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?2015 Society of Economic Geologists, Inc.

Economic Geology, v. 110, pp. 1925–1952

A Detailed Assessment of Global Rare Earth Element Resources:

Opportunities and Challenges*

Zhehan Weng,1,? Simon M. Jowitt,2 Gavin M. Mudd,1 and Nawshad Haque3

1 Environmental Engineering, Department of Civil Engineering, Monash University, Wellington Road, Clayton, VIC 3800, Australia

2 School of Earth, Atmosphere and Environment, Monash University, Wellington Road, Clayton, VIC 3800, Australia

3 CSIRO Mineral Resources, Private Bag 10, Clayton South, VIC 3169, Australia

Abstract

Rare earth elements (REE) are indispensable to infrastructure, technology, and modern lifestyles, which

has led to an increasing demand for these elements. The current global rare earth oxides (REO) market is

dominated by Chinese production, which peaked in 2006 at 133,000 tonnes REO per year, accounting for some

97.1% of global production, causing concern about the long-term supply of REE resources. Although the REE

consist of 17 individual elements (15 lanthanides plus scandium and yttrium) that are hosted by numerous

types of mineralization, the relatively modest scale of the global REE mining sector has limited our knowledge

of REE mineral resources and mineralizing systems compared to metals such as copper and iron, which are

produced in much larger quantities.

In order to quantitatively analyze the mineralogy, concentrations, and geologic types of REE deposits, we

compiled a global dataset of REE mineral resources based on the most recently available data (2013–2014).

This compilation yields minimum global contained total rare earth oxides plus yttrium oxide (TREO + Y)

resources of 619.5 Mt split between 267 deposits. Deposits with available grade and tonnage data (260 of the

267 deposits in our database) contain some 88,483 Mt of mineral resources at an average concentration of

0.63% TREO + Y, hosting 553.7 Mt TREO + Y. Of the 267 total deposits in our database, some 160 have min-

eral resources reported using statutory mining codes (e.g., JORC, NI43-101, SAMREC), with the remaining

107 projects having CRIRSCO-noncompliant mineral resources that are based on information available in the

industry literature and peer-reviewed scientific articles.

Approximately 51.4% of global REO resources are hosted by carbonatite deposits, and bastn?site, monazite,

and xenotime are the three most significant REE minerals, accounting for >90% of the total resources within

our database. In terms of REE resources by individual country, China dominates currently known TREO +

Y resources (268.1 Mt), accounting for 43% of the global REO resources within our database, with Australia,

Russia, Canada, and Brazil having 64.5, 62.3, 48.3, and 47.1 Mt of contained TREO + Y resources, respectively.

Some 84.3 Mt TREO + Y is hosted within tailings (dominated by tailings from Bayan Obo but with smaller

resources at Palabora, Steenkampskraal, and Mary Kathleen) and 12.4 Mt TREO + Y is hosted by monazite

within heavy mineral sands projects, illustrating the potential for REO production from resources other than

traditional hard-rock mining.

Global REE resources are dominated by the light REE, having an average light REO (LREO; La-Gd) to

heavy REO (Tb-Lu and Y) ratio of 13:1. These REE deposits contain an average of 81 ppm Th and 127 ppm U,

indicating that radioactive waste associated with REE extraction and refining could be a concern. Modeling

the 2012 global production figures of 110 kt TREO + Y combined with an assumed 5% annual growth in REE

demand indicates that known REE resources could sustain production until 2100 and that geologic scarcity is

not an immediate problem. This suggests that other issues such as environmental, economic, and social factors

will strongly influence the development of REE resources.

Introduction

Rare earth elements (REE) have crucial industrial uses and are indispensable to the development of modern defense sys-tems, green technologies, and electronic applications. This is exemplified by REE alloys and permanent magnets, both of which are considered essential for renewable energy technol-ogy (e.g., electric vehicles, energy-efficient lighting, and wind power turbines). From a production perspective, the REE are primarily reported as rare earth oxides (REO; U.S. Environ-mental Protection Agency [USEPA], 2012), and the growth of REE-dependent technologies and applications is expected to significantly increase global demand for the REO over coming decades (U.S. Department of Energy [USDOE], 2010; Hoen-derdaal et al., 2013; Humphries, 2013).

The global REO market peaked in 2006 with 133,000 tonnes (t) of produced REO and is dominated by C hinese produc-tion, which accounted for 97.1% of global production in 2006 (United States Geological Survey [USGS], 1997–2015). Histor-ical global REO production is shown in Figure 1. For various political, economic, and environmental reasons, the C hinese government from about 2006 implemented mandatory export restrictions on REE, tungsten (W), and molybdenum (Mo) (State C ouncil Information Office of the People’s Republic of China [SCIO], 2012). From 2006 to 2011, the REO export quota for Sino-foreign joint ventures in China decreased from 16,070 to 7,746 t, whereas domestic REE producers and trad-ers had export quotas reduced from 45,000 to 22,512 t (Morri-son and Tang, 2012). These restrictions led to a decrease in the

0361-0128/15/4355/1925-28 1925Submitted: August 19, 2014 Accepted: June 12, 2015

? Corresponding author: e-mail, zhehan.weng@https://www.wendangku.net/doc/f12989873.html,

*A digital supplement to this paper is available at http://economicgeology. org/ and at https://www.wendangku.net/doc/f12989873.html,/.

1926

WENG ET AL.

Chinese REO export quota from 61,560 t in 2006 to 30,246 t in 2011. In addition, China’s annual REO production also gradu-ally declined from 133,000 t in 2006 to 95,000 t in 2013 (USGS, 1997–2015). These restrictions on REO exports were coinci-dent with an internal drive in C hina to encourage domestic REO consumption, including high-end and high-tech REE-related processing and manufacturing. The Chinese restrictions on REO exports caused a significant increase in global REO prices (Humphries, 2013), although these prices have declined recently (USGS, 1997–2015). These quotas also highlighted concerns about the future supply of critical metals, driven not only by economics but also by geopolitical considerations, industrial and economic interests, supply monopoly, and pri-oritization of domestic downstream industries (Hayes-Labruto et al., 2013; Moss et al., 2013a, b; Wübbeke, 2013). This was noted by the World Trade Organization (WTO), which in 2014 announced the settlement of China’s REE export dispute and the removal of the Chinese REE export quota (WTO, 2014).Nevertheless, China’s REE export restrictions exemplify the risk inherent in having the global supply of the REO depen-dent on a dominant supplier or country, which obviously poses significant risks to the security of supply of these impor-tant elements. This situation has led to a widespread inter-est in quantifying the availability of these important elements (e.g., USDOE, 2010; Moss et al., 2011; Naden, 2014). Thus, there is need for a comprehensive assessment of global REE mineral resources to identify key opportunities, uncertainties, and challenges for the global REE industry. The critical aspects needed for such an assessment include identifying major REE mineral deposit types, classifying these deposits by REE mineralogy, and identifying the presence or absence of potential by-/co-products (e.g., Fe, Ti, Nb, and Zr) and/or hazardous impurities (e.g., U and Th). These data will provide a rigorous foundation for industries and governments to ini-tiate the development of sustainable, secure, and economic global REE supplies.

The International Union of Applied and Pure C hemistry (IUPAC) defines the REE as the 15 lanthanide elements plus Sc and Y, as shown in Table 1 (IUPAC , 2005). Each of the REE has distinctive characteristics and usages, with the lan-thanide elements divided by electron shell configuration into the light REE (LREE; La to Gd) and the heavy REE (HREE; Tb to Lu), although the mining industry does not currently use such a definitive classification of the split between LREE and HREE, with some projects (e.g., Buckton, Browns Range, etc.) defining the LREE as including La, C e, Pr, and Nd, whereas the HREE (as reported by the mining companies involved) include Sm, Eu, and Gd (e.g., Eccles et al., 2013). Furthermore, the term medium REE (MREE; Sm to Gd) is also used in some industrial reporting (e.g., Ashram, Charley C reek), but does not have a formal IUPAC classification. Y and Sc are not formally classified as either LREE or HREE but have a chemical affinity with the lanthanide group of ele-ments, with these chemical affinities meaning that Y is also

100

120

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1950196019701980199020002010

A n n u a l P r o d u c t i o n (k t T R E O +Y )

Fig. 1. Historical TREO + Y production split by country. Average global REO production data are from the U.S. Bureau of Mines (USBoM, 1927–1934, 1933–1996) and the U.S. Geological Survey (USGS, 1901–1927, 1994–2011, 1997–2015). Australian REO are based on monazite production data, assuming a minimum of 60% contained TREO + Y (BoMRGG, 1960–1985).

A DETAILED ASSESSMENT OF GLOBAL RARE EARTH ELEMENT RESOURCES: OPPORTUNITIES AND CHALLENGES 1927

often considered an HREE. The short half-life of Pm means that it is rarely extracted during the exploitation of REE min-eral deposits but, rather, may be produced as by-product from the nuclear industry, and as such is excluded from our dataset. Here, we split the REE according to the IUPAC classification into the LREE (La, C e, Pr, Nd, Sm, Eu, and Gd) and the HREE (Tb, Dy, Ho, Er, Tm, Yb, and Lu).

In contrast to their name, some of the REE are relatively abundant in the Earth’s crust and, although typical REE abundances in the Earth’s upper crust vary significantly, Ce and La have average crustal concentrations of 63 and 31 parts per million (ppm), respectively—both higher than the aver-age crustal concentrations of Cu (28 ppm) and Pb (17 ppm; Rudnick and Gao, 2003). In comparison, Tm and Lu have average crustal concentrations of 0.3 and 0.31 ppm, respec-tively, much lower than the majority of other economically important metals, but still higher than Au, Ag, and the plati-num group elements (Rudnick and Gao, 2003).

The REE are rarely (if ever) present as native metals in the natural environment; instead, they often substitute for other elements within the matrix of certain minerals, espe-cially phosphates and carbonates. At present, the most impor-tant economic REE-bearing minerals are bastn?site ((Ce,La) (CO3)F), monazite ((Ce,La,Nd,Th)PO4), and xenotime (YPO4; Jordens et al., 2013), although the REE can substitute into the matrix of more than 200 individual minerals (Jones et al., 1996). The substitution-dominated nature of REE minerals and the low difference in density between these minerals and their associated gangue means that REE ores are complicated to process, especially when compared to more commonly pro-cessed sulfide and oxide ores (e.g., Cu, Pb, and Zn). In addi-tion, the chemical similarities between the REE mean that the separation and purification of individual REE, a necessary step in the vast majority of end uses, is also difficult, with both concentration and refining being chemically and energy inten-sive (USEPA, 2012). Furthermore, the geologic and mineral-ogical variability of REE deposits means that the extraction, concentration, and processing of REE ores is highly variable from project to project, and is often deposit type or even indi-vidual deposit specific. The geochemical behavior of the REE also means that REE-bearing minerals often contain uranium and thorium, as is evidenced by the high concentrations of Th that are often present in REE-bearing monazite (Long et al., 2010), with significant amounts of U also present in or asso-ciated with REE-enriched mineral deposits (USEPA, 2012). These processing difficulties and complexities are indicative of the risk factors inherent in REE exploration, mining, and processing, which have previously hindered the economic development of potential REE resources.

Here, we present a quantitative global REE dataset based on mineral resources reported using various statutory reporting standards, geologic studies, and government assessments, and use these data to provide an overview of differing REE mineral deposit types, tonnages, TREO + Y concentrations, principal mineralogies, individual REE concentrations, and significant by-/co-products or impurities. This dataset provides a basis for the quantitative analysis of the opportunities, challenges, and uncertainties inherent within the global REE supply chain.

