The first data on U-Th mineralization in the Shkhara paleozoic crystalline massif, the greater Caucasus

A granite vein with a thickness of ∼ 2-3 m exposed in the headwaters of the Enguri River, with elevated radiation (μ Sv/h fluctuates in the range of ∼ 1-3) has been studied in detail. It is located along the Main Thrust of the Greater Caucasus, in the Upper Paleozoic biotite-bearing migmatites of the Shkhara massif. The vein represents hydrothermally altered rock composed of a biotite-quartzplagioclase assemblage, whose zircon LA-ICP- ²⁰⁶ Pb/²³⁸U age was determined to be late Variscan (310.2±7). It is slightly fragmented and fractured, where the existing fractures and nests are filled with quartz and thorianite-uraninite veins. According to ICP-MS-ES multielement analysis, in this vein, the Th content varies from ∼26 ppm ∼50 ppm, the U - varies between ∼55 ppm and ∼290 ppm, while the content of all other chemical elements is within the normal concentrations. Of particular interest in this vein is an elevated concentration of uranium, as it is almost 100-200 times higher than normal. Those are industrial contents for the vein-type deposits. Based on the conducted research, it has been found that there is full correlation between the studied vein and of U-bearing granitic veins of different regions of the world, by genesis, composition, localization and age. Based on these data, we suppose that the Late Variscan hydrothermal plagiogranite veins, which are localized in the shear zones of the Shkhara massif granite-migmatite complex and entirely the Main Range Zone of the Greater Caucasus, may be potentially U-bearing. (author)