Uranium and thorium: The extreme diversity of the resources of the world’s energy minerals

Abstract

Uranium and thorium represent two elements which can be used for the production of energy. The types of uranium deposits, the mechanisms driving their genesis and their resources are relatively well known because extensive exploration programs and scientific research projects have been developed worldwide since the early 1950s. However, there are still several types of U deposits which have been underexplored such as those related to Na-metasomatism, and several others with low uranium grade but large tonnages such as phosphates, which mining has been discontinued, but which may become significant resources in the future depending of the evolution of the U prices. At the opposite, the types of Th deposits, their genesis and their resources are poorly known because of the extremely limited commercial use of this commodity. Recent evaluations of the Th resources show however that they may be as important as identified U resources, but a better evaluation of the cost of Th extraction for most of these resources is crucially needed. However, as the Th cycle does not need the costly enrichment process required for the use of uranium in most nuclear reactors and that the totality of Th can be burned in a nuclear power station, at least theoretically, the cost of thorium extraction can probably be significantly higher than that of U. U deposits are extremely diverse and may be formed at nearly all steps of the geological cycle, whereas Th deposits dominantly result from concentration during two major types of processes: magmatic fractionation of peralkaline complexes, associated carbonatites as an incompatible element and associated fluid fractionation from these types of melt, and as heavy mineral accumulation in placer-type deposits, essentially as monazite. Uranium is already widely used for energy production, but only a very small part of it is burned in the present nuclear reactors. A great variety of nuclear materials are produced during the U nuclear cycle: depleted U, spent fuel, reprocessed U, reprocessed Pu and military highly enriched U and Pu, which can be transformed to usable fuel in the present and future generations of nuclear power stations for a sustainable use of these resources. The present review of available and potentially available nuclear fuel resources in the world shows that these resources are considerable and can be largely increased with increasing exploration, the improvement of processing of low grade - large tonnage deposits (phosphates, black shales) - of refractory ore associated with peralkaline intrusions, the spreading of recycling spent U fuel and the development of new technologies for burning 238 U and 232 Th in new generations of nuclear power reactors.