Rare Earth Element Mineral Deposits in the 

United States

U.S. Department of the Interior

U.S. Geological Survey

Circular 1454

Version 1.1, April 2019
Cover. Rare earth elements and their uses as part of our everyday life. Photographs of 

minerals and high-technology devices used with permission from https://www.PEXELS.com; 

Rob Lavinsky, https://www.iRocks.com/; https://geology.com/. Photograph of Mountain Pass 

mine by Bradley Van Gosen.
Rare Earth Element Mineral Deposits in the 

United States

By Bradley S. Van Gosen, Philip L. Verplanck, and Poul Emsbo

U.S. Department of the Interior

U.S. Geological Survey

Circular 1454

Version 1.1, April 2019
U.S. Department of the Interior

DAVID BERNHARDT, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia

First release: 2019

Revised: April 15, 2019 (ver 1.1)

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Suggested citation:

Van Gosen, B.S., Verplanck, P.L., and Emsbo, Poul, 2019, Rare earth element mineral deposits in the United States 

(ver 1.1, April 15, 2019): U.S. Geological Survey Circular 1454, 16 p., https://doi.org/10.3133/cir1454.

Library of Congress Cataloging-in-Publication Data

Names: Van Gosen, B. S. (Bradley S.), 1960- author. | Verplanck, Philip L., 

 author. | Emsbo, Poul, author. | Geological Survey (U.S.), issuing body.

Title: Rare earth element mineral deposits in the United States / by Bradley 

S. Van Gosen, Philip L. Verplanck, and Poul Emsbo.

Other titles: U.S. Geological Survey circular ; 1454.

Description: Reston, Virginia : U.S. Department of the Interior, U.S. 

 Geological Survey, 2019. | Series: Circular, ISSN 1067-084X ; 1454 | 

 Includes bibliographical references.

Identifiers: LCCN 2019016090 | ISBN 9781411342941 (paperback)

Subjects: LCSH: Rare earth metals--United States. | Rare earth 

 metals--Industrial applications--United States.

Classification: LCC TA480.R3 V36 2019 | DDC 553.4/940973--dc23 | SUDOC I 

 19.4/2:1454

LC record available at https://lccn.loc.gov/2019016090

ISSN 1607-084X (print) 

ISSN 2330-5703 (online)

ISBN 978-1-4113-4294-1
iii

Contents

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

Introduction.....................................................................................................................................................1

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

Supply Concerns............................................................................................................................................4

Principal Rare Earth Element Minerals in Economic Nonfuel Mineral Deposits................................5

Rare Earth Element Mineral Deposit Types in the United States...........................................................7

Carbonatite REE-Bearing Deposits....................................................................................................9

Alkaline Igneous REE Deposits...........................................................................................................9

Rare Earth Elements in Sedimentary Phosphate Deposits..........................................................11

Vein Deposits.......................................................................................................................................12

Iron Oxide-Apatite Deposits (IOA) ...................................................................................................12

Monazite-Xenotime-Bearing Placer Deposits (Heavy-Mineral Sands) ....................................12

Ion-Adsorption Clay Deposits (REE in Granite-Derived Regolith)...............................................13

Summary........................................................................................................................................................13

References....................................................................................................................................................14

Figures

1. Rare earth elements (REEs) are used in the components of many high-technology

devices that are part of our everyday life, such as those shown here ...............................2

2. Periodic table of the elements....................................................................................................3

3. Mountain Pass mine, southeastern California, June 2018 ....................................................5

4. Rare earth element (REE) deposits in the United States discussed in this report.............6

5. World mine production of rare-earth oxides, by country and year, from 1960 to 2012.

The layers of the graph are placed one above the other, forming a cumulative total ......7

6. Principal ore minerals recovered for rare earth elements (REE) are bastnäesite,

monazite, xenotime, and apatite ................................................................................................8

7. Outcrop of rare earth element (REE)-rich “vein-dike” intrusions (dark vertical layers) 

in the Dotson zone on Bokan Mountain, southern part of Prince of Wales Island, 

southeastern Alaska ..................................................................................................................10

8. Two-meter-thick outcrop of Upper Ordovician, high-grade REE phosphorite .................11

Tables

1. Rare earth elements and their applications.............................................................................4

2. Principal rare earth element (REE) minerals in various economic REE deposits and

their ideal chemical formula .......................................................................................................7
iv

Conversion Factors

International System of Units to U.S. customary units

Multiply By To obtain

Length

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

square meter (m2) 0.0002471 acre 

square kilometer (km2) 0.3861 square mile (mi2)

Mass

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

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

Abbreviations

Eu europium

Gd gadolinium

HREE heavy rare earth element

IOA iron oxide apatite

km kilometer

La lanthanum

km2 square kilometer

LREE light rare earth element

m meter

m2 square meter

Nd neodymium

Pm promethium

REE rare earth element

REO rare earth oxide

Sc scandium

t metric ton

Tb terbium

USGS U.S. Geological Survey

Y yttrium
Rare Earth Element Mineral Deposits in the United States

By Bradley S. Van Gosen, Philip L. Verplanck, and Poul Emsbo

regolith). A better understanding of these mineral deposits will 

assist in identifying domestic resources to help alleviate the 

dependence on imported REEs. 

The economic development of REE mineral deposits is 

affected by many factors beyond mining, such as commodity 

prices and mineral processing costs. Most of the REEs are 

hosted by minerals that have complex chemical formulas; 

this presents more challenges to process and extract the 

REEs. Continued advancements and refinements in mineral 

processing techniques may allow REE deposits with complex 

mineralogy to be economically developed in the future.

Introduction

Rare earth elements (REEs) have unique physical and 

chemical properties that have become vital to a broad range 

of high-technology industries (summarized in Goonan, 2011; 

Van Gosen and others, 2014b, 2017). The REE elements 

include the 15 lanthanide elements, and along with scandium 

and yttrium, are critical in the production of cell phones, 

computers, fluorescent and light-emitting-diode (LED) lights, 

and flat-screen monitors (televisions and computer monitors). 

The REEs are also fundamental components in high-strength 

magnets used in the generators of wind turbines and in newgeneration batteries as well as many components in hybrid and 

electric vehicles, all of which underpin emerging clean-energy 

technologies. The unique properties of REEs are indispensable 

to defense applications, such as in the production of jet 

engines, missile guidance systems, antimissile defense 

systems, satellites, and communication systems (U.S. 

