U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2016–5089–A

Prepared in cooperation with the Bureau of Land Management

Overview with Methods and Procedures of the U.S. Geological 

Survey Mineral-Resource Assessment of the Sagebrush Focal 

Areas of Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Chapter A of

Mineral Resources of the Sagebrush Focal Areas of Idaho, Montana, Nevada, 

Oregon, Utah, and Wyoming
COVER. Photograph of sagebrush lands in southwestern Wyoming (U.S. Geological Survey photograph by Anna Wilson).
Overview with Methods and Procedures of 

the U.S. Geological Survey Mineral-Resource 

Assessment of the Sagebrush Focal Areas of 

Idaho, Montana, Nevada, Oregon, Utah, and 

Wyoming

By Warren C. Day, Jane M. Hammarstrom, Michael L. Zientek, and Thomas P. Frost, editors

With additional sections by Eric D. Anderson, Donald I. Bleiwas, Ronald M. Drake II, Jacob 

DeAngelo, Connie L. Dicken, Gregory L. Fernette, Helen W. Folger, Stuart A. Giles, Jonathan 

M.G. Glen, Aimee E. Graeber, Matthew Granitto, Gregory L. Gunther, Jon E. Haacke, 

Cassandra K. Hennings, M. Christopher Jenkins, Karen D. Kelley, Duc M. Nguyen, Heather 

L. Parks, David A. Ponce, Barnaby Rockwell, Carma A. San Juan, Elizabeth S. Sangine, Peter 

N. Schweitzer, Steven M. Smith, John C. Wallis, Colin F. Williams, and Douglas B. Yager

Chapter A of

Mineral Resources of the Sagebrush Focal Areas of Idaho, Montana, 

Nevada, Oregon, Utah, and Wyoming

Edited by Warren C. Day, Thomas P. Frost , Jane M. Hammarstrom, and Michael L. Zientek

Prepared in cooperation with the Bureau of Land Management

Scientific Investigations Report 2016–5089–A

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Director

U.S. Geological Survey, Reston, Virginia: 2016

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Suggested citation:

Day, W.C., Hammarstrom, J.M., Zientek, M.L., and Frost, T.P., eds., 2016, Overview with methods and procedures of 

the U.S. Geological Survey mineral-resource assessment of the Sagebrush Focal Areas of Idaho, Montana, Nevada, 

Oregon, Utah, and Wyoming: U.S. Geological Survey Scientific Investigations Report 2016–5089–A, 211 p., 

http://dx.doi.org/10.3133/sir20165089A.

ISSN 2328-0328 (online)
iii

Foreword

Scientific Investigations Report 2016–5089 and accompanying data releases are the products of the U.S. 

Geological Survey (USGS) Sagebrush Mineral-Resource Assessment (SaMiRA). The assessment was done 

at the request of the Bureau of Land Management (BLM) to evaluate the mineral-resource potential of some 

10 million acres of Federal and adjacent lands in Idaho, Montana, Nevada, Oregon, Utah, and Wyoming. The 

need for this assessment arose from the decision by the Secretary of the Interior to pursue the protection of 

large tracts of contiguous habitat for the greater sage-grouse (Centrocercus urophasianus) in the Western 

United States. One component of the Department of Interior plan to protect the habitat areas includes 

withdrawing selected lands from future exploration and development of mineral and energy resources, 

including copper, gold, silver, rare earth elements, and other commodities used in the U.S. economy. The 

assessment evaluates the potential for locatable minerals such as gold, copper, and lithium and describes 

the nature and occurrence of leaseable and salable minerals for seven Sagebrush Focal Areas and additional 

lands in Nevada (“Nevada additions”) delineated by BLM. Supporting data are available in a series of USGS 

data releases describing mineral occurrences (the USGS Mineral Deposit Database or “USMIN”), oil and gas 

production and well status, previous mineral-resource assessments that covered parts of the areas studied, 

and a compilation of mineral-use cases based on data provided by BLM, as well as results of the locatable 

mineral-resource assessment in a geographic information system. The present assessment of mineralresource potential will contribute to a better understanding of the economic and environmental trade-offs 

that would result from closing the designated 10 million acres of Federal lands to mineral entry.

The initial request for USGS involvement in this resource assessment occurred in October 2015, with a 

need to provide a report to BLM by mid-July 2016 to inform the National Environmental Policy Act (NEPA) 

process and environmental impact statement (EIS) preparation. Such a short timeframe required mobilizing 

a large number of USGS Mineral Resources Program staff to focus on the SaMiRA project, which began in 

November 2015 with a series of programwide teleconferences to get the project rolling. All of the 61 staff 

members enlisted to work on the project, including three emeritus scientists who are experts in assessment 

and in the geology of the areas under consideration, put aside other research and dedicated themselves 

to this new effort. The first step was to assemble the many types of data needed, including geology, 

geophysics, geochemistry, location of known deposits, production history, current exploration results, and 

information from State geological surveys and industry.

By the end of January 2016, the assessment teams were working hard to evaluate the myriad data needed 

for the assessments. State geological surveys were invited to participate in the process, and meetings were 

held over a period of several weeks in February and March in Butte, Montana; Denver, Colorado; Menlo Park, 

California; Moscow, Idaho; and Reno, Nevada, to conduct the assessment workshops and present the results 

to the State geological surveys for their feedback. The immense task of report writing and figure preparation 

began during and following the assessment meetings, always mindful of the looming July deadline. The 

support of the USGS Science Publishing Network is gratefully acknowledged in getting these reports finished 

in time to meet the BLM’s EIS and NEPA deadlines.

We are, as individuals and as an organization, proud of these reports and the dedication and hard work of 

all the scientists and specialists who worked to produce them. We hope these volumes serve to inform the 

decisions regarding the future of these Federal lands in the West, the protection of greater sage-grouse and 

their habitat, and the economies of the Western States. Although we sought information and advice from 

numerous outside contributors, the results of this study are solely those of the USGS.

Larry Meinert, Program Coordinator, Mineral Resources Program, USGS
iv

Preface

Landscape-scale conservation efforts by the Bureau of Land Management (BLM), U.S. Fish and 

Wildlife Service (FWS), the U.S. Forest Service (USFS), State agencies, private landowners, 

and other partners are striving to conserve the breeding sagebrush habitat for the greater 

sage-grouse (Centrocercus urophasianus) across 11 Western States. In September 2015, the 

FWS decided that the greater sage-grouse did not warrant protection under the Endangered 

Species Act. Concurrent with this decision, the BLM and USFS finalized land-use plans for the 

Federal lands containing sagebrush habitat, consisting of more than 165 million acres, of which 

10 million acres (15,625 square miles) of BLM and National Forest System lands have been 

proposed for withdrawal from mineral entry across Idaho, Montana, Nevada, Oregon, Utah, 

and Wyoming. An additional 394,289 acres (616 square miles) in Nevada (termed the “Nevada 

additions”) were also evaluated by the U.S. Geological Survey (USGS), at the request of the 

BLM, that were proposed by the State of Nevada for consideration. The land-use plans outline 

management practices aimed at conserving viable sagebrush habitats that support the greater 

sage-grouse across large areas termed Sagebrush Focal Areas (SFAs). The SFAs contain lands 

that have been proposed for withdrawal (“withdrawal areas”) from location and entry under the 

U.S. mining laws, subject to valid existing rights.

The USGS Sagebrush Mineral-Resource Assessment (SaMiRA) project was initiated in 

November 2015 and supported by the BLM to (1) assess locatable mineral-resource potential 

and (2) to describe leasable and salable mineral resources for the seven SFAs and Nevada 

additions. Because of the limited duration of the SaMiRA project, the effort focused on 

publically available geoscience data. Additionally, the State geological surveys of Idaho, 

Montana, Nevada, Oregon, Utah, and Wyoming provided valuable mineral resource and geologic 

data, as well as scientific expertise. Information was solicited directly by the USGS from the 

mineral industry, as well as through BLM’s public comment process, regarding any information 

the mineral industry wished to make public and have considered in the assessment. However, 

the conclusions presented herein are solely those of the USGS.
v

Acknowledgments

This endeavor has been made possible through the combined efforts of numerous people 

throughout the Bureau of Land Management (BLM) and the U.S. Geological Survey (USGS). 

Rick Deery, Mitchell Leverette, Adam Merrill, and Thomas (Scott) Murrellwright (BLM Division 

of Solid Minerals, Washington, D.C.) have provided crucial guidance that set the overall 

direction of the project. John Varner and Anthony Titolo and their colleagues at the BLM’s 

National Operations Center, Denver, Colorado, provided the claim and lease information from 

the BLM Legacy Rehost System, or LR2000, database and the geospatial portrayals of the 

various components of land status within the Sagebrush Focal Areas (SFAs) and proposed 

withdrawal area boundaries. From the BLM in Montana, we particularly thank Dave Williams, 

Craig Towery, Joan Gabelman, and Nate Arave.

State geological surveys and other State agencies provided valuable input for the area 

assessments. In Idaho, Ed Ratchford, State Geologist, and Renee Breedlovestrout, Dennis 

Feeney, Virginia Gillerman, Reed Lewis, William Phillips, and Christopher Tate provided 

feedback on the assessment results. For Montana, Dick Berg (emeritus) from the Montana 

Bureau of Mines and Geology provided information on industrial minerals, and John Metesh, 

Thomas Patton, Jay Gunderson, Peggy Delaney, Phyllis Hargrave, and Stan Korzeb also provided 

important feedback. Jay Gunderson of the Montana Board of Oil and Gas Conservation provided 

oil and gas field boundaries. From the Montana Department of Environmental Quality, we 

particularly thank Warren McCullough, Robert Cronholm, Herb Rolfes, Wayne Jepson, Ed 

Coleman, Chris Yde, and Chris Cronin. James E. Faulds, State Geologist for Nevada, made 

certain that the USGS assessment team covering areas in Nevada was aware of the recent 

report released by the State on mineral and energy resources in the Nevada part of the SFAs. 

From the Oregon Department of Geology and Mineral Industries, Robert Houston and Ian Madin 

participated in the Nevada Borderlands assessment meetings. Ken Krahulec, Minerals Section 

Manager, from the Utah Geological Survey, participated in the Nevada Borderlands assessment 

meetings. In addition, Andrew Rupke, industrial minerals geologist from the Utah Geological 

Survey, participated in the Wyoming-Utah assessment meetings. This effort was also greatly 

improved through discussions in the Wyoming-Utah assessment meetings with Wyoming State 

Geological Survey staff, including Tom Drean, Director, and geologists Wayne Sutherland and 

Robert Gregory.

Acquisition, archiving, and analysis of multiple types of geospatial data were the backbone of 

the project. Numerous geographic information system (GIS) databases were developed from 

existing reports, data releases, company reports, and State sources, which in many instances 

had to be converted into digital geospatial format to allow for analysis. The USGS GIS group 

in Denver, Colorado, was led by Carma San Juan and included Paul Denning, Stuart Giles, and 

John Horton. Connie Dicken in Reston, Virginia, provided database, GIS, and land-status support. 

Pam Cossette, Heather Parks, and John Wallis from Spokane, Washington, provided GIS and 

graphics expertise.

Mineral-resource information compiled by USGS staff was key to the analysis. This included 

the Mineral Resource Data System (MRDS) and the new Mineral Deposit Database (USMIN) 

project, which is partly funded by the BLM and is being developed by Gregory Fernette and 

Peter Schweitzer. The geochemical database compilation was done by Karen Duttweiler-Kelly, 
vi

Matthew Granitto, Douglas Yager, and Stephen Smith. The geophysical data were compiled and 

processed by Eric Anderson and David Ponce; Barnaby Rockwell provided data and guidance 

on interpretation of remote sensing data. A number of USGS energy experts contributed 

data and analysis for uranium, geothermal energy, oil and gas, and coal (see below). Donald 

Bleiwas, Beth Sangine, and the staff of the USGS National Minerals Information Center (NMIC) 

contributed commodity information and expertise.

Before writing began, the individual area preliminary assessment tracts were reviewed by an 

“Assessment Oversight Committee” (AOC) comprised of USGS project leads and scientists of the 

project to evaluate completeness and consistency from area to area. AOC leads include Thomas 

Frost, Jane Hammarstrom, and Michael Zientek. Panelists include Donald Bleiwas, Warren Day, 

Jeffrey Mauk, Mark Mihalasky, Gilpin Robinson, and Bradley Van Gosen.

The following provides an outline of the SaMiRA project structure and lists the names of 

contributors.

SaMiRA Project Coordination

Warren C. Day, co-lead

Thomas P. Frost, co-lead

North-Central Montana SFA Team

B. Carter Hearn, Jr. (Emeritus)

Jeffrey L. Mauk, lead

Heather L. Parks

Michael L. Zientek

North-Central Idaho SFA Team

Mary Ellen Benson

Stephen E. Box

Albert H. Hofstra

David A. John

Karen Lund, lead

Gilpin R. (Rob) Robinson

Bradley S. Van Gosen

Lukas Zürcher

Southwestern and South-Central Wyoming and Bear River Watershed SFA Team

Mary Ellen Benson

Timothy S. Hayes

Bradley S. Van Gosen

Anna B. Wilson, lead

Douglas B. Yager

Nevada Borderland SFAs Team

Mary Ellen Benson
vii

Joseph P. Colgan

Edward A. du Bray

Susan Hall

Albert H. Hofstra

David A. John

Steve Ludington (Emeritus)

Mark J. Mihalasky

James J. Rytuba (Emeritus)

Lisa L. Stillings

Peter G. Vikre, lead

Lukas Zürcher

Mineral-Resource Assessment Team

Jane M. Hammarstrom, co-lead

Mark J. Mihalasky

Gilpin R. (Rob) Robinson

Michael L. Zientek, co-lead

Geospatial Information Systems (GIS) and Enterprise Network Team

Pamela M. Cossette

Randall E. Dailey, Enterprise Network lead

Paul D. Denning

Connie L. Dicken

Stuart A. Giles

John D. Horton

Heather L. Parks

Carma A. San Juan, lead

John C. Wallis, contractor

Geochemistry Team

Helen W. Folger

Stuart A. Giles

Matthew Granitto

Karen D. Kelley, co-lead

Steven M. Smith, co-lead

Doug B. Yager

Remote Sensing Team

Barnaby W. Rockwell

Geophysics Team

Eric D. Anderson, lead

David A. Ponce
viii

Energy Resources Team

Jacob DeAngelo, geothermal resources

Ronald M. Drake, oil and gas resources

Jonathan M.G. Glen, geothermal resources

Gregory L. Gunther, energy resource GIS

Jon E. Haacke, coal resources

Susan M. Hall, uranium resources

Colin F. Williams, geothermal resources

Mineral Deposit, Commodity, and Database Teams

Donald I. Bleiwas, co-lead NMIC Team

Gregory L. Fernette, lead USMIN (see Fernette and others, this volume, for additional 

acknowledgments)

Peter N. Schweitzer, lead MRDS

Elizabeth S. Sangine, co-lead NMIC Team (see Sangine, appendix 5, for additional 

acknowledgments)

Assessment Oversight Committee

Thomas P. Frost, Jane M. Hammarstrom, Michael L. Zientek, leads

Donald I. Bleiwas

Warren C. Day

Jeffrey L. Mauk

Mark J. Mihalasky

Gilpin R. (Rob) Robinson

Bradley S. Van Gosen

Scientific Peer and GIS Metadata Reviewers

Arthur A. Bookstrom, chapter C

William F. Cannon, chapter E

Mark E. Gettings, chapter D

Christopher S. Holm-Denoma, chapter D

Michaela R. Johnson, metadata

Victoria E. Langenheim, chapter A

Keith R. Long, chapter A

Celestine N. Mercer, chapter C

Barry C. Moring, metadata

William I. Ridley, chapter A

Klaus J. Schulz, chapter E

Ryan D. Taylor, chapter B

Charles H. Thorman (emeritus), chapter B

Erin Todd, chapter C

Philip L. VerPlanck, chapter A

Kathryn E. Watts, chapter B
ix

Mineral-Deposit Models

Mary Ellen Benson

Susan Hall

Jane M. Hammarstrom

David A. John

Mark J. Mihalasky

Gilpin R. (Rob) Robinson

Lisa L. Stillings

Bradley S. Van Gosen

Michael L. Zientek 
x

Contents

Foreword ........................................................................................................................................................iii

Preface ...........................................................................................................................................................iv

Acknowledgments.........................................................................................................................................v

Section A. Overview of the U.S. Geological Survey Sagebrush Mineral-Resource Assessment 

(SaMiRA) Project..............................................................................................................................1

By Warren C. Day, Jane M. Hammarstrom, Michael L. Zientek, and Thomas P. Frost

Abstract..................................................................................................................................................1

Introduction............................................................................................................................................2

Lands Involved.......................................................................................................................................3

Project Overview...................................................................................................................................3

Who Did the Work?...............................................................................................................................5

Data Sources.........................................................................................................................................5

Geologic Map Data...............................................................................................................................5

References Cited...................................................................................................................................6

Section B. Mineral-Resource Information ..............................................................................................11

By Gregory L. Fernette, Peter N. Schweitzer, and Elizabeth S. Sangine

USMIN Project Mineral-Resource Data for the USGS SaMiRA Project...................................11

By Gregory L. Fernette

Introduction.................................................................................................................................11

Data Compilation........................................................................................................................12

Data Files and Sources.............................................................................................................12

Prospect- and Mine-Related Features..........................................................................12

Mining Districts.................................................................................................................14

Mineral Occurrences.......................................................................................................14

Mine Sites ..........................................................................................................................17

Active Exploration Sites...................................................................................................18

Mineral Production Data .................................................................................................18

Mineral-Resource Data ...................................................................................................19

Acknowledgments.....................................................................................................................19

Mineral Resources Data System (MRDS) ......................................................................................19

By Peter N. Schweitzer

Mineral-Resource Data from the USGS National Mineral Information Center........................20

By Elizabeth S. Sangine

References Cited.................................................................................................................................20

Section C. Geochemical Data....................................................................................................................23

By Steven M. Smith, Karen D. Kelley, Helen W. Folger, Douglas B. Yager, Matthew 

Granitto, and Stuart A. Giles

Introduction..........................................................................................................................................23

Databases Used to Build the SaMiRA Datasets............................................................................23

NURE-HSSR (collected 1976–1980).........................................................................................23

NGS (2008 release) ....................................................................................................................23

NGS-NURE ..................................................................................................................................23

NGDB (mid-1960s through 2007)..............................................................................................23
xi

NASGLP Soils (2013 data release) ..........................................................................................24

Compilation and Evaluation of Data for the SaMiRA Dataset .....................................................24

Analytical Methods ...................................................................................................................25

Statistical Summaries ...............................................................................................................29

Determination of Threshold Values for SedsSoils and Rocks............................................29

Determination of Threshold Values for Concentrates .........................................................31

Interpolated Geochemistry Grids.....................................................................................................31

Geographic Information Systems and Symbolized Layers ..........................................................32

References Cited.................................................................................................................................32

Section D. Geophysical Data and Methods Used in Mineral-Resource Assessments within the 

Sagebrush Focal Areas.................................................................................................................37

By Eric Anderson and David A. Ponce

Introduction..........................................................................................................................................37

Geophysical Methods ........................................................................................................................38

Magnetic and Gravity................................................................................................................38

Radiometric.................................................................................................................................38

Geophysical Data................................................................................................................................39

Aeromagnetic Data ...................................................................................................................39

Gravity Data ................................................................................................................................44

Radiometric Data .......................................................................................................................44

Derivative Geophysical Products.....................................................................................................47

Reduction-to-the-Pole (RTP) of Magnetic Data ...................................................................47

Total Horizontal Gradient of Magnetic and Gravity Data ....................................................47

First Vertical Derivative of Magnetic and Gravity Data.......................................................47

Tilt Derivative of Magnetic and Gravity Data ........................................................................47

Analytic Signal of Magnetic and Gravity Data......................................................................48

Radioelement Element and Ratio Maps of Radiometric Data ............................................48

Depth Estimates .........................................................................................................................48

Magnetic Methods ...........................................................................................................48

Gravity Methods................................................................................................................48

Pluton Mapping..........................................................................................................................50

Diatreme Mapping.....................................................................................................................53

Large-Scale Fractures in Nevada and Idaho........................................................................53

General Discussion.............................................................................................................................53

References Cited.................................................................................................................................53

Section E. Remote Sensing ........................................................................................................................57

By Barnaby W. Rockwell

References Cited.................................................................................................................................57

Section F. BLM Legacy Rehost System (LR2000)....................................................................................59

By Connie L. Dicken and Carma San Juan

Coal........................................................................................................................................................59

Geothermal...........................................................................................................................................59

Mineral Materials Disposal...............................................................................................................59

Mining Claims......................................................................................................................................60

Non-Energy Solid Minerals...............................................................................................................60

Oil and Gas Leasing............................................................................................................................60
xii

Notices and Plans (Surface Management)....................................................................................60

References Cited.................................................................................................................................60

Section G. Previous Mineral-Resource Assessment Data Compilation.............................................61

By Heather L. Parks, Michael L. Zientek, M. Christopher Jenkins, Cassandra K. 

Hennings, John C. Wallis, and Duc M. Nguyen

References Cited.................................................................................................................................62

Section H. Mineral-Resource Assessment for Locatable Minerals ...................................................65

By Jane Hammarstrom and Michael L. Zientek

Introduction..........................................................................................................................................65

A Geologically Based Assessment Approach ...............................................................................65

Mineral-Deposit Types and Models........................................................................................65

Mineral Systems ........................................................................................................................66

Map Scale and Resolution .......................................................................................................68

Assessment Process..........................................................................................................................68

Mineral-Resource Tracts..........................................................................................................68

Buffers.... ............................................................................................................................70

Using Near Distance and Density Mapping to Map Areas with Mineral 

Potential................................................................................................................73

Geostatistical Analysis ....................................................................................................74

Mineral-Resource Potential and Certainty............................................................................74

SaMiRA Assessment Guidelines.............................................................................................74

References Cited.................................................................................................................................76

Section I. Locatable Mineral Market-Demand Analysis Commodity Profiles ...................................79

By Donald Bleiwas

Section J. Energy Mineral Resources......................................................................................................81

By Jonathan M.G. Glen, Jacob DeAngelo, Colin F. Williams, Jon E. Haacke, 

Ronald M. Drake II, Gregory L. Gunther, Stuart A. Giles, and Aimee E. Graeber

Geothermal Energy Resources.........................................................................................................81

By Jonathan M.G. Glen, Jacob DeAngelo, and Colin F. Williams

Introduction.................................................................................................................................81

Overview of USGS Geothermal-Resource Assessments and Definitions........................81

Conventional Geothermal Resources.....................................................................................81

Unconventional Geothermal Resources................................................................................82

2008 USGS National Resource Assessment .........................................................................82

Identified Geothermal Systems ...............................................................................................82

Undiscovered Geothermal Resources ...................................................................................82

Enhanced Geothermal Systems (EGS) Resources...............................................................87

Geothermal Provinces ..............................................................................................................87

Great Basin Province ................................................................................................................87

Snake River Plain.......................................................................................................................87

Methods Used for Reporting the Coal Resources.........................................................................88

By Jon E. Hacke

Methods Used for Reporting the Oil and Gas Resources ............................................................88

By Ronald M. Drake II, Gregory L. Gunther, Stuart A. Giles, and Aimee E. Graeber

Introduction.................................................................................................................................88

Methodology...............................................................................................................................91
xiii

References Cited.................................................................................................................................91

Glossary.........................................................................................................................................................93

References Cited.................................................................................................................................98

Appendix 1. List of Locatable, Leasable, and Salable Minerals ........................................................100

Appendix 2. Mineral-Potential Classification System .........................................................................102

Level of Potential .....................................................................................................................102

Level of Certainty .....................................................................................................................102

Reference Cited .......................................................................................................................102

Appendix 3. Mineral-Deposit Models.....................................................................................................105

Magmatic Systems...........................................................................................................................109

Diatreme-Hosted Diamond.....................................................................................................110

Basalt-Hosted Sunstone.........................................................................................................112

Hydrothermal—Plutonic Rock Associated System ....................................................................113

Porphyry Copper......................................................................................................................114

Arc-Related Porphyry Molybdenum (low fluorine) ............................................................115

Copper Skarn............................................................................................................................116

Tungsten Skarn.........................................................................................................................117

Lead-Zinc Skarn.......................................................................................................................118

Polymetallic Replacement......................................................................................................119

Polymetallic Vein......................................................................................................................120

Tungsten Vein ...........................................................................................................................122

Molybdenum-Tungsten Greisen............................................................................................124

Distal Disseminated Silver-Gold............................................................................................125

Carlin-Type Gold (Silver, Mercury, Antimony).....................................................................126

Hydrothermal—Volcanic Rock Associated System ...................................................................128

Epithermal Gold-Silver (Mercury) .........................................................................................129

Volcanogenic Uranium............................................................................................................131

Stanley District (Idaho)-Type Uranium.................................................................................133

Volcanic Opal and Specialty Gemstones.............................................................................135

Hectorite (Lithium-Rich Clay) and Specialty Clay...............................................................136

Hydrothermal—Exhalative-Magmatic Processes System........................................................137

Volcanogenic Massive Sulfide (Besshi-subtype VMS).....................................................138

Hydrothermal—Exhalative-Sedimentary Processes System ...................................................140

Sedimentary-Exhalative (SEDEX) Lead-Zinc-Silver...........................................................141

Bedded Barite...........................................................................................................................143

Hydrothermal—Metamorphic Rock Associated System...........................................................145

Orogenic Low Sulfide Gold-Quartz Veins.............................................................................146

Sedimentary System (formed during or after the conversion from sediment to 

sedimentary rock) ...............................................................................................................148

Bentonite...................................................................................................................................149

Dolomite (high-purity) .............................................................................................................151

Sediment-Hosted Stratabound Copper................................................................................153

Sandstone Uranium (Roll Front) in Intermontane Basins..................................................155

Hydroallogenic Volcanic-Hosted Uranium..........................................................................156

Zeolites (Closed-Basin Subtype)...........................................................................................158

Zeolites (Open-Basin Subtype)..............................................................................................160
xiv

Sedimentary System (formed during deposition of the sediment) ...........................................162

Banded Iron Formation (Algoma type) .................................................................................163

Lacustrine Diatomite ...............................................................................................................165

Surficial-Mechanical (Placer) Mineral System...........................................................................167

Heavy Mineral Placers ...........................................................................................................168

Placer and Paleoplacer Gold.................................................................................................170

Other (Non-Locatable) Deposit Types ...........................................................................................172

Dimension Stone (Sandstone and Quartzite) ......................................................................173

Sand and Gravel.......................................................................................................................175

Volcanic Ash (cinders and pumice)......................................................................................177

Perlite.........................................................................................................................................178

Appendix 4. Strategic and Critical Materials ........................................................................................179

References Cited...............................................................................................................................179

Appendix 5. Market-Demand Commodity Profiles ...............................................................................181

Antimony.............................................................................................................................................181

References Cited .....................................................................................................................181

Barite...................................................................................................................................................182

References Cited .....................................................................................................................183

Bentonite Clay ...................................................................................................................................183

References Cited .....................................................................................................................184

Copper.................................................................................................................................................185

References Cited .....................................................................................................................186

Diatomite ............................................................................................................................................186

References Cited .....................................................................................................................187

Dimension Stone—Quartzite ..........................................................................................................187

References Cited .....................................................................................................................188

Gallium................................................................................................................................................188

References Cited .....................................................................................................................189

Gemstones .........................................................................................................................................190

References Cited .....................................................................................................................191

Gold...... ...............................................................................................................................................191

References Cited .....................................................................................................................192

Gypsum...............................................................................................................................................192

References Cited .....................................................................................................................192

Iron Ore...............................................................................................................................................193

References Cited .....................................................................................................................194

Lead.....................................................................................................................................................194

References Cited .....................................................................................................................195

Lithium.................................................................................................................................................195

References Cited .....................................................................................................................196

Mercury..............................................................................................................................................196

References Cited .....................................................................................................................197

Molybdenum......................................................................................................................................197

References Cited .....................................................................................................................198

Rare Earth Elements.........................................................................................................................199

References Cited .....................................................................................................................200
xv

Figures

A1. Map of the Sagebrush Focal Areas (SFAs) studied for the Sagebrush Mineral-Resource 

Assessment (SaMiRA) project, Western United States...................................................................... 4

B1. Map of the Sagebrush Focal Areas (SFAs) studied for the Sagebrush Mineral-Resource 

Assessment (SaMiRA) project, Western United States....................................................................13

B2. Map of the mining districts in and near Sagebrush Focal Areas (SFAs) for the Sagebrush 

Mineral-Resource Assessment (SaMiRA) project, Western United States................................15

C1. Map showing the distribution of all geochemistry sample sites for the Sagebrush Focal 

Areas (SFA) studied in the Sagebrush Mineral-Resource Assessment (SaMiRA) project, 

Western United States...............................................................................................................................26

C2. Example diagram showing copper concentrations in parts per million (ppm) in streamsediment and soil samples (SedsSoils) from the Sheldon-Hart Mountain National Wildlife 

Refuge, Southern Idaho and Northern Nevada, and Southeastern Oregon and NorthCentral Nevada Sagebrush Focal Areas...............................................................................................29

C3. Diagram showing dimensions of inverse distance weighted (IDW) grid cell used for 

geochemical data in the Sagebrush Mineral-Resource Assessment (SaMiRA) project........32

D1. Map showing airborne magnetic surveys that intersect a rectangular region 

encompassing a 25-kilometer buffer surrounding Sagebrush Focal Areas (SFAs), Western 

United States.................................................................................................................................................40

D2. Map showing total magnetic intensity (TMI) in the Western United States................................41

D3. Complete Bouguer gravity anomaly map for four rectangular regions surrounding 

Sagebrush Focal Areas (SFAs) in the Western United States, which was created as part of 

the Sagebrush Mineral-Resource Assessment (SaMiRA) project................................................45

D4. Ternary radiometric map of the Western United States....................................................................46

D5. Map of Euler depth estimates overlain on a reduced-to-pole (RTP) magnetic-anomaly 

map of the North-Central Montana Sagebrush Focal Area.............................................................49

D6. Isostatic-anomaly map and basin-thickness estimates derived from gravity inversions over 

the North-Central Idaho Sagebrush Focal Area .................................................................................51

Silver....................................................................................................................................................201

References Cited .....................................................................................................................201

Specialty Clay—Hectorite...............................................................................................................202

References Cited .....................................................................................................................202

Titanium Mineral Concentrates......................................................................................................203

References Cited .....................................................................................................................204

Tungsten.............................................................................................................................................204

References Cited .....................................................................................................................205

Uranium (U3O8)...................................................................................................................................206

References Cited .....................................................................................................................207

Vanadium............................................................................................................................................207

References Cited .....................................................................................................................208

Zeolites ...............................................................................................................................................209

References Cited .....................................................................................................................210

Zinc......................................................................................................................................................210

References Cited .....................................................................................................................211

Acknowledgments.....................................................................................................................................211
xvi

D7. Map of residual magnetic anomalies used to help map plutons in North-Central Idaho 

Sagebrush Focal Area................................................................................................................................52

H1. Illustration of a schematic cross section of possible deposit types associated with a 

hydrothermal-plutonic rock associated system..................................................................................66

H2. Illustration showing an example of datasets used to develop a mineral-resource tract for 

porphyry copper and skarn deposits......................................................................................................71

H3. Matrix of possible mineral potential and certainty designations and criteria used for the 

mineral-resource assessment for locatable minerals in the Sagebrush Mineral-Resource 

Assessment (SaMiRA) project.................................................................................................................75

J1. Geothermal-favorability map showing the relative favorability of occurrence for 

conventional moderate- to high-temperature geothermal resources across the western 

contiguous United States ..........................................................................................................................83

J2. Geothermal-temperature map showing temperature in degrees Celsius (°C) at 6-kilometers 

(km) depth across the western contiguous United States that provides a proxy for the 

favorability of occurrence for enhanced geothermal systems (EGS) resources.......................84

J3. Geothermal-favorability map for the region of Sagebrush Focal Areas (SFAs), 

Western United States, showing logistic regression results for geothermal 

favorability spanning the areas proposed for withdrawal................................................................85

J4. Geothermal-temperature map for the region of Sagebrush Focal Areas (SFAs), Western 

United States, showing temperature in degrees Celsius (°C) at 6-kilometers (km) depth, 

which provides a proxy for enhanced geothermal systems (EGS) favorability spanning the 

areas proposed for withdrawal ...............................................................................................................86

J5. Map of known coal occurrences for the region of the Sagebrush Focal Areas (SFAs), 

Western United States...............................................................................................................................89

J6. Map showing the 1⁄4 section-level cell summary oil and gas exploration and well-type information from the propriety IHS Energy Group (2016) database and from Gunther and others 

(2016b) used for the Sagebrush Mineral-Resource Assessment (SaMiRA) project.................90

Tables

 B1. District data theme attribute fields used for the Sagebrush Mineral-Resource Assessment 

(SaMiRA) project, Western United States............................................................................................14

 B2. Mineral-occurrence data theme attribute fields used for the Sagebrush Mineral-Resource 

Assessment (SaMiRA) project, Western United States....................................................................16

 B3. Mines data theme attribute fields used for the Sagebrush Mineral-Resource Assessment 

(SaMiRA) project, Western United States............................................................................................17

 B4. Exploration data theme attribute fields used for the Sagebrush Mineral-Resource 

Assessment (SaMiRA) project, Western United States....................................................................18

 C1. Number of samples listed by sample media type for Sagebrush Focal Areas (SFA) studied in 

the Sagebrush Mineral-Resource Assessment (SaMiRA) project, Western United States...25

 C2. Analytical methods used for the Sagebrush Mineral-Resource Assessment (SaMiRA) 

project soil and stream-sediment samples (SedsSoils), concentrate samples, and rock 

samples..........................................................................................................................................................27
xvii

 C3. Abundance values for stream-sediment and soil samples (SedsSoils) and rocks 

used in the Sagebrush Mineral-Resource Assessment (SaMiRA) project ......................30

 D1. List of filtered or transformed geophysical datasets generated for the Sagebrush Focal 

Areas as part of the Sagebrush Mineral-Resource Assessment (SaMiRA) project ..........42

 D2. Aeromagnetic surveys used to generate new, higher resolution compilations for 

the Sagebrush Focal Areas (SFAs) as part of the Sagebrush Mineral-Resource 

Assessment (SaMiRA) project .................................................................................................42

 D3. Specifications for State-compilation of magnetic data over the Sagebrush Focal Areas 

(SFAs) as part of the Sagebrush Mineral-Resource Assessment (SaMiRA) project..........44

 D4. Reduction-to-the-pole (RTP) parameters used to transform magnetic-intensity 

anomaly data as part of the Sagebrush Mineral-Resource Assessment (SaMiRA) 

project...........................................................................................................................................47

 D5. Density-depth functions used to constrain final basin gravity fields as part of the 

Sagebrush Mineral-Resource Assessment (SaMiRA) project...........................................50

 G1. Geodatabases containing mineral-resource assessment geographic information 

system (GIS) data that covered the Sagebrush Mineral-Resource Assessment 

(SaMiRA) study areas compiled from preexisting reports .......................................................62

 H1. Relation between classes of mineral deposits, mineral systems, and mineral-deposit 

types with locatable commodities used in the Sagebrush Mineral-Resource 

Assessment (SaMiRA) project .................................................................................................67

 H2. Guide to map scale, detectable size of a map feature, and resolution ................................68

 H3. Example data table for a mineral-resource tract used in the Sagebrush MineralResource Assessment (SaMiRA) project...............................................................................69

 H4. Example of mineral-resource tract criteria used in the Sagebrush Mineral-Resource 

Assessment (SaMiRA) project for Carlin-type gold deposits in the Southeastern Oregon 

and North-Central Nevada, Southern Idaho and Northern Nevada, and Sheldon-Hart 

Mountain National Wildlife Refuge Complex of Oregon Sagebrush Focal Areas...............70

 H5. Relations among mineral occurrences, deposits, prospects, and showings used in 

the Sagebrush Mineral-Resource Assessment (SaMiRA) project ....................................72

 H6. Sources of information for classifying mineral occurrences as deposits or 

prospects used in the Sagebrush Mineral-Resource Assessment (SaMiRA) 

project...........................................................................................................................................72

 H7. Summary statistics for the areal extent of mineralized rock and alterations systems 

associated with various deposit types and suggested buffer radius for tract 

delineation used in the Sagebrush Mineral-Resource Assessment (SaMiRA) 

project...........................................................................................................................................73

 H8. Examples of near distance calculations that were considered for kernel-density 

mapping used in the Sagebrush Mineral-Resource Assessment (SaMiRA) project......73

 H9. Direct and indirect evidence indicators for assigning mineral potential used in the 

Sagebrush Mineral-Resource Assessment (SaMiRA) project...........................................74

 3-1. Typical mining methods for mineral-deposit types assessed within the Sagebrush 

Mineral-Resource Assessment (SaMiRA) study areas .....................................................106

 4-1. Elemental listing of materials stockpiled by the Defense Logistics Agency ....................179

 4-2. Potential acquisitions of materials selected by the Defense Logistics Agency for 

fiscal year 2016..........................................................................................................................179
xviii

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

yard (yd) 0.9144 meter (m)

Area

acre 4,047 square meter (m2)

acre 0.4047 hectare (ha)

acre 0.4047 square hectometer (hm2) 

acre 0.004047 square kilometer (km2)

square foot (ft2) 929.0 square centimeter (cm2)

square foot (ft2) 0.09290 square meter (m2)

square inch (in2) 6.452 square centimeter (cm2)

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

barrel (bbl; petroleum, 1 barrel=42 gal) 0.1590 cubic meter (m3) 

Mass

ounce, troy (oz) 31.103 gram (g) 

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

ton, short (2,000 lb) 0.9072 metric ton (t) 

ton, long (2,240 lb) 1.016 metric ton (t) 

[U.S. customary units to International System of Units]

Conversion Factors

[International System of Units to U.S. customary units]

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

kilometer (km) 0.5400 mile, nautical (nmi) 

meter (m) 1.094 yard (yd) 

Area

square meter (m2) 0.0002471 acre 

square kilometer (km2) 247.1 acre

square centimeter (cm2) 0.001076 square foot (ft2)

square meter (m2) 10.76 square foot (ft2) 

square centimeter (cm2) 0.1550 square inch (ft2) 

square kilometer (km2) 0.3861 square mile (mi2)

Volume

cubic meter (m3) 6.290 barrel (petroleum, 1 barrel = 42 gal)

cubic meter (m3) 264.2 gallon (gal) 

cubic meter (m3) 0.0002642 million gallons (Mgal) 

cubic centimeter (cm3) 0.06102 cubic inch (in3) 
xix

Multiply By To obtain

cubic meter (m3) 35.31 cubic foot (ft3)

cubic meter (m3) 1.308 cubic yard (yd3) 

cubic kilometer (km3) 0.2399 cubic mile (mi3) 

cubic meter (m3) 0.0008107 acre-foot (acre-ft) 

Mass

gram (g) 0.032 ounce, troy (oz)

gram (g) 0.03527 ounce, avoirdupois (oz)

kilogram (kg) 2.205 pound avoirdupois (lb)

metric ton (t) 1.102 ton, short [2,000 lb]

metric ton (t) 0.9842 ton, long [2,240 lb]

Density

kilogram per cubic meter (kg/m3) 0.06242 pound per cubic foot (lb/ft3) 

gram per cubic centimeter (g/cm3) 62.4220 pound per cubic foot (lb/ft3) 

Supplemental Information

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as °F = (1.8 × 

°C) + 32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as °C = (°F – 

32) / 1.8.

Datum

Vertical coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.
xx

Abbreviations

Ad andradite (iron-rich garnet)

AMIS Automated Minerals Information System

AOC Assessment Oversight Committee

API American Petroleum Institute

AR “as received”

ASTER Advanced Spaceborne Thermal Emission and Reflection Radiometer

ASTM American Society for Testing and Materials

AU assessment unit (oil and gas)

BCF, BCFG billion cubic feet (of gas) 

BHT bottom-hole temperature

BLM Bureau of Land Management

BRW Bear River Watershed (Sagebrush Focal Area)

Bt billion metric tons

BV “best value”

CAGR compound annual growth rate

CAI color alteration index

CFR Code of Federal Regulations 

CIGS copper-indium-gallium selenide

CSA Canadian Standards Association

CSM clay-sulfate-mica

CSAMT controlled-source audiofrequency magnetotellurics

DLA Defense Logistics Agency

DOD U.S. Department of Defense

DOE U.S. Department of Energy

DOI U.S. Department of the Interior

EGS enhanced geothermal system

EIS Environmental Impact Statement

ETM+ Landsat 7 Enhanced Thematic Mapper Plus

FLPMA Federal Land Policy and Management Act of 1976

f.o.b. free on board

FWS U.S. Fish and Wildlife Service

g/t gram per metric ton

Ga giga-annum or billions of years ago
xxi

GFTZ Great Falls Tectonic Zone

GHC Geo-Heat Center

GIS geographic information system

HSSR Hydrogeochemical and Stream Sediment Reconnaissance

IDW inverse distance weighted

LEDs light-emitting diodes

LLD lower limit(s) of determination

m.y. millions of years

Ma mega-annum or millions of years ago

MAS Minerals Availability System

MCF thousand cubic feet of gas

MILS Mineral Industry Location System

MMBO million barrels of oil

MMBNGL million barrels of natural gas liquids

MOP muriate of potash

Moz million troy ounces

MRDS Mineral Resources Data System

Mt million metric tons

MTU metric ton unit

MVT Mississippi-Valley-type

MW megawatt

MWe megawatt electricity

NASGLP North American Soils Geochemical Landscape Project

NBMG Nevada Bureau of Mines and Geology

NDS National Defense Stockpile

NEPA National Environmental Policy Act of 1989

NGDB National Geochemical Database

NGL natural gas liquids

NGS National Geochemical Survey

NMIC USGS National Minerals Information Center

NOAA National Oceanic and Atmospheric Administration

NOGA USGS National Oil and Gas Assessment

NURE National Uranium Resource Evaluation

NWR National Wildlife Refuge

opt troy ounce per metric ton
xxii

oz troy ounce 

PGE platinum-group element

PGM platinum-group metal

PLSS Public Land Survey System

ppm parts per million

REE rare earth element

REOE rare earth oxide equivalent(s)

RMOTC Rocky Mountain Oilfield Testing Center

ROD Record of Decision

RTP reduction-to-the-pole

SaMiRA Sagebrush Mineral-Resource Assessment

SEDAR Canadian System for Electronic Document Analysis and Retrieval

SEDEX sedimentary exhalative

SFA Sagebrush Focal Area

SG specific gravity

SI structural index

SOP sulfate of potash

SWIR shortwave-infrared (region of the electromagnetic spectrum)

t metric ton

TCM Tax Court Memorandum

Th/K thorium/potassium ratio

TMI total magnetic intensity

TOMS Topographically Occurring Mine Symbols

TPS total petroleum system

UMOS Utah Mineral Occurrence System

USBM former U.S. Bureau of Mines

USFS U.S. Forest Service

USGS U.S. Geological Survey

USMIN USGS Mineral Deposit Database

VMS volcanogenic massive sulfide

wt.% weight percent

WYO Southwestern and South-Central Wyoming (Sagebrush Focal Area)
xxiii

Chemical Symbols and Formulas Used 

Ag silver Gd gadolinium

Al aluminum Ge germanium

Al2O3 aluminum oxide H hydrogen

Ar Argon H2S hydrogen sulfide

As arsenic Hf hafnium

Au gold Hg mercury

B boron Ho holmium

Ba barium In indium

BaSO4 barium sulfate Ir iridium

Be beryllium K potassium

Bi bismuth K2O potassium oxide

Br bromine La lanthanum

C carbon Li lithium

Corg organic carbon Lu lutetium

CO carbon monoxide Mg magnesium

CO2 carbon dioxide MgO magnesium oxide

Ca calcium Mn manganese

CaO calcium oxide Mo molybdenum

Cd cadmium N nitrogen

Ce cerium NH3 ammonia

CH4 methane Na sodium

Cl chlorine NaCl sodium chloride

Co cobalt Na2O sodium oxide

Cr chromium Nb niobium

Cs cesium Nd neodymium

Cu copper Ni nickel

Dy dysprosium O oxygen

Er erbidium Os osmium

Eu europium P phosphorous

F fluorine P4 elemental (white) phosphorus

Fe iron PO4 phosphate

Fe2O3 ferric iron oxide P2O5 phosphorous pentoxide

Ga gallium Pb lead

GaAs gallium arsenide Pd palladium

GaN gallium nitride Pr praseodymium
xxiv

Pt platinum Te tellurium

Rb rubidium Th thorium

Re rhenium Ti titanium

Rh rhodium TiO2 titanium dioxide

Ru ruthenium Tm thulium

S sulfur Tl thallium

Sb antimony U uranium

Sc scandium U3O8 triuranium octaoxide (yellowcake)

Se selenium V vanadium

Si silicon V2O5 vanadium pentoxide

SiO2 silicon dioxide (silica) W tungsten

Sm samarium WO3 tungsten trioxide

Sn tin Y yttrium

Sr strontium Yb ytterbium

Ta tantalum Zn zinc

Tb terbium Zr zirconium

Mineral Formulas Used 

adularia KAlSi

3

O8

alunite KAl3(SO4)

2

(OH)

6

andradite (garnet) Ca3Fe3+

2

(SiO4)

3

ankerite Ca(Fe,Mg,Mn)(CO3)

2

argentite Ag2S

arsenopyrite FeAsS

barite BaSO4

bornite Cu5FeS4

cassiterite SnO2

chalcocite Cu2S

chalcopyrite CuFeS2

cinnabar HgS

clinoptililite (zeolite) (Ca, Na,K6[Al6Si3O72] ·~20H2O

coffinite U[SiO4,(OH)4]
xxv

corderoite Hg

3

S

2

Cl

2

dolomite CaMg(CO

3

)

2

erionite (zeolite) (Ca,Na,K)10[Al10Si26O72]·~30H

2

O

fluorite CaF

2

galena PbS

hectorite (smectite clay) Na

3

(Mg,Li)

3

Si

4

O10(F,OH)

2

hematite Fe

2

O

3

ilmenite FeTiO

3

kaolinite Al

2

Si

2

O

5

(OH)

4

leucite K(AlSi

2

O

6

)

magnetite Fe

3

O

4

molybdenite MoS

2

molybdite MoO

3

monazite (Ce,La,Th,Nd)PO

4

montmorillonite (Na,Ca)0.33(Al,Mg)

2

(Si

4

O10)(OH)

2 · nH2

O

nepheline Na

3

KAl

4

Si

4

O16

opal SiO

2

·nH

2

O

phillipsite (zeolite) (Ca,Na,K)4-7[Al4-7Si2-9O32]·12H

2

O

powellite CaMoO

4

pyrite FeS

2

quartz SiO

2

rutile TiO

2

scheelite CaWO

4

siderite FeCO

3

sillimanite Al

2

SiO

5

sylvite KCl

sylvinite KCl+NaCl

sphalerite (Zn,Fe)S

staurolite Fe

2

Al

9

Si

4

O23(OH)

stilpnomelane (K,Ca,Na)(Fe2+,Mg,Fe3+)

8

(Si,Al)12(O,OH)27·nH

2

O

tetrahedrite (Cu,Fe,Ag,Zn)12Sb

4

S13

uraninite UO

2

xenotime YPO

4

zircon ZrSiO

4

Overview with Methods and Procedures of the U.S. 

Geological Survey Mineral-Resource Assessment of 

the Sagebrush Focal Areas of Idaho, Montana, Nevada, 

Oregon, Utah, and Wyoming

By Warren C. Day, Jane M. Hammarstrom, Michael L. Zientek, and Thomas P. Frost, editors

With additional sections by Eric D. Anderson, Donald I. Bleiwas, Ronald M. Drake II, Jacob DeAngelo, Connie 

L. Dicken, Gregory L. Fernette, Helen W. Folger, Stuart A. Giles, Jonathan M.G. Glen, Aimee E. Graeber, 

Matthew Granitto, Gregory L. Gunther, Jon E. Haacke, Cassandra K. Hennings, M. Christopher Jenkins, Karen 

D. Kelley, Duc M. Nguyen, Heather L. Parks, David A. Ponce, Barnaby Rockwell, Carma A. San Juan, Elizabeth 

S. Sangine, Peter N. Schweitzer, Steven M. Smith, John C. Wallis, Colin F. Williams, and Douglas B. Yager

Section A. Overview of the U.S. Geological Survey Sagebrush 

Mineral-Resource Assessment (SaMiRA) Project

By Warren C. Day, Jane M. Hammarstrom, Michael L. Zientek, and Thomas P. Frost

Abstract

This report, chapter A of Scientific Investigations Report 

2016–5089, provides a project overview and a consolidated 

resource for the methods, procedures, and voluminous 

fundamental reference information used throughout the 

Sagebrush Mineral-Resource Assessment (SaMiRA) 

project. Mineral occurrence and deposit information is a key 

component of assessments for non-energy minerals. Data were 

used from several major databases. The new U.S. Geological 

Survey (USGS) Mineral Deposit Database project (USMIN) 

(Fernette, section B) provides a modern compilation that 

captures all information publically available through historical 

records, Federal and State databases, company reports, and 

from the Bureau of Land Management’s (BLM) public 

comments on the proposed withdrawal action of greater sagegrouse (Centrocercus urophasianus) habitat received by the 

USGS on April 4, 2016. USMIN provides updated location 

and mineral information on mine sites, mining districts, areas 

of active exploration, and production data. The USGS Mineral 

Resource Data System (MRDS) legacy database (Schweitzer, 

section B) contains mineral-resource information used in the 

SaMiRA project. The Automated Minerals Information System 

(AMIS) database operated by the USGS (see Sangine, section 

B) contains proprietary mineral data that, when aggregated 

to assure that the individual operators were not identified, 

provided a list of active facilities in the project area.

Geochemical data for approximately 26,300 stream 

sediment and soil samples, 3,700 heavy concentrate 

fractions, and 6,890 rock samples were compiled from 

USGS geochemical databases for the SaMiRA project. 

After statistical evaluation, selected elements indicative of a 

wide variety of mineral-deposit types were used to identify 

areas with mineral potential (Smith and others, section C). 

Geophysical methods are powerful tools to map geologic 

materials that have differing physical properties in areas 
2 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

that are both exposed on the land surface and concealed 

beneath thick sequences of overburden. Such information 

helps define mineral-potential tracts like those used in the 

SaMiRA project. Anderson and Ponce (section D) review the 

magnetic susceptibility, density, and radioactivity data sources 

and analytical methods used. Rockwell (section E) describes 

remote-sensing data used for the project. 

The BLM’s Legacy Rehost System, or LR2000, database 

provides a compendium of information on mineral-use 

authorizations for oil, gas, and geothermal leasing, rights-ofways, coal and other mineral development, land and mineral 

titles, mining claims, withdrawals, classifications, and more 

on Federal lands or on Federal mineral estates. The LR2000 

data used in the SaMiRA reports as described by Dicken and 

San Juan (section F) are as of March 6, 2016. To expedite the 

locatable mineral-resource assessments and consolidate the 

LR2000 data for the leasable and salable minerals, Dicken 

and San Juan built a geographic information system (GIS) 

database that relates the attributes to allow for statistical 

analysis of claim- and lease-density information for numerous 

commodities.

The primary focus of the SaMiRA project was to 

provide qualitative mineral-resource assessments for the 

significant locatable mineral commodities. Mineral-deposit 

models provide powerful tools to integrate various geologic, 

geochemical, geophysical, and mineral-deposit data to develop 

the locatable mineral assessment tracts. Parks and others 

(section G) compiled data on previous mineral assessments 

that overlap the SaMiRA project area. Hammarstrom and 

Zientek (section H) review the principal mineral-deposit 

types and mineral systems applicable to the vast landscape of 

the SaMiRA project area. They provide an overview of the 

assessment methods and procedures for creating the tracts for 

locatable mineral resources, evaluating the potential and level 

of certainty for the tracts, and the assessment guidelines used. 

The geospatial data for all of the locatable mineral resources 

assessed for the SaMiRA project are presented in San Juan and 

others (2016). 

The BLM requested present and potential future 

market-demand analyses for the locatable minerals. Bleiwas 

(section I) provides a general description of domestic 

production and a qualitative assessment of inferred future 

market demands for the important locatable minerals 

identified to have a moderate or high potential for occurrence 

within the proposed withdrawal areas.

The SaMiRA project was tasked with describing the 

nature and occurrence of the leasable and salable minerals 

relevant for each Sagebrush Focal Area (SFA). Leasable 

minerals include energy-resource commodities and fertilizer 

minerals such as potash. The evaluation of energy minerals 

was based on previous USGS assessments and the information 

from the BLM’s LR2000 database. Glen and others (sectionJ) 

provide a review of the source information, an overview of 

previous USGS geothermal-assessment reports, discussion 

of the identified geothermal systems, and context for the 

geothermal-energy setting for the major geothermal provinces 

of the project area. Coal is a vital energy resource for the 

Nation; Haacke (section J) provides a brief overview on 

how coal resource information was incorporated into each 

of the assessment reports. Oil and gas development plays an 

important part in land-use planning for the BLM. Drake and 

others (section J) review the Total Petroleum System (TPS) 

methodology used in USGS oil and gas assessments. A TPS is 

a naturally occurring hydrocarbon-fluid system that presumes 

that migration pathways exist now or existed in the past and 

that they connect the provenance with the accumulations. 

Such concepts led to the assessments that were used in the 

individual SFA reports.

The extensive appendixes that accompany this report are 

a major resource used throughout the SaMiRA project. They 

provide a comprehensive listing of the individual locatable, 

leasable, and salable minerals; mineral-potential classification 

system used; a general glossary of terms; a consolidation of 

the applicable mineral-deposit models; and market-demand 

commodity profiles for the locatable mineral commodities that 

have moderate to high potential of occurrence.

Introduction

In September 2015, the Bureau of Land Management 

(BLM) and U.S. Forest Service (USFS) finalized land-use 

plans for regions containing sagebrush habitat for more 

than 165 million acres of public and National Forest System 

lands across in Idaho, Montana, Nevada, Oregon, Utah, and 

Wyoming. The intent of the plans is to provide guidance on 

land-management practices to conserve viable sagebrush 

ecosystems that support the greater sage-grouse (Centrocercus 

urophasianus; hereafter sage-grouse). The plans, released as 

Records of Decision (RODs) for the Great Basin greater sagegrouse sub-regions (Bureau of Land Management, 2015a) and 

for the Rocky Mountain region (Bureau of Land Management, 

2015b), identified Sagebrush Focal Areas (SFAs), which are 

landscape-scale unconsolidated and contiguous tracts of land 

that contain high breeding population densities of sage-grouse 

and high quality sagebrush ecosystems (see Bureau of Land 

Management, 2015c). Notification of the extent of the SFAs 

was initially given in September 2015 in the Federal Register 

(U.S. Department of the Interior, 2015a), with subsequent 

corrections to the legal land descriptions in October 2015 

(U.S. Department of the Interior, 2015b).

The BLM and USFS RODs of September 2015 

recommended withdrawal from location and entry under 

U.S. mining laws. To inform the decision on whether to 

withdraw the SFAs from mineral entry, the BLM requires a 

mineral-resource assessment be completed to identify mineral 

resources within the proposed area of withdrawal. Mineralpotential reports are required to satisfy the requirements of 43 

CFR 2310.3-2, “Development and processing of casefile for 

submission to the Secretary.” The analysis needs to provide 

information on the general geology, known mineral deposits, 

past and present mineral production, mining claims, and 
Section A. Overview of the USGS Sagebrush Mineral-Resource Assessment (SaMiRA) Project 3

mineral leases, as well as an evaluation of future mineral 

potential and a review of mineral economics.

The USGS initiated the Sagebrush Mineral-Resource 

Assessment (SaMiRA) project in November 2015. There 

are seven SFAs discussed herein—(1) North-Central Idaho, 

(2) North-Central Montana, (3) Southeastern Oregon and 

North-Central Nevada, (4) Southern Idaho and Northern 

Nevada, (5) Sheldon-Hart Mountain National Wildlife Refuge 

Complex of Oregon, (6) Bear River Watershed of Utah, and 

(7) Southwestern and South-Central Wyoming. In February 

2016, the BLM requested assessments of two additional areas 

in Nevada, termed the “Nevada additions,” which lie to the 

south of the Southern Idaho and Northern Nevada SFA and 

the Southeastern Oregon and North-Central Nevada SFA (fig. 

A1). The Nevada additions were proposed by the Governor 

of Nevada in January 2016 (http://gov.nv.gov/uploadedFiles/

govnvgov/Content/News_and_Media/Press/2016_Images_

and_Files/Final Transmittal Letter 1.15.16 Signed-reducedcombined.pdf).

The data used throughout this report are based on 

publicly available sources. Very limited new field data and 

no new geochemical or geophysical data were collected 

because of the limited time available to provide preliminary 

information to the BLM by July 15, 2016. Because the 

proposed withdrawal only affects locatable minerals, these 

reports focus on the potential for and provide market analysis 

only on those mineral commodities that are classified as 

“locatable” minerals under the General Mining Act of 1872 

(30 U.S.C. 22–42) that are important to the regional, national, 

and international economies (see appendix 1). The present and 

potential future market-demand analysis is focused on current 

use and U.S. domestic production to provide a qualitative 

assessment of inferred future market demands for the relevant 

locatable minerals. These reports also review the current 

situation, but not future potential, for leasable minerals (such 

as, oil, gas, coal, geothermal energy minerals, and phosphate 

deposits) and salable minerals (such as, sand and gravel 

resources). The USGS relied on the BLM’s LR2000 database 

for information on mining claims, mineral leases, mineralmaterial sales contracts, and surface-management (43 CFR 

3809) authorizations.

This report summarizes the approach taken to provide 

mineral-resource information to the BLM, with discussions on 

the sources of data incorporated, mineral-resource assessment 

methods, the mineral-deposit models employed, and an 

analysis of the market demand.

Lands Involved

The U.S. Department of the Interior (DOI) (2015a, b) 

defined the initial legal boundaries of the proposed lands for 

withdrawal from mineral entry within the SFAs. There are 

three important terms used in these reports that reference 

the lands under consideration by the BLM for conservation 

actions (fig. A1)—(1) Sagebrush Focal Areas (SFAs), (2) the 

part of the SFAs that are under consideration and proposed for 

withdrawal from mineral entry (“withdrawal areas”), and (3) 

Public Land Survey System (PLSS) boundaries, which are the 

boundaries of the townships that contain proposed withdrawal 

areas.

The SFAs are broad landscape-scale regions considered 

to have high breeding-population densities of sage-grouse 

and existing high-quality sagebrush habitat within the 

Western Association of Fish and Wildlife Agencies sagegrouse management zones. Only some parts of the SFAs are

proposed for withdrawal from locatable mineral entry. Within 

the SFAs, some lands, such as BLM wilderness study areas, 

have already been excluded from mineral entry. There are 

also inholdings of State and private lands within the SFAs. 

Examples include the two sections set aside in every PLSS 

township to support State schools, mineral patents, and 

homesteads. With these exclusions, the proposed withdrawal 

areas have irregular and patchy shapes. To ensure complete 

coverage of the withdrawal areas, USGS used a study area that 

is made up of all the townships that include areas proposed 

for withdrawal. The townships include those first described 

by BLM (Bureau of Land Management, 2015c), as formally 

proposed by DOI (U.S. Department of the Interior, 2015a, b), 

plus amendments proposed by the State of Nevada on January 

15, 2016 (http://gov.nv.gov/uploadedFiles/govnvgov/Content/

News_and_Media/Press/2016_Images_and_Files/Final 

Transmittal Letter 1.15.16 Signed-reduced-combined.pdf), and 

further amended by BLM through correspondence (Anthony 

Titolo, BLM, written commun., April 22, 2016). The adjacent 

PLSS township boundaries were dissolved to define the study 

area and then modified to exclude Native American lands, 

which are sovereign and exempt from withdrawal, that are 

inside the study area (fig. A1). Inclusion of lands in the USGS 

mineral assessment that are not part of the formally proposed 

withdrawal areas has no implications regarding land value, 

management alternatives, or recommendation for disposition. 

They were included only to assure continuity in evaluation of 

the regional geologic information to inform the assessment of 

the proposed withdrawal areas.

A 25-kilometer (km) buffer zone beyond the outermost 

PLSS boundary was defined within which the USGS compiled 

the geologic, geochemical, geophysical, and mine and 

mineral-deposit data, to assure completeness, although the 

analysis does not include the buffer areas. This assured that the 

USGS effort captured the pertinent data adjacent to the PLSS 

townships and consequently, all data relevant to the proposed 

withdrawal areas.

Project Overview

The BLM uses legal definitions that group minerals 

into three categories—(1) locatable minerals (General 

Mining Act of 1872, 30 U.S.C. 22–42), including most 

metallic commodities and many high-unit value industrial 

commodities), (2) leasable minerals (Mineral Leasing Act of 
4 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

WASHINGTON

MONTANA

IDAHO

OREGON WYOMING

CA

UTAH

NEVADA

COLORADO

Lakeview

Winnemucca

Elko

Twin Falls

Boise

Pocatello

Logan

Salt Lake City

Rock Springs

Lewistown

84

82

84

25

86

80

90

90

15

94

80

90

15

15

120° 116° 112° 108°

46°

42°

Southeast Oregon and North-Central Nevada SFA

Sheldon-Hart Mountain NWR Complex SFA

Southern Idaho and Northern Nevada SFA

Southwestern and South-Central Wyoming SFA

Proposed Nevada additions

Base modified from U.S. Geological Survey DEM digital data. Boundary data from BLM (2016). 

Roads and political data from Esri (2013). USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 114° W, latitude of origin, 37.5° N. North American Datum of 1983.

0 50 100 150 200 MILES

0 50 100 150 200 KILOMETERS

USGS study area boundary

Bear River Watershed SFA

North-Central Montana SFA

North-Central Idaho SFA

EXPLANATION

Map

area

Study areas

CANADA

UT

MT

ID

NV

OR

CO

WY

KS

NB

CA

WA

SD

ND

AZ NM TX

Study areas

Figure A1. Map of the Sagebrush Focal Areas (SFAs) studied for the Sagebrush Mineral-Resource Assessment (SaMiRA) project, 

Western United States. USGS, U.S. Geological Survey; NWR, National Wildlife Refuge.
1920, 30 U.S.C. 181 et seq.), including energy and fertilizer 

minerals), and (3) salable minerals (Mineral Materials Act 

of 1947, 30 U.S.C. 601 et seq.), which includes common 

varieties of sand, stone, gravel, pumice, pumicite, cinders, 

and clay. A listing of the mineral commodities and their 

classification is given in appendix 1.

For this study, the USGS integrated publically available 

regional-scale geoscience data to discuss the mineral potential 

(current condition and future potential) for locatable minerals 

in the seven SFAs and the Nevada additions and provide a 

summary of the current condition for the most important leasable 

and salable minerals. The mineral-assessment reports follow 

the general guidelines outlined in BLM Manual Sections 3031 

(Bureau of Land Management, 1985) and 3060 (Bureau of Land 

Management, 1994) using the best data from the published 

literature and USGS and BLM databases. The BLM requested that 

the USGS mineral-resource assessments use the overall method 

summarized by Goudarzi (1984), which prescribes a qualitative 

approach to evaluating mineral-resource potential (none, low, 

moderate, or high) with levels of certainty dependent on the 

available evidence for the occurrence of a given mineral-deposit 

type (for example, least certain with insufficient evidence to most 

certain with abundant direct and indirect evidence). Appendix 2 

provides a description of the criteria for determining the levels 

of mineral potential and certainty as requested by BLM. The 

geospatial data that outline the assessment tracts, potential for 

occurrence, and levels of certainty for the mineral deposit types 

that often contain the locatable minerals using the BLM guidelines 

discussed above are given in San Juan and others (2016).

Who Did the Work?

The assessment work was done by a multidisciplinary 

team of USGS geologists, economic geologists, geophysicists, 

geochemists, mineral commodity specialists, and GIS experts. 

These geoscientists reached out to the State geological surveys 

(or equivalent) for Idaho, Montana, Nevada, Oregon, Utah, 

and Wyoming to gather the most recent geologic and mineral 

information available. The State geological surveys provided 

invaluable data and expertise that informed the USGS effort.

Reports for this study include other chapters of Scientific 

Investigations Report 2016–5089 by Mauk and others (in press) for 

the North-Central Montana SFA assessment study and Lund and 

others (in press) for the North-Central Idaho SFA. Vikre and others 

(in press) combined three SFAs that occur along the northern Nevada 

border (Sheldon-Hart Mountain National Wildlife Refuge, Southeast 

Oregon and North-Central Nevada, and Southern Idaho and Northern 

Nevada SFAs) and the Nevada additions into one report. Vikre and 

others (in press) provides a coherent summary over a large region, 

yet presents mineral-potential results for the individual SFAs and 

Nevada additions. Similarly, the discussion of the geologic overview 

and potential mineral-deposit types for the Bear River Watershed, 

Utah, and the Southwestern and South-Central Wyoming SFAs was 

combined by Wilson and others (in press).

Data Sources

The USGS mineral-resource assessments for the locatable 

mineral commodities are based on integration of the available 

digital geospatial information that address the favorability 

criteria defined by the specific mineral-deposit models 

applicable to the SFA under consideration. The mineral-deposit 

models (see appendix 3) are extremely powerful tools that 

simplify the complex ore-forming processes into criteria that 

can be used to estimate the favorability of landscape-scale tracts 

such as the SFAs. The models are syntheses of key features of 

the mineral deposits that include succinct geologic descriptions, 

associated mineral commodities, key features of the geologic 

environment of formation, ore controls, and economic factors 

for each deposit type. Mineral-deposit models provide 

rigorous constructs that specify the geologic, geochemical, and 

geophysical features that lead to formation of a given mineraldeposit type. Mineral-deposit models can be highly detailed 

(for example, Hayes and others, 2015), the full application of 

which demands detailed datasets such as isotope geochemical 

studies, detailed geologic mapping, alteration mineralogical 

studies, multispectral remote-sensing studies, and high-precision 

geophysical data. Such detailed models are extremely powerful 

at the ore-deposit to district-scales and can lead to discovery 

of individual mineral deposits. In contrast, the generalized oredeposit models compiled by and used for the SaMiRA study 

(appendix 3), which rely on large, regional-scale geoscience 

datasets to delineate tracts of the locatable mineral commodities, 

result in landscape-scale qualitative mineral-resource 

assessments that meet the requirements of the regulations 

followed by the BLM. The following is a brief description of 

the major datasets that were combined with the mineral-deposit 

models that underpin delineation of the resource-potential tracts 

for the locatable minerals.

Geologic Map Data

Geologic maps provide a fundamental building block for 

mineral-resource assessments. The USGS relied on publically 

available geologic maps published at a variety of scales to conduct 

the resource analyses. Digital geologic map compilations for 

this project built on the approach taken by Ludington and others 

(2005), Stoeser and others (2005), and Zientek and others (2005) 

for geologic maps of the Western United States and included 

the maps from the California (Saucedo and others, 2000), Idaho 

(Bond and others, 1978; Lewis and others, 2012), Montana (Vuke 

and others, 2007), Nevada (Crafford, 2007), Oregon (Walker 

and others, 2002), Utah (Hintze and others, 2000), and Wyoming 

(Green and Drouillard, 1994) at their original scales. The digital 

geologic map compilations do not resolve map-unit discontinuities 

along the borders between the States nor the inherent differences 

in mapping styles and scales between the source maps. However, 

their compilation provided a useful first-order dataset where more 

detailed published digital geologic maps were not available.

Section A. Overview of the USGS Sagebrush Mineral-Resource Assessment (SaMiRA) Project 5
6 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Several more-detailed geologic maps were used to 

refine the assessment-tract boundaries and identify key 

lithologic information to help delineate the assessment tracts 

for locatable mineral-resource potential. For Idaho, the 

1:100,000-scale maps of Link and others (1995), Evans and 

Green (2003), Kuntz and others (2007), Skipp and others 

(2009), and Othberg and others (2012) were incorporated in 

the assessments along with the 1:250,000-scale maps of Worl 

and others (1991), Fisher and others (1992), Wilson and Skipp 

(1994), and Worl and Johnson (1995).

The digital geologic-map data used for Montana were a 

series of 1:100,000-scale, 30’×60’ quadrangle maps developed 

by the Montana Bureau of Mines and Geology (http://www.

mbmg.mtech.edu/gis/gis-datalinks.asp). The maps used 

include the Dodson (Bergantino, 2001), Fort Peck Lake East 

(Wilde and Bergantino, 2004a), Fort Peck Lake West (Wilde 

and Bergantino, 2004b), Glasgow (Bergantino, 1999a), Jordan 

(Wilde and Vuke, 2004a), Malta (Bergantino, 1999b), Winnett 

(Porter and Wilde, 1993), Sand Springs (Wilde and Vuke, 

2004b), and Zortman (Porter and Wilde, 2001) quadrangles.

The digital geospatial information incorporated for 

assessments of the SFAs in Nevada included sources from 

several map scales. The 1:250,000-scale Crafford (2007) 

map formed the basic reference for the statewide data. This 

was augmented by data on intrusive rocks from du Bray 

and Crafford (2007). Reheis (1999) provided constraints on 

the extent of Pleistocene-aged lake deposits. In addition to 

the Oregon geologic map of Miller and others (2002), we 

incorporated data from the Oregon Department of Geology 

and Mineral Industries released in the GIS data compilation of 

Smith and Roe (2015).

For Utah, the Hinze and others (2000) State-scale 

geologic map was used. The primary source of digital geologic 

information used for the assessment of the Bear River 

Watershed was the 1:100,000-scale map of Dover (1995) for 

the Logan 30’×60’ quadrangle.

The digital geologic map information used for the 

mineral-resource assessments for Wyoming included the 

digital geologic-map compilation of Green and Drouillard 

(1994), which was based on the 1:500,000-scale mapping 

of Love and Christiansen (1985). More detailed geologic 

data were captured from the 1:100,000-scale mapping of 

M’Gonigle and Dover (2004), Sutherland and Hausel (2006), 

Johnson and Sutherland (2009), Jones and Scott (2010), and 

Sutherland and Luhr (2011).

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Section A. Overview of the USGS Sagebrush Mineral-Resource Assessment (SaMiRA) Project 7
8 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

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the South Pass 30’×60’ quadrangle, Fremont and Sweetwater 

Counties, Wyoming: Wyoming State Geological Survey Map 

Series 70, 1 sheet, scale 1:100,000.

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geologic map of the Farson 30’×60’ Quadrangle, Sweetwater, 

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E.A., Fernette, G.L., Glen, J.M.G., Haacke, J.E., Hall, 

S.M., Hofstra, A.H., John, D.A., Ludington, S., Mihalasky, 

M.J., Rytuba, J.J., Shaffer, B.N., Stillings, L.L., Wallis, 

J., Williams, C.F., Yager, D.B., and Zürcher, L., in press, 

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Survey Scientific Investigations Report 2016–5089–B, http://

dx.doi.org/10.3133/sir20165089.

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and structure contour map of the Fort Peck Lake 

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ftPeckLakeEast.pdf.

Wilde, E.M., and Bergantino, R.N., 2004b, Geologic 

and structure contour map of the Fort Peck Lake 

West 30’×60’ quadrangle, eastern Montana: Montana 

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15, 2016, at http://www.mbmg.mtech.edu/pdf_100k/

ftPeckLakeWest.pdf.

Wilde, E.M., and Vuke, S.M., 2004, Geologic map of the 

Jordan 30’×60’ quadrangle, eastern Montana: Montana 

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p., 1 sheet, scale 1:100,000, accessed March 15, 2016, 

at http://www.mbmg.mtech.edu/pdf_100k/jordan.pdf.

Wilde, E.M., and Vuke, S.M., 2004, Geologic map of the 

Sand Springs 30’×60’ quadrangle, eastern Montana: 

Montana Bureau of Mines and Geology Open-File 

Report 515, 8 p., 1 sheet, scale 100,000, accessed 

March 15, 2016, at http://www.mbmg.mtech.edu/

pdf_100k/sandSprings.pdf.

Wilson, A.B., Hayes, T.S., Benson, M.E., Yager, D.B., Anderson, E.D., 

Bleiwas, D.I., DeAngelo, J., Dicken, C.L., Drake, R.M., II, Fernette, 

G.L., Giles, S.A., Glen, J.M.G., Haacke, J.E., Horton, J.D., Parks, H.L., 

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resources of the Southwestern and South-Central Wyoming Sagebrush 

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Focal Area, Wyoming and Utah: U.S. Geological Survey Scientific 

Investigations Report 2016–5089–E, http://dx.doi.org/10.3133/

sir20165089.

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http://pubs.usgs.gov/bul/b2064-a/.

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of the Hailey 1°×2° quadrangle, Idaho: U.S. Geological Survey OpenFile Report 91–340, 1 sheet, scale 1:250,000, accessed March 15, 

2016, at http://ngmdb.usgs.gov/Prodesc/proddesc_18123.htm.

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Carlson, M.H., Green, G.N., Frost, T.P., Boleneus, D.E., Evans, K.V., 

Van Gosen, B.S., Wilson, A.B., Larsen, J.C., Kayser, H.Z., Kelley, 

W.N., and Assmus, K.C., 2005, Spatial databases for the geology of 

the Northern Rocky Mountains-Idaho, Montana, and Washington: 

U.S. Geological Survey Open-File Report 2005–1235, 201 p., scale 

1:100,000 and 1:250,000, accessed March 15, 2016, at http://pubs.usgs.

gov/of/2005/1235/.

Section A. Overview of the USGS Sagebrush Mineral-Resource Assessment (SaMiRA) Project 9

Section B. Mineral-Resource Information

By Gregory L. Fernette, Peter N. Schweitzer, and Elizabeth S. Sangine

This discussion on mineral-resource information used in 

the SaMiRA project consists of three sections. The first section 

describes the U.S. Geological Survey (USGS) Mineral Deposit 

Database (USMIN) data compilation developed for the Bureau 

of Land Management. The second section describes the USGS 

Mineral Resources Data System (MRDS). The third section 

describes the data contributed by the USGS National Minerals 

Information Center (NMIC).

USMIN Project Mineral-Resource Data 

for the USGS SaMiRA Project

By Gregory L. Fernette

Introduction

Mineral-occurrence, mining, and mineral-exploration 

information is one of the foundations for developing mineralresource assessments such as the U.S. Geological Survey (USGS) 

Sagebrush Mineral-Resource Assessment (SaMiRA) project done 

for the Bureau of Land Management (BLM). The BLM mineralresource assessment guidelines outlined in BLM Manual Sections 

3031 (Bureau of Land Management, 1985) and 3060 (Bureau of 

Land Management, 1994) require that mineral-assessment reports 

contain information on current and past mining, exploration 

activity, and known mineral occurrences. The USGS has an 

ongoing project, the USGS Mineral Deposit Database (USMIN), 

whose objective is to develop a new geospatial database of the 

mineral resources of the United States. Personnel working on 

this project were temporarily retasked to work exclusively on the 

SaMiRA Project.

This report describes the type, source, and nature of the 

mineral-resource data compiled for the assessment by the USMIN 

project, which was used along with other data throughout the 

USGS SaMiRA project. The data compiled for the SaMiRA 

assessment differs somewhat in structure from that being compiled for USMIN. The mineral-resource data for SaMiRA were 

compiled as a series of GIS data “themes” designed to meet the 

requirements of BLM assessments. Previously compiled USMIN 

GIS data showing mine- and prospect-related features from USGS 

topographic maps were also made available to the SaMiRA 

project. 

A core part of the USGS Mineral Resources Program’s 

mission is to inventory the mineral resources of the United States. 

Consequently, the USGS has a long history of publishing maps 

and reports on domestic mineral resources. The first USGS digital 

mineral-resource database began to be built in late 1960s and was 

released in 1972 as the Computerized Resources Information 

Bank (CRIB) (Calkins and others, 1973). The name was changed 

in the early 1980s to the Mineral Resource Data System (MRDS). 

The MRDS database was used to manage descriptive data about 

mines, prospects, and mineral occurrences (Arndt, 1990). Much of 

the data in MRDS were entered during the 1970s and 1980s, when 

USGS conducted numerous mineral-resource assessments for the 

U.S. Forest Service (USFS) and the BLM.

The U.S. Bureau of Mines (USBM) concurrently developed 

two digital databases—the Minerals Availability System (MAS) 

and the Mineral Industry Location System (MILS) (Berg and 

Carrillo, 1980; Babitzke and others, 1982). The primary purpose 

of the MAS/MILS databases was to support the minerals-supply 

analysis function of the USBM (Davidoff, 1980). After closure of 

the USBM in 1996, the MAS/MILS databases were transferred to 

the USGS (McFaul and others, 2000).

The MAS/MILS and MRDS databases were merged into a 

single Oracle database, which was available on the USGS Mineral 

Resources Data Web site (http://mrdata.usgs.gov). The database 

now has a total of about 303,000 records, of which some 270,000 

are for sites in the United States (U.S. Geological Survey, 2016). 

Work thereafter concentrated on improving the Oracle database 

interface with little updating of data. In 2012, the USMIN project 

began with the objective of providing an up-to-date, comprehensive, site-specific, geospatial database of the mines, mineral 

regions, and mineral occurrences of the United States. The 

following year an interagency agreement covering the USMIN 

project was implemented with the BLM Solid Minerals Program, 

whereby BLM provided additional funding for the project.

The reasons for the development of the new USMIN 

database include the following:

• Advances in Geographic Information Systems (GIS) 

software and data delivery mechanisms via the Internet 

allow for the use and analysis of large landscape-scale 

datasets of which mineral resources are a part.

• New technology for data capture, such as “heads up” 

digitizing from georeferenced raster images of paper 
12 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

maps, allows the rapid capture of accurate locations 

and other digital data.

• New sources of data, such as digital air photos and 

high-resolution satellite imagery, allow for the rapid 

and efficient capture of spatial data.

• New laws that require permitting of mine sites at both 

the State and Federal level provide new sources of 

timely data on the nature and location of mine sites, 

which can be incorporated into a national database.

An underlying concept of USMIN is to transition USGS 

mineral-resource information from the traditional “point with 

attributes” style of database into the geospatial realm where the 

data also include the spatial elements of mineral resources, such as 

the footprints of the mineral deposits and the spatial extent of mine 

features and mineral regions.

The USMIN database has three feature groups—(1) 

mineral occurrences, (2) mineral regions, and (3) mine 

features. Each feature group contains spatial data in the 

form of points and polygons, but all features are tied to 

point locations. Feature locations are captured primarily 

by “heads up” digitizing from georeferenced maps and (or) 

imagery. Point locations are captured for all features and, 

where available, the polygons that outline the footprint of a 

given feature. In USMIN, a mineral occurrence is considered 

“a concentration of a mineral (usually, but not necessarily, 

considered in terms of some commodity, such as copper, 

barite, or gold) that is considered valuable by someone 

somewhere, or that is of scientific or technical interest” 

(Cox and Singer, 1986). Mineral occurrences are classified 

as deposits, prospects, or showings. A mineral deposit is a 

mineral occurrence that has a defined size and grade as shown 

by past production and (or) a resource estimate. A mineral 

prospect is a mineral occurrence where there is sufficient data 

to describe at least two dimensions of the occurrence and its 

commodity. A mineral showing is a site where a potentially 

valuable mineral is present. Mineral regions are geographic 

features, such as mining districts, mineral belts, and mineral 

provinces that are associated with mineral-resource data. 

Mine features are those features created as part of the process 

of mining mineral deposits, such as mine shafts, adits, open 

pits, and waste piles. As noted above, the structure of the data 

compiled for SaMiRA, where the data was organized into 

“themes,” differs from that in USMIN and includes a data 

theme for Active Exploration Sites. This data is not a part 

of USMIN but was added to the SaMiRA data specifically to 

meet the requirements of BLM assessment reports.

Data Compilation

Work on the USMIN project started in 2012 with an 

emphasis on augmenting and complementing existing USGS 

data and laying the foundation for the eventual geospatial 

database. An early focus of the project was on compiling 

data on active mineral exploration sites and active mines 

in the United States, as most of the data in MRDS had not 

been updated since the 1980s. For the SaMiRA project, the 

data compilation effort focused on those lands proposed for 

withdrawal including a 25-kilometer (km) buffer that enclosed 

the Public Land Survey System (PLSS) township boundaries 

that include the proposed withdrawal areas in the seven 

Sagebrush Focal Areas (SFA) and two additions in Nevada 

(fig. B1).

The data were compiled from all publicly available sources 

including USGS publications, data from other Federal agencies, 

State geological surveys, other State agencies, geological 

societies, and mineral-industry data. A considerable amount of 

additional data came from sources such as industry Web sites, 

press releases, presentations, annual reports, and technical 

reports filed with regulatory agencies. An important example 

is the technical reports prepared in accordance with Canadian 

National Instrument 43-101, referred to as “NI 43-101 Reports.” 

Completed preliminary maps of active mines and exploration 

sites were sent to the State geological surveys of Montana, 

Wyoming, Idaho, Utah, Nevada and Oregon for review and 

comment. Data were also sent to BLM and U.S. Forest Service 

geologists in the affected regions. Maps of active mine and 

exploration sites were also displayed at the annual meeting of 

the American Exploration and Mining Association (AEMA) in 

December 2015. Industry and government agency personnel 

at the meeting were invited to review the maps and the site 

listings and identify missing sites. In April 2016, BLM provided 

the USGS with copies of public comments received on the 

proposed land withdrawals. Comments specific to mineral 

resources were reviewed to insure that any specific mineral 

occurrences, mines, and (or) exploration sites mentioned were 

in the data being used by the assessment teams.

Data Files and Sources

USMIN project data used in the SaMiRA project are 

presented as six data themes, described below. One of these 

themes for prospect- and mine-related sites, is a subset of a 

larger database that was published separately (Fernette and 

others, 2016b). The data described here are being published as 

a USGS data release (Fernette and others, 2016a).

Prospect- and Mine-Related Features

Locations of historical or past mining sites were compiled 

by capturing prospect- and mine-related symbols from USGS 

7.5- and 15-minute topographic maps. In the SaMiRA region, 

mine symbols are shown on USGS topographic maps published 

between 1935 to 2006. Early in the USMIN project, it was 

decided to capture these data as a first step in developing a 

GIS of mines in the United States. The process and rationale 

were based on the Abandoned Mine Lands programs of the 

Nevada Division of Minerals (Hess, 2001) and the California 

Department of Conservation’s Abandoned Mine Lands Unit 

(California Department of Conservation, 2013).
WASHINGTON

MONTANA

IDAHO

OREGON WYOMING

CA

UTAH

NEVADA

COLORADO

Lakeview

Winnemucca

Elko

Twin Falls

Boise

Pocatello

Logan

Salt Lake City

Rock Springs

Lewistown

84

82

84

25

86

80

90

90

15

94

80

90

15

15

120° 116° 112° 108°

46°

42°

Base modified from U.S. Geological Survey DEM digital data.

Boundary data from BLM (2016). Roads and political data from Esri (2013).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 114° W, latitude of origin, 37.5° N.

North American Datum of 1983.

0 50 100 150 200 MILES

0 50 100 150 200 KILOMETERS

Map

area

CANADA

UT

MT

ID

NV

OR

CO

WY

KS

NB

CA

WA

SD

ND

AZ NM TX

Southeast Oregon and North-Central Nevada SFA

Sheldon-Hart Mountain NWR Complex SFA

Southern Idaho and Northern Nevada SFA

Southwestern and South-Central Wyoming SFA

Proposed Nevada additions

USGS study area boundary

Bear River Watershed SFA

North-Central Montana SFA

North-Central Idaho SFA

EXPLANATION

Study areas

Figure B1. Map of the Sagebrush Focal Areas (SFAs) studied for the Sagebrush Mineral-Resource Assessment (SaMiRA) project, 

Western United States. USGS, U.S. Geological Survey; NWR, National Wildlife Refuge.

Section B. Mineral-Resource Information 13
14 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

The historical mine site data were captured by digitizing 

from georeferenced raster images of historic topographic maps of 

the United States obtained from the USGS Historical Topographic 

Map Collection (see http://ngmdb.usgs.gov/maps/TopoView/). 

Mine sites were digitized and attributed with the source map name 

and date and the feature type. Locational accuracy for data derived 

from 7.5-minute quadrangle (1:24,000-scale) topographic maps 

is estimated to be about 100 feet. The most common features 

captured were mineshafts, adits, open pit mines, and prospect 

pits. In the mineral-resource assessment process, these data can be 

used to highlight areas of past mining activity, which is one of the 

requirements of the BLM mineral-assessment reports.

Mining Districts

Mining districts are historical administrative areas 

organized by miners under the mining laws of the United States. 

They typically comprise an area covering a group of mines that 

often exploit the same or similar commodity such as gold or 

silver. Considerable mineral-resource information, including 

production data, is tied to mining districts, and they have been 

the focus of many USGS studies (Hill, 1912; Koschmann and 

Bergendahl, 1968).

Mining districts were being compiled as a part of the 

Mineral Regions USMIN feature group, and data in progress 

was extracted for the SaMiRA Project. Most district locations 

were obtained from compilations by the State geological 

surveys of Nevada (Tingley, 1998), Utah (Doelling and Tooker, 

1983; Utah Geological Survey, 2012), Idaho (Ross, 1941; 

Gustafson, 1987), Montana (Chavez, 1994), and Wyoming 

(Gregory and others, 2010; Harris and others, 1985). For 

Oregon, district locations were compiled primarily from 

Bradley (1982) and Gilluly and others (1933).

Table B1. District data theme attribute fields used for the Sagebrush Mineral-Resource Assessment (SaMiRA) project, Western United 

States.

Field name Description

Name Primary name of the district.

Other name Other names for the district.

State State in which the district is located.

Commodity(s) Commodities present in mineral deposits in the district.

Commodity group Group to which the commodities belong: metallic minerals, nonmetallic and industrial minerals, gemstones, 

and uranium.

Deposit model number(s) ID numbers for the USGS deposit models of mineral deposits present in the district.

Deposit model name(s) Names of the USGS deposit models of mineral deposits present in the district.

Geoenvironmental model(s) Names of the USGS geoenvironmental deposit models for mineral deposits present in the district.

Remarks Additional data or comments on the data.

References Source of the location and other data for the district.

Associated polygon Whether or not there is a shape associated with the point (yes/no).

Polygon definition Description of the nature of the polygon.

Mining district locations are areas represented as polygons. 

In the GIS data, all districts also have a point location, which 

is typically the centroid of the polygon. Mining-district data 

attributes are shown in table B1. The distribution of mining 

districts in the SaMiRA region is shown on figure B2.

All commodities associated with mineral occurrences 

located within a district are recorded whether they have been 

mined or not, contingent on the available data. Commodity 

groups for districts include metallic minerals (excluding 

uranium), industrial minerals, gemstones, and uranium. The 

USGS mineral-deposit models for mineral deposits present 

in a district were extracted from the Mineral Occurrence data 

theme. Geoenvironmental deposit models were derived from 

the equivalency relationship in du Bray (1995).

Mining districts can be used as a part of the mineralresource assessment process, as they highlight areas of past 

mining activity, groupings of mineral occurrences, and provide 

a focus for the discussion of other data such as production.

Mineral Occurrences

The locations of mineral occurrences were compiled 

from a variety of sources. Early in the USMIN project a 

review of the literature with the objective of identifying 

existing mineral-resource databases that could be incorporated 

into USMIN eliminated the need for a completely new data 

compilation. The State geological surveys of Oregon, Idaho, 

and Utah have published mineral occurrence databases that 

include the SaMiRA assessment areas. For the SaMiRA 

project, data were compiled on a state-by-state basis with 

USGS, USBM, and other data being added to State data. A 

large number of mineral occurrences were found through the 

USMIN compilation of active exploration projects.
Figure B2. Map of the mining districts in and near Sagebrush Focal Areas (SFAs) for the Sagebrush Mineral-Resource Assessment 

(SaMiRA) project, Western United States. USGS, U.S. Geological Survey; BLM, Bureau of Land Management.

WASHINGTON

MONTANA

IDAHO

OREGON WYOMING

CA

UTAH

NEVADA

COLORADO

Lakeview

Winnemucca

Elko

Twin Falls

Boise

Pocatello

Logan

Salt Lake City

Rock Springs

Lewistown

§ ̈¦84

§ ̈¦82

§ ̈¦84

§ ̈¦25

§ ̈¦86

§ ̈¦80

§ ̈¦90

§ ̈¦90

§ ̈¦15

§ ̈¦94

§ ̈¦80

§ ̈¦90

§ ̈¦15

§ ̈¦15

120° 116° 112° 108°

46°

42°

Base modified from U.S. Geological Survey DEM digital data.

Boundary data from BLM (2016). Roads and political data from Esri (2013).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 114° W, latitude of origin, 37.5° N.

North American Datum of 1983.

0 50 100 150 200 MILES

0 50 100 150 200 KILOMETERS

EXPLANATION

USGS study area boundary

BLM proposed withdrawal areas

Map Mining districts area

CANADA

UT

MT

ID

NV

OR

CO

WY

KS

NB

CA

WA

SD

ND

AZ NM TX

Study areas

Section B. Mineral-Resource Information 15
16 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Table B2. Mineral-occurrence data theme attribute fields used for the Sagebrush Mineral-Resource Assessment (SaMiRA) project, 

Western United States.

Field name Description

Name Primary name of the occurrence.

Other name Other names for the occurrence.

State State in which the occurrence is located.

Feature type Classification of occurrence as deposit, prospect, or showing.

Exploration project Name of exploration project associated with the mineral occurrence.

Commodity(s) Commodities present in mineral occurrence.

Commodity group Group to which the commodities belong: metallic minerals, nonmetallic and industrial minerals, stone, sand and 

gravel, gemstones, and uranium.

Deposit model number(s) ID numbers for the USGS deposit models of mineral deposits present in the district.

Deposit model name(s) Names of the USGS deposit models of mineral deposits present in the district.

Deposit model source Source of the deposit model(s).

Geoenvironmental model(s) Names of the USGS geoenvironmental deposit models for mineral deposits present in the district.

Remarks Additional data or comments on the data.

References Reference for the primary source of the location and other data for the occurrence.

Associated polygon Whether or not there is a shape associated with the point (yes/no).

Polygon definition Description of the nature of the polygon.

For the State of Nevada, the primary sources of data 

were commodity reports produced by the Nevada Bureau 

of Mines and Geology (NBMG); for example, Stager and 

Tingley (1988), Papke and Castor (2003), Davis and others 

(2006), and the county reports on Elko, Humboldt and 

Washoe Counties (Willden, 1964; Bonham, 1969; Lapointe 

and others, 1991). Active mines and exploration sites were 

compiled from annual reports by the Nevada Division of 

Minerals and the NBMG and through a search of company 

activities in mining publications on the Web. Locations of 

material sites and gravel pits were obtained from the Nevada 

Department of Transportation. Active mine and exploration 

sites were identified from permits of the Nevada Department 

of Environmental Protection, the BLM, and USFS. Significant 

data were also collected from publications of the Geological 

Society of Nevada. Data from these sources were captured and 

then reconciled into single data layers. 

For Oregon, data were extracted from the Oregon 

Department of Geology and Mineral Industries Mineral 

Information Layer MILO-2 (Oregon Department of Geology and 

Mineral Industries, 2010). This was augmented with data from 

other sources, including BLM Plans of Operations, company data, 

and USGS and USBM reports.

For Utah, the Utah Mineral Occurrence System (Utah 

Geological Survey, 2015) was the primary data source. This 

was augmented by data from the Utah Geological Association, 

company data, and USGS and USBM reports. 

The primary sources of mineral occurrence data in Idaho 

were the Idaho Geological Survey’s Database of Mines and 

Prospects and the Database of Select Aggregate Material Sources 

(Idaho Geological Survey, 2015; Tate and others, 2015). These 

data were augmented by reports of the USGS and USBM.

For Wyoming, the primary data sources were Wilson and 

others (2001), Wilson (2014), and Wyoming Geological Survey 

maps and publications (Harris and others, 1985; Hausel, 1986, 

1989; Harris, 2004; Gregory and others, 2010). These data were 

augmented by company data collected by the USMIN project.

For Montana, the primary data sources were MRDS (U.S. 

Geological Survey, 2016) and the Montana Abandoned and 

Inactive Mines Database (Montana Bureau of Mines and Geology, 

2006). Additional data were added from other USGS databases, 

including Klein (2004), and Spanski (2001, 2004), as well as from 

company data.

Attributes assigned to mineral occurrences in the GIS data 

were limited to those judged most critical for assessment purposes 

(table B2). The key geological attributes were commodity and 

mineral-deposit model. The mineral-deposit model ascribed to 

each occurrence was derived from the source data inasmuch as 

no mineral deposit classification was done by USMIN project 

personnel. Geoenvironmental models were assigned by using the 

equivalency relation in du Bray (1995).

A primary objective of the compilation of mineral 

occurrences was to develop accurate locations, commodity data, 

deposit models, source references, and where available production 

and resource (grade-tonnage) data. Industry data were one of the 

most important sources for accurate locations, deposit outlines (or 

footprints), and resource data. Whenever a deposit footprint was 

available, it was captured as a polygon that is associated with the 

point location. The meaning of the deposit footprint is variable. In 

some deposits that were at the resource estimation stage at the time 

of the data compilation, there were often maps showing the extent 

of the estimated resource. In other cases, a grade limit or gradethickness map might be available. Older reports tended to show 

the limit of mineralization.
Mine Sites

A discussion of current and past mining activity is a required 

part of the BLM mineral-assessment reports. Data on mines, both 

active and closed, in the assessment areas were compiled from 

a number of sources to form the Mines data theme. The USGS 

National Mineral Information Center (NMIC) publishes data on 

active mines and mineral processing plants in the United States 

(U.S. Geological Survey, 2005) and provided the 2011 version of 

these data to the SaMiRA project. These data include only mines 

that voluntarily report data to NMIC. In the USMIN project these 

data are augmented by data collected from other sources such as 

the Mine Safety and Health Administration (MSHA) and other 

Federal and State agencies so that as complete an inventory of 

mines as possible could be compiled. Amongst valuable sources of 

data on active mines in the SaMiRA region are State agency data 

for mine permits and BLM and USFS Plans of Operations.

In the State of Nevada, locations of active mines are 

published annually by the Nevada Division of Minerals and the 

Nevada Bureau of Mines and Geology (NBMG) in their Major 

Mines of Nevada Special Publication series. This series provides 

location and production data for most mines in Nevada. Additional 

sources of data were the NBMG maps of mines and energy 

resources (for example, Hess and Davis, 2010). The Nevada 

Department of Environmental Protection provides the locations of 

mining permits on its Web site (http://ndep.nv.gov). The Nevada 

Department of Transportation Material Site Atlas contains the 

locations of gravel and borrow pits (Nevada Department of 

Transportation, 2013).

For Utah, a GIS database of mine permit locations was 

obtained from the Utah Division of Oil Gas and Mining (Utah 

Division of Oil Gas and Mining, 2016). Mine locations are also 

published by the Utah Geological Survey (Bon and Heuscher, 

2008; Bon and Wakefield, 2008).

Mine locations and current status of mine sites in Oregon 

were obtained from permit data from the Oregon Department of 

Geology and Mineral Industries (Oregon Department of Geology 

and Mineral Industries, 2015).

Data on active mines in Wyoming were provided by 

the Land Quality Division of the Wyoming Department 

of Environmental Quality (Wyoming Department of 

Environmental Quality, 2015). Additional information was 

obtained from the Annual Reports of the Wyoming State 

Inspector of Mines (Wyoming Department of Workforce 

Services, 2013, 2014).

Locations of open-cut mines in Montana were obtained 

from the Montana Department of Environmental Quality, 

Open Cut Mining Program (Montana Department of 

Environmental Quality, 2015). Further data were obtained 

from the annual presentations of the Montana Bureau of Mines 

and Geology (for example, McCullogh, 2014) and BLM Plans 

of Operations.

In Idaho, locations of active mines were obtained from 

the annual mineral industry reports of the Idaho Geological 

Survey (for example, Gillerman, 2014), the Idaho Geologic 

Survey aggregate site database (Tate and others, 2015), and 

from BLM and USFS field office personnel.

The attributes for the mines data theme are listed in 

table B3. The data-capture process for mines emphasized 

accurate locations and status data that were as timely as 

possible. Permit data were checked using digital air photos, 

and locations were corrected to the actual site of the mining 

activity. Where applicable, notes on the current level of 

activity, as visible on air photos, were made.

Table B3. Mines data theme attribute fields used for the Sagebrush Mineral-Resource Assessment (SaMiRA) project, Western United 

States.

Field name Description

Name Primary name of the mine.

Other name Other names for the mine.

State State in which the mine is located.

Operator Name of the operator of the mine based on the source data.

Commodity(s) Commodities being mined.

Commodity group Group to which the commodities belong: metallic minerals, nonmetallic and industrial minerals, 

gemstones, stone, sand and gravel, uranium, and coal.

Current status Activity status of the mine—active, inactive (closed), unknown.

Status date Year of the status data.

Remarks Additional data or comments on the data.

References Source(s) of the location and other data for the mine.

Section B. Mineral-Resource Information 17
18 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Active Exploration Sites

BLM mineral-resource assessment guidelines require 

a discussion of current and past exploration activity in the 

assessment areas. The collection of information on the location 

and nature of active mineral-exploration projects in the United 

States was one of the principal components of the USMIN 

data compilation effort before the SaMiRA project. Previously 

collected and newly compiled data for exploration projects within 

the SaMiRA areas were compiled into the Exploration Sites data 

theme. Exploration projects were classed as “active” if data on 

exploration activity within the past 10 years could be found. Key 

sources for the SaMiRA project area were the annual exploration 

reports and other reports of the NBMG, Idaho Geological 

Survey, Utah Geological Survey, Wyoming Geological Survey, 

Oregon Department of Mineral Industries, and Montana Bureau 

of Mines and Geology. Other data were collected from mining 

trade publications, such as the Canadian and American Mines 

Handbook, the Northern Miner, and Mining News.

Additional important sources of information were the 

individual mining company Web sites and technical reports filed 

in the Canadian System for Electronic Document Analysis and 

Retrieval (SEDAR) on-line database (http://www.sedar.com/). 

An extensive review of the Web sites of mining and exploration 

companies had been started in 2013, and this data was used in 

the SaMiRA project. Where Web sites contained information 

on exploration projects, the data were captured by printing to a 

.pdf file. For Canadian companies, National Instrument 43-101 

technical reports (NI 43-101 Reports) were searched for using the 

SEDAR on-line database and company Web sites. These reports 

are a significant source of data on project history, mine production, 

the resources of mineral deposits, and typically also contain a 

description of the property history. Exploration sites were located 

as points and, where available, polygons showing the aerial extent 

of the project or property. “Properties” can be blocks of mining 

claims or exploration target areas. The sites were attributed with 

data on ownership, exploration status, and commodity (table B4).

Mineral Production Data

BLM mineral-assessment reports are required to 

present data on current and past mine production within the 

assessment areas. Production data for mines within the buffer 

zone surrounding the SFAs were compiled from a variety of 

sources. Reported production data were then converted to 

standard units and formatted for presentation in the production 

data theme. This data theme contains a summary of available 

production data, including ore tonnage, value, and (or) 

amounts of commodities produced.

For Nevada, the annual Major Mines of Nevada reports 

published by the Nevada Division of Minerals and NBMG 

contain production data and locations for major mines. 

Production data for past-producing mines were compiled from 

other NBMG reports and company reports. Important sources 

of information included Couch and Carpenter (1943), Lapointe 

and others (1991), Bailey and Phoenix (1944), and Stager 

and Tingley (1988). Production data for past producing mines 

in Idaho was found in Staff Reports of the Idaho Geological 

Survey and in the Idaho Mines and Prospects Database 

(Idaho Geological Survey, 2015). The data in the Mines and 

Prospect database are presented as ranges. For the Production 

data theme, the minimum values in each range were used. 

Significant additional mine production data for Idaho were 

found in Spanski (2004).

Field name Description

Name Primary name of the exploration site.

Other name Other names for the exploration site.

State State in which the exploration site is located.

Operator Name of the operator of the exploration site based on the source data.

Commodity(s) Commodities present at exploration site.

Commodity group Group to which the commodities belong: metallic minerals, nonmetallic and industrial minerals, stone, 

sand and gravel, gemstones, and uranium.

Current status Activity status of the exploration site: active, development, drilling, early, resource, no data, uncertain.

Status date Year of the status data.

Remarks Additional data or comments on the data.

References Source of the location and other data for the exploration site.

Associated polygon Whether or not there is a shape associated with the point (yes/no).

Polygon definition Description of the nature of the polygon.

Table B4. Exploration data theme attribute fields used for the Sagebrush Mineral-Resource Assessment (SaMiRA) project, Western 

United States.
The principal sources of mine production data in Wyoming 

were Gregory and others (2010), Hausel (1986), and the Wyoming 

Mines Inspector annual reports (Wyoming Department of 

Workforce Services, Office of Mine Inspector, 2014). 

NI 43-101 reports are also valuable sources of data for both 

currently active and formerly active mines. For active mines, the 

Web sites and annual reports of the operators were consulted.

Mineral-Resource Data

The BLM mineral-assessment reports are also required to 

contain information on the resources contained in known mineral 

deposits in the assessment area. Data on the resources (tonnage 

and grade) of mineral deposits located in the 25-km buffer zone 

around the SFAs were compiled to develop the Resource data 

theme. This data theme includes summaries of the tonnage and 

grade of mineral deposits for which data were available. For many 

deposits, these data were discovered during the compilation of 

data on active exploration projects. Projects at the resource stage 

frequently present resource data in NI 43-101 reports, which were 

the major source of recent resource estimates. Other sources of 

data included USGS and USBM reports, such as Wilderness Study 

reports and USGS mineral-resource assessment data (for example, 

Spanski, 2004). For the Resource data theme, all categories of 

resources such as “reserves” and “resources” were combined into 

a total tonnage and average grade for each deposit.

Acknowledgments

Many people contributed to the USMIN data compilation 

process. USGS contractors Jesse Bellora, Marie Bartels, 

Stephanie Gallegos, Jeremy Jordan, Kathleen Tureck, and 

Adam Chapman worked on the SaMiRA data compilation. 

Lauren Foiles, Meredith Burger, Ryan Finley, Shauna Bladt, 

Brandon Gill, Chris Karns, Nicole Demontigny, Josef 

Bourgeois, Saige Sanchez, and Sara Hartman worked on the 

USMIN project in prior years and laid the foundation for 

the SaMiRA data. Carma San Juan, Peter Schweitzer, John 

Horton, Stu Giles, Paul Denning, Damon Bickerstaff, and E.G. 

Boyce of the USGS provided abundant technical assistance 

and advice.

Our colleagues in the BLM and USFS kindly reviewed our 

data and shared their on-the-ground knowledge. From the BLM, 

we would like to thank Jeff Clauson, Joe Larsen, Ken Gardner, 

Adam Merril, Rick Deery, Larry Garahana, Deb MacFarland, 

Micheal Jackson, Marilyn Wegweiser, Chris Rye, Jeff Clawson, 

Tim Barnes, and Ricky Wells. From the USFS, we thank Greg 

Graham, Susan Elliott, and Amanda Kriwox. Our colleagues 

and friends with the State geological surveys of Montana, Idaho, 

Wyoming, Utah, Nevada, and Oregon kindly reviewed the 

USMIN data and gave of their unparalleled local knowledge. In 

particular, we thank Clark Niewendorp, Oregon Department of 

Geology and Mineral Industries; Ken Krahulec, Utah Geological 

Survey; John Muntean, Nevada Bureau of Mines and Geology; 

Richard Perry, Nevada Division of Minerals; Wayne Sutherland, 

Wyoming State Geological Survey; and Virginia Gillerman and 

Chris Tate, Idaho Geological Survey. Personnel at numerous other 

State agencies asked only that their agencies and departments be 

acknowledged. These agencies include the Nevada Department 

of Transportation, the Nevada Department of Environmental 

Protection, the Montana Division of Environmental Quality, the 

Utah Division of Lands, and the Wyoming Land Quality Division.

Finally, we would like to thank Mitch Leverette, Rick 

Deery, and Mike Nedd of the Solid Minerals Program of 

the BLM for their leadership in developing the cooperative 

agreement between USGS and BLM.

Mineral Resources Data System (MRDS)

By Peter N. Schweitzer

Several sources of mineral deposit information were used 

for the U.S. Geological Survey (USGS) Sagebrush MineralResource Assessment (SaMiRA) reports. One such data source 

for mine and mineral-district information is available through 

the Mineral Resources Data System (MRDS) (U.S. Geological 

Survey, 2016). MRDS contains global mineral-resource 

occurrence data, most thoroughly within the United States. 

The database contains the records previously provided in the 

Mineral Resource Data System (MRDS) of the USGS and the 

Mineral Availability System/Mineral Industry Locator System 

(MAS/MILS) of the U.S. Bureau of Mines.

MRDS is a large and complex relational database 

developed over several decades by hundreds of researchers 

and collaborators. The content of MRDS records was drawn 

from reports previously published or made available to USGS 

researchers, some of which are no longer available.

The information contained in MRDS reflects the 

limitations of the material used as sources, and its recency 

is that of the date of the source reports. Mining operations 

are continually evolving and global mineral economies 

represent a dynamic flow of information. Consequently, 

MRDS does not reflect up-to-date changes to the operating 

status of mines, ownership, land status, production figures, 

and estimates of reserves and resources or the nature, size, and 

extent of workings. However, the geological characteristics 

of the mineral resource are likely to remain correct and are 

very useful for understanding the deposit type and mineral 

commodities present for the major and many of the smaller 

mines, occurrences, and prospects.

Section B. Mineral-Resource Information 19
20 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Mineral-Resource Data from the USGS 

National Mineral Information Center

By Elizabeth S. Sangine

The Automated Minerals Information System (AMIS) 

database operated by the U.S. Geological Survey (USGS) 

National Minerals Information Center (NMIC) is a large 

and complex database developed over several decades based 

on surveys conducted annually on mineral commodities. 

More than 140 surveys are conducted annually on mineral 

commodities from domestic producers. More than 

18,000 domestic producer and consumer establishments 

voluntarily complete about 40,000 survey forms annually. 

In developing lists of companies to canvass for each of 

the commodities, NMIC specialists monitor the published 

literature, review company reports, review commodityspecific reports prepared by industry, and gather information 

from conferences, field trips, and industry and Government 

contacts.

The NMIC AMIS database has comprehensive mineralcommodity data from the 1980s to the present. Mining 

operations are continually evolving, and AMIS houses both 

historical and current production figures and estimates of 

production. The USGS canvass forms contain a proprietary 

data banner that describes the treatment of the company data 

collected. The proprietary information is considered sensitive 

and usually contains commercially valuable business data, 

such as production figures and consumption projections. 

Before specific statistics can be published, a determination 

must be made as to whether the publication would result 

in the disclosure of proprietary data. In order to publish 

production data, the policy is that there must be three or 

more companies contributing to an aggregated statistic; 

however, if the minerals statistic under consideration does 

have three or more companies but one company contributes 

more than 75 percent of the total, or two companies 

contribute more than 90 percent, then the figure cannot be 

published because the preponderance of the data released is 

considered proprietary.

For the Sagebrush Mineral-Resource Assessment 

(SaMiRA) project, NMIC staff queried the AMIS database 

for active facilities using States and counties with assessment 

areas contained within. A listing of the facility names 

and physical locations, latitudes and longitudes, was 

then provided for mapping against the specific proposed 

withdrawal areas. Specific production figures were not 

provided for these facilities, as that would violate business 

proprietary rules.

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Wilson, A.B., 2014, Uranium in the Wyoming Landscape 

Conservation Initiative Study Area, southwestern Wyoming: U.S. 

Geological Survey Open-File Report 2014–1123, 33 p., 1 plate, 

accessed May 1, 2016, at http://dx.doi.org/10.3133/ofr20141123.

Wilson, A.B., Klein, T.L., and Heran, W.D., 2001, Databases and 

simplified geology for mineralized areas, claims, mines and 

prospects in Wyoming: U.S. Geological Survey Open-File Report 

2001–0497, 17 p., accessed May 1, 2016, at https://pubs.usgs.gov/

of/2001/ofr-01-0497/.

Wyoming Department of Environmental Quality, 2015, A viewer 

of land quality active permits: Wyoming Department of 

Environmental Quality online viewer and database, accessed 

December 23, 2015, at https://gis.deq.wyoming.gov/maps/lqd_

permit_public/index.html.

Wyoming Department of Workforce Services, Office of Mine 

Inspector, 2013, Annual report of the State Inspector of Mines 

for the year 2013: Wyoming Department of Workforce Services, 

115 p., accessed May 18, 2016, at http://wyomingworkforce.

org/_docs/mines/ar/2013.pdf.

Wyoming Department of Workforce Services, Office of Mine 

Inspector, 2014, Annual Report of the State Inspector of Mines 

for the year ending December 31, 2014: Wyoming Department 

of Workforce Services, Office of Mine Inspector, 115 p., 

accessed May 18, 2016, at http://wyomingworkforce.org/_docs/

mines/ar/2014.pdf.
Section C. Geochemical Data

By Steven M. Smith, Karen D. Kelley, Helen W. Folger, Douglas B. Yager, Matthew Granitto, and Stuart A. Giles

Introduction

The geochemical datasets used for the assessments of the 

Bureau of Land Management (BLM) Sagebrush Focal Areas 

(SFA) were compiled from U.S. Geological Survey (USGS) 

geochemical databases and include soil and stream-sediment 

(primarily, but not exclusively, <80 and <100 mesh) samples 

(hereafter referred to as SedsSoils), concentrate fractions 

from sediment and soil samples (hereafter referred to as 

concentrates), and rock samples. The samples were collected 

and analyzed over a period of 50 years from the mid-1960s 

through 2013. After statistical evaluation, selected elements 

(silver, gold, and others) indicative of a wide variety of 

mineral-deposit types were plotted, either as point plots (rock, 

concentrates, and SedsSoils) or interpolated grids (SedsSoils 

only). A summary of the data sources, methods for statistical 

evaluation and determination of threshold values, replacement 

of lower limits of determination (LLD) required for gridding, 

and GIS methods are provided below.

Databases Used to Build the SaMiRA 

Datasets

Multiple USGS databases were evaluated for inclusion in the 

Sagebrush Mineral-Resource Assessment (SaMiRA) geochemical 

datasets. These are listed below with brief descriptions.

NURE-HSSR (collected 1976–1980)

The National Uranium Resource Evaluation (NURE) 

program included a Hydrogeochemical and Stream Sediment 

Reconnaissance (HSSR) task that collected and analyzed more 

than 300,000 sediment and soil samples from Alaska and the 

conterminous United States between 1976 and 1980. These data 

were compiled, reformatted, and released online by Smith (1997) 

and are available from the USGS Mineral Resources On-Line 

Spatial Data Web site (http://mrdata.usgs.gov/nure/sediment). 

The NURE-HSSR samples in the SaMiRA area were collected or 

analyzed under the auspices of three U.S. Department of Energy 

National Laboratories—Oak Ridge Gaseous Diffusion Plant 

(OR), Los Alamos National Laboratory (LA), and Savannah River 

National Laboratory (SR). Because multiple analytical methods 

in different laboratories were used, the NURE-HSSR database 

contains analytical bias between areas covered by each laboratory. 

The NURE-HSSR program was terminated before collection and 

analyses of samples from the entire United States were completed.

NGS (2008 release)

The National Geochemical Survey (NGS) was a USGS 

project tasked with creating complete geochemical coverage of the 

United States at a scale of one sample per 289 square kilometers 

(km2). The project (1) reanalyzed selected NURE-HSSR samples, 

(2) assembled other similar reanalyzed NURE-HSSR sample 

datasets, and (3) collected and analyzed additional samples where 

the NURE program was incomplete. This database was published 

(U.S. Geological Survey, 2004), and the data (as of the 2008 

release) are available from the USGS Mineral Resources On-Line 

Spatial Data Web site (http://mrdata.usgs.gov/geochem).

NGS-NURE

Analytical bias displayed by many elements, due to the 

use of multiple analytical methods and labs, was characteristic 

of the original NURE-HSSR data. The NGS project described 

above was designed to reanalyze approximately 13 percent 

of the available NURE-HSSR samples using a 40-element 

inductively coupled plasma atomic emission spectrometry 

(ICP-AES) (Briggs, 2002) or ICP-MS (Briggs and Meier, 

2002) method. The availability of new analyses by consistent 

methodology creates the possibility to mathematically level 

the NURE-HSSR data and remove most of the analytical bias. 

A review of overlapping analyses revealed that leveling was 

possible for 29 elements (Al, As, Au, Be, Ca, Ce, Co, Cu, Eu, 

Fe, K, La, Li, Lu, Mg, Mn, Mo, Na, Ni, P, Pb, Sc, Sm, Ti, U, 

V, Y, Yb, and Zn; chemical symbols are defined in the front 

matter of this report). A revised NGS-NURE database was 

created by combining the NGS and the leveled NURE-HSSR 

datasets. This process and database is described by Smith and 

others (2015) and the database is currently being prepared for 

release on the USGS Mineral Resources On-Line Spatial Data 

Web site (http://mrdata.usgs.gov/).

NGDB (mid-1960s through 2007)

The National Geochemical Database (NGDB) is a 

compilation of geochemical records from samples collected for 

various USGS projects and analyzed by USGS laboratories from 

the mid-1960s until the present, although currently only data 
24 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

through 2007 have been released. Because samples in the NGDB 

were originally collected and analyzed for multiple purposes, 

there is a large variety of geologic materials (for example, rocks, 

sediments, soils, concentrates), sampling densities, requested 

analytical procedures, and number of elements analyzed. Many of 

these samples came from mineral-resource assessment studies of 

1°×2° quadrangles or BLM Wilderness Study Areas. The NGDB 

also contains reanalyzed NURE-HSSR samples from the NGS 

and other USGS projects. The NGDB rock, soil, sediment, and 

concentrate data (through 2007) are available from the USGS 

Mineral Resources On-Line Spatial Data Web site (http://mrdata.

usgs.gov/ngdb).

NASGLP Soils (2013 data release)

The North American Soils Geochemical Landscape Project 

(NASGLP) collected and analyzed topsoil and C-horizon 

soil from the conterminous United States at a density of 

one sample per 1,600 km2. These samples were collected in 

conjunction with similar projects in Canada and Mexico. The 

use of randomly selected sites within a grid that covered the 

entire conterminous United States makes this an ideal dataset 

to use for the determination of elemental baseline or regional 

background concentrations for U.S. soils. These data were 

published (Smith and others, 2013) and are available from the 

USGS Mineral Resources On-Line Spatial Data Web site (http://

mrdata.usgs.gov/ds-801).

Compilation and Evaluation of Data for 

the SaMiRA Dataset

Data for concentrates, rocks, sediment, and soils were 

extracted exclusively from the NGDB (U.S. Geological Survey, 

2016a–d). The combined dataset for SedsSoils was derived from 

all of the available USGS databases described above. However, 

most records for SedsSoils within the SaMiRA areas were pulled 

from the NGS-NURE database. Additional records were added 

from the NGDB and the NASGLP databases (A-horizon soils only 

because they were more likely to be consistent with the variety 

of other soil samples from other databases). Many samples were 

represented by duplicate records in the NGDB and NGS-NURE 

databases. Considerable effort was made to remove duplication 

and preserve the best information for each of the overlapping 

records. Every record in the SedsSoils database is identified by its 

data source:

1. NASGLP A-Horizon Soils—A-horizon soil records with 

chemistry and sample description information derived from 

the NASGLP database.

2. NGDB SedsSoils-with NGDB BV chemistry—Sample 

records pulled exclusively from the NGDB database with 

“best value” (BV) chemistry (Granitto and others, 2013) as 

described below.

3. NGSNURE-Leveled NURE plus NURE—Records for 

samples collected during the NURE program, analyzed only 

by NURE laboratories. The sample descriptive information 

comes from the NURE-HSSR database (Smith, 1997), 

and the chemistry for 29 leveled elements was obtained 

from the NGS-NURE database of Smith and others (2015). 

Additional chemistry for Ag, B, Ba, Cd, Cr, Cs, Dy, Hf, Nb, 

Rb, Sb, Se, Sn, Sr, Th, W, and Zr was added directly from 

the original NURE-HSSR database.

4. NGS-NURE-with NGS chemistry—Sample records from 

the NGS database that were not found in the NGDB. 

Most of these were NURE-HSSR samples reanalyzed by 

USGS projects using non-USGS commercial or university 

laboratories. The sample descriptive information and the 

chemistry were combined from the NGS-NURE and NGS 

databases.

5. NGSNURE-with NGDB BV chemistry—Sample records 

from the NGS database that were duplicated in the NGDB. 

The sample descriptive information was obtained from the 

NGS-NURE database and the more complete “best value” 

chemistry (Granitto and others, 2013) was added from the 

NGDB.

When compilation of the datasets was complete, records 

were examined to remove samples that were not appropriate 

for the purpose of assessing the mineral potential of the BLM 

SFAs. Examples of samples removed include (1) those that 

were collected at depths greater than 1 meter below the surface 

(primarily drill cores), (2) those identified as mill products (for 

example, tailings, slag), and (3) those with no relevant chemical 

data. Surface samples collected at mine sites were not removed.

The NGDB contains many records with poor coordinate 

precision or accuracy. In the past, it was common to report sample 

coordinates that were less precise than the nearest second of 

latitude or longitude. Although the actual accuracy of a coordinate 

location is dependent on the care given by the submitter and 

cannot be assessed without other information, it is possible to 

assess the apparent coordinate precision, defined as the precision 

level to which a coordinate was reported (for example, nearest 

second, minute, degree, and fraction thereof). The apparent 

reported coordinate precision was determined for every latitude 

and longitude value. Because it is possible that a few coordinates 

in a batch (job) of samples actually did plot on what appears to be 

a less precise coordinate, each sample job was assessed based on 

the best apparent coordinate precision of samples within the batch. 

If coordinates in a job were not provided to the nearest 15 seconds 

or better (±760 feet or ± 0.14 miles), samples were removed. 

After jobs with imprecise coordinates were removed, individual 

samples with poor apparent precision were assessed and, where it 

was evident that precision within a job was not maintained, those 

samples were also removed.

The duplication of samples at single sites was also assessed 

(after removal of samples with poor coordinate precision). 

Some additional jobs or batches of samples were removed 

when it became evident that the submitter had used only a 
single coordinate instead of accurate coordinates for a study. For 

example, samples were removed for a couple of soil surveys, 

known to have been collected on a traverse or grid, when all 

samples had the same single-site coordinates. Several rock 

samples with similar problems were also removed. However, 

within the existing database, a large number of rocks plotting at 

single sites more likely represent multiple sample collections from 

a single locality.

Finally, the analytical values were examined, and a few 

samples were checked against the original laboratory paperwork 

to correct or remove bad values that had been mistakenly entered. 

Another common issue was the use of two or more analytical 

methods on a sample or batch of samples, resulting in multiple 

values for the same element. This situation occurred most commonly 

when more than one multielement analytical package was used 

(typically with the second one containing some of the same elements 

but with better LLDs). To ensure that the most appropriate single 

value for each element was preserved in the database, we used 

the “best value” (BV) method as described by Granitto and others 

(2013). Because of the multitude of analytical methods used on 

these samples, there was also a large variation of LLDs for many 

elements—sometimes greatly exceeding the average crustal 

abundance of that element. For example, the median value for 

tellurium (Te) in the A-horizon soils throughout the conterminous 

United States (Smith and others, 2013) is 0.03 milligrams per 

kilogram (mg/kg) or parts per million (ppm), but the LLDs for Te in 

the SedsSoils database were <0.02, <0.05, <0.1, <0.2, <0.5, <50, and 

<2,000 ppm, whereas the maximum detected value is 1.6 ppm Te. It 

was determined that, in the case of Te, the values of <50 and <2,000 

ppm were not useful for a mineral-resource assessment, and so these 

two LLD values were removed from the data. In summary, two rules 

were applied when determining which of multiple LLDs were not 

useful for the assessment:

1. For elements that were less than 40 percent censored (“censored” indicates values that are less than the LLD, for 

example, <0.5 ppm, which is the LLD in this case), high 

LLDs were removed when they exceeded 2 times the crustal 

abundance or median topsoil value in the United States, as 

determined by Smith and others (2013).

2. For elements that were 40 percent or more censored, two 

additional conservative criteria were applied—(1) the LLD of 

the method or methods with the majority of detected values 

was kept, even if it exceeded two times the estimated crustal 

abundance of the element in that media; and (2) high LLDs 

were not removed if they significantly changed the median 

and upper quartile statistics of the population.

Because heavy-mineral concentrates have undergone a 

concentration factor of 1,000 to 10,000 times the original source 

material (method for obtaining heavy-mineral concentrates is 

described in later section), even seemingly high LLDs can be 

meaningful. No LLD values were removed from the concentrate 

database.

The resulting database for the SaMiRA project is summarized 

in table C1 and distinguished based on sample media type within 

each of the four SFAs. Analyses from a total of 26,343 SedsSoils, 

6,890 rock samples, and 3,717 concentrates were used in this 

evaluation. Data within the Public Land Survey System (PLSS) 

areas were included, as well as within a 25-kilometer (km) buffer 

zone around each SFA in order to incorporate geochemical trends 

that could fall near the edge of the SFAs. The distribution of samples 

is shown in figure C1.

Analytical Methods

The SaMiRA database contains reported values obtained by 

analytical methods provided by multiple laboratories. In general, 

samples were collected and analyzed from the mid-1960s to the 

mid-2000s, and there were significant developments in analytical 

methods during that timeframe. Table C2 lists the analytical 

methods used. The method codes are included as a column in the 

sediment, soil, rock, and concentrate databases.

Table C1. Number of samples listed by sample media type for 

Sagebrush Focal Areas (SFA) studied in the Sagebrush MineralResource Assessment (SaMiRA) project, Western United States.

[SedsSoils, soil and stream-sediment samples] 

SFA SedsSoils Concentrates Rocks

Nevada border1 13,103 1,458 2,552

North-Central Idaho 8,624 1,905 3,765

Wyoming/Utah2 2,293 354 496

Montana 2,323 0 77

Total 26,343 3,717 6,890

1

Includes Sheldon-Hart Mountain National Wildlife Refuge, Southeast Oregon 

and North-Central Nevada, and Southern Idaho and Northern Nevada SFAs.

2

Includes Bear River Watershed of Utah and Southwestern and South-Central 

Wyoming.

Section C. Geochemical Data 25
26 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming 104° 108° 112° 116° 120° 48° 46° 44° 42°124° MONTANA IDAHO OREGON WYOMING WASHINGTON NEVADA UTAH CALIFORNIA North-Central MT BufferWY-UT Buffer North-Central ID Buffer NV Border Buffer Townships that contain proposed withdrawal areas Extent of 25-km buffer around townships USA Contiguous Albers Equal Area Conic projection. Datum: North American Datum 1983. Central Meridian: 114°00' W Latitude of origin: 37.5° N. Standard parallel 1: 29.5° N Standard parallel 2: 45.5° N.

0 100 200 20 40 60 80 MILES

0 100 200 20 40 60 80 KILOMETERS

NV

ID OR

MT

WY

UT

WA

CO CA

Map area

Wyoming-Utahbuffered area

North-CentralIdaho buffered area

Nevada Borderbuffered area

North-Central Montana

buffered area

EXPLANATION

SedSoil sample sitesRock sample sitesConcentrate sample sites

Chapter A Figure C1. Figure C1. Map showing the distribution of all geochemistry sample sites for the Sagebrush Focal Areas (SFA) studied in the Sagebrush Mineral-Resource Assessment (SaMiRA) project, Western United States. See figure A1 for SFA boundaries and names. SedSoil, soil and stream-sediment.
Table C2. Analytical methods used for the Sagebrush Mineral-Resource Assessment (SaMiRA) project soil and stream-sediment 

samples (SedsSoils), concentrate samples, and rock samples.

[NURE, National Uranium Resource Evaluation; DIBK, diisobuytl ketone, an extraction solvent sometimes written as di iso butyl; MIBK, methyl isobutyl ketone, an 

organic solvent; Aliquat 336, trioctylmethylammonium chloride; HF, hydrofluoric acid; other chemical symbols are defined in the front matter of this report]

Analytical 

method code Analytical method description Reference

AA_CV Mercury by cold-vapor atomic absorption spectrometry after multi-acid digestion and solution. Brown and others, 2002

AA_CV_WO Mercury by cold-vapor atomic absorption spectrometry after wet oxidation from multi-acid 

digestion and solution.

Huffman and others, 1972

AA_F_Fuse Major and minor elements by flame atomic absorption spectrometry after LiBO2/Li2B4O7 fusion 

digestion.

Shapiro, 1975

AA_F_HBr Gold and tellurium by flame atomic absorption spectrometry after HBr-Br2 digestion and selective 

organic extraction with Aliquat 336-MIBK.

O’Leary and Meier, 1996

AA_F_HF Major and minor elements by flame atomic absorption spectrometry after multi-acid digestion 

with HF.

Doughten and Grossman, 1993; 

Aruscavage and Crock, 1987

AA_FE Sodium and potassium by flame emission spectrometry (flame photometry) after HF-HClO4

dissolution or LiBO2 fusion.

Fries and others, 1996; Jackson 

and others, 1987

AA_GF_HBr Gold and tellurium by graphite furnace atomic absorption spectrometry after HBr-Br2 digestion 

and selective organic extraction with Aliquat 336-MIBK.

O’Leary and Meier, 1996

AA_GF_HF Arsenic, gold, bismuth, indium, antimony, tellurium and thallium by graphite furnace atomic 

absorption spectrometry after multi-acid digestion with HF and selective organic extraction 

with Aliquat 336-MIBK.

Doughten and Grossman, 1993

AA_GF_ST Thallium by graphite furnace atomic absorption spectrometry after Na2O2 sinter, HCl-HNO3

dissolution, and selective organic extraction with DIBK.

Modified from Doughten and 

Grossman, 1993

AA_HG_Acid Selenium by flow injection or continuous flow hydride generation-atomic absorption spectrometry 

after digestion with HNO3-HCl-H2SO4-KMnO4.

Modified from Doughten and 

Grossman, 1993

AA_HG_HF Arsenic, antimony, selenium and tellurium by flow injection or continuous flow hydride 

generation-atomic absorption spectrometry after multi-acid digestion with HF.

Hageman and others, 2002

AA_HG_ST Arsenic and antimony by flow injection or continuous flow hydride generation-atomic absorption 

spectrometry after Na2O2 sinter digestion.

Modified from Hageman and 

Welsch, 1996

AA_TR Mercury by thermal release and atomic absorption spectrometry after heating (Vaughn-McCarthy 

method).

Ward and others, 1969

AES_Fuse Major and minor elements by inductively coupled plasma-atomic emission spectrometry after 

Li2B4O7 fusion digestion.

Doughten and Grossman, 1993

AES_HF Major and minor elements by inductively coupled plasma-atomic emission spectrometry after 

digestion with HF-HCl-HNO3-HClO4.

Briggs, 2002

AES_HF_REE Rare earth elements by ion exchange and inductively coupled plasma-atomic emission 

quantitative spectrometry after HF-HCl-HNO3-HClO4 digestion.

Lichte and others, 1987

AES_IE Molybdenum, niobium and tungsten by inductively coupled plasma-atomic emission quantitative 

spectrometry after HF-HCl-HNO3-HClO4 digestion and ion exchange separation.

Doughten and Aruscavage, 1996

CB_IRC Carbon and sulfur by infrared detection after combustion. Brown and Curry, 2002a; Brown 

and Curry, 2002b

CB_TC Total carbon and organic carbon by thermal conductivity detection after combustion. Jackson and others, 1987

CB_TT Sulfur by iodometric titration after combustion. O’Leary, 1990

CM_Acid Arsenic by colorimetry after Na2O2 sinter digestion. Brown and others, 1975

CM_Fuse Major and minor elements by colorimetric spectrophotometry after fusion digestion. Shapiro, 1975

CM_HF Vanadium and tungsten by colorimetric spectrophotometry after multi-acid digestion with HF. Wilson and others, 1987

CM_HSF Fluorine by colorimetric spectrophotometry after H2SiF6 digestion and chemical separation. Shapiro, 1975

CM_ST Chloride by colorimetric spectrophotometry after Na2CO3 and ZnO sinter digestion. Jackson and others, 1987

CP Organic carbon, carbonate carbon and totals by computation. Jackson and others, 1987

DN Uranium and thorium by delayed neutron activation counting. Knight and McKown, 2002

Section C. Geochemical Data 27
28 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Analytical 

method code Analytical method description Reference

EDX Minor elements by energy-dispersive X-ray fluorescence spectrometry. Siems, 2002

ES_Q Major and minor elements by quantitative emission spectrography. Golightly and others, 1987

ES_SQ Major and minor elements by semi-quantitative emission spectrography. Skeen and Crandell, 1989; 

Adrian and others, 1996

FA_DC Gold by direct current plasma-atomic emission spectroscopy or atomic absorption 

spectrophotometry after PbO fire assay chemical separation.

Modified from Wilson and 

others, 1987

FA_MS Platinum-group elements by inductively coupled plasma-mass spectrometry after NiS fire assay 

chemical separation.

Meier and others, 1996

FL_HF Uranium by fluorimetry after multi-acid digestion with HF. O’Leary and Meier, 1986

GRC Uranium by gamma counting. Grimaldi and others, 1954

ISE_Fuse Fluoride by ion specific electrode after fusion digestion. O’Leary and Hopkins, 1990; 

Pribble, 1996

ISE_HF Chloride by ion specific electrode after fusion digestion or multi-acid digestion with HF. Aruscavage, 1996

MS_HF Major and minor elements by inductively coupled plasma-mass spectrometry after HF-HClHNO3

-HClO4 digestion.

Briggs and Meier, 2002

MS_ST_REE Rare earth elements by inductively coupled plasma-mass spectrometry after Na2O2 sinter 

digestion.

Meier and Slowik, 2002

NA_LC Major and minor elements by long count instrumental neutron activation analysis. Budahn and Wandless, 2002b

NA_REE Rare earth elements by long count instrumental neutron activation analysis. Wandless, 1987

NA_SC Major and minor elements by short count instrumental neutron activation analysis. Budahn and Wandless, 2002a

NURE-LA2 Minor elements by energy-dispersive X-ray fluorescence spectrometry, from NURE program, Los 

Alamos National Laboratory.

Grimes, 1984

NURE-LA3 Minor elements by energy-dispersive X-ray fluorescence spectrometry, from NURE program, Los 

Alamos National Laboratory.

Grimes, 1984

NURE-LA5 Major and minor elements by long count instrumental neutron activation analysis, from NURE 

program, Los Alamos National Laboratory.

Grimes, 1984

NURE-Level Major and minor elements in NURE sediment and soil samples, leveled for the conterminous 

United States to eliminate laboratory and analytical method bias, multiple analytical methods 

used per element.

Smith and others, 2015

NURE-OR7 Major and minor elements by inductively coupled plasma-atomic emission spectrometry after 

digestion with HF-HCl-HNO3-HClO4, from NURE program, Oak Ridge Gaseous Diffusion 

Plant.

Grimes, 1984

NURE-OR8 Arsenic and selenium by flow injection or continuous flow hydride generation-atomic absorption 

spectrometry after multi-acid digestion with HF, from NURE program, Oak Ridge Gaseous 

Diffusion Plant.

Grimes, 1984

NURE-ORSN Tin by flame atomic absorption spectrometry after multi-acid digestion with HF, from NURE 

program, Oak Ridge Gaseous Diffusion Plant.

Grimes, 1984

NURE-SR2 Major and minor elements by long count instrumental neutron activation analysis, from NURE 

program, Savannah River Laboratory.

Grimes, 1984

NURE-SR3AA Major and minor elements by flame atomic absorption spectrometry after digestion with 

HF-HNO3-HClO4, HNO3-HClO4, or K2S2O7 fusion, from NURE program, Savannah River 

Laboratory.

Grimes, 1984

NURE-SR3CA Phosphorus, niobium and tungsten by colorimetry after HF-HNO3-HClO4 digestion (P) or K2S2O7

fusion (Nb-W), from NURE program, Savannah River Laboratory.

Grimes, 1984

NURE-SR3XX Arsenic and selenium by flow injection or continuous flow hydride generation-atomic absorption 

spectrometry after multi-acid digestion with HF (?), from NURE program, Savannah River 

Laboratory.

Grimes, 1984

WDX_Fuse Major and minor elements by wavelength-dispersive X-ray fluorescence spectrometry after LiBO2

fusion digestion.

Taggart and Siems, 2002

Table C2.—Continued
Statistical Summaries

Elements of most interest for the mineral assessment 

include Ag, As, Au, Be, Bi, Ce, Co, Cr, Cu, Dy, Ga, Ge, Hg, La, 

Li, Mn, Mo, Nb, Ni, Pb, Re, platinum-group elements (Ir, Os, 

Pd, Pt, Rh, and Ru), Sb, Sn, Te, Th, Tl, U, V, W, Y, Yb, and Zn, 

many of which are pathfinder elements for a variety of deposit 

types known to occur within or near one or more of the SFAs. 

Summary statistics were calculated for these elements in each 

of the three media types (SedsSoils, concentrates, and rocks). 

Distribution diagrams (histograms and boxplots) were constructed 

(for example, fig. C2) based only on the samples with values 

greater than the LLD, that is, uncensored values). This interval 

was selected to identify and evaluate the range of values that can 

reflect enrichment in these particular pathfinder elements. For 

the SedsSoils and rock databases, we also calculated minimum, 

maximum, and median values (for uncensored data). The four 

upper threshold values (determined by methods described below) 

are shown on each boxplot/histogram diagram, and are consistent 

with those used to create the point plots and grid maps.

Determination of Threshold Values for SedsSoils 

and Rocks

The purpose of geochemistry in mineral-resource 

assessments is to determine concentrations of elements Copper, in parts per million

0

Count

1,000 2,000 3,000

1,000

10

1

Median 25% to 75%

Outliers

T1

T2

T3

T4

Number of samples

Minimum

Maximum

Median

No. censored

No. uncensored

Total analysed

Percentage of censored

values (of total analyzed)

10,051

1

907

26

26

10,051

10,077

0.3

Figure C2. Example diagram showing 

copper concentrations in parts per 

million (ppm) in stream-sediment and 

soil samples (SedsSoils) from the 

Sheldon-Hart Mountain National Wildlife 

Refuge, Southern Idaho and Northern 

Nevada, and Southeastern Oregon 

and North-Central Nevada Sagebrush 

Focal Areas (see section A, fig. A1). The 

histograms and boxplot diagrams and 

median are based on uncensored (above 

lower limits of determination, LLD) data 

only, but the percentage of censored 

data is shown in statistics table in the 

diagram (N, number). T1, T2, T3, and 

T4 are the threshold values (see text 

for description). T1 = 2–3× background 

(green line), T2 = 4–7× background 

(yellow line), T3 = 8–15× background 

(orange line), and T4 = >16× background 

(red line). %, percent.

that are relatively high compared to a threshold value (and 

thus, could potentially record proximity to mineral deposits 

containing those elements). Methods for determination of 

threshold values for a given dataset are varied, and it is 

critical to use one that is best suited for the goal of assessing 

mineral potential. Calculation of percentile values is a 

common method, and doing so will always produce element 

classes that are “anomalous” (for example, >90th percentile) 

with respect to the dataset as a whole; however, the absolute 

concentrations of an element in samples represented by these 

>90th percentile classes may not always be high (and thus, 

potentially not reflective of mineral deposits). Such false 

anomalies are not always meaningful for mineral-resource 

assessments. Hence, we chose a method that is consistent 

across all of the SFAs and would not elevate any element to 

anomalous status without justification. To do this, we used 

estimates of natural element abundance (described below) 

as the basis for classifying element concentrations. For 

SedsSoils, we primarily used the median value for A-horizon 

soils determined from samples collected throughout the 

entire conterminous United States (Smith and others, 

2013). For rocks, we primarily used the crustal abundance 

estimates, also known as the Clarke Index, compiled by 

Fortescue (1992). For a few elements, it was necessary to 

obtain abundance values from other sources. Table C3 lists 

the abundance values (expressed in parts per million unless 

mentioned otherwise) used for SedsSoils and rocks.

Section C. Geochemical Data 29
30 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Table C3. Abundance values for stream-sediment and soil samples (SedsSoils) and rocks used in the Sagebrush Mineral-Resource 

Assessment (SaMiRA) project.

[All values in parts per million (ppm) unless otherwise noted; wt.%, elements reported in weight percent; chemical symbols are defined in the front matter of this report]

Sediments and Soils1 Rocks2

Element Abundance Element Abundance Element Abundance Element Abundance

Ag3 0.27 Sc 6.1 Ag 0.08 Mo 1.2

Al wt.% 4.71 Se 0.2 Al wt.% 8.36 Na wt.% 2.27

As 5.2 Sm3 3.96 As 1.8 Nb 20

Au4 0.004 Sn 1.3 Au 0.004 Nd 39.6

B5 26 Sr 122 B 9 Ni6 75

Ba 512 Ta3 0.68 Ba 390 P wt.% 0.112

Be 1.3 Te3 0.03 Be 2 Pb 13

Bi 0.16 Th 7.7 Bi6 0.17 Pd 0.015

Ca wt.% 0.74 Ti wt.% 0.24 Br 2.5 Pr 9.1

Cd 0.2 Tl 0.4 Ca wt.% 4.66 Pt 0.0005

Ce 51.7 U 2 Cd 0.16 Rb 78

Co 7.8 V 54 Ce 66.4 Re 0.0007

Cr 31 W 0.8 Cl 126 Rh 0.0002

Cs3 3.71 Y 14.5 Co 29 Ru 0.001

Cu 14.8 Yb3 1.99 Cr 122 S wt.% 0.034

Dy3 3.42 Zn 59 Cs 2.6 Sb 0.2

Eu3 0.77 Zr5 180 Cu 68 Sc 25

Fe wt.% 1.99 Dy 5 Se7 0.15

Ga 11.2 Er 3.46 Sm 7.02

Hf3 5.55 Eu 2.14 Sn 2.1

Hg 0.02 F wt.% 0.0544 Sr 384

K wt.% 1.5 Fe wt.% 6.22 Ta 1.7

La 25.7 Ga 19 Tb 1.18

Li 20 Gd 6.14 Te 0.004

Lu3 0.3 Ge 1.5 Th 8.1

Mg wt.% 0.46 Hf 2.8 Ti wt.% 0.632

Mn wt.% 0.05 Hg 0.086 Tl 0.72

Mo 0.78 Ho 1.26 Tm 0.5

Na wt.% 0.69 In 0.24 U 2.3

Nb 8.6 Ir 0.000002 V 136

Nd3 20.8 K wt.% 1.84 W 1.2

Ni 13.8 La 34.6 Y 31

P wt.% 0.055 Li 18 Yb 3.1

Pb 17.8 Lu 0.54 Zn 76

Rb 65.8 Mg wt.% 2.764 Zr 162

Sb 0.57 Mn wt.% 0.106

1

Sediment and soil abundance values from A-horizon median values of Smith and others (2013) unless otherwise noted.

2

Rock crustal abundance values from Fortescue (1992) Clarke Index unless otherwise noted.

3

Salminen and others (2005) topsoil median.

4

Fortescue (1992) Clarke index.

5

Shacklette and Boerngen (1984).

6

Taylor (1964).

7

Gao and others (1998).
To map abundances in terms of classified ranges, the 

following scheme was used: background range was determined 

to be between 0.5× and 1.5× the abundance value; 2× background 

is the range from 1.5× to 2.5× abundance; 3× background is the 

range from 2.5× to 3.5× abundance, and so on. Classification 

ranges or multiples of background for each element were grouped 

in a pseudo-logarithmic scale of <background, background, 2–3× 

background, 4–7× background, 8–15× background, and >16× 

background. The thresholds (T1, T2, T3, and T4) between the 

upper four classification ranges were then assigned the values 

of 1.5×, 3.5×, 7.5×, and 15.5× abundance, respectively. These 

thresholds are indicated by colored lines on histograms and 

boxplots (fig. C2). 

Determination of Threshold Values for 

Concentrates

Many USGS mineral-resource assessment projects used 

concentrate samples that were derived from samples of stream 

sediment, soil, and less commonly, rock. These concentrates were 

processed by a variety of methods to concentrate the heavymineral fraction. These techniques commonly enhanced the 

concentration of selected minerals from 1,000 to more than 10,000 

times their concentration in the original material and permitted 

the determination of elements in some samples that could not 

otherwise be detected.

Almost all concentrates were initially processed by panning 

the sample with a gold pan to remove clay, organic material, and 

the majority of lighter density minerals (primarily quartz and 

feldspar). A sample prepared to this point is known as a panned 

concentrate. Some of these panned concentrate samples were 

not processed further before geochemical analysis. Alternately, 

a panned concentrate might have had magnetite removed with 

a hand magnet before submittal. A larger proportion of panned 

concentrate samples were taken to the laboratory and processed by 

a heavy liquid, usually bromoform, which concentrated minerals 

with specific gravities of greater than about 2.8. This was usually 

followed by an electromagnetic separation (Frantz Isodynamic 

Separator) to create three magnetic splits of the heavy-mineral 

sample—(1) strongly magnetic minerals (C1 fraction), primarily 

magnetite and ilmenite; (2) weakly magnetic minerals (C2 

fraction), including most of the iron and manganese oxides and 

ferromagnesian silicates; and (3) very weakly to nonmagnetic 

minerals (C3 fraction), primarily consisting of zircon, apatite, 

and titanite but also including many ore-related oxide and sulfide 

minerals. The C3 fraction, commonly referred to as a nonmagnetic 

heavy-mineral concentrate, was commonly analyzed. The C1 and 

C2 fractions were occasionally analyzed.

Unfortunately, much of this concentrate processing 

information was not stored in the USGS geochemical databases. 

These older databases have now been combined into the 

NGDB, and a large, but still incomplete, effort has been made to 

distinguish various types of concentrates in the data. Therefore, 

the SaMiRA concentrate database contains a mixture of all of 

these types of concentrates. Thus, the data cannot be treated 

as a consistent sample medium but must be interpreted as a 

secondary source of information in areas that contain enhanced 

concentrations of elements of interest.

Unlike sediments, soils, or rocks, there are no relevant 

databases or crustal abundance estimates for concentrates that 

can be used to create classes of values by element. Using the 

SaMiRA concentrate data alone, we classified the data based 

on percentiles for the entire population (including values 

below lower detection limits) for each element. The chosen 

percentile classes for plotting concentrate data were as follows: 

not detected; <25th percentile; 25–50th percentile; 50–75th 

percentile; 75–90th percentile; 90–97.5th percentile; and 

>97.5th percentile. These seven classes allowed us to use the 

same colored dot symbols that we used for the Sediment/Soil 

and Rock geochemistry layers. Some highly censored elements, 

like Ag only had three classes—not detected, 90–97.5th 

percentile, and >97.5th percentile. Four elements (As, Au, Cd, 

and Sb) were so extremely censored that we had to modify these 

classes slightly to Not Detected, 97.5–99th percentile, and >99th 

percentile. Two elements (Ti and Zr) had so many “greater 

than” values that we could not distinguish the upper end of the 

spectrum and had to make the last class as >75th percentile.

Interpolated Geochemistry Grids

Before gridding, samples with elemental concentrations 

below the LLD were replaced with an arbitrary value of 1⁄2 the 

lowest measured concentration. For some samples the LLDs 

were too high to be meaningful and those samples values were 

replaced with null values.

Geochemical data were gridded using an inverse distance 

weighted (IDW) algorithm and Geosoft MontajTM software. 

The data were projected to the Albers equal-area conic with 

the datum of NAD 83 and a central meridian of −114° before 

gridding. The parameters used for IDW are (1) grid cell size: 1 

km; (2) weighting power: 2; (3) weighting slope: 1; (4) search 

radius: 4 km; (5) blanking distance: 4 km; (6) cells to extend 

beyond data: 0; (7) log option: linear; and (8) log minimum: 

1. The grids were converted from Geosoft file (.grd) formats 

to Arc View Binary Grid (.flt) formats before being imported 

into an ArcGIS version 10.3.1 geodatabase. A typical sample 

would be located in the center of a 1-km2 cell, and the gridding 

algorithm searched 4 km around this unit cell for neighboring 

samples (fig. C3). The value of neighboring samples influenced the values in the surrounding cells according to the distances from each unit cells. When more than one sample was 

located within a single cell, the algorithm took the average of 

the values for the unit cell value.

In ArcGIS, the grids were classified into six intervals 

based on elemental abundance concentrations of soils (tables 

C3 and C4). These intervals were ranked and colored in order 

of increasing concentration from blue to red. A buffer area 

extending 25 km outside of the study area was included to 

capture any trends that could exist near the PLSS boundaries. 

Section C. Geochemical Data 31
32 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

The IDW grids, when combined with dot plots, yield a stable 

backdrop for comparing the different focal areas and for 

assessing areas that appear anomalous.

Geographic Information Systems and 

Symbolized Layers

To calculate spatially accurate sample locations and grids, all 

sample-site coordinates must be in a single geographic coordinate 

system. Sample sites with coordinates that were not already in the 

World Geodetic System of 1984 (WGS84) were selected by existing 

projection and exported into a working geographic information 

system (GIS) (Esri ArcGIS 10.3.1) as feature classes. The data in 

a particular projection were loaded into an ArcGIS map document 

with a WGS84 coordinate system and then had WGS84 coordinates 

calculated and appended to the data using the Xtools Pro for ArcGIS 

11.1 extension. The new WGS84 coordinates were then extracted 

from the various sub-datasets and merged back into the Microsoft 

Access data tables. When all WGS84 coordinates were added, and 

the data collection, selection, and geochemistry preparation were 

Search radius = 4 km Sample site

IDW Grid Cell

1 km

1 km

Chapter A Figure C3.

Figure C3. Diagram showing dimensions of inverse distance weighted (IDW) grid cell used for 

geochemical data in the Sagebrush Mineral-Resource Assessment (SaMiRA) project. km, kilometer.

complete, the data were assembled into final Access database tables 

for conversion into the project GIS.

After the geochemistry geodatabases were constructed 

and the feature classes, tables, and prediction grids were 

generated, the elements for each sample media type were 

classified (binned into ranges) and symbolized according to 

class divisions determined for each element. See previous 

discussions on determination of threshold values for details on 

class divisions.

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Taylor, S.R., 1964, The abundance of chemical elements 

in the continental crust—A new table: Geochimica et 

Cosmochimica Acta, v. 28, no. 8, p. 1273–1285.

U.S. Geological Survey, 2004, The National Geochemical 

Survey; database and documentation, version 5.0 (2008): 

U.S. Geological Survey Open-File Report 2004–001, 

accessed March 15, 2016, at http://mrdata.usgs.gov/

geochem/doc/home.htm.

U.S. Geological Survey, 2016a, National Geochemical 

Database—Concentrate: U.S. Geological Survey Web site, 

accessed July 14, 2016, at http://mrdata.usgs.gov/ngdb/

concentrate.

U.S. Geological Survey, 2016b, National Geochemical 

Database—Rock: U.S. Geological Survey Web site, 

accessed July 14, 2016, at http://mrdata.usgs.gov/ngdb/rock.

U.S. Geological Survey, 2016c, National Geochemical 

Database—Sediment: U.S. Geological Survey Web site, 

accessed July 14, 2016, at http://mrdata.usgs.gov/ngdb/

sediment.

U.S. Geological Survey, 2016d, National Geochemical 

Database—Soil: U.S. Geological Survey Web site, accessed 

July 14, 2016, at http://mrdata.usgs.gov/ngdb/soil.

Wandless, G.A., 1987, Radiochemical neutron activation 

analysis of geologic materials, in Baedecker, P.A., ed., 

Methods for geochemical analysis: U.S. Geological Survey 

Bulletin 1770, p. J1–J8, accessed March 15, 2016, at http://

pubs.er.usgs.gov/publication/b1770.

Ward, F.N., Nakagawa, H.N., Harms, T.F., and VanSickle, 

G.H., 1969, Atomic-absorption methods of analysis useful 

in geochemical exploration: U.S. Geological Survey 

Bulletin 1289, p. 41–42, accessed March 15, 2016, at http://

pubs.er.usgs.gov/publication/b1289.

Wilson, S.A., Kane, J.S., Crock, J.G., and Hatfield, D.B., 

1987, Chemical methods of separation for optical emission, atomic absorption spectrometry, and colorimetry, in

Baedecker, P.A., ed., Methods for geochemical analysis: 

U.S. Geological Survey Bulletin 1770, p. D1–D14, accessed 

March 15, 2016, at http://pubs.er.usgs.gov/publication/

b1770.

Section C. Geochemical Data 35

Section D. Geophysical Data and Methods Used in MineralResource Assessments within the Sagebrush Focal Areas

By Eric D. Anderson and David A. Ponce

Introduction

Geophysical investigations help assess the mineralresource potential of the Sagebrush Focal Areas (SFAs) in parts 

of Idaho, Montana, Nevada, Oregon, Utah, and Wyoming. 

Magnetic, gravimetric, and radiometric methods help map 

variation in the physical and geochemical properties of rocks 

both at and near the Earth’s surface. Thus, publically available 

datasets have been described, processed, and interpreted to help 

provide a better understanding of the mineral-resource potential 

of the SFAs. Magnetic and gravity data transforms, including 

reduction-to-the-pole, total horizontal gradient, first vertical 

derivative, tilt derivative, and analytic signal were applied 

to facilitate interpretation. Similarly, radiometric data were 

ratioed to help further discriminate the radiogenic variations/

compositions of surface material.

Magnetic data sources include existing compilations, 

both at the national- and State-scale, as well as individual 

survey datasets. The data provide information on the lateral 

distribution of magnetic material within the Earth’s crust, 

and in all SFAs these data were most effective for mapping 

plutonic rocks that could be associated with mineral systems. 

Magnetic data were also used to provide depth estimates 

to magnetic sources and showed that in Montana magnetic 

sources are likely too deep to be of interest for mineral 

extraction.

Gravity data from national-scale compilations are 

relatively coarse over the SFAs, thereby making them less 

useful for mapping lateral changes in rock types. These data 

are more effective for understanding basin thickness within 

the Basin and Range Province. Gravity inversions provide 

an estimate of the thickness of low-density basin fill, thereby 

helping to map depth to bedrock that could host mineral 

resources beneath basin fill.

Radiometric data provide information on the distribution 

of potassium, thorium, and uranium at the Earth’s surface. 

Changes in the relative abundances of these elements can 

reflect rock types or hydrothermal alteration that could 

be associated with mineral deposits. In the SFAs, the 

radiometric data complemented geologic maps and helped 

differentiate subtle changes in rock compositions. Geophysical 

investigations of the Sagebrush Mineral-Resource Assessment 

(SaMiRA) focal areas are part of an interagency effort by 

the U.S. Geological Survey (USGS) and Bureau of Land 

Management (BLM) to help characterize the mineral resources 

of parts of Idaho, Montana, Nevada, Oregon, Utah, and 

Wyoming. The seven Sagebrush Focal Areas (SFAs) are Bear 

River Watershed, North-Central Idaho, North-Central Montana, 

Southeastern Oregon and North-Central Nevada, Sheldon-Hart 

Mountain National Wildlife Refuge Complex, Southern Idaho 

and Northern Nevada, and Southwestern and South-Central 

Wyoming. For the purpose of geophysical data interpretation, 

the seven SFAs have been grouped into four areas based 

on proximity to each other. The areas and contained SFAs 

include (1) Area A: Sheldon-Hart Mountain National Wildlife 

Refuge Complex, Southeastern Oregon and North-Central 

Nevada, and Southern Idaho and Northern Nevada; (2) Area 

B: North-Central Idaho; (3) Area C: Bear River Watershed 

and Southwestern and South-Central Wyoming; and (4) Area 

D: North-Central Montana. This report section describes the 

geophysical methods, datasets, and analyses used to aid in the 

mineral-resource assessment of the SFAs.

Geophysical methods map geologic materials that have 

differing physical and (or) geochemical properties. In this 

study, the geophysical methods used magnetic, gravity, and 

radiometric data, which reflect variations in magnetization, 

density, and radioactivity, respectively. The geophysical 

methods are most effective where the rock properties vary 

considerably. Physical property variation can occur along 

and across geologic structures, across rock type contacts, 

or within a mineral deposit. For example, (1) structures that 

juxtapose differing rock types can show changes in physical 

properties; (2) structures can provide pathways for reactive 

hydrothermal fluids that can alter the physical properties of 

rocks; (3) the distribution of igneous rocks, both intrusive 

and extrusive, can lead to abrupt physical property changes; 

(4) sedimentary-rock layers within basins can have differing 

physical properties as a function of lithology; (5) the physical 

properties of a sedimentary-rock cover as a whole can differ 

from the underlying basement; (6) metamorphic rocks can 

have different physical properties; (7) hydrothermal fluids 

within, and surrounding, a mineral deposit can alter the host 

rock physical properties; and (8) mineral deposits themselves 

can have physical properties that contrast with the surrounding 

host rocks. Geophysical methods take advantage of these 

changes in the rock properties and can help identify the 

structures, host rocks, and hydrothermal systems that may be 

associated with ore deposit formation.
38 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Qualitative interpretation of magnetic and gravity 

anomalies helps produce a geology map based on anomaly 

patterns. The resultant maps can assist with identifying nearsurface favorable lithology or structures that host mineral 

deposits. Digital enhancements of these data can further 

facilitate interpretations. Enhancements include mathematical 

filters, or transforms, which can highlight areas of contrasting 

physical properties at both shallow and deep crustal levels. 

A gradient, or derivative, filter is commonly employed to 

emphasize changes in the dataset that may represent a geologic 

contact between bodies of contrasting physical properties. 

Filters can highlight anomalies of certain frequencies, or 

wavelengths, within the data that may represent a particular 

lithology or source depth. High-pass filters enhance the higher 

frequency, or short-wavelength, component of the dataset 

that generally corresponds to shallow sources. In contrast, a 

low-pass filter will highlight the lower frequency, or longwavelength, component of the dataset that may correspond to 

deeper sources.

Quantitative interpretation of magnetic and gravity 

anomalies, such as forward and inverse mathematical models, 

seeks to better understand the distribution of physical 

properties at depth. Depth to magnetic and gravity sources can 

be estimated to help develop a three-dimensional framework 

for subsurface geology. Such interpretations help to assess for 

mineral resources that are under cover.

Geophysical Methods

Magnetic and Gravity

Magnetic and gravity methods, commonly referred 

to as potential-field methods, have been used for geologic 

mapping and mineral-resource assessments (Grant, 1985; 

Hinze, 1985; Blakely, 1995; Clark, 1997; 1999; Nabighian 

and others, 2005a, b). They can provide a nearly continuous 

set of observations over large areas. Magnetic and gravity data 

are collected and processed in such a way that they reflect 

lateral changes in subsurface magnetization and density, 

respectively. Because the known spectrum of rock types 

can have several orders of magnitude variation in magnetic 

properties and can vary in density by about a factor of two, 

magnetic and gravity data provide powerful subsurface 

mapping tools. Gravity data are typically more difficult to 

process because effects not related to geology have to be 

removed. Such effects include the tidal attraction of the Moon 

and Sun, instrument drift, changes in gravity with elevation, 

changes in gravity with latitude, the Earth’s curvature, and 

the surrounding topographic terrain. Magnetic data are simply 

corrected for diurnal variations in the Earth’s magnetic field, 

magnetic effects of the aircraft (if applicable), and a regional 

geomagnetic model of the Earth.

Magnetic data provide information on the distribution of 

magnetic minerals, mainly magnetite, within the crust. These 

data can be used to map areas of magnetite variability within 

a hydrothermal system or more commonly to map magnetic 

patterns and trends that may reflect differing rock types and 

structures proximal to mineral deposits. Magnetic anomalies 

are caused by two different kinds of magnetism—induced 

and remanent. The induced component is mostly determined 

by magnetic susceptibility of the rock and is proportional 

to the magnetic field in which it is measured. The remanent 

component depends on the thermal, mechanical, and magnetic 

history of the rock and is independent of the field in which 

it is measured. In general, but not exclusively, the induced 

component is predominant, especially for Cenozoic volcanic 

rocks. Magnetic anomalies measured on rocks that carry 

significant remanent magnetization not aligned with the 

inducing field can be difficult to interpret.

Gravity data provide information on variations in 

subsurface rock density. In general, igneous and metamorphic 

rocks have higher densities than sedimentary rocks. For igneous 

rocks, increasing density tends to be negatively correlated 

with silica content. Thus, felsic rocks have low densities, 

intermediate rocks have moderate densities, and mafic and 

ultramafic rocks have highest densities. For sedimentary 

rocks, evaporites generally have low densities, siliciclastics 

have moderate densities, carbonates have high densities, and 

iron formations tend to be most dense. Gravity anomalies 

are centered over the source body and, similar to magnetic 

anomalies, will broaden with increasing distance from the 

source body.

Radiometric

The radiometric method measures gamma radiation 

intensities from the radioactive decay of potassium (K), 

thorium (Th), and uranium (U) within the upper few 

centimeters of the Earth’s surface (Dickson and Scott, 

1997). Intensities can then be converted into elemental 

concentrations. These elements are the three most abundant 

radioactive elements present in various proportions in all 

rocks and soils. A measured intensity value from airborne 

data is an average element concentration over a surface area, 

the areal extent of which is determined by the altitude of the 

aircraft. Radiometric data are calibrated and corrected for 

instrument spikes, cosmic background, and height-related 

scattering. Airborne radiometric data are interpreted in terms 

of surface chemistry and presented as individual element 

maps or the ratio of two elements that aid the recognition of 

lithologic units. Linear features within the data may indicate 
the presence of faults, or structures, which can be favorable 

for mineral-deposit types. In general, felsic igneous rocks 

have higher radioelement concentrations than mafic rocks; 

whereas the radioelement concentration in sedimentary rocks 

reflects the parent source rocks (Dickson and Scott, 1997).

Geophysical Data

The magnetic, gravity, and radiometric data assembled 

for the mineral-resource assessments within the SFAs 

are derived from publically available databases. For each 

compiled dataset, several basic data-processing steps were 

conducted. Each dataset was projected into a common map 

projection (Albers equal-area conic with central meridian 

of −114.0° longitude). The final processed datasets were 

subset to remove all data outside of regions that encompass a 

25-kilometer (km) buffer surrounding the SFAs.

The U.S. Department of Energy as part of the 

National Uranium Resource Evaluation (NURE) program 

systematically collected airborne radiometric and magnetic 

data across the United States. The primary goal for the 

program was to identify uranium resources, and thus the 

airborne surveys were optimized for radiometric data 

collection. The airborne NURE datasets provide the most 

comprehensive radiometric and magnetic data coverage over 

the SFAs (Duval, 1999; Hill and others, 2009) and are the 

framework for the magnetic and radiometric compilations 

described below.

Aeromagnetic Data

Aeromagnetic data available as individual surveys 

and existing compilations were used to help understand 

the geologic setting and associated mineral deposits within 

the SFAs. The existing compilation that covers the United 

States, Canada, and Mexico has relatively low resolution 

of 1,000-meter (m) grid cells (Bankey and others, 2002), 

whereas the individual State compilations have higher 

resolution of 500-m grid cells (for example, Montana: 

McCafferty and others, 1998; Nevada: Kucks and others, 

2006; Oregon: Roberts and others, 2008; and Wyoming: 

Kucks and Hill, 2000). The individual aeromagnetic survey 

datasets, available from the USGS Mineral Resources 

On-Line Spatial Data Web site (http://mrdata.usgs.gov/), 

exist in two forms—(1) digital, where original flight-line 

data are digitally preserved or (2) digitized, where analog 

contour maps have been digitized (no flight-line data are 

available). The individual surveys were designed for many 

purposes; as such their coverage varies considerably in both 

areal extent and anomaly resolution (fig. D1). In the focal 

areas, the flight-line spacing ranges from less than about 

800 m to about 8,000 m. The flight-line height ranges from 

about 120 m above ground to 3,960 m barometric elevation. 

Thus, most of the focal areas have low spatial and anomaly 

resolution. Because of low resolution, shallow magnetic 

sources of limited areal extent may not be well resolved in 

some parts of the aeromagnetic maps. Thus, these datasets 

are not adequate to map individual mineral deposits that have 

limited areal extent; instead these data are more useful for 

imaging the regional geologic framework within which the 

mineral resources occur.

The national-scale magnetic compilation data covering 

the study area were obtained from the magnetic anomaly 

map of North America (Bankey and others, 2002). In this 

compilation, all survey data were reduced using industry 

standard techniques (Luyendyk, 1997). The data were corrected 

for the Earth’s magnetic field and diurnal variations, upward 

or downward continued to a common datum of 305 m above 

the topography, and merged to produce a uniform anomaly 

map with grid spacing of 1,000 m. The resultant total magnetic 

intensity anomaly data (fig. D2) were the initial dataset from 

which subsequent data transforms, described below, were 

derived (table D1).

In addition, the individual surveys that encompass the 

focal areas were used to generate relatively high-resolution 

compilations with grid cell spacing of 500 m for the SFAs. 

The surveys within and surrounding the SFAs were assessed 

for quality, and the best available datasets were used to 

generate new, higher resolution compilations (table D2). The 

survey specifications varied considerably with flight-line 

spacing between 800 and 8,000 m and a range in flight-line 

altitude from 120 m above ground to 3,960 m barometric 

elevation. The NURE data were collected at low altitudes 

along relatively widely spaced flight lines. Such a survey 

geometry can cause problems when gridding flight-line data 

over magnetic sources. Artifacts can be introduced into the 

data in the form of lineations perpendicular to flight lines. 

To reduce these artifacts, the NURE flight-line data were 

continued to 305 m height before gridding. Where necessary, 

data gaps between individual surveys were filled using the 

existing State compilations (table D3). All survey data were 

corrected for the Earth’s magnetic field and diurnal variations, 

upward or downward continued to a constant elevation of 

305 m above the ground, gridded using a minimum curvature 

algorithm, and merged to produce a uniform map with a 

grid spacing of 500 m. These data have a grid resolution 

four times higher than that of the national scale. The new 

compilations, although initially composed of surveys acquired 

with different specifications, allow seamless interpretation of 

magnetic anomalies across survey boundaries within the SFAs 

and provide the initial dataset from which subsequent data 

transforms described below were derived (table D1).

Section D. Geophysical Data and Methods Used in Mineral-Resource Assessments within the Sagebrush Focal Areas 39
40 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Figure D1. Map showing airborne magnetic surveys that intersect a rectangular region encompassing a 25-kilometer buffer 

surrounding Sagebrush Focal Areas (SFAs), Western United States. Data available through the U.S. Geological Survey (USGS) 

Mineral Resource Program on-line spatial data Web site (http://mrdata.usgs.gov/).

120° 116° 112° 108°

46°

42°

0 50 100 150 MILES

0 50 100 150 200 KILOMETERS

Political boundaries from Esri (2013).

Shaded relief from Esri (2008).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 114° W., latitude of origin, 37.5° N.

MONTANA

IDAHO

WASHINGTON

OREGON

WYOMING

COLORADO

NEVADA UTAH

AREA D

AREA B

AREA C

AREA A

Map

area

Flight-line spacing (meters)

less than 800 

800 to 1,600

1,600 to 4,800

4,800 to 8,000

greater than 8,000

EXPLANATION

USGS study area boundary

Map

area

CANADA

UT

MT

ID

NV

OR

CO

WY

KS

NB

CA

WA

SD

ND

AZ NM TX

Study areas
Figure D2. Map showing total magnetic intensity (TMI) in the Western United States (Bankey and others, 2002). These data were 

subset to the four rectangular regions (black boxes) surrounding Sagebrush Focal Areas (SFAs; see section A, fig. A1) and provided 

the basis for subsequent data transforms (table D1). USGS, U.S. Geological Survey. nT, nanotesla.

120° 116° 112° 108°

46°

42°

0 50 100 150 MILES

0 50 100 150 200 KILOMETERS

Political boundaries from Esri (2013).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 114° W., latitude of origin, 37.5° N.

MONTANA

IDAHO

WASHINGTON

OREGON

WYOMING

UTAH COLORADO NEVADA

Map

area

CANADA

UT

MT

ID

NV

OR

CO

WY

KS

NB

CA

WA

SD

ND

AZ NM TX

Study areas

Total magnetic intensity (nT)

-300 -100 -50 0 100 450

EXPLANATION

USGS study area boundary

Area D

Area C

Area A

Area B

Section D. Geophysical Data and Methods Used in Mineral-Resource Assessments within the Sagebrush Focal Areas 41
42 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Table D1. List of filtered or transformed geophysical datasets generated for the Sagebrush Focal Areas (SFAs; see section A, fig. A1) 

as part of the Sagebrush Mineral-Resource Assessment (SaMiRA) project.

Dataset Description

Magnetic compilations:

TMI Total magnetic intensity anomaly map.

RTP Reduced-to-pole transform of total magnetic intensity anomaly map.

RTP-HGD Total horizontal gradient of the reduced-to-pole anomaly map.

RTP-1VD First vertical derivative of the reduced-to-pole anomaly map.

RTP-TDR Tilt derivative (or tilt angle) of the reduced-to-pole anomaly map; Also, vector file of –45, 0, 45 degree contours for tilt-depth 

estimates.

RTP-TDR-HGD Horizontal gradient of the tilt derivative of the reduced-to-pole anomaly map.

RTP-AS Analytic signal of the reduced-to-pole anomaly map.

Gravity compilation:

CBA Complete Bouguer anomaly map.

ISO Isostatic anomaly map.

ISO-HGD Total horizontal gradient of the isostatic anomaly map.

ISO-1VD First vertical derivative of the isostatic anomaly map.

ISO-TDR Tilt derivative (or tilt angle) of the isostatic anomaly map; Also, vector file of -45, 0, 45 degree contours for tilt-depth estimates.

ISO-TDR-HGD Horizontal gradient of the tilt derivative of the isostatic anomaly map.

Radiometric compilation:

K Potassium map.

TH Thorium map.

U Uranium map.

U:TH Uranium to thorium (ratio) map.

TH:U Thorium to potassium (ratio) map.

U:K Uranium to potassium (ratio) map.

U2:K Uranium squared to thorium (ratio) map.

K-TH-U Ternary image where red=potassium, green=thorium, blue=uranium.

Survey name Type Focal 

area(s)

Year 

flown

Line spacing 

(m)

Survey 

height (m) URL

Modoc North-central Digitized A 1957 3,200 2,1001 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=CA03c

Modoc South-central Digitized A 1957 3,200 2,4501 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=CA03d

Modoc East Digitized A 1957 3,200 2,9001 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=CA03e

Idaho Regional ‘69 Digitized A, B 1969 8,000 3,6501 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=0667

Susanville NURE A 1965 8,000 120 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=NURE-295

Boise NURE A 1976 4,800 120 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=NURE-227

Jordan Valley NURE A 1973 4,800 120 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=NURE-250

Table D2. Aeromagnetic surveys used to generate new, higher resolution compilations for the Sagebrush Focal Areas (SFAs) as part 

of the Sagebrush Mineral-Resource Assessment (SaMiRA) project.

[NURE, National Uranium Resource Evaluation; Focal areas: A, Sheldon-Hart Mountain National Wildlife Refuge Complex, Southeastern Oregon and North-Central 

Nevada, and Southern Idaho and Northern Nevada; B, North-Central Idaho; and C, Bear River Watershed and Southwestern and South-Central Wyoming]
1

Barometric survey.

Survey name Type Focal 

area(s)

Year 

flown

Line spacing 

(m)

Survey 

height (m) URL

Brigham City NURE A, C 1962 8,000 120 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=NURE-270

Toole NURE A 1970 8,000 120 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=NURE-296

Challis NURE B 1963 4,800 120 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=NURE-210

Elk City NURE B 1982 4,800 120 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=NURE-186

Dubois NURE B 1976 4,800 120 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=NURE-194

Dillon NURE B 1962 4,800 120 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=NURE-171

Ashton NURE B 1972 8,000 120 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=NURE-207

Bozeman NURE B 1972 4,800 120 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=NURE-178

Driggs NURE B 1972 4,800 120 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=NURE-229

Preston NURE B, C 1978 8,000 120 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=NURE-252

Pocatello NURE C 1976 8,000 120 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=NURE-243

Ogden NURE C 1978 4,800 120 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=NURE-283

Rock Springs NURE C 1962 4,800 120 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=NURE-287

Lander NURE C 1978 8,000 120 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=NURE-260

Wind River Digitized C 1969 1,600 3,9501 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=0669

Wind River Basin Digital C 1974 3,200 120 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=6001

Bonneville Digitized C 1969 8,000 3,6501 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=0664

Idaho Thrust Belt Digitized C 1963 1,600 2,7501 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=0523

Mt. Naomi Digital C 1981 800 305 http://mrdata.usgs.gov/magnetic/showsurvey.php?id=3188

Section D. Geophysical Data and Methods Used in Mineral-Resource Assessments within the Sagebrush Focal Areas 43

Table D2. Aeromagnetic surveys used to generate new, higher resolution compilations for the Sagebrush Focal Areas (SFAs) as part 

of the Sagebrush Mineral-Resource Assessment (SaMiRA) project.—Continued
44 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Gravity Data

Gravity stations were compiled from the Pan-American 

Center for Earth and Environmental Studies (PACES) 

U.S. Gravity Database accessed January 5, 2016, at http://

irpsrvgis08.utep.edu/viewers/Flex/GravityMagnetic/

GravityMagnetic_CyberShare/ (Hildenbrand and others, 

2002; Aldouri and Keller, 2011). The gravity-station spacing 

is irregular and coarse, having approximately 0.1 stations per 

square kilometer. Gravity-station data were processed using 

standard data reduction techniques (Hinze and others, 2005) 

and include the following corrections: (1) an Earth-tide 

correction, which corrects for tidal effects of the Moon and 

Sun; (2) an instrument-drift correction, which compensates 

for drift in the instrument’s spring; (3) a latitude correction, 

which accounts for variation in the Earth’s gravity with 

latitude; (4) free-air correction, which accounts for the 

variation in gravity due to elevation relative to sea level; (5) 

a Bouguer correction, which corrects for the attraction of 

material between the station and sea level; (6) a curvature 

correction, which corrects the Bouguer correction for the 

effect of the Earth’s curvature; and (7) a terrain correction, 

which removes the effect of topography to a radial distance 

of 167 km from the station. Gravity-station data were 

gridded using a minimum curvature algorithm at an interval 

of 500 m to produce complete Bouguer anomaly datasets 

over the four areas (fig. D3). The Bouguer anomaly data 

were the initial starting point from which the gravity data 

transforms described below were derived (table D1). For 

each area, an isostatic correction was applied to remove the 

long-wavelength variations in the gravity field related to 

the compensation of topographic loads. For this reduction, 

the digital elevation model (Lukas and others, 2015) was 

resampled to 500 m. A 2.67-gram per cubic centimeter 

(g/cm3) Bouguer density and a 0.35-g/cm3 Moho density 

contrast were assumed.

Radiometric Data

Radiometric data over the SFAs were derived from 

previously released map compilations across the United 

States (Duval and others, 2005). The original data were 

acquired as part of the National Uranium Resource 

Evaluation (NURE) program in the 1970s. The NURE 

flight-line spacing over the SFAs varied from 3,200 m to 

8,000 m and had a nominal terrain clearance of 120 m. 

The flight-line data were previously processed to produce 

internally consistent data (Duval, 1999; Duval and Riggle, 

1999). Data corrections included compensation for aircraft 

and cosmic radiation background, altitude variations, 

Compton scattering, and airborne bismuth-214. The data 

were subsequently converted from counts per second to 

concentration values. The compiled radiometric data provide 

a uniform suite of maps showing potassium, thorium, and 

uranium concentrations within the upper few centimeters of 

surface material at a grid spacing of 2,000 m. These data can 

be combined in single display by producing a ternary image 

where potassium, thorium, and uranium concentrations are 

displayed as red, green, and blue, respectively (fig. D4). 

The concentration maps form the basis for additional data 

transforms (table D1) described below.

Table D3. Specifications for State-compilation of magnetic data over the Sagebrush Focal Areas (SFAs) as part of the Sagebrush 

Mineral-Resource Assessment (SaMiRA) project.

State Grid interval, in meters Datum, in meters Reference

California 1,000 305 Roberts and Jachens, 1999

Idaho 1,000 305 McCafferty and others, 1999

Montana 500 305 McCafferty and others, 1998

Nevada 500 305 Kucks and others, 2006

Oregon 500 305 Roberts and others, 2008

Utah 1,000 3,8101 Bankey and others, 1998

Wyoming 500 305 Kucks and Hill, 2000

1

Barometric altitude.
Figure D3. Complete Bouguer gravity anomaly map for four rectangular regions surrounding Sagebrush Focal Areas (SFAs; 

see section A, fig. A1) in the Western United States, which was created as part of the Sagebrush Mineral-Resource Assessment 

(SaMiRA) project. USGS, U.S. Geological Survey. mGal, milligal.

120° 116° 112° 108°

46°

42°

Area D

Area A

Area C

Map

area

Study areas

CANADA

UT

MT

ID

NV

OR

CO

WY

KS

NB

CA

WA

SD

ND

AZ NM TX

Study areas

0 50 100 150 MILES

0 50 100 150 200 KILOMETERS

Political boundaries from Esri (2013).

Shaded relief from Esri (2008).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 114° W., latitude of origin, 37.5° N.

MONTANA

IDAHO

WASHINGTON

OREGON

WYOMING

COLORADO NEVADA UTAH

Area B

-250 -200 -175 -150 -130 -75

Complete Bouguer anomaly (mGal)

USGS study area boundaries

EXPLANATION

Section D. Geophysical Data and Methods Used in Mineral-Resource Assessments within the Sagebrush Focal Areas 45
46 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Figure D4. Ternary radiometric map of the Western United States (Duval and others, 2005). These data were subset to four 

rectangular regions (black boxes) surrounding the Sagebrush Focal Areas (SFAs; see section A, fig. A1) and provided the basis for 

subsequent data transforms (table D1) used as part of the Sagebrush Mineral-Resource Assessment (SaMiRA) project. USGS, U.S. 

Geological Survey.

120° 116° 112° 108°

46°

42°

0 50 100 150 MILES

0 50 100 150 200 KILOMETERS

Political boundaries from Esri (2013).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 114° W., latitude of origin, 37.5° N.

MONTANA

IDAHO

WASHINGTON

OREGON

WYOMING

UTAH COLORADO

NEVADA

Area B

Area C

Area D

Thorium Uranium

Potassium

Area A

USGS study area boundaries

EXPLANATION

Map

area

CANADA

UT

MT

ID

NV

OR

CO

WY

KS

NB

CA

WA

SD

ND

AZ NM TX

Study areas
Derivative Geophysical Products

Reduction-to-the-Pole (RTP) of Magnetic Data

The reduction-to-pole (RTP) transform better aligns 

magnetic anomalies with causative sources (Baranov and 

Naudy, 1964; Blakely, 1995). The transform removes the 

effect of the direction of the Earth’s magnetic field and the 

direction of magnetization by transforming the data to their 

expression at a vertical field and magnetization as if measured 

at the north magnetic pole. This transformation approximately 

centers magnetic anomalies over their sources and will 

produce a symmetrical anomaly over a symmetrical source. 

Remanent magnetization is assumed to be either negligible or 

in the same direction as the Earth’s magnetic field. The total 

magnetic-intensity anomaly data were transformed to RTP 

data using parameters described in table D4.

