Sedimentary Environment of Mn-bearing Carbonate from the Muhu Manganese Deposit in Malkansu, West Kunlun: Evidences from Fusulinids and C-O-Sr Isotopes

Muhu Manganese Deposit is an important typical manganese deposit in the eastern part of the Malkansu Manganese Belt. Manganese ore bodies are mainly hosted in a set of clastic-carbonate rocks. Fossils from the top of manganese-bearing rock series are mainly Quasifusulina, include Quasifusulina tennissima (Schellwien), Quasifusulina phaselus (Lee), Quasifusulina paracompacta (Chang), and two unidentified species, indicating that the geological age of the manganese-bearing strata should be the Late Carboniferous. The δ¹³C_PDB values of surrounding rock range from -2.06‰ to 3.99‰; δ¹⁸O_PDBvalues range from -13.35‰ to-7.49‰; and ⁸⁷Sr/⁸⁶Sr values range from 0.707 70 to 0.707 97. In contrast, the δ¹³C_PDB values of rhodochrosite range from -16.60‰ to-1.95‰; δ¹⁸O_PDB values range from -11.51‰ to-4.48‰; and ⁸⁷Sr/⁸⁶Sr values range from 0.707 64 to 0.707 90. Comprehensive analysis reveals that the Mn-bearing rock series in Muhuhu Manganese Deposit developed in a shallow shelf with warm, normal salinity, and relatively strong hydrodynamic force. The water column is clear, but comparatively turbid compared to carbonate platform sedimentary environment. The deposition of carbonate rocks and manganese deposits was affected by surface water, and the formation of rhodochrosite is associated with the reduction of organic matter.