The composition of ore-forming minerals in rare-metal alkaline granites of the Zashikhinsky massif (Irkutsk region)
Alymova N. V., Vladykin N. V., Dokuchits E. Yu.
Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2021. V. 150. N 1. P. 76-91
The Zashikhinsky alkaline-granite massif, with the unique Ta–Nb–Zr–REE ore deposit, is located in the Irkutsk region and associates with the Late-Paleozoic East Sayan zone of rare-metal magmatism. Three facial varieties of granites were identified according to their differentiation and ore-bearing potential. These granite varieties include: (1) amphibole-bearing quartz-microclinealbite facies, (2) quartz-albite-microcline granites, (3) quartz-albite granites altered to albitites. These rocks show high concentrations of heavy rare earth elements and significant Nb/Ta ratios. Minerals, which concentrate rare elements, are represented by columbite, niobium rutile, zircon, xenotimum, and gagarinite. The long-term crystallization differentiation of the melt with a accumulation of inconsistent elements contributed to formation of rare-metal mineralization. Enrichment of granites in REE, Zr, Nb, and Ta testifies for initial enrichment of alkaline-granitic melts with ore components. Rocks of the Zashikhinsky massif originated from the magma of “transitional composition” and are characterized by mineral parageneses which are intermediate between parageneses of alkaline agpaite and Li-F granites.
Keywords: columbite, mineral concentrators, rare elements, rare-metal granites, Zashikhinsky deposit, East Sayan