Total Horizontal Gradient of Magnetic and 

Gravity Data

The total horizontal gradient of potential-field data maps 

the edges of anomaly sources (Cordell and Grauch, 1985; 

Grauch and Cordell, 1987). The transform, which assumes 

a vertical contact and vertical magnetization for the case 

of magnetic sources, produces maxima coincident with the 

contact. If a body is dipping or the source is narrow, the total 

horizontal gradient response will be displaced; however, 

displacement is only normally significant in high-resolution 

data (Grauch and Cordell, 1987). To help map geologic 

contacts and structures, the total horizontal gradient method 

was applied to the RTP, isostatic anomaly, and tilt derivatives 

(see below) of the RTP and isostatic anomaly data (table D1).

First Vertical Derivative of Magnetic and Gravity 

Data

The first vertical derivative (for example, Evjen, 1936; 

Blakely, 1995) amplifies short-wavelength anomalies and typically 

highlights steep gradients along edges of shallow sources. Thus, 

local features are sharpened at the expense of broad or regional 

features that can often mask shallow anomalies. Although 

horizontal gradients mentioned above enhance edges of causative 

features, vertical derivatives narrow the width of the anomaly 

and help to better constrain the location of the causative feature. 

Because first vertical derivative maps reflect shallow sources, they 

are also useful for correlating geophysical anomalies with exposed 

surface geology. In addition, the first vertical derivative of gravity 

anomalies is equivalent to a pseudomagnetic transformation and 

thus can be used to compare gravity anomalies with observed 

magnetic anomalies (for example, Simpson and others, 1986).

Tilt Derivative of Magnetic and Gravity Data

The tilt derivative and its total horizontal gradient are useful 

tools for enhancing causative sources and can be less sensitive 

to noise than other higher order derivatives (Miller and Singh, 

1994; Verduzco and others, 2004). The tilt derivative is defined 

as the arctangent of the ratio of the first vertical derivative of the 

potential field to the horizontal gradient of the field. The ratio of 

the derivatives helps to overcome the large dynamic range in the 

size of the gradients, whereas the arctangent places the ratio in 

the range of –90° and 90°. The result is a map sensitive to both 

shallow and deep sources, where positive values occur over the 

source, zero values occur along the edge of vertical contacts, 

and negative values occur outside the source region. The total 

horizontal gradient method can be applied to the tilt derivative to 

indicate the anomaly edge in shallow basement targets (Verduzco 

and others, 2004). The tilt-depth method provides a rapid way 

to estimate source depths (Salem and others, 2007; Fairhead and 

Table D4. Reduction-to-the-pole (RTP) parameters used to transform magnetic-intensity anomaly 

data as part of the Sagebrush Mineral-Resource Assessment (SaMiRA) project.

[Focal areas: A, Sheldon-Hart Mountain National Wildlife Refuge Complex, Southeastern Oregon and North-Central 

Nevada, and Southern Idaho and Northern Nevada; B, North-Central Idaho; C, Bear River Watershed and Southwestern 

and South-Central Wyoming; and D, North-Central Montana; nT, nanotesla]

Focal area Longitude Latitude Field strength, in nT Inclination Declination

A -117.011 42.1205 53,190 66.3 15.3

B -113.39 43.7846 54,683 68.4 14.6

C -110.17 42.0032 54,264 67.6 12.9

D -107.952 47.73 57,207 72.6 13.0

Section D. Geophysical Data and Methods Used in Mineral-Resource Assessments within the Sagebrush Focal Areas 47
48 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

others, 2011). This method estimates the depth to a vertical contact 

by calculating half the distance between the -45° and 45° tilt angle.

Analytic Signal of Magnetic and Gravity Data

The analytic signal can be computed from the horizontal 

and vertical gradients of potential-field data in both two and three 

dimensions (Nabighian, 1972; Roest and others, 1992). The result 

depends on the geometry of the source body, not its magnetization, 

such that all bodies with the same geometry have the same analytic 

signal. The analytic signal can be used to determine location and 

estimate the depth of causative bodies (Nabighian, 1972; Roest 

and others, 1992). Because the analytic signal is independent of 

the direction of magnetization, it can also be used to estimate the 

magnetization of source bodies (for example, Blakely, 1995). 

The analytic signal peaks are symmetrical and occur directly over 

the edges of wide bodies and directly over the centers of narrow 

bodies. Thus, the analytic signal maps can be used to map source 

contacts and geometries.

Radioelement Element and Ratio Maps of 

Radiometric Data

Radiometric data map major variations in the radioelement 

concentrations in soil and exposed rock. Minor variations 

in radioelement concentration within rock units can be due 

to lithological changes, weathering, or mineralizing events 

(Dickson and Scott, 1997). These minor variations can be 

enhanced using ratios of the radiometric data. Ratio maps have 

the added advantage of being able to discriminate areas where 

relative concentrations of elements have increased or decreased 

possibly as a result of hydrothermal alteration within an ore 

system. For example, potassium enrichment associated with 

formation of potassium-rich bearing minerals formed during 

hydrothermal event(s) can be imaged using the potassium/

thorium ratio. Potassium and thorium generally covary with 

changing silica content in unaltered rocks. Because thorium 

is relatively immobile during hydrothermal alteration, the 

potassium/thorium ratio map may better show potassically 

altered rocks than potassium concentrations alone (Dickson and 

Scott, 1997; Shives and others, 2000).

Depth Estimates

Magnetic Methods

Euler deconvolution is a semiautomated way to estimate 

source position and depths (Reid and others, 1990; Phillips, 2002). 

The calculated depths are dependent on the source geometry. For 

this reason, a structural index (SI) term is used as a measure of the 

rate of change of a field with distance. The SI changes with source 

geometry such that geologic contacts, vertical dikes, vertical 

pipes, and spheres (or point sources) have a SI of 0, 1, 2, and 3, 

respectively. A SI that is too low gives depths that are too shallow, 

whereas one that is too high gives estimates that are too deep. A 

data window size is chosen such that it incorporates substantial 

variation of the magnetic field, but is small enough to minimize 

significant contributions from multiple sources.

The Euler deconvolution method was used in the NorthCentral Montana SFA to better understand the source depth 

of the northeast-trending RTP magnetic anomalies (fig. D5). 

The anomalies have been previously interpreted as reflecting 

Paleoproterozoic oceanic-arc rocks that accreted to the Archean 

Wyoming craton margin (Sims and others, 2004). Near the NorthCentral Montana SFA, Precambrian rocks are exposed as roof 

pendants in the Tertiary plutonic rocks within the Little Rocky 

Mountains. Recently digitized high-resolution aeromagnetic data 

(Anderson and others, 2016) indicate that the Tertiary plutonic 

rocks also appear to contribute to the northeast-trending anomalies.

The depth estimates presented here are for source 

geometries that represent the contact of plutonic bodies. 

Structural indices of 0.0, 0.5, and 1.0 were chosen and estimates 

were generated for window sizes that ranged from 2,500 to 

8,500 m. The solutions were subset to a 1,000-m buffer along the 

maximum total horizontal gradient associated with the northeasttrending magnetic anomalies. The results were compared to a 

structure contour map to top of Precambrian crystalline rock 

based on geology and drill-hole information that indicates the 

top of Precambrian rocks deepens from about 1,500 m east of 

the Little Rocky Mountains to more than 2,500 m just east of the 

eastern extent of the North-Central Montana SFA (Bergantino and 

Clark, 1985).

The preferred results were calculated from the RTP data 

using an SI of 0.5 and a window size of 8,500 m (fig. D5). The 

results show good clustering of solutions along the total horizontal 

gradients of the RTP data. The northeast-trending anomalies 

appear to have sources typically greater than 2,000 m depth. This 

agrees generally with the reported depths to the top of Precambrian 

basement, which range from 1,500 to 2,500 m depth (Bergantino 

and Clark, 1985). Shallow sources occur over the Little Rocky 

Mountains that likely reflect the outcropping Tertiary plutonic 

rocks. Two areas within the north-central Montana Sagebrush 

Focal Area indicate relatively shallow magnetic sources—(1) 

approximately 50 km southeast of the Little Rocky Mountains are 

clusters of shallow solutions ranging from 500 to 2,000 m, and (2) 

approximately 35 km east-southeast of Malta, Montana, is another 

cluster of depth solutions that range mostly from 500 to 2,000 m. 

Both areas may represent Mesozoic to Cenozoic igneous rocks.

Gravity Methods

Previously, an iterative gravity inversion method was 

used to determine the thickness of Cenozoic basin deposits 

in Nevada and Utah (Jachens and Moring, 1990; Saltus and 

Jachens, 1995). The depth-to-basement method separates the 

gravity field into two components—(1) the field caused by preCenozoic basement rocks and (2) the field caused by overlying 

younger basin deposits. An initial basement gravity field is 

determined by using just those gravity measurements located 
Figure D5. Map of Euler depth estimates overlain on a reduced-to-pole (RTP) magnetic-anomaly map of the North-Central 

Montana Sagebrush Focal Area (SFA; see section A, fig. A1). Map was generated as part of the Sagebrush Mineral-Resource 

Assessment (SaMiRA) project. nT, nanotesla.

PHILLIPS

COUNTY

GARFIELD COUNTY

VALLEY COUNTY

BLAINE COUNTY

FERGUS COUNTY

PETROLEUM COUNTY

Fort Peck LakeFort Peck Lake

Roy

Hays

Malta

Jordan Hilger

Glasgow

Lodge Pole

Little Rocky

Mountains

109° 108° 107°

48°

47°30'

IDAHO

MONTANA

WYOMING

OREGON

NEVADA UTAH

Map area

Study area

0 10 20 30 MILES

0 20 40 KILOMETERS

Political boundaries from Esri (2013).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 108° W., latitude of origin, 36.5° N.

Reduced-to-pole magnetics (nT)

-325

-170

-100

0

-100

300

Depth estimate (meters)

0 to 500

501 to 1,000

1,001 to 1,500

1,501 to 2,000

2,001 to 2,500

2,501 to 3,000

3,001 to 5,000

Proposed withdrawal area

EXPLANATION

Study area

Section D. Geophysical Data and Methods Used in Mineral-Resource Assessments within the Sagebrush Focal Areas 49
50 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

on pre-Cenozoic basement outcrops. The initial basement 

gravity field is only approximate, because measurements 

located on basement are influenced by the gravity effect of 

low-density deposits in nearby basins, especially for those 

measurements near the edge of the basins. The difference 

between the isostatic gravity and basement gravity fields 

provides the first estimate of the basin gravity field, which is 

inverted to provide the first estimate of the basin depth and 

shape. The gravitational effects of the basins are subtracted 

from each measurement located on basement, and a new and 

improved basement gravity field is determined. This process 

is repeated until successive iterations converge. Inversion of 

the final basin gravity field constrained with a density-depth 

function (table D5) and geology yields an estimate of the 

depth to pre-Cenozoic basement. The density of basement 

rocks is allowed to vary horizontally, whereas the density of 

basin-filling deposits increases with depth according to the 

density-depth relations shown in table D5. The density-depth 

function is based on density information from rock samples, 

geophysical well logs, and borehole gravity data. A densitydepth profile representative for the state of Nevada (Jachens 

and Moring, 1990) was used for sedimentary and volcanic 

deposits.

A number of limitations are inherent in the gravity data 

themselves, as well as in the inversion process. Uncertainties 

are related to the distribution of gravity data, especially for 

measurements on basement outcrops, the assumed densitydepth function, accuracy or scale of the geologic mapping, 

simplifying assumptions regarding concealed geology, and 

the distribution of basement outcrops. The depth-to-basement 

process itself is regional in scope, and caution should be 

exercised when using these results at a scale greater than about 

1:250,000. A more detailed discussion of the limitations and 

accuracy of the method are provided by Jachens and Moring 

(1990).

In the North-Central Idaho SFA, three-dimensional (3-D) 

gravity inversions were used to map areas in the Pahsimeroi 

and Lemhi Valleys where the thickness of Cenozoic basins 

exceeds 1,000 m, a depth that is nonpermissive for economic 

extraction of hard rock mineral resources. The gravity inversion 

Table D5. Density-depth functions used to constrain final 

basin gravity fields as part of the Sagebrush Mineral-Resource 

Assessment (SaMiRA) project.

[g/cm3, gram per cubic centimeter]

Depth range, in 

kilometers

Sedimentary density 

contrast, in g/cm3

Volcanic density 

contrast, in g/cm3

0–0.2 -0.65 -0.45

0.2–0.6 -0.55 -0.40

0.6–1.2 -0.35 -0.35

>1.2 -0.25 -0.25

method assumed a two-layer model with 0.3-g/cm3 density 

contrast (Liberty and others, 2006) that consisted of low-density 

basins underlain and surrounded by higher density material 

representing pre-Cenozoic bedrock. Three datasets were used 

to constrain the inversion—isostatic anomaly, topography, 

and mapped geology. The isostatic anomaly map (described 

above) characterized the observed anomalous gravity field. The 

topography was defined by a digital elevation model (DEM) 

generated as part of the USGS 3D Elevation Program (Lukas 

and others, 2015). Mapped surface lithologies were used to 

define lateral extent of basin and bedrock materials (Lewis and 

others, 2012). The basin thickness was initially set at 1,000 m 

below topography. The inversion process iteratively adjusted 

the basin thickness until the predicted gravity field adequately 

matched that of the observed gravity field. The inversions over 

the Pahsimeroi and Lemhi Valleys were run separately. The 

Pahsimeroi Valley inversion was first run and parameters were 

adjusted until areas within the basin agreed well with seismicreflection data (Liberty and others, 2006). The inversions over 

the Lemhi Valley were then run using similar parameters and 

areas of overlap were inspected for consistency. The results 

were then contoured and the 1,000 m-depth contour helped 

define tract boundaries by indicating depths too deep for mineral 

resource extraction (fig. D6).

Pluton Mapping

Isostatic gravity, aeromagnetic, and the horizontal 

gradient of gravity and magnetic anomalies were used to infer 

the lateral extent of known and unknown granitoid plutons in 

Nevada (Grauch and others, 1988; Grauch, 1996). Although 

aeromagnetic data (Hildenbrand and Kucks, 1988) and their 

correlation to mapped granitic rocks (Stewart and Carlson, 

1978) was primarily used, isostatic- and basement-gravity 

maps of Nevada (Jachens and Moring, 1990; Saltus and 

Jachens, 1995) were also used to supplement the aeromagnetic 

interpretations. Because mineral-resource deposits are often 

spatially or temporally associated with granitic plutons, their 

inferred horizontal extent plays a major role in mineralresource assessments.

In the North-Central Idaho SFA, plutons were also 

mapped using transformed RTP data. The upward continuation 

transformation calculates the magnetic field at an elevation 

higher than that at which it was originally measured. This 

transform attenuates near-surface effects and accentuates the 

anomalies from deeper magnetic sources (Blakely, 1995). A 

common technique to enhance near-surface sources, such as 

shallow plutons, is to upward continue magnetic data a short 

distance to generate a regional field and then subtract this 

regional field from the original dataset. The resulting map is a 

high-frequency-passed magnetic field associated with shallow 

sources. Using a 1,000-m upward-continuation distance and 

the RTP field, the resultant anomalies helped map near-surface 

plutons in North-central Idaho SFA (fig. D7).
Figure D6. Isostatic-anomaly map and basin-thickness estimates derived from gravity inversions over the North-Central Idaho 

Sagebrush Focal Area (SFA; see section A, fig. A1). Map was generated as part of the Sagebrush Mineral-Resource Assessment 

(SaMiRA) project. USGS, U.S. Geological Survey.

114° 112°

44°

43°

-50 -30 -20 -15 0 10

Isostatic anomaly, in milligals

0 15 30 45 MILES

0 15 30 45 60 KILOMETERS

USGS study area boundaries

Gravity station

Basin thickness (meters)

500

1,000

1,500

2,000

2,500

EXPLANATION

IDAHO

MONTANA

OREGON

NEVADA UTAH

WYOMING

Map area

Lemhi Valley Pahsimeroi Valley

Political boundaries from Esri (2013).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 114° W., latitude of origin, 37.5° N.

Section D. Geophysical Data and Methods Used in Mineral-Resource Assessments within the Sagebrush Focal Areas 51
52 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Figure D7. Map of residual magnetic anomalies used to help map plutons in North-Central Idaho Sagebrush Focal Area (SFA). Map 

was generated as part of the Sagebrush Mineral-Resource Assessment (SaMiRA) project. USGS, U.S. Geological Survey.

114° 112°

44°

43°

0 15 30 45 MILES

0 15 30 45 60 KILOMETERS

EXPLANATION

USGS study area boundary

IDAHO

MONTANA

OREGON

NEVADA UTAH

WYOMING

Map area

Residual magnetic anomaly (nT)

-25 -10 -5 0 5 20

Political boundaries from Esri (2013).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 114° W., latitude of origin, 37.5° N.
Diatreme Mapping

In 1981, Anaconda Minerals Company collected highresolution aeromagnetic data over the Missouri Breaks diatremes 

in Montana. The survey was flown along north-south flight lines 

spaced 200 m at a nominal terrain clearance of 130 m. The analog 

contour maps of these data were digitized (Anderson and others, 

2016) and digitally enhanced. The RTP anomaly map shows 

discrete magnetic highs over mapped diatremes. The analytic 

signal also images these rocks and suggests the location of 

additional diatremes in the shallow subsurface.

Large-Scale Fractures in Nevada and Idaho

On the basis of gravity and aeromagnetic data, Ponce and 

Glen (2002) interpreted large-scale fractures across northern 

Nevada and extending into Idaho that are probably related to 

the inception of the Yellowstone Hotspot. These features are 

particularly evident in aeromagnetic data as linear positive 

anomalies, but some are also prominently expressed in gravity 

data. These geophysical lineaments represent major crustal 

discontinuities within the Earth that are interpreted to have formed 

as a result of mid-Miocene rift-related magmatism.

These large-scale features may have served as conduits for 

ore-forming hydrothermal solutions and are both spatially and 

temporally associated with mid-Miocene epithermal gold-silver 

deposits (Ponce and Glen, 2002). The statistical proximity of these 

arcuate features to mid-Miocene and younger epithermal gold-silver 

deposits suggests that they may serve as a guide to future epithermal 

mineral-resource potential in Nevada, Oregon, and Idaho.

General Discussion

Gravity and magnetic anomalies can be used to infer the 

subsurface structure of known or unknown geologic features, 

where a physical-property contrast occurs across the geologic 

boundaries. Typically, gravity anomalies reflect lateral (horizontal) 

density variations in the middle to upper crust. Thus, isostaticgravity anomalies can be used to infer the subsurface structure 

of known or unknown geologic features. In general, gravity 

anomalies reflect carbonate rocks, calderas, deep sedimentary 

basins, plutons, and linear geologic features such as faults. Many 

of these features play an important role in assessing the mineralresource potential across the SFAs.

Magnetic anomalies typically reflect lateral changes in 

rock magnetic properties and can be analyzed to gain insights 

into the three-dimensional nature of the causative source. In 

general, short-wavelength, high-amplitude magnetic anomalies 

are caused by moderately to strongly magnetic volcanic 

rocks, whereas broad circular long-wavelength magnetic 

anomalies reflect magnetic granitoid intrusions or other mafic 

basement rocks. Many of these features play an important 

role in ore formation, and their distribution is important to the 

understanding of the mineral-resource potential of the area. 

The diverse physical properties of rock units that underlie 

this region are well suited to geophysical investigations. The 

contrast in magnetic properties between pre-Cenozoic rocks, 

volcanic rocks, and alluvium produces a distinctive pattern 

of anomalies that can be used to determine the sources of the 

anomalies and their subsurface extent.

Radiometric data map the surficial variation in 

potassium, thorium, and uranium concentrations. These data 

map lateral changes in geologic material and complement 

geologic maps. Ore deposits can have preferential host or 

source rocks, which may be imaged by the data. In addition, 

the hydrothermal systems associated with ore deposits can 

alter the concentrations of potassium, thorium, and uranium, 

thereby making them an effective dataset for mineral-resource 

assessment. However, because of the relatively low spatial 

resolution of the data over the SFAs, these data are most useful 

for lithologic mapping. The contrast in radioactivity between 

Paleozoic sedimentary rocks, volcanic rocks, and plutonic 

rocks made these data effective for understanding their 

surficial distribution throughout the SFAs.

Most Paleozoic rocks are relatively nonmagnetic within 

the study area, whereas intrusive rocks are, in general, 

moderately magnetic and are associated with magnetic 

highs. Tertiary volcanic rocks are strongly magnetic with 

variable magnetic properties, and they play significant roles 

in assessing the mineral-resource potential and extensional 

history of the area. Thick accumulations of these volcanic 

rocks are present throughout the study area. Alluvial deposits 

within the study area are essentially nonmagnetic and most 

basins have subdued magnetic anomalies with the exception of 

those basins that may contain volcanic centers, buried volcanic 

rocks, or buried granitic rocks.

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Section D. Geophysical Data and Methods Used in Mineral-Resource Assessments within the Sagebrush Focal Areas 55
56 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

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Section E. Remote Sensing

By Barnaby W. Rockwell

The occurrence and mineralogy of exposed, 

hydrothermally altered rocks related to locatable mineralresource potential in the U.S. Geological Survey (USGS) 

Sagebrush Mineral-Resource Assessment (SaMiRA) project 

study areas were assessed using digital geospatial data 

derived from spectral analysis of satellite remote sensing 

data. Maps of alteration types and key mineral groups derived 

from automated analysis of Advanced Spaceborne Thermal 

Emission and Reflection Radiometer (ASTER) data were the 

most important source of surface mineralogical information 

(Rockwell, 2012). Maps of mineral groups derived from 

automated analysis of Landsat 7 Enhanced Thematic Mapper 

Plus (ETM+) data were used to verify occurrences of 

anomalous mineral concentrations observed using the ASTERderived maps, especially in areas with abundant dry vegetation 

that can complicate remote sensing-based mineral mapping, 

such as the northern Great Basin (Rockwell, 2013). In northern 

Nevada, maps of quartz and carbonate abundance derived 

from analysis of ASTER thermal infrared data were used to 

identify jasperoids associated with Carlin-type gold deposits 

and hydrothermal quartz in areas of potential epithermal 

gold-silver mineralization (Rockwell and Hofstra, 2008). 

The mineral maps used for the mineral-resource assessment 

are available through an online viewer and associated data 

services (Rockwell and others, 2015).

The maps of surficial mineralogy were not used as the 

sole criteria for defining permissive tracts in the mineralresource assessment but locally were used to refine the 

boundaries of tracts for epithermal gold-silver and intrusionrelated deposits for which hydrothermal alteration is an 

important characteristic of the deposit type. The areas defined 

by mapped occurrences of the “sericite and (or) smectite” 

mineral group from the ASTER-derived data exhibited high 

correlation with known bentonite claims, mines, and exposures 

of thin, light-colored, bentonite-bearing beds interpreted 

using aerial imagery within widespread shales of the Bearpaw 

Formation in the North-Central Montana Sagebrush Focal 

Area. As a result, the ASTER-derived data were used as an 

important criterion for the delineation of permissive tracts 

for bentonite in that study area. Strong hematitic alteration 

associated with sediment-hosted “roll front” uranium deposits, 

such as that mapped using both the ASTER and ETM+ 

data in sandstones on Red Rim, 21 kilometers southwest 

of Rawlins, Wyoming, is another example of an alterationrelated mineralogical signature used as an assessment 

criterion for a specific deposit type. Integration of various 

data types, including data of known mineral deposits, claims, 

permissive lithologic map units, airborne geophysics, regional 

geochemistry, and remote sensing typically yields higher 

confidence levels when defining permissive tracts, and the 

mineral maps derived from remote sensing play a key role in 

that process for certain deposit types.

References Cited

Rockwell, B.W., 2012, Description and validation of 

an automated methodology for mapping mineralogy, 

vegetation, and hydrothermal alteration type from ASTER 

satellite imagery with examples from the San Juan 

Mountains, Colorado: U.S. Geological Survey Scientific 

Investigations Map 3190, 35 p. pamphlet, 5 map sheets, 

scale 100,000, accessed March 15, 2016, at http://pubs.usgs.

gov/sim/3190/.

Rockwell, B.W., 2013, Automated mapping of mineral groups 

and green vegetation from Landsat Thematic Mapper 

imagery with an example from the San Juan Mountains, 

Colorado: U.S. Geological Survey Scientific Investigations 

Map 3252, 25 p. pamphlet, 1 map sheet, scale 325,000, 

accessed March 15, 2016, at http://pubs.usgs.gov/sim/3252/.

Rockwell, B.W., Bonham, L.C., and Giles, S.A., 2015, USGS 

national map of surficial mineralogy: U.S. Geological 

Survey Web site, accessed March 15, 2016, at http://

cmerwebmap.cr.usgs.gov/usminmap.html.

Rockwell, B.W., and Hofstra, A.H., 2008, Identification of 

quartz and carbonate minerals across northern Nevada using 

ASTER thermal infrared emissivity data—Implications for 

geologic mapping and mineral resource investigations in 

well-studied and frontier areas: Geosphere, v. 4, no. 1, p. 

218–246, doi:10.1130/GES00126.1, accessed March 15, 

2016, at http://geosphere.gsapubs.org/content/4/1/218.

Section F. BLM Legacy Rehost System (LR2000)

By Connie L. Dicken and Carma San Juan

The Bureau of Land Management’s (BLM) Legacy 

Rehost System, or LR2000, contains legal descriptions of 

BLM lands. LR2000 provides reports on BLM land- and 

mineral-use authorizations for oil, gas, and geothermal leasing, 

rights-of-ways, coal and other mineral development, land and 

mineral title, mining claims, withdrawals, classifications, and 

more on Federal lands or on Federal mineral estates (Bureau 

of Land Management, 2016).

The LR2000 database was queried for relevant data for 

the seven focal areas in the Western United States included 

in the Sagebrush Mineral-Resource Assessment (SaMiRA) 

project. The BLM compiled tabular queries and reports to 

generate data spreadsheets that were processed and delivered 

to U.S. Geological Survey (USGS) as spatial information; 

BLM reported an expected accuracy of 90 percent for the data 

provided (John Varner, BLM, written commun., 2016).

Spatial data were compiled by BLM and delivered 

to USGS on March 6, 2016, using the data extracted from 

LR2000 for the study area. The data included polygon feature 

classes and nonspatial tables in an Esri file geodatabase format 

to be used in a geographic information system (GIS). The 

database contained seven feature classes—coal, geothermal, 

mineral materials, mining claims, non-energy solid minerals, 

oil and gas, and notices and plans. Each feature class was 

comprised of a polygon file of Public Land Survey System 

(PLSS) sections and a nonspatial related table. The PLSS is 

used to describe and subdivide land in the United States. The 

PLSS is typically divided into 6-mile-square townships and 

those townships are then subdivided into 36 one-mile-square 

sections (U.S. Geological Survey, 2016).

To work with the data in a more simplified way, the 

related tables were merged with the spatial sections and 

processed so that the data could be easily queried. The 

processing required the creation of frequency tables for 

each feature class and removing duplicate entries. After the 

frequency tables were complete, those tables were joined with 

corresponding feature class based on a unique attribute. This 

process allowed the nonspatial tables to be connected with 

polygon sections in a one-to-one relation. The next step was to 

combine sections that contained the same unique case number, 

which was done by dissolving polygon section boundaries. 

This allowed users to visualize the data in a GIS, as well 

as define queries to show spatial distribution of the data. 

Status and number of mining claims, mineral leases, mineralmaterial sales sites, and surface-management (43 CFR 3809) 

authorizations were provided as summary tables for each 

focal area based on the processed LR2000 data. The processed 

LR2000 data for the SaMiRA project are available in a data 

release (Dicken and San Juan, 2016).

Each of the seven feature classes was used for the 

mineral-resource assessment. The following descriptions were 

provided by BLM for each dataset.

Coal

Nonrenewable energy.—The Mineral Leasing Act of 

1920, as amended, and the Mineral Leasing Act for Acquired 

Lands of 1947, as amended, gives the BLM responsibility for 

coal leasing on approximately 570 million acres where the 

coal mineral estate is owned by the Federal Government. The 

surface estate of these lands could be controlled by BLM, the 

U.S. Forest Service, private landowners, State landowners, or 

other Federal agencies. Not all public lands are available for 

coal exploration or leasing. The purpose of the coal-screening 

part of the land-use planning process (43 CFR 3420.1-4) is 

to identify those Federal lands that are acceptable for further 

consideration for coal leasing and development.

Geothermal

Renewable energy.—Geothermal energy is the use of 

steam and hot water generated by heat from the Earth to 

perform work. Geothermal resources include (1) all products 

of geothermal processes, including indigenous steam, hot 

water, and hot brines; (2) steam and other gases, hot water, 

and hot brines resulting from water, gas, or other fluids 

artificially introduced into geothermal formations, heat or 

other associated energy found in geothermal formations, and 

any byproducts.

Mineral Materials Disposal

43 CFR 3600.—This law applies to disposal of sand, 

gravel, and other mineral and vegetative materials that are 

not subject to mineral leasing or location under the mining 

laws. Mineral materials means, but is not limited to, petrified 

wood and common varieties of sand, stone, gravel, pumice, 

pumicite, cinders, and clay. Mineral materials are some of our 
60 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

most basic natural resources, such as sand, gravel, dirt, and 

rock, used in every day building and other construction uses. 

These materials generally are bulky and have a low unit price.

Mining Claims

A mining claim on Federal land gives exclusive rights to 

develop the minerals under the claim beginning on the date the 

mining claim was located. Within a mining claim, the surface 

lands remain open to the public for other multiple uses. A 

mining claim is located in order to acquire the right to develop 

the mineral values in a specified area. Locating a mining claim 

requires a discovery of a valuable mineral.

Non-Energy Solid Minerals

The BLM leases certain solid minerals, such as 

phosphate, sodium, potassium, sulfur, gilsonite, or a hardrock 

mineral, on public and other Federal lands. The BLM can 

also lease these minerals on certain private lands, provided 

the mineral rights are owned by the Federal Government. 

Prospecting permits are issued under 43 CFR 3505 in areas 

where it is not known a mineral deposit exists. A prospecting 

permit provides the exclusive right to prospect and explore for 

leasable mineral deposits.

Oil and Gas Leasing

Leasable minerals include energy resources of coal, 

phosphate, oil, oil shale, and gas on the public domain as 

designated by the Mineral Leasing Act of 1920, as amended. 

An oil and gas lease grants the lessee the right to explore and 

drill for, extract, remove, and dispose of oil and gas deposits, 

except helium, that may be found in the leased lands.

Notices and Plans (Surface 

Management)

Surface-management notices and plans refers to all 

surface disturbing activity conducted under the General Mining 

Act of 1872 (30 U.S.C. 22–42), as amended, and the Federal 

Land Policy and Federal Land Policy and Management Act 

of 1976 (FLPMA; Pub. L. 94–579; 90 Stat. 2743), as well 

other laws. Notices and plans facilitate the administration of 

exploration, mining, and milling activities on the public lands, 

or interests in such lands, in order to prevent unnecessary or 

undue degradation of the lands.

References Cited

Bureau of Land Management, 2016, Bureau of Land 

Management’s Land and Mineral Legacy Rehost 2000 

System—LR2000: Bureau of Land Management Web site, 

accessed March 7, 2016, at http://www.blm.gov/lr2000/.

Dicken, C.L., and San Juan, Carma, 2016, Bureau of Land 

Management’s Land and Mineral Legacy Rehost System 

(LR2000) mineral use cases for the Sagebrush MineralResource Assessment, Idaho, Montana, Nevada, Oregon, 

Utah, and Wyoming: U.S. Geological Survey data release, 

http://dx.doi.org/10.5066/F7RX996K.

U.S. Geological Survey, 2016, The National Map—The Public 

Land Survey System (PLSS): U.S. Geological Survey Web 

site, accessed April 28, 2016, at http://nationalmap.gov/

small_scale/a_plss.html.
Section G. Previous Mineral-Resource Assessment Data 

Compilation

By Heather L. Parks, Michael L. Zientek, M. Christopher Jenkins, Cassandra K. Hennings, John C. Wallis, and 

Duc M. Nguyen

For the Sagebrush Mineral-Resource Assessment 

(SaMiRA) project, mineral-potential maps from previous 

mineral-resource assessments that covered the project area 

were compiled into raster or vector geographic information 

system (GIS) databases. Georeferenced tract-map images 

from Bureau of Land Management (BLM) and U.S. Forest 

Service (USFS) wilderness study summary reports were 

used, along with multiple other mineral-potential reports 

that were done under the U.S. Geological Survey (USGS) 

Conterminous United States Mineral Assessment Program 

(CUSMAP) program and for USGS assessments of U.S. 

National Forests. In the previous studies, assessment 

results were described using different schemes. The BLM 

used “qualitative categorical,” and others used the USGS 

“three-part form” (Singer and Menzie, 2010). For this 

compilation, we captured the information as presented but 

also standardized nomenclature when we could in Parks and 

others (2016).

We reviewed BLM and USFS wilderness study 

summary reports along with BLM Surface Management 

Agency GIS data to help locate the reports that covered the 

SaMiRA project areas. The USFS wilderness studies were 

summarized in USGS Professional Paper 1300 (Marsh and 

others, 1984). The BLM wilderness studies were summarized 

in unpublished reports for Montana and Wyoming and 

published reports for Idaho, Oregon, and Nevada (Diggles, 

1991; U.S. Geological Survey Central Mineral Resources 

and U.S. Bureau of Mines Western Field Operations Center, 

1989; Conrad, 1990). We did not locate a summary report for 

Utah but consulted the BLM Surface Management Agency’s 

Special Public Purpose Withdrawal Areas GIS data to double 

check that there were no assessments covering the SaMiRA 

Utah areas (DOI–BLM, National Operations Center—

Division of Information Resource Management, 2016). 

Fifty-nine mineral potential reports covering the SaMiRA 

project areas were located, and 134 mineral potential maps 

shown in these reports were either extracted from report 

.pdf files or scanned and then georeferenced using ArcGIS. 

The georeferenced images were imported into four ArcGIS 

raster mosaic datasets, one for each of the four report areas—

MT.gdb, NC_IDAHO.gdb, NV_ID_OR.gdb, and WY.gdb. 

The MT.gdb raster mosaic dataset contained 7 georeferenced 

images, NV_ID_OR.gdb contained 66 georeferenced images, 

NC_IDAHO.gdb contained 60 georeferenced images, and the 

WY.gdb contained 1 georeferenced image.

When viewed in ArcMap, the raster mosaic dataset 

appears as a group of three layers under the mosaic dataset. 

The first item in the group is the “Boundary,” which 

contains a single polygon representing the extent of all 

images in the dataset. The second item is the “Footprint,” 

which contains a polygon representing the extent of each 

individual image in the dataset. The “Footprint” layer also 

contains the attribute-table data associated with each of the 

images. The third item is the “Image” layer and contains 

the images in the dataset. The images are overlapping 

and must be selected and locked or queried in order to be 

viewed one at a time. To select and lock an image, rightclick on the “Footprint” layer in the table of contents 

window and hover over “Selection,” then click “Lock To 

Selected Rasters.” Another way to view a single image 

is to run a definition query on the image. This is done by 

right clicking on the raster mosaic in the table of contents 

and opening the layer properties box. Then click on the 

“Definition Query” tab and create a query for the desired 

image.

The images were clipped to the extent of the map 

and all explanatory text gathered from map explanations 

or report text was imported into the raster mosaic dataset 

database as attributes. The data compiled into the attribute 

tables contained the figure caption from the original map. 

In addition, the images were catalogued according the 

legal definition of mineral resources—metallic, nonmetallic, leasable non-fuel, leasable fuel, geothermal, 

paleontological, and salable. This allows users to view the 

image along with information about the images without the 

need for referring back to the source report.

Some previous mineral-resource assessments were 

available in vector GIS format. We searched for reports 

covering the SaMiRA project area and compiled the GIS 

vector data. The original data was both in ArcInfo coverage 

and shapefile format. The coverages were converted to 

shapefiles, and then these and the other shapefiles were 

imported into ArcGIS geodatabases. Table G1 lists the 

geodatabases and reports used in the compilation.
62 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Table G1. Geodatabases containing mineral-resource assessment geographic information system (GIS) data that covered the 

Sagebrush Mineral-Resource Assessment (SaMiRA) study areas compiled from preexisting reports. 

[USGS, U.S. Geological Survey]

Geodatabase name Source report number and title Reference

IdMt_USGS_OFR2007_1101_Asmt.gdb USGS Open-File Report 07–1101: A compilation 

of spatial digital databases for Selected U.S. 

Geological Survey nonfuel mineral-resource 

assessments for parts of Idaho and Montana

Carlson and others, 2007

IdOr_USGSar2016_MJA_Asmt.gdb USGS unpublished data, Oregon and Idaho James Evans, USGS, written commun., 1999

Nv_USGSofr96-712_1996_Asmt.gdb USGS Open-File Report 96–712: Metallic 

mineral resources in the U.S. Bureau of Land 

Management’s Winnemucca District and Surprise 

Resource Area, northwest Nevada and northeast 

California

Peters and others, 1996

Nv_USGSofr2004-1245_2004_Asmt.gdb USGS Open-File Report 04–1245: Spatial databases 

of the Humboldt Basin mineral-resource 

assessment, northern Nevada

Mihalasky and Moyer, 2004

NV_USGSar_Sheldon_2010_Asmt.gdb USGS unpublished data, Oregon and Nevada James Rytuba and others, written commun., 2009

US_USGSc1178_2000_and_PacNW_

USGSofr682_1996_Asmt.gdb

USGS Circular 1178: 1998 Assessment of 

Undiscovered deposits of gold, silver, copper, 

lead, and zinc in the United States

U.S. Geological Survey National MineralResource Assessment Team, 1998

USGS Open-File Report 95–682: Assessment of 

undiscovered mineral resources in the Pacific 

Northwest—A contribution to the Interior 

Columbia Basin Ecosystem Management Project

Box and others, 1996

The original GIS data had varying data structures, and 

therefore, we reformatted the data so that all of the GIS 

files had a consistent attribute-table structure. We referred 

to the report text in some instances to fill in missing data 

into the attribute tables. We used two basic attributetable structures—one for reports that had quantitative 

data and one for reports with qualitative data. We set up a 

general attribute table structure, which contained fields for 

information on the deposit type assessed, assessment rank, 

type of assessment, and tract name and identifier. For the 

attribute table of the quantitatively assessed reports that 

used the USGS three-part form of assessment, we added 

additional fields for the deposit model name and number, 

probabilistic assessment results data, and estimators.

These results were crucial in defining what deposit types 

needed to be assessed for this project. The deposit types 

assessed were compiled and distributed to all assessment 

teams as part of the evaluation of what expertise and data 

would be needed. This compilation helped to determine 

what deposit models needed to be developed (appendix 3). 

Assessment teams used the results to guide mineral-potential 

assessment. Assessment Oversight Committee (AOC) 

members used the compilation to assess the work done by 

the assessment teams.

References Cited

Box, S.E., Bookstrom, A.A., Zientek, M.L., Derkey, P.D., Ashley, 

R.P., Elliott, J.E., and Peters, S.G., 1996, Assessment of 

undiscovered mineral resources in the Pacific Northwest—A 

contribution to the Interior Columbia Basin Ecosystem 

Management Project: U.S. Geological Survey Open-File Report 

95–682, 432 p., and GIS data, also available at http://pubs.usgs.

gov/of/1995/of95-682/.

Carlson, M.H., Zientek, M.L., Causey, J.D., Kayser, H.Z., Spanski, 

G.T., Wilson, A.B., Van Gosen, B.S., and Trautwein, C.M., 

2007, A compilation of spatial digital databases for selected 

U.S. Geological Survey nonfuel mineral resource assessments 

for parts of Idaho and Montana: U.S. Geological Survey 

Open-File Report 2007–1101, v. 1.0, 34 p., and GIS data, also 

available at http://pubs.usgs.gov/of/2007/1101/.

Conrad, J.E., ed., 1990, Mineral summaries for Nevada—U.S. 

Bureau of Land Management wilderness study areas: U.S. 

Geological Survey Open-File Report 90–638, 373 p.

Diggles, M.F., ed., 1991, Mineral summaries for Oregon—U.S. 

Bureau of Land Management wilderness study areas: U.S. 

Geological Survey Open-File Report 91–139, 298 p.
DOI–BLM, National Operations Center—Division of 

Information Resource Management, 2016, Surface 

Management Agency (Special Public Purpose—

Withdrawal Areas): Bureau of Land Management 

Geocommunicator Web page, accessed May 11, 2016, at 

http://www.geocommunicator.gov/ArcGIS/rest/services/

SurfaceManagementAgency/MapServer.

Marsh, S.P., Kropschot, S.J., and Dickinson, R.G., eds., 1984, 

Wilderness mineral potential—Assessment of mineralresource potential in U.S. Forest Service lands studied 

1964–1984: U.S. Geological Survey Professional Paper 

1300, v. 2, p. 552–1183.

Mihalasky, M.J., and Moyer, L.A., 2004, Spatial databases of 

the Humboldt Basin mineral resource assessment, northern 

Nevada: U.S. Geological Survey Open-File Report 2004–

1245, 17 p., and GIS data, also available at http://pubs.usgs.

gov/of/2004/1245/.

Parks, H.L., Zientek, M.L., Jenkins, M.C., Hennings, C.K., 

Wallis, J.C., Nguyen, D.M., and Cossette, P.M., 2016, 

Previous mineral resource assessment data compilation for 

the U.S. Geological Survey Sagebrush Mineral-Resource 

Assessment project: U.S. Geological Survey data release, 

http://dx.doi.org/10.5066/F7736P0C.

Section G. Previous Mineral-Resource Assessment Data Compilations 63

Peters, S.G., Nash, J.T., John, D.A., Spanski, G.T., King, 

H.D., Connors, K.A., Moring, B.C., Doebrich, J.L., 

McGuire, D.J., Albino, G.V., Dunn, V.C., Theodore, T.G., 

and Ludington, S.D., 1996, Metallic mineral resources 

in the U.S. Bureau of Land Management’s Winnemucca 

District and Surprise Resource Area, northwest Nevada 

and northeast California: U.S. Geological Survey OpenFile Report 96–712, 146 p., and 11 plates, also available at 

http://pubs.er.usgs.gov/publication/ofr96712.

Singer, D.A., and Menzie, W.D., 2010, Quantitative mineral 

resource assessments—An integrated approach: New York, 

Oxford University Press, 219 p.

U.S. Geological Survey Central Mineral Resources and 

U.S. Bureau of Mines Western Field Operations Center, 

1989, Mineral summaries, Bureau of Land Management 

wilderness study areas, Idaho: Bureau of Land 

Management, Idaho Briefing Book, 187 p.

U.S. Geological Survey National Mineral Resource 

Assessment Team, 1998, Assessment of undiscovered 

deposits of gold, silver, copper, lead, and zinc in the United 

States: U.S. Geological Survey Circular 1178, 22 p., and 

GIS data. [Also available at http://pubs.usgs.gov/circ/

c1178/.]

Section H. Mineral-Resource Assessment for Locatable Minerals

By Jane M. Hammarstrom and Michael L. Zientek

Introduction

The objective of this project is to provide a description of 

mineral potential of the Sagebrush Focal Areas (SFAs) evaluated in 

the Sagebrush Mineral-Resource Assessment (SaMiRA) project in 

narrative form and on maps that can be used by others to evaluate 

reasonably foreseeable development in the study area. For this study, 

the assessment of mineral potential is required only for locatable 

minerals. Leasable and salable minerals are discussed in the reports 

prepared for the focal areas, but their potential was not evaluated.

Bureau of Land Management (BLM) focal areas in Montana, 

Wyoming and Utah, central Idaho, and the Oregon-Nevada-Idaho 

area were assessed by four different teams, each of whom produced 

an assessment report for their region. Each team (1) identified the 

possible mineral-deposit types for locatable commodities that could 

be present within the focal areas identified by the BLM for possible 

withdrawal from future mineral activity, (2) outlined those areas 

that could contain different types of mineral deposits on the basis of 

geology and other publically available data, and (3) evaluated the 

level of mineral-resource potential and level of certainty associated 

with the outlined areas using BLM assessment categories. In this 

study, areas that have potential for one or more types of mineral 

deposits are called mineral-resource tracts.

A Geologically Based Assessment 

Approach

The potential for mineral resources is a prediction of the 

likelihood of the occurrence of these resources. The specific form 

of the assessment qualitatively classifies mineral potential into 

categories based on the level of potential and the level of certainty 

as specified in BLM Manual Sections 3031 and 3060. The level 

of potential is based on favorable geologic environment, inferred 

geological processes, mineral occurrences, and other evidential 

data such as geochemistry and geophysics. The level of certainty is 

based on the amount of direct and indirect evidence to support the 

interpretation of the level of potential. For this study, a geologically 

based assessment method used the interrelated concepts of mineraldeposit types and mineral systems to evaluate mineral-resource 

potential. Models based on these concepts provide a predictive 

capability largely based on analogy with well-characterized mineral 

deposits and research on geologic processes of ore formation.

In this study, we report mineral potential by deposit type, 

rather than commodity, to facilitate the evaluation of reasonably 

foreseeable development. We use our understanding of geologic 

processes to define favorable geologic environments and elevated 

mineral potential. This assessment addresses the potential for 

deposits that may occur within the upper 1 kilometer (km) of the 

Earth’s surface. Exploration and development of deeper-seated 

deposits is technically feasible but extremely costly.

Mineral-Deposit Types and Models

A mineral deposit is a mineral concentration of sufficient 

size and quality that it might, under the most favorable of 

circumstances, be considered to have potential for economic 

development. Most mineral commodities occur in a variety of 

different types of mineral deposits. Gold, for example, occurs 

in surficial concentrations as placer deposits, in some volcanic 

environments as epithermal vein deposits, in metamorphic terrains 

as orogenic gold deposits, and as a coproduct in porphyry copper 

deposits that form in shallowly emplaced igneous intrusions.

Mineral deposits that share characteristics, in terms of how 

they form, their inherent value (tonnage and grade), the mining 

and beneficiation methods that can be used to develop them, and 

the remediation that must be done to minimize environmental 

impacts of mining are grouped into types. Mineral-deposit models 

are descriptive summaries of mineral-deposit types, used primarily 

for classifying occurrences into types but also for providing 

descriptive information on the favorable geologic setting.

Mineral-deposit models describe the essential attributes of 

each types of mineral deposit (Cox and others, 1986). The function 

of the model is to provide the geologist with information that 

they can interpret and use to discriminate (1) possible mineralized 

environments from barren environments and (2) types of known 

deposits from each other. Within the Bureau of Land Management 

(BLM), mineral-deposit models are used for resource assessment 

to classify land as to its potential for mineral and energy resources 

(Fisher and Juilland, 1986).

Descriptive mineral-deposit models such as the U.S. 

Geological Survey (USGS) models of Cox and Singer (1986) 

and the BLM models compiled by Fisher and Juilland (1986) 

list characteristics of the geologic environments in which the 

deposits are found and identifying characteristics of deposits. 

The deposit description includes information on host rocks, 

mineralogy, alteration, and geochemical and geophysical 

anomalies that are used by the assessment geologists to 

recognize the deposit type and to discriminate one deposit type 

from another. Mineral-deposit models compiled for the SFAs 

are included as appendix 3.
66 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Mineral Systems

Individual mineral deposits can be small parts of much larger 

mineralizing systems. For example, porphyry copper deposits, 

associated skarns, polymetallic veins, and epithermal precious-metal 

veins can all be reflections of a hydrothermal system associated with 

plutonic rocks (fig. H1). Similarly, sediment-hosted copper deposits 

and Mississippi-Valley-type zinc-lead-silver deposits are associated 

with regional fluid flow involving basinal brines in areas that lack 

active magmatism.

Knowledge of processes that control where mineral deposits 

form at regional and local scales is used to describe favorable 

geologic environments and can be expressed by mineral systems 

models. These models differ from simply descriptive models of 

mineral-deposit types, because they explicitly integrate research 

on geologic process. Commonly, mineral system models use 

“source-transport-trap” as a way to summarize information 

(Magoon and Dow, 1994; Wyborn and others, 1994; Magoon 

and Schmoker, 2000), but any model that summarizes a processbased understanding could be used. Mineral system models were 

developed for exploration targeting and mineral potential mapping.

Mineral-system models use components and processes to 

organize ideas about how different mineral-deposit types form. 

For example, hydrothermal mineral deposits can be understood by 

EXPLANATION

Host rocks, including limestone beds

Granodiorite/monzonite 

 (precursor pluton)

Porphyry stock overprinted with alteration 

Rock type

Intermediate argillic

Advanced argillic

Phyllic

Hydrothermal breccia

Propylitic

Potassic

Fault Skarn

Alteration

K

K K

K

Porphyry dike

Overburden

3

2

1

0 0

1

4 KILOMETERS

3 MILES

2

0 1 2 3 4 KILOMETERS

0 1 2 3 4 MILES

K

K

K

K K

K

K

K

K

K K

K

K

K

K

K K

K

K

K K

K K K

K

K

K

K K

K

K K

K

K

K

K

K

K K

K

K

K K

K

K K

K

K K

K

K K K

K K

K

K K

K

K K

K K

Cu 

skarn

Distal 

skarn

Pb-Zn 

skarn Polymetallic

replacement

Polymetallic 

 veins Porphyry Cu

Epithermal 

 veins

Figure H1. Illustration of a 

schematic cross section of possible 

deposit types associated with 

a hydrothermal-plutonic rock 

associated system.
Table H1. Relation between classes of mineral deposits, mineral systems, and mineral-deposit types with locatable commodities used 

in the Sagebrush Mineral-Resource Assessment (SaMiRA) project.

[Systems represent a subjective classification of deposit types adopted for SaMiRA to group deposit types that share some broad genetic characteristics or 

processes of formation. Note that some of the models listed in appendix 3 cover multiple deposit types, such as hectorite and specialty clay. In addition, some 

mineral-resource tracts were developed for multiple deposit types, such as both porphyry copper and copper skarn. SEDEX, sedimentary exhalative deposits]

General class System Deposit type

Magmatic Magmatic–directly related to igneous processes Diatreme-hosted diamond

Basalt-hosted sunstone

Hydrothermal Hydrothermal–plutonic rock associated Porphyry copper

Arc-related porphyry molybdenum (low-fluorine)

Climax-type porphyry molybdenum

Copper skarn

Lead-zinc skarn

Molybdenum-tungsten greisen

Tungsten skarn

Tungsten vein

Polymetallic replacement

Polymetallic vein

Distal-disseminated silver-gold

Carlin-type gold (silver, mercury, antimony)

Hydrothermal–volcanic rock associated Epithermal gold-silver (mercury)

Jasperoid precious metal

Epithermal gypsum

Volcanogenic uranium (Aurora and Kings River types)

Stanley district (Idaho)-type uranium 

Volcanic rock-hosted opal

Specialty gemstone

Hectorite (lithium-rich clay) 

Specialty clay

Hydrothermal–exhalative-magmatic processes Volcanogenic massive sulfide (Besshi-subtype)

Hydrothermal–exhalative-sedimentary processes SEDEX lead-zinc-silver

Bedded barite

Hydrothermal–metamorphic rock associated Orogenic low-sulfide gold-quartz vein

Sedimentary Sedimentary (formed during or after the conversion from sediment to sedimentary rock)Bentonite

Dolomite (high purity)

Sediment-hosted stratabound copper

Sandstone uranium (roll front) in intermontane basins

Hydroallogenic volcanic-hosted uranium

Zeolite

Sedimentary (formed during deposition of the sediment) Iron formations (Algoma and Superior subtypes)

Lacustrine diatomite

Surficial Surficial–mechanical (placer) Heavy mineral placer

Placer gold

Paleoplacer gold 

considering the source of the ore-forming fluid, its physical and 

chemical character, the mechanisms for dissolving and transporting 

ore-forming components, and the causes of precipitation from it 

(Skinner and Barton, 1973). Sites where appropriate combinations 

of structural, chemical, and physical conditions that force oremineral precipitation reactions are called ore traps (Reed, 1997). 

The deposition of ore minerals will not occur unless all the essential 

components are present and processes occur in the correct sequence 

and location (Magoon and Dow, 1994; Kreuzer and others, 2008; 

McCuaig and others, 2010).

Mineral systems models serve two functions in mineralresource assessments. All components and processes that relate to 

mineral-deposit type can be systematically evaluated to identify 

areas where a mineral-forming system could be present. Another 

function of these models is to use the components and processes 

of the mineral-system model to define the assessment unit in areas 

where the existence of a mineral-forming system is known from the 

presence of deposits and prospects.

The types of mineral deposits that may occur within the focal 

areas are grouped in mineral systems associated with magmatic, 

hydrothermal, sedimentary, or surficial geologic processes (table H1). 

Within a given mineral system, a variety of different types of deposits 

can form. The occurrence of porphyry copper deposits for example, 

suggests that the hydrothermal-plutonic mineral system may have also 

formed skarns or replacement deposits or other deposit types where 

metals are transported in magmatic fluids interacting with meteoric 

water in a plutonic setting. The mineral-system concept provides a 

framework for considering what could occur in a given setting.

Section H. Mineral-Resource Assessment for Locatable Minerals 67
68 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Map Scale and Resolution

We assume that the scale at which the data are needed is 

about 1:100,000 to 1:250,000. For a given scale, the minimum 

map unit is the size in map units below which a narrow feature 

can be reasonably represented by a line and an area by a point. 

USGS map standards state that the minimum polygon size on 

maps is about 1 square millimeter (mm2) (GDS-FGDC, 2006). 

For 1:100,000-scale maps, 1 mm2 corresponds to 0.01 square 

kilometer (km2) (10,000 square meters, m2). For 1:250,000-

scale maps, 1 mm2 corresponds to 0.063 km2 (62,500 m2). The 

acceptable error for USGS maps is about 1/50th of an inch (U.S. 

Geological Survey, 1999), which corresponds to 50 meters (m)

for 1:100,000-scale maps and 100 m for 1:250,000-scale maps.

In 1987, Waldo Tobler, analytical cartographer (now emeritus 

from University of California-Santa Barbara) wrote, “The rule 

is: divide the denominator of the map scale by 1,000 to get 

the detectable size in meters. The resolution is one half of this 

amount” (Nagi, 2010). This rule is a useful guide to keep in mind 

when applying geographic information system (GIS) tools in 

assessment (table H2). 

Table H2. Guide to map scale, detectable size of a map feature, 

and resolution.

Map 

scale

Detectable size, in 

meters

Raster resolution, in 

meters

1:100,000 100 50

1:250,000 250 125

Assessment Process

The focal area assessment teams followed a number of steps 

or procedures to conduct the assessment of mineral potential. In 

general, the steps were:

1. Work with project managers to understand the scope of 

work and the anticipated end use of the assessment. This 

started with a project meeting in December 2015 and 

continued throughout the course of the assessment work.

2. Determine which mineral-deposit types and commodities 

need to be assessed and make sure appropriate models 

are available. This was done by using the expertise of 

USGS scientists who have worked in the study areas 

and by reviewing results of previous mineral-resource 

investigations and assessments in the study area.

3. Gather and compile data such as geology, mineral 

occurrences, mineral exploration, rock alteration 

inferred from satellite imagery, soil and stream-sediment 

geochemistry, and potential-field geophysics. Many of the 

datasets used for these assessments are described in other 

sections of this report. 

4. Enhance existing datasets as needed from larger scale 

geologic maps and geological literature. 

5. Construct preliminary maps showing areas with mineral 

potential

6. Conduct a workshop to revise the preliminary maps and 

assign levels of mineral potential and certainty. In most 

cases, representatives from State geological surveys were 

observers or participants at the workshops.

7. Present results of the assessment to an evaluation panel.

8. Prepare report for technical review.

Before each workshop, the assessment teams developed a 

list of possible mineral-deposit types and commodities to consider, 

classified known deposits and prospects in terms of deposit type, 

and identified mineral-deposit models needed to conduct the 

assessment. The assessment teams evaluated available data and 

developed preliminary mineral-resource tracts. 

At the workshops, the teams refined the tracts and 

assigned a mineral potential and level of certainty to 

each tract. The tracts were compared to compilations that 

summarized the level of mineral activity as indicated by 

authorized and closed mining claims, surface-management 

notices and plans, and a compilation of active exploration 

areas from literature. The rationale for tract delineation and 

the classification potential and certainty were recorded and 

summarized in a tabular format (table H3).

Following each workshop, the mineral-potential tracts 

were refined, and any unresolved issues identified during the 

assessment workshops were addressed. Each focal area team 

prepared a presentation for an evaluation panel composed 

of five scientists who were not directly involved in the 

assessment of the focal area. The selection of mineral-deposit 

models, rationale for mineral-resource tracts, and classification 

of mineral potential for locatable commodities were evaluated 

by the panel and comments were communicated to the 

assessment team prior to final report preparation. The panel 

also evaluated the information presented for leasable and 

salable commodities. This evaluation process provided a check 

on consistency in applying the assessment criteria throughout 

the focal areas.

Mineral-Resource Tracts

According to BLM guidelines, when known geologic 

conditions in an area fit a model, they define a “favorable 

geologic environment.” Mineral-resource specialists determine 

favorable geologic environments by integrating and assessing 

different lines of evidence (Bureau of Land Management, 1985):

A. Favorable rocks (lithostratigraphic suitability).

B. Favorable geologic structure (faults, folds, and other 

 structural features).
Section H. Mineral-Resource Assessment for Locatable Minerals 69

Table H3. Example data table for a mineral-resource tract used in the Sagebrush Mineral-Resource Assessment (SaMiRA) project.

[BLM, Bureau of Land Management; MRDS, Mineral Resources Data System; USMIN, U.S. Geological Survey Mineral Deposit Database project; PLSS, 

Public Land Survey System; ASTER, Advanced Spaceborne Thermal Emission and Reflection Radiometer]

Focal Area: 

Mineral-resource tract name:

Tract identifier:

State:

County(ies):

Mineral-Deposit Types:

Commodities:

Mineral potential (H, M, L) See appendix 2 for definitions. Level of certainty (A, B, C, D)

Basis for tract Fundamental basis for the tract (for example, Cretaceous arc segment, Triassic basin) 

Previous assessment(s) Yes or No? Overlapped by a permissive tract from a previous assessment ranked high? 

Favorable rocks

(litho-stratigraphic suitability)

Source map and scale

Map units

Favorable geologic structures

(faults, folds, other)

Fault bounded? Regional trend? Folds?

Describe or state no data.

Evidence from mineral occurrences

(specify dataset: MRDS, USMIN, other)

Deposits (production or mineral inventory within 500 meters of PLSS boundary)

Related deposit type

Prospects

Occurrences of possible related commodity

Evidence of rock alteration

(maturation, hydrothermal alteration)

Alteration mapped or described in literature

Landsat alteration

ASTER alteration

Geochemical evidence Anomalies or other data

Geophysical evidence Anomalies or other data

Evidence from other sources For example, depth to basement, mineralogy, petrology, and so forth

Exploration history

(BLM data) 

Plans of operations for appropriate commodity

Active notices for an appropriate commodity

Closed plans of operations for appropriate commodity

Active lode claims

Active placer claims

USMIN data Active exploration areas 

Additional notes and references

C. Evidence of rock alteration (maturation, hydrothermal

 alteration).

D. Geochemical evidence (anomalies).

E. Geophysical evidence (anomalies).

F. Evidence from mineral occurrences.

G. Evidence from other sources (depth to basement, 

 mineralogy, and so forth).

Mineral-resource tracts were constructed by identifying the 

appropriate geological environments and the deposit types likely 

to occur in each focal area (see table H4 for an example). When 

data and time permit, computational techniques can be used to 

map mineral potential by combining digital files for the different 

types of evidence as listed above. For this study, a single 

computational approach was not possible, given the quality of 

the data and the diversity of deposit types and mineral systems 

that were present. The areal extent of a particular mineralresource tract varies by mineral system and by deposit type. 

Experts determined what data and approach was best suited 

to map areas with mineral potential. In the following sections, 

we give some examples of how mineral potential was mapped. 

Specific descriptions are included with each focal area report.

A mineral-resource tract for a hydrothermal mineral system 

associated with plutonic rocks, for example, could contain 

porphyry deposits, as well as associated deposit types such as 

skarn and replacement deposits in carbonate rocks, polymetallic 

veins, and distal disseminated deposits. In some cases, mineralresource tracts for one deposit type are coincident with tracts 

for other deposit types. However, the mineral potential and 

uncertainty are assigned by deposit type. Shallow-level magmatic 

rocks formed at convergent tectonic-plate margins are indicative 

of the favorable environment for porphyry copper deposits. For 

some deposit types, criteria were established by defining very 

specific lithologies. Skarns, for example, typically form at the 

contact of limestone with a calcalkaline pluton. For polymetallic 
70 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Table H4. Example of mineral-resource tract criteria used in the Sagebrush Mineral-Resource Assessment (SaMiRA) project for 

Carlin-type gold deposits in the Southeastern Oregon and North-Central Nevada, Southern Idaho and Northern Nevada, and SheldonHart Mountain National Wildlife Refuge Complex of Oregon Sagebrush Focal Areas (SFAs; see section A, fig. A1).

[km, kilometer]

Necessary criteria for a mineral-resource tract

1. Areas underlain by continental crust and subcontinental lithospheric mantle (for example, east of the initial strontium 0.706 crustal 

discontinuity).

2. Areas within the limits of the southward sweeping Eocene calcalkaline magmatic arc.

3. Cambrian to Permian marine calcareous or dolomitic sedimentary rocks deposited along the western margin of the United States in slope, 

shelf, foreland basin, and overlap settings, as well as rocks of the Havallah Basin. The largest deposits are in Ordovician, Silurian, and 

Devonian slope facies near the platform margin below the Roberts Mountains allochthon. Nevada border map units: PzMzs, Pzrm, Pzh. 

State of Nevada map units include Nolan, Basin, Slope, Shelf, Foreland, Overlap, and Golconda.

4. Aforementioned sedimentary host rocks are within 1 km of present surface. In other words less than 1 km of sedimentary, volcanic, or 

alluvial cover.

veins to form, structural controls such as faults are more important 

than host rock because the structures provide hydrothermal fluid 

transport pathways through a variety of rock types. 

In addition to permissive geology for the deposit type, 

the tract is drawn to include any direct evidence of mineral 

occurrences, such as deposits that have a defined resource, active 

exploration projects for the deposit type, and (or) BLM permits, 

as well as indirect evidence, such as geochemical anomalies, 

mineral showings of a commodity that could be related to the 

deposit type, and (or) alteration (fig. H2). Mineral occurrences 

include mineral deposits, mineral prospects, and mineral 

showings. Table H5 lists the criteria used to assign mineraloccurrence data to one of these three categories. The essential 

distinction between a deposit and a prospect is that a deposit has 

a formal mineral inventory (table H6). The nature and density 

of mineral occurrences, the nature and density of alteration 

appropriate for the deposit type, and the level of exploration 

and mining activity indicated by BLM permits and claims were 

also considered in delineating the extent, potential, and level of 

certainty associated with each tract. A mineral-resource tract may 

or may not contain known deposits or prospects.

In some cases, a geologic structure such as a fault provided 

a tract boundary. Geophysical data (chapter C) provided guidance 

on areas where shallow buried plutons might exist or areas of 

thick basin cover (>1 km) are present. Although deposits can 

occur at greater depth, this assessment only considered the mineral 

potential within the upper 1 km of the surface.

A number of tools are available for processing data to facilitate 

making mineral-resource tracts. These include the application of 

buffer distances around known deposits or particular map units and 

using geospatial tools to examine the density of mineral occurrences. 

These tools, used in conjunction with the other available data, aid 

the delineation of the spatial extent of mineral-resource tracts, as 

described in the focal area reports. The mineral-resource tracts for 

locatable minerals for the SaMiRA project are provided in a data 

release of spatial data (San Juan and others, 2016). Mineral potential 

and level of certainty are included in the tract attributes.

Buffers

The geoprocessing buffer tool in ArcGIS can be used to 

simplify complex shapes, address cartographic uncertainty, 

approximate the size of a feature that is not mapped, and (or) 

determine an appropriate search radius for adjacent deposits. 

Buffering was used by most of the assessment teams. Most of the 

geologic-map databases used in the assessment combine geologic 

bedrock and surficial geologic units. If a favorable geologic unit is 

selected from the database, the polygon commonly has a complex 

shape because of intersecting surficial geologic units. Buffering 

can be used to fill in areas underlain by alluvium to make a 

polygon that more closely represents the bedrock extent of the 

permissive unit.

Buffering was also used to approximate the extent of 

hydrothermal alterations systems that are associated with 

hydrothermal deposit types. Hydrothermal mineral deposits are 

the most common mineral-deposit types, but direct evidence of 

the areal extent of hydrothermal alteration is almost never shown 

on regional-scale (1:100,000–1:250,000) geologic maps. For 

some hydrothermal mineral deposits, the sizes of areas underlain 

by mineralized or altered rock have been compiled and summary 

statistics can be calculated. For example, these data have been 

compiled for porphyry copper deposits (Singer and others, 

2008), polymetallic veins (Bliss, 1994), and sediment-hosted 

gold deposits (Berger and others, 2014). Using the information 

compiled for these systems, a buffer radius was selected and 

applied to data points that provided direct evidence for the 

presence of a hydrothermal mineral occurrence (of a given type).

Depending on the scale of available geologic maps, 

deposit type, and the occurrence of unexposed mineral deposits, 

the presence of a mineral system may not always be readily 

inferred from a geologic map. In such cases, the mapped mineral 

occurrences can serve as the primary sampling method for 

delineating the extent of a mineral-resource tract. The approximate 

diameter of well-exposed pluton-related hydrothermal systems 

ranges from just a few hundred meters to tens of kilometers 
Figure H2. Illustration showing an example of datasets used to develop a mineral-resource tract for porphyry copper and skarn 

deposits. The final tract outline encompasses the permissive map unit, the mineral occurrences, alteration, and areas of exploration 

interest based on Bureau of Land Management (BLM) records. PLSS, Public Land Survey System; ASTER, Advanced Spaceborne 

Thermal Emission and Reflection Radiometer; USMIN, U.S. Geological Survey Mineral Deposit Database.

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D !D D! !

D

D

D

!

D

Deposit

Prospect

 Showing

Mineral occurrences

 (metallic)

Geology

Jgr, Jurassic granodiorite pluton $ " "

$

Geochemistry

"

$

Rock

Copper anomalies

(Cu > 16 x background)

Stream sediments 

and soils

BLM mining plans

 and notices

PLSS sections

 with notices 

 for copper or 

 gold

BLM active lode claims

 per PLSS section 

1-8

9–20

21–33

34–44

45–74

ASTER alteration

Areas with 

 concentrations 

 of argillic and

 jarositic alteration

Final mineral resource tract 

Section boundary

Proposed withdrawal

Select permissive lithology

for a hydrothermal-plutonic 

rock associated system 

from a geologic map

Plot mineral occurrences

(USMIN data)

Evaluate geochemical data

Evaluate mining activity

Evaluate mining activity Evaluate alteration 

1 mile

1 mile

 Chapter A Figure H2

Section H. Mineral-Resource Assessment for Locatable Minerals 71
72 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Table H5. Relations among mineral occurrences, deposits, prospects, and showings used in the Sagebrush Mineral-Resource 

Assessment (SaMiRA) project.

Name Name Criteria Notes

Mineral 

occurrence

Mineral 

deposit

Has a formally defined (drill-indicated) mineral-resource estimate; does not 

need to be economic (include sites with resources, as well as reserves)

May be able to categorize by 

deposit type

Mineral 

prospect

Significant exploration site; drilling; plan-of-operation May be able to categorize by 

deposit type

Mineral 

showing

Exploration target; minor occurrence May only know commodities 

present

Table H6. Sources of information for classifying mineral occurrences as deposits or prospects used in the Sagebrush MineralResource Assessment (SaMiRA) project.

[BLM, Bureau of Land Management; USFS, U.S. Forest Service; NI, National Instrument]

Sources of information on mineral inventory Deposit Prospect

Formal mineral inventory (supported by drilling 

and sampling as appropriate for deposit type).

No formal mineral inventory; some geologic 

estimates of resources may be in older 

literature.

Companies listed on Canadian, Australian, 

London stock exchanges

Feasibility study completed and reserves 

reported.

Resources reported (Annual reports; NI 43-101 

reports).

Information may be on company Web pages; 

usually for junior companies; almost never 

for majors.

Companies listed on U.S. stock exchange Reserves reported in company annual reports.

USFS and BLM Pending patent application.

Plan of operation indicating extensive drilling 

and sampling.

Notice of intent.

Federal and (or) State regulatory agencies Pending or approved mining permit

Environmental impact studies or environmental 

analysis reports studies or reports.

Mineral occurrences database Past production, reserves, and measured and 

indicated resources.

Inactive (closed) or abandoned mine.

Incompletely characterized mineral resources; 

may be some drilling.

Imagery Mine pit and operations may be visible. Surface disturbance and evidence of exploration 

such as trenches or drill pads.

Privately held companies Information usually not reported. Information usually not reported.

(Sillitoe, 2010). The maximum radius that would be appropriate 

to depict the uncertainty in the location of a hidden or unmapped 

part of a mineral system related to a sampling point (mineral 

occurrence) that encounters the system would be half that distance 

(probably less than 10 km). The footprint of porphyry copper 

systems, the archetype of pluton-related systems, for example, 

was documented by Berger and others (2008). The median radius 

for those systems is about 5 km, and the 90th percentile is about 

2.6 km (table H7). These data represent minimum sizes, because 

parts of many porphyry systems are covered. Thus, about 3 km 

may serve as an appropriate buffer radius around a porphyry-type 

mineral occurrence as a tool for developing mineral-resource tracts 

for porphyry copper deposits.

The polygons created by buffering the mineral occurrence 

points formed the basis for many of the mineral-potential tracts in 

some reports. What buffer radius should be used to approximate 

the size of a hydrothermal system for a known mineral-occurrence 

point? Histograms of available data show that alteration areas 

are right skewed for a given deposit type (similar to tonnage 

values). Some assessors wanted to use a buffer radius that would 

approximate the maximum size of an alteration area; others argued 

that the buffer radius should be closer to the mean or median 

value. The recommended radius is based on the 90th percentile 

(table H7).

Users of the mineral-resource tracts should consult the 

tract descriptions in the SaMiRA reports for each SFA to 

understand the rationale for the buffer radius, the value that 

was used (maximum, mean, or other), and how it was applied 

(to data points corresponding to a mineral occurrence of a 

given deposit type).
Using Near Distance and Density Mapping to 

Map Areas with Mineral Potential

Other geoprocessing tools were used to examine the distance 

relations between one site and another as a guide to delineating 

mineral-resource tracts. In applying these tools, the spatial relation 

of, for example, metallic-mineral sites relative to each other can 

be determined using a proximity tool to compute the distance that 

one would have to search from a given site to reach other sites. 

The results of generating a “near distance table” provide a guide to 

the distance beyond which it would be highly unlikely that another 

site would be found 

Mineral occurrences tend to be spatially clustered. Statistics 

that summarize the nearest distance between spatially clustered 

points were used in the development of some mineral-potential 

tracts when the distribution of mineral occurrences could not 

be related to features on geologic maps. In the absence of other 

Section H. Mineral-Resource Assessment for Locatable Minerals 73

Table H7. Summary statistics for the areal extent of mineralized rock and alterations systems associated with various deposit types 

and suggested buffer radius for tract delineation used in the Sagebrush Mineral-Resource Assessment (SaMiRA) project.

Deposit 90th 

percentile

75th 

percentile 

(quartile)

50th 

percentile 

(median)

25th 

percentile 

(quartile)

10th 

percentile Mean Number

Buffer radius 

based on 90th 

percentile 

(assuming 

circle), in 

kilometers

Reference

Deposit, ore body, or ore

Volcanogenic massive 

sulfide

0.52 0.11 0.02 0.00 0.00 0.18 126 0.4 Mosier and others, 2009

Sediment-hosted gold 2.85 1.30 0.40 0.13 0.04 1.04 112 1.0 Berger and others, 2014

Porphyry copper 2.65 1.53 0.60 0.27 0.10 1.25 174 0.9 Singer and others, 2008

Sediment-hosted zinc-lead 15.70 4.70 1.00 0.40 0.24 38.96 129 2.2 Singer and others, 2009

Sediment-hosted 

stratabound copper

50.11 9.90 1.55 0.53 0.15 19.40 55 4.0 Taylor and others, 2013

Nickel-cobalt laterite 70.40 33.00 9.40 3.15 1.06 24.10 93 4.7 Berger and others, 2011

Alteration or target area

Volcanogenic massive 

sulfide

49.35 8.53 1.04 0.00 0.00 8.76 12 4.0 Mosier and others, 2009

Mixed base-and-precious 

metal veins

23.00 No data 2.90 No data 0.36 No data 49 2.7 Bliss, 1994

Sediment-hosted zinc-lead 17.28 9.33 3.20 0.43 0.14 5.63 17 2.3 Singer and others, 2009

Porphyry copper 21.00 12.00 5.10 2.00 0.85 8.92 184 2.6 Singer and others, 2008

information, the maximum near distance between clustered points 

for a given type of mineral occurrence was used as the buffer 

distance to establish the farthest search area for that deposit type. 

In some cases, this was used to define the lowest ranked mineral 

tracts in this study (low levels of potential and confidence).

To define areas of higher confidence, density of mineraloccurrence points was calculated using the kernel-density tool 

in ArcGIS. This tool calculates a magnitude-per-area from the 

point features to illustrate the spatial density of sites. Tobler’s 

first law of geography (http://support.esri.com/other-resources/

gis-dictionary/term/Tobler’s%20First%20Law%20of%20

Geography) was used when generating kernel-density maps for 

SaMiRA (table H8). ArcGIS usually asks for cell size of output 

raster, and the information in table H2 was used to determine 

an appropriate value. The 90th-percentile value near distance 

was used as the search radius when performing this calculation. 

This value was chosen because a search distance of this radius 

Table H8. Examples of near distance calculations that were considered for kernel-density mapping used in the Sagebrush MineralResource Assessment (SaMiRA) project.

[MRDS, U.S. Geological Survey Mineral Resource Database; USMIN, U.S. Geological Survey Mineral Deposit Database project]

Data Number of 

points

Near-distance, 90th 

percentile, in meters

Near-distance, 95th 

percentile, in meters

Missouri River Breaks diatremes 86 3,923 11,220

Leucite Hills diatremes 25 7,123 7,643

Bedded barite in MRDS and USMIN in Sagebrush Focal Areas in Nevada 2,700 3,300

Carlin‐type gold deposits in Nevada 4,200 12,000
74 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

should find most (90 percent) of the mineral occurrences used in 

the calculations. The resulting density maps were classified into 

groups and used to map level of certainty. This approach was 

used for assessing diamond potential associated with diatremes 

and related intrusions in Montana (Missouri River Breaks field) 

and Wyoming (Leucite Hills).

Geostatistical Analysis

Geostatistical models were used to model where bentonite 

should crop out in the assessment for bentonite in the Montana 

focal area. The models were also used to create surfaces that 

represent the bentonite layers or the interval containing the 

bentonite layers. Those modeled surfaces were then intersected 

with a digital elevation model to create a map showing where 

bentonite layers should crop out.

Mineral-Resource Potential and Certainty

The assessment methodology used in this report follows 

the BLM assessment guidelines and relies on subjective 

assessment. For locatable minerals, areas are assigned high, 

moderate, low, or no mineral-resource potential according to 

the degree of likelihood that geologic processes operated in 

an area in such a way as to permit accumulation of resources 

(appendix 2). If no useful data are available, the designation 

ND (not determined) is used. In addition to the level of 

mineral-resource potential, a level of certainty is applied to 

document the quality and quantity of data available to support 

the assigned level of potential (appendix 2). These levels range 

from A (least certain) to D (most certain), depending on the 

evidence to support the possible existence of mineral resources 

on the mineral-resource tract. Known deposits, for example, 

provide direct evidence of mineral resources, whereas a 

geochemical anomaly or a mineral showing might represent 

indirect evidence of mineral resources.

The definitions of these levels of resource potential were 

developed by Goudarzi (1984) and adopted by BLM (1985). The 

range of possible mineral-potential classifications for a given 

mineral-resource tract is illustrated in figure H3. The assessment of 

mineral potential and level of certainty assigned to mineral-resource 

tracts depends on consideration of BLM evidence factors. For 

example, a mineral-resource tract assigned an H/D classification has 

a high potential for mineral resources and a high level of certainty. 

By definition, mineral-resource tracts have at least a low potential 

because the tract is based on some geologic evidence that indicates 

that the area is permissive for the occurrence of the deposit type. 

Additional types of evidence are necessary to warrant a designation 

of moderate or high mineral potential.

A practical way to interpret the different subjective levels 

might be that most mining companies would be willing to risk 

exploration dollars in an area with high potential, whereas areas 

with moderate potential might be attractive to some optimistic 

investors but not to more conservative ones (Ludington, 2006). 

The level of certainty of the assigned resource potential reflects 

the amount and quality of useful data available at the time of 

the assessment. As new or more detailed information becomes 

available, the resource potential and level of certainty in an area 

can change. The designation of an area as having high potential 

does not necessarily imply that deposits that might be discovered 

there could be developed and operated successfully. When 

information is available about resource quality that might bear on 

the economic viability of deposits, it is presented separately from 

the potential designation.

SaMiRA Assessment Guidelines

The guidelines adopted for assigning mineral potential 

and level of certainty for locatable minerals in SaMiRA are 

summarized in figure H3. Specific rationales for each permissive 

tract are cited in the focal area reports. The tract example shown 

in figure H2 would be classified as H/D because of the abundant 

direct evidence illustrated by the occurrence of deposits with 

production, prospects, and exploration activity, and the indirect 

evidence from geochemistry and alteration. Examples of 

datasets that provided direct and indirect evidence to support the 

interpretation of the level of potential and certainty are listed in 

table H9. Direct evidence indicates that the mineral occurrence can 

be assigned to a deposit type or that mineralized rock is present. 

These guidelines, in combination with the subject matter expertise 

of the assessment teams, determined the final designation of each 

mineral-resource tract.

Table H9. Direct and indirect evidence indicators for assigning mineral potential used in the Sagebrush Mineral-Resource Assessment 

(SaMiRA) project.

[ASTER, Advanced Spaceborne Thermal Emission and Reflection Radiometer]

Criteria

Mineral occurence databases

Geochemistry 

of soils, stream 

sediments, and 

rocks

ASTER 

anomalies

Regionalscale 

geophysics

43 CFR 

3809 

permits

Mining 

claims

Current or historical 

deposit with 

identified resources, 

past production, or 

active exploration

Prospect or 

showing

Direct evidence of a 

particular deposit type

X

Direct evidence that 

mineralized rock is present

X X X Maybe

Indirect only X X X X
Figure H3. Matrix of possible mineral potential and certainty designations and criteria used for the mineral-resource 

assessment for locatable minerals in the Sagebrush Mineral-Resource Assessment (SaMiRA) project. Levels of resource 

potential: N, none; L, low; M, moderate; H, high. Levels of certainty: A, insufficient evidence; B, indirect evidence; C, direct 

evidence; D, abundant evidence. USMIN, U.S. Geological Survey Mineral Deposit Database.

Level of certainty

A B C D

N

L

M

H

Level of resource potential

H/A

M/A

L/A

H/B

M/B

L/B

H/C

M/C

L/C

H/D

M/D

L/D

N/D

High potential with 

insufficient evidence

Moderate potential 

 with insufficient 

evidence

Low potential with 

insufficient evidence

High potential with 

indirect evidence

Moderate potential 

 with indirect evidence

Low potential with 

indirect evidence

High potential with 

direct evidence

Moderate potential

with direct evidence

Low potential with 

direct evidence

High potential with 

abundant direct and

indirect evidence

Moderate potential with 

abundant direct and

indirect evidence

Low potential with 

abundant direct and

indirect evidence

No potential

Current production/significant inventor.

Significant past production.

Active or pending notices or mine plans.

Numerous active claims.

USMIN active exploration.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Historic mining.

Historic claims.

No active notices or mine plans.

No active exploration. 

No claims.

No other applicable data.

Permissive host rocks +/- previous assessment 

Permissive host rocks +/- previous assessment

Permissive host rocks +/- previous assessment 

Few active claims.

Historic mining. 

No USMIN active exploration. 

No active notices or mine plans.

Minor past production.

Attractive exploration targets.

Active or pending notices or mine plans.

Numerous active claims.

USMIN active exploration.

Attractive exploration targets.

Active or pending notices or mine plans.

Numerous active claims.

USMIN active exploration.

Contains 2 or more of the following:

Current production/significant inventory.

Significant past production.

Active or pending notices or mine plans.

Numerous active claims.

USMIN active exploration.

Contains 1 or more of the following:

Minor past production.

Attractive exploration targets.

Active or pending notices or mine plans.

Numerous active claims.

USMIN active exploration.

Attractive exploration targets.

Active or pending notices or mine plans.

Numerous active claims.

USMIN active exploration.

Chapter A Figure H3 (Appendix fig. for all other chapters)

Contains 2 or more of the following: Contains 2 or more of the following:

Contains 1 or more of the following: Contains 1 or more of the following:

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Reserved for a specific type of 

resource in a well-defined area. For 

example, it is appropriate to say that 

there is no oil potential in an area 

where the only rocks present are 

unfractured Precambrian granite, 

but the term ”low” is appropriate if 

there is a slight possibility for the 

presence of resources.

Section H. Mineral-Resource Assessment for Locatable Minerals 75
76 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

References Cited

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2008, Preliminary model of porphyry copper deposits: 

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55 p., accessed May 15, 2009, at http://pubs.usgs.gov/

of/2008/1321.

Berger, V.I., Mosier, D.L., Bliss, J.D., and Moring, B.C., 2014, 

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Section H. Mineral-Resource Assessment for Locatable Minerals 77

Section I. Locatable Mineral Market-Demand Analysis 

Commodity Profiles

By Donald I. Bleiwas

The present and potential future market-demand analyses 

were developed to provide a general description of domestic 

production and a qualitative assessment of inferred future market 

demands for the important locatable minerals identified to have a 

moderate and high potential for occurrence within the proposed 

withdrawal areas in the Bureau of land Management (BLM) 

Sagebrush Focal Areas (SFAs; see section A, fig. A1). A table 

of strategic and critical materials is provided in appendix 4. A 

complete listing of the market-demand commodity profiles are 

provided in appendix 5.

Individual mineral-commodity profiles contained in 

the market-demand analysis section were developed by U.S. 

Geological Survey (USGS) minerals and materials specialists 

in the National Minerals Information Center (NMIC). The 

NMIC’s primary mission is to collect, monitor, and analyze data 

on domestic and foreign nonfuel mining and mineral-processing 

industries and markets for more than 90 mineral commodities 

essential to the U.S. economy and national security.

The sources of information used for developing the 

mineral-commodity profiles include academia, Federal, State 

and local agencies, industry contacts, international and domestic 

organizations, publications, questionnaires and surveys, and site 

visits.

Each mineral-commodity profile contains descriptive and 

statistical information that address domestic and global production, 

domestic consumption, historical and recent prices, major uses, 

recycling, stocks, shipments, the strategic and critical nature of the 

commodity, and trade. In some cases, recent mine production in 

or proximal to the proposed withdrawal area is discussed in each 

commodity profile.

Section J. Energy Mineral Resources

By Jonathan M.G. Glen, Jacob DeAngelo, Colin F. Williams, Jon E. Haacke, Ronald M. Drake II, Gregory L. 

Gunther, Stuart A. Giles, and Aimee E. Graeber

This section on energy mineral resources data compiled 

for the Sagebrush Mineral-Resource Assessment (SaMiRA) 

project consists of three subsections. The first section 

describes geothermal energy resources. The second section 

provides an overview of methods used for reporting coal 

resources. The third section describes the methods used in 

reporting oil and gas data.

Geothermal Energy Resources

By Jonathan M.G. Glen, Jacob DeAngelo, and Colin 

F. Williams

Introduction

Geothermal energy constitutes one of the Nation’s 

largest sources of renewable electric power. Its potential is 

an important consideration given that current projections 

indicate the United States will need to increase its electrical 

power generating capacity by approximately 25 percent over 

the next 25 years (Energy Information Administration, 2015). 

Although the installed capacity of geothermal (approximately 

3,000 megawatts-electric or MWe) falls short of meeting 

the Nation’s entire power needs, it constitutes a potentially 

significant part of the estimated available resources based on 

recent assessments. With potential advances in exploration 

and development technologies, these resources could provide 

a substantial source of baseload electric power. Owing to 

government mandates and incentives for renewable energy, 

it is expected that the demand for geothermal energy will 

continue to grow, and, given the concentration of geothermal 

resources in the Western United States, a substantial part of 

this growth could occur on public lands. This section, which 

provides a review of the geothermal resource potential of the 

proposed Sagebrush Focal Areas, is based on the results of 

the USGS 2008 assessment of the Nation’s moderate- and 

high-temperature geothermal resources (Williams and others, 

2008b) that includes a provisional assessment of Enhanced 

Geothermal Systems (EGS), as well as earlier USGS and 

State-level inventories and assessments.

Overview of USGS Geothermal-Resource 

Assessments and Definitions

Comprehensive efforts to assess the geothermal resources of 

the United States began after passage of the Geothermal Energy 

Research, Development, and Demonstration Act of 1974, which 

assigned responsibility for the evaluation and assessment of 

geothermal resources to the USGS through the U.S. Department 

of the Interior. The USGS produced three national geothermalresource assessments in the following 8 years, USGS Circular 726, 

Assessment of Geothermal Resources of the United States-1975 

(White and Williams, 1975), USGS Circular 790, Assessment 

of Geothermal Resources of the United States–1978 (Muffler, 

1979), and USGS Circular 892, Assessment of Low-temperature 

Geothermal Resources of the United States–1982 (Reed, 1983). 

After the passage of the Energy Policy Act of 2005, the USGS 

produced an updated assessment of the moderate-temperature 

(90 to 150 degrees Celsius, °C) and high-temperature (>150 °C) 

geothermal resources of the United States (Williams and others, 

2008a, b). In the 2008 assessment, the USGS provided estimates 

of the geothermal electrical power generation potential from 

identified and undiscovered resources and included a provisional 

estimate of the power-production potential of Enhanced 

Geothermal Systems (EGS) techniques, which involve the creation 

of producing geothermal reservoirs in low-permeability rock units.

All four of these national geothermal assessments 

consider both identified and undiscovered resources and use 

the following definitions established for the USGS by Muffler 

and Cataldi (1978). The geothermal-resource base is all of 

the thermal energy in the Earth’s crust beneath a specific 

area, measured from the local mean annual temperature. The 

geothermal resource is that part of the resource base at depths 

shallow enough to be tapped by drilling in the foreseeable future 

that can be recovered as useful heat economically and legally at 

some reasonable future time. Similarly, the geothermal reserve 

is the identified part of the resource that can be recovered 

economically and legally at the present time using existing 

technology.

Conventional Geothermal Resources

In the context of this report, geothermal resources are 

divided into two categories—conventional and unconventional. 

Conventional resources are those associated with geothermal 

systems defined by Muffler (1979) as “any regionally localized 
82 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

geological setting where naturally occurring parts of the Earth’s 

thermal energy are transported close enough to the Earth’s 

surface by circulating steam or hot water to be readily harnessed 

for use.” These geothermal (or alternatively, hydrothermal) 

systems involve the natural vertical movement of water through 

either free or forced convection (for example, Duffield and 

Sass, 2003). All of the geothermal systems developed for 

commercial electric power generation in the United States fall 

in this category. Within this framework, identified hydrothermal 

systems are divided into three temperature classes—low 

temperature (<90 °C), moderate temperature (90 to 150 °C), 

and high temperature (>150 °C). High-temperature systems 

include both liquid- and vapor-dominated resources. Moderatetemperature systems are principally liquid dominated, and 

all low-temperature systems are liquid dominated. All three 

temperature classes are suitable for direct-use applications, but 

in general only moderate- and high-temperature systems are 

economically viable for electric power generation. The heat 

source of a hydrothermal system can be characterized as either 

magmatic or amagmatic. Magmatic geothermal reservoirs, 

which derive their heat from shallow-crustal magma bodies, 

are typically larger and higher in temperature than amagmatic 

systems that owe their heat to deep circulating fluids within the 

background geothermal gradient of the upper crust (Coolbaugh 

and others, 2006).

