Uranium Mineral Systems of Southeastern Eurasia

The territory of Southeastern Eurasia includes areas of Russian Transbaikalia, Mongolia and China, where hydrothermal and infiltration uranium deposits are widespread, formed in the Mesozoic–Cenozoic period in the area of postplatform tectonic-magmatic activation or, in terms of plate tectonics, in an “extensive rift system.” It is shown that the accumulation of ore-bearing volcanogenic-sedimentary strata and uranium mineralization of different genesis is synchronized in time with the processes of rifting and magmatism, which in turn are a consequence of the interaction of the Eurasian, Indian, and Pacific plates. The stretching conditions ensured the emergence of depressions in which sedimentary basins and volcano-tectonic structures were formed. The successive alternation of orogenic uplifts and riftlike depressions in the Mesozoic–Cenozoic period created favorable hydrodynamic conditions for the emergence of uranium mineral systems in this area, from Late Jurassic to Early Cretaceous hydrothermal to late Cenozoic infiltration systems. Hydrothermal and infiltration uranium systems of Southeastern Eurasia are characterized by multifluidity associated with a variety of processes of formation of solutions circulating in the depths of the territories of development of tectonic-magmatic activation. In these systems, due to the emergence of hydraulic gradients as a result of relief differentiation, cold meteoric waters capable for carrying uranium entered from the surface. Thermal fluids formed above magmatic chambers and thermal brines formed in deep horizons of sedimentary basins came from the basement or depths of the basins to the same systems. The potential of uranium volcanogenic ore genesis is associated with the development of thermoconvective circulation of uranium-transporting fluids whereas the potential for infiltration formation of exogenous mineralization was most fully realized in the arid climate zone. High-grade uranium mineralization was formed in areas where solutions of different genesis were mixed, which indicates such an important characteristic of mineral systems as multifluidity.