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The Exploration for New rare earth Deposits Outside of China

J.Standing, 2014

Introduction

Rare Earth Elements (REE) are essential components within modern technology; computers, smartphones, and televisions are just some of the products that contain small amounts of REE. CO2 reducing technology such as; hybrid electric vehicles, maglev trains, catalytic convertors, and wind turbines, require around 25% of the REE market, with this increasing as the technology becomes more widespread (Chakhmouradian & Wall, 2012). The use of REE in defense technology such as; precision guided weapons and stealth technology also makes REE a strategic commodity, as substitute components are less effective (Szumigala, 2011).

What are Rare Earth Elements?

Rare Earth Elements (REE) are a groups of elements that are subdivide into “Heavy Rare Earths” (HREE) and “Light Rare Earths” (LREE) and occur together on the periodic table, as seen in Figure 1 (Szumigala, 2011).

Figure 1: Periodic table highlighting the REE and their position in the periodic table (Szumigala, 2011)

Figure 1 shows LREEs have a low-atomic number (La 57 – 62 Sm) whilst HREEs are heavier and have a higher atomic number (Eu 63 - Lu 71).

Despite the name “rare earth elements” they are surprisingly abundant within the Earth crust, for example Cerium is the 25th most abundant element in the crust far exceeding most precious metals, what is rare are economically viable deposits (Chakhmouradian & Wall, 2012).

Geological occurrence of REEs

Over 200 minerals contain significant REE, but three are the most economically important; basnaesite (Ce,La) (CO3) (OH,F), xenotime (YPO4) and monazite (Ce,La,Nd,Th) PO4, (Sukumaran 2012). These and other less significant, but economical minerals, e.g. Eudialyte and Allanite, occur in concentrations that enrich various rock types, as illustrated in Figure 2 which shows some of the worlds major REE deposit types in a tectonic context (Chakhmouradian & Wall, 2012).

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Figure 2: Types of major REE deposits and their tectonic setting (Chakhmouradian and Wall 2012)

China’s Dominance of the market and the need for alternative supplies

China has been the dominant producer of REEs since the mid-1980s and by 2009, as shown in figure 3, supplied over 94% of the world demand. China contains unusually large REE deposits that account for approximately 50% of the current known global reserves. This has allowed China to sell REEs at low prices, other mines around the world, for example Mountain Pass, USA, were unable to compete and were either closed or mothballed (Kynicky, et al 2012) (Szumigala, 2011).

Figure 3 – Global Rare Earth Supply 2009 (Chen, 2011)

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China’s advantage is not just the amount of REE reserves available but also the diversity of its deposits:

§ Bayan Obo is currently classed as the largest REE deposit on Earth, hosted within Proterozoic dolomitic marble affected by carbonatitic fluids, the deposit is rich in LREEs contained within basnaite and monazite. This world-class reserve is largely the reason for China global dominance.

§ South China Ion-adsorption clays have been mined since the 1970s and are currently the most important source of HREEs, these have been formed by the lateritic weathering of felsic rocks that contain REEs.

§ A number of high-grade REE deposits that have also been discovered within the Carbonites of the Himalayan Mianning - Dechang orogenic belts.

With all its deposits, and control of REE exploration projects outside of its borders, China continues to dominate the market. (Kynicky, et al 2012)

China the largest producer and also the largest consumer of REEs, mainly in electronics manufacturing for export and domestic markets. In 2010, in order to ensure supplies for domestic manufacturing, China announced a 72% restriction to REE exports, followed by 35% in the first half of 2011, generating a sharp rise in the price of REEs. China’s unpredictability on exports, due to its concentration on domestic interests and economic development, coupled with an ever increasing global demand means that by 2015 observers are predicting a supply shortfall (Kynicky, et al 2012) (Szumigala, 2011).

This forecast means that countries outside of China need to considerably increase their own production which has led to mines reopening, and even expanding, e.g. Mountain Pass, USA. The need to find new alternative deposits, has generated over 200 REE exploration projects worldwide. The USGS estimated in 2009 the global reserves of REEs at around 99 million tons, as illustrated in figure 4. (Steenfelt, 2012) (Kanazawa, 2005) (Chen 2011).

