Rare metal mineralization in albite-bearing granites of Western Trans-Baikal

Research subject. The article presents results of mineralogical and geochemical investigation of albite-bearing granites with high concentrations of trace elements located in the Western Trans-Baikal region. Methods. The composition of rocks was determined by the methods of classical silicate analysis, X-ray fluorescence and ICP-MS analysis. Microstructural features, relationships and homogeneity of minerals were studied using an electron microscope LEO-1430 equipped with an energy dispersive spectrometer Inca Energy-300. Isotopic compositions of oxygen were carried out using a mass spectrometer Finigan MAT 253 in the mode of a constant helium flow. Results. Ore mineralization is specified by the presence of Nb-bearing and less REE-bearing minerals. The studied rocks were divided into two groups: albitized granites, and deep albitized granites and albitites. These groups differ in terms of the presence of accessory minerals. The deep albitized granites and albitites belong to alkaline riebeckite-albite granites containing Nb-, Zr-, Y- and REE-bearing minerals. These rocks contain Y-bearing minerals - thalenite and yttrialite, with an up to 4 wt % inclusion of Y 2 O 3 in titanite, chevkinite, thorite and monazite. In contrast, the albitized granites contain fewer amounts of Y and HREE along with LREE-bearing minerals (monazite, allanite, fluocerite, samarskit). Conclusion. The selected groups of rocks have been analyzed in terms of their mineral and geochemical characteristics. The main Nb-bearing mineral in albitized granites is columbite. Minerals from albitites are rich in Y and HREE. The isotopic investigation has shown involvement of a magmatic-derived fluid in the rock formation process.