic and 

topographic maps.

Within and near the study area, the total relief of the 

residual magnetic anomaly field is only about 150 nT, in 

the form of an east-west-trending ridgelike high through the 

approximate center of the study area. Magnetic anomalies 

are very smooth and appear to be due to sources 1 mi or 

more below the observation plane, that is, at least 0.2 mi 

below the ground surface. Within the study area, anomaly 

amplitude does correlate somewhat with topography, but 

topography appears to produce only a small perturbation of 

the anomaly shapes. All anomalies observed within the 

study area are parts of regional anomalies extending well 

beyond the boundaries of the study area. The trends of the 

gradients of these anomalies are parallel to and in many 

cases coincident with mapped fault zones along northeast, 

northwest, and north-northwest trends. The sources of the 

magnetic anomalies are inferred to be faulted blocks of 

magnetic basement, and no indications of near-surface 

structures were observed in the magnetic data, both because 

of the large terrain clearance (0.75-1.0 mi) of the data 

observation level and the relatively nonmagnetic character 

of the surface rocks.

Linear features in Landsat multispectral scanner (MSS) 

images at a scale of 1:800,000 were mapped by photogeologic interpretation for the region of southeastern Oregon, 

and trend concentration maps were made. Linear features 

are the topographic and spectral expression of rock feature 

patterns and other structural and lithologic lineaments. 

This expression can be enhanced or subdued by scanner 

resolution, sun orientation, atmospheric phenomena, and 

vegetation. Analysis of linear features in conjunction with 

geologic and geophysical maps may reveal relations such 

as fracture control of mineralization.

Linear features of every orientation are well expressed 

on the surface in southeastern Oregon, except in terrains 

underlain by volcanic rocks. Areas may have preferred 

trends related to faults, if locally important, or to rock joint

Mineral Resources of the Orejana Canyon Wilderness Study Area, Harney County, Oregon B7
systems. The study area has no prominent linear features 

within it. However, linear features in the region around the 

study area have two prominent trends. The dominant trend 

is N. 20° W., but linear features with this trend are concentrated north and west of the study area. Linear features 

with the second trend, N. 20° E., lie to the northwest of the 

study area.

Mineral and Energy Resource Potential

Geologic, geochemical, and geophysical studies suggest that only minor mineralization may have occurred in 

the study area. Field examination of outcrops did not 

disclose evidence of extensive or pervasive alteration associated with mineralization. Geochemical studies, however, 

show some indications of hydrothermal activity that may be 

associated with mineralization. Three rock samples, taken 

by the U.S. Bureau of Mines from exposures along the 

Orejana Rim escarpment, had slightly anomalous concentrations of gold, silver, lead, bismuth, arsenic, and antimony. The north-south-trending fault that formed the 

Orejana Rim escarpment may have served as a pathway for 

metal-bearing hydrothermal fluids. These anomalies may 

reflect low-grade gold-silver mineralization, perhaps in epithermal veins or in hot-spring gold-silver deposits (Berger, 

1986). There is low potential for gold and silver resources, 

certainty level B, in low-grade, bulk-mineable deposits 

along the west side of the study area (fig. 2).

Anomalous concentrations of tin, produced by wood 

tin (cassiterite) in five heavy mineral concentrates from 

stream sediments, and an anomalous tin concentration in 

one rock sample, were found in samples collected from 

drainages underlain by a rhyolite ash-flow tuff just north of 

the study area. A deposit type suggested by this tin anomaly is the rhyolite-hosted tin deposit (Reed and others, 

1986). The abundant lithophysae in the welded ash-flow 

tuff suggest late-stage, vapor-phase alteration that may 

have remobilized and concentrated tin. There is low resource potential for tin, certainty level B, mostly north of 

the study area, but including the northwest corner of the 

study area.

The dominantly volcanic rocks exposed in the study 

area are unlikely to have significant hydrocarbon content, 

but older Tertiary sedimentary rocks containing carbonaceous source beds may underlie the study area at depth. 

High heat flow associated with volcanism, however, would 

most likely have driven off any preexisting hydrocarbons. 

The study area has a low potential for oil and gas resources, 

certainty level B (Fouch, 1983).

There are no hot springs or other indications of geothermal activity in or near the study area (Bliss, 1983), so 

there is no geothermal resource potential in the study area, 

certainty level D. No diatomite or lacustrine rocks of any 

kind were observed in the bedrock underlying the study 

area, so there is no potential for undiscovered resources of

diatomite, certainty level D. Although minor zeolite occurrences and poorly developed perlite occurrences were noted 

in the Orejana Canyon study area, these occurrences do not 

constitute resources, and there is no potential for undiscovered resources of these commodities, with a certainty level 

of D.

REFERENCES CITED

Beikman, H.M., Hinkle, M.E., Frieders, Twila, Marcus, S.M., and 

Edward, J.R., 1983, Mineral surveys by the Geological Survey and the Bureau of Mines of Bureau of Land Management 

Wilderness Study Areas: U.S. Geological Survey Circular 

901, 28 p.

Benjamin, D.A., 1987, Mineral resources of the Orejana Canyon 

study area, Hamey County, Oregon: U.S. Bureau of Mines 

Open-File Report MLA 46-87, 12 p.

Berger, B.R., 1986, Descriptive model of hot-spring Au-Ag, in 

Cox, D.P., and Singer, D.A., eds., Mineral deposit models: 

U.S. Geological Survey Bulletin 1693, p.143-144.

Bliss, J.D., 1983, Basic data for thermal springs and wells as 

recorded in GEOTHERM: U.S. Geological Survey Open-File 

Report 83^35, 342 p.

Carlson, R.W., and Hart, W.K., 1987, Crustal genesis on the 

Oregon plateau: Journal of Geophysical Research, v. 92, no. 

