Genesis of manganese ore occurrences of the Olkhon Terrane

Geological and mineralogical data are reported on the manganese occurrences of the Olkhon terrane (Western Baikal region), which are localized in metadolerites of the Ustkrestovsky Complex, high-temperature mafic hornfels, granites, calcitic marbles and calciphyres, and occasionally are developed as separate veins in gneiss granites or small lenses in quartzites. Most of them are made up of high-temperature mineral assemblages ( Opx + Cpx + Pl + Ilm ± Grt ± Bt ± Amp ), the main manganese carriers in which are ferrorhodonite (33–36 wt % MnO), orthopyroxene (6–12 wt % MnO), and ilmenite (3–16 wt % MnO). Obtained data are in conflict with traditional concepts that these rocks are gondites (manganese-rich metamorphosed sediments) or that manganese flux in carbonate sediments was related to the volcanic activity that occurred simultaneously with sedimentation at about 500 Ma. The diversity of manganese occurrences was produced by metasomatic processes that occurred almost simultaneously with regional metamorphism and emplacement of subalkaline mafic bodies during collisional tectonogenesis (about 470 Ma).