Geochemistry and chemical U-Pb dating of U-Th mineralization of the Shkhara crystalline massif, Greater Caucasus,  Georgia

The Greater Caucasus orogenic belt is the northernmost expression of the Caucasus and is linked to the southern 1Institute of Earth Sciences margin of the Precambrian Scythian Platform. In its structure two major formations are distinguished: pre-Jurassic crystalline basement and Meso-Cenozoic sedimentary formations. The basement complex is thrust over the Lower Jurassic formations along the Main Thrust of the Greater Caucasus (Gamkrelidze et al.,2020).       The Shkhara massif, part of the crystalline basement, is located in the central, highest, elevation portion of the Greater Caucasus at the headwaters of the Enguri River.  The massif  forms a large ridge 15 km long and 5 km high and is composed predominantly of Lower to mid-Paleozoic biotite gneisses and migmatites and cut through by a granitoid pluton of the Variscan generation. The zircon U-Pb age of granodiorite   of the Shkhara pluton corresponds to 316.9±8.8 Ma (Okrostsvaridze et al., 2022a).         U-Th mineralization was discovered in the biotite gneisses and migmatites of the Shkhara massif along the Main Thrust of the Greater Caucasus (Okrostsavridze et al., 2022b).  Uranium and thorium mineralization is associated with uraninite veins and nests, which are formed in biotite plagiogranites and migmatites. The content of Th in this rock varies from 26 to 51 ppm and the content of U changes from 55 to 299 ppm       For the first time, we studied the geochemistry and chemical U-Pb age of  Shkhara uraninite veins, on the JXA-8230 electron probe microanalyzer, of the  German GeoResearch Center in Potsdam. Geochemical studies have shown that the uranium mineral is high-temperature Th-bearing uraninite that   consists  of  uranium,  thorium, lead and yttrium. In these veins, the UO2 composition varies from 79.5% to 82.6 %, ThO2 – from 6.7% to 8.4 %, PbO – from 2.95 to 3.9%, Y2O3 – from 1.15 to 3.77%.  As for the chemical U-Pb age of the veins, it ranges from 286 to 290 Ma. The analysis of the obtained data shows that   the Shkhara uraninite mineralization was formed in pos-orogenic extension regime of the Greater Caucasus, which is in full correlation   with the vein-type uranium deposits similar to different regions of the world, including the central European Variscides. References      Gamkrelidze, I., Shengelia D., Chchindaze G., Lee Y. H., Okrostsvaridze, A., Beridze G., 2020.  U-Pb LA-ICP-MS dating of zoned zircons from the Greater Caucasus pre-Alpine crystalline basement: Geologica Carpatica, v. 71, no. 3, pp. 249-263.       Okrostsvaridze A., Bluashvili D., Gogoladze S., Gabrielashvili R., 2022a. The discovery of U mineralization in the late Variscan plagiogranite vein of the Shkhara crystalline massif (Greater Caucasus, Georgia) Geologica Balcanica, vo.51, no.1, pp. 3–14.       Okrostsvaridze A., Lee Y.-H., Tormey D., Skhirtlade I., 2022b. U-Pb zircon chronological constraints for three stages of syn-orogenic plutonic magmatism of the Greater Caucasus Svaneti segment, Georgia. Episodes, vo. 76, no. 3, pp. 1-15.