U–Th–REE Mineralization of the Bystrinsk Skarn-Porphyry Au–Cu–Fe Deposit (Eastern Transbaikalia): Typomorphic Characteristics, Peculiarities of Formation, and Genetic Implications

In the article typomorphic characteristics and peculiarities of formation of U–Th–REE mineralization first discovered in the Bystrinsk Cu–Au–Fe skarn-porphyry deposit are considered. It is shown that this mineralization was formed at high temperatures as a result of (1) magmatic (in skarns) and (2) early postmagmatic (porphyry-type mineralization) magmatic-hydrothermal processes in connection with Mesozoic magmatism of the Shakhtama complex. The peculiarities and differences of these two types of U–Th–REE mineralization are established. Transit of U, Th, and REE was carried out by chloride subalkaline reduced fluids at temperatures above 700° in skarns and similar anionic compositions, but lower-temperature (522°C) and more oxidized during the formation of porphyry-type mineralization. A brief comparative analysis is carried out of the characteristic features of uranium mineralization of the Bystrinsk deposit and some skarn U-deposits, as well as the unique uranium Streltsovsk ore field, which, like the Bystrinsk deposit, is located in the Argun structural-formation zone and associated with late derivatives of Mesozoic magmatism, similarly to the magmatism of the Shakhtama complex in terms of indicator characteristics.