Geochemical Characteristics And Metallogenic Regularity Of The Xiaochayuan Manganese Deposit In Xiushan,Chongqing

Xiaochayuan manganese deposit in Xiushan,Chongqing is rich in resources and there are important research significance.Previous studies on the sedimentary environment and mineralization of manganese deposits in the area have gained some understanding,but the metