U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2010–5220

The Principal Rare Earth Elements Deposits of the

United States—A Summary of Domestic Deposits

and a Global Perspective

Sm

Gd Pr

La

Nd

Ce
Cover photo: Powders of six rare earth elements oxides. Photograph by Peggy Greb, Agricultural Research Center of 

United States Department of Agriculture.
The Principal Rare Earth Elements Deposits

of the United States—A Summary of 

Domestic Deposits and a Global Perspective

By Keith R. Long, Bradley S. Van Gosen, Nora K. Foley, and Daniel Cordier

Scientific Investigations Report 2010–5220

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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Suggested citation:

Long, K.R., Van Gosen, B.S., Foley, N.K., and Cordier, Daniel, 2010, The principal rare earth elements deposits of the 

United States—A summary of domestic deposits and a global perspective: U.S. Geological Survey Scientific 

Investigations Report 2010–5220, 96 p. Available at http://pubs.usgs.gov/sir/2010/5220/.
iii

Contents

Introduction and Background......................................................................................................................1

The Rare Earth Elements ..............................................................................................................................3

Basic Geology of Rare Earth Elements .............................................................................................3

Mineralogy of United States Deposits ..............................................................................................7

References Cited.................................................................................................................................14

Current Sources and Domestic Reserves ...............................................................................................15

Concentration of Supply ....................................................................................................................15

Risk of Supply Interruption................................................................................................................17

Domestic and World Resources.......................................................................................................18

Developing Rare Earth Elements Resources .................................................................................19

Developing a Rare Earth Elements Mine ........................................................................................21

Summary...............................................................................................................................................23

References Cited.................................................................................................................................24

The Principal Rare Earth Elements Deposits of the United States......................................................27

Glossary of Terms ...............................................................................................................................27

References Cited.................................................................................................................................27

Alaska— Bokan Mountain...........................................................................................................28

Salmon Bay...................................................................................................................35

California— Mountain Pass Deposit and Mine.............................................................................36

Music Valley Area........................................................................................................40

Colorado— Iron Hill Carbonatite Complex.....................................................................................41

Wet Mountains Area ...................................................................................................45

Idaho— Diamond Creek Area ...................................................................................................49

Hall Mountain ...............................................................................................................51

Lemhi Pass district, Idaho–Montana........................................................................53

Illinois— Hicks Dome ...................................................................................................................56

Missouri— Pea Ridge Iron Deposit and Mine..............................................................................57

Nebraska— Elk Creek Carbonatite ..................................................................................................63

New Mexico— Capitan Mountains.......................................................................................................65

El Porvenir District.......................................................................................................66

Gallinas Mountains......................................................................................................67

Gold Hill Area and White Signal District..................................................................69

Laughlin Peak Area......................................................................................................70

Lemitar and Chupadera Mountains ..........................................................................71

Petaca District..............................................................................................................72

Red Hills Area...............................................................................................................73

Wind Mountain, Cornudas Mountains .....................................................................74

New York— Mineville Iron District ..................................................................................................75

Wyoming— Bear Lodge Mountains................................................................................................78

Phosphorite Deposits in the Southeastern United States ....................................................................80

Placer Rare Earth Elements Deposits ......................................................................................................84

Idaho—Placer Deposits .............................................................................................................................86

North and South Carolina—Placer Deposits..........................................................................................90

Florida and Georgia—Beach Placer Deposits .......................................................................................93
iv

Figures

Index map of the principal rare earth elements districts in the United States ...................................2

The Rare Earth Elements

1. Periodic table of the elements....................................................................................................4

2. Rare earth elements mineral-processing flow sheet for the Mountain Pass mine, 

California ........................................................................................................................................8

Current Sources and Domestic Reserves

3. Criticality matrix for selected imported metals......................................................................17

Alaska

4. Simplified geologic map of Bokan Mountain, Alaska...........................................................29

5. Map of major vein and dike systems associated with Bokan Mountain, Alaska ............32

California

6. Google Earth image of Mountain Pass mining district, California......................................37

7. Photograph of northwest-facing view of Mountain Pass district, California...................38

8. Photograph of dolomitic carbonatite of Sulphide Queen orebody, California..................38

Colorado

9. Photograph of northwest-facing view of Iron Hill, Colorado...............................................42

10. Photograph of outcrop of pyroxenite unit in Iron Hill carbonatite complex, Colorado...44

11. Photograph of Sewell Ranch thorium vein, Wet Mountains, Colorado.............................46

12. Photograph of west-facing view of McClure Mountain, Colorado ....................................47

Idaho

13. Photograph of view to west of Lemhi Pass, Idaho-Montana boundary ............................54

14. Photograph of outcrop of Wonder vein, Lemhi Pass district, Idaho-Montana ................54

Missouri

15. Generalized geologic map of 2275 level of Pea Ridge iron mine, Missouri ......................59

New York

16. Map of Mineville district, New York ........................................................................................76

Phosphorite Deposits in the Southeastern United States

17. Map of locations of phosphogenic provinces of the southeastern United States ..........81

Placer Rare Earth Elements Deposits

18. Photograph of heavy-mineral layers in quartz beach sand, Chennai, India.....................84

Idaho—Placer Deposits

19. Generalized map of known monazite placer districts, Idaho..............................................87

20. Photograph of Porter Brothers dredge, Bear Valley, Idaho ................................................88

North and South Carolina—Placer Deposits

21. Map of monazite placers of North and South Carolina........................................................91

Florida-Georgia—Beach Placer Deposits

22. Map of locations of Recent and Pleistocene sands, Georgia.............................................94

23. Map of sample and mine locations of monazite, Georgia and Florida...............................95
v

Tables

The Rare Earth Elements

1. Estimates of the crustal abundances of rare earth elements...............................................5

2. Classification of rare earth elements–bearing mineral deposits .........................................6

3. Rare earth elements, thorium, and uranium content of minerals.........................................9

4. Dominant rare earth elements–bearing minerals in the United States.............................11

5. Distribution of rare earth elements in selected rare earth elements deposits ................12

6. Usage of rare earth elements...................................................................................................13

7. Production of rare earth elements mines in 2009..................................................................13

Current Sources and Domestic Reserves

8. World production and reserves of rare earth elements minerals in 2009.........................15

9. Measures of concentration for selected world metal mining industries..........................16

10. Domestic reserves and resources of rare earth elements..................................................19

11. Reserves and resources of rare earth elements outside of the United States................20

12. Time required to obtain permits, construct, and commission recent metal mines 

in the United States ....................................................................................................................22

13. Time required to develop selected mines outside of the United States............................24

Alaska—Bokan Mountain

14. Uranium production from the Ross-Adams mine, Alaska....................................................30

15. Dimensions of main orebodies at Bokan Mountain, Alaska................................................31

16. Resource estimates for main prospects on Bokan Mountain, Alaska, and 

surrounding property .................................................................................................................33

Colorado—Iron Hill

17. Median concentrations of rare earth elements in carbonatite stock and pyroxenite

unit at Iron Hill, Colorado...........................................................................................................43

Idaho—Hall Mountain, Last Chance

18. Concentrations of rare earth elements in vein samples from Hall Mountain, Idaho ......51

19. Concentrations of rare earth elements in samples from Last Chance vein, 

Idaho-Montana ...........................................................................................................................55

Missouri—Pea Ridge

20. Rare earth elements and thorium concentrations in four breccia pipes at 

Pea Ridge, Missouri ...................................................................................................................60

China—Two Chinese deposits

21. Rare earth elements oxide concentrations of two Chinese deposits compared with 

major U.S. deposits.....................................................................................................................61

Wyoming—Bear Lodge Mountains

22. Typical rare earth elements distribution in Bear Lodge Mountains deposit, 

Wyoming.......................................................................................................................................79
vi

Abbreviations Used in This Report

cm centimeter

ft foot

ft3 cubic foot

g/cm3 gram per cubic centimeter

in. inch

km kilometer

km2 square kilometer

kt thousand metric tons

lb pound

m meter

mi mile

mi2 square mile

mm millimeter

ppm parts per million

t metric ton

HREE heavy rare earth elements

LREE light rare earth elements

REE rare earth elements 

U.S. United States

USGS United States Geological Survey

REO rare earth oxide

TREO total rare earth oxide

WGS84 World Geodetic System of 1984 (the reference coordinate system used by 

 global positioning systems)
Introduction and Background

The rare earth elements (REE) are fifteen elements with 

atomic numbers 57 through 71, from lanthanum to lutetium 

(“lanthanides”), plus yttrium (39), which is chemically similar 

to the lanthanide elements and thus typically included with the 

rare earth elements. Although industrial demand for these elements is relatively small in tonnage terms, they are essential 

for a diverse and expanding array of high-technology applications. REE-containing magnets, metal alloys for batteries and 

light-weight structures, and phosphors are essential for many 

current and emerging alternative energy technologies, such as 

electric vehicles, energy-efficient lighting, and wind power. 

REE are also critical for a number of key defense systems and 

other advanced materials.

Section 843 of the National Defense Authorization Act 

for Fiscal Year 2010, Public Law 111-84, directs the Comptroller General to complete a report on REE materials in the 

defense supply chain. The Office of Industrial Policy, in collaboration with other U.S. Government agencies, has initiated 

(in addition to this report) a detailed study of REE. This latter 

study will assess the Department of Defense’s use of REE, as 

well as the status and security of domestic and global supply 

chains. That study will also address vulnerabilities in the supply chain and recommend ways to mitigate any potential risks 

of supply disruption. To help conduct this study, the Office of 

Industrial Policy asked the U.S. Geological Survey (USGS) 

to report on domestic REE reserves and resources in a global 

context. To this end, the enclosed report is the initial USGS 

contribution to assessing and summarizing the domestic REE 

resources in a global perspective.

In 2009, the Mineral Resources Program of the USGS 

organized a new project under the title Minerals at Risk and 

For Emerging Technologies in order to evaluate mineral 

resource and supply issues of rare metals that are of increasing 

importance to the national economy. Leaders and members of 

this project, with the assistance of the USGS National Minerals Information Center, prepared the enclosed USGS report 

on domestic REE resources. The USGS Mineral Resources 

Program has investigated domestic and selected foreign REE 

resources for many decades, and this report summarizes what 

has been learned from this research. The USGS National 

Minerals Information Center (formerly Minerals Information 

Team) has monitored global production, trade, and resources 

for an equally long period and is the principal source of statistics used in this report.

The objective of this study is to provide a nontechnical 

overview of domestic reserves and resources of REE and 

possibilities for utilizing those resources. At the present time, 

the United States obtains its REE raw materials from foreign 

sources, almost exclusively from China. Import dependence 

upon a single country raises serious issues of supply security. 

In a global context, domestic REE resources are modest and 

of uncertain value; hence, available resources in traditional 

trading partners (such as Canada and Australia) are of great 

interest for diversifying sources of supply. This report restates 

basic geologic facts about REE relevant to assessing security 

of supply, followed by a review of current United States consumption and imports of REE, current knowledge of domestic 

resources, and possibilities for future domestic production. 

Further detail follows in a deposit-by-deposit review of the 

most significant domestic REE deposits (see index map). 

Necessary steps to develop domestic resources are discussed 

in a separate section, leading into a review of current domestic 

exploration and a discussion of the value of a future national 

mineral resource assessment of REE. The report also includes 

an overview of known global REE resources and discusses the 

reliability of alternative foreign sources of REE.

The Principal Rare Earth Element Deposits of the 

United States—A Summary of Domestic Deposits 

and a Global Perspective

By Keith R. Long,1 Bradley S. Van Gosen,2 Nora K. Foley,3 and Daniel Cordier3

1

U.S. Geological Survey, Tucson, Arizona

2

U.S. Geological Survey, Denver, Colorado

3

U.S. Geological Survey, Reston, Virginia
2 The Principal Rare Earth Elements Deposits of the United States Bear Lodge Mtns WY Bokan Mtn, AKSalmon Bay, AK Hall MtnDiamond Creek Lemhi Pass ID MT

Elk Creek

NE

Wet Mtns

Iron Hill

CO

Pea Ridge

MO

IL

HicksDome

Mineville

NY

Laughlin Peak

El Porvenir

Petaca

Gallinas Mtns

Capitan

Mtns

Wind Mtn

Lemitar Mtns Chupadera Mtns

GoId Hill

Red Hills

NM

Mountain Pass

Music

Valley

CA

Placers

NC

SC Placers

Placers

FL

GA

Land-pebble Phosphate Field

Principal rare earth elements districts in the United States, which are described in this report.
The Rare Earth Elements 3

The Rare Earth Elements

The rare earth elements (REE) comprise 15 elements 

that range in atomic number from 57 (lanthanum) to 71 

(lutetium) on the periodic table (fig. 1). These elements are 

also commonly referred to as “lanthanides.” Yttrium (atomic 

number = 39) is also included with the REE group, because it 

shares chemical and physical similarities with the lanthanides.

Traditionally, the REE are divided into two groups on the 

basis of atomic weight: the light rare earth elements are lanthanum through europium (atomic numbers = 57 through 63); 

and the heavy rare earth elements are gadolinium through 

lutetium (atomic numbers = 64 through 71). Yttrium (atomic 

number = 39), although light, is included with the heavy REE 

group because of its common chemical and physical affiliations 

with the heavy REE in nature.

Most of the REE are not as rare as the group’s name 

suggests. They were named rare earth elements because most 

were identified during the 18th and 19th centuries as oxide 

components within seemingly rare minerals. Cerium is the 

most abundant REE, and it is actually more common in the 

Earth’s crust than is copper or lead. All of the REE except 

promethium are more abundant than silver or mercury (Taylor 

and McLennan, 1985). The rare earth elements are commonly 

found together in the Earth’s crust because they share a trivalent charge (+3) and similar ionic radii. Detailed information 

on the REE is described in Emsley (2001), and an overview of 

the geology, production, and economics of REE is provided by 

Castor and Hedrick (2006).

Basic Geology of Rare Earth Elements

Several geologic aspects of the natural occurrence of rare 

earth elements strongly influence the supply of rare-earthelements raw materials. These geologic factors are presented 

as statements of facts followed by a detailed discussion. This 

section is placed before the balance of the report because an 

understanding of these facts is critical to the discussion that 

follows and should be read first.

Although rare earth elements are relatively abundant in the 

Earth’s crust, they are rarely concentrated into mineable ore 

deposits.

The estimated average concentration of the rare earth 

elements in the Earth’s crust, which ranges from around 150 

to 220 parts per million (table 1), exceeds that of many other 

metals that are mined on an industrial scale, such as copper 

(55 parts per million) and zinc (70 parts per million). Unlike 

most commercially mined base and precious metals, however, 

rare earth elements are rarely concentrated into mineable ore 

deposits. The principal concentrations of rare earth elements 

are associated with uncommon varieties of igneous rocks, 

namely alkaline rocks and carbonatites. Potentially useful concentrations of REE-bearing minerals are also found in placer 

deposits, residual deposits formed from deep weathering of 

igneous rocks, pegmatites, iron-oxide copper-gold deposits, 

and marine phosphates (table 2).

Alkaline igneous rocks form from cooling of magmas 

derived by small degrees of partial melting of rocks in the 

Earth’s mantle. The formation of alkaline rocks is complex 

and not fully understood but can be thought of as a geologic 

process that extracts and concentrates those elements that do 

not fit into the structure of the common rock-forming minerals. The resulting alkaline magmas are rare and unusually 

enriched in elements such as zirconium, niobium, strontium, 

barium, lithium, and the rare earth elements. When these magmas ascend into the Earth’s crust, their chemical composition 

undergoes further changes in response to variations in pressure, temperature, and composition of surrounding rocks. The 

result is an astonishing diversity of rock types that are variably enriched in economic elements, including the rare earth 

elements. The mineral deposits associated with these rocks 

are likewise quite diverse and awkward to classify, in that the 

distinctive features of these deposits and their rarity can result 

in classifications that have only one or a few known examples.

Classification of ores related to alkaline rocks is also 

controversial. Table 2 presents a relatively simple classification that follows analogous categories for deposits related to 

nonalkaline igneous rocks. Some of the more unusual alkaline 

rocks that host, or are related to, REE ores are carbonatite and 

phoscorite, igneous rocks composed principally of carbonate 

and phosphate minerals, respectively. Carbonatites, and especially phoscorites, are relatively uncommon, as there are only 

527 known carbonatites in the world (Woolley and Kjarsgaard, 

2008). Economic concentrations of REE-bearing minerals 

occur in some alkaline rocks, skarns and carbonate-replacement 

deposits associated with alkaline intrusions, veins and dikes 

cutting alkaline igneous complexes and surrounding rocks, and 

soils and other weathering products of alkaline rocks.

Weathering of all types of rocks yields sediments that are 

deposited in a wide variety of environments, such as streams 

and rivers, shorelines, alluvial fans, and deltas. The process of 

erosion concentrates denser minerals, most notably gold, into 

deposits known as placers. Depending on the source of the 

erosion products, certain rare earth elements−bearing minerals, such as monazite and xenotime, can be concentrated along 

with other heavy minerals. The source need not be an alkaline 

igneous rock or a related rare-earth deposit. Many common 

igneous, metamorphic, and even older sedimentary rocks contain enough monazite to produce a monazite-bearing placer. 

As a result, monazite is almost always found in any placer 

deposit. However, the types of placers with the greatest concentrations of monazite are typically ilmenite−heavy mineral 

placers, which have been mined for titanium oxide pigments, 

and cassiterite placers, which are mined for tin.

In tropical environments, rocks are deeply weathered to 

form a unique soil profile consisting of laterite, an iron- and 

aluminum-rich soil, as much as many tens of meters thick. 

The processes of soil formation commonly concentrate heavy 

minerals as residual deposits, resulting in an enriched-metal 

layer over the underlying, unweathered bedrock. When a rareearth deposit undergoes such weathering, it may be enriched 

in rare earth elements in concentrations of economic interest. 
4

The Principal Rare Earth Elements Deposits of the United States

Figure 1. Periodic table of the elements. The rare earth elements comprise 15 elements, which range in atomic number from 57 to 71, including lanthanum (La) to lutetium (Lu). The elements are also commonly referred to as “lanthanides.” Yttrium (Y, atomic number 39) is also typically included with the rare earth elements group because it shares chemical, physical, and application properties with the lanthanides.
The Rare Earth Elements 5

Table 1. Estimates of the crustal abundances of rare earth elements. 

[Rare earth elements listed in order of increasing atomic number; yttrium (Y) is included with these elements because it shares chemical and physical similarities 

with the lanthanides. Unit of measure, parts per million] 

A particular type of REE deposit, the ion-absorption type, is 

formed by the leaching of rare earth elements from seemingly 

common igneous rocks and fixing the elements onto clays in 

soil. These deposits are only known in southern China and 

Kazakhstan and their formation is poorly understood.

Among pegmatites, a group of very coarse grained 

intrusive igneous rocks, the niobium-yttrium-fluorine family, comprises a large number of subtypes formed in different geologic environments. These subtypes are granitic in 

composition and are usually found peripheral to large granitic 

intrusions. In general, however, rare earth elements−bearing 

pegmatites are generally small and are of economic interest 

only to mineral collectors.

The iron-oxide copper-gold type of deposit has been 

recognized as a distinct deposit type only since the discovery 

of the giant Olympic Dam deposit in South Australia in the 

1980s. The Olympic Dam deposit is unusual in that it contains 

large amounts of rare earth elements and uranium. An economic method for recovering rare earth elements from these 

deposits has not yet been found. Many other deposits of this 

type have been identified around the world, but information 

on their rare earth elements content is generally lacking. Trace 

amounts of rare earth elements have also been identified in 

magnetite-apatite replacement deposits.

Karst bauxites, aluminum-rich soils that accumulate in 

cavernous limestone (underlying karst topography) in Montenegro and elsewhere, are enriched in rare earth elements, 

but the resulting concentrations are not of economic interest 

(Maksimović and Pantó, 1996). The same can be said for 

marine phosphate deposits, which can contain as many as 

0.1 percent REE oxides (Altschuler and others, 1966). As 

a result, recovery of rare earth elements as a byproduct of 

phosphate fertilizer manufacture has been investigated.

The ores of rare earth elements are mineralogically and 

chemically complex and commonly radioactive.

In many base and precious metal deposits, the metals 

extracted are highly concentrated in a single mineral phase, such 

as copper in chalcopyrite (CuFeS2

) or zinc in sphalerite (ZnS). 

Separation of a single mineral phase from rock is a relatively 

easy task. The final product is a concentrate typically sent to a 

smelter for final extraction and refining of the metals. Zinc, for 

example, is almost entirely derived from the mineral sphalerite, such that the global zinc smelting and refining industry has 

developed a highly specialized treatment of this mineral. Thus, 

production of zinc has a pronounced cost advantage in that a 

single standard technology is used, and the development of a 

new zinc mine is a largely conventional process.

Rare earth 

element

Mason 

and Moore 

(1982)

Jackson and 

Christiansen 

(1993)

Sabot and 

Maestro 

(1995)

Wedephol 

(1995)

Lide 

(1997)

McGill 

(1997)

Lanthanum

Cerium

Praseodynium

Neodymium

Samarium

Europium

Gadolinium

Terbium

Dysprosium

Holmium

Erbium

Thulium

Ytterbium

Lutetium

Yttrium

Scandium

30

60

8.2

28

6

1.2

5.4

0.9

3

1.2

2.8

0.5

3.4

0.5

33

22

29

70

9

37

8

1.3

8

2.5

5

1.7

3.3

0.27

0.33

0.8

29

18

46

5.5

24

6.5

0.5

6.4

0.9

5

1.2

4

0.4

2.7

0.8

28

10

30

60

6.7

27

5.3

1.3

4

0.65

3.8

0.8

2.1

0.3

2

0.35

24

16

39

66.5

9.2

41.5

7.05

2

6.2

1.2

5.2

1.3

3.5

0.52

3.2

0.8

33

22

5 to 18

20 to 46

3.5 to 5.5

12 to 24

4.5 to 7

0.14 to 1.1

4.5 to 6.4

0.7 to 1

4.5 to 7.5

0.7 to 1.2

2.5 to 6.5

0.2 to 1

2.7 to 8

0.8 to 1.7

28 to 70

5 to 10

Total 206.1 205.2 159.9 184.3 242.17
6 The Principal Rare Earth Elements Deposits of the United States

Table 2. Classification of rare earth elements–bearing mineral deposits.

Association Type Example

Peralkaline igneous rocks Magmatic (alkali-ultrabasic) Lovozero, Russia.

Pegmatite dikes (alkali-ultrabasic) Khibina Massif, Russia.

Pegmatite dikes (peralkaline) Motzfeldt, Greenland.

Hydrothermal veins and stockworks Lemhi Pass, Idaho.

Volcanic Brockman, Western Australia.

Metasomatic-albitite Miask, Russia.

Carbonatites Magmatic Mountain Pass, California.

Dikes and dialational veins Kangakunde Hill, Malawi.

Hydrothermal veins and stockworks Gallinas Mtns., New Mexico.

Skarn Saima, China.

Carbonate rock replacement Bayan Obo, China.

Metasomatic-fenite Magnet Cove, Arkansas.

Iron oxide copper-gold Magnetite-apatite replacement Eagle Mountain, California.

Hematite-magnetite breccia Olympic Dam, South Australia.

Pegmatites Abyssal (heavy rare earth elements) Aldan, Russia.

Abyssal (light rare earth elements) Five Mile, Ontario.

Muscovite (rare earth elements) Spruce Pine, North Carolina.

Rare earth elements-allanite-monazite South Platte, Colorado.

Rare earth elements-euxenite Topsham, Maine.

Rare earth elements-gadolinite Ytterby, Sweden.

Miarolitic-rare earth elements-topaz-beryl Mount Antero, Colorado

Miarolitic-rare earth elements-gadolinite-fergusonite Wasau complex, Wisconsin.

Porphyry molybdenum Climax-type Climax, Colorado.

Metamorphic Migmatized gneiss Music Valley, California.

Uranium–rare earth elements skarn Mary Kathleen, Queensland.

Stratiform phosphate residual Platform phosphorite Southeast Idaho.

Carbonatite-associated Mount Weld, Western Australia.

Granite-associated laterite South China.

Baddeleyite bauxite Poços de Caldas, Brazil.

Karst bauxite Montenegro.

Paleoplacer Uraniferous pyritic quartz pebble conglomerate Elliot Lake, Ontario.

Auriferous pyritic quartz pebble conglomerate Witwatersrand, South Africa.

Placer Shoreline Ti–heavy mineral placer Cooljarloo, Western Australia.

Tin stream placer Malaysia.
The Rare Earth Elements 7

Current mineral-processing practice is capable of sequential separation of multiple mineral phases but it is not always 

cost effective to do so. When elements of interest are found in 

two or more mineral phases, each requiring a different extraction technology, mineral processing is relatively costly. Many 

rare earth elements deposits contain two or more rare earth 

elements−bearing phases. Therefore, rare earth elements deposits in which the rare earth elements are largely concentrated in 

a single mineral phase have a competitive advantage. To date, 

REE production has largely come from single-mineral-phase 

deposits, such as Bayan Obo (bastnasite), Mountain Pass (bastnasite), and heavy-mineral placers (monazite).

Rare earth elements−bearing minerals, once separated, 

contain as many as 14 individual rare earth elements (lanthanides and yttrium) that must be further separated and 

refined. The complexity of extracting and refining rare earth 

elements is illustrated by a metallurgical flow sheet for the 

Mountain Pass mine in California (fig. 2). Unlike metal sulfides, which are chemically simple compounds, REE-bearing 

minerals are quite complex (table 3). Base metal sulfide ores, 

such as sphalerite (ZnS), are typically smelted to burn off sulfur 

and separate impurities from the molten metal. The resulting 

metal is further refined to near purity by electrolysis. Rare earth 

elements, on the other hand, are typically extracted and refined 

through dozens of chemical processes to separate the different 

rare earth elements and remove impurities.

The principal deleterious impurity in REE-bearing minerals is thorium, which imparts an unwanted radioactivity to the 

ores. Because radioactive materials are difficult to mine and 

handle safely, they are heavily regulated. When a radioactive 

waste product is produced, special disposal methods must be 

used. The cost of handling and disposing of radioactive material is a serious impediment to the economic extraction of the 

more radioactive REE-rich minerals, in particular monazite, 

which typically contains considerable amounts of thorium. In 

fact, imposition of tighter regulations on the use of radioactive 

minerals drove many sources of monazite out of the rare earth 

elements market during the 1980s.

The complex metallurgy of rare earth elements is compounded by the fact that no two REE ores are truly alike. As 

a result, there is no standard process for extracting the REEbearing minerals and refining them into marketable rare earth 

compounds. To develop a new rare earth elements mine, the ores 

must be extensively tested by using a variety of known extraction methods and a unique sequence of optimized processing 

steps. Compared with a new zinc mine, process development for 

rare earth elements costs substantially more time and money.

Mineralogy of United States Deposits

The main REE-bearing minerals found in the United 

States are euxenite, bastnasite, xenotime, monazite, and 

allanite. Samarskite, aeschynite, fergusonite, parisite, synchisite, tengerite, ancylite, florencite, britholite, kainosite, and 

thalenite have also been identified in United States deposits 

(table 4). Euxenite [(Y,Er,Ce,U,Pb,Ca)(Nb,Ta,Ti)2

(O,OH)6]is 

an oxide mineral that forms a series with the mineral polycrase 

[(Y,Ca,Ce,U,Th)(Ti,Nb,Ta)2

O6]. Other rare earth elements oxide 

(REO) minerals, such as fergusonite, aeschynite, and samarskite, have similar properties, making identification in hand 

sample difficult. Euxenite is black with a tabular to prismatic 

habit, making it indistinguishable from rutile, a common oxide 

mineral, when found in massive form. However, euxenite does 

not have any cleavage planes and, unlike rutile, has a conchoidal fracture. Furthermore, because euxenite is ordinarily found 

in granite pegmatites, it is commonly associated with quartz, 

feldspars, columbite (now called ferrocolumbite), tantalite (now 

called ferrotantalite or manganocolumbite), and monazite.

Bastnasite (also spelled bastnäsite or bastnaesite) is a rare 

REE-bearing carbonate mineral [(Ce, La,Y)CO3

F] that forms a 

series with the mineral hydroxyl-bastnasite [(Ce,La)CO3

(OH,F)]. 

Bastnasite can be pale white, tan, gray, brown, yellow, or pink, 

with a pearly, vitreous, or greasy to dull luster. Bastnasite usually forms small rounded hexagonal or short prismatic crystals, 

though it can also form rosettes and spheres. Both massive and 

granular varieties have been observed. Bastnasite is closely 

related to the mineral parisite [Ca(Ce,La)2

(CO3)

3

F2] and has 

been known to replace crystals of allanite.

Xenotime is a Y-bearing phosphate mineral (YPO4

) and 

can be yellowish brown to reddish brown with a vitreous to 

resinous luster. Less common colors include gray, salmon 

pink, and green. Xenotime is usually an accessory mineral in 

acidic and alkaline rocks, though it has been observed in mica 

schists and quartz-rich gneisses; it may also be a detrital mineral. Xenotime can easily be confused with zircon because of 

similarities in crystal habit and overall appearance. However, 

xenotime is not as hard as zircon and demonstrates perfect 

{100} cleavage.

Monazite is a REE- and thorium-bearing phosphate mineral [(Ce,La,Y,Th)PO4

] and typically contains 60–62 percent 

total rare-earth oxides. Monazite’s resistance to chemical 

weathering and its high specific gravity account for its association with other resistant heavy minerals such as ilmenite, 

magnetite, rutile, and zircon. Because monazite is radioactive, 

however, grains can be metamict, which means they have lost 

their crystalline structure owing to radioactive decay. Crystals 

of monazite are yellow to brown or orange-brown with a vitreous and resinous or adamantine luster. Monazite grains are 

usually equant to prismatic with wedge-shaped terminations. 

Both granular and massive forms exist.

Allanite [Ca(Ce,La,Y,Ca)Al2

(Fe2+,Fe3+)(SiO4)(Si2O7)

O(OH)], which belongs to the epidote mineral group, is 

one of the more common REE-bearing minerals in igneous 

rocks but is rarely concentrated enough to be an ore of REE. 

Allanite grains are tabular and usually black, though dark 

brown to brownish violet varieties also occur. Allanite has a 

conchoidal fracture and is commonly metamict because of the 

radioactive decay of thorium. The presence of a halo or dark 

ring inside the mineral grain is also an effect of its radioactivity. Most commonly, allanite is found as an accessory mineral 

in igneous rocks, such as granites, syenites, diorites, and 

associated pegmatites.
8 The Principal Rare Earth Elements Deposits of the United States

Crushing

Grinding

Classification

Conditioner 1 Conditioner 2

Conditioner 6 Conditioner 5 Conditioner 4 Conditioner 3

Rougher 

Flotation

Cleaner 

Flotation 1

Cleaner 

Flotation 2, 3, 4

Scavenger 

Flotation Tailings

(1 to 2% REO)

Thickener

Drum Filter

Regrind Rotary Kiln 

Dryer

Oxidizing Roast Acid Leach Thickener and 

Filter

Redox 

Separation

Filter SX Mixers SX Loading 

Mixer-Settlers

SX Stripping 

Mixer-Settlers

Eu Redox 

Separation

La Nd Pr SX 

Separation

Nd Pr SX 

Separation

Eu Purification

Precipitation

Filter

Calcination

Sm Gd SX 

Separation

Precipitation

Filter

Calcination

Precipitation

Filter

Calcination

Acid Treatment

Nitrification

Precipitation

Filter

Calcination

Precipitation

Filter

Calcination

Bastnasite Ore

(7% REO)

Steam Steam

Steam Steam

Soda Ash

Fluosilicate

Ammonium 

Lignin 

Sulfonate

Steam

Tall Oil C-30

HCl

Bastnasite 

Concentrate 

(60% REO)

Bastnasite 

Concentrate 

(70% REO)

Bastnasite 

Concentrate 

(85% REO)

Ce 

Concentrate 

(57% CeO2)

Ce Carbonate 

(90% CeO2 )

Gd Oxide Sm Oxide Eu Oxide

La Chloride

HCl

HNO3

La(NO3)3

Pr Oxide

Nd Oxide

Figure 2. Rare earth elements mineral-processing flow sheet for the Mountain Pass mine, California, about 

1995. From one type of ore, no less than 12 rare earth elements products were obtained. REO, rare earth oxides; 

Ce, cerium; Eu, europium; Gd, gadolinium; La, lanthanum; Nd, neodymium; Pr, praseodymium; Sm, samarium; HCl, 

hydrochloric acid. (Gupta and Krishnamurthy (2005), Castor and Hedrick (2006)).
The Rare Earth Elements 9

Table 3. Rare earth elements, thorium, and uranium content of minerals found in rare earth elements deposits.—Continued

[--, not available; REO, rare earth elements oxides. Minerals in bold have historically been processed to recover rare earth elements. Small quantities of other 

minerals may be found in deposits that are or have been mined or in unmined deposits]

Mineral Formula

Content (weight percent)

 REO ThO2

 UO2

Allanite (Ce) (Ce,Ca,Y)2(Al,Fe2+,Fe3+)3(SiO4)3(OH) 3 to 51 0 to 3 --

Allanite (Y) (Y,Ce,Ca)2(Al,Fe3+)3(SiO4)3(OH) 3 to 51 0 to 3 --

Anatase (Ti,REE)O2 -- -- --

Ancylite (Ce) SrCe(CO3

)2OH·H20 46 to 53 0 to 0.4 0.1

Bastnasite (Ce) (Ce,La)(CO3

)F 70 to 74 0 to 0.3 0.09

Brannerite (U,Ca,Y,Ce)(Ti,Fe)2

O6 -- -- --

Britholite (Ce) (Ce,Ca)5(SiO4,PO4)

3

(OH,F) 56 1.5 --

Brockite (Ca,Th,Ce)(PO4)·H2O -- -- --

Calcio-ancylite (Ce) (Ca,Sr)Ce3

(CO3)4(OH)3·H2O 60 -- --

Cerianite (Ce) (Ce4+,Th)O2 -- -- --

Cerite (Ce) Ce9

Fe3+(SiO2)6[(SiO3)(OH)](OH)3 -- -- --

Cheralite (Ca,Ce,Th)(P,Si)O4 -- ≤30 --

Chevkinite (Ca,Ce,Th)4(Fe2+,Mg)2(Ti,Fe3+)3Si4O22 -- -- --

Churchite (Y) YPO4·H2O -- -- --

Crandallite CaAl3

(PO4)2(OH)5·H2O -- -- --

Doverite YCaF(CO3

)2 -- -- --

Eudialyte Na4(Ca,Ce)2(Fe2+,Mn2+,Y)ZrSi8O22(OH,Cl)2 1 to 10 -- --

Euxenite (Y) (Y,Ca,Ce,U,Th)(Nb,Ta,Ti)2O6 -- -- --

Fergusonite (Ce) (Ce,La,Y)NbO4 -- -- --

Fergusonite (Y) YNbO4 -- -- --

Florencite (Ce) CeAl3

(PO4)2(OH)6 -- 1.4 --

Florencite (La) (La,Ce)Al3

(PO4)2(OH)6 1.4

Fluocerite (Ce) (Ce,La)F3 -- -- --

Fluocerite (La) (La,Ce)F3 -- -- --

Fluorapatite (Ca,Ce)5

(PO4)3F 0 to 21 0 to 0.01

Fluorite (Ca,REE)F -- -- --

Gadolinite (Y) Y2

Fe2+Be2Si2O10 40 -- --

Gagarinite (Y) NaCaY(F,Cl)6 -- -- --

Gerenite (Y) (Ca,Na)2

(Y,REE)3Si6O18·2H2O -- -- --

Gorceixite (Ba,REE)Al3[(PO4)2(OH)5]·H2O -- -- --

Goyazite SrAl3

(PO4)

2

(OH)5·H2O -- 1.4 --

Hingganite (Y) (Y,Yb,Er)2

Be2Si2O8(OH)2 -- -- --

Iimoriite (Y) Y2(SiO4)(CO3) -- -- --

Kainosite (Y) Ca2(Y,Ce)2Si4O12(CO3)·H2O -- -- --

Loparite (Ce) (Ce,Na,Ca)(Ti,Nb)O3 32 to 34 -- --
10 The Principal Rare Earth Elements Deposits of the United States

Lateritic deposits—highly weathered soil horizons, 

rich in iron and aluminum oxide minerals, which develop 

in a tropical or forested warm environment—have been 

studied as a potential source of REE; these lateritic REE 

deposits may contain large resources when they overlie lowgrade primary sources, such as carbonatites and syenites. 

At present, however, only two districts (both in southern 

China) have been mined in this capacity. These surficial clay 

deposits account for 14 percent of Chinese REE production (Wu and others, 1996). The ore is referred to as REEbearing ionic absorption clay and forms weathering crusts 

over granite (Ren, 1985; Wu and others, 1996). Laterite clays 

from Longnan in the Jiangxi Province yield heavy REE- and 

Y-rich material whereas ore from Xunwu is light REE−rich 

(O’Driscoll, 2003).

The relative abundance of rare earth elements within and 

among deposits is highly variable, but light rare earth 

Table 3. Rare earth elements, thorium, and uranium content of minerals found in rare earth elements deposits.—Continued

[--, not available; REO, rare earth elements oxides. Minerals in bold have historically been processed to recover rare earth elements. Small quantities of other 

minerals may be found in deposits that are or have been mined or in unmined deposits]

Mineral Formula

Content (weight percent)

 REO ThO2

 UO2

Monazite (Ce) (Ce,La,Nd,Th)PO4 35 to 71 0 to 20 0 to 16

Parisite (Ce) Ca(Ce,La)2(CO3)3F2 59 0 to 0.5 0 to 0.3

Perovskite (Ca,REE)TiO3 ≤37 0 to 2 0 to 0.05

Pyrochlore (Ca,Na,REE)2

Nb2O6(OH,F) -- -- --

Rhabdophane (Ce) (Ce,La)PO4·H2O -- -- --

Rhabdophane (La) (La,Ce)PO4

·H2O -- -- --

Rinkite (rinkolite) (Ca,Ce)4Na(Na,Ca)2Ti(Si2O7)2F2(O,F)2 -- -- --

Samarskite (REE,Fe2+,Fe3+,U,Th,Ca)(Nb,Ta,Ti)O4 -- -- --

Sphene (titanite) (Ca,REE)TiSiO5 ≤3 -- --

Steenstrupine (Ce) Na14Ce6

Mn2Fe2(Zr,Th)(Si6O18)2(PO4)7·3H2O

Synchysite (Ce) Ca(Ce,La)(CO3

)2F 49 to 52 1.6 --

Synchysite (Y) (doverite) Ca(Y,Ce)(CO3

)2F -- -- --

Thalenite (Y) Y3

Si3O10(F,OH) -- -- --

Thorite (Th,U)SiO4 ≤3 -- 10 to 16

Uraninite (U,Th,Ce)O2 -- -- --

Vitusite (Ce) Na3

(Ce,La,Nd)(PO4)2 -- -- --

Xenotime (Y) YPO4 52 to 67 -- 0 to 5

Yttrofluorite (Ca,Y)F2 -- -- --

Zircon (Zr,REE)SiO4 -- 0.1 to 0.8 --

elements are typically more abundant than heavy rare earth 

elements.

The relative proportion of the different rare earth elements in an orebody is quite variable (table 5). The chief 

differences can be seen in the relative proportion of light to 

heavy rare earth elements. REE orebodies are typically somewhat enriched in the light REE—lanthanum to gadolinium—

compared with average crustal abundances. In comparison, 

most rare earth ores are notably depleted in the heavy REE—

terbium to lutetium. A minority of deposits are relatively 

enriched in heavy REE, most commonly those that contain 

xenotime as the principal REE mineral.

Given that each individual rare earth element has its own 

particular uses and market (table 6), the proportions of the 

various rare earth elements in a deposit are unlikely to parallel 

those of demand for rare earth elements. For instance, the most 

abundant rare earth element, cerium, is available in quantities 
The Rare Earth Elements 11

Table 4. Dominant rare earth elements–bearing minerals identified in the United States.

Mineral Formula

Oxides

Aeschynite (Ce,Th,Ca...)[(Ti,Nb,Ta)2O6]

Euxenite (Y,Er,Ce,U,Pb,Ca)(Nb,Ta,Ti)2

(O,OH)6

Fergusonite YnbO4

Samarskite (Y,Er,Fe,Mn,Ca,U,Th,Zr)(Nb,Ta)2(O,OH)6

 Carbonates

Ancylite Sr(Ce,La)(CO3

)

2

(OH)·(H2O)

Bastnasite (Ce, La,Y)CO3

F

Parisite Ca(Ce,La)2

(CO3)3F2

Synchisite Ca(Ce,Nd,Y,La)(CO3)2F

Tengerite Y2

(CO3)3•n(H2O)

 Phosphates

Britholite (Na,Ce,Ca)5

(OH)[(P,Si)O4]3

Florencite (La,Ce)Al3(PO4)2(OH)6

Monazite (Ce,La,Th,Nd,Y)PO4

Xenotime YPO4

 Silicates

Allanite Ca(Ce,La,Y,Ca)Al2

(Fe2+,Fe3+)(SiO4)(Si2O7)O(OH)

Kainosite Ca2

(Ce,Y)2(SiO4)3CO3·H2O

Thalenite Y2

[Si2O7]

that exceed demand for traditional uses (Heymann, 2010). 

