New data on REE and rare-metal mineralization in pegmatites of the Slyudyanogorsk muscovite deposit in the Southern Urals

The Slyudyangorsk muscovite deposit in the southern Urals was explored and mined in 1926–1957. By the mid-1950s, 104 veins of quartz–feldspar pegmatites including 21 muscovite-bearing veins have been found. Pegmatites with giant black Y-bearing epidote crystals are crosscut by veins with giant muscovite crystals, which, in turn, are intersected by veins of two-mica–quartz–two-feldspar pegmatites with rare-metal and REE mineralization. Microprobe data on compositions of complex Ti–Ta–Nb oxides [fergusonite-(Y), samarskite-(Y), euxenite-(Y), polycrase-(Y), columbite-(Fe), pyrochlore supergroup] are characterized, as well as of uraninite, ilmenorutile, scheelite, Y-bearing epidote, certain sulfides and rock-forming minerals from the Slyudyanogorsk deposit. The morphology and interrelation of minerals indicate that they are the result of crystal growth in cavities rather than of metasomatic replacement of gneisses, as has been suggested earlier. Thus, it is more promising for rare-metal and REE minerals in the Slyudorudnik area to be found in igneous rocks (granitic muscovite–quartz–feldspar pegmatites with the Nb–Ta–Ti–Y–U–W–Mo mineralization) than in metasomatic rocks.