MINERALOGY AND INCLUSIONS IN RARE METAL CARBONATITES SREDNYAYA ZIMA (EASTERN SAYAN)

The studied carbonatites of the Srednyaya Zima alkaline massif belong to calcitic carbonatites. The main rock-forming mineral of carbonatites is calcite. Minor minerals are represented by biotite of the annite-phlogopite series, fluorapatite, nepheline, ilmenite, pyrite, pyrrhotite, galena, as well as secondary feldspars - albite and potassium feldspar. Accessory minerals of carbonatites are pyrochlore, zircon, burbankite, magnetite, rutile, titanite, strontianite and barite. In the zircon of the carbonatites of the Srednyaya Zima massif, several generations of inclusions have been identified that characterize the composition of the melts of rare metal carbonatites and its subsequent evolution. According to the study of primary melt inclusions, the carbonatite melt in zircon had an alkaline-carbonate composition, with a high content of Ca, Na, CO2, OH, F and increased concentrations of Sr, Ba, Mg, Fe, Mn, Ti, U, rare metals Nb and Ta , as well as Zr and Si. The inclusions were captured by zircon at the initial stages of crystallization of the liquidus mineral and in composition were as close as possible to the composition of the parental melts of the Srednyaya Zima carbonatites.