Government Accountability Office, 2016) (fig. 1). 

The critical role of REEs in high-tech industries 

has created a surge in demand and, considering there is a 

near-monopoly reliance on imports from a single country, 

have made the Nation vulnerable to supply disruptions 

(McCullough and Nassar, 2017; Fortier and others, 2018). 

This report summarizes the U.S. Geological Survey (USGS) 

efforts to identify and inventory U.S. sources of REEs to aid in 

ensuring our Nation’s mineral resource needs. 

Abstract

Because of their unique special chemical properties, many 

of the metals in the group of rare earth elements (REEs) have 

essential applications in 21st century technologies. Examples 

of products that use REEs are cell phones, computers, fluorescent and light-emitting-diode lights, flat-screen television and 

computer monitors, and in high-strength magnets used by clean 

energy technologies such as the generators of wind turbines 

and batteries of hybrid and electric vehicles. REEs are used 

in many defense applications, such as in components of jet 

engines, missile guidance systems, antimissile defense systems, 

satellites, and communication systems.

The rare earth elements have become vital to manufacturing numerous high-tech products, which has been accompanied 

by a large increase in their demand. At the same time, there 

has been concern by the United States and many other Nations 

about the near-monopoly of mining, processing, and supply of 

REEs from one Nation, China. Between 2011 and 2017, China 

produced approximately 84 percent of the world’s REEs, and 

during this time the United States only produced REEs between 

2012 and 2015. The U.S. production came entirely from 

the Mountain Pass mine in California, providing only about 

4 percent of the world REE supply. Because REEs are essential 

for technological applications and are primarily supplied by 

one Nation, there has been an increased concern in identifying 

new sources of REEs, including economic REE deposits.

In response to these concerns, since 2009, the U.S. 

Geological Survey (USGS) has conducted numerous studies 

focused on the distribution, geology, and potential resources 

for the REE-bearing mineral deposits in the United States. 

The basic characteristics of mineral deposit types that host 

REE enrichments in the United Sates are summarized in this 

report, with selected examples. Several types of REE-enriched 

mineral deposits are reviewed, including deposits in carbonatites, alkaline igneous rocks, sedimentary phosphate-rich 

rocks (phosphorite), regions containing REE-rich veins, iron 

oxide deposits containing REE-bearing apatite, monazitexenotime-bearing placer deposits (heavy-mineral sands), 

and ion-adsorption clay deposits (REE in granite-derived 
2 Rare Earth Element Mineral Deposits in the United States

Figure 1. Rare earth elements (REEs) are used in the components of many high-technology devices that are part of our everyday life, 

such as those shown here. Green energy uses many REEs, including in the batteries and other modules of hybrid and electric cars, 

and the generators of wind turbines, which require strong permanent magnets containing neodymium-iron-boron. There are numerous

defense applications of REEs, such as in the production of jet engines, missile guidance systems, antimissile defense systems, satellites, 

and communication systems. Photographs used with permission from https://www.PEXELS.com.
1A 8A

2A

3B 4B 5B 6B 7B 8B 11B 12B

3A 4A 5A 6A 7A

element names in blue are liquids at room temperature

element names in red are gases at room temperature

element names in black are solids at room temperature

Periodic Table of the Elements

Los Alamos National Laboratory Chemistry Division

39

*

**

As

39.10

85.47

132.9

(223)

9.012

24.31

40.08

87.62

137.3

(226)

44.96

88.91

47.88

91.22

178.5

(267) (268) (269) (270) (277) (278) (281) (282) (285) (286) (289) (289) (293) (294) (294)

50.94

92.91

180.9

52.00

95.96 

183.9

54.94

(98)

186.2

55.85

101.1

190.2 192.2

102.9

58.93 58.69

106.4

195.1 197.0

107.9

63.55 65.39

112.4

200.5

10.81

26.98

12.01

28.09

14.01

69.72 72.64

114.8 118.7

204.4 207.2

30.97

74.92

121.8

209.0 (209) (210) (222)

16.00 19.00 20.18

4.003

32.06 35.45 39.95

78.96 79.90 83.79

127.6 126.9 131.3

140.1 140.9 144.2 (145) 150.4 152.0 157.2 158.9 162.5 164.9 167.3 168.9 173.0 175.0

232

138.9

(227) 231 238 (237) (244) (243) (247) (247) (251) (252) (257) (258) (259) (262)

Tc

43

11

1

3 4

12

19 20 21 22 23 24 25 26 27 28 29 30

37 38 40 41 42 44 45 46 47 48

55 56

58 59 60

72 73 74 75 76 77 78 79 80

87 88

90

57

89 91 92 93 94 95 96

104 105 106 107 108 109 110 111 112

61 62 63 64 65 66 67

97 98 99

68 69 70 71

100 101 102 103

31

13 14 15 16 17 18

32 33 34 35 36

49 50 51 52 53 54

81 82 83 84 85 86

5 6 7 8 9 10

2

113 114 115 116 117 118

3/13/17

Th

Li

Na

K

Rb

Cs

Fr

Be

Mg

Ca

Sr

Ba

Ra

Sc Ti V Cr Mn Fe Co Ni Cu Zn

Y Zr Nb Mo Ru Rh Pd Ag Cd

Hf Ta W Re Os Ir Pt Au Hg

H He

Ne

Ar

Kr

Xe

F

Cl

N O

Br

Rf Db Sg Bh Hs Mt Ds Rg Cn

B C

Al Si P S

Ga Ge Se

In Sn Sb Te I

Tl Pb Bi Po At Rn

Nh Fl Mc Lv Ts Og

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Ac Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

hydrogen

barium

francium radium

strontium

sodium

vanadium

lithium beryllium

magnesium

potassium calcium

rubidium

cesium

helium

boron carbon nitrogen oxygen fluorine neon

aluminum silicon phosphorus sulfur chlorine argon

scandium titanium chromium manganese iron cobalt nickel copper zinc gallium germanium arsenic selenium bromine krypton

yttrium zirconium niobium molybdenum technetium ruthenium rhodium palladium silver cadmium indium tin antimony tellurium iodine xenon

hafnium

cerium praseodymium neodymium promethium samarium europium gadolinium terbium dysprosium holmium erbium thulium ytterbium lutetium

tantalum tungsten rhenium osmium iridium platinum gold mercury thallium lead bismuth polonium astatine radon

thorium

lanthanum

actinium protactinium uranium neptunium plutonium americium curium berkelium californium einsteinium fermium mendelevium nobelium lawrencium 

rutherfordium dubnium seaborgium bohrium hassium meitnerium darmstadtium roentgenium copernicium nihonium flerovium moscovium livermorium tennessine oganesson