Unconventional Geothermal Resources

In addition to conventional hydrothermal resources, there 

are several geothermal-resource types that have the technical 

potential either for electric power generation, reductions in 

demand for other nonrenewable sources of energy, or directuse applications but have not yet been adopted commercially. 

These resources include deep high-temperature sedimentary 

basins; especially geothermal resources colocated with oil and 

gas accumulations or zones of geopressured fluids, and EGS. 

Enhanced geothermal systems are the part of a geothermal 

resource for which a measureable increase in production over its 

natural state is or can be attained through mechanical, thermal, 

and (or) chemical stimulation of the reservoir rock (Williams 

and others, 2011).

This section, dealing with the geothermal-resource 

potential of Sagebrush Focal Areas, is primarily based on 

results from the 2008 assessment that addresses moderatetemperature (90 to 150 °C) and high-temperature (greater than 

150 °C) conventional and EGS systems capable of electric 

power generation. In addition, low-temperature systems 

that may offer important direct-use applications are briefly 

discussed. Also considered are sedimentary-basin resources 

that may hold substantial future potential when technologies 

have improved to allow commercial exploitation of those 

resources for electric power generation and other applications, 

such as in Utah and Wyoming.

2008 USGS National Resource Assessment

The USGS 2008 national resource assessment (Williams and 

others, 2008b) assessed the electric power generation potential 

of geothermal resources in the United States. These resources are 

concentrated in 13 States that include all 6 of the States (Idaho, 

Montana, Nevada, Oregon, Utah, and Wyoming) spanned by 

the Sagebrush Focal Areas (SFAs). The assessment considered 

conventional moderate-temperature (90 to 150 °C) and hightemperature (greater than 150 °C) geothermal systems located 

on private or accessible public lands and included a provisional 

estimate of the power-generation potential from the application of 

unconventional, EGS technology.

The assessment of conventional resources addresses those 

that can be accessed and exploited in the foreseeable future with 

existing methods and technology (Williams and others, 2011). In 

contrast, the provisional EGS assessment addresses EGS resources 

that are within depths accessible with existing technology but that 

will require methods and technology presently being developed, 

which have not yet been established as commercially viable 

(Department of Energy, 2008), for stimulation of the reservoir.

Identified Geothermal Systems

The majority of identified moderate- and high-temperature 

geothermal systems across the Western United States occur 

within the Great Basin Province and Snake River Plain (fig.J1). 

These are resources that are known and characterized by in-situ 

measurements through drilling or other lines of evidence 

such as geochemical, geophysical, and geological surveys. 

There are numerous low- and moderate- to high-temperature 

identified geothermal systems that occur within and around the 

proposed withdrawal areas (figs. J1–J4). Although there are 

currently no installed geothermal power plants located with the 

proposed withdrawal areas, there are four producing sites that 

lie within 100 kilometers (km) of the withdrawal boundaries in 

Oregon, Idaho, and Nevada, as well as sites under development 

(according to the National Renewable Energy Laboratory; 

http://www.nrel.gov/gis/geothermal.html) in those States and 

Utah (figs. J3 and J4; see individual SFA reports for further 

information).

Undiscovered Geothermal Resources

Undiscovered geothermal resources were assessed 

for the Western States that contain identified moderateand high-temperature geothermal systems in the 2008 

assessment. The assessment was based in part on a series of 

Geographic Information Systems (GIS) weights-of-evidence 

and logistic regression analyses through which geothermal 

potential was modeled using a weighted combination of 

evidence layers derived from mappable geologic and tectonic 
Figure J1. Geothermal-favorability map showing the relative favorability of occurrence for conventional moderate- to high-temperature 

geothermal resources across the western contiguous United States (after Williams and others, 2008b). Warmer colors equate with higher 

favorability. Identified geothermal systems are represented by black dots. USGS, U.S. Geological Survey.

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EXPLANATION

Section J. Energy Mineral Resources 83
84 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

0 60 120 180 MILES

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EXPLANATION

greater than 250

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Figure J2. Geothermal-temperature map showing temperature 

in degrees Celsius (°C) at 6-kilometers (km) depth across the 

western contiguous United States that provides a proxy for the 

favorability of occurrence for enhanced geothermal systems (EGS) 

resources. Warmer colors equate with higher temperatures (and 

higher EGS favorability). Dots indicate temperature-gradient wells 

colored according to their estimated heat-flow values. USGS, U.S. 

Geological Survey.
Figure J3. Geothermal-favorability map for the region of Sagebrush Focal Areas (SFAs; see section A, fig. A1), Western United 

States, showing logistic regression results for geothermal favorability (after Williams and others, 2008b) spanning the areas 

proposed for withdrawal. Warmer colors equate with higher favorability. USGS, U.S. Geological Survey; SaMiRA, Sagebrush 

Mineral-Resource Assessment.

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EXPLANATION

Geothermal operating sites (October 26, 2015)

Moderate- and high-temperature

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USGS SaMiRA project report areas

USGS study area boundary

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Section J. Energy Mineral Resources 85
86 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Figure J4. Geothermal-temperature map for the region of Sagebrush Focal Areas (SFAs; see section A, fig. A1), Western United 

States, showing temperature in degrees Celsius (°C) at 6-kilometers (km) depth, which provides a proxy for enhanced geothermal 

systems (EGS) favorability spanning the areas proposed for withdrawal. Warmer colors equate with higher temperatures (and 

higher EGS favorability). USGS, U.S. Geological Survey; SaMiRA, Sagebrush Mineral-Resource Assessment.

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USGS study area boundary

EXPLANATION

Temperature at 6-km depth (oC)

greater than 250

225.1 to 250

200.1 to 225

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150.1 to 175

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features available in digital databases (Coolbaugh and others, 

2005; Williams and DeAngelo, 2008; Williams and others, 

2009). The spatial variations in probability for the presence 

of a geothermal system were determined by mapping the 

presence or absence of various indicators comprising 

evidence layers that were weighted for their influence on the 

feature of interest.

Based on the 2008 assessment, the mean estimated 

power production potential from undiscovered geothermal 

resources is more than three times that from identified 

geothermal systems (more than 30,000 MWe versus 

approximately 9,000 MWe, respectively). These results 

indicate that additional exploration for undiscovered systems 

could substantially augment the potential exploitable 

resources. A plot of relative geothermal-resource favorability 

of both identified and undiscovered systems is given in 

figures J1 and J3. As indicated by the geothermal-favorability 

maps, regions with significant geothermal potential but few 

identified geothermal systems include parts of the proposed 

SFAs. The favorability scale in these maps is set relative to 

the average favorability for the occurrence of moderate- and 

high-temperature geothermal systems in the Western United 

States, which has significantly greater geothermal resource 

potential than east of the Rocky Mountains. Consequently, 

low values of favorability should be evaluated in this context 

and not considered an absolute measure of resource absence. 

Enhanced Geothermal Systems (EGS) Resources

Enhanced Geothermal Systems involve efforts to 

engineer geothermal reservoirs where they did not previously 

exist by stimulating the host rock to generate permeable 

pathways for the circulation of hot water or steam necessary 

for electrical power generation. Although this has yet to be 

demonstrated on a commercial basis in the United States, 

EGS are the focus of substantial research and development 

worldwide due to their vast resource potential. For the 

2008 provisional estimates of EGS potential (Williams 

and others, 2008b), the dominant factor determining the 

favorability of occurrence for EGS resources is the presence 

of elevated temperatures at viable drilling depths (Williams 

and DeAngelo, 2011). As a simple proxy for the detailed 

assessment analyses EGS potential is represented in figures 

J2 and J3, as well as subsequently in the regional sections, by 

the estimated temperature at a depth of 6 km. The provisional 

estimate of EGS resources indicates that the EGS electric 

power production potential is significantly larger than from 

conventional geothermal resources (~500,000 megawatts, 

MW, versus ~30,000 MW) and represents approximately 

half of the current installed electric power generating 

capacity in the United States (Williams and others, 2008b). 

In comparison to the geothermal-favorability map (fig. J1), 

the high crustal heat flow favorable for EGS development 

(fig.J2) is much more uniformly distributed across the 

Western United States.

Geothermal Provinces

The Western United States is a region characterized 

by active tectonics and magmatism that has resulted in an 

elevated conductive thermal gradient capable of driving 

hydrothermal convection of water along permeable pathways 

in the crust. Hydrothermal systems driven by magmatic 

sources are typically concentrated along the western margin of 

the actively extending tectonic zones within the Great Basin 

and along the Snake River Plain, whereas those that result 

from amagmatic sources tend to be associated with basin and 

range settings. Extensive geothermal resources relevant to the 

present study occur principally in the northern Great Basin, 

Snake River Plain, and their surroundings (including the basin 

and range north of the plain, Oregon-Idaho Graben, and the 

High Lava Plains).

Great Basin Province

The Great Basin Province is a broad, highly extended 

basin and range province characterized by significantly elevated 

heat flow relative to the rest of the continental craton (Sass 

and others, 2005). It represents one of the largest geothermal 

provinces in the world and hosts more than 20 operating power 

plants that support roughly 550 MW of installed capacity. 

Estimates based on the 2008 National assessment (Williams 

and others, 2008b) suggest that the province has the potential of 

producing ~30,000 MW. Most of the geothermal systems within 

the Great Basin Province are believed to be primarily faultcontrolled and not related to magmatic heat sources residing in 

the upper crust. Furthermore, many of these systems have little 

or no surface manifestation (Faulds and Hinz, 2015; Coolbaugh 

and others, 2006). Given the presence of such “blind” systems, 

assessments may underestimate the region’s full geothermal 

potential. The high geothermal potential of the province is 

attributed to significant crustal thinning from high extensional 

strain rates (Blewitt and others, 2005; Faulds and others, 2012) 

that have led to elevated geothermal gradients.

Snake River Plain

The Snake River Plain is a major physiographic feature 

of the Western United States that forms a continuous arcuate 

topographic depression extending from the Oregon-Idaho 

border, across southern Idaho, to northwest Wyoming. 

The western plain represents a rift graben that developed 

~11–12 million years ago (Ma) with the eruption of silicic 

volcanic rocks, and it is filled with thick sequences (several 

kilometers) of late Cenozoic lacustrine sediments. In 

contrast, the eastern plain forms a topographic depression 

thought to represent an expression of a mantle plume that 

heats the base of the continental crust in response to the 

northeast migration of the Yellowstone hotspot from the 

south-central Snake River Plain to its present location at 

Yellowstone as the North American Plate passed over the 

Section J. Energy Mineral Resources 87
88 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

plume. The eastern plain is filled with a thick sequence 

of basalts that blanket a series of caldera complexes and 

associated silicic volcanic rocks that were all emplaced 

during passage of the hotspot.

The Snake River Plain and its surroundings represent 

one of the highest heat flow provinces in North America. 

The thermal anomaly associated with the plain originates 

from a thinned lithosphere, voluminous silicic volcanism, 

and extensive intrusions emplaced into the middle and 

lower crust. Very high heat-flow values are expected for 

the youngest part of the plain that have experienced recent 

(in the past 2,000 years) basaltic volcanism (Brott and 

others, 1978, 1981). Although the Snake River Plain and 

surroundings likely represents an important geothermal 

resource area (Fleischmann, 2006; Shervais and others, 

2016; Welhan, 2016), much of the eastern plain’s expected 

high heat flow is masked by shallow groundwater flow 

(Brott and others, 1981). This leads to relatively low heatflow values observed along the axis of the plain (with the 

exception of a few deep boreholes that penetrate below the 

base of the aquifer). Although the most recent volcanism 

occurs in the eastern Snake River Plain, relatively young 

(~200,000 years ago) basaltic volcanism has also occurred in 

the west. Elevated heat-flow values mark the margins of the 

western Snake River Plain, where it is believed that the heatflow pattern is influenced by crustal-scale thermal refraction 

imposed by the thick sequence of sediments infilling the 

western graben.

Methods Used for Reporting the Coal 

Resources

By Jon E. Haacke

Coal is a major energy source in the United States. Although 

its contribution has diminished significantly in recent years, as of 

2014 some 39 percent of U.S. electricity generation came from 

coal (U.S. Energy Information Administration, 2015). More than 

half of U.S. coal production comes from the Western States. 

Because so much is on lands with Federal mineral ownership, 

coal resources in the Western United States have been extensively 

evaluated by the U.S. Geological Survey (USGS).

The USGS divides the United States into coal regions that are 

known to contain coal and (or) lignite (East, 2013). The regions 

are further subdivided into coal fields, which are those areas that 

are or have been actively mined or that have significant potential 

to be mined.

Coal assessments by the USGS can be unofficially divided 

into four levels of detail:

1. Presence of coal.—At the simplest level is a geologic 

study to identify those areas that have any coal deposits.

2. Estimation.—An estimate of coal resources based on 

general knowledge of the geology.

3. Zonal.—A more detailed study of coal resources to 

add up all the coal at a given thickness and at some 

maximum depth, such as coal greater than 30-inches 

thick and at a depth no greater than 1,000 feet.

4. Resources and Reserves.—The most detailed approach 

involves bed-by-bed correlation, calculation of available 

coal resources, and evaluation of the economically 

minable reserves.

For the coal assessment of the Sagebrush Focal Areas (SFAs; 

see section A, fig. A1), the first step was to determine those areas 

that were within any of the coal regions. For those focal areas in 

known coal areas, publications of the USGS and other sources 

were referenced.

The majority of the SFAs are not within regions of known 

coal occurrences (fig. J5). In the late 1990s, the National Coal 

Resource Assessment (Fort Union Coal Assessment Team, 1999) 

studied much of the Western United States; however, none of 

the focal areas were assessed. For those focal areas within coalbearing regions, there is low economic potential. None of the 

focal areas are within the higher (zonal or resource and reserves) 

assessment levels. The only area with estimated coal resources is a 

small part of the Bear River Watershed SFA.

Methods Used for Reporting the Oil and 

Gas Resources

By Ronald M. Drake II, Gregory L. Gunther, Stuart A. 

Giles, and Aimee E. Graeber

Introduction

The U.S. Geological Survey (USGS) was tasked with 

providing a summary of published oil and gas assessments that 

overlie the land tracts for the Sagebrush Focal Areas (SFAs; see 

section A, fig. A1). The USGS oil and gas assessments were 

conducted at a basin scale using the Total Petroleum System 

(TPS) concept. As defined by Magoon and Schmoker (2000), 

the TPS approach considers the source rock, reservoir rock, seal 

rock, and overburden rock and processes of generation, migration, 

accumulation, and trap formation for discovered and undiscovered 

accumulations. A TPS is a naturally occurring hydrocarbon-fluid 

system that presumes that migration pathways exist now or in the 

past, and they connect the provenance with the accumulations. 

Therefore, the goal of the previous assessments was to map this 

natural fluid system, or TPS, in three-dimensional space through 

time to locate, define, and evaluate those areas for undiscovered 

hydrocarbons (Magoon and Schmoker, 2000).
Figure J5. Map of known coal occurrences for the region of the Sagebrush Focal Areas (SFAs; see section A, fig. A1), Western 

United States. Coal regions from East (2013). USGS, U.S. Geological Survey.

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Section J. Energy Mineral Resources 89
90 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming Figure J6. Map showing the 1⁄4 section-level cell summary oil and gas exploration and well-type information from the propriety IHS Energy Group (2016) database and from Gunther and others (2016b) used for the Sagebrush Mineral-Resource Assessment (SaMiRA) project. USGS, U.S. Geological Survey; BLM, 

Bureau of Land Management.

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Base modified from U.S. Geological Survey DEM data (2016).

Political boundaries and roads from Esri (2013).

Withdrawl area boundaries from BLM (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 114° W., latitude of origin, 37.5° N.

North American Datum of 1983.

0 50 100 150 200 MILES0 50 100 150 200 KILOMETERS

Maparea

Study areas

CANADA

MT

UT

ID

NV

OR

CO

WY

KS

NB

WA

CA

SD

ND

AZ TX NM

Study areas

EXPLANATION

Exploration well type Base data
Methodology

A geographic information system (GIS) dataset was created 

that combined the Sagebrush Mineral-Resource Assessment 

(SaMiRA) township areas (as defined by the BLM) and USGS 

oil and gas assessment boundaries. A query was run within the 

GIS for intersecting assessment units within the Public Land 

Survey System (PLSS) townships containing SFAs. The resulting 

table related each PLSS Township with any correlating USGS 

oil and gas assessment unit or play. If an assessment was done in 

1995, then the terminology used was “Play,” and, after 1995, the 

terminology became “Assessment Unit” (AU). In many cases, 

more than one play or assessment unit (AU) was present within 

a PLSS Township. The table created lists each PLSS Township 

and the associated play or AU, the name of the AU or play, the 

publication title, and a URL link to the published USGS geologic 

assessment report. The published USGS assessment reports 

include many details regarding the source rocks, reservoir rocks, 

type of trap, reservoir properties, and resource potential. In some 

cases, many AUs or plays overlie a township. A table of oil and 

gas plays and AUs for each SFA is given in the corresponding 

SaMiRA report chapter as an appendix.

Using the list of AUs and plays that overlap the SFA 

townships, we were able to report the assessed potential oil and 

gas resources for those AUs and plays. The assessed resources 

are for areas larger than the SFA’s PLSS township boundary. The 

assessment units and plays are usually basin size in scale.

Map figures provided in each individual SFA report 

incorporate borehole data from the IHS Energy Group (2016) 

and from Gunther and others (2016a, b) for well type and oil and 

gas production data. Although these data are proprietary, we were 

able to summarize the data by showing the majority type of wells 

at the 1⁄4 section scale (fig. J6). These maps have been added to 

the reports for each SFA if there was production within a PLSS 

township containing a given proposed withdrawal area.

Nearly all oil and gas production occurred outside of the 

proposed withdrawal areas. For example, only one inactive well 

in Sweetwater County, Wyoming, produced a minor amount of oil 

and gas within the proposed withdrawal areas (IHS Energy Group, 

2016). Although there are many assessed potential oil and gas 

resources near the proposed withdrawal areas, there has not been 

any significant hydrocarbon production within them.

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belt of southeast Idaho: Proceedings, 41st Workshop on 

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2016, at https://pangea.stanford.edu/ERE/db/GeoConf/

papers/SGW/2016/Welhan.pdf.

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geothermal resources of the United States–1975: U.S. 

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2016, at http://pubs.usgs.gov/circ/1975/0726/report.pdf.

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potential in the Western United States: Transactions of the 

Geothermal Resources Council, v. 32, p. 181–187.

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approaches and associated uncertainties in the estimation 

of temperatures in the upper crust of the Western United 

States: Transactions of the Geothermal Resources Council, 

v. 35, p. 1599–1606.

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Updating the classification of geothermal resources: 

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Engineering, Stanford University, Stanford, California, 7 

p., accessed March 10, 2016, at https://pangea.stanford.edu/

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2009, Quantifying the undiscovered geothermal resources 

of the United States: Transactions of the Geothermal 

Resources Council, v. 33, p. 995–1003, accessed March 10, 

2016, at https://pubs.er.usgs.gov/publication/70158979.

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review of methods applied by the U.S. Geological Survey 

in the assessment of identified geothermal resources: 

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Galanis, S.P., Jr., 2008b, Assessment of moderate- and hightemperature geothermal resources of the United States: U.S. 

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Glossary 93

Glossary

B

base metal A metal inferior in value to gold and silver, a term 

generally applied to the commercial metals such as copper and 

lead (Bureau of Land Management, 2000).

base metals Those metals usually considered to be of lesser 

value and of greater chemical reactivity compared to the noble 

or precious) metals, most commonly copper, lead, zinc, and tin 

(NRC, 1999).

beneficiation Improvement of the grade of ores by milling, 

flotation, sintering, gravity concentration, or other processes. Also 

termed “concentration” (National Research Council, 1999). The 

dressing or processing of ores to (1) regulate the size of a desired 

product, (2) remove unwanted constituents, and (3) improve the 

quality, purity, or assay grade of a desired product. Beneficiation 

includes concentration or other preparation of ore for smelting 

by drying, flotation, or magnetic separation (Bureau of Land 

Management, 2000).

bentonite A rock consisting of clay minerals formed from the 

decomposing of volcanic ash. Commonly bentonite can readily 

absorb or adsorb water and swell accordingly (Bureau of Land 

Management, 2000).

BLM Bureau of Land Management.

C

casual use Mining activities that only negligibly disturb Federal 

lands and resources. Casual use generally includes the collecting 

of geochemical, rock, soil, or mineral specimens using hand 

tools, hand panning, and nonmotorized sluicing. It also generally 

includes use of metal detectors, gold spears, and other batteryoperated devices for sensing the presence of minerals, and hand 

and battery-operated drywashers. Operators may use motorized 

vehicles for casual-use activities if the use conforms to the 

regulations governing such use, off-road vehicle use designations 

in BLM land-use plans, and temporary closures. Casual use does 

not include use of mechanized earth-moving equipment, truckmounted drilling equipment, suction dredges, motorized vehicles 

in areas designated as closed to off-road vehicles, chemicals, 

or explosives. It also does not include occupancy or operations 

where the cumulative effects of the activities result in more than 

negligible disturbance. Under casual use, operators do not have 

to notify BLM, and operations do not need to be approved. But 

operations are subject to monitoring by BLM to ensure that 

Federal lands do not undergo unnecessary or undue degradation. 

Casual use operations must be reclaimed (Bureau of Land 

Management, 2000).

claim See mining claim (Bureau of Land Management, 2000).

common variety minerals Mineral materials that do not have a 

special quality, quantity, character, or location that makes them 

of unique commercial value. On public lands such minerals are 

considered salable and are disposed of by sales or by special 

permits to local governments (National Research Council, 

1999). Stone, gravel, pumice, pumicite, and cinders that, though 

possibly having value for trade, manufacture, the sciences, or 

the mechanical or ornamental arts, do not have a distinct, special 

value for such use beyond normal uses. On Federal lands such 

minerals are considered salable and are disposed of by sales or by 

special permits to local governments. (National Research Council, 

1999). See salable minerals, mineral materials, and uncommon 

variety minerals.

critical minerals Minerals essential to the national defense, the 

procurement of which in war, although difficult, is less serious 

than those of strategic minerals because they can be either 

domestically produced or obtained in more adequate amounts 

or are less essential, and for which some degree of conservation 

and distribution control is needed (Bureau of Land Management, 

2000). See strategic minerals.

D

development (mineral) The preparation of a proven deposit for 

mining (Bureau of Land Management, 2000).

discovery As used in this report, initial recognition and 

demonstration of the presence of valuable mineral within a 

claim (National Research Council, 1999). The knowledge of the 

presence of valuable minerals within or close enough to a location 

to justify a reasonable belief in their existence. Discovery is an 

extremely important to public-lands mining because the General 

Mining Act of 1872 (30 U.S.C. 22–42) provides that mining 

claims can be located only after a discovery is made. Discovery 

was first legally defined in a landmark Department of the Interior 

1894 land decision—Castle versus Womble. The definition, now 

known as the “Prudent Person Test, ‘described a discovery as’...

where minerals have been found and the evidence is of such a 

character that a person of ordinary prudence would be justified in 

the further expenditure of his labor and means, with a reasonable 

prospect of success in developing a valuable mine . . .” (Bureau of 

Land Management, 2000).

E

entry An application to acquire title to public lands (Bureau of 

Land Management, 2000).
94 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

environmental assessment (EA) A concise public document 

for which a Federal agency is responsible that does the 

following: (1) briefly gives enough evidence and analysis 

for determining whether to prepare an environmental 

impact statement (EIS) or a finding of no significant impact 

(FONSI), (2) aids an agency’s compliance with the National 

Environmental Act when no EIS is needed, and (or) (3) 

facilitates preparing an EIS when one is needed (Bureau of 

Land Management, 2000).

environmental impact statement (EIS) A document required 

by the National Environmental Policy Act (NEPA) for certain 

actions “significantly affecting the quality of the human 

environment.”

evaporite Sedimentary rock formed by the evaporation 

of a saline solution. Examples include rock salt, gypsum, 

and chemically precipitated limestone (Bureau of Land 

Management, 2000).

exploration The work of investigating a mineral deposit 

to determine by geological surveys, geophysical surveys, 

geochemical surveys, boreholes, pits, and underground 

workings if it is feasible to mine. Exploration is undertaken 

to gain knowledge of the size, shape, position, characteristics, 

and value of the deposit. For 43 CFR 3809 regulations, 

exploration means creating surface disturbance that is greater 

than casual use and that includes sampling, drilling, or 

developing surface or underground workings to evaluate the 

type, extent, quantity, or quality of mineral values present. 

Exploration does not include activities where material 

is extracted for commercial use or sale (Bureau of Land 

Management, 2000).

F

Federal Land Policy and Management Act (FLPMA) The act 

that (1) set out for the Bureau of Land Management standards 

for managing the public lands, including land-use planning, 

sales, withdrawals, acquisitions, and exchanges; (2) authorized 

the setting up of local advisory councils representing 

major citizens groups interested in land-use planning and 

management; (3) established criteria for review of proposed 

wilderness areas; and (4) provided guidelines for other aspects 

of public land management such as grazing (Bureau of Land 

Management, 2000).

ferrous metals Metals commonly occurring in alloys with 

iron, such as chromium, nickel, manganese, vanadium, 

molybdenum, cobalt, silicon, tantalum, and columbium 

(niobium) (National Resource Council, 1999).

FWS U.S. Fish and Wildlife Service.

G

General Mining Act of 1872 (30 U.S.C. 22–42) The Federal 

act of May 10, 1872, that, with its amendments, formed the 

framework for the mining of locatable minerals on the public 

lands. This law declared that “valuable” mineral deposits 

rather than simply “mineral deposits” were to be free and open 

to exploration and purchase, limited individual claims to 20 

acres, required $100 worth of assessment work yearly, and 

allowed milling or processing claims of 5 acres or less to be 

entered on nonmineral lands (Bureau of Land Management, 

2000).

geophysical exploration The use of geophysical instruments 

and methods to determine subsurface conditions by analyzing 

such properties as specific gravity, electrical conductivity, or 

magnetic susceptibility (Bureau of Land Management, 2000).

H

hardrock Locatable minerals that are neither leasable 

minerals (oil, gas, coal, oil shale, phosphate, sodium, 

potassium, sulfur, asphalt, or gilsonite) nor salable mineral 

materials (for example, common variety sand and gravel). 

Hardrock minerals include, but are not limited to, copper, lead, 

zinc, magnesium, nickel, tungsten, gold, silver, bentonite, 

barite, feldspar, fluorspar, and uranium. (Bureau of Land 

Management, 2000b) Usually refers to rock types or mining 

environments where the rocks are hard and strong and where 

blasting is needed to break them for effective mining. As 

used in this report, the term hardrock minerals are defined 

synonymous with “locatable minerals.”

heavy metal Any of the metals that react readily with 

dithizone, including zinc, copper, cobalt, lead, bismuth, 

gold, cadmium, iron, manganese, nickel, tantalum, tellurium, 

platinum, and silver (Bureau of Land Management, 2000).

I

industrial minerals Rock and minerals that are not produced as 

sources of metals and are not mineral fuels. Examples include 

salt, gravels, building materials, talc, and sands (Bureau of Land 

Management, 2000).

L

leasable minerals A legal term that identifies a mineral or 

mineral commodity that is leasable by the Federal Government 

under the Mineral Leasing Act of 1920 and similar legislation. 

Leasable minerals include oil, gas, sodium, potash, phosphate, 
coal, and all minerals on acquired lands (NRC, 1999) 

(examples are given in appendix 1). Minerals whose extraction 

from Federal land requires a lease and the payment of 

royalties. Leasable minerals include coal, oil and gas, oil shale 

and tar sands, potash, phosphate, sodium, and geothermal 

steam (Bureau of Land Management, 2000).

locatable minerals A legal term that identifies minerals 

acquired through the General Mining Act of 1872 (30 U.S.C. 

22–42), as amended (examples are given in appendix 1). 

Locatable minerals are distinguished from federally owned 

minerals that are disposed of by leasing (see leasable minerals). 

In some situations, the term “hardrock minerals” is applied to 

locatable minerals (National Research Council, 1999). Minerals 

that may be acquired under the General Mining Act of 1872, as 

amended (Bureau of Land Management, 2000).

location The act of taking or appropriating a parcel of mineral 

land, including the posting of notices, the recording thereof when 

required, and marking the boundaries so they can be readily 

traced; also the claim acquired by an act of location. See mining 

claim (Bureau of Land Management, 2000).

lode claim A public lands mining claim that contains 

valuable minerals occurring in a vein or lode (Bureau of Land 

Management, 2000).

lode A mineral deposit in solid rock (Bureau of Land 

Management, 2000).

M

millsite A site located on nonmineral land and used for erecting 

a mill or reduction works, or for other uses reasonably incident 

to support of a mine. Millsites are limited to 5 acres and may be 

located either by metes and bounds or by legal subdivision. See 

location and mining claim (Bureau of Land Management, 2000).

mine An opening or excavation in the earth for extracting 

minerals (Bureau of Land Management, 2000).

mineral activity Mining and mineral exploration (Bureau of Land 

Management, 2000).

mineral assessment The determination of mineral potential, 

including the process for making that determination. Assessment 

usually does not include calculations of value or quantity, although 

these data may be part of an assessment where they are already 

known (Bureau of Land Management, 1985).

mineral claimant A person, association, corporation, or 

government that claims minerals rights or title in the public lands 

(Bureau of Land Management, 2000).

mineral entry The filing of a claim on public land to obtain 

the right to any minerals it may contain (Bureau of Land 

Management, 2000).

mineral materials Materials such as common varieties of sand, 

stone, gravel, pumice, pumicite, and clay, that are not obtainable 

under the mining or leasing laws but that can be acquired under 

the Mineral Materials Act of 1947, as amended. See common 

variety minerals (Bureau of Land Management, 2000).

mineral occurrence A concentration of mineral that is considered 

to be valuable or that is of technical or scientific interest (National 

Research Council, 1999).

mineral prospect A mineral property whose value has not been 

proved by exploration (Bureau of Land Management, 2000).

mineral resource “A concentration of naturally occurring solid, 

liquid, or gaseous materials in or on the Earth’s crust in such form 

that economic extraction of a mineral resource is currently or 

potentially feasible (after USGS Circular 831, p.1)” (Bureau of 

Land Management, 1985).

mineral rights Ownership of all minerals, including all rights 

needed for access, exploration, development, mining, ore dressing, 

and transportation (Bureau of Land Management, 2000).

mineral Several other common meanings, but the following 

are used in this report: Any natural resource extracted from the 

earth for human use; for example, ores, salts, coal, or petroleum 

(National Research Council, 1999). Any solid or fluid inorganic 

substance that can be extracted from the earth for profit (Bureau of 

Land Management, 2000).

mineral species Term used in this report to distinguish specific 

mineralogical species from the unmodified term “mineral” as 

defined above (National Research Council, 1999).

mineralization The processes taking place in the Earth’s crust 

resulting in the formation of valuable minerals or ore bodies 

(Bureau of Land Management, 2000).

mineralogy The study of minerals—their formation, occurrence, 

properties, composition, and classification (Bureau of Land 

Management, 2000).

mining claim A parcel of land that a miner takes and holds 

for mining purposes, having acquired the right of possession 

by complying with the General Mining Act of 1872 and local 

laws and rules. A single mining claim may contain as many 

adjoining locations as the locator may make or buy. There 

are four categories of mining claims: lode, placer, millsite, 

and tunnel site. For 43 CFR 3809 regulations, mining claim 

means any unpatented mining claim, millsite, or tunnel site 

Glossary 95
96 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

located under the mining laws. The term also applies to mining 

claims and millsites that were located in the California Desert 

Conservation Area and patented after the enactment of the 

Federal Land Policy and Management Act of 1976 (Bureau of 

Land Management, 2000). See location, lode claim, placer 

claim, millsite, and tunnel site claim. 

mining district An area, usually designated by name, with 

described or understood boundaries, where minerals are found 

and mined under rules prescribed by the miners, consistent 

with the General Mining Act of 1872 (Bureau of Land 

Management, 2000).

mining laws The Lode Law of July 26, 1866, as amended 

(14 Stat. 251); the Placer Law of July 9, 1870, as amended 

(16 Stat. 217); and the General Mining Act of May 10, 1872, 

as amended (17 Stat. 91); as well as all laws supplementing 

and amending those laws, including the Building Stone Act of 

August 4, 1892, as amended (27 Stat. 348); the Saline Placer 

Act of January 31, 1901 (31 Stat. 745); the Surface Resources 

Act of 1955 (30 U.S.C. 611-614); and the Federal Land 

Policy and Management Act of 1976 (43 U.S.C. 1701 et seq.) 

(Bureau of Land Management, 2000).

mining location A mining claim on the public lands (Bureau of 

Land Management, 2000).

N

National Environmental Policy Act (NEPA) The Federal law, going 

into effect on January 1, 1970, that established a national policy for 

the environment and requires Federal agencies (1) to become aware 

of the environmental ramifications of their proposed actions, (2) to 

fully disclose to the public proposed Federal actions and provide 

a mechanism for public input to Federal decision-making, and (3) 

to prepare environmental impact statements for every major action 

that would significantly affect the quality of the human environment 

(Bureau of Land Management, 2000).

notice level operation A mining or exploration operation on 

BLM land involving more than casual use but requiring that the 

operator submit only a notice rather than a plan of operations. It 

is limited to an area of disturbance of 5 or fewer acres (National 

Research Council, 1999). 

O

open-pit mining A surface mining method in which overlying 

rock and soil are removed to expose an ore body, which is 

then drilled, blasted, and hauled from the pit (Bureau of Land 

Management, 2000).

operations All functions, work, facilities, and activities on public 

lands in connection with prospecting, exploration, discovery, and 

assessment work, development, extraction, and processing of 

mineral deposits locatable under the mining laws; reclamation of 

disturbed areas; and all other reasonably incident uses, whether 

on a mining claim or not, including the building of roads, 

transmission lines, pipelines, and other means of access across 

public lands for support facilities. 

operator Any person who manages, directs, or conducts mining 

operations at a project area, including a parent entity or an affiliate 

who materially participates in such management, direction, or 

conduct. An operator on a particular mining claim may also be the 

mining claimant (Bureau of Land Management, 2000).

ore The naturally occurring material from which a mineral or 

minerals of economic value can be extracted profitably or to 

satisfy social or political objectives (National Research Council, 

1999).

ore body A mineralized mass whose characteristics have been 

determined and deemed commercially viable. The term ore body 

is used once the economic limits of the mineralized mass and its 

grade have been examined (Bureau of Land Management, 2000).

ore reserves The part of a mineral deposit that can be profitably 

mined. Use of this term implies detailed knowledge of all the 

geological, engineering, economic, and environmental parameters 

that might affect the profitability of an operation. For a new 

mining project or for the mining of new zones in an existing mine, 

a formal feasibility study is conducted to evaluate all the project’s 

parameters (Bureau of Land Management, 2000).

ore deposit A mineral deposit of high enough quality to be mined 

at a profit (Bureau of Land Management, 2000).

P

patent The instrument by which the Federal Government conveys 

title to public lands (Bureau of Land Management, 2000).

placer claim A mining claim located on gravel or ground whose 

mineral contents are extracted by the use of water (Bureau of Land 

Management, 2000).

placer deposit A mass of gravel, sand, or similar material 

resulting from the crumbling and erosion of solid rocks containing 

particles of gold or other valuable minerals that have been derived 

from rocks or veins (Bureau of Land Management, 2000).

placer mining A method of mining in which the overburden 

is removed to expose gold-bearing gravel deposits beneath. 

The gravel is then sluiced to separate the gold (Bureau of Land 

Management, 2000).

placer An alluvial deposit of sand and gravel containing valuable 

minerals such as gold (Bureau of Land Management, 2000).
plans of operations Plans for mining exploration or development 

on BLM land involving more than 5 acres or a plan for mining 

where the operator with preexisting, valid claims intends to mine 

in an area of critical environmental concern or a wilderness area. 

Also a plan required for mining or exploration on U.S. Forest 

Service lands whenever the U.S. Forest Service determines that 

the operation will result in “significant” disturbance of the land 

surface (National Research Council, 1999).

precious metal A general term for gold, silver, or any of the 

metals of the platinum group (Bureau of Land Management, 

2000). Any of several relatively scarce and valuable metals, such 

as gold, silver, and the platinum-group metals (National Research 

Council, 1999).

priority habitat management area (PHMA) BLM-administered 

lands as having the highest habitat value for maintaining 

sustainable sage-grouse populations. These areas are larger than 

the SFAs.

project area The area of land on which an operator conducts 

mining operations, including the area needed for building or 

maintaining of roads, transmission lines, pipelines, or other means 

of access (Bureau of Land Management, 2000).

public lands Any land and interest in land owned by the 

United States and administered by the Secretary of the Interior 

through the Bureau of Land Management, without regard to 

how the United States acquired ownership, except for (1) land 

located on the Outer Continental Shelf and (2) land held for 

the benefit of Indians, Aleuts, and Eskimos (Bureau of Land 

Management, 2000).

Public Lands Survey System (PLSS) boundary or “study area” 

The aggregate of all townships shown at various times since 

October 2015 on BLM Web sites, the Records of Decision 

(Bureau of Land Management, 2015a, b), or in written 

communication from BLM (Anthony Titolo, April 20, 2016) as 

those that include the “withdrawal areas.”

R

rare earth metals A group of widely distributed metals 

consisting of the elements scandium, yttrium, and 15 elements 

of atomic numbers 57 to 71, inclusive. These metals have the 

same arrangement of the two external shells of electrons in their 

atoms and resemble one another closely in chemical and physical 

properties, being thus most difficult to separate from each other. It 

is for this property, rather than their actual rarity in nature, that they 

are so described (Bureau of Land Management, 2000).

record of decision (ROD) A document signed by a responsible 

official recording a decision that was preceded by the 

preparing of an environmental impact statement (Bureau of 

Land Management, 2000).

reserve “That portion of a mineral resource from which a mineral 

commodity can be economically and legally extracted at the time 

of determination (after USGS Circular 831, p. 2)” (Bureau of Land 

Management, 1985).

resource management plan (RMP) A BLM planning document, 

prepared in accordance with Section 202 of the Federal Land 

Policy and Management Act that presents systematic guidelines 

for making resource management decisions for a resource area. An 

RMP is based on an analysis of an areas’ resources, their existing 

management, and their capability for alternative uses. RMPs are 

issue oriented and developed by an interdisciplinary team with 

public participation (Bureau of Land Management, 2000).

S

sagebrush focal area or “SFA” FWS has identified as important 

landscape blocks with high breeding-population densities of 

greater sage-grouse (Centrocercus urophasianus), existing 

high quality sagebrush habitat, and a preponderance of Federal 

ownership or protected area that serves to anchor the conservation 

value of the landscape. “The BLM and USFS plans will focus the 

highest protections in the SFAs.” (http://www.blm.gov/wo/st/en/

prog/more/sagegrouse/documents_and_resources.html)

salable minerals A legal term that defines mineral commodities 

that are sold by contract from the Federal Government. These 

are generally construction materials and aggregates. (National 

Research Council, 1999). See appendix 1.

segregation Any act such as a withdrawal or exchange that 

suspends the operation of the public land laws. See withdrawal

(Bureau of Land Management, 2000).

SFA Sagebrush Focal Area

strategic minerals Minerals essential to the national defense 

for the supply of which during war we are wholly or partly 

dependent on sources outside the continental limits of the 

United States, and for which strict measures are needed to 

control conservation and distribution. See critical minerals

(Bureau of Land Management, 2000).

study area See Public Lands Survey System (PLSS) boundary

T

trace metals Metals that are present in small concentrations 

(Bureau of Land Management, 2000).

troy ounce A unit of measure based on troy weight (12 ounces 

to a pound) and equal to 1.09714 avoirdupois ounces. (An 

avoirdupois ounce is the conventional U.S. weight measure in 

which 16 ounces equal 1 pound.)

Glossary 97
98 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

tunnel site claim A mining claim located to secure an area 

for a tunnel. A tunnel site claim may be located on land where 

a tunnel is run to develop a vein or lode, or for intersecting 

unknown veins or lodes. See location and mining claim

(Bureau of Land Management, 2000).

U

uncommon variety minerals On the Federal lands stone, 

gravel, pumice, pumicite, and cinder deposits that have 

distinct and special properties making them commercially 

valuable for use in a manufacturing, industrial, or processing 

operation. Such minerals are locatable under the General 

Mining Act of 1872, as amended. In determining a deposit’s 

commercial value, the following factors may be considered: 

quality and quantity of the deposit, geographic location, 

accessibility to transportation, and proximity to market or 

point of use (National Research Council, 1999).

USFS U.S. Forest Service.

USGS U.S. Geological Survey.

wilderness area A congressionally designated area of 

undeveloped Federal land retaining its primeval character 

and influence, without permanent improvements or human 

habitation, that is protected and managed to preserve its 

natural conditions and that (1) generally appears to have been 

affected mainly by the forces of nature, with human imprints 

substantially unnoticeable; (2) has outstanding opportunities 

for solitude or a primitive and unconfined type of recreation; 

(3) has at least 5,000 acres or is large enough to make practical 

its preservation and use in an unimpaired condition; and (4) 

may also contain ecological, geological, or other features of 

scientific, educational, scenic, or historic value (Bureau of 

Land Management, 2000).

wilderness study area On BLM-managed lands, a roadless area 

that has been inventoried (but not designated by Congress) and 

found to have wilderness characteristics as described in Section 

603 of the Federal Land Policy and Management Act of 1976 

(FLPMA; Pub. L. 94–579; 90 Stat. 2743) and section (c) of 

the Wilderness Act of 1964 (PUB. L. 88–577). BLM manages 

wilderness study areas to protect their wilderness characteristics 

until Congress decides whether to designate them as wilderness 

(Bureau of Land Management, 2000).

withdrawal areas, or “withdrawals” Informal term used 

within these reports to identify those Federal lands within the 

Sagebrush Focal Areas (SFAs) that are proposed for closure 

to locatable mineral entry subject to valid existing rights. The 

proposed withdrawal areas are a subset of lands within the 

larger SFAs.

References Cited

Bureau of Land Management, 1985, Energy and mineral resource 

assessment: Washington, D.C., U.S. Department of Interior, 

Bureau of Land Management, accessed March 15, 2016, at http://

www.blm.gov/wo/st/en/info/regulations/Instruction_Memos_

and_Bulletins/blm_manual.html.

Bureau of Land Management, 2000, Surface management 

regulations for locatable mineral operations: Bureau of Land 

Management, Final Environmental Impact Statement, v. 1, 

664 p., accessed May 25, 2016, at https://archive.org/details/

surfacemanagemen01/.

Bureau of Land Management, 2015a, Record of Decision and 

approved resource management plan amendments of the Great 

Basin region, including the greater sage-grouse sub-regions of 

Idaho and Southwestern Montana, Nevada and northeastern 

California: Washington, D.C., U.S. Department of Interior, 

Bureau of Land Management, September 2015, accessed 

March 15, 2016, at http://www.blm.gov/style/medialib/blm/

wo/Communications_Directorate/public_affairs/sage-grouse_

planning/documents.Par.44118.File.dat/GB%20ROD.pdf.

Bureau of Land Management, 2015b, Record of Decision and 

approved resource management plan amendments for the Rocky 

Mountain region, including the greater sage-grouse sub-regions 

of Lewiston, North Dakota, Northwest Colorado, Wyoming, and 

the approved resource management plans for Billings, Buffalo, 

Cody, HiLine, Miles City, Pompeys Pillar National Monument, 

South Dakota, Worland: Washington, D.C., U.S. Department of 

Interior, Bureau of Land Management, September, 2015, accessed 

March 15, 2016, at http://www.blm.gov/style/medialib/blm/

wo/Communications_Directorate/public_affairs/sage-grouse_

planning/documents.Par.57493.File.dat/RM%20ROD.pdf.

National Research Council, 1999, Hardrock mining on Federal 

Lands: Washington, D.C., National Academy Press, 260 p., 

accessed May 25, 2016, at http://www.nap.edu/catalog/9682/

hardrock-mining-on-federal-lands.
Appendixes 1–5
Appendix 1. List of Locatable, Leasable, and Salable Minerals

[BLM, Bureau of Land Management]

Mineral commodity BLM designation Comment

Primarily locatable minerals

Aluminum Locatable None

Antimony Locatable None

Barite Locatable None

Bentonite Locatable None

Beryllium Locatable None

Bismuth (byproduct) Locatable None

Building stone Locatable or salable Not all building stone is locatable. Much building stone requires a mineral material 

sale contract. The determination is made by a BLM Certified Examiner.

Calcium borates Locatable Calcium borates are locatable minerals. Sodium borates are leasable minerals.

Carbon Locatable Carbon is not usually a metal in the Mendeleev Periodic Chart of the Elements. It is 

included in this list as a metal because of its metallic properties, such as being a 

conductor of electricity, which is useful in certain green energy batteries. Carbon is 

also locatable as an industrial mineral, and as diamond.

Chromium Locatable None

Cobalt Locatable None

Decorative stone Locatable or salable Most decorative stone requires a mineral material sales contract. Only uncommon 

varieties of decorative stone may be acquired using mining claims.

Diamond Locatable None

Diatomite Locatable None

Fluorspar Locatable Also known as fluorite.

Gallium Locatable None

Garnet Locatable None

Gemstones Locatable or salable Most nonprecious and semiprecious gemstones require a mineral material sale 

contract. But most production comes from hobby collection on mining claims.

Geodes Primarily salable Geodes are seldom locatable. Only uncommon varieties of geodes are.

Gypsum Locatable None

Iron Locatable None

Lead Locatable None

Limestone Locatable or salable None

Lithium Locatable Lithium is locatable in solid mineral form, such as lepidolite and hectorite, and also in 

ionic form in subsurface brines.

Magnesium Locatable None

Mercury Locatable None

Mica Locatable None

Mineral Specimens Rarely locatable Mineral specimens are seldom locatable. Only uncommon varieties of geodes are 

considered locatable.

Niobium Locatable Also called columbium.

Perlite Locatable None

Platinum-group metals Locatable Platinum-group metals (PGMs) commonly occur together and include platinum, 

palladium, rhodium, ruthenium, osmium, and iridium.

Pozzolan Locatable Pozzolan is a naturally occurring additive to concrete. When pozzolan meets 

specifications, it increases the strength of the resulting structure. Pozzolan can 

generally replace portland cement in the concrete by about one-to-one. Doing so 

reduces the emission of carbon dioxide (CO2) during the production of the portland 

cement. Not a specific mineral; can be from volcanic ash, pumice, or diatomaceous 

earth.

Pumice (greater than 2 

inches diameter)

Locatable By Act of Congress, to be locatable, pumice must have at least one dimension that is 2 

inches or larger.
Mineral commodity BLM designation Comment

Primarily locatable minerals—Continued

Rare Earth Elements Locatable Elements commonly referred to as rare earths include yttrium, scandium, lanthanum, 

cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, 

terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

Silica and Silica Sand (high 

purity or uncommon 

variety)

Locatable Silica must be high purity, suitable for an uncommon use. Silica sand must be an 

uncommon variety, such as proppant sand for hydrofracking.

Silver Locatable None

Sulfur Locatable or leasable None

Tantalum Locatable None

Tellurium Locatable None

Thorium Locatable None

Tin Locatable None

Titanium Locatable None

Travertine Locatable None

Tungsten Locatable None

Uranium Locatable None

Vanadium Locatable None

Vermiculite Locatable None

Zeolite Locatable None

Zinc Locatable None

Zirconium Locatable None

Leasable minerals

Bituminous rock Leasable None

Coal Leasable None

Geothermal energy Leasable None

Native asphalt Leasable None

Oil and gas Leasable None

Phosphate Leasable None

Potash Leasable None

Solid and semisolid bitumen Leasable None

Sulfur Leasable None

Iodides Leasable None

Helium Leasable None

Magnesium evaporites Leasable Or “bitterns”

Primarily salable minerals

Sand Salable None

Stone Salable None

Gravel Salable None

Pumice Salable None

Pumicite Salable None

Cinders Salable None

Clay (common) Salable None

Decorative stone Salable None

Building stone (common) Locatable or salable None

Gemstones Locatable or salable None

Limestone Locatable or salable None

Appendix 1 101
Appendix 2. Mineral-Potential Classification System

The approach to classification of the qualitative mineralresource potential for locatable minerals followed that prescribed 

in Bureau of Land Management (BLM) Manual Sections 3031 

and 3060 defined originally by Goudarzi (1984).

Level of Potential

N. The geologic environment, the inferred geologic processes, 

and the lack of mineral occurrences do not indicate 

potential for accumulation of mineral resources.

L. The geologic environment and the inferred geologic 

processes indicate low potential for accumulation of 

mineral resources.

M. The geologic environment, the inferred geologic processes, 

and the reported mineral occurrences or valid geochemical/

geophysical anomaly indicate moderate potential for 

accumulation of mineral resources.

H. The geologic environment, the inferred geologic 

processes, the reported mineral occurrences and (or) valid 

geochemical/geophysical anomaly, and the known mines or 

deposits indicate high potential for accumulation of mineral 

resources. The “known mines and deposits” do not have 

to be within the area that is being classified but have to be 

within the same type of geologic environment.

ND. Minerals potential not determined due to lack of useful 

data. This does not require a level of certainty qualifier.

Level of Certainty

A. The available data are insufficient and (or) cannot be 

considered as direct or indirect evidence to support or 

refute the possible existence of mineral resources within 

the respective area.

B. The available data provide indirect evidence to support 

or refute the possible existence of mineral resources.

C. The available data provide direct but quantitatively 

minimal evidence to support or refute the possible 

existence of mineral resources.

D. The available data provide abundant direct and indirect 

evidence to support or refute the possible existence of 

mineral resources.

For the determination of “no potential” use N/D. This 

class shall be seldom used, and when used it should be for a 

specific commodity only. For example, if the available data 

show that the surface and subsurface types of rock in the 

respective area is batholithic (igneous intrusive), one can 

conclude, with reasonable certainty, that the area does not 

have potential for coal.

As used in this classification, potential refers to potential 

for the presence (occurrence) of a concentration of one or 

more energy and (or) mineral resources. It does not refer to 

or imply potential for development and (or) extraction of 

the mineral resource(s). It does not imply that the potential 

concentration is or may be economic, that is, could be 

extracted profitably. 

Reference Cited

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

survey reports on public lands: U.S. Geological Survey 

Open-File Report 84–787, 41 p., accessed December 9, 2015, 

at https://pubs.er.usgs.gov/publication/ofr84787.
Level of certainty

A B C D

N

L

M

H

Level of resource potential

H/A

M/A

L/A

H/B

M/B

L/B

H/C

M/C

L/C

H/D

M/D

L/D

N/D

High potential with 

insufficient evidence

Moderate potential 

 with insufficient 

evidence

Low potential with 

insufficient evidence

High potential with 

indirect evidence

Moderate potential 

 with indirect evidence

Low potential with 

indirect evidence

High potential with 

direct evidence

Moderate potential

with direct evidence

Low potential with 

direct evidence

High potential with 

abundant direct and

indirect evidence

Moderate potential with 

abundant direct and

indirect evidence

Low potential with 

abundant direct and

indirect evidence

No potential

Current production/significant inventor.

Significant past production.

Active or pending notices or mine plans.

Numerous active claims.

USMIN active exploration.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Historic mining.

Historic claims.

No active notices or mine plans.

No active exploration. 

No claims.

No other applicable data.

Permissive host rocks +/- previous assessment 

Permissive host rocks +/- previous assessment

Permissive host rocks +/- previous assessment 

Few active claims.

Historic mining. 

No USMIN active exploration. 

No active notices or mine plans.

Minor past production.

Attractive exploration targets.

Active or pending notices or mine plans.

Numerous active claims.

USMIN active exploration.

Attractive exploration targets.

Active or pending notices or mine plans.

Numerous active claims.

USMIN active exploration.

Contains 2 or more of the following:

Current production/significant inventory.

Significant past production.

Active or pending notices or mine plans.

Numerous active claims.

USMIN active exploration.

Contains 1 or more of the following:

Minor past production.

Attractive exploration targets.

Active or pending notices or mine plans.

Numerous active claims.

USMIN active exploration.

Attractive exploration targets.

Active or pending notices or mine plans.

Numerous active claims.

USMIN active exploration.

Chapter A Figure H3 (Appendix fig. for all other chapters)

Contains 2 or more of the following: Contains 2 or more of the following:

Contains 1 or more of the following: Contains 1 or more of the following:

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Reserved for a specific type of 

resource in a well-defined area. For 

example, it is appropriate to say that 

there is no oil potential in an area 

where the only rocks present are 

unfractured Precambrian granite, 

but the term ”low” is appropriate if 

there is a slight possibility for the 

presence of resources.

Appendix 2 103

Appendix 3. Mineral-Deposit Models

Concise mineral-deposit models for the mineral-deposit 

types that were considered for the Sagebrush Mineral-Resource 

Assessment (SaMiRA) study are included in this appendix, 

grouped by the mineral systems adopted for this study. See section 

H for a discussion of mineral systems and mineral deposits. These 

mineral-deposit models are based on the references cited for each 

model. See the complete reference for additional information 

on the deposit type. The table that accompanies this appendix 

contains additional information about these deposit types such 

as an association of the deposit type with metallic or nonmetallic 

commodities and strategic or critical minerals (table 3-1). In 

addition, the most common mining methods associated with each 

deposit type are listed using Bureau of land management (BLM) 

mining method classifications (A. Merrill, written commun., May 

2016). The last two columns of the table list median tonnages 

and references for the deposit types that have published tonnage 

models. The populations of deposits used to construct the cited 

tonnage models may or may not be appropriate for the study 

area; these are simply provided as a general guide to the order of 

magnitude of tonnages typically associated with the deposit type 

throughout the world. (Note that chemical symbols used in the 

tables below are defined in the front matter of this report.)
106 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming Table 3-1. Typical mining methods for mineral-deposit types assessed within the Sagebrush Mineral-Resource Assessment (SaMiRA) study areas. [Deposit types are grouped by mineral system. X, typical mining method; -, unlikely mining method; median ore tonnage based on a population of well-characterized deposits of the type; see individual models for median tonnage source references] Deposit types in the study area Metallic/ nonmetallic Contains strategic or critical materials Industrial mineral mine Casual use/ suction dredging Placer mining, small (<5 acres) Placer mining, large (>5 acres) Open pit mine, small (<5 acres) Open pit mine, large (>5 acres) Underground mine, small (<5 acres) Underground mine, large (>5 acres) Median ore tonnage, in million metric tons Median tonnage source Magmatic–directly related to igneous processes Diatreme-hosted diamond Nonmetallic No - - - - X

X - X 26 Bliss (1992)

Basalt-hosted sunstone Nonmetallic No - - - - X

X - - No data -

Hydrothermal–plutonic rock associated

Porphyry copper Metallic No - - - - - X - Unlikely, if so, 

block cave

240 Singer and others (2008)

Arc-related porphyry 

molybdenum (lowfluorine)

Metallic Yes, molybdenum - - - - - X - Unlikely, if so, 

block cave

94 Cox and Singer (1986)

Climax-type porphyry 

molybdenum

Metallic Yes, molybdenum - - - - - X - X 200 Cox and Singer (1986)

Copper skarn Metallic No - - - - X

X

X

X 0.56 Cox and Singer (1986)

Lead-zinc skarn Metallic No - - - - - X - X 1.4 Cox and Singer (1986)Molybdenum-tungsten 

greisen 

Metallic Yes, molybdenum 

and tungsten

- - - - - X - X No data Cox and Singer (1986)

Tungsten skarn Metallic Yes, tungsten - - - - - X - X 1.1 Cox and Singer (1986)Tungsten vein Metallic Yes, tungsten - - - - X

X

X

X 0.56 Cox and Singer (1986)

Polymetallic replacement Metallic No - - - - X

X 1.8 Cox and Singer (1986)

Polymetallic vein Metallic Yes, tungsten - - - - X

X

X

X 0.0076 Cox and Singer (1986)

Distal disseminated silvergold Metallic No - - - - - X - X 7.4 Cox and Singer (1990)Carlin-type gold-silver Metallic No - - - - - X - X 5.7 Berger and others (2008)

Hydrothermal–volcanic rock associated

Epithermal gold-silver 

(mercury) [includes jasperoid precious metal and epithermal gypsum]

Metallic Yes, mercury - - - - - X - X Many deposit 

types in this category

-

Volcanogenic uranium Metallic No - - - - X

X

X

X 0.34 Cox and Singer (1986)

Stanley district (Idaho)-type 

uranium 

Metallic No - - - - X - X - -

Volcanic opal and specialty 

gemstones

Nonmetallic No - - - - X

X - X No data -

Hectorite (lithium-rich clay) 

and specialty clays

Metallic Yes

X - - - - X - - No data -
Deposit types in the study 

area

Metallic/

nonmetallic

Contains strategic 

or critical 

materials

Industrial 

mineral 

mine

Casual 

use/

suction 

dredging

Placer 

mining, 

small 

(<5 acres)

Placer 

mining, 

large 

(>5 acres)

Open pit 

mine, small 

(<5 acres)

Open pit 

mine, 

large 

(>5 acres)

Underground 

mine, small 

(<5 acres)

Underground 

mine, large 

(>5 acres)

Median ore 

tonnage, in 

million metric 

tons

Median tonnage source

Hydrothermal–exhalative-magmatic processes 

Volcanogenic massive sulfide (Besshi-subtype) Metallic No - - - - X X X X 0.22 Cox and Singer (1986)

Hydrothermal–exhalative-sedimentary processes

SEDEX lead-zinc-silver Metallic No - - - - - X - X 15 Cox and Singer (1986)Bedded barite Nonmetallic No - - - - X X - X 1.24 Orris (1992)

Hydrothermal–metamorphic rock associated

Orogenic low-sulfide goldquartz veins (tonnage for 

Chugach-type)

Metallic No - - - - X X X X 0.0032 Bliss (1992)

Sedimentary (formed during or after the conversion from sediment to sedimentary rock ) 

Bentonite Nonmetallic No - - - - X X - - No data -Dolomite (High purity) Nonmetallic No X - - - X X - - No data -Sediment-hosted stratabound 

copper

Metallic No - - - - - X - X 10 Zientek and others 

(2013)

Sandstone uranium (rollfront) in intermontane 

basins

Metallic ??? - - - - - X - X No data -

Hydroallogenic volcanichosted uranium Metallic ??? - - - - - X - X No data -Zeolites (closed system 

subtype) 

Nonmetallic No - - - - X X - - No data -

Zeolites (open system 

subtype)

Nonmetallic No - - - - X X - - No data -

Sedimentary (formed during deposition of the sediment)

Banded iron formations 

(Algoma and Superior subtypes)

Metallic No - - - - X - X 170 Cox and Singer (1986)

Lacustrine diatomite Nonmetallic No X X X - - No data -

Surficial –mechanical (placer)

Heavy mineral placer Metallic Yes - X X X - - - - No data -Placer and paleoplacer gold Metallic No - X X X - - - - 1.1 Cox and Singer (1986)

Table 3-1.—Continued

Appendix 3 107
108 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming Deposit types in the study area Metallic/ nonmetallic Contains strategic or critical materials Industrial mineral mine Casual use/ suction dredging Placer mining, small (<5 acres) Placer mining, large (>5 acres) Open pit mine, small (<5 acres) Open pit mine, large (>5 acres) Underground mine, small (<5 acres) Underground mine, large (>5 acres) Median ore tonnage, in million metric tons Median tonnage source Other (non-locatable) mineral-deposit types Dimension stone (sandstone and quartzite) Nonmetallic No

X - - - X

X - - No data -

Sand and gravel Nonmetallic No

X - - - X - - No data -

Volcanic ash (pumice and 

cinders)

Nonmetallic No

X - - - X

X - - No data -

Perlite Nonmetallic No

X - - - X

X - - No data -

References

Berger, B.R., Ayuso, R.A., Wynn, J.C., and Seal, R.R., 2008, Preliminary model of porphyry copper deposits: U.S. Geological Survey Open-File Report 2008–1321, 55 p., accessed May 15, 2009, at http://

pubs.usgs.gov/of/2008/1321.

Bliss, J.D., 1992, Grade and tonnage model of Chugach-type low sulfide Au-quartz veins, in Bliss, J.D., ed., Developments in mineral deposit modeling: U.S. Geological Survey Bulletin 2004, p. 44–46, 

accessed May 20, 2016, at https://pubs.er.usgs.gov/publication/b2004.

Cox, D.P., and Singer, D.A., eds., 1986, Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 55. [Also available at https://pubs.usgs.gov/bul/b1693/.]Cox, D.G., and Singer, D.A., 1990, Descriptive and grade-tonnage models for distal disseminated Ag-Au deposit—A supplement to U.S. Geological Survey Bulletin 1693: U.S. Geological Survey OpenFile Report 90–282, 7 p. [Also available at https://pubs.er.usgs.gov/publication/ofr90282.]Orris, G.J., 1992, Grade and tonnage model of bedded barite, in Orris, G.J., and Bliss J.D., eds., Industrial minerals deposit models—Grade and tonnage models: U.S. Geological Survey Open-File Report 

92–437, p. 40–42, accessed May 10, 2016, at https://pubs.usgs.gov/of/1992/0437/report.pdf.

Singer, D.A., Berger, V.I., and Moring, B.C., 2008, Porphyry copper deposits of the World—Database and grade and tonnage models, 2008: U.S. Geological Survey Open-File Report 2008–1155, http://

pubs.usgs.gov/of/2008/1155/.

Zientek, M.L., Hayes, T.S., and Taylor, C.D., 2013, Grade and tonnage relations for sediment-hosted stratabound copper deposits, chap. 2 of Taylor, C.D., Causey, J.D., Denning, P.D., Hammarstrom, J.M., 

Hayes, T.S., Horton, J.D., Kirschbaum, M.J., Parks, H.L., Wilson, A.B., Wintzer, N.E., and Zientek, M.L., Descriptive models, grade-tonnage relations, and databases for the assessment of sedimenthosted copper deposits—With emphasis on deposits in the Central African Copperbelt, Democratic Republic of the Congo and Zambia: U.S. Geological Survey Scientific Investigations Report 2010–5090–J, p. 17–59, http://pubs.usgs.gov/sir/2010/5090/j/.

Table 3-1.—Continued
Deposit types in the study area

Diatreme-hosted diamond 

Basalt-hosted sunstone

Magmatic Systems

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Synonyms Diamond-bearing kimberlite pipes, diamond pipes, group-1 kimberlites.

Commodities Diamond.

Description Diamonds in kimberlite diatremes and other alkaline mafic rocks. Kimberlites are volatile-rich, potassic ultrabasic rocks 

with macrocrysts (and sometimes megacrysts and xenoliths) set in a fine-grained matrix.

Geological environment

Rock types Small hypabyssal intrusions that grade upwards into diatreme breccias near surface and pyroclastic rocks in the crater facies at surface. Kimberlites are volatile-rich, potassic ultrabasic rocks that commonly exhibit a distinctive inequigranular 

texture resulting from the presence of macrocrysts (and sometimes megacrysts and xenoliths) set in a fine-grained matrix. The megacryst and macrocryst assemblage in kimberlites includes anhedral crystals of olivine, magnesian ilmenite, 

pyrope garnet, phlogopite, Ti-poor chromite, diopside, and enstatite. Some of these phases may be xenocrystic in origin. 

Matrix minerals include microphenocrysts of olivine and one or more of monticellite, perovskite, spinel, phlogopite, 

apatite, and primary carbonate and serpentine.

Kimberlites crosscut all types of rocks.

Age range Any age except Archean for host intrusions. Economic deposits occur in kimberlites from Proterozoic to Tertiary in age. 

The diamond ages vary from early Archean to as young as 990 Ma.

Depositional environment Kimberlites rise quickly from the mantle and are emplaced as multistage, high-level diatremes, tuff-cones and rings, and 

hypabyssal dikes and sills.

Tectonic setting(s) Ancient stable cratons, alkalic rock provinces, regions of crustal tension with deep-seated fractures, broad anticlines and 

synclines with deep-seated fractures, and regions of low geothermal gradient.

Associated deposit types Diamonds can be concentrated, by weathering to produce residual concentrations, or within placer deposits. Lamproitehosted diamond deposits form in a similar manner, but the magmas may be of different origin.

Deposit description

Ore mineralogy Diamond

Alteration Serpentinization in many deposits; silicification or bleaching along contacts. Secondary calcite, quartz, and zeolites can 

occur on fractures. Diamonds can undergo graphitization or resorption.

Ore controls Kimberlites typically occur in fields comprising as much as 100 individual intrusions, often grouped in clusters. Each field 

can exhibit considerable diversity with respect to the petrology, mineralogy, mantle xenolith and diamond content of 

individual kimberlites. Economically diamondiferous and barren kimberlites can occur in close proximity. Controls 

on the differences in diamond content between kimberlites are not completely understood. They may be due to depths 

of origin of the kimberlite magmas (above or below the diamond stability field); differences in the diamond content of 

the mantle sampled by the kimberlitic magma; degree of resorption of diamonds during transport; flow differentiation; 

batch mixing; or some combination of these factors.

Geochemical signatures Elevated Ti, Cr, Ni, Mg, Ba and Nb in overlying residual soils. However, caution must be exercised as other alkaline rocks 

can give similar geochemical signatures.

Geophysical signature Geophysical techniques are used to locate kimberlites but give no indication as to their diamond content. Ground and 

airborne magnetometer surveys are commonly used; kimberlites can show as either magnetic highs or lows. In 

equatorial regions, the anomalies are characterized by a magnetic dipolar signature in contrast to the “bulls-eye” pattern 

in higher latitudes. Some kimberlites, however, have no magnetic contrast with surrounding rocks. Some pipes can 

be detected using electrical methods (for example, electromagnetic and very low frequency, resistivity) in airborne 

or ground surveys. These techniques are particularly useful where the weathered, clay-rich, upper parts of pipes are 

preserved because they are conductive and may contrast sufficiently with the host rocks to be detected. Ground-based 

gravity surveys can be useful in detecting kimberlites that have no other geophysical signature and in delineating pipes. 

Deeply weathered kimberlites or those with a thick sequence of crater sediments generally give negative responses and 

where fresh kimberlite is found at surface, a positive gravity anomaly may be obtained.

Economic factors

Grade and tonnage The amount of diamond contained within diamond bearing pipes is extremely small, with commercially mineable 

concentrations ranging from .01 ppm to 0.80 ppm (0.04 to 4.0 carats per ton). The clarity, size, shape, color, and volume 

of diamonds within a pipe need to be carefully determined before the true economic potential of a diamond-bearing pipe 

can be determined.

Diatreme-Hosted Diamond

[km, kilometer; t, metric ton; g/t, grams per metric ton; ppm, parts per million; Ma, mega-annum or millions of years ago]
Importance Major source of gem and industrial diamonds. On a worldwide basis only about 10 percent of known kimberlites are 

diamond-bearing and only one or two percent of kimberlites contain economic quantities of diamond.

Other assessment and exploration guides

Indicator minerals are used extensively in the search for kimberlites and are one of the most important tools, other than bulk sampling, to assess the 

diamond content of a particular pipe. Chrome pyrope and eclogitic garnet, chrome diopside, picroilmenite, chromite and, to a lesser extent, olivine in 

surficial materials (tills, stream sediments, loam, etc.) indicate a kimberlitic source.

Mineral chemistry is used extensively to help determine whether the kimberlite source is diamondiferous or barren. Diamond-bearing kimberlites can 

contain high-Cr, low-Ca pyrope garnets (G10 garnets), sodium-enriched eclogitic garnets, high-Cr chromites with moderate to high Mg contents, and 

magnesian ilmenites.

Examples

In/near focal areas Kimberlites occur in north-central Montana; however, only one microdiamond has been reported.

Elsewhere Koala, Panda, Sable, Fox and Misery (Northwest Territories, Canada); Kimberly, Premier and Venetia (South Africa)

References

Hearn, Jr., B.C., 1968, Diatremes with kimberlite affinities in north-central Montana: Science, v. 159, p. 622–625.

Michalski, T.C., and Modreski, P.J., 1991, Descriptive model of diamond-bearing kimberlite pipes, in Orris, G.J., and Bliss, J.D., eds., Some industrial 

mineral deposit models: U.S. Geological Survey Open-File Report 91–11–A, p. 1– 5, accessed April 15, 2016, at http://pubs.usgs.gov/of/1991/ofr-91-

0011-a/ofr-91-0011a.pdf.

Mitchell, R.H., 1993, Kimberlites and lamproites—Primary sources of diamond, in Sheahan, P.A., and Cherry, M.E., eds., Ore Deposit Models, v. II: 

Geoscience Canada, Reprint Series 6, p. 13–28.

Pell, J., 1998, Kimberlite-hosted diamonds, in Geological Fieldwork 1997, British Columbia Ministry of Employment and Investment, Paper 1998–1, p. 

24L–1 to 24L–4.

Kjarsgaard, B.A., 2007, Kimberlite diamond deposits, in Goodfellow, W.D., ed., Mineral deposits of Canada—A synthesis of major deposit types, district 

metallogeny, the evolution of geological provinces, and exploration methods: Geological Association of Canada, Mineral Deposits Divisions, Special 

Publication No. 5, p. 245–272.

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Basalt-Hosted Sunstone

[t, metric ton; N/A, not applicable]

Synonyms Gem labradorite feldspar.

Commodities Sunstone.

Description Gem-quality labradorite in weathered basalt flows that exhibit adventurescence, a light reflectance phenomenon 

caused by inclusions of copper (in Oregon) or hematite (other localities).

Geological environment

Rock types In Oregon, sunstone occurs locally in a weathered basalt flow that is part of a classic volcanic highland typified 

by shield volcanoes, cinder cones, large bodies of ashfall tuffs, regionally extensive basalt flows of varying 

thicknesses, and locally extensive red cinder beds.

Deposit description

Ore mineralogy Labradorite

Alteration Groundmass of gem-bearing zones at the Ponderosa Mine is highly weathered to unconsolidated reddish-brown 

material.

Ore controls Sunstone occurs as phenocrysts in a moderately to heavily weathered scoriaceous porphyritic basalt of 

calcalkaline affinity composed of labradorite feldspar and basaltic glass, with minor olivine and magnetite/

ilmenite present as accessory phases. The vesicles are filled to varying amounts with nonspecific clay and 

feldspar alteration products. 

Geochemical signatures N/A

Geophysical signature N/A

Economic factors

Grade and tonnage At the Ponderosa Mine in Oregon, 500,000 t of ore is estimated to contain 200 t of gem material.

Importance The premier U.S. gem-quality feldspar is the red labradorite, known as sunstone, mined in Oregon. Large 

quantities of gem-quality labradorite from deposits in southeastern Oregon for many years. The common 

color of Oregon sunstone is straw-yellow, it also can be pink, peach, red, salmon red-orange, red-green, and 

blue-green. It also can be bicolored and tricolored in combinations of yellow, red, and green, and a small 

percentage is dichroic and trichroic. 

In 1988, the availability and quality of sunstone, other than the standard yellow Oregon variety, drastically 

increased with the discovery of the Ponderosa Mine. The vivid-red faceted stones and cabochons from this 

mine set a new world standard sunstone. The opening of the mine also increased the supply of peach, salmon 

red-orange, red-green, green, blue-green, and bicolored and tricolored in combinations of yellow, red, and 

green. For the first time ever, there was a continuous U.S. supply of the more desirable colors in sizes needed 

by the jewelry industry. The largest faceted high-quality red sunstone is more than 10 carats. The supply from 

this and other developed deposits will continue to be adequate for many years into the future. 

Other assessment and exploration guides

N/A

Examples

In/near focal areas Ponderosa Mine, Oregon; Dust Devil Mine, Oregon; Sunstone Butte Mine, Oregon.

References

Brown, D.E., McLean, G.D., and Black, G.L., 1981, Preliminary geology and geothermal potential of the southern Harney Basin: Oregon 

Department of Geology and Mineral Industries, Open File Report 0–80–07.

Johnston, C.L., Gunter, M.E., and Knowles, C.R., 1991, Sunstone labradorite from the Ponderosa mine, Oregon: Gems and Gemology, v. 27, no. 4, 

p. 220–233.

Pay, Duncan, Weldon, Robert, McClure, Shane, and Schumacher, Kevin, 2013, Three occurrences of Oregon sunstone: Gems and Gemology, v. 49, 

no. 3, 162–171, accessed April 28, 2016, at http://www.gia.edu/gems-gemology/FA13-oregon-sunstone-pay.

U.S. Bureau of Mines, 1995, An overview of production of specific U.S. gemstones: U.S. Bureau of Mines Special Publication 14–95, accessed April 

21, 2016, at http://minerals.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/index.html.
Hydrothermal—Plutonic Rock Associated System

Deposit types in the study area

Porphyry copper 

Arc-related porphyry molybdenum (low-fluorine)

Copper skarn

Tungsten skarn

Lead-zinc skarn 

Polymetallic replacement

Polymetallic vein

Tungsten vein

Molybdenum-tungsten greisen 

Distal disseminated silver-gold

Carlin-type gold-silver

Appendix 3 113
114 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Porphyry Copper

[wt.%, weight percent; g/t, grams per metric ton; Mt, million metric tons; avg, average; km, kilometer]

Synonyms Calkalkaline porphyry.

Commodities Cu, Mo, Au, Ag.

Description Porphyry copper deposits consist of disseminated copper minerals and copper minerals in veins and breccias that are 

relatively evenly distributed in large volumes of rock, forming high tonnage (>100 Mt), low to moderate grade 

(0.3–2.0 wt.% Cu) ores. Host rocks are altered and genetically related granitoid porphyry intrusions and adjacent wall 

rocks.

Geological environment

Rock types Tonalite to monzogranite or syenitic porphyry intruding granitic, volcanic, calcareous sedimentary, and other rocks.

Textures Porphyry has closely spaced phenocrysts and microaplitic quartz-feldspar groundmass.

Age range Mainly Mesozoic and Cenozoic, but may be any age.

Depositional environment High-level intrusive complexes that commonly include stocks, dikes, and breccia pipes. Many deposits are focused 

in swarms of porphyry dikes that may radiate from larger intrusions or batholiths. The deposits form at shallow 

(mostly 6 km or less) depth by fluids exsolved from underlying crystallizing magmas emplaced at greater than 

3–10-km depth in the upper crust and by external waters heated by those magmas.

Tectonic setting(s) Localized in time and space within magmatic arcs along convergent plate margins where subduction of oceanic crust 

and arc-type magmatism generates hydrous, oxidized upper crustal granitoids genetically related to ores. Arc crust is 

relatively thick, and there is evidence for broadly coeval compressional or transpressional tectonism.

Associated deposit types Skarns (Cu, Fe, Au, Zn), polymetallic replacement, polymetallic veins, distal-disseminated Au-Ag, epithermal veins.

Deposit description

Ore mineralogy Hypogene: Chalcopyrite+pyrite±molybdenite; chalcopyrite+magnetite±bornite± Au; assemblages may be superposed. 

Quartz+K-feldspar+biotite±anhydrite; quartz+sericite+clay minerals. Late veins of enargite, tetrahedrite, galena, 

sphalerite, and barite in some deposits. Supergene: brochantite, copper pitch, cuprite, native copper, tenorite, chrysocolla, 

neotocite, malachite, and atacamite.

Alteration Major alteration types are (1) potassic, (2) sericitic, (3) advanced argillic, (4) intermediate argillic, (5) propylitic, (6) sodiccalcic and sodic, (7) greisen, and (8) skarn. Weathering can form an enriched oxide zone above sulfide ore.

Ore controls Stockwork veins in porphyry, along porphyry contact, and in favorable country rocks such as carbonate rocks, mafic igneous rocks, and older granitic plutons.

Geochemical signatures Cu+Mo±Au+Ag+W+B+Sr center, Pb, Zn, Au, As, Sb, Se, Te, Mn, Co, Ba, and Rb outer. Locally Hg and Sn form most 

distal anomalies. High S in all zones. Some deposits have weak U anomalies.

Geophysical signature Ore zones can be associated with magnetite-rich rocks and are indicated by magnetic surveys. Intensely hydrothermally 

altered rocks, with quartz-pyrite-sericite (phyllic) alteration produce magnetic and resistivity lows. Pyritic haloes 

surrounding ore respond well to induced polarization (IP) surveys but in sulfide-poor systems the ore itself provides the 

only significant IP response. 

Remote sensing: In areas of good exposure with limited vegetation, airborne and spaceborne multispectral and 

hyperspectral imaging systems can be used to map alteration mineral associations and their spatial relations in porphyry 

copper systems. Hydrothermal minerals characteristic of sericitic, intermediate and advanced argillic, and propylitic 

alteration, iron oxides and hydroxides, and silica can be remotely mapped using their distinctive absorption features in 

the visible near-infrared through short-wave infrared and thermal-infrared wavelengths.

Economic factors

Grade and tonnage Cu grades vary from 0.03 to 2 wt.%; avg 0.44 wt.%. Mo grades vary from < 0.001 to 0.1 wt.%; avg 0.019 wt.%. Au varies 

from 0.001 to 6.6 g/t; avg 0.31 g/t. Ag varies from 0.08 to 65 g/t; avg 3.2 g/t. Tonnages range from 2 to 21,000 Mt.

Importance Porphyry copper deposits supply about 60 percent of the world’s copper.

Examples

In/near focal area Contact, Nevada.

Elsewhere Bingham, Utah; Yerington and Ann Mason, Nevada; Butte, Montana.

References

John, D.A., Ayuso, R.A., Barton, M.D., Blakely, R.J., Bodnar, R.J., Dilles, J.H., Gray, Floyd, Graybeal, F.T., Mars, J.C., McPhee, D.K., Seal, R.R., Taylor, 

R.D., and Vikre, P.G., 2010, Porphyry copper deposit model, chap. B of Mineral deposit models for resource assessment: U.S. Geological Survey 

Scientific Investigations Report 2010–5070–B, 169 p., accessed April 15, 2016, at http://pubs.usgs.gov/sir/2010/5070/b/.
Arc-Related Porphyry Molybdenum (low fluorine)

[wt.%, weight percent; Mt, million metric tons]

Synonyms Low-fluorine stockwork molybdenum, fluorine-poor, granodiorite-type, calcalkaline-type, differentiated monzogranite class, 

Endako-type, subduction-related porphyry molybdenum, porphyry molybdenum.

Commodities Mo, W.

Description Stockwork of molybdenite-bearing quartz veinlets and fractures in intermediate to felsic intrusive rocks and associated 

country rocks. Deposits are low grade but large and amenable to bulk mining methods.

Geological environment

Rock types Diorite to granite (mostly 65–77 wt.% SiO2

, most commonly quartz monzonite and granodiorite. Generally, peraluminous 

I-type granitoids. 

Textures Ore is predominantly structurally controlled; mainly stockworks of crosscutting fractures and quartz veinlets, also veins, vein 

sets, and breccias

Age range Mostly Late Jurassic through Tertiary in the western cordillera of North America.

Depositional environment High-level to subvolcanic felsic intrusive centers; multiple stages of intrusion are common. Typically, deeper-seated settings 

than for porphyry copper deposits.

Tectonic setting(s) Subduction-related magmatic arcs at convergent plate margins. Close association with calcalkalic continental magmatic arcs; 

deposits form almost exclusively within continental crust.

Associated deposit types Mo-bearing skarns, Ag-Pb-Zn veins.

Deposit description

Ore mineralogy Molybdenite. Chalcopyrite, scheelite, and galena are generally subordinate.

Alteration Core zone of potassic and silicic alteration characterized by hydrothermal K-feldspar, biotite, quartz, ±anhydrite. K-feldspar 

and biotite commonly occur as alteration selvages on mineralized quartz veinlets and fractures but may be pervasive in 

areas of intense fracturing and mineralization. 

Phyllic alteration typically surrounds and may be superimposed to various degrees on the potassic-silicic core; it consists 

mainly of quartz, sericite and carbonate. Phyllic alteration is commonly pervasive and may be extensive. 

Propylitic alteration (chlorite and epidote) may extend for hundreds of meters beyond the zones of potassic- silicic and 

phyllic alteration. 

Argillic alteration, where present, characterized by clay minerals (kaolinite) typically overprinted on the other types of 

alteration

Ore controls Quartz veinlet and fracture stockwork zones superimposed on intermediate to felsic intrusive rocks and surrounding country 

rocks; multiple stages of mineralization common.

Geochemical signatures Pathfinder elements: Mo, Se, Re, As, Pb, Zn. Stream-sediment anomalies: Mo, W, F, Cu, Pb, Zn, Ag. Heavy mineral 

concentrates: Mo, W, Pb.

Geophysical signature Ring of magnetic high anomalies may be present around a deposit if magnetite- or pyrrhotite-bearing hornfels or skarn 

occurs. Radiometric surveys may show potassic alteration zones. Overall low total sulfide content (generally <5 volume 

percent) reduces the usefulness of many geophysical methods; in many aspects, signatures of barren intrusions resemble 

those of productive intrusions.

Economic factors

Grade and tonnage Deposits are low-grade (0.03–0.22 wt.% Mo), but large (commonly >50 Mt), which makes them amenable to bulk-mining 

open-pit methods. Typical size is 100 Mt at 0.1 to 0.2 wt.% Mo.

Importance Porphyry Mo deposits associated with low-F felsic intrusive rocks are a major source of world molybdenum production. 

Essentially all Mo production in the United States and Canada comes from these and from porphyry Cu-Mo-Au deposits.

Other assessment and exploration guides

Magmatic belts that formed above subduction zones along convergent plate boundaries, in regions that already have discovered deposits and prospects.

Known arc-related porphyry molybdenum deposits are found in mountain belts where known porphyry copper mineralization also is located. However, 

many mountain belts where porphyry copper deposits are found do not contain any, as of yet discovered, arc-related porphyry molybdenum deposits.

Potassic alteration grading outward or upward into phyllic alteration is a diagnostic feature.

Examples

In/near focal areas

Elswhere

Thompson Creek, Idaho.

Cannivan Gulch, Montana; Endako, British Columbia.

References

Sinclair, W.D., 1995, Porphyry Mo (Low-F-type), in Lefebure, D.V. and Ray, G.E., eds., Selected British Columbia mineral deposit profiles, volume 1—

Metallics and coal: British Colombia Ministry of Energy of Employment and Investment, Open File 1995–20, p. 93–96, accessed April 15, 2016, at 

http://www.empr.gov.bc.ca/MINING/GEOSCIENCE/MINERALDEPOSITPROFILES/Pages/Introduction.aspx.

Taylor, R.D., Hammarstrom, J.M., Piatak, N.M., and Seal, R.R. II, 2012, Arc-related porphyry molybdenum deposit model, chap. D of Mineral deposit 

models for resource assessment: U.S. Geological Survey Scientific Investigations Report 2010–5070–D, 64 p., accessed April 25, 2016, at http://pubs.

usgs.gov/sir/2010/5070/d/.

Appendix 3 115
116 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Synonyms Pyrometasomatic and contact metasomatic copper deposits.

Commodities Cu, Au, Ag, Mo, W, magnetite.

Description Cu-dominant mineralization (generally chalcopyrite) genetically associated with a skarn gangue (includes calcic and 

magnesian Cu skarns).

Geological environment

Rock types Tonalite to monzogranite intruding carbonate rocks or calcareous clastic rocks.

Age range Mainly Mesozoic, but may be any age.

Depositional environment Miogeosynclinal sequences intruded by felsic plutons.

Tectonic setting(s) Most common where Andean-type plutons intrude older continental-margin carbonate sequences. Can be associated with 

oceanic island arc plutonism. Commonly associated with porphyry copper deposits intrusive into carbonate rocks. 

Associated deposit types Porphyry Cu deposits, other skarns (Au, Fe, Zn-Pb), and replacement Pb-Zn-Ag deposits.

Deposit description

Ore mineralogy Moderate to high sulfide content. Chalcopyrite ± pyrite ± magnetite in inner garnet-pyroxene zone. Bornite ± chalcopyrite 

±sphalerite ± tennantite in outer wollastonite zone. Hematite, pyrrhotite, or magnetite may predominate (depending on 

oxidation state). Scheelite and traces of molybdenite, bismuthinite, galena, cosalite, arsenopyrite, enargite, tennantite, 

loellingite, cobaltite, and tetrahedrite may be present.

Alteration Diopside+andradite center; wollastonite+tremolite outer zone; marble peripheral zone. Igneous rocks may be altered to 

epidote+pyroxene+garnet (endoskarn). Retrograde alteration to actinolite, chlorite, and clays may be present.

Ore controls Irregular or tabular ore bodies tend to form in carbonate rocks and (or) calcareous volcanic rocks or tuffs near igneous 

contacts. Pendants within igneous stocks can be important. Cu mineralization is present as stockwork veining and 

disseminations in both endo and exoskarn; it commonly accompanies retrograde alteration.

Geochemical signatures Rock analyses may show Cu-Au-Ag-rich inner zones grading outward through Au-Ag zones with high Au:Ag ratios to an 

outer Pb-Zn-Ag zone. Co-As-Sb-Bi-Mo-W geochemical anomalies are present in the more reduced Cu skarn deposits.

Geophysical signature Magnetics: plutons, batholiths, and regional geology/structure can be imaged. Oxidized plutons generally produce mag 

highs, whereas reduced plutons produce mag lows. Highs/lows also depend on contrast with host rocks. More oxidized 

in island-arc versus continental arc. Thick sedimentary pile of host rocks may reduce magmas during assimilation, 

thereby reducing magnetic response. Magnetite may be produced (sodic-calcic, K-feldspar, propylitic zones) or 

destroyed (phyllic and argillic, advanced argillic zones) during hydrothermal alteration processes, but regional 

geophysical surveys are unlikely to see hydrothermal system because of low resolution. Gravity: regional geology/

structure. Radiometrics: lithology and hydrothermal alteration potassium enrichment (Th/K).

Economic factors

Grade and tonnage Average 1 to 2 wt.% copper. Worldwide, they generally range from 1 to 100 Mt, although some exceptional deposits 

exceed 300 Mt.

Importance Historically, these deposits were a major source of copper, although porphyry deposits have become much more important. 

However, major Cu skarns are still worked throughout the world, including in China and the United States.

Other assessment and exploration guides

Limestone/carbonate rocks proximal to calcalkaline intrusive complexes.

Limestone converted to marble.

Porphyry copper deposits; many skarns are porphyry-copper related.

Endoskarn alteration in intrusions; hornfels around intrusions. 

Close proximity to stock contacts with oxidized skarn mineralogy dominated by andraditic garnet. 

Zoning from garnet near the pluton to pyroxene to vesuvianite or wollastonite at the marble contact.

Examples

In/near focal areas Contact, Nevada; Empire Mine, Idaho.

Elsewhere Carr Fork, Utah; Mason Valley, Copper Canyon, and Victoria, Nevada.

References

Einaudi, M.T., 1981, Skarns associated with porphyry plutons. I—Description of deposits, southwestern North America, II—General features and origin, 

in Titley, S. R., ed., Advances in geology of the porphyry copper deposits of southwestern North America: Tucson, University of Arizona Press, 

p. 139–183.

Meinert, L.D., 2005, World skarn deposits, in Hedenquist, J.W., Thompson, J.F.H., Goldfarb, R.J., and Richards, J.P., eds., Economic Geology—One 

hundredth anniversary volume 1905–2005: Littleton, Colorado, Society of Economic Geologists, Inc., p. 299–336.

Copper Skarn

[wt.%, weight percent; Mt, million metric tons]
Tungsten Skarn

[wt.%, weight percent; Mt, million metric tons]

Synonyms Pyrometasomatic or contact metasomatic tungsten deposits.

Commodities W, Mo, Cu, Sn, Zn.

Description Scheelite-dominant mineralization genetically associated with a skarn gangue.

Geological environment

Rock types Pure and impure limestones, calcareous to carbonaceous pelites. Associated with tonalite, granodiorite, quartz 

monzonite and granite of both I- and S-types. W skarn-related granitoids, compared to Cu skarn- related plutonic 

rocks, tend to be more differentiated, more contaminated with sedimentary material, and have crystallized at a 

deeper structural level.

Age range Mainly Mesozoic, but may be any age.

