부산대학교 도서관

The causes of metasomatic albitization of host rocks and the formation of the accompanying thorium mineralization in uranium deposits of the Streltsovka ore field located in the Streltsovka volcanic caldera are considered. Data provided by the authors and published data allow us to conclude that the process of hydrothermal albitization does not require additional Na input by the magmatogenic fluids. It could have originated from the host rocks due to pre-ore acid leaching; accessory minerals in the same rocks were a source of Th. The increase in the pH value necessary for the deposition of albite under low-T conditions is ensured by a sharp change in the physicochemical conditions due to seismotectonic impulses. The latter were accompanied by opening of the fault and fracture systems, a decrease in pressure (decompression), and degassing. The alkaline character of the fluids that caused albitization is also emphasized by the behavior of trace and rare-earth elements. It is likely that thorium migrated in a sodium alkaline environment probably in the form of mobile tetra- or pentacarbonates: Na4[Th(CO3)4] or Na6[Th(CO3)5]. [ABSTRACT FROM AUTHOR]