1.008

6.94

22.99

Lanthanide Series*

Actinide Series**

1s1

[Ar]4s23d104p [Ar]4s23d3 3 [Ar]4s13d10

[Ne]3s23p6 [Ne]3s23p4

[Ar]4s1 [Ar]4s23d10

1s2

[He]2s1 [He]2s2

[Ar]4s23d7

[Ne]3s23p5

[He]2s22p1 [He]2s22p2 [He]2s22p3

[Ar]4s23d5

[He]2s22p4 [He]2s22p5 [He]2s22p6

[Ar]4s23d104p5

[Ne]3s1 [Ne]3s23p1 [Ne]3s23p3 [Ne]3s23p2

[Rn]7s25f146d2

[Ne]3s2

[Ar]4s2 [Ar]4s23d1 [Ar]4s23d2 [Ar]4s13d5 [Ar]4s23d6 [Ar]4s23d8 [Ar]4s23d104p1 [Ar]4s23d104p2 [Ar]4s23d104p4 [Ar]4s23d104p6

[Kr]5s1 [Kr]5s2 [Kr]5s24d1 [Kr]5s24d2 [Kr]5s14d4 [Kr]5s14d5 [Kr]5s24d5 [Kr]5s14d7 [Kr]5s14d8 [Kr]4d10 [Kr]5s14d10 [Kr]5s24d10 [Kr]5s24d105p1 [Kr]5s24d105p2 [Kr]5s24d105p3 [Kr]5s24d105p4 [Kr]5s24d105p5 [Kr]5s24d105p6

[Xe]6s1 [Xe]6s2

[Xe]6s24f15d1 [Xe]6s24f3 [Xe]6s24f4 [Xe]6s24f5 [Xe]6s24f6 [Xe]6s24f7 [Xe]6s24f75d1 [Xe]6s24f9 [Xe]6s24f10 [Xe]6s24f11 [Xe]6s24f12 [Xe]6s24f13 [Xe]6s24f14 [Xe]6s24f145d1

[Xe]6s24f145d2 [Xe]6s24f145d3 [Xe]6s24f145d4 [Xe]6s24f145d5 [Xe]6s24f145d6 [Xe]6s24f145d7 [Xe]6s14f145d9 [Xe]6s14f145d10 [Xe]6s24f145d10 [Xe]6s24f145d106p1 [Xe]6s24f145d106p2 [Xe]6s24f145d106p3 [Xe]6s24f145d106p4 [Xe]6s24f145d106p5 [Xe]6s24f145d106p6

[Rn]7s1 [Rn]7s2

[Rn]7s26d2

Xe]6s25d1

[Rn]7s26d1 [Rn]7s25f26d1 [Rn]7s25f36d1 [Rn]7s25f46d1 [Rn]7s25f6 [Rn]7s25f7 [Rn]7s25f76d1 [Rn]7s25f9 [Rn]7s25f10 [Rn]7s25f11 [Rn]7s25f12 [Rn]7s25f13 [Rn]7s25f14 [Rn]7s25f146d1

[Rn]7s25f146d3 [Rn]7s25f146d4 [Rn]7s25f146d5 [Rn]7s25f146d6 [Rn]7s25f146d7 [Rn]7s15f146d9 [Rn]7s15f146d9 [Rn]7s15f146d9 [Rn]7s27p15f14

6d10 (predicted)

[1] [Rn]7s27p25f14

6d10(predicted)

[2] [Rn]7s27p35f14

6d10(predicted)[1] [Rn]7s27p45f146d10(predicted)

[1] [Rn]7s27p55f14

6d10(predicted)[4] [Rn]7s27p65f14

6d10(predicted)

[1][2]

Rare Earth Elements 3

Rare Earth Elements

The REEs, also referred to as the lanthanides or lanthanoids, include elements from lanthanum (fig. 2, atomic 

number 57) to lutetium (atomic number 71) on the periodic 

table of elements. Promethium (Pm, atomic number = 61), 

is excluded, because it is not naturally occurring. Yttrium 

(Y, atomic number = 39) shares chemical and physical similarities with the lanthanides and thus is often included in the 

REE group of elements. Scandium (Sc, atomic number = 21) 

is chemically similar to and sometimes included with the 

REEs. However, scandium does not commonly occur in 

significant quantities in the same mineral deposits with the 

lanthanides and yttrium.

Figure 2. Periodic table of the elements.

The REEs are traditionally divided into two informal 

groups based on their atomic weight (table 1). Lanthanum 

through gadolinium (atomic numbers 57 through 64) are 

grouped as light rare earth elements (LREEs) and terbium 

through lutetium (atomic numbers 65 through 71) as the heavy 

rare earth elements (HREE). Some authorities, including the 

International Union of Pure and Applied Chemistry, include 

europium and gadolinium within the group of heavy REEs. 

Yttrium, although atomically light (atomic number 39), is 

included with the HREE group because it shares common 

chemical and physical properties with the HREEs. In general, 

the HREE group is particularly important to emerging technologies, less abundant, and harder to source than the LREEs, 

and thus command a higher price.
4 Rare Earth Element Mineral Deposits in the United States

Supply Concerns

From the mid-1960s to the early 1990s, the United 

States was the world’s largest REE-producing country, with 

production coming entirely from the Mountain Pass mine in 

southeastern California (figs. 3 and 4). In the late 1980s, China 

began mining their in-country REE deposits, processing their 

ore and extracting and separating the individual REEs for use 

in products, which they also manufactured. China quickly 

gained control of global REE production, providing 95 percent 

of the global market of processed REE by 2011 (fig. 5). 

Between 2011 and 2017, China produced approximately 

84 percent of the world’s REEs, followed by Australia with 

about 8 percent of production (Gambogi, 2019). Within this 

period, the United States only produced REEs between 2012 

and 2015, entirely from the Mountain Pass mine, which 

contributed only about 4 percent of the world REE supply. 

Meeting the growing need for HREEs has been 

particularly challenging because efforts to identify 

economically feasible HREE-enriched deposits outside 

of China have generally been unsuccessful. The world’s 

principal source of HREEs are unusual clay deposits in 

southern China, which are profitable because of their 

relatively low-cost mining and chemical extraction methods 

and less stringent environmental restrictions. A global search 

for similar clay deposits is ongoing, including the southeastern United States. 

