Study On Microscopic Characteristics Of The Ore And Metallogenic Genesis Of The Datangpo Type Manganese Deposit In Xiushan

The Datangpo manganese deposit in the Xiushan area of Chongqing is one of the typical“Dangtangpo”manganese ore deposits in China.The mineral composition is complex,and the manganese minerals are poorly crystalline and fine-grained.Therefore,the microcosmic research of predecessors to manganese ore mineral is very shallow,and at the same time,the origin of the manganese deposits and the sources of the ore-forming materials have not yet been determined.Field geological surveys,indoor rock flake observation,and geochemical studies have shown that the black manganese-bearing rock series of the Manganese deposits at the bottom of the first section of the Datangpo Formation in the Xiushan area of Chongqing is a combination of rhodochrosite-carbonaceous shale,rhodochrosite,and manganese-containing carbonic acid.Salt Rock-Sandy shale.Manganese ore mainly has three types:block,lamellar and sand-like;The ore is mainly composed of mud crystal structure,microsphere structure,and microscopic scaly structure;It has a massive structure,a lamellar structure,and a sand-like structure;The main composition of manganese ore is rhodochrosite,which is in the form of cocoon,fish-like,lens-like,associated with carbonaceous mud and fine sand,distributed in strips or scattered,sometimes confessed to dissolving quartz particles or accounted for by pyrite.Quartz is angular,irregular,and pyroclastic;At the same time,there was a pyrite vein filling,indicating that it was in an oxygen-deficient environment.The MgO/CaO value of the manganese ore sample reflects the formation of manganese ore in a relatively dry climatic environment.The m value?m=100×MgO/Al2O3?indicates that the manganese ore is formed in a shallow sea-continent transition environment.The Al₂O₃/?Al₂O₃+Fe₂O₃?,Al/?Al+Fe+Mn?ratios,and the Na₂O/K₂O-SiO₂ mineralization structural environmental discrimination diagrams indicate that the manganese-bearing rock series formed on the passive continental margin.The characteristics of U/Th,Ni/Co,V/Cr,V/?V+Ni?and V/?Cr+V?ratio,Ce/La ratio and lgCe/Ce*reflect that manganese ore formation has undergone oxidative-anoxic processes.,Formed in an oxygen-deficient environment.The C isotope has a significant negative bias and is characterized by a submarine hot spring.The background value of^?34S in seawater is higher,reflecting the formation of manganese ore in a closed-and-semi-enclosed confined environment.The source of ore-forming material was mainly submarine hydrothermal fluid,and a small amount of terrestrial manganese was denuded and entered the ancient sea basin.The formation of manganese ore is divided into four stages:Mn²⁺enrichment in anoxic water bodies with poor oxidative-reducing delamination;Supersaturated precipitation of MnO₂ in the upper oxidation zone in stratified seawater;Short-term seafloor oxidation events bring MnO₂ precipitates into the bottom of the basin,and a large amount of MnO₂ precipitates accumulate at the bottom.After the oxygen at the bottom is exhausted,the seawater is reconstructed by oxidation-reduction stratification.In the H₂S-rich water body at the bottom of the basin,organic matter,natural gas hydrates,and anaerobes combine to convert the MnO₂ deposit to MnCO₃and form diagenesis.Manganese mine.