Depositional environment Contacts and roof pendants of batholith and thermal aureoles of apical zones of stocks that intrude carbonate rocks.

Tectonic setting(s) Continental margin, synorogenic plutonism intruding deeply buried sequences of eugeoclinal carbonate-shale 

sedimentary rocks. Can develop in tectonically thickened packages in back-arc thrust settings.

Associated deposit types Other skarn types (Sn, Mo, Zn-Pb, W).

Deposit description

Ore mineralogy Scheelite ± molybdenite ± chalcopyrite ±pyrrhotite ± sphalerite ± arsenopyrite ± pyrite ± powellite. May contain 

trace wolframite, fluorite, cassiterite, galena, marcasite and bornite. Reduced types are characterized by pyrrhotite, 

magnetite, bismuthinite, native bismuth and high pyrrhotite:pyrite ratios. Variable amounts of quartz-vein stockwork 

(with local molybdenite) can cut both the exoskarn and endoskarn.

Alteration Exoskarn alteration: Inner zone of diopside-hedenbergite±grossular-andradite±biotite±vesuvianite, with outer barren 

wollastonite-bearing zone. An innermost zone of massive quartz may be present. Late stage spessartine±almandin

e±biotite±amphibole±plagioclase±phlogopite±epidote±fluorite±sphene. Exoskarn envelope can be associated with 

extensive areas of biotite hornfels. Endoskarn alteration: Pyroxene±garnet±biotite±epidote±amphibole±muscovite±

plagioclase±pyrite±pyrrhotite±trace tourmaline and scapolite; local greisen developed.

Ore controls Carbonate rocks in extensive thermal aureoles of intrusions; gently inclined bedding and intrusive contacts; structural 

and (or) stratigraphic traps in sedimentary rocks and irregular parts of the pluton/country rock contacts.

Geochemical signatures W, Cu, Mo, As, Bi, and B. Less commonly Zn, Pb, Sn, Be, and F.

Geophysical signature Magnetic and induced polarization surveys can be used to outline the surface projection of ore bodies because 

magnetite, pyrrhotite, and other sulfide minerals are common in these deposits. Although skarns typically have a 

positive density contrast relative to adjacent intrusions and carbonate rocks, gravity surveys are not commonly used 

due to high cost and nonspecificity for ore. Remote-sensing techniques can effectively identify carbonate terranes 

and iron enrichment in skarns if skarn is exposed. In some cases, contacts between intrusions and sedimentary rocks 

can be mapped and carbonate rocks can be distinguished from noncarbonate rocks.

Economic factors

Grade and tonnage Grades range between 0.4 and 2 wt.% WO3

 (typically 0.7 wt.%). Deposits vary from 0.1 to >30 Mt.

Importance Historically, skarn deposits have accounted for nearly 60 percent of the Western world’s tungsten production.

Other assessment and exploration guides

Reduced W skarns form in carbonaceous rocks and (or) at greater depth.

Oxidized W skarns form in hematitic or noncarbonaceous rocks, and (or) at shallower depths.

Late retrograde alteration is an important factor in many W skarns because, during retrogression, the early low-grade mineralization is often scavenged 

and redeposited into economic high-grade ore zones.

Dolomitic rocks tend to inhibit the development of W skarns; consequently, magnesian W skarns are uncommon.

Examples

In/near focal areas None. 

Elsewhere Osgood Range, Nevada; Pine Creek, California.

References

Cox, D.P., 1986, Descriptive model of W skarn deposits, in Cox, D.P. and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey, Bulletin 

1693, p. 55. [Also available at https://pubs.usgs.gov/bul/b1693/.]

Meinert, L.D., 2005, World skarn deposits, in Hedenquist, J.W., Thompson, J.F.H., Goldfarb, R.J., and Richards, J.P., eds., Economic Geology—One 

hundredth anniversary volume 1905–2005: Littleton, Colorado, Society of Economic Geologists, Inc., p. 299–336.

Ray, G.E., 1995, W skarns, in Lefebure, D.V. and Ray, G.E., eds., Selected British Columbia mineral deposit profiles, volume 1—Metallics and coal: 

British Columbia Ministry of Energy of Employment and Investment, Open File 1995-20, p. 71–74, accessed April 25, 2016, at http://www.empr.

gov.bc.ca/Mining/Geoscience/PublicationsCatalogue/OpenFiles/1995/Pages/1995-20.aspx.

Appendix 3 117
118 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Lead-Zinc Skarn

[wt.%, weight percent; Hd, hedenbergite; Jo, johannsenite; Mt, million metric tons; m, meter; CSAMT, controlled-source audiofrequency magnetotellurics]

Synonyms Pyrometasomatic or contact metasomatic Pb-Zn deposits.

Commodities Pb, Zn, Ag, (Cu, Cd, W, Au).

Description Galena and (or) sphalerite-dominant mineralization genetically associated with a skarn gangue.

Geological environment

Rock types Host rocks vary from high-level skarns in thick limestones, calcareous tuffs and sediment to deeper level skarns in marbles 

and calcsilicate-bearing migmatites. Associated intrusive rocks are granodiorite to leucogranite, diorite to syenite (mostly 

quartz monzonite). Pb-Zn skarns tend to be associated with small stocks, sills and dikes and less commonly with larger 

plutons. The composition of the intrusions responsible for many distal Pb-Zn skarns is uncertain.

Age range Mainly Mesozoic.

Depositional environment Commonly occur along igneous or stratigraphic contacts, as subvertical chimneys or veins along faults and fissures, and as 

subhorizontal blankets. Pb-Zn skarn deposits formed either at higher structural levels or distal to the intrusions tend to be 

larger and more Mn- rich compared to those formed at greater depths or more proximal.

Tectonic setting(s) Plutonism. Pb-Zn skarns occur at a wide range of depths, being associated with subvolcanic aphanitic dikes and high-level 

breccia pipes, as well as deep-level batholiths.

Associated deposit types Porphyry Cu deposits, other skarns (Au, Fe, Zn-Pb), and replacement Pb-Zn-Ag deposits 

Deposit description

Ore mineralogy Sphalerite±galena±pyrrhotite±pyrite±magnetite±arsenopyrite±chalcopyrite±bornite. Other trace minerals reported include 

scheelite, bismuthinite, stannite, cassiterite, tetrahedrite, molybdenite, fluorite, and native gold.

Proximal skarns tend to be richer in Cu and W, whereas distal skarns contain higher amounts of Pb, Ag, and Mn.

Alteration Exoskarn alteration: Mn-rich hedenbergite (Hd30–90, Jo10–50), andraditic garnet (Ad20–100, Spess2–10) ±wollastonite±bustamite±r

hodonite. Late-stage Mn-rich actinolite± epidote±ilvaite±chlorite±dannermorite±rhodochrosite±axinite.

Endoskarn alteration: Highly variable in extent of development, and in many of the distal Pb-Zn skarns the nature of the 

endoskarn is unknown. However, Zn-rich skarns formed near stocks are often associated with abundant endoskarn that 

may equal or exceed the exoskarn. Endoskarn mineralogy is dominated by epidote±amphibole±chlorite±sericite with 

lesser rhodonite±garnet± vesuvianite±pyroxene±K-feldspar±biotite and rare topaz. Marginal phases may contain greisen 

and (or) tourmaline.

Ore controls Carbonate rocks, particularly along structural and (or) lithologic contacts (shale-limestone contacts or pre-ore dikes). 

Deposits may occur considerable distances (100–1,000 m) from the source intrusions.

Geochemical signatures Pb, Zn, Ag, Cu, Mn, As, Bi, W, F, Sn, Mo, Co, Sb, Cd, and Au

Geophysical signature Generally good induced polarization response. Galena-rich ore bodies may be marked by gravity anomalies whereas 

pyrrhotite-rich mineralization may be detected by magnetic surveys. CSAMT may also be a useful exploration system.

Economic factors

Grade and tonnage Pb-Zn skarns tend to be small (<3 Mt) but can reach 45 Mt, grading as much as 15 wt.% Zn, 10 wt.% Pb and > 150 g/t Ag 

with substantial Cd. Cu grades are generally < 2 wt.%. Some deposits contain Au.

Importance Important past and current producers exist in Mexico, China, United States (New Mexico and California), and Argentina.

Other assessment and exploration guides

Thick limestones distal to small granitoid stocks. 

Structural traps and lithological contacts.

Exoskarns with low garnet/pyroxene ratios.

Mn-rich pyroxenes.

Examples

In/near study area White Knob Mine and Champion Group, Idaho.

Elsewhere Hanover-Fierro district, New Mexico.

References

Cox, D.P., 1986, Descriptive model of Zn-Pb skarn deposits, in Cox, D.P. and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey, Bulletin 

1693, p. 90. [Also available at https://pubs.usgs.gov/bul/b1693/.]

Meinert, L.D., 2005, World skarn deposits, in Hedenquist, J.W., Thompson, J.F.H., Goldfarb, R.J., and Richards, J.P., eds., Economic Geology—One 

hundredth anniversary volume 1905–2005: Littleton, Colorado, Society of Economic Geologists, Inc., p. 299–336.

Mosier, D.L., 1986, Grade and tonnage model of Zn-Pb skarn deposits, in Cox, D.P. and Singer, D.A., eds., Mineral deposit models: U.S. Geological 

Survey, Bulletin 1693, p. 90–93. [Also available at https://pubs.usgs.gov/bul/b1693/.]

Ray, G.E., 1995, Pb-Zn skarns, in Lefebure, D.V., and Ray, G.E., eds., Selected British Columbia mineral deposit profiles, volume 1—Metallics and coal: 

British Columbia Ministry of Energy of Employment and Investment, Open File 1995-20, p. 61–62, accessed April 15, 2016, at http://www.empr.gov.

bc.ca/Mining/Geoscience/PublicationsCatalogue/OpenFiles/1995/Pages/1995-20.aspx.
Polymetallic Replacement

[wt.%, weight percent; Mt, million metric tons; SEDEX, sedimentary exhalative deposits]

Synonyms Manto.

Commodities Ag, Pb, Zn, Cu (byproduct Au, Sn, Bi).

Description Hydrothermal, epigenetic, Ag, Pb, Zn, Cu minerals in massive lenses, pipes in limestone, dolomite, or other soluble rock near 

igneous. Most massive ore contains more than 50 percent sulfide minerals.

Geological environment

Rock types Hosted by limestone and dolostone. The carbonates are typically within a thick sediment package with siliciclastic rocks 

that is cut by granite, quartz monzonite, and other intermediate to felsic hypabyssal, porphyritic lithologies. There may be 

volcanic rocks in the sequence, or more commonly above, which are related to the intrusive rocks.

Age range Many are late Mesozoic to early Cenozoic; age is not important.

Depositional environment Carbonate host rocks that commonly occur in broad sedimentary basins, such as epicratonic shelf. Replacement by solutions 

emanating from volcanic centers and epizonal plutons. Calderas may be favorable. Can be distal to skarns and intrusions. 

Tectonic setting(s) Intrusions emplaced into miogeoclinal to platformal, continental settings. Most deposits occur in mobile belts that have 

undergone moderate deformation and have been intruded by small plutons.

Associated deposit types Base-metal skarns, porphyry Cu.

Deposit description

Ore mineralogy Sphalerite, galena, pyrite, chalcopyrite, marcasite; arsenopyrite, pyrargyrite/proustite, enargite, tetrahedrite, geocronite, 

electrum, digenite, jamesonite, jordanite, bournonite, stephanite, polybasite, rhodochrosite, sylvanite, calaverite. Chimneys 

may be more Zn-rich, Pb-poor than manto deposits.

Alteration Limestone wallrocks are commonly dolomitized and (or) silicified, whereas shale and igneous rocks are argillized and 

chloritized. Jasperoid occurs in some U.S. examples.

Ore controls The irregular shapes of these deposits and their occurrence in carbonate hosts emphasize the importance of ground 

preparation in controlling fluid channels and depositional sites. Controls include faults, fault intersections, fractures, 

anticlinal culminations, bedding channelways (lithologic contrasts), karst features and pre-existing permeable zones. In 

several districts karst development associated with unconformities is believed to have led to development of open spaces 

subsequently filled by ore. Some deposits are spatially associated with dikes.

Geochemical signatures Elevated Pb-Zn±Cu±Au±Ag±Mo±As±Bi±Sb. In some districts, ore proximal to igneous intrusions is Cu- and Au rich, and 

grades laterally (and sometimes vertically) into Pb-Zn-Ag ore. A distal, Mn-enriched zone is present in some districts. 

Elevated Ba and Ag in jasperoid.

Geophysical signature Magnetics: Igneous intrusions at depth may be imaged. Felsic character suggests a low magnetic response. Also, intrusions 

commonly emplaced into miogeoclinal to platformal, continental settings so should consider potential for sedimentary 

rocks to reduce oxygen fugacity of magma.

Gravity: Igneous intrusions at depth may be imaged.

Radiometrics: Lithology and alteration patterns may be evident.

Economic factors

Grade and tonnage Deposits are small (10,000 t) to very large (as much as 30–40 Mt). Individual deposits average about a million metric tons 

grading tens to hundreds of g/t Ag and approximately 5 to 20 wt.% combined Pb-Zn. 

Importance As sources of base metals, manto deposits are overshadowed on a world scale by the giant syngenetic classes such as SEDEX 

and volcanogenic massive sulfide deposits. However, because of their high precious metal contents, they provide exciting 

targets for small producers.

Other assessment and exploration guides

Concentration of Ag-Pb-Zn vein deposits in or near carbonates.

Structural controls include regional faults, folds, fractures, fissures, and caverns.

Mantos and chimneys are usually carbonate-hosted and remote from intrusions (relative to skarns).

Examples

In/near focal areas Copper Mountain Mine, Idaho.

Elsewhere Park City, Utah; Leadville, Colorado; Northern Mexico.

References

Megaw, P.K.M., Ruiz, Joaquin, and Titley, S.R., 1988, High-temperature, carbonate-hosted Ag-Pb-Zn(Cu) deposit of northern Mexico: Economic 

Geology, v. 83, p. 1856–1885. 

Nelson, J.L., 1996, Polymetallic mantos Ag-Pb-Zn, in Lefebure, D.V. and Hõy, T., eds., Selected British Columbia mineral deposit profiles, volume 2—

Metallic deposits: British Columbia Ministry of Employment and Investment, Open File 1996-13, p. 101–104, accessed April 25, 2016, at http://www.

empr.gov.bc.ca/MINING/GEOSCIENCE/MINERALDEPOSITPROFILES/LISTBYDEPOSITGROUP/Pages/JManto.aspx.

Vikre, P.G., 1998, Intrusion-related polymetallic carbonate replacement deposits in the Eureka District, Eureka County, Nevada: Nevada Bureau of Mines 

and Geology Bulletin 110, 52 p.

Appendix 3 119
120 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Polymetallic Vein

[wt.%, weight percent; km, kilometer; t, metric ton; g/t, grams per metric ton; m, meter]

Synonyms Felsic-intrusion-associated Ag-Pb-Zn veins, clastic metasediment-hosted silver-lead-zinc veins.

Commodities Ag, Pb, Zn (Cu, Au, Mn).

Description Quartz-carbonate veins with Au and Ag associated with base-metal sulfides related to hypabyssal intrusions in 

sedimentary and metamorphic terranes.

Geological environment

Rock types These deposits are principally hosted by sedimentary rocks (dolomite, limestone, sandstone, and shale) that 

have been intruded by intermediate- to felsic-composition igneous stocks, dikes, and sills. Many veins are 

associated with dikes following the same structures.

Age range Proterozoic or younger. Most are Mesozoic and Cenozoic, but may be any age.

Depositional environment Metasediment host: Veins are emplaced along faults and fractures in sedimentary basins dominated by clastic 

rocks that have been deformed, metamorphosed and intruded by igneous rocks. Veins postdate deformation 

and metamorphism.

Igneous host: Veins typically occur in country rock marginal to an intrusive stock. Typically veins crosscut 

volcanic sequences and follow volcano- tectonic structures, such as caldera ring-faults or radial faults. In 

some cases the veins cut older intrusions.

Tectonic setting(s) These veins occur in virtually all tectonic settings except oceanic, including continental margins, island arcs, 

continental volcanic and cratonic sequences.

Associated deposit types Polymetallic replacement, porphyry, skarn, placer Au.

Deposit description

Ore mineralogy Galena, sphalerite, tetrahedrite-tennantite, sulfosalts including pyrargyrite, stephanite, bournonite and acanthite, 

native silver, chalcopyrite, pyrite, arsenopyrite, stibnite.

Silver minerals often occur as inclusions in galena; native gold and electrum in some deposits. Au grades are 

normally low for the amount of sulfides present.

Rhythmic compositional banding sometimes present in sphalerite.

Some veins contain more chalcopyrite and gold at depth.

Alteration Generally wide propylitic zones and narrow sericitic and argillic zones.

Silicification of carbonate rocks to form jasperoid.

Ore controls Regional faults, fault sets, and fractures are an important ore control; however, veins are typically associated 

with second order structures. In igneous rocks the faults may relate to volcanic centers. Significant deposits 

are restricted to competent lithologies. Dikes are often emplaced along the same faults and may be roughly 

contemporaneous with mineralization. Polymetallic veins are typically steeply dipping, narrow tabular or 

splayed veins and commonly occur as sets of parallel and offset veins. Individual veins vary from cm as 

much as more than 3-m wide and can be followed from a few hundred to more than 1,000 m in length and 

depth. Veins may widen to tens of meters in stockwork zones.

Areas of high permeability: intrusive contacts, fault intersections, and breccia veins and pipes. Replacement ore 

bodies may form where structures intersect carbonate rocks

Geochemical signatures Zn, Cu, Pb, As, Au, Ag, Mn, Ba, Cd. Anomalies zoned outward from Cu-Au to Zn-Pb-Ag to Mn at periphery.

Geophysical signature Magnetics: Veins are unlikely to be evident, but plutons below may be imaged depending on tectonic setting 

in which they formed (continental margins, island arcs, continental volcanic and cratonic sequences). More 

oxidized magmas will result in plutons with stronger magnetic response. Gravity: Regional geology/structure 

can be imaged. Relatively large underlying plutons or batholiths can be imaged.

Radiometrics: Lithology and alteration can be imaged.

Economic factors

Grade and tonnage Median size 7,600 t at 9 wt.% Pb, 2.1 wt.% Zn, 820 g/t Ag, and 13 g/t Au. Polymetallic veins of two types 

appear to exist—a base-metal polymetallic vein worked primarily for a base metal or metals and silver and a 

gold-silver polymetallic vein with copper, lead, and zinc production
Importance Ubiquitous in many setting. These veins were a significant source of Ag, Pb, and Zn until the 1960s. They have 

declined in importance as industry focused more on syngenetic massive sulfide deposits. Larger polymetallic 

vein deposits are still attractive because of their high grades and relatively easy beneficiation. They are 

potential sources of cadmium and germanium.

Other assessment and exploration guides

Presence of vein deposits.

Presence of base or precious metals in rock or stream-sediment samples.

Presence of faults, breccias, shear zones, fault intersections, or intrusive contacts. Strong structural control on veins and common occurrence 

of deposits in clusters can be used to locate new veins.

Presence of Mesozoic or Tertiary plutons or hypabyssal igneous bodies.

Near-surface fractures and breccias within thermal aureole of clusters of small intrusions.

Some polymetallic veins are found surrounding intrusions with porphyry deposits or prospects.

Examples

In/near focal areas Valley View Mine, Idaho.

Elsewhere Wallapi district, Arizona; Marysville district, Montana.

References

Bliss, J.D., and Cox, D.P., 1986, Grade and tonnage model of polymetallic veins, in Cox, D.P. and Singer, D.A., eds., Mineral deposit 

models: Geological Survey Bulletin 1693, p. 125–129. [Also available at http://pubs.usgs.gov/bul/b1693/.]

Cox, D.P., 1986, Descriptive model of polymetallic veins, in Cox, D.P. and Singer, D.A., eds., Mineral deposit models: Geological Survey 

Bulletin 1693, p. 125–129. [Also available at http://pubs.usgs.gov/bul/b1693/.]

Lefebure, D.V., and Church, B.N., 1996, Polymetallic veins Ag-Pb-Zn±Au, in Lefebure, D.V. and Hõy, eds., Selected British Columbia 

mineral deposit profiles, volume 2—Metallic deposits: British Columbia Ministry of Energy of Employment and Investment, Open File 

1996-13, p. 67–70, accessed April 25, 2016, at http://www.empr.gov.bc.ca/Mining/Geoscience/MineralDepositProfiles/Pages/default.aspx.

Appendix 3 121
122 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Tungsten Vein

[wt.%, weight percent; km, kilometer; t, metric ton; g/t, grams per metric ton; REE, rare earth elements]

Synonyms Quartz-wolframite veins.

Commodities W, Mo, Sn.

Synoptic statement Magmatic hydrothermal veins associated with granitic rocks and pegmatites. 

Description Simple to complex fissure filling or replacement quartz veins, including discrete single veins, swarms or systems of veins, or 

vein stockworks, that contain mainly wolframite series minerals (huebnerite-ferberite).

Geological environment

Rock types Granitic plutonic rocks, especially late-stage, highly evolved, specialized biotite and (or) muscovite (S-type or A-type) 

ilmenite series granites and leucogranites.

Age range Paleozoic to late Tertiary.

Depositional environment Tensional fractures in epizonal granitic plutons and their wallrocks.

Tectonic setting(s) Belts of granitic plutons derived from remelting of continental crust.

Country rocks are metamorphosed to greenschist facies.

Associated deposit types Sn skarn, W skarn, Sn replacement, complex Sn-Ag-sulfide veins, Climax-type Mo deposits, and Mo vein and greisen 

deposits.

Deposit description

Ore mineralogy In general, the most common minerals in tungsten vein deposits in addition to quartz are: wolframite series minerals 

(huebnerite-ferberite), molybdenite, bismuthinite, pyrite, pyrrhotite, arsenopyrite, bornite, chalcopyrite, scheelite, 

cassiterite, beryl, mica, and fluorite.

Alteration Alteration directly associated with ore includes greisenization, albitization, and (or) tourmalinization. Deepest zones, 

pervasive albitization; higher pervasive to vein-selvage pink K-feldspar replacement with minor disseminated REE 

minerals; upper zones, vein selvages or zinnwaldite (greisen). Chloritization. Widespread tourmaline alteration at Isla de 

Pines deposit, Cuba. 

Ore controls Swarms of parallel veins cutting granitic rocks or sedimentary rocks near igneous contacts.

Geochemical signatures W, Mo, Sn, Bi, As, Cu, Pb, Zn, Be, F. Soil and stream sediment may have elevated tin and tungsten contents (tens to 

hundreds of ppm) and may contain anomalous abundances of elements characteristic of specialized granites (F, Rb, Be, 

Nb, Ta, Mo, U, Th, Li, and REE). Other possible pathfinder elements are As, Bi, B, Cu, Pb, and Zn.

Geophysical signature Magnetics: Plutons generated from remelting of continental crust. I-type granites can produce relatively high magnetic 

anomalies, whereas S-type granites are likely to be reduced, having low magnetic response. Regional geology/structure 

can be imaged. 

Gravity: Orogenic granites can have low gravity response. Radiometrics: Host rock lithology and alteration patterns can be 

imaged.

Economic factors

Grade and tonnage The most common tungsten vein deposits are quartz-wolframite veins. These range from less than 0.1 to about 10 million Mt 

of ore containing 0.4 to 1.6 wt.% WO3; median size and grade is 680,000 Mt and 0.81 wt.% WO3.

Importance Relative to W skarn deposits, W vein systems typically have smaller tonnages and comparable grades. 

Other assessment and exploration guides

Veins and greisen deposits are found within or near highly evolved, rare-metal enriched plutonic rocks, especially near contacts with surrounding country 

rock; settings in or adjacent to cupolas of subsurface granitic batholiths are particularly favorable.

Deposits may be endocontact or exocontact. Exocontact deposits usually are in pelitic and arenaceous sedimentary or metamorphic rocks and within 

the contact metamorphic aureole of a pluton. Most endocontact deposits, are in or near cupolas and ridges developed on the roof or along margins of 

granitoids.

Wolframite persists in soils and stream sediments; stolzite and tungstite may occur as weathering products.

Zoned alteration has been identified in some tungsten vein systems, upper parts of veins have well developed greisen zones; middle parts have quartz-rich 

greisen and silicification; and lower parts have K-feldspar-rich greisen. Higher tungsten grades are found in the upper and middle parts of veins.

Examples

In/near focal areas Round Mountain, Nevada.

Elsewhere Hamme district, North Carolina; Isla de Pines, Cuba.
References

Cox, D.P., and Bagby, W.C., 1986, Descriptive model of W veins, in Cox, D.P. and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey 

Bulletin 1693, p. 64. [Also available at http://pubs.usgs.gov/bul/b1693/.]

Elliott, J.E., Kamilli, R.J., Miller, W.R., and Livo, K.E., 1995, Vein and greisen Sn and W deposits, in du Bray, E.A., ed., Preliminary compilation of descriptive geoenvironmental mineral deposit models: U.S. Geological Survey Open-File Report 95–0831, p. 62–69. [Also available at http://pubs.usgs.

gov/of/1995/ofr-95-0831/.]

Jones, G.M., and Menzie, W.D., 1986, Grade and tonnage model of W veins, in Cox, D.P. and Singer, D.A., eds., Mineral deposit models: Geological 

Survey Bulletin 1693, p. 65–66. [Also available at http://pubs.usgs.gov/bul/b1693/.]

Menzie, W.D., Jones, G.M., and Elliott, J.E., 1992, Tungsten—Grades and tonnages of some deposits, in DeYoung, J.H., Jr., and Hammarstrom, J.M., 

eds., Contributions to commodity geology research: U.S. Geological Survey Bulletin 1877, p. J1–J7, accessed May 25, 2016, at https://pubs.usgs.gov/

bul/1877/report.pdf.

Shawe, D.R., Foord, E.E., and Conklin, N.M., 1984, Huebnerite veins near Round Mountain, Nye County, Nevada: U.S. Geological Survey Professional 

Paper 1287, 48 p.

Appendix 3 123
124 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Molybdenum-Tungsten Greisen

[wt.%, weight percent; ppm, parts per million; km, kilometer; Mt, million metric tons;*, based on 10 well-described deposits, including 5 in Nevada]

Synonyms and subtypes Molybdenite in greisens, quartz and quartz-muscovite veins, and sheeted veins and veinlets, often with wolframite 

(scheelite).

Commodities Mo, W.

Description Fine- to coarse-grained molybdenite, molybdenite and wolframite (scheelite) in greisenized granites, massive greisen 

bodies, quartz veins and veinlets in greisen and greisenized adjacent rocks in the endocontact zone (endogreisen) and 

exocontact zone (exogreisen) of granites and alaskites.

Geological environment

Rock types Granites with 73–75 percent SiO2

, K2O>Na2O (1.1–2.5), Al2O3 >12.5–13 percent, low CaO (<1.0), variations in F content, 

lack of contamination process, nonspecialized. Multiphase hypabyssal plutons (10–1,000 km2) with intermineral and 

postmineral dikes.

Age range Proterozoic (1,000–2,650 Ma), Hercynian (292–348 Ma), Cimmerian (140–210 Ma).

Depositional environment Apical lobes of multiphase plutons and adjacent rocks.

Tectonic setting(s) Extensional zones in continental rifts. Endocontact and exocontact zones of batholiths, stocks, and cupolas.

Deposit description

Ore mineralogy Molybdenite, wolframite, scheelite, bismuthinite, cassiterite; quartz, muscovite, fluorite, topaz, K-feldspar, lepidolite, 

zinnwaldite.

Alteration Greisenization, albitization, microclinization, silicification, and sericitization.

Ore controls Lobes of granite plutons, system of fractures, chemistry of adjacent rocks.

Geochemical signatures Primary anomalies of Mo, W, Sn, Bi, Ag, Li, Zn, and Pb.

Secondary anomalies in soil, stream sediments and plants of Mo, W, Sn, Bi, Cu, Zn, and Ag.

Elevated Re in molybdenite, >50 ppm.

Geophysical signature Thick crust (>40 km), regional and local gravity anomalies with positive electric anomalies (halo of pyrite 

mineralization surrounds bodies); distinct U/Th as well as magnetic anomalies in close proximity to the 

greisen.

Associated deposit types Porphyry Cu, Cu skarn, Pb-Zn skarn, Au skarn polymetallic veins, polymetallic replacement and replacement Mn deposits.

Economic factors 

Grade and tonnage* Each molybdenum-tungsten greisen deposit represents a different level of emplacement. Taken together, they define a 

composite greisen column, which may be represented by distinct grade and tonnage models. Proximal deposits have a 

mean tonnage of 0.43 Mt and a mean grade of 0.17 wt.% Mo. Distal deposits have a mean tonnage of 40 Mt and a mean 

grade of 0.081 wt.% Mo.

Importance Greisen deposits are one of the most important sources of rare metals, and contain a large part of the world’s mineable 

reserves of tungsten, tin, beryllium, and molybdenum, and significant resources of tantalum, niobium, and rare earth 

elements (REE).

Assessment and Exploration Guides

Molybdenum-tungsten greisen is a distinct type of mineral deposit, apparently confined to granitic plutons in extensional rift zones in Proterozoic, 

Hercynian and Cimmerian continental plates, and primarily found in areas with thick crust in Asia.

General prospecting guides include extensional zones where crustal thickness is more than 40–45 km. Regional negative gravity anomalies, that may 

represent felsic plutons are also indicative. General analysis of geologic (petrologic and petrochemical) data, combined with the results of regional 

geophysical surveys, can lead to the delineation of potential targets. 

Experience in exploration for this type of deposit in different countries shows that subsequent fieldwork must include geochemical surveys (rock, soil, or 

stream sediments), detailed gravimetric measurements, and aeromagnetic surveys. These methods usually detect the ore-bearing granites, particularly 

hidden plutons or their cupolas. Local negative gravity and positive magnetic anomalies may outline unexposed plutons, the specific characteristics of 

roof morphology (lobes), and variations in the thickness of granites (roots). Zonal dispersion of lead, zinc and copper from one side and molybdenum, 

tungsten, tin and bismuth from the other indicates the polarity, or symmetry of the metallized system. Separation of tungsten and molybdenum within a 

district, with tungsten dominant, might be the sign of an unexposed, compound mineral deposit

Although molybdenum-tungsten greisen deposits have many similarities with Climax-type deposits, they seem to form at greater depths, in a mostly 

plutonic environment. 

Examples

In/near focal areas Springs W deposit, Nevada.

Elsewhere Mount Pleasant, Canada; Koktenkol, Akchatau, Bainazar, Kazakhstan; Yugodzir, Mongolia.

References

Kotlyar, B.B., Ludington, Steve, and Mosie, D.L., 1996, Descriptive, grade, and tonnage models for molybdenum-tungsten greisen deposits: U.S. 

Geological Survey Open-File Report 95–584, 16 p. [Also available at https://pubs.er.usgs.gov/publication/ofr95584.]
Distal Disseminated Silver-Gold

[g/t, grams per metric ton; Mt, million metric tons;*, based on 10 well-described deposits, including 5 in Nevada]

Synonyms and subtypes Sediment-hosted Ag-Au, disseminated Ag.

Commodities Ag, Au, (Sb).

Description Disseminated Ag and Au mainly in sedimentary rocks distal to porphyry Cu, skarns, and polymetallic veins. The deposits 

are somewhat similar to sediment-hosted Au deposits, but have significantly higher Ag grades and base-metal contents.

Geological environment

Rock types Carbonate and elastic sedimentary rocks associated with felsic hypabyssal or subvolcanic intrusions.

Age range Mesozoic-Tertiary in Western United States; may be any age.

Depositional environment Shelf and basinal sedimentary rocks are folded and faulted and intruded by I-type granitic rocks.

Tectonic setting(s) Continental margins.

Deposit description

Ore mineralogy Native Au, native Ag, electrum, argentite, Ag sulfosalts, tetrahedrite, stibnite, galena, sphalerite, chalcopyrite, pyrite, 

marcasite, and arsenopyrite; at Cove deposit in Nevada, stannite and canfieldite.

Alteration Silicification and decalcification of carbonate rocks; sericite-clay in elastic rocks. Differs from deposit to deposit in 

Nevada.

Ore controls Deposits commonly occur in skarn and polymetallic vein and replacement districts outboard of all other types of 

mineralization. Fracture permeability is the most important ore control. Primary rock permeability may be important 

locally.

Geochemical signatures Ag±Au±Pb±Mn±Zn±Cu± Sb±As±Hg±Te; Mn. Ag:Au ratios are highly variable. (For Nevada deposits: Candelaria, 400:1; 

Taylor, 143:1; Hilltop, <2:1).

Geophysical signature None.

Associated deposit types Porphyry Cu, Cu skarn, Pb-Zn skarn, Au skarn polymetallic veins, polymetallic replacement and replacement Mn deposits.

Economic factors 

Grade and tonnage* Tonnages range from <1 to 81 Mt; Au grades range from 0 to 4.8 g/t; Ag grades range from 2 to 142 g/t.

Importance Deposits are a significant source of silver; the Cove deposit in Nevada is the fourth largest silver producer in the history of 

Nevada. 

Other assessment and exploration guides

Structural setting: Shear zones, axial plane fractures in folded rocks.

Ore deposit geometry: Irregular bodies, locally conformable to bedding.

Weathering: Leaching and redeposition of Ag as cerargyrite forms bonanza deposits (White Pine district, Nevada; Vekol, Arizona).

Gangue minerals: Quartz, rhodochrosite, Ag-rich manganocalcite.

Depth: Typically form at higher crustal levels than porphyry copper deposits.

Examples

In/near focal areas Vipont, Nevada.

Elsewhere Taylor, Candelaria, Star Pointer, Cove deposits, White Pine district, Nevada; Tecoma, Utah; Vekol, Tombstone, and 

Hardshell, Arizona.

References

Cox, D.P., 1992, Descriptive model of distal disseminated Ag-Au, in Bliss, J.D., Developments in mineral deposit modeling: U.S. Geological Survey 

Bulletin 2004, p. 19, accessed April 25, 2016, at http://pubs.usgs.gov/bul/b2004/model19c.pdf.

Cox, D.P., and Singer, D.A., 1992, Grade and tonnage model of distal disseminated Ag-Au, in Bliss, J.D., Developments in mineral deposit modeling: U.S. 

Geological Survey Bulletin 2004, p. 20–22, accessed April 25, 2016, at http://pubs.usgs.gov/bul/b2004/model19c.pdf.

Theodore, T.G., 1998, Large distal-disseminated precious-metal deposits, Battle Mountain mining district, Nevada, in Tosdal, R.M., ed., Contributions to 

the gold metallogeny of northern Nevada: U.S. Geological Survey Open-File Report 98–338–B, p. 253–258, accessed April 25, 2016, at http://pubs.

usgs.gov/of/1998/of98-338/of98_338.pdf.

Appendix 3 125
126 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Carlin-Type Gold (Silver, Mercury, Antimony)

[%, percent; wt.%, weight percent; g/t, grams per metric ton; Mt, million metric tons; °C, degrees Celsius; m, meter; ASTER, Advanced Spaceborne Thermal 

Emission Radiometer]

Synonyms and subtypes Sediment-hosted gold, Micro-disseminated gold, Micron gold. 

Commodities Au. Byproducts: Ag, Hg, Sb.

Description Epigenetic, replacement, disseminated, auriferous pyrite deposits at intersections of high angle faults and permeable 

reactive sedimentary rocks. 

Geological environment

Rock types Most deposits are hosted in Paleozoic, marine, carbonaceous, pyritic, and calcareous and (or) dolomitic sedimentary rocks 

deposited on the slope near the carbonate platform margin. Some deposits are hosted in marginal basin, shelf, foreland 

basin, and overlap sequences. Others occur in dolomitize limestones, contact metamorphic aureoles of Mesozoic 

intrusions, and Jurassic lamprophyre dikes. 

Age range Mostly Eocene.

Depositional environment Epizone, subvolcanic, a few 100 to 5,000 m below the paleosurface.

Temperature 100–240 °C, 0–9 wt.% NaCl, pH < 5, CO2 < 4 mole%, CH4 <0.4 mole%, H2S 10-1-10-2 molar.

Gold-bearing disseminated pyrite precipitates where H2S-bearing hydrothermal fluids react with iron-bearing minerals or 

external fluids in sedimentary rocks.

Tectonic setting(s) Underlain by attenuated continental crust and subcontinental lithospheric mantle (east of Sri

 0.706 line). Mineral belts 

occur along reactivated basement faults produced during Neoproterozoic rifting and formation of the continental 

margin. Typically in carbonate rocks below a less permeable cap of shaley siliciclastic rocks, such as the Roberts 

Mountains allochthon. Districts are restricted to a region affected by a southward sweeping Eocene subduction-related 

magmatism. Eocene felsic dikes are frequently present.

Deposit description

Ore mineralogy Most of the gold and trace elements reside in micron-sized disseminated pyrite that often forms rims on diagenetic pyrite. 

Common open-space filling minerals include drusy quartz, calcite, barite, stibnite, orpiment, and realgar. Rare minerals 

include native gold, cinnabar, lorandite, getchellite, and galkhaite. Micron-sized native gold occurs in jasperoid and in 

supergene goethite pseudomorphs of pyrite.

Alteration Ore pyrite was produced by sulfidation of iron-bearing minerals, silicification to form jasperoid, dissolution of carbonate 

minerals, argillization of silicate minerals, and mobilization of preexisting organic carbon. Ammonium phyllosilicates 

are present locally.

Ore controls Intersections of faults and permeable reactive strata, sedimentary breccias, karsted unconformities, dolomitized 

limestones, calcsilicate hornfels, lamprophyre dikes, and hydrothermal dissolution collapse breccias. 

Geochemical signatures Common pathfinder elements in rock, soil, and stream sediment: Au, As, Sb, Tl, Hg. Au/Ag generally more than three and 

often much higher. Base metals and Ag generally are not anomalous.

Geophysical signature Aeromagnetics: Map the distribution of plutons and dikes.

Radiometrics: Detect shaley cap rocks (K high) and Valmy quartzites (K, Th, U low).

Gravity: Map regional structures associated with deposits and underlying intrusive rocks.

Remote sensing: ASTER data permit recognition of carbonate host rocks, quartzites, argillaceous cap rocks, jasperoid, 

ferric iron (oxidized pyrite), and clay minerals.

Electrical methods: Delineating low-resistivity zones associated with organic carbon, clay, or sulfide-rich zones at shallow 

levels. Magnetotelluric methods can detect crustal scale features.

Seismic methods: Detect the thickness of alluvial or volcanic cover.

Economic factors 

Grade and tonnage Au grade 0.7–34 g/t (range).

Tonnage 0.3–700 Mt (range) .
Importance The wide range of tonnage-grade characteristics make the deposits amenable to both open-pit and underground mining.

Other assesment and exploration guides

Subcontinental lithospheric mantle may have been hydrated and enriched in Au by Mesozoic subduction- and rift-related magmatism.

Metalliferous black shales may be a potential source for Au and trace elements in the deposits.

Sedimentary facies and sequence stratigraphy.

Regional and local structural features. For example, extensional step-over faults within strike-slip fault zones and dilatant fracture systems on margins of 

Mesozoic plutons.

In areas with low ground water tables, supergene oxidation of pyrite allows Au recovery by low-cost cyanide heap leach methods.

Information on depth of post-mineralization cover and depth of erosion.

Exploration and drilling history.

 Examples

In/near focal areas Doby George, Nevada.

Nevada gold trends Independence, Getchell, Carlin, Battle Mountain-Eureka, Alligator Ridge, Long Canyon.

References

Berger, V.I., Mosier, D.L., Bliss, J.D., and Moring, B.C., 2014, Sediment-hosted gold deposits of the world—Database and grade and tonnage models 

(ver. 1.1, June 2014): U.S. Geological Survey Open-File Report 2014–1074, 46 p., accessed April 25, 2016, at http://dx.doi.org/10.3133/ofr20141074. 

Cook, H.E., 2015, The evolution and relationship of the western North American Paleozoic carbonate platform and basin depositional environments to 

Carlin-type gold deposits in the context of sequence stratigraphy, in Pennell, W.M., and Garside, L.J., eds., New concepts and discoveries: Geological 

Society of Nevada Symposium 2015, p. 1–80. 

Cline, J.S. Hofstra, A.H., Muntean, J.L, Tosdal, R.M. and Hickey, K.A., 2005, Carlin-type gold deposits in Nevada—Critical geologic characteristics and 

viable models: Economic Geology, 100th Anniversary Volume, p. 451–484.

Emsbo, Poul, Groves, D.I., Hofstra, A.H., and Bierlein, F.P., 2006, The giant Carlin gold province—A protracted interplay of orogenic, basinal, and 

hydrothermal processes above a lithospheric boundary: Mineralium Deposita, v. 41, p. 517–525.

Hofstra, A.H., and Cline, J.S., 2000, Characteristics and models for Carlin-type gold deposits, chapter 5, in Hagemann, S.G., and Brown, P.E., eds., Gold in 

2000: Reviews in Economic Geology, v. 13, p. 163–220. 

Large, R.R., Bull, S.W., and Maslennikov, V.V., 2011, A carbonaceous sedimentary source-rock model for Carlin-type and orogenic gold deposits: 

Economic Geology v.106, p. 331–358.

Muntean, J.L., Cline, J.S., Simon, A.C., and Longo, A.A., 2011, Magmatic–hydrothermal origin of Nevada’s Carlin-type gold deposits: Nature Geoscience 

v. 4, p. 122–127.

Appendix 3 127
128 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Hydrothermal—Volcanic Rock Associated System

Deposit types in the study area

Epithermal gold-silver (mercury)

Volcanogenic uranium

Stanley district (Idaho)-type uranium

Volcanic opal and specialty gemstones

Hectorite (lithium-rich clay) and specialty clays
Epithermal Gold-Silver (Mercury)

[g/t, grams per metric ton; Mt, million metric tons;*, based on 90 well-described deposits; CSMAT, controlled-source audio magnetotelluric surveys]

Synonyms and subtypes Quartz-alunite (high-sulfidation), quartz-adularia (low sulfidation), hot spring deposits. Quartz-adularia subtypes include 

layered vein and polymetallic variants. Alkaline igneous rock-related epithermal gold deposits. Bonanza ores (>1 troy 

ounce gold per ton (34.3 g/t).

Commodities Au, Ag. Byproducts: Pb, Zn, Cu, and (or) Hg (quartz-adularia); Cu (quartz-alunite), gypsum.

Description Epithermal gold-silver deposits are shallowly formed vein, stockwork, disseminated, and replacement deposits that are mined 

primarily for their gold and silver contents. Hot-spring-type mercury deposits are commonly the near-surface expression of 

hot-spring type gold-silver deposits that occur at deeper levels below mercury-enriched sinter. Epithermal gypsum forms 

where carbonate host rocks are altered by sulfur-bearing hydrothermal fluids. 

Geological environment

Rock types Most commonly hosted by alkaline to calcalkaline volcanic rocks and hypabyssal intrusions that range in composition 

from mafic to felsic, but generally fall into suites of andesite-dacite±rhyolite compositions or bimodal basalt-rhyolite 

compositions. Rocks of the andesite-dacite±rhyolite suite mostly have calcalkaline compositions, whereas some bimodal 

basalt-rhyolite suites have tholeiitic compositions, notably rocks associated with quartz-adularia deposits of the northern 

Nevada rift that are related to extension and hot spot or mantle plume magmatism in a back arc setting. Hosts for some 

deposits are silica-undersaturated, highly alkali-rich (Na2O + K2O) rocks ranging from felsic phonolites to ultramafic 

lamprophyres. Other igneous, sedimentary, and metamorphic rock types also can host deposits.

Age range Mostly of Cenozoic age, which reflects preferential preservation of these shallowly formed deposits in tectonically active 

regions. Deposits as old as 1.9 billion years are preserved within some cratons.

Depositional environment Quartz-alunite deposits: Lava domes and flows, diatremes, tuff rings, maars, and intrusive breccias associated with diatremes; 

uplands and basins with pyroclastic and volcaniclastic rocks.

Quartz-adularia, layered vein, and hot springs deposits: Lava domes and flows; uplands and basins with pyroclastic and 

volcaniclastic rocks; dikes.

Quartz-adularia, polymetallic deposits: Lava domes and flows, diatremes, tuff rings, maars, and intrusive breccias associated 

with diatremes; uplands and basins with pyroclastic and volcaniclastic rocks.

Tectonic setting(s) Form from subaerial hydrothermal systems in volcanic arcs at convergent plate margins in continental and oceanic settings, 

in continental-margin back arcs, in rifts, and in intraplate environments.

Deposit description

Ore mineralogy Quartz-alunite: Gold, electrum, Au-Ag tellurides, Ag-bearing tennantite-tetrahedrite, enargite, luzonite, chalcopyrite, 

numerous Au-Ag-Cu-As-Sb-Bi-Sn-Te-Se-S minerals.

Quartz-adularia, layered veins: Electrum, Ag sulfides, selenides and sulfosalts; low Ag/Au; generally no other metals 

recovered.

Quartz-adularia, polymetallic: Electrum, Ag sulfides and sulfosalts; Ag-bearing tetrahedrite-tennantite; high Ag/Au; 

chalcopyrite, galena, sphalerite.

Alkaline igneous rock-related epithermal gold deposits: native Au, numerous telluride minerals, auriferous pyrite.

Hot springs deposits: cinnabar, metacinnabar, tiemannite, HgSeS minerals, sulfur.

Alteration Quartz-alunite: Zoned. Inner residual (vuggy) quartz grading progressively outward to quartz-alunite; kaolinite (dickite) or 

pyrophyllite; illite; montmorillonite; distal chlorite-calcite ± epidote. All + pyrite.

Quartz-adularia: Zoned: inner quartz/chalcedony ± adularia, carbonate, grading progressively outward to sericite/illite ± 

adularia; mixed layer clay ± chlorite; distal chlorite-calcite ± epidote. All + pyrite.

Epithermal deposits may be overlain by zones of steam-heated opal, kaolinite, alunite, and (or) montmorillonite. Silica sinter 

overlies some quartz-adularia deposits. Gypsum replacement bodies occur in some systems. 

Hot-spring Hg deposits: Volcanic host rocks and associated clastic sedimentary rocks are altered to an assemblage of 

adularia, quartz, and sericite at depth, and in the near surface, to an advanced argillic alteration assemblage of kaolinite, 

alunite, and cristobalite that commonly contains elemental sulfur. Some of these deposits are hosted in hot-spring sinter 

that was deposited at the surface and that consists of banded silica phases and beds of hydrothermal eruption breccia.

Ore controls Breccias (magmatic, tectonic, hydrothermal, diatreme); faults, fractures, voids; fault intersections.

Geochemical signatures Au, Ag, As, Sb, Hg ±Tl, F, Mo, Se, Te, and W are generally enriched in and near epithermal deposits; combinations of Ba, 

Cu, Zn, Pb, Sn, and Bi may or may not be present. Hot-spring Hg deposits: Hg, Li, B, As, Sb, Au, Ag, Th, and W.

Appendix 3 129
130 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Geophysical signature Aeromagnetics: Hydrothermal fluids can destroy magnetite; therefore, pervasively altered volcanic rock appears as areas 

of subdued magnetic anomalies (magnetic quiet zones) relative to high-amplitude, short-wavelength anomalies of 

surrounding unaltered volcanic rock.

Radiometrics: Central zone of K metasomatism in quartz-adularia deposits characterized by enriched K/Th values, which 

may be particularly pronounced in alkaline igneous rock-related epithermal gold deposits.

Gravity: Useful in mapping and characterizing regional structures associated with deposits, such as concealed basins, 

calderas, and underlying intrusive rocks. High-resolution gravity measurements may directly characterize hydrothermal 

alteration, which may reduce porosity, thereby increasing density.

Remote sensing: Host rocks are commonly enriched in hydrothermal minerals that have diagnostic absorption features in the 

visible (VIS), near-infrared (NIR), shortwave-infrared (SWIR), and thermal infrared (TIR) regions of the electromagnetic 

spectrum. ASTER data permit mineralogical differentiation of various alteration types (argillic, phyllic, alunitic), carbonate 

minerals, and high concentrations of quartz.

Electrical methods: Hydrothermal alteration associated with gold mineralization commonly involves the replacement of 

host rocks by clay and sulfide minerals, which can decrease electrical resistivity by several orders of magnitude, and 

silicification or quartz veining, which increases resistivity. Methods focused on shallow parts of the crust are useful in 

delineating low-resistivity zones associated with clay or sulfide-rich alteration or highly resistive zones dominated by 

quartz veins or silicification. CSAMT now widely used.

Economic factors 

Grade and tonnage* Quartz-alunite Quartz-adularia

Au grade 3.8 g/t (avg), 0.45–17 g/t (range) 9.9 g/t (avg), 0.26–68 g/t (range)

Ag grade 53 g/t (avg), 2.4–600 g/t (range) 164 g/t (avg), 1.6–1,100 g/t (range)

Tonnage 170 Mt (avg), 1.2–1,700 Mt (range) 142 Mt (avg), 0.1–2,300 Mt (range)

Importance These deposits are attractive because of their relatively rich gold and silver grades, their wide range of tonnage-grade characteristics, including bonanza grades, which are amenable to both underground and bulk tonnage mining, and in some cases, 

recovery of byproducts.

Other assessment and exploration guides

Known epithermal deposits and prospects.

Volcanic and volcaniclastic rocks coeval with similar rocks known to host deposits.

Hydrothermal alteration known to accompany epithermal deposits.

Regional and local structural features (for example, extensional stepover zones within strike-slip fault zones).

Some hot-spring Hg deposits occur in hot-spring sinter that consists of layered or bedded silica phases and hydrothermal eruption breccia.

Shallow hydrothermal features, such as sinters, stratiform alteration zones, and hydrothermal eruption breccias.

Information on depth of post-mineralization cover and depth of erosion.

Exploration and drilling history.

Examples

In/near focal areas Buckskin Mountain, Nevada (quartz-adularia, layered vein).

Zortman-Landusky, Montana (alkaline igneous rock-related).

Clear Creek gypsum mine, Idaho.

Elsewhere Quartz-alunite: Goldfield, Nevada; Summitville, Colorado. 

Quartz-adularia, layered veins: Midas, Round Mountain, and Sleeper, Nevada.

Quartz-adularia, polymetallic: Comstock Lode and Tonopah, Nevada.

Alkaline igneous rock-related: Cripple Creek, Colorado; Golden Sunlight, Montana; Ladolam and Porgera, Papua New 

Guinea.

References

John, D.A., USGS, written commun., 2016.

Kelley, K.D., and Spry, P.G., 2015, Critical elements in alkaline igneous rock-related epithermal gold deposits: Reviews in Economic Geology, v. 18, p. 

195–216. 

Rytuba, J.J., 2002, Mercury geoenvironmental models, in Seal, R.R., II, and Foley, N.K., eds., Progress on geoenvironmental models for selected mineral 

deposit types: U.S. Geological Survey Open-File Report 02–195–J, p. 161–175, accessed February 9, 2016, at http://pubs.usgs.gov/of/2002/of02-195/

OF02-195J.pdf.

Skipp, Betty, Hassemer, Jerry R., Kulik, D.M., Sawatzky, Leszcykowski, A.M., and Winters, R.A., 1988, Mineral resources of the Eighteenmile Wilderness Study Area, Lemhi County, Idaho: U.S. Geological Survey Bulletin 1718-B, 22 p. [Also available at http://pubs.usgs.gov/bul/1718b/report.pdf.]
Volcanogenic Uranium

[wt.%, weight percent; ft, feet; mi2, square miles]

Synonyms

Commodities Uranium (sometimes associated mineable fluorite, molybdenum, mercury).

Description Uranium minerals associated with felsic volcanic in caldera systems.

Geological environment

Rock types Felsic volcanic rocks and associated volcanoclastic sediments and tuffs. Uranium enrichment increases with differentiation to 

more felsic composition, and deposits are most common in rocks with aluminous and alkaline affinities and high fluorine 

content (Cuney and Kyser, 2009). 

Age range Proterozoic through Tertiary

Depositional environment Felsic volcanic centers: Both fracture zones and volcanoclastic sediments, tuffs and permeable lava flows associated that 

make up felsic volcanic complexes.

Tectonic setting(s) Diverse tectonic settings, including rifts, hot spots (McDermitt caldera, Nevada), back arcs, and subduction zones where the 

stress field has shifted from compressional to extensional.

Associated deposit types Mercury, fluorite, and molybdenum.

Deposit description

Ore mineralogy Uraninite, pitchblende and coffinite with brannerite and uranothorite in more alkaline volcanic rocks. Associated fluorite and 

molybdenite in most volcanogenic uranium deposits; rare earth elements, thorium and zirconium in peralkaline volcanic 

systems. Polymetallic deposits (with copper, lead, silver, and zinc) in Europe and Asia are the result of a multistage 

hydrothermal history.

Alteration Pre-ore alteration: alkali metasomatism with quartz, sericite, pyrite and carbonate mineral veining. Ore-stage alteration: 

uranium minerals associated with argillic alteration and fluorite. Post-ore alteration: redistribution of uranium and latestage carbonate minerals, sulfates and additional argillic alteration. 

Ore controls Ore hosted in two settings: (1) vein and stockwork deposits filling fractures and faults and stratabound deposits hosted in 

permeable eruption breccia and (2) flow breccia and volcanoclastic rocks with associated fractures or feeder zones. Ore 

control may be reduction, with reducing phases including reduced sulfur species, ferrous iron and carbonaceous matter, 

or, in volcanoclastic sediments, hydrogen sulfide. Alternatively ore may have formed during boiling of ore-forming fluids 

with loss of CO2 and fluoride destabilizing soluble uranium complexes (Cunningham and others, 1998) or by decreasing 

oxygen fugacity in parts of the volcanic complex. 

Geochemical signatures Elevated uranium, fluoride, and molybdenum in rock, water, soil, and stream sediments. Concealed deposits may be 

identified by elevated radon in soil gas samples and uranium and indicator elements (U, F, Mo) in groundwater.

Geophysical signature Radiometric signatures that detect uranium enrichment in both deposits and elevated uranium in host rocks. 

Economic factors

Grade and tonnage Vein and stockwork deposits extend for tens to several hundreds of meters along strike and tens to hundreds of meters in dip. 

Stratabound deposits can extend for hundreds of meters laterally and range from less than one to tens of meters in thickness. These deposits have low to moderate grades of 0.05 to 0.23 wt.% U3

O8. Known deposits range from relatively small 

deposits of a few thousand pounds. U3O8 to the Stretsovskoye district, which contains over 250 million pounds U3O8. 

Within the U.S., known deposits in Idaho, Nevada, Oregon and Utah produced an estimated 2 million pounds U3O8 during 

mining from the 1950s to 1970s.

Importance Worldwide volcanogenic uranium deposits contain about 1.2 billion pounds of U3

O8, which is about 6 percent of the world’s 

known global resources (International Atomic Energy Agency, 2009). Within the U.S. potential resources within volcanic 

rocks are estimated to be 232 million pounds of U3O8 (Department of Energy, 1980).

Other assessment and exploration guides

Areas favorable to these deposits typically have basement rocks that are enriched in uranium. Crustal thinning accompanied by partial melting and hydrothermal fluid interaction with this enriched crust is thought to contribute uranium to the felsic volcanic rocks that host the deposits.

Multiple overprinting volcanic episodes may help concentrate uranium in later stage melts and hydrothermal fluids.

The identification of regions with progressive concentration of uranium by successive magmatic episodes may help identify favorable terrain.

Examples

In/near focal areas McDermitt Caldera District (Aurora, Bretz, Moonlight deposits), Nevada–Oregon.

Appendix 3 131
132 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Elsewhere Streltsovskoye, Russia.

References

Breit, G.N., and Hall, S.M., 2011, Deposit model for volcanogenic uranium deposits: U.S. Geological Survey Open-File Report 2011–1255, 5 p., accessed 

May 10, 2016, at http://pubs.usgs.gov/2011/1255/.

Cuney, M., and Kyser, K., 2009, Recent and not-so-recent developments in uranium deposits and implications for exploration: Mineralogical Association 

of Canada, Short Course Series, v. 39, 257 p.

Cunningham, C.G., Rasmussen, J.E., Steven, T.A., Rye, R.O., Rowley, P.D., Romberger, S.B. and Selverstone, J., 1998, Hydrothermal uranium deposits 

containing molybdenum and fluorite in the Marysvale volcanic field, west-central Utah: Mineralium Deposits, v.33, p. 477–494.

Department of Energy, 1980, An assessment report on uranium in the United States of America: U.S. Department of Energy Report, GJO-111 (80), 157 p.

International Atomic Energy Agency, 2009, International Atomic Energy Agency world distribution of uranium deposits (UDEPO) with uranium deposit 

classification: Vienna, Austria, International Atomic Energy Agency, IAEA-TECHDOC-1629, 117 p.

Nash, J.T., 2010, Volcanogenic uranium deposits: geology and geochemical processes, and criteria for resource assessment: U.S. Geological Survey OpenFile Report 2010–1001, 98 p. [Also available at http://pubs.usgs.gov/of/2010/1001/.]
Stanley District (Idaho)-Type Uranium

[Mt, million metric tons]

Synonyms Unconformity sandstone-conglomerate-hosted uranium; vein-hosted uranium.

Commodities Uranium.

Description In the Stanley district, the uranium deposits occur in two geologic settings: (1) as disseminated uranium minerals 

within fluvial-channel arkosic sandstones and conglomerates that rest on the eroded surface of the Cretaceous Idaho 

batholith and immediately beneath the Eocene Challis Volcanic Group and (2) as thin pockets of uranium minerals 

in silicified fractures that cut through the granitoid rocks of the batholith (Kern, 1959; Johnson and others, 1995a, 

1995b; Van Gosen and others, 2006).

Geological environment

Rock types Arkosic sandstones and conglomerates and thin siliceous veins in granitic rocks.

Age range Uranium deposition is likely to be Eocene, perhaps younger.

Depositional environment Microscopic textures in the uranium minerals suggest that the uranium mineralization in the strata-bound deposits is 

genetically linked to the widespread hydrothermal alteration in the area that was associated with igneous intrusions 

related to the eruption of the Eocene Challis Volcanic Group (Van Gosen and others, 2006).

Tectonic setting(s) Mid-cratonic setting in volcanic terranes.

Deposit description

Ore mineralogy Uraninite; meta-autunite; uranophane; a calcium uranium phosphate mineral (autunite? phosphuranylite?); kasolite, a 

member of the phosphuranylite-renardite series; beta-uranophane; clarkeite; schoepite; and vandendriesscheite (see 

Choate, 1962, p. 31; Van Gosen and others, 2006).

Alteration Microscopic alteration of minerals in the U-mineralized intervals.

Ore controls Uranium mineralization is confined to fluvial-channel arkosic sandstones and conglomerates that rest upon the eroded 

surface of the Cretaceous Idaho batholith and immediately beneath the Eocene Challis Volcanic Group and (2) as thin 

pockets of uranium minerals in silicified fractures that cut through the granitoid rocks of the Idaho batholith. Organic 

matter and sulfide minerals in the sedimentary hot rocks provided reductant materials for the precipitation of the 

uranium minerals.

Geochemical signature U, As, Ca, P.

Geophysical signature Radioactivity is the principal geophysical signature; radiometric surveys can locate radioactive concentrations. 

Electromagnetic surveys may be useful in detecting conductive sulfides in paleo-channels. Ground-penetrating radar 

may be useful in delineating the geometry of shallow paleo-channels.

Economic factors

Grade and tonnage The average grade (about 0.18 weight percent U3

O8) of the uranium deposits mined in the Stanley district was 

comparable to other U.S. producers during the late 1950s and early 1960s, but the district’s output (no more than 

8,000 metric tons of uranium ore per year) and its mines were relatively small.

Importance Small production of uranium ore came from mines in the Stanley district from 1957 to 1962, making it the first 

commercial uranium district in Idaho. This district comprised at least 27 uranium mines and prospect claim groups, 

scattered across an area of about 10 square miles.

Other assessment and exploration guides

Identify Tertiary sandstones and conglomerates that rest of the surface of granitoid plutonic rocks of the Idaho Batholith and occur immediately below 

volcanic and volcaniclastic rocks of the Eocene Challis Volcanics.

Survey the appropriate sedimentary units and stratigraphic horizons for radioactivity using airborne radiometric surveys, followed up by on-the-ground 

radiometric surveys (scintillometer or Geiger counter).

Economic deposits of this type typically are exploited only if they lie at or within a few tens of meters of the surface due to their modest uranium 

concentrations and tonnage.

Examples

In/near focal areas Central Idaho where Challis Volcanics lie in contact with the Idaho batholith.

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Elsewhere The uranium deposits of the Marysvale volcanic field in west-central Utah comprise another uranium district with 

geologic characteristics generally similar to those of the Stanley district. Uranium in the Marysvale volcanic field occurs in a variety of geologic settings, including hydrothermal vein deposits and sedimentary-trap deposits in basin-fill 

sediments (Steven and others, 1981).

References

Choate, Raoul, 1962, Geology and ore deposits of the Stanley area: Idaho Bureau of Mines and Geology Pamphlet No. 126, 122 p.

Johnson, K.M., and Cookro, T.M., 1995a, Stratiform uranium deposits in sedimentary rocks, in Fisher, F.S., and Johnson, K.M., eds., Geology and mineral 

resource assessment of the Challis 1° × 2° quadrangle, Idaho: U.S. Geological Survey Professional Paper 1525, p. 167–168.

Johnson, K.M., and Cookro, T.M., 1995b, Uranium veins, in Fisher, F.S., and Johnson, K.M., eds., Geology and mineral resource assessment of the Challis 

1°×2° quadrangle, Idaho: U.S. Geological Survey Professional Paper 1525, p. 119–121.

Kern, B.F., 1959, Geology of the uranium deposits near Stanley, Custer County, Idaho: Idaho Bureau of Mines and Geology Pamphlet 117, 40 p.

Steven, T.A., Cunningham, C.G., and Machette, M.N., 1981, Integrated uranium systems in the Marysvale volcanic field, west-central Utah, in Goodell, 

P.C., and Waters, A.C., eds., Uranium in volcanic and volcaniclastic rocks: American Association of Petroleum Geologists Studies in Geology No. 13, p. 

111–122.

Van Gosen, B.S., Hammarstrom, J.M., Eppinger, R.G., Briggs, P.H., Crock, J.G., Meier, A.L., Sutley, S.J., Theodorakos, P.M., and Hageman, P.L., 2006, 

A reconnaissance geochemical and mineralogical study of the Stanley uranium district, Custer County, central Idaho: U.S. Geological Survey Scientific 

Investigations Report 2005–5264, 54 p., accessed May 10, 2016, at http://pubs.usgs.gov/sir/2005/5264/.
Volcanic Opal and Specialty Gemstones

Synonyms Hydrothermal opal, precious opal in volcanic sequences.

Commodities Gem opal (common opal, chalcedony, jasper, agate), geodes, petrified wood, picture rock.

Description Opal (hydrated silica) in seams of volcanic ash or lahars sandwiched between successive lava flows. It occurs mainly as 

open space fillings and impregnations. Common opal, opalized wood, and “fire opal” are widespread within Triassic or 

younger volcanic sequences, but precious opal is rare. Where opal occurs in massive volcanic rocks, it occurs also as 

open-space fillings; however, the opal-bearing areas are much smaller. Regardless of volcanic host rock, the precious 

opal occurrences are discrete, whereas common opal occurs over large areas.

Geological environment

Rock types Rhyolite, basalt, andesite and trachyte lavas, lahars and other volcaniclastic rocks. Associated rocks are perlite, bentonite, 

scoria, volcanic ash and diatomite; volcanic rocks may be intercalated with lacustrine sedimentary rocks.

Age range Tertiary or younger, commonly Miocene.

Depositional environment Volcanic sequences formed in subaerial or shallow marine environments where porous, pyroclastic or lacustrine rocks are 

interbedded with lava flows.

Tectonic setting(s) Volcanic arcs, rifts, collapsed calderas, hot-spot related volcanism, and others.

Deposit description

Ore mineralogy Precious opal; “fire opal,” chalcedony, agate, common opal.

Alteration

Ore controls

Opal-bearing cavities may have zeolite and celadonite coatings, but so do the barren cavities. There is no known alteration 

that is specific to precious opal.

Open spaces and other permeable zones open to the silica-bearing solutions. Spencer deposit, Idaho: precious opal occurs as 

one or more thin layers within common opal partially filling gas cavities within a rhyolite-obsidian flow.

Virgin Valley, Nevada: opal occurs primarily as replacement of wood, as replacement of conifer cones, as nodules filling 

void spaces in clay.

Opal Butte, Oregon: opals are found in rhyolite geodes (thunder eggs) in a perlite that has altered to a pastel-colored clay. 

Geochemical signatures Mn oxide fracture coating proximal to some deposits. Indicators of epithermal deposits. Opal at Virgin Valley, Nevada is 

uraniferous.

Economic factors 

Grade and tonnage Grade and tonnage for volcanic-hosted opal deposits are not well documented, because the opal extraction is done by smallscale operations.

Importance Volcanic rock-hosted opal deposits are numerous, but most of today’s high-quality opal production comes from Australian 

sedimentary-hosted deposits.

Other assessment and exploration guides

Boulder tracing is commonly used in opal exploration.

Unmetamorphosed or weakly metamorphosed (zeolite facies) terrains (gem opal deteriorates and becomes brittle if subject to moderate temperatures).

Tertiary or younger volcanic rocks. 

Areas containing known occurrences of precious or common opal, opalized wood and possibly chalcedony. 

Opal occurrences hosted by volcaniclastic rocks are commonly confined to the same lithologic unit over a large area. 

Presence of warm springs in an appropriate setting.

Examples

In/near focal areas Virgin Valley, Nevada.

Elsewhere Blue Fire Opal Mine, Idaho.

References

Paradis, S., Simandl, G.J. and Sabina, A., 1999, Opal deposits in volcanic sequences, in Simandl, G.J., Hora, Z.D., and Lefebure, D.V., eds., Selected 

British Columbia mineral deposit profiles, volume 3—Industrial Minerals: British Columbia Ministry of Energy and Mines, Open File 1999-10, 

accessed April 26, 2016, at http://www.empr.gov.bc.ca/Mining/Geoscience/MineralDepositProfiles/Pages/default.aspx.

Staatz, M.H., and Bauer, H.L., Jr., 1961, Virgin Valley opal district, Humboldt County, Nevada: U.S. Geological Survey Circular 142, 7 p. [Also available 

at http://pubs.usgs.gov/circ/0142/report.pdf.]

U.S. Bureau of Mines, 1995, An overview of production of specific U.S. gemstones: U.S. Bureau of Mines Special Publication 14-95, accessed February 

4, 2016, at http://minerals.er.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/contents.html.

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136 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Hectorite (Lithium-Rich Clay) and Specialty Clay

[ppm, parts per million; wt.%, weight percent; kt, thousand metric tons]

Synonyms Lithium (Li) smectite, high-Li clay.

Commodities Hectorite, Li, bentonite, specialty clays for drilling fluid additives and organoclays.

Description Li- and Mg-rich smectite clay; “greasy” when wet, color ranges from bright white to pink pastel to dark-green and brown. 

Found in playa and caldera sediments.

Geological environment

Rock types Volcanic ash, preexisting smectites, lacustrine sediments in high Mg evaporative lakes.

Textures Inherited from parent lacustrine sediments, may be thin or thickly bedded and laterally extensive. Hydrous with “greasy” 

fresh surface; dries to a blocky texture. Weathered surfaces may develop a “popcorn” texture.

Age range Miocene-Holocene.

Depositional environment Hydrologically closed basin containing evaporative lakes with discharge of geothermal waters. Geothermal waters provide 

the Li, previously leached from ash and alkaline volcanic rocks.

Tectonic setting(s) Basin-and-Range or other rift settings characterized by rhyolitic volcanism, crustal extension, hydrothermal activity, 

and high rates of sedimentation.

Associated deposit types Uranium, mercury, zeolites, bentonite, borate, gypsum, diatomite, dolomite, magnesite.

Deposit description

Ore mineralogy Hectorite, saponite, stevensite, bentonite.

Alteration Clays may expand with moisture, leading to “popcorn weathering”; lithium may be lost through leaching or cation 

exchange; burial and diagenesis may convert smectite minerals to illite or chlorite. 

Ore Controls Extent of lacustrine sediments, geothermal source of Li.

Geochemical signatures Li >300 ppm; ±F, U, Be, B enrichment; high Mg, low Al content.

Geophysical signature Seismic surveys may delineate extent and thickness of lacustrine sediments, and basin depth.

Economic factors

Grade and tonnage Hectorite from Hector, California, contains approx. 0.7 wt.% Li. The Kings Valley deposit (McDermitt caldera, Nevada) 

contains a measured resource of 50,700 kt grading at >0.312 wt.% Li, and 1,370 kt grading at >0.529 wt.% Li.

Importance Specialty clays for use as drilling fluid additives, organoclays, cosmetics, paints, medications.

Examples

In/near focal areas Kings Canyon mine, McDermit Caldera, Nevada-Oregon border.

Elsewhere Hector Mine, Hector, California.

Lyles Hectorite Mine, Yavapai County, Arizona.

References

Asher-Bolinder, Sigrid, 1991, Descriptive model of lithium in smectites of closed basins, Model 25l.3(T), in Orris, G.J., and Bliss, J.D., eds., Some 

industrial mineral deposit models—Descriptive deposit models. U.S. Geological Survey Open-File Report 91–11–A, p. 11–12.

Asher-Bolinder, Sigrid, 1982, Lithium-rich clays, in Erickson, Ralph L., ed., Characteristics of mineral deposit occurrences, U.S. Geological Survey OpenFile Report 82–795, p. 225–228.

Garrett, D., 2004, Handbook of lithium and natural calcium chloride—Their deposits, processing, uses and properties: Amsterdam, Elsevier Academic 

Press, 476 p.

Rytuba, J.J., and Glanzman, Richard K., 1979, Relation of mercury, uranium, and lithium deposits to the McDermitt caldera complex, Nevada-Oregon, in

Ridge, J.D., ed., Papers on mineral deposits of North America: Nevada Bureau of Mines and Geology Report 33, p. 109–117.

Western Lithium Corporation, 2014, Updated NI 43–101 Technical Report, Kings Valley property, Humboldt County, Nevada: Western Lithium 

Corporation, accessed April, 15, 2016, at http://www.westernlithium.com/wp-content/uploads/2015/01/NI43101May92014.pdf.
Hydrothermal—Exhalative-Magmatic Processes System

Deposit types in study area

Volcanogenic massive sulfide

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138 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Volcanogenic Massive Sulfide (Besshi-subtype VMS)

[wt.%, weight percent; km, kilometer; t, metric ton; g/t, grams per metric ton; VMS, volcanogenic massive sulfide]

Synonyms Mafic-siliciclastic VMS, volcanogenic sulfide, volcanic massive sulfide.

Commodities Cu, Pb, Zn, Ag (Au, Co, Sn, Mo, Cd).

Description Stratabound concentrations of sulfide minerals precipitated from hydrothermal fluids in extensional seafloor environments. Thin sheets of massive to well layered base-metal sulfide minerals in interlayered, terrigenous clastic rocks and 

calcalkaline basaltic to andesitic tuffs and flows.

Geological environment

Rock types Mainly shales, greywackes, sandstones, local dolomitic shales, basaltic sills and flows. Clastic sedimentary rocks and 

marine volcanic rocks; basaltic tuffs and flows, shale and siltstone, commonly calcareous; less commonly chert and Fe 

formations. Possibly ultramafics and metagabbro in sequence.

Age range Mainly Paleozoic and Mesozoic.

Depositional environment Besshi subtype: Terrigenous clastic rocks associated with marine volcanic rocks and sometimes carbonate rocks; these 

may overlie platformal carbonate or clastic rocks.

Tectonic setting(s) Oceanic extensional environments, such as back-arc basins, oceanic ridges close to continental margins, or rift basins in 

the early stages of continental separation rift separation.

Associated deposit types Cu, Zn veins.

Deposit description

Ore mineralogy Pyrite, pyrrhotite, chalcopyrite, sphalerite, cobaltite, magnetite, galena, bornite, tetrahedrite, cubanite, stannite, molybdenite, arsenopyrite, marcasite.

Alteration Difficult to recognize because of metamorphism. Chloritization of adjacent rocks is noted in some deposits. Similar to 

gangue mineralogy—quartz, chlorite, calcite, siderite, ankerite, pyrite, sericite, and graphite.

Ore controls Difficult to recognize; early (syndepositional) faults and mafic volcanic centers. Deposits are thin, but laterally extensive 

and tend to cluster in en echelon pattern.

Geochemical signatures Cu, Zn, Ag, Co/Ni>1; Mn halos, Mg enrichment, Cu, Pb, Zn, Ag, As, Au, Bi, Cd, Hg, In, Sb, Sn, and Tl.

Geophysical signature Magnetics: Regional geology/structure. Gravity: Regional geology/structure. Radiometrics: Lithology.

Economic factors

Grade and tonnage The type-locality Besshi deposits average 0.22 Mt, containing 1.5 wt.% Cu, 2–9 g/t Ag, and 0.4–2 wt.% Zn.

Importance Minor global significance. 

Other assessment and exploration guides

Mafic volcanic rocks (tholeiitic, less commonly alkalic) associated with clastic rocks.

Mn-rich garnets in metamorphosed exhalative horizons.

Presence of a submarine volcanosedimentary sequence having an age that falls within a time period containing numerous VMS deposits with large 

aggregate tonnages and base metal contents.

Evidence of an extensional geodynamic setting and synvolcanic faulting as reflected in distinctive compositions of volcanic and synvolcanic intrusive 

rocks.

Presence of coarse volcanic breccias or felsic domes indicating proximity to a volcanic center.

Occurrence of exhalites, especially those containing barite and (or) high concentrations of Cu, Zn, or Pb.

Favorable marine volcanosedimentary units including felsic or mafic lavas or tuffs, coarse breccias, and rhyolite domes that host mineralization within the 

same belt.

VMS-type prospects or occurrences including stratabound sulfides and discordant veins.

Evidence of VMS-type alteration zones represented by abundant chlorite or white mica, or their metamorphosed equivalents; abundant tourmaline and (or) 

gahnite.

Synvolcanic structures such as growth faults, calderas, and fault intersections, which may have focused fluid flow and localized sulfide mineralization.

Local fine-grained, highly carbonaceous or graphitic sedimentary rocks that record breaks in volcanism and in most cases indicate coeval anoxic or sulfidic 

bottom waters that prevented seafloor weathering and oxidation of sulfides.

Large synvolcanic sills and (or) dikes, which typically occur in the stratigraphic footwall of the deposits, having served as sources of heat to drive the 

hydrothermal systems.

Abundant chlorite or white mica and their metamorphosed equivalents (including Al-rich minerals), as evidence of VMS-type alteration.

Examples

In/near focal areas Rio Tinto, Nevada.
Elsewhere Windy Craggy, British Columbia; Besshi, Japan.

References

Franklin, J.M., Lydon, J.W., and Sangster, D.M., 1981, Volcanic-associated massive sulfide deposits: Economic Geology, 75th Anniversary Volume, 

p. 485−627.

Hõy, Trygve, 1995, Besshi massive sulphide, in Selected British Columbia mineral deposit profiles, volume 1—Metallics and Coal, in Lefebure, D.V., and 

Ray, G.E., eds., British Columbia Ministry of Energy of Employment and Investment, Open File 1995−20, p. 49−50, accessed April 26, 2016, at http://

www.empr.gov.bc.ca/Mining/Geoscience/MineralDepositProfiles/Pages/default.aspx.

Shanks, W.C. Pat, III, and Thurston, Roland, eds., 2012, Volcanogenic massive sulfide occurrence model: U.S. Geological Survey Scientific Investigations 

Report 2010−5070–C, 345 p., accessed February 7, 2016, at http://pubs.usgs.gov/sir/2010/5070/c/.

Appendix 3 139
140 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Hydrothermal—Exhalative-Sedimentary Processes System

Deposit types in the study area

SEDEX (sedimentary exhalative deposits) lead-zinc-silver

Bedded barite
Sedimentary-Exhalative (SEDEX) Lead-Zinc-Silver

[wt.%, weight percent; Mt, million metric tons; g/t, grams per metric ton; m, meter; km, kilometer; °C, degree Celsius; SEDEX sedimentary exhalative; MVT, 

Mississippi-Valley-type]

Synonyms Shale-hosted Zn-Pb-Ag, sediment-hosted massive sulfide Zn-Pb-Ag, SEDEX Zn-Pb.

Commodities Zn, Pb, Ag (minor Cu, barite).

Synoptic statement Hydrothermal deposit formed by the exhalation of metalliferous sedimentary brines into seawater.

Description Beds and laminations of sphalerite, galena, pyrite, pyrrhotite and rare chalcopyrite, with or without barite, in euxinic 

clastic marine sedimentary strata. Deposits are typically tabular to lensoidal in shape and range from centimeters to 

tens of meters thick. Multiple horizons may occur over stratigraphic intervals of 1,000 m or more.

Geological environment

Rock types Carbonaceous black shale, siltstone, cherty argillite and chert. Thin interbeds of turbiditic sandstone, granule to pebble 

conglomerate, pelagic limestone and dolostone, although volumetrically minor, are common. Evaporites, calcareous 

siltstone and mudstone are common in shelf settings. Small volumes of volcanic rocks, typically tuff and submarine 

mafic flows, may be present within the host succession. Slump breccia, fan conglomerates and similar deposits occur 

near synsedimentary growth faults. Rapid facies and thickness changes are found near the margins of second and 

third order basins. In some basins high-level mafic sills with minor dikes are important.

Textures Sulfide and barite laminae are usually very finely crystalline where deformation is minor. In intensely folded deposits, 

coarser grained, recrystallized zones are common. Sulfide laminae are typically monomineralic.

Age range Middle Proterozoic, Early Cambrian, early Silurian and Middle to Late Devonian to Mississippian. The middle 

Proterozoic and Devonian-Mississippian events are recognized worldwide.

Depositional environment Large evaporative shallow-water epeiric carbonate platforms.

Tectonic setting(s) Intracratonic or epicratonic sedimentary basin.

Associated deposit types Mississippi-Valley type (MVT), bedded barite, iron formation, phosphate.

Deposit description

Ore mineralogy Sphalerite, galena, pyrite, pyrrhotite ± chalcopyrite. Barite may or may not be a major component of the ore zone. 

Trace marcasite, arsenopyrite, bismuthinite, molybdenite, enargite, millerite, freibergite, cobaltite, cassiterite, 

valleriite and melnikovite have been reported from these deposits. 

Alteration Alteration varies from well-developed to nonexistent. In some deposits a stockwork and disseminated feeder zone 

lies beneath, or adjacent to, the stratiform mineralization. Alteration minerals, if present, include silica, tourmaline, 

carbonate, albite, chlorite and dolomite. They formed in a relatively low temperature environment. Celsian, Bamuscovite and ammonium clay minerals have also been reported but are probably not common.

Ore controls Favorable sedimentary sequences, major structural breaks, basins.

Geochemical signatures Typically zoned with Pb found closest to the vent grading outward and upward into more Zn-rich facies. Cu is usually 

found either within the feeder zone of close to the exhalative vent. Barite, exhalative chert and hematite-chert iron 

formation, if present, are usually found as a distal facies. Phosphate may occur in temporal association with Pb and 

Zn. Sedimentary rocks such as pelagic limestone interbedded with the ore zone may be enriched in Mn. NH3 Zn, Pb, 

and Mn anomalies at some deposits. The host stratigraphic succession may also be enriched in Ba on a basinwide 

scale. Dispersion halos and zoning of Fe, Ba, and Si at distances of tens and even hundreds of km from deposits. If 

phosphate occurs as apatite, may have enrichments of U and rare earth elements.

Geophysical signature Magnetics: Regional geology/structure. Basin geometry. Gravity: Regional geology/structure. Radiometrics: Lithology, 

weak radioactivity in some deposits. Presence of graphite-rich zones in the host sedimentary rocks can complicate 

the interpretation of electromagnetic conductors.

Economic factors

Grade and tonnage SEDEX deposits range from 0.01 to 746 Mt, with a median size of 10 Mt. Median ore grades are: 2.26 wt.% Pb, 5.55 

wt.% Zn, 0.6 wt.% Cu, and 45 g/t Ag.

Appendix 3 141
142 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Importance SEDEX deposits produce a significant proportion of the world’s Zn and Pb. Their large tonnage potential and 

associated Ag values make them an attractive exploration target.

Other assessment and exploration guides

All SEDEX deposits occur in intracratonic or epicratonic sedimentary basins. 

Depth to crystalline basement greater than 3 km (to achieve required fluid temperatures 100 °C).

Organic-rich black shale or siltstone with greater than 1 wt.% Corg.

Brine salinity source: Saline brine (>17 percent TDS) is necessary to form a SEDEX deposit. Basin-scale processes are required to produce the 

volume of brine necessary to form a deposit. Thus, direct geologic evidence for saline brine generation (such as evaporite minerals, breccias 

indicating salt dissolution or escape, or regional dolomitized platforms sequences) is required. 

Basinwide organic-rich metalliferous black shales and PO4, Fe, and Mn deposits may identify prospective sedimentary intervals in basins.

Areas within a few to tens of kilometers of large basin-bounding faults that control second-order features within sedimentary basins are highly 

favorable.

Synsedimentary faulting as indicated by abrupt and truncated facies boundaries in platform-to-slope transition, thick debris flows, intraformational 

breccias, changes in isopach thicknesses, and synsedimentary slump structures are highly useful indicators of favorable stratigraphic horizons for 

ore.

Extensive dolomitization of platform carbonate rocks and alkali-altered platform and rift-phase clastic sedimentary rocks are strong indicators of 

productive SEDEX basins.

On a local scale, faults that were fluid conduits may be identified by wallrock alteration with Fe- and Mn-rich carbonate rocks or silicification, and 

perhaps tourmalinization.

MVT-style mineralization and higher temperature dolomite along platform margins may be a strong indicator of the fluid-flow systems that form 

SEDEX deposits.

Examples

In/near focal areas Triumph, Idaho.

Elsewhere Red Dog, Alaska; Sullivan, British Columbia.

References

Emsbo, Poul, 2009, Geologic criteria for the assessment of sedimentary exhalative (SEDEX) Zn-Pb-Ag deposits: U.S. Geological Survey Open-File 

Report 2009−1209, 21 p., accessed February 1, 2016, at http://pubs.usgs.gov/of/2009/1209/.

Leach, D.L., Sangster, D.F., Kelley, K.D., Large, R.R., Garven, G., Allen, C.B., Gutzmer, J., and Walters, S., 2005, Sediment-hosted lead-zinc 

deposits—A global perspective, in Hedenquist, J.W., Thompson, J.F.H., Goldfarb, R.J., and Richards, J.P., eds., Economic Geology—One 

hundredth anniversary volume 1905–2005: Littleton, Colorado, Society of Economic Geologists, Inc., p. 561–607.

MacIntyre, Don, 1995, Sedimentary exhalative Zn-Pb-Ag, in Lefebure, D.V., and Ray, G.E., eds., Selected British Columbia mineral deposit profiles, 

volume 1—Metallics and Coal: British Columbia Ministry of Energy of Employment and Investment, Open File 1995-20, p. 37–39, accessed April 

2, 2016, at http://www.empr.gov.bc.ca/Mining/Geoscience/MineralDepositProfiles/Pages/default.aspx.
Bedded Barite

[wt.%, weight percent; Mt, million metric tons; SEDEX, sedimentary exhalative deposits; PGE, platinum-group elements; REE, rare earth elements]

Synonyms Sediment-hosted, stratiform barite.

Commodities Ba.

Description Sedimentary-hosted, stratiform or lens-shaped barite bodies that may reach over ten meters in thickness and several 

kilometers in strike length. Some Ba-rich rocks are lateral distal equivalents of shale-hosted Pb-Zn (SEDEX) deposits. 

Geological environment

Rock types Carbonaceous and siliceous shales, siltstones, cherts, argillites, turbidites, sandstones, dolomites and limestones. Chert is 

abundant in continental margin types. Clastics deposit in turbidity currents common in cratonic rift types.

Age range Deposits are hosted by rocks of Archean to Mesozoic ages but are most common in rocks of the Phanerozoic, especially 

mid to late Paleozoic in age.

Depositional environment Sedimentary depositional environment is mainly half-grabens and basins of second or third order. Although Zn-Pb-barite 

(SEDEX) deposits may require euxinic environment to stabilize sulfides, more oxidized depositional environment may 

be the key for deposition of high-grade (nearly sulfide-free) barite deposits.

Tectonic setting(s) Continental margin types deposited in ocean basins between subduction zone and passive continental margin. (Nevada 

type). Cratonic rift types are deposited in intracratonic rifts with strong local relief (German type).

Associated deposit types Shale-hosted Zn-Pb deposits, Irish-type massive sulfide deposits, sedimentary manganese deposits, and vein barite deposits. In oxygen starved basins, barite deposits may be stratigraphically associated with black shales enriched in phosphates, vanadium, REE and uranium mineralization, and possibly shale-hosted Ni-Mo-PGE deposits.

Deposit description

Ore mineralogy Barite.

Alteration None in most cases. Secondary barite veining. Weak to moderate sericitization reported in, or near, some deposits in 

Nevada.

Ore controls Syndepositional faults are extremely important for SEDEX deposits that are commonly proximal to the vents but may not 

be essential for all sediment-hosted stratabound barite deposits.

Geochemical signatures Ba enrichment on the scale of the basin and other indicators of shale-hosted Zn-Pb deposits, such as high values of Zn, Pb, 

Mn, Cu, and Sr, in rock and stream sediment samples. Strongly anomalous Ba values in stream sediments and heavy 

mineral concentrates are only found in close proximity to barite mineralization because barite abrades rapidly during 

stream sediment transportation. The difference between 87Sr/86Sr ratios of barite and coeval seawater may be used to 

distinguish between cratonic rift (potentially SEDEX-related) barite occurrences and those of peripheral foreland basins. 

Geophysical signature Deposit may correspond to a gravity high.

Economic factors

Grade and tonnage Deposits range from less than 1 to more than 25 Mt grading 30 wt.% to over 95 wt.% barite with a median size of 1.24 Mt 

containing 87.7 wt.% BaSO4 (Orris, 1992).

Importance Main source of industrial barite, which is used in drilling fluids in the oil and gas industry. 

Other assessment and exploration guides

Appropriate tectonic and depositional setting.

Some barite deposits display breccias and slump structures.

In metamorphosed areas, barite may be remobilized forming veinlets and (or) recrystallized.

Proximity to known occurrences of barite, shale-hosted SEDEX, or Irish-type massive sulfide occurrences.

Exhalative chert, hematite-chert iron formations, and regional Mn marker beds.

Vegetation “kill zones” coincide with some barite occurrences.

Examples

In/near focal areas Snake Mountains, Nevada.

Appendix 3 143
144 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Elsewhere Argenta, Rossi, Greystone, Big Ledge Mines, Nevada.

References

Maynard, J.B., and Okita, P.M., 1991, Bedded barite deposits in the United States, Canada, Germany, and China—Two major types based on tectonic 

setting: Economic Geology, v. 86, p. 364–376.

Orris, G.J., 1992, Grade and tonnage model of bedded barite, in Orris, G.J., and Bliss J.D., eds., Industrial minerals deposit models—Grade and tonnage 

models: U.S. Geological Survey Open-File Report 92–437, p. 40–42, accessed May 10, 2016, at https://pubs.usgs.gov/of/1992/0437/report.pdf.

Paradis, S., Simandl, G.J., MacIntyre, D., and Orris, G.J., 1998, Sedimentary-hosted, stratiform barite, in Geological Fieldwork 1997: British Columbia 

Ministry of Employment and Investment, Paper 1998–1, p. 24F-1 to 24F-4.

Shawe, D.R., Poole, F.G., and Brobst, D.A., 1967, Bedded barite in East Northumberland Canyon, Nye County, Nevada: U.S. Geological Survey Circular 

555, 8 p.