Heavy dependence on a single country as a source of 

the REEs has led to concern from many groups, including 

high dependence on new electronic, computer, and green 

technologies by countries such as the United States, Japan, 

and the European Union. The U.S. Defense Department 

has expressed these concerns and commissioned studies to 

evaluate the concentration of the REE supply chain in China 

(U.S. Government Accountability Office, 2016). These 

reports emphasize the “criticality” of the recent REEs situation, the limited sources for supply, and the important role of 

REEs in our modern technologies and economies (National 

Research Council, 2008; European Commission, 2010; U.S. 

Department of Energy, 2011). The significant increases in 

applications and demands for REEs has led to an increased 

interest in identifying new sources that include extraction from 

mineral deposits, extraction from coal-based resources, and 

recycling of products containing REEs. The Department of 

Energy is currently (2019) evaluating technologies to recover 

REEs and other critical minerals from coal and coal-based 

resources (https://www.netl.doe.gov/coal/rare-earth-elements). 

Recycling efforts have focused on recovering REEs from light 

bulbs and electronics. In response to these national concerns 

the U.S. Geological Survey (USGS) has been investigating the 

REE-bearing mineral deposits in the United States to better 

inform stakeholders on the characteristics of the domestic, inthe-ground REE resources (Long and others, 2010; Van Gosen 

and others, 2014a, 2014b, 2017; McCafferty and others, 2014; 

Table 1. Rare earth elements and their applications.

Element Symbol Atomic 

number Example applications

Light rare earth elements

Lanthanum La 57 Optical glass, nickel-metal-hydride batteries

Cerium Ce 58 Colored glass (flat-panel displays), automobile catalytic converters

Praseodymium Pr 59 Super-strong magnets, metal alloys, specialty glass, lasers

Neodymium Nd 60 Permanent magnets

Samarium Sm 62 Permanent magnets, nuclear reactor control rods, lasers

Europium Eu 63 Optical fibers, visual displays, lighting

Gadolinium Gd 64 Shielding in nuclear reactors, X-ray and magnetic resonance imaging scanning systems

Heavy rare earth elements

Terbium Tb 65 Visual displays, fuel cells, lighting

Dysprosium Dy 66 Permanent magnets, lighting

Holmium Ho 67 Lasers, high-strength magnets, glass coloring

Erbium Er 68 Glass coloring, fiber optic cables

Thulium Tm 69 Lasers, portable X-ray machines

Ytterbium Yb 70 Stainless steel, lasers

Lutetium Lu 71 Petroleum refining

Yttrium Y 39 Metal alloys, visual displays, lasers, lighting
Principal Rare Earth Element Minerals in Economic Nonfuel Mineral Deposits 5

Figure 3. Mountain Pass mine, southeastern California, June 2018. The ore body, called the Sulphide Queen deposit, is a large tabular 

carbonatite intrusion, thought to be the largest rare earth element deposit in the United States. The deposit was discovered in 1949. 

Mining of the deposit began in 1952 and continued with nearly continuous production until 2002, resumed from 2012 to 2015, and began 

again in 2017 under new ownership. Photograph by Bradley Van Gosen.

Verplanck and others, 2014; Emsbo and others, 2015, 2016; 

Foley and Ayuso, 2015; Day and others, 2016; Hofstra and 

others, 2016; Karl and others, 2016; Senguta and Van Gosen, 

2016; McCullough and Nassar, 2017; Shah and others, 2017; 

Bellora and others, 2018; Fortier and others, 2018; Dicken and 

others, 2019; Hammarstrom and Dicken, 2019). This report 

briefly summarizes the principal types of mineral deposits in 

the United States known to contain elevated concentrations of 

the REEs, with examples of each.

Principal Rare Earth Element Minerals 

in Economic Nonfuel Mineral Deposits

Although at least 245 individual REE-bearing minerals 

have been identified, only a few minerals contribute the majority of the REE concentrations in economic nonfuel mineral 

deposits. These minerals are bastnäesite (also spelled bastnäsite), monazite, and xenotime (table 2; fig. 6). In addition, 

the phosphate mineral apatite is a potentially important source 

of REEs because it can contain a substantial amount of REEs 

due to its crystal structure. These minerals tend to be enriched 

in either light or heavy REEs, but not equally.

Bastnäesite.—A REE-carbonate-fluorine mineral 

(table 2), is the main ore mineral in carbonatite REE deposits, 

including the three largest REE mines, Bayan Obo and 

Maoniuping deposits in China and the Mountain Pass deposit, 

California. Because these carbonatite-hosted deposits are the 

largest global sources of REEs, especially the LREEs, bastnäesite may be considered the most important REE mineral. 

Bastnäesite commonly occurs with two other REE-carbonatefluorine minerals, synchysite and parisite. Bastnäesite contains 

up to 75 weight-percent REE oxides and is highly enriched in 

the LREEs. The separation and processing for bastnäesite is 

well established. For these reasons, bastnäesite accounts for 

the majority of the LREE production in the world. 

Monazite.—A REE-phosphate mineral (table 2), was 

the primary REE ore mineral prior to the discovery of 

bastnäesite-rich deposits. Monazite, the most common REE 

mineral, occurs in a range of geologic environments and 

is typically enriched in the LREEs. Historically, monazite 

was extracted from placer deposits—stream and coastal 

sediments—because monazite resists chemical and physical 

weathering and has a relatively high density, allowing it to 

be transported but not destroyed and ultimately sorted by 

the actions of water and (or) wind into discrete layers with 

other heavy minerals in these depositional environments 
6 Rare Earth Element Mineral Deposits in the United States

Figure 4. Rare earth element (REE) deposits 

in the United States. Numbers on map 

indicate locations of deposits discussed in 

this report. 1, Mountain Pass, California—

Carbonatite deposit; 2, Lemhi Pass, Idaho 

and Montana—REE-bearing veins; 3, Bear 

Lodge, Wyoming—Carbonatite deposit; 

4, Wet Mountains, Colorado—REE-bearing 

veins; 5, Elk Creek, Nebraska—Carbonatite 

deposit; 6, Pea Ridge, Missouri—Iron-oxide 

apatite deposit (IOA); 7, Upper Ordovician 

phosphorites (gray areas in Arkansas, 

Illinois, Indiana, Iowa, Minnesota, Missouri, 

and Wisconsin)—REE-bearing phosphorites; 

8, Clay deposits at Stewartsville pluton, 

Virginia—Ion-adsorption clay deposits (REE 

in granite-derived regolith); 9, Mineville iron 

mining district, New York—Iron-oxide apatite 

deposits (IOA); 10, Atlantic Coastal Plain 

(yellow areas in Maryland, Virginia, North 

Carolina, South Carolina, Georgia, Florida, 

and Alabama)—Monazite-Xenotime-bearing 

placer deposits (heavy-mineral sands); 

11, Bokan Mountain, Prince of Wales Island, 

Alaska—REE-bearing veins in an alkaline 

igneous complex.

