Mineralogy of manganese skarns, genetically related to alkaline granites (on the example of the Ufa mine, Southern Urals)
Skarns of spessartine-rhodonite composition were detected in the Southern part of the Ufalei metamorphic block within limits of the Ufimian iron mine deposit (Central Uralian uplift, Southern Urals). The skarns are associated with the zone of ferruginous quartzite layer, which are intersected by the vein of granite pegmatites, occurring among the Riphean-Vendian metagabbroids and granite-gneisses (1350-590 Ma) and alkaline granites with aegirine and riebeckite (290-270 Ma). Manganese mineralization is presented by two associations: skarn (rhodonite, spessartine, johansennite, pyroxmangite, magnetite) and aposkarn metasomatites (ferromangnesian garnets, amphiboles and biotite). Aposkarn metasomatites are accompanied by barite, quartz and sulfides (pyrite, chalcopyrite, alabandite). On its chemical composition the researched rhodonite (SiO2 - 46.0-47.0, FeO - 8.5-9.0, MnO - 36.0-37.0, CaO - 5.0-6.0, ZnO - 0.5-0.8 wt %) sharply different from the composition of rhodonite of the deposits Uralian “manganese spar” (SiO2 - 46.0, FeO - 0.2-0.3, MnO - 50.0-51.0, CaO - 3.0-3.3 wt %). Spessartine, accompanying rhodonite, has zonal structure - from center to periphery the component content in them varies from spessartine to almandine-spessartine. On chemical activity and chemical properties they are close to manganese amphiboles of a number of the Uralian rhodonite deposits (Kurganovo, etc.). Constant presence of berillium mineralization (helvite, genthelvite, phenacite and oth.) in manganese skarns makes it possible to assume a possibility of finding helvite mineralization in skarns and aposkarn metasomatites of the Ufimian mine. A wide development in the mine area of alkaline granites with aegirine, riebeckite also allows believe, that the studied manganese skarns are genetically associated with the A-type alkaline granites.