Most REE deposits currently (2010) considered for development are enriched in light REE and would likely flood the 

market for cerium if put into production. By contrast, heavy 

REE are in short supply with limited reserves. Certain rare 

earth elements, such as lutetium, presently have no market and 

are not worth recovering at this time.

Rare earth elements are typically obtained as a byproduct or 

coproduct of mining other mineral commodities.

When the economic viability of a mining project is 

assessed, the potential mineral products are divided into 

principal products and byproducts. The principal product, 

for example zinc in a zinc mine, contributes most to the 

value of the minerals produced. Generally, returns from the 

principal product are sufficient to pay the costs of mining 

and processing. All other products are referred to as byproducts, whose returns typically bolster the overall profitability of a mine. Where two or more products of essential 

value are obtained, they are called coproducts. A salient 

feature of rare earth elements mining is that REE-rich 

minerals may be byproducts or coproducts of mining other 

mineral commodities.

Mine production decisions are driven by demand for 

principal products, not for byproducts. Thus, production 

of byproduct REE will vary subject to changes in demand 

for principal products and will be relatively unresponsive 

to demand for REE. China currently (2010) accounts for 

about 96 percent of global rare earth elements production 

(table 7). Of a total production of 120,000 metric tons, 

about 55,000 metric tons was produced as a byproduct of 

the Bayan Obo iron mine. This fact means that at least 44 

percent of world rare earth elements production is a byproduct. Of the remaining Chinese production, about 25,000 

metric tons is produced in southern China as a primary 

product from ion-adsorption deposits. The status of remaining Chinese production is unclear. The balance of global 

REE production is as a byproduct. Conceivably, as much as 

90 percent of global rare earth elements production is as a 

byproduct or coproduct.
12

The Principal Rare Earth Elements Deposits of the United States Table 5. Distribution of rare earth elements in selected rare earth elements deposits. [Rare earth elements listed in order of increasing atomic number; yttrium (Y) is included with these elements because it shares chemical and physical similarities with the lanthanides] Rare earth element Average upper crustal abundance (percent) Wedepohl (1995) Bastnasite Mountain Pass, USA (percent) Castor (2008) Bastnasite Bayan Obo, China (percent) Hedrick (2004) Monazite Green Cove Spring, USA (percent) Hedrick (2004) Xenotime Lehat, Malaysia (percent) Hedrick (2004) High Y REE laterite Longnan, China (percent) Hedrick (2004) Low Y REE laterite Xunwu, China (percent) Hedrick (2004) Bulk ore Bear Lodge, USA (percent) Castor (2008) Bulk ore Strange Lake, Canada (percent) Castor (2008) Lanthanum 19.3 33.8 23.0 17.5 1.2 1.8 43.4 30.4 4.6 Cerium 39.2 49.6 50.0 43.7 3.1 0.4 2.4 45.5 12.0 Praseodynium 3.8 4.1 6.2 5.0 0.5 0.7 9.0 4.7 1.4 Neodymium 15.5 11.2 18.5 17.5 1.6 3.0 31.7 15.8 4.3 Samarium 2.8 0.9 0.8 4.9 1.1 2.8 3.9 1.8 2.1 Europium 0.6 0.1 0.2 0.2 Trace 0.1 0.5 0.4 0.2

Gadolinium 1.7 0.2 0.7 6.6 3.5 6.9 3.0 0.7 2.5

Terbium 0.3 0.0 0.1 0.3 0.9 1.3 Trace 0.1 0.3

Dysprosium 1.7 0.0 0.1 0.9 8.3 6.7 Trace 0.2 8.2

Holmium 0.4 0.0 Trace 0.1 2.0 1.6 Trace 0.0 1.7

Erbium 1.3 0.0 Trace Trace 6.4 4.9 Trace 0.0 4.9

Thulium 0.2 0.0 Trace Trace 1.1 0.7 Trace <0.01 0.7

Ytterbium 0.9 0.0 Trace 0.1 6.8 2.5 0.3 0.5 4.0

Lutetium 0.2 Trace Trace Trace 1.0 0.4 0.1 <0.01 0.4

Yttrium 12.3 0.1 Trace 2.5 61.0 65.0 8.0 <0.01 52.8
The Rare Earth Elements 13

Table 6. Useage of rare earth elements.

[Each rare earth element has its own applications and market. Source: Lynas Corporation (2010)]

Application La Ce Pr Nd Sm Eu Gd Tb Dy Y Other

Magnets -- -- 23.4 69.4 -- -- 2 0.2 5 -- --

Battery alloys 50 33.4 3.3 10 3.3 -- -- -- -- -- --

Metal alloys 26 52 5.5 16.5 -- -- -- -- -- -- --

Auto catalysts 5 90 2 3 -- -- -- -- -- -- --

Petroleum refining 90 10 -- -- -- -- -- -- -- -- --

Polishing compounds 31.5 65 3.5 -- -- -- -- -- -- -- --

Glass additives 24 66 1 3 -- -- -- -- -- 2 4

Phosphors 8.5 11 -- -- -- 4.9 1.8 4.6 -- 69.2 --

Ceramics 17 12 6 12 -- -- -- -- -- 53 --

Other 19 39 4 15 2 -- 1 -- -- 19 --

Table 7. Production of rare earth elements mines in 2009. 

[Source: USGS Mineral Commodity Summaries (U.S. Geological Survey, 2010). TREO, total rare earth elements oxide]

Country Mine 2009 output

(metric tons TREO) Primary product Byproduct

Brazil Buena Norte 650 Ilmenite concentrate Monazite concentrate.

China Bayan Obo 55,000 Iron ore Bastnäsite concentrate.

Sichuan1 10,000 Bastnäsite concentrate

South China1 45,000 Rare earth elements

India Heavy-mineral sands 2,700 Ilmenite concentrate Monazite concentrate.

Malaysia Ipoh sand plant 380 Cassiterite concentrate Xenotime concentrate.

Russia Lovozero 2,500 Loparite concentrate Rare earth elements chloride.

1

Many small producers and a few medium-large producers. The Chinese rare earth elements–mining industry is currently (2010) undergoing governmentdirected rationalization to reduce the number of producers.
14 The Principal Rare Earth Elements Deposits of the United States

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484 p.

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Current Sources and Domestic Reserves 15

Current Sources and Domestic 

Reserves

The United States currently imports all of its rare earth 

elements (REE) raw materials from foreign sources, principally China (U.S. Geological Survey, 2010). This has not 

always been the case. The USGS annually reports global and 

domestic production and trade in REE in its publications 

Minerals Yearbook and Mineral Commodity Summaries. 

Prior to 1998, when production from the Mountain Pass 

mine in California was curtailed, the United States produced 

most of the light REE consumed domestically and by free 

market countries. Heavy REE were obtained from imported 

monazite concentrates. That changed in the 1980s after China 

became the dominant global supplier of light and heavy REE 

(Papp and others, 2008). In 2002, the Mountain Pass mine 

in California, the sole domestic producer of REE minerals, 

shut down. Although the mine has continued to produce REE 

materials from stockpiled raw materials, no new REE ores are 

being mined. Since then, the United States has obtained all of 

its REE raw materials from imports, principally from China. 

China accounts for 95 percent of global REE production 

despite having only 36 percent of identified world reserves 

(table 8).

Concentration of Supply

The high concentration of production of REE in one 

country is not unusual for a minor metal commodity. For 

example, a single mine in the United States supplies 86 

percent of world demand for beryllium and two mines in 

Brazil account for 92 percent of world niobium production 

(U.S. Geological Survey, 2010). Such concentration of supply, 

which has long been of concern in regard to price manipulation, also raises issues related to reliability of supply. Given an 

equal risk of a natural disaster, industrial accident, labor strike, 

political strife, or anything else that might interrupt production, a single source of supply is inherently more risky than 

multiple sources of supply. Even though these various risks are 

not equal among countries, concentration of supply is a key 

indicator of mineral-supply risk.

Table 9 compares the supply situation of REE with other 

internationally traded minerals using several measures of concentration. These measures are used by economists to study 

market concentration and by regulators for antitrust purposes. 

In table 9, concentration ratios, abbreviated CR2 and CR3, 

measure the total percent share in United States imports and 

world production of the top two or top three supplier countries, respectively. A high percentage, such as the CR2 of 94 

percent and CR3 of 96 percent shown for REE (excluding 

Table 8. World production and reserves of rare earth elements minerals in 2009.

[In 2009, China produced 95 percent of world rare earth elements although it had only 36 percent of 

rare earth elements reserves. TREO, total metric tons of rare earth oxides]

2009

Production Reserves

Country

TREO Share TREO Share 

(metric tons) (percent) (metric tons) (percent)

Australia 0 0 5,400,000 5

Brazil 650 0.5 48,000 0.05

China 120,000 95 36,000,000 36

Commonweath of 

Independent States 2,500 2 19,000,000 19

India 2,700 2 3,100,000 3

Malaysia 380 0.3 30,000 0.03

United States 0 0 13,000,000 13

Other 0 0 22,000,000 22

Total 126,230 99,000,000
16 The Principal Rare Earth Elements Deposits of the United States

Table 9. Measures of concentration for selected world metal mining industries.

[CR2 and CR3, two-county and three-country concentration ratios, respectively. NHI, normalized Herfindahl index. The higher the index, the more concentrated are mineral production and United States imports. CR2 and CR3 are rounded to the nearest percent resulting, in some cases, in a slight discrepancy 

between the concentration ratios and the normalized Herfindahl index. RI, country risk index. See text for an explanation of indices. Data are for 2007, the 

latest year for which complete information is available from the U.S. Geological Survey (2010)]

Mineral

commodity

Import 

reliance 

(percent)

United States imports

(percent)

World production

(percent)

CR2 CR3 NHI RI CR2 CR3 NHI RI

Antimony 86 90 98 0.42 1.9 91 94 0.77 2.3

Bauxite and 

alumina

100 50 64 0.19 4.6 46 58 0.16 2.8

Bismuth 95 62 80 0.26 0.8 75 90 0.29 2.3

Cobalt 78 43 56 0.13 1.7 52 63 0.20 1.4

Copper 37 75 88 0.32 1.5 44 51 0.16 2.4

Gallium 99 57 73 0.21 1.3 51 65 0.19 1.9

Indium 100 72 81 0.31 1.3 68 76 0.36 1.4

Manganese 100 54 65 0.21 2.9 46 64 0.17 2.8

Nickel 17 59 68 0.23 1.0 32 46 0.10 2.6

Niobium 100 96 97 0.79 2.7 100 100 0.90 2.9

Platinum 94 50 65 0.17 1.5 91 94 0.63 2.9

Rare earth

elements

100 94 96 0.83 1.9 99 100 0.94 2.0

Rhenium 86 95 98 0.81 1.8 59 68 0.26 2.3

Tantalum 100 35 50 0.13 1.6 75 85 0.35 2.0

Tin 79 69 79 0.31 3.2 74 91 0.30 3.3

Titanium 64 85 94 0.39 3.3 55 77 0.23 2.2

Tungsten 70 50 69 0.19 3.3 81 86 0.57 2.3

Vanadium 100 66 74 0.35 1.5 72 97 0.33 1.5

Yttrium 100 96 99 0.78 1.8 100 100 0.98 2.0

Zinc 58 67 82 0.19 1.1 52 66 0.19 1.9

yttrium and scandium), indicates that imports and world 

production are principally derived from one or two countries. 

A third measure is the Herfindahl index (Stigler, 1983), which 

was originally developed to measure the degree of competition in an industry. It is calculated according to the equation

2

1

n

i

i

HI s == ∑ ,

where si is the share in global production or United States 

imports by country i with n countries. The larger this index, 

the more concentrated are world production and United States 

imports by country. The Herfindahl index can be normalized

1

1 1

HI

n NHI

n

−

=

−

such that the index ranges from 0 to 1.0, which facilitates 

comparison between different mineral commodities. A normalized Herfindahl Index of 1.0 indicates concentration in a single 

country; an index of 0 indicates that all countries have exactly 

the same share in United States imports or world production.

As shown in table 9, all three of these indices place 

REE (including yttrium) at the top of all mineral commodities in terms of concentration of United States imports and 
Current Sources and Domestic Reserves 17

world production. Antimony and niobium, which are mostly 

produced in China and Brazil, respectively, have very similar 

concentration indices. Rhenium is an example of a mineral 

commodity that the United States largely imports from a single 

country, Chile, but whose global production is not particularly 

concentrated.

On the basis of these data, it is no exaggeration to say 

that China dominates the world REE industry. This dominance 

is attributable to China’s large, high-quality resources of REE 

coupled with minimal capital investment, low labor costs, and 

lack of environmental regulation (Hurst, 2010). Referring back 

to table 8, China has only about a third of global REE; hence, 

a lower cost of production is a reasonable explanation for 

China’s position as the world’s dominant REE producer. Papp 

and others (2008) show that REE prices dropped dramatically 

from 1997 to 2008, consistent with the introduction of significant amounts of lower priced Chinese REE.

Risk of Supply Interruption

Assessing our nation’s vulnerability to mineral-supply 

disruptions is a classic exercise in risk analysis. The analysis 

has two components: the nature and probability of threats, and 

assessment of potential impact. Quantitative measurement 

of these components would be useful in ranking the relative 

security of supply of the various mineral commodities used 

and imported by the United States. A first step was made by a 

special committee of the National Research Council when it 

recommended the criticality matrix as a tool for assessing mineral supply risk (National Research Council, 2008). The criticality matrix is a plot that subjectively contrasts supply risk on 

one axis and the effect of supply restriction on the other. The 

authors of the study ranked various imported metals, including 

REE, on a scale of 1 to 4 (low to high) as shown in figure 3. 

Rare earth elements were ranked 4 (high) for supply risk and 3 

(moderately high) for effect of supply restriction.

An analysis of the effect of supply restrictions requires 

a level of economic analysis that is outside the traditional 

responsibilities of the U.S. Geological Survey and beyond 

the scope of this report. Long (2009) proposed combining 

the quantitative measures of concentration discussed above 

with measures of country risk to obtain a relative ranking of 

minerals by supply risk. A similar approach was independently 

adopted by the Raw Materials Supply Group of the European 

Union in a recent study of European mineral security (Raw 

Materials Supply Group, 2010). The European Union study 

does include a rough measure of the economic effect of a 

mineral supply disruption.

There are many measures of country risk from which 

to choose. Long (2009) used the Country Risk Classification 

that is published annually by the Organization for Economic 

Co-operation and Development (Organization for Economic 

Co-Operation and Development, 2008). This classification is a 

measure of a country’s credit risk or likelihood that a country 

will service its external debt. Countries are subjectively ranked 

on a scale from 0 to 7, where 0 is the lowest degree of risk and 

7 the highest. An aggregate country risk index for a commodity is obtained as the sum of individual country risk indices 

weighted by share in United States imports or world production (table 9). This aggregate country risk index likewise falls 

on the scale of 0 to 7. Table 9 illustrates how these indices and 

ratios can be used. Comparison of concentration indices for 

Supply Risk

1 (low)

2

3

4 (high)

1 (low) 2 3 4 (high)

Impact of Supply Restriction

Copper

Gallium

Indium

Lithium

Manganese

Niobium

Platinum Group Metals

 Palladium

 Platinum

 Rhodium

Rare Earth Elements

Tantalum

Titanium

Vanadium

Figure 3. Criticality matrix for selected imported metals (National Research Council, 2008).
18 The Principal Rare Earth Elements Deposits of the United States

United States imports and for world production shows whether 

imports are more concentrated than global production, thus 

indicating opportunities for further diversification of supply. A 

high import concentration index with a low country risk index 

suggests that imports are obtained from stable trading partners 

such as Canada and Australia. High indices across the board 

are cause for greatest concern and indicate those commodities 

that are of greatest risk.

The European Union study (Raw Materials Supply 

Group, 2010) used the World Bank’s World Governance 

Indicators as a measure of political risk. The World Bank 

estimates six governance indicators: voice and accountability, 

political stability, government effectiveness, regulatory quality, rule of law, and control of corruption (World Bank, 2010). 

The European Union study unfortunately does not specify 

which indicator was used or, if all indicators were used, how 

they were combined. The U.S. Geological Survey has identified other indicators of country risk, such as the Economic 

Freedom Score (Heritage Foundation, 2010), the Corruption 

Perceptions Index (Transparency International, 2010), and 

rankings of countries for mining investment (Behre Dolbear, 

2010; McMahon and Cervantes, 2010).

Aside from an indicator of country risk, the European 

Union study also used a subjective ranking of the degree to 

which other minerals can substitute for the mineral in question, measures of recycling rates and environmental policy 

risk, and a rescaled Herfindahl index to measure mineral supply concentration. Using these indicators, some 14 metals and 

minerals were shortlisted as critical raw materials for European Union member nations, “critical” in this case signifying 

a high degree of both supply risk and economic importance. 

The shortlisted metals and minerals are antimony, beryllium, 

cobalt, fluorspar, gallium, germanium, graphite, indium, magnesium, niobium, platinum group metals, REE, tantalum, and 

tungsten (Raw Materials Supply Group, 2010). Long (2009) 

listed 15 metals and minerals: antimony, barite, chromite, 

cobalt, fluorspar, gallium, graphite, indium, niobium, platinum 

group metals, REE, rhenium, tantalum, titanium, and tungsten 

as those minerals with the greatest supply risk to the United 

States economy. The two lists are very similar. The differences 

are beryllium, which is imported by Europe from the United 

States; barite, critical to the US oil and gas industry; and chromite, rhenium, and titanium, whose supply was rated as less 

risky in the European Union report.

In both the USGS and European Union studies of mineral supply risk, REE rank highest as mineral raw materials 

of critical concern, given uncertain future supplies and their 

importance to advanced industrial economies. Neither of 

these studies addressed measures to mitigate these risks but 

each did recommend further study, including examination of 

mineral policy options. There are geologic factors, however, 

that should be considered in future studies of REE supply, 

such as the extent and quality of domestic REE resources, 

undeveloped resources in other low-risk countries, and 

the time it takes to develop these resources into producing 

mines.

Domestic and World Resources

The main body of this report is a review of the geology 

and known mineral resources of the principal domestic United 

States deposits of REE minerals discovered to date (2010). 

These resources are summarized in table 10. It is important to 

recognize that resource estimates are of differing accuracy and 

reliability, depending on the degree of exploration undertaken 

to date. Many of the estimates in table 10 are obtained by 

inference from surface exposures of mineralization, a small 

number of samples, and inferences or assumptions about 

how deep mineralization extends. Some deposits have been 

explored at depth by core drilling. A very few have been 

drilled on a narrowly spaced grid sufficient for an estimate of 

how much mineralized material may be economic to mine. 

The potential economic viability of any of these resources can 

be reliably assessed only with sufficient drilling, pilot plant–

scale metallurgical testing, and definitive economic analysis. 

Only one domestic deposit, Mountain Pass, California, meets 

those criteria and can be reported to contain a sizable reserve 

of REE-bearing ore.

Table 11 reports reserves and resources in REE deposits 

worldwide, divided into three categories. The first category 

comprises deposits sufficiently explored to estimate a mine 

plan resource. Although a mine has been designed or already 

exists for each of these deposits, they have not been demonstrated to be economically viable by means of a definitive 

feasibility study; hence, they are classed as resources. The 

second category comprises measured, indicated, and inferred 

resources for well-explored deposits that have not yet been 

subject to a feasibility study that includes a mine design. 

The third category, unclassified resources, is a mixed bag of 

known resources that are unlikely to be exploited, such as 

Pilanesberg, South Africa, which is now within a national 

park, and the Olympic Dam mine, Australia, where extensive 

study has found that REE are not economic to recover even 

as a byproduct. Other deposits in this category have been 

little explored and the resources are inferred from surface 

exposures and limited sampling. No reliable data are available for mines and deposits in China, Russia, and North 

Korea.

The first two categories of resources are the only shortand medium-term sources of additional REE that might 

contribute to the global supply. These categories will likely 

be augmented through further exploration at existing mines 

and development projects. It is possible that long-term supply 

can be met through exploration of known deposits that have 

had little or no drilling and by the discovery of new deposits. 

The projects listed in the first two of the categories shown in 

tables 10 and 11 put an upper limit on a near-term potential for 

production of REE mineral supplies. This limit can be put at 

about 14 million tons of contained total REE oxides (TREO), 

with a country risk index of near zero because almost all of 

that production potential is in the United States, Australia, and 

Canada.
Current Sources and Domestic Reserves 19

Table 10. Domestic reserves and resources of rare earth elements, excluding heavy-mineral placer and phosphate deposits. 

[TREO, total rare earth oxides. Reserves proven and probable classified according to definitions and standards of the Securities and Exchange Commission 

(Securities and Exchange Commission = http://www.sec.gov/index.htm). Inferred resources classified according to the standards of Canadian National Instrument 

43-101 (Canadian National Instrument 43-101 = http://www.ccpg.ca/profprac/index.php?lang=en&subpg=natguidelines). Unclassified resources based on little 

or no drilling. For data on resources in heavy-mineral placer and phosphate deposits, which are not of economic interest, see Jackson and Christiansen (1993)] 

Deposit Tonnage

(metric tons)

Grade

(percent TREO)

Contained TREO

(metric tons) Source

Reserves—Proven and probable

Mountain Pass, California 13,588,000 8.24 1,120,000 Molycorp, Inc. (2010).

Resources—Inferred

Bear Lodge, Wyoming 10,678,000 3.60 384,000 Noble and others (2009).

Resources—Unclassified

Bald Mountain, Wyoming 18,000,000 0.08 14,400 Osterwald and others (1966).

Bokan Mountain, Alaska 34,100,000 0.48 164,000 Keyser and Kennedy (2007).

Diamond Creek, Idaho 5,800,000 1.22 70,800 Staatz and others (1979).

Elk Creek, Nebraska 39,400,000 Molycorp, Inc. (1986).

Gallinas Mtns., New Mexico 46,000 2.95 1,400 Jackson and Christiansen (1993).

Hall Mountain, Idaho 100,000 0.05 50 Staatz and others (1979).

Hick’s Dome, Illinois 14,700,000 0.42 62,000 Jackson and Christiansen (1993).

Iron Hill, Colorado 2,424,000,000 0.40 9,696,000 Staatz and others (1979).

Lemhi Pass, Idaho 500,000 0.33 1,650 Staatz and others (1979).

Mineville, New York 9,000,000 0.9 80,000 McKeown and Klemic (1956).

Music Valley, California 50,000 8.6 4,300 Jackson and Christiansen (1993).

Pajarito, New Mexico 2,400,000 0.18 4,000 Jackson and Christiansen (1993).

Pea Ridge, Missouri 600,000 12 72,000 Grauch and others (2010).

Scrub Oaks, New Jersey 10,000,000 0.38 38,000 Klemic and other (1959).

Wet Mountains, Colorado 13,957,000 0.42 59,000 Jackson and Christiansen (1993).

Long-term prospects for the discovery of new reserves 

and resources depend on sufficient exploration. About 150 

projects worldwide that are prospecting and exploring for rare 

earth elements are known to the U.S. Geological Survey (U.S. 

Geological Survey, 2010). Most of this activity began in the 

last 2 years and it will be some time before results are known. 

Whether this exploration further diversifies REE mineral supplies depends on discovering deposits of adequate size and 

quality in the right countries. Probability of discovery requires 

a quantitative mineral resource assessment, which has never 

been done for REE minerals in any country. The last REE 

deposit discovered and developed into a mine in the United 

States was the Mountain Pass mine in California, discovered in 

1949 and put into production in 1953. That was more than 50 

years ago and is not indicative of the time required to discover 

and develop REE deposits in today’s regulatory climate. During the past 50 years outside of China, there has been little REE 

exploration and almost no mine development; hence, we have 

no real REE exploration and development record to draw upon 

for assessing the future pace of discovery and development.

Developing Rare Earth Elements Resources

Rare earth elements resources are distributed between 

many mineral deposits, but only a proportion will be economic 

to develop and mine. By convention, that portion of resources 

that is economic to mine is classified as a “reserve.” That a rare 

earth deposit contains reserves does not mean that it will be 

developed and mined—it means only that it is economic to do 

so. Among the many rare earth reserves available, mining companies will select the most profitable to develop, potentially 

leaving less profitable reserves undeveloped. Reserves may 

also be undeveloped because of adverse land use restrictions, 

civil strife, and a host of other political and social factors. 

Developing a new mine requires a prolonged effort of 

prospecting, exploration, process development, feasibility 

studies, permitting, construction, and commissioning. These 

efforts are broadly sequential but commonly overlap. The 

time required to complete all steps is variable but appreciable, 

particularly compared with the time typically required by nonextractive industries. Studies of the time required to complete 
20 The Principal Rare Earth Elements Deposits of the United States

Table 11. Reserves and resources of rare earth elements outside of the United States, excluding heavy-mineral placer and phosphate 

deposits.—Continued

[TREO, total rare earth elements oxides. Heavy-mineral placers are mined for rare earth elements in only a few places, such as India and Malaysia, and reserve 

information is unavailable. Reserves and resources classified according to one of several national standards, such as Canadian National Instrument 43-101, 

JORC, and SAMREC codes. (JORC, The Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves (JORC Code, 2004 

edition) (http://www.jorc.org/); SAMREC, South African Mineral Resource Committee, http://www.samcode.co.za/downloads/SAMREC2009.pdf).) Unclassified resources based on little or no drilling. Reliable data on rare earth elements reserves and resources in China, North Korea, and Russia are not available. 

Where reserves and resources are given for the same deposit, resources include reserves. For data on other resources in heavy-mineral placers and in phosphate 

deposits, see Jackson and Christiansen (1993)]

Deposit Tonnage

(metric tons)

Grade

(percent TREO)

Contained 

TREO

(metric tons)

Source

Measured-in-pit resources

Brockman, Australia 4,290,000 0.2 8,600 Chalmers (1990).

Mount Weld, Australia 2,100,000 15.5 326,000 Lynas Corporation (2010).

Thor Lake (Lake Zone), Canada 12,010,000 1.70 204,000 Paul and Stubens (2009).

Steenkampskraal, South Africa 249,500 11.80 29,500 Great Western Minerals Group Ltd. (2009).

Measured, indicated, inferred resources

Brockman, Australia 50,000,000 0.23 115,000 Chalmers (1990).

Cummins Range, Australia 4,170,000 1.72 72,000 Navigator Resources Ltd. (2009).

Dubbo, Australia 73,200,000 0.89 651,500 Alkane Resources (2010).

Mount Weld, Australia 15,020,000 8.60 1,292,000 Lynas Corporation (2010).

Narraburra, Australia 55,000,000 0.03 16,500 Capital Mining Ltd. (2009).

Nolans Bore, Australia 30,300,000 2.80 849,000 Arafura Resources Ltd. (2010).

Hoidas Lake, Canada 2,847,000 2.00 57,000 Dunn (2009).

Strange Lake, Canada 137,639,000 0.97 1,335,000 Daigle and Maunula (2010).

Thor Lake (Lake Zone), Canada 175,930,000 1.43 2,516,000 Paul and Stubens (2009).

Thor Lake (North T), Canada 1,136,000 0.71 8,000 Palmer and Broad (2007).

Zeus (Kipawa), Canada 2,270,000 0.11 2,500 Knox and others (2009).

Kvanefjeld, Greenland 457,000,000 1.07 4,890,000 Greenland Minerals and Energy Ltd. 

(2009).

Kangankunde Hill, Malawi 2,500,000 4.24 107,000 Lynas Corporation Ltd. (2007).

Unclassified resources

John Galt, Australia 382,000 7.96 30,400 Northern Uranium Ltd. (2010).

Olympic Dam, Australia >2,000,000,000 0.50 >10,000,000 Oreskes and Einaudi (1990).

Yangibana, Australia 3,500,000 1.70 59,500 Jackson and Christiansen (1993).

Araxá, Brazil 450,000,000 1.80 8,100,000 Filho and others (2005).

Catalão I, Brazil 10,000,000 0.90 90,000 Hirano and others (1990).

Pitinga, Brazil 164,000,000 0.15 246,000 Bastos Neto and Pereira (2009).

Poços de Caldas, Brazil 115,000 Wedow (1967).

Seis Lagos, Brazil 2,900,000,000 1.50 43,500,000 De Sousa (1996).

Tapira, Brazil 5,200,000 10.5 546,000 Hirano and others (1990).

Kasagwe, Burundi 67,000 1.50 1,000 Jackson and Christiansen (1993).
Current Sources and Domestic Reserves 21

Table 11. Reserves and resources of rare earth elements outside of the United States, excluding heavy-mineral placer and phosphate 

deposits.—Continued

[TREO, total rare earth elements oxides. Heavy-mineral placers are mined for rare earth elements in only a few places, such as India and Malaysia, and reserve 

information is unavailable. Reserves and resources classified according to one of several national standards, such as Canadian National Instrument 43-101, 

JORC, and SAMREC codes. (JORC, The Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves (JORC Code, 2004 

edition) (http://www.jorc.org/); SAMREC, South African Mineral Resource Committee, http://www.samcode.co.za/downloads/SAMREC2009.pdf).) Unclassified resources based on little or no drilling. Reliable data on rare earth elements reserves and resources in China, North Korea, and Russia are not available. 

Where reserves and resources are given for the same deposit, resources include reserves. For data on other resources in heavy-mineral placers and in phosphate 

deposits, see Jackson and Christiansen (1993)]

Deposit Tonnage

(metric tons)

Grade

(percent TREO)

Contained 

TREO

(metric tons)

Source

Oka, Canada 210,000,000 0.127 267,000 Orris and Grauch (2002).

Mrima Hill, Kenya 6,000,000 16.2 972,000 Pell (1996).

Ak-Tyuz, Kyrgyzstan 15,000,000 1.00 150,000 Malyukova and others (2005).

Karajilga, Kyrgyzstan 957,000 0.70 6,700 Bogdetsky and others (2001).

Kutessai II, Kyrgyzstan 20,228,000 0.22-0.3 <60,000 Stans Energy Corp. (2010).

Sarysai, Kyrgyzstan 7,000,000 0.20 14,000 Bogdetsky and others (2001).

Pilanesberg, South Africa 13,500,000 0.70 94,500 Lurie (1986).

Zandkopsdrift, South Africa 31,500,000 3.60 1,130,000 Frontier Minerals (2009).

Kizilcaören, Turkey 4,695,000 2.78 130,500 Morteani and Satir (1989).

Dong Pao, Vietnam 500,000,000 1.40 7,000,000 Kušnir (2000).

Mau Xe North, Vietnam 557,000,000 1.40 7,800,000 Kušnir (2000).

this process typically examine the interval between recognition 

of a potentially economic deposit and the commencement of 

commercial production. Peters (1966) examined the development history of a large number of mines and divided them into 

four classes. The first class requires a preproduction period of 2 

years or less. This class of mine is characterized by simple ores 

of high unit value, the applicability of conventional mining 

and mineral processing methods, the absence of need for much 

additional transportation or power infrastructure, an assured 

market, and the requirement for only short-term financing. A 

modern example in this class would be a small- to mediumsized open pit-heap leach gold deposit in Nevada. Gold has a 

high unit value and ready market. The pertinent mining and 

mineral processing technology is also simple and well-known, 

with excellent local infrastructure, and regulatory authorities 

have much experience with this type of mining.

The other three categories are characterized by increasing complexity of ores, size of operations, infrastructure and 

financing needs, and lower unit values. The last category has 

a preproduction period of 7 years or more. A modern example 

would be a nickel laterite mine, the metallurgy of which is 

quite troublesome; many such nickel mines have required in 

excess of 10 years of process development plus delays because 

of market timing. Developing a new nickel laterite mine is 

best timed to open during a period of high nickel prices. A new 

REE mine would almost certainly fall into this last category 

for many of the same reasons—complex metallurgy and 

restricted opportunities for market entry.

The time to develop a mine in each category is likely to 

take longer today than it did when Peters (1966) did his study. 

Most modern mines are developed under a comprehensive 

regulatory environment where, in the United States at least, 

environmental studies, due diligence studies by financing 

sources, permitting, public participation, and due process 

require substantial amounts of time. Further delays may be 

caused by public controversy and litigation against a proposed 

mine. These delays are illustrated in table 12, which tallies the 

time it took to develop metal mines that opened in the United 

States since 2000. The time to obtain a permit has required as 

many as 17 years, and one mine, the Pogo, Alaska gold mine, 

was developed under an expedited permitting schedule that still 

took 7 years. For a small gold mine in Nevada, once permits 

were obtained, the time to construct and put a mine into operation took 1 month. For the Kensington, Alaska, gold mine, 

however, whose operating permits were contested in the courts, 

the process lasted 63 months. Ramp-up times for new mines 

took from 2 to 12 months; the longest was for Pogo, Alaska, 

which had unexpected metallurgical difficulties.

Developing a Rare Earth Elements Mine

The first step in developing a new REE mine is to locate 

a suitable REE deposit. Exploration for new deposits may 

be in either of two contexts: greenfield exploration to find 

new deposits in areas not previously mined and brownfield 

exploration in and adjacent to current and past mining activity. 
22 The Principal Rare Earth Elements Deposits of the United States

Table 12. Time required to obtain permits, construct, and commission recently opened metal mines in the United States.

[NYA, not yet achieved, production not yet begun or commercial operations not achieved; PGE, platinum group elements. Yes, long permitting and development 

delays because of litigation by government agencies and nongovernmental organizations]

Mine Commodity Permitting 

began

Permitting 

completed

Production 

began

Commercial 

operations 

began

Litigation 

reported

Alta Mesa, Texas U 1999 2004 10/2005 1/2006

Arizona 1, Arizona U mid-2007 2009 NYA NYA Yes.

Ashdown, Nevada Mo Au 2/2004 11/2006 12/2006 NYA

Buckhorn, Washington Au 1992 9/2006 10/2008 11/2008 Yes.

Carlota, Arizona Cu 2/1992 6/2007 12/2008 1/2009 Yes.

Eagle, Michigan Ni Cu Co PGE 4/2004 1/2010 NYA NYA Yes.

East Boulder, Montana PGE 1995 1998 6/2001 1/2002

Kensington, Alaska Au 3/1988 6/2005 9/2010 NYA Yes.

Leeville, Nevada Au 7/1997 8/2002 10/2006 4th quarter 2006

Lisbon Valley, Utah Cu 2/1996 7/2004 1st quarter 2006 NYA Yes.

Pend Oreille, Washington Zn 1992 9/2000 1/2004 8/2004

Phoenix, Nevada Au 1/1999 1/2004 10/2006 4th quarter 2006

Pogo, Alaska Au 12/1997 4/2004 2/2006 4/2007

Rock Creek, Alaska Au 2003 8/2006 9/2008 NYA Yes.

Rossi (Storm), Nevada Au 1990 3Q/2006 3/2007 12/2007

Safford, Arizona Cu 4/1998 7/2006 4th quarter 2007 2nd half 2008 Yes.

Turquoise Ridge, Nevada Au 9/1995 5/2003 2004 NYA

Greenfield exploration may target frontier areas with no previ- In the case of REE, very little exploration has ever been 

ous exploration or may follow up on past exploration results. done and the most intense period ever of direct exploration 

Brownfield exploration includes searching for extensions to for REE is currently underway (2010). Many important past 

known reserves and resources within or near a mine as well as discoveries have been serendipitous—the world’s largest REE 

new deposits in the vicinity of existing operations. The latter mine, Bayan Obo in China, was first mined for iron ore. The 

may extend the life of an existing mine or result in the com- “funny” steel produced from this ore was investigated and 

plete redevelopment of a former mine. found to be contaminated with REE (Laznicka, 2006). MounExploration is an uncertain process conducted with tain Pass, California, was found in the course of a U.S. Geologlimited capital. An explorer’s objective is to find a deposit ical Survey radioactivity reconnaissance project that expected 

of the targeted type, size, and quality with the least amount to find uranium. Many REE-bearing carbonatite deposits were 

of expense. Thus, any particular location of merit is rarely initially explored as a source of niobium or phosphates.

exhaustively explored. Exploration will proceed on the basis The discovery of a REE deposit must be proved by extenof favorable indicators so long as objectives are met within sive trenching, drilling, and sampling. Drilling will initially 

budget. An exploration project will be curtailed if evidence be on a widely spaced grid to evaluate the extent and richness 

is found that contraindicates the prospectivity of the target or of mineralization. If results are favorable, the deposit will be 

if results are insufficient to justify further work. Exploration drilled on progressively narrower spacing until a measured 

commonly runs in cycles, prompted by short- to medium-term resource of adequate size is established. Concurrently, baseline 

increases in mineral prices. The low side of a price cycle may environmental studies will be completed and bulk samples 

prompt little or no exploration activity. Any particular prospect obtained for metallurgical testing. A conceptual mine plan 

may undergo many episodes of exploration by different parties and metallurgical plan will be engineered and a preliminary 

during many decades; the exploration episodes are motivated economic feasibility study undertaken. If the results of these 

by price cycles, new cost-saving technology, improved explora- studies are favorable, further work will develop an optimized 

tion concepts and methods, and the vagaries of land access and mine plan, validate metallurgical processing on a pilot plant 

exploration management. scale, begin application for permits, and conduct a definitive 
Current Sources and Domestic Reserves 23

economic feasibility study. If the results of the feasibility study 

are positive, financing will be sought and permitting further 

advanced along with detailed plant engineering. Permitting will typically require an approved plan of operations, a 

positive environmental impact study, and some kind of final 

permission by a government agency. If external financing is 

required, an independent due diligence study will verify the 

results of the feasibility study.

Once financing and regulatory approval are in place, a 

construction decision will be announced. Ongoing detailed 

engineering design will be completed, long lead-time items 

will be ordered, construction work will be bid on, and contracts will be awarded. Construction begins as soon as possible 

and is executed quickly to minimize interest and opportunity 

costs. As mine components are completed, they will be tested 

and placed in operation with a ramp-up period until full commercial production at the planned output rate is achieved. The 

ramp-up process may be completed smoothly in a matter of 

months or may encounter unanticipated difficulties that require 

an extended period of time to solve. Some mines have failed 

at this stage because of ore grades that are lower than expected 

or metallurgical processes that do not work as planned.

Up to this point, a mining company has been spending 

large amounts of money without any revenue from mineral 

sales. Capital must be supplied internally, from net revenues of 

a mining company’s other operations, or externally from banks 

or investors. The cost of borrowing these funds is considerable and repayment cannot even start until a mine goes into 

production. The largest of currently (2010) proposed new REE 

mining operations, including Mountain Pass, California, have 

reported premining capital requirements of a half a billion 

dollars or more.

A mine will operate until reserves are exhausted. Today, 

mine closure and reclamation are planned before a mine is 

built; reclamation is undertaken concurrent with operations 

wherever possible. Mobile equipment and structures are 

removed. Roads, waste stockpiles, tailings, and surface facilities are also reclaimed in an attempt to restore the land to its 

previous use and appearance. Large open pits are not typically 

backfilled because of the large energy and CO2

 emissions costs 

of doing so. Instead, to minimize environmental impact they 

are reclaimed as landscape features.

Only one REE mine, at Mountain Pass, California, has 

ever been developed in the United States. That occurred in the 

early 1950s and is not illustrative of what is required to develop 

such a mine today. Nickel laterite deposits were suggested 

above as a useful analog for the development of a new REE 

mine. This comparison is particularly apt for a REE laterite 

deposit, such as Mount Weld, Australia. Niobium-bearing 

carbonatites are another close analog. These two deposit 

types share complex and difficult metallurgy and typically 

require extended periods of time to develop. The time that was 

required to bring into production recently developed nickel 

laterite mines and most niobium carbonatite mines is shown 

in table 13. All of these mines were developed outside of the 

United States and the permitting delays noted in table 12 do not 

pertain in this case.

The time from discovery to initial production for the 

mines listed in table 13 range from 5 to 50 years, permitting 

to initial production 1 to 7 years, and ramp-up times were 3 to 

42 months, except in the case of Araxá, Brazil, which suffered 

some unusual political delays. These development times are 

in line with the results of Peters (1966) and indicate that in 

some instances a relatively rapid pace of development can be 

obtained. It should be noted, however, that the most advanced 

REE projects other than Mountain Pass, California, namely 

Mount Weld and Dubbo in Australia, have required years of 

metallurgical testing and development and fall into the fourth, 

7-year-or-more category of Peters (1966).

Summary

United States domestic reserves and inferred resources 

of REE are approximately 1.5 million tons, which are large 

compared with peak domestic consumption of REE of 10,200 

tons in 2007 (U.S. Geological Survey, 2010). How much of 

that reserve and resource will be economically available, 

when, and at what rate, cannot be addressed with the data at 

hand. It can be said that the reserves and inferred resources 

reported in table 10 are of light REE and that these two potential mines may not be able to meet domestic needs for heavy 

REE with the production plans currently (2010) proposed. The 

pipeline of new REE projects within the United States is rather 

thin, with 10 out of 150 REE exploration projects identified 

worldwide. If we extend our analysis to reliable trading partners, such as Australia and Canada, prospects for diversifying 

supply and meeting future demand are considerably improved. 

Unfortunately, the time required for development of new REE 

mines is on the order of at least a decade, perhaps much longer 

in the United States, and forecasting future supply that far into 

the future is hazardous.

The lack of mining industry exploration of REE 

deposits in the last few decades is paralleled by a low level 

of geological research. The U.S. Geological Survey has 

demonstrated in related studies that the first step in improving our understanding of REE resources and prospects for 

further discoveries is to conduct national and global mineral resource assessments. Rare earth elements are one of 

the commodities under consideration for the next National 

Resource Assessment, scheduled to begin in 2012. Preliminary work is underway as part of the Minerals at Risk and for 

Emerging Technologies Project, which will be completed at 

the end of Fiscal Year 2011.
24 The Principal Rare Earth Elements Deposits of the United States

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Table 13. Time required to develop selected mines outside of the United States. 

