Jacobsite as an indicator of genrsis of manganese ore of the Ushkatyn-III deposit (Central Kazakhstan)

Jacobsite is a characteristic minor mineral of manganese ores at the Ushkatyn-III deposit in Central Kazakhstan. It mainly associates with hausmannite, tephroite, sonolite, friedelite, pennantite and calcite in the bulk mass of ores. A similar association, but without hausmannite, is also characteristic of jacobsite from veinlets intersecting the bulk mass ore. The chemical composition of jacobsite varies from Mn1.5Fe1.5O4 to MnFe2O4. A mineral with a high content of manganese (1 atoms per formula unit (apfu)) dominates the bulk mass of ores, while the veins are dominated by stoichiometric jacobsite (Mn ~1 apfu). The mineral composition of ores was formed in the process of low-grade metamorphism of metal-bearing deposits of hydrothermal-sedimentary genesis. The formation of jacobsite in metamorphosed metal-bearing deposits occurs under reducing conditions. With an increase in oxygen fugacity (oxidation potential), jacobsite is replaced by the association of hausmannite with hematite. Crystallization of jacobsite in the veinlets intersecting the hausmannite ores is carried out due to the entry of iron-containing hydrothermal solutions into them. It is assumed that jacobsite veinlets serve as mineralogical markers through seepage of ore-bearing hydrothermal structures («feeding channels») producing manganese-rich ores.