Thermal Convection of Fluids as a Possible Mechanism for the Formation of the Unique Streltsovka and Antei Uranium Deposits (Eastern Transbaikalia)

Resumo

The hydrothermal molybdenum–uranium deposits of the Streltsovka ore field are localized in a volcanic caldera of Late Mesozoic age. The paper presents the results of numerical modeling of free thermal convection of fluids in the residual thermal field of the consolidated magma chamber of the Streltsovka caldera, which justifies the idea of thermoconvective mechanism for the formation of the structurally conjugate Streltsovka and Antei deposits. The process of fluid heat and mass transfer in the Antei–Streltsovka oreforming system self-organized into a convection cell with a fluid circulation circuit including a descending convection branch along the ring-fault zone of the caldera, a lateral flow branch from the descending to the ascending convection branch in the caldera’s basement rocks, an ascending convection branch along faults of the Antei deposit, and a lateral return branch from the ascending to the descending convection branch along the caldera’s volcano-sedimentary rock fill, in which the ores of the Streltsovka deposit are localized. At the same time, formation of the total reserves of the Antei–Streltsovka deposit, largest in this ore field, was facilitated by uranium sourced, during the hydrothermal ore-forming process, not only from the uranium-rich rocks of the consolidated magma chamber, but also from the granitic host rocks of the Streltsovka caldera basement.