[These mines selected as close analogs of the mining and metallurgical methods required by a rare earth elements mine. NYA, commercial production 

not yet achieved]

Mine Country Commodity Discovery

date

Permitting

completed

Production

began

Commercial

operations

began

Ambatovy Madagascar Ni Co 1960 3/2007 Late 2010 NYA

Araxa Brazil Nb 1955 1960 1st quarter 1961 1966

Barco Alto Brazil Ni 1981 12/2006 3/2010 2011

Bulong Australia Ni 1971 9/1996 3/1999 9/1999

Catalão I Brazil Nb 1970 1974 1976 1977

Cawse Australia Ni Co 1994 9/1996 1/1999 6/2000

Goro New Caledonia Ni Co 1982 10/2004 Late 2010 NYA

Murrin Murrin Australia Ni Co 1984 5/1996 5/1999 12/2003

Niobec Canada Nb 6/1967 11/1973 1/1976 3/1976

Onça Puma Brazil Ni 1970s 8/2005 3rd quarter 2010 Early 2011

Raventhorpe Australia Ni Co Late 1960s 3/2004 10/2007 NYA

Urumu Utsumi Brazil U 1971 1975 7/1981 1982

Vermelho Brazil Ni 1966 7/2005 4th quarter 2012 NYA
Current Sources and Domestic Reserves 25

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The Principal Rare Earth Elements Deposits of the United States 27

The Principal Rare Earth Elements 

Deposits of the United States

The largest rare earth elements (REE) deposits in the 

United States are found in carbonatites and alkaline igneous 

rocks and are concentrated in veins genetically and spatially 

associated with alkaline igneous intrusions. The association 

of REE with alkaline igneous rocks also places REE in close 

association with minerals that host other valuable elements, 

such as titanium, niobium, phosphorus, and thorium (Van 

Gosen and others, 2009).

The major REE deposits in the United States are found in 

• Carbonatites and alkaline igneous complexes; 

• Veins related to alkaline intrusions; 

• Some iron ore deposits associated with magmatichydrothermal processes; and

• Stream and beach deposits (placers) derived from the 

erosion of alkaline igneous terranes.

The principal REE districts in the United States are 

briefly summarized in this report. More-detailed descriptions 

of these districts and their mineral deposits are available in 

the References Cited section. The Mountain Pass REE mine, 

California, may resume operation within the next 2 years, and 

some of the districts mentioned in this report have experienced 

recent exploration activity to evaluate their REE resource 

potential.

Glossary of Terms

Alkaline igneous rock: A series of igneous rocks that formed 

from magmas and fluids so enriched in alkali elements 

that sodium- and potassium-bearing minerals form constituents of the rock in much greater proportion than normal igneous rocks. For detailed discussions of alkaline 

igneous rocks and their scattered geographic distribution 

refer to Sorensen (1974) and Woolley (1987).

Carbonatite: A rare, carbonate igneous rock formed by 

magmatic or metasomatic processes. Most carbonatites consist of 50 percent or more primary carbonate 

minerals, such as calcite, dolomite, and ankerite. They 

are genetically associated with, and therefore typically 

occur near, alkaline igneous rocks. Thorough treatises on 

carbonatites are provided by Tuttle and Gittins (1966), 

Heinrich (1980), and Bell (1989).

Epithermal: Mineral veins and ore deposits formed within 

the Earth’s crust from warm water at shallow depths and 

relatively low temperatures (50–200°C), generally at 

some distance from the magmatic source.

Hypabyssal: An igneous intrusion that solidified at shallow 

depths before reaching the Earth’s surface.

References Cited

Bell, Keith, ed., 1989, Carbonatites—Genesis and evolution: 

Boston, Mass., Unwin Hyman Ltd., 618 p.

Heinrich, E.W., 1980, The geology of carbonatites: Huntington, N.Y., Robert E. Krieger Publishing Company, 585 p.

Sorensen, H., ed., 1974, The alkaline rocks: London, John 

Wiley, 622 p.

Tuttle, O.F., and Gittins, J., 1966, Carbonatites: New York, 

Interscience Publishers, 591 p.

Van Gosen, B.S., Gillerman, V.S., and Armbrustmacher, T.J., 

2009, Thorium deposits of the United States—Energy 

resources for the future?: U.S. Geological Survey Circular 1336, 21 p. (Also available at http://pubs.usgs.gov/

circ/1336/.)

Woolley, A.R., 1987, Alkaline rocks and carbonatites of the 

World—Part I, North and South America: Austin, Tex., 

University of Texas Press, 216 p.
28 The Principal Rare Earth Elements Deposits of the United States

Alaska—Bokan Mountain

Location: Southern area of Prince of Wales Island, the southernmost island in Alaska. Latitude: 54.91299 N., Longitude: 132.13509 W.; datum: WGS84

Deposit type and basic geology: Several northwest-trending 

“vein-dike” systems cut linearly through a zoned, peralkaline granite pluton. The vein-dike deposits contain rare 

earth elements, thorium, and uranium concentrations of 

several percent each. Individual vein-dike systems extend 

as much as 2.6 km (1.6 mi) along strike, composed of 

multiple, subparallel, thin veins that individually rarely 

exceed 1.5 m (5 ft) in width.

Status: Active, ongoing exploration and assessment of the 

rare earth elements vein systems in the district by Ucore 

Rare Metals; its exploration work in the district began in 

2007 and has continued into the 2010 field season (http://

www.ucoreraremetals.com/bokan.asp). 

Production: Between 1957 and 1971, the Ross-Adams mine 

was operated by three different companies to fulfill a contract with the Atomic Energy Agency; it produced roughly 

85,000 tons (77,000 metric tons) of ore with a grade of 

about 1 percent uranium oxide and 3 percent thorium 

oxide.

Estimated resources: An assessment by the U.S. Bureau of 

Mines (Warner and Barker, 1989) suggested that collectively the vein-dike systems in the district represent a 

resource of 6.8 million tons (6.2 metric tons) of ore that 

average 0.264 percent rare earth elements, about onethird of which is yttrium. Recent assay results released by 

Ucore Rare Metals suggest that in some of the vein-dike 

deposits the rare earth elements content (dominated by 

yttrium) can locally exceed 11 percent.

Detailed Discussion

Bokan Mountain is situated near the southern tip of 

Prince of Wales Island, which is the southernmost island in 

the Alaska panhandle and which covers an area of about 7–10 

km2 (3–4 mi2) (fig. 4) (Warner and Barker, 1989; Philpotts 

and others, 1998). The Upper Triassic to Middle Jurassic host 

rock (Lanphere and others, 1964; De Saint-Andre and others, 

1983) is a riebeckite-acmite−bearing peralkaline granite with 

a crudely circular shape that intruded Paleozoic igneous and 

sedimentary rocks (Staatz, 1978). The core riebeckite granite 

porphyry contains subordinate aplitic aegirine granite and is 

surrounded by an outer annulus composed of predominantly 

aegirine granite porphyry (Thompson, 1988; Philpotts and 

others, 1998). Pegmatite-aplites with thorium, rare earth elements (REE), and low levels of gold are also present on Bokan 

Mountain and were emplaced in contact zones around the 

intrusive granite (Staatz, 1978; Warner and Barker, 1989; Philpotts and others, 1998). In addition, various dikes cut across 

all of the rocks near Bokan Mountain, with compositions that 

include andesite, dacite, basalt, lamprophyre, quartz, monzonite, rhyolite, aplite, and quartz latite (Warner and Barker, 

1989). Some of the more felsic dikes contain high levels of 

accessory Nb, REE, and Th.

The aplitic pegmatites are found throughout the peralkaline granite and range in shape from lensoidal bodies to 

elongated pods. Examples are radioactive pegmatites exposed 

in the IML prospects on the east flank of Bokan Mountain, 

about 1 km (0.6 mi) north-northwest of the Ross-Adams mine 

(MacKevett, 1963; Warner and Barker, 1989). Most of the 

pegmatites contain complex mineralogies that include quartz, 

albite, aegirine, and zircon, with variable amounts of allanite, 

ilmenite, riebeckite, arsenopyrite, and fluorite (Warner and 

Barker, 1989). Because of alteration of riebeckite, along the 

border zone pegmatites typically contain disseminated iron 

and titanium spinels, as well as magnetite. The cores of the 

pegmatites consist of milky white massive quartz. The trace 

element compositions of the pegmatites is equally complex 

and may contain elevated percentages of Au, Be, Nb, REE, 

hafnium (Hf), Li, Ta, Sn, Th, U, Y, and Zr. The wall rock 

also contains a halo that is enriched in these elements, with 

minerals that include aegirine, sericite, and hematite alteration 

(Warner and Barker, 1989). Feldspar is largely altered to clay 

minerals.

In 1955, uranium was discovered in the shear zones and 

fractures at Bokan Mountain. However, the Ross-Adams mine 

was the only commercially productive open pit mine in the 

area. The Ross-Adams mine extracted ore from the RossAdams pipe on the Cub claim, which lies along the contact 

between aegirine syenite and aegirine granite porphyry. An 

irregularly shaped north-northwest-trending body, the pipe 

measures 24 m (79 ft) across and was mined along strike for 

more than 300 m (984 ft) (Thompson, 1988). Between 1957 

and 1971, the Ross-Adams mine was operated by three different companies and produced roughly 85,000 tons of ore with a 

grade of about 1 percent U3

O8 and 3 percent ThO2 (Stephens, 

1971; Thompson, 1988; Warner and Barker, 1989). Climax 

Molybdenum operated the mine from 1957 to 1959 and 

produced 315,000 lb of U3

O8, and Standard Metals produced 

another 300,000 lb of U3

O8 between 1959 and 1964 (table 14). 

From 1970–1971, Newmont Exploration produced 687,000 lb 

of U3

O8, at which time operations were suspended, leaving 

approximately 365,000 tons of uranium ore unmined (Warner 

and Barker, 1989).

A private report for the U.S. Department of Agriculture 

of work conducted by Kent and Sullivan (2004) indicates 

that a total of 90,700 tons of uranium ore with an unknown 

grade has been produced at the Ross-Adams mine; in contrast, 

Cathrall (1994) reports that a total of 209,400 tons of 1 percent 

uranium oxide (U3

O8) ore was produced. Several companies, 

including Standard Metals, Cotter Corp., Union Carbide, 

Santa Fe Minerals, Dome Minerals, and Humble Oil, conducted exploration drilling on the Bokan Mountain property 

during 1971–1981 (Kent and Sullivan, 2004). The property 

is currently (2010) under study by Ucore Rare Metals; the 
Alaska—Bokan Mountain 29

Prince of Wales Island

Ross Adams Mine

Bokan Mountain

Aegirine granite porphyry

Fine-grained riebeckite granite porphyry

Riebeckite aplite porphyry

Felty-aegirine granite

Border zone pegmatite-aplite

Riebeckite granite porphyry

Riebeckite-aegirine aplite

0 1 2 KILOMETERS

54°54'30"

132°8'30"

EXPLANATION

Figure 4. Simplified geologic map of Bokan Mountain, Alaska. Modified from Thompson (1988).
30 The Principal Rare Earth Elements Deposits of the United States

company began an intensive new exploration program in 2007 

that continued to the present throughout an area of about 20 

mi2

 that includes the Ross-Adams mine property (http://www.

ucoreraremetals.com/bokan.asp). Preliminary reports based on 

these new data suggest an inverse relationship between U and 

REE; U is located near the margin of the granite complex and 

more abundant REE more distant from the intrusive complex. 

However, ore having a high percentage of U is generally also 

enriched in REE—especially the heavy rare earth elements 

(HREE), Y, Zr, Be, and Nb. For example, Ucore Rare Metals 

reports finding about 6 m of core having a grade of 0.26 percent light rare earth elements (LREE) and 3.6 percent HREE 

in the orebody’s I & L vein system.

Rare earth elements–bearing uraniferous orebodies also 

lie in the northwest-striking shear zones within the stock 

granite, where they measure as thick as 3 m (3.3 ft) and as 

long as 30 m (98 ft) along strike (Thompson, 1988). The 

main uranium minerals include uranothorite and coffinite in 

a gangue of quartz and feldspar (Warner and Barker, 1989; 

Heylmun, 1999). Typically, uranothorite is the dominant 

ore mineral; it forms yellowish to brownish ovoids that are 

0.2 to 2 mm in diameter (Thompson, 1988). Hematite may 

be found as rims on uranothorite grains or in fine veinlets 

that extend along microfractures between ovoids. Less than 

2 percent of the ore also consists of sulfide species such as 

pyrrhotite, pyrite, chalcopyrite, galena, sphalerite, marcasite, acanthite, and bornite (Thompson, 1988). Within and 

adjacent to the orebodies, pervasive hydrothermal albite and 

minor amounts of chlorite, fluorite, calcite, quartz, sericite, and tourmaline precipitated during wall-rock alteration 

(Thompson, 1988).

In addition to the mineralized shear zones, U- and REEmineralized veins and dikes extend out from Bokan Mountain 

all the way to the West Arm of Kendrick Bay. Most of the 

veins and dikes are parallel to subparallel (table 15) and crop 

out on the southeast side of Bokan Mountain, although an 

exception is the Geiger dike, which is located on the northwest 

side of the mountain (fig. 5). Overall, the veins and dikes tend 

to bifurcate and anastomose, especially away from the granite 

stock, which makes them appear more like members of a system rather than individual bodies (Philpotts and others, 1998). 

On the whole, ore mineralization is confined to microfractures 

in the dikes or the interstices between larger silicate grains 

(Warner and Barker, 1989). For example, the I & L vein system strikes west-northwest (table 15) and is located within the 

peralkaline granite stock on the east side of Bokan Mountain 

(MacKevett, 1963; Warner and Barker, 1989). The system 

measures 2.6 km (1.6 mi) long and is composed of many thin, 

subparallel veins that individually rarely exceed 1.5 m (5 ft) 

in width (Staatz, 1978; Warner and Barker, 1989). Of the 

two main splays in the I & L vein system, the western splay 

(closest to the Bokan Mountain granite) is hosted by limonitestained peralkaline granite and pegmatite (Warner and Barker, 

1989). The Dotson dike system terminates in the northwest 

at a right-lateral offset to the I & L vein system and extends 

about 2 km (1.2 mi) to the southeast; this system of veins has 

a width around 1 km (0.6 mi) (Staatz, 1978; Philpotts and 

others, 1998). The Dotson dike system likely extends southeastward beneath the West Arm of Kendrick Bay (Warner and 

Barker, 1989). The Geiger dike extends northerly from near 

an aplite outlier of the peralkaline granite to the north shore of 

South Arm Moira Sound; it is a continuous dike system of one 

to five or more parallel, radioactive dikes (Warner and Barker, 

1989). The Cheri dike system consists of steeply dipping, 

subparallel, radioactive dikes that cut albitized quartz diorite 

country rock (Warner and Barker, 1989). In some places, 

pyroxene-rich masses appear within the dikes whereas magnetite, pyrite, and epidote appear along the edges. Rare fluorite 

and secondary uranium have also been identified within all of 

these “vein-dike” systems (Warner and Barker, 1989).

The Upper Cheri dikes are subparallel to and southwest 

of the Cheri dikes. On the whole, the dikes are very similar to 

those of the Cheri dike system, with comparable mineralogy, 

structure, setting, radioactivity, and intrusive characteristics 

(Warner and Barker, 1989). The Geoduck dikes can be traced 

southeasterly along a strike of N. 40°–50°W. for about 2.9 

km (1.8 mi) (Warner and Barker, 1989) (table 15). Texturally, 

the dikes are fine to medium grained and granular and banded 

or cut by veinlets of quartz or opaque minerals. In addition, 

the Geoduck dike system has, for most of its strike length, 

chlorite- and epidote-altered pyritic quartz diorite wall rocks 

(Warner and Barker, 1989).

Table 14. Uranium production from the Ross-Adams mine, Alaska.

[Source: Warner and Barker, 1989. Stephens (1971) reported 83,000 tons of uranium ore at about 1% U3O8. Kent and Sullivan (2004) reported 

90,700 tons of ore of unknown grade. Cathrall (1994) reported 209,400 tons of 1 percent U3O8, making the total U3O8 produced 4.2 million pounds. 

lb, pound]

Year Mining company Amount mined (tons) U3O8 produced (lb) Grade (percent U3O8)

1957 Climax Molybdenum Corp. 15,000 315,000 1.05

1959–1964 Standard Metals Corp. 15,000 300,000 1.0 

1970–1971 Newmont Exploration, Ltd. 55,600 687,000 0.62

Total 85,600 1,302,000

Weighted average 0.76
Alaska—Bokan Mountain 31

The veins and dikes are of importance because they contain anomalously high amounts of Be, Nb, REE, Ta, and Hfrich zirconium (table 16). From 1984 to 1987, the U.S. Bureau 

of Mines investigated several prospects on Bokan Mountain 

and in the surrounding area, including the mineralized dikes. 

Collectively, the dikes indicate a resource of 6.8 million tons 

of ore that average 0.264 percent REE oxides, about one-third 

yttrium (Warner and Barker, 1989). In addition, the dikes are 

extensively enriched in yttrium and heavy rare earth elements 

(HREE) relative to the light rare earths (LREE); yttrium is 

present at 1,000 times its normal crustal abundance. This composition contrasts with REE deposits elsewhere in the United 

States and is important because most of the HREE and yttrium 

in the United States is imported (Warner and Barker, 1989). 

The most abundant REE are, in order of generally decreasing 

abundance, Y, Ce, Nd, La, and Sm. Gadolinium, Dy, Ho, Er, 

and Tm are also present in variable and sometimes noteworthy 

concentrations (Warner and Barker, 1989). On average, the 

dikes also contain 0.727 percent zirconium oxide and 0.155 

percent niobium oxide, while the amount of thorium and 

uranium in the dikes is negligible. Trace to minor amounts of 

other valuable elements are also present, including Be, Ga, Ge, 

Au, Hf, Pb, Li, Pd, Rb, Ag, Sr, Ta, Sn, V, and Zn.

The minerals of the euxenite-polycrase series host most 

of the Nb found in the dikes, though minor amounts are 

also contained in columbite (now called ferrocolumbite), 

aeschynite, and fergusonite (Warner and Barker, 1989). 

Thalenite, or its alteration product tengerite, contains the 

observed Y as well as inclusions of xenotime. Other REE are 

contained within the minerals bastnasite, parisite, synchysite, 

xenotime, and monazite. Thorium and uranium are present 

in thorite and uranothorite. Other minerals identified in the 

dikes include aegirine, barite, biotite, calcite, epidote, fluorite, 

galena, iron oxides, magnetite, microcline, microperthite, 

native silver, pyrite, riebeckite, sphalerite, and zircon. Philpotts and others (1998) examined a 3-km (1.9 mi) transect 

from the margin of the Bokan Mountain peralkaline granite 

stock along a micro-pegmatite and aplite vein-dike system 

enriched in Y-REE-Zr-Nb, and they identified minerals such 

as arfvedsonite, taeniolite, and gittinsite, as well as several 

other REE-, Zr-, and Nb-bearing phases. By use of various 

analytical methods, the examined transect was found to be 

generally enriched in Y and HREE and to have a pronounced 

negative Eu anomaly, which largely agrees with the results 

obtained by Warner and Barker (1989) for several dike systems in the Bokan Mountain area.

Similar to the mineralogy of the dike systems, the 

mineralogy of the I & L vein system is complex. In particular, U, Th, and REE are present in several different minerals 

from different parts of the veins, and they are usually in a 

gangue dominated by quartz and albite (Staatz, 1978; Keyser 

and McKenney, 2007). Generally, U is located in Th-bearing 

uraninite, although it can be found in brannerite in some of the 

transverse veins (Staatz, 1978). Secondary U minerals, such 

as kasolite and sklodowskite, have been identified, but they 

are rare (Keyser and McKenney, 2007). In the northwest part 

of the vein system, thorite is the main thorium mineral, while 

allanite is found in the southeastern part of the system as well 

as in the transverse veins. Other rare earth minerals besides 

allanite include bastnasite, xenotime, and monazite. However, 

Table 15. Dimensions of main orebodies in the Bokan Mountain district, Alaska.

[m, meter; --, not available]

Prospect Deposit type Trend Length 

(m)

Average 

width 

(m)

Estimated 

depth 

(m)

Source

Dotson shear zone Shear zone, 

fracture controlled -- -- 3.0 -- Warner and Barker (1989).

Ross-Adams pipe Shear zone, 

fracture controlled N-NW 300 24 -- Thompson (1988).

Cheri Dike N. 45° W. 1,097 0.9 264 Warner and 

Barker (1989).

Upper Cheri Dike -- 366 1 -- Warner and 

Barker (1989).

Dotson Dike -- 2,134 0.9 762 Warner and 

Barker (1989).

Geiger Dike N. 15° E. to 

N. 30° W. 1,707 1.5 762 Warner and Barker (1989).

Geoduck Dike N. 40° W. to 

N. 50° W. 2,896 0.5 762 Warner and Barker (1989.

I & L vein system Dike NW 2,600 ≤1.5 -- Staatz (1978).
32 The Principal Rare Earth Elements Deposits of the United States

0 2 MILES

South Arm

Bokan 

Mountain

Lake

Geiger

Kendrick

Bay

I & L

X

Lake

West Arm

Lake

Dotson

Dotson CreekUpper Cheri

Cheri

Geoduck

Cheri

Perkins Creek

Ross

Adams

N

Figure 5. Map of major vein and dike systems associated with Bokan Mountain, Alaska. Modified from 

Heylmun (1999).

the distribution of the REE oxides is unusual in that one part 

of a vein may contain mostly LREE (for example, bastnasite) 

whereas another part of the same vein has predominantly 

HREE (for example, xenotime) (Staatz, 1978).

In addition, the I & L vein system contains anomalous 

amounts of Be, Nb, Zr, Ba, Sr, Sn, Pb, Zn, Cu, and Mo (table 

16). Most of the Nb-rich minerals are located in euxenitepolycrase or columbite-tantalite series. (Columbite and tantalite are obsolete names for a mineral series; columbite is now 

named ferrocolumbite (Fe2+Nb2

O6), which forms two minerals 

series, one with ferrotantalite (Fe2+Ta2O6) and the other with 

manganocolumbite [(Mn2+,Fe2+)(Nb,Ta)2

O6)].

Commonly, these minerals are associated with zircon as 

microveinlets. Alternatively, these minerals may replace albite 

and quartz in the vein matrix. Other minerals include aegirine, 

barite, biotite, calcite, epidote, fluorite, galena, iron oxides, 

potassium feldspar, magnetite, pyrite, riebeckite, native silver, 

and sphalerite (Staatz, 1978).

Many of the dikes in the Bokan Mountain area crop out 

in heavily forested areas and thus the bedrock is covered by 

thick vegetation (Warner and Barker, 1989). For instance, the 

Upper Cheri dike system can be traced only intermittently 

because of muskeg cover, glacial till, or obscuration by 

hillside talus where it is open-ended. On the northwest end 

of the Upper Cheri, the dike system passes under a low-lying 

creek valley (Warner and Barker, 1989). Heavy soil cover 

also prohibits detailed mapping in the I & L vein system. In 

addition, accessibility to the area is limited given that the 

topography of the Bokan Mountain area ranges from moderately steep to precipitous (Keyser and McKenney, 2007). 

Although deep-water marine access is available to and from 

Ketchikan and Prince Rupert by way of Kendrick Bay and 

Moira Sound, accessing more remote sections of the area 

must be achieved by helicopter, boat, or on foot. In spite of 

these limitations, the mineralization could have considerable 

economic potential.
Alaska—Bokan Mountain

33

Table 16. Resource estimates for main prospects on Bokan Mountain, Alaska, and surrounding property.[%, percent; --, not available. Source of data: Warner and Barker (1989) and Keyser and McKenney (2007)]

Prospect Resource (tons) U O3 8 (percent) Nb O2 5 (percent) ThO2 (percent) Y O2 3 (percent) ZrO2 (percent) REO (percent) BeO (percent) Ta O2 5 (percent)

Indicated Inferred

Cheri1 -- 73,000 0.012 0.089 0.025 0.095 0.320 0.281 0.025 0.01

Cheri1 -- 458,000 0.020 0.175 0.042 0.222 0.650 0.461 0.03 0.01Cheri1 4,443,000 -- 0.014 0.123 0.032 0.180 0.410 0.352 0.025 0.01

Upper Cheri 481,000 -- 0.014 0.099 0.025 0.159 0.460 0.411 -- --

Dotson shear zone -- 2,039,000 0.009 0.083 0.071 0.113 0.009 0.132 -- --

Dotson dike1 8,490,000 -- 0.011 0.103 0.052 0.138 0.260 0.21 0.16 0.026

Geiger1 -- 2,450,000 0.021 0.219 0.009 0.168 2.430 0.458 -- 0.014

Geiger1 4,693,000 -- 0.021 0.219 0.168 2.430 0.458 -- 0.014

Geiger1 2,600,000 -- 0.008 0.062 0.009 0.163 1.000 0.149 -- --

Geoduck1 -- 1,378,000 0.015 0.148 0.031 0.374 0.640 0.375 0.028 --

Geoduck1 9,528,000 -- 0.012 0.112 0.021 0.200 0.390 0.319 0.028 --

I & L -- 21,000 0.094 0.186 0.114 -- 0.094 -- -- --

I & L -- 23,000 -- 0.096 -- -- -- -- -- --

I & L -- 50,000 -- 0.100 -- -- -- -- -- --

I & L -- 6,000 -- 0.300 -- -- -- -- -- --

I & L 37,000 -- -- 0.100 -- -- -- -- -- --

I & L 5,000 -- -- 0.300 -- -- -- -- -- --

ILM 586,000 -- 0.017 0.176 -- 0.083 3.340 0.353 -- --

Ross-Adams mine -- 365,000 0.17 -- 0.460 0.400 0.320 0.32 -- --

Sunday Lake 27,000 -- 0.59 0.070 3.640 1.030 0.380 0.329 -- --

Total 30,890,000 6,863,000

1Trace percentages of Ge, Hf, Pb, Zn, and Au also present.
34 The Principal Rare Earth Elements Deposits of the United States

References Cited

Cathrall, J.B., 1994, Geochemical survey of the Craig study 

area—Craig and Dixon Entrance quadrangles and the 

western edges of the Ketchikan and Prince Rupert 

quadrangles, southeast Alaska: U.S. Geological Survey 

Bulletin 2082, 52 p., 1 plate.

De Saint-André, B., Lancelot, J.R., and Collot, B., 1983, 

U-Pb geochronology of the Bokan Mountain peralkaline 

granite, southeastern Alaska: Canadian Journal of Earth 

Sciences, v. 20, no. 2, p. 236–245.

Heylmun, E.B., 1999, Rare earths at Bokan Mountain, Alaska: 

International California Mining Journal, v. 68, no. 5, 

p. 44–46.

Kent, S., and Sullivan, C., 2004, 2004 Preliminary assessment/

site inspection report, Ross Adams uranium mine, Prince 

of Wales Island, Alaska: Private report for USDA Forest 

Service, Kent & Sullivan, Inc.

Keyser, H.J., and McKenney, J., 2007, Geological Report on 

the Bokan Mountain Property, Prince of Wales Island, 

Alaska: Private report for Landmark Minerals, Inc., 48 p.

Lanphere, M.A., MacKevett, Jr., E.M., and Stern, T.W., 1964, 

Potassium-argon and lead-alpha ages of plutonic rocks, 

Bokan Mountain area, Alaska: Science, v. 145, no. 3633, 

p. 705–707.

MacKevett, E.M., Jr., 1963, Geology and ore deposits of the 

Bokan Mountain uranium-thorium area, southeastern 

Alaska: U.S. Geological Survey Bulletin 1154, 125 p., 

5 plates.

Philpotts, J.A., Taylor, C.D., Tatsumoto, M., and Belkin, H.E., 

1998, Petrogenesis of late-stage granites and Y-REE-ZrNb-enriched vein dikes of the Bokan Mountain stock, 

Prince of Wales Island, southeastern Alaska: U.S. Geological Survey Open-File Report 98–0459, 71 p.

Staatz, M.H., 1978, I and L uranium and thorium vein system, 

Bokan Mountain, southeastern Alaska: Economic Geology, v. 73, no. 4, p. 512–523.

Stephens, F.H., 1971, The Kendrick Bay project: Western 

Miner, v. 44, no. 10, p. 151–158.

Thompson, T.B., 1988, Geology and uranium-thorium mineral 

deposits of the Bokan Mountain granite complex, southeastern Alaska: Ore Geology Reviews, v. 3, p. 193–210.

Warner, J.D., and Barker, J.C., 1989, Columbium- and rareearth element-bearing deposits at Bokan Mountain, 

southeast Alaska: U.S. Bureau of Mines Open File 

Report 33–89, 196 p.
Alaska—Salmon Bay 35

Alaska—Salmon Bay

Location: Northeast shore of Prince of Wales Island, the 

southernmost island in Alaska. Latitude: 56.31915 N., 

Longitude: 133.17145 W.; datum: WGS84

Deposit type and basic geology: Short, irregular, and lenticular veins of radioactive carbonate-hematite crop out 

along the coast for about 13 km (8 mi). Some veins can be 

traced for more than 91 m (300 ft) between the low-tide 

line and forest cover. The veins cut the Salmon Bay greywacke, a thick formation of Silurian age. On average, the 

veins are 5–8 cm (2–3 in.) wide, though they normal range 

from less than 2 cm (1 in.) to as much as 0.76 m (2.5 ft). A 

few veins reach 1.5–3 m (5 to 10 ft) in width.

Status: Apparently little geologic work has been done in this 

area since the 1950s.

Production: No past production.

Estimated resources: The average of seven samples taken 

from one of the more radioactive veins was 0.034 percent equivalent uranium (eU) or 0.156 percent equivalent 

thorium (eTh), which equates to 0.178 percent equivalent 

ThO2

 (eThO2) (Houston and others, 1955). The fluorinerich carbonates from the highest-grade rare earth elements 

vein yield an average content of 0.79 percent rare earth 

oxides. Because of the short, lenticular, and irregular 

nature of the veins, the average grade or total reserves was 

not calculated. 

Detailed Discussion

Reconnaissance for radioactive deposits in southeastern 

Alaska in 1952 identified radioactive minerals in the vicinity 

of Salmon Bay, Alaska, located on the northeastern shoreline 

of Prince of Wales Island. Short, irregular, and lenticular veins 

of radioactive carbonate-hematite crop out along the coast for 

about 13 km (8 mi), roughly 5 km (3 mi) northwest and 8 km 

(5 mi) southeast of Salmon Bay (Houston and others, 1955). 

Some of the veins can be traced, however, for more than 91 m 

(300 ft) between the low-tide line and forest cover. The veins 

cut the Salmon Bay greywacke, a thick formation of Silurian 

age that ranges in color from reddish brown to grayish green 

(Houston and others, 1955). On average, the veins are 5–8 

cm (2–3 in.) wide, though they normally range from less than 

2 cm (1 in.) to as many as 0.76 m (2.5 ft). A few veins reach 

1.5–3 m (5 to 10 ft) in width.

The predominant minerals in the veins are dolomiteankerite and alkali feldspar, with lesser amounts of hematite, 

pyrite, siderite, magnetite, quartz, chalcedony, and chlorite 

(Houston and others, 1955). Other minerals identified include 

parisite, bastnasite, muscovite, fluorite, apatite, thorite, zircon, 

monazite, epidote, topaz, garnet, chalcopyrite, and marcasite. 

The radioactivity in the veins is caused by thorite and monazite, both of which contain thorium. The fluorcarbonates 

parisite and bastnasite are found in nonradioactive carbonatehematite veins, which are also located along the coast and are 

wider than the radioactive veins. Of the two fluorcarbonates, 

parisite is more abundant and appears to be a late-stage mineral that fills in small vugs or was deposited along fractures in 

the host carbonate vein (Houston and others, 1955).

Seven samples taken from one of the more radioactive 

veins averaged 0.034 percent equivalent uranium (eU) or 

0.156 percent equivalent thorium (eTh), which equates to 

0.178 percent equivalent ThO2

 (eThO2) (Houston and others, 1955). The fluorcarbonates from the highest-grade rare 

earth vein yield an average content of 0.79 percent rare earth 

oxides. Because of the short, lenticular, and irregular nature 

of the veins, no calculation of the average grade or total 

reserves was attempted. However, analyses of samples from 

the Paystreak vein on Pitcher Island were sufficient to enable 

preliminary estimates. Houston and others (1955) reported 

approximately 68.6 lb (31 kg) of Th or 78.1 lb (35.4 kg) of 

ThO2 per foot (0.3 m) of depth for the 100-ft (30.5-m) portion 

of the vein sample.

Additional exploration of the Salmon Bay deposit is 

necessary to more fully evaluate the economic potential of 

this resource, as little work has been done in this area since 

the 1950s.

Reference Cited

Houston, J.R., Velikanje, R.S., Bates, R.G., and Wedow, 

H., Jr., 1955, Reconnaissance for radioactive deposits in 

southeastern Alaska, 1952: U.S. Geological Survey Trace 

Elements Investigations Report 293, 58 p.
36 The Principal Rare Earth Elements Deposits of the United States

California—Mountain Pass Deposit 

and Mine

Location: Northeastern corner of San Bernardino County, 

California. Latitude: 35.47812 N., Longitude: 115.53068 

W.; datum: WGS84

Deposit type and basic geology: A massive carbonatite called 

the Sulphide Queen body forms the core of the Mountain 

Pass igneous complex and hosts the bulk of the rare earth 

elements resources in the district. This carbonatite body 

has an overall length of 730 m (2,395 ft) and average 

width of 120 m (394 ft). The typical ore contains about 

10–15 percent bastnasite (the ore mineral), 65 percent 

calcite or dolomite (or both), and 20–25 percent barite, 

plus other minor accessory minerals (Castor and Nason, 

2004). The Sulphide Queen carbonatite body is the largest 

known mass of high-grade rare earth elements ore in the 

United States.

Status: Molycorp ceased its mining of the Mountain Pass rare 

earth elements deposit in 2002 when its permit expired. In 

2009, Molycorp announced its intentions to resume mining at Mountain Pass by the year 2012. 

Production: Rare earth elements were mined in the district 

beginning in 1952, with nearly continuous production 

until 2002. The mine’s peak output, around 1990, was 

20,000 metric tons/year (22,000 tons/year) of rare earth 

elements oxides.

Estimated resources: Molycorp estimates that the remaining 

deposit holds 20 to 47 million metric tons (22 to 52 million tons) of ore with an estimated average grade of 8.9 

percent rare earth elements oxide.

Detailed Discussion

The Mountain Pass deposit sits near the eastern edge of 

the Mohave Desert in the northeastern corner of San Bernardino County, California. It lies just north of Interstate Highway 15 near Mountain Pass, about 60 mi (96 km) southwest of 

Las Vegas, Nevada (figs. 6 and 7). 

The Mountain Pass deposit is commonly recognized as 

the largest known rare earth elements (REE) resource in the 

United States, with current reserves estimated to be greater 

than 20 million metric tons of ore with an average grade of 8.9 

percent rare earth elements oxide (Castor and Hedrick, 2006). 

A massive carbonatite called the Sulphide Queen body forms 

the core of the Mountain Pass igneous complex and hosts the 

bulk of the REE mineral resources in the district. This carbonatite body has an overall length of 730 m (2,395 ft) and 

average width of 120 m (394 ft) (Olson and others, 1954). The 

typical ore contains about 10–15 percent bastnasite (the ore 

mineral), 65 percent calcite or dolomite (or both), and 20–25 

percent barite, plus other minor accessory minerals (Castor 

and Nason, 2004). The Sulphide Queen carbonatite body is 

the largest known mass of high-grade REE ore in the United 

States. Light REE are preferentially concentrated in the Mountain Pass ore (Castor, 2008). 

Molycorp ceased its mining of the Mountain Pass REE 

deposit in 2002 when its permit expired. However, in 2009, 

Molycorp announced its intentions to resume mining at Mountain Pass by the year 2012. The mine’s open pit—inactive 

since 2002—covers about 22 hectares (55 acres ) of area 

and is about 122 m (400 ft ) deep. In July 2009, Molycorp 

reached agreement with Arnold Magnetic Technologies Corp. 

of Rochester, New York, to make permanent magnets using 

REE mined at Mountain Pass (Mining Engineering, 2009). 

Molycorp announced that “Plans call for mining to resume 

at Mountain Pass by 2012, at the rate of about 972 t/d [972 

metric tons per day; 1,000 tons per day] of ore, enough to 

produce 20 kt [20,000 metric tons; 22,000 tons] of rare earth 

oxides for sale each year” (Mining Engineering, 2009, p. 8); it 

has received approval to double its output volume with time. 

The mine’s peak output 20 years ago was 20,000 metric tons 

per year of rare earth oxides (Mining Engineering, 2009). 

Molycorp estimates that the remaining deposit holds 20 to 

47 million metric tons (22 to 52 million tons) of ore (Mining 

Engineering, 2009). 

The Sulphide Queen carbonatite stock and nearby carbonatite dikes are associated with Proterozoic, potassium-rich 

igneous rocks—biotite shonkinite, hornblende and biotite 

syenite, and granite—that intruded Precambrian metamorphic 

and igneous rocks (Olson and others, 1954; Castor, 2008). The 

Sulphide Queen body was originally mapped as three rock 

types with local variations—gray calcite-barite rock (fig. 8), 

ferruginous dolomitic rock, and silicified carbonate rock 

(Olson and others, 1954). All phases of the stock contain bastnasite. Age determinations indicate that the Sulphide Queen 

carbonatite was emplaced 1375±5 million years ago (DeWitt 

and others, 1987), about 25–35 million years after the alkaline 

igneous intrusions in the district (Castor, 2008).

In addition to the massive Sulphide Queen carbonatite 

stock, several carbonatite dikes are exposed in the Mountain 

Pass district. These dikes include the Birthday veins north 

and northwest of the Sulphide Queen mass and other carbonatite dikes southeast of the stock. The Sulphide Queen 

stock and the carbonatite dikes are exposed across an area 

of less than 1 mi2

 in the district. The carbonatite dikes range 

from a few inches to about 6 m (20 ft) in thickness and 

can be exposed for as much as 122 m (400 ft) along strike 

(Olson and others, 1954). Like the Sulphide Queen stock, 

the carbonatite dikes are abundant in calcite (as much as 90 

percent of the dike) and barite (as much as 30 percent); but 

in contrast to the stock, individual dikes may or may not contain bastnasite. Accessory minerals include siderite, quartz, 

fluorite, galena, pyrite, apatite, crocidolite, wulfenite, biotite, 

thorite, hematite, magnetite, goethite, and potassium feldspar 

(Olson and others, 1954; Castor and Nason, 2004; Castor, 2008). The carbonatite dikes range in total REE oxide 

content from 2.03 to 18.64 percent (Olson and others, 1954; 

Staatz and others, 1980).
California—Mountain Pass Deposit and Mine 37

The REE content of the Mountain Pass district was first 

discovered in April 1949, when a couple of uranium prospectors noted modest radioactivity on their Geiger counter on 

Sulphide Queen hill and at the Birthday vein, located 1,219 m 

(4,000 ft) to the northwest (radioactivity reflected the thorium 

content of the carbonatite). They grabbed samples of radioactive rock and took it to the U.S. Bureau of Mines office in 

Boulder City, Nevada. Analyses of the samples by the Bureau 

of Mines, confirmed by laboratories of the USGS, found 

that the rock was rich in bastnasite—a rare earth–carbonatefluorine mineral—which subsequently became the primary 

ore mineral of Mountain Pass. Later in 1949, the prospectors 

filed claims on the Birthday vein system. In November of 

1949, the USGS initiated a high-priority field study of the 

Mountain Pass district, which mapped, described, and sampled 

the district in detail; this field work led to the discovery of 

the massive Sulphide Queen carbonatite stock (Shawe, 1953; 

Olson and others, 1954).

Mappers collected 59 outcrop samples of the Sulphide 

Queen stock, which in total showed an average content of 6.9 

percent REE oxides. Molybdenum Corporation of America 

(later “Molycorp”) purchased the claims from the prospectors 

in February 1950 and prepared plans to mine these bastnasite 

deposits. In 1952, Molybdenum Corporation of America began 

Figure 6. Google Earth image of the Mountain Pass mining district, California. Molycorp’s open pit mine—inactive since 2002—is at 

the center of this view; the pit covers about 55 acres (22 hectares) and is about 400 ft (122 m) deep. (Image used with permission of 

Google.)
38 The Principal Rare Earth Elements Deposits of the United States

Figure 7. Northwest-facing view of Mountain Pass district, California, about 1997, viewed from the Mineral Hill area south of Interstate 

Highway 15. An outcrop of ultrapotassic rock is in the right foreground. (Photograph by Stephen B. Castor, Nevada Bureau of Mines and 

Geology; used with permission.)

Figure 8. Dolomitic carbonatite (“beforsite,” described by Castor, 2008) of the 

Sulphide Queen orebody, Mountain Pass district, California. This sample is very 

high grade ore; it contains more than 12 percent rare earth oxide. bar, barite 

phenocrysts; b+cc, fine-grained bastnasite mixed with calcite; brown to yellow 

mineral is dolomite. (Photograph by Stephen B. Castor, Nevada Bureau of Mines 

and Geology; used with permission.)
California—Mountain Pass Deposit and Mine 39

mining of the surface outcrops and built small processing 

facilities in the district. The early prospecting and discovery 

history of the Mountain Pass district is thoroughly described 

by D.F. Hewett, as the foreword to Olson and others (1954). 

