Geochemical properties and mineralization of thorium

Abstract

Thorium, a naturally occurring radioactive element, is widely distributed across diverse geological environments. As a typical lithophilic element, thorium exhibits strong affinity towards oxygen, readily integrating into silicate melts, primarily concentrating in the lithosphere. During the magmatic phase, thorium's geochemical behavior is akin to that of U, Ce, and Zr, and as an incompatible element, it remains in the residual melts of the latter stages of magmatic evolution. Thorium is enriched in acidic, pegmatitic, and alkaline rocks, leading to the formation of thorium-bearing phosphate minerals such as monazite. Alkaline carbonatitic fluids are capable of enriching rare earth elements and thorium, closely associating thorium deposits with igneous carbonatites. In surface processes, thorium's geochemical properties are relatively inert, allowing it to be preserved within the stable lattice of thorium-bearing minerals and form placer deposits. Globally, thorium resources are primarily found in carbonatite rocks, placer, and vein deposits, with monazite being one of the main sources. According to a report jointly published by the International Atomic Energy Agency and the Nuclear Energy Agency, the global thorium resources currently exceed 6.3 million tons, predominantly distributed in countries like India, Brazil, Australia, and the United States. The mineralization period of thorium is mainly concentrated in the Precambrian and Mesozoic, followed by the Paleozoic and Cenozoic. In China, thorium resources are relatively abundant, mostly associated with rare earth element deposits, yet their utilization rate remains low due to factors such as sorting technology. Thorium is a vital raw material in the space technology industry and a significant future nuclear fuel; thus, rational development and strategic protection of thorium resources should be strengthened, along with appropriate strategic reserves.