ALASKA

TEXAS

OKLAHOMA

KANSAS

COLORADO

NEW MEXICO

ARIZONA

CALIFORNIA

NEVADA

OREGON

IDAHO

MONTANA

WYOMING

NORTH DAKOTA

SOUTH DAKOTA

NEBRASKA

MINNESOTA

WISCONSIN

MICHIGAN

ILLINOIS

KENTUCKY

TENNESSEE

SOUTH

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Base from U.S. Geological Survey digital data, 

The National Map, 1:2,000,000, 2018

Albers Equal-Area Conic projection

Standard parallels 29°30' N. and 45°30' N. 

Central meridian 96°30' W. latitude of origin 23° N. 

North American Datum of 1983 

Base from U.S. Geological Survey digital data, 

The National Map, 1:2,000,000, 2018

Albers Equal-Area Conic projection

Standard parallels 55° N. and 65° N. 

Central meridian 154° W. latitude of origin 50° N. 

North American Datum of 1983 
Rare Earth Element Mineral Deposit Types in the United States 7

(Sengupta and Van Gosen, 2016). Monazite can occur in 

carbonatite-related REE deposits as a primary mineral phase 

(crystallized from magma, as in the Mountain Pass deposit) or 

as a secondary (replacement) mineral in the weathered zone 

(for example, the carbonatites of Mount Weld, Western Australia, and Araxá, Brazil). The weight percent of REEs within 

monazite is quite variable depending on what other elements 

are present. Monazite typically contains small amounts of 

thorium, making it radioactive.

Xenotime.—A yttrium (Y)-phosphate mineral (table 2), 

has been a source of REEs as a byproduct commodity in river 

placer mines. Because yttrium has a similar charge and ionic 

radius to other HREEs, xenotime generally contains substantial amounts of the HREEs. Xenotime’s crystal structure can 

accommodate significant quantities of uranium and thorium, 

which can contribute to environmental and handling issues 

when this mineral is separated and stockpiled, similar to the 

radioactivity issues associated with monazite. Because xenotime is enriched in the more valuable HREEs, it has become 

an important exploration target.

Apatite.—A calcium-phosphate mineral (table 2), is an 

important source of phosphate. It may also contain significant 

quantities of REEs. Apatite occurs in a range of rock types 

and can be LREE- or HREE-enriched, although they are most 

commonly LREE. Apatite may be an important source of 

REEs in some carbonatites (for example Mushgai Khudag, 

Mongolia) and iron-oxide apatite deposits (Pea Ridge, 

Missouri, and Mineville, New York; fig. 4).

Rare Earth Element Mineral Deposit 

Types in the United States

REEs are relatively common in the Earth’s crust; however, economic concentrations of these elements are not 

commonplace and the REEs tend to concentrate in uncommon rock types. The generalized characteristics of mineral 

deposit types that host REE enrichments are briefly described 

in this section, with selected occurrences in the United States 

that may have the potential to mitigate the dependence on 

imported REEs. More detailed discussions on the principal 

REE deposits and districts of the United States are provided in 

140,000

120,000

100,000

80,000

60,000

40,000

20,000

0

Rare-earth oxide mine production, in metric tons

1960 1965 1970 1975 1980 1985

Year

China

United States

Other countries

EXPLANATION

1990 1995 2000 2005 2010

Figure 5. World mine production of rare-earth oxides, by country and year, from 1960 to 2012. The 

layers of the graph are placed one above the other, forming a cumulative total. Data are from Kelly and 

Matos, 2014. 

Table 2. Principal rare earth element (REE) minerals in various 

economic REE deposits and their ideal chemical formula.

Mineral Formula

Bastnäesite REECO3F

Paristite CaREE2(CO3)3F2

Synchysite CaREE(CO3)2F)

Monazite (REE,Th)PO4

Xenotime (Y,HREE,Th,U)PO4

Apatite (Ca,REE)5(PO4)3(F,Cl,OH)
8 Rare Earth Element Mineral Deposits in the United States

Figure 6. Principal ore minerals recovered for rare earth elements (REE) are bastnäesite, monazite, xenotime, and apatite. 

A, Bastnäesite, an REE-carbonate-fluorine mineral, is the primary ore mineral in the world’s largest REE deposits, and the principal source 

of the global LREE supply. Photograph by Rob Lavinsky, https://www.iRocks.com/. B, Monazite, an REE-thorium-phosphate mineral, has 

been separated from ancient and modern beach sands as a coproduct of the recovery of economic titanium minerals. Monazite was the 

primary REE ore mineral prior to the mining of bastnäesite-rich, hard rock deposits. Photograph from https://geology.com/. C, Xenotime, 

a yttrium-phosphate mineral, has been a source of REEs as a byproduct commodity in river placer mines. Because yttrium has a similar 

charge and ionic radius to other heavy rare earth elements (HREE), xenotime generally contains substantial amounts of the HREEs. 

Photograph by Rob Lavinsky, https://www.iRocks.com/. D, Fluorine-bearing apatite, a calcium-phosphate mineral. Apatite occurs in a 

range of rock types and can contain significant quantities of light rare earth elements (LREE) or HREEs, although most commonly LREE. 

Apatite may be an important source of REEs in some carbonatites and iron-apatite deposits (Pea Ridge, Missouri, and Mineville, New 

York). Photograph by Rob Lavinsky, https://www.iRocks.com/.

A B

C D
Rare Earth Element Mineral Deposit Types in the United States 9

Long and others (2010), datasets in Bellora and others (2019), 

and numerous references cited in these reports. Exploration 

for REE deposits, data on the size and concentrations of REEs 

(tonnage and grade) in well explored and developed deposits, 

and environmental considerations in mining of REE deposits 

are discussed in Van Gosen and others (2017).