Although the report is more than half a century old and 

was written prior to large-scale mining in the district, the USGS 

report of Olson and others (1954) remains the most comprehensive published report on the geology of the Mountain Pass 

district. The geologic mapping, lithologic descriptions, and 

mineralogy described in the report have been proven through 

the several decades of development to be an accurate geologic 

accounting of the district. The results of more recent geologic 

and geochemical research in the district, which includes subsurface information, are detailed by Castor (2008).

References Cited

Castor, S.B., 2008, The Mountain Pass rare-earth carbonatite 

and associated ultrapotassic rocks, California: The Canadian 

Mineralogist, v. 46, no. 4, p. 779–806.

Castor, S.B., and Hedrick, J.B., 2006, Rare earth elements, in 

Kogel, J.E., Trivedi, N.C., Barker, J.M., and Krukowski, 

S.T., eds., Industrial minerals & rocks—Commodities, markets, and uses (7th ed.): Littleton, Colo., Society for Mining, 

Metallurgy, and Exploration, Inc. (SME), p. 769–792.

Castor, S.B., and Nason, G.W., 2004, Mountain Pass rare earth 

deposit, California, in Castor, S.B., Papke, K.G., and Meeuwig, R.O., eds., Betting on industrial minerals—Proceedings of the 39th Forum on the Geology of Industrial Minerals, Reno/Sparks, Nev., May 18–24, 2003: Nevada Bureau 

of Mines and Geology Special Publication 33, p. 68–81.

DeWitt, Ed, Kwak, L.M., and Zartman, R.E., 1987, U-Th-Pb 

and 40Ar/39Ar dating of the Mountain Pass carbonatite and 

alkalic igneous rocks, S.E. Cal. [abs.]: Geological Society 

of America Abstracts with Programs, v. 19, no. 7, p. 642.

Mining Engineering, 2009, Rare earths mine to come back on 

line to fuel green cars: Mining Engineering, v. 61, no. 10, 

[October 2009], p. 8.

Olson, J.C., Shawe, D.R., Pray, L.C., and Sharp, W.N., 1954, 

Rare-earth mineral deposits of the Mountain Pass district, 

San Bernardino County, California: U.S. Geological Survey 

Professional Paper 261, 75 p.

Shawe, D.R., 1953, Thorium resources of the Mountain Pass 

district, San Bernardino County, California: U.S. Geological Survey Trace Elements Investigations Report 251, 

73 p., 4 plates.

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.
40 The Principal Rare Earth Elements Deposits of the United States

California—Music Valley Area

Location: Sixteen km (10 mi) southeast of Twentynine Palms 

in Riverside County, southern California. Latitude: 

33.98423 N., Longitude: 115.93254 W.; datum: WGS84

Deposit type and basic geology: The xenotime deposits of 

the Music Valley area are situated within the Pinto Gneiss 

of probable Precambrian age. Biotite-rich zones in the 

gneiss can contain abundant orange xenotime grains, 

commonly forming 10–15 percent of the biotite zones and 

locally comprising about 35 percent xenotime.

Status: A reported deposit with apparently no current exploration activity.

Production: These deposits had no past production. Smallscale exploration of these deposits during the late 1950s 

investigated their radioactivity.

Estimated resources: No resource estimate has been made for 

this district. In 1957, rock chip samples were collected in 

radioactive, biotite-rich intervals of the Pinto Gneiss that 

had been exposed in exploration prospect pits. Results 

from five samples found 3.5 to 8.8 weight percent yttrium.

Detailed Discussion

Music Valley lies in the Pinto Mountains about 16 km 

(10 mi) southeast of Twentynine Palms in Riverside County, 

southern California, and just to the northeast of Joshua Tree 

National Park. During 1949 and 1952, reconnaissance ground 

and airborne radiometric prospecting by the USGS in conjunction with the U.S. Atomic Energy Commission led to 

the discovery of radioactivity anomalies in the Music Valley 

area. This discovery led to local exploration efforts to find the 

source of the radioactivity. By 1959, only traces of uranium 

had been found in this area, but localized concentrations of 

xenotime suggest that the radioactivity originated in thorium 

rather than uranium.

All of the xenotime deposits of the Music Valley area 

lie within the Pinto Gneiss of probable Precambrian age 

(Evans, 1964), the oldest rock unit exposed in this area. The 

Pinto Gneiss consists of roughly equal amounts of quartz 

and plagioclase feldspar, and it averages approximately 35 

percent biotite (Evans, 1964). Accessory minerals present in 

trace amounts in the gneiss include sericite, apatite, magnetite, 

zircon, and sphene, and local monazite, actinolite, orthoclase, 

microcline, perthite, and muscovite. Biotite-rich zones in 

the gneiss can contain abundant orange xenotime grains that 

commonly form 10–15 percent of the biotite zones and locally 

comprise about 35 percent xenotime (Evans, 1964). 

In the Music Valley area, xenotime concentrations are 

distributed throughout a northwest-trending zone that is about 

4.8 km (3 mi) in width by 9.7 km (6 mi) in length. According 

to Evans (1964, p. 10): “Xenotime is almost entirely confined 

to the Pinto Gneiss where it is irregularly distributed and only 

locally concentrated in sufficient quantity to give an abnormal 

radioactive anomaly. It nearly always occurs in biotite-rich 

lenses, pods, and folia.”

In 1957, rock-chip samples were collected in radioactive, 

biotite-rich intervals of the Pinto Gneiss that had been exposed 

in exploration prospect pits. Five rock-chip samples collected 

from the most radioactive prospect, the U-Th deposit, found 

the following concentrations (Evans, 1964, table 2, p. 21):

Element Concentration 

(wt percent)

Y 3.5–8.8

La 0.26–0.34

Ce 0.47–0.94

Nd 0.24–0.41

Dy 0.22–0.41

Yb 0.46–0.75

Th 0.31–0.49

To better evaluate the potential rare earth elements 

resources within the Music Valley area requires additional 

detailed mapping, sampling and analyses, and perhaps core 

drilling.

Reference Cited

Evans, J.R., 1964, Xenotime mineralization in the southern 

Music Valley area, Riverside County, California: California 

Division of Mines and Geology Special Report 79, 24 p.
Colorado—Iron Hill Carbonatite Complex 41

Colorado—Iron Hill Carbonatite 

Complex

Location: Located near the small town of Powderhorn, about 

35 km (22 mi) south-southwest of Gunnison, Colorado. 

Latitude: 38.25319 N., Longitude: 107.05328 W.; datum: 

WGS84

Deposit type and basic geology: A massive carbonatite 

stock forms the core of the Iron Hill carbonatite complex. 

The carbonatite stock is enriched in rare earth elements, 

niobium, and thorium; the adjacent pyroxenite unit is 

enriched in these elements also and in substantial amounts 

of titanium.

Status: Since 1990, Teck Resources Ltd. has owned many 

of the patented claims within this intrusive complex. Its 

interests have focused on the substantial titanium resource 

within the pyroxenite unit of the complex. Currently 

(2010), it appears that Teck Resources is not actively 

conducting work at this property.

Production: No mineral resources have been produced from 

this intrusive complex, despite its varied and substantial 

mineral resources (Van Gosen and Lowers, 2007).

Estimated resources: The U.S. Geological Survey (Staatz 

and others, 1979) estimated that the carbonatite stock of 

Iron Hill contains 655.6 million metric tons (722.7 million 

tons) of carbonatite. On the basis of the averaged analytical results of 28 samples of the carbonatite stock—0.4 

percent total rare earth elements oxides and 0.004 percent thorium oxide—Staatz and others (1979) calculated 

potential reserves within the stock of 2.6 million metric 

tons (2.865 million tons) of rare earth elements oxides and 

28,190 metric tons (31,080 tons) of thorium oxide. Applying an average grade of 0.057 percent niobium oxide, 

Staatz and others (1979) estimated a reserve of 374,000 

metric tons (412,000 tons) of niobium oxide in the carbonatite stock of Iron Hill. For an area of the pyroxenite unit, 

Teck Resources reported that “mineable proven, probable 

and possible reserves***are 41.8 million tonnes [46 million tons] grading 13.2% TiO2

 [titanium oxide] within an 

open-ended global proven, probable and possible geologic 

resource of 1.6 billion tonnes [1.8 billion tons] grading 

10.9% TiO2” (Shaver and Lunceford, 1998, p. 63).

Detailed Discussion

The Iron Hill carbonatite complex is exposed for 31 km2

(12 mi2) near the small town of Powderhorn, about 35 km 

(22 mi) south-southwest of Gunnison, Colorado. The intrusion is alkaline with a prominent carbonatite stock at its core. 

This intrusive complex is noteworthy because of its classic 

geology and its mineral resource potential (Van Gosen and 

Lowers, 2007). This intrusive complex was described by 

Olson and Hedlund (1981, p. 5) as “the best example of the 

carbonatite-alkalic rock association in the United States and is 

one of the outstanding occurrences in the world, comparable to 

many of the classic areas in Africa and other continents.” The 

primary rock types of the complex are, from oldest to youngest, pyroxenite, uncompahgrite, ijolite, nepheline syenite, and 

carbonatite (Olson, 1974; Hedlund and Olson, 1975; Olson 

and Hedlund, 1981; Armbrustmacher, 1983). Substantial 

titanium concentrations have been measured in the pyroxenite 

unit, which is thought to host the largest titanium (Ti) resource 

in the United States (Thompson, 1987; Shaver and Lunceford, 

1998; Van Gosen and Lowers, 2007). The carbonatite stock 

is enriched in rare earth elements (REE), niobium (Nb), and 

thorium (Th); the pyroxenite unit is also enriched in these elements plus vanadium (V). Thus, it may be economic to extract 

several resources from this complex with a well-coordinated 

mine and mill plan. Thus far, none of these resources has been 

developed at Iron Hill.

A dolomitic carbonatite stock was the last major igneous phase of the Iron Hill intrusive complex. The stock 

forms Iron Hill (fig. 9) and the ridge to its northwest, and 

it is exposed throughout an area of about 3.7 km (2.3 mi) 

long by 1.9–0.8 km (1.2–0.5 mi) wide, making it the largest exposed carbonatite mass in the United States. Staatz and 

others (1979) estimated that the carbonatite stock of Iron Hill 

contains 655.6 million metric tons (722.7 million tons) of 

carbonatite. On the basis of the averaged analytical results 

of 28 samples of the carbonatite stock—0.4 percent for total 

rare earth oxides and 0.004 percent ThO2

—Staatz and others 

(1979) calculated potential reserves within the stock of 2.6 

million metric tons (2.865 million tons) of rare earth elements 

oxides and 28,190 metric tons (31,080 tons) of ThO2

. Recent 

sampling of the Iron Hill carbonatite stock by Van Gosen 

(2008) found median values (from 13 samples) of 0.19 percent 

total rare earth oxides (table 17) and 0.0035 percent ThO2

; 

this result represents estimated resources within the stock of 

about 1.22 million metric tons (1.34 million tons) of rare earth 

elements oxides and about 23,000 metric tons (25,300 tons) 

of ThO2

. (Median values were used for the Van Gosen (2008) 

data because a few individual results exceeded the upper 

analytical limit of detection for an element.) 

Applying an average grade of 0.057 percent Nb2

O5, Staatz 

and others (1979) estimated a reserve of 374,000 metric tons 

(412,000 tons) of Nb2

O5 in the carbonatite stock of Iron Hill. 

Armbrustmacher and Brownfield (1979) found 0.003 to 0.2 

weight percent Nb (niobium) in 28 samples of the carbonatite 

stock. Van Gosen (2008) found median values of 0.0595 weight 

percent Nb2

O5 from 13 samples of the stock, suggesting an estimated resource of 390,000 metric tons (430,000 tons) of Nb2

O5.

As noted earlier, the pyroxenite unit of the Iron Hill 

complex is enriched in titanium and likely is the largest titanium resource in the United States. In 1968, Buttes Gas & Oil 

Company purchased the properties of the Iron Hill intrusive 

complex. It focused its exploration and development primarily 

on titanium resources in the perovskite-rich pyroxenite on the 

northeast side of the Cimarron fault (Thompson, 1983). Exploration by Buttes Gas & Oil continued at the site into the 1980s. 
42 The Principal Rare Earth Elements Deposits of the United States

A 1976 newspaper article in the Denver Post (February 25, 

1976, p. 31) reported that company officials stated that their 

studies had identified 419 million tons (380 metric tons) of 

reserves averaging 12 percent TiO2. Thompson (1987, p. 27) 

noted, “In 1976, Kaiser Engineers, Inc. prepared a computer 

ore reserve analysis indicating a reserve of 390,000,000 tons 

(350 million metric tons) assaying 11.5 percent TiO2. Since 

1976, additional drilling has increased the reserve to at least 

500 million tons (450 million metric tons) of about the same 

grade.” Thompson (1983, 1987) summarizes the exploration 

work at Iron Hill during the 1970s and 1980s by Buttes Gas 

& Oil and its subsidiary companies, and he describes the processing steps that were being considered to most effectively 

extract titanium from the rock.

In 1990, Teck Resources Ltd. entered into a joint venture 

partnership with Buttes Gas & Oil Company to explore 

the titanium resources of the Iron Hill intrusive complex. 

In 1994, Teck Resources purchased 100 percent interest in 

the properties. Since then (and by 2010), Teck Resources 

delineated an orebody within the pyroxenite rock in the 

northeastern area of the intrusive complex, calculated reserve 

estimates, and conducted mineral processing, marketing, 

and environmental baseline studies to evaluate the economic 

viability of developing these titanium resources (Shaver and 

Lunceford, 1998). Teck Resources reported that “mineable 

proven, probable and possible reserves...are 41.8 million 

metric tons (46 million tons) grading 13.2 percent TiO2

 within 

an open-ended global proven, probable and possible geologic 

resource of 1.6 billion metric tons (1.8 billion tons) grading 

10.9 percent TiO2

” (Shaver and Lunceford, 1998, p. 63).

More recently, Van Gosen (2008) collected 24 widely 

scattered near-surface samples of the pyroxenite unit in 

the northern part of the intrusive complex (fig. 10). Results 

showed a high concentration of 5.74 percent Ti (titanium) with 

a median value of 3.2 percent Ti content. For comparison, Best 

(1982, p. 615) reported that the titanium content of typical 

pyroxenite is approximately 0.88 percent. Also, Upton (1967, 

p. 283) reported that the Iron Hill pyroxenite contained the 

highest titanium concentrations among his example chemistries of alkaline pyroxenites worldwide.

Similar to the central carbonatite stock, the pyroxenite unit at Iron Hill also is enriched in rare earth elements 

(table 17), niobium, and thorium and, additionally, vanadium. 

Pyroxenite samples collected by Van Gosen (2008) contained 

median values of 0.143 percent total rare earth elements oxide 

content (table 2), 0.036 percent Nb2

O5, 0.0025 percent ThO2, 

and 0.046 percent V2O5.

The high REE resource estimates at Iron Hill, Colorado, 

are biased by the very large volume of the host rocks—the 

carbonatite and the pyroxenite unit—which are exposed 

throughout very large areas and extend at depth for at least 

several hundreds of meters. Also, note that REE concentrations at Iron Hill—about 0.14–0.19 percent REE oxide—are 

substantially lower than the concentrations in the Mountain 

Pass carbonatite deposit (California), which reportedly averages 8.9 percent rare earth oxide.

Figure 9. Northwestfacing view of Iron 

Hill, Gunnison County, 

southwestern Colorado. 

Iron Hill is formed by a 

massive carbonatite stock 

that forms the center of an 

alkaline intrusive complex. 

This complex hosts 

many mineral resources, 

including titanium, 

niobium, rare earth 

elements, and thorium 

(Van Gosen and Lowers, 

2007). The carbonatite 

stock is estimated to 

consist of 655.6 metric tons 

of carbonatite containing 

2.6 million metric tons 

of rare earth elements 

oxides, 28,200 metric tons 

of thorium oxide, and 

373,700 metric tons of 

niobium oxide (Staatz and 

others, 1979, p. 30). 
Colorado—Iron Hill Carbonatite Complex 43

Table 17. Median concentrations of rare earth elements in samples of carbonatite stock and pyroxenite unit, Iron Hill 

carbonatite complex, Colorado.

[Rare earth elements listed in order of increasing atomic number; yttrium (Y) is included with these elements because it shares chemical and physical 

similarities with the lanthanides. ppm, parts per million; wt percent, weight percent. Data from Van Gosen (2008)]

Carbonatite stock (13 samples) Pyroxenite unit (24 samples)

Element Median value

(ppm) Oxide Oxide equivalent (wt percent) Element Median value (ppm) Oxide Oxide equivalent (wt percent)

La

Ce

Pr

Nd

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

Y

344

681

89.7

337

47.8

11

33.7

3.72

8.04

1.10

2.63

0.29

1.6

0.17

27.9

La2 3 O

Ce O2 3

Pr O2 3

Nd O2 3

Sm2 3 O

Eu O2 3

Gd O2 3

Tb O2 3

Dy O2 3

Ho O2 3

Er2 3 O

Tm2 3 O

Yb O2 3

Lu O2 3

Y O2 3

0.040

0.080

0.010

0.039

0.006

0.001

0.004

0.0004

0.0009

0.0001

0.0003

0.00003

0.0002

0.00002

0.004

La

Ce

Pr

Nd

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

Y

264

508

60.2

227

39.1

10.6

31.1

3.64

14.1

2.04

4.48

0.45

2.5

0.29

47.8

La O2 3

Ce O2 3

Pr O2 3

Nd O2 3

Sm2 3 O

Eu O2 3

Gd O2 3

Tb O2 3

Dy O2 3

Ho O2 3

Er2 3 O

Tm2 3 O

Yb O2 3

Lu O2 3

Y O2 3

0.031

0.060

0.007

0.026

0.005

0.001

0.004

0.0004

0.002

0.0002

0.0005

0.00005

0.0003

0.00003

0.006

Total 1,590 0.186 1,215 0.143
44 The Principal Rare Earth Elements Deposits of the United States

References Cited

Armbrustmacher, T.J., 1983, The complex of alkaline rocks 

at Iron Hill, Powderhorn district, Gunnison County, 

Colorado, in Handfield, R.C., ed., Gunnison Gold Belt 

and Powderhorn Carbonatite Field Trip Guidebook, 

1983: Denver Region Exploration Geologists Society, 

p. 28–31.

Armbrustmacher, T.J., and Brownfield, I.K., 1979, The carbonatite stock at Iron Hill, Gunnison County, Colorado—

Chemical and mineralogical data: U.S. Geological Survey 

Open-File Report 79–537, 10 p.

Best, M.G., 1982, Igneous and metamorphic petrology: San 

Francisco, Calif., W.H. Freeman and Company, 630 p.

Hedlund, D.C., and Olson, J.C., 1975, Geologic map of the 

Powderhorn quadrangle, Gunnison and Saguache Counties, 

Colorado: U.S. Geological Survey Geologic Quadrangle 

Map GQ–1178, scale 1:24,000.

Olson, J.C., 1974, Geologic map of the Rudolph Hill 

quadrangle, Gunnison, Hinsdale, and Saguache Counties, 

Colorado: U.S. Geological Survey Geologic Quadrangle 

Map GQ–1177, scale 1:24,000.

Olson, J.C., and Hedlund, D.C., 1981, Alkalic rocks and 

resources of thorium and associated elements in the 

Powderhorn district, Gunnison County, Colorado: U.S. 

Geological Survey Professional Paper 1049–C, 34 p.

Shaver, K.C., and Lunceford, R.A., 1998, White Earth Project, 

Colorado—The largest titanium resource in the United States: 

Canadian Industrial Minerals Bulletin, v. 91, p. 63–65.

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.

Thompson, J.V., 1983, Economic potential of the carbonatite 

and alkalic stock at Powderhorn, Gunnison County, Colorado, in Handfield, R.C., ed., Gunnison Gold Belt and Powderhorn Carbonatite Field Trip Guidebook, 1983: Denver 

Region Exploration Geologists Society, p. 32–42.

Thompson, J.V., 1987, Titanium resource in Colorado equals 

all other US deposits: Engineering and Mining Journal, v. 

188, no. 7, p. 27–30.

Upton, G.J., 1967, Alkaline pyroxenites, in Wyllie, P.J., ed., Ultramafic and related rocks: New York, John Wiley, p. 281–288.

Van Gosen, B.S., 2008, Geochemistry of rock samples collected from the Iron Hill carbonatite complex, Gunnison 

County, Colorado: U.S. Geological Survey Open-File 

Report 2008–1119, 27 p. and 2 spreadsheet data files. (Also 

available at http://pubs.usgs.gov/of/2008/1119/)

Van Gosen, B.S., and Lowers, H.A., 2007, Iron Hill (Powderhorn) carbonatite complex, Gunnison County, CO—A 

potential source of several uncommon mineral resources: 

Mining Engineering, v. 59, no. 10, [October 2007], p. 56–62. 

Figure 10. Outcrop of 

pyroxenite unit in the 

northern part of the Iron 

Hill carbonatite complex, 

southwestern Colorado. 

Analyses of 24 widely 

scattered samples of 

this pyroxenite unit 

collected throughout 

the complex contained 

median abundances of 5.3 

percent titanium oxide, 

0.06 percent cerium oxide, 

0.143 percent total rare 

earth elements oxides, 

0.036 percent niobium 

oxide, 0.0025 percent 

thorium oxide, and 0.046 

percent vanadium oxide 

(Van Gosen, 2008).
Colorado—Wet Mountains Area 45

Colorado—Wet Mountains Area

Location: In the Wet Mountains and surrounding area in 

Fremont and Custer Counties of south-central Colorado. 

Latitude: 38.16695 N., Longitude: 105.21388 W.; datum: 

WGS84

Deposit type and basic geology: Thorium (Th) and rare 

earth elements (REE) are noted in veins, syenite dikes, 

fracture zones, and carbonatite dikes (Armbrustmacher, 

1988) associated with three Cambrian alkaline complexes 

(Olson and others, 1977) that intruded the surrounding 

Precambrian terrane. Thorium-REE−mineralized veins 

and fracture zones, which are distal to the three alkaline 

intrusive complexes, have the highest economic potential for thorium and rare earth elements resources. The 

thorium-REE veins and fracture zones are linear features, 

typically 1–2 m (3.3–6.6 ft) thick, but a few are as much 

as 15 m (49 ft) thick. Some individual thorium veins can 

be traced in outcrop for 1.5 km (0.9 mi) and some radioactive fracture zones as much as 13 km (8 mi). Most of 

these vein and fracture-zone deposits lie within a 57 km2

(22 mi2) tract of Precambrian gneiss and migmatite 

located south and southeast of a quartz syenite complex 

at Democrat Creek. Christman and others (1953, 1959) 

mapped nearly 400 veins in this area.

Status: No apparent exploration activity is underway in this 

district at present (2010). Many of the prospective vein 

and fracture-zone deposits occur on private lands.

Production: No thorium or rare earth elements have been 

produced from the district. Modest exploration activity, 

apparently during the 1950s, prospected the radioactive 

veins in the district; the prospecting included shallow 

trenching.

Estimated resources: The U.S. Geological Survey (Armbrustmacher, 1988) estimated that the vein and fracture 

zone deposits of the Wet Mountains area contain the following resources:

• Thorium oxide (ThO2)

Reserves of 58,200 metric tons (64,200 tons);

Probable potential resources of 145,600 metric tons 

(160,500 tons);

• Total light rare earth elements

Reserves of 26,600 metric tons (29,300 tons);

Probable potential resources of 66,500 metric tons 

(73,270 tons) 

• Total heavy rare earth elements

Reserves of 17,700 metric tons (19,540 tons); 

Probable potential resources of 44,300 metric tons 

(48,850 tons).

(This estimate was based on average concentrations of 0.46 

percent ThO2

, 0.21 percent total light rare earth elements 

oxides, and 0.14 percent total heavy rare earth elements 

oxides.)

Detailed Discussion

This thorium-rare earth elements (REE) district, located 

in Fremont and Custer Counties of south-central Colorado, 

may be comparable in thorium and REE resources to the 

Lemhi Pass district of Idaho-Montana. Thorium-REE deposits 

are exposed throughout an area of about 60 km (37 mi) north 

to south by 24 km (15 mi) west to east. Thorium and REE are 

found in veins, syenite dikes, fracture zones, and carbonatite 

dikes (Armbrustmacher, 1988) associated with three Cambrian 

alkaline complexes (Olson and others, 1977) that intruded 

the surrounding Precambrian terrane. These three alkaline 

complexes are the McClure Mountain Complex (Shawe and 

Parker, 1967; Armbrustmacher, 1984), the Gem Park Complex 

(Parker and Sharp, 1970), and the complex at Democrat Creek 

(Armbrustmacher, 1984). The thorium-REE-mineralized 

veins and fracture zones, which are distal to the three alkaline 

intrusive complexes, have the highest economic potential for 

thorium and REE resources. 

On the basis of 201 samples of veins and fracture zones, 

the USGS (Armbrustmacher, 1988) estimated that the vein and 

fracture zone deposits of the Wet Mountains area contain the 

following resources:

• Thorium oxide (ThO2)

Reserves of 58,200 metric tons (64,200 tons);

Probable potential resources of 145,600 metric tons 

(160,500 tons);

• Total light rare earth elements

Reserves of 26,600 metric tons (29,300 tons);

Probable potential resources of 66,500 metric tons 

(73,270 tons);

• Total heavy rare earth elements 

Reserves of 17,700 metric tons (19,540 tons); and

Probable potential resources of 44,300 metric tons 

(48,850 tons).

This estimate incorporates average concentrations of 0.46 

percent ThO2, 0.21 percent total light REE oxides, and 0.14 

percent total heavy REE oxides.

The thorium-REE veins and fracture zones are linear 

features, typically 1–2 m (3.3–6.6 ft) thick, but a few are as 

much as 15 m (49 ft) thick (fig. 11). Some individual thorium 

veins can be traced in outcrop for 1.5 km (0.9 mi) and some 

radioactive fracture zones for as much as 13 km (8 mi). Most 

of these vein- and fracture-zone deposits are distributed within 

a 57 km2

 (22 mi2) tract of Precambrian gneiss and migmatite 

located south and southeast of a quartz syenite complex at 

Democrat Creek. Christman and others (1953, 1959) mapped 
46 The Principal Rare Earth Elements Deposits of the United States

nearly 400 veins in this area. The dominant minerals forming 

these veins are smoky and clear quartz, microcline, barite, iron 

oxides, carbonates, and accessory rutile and sulfide minerals. 

Waxy, red thorite is the primary thorium mineral.

Thorium-REE minerals in the Wet Mountains district 

are also deposited in carbonatite dikes and small plugs. The 

carbonatite dikes are especially associated with the McClure 

Mountain complex (Staatz and Conklin, 1966). The carbonatites take a variety of forms, such as composite dikes 

with two or more generations of carbonate side by side with 

lamprophyre (Heinrich and Salotti, 1975; Armbrustmacher 

and others, 1979); phreatic explosion breccia pipes satellite 

to the McClure Mountain complex (the Pinon Peak breccia 

pipes of Heinrich and Dahlem, 1967); and siliceous carbonate 

dikes associated with amethyst veining (the Amethyst carbonatites of Heinrich and Shappirio, 1966). Armbrustmacher 

(1979) separated the carbonatites into two groups: replacement 

carbonatites and primary magmatic carbonatites. Replacement 

carbonatites have microscopic textures that indicate the nearly 

0

0

1 FOOT

1 METER

Gneiss Quartz-barite-limonite-thorite vein Gneiss

complete pseudomorphous replacement of relict igneous dike 

minerals by carbonate minerals. The replacement carbonatite 

dikes have ThO2 contents of <0.1 percent (Armbrustmacher 

and Brownfield, 1978). In contrast, the primary magmatic 

carbonatite dikes do not display mineral replacement textures 

and are enriched in elements and minerals typical of magmatic 

carbonatites, such as thorium, niobium, and REE that reside 

in the minerals thorite, bastnasite, synchysite, ancylite, and 

monazite. Thorium concentrations in the primary magmatic 

carbonatite dikes commonly exceed 0.1 percent ThO2. However, thorium is more concentrated and is present in greater 

volume in the quartz–iron oxide–barite vein and fracture-zone 

deposits of the district in comparison with the carbonatites 

(Armbrustmacher, 1988).

From 52 samples of primary magmatic carbonatite in the 

Wet Mountains area, Armbrustmacher (1988) found average 

concentrations of 0.17 percent ThO2 and 2.15 percent total rare 

earth oxides. Armbrustmacher (1988) calculated that the seven 

largest carbonatite dikes in the district contain the following:

Figure 11. Sewell Ranch thorium vein (between yellow lines), Wet Mountains, Custer 

County, south-central Colorado. This northwest-southeast-trending Cambrian vein, 9 ft (2.7 

m) wide here, cuts about perpendicular to foliation of Precambrian mafic gneiss country 

rock. Analysis of outcrop samples of this vein collected by this study found 762 ppm Th 

(0.087 percent Th oxide); 495 ppm La; 1,280 ppm Ce; 752 ppm Nd; 296 ppm Sm; 78.5 ppm Eu; 

174 ppm Gd; 16.2 ppm Tb; 14.5 ppm Ho; 4.16 ppm Tm; 25.2 ppm Yb; and 3.42 ppm Lu.
Colorado—Wet Mountains Area 47

• ThO2

Reserves of 119 metric tons (131 tons);

Probable potential resources of 683 metric tons 

(753 tons);

• Total REE oxides 

Reserves of 2,270 metric tons (2,500 tons);

Probable potential resources of 12,970 metric tons 

(14,300 tons).

The Wet Mountains area also contains thin (≤2 m thick) 

red syenite dikes that contain anomalous thorium and REE, 

particularly where the dikes are located nearest the intrusive 

centers. The syenite dikes are composed primarily of alkali 

feldspar and ferric oxides, with trace amounts of thorite, 

barite, rutile, xenotime, bastnasite, and brockite (Armbrustmacher, 1988). Samples of red syenite veins analyzed by this 

study found only 30–40 parts per million (ppm) Th, equivalent 

to 0.0034–0.0046 percent ThO2, and 590–680 ppm total rare 

earth elements. Cerium accounts for about 40 percent of the 

rare earth content of the syenite dikes.

Sampling and geochemical analyses completed during 

this study showed that the syenite, mafic, and ultramafic rock 

units that form the core of the three intrusive complexes do 

not contain particularly large concentrations of thorium or 

REE. Samples of the quartz syenite pluton of the complex at 

Democrat Creek had an average content of 62 ppm Th (0.007 

percent ThO2) and 700 ppm total rare earth elements. Gabbro 

and pyroxenite units of the Gem Park complex showed no 

greater than 13 ppm Th and average total rare earth elements 

content of 190 ppm. In the McClure Mountain complex, all 

samples of the plutonic units of hornblende-biotite syenite 

(fig. 12), nepheline syenite, pyroxenite, and gabbro contained 

less than10 ppm Th and no more than 355 ppm total rare earth 

elements content.

Figure 12. West-facing view of McClure Mountain, Fremont County, Colorado. The mountain is composed of a 

hornblende-biotite syenite phase of McClure Mountain complex. This stock is genetically related to thorium-rare earth 

elements vein deposits of Wet Mountains area. However, this rock unit and other core units of three intrusive complexes 

in this area contain only modest concentrations of thorium and rare earth elements. The thorium- and rare earth–bearing 

minerals crystallized in epigenetic vein and fracture-zone deposits distal to the alkaline intrusive complexes. 
48 The Principal Rare Earth Elements Deposits of the United States

References Cited

Armbrustmacher, T.J., 1979, Replacement and primary magmatic carbonatites from the Wet Mountains area, Fremont 

and Custer Counties, Colorado: Economic Geology, v. 74, 

no. 4, p. 888–901.

Armbrustmacher, T.J., 1984, Alkaline rock complexes in the 

Wet Mountains area, Custer and Fremont Counties, Colorado: U.S. Geological Survey Professional Paper 1269, 

33 p.

Armbrustmacher, T.J., 1988, Geology and resources of thorium and associated elements in the Wet Mountains area, 

Fremont and Custer Counties, Colorado: U.S. Geological 

Survey Professional Paper 1049–F, 34 p., 1 plate.

Armbrustmacher, T.J., and Brownfield, I.K., 1978, Carbonatites in the Wet Mountains area, Custer and Fremont Counties, Colorado—Chemical and mineralogical data: U.S. 

Geological Survey Open-File Report 78–177, 6 p., 3 sheets.

Armbrustmacher, T.J., Brownfield, I.K., and Osmonson, L.M., 

1979, Multiple carbonatite dike at McClure Gulch, Wet 

Mountains alkalic province, Fremont County, Colorado: 

The Mountain Geologist, v. 16, no. 2, p. 37–45.

Christman, R.A., Brock, M.R., Pearson, R.C., and Singewald, 

Q.D., 1959, Geology and thorium deposits of the Wet 

Mountains, Colorado—A progress report: U.S. Geological 

Survey Bulletin 1072–H, 535 p.

Christman, R.A., Heyman, A.M., Dellwig, L.F., and Gott, G.B., 

1953, Thorium investigations 1950–52, Wet Mountains, Colorado: U.S. Geological Survey Circular 290, 40 p., 5 plates.

Heinrich, E.W., and Dahlem, D.H., 1967, Carbonatites and 

alkalic rocks of the Arkansas River area, Fremont County, 

Colorado, 4—The Pinon Peak breccia pipes: American 

Mineralogist, v. 52, nos. 5 and 6, p. 817–831.

Heinrich, E.W., and Salotti, C.A., 1975, A colloform carbonatite, McCoy Gulch, Fremont County, Colorado: The 

Mountain Geologist, v. 12, no. 3, p. 103–111.

Heinrich, E.W., and Shappirio, J.R., 1966, Alkalic rocks 

and carbonatites of the Arkansas River Canyon, Fremont 

County, Colorado, 3—The Amethyst carbonatites: American Mineralogist, v. 51, no. 7, p. 1088–1106.

Olson, J.C., Marvin, R.F., Parker, R.L., and Mehnert, H.H., 

1977, Age and tectonic setting of lower Paleozoic alkalic and mafic rocks, carbonatites, and thorium veins in 

south-central Colorado: U.S. Geological Survey Journal of 

Research, v. 5, no. 6, p. 673–687.

Parker, R.L., and Sharp, W.N., 1970, Mafic-ultramafic igneous 

rocks and associated carbonatites of the Gem Park Complex, Custer and Fremont Counties, Colorado: U.S. Geological Survey Professional Paper 649, 24 p.

Shawe, D.R., and Parker, R.L., 1967, Mafic-ultramafic layered 

intrusion at Iron Mountain, Fremont County, Colorado: U.S. 

Geological Survey Bulletin 1251–A, 28 p.

Staatz, M.H., and Conklin, N.M., 1966, Rare-earth thorium 

carbonate veins of the Road Gulch area, northern Wet 

Mountains, Colorado, in Geological Survey research, 1966, 

Chapter B: U.S. Geological Survey Professional Paper 

550–B, p. 130–133.
Idaho—Diamond Creek Area 49

Idaho—Diamond Creek Area

Location: This vein district lies on the eastern slope of the 

Salmon River Mountains, about 13 km (8 mi) northnorthwest of Salmon, Idaho. Veins of the Diamond Creek 

district are found throughout an area only 4 km (2.5 mi) 

long by 0.8 km (0.5 mi) wide. Latitude: 45.29112 N., Longitude: 113.95174 W.; datum: WGS84

Deposit type and basic geology: The veins are hosted by 

Proterozoic quartzite and siltite and by Mesoproterozoic 

granite. The Diamond Creek veins are mineral fillings in 

fractured and sheared bedrock; the veins are as much as 

7.6 m (25 ft) thick in the metasedimentary rocks (quartzite and siltite) but rarely more than 0.6 m (2 ft) thick in 

the granite (Staatz and others, 1979). These veins contain 

considerable amounts of hydrous iron oxide minerals, 

accompanied by disseminated thorium−rare earth elements−bearing minerals. The vein deposits with copious 

amounts of yellow-to-brown iron oxides (limonite and 

goethite) appear to contain the highest thorium (Th) and 

rare earth elements (REE) concentrations.

Status: No apparent exploration activity is underway in this 

district at present (2010). Within the last decade, Thorium 

Energy Inc. sampled vein deposits in the district.

Production: No thorium or rare earth elements have been 

produced from the district. In the Diamond Creek area, the 

larger veins were explored to evaluate their radioactivity 

in the latest 1940s into the early 1950s by use of bulldozed 

trenches, short adits, and hand-dug pits (Anderson, 1958). 

Most of the Diamond Creek area is soil covered, and thus 

the veins are exposed only by workings and road cuts.

Estimated resources: Sampling of the veins of the Diamond 

Creek district by the U.S. Geological Survey (Staatz and 

others, 1979, eight samples) found total REE oxide contents of 0.59 to 5.51 percent and thorium oxide contents 

of 0.04 to 1.71 percent (only one sample had more than 

1 percent ThO2

). Most of the samples were more greatly 

enriched in the light REE compared with the heavy REE. 

Staatz and others (1979) estimated total reserves for the 

district of 2,870 tons (2,600 metric tons) of total rare-earth 

oxides and total probable potential resources of 75,500 tons 

(68,500 metric tons) of total REE oxides, using an average 

grade of 1.22 percent total REE oxides. Recent exploration and sample analysis by Thorium Energy Inc. supports 

the previous data reported by the USGS and the Atomic 

Energy Commission., including average total REE content 

of 0.80 percent and thorium content of 0.12 percent.

Detailed Discussion

The Diamond Creek district in eastern Idaho contains 

thorium- and rare earth elements (REE)-bearing veins similar to those in the Lemhi Pass district, 56 km (35 mi) to the 

southeast. This vein district lies on the eastern slope of the 

Salmon River Mountains, about 13 km (8 mi) north-northwest 

of Salmon, Idaho. Veins of the Diamond Creek district are 

found across an area of only 4 km (2.5 mi) long by 0.8 km (0.5 

mi) wide (Anderson, 1958; Staatz and others, 1979). The veins 

are hosted by Proterozoic quartzite and siltite and by Mesoproterozoic granite (Evans and Zartman, 1990; Evans and Green, 

2003). Similar in general appearance to the veins of Lemhi 

Pass, the Diamond Creek veins are mineral fillings in fractured 

and sheared bedrock; the veins are as much as 7.6 m (25 ft ) 

thick in the metasedimentary rocks (quartzite and siltite), but 

rarely more than 0.6 m (2 ft ) thick in the granite (Staatz and 

others, 1979).

In the Diamond Creek area, the larger veins were 

explored in the latest 1940s into the early 1950s by use of 

bulldozed trenches, short adits, and hand-dug pits (Anderson, 

1958). Most of the Diamond Creek area is soil covered, and 

thus the veins are exposed only by workings and road cuts. 

Only eight veins have been identified in the district, traced 

along strike for 33.5 to 780 m (110 to 2,560 ft ) (Anderson, 

1958; Staatz and others, 1979). The eight veins vary from 0.15 

to 7.6 m (0.5 to 25 ft ) in thickness (Staatz and others, 1979). 

They contain considerable amounts of hydrous iron oxide minerals, accompanied by disseminated thorium-REE minerals.

In the Diamond Creek district, the vein deposits with 

copious amounts of yellow to brown iron oxides (limonite 

and goethite) appear to contain the highest thorium and REE 

concentrations (Anderson, 1958). Quartz, limonite, and 

goethite form the bulk of the veins, with locally abundant 

fluorite, potassium feldspar, hematite, and biotite (Anderson, 

1958; Staatz and others, 1979). The primary thorium and REE 

mineral is monazite (Staatz and others, 1979). Thorium also 

occurs in minor amounts in brockite and thorite, and xenotime 

and bastnasite have been identified in trace amounts (Staatz 

and others, 1979).

Sampling of the veins of the Diamond Creek district by 

Staatz and others (1979, eight samples) found total REE oxide 

contents of 0.59 to 5.51 percent and thorium oxide contents of 

0.04 to 1.71 percent (only one sample had more than 1 percent 

ThO2

). Most of the samples were more greatly enriched in the 

light REE than in the heavy REE. Staatz and others (1979) 

estimated total reserves for the district of 2,870 tons (2,600 

metric tons) of total rare-earth oxides and total probable 

potential resources of 75,500 tons (68,500 metric tons) of total 

REE oxides, using an average grade of 1.22 percent total REE 

oxides.

Recent exploration and sample analysis by Thorium 

Energy Inc. supports the previous data reported by the USGS 

and the Atomic Energy Commission., including average total 

REE content of 0.80 percent and thorium content of 0.12 

percent. Hedrick (2010) reports, “A preliminary estimate of 

the amounts of REE in the deposit are 22,400 t (metric tons) 

of cerium, 17,125 of neodymium, 8,220 t of lanthanum, 5,480 

t of samarium, 4,795 t of yttrium, 3,425 t of praseodymium, 

3,425 t of gadolinium, 1,370 t of dysprosium and europium 

each, and a total of 685 t of the remaining heavy rare earths.” 

(One ton (2,000 lb) is equal to 0.9072 metric tons.)
50 The Principal Rare Earth Elements Deposits of the United States

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 

No. 115, 81 p.

Evans, K.V., and Green, G.N., 2003, Geologic map of the 

Salmon National Forest and vicinity, east-central Idaho: 

U.S. Geological Survey Geologic Investigations Series Map 

I–2765, scale 1:100,000, 2 sheets, 19 p. pamphlet.

