Oolitic Ironstones and Carbonate Mn Ores of Marsyaty Deposit (Northern Urals, Russia): Key Study of Mineralogy and Geochemistry

This article describes the mineralogical and geochemical features of the Marsyaty sedimentary deposit of Fe and Mn ores in the Northern Urals (Russia). Oolitic ironstones are localized in coastal sandstones of the Cenomanian age. Сarbonate Mn ores lies within siliciclastic sediments of the Lower Paleocene and are separated from the oolitic ironstone by a layer of gravel. Authigenic iron oxyhydroxides, chamosite/bertierite and superimposed siderite predominate in the ironstones; kaolinite, apatite, perhamite, calcite and dolomite are minor and rare. Rhodochrosite and rencieite are major minerals of the Mn ore; layer Mn-silicates (caryopilite, parsettensite?) are minor and rare. Both ore types contain authigenic glauconite, montmorillonite, sulfides (sphalerite/wurtzite, galena, pyrite), gibbsite/boemite, REE phosphates. The detrital component of both types of ores is represented by clasts of quartz, ilmenite, zircon, monazite, epidote, titanite, muscovite, and feldspars. The δ13Сcarb varies from -18.5 to -23.3 in carbonate ironstone and -10.0 to -41.0 ‰ PDB in manganese ore. The light isotopic composition of carbon and numerous organic relics indicate the participation of microbes in both types carbonate ore formation process. It is concluded that iron and manganese ores belong to a joint transgressive series of sedimentary rocks that arose sequentially during the evolution of the West-Siberian basin. The unique feature of the Marsyaty deposit is that, within a limited area and over a short geological period, favorable conditions were realized first for the accumulation of iron and manganese, and then only for manganese.