Torres, M.E., Bohrman, Gerhard, Dube, T.E., and Poole, F.G., 2003, Formation of modern and Paleozoic stratiform barite at cold methane seeps on 

continental margins: Geology, v. 31, p. 897–400.
Hydrothermal—Metamorphic Rock Associated System

Deposit types in the study area

Orogenic low-sulfide gold-quartz veins 

Appendix 3 145
146 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Orogenic Low Sulfide Gold-Quartz Veins

[km, kilometer; t, metric tons; g/t, grams per metric ton; °C, degree Celsius]

Synonyms Turbidite-hosted gold, low-sulfide gold quartz veins, mesothermal gold, greenstone gold, Slate Belt gold, Mother Lode 

type, Homestake type.

Commodities Au.

Description Structurally controlled lode gold in massive persistent quartz veins mainly in regionally metamorphosed volcanic rocks, 

volcanic sedimentary rocks, and banded iron formation.

Geological environment

Rock types A wide range of potential rock types within deformed and metamorphosed host terranes; greenstone belts; turbidites, banded 

iron formation. Mainly greenschist metamorphic grade rocks, less commonly amphibolite facies, rare granulite facies.

Age range Archean to present.

Depositional environment Adjacent to major, regionally extensive, deep crustal fault zones with deposit locations controlled by secondary faults. Gold 

is deposited from near-neutral pH, low-moderate salinity, and high CO2 hydrothermal fluids within, or in proximity to, 

zones of brittle and (or) ductile deformation; transported in solution along permeable large-scale fault zones; temperatures of deposition are ± 350 oC, at depths ranging from 4 to 12 km. 

Tectonic setting(s) Archaean granite-greenstone terrain.

Terrains of turbiditic metasedimentary rocks.

Continental margin accretionary (oceanic-continental) and collisional continent-continent) orogens.

Associated deposit types Placer and paleoplacer gold deposits.

Deposit description

Ore mineralogy Gold, electrum, arsenopyrite, pyrite, pyrrhotite (minor chalcopyrite, sphalerite, galena, and telluride minerals). Au/Ag ratios 

>1. Mineralogy of deposits is limited, in descending order, to quartz, carbonates, alkali feldspar (usually albite), sericite, 

pyrite, and minor amounts of tourmaline, arsenopyrite, scheelite, molybdenite. No significant base metals.

Alteration Intense carbonate alteration is always present (ankerite, dolomite, calcite, magnesite). A progression from calcite to Fecarbonate can often be observed toward the deposit.

Chlorite is an important alteration product when the wall rock is mafic.

Fe-sulfide (commonly as pyrite) is ubiquitous.

Silicification (an increase in modal quartz).

Alteration is most obvious when it occurs within low-grade rocks.

Ore controls Commonly near major regional faults/shear zones but located in secondary faults and (or) near hinge zones of folds. Ore 

bodies typically strike parallel to subparallel to the host structures. Major regional structures often along terrane or block 

boundaries serve as fluid pathways.

Geochemical signatures Common pathfinder elements: Ag, As, Au, B, Bi, Hg, Sb, Te, and W. Local, low-level enrichment of Cu, Pb, and Zn may 

occur in some deposits.

Geophysical signature Faults indicated by linear magnetic anomalies.

Areas of alteration indicated by negative magnetic anomalies due to destruction of magnetite as a result of carbonate 

alteration.

Airborne and ground magnetic and gravity surveys to map bedrock geology including deformation zones.

Airborne and ground electromagnetic surveys to outline deformation zones, especially those that contain graphitic gouge 

and S-rich zones.

Linear resistivity survey lows may locate fault structures; resistivity highs may be associated with massive quartz veins.

Radiometric surveys may aid in defining areas of potassium alteration. 

Seismic-reflection surveys to locate linear fault zones.

Economic factors

Grade and tonnage World-class deposits range from about 100 to 5,000 t. Typical grades 4 to 20 g/t Au. 
Importance These deposits are a major source of global gold production.

Other assessment and exploration guides

Placer gold or elevated gold in stream sediment samples is an excellent regional and property-scale guide to gold-quartz veins.

Ore shoots can have many forms that are related to the wide variety of second and third-order structures that can develop in (or be used by) strike-slip fault 

systems.

Broad “deformation envelopes” adjacent to regional listric faults where associated with carbonate alteration.

Alteration and structural analysis can be used to delineate prospective ground. Economic gold concentration in a deformation zone is often located in 

places where increased extension has occurred, such as in pull-apart basins.

Mineralization is often contemporaneous with spatially associated granitic intrusions but not genetically related to them.

Within carbonate alteration zones, gold is typically only in areas containing quartz, with or without sulfides.

Serpentinite bodies, if present, can be used to delineate favorable regional structures. Largest concentrations of free gold are commonly at, or near, the 

intersection of quartz veins with serpentinized and carbonate-altered ultramafic rocks.

Examples

In/near focal areas South Pass, Wyoming; Buffalo Hump, Elk City, Yellow Pine, and Boise Basin in central Idaho.

Elsewhere Grass Valley, California; Timmins District, Ontario; Val d’Or District, Quebec; Homestake, South Dakota.

References

Ash, Chris, and Alldrick, Dani, 1996, Au-quartz veins, in Lefebure, D.V., and Hõy, T., eds., Selected British Columbia mineral deposit profiles, volume 

2—Metallic deposits: British Columbia Ministry of Employment and Investment, Open File 1996-13, p. 53–56, accessed April 4, 2016, at http://www.

empr.gov.bc.ca/Mining/Geoscience/MineralDepositProfiles/Pages/default.aspx.

Bliss, J.D., 1992, Grade and tonnage model of Chugach-type low sulfide Au-quartz veins, in Bliss, J.D., ed., Developments in mineral deposit modeling: 

U.S. Geological Survey Bulletin 2004, p. 44–46, accessed May 20, 2016, at https://pubs.er.usgs.gov/publication/b2004.

Drew, L.J., 2003, Low-sulfide quartz gold deposit model: U.S. Geological Survey Open-File Report 03–077, 24 p., accessed February 7, 2016, at http://

pubs.usgs.gov/of/2003/of03-077/of03-077.pdf.

Goldfarb, R.J., Baker, T., Dubé, B., Groves, D.I., Hart, C.J.R., and Gosselin, P., 2005, Distribution, character, and genesis of gold deposits in metamorphic 

terranes, in Hedenquist, J.W., Thompson, J.F.H., Goldfarb, R.J., and Richards, J.P., eds., Economic Geology One Hundredth Anniversary Volume 

1905–2005: Society of Economic Geologists, p. 407–450.

Goldfarb, R.J., Groves, D.I., and Gardoll, S., 2001, Orogenic gold and geologic time—A global synthesis: Ore Geology Reviews, v. 18, p. 1–75.

Groves D.I., Goldfarb R.J., Gebre-Mariam M., Hagemann S.G., and Robert, F., 1998, Orogenic gold deposits—A proposed classification in the context of 

their crustal distribution and relationship to other gold deposits: Ore Geology Reviews, v. 13, p. 7–27.

Appendix 3 147
148 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Sedimentary System (formed during or after the conversion from sediment to 

sedimentary rock)

Deposit types in the study area

Bentonite

Dolomite (high purity)

Sediment-hosted stratabound copper

Sandstone uranium (rollfront) in intermontane basins

Hydroallogenic volcanic-hosted uranium 

Zeolites (closed system subtype) 

Zeolites (open system subtype)
Bentonite

[Mt, million metric tons; m, meter; km, kilometer]

Synonyms Sodium (Na) bentonite, calcium (Ca) bentonite, swelling bentonite, nonswelling bentonite, hydrothermal bentonite, 

Wyoming bentonite, southern bentonite, montmorillonite.

Commodities Na bentonite, Ca bentonite, hydrothermal bentonite.

Description Any material composed of smectite clay minerals, whose properties are dictated by the dominant smectite clay mineral.

Geological environment

Rock types Parent materials are felsic to intermediate volcanic rock, ash, and tuff.

Textures Inherited from parent volcanic tuff or ash, clay deposits can be thinly bedded and laterally extensive, or they can be lensshaped and massively bedded bodies with thickness 1–6 m.

Age range Almost all commercial deposits are either Cretaceous or Tertiary 

Depositional environment Felsic to intermediate volcanism producing volcanic ash and (or) feldspar-rich rocks which are subsequently altered to clay 

by reaction with alkaline, marine-, or hydrothermal waters.

Tectonic setting(s) Stable marine or fluvial-lacustrine basins. Hydrothermal bentonites form near conduits for thermal fluids.

Associated deposit types Diatomite, other clay minerals, limestone, dolomite, zeolites.

Deposit description

Ore mineralogy Na- and Ca-bentonite, montmorillonite, and other smectite clays.

Alteration Leaching of Mg and Fe from bentonite may lead to formation of kaolinite, burial and diagenesis may convert smectite 

minerals to illite or chlorite. Abundance decreases with depth of burial; smectites become rare when buried >4 km.

Ore controls For sedimentary bentonites: proximity of volcanism to alkaline marine basin; for hydrothermal bentonites: faults and 

fractures for fluid migration and reactive host rocks. 

Geochemical signatures Formed from alteration of volcanic ash and tuffs; often found containing feldspar, biotite, quartz, pyroxene, and zircon that 

were phenocryts in the original volcanic material. Na bentonite contains exchangeable Na ions and may increase 15–20 

times in volume when wetted with water. Ca bentonite contains exchangeable Ca ions and may increase as much as five 

times in volume in the presence of water.

Geophysical signature Seismic surveys may delineate extent and thickness of bentonite beds and basin depth.

Economic factors

Grade and tonnage Almost 90 percent of Na bentonite comes from Wyoming and Montana; 45 percent of Ca bentonite comes from Mississippi 

and Alabama. 

Importance Na bentonite (swelling): used in drilling mud, foundry sand bond, iron-ore pelletizing, bleaching liquids, filler, sealant, 

nondrip paint, putty adhesives, liquid fertilizer suspensions, and animal feed.

Ca bentonite (nonswelling): used as foundry sand bond, filler, catalyst, absorbent (kitty litter and oil and grease absorbents), 

water treatment filters, ceramic glazes, and used as “Fuller’s earth” for cleaning agent and decolorizing oils.

Hydrothermal bentonite: decolorizing oils, filler, filtration, pesticide carrier. 

Examples

In/near focal areas Ivanhoe Creek, Ca bentonite, Elko County, Nevada.

Glasgow and Malta areas, Na bentonite, Montana.

Ben-Jel bentonite mine, 22 km west of Grand View, Owyhee County, Idaho, 4.6 m thick bentonite bed overlying siliceous 

volcanic tuff.

Liddy Hot Springs bentonite occurrence, 3-m clay beds.

Appendix 3 149
150 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Elsewhere Clay Spur Na Bentonite Bed, Cretaceous Mowry Shale near Black Hills in Wyoming and South Dakota.

Sandy Ridge, a Ca bentonite at the base of the Late Cretaceous Ripley Formation, southeastern Lowndes County, Alabama.

References

Dean, L.S., 2008, Minerals in the economy of Alabama, 2007, Geological Survey of Alabama, Information Series 64R, 36 p.

Geitgey, Ronald P., 1989, Industrial Minerals in Oregon: Oregon Geology, v. 51, p. 123–129.

Hosterman, J.W., 1984, Ball clay and bentonite deposits of the central and western Gulf of Mexico coastal plain, United States: U.S. Geological Survey 

Bulletin 1558–C, 28 p.

Hosterman, J.W., and Orris, G.J., 1998, Preliminary descriptive model of sedimentary bentonite—Deposit subtype—Sodium bentonite, model 28e.2, in

Orris, G.J., ed., Additional descriptive models of industrial mineral deposits: U.S. Geological Survey Open-File Report 98–505, p. 24–26.

Hosterman, J.W., and Orris, G.J., 1998, Preliminary descriptive model of sedimentary bentonite—Deposit subtype—Calcium bentonite, model 28e.1, in

Orris, G.J., ed., Additional descriptive models of industrial mineral deposits: U.S. Geological Survey Open-File Report 98–505, p. 27–29.

Hosterman, J.W., and Orris, G.H., 1995, Preliminary descriptive model of hydrothermal bentonite, model 25l.1, in Orris, G.J., ed., Additional descriptive 

models of industrial mineral deposits: U.S. Geological Survey Open-File Report 98–505, p. 18–20.

Hosterman, J J.W., 1973, Clays, in Brobst, D.A., and Pratt, W.P., eds., United States Mineral Resources: U.S. Geological Survey Professional Paper 820, p. 

123–131.

Hosterman, J.W., and Peterson, Sam H., 1992, Bentonite and Fuller’s earth resources of the United States: U.S. Geological Survey Professional Paper 1522, 

50 p.

Rogers, M.C., 2011, Model B-9, bentonite, in Saskatchewan descriptive mineral deposit models: Saskatchewan Ministry of Energy and Resources, Open 

File Report 2014-2, p. B-9-1 to B-9-2. accessed July 15, 2016, at http://www.publications.gov.sk.ca/details.cfm?p=79909.
Dolomite (high-purity)

[km, kilometer; t, metric ton; wt.%, weight percent]

Synonyms Dolostone, dolomitite, dolospar. 

Commodities Dolomite (aggregate, filler). Sometimes dolomite may be a byproduct of quarrying limestone.

Description A bedded or massive carbonate sedimentary rock that occurs as tabular bodies concordant with stratigraphy and beds 

as much as tens of meters thick and zones controlled by faults and permeable zones. Dolomite contains more than 

90 percent of the mineral dolomite and is usually a finely crystalline and slightly porous rock. Calcite is the most 

common other mineral.

Geological environment

Rock types Dolomites are often found within thicker sedimentary sequences with associated limestones, dolomitic limestones, 

argillites, sandstones, and evaporates. In island arcs, dolomites often have a volcanic component, such as tuffaceous 

rocks, sills, submarine lavas, palagonite breccias, and sometimes cherty layers and interbeds.

Age range Dolomite can be any age, but the ages of dolomitization for secondary deposits often are not well defined. Largescale regional dolomitization in western Canada has been linked to fluid circulation taking place during DevonianMississippian and Late Cretaceous-Tertiary periods. Generally these deposits are believed to be concurrent with 

large-scale tectonic activity.

Depositional environment Dolomite is most common as a secondary replacement of marine sedimentary rocks that were a slightly magnesian 

calcium carbonate that was frequently aragonite originally and later recrystallized into calcite. Circulating ground 

water (sea water, hypersaline brine, pore water) containing magnesium reacted with the calcium carbonate to 

produce dolomitic limestones and dolomites. Dolomite may also form as a primary sediment, but this is not very 

common.

Tectonic setting(s) Dolomite is more common in Holocene and ancient continental shelf and subsiding marginal marine environments; 

however, economically attractive deposits also occur in island arc environments.

Associated deposit types Mississippi Valley Type Pb, Zn, barite, fluorspar deposits, limestone, accumulations of oil and natural gas, and 

hydrogen sulfide. 

Deposit description

Ore mineralogy Dolomite (may occur with quartz, brucite, calcite, chert, kaolinite, illite, sometimes bitumen).

Alteration Dolomite is typically an alteration product. It may be accompanied by a variety of sulfides (pyrite, sphalerite, galena), 

Fe-Mn-Mg-Ca carbonates, chlorite, barite, gypsum or anhydrite, and fluorspar. High-temperature/low-pressure 

metamorphism may result in converting dolomite into a mixture of periclase (MgO) and calcite. Periclase in nature 

easily alters into brucite Mg(OH)2.

Ore controls Ore control reflects the mode and intensity of dolomitization. In some deposits a primary control is the chemical 

composition of the carbonate rock; in some others it is the upper and lower limits of the original limestone bed. For 

some deposits, the locations where fluid pathways along faults and permeable zones intersect reactive carbonate 

rocks are the control on the location of the replacement zones.

Geochemical signatures High magnesium in carbonate rock.

Geophysical signature Although karst features in dolomite are rather uncommon, resistivity and gravity could be used to outline karstaffected areas.

Economic factors

Grade and tonnage Commercial dolomite must be very high-purity carbonate rock and almost stoichiometric in composition (30.4 wt.% 

CaO and 21.9 wt.% MgO). Industry specifications are set for the calcined product—that is, a dolomitic lime. 

Depending on the end use, the limits for impurities are usually between 0.1 and 4.5 wt.% Fe2O3, SiO2 between 0.5 

and 1.0 wt.%, and Al2O3 between 0.3 and 0.8 wt.%.

Appendix 3 151
152 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Importance Very important as a source of magnesium to improve fluidity of molten product, such as in the production of mineral 

wool, float glass, and slag in metallurgical process. As agriculture soil conditioner; the magnesium content 

improves the neutralizing power and helps to retain the soil nutrients better than pure limestone. In many other end 

uses dolomite can be substituted by some other industrial minerals.

Other assessment and exploration guides

Sometimes yellow or brown color of outcrops; sandy talus.

Because of lower solubility of dolomite relative to calcite, dolomite does not fizz with diluted hydrochloric acid.

Ore control reflects the mode and intensity of dolomitization. In some deposits a primary control is the chemical composition of the carbonate rock, 

in some others it is the upper and lower limits of the original limestone bed. For some deposits, the locations where fluid pathways along faults and 

permeable zones intersect reactive carbonate rocks are the control on the location of the replacement zones.

Mining of high purity dolomite requires more exploration and quality control, and is more costly than mining dolomite for aggregate use. 

Examples

In/near focal areas None.

Elsewhere Mill Creek, Oklahoma; northeastern Illinois.

References

Hopkins, D.A., 2002, Value added refractory dolomite—A case study, in Scott, P.W., and Bristow, C.M., eds., Industrial minerals and extractive industry 

geology: London, Geological Society of London, p. 167–168. 

Hora, Z.D., 1999, Dolomite (R10), in Simandl, G.J., Hora, Z.D., and Lefebure, D.V., eds., Selected British Columbia mineral deposit profiles, volume 

3—Industrial Minerals: British Columbia Ministry of Energy and Mines, Open File 1999-10, accessed March 15, 2016, at http://www.empr.gov.

bc.ca/Mining/Geoscience/MineralDepositProfiles/Pages/default.aspx. 
Sediment-Hosted Stratabound Copper

[Mt, million metric tons; wt.%, weight percent; g/t, grams per metric ton; Ma, mega-annum or millions of years ago]

Synonyms Sediment-hosted stratiform Cu, Cu sandstone, sandstone Cu; sandstone Cu deposits are one of three subtypes: (1) reduced 

facies-type, (2) sandstone Cu-type, and (3) red bed-type.

Commodities Cu, Ag, or Co.

Description Bodies of disseminated, cementing, and veinlet-hosted copper (Cu) minerals that are peneconformable with their 

sedimentary or metasedimentary host rocks. Deposits are characterized by strong zoning of the ore minerals laterally 

along and across the bedding, from pyrite, to chalcopyrite, to bornite, to chalcocite, and to hematite.

Geological environment

Rock types Typically well-sorted feldspathic to arkosic sandstones. Where conglomeratic, they typically have only mud intraclasts and 

are not polymictic. These rocks were probably reservoir rocks for petroleum before copper minerals were deposited; 

petroleum was probably sour gas, for most cases. 

Age range Limited to sedimentary or metasedimentary formations younger than 2,300 Ma, when free oxygen first appeared in Earth’s 

atmosphere and the earliest red beds formed.

Depositional environment Sandstone-type host rocks were deposited in subtidal nearshore, beach, eolian, and fluvial environments. Various 

depositional environments that are among deltaic topset beds. Host rocks at Spar Lake are the lower quartzite beds of 

the upper member of the Revett Formation of the Belt Supergroup, which were deposited in a prograding beach and bar 

nearshore environment, and middle quartzite host rocks were deposited by laterally shifting subtidal channels.

Tectonic setting(s) SSC deposits formed in sedimentary basins that now vary from virtually undeformed to intensely folded, thrust-faulted, 

and the host rocks metamorphosed. Host sedimentary-rock sequences were deposited within 20 to 30 degrees of the 

paleo-equator, associated with hot, dry climates that produced thick packages of red beds and commonly also produced 

evaporites.

Associated deposit types Volcanic red bed Cu, tabular sandstone-hosted U-V.

Deposit description

Ore mineralogy Chalcocite and bornite zones are typically the ore zones. Mineral zonation both laterally and vertically from pyrite to 

chalcopyrite to bornite to chalcocite to hematite is characteristic. Less common ore minerals include digenite, djurleite, 

covellite, sulfur-rich bornite±carrollite, Co-rich pyrite, and native silver. Chalcocite, bornite, and digenite are commonly 

argentiferous.

Alteration Alteration gangue minerals are zonally arranged, with their zone boundaries parallel to the zonation of sulfide minerals. 

Authigenic hematite lining and filling pores is present in chalcocite zones of most deposits. Authigenic K-feldspar 

may occur as overgrowths on detrital K-feldspar grains and as cements and replacements. Authigenic chlorite. Fe- and 

Mn-rich calcite cement. Na-rich alteration accompanies mobilization and transport (sodium sulfate minerals, albite, or 

analcime, and at higher metamorphic grade, sodic amphibole riebeckite). 

Ore controls Traps to create gas reservoirs include anticlines, fault traps, and combination traps produced by pre-ore folding and 

faulting. Faults at high angles to host beds are common, and some fed cupriferous oxidizing ore fluids to the gas 

reservoirs. 

Geochemical signatures Cu, Ag, and Co. Ag is useful in the sandstone Cu mineralizing system of the Revett Formation, because anomalies with Cu 

and Ag are distinct from anomalies associated with other types of deposits. Other potential pathfinder elements include 

Pb, Zn, As, Hg, Mn, and Ba.

Geophysical signature Gravity, magnetic, and electromagnetic surveys to map basement topography, bedrock geology, and basin and subbasin 

margins. Seismic reflection or refraction surveys can identify basin and subbasin margins, anticlines, stratigraphic traps, 

and combination. Radiometrics can be used to image lithology and alteration. Induced polarization (IP) may be effective 

in direct sensing of deposits. Remote sensing of colors using Landsat imagery or remote sensing of ferric oxides using 

Landsat imagery can be used to map pre-ore bleaching of red beds.

Economic factors

Grade and tonnage Tonnages range from about 2 to 90 Mt, although the largest is 1,311 Mt; median size 10 Mt; Grades range from about 0.5 

to 2.6 wt.% Cu, median 1.2 wt.% Cu; Ag grades 5 to 100 g/t.

Appendix 3 153
154 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Importance Sediment-hosted stratabound copper deposits account for approximately 20 percent of the world’s past production and 

known resources of copper. Although such deposits are common throughout the world, economically significant 

deposits are rare.

Other assessment and exploration guides

Evidence of essential ore system components:

Source rocks for copper, typically oxidized (hematite-stable) siliciclastic sediment or mafic subaerial volcanic rocks.

Hematite-stable (oxidized) subsurface sedimentary brines capable of dissolving and transporting copper in solution.

Brines moving generally in the direction of dewatering of a sedimentary basin. Evidence of brine can include bedded evaporite or casts, molds of halite, 

gypsum, and other evaporite minerals nearby.

Rock seals confining beds, stratigraphic pinchouts, and (or) anticlinal traps (focus fluid flow of the copper-bearing brines to rocks that contain organic 

material that will cause sulfide mineral precipitation).

Organic-rich sedimentary rocks that serve as source rocks for natural gas, oil, and H2S, that cause the precipitation of copper from an oxidized subsurface 

sedimentary brine.

In terrains that have known sandstone Cu deposits, anticlines, areas with known stratigraphic traps, and those with known combination traps are more 

favorable than other parts of broadly permissive areas.

Areas of natural-gas production within basins that have known sandstone Cu deposits.

Host rocks overlie or are enclosed within thick (greater than 300 meters and commonly greater than 1 kilometer) sequences of red beds. The association 

with red beds is an important distinction from other Cu deposits found in sedimentary rocks.

Examples

In/near focal areas Griggs mine, Wyoming.

Elsewhere Spar Lake, Belt-Purcell Basin, Montana; Udokan, Transbaikalian Russia; Chu Sarysu Basin, Kazakhstan; Chuxiong Basin, 

China.

References

Hayes, T.S., Cox, D.P., Piatak, N.M., and Seal, R.R., II, 2015, Sediment-hosted stratabound copper deposit model: U.S. Geological Survey Scientific 

Investigations Report 2010–5070–M, 147 p., accessed March 15, 2016, at http://dx.doi.org/10.3133/sir20105070M.

Zientek, M.L., Wintzer, N.E., Hayes, T.S., Parks, H.L., Briggs, D.A., Causey, J.D., Hatch, S.A., Jenkins, M.C., and Williams, D.J., 2015, Qualitative 

assessment of selected areas of the world for undiscovered sediment-hosted stratabound copper deposits: U.S. Geological Survey Scientific 

Investigations Report 2010–5090–Y, 143 p., and spatial data, accessed March 15, 2016, at http://dx.doi.org/10.3133/sir20105090Y.
Sandstone Uranium (Roll Front) in Intermontane Basins

[wt.%, weight percent; km, kilometer; t, metric ton; g/t, grams per metric ton]

Synonyms Roll front U.

Commodities U.

Description Microcrystalline uranium oxides and silicates deposited from groundwater in localized reduced environments within fine- to 

medium-grained sandstone beds; some uranium oxides also deposited during redistribution by ground water at interface 

between oxidized and reduced ground.

Geological environment

Rock types Host rocks are feldspathic or tuffaceous sandstone. Pyroclastic material is felsic in composition. Mudstone or shale 

commonly above and (or) below sandstones hosting diagenetic ores that have channeled and focused uraniferous 

groundwater.

Age range Jurassic to Oligocene sandstones in the Wyoming basin province, with most mineralization in the Paleocene Fort Union, 

Oligocene Wasatch, Wind River, and Battle Spring Formations. 

Depositional environment Intracratonic basins, fluvial channels, braided stream deposits. Contemporaneous felsic volcanism or eroding felsic plutons 

are sources of U. 

Tectonic setting(s) Stable platform or foreland-interior basin; adjacent major uplifts provide favorable topographic conditions.

Associated deposit types Tabular remnant or “lag” deposits. 

Deposit description

Ore mineralogy At the roll-front, uraninite, coffinite, uranyl sulfate, uranium vanadates, arsenic with pyrite, ferroselite, marcasite, and 

molybdenite

Alteration The alteration zone on the oxidized side of the roll front is characterized by bleached sand containing limonite, hematite, 

magnetite, and nontronite. Adjacent-to-ore siderite, ferroselite, and goethite with vanadium and arsenic enrichment. At 

the roll-front interface, carbonate-cemented sand with iron oxides, siderite, ferroselite, and goethite.

Ore controls Permeable sandstone sequences with low dips and adequate recharge to facilitate the movement of uranium rich groundwater 

into the sequence; felsic plutons or felsic tuffaceous sediments adjacent to or above host rock are favorable source for U. 

Groundwater flow as controlled by paleohighs (Casper arch southwest of Powder River Basin and the Granite Mountains 

adjacent to the Shirley, Wind River, and Great Divide Basins in Wyoming) Regional redox interface marks locus of ore 

deposition and has been attributed to amorphous organic material, petroleum, and natural gas within host sediments. 

Coalified logs and other vegetal remains behind the oxidized roll fronts yield remnant or lag deposits of uranium. 

Geochemical signatures U, V, Mo, Se, locally Cu, and Ag. Anomalous radioactivity from daughter products of U. Typical zoning across a roll front is 

Se/V–U–Mo/As.

Geophysical signature Magnetics: Regional geology/structure. Gravity: Regional geology/structure. Radiometrics: Lithology that may focus 

grounwater flow (stream channels)

Economic factors

Grade and tonnage Sandstone-hosted deposits of all types in the United States range in size from 1 to 40 million pounds of U3

O8 and grade from 

0.07 to 0.9 wt.% U3O8. Roll-front deposits fall on the small size of this range and are characterized by their poddy nature 

along extensive roll-front systems. Within the Great Divide Basin, Sheep Mountain contains 16 million pounds of U3O8

(average grade 0.131 wt.% U3O8). 

Importance The majority of the ~ 4–5 million pounds of uranium currently being produced in the Untied States is from roll-front deposits in 

Wyoming. The Sheep Mountain deposit has produced uranium and is under development by Energy Fuels Resources, Inc.

Other assessment and exploration guides

Anomalous radon and helium over mineralization.

Areas where oxygenated waters migrating through an aquifer with traces of dissolved uranium encounter a reducing zone and precipitate uranium along with 

other metals

Examples

In/near focal areas Great Divide Basin, Wyoming.

Elsewhere Gas Hills, Wyoming.

References

Boberg, W.W., 2010, The nature and development of the Wyoming uranium province: Society of Economic Geologists Special Publication 15, p. 653–674.

Mickle, D.G., and Mathews, G.W., 1978, Geologic characteristics of environments favorable for uranium deposits: U.S. Department of Energy Publication 

GJBS-67 (78), 250 p.

Turner-Peterson, C.E., and Hodges, C.A., 1986, Descriptive model of sandstone U, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. 

Geological Survey Bulletin 1693, p. 209–210. [Also available at http://pubs.usgs.gov/bul/b1693/.]

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156 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Hydroallogenic Volcanic-Hosted Uranium

[wt.%, weight percent; ft., feet; mi2, square mile; lb, pound; NURE, National Uranium Resource Evaluation]

Synonyms Epigenetic, supergene.

Commodities Uranium.

Description Hydroallogenic deposits form when uranium-enriched fluids are released from volcanic source rocks, transported by 

aqueous solutions, and concentrated in the same or nearby rocks.

Geological environment

Rock types Highly variably lithologies, with porosity and permeability the determining parameters. At Mountain City, deposits 

are hosted within Tertiary arkosic sandstone and conglomerate with intercalated clay, shale, and tuffaceous and 

volcanoclastic rocks. Mineralization is also noted in shear zones and joints within these sedimentary rocks and 

underlying granites. Deposits are associated with rhyolitic to andesitic welded to unwelded air-fall and ash-flow tuff, 

agglomerate, and granite.

Age range Tertiary.

Depositional environment At Mountain City: Tertiary conglomerate, sandstone and volcanoclastic rocks that collected in paleochannels or lows. 

Shear zones and joints within volcanic rocks, granite, and granitic grus. Within these rocks, charcoal, carbonaceous 

debris, and clay; trace pyrite is an important reductant.

Tectonic setting(s) Volcanic settings favorable for groundwater circulation by faults and fractures.

Associated deposit types Volcanogenic uranium deposits.

Deposit description

Ore mineralogy Most commonly uraniferous silica (chert/opal), uranosilicates, and (or) epigenetic uranium minerals (autunite, torbernite, 

soddyite, and carnotite).

At Mountain City uranyl phosphates: Autunite (hydrated calcium uranyl phosphate Ca(UO2)

2

(PO4)

2

·10-12 H2O), 

torbernite (hydrated copper uranyl phosphate Cu(UO2)

2

(PO4)

2

·12 H2O), and meta-torbernite (Cu(UO2)

2

(PO4)

2

·8 H2O).

Alteration Host rocks usually silicified with widespread zeolitization and calcification.

At Mountain City, diagenesis by groundwater alters feldspars to kaolinite and sericite; mafic rock constituents to iron 

oxide and chlorite; and tuffaceous material to montmorillonite and devitrifies the groundmass and quartz grains. This 

alteration presumably leaches uranium from source rocks.

Ore controls Uranium minerals occur in (1) aureoles around the contact of the host rock with intrusive or effusive body from which 

mineralizing fluids originate, (2) tabular or lenticular units that follow bedding and permeable zones within sedimentary 

host rocks, (3) permeable Tertiary sediments deposited in paleochannels or lows developed on a Tertiary weathering 

surface, and (4) shear zones, fault breccias, and joints within volcanic rocks, granite, and grus.

Geochemical signatures Few geochemical signatures of this deposit type are described nationwide. At Mountain City, elevated uranium and 

molybdenum in rock, surface water and groundwater, and soil and stream sediments samples. 

Geophysical signature Ground radiometric signatures detect uranium enrichment in discrete deposits. 

Economic factors

Grade and tonnage These occurrences are highly variable in size and concentration. Deposits contain trace to 1–2 wt.% U3

O8, and individual 

deposits have historically produced a few thousand pounds of U3O8.

In the Mountain City area, cumulative production was 18,617 lb U3O8, as follows:

Rim Rock Mine, 4,240 lb U3O8 (average grade 0.28 wt.% U3O8); 

Race Track Mine 9,866 lb U3O8 (average grade 0.24 wt.% U3O8);

South Fork and Pixley Claims 4,511 lb U3O8 (average grade 0.12 wt.% U3O8). 

Deposits were mined from workings that are several hundred feet long; mineralization is described as a few to tens of feet 

thick.
Importance Past production, relatively high uranium grades and widespread distribution of these deposits is noteworthy.

For the hydroallogenic class of deposits, nationwide in all resource categories (probable, possible and speculative) NURE 

estimated 157 million pounds U3O8 in the $30/lb U3O8 cost category and 716 million lb U3O8 in the $100/lb cost 

category (1980s prices). Most of this potential resource was identified in the Basin and Range resource region where, 

NURE estimated 148 million lb U3O8 in the $30/lb U3O8 cost category and 653 million pounds U3O8 in the $100/lb cost 

category. Note that the higher cost category is cumulative.

Other assessment and exploration guides

Potential sources for leachable uranium including tuffaceous material and possibly granitic rocks.

Permeable sediments deposited on a paleo-topographic surface that allows transport of uranium-rich groundwater into host rocks.

Reductants within host rocks including charcoal, carbonaceous debris, clay, and pyrite.

Examples

In/near focal areas Nine deposits identified in the Mountain City region, Wells quadrangle, Nevada and Idaho.

Elsewhere Truckee Formation (Tertiary) in Nevada.

References

Mickle, D.G., and Matthews, G.W., eds., 1978, Geologic characteristics of environments favorable for uranium deposits: U.S. Department of Energy 

Report GJBX-67 (78), 250 p.

Proffitt, J.L., Mayerson, D.L., Parker, D.P., Wolverson, N., Antrim, D., Berg, J., and Witzel, F., 1982, National uranium resource evaluation, Wells 

quadrangle, Nevada, Idaho and Utah: U.S. Department of Energy publication PGJ/F-070 (82), 246 p.

Appendix 3 157
158 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Zeolites (Closed-Basin Subtype)

[cm, centimeter; m, meter; wt.%, percent]

Synonyms Closed-system zeolites.

Commodities Analcime, chabazite, clinoptilolite, erionite, mordenite, phillipsite.

Byproducts: bentonite, fluorite, pumicite, potassium feldspar.

Description Microcrystalline zeolite-bearing vitric tuff that consists chiefly of analcime, chabazite, clinoptilolite, mordenite, 

phillipsite, and sometimes erionite. Deposit may consist of one or several stacked zeolite layers separated by 

subeconomic or barren beds.

Geological environment

Rock types Rhyolitic to dacitic, vitric tuff. Associated to rocks include bedded evaporites (trona, halite, borates), mudstone, diatomite, 

oil shale.

Age range Late Paleozoic to Holocene, but most deposits are Cenozoic.

Depositional environment Lacustrine basins that received silicic, vitric material either directly by airfall or by reworking. The saline lake water 

commonly was of the sodium carbonate-bicarbonate variety and had a pH of 9 or greater. These lakes are common in 

arid and semi-arid regions where annual evaporation exceeds rainfall.

Tectonic setting(s) Closed hydrographic basins in either block-faulted terrains (such as the Basin and Range Province) or trough valleys 

associated with rifting. Lakes are commonly in block-faulted terranes or rift valleys.

Associated deposit types Continental-basin bedded evaporites; finely crystalline, disseminated fluorite in lacustrine rocks.

Deposit description

Ore mineralogy Analcime, chabazite, clinoptilolite, erionite, mordenite, phillipsite. 

Alteration In certain highly alkaline and saline lacustrine deposits, siliceous and alkali zeolites have been replaced during late 

diagenesis by analcime or potassium feldspar in the central part of the basin.

Ore controls Grain size and permeability of the host silicic, alkali-rich, vitric tuff. Salinity, pH, and ratios of alkali and alkaline-earth ions 

in the pore water are important.

Geochemical signatures B, Li in lacustrine environment of sodium carbonate-bicarbonate type.

In most cases, zeolites can be detected and positively identified only by direct analytical techniques, such as x-ray 

diffraction. Lithogeochemistry may be a useful tool.

Geophysical signature Possible use of color-composite imagery from airborne multispectral scanner data to distinguish zeolitic tuffs.

Magnetics: Regional geology/structure. Gravity: Regional geology/structure. Radiometrics: Lithology.

Other assessment and exploration guides

Regional depositional environment of silicic, vitric tuffs in an alkaline, saline-lake deposit.

Alteration of tuff to zeolite require high alkalinity and lake brines rich the HCO3 ion.

Host rock of vitric tuff of rhyolitic or dacitic composition; lateral zonation of zeolites and associated silicate minerals.

Ashfalls of glassy tuffs into alkaline-saline playas or rift lakes are ideal settings for high-grade deposits.

Unmetamorphosed or very low metamorphic-grade environments.

Molds of saline minerals, chemical delta of calcite or aragonite, associated dolomitic mudstone, occurrence of bedded or nodular chert.

Zeolites are finely crystalline and resemble bedded diatomite, feldspar, or bentonite in outcrop. Combination of x-ray diffraction and ammonia cation 

exchange capacity (CEC) are essential in the early screening of zeolite prospects.

Concentric zonation and lateral gradation in a basinward direction of unaltered volcanic glass to alkali-rich, silicic zeolites to analcime and then to 

potassium feldspar in the central part of the depositional basin.

Economic factors

Grade and tonnage Thickness of the zeolitic tuffs commonly ranges from 10 cm to 10 m. Areal extent is commonly tens to hundreds of square 

kilometers. The cutoff grade varies greatly. For example, a 10 to 20 cm thick ore bed at Bowie contains 60 to 80 wt.% 

chabazite. Obviously, this zone would not have been economic if the main ore mineral was clinoptilolite. Most of the 

commercial clinoptilolite deposits contain between 50 wt.% and 90 wt.% zeolite.

Importance This deposit type contains the largest variety of zeolite species, accounts for most of the present zeolite production in the 

United States, and is an important source for chabazite, erionite, and phillipsite in the United States.

Examples

In /near focal areas McDermitt caldera, Nevada; Bear River zeolite deposit, southeast Idaho.
Elsewhere Miocene-Pliocene Big Sandy Formation, Mohave County, Arizona; Bowie deposit, Arizona.

References

Eyde, T.H., and Holmes, D.A., 2006, Zeolites, in Kogel, J.E., Trivedi, N.C., Barker, J.M., and Krukowski, S.T., eds., Industrial minerals and rocks: 

Littleton, Colo., Society for Mining, Metallurgy, and Exploration, Inc., p. 139–165.

Sheppard, R.A., 1991, Descriptive model of sedimentary zeolites, deposit subtype—Zeolites in tuffs of saline, alkaline-lake deposits in Orris, G.J., and 

Bliss, J.D., eds., Some industrial mineral deposit models—Descriptive models: U.S. Geological Survey Open-File Report 91-11–A, p. 19–21, accessed 

February 1, 2016, at http://pubs.usgs.gov/of/1991/ofr-91-0011-a/ofr-91-0011a.pdf.

Sheppard, R.A., and Simandl, G.J., 1999, Closed-basin zeolites, in Simandl, G.J., Hora, Z. D., and Lefebure, D.V., eds., Selected British Columbia mineral 

deposit profiles, volume 3—Industrial Minerals: British Columbia Ministry of Energy and Mines, Open File 1999-10, accessed February 1, 2016, at 

http://www.unalmed.edu.co/~rrodriguez/MODELOS/columbia/Closed%20Basin%20Zeolites.htm.

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160 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Zeolites (Open-Basin Subtype)

[cm, centimeter; m, meter; wt.%, percent]

Synonyms Open-system zeolites.

Commodities Chabazite, clinoptilolite, mordenite, phillipsite (bentonite, pumicite).

Description Microcrystalline zeolites crystallized in relatively thick, generally nonmarine tephra sequences that commonly show a 

more or less vertical zonation of zeolites and associated silicate minerals and that reflects the chemical modification of 

meteoric water as it flowed through the vitric sequence. The zeolites crystallized in the postdepositional environment 

over periods ranging from thousands to millions of years.

Geological environment

Rock types Tuffs having a broad compositional range, including rhyolite to dacite, trachyte or phonolite, and basalt to basanite. The 

silicic tuffs commonly were deposited as nonwelded ash flows. Associated with rhyolite to basalt flows; fluviatile 

mudstone, sandstone, and conglomerate; diatomite.

Age range Mesozoic to Holocene, but most are Cenozoic.

Depositional environment Most deposits are nonmarine (fluviatile and lacustrine), but some are shallow marine.

Tectonic setting(s) Variety of nonmarine and shallow marine basins in volcanic terrains. Some thick tuffaceous deposits were air-laid onto the 

land surface and not into water.

Associated deposit types The zonation of the open-system type of zeolite deposit is similar to the upper zones of burial diagenesis (burial 

metamorphism) that affected thick sequences of silicic, vitric tuffs. Associated deposits include pumicite and bentonite.

Deposit description

Ore mineralogy Chabazite, clinoptililite, mordenite, phillipsite.

Alteration In silicic tuff sequences, the alkali-rich siliceous zeolites (clinoptilolite and mordenite) in the upper part of the deposit are 

replaced at depth by analcime, potassium feldspar, and (or) albite.

Ore controls Grain size and permeability of host tuff; flow of meteoric water downward in an open hydrologic system; hydrolysis 

and solution of vitric material by the subsurface water in the upper part of the system raised the pH, activity of SiO2, 

and content of dissolved solids to values where zeolites crystallized; resulted in a vertical or near-vertical zonation 

of zeolites and other authigenic minerals; composition of the vitric material may have dictated which zeolite species 

precipitated; clinoptilolite and mordenite are common in silicic tuffs, but chabazite and phillipsite are common in mafic 

or trachytic tuffs.

Geochemical signatures None recognized. In most cases, zeolites can be detected and positively identified only by direct analytical techniques, 

such as x-ray diffraction. Lithogeochemistry may be a useful tool.

Geophysical signature Possible use of color-composite imagery from airborne multispectral scanner data to distinguish zeolitic alteration.

Other assessment and exploration guides

Regional depositional environment containing thick sequence of vitric tuffs of Cenozoic age.

Very low grade or unmetamorphosed volcaniclastic sequences typically containing large proportions of ignimbrites.

Vertical zonation of zeolites and associated authigenic silicate minerals in thick (hundreds to thousands of meters) tuffaceous sequences, especially 

siliceous tuffs of Neogene age that were air-laid on land. The vertical zonation commonly is (from top to bottom) unaltered vitric material±smectite to 

clinoptilolite±mordenite±opal-(cristobilite-tridymite) to analcime±potassium feldspar±quartz and then to albite±quartz. This zonation may cut across 

bedding.

Thickness of the zeolitic tuffs commonly ranges from hundreds to thousands of meters. Areal extent is commonly hundreds to thousands of square 

kilometers.

Zeolitic tuffs commonly resist weathering and may be ledge formers.

Economic factors

Grade and tonnage The value of zeolite deposits varies depending on the end product use and zeolite species present. Properties, such as 

cation exchange capacity for radionuclides, heavy metals or NH+4, are more meaningful than grade. This is because 

these properties are commonly different for the same zeolite species originating from two distinct deposits. The 

zeolite content of better deposits currently mined is estimated to have zeolite content above 60 wt.%, but may 

reach over 80 wt.%. Deposits supplying materials to control the odor to local farms may have zeolite content well 

below 50 wt.%, but must be close to the market.

The Si/Al ratio and exchangeable cation ratios of the zeolites affect certain uses. Cation exchange capacity and adsorption 

capacity for various gases are important. Color (due to iron staining) and the abundance of nonzeolitic minerals may 

limit use.
Importance Important sources of natural clinoptilolite and mordenite. Bentonite, attapulgite, and other materials known for their high 

absorbency may be cost effective alternatives to zeolites for specific ion exchange applications.

Examples

In /near focal areas Miocene Paintbrush Group tuffs, tuffaceous beds of Calico Hills, and Crater Flat Group tuffs at Yucca Mountain, Nye 

County, Nevada (clinoptilolite and mordenite).

Elsewhere Oligocene-Miocene John Day Formation, Oregon (clinoptilolite).

Death Valley Junction, California (clinoptilolite).

References

Eyde, T.H., and Holmes, D.A., 2006, Zeolites, in Kogel, J.E., Trivedi, N.C., Barker, J.M., and Krukowski, S.T., eds., Industrial minerals and rocks: 

Littleton, Colo., Society for Mining, Metallurgy, and Exploration, Inc. (SME), p. 139–165.

Sheppard, R.A., 1991, Descriptive model of sedimentary zeolites, Deposit subtype-zeolite in tuffs of open hydrologic systems, in Orris, G.J., and Bliss, 

J.D., eds., Some industrial mineral deposit models—Descriptive models: U.S. Geological Survey Open-File Report 91-11–A, p. 16–18, accessed 

February 1, 2016, at http://pubs.usgs.gov/of/1991/ofr-91-0011-a/ofr-91-0011a.pdf.

Sheppard, R.A., and Simandl, G.J., 1999, Open-system zeolites D01, in Simandl, G.J., Hora, Z.D., and Lefebure, D.V., eds., Selected British Columbia 

mineral deposit profiles, volume 3—Industrial Minerals: British Columbia Ministry of Energy and Mines, Open File 1999-10, accessed February 1, 

2016, at http://www.unalmed.edu.co/~rrodriguez/MODELOS/columbia/Closed%20Basin%20Zeolites.htm.

Appendix 3 161
162 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Sedimentary System (formed during deposition of the sediment)

Deposit types in the study area

Banded iron (Algoma type)

Lacustrine diatomite 
Banded Iron Formation (Algoma type)

[wt.%, weight percent; Mt, million metric tons; nT, nanotesla; Ga, giga-annum or billions of years; REE, rare earth elements]

Synonyms Volcanogenic iron formation, banded iron formation (BIF), taconite, itabirite.

Commodities Fe (Mn).

Description Oxide and carbonate lithofacies that contain 20 to 40 wt.% Fe as alternating layers and beds of micro- to macrobanded chert or quartz, magnetite, hematite, pyrite, pyrrhotite, iron carbonates, iron silicates, and manganese oxide 

and carbonate minerals. The deposits are interbedded with volcanic rocks, greywacke, and turbidite and pelitic 

sedimentary rocks; the sequences are commonly metamorphosed.

Geological environment

Rock types Mafic to felsic submarine volcanic rocks and deep-water elastic and volcaniclastic sedimentary rocks. Pillowed 

greenstones, intermediate to felsic tuffs and agglomerates, poorly sorted clastic sedimentary rocks. Also, greywacke, 

black shale, argillite, and chert interlayered with pyroclastic and other volcaniclastic beds or their metamorphic 

equivalents. Algoma-type iron formations and associated stratiform sedimentary rocks commonly show a prolific 

development of different facies types within a single stratigraphic sequence.

Age range Most widely distributed and achieve the greatest thickness in Archean terranes (2.9 to 2.5 Ga).

Depositional environment Volcano-sedimentary basins (greenstone belts of Precambrian shields) generally with rapid turbidite sedimentation and 

thick volcanic accumulations.

Tectonic setting(s) Volcanic arcs and at spreading ridges. Tectonically active Precambrian shields, most commonly preserved in Precambrian 

shields.

Associated deposit types Kuroko massive sulfides, Homestake Au deposits.

Deposit description

Ore mineralogy Magnetite, hematite; some deposits consist of siderite interbedded with pyrite and pyrrhotite.

Alteration No syngenetic alteration, but commonly metamorphosed to varying degrees and weathered.

Ore controls Iron-rich stratigraphic horizons with little clastic sedimentation, often near volcanic centers. Some Algoma-type ironformations contain ore deposits due to metamorphic enhancement of grain size or structural thickening of the mineralized horizon.

Geochemical signatures Elevated values for Fe and Mn; at times elevated values for Ni, Au, Ag, Cu, Zn Pb, Sn, W, REE, and other minor 

elements.

Geophysical signature Gravity and magnetic methods can be used to delineate greenstone belts within granite-greenstone terranes at provincial 

to regional scales. Magnetic low and gravity high anomalies are usually associated with relatively nonmagnetic, dense 

greenstone terranes, whereas magnetic high and gravity low anomalies are usually associated with magnetic, lowdensity granitic. Gravity and magnetic methods can also be used for deposit-scale iron-formation studies. Most ironformation is associated with positive, high-amplitude gravity anomalies because it contains elevated abundances of 

high-density iron minerals, including magnetite and hematite. The magnetic signature of an iron formation is usually 

one to two orders of magnitude greater than that of its host rock.

Remote-sensing imaging spectroscopy can also be used in regional exploration because iron ore minerals and their alteration products have distinct spectral signatures.

The magnetic character of an iron formation is dependent on magnetic mineral content, alteration, structural attitude, and 

remanent magnetization. Iron formation with low magnetite content, or deposits in which magnetite has been oxidized 

to nonmagnetic hematite, produce low-amplitude anomalies of tens to hundreds of nT. Flat-lying deposits with normal 

magnetic polarization typically produce positive anomalies of about several thousand nT. Steeply dipping or folded 

iron-formation dominated by remanent magnetic polarization can produce anomalies with extremely high positive 

amplitudes of as much as tens of thousands of nT.

Electrical and electromagnetic methods are generally not applied to iron-formation exploration because the ore is resistive owing to high silica (chert) content. However, electrical techniques could be used to locate conductive sulfide 

facies or to delineate graphitic shale horizons associated with ore deposits.

Economic factors

Grade and tonnage Ore bodies range in size from about 1,000 to less than 100 Mt with grades ranging from 15 to 45 wt.% Fe, averaging 25 

wt.% Fe. Precambrian deposits usually contain less than 2 wt.% Mn.

Appendix 3 163
164 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Importance Algoma-type iron-formations are widely distributed and may provide a convenient local source of iron ore. No deposits 

of this type are currently mined in the United States.

Other assessment and exploration guides

Discrete, well-defined magnetite and hematite lithofacies of iron formation are preferred with a minimum of other lithofacies and clastic sediment interbedded in the crude ore.

Iron formations are usually large regional geological features that are relatively easy to define.

Detailed stratigraphic information is an essential part of the database required for defining grade, physical and chemical quality, and beneficiation and 

concentration characteristics of the ore.

Basin analysis and sedimentation modeling enable definition of factors that controlled the development, location and distribution of different iron formation lithofacies. 

Examples

In/near focal areas Atlantic City-South Pass, Wyoming.

Elsewhere Archean examples: Vermillion iron formation, Minnesota; Sherman Mine, Temagami, Ontario; Helen Mine, Wawa, 

Ontario; early Proterozoic example: Wadi Sawawin, Saudi Arabia.

References

Cannon, W.F., 1986, Descriptive model of Algoma Fe, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 

1693, p. 198.

Cannon, W.F., Hadley, D.G., and Horton, R.J., 1995, Algoma Fe deposits, in du Bray, E.A., ed., Preliminary compilation of descriptive geoenvironmental 

mineral deposit models: U.S. Geological Survey Open-File Report 95–0831 p. 209–214. [Also available at http://pubs.usgs.gov/of/1995/ofr-95-0831/.]

Gross, G.A., 1996, Algoma-type iron-formation, in Lefebure, D.V. and Hõy, T., eds., Selected British Columbia mineral deposit profiles, volume 2—

Metallic deposits: British Columbia Ministry of Employment and Investment, Open File 1996–13, p. 25–28, accessed April 23, 2016, at http://www.

empr.gov.bc.ca/Mining/Geoscience/MineralDepositProfiles/Pages/default.aspx.
Lacustrine Diatomite

[wt.%, weight percent; ft, feet; mi2, square mile; m.y., million years]

Synonyms Diatomaceous earth, kieselguhr, bog deposits.

Commodities Diatomaceous earth.

Description A chalk-like, soft, earthy siliceous sedimentary rock composed of diatoms. Lacustrine diatomite deposits formed in 

fresh to brackish water, generally associated with volcanism, found worldwide both in paleosediments and in recent 

lake sediments. Large amount of silica necessary for thick accumulations of diatoms is from the weathering and 

decomposition of silica rich volcanic rocks where silica is transported to the lake through runoff, groundwater, and hot 

or cold springs.

Geological environment

Rock types Diatomaceous lake sediments are typically hosted in volcanic rocks (craters, maars) and volcanic and sedimentary rocks 

(interbedded volcanic flows or tuffs).

Age range Miocene to Recent. Occurrences noted as early as Late Eocene. Diatomite deposits in the Great Basin region formed in 

some Neogene basins in response to different regional and local processes over the past 16 to 17 m.y.

Depositional environment Depositional conditions necessary for thick diatom accumulations: extensive, shallow basins for photosynthesis; abundant 

supply of soluble silica and nutrients; absence of toxic or growth-inhibiting constituents; sustained high rates of diatom 

reproduction; minimal clastic, chemical, and organic contamination; and a low energy environment for preservation of 

the delicate diatom structure.

Tectonic setting(s) Typically found in volcanic terrain. Often associated with crustal extension, such as in the Basin and Range Province of the 

Western United States.

Associated deposit types Trona, gypsum.

Deposit description

Ore mineralogy Diatomaceous silica, opal-cristobalite.

Alteration Diagenetic and postdiagenetic products can include various cements, chert phases, zeolites, and clay minerals, many of 

which form at the expense of the original sediment and diatoms, which undergo a structural transformation almost 

immediately after deposition, with a subsequent change to more stable silica phases. 

Ore controls The formation and localization of ore is controlled by the physical and chemical boundaries of the regional depositional 

environment.

Geochemical signatures None?

Geophysical signature Magnetics: regional geology/structure. Gravity: regional geology/structure. Radiometrics: lithology. Apparent resistivity 

and refraction seismic surveys have been used as exploration tools. Varying thermal characteristics of diatomaceous 

sediments have been noted using narrow pass-band infrared imagery.

Economic factors

Grade and tonnage Deposits commonly extend over areas of 1 to 25 mi2

 and attain thicknesses of 10 to >200 ft. Deposits covering <1 mi2 and 

<10 feet thick are generally uneconomic. Chemical analyses: 80.0–95.0 wt.% SiO2, 1.0–6.0 wt.% Al2O3, 0.4–2.2 wt.% 

Fe2O3, 0.2–3.5 wt.% CaO, and minor to trace amounts of TiO2, MgO, Na2O, K2O, and P2O5.

Importance The United States is the world’s largest producer of diatomite.

Other assessment and exploration guides

Tectonostratigraphic setting.

Basinal sediments.

Overburden typically <5:1.

Examples

In/near focal areas Dickshooter deposit, Idaho.

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166 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Elsewhere Juntura and Otis basins, Oregon.

References

Shenk, J.D., 1991, Lacustrine diatomite, in Orris, G.J., and Bliss, J.D., Some industrial mineral deposit models; descriptive deposit models: U.S. 

Geological Survey Open-File Report 91–11–A, p. 26–30. 

Wallace, A.R., 2003, Regional geologic setting of Late Cenozoic lacustrine diatomite deposits, Great Basin and surrounding region—Overview and 

plans for investigation, in Bliss, J.D., Moyle, P.R., and Long, K.R., eds. Contributions to industrial-mineral research: U.S. Geological Survey Bulletin 

2209–B, 16 p. [Also available at http://pubs.usgs.gov/bul/b2209/.]

Wallace, A.R., Frank, D.G., and Founie, Alan, 2006, Freshwater diatomite deposits in the Western United States: U.S. Geological Survey Fact Sheet 

2006–3044, 2 p. [Also available at http://pubs.usgs.gov/fs/2006/3044/.]
Surficial-Mechanical (Placer) Mineral System

Deposit types in the study area

Heavy mineral placer

Placer and paleoplacer gold

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168 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Heavy Mineral Placers

[wt.%, percent; Mt, million metric tons; REE, rare earth elements; PGE, platinum-group elements]

Synonyms Placer deposits, placer heavy mineral deposits, black sand deposits, stream placers

Commodities Ti-minerals (ilmenite, rutile), zircon, monazite, ± garnet, cassiterite, sillimanite, staurolite, xenotime, PGE

Description Concentrations of water-deposited minerals with high specific gravities; formed by the physical-mechanical concentration of 

bedrock minerals freed by weathering, then deposited and reworked in fluvial environments.

Geological environment

Rock types Unconsolidated to weakly consolidated layers of fluvial sediments (alluvium).

Age range Quaternary; principally modern, Holocene and Pleistocene alluvial sediments.

Depositional environment Ancient and modern alluvial valleys fed by streams and rivers that drain terranes where abundant high-grade metamorphic 

rocks or igneous rocks crop out. Streams carry the sediments to valleys, where they are deposited and reworked by fluvial 

processes.

Tectonic setting(s) Various.

Deposit description

Ore mineralogy Mainly gold, ilmenite, rutile, zircon, monazite; occasionally cassiterite, xenotime

Alteration None

Ore controls High-grade metamorphic or heavy mineral-rich igneous are source rocks. Fluvial processes in streams and rivers concentrate 

the heavy-minerals.

Geochemical signatures Ti, Hf, REE, Th, U, Nb, and Ta in stream sediments can be pathfinder elements for gold (Au), ilmenite (FeTiO3

), rutile 

(TiO2), zircon ((Zr,Hf,U)SiO4), monazite ((Ce,La,Y,Th)PO4), xenotime (YPO4), platinum-group minerals, and euxenite 

((Y,Ca,Ce,U,Th)(Ti,Nb,Ta)2O6).

Geophysical signature High-resolution magnetic, gravity, and seismic-reflection surveys can map paleotopography and outline paleochannels; 

electromagnetic surveys may be useful in detecting conductive material in paleochannels; ground-penetrating radar may 

be useful in delineating the geometry of shallow channels and deposits; and radiometric surveys can locate radioactive 

heavy-mineral concentrations.

Economic factors

Grade and tonnage Grade and tonnage in fluvial placers can vary considerably (see Robertson and Storch, 1955; Anderson, 1958; Storch and 

Holt, 1963; Staatz and others, 1979, 1980). The average heavy-mineral content of Idaho placers sampled by the U.S. 

Bureau of Mines ranged from 0.10 to 1.06 wt.% of the sediments, with an average of 0.5 wt.% (Staatz and others, 1980).

Importance Heavy-minerals sands are a principal source of Zr and a primary source of Ti for the TiO2

 pigments industry. However, 

currently these elements are almost entirely produced from heavy-mineral sands deposited in coastal environments. 

Heavy mineral placers are significant sources of Au in some areas of the United States, such as Alaska, and also in some 

countries elsewhere (Yeend and others, 1989).

Other assessment and exploration guides

Identify streams and rivers that drain terranes with outcropping (1) abundant high-grade metamorphic or igneous rocks or (2) ore bodies that host native 

gold, electrum, or platinum-group minerals

Restrict the assessment areas to unconsolidated or weakly consolidated Quaternary fluvial sediments as a first-level exploration and assessment guideline.

Detailed geologic mapping that distinguishes amongst Quaternary sedimentary units can benefit the search for deposits. For example, alluvium is the target 

host of heavy mineral sands, whereas landslide and colluvium generally lack the sorting necessary to form concentrations of heavy minerals.

Limited only to near-surface, unconsolidated or weakly consolidated alluvial sediments. Economic deposits of this type, regardless of their heavy-mineral 

content (grade), typically are exploited only if they lie at or within a few tens of meters of the surface.

Examples

In/near focal area Central Idaho valleys that are within or adjacent to the Idaho batholith (Staatz and others, 1980).
Elsewhere Stream deposits in the Piedmont region of North Carolina and South Carolina (Staatz and others, 1979).

References

Anderson, A.L., 1958, Uranium, thorium, columbium, and rare earth deposits in the Salmon region, Lemhi County, Idaho: Idaho Bureau of Mines and 

Geology Pamphlet 115, 81 p.

Force, E.R., and Creely, Scott, 2000, Titanium mineral resources of the western U.S.—An update: U.S. Geological Survey Open-File Report 00–442, 37 p.

Jones, J.V., III, Karl, S.M., Labay, K.A., Shew, N.B., Granitto, M., Hayes, T.S., Mauk, J.L., Schmidt, J.M., Todd, E., Wang, B., Werdon, M.B., and Yager, 

D.B., 2015, GIS-based identification of areas with mineral resource potential for six selected deposit groups, Bureau of Land Management Central 

Yukon Planning Area, Alaska: U.S. Geological Survey Open-File Report 2015–1021, 78 p., 5 appendixes, 12 pls., accessed May 1, 2016, at http://dx.doi.

org/10.3133/ofr20151021. 

Garnett, R.H.T., and Bassett, N.C., 2005, Placer deposits, in Hedenquist, J.W., Thompson, J.F.H., Goldfarb, R.J., Richards, J.P., eds., Economic Geology 

one hundredth anniversary volume 1905–2005: Society of Economic Geologists, p. 813–843.

Robertson, A.F., and Storch, R.H., 1955, Rock Creek radioactive mineral placer area, Blaine County, Idaho: U.S. Atomic Energy Commission RME–3129, 

25 p.

Storch, R.H., and Holt, D.C., 1963, Titanium placer deposits of Idaho: U.S. Bureau of Mines Report of Investigations 6319, 69 p.

Staatz, M.H., Armbrustmacher, T.J., Olson, J.C., Brownfield, I.K., Brock, M.R., Lemons, J.F., Jr., Coppa, L.V., and Clingan, B.V., 1979, Principal thorium 

resources in the United States: U.S. Geological Survey Circular 805, 42 p.

Staatz, M.H., Hall, R.B., Macke, D.L., Armbrustmacher, T.J., and Brownfield, I.K., 1980, Thorium resources of selected regions in the United States: U.S. 

Geological Survey Circular 824, 32 p.

Yeend, W., and Shawe, D.R., 1989, Gold in placer deposits: U.S. Geological Survey Bulletin 1857–G, 19 p.

Youngson, J. H., and Craw, D., 1995, Evolution of placer gold deposits during regional uplift, central Otago, New Zealand: Economic Geology, v. 90, 

p. 731–745.

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170 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Placer and Paleoplacer Gold

[g/t, grams per metric ton; Mt, million metric tons; PGE, platinum-group elements]

Synonyms Holocene placer deposits; terrace placers; fluvial, alluvial, colluvial placers, buried-channel placers, paleoplacers.

Commodities Au, platinum-group elements (PGEs), and Sn.

Description Concentrations of valuable detrital (gold, PGE, cassiterite) formed by sedimentary processes where the high specific 

gravity of the minerals results in their concentration at or near the surface, usually in Holocene fluvial deposits or in 

buried valleys (typically with at least several meters of overlying barren material, usually till, clay or volcanic rocks), 

mainly as channel-lag and gravel-bar deposits.

Geological environment

Rock types Generally mature, well-sorted, fine to coarse-grained, quartz-rich sands and sandstones, and mature, well-rounded, clastsupported, quartz-rich gravels and conglomerates.

Age range Mainly Tertiary and Quaternary. Older paleoplacers are rare due to poor long-term preservation of deposits in high-relief, 

subaerial environments.

Depositional environment Surficial fluvial placer: large, high-order, stream channels and along bedrock in high-energy, steep-gradient, low-sinuosity, 

single-channel streams.

Alluvial fan, fan-delta and delta deposit: relatively unconfined depositional settings dominated by massive or graded 

sands and gravel.

Colluvial placers: develop from residual deposits associated with primary lode sources by sorting associated with 

downslope migration of heavy minerals.

Paleoplacers: Incised paleochannels in mountainous areas such as high-gradient narrow bedrock-floored valleys 

(paleogulches); high-level, abandoned tributary valleys with intermediate gradients large, buried trunk valleys (on the 

order of 100 meters deep, a few hundred meters wide and >1 km long) with low channel gradients; channels buried in 

modern alluvial valleys with gradients similar to the modern streams.

Tectonic setting(s) Stable intracratonic basin, platform, and intermontane plateau settings characterized by long periods of erosion and 

reworking of clastic sediments; accretionary orogenic belts, commonly in proximity to major faults that expose the 

bedrock sources to weathering and erosion.

Associated deposit types The source mineral-deposit type will determine the type of placer deposit (lode gold deposit will erode to produce placer 

gold).

Deposit description

Ore mineralogy Native gold, gold nuggets, flakes, and grains, electrum, PGE minerals, cassiterite (gems).

Alteration Fe and Mn oxide precipitates common; Ag-depleted rims of Au grains increase in thickness with age.

Ore controls Fluvial settings: channel irregularities, bedrock depressions and below natural riffles created by fractures, joints, cleavage, 

faults, foliation or bedding planes that dip steeply and are oriented perpendicular or oblique to stream flow. Basal 

gravels over bedrock typically contain the highest placer concentrations. Fine-grained placer concentrations occur 

where channel gradients abruptly decrease or stream velocities lessen.

Gold in alluvial fan placers is found in debris- flow sediments and in interstratified gravel, sand and silt.

Colluvial placers are best developed on steeper slopes, generally over a weathered surface and near primary lode sources.

Geochemical signatures Anomalous concentrations of Au, Ag, Hg, As, Cu, Fe, Mn, Ti, or Cr in stream sediments. Au fineness (relative Ag content) 

and trace element geochemistry (Hg, Cu) of Au particles can be used to relate placer and lode sources. 

Geophysical signature Magnetic, gravity, and seismic-reflection surveys to map paleotopography and outline paleochannels; inducedpolarization/resistivity surveys to locate conductive disseminated mineralization; electromagnetic surveys may be 

useful in detecting conductive material in paleochannels; ground-penetrating radar may be useful in delineating 

the geometry of shallow channels and deposits; and radiometric surveys to locate radioactive heavy-mineral 

concentrations.

Economic factors

Grade and tonnage Deposits are typically high tonnage (0.1 to 100 Mt) but low grade (0.05-0.25 g/t Au, 50-200 g/t Sn). Placer concentrations 

are highly variable both within and between individual deposits. 
Importance Historically, placer gold deposits accounted for more than two-thirds of the world’s gold. Shallow alluvial placers also 

account for a large part of world tin (mainly from Southeast Asia and Brazil) and diamond (Africa) production.

Other assessment and exploration guides

Quartz pebble conglomerates near lode gold sources.

Recognition of paleochannels in stratigraphy.

Panning and other methods of gravity sorting are used to identify concentrations of gold and other heavy minerals. Many placer gold 

paystreaks overlie clay beds or dense tills and in some camps these “false bottom” paystreaks are important.

Examples

In/near focal areas Yankee Fork placers, Idaho; Homestake paleoplacer, Idaho.

Elsewhere Klondike Au district, Yukon.

References

Garnett, R.H.T., and Bassett, N.C., 2005, Placer deposits, in Hedenquist, J.W., Thompson, J.F.H., Goldfarb, R.J., and Richards, J.P., eds., Economic 

Geology one hundredth anniversary volume 1905–2005, Society of Economic Geologists, p. 813–843.

Levson, V.M., 1995, Surficial placers, in Lefebure, D.V., and Ray, G.E., eds., Selected British Columbia mineral deposit profiles: British Columbia 

Geological Survey, Open File 1995–20, p. 21–23.

Levson, V.M., and Giles, T.R., 1995, Buried-channel placers, in Lefebure, D.V., and Ray, G.E., eds., Selected British Columbia mineral deposit profiles: 

British Columbia Geological Survey, Open File 1995–20, p. 25–28.

Yeend, W.E., 1986, Descriptive model of placer Au-PGE, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey, Bulletin 

1693, p. 261.

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172 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Other (Non-Locatable) Deposit Types

Deposit types in the study area

Dimension stone (sandstone and quartzite)

Sand and gravel

Volcanic ash (pumice and cinders)

Perlite
Dimension Stone (Sandstone and Quartzite)

[m, meter; t, metric ton; wt.%, weight percent; SEDEX, sedimentary exhalative; VMS, volcanogenic massive sulfide]

Synonyms High silica quartzite, quartz sandstone, silica rock silicastone. Bluestone, brownstone, freestone, arkose, greywacke, 

quartzite.

Commodities Building stone.

Description Uniform massive beds of sandstone with very few and well-spaced (more than 1 m) fractures and bedding planes. 

Sandstone must be suitable to be removed from a quarry face in square shaped blocks that are 10 t or larger with 

minimum waste. Metamorphic equivalent (quartzite) of uniform, massive beds of siliceous sediments, such as 

sandstone. These beds are commonly formed in sedimentary sequences. They have high silica contents with very 

limited impurities, usually less than 1 wt.%.

Geological environment

Rock types Siliceous sediments are found with a variety of clastic and carbonate rocks; quartzites are the metamorphic 

equivalents.

Age range Precambrian to Tertiary.

Depositional environment Shallow continental shelf, inland sea or large continental lacustrine basins with low energy environment and a steady 

supply of well sorted, detrital, sand size particles. The mineral composition is influenced by the regional climate 

over the source area; speed, type and intensity of weathering and speed of transport into the sedimentary basin.

Non-locatable tectonic setting(s) Quartzites are found in orogenic belts of all ages.

Associated deposit types Siliceous sediments—building stone; cherts—SEDEX and VMS deposits, marine diatomite.

Deposit description

Ore mineralogy Quartz; chert can also have other forms of amorphous and microcrystalline silica.

Alteration Secondary Fe-Mn hydroxides and (or) calcium carbonate along fractures.

Ore controls Source terrains that minimize impurities and depositional environments that includes long or repeated 

transportation with intensive wear of particles which includes separation from other silicates like feldspars for 

example. This may occur both by physical as well as chemical weathering.

Geochemical signatures In general, more than 98 wt.% silica with traces of other elements. High silica contents and low aluminosilicate and 

carbonate contents.

Geophysical signature Only applicable where there is significant contrast in physical rock properties of silica-rich rocks with surrounding 

rocks.

Economic factors

Grade and tonnage Each use has its very specific requirement for the particle size and shape, physical strength and permissible amounts 

of different impurities. Generally silica contents have to be 98 wt.% with significant impurities removable by 

processing.

Even high-purity orthoquartzite usually contains minute titanium minerals, which are detrimental for silicon metal 

(even at 0.2% TiO2). Also, even trace of Ca can, as well as iron oxide and alumina, make silica unacceptable for 

specific end use.

Tonnage for 28 sandstone/quartzite silica deposits range from 0.3 to 42 Mt with grades of 87 to 97 wt.% SiO2. 

Importance Used for building and construction and decorative stone.

Other assessment and exploration guides

Large smooth bedrock exposures in cuts, on valley slopes and along shorelines lacking fragmented rock are good indicators. An air photo study can 

identify large outcrop areas and boulder fields.

Look for resistant ridges and outcrops and absence of impurities in hand sample visible to the naked eye.

Usually weather resistant, resulting in morphological highs.

Massive beds of thickness more than 1 m, may be layered or cross bedded, and uniform in appearance.

Deposits commonly extend over areas of at least several square kilometers. Usually the deposits are horizontal or tilted, and rarely folded.

Appendix 3 173
174 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Examples

In/near focal areas Idaho.

Elsewhere Texas, Indiana, Wisconsin, Massachusetts, Georgia.

References

Hora, Z.D., 1999, Silica-rich rocks, in Simandl, G.J., Hora, Z.D., and Lefebure, D.V., eds., Selected British Columbia mineral deposit profiles, 

volume 3—Industrial Minerals, Model R07: British Columbia Ministry of Energy and Mines, Open File 1999-10, accessed February 15, 2016, at 

http://www.empr.gov.bc.ca/Mining/Geoscience/MineralDepositProfiles/. 

Hora, Z.D., 1999, Dimension stone—Sandstone, in Simandl, G.J., Hora, Z.D., and Lefebure, D.V., eds., Selected British Columbia mineral deposit profiles, volume 3—Industrial Minerals, Model R06: British Columbia Ministry of Energy and Mines, Open File 1999-10, accessed February 15, 2016, at 

http://www.empr.gov.bc.ca/Mining/Geoscience/MineralDepositProfiles/.

Orris, G.J., 1992, Preliminary grade and tonnage model of sandstone/quartzite silica, in Orris, G.J., and Bliss, J.D. Industrial minerals deposit models—

Grade and tonnage models: U.S. Geological Survey Open-File Report 92-437, 84 p., accessed April 25, 2016, at http://pubs.usgs.gov/of/1992/ofr-92-

0593/593in.pdf.
Sand and Gravel

[km, kilometer; t, metric ton; kt, thousand metric tons; g/t, grams per metric ton; ASTM, American Society for Testing and Materials; CSA, Canadian Standards Association]

Synonyms Aggregate, granular deposits, fluvial and glaciofluvial sediments, ice-contact deposits, outwash, alluvial sand and gravel, 

beach sand and gravel.

Commodities All-purpose construction aggregate, special fill, railroad ballast.

Description Surficial sediment of sand and gravel deposited as a stream channel and terrace deposits, alluvial fans, and glacial or 

marine deposits. 

Geological environment

Rock types Usually poorly to moderately well-sorted pebble, cobble and (or) boulder gravel with variable proportions of fine- to 

coarse-grained sand; deltaic deposits locally interbedded with glaciomarine or glaciolacustrine silts and clays; ice–

proximal glaciofluvial deposits commonly interbedded with till or glaciogenic debris flow deposits; fluvial sands and 

gravels often overlain by floodplain silts and organic deposits.

Age range Mainly Holocene and Pleistocene in glaciated areas; Holocene to Tertiary in unglaciated regions.

Depositional environment Streams, alluvial fans, glaciated areas.

Tectonic setting(s) Generally unimportant. Sand and gravel deposits occur in high energy stream sediments in all tectonic belts. In coastal 

areas, isostatic or tectonic uplift produces raised landforms that are readily mined.

Associated deposit types Placer deposits of gold, platinum-group elements (PGE), gemstones and garnet.

Deposit description

Ore mineralogy Composition of aggregate particles depends on the source areas. Provenance is also a major factor in determining the 

quality of the resulting aggregate product. Bedded and schistose rocks usually provide lower quality products, whereas 

massive igneous rocks and metamorphic rocks, such as gneisses and quartzites, produce better quality aggregate. In 

sedimentary source areas, limestones and cemented sandstones are better than shales, siltstones, or weak sandstone.

Alteration Soft and weak rocks are a deleterious component of every type of construction aggregate. Prolonged weathering may 

weaken some otherwise competent rock types. This is particularly true for older Pleistocene and Tertiary deposits in 

glaciated areas, and for all deposits in nonglaciated areas. Percolating groundwater may result in coating of gravel 

particles with calcium carbonate, clay, or iron hydroxides. Such coatings may negatively affect the strength and 

durability of bonding with cement in concrete structures.

Ore controls The composition of the bedrock in the source area has a major impact on aggregate quality. A variety of factors influence 

the usability of granular sediment for individual products, which frequently have distinct quality requirements. Quality 

of construction aggregate for particular end uses is controlled by a number of physical and chemical parameters 

specified in ASTM and CSA Standards. The main factors influencing suitability for different end uses are the relative 

proportions of competent rock types, components reactive with cement like chert, other amorphous silica varieties, 

volcanic glass, sulfides, and organics like peat. Other important criteria include the absence of clay and silt; clean clast 

surfaces; isometric shapes and granulometric composition. Sometimes in the absence of a quality aggregate, some 

granular deposits can be improved by more sophisticated processing. Use of a different type or higher proportion of 

cement in a concrete mix may be another solution.

Geochemical signatures None.

Geophysical signature Ground-penetrating radar can delineate the geometry, structure, and thickness of granular deposits provided they are not 

overlain by clay or clay-rich till. Shallow seismic and resistivity surveys can help outline the thickness and homogeneity 

of a granular deposit, particularly the presence of clay layers or till, and depth of the groundwater level.

Economic factors

Grade and tonnage Grade is determined by ASTM or CSA specifications and can be highly variable, depending on location and intended 

use. Tonnage also can vary widely. For example, even a small deposit of a few hundred thousand tons may be an 

important source for local use in populated areas. Such a deposit, however, must contain aggregate that does not require 

complicated processing. Similar examples are borrow pits used in road construction and maintenance.

Appendix 3 175
176 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Importance Sand and gravel are the main, basic construction materials for building cities and infrastructure. Building an average 

family home requires about 100 t of aggregate; for a school it takes approximately 15,000 t; for 1 km of 4-lane 

highway, between 40 and 60 kt of aggregate are needed.

Other assessment and exploration guides

Geologic maps serve as a primary source of information for beginning the search for new sources of aggregate.

Examples

In/near focal areas All focal areas have sand and gravel (salable minerals). 

References

Hora, Z.D., 1999, Sand and gravel, in Simandl, G.J., Hora, Z.D., and Lefebure, D.V., eds., Selected British Columbia mineral deposit profiles, 

volume 3—Industrial Minerals: British Columbia Ministry of Energy and Mines, Open File 1999-10, accessed February 15, 2016, at http://www.

empr.gov.bc.ca/Mining/Geoscience/MineralDepositProfiles/.

Knepper, D.H., Jr., Langer, W.H., and Miller, S.H., 1994, Remote sending and airborne geophysics in the assessment of natural aggregate resources: U.S. 

Geological Survey Open-File Report 94–158, 62 p, accessed April 25, 2016, at https://pubs.er.usgs.gov/publication/ofr94158.

Langer, W.H., 1988, Natural aggregates of the conterminous United States: U.S. Geological Survey Bulletin 1594, 33 p.
Volcanic Ash (cinders and pumice)

[km, kilometer; t, metric ton; Mt, million metric tons; ASTM, American Society for Testing and Materials]

Synonyms Volcanic scoria, volcanic ejecta, agglomerate, pyroclastics, lapilli, tuff.

Commodities Lightweight aggregate, landscaping aggregate, anti-skid sand, stonewashing pumice, “lava (barbecue) rock,” pozzolan, 

abrasive powders, absorbents, insulation fill, filler, filtration media.

Description Unconsolidated pumice, cinder and other pyroclastic deposits are usually found near a volcanic vent or edifice. It is 

typically the vesicular pyroclastic material that is exploited because of its appearance or attractive strength to weight 

ratio. Pumice occurs in felsic pyroclastic flows, air-fall blankets, and flow domes; cinder usually forms basaltic 

pyroclastic tephra cones and blankets.

Geological environment

Rock types Ash, lapilli, and agglomerate pyroclastic deposits. Associated with lava flows, high-level dikes, ash flows, and flow domes. 

All these rock types can vary in composition from rhyolite to basalt.

Age range Any age, although preserved deposits are commonly Tertiary to Holocene.

Depositional environment Pumice in calderas, lava flow dome complexes and Plinian-type central eruptions. Blanket deposits are found in the vicinity of stratovolcanoes.

Tectonic setting(s) Volcanic arcs and rift zone belts.

Associated deposit types Perlite, open and closed system zeolites, and andesite dimension stone. Secondary deposits are produced by erosion of 

primary deposits and subsequent deposition in stream and riverbeds, for example, in Kansas and Oklahoma or along the 

Waikato and Wanganui Rivers in New Zealand.

Deposit description

Ore Pumice, cinder, volcanic ash, bombs, blocks.

Alteration Clay minerals, alunite, zeolites, hematite, limonite.

Ore controls Pumice, a product of highly viscous rhyolite magma, commonly forms an ashfall blanket surrounding the source vent. 

Its thickness depends on intensity and longevity of eruption. Large volumes of pumice and pumiceous rhyolite also 

accumulate in the upper parts of rhyolite and obsidian flow domes, as well in ash-flow tuffs in calderas. Volcanic cinder, 

because of low viscosity and higher density of the mafic magma, is more concentrated in proximity to the vent as coneshaped deposits.

Geochemical signatures For pumice, look for rhyolite compositions.

Geophysical signature Ground-penetrating radar can delineate structure and thickness of a pyroclastic deposit. Shallow seismic surveys can help 

to outline the presence of lave flows or dikes in cinder cones, as well as the boundary between pumiceous rhyolite and 

nonporous rock facies.

Economic factors

Grade and tonnage Deposits range in size from 10,000 t to 10 Mt, although occasionally, deposits may reach 400 Mt. The average production 

from a single deposit in Western United States is approximately 35,000 t per year for cinder and 10,000 t per year for 

pumice. Use of a lightweight aggregate has several ASTM specifications for particle sizing and unit weight, so do some 

specific end uses, like stone washing.

Importance Regionally important as a specialty aggregate, but represents only a small part of the overall aggregate market in North 

America (0.1 percent in the year 2000).

Lightweight aggregate transportation costs ultimately determine the geographic extent of the market, as it can be 

substituted by expanded shales and similar products. Only specialty products, like “barbecue lava rock,” stone-washing 

pumice, absorbents, landscaping cinder, and filter media can reach more distant markets. The demand for these specialty 

products is only a fraction of total production.

Other assessment and exploration guides

Proximity to volcanic vents, particularly on the downwind side.

Areas with remnant volcanic edifices.

Remote sensing and air photo interpretation are useful to map the limits of cinder and pumice blanket areas.

Examples

In/near focal areas All focal areas except North-Central Montana. 

References

Hora, Z.D., 1999, Volcanic ash. Cinders and Pumice, in Simandl, G.J., Hora, Z.D., and Lefebure, D.V., eds., Selected British Columbia mineral deposit 

profiles, volume 3—Industrial Minerals: British Columbia Ministry of Energy and Mines, Open File 1999-10, accessed February 15, 2016, at http://

www.empr.gov.bc.ca/Mining/Geoscience/MineralDepositProfiles/.

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178 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Perlite

[wt.%, weight percent; km, kilometer; t, metric ton; g/t, grams per metric ton; kg, kilogram; Mt, million metric tons; °C, degree Celsius; ASTM, American 

Society for Testing and Materials]

Synonyms Onion skin rhyolitic glass, pitchstone, obsidian.

Commodities Expanding perlite (pumice, foundry flux, synthetic zeolite feedstock).

Description Hydrated volcanic glass, usually of rhyolite composition, formed through secondary alteration by the incorporation of 

water into the glass/silica structure. It is often distinguished by vitreous, pearly luster and concentric (onion skin) 

fractures. When heated, it will expand as much as 10 to 40 times its original volume.

Geological environment

Rock types Perlite is hosted by flow domes and lava flows of rhyolite composition. Most obsidian contains less than 1 wt.% of total 

water (water left after heating to 105 °C); the hydration of perlite increases the water content level to 2 to 5 wt.% but 

may reach as much as 10 wt.%.

Age range Normally Tertiary through middle Quaternary, occasionally older.

Depositional environment Rapidly cooled volcanic rocks of rhyolite composition occurring as the glassy parts of domes and flows, vitric tephra, chill 

margins of dikes and sills, and welded ash-flow tuffs.

Tectonic setting(s) Orogenic rift belts and volcanic arcs.

Associated deposit types Vitric tephra, ash-flow tuffs, pumiceous rhyolite and pumicite.

Deposit description

Ore Expandable hydrated siliceous volcanic glass. Most commercial perlites are “high silica rhyolites” with 75 to 77.5 wt.% 

SiO2. In a few countries, obsidian and pitchstone are also expanded.

Alteration Because volcanic glass is unstable, devitrification changes Tertiary age or older volcanic glass into a microcrystalline 

equivalent (there may be some rare exceptions of older volcanic glass being preserved). Alteration can introduce clay 

minerals and (or) chalcedony and can produce deposits of halloysite.

Ore controls Perlite forms carapaces that partially or fully comprise extrusive domes and flows and tephra and tuff beds, where percolating meteoric water had access to hydrate the glassy volcanic material. Because felsic flows are viscous, most perlite 

deposits form close to the volcanic vent.

Geochemical signatures Felsic volcanic rocks with more than 65 wt.% silica, preferably greater, as much as 75 wt.%; water contents of 2 to 10 wt.%.

Geophysical signature Hydrated glass can be distinguished from nonhydrated obsidian by electrical properties.

Economic factors

Grade and tonnage Average perlite has an expanded density between 20 and 40 kg per cubic meter. Some deposits can contain as much as 

15 percent nonperlite material. The quality of perlite products is controlled by performance standards developed by 

the Perlite Institute, as well as ASTM specifications. Deposits range in size from less than 5 Mt to more than 100 Mt. 

Annual production in North America is reported between 500,000 and 600,000 t annually. It comes from 10 production 

centers in the Western United States.

Importance Important for horticulture and for construction products. Expanded perlite has a very limited number of substitutes; 

therefore, it may be shipped considerable distances. For example, Greece has exported perlite to the eastern seaboard of 

North America, whereas New Mexico supplies Canada and numerous Eastern U.S. locations. Perlite is usually mined 

from open pits (the Caliente deposit in Nevada is underground) and processed in expanding plants located in market 

areas. Raw perlite is shipped by truck or by rail and boat to more distant processing plants. The average capacity of 

an expanding plant is about 10,000 t per year. As a relatively large volume product, perlite products are sensitive to 

transportation costs.

Other assessment and exploration guides

A small portable blowtorch is the most effective field test. A potential perlite either expands or decrepitates; nonexpanding rock just glows red. 

Detailed mapping must delineate rock type, perlite textures, and the abundance of contaminants, such as clay, felsite, phenocrysts, and obsidian.

A great variability of textures and zonation require careful deposit modeling.

For drilling the potential deposit, the core diameter must be large enough to ensure high and representative core recovery.

Examples

In/near focal areas Caliente, Nevada.

Elsewhere Grants, Socorro, New Mexico; Malad City, Idaho.

References

Hora, Z.D., 1999, Perlite, in Simandl, G. J., Hora, Z.D., and Lefebure, D.V., eds., Selected British Columbia mineral deposit profiles, volume 3—Industrial 

Minerals: British Columbia Ministry of Energy and Mines, Open File 1999-10, accessed February 15, 2016, at http://www.empr.gov.bc.ca/Mining/Geoscience/MineralDepositProfiles/.
There is no global consensus on a definition for “strategic 

and critical” commodities. In general, it has been accepted as 

those materials that are considered vital to support societal 

requirements and Government policy. The Defense Logistics 

Agency, Strategic Materials, in the U.S. Department of 

Defense, is the leading U.S. agency for the analysis, planning, 

procurement, and management of materials critical to national 

security. Among the agency’s many functions, is the acquiring, 

upgrading, rotating, and disposing of materials needed to 

support national defense as authorized under the Strategic and 

Critical Material Act (50 U.S.C. 98 et seq.)(Defense Logistics 

Agency, 2016). The stocks held by the agency include 

mineral-based commodities (alloys, compounds, metals, and 

minerals) that are not found or produced in sufficient quantity 

in the United States to meet the Nation’s requirements and 

results in a dependence on foreign sources. 

Table 4-1 lists most of the elements of the non-fuel mineralbased commodities held as stock by Defense Logistics Agency 

(DLA), as of September 30, 2015 (U.S. Geological Survey, 2016). 

Table 4-1. Elemental listing of materials stockpiled by the Defense Logistics Agency. 

[Materials in the inventory may be in the form of mineral ores and concentrates but are more commonly held as advanced 

materials alloys, compounds, or metals (U.S. Geological Survey, 2016)]

Stockpiled material

Beryllium Manganese Tantalum 

Chromium Mercury Tin

Cobalt Nickel Titanium 

Columbium Platinum-group elements Tungsten 

Germanium Silicon Zinc

Lithium Talc

Table 4-2. Potential acquisitions of materials selected by the Defense Logistics Agency for fiscal year 2016.

[Materials may be in the form of alloys, metals, compounds, or advanced materials (Defense Logistics Agency, 2016)]

Potential acquisitions

Boron carbide Germanium metal Triamino-trinitrobenzene 

Carbon fibers Lithium cobalt oxide Tungsten-rhenium alloy

Cadmium Zinc Tellurium Lithium-nickel-cobalt-aluminum oxide Yttrium oxide

Dysprosium metal Mesocarbon microbeads 

Ferro-niobium Tantalum

Table 4-2 lists proposed additions of non-fuel mineral commodities 

in fiscal year 2016 (Defense Logistics Agency, 2016). 

None of the locatable mineral commodities containing 

the elements listed in tables 1 and 2 are currently produced in 

significant amount and (or) as the primary source of revenue from 

mines operating within the assessment area; however, they may be 

produced as minor byproducts. Individual market demand profiles 

include a discussion related to a mineral commodity’s strategic and 

critical importance.