Evans, K.V., and Zartman, R.E., 1990, U-Th-Pb and Rb-Sr 

geochronology of middle Proterozoic granite and augen 

gneiss, Salmon River Mountains, east-central Idaho: Geological Society of America Bulletin, v. 102, no. 1, p. 63–73.

Hedrick, J.B., 2010, Rare earths (advance release), in 2007 

Minerals yearbook: U.S. Geological Survey, 19 p., accessed 

September 8, 2010, at http://minerals.usgs.gov/minerals/

pubs/commodity/rare_earths/myb1-2007-raree.pdf.

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.
Idaho—Hall Mountain 51

Idaho—Hall Mountain

Location: Veins crop out in an area of about 2.6 km2 (1⁄2 mi2)—

1,830 m (6,000 ft) by 305 m (1,000 ft) wide—on Hall 

Mountain in northernmost Idaho. Hall Mountain lies 1.6 

km (1 mi) south of the United States−Canada border and 

4.8 km (3 mi) east of the border station of Porthill, Idaho. 

Latitude: 48.98584 N., Longitude: 116.41887 W.; datum: 

WGS84

Deposit type and basic geology: The veins of Hall Mountain 

cut Precambrian quartzite and quartz diorite. They range 

in exposed length from 1.8 m (6 ft) to 213 m (700 ft) 

and in width from 0.18 m (0.6 ft) to 4 m (13 ft). Thorite 

is the primary thorium- and rare earth elements–bearing 

mineral; quartz and calcite are the most abundant gangue 

minerals, associated with chlorite magnetite, limonite, 

pyrite, and biotite, along with numerous minor and trace 

minerals. A total of 30 minerals were identified by Staatz 

(1972).

Status: No active exploration has been reported in this district. 

Production: No mineral resources have been produced from 

this district.

Estimated resources: The U.S. Geological Survey (Staatz 

and others, 1979) determined that the possible reserves 

in this district are limited to thorium resources in only a 

few large veins. They estimate that the thorium reserves 

are 104,300 metric tons (115,000 tons) of vein material 

averaging 4.0 percent thorium oxide. They suggest that 

the rare earth elements are probably not economical in 

this district because of their low overall concentrations 

(average about 0.05 percent rare earth elements oxides).

Detailed Discussion

Thorium and REE-rich veins crop out in an area of about 

2.6 km2 (1⁄2 mi2

)—1,830 m (6,000 ft) by 305 m wide (1,000 

ft)—on Hall Mountain in northernmost Idaho. Hall Mountain 

lies 1.6 km (1 mi) south of the United States-Canada border 

and 4.8 km (3 mi) east of the border station of Porthill, Idaho. 

Veins in this area can contain considerable thorium content, 

locally with as much as 21 percent ThO2 (Staatz, 1972); 

however, their rare earth elements content is usually much less 

than their thorium content. As reported by Staatz and others 

(1974, p. 677), “Total rare-earth content of these veins ranges 

from 0.00111 to 0.197 percent in 12 samples from 10 veins; 

the thoria (ThO2) content, from 0.011 to 5.84 percent.” Staatz 

(1972, p. 240) reported, “The thorium content of 23 samples 

from 11 veins ranged from 0.0095 to 21 percent. Twelve 

samples had a thorium content greater than 1 percent.”

The veins of Hall Mountain cut Precambrian quartzite 

and quartz diorite. They range in exposed length from 1.8 

to 213 m (6 to 700 ft) and vary in width from 0.18 to 4 m 

(0.6 to 13 ft). Thorite is the primary thorium- and rare earth 

elements−bearing mineral; quartz and calcite are the most 

abundant gangue minerals, associated with chlorite magnetite, 

limonite, pyrite, and biotite, along with numerous minor and 

trace minerals. A total of 30 minerals were identified by Staatz 

(1972).

According to the analyses of Staatz and others (1979), 

the possible reserves in this district are limited to thorium 

resources in only a few large veins. They estimate that the thorium reserves are 104,300 metric tons (115,000 tons) of vein 

material averaging 4.0 percent ThO2

. They suggest that the 

rare earths are probably not economical in this district because 

of their low overall concentrations (average about 0.05 percent 

rare earth elements oxides). The distribution of rare earth elements in the Hall Mountain veins, on the basis of the average 

concentrations of 10 vein samples reported by Staatz and others (1974), is summarized in table 18.

Table 18. Mean concentrations of rare earth elements measured 

in 10 vein samples, Hall Mountain, Idaho.

[Rare earth elements listed in order of increasing atomic number; yttrium (Y) 

is included with these elements because it shares chemical and physical similarities with the lanthanides. wt percent, weight percent. Data averaged from 

analyses reported by Staatz and others (1974, table 1)]

Oxide Average

wt percent

La2

O3 0.0013

Ce2

O3 0.0053

Pr2

O3 <0.0006

Nd2

O3 0.0016

Sm2

O3 0.0011

Eu2

O3 <0.0018

Gd2

O3 0.0041

Tb2

O3 <0.0018

Dy2

O3 0.0034

Ho2

O3 <0.0012

Er2

O3 0.0024

Tm2

O3 <0.0017

Yb2

O3 0.0025

Lu2

O3 <0. 0014

Y2

O3 0.0315

Total 0.0512
52 The Principal Rare Earth Elements Deposits of the United States

References Cited

Staatz, M.H., 1972, Thorium-rich veins of Hall Mountain in 

northernmost Idaho: Economic Geology, v. 67, no. 2, 

p. 240–248.

Staatz, M.H., Shaw, V.E., and Wahlberg, J.S., 1974, Distribution and occurrence of rare earths in the thorium veins 

on Hall Mountain, Idaho: Journal of Research of the U.S. 

Geological Survey, v. 2, no. 6, p. 677–683.

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. 
Idaho—Lemhi Pass District, Idaho-Montana 53

Idaho—Lemhi Pass District, IdahoMontana

Location: The Lemhi Pass district contains numerous vein 

deposits enriched in thorium and rare earth elements 

(REE) within a 140 km2 (54 square mi) core of a larger 

400 km2 (154 mi2) area in the central Beaverhead Mountains; the district straddles the Continental Divide on the 

Montana-Idaho border. Latitude: 44.93728 N., Longitude: 

113.46451 W.; datum: WGS84

Deposit type and basic geology: Within the Lemhi Pass district, Staatz (1972; Staatz and others, 1979) mapped 219 

veins enriched in thorium and rare earth elements (REE). 

Most of these veins are quartz-hematite-thorite veins 

that fill fractures, shears, and brecciated zones in Mesoproterozoic quartzite and siltite host rocks. Thorium and 

REE also appear in monazite-thorite-apatite shears and in 

replacements with specularite, biotite, and alkali feldspar. 

The thorium-REE veins of the district range from 1 m (3.3 

ft) to at least 1,325 m (4,347 ft) in length and from a few 

centimeters (1 in.) to as much as 12 m (39 ft) in width. 

The Last Chance vein—1,325 m (4,348 ft) long and 3–8 

m (10–26 ft) wide for most of its length—is the longest 

and widest vein in the district.

Status: During the last decade (prior to 2010), Thorium 

Energy Inc. has evaluated the thorium and REE resources 

in the vein systems of the district. 

Production: No thorium or REE have been produced from 

this district. Past exploration and development in these 

vein deposits focused on their thorium content; earlier 

development trenched several veins and produced modest 

underground workings in the Last Chance vein.

Estimated resources: This district is thought to represent the 

largest concentration of thorium resources in the United 

States (Van Gosen and others, 2009). On average, the 

thorium veins of the district have roughly equal concentrations of thorium and total rare earth elements. Thus, 

the REE resources of the vein deposits of the Lemhi Pass 

district are approximately equal to its thorium resource. 

Earlier studies by the USGS estimated that the Lemhi 

Pass district contains total reserves of 64,000 metric 

tons (70,500 tons) of thorium oxide (ThO2

) and probable 

potential resources of an additional 121,000 metric tons 

(133,000 tons) (Staatz and others, 1979). The 10 largest veins, with an average grade of 0.43 percent ThO2

, 

represent 95 percent of the district’s identified thorium 

resources. Using a compilation of surface, underground, 

and drilling assays, the Idaho Energy Resource Company 

reported a “quantitative proven” reserve of 176 metric 

tons (194 tons) of ThO2 within the Last Chance vein and 

a possible resource of 2,000 metric tons (2,200 tons) of 

additional ThO2 (Idaho Energy Resource Company, written commun., 2008).

Detailed Discussion

The Lemhi Pass district contains numerous vein deposits enriched in thorium and rare earth elements (REE) within 

a 140 km2 (54 mi2) core of a larger 400 km2 (154 mi2) area in 

the central Beaverhead Mountains; the district straddles the 

Continental Divide on the Montana-Idaho border (fig. 13). 

This district is thought to represent the largest concentration 

of thorium resources in the United States (Van Gosen and 

others, 2009). Earlier studies by the USGS estimated that the 

Lemhi Pass district contains total reserves of 64,000 metric 

tons (70,550 tons) of thorium oxide (ThO2) and probable 

potential resources of an additional 121,000 metric tons

(133.400 tons) (Staatz and others, 1979). The 10 largest 

veins, with an average grade of 0.43 percent ThO2, represent 95 percent of the district’s identified thorium resources. 

Using a compilation of surface, underground, and drilling 

assays, the Idaho Energy Resource Company reported a 

“quantitative proven” reserve of 176 metric tons (194 tons) 

of ThO2

 within the Last Chance vein and a possible resource 

of 2,000 metric tons (2,200) of additional ThO2 (Idaho 

Energy Resource Company, written commun., 2008). On 

average, the thorium veins of the district have roughly equal 

concentrations of thorium and total rare earth elements. 

Thus, the REE resources of the vein deposits of the Lemhi 

Pass district are approximately equal to its thorium resource. 

The Last Chance vein and the Wonder vein (fig. 14) are 

the only deposits in the district that have been sampled by 

underground or drill-hole access. Much exploration potential 

exists in the district. 

Within the Lemhi Pass district, Staatz (1972) and Staatz 

and others (1979) mapped 219 veins enriched in thorium and 

REE. Most of these veins are quartz-hematite-thorite veins, 

which fill fractures, shears, and brecciated zones in Mesoproterozoic quartzite and siltite host rocks. Thorium and 

REE also are present in monazite-thorite-apatite shears and 

replacements with specularite, biotite, and alkali feldspar. 

The thorium-REE veins of the district range from 1 m (3.3 ft) 

to at least 1,325 m (4,347 ft) in length and from a few centimeters (1 in.) to as much as 12 m (39 ft) in width. The Last 

Chance vein—1,325 m (4,348 ft) long and 3–8 m (10–26 ft) 

wide for most of its length—is the longest and widest vein 

in the district; this vein also represents the largest individual 

thorium and REE resource in the district. Fifteen thorium 

veins in the district exceed 300 m (984 ft) in length. Some of 

the veins contain carbonate minerals, such as calcite, siderite, 

and ankerite, and local fluorite. Rare earth elements- and 

thorium-bearing allanite and monazite are locally abundant. 

Other reported ore minerals include brockite, xenotime, and 

thorite. The primary gangue minerals are quartz, hematite, 

limonite, apatite, potassium feldspar, biotite, albite, and 

barite. Most of the veins are extensively weathered and have 

abundant iron-oxide staining. The district also hosts small 

quartz-copper-gold (and rare molybdenum) veins, and some 

of the thorium veins contain very small amounts of base metals, such as copper, iron, manganese, lead, and zinc. 
54 The Principal Rare Earth Elements Deposits of the United States

Lemhi Pass

Figure 13. View to west of Lemhi Pass, Idaho-Montana. The ridge, a part of Beaverhead 

Mountains, forms a segment of the Continental Divide and the Idaho-Montana border; 

Montana is in foreground and Idaho is in the distance. More than 200 rare earth elements- and 

thorium-rich veins in this area form the Lemhi Pass district.

Figure 14. Outcrop of Wonder vein (between red lines), Lemhi Pass district, Idaho-Montana, 

exposed in a mined bench. Vein is heavily oxidized and consists mainly of silica, likely some 

carbonate, and iron oxide minerals with thorite and altered thorite. Host rock is Precambrian 

quartzite and siltite.
Idaho—Lemhi Pass District, Idaho-Montana 55

The thorite veins of the Lemhi Pass district are approximately equally enriched in thorium and REE; the ratio of 

thorium to REE concentrations in the veins averages around 

1:1. Staatz (1972) reported the REE analyses of 31 vein 

samples, which showed total REE-oxide contents ranging 

from 0.073 to 2.20 percent, with an average value of 0.428 

percent (very similar to the average thorium oxide content 

of 0.43 percent found in the 10 largest veins in the district). 

Table 19 lists the average distribution of the rare earth elements reported by Staatz (1972, table 5) from the analyses 

of nine samples of the Last Chance vein. The district’s 

thorium veins are most commonly enriched in the middle 

REE (especially neodymium), with some veins apparently 

enriched more in the heavy REE (Staatz, 1972, p. 76–77). 

Using modern techniques in recent analytical work, the Idaho 

Geological Survey and industry (Idaho Energy Resource 

Company in 1991; Thorium Energy in 2008) has confirmed 

the overall thorium and REE concentrations and the unusual 

Table 19. Mean concentrations of rare earth elements measured 

in samples of Last Chance vein, Idaho-Montana.

[Rare earth elements listed in order of increasing atomic number; yttrium (Y) 

is included with these elements because it shares chemical and physical similarities with the lanthanides. wt percent, weight percent. Last Chance is the 

largest vein in the Lemhi Pass district, Idaho-Montana. Data averaged from 

nine samples of the vein reported by Staatz (1972, table 5)]

Oxide Average

wt percent

La2

O3 0.033

Ce2

O3 0.082

Pr2

O3 0.014

Nd2

O3 0.127

Sm2

O3 0.087

Eu2

O3 0.027

Gd2

O3 0.056

Tb2

O3 0.003

Dy2

O3 0.008

Ho2

O3 <0.003

Er2

O3 0.002

Tm2

O3 <0.003

Yb2

O3 <0.003

Lu2

O3 <0.003

Y2

O3 0.015

Total 0.454

enrichments in middle REE-group minerals. Hedrick (2010) 

reported, “Based on average percentages of individual REE 

by recent sampling and previous analyses by Idaho Energy 

Reserves Co. (a subsidiary of Idaho Power Co.), the Lemhi 

Pass District had resources, in order of increasing atomic 

number, 77,345 t of yttrium; 25,780 t of lanthanum; 69,980 

t of cerium; 11,050 t of praseodymium; 66,296 t of neodymium; 40,515 t of samarium; 14,735 t of europium; 40,515 t of 

gadolinium; 1,840 of terbium; 14,730 t of dysprosium; 1,840 

t each of holmium and ytterbium; and about 929 t or less 

each of erbium, thulium, and lutetium.”

References Cited

Hedrick, J.B., 2010, Rare earths (advance release), in 2007 

Minerals yearbook: U.S. Geological Survey, 19 p. accessed 

September 8, 2010, at http://minerals.usgs.gov/minerals/

pubs/commodity/rare_earths/myb1-2007-raree.pdf.

Staatz, M.H., 1972, Geology and description of the thoriumbearing veins, Lemhi Pass quadrangle, Idaho and Montana: 

U.S. Geological Survey Bulletin 1351, 94 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.

Van Gosen, B.S., Gillerman, V.S., and Armbrustmacher, T.J., 

2009, Thorium deposits of the United States—Energy 

resources for the future?: U.S. Geological Survey Circular 1336, 21 p. (Also available at http://pubs.usgs.gov/

circ/1336/.)
56 The Principal Rare Earth Elements Deposits of the United States

Illinois—Hicks Dome

Location: Hicks Dome is located in Hardin County, southernmost Illinois. Latitude: 37.53131 N., Longitude: 88.36873 

W.; datum: WGS84

Deposit type and basic geology: The dome-shaped structure, 

approximately 14.5 km (9 mi) in diameter, was formed 

by the displacement of sedimentary rocks at least 1,200 

m (3,940 ft) upward above an alkaline intrusion at depth. 

More than 600 m (1,970 ft) of sedimentary rocks, mostly 

limestone, were pushed up by the explosive intrusion 

of magmatic fluids. A hole drilled near the apex of the 

dome (Brown and others, 1954) intersected a mineralized 

breccia at a depth of 490 m (1,607 ft), which continues to 

the bottom of the hole at 897 m (2,944 ft). Mineralization 

in the breccia contains thorium and rare earth elements, 

tentatively identified as residing in monazite, and is 

found in association with florencite, a cerium-aluminum 

phosphate; gangue minerals are fluorspar, calcite, quartz, 

minor pyrite, and traces of sphalerite and galena.

Status: Currently (2010), no exploration appears to be active 

at this feature.

Production: No mineral resources have been produced from 

this intrusive complex.

Estimated resources: Resources have not been estimated. 

Eight samples of drill core, each 7.6–9.1 m (25–30 ft) 

long, contained thorium concentrations of 0.007−0.18 

percent thorium oxide (Brown and others, 1954). Rare 

earth elements content in the eight drill-core samples 

was 0.1–0.99 weight percent yttrium; 0.01–0.099 weight 

percent lanthanum, cerium, neodymium, and dysprosium; 

and 0.001–0.0099 weight percent ytterbium (Trace, 1960). 

These samples represent only 64 m (210 ft) of a breccia 

zone enriched in thorium and rare earth elements; this 

zone could extend throughout a large area across the roof 

of Hicks Dome.

Detailed Discussion

Hicks Dome, in Hardin County of southernmost Illinois, overlies a potentially wide area of rare earth elements 

(REE) and thorium (Th) mineralization at depth. The domeshaped structure, approximately 14.5 km (9 mi) in diameter, 

was formed by the displacement of sedimentary rocks at 

least 1,200 m (3,940 ft) upward above an alkaline intrusion 

at depth. More than 600 m (1,970 ft) of sedimentary rocks, 

mostly limestone, were pushed up by the explosive intrusion 

of magmatic fluids (Heyl and others, 1965). A hole drilled near 

the apex of the dome (Brown and others, 1954) intersected a 

mineralized breccia at a depth of 490 m (1,607 ft), which continues to the bottom of the hole at 897 m (2,944 ft). Mineralization in the breccia includes fluorspar, calcite, quartz, minor 

pyrite, and traces of sphalerite and galena. Eight samples of 

this drill core, each 7.6–9.1 m (25–30 ft) long, contained 0.007 

to 0.18 percent ThO2

 (Brown and others, 1954). REE content 

in the eight drill-core samples was 0.1–0.99 weight percent 

Y; 0.01–0.099 weight percent for La, Ce, Nd, and dysprosium 

(Dy); and 0.001–0.0099 weight percent ytterbium (Yb) (Trace, 

1960). These samples represent only 64 m (210 ft) of a breccia 

zone enriched in Th-REE; this zone could extend throughout a 

large area across the roof of Hicks Dome.

Shallow diamond drilling and trenching sampled an 

area of radioactive breccia atop Hicks Dome in which the 

radioactive mineral was tentatively identified as monazite, 

and found, in association with florencite, a cerium-aluminum 

phosphate (Trace, 1960). A surface sample from a trench 

contained 0.1–0.5 weight percent Th plus REE, including 

0.5–1 weight percent Ce and La, 0.1–0.5 weight percent 

Nd, 0.05–0.1 weight percent praseodymium (Pr), 0.01–0.05 

weight percent terbium (Tb), and 0.005–0.01 weight percent 

Yb (Trace, 1960).

Using airborne gamma-ray data, Pitkin (1974) delineated the large extent of the radioactivity anomaly at Hicks 

Dome, which arises because of its thorium content. However, 

the apparent depth of this REE-thorium deposit may limit 

its resource potential. Much more surface and subsurface 

exploration is necessary to evaluate the extent and grade of 

this deposit.

References Cited

Brown, J.S., Emery, J.A., and Meyer, P.A., Jr., 1954, Explosion pipe in test well on Hicks Dome, Hardin County, 

Illinois: Economic Geology, v. 49, no. 8, p. 891–902.

Heyl, A.V., Brock, M.R., Jolly, J.L., and Wells, C.E., 1965, 

Regional structure of the southeast Missouri and IllinoisKentucky mineral districts: U.S. Geological Survey Bulletin 

1202–B, 20 p., 3 plates.

Pitkin, J.A., 1974, Preliminary thorium daughter contour map 

and profiles of the Hicks Dome area, Hardin County, Illinois: U.S. Geological Survey Open-File Report 74–157, 9 p.

Trace, R.D., 1960, Significance of unusual mineral occurrence at Hicks Dome, Hardin County, Illinois, in Short 

papers in the geological sciences, Geological Survey 

research, 1960: U.S. Geological Survey Professional Paper 

400–B, p. B63–B64.
Missouri—Pea Ridge Iron Deposit and Mine 57

Missouri—Pea Ridge Iron Deposit and 

Mine

Location: The Pea Ridge iron orebody and mine site is 

located in Washington County, Missouri, about 97 km (60 

mi) southwest of St. Louis. Latitude: 38.12621 N., Longitude: 91.04766 W.; datum: WGS84

Deposit type and basic geology: Rare earth elements 

(REE)−bearing breccia pipes cut through the Pea Ridge 

massive magnetite-iron orebody. The Pea Ridge deposit 

is hosted by Precambrian volcanic rocks of the St. Francois terrane of southeastern Missouri. The magnetite-rich 

orebody is interpreted as a high-temperature, magmatichydrothermal deposit (Sidder and others, 1993) in 

ash-flow tuffs and lavas, which may have formed in the 

root of a volcanic caldera (Nuelle and others, 1991). Four 

mapped REE-bearing breccia pipes steeply crosscut the 

magnetite-hematite orebody and its altered rhyolite host 

rock. Exposed portions of the breccia pipes are as much 

as 60 m (197 ft) in horizontal length and as much as 15 m 

(49 ft) in width; the pipes extend below the mined levels 

to an undetermined depth (Seeger and others, 2001). 

Rare earth elements–bearing minerals in the breccia 

pipes include monazite, xenotime, and minor bastnasite 

and britholite. The REE concentrations reported in the 

breccia pipes are consistently high but variable. Nuelle 

and others (1992, p. A1) state, “Total REE oxide content 

of samples of the groundmass material, which are not 

diluted with lithic fragments, average about 20 weight 

percent.” Seeger and others (2001, p. 2) state, “Total 

REE oxide concentrations of grab samples range from 

about 2.5 to 19 weight percent.” Bulk sampling by the 

U.S. Bureau of Mines found REE oxides concentrations 

ranging from 7 to 25 weight percent and an average of 

12 weight percent (Vierrether and Cornell, 1993).

Status: Currently (2010), there is no active development in 

this deposit. In 2005, Upland Wings formed Wings Enterprises, with the intent to reclaim iron ore at the site and 

produce iron from its large surface reserves (http://www.

wingsironore.com/).

Production: In 1957, the deposit was first developed by the 

Bethlehem Steel and St. Joseph Lead Company, under the 

name Meramec Mining Company. In 1964, iron production began from this deposit. The mine operated from 

1964 to 2001 with three interruptions, producing more 

than 30 million tons (27 million metric tons) of pellets, 

fines, heavy media, and other iron products. In 1990, the 

mine lost its last iron-ore-pellet customer and began to 

produce specialty products. The Pea Ridge mine continued to operate while iron ore prices fell during the 1990s, 

but in 2001 the mine went into bankruptcy. In 2001, 

Upland Wings, Inc., purchased the Pea Ridge Iron Ore 

mine properties and all of its mineral rights.

Estimated resources: A U.S. Bureau of Mines report by 

Whitten and Yancey (1990) estimated that the breccia 

pipes contain about 600,000 metric tons (660,000 tons) of 

REE reserves with an average grade of 12 percent REE 

oxides. The report does not indicate the data used to calculate this estimate. However, a similar value of 600,000 

short tons is mentioned as a note on another internal company memo (provided by Jim Kennedy, electronic communication, October 2008); that memo is dated 10-25-89 

and signed by Larry J. Tucker (retired Pea Ridge mine 

superintendent); supporting calculations for this value 

are missing. A copy of another internal company memo 

(provided by Jim Kennedy, electronic communication, 

October 2008 and dated 11-22-88 and signed by Larry 

J. Tucker) indicates that there is a combined, probable 

reserve in two of the breccia pipes of approximately 

250,000 metric tons (276,000 tons) of mineralized rock, 

grading about 13 percent REE (note: weight percent, not 

oxide equivalent). The surface tailings contain additional 

lanthanide resources primarily in fine-grained, REEbearing minerals, chiefly monazite and xenotime, that 

form inclusions within apatite. The apatite also contains 

minor amounts of REE in its structure; apatite is found 

in variable concentrations throughout the iron orebody 

(Vierrether and Cornell, 1993).

Detailed Discussion

Rare earth elements (REE)−bearing breccia pipes cut 

through the Pea Ridge massive magnetite iron-orebody in 

Washington County, Missouri, about 97 km (60 mi) southwest 

of St. Louis. The iron deposit as a whole contains concentrations of REE that may be economically recoverable as a 

primary product or as a byproduct of iron ore production. 

The Pea Ridge massive magnetite deposit is hosted by 

Precambrian volcanic rocks of the St. Francois terrane of southeastern Missouri; this volcanic-plutonic province is composed 

of Mesoproterozoic rhyolitic ash-flow tuffs, lava flows, and 

granitic plutons (Kisvarsanyi, 1980). The St. Francois terrane 

contains eight known Mesoproterozoic magnetite-hematite 

deposits and forms an iron metallogenic province (Kisvarsanyi 

and Proctor, 1967) that hosts nearly 1 billion metric tons of 

identified ore (Arundale and Martin, 1970). The Pea Ridge 

massive magnetite orebody has been interpreted as a hightemperature, magmatic-hydrothermal deposit (Sidder and others, 1993) in ash-flow tuffs and lavas, which may have formed 

in the root of a volcanic caldera (Nuelle and others, 1991).

The Pea Ridge deposit is covered by Cambrian and 

Ordovician sedimentary rocks that unconformably overlie the 

deposit and the underlying Precambrian rocks. The orebody 

lies discordant to the host volcanic rocks, striking N. 60° E. 

with a nearly vertical dip, whereas the host volcanic rocks 

strike N. 80° W. and dip 75° NE. (Emery, 1968). The primary 

host for the iron orebody is altered rhyolite tuff (Nuelle and 

others, 1992). This massive iron deposit is estimated to contain more than 100 million short tons of ore (Arndt, 1981). 
58 The Principal Rare Earth Elements Deposits of the United States

The deposit area contains nine mappable rock units: 

amphibole-quartz rock; heterolithic breccia; pseudobreccia; 

magnetite; hematite; silicified rock; REE mineral-bearing 

breccia pipes; mafic dikes; and aplite dikes (Nuelle and others, 1992; Seeger and others, 2001). Four mapped lanthanide-bearing breccia pipes (X11, V12, X13, V14) steeply 

crosscut the magnetite-hematite orebody and its altered 

rhyolite host rock (fig. 15); the pipes are situated along the 

footwall and eastern edge of the iron orebody (Seeger and 

others, 2001). Exposed portions of the breccia pipes are as 

much as 60 m (197 ft) in horizontal length and as much as 

15 m (49 ft) in width; the pipes extend below the mined 

levels to an undetermined depth (Seeger and others, 2001). 

One of the pipes is exposed for 120 m (394 ft) vertically. As 

described by Seeger and others (2001, p. 2), the four breccia 

pipes of the Pea Ridge deposit consist of the following:

“Fragments of rhyolite, iron oxide, and silicified rock 

in a groundmass of rock flour, feldspar, chlorite, barite, apatite, monazite, xenotime, quartz, and calcite. 

Volcanic rock fragments range from less than 1 mm 

to about 0.5 m in diameter, are subrounded to angular 

with moderate to high sphericity, and have undergone 

potassium metasomatism. Specularite [iron oxide] 

fragments are angular, are as long as several meters, 

and have low to moderate sphericity.”

The REE-bearing minerals in the breccia pipes include 

monazite, xenotime, and minor bastnasite and britholite. 

Nuelle and others (1992) describe the monazite and xenotime as forming radial crystal aggregates and granular 

crystals 0.5–1.9 mm (0.02—0.75 in.) across; these minerals 

also replace microfragments in the wall rock and within the 

groundmass fill fractures in barite and potassium feldspar 

crystals. The mineralogy of Pea Ridge is summarized by 

Nuelle (1998), and its mineral paragenesis and alteration 

zones are described by Sidder and others (1993). Gold, tin, 

and silver are unevenly distributed in the breccia pipes and in 

both the hematite and silicified zones (Husman, 1989). Nuelle 

and others (1992) report localized gold concentrations as 

much as 371 parts per million.

The REE oxide concentrations are relatively high within 

the breccia pipes of the Pea Ridge deposit. The REE abundances reported in the breccia pipes are consistently high but 

variable. Nuelle and others (1992, p. A1) state, “Total REE 

oxide content of samples of the groundmass material, which 

are not diluted with lithic fragments, average about 20 weight 

percent.” Seeger and others (2001, p. 2) state, “Total REE 

oxide concentrations of grab samples range from about 2.5 

to 19 weight percent.” Bulk sampling by the U.S. Bureau 

of Mines found REE oxides concentrations ranging from 7 

to 25 weight percent and an average of 12 weight percent 

(Vierrether and Cornell, 1993). The size of the REE resource 

in the four breccia pipes has not been determined and these 

pipes are open downward. A copy of an internal company 

memo (provided by Jim Kennedy, electronic communication, 

October 2008, dated 11-22-88 and signed by Larry J. Tucker, 

retired Pea Ridge mine superintendent) indicates that there is a 

combined, probable reserve for pipes X11 and X13 of approximately 250,000 metric tons of mineralized rock, grading about 

13 percent REE (note: weight percent, not oxide equivalent). 

The reserves were calculated for the volume between levels 

2275 and 2675 by using a density of 2,000 lb per 9 cubic foot 

(ft3

) (approximately 3.56 gram per cubic centimeter (g/cm3)). 

(Working levels in the mine, now flooded, are named for their 

depth below the collar of the shaft; the uppermost level was at 

1,375 ft and the deepest level was at 2,675 ft.)

A U.S. Bureau of Mines report by Whitten and Yancey 

(1990) estimated that the breccia pipes contain about 600,000 

metric tons of REE reserves with an average grade of 12 

percent REE oxides. The report does not indicate the data 

used to calculate the 600,000 metric ton resource estimate. 

However, a similar value of 600,000 short tons is mentioned 

as a note on another internal company memo (provided by 

Jim Kennedy, electronic communication, October 2008) that 

is dated 10-25-89 and signed by Larry J. Tucker; supporting 

calculations for this value are missing. The surface tailings 

contain additional lanthanide resources, primarily in finegrained, REE-bearing minerals, chiefly monazite and xenotime, that form inclusions within apatite. The apatite also 

contains minor amounts of REE in its structure; apatite is 

found in variable concentrations throughout the iron orebody 

(Vierrether and Cornell, 1993).

The rare earth elements in the breccia pipes of the Pea 

Ridge are dominated by the light REE lanthanum (La) and 

cerium (Ce), but the pipes are also relatively enriched in 

heavy REE, including dysprosium (Dy), holmium (Ho), 

erbium (Er), ytterbium (Yb), lutetium (Lu), and yttrium (Y) 

(table 20). The REE (lanthanide) resources of Pea Ridge are 

proportionally more concentrated in these heavy REE than is 

true of most other U.S. deposits (table 21). The REE distribution in the Pea Ridge deposit was generally confirmed by 

a recent USGS study, which collected limited samples of 

tailings and drill core at the site (Grauch and others, 2010). 

Although the total REE oxide resource at Pea Ridge (72,000 

metric tons) is very small in comparison with the Mountain 

Pass deposit (2.58 million metric tons), the Pea Ridge deposit 

may be viewed as a potential source of heavy REE as a 

byproduct of iron ore production.

The Pea Ridge magnetite deposit was identified in 1950 

from a prominent magnetic anomaly. In 1957, the deposit was 

first developed by the Bethlehem Steel and St. Joseph Lead 

Company, under the name Meramec Mining Company. In 

1964, production began from this deposit. The mine operated 

from 1964 to 2001, with three interruptions, and produced 

more than 30 million tons (27 million metric tons) of pellets, 

fines, heavy media, and other iron products. In 1990, the mine 

lost its last iron-ore-pellet customer and began to produce specialty products (information from the Wing Enterprises Web 

site, http://www.wingsironore.com/). In contrast, Nuelle (1998) 

reported a much higher historic production and stated, “to date 

[March 1998], Pea Ridge has produced 50.7 million metric 

tons of iron ore.”
Missouri—Pea Ridge Iron Deposit and Mine 59 mabn mabo mabo mpbn mpbn vr

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LIST OF MAJOR MAP UNITS

MIDDLE PROTEROZOIC UNITSRare earth mineral-bearing breccia pipesSilicified rockHematite zoneMagnetite zoneAmphibole-quartz rockVolcanic rocks

bp

sr

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where projected or inferred. 

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abandoned areas.

70

200 200 0 400 feet

MISSOURI

X-11 pipe

V-12 pipe X-13 pipe V-14 pipe

Figure 15. Generalized geologic map of the 2275 level of the Pea Ridge iron mine, Washington County, Missouri. Map from Grauch and others (2010), who adapted it from Seeger and others (2001).
60 The Principal Rare Earth Elements Deposits of the United States

The Pea Ridge mine continued to operate while iron ore 

prices fell during the 1990s, but in 2001 the mine went into 

bankruptcy. Later that year, Upland Wings, Inc. purchased 

the Pea Ridge Iron Ore mine properties and all of its mineral 

rights. In 2005, Upland Wings formed Wings Enterprises, 

with the intent to reclaim iron ore at the site and produce iron 

from its large surface reserves. Wings Enterprises suggests 

that its reclamation production facility can produce more than 

30 short tons per hour of 70 percent Fe (95 percent magnetite) 

ore material from its estimated 300,000 short tons of surface 

reserve.

Table 20. Rare earth elements and thorium concentrations in four breccia pipes, Pea Ridge deposit, 

Missouri.

[Rare earth elements listed in order of increasing atomic number; yttrium (Y) is included with these elements because it 

shares chemical and physical similarities with the lanthanides. --, not available. Data from internal company memo by 

Larry J. Tucker, dated 10-25-89 (Jim Kennedy, electronic communication, October, 2008)]

Element Breccia pipe

X-11

(percent)

V-12

(percent)

X-13

(percent)

V-14

(percent)

La 4.45 2.70 2.95 2.05

Ce 8.00 4.50 4.95 4.05

Pr 0.68 -- 0.41 0.34

Nd 2.15 -- 1.50 1.10

Sm 0.42 -- 0.33 0.24

Eu 0.03 -- 0.03 0.02

Gd 0.15 -- 0.18 0.08

Tb -- -- -- --

Dy 0.19 -- 0.18 0.09

Ho 0.03 -- 0.03 0.01

Er 0.09 -- 0.09 0.04

Tm -- -- -- --

Yb 0.16 -- 0.12 0.06

Lu 0.02 -- 0.01 --

Y 0.70 0.69 0.67 0.36

Th 0.63 -- 0.23 0.41

The Pea Ridge mine site, currently inactive (2010), contains an iron mine, mill, iron-pellet-making facility, and large 

piles of milled iron-ore tailings resulting from its earlier operation. The property now has two large tailings lakes flanked by 

extensive waste and tailings piles; most have vegetation cover, 

and several contain smaller ponds and wetlands. There are also 

several small, dry tailings ponds and a variety of ore stockpiles. 

Tailings underlie approximately 180 acres in total. The entire 

property is currently owned by Jim Kennedy, the president of 

Wings Enterprises, Inc., in Saint Louis, Missouri (http://www.

wingsironore.com/).
Missouri—Pea Ridge Iron Deposit and Mine 61

Table 21. Rare earth elements oxide concentrations of two world-class Chinese rare earth elements deposits compared with 

concentrations in major United States rare earth elements deposits.

[Rare earth elements listed in order of increasing atomic number; yttrium (Y) is included with these elements because it shares chemical and physical similarities with the lanthanides. --, not available. Values listed below were calculated by combining data from sources providing either tonnage or rare earth elements 

distribution]

Rare earth 

oxide

Bayan Obo 

deposit1

(metric tons)

China Clay 

deposits2

(metric tons)

Mountain Pass 

deposit3

(metric tons)

Iron Hill 

carbonatite4

(metric tons)

Pea Ridge 

deposit5

(metric tons)

Lemhi Pass 

district6

(metric tons)

La O2 3

Ce O2 3

Pr O2 3

Nd O2 3

Sm2 3 O

Eu O2 3

Gd O2 3

Tb O2 3

Dy O2 3

Ho O2 3

Er2 3 O

Tm2 3 O

Yb O2 3

Lu O2 3

Y O2 3

15,267,052

23,720,328

1,734,339

6,083,552

616,088

99,822

247,460

23,884

56,584

12,594

14,270

3,376

2,364

490

117,798

193,001

311,762

40,529

135,197

38,165

3,430

29,699

4,282

22,994

4,918

14,401

2,059

10,755

1,627

187,181

872,120

1,279,918

106,337

288,040

21,939

2,710

5,420

413

878

103

155

52

52

--

3,355

264,469

522,907

68,838

257,716

36,340

8,352

25,464

2,806

6,051

826

1,973

216

1,195

125

23,228

18,275

32,298

2,862

9,474

1,963

158

808

--

903

137

430

--

662

88

3,942

4,672

11,584

1,984

17,903

12,264

3,776

7,872

448

1,128

--

256

--

--

--

2,113

Total 48,000,000 1,000,000 2,581,490 1,220,506 72,000 64,000

1

Bayan Obo deposit, Inner Mongolia, China: Berger and others (2009) indicate that Bayan Obo has 800 million metric tons of ore at 6 percent REE oxide 

content. Rare earth elements distribution is based on the average of three analyses of mineralized material from the East Ore Deposit; data from Yang and others 

(2009). 

2

China Clay deposits, southern China: Clark and Zheng (1991) indicate that the combined rare earth elements oxide content of all the China Clay deposits is at 

least 1 million metric tons. Rare earth elements distribution is based on a single ore concentrate (Grauch and others, 2010, table 4).

3

Mountain Pass deposit, California: Castor and Nason (2004) indicate that Mountain Pass contains estimated reserves of 29 million metric tons of ore at 8.9 

wt. percent rare earth elements oxides (by using a 5 percent cutoff). Rare earth elements distribution calculated from data in Castor (2008) from rare earth elements oxide contents in concentrate.

4

Iron Hill carbonatite, Colorado: Staatz and others (1979) estimated that the carbonatite stock of Iron Hill consists of 655.6 million metric tons of carbonatite. 

Rare earth elements oxide resources were calculated from median concentrations measured by Van Gosen (2008) in 13 samples of the Iron Hill stock.

5

Pea Ridge deposit, Missouri: Whitten and Yancey (1990) indicate that Pea Ridge contains 600,000 metric tons of ore with an average tenor of 12 percent 

rare earth elements oxides. Rare earth elements distribution is based on the average of composite assays of samples from four breccia pipes (Grauch and others, 

2010).

6

Lemhi Pass district, Idaho-Montana: Rare earth elements distribution is based on the average of analyses of nine samples of the Last Chance vein, reported 

by Staatz (1972). 

References Cited Berger, V.I., Singer, D.A., and Orris, G.J., 2009, Carbonatites 

of the world, explored deposits of Nb and REE—Database 

Arndt, R.H., 1981, The mineral industry of Missouri, in Min- and grade and tonnage models: U.S. Geological Survey 

erals Yearbook, 1978–79, Volume II, Area reports—Domes- Open-File Report 2009–1139, 17 p. plus database. (Also 

tic: U.S. Bureau of Mines, p. 299–314. available at http://pubs.usgs.gov/of/2009/1139/)

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deposit, California, in Castor, S.B., Papke, K.G., and Meeuwig, R.O., eds., Betting on industrial minerals—Forum 

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Thailand, Prince of Songkla University, p. 577–601.

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American Institute of Mining, Metallurgical, and Petroleum 

Engineers, Inc., p. 359–369.

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Missouri: U.S. Geological Survey Open-File Report 

2010–1080, 15 p. (Also available at http://pubs.usgs.gov/

of/2010/1080/.)

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Open-File Report OFR–89–78–MR, 18 p.

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content of magnetites and hematites, southeast Missouri iron 

metallogenic province, U.S.A.: Economic Geology, v. 62, 

no. 4, p. 449–471.

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County, Missouri: Rocks & Minerals, v. 73, issue 2, p. 90–97.

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1992, Geology and mineral paragenesis of the Pea Ridge 

iron ore mine, Washington County, Missouri—Origin of the 

rare-earth-element- and gold-bearing breccia pipes, Chapter 

A, in Day, W.C., and Lane, D.E., eds., Strategic and critical 

minerals in the midcontinent region, United States: U.S. 

Geological Survey Bulletin 1989–A, p. A1–A11.

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Sidder, G.B., 1991, Structural setting and control of the Pea 

Ridge magnetite deposit, Middle Proterozoic St. Francois 

terrane, Missouri [abs.]: Geological Society of America 

Abstracts with Programs, v. 23, no. 5, p. 292.

Seeger, C.M., Nuelle, L.M., Day, W.C., Sidder, G.B., 

Marikos, M.A., and Smith, D.C., 2001, Geologic maps and 

cross sections of mine levels at the Pea Ridge iron mine, 

Washington County, Missouri: U.S. Geological Survey 

Miscellaneous Field Studies Map MF–2353, version 1.0, 

6 p. pamphlet, 5 sheets.

