LITHIUM IN THE SUBSOIL OF UKRAINE Part 7. Genesis of lithium-bearing objects: rare-metal granites of the Ukrainian Shield

Abstract

In the genetic sense, the following lithium-bearing objects have been characterized: vein Li-F granites and areal Liznykivsky granites of the Korosten pluton, rare-metal granites of the Kamianomohylsky complex, and ongonites of the Azov region. Most researchers consider Li-F granites as the final phase of magmatism of the Korostensky complex. Our conclusion differs from the mainstream view: vein Li-F granites of the pluton are products of crystallization of deep fluid flows that penetrated into the fissure cavities of the pluton rocks after the formation of magmatic massifs. In our opinion, the Liznykivsky granites are metasomatic formations that have developed on different-age rapakivi-like biotite-amphibole granites under the influence of deep fluid flows. The rare-metal granites of the Kamianomohylsky complex form three massifs in the Azov region: Kamiana Mohyla, Katerynivsky and Starodubivsky. Initially, all granite massifs were formed in the process of crystallization of magmatic melt, which later changed to metasomatic alteration of granites. Post-magmatic changes in granites that contributed to the development of rare metal mineralization include: 1) biotitization; 2) microclinization; 3) early albitization; 4) greisenization; 5) late albitization. According to the data of thermobarogeochemical studies, the stage-by-stage development of the post-magmatic alteration of the Kamiana Mohyla granitoids was substantiated and physicochemically characterized: microclinization (500-600 °С), albitization (430 °С), topazization (430 °С), silicification (430-440 °С), sulfidization (320 °С), late albitization (290-420 °С), crystallization of xenotime (200-210 °С), vein fluoritization and the growth of fluorite crystals (125-155 °С). The crystallization of ongonites took place at high temperature, which was 1140 °C at the final stage of quartz phenocrysts growth.