Table 1. Summary of the Chemistry and Average Crustal Abundances of the REE1

Element Atomic IUPAC Average crust

abbreviation number Element name classification2 (ppm)3 Usages

La 57 Lanthanum Light 31 Optics, batteries, catalysis, hydrogen storage

Ce 58 Cerium Light 63 Chemical applications, coloring, polishing glass, catalysis,

hybrid vehicles

Pr 59 Praseodymium Light 7.1 Magnets, lighting, optics

Nd 60 Neodymium Light 27 (SmCo) magnets, lighting, lasers, optics, hybrid vehicle

batteries

Pm 61 Promethium Light – Limited use due to radioactivity, used in luminous paint and

atomic batteries; very rare in nature (due to its short

half-life)

Sm 62 Samarium Light 4.7 Magnets, lasers, masers, lightweight magnets

Eu 63 Europium Light 1 Lasers, lighting, medical applications

Gd 64 Gadolinium Light 4 Magnets, glassware, lasers, X-ray contrast agent, computer

applications, medical applications

Tb 65 Terbium Heavy 0.7 Lasers, lighting, lightweight magnets

Dy 66 Dysprosium Heavy 3.9 Magnets, lasers, hybrid vehicle batteries

Ho 67 Holmium Heavy 0.83 Lasers

Er 68 Erbium Heavy 2.3 Lasers, medical applications, neutron-absorbing control rods

in nuclear industry

Tm 69 Thulium Heavy 0.3 X-ray generation

Yb 70 Ytterbium Heavy 2 Lasers, chemical industry applications

Lu 71 Lutetium Heavy 0.31 Medical applications, chemical industry applications

Sc 21 Scandium N/A 14 Alloys in aerospace engineering, lighting, fuel cells

Y 39 Yttrium Heavy 21 Lasers, superconductors, microwave filters, lighting, ceramic

– = concentration too low to assess as a result of the short radioactive half-life of this element

1 Adapted from Weng et al. (2013)

2 The chemical classification of the REE uses the configuration of electrons in the outer shell of the element, with the LREE having no paired clockwise- and counterclockwise-spinning electrons, whereas the HREE have both clockwise- and counterclockwise-spinning electrons; Sc and Y are chemically similar to these elements and are also included, with Y classified as a heavy rare earth element, although the properties of Sc are not similar enough to either LREE or HREE to allow further chemical classification

3 From Rudnick and Gao (2003)

1928 WENG ET AL.

Methodology

REE deposit types and mineralogy

Understanding REE mineral deposit types and the miner-alogy of potential REE deposits is crucial for exploration tar-geting and determining the feasibility of mining operations, processing, and refining. Therefore, we have classified our database using a range of differing mineral deposits types; this classification was first published by Weng et al. (2013) and has been expanded and slightly adapted to reflect the range of known REE deposits. Our classification is obviously a sim-plification of the natural complexity of REE deposits, which has led to the formulation and implementation of numerous other classification schemes; for example, the United States Geological Survey (Long et al., 2010) classification splits REE deposits into a total of 34 different types of mineral deposits, whereas the British Geological Survey (Walters et al., 2010) uses a simpler split of primary deposits of igneous and hydrothermal origin or secondary deposits concentrated by sedimentary processes and weathering. Here, we con-sider both the geologic processes involved in the formation of REE deposits and the mineralogy of individual deposits in our classification scheme (shown in Table 2). This classifica-tion splits REE deposits into three broad categories relating to the dominant processes that formed the REE mineraliza-tion (i.e., igneous, hydrothermal, or secondary/sedimentary processes), before further subdividing into 14 subclassifica-tions (carbonatite, alkaline complexes and pegmatites, felsic volcanic, granites and granitic pegmatites, iron oxide copper-gold (IOCG), granite-related skarn, carbonatite-related skarn, hydrothermal undifferentiated, heavy mineral sands (HMS), laterites/soils/clays, tailings, shale hosted, alluvial/placer, and sedimentary undifferentiated deposits) that are used to clas-sify individual mineral deposits within our database. It should be noted that this classification, as with all mineral deposit-type classifications, is reliant on the amount of information available, as epitomized by the world’s most important REE deposit at Bayan Obo; the formation of this REE deposit is still controversial (e.g., Yang and Le Bas, 2004; Yang et al., 2011; Smith et al., 2015) and, thus, we can only rely on current knowledge and the geologic evidence available within both published and industry literature (e.g., NI43-101 reports) to classify the deposits within our database. In addition, as is often the case for mineral deposits (e.g., Jowitt et al., 2013a), a given mining camp or even resource may contain two or more REE deposit types (Jones et al., 1996; Lai and Yang, 2013; Weng et al., 2013); where this is the case, we have classified a given deposit by the dominant (i.e., most contained REE) deposit type. Several of the hydrothermal deposits in our data-base are of uncertain origin but are definitively linked with magmatic bodies; we have classified these as skarns, although this terminology may not be strictly correct. Finally, a few of the deposits in our database have definitive hydrothermal or sedimentary origins but could not be classified further, either as a result of a lack of research or because the deposits them-selves were poorly understood; these remain classified simply as hydrothermal or sedimentary undifferentiated within our database. We have also classified the Hangaslampi resource as hydrothermal and undifferentiated because, although the deposit is an orogenic gold deposit that also contains C o,

Table 2. Classification of REE Mineral Deposit Types Used During This Study1

Process Mineral deposit type Key examples

Igneous Silica undersaturated Carbonatite Bayan Obo, China; Araxá, Brazil; Karonge, Burundi;

Mountain Pass, USA; Nolans Bore, Australia;

Steenkampskraal, South Africa

Alkaline complexes and Khibina and Lovozero, Russia; Norra K?rr, Sweden;

alkaline pegmatites Bokan, USA; Thor Lake, Canada; Kipawa Lake,

Canada; Kola Peninsula, Russia

Silica saturated to oversaturated Felsic volcanic Round Top, USA; Foxtrot, Canada

Granites and Khibina Massif, Russia; Motzfeldt, Greenland;

granitic pegmatites Ytterby, Sweden

Hydrothermal Iron oxide copper-gold (IOCG) Olympic Dam, Australia; Milo, Australia

Skarn Granite related Mary Kathleen, Australia

Carbonatite related John Galt, Australia; Saima, China

Undifferentiated Mount Gee, Australia

Secondary/sedimentary Heavy mineral sands (HMS) WIM150, Australia; monazite stockpile in India

(IREL)

Laterite/soil/clay Tantalus, Madagascar

Tailings Steenkampskraal, South Africa; Port Pirie, Australia;

Mary Kathleen, Australia

Shale hosted Buckton, Canada

Alluvial/placer Charley Creek, Australia; India; Sri Lanka; Florida,

USA

Undifferentiated Korella, Australia

1 Adapted from Weng et al. (2013)

A DETAILED ASSESSMENT OF GLOBAL RARE EARTH ELEMENT RESOURCES: OPPORTUNITIES AND CHALLENGES 1929

the nature and association of the REE with this mineraliza-tion remain unclear—especially as, although the Co and Au resources within this deposit are reported according to the JORC code, the grade and tonnage of the REE within this deposit remain conceptual and are not currently code compli-ant. This lack of code compliance for the REE resource within this project also means that this deposit REE resource has a low confidence rating. The next section provides a brief out-line of the differing categories and processes involved in REE deposit formation, and the reader is referred to Weng et al. (2013) and references therein for more detailed descriptions. The REE are highly incompatible in the majority of mag-matic systems, meaning that these elements are concentrated in magmas that form as the result of low-degree partial melt-ing of the mantle; this is especially true of metasomatically enriched regions of the mantle that may contain higher con-centrations of the REE compared to those expected for typi-cal primitive mantle. The incompatibility of the REE means that low-degree partial melts can contain very high concentra-tions of these elements (e.g., C hakhmouradian and Zaitsev, 2012; Jordan et al., 2015), although this also means that these elements can be concentrated during significant fraction-ation or differentiation, with the REE eventually crystallizing out as REE minerals during late-stage fractionation, rather than within earlier fractionated minerals (e.g., Medlin et al., 2015)—a process that can also lead to the formation of vola-tile-rich pegmatitic magmas. This means that the majority of igneous REE deposits are related either to rock formed from magmas generated by very low degree partial melting (and other associated processes) or by extreme fractionation. Igne-ous rocks with high REE concentrations, such as carbonatites or alkaline igneous complexes, also form ideal sources for REE-enriched hydrothermal fluids, leading to several REE deposits that contain both primary igneous and hydrothermal REE mineralization (e.g., Bayan Obo).

The REE are thought to be generally immobile during the majority of hydrothermal processes, indicating that the mobilization and the effective deposition and concentration of these elements may require atypical hydrothermal activity. In addition, our hydrothermal REE deposit classification con-siders very high temperature systems that are, for example, associated with the formation of pegmatites to fall within the igneous category of deposits. Both high-temperature magma-tohydrothermal and F- and Cl-bearing hydrothermal systems are frequently associated with the formation of REE-enriched hydrothermal mineralization and hydrothermal REE mineral deposits, although the two systems are not mutually exclusive (e.g., Williams-Jones et al., 2012; Jowitt et al., 2013b; Weng et al., 2013). These systems are thought to dominate the for-mation of hydrothermal REE deposits, as (1) the REE are more soluble in high-temperature hydrothermal fluids than lower-temperature fluids (Williams-Jones et al., 2012) and (2) hydrothermal fluids that contain significant amounts of F, Cl, and Li ligands can also mobilize significant amounts of the REE, in addition to elements such as U that are often associ-ated with the REE (e.g., McPhie et al., 2011; Williams-Jones et al., 2012), although the exact role of F in the mobilization of the REE and the formation of REE mineral deposits remains contentious (e.g., Skirrow et al., 2007; McPhie et al., 2011; Williams-Jones et al., 2012; Ernst and Jowitt, 2013). Both high-temperature and high-F and -C l hydrothermal fluids most likely deposit their REE during interaction with cooler and pH-neutralizing rocks or fluids (e.g., Williams-Jones et al., 2012), although REE deposition may not always be syn-chronous with the deposition of other metals, such as Cu, Au, or U—as, for example, may be the case at the Hangaslampi deposit, as discussed above.

The fact that REE-bearing minerals are often somewhat denser than most silicate minerals (although not to the same extent as, say, native Au or sulfide minerals) and are refractory and resistant to both alteration and weathering means that they are often preferentially concentrated into sedimentary or secondary deposits during erosion, transportation, and depo-sition. This has led to the formation of a diverse range of sedi-mentary (e.g., shale-hosted REE deposits), secondary (e.g., laterite), or placer (e.g., alluvial deposits)-type REE deposits, with the latter two types of deposit containing REE miner-alization that is often associated with other dense, refractory minerals (e.g., zircon, rutile, and ilmenite). Although both placer and HMS deposits may result from similar geologic processes, the minerals they target may differ significantly. For example, placer REE deposits like Charley Creek domi-nantly target REE-enriched minerals such as monazite and xenotime, whereas HMS operations usually target ilmenite, rutile, and zircon, and may produce monazite as a by-product. Hence, placer REE and HMS deposits have very different REE production potentials, meaning that we separate these deposits into two differing classification categories. Our placer category also includes ancient paleoplacer deposits that have been upgraded by postdepositional hydrothermal or meta-morphic activity, but anthropogenic secondary placer or tail-ings deposits, such as the REE-enriched tailings resource at Mary Kathleen, which formed as a result of mining of primary skarn mineralization, have been classified as a separate tail-ings category within the overall secondary/sedimentary class of REE deposits (Table 2).

REE mineral deposits host a wide and diverse range of REE-bearing minerals, the most economically important of which are bastn?site, monazite, and xenotime. These are just three of the more than 200 minerals known to contain essential or significant amounts of the REE (Jones et al., 1996; Christie et al., 1998; Hoatson et al., 2011), all of which form as a result of a wide range of geologic processes and, thus, are found in a diverse range of igneous, sedimentary, and metamorphic rocks. This means that understanding the processes that form these mineral deposits and their REE-bearing minerals is crucial not only for exploration but also for designing and operating ore processing routes as well as REE processing facilities (Interna-tional Atomic Energy Agency [IAEA], 2011a). Given this, we also have classified the REE deposits in our compilation by the dominant REE mineral or minerals within the deposit; as with the mineral deposit classification outlined above, individual deposits may contain a range of undisclosed REE minerals, but our classification focuses on publicly available information taken either from statutory mining code-based reports or from previously published geologic research.

Mineral Resource Accounting

Global REE production has long been dominated by car-bonatite or weathered carbonatite deposits, such as Bayan

1930 WENG ET AL.

Obo in China, Mountain Pass in the United States, and Mount Weld in Australia. However, as discussed above, various types of mineral deposits, including alkaline complexes and pegma-tites (e.g., Tanbreez in Greenland, Strange Lake in Canada), felsic volcanic rocks (e.g., Round Top in the United States), shale-hosted (e.g., the Grande-Vallée complex and Buckton in C anada), and HMS (e.g., WIM 150/200 in Australia and monazite stockpiles in India) deposits, can contain significant amounts of REE mineral resources and could potentially become major REO producers. The mineralogy, grades, ton-nages, and mineral processing used in the exploitation of all these REE deposits have not been systemically analyzed in the literature to date, and each deposit type contains different concentrations of the individual REE and differing propor-tions of the LREE and the HREE, further complicating the issue of refined REO production. The increasing demand for the REE has also accelerated exploration and the push for extraction from all differing types of REE deposits, either as a target commodity or as a by-product of other elements, such as Fe, Nb, Zr, Ti, and U.

