Composition and thermochronology of alkaline granites of Ingur massif: to problem of detection of factors contributing to formation of rare-metal mineralization in alkaline granites of Western Transbaikalia

The article considers the question of what factors contributed to the formation of rare metal mineralization in alkaline granites of Western Transbaikalia. It is based on the results of comparison of petro-geochemical characteristics of alkaline granitoids of nearby ore-bearing Ingur and ore-free Sherbakhtinsky massifs. The rocks of these massifs form a common series of compositions with variations from syenites to alkaline granites (in the Sherbakhtinsky massif) and from alkaline granites to pegmatites (in the Ingur massif). The formation of this series of rocks is associated with a deep differentiation of the original magma common to both massifs, accompanied by a sequential decrease in magnesiality and the accumulation of rare elements (Be, Ta, Nb, Th, U, HREE) in residual melts. They reach the highest values in the pegmatites of the Ingur massif, in which rare metal mineralization appears. Its formation is associated with the fact that, according to thermochronological studies, the Ingur massif for 6 million years was located in the temperature range from 900° to 500°. Such a long stay in the region of high temperatures was accompanied not only by deep differentiation of residual melts, but also stimulated fluid activity, which contributed to the redistribution and accumulation of ore elements in pegmatites.