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Kisvarsanyi, E.B., 1993, Mineralogic and fluid-inclusion 

studies of the Pea Ridge iron-rare-earth-element deposit, 

southeast Missouri, Chapter U, in Scott, R.W., Jr., Detra, 

P.S., and Berger, B.R., eds., Advances related to United 

States and international mineral resources—Developing 

frameworks and exploration technologies: U.S. Geological 

Survey Bulletin 2039, p. 205–216.

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U.S. Geological Survey Bulletin 1351, 94 p.

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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.

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County, Colorado: U.S. Geological Survey Open-File 

Report 2008–1119, 27 p. and 2 spreadsheet data files. (Also 

available at http://pubs.usgs.gov/of/2008/1119/)

Vierrether, C.W., and Cornell, W.L., 1993, Rare-earth occurrences in the Pea Ridge tailings: U.S. Bureau of Mines 

Report of Investigations 9453, 10 p.

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rare-earth mineralogy at the Pea Ridge deposit, Missouri: 

U.S. Bureau of Mines Report of Investigations 9331, 9 p.

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Yong-Fei, 2009, Geochemical constraints on the genesis 

of the Bayan Obo Fe-Nb-REE deposit in Inner Mongolia, China: Geochimica et Cosmochimica Acta, v. 73, p. 

1417–1435.
Nebraska—Elk Creek Carbonatite 63

Nebraska—Elk Creek Carbonatite

Location: Located near the small town of Elk Creek in 

southeastern Nebraska. Latitude: 40.26861 N., Longitude: 

96.18333 W.; datum: WGS84

Deposit type and basic geology: A buried, rare earth elements (REE)- and niobium (Nb)-rich carbonatite mass, 

referred to as the Elk Creek carbonatite, lies in the subsurface about 1.6 km (1 mi) southwest of the small town 

of Elk Creek in southeastern Nebraska. On the basis of 

exploration drilling and the extent of magnetic and gravity 

anomalies, the carbonatite mass at depth appears to have 

its center beneath section 33, township 4 north, range 11 

east. The entire oval-shaped, subsurface body, which is 

recognized by a geophysical anomaly caused by the carbonatite and associated intrusive rocks, is about 7 km (4.3 

mi) in diameter. Analyses of drill core showed the intrusion at depth comprised mostly massive to brecciated, 

apatite- and pyrochlore-bearing dolomitic carbonatite (89 

percent), along with fenitized basalt, lamprophyre, and 

syenite (totaling 11 percent). Major-element analyses suggest that the carbonate mass is a magnesian carbonatite 

(dolomitic), generally similar in gross chemical composition to the Iron Hill (Powderhorn) carbonatite stock in 

southwestern Colorado. The REE are hosted principally 

by the minerals bastnasite, parisite, and synchisite and 

by smaller amounts of monazite (Xu, 1996). Niobium 

was deposited in pyrochlore. The U.S. Geological Survey 

obtained a potassium-argon age on biotite in the carbonatite of 544±7 million years old (Xu, 1996).

Status: On May 4, 2010, Quantum Rare Earth Developments 

Corp. announced that it had acquired the Elk Creek carbonatite properties (http://www.quantumrareearth.com/).

Production: No mineral resources have been produced from 

this intrusion.

Estimated resources: It has been reported that the Elk 

Creek carbonatite may represent the largest niobium 

(Nb) resource in the United States. Quantum Rare Earth 

Developments Corporation reported several assay results 

from Molycorp’s earlier drilling program. Reportedly, 

drilling within the core zone found high-grade niobium 

contents, estimated at “39.4 million tons of 0.82 percent 

Nb2

O5 and is open to the north, west and at depth (Molycorp, Inc., internal memorandum, Feb 05/1986).” In the 

widely spaced drilling surrounding the core zone, “at 

least 18 of the surrounding holes intersected greater than 

6.1 m (20 ft) of greater than 1.0 percent REO (total rare 

earth oxides), while at least 17 of the surrounding holes 

intersected greater than 3.05 m (10 ft) of greater than 0.6 

percent Nb2O5.” Quantum reports assay intervals that 

range from 1.02 to 3.12 percent total rare earth elements 

oxide. They also note, “Most of the historic drill core, 

sample rejects, and pulps from Molycorp’s exploration are 

available for review and sampling.”

Detailed Discussion

A buried, rare earth elements (REE)– and niobium-rich 

carbonatite mass, referred to as the Elk Creek carbonatite, lies 

in the subsurface about 1.6 km (1 mi) southwest of the small 

town of Elk Creek in southeastern Nebraska. On the basis of 

exploration drilling results and the extent of magnetic and 

gravity anomalies, the carbonatite mass at depth appears to 

have its center beneath section 33, township 4 north, range 11 

east. The entire oval-shaped, subsurface body, which is recognized by a geophysical anomaly caused by the carbonatite and 

associated intrusive rocks, is about 7 km (4.3 mi) in diameter; 

it straddles the boundary between Johnson County and Pawnee 

County (Carlson and Treves, 2005). 

In 1970, a regional geophysical program detected a 

nearly circular, concurrent magnetic and gravity anomaly 

in this area. This area of Nebraska is blanketed by loess and 

glacial till that overlies Pennsylvanian marine carbonates and 

shale. Exploratory drilling in this area had previously encountered Precambrian granitic and metamorphic rocks at depths of 

600 ft (183 m) (Carlson and Treves, 2005). Modeling by Burfeind and others (1971) of the geophysical data collected over 

the anomaly suggested a cylindrical body with an indefinite 

length and a radius of 5,500 ft (1,676 m), which was beveled 

on the basement surface at a depth of about 600 ft (183 m). A 

test hole was drilled into the anomaly, which found 45 ft (13.7 

m) of unconsolidated cover of Quaternary loess and glacial till 

overlying 583 ft (178 m) of Upper and Middle Pennsylvanian 

carbonates and shale. At a depth of 630 ft (192 m), the drilling 

hit an iron-rich, silicate-bearing carbonate rock. This discovery prompted a drill-coring program, which recovered carbonate rocks from depths of 665 ft (203 m) to 1,000 ft (305 m) 

(Carlson and Treves, 2005). Core drilling into the geophysical 

anomaly during the 1970s and 1980s by the State of Nebraska, 

Cominco American, and Molycorp, Inc. resulted in at least 113 

core holes. Molycorp completed 106 of the test holes, recovering about 80,000 ft (24,384 m) of cores and rotary samples 

(Carlson and Treves, 2005). The deepest hole reached a depth 

of 3,406 ft (1,038 m) and bottomed in carbonatite.

As part of his doctoral dissertation project, Xu (1996) 

examined 5,927 ft (1,807 m) of core obtained from the carbonatite complex. He reported that the core studied comprised 

mostly massive to brecciated, apatite- and pyrochlore-bearing 

dolomitic carbonatite (89 percent), along with fenitized basalt, 

lamprophyre, and syenite (totaling 11 percent). Major-element 

analyses suggest that the carbonate mass is a magnesiocarbonatite, generally similar in major chemical composition to 

the Iron Hill (Powderhorn) carbonatite stock in southwestern 

Colorado. The REE are hosted principally by the minerals 

bastnasite, parisite, and synchisite and by smaller amounts of 

monazite (Xu, 1996). Niobium resides in pyrochlore. The U.S. 

Geological Survey obtained a potassium-argon age on biotite 

in the carbonatite of 544±7 million years old (Xu, 1996). 

On May 4, 2010, Quantum Rare Earth Developments 

Corp. announced that it had acquired the Elk Creek carbonatite 

properties (http://www.quantumrareearth.com/). In its press 
64 The Principal Rare Earth Elements Deposits of the United States

release, Quantum reported several assay results from Molycorp’s earlier drilling program, which included: detailed drilling of 25 holes within a core (central) zone of the 7-km (4.3-

mi) diameter geophysical anomaly and holes spaced about 

610 m (2,000 ft) apart surrounding the core zone. Reportedly, 

the drilling within the core zone found high-grade niobium 

contents, estimated at “39.4 million tons of 0.82 percent Nb2O5

and is open to the north, west and at depth (Molycorp, Inc. 

internal memorandum, Feb 05/1986).” In the widely spaced 

drilling surrounding the core zone, “least 18 of the surrounding holes intersected greater than 20 feet (6.1 metres) of 

greater than 1.0% REO [total rare earth oxides], while at least 

17 of the surrounding holes intersected greater than 10 feet 

(3.05 metres) of greater than 0.6% Nb2O5.” Quantum reports 

assays intervals that range from 1.02 to 3.12 percent total rare 

earth oxide. They also note, “Most of the historic drill core, 

sample rejects, and pulps from Molycorp’s exploration are 

available for review and sampling.”

References Cited

Burfeind, W.J., Carlson, M.P., and Smith, Russell, 1971, The 

Elk Creek geophysical anomaly, Johnson and Pawnee 

Counties, Nebraska [abs.]: Geological Society of America 

Abstracts with Programs, v. 3, no. 4, p. 254.

Carlson, M.P., and Treves, S.B., 2005, The Elk Creek Carbonatite, southeast Nebraska—An overview: Natural Resources 

Research, v. 14, no. 1, p. 39–45.

Xu, Anshun, 1996, Mineralogy, petrology, geochemistry and 

origin of the Elk Creek Carbonatite, Nebraska: Lincoln, 

Nebr., University of Nebraska, Ph.D. dissertation, 299 p.
New Mexico—Capitan Mountains 65

New Mexico—Capitan Mountains

Location: Thin veins containing thorium and rare earth elements crop out on the south flank of the Capitan Mountains in Lincoln County, south-central New Mexico. 

Latitude: 33.61059 N., Longitude: 105.45051 W.; datum: 

WGS84

Deposit type and basic geology: The radioactive deposits in 

this district are veins composed of angular fragments of 

alaskite cemented by quartz. Staatz (1974) identified 12 

breccia veins in the district, ranging from 10 to 150 ft (3 to 

46 m) in length and 1⁄4 in. to 8 ft (6 mm to 2.4 m) in thickness. The principal thorium-bearing mineral in these veins 

is thought to be allanite, accompanied by considerable 

quantities of quartz, purple fluorite, limonite, and possibly 

tourmaline (Griswold, 1959).

Status: Currently (2010), there appears to be no active 

exploration in this district. The deposits were apparently 

discovered in the early 1950s during the era of extensive 

prospecting for radioactivity anomalies. Radioactive veins 

in the Capitan Mountains were prospected in the middle 

to late 1950s by numerous bulldozer cuts but never further 

developed (Griswold, 1959). The primary focus of the 

late 1950s exploration of the veins of this district was its 

thorium potential. A thorium mill was constructed by New 

Mexico Thorium Company, but it never processed ore 

(McLemore, 1983). The ruins of the mill were subsequently removed by the U.S. Forest Service. 

Production: No mineral resources have been produced from 

these vein deposits.

Estimated resources: Thorium and REE resources in the 

district have not been estimated. Staatz (1974) analyzed 17 

samples of these veins and found thorium contents of less 

than 0.01 to as much as 1.12 percent. Reportedly, some 

assays of vein material showed as much as 1.7 percent 

thorium (Griswold, 1959). Thorium was assayed as the 

target commodity in the breccia veins of the southern 

Capitan Mountains, but REE concentrations are likely to 

coexist in these deposits. McLemore and others (1988, 

p. 4) noted that a “select sample assayed 2,500 ppm La, 

4,350 ppm Ce, and 330 ppm Y.”

Detailed Discussion

Thin veins containing thorium and rare earth elements 

(REE) crop out on the south flank of the Capitan Mountains in 

Lincoln County, south-central New Mexico. The deposits were 

apparently discovered in the early 1950s during the era of 

extensive prospecting for radioactivity anomalies. Radioactive 

veins in the Capitan Mountains were prospected in the middle 

to late 1950s by numerous bulldozer cuts but never further 

developed (Griswold, 1959). The radioactivity in the veins 

originates primarily in thorium and in much lesser amounts of 

uranium.

The radioactive deposits in this district are veins composed of angular fragments of alaskite cemented by quartz. 

Staatz (1974) identified 12 breccia veins in the district, ranging 

from 10 to 150 ft (3 to 46 m) in length and 1⁄4 in. to 8 ft (6 mm 

to 2.4 m) in thickness. He analyzed 17 samples of these veins 

and found thorium contents of less than 0.01 to 1.12 percent. 

Reportedly some assays of vein material showed as much as 

1.7 percent thorium (Griswold, 1959). The principal thoriumbearing mineral in these veins is thought to be allanite, which 

is accompanied by considerable quantities of quartz, purple 

fluorite, limonite, and possibly tourmaline (Griswold, 1959).

The primary focus of the late 1950s exploration of this 

district’s veins was their thorium potential. A thorium mill was 

constructed by New Mexico Thorium Company, but it never 

processed ore (McLemore, 1983). The ruins of the mill were 

subsequently removed by the U.S. Forest Service. 

Thorium was assayed as the target commodity in 

the breccia veins of the southern Capitan Mountains, but 

REE concentrations are likely to coexist in these deposits. 

McLemore and others (1988, p. 4) noted that a “select sample 

assayed 2,500 ppm La; 4,350 ppm Ce; and 330 ppm Y.” 

References Cited

Griswold, G.B., 1959, Mineral deposits of Lincoln County, 

New Mexico: New Mexico Bureau of Mines and Mineral 

Resources Bulletin 67, 117 p., 12 plates.

McLemore, V.T., 1983, Uranium and thorium occurrences 

in New Mexico—Distribution, geology, production, and 

resources, with selected bibliography: New Mexico Bureau 

of Mines and Mineral Resources Open-File Report 183, 180 

p. text, 6 appendixes. 

McLemore, V.T., North, R.M., and Leppert, Shawn, 1988, 

REE, niobium, and thorium districts and occurrences in 

New Mexico: New Mexico Bureau of Mines and Mineral 

Resources Open-File Report 324, 27 p., 2 plates.

Staatz, M.H., 1974, Thorium veins in the United States: Economic Geology, v. 69, no. 4, p. 494–507.
66 The Principal Rare Earth Elements Deposits of the United States

New Mexico—El Porvenir District

Location: The El Porvenir or Hermit Mountain district lies 

about 24 km (15 mi) northwest of Las Vegas and 4.8 km 

(3 mi) north of Porvenir, on the eastern edge of the Las 

Vegas Range, San Miguel County, north-central New 

Mexico. Latitude: 35.74237 N., Longitude: 105.42377 W.; 

datum: WGS84

Deposit type and basic geology: The bulk of Hermit Mountain is formed by a pink, coarse-grained Precambrian 

granite that is cut by pegmatite dikes and quartz veins 

(Robertson, 1976). Some of the pegmatites reportedly 

contain monazite and rare earth elements mineralization. 

Little published information is available on the chemistry 

of these pegmatites, but the data that are available suggest 

that anomalous rare earth elements concentrations are 

present.

Status: Currently (2010), there appears to be no active exploration in this district. 

Production: No mineral resources have been produced from 

these occurrences.

Estimated resources: Thorium and rare earth elements 

resources in the district have not been estimated. 

McLemore and others (1988) report that samples of 

“quartzite” contain 546 parts per million (ppm) thorium (Th), 582 ppm lanthanum (La), and 1,160 ppm 

yttrium (Y). These data presumably refer to a quartz-rich 

pegmatite.

Detailed Discussion

The El Porvenir or Hermit Mountain district lies about 

24 km (15 mi) northwest of Las Vegas and 4.8 km (3 mi) 

north of Porvenir, on the eastern edge of the Las Vegas Range, 

San Miguel County, north-central New Mexico. The bulk of 

Hermit Mountain is formed by a pink, coarse-grained Precambrian granite, which is cut by pegmatite dikes and quartz 

veins (Robertson, 1976). Some of the pegmatites reportedly 

contain monazite and rare earth elements mineralization. Little 

published information is available on the chemistry of these 

pegmatites, but the data that are available suggest that anomalously high rare earth elements concentrations are present. For 

example, McLemore and others (1988) report that samples of 

“quartzite” contain 546 parts per million (ppm) Th, 582 ppm 

La, and 1,160 ppm Y. These data presumably refer to a quartzrich pegmatite.

References Cited

McLemore, V.T., North, R.M., and Leppert, Shawn, 1988, 

REE, niobium, and thorium districts and occurrences in 

New Mexico: New Mexico Bureau of Mines and Mineral 

Resources Open-File Report 324, 27 p., 2 plates.

Robertson, J.M., 1976, Mining districts of northeastern New 

Mexico, in Ewing, R.C., and Kues, B.S., eds., Guidebook 

of Vermejo Park, northeastern New Mexico, New Mexico 

Geological Society Twenty-seventh Field Conference, September 30, October 1 and 2, 1976: New Mexico Geological 

Society, p. 257–262.
New Mexico—Gallinas Mountains 67

New Mexico—Gallinas Mountains

Location: Gallinas mining district lies in the Gallinas Mountains, about 16 km (10 mi) west of the town of Corona 

in Lincoln County, central New Mexico. Latitude: 

34.19368 N., Longitude: 105.73744 W.; datum: WGS84

Deposit type and basic geology: The cerium-rich mineral 

bastnasite precipitated in fluorite-copper sulfide deposits 

in the Gallinas Mountains. The fluorite-copper-bastnasite 

deposits form veins and fill brecciated zones in sandstones and siltstones of the Permian Yeso Formation. 

Only two fluorspar deposits were found in porphyritic 

trachyte; all other fluorspar deposits in the district are 

hosted by sandstone and siltstones of the Yeso Formation. 

The porphyritic character of the trachyte and the character of the mineral deposits (low-temperature mineral 

assemblage, brecciation, infilling of open spaces) suggest 

that the intrusions and mineralizing events were shallow 

(hypabyssal). The fluorite-copper-bastnasite deposits of 

the Gallinas district are found in two settings within the 

sandstones and siltstones of the Yeso Formation: as veins 

that fill thin fissures (1–3 in. (2.5–7.6 cm) wide] in highly 

fractured zones, and as mineral-rich masses that fill open 

spaces and veinlets in breccia zones. The brecciated 

zones were formed by faulting and are therefore regarded 

as fault breccias. In both settings, fluorite is the most 

abundant mineral.

Status: Currently (2010), there appears to be no active 

exploration in this district. 

Production: In 1953–54, the Gallinas mining district produced small amounts of fluorspar-rich ore (for fluorine); 

output is estimated to have been less than 2,000 tons 

(1,800 metric tons) (Griswold, 1959). During 1954–55, 

the Conqueror No. 9 claim produced approximately 60 

tons (54 metric tons) of bastnasite (a cerium-rich mineral) 

concentrate from these same fluorspar deposits, which 

was processed nearby in Gallinas at a small mill owned 

by the United States Rare Earths, Inc. (Griswold, 1959). 

In 1956, the New Mexico Copper Corp. produced about 

300 tons (270 metric tons) of copper-lead-fluorspar ore 

from its Conqueror claim in the Gallinas district, of which 

about 11 tons (10 metric tons) of bastnasite ore concentrate from the Conqueror No. 10 claim.

Estimated resources: Soule (1946) estimated that bastnasite forms about 5 percent of the breccia deposits. Soule 

(1946) analyzed hand-picked grains of bastnasite from the 

Gallinas district and found that the bastnasite contained 

74.39 percent total rare earth elements oxides: 25.61 

percent cerium oxide and 48.78 percent other rare earth 

elements oxides. No resource estimate of the potential 

fluorspar and bastnasite tonnage within the Gallinas 

district has been published.

Detailed Discussion

The cerium-rich mineral bastnasite formed within 

fluorite-copper sulfide deposits in the Gallinas Mountains, 

about 16 km (10 mi) west of the town of Corona in Lincoln 

County, central New Mexico. In 1953–54, the Gallinas mining district produced small amounts of fluorspar-rich ore (for 

fluorine); output is estimated to have been less than 2,000 tons 

(1,800 metric tons) (Griswold, 1959). During 1954–55, the 

Conqueror No. 9 claim produced approximately 60 tons 

(54 metric tons) of bastnasite concentrate from these same 

fluorspar deposits, which was processed nearby in Gallinas 

at a small mill owned by the United States Rare Earths, Inc. 

(Griswold, 1959). In 1956, the New Mexico Copper Corp. 

produced about 300 tons (270 metric tons) of copper-leadfluorspar ore from its Conqueror claim in the Gallinas district, 

of which about 11 tons (10 metric tons) was bastnasite ore 

concentrate from the Conqueror No. 10 claim.

The Gallinas Mountains consist of Lower Permian sedimentary rocks that were domed, uplifted, faulted, and fractured during the emplacement of middle(?) Tertiary laccoliths 

composed mainly of alkaline trachyte and rhyolite (Perhac, 

1970). The fluorite-copper-bastnasite deposits form veins and 

fill brecciated zones in sandstones and siltstones of the Permian Yeso Formation. Only two fluorspar deposits were found in 

porphyritic trachyte; all other fluorspar deposits in the district 

are hosted by sandstone and siltstones of the Yeso Formation. 

The district’s fluorite-copper-bastnasite deposits are interpreted to result from epithermal (relatively low temperature) 

mineralization related to the intrusion of the alkaline trachyte 

(Perhac and Heinrich, 1964; Perhac, 1970). The porphyritic 

character of the trachyte and the character of the mineral 

deposits (low-temperature mineral assemblage, brecciation, 

and infilling of open spaces) suggest that the intrusions and 

mineralizing events occurred at shallow depths (hypabyssal). 

The fluorite-copper-bastnasite ore of the Gallinas district 

was deposited in two settings within the sandstones and 

siltstones of the Yeso Formation: as veins that fill thin fissures 

(1–3 inches (2.5–7.6 cm wide) in highly fractured zones, and 

as mineral-rich masses that fill open spaces and veinlets in 

breccia zones. The brecciated zones were formed by faulting 

and are therefore regarded as fault breccias. In both settings, 

fluorite is the most abundant mineral. Fluorite content in the 

breccia deposits averages about 60 percent (Soule, 1946). 

Barite, calcite, and quartz are next in abundance (Soule, 1946; 

Perhac, 1970). Other associated minerals are pyrite, galena, 

chalcopyrite, mimetite, sphalerite, conichalcite, chalcocite, 

wulfenite, malachite, azurite, vanadinite, mottramite, cerussite, 

chrysocolla, agardite (yttrium-bearing mineral), and bastnasite (Glass and Smalley, 1945; Griswold, 1959; Perhac, 1970; 

DeMark, 1980). 

The bastnasite ore forms thin, tabular, waxy yellow, 

transparent to translucent crystals 1 to 10 mm in length, usually about 4 mm (0.16 in.) in width and embedded in fluorite 
68 The Principal Rare Earth Elements Deposits of the United States

(Glass and Smalley, 1945; Soule, 1946; DeMark, 1980). 

Soule (1946) estimated that bastnasite forms about 5 percent 

of the breccia deposits. Soule (1946) analyzed hand-picked 

grains of bastnasite from the Gallinas district and found that 

the bastnasite contained 74.39 percent total rare earth elements oxides: 25.61 percent cerium oxide and 48.78 percent 

other rare earth elements oxides. No resource estimate of the 

potential fluorspar and bastnasite tonnage within the Gallinas 

district has been published.

References Cited

DeMark, R.S., 1980, The Red Cloud mines, Gallinas Mountains, New Mexico: The Mineralogical Record, v. 2, no. 11, 

p. 69–72.

Glass, J.J., and Smalley, R.G., 1945, Bastnasite: American 

Mineralogist, v. 30, nos. 9 and 10, p. 601–615.

Griswold, G.B., 1959, Mineral deposits of Lincoln County, 

New Mexico: New Mexico Bureau of Mines and Mineral 

Resources Bulletin 67, 117 p., 12 plates.

Perhac, R.M., 1970, Geology and mineral deposits of the 

Gallinas Mountains, Lincoln and Torrance Counties, 

New Mexico: New Mexico Bureau of Mines and Mineral 

Resources Bulletin 95, 51 p., 2 plates.

Perhac, R.M., and Heinrich, E.W., 1964, Fluorite-bastnaesite 

deposits of the Gallinas Mountains, New Mexico and 

bastnaesite paragenesis: Economic Geology, v. 59, no. 2, p. 

226–239.

Soule, J.H., 1946, Exploration of Gallinas fluorspar deposits, 

Lincoln County, N. Mex.: U.S. Bureau of Mines Report of 

Investigations 3854, 25 p.
New Mexico—Gold Hill Area and White Signal District 69

New Mexico—Gold Hill Area and 

White Signal District

Location: The White Signal district is located in Grant 

County, southwestern New Mexico. The adjacent Gold 

Hill area lies near the crest of the Burro Mountains. 

Latitude: 32.45400 N., Longitude: 108.50603 W.; datum: 

WGS84

Deposit type and basic geology: Rare earth elements (REE)–

thorium−bearing minerals form pods and lenses within 

pegmatites hosted by the Proterozoic Burro Mountain 

granite in the western part of the White Signal district. 

Quartz, muscovite, and microcline are the primary minerals of these pegmatites. Large euhedral crystals of euxenite [Y,Ca,Ce,U,Th)(Nb,Ta,Ti)2

O6] are found locally, and 

some crystals are several inches long (Gillerman, 1964). 

Other REE-bearing minerals reported in the pegmatites 

are allanite and samarskite (Richter and others, 1986). In 

the Gold Hill area, near the crest of the Burro Mountains, 

the same REE-bearing minerals are hosted in similar 

but larger pegmatites that also cut the Burro Mountain 

granite (Hedlund, 1978). The primary pegmatite minerals are milky quartz, microcline, albite, and muscovite 

with accessory biotite, magnetite, garnet, fluorite, and 

REE-bearing minerals such as allanite, euxenite, and 

samarskite.

Status: Currently (2010), there appears to be no active 

exploration in this district. 

Production: Shallow prospect pits were dug into the pegmatites in order to explore their radioactivity, presumably 

during the 1950s, but no further development is reported. 

Estimated resources: No report of the REE concentrations in 

these pegmatites has been published, but thorium concentrations can reach as high as 0.72 percent (Staatz, 1974).

Detailed Discussion

Rare earth elements (REE)−thorium−bearing minerals form pods and lenses within pegmatites hosted by the 

Proterozoic Burro Mountain granite in the western part of the 

White Signal district, which lies in Grant County, southwestern New Mexico (Gillerman, 1964; Richter and Lawrence, 

1983; Richter and others, 1986). Shallow prospect pits were 

dug into the pegmatites in order to explore their radioactivity, presumably during the 1950s, but no further development 

is reported. 

Quartz, muscovite, and microcline are the primary minerals of these pegmatites. Large euhedral crystals of euxenite 

[Y,Ca,Ce,U,Th)(Nb,Ta,Ti)2

O6] are found locally, and some 

crystals are several inches long (Gillerman, 1964). Other REEbearing minerals reported in the pegmatites are allanite and 

samarskite (Richter and others, 1986). No analyses of the REE 

concentrations in these pegmatites have been reported.

In the Gold Hill area, near the crest of the Burro Mountains, the same REE-bearing minerals are hosted in similar 

but larger pegmatites that also cut the Burro Mountain granite 

(Hedlund, 1978). These pegmatites were prospected by small 

pits between 1952 and 1955. However, “the amount and 

concentration of rare-earth minerals was so small that work 

was soon stopped” (Gillerman, 1964, p. 127). The primary 

pegmatite minerals are milky quartz, microcline, albite, and 

muscovite with accessory biotite, magnetite, garnet, fluorite, 

and the REE-bearing minerals, such as allanite, euxenite, and 

samarskite. No report of the REE concentrations in these pegmatites has been published, but Th concentrations can reach as 

high as 0.72 percent (Staatz, 1974).

References Cited

Gillerman, Elliott, 1964, Mineral deposits of western Grant 

County, New Mexico: New Mexico Bureau of Mines and 

Mineral Resources Bulletin 83, 213 p., 11 plates.

Hedlund, D.C., 1978, Geologic map of the Gold Hill quadrangle, Hidalgo and Grant Counties, New Mexico: U.S. Geological Survey Miscellaneous Field Studies Map MF–1035, 

scale 1:24,000.

Richter, D.H., and Lawrence, V.A., 1983, Mineral deposit map 

of the Silver City 1° x 2° quadrangle, New Mexico and Arizona: U.S. Geological Survey Miscellaneous Investigations 

Series Map I–1310–B, scale 1:250,000.

Richter, D.H., Sharp, W.N., Watts, K.C., Raines, G.L., Houser, 

B.B., and Klein, D.P., 1986, Maps showing mineral resource 

assessment of the Silver City 1° x 2° quadrangle, New 

Mexico and Arizona: U.S. Geological Survey Miscellaneous Investigations Series Map I–1310–F, 24 p. pamphlet, 

1 sheet, various scales.

Staatz, M.H., 1974, Thorium veins in the United States: Economic Geology, v. 69, no. 4, p. 494–507.
70 The Principal Rare Earth Elements Deposits of the United States

New Mexico—Laughlin Peak Area

Location: Thorium (Th)- and rare earth elements–rich veins 

are intruded throughout an area of about 12 km2

 (4.6 mi2) 

near Laughlin Peak, about 38 km (24 mi) southeast of 

Raton in Colfax County, northeastern New Mexico. 

Latitude: 36.58156 N., Longitude: 104.22953 W.; datum: 

WGS84

Deposit type and basic geology: In this area, Staatz (1985) 

mapped 29 veins ranging from 0.5 to 550 m (1.6 to 1,800 

ft) in length and 0.2 to 70 cm (0.08 to 28 in.) in thickness. Thorium- and REE-bearing minerals in the veins 

include brockite, xenotime, and crandallite. The brockite 

and xenotime are mainly enriched in the yttrium-group 

(heavy) rare earths, whereas the crandallite contains 

mostly cerium-group (light) rare earth elements. The veins 

are steeply dipping and lie along fracture zones, cutting 

mostly trachyte and Dakota Sandstone but also intrusive 

breccia and trachyandesite. The gangue minerals are 

mostly potassium feldspar, quartz, or calcite, and lesser 

amounts of goethite, magnetite, barite, zircon, rutile, and 

a manganese oxide. One small carbonatite dike was found 

2.7 km (1.7 mi) south of the mapped area.

Status: Currently (2010), there appears to be no active 

exploration in this district. 

Production: Prospecting for radioactive deposits began in 

the Laughlin Peak area in the early 1950s; small pits and 

trenches were dug along the veins. These prospects were 

subsequently sampled by Staatz (1985).

Estimated resources: Thorium and REE resources in the 

district have not been estimated. Staatz (1985) found 

that most of the veins contain higher concentrations of 

the yttrium-group REE than the cerium group, and veins 

with high yttrium-group concentrations usually also have 

a high thorium content. Sampling by Staatz (1985, p. 1) 

found, “Thorium content of 30 samples ranges from 30 

to 24,200 ppm (parts per million), and the total rare-earth 

content from 147 to 19,030 ppm.” These amounts equate 

to REE concentrations of about 0.018 to 2.34 percent total 

REE oxide.

Detailed Discussion

Thorium (Th)- and rare earth elements (REE)-rich veins 

crop out throughout an area of about 12 km2

 (4.6 mi2) near 

Laughlin Peak, about 38 km (24 mi) southeast of Raton in 

Colfax County of northeastern New Mexico. Staatz (1985) 

mapped 29 veins in this area, ranging from 0.5 to 550 m (1.6 

to 1,800 ft) in length and 0.2 to 70 cm (0.08 to 28 in.) in thickness. Thorium- and REE-bearing minerals in the veins include 

brockite, xenotime, and crandallite. Thorite and monazite are 

absent. The brockite and xenotime are mainly enriched in the 

yttrium-group (heavy) rare earths, whereas the crandallite 

contains mostly cerium-group (light) rare earth elements. 

Staatz (1985) found that most of the veins contain higher 

concentrations of yttrium-group REE than cerium-group REE, 

and veins with high yttrium-group values usually have a high 

Th content. Sampling by Staatz (1985, p. 1) found, “Thorium 

content of 30 samples ranges from 30 to 24,200 ppm (parts per 

million), and the total rare-earth content from 147 to 19,030 

ppm.” These amounts equate to REE concentrations of about 

0.018 to 2.34 percent total REE oxide.

The veins are steeply dipping and lie along fracture 

zones, cutting mostly trachyte and Dakota Sandstone but also 

intrusive breccia and trachyandesite. The gangue minerals 

are mostly potassium feldspar, quartz, or calcite, and lesser 

amounts of goethite, magnetite, barite, zircon, rutile, and a 

manganese oxide. One small carbonatite dike was found 2.7 

km (1.7 mi) south of the mapped area (Staatz, 1985). The 

igneous rocks that are spatially associated with the veins have 

alkaline compositions of phonolite, trachyte, trachyandesite, 

and basalt. These rocks are also anomalous in REE, especially 

light REE, and show total REE contents of 173–807 ppm. 

The veins do not cut phonolite or basalt, but Staatz (1985) 

suggested that the source of the Th and REE in the veins was 

the magma that formed the phonolite during the Oligocene, 

because samples of the phonolite showed Th and REE contents much higher than samples of other associated igneous 

rocks.

Prospecting for radioactivity began in the Laughlin Peak 

area in the early 1950s; small pits and trenches were dug along 

the veins. These prospects were subsequently sampled by Staatz (1985). Additional exploration is necessary to evaluate the 

full REE resource potential of this area, but the geologic mapping and descriptions by Staatz (1985, 1986, 1987) provide a 

solid framework for further work here.

References Cited

Staatz, M.H., 1985, Geology and description of the thorium 

and rare-earth veins in the Laughlin Peak area, Colfax 

County, New Mexico: U.S. Geological Survey Professional 

Paper 1049–E, 32 p., 1 plate, scale 1:12,000.

Staatz, M.H., 1986, Geologic map of the Pine Buttes quadrangle, Colfax County, New Mexico: U.S. Geological Survey 

Geologic Quadrangle Map GQ–1591, scale 1:24,000.

Staatz, M.H., 1987, Geologic map of the Tres Hermanos Peak 

quadrangle, Colfax County, New Mexico: U.S. Geological 

Survey Quadrangle Map GQ–1605, scale 1:24,000.
New Mexico—Lemitar and Chupadera Mountains 71

New Mexico—Lemitar and Chupadera 

Mountains

Location: Carbonatite dikes and veins occur in the Lemitar 

Mountains in west-central New Mexico, and more than a 

dozen similar carbonatite dikes are known to be located 

to the south within the adjacent Chupadera Mountains. 

These mountain ranges lie west of San Antonio, Socorro, 

and Lemitar in Socorro County, New Mexico. Latitude: 

34.15398 N., Longitude: 106.98623 W.; datum: WGS84, 

and Latitude: 33.85285 N., Longitude: 106.95781 W.; 

datum: WGS84

Deposit type and basic geology: More than 100 carbonatite 

dikes and veins that contain rare earth elements (REE) 

cut Precambrian metamorphic and granitic terrane in 

the Lemitar Mountains, and more than a dozen similar 

carbonatite dikes intruded Precambrian metamorphic rocks 

to the south within the adjacent Chupadera Mountains 

(McLemore, 1983, 1987; Van Allen and others, 1986). 

The carbonatite intrusions range from less than 1 cm (0.4 

in.) thick—veins—to more than 1 m (3.3 ft) thick—dikes 

(McLemore, 1983, 1987). A few of the dikes can be traced 

in outcrop for as much as 600 m (1,970 ft). Subparallel sets 

of carbonatites locally form dike swarms. Alkaline igneous 

rocks are lacking in these mountain ranges, so their igneous 

source presumably lies at depth (McLemore, 1987). Age 

determinations by the potassium-argon method suggest that 

the carbonatites are Ordovician (449±16 million years old, 

McLemore, 1987) and thus represent a part of widespread 

Cambrian-Ordovician igneous activity in New Mexico.

Status: Currently (2010), there appears to be no active 

exploration in this district. 

Production: No mineral resources have been produced from 

these vein deposits. Because uranium and thorium in the 

carbonatite dikes make the dikes radioactive, they were 

identified in 1954 during a uranium exploration program 

conducted by United Geophysical Corp. (Van Allen and 

others, 1986). 

Estimated resources: Thorium and REE resources in the 

district have not been estimated. McLemore and others 

(1988) reported a maximum concentration from selected 

samples of 1,950 parts per million (ppm) thorium (0.195 

percent) and 0.25 weight percent uranium oxide. Van 

Allen and others (1986) and McLemore and others (1988) 

report maximum concentrations from select carbonatite 

samples as 0.19 weight percent total REE; 700 ppm Y; 

4,900 ppm cerium (Ce); and 1,700 ppm lanthanum (La).

Detailed Discussion

More than 100 carbonatite dikes and veins that contain 

rare earth elements (REE) cut Precambrian metamorphic 

and granitic terrane in the Lemitar Mountains in west-central 

New Mexico, and more than a dozen similar carbonatite dikes 

intruded Precambrian metamorphic rocks to the south within 

the adjacent Chupadera Mountains (McLemore, 1983, 1987; 

Van Allen and others, 1986). These north-south-trending mountain ranges lie west of San Antonio, Socorro, and Lemitar in 

Socorro County, New Mexico. The carbonatite intrusions range 

from less than 1 cm (0.4 in.) thick—veins—to more than 1 m 

(3.3 ft) thick—dikes (McLemore, 1983, 1987). A few of the 

dikes can be traced in outcrop for as much as 600 m (1,970 ft). 

Subparallel sets of carbonatites locally form dike swarms. 

The carbonatite dikes occupy sets of fractures apparently 

related to rifting of the adjacent Rio Grande Rift. Alkaline 

igneous rocks are lacking in these mountain ranges, so the 

dikes’ igneous source presumably lies at depth (McLemore, 

1987). Age determinations by the potassium-argon method 

suggest that the carbonatites are Ordovician (449±16 million 

years old, McLemore, 1987) and thus represent a part of widespread Cambrian-Ordovician igneous activity in New Mexico.

Because uranium and thorium in the carbonatite dikes 

make the dikes radioactive, they were identified in 1954 during 

a uranium exploration program conducted by United Geophysical Corp. (Van Allen and others, 1986). Although they were 

described at that time as “radioactive-calcite veins” they were 

later classified as carbonatites in 1978 by Tenneco geologists. 

McLemore and others (1988) reported a maximum concentration 

from selected samples of 1,950 ppm thorium (0.195 percent) and 

0.25 weight percent U3

O8. Although the uranium correlates with 

yttrium in carbonatites of the Chupadera Mountains, no specific 

uranium or yttrium mineral was identified (McLemore, 1983; 

Van Allen and others, 1986). The gangue mineralogy of these 

carbonatites is detailed by McLemore (1983, 1987).

Overall, the REE concentrations found in the carbonatite 

dikes in both mountain ranges were quite variable. Van Allen 

and others (1986) and McLemore and others (1988) report 

maximum concentrations from select carbonatite samples as 

0.19 weight percent total REE; 700 ppm Y; 4,900 ppm cerium 

(Ce); and 1,700 ppm lanthanum (La).

References Cited

McLemore, V.T., 1983, Carbonatites in the Lemitar and 

Chupadera Mountains, Socorro County, New Mexico, in

Chapin, C.E., ed., Socorro Region II, New Mexico Geological Society Thirty-fourth Annual Field Conference, October 

13–15, 1983: New Mexico Geological Society, p. 235–240.

McLemore, V.T., 1987, Geology and regional implications of 

carbonatites in the Lemitar Mountains, central New Mexico: 

Journal of Geology, v. 95, no. 2, p. 255–270.

McLemore, V.T., North, R.M., and Leppert, Shawn, 1988, 

REE, niobium, and thorium districts and occurrences in 

New Mexico: New Mexico Bureau of Mines and Mineral 

Resources Open-File Report 324, 27 p., 2 plates.

Van Allen, B.R., Emmons, D.L., and Paster, T.P., 1986, Carbonatite dikes of the Chupadera Mountains, Socorro County, 

New Mexico: New Mexico Geology, v. 8, no. 2, p. 25–29.
72 The Principal Rare Earth Elements Deposits of the United States

New Mexico—Petaca District

Location: The Petaca district is located between Ojo Caliente 

and Tres Piedras, in Rio Arriba County, north-central New 

Mexico. Latitude: 36.58835 N., Longitude: 106.07170 W.; 

datum: WGS84

Deposit type and basic geology: Thorium- and rare earth 

elements (REE)−bearing pegmatites crop out in Precambrian rocks in the southeastern Tusas Mountains (Bingler, 

1968). The pegmatites of the Petaca district take a variety 

of shapes, such as dikes, sills, pipes, pods, troughs, and 

irregular forms. The pegmatites crop out for 75 to 1,430 ft 

(23 to 436 m) in length (an average outcrop length is 410 

ft (125 m)), and they have an average width of 30 to 35 ft 

(9 to 11 m) (Bingler, 1968). Elevated REE concentrations 

in Petaca district pegmatites mainly reflect the mineral 

samarskite, a REE-iron-uranium-thorium-niobium-tantalum-titanium−bearing oxide.

Status: Currently (2010), there appears to be no active 

exploration in this district. 

Production: A number of pegmatites in the district were 

mined for their large books of muscovite mica crystals, 

beginning in 1870 and continuing intermittently until 

1944 (Bingler, 1968). 

