Mineralogy and metamorphism conditions of manganese ore at the South Faizulino deposit, the southern Urals, Russia

Abstract

The mineralogy of slightly metamorphosed manganese ore at the South Faizulino hydrothermalsedimentary deposit in the southern Urals has been studied; 32 minerals were identified. Quartz, hausmannite, rhodochrosite, tephroite, ribbeite, pyroxmangite, and caryopilite are major minerals; calcite, kutnahorite, alleghanyite, spessartine, rhodonite, clinochlore, and parsettensite are second in abundance. This mineralic composition was formed in the process of gradual burial of ore beneath the sequence of Middle Devonian-Lower Carboniferous rocks. The highest parameters of metamorphism are T ≈ 250°C and P ≈ 2.5 kbar. The relationships between minerals and their assemblages made it possible to reconstruct the succession of ore transformation with gradually increasing temperature and pressure. Manganese accumulated in the initial sediments as oxides and a gel-like Mn-Si phase. Rhodochrosite and neotocite were formed at the diagenetic stage. In the course of a further increase in temperature and pressure, neotocite was replaced with caryopilite; ribbeite, tephroite, pyroxmangite, and other silicates crystallized afterwards. In addition to the PT parameters, the formation of various metamorphic mineral assemblages was controlled by the Mn/(Mn + Si) ratio in ore and XCO2 in pore solution. The latter parameter was determined by the occurrence of organic matter in the ore-bearing rocks. Ore veinlets as products of local hydrothermal redistribution of Mn, Si, and CO2 were formed during tectonic deformations in the Middle Carboniferous and Permian.