Occurrence state and enrichment mechanism of cobalt in the cobalt-manganese deposit within the Ediacaran Doushantuo Formation in the Shiqian area, Guizhou Province, China

The sedimentary-supergene weathering cobalt-manganese (Co-Mn) deposits are extensively developed in southern China. However, at present, there is still a lack of precise constraints on the occurrence state and enrichment mechanism of cobalt in this type of Co-Mn deposits. Here, we have conducted the mineralogical and elemental mapping analyses of ores within the Ediacaran Doushantuo Formation of the Zhongba Co-Mn deposit in the Shiqian area, Guizhou Province, based on the elemental geochemical compositions of the cobalt-manganese ores of the Zhongba Co-Mn deposit. The results show that the primary Mn-bearing minerals in the Zhongba Co-Mn deposit are hollandite, pyrolusite, braunite, and Mn-bearing hematite, with minor todorokite. Especially, Co occurred predominantly in the forms of adsorption and partly isomorphic substitution within manganese oxides and partially in Mn-bearing iron oxides. Its enrichment is attributed to the adsorption (Co(II)) and oxidation/displacement (Co(III)/Mn(IV)) on the surface of manganese oxides. The integrative analysis of the evolution of paleotectonics, paleogeography, and paleocean during the middle and late Neoproterozoic period, as well as the later tectonic uplift evolution, suggests that the extraordinary enrichment/mineralization of Co in the Zhongba Co-Mn deposit in the Shiqian area was resulted from the combined effects of the early diagenetic process and the later surface-induced weathering process in the embryonic layer of Mn-bearing carbonates. Especially, the initial enrichment and re-enrichment/mineralization of Co were triggered by the surface adsorption and oxidation/replacement of manganese oxides during the early diagenetic stage and the later supergene weathering stage, respectively. This study reveals that the dual controlling mechanism of the respectively formed manganese oxides at the early diagenetic stage and the later surface weathering stage on the Co enrichment/mineralization of the Co-Mn deposit can be used to, interpret the Co enrichment/mineralization processes in other sedimentary-supergene weathering type of Co-Mn deposits throughout geological history.