Mineral Composition of Rare-Metal Metasomatic Rocks of the Ufaley Metamorphic Complex (Vein 175 of the Kyshtym Quartz-Vein Deposit, Slyudorudnik, South Urals)

The article considers the geological position and mineral composition of rare-metal (TR) metasomatites with a pegmatoid structure and forming lenticular bodies. TR metasomatites are spatially and genetically related to carbonatites and form single bodies. The latter are spatially related and have the same geological position with industrial bodies of vein, granular quartz. Unlike cabonatites, metasomatites are crushed and boudinated. The uniqueness of metasomatites is due to unusually large xenotime crystals. Most minerals involved in the structure of metasomatites contain abnormally high isomorphic impurities of Y. In the composition of yttrium-bearing epidote and yttrium-bearing titanite, its amount is slightly more than 8 wt. % Y2O3. Fergusonite-(Y) and a mineral whose composition approaches the idealized formula YAlSiO5 are present as inclusions in yttrium titanite. In apatite-II, formed in certain areas during recrystallization (granulation) of apatite-I, the total content of yttrium and heavy rare earth elements signi cantly exceeds 10 wt. %. Fergusonite-(Y) and a microinclusion, the composition of which corresponds to a complex oxide with the formula Ca2Y2O5, are present as inclusions at the grain boundary. The unusual composition of metasomatites and the speci c structure of TR-metasomatites indicate a long process of their formation and metasomatic nature. At present, metasomatite lenses occur in rocks that have undergone metamorphism at the level of amphibolite facies.