In order to justify the economic feasibility and planning of a mineral deposit, mining companies commonly use statutory codes for assessing and reporting mineral resources, with Aus-tralia using the Joint Ore Reserves Committee (JORC) Code (Stephenson, 2001; Australasian Institute of Mining and Met-allurgy [AusIMM] et al., 2012), Canada using the CIM code and National Instrument 43-101 (NI 43-101; Ontario Securi-ties Commission [OSC], 2011), South Africa using the South African Mineral Resource C ommittee (SAMREC) code (South African Mineral Resource Committee Working Group [SAMRC WG], 2009), and similar codes or standards exist-ing in the United States, China, Russia, and Europe. In 1994, the Committee for Mineral Reserves International Reporting Standards (also known as CRIRSCO) established an interna-tional standard on mineral reserve-resources reporting, with current members of CRIRSCO including Australia, Canada, Chile, Europe, Russia, South Africa, and the United States. As discussed by Mudd et al. (2013a) and others, there are two primary categories used to classify a mineral deposit: ore reserves and mineral resources. Ore reserves typically have a high probability of profitable production and can be the basis of a technically and economically viable project, whereas min-eral resources have reasonable uncertainties within certain modifying factors (e.g., mining, processing, metallurgical, infrastructure, economic, marketing, legal, environmental, social implications, governmental policy, etc.) for eventual economic extraction (e.g., AusIMM et al., 2012). C ommon definitions include the following:

1. Ore reserves: Assessments demonstrate at the time of reporting that profitable extraction could reasonably be justi-fied. Ore reserves are subdivided, in order of increasing con-fidence, into probable ore reserves and proved ore reserves.

2. Mineral resources: The location, quantity, grade, geo-logic characteristics, and continuity of a mineral resource are known such that there are reasonable prospects for eventual economic extraction, although not all modifying factors have been assessed and, hence, some uncertainty remains. Mineral resources are subdivided, in order of increasing geologic con-fidence, into inferred, indicated, and measured categories. An inferred mineral resource, where geologic evidence is suffi-cient to imply but not verify geologic and grade (or quality) continuity, has a lower level of confidence than is inherent within measured or indicated mineral resources and, there-fore, cannot be directly converted to ore reserves. It is reason-ably expected that the majority of inferred mineral resources could be upgraded to indicated mineral resources with con-tinued exploration (AusIMM et al., 2012).

Some studies undertaken by various geologic, scien-tific, and governmental organizations assess global REE resources, summarized in Table 3, with the majority based on regional or global geologic estimates (e.g., Indian Bureau of Miners [IBM], 2014), or are focused on limited mineral resources/mineral reserves assessments for individual coun-tries (e.g., C hristie et al., 1998; Hoatson et al., 2011). As such, these assessments cannot provide a realistic and sys-tematic dataset of global REE mineral resources that can be used for predicting the global security of supply of these

Table 3. USGS Reserves and Reserves Base Values for the REO, Including Respective National Resource Estimates, and

Cumulative REO Production by Country to 2013 (in Mt REO)

Reserves Reserves Reserves Reserves National resource Cumulative REO ountry (2008)1 (2010) (2013) (2014) estimate production USA 13 13 13 1.8 ND 0.56

Australia 5.2 1.6 2.1 3.2 582 0.16

Brazil 0.05 0.05 22 22 ND 0.012

C hina 27 55 55 55 1823 2.04

India 1.1 3.1 3.1 3.1 64 0.077 Malaysia 0.03 0.03 0.03 0.03 ND 0.019 Russia and Commonwealth of Independent States 19 19 ND ND ND 0.061 Other 22 22 41 41 ND 0.007 Total5 885 1105 1405 1305 2.94

Notes: Reserves from USGS (1997–2015); ND = no data

1Reserves base in 2008 was 150 Mt REO, suggesting an additional 62 Mt REO to the reserves

2Total mineral resources estimate for Australia (Britt et al., 2015)

3National resource estimate for China is from CSRE (2002)

4India assumes 60% REO from reported monazite resources from IBM (2014); historical Australian production is from BoMRGG (1960–1985) with an assumed 60% REO conversion rate from reported monazite production

5Totals rounded down to two significant figures

A DETAILED ASSESSMENT OF GLOBAL RARE EARTH ELEMENT RESOURCES: OPPORTUNITIES AND CHALLENGES 1931

critical elements. The most widely cited group that pub-lishes such estimates is the USGS, which publishes approxi-mate reserve estimates for numerous metals and minerals in its annual Mineral Commodity Summaries (USGS, 1997–2015). Recent estimates of REO reserves, mineral resources (depending on source organization), and annual and cumu-lative production (see Table 3) suggest global REO reserves of about 130 Mt in 2014. In reality, mining companies tend to demonstrate an ore reserve of a mining project using the minimal investment required to justify its profitability. How-ever, given that ore reserves are determined by a range of compulsory “modifying factors” (see above), additional min-eral resources that are known but not quantified as reserves are excluded from formal ore reserve estimates. This means that ore reserves generally represent only a small part of an often continuous orebody, with long-term production plan-ning involving the continual upgrade of mineral resources to ore reserves and then production, commonly as a project is operating (e.g., Jowitt et al., 2013a; Mudd et al., 2013a, b). As summarized in Hellman and Duncan (2014, p. 111), “there are no special issues relating to the mechanics of the estimation of REE mineral resources which appear similar in mineralization style to primary and supergene enriched C u deposits,” meaning that all categories of REE min-eral resources could potentially contribute to future REE reserves, as has been documented by previous research (e.g., Jowitt et al., 2013a; Mudd et al., 2013a, b).

In order to realistically analyze the long-term prospects for global recoverable REE, this study focuses on REE mineral resources that include all measured, indicated, and inferred resources by individual projects or deposits reported under statutory codes or other robust technical literature. In addi-tion, resources based on the former and the latter are clearly differentiated by assessing and quantifying the reliability of these data. However, the complexities in REE mineralization and the somewhat limited global scale of REE mining mean that significant variations exist within current REE resource reporting. For example, company reports that comply with the CIM reporting code and NI 43-101 usually provide details of mineral deposit types, REE mineralogies, TREO + Y con-centrations, LREE/HREE fractions, and orebody tonnages, whereas JORC code-based projects typically only report ore-body tonnages and TREO + Y concentrations. Therefore, we have compiled information from other sources, including the technical literature and published peer-reviewed articles, to provide sufficient detail on each deposit to ensure the dataset presented here is as comprehensive as possible. Furthermore, the fact that there are numerous deposits that contain signifi-cant amounts of the REE that are not formally reported (e.g., Olympic Dam) means that some of the data in our compila-tion are based on the best available code-noncompliant data from the technical literature. Taking into account the uncer-tainties inherent in combining these different sources of REE mineral resource data, we divided our dataset into three dif-ferent categories of reliability using the approach outlined in Mudd et al. (2013b):

1. High: Tonnage and TREO + Y concentrations are pro-vided by reporting code-compliant data (e.g., JORC, CIM/NI 43-101, SAMREC, etc.).

2. Medium: Tonnages are reported as code-compliant data, with TREO + Y concentrations provided through additional code-noncompliant technical information.

3. Low: Information is derived from government reports or from other technical literature with code-noncompliant data. From a production perspective, REE minerals are extracted as target or important commodities through conventional min-ing operations (e.g., Mountain Pass) but are also produced as by-/co-products from various sources, including base metal mining (e.g., iron production in Bayan Obo, C hina), HMS mining (e.g., monazite production in India), loparite mining (e.g., Lovozero, Russia), and so on. In addition, the REE could potentially be extracted as a by-product of phosphate mineral production (e.g., Araxá, Brazil), U mining (Mary Kathleen, Australia), and deep-sea mining (e.g., Kato et al., 2011). Monazite is one of the most significant REE minerals in terms of potential REO production, is a relatively minor con-stituent (commonly ≤2% of the contained total heavy min-erals) of many HMS deposits, and is usually treated as an impurity during titanium mineral (primarily ilmenite, rutile, and leucoxene) and zircon production (IAEA, 2011a). As shown in Figure 1, Australia produced monazite concentrates containing a minimum of 60% contained REO (Bureau of Mineral Resources, Geology and Geophysics [BoMRGG], 1960–1985) up to the mid-1990s, and became the largest monazite producer in the world in 1985, producing some 18,735 t of monazite (BoMRGG, 1960–1985). Although the Australian HMS industry does not currently export monazite for REO production (Australian Safeguards and Non-Pro-liferation Office [ASNO], 2014), the significant amounts of REO present in currently exploited and known HMS deposits and projects could become an important future source of the REE. Other countries like China, India, Russia, and Canada also have similar potential in terms of REO production from monazite extracted from placer, HMS, or hard-rock deposits. It should be noted that variations in geologic setting and for-mation processes mean that the TREO + Y concentrations within monazite in individual monazite-dominant deposits vary significantly, from an average of 35% in Vietnam (IAEA, 2011a) to 71% (Long et al., 2010). However, monazite contains significant amounts of Th, meaning that any REO produced from this material may leave a radioactive residue, although the concentration of Th (reported as a single element rather than as an oxide) within monazite also varies between 1.2% and 21.9% (van Emden et al., 1997; Hoatson et al., 2011). Here, we estimate the potential REO resources contained in HMS projects using a moderate but robust assumption that the monazite within all reported monazite resources in our database contains 55% TREO + Y and 7% Th.

In addition, a significant amount of potential REE resources (e.g., deep-sea REE mining, nuclear reprocessing, electronic waste recycling, etc.) have not yet been systematically stud-ied or reported as a consequence of lack of exploration and the targeting of other elements rather than the REE as the main commodity to be exploited in a given deposit/prospect. Some REE projects also do not report any code-compliant data and, thus, cannot be considered to be equivalent to min-eral resources and have been excluded from our dataset. For example, the Jongju deposit in North Korea is claimed to

1932 WENG ET AL.

include some 216.2 Mt of contained TREO resources (Pacific C entury Rare Earths Minerals Limited [PC REML], 2012), but this reporting is not code based or compliant with any other technical standard for quantifying mineral resources. This, combined with the fact that very little is known about this controversial purported deposit, means that we have deliberately excluded it from our dataset. Furthermore, some past REO producers have not been systemically analyzed and reported (e.g., placer/HMS-derived monazite production in Sri Lanka or monazite from tin mining in Malaysia); these uncertainties mean that, although these resources probably exist, quantifying them with any degree of certainty remains impossible, and they have therefore not been included in this paper.

The compiled data presented in this study should therefore be considered a minimum estimate of current global REE resources, especially as the majority of the resources within our database are from code-based reporting or are derived from the best available code-noncompliant data from the lit-erature and published peer-reviewed articles (as undertaken by Mudd et al., 2013a, b). We have also provided the full dataset, including resources for individual REE deposits, as supplementary information to this paper.

Results and Analysis

Our minimum estimate of global REO mineral resources is given in Table 4, with resources split by country given in Table 5. It should be noted that our overall database includes seven projects for which only total contained REO tonnages were available (HMS deposits in Andhra Pradesh, Bihar, Ker-ala, Odisha, Tamil Nadu, and West Bengal in India and the ion-adsorption clay deposits of the southern seven provinces of C hina); these projects are included in our overall REO resource calculations but are not included in any other cal-culations. Our compilation indicates that current global REO resources stand at 619.5 million tonnes (Mt) TREO + Y within 267 deposits, with the 260 deposits that have reported tonnage and grade data including 88,483 Mt of mineral resources at an average TREO+Y grade of 0.63%; this is further split into 111, 199, and 310 Mt TREO + Y in 65, 126, and 76 deposits within high-, medium-, and low-reliability categories, respectively. Current TREO + Y resources are dominated by the LREE, with an average light REO (LREO; La-Gd) to heavy REO (HREO) + Y (Tb-Lu and Y oxides) ratio of 13:1, although it should be noted that the HREO here include Y, which is much more abundant than HREE such as Lu and Tb. Splitting the resources in our database by individual country indicates that China dominates known contained REO resources, with some 43% of global REO resources (268.1 Mt TREO + Y), followed by Australia, Russia, C anada, and Brazil with resources of 64.5, 62.3, 48.3, and 47.1 Mt contained TREO + Y, respec-tively. These results significantly exceed the current estimates of global REO reserves from the USGS (although our data are resource rather than reserve based) and the various national resource estimates that are summarized in Table 3.

