Discovery of Late Carboniferous high-grade carbonate-hosted manganese mineralization in the Maerkansu Area of the Western Kunlun Orogen, Northwest China

The Aoertuokanashi deposit located in the Western Kunlun Orogen is the first known Late Carboniferous large high-grade carbonate-hosted Mn deposit in the world and it has been mined since 2018. The deposit is considered to have formed in a back-arc basin developed during the northward subduction of the Paleo-Tethys Ocean beneath the Tarim Block. The Re-Os isotope isochron age of Mn ore at the Aoertuokanashi deposit is 302 ± 9 Ma. The minimum initial 187Os/188Os values obtained from the deposit is 0.28, which indicates the presence of a mantle source for the mineralization. The Aoertuokanashi deposit is similar in age to the 301 ± 5 Ma Wajilitag kimberlite in the Tarim Block, which is considered to be the initial magmatic pulse triggered by the Tarim mantle plume. The Late Carboniferous Aoertuokanashi Mn deposit was likely promoted by igneous activity from the Tarim mantle plume.The Aoertuokanashi deposit shows geochemical characteristics of hot water activity in a back-arc basin. The Mn mineralization is hosted in the restricted platform facies. Framboidal pyrite, typical biomat, and authigenic quartz are observed in the Mn deposit, indicating the influence of microbial processes. The sedimentary facies show a starving basin feature that can enhance microbial mediation. The d13CV-PDB values of mineralized rocks (from -19.5 to -8.2‰) are more negative than those of wall rocks (from -5.3 to +4.2‰), whereas the d13CV-PDB values (around -29‰) of kerogen for the Mn ore are significantly lower than those of the whole rock. These compositions indicate that the reducing function of organic matter played an important role in Mn mineralization. In the inferred extensional tectonic environment, under the influence of a mantle plume, the stratum with strong hot water activities and a large amount of organic matter becomes the focal point for the formation of carbonate type manganese ore deposit.