References Cited

Defense Logistics Agency, 2016, Strategic materials: Defense 

Logistics Agency Web site, accessed on March 18, 2016, at 

http://www.dla.mil/HQ/Acquisition/StrategicMaterials.aspx.

U.S. Geological Survey, 2016, Mineral commodity summaries 

2016: U.S. Geological Survey, 202 p., accessed on March 18, 

2016, at http://dx.doi.org/10.3133/70140094.

Appendix 4. Strategic and Critical Materials

Appendix 5. Market-Demand Commodity Profiles

The following market-demand profiles for the locatable 

mineral commodities relevant to the Sagebrush MineralResource Assessment (SaMiRA) project conducted by the 

U.S. Geological Survey (USGS) are listed in alphabetical 

order below by commodity:

Antimony

Alloys containing antimony are used in a variety of 

applications, including lead-acid storage batteries and solders for 

joining pipes that carry potable water. Antimony is converted to 

antimony trioxide, which is primarily used in the flame-retardant 

industry in applications such as children’s clothing and aircraft 

seats (U.S. Geological Survey, 2013).

Publications of the USGS National Minerals Information 

Center reported that no marketable antimony was recovered 

from mines in the United States in 2014 and 2015. In 2013, one 

operation in Pershing County, Nevada, produced less than 1,000 

metric tons (t) of unprocessed ore that is not within the assessment 

area. Information regarding the ore’s antimony content was not 

available. The company experienced financial challenges during 

2014, and the mine was place on care-and-maintenance status in 

early 2015. Although no or only negligible quantities of antimony 

have been recovered from domestic mines since 2000, the 

United States produced an average of 326 t per year of antimony 

contained in ore and concentrates from 1993 through 1999. Most 

of this antimony was recovered as a byproduct from silver-copper 

sulfide ore mined primarily in northern Idaho. There has also been 

some intermittent mining in central Idaho (Yellow Pine District) 

near Stibnite from 1925 to 1997. Midas Gold Corp. is considering 

the reactivation of the Yellow Pine property. Although, it is 

primarily a gold project, the deposit contains significant amounts 

of potentially recoverable antimony (Midas Gold Corp., 2016).

Primary antimony metal and oxides were produced 

from imported concentrates at a smelter in Montana. In 2014, 

approximately 4,230 t of secondary antimony was recovered, 

almost entirely as a component of lead alloys from recycled leadacid batteries at secondary lead smelters. 

The United States relies on foreign sources of raw and 

processed antimony to meet its commercial and strategic 

requirements. In 2014, the United States imported approximately 

24,200 t of antimony contained in concentrates, raw metal, and 

other unwrought forms, and net import reliance, as a percentage 

of apparent consumption, was 84 percent. In 2014, China 

accounted for 76 percent of global antimony mine production 

and for 76 percent of antimony metal and oxide (metal content) 

imported to the United States. In 2014, world antimony mine 

production was estimated to be 158,000 t. Other major producers 

and their percentage share of world production in 2014 were 

Russia (approximately 6 percent); Australia (4 percent); and 

Bolivia, Tajikistan, and Turkey (3 percent each). From the year 

2000 through 2014, the compound annual growth rate of world 

antimony production was 2 percent. 

The U.S. Defense Logistics Agency does not hold a 

stockpile of antimony, although it is monitored for supply 

adequacy. Antimony sulfide is used by the U.S. Department 

of Defense (DOD) as a constituent in percussion primers for 

ammunition. Currently, there are few, if any, substitutes for 

antimony sulfide that meet DOD requirements, and sources of 

antimony sulfide are primarily limited to China. Antimony is not 

typically categorized as a critical metal (National Science and 

Technology Council, 2016).

The average annual antimony price since the year 2000 

ranged from a low of about $1,430 per metric ton ($/t) in 2001 to 

a high of $14,300/t in 2011. In 2015, the nominal average price 

of antimony had dropped to approximately $7,200/t (Kelly and 

Matos, 2007; Llewellyn, 1993; Guberman, 2015, 2016). 

References Cited

Guberman, D.E., 2015, Antimony [advanced release] in Metals 

and minerals: U.S. Geological Survey, Minerals Yearbook 

2013, v.1, p. 6.1–6.8, accessed February 9, 2016, at http://

minerals.usgs.gov/minerals/pubs/commodity/antimony/

myb1-2013-antim.pdf.

Guberman, D.E., 2016, Antimony: U.S. Geological Survey 

Mineral Commodity Summaries 2016, p.24–25, accessed 

February 4, 2016, at http://minerals.usgs.gov/minerals/pubs/

commodity/antimony/mcs-2016-antim.pdf.

Kelly, T.D., and Matos, G.R., compilers, 2007, Historical 

statistics for mineral and material commodities in the 

United States: U.S. Geological Survey Data Series 140, ver. 

2011, accessed February 4, 2016, at http://minerals.usgs.

gov/minerals/pubs/historical-statistics/.

Llewellyn, T.O., 1993, Antimony: U.S. Bureau of Mines 

Mineral Commodity Summaries 1993, p. 22–23.

Midas Gold Corp., 2016, Midas Gold projects: Midas 

Gold Corp. Web page, accessed March 10, 2016, at 

http://www.midasgoldinc.com/s/goldenmeadows.

asp?ReportID=445651.

National Science and Technology Council, 2016, Assessment 

of critical minerals—Screening methodology and initial 

application: National Science and Technology Council, 

Subcommittee on Critical and Strategic Mineral Supply 

Chains of the Committee on Environment, Natural 

Resources, and Sustainability, 47 p., accessed March 10, 

2016, at https://www.whitehouse.gov/sites/default/files/

microsites/ostp/NSTC/csmsc_assessment_of_critical_

minerals_report_2016-03-16_final.pdf.
182 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

U.S. Geological Survey, 2013, Metal prices in the United States 

through 2010: U.S. Geological Survey Scientific Investigations 

Report 2012–5188, p. 7–12, accessed February 10, 2016, at 

http://pubs.usgs.gov/sir/2012/5188/.

Barite

Barite is the mineralogical name for barium sulfate 

(BaSO4), also known as barytes. In pure form, it has the highest 

specific gravity of any nonmetallic mineral, which makes it 

useful as a filler, extender, and weighting agent in a wide variety 

of applications including cement, paints, plastics, and rubber. 

However, its primary use is as a weighting agent in fluids used in 

the drilling of oil and natural gas wells. Globally, more than 80 

percent of barite is used for this purpose (The Barytes Association, 

undated), and in the United States this use exceeds 97 percent. 

For most applications, barite needs to be ground to a small 

uniform size before use. The American Petroleum Institute 

(API) sets specifications for barite used in drilling fluids. The 

most important characteristic of barite used in drilling mud is 

its specific gravity (SG), and until 2010, the API specification 

called for a minimum SG of 4.2. After concerns developed about 

dwindling reserves of 4.2-SG barite in the United States, the API 

issued a new edition of API Specification 13A, Specification 

for Drilling Fluids Materials, adding specifications for 4.1-SG 

barite (American Petroleum Institute, 2010). Since the adoption 

of the 4.1-SG specification, 4.1 and sub 4.1-SG barite gained 

widespread acceptance in the U.S. drilling industry. Barite’s other 

advantageous properties include low abrasion, low oil absorption, 

chemical and physical inertness, nontoxicity, low solubility, and 

being relatively inexpensive in comparison to alternatives.

The United States was the world’s fourth-ranked producer 

of barite, producing approximately 8 percent of total world 

production in 2014. The leading producers and their percentage 

share of world production were China (44 percent), India (19 

percent), and Morocco (11 percent) (McRae, 2015a). The United 

States is the world’s leading barite consumer, using an average of 

approximately 3 million metric tons (Mt) per year for the past 10 

years. Nearly all U.S. production is used domestically. Domestic 

barite production peaked in the early 1980s, when more than 2 Mt 

was produced annually. A large decrease in domestic consumption, 

coupled with the availability of low-priced foreign imports 

contributed to a sudden decrease in domestic barite production in 

the mid-1980s (Bleiwas and Miller, 2015; Kelly and Matos, 2014). 

During this same time period, China surpassed the United States 

as the world’s leading barite producer, and U.S. imports surpassed 

domestic production. Since 2000, the United States net import 

reliance, as a percentage of apparent consumption, has averaged 

approximately 80 percent. Barite is not considered a critical or 

strategic mineral under any of the widely accepted definitions.

Although numerous States have historically produced barite, 

barite mine production in Nevada has long led all other domestic 

production, the bulk of which has been concentrated in Elko 

(located within or near the boundaries of the assessment area) and 

Lander Counties. The Big Ledge Mine in Elko is within the Public 

Land Survey System (PLSS) and has historically produced barite 

as the need arises. It was restarted in 2007 by Spirit Minerals, LP, 

and operated currently by National Oilwell Varco, LP. Nevada 

is thought to contain the leading share of U.S. barite resources. 

Since 2007, USGS estimated that U.S. barite reserves were 

approximately 15 Mt, most of which is located in ore deposits 

in Nevada (Miller, 2007; McRae, 2015a). It should be noted that 

the latest revision to the reserve estimate was made when 4.2-SG 

barite was the industry standard and before the widespread usage 

of 4.1 and sub 4.1-SG barite. 

After peaking in the early 1980s, consumption trended 

downward through 2003, and U.S. barite consumption began 

resurgence in 2005 owing to advances in the application of 

horizontal drilling techniques and hydraulic fracturing in 

onshore shale and other tight formations. Concern was growing, 

however, within the barite industry about an imminent shortage 

of 4.2 SG barite. 

As a consequence, exploration and development projects 

have been very active in northeastern Nevada in the past 

decade. Three oil services companies have either opened or 

begun development of new mines, two in Lander County 

and one in Elko County. A fourth company completed an 

expansion project of its mine in Elko County and the Bureau 

of Land Management announced in late 2015 that it was 

preparing an environmental impact statement for another 

expansion that would extend mine life by an additional 8 years 

(Bureau of Land Management, 2015). These same companies 

have also invested in processing capacity. In 2005, Nevada’s 

grinding mill capacity was estimated to be 650,000 metric 

tons per year (Roskill Information Services, Ltd., 2006, p. 

152). In 2015, grinding capacity was an estimated 1.7 Mt per 

year, more than double the amount of current annual mine 

production (Allen, 2015). 

Numerous smaller projects have also received permits; 

primarily projects reprocessing tailings piles at abandoned mine 

operations. Because barite is often associated with gold deposits, 

gold exploration companies have been known to enter into 

agreements allowing other companies to explore for barite on their 

properties (McRae, 2015b). It is unknown if any of these projects 

have come to fruition.

Since 1990, the price of barite per metric ton ($/t), 

expressed in constant 1998 U.S. dollars was lowest in 2003 at 

about $40/t to high of about $96/t in 2012 (Kelly and Matos, 

2014). The price of crude barite had increased significantly from 

the mid-2000s through 2014 in response to increased demand 

for domestic drilling by the oil and gas industry. In 2014, the 

average 1998 U.S. dollar unit value for crude barite was $93/t, 

free on board (f.o.b.), mine. 

The number of operating drill rigs exploring for oil and gas 

traditionally has been a good barometer of barite consumption or 

industry stockpiling. The monthly average of drill rigs operating 

in December 2014 was 1,882, which by December 2015 had 

decreased to 714. Petroleum production in the United States 

is expected to decline through 2017, and many companies are 

expected to scale back investment in new projects (U.S. Energy 

Information Administration, 2016). The decrease in drilling 
activity is estimated to have reduced domestic barite consumption 

by approximately 25 percent to 30 percent in 2015. Because of 

this decline, it is likely that many of the aforementioned barite 

exploration and development projects have been put on hold 

until oil prices stabilize. However, a return to growth in the 

U.S. onshore oil and gas industry will necessitate a return to 

development of barite resources.

References Cited

Allen, John, 2015, Barytes sourcing and marketing: IMFormed 

Oilfield Minerals and Markets Forum Houston 2015, Houston, 

Texas, May 27–29, Presentation.

American Petroleum Institute, 2010, API Specification 13A 18th 

Edition, August 2010: American Petroleum Institute, accessed 

March 11, 2016, at http://www.api.org/~/media/Files/Certification/

Monogram-APIQR/program-updates/13A-18th-Edition-PurchGuidlines-R1-2011-12-06.pdf.

Barytes Association, The, [undated], What is barytes?—Introduction: 

Derbyshire, United Kingdom, The Barytes Association, accessed 

March 10, 2016, at http://www.barytes.org/barytes.html.

Bleiwas, D.I., and Miller, M.M., 2015, Barite—A case study of 

import reliance on an essential material for oil and gas exploration 

and development drilling: U.S. Geological Survey Scientific 

Investigations Report 2014–5230, 6 p., accessed March 10, 2016, 

at http://dx.doi.org/10.3133/sir20145230.

Bureau of Land Management, 2015, BLM seeks input on proposed 

Rossi mine expansion: Bureau of Land Management news release, 

Sept. 15, accessed March 10, 2016, at http://www.blm.gov/nv/st/

en/info/newsroom/2015/september/blm_seeks_public_input.html.

Kelly, T.D., and Matos, G.R., comps., 2014, Historical statistics 

for mineral and material commodities in the United States: U.S. 

Geological Survey Data Series 140, accessed March 10, 2016, at 

http://minerals.usgs.gov/minerals/pubs/historical-statistics/.

McRae, M.E., 2015a, Barite: U.S. Geological Survey Mineral 

Commodity Summaries 2015, p. 24–25, accessed January 25, 

2016, at http://minerals.usgs.gov/minerals/pubs/commodity/

barite/mcs-2015-barit.pdf.

McRae, M.E., 2015b, Barite in Metals and minerals: U.S. 

Geological Survey, Minerals Yearbook 2013, v.1, p. 9.1–9.8, 

accessed January 25, 2016, at http://minerals.usgs.gov/minerals/

pubs/commodity/barite/myb1-2013-barit.pdf.

Miller, M.M., 2007, Barite: U.S. Geological Survey Mineral 

Commodity Summaries 2007, p. 30–31, accessed January 25, 

2016, at http://minerals.usgs.gov/minerals/pubs/commodity/

barite/mcs-2008-barit.pdf.

Roskill Information Services, Ltd., 2006, The economics of barytes: 

Roskill Information Services, Ltd., 2006, 254 p.

U.S. Energy Information Administration, 2015, Short-term energy 

outlook (STEO): U.S. Energy Information Administration, 12 p., 

accessed March 10, 2016, at http://www.eia.gov/forecasts/steo/pdf/

steo_full.pdf.

Bentonite Clay

Bentonite predominantly consists of smectite-group minerals 

(usually montmorillonite) with minor amounts of feldspar, biotite, 

and quartz. Bentonite is divided into two major types, nonswelling 

(calcium rich) and swelling (sodium rich). Nonswelling bentonite 

is used primarily as a binding agent for pelletization of iron ore 

and foundry sand, as well as for water treatment and filtering. 

The molecular structure of bentonite with sodium as the major 

exchangeable cation enables it to absorb several times its dry 

weight in fluid. The swelling behavior of the clay makes it useful 

as an important component in drilling muds required for drilling 

in oil and gas exploration and development, as an impermeable 

liner for isolating fluids from the environment, and for pet-waste 

absorbents (Flanagan, 2016; Industrial Minerals Association–

North America, 2016; Virta, 2015).

In 2014, the USGS National Minerals Information Center 

(NMIC) reported that the United States produced a combined total 

of 25.9 million metric tons (Mt) of six types of clays. At 4.8 Mt, 

bentonite clay represented about 19 percent of the total clay sold 

or used by domestic producers in 2014. Swelling clays represented 

about 95 percent of that amount (Flanagan, 2016; Virta, 2015). 

In 2013, Alabama was the leading domestic producer of 

nonswelling bentonite, followed by Mississippi and California 

(Virta, 2015). These States are not included in the assessment area.

In 2013, Wyoming led all States in the production of swelling 

bentonite with a 97 percent share, followed, in descending order 

of tonnage, by Utah, Texas, California, Oregon, Nevada, Montana, 

and Colorado (Virta, 2015). The States, which include the 

assessment area, are briefly discussed in the following paragraphs 

in descending order of estimated production.

Much of Wyoming’s bentonite production originated in Big 

Horn County, which is outside of the SaMiRA project assessment 

area. Since 2005, bentonite production has been reported in Crook, 

Hot Springs, Johnson, Natrona, Washakie, and Weston Counties. 

None of these counties are included in the assessment area (U.S. 

Geological Survey, 2008e, 2015e).

Utah has produced bentonite since 2005 in Sanpete and 

Sevier Counties. The two counties are not included in the 

assessment area (U.S. Geological Survey, 2008d, 2015d). 

Bentonite production in Oregon has been reported since 2005 

in Malheur County, which is included in the assessment area, and 

in Crook County, which is not included in the assessment area 

(U.S. Geological Survey 2008c, 2015c) 

Bentonite production in Montana has been reported in Carter 

County, Montana, since 2005, which is outside of the assessment 

area. New operations in Valley County are within the assessment 

area (U.S. Geological Survey 2008a, 2015a). 

Bentonite production has been reported since 2005 in the 

Nevada counties of Esmeralda, Humboldt (possibly hectorite and 

Appendix 5 183
184 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

not bentonite), Nye, and Pershing. Humboldt County is in the 

assessment area, but the others are not (U.S. Geological Survey 

2008b, 2015b).

It is possible that bentonite was mined within the assessment 

area and not identified for reasons which may include (1) clay 

production reported without identifying type(s), (2) incomplete and 

inconsistent reporting, and (3) intermittent low-tonnage production.

In 2014, the quantity of bentonite sold and used in the United 

States of 4.8 Mt was more than the 3.47 Mt that was sold and used 

in 1990. From 1990 to 2014, the compound annual growth rate in 

production was approximately 1.4 percent. The trend of increasing 

domestic production of bentonite from the mid-1990s was driven 

by its increased use as pet-waste absorbent and in domestic drilling 

for oil and gas exploration and development. Domestic production 

of bentonite has leveled off somewhat in recent years as demand 

for conventional drilling has decreased in response to weaker 

petroleum prices, increased use of proppants made from kaolin 

for horizontal drilling, and increases in the amount of imported 

bentonite (Flanagan, 2016; Kelly and Matos, 2007; Virta, 1993, 

1994, 1996, 2004, 2015).

In 2014, approximately 22,000 metric tons (t) of bentonite 

was imported to the United States. This was a significant increase 

from 1990, when about 2,045 t were imported, but still only 

represents less than one-half of one percent of domestic usage. The 

principal sources of bentonite imports in 2013 were Mexico (43 

percent), China (23 percent), Egypt (13 percent), and the United 

Kingdom (12 percent) (Virta, 2015 Kelly and Matos, 2007). 

In 2014, the United States exported about 901,000 t of 

bentonite, or about 19 percent of estimated domestic sales. Canada 

was the primary recipient of U.S. bentonite exports (49 percent), 

followed by Japan (11 percent) and China (6 percent). For the 

years 1990 through 2014, exports reached a high of 1.43 Mt, but 

declined shortly thereafter in response to the global recession 

(Flanagan, 2016; Virta, 2015). 

The United States is a net exporter of bentonite. The 

U.S. bentonite industry is able to meet domestic demand with 

relatively low imports while at the same time continuing to export 

comparatively high tonnages of the clay (Flanagan, 2016).

Apparent consumption of bentonite in the United States 

was approximately 2.78 Mt in 1990 and trended upward to about 

3.48 Mt in 2013. Apparent consumption increased during the 

24-year period as a function of growing demand for use in drilling 

muds and absorbents, which was met by an increase in domestic 

production and imports relative to the amount of bentonite 

exported (Kelly and Matos, 2007). 

The U.S. Defense Logistics Agency does not hold a stockpile 

of bentonite, and the commodity is not considered of strategic 

or critical importance. The United States has large reserves 

and significant production. The United States does not rely on 

imports to meet its commercial and strategic requirements for the 

commodity. 

From 1990 to 2014, the total world bentonite mine 

production increased from 9.6 Mt to an estimated 16.1 Mt, for an 

average compound annual growth rate of 2.2 percent. In 1990, the 

United States was the world leader in bentonite production with 

3.47 Mt that represented a 36 percent share of world production. In 

2014, the United States maintained its position as the world leader 

in bentonite production with 4.8 Mt, albeit with a lower percentage 

share of 30 percent. Other major producers of bentonite in 2014 

and estimates of their respective share of global production were 

China (22 percent) and Greece and India (about 7 percent each). 

The increase in world bentonite production was driven primarily 

by demand in the oil and gas energy sector and the broad uses 

of the clay as an absorbent and binder in iron ore pelletizing and 

foundry sand to meet the needs of a growing global population 

(Flanagan, 2016; Kelly and Matos, 2007; Virta, 1992). 

The average annual unit value per metric ton ($/t) of 

bentonite, expressed in constant 1998 U.S. dollars, ranged from 

a low of $17.10/t in 2008 during the global recession to a high of 

about $45.50/t in 2014. The increase in price over the past several 

years was primarily driven by higher demand for drilling mud. 

The price and level of demand for bentonite may be somewhat 

lessened over the next few years as if drilling for oil and gas 

continues to decrease (Flanagan, 2016; Kelly and Matos, 2007; 

Virta, 1992, 1993, 2004, 2015).

References Cited

Flanagan, D.M., 2016, Clays: U.S. Geological Survey Mineral Commodity Summaries 2016, p. 50–51, accessed February 22, 2016, 

at http://minerals.usgs.gov/minerals/pubs/commodity/clays/mcs2016-clays.pdf.

Industrial Minerals Association–North America, 2016, What is 

bentonite?: Washington, DC, Industrial Minerals Association–

North America, accessed March 3, 2016, at http://www.ima-na.

org/?page=what_is_bentonite.

Kelly, T.D., and Matos, G.R., comps., 2007, Historical statistics 

for mineral and material commodities in the United States: U.S. 

Geological Survey Data Series 140, ver. 2011, accessed February 

22, 2016, at http://minerals.usgs.gov/minerals/pubs/historicalstatistics/.

U.S. Geological Survey, 2008a, The mineral industry of Montana, in

Area reports—Domestic: U.S. Geological Survey Minerals Yearbook, 2005, v. II, p. 28.1–28.7, accessed March 3, 2016, at http://

minerals.usgs.gov/minerals/pubs/state/2005/myb2-2005-mt.pdf.

U.S. Geological Survey, 2008b, The mineral industry of Nevada, in

Area reports—Domestic: U.S. Geological Survey Minerals Yearbook, 2005, v. II, p. 30.1–30.12, accessed March 3, 2016, at http://

minerals.usgs.gov/minerals/pubs/state/2005/myb2-2005-nv.pdf.

U.S. Geological Survey, 2008c, The mineral industry of Oregon, 

in Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook, 2005, v. II, p. 39.1–39.4, accessed March 3, 2016, 

at http://minerals.usgs.gov/minerals/pubs/state/2005/myb2-

2005-or.pdf.

U.S. Geological Survey, 2008d, The mineral industry of Utah, in Area 

reports—Domestic: U.S. Geological Survey Minerals Yearbook, 

2005, v. II, p. 47.1–47.9, accessed March 3, 2016, at http://

minerals.usgs.gov/minerals/pubs/state/2008/myb2-2008-ut.pdf.
U.S. Geological Survey, 2008e, The mineral industry of Wyoming, 

in Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook, 2005, v. II, p. 53.1–53.6, accessed March 3, 2016, 

at http://minerals.usgs.gov/minerals/pubs/state/2005/myb2-

2005-wy.pdf.

U.S. Geological Survey, 2015a, The mineral industry of Montana, 

in Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook, 2010–2011, v. II, p. 28.1–28.12, accessed March 3, 

2016, at http://minerals.usgs.gov/minerals/pubs/state/2010_11/

myb2-2010_11-mt.pdf.

U.S. Geological Survey, 2015b, The mineral industry of Nevada, 

in Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook, 2010–2011, v. II, p. 30.1–30.17, accessed March 3, 

2016, at http://minerals.usgs.gov/minerals/pubs/state/2010_11/

myb2-2010_11-nv.pdf.

U.S. Geological Survey, 2015c, The mineral industry of Oregon, 

in Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook, 2010–2011, v. II, p. 39.1–39.9, accessed March 3, 

2016, at http://minerals.usgs.gov/minerals/pubs/state/2010_11/

myb2-2010_11-or.pdf.

U.S. Geological Survey, 2015d, The mineral industry of Utah, in

Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook, 2010–2011, v. II, p. 47.1–47.14, accessed March 3, 

2016, at http://minerals.usgs.gov/minerals/pubs/state/2010_11/

myb2-2010_11-ut.pdf.

U.S. Geological Survey, 2015e, The mineral industry of Wyoming, 

in Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook, 2010–2011, v. II, p. 53.1–53.8, accessed March 3, 

2016, at http://minerals.usgs.gov/minerals/pubs/state/2010_11/

myb2-2010_11-wy.pdf.

Virta, R.L., 1992, Clay, in Metals and minerals: U.S. Bureau of 

Mines, Minerals Yearbook 1992, v. 1, p. 379–412, accessed 

February 22, 2016, at http://minerals.usgs.gov/minerals/pubs/

commodity/clays/190494.pdf.

Virta, R.E., 1993, Clays: U.S. Bureau of Mines Mineral 

Commodity Summaries 1993, p. 48–49.

Virta, R.L., 1994, Clay, in Metals and minerals: U.S. Bureau 

of Mines, Minerals Yearbook 1994, v. 1, p. 1–23, accessed 

February 22, 2016, at http://minerals.usgs.gov/minerals/pubs/

commodity/clays/190494.pdf.

Virta, R.L., 1996, Clays: U.S. Geological Survey Mineral 

Commodity Summaries 1995, p. 44–45, accessed on February 

22, 2016, at http://minerals.usgs.gov/minerals/pubs/commodity/

clays/claysmcs96.pdf.

Virta, R.L., 2004, Clay and shale, in Metals and minerals: U.S. 

Geological Survey, Minerals Yearbook 2004, v. 1, p. 18.1–

18.28, accessed February 22, 2016, at http://minerals.usgs.gov/

minerals/pubs/commodity/clays/claysmyb04.pdf.

Virta, R.L., 2015, Clay and shale [advanced release], in Metals and 

minerals: U.S. Geological Survey, Minerals Yearbook 2013, v. 1, 

p. 18.1–18.22, accessed February 22, 2016, at http://minerals.usgs.

gov/minerals/pubs/commodity/clays/myb1-2013-clays.pdf.

Copper

Copper finds its major use in electrical applications 

distributed throughout all sectors of the global economy through 

use in the generation and distribution of electricity, signal transfer, 

and the circuitry of electronic devices. Other uses include 

plumbing tube, heat exchangers, building hardware, and roofing, 

and coinage. 

Publications of the USGS National Minerals Information 

Center (NMIC) reported that in 2014 the United States 

remained the world’s fourth-ranked mine producer of copper, 

behind Chile, China, and Peru, and accounted for approximately 

7 percent of global production. Although from 1990 through 

2014 U.S. copper mine production decreased at a compound 

annual rate of 1 percent, from 1990 through 1997, copper mine 

production rose by 22 percent to a record-high 1.94 million 

metric tons (Mt) before trending downward to 1.11 Mt in 

2010. From 2011 through 2014, U.S. mine production trended 

upward, increasing by 22 percent from 1.11 Mt through 1.36 Mt 

(Brininstool, 2016).

Mine production during the next several years will likely 

remain close to the current level. The principal mining States for 

copper were, in descending order of production, Arizona, Utah, 

New Mexico, Nevada, and Montana, which altogether accounted 

for more than 99 percent of domestic production (Brininstool, 

2016). No significant copper production has been reported within 

the assessment area since at least 1990. Nearly all of the copper in 

the United States is recovered from ore extracted from large openpit mines that used conventional flotation to produce concentrate 

for smelting and refining or leaching and solvent extractionelectrowinning methods to recover refined copper.

The United States exports a significant amount of copper 

concentrate for offshore smelting and refining. In 2014, it was 

estimated that U.S. copper ore reserves contained approximately 

35 Mt of copper. In addition to 1.05 Mt of domestic primary 

refined copper production in 2014, an additional 796 thousand 

metric tons of copper was recovered from scrap. There are 

also large producer, merchant, and consumer stocks of copper 

maintained in the United States. The U.S. Defense Logistics 

Agency does not hold a stockpile of copper, having liquidated 

its inventories in 1993. Historically, copper has been considered 

a strategic and critical material, with various price controls, 

export controls, Government stockpiling, and production 

incentives through the World Wars and the Vietnam War. The 

United States currently produces a significant amount of copper 

relative to its reduced consumption levels, and domestically 

imported supplies of copper are varied and generally from the 

Western Hemisphere. Therefore, copper is no longer categorized 

as a strategic and critical commodity despite its importance to 

the U.S. economy.

Appendix 5 185
186 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

The United States relies on foreign sources of raw and 

processed copper to supplement its commercial and strategic 

requirements. In 2014, U.S. apparent consumption of refined 

copper was approximately 1.78 Mt. In 1990, net import reliance, 

as a percentage of apparent consumption, was 3 percent. By 

2014, net import reliance had increased to 31 percent as a result 

of increased exports of concentrates for offshore treatment 

because of decreased domestic smelting and refining capacity 

(Brininstool, 2016). 

From 1990 to 2014, the total world copper mine production 

more than doubled at an average compound annual growth 

rate of nearly 4 percent (Brininstool, 2016; Kelly and Matos, 

2007). Since 2000, world refined copper production increased 

at average compound annual growth rate of approximately 2.6 

percent, reaching about 21 Mt in 2014 with about 18 percent 

from secondary sources. The general trend of increased copper 

production reflects the growing global demand for use in 

consumer products, such as appliances and automobiles, and 

for building and upgrading infrastructure in China, India, and 

other developing economies. China has emerged as the leading 

driver for global demand, accounting for more than 40 percent 

of global consumption since 2011 and about 48 percent in 2014 

(International Copper Study Group, 2016, p. 19). Barring global 

economic recession, the trend of increasing consumption may 

continue for the balance of the decade.

The average annual domestic producer price per pound 

of copper in nominal dollars over the past decade ranged from 

a low of $1.73 per pound in 2005 to a high of $4.06 in 2011 

(Kelly and Matos, 2007). The price of the metal declined 

throughout 2015. In 2015, the average producer price was 

$2.56 per pound (M. Brininstool, USGS, written commun., 

January 21, 2016). In general, higher prices reflect periods of 

greater demand and a tightening of supply.

References Cited

Brininstool, M., 2016, Copper: U.S. Geological Survey Commodity 

Summaries 2015, p. 54–55, accessed on February 4, 2016, at 

http://minerals.usgs.gov/minerals/pubs/mcs/2016/mcs2016.pdf.

International Copper Study Group, 2016, December 2015 Copper 

Bulletin: Lisbon Portugal, International Copper Study Group, 

February 22, 53 p.

Kelly, T.D., and Matos, G.R., comps., 2007, Historical statistics 

for mineral and material commodities in the United States: 

U.S. Geological Survey Data Series 140, ver. 2011, accessed 

on February 4, 2016, at http://minerals.usgs.gov/minerals/pubs/

historical-statistics/.

Diatomite

Diatomite is a chalk-like, soft, friable, earthy, very finegrained, siliceous sedimentary rock comprised of fossilized diatom 

remains. Diatomite is used for filter aids (55 percent), as a cement 

additive (21 percent), as a filler (14 percent), as an absorbent (9 

percent), and in other applications (Crangle, 2013, 2016).

The USGS National Minerals Information Center (NMIC) 

reported that about 901,000 metric tons (t) of processed diatomite 

ore was sold and used by producers in the United States in 2014. 

The United States ranked first in global diatomite mine production. 

In 2014, diatomite was produced from mines in California, 

Nevada, Oregon, and Washington (Crangle, 2016). Diatomite 

production is ongoing or has occurred in the assessment area 

States since 2005 in the Nevada counties of Elko, Humboldt, 

and Washoe. Diatomite was previously mined in Lake County, 

Oregon, and a deposit was identified in Camas County, Idaho 

(Powers, 1947; Taylor, 1994).

In 2014, 901,000 t of diatomite was sold and used by 

producers, significantly more than the 631,000 t in 1990. The 

average annual growth rate was 1.5 percent over the period. In 

2014, U.S. diatomite reserves were estimated to be 250 million 

metric tons (Mt). The apparent consumption of diatomite in the 

United States increased from 488,000 t in 1990 to 823,000 t in 

2014 (Crangle, 2016; Kelly and Matos, 2007). 

In 2014, the United States exported about 82,000 t of 

diatomite compared to 488,000 t exported in 1990. The decrease 

in exports reflects the increased domestic consumption, as well 

as increases in production among some competing foreign 

producers, such as China. Approximately 4,000 t of diatomite 

were imported for domestic consumption in 2014 compared to 

1,000 t in 1990. Imports have not been a significant component of 

domestic consumption (Crangle, 2016; Kelly and Matos, 2007). 

For 2011–14, three countries accounted for 80 percent of U.S. 

diatomite imports—Mexico (30 percent), Canada (26 percent), 

and France (24 percent) (Crangle, 2016).

The United States is a net exporter of diatomite making its 

net import reliance as a percentage of apparent consumption zero 

for 2014, which has been the case since at least 1990 (Crangle, 

2016; Davis, 1992).

The U.S. Defense Logistics Agency does not hold a stockpile 

of diatomite. Diatomite is not considered a strategic or critical 

commodity because of substantial U.S. production and substantial 

reserves and stocks held by producers and consumers (Crangle, 

2016; Davis, 1992). In addition, substitutes exist for diatomite in 

most applications.

From 1990 to 2014, total world diatomite production 

increased from 1.68 Mt to 2.26 Mt for an average annual growth 

rate of about 1.2 percent. In 2014, the United States was the 

world leader in diatomite production with 901,000 t, which 

represented a 40 percent share. Other major diatomite producers 

in 2014 and their respective share of global production were 

China (19 percent), Peru (6 percent), and Argentina (4 percent). 

In 1994, China represented about 11 percent of world production 

(Taylor, 1994). Production in China for the years 1990–93 was 

not available.

According to reported by U.S. diatomite producers, the 

average unit value per metric ton ($/t) of diatomite ranged from 

a high of $283/t in 1993 to a low of about $170/t in 2009. In 

2014, the average unit value of diatomite in nominal dollars was 

approximately $298/t (Kelly and Matos, 2007; Crangle, 2016).
References Cited

Crangle, R.D., Jr., 2013, Diatomite [advanced release], in Metals 

and minerals: U.S. Geological Survey, Minerals Yearbook 2014, 

v. 1, p. 22.1–22.5, accessed February 9, 2016, at http://minerals.

usgs.gov/minerals/pubs/commodity/lead/myb1-2010-lead.pdf.

Crangle, R.D., Jr., 2016, Diatomite: U.S. Geological Survey 

Mineral Commodity Summaries 2016, p. 58–59, accessed 

February 4, 2016, at http://minerals.usgs.gov/minerals/pubs/

mcs/2016/mcs2016.pdf.

Davis, L.L., 1992, Diatomite: U.S. Bureau of Mines Mineral 

Commodity Summaries 1992, p. 60–61.

Kelly, T.D., and Matos, G.R., comps., 2007, Historical statistics 

for mineral and material commodities in the United States: 

U.S. Geological Survey Data Series 140, ver. 2011, accessed 

on February 4, 2016, at http://minerals.usgs.gov/minerals/pubs/

historical-statistics/.

Powers, H.A., 1947, Diatomite deposits of southwestern Idaho, 

Idaho mineral resources report no. 4: Moscow, Idaho, School 

of Mines, University of Idaho and Idaho Bureau of Mines and 

Geology, 27 p., accessed February 11, 2016, at http://www.

idahogeology.org/PDF/Mineral_Resource_Reports_(MR)/

MR-04.pdf.

Taylor, H.A., 1994, Diatomite, in Metals and minerals: U.S. 

Bureau of Mines Minerals Yearbook 1994, v. 1, accessed 

February 9, 2016, at http://minerals.usgs.gov/minerals/pubs/

commodity/diatomite/250494.pdf.

Dimension Stone—Quartzite

Dimension stone can be defined as a natural rock material 

quarried for the purpose of obtaining blocks or slabs that 

meet specifications as to size (width, length, and thickness) 

and shape. Color, grain texture and pattern, and surface finish 

of the stone are aesthetically desirable properties. Durability 

(essentially based on mineral composition, hardness, and past 

performance), strength, and the ability of the stone to take a 

polish are other important selection criteria. In addition to these 

desirable characteristics, a deposit will only have economic 

value if the rock is amenable to mining at a profit. Important 

criteria include the geometry of the deposit, orientation, and the 

site’s access to infrastructure. 

Although a variety of igneous, metamorphic, and 

sedimentary rocks are used as dimension stone, the principal rock 

types are granite, limestone, marble, sandstone (which includes 

quartzite), and slate. Other varieties of dimension stone that are 

normally considered to be special minor types include alabaster 

(massive gypsum), soapstone (massive talc), and various products 

fashioned from natural stone (Dolley, 2015). 

The USGS National Minerals Information Center 

(NMIC) reported that approximately 2.47 million metric 

tons (Mt) of dimension stone valued at $470 million was 

sold or used by U.S. producers in 2014. Dimension stone 

was produced by 216 companies operating 293 quarries in 

34 States. Leading producer States were, in descending order 

by tonnage, Texas, Indiana, Wisconsin, Massachusetts, and 

Georgia. These five States accounted for about 66 percent of 

the production and contributed about 63 percent of the value 

of domestic production. Approximately 42 percent by tonnage 

of dimension stone sold or used was limestone, followed by 

granite (21 percent), sandstone (which includes quartzite; 17 

percent), miscellaneous stone (16 percent), marble (2 percent), 

and slate (2 percent). By value, the leading sales or uses were 

for limestone (38 percent), followed by granite (25 percent), 

miscellaneous stone (18 percent), sandstone (which includes 

quartzite; 11 percent), marble (4 percent), and slate (4 percent) 

(Dolley, 2016). 

Quartzite, a metamorphosed sandstone, has been 

identified as a dimension and dressed stone that has been 

quarried in or proximal to the assessment area in Idaho. As 

there is a wide variety among the types and uses of dimension 

stone, a full discussion of types other than quartzite is beyond 

the scope necessary for the assessment area. The USGS 

does not publish statistical information specific to quartzite 

dimension stone. Statistical data related to quartzite production 

is aggregated with sandstone statistics. Quartzite represents 

a relatively small percentage of the stone included in the 

category, and in some cases, quartzite may be reported to the 

USGS as sandstone. Detailed information on production from 

individual sites is often considered confidential by companies 

and is therefore not published.

Rough stone represented 59 percent of the tonnage and 

49 percent of the value of all the dimension stone sold or used 

by domestic producers, including exports. The leading uses 

and distribution of rough stone, by tonnage, were in building 

and construction (58 percent) and in irregular-shaped stone (27 

percent). Dressed stone (usually cut to shape and sometimes 

smoothed) was primarily sold for facades and partially squared 

pieces (44 percent), curbing (20 percent), and flagging (11 

percent), by tonnage (Dolley, 2016). 

In 2014, approximately 63,700 metric tons (t) of dimension 

stone, most of which was slate, was produced in Idaho. It had a 

nominal value of $8.64 million. Quarries that have produced the 

majority of Idaho’s quartzite decorative and dimension stone are 

located outside the cities of Clayton in Custer County and Oakley 

in Cassia County. Decorative quartzite and dimension-stone 

production from Idaho’s famous “Oakley Stone,” a micaceous 

quartzite quarried on Middle Mountain, was reported by the 

USGS in Cassia County, Idaho, in 2000–11. The Three Rivers 

Quarry near Clayton in Custer County reported production 

of 18,000 t of argillaceous quartzite, probably a fine-grained 

quartzite dimension stone used for flagstone, in 2002 (U.S. 

Geological Survey, 2004). Production was 23,000–27,000 t 

in 2006 and 32,000 t in 2007. Production data for prior and 

subsequent years were withheld to avoid disclosing company 

proprietary data (Dolley, 2007; U.S. Geological Survey, 2002a, b, 

2003, 2005, 2008, 2009, 2010, 2012, 2014, and 2015). 

Appendix 5 187
188 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Examples of the applications of quartzite produced by 

companies in Cassia County include flagstone, hearths and 

mantels, retaining walls, steps, table tops, tile, and veneer 

(Northern Stone Supply, Inc., 2016). It is likely that similar 

products are also produced by operations in Custer County. 

On-site prices for the types of quartzite products vary 

significantly. Determining factors include the amount of 

finishing work, dimensions, and shape. It is likely that the bulk 

of sales of quartzite products shipped from Idaho are limited 

to regional markets because transportation is a major cost 

component.

The U.S. Defense Logistics Agency does not hold a 

stockpile of quartzite or any type of dimension stone. It is 

not considered a strategic or critical commodity because it is 

mostly for decorative purposes and numerous materials are 

readily available that can serve as a substitute for use in its 

applications.

References Cited

Dolley, T.P., 2007, Stone, dimension [advanced release], in Metals 

and minerals: U.S. Geological Survey, Minerals Yearbook 

2005, v. 1, p. 72.1–72.13, accessed March 11, 2016, at http://

minerals.usgs.gov/minerals/pubs/commodity/stone_dimension/

dstonmyb05.pdf.

Dolley, T.P., 2015, Stone, dimension [advanced release], in Metals 

and minerals: U.S. Geological Survey, Minerals Yearbook 2013, 

v. 1, p. 72.1–72.14, accessed March 9, 2016, at http://minerals.

usgs.gov/minerals/pubs/commodity/stone_dimension/myb1-

2013-stond.pdf.

Dolley, T.P., 2016, Stone (dimension): U.S. Geological Survey 

Mineral Commodity Summaries 2016, p. 152–153, accessed 

March 9, 2016, at http://minerals.usgs.gov/minerals/pubs/

commodity/stone_dimension/mcs-2015-stond.pdf.

Northern Stone Supply, Inc., 2016, Products: Oakley, Idaho, 

Northern Stone Supply, Inc., accessed March 10, 2016, at http://

www.northernstonesupply.com/quarries/index.html.

U.S. Geological Survey, 2002a, The mineral industry of Idaho, 

in Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook 2000, v. II, p. 14.1–14.5, accessed March 9, 2016, 

at http://minerals.usgs.gov/minerals/pubs/commodity/stone_

dimension/800400.pdf.

U.S. Geological Survey, 2002b, The mineral industry of Idaho, 

in Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook 2004, v. II, p. 14.1–14.6, accessed March 11, 2016, 

at http://minerals.usgs.gov/minerals/pubs/commodity/stone_

dimension/dimsmyb02.pdf.

U.S. Geological Survey, 2003, The mineral industry of Idaho, in 

Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook 2001, v. II, p. 14.1–14.5, accessed March 11, 2016, 

at http://minerals.usgs.gov/minerals/pubs/commodity/stone_

dimension/dimsmyb01.pdf.

U.S. Geological Survey, 2002, The mineral industry of Idaho, in Area 

reports—Domestic: U.S. Geological Survey Minerals Yearbook, 

2002, v. II, p. 14.1–14.5, accessed March 3, 2016, at http://

minerals.usgs.gov/minerals/pubs/state/2002/idstmyb02.pdf.

U.S. Geological Survey, 2005, The mineral industry of Idaho, in 

Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook 2003, v. II, p. 14.1–14.5, accessed March 11, 2016, at 

http://minerals.usgs.gov/minerals/pubs/state/2003/idstmyb03.

pdf.

U.S. Geological Survey, 2008, The mineral industry of Idaho, in 

Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook 2005, v. II, p. 14.1–14.7, accessed March 9, 2016, 

at http://minerals.usgs.gov/minerals/pubs/state/2005/myb2-

2005-id.pdf.

U.S. Geological Survey, 2009, The mineral industry of Idaho, in 

Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook 2006, v. II, p. 14.1–14.7, accessed March 9, 2016, 

at http://minerals.usgs.gov/minerals/pubs/state/2005/myb2-

2005-id.pdf.

U.S. Geological Survey, 2010, The mineral industry of Idaho, in 

Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook 2007, v. II, p. 14.1–14.5, accessed March 9, 2016, 

at http://minerals.usgs.gov/minerals/pubs/commodity/stone_

dimension/myb1-2007-stond.pdf.

U.S. Geological Survey, 2012, The mineral industry of Idaho, in 

Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook 2008, v. II, p. 14.1–14.5, accessed March 9, 2016, 

at http://minerals.usgs.gov/minerals/pubs/state/2008/myb2-

2008-id.pdf.

U.S. Geological Survey, 2014, The mineral industry of Idaho, in 

Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook 2009, v. II, p. 14.1–14.6, accessed March 9, 2016, 

at http://minerals.usgs.gov/minerals/pubs/state/2009/myb2-

2009-id.pdf.

U.S. Geological Survey, 2015, The mineral industry of Idaho, in 

Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook 2010–2011, v. II, p. 14.1–14.11, accessed March 9, 

2016, at http://minerals.usgs.gov/minerals/pubs/state/2010_11/

myb2-2010_11-id.pdf.

Gallium

Mined gallium is recovered globally as a byproduct 

of processing bauxite and zinc ores. Gallium is used in 

microelectronic components of a wide variety of products. 

The components include gallium arsenide (GaAs), gallium 

nitride (GaN), and copper-indium-gallium selenide (CIGS) 

direct band-gap semiconductors. GaAs and GaN are used in 

the manufacture of light-emitting diodes (LEDs), laser diodes, 

photo detectors, and solar cells. These devices are important for 
the aerospace and telecommunications industries. They are also 

used in the production of highly specialized integrated circuits, 

semiconductors, and transistors to help regulate the flow of 

electricity and amplify power. These components are necessary for 

high-performance computers and smartphones (cellular telephones 

that have advanced personal computer-like functionality). Power 

transistors made with GaN operate at higher voltages and with a 

higher power density than those made with GaAs. The types and 

numbers of products that use advanced GaN based transistors are 

expected to increase in the future. CIGS was developed to make 

lightweight and durable thin-film photovoltaics that have a high 

absorption coefficient and applications in the manufacture of solar 

cells (Foley and Jaskula, 2013).

GaAs applications accounted for about 80 percent of 

the worldwide gallium market, whereas GaN and CIGS 

applications accounted for about 7 percent and 5 percent, 

respectively. Various other applications accounted for the 

remaining 8 percent (Jaskula, 2015).

Domestically, GaAs and GaN wafers used in integrated 

circuits and optoelectronic devices accounted for approximately 

75 percent of gallium consumption. Uses in the United States 

include integrated circuits for defense applications, highperformance computers, and telecommunications equipment. 

Optoelectronic devices, which include laser diodes, LEDs, 

photodetectors, and solar cells, accounted for nearly all of the 

remaining gallium consumption (Jaskula, 2016).

Publications of the USGS National Minerals Information 

Center (NMIC) reported that in 2014, the United States did not 

recover gallium metal from domestic mining and has not done 

so since 1987. The Cordero primary gallium project, located 

within the assessment area, has been actively explored, but no 

production has been reported (Business Wire, 2005). The U.S. 

Geological Survey publishes detailed analyses and statistical data 

related to gallium derived from mining (gallium metal), GaAs 

wafers, and GaN wafers. GaAs and GaN wafers are manufactured 

products; the major focus of the following discussion is unwrought 

gallium metal, “waste,” and “scrap,” as it is more relevant to the 

methodology applied to the assessment area as it relates to mining 

(Jaskula, 2015, 2016).

Gallium is not recovered from old scrap in the United 

States; however, substantial quantities of domestic and imported 

new scrap generated in the manufacture of GaAs-based devices 

are reprocessed to recover high-purity gallium at one facility in 

Utah. The amounts and type of exported scrap are not available 

(Jaskula, 2016).

Approximately 53.9 metric tons (t) of unwrought gallium 

waste and scrap were imported and consumed in the United 

States in 2014. Imports have increased significantly since 1990, 

when only 9.9 t were imported. The rise reflects the increase in 

domestic waste-processing capacity and the Nation’s demand for 

the production of electronic circuitry and other products that use 

the metal. The compound average annual growth rate in imports 

of nearly 7 percent over the time period reflects the increase in 

demand for technologically advanced products and growth in 

domestic manufacturing. For the years 2011–14, Germany was 

the leading import source with a 35 percent share. Other major 

import sources and their percentage shares were China (26 percent), 

United Kingdom (22 percent), and Ukraine (9 percent) (Jaskula, 

2016; Kelly and Matos, 2007). The United States does not have 

a vertically integrated gallium mining and processing industry 

and therefore relies completely on foreign imports to meet the 

Nation’s commercial and strategic requirements. Since 2000, the 

net import reliance of the United States, as a percentage of apparent 

consumption has been estimated at 99 or 100 percent (Jaskula, 

2016; Kramer, 2001).

Gallium is considered a strategic and critical mineral material 

because of total or nearly total U.S. import reliance and gallium’s 

use in advanced commercial and military applications. GaAs- and 

GaN-based integrated circuits are used in many defense-related 

applications because of their unique properties, and no effective 

substitutes exist in these applications. The U.S. Defense Logistics 

Agency, however, does not hold a stockpile of gallium (Jaskula, 

2016). From 1990 to 2014, the total amount of byproduct lowgrade primary gallium recovered annually from global mines 

increased from approximately 37 to 438 t. The compound average 

annual increase of nearly 11 percent reflects the growth in global 

demand for use in a wide array of applications in advanced 

technologies. This rate of growth exceeds that of base metals and 

many other mineral commodities. In 2014, gallium recovered 

from mining was estimated to be 438 t, significantly below the 

estimated world capacity of 670 t, owing to large inventories 

of primary gallium. China is by far the leading primary gallium 

producer and possessed more than 80 percent of global production 

capacity. China’s primary gallium production capacity expanded 

to approximately 550 t per year in 2014 from 140 t in 2010 on the 

expectations of increases in LED backlighting and general lighting 

demand. The other major primary gallium producing countries are 

Germany, Hungary, Japan, Kazakhstan, Republic of South Korea, 

Russia, and Ukraine (Jaskula, 2015, 2016; Kelly and Matos, 2007; 

Brian Jaskula, gallium commodity specialist, USGS, oral commun., 

March 15, 2016).

The average annual price per kilogram of gallium

($/kg), expressed in constant 1998 U.S. dollars for the purpose 

of comparison for the years 1990–15, was at a low of 

$203/kg ($295/kg in nominal dollars) in 2015 owing to China’s 

continued overproduction and continued stock buildup of 

low-grade primary gallium. Prices attained a high of $626/kg 

in 1999, when gallium supply became tight because of high 

demand in the telecommunications industry (Jaskula, 2010, 

2016; Kelly and Matos, 2007; Kramer, 2001). 

References Cited

Business Wire, 2005, Gold Canyon reports greater than 90 percent 

recovery of gallium at Cordero: Business Wire, accessed 

on March 21, 2016, at http://www.businesswire.com/news/

home/20050726005839/en/Gold-Canyon-Reports-Greater-90-

Recovery-Gallium. 

Foley, Nora, and Jaskula, Brian, 2013, Gallium—A smart metal: U.S. 

Geological Survey Fact Sheet 2013–3006, 2 p., accessed March 

15, 2016, at http://pubs.usgs.gov/fs/2013/3006/.

Appendix 5 189
190 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Jaskula, B.W., 2010, Gallium: U.S. Geological Survey Mineral 

Commodity Summaries 2010, p. 58–59, accessed on March 15, 

2016, at http://minerals.usgs.gov/minerals/pubs/commodity/

gallium/mcs-2010-galli.pdf.

Jaskula, B.W., 2015, Gallium [advanced release], in Metals 

and minerals: U.S. Geological Survey, Minerals Yearbook 

2013, v. 1, p. 27.1–27.8, accessed March 14, 2016, at http://

minerals.usgs.gov/minerals/pubs/commodity/gallium/myb1-

2013-galli.pdf.

Jaskula, B.W., 2016, Gallium: U.S. Geological Survey Mineral 

Commodity Summaries 2016, p. 64–65, accessed on March 14, 

2016, at http://minerals.usgs.gov/minerals/pubs/commodity/

gallium/mcs-2016-galli.pdf.

Kelly, T.D., and Matos, G.R., comps., 2007, Historical statistics 

for mineral and material commodities in the United States: 

U.S. Geological Survey Data Series 140, ver. 2011, accessed 

February 4, 2016, at http://minerals.usgs.gov/minerals/pubs/

historical-statistics/.

Kramer, B.W., 2001, Gallium: U.S. Geological Survey Mineral 

Commodity Summaries 2000, p. 60–61, accessed on March 14, 

2016, at http://minerals.usgs.gov/minerals/pubs/commodity/

gallium/460301.pdf.

Gemstones

At least three gemstones are known to be produced in or 

proximal to the SaMiRA project assessment area—aventurine, 

precious opal, and sunstone.

Aventurine, also known as aventurine quartz, is a 

type of light- to dark-green quartz that exhibits a metallic 

iridescence or glittering (aventurescence), which is caused 

by light reflecting off of included fuchsite (green mica) 

flakes. Sometimes it occurs with red- or golden-brown color 

exhibiting metallic iridescence caused by included hematite 

flakes. It is cut into cabochons (unfaceted stones) and is carved 

into ornamental objects. Aventurine deposits are found in 

Austria, Brazil, India, Russia, Tanzania, and the United States 

(Schumann, 1998, p.122). 

Opal is a mineraloid in the form of hydrated amorphous 

silicon dioxide and is generally classified as common opal or 

precious opal. It is valued as a precious opal for the intense 

rainbow of colors displayed as it diffracts and refracts light 

when it is shaped and polished to produce cabochons and, 

less commonly, cut and faceted. The value of precious opal 

can vary significantly and depends largely on the size of 

the gem, the intensity and range of colors it displays, and 

uniformity of the stone (Geology.org, 2016). A large part 

of the world’s precious opal is mined in Australia, but it 

is also mined in significant quantities in Brazil, Ethiopia, 

Guatemala, Honduras, Indonesia, Japan, Mexico, Russia, and 

the United States. Common opal is usually milky in color, 

opaque, and may be used in jewelry and may have value to 

mineral collectors. It does not usually share the more-valued 

“rainbow” of colors and other characteristics of precious 

opal and is rarely considered a gemstone. Common opal 

has relatively low value and is mined in many countries 

(Schumann, 1998, p. 150–152).

Sunstone, also known as aventurine feldspar, is a type 

of clear, blue, green, orange-brown, red-brown, or yellow 

oligoclase feldspar that exhibits aventurescence caused by light 

reflecting off included copper, hematite, or goethite platelets 

or flakes. It typically is cut into cabochons and is sometimes 

faceted. Sunstone deposits are found in Canada, India, 

Madagascar, Norway, Russia, and the United States (Schumann,

1998, p. 166). Sunstone is the State gemstone of Oregon.

The USGS National Minerals Information Center 

(NMIC) reports on a wide range of statistical data related 

to the domestic and global production of gemstones with a 

focus on natural and synthetic gemstones, such as diamonds, 

emeralds, pearls, and rubies (Olson, 2014, 2016). The NMIC 

does not publish information on the carat weight of individual 

gemstone types produced by State, but does provide information 

on the estimated value of total gemstone production by State 

through a voluntary survey of mining companies. Statistics 

may underestimate actual production owing to the relatively 

low level of response to surveys and the amount of unreported 

production by individual collectors. 

The total value of aventurine production in 2014 is withheld 

to avoid revealing company proprietary data. Commercial 

aventurine production and collection by hobbyists takes place in 

Utah. Production of aventurine in or proximal to the assessment 

area includes Northern Stone Supply’s aventurine operation in 

Box Elder County, Utah. 

The NMIC reported that in 2013 the total value of opal 

production in the United States was approximately $93,000 and 

represented less than 1 percent of the total estimated value of 

domestic natural gemstone production. Preliminary estimates 

suggest that the value of opal production in 2014 was about 5 

percent lower (Olson, 2016). Commercial opal production and 

collection by hobbyists takes place in Arizona, California, Idaho, 

Louisiana, Nevada, and Oregon. Production of precious and 

common opal in or proximal to the assessment area includes the 

Spencer Mine in Clark County, Idaho, and several mines in the 

Virgin Valley area and in the Calico Mountains in Humboldt County, 

Nevada (Austin, 1995; U.S. Geological Survey, 2015; Olson, 2016). 

The total value of 2013 sunstone production in the United 

States was approximately $576,000 and represented about 6 

percent of the total estimated value of domestic natural gemstone 

production. Preliminary estimates suggest that the value of 

sunstone production was slightly less in 2014. Production of 

sunstone in or proximal to the assessment area includes several 

mines in Harney, Jackson, and Lake Counties, Oregon (Olson, 

2016), including the Dust Devil Mining Company, which operates 

a fee digging sunstone mine near Plush, Oregon.

Aventurine, precious opal and sunstone are not considered 

to have strategic or critical importance to the United States. Their 

value is solely based on their actual or speculative desirability for 

personal adornment. 
References Cited

Austin, G.T., 1995 Opal, in Gemstones—An overview of 

production of specific U.S. gemstones: U.S. Bureau of Mines 

Special Report 14-95, accessed February 19, 2016, at http://

minerals.er.usgs.gov/minerals/pubs/commodity/gemstones/

sp14-95/opal.html. 

Gemdata.org, 2016, Common opal: Gemdata.org Web page, 

accessed on February 19, 2016, at http://www.gemdat.org/gem5981.html.

Geology.com, 2016, Precious opal: Gemdata.org Web page, 

accessed on February 19, 2016, at http://geology.com/

gemstones/opal/precious-opal.shtml.

Olson, D.W., 2014 Gemstones, in Metals and minerals: U.S. 

Geological Survey, Minerals Yearbook 2014, v. 1. p. 62–63, 

accessed May 23, 2016, at http://minerals.usgs.gov/minerals/

pubs/mcs/2014/mcs2014.pdf.

Olson, D.W., 2016, Gemstones, in Metals and minerals: U.S. 

Geological Survey, Minerals Yearbook 2013, v. 1, p. 29.1–

29.25, accessed February 19, 2016, at http://minerals.usgs.gov/

minerals/pubs/commodity/gemstones/myb1-2013-gemst.pdf.

Schumann, Walter, 1998, Gemstones of the world: New York, 

Sterling Publishing Co., Inc., 273 p.

Gold

Publications of the USGS National Minerals Information 

Center (NMIC) reported that in 2014, U.S. mines produced 

about 210 metric tons (t) of gold as a primary product and as 

coproduct or byproduct of other metals mining and processing; 

U.S. output ranked fourth in the world. Mines in Nevada and 

Alaska, the two leading producing States, accounted for about 

72 percent and 15 percent, respectively, of domestic gold mine 

production in 2014. The remainder, in descending order of 

production, was from mines in Colorado, Utah, Washington, 

California, Montana, South Dakota, Arizona, and New 

Mexico, (George, 2016). 

Within the assessment area, gold production was reported 

in Custer and Lemhi Counties, Idaho; in Fergus and Phillips 

Counties, Montana; and, most significantly, in Elko and Humboldt 

Counties, Nevada (Environmental Working Group, 2016; U.S. 

Geological Survey, 2015a, b). Gold production in these States is 

not within the specified proposed withdrawal areas, at the time 

of this analysis, but production in Elko and Humboldt Counties 

in Nevada, does fall within a 25-kilometer (km) zone outside 

the study area. In 2014, approximately 30 percent of all gold 

production in Nevada came from mines within the 25-km buffer 

zone in Elko and Humboldt Counties.

In 2014, the U.S. mine production of gold was about 

210t, significantly less than the estimated 294 t that was 

produced in 1990. Although gold production declined by an 

average compound annual rate of about 1.4 percent from 1990 

through 2014, production rose to a record-high level of 366 t 

in 1998, owing to development of open-pit leach operations in 

the Carlin trend. The decline in domestic gold mine production 

since 1998 can be attributed to a combination of increasing 

costs, lower ore grades, decreased ore throughput at some 

mines, closure of some mines, and, reduced output from 

copper mines. During this period, an increased share of copper 

mine production was from leaching methods that preclude the 

recovery of gold. In 2014, it was estimated that U.S. gold ore 

reserves contained approximately 3,000 t of gold (George, 

2016; Kelly and Matos, 2007).

In addition to domestically mined gold, an additional 

140 t of the metal was recovered from the recycling of scrap 

in 2014; a substantial increase from 1990 when 44 t was 

recovered. 

In 2014, the United States exported about 500 t of gold 

in refined bullion, doré, concentrates, and precipitates and 

imported approximately 308 t for domestic consumption. Four 

countries supplied 81 percent of U.S. imports—Mexico (41 

percent), Canada (19 percent), Colombia (13 percent), and 

Peru (8 percent (George, 2016).

For 2014, U.S. consumption of gold was estimated to be 

150 t, significantly lower than in 1990 when it was estimated 

to be 215 t. The United States has long been a net exporter 

of gold; however, large unreported investor stock changes 

preclude calculation of meaningful net import reliance 

(George, 2016; Kelly and Matos, 2007).

The U.S. Defense Logistics Agency does not hold a 

stockpile of gold. Gold is not considered a strategic or critical 

commodity. The United States has substantial production 

and stocks of gold held by industry and investors, the U.S. 

Treasury Department, and commodity exchanges. The 

U.S. Department of Defense operates a Government-wide 

secondary precious-metals recovery program (George, 2016). 

From 1990 to 2014, total world mine production of gold 

increased from 2,180 to 2,990 t at an average compound 

annual growth rate of about 1.5 percent. In 2014, China led 

the world in mined gold production with 450 t. This was 

a significant increase from 1990 when China produced an 

estimated 100 t. Other major gold producers in 2014, and 

their respective shares of global production, were Australia 

(9 percent); Russia (8 percent); the United States (7 percent); 

Canada, Peru, and South Africa (5 percent each); and Mexico 

(4 percent). The increase in world gold output from 1990 to 

2014 has been driven by an overall increase in the demand 

for the metal in electronics and jewelry and as an investment 

vehicle, especially among some Asian countries, notably India 

(George, 2016; Kelly and Matos, 2007).

The average annual gold price per troy ounce, expressed 

in constant 1998 U.S. dollars, since 1990, ranged from a low 

of about $250 per troy ounce ($8,060,000/t) in 2001 to a high 

of $1,673 per troy ounce in 2012 ($38,200,000/t). In 2015, the 

average price of gold in nominal dollars was approximately 

$1,163 per troy ounce ($32,262,000/t) (Kelly and Matos, 

2007; George, 2016).

Appendix 5 191
192 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

References Cited

Environmental Working Group, 2016, Who owns the West: 

Environmental Working Group Web page, accessed on 

February 16, 2016, at http://www.ewg.org/mining/plans/index.

php?stab=ID&fips.

George, M.W., 2016, Gold: U.S. Geological Survey Mineral 

Commodity Summaries 2016, p.72–73, accessed on February 

4, 2016 at http://minerals.usgs.gov/minerals/pubs/mcs/2016/

mcs2016.pdf.

Kelly, T.D., and Matos, G.R., comps., 2007, Historical statistics 

for mineral and material commodities in the United States: 

U.S. Geological Survey Data Series 140, ver. 2011, accessed 

February 4, 2016, at http://minerals.usgs.gov/minerals/pubs/

historical-statistics/.

U.S. Geological Survey, 2015a, The mineral industry of Utah, in 

Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook 2010–2011, v. II, p. 47.1–47.14, accessed February 4, 

2016, at http://minerals.usgs.gov/minerals/pubs/state/2010_11/

myb2-2010_11-ut.pdf.

U.S. Geological Survey, 2015b, The mineral industry of Nevada, 

in Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook 2010–2011, v. II, p. 30.1–30.17, accessed February 4, 

2016, at http://minerals.usgs.gov/minerals/pubs/state/2010_11/

myb2-2010_11-nv.pdf.

Gypsum

The USGS National Minerals Information Center 

(NMIC) reported that the United States produced gypsum 

from about 54 mines in 16 States in 2014. The United States 

was the world’s third-ranked mine producer of crude gypsum 

with 11 million metric tons (Mt) accounting for nearly 5 

percent of world production. Domestic reserves of crude 

gypsum were estimated to be 700 Mt. The United States and 

other countries also produce significant tonnages of synthetic 

gypsum, which is predominantly generated as a byproduct at 

coal-fired electrical power plants. In 2014, the United States 

sold approximately 15 Mt of synthetic gypsum, most of which 

was produced from flue-gas desulfurization (FGD) systems at 

coal-fired electric power plants. Some gypsum scrap that was 

generated by wallboard manufacturing, wallboard installation, 

and building demolition in the United State was recycled. The 

recycled gypsum was used primarily for agricultural purposes 

and feedstock for the manufacture of new wallboard.

In 2015, the leading crude gypsum-producing States 

were, in descending order of production, Oklahoma, Texas, 

Nevada, Kansas, Iowa, and Arkansas, which together 

accounted for 70 percent of total domestic output (Crangle, 

2015a, b, 2016). Ongoing or previous gypsum mining 

activities in the States or counties within the assessment areas 

studied include Washoe County in northwestern Nevada, but 

these locations were not within the proposed withdrawal area 

(State of Nevada, 2015, p. 15–24; Weissenborn, 1963).

A significant driver for gypsum production is the demand 

for its use as a component of wallboard and portland cement in 

the construction industry. From 1990 to 2014, total annual world 

mined gypsum production more than doubled from approximately 

104 to 244 Mt for an average annual growth rate of about 3.5 

percent. The effect of the global recession in 2008 was reflected by 

a decrease in world production in response to decreased demand 

for gypsum (Kelly and Matos, 2007). Increased use of wallboard 

in Asia, coupled with new gypsum-product manufacturing plants, 

spurred increased production and consumption in that region. 

As wallboard becomes more widely used in other regions, the 

trend of worldwide production of gypsum is expected to increase. 

In 2014, the United States apparent consumption of crude and 

synthetic gypsum was 25.7 Mt, about 15 percent higher than 

1990. However, domestic production of crude gypsum decreased 

over the same period from 16 Mt to 11 Mt and synthetic gypsum 

production increased from 735,000 to 11 Mt. In 1990, 8.7 Mt of 

crude gypsum was imported and about 129,000 t was exported, 

but in 2014, imports of crude gypsum had decreased to 3.7 Mt 

and exports had decreased to 67,000 t. From 2011 through 2014, 

the leading import sources of crude gypsum and their percentage 

shares were Mexico (42 percent), Canada (35 percent), and Spain 

(22 percent) (Davis, 1992; Crangle, 2016). The U.S. net-import 

reliance as a percentage of apparent consumption was 14 percent 

in 2014.

The U.S. Defense Logistics Agency does not maintain an 

inventory of gypsum. Gypsum is not considered either of critical 

or strategic importance because of the numerous domestic sources, 

both crude and synthetic, and the significant number of foreign 

producers.

In 2014, approximately 80 countries produced mined gypsum 

for a total of about 244 Mt. China was the leading producer 

with an estimated 129 Mt and accounted for an approximately 

53 percent share of world crude gypsum production. China is 

likely to maintain its position for the foreseeable future. The other 

leading producers were Iran and Turkey, each representing a 6 

percent share of world production, followed by the United States 

accounting for nearly 5 percent (Crangle, 2016).

The average annual price per metric ton ($/t) of the total 

value of domestic sales of calcined and uncalcined gypsum 

in nominal dollars was about $12.00/t in 2014. Since 1990, 

average annual price per metric ton has ranged from a low 

of $9.70/t in 1992 to a high of $15.90/t in 2005 (Kelly and 

Matos, 2007). In 2014, the average nominal price for crude 

gypsum was approximately $9.00/t, free on board at the mine 

(Crangle, 2016).

References Cited

Crangle, R.C., Jr., 2015a, Gypsum, in Metals and minerals: U.S. 

Geological Survey, Minerals Yearbook 2013, v. 1, p. 33.1–

33.10, accessed February 3, 2016, at http://minerals.usgs.gov/

minerals/pubs/commodity/gypsum/myb1-2013-gypsu.pdf.
Crangle, R.C., Jr., 2015b, Gypsum: U.S. Geological Survey 

Mineral Commodity Summaries 2014, p. 94–95, accessed 

February 4, 2016, at http://minerals.usgs.gov/minerals/pubs/

mcs/2015/mcs2015.pdf.

Crangle, R.C., Jr., 2016, Gypsum: U.S. Geological Survey Mineral 

Commodity Summaries 2015, p. 76–77, accessed February 

4, 2016, at http://minerals.usgs.gov/minerals/pubs/mcs/2016/

mcs2016.pdf.

Davis, L.L., 1992, Gypsum: U.S. Bureau of Mines Mineral 

Commodity Summaries 1992, p. 78–79.

Kelly, T.D., and Matos, G.R., comps., 2007, Historical statistics 

for mineral and material commodities in the United States: 

U.S. Geological Survey Data Series 140, ver. 2011, accessed 

February 4, 2016, at http://minerals.usgs.gov/minerals/pubs/

historical-statistics/.

State of Nevada, 2015, Directory of Nevada mine operations, 

January–December, 2014: Carson City, Nevada, State of 

Nevada, Department of Business and Industry, Division of 

Industrial Relations, Mine Safety and Training Section, August 

19, 2015, 324 p., accessed February 4, 2016, at http://dir.

nv.gov/uploadedFiles/dir.nv.gov/content/MSATS/Features/

Complete%20Mine%20Directory.pdf.

Weissenborn, A.E., 1963, Mineral and water resources of 

Montana: Montana Bureau of Mines and Geology, Special 

Publication No. 28, accessed February 5, 2016, at http://www.

mbmg.mtech.edu/sp28/contents.htm.

Iron Ore

The principal ore minerals of iron are hematite, magnetite, 

siderite, and goethite. An estimated 98 percent of the ore shipped 

in the world is consumed in the manufacture of iron and steel. 

The remaining 2 percent is used in the manufacture of cement, 

heavy-medium materials, pigments, ballast, agricultural products, 

or specialty chemicals, among other uses. As a result, demand 

for iron ore is tied directly to the production of raw steel, the 

availability and cost of high-quality ferrous scrap, and the 

percentage of steel produced using basic oxygen furnaces.

Publications of the USGS National Minerals Information 

Center (NMIC) reported that in 2014 the United States produced 

55.9 million metric tons (Mt) of iron ore for use in steel production 

and ranked eighth in global iron-ore production. All of the ore 

is recovered from surface operations. Mines in Michigan and 

Minnesota shipped 98 percent of the usable iron ore in the United 

States (Tuck, 2016). Iron-ore production has not occurred in the 

assessment area within the past 10 years; however, production was 

reported in Utah County, Utah, in 1990 and in Fremont County, 

Wyoming, until about 1983 (Jeske and Gloyn, 1991; Starch and 

Glass, 1984).

In 2014, U.S. mine production of iron ore was slightly lower 

than the estimated 56.4 Mt that were produced in 1990. Except for 

a drop in production in the years surrounding the global recession, 

domestic iron-ore production has been relatively stable since 

1990. In 2014, it was estimated that U.S. iron-ore reserves were 

approximately 11.5 billion metric tons (Bt) of crude ore, which is 

equivalent to a 3.5 Bt of iron (Tuck, 2016).

In 2014, the United States exported about 12.1 Mt of iron 

ore compared with 3.2 Mt in 1990. The increase in exports 

followed the increasing trade of iron and steel between Canada, 

Mexico, and the United States as domestic iron-ore producers 

expanded their iron and steel operations throughout North 

America. Approximately 5.1 Mt of iron ore were imported for 

domestic consumption in 2014 compared with 18.1 Mt in 1990. 

The decrease in iron-ore imports was a result of decreased 

domestic steel production. The countries importing the most 

U.S. iron ore during 2011–14, and their respective shares, were 

Canada (56 percent), Brazil (35 percent), Sweden (3 percent), 

and Argentina (2 percent) (Tuck, 2016). 

Apparent consumption of iron ore in the United States has 

declined by 36 percent to 45.9 Mt in 2014 from 71.4 Mt in 1990. 

This trend resulted from decreasing imports and increasing exports 

of iron ore and reduced domestic steel production. The United 

States was a net exporter of iron ore in 2014 in contrast to 1990, 

when net import reliance as a percentage of apparent consumption 

was 21 percent.

The U.S. Defense Logistics Agency does not hold a stockpile 

of iron ore (Tuck, 2014, 2016). Iron ore is not considered a 

strategic or critical commodity because of substantial U.S. 

production, well-established domestic steel manufacturing, steel 

recycling, reliable import sources, and abundant stocks held by 

producers and consumers. The greatest risk to the domestic ironore industry lies in rising levels of steel imports, which increased 

by nearly one-third from 2013 to 2014. The sustained increase has 

directly affected the iron and steel industry causing iron-ore mines 

and iron-based steel production facilities to be idled, reducing 

the overall domestic capacity for raw steel production. Iron and 

steel is essential all aspects of the U.S. economy, because it is a 

critical component of all modern technology sectors, including 

agriculture, communications, defense, manufacturing, and 

transportation.

From 1990 to 2014, the total world iron-ore production 

increased from 982 Mt to 3.4 Bt, for an average compound 

annual growth rate of about 8.9 percent. During this period of 

time, U.S. production varied only slightly, while production in 

some other countries increased significantly. Iron-ore production 

rose nearly sixfold in Australia, nearly threefold in Brazil, and 

nearly fourteenfold in China from 1990 through 2014. Much 

of the increased production was to supply increased demand 

by China’s steel industry for domestic construction goods, 

manufacture of consumer goods, and export. In 2014, China 

was the world leader in iron-ore production with 1,510 Mt, 

which represented a 44 percent share; however, unlike most 

of the reported global iron-ore production, which has an iron 

content averaging 62.5 percent iron content, China reports ore 

production as crude ore, which has an estimated iron content 

of 20 percent to 30 percent. Other major iron-ore producers 

in 2014, and estimates of their respective share of global 

production, were Australia (23 percent), Brazil (12 percent), 

Appendix 5 193
194 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

India (4 percent), and Russia (3 percent) (Kelly and Matos, 

2007; Kuck, 1992; Tuck, 2016).

The average annual unit value of iron ore, expressed in 

constant 1998 U.S. dollars for the purpose of comparison, has 

varied since 1990 but reached a low of about $22/t in 2001 

to a high of $74/t in 2010. The increase in iron-ore unit value 

beginning around 2004 was driven to a large extent by high 

demand from China. Prices began to weaken in 2014 as demand 

began to wane. In 2014, the average price of iron ore in nominal 

dollars was approximately $92.78/t (Kelly and Matos, 2007; 

Tuck, 2016).

References Cited

Jeske, R.E., and Gloyn, R.W., 1991, The mineral industry of Utah, 

in Area reports—Domestic: U.S. Bureau of Mines Minerals 

Yearbook 1991, v. II, p. 515–528, accessed February 11, 

2016, at http://digicoll.library.wisc.edu/cgi-bin/EcoNatRes/

EcoNatRes-idx?type=turn&entity=EcoNatRes.MinYB1991v2.

p0528&id=EcoNatRes.MinYB1991v2&isize=M.

Kelly, T.D., and Matos, G.R., comps., 2007, Historical statistics 

for mineral and material commodities in the United States: U.S. 

Geological Survey Data Series 140, ver. 2011, accessed February 

4, 2016, at http://minerals.usgs.gov/minerals/pubs/historicalstatistics/.

Kuck, P.H., 1992, Iron ore, in Metals and minerals: U.S. Bureau 

of Mines, Minerals Yearbook 1990, v. 1, p. 559–606, accessed 

March 4, 2016, at http://digicoll.library.wisc.edu/cgi-bin/

EcoNatRes/EcoNatRes-idx?type=turn&entity=EcoNatRes.

MinYB1990v1.p0610&id=EcoNatRes.MinYB1990v1&isize=M.

Starch, K.E., and Glass, G.B., 1984, The mineral industry of 

Wyoming, in Area reports—Domestic: U.S. Bureau of Mines 

Minerals Yearbook 1982, v. II, p. 591–601, accessed February 

11, 2016, at http://digicoll.library.wisc.edu/cgi-bin/EcoNatRes/

EcoNatRes-idx?type=turn&entity=EcoNatRes.MinYB1991v2.

p0528&id=EcoNatRes.MinYB1991v2&isize=M.

Tuck, C.A., 2014, Iron ore, in Metals and minerals: U.S. Geological 

Survey, Minerals Yearbook 2012, v.1, p. 39.1–39.18, accessed 

February 10, 2016, at http://minerals.usgs.gov/minerals/pubs/

commodity/iron_ore/myb1-2012-feore.pdf.

Tuck, C.A., 2016, Iron ore: U.S. Geological Survey Mineral 

Commodity Summaries 2016, p. 90–91, accessed February 

10, 2016, at http://minerals.usgs.gov/minerals/pubs/mcs/2016/

mcs2016.pdf.

Lead

The major application for lead is in all types of lead-acid 

storage batteries. Other significant uses included ammunition, 

oxides in glass and ceramics, casting metal, and sheet lead. The 

remainder is consumed in solders, bearing metals, brass and 

bronze billets, covering for cable, caulking lead, and extruded 

products (Guberman, 2015, 2016).

Publications of the USGS National Minerals Information 

Center (NMIC) reported that in 2014 the United States 

produced about 379,000 metric tons (t) of lead in concentrates 

as a principal product, coproduct, or byproduct of mining. Lead 

is recovered from ore extracted from underground or open pit 

mines and concentrated using conventional flotation methods. In 

2014, the United States ranked third in global mine production 

of lead. Mines in Alaska and Missouri accounted for most of 

the domestic mined lead production in 2014. The remaining 

production came from mines in Shoshone County, Idaho, and 

in Pend Oreille County, Washington (Gabby, 2007; Guberman, 

2012, 2015). Lead production is ongoing or has occurred 

since 2005 in Jefferson County, Montana, and Shoshone 

County, Idaho (U.S. Geological Survey, 2015a, b, c). No mine 

production of lead was reported in the assessment areas or the 

25-kilometer (km) buffers. In 2014, the U.S. mine production 

of lead in concentrates was about 379,000 t, significantly less 

than the 497,000 t produced in 1990. The compound annual 

growth rate has been about negative 1 percent in domestic lead 

mine production during the period, which can be attributed to 

a combination of shutdowns and curtailments at zinc and lead 

mines. Mine production of lead remained essentially unchanged 

from 2011 to 2013. In 2014, it was estimated that U.S. ore 

reserves contained approximately 5 million metric tons (Mt) of 

lead (Guberman, 2016; Kelly and Matos, 2007).

In 1990, approximately 404,000 t of primary refined lead was 

produced from domestic and imported concentrates by domestic 

refiners. In 2014, as a result of plant closures, the United States did 

not produce any primary refined lead. All domestically produced 

lead concentrates were exported and essentially no concentrates 

were imported. It is unlikely that lead concentrates will be smelted 

and refined in the United States before the end of the decade or 

perhaps the foreseeable future.

In 2014, in addition to domestically mined lead, 1.13 Mt 

of lead was recovered from the recycling of scrap, an increase 

from 1990 when about 922,000 t was recovered. Spent lead-acid 

batteries are the primary source of lead recovered from recycling 

(Guberman, 2016; Woodbury, 1992).

In 2014, the United States exported about 356,000 t of 

lead in concentrates plus 60,000 t of refined-lead (wrought and 

unwrought). Approximately 596,000 t of refined lead (wrought 

and unwrought) was imported for consumption in 2014 compared 

with 97,000 t in 1990. The increase reflects reduced domestic 

mine production and closures of U.S. primary lead smelters and 

refineries. For the years 2011–14, five countries accounted for 

90 percent of refined-lead (wrought and unwrought) imports—

Canada (57 percent), Mexico (20 percent), Peru (5 percent), and 

Australia and Kazakhstan (4 percent each) (Guberman, 2016).

Apparent consumption of lead in the United States has 

increased from 1,300 Mt in 1990 to 1,670 Mt in 2014, primarily 

owing to increased consumption for use in lead-acid batteries 

(Guberman, 2015; Woodbury, 1992). 

The United States became increasingly reliant on imports 

of refined lead from 1990 through 2014, primarily owing to 
the closures of all primary lead refineries. In 2014, net import 

reliance as a percentage of apparent consumption of refined lead 

was 32 percent, a substantial increase from 1990 when it was 3 

percent (Guberman, 2015; Woodbury, 1992).

The U.S. Defense Logistics Agency does not hold a 

stockpile of lead. Lead is not considered a strategic or critical 

material because of substantial U.S. production of lead from 

recycling, reliable sources for imports, and sufficient stocks held 

by producers and consumers (Guberman, 2016). Although not 

held in the stockpile, the U.S. Department of Defense (DOD) has 

modeled for potential shortfalls of lead and looked into substitutes 

for specific applications that are vital to DOD. Refined lead is 

not considered to be difficult to obtain; however, there are some 

military applications, such as high-purity refined lead used in 

batteries for submarines, that use types of lead that have limited 

supply sources.

From 1990 through 2014, total world mine production 

of lead increased from 3.37 Mt to 4.87 Mt for an average 

compound annual growth rate of about 1.6 percent. In 2014, 

China was the leading world producer of mined lead with 

2.4 Mt, accounting for 49 percent of world lead production. 

This was a significant increase from 1990 when China produced 

an estimated 315,000 t or about 9 percent of world mine 

production. Other major lead producers in 2014 were Australia 

(15 percent), United States (8 percent), Peru (6 percent), and 

Mexico (5 percent). The increase in world lead-mine production 

during that time period was driven primarily by increases in 

consumption in China and other developing nations (Guberman, 

2015; Kelly and Matos, 2007; Woodbury, 1992). 

The average annual lead price, expressed in constant 1998 

U.S. dollars since the year 1990, ranged from a low of about $855 

per metric ton in 2003 to a high of $2,150 per metric ton in 2007. 

The elevated price of the metal in 2007 was a result of increased 

global consumption, most notably in China, and a decline in global 

stocks. Prices decreased in subsequent years, partially owing to a 

global economic slowdown and more moderate increases in lead 

consumption in China. In 2014, the average annual price of lead 

expressed in constant 1998 U.S. dollars was approximately $1,610 

per metric ton (Kelly and Matos, 2007; Guberman, 2016).

References Cited

Gabby, P.N., 2007, Lead, in Metals and minerals: U.S. Geological 

Survey, Minerals Yearbook 2005, v. 1, p. 43.1–42.19, accessed 

February 9, 2016, at http://minerals.usgs.gov/minerals/pubs/

commodity/lead/leadmyb05.pdf.

Guberman, D.E., 2012, Lead [advanced release], in Metals and 

minerals: U.S. Geological Survey, Minerals Yearbook 2010, v. 1, 

p. 42.1–42.18, accessed February 9, 2016, at http://minerals.usgs.

gov/minerals/pubs/commodity/lead/myb1-2010-lead.pdf.

Guberman, D.E., 2015, Lead [advanced release], in Metals and 

minerals: U.S. Geological Survey, Minerals Yearbook 2013, v. 1, 

p. 42.1–42.16, accessed February 9, 2016, at http://minerals.usgs.

gov/minerals/pubs/commodity/lead/myb1-2013-lead.pdf.

Guberman, D.E., 2016, Lead: U.S. Geological Survey Mineral 

Commodity Summaries 2016, p.72–73, accessed February 

4, 2016 at http://minerals.usgs.gov/minerals/pubs/mcs/2016/

mcs2016.pdf.

Kelly, T.D., and Matos, G.R., comps., 2007, Historical statistics 

for mineral and material commodities in the United States: 

U.S. Geological Survey Data Series 140, ver. 2011, accessed 

February 4, 2016, at http://minerals.usgs.gov/minerals/pubs/

historical-statistics/.

U.S. Geological Survey, 2015a, The mineral industry of Idaho, 

in Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook 2010–2011, v. II, p. 14.1–14.11, accessed February 4, 

2016, at http://minerals.usgs.gov/minerals/pubs/state/2010_11/

myb2-2010_11-id.pdf.

U.S. Geological Survey, 2015b, The mineral industry of Montana, 

in Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook 2010–2011, v. II, p. 28.1–28.12, accessed February 4, 

2016, at http://minerals.usgs.gov/minerals/pubs/state/2010_11/

myb2-2010_11-mt.pdf.

U.S. Geological Survey, 2015c, The mineral industry of Utah, in 

Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook 2010–2011, v. II, p. 47.1–47.14, accessed February 4, 

2016, at http://minerals.usgs.gov/minerals/pubs/state/2010_11/

myb2-2010_11-ut.pdf.

Woodbury, W.D., 1992, Lead, in Metals and minerals: U.S. Bureau 

of Mines Minerals Yearbook 1992, v. 1, p. 709–733, accessed 

February 9, 2016, at http://digicoll.library.wisc.edu/cgi-bin/

EcoNatRes/EcoNatRes-idx?type=turn&entity=EcoNatRes.

MinYB1992v1.p0741&id=EcoNatRes.

MinYB1992v1&isize=M.

Lithium

Although lithium markets vary by location, global end-use 

markets are estimated as follows: batteries, 35 percent; ceramics 

and glass, 32 percent; lubricating greases, 9 percent; air treatment 

and continuous-casting mold-flux powders, 5 percent each; 

polymer production, 4 percent; primary aluminum production, 

1 percent; and other uses, 9 percent. Lithium consumption for 

batteries has increased significantly in recent years because 

rechargeable lithium batteries are used extensively in the growing 

market for portable electronic devices and increasingly are used 

in electric tools, electric vehicles, and grid-storage applications. 

Lithium minerals are used directly as ore concentrates in ceramics 

and glass applications worldwide (Jaskula, 2016).

The USGS National Minerals Information Center (NMIC) 

reported that in 2015 the United States continued to produce 

lithium from one lithium-brine operation located at Silver Peak 

in Esmeralda County, Nevada (Jaskula, 2016). In 2013, the 

mine produced approximately 870 metric tons (t) of lithium 

and represented about 3 percent of world production. Historical 

production statistics for the Silver Peak operation are withheld 

Appendix 5 195
196 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

to avoid disclosing company proprietary data in most years 

(Jaskula, 2015).

The United States was the world’s leading producer 

until the late-1990s, when relatively low-cost lithium 

production recovered from subsurface lithium-rich brines in 

Chile underwent significant growth. In response to the lower 

market prices, hard-rock mining operations in North Carolina 

decreased production and eventually closed.

The recovery of lithium from scrap is an emerging industry, 

and only a relatively small quantity of lithium is recovered from 

the secondary sources such as batteries (Jaskula, 2015).

The estimated consumption of lithium in the Untied States 

from 1990 to 2014 ranged from a high of 2,800 metric tons (t) for 

the years 1997–2000 (when the two largest lithium-consuming 

sectors were ceramics and glass and primary aluminum 

production) to 1,100 t in 2002 (owing to the closure of several 

major aluminum smelters and a large cookware factory) and 2010 

(owing to the economic downturn which began in 2008).

The United States relies on foreign sources of lithium 

carbonate, lithium hydroxide, and other lithium compounds to 

supplement its commercial and strategic requirements. In 2014, 

the United States imported approximately 2,120 t and exported 

about 1,420 t of lithium contained in a variety of different lithium 

compounds. In the 1990s until about 2001, the United States was 

a net exporter of lithium. With the closure of mines in the United 

States and increased imports for consumption, import reliance has 

increased. In 2014, net import reliance was estimated to be greater 

than 60 percent. From 2011 through 2014, the two leading import 

sources of lithium to the United States were Chile, with an average 

58 percent share, and Argentina, with a 38 percent share of total 

imports. China supplied 3 percent of total U.S. imports over the 

same period (Jaskula, 2016).

The Defense Logistics Agency (DLA) Strategic Materials 

maintains the National Defense Stockpile (NDS) of strategic 

and critical materials to supply the military, industrial, and 

essential civilian needs of the United States for national defense. 

In an effort to modernize the NDS by acquiring new materials 

needed for defense applications, the DLA announced plans to 

acquire 150 kilograms (kg) of lithium cobalt oxide and 540 kg 

of lithium nickel cobalt aluminum oxide during fiscal year 2015. 

The materials are to be used for cathodes in lithium-ion batteries. 

By the end of 2015, the NDS had acquired stocks of 241 kg of 

lithium cobalt oxide and 690 kg of lithium nickel cobalt aluminum 

oxide, with plans to make additional purchases in the subsequent 

years (Defense Logistics Agency Strategic Materials, 2014, 2015; 

Jaskula, 2016). 