Carbonatite REE-Bearing Deposits

These deposits are hosted in unusual igneous intrusions—carbonatites—that are composed of 50 percent or more 

carbonate minerals, mainly calcite and dolomite, reflecting 

carbonate-rich source magmas (Verplanck and others, 2014). 

Large carbonatite bodies in China (for example, Bayan Obo, 

Maoniuping, Daluxiang, and Weishan) have been the sources 

of most of the global REE production for many years. Bastnäesite is the primary REE ore mineral in most carbonatites 

and can be accompanied by REE-bearing synchysite, parisite, 

monazite, and apatite, with occasional contributions from 

secondary xenotime that may form in weathered ore, such as 

in the Mount Weld deposit in Western Australia. Carbonatites 

tend to have the highest total REE concentrations of any igneous rocks. While the extraordinarily large carbonatite deposits 

are proven producers and large enough such that a single 

deposit can produce much of the world’s LREEs demand, they 

are typically depleted in HREE and, thus incapable of producing significant quantities of the important HREEs. 

The Mountain Pass deposit in southeastern California 

(fig. 3) is the largest known REE deposit in the United States 

(Verplanck and others, 2014; Van Gosen and others, 2017). This 

deposit produced most of the REEs mined in the United States 

since the late 1960s (fig. 5) and contains proven and probable 

reserves totaling 18.4 million metric tons of carbonatite ore 

averaging 7.98 percent rare earth oxide (REO) using a cutoff 

grade of 5 percent REO (Molycorp, Inc., 2012). In 2018, the 

mine was reopened and is currently (2019) producing a bastnäesite concentrate from the ore body that primarily consists of 

calcite, dolomite, barite, and bastnäesite in varying proportions.

Other REE-rich carbonatites in the United States include 

the Bear Lodge deposit in northeastern Wyoming and the Elk 

Creek deposit in southeastern Nebraska (fig. 4) (Long and 

others, 2010). The Bear Lodge carbonatite complex has been 

thoroughly drilled with proven plus probable resources of 

15.6 million metric tons of ore averaging 2.78 percent total 

REO (Rare Element Resources, Ltd., 2015). The Elk Creek 

deposit is a REE- and niobium-rich carbonatite that lies about 

200 meters (m) below the surface; it was discovered in 1970 

by a regional airborne geophysical survey (Long and others, 

2010). Core drilling into the Elk Creek carbonatite during the 

1970s, 1980s, and more recently in the 2010s has identified 

many intervals containing from 1 to more than 3 percent total 

REO. Recent (2019) developers of the Elk Creek property 

(NioCorp Developments, Ltd.) have emphasized the carbonatite’s potential resources of niobium, scandium, and titanium. 

Alkaline Igneous REE Deposits

These deposits are hosted in alkaline igneous 

rocks, another uncommon group of igneous rock that are 

geochemically characterized by depletion in silica relative to 

sodium, potassium, and calcium in comparison to “typical,” 

more silica-rich igneous rocks (Verplanck and others, 2014). 

Deposits in alkaline igneous rocks have been relatively small 

contributors to the global REE supply, but alkaline-hosted 

deposits have become important exploration targets, because 

they tend to be more enriched in the heavy HREEs than carbonatites and most other REE deposit types. 

An example of an alkaline igneous-related REE deposit 

in the United States occurs at Bokan Mountain in a southern part of Prince of Wales Island, southeastern Alaska. The 

deposit consists of vein-like intrusions (thin dikes) containing REEs, thorium, and uranium concentrations of several 

percent each. The principal vein-dike system, the Dotson 

zone, extends for at least 2.6 kilometers (km) in length and is 

composed of numerous, subparallel, thin dikes that are 1.5 m 

or less in width, forming a zone of about 50 m in total width 

(fig. 7). The REE mineralogy in these vein dikes is complex 

and fine-grained, with more than two dozen distinct REE 

minerals. These REE minerals occur in a variety of types, 

including oxide, silicate, phosphate, and carbonate minerals. 

Based on extensive drilling of the Dotson zone and adjacent I 

and L zone by Ucore Rare Metals Ltd. (Robinson and others, 

2011), the vein dikes have a combined inferred resource of 

5.275 million metric tons (Mt) of rock averaging 0.262 percent 

HREE oxides and 0.392 percent LREE oxides (Robinson and 

others, 2011). 
10 Rare Earth Element Mineral Deposits in the United States

Figure 7. Outcrop of rare earth element 

(REE)-rich “vein-dike” intrusions (dark vertical 

layers) in the Dotson zone on Bokan Mountain, 

southern part of Prince of Wales Island, 

southeastern Alaska. The vein-like dikes 

were emplaced by REE-bearing magmas, and 

subsequently altered multiple times by heated 

fluids. These vein dikes contain at least two 

dozen REE-bearing mineral phases, in forms of 

silicates, carbonates, phosphates, and oxide 

minerals. Photographs by Bradley Van Gosen.

Bokan Mountain
Rare Earth Element Mineral Deposit Types in the United States 11

Rare Earth Elements in Sedimentary Phosphate 

Deposits

USGS research has discovered that francolite (a carbonate-rich apatite mineral), common to some sedimentary 

phosphate-rich rocks (phosphorite), is highly enriched in 

HREEs. A continent-scale assessment has identified several 

unmined HREE-bearing phosphorites in the United States 

that are exposed over large areas (Emsbo and others, 2015, 

2016). This research has also demonstrated that REEs vary 

in a secular fashion because of oceanic redox state transitions 

during specific time periods in Earth’s history. The consistency of REE abundances within individual time horizons 

has identified time periods—Late Mississippian, Devonian, 

and Ordovician—as particularly favorable for the formation 

of phosphorites with high-REE abundances. For example, 

an Upper Ordovician horizon may rank as one of the largest 

concentrations of HREEs in the world. This nearly horizontal 

horizon occurs at, or just below the surface, over an area of 

2,000 square kilometers (km2) in northern Arkansas (fig. 8). 

Samples from more than 100 km2 of this 1.5-m-thick horizon 

have remarkably homogenous REE abundances, estimated to 

comprise 235 Mt of phosphate rock with 1.3 Mt of extractable 

total REE, of which 0.37 Mt are HREE, which is nearly twice 

the HREE content of the south China clays deposits (Emsbo 

and others, 2015). Moreover, this ore horizon extends in the 

shallow subsurface throughout Missouri and Indiana. Several 

samples of thin, irregularly distributed Upper Devonian phosphorites occurrences in the midcontinent region of the central 

United States reveal high HREE concentrations (orders of 

magnitude higher than the producing south China deposits). 

