Geology and ore formation at the Yuzhno-Shameiskoe molybdenum deposit, Middle Urals, Russia

The Yuzhno-Shameiskoe molybdenum deposit belongs to the tungsten-molybdenum type and is associated with the Malyshevsk granite massif of Early Mesozoic age (240 - 220 Ma). The deposit is a steeply dipping linear fluorite-quartz veinlet stockwork (1.2 x 0.2 x 0.26 km), which is situated at the eastern exo- and endocontacts of the granite massif and located along a buried additional crest of the contact surface. Around the crest, the host apovolcanogenic amphibole schists of Early Ordovician are heavily biotitized (+ epidote + calcite) and cut by numerous granite apophyses. Ore-bearing granites are altered with feldspar granulation and poor muscovitization. Ore-bearing granites with quartz veinlets and ore-free homogeneous granites have similar concentrations of silica and total alkalies. Two ore types are distinguished in the deposit: (a) apogranitic and (b) complex apogranitic-metasomatic in the exocontact of granites. The ore mineralization is veined and, less commonly, disseminated. The ore veinlets are composed of quartz, fluorite, pyrite, and molybdenite. Molybdenite contains 1.26% W, 40 - 60 ppm Re, and 15 ppm Bi. Rare grains of scheelite occur in ores of the exocontact. Several discrete thin ore bodies with scheelite mineralization are revealed at the southeastern flank of the deposit. The specific features of the molybdenum mineralization and composition of ore-bearing granites can best be described in the context of the model of liquation of granitic melt that is rich in F and favorable for molybdenum concentration.