Composition of Chromitites from Ultramafites Framing the Sysert Complex (Mount Kron, Middle Urals)

The paper presents the results of a study of the mineralogy of chromitites from an ancient mine located on the slope of Mount Kron near the village of Raskuikha in the Middle Urals. Geologically, the studied chromitites form small lens-shaped bodies in apodunite and apoharzburgite serpentinites of the Early and Middle Ordovician. Ultrabasites are linear bodies confined to the melange zone developed in the northwestern exocontact of the Sysert metamorphic complex. It has been established that chromitites are represented by primary aluminous magnesiochromite, which, under the conditions of the greenschist facies of metamorphism, was transformed into magnesian and ferruginous chromite. Microprobe analysis determined that the green garnet that makes up the cement in chromitites and the brushes of crystals on it is uvarovite with a content of 53-63 % uvarovite end-member, up to 28 % grossular end-member and up to 22 % andradite end-member. Nine sulfides have been identified in chromitites: godlevskite, nickel pentlandite, heazlewoodite, millerite, chalcopyrite, pyrite, bornite, galena and geerite. The formation of such rich mineralization is associated with the metamorphism of chromitites and their subsequent hydrothermal development.