The REEs in sedimentary phosphorites are nearly 

100 percent extractable, using technologies currently (2019) 

used in the phosphate fertilizer industry in the United States 

(Emsbo and others, 2015). The scale of the domestic fertilizer 

industry, which produces 30 million metric tons per year, suggests that byproduct REE production from phosphate mines 

could meet much of the Nation’s HREE demand (Emsbo and 

others 2015, 2016). Furthermore, the ease of beneficiation and 

chemical dissolution of sedimentary francolite suggests that 

higher-grade phosphorite deposits might constitute stand-alone 

REE deposits. 

Figure 8. Two-meter-thick outcrop of Upper Ordovician, high-grade REE phosphorite in Arkansas. The unit’s thickness and REE 

concentration is remarkably homogeneous and the unit occurs at, or just below the surface more than 2,000 square kilometers in Arkansas. 

This phosphorite unit can also be traced into the shallow subsurface into adjacent Missouri and to Indiana. Photograph by Poul Emsbo.
12 Rare Earth Element Mineral Deposits in the United States

Vein Deposits

Mineral districts with multiple REE-rich veins of 

equivocal origin also exist. Most of these vein deposits are 

interpreted to be related to alkaline igneous rocks, which 

are not exposed at the surface and have not been confirmed 

by drilling. An example of vein-hosted REE mineralization 

occurs in the Lemhi Pass district along the Montana–Idaho 

border (fig. 4). This district contains 219 mapped quartz-rich 

veins with elevated concentrations of REEs and thorium 

(Staatz, 1979). Most of these veins are made up primarily of 

quartz and iron-oxide minerals with thorite (ThSiO4) and finegrained REE-bearing minerals, including monazite, allanite 

[(CaCe)(Al2Fe2+)(Si2O7)(SiO4)O(OH)], and apatite. The veins 

fill elongate fractures that cut through Precambrian metamorphic rocks. The REE-thorium-rich veins are as much as 

1,325 m in length and 12 m in width. The veins of the Lemhi 

Pass district contain approximately equal concentrations of 

REEs and thorium, with an average REO and thorium content 

that is about 0.43 percent for each (Staatz, 1979). The underlying source of these veins, most likely alkaline intrusions, is 

unresolved (Gillerman, 2008). There is little surface evidence 

of intrusions and no deep drilling has been done in the Lemhi 

Pass district that could potentially reveal buried intrusions. 

The Wet Mountains area of south-central Colorado 

hosts a district of REE-thorium-rich veins that formed along 

fractured zones that cut a Precambrian metamorphic terrane 

(fig. 4) (Armbrustmacher, 1988). The Wet Mountains mineral 

district is spatially associated with alkaline igneous intrusions, 

presumed to be genetically related to the REE-thorium veins. 

Most of these vein deposits lie within a 57 km2 area. The veins 

and mineralized fracture zones are linear features, typically 1 to 

2 m thick and as much as 15 m thick. Some veins can be traced 

for 1.5 km and some of the fracture zones can be traced for as 

much as 13 km. The veins and fracture zones average 0.21 percent LREE and 0.14 percent HREE (Armbrustmacher, 1988).

Iron Oxide-Apatite Deposits (IOA)

Massive iron oxide deposits of magmatic-hydrothermal 

origin can contain elevated concentrations of REEs, primarily 

occurring in the mineral apatite. The iron deposits that host 

elevated REE concentrations are commonly referred to as iron 

oxide-apatite (IOA) deposits, often considered a subgroup 

of the more generalized category of iron oxide-copper-gold 

(IOCG) deposits. Examples of massive IOA deposits in the 

United States containing enrichments in REEs are the Pea 

Ridge deposit in southeast Missouri and the Mineville district 

in northern New York (fig. 4).

The Pea Ridge magnetite-hematite IOA ore body is 

hosted by Mesoproterozoic volcanic rocks of southeastern 

Missouri. The magnetite-rich bodies are interpreted as the 

products of high-temperature, magmatic-hydrothermal processes that may have formed within the root zone of a volcanic 

caldera. In the Pea Ridge iron deposit, four REE-bearing 

breccia pipes steeply crosscut the magnetite-hematite orebody 

and surrounding host rock. Exposed portions of the breccia 

pipes are as much as 60 m in horizontal length and as much 

as 15 m in width; the pipes extend below the mined levels to 

an undetermined depth. The primary REE-bearing minerals in 

the breccia pipes are monazite, xenotime, and a fluorine-rich 

REE-bearing apatite. As a result, these breccia pipes contain 

REE of several percent (Day and others, 2016; Hofstra and 

others, 2016).

Other IOA deposits were mined in the Mineville iron district, New York, located in the northeastern part of the Adirondack Mountains (fig. 4). The ore bodies are massive magnetite 

deposits intricately folded and faulted within a complex suite 

of Precambrian metamorphic and igneous rocks. Past mining 

of the magnetite deposits for iron produced large tailing piles 

in the Mineville district. Some of the iron ores, and many of 

the remaining waste rock piles, contain REE-bearing apatite. 

The REEs reside mainly within apatite in these iron deposits 

(McKeown and Klemic, 1956). An estimated two-thirds of 

the district’s tailings were derived from apatite-bearing ores, 

which would represent an estimated 9 million tons of REEbearing tailings. These tailings represent a potential source for 

yttrium and other HREEs (Staatz and others, 1980).

Monazite-Xenotime-Bearing Placer Deposits 

(Heavy-Mineral Sands)

Heavy-mineral sands are sedimentary deposits of dense 

(heavy) minerals that accumulate with sand, silt, and clay in 

coastal and alluvial environments, locally forming economic 

concentrations of heavy minerals (Van Gosen and others, 

2014a). Expansive coastal deposits of heavy-mineral sands are 

the main source of titanium feedstock for the large titanium 

dioxide pigments industry, through recovery of the minerals 

ilmenite (Fe2+TiO3), rutile (TiO2), and leucoxene (an alteration 

product of ilmenite). Heavy-mineral sands are also the principal source of zircon (ZrSiO4

), often recovered as a coproduct, 

for use mostly in refractory products. 

