The geological characteristics of marine sedimentary manganese deposits associated with ophiolitic mélange: A case study of the Kuoshibulake manganese deposit in the Altun orogenic belt

The Kuoshibulake sedimentary manganese deposit is located in the western section of the Hongliugou-Lapeiquan ophiolite mélange belt on the northern margin of the Altun orogenic belt. This manganese deposit is newly discovered. The initial exploration indicates that the size of the deposit is of medium to large scale. Previous studies have shown that the main host rocks in the mining area are the siliceous rocks and siliceous dolomites in the upper part of the Early Paleozoic Hongliugou Group. The main ore bodies are significantly controlled by the lithology of the strata, but it has been modified and superimposed by later hydrothermal fluids and secondary oxidation processes. The main ore minerals are psilomelane, pyrolusite and manganosite. Primary rhodochrosite is also observed in the deep layer. Based on the collection of regional geological data, this paper conducted a preliminary study on the type, geological characteristics and genesis of the deposit through methods such as geological profile measurement, observation of ore mineral composition and texture, and in-situ microanalysis. The results show that the host rocks of the Kuoshibulake sedimentary manganese deposit are mainly siliceous rocks, and both the siliceous rocks and the manganese ore layer belong to the oceanic sediments in the ophiolitic mélange. The formation of manganese deposits mainly occurred through three periods: Early Ordovician marine sedimentation, the metamorphic hydrothermal transformation during the Late Ordovician to Early Silurian collision and orogeny process, and secondary oxidation. This study will provide a case to understand the geological characteristics and formation processes of manganese deposits related to ophiolitic mélange, and also offer a reference for enriching the theory of sedimentary manganese mineralization.