The Slyudyanogorsk muscovite deposit in the Middle Ural

Abstract

The Slyudyanogorsk muscovite deposit of the central Urals has been known since 1884, but little geologic data are available in the literature. The muscovite occurrences are restricted to pegmatites found near the contact of the Late Precambrian Slyudyanogorsk Formation and the unconformably overlying Kurta Formation of Ordovician age. The country rock is dominantly metasedimentary in origin. Migmatization of schists is common and migmatites may be traced into pegmatites. The pegmatites may be classified on the basis of form into lens- and net-like veins and pipes that may be concordant or discordant to schistosity. Conformable pegmatites usually have higher mica contents and are distinctive in their extension to great depths. Transverse cutting types of pegmatites taper rapidly downward and are usually mica-free. On the basis Of composition, pegmatites may be divided into plagioclase (albite-oligoclase) and microcline varieties. Commercial muscovite occurrences are restricted to plagioclase pegmatites, as are the accessory ore minerals (molybdenite, chalcopyrite, pyrrhotite). The mica-bearing pegmatites usually have a more complex structure (zonal, cellular) than the massive mica-free pegmatites. The character and structure of the mica-bearing pegrnatites, the relicts of biotite within sheet muscovite and muscovite aggregates, the enlargement and replacement of biotite by muscovite in the surrounding wall rock, and the high iron content of the muscovite .suggest that muscovite is metasomatic after biotite in pegmatites that have formed from the wall rock by migmatization, recrystallization, and metasomatism. — R. D. DeRudder.