Global REEs Reserves according to USGS 2009 (Chen, 2011)

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Large alternative REE discoveries

USA

The USA has a number of REE deposits, the main being the Mountain Pass deposit. This is the second largest known REE deposit following Bayan Obo, and the largest LREE deposit of economical significance in North America. The ore body consists of a carbonate sill approximately 75m thick with substantial LREE mineralization occurring predominantly as bastnasite. Molycorp, the operating company, estimated the reserves at around 16.7 million tonnes in April 2012. (Kanazawa, 2005) (Mariano and Mariano, 2 012).

After Mountain Pass the next largest operation with respect to tonnage is the Bear Lodge Carbonatite, Wyoming, The Bear Lodge Mountains form a dome containing over 30 igneous bodies and may prove to be a substantial source of LREEs. Rare Earth Resources Ltd estimated the resource size to be in the region of 6.8 million tonnes (Mariano and Mariano, 2012).

Exploration projects within North America have centered mainly around Peralkaline Igneous occurrences with no fewer than six active exploration projects underway or being revisited from previous exploration, it is believed that these igneous occurrences contain substantial quantities of REEs, including the more valuable HREE’s in economically beneficial quantities (Mariano and Mariano, 2012).

Greenland

Greenland recently awarded a number of licenses to companies, allowing them to explore known rock complexes, such as carbonatites (these have been highlighted since the largest known REE deposits in the world Bayan Obo and Mountain Pass are both carbonatites), also carbonaceous sediments, and alkaline magnetic complexes, the distribution of which are shown in Figure 4, and identify the economic REE potential contained within the mineralization of these complexes, (Steenfelt, 2012).

Figure 4 – Map showing the main tectono-stratigraphical units of Greenland (Steenfelt, 2012)

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The most promising prospects are concentrated in southern Greenland, in particular the Gardar alkakine complexes where a major input of REE in to the crust is evident, generating a potential future world-class REE deposit. In addition to the major discoveries in the Gardar province there are also REE deposits in the Sarfarroq carbonatites, and the Palaeoproterozoic supracrutals in the Karrat Group, the locations of all these are highlighted on Figure 4, with the reserve estimates, as of September 2011, shown in Table 1. Added to the primary deposits, discussed below, there are a number of on going proposed prospects, for example the Cretaceous monazite-bearing paleoplacer at Milne Land in eastern Greeenland. It has been suggested that Greenland has the potential to deliver around 25% of global demand in the future and become Europe’s major REE source (Steenfelt, 2012), (Charles et al, 2013).

Table 1 – Resource estimates for REE prospects in Greenland, September 2011 (Steenfelt, 2012)

Oceanic Deposits

The search for new REE deposits has uncovered a new source within the world’s oceans, these deposits, if exploitable (due to environmental, logistic, and political issues, could prove sufficient to satisfy global demand (Sukumaran, 2012).

The main focus of research has been in the Pacific Ocean, here Japanese Geologists have discovered huge deposits of REE in the pelagic clay sediments at depths of 4000m – 5000m. These deposits, highlighted in figure 5, are associated with mid-ocean ridge hydrothermal activity, with hydrothermal plumes taking up REEs from ambient seawater. The study of drill core samples from a number of sites show that two regions; eastern South Pacific and central North Pacific, both contain pelagic muds, that are rich in REEs. The deposit in the eastern South Pacific having concentrations as high, if not greater, than those in recorded in the ion-absorbed clays of South China, with HREEs being twice as abundant (REE 500-2000ppm, HREE 50-200ppm). The deposit in the central North Pacific has lower concentration but still economically significant (REE 400-1000ppm, HREE 70-180 ppm). It has been estimated that 1 sq. km around one of the sampling sites could satisfy one-fifth of the current world consumption of REEs, making these the REE-rich mud in the Pacific Ocean a highly promising future resource. (Kato et al, 2011), (Balaram et al, 2012).

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Figure 5 : Distribution of average REY contents for surface sediments (<2m in depth) in the Pacific Ocean. Circles represent DSDP/ODP sites and squares represent the University of Tokyo piston core sites, with colours corresponding to the dominant origin of surface sediments. Open symbols are sites lacking samples from the sediment surface. Contours represent helium-3 anomalies (_3He) of mid-depth seawater12. REY-rich mud with average REY >400 ppm is designated as a potential resource in this study. (Kato et. Al. 2011)

Another potential REE resource within the worlds ocean basins is the Fe-Mn crust and nodule deposits on and around seamounts. Formed by hydrogeneric precipitation, and highly enriched in REEs, the initial research was in the Pacific Ocean. Hein, et. al. 2012 anayised cores of Fe-Mn crust and nodules in the Pacific Ocean, and found that there is an excellent commercial opportunity as nodules can easily extracted, however their REE concentrations are lower than the Fe-Mn crusts, which can also be exploited if engineering obstacles can be overcome. Zhang, et. al 2012, studied Fe-Mn crusts and nodules in both the Pacific and Indian Oceans, pictures of samples obtained are shown in Figure 6, with the sample distribution shown in Figure 7.

