Jackson and Christiansen reported in 1993 in U.S. Geological Survey Circular 930-N that bastnaesite, monazite, and xenotime are currently the most important rare-earth minerals. Bastnaesite occurs as a primary mineral in carbonatites. Monazite and xenotime also can be found in primary deposits but are recovered principally from heavy-mineral placers that are mined for titanium or tin. Each of these minerals has a different composition of the 15 rare-earth elements.
World resources of economically exploitable rare-earth oxides (REO) are estimated at 93.4 million metric tons in place, composed of 93 percent in primary deposits and 7 percent in placers. The average mineral composition is 83 percent bastnaesite, 13 percent monazite, and 4 percent of 10 other minerals. Annual global production is about 67,000 metric tons of which 41 percent is from placers and 59 percent is from primary deposits; mining methods consist of open pits (94 percent) and dredging (6 percent).
This output could be doubled if the operations that do not currently recover rare earths would do so. Resources are more than sufficient to meet the demand for the predictable future. About 52 percent of the world's REO resources are located in China. The 1993 ranking of other countries is as follows:
- Namibia (22 percent),
- United States (15 percent),
- Australia (6 percent), and
- India (3 percent).
Conversely, 38 percent of the production is in China, 33 percent in the United States, 12 percent in Australia, and 5 percent each in Malaysia and India. Several other countries, including Brazil, Canada, South Africa, Sri Lanka, and Thailand, make up the remainder. Markets for rare earths are mainly in the metallurgical, magnet, ceramic, electronic, chemical, and optical industries.
Rare earths improve the physical and rolling properties of iron and steel and add corrosion resistance and strength to structural members at high temperatures. Samarium and neodymium are used in lightweight, powerful magnets for electric motors. Cerium and yttrium increase the density and heat resistance of sintered ceramics. Yttrium and gadolinium contribute to the efficiency of electronic switches and sensors. Cerium improves the effectiveness of catalysts in the petroleum and automotive industries. Cerium oxides speed glass melting and are used to polish glass by chemical, rather than mechanical, means. Cerium, europium, terbium, and yttrium, as phosphoric compounds, promote the vivid colors of television screens. Consumption of rare earths is expected to grow by about 2.6 percent per year (1993).
International trade in rare-earth concentrates, compounds, and metals is complicated and vigorous. Countries like Australia and Sri Lanka export their monazite concentrates without treatment. Other nations, such as Brazil and India, convert their monazite concentrates to specific compounds. Japan, South Korea, France, West
Germany, and the United Kingdom import concentrates.
Note: FIGURE 18. U.S. imports of rare-earth products in 1989, by country (see table 20). and compounds for their electronic and ceramic industries. The United States imports about 5,000 metric tons of monazite concentrates and 10,100 metric tons per year of rare-earth compounds and metals (mainly from France) and exports about 2,000 metric tons per year of rare-earth products (mostly to Japan).
PART II-SELECTED INVENTORY INFORMATION FOR REO DEPOSITS AND DISTRICTS
Tables 21 and 22 contain information from the International Strategic Minerals Inventory record forms for REO deposits and districts. Only selected items of information about the geology and location (table 21) and mineral production and resources (table 22) of the deposits are listed in this publication, albeit of 1993 vintage.
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