Estimated resources: Thorium and REE resources in the 

district have not been estimated. McLemore and others (1988) reported an average niobium content of 0.04 

percent in 87 pegmatites of the district. Monazite accounts 

for the pegmatites’ high thorium content. An analysis 

of the Globe pegmatite in the district found 10,332 ppm 

thorium (McLemore and others, 1988). McLemore and 

others (1988, p. 4) reported the following REE analysis of 

a sample of the Globe pegmatite: “600 ppm Y, 660 ppm 

Yb, 396 ppm Er, 186 ppm Gd, 3,117 ppm [total] REE + 

Y.” Otherwise, the REE content of the pegmatites of the 

Petaca district has not been published.

Detailed Discussion

Thorium- and rare earth elements (REE)–bearing pegmatites are exposed in the Petaca district, located between 

Ojo Caliente and Tres Piedras, in Rio Arriba County, northcentral New Mexico. The pegmatites crop out in Precambrian 

rocks in the southeastern Tusas Mountains (Bingler, 1968). 

The pegmatites of the Petaca district take a variety of shapes, 

such as dikes, sills, pipes, pods, troughs, and irregular forms. 

The pegmatite forms and their characteristics are described 

in detail by Jahns (1946). They crop out for 75 to 1,430 ft (23 

to 436 m) in length (an average outcrop length is 410 ft (125 

m)), and they have an average width of 30 to 35 ft (9 to 11 m) 

(Bingler, 1968).

The primary minerals of the Petaca district pegmatites 

are microcline, quartz, plagioclase, and muscovite. A number 

of pegmatites in the district were mined for their large books 

of muscovite mica crystals beginning in 1870 and continuing 

intermittently until 1944 (Bingler, 1968). Almost 50 accessory 

minerals have been identified; the most common is spessartite (now called spessartine) garnet, columbite-tantalite 

[(Fe,Mn)(Nb,Ta)2

O6], fluorite, beryl, monazite, samarskite, 

and ilmenite-magnetite (Wright, 1948; Redmon, 1961; 

Bingler, 1968). (Columbite and tantalite are obsolete names 

for a mineral series; columbite is now named ferrocolumbite 

(Fe2+Nb2O6), which forms two minerals series, with ferrotantalite (Fe2+Ta2

O6) and with manganocolumbite [(Mn2+,Fe2+)

(Nb,Ta)2O6)].

The elevated concentrations of niobium (Nb) and tantalum (Ta) in the pegmatites arise from Nb- and Ta-bearing minerals. For example, McLemore and others (1988) reported an 

average of Nb content of 0.04 percent in 87 pegmatites of the 

district. Similarly, monazite accounts for the pegmatites’ high 

Th content. Specifically, analysis of the Globe pegmatite in the 

district found 10,332 ppm Th (McLemore and others, 1988).

Elevated REE concentrations in Petaca district pegmatites 

mainly reflect the mineral samarskite, an REE-iron-uraniumthorium-niobium-tantalum-titanium−bearing oxide. The REE 

are reportedly restricted to albite-rich zones in the pegmatites. 

McLemore and others (1988, p. 4) reported this REE analysis 

of a sample of the Globe pegmatite: “600 ppm Y, 660 ppm Yb, 

396 ppm Er, 186 ppm Gd, 3,117 ppm [total] REE + Y.” Otherwise, the REE content of the pegmatites of the Petaca district 

has not been published.

References Cited

Bingler, E.C., 1968, Geology and mineral resources of Rio 

Arriba County, New Mexico: New Mexico Bureau of Mines 

and Mineral Resources Bulletin 91, 158 p., 8 plates.

Jahns, R.H., 1946, Mica deposits of the Petaca district, Rio 

Arriba County, New Mexico: New Mexico Bureau of Mines 

and Mineral Resources Bulletin 25, 294 p., 25 plates.

McLemore, V.T., North, R.M., and Leppert, Shawn, 1988, 

REE, niobium, and thorium districts and occurrences in 

New Mexico: New Mexico Bureau of Mines and Mineral 

Resources Open-File Report 324, 27 p., 2 plates.

Redmon, D.E., 1961, Reconnaissance of selected pegmatite 

districts in north-central New Mexico: U.S. Bureau of 

Mines Information Circular 8013, 79 p.

Wright, L.A., 1948, The Globe pegmatite, Rio Arriba County, 

New Mexico: American Journal of Science, v. 246, no. 11, 

p. 665–688. 
New Mexico—Red Hills Area 73

New Mexico—Red Hills Area

Location: Dike-like and tabular bodies containing thorium 

and rare earth elements are exposed in the Red Hills area 

of the southern Caballo Mountains, Sierra County, New 

Mexico. They crop out across an area of about 7.8 square 

km (3 mi2), which is centered about 4 km (2.5 mi) southeast of Caballo dam. Latitude: 32.86293 N., Longitude: 

107.25655 W.; datum: WGS84

Deposit type and basic geology: At least 45 radioactive, 

dike-like and tabular, deep-red bodies of syenite that 

crop out in the Red Hills area are modestly enriched in 

heavy rare earth elements (HREE). These coarse-grained, 

microcline-rich syenites range from 1 to 100 m (3.3 to 

328 ft) in length and several centimeters to 10 m (1 in. 

to 33 ft) in width (McLemore, 1986). The syenite bodies 

are composed mainly of microcline and contain lesser 

amounts of quartz, muscovite, hematite, goethite, chlorite, 

and plagioclase and accessory apatite, zircon, calcite, 

fluorite, limonite, magnetite, and barite. The radioactivity 

originates in uranium and thorium residing in with spinel, 

rutile, anatase, thorite, thorogummite, and possibly uraninite (Staatz and others, 1965; McLemore, 1986).

Status: Currently (2010), there appears to be no active 

exploration in this district.

Production: No mineral resources have been produced from 

these vein deposits.

Estimated resources: Thorium or REE resources in the 

district have not been estimated. Subsurface sampling 

is necessary in this area to determine if a larger syenite 

mass exists at depth, and if such a mass is consistently 

enriched in the heavy REE. Samples of the microclinerich (syenite) bodies in the Red Hills by Staatz and others 

(1965) contained thorium concentrations as much as 0.44 

weight percent and modest to undetectable concentrations 

of the light REE. However, the proportion of heavy REE 

was higher. In particular, yttrium concentrations were as 

much as 0.19 weight percent (Staatz and others, 1965; 

McLemore, 1986).

Detailed Discussion

At least 45 radioactive, dike-like and tabular, deep-red 

bodies of syenite that are modestly enriched in heavy rare 

earth elements (REE) are exposed in the Red Hills area of the 

southern Caballo Mountains, Sierra County, New Mexico (Staatz and others, 1965; McLemore, 1983, 1986). These coarsegrained, microcline-rich syenites range from 1 to 100 m (3.3 

to 328 ft) in length and several centimeters to 10 m (1 in. to 

33 ft) in width (McLemore, 1986). They crop out across an 

area of about 7.8 square km (3 mi2

), which is centered about 

4 km (2.5 mi) southeast of Caballo dam. The syenite bodies 

are composed mainly of microcline, with lesser amounts of 

quartz, muscovite, hematite, goethite, chlorite, and plagioclase, and accessory apatite, zircon, calcite, fluorite, limonite, 

magnetite, and barite. The radioactivity originates in uranium 

and thorium that resides in with spinel, rutile, anatase, thorite, 

thorogummite, and possibly uraninite (Staatz and others, 1965; 

McLemore, 1986). 

Samples of the microcline-rich (syenite) bodies in the 

Red Hills by Staatz and others (1965) contained thorium 

concentrations as much as 0.44 weight percent and modest to 

undetectable concentrations of the light REE. However, the 

proportion of heavy REE was higher. In particular, yttrium 

concentrations were as much as 0.19 weight percent (Staatz 

and others, 1965; McLemore, 1986). Subsurface sampling 

is necessary in this area to determine if a larger syenite mass 

exists at depth, and if such a mass is consistently enriched in 

the heavy REE.

References Cited

McLemore, V.T., 1983, Uranium and thorium occurrences 

in New Mexico—Distribution, geology, production, and 

resources, with selected bibliography: New Mexico Bureau 

of Mines and Mineral Resources Open-File Report 183, 

180 p. text, 6 appendixes. 

McLemore, V.T., 1986, Geology, geochemistry, and mineralization of syenites in the Red Hills, southern Caballo 

Mountains, Sierra County, New Mexico—Preliminary 

observations, in Clemons, R.E., King, W.E., and Mack, 

G.H., eds., Truth or Consequences region, New Mexico 

Geological Society Thirty-seventh Annual Field Conference, October 16–18, 1986: New Mexico Geological 

Society, p. 151–159.

Staatz, M.H., Adams, J.W., and Conklin, N.M., 1965, Thorium-bearing microcline-rich rocks in the southern Caballo 

Mountains, Sierra County, New Mexico, in Geological 

Survey Research 1965, Chapter D: U.S. Geological Survey 

Professional Paper 525–D, p. 48–51.
74 The Principal Rare Earth Elements Deposits of the United States

New Mexico—Wind Mountain, 

Cornudas Mountains

Location: Wind Mountain is located in Otero County, New 

Mexico, and is one of the largest uplifted areas of the Cornudas Mountains. Wind Mountain stands about 80 km (50 

mi) east of El Paso, just north of the New Mexico−Texas 

boundary. Latitude: 32.02382 N., Longitude: 105.50162 

W.; datum: WGS84

Deposit type and basic geology: Wind Mountain was formed 

by a laccolith of porphyritic nepheline syenite that rises 

about 2,500 ft (762 m) above the surrounding Diablo Plateau (Holser, 1959). Dikes and sills of nepheline syenite 

and syenite cut the main mass of the laccolith. At least 

some of these dikes and sills contain thorium, uranium, 

and rare earth elements (REE) mineralization (McLemore, 

1983). The alkaline dikes and sills reportedly also contain 

anomalous concentrations of beryllium (Be), niobium 

(Nb), lithium (Li), nickel (Ni), tin (Sn), zirconium (Zr), 

and fluorine (F, in fluorite).

Status: Currently (2010), there appears to be no active 

exploration in this district. 

Production: No mineral resources have been produced from 

these dikes and sills.

Estimated resources: Thorium and REE resources in the 

district have not been estimated. McLemore and others (1988) analyzed a dike sample collected from Wind 

Mountain and reported 700 parts per million (ppm) 

lanthanum (La), 270 ppm neodymium (Nd), and 242 ppm 

yttrium (Y). However, a full rare earth elements resource 

evaluation of the Wind Mountain uplift would require 

much more sampling than has been conducted thus far.

Detailed Discussion

Wind Mountain, in Otero County, New Mexico, is one 

of the largest uplifted areas of the Cornudas Mountains, a 

mountain range that straddles the New Mexico−Texas border 

east of El Paso, Texas. The Cornudas Mountains, the northern 

end of an alkaline magmatic belt that was emplaced about 35 

million years ago, extends from southern New Mexico, across 

Texas, and into Mexico. Wind Mountain itself lies about 80 

km (50 mi) east of El Paso, just north of the New MexicoTexas boundary. 

Wind Mountain was formed by a large alkaline intrusion, 

a laccolith of porphyritic nepheline syenite that rises about 

2,500 ft (762 m) above the surrounding Diablo Plateau (Holser, 1959). Dikes and sills of nepheline syenite and syenite cut 

the main mass of the laccolith. At least some of these dikes 

and sills contain Th, U, and rare earth elements mineralization 

(McLemore, 1983). The alkaline dikes and sills reportedly also 

contain anomalously high concentrations of beryllium (Be), 

niobium (Nb), lithium (Li), nickel (Ni), tin (Sn), zirconium 

(Zr), and fluorine (F, in fluorite). McLemore and others (1988) 

analyzed a dike sample collected from Wind Mountain and 

reported concentrations of 700 ppm lanthanum (La), 270 ppm 

neodymium (Nd), and 242 ppm yttrium (Y). However, a full 

rare earth elements resource evaluation of the Wind Mountain uplift would require much more sampling than has been 

completed thus far.

References Cited

Holser, W.T., 1959, Trans-Pecos region, Texas and New 

Mexico, in Warner, L.A., Holser, W.T., Wilmarth, V.R., and 

Cameron, E.N., Occurrence of nonpegmatite beryllium in 

the United States: U.S. Geological Survey Professional 

Paper 318, p. 130–143.

McLemore, V.T., 1983, Uranium and thorium occurrences 

in New Mexico—Distribution, geology, production, and 

resources, with selected bibliography: New Mexico Bureau 

of Mines and Mineral Resources Open-File Report 183, 

180 p. text, 6 appendixes. 

McLemore, V.T., North, R.M., and Leppert, Shawn, 1988, 

REE, niobium, and thorium districts and occurrences in 

New Mexico: New Mexico Bureau of Mines and Mineral 

Resources Open-File Report 324, 27 p., 2 plates.
New York—Mineville Iron District 75

New York—Mineville Iron District

Location: The Mineville iron district includes the iron ores 

once mined in the Mineville, New York, area, located 

in the northeastern part of the Adirondack Mountains, 

on the west side of Lake Champlain. Most of the former 

iron mines are near the towns of Mineville and Port 

Henry in Essex County, New York. This district of iron 

deposits extends for approximately 78 km2 (30 mi2). 

Latitude: 44.06403 N., Longitude: 73.49239 W.; datum: 

WGS84

Deposit type and basic geology: Thorium and rare earth 

elements (REE) reside within apatite in iron ores once 

mined in the Mineville, New York, area. The primary 

apatite-rich iron deposits are the Old Bed, Cheever, and 

Smith bodies; the Cheever and Smith orebodies have 

been mined out. The orebodies are magnetite deposits 

that are intricately folded and faulted within a complex 

suite of Precambrian metamorphic and igneous rocks. 

The host rocks have both mafic and felsic compositions 

that include augite syenites, granite, gabbro and diorite 

(Kemp, 1908; Staatz and others, 1980). The iron deposits 

are mainly magnetite, martite, and apatite, with gangue 

minerals of augite, hornblende, albite, quartz, pyrite, 

and tourmaline (McKeown and Klemic, 1956). The iron 

deposits in the Mineville–Port Henry area that are high 

in apatite are also enriched in phosphorous, thorium, and 

REE, because these elements are concentrated within 

the apatite grains. In addition, the ore mineral magnetite 

is intergrown with 1–3 mm (0.04–0.12 in.) long, riceshaped grains of apatite.

Status: Currently (2010), there is no reported exploration or 

development in this district. 

Production: Iron ore was mined from the district intermittently from 1804 until the last operation closed in 1971. 

A detailed mining history of the district is summarized by 

Staatz and others (1980).

Estimated resources: Currently, large tailings piles and 

unmined parts of magnetite orebodies in the Mineville 

district contain REE-bearing apatite-rich rock. Staatz 

and others (1980) estimated that about two-thirds of 

the tailings piles were derived from apatite-rich ores, 

which would represent about 9 million metric tons (10 

million tons) of the tailings. Using an average grade of 

about 8 percent apatite content, approximately 720,000 

metric tons (790,000 tons) of apatite could be present 

in the tailings dumps in the district. McKeown and 

Klemic (1956) reported an average rare earth oxide 

content of 11.14 percent in 14 samples of apatite separated from the Old Bed, Joker, and Smith orebodies. 

Thus, the tailings dump piles could contain approximately 80,200 metric tons (88,400 tons) of rare earth 

oxides. 

Detailed Discussion

Thorium and rare earth elements (REE) are incorporated 

within apatite in iron ores once mined in the Mineville, New 

York, area, located in the northeastern part of the Adirondack 

Mountains, on the west side of Lake Champlain (fig. 16). 

Most of the former iron mines are near the towns of Mineville 

and Port Henry in Essex County, New York. This district of 

iron deposits extends for approximately 78 km2 (30 mi2). The 

primary apatite-rich iron deposits are the Old Bed, Cheever, 

and Smith bodies; the Cheever and Smith orebodies have been 

mined out. Iron ore was mined from the district intermittently 

from 1804 until the last operation closed in 1971. A more 

detailed mining history of the district is summarized by Staatz 

and others (1980). 

The orebodies are magnetite deposits that are intricately 

folded and faulted within a complex suite of Precambrian 

metamorphic and igneous rocks. The host rocks have both 

mafic and felsic compositions that include augite syenites, 

granite, gabbro, and diorite (Kemp, 1908; Staatz and others, 

1980). The granite has felsic Na- and K-rich compositions that 

alternate with more basic, amphibole-, pyroxene-, and phlogopite-bearing rocks. Overlying the igneous sequence rests a 

metasedimentary series that contains Proterozoic marbles, 

calc-silicates and gneisses. The iron deposits are mainly magnetite, martite, and apatite, with gangue minerals of augite, 

hornblende, albite, quartz, pyrite, and tourmaline (McKeown 

and Klemic, 1956). Pegmatites crosscut the magnetite ore and 

consist of quartz, feldspar ± magnetite ± allanite, and minor 

scapolite, titanite, epidote, and zircon. 

The iron deposits in the Mineville–Port Henry area that 

are high in apatite content are also enriched in phosphorous, 

thorium, and REE, because these elements are concentrated within the apatite grains. In addition, the ore mineral 

magnetite is intergrown with 1–3 mm (0.04–0.12 in.) long, 

rice-shaped grains of apatite. The apatites can take several 

colors, such as reddish brown, green, white, or transparent. 

The reddish-brown variety is the most common. The reddishbrown color of the apatite, also referred to as fluorapatite, is 

most likely generated by infiltration or inclusions of hematite 

along fractures or within the crystal structure.

According to Staatz and others (1980, p. 29), “The 

reddish-brown apatite contains between 5.8 and 20.6 percent 

total rare earths, the green variety between 0.5 and 2.0 percent, 

and the white and transparent varieties only trace amounts.” 

Monazite, bastnasite, and hematite fill microfractures in the 

apatites and also form coatings on the apatites as well. In 

addition, microscopic phases of secondary thorite, allanite, 

and parisite have been noted in some apatite crystals. Monazite, thorite, allanite, and bastnasite are enriched in thorium 

and REE. Kainosite has also been observed in edenite under 

a polarizing microscope and scanning electron microscope 

(Lupulescu and Pyle, 2008).

Allanite located in the pegmatite bodies, host gneiss, or 

pyroxene-rich rocks is rich in cerium. The allanite crystals with 

a pegmatitic origin are very large, 20 to 25 cm (7.9 to 9.8 in.) 
76 The Principal Rare Earth Elements Deposits of the United States

Mineville

Moriah

Center

Witherbee

Moriah

CHEEVER

MINE

BARTON HILL

MINE

x

x

x

FISHER HILL

MINE

SMITH

MINE

SHERMAN

MINE

x x

Bartlett

Pond

PILFERSHIRE

x MINE

Location of

detailed map

x

1 MILE

McKenzie

McKenzie

Brook

Brook

MINEVILLE MINES

xDELAWARE

AND

HUDSON

Brook

Bartlett

Brook

Lake Champlain

0

L C and M

Road

Water

Railroad

Mine location

Port

Henry

Lake

Champlain

Figure 16. Mineville district in Essex County, New York. Modified from McKeown and Klemic (1956).
New York—Mineville Iron District 77

long, 6 to 20 cm (2.4 to 7.9 in.) wide, and 2.5 to 5 cm (1 to 2 in.) 

thick, with smooth surfaces and conchoidal fractures (Blake, 

1858). Allanite crystals associated with quartz and monazite 

(Ce) are large, smooth-faced, and metamict (Lupulescu and 

Pyle, 2008). In the pyroxene rocks, the metamict allanite has 

decomposed to monazite (Ce), which contains a rim of Y-dominant allanite that is dark brown and strongly pleochroic.

In the iron ores of the Mineville–Port Henry area, two 

generations of monazite can be distinguished largely on the 

basis of their relationships with other minerals. Within the 

pegmatites, monazite (Ce) ranges from 1–3 mm (0.04–0.12 

in.) to almost 1 cm (0.39 in.) and appears to be associated with 

or inclusions in allanite, both of which are embedded in quartz 

(Lupulescu and Pyle, 2008). Monazite also formed as a minute, secondary mineral because of the breakdown of allanite in 

the pyroxene-rich rocks.

Currently, large tailings piles and unmined parts of magnetite orebodies in the Mineville district contain REE-bearing 

apatite-rich rock. Staatz and others (1980) estimated that about 

two-thirds of the tailings piles were derived from apatite-rich 

ores, which would represent about 9 million metric tons of the 

tailings. Using an average grade of about 8 percent apatite, 

approximately 720,000 metric tons of apatite could be present in the tailings dumps in the district. McKeown and Klemic 

(1956) reported an average rare earth elements–oxide content 

of 11.14 percent in 14 samples of apatite separated from the 

Old Bed, Joker, and Smith orebodies. Thus, the tailings dump 

piles could contain approximately 80,200 metric tons of rare 

earth oxides. Uranium and thorium contents average 0.032 

percent and 0.15 percent, respectively. Spectrographic analyses 

also reveal that yttrium is one of the main REE contained in 

apatite, making the tailings a potential source for the yttriumgroup REE (McKeown and Klemic, 1956).

References Cited

Blake, W.P., 1858, Lanthanite and allanite in Essex County, 

N.Y.: American Journal of Science and Arts, Series 2, v. 26, 

no. 76, p. 245–246.

Kemp, J.F., 1908, The Mineville-Port Henry group, in Newland, 

D.H., and Kemp, J.F., Geology of the Adirondack magnetic 

iron ores: New York State Museum Bulletin 119, p. 57–88.

Lupulescu, Marion, and Pyle, Joseph, 2008, Mining history, 

mineralogy and origin of the gneiss (granite)-hosted Fe-PREE and Fe oxide and gabbro-hosted Ti-Fe oxide deposits 

from the Mineville-Port Henry Region, Essex County, NY, 

in Selleck, B.W., ed., Field trip guidebook for the 80th 

annual meeting of the New York State Geological Association: New York, N.Y., Guidebook-New York State 

Geological Association, v. 80, p. 117–129.

McKeown, F.A., and Klemic, Harry, 1956, Rare-earth-bearing 

apatite at Mineville, Essex County, New York: U.S. 

Geological Survey Bulletin 1046–B, p. 9–23.

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.
78 The Principal Rare Earth Elements Deposits of the United States

Wyoming—Bear Lodge Mountains

Location: Rare earth elements (REE)–thorium deposits are 

exposed in the southern Bear Lodge Mountains, about 8 

km (5 mi) northwest of Sundance, Crook County, Wyoming. Latitude: 44.49215 N., Longitude: 104.44133 W.; 

datum: WGS84

Deposit type and basic geology: The REE-thorium deposits and nearby gold mineralization of the southern Bear 

Lodge Mountains are hosted by middle Tertiary alkaline 

intrusions. These intrusions are Eocene (38.3−50 million 

years old) and consist primarily of phonolite and trachyte 

(Staatz, 1983). They intruded Paleozoic and Mesozoic 

sedimentary rocks, forming a dome about 13 km (8 mi) 

long by 10 km (6 mi) wide. Breccia bodies are associated 

with the igneous intrusions, such as a heterolithic diatreme breccia near Bull Hill. Rare earth elements–bearing 

carbonatite dikes intruded near the Bull Hill diatreme; the 

dikes are surrounded by a large zone of low-grade REE 

mineralization that fills thin, narrow stockwork fractures 

within the large alkaline intrusions. These thorium and 

REE deposits crop out throughout an area of about 16 

km2

 (6 mi2) (Staatz, 1983). The igneous core of the dome 

is microfractured and altered, thereby forming disseminated deposits. The REE and thorium mineralization 

precipitated within thin fractures as coatings and veinlets 

as much as 6 mm thick. The coatings and veinlets consist 

predominantly of iron and manganese oxide minerals, 

along with potassium feldspar and quartz. The REE and 

thorium are incorporated into the minerals monazite, 

thorite, and brockite.

Status: During the last few field seasons, Rare Element 

Resources, Ltd., has explored for REE (http://www.

rareelementresources.com/s/Home.asp), focused primarily on Bull Mountain (near the center of the dome) and 

areas just to the west and southeast of Bull Mountain, 

where numerous carbonatite dikes are exposed. The 

company drilled again in the summer months of 2010.

Production: No mineral resources have been produced from 

these vein deposits thus far (2010).

Estimated resources: Rare Element Resources, Ltd., has 

delineated three mineralogical zones in the Bear Lodge 

Mountain deposits dependent on depth of weathering—

oxide, transitional, and unoxidized. As of 2010, they 

estimate that the oxide zone—the near-surface part of the 

“Bull Hill deposit”—hosts 4.5 million tons at 4.3 percent 

REE oxides. They suggest that the total inferred resource 

of the deposit is 9.8 million tons averaging 4.1 percent 

REE oxides. During 2009, the company drilled five holes 

just northwest of Bull Mountain through a total of 5,141 

vertical feet of veins and dikes; there, total REE oxide 

concentrations ranged from 2.08 to 9.12 percent.

Detailed Discussion

Disseminated and vein rare earth elements (REE)–

thorium deposits are located in the southern Bear Lodge 

Mountains, about 8 km (5 mi) northwest of Sundance, Crook 

County, Wyoming. These REE deposits have been the focus 

of recent exploration and resource evaluation by Rare Element Resources, Ltd. (http://www.rareelementresources.

com/s/Home.asp). Three decades ago, the geology and 

thorium-REE resources of this district were studied by the 

USGS (Staatz, 1983). 

The REE-thorium deposits and nearby gold (Au) mineralization of the southern Bear Lodge Mountains are hosted 

by middle Tertiary alkaline intrusions. These intrusions are 

Eocene (38.3−50 million years old) and consist primarily of 

phonolite and trachyte (Staatz, 1983). They intruded Paleozoic and Mesozoic sedimentary rocks, forming a dome about 

13 km (8 mi) long by 10 km (6 mi) wide. The flanks of the 

central intrusive mass (phonolite and trachyte) are cut by small 

plugs, dikes, and sills that are also of alkaline affinity (high 

potassium and low silica content), which include lamprophyre, 

syenite, nepheline syenite, and latite. These alkaline igneous 

rocks crop out in a northwest-trending, oval-shaped area 9 km 

(5.6 mi) long by 4 km (2.5 mi) wide (Staatz and others, 1979; 

Staatz, 1983, his plate 1). Breccia bodies are associated with 

the igneous intrusions, such as a heterolithic diatreme breccia 

near Bull Hill. Rare earth elements–bearing carbonatite dikes 

also intruded near the Bull Hill diatreme; these dikes are surrounded by a large zone of low-grade REE mineralization that 

fills thin, narrow stockwork fractures within the large alkaline 

intrusions. These thorium and REE deposits crop out throughout an area of about 16 km2

 (6 mi2) in the southern Bear Lodge 

Mountains (Staatz, 1983).

The igneous core of the dome is microfractured and 

altered, thereby forming the disseminated deposits. REE and 

Th mineralization precipitated within thin fractures as coatings and veinlets as much as 6 mm thick. The coatings and 

veinlets consist predominantly of iron and manganese oxide 

minerals, along with potassium feldspar and quartz. The REE 

and thorium occupy sites in the minerals monazite, thorite, 

and brockite. On the basis of 52 samples collected within an 

area of 2.4 by 1.6 km (1.5 by 1 mi), where the alkaline rock 

has numerous small veinlets, Staatz and others (1979, p. 27) 

delineated three subareas:

“(1) The northern area has an average grade of 0.023 

percent ThO2

 and 0.75 percent combined rare-earth 

oxides, (2) the central area has an average grade of 

0.042 percent ThO2 and 1.71 percent combined rareearth oxides, and (3) the southern area has an average grade of 0.035 percent ThO2

 and 1.35 percent 

combined rare-earth oxides.”

They also noted that drilling “indicates that the veining 

extends at least 1,200 ft (365 m) below the surface.” 
Wyoming—Bear Lodge Mountains 79

In a broader sampling survey, Staatz (1983) collected a 

total of 341 samples throughout an area of 10.6 km2 (4.1 mi2) 

across the exposed core of the Bear Lodge dome (centered 

along Taylor Divide and Bull Hill). He found that the REE 

content of the disseminated deposits was about 27 times greater 

than their Th content. Staatz (1983, p. 1) reported, “Total rareearth content of these samples ranged from 47 to 27,145 ppm, 

and the thorium content from 9.3 to 990 ppm. The amount of 

total rare earths of individual samples shows little correlation 

with that of thorium.” Staatz (1983, p. 1) also stated,

“These deposits could be mined by open pit. The 

Bear Lodge disseminated deposits have one of the 

largest resources of both total rare earths and thorium in the United States, and although the grade of 

both commodities is lower than some other deposits, 

their large size and relative cheapness of mining 

make them an important future resource.”

Vein deposits in the southern Bear Lodge Mountains were 

defined by Staatz (1983) as all tabular bodies at least 5 cm (2 

in.) in thickness. Staatz (1983) mapped 26 veins in the core 

of the Bear Lodge uplift and described them all as thin and 

short—the longest vein is exposed for 137 m (450 ft). Gangue 

minerals are mostly potassium feldspar and quartz, with limonite, hematite, and manganese oxides. The REE and thorium 

in these veins is observed in monazite, brockite, and bastnasite. Staatz (1983, p. 1) reported, “Thorium content of 35 

[vein] samples ranged from 0.01 to 1.2 percent, and the total 

rare-earth content of 21 samples from 0.23 to 9.8 percent.”

Rare Element Resources, Ltd., has focused its recent REE 

exploration efforts (http://www.rareelementresources.com/s/

Home.asp) on Bull Mountain (near the center of the dome) and 

areas just to the west and southeast of Bull Mountain, where 

numerous carbonatite dikes are exposed. It has delineated three 

mineralogical zones in these deposits dependent on depth of 

weathering—oxide, transitional, and unoxidized (Ranta and 

Clark, 2010). As of 2010, they estimate that the oxide zone (the 

near-surface part of the “Bull Hill deposit”) hosts 4.5 million 

tons at 4.3 percent REE oxides. They suggest that the total 

inferred resource of the deposit is 9.8 million tons averaging 

4.1 percent REE oxides. During 2009, the company drilled five 

holes just to the northwest of Bull Mountain through a total of 

5,141 vertical feet of veins and dikes; there, total REE oxide 

concentrations ranged from 2.08 to 9.12 percent. The company 

drilled again in the summer of 2010, which will further update 

and refine its REE resource estimates for this district. The 

rare earth elements distribution in these deposits is apparently 

weighted toward light REE, as shown in table 22.

Rare Element Resources has focused on the oxide portions of 

the Bull Hill deposit because this material has displayed favorable 

recovery in its metallurgical testing (Ranta and Clark, 2010). The 

loose, friable character of this material and fine-grained nature of 

the REE minerals have reportedly shown a 90 percent recovery of 

REE with a 13 percent REE oxide grade in the less-than-25-mm 

(1-in.) fraction by employing a process using simple crushing to 

less than 1⁄4 in., scrubbing, and screening (Ranta and Clark, 2010).

References Cited

Ranta, Don, and Clark, Jim, 2010, Geology and evaluation of 

the Bear Lodge rare-earths project, Wyoming [unpublished 

abs.]: Presentation to the Denver Region Exploration Geologists’ Society, January 4, 2010, Lakewood, Colo.

Staatz, M.H., 1983, Geology and description of thorium and 

rare-earth deposits in the southern Bear Lodge Mountains, 

northeastern Wyoming: U.S. Geological Survey Professional Paper 1049–D, 52 p., 2 plates.

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.

Table 22. Typical rare earth elements distribution in the Bear 

Lodge Mountains deposit, Wyoming.

[Rare earth elements listed in order of increasing atomic number; yttrium (Y) is 

included with these elements because it shares chemical and physical similarities with the lanthanides. Elements listed in order of increasing atomic number. 

Each sample is a composite metallurgical sample. The most abundant rare earth 

elements in this deposit (in bold) are light rare earths elements. Source: Rare 

Element Resources, Ltd. (http://www.rareelementresources.com/s/Home.asp)]

Rare earth

element

Oxide sample

(percent)

Unoxidized sample

(percent)

Lanthanum 29.3 32.5 

Cerium 45.0 46.4 

Praseodymium 4.8 4.3 

Neodymium 16.8 13.7 

Samarium 2.0 1.4 

Europium 0.4 0.3 

Gadolinium 0.8 0.6 

Terbium 0.1 0.0 

Dysprosium 0.2 0.2 

Yttrium 0.5 0.5 

Total 99.9 99.9 
80 The Principal Rare Earth Elements Deposits of the United States

Phosphorite Deposits in the 

Southeastern United States

Location: Phosphorite deposits are found in the southeastern 

United States along the Atlantic Coastal Plain from North 

Carolina to the center of the Florida peninsula, forming a 

large phosphogenic province that has been subdivided into 

the Carolina Phosphogenic Province and the Florida Phosphogenic Province (Riggs, 1984). Phosphate deposits are 

also found in Virginia and Tennessee. Latitude: 27.58021 

N., Longitude: 81.94569 W.; datum: WGS84

Deposit type and basic geology: Cathcart (1949) identified 

three main types of phosphatic rock in Florida: landpebble phosphate, hard-rock phosphate, and river-pebble 

phosphate. Only the land-pebble deposits contain a 

substantial amount of uranium and, in some places, also 

contain rare earth elements. The most productive area 

of the land-pebble district is in Polk and Hillsborough 

Counties, which are located in the west-central part of the 

Florida peninsula and include the upper Tertiary Hawthorn 

Group and Bone Valley Formation. As such, mining of 

phosphate in Florida has been concentrated in this area 

(Cathcart and others, 1952). This region has been referred 

to more recently as the central Florida phosphate district 

(Van Kauwenberg and McClellan, 1990). 

Status: Mining for phosphate in Florida dates back to 1883 

in hard-rock deposits located near Hawthorne in Alachua 

County; the bulk of phosphorite is used for fertilizer. 

In 2009, 27.2 million metric tons (30 million tons) of 

phosphate rock were mined (Jasinksi, 2010), compared 

with 38.2 million metric tons (42.1 million tons) in 1973 

(Stowasser, 1975). According to Jasinski (2010, p. 118): 

“In 2009, U.S. phosphate rock production and reported 

usage were at their lowest point since the mid-1960s, 

and consumption was at its lowest level since the early 

1970s.” The sharp decline is partly the result of a global 

economic crisis that started in 2008 when phosphate 

fertilizer producers were left with high inventories of 

both phosphate rock and fertilizer as farmers held out for 

lower prices (Jasinksi, 2010). The Atlantic Coastal Plain 

deposits in Florida and North Carolina account for about 

85 percent of production; the majority of phosphate comes 

from Florida. 

Production: Rare earth elements have not been extracted as a 

byproduct from the phosphate deposits of the southeastern 

United States.

Estimated resources: No one has estimated the potential 

resource of rare earth elements in phosphate deposits in 

the southeastern United States. Analyses of phosphate 

rock from the Bone Valley Formation indicate that the rare 

earth elements yttrium (Y) and lanthanum (La) are present 

(McKelvey and others, 1951). Samples from the Noralyn 

mine ranged from 0.01 to 0.1 percent Y, while those from 

the Bonny Lake mine varied from 0.001 to 0.01 percent 

Y. Although only one of the Bonny Lake mine samples 

contained La, all of the samples from the Noralyn mine 

contained 0.001 to 0.01 percent La.

Detailed Discussion

Phosphorite deposits are found in the southeastern United 

States along the Atlantic Coastal Plain from North Carolina 

to the center of the Florida peninsula, forming a large phosphogenic province that has been subdivided into the Carolina Phosphogenic Province and the Florida Phosphogenic 

Province (Riggs, 1984). Phosphate deposits are also found in 

Virginia and Tennessee. Mining for phosphate in Florida dates 

back to 1883 in hard-rock deposits located near Hawthorne 

in Alachua County (Florida Institute of Phosphate Research 

(FIPR), 2010); the bulk of phosphorite is used for fertilizer. 

In 2009, 27.2 million metric tons (30 million tons) of phosphate rock were mined (Jasinksi, 2010), compared with 38.2 

million metric tons (42.1 million tons) in 1973 (Stowasser, 

1975). According to Jasinski (2010, p. 118): “In 2009, U.S. 

phosphate rock production and reported usage were at their 

lowest point since the mid-1960s, and consumption was at its 

lowest level since the early 1970s.” The sharp decline is partly 

the result of a global economic crisis that started in 2008 when 

phosphate fertilizer producers were left with high inventories 

of both phosphate rock and fertilizer as farmers held out for 

lower prices (Jasinksi, 2010). In addition, the richest orebodies 

in Florida have been depleted, resulting in massive consolidation of phosphate mining companies in the State. The Atlantic 

Coastal Plain deposits in Florida and North Carolina account 

for about 85 percent of production, and the majority of phosphate comes from Florida.

Cathcart (1949) identified three main types of phosphatic 

rock in Florida: land-pebble phosphate, hard-rock phosphate, 

and river-pebble phosphate. Only the land-pebble deposits 

contain a substantial amount of uranium and, in some places, 

also contain rare earth elements (REE). Historically, the most 

productive area of the land-pebble district occurs in Polk and 

Hillsborough Counties, which are located in the west-central 

part of the Florida peninsula, and which contain the Hawthorn 

Group and Bone Valley Formation. As such, mining of phosphate in Florida, which began in 1888, has been concentrated 

in this area (Cathcart and others, 1952). This region has been 

referred to more recently as the central Florida phosphate district (Van Kauwenberg and McClellan, 1990). As time passed, 

the mining became more concentrated in the Four Corners 

Area (southwest of Orlando), as operations moved down dip 

to the south and west.

The central Florida platform, or phosphate district, is 

a shield-shaped area (fig. 17) that is about 7,252 km2 (2,800 

mi2) and includes Polk, Hillsborough, Hardee, Manatee, 

Sarasota, DeSoto, and Highland Counties (Cathcart, 1949). 

The middle Miocene Hawthorn Group is found throughout 

the entire Florida peninsula, except within the Ocala High (or 

“Ocala Upland”) and the Sanford High. The Hawthorn Group 
Phosphorite Deposits in the Southeastern United States 81

Mid-Carolina

Platform High

Ocala

High

Carolina

Phosphogenic

Province

2000 m

2000 m

700 m

100 m 

700 m 

100 m

200 m

Florida

Phosphogenic

Province

200 m

Bahama

Banks

200 m

700 m

Blake Plateau

Atlantic Ocean

Hatteras

Embayment

Miocene upland areas

Phosphogenic provinces

Southeast

Georgia

Embayment

82° 78° 74°

28°

36°

NORTH CAROLINA

GEORGIA

FLORIDA

SOUTH

CAROLINA

Figure 17. Phosphogenic provinces of the southeastern United States. Modified from Van Kauwenbergh 

and McClellan (1990).
82 The Principal Rare Earth Elements Deposits of the United States

contains considerable phosphorite (Riggs, 1980). A preliminary investigation report by Cathcart and others (1952) divides 

the Hawthorn Group into three lithologic units: a lowermost 

unit containing dolomite, phosphatic marls, limestone, and 

clay and quartz sands; a middle series of interbedded phosphatic sands, clays, and sandy clays; and an uppermost unit 

consisting of dolomites and dolomitic limestone. In general, 

the phosphorite grains range in size from less than 0.1 mm to 

10 cm (0.0039 to 3.937 in.) in diameter. 

Uncomformably overlying the Hawthorn Group, the 

Bone Valley Formation contains phosphate that is typically a 

higher grade, most likely the result of mechanical reworking 

and subsequent precipitation during the Pliocene (Cathcart, 

1949). As a result, the Bone Valley Formation is a lithochemical sequence in which the phosphorite appears sporadically 

in irregular concentration and distribution (Riggs, 1980). The 

formation consists of a lower zone of poorly sorted clay, silt, 

sand, and gravel (Cathcart and others, 1952). Nearly all the 

gravel in this unit, as well as a large part of the sand and clay, 

is phosphate, specifically carbonate-fluorapatite (Cathcart 

and others, 1952; Altschuler and others, 1952). The rest of 

the sand consists of quartz, with minor amounts of feldspar 

and trace amounts of ilmenite, zircon, tourmaline, staurolite, 

and other minerals. The clay minerals include palygorskite, 

montmorillonite, and kaolinite. The minerals in the upper 

zone of the Bone Valley Formation are quartz sand, wavellite 

and pseudowavellite (aluminum phosphates), crandallite, and 

kaolinite.

Uranium (U) in the Bone Valley Formation has a maximum concentration of 0.02 percent uranium in the basal 

section and an average concentration of about 0.01 percent 

uranium (Cathcart, 1949). In the Hawthorn Group, there is a 

low content of uranium in fresh, unweathered material. However, after leaching, the phosphate-rich rocks of the Hawthorn 

Group yield a maximum of 0.01 percent U. In Manatee and 

Hardee Counties, which are south of the high-grade district, 

only minor amounts of uranium occur in the Bone Valley, 

Hawthorn, and overlying Pleistocene sand formations.

In addition to uranium, semiquantitative spectrographic 

analyses on phosphate rock from the Bone Valley Formation 

indicate that the rare earth elements yttrium (Y) and lanthanum (La) are present (McKelvey and others, 1951). Samples 

from the decommissioned Noralyn mine range from 0.01 to 

0.1 percent Y while those from the decommissioned Bonny 

Lake mine range from 0.001 to 0.01 percent Y. Although 

only one of the Bonny Lake mine samples contains La, all 

of the samples from the Noralyn mine contain 0.001 to 0.01 

percent La.

Several metals are also present in nearly all samples from 

the Bone Valley Formation such as vanadium, manganese, 

chromium, barium, strontium, and titanium, with concentrations that range from 0.01 to 0.1 percent (McKelvey and 

others, 1951). Nickel, copper, zirconium, and lead are also 

present in amounts greater than 0.001 percent. The Bonny 

Lake mine samples contain 0.001 to 0.01 percent tin whereas 

those from the Noralyn mine contain 0.0001 to 0.001 percent. 