In terms of principal deposit types, the majority of the cur-rent global REO resources are hosted by carbonatites, which contain some 318.6 Mt of TREO + Y within 67 individual projects. In addition, a further 84.3, 80.5, 60.3, 53.9, and 12.4 Mt of TREO + Y resources are hosted by tailings, alka-line complexes and pegmatites, laterite/soil/clay, IOCG, and HMS deposits, with an additional 9.5 Mt in other categories. However, it should be noted that REO resource estimates within several deposit-type categories (e.g., tailings, laterite/ soil/clay, and IOCG) are biased by the presence of one or two giant projects within each category; for example, the Bayan Obo tailings alone contains 83 out of a total of 84.3 Mt con-tained TREO + Y in our tailings category, and 53 Mt of the total 53.9 Mt TREO + Y within IOCG deposits is within the Olympic Dam project. In both cases, these REO resources have been classified as low-reliability data, further indicating the lower reliability of the resource estimates within these categories.

The relationship between TREO + Y grades and mineral resources for various deposit types is illustrated in Figure 2. C arbonatite deposits dominate ore grades and contained REO whereas other deposit types, such as alkaline complexes and pegmatite, alluvial and placer deposits, and felsic volcanic rocks, have moderate REE grades but highly variable total mineral resources, and HMS and shale-hosted projects are typically low grade but bulk tonnage (≥1,000 Mt).

Figure 3 illustrates the relationship between TREO + Y grades and principal REE mineralogy, with the ionic clay clas-sification in this diagram including both deposits with REE resources associated with ion-adsorption clays and shale-hosted deposits that have REE mineralogies dominated by clay minerals. Global REO production is dominated by bastn?site extraction (e.g., Bayan Obo, Mountain Pass), with bastn?site-based REE projects also having the highest average TREO + Y concentration of 3.27%, although the tonnages of all of these deposits vary significantly. Monazite-based REE projects have the most significant variations in both tonnage and grade, with some hard-rock monazite projects (e.g., Tomtor, Steenkamp-skraal, etc.) having TREO + Y grades >10%, but the major-ity of monazite-based HMS projects have average TREO + Y grades of 0.01%. Furthermore, these HMS projects tend to contain significant amounts of mineral resources (>1,000 Mt) but have low to very low TREO + Y grades that reflect the importance of other non-REE minerals (e.g., ilmenite, rutile, and zircon) in these deposits (<0.1% TREO + Y). Cumulative frequency curves for TREO + Y concentrations and contained TREO + Y tonnages are given in Figure 4. The median size of the 260 REE deposits with grade and ton-nage data in our database is 0.04 Mt TREO + Y at a median grade of 0.23% TREO + Y. Some 82% of these projects con-tain <1 Mt contained TREO + Y, with 4% of the deposits in our database containing >10 Mt TREO + Y, indicating the

Table 4. Total REE Mineral Resources by Reliability Classification

Average

Reliability Mineral TREO + Y TREO + Y No. of level resources (Mt) grades (%) (Mt) deposits High 19,314 0.58 111 65 Medium 45,138 0.44 199

126 Low 24,031 1.011310 76 Total 88,483 0.631619 267

1Average TREO + Y grade calculation does not include the seven depos-its without available grade and tonnage data

A DETAILED ASSESSMENT OF GLOBAL RARE EARTH ELEMENT RESOURCES: OPPORTUNITIES AND CHALLENGES 1933

Table 5. Total Global REO Resources Split by Country and Deposit Type and Listed with Potential By-/Co-products

No. of % HREO % TREO REO Th U Other Country Deposit type deposits Mt ore % LREO + Y + Y (kt) (ppm) (ppm) metals Afghanistan

C arbonatite 1 37 NR NR 3.6 1,334 NR 500 Ba-Sr

C arbonatite 1 5.6 NR NR 2.1 118 NR NR NR

Argentina

Australia Alkaline complex and pegmatites 2 146 NR NR 0.39 573 54(1) NR Zr-Nb-Ta Alluvial/placer 1 805 0.020(1) 0.010(1) 0.029 235 NR NR NR

C arbonatite 11 78 7.7(2) 0.21(2) 3.3 2,533 41(1) 148(1) Fe-P-Al

skarn 1 0.05 NR NR 0.35 0.18 NR NR NR

C arbonatite-related

volcanic 1 36 0.040 0.17 0.21 76 NR NR NR Felsic

Granite-related

skarn 5 54 2.236 0.11 2.4 1,264 27(4) 153 Zr-Nb-Hf Hydrothermal undifferentiated 1 44 NR NR 0.12 53 NR 509 NR

C G 2 9,763 0.049(1) 0.010(1) 0.55 53,810 NR 2,20(1) Cu-Fe-Au

Sedimentary undifferentiated 1 14 NR NR 0.07 9.6 NR NR NR

Tailings 2 5.7 0.65(1) 0.32(1) 6.3 354 NR 159 NR

Heavy mineral sands 83 18,275 0.0012(1) 0.00(1) 0.029 5,611 34(83) NR Ti-Fe- Zr

Subtotal 110 29,221 0.15(12) 0.010 (12) 0.22 64,519 34(88) 295(10) Brazil C arbonatite 5 3,338 4.1(1) 0.070(1) 1.4 47,111 NR NR Al-Fe-P-Nb Canada Alkaline complex and pegmatites 6 991 0.81(5) 0.24(5)0.96 9,499 226(4) 49(2) Al-Fe-Ga-

Ta-Zr-Be-Hf Alluvial/placer 3 160 0.13 0.0084 0.14 227 245(2) 416 Sc

C arbonatite 7 2,470 1.5(6) 0.049(6) 1.5 36,551 377(3) NR Nb-Fe-Mn

volcanic 1 14 0.83 0.18 1.0 146 NR NR Zr-Nb Felsic

Shale hosted 3 6,249 0.13(2) 0.010(2) 0.031 1,915 10(2) 9(2) Zn-Cu-Co-

V-Ni-Mo-

Sc-Li-Si-Mg Subtotal 20 9,884 0.49(17) 0.038(17) 0.49 48,338 71(11) 24(7)

C hina C arbonatite 6 1,614 5.9(1) 0.058(1) 7.6 122,591 334(1) NR Nb-Fe-F

Laterite/soil/clay 1 NR NR NR NR 59,900 NR NR NR

Tailings 1 1,200 NR NR 7.0 83,400 378(1) NR Nb-Fe-F

Shale hosted 1 4,400 NR NR 0.05 2,200 NR NR NR

Subtotal 9 9,070 5.9(1) 0.058(1) 2.31268,092 353(2) NR Finland Alkaline complex and pegmatites 1 0.46 NR NR 1.1 11 1,200 250 Nb-Zr

C arbonatite 1 0.86 NR NR 0.71 7 NR NR Pb

Hydrothermal 1 0.60 NR NR 0.022 0 NR 100 C o-Au

Subtotal 3 2 NR NR 1.2 18 1,200(1) 220(2) Gabon C arbonatite 1 380 NR NR 2.5 9,576 NR NR Nb

C arbonatite 1 4.4 NR NR 0.45 20 NR NR NR

Germany

Greenland Alkaline complex and pegmatites 6 5,622 0.56 0.14 0.70 39,512 232(3) NR Nb-Zr-Ta

C arbonatite 1 12 1.4 0.010 1.4 176 NR NR NR

Subtotal 7 5,635 0.57 0.14 0.70 39,688 232(3) NR India Alluvial/placer 1 104 NR NR 1.5 1,549 NR NR NR

C arbonatite 1 12 NR NR 1.1 123 NR NR NR

Heavy mineral sands 6 NR NR NR NR 5,885 NR NR NR

Subtotal 8 115 NR NR 1.41 7,557 NR NR NR Kenya C arbonatite 2 163 3.6(1) 0.27(1) 3.9 6,286 450(1) 26(1) Nb Kyrgyzstan Alkaline complex and pegmatites 1 18 0.15 0.11 0.26 47 NR NR NR

C arbonatite 1 7 NR NR 0.20 14 NR NR NR

Granites and granitic pegmatites 2 16 NR NR 0.98 157 NR NR NR

Subtotal 4 41 0.15(1) 0.11(1) 0.53 217 NR NR Nb Madagascar Laterite/soil/clay 1 435 0.067 0.014 0.08 351 44 8 Zr-Nb-Ga-

Sn-Ta Malawi C arbonatite 4 63 1.2(2) 0.070(2) 1.4 867 297(1) 12(1) P, Nb Mauritania

C arbonatite 1 0.1 NR NR 4.4 4 NR NR NR

Mongolia Alkaline complex and pegmatites 1 425 NR NR 0.40 1,713 NR NR NR

C arbonatite 2 368 NR NR 1.6 5,895 NR NR NR

Subtotal 3 793 NR NR 0.96 7,608 NR NR NR Mozambique C arbonatite 1 1.1 NR NR 2.1 23 NR NR P-Nb Heavy mineral sands 9 8,145 NR NR 0.009 758 NR NR Ti-Fe-Zr

Subtotal 10 8,146 NR NR0.015 781 NR NR Namibia C arbonatite 1 8 NR NR 3.0 240 NR NR NR Norway Alkaline complex and pegmatites 3 87 NR NR 0.25 219 490(1) NR Nb-Zr-Ta

C arbonatite 1 486 NR NR 0.90 4,374 NR NR NR

Granites and granitic pegmatites 3 104 NR NR 0.13 131 NR NR NR

undifferentiated 1 0.050 NR NR 0.20 200 NR 900(1) Sc Hydrothermal

Subtotal 8 677 NR NR 0.72 4,924 490(1) 900(1) Peru Heavy mineral sands 2 1,329 NR NR 0.010 125 NR NR NR Russia Alkaline complex and pegmatites 18 5,259 NR NR 0.52 27,145 NR NR P-Nb-Ta

C arbonatite 2 605 NR NR 5.8 35,199 NR NR Zr-Nb

Subtotal 20 5,864 NR NR 1.1 62,344 NR NR Saudi Arabia Alkaline complex and pegmatites 5 439 0.060 0.16 0.20 911 415 113 Zr-Nb-Sn-Ta

1934

WENG ET AL.importance of these giant deposits in terms of global REE supply both now and in the future. About 68% of the REE deposits in our database have TREO + Y grades <1% whereas 1% of projects have TREO + Y concentrations >10%. The top 25 REE projects by concentrations and contained TREO + Y tonnages are shown in Tables 6 and 7, including concentra-tions of individual REE and Sc where available. Both of these tables are dominated by carbonatite-hosted REE deposits, suggesting that this deposit type could continue to be the dominant source of the LREE production for the foresee-able future. However, other crucial factors, such as the lack of known HREE resources combined with the high demand for this subset of the REE, hazardous impurities, and process-ing efficiency, also need to be considered when assessing the global REO supply chain. There are still uncertainties within mineral resource estimates for even the most significant REE projects, which certainly limits a highly accurate assessment of global REE resources. This is exemplified by the uncertain-ties surrounding the Bayan Obo deposit, the world’s largest REO producer since the mid-1980s, and the ionic clay-hosted REE deposits in the seven southern provinces of China (e.g., Fujian, Guangxi, etc.) that dominate the global supply of the HREE; these projects have only medium- to low-confidence mineral resource estimates, with limited or even no informa-tion on their mineralogy and details of the individual REE concentrations within these deposits.