B7, p. 6191-6206.

Crock, J.G., Briggs, P.H., Jackson, L.L., and Lichte, F.E., 1987, 

Analytical methods for the analysis of stream sediments and 

rocks from wilderness study areas: U.S. Geological Survey 

Open-File Report 87-84, 35 p.

Fiebelkorn, R.B., Walker, G.W., MacLeod, N.S., McKee, E.H., 

and Smith, J.G., 1982, Index to K-Ar determinations for the 

state of Oregon: U.S. Geological Survey Open-File Report 

82-596, 40 p.

Fouch, T.D., 1983, Petroleum potential of wilderness lands in 

Oregon in Miller, B.W., ed., Petroleum potential of wilderness 

lands in the western United States: U.S. Geological Survey 

Circular 902, p. J1-J5.

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

reports on public lands: U.S. Geological Survey Open-File 

Report 84-787, 51 p.

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

alternating-current spark emission spectrographic field methods for the semiquantitative analysis of geologic materials: 

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

Helfferich, Friedrich, 1964, A simple identification reaction for 

zeolites (molecular sieves): The American Mineralogist, v. 

49, nos. 11 and 12, p. 1752-1754.

Lawrence, R.D., 1976, Strike-slip faulting terminates the Basin 

and Range Province in Oregon: Geological Society of 

America Bulletin, v. 87, p. 846-850.

McKee, E.H., Duffield, W.A., and Stern, R.J., 1983, Late Miocene and early Pliocene basaltic rocks and their implications 

for crustal structure, northeastern California and south-central 

Oregon: Geological Society of America Bulletin, v. 94, p. 

292-304.

McKelvey, V.E., 1972, Mineral resource estimates and public 

policy: American Scientist, v. 60, p. 32-40.

B8 Mineral Resources of Wilderness Study Areas: South-Central Oregon
O'Leary, R.M., and Viets, J.G., 1986, Determination of antimony, 

arsenic, bismuth, cadmium, copper, lead, molybdenum, silver, 

and zinc in geologic materials by atomic absorption spectrometry using a hydrocloric acid-hydrogen peroxide digestion: Atomic Spectroscopy, v. 7, p. 4-8.

Reed, B.L., Duffield, Wendell, Ludington, S.D., Maxwell, C.H., 

and Richter, D.H., 1986, Descriptive model of rhyolite-hosted 

Sn, in Cox, D.P., and Singer, D.A., eds., Mineral deposit 

models: U.S. Geological Survey Bulletin 1693, p. 168.

Thompson, C.E., Nakagawa, H.M., and VanSickle, G.H., 1968, 

Rapid analysis for gold in geologic materials: U.S. Geological Survey Professional Paper 600-B, p. B130-B132.

U.S. Bureau of Land Management, 1985, Oregon Wilderness 

Environmental Impact Statement, v. 2, p. 81-93.

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

Geological Survey Circular 831, 5 p.

U.S. Geological Survey, 1972, Aeromagnetic map of the Adel and 

parts of the Burns, Boise, and Jordan Valley 1° x 2° quadrangles, Oregon: U.S. Geological Survey Open-File Report 

72-390, scale 1:250,000.

Walker, G.W., 1977, Geologic map of Oregon east of the 121st 

meridian: U.S. Geological Survey Miscellaneous Geological 

Investigations Map 1-902, scale 1:500,000.

Walker, G.W., and Repenning, C.A., 1965, Reconnaissance geological 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.

Mineral Resources of the Orejana Canyon Wilderness Study Area, Harney County, Oregon B9

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.

rz

LU

2

LU 

U

C£

a

Uo

>LU

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. 1268-1270.

Taylor, R.B., Stoneman, R.J., and Marsh, S.P., 1984, An assessment of the mineral resource potential of the San Isabel National Forest, south-central Colorado: U.S.

Geological Survey Bulletin 1638, p. 40-42. 

Goudarzi, G.H., compiler, 1984, Guide to preparation of mineral survey reports on public lands: U.S. Geological Survey Open-File Report 84-0787, p. 7, 8.

B12 Mineral Resources of Wilderness Study Areas: South-Central Oregon
RESOURCE/RESERVE CLASSIFICATION

ECONOMIC

MARGINALLY 

ECONOMIC

SUBECONOMIC

IDENTIFIED RESOURCES

Demonstrated

Measured

Rese

Indicated

;rves

Marginal 

Reserves

Demonstrated 

Subeconomic

Resources

i

Inferred

Inferred 

Reserves

Inferred 

Marginal 

Reserves

Inferred 

Subeconomic 

Resources

UNDISCOVERED RESOURCES

Probability Range

Hypothetical Speculative

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.

Mineral Resources of the Orejana Canyon Wilderness Study Area, Harney County, Oregon B13
GEOLOGIC TIME CHART

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

EON

Phanerozoic

Proterozoic

Archean

ERA

Cenozoic

Mesozoic

Paleozoic

Late Proterozoic

Middle Proterozoic

Early Proterozoic

Late Archean

Middle Archean

Early Archean

PERIOD

Quaternary

Tertiary

Neogene 

Subperiod

i 3'GOJjGnG

Ct ihirtorifvi *JUU|JC?I Iwvl

Cretaceous

Jurassic

Triassic

Permian

Carboniferous 

Periods

Pennsylvanian

Mississippian

Devonian

Silurian

Ordovician

Cambrian

pre-Archean2

/7or\n?^

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 Ma)

0.010

 1.7

5

f\ M

2Q

55

 66

3D

1 la

205

 290

 360

 410

 435

*J / \J

 1600 

 2500

 3000

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

informal time term without specific rank.

B14 Mineral Resources of Wilderness Study Areas: South-Central Oregon

GPO 585-045/78060
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