McKelvey and others (1951) also report gallium in all samples 

from the two mines.

Although the distribution of the metals is unknown, the 

REE, U, Ba, and Sr are most likely located in the carbonatefluorapatite (francolite) lattice or absorbed on its surface 

(Cathcart and others, 1952; Clarke and Altschuler, 1958). In 

addition, because of the small quantities of the various elements, recovery may be possible only when ore is taken into 

acid solution. More recent research regarding the rare earth 

geochemistry of phosphorites suggests that the two main 

factors influencing REE concentrations in marine sedimentary phosphates are primary compositional differences and 

postdepositional processes such as diagenesis, the removal 

of mineral species, and reworking of deposits by winnowing action (Van Kauwenbergh and McClellan, 1990). While 

the North Carolina phosphorites appear to be unaltered, 

the Florida phosphorites have undergone postdepositional 

alteration through the removal of carbonate mineral species, 

systematic decarbonatization of francolite, deposition of iron 

and aluminum phosphates and of clay minerals in alteration 

profiles.

MacArthur and Walsh (1984) determined that the abundance of REE in francolite reflects the REE source and mechanism of incorporation. Zanin and Zamirailova (2009) suggested that the REE concentrations of supergene phosphorites 

are the result of weathering, the physicochemical conditions of 

phosphorite formation, presence of a biogenic component, and 

structural type of the phosphorites. In particular, phosphorite 

from the weathering zone of sedimentary rocks, such as those 

that are found in Florida and Tennessee, yield an average total 

REE content of 27 ppm (Zanin and Zamirailova, 2009).

Further research on the REE and trace metal contents 

of Florida phosphorites is critical to more fully assessing its 

viability as an economic resource. Additional REE and trace 

metal work on the North Carolina phosphorites is also warranted, as little has been reported at this point.

References Cited

Altschuler, Z.S., Cisney, E.A., and Barlow, I.H., 1952, X-ray 

evidence of the nature of carbonate-apatite: Bulletin of the 

Geological Society of America, v. 63, p. 1230–1231.

Cathcart, J.B., 1949, Distribution of uranium in the Florida 

phosphate field: U.S. Geological Survey Trace Elements 

Investigations Report 85, 18 p.

Cathcart, J.B., Blade, L.V., Davidson, D.F., and Ketner, K.B., 

1952, The geology of the Florida land-pebble phosphate 

deposits: U.S. Geological Survey Trace Elements Investigations Report 265, 21 p.

Clarke, R.S., Jr., and Altschuler, Z.S., 1958, Determination of 

the oxidation state of uranium in apatite and phosphorite 

deposits: Geochimica et Cosmochimica Acta, v. 13, 

p. 127–142.
Phosphorite Deposits in the Southeastern United States 83

Florida Institute of Phosphate Research (FIPR), 2010, 

accessed September 8, 2010, at http://www.fipr.state.fl.us/

research-area-mining.htm#History.

Jasinski, S.M., 2010, Phosphate rock: U.S. Geological Survey 

Mineral Commodity Summaries 2010, p. 118–119, accessed 

October 6, 2010, at http://minerals.usgs.gov/minerals/pubs/

commodity/phosphate_rock/mcs-2010-phosp.pdf.

McArthur, J.M., and Walsh, J.N., 1984, Rare-earth geochemistry of phosphorites: Chemical Geology, v. 47, p. 191–220.

McKelvey, V.E., Cathcart, J.B., and Worthing, H.W., 1951, 

Preliminary note on the minor-metal content of Florida 

phosphate rock: U.S. Geological Survey Trace Elements 

Memorandum Report 236, 6 p.

Riggs, S.R., 1980, Intraclast and pellet phosphorite sedimentation in the Miocene of Florida: Journal of the Geological 

Society, v. 137, p. 741–748.

Riggs, S.R., 1984, Paleoceanographic model of Neogene 

phosphorite deposition, U.S. Atlantic Continental Margin: 

Science, v. 223, no. 4632, p. 123–131.

Stowasser, W.F., 1975, Phosphate rock, in Minerals Yearbook 

1973, v. 1, Metals, Minerals, and Fuels: U.S. Bureau of 

Mines, p. 1019–1035.

Van Kauwenbergh, S.J., and McClellan, G.H., 1990, Comparative geology and mineralogy of the southern United States 

and Togo phosphorites: Geological Society of London, 

Special Publications, v. 52, p. 139–155.

Zanin, Y.N., and Zamirailova, A.G., 2009, Rare earth elements in supergene phosphorites: Geochemistry International, v. 47, p. 282–296.
84 The Principal Rare Earth Elements Deposits of the United States

Placer Rare Earth Elements Deposits

Placer deposits are sand, silt, and cobble-size sediments 

deposited in streams, rivers, and beaches, also referred to as 

“alluvial” deposits. Globally and in the United States, alluvial accumulations of monazite are a valuable type of rare 

earth elements (REE)–thorium (Th) deposit. For example, 

the alluvial monazite deposits of the Coastal Belt of southernmost India are thought to represent one of the largest 

thorium resources in the world. The monazite deposits 

of southern India contain detrital heavy minerals and are 

found in piedmont lakes, shallow seas, parts of the beaches 

(fig. 18), sand bars across the mouth of rivers, deltas, and 

sand dunes behind the beaches (Bhola and others, 1958). A 

study by Mahadevan and others (1958) estimated that the 

beach sands of the southwestern coast of India alone contain 

estimated reserves of 446,400 metric tons (492,200 tons) of 

monazite, in which the ThO2 content of the monazite ranges 

from 7.5 to 9 percent.

Monazite’s resistance to chemical weathering and high 

specific gravity account for its association in alluvial (placer) 

deposits with other resistant heavy minerals such as ilmenite, 

magnetite, rutile, and zircon. Monazite weathers from alkaline 

crystalline rocks of the surrounding region and is transported 

downstream and deposited by alluvial processes. 

In the United States, alluvial deposits of monazite 

are known in the Carolina Piedmont of North and South 

Carolina, the beach deposits of northeastern Florida through 

southeastern Georgia, and the intermontane valleys of Idaho. 

In the past, these unconsolidated stream deposits were mined 

by small-scale sluices (Idaho and North and South Carolina) 

and dredges (Idaho); beach sands were mined by large shovels 

(Florida and Georgia). Sluicing instantly produces a heavymineral separate, but even in the case of the dredge or shovel 

operations, the heavy-mineral separation was still performed 

at the site. Thus, the mining of REE and thorium from alluvial 

deposits has the advantages of relative ease of mining and 

rapid mineral separation, in contrast to hard-rock mining. 

Another benefit of placer deposits is the potential for coproducts. Coproducts can include REE and thorium obtained from 

monazite; titanium from ilmenite and rutile; iron from magnetite; zirconium and hafnium from zircon; and industrial-grade 

garnet, staurolite, tourmaline, kyanite, and sillimanite, which 

are used as abrasives and refractory minerals.

The three monazite placer districts highlighted in this 

report—North and South Carolina stream deposits, FloridaGeorgia beaches, and Idaho stream deposits—are the largest 

volume alluvial REE-thorium deposits known in the United 

States. The geology and estimated monazite resources of these 

districts have been well described by Staatz and others (1979, 

the North and South Carolina placer deposits, p. 33–39) and 

Staatz and others (1980, the Idaho stream placers, p. 9–18, and 

the Florida beach deposits, p. 3–9); numerous references cited 

therein provide more detailed information on these deposits. 

Thus, here we only briefly summarize the findings of these 

earlier studies.

Figure 18. Heavy-mineral layers (“black sand”) in a quartz beach sand, Chennai, India. A penny 

provides a scale. (Photograph by Mark A. Wilson, Department of Geology, The College of Wooster, 

Wooster, Ohio; used with permission.)
Placer Rare Earth Elements Deposits 85

References Cited

Bhola, K.L., Chatterji, B.D., Dar, K.K., Mahadevan, C., 

Mahedevan, V., Mehta, N.R., Handi, N., Nanhi, H., Narayandas, G.R., Sahasrabudhe, G.H., Shirke, V.G., and Udas, G.R., 

1958, A survey of uranium and thorium occurrences in India, 

in Proceedings of the Second United Nations International 

Conference on the Peaceful Uses of Atomic Energy, Geneva, 

Switzerland, September 1–13, 1958—Volume 2, Survey of 

raw material resources: Geneva, United Nations Publication, 

p. 100–102.

Mahadevan, V., Narayana Das, G.R., and Nagaraja Roa, N., 

1958, Prospecting and evaluation of beach placers along 

the Coastal Belt of India, in Proceedings of the Second 

United Nations International Conference on the Peaceful 

Uses of Atomic Energy, Geneva, Switzerland, September 

1–13, 1958—Volume 2, Survey of raw material resources: 

Geneva, United Nations Publication, p. 103–106.

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.
86 The Principal Rare Earth Elements Deposits of the United States

Idaho—Placer Deposits

Location: At least 11 monazite-bearing placer districts exist 

in the valleys of a region extending north of Boise, 

Idaho, and along the western flank of the Idaho batholith. 

Latitude: 44.40416 N., Longitude: 115.35356 W.; datum: 

WGS84

Deposit type and basic geology: Monazite-bearing alluvial 

stream deposits (placers) exist in the valleys of a region 

that extends north of Boise, Idaho along the western flank 

of the Idaho batholith. The primary source of the resistant 

rare earth elements (REE)–thorium-bearing minerals in 

the Idaho placers is thought to be the Idaho batholith, 

in particular the quartz monzonite and pegmatite phases 

of the batholith (Mackin and Schmidt, 1957). The most 

common heavy minerals in the alluvial deposits (in generally decreasing amounts) are ilmenite, magnetite, sphene, 

garnet, monazite, euxenite, zircon, and uranothorite 

(uranium-rich thorite). In addition to REE and thorium 

from monazite and euxenite, the Idaho placer deposits 

(and the abandoned historic dredge waste piles) contain 

coproducts of titanium (in ilmenite), and niobium and 

tantalum (in euxenite).

Status: Currently (2010), there is no active exploration in this 

district.

Production: In the 1950s, two areas of west-central Idaho 

were mined by dredges for monazite, Long Valley and 

Bear Valley. Beginning in September 1950, Long Valley 

was worked by three dredges that had earlier been used 

to recover gold but later were converted (with assistance 

from the U.S. Bureau of Mines under the sponsorship of 

the U.S. Atomic Energy Commission) to recover monazite. The history of these dredging operations is described 

by Argall (1954) and Staatz and others (1980, p. 9–16, 

and references cited therein). During this 5-year period, 

Staatz and others (1980) estimated that the three dredges 

recovered 6,430 metric tons (7,085 tons) of monazite 

containing 269 metric tons (297 tons) of thorium oxide. 

Dredging ended here in mid-1955, when the government 

stockpile order was fulfilled. The Bear Valley placers 

were worked by first one dredge in 1955, then a second 

in 1956, with the intent to recover Nb and Ta for another 

Federal government contract. According to Staatz and 

others (1980, p. 10), “from alluvium of Bear Valley, 2,049 

short tons [1,858 metric tons] of euxenite, 83.5 tons [75.7 

metric tons] of columbite, and 54,862 tons [49,760 metric 

tons] of ilmenite were recovered.” No records of monazite 

recovery were kept.

Estimated resources: U.S. Geological Survey geologists 

(Staatz and others, 1980) extensively reviewed results of 

the 1950s government dredging program in central Idaho. 

They determined that the five most important monazite 

districts are Long Valley, Bear Valley, the Boise Basin, 

the Burgdorf-Warren area, and the Elk City–Newsome 

area. The reported thorium oxide contents of monazite in 

the Idaho placer deposits range from 2.2 to 6.24 percent. 

The few analyses of REE in monazites from Idaho placers 

indicate that these monazites contain 63 percent total REE 

oxides Staatz and others (1980). Staatz and others (1980) 

calculated thorium reserves for each of the five major 

placer districts individually; in total, the five districts have 

total reserves of about 9,130 metric tons (10,060 tons) of 

thorium oxide. The REE resources of the five placer districts would presumably be at least ten times the thorium 

resource, because the typical monazite contains about 63 

percent total REE oxides and 2.2–6.24 percent thorium 

oxide.

Detailed Discussion

At least 11 monazite-bearing placer districts exist in 

the valleys of a region extending north of Boise, Idaho, and 

along the western flank of the Idaho batholith (fig. 19). Monazite was first recognized here in 1896 as the heavy, yellow 

to brownish-yellow mineral that collected with other heavy 

minerals and gold within the sluice boxes of gold placer 

operations in the Boise Basin near Idaho City, Centerville, 

and Placerville (Lindgren, 1897). In 1909, a mill designed to 

capture the monazite was built by the Centerville Mining and 

Milling Co. Only a small amount of monazite concentrate 

was produced for its thorium content before the mill burned 

down in a forest fire in 1910.

In the 1950s, two areas of west-central Idaho were mined 

by dredges for monazite recovery, Long Valley and Bear 

Valley (figs. 19 and 20). Beginning in September 1950, Long 

Valley was worked by three dredges that were earlier used to 

recover gold but later were converted (with assistance from 

the U.S. Bureau of Mines under the sponsorship of the U.S. 

Atomic Energy Commission) to recover monazite. The history 

of these dredging operations is described by Argall (1954) and 

Staatz and others (1980, p. 9–16, and references cited therein). 

The heavy minerals recovered in the Long Valley district 

were dominated by ilmenite (84 percent of heavy minerals), 

followed by monazite (8 percent), garnet (5 percent), and 

zircon (3 percent). During this 5-year period, Staatz and others 

(1980) estimated that the three dredges recovered 6,430 metric 

tons (7,085 tons) of monazite containing 269 metric tons 

(297 tons) of thorium oxide. The dredging ended here in mid1955, when the government stockpile order was fulfilled.

Rare earth elements (REE) and thorium were also 

unintentionally recovered within the minerals euxenite and 

monazite from the Bear Valley placers. The Bear Valley placers were worked by first one dredge in 1955, then a second 

in 1956, with the intent to recover Nb and Ta for another 

Federal government contract. According to Staatz and others 

(1980, p. 10), “from alluvium of Bear Valley, 2,049 short 

tons [1,858 metric tons] of euxenite, 83.5 tons [75.7 metric 

tons] of columbite, and 54,862 tons [49,760 metric tons] of 

ilmenite were recovered.” No records of the monazite 

recovery were kept.
Idaho—Placer Deposits 87

42°

43°

44°

45°

46°

47°

48°

49°

117° 116°

115°

114°

113° 112°

8

5

6

4

1

3

11

10

2 7

9

IDAHO

Boise

EXPLANATION

 1 Long Valley

 2 Bear Valley

 3 Boise Basin

 4 Burgdorf Warren area

 5 Elk City–Newsome area

 6 Dixie-Florence area

 7 Stanley Basin

 8 Clearwater River

 9 Salmon River

10 Rock Creek–Camp Creek area

11 Dismal Swamp 

Monazite placer districts

3 Placer locality and number

Approximate boundary of

Idaho batholith

0

0 50 100 150 KILOMETERS

50 100 MILES

Figure 19. Generalized map of known monazite placer districts in Idaho. From Staatz 

and others (1980).
88

The Principal Rare Earth Elements Deposits of the United States

Figure 20. Porter Brothers dredge in Bear Valley, Idaho, worked columbium (now called niobium)-tantalum placer deposits. This dredge operated from 1955 to 1960; exact date of photograph is unknown. Monazite was produced as a byproduct from these placer deposits. (Photograph from Savage (1961, fig. 13); used with permission of Idaho Geological Survey.)
Idaho—Placer Deposits 89

Most of the Idaho monazite resource data used by Staatz 

and others (1980) came from a 1950s program in which the 

U.S. Atomic Energy Commission funded the U.S. Bureau of 

Mines to identify new domestic monazite reserves (Storch and 

Holt, 1963). The USGS (Staatz and others, 1980) extensively 

reviewed results of this program, as attested by U.S. Bureau 

of Mines literature, interviews with former dredge companies, and field reconnaissance and sampling of the major 

monazite placer districts in Idaho. They determined that the 

five most important monazite districts are Long Valley, Bear 

Valley, the Boise Basin, the Burgdorf-Warren area, and the Elk 

City–Newsome area. The reported thorium oxide contents of 

monazite in the Idaho placer deposits range from 2.2 to 6.24 

percent. The few analyses of REE in monazites from Idaho 

placers indicated that these monazites contain 63 percent total 

REE oxides Staatz and others (1980). Staatz and others (1980) 

calculated thorium reserves for each of the five major placer 

districts individually; in total, the five districts have total 

reserves of about 9,130 metric tons (10,060 tons) of thorium 

oxide.The REE resources of the five placer districts would 

presumably be at least 10 times the thorium resource, because 

the typical monazite contains about 63 percent total REE 

oxides and 2.2–6.24 percent thorium oxide.

The primary source of the resistant REE-thorium−

bearing minerals in the Idaho placers is thought to be the 

Idaho batholith, in particular the quartz monzonite and pegmatite phases of the batholith (Mackin and Schmidt, 1957). 

The most common heavy minerals in the alluvial deposits (in 

generally decreasing amounts) are ilmenite, magnetite, sphene, 

garnet, monazite, euxenite, zircon, and uranothorite (uraniumrich thorite). In addition to REE and thorium from monazite 

and euxenite, the Idaho placer deposits (and the abandoned 

historic dredge waste piles) contain coproducts of titanium (in 

ilmenite), and niobium and tantalum (in euxenite). 

References Cited

Argall, G.O., Jr., 1954, New dredging techniques recover 

Idaho monazite: Mining World, v. 16, no. 2, p. 26–30.

Lindgren, W., 1897, Monazite from Idaho: The American 

Journal of Science, Fourth Series, v. 4, p. 63–64.

Mackin, J.H., and Schmidt, D.L., 1957, Uranium and 

thorium-bearing minerals in placer deposits in Idaho: 

Idaho Bureau of Mines and Geology, Mineral Resources 

Report 7, 9 p.

Savage, C.N., 1961, Economic geology of central Idaho blacksand placers: Idaho Bureau of Mines and Geology Bulletin 

17, 160 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.

Storch, R.H., and Holt, D.C., 1963, Titanium placer deposits 

of Idaho: U.S. Bureau of Mines Report of Investigations 

No. 6319, 69 p.
90 The Principal Rare Earth Elements Deposits of the United States

North and South Carolina—Placer 

Deposits

Location: The high-grade monazite placers of the Piedmont of 

North Carolina and South Carolina are deposited between 

the Catawba River in the northeast and the Savannah River 

in the southwest, along a belt that extends from eastcentral Virginia southwestward into Alabama. Latitude: 

33.40277 N., Longitude: 81.79004 W.; datum: WGS84

Deposit type and basic geology: Monazite-bearing alluvial 

stream deposits (placers) exist in the valleys of the Piedmont of North Carolina and South Carolina. The streamsediment deposits in this region are generally consistent 

in character; the heavy-mineral concentrations are greatest 

in the headwaters areas. The alluvium is deposited in flat 

valleys, forming well-bedded, poorly graded layers of 

unconsolidated sediment. Stacked layers contain gravel, 

sand, clay, and clayey silt, at an average total thickness 

of about 4.5 m (15 ft) (Staatz and others, 1979). Monazite typically is found in all units, but it is generally most 

abundant in the basal gravel layers and least abundant in 

the clay layers. According to Staatz and others (1979), 

the heavy-mineral content of the placer deposits of the 

Piedmont region ranges from 0.15 to 2.0 percent; monazite makes up about 3.5–13 percent of the heavy minerals. 

Other parts of the heavy-mineral fraction include ilmenite, 

20–70 percent; garnet, 2–50 percent; rutile, 0.3–7 percent; 

zircon, trace to 14 percent; and sillimanite and kyanite 

together, trace to 20 percent. In some placers, additional 

heavy minerals include epidote, magnetite, xenotime, 

tourmaline, sphene, staurolite, andalusite, and an unidentified black radioactive mineral (Staatz and others, 1979). 

Analysis of 52 samples of alluvial monazite from this 

region (Mertie, 1975) found that the monazite contains 

60–63 percent total rare earth elements (REE) oxides and 

2.5–7.8 percent thorium oxide content, with a mean value 

of 5.67 percent thorium. 

Status: Currently (2010), there is no reported exploration in 

this region. 

Production: In 1887, a few short tons of monazite were 

produced from stream deposits in the Piedmont region of 

North and South Carolina, giving this region the distinction of being the world’s first supplier of thorium (Olson 

and Overstreet, 1964). Monazite-bearing placers of this 

region were worked by small-scale sluice operations from 

1887 to 1911 and 1915 to 1917; they produced a total of 

4,973 metric tons (5,483 tons) of monazite (Overstreet 

and others, 1968). Monazite mining ended here in 1917 

because beach deposits in India and Brazil were producing thorium at lower cost. 

Estimated resources: For the 13 largest placer deposits of 

the Piedmont region of North and South Carolina, Staatz 

and others (1979) estimated total reserves of about 4,800 

metric tons (5,300 tons) of thorium oxide and potential 

thorium resources seven times as high. Using mean concentrations of REE oxides (60–63 percent) and thorium 

oxide (5.67 percent) found in monazite from these placer 

deposits, a REE resource of roughly 53,000 metric tons 

(58,400 tons) of REE oxide is suggested. 

Detailed Discussion

In 1887, a few short tons of monazite were produced 

from stream deposits in the Piedmont region of North and 

South Carolina, giving this region the distinction of being the 

world’s first supplier of thorium (Olson and Overstreet, 1964). 

Monazite-bearing placers of this region were worked by 

small-scale sluice operations from 1887 to 1911 and 1915 to 

1917; they produced a total of 4,973 metric tons (5,483 tons) 

of monazite (Overstreet and others, 1968). Monazite mining 

ended here in 1917, not because reserves had been exhausted 

but rather because the beach deposits of India and Brazil were 

producing thorium at lower cost. 

The high-grade monazite placers of the Piedmont of 

North Carolina and South Carolina are deposited between the 

Catawba River in the northeast and the Savannah River in the 

southwest (fig. 21), along a belt that extends from east-central 

Virginia southwestward into Alabama (Mertie, 1975). The 

stream-sediment deposits in this region are generally consistent in character; the heavy-mineral concentrations are greatest 

in the headwaters areas. The alluvium is deposited in flat valleys, forming well-bedded, poorly graded layers of unconsolidated sediment. Stacked layers contain gravel, sand, clay, and 

clayey silt, at an average total thickness of about 4.5 m (15 ft) 

(Staatz and others, 1979). Monazite typically is found in all 

units, but it is generally most abundant in the basal gravel layers and least abundant in the clay layers. 

The Piedmont region is underlain by crystalline, highgrade metamorphic rocks intruded by quartz monzonite and 

pegmatite. The monzonite and pegmatite intrusions may be 

monazite bearing or monazite free. Overstreet (1967) suggested that the primary source of the alluvial monazite was 

the high-grade metamorphic rocks, particularly sillimanite 

schist. Other metamorphic rocks in the area include mica and 

hornblende gneisses, amphibolites, and additional varieties 

of schist (Mertie, 1975). Other igneous country rocks include 

diorite, rhyolite with associated pyroclastic rocks, gabbro, 

diabase, ultrabasic rocks, and several kinds of granite, such as 

monzonite, quartz monzonite, and granodiorite. 

Various rivers carried monazite and other heavy minerals 

eastward from the Piedmont region, such that all the regions 

in the Coastal Plain may have also received various amounts 

of heavy minerals (Staatz and others, 1979). In particular, 

the Late Cretaceous Tuscaloosa Formation received a large 

amount of monazite, albeit widely dispersed. Although 

this area has not been as well explored as the Piedmont, it 

is known that the Tuscaloosa directly overlaps the crystalline rocks of the Piedmont and that streams in the area have 

reworked the Tuscaloosa sand so that in places heavy-mineral 
North and South Carolina—Placer Deposits 91

80 KILOMETERS

0 50 MILES

0

NORTH CAROLINA

SOUTH CAROLINA

Charlotte

Asheville

Gaffney

Columbia

Aiken

Laurens

Greenville

Anderson

GEORGIA

NORTH CAROLINA

TENNESSEE

River

FALL

LINE

Savannah

River

River

Broad

Saluda

Enoree

Tyger

River

River

River

Pacolet

Shelby

Monazite placers

Catawba

River

Horse

Creek

34o

35o

36o

83o 82o 81o 80o

Figure 21. Map of monazite placers of North Carolina and South Carolina. Modified from Staatz and others (1979).
92 The Principal Rare Earth Elements Deposits of the United States

placers containing monazite have been identified (Staatz and 

others, 1979). The best-known placer is Horse Creek, which 

is southwest of Aiken, South Carolina, and was the site of 

the first large-scale mining of stream placers for monazite 

and other heavy minerals in the Carolinas. Dredging in this 

area between the summers of 1955 and 1958 (Williams, 

1967) found heavy-mineral contents of about 1−1.5 percent, 

of which fraction monazite formed about 8 percent (Mertie, 

1975). Overall, these dredging operations recovered monazite, 

ilmenite, rutile, zircon, and staurolite (Williams, 1967).

According to Staatz and others (1979), the heavy-mineral 

content of the placer deposits of the Piedmont region ranges 

from 0.15 to 2.0 percent, and monazite forms about 3.5–13 

percent of the heavy minerals. Other parts of the heavymineral fraction contain ilmenite, 20–70 percent; garnet, 2–50 

percent; rutile, 0.3–7 percent; zircon, trace to 14 percent; and 

sillimanite and kyanite together, trace to 20 percent. In some 

placers, additional heavy minerals include epidote, magnetite, xenotime, tourmaline, sphene, staurolite, andalusite, and 

an unidentified black radioactive mineral (Staatz and others, 

1979). Analysis of 52 samples of alluvial monazite from this 

region (Mertie, 1975) found that the monazite contains 60–63 

percent total REE oxides and 2.5–7.8 percent (mean, 5.67 

percent) thorium oxide. 

The Fall Line is the sharp topographic break that marks 

the boundary between the Piedmont and the Coastal Plain 

(fig. 21). East of the Fall Line, the heavy-mineral distribution 

in two deposits (the only ones for which data are available) 

shows several differences from that of the Piedmont. First, 

the abundance of staurolite increases to 7 and 38 percent of 

the two deposits (Kline and others, 1954, p. 27; Mertie, 1975, 

p. 27). Rutile and zircon are also more abundant in these 

deposits than in the Piedmont placers; rutile makes up 15 and 

10 percent of the heavy-mineral content and zircon 19 and 11 

percent. However, monazite concentrations are similar to those 

in placers in the Piedmont.

For the 13 largest placer deposits of the Piedmont region 

of North and South Carolina, Staatz and others (1979) estimated total reserves of about 4,800 metric tons (5,300 tons) 

of thorium oxide, with potential thorium resources seven 

times as high. However, using the mean concentrations of 

REE oxides (60–63 percent) and thorium oxide (5.67 percent) 

found in monazite from these placer deposits, a REE resource 

of roughly 53,000 metric tons (58,400 tons) of REE oxide 

is suggested. The estimate of Staatz and others (1979) was 

based on regional monazite resource studies by Overstreet 

and others (1959) and Overstreet (1967), and on studies of 

individual drainage basins by several others (see Staatz and 

others, 1979, p. 37). Future exploration for monazite placer 

deposits in the Mid-Atlantic region can be aided by regional 

stream-sediment geochemistry datasets assembled by the 

USGS (Grosz, 1993).

References Cited

Grosz, A.E., 1993, Use of geochemical surveys in Ti-Hf-REETh-U placer exploration—A mid-Atlantic-States example 

(Chapter R), in Scott, R.W., Jr., Detra, P.S., and Berger, 

B.R., eds., Advances related to United States and international mineral resources—Developing frameworks and 

exploration technologies: U.S. Geological Survey Bulletin 

2039, p. 181–188.

Kline, M.H., Griffith, R.F., and Hansen, L.A., 1954, Hollow 

Creek monazite placer, Aiken County, South Carolina: U.S. 

Atomic Energy Commission Report RME–3127, 29 p.

Mertie, J.B., Jr., 1975, Monazite placers in the southeastern 

Atlantic States: U.S. Geological Survey Bulletin 1390, 41 p.

Olson, J.C., and Overstreet, W.C., 1964, Geologic distribution 

and resources of thorium: U.S. Geological Survey Bulletin 

1204, 61 p.

Overstreet, W.C., 1967, The geologic occurrence of monazite: 

U.S. Geological Survey Professional Paper 530, 327 p., 2 

plates.

Overstreet, W.C., Theobald, P.K., Jr., and Whitlow, J.W., 1959, 

Thorium and uranium resources in monazite placers of the 

western Piedmont, North and South Carolina: Mining 

Engineering, v. 11, no. 7, p. 709–714.

Overstreet, W.C., White, A.M., Whitlow, J.W., Theobald, 

P.K., Jr., Caldwell, D.W., and Cuppels, N.P., 1968, Fluvial 

monazite deposits in the southeastern United States: U.S. 

Geological Survey Professional Paper 568, 85 p., 9 plates.

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.

Williams, Lloyd, 1967, Heavy minerals in South Carolina: 

Columbia, S.C., South Carolina State Development Board, 

Division of Geology, Bulletin No. 35, 35 p.
Florida-Georgia—Beach Placer Deposits 93

Florida-Georgia—Beach Placer 

Deposits

Location: Monazite accumulations are situated in the modern 

and raised Pleistocene and Pliocene beach deposits of 

northeastern Florida and southeastern Georgia. Latitude: 

29.85997 N., Longitude: 81.73711 W.; datum: WGS84

Deposit type and basic geology: The modern and raised 

Pleistocene and Pliocene beach deposits of northeastern 

Florida and southeastern Georgia host low-grade but 

persistent concentrations of monazite. Heavy minerals 

constitute a small part of the modern beach sands, and 

monazite forms a small part of the heavy minerals. However, because of the large tonnage of suitable beach-sand 

deposits and the ease of mining and processing this material, these beach deposits represent a potential rare earth 

elements (REE) and thorium resource. The most abundant 

heavy mineral in the southeastern United States shoreline 

deposits is ilmenite, which in many places forms more 

than 50 percent of the heavy-mineral fraction; monazite 

forms a minor part of the heavy-mineral fraction, usually 

less than 1 percent (Staatz and others, 1980). Monazite 

from the Florida beach placers contains about 50–60 

percent total REE oxides (Kremers, 1958; Staatz and others, 1980) and 4–5 percent thorium oxide (Calver, 1957). 

Small amounts of uranium, averaging 0.55 percent, are 

also present in the monazite (Calver, 1957).

Status: Currently (2010), there is no reported exploration in 

this district. 

Production: Some of the former heavy-mineral operations 

in the Pleistocene beach deposits of Florida were once 

domestic suppliers of monazite. Staatz and others (1980, 

p. 3) reported, “During 1978 monazite was produced 

from two of the three operating heavy-mineral deposits 

in Florida: Titanium Enterprises at Green Cove Springs 

and Humphrey Mining Corp. at Boulogne recovered 

monazite as a byproduct.” Trace amounts of monazite 

were also mined from the large Trail Ridge orebody south 

of Jacksonville in 1949 by E.I. du Pont de Nemours and 

Company. Overall, these deposits were mined primarily 

for titanium (in ilmenite and rutile), which was used by 

the pigment industry. Other minerals sold from the three 

deposits include kyanite, sillimanite, staurolite, garnet, 

zircon, and the host sand itself. Mining ceased in this area 

in late 1978 because of increasing environmental regulations that made mining operations more costly.

Estimated resources: Staatz and others (1980) estimated 

that the beach placer deposits of this region contain total 

reserves of about 198,000 metric tons (218,000 tons) of 

rare earth elements oxides, 14,700 metric tons (16,200 

short tons) of thorium oxide, and 1,490 metric tons (1,640 

tons) of uranium oxide, all of which are hosted in 330,000 

metric tons (364,000 tons) of monazite. 

Detailed Discussion

The modern and raised Pleistocene and Pliocene beach 

deposits of northeastern Florida and southeastern Georgia host 

low-grade but persistent concentrations of monazite (figs. 22 

and 23). Heavy minerals constitute a small part of the modern 

beach sands, and monazite forms a small part of the heavy 

minerals. However, because of the large tonnage of suitable 

beach sand deposits and the ease of mining and processing 

this material, these beach deposits represent a potential rare 

earth elements (REE) and thorium resource. Staatz and others 

(1980) estimated that the beach placer deposits of this region 

contain total reserves of about 198,000 metric tons (218,000 

tons) of REE oxides, 14,700 metric tons (16,200 short tons) of 

thorium oxide, and 1,490 metric tons (1,640 tons) of uranium 

oxide, all of which are hosted in 330,000 metric tons (364,000 

tons) of monazite. 

Some of the heavy-mineral operations in the Pleistocene beach deposits of Florida were once domestic suppliers 

of monazite (fig. 23). Staatz and others (1980, p. 3) noted, 

“During 1978 monazite was produced from two of the three 

operating heavy-mineral deposits in Florida: Titanium Enterprises at Green Cove Springs and Humphrey Mining Corp. 

at Boulogne recovered monazite as a byproduct.” Trace 

amounts of monazite were also mined from the large Trail 

Ridge orebody south of Jacksonville in 1949 by E.I. du Pont 

de Nemours and Company. The Boulogne orebody underlies 

an area of about 4 km2

 (1.5 mi2) and was mined to a depth of 

4.6 m (15 ft), whereas the Trail Ridge deposit has been traced 

for about 29 km (18 mi) (Staatz and others, 1980). 

Overall, these deposits were mined primarily for titanium 

(in ilmenite and rutile), which was used by the pigment industry. Other minerals sold from the three deposits include kyanite, 

sillimanite, staurolite, garnet, zircon, and the host sand itself. 

Mining ceased in this area in late 1978 because of increasing environmental regulations that made mining operations 

more costly. Steep increases in coastal real-estate values also 

influenced the situation, such that the heavy-mineral concentrations in the modern beaches became much less valuable than 

the real estate they occupy. Nonetheless, while the modern 

beaches hosted most of the early heavy-mineral operations, the 

older inland beaches are larger, have more uniform distribution 

of heavy minerals, and are not as vulnerable to severe storms, 

which made them favorable before the real estate market skyrocketed (Overstreet, 1967, p. 125). Staatz and others (1980, p. 

3–4, and references cited therein) describe the mining history 

of the heavy-mineral beach placers of the northeastern Florida 

and southeastern Georgia area in greater detail.

In general, the monazite-bearing sands in the raised 

Pleistocene and Pliocene beach deposits lie as much as 80 

km (50 mi) inland, making them deposits of former shorelines. These relict shorelines, which lie 3–33 m (10–108 ft) 

above the sea level, have been noted in the outer coastal plain 

region from Maryland to Florida. Once referred to as “marine 

terraces,” the relict shorelines were divided into different 

levels on the basis of elevation and tectonic stability and then 
94 The Principal Rare Earth Elements Deposits of the United States

ATLANTIC OCEAN

B1–B9

R1–R6

S1–S9

P1–P8 

Beach sands

River sands

Silver Bluff sands

Pamlico sands

Silver Bluff shoreline

Pamlico shoreline

EXPLANATION

0 20 MILES

Altamaha 

River

R4 R5

R3

R2

R1 R6

P7

P8 S9

S8

Jekyll

Island

B9

B8

B4

B6

B5

B4

S7

B3

B2

B1

S6

S5

S4

S3

S2

S1

P2

P1

P3

P4

P6 P5

31°20'

81°20'

Figure 22. Map of Recent and Pleistocene sands of Georgia. Modified from Neiheisel (1962).

correlated with interglacial stages (MacNeil, 1950; Doering, 

1960). Further investigation revealed that the relict shorelines 

more closely resembled barrier islands, suggesting that the 

coastal plain was warped during the Pleistocene (Winkler and 

Howard, 1977). Because monazite contains radioactive thorium, future monazite exploration in the eastern United States 

coastal plain areas can benefit from several aeroradiometric 

maps that were compiled and interpreted by the USGS (Force 

and others, 1982; Grosz, 1983; Grosz and others, 1989; Owens 

and others, 1989).

The monazite and associated heavy minerals in the 

relict shoreline deposits of the southeastern United States 

were eroded from crystalline rocks of the Piedmont province (Mertie, 1953), carried towards the Atlantic Ocean by 

streams and rivers, and eventually redeposited by coastal 

processes. The natural concentration of heavy minerals in the 

shoreline area is a multistage process that involves transport 

by longshore drift; gravity separation by specific gravity, 

particle size, and shape; differential chemical weathering 

(Neiheisel, 1962); wave action; and, in some parts of the 

coastal environment, the actions of tides. All of these forces 

rework the sediments in the shoreline environments through 

time and naturally concentrate the heavy minerals (see Force, 

1991, p. 73–84). 

Although the most abundant heavy mineral in the southeastern United States shoreline deposits is ilmenite, which in 

many places composes more than 50 percent of the heavymineral fraction, monazite usually forms less than 1 percent of 

the heavy-mineral fraction (Staatz and others, 1980). Zircon 

generally composes 10–20 percent of the heavy minerals. 

Monazite from the Florida beach placers contains about 50–60 

percent total REE oxides (Kremers, 1958; Staatz and others, 

1980) and 4–5 percent thorium oxide (Calver, 1957). Small 

amounts of uranium are also present in the monazite, averaging 0.55 percent (Calver, 1957). 

Despite the low concentrations of monazite (and thus, 

REE and thorium) in the typical coastal placer deposit of the 

southeastern United States, these deposits have three distinct 

advantages as potential sources of REE and thorium: they are 

relatively easy to excavate; it is relatively easy to separate the 

heavy-mineral fraction onsite; and they contain several salable 

mineral products. Mining in both beach placers and on relict 

shorelines is possible using open-pit methods, and overburden is 

rarely greater than 4–5 m (13–16 ft) thick. In addition, groundwater in Florida and Georgia is shallow enough that monazite 

and other heavy minerals can be mined by a dredge floating on 

a pond (Staatz and others, 1980). However, at present the Boulougne and Jacksonville deposits are essentially mined out.
Florida-Georgia—Beach Placer Deposits 95

Starke

x

St. Augustine

Blackshear

Waycross

Nahunta

Woodbine

Folkston

MacClenny

GEORGIA

FLORIDA

Okefenokee

Swamp

Brunswick

St. Marys River

Fernandia

Jacksonville

x

Green Cove Springs St. Johns 

River

Monazite-bearing

No monazite

X Mine

0 25 MILES

82°20' 82°00' 81°40'

30°00'

31°00'

31°15'

Figure 23. Sample and mine locations of monazite in southeastern Georgia and northeastern 

Florida. Modified from Mertie (1975).
96 The Principal Rare Earth Elements Deposits of the United States

References Cited

Calver, J.L., 1957, Mining and mineral resources: Florida 

Geological Survey Bulletin 39, 132 p.

Doering, J.A., 1960, Quaternary surface formations of southern part of Atlantic Coastal plain: Journal of Geology, v. 68, 

no. 2, p. 182–202.

Force, E.R., 1991, Geology of titanium-mineral deposits: 

Geological Society of America Special Paper 259, 112 p.

Force, E.R., Grosz, A.E., Loferski, P.J., and Maybin, A.H., 

1982, Aeroradioactivity maps in heavy-mineral exploration—Charleston, South Carolina, area: U.S. Geological 

Survey Professional Paper 1218, 19 p., 2 plates.

Grosz, A.E., 1983, Application of total-count aeroradiometric 

maps to the exploration for heavy-mineral deposits in the 

Coastal Plain of Virginia: U.S. Geological Survey Professional Paper 1263, 20 p., 5 plates.

Grosz, A.E., Cathcart, J.B., Macke, D.L., Knapp, M.S., 

Schmidt, Walter, and Scott, T.M., 1989, Geologic interpretation of the gamma-ray aeroradiometric maps of central 

and northern Florida: U.S. Geological Survey Professional 

Paper 1461, 48 p., 5 plates.

Kremers, H.E., 1958, Commercial thorium ores: Society of 

Mining Engineers of American Institute of Mining Engineers preprint 589A18, p. 1–14.

MacNeil, F.S., 1950, Pleistocene shore lines in Florida and 

Georgia: U.S. Geological Survey Professional Paper 221–F, 

p. 95–107, 7 plates.

Mertie, J.B., Jr., 1953, Monazite deposits of the southeastern 

Atlantic States: U.S. Geological Survey Circular 237, 31 p., 

1 plate.

Mertie, J.B., Jr., 1975, Monazite placers in the southeastern 

Atlantic States: U.S. Geological Survey Bulletin 1390, 41 p.

Neiheisel, James, 1962, Heavy-mineral investigation of Recent 

and Pleistocene sands of Lower Coastal Plain of Georgia: Geological Society of America Bulletin, v. 73, no. 3, p. 365–374.

Overstreet, W.C., 1967, The geologic occurrence of monazite: 

U.S. Geological Survey Professional Paper 530, 327 p., 

2 plates.

Owens, J.P., Grosz, A.E., and Fisher, J.C., 1989, Aeroradiometric map and geologic interpretation of part of the Florence 

and Georgetown 1° x 2° quadrangles, South Carolina: U.S. 

Geological Survey Miscellaneous Investigations Series Map 

I–1948–B, 1 sheet, scale 1:250,000.

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.

Winkler, C.D., and Howard, J.D., 1977, Correlation of tectonically deformed shorelines on the southern Atlantic coastal 

plain: Geology, v. 5, no. 2, p. 123–127.

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Flagstaff, AZ 86001

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