The global distribution of REO resources split by coun-try and by principal deposit types is shown in Figure 5. The TREO + Y resources in our database are led by China, which contains some 43% of known global TREO + Y resources, with lesser amounts in Australia (10%), Russia (10%), Brazil (8%), Canada (8%), Greenland (6%), and the United States (3%); the 57% of global TREO + Y resources outside C hina are located in 27 different countries, indicating a diverse range of

South Africa Carbonatite 4 6,444 1.8 0.10 0.17 10,847 25,291(1) 506(1) Nb-Sc-P

Tailings 3 297 6.4(2) 0.56(2) 0.15 448 NR NR NR

Alkaline 2 14 16(1) 1.0(1) 1.19 165 NR NR NR Subtotal 9 6,755 1.82(5) 0.10(6) 0.17 11,461 25,291(3) 506(3)Sweden Alkaline complex and pegmatites 1 58 0.31 0.27 0.59 341 10 10 Zr-Hf Alluvial/placer 1 12 0.35 0.15 0.50 62 NR NR NR Shale hosted 1 200 NR NR 0.11 220 NR NR NR Subtotal 3 271 0.32(2) 0.25(2) 0.23 624 10(1) 10(1)Tanzania C arbonatite 2 198 2.2(1) 0.019(1) 2.3 4,505 NR NR NR

Turkey Alkaline complex and pegmatites 3 530 0.060(2) 0.010(2) 0.071 402 34(2) 7(2) Fe-Ti-Ga

C arbonatite 1 30 NR NR 3.1 942 NR NR NR Subtotal 4 560 0.060(2) 0.010(2) 0.24 1,344 34(2) 7(2)USA Alkaline complex and pegmatites 2 31 0.37(1) 0.21(1) 0.26 78 73(1) 58(1) Zr-Nb Alluvial/placer 1 18 NR NR 0.08 14 NR NR NR

C arbonatite 7 2,643 4.0(2) 0.050(2) 0.54 14,140 44(2) 12(2) NR

Felsic volcanic 1 1,034 0.020 0.040 0.064 662 NR NR NR Granite-related skarn 2 6 NR NR 1.2 71 NR NR NR Granites and granitic pegmatites 1 0.05 NR NR 8.6 4 NR NR NR Hydrothermal undifferentiated 2 128 NR NR 0.37 476 NR NR NR Tailings 1 9 0.65 0.24 0.89 80 NR NR NR IO C G 2 0.6 NR NR 12 72 NR NR NR

Subtotal 19 3,861 0.27(5)

0.050(5) 0.40 15,621 44(3) 12(3)Vietnam C arbonatite 2 1,057 NR NR 1.4 14,798 NR NR NR Zambia C arbonatite 1 130 NR NR 0.30 390 NR NR Nb-P The world Alkaline complex and pegmatites 51 13,621 0.52(22) 0.14(22) 0.59 80,510 213(17) 122(16)

Alluvial/placer 7 1,099 0.050(5) 0.010(5) 0.19 2,087 245(2) 416(3) C arbonatite 68 21,993 3.2(20) 0.060(20) 1.4 318,650 190(9) 20(6)

C arbonatite-related skarn 1 0.05 NR NR 0.35 0.18 NR NR Felsic volcanic 3 1,084 0.030 0.050 0.081 884 NR NR Granite-related skarn 7 60 2.2(5) 0.11(5) 2.2 1,335 27(4) 153(5) Granites and granitic pegmatites 6 120 NR NR 0.24 292 NR NR Sedimentary undifferentiated 1 14 NR NR 0.07 10 NR NR Heavy mineral sands 100 27,747 0.0012(1) 0.00(1) 0.0231 12,392 37(82) NR Hydrothermal undifferentiated 5 173 NR NR 0.31 529 NR 503(3)

IO C G 4 9,774 0.049(1) 0.010(1) 0.55 53,920 NR 220(1)

Laterite/soil/clay 2 435(1) 0.067(1) 0.014(1) 0.081 60,251 44(1) 8(1)

Shale hosted 5 6,449 0.13(2) 0.010(2) 0.067 4,335 10(2) 16(3) Tailings 7 1,512 0.67(4) 0.24(4) 5.6 84,282 378(1) 159(2)

Total 267 88,483 0.93(64) 0.070(64) 0.631 619,477 81(118) 127(40)

Notes: Superscript numbers in parentheses denote the number of deposits used to derive the LREO-HREO values in this table; these are different from

the values for the TREE since all deposits were used for TREO calculations; for example, the two known Australian carbonatite deposits with fully reported REE concentrations were used to to derive the LREO and HREO percentages within the table, but the TREO statistics are based on all 11 deposits, as TREO data are reported for all of these projects; values are rounded down to two significant figures; NR = not reported 1Average TREO + Y grade calculation does not include the seven deposits without available grade and tonnage data

Table 5. (Cont.)

No. of % HREO % TREO REO

Th U Other Country Deposit type deposits Mt ore % LREO + Y + Y (kt) (ppm) (ppm) metals

A DETAILED ASSESSMENT OF GLOBAL RARE EARTH ELEMENT RESOURCES: OPPORTUNITIES AND CHALLENGES

1935

0.001

0.01

0.1

0.001

0.010.1110100100010000

O r e G r a d e (%T R E O +Y )

Mineral Resources (Mt)

Fig. 2. TREO + Y grades versus mineral resources split by principal REE deposit types.

0.001

0.01

0.1

0.001

0.010.1110100100010000

O r e G r a d e

(%T R E O +Y )

Mineral Resources (Mt)

Fig. 3. TREO +Y grades versus mineral resources split by principal REE mineralogy. The ionic clay classification in this diagram includes both deposits with REE resources associated with ion-adsorption clays and shale-hosted deposits that have REE mineralogies dominated by clay minerals

1936

WENG ET AL.

possible future REE suppliers. The majority of REE deposits are hosted by carbonatites (51.4%), with significant amounts of the REE hosted by tailings (13.6%), alkaline complexes and pegmatites (13.0%), lateritic or clay-related deposits (9.7%), and IOCG deposits (8.7%). However, as discussed previously, these results are heavily skewed by one or two megaprojects in certain categories (e.g., Bayan Obo tailings contain 83 of 84 Mt TREO + Y within the tailings category and Olympic Dam accounts for 53 of 54 Mt TREO + Y in IOCG deposits), making these deposit-type categories seemingly much more attractive for exploration than they actually are.

From a production perspective, each of the individual REE have similar but distinctive chemical characteristics, miner-alogies, ore grades, uses, and demands, meaning that each of these elements have differing economic values. This complex-ity means that traditional economic aspects, such as mineral resources, ore grades, and the size of an orebody, may not be enough to determine the long-term economic feasibility of an REE deposit. This, in turn, means that additional fac-tors, including the relative abundances of the LREE and the HREE and the concentrations of the individual REE within a project, are crucial considerations during economic assess-ment and operational planning activities associated with REE mining projects. As illustrated in Figure 6 and Table 8, the majority of current reported REE mineral resources with reported individual elemental REE concentrations are LREE dominated, containing especially high concentrations of C e (~100 Mt contained C e), La (~55 Mt), and Nd (~24 Mt), whereas HREE resources are dominated by 9.9 Mt Y fol-lowed by 1.5 Mt Dy, 0.98 Mt Er, and 0.96 Mt Yb, a distribu-tion that is similar to the relative abundance of these elements

in the Earth’s crust (e.g., Rudnick and Gao, 2003). The rest of

P e r c e n t (C u m u l a t i v e )

Ore Grade (% TREO+Y)

P e r c e n t (C u m u l a t i v e )

Contained TREO+Y (Mt)

Fig. 4. Cumulative frequency curves for contained total rare earth oxides (above) and ore grades (below).

A DETAILED ASSESSMENT OF GLOBAL RARE EARTH ELEMENT RESOURCES: OPPORTUNITIES AND CHALLENGES

1937

T a b l e 6. T h e 25 H i g h e s t -G r a d e R E E D e p o s i t s L i s t e d b y T R E O + Y G r a d e a n d w i t h S p l i t s o f I n d i v i d u a l R E E C o n c e n t r a t i o n s

M i n e r a l P r i n c i p a l R e l i a b i l i t y T R E O + r e s o u r c e s L a C e P r N d S m E u G d T b D y P r o j e c t C o u n t r y d e p o s i t t y p e l e v e l R E E m i n e r a l o g y Y (%) (M t )

(p p m ) (p p m ) (p p m ) (p p m ) (p p m ) (p p m ) (p p m ) (p p m ) (p p m )S t e e n k a m p s k r a a l S o u t h A f r i c a A l k a l i n e H i g h M o n a z i t e 17 0.42 30,333 62,532 7,257 26,462 4,156 86 2,881 318 1,442

T o m t o r R u s s i a C a r b o n a t i t e L o w M o n a z i t e , p y r o c h l o r e 12 150 N R N R N R N R N R N R N R N R N R P e a R i d g e U S A I O C G L o w M o n a z i t e , x e n o t i m e , 12 0.60 N R N R N R N R N R N R N R N R N R b a s t n ?s i t e M o u n t W e l d C L D A u s t r a l i a C a r b o n a t i t e H i g h M o n a z i t e , r h a b d o p h a n e , c h u r c h i t e 10 15 19,810 39,497 4,290 15,123 2,047 445 920 76 212M u s i c V a l l e y U S A G r a n i t e L o w X e n o t i m e 8.6 0.050 N R N R N R N R N R N R N R N R N R M o u n t a i n P a s s U S A C a r b o n a t i t e M e d i u m B a s t n ?s i t e 8.0 17 23,003 33,803 2,811 7,639 585 72 145 11 24S t e e n k a m p s k r a a l S o u t h A f r i c a T a i l i n g s H i g h M o n a z i t e 7.1 0.0092 15,990 18,671 3,745 13,703 2,111 81 1,528 174 860 (U p p e r T a i l i n g s D a m )B a y a n O b o C h i n a T a i l i n g s L o w B a s t n ?s i t e , m o n a z i t e , 7.0 1,200 N R N R N R N R N R N R N R N R N R (T a i l i n g s D a m ) x e n o t i m e S t e e n k a m p s k r a a l S o u t h A f r i c a T a i l i n g s H i g h M o n a z i t e 6.9 0.029 15,433 17,684 3,845 13,375 2,156 86 1,562 174 871 (L o w e r T a i l i n g s D a m )M a r y K a t h l e e n A u s t r a l i a T a i l i n g s L o w N R 6.4 5.5 N R N R N R N R N R N R N R N R N R B a y a n O b o C h i n a C a r b o n a t i t e M e d i u m B a s t n ?s i t e , m o n a z i t e , 5.9 1,540 12,628 26,012 2,785 7,943 661 207 310 45 141 x e n o t i m e D a l u c a o C h i n a C a r b o n a t i t e L o w N R 5.0 0.76 N R N R N R N R N R N R N R N R N R C h i l w a I s l a n d M a l a w i C a r b o n a t i t e L o w A p a t i t e , b a s t n ?s i t e , 5.0 0.38 N R N R N R N R N R N R N R N R N R fl o r e n c i t e , fl u o r i t e , p y r i t e M o u n t W e l d A u s t r a l i a C a r b o n a t i t e H i g h R h a b d o p h a n e , m o n a z i t e , D u n c a n c h u r c h i t e 4.8 9.0 10,257 16,262 1,963 7,419 1,180 322 835 109 535B o u N a g a M a u r i t a n i a C a r b o n a t i t e L o w A p a t i t e , b a r i t e , b a s t n ?s i t e , 4.4 0.10 N R N R N R N R N R N R N R N R N R fl u o r i t e , m o n a z i t e K a n g a n k u n d e M a l a w i C a r b o n a t i t e H i g h M o n a z i t e , b a s t n ?s i t e 4.2 3.5 10,774 17,991 1,703 5,089 384 70 132 26 296A r a x á B r a z i l C a r b o n a t i t e H i g h M o n a z i t e , a p a t i t e 4.2 28 10,062 17,742 1,631 4,995 541 122 250 26 105M u l u o z h a i C h i n a C a r b o n a t i t e L o w B a s t n ?s i t e 4.0 0.45 N R N R N R N R N R N R N R N R N R R u r i C o m p l e x K e n y a C a r b o n a t i t e L o w B a s t n ?s i t e , e u d i a l y t e , fl u o r i t e , m o n z i t e 3.9 3.8 N R N R N R N R N R N R N R N R N R M r i m a H i l l K e n y a C a r b o n a t i t e H i g h A p a t i t e , m a g n e t i t e , b a r i t e , 3.9 159 8,658 14,135 1,428 4,969 697 196 503 62 308 fl u o r i t e C h u k t u k o n s k o y e R u s s i a C a r b o n a t i t e M e d i u m A p a t i t e (f r a n c o l i t e ), b a r i t e , 3.8 455 N R N R N R N R N R N R N R N R N R c e r i a n i t e , h e m a t i t e , i l m e n i t e , m o n a z i t e K h a n n e s h i n A f g h a n i s t a n C a r b o n a t i t e L o w M o n a z i t e , s y n c h y s i t e , b a s t n ?s i t e 3.6 37 N R N R N R N R N R N R N R N R N R L u g i n G o l M o n g o l i a C a r b o n a t i t e L o w B a s t n ?s i t e , fl u o r i t e , p a r i s i t e , 3.2 0.72 N R N R N R N R N R N R N R N R N R p y r i t e , r u t i l e , s y n c h y s i t e K i z i l c a o r e n T u r k e y C a r b o n a t i t e L o w B a s t n ?s i t e , b r a u n i t e , fl u o r i t e 3.1 30 N R N R N R N R N R N R N R N R N R O n d u r u k u r m e N a m i b i a C a r b o n a t i t e L o w M o n a z i t e 3.0 8.0 N R N R N R N R N R N R N R N R N R C o m p l e x

1938

WENG ET AL.