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Figure 6: Morphological features of Fe-Mn nodules (a1, a2) and crusts (b1,b2). (Zhang, et. al. 2012)

Figure 7: Map of the sample distribution. (Zhang, et. al. 2012)

Zhang, et. al attributes the high levels of REE enrichment to hydrogenic processes and the absorption of REEs from seawater with the crust is more enriched than the nodules. Zhang, et. al suggests that REEs can also be absorbed from the sediments, where the REEs are derived from seamount weathering, and possibly from weathered terrigenous material.

Similar studies in the Indian Ocean have focused on cobalt-rich crust deposited on seamounts. This area is being investigated as a potential resource for REEs, initial research at the Afanasy Niktin Seamount suggests that REE enrichment could be higher than that discovered in the Central Pacific, although it is acknowledged that a more detailed exploration study is required in order to estimate the resource potential. Samples obtained by dredging the seamount found that REE enrichment with average concentrations shown in Table 2 (Balaram et al, 2012).

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Table 2: Average concentrations of yttrium and REEs (µg/g) in the Fe-Mn crust from ANS, (Balaram et. al. 2012)

The Atlantic Ocean has also been studied, but on a more limited scale, in Atlantic Ocean, sediment cores, obtained using a ROV from a number of locations on the Lucky Strike Hydrothermal Field in the Mid-Atlantic Ridge, had been studied, a map of the area and the positions of the cores taken are shown in Figure 8 (Dias, et. al, 2007).

Figure 8: Area between the Pico Fracture Zone (PFZ) and the Oceanographer Fracture Zone (OFZ) along the Mid-Atlantic Ridge (MAR), south of the Azores Triple Point (ATZ) showing the Lucky Strike segment (PO1) and hydrothermal field. (Dias, et. al, 2007)

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Analysis of the sediment cores, shown in Table 3, showed high REE concentrations with LREE enrichment in the top half of the cores and HREE enrichment in the bottom half of the cores.

Table 3: REE concentrations from on of the Lucky Strike Sediment Cores (Dias, et. al, 2007)

As with the sediment cores studied from the Pacific Ocean, the REE enrichment of these sediments was related to hydrothermal processes, where seawater penetrates through cracks in the crust, undergoes high temperature chemical reactions with the crustal rocks, then is precipitated through hydrothermal vents. The vents themselves become enriched with metals and REEs, which spread to the surrounding sediments. Four sediment cores obtained by and ROV from the Condor Seamount on the Mid-Atlantic Ridge were studied by Caetano, et. al. 2013, a map of the Condor Seamount and the sampled areas are shown in Figure 9.

Figure 9: Location of the Condor Seamount and the sampled cores (Caetano, et al. 2013)

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The four cores showed a variation in concentrations of REEs, with those from the base of the seamount more highly enriched than from the other locations. The conclusions of Caetano, et. al. was that the high concentrations of REEs were related mainly to volaniclastic debris due to weathering of the slopes, this differs to the conclusions offered by Kato, et. al. and Dias, et. al, who state that hydrothermal processes are the main driving factor. A more varied study, of cores taken from 10 seamounts in the N/E Atlantic (see Figure 10 for the location of the sample sites) by Muinos, et. al 2013, shows that, as with the deposits in the Indian and Pacific Oceans, hydrogeneric precipitation processes have enriched the crust. The samples, analysed by X-Ray diffraction, showed significant REE enrichment at all sites with little variation in the concentration quantities. The researchers concluded that the Fe-Mn deposits could provide an important future metal resource, whilst acknowledging that future studies are required to quantitatively assess the resources’ potential. Overall the studies show that as with the Pacific and Indian Oceans, the Atlantic offers huge REE resource potential.

Figure 10: Map showing the bathymetry, the location of the sample sites and the limits of the Portuguese EEZ. (Muinos, et. al

2013)

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Future Scenarios

China will continue to dominate the global REE market for the foreseeable future, however with supply restrictions from China and the success of the various land-based projects outside of China, their supply could fall to around 37% creating a multi-supply system (Chen 2011).