In some deposits, monazite is recovered as a byproduct 

mineral, sought for its REEs and thorium (Sengupta and 

Van Gosen, 2016). Monazite is one the heaviest minerals in 

the heavy-mineral suite and can be the dominant REE- and 

thorium-bearing mineral in heavy-mineral sands. This monazite 

is mainly derived from the erosion of igneous and high-grade 

metamorphic rocks that lie inland of the rivers and coastal plain. 

Monazite is resistant to chemical and physical weathering, thus 

can survive the arduous trip from a distant bedrock source to its 

deposition in a stream, river, or a coastal plain environment.

Byproduct monazite has been recovered in Australia, 

Brazil, China, Indonesia, Korea, Malaysia, New Zealand, Sri 

Lanka, Thailand, Zaire, and the United States, derived mainly 

from the mining of heavy-mineral sands deposits in ancient 

and modern coastlines, as well as from some inland stream 

and river (alluvial) deposits. Recently, monazite has been 

recovered from modern coasts in India, Sri Lanka, and Brazil, 

and alluvial placers in Malaysia and Thailand (Van Gosen and 

others, 2014a).
Summary 13

Recent regional-scale studies of the Atlantic Coastal Plain 

of the southeastern United States by the USGS have identified 

(1) areas with elevated concentrations of thorium in coastal 

sediments, indicative of monazite, based on data measured 

from regional airborne radiometric surveys (Shah and others, 

2017); and (2) areas of high titanium content based on stream 

sediment sampling surveys across the coastal plain (fig. 4) 

(Van Gosen and Ellefsen, 2018). These studies suggest that 

large areas of the Atlantic Coastal Plain are permissive for 

deposits of titanium-bearing heavy-mineral sands that also 

contain monazite, a potential source of REEs.

Ion-Adsorption Clay Deposits (REE in GraniteDerived Regolith)

Clay deposits in southern China are the world’s primary 

sources of the HREEs. This deposit type is informally referred 

to as south China clay deposits, and more formally as ionadsorption clay deposits or REE in granite-derived regolith. 

These deposits formed through the intensive weathering 

of REE-bearing granites in regions that experienced warm 

climates with moderate to intensive rainfall. The generalized 

processes that formed these deposits are

• The REEs are leached by groundwater from REEbearing granites (the bedrock).

• Intensive weathering formed thick clay-rich zones of 

soils (laterite) atop the granites.

• The REEs, sourced from the underlying granite, were 

mobilized and became weakly attached (by ionadsorption) onto the clays.

• The regions remained stable such that the weathered 

material is not removed by erosion.

Although these clay deposits typically contain modest REE 

concentrations (approximately 0.03 to 0.2 percent REEs), they 

have become economically viable deposits, because (1) they are 

preferentially enriched in the high-value HREEs; (2) the REEs 

are easily extracted from the clays with weak acids; and (3) mining costs are low.

A USGS study (Foley and Ayuso, 2015) identified REEbearing clay deposits overlying weathered granite plutons in 

southeastern United States with several characteristics in common with the south China clay deposits. Comparisons showed 

similarities in mineralogy, inferred processes of formation, and 

REE concentrations.

Summary

Most rare earth elements (REE) deposits tend to be 

preferentially enriched in either the light rare earth elements 

(LREE) or the heavy rare earth elements (HREE). Carbonatites, for example, are enriched in minerals of the bastnäesite 

group, which are LREE rich. Because of this mineralogy, 

combined with the large size of the world-class carbonatite 

bodies, they currently fulfill most of the global LREE demand. 

Coastal deposits of heavy-mineral sands are mined for their 

titanium minerals, but many also contain accessory grains 

of monazite, which can be easily extracted from the sands. 

Monazite is LREE rich and is an additional source of LREEs; 

however, monazite is more difficult to dissolve and process.

Meeting the growing need for HREEs is more challenging, because efforts to identify additional economically feasible 

HREE-rich deposits has been less successful. Alkaline igneous 

intrusions are often more enriched in the HREEs relative to the 

common igneous rocks, but the ore mineralogy of these deposits can be complex and require specialized mineral separation 

techniques. Piles of mine-waste materials produced from the 

past mining of some iron deposits (for example, iron-oxide 

apatite deposits), specifically the iron ores that contain HREEbearing apatite, may offer another potential secondary HREE 

resource that has yet to be exploited. U.S. Geological Survey 

research has also delineated HREE-bearing sedimentary 

phosphate-rich rocks (phosphorite) that are exposed over large 

areas of the midcontinent of the United States. Many of these 

phosphorites are enriched in readily extractable HREEs, thus 

being a potentially large, but undeveloped HREE resource.

Alaska has considerable potential for undiscovered 

critical minerals, including REE-bearing deposits. A recent 

(2016) USGS study used a data-driven, geographic information system (GIS)-implemented method to identify areas that 

have mineral resource potential in Alaska, which included 

an evaluation for deposits of REEs with thorium, yttrium, 

and niobium (and sometimes also uranium and zirconium) 

associated with peralkaline to carbonatitic igneous intrusive 

rocks. The prospectivity analysis identified not only areas of 

known REE-enrichments and prospects, such as the Bokan 

Mountain peralkaline system and the Tofty carbonatite system, 

but also highlighted areas with high potential in areas not 

previously considered to be prospective for REEs. Several of 

these regions are the focus of ongoing USGS studies to better 

characterize and interpret the geologic framework and metallogeny for REE mineral potential.

Within the United States many mineral deposits contain 

concentrations of REEs, but to date, the Mountain Pass mine of 

southeastern California has been the only substantial producer. 

The economic development of REE mineral deposits hinges 

on a variety of factors, which include commodity prices and 

the entirety of extraction costs. Unlike many traditional metal 

commodities hosted in relatively simple minerals (as examples, 

copper in chalcopyrite [CuFeS] or lead in galena [PbS]), most 

of the REEs are hosted by minerals that have complex chemical formulas, presenting more of a challenge to process and 

extract the REEs. Furthermore, once the REEs are separated 

as a group from a mineral, individual REEs must be separated 

from the other REEs to produce a final product; for example, 

neodymium is separated from other light REEs for use by the 

magnet industry. Advancements and refinements in mineral 

processing techniques may allow mineralogically complex 

REE deposits to be more readily developed in the future.
14 Rare Earth Element Mineral Deposits in the United States

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Van Gosen and others—Rare Earth Element Mineral Deposits in the United States—Circular 1454

ISSN 1607-084X (print)

ISSN 2330-5703 (online)

https://doi.org/10.3133/cir1454