T a b l e 6. (C o n t .)

H R E O P r i n c i p a l R e l i a b i l i t y H o E r T m Y b L u Y S c L R E E H R E E L R E O + Y P r o j e c t C o u n t r y d e p o s i t t y p e l e v e l R E E m i n e r a l o g y (p p m ) (p p m ) (p p m ) (p p m ) (p p m ) (p p m ) (p p m ) (p p m ) (p p m ) (%) (%)

S t e e n k a m p s k r a a l S o u t h A f r i c a A l k a l i n e H i g h M o n a z i t e 224 467 45 191 23 5,474 N R 133,708 8,185 16 1T o m t o r R u s s i a C a r b o n a t i t e L o w M o n a z i t e , p y r o c h l o r e N R N R N R N R N R N R N R N R N R N R N R P e a R i d g e U S A I O C G L o w M o n a z i t e , x e n o t i m e , N R N R N R N R N R N R N R N R N R N R N R b a s t n ?s i t e M o u n t W e l d C L D A u s t r a l i a C a r b o n a t i t e H i g h M o n a z i t e , r h a b d o p h a n e , 25 51 8.5 26 N R 582 N R 82,132 981 9.6 0.12 c h u r c h i t e M u s i c V a l l e y U S A G r a n i t e L o w X e n o t i m e N R N R N R N R N R N R N R N R N R N R N R M o u n t a i n P a s s U S A C a r b o n a t i t e M e d i u m B a s t n ?s i t e 2.8 4.2 1.4 1.4 N R 82 N R 68,059 126 8.0 0.02S t e e n k a m p s k r a a l S o u t h A f r i c a T a i l i n g s H i g h M o n a z i t e 87 262 25 88 8.8 3,009 N R 55,827 4,514 6.5 0.55 (U p p e r T a i l i n g s D a m )B a y a n O b o C h i n a T a i l i n g s L o w B a s t n ?s i t e , m o n a z i t e , N R N R N R N R N R N R N R N R N R N R N R (T a i l i n g s D a m ) x e n o t i m e S t e e n k a m p s k r a a l S o u t h A f r i c a T a i l i n g s H i g h M o n a z i t e 87 262 26 26 9 3,071 N R 54,141 4,527 6 0.56 (L o w e r T a i l i n g s D a m )M a r y K a t h l e e n A u s t r a l i a T a i l i n g s L o w N R N R N R N R N R N R N R N R N R N R N R N R B a y a n O b o C h i n a C a r b o n a t i t e M e d i u m B a s t n ?s i t e , m o n a z i t e , N R 31 N R 91 23 157 N R 50,546 489 5.9 0.06 x e n o t i m e D a l u c a o C h i n a C a r b o n a t i t e L o w N R N R N R N R N R N R N R N R N R N R N R N R C h i l w a I s l a n d M a l a w i C a r b o n a t i t e L o w A p a t i t e , b a s t n ?s i t e , N R N R N R N R N R N R N R N R N R N R N R fl o r e n c i t e , fl u o r i t e , p y r i t e M o u n t W e l d A u s t r a l i a C a r b o n a t i t e H i g h R h a b d o p h a n e , m o n a z i t e , 80 173 17 76 9 1,969 N R 38,238 2,969 4.5 0.36 D u n c a n c h u r c h i t e B o u N a g a M a u r i t a n i a C a r b o n a t i t e L o w A p a t i t e , b a r i t e , b a s t n ?s i t e , N R N R N R N R N R N R N R N R N R N R N R fl u o r i t e , m o n a z i t e K a n g a n k u n d e M a l a w i C a r b o n a t i t e H i g h M o n a z i t e , b a s t n ?s i t e 3.7 3.7 3.7 N R N R 3.3 N R 36,143 336 4.2 0.04A r a x á B r a z i l C a r b o n a t i t e H i g h M o n a z i t e , a p a t i t e 15 29 2 15 0 374 N R 35,342 565 4.1 0.07M u l u o z h a i C h i n a C a r b o n a t i t e L o w B a s t n ?s i t e N R N R N R N R N R N R N R N R N R N R N R R u r i C o m p l e x K e n y a C a r b o n a t i t e L o w B a s t n ?s i t e , e u d i a l y t e , N R N R N R N R N R N R N R N R N R N R N R fl u o r i t e , m o n z i t e M r i m a H i l l K e n y a C a r b o n a t i t e H i g h A p a t i t e , m a g n e t i t e , 54 133 17 90 12 1,517 N R 30,585 2,193 3.6 0.27 b a r i t e , fl u o r i t e C h u k t u k o n s k o y e R u s s i a C a r b o n a t i t e M e d i u m A p a t i t e (f r a n c o l i t e ), b a r i t e , N R N R N R N R N R N R N R N R N R N R N R c e r i a n i t e , h e m a t i t e , i l m e n i t e , m o n a z i t e K h a n n e s h i n A f g h a n i s t a n C a r b o n a t i t e L o w M o n a z i t e , s y n c h y s i t e , N R N R N R N R N R N R N R N R N R N R N R b a s t n ?s i t e L u g i n G o l M o n g o l i a C a r b o n a t i t e L o w B a s t n ?s i t e , fl u o r i t e , p a r i s i t e , N R N R N R N R N R N R N R N R N R N R N R p y r i t e , r u t i l e , s y n c h y s i t e K i z i l c a o r e n T u r k e y C a r b o n a t i t e L o w B a s t n ?s i t e , b r a u n i t e , fl u o r i t e N R N R N R N R N R N R N R N R N R N R N R O n d u r u k u r m e N a m i b i a C a r b o n a t i t e L o w M o n a z i t e N R N R N R N R N R N R N R N R N R N R N R C o m p l e x

N R = n o t r e p o r t e d

A DETAILED ASSESSMENT OF GLOBAL RARE EARTH ELEMENT RESOURCES: OPPORTUNITIES AND CHALLENGES

1939

T a b l e 7. T h e 25 L a r g e s t (b y c o n t a i n e d R E O ) R E E D e p o s i t s w i t h a B r e a k d o w n i n t o I n d i v i d u a l R E E C o n c e n t r a t i o n s

M i n e r a l P r i n c i p a l R e l i a b i l i t y T R E O + r e s o u r c e s L a C e P r N d S m E u G d T b D y P r o j e c t

C o u n t r y d e p o s i t t y p e l e v e l R E E m i n e r a l o g y Y (M t ) (M t ) (p p m ) (p p m ) (p p m ) (p p m ) (p p m ) (p p m ) (p p m ) (p p m ) (p p m )

B a y a n O b o

C h i n a

C a r b o n a t i t e M e d i u m B a s t n ?s i t e , m o n a z i t e , 92

1,540 12,628 26,012 2,785 7,943 661 207 310 45 141

x e n o t i m e B a y u n O b o C h i n a T a i l i n g s L o w B a s t n ?s i t e , m o n a z i t e , 83

1,200 N R N R N R N R N R N R N R N R

N R

(t a i l i n g s d a m ) x e n o t i m e S o u t h e r n s e v e n C h i n a L a t e r i t e / L o w I o n -a d s o r p t i o n c l a y

N R N R N R N R N R N R N R N R

N R

p r o v i n c e s (F u j i a n ,

s o i l /c l a y G u a n g x i , e t c .)O l y m p i c D a m A u s t r a l i a I O C G

M e d i u m G r a n i t e -r i c h b r e c c i a s , 53

9,576 1,705 2,561 N R N R N R N R

N R

fl o r e n c i t e , m o n a z i t e , x e n o t i m e M o r r o d o s S e i s L a g o s B r a z i l C a r b o n a t i t e L o w N R 43 2,898 N R N R N R N R N R N R N R N R N R W e i s h a n C h i n a C a r b o n a t i t e L o w B a s t n ?s i t e 30 1,856 N R N R N R N R N R N R N R N R N R T a n b r e e z G r e e n l a n d A l k a l i n e H i g h E u d i a l y t e 28 4,300 1,157 2,145 208 780 150 20 163 33 189S a i n t -H o n o r é C a n a d a C a r b o n a t i t e H i g h B a s t n ?s i t e , a l l a n i t e , 18

1,058 3,577 6,801 743 2,573 281 60 130 11 36

C o m l p e x a p a t i t e , m o n a z i t e T o m t o r R u s s i a C a r b o n a t i t e L o w M o n z i t e , p y r o c h l o r e 18 150 N R N R N R N R N R N R

N R N R N R C h u k t u k o n s k o y e R u s s i a C a r b o n a t i t e M e d i u m A p a t i t e , b a r i t e , c e r i a n i t e , 17

455 N R N R N R N R

N R

h e m a t i t e , i l m e n i t e , m o n a z i t e I r o n H i l l U S A C a r b o n a t i t e

L o w M o n a z i t e , b a s t n ?s i t e

9.7

2,424 N R N R N R

N R

(P o w d e r h o r n , C e b o l l a C r e e k ) M a b o u n i e G a b o n C a r b o n a t i t e

L o w B a s t n ?s i t e , m o n a z i t e , 9.6

380 N R N R

N R

p y r i t e , p y r o c h l o r e , s y n c h y s i t e , x e n o t i m e P a l a b o r a S o u t h A f r i c a

C a r b o n a t i t e

L o w A p a t i t e , p y r o x e n i t e

9.6

297 N R

N R

(P h a l a b o r w a ) C o m p l e x M a u X e N o r t h V i e t n a m C a r b o n a t i t e L o w B a s t n ?s i t e 7.8 557 N R N R N R N R N R N R N R N R N R N i o b e c R E E z o n e C a n a d a C a r b o n a t i t e H i g h B a s t n ?s i t e , a l l a n i t e , 7.7

467

3,452

6,756

742

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293

140

a p a t i t e , m o n a z i t e D o n g P a o V i e t n a m C a r

b o n a t i t e L o w B a s t n ?s i t e 7.0 500 N R N R N R N R N R N R N R N R N R L o v o z e r o R u s s i a A l k a l i n e M e d i u m L o p a r i t e , m a g n e t i t e , 7

612

N R

e u d i a l y t e , r i n k i t e , a n c y l i t e , m o s a n d r i t e K v a n e

f j e l d G r e e n l a n d A l k a l i n e H i

h L u j a v r

i t e 6.6 619 N R N R N R N R N R N R N R N R N R M r i m a H i l l K e n y a C a r b o n a t i t e H i g h A p a t i t e , m a g n e t i t e , 6.1

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308

b a r i t e , fl u o r i t e A s h r a m (E l d o r ) C a n a d a C a r b o n a t i t e H i g h M o n a z i t e , b a s t n ?s i t e , 6.1

423

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618

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284

157

x e n o t i m e M u s h a g a i K h u d a g M o n g o l i a C a r b o n a t i t e L o w B a s t n ?s i t e , c e l e s t i t e , 5.9

367

N R

(M u s h u g a y -

fl u o r i t e , e t c .

K h u d u k ) N g u a l l a T a n z a n i a C a r b o n a t i t e H i g h B a s t n ?s i t e 4.4 195 5,237 9,326 902 3,167 326 69 149 13 32S t r a n g e L a k e C a n a d a A l k a l i n e H i g h A l l a n i t e , t i t a n i t e , 4.4

492 1,034 2,228 248 954 207 9.0 201 40 276

p y r o c h l o r e , g a d o l i n i t e F e n N o r w a y C a r b o n a t i t e L o w A l l a n i t e , m o n a z i t e , 4.4

486

N R

b a s t n ?s i t e T h o r L a k e / C a n a d a A l k a l i n e H i g h M o n a z a t i t e , h u a n g h o i t e , 4.3

312 1,612 4,641 609 2,263 446 53 369 47 216

N e c h a l a c h o (B a s a l

c e b a i t e , q a q a r s s u k i t e

a n d U p p e r z o n e s )

1940

WENG ET AL.

T a b l e 7. (C o n t .)