With REE’s becoming more valuable due to supply many countries and companies are funding deep-sea research, should the exploitation Oceanic deposits become a reality this could see China’s percentage fall further especially considering oceanic deposits are depleted in the radioactive elements Thorium and Uranium that are often associated with REE deposits and can cause environmental issues during mining and processing of REEs. The future of the REE industry is certainly promising and more interesting than previously thought (Chakhmouradian & Wall, 2012), (Kato et al, 2011).

References

BALARAM, V., BANAKAR, V., SUBRAMANYAM, K., ROY, P., SATYANARAYAN, M., RAMMOHAN, M. and SAWANT, S., 2012. Yttrium and rare earth element contents in seamount cobalt crusts in the Indian Ocean. Current science, 103, pp. 1334-1338.

CAETANO, M., VALE, C., ANES, B., RAIMUNDO, J., DRAGO, T., SCHIMDT, S., NOGUEIRA, M., OLIVEIRA, A. and PREGO, R., 2013. The Condor seamount at Mid-Atlantic Ridge as a supplementary source of trace and rare earth elements to the sediments. Deep Sea Research Part II: Topical Studies in Oceanography, .

CHAKHMOURADIAN, A.R. and WALL, F., 2012. Rare earth elements: Minerals, mines, magnets (and more). Elements, 8(5), pp. 333-340.

CHARLES, N., TUDURI, J., GUYONNET, D., MELLETON, J. and POURRET, O., 2013. Rare earth elements in Europe and Greenland: a geological potential? An overview, 12th meeting of the Society of Geology Applied to Mineral Deposits (SGA) 2013, pp. 12-15.

CHEN, Z., 2011. Global rare earth resources and scenarios of future rare earth industry. Journal of rare earths, 29(1), pp. 1-6.

DIAS, A., MILLS, R., TAYLOR, R., FERREIRA, P. and BARRIGA, F., 2008. Geochemistry of a sediment push-core from the Lucky Strike hydrothermal field, Mid-Atlantic Ridge. Chemical Geology, 247(3), pp. 339-351.

HEIN, J.R., MIZELL, K., KOSCHINSKY, A. and CONRAD, T.A., 2012. Deep-ocean mineral deposits as a source of critical metals for high-and green-technology applications: Comparison with land-based resources. Ore Geology Reviews, .

KANAZAWA, Y. and KAMITANI, M., 2006. Rare earth minerals and resources in the world. Journal of Alloys and Compounds, 408, pp. 1339-1343.

KATO, Y., FUJINAGA, K., NAKAMURA, K., TAKAYA, Y., KITAMURA, K., OHTA, J., TODA, R., NAKASHIMA, T. and IWAMORI, H., 2011. Deep-sea mud in the Pacific Ocean as a potential resource for rare-earth elements. Nature Geoscience, 4(8), pp. 535-539.

KYNICKY, J., SMITH, M.P. and XU, C., 2012. Diversity of rare earth deposits: The key example of China. Elements, 8(5), pp. 361-367.

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MARIANO, A.N. and MARIANO, A., 2012. Rare earth mining and exploration in North America. Elements, 8(5), pp. 369-376.

MUINOS, S.B., HEIN, J.R., FRANK, M., MONTEIRO, J.H., GASPAR, L., CONRAD, T., PEREIRA, H.G. and ABRANTES, F., 2013. Deep-sea Fe-Mn Crusts from the Northeast Atlantic Ocean: Composition and Resource Considerations. Marine Georesources & Geotechnology, 31(1), pp. 40-70.

STEENFELT, A., 2012. Rare earth elements in Greenland: known and new targets identified and characterised by regional stream sediment data. Geochemistry: Exploration, Environment, Analysis, 12(4), pp. 313-326.

SUKUMARAN, P., 2012. The need to explore for rare earth minerals. Current science, 102(6), pp. 839.

SZUMIGALA, D., 2011. Rare Earth Elements–A Brief Overview of these elements, including their uses, worldwide resources and known occurrences in Alaska. Office of Governor Sean Parnell, .

ZHANG, Z., DU, Y., GAO, L., ZHANG, Y., SHI, G., LIU, C., ZHANG, P. and DUAN, X., 2012. Enrichment of REEs in polymetallic nodules and crusts and its potential for exploitation. Journal of Rare Earths, 30(6), pp. 621-626.