**5. Resources**

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 in terms of classification as identified U resources.

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,


**Table 2.** Identified resources of thorium [9].

Norway, Finland, and Sweden). Some other thorium resources are coupled with various uranium deposits in Canada, the USA, South Africa, and Kazakhstan. Thorium in Kazakhstan could be recovered as a by-product together with REO bounded on complex U-REE-Th ores. These ores are recently processed in the SARECO plant by Stepnogorsk [9].