From 1990 to 2014, total annual world lithium production, 

excluding U.S. production, increased from approximately 5,400 

to 31,700 t for a compound average annual growth rate of more 

than 7.5 percent. The effect of the global recession is reflected by 

a short term, but significant decrease, in world production in 2009 

(Kelly and Matos, 2007). A significant driver for increased world 

lithium production was the rise in demand for lithium compound 

use in rechargeable lithium-ion battery applications for electronic 

devices and electric and hybrid vehicles. Consumer demand in this 

sector is anticipated to continue to increase, barring technological 

breakthroughs using different materials, economic downturns, and 

other factors. In 2014, Australia led the world in mined lithium 

production with a nearly 42 percent share, all of which was 

contained in lithium minerals. Other countries with significant 

lithium production included Chile, Argentina, and China, with 

36, 10, and 7 percent shares of world production, respectively. 

Lithium in Argentina and Chile is recovered from brine deposits, 

and lithium from China is recovered from a combination of 

brine and mineral deposits. In 2014, world lithium reserves were 

estimated at 14 million metric tons; with about 3 percent located in 

the United States.

The average annual unit value per metric ton ($/t) of lithium 

content since 1990, expressed in constant 1998 U.S. dollars, has 

ranged from a low of $1,220/t in 2005 to a high of $5,040 in 1991 

(Kelly and Matos, 2007). Prices are weighted toward lithium 

carbonate, because it is produced in the largest quantity and has the 

highest combined value among lithium compounds. The average 

unit value for lithium carbonate in 2014 was $3,110/t (Jaskula, 

2016). In general, higher prices reflect periods of greater demand 

and a tightening of supply.

References Cited

Defense Logistics Agency Strategic Materials, 2014, Annual 

materials plan for FY 2015 for possible acquisition of new NDS 

stocks: Defense Logistics Agency Strategic Materials, October 

2, 1 p., accessed March 10, 2016, at http://www.dla.mil/

Portals/104/Documents/StrategicMaterials/3088%20FY15%20

AMP_ACQ.pdf.

Defense Logistics Agency Strategic Materials, 2015, Annual 

materials plan for FY 2015 for possible acquisition of new NDS 

stocks: Defense Logistics Agency Strategic Materials, October 

1, 1 p., accessed March 10, 2016, at http://www.dla.mil/

Portals/104/Documents/StrategicMaterials/3088%20FY15%20

AMP_ACQ.pdf.

Jaskula, B.W., 2015, Lithium: U.S. Geological Survey Commodity 

Summaries 2014, p. 94–95, accessed February 4, 2016, at http://

minerals.usgs.gov/minerals/pubs/mcs/2015/mcs2015.pdf.

Jaskula, B.W., 2016, Lithium: U.S. Geological Survey Commodity 

Summaries 2015, p. 100–101, accessed February 4, 2016, at 

http://minerals.usgs.gov/minerals/pubs/mcs/2016/mcs2016.pdf.

Kelly, T.D., and Matos, G.R., comps., 2007, Historical statistics 

for mineral and material commodities in the United States: 

U.S. Geological Survey Data Series 140, ver. 2011, accessed 

February 4, 2016, at http://minerals.usgs.gov/minerals/pubs/

historical-statistics/.

Mercury

Publications of the USGS National Minerals Information 

Center (NMIC) reported that mercury has not been produced as 

a principal mineral commodity in the United States since 1992. 
From 1990 to 1992, the United States produced a total of 684 t. 

About 70 percent of the production originated from the McDermitt 

Mine located in Humboldt County, Nevada, which closed in 

late-1990 (Reese, 1989, 1990, 1991). The balance of the domestic 

mercury-mine production during that period was as a byproduct 

of the pyrometallurgical treatment of sulfidic refractory gold 

concentrates in the Nevada counties of Elko, Eureka, Humboldt, 

Mineral, Nye, Washoe, and White Pine; Napa County, California; 

and Tooele County, Utah. In 2015, mercury continued to be 

recovered as a product of processing gold-silver ore at several 

mines in Nevada; however, production data were not reported. 

Mercury is also recovered by recycling batteries, compact 

and traditional fluorescent lamps, dental amalgam, medical 

devices, and thermostats, as well as mercury-contaminated 

soils (George, 2016). Owing to mercury’s toxicity and concerns 

for the environment and human health, overall world mercury 

consumption has declined. Most of the metal’s current end use is 

in chlor-alkali plants for the production of chlorine and sodium 

hydroxide (only two plants using mercury remained operating in 

the United States in 2015) and for the recovery of gold by artisanal 

miners, mostly in developing countries. The trend of decreasing 

global consumption is reflected in global mercury mine production 

statistics for the years 1990 to 2014, which has contracted from 

4,100 metric tons (t) to 2,350 t for an average compound annual 

rate of decline of just more than 2 percent. It is likely that this 

trend will continue for the balance of the decade. In 2014, China 

produced an estimated 1,600 t of primary mercury and accounted 

for 68 percent of world production. Statistical data on mercury 

production in Mexico is incomplete, but based on the country’s 

level of exports, it is likely they were the second leading producer 

with about a 21 percent share of world production (George, 2016). 

China is expected to continue to be the world’s major producer for 

the foreseeable future.

At the end of 2014, an inventory of 4,436 t of mercury 

was held in storage at the Hawthorne Army Depot, Hawthorne, 

Nevada, and about 1,200 t of mercury was held by the U.S. 

Department of Energy, Oak Ridge, Tennessee. Sales of mercury 

from the National Defense Stockpile remained suspended. 

Beginning in January 1, 2013, the export of elemental mercury 

from the United States was banned, with some exceptions, under 

the Mercury Export Ban Act of 2008. Less than 1 t of mercury 

was exported in 2013, and no exports have been recorded in 

subsequent years. Imports for consumption to the United States 

declined substantially from 249 t in 2012 to 49 t in 2014 (George, 

2015, 2016). Mercury is not considered a strategic and critical 

material, mainly because of its (1) limited remaining applications 

as determined by legislation, (2) substitution by other materials 

through advances in technology, and (3) large inventories.

The average free-market price in nominal dollars for 

mercury has remained unchanged at about $53,700 per metric 

ton ($/t) ($1,850 per flask) since 2011. Expressed in constant 

1998 U.S. dollars, for the purpose of comparison, the price of 

mercury has increased nearly four-fold since 1990, when the price 

of mercury was $9,020/t. Two major factors contributed to the 

substantial increase in the price of mercury beginning in about 

2009. Supply decreased from primary production, owing to the 

increase in regulation of the production and trade of mercury, and 

secondary production decreased, owing to reduced availability 

from recycling. Secondly, an increase in demand for mercury 

in the artisanal and small-scale mining industry resulted from a 

substantial increase in the price of gold. 

References Cited

George, M.W., 2015, Mercury: U.S. Geological Survey Mineral 

Commodity Summaries 2014, p. 102–103, accessed on 

February 4, 2016, at http://minerals.usgs.gov/minerals/pubs/

mcs/2015/mcs2015.pdf.

George, M.W., 2016, Mercury: U.S. Geological Survey Mineral 

Commodity Summaries 2016, p. 108–109, accessed on 

February 4, 2016, at http://minerals.usgs.gov/minerals/pubs/

mcs/2016/mcs2016.pdf.

Reese, R.G., Jr., 1989, Mercury, in Minerals Yearbook 1989, Staff, 

Branch of Nonferrous Metals, p. 705–708 accessed on February 

4, 2016, at http://digicoll.library.wisc.edu/cgi-bin/EcoNatRes/

EcoNatRes-idx?type=article&did=EcoNatRes.MinYB1989v1.

i0049&id=EcoNatRes.MinYB1989v1&isize=M.

Reese, R.G., Jr., 1990, Mercury, in Minerals Yearbook 1990, 

p. 743–747, v. 1, accessed March 15, 2016, at http://

digicoll.library.wisc.edu/cgi-bin/EcoNatRes/EcoNatResidx?type=article&did=EcoNatRes.MinYB1990v1.

RReese&id=EcoNatRes.MinYB1990v1&isize=M.

Reese, R.G., Jr., 1991, Mercury, in Minerals Yearbook 

1991, p. 989–995, accessed March 15, 2016, at http://

digicoll.library.wisc.edu/cgi-bin/EcoNatRes/EcoNatResidx?type=article&did=EcoNatRes.MinYB1991v1.

RReese&id=EcoNatRes.MinYB1991v1&isize=M.

Molybdenum

Molybdenum is a refractory metallic element used 

principally as an alloying agent in cast iron, steel, and superalloys 

to enhance hardenability, strength, toughness, and wear-and 

corrosion resistance. Other uses for molybdenum are in catalysts, 

chemicals, lubricants, and pigments (Polyak, 2015a, b).

The USGS National Minerals Information Center (NMIC) 

reported that in 2014, the United States produced 68,200 metric 

tons (t) of molybdenum in concentrates from 13 mines as either a 

primary product or byproduct of mining, ranking second in global 

mine production. In 2014, molybdenum was recovered from 5 

mines in Arizona, 2 in Colorado, and 1 mine each in Montana, 

Nevada, and Utah. Molybdenum production is ongoing or has 

occurred within the States included in the assessment area since 

2005 in Custer County, Idaho; Silver Bow County, Montana; 

White Pine County, Nevada; and Salt Lake County, Utah (Polyak, 

2013, 2016). There are two molybdenum mines—Thompson 

Creek in Custer County and Ashdown Mine in Humboldt County, 

Nevada, that are within 25 kilometers (km) of the assessment area. 

Appendix 5 197
198 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

The Thompson Creek went on care and maintenance status in 

December 2014. There was no production in 2015. The Ashdown 

Mine has been closed since early 2012. 

In 2014, U.S. mine production of molybdenum was about 

68,200 t contained in concentrate, about 11 percent more than 

the estimated 61,600 t of molybdenum contained in concentrates 

that was produced in 1990. The average compound annual rate 

of growth was less than half of a percent. In 2014, estimated U.S. 

molybdenum ore reserves contained approximately 2.7 million 

metric tons (Mt) of molybdenum (Polyak, 2016).

Molybdenum is recycled as a component of catalysts, ferrous 

scrap, and superalloy scrap. The recycling of steel, which contains 

molybdenum as an alloying agent (the major use of molybdenum), 

is the most significant source of recovered molybdenum from 

secondary sources. Molybdenum is not separated and remains as 

a component of the reused steel. Currently, no processes for the 

separate recovery and refining of secondary molybdenum from 

its alloys are used. Data regarding the amount of molybdenum 

contained in the recycled steel are not available. 

Approximately 25,300 t of molybdenum contained in 

concentrates (mostly as molybdenum trioxide) and other 

molybdenum-containing materials, such as ferromolybdenum, 

were imported for consumption to the United States in 2014, 

compared with 2,560 t in 1990. Total imported molybdenum 

ores and concentrates (roasted and unroasted) increased from 

about 433 t of contained molybdenum in 1990 to 15,770 t in 

2014. For the years 2011–14, Mexico was the leading source 

of imported molybdenum ores and concentrates with a 31 

percent share. Other major import sources during that time 

period and their share of imports were Canada (28 percent), 

Peru (23 percent), and Chile (17 percent) (Blossom, 1992, 

1993; Polyak, 2015a, 2016).

The quantity of imported ferromolybdenum, also a 

component of molybdenum imports, increased from 1990 to 

2014 from 871 to 5,110 t of contained molybdenum (Blossom, 

1993; Polyak, 2015). The increases reflect higher production 

of specialty steels in the United States, mainly in full alloy 

steels for the construction and transport industry. For the years 

2011–14, Chile was the leading source of ferromolybdenum 

with 83 percent, followed by Canada with 9 percent (Blossom, 

1992, 1993; Polyak, 2015, 2016).

In 2014, the United States exported about 65,100 t of 

molybdenum contained in various products, most of which was 

contained in roasted concentrates (molybdenum trioxide), a 

significant increase from 1990 when the United States exported 

43,400 t (Blossom, 1993; Polyak, 2016). 

In the United States, molybdic oxide and ferromolybdenum 

are used principally in steels, with a significant volume of oxide 

being used in catalysts. Ammonium and sodium molybdate are 

used in pigments, catalysts, and other chemical uses. Molybdenum 

metal (mostly powder) products are used mainly in mill products 

and nonferrous alloys. Apparent consumption of molybdenum in 

the United States has increased from about 20,300 t in 1990 to an 

estimated 27,900 t in 2014 (Blossom, 1992, 1993; Polyak, 2016). 

The U.S. Defense Logistics Agency does not hold a stockpile 

of molybdenum (Polyak, 2016). Molybdenum is not considered a 

strategic or critical commodity because of the Nation’s substantial 

mine production and capacity of processing facilities and stocks 

held by consumers and producers. The United States has been a 

net exporter of molybdenum in various forms and compounds for 

several decades. For that reason, the United States is not reliant on 

imported molybdenum. 

From 1990 to 2014, world production of molybdenum 

in concentrate increased from 112,000 to 281,000 t, for an 

average compound annual growth rate of about 4 percent. 

In 2014, China was the world leader in the production of 

molybdenum in concentrate with 103,000 t, which represented 

a 37 percent share. This was a significant increase from 

1990, when the China produced an estimated 2,000 t of 

molybdenum in concentrate and represented a 2 percent share 

of world production. Other major producers of molybdenum 

in concentrate in 2014 were the United States (24 percent), 

Chile (17 percent), Peru (6 percent), and Mexico (5 percent) 

(Blossom, 1992, 1993; Polyak, 2016). Molybdenum 

consumption has continued to increase, owing to increases 

in China’s industrial growth fueled by steel manufacturers 

producing higher-grade steel products for domestic consumption 

in China, as well as to increase steel exports. The principal 

areas of molybdenum growth are expected to be in the use of 

stainless and other steels containing molybdenum in aerospace 

and aircraft-engine components, chemical and petrochemical 

processing plants, motor-vehicle components, nuclear power 

plants, and in wind power generation components.

The average annual molybdenum price per metric ton 

($/t) of molybdenum contained in technical-grade molybdic 

oxide, expressed in constant 1998 U.S. dollars for the purpose 

of comparison since the year 1990, ranged from a low of about 

$4,780/t ($2.16/per pound) in 2001 to a high of $58,500/t 

(26.53/per pound) in 2005. The sharp rise in the price of the 

metal in 2005 was a result of high demand by China and tight 

supply. Prices dropped in subsequent years in response to 

increased production followed by weakened demand for the 

metal in most major molybdenum-consuming nations during 

the global recession. In 2014, the average price of molybdenum 

contained in technical-grade molybdic oxide in nominal dollars 

was approximately $25,840/t ($11.72/per pound). Metal prices, 

in general, decreased during the 2014–15 period in response 

to decreasing demand and oversupply (Blossom, 1992, 1993; 

Kelly and Matos, 2007; Polyak, 2015a, 2016).

References Cited

Blossom, J.W., 1992, Molybdenum: U.S. Bureau of Mines 

Mineral Commodity Summaries 1992, p. 118–119.

Blossom, J.W., 1993, Molybdenum, in Metals and minerals: 

U.S. Bureau of Mines Minerals Yearbook 1993, v. 

1, p. 669–683, accessed February 10, 2016, at http://

digicoll.library.wisc.edu/cgi-bin/EcoNatRes/EcoNatResidx?type=turn&entity=EcoNatRes.MinYB1993v1.

p0683&id=EcoNatRes.MinYB1993v1&isize=M.
Kelly, T.D., and Matos, G.R., comps., 2007, Historical 

statistics for mineral and material commodities in the 

United States: U.S. Geological Survey Data Series 140, ver. 

2011, accessed on February 10, 2016, at http://minerals.

usgs.gov/minerals/pubs/historical-statistics/.

Polyak, D.E., 2013, Molybdenum [advanced release], in

Metals and minerals: U.S. Geological Survey, Minerals 

Yearbook 2013, v.1, p. 50.1–50.12, accessed February 10, 

2016, at http://minerals.usgs.gov/minerals/pubs/commodity/

molybdenum/myb1-2013-molyb.pdf.

Polyak, D.E. 2015a, Molybdenum [advanced release], in

Metals and minerals: U.S. Geological Survey, Minerals 

Yearbook 2014, v.1, p. 50.1–50.12, accessed February 10, 

2016, at http://minerals.usgs.gov/minerals/pubs/commodity/

molybdenum/myb1-2014-molyb.pdf.

Polyak, D.E., 2015b, Molybdenum: U.S. Geological Survey 

Mineral Commodity Summaries 2015, p.106–107, accessed 

February 10, 2016, at http://minerals.usgs.gov/minerals/

pubs/commodity/molybdenum/mcs-2016-molyb.pdf.

Polyak, D.E., 2016, Molybdenum: U.S. Geological Survey 

Mineral Commodity Summaries 2016, p.112–113, accessed 

February 10, 2016, at http://minerals.usgs.gov/minerals/

pubs/commodity/molybdenum/mcs-2016-molyb.pdf.

Rare Earth Elements

The rare earth elements (REE) include the lanthanide 

elements with atomic numbers 57 through 71, plus scandium 

and yttrium. The lanthanides include, in order of atomic number, 

lanthanum, cerium, praseodymium, neodymium, promethium, 

samarium, europium, gadolinium, terbium, dysprosium, holmium, 

erbium, thulium, ytterbium, and lutetium (International Union of 

Pure and Applied Chemistry, 2005). 

The principal ores from which REE are extracted are 

characterized by the minerals bastnäsite, loparite, monazite, 

lateritic ion-adsorption clays, and xenotime. Bastnäsite, the 

leading ore mineral source of REE in the world, is enriched with 

cerium, lanthanum, neodymium, praseodymium, and other REE. 

Bastnäsite, a fluorocarbonate mineral, is produced in China and 

formerly in the United States. Loparite, which is an oxide mineral, 

is produced at one mine in Russia near Revda, Murmansk Oblast, 

and further processed into REE compounds in Solikamsk, Perm 

Oblast. Monazite is a phosphate mineral that contains REE and 

the radioactive element thorium. Although monazite has been 

and could be produced as a byproduct of many heavy-mineral 

operations, limited demand for thorium, and in some cases, 

environmental concerns associated with radioactivity, had led 

most producers outside of China to stop recovering monazite; 

however, recent efforts in India and elsewhere may be reversing 

this trend. REE mineral concentrates containing mostly supergene 

(enriched) monazite low in thorium are produced in Australia 

and then exported to Malaysia to be further processed into REE 

compounds. Xenotime, a phosphate mineral rich in yttrium and 

certain other REE, has been produced from tin-bearing cassiterite 

deposits and is a potential byproduct from the production of 

heavy-mineral placer deposits. Like most REE minerals, xenotime 

may contain some level of thorium. 

Lateritic deposits in southern China contain clays that have 

rare earth ions adsorbed into their mineral surfaces. These deposits 

make up the world’s principal supply source of yttrium and the 

heavy REE (terbium, dysprosium, holmium, erbium, thulium, 

ytterbium, and lutetium).

Rare earth elements (individually and in combination with 

other REE) are used in a wide range of applications, including 

batteries, catalysts, ceramics, electronics, glass, lasers, medicine, 

permanent magnets, phosphors, polishes, and a host of metal 

alloys including aluminum-base, iron-base, magnesium-base, 

and super alloys. In 2014, the domestic consumption of rare 

earths by end use was as follows, in decreasing order: catalysts 

(60 percent), metallurgical applications and alloys (10 percent), 

ceramics and glass (10 percent), glass polishing (10 percent), 

and other (10 percent). The China Rare Earth Association 

reported that China’s rare earth oxide equivalents (REOE) 

consumption in 2014 was 90,000 metric tons (t). The end 

use distribution in China was, in descending order, magnets 

(35 percent), polishing (18 percent), catalysts (15 percent), 

ferrosilicon (8 percent), hydrogen alloys (8 percent), aluminum 

alloys (6 percent), phosphors (2 percent), and magnesium alloys 

(0.2 percent). Rare earth demand in China was forecast to 

increase to 149,000 t by 2020.

In 2014, bastnäsite was mined by one company in the 

United States at Mountain Pass, California. The mine produced 

5,400 t of REOE contained in mineral concentrates that were 

processed into downstream rare earth compounds. In October 

2015, the mine shut down after nearly 4 years of continuous 

operation. The Mountain Pass mine was first developed in 

the 1950s and was idle from 2002 through 2011. Although 

the operation continued to process previously mined ore, no 

domestic mine production of REE was reported during those 

years. Domestic production in 2014 was significantly less than 

the estimated 22,700 t of REOE produced in 1990. Domestic 

production ceased in the early 1990s from the processing of 

monazite as a byproduct from heavy-mineral sands in Florida 

and North Carolina. No production of REE have been reported 

within the assessment area, although they may have been 

contained in heavy-mineral placers and not recovered. In 2014, 

it was estimated that U.S. reserves contained approximately 

1.8 million metric tons of REOE (Bleiwas and others, 2013; 

Gambogi, 2016a, b; Hedrick, 1992, 1993, 1994; Kelly and 

Matos, 2007).

In addition to domestically mined material, a limited amount 

of REE was recovered from the recycling of batteries, permanent 

magnets, and fluorescent lamps (Gambogi, 2016a). 

In 2014, the United States exported about 6,180 t of 

REOE contained in various rare earth compounds and metals. 

During the period 1990 to 2014, U.S. exports have varied 

between 5,360 t and 13,000 t, often fluctuating based on market 

conditions. Outside of China, the United States has been a 

Appendix 5 199
200 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

leading consumer of rare earths. The characteristics (elemental 

composition, type of compound, purity, and other qualities) of 

rare earth exports have changed over time because of the loss of 

downstream processing capabilities (Gambogi, 2016a).

In 2014, an estimated 11,600 t of REOE contained in various 

rare earth compounds and metals were imported to the United 

States. Increases in imports since 2012 reflect lower prices for 

rare earth compounds and metals. The leading import sources and 

their respective percentage shares for rare earth compounds and 

metals for the years 2011–14 were China (71 percent), Estonia 

(7 percent), and France and Japan (6 percent each) (Gambogi, 

2016a). 

Domestic consumption in 2014 was estimated at 17,000 t of 

REOE, significantly less than in 1990 when it was an estimated 

28,700 t. Much of the decrease reflects reduced consumption 

by intermediate processors of rare earth compounds (Gambogi, 

2016a; Kelly and Matos, 2007).

Net import reliance, as a percentage of apparent consumption 

in 2014, was estimated at 68 percent, an increase from 1990 when 

it was estimated at 20 percent. The significant change in import 

reliance from 1990 to 2014 reflects the reductions in domestic 

mining and processing of REE compounds (Gambogi, 2016a, b; 

Kelly and Matos, 2007).

Rare earths are important to numerous defense applications 

such as such as aircraft, communications, drive motors, 

electronics, lasers, optics, precision-guided missiles, radar, and 

smart bombs. The Defense Logistics Agency, Strategic Materials 

Division (DLA–SM) has conducted numerous assessments in 

regard to availability of REE for defense applications, and the 

Department of Defense has recommended that Congress authorize 

the acquisition of specific materials to mitigate the potential 

shortfalls. In the fiscal year 2014 National Defense Authorization 

Act, Congress authorized the acquisition of dysprosium and 

yttrium (Gambogi, 2016a; Grasso, 2013; Ucore Rare Metals, Inc., 

2015). 

From 1990 to 2014, the total world REOE mine production 

increased to 123,000 t from 52,900 t for an average compound 

annual growth rate of nearly 4 percent. The upward trend reflects 

technological advances that increased demand for REE used in 

materials such as batteries, catalysts, and magnets. In 2014, China 

produced 105,000 t of REOE and accounted for 85 percent of 

world production. This was a significant increase from 1990, when 

China produced an estimated 16,500 t and accounted for about 30 

percent of world production. Other producers of mined REE in 

2014, and estimates of their respective share of global production 

were Australia (7 percent), the United States (4 percent), and 

Russia and Thailand (about 2 percent each) (Hedrick, 1992, 1993, 

1994; Gambogi, 2016a, b; Kelly and Matos, 2007). In general, 

the price per unit of the heavy REE is considerably higher than 

for light REE (lanthanum, cerium, praseodymium, neodymium, 

samarium, europium, and gadolinium). This price differential is 

driven by scarcity and higher processing costs.

Because of their importance for advanced technologies, 

the upward trend in demand for REE is likely to continue. The 

price of REE and their compounds vary considerably and are 

often negotiated by contract. Examples of published prices 

at yearend 2014 ranged from a low of 4 to 5 U.S. dollars per 

kilogram ($/kg) for cerium oxide (99.5 percent minimum) 

to a high of $680–730/kg for europium oxide (99.9 percent 

minimum). In general, the prices for REE dropped significantly 

from prices published during the past several years as the 

available supply has exceeded growth in demand (Gambogi, 

2016a, b).

References Cited

Bleiwas, D.I., and Gambogi, Joseph, 2013, Preliminary estimates 

of the quantities of rare earth elements contained in selected 

products and in imports of semi manufactured products to the 

United States, 2010: U.S. Geological Survey Open-File Report 

2013–1072, 14 p., accessed March 8, 2016, at http://pubs.usgs.

gov/of/2013/1072/.

Gambogi, Joseph, 2016a, Rare earths: U.S. Geological Survey 

Mineral Commodity Summaries 2016, p. 134–135, accessed 

March 8, 2016, at 4, 2016, at http://minerals.usgs.gov/minerals/

pubs/commodity/rare_earths/mcs-2016-raree.pdf.

Gambogi, Joseph, 2016b, Rare earths [advanced release], in

Metals and minerals: U.S. Geological Survey, Minerals 

Yearbook 2013, v. 1, p. 60.1–60.17, accessed March 8, 2016, at 

http://minerals.usgs.gov/minerals/pubs/commodity/rare_earths/

myb1-2013-raree.pdf.

Grasso, Valerie, 2013, Rare Earth Elements in National 

Defense—Background, Oversight Issues, and Options 

for Congress: Washington, D.C., Congressional Research 

Service, December 23.

Hedrick, J.B., 1992, Rare earth metals: U.S. Bureau of Mines 

Mineral Commodity Summaries 1992, p. 140–141. 

Hedrick, J.B., 1993, Rare earth metals: U.S. Bureau of Mines 

Mineral Commodity Summaries 1993, p. 138–139. 

Hedrick, J.B., 1994, Rare earths, in Metals and minerals: U.S. 

Geological Survey, Minerals Yearbook 1994, v. 1, p. 1–10, 

accessed March 8, 2015, at http://minerals.usgs.gov/minerals/

pubs/commodity/rare_earths/740494.pdf.

International Union of Pure and Applied Chemistry, 

2005, Nomenclature of Inorganic Chemistry—IUPAC 

Recommendations 2005, accessed March 14, 2016, at 

http://www.iupac.org/fileadmin/user_upload/databases/

Red_Book_2005.pdf.

Kelly, T.D., and Matos, G.R., comps., 2007, Historical 

statistics for mineral and material commodities in the 

United States: U.S. Geological Survey Data Series 140, ver. 

2011, accessed February 4, 2016, at http://minerals.usgs.

gov/minerals/pubs/historical-statistics/.

Ucore Rare Metals, Inc., 2015, Rare earths: Ucore Rare Metals, 

Inc., Web site, accessed on March 14, 2016, at http://ucore.com.
Silver

Traditional use categories for silver include coin and medal 

fabrication; industrial applications, including electrical and 

electronics components; jewelry and silverware; and photography 

(Virta, 2015).

Publications of the USGS National Minerals Information 

Center (NMIC) reported that in 2014 the United States mined 

about 1,180 metric tons (t) of silver as the principal product, 

coproduct, or byproduct from mines in 11 States. Combined, 

these mines accounted for approximately 4 percent of global 

silver mine production. In 2013, the principal mining States for 

silver were, in descending order of production, Alaska, Nevada, 

Idaho, and Utah. In Nevada, silver production is ongoing or 

has recently occurred in the gold producing counties of Elko, 

Esmeralda, Eureka, Humboldt, Pershing, Lander, Mineral, Nye, 

and White Pine (U.S. Geological Survey, 2015a). One silver 

producing company is within 25-kilometer (km) of the study area 

in Elko County, Nevada. In Idaho, silver production comes from 

two mines in Shoshone County. In Utah, silver is currently being 

produced in Salt Lake County, primarily from the Bingham Mine 

(U.S. Geological Survey, 2015b). In 2014, U.S. mine production 

of silver was about 1,180 t, which was significantly less than 

the 2,120 t that was produced in 1990. The overall decrease in 

silver domestic production can be attributed to a combination of 

increasing costs, lower ore grades, mine closures, and a decrease 

in the proportion of copper recovered through conventional 

flotation and smelting. Copper ores processed through leaching 

and solvent extraction-electrowinning do not yield any silver. 

Although the price of silver increased significantly from 1990 to 

its record-high level in 2011, silver mine production in the United 

States generally trended downward through several cycles from 

its near peak level in 1990 by an average compound annual rate 

of decline of about 1 percent. In addition to domestically mined 

silver, an additional 1,400 t of the silver was recovered from new 

and old scrap in 2014, a decrease of about 16 percent from the 

1,675 t that was recovered in 1990. In 2014, it was estimated that 

U.S. ore reserves contained approximately 570,000 t of silver 

(George, 2016; Hilliard, 2000; Reese, 1992).

In 2014, the United States exported about 383 t of silver 

in concentrates and refined bullion and doré and imported 

approximately 4,960 t for domestic consumption. From 2011 

through 2014, four countries accounted for 87 percent of U.S. 

imports. The country shares were Mexico (54 percent), Canada 

(26 percent), Poland (4 percent), and Peru (3 percent).

In 2014, the U.S. apparent consumption of silver was 

estimated to be 7,150 t, significantly higher than in 1990 when it 

was estimated at 4,355 t. A net decrease in consumption of silver 

in photographic applications was more than offset by increased 

consumption in other industrial uses, jewelry, and investment 

holdings. Net import reliance in 2014, as a percentage of apparent 

consumption, was estimated at 64 percent. Although the United 

States is a net importer of silver, changes in unreported investor 

stocks precluded calculations for reliable estimates of import 

reliance for the period 1990–97, but import reliance in 1998 was 

estimated at 14 percent.

The U.S. Defense Logistics Agency does not hold a 

stockpile of silver. Silver is not considered a strategic and critical 

commodity because of adequate supplies from substantial 

domestic production from primary and secondary sources; 

stocks held by industry, investors, traders, and the U.S. Treasury 

Department; and availability from multiple import sources 

(George, 2016; Hilliard, 2000; Reese, 1992). 

In 2013, about 29 percent of global silver mine production 

was from primary silver ores, 38 percent was from lead and 

zinc ores, 20 percent from copper ores, 13 percent from gold 

ores, and less than 1 percent was from other types of mining 

operations (Virta, 2015). From 1990 through 2014, total world 

mine production of silver increased from 16,600 to 26,800 t for 

an average compound annual growth rate of nearly 2 percent. 

In 2014, Mexico was the leading mine producer of silver and 

accounted for 19 percent of global production. Other major 

silver producers were China (15 percent); Peru (14 percent); 

Australia and Chile (6 percent each); Bolivia, Poland, and 

Russia (5 percent each); and the United States (4 percent). 

China’s silver production has increased more than thirtyfold 

from approximately 130 t in 1990 to 4,060 t in 2014. The 

increase in world silver production from 1990 to 2014 has been 

driven by an overall increase in consumption for electronics and 

jewelry and for demand as an investment vehicle.

Market sectors for silver consumption have changed 

since the early 1990s. For example, consumption in the 

photographic sector, which in 1990 used about 50 percent of 

total U.S. silver consumption, decreased to 8 percent in 2014 

with the increase in use of digital photography (George, 2016; 

Reese, 1992).

The average annual silver price per troy ounce, ranged from 

a low of about $4.00 per troy ounce ($1,300/t) in 2001 to a high 

of nearly $36 per troy ounce in 2011 ($1,130,000/t). In 2014, the 

average price of silver was approximately $13.00 per troy ounce 

(Kelly and Matos, 2007; George, 2016).

References Cited

George, M.W., 2016, Silver: U.S. Geological Survey Mineral 

Commodity Summaries 2016, p.152–153, accessed on 

February 4, 2016, at http://minerals.usgs.gov/minerals/pubs/

commodity/silver/mcs-2016-silve.pdf.

Hilliard, H.E., 2000, Silver: U.S. Geological Survey Mineral 

Commodity Summaries 2000, p. 152–153, accessed on 

February 4, 2016, at http://minerals.usgs.gov/minerals/pubs/

commodity/silver/880300.pdf.

Kelly, T.D., and Matos, G.R., comps., 2007, Historical 

statistics for mineral and material commodities in the 

United States: U.S. Geological Survey Data Series 140, ver. 

2011, accessed on February 4, 2016, at http://minerals.usgs.

gov/minerals/pubs/historical-statistics/.

Reese, R.G., Jr., 1992, Silver: U.S. Geological Survey Mineral 

Commodity Summaries 1992, p. 160–161.

Appendix 5 201
202 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

U.S. Geological Survey, 2015a, The mineral industry of Nevada, 

in Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook 2010–2011, v. II, p. 30.1–30.17, accessed February 4, 

2016, at http://minerals.usgs.gov/minerals/pubs/state/2010_11/

myb2-2010_11-nv.pdf.

U.S. Geological Survey, 2015b, The mineral industry of Utah, 

in Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook 2010–2011, v. II, p. 47.1–47.14, accessed February 4, 

2016, at http://minerals.usgs.gov/minerals/pubs/state/2010_11/

myb2-2010_11-ut.pdf.

Virta, R.L., 2015, Silver: U.S. Geological Survey Minerals 

Yearbook 2013, p. 68.1–68.13, v. 1, accessed on February 8, 

2016, at http://minerals.usgs.gov/minerals/pubs/commodity/

silver/myb1-2013-silve.pdf.

Specialty Clay—Hectorite

Hectorite is a bright white lithium-rich magnesium silicate 

mineral that belongs to the smectite clay group. Hectorite occurs 

in mineral deposits and can also be produced synthetically. 

The mineral’s unique physical and chemical properties make 

it useful for applications such as increasing thermal stability 

and viscosity in ceramics and oil-based drilling mud and for 

adding color, spreadability, and viscosity in deodorants, facial 

cleansers, moisturizers, shampoos, and paints (Dell, 1996; Paint 

& Coatings Industry, 2004; Schlumberger, Ltd., 2016; Western 

Lithium USA Corp., 2016). Statistics on the distribution of 

domestic and global end-use markets are not available; however, 

in recent years hectorite clay products have been increasingly 

used in drilling muds by the oil and gas industry for directional 

drilling in unconventional reservoirs and deep drilling in high 

pressure-high temperature environments, owing to the mineral’s 

inherent high temperature thermal stability (Lithium Americas 

Corp., 2016a, b).

Natural hectorite production data are not published to 

avoid revealing company proprietary information, but the 

United States continues to be world’s largest natural hectorite 

producer, with surface mines in Hector, California, (the origin of 

the mineral’s name) and the Kings Valley deposit in Humboldt 

County, Nevada. Some intermittent hectorite production also 

has been reported from the Disaster Peak Mine in Humboldt 

County, Nevada (Nevada Bureau of Mines and Geology, 2008, 

2013). The United States does not rely on foreign sources of 

hectorite to supplement its commercial requirements. The 

Hector Mine is currently the world’s leading producer of natural 

hectorite. The Kings Valley Mine came on-line at the end of 

2014 and is within the Nevada assessment area. The company 

that operates the Kings Valley Mine has indicated that it may 

also become a source of lithium as the company continues 

toward a feasibility study and permitting of possible lithium 

extraction (Western Lithium USA Corp., 2014, 2015).

The Defense Logistics Agency (DLA) maintains the National 

Defense Stockpile (NDS) of strategic and critical materials to 

supply the military, industrial, and essential civilian needs of the 

United States for national defense. Hectorite is not considered a 

strategic or critical mineral.

The price of hectorite clay and hectorite-based products are 

not published in industry literature. Prices are usually negotiated 

between the seller and buyer. In 2015, Hectatone®, a hectoritebased specialty product for use in high pressure-high temperature 

drilling applications, was reported to sell in the range of $2,000–

4,500 per short ton, free on board (f.o.b.) (IMFORMED Industrial 

Mineral Forums & Research, Ltd., 2015).

References Cited

Dell, Don, 1996, Hectorite as a critical element in 

manufacturing high-grade ceramic slips, bodies, and glazes, 

in A collection of papers presented at the 97th annual 

meeting and the 1995 Fall meetings of the Materials & 

Equipment/Whitewares Divisions: Ceramic engineering 

and science proceedings, April 30–May 3, 1995, Cincinnati, 

Ohio and September 13–16, 1995, Virginia Beach, Virginia, 

v. 17, issue 1, p. 70–71, accessed on March 22, 2016, at 

http://samples.sainsburysebooks.co.uk/9780470316375_

sample_378778.pdf.

IMFORMED Industrial Mineral Forums & Research, 

Ltd., 2015, World’s second hectorite source on stream: 

IMFORMED Industrial Mineral Forums & Research, Ltd., 

accessed March 24, 2016, at http://imformed.com/worldssecond-hectorite-source-on-stream/.

Lithium Americas Corp., 2016a, Applications: Vancouver, 

British Columbia, Canada, Lithium Americas Corp., 

accessed March 24, 2016, at http://www.hectatone.com/

drilling-additives-applications/.

Lithium Americas Corp., 2016b, Introducing Lithium 

Americas formerly Western Lithium: Vancouver, British 

Columbia, Canada, Lithium Americas Corp., accessed 

March 22, 2016, at http://www.westernlithium.com/about/

overview/.

Nevada Bureau of Mines and Geology, 2008, The Nevada 

mineral industry 2007: Carson City, Nevada, Nevada 

Bureau of Mines and Geology special publication MI–2007, 

180 p.

Nevada Bureau of Mines and Geology, 2013, The Nevada mineral 

industry 2011: Carson City, Nevada, Nevada Bureau of Mines 

and Geology special publication MI–2011, 160 p.

Paint & Coatings Industry, 2004, The innovation of hyperdispersible hectorite clays for automotive applications: Paint & 

Coatings Industry, May 1, accessed March 24, 2016, at http://

www.pcimag.com/articles/84353-the-innovation-of-hyperdispersible-hectorite-clays-for-automotive-applications.

Schlumberger, Ltd., 2016, Oilfield glossary—Hectorite: 

Schlumberger, Ltd., accessed March 22, 2016, at http://www.

glossary.oilfield.slb.com/Terms/h/hectorite.aspx.
Western Lithium USA Corp., 2014, Updated NI 43-101 technical 

report, Kings Valley property, Humboldt County, Nevada: 

Western Lithium USA Corp., accessed on March 22, 2016, at 

http://www.westernlithium.com/wp-content/uploads/2015/01/

NI43101May92014.pdf.

Western Lithium USA Corp., 2015, Western Lithium announces 

investor conference call—Provides updates on projects in 

Argentina and Nevada: Toronto, Ontario, and Vancouver, 

British Columbia, Canada, Western Lithium USA Corp. press 

release, December 17, accessed March 25, 2016, at http://www.

westernlithium.com/wp-content/uploads/2015/12/WLC_NR_

Dec172015.pdf.

Titanium Mineral Concentrates

Most titanium is not consumed in its metal form but is 

consumed as titanium dioxide (TiO2), a white pigment used in 

paints, paper, and plastics because of its whiteness, brightness, 

and opacity. On a gross weight basis, 95 percent of domestic 

consumption of titanium mineral concentrates was used to produce 

TiO2 pigment in 2014. The remaining 5 percent was used to 

produce metal and other miscellaneous products, including fluxes 

and welding-rod coatings. Because of the high strength-to-weight 

ratio of its alloys and their resistance to corrosion, titanium metal 

is an important strategic and critical material and is used widely 

for high-performance military and civilian aircraft in both engines 

and airframes (Bedinger, 2016).

Titanium minerals of economic importance include 

ilmenite, leucoxene, and rutile. Mining of titanium minerals 

is usually performed by surface-mining operations using 

dredging and dry-surface mining techniques for the recovery of 

heavy minerals, which include titanium mineral concentrates. 

Separation by gravity is used to isolate the heavy-mineral 

components. Further processing and separation of the heavymineral suite is accomplished using magnetic and electrostatic 

circuits, with ilmenite and rutile being the two principal mineral 

concentrates for titanium. Ilmenite is the most abundant 

titanium mineral and has a stoichiometric TiO2 content of 

53 percent, but intercalation and weathering causes the TiO2

content to vary significantly. Rutile, a naturally occurring 

TiO2 mineral with contained TiO2 of about 95 percent, is less 

abundant. Ilmenite is often processed to produce a titanium 

concentrate, either as synthetic rutile or titaniferous slag. 

Although numerous technologies are used to produce synthetic 

rutile, nearly all are based on either selective leaching or thermal 

reduction of iron and other impurities in ilmenite (Bedinger, 

2015; Gambogi, 2001; Kelly and Matos, 2007).

Because of heavy-mineral placer occurrences in or near 

the assessment area, rutile and ilmenite production derived 

from domestic mining operations is the major focus of 

this discussion. A search of U.S. Bureau of Mines, USGS, 

and other publications has not indicated any commercial 

production of ilmenite or other titanium ore minerals as a 

principal commodity within the assessment area since at least 

1990. There are some Idaho placer deposits and abandoned 

historical dredge waste piles that contain ilmenite (Anderson, 

1958; Storch and Holt, 1963), but there is no evidence that it 

was ever recovered as a salable product. 

In 2014, U.S. mine production1 of ore concentrates, from 

two mines in Virginia and one mine in Florida, was about 

100,000 metric tons (t) of contained TiO2, significantly less 

than the 300,000 t of contained TiO2 produced in 2000.2 For 

the years 2000–14, domestic mine production averaged about 

200,000 t of contained TiO2 and has trended downward since 

2007, owing to a combination of shutdowns and production 

curtailments resulting from factors such as depletion of reserves 

and economic factors. In 2015, both mine operations in Virginia 

were scheduled to shut down, but there were also plans in 

place to mine heavy-mineral concentrates in Georgia and New 

Jersey. In 2014, it was estimated that U.S. reserves contained 

approximately 2 million metric tons (Mt) of TiO2. No titanium 

concentrates were recycled in the United States, but titanium 

metal was recycled (Bedinger, 2016; Kelly and Matos, 2007).

Because domestic consumption has exceeded domestic 

production of titanium mineral concentrates, the United States 

has been import reliant for the entire period of consideration. 

In 2000, the United States was 79 percent net import reliant 

and in 2014 was 92 percent net import reliant. From 2011 to 

2014, four countries represented 94 percent of U.S. imports 

of titanium mineral concentrates—South Africa (35 percent), 

Australia (31 percent), Canada (17 percent), and Mozambique 

(11 percent) (Gambogi, 2002; Bedinger, 2016).

From 2000 to 2014 the total world mine production of 

contained TiO2 in ilmenite concentrates increased by 29 percent 

from an estimated 4.70 Mt to 6.04 Mt of contained TiO2

concentrate for an average compound annual growth rate over 

the period of about 2 percent. The increase in production of 

concentrates was brought about to a large extent by increased 

demand by China (Gambogi, 2002; Kelly and Matos, 2007; 

Bedinger, 2016).

In 2014, China was the leading world mine producer of 

Ilmenite concentrates with 960,000 t of contained TiO2, 16 

percent of global production. This was a significant increase from 

2000 when China produced about 150,000 t of contained TiO2, 

less than 5 percent of global production. Australia was the world’s 

leading producer in 2000—1.5 Mt of contained TiO2, which 

was about 31 percent of world production. By 2014, Australia 

produced 910,000 t of contained TiO2, 15 percent of global 

production (Bedinger, 2016; Gambogi, 2002).

Other major producers in 2014, and their respective 

share of global Ilmenite production, were South Africa (10 

percent), Vietnam (9 percent), and Mozambique (8 percent). 

The market for titanium mineral concentrates is expected 

to continue to be driven by the production of TiO2 pigment 

(Bedinger, 2016).

1

Domestic mine production was rounded to one significant digit to avoid 

disclosing company proprietary data.

2

Domestic mine production for the years 1983–99 were not published to 

avoid the disclosure of company confidential data.

Appendix 5 203
204 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

World production of TiO2 contained in natural rutile 

concentrate increased from about 390,000 t in 2000 to 

470,000 t in 2014, an average compound annual-growth 

rate over the period of about 1.3 percent. The increase in 

production of natural rutile concentrates resulted from the 

development of mines in Sierra Leone beginning in 2006. 

World production of TiO2 in natural rutile concentrates was 

subordinate to that of ilmenite concentrate over the entire 

period. In 2014, Australia was the world leader in mined 

natural rutile production—about 190,000 t of contained TiO2

with a 40 percent share. This was a decrease from 2000 when 

the country produced an estimated 195,000 t, 58 percent of 

world mine production. In 2014, Sierra Leone produced about 

110,000 t of contained TiO2, about 23 percent of TiO2 in natural 

rutile concentrates(Bedinger, 2016; Gambogi, 2002, 2003; 

Kelly and Matos, 2007).

Other major natural rutile producers in 2014, and their 

respective production percentage share of global TiO2 contained 

in rutile concentrates, were Ukraine (13 percent), South Africa 

(11 percent), and Kenya (5 percent) (Bedinger, 2016).

The price per metric ton ($/t) of ilmenite concentrate 

(54 percent of contained TiO2 free on board (f.o.b.) Australian 

port), expressed in constant 2000 U.S. dollars for the purpose 

of comparison since the year 2000, ranged from a low of 

about $59/t ($73/t nominal) in 2009 to a high of $225 in 2012 

($300/t nominal). Prices were depressed in 2009 in response to 

weakened demand during the global recession but rebounded 

as world economic conditions improved and demand 

increased, with China’s increased consumption being a major 

contributing factor. In 2014, the average price of ilmenite 

concentrate was approximately $113/t ($155/t nominal) 

(Gambogi, 2011; Bedinger, 2016; Kelly and Matos, 2007).

The price per metric ton ($/t) of natural rutile 

concentrate, 95 percent contained TiO2, f.o.b, Australian 

ports, expressed in constant 2000 U.S. dollars for the purpose 

of comparison since the year 2000, ranged from a low of 

about $402/t ($430/t nominal) in 2003 to a high of $1,650 

in 2012 ($2,200/t nominal). Prices increased significantly 

beginning in 2011 in response to increased demand. 

China’s consumption was a major contributing factor. In 

2014, the average price of rutile concentrate in dollars was 

approximately $691/t ($950/t nominal) (Bedinger, 2016; 

Gambogi, 2005; Kelly and Matos, 2007).

References Cited

Anderson, A.L., 1958, Uranium, thorium, columbium, and rare 

earth deposits in the Salmon region, Lemhi County, Idaho: 

Idaho Bureau of Mines and Geology Pamphlet 115, 81 p.

Bedinger, G.M., 2015, Titanium [advanced release], in Metals 

and minerals: U.S. Geological Survey, Minerals Yearbook 

2013, v. 1, p. 78.1–78.14, accessed February 12, 2016, at 

http://minerals.usgs.gov/minerals/pubs/commodity/titanium/

myb1-2013-titan.pdf.

Bedinger, G.M., 2016, Titanium mineral concentrates: U.S. 

Geological Survey Mineral Commodity Summaries 2016, 

p.178–179, accessed February 10, 2016, at http://minerals.

usgs.gov/minerals/pubs/commodity/titanium/mcs-2016-

timin.pdf.

Gambogi, Joseph, 2001, Titanium, in Metals and minerals: 

U.S. Geological Survey, Minerals Yearbook 2001, v. 1, p. 

79.1–79.16, accessed February 12, 2016, at http://minerals.

usgs.gov/minerals/pubs/commodity/titanium/670400.pdf.

Gambogi, Joseph, 2002, Titanium mineral concentrates: U.S. 

Geological Survey Mineral Commodity Summaries 2002, 

p.176–177, accessed March 10, 2016, at http://minerals.

usgs.gov/minerals/pubs/commodity/titanium/673302.pdf.

Gambogi, Joseph, 2003, Titanium in Metals and minerals: 

U.S. Geological Survey, Minerals Yearbook 2003, v. 1, p. 

78.1–78.16, accessed March 9, 2016, at http://minerals.usgs.

gov/minerals/pubs/commodity/titanium/titanmyb03.pdf.

Gambogi, Joseph, 2004, Titanium, in Metals and minerals: 

U.S. Geological Survey, Minerals Yearbook 2004, v. 1, p. 

78.1–78.17, accessed March 9, 2016, at http://minerals.usgs.

gov/minerals/pubs/commodity/titanium/titanmyb04.pdf.

Gambogi, Joseph, 2005, Titanium, in Metals and minerals: 

U.S. Geological Survey, Minerals Yearbook 2005, v. 1, p. 

176–177, accessed March 9, 2016, at http://minerals.usgs.

gov/minerals/pubs/commodity/titanium/titanmyb05.pdf.

Gambogi, Joseph, 2011, Titanium mineral concentrates: U.S. 

Geological Survey Mineral Commodity Summaries 2011, 

p.178–179, accessed March 10, 2016, at http://minerals.

usgs.gov/minerals/pubs/commodity/titanium/mcs-2011-

timin.pdf.

Kelly, T.D., and Matos, G.R., comps., 2007, Historical 

statistics for mineral and material commodities in the 

United States: U.S. Geological Survey Data Series 140, ver. 

2011, accessed February 4, 2016, at http://minerals.usgs.

gov/minerals/pubs/historical-statistics/.

Storch, R.H., and Holt, D.C., 1963, Titanium placer deposits 

of Idaho: U.S. Bureau of Mines Report of Investigations 

6319, 69 p.

Tungsten

The leading use of tungsten is in cemented carbides. 

Cemented carbides (also called hardmetals) are wearresistant materials used by the construction, metalworking, 

mining, and oil and gas drilling industries. Tungsten metal 

contacts, electrodes, filaments, wires, and other products are 

used in electrical, electronic, heating, lighting, and welding 

applications. Tungsten is also used to make corrosion- and 

wear-resistant alloy parts and coatings; specialty steels for 
pipes, tools, and valves; superalloys for turbine engine parts; 

and tungsten heavy alloys (also called “heavy-metal alloys”) 

for armaments, heat sinks, and high-density applications, 

such as weights and counterweights. Tungsten, often in 

combination with less-dense materials, is used as a substitute 

for lead in ammunition, fishing weights, hunting shot, 

radiation shielding, wheel weights, and other high-density 

applications. Tungsten chemicals are used to make catalysts, 

corrosion-resistant coatings, dyes and pigments, fire-resistant 

compounds, lubricants, phosphors, and semiconductors (U.S. 

Geological Survey, 2013; Shedd, 2015a). 

The USGS National Minerals Information Center 

(NMIC) reported that in 2014 the only tungsten concentrate 

production in the United States was from a mine north of 

Los Angeles, California. Historically, tungsten has been 

produced from, or was present at, numerous mines in the 

following counties that were within 25 kilometers (km) of the 

assessment area—Blaine, Butte, Camas, Custer, Elmore, and 

Lemhi Counties in Idaho; Beaverhead County in Montana; 

Elko, Humboldt, and Washoe Counties in Nevada; Box 

Elder and Summit Counties in Utah; and Fremont County in 

Wyoming. Annual tungsten production statistics for domestic 

mines have not been published by USGS since 1987. U.S. 

tungsten concentrate production contracted significantly in 

the early 1980s, when mines and beneficiation plants, most 

of which were located in California and Nevada, shut down 

in response to reduced consumption owing to a worldwide 

recession, a significant increase in low-priced exports of 

tungsten concentrates and intermediate products from China, 

and a precipitous drop in the price of tungsten concentrate 

(U.S. Geological Survey, 2013). In 2014, it was estimated that 

U.S. tungsten reserves were approximately 140,000 metric 

tons (t), most of which were located in California (Shedd, 

2015b).

Apparent consumption of all forms of tungsten in the 

United States in 1990 was approximately 8,500 t and increased 

to 15,000 t by 2014. The increase was due in large part to the 

increase in U.S. industrial activity during that period. 

The United States relies on foreign sources of tungsten 

concentrate and other tungsten-bearing materials, such as 

ammonium paratungstate and ferrotungsten, to supplement its 

commercial and strategic requirements. Shipments of tungsten 

materials from the National Defense Stockpile (NDS), 

which is administered by the U.S. Defense Logistics Agency 

Strategic Materials, and consumption of tungsten-bearing 

scrap also contribute to U.S. supply.

In 2014, the United States imported 12,800 t of tungsten 

contained in concentrates and other forms and exported 6,660 t. 

For 2011–14, China was the leading supplier, with a 40 percent 

share. Bolivia and Canada each represented an 8 percent share 

and Germany a 6 percent share. The balance of 38 percent was 

imported from more than 50 other countries. In 1990, U.S. 

net import reliance, as a percentage of apparent consumption, 

was estimated to be 81 percent. By 2014, import reliance had 

dropped to 43 percent mainly as a result of increased scrap 

consumption (Shedd, 2016).

In 2014, NDS held 11,600 t of tungsten in concentrate 

(Shedd, 2016). Government stockpiling is a means of reducing 

potential supply disruptions. Although the United States is a 

leading tungsten consumer, it has limited mine production and 

is highly reliant on imports for its tungsten needs. Tungsten’s 

high concentration of world production in a single country 

(China) increases the risk of supply disruption. These factors, 

combined with tungsten’s importance in a wide variety of 

commercial, industrial, and military uses and the limited options 

for substitution in most applications, are reasons why it has 

been identified as a strategic and (or) critical material by the 

U.S. Defense Logistics Agency Strategic Materials and other 

organizations.

From 1990 through 2014, world tungsten concentrate 

production expanded at a compound annual growth rate of 

approximately 2 percent, reaching 86,800 t of contained tungsten 

in 2014. China produced about 71,000 t (82 percent of world 

tungsten concentrate production) in 2014, a significant increase 

from 1990 when the country produced an estimated 32,000 t (62 

percent of world production). China’s increase can be explained 

in part by the country’s investment in its domestic industries to 

produce goods for internal consumption and export. Other leading 

tungsten concentrate producers in 2014 were Vietnam (5 percent) 

and Canada and Russia (3 percent each) (Shedd, 2016).

Tungsten materials are not traded on the London Metal 

Exchange, Ltd., but are traded on some Chinese exchanges. Most 

tungsten sales are negotiated between producers and consumers 

or between traders and consumers. Prices published by trade 

journals, such as Metal Bulletin, Platts Metals Week, and CRU 

Ryan’s Notes, are derived from information collected from 

consumers, producers, and traders. The average annual U.S. spot 

market price of tungsten concentrate per metric ton unit (MTU) 

of tungsten trioxide (WO3) in nominal dollars over the past 15 

years ranged from a low of approximately $47/MTU in 1999 to a 

high of about $358/MTU in 2012. A metric ton unit is equivalent 

to 10 kilograms (kg). For the purpose of comparison, the U.S. 

free-market price of ammonium paratungstate (the most important 

chemical precursor for most tungsten products), expressed 

in constant 1998 U.S. dollars per metric ton ($/t) of tungsten, 

ranged from a low of $6,920/t in 1999 to a high in 2012 of 

$40,200/t. During this period, China’s economy grew, its tungsten 

consumption increased, and its control over tungsten production 

and exports was strengthened. Prices trended downward beginning 

in 2013 and into 2015, as world tungsten-concentrate production 

was in oversupply, owing to an economic slowdown in China and 

weak economic conditions elsewhere (U.S. Geological Survey, 

2015; Shedd, 2013, 2015b, 2016).

References Cited

Shedd, K.B., 2015a, Tungsten, in Metals and minerals: U.S. 

Geological Survey, Minerals Yearbook 2013, v. 1, p. 

79.1–79.20, accessed January 25, 2016, at http://minerals.

usgs.gov/minerals/pubs/commodity/tungsten/myb1-2013-

tungs.pdf.

Appendix 5 205
206 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Shedd, K.B., 2015b, Tungsten: U.S. Geological Survey 

Mineral Commodity Summaries 2015, p. 174–175, accessed 

January 25, 2016, at http://minerals.usgs.gov/minerals/pubs/

commodity/tungsten/mcs-2015-tungs.pdf.

Shedd, K.B., 2016, Tungsten: U.S. Geological Survey Mineral 

Commodity Summaries 2016, p. 180–181, accessed 

March 3, 2016, at http://minerals.usgs.gov/minerals/pubs/

commodity/tungsten/mcs-2016-tungs.pdf.

U.S. Geological Survey, 2013, Tungsten, in Metal prices in 

the United States through 2010: U.S. Geological Survey 

Investigations Report 2012–5188, p. 187–193, accessed 

February 10, 2016, at http://pubs.usgs.gov/sir/2012/5188/.

U.S. Geological Survey, 2015, Tungsten statistics, in Kelly, 

T.D., and Matos, G.R., comps., Historical statistics for 

mineral and material commodities in the United States: 

U.S. Geological Survey Data Series 140, accessed March 9, 

2016, at http://minerals.usgs.gov/minerals/pubs/historicalstatistics/.

Uranium (U3O8)

The primary use for uranium is as a fuel for generating 

electricity in nuclear power plants. Globally there are 439 operating 

reactors, 99 of which are in the United States (International Atomic 

Energy Agency, 2016). Other uses for uranium include nuclear 

medicine, nuclear weapons, and propulsion. Depleted uranium 

is used as ballast, high-density projectiles in weaponry, and as a 

material for shielding from radiation. 

Mining uranium has been accomplished by conventional 

mining techniques and through in-situ mining, where aqueous 

fluids are pumped through a porous ore deposit. Historically, 

a significant amount of U.S. uranium-mine production 

was located in the Western United States but outside of the 

assessment area. Carnotite ore produced on the Colorado 

Plateau of western Colorado and eastern Utah was a major 

source of domestic supply. Exploration for uranium has 

occurred within many parts in or proximal to the assessment 

area; production has occurred in Custer County, Idaho; Lake 

and Malheur Counties, Oregon; and Converse, Freemont, and 

Sweetwater Counties, Wyoming (Petersen, 1969; University of 

Wyoming, 2010; Van Gosen and others, 2005). 

The United States produced an estimated 2,200 metric 

tons (t) of U3O8 equivalents3 in 2014, which represented about 4 

percent of world production. Production has recently taken place 

from 2 underground mines in Mohave County, Arizona, and 

San Juan County, Utah; and 8 in-situ leach operations in Dawes 

County, Nebraska; Brooks, Duval, and Karnes Counties, Texas; 

and Campbell, Converse, Johnson, and Sweetwater Counties, 

Wyoming. Some byproduct uranium was recovered from 

3

Units of production are often expressed in the literature as uranium (U) 

and triuranium octoxide (U3O8). All units expressed in source literature as U 

were adjusted to U3O8 equivalents by multiplying by 1.179 for the purpose of 

consistency.

phosphate mining in the Western United States (St. George News, 

2013; U.S. Energy Information Administration, 2015; Uranium 

Producers of America, 2014).

In 1993, the United States produced approximately 952 t 

of U3O8 equivalents from mills and in-situ mining, which was 

significantly less than the 2,200 t of U3O8 equivalents produced in 

2014. The average compound annual rate of growth in production 

of about 4 percent over the 22-year time period can be attributed 

the development of relatively low-cost in-situ mining, the source 

for most of domestic uranium production. Many U.S. hard-rock 

mines have closed or suspended operation over the past two 

decades as a result of high costs, reserve depletion, and other 

factors. Uranium reserves in the United States are estimated at 

163,000 t of U3O8 equivalents at prices of as much as $220,460 

per metric ton ($100 per pound) of U3O8 equivalents (U.S. Energy 

Information Administration, 2015). 

In 2014, the United States imported approximately 23,000 t 

of U3O8 equivalents to meet its commercial-civilian requirements. 

In 1990, the United States imported approximately 12,000 t of 

U3O8 equivalents, but by 1992, as some U.S. operations closed and 

few new mines were developed in response to decreasing prices, 

imports had increased to 21,000 t of U3O8 equivalents. Domestic 

production rebounded with the development of relatively low-cost 

in-situ mining. In 2014, Kazakhstan was the leading import source 

with a 23 percent share. Other major importers and their percentage 

share were Australia (21 percent), Canada (20 percent), Russia 

(14 percent), and Namibia (9 percent) (U.S. Energy Information 

Administration, 1995; U.S. Energy Information Administration, 

2015; Organization of Economic Cooperation and Development, 

2000). Data regarding the amount of exports of uranium-containing 

compounds from the United States are not available.

Uranium compounds are not part of the National Defense 

Stockpile managed by the Defense Logistics Agency within 

the U.S. Department of Defense. The National Nuclear 

Security Administration within the U.S. Department of Energy 

(DOE) controls an inventory of excess uranium from military 

use. DOE’s inventories of uranium come from various sources, 

including governmental weapons programs, from its own 

former enrichment activities, and from inventories of natural 

uranium of Russian origin. Inventories of uranium are also 

held by domestic producers and consumers. According to the 

U.S. Energy Information Administration, at the end of 2014, 

commercial inventories were estimated to include 61,100 t of 

U3O8 equivalents. Data regarding U.S. supplier inventories 

of natural and enriched uranium hexafluoride (UF6) were 

withheld (U.S. Energy Information Administration, 2015).

In 1990, approximately 56,000 t of U3O8 equivalents were 

produced from mines worldwide. Production continued to 

remain near this level through the 1990s into the early 2000s, as 

secondary-sourced materials were available from recycled nuclear 

warheads and other sources (Underhill and Müller-Kahle, 1993; 

World Nuclear Association, 2015). Total world mine production 

of U3O8 equivalents increased nearly every year since 2004, when 

47,400 t of U3O8 equivalents were produced. In 2014, world 

production of U3O8 from mining was estimated at 66,300 t of U3O8

equivalents. The increase over the past 10 years has been driven 
by the decrease in secondary sources and demand for fueling 

nuclear power plants. In 2014, Kazakhstan was the world’s leading 

in producer with 27,300 t of U3O8 equivalents, which represented a 

41 percent share. This was a significant increase from that of 2007 

when Kazakhstan produced about 7,800 t of U3O8 equivalents. 

Other major producers in 2014 and their respective share of global 

production were Canada (16 percent), Australia (9 percent), Niger 

(7 percent), Namibia (6 percent), Russia (5 percent), Uzbekistan 

(4 percent), United States (4 percent), and China (3 percent) 

(World Nuclear Association, 2015).

Uranium is not traded on an open market like most other 

mineral commodities. Buyers and sellers generally negotiate 

contracts privately. The average annual spot price per metric ton 

($/t) of U3O8 equivalents, expressed in constant 1998 U.S. dollars 

since the year 1990, ranged from a low of about $855/t ($7 per 

pound, $/lb) in 1991 to a high of $2,150/t ($107/lb) in 2007 

(Cameco, 2016). The elevated price of U3O8 equivalents in 2007 

was a result of concerns related to potential interruptions of supply, 

anticipation of an increase in demand from China and India, and 

reduced availability of weapons-grade uranium for recycling. 

Prices dropped in subsequent years when the concerns did not 

materialize to the extent expected. In early 2016, the nominal price 

of U3O8 was approximately $75,000 per t ($34/lb) (Johnson, 2010; 

UXC, 2016; U.S. Energy Information Administration, 2015).

References Cited

Cameco, 2016, Uranium price: Cameco Web page, accessed on 

February 16, 2016, at https://www.cameco.com/invest/markets/

uranium-price.

International Atomic Energy Agency, 2016, Operational & longterm shutdown reactors: International Atomic Energy Agency 

Web page, accessed on March 10, 2016, at https://www.iaea.

org/PRIS/WorldStatistics/OperationalReactorsByCountry.aspx.

Johnson, Toni, 2010, Global uranium supply and demand: Council 

on Foreign Relations, accessed on February 16, 2016, at http://

www.cfr.org/world/global-uranium-supply-demand/p14705.

Organization of Economic Cooperation and Development, 2000,

Uranium 1999—Resources, production and demand—A 

joint Report by the OECD Nuclear Energy Agency and 

the International Atomic Energy Agency: Organization of 

Economic Cooperation and Development accessed on February 

16, 2016, at https://www.oecd-nea.org/ndd/pubs/2000/2369-

uranium-1999.pdf.

Petersen, N.V., 1969, Uranium, Mineral and water resources 

of Oregon: Oregon Department of Geology and Mineral 

Industries, Bulletin 64, p. 180–184.

St. George News, 2013, Operations resume at uranium 

mine in Mohave County: St. George News, accessed on 

March 16, 2016, at http://www.stgeorgeutah.com/news/

archive/2013/05/10/operations-resume-at-uranium-mine-inmohave-county/#.Vumt301f2Ax.

Underhill, D.H., and Müller-Kahle, E., 1993, World uranium 

supply and demand—The changing market: International 

Atomic Energy Agency Bulletin, v. 3/1993, accessed 

on February 16, 2016, at https://www.iaea.org/sites/

default/files/publications/magazines/bulletin/bull35-

3/35302680813.pdf.

U.S. Energy Information Administration, 1995, Uranium 

industry annual report: U.S. Department of Energy, 

accessed on March 10, 2016, at https://www.eia.gov/

uranium/marketing/archive/047894.pdf.

U.S. Energy Information Administration, 2015, 2014 domestic 

uranium production report: U.S. Department of Energy, 

accessed on February 16, 2016, at http://www.eia.gov/

uranium/production/annual/pdf/dupr.pdf.

University of Wyoming, 2010, An overview of uranium 

production of Wyoming: University of Wyoming, School 

of Energy Resources, accessed on February 17, 2016, at 

http://www.uwyo.edu/ser/_files/docs/conferences/2010/

uraniumforum/uraniumforumwhitepaper.pdf.

Uranium Producers of America, 2014, Uranium in America, 

accessed on February 16, 2016, at http://www.theupa.org/

uranium_in_america/.

UXC, 2016, U3O8 prices [publishing information]: UXC Web 

page, accessed on February 16, 2016, at http://www.uxc.

com/p/prices/UxCPrices.aspx.

Van Gosen, B.S., Hammarstrom, J.M., Eppinger, R.G., 

Briggs, P.H., Crock, J.G., Meier A.L., Sutley, S.J., 

Theodorakos, P.M., and Hageman, P.L., 2005, A 

reconnaissance geochemical and mineralogical study of 

the Stanley Uranium District, Custer County, Central 

Idaho: U.S. Geological Survey Scientific Investigations 

Report 2005–5264, 54 p., accessed February 16, 2016, at 

http://pubs.usgs.gov/sir/2005/5264/.

World Nuclear Association, 2015, Uranium production figures, 

2004–2014: World Nuclear Association, accessed on February 

16, 2016, at http://www.world-nuclear.org/information-library/

facts-and-figures/uranium-production-figures.aspx.

Vanadium

Metallurgical use, primarily as an alloying agent for iron 

and steel, accounted for about 93 percent of domestic vanadium 

consumption in 2014. The vanadium industry is thus heavily 

dependent on the demand cycles from steel production. Other uses 

for vanadium are in chemical applications, specifically in catalysts. 

A growing use of vanadium is in rechargeable vanadium redox 

batteries, which may have significant potential for use in large 

power-grid applications and for electric vehicles (Polyak, 2016a, b).

The USGS National Minerals Information Center (NMIC) 

reported that in 2014 the United States did not produce any 

Appendix 5 207
208 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

vanadium as a byproduct or coproduct of mining uranium. The 

United States is a significant producer of vanadium pentoxide, 

ferrovanadium, and other vanadium products, although their 

production is almost exclusively from secondary and imported 

materials. From 1990 through 2014, mined vanadium production 

peaked at 3,730 metric tons (t) in 1999, most of which was 

produced as a coproduct from the mining of uraniferous 

sandstones on the Colorado Plateau. No vanadium was produced 

as a coproduct from 2000 through 2007 as a consequence of 

poor market conditions in the primary uranium industry and the 

Western U.S. phosphate industry. The uranium industry revived 

somewhat in 2008, and vanadium was once again produced as a 

coproduct from carnotite ores on the Colorado Plateau until 2014. 

In 2013, 591 t of vanadium was produced as a coproduct, but none 

was produced in 2014 or 2015. This vanadium production was 

outside the assessment area.

In the 1980s, Idaho followed Colorado as the second 

ranked producer of vanadium from mining. The ore was mined 

from vanadiferous phosphate ores in the Phosphoria Formation, 

which extends into the assessment area, although essentially 

all of the vanadium was produced from phosphate ores mined 

from outside the boundaries. The vanadium was extracted from

ferrophosphorous slag, which was generated during the processing 

of phosphate ore to produce elemental phosphorous. Some minor 

amounts of vanadium may have been recovered from ores shipped 

from mines within the assessment area, but no production of 

vanadium has occurred from phosphate ores in Idaho since about 

2000 (Judd and others, 1986; Kelly and Matos, 2007; Minarik 

and Gilleman, 1991; Ohl and Davis, 1991; Polyak, 2016a, b; U.S. 

Geological Survey, 2012).

Vanadium, contained in black shales in Eureka County, 

Nevada, also outside of the assessment area, have been 

investigated and evaluated for potential development (Miningtechnology.com, 2016).

Statistical data on the amount of vanadium recovered 

from catalysts and specialty alloys in the United States through 

recycling are not available. Vanadium is recycled incidentally 

as a constituent of ferrous and nonferrous scrap (Goonan, 2011; 

Polyak, 2016a, b). 

In 2014, the United States exported about 1,000 t of 

vanadium contained in various products, significantly less than 

that in 1990 when exports totaled 3,920 t, which were the highest 

for the period 1990 to 2014. The compound average rate of decline 

was estimated to be about 5.5 percent. A large part of the decrease 

can be attributed to the decline of domestic mine production 

(Kelly and Matos, 2007).

The United States does not import vanadium ores or 

concentrates produced directly from mining but does import 

significant tonnages of vanadium contained in ferrovanadium, 

vanadium pentoxide, and other materials, such as vanadiumbearing ash and slag, that require further processing. In 2014, 

the quantity of vanadium contained in imported materials was 

estimated to be 13,700 t, the highest for the period analyzed. 

The compound annual growth rate (CAGR) from 1990 to 2014 

was estimated at 4.5 percent. The major sources for imported 

ferrovanadium for 2011–14 were Czech Republic (43 percent), 

Canada (22 percent), Republic of Korea (18 percent), and Austria 

(14 percent). For vanadium pentoxide, the leading import sources 

were South Africa (40 percent), Russia (35 percent), and China 

(18 percent). For ash and other residues, the major import sources 

were Canada (80 percent) and Mexico (13 percent).

Apparent consumption of vanadium in the United States has 

increased from 4,080 t in 1990 to 12,400 t in 2014 for a CAGR of 

about 3.9 percent over the period (Kelly and Matos, 2007; Polyak, 

2016a). U.S. import reliance for vanadium was estimated to be 

100 percent in 2014, as a consequence of increased imports and no 

primary domestic production.

The U.S. Defense Logistics Agency did not maintain a 

stockpile of vanadium in 2015. In the early 1990s, approximately 

651 t of vanadium contained in various materials was held in the 

stockpile.

Vanadium has been considered a strategic and critical 

material for its essential use in defense, energy, and construction 

applications, as well as its limited substitutability. Sharp increases 

in prices that occurred between 2003 and 2008 caused some 

steelmakers, particularly in China, to switch from vanadium to 

niobium. However, replacement of vanadium requires significant 

technical adjustments to steel production to ensure that product 

specifications and quality are not compromised. Therefore, 

substitution is normally not considered for short-term changes in 

market conditions. 

In 2014, approximately 82,700 t of vanadium was mined 

globally. China was the world leader with a 54 percent share. In 

2014, China’s production was nearly 10 times than that of 1990 

and reflected the country’s accelerated industrialization over this 

time period. Other leading producers of mined vanadium in 2014, 

and their respective share of world production, were South Africa 

(25 percent) and Russia (18 percent).

The average annual price per metric ton ($/t) of contained 

vanadium, expressed in constant 1998 U.S. dollars for the purpose 

of comparison since the year 1990, ranged from a low of about 

$4,780/t in 2002 to a high of $53,500 /t in 2005 (Kelly and Matos, 

2007). Industry analysts ascribed the low price in 2002 to an 

increase in global supply of material. The price rise in 2005 was 

primarily owing to strong demand in the steel and aerospace 

industries and the inability of producers to increase production 

of vanadium in a timely manner (Magyar, 2006). In 2015, the 

nominal price was $9,700/t of contained vanadium. Prices have 

declined since 2009 in response to reduced global demand for 

steels, triggered to a large extent by a slowdown of the economy in 

China (Polyak, 2016a).

References Cited

Goonan, T.G., 2011, Vanadium recycling in the United States in 

2004: U.S. Geological Survey Circular 1196–S, 23 p., accessed 

February 16, 2016, at http://pubs.usgs.gov/circ/circ1196-S/.

Judd, J.C., Sandberg, R.G., and Huiatt, J.L., 1986, Recovery of 

vanadium, uranium, and phosphate from Idaho phosphorite 

ores: U.S. Bureau of Mines Report of Investigation 9025, 15 p.
Kelly, T.D., and Matos, G.R., comps., 2007, Historical statistics 

for mineral and material commodities in the United States: 

U.S. Geological Survey Data Series 140, ver. 2011, accessed 

February 4, 2016, at http://minerals.usgs.gov/minerals/pubs/

historical-statistics/.

Magyar, M.M., 2006, Vanadium: U.S. Geological Survey Mineral 

Commodity Summaries 2006, p.184–185, accessed February 

14, 2016, at http://minerals.usgs.gov/minerals/pubs/mcs/2006/

mcs2006.pdf.

Minarik, R.J., and Gillerman, V.S., 1991, The mineral industry 

of Idaho, in Area reports—Domestic: U.S. Bureau of Mines 

Minerals Yearbook 1989, v. II, p. 157–166.

Mining-technology.com, 2016, Gibellini vanadium, project 

Nevada, United States of America: Mining-technology.com 

Web site, accessed February 16, 2016, at http://www.miningtechnology.com/projects/gibellini-vanadium-project/).

Ohl, J.P., and Davis, M.W., 1991, The mineral industry of 

Colorado, in Area reports—Domestic: U.S. Geological Survey 

Minerals Yearbook 1989, v. II, p. 103–114. 

Polyak, D.E., 2016a, Vanadium: U.S. Geological Survey Mineral 

Commodity Summaries 2016, p.182–183, accessed February 

16, 2016, at http://minerals.usgs.gov/minerals/pubs/commodity/

vanadium/mcs-2016-vanad.pdf.

Polyak, D.E., 2016b, Vanadium [advanced release], in Metals and 

minerals: U.S. Geological Survey, Minerals Yearbook 2014, v. 

1, p. 80.1–80.10, accessed February 16, 2016, at http://minerals.

usgs.gov/minerals/pubs/commodity/vanadium/myb1-2013-

vanad.pdf.

U.S. Geological Survey, 2012, The mineral industry of Idaho, in

Area reports—Domestic: U.S. Geological Survey Minerals 

Yearbook 2008, v. II, p. 14.1–14.6.

Zeolites

Zeolites are hydrated aluminosilicate minerals with loosely 

bound alkali and alkaline-earth metals within the crystalline 

structure that can be exchanged by water or other cations. Zeolite 

deposits in the United States occur predominantly in Arizona, 

California, Idaho, Nevada, New Mexico, Oregon, Texas, and 

Wyoming. Zeolite minerals present within these deposits are 

chabazite, clinoptilolite, erionite, mordenite, and phillipsite (Eyde 

and Holmes, 2006). 

In 2014, the USGS National Minerals Information 

Center (NMIC) reported that the United States produced 

about 64,100 metric tons (t) of natural zeolite. Chabazite was 

mined in Arizona, and clinoptilolite was mined in California, 

Idaho, New Mexico, Oregon, and Texas. New Mexico was the 

leading natural zeolite-producing State, followed by Texas, 

Idaho, California, Oregon, and Arizona (Virta and Flanagan, 

2015). Areas within or proximal to the assessment area where 

natural zeolite production is ongoing or has occurred since 

2005 include Franklin and Owyhee Counties, Idaho; Nye 

County, Nevada; Malheur County, Oregon; and Sweetwater 

County, Wyoming (Flanagan, 2016; Virta, 2002, 2006, 2010; 

Virta and Flanagan, 2015). Due to obligations to withhold 

company confidential data, no specific production amounts can 

be provided. Zeolite deposits in the United States are mined by 

surface methods.

Domestic uses for natural zeolites are, in decreasing order 

by tonnage, animal feed, odor control, water purification, other 

end uses, pet litter, wastewater treatment, gas absorbents (and air 

filtration), fertilizer carriers, oil absorbents, desiccants, catalysts, 

fungicide or pesticide carriers, aquaculture, and cement. Animal 

feed, odor control, water purification, pet litter, and wastewater 

treatment accounted for nearly 80 percent of the domestic sales 

tonnage (Virta and Flanagan, 2015). On a global basis, domestic 

mine production was about 2 percent of world production but 

sufficient for domestic consumption (Flanagan, 2016). Domestic 

reserves of zeolites are not quantified, but are considered adequate 

for the foreseeable future.

In 2014, approximately 64,100 t of natural zeolite was 

produced in the United States, compared to 1990 when 

production was 15,600 t. The compound annual growth rate of 

about 6 percent over the period can be attributed to a significant 

extent on the increased domestic consumption of zeolite 

in animal feed. Sales for cement, odor control, wastewater 

treatment, and water purification applications also increased in 

the past 10 years, although expansion of these markets has not 

been as great as with animal feed (Flanagan, 2016; Virta, 1993, 

2002, 2006, 2010; Virta and Flanagan, 2015).

Nearly all imports and exports of zeolites are synthetic 

zeolite products. Comprehensive statistics distinguishing between 

the quantities of natural or synthetic zeolite products are not 

available because zeolite trade data are included under a category 

for miscellaneous mineral substances. In 2014, the United States 

exported an estimated 175 t of zeolites compared to an estimated 

3,000 to 7,000 t in 2005. Imports have not been a significant 

component of domestic consumption. Zeolite imports were 

estimated to be only 25 t in 2014 and probably have not exceeded 

500 t in any of the past 10 years (Virta, 2002, 2006, 2010; Virta 

and Flanagan, 2015; Flanagan, 2016). The United States was a net 

exporter of natural zeolites in 2014 (Flanagan, 2016) and has been 

so for at least the past 20 years.

The U.S. Defense Logistics Agency does not hold a stockpile 

of zeolites. Zeolites are not considered a strategic or critical 

commodity because domestic production is adequate to meet 

demand and substantial reserves exist (Flanagan, 2016).

In 2014, total world zeolite production was approximately 

2.75 million metric tons. U.S. production represented about 2 

percent of this amount. China dominates the world production 

of natural zeolite, with an estimated 73 percent, followed by the 

Republic of Korea, the world’s second ranked producer, with 8 

percent. 

In 2014, the price per metric ton ($/t) of zeolite sold 

in bulk shipments typically ranged from $100/t to $230/t 

(Flanagan, 2016).

Appendix 5 209
210 Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

References Cited

Eyde, T.H., and Holmes, D.A., 2006, Zeolites, in Kogel, J.E., 

Trivedi, N.C., Barker, J.M., and Krukowski, S.T., eds., 

Industrial minerals and rocks (7th ed.): Littleton, Colorado, 

Society for Mining, Metallurgy, and Exploration Inc., p. 

1039–1064.

Flanagan, D.M., 2016, Zeolites (natural): U.S. Geological Survey 

Mineral Commodity Summaries 2016, p. 190–191, accessed 

March 7, 2016, at http://minerals.usgs.gov/minerals/pubs/

commodity/zeolites/mcs-2016-zeoli.pdf.

Virta, R.L., 1993, Zeolites in 1993: U.S. Bureau of Mines Mineral 

Industry Surveys, 6 p., accessed March 7, 2016, at http://

minerals.usgs.gov/minerals/pubs/commodity/zeolites/myb1-

1993-zeoli.pdf. 

Virta, R.L., 2002, Zeolites, in Metals and minerals: U.S. 

Geological Survey Minerals Yearbook 2002, v. 1, p. 84.1–84.3, 

accessed March 7, 2016, at http://minerals.usgs.gov/minerals/

pubs/commodity/zeolites/zeolmyb02.pdf.

Virta, R.L., 2006, Zeolites, in Metals and minerals: U.S. 

Geological Survey Minerals Yearbook 2005, v. 1, p. 84.1–84.3, 

accessed March 7, 2016, at http://minerals.usgs.gov/minerals/

pubs/commodity/zeolites/zeolimyb05.pdf.

Virta, R.L., 2010, Zeolites, in Metals and minerals: U.S. 

Geological Survey Minerals Yearbook 2008, v. 1, p. 83.1–83.3, 

accessed March 7, 2016, at http://minerals.usgs.gov/minerals/

pubs/commodity/zeolites/myb1-2008-zeoli.pdf.

Virta, R.L., and Flanagan, D.M., 2015, Zeolites, in Metals and 

minerals: U.S. Geological Survey Minerals Yearbook 2014, v. 

1, p. 83.1–83.3, accessed March 7, 2016, at http://minerals.usgs.

gov/minerals/pubs/commodity/zeolites/myb1-2014-zeoli.pdf.

Zinc

Zinc is used mostly for galvanizing steel, where it acts as a 

protective coating against corrosion. Zinc is also consumed for 

the production of zinc-based alloys for the die-casting industry, 

as a component of brass and bronze, and in chemical compounds, 

including zinc oxide used in tire manufacturing and zinc sulfate for 

fertilizers.

Publications of the USGS National Minerals Information 

Center (NMIC) reported that in 2014 the United States 

produced 832,000 metric tons (t) of zinc in concentrate and was 

the world’s fourth-ranked mine producer of zinc behind China, 

Australia, and Peru, accounting for approximately 6 percent of 

global production (Tolcin, 2016). U.S. zinc-mine production has 

increased at a compound annual growth rate of about 2 percent 

in the past 25 years, mostly owing to increased production in 

Alaska beginning in the mid-to-late 1990s. 

In 2014, zinc was produced in five States; Alaska was the 

leading zinc-producing State, followed by Tennessee, Missouri, 

Idaho, and Washington. No significant zinc production has 

been reported in or near the assessment area since at least 1990. 

Zinc was recovered from ore extracted from both open-pit and 

underground mines that used conventional flotation to produce 

concentrate for smelting and refining. In 2014, U.S. proven and 

probable ore reserves contained approximately 11 million metric 

tons (Mt) of zinc (Tolcin, 2016).

In 1990, approximately 263,000 t of zinc metal was 

produced from domestic and imported concentrates by domestic 

smelters (Jasinski, 1993). By 2014, as a result of plant closures 

and suspensions for various reasons, zinc production at primary 

smelters more than halved to approximately 110,000 metric tons 

(t). It is unlikely that new production capacity for processing zinc 

concentrates will be constructed in the United States before the 

end of the decade or perhaps the foreseeable future. An additional 

70,000 t of zinc metal was recovered by secondary smelters from 

the recycling of scrap in 2014 (Tolcin, 2016).

The United States exports a significant amount of zinccontaining concentrates to foreign smelters and imported 

most of the zinc metal it consumed. In 2014, U.S. exports 

of zinc in concentrate were 644,000 t, whereas imports were 

less than 500 t, and imports of refined zinc were 805,000t, 

whereas exports were 20,000 t. Zinc in concentrate was 

exported primarily to Canada (35 percent), the Republic of 

Korea (87 percent), and Spain (11 percent), and refined zinc 

was imported mostly from Canada (55 percent), Australia 

(14 percent), and Mexico (13 percent) (Jasinski, 1993; Jolly, 

1993; Tolcin, 2016). 

In 2014, U.S. apparent consumption of refined zinc 

was 965,000 t. From 1992 to 2008, annual apparent 

consumption exceeded 1 Mt, reaching a high of 1.43 Mt in 

1999. Consumption declined in 2008 after the global economic 

recession began in late 2007 and fell to less than 1 Mt in 2009. 

Although the recession ended in 2009, consumption remained 

less than 1 Mt from 2010 to 2014, owing mostly to increased 

imports of galvanized steel from China (Kelly and Matos, 

2007; Tolcin, 2016).

The U.S. Defense Logistics Agency holds a stockpile of 

about 7,000 t of zinc (Tolcin, 2016). As such, zinc continues 

to be considered a strategic or critical commodity, although 

domestically imported supplies of zinc are varied with a 

substantial amount sourced from North American Free Trade 

Agreement partners.

In the past 25 years, global zinc-mine production 

increased by a compound annual growth rate of 2.6 percent, 

from 7.15 Mt in 1990 to 13.3 Mt in 2014. During this period 

of time, China had the most substantial increase in zinc 

production and became the leading global producer—from 

producing 660,000 t of zinc in concentrate in 1990 (9 percent 

of the world’s total) to producing 4.93 Mt in 2014 (37 percent 

of the world’s total). Other major producers of mined zinc in 

2014, and their share of global production, were Australia (12 

percent), Peru (10 percent), United States (6 percent), India 

(5 percent), and Mexico (5 percent). The increase in world 

zinc production has been driven primarily by an upsurge in 

demand in China for galvanized steel and other materials used 
in construction and consumer goods (Jasinski, 1993; Tolcin, 

2015, 2016). 

The average annual North American price for special high 

grade (SHG) zinc, expressed in constant 1998 U.S. dollars for the 

purpose of comparison since the year 1990, ranged from a low of 

about $772 per metric ton ($0.35 per pound in 2002) to a high of 

$2,830 per metric ton ($1.28 per pound) in 2006. Prices dropped 

shortly thereafter in response to weakened demand for the metal 

in most major zinc-consuming nations during the global recession, 

with China being an exception. Prices recovered somewhat in 

2011 and 2012 but softened thereafter as demand for the metal 

lessened. In 2014, the average price of zinc in nominal dollars was 

approximately $2,359 per metric ton ($1.07 per pound) (Kelly and 

Matos, 2007; Tolcin, 2016).

References Cited

Jasinski, S.M., 1993, Zinc, in U.S. Bureau of Mines Minerals 

Yearbook 1993, v. 1, p. 1279–1292, accessed February 9, 

2016, at http://digicoll.library.wisc.edu/cgi-bin/EcoNatRes/

EcoNatRes-idx?type=article&did=EcoNatRes.MinYB1993v1.

SJasinski&id=EcoNatRes.MinYB1993v1&isize=M.

Jolly, J.H., 1993, Zinc: U.S. Bureau of Mines Mineral Commodity 

Summaries 1993, p.196–197.

Kelly, T.D., and Matos, G.R., comps., 2007, Historical statistics 

for mineral and material commodities in the United States: U.S. 

Geological Survey Data Series 140, ver. 2011, accessed February 

4, 2016, at http://minerals.usgs.gov/minerals/pubs/historicalstatistics/.

Tolcin, A.C., 2015, Zinc [advanced release], in Metals and minerals: 

U.S. Geological Survey, Minerals Yearbook 2013, v. 1, p. 

84.1–84.13, accessed February 9, 2016, at http://minerals.usgs.

gov/minerals/pubs/commodity/zinc/myb1-2013-zinc.pdf.

Tolcin, A.C., 2016, Zinc: U.S. Geological Survey Mineral 

Commodity Summaries 2016, p.192–193, accessed February 

4, 2016, at http://minerals.usgs.gov/minerals/pubs/mcs/2016/

mcs2016.pdf.

Acknowledgments

Several people made valuable contributions to the 

information provided by the USGS National Mineral Information 

Science Center (NMIC). These include George M. Bedinger, 

Donald I. Bleiwas, Robert D. Crangle, Jr., Daniel M. Flanagan, 

Joseph Gambogi, Micheal W. George, David I. Guberman, Brian 

W. Jaskula, Michele E. McRae, Donald W. Olson, Désirée E. 

Polyak, Kim B. Shedd, Amy C. Tolcin, and Christopher A. Tuck.

Appendix 5 211

Menlo Park Publishing Service Center, California

Manuscript approval date June 14, 2016

Edited by James W. Hendley II

Design and layout by Cory Hurd
Day and others—Overview of USGS Mineral-Resource Assessment of Sagebrush Focal Areas—Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

—Scientific Investigations Report 2016–5089–A

ISSN 2328-0328 (online)

http://dx.doi.org/10.3133/sir20165089A