Mineral Composition of Rare-Metal Metasomatic Rocks of the Ufaley Metamorphic Complex (Vein 175 of the Kyshtym Quartz-Vein Deposit, Slyudorudnik, Southern Urals)
摘要
The present paper considers the geological position and mineral composition of rare-metal (RM) pegmatoid metasomatic rocks, which form lenticular bodies. The single bodies of RM metasomatic rocks are spatially and genetically related to carbonatites. In addition, these bodies are spatially related with industrial vein, granular quartz bodies and have the same geological position. Unlike carbonatites, metasomatic rocks are crushed and boudined. These metasomatic rocks are unique due to the presence of unusually large xenotime crystals. Most minerals involved in the structure of these rocks contain abnormally high isomorphic yttrium impurity. In the composition of Y-bearing epidote and Y-bearing titanite, its amount is about 8 wt % Y2O3. Fergusonite-(Y) and a mineral with the idealized formula YAlSiO5 are present as inclusions in yttrium titanite. In apatite-II, which formed locally during recrystallization (granulation) of apatite-I, the total Y + HREE content significantly exceeds 10 wt %. Fergusonite-(Y) and a microinclusion, corresponding to a complex oxide with the formula Ca2Y2O5, are present as inclusions at the grain boundary of apatite-II. The unusual composition of metasomatic rocks and the specific structure of RM metasomatic rocks indicate a long process of their formation and metasomatic origin. At present, metasomatic lenses occur in rocks that experienced amphibolite-facies metamorphism.