H R E O T R E O P r i n c i p a l R e l i a b i l i t y H o E r T m Y b L u Y S c L R E E H R E E L R E O + Y + Y P r o j e c t

C o u n t r y d e p o s i t t y p e l e v e l R E E m i n e r a l o g y (p p m ) (p p m ) (p p m ) (p p m ) (p p m ) (p p m ) (p p m ) (p p m ) (p p m ) (%) (%) (%)

B a y a n O b o

C h i n a

C a r b o n a t i t e M e d i u m B a s t n ?s i t e , m o n a z i t e , N R

31 N R 91 23 157 N R 50,546 489 5.9 0.06 5.9

x e n o t i m e B a y u n O b o C h i n a T a i l i n g s L o w B a s t n ?s i t e , m o n a z i t e , N R

N R N R N R N R N R N R N R N R N R N R

7.0

(t a i l i n g s d a m ) x e n o t i m e S o u t h e r n s e v e n C h i n a L a t e r i t e / L o w I o n -a d s o r p t i o n c l a y

N R

N R N R N R N R N R N R N R N R N R N R

N R

p r o v i n c e s (F u j i a n , s o i l /c l a y

G u a n g x i , e t c .)O l y m p i c D a m A u s t r a l i a I O C G M e d i u m G r a n i t e -r i c h b r e c c i a s , N R N R N R N R N R N R N R N R N R N R

N R

0.55

fl o r e n c i t e , m o n a z i t e , x e n o t i m e M o r r o d o s S e i s L a g o s B r a z i l C a r b o n a t i t e L o w N R N R N R N R N R N R N R N R N R N R N R N R 1.5W e i s h a n C h i n a C a r b o n a t i t e L o w B a s t n ?s i t e N R N R N R N R N R N R N R N R N R N R N R N R T a n b r e e z G r e e n l a n d A l k a l i n e H i g h E u d i a l y t e 39 156 20 130 20 1,235 N R 4,622 1,820 0.50 0.15 0.65S a i n t -H o n o r é C a n a d a C a r b o n a t i t e H i g h B a s t n ?s i t e , a l l a n i t e , 4.4 7.9 0.88 0.88 0.88 513 N R 14,165 575 1.66 0.07 1.7

C o m l p e x a p a t i t e , m o n a z i t e T o m t o r R u s s i a C a r b o n a t i t e L o w M o n z i t e , p y r o c h l o r e N R

N R N R N R N R N R N R N R N R N R N R 12C h u k t u k o n s k o y e R u s s i a C a r b o n a t i t e M e d i u m A p a t i t e , b a r i t e , c e r i a n i t e , N R

N R N R N R N R N R N R

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3.8

h e m a t i t e , i l m e n i t e , m o n a z i t e I r o n H i l l (P o w d e r h o r n , U S A C a r b o n a t i t e

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0.40

C e b o l l a C r e e k )M a b o u n i e G a b o n C a r b o n a t i t e L o w

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N R N R N R N R

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2.5

p y r i t e , p y r o c h l o r e , s y n c h y s i t e , x e n o t i m e P a l a b o r a S o u t h C a r b o n a t i t e

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N R N R N R

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0.15

(P h a l a b o r w a ) A f r i c a

C o m p l e x M a u X e N o r t h V i e t n a m C a r b o n a t i t e L o w B a s t n ?s i t e N R

N R N R

N R

1.4

N i o b e c R E E z o n e C a n a d a C a r b o n a t i t e H i g h B a s t n ?s i t e , a l l a n i t e , a p a t i t e , m o n a z i t e 4.4 8 1.9 N R 0.70 74 28 11,443 140 1.34 0.02 1.7D o n g P a o V i e t n a m C a r b o n a t i t e L o w B a s t n ?s i t e N R N R N R N R N R N R N R N R N R N R N R 1.4L o v o z e r o R u s s i a A l k a l i n e M e d i u m L o p a r i t e , m a g n e t i t e , N R

N R N R

N R

1.1

e u d i a l y t e , r i n k i t e , a n c y l i t e , m o s a n d r i t e K v a n e

f j e l d G r e e n l a n d A l k a l i n e H i

h L u j a v r

i t e N R N R N R N R N R 680 N R N R N R 0.93 0.13 1.1M r i m a H i l l K e n y a C a r b o n a t i t e H i g h A p a t i t e , m a g n e t i t e , 54

133

1,517

N R

30,585

2,193

3.58

0.27

3.9

b a r i t e , fl u o r i t e A s h r a m (E l d o r ) C a n a d a C a r b o n a t i t e H i g h M o n a z i t e , b a s t n ?s i t e , 9

1.8

N R

12,157

132

1.36

0.07

1.4

x e n o t i m e M u s h a g a i K h u d a g M o n g o l i a C a r b o n a t i t e L o w B a s t n ?s i t e , c e l e s t i t e , N R

N R

1.6

(M u s h u g a y -K h u d u k ) fl u o r i t e , e t c .N g u a l l a T a n z a n i a C a r b o n a t i t e H i g h B a s t n ?s i t e 4.0 12 N R 4.0 N R 86 N R 19,177 151 2.2 0.02 2.3S t r a n g e L a k e C a n a d a A l k a l i n e H i g h A l l a n i t e , t i t a n i t e , 60

191

192

1,710

N R

4,881

2,524

0.57

0.31

0.89

p y r o c h l o r e , g a d o l i n i t e F e n N o r w a y C a r b o n a t i t e L o w A l l a n i t e , m o n a z i t e , N R

N R

0.90

b a s t n ?s i t e T h o r L a k e / C a n a d a A l k a l i n e H i g h M o n a z a t i t e , h u a n g h o i t e , 36

836

N R

9,993

1,315

1.2

0.16

1.4

N e c h a l a c h o (B a s a l

c e b a i t e , q a q a r s s u k i t e

a n d U p p e r z o n e s )

N R = n o t r e p o r t e d

A DETAILED ASSESSMENT OF GLOBAL RARE EARTH ELEMENT RESOURCES: OPPORTUNITIES AND CHALLENGES

1941

the HREE have resources that are an average of three orders of magnitude lower than the other REE (e.g., 0.34 Mt Tb, 0.26 Mt Ho, and 0.16 Mt Lu). This is reflected by the grades within our database, where C e, La, and Nd have average grades of 3,379, 1,853, and 823 ppm, respectively, compared

to the average grades of 464, 52, and 33 ppm for Y, Dy, and Er, respectively.

The average distribution of the individual REE within indi-vidual deposit types is summarized in Table 9. These data indi-

cate that IOCG, carbonatite, and hydrothermal projects are

Fig. 5. Percentage of global REO resources split by country (left) and by principal deposit type (right). The “other” category of the global REO resources split by country summarized REO resource data from all the other countries (e.g., Afghanistan, Argentina, Finland, Peru, Sweden, etc.) covered in our dataset. The details of all countries’ REO resources are presented in Table 5. The “other” category of the global REO resources by principal deposit types includes REO resources from granites and granitic pegmatites, sedimentary undifferentiated, carbonatite-related skarn, and hydrothermal undiffer-entiated types of deposits.

100

1000

10000

100000

1000000

R E E R e s o u r c e s (k t )

Fig. 6. Summary of individual REE resources with reported data and average estimates. Average estimates are calculated based on weighted average grade of each individual REE + Y.

1942

WENG ET AL.

T a b l e 8. S u m m a r y o f M i n e r a l R e s o u r c e s a n d R E E G r a d e s b y D e p o s i t T y p e , I n c l u d i n g M e a n a n d S t a n d a r d D e v i a t i o n V a l u e s

M i n e r a l r e s o u r c e s D e p o s i t t y p e (M t )

L a (p p m )

C e (p p m ) P r (p p m ) N d (p p m ) S m (p p m ) E u (p p m ) G d (p p m )

T b (p p m )

A l k a l i n e c o m p l e x a n d 13,621

1,002 ± 6,799 (19)

1,957 ± 14,019 (19) 213 ± 1,883 (13) 795 ± 6,867 (14) 154 ± 1,069 (14) 21 ± 35 (14) 157 ± 736 (14) 31 ± 79 (14)

p e g m a t i t e s (51)A l l u v i a l /p l a c e r (7) 1,099 94 ± 207 (5) 187 ± 464 (5) 19 ± 58 (5) 68 ± 231 (5)

13 ± 55 (5)

1.5 ± 0.4 (4) 10 ± 62 (5) 2 ± 11 (5)C a r b o n a t i t e (68) 21,993 7,093 ± 5,918 (21) 13,886 ± 10,012 (21) 1,490 ± 980 (21) 4,286 ± 3,275 (21) 443 ± 427 (21) 120 ± 102 (20) 217 ± 230 (20) 30 ± 27 (20) F e l s i c v o l c a n i c (3) 1,084 41 ± 889 125 ± 1,870 15 ± 210 48 ± 765 15 ± 130 0.4 ± 6 15 ± 96 5 ± 14H e a v y m i n e r a l s a n d s (100) 27,747

2.3 (1) 4.9 (1) 0.6 (1) 2.0 (1) 0.3 (1) 0.09 (1) 0.2 (1) 0.03 (1)G r a n i t e -r e l a t e d s k a r n (7) 60 3,707 ± 1,813 (5) 9,450 ± 4,632 (5) 1,152 ± 565 (5) 4,018 ± 1,931 (5) 465 ± 171 (5) 80 ± 28 (5) 238 ± 175 (5) 25 ± 46 (5)I O C G (4) 9,764 1,675 ± 1,115 (2) 2,516 ± 1,654 (2) 21 (1) 69 (1) 10 (1) 4 (1) 9 (1) N /A L a t e r i t e /s o i l /c l a y (2) 435 (1) 145 (1) 265 (1) 30 (1) 99 (1) 18 (1) 2 (1) 15 (1) 2 (1)S h a l e h o s t e d (5) 6,449 41 ± 1 (2) 72 ± 2 (2) 9 (2) 34 ± 0.4 (2) 7 ± 0.1 (2) 1 (2) 6 (2) 1 (2)T a i l i n g s (7) 1,512 1,289 ± 7,846 (4) 2,426 ± 9,235 (4) 287 ± 2,097 (4) 1,215 ± 7,445 (4) 230 ± 1,165 (4) 30 ± 39 (4) 273 ± 809 (4) 142 ±62 (4)A v e r a g e R E E g r a d e (p p m ) 1,853 ± 6,110 (63) 3,379 ± 10,798 (63) 271 ± 1,328 (57) 823 ± 4,712 (56) 101 ± 696 (57) 23 ± 81 (55) 67 ± 474 (56) 11 ± 56 (55) R e p o r t e d R E E 55,060 100,391 8,079 24,450

3,006 671 1,999

341

r e s o u r c e s (k t )A v e r a g e e s t i m a t e (k t )

163,959 298,983 23,979 72,821 8,937 2,035

5,928

973

M i n e r a l

r e s o u r c e s D e p o s i t t y p e (M t )

D y (p p m )

H o (p p m ) E r (p p m ) T m (p p m )

Y b (p p m )

L u (p p m )

Y (p p m ) S c (p p m )

A l k a l i n e c o m p l e x a n d 13,621 170 ± 362 (14)

35 ± 57 (13) 132 ± 120 (14) 17 ± 13 (12)

114 ± 66 (14)

17 ± 9 (12)

1,051 ± 1,544 (27) 11 ± 0.46 (2)

p e g m a t i t e s (51)A l l u v i a l /p l a c e r (7) 1,099 8 ± 65 (5)

2 ± 15 (5) 4 ± 39 (5) 0.6 ± 6 (4) 4 ± 35 (5) 0.5 ± 4 (4) 42 ± 362 (5) 5 (1)C a r b o n a t i t e (68) 21,99

3 89 ± 126 (20) 9 ± 126 (18) 23 ± 4

4 (19) 2 ±

5 (15) 38 ± 30 (18) 9 ±

6 (13) 274 ± 489 (21) 29 ± 11 (2) F e l s i c v o l c a n i c (3) 1,084 38 ± 83 3

7 ± 1 (2) 3

8 ± 5

9 8 ± 6 59 ± 33 9 ± 4 253 ± 426 N /A H e a v y m i n e r a l s a n d s (100) 27,747 0.06 (1) 0.01 (1) 0.02 (1) N /A 0.01 (1) 0.01 (1) 0.2 (1) N /A G r a n i t e -r e l a t e d s k a r n (7) 60 128 ± 362 (5) 22 ± 88 (5) 59 ± 272 (5) 8 ± 40 (5) 46 ± 240 (5) 7 ± 33 (5) 634 ± 2,255 (5) N /A I O C G (4) 9,764 7 (1) N /A 4 (1) N /A N /A N /A 41 (1) N /A L a t e r i t e /s o i l /c l a y (2) 435 (1) 13 (1) 3 (1) 8 (1) 1 (1) 7 (1) 1 (1) 75 (1) N /A S h a l e h o s t e d (5) 6,449 5 ± 0.2 (2) 1 (2) 3 (2) 41 ± 1 (2) 3 (2) 0.5 ± 0.1 (2) 32 ± 1 (2) 12 ± 2 (2)T a i l i n g s (7) 1,512 150 ± 380 (4) 46 ± 21 (4) 133 ± 84 (4) 39 ± 17 (4) 137 ± 246 (4) 46 ± 23 (4) 1,304 ± 1,021 (4) 194 (1)A v e r a g e R E E g r a d e (p p m ) 52 ± 282 (56) 9 ± 51 (52) 33 ± 142 (55) 4 ± 21 (46) 32 ± 130 (52) 5 ± 18 (45) 464 ± 1,397 (71) 13 ± 63 (8) R e p o r t e d R E E 1,532

263 983 124

959

158 9,902 82

r e s o u r c e s (k t )A v e r a g e e s t i m a t e (k t )

4,601 796 2,920

354 2,831

442 41,056 1,150

N o t e s : P a r e n t h e s e s i n d i c a t e n u m b e r o f d a t a p o i n t s u s e d t o c a l u l a t e e a c h v a l u e ; “a v e r a g e e s t i m a t e s ” a r e c a l c u l a t e d b a s e d o n a w e i g h t e d a v e r a g e g r a d e f o r i n d i v i d u a l e l e m e n t s ; N /A = d a t a n o t a v a i l a b l e

A DETAILED ASSESSMENT OF GLOBAL RARE EARTH ELEMENT RESOURCES: OPPORTUNITIES AND CHALLENGES

1943

unsurprisingly LREE dominated, containing >90% LREE or Ce and La where specified for individual deposits. Felsic vol-canic, granite-related, and alkaline deposits usually have REO resources that contain more HREE, although, again, a lack of available individual element data for all projects has lim-ited our capacity to assess the full picture of REE distribution within all potential REE deposits. However, even given this, there are significant differences in the distribution of the indi-vidual REE (especially the HREE) in the resources evident in Table 9, a fact that has implications for targeting of deposit types that preferentially contain the more valuable HREE.Despite the significance of individual REE concentrations, most mining companies rarely provide REE resource esti-mates that contain these crucial data, with only 71 of the 260 deposits within our database reporting individual REE con-centration data, and a further 10 deposits that only report Y concentrations rather than individual concentrations for all of the REE. This situation is also exemplified by the data shown in Tables 6 and 7, where individual REE concentrations are not reported for some of the most significant REE projects in our database (e.g., the Tomtor project in Russia, the Pea Ridge deposit in the United States, and the Morro dos Seis Lagos deposit in Brazil). This insufficient reporting means that our database contains significant variations in average REE concentrations (especially the HREE) for different types of REE mineral deposits, which could be attributed to the natu-ral variability of these deposits, the changing geologic settings of these REE projects, a lack of sufficient data and associated reporting to provide a comprehensive picture for each type of deposit, or some combination of all of these factors.

Average individual concentrations were calculated for indi-vidual deposit types to provide an estimate of the distribu-tion of the individual REE within individual projects; these data were then used to estimate individual REE resources within the 196 of the 260 deposits in our dataset that do not have formally reported individual REE concentrations. This approach involves assessing the individual REE resources within a given type of REE deposit using the compiled total mineral resources from all deposits in the same deposit-type category combined with corresponding weighted average REE fractions calculated for those deposits that reported individual REE concentrations within this deposit class. This assessment confirms that significant differences are present between LREE and HREE resources (as summarized in Fig. 6 and Table 8), and our estimates indicate that Ce is the most abundant of all of the REE within our database (~299 Mt contained elemental Ce), followed by La (~164 Mt), with Y unsurprisingly dominating the HREE budget of these depos-its (~41 Mt contained elemental Y). Although, chemically, Y does not belong to the lanthanide group of elements, it con-stitutes more than 56% of the entire HREE metal resource, further indicating the natural scarcity of critical HREE like Dy, Yb, and Lu. Despite the insufficient reported data and uncertainties involved in these scenarios, the three orders of magnitude difference between LREE and HREE resources again indicates that global REE resources contain far lower amounts of the HREE than the LREE.

The complex substitution-dominated mineralogy of the REE and the relatively limited scale of global REE mining means that REE deposits are associated with a wide range

T a b l e 9. A v e r a g e P r o p o r t i o n a l D i s t r i b u t i o n s o f t h e R E E S p l i t b y D e p o s i t T y p e

L a C e P r N d S m E u G d T b D y H o E r T m Y b L u Y D e p o s i t t y p e

(w t %) (w t %) (w t %) (w t %) (w t %) (w t %) (w t %) (w t %) (w t %) (w t %) (w t %) (w t %) (w t %) (w t %) (w t %)

N o .

A l k a l i n e 17 33 3.6 14 2.6 0.36 2.7 0.53 2.9 0.60 2.3 0.29 1.9 0.29 18 27

A l l u v i a l /p l a c e r 21 41 4.2 15 2.9 0.33 2.2 0.44 1.8 0.44 0.88 0.13 0.88 0.11 9.2 5C a r b o n a t i t e 25 50 5.3 15 1.6 0.43 0.77 0.11 0.32 0.032 0.082 0.0071 0.14 0.032 0.98 21F e l s i c v o l c a n i c 5.8 18 2.1 6.8 2.1 0.057 2.1 0.71 5.4 5.24 5.4 1.1 8.4 1.3 36 3G r a n i t e -r e l a t e d s k a r n 18 47 5.7 20.1 2.3 0.40 1.2 0.1 0.6 0.11 0.29 0.040 0.23 0.035 3.2 5H e a v y m i n e r a l s a n d 21 46 5.6 19 2.8 0.84 1.9 0.28 0.56 0.093 0.19 N R 0.093 0.093 1.9 1I O C G 38 58 0.48 1.6 0.23 0.092 0.21 N R 0.1607 N R 0.092 N R N R N R 0.941 2L a t e r i t e /s o i l /c l a y 21 39 4.4 14 2.6 0.29 2.2 0.29 1.9 0.44 1.2 N R 1.0 0.15 11 1S h a l e h o s t e d 16 28 3.5 13 2.7 0.39 2.3 0.39 1.9 0.39 1.2 16 1.2 0.19 12 2T a i l i n g s

17 31 3.7 16 3.0 0.39 3.5 1.8 1.9 0.59 1.7 0.50 1.8 0.59 17 4

N o . = n u m b e r o f d e p o s i t s w i t h r e p o r t e d i n d i v i d u a l R E E c o n c e n t r a t i o n s ; N R = n o t r e p o r t e d

1944 WENG ET AL.

of critical co- and by-product elements (e.g., Zr, Nb, Li, Hf, Ta, etc.). However, the relationship between these co- and by-products and the differing types of REE deposits has not as yet been fully assessed. As summarized in Table 5 and the supplementary information, our compiled dataset provides an initial step in quantitatively assessing these relationships.

A number of alkaline complex and pegmatite REE deposits contain reported economic concentrations of Zr (16 out of 48) and Nb (15 out of 48), suggesting (as expected) a link between these deposits and Zr and Nb enrichment. The car-bonatite deposits that dominate global REE resources are variably enriched in a wide variety of by- and co-product ele-ments, such as Nb, Zr, Fe, Sr, and F, whereas shale-hosted REE deposits contain the most diverse by-/co-products, including Zn, Cu, Co, V, Ni, Mo, Sc, Li, Al, and pure silica, among others. Th and U are the two most common radio-active impurities reported within the REE deposits in our database (118 deposits report Th grades and 40 deposits provide U concentrations), with average concentrations of 81 ppm Th and 127 ppm U. It should be emphasized that our study is primarily based on reported mineral resources that provide information on geologic probability rather than economic feasibility for extraction. However, this, in turn, also indicates that a significant amount of coexisting and economically important elements may be present within these REE deposits. These elements either are not present at sufficient concentrations, have not undergone sufficient metallurgical testing to be reported as yet, or may not be extractable as a result of processing difficulties or prohibitive costs to be classified as part of individual reported mineral resources and, hence, have not been included in our dataset. Discussion: Assessing Rare Earth Element Resources Shifting from one dominant supplier (i.e., C hina) to a more diverse global REO supply chain is crucial for ensur-ing long-term REE resource security and meeting growing global demands for the REE. Our database indicates that global known REE resources are some 619.5 Mt TREO + Y hosted by 267 deposits, with the 260 deposits that have known grades and tonnages having an average concentration of 0.63% TREO + Y (Table 4), with 111, 199, and 310 Mt contained TREO + Y in high-, medium-, and low-reliability category deposits, respectively. Current TREO + Y resources are dominated by the LREE, with an average LREO (La-Gd) to HREO (Tb-Lu + Y) ratio of 13:1. Although China hosts sig-nificant TREO + Y resources (~268 Mt) and the largest oper-ating REE project (i.e., Bayan Obo; Table 5), some 57% of the global TREO + Y resources within our database are hosted by deposits outside of China (Fig. 5). These deposits are located in a number of different countries, including Australia (e.g., Mt. Weld, Nolans Bore, etc.), Canada (Niobec, Nechalacho, etc.), Brazil (Araxá, etc.), Russia (Tomtor, C huktukonskoye, etc.), and Greenland (Tanbreez, Kvanefjeld, etc.), all of which host numerous potential REE deposits containing abundant REO resources. From a geographic perspective, the transi-tioning of these potential deposits into production means that they could become significant suppliers within the global REE market and therefore mitigate any potential supply risks associated with the dependence on a single supplier. How-ever, C hina’s monopoly within the global REE industry is not only based upon the largest REO resource endowment but also benefits from its dominant position in REE process-ing, specialized human capital, particular technical expertise, alloying, and downstream manufacturing (USDOE, 2010). In order to cope with these challenges, a significant amount of time and resources will be required to establish a competi-tive and sustainable REE supply chain outside China; hence, any change toward a more diverse global REE market must necessarily be gradual.

Various estimates of global REE resources have been pub-lished by different geological, scientific, and governmental organizations (Table 3), with the majority of these estimates focused on REE ore reserves. In comparison, our approach is based on reported project-specific mineral resources that are categorized by the reliability of the available data (i.e., high, medium, and low). This study inevitably involves a variety of uncertainties, as illustrated by the large number of medium- (126 out of 267 projects) and low- (76 out of 267 projects) reliability resources in our dataset. This is exemplified by the Bayan Obo deposit, which, despite the fact that it has been the largest operating REE mine in the world since the 1960s, has an uncertain resource, with many reports including highly variable mineral resource estimates for the deposit, such as one from the Chinese Society of Rare Earths (CSRE, 2002), which reported that Bayan Obo contained 43.5 Mt TREO + Y “industrial reserves” plus 106 Mt “measured reserves,” com-pared to one from the Ministry of Land and Resources of the People’s Republic of China (MoLRPRC, 2012), which pub-lished a reserve estimate for Bayan Obo of 91.59 Mt of con-tained TREO + Y in addition to other critical minerals such as Nb (2.16 Mt contained Nb2O5). This just highlights some of the uncertainties involved in predicting the security of future supplies of the REE and other critical metals.

Similar uncertainties also surround the REE resources within Australia’s Olympic Dam deposit. According to Geo-science Australia, Olympic Dam contained about 53 Mt TREO + Y in December 2011 (Hoatson et al., 2011), which, when combined with the published 2011 total mineral resource of 9,292 Mt (BHP Billiton Ltd. [BHPB], 2011a), suggests an approximate grade of 0.55% TREO + Y for the deposit. The deposit is also known to contain about 2,000 ppm La and 3,000 ppm Ce (Oreskes and Einaudi, 1990), suggest-ing a combined La-Ce oxide grade of 0.59% (using an X2O3 formula). C ombining these concentrations with an assump-tion that all of the other REE within the deposit form some 10% of the total REE budget within Olympic Dam (i.e., 90% La and Ce, as the deposit is known to be LREE domi-nated; Oreskes and Einaudi, 1990; Reeves et al., 1990) and a decline in the REO grade of the deposit by one-third (in accordance with declining C u grades in reported mineral resources for Olympic Dam) suggests that Olympic Dam has an approximate grade of 0.48% TREO + Y, consistent with previous research (Oreskes and Einaudi, 1990; Reeves et al., 1990). However, despite the fact that Olympic Dam contains a significant amount of the REE, BHP Billiton has no plans to attempt to convert this potential resource into production (BHPB, 2011b), meaning that other information on this proj-ect, such as mineralogy and individual REE concentrations, are not included within annual mineral resource reporting for the Olympic Dam deposit (e.g., BHPB, 2012).