**6. Production**

The Lemhi Pass district on the Montana-Idaho border in the USA contains numerous thoriumrich veins in the central Beaverhead Mountains. This district is thought to represent the largest concentration of thorium resources in the USA. The district contains total reserves of 64,000

tures, shears, and brecciated zones in quartzitic rocks. Rare-earth- and Th-bearing allanite and monazite are locally abundant. The thorite veins of the Lemhi Pass district are approximately equally enriched in thorium and REE. The total REE-oxide contents range from 0.07 to 2.20 wt.%, with an average value of 0.43 wt.%. The average concentrations of Th are 0.43 wt.%. [11]. At Steenkampskraal (South Africa) from the 1950s to 1963 about 50,000 tons of monazite concentrates were extracted, which contained between 3.3 and 7.6 wt.% Th before operation of the mine was halted. New economic assessment of this deposit was completed in 2012 and

The Nolans Bore deposit in the Northern Territory (Australia) is coupled with mineralized shear zones evolved in variably deformed and altered granitic gneiss, pegmatite, and minor calcsilicate rocks. Massive fluorapatite dykes enriched in REE and Th form the mineralization. The thorium content of Nolans Bore fluorapatite generally ranges from 0.07 to 0.59 wt.% Th

The by-product nature of the occurrence of thorium and a lack of economic interest has meant that thorium resources have seldom, if over, been accurately defined. Information on thorium resources was published in a joint report by the OECD Nuclear Energy Agency and the International Atomic Energy Agency (IAEA)—"Red Books" between 1965 and 1981, typically using the same terminology as for uranium resources at that time (e.g., reasonably assured resources and estimated additional resources I and II, the latter two categories which are recently termed inferred and prognosticated resources, respectively). No further information was published until 2003 when a global estimate of thorium resources of 4.5 million Th was presented in the 2003 Reed Book. A more comprehensive report was presented in the 2007 Red Book where resource estimates were given by deposit type and by countries and this was updated in the 2009 edition. Currently, the worldwide thorium resources by major deposit types are estimated to total about 6.2 million tons Th, including undiscovered resources (**Table 1**). In 2011 and 2013, the IAEA conducted technical meetings on thorium resources. Based on the inputs given in the meetings and details available in other open sources, identified uranium resources, regardless of resource category or cost category, have been updated for 16 countries and published in the most recent Red Book (**Table 2**) [9]. However, these identified resources (reasonably assured and inferred resources) may not have the same meaning

The main world resources of thorium are associated with monazite placer deposits in India, Brazil, Australia, the USA, Egypt, and Venezuela. The second most important thorium resources could be mined as by-product of REO from carbonatites (China, Greenland,

currently were established resources of 86,900 wt.% of REO [9].

208 Descriptive Inorganic Chemistry Researches of Metal Compounds

in terms of classification as identified U resources.

[20]. Most of mineralized veins are quartz-hematite-thorite veins, which fill frac-

tons of ThO2

(average 0.23 wt.% Th) [21].

**5. Resources**

The monazite concentrates arte recently produced only in five countries (**Table 3**) [22]. However, substantial but unquantifiable quantities of thorium produced China during the processing of domestic and imported mineral concentrates for production of rare-earth compounds. Issues associated with thorium's natural radioactivity are a significant deterrent to its commercial use. Limited global demand for thorium continued to create an oversupply of thorium compounds and residues. Excess thorium that was not designated for commercial use was either disposed of as a low-level radioactive waste or stored. Although research into thorium-fuelled nuclear reactor continues, there are recently no industrial-scale nuclear reactors using thorium.


**Table 3.** World production of monazite concentrates [22].

Recently, worldwide only minor amounts of ThO2 are typically used annually. Principal uses include chemical catalysts, lighting, welding electrodes, and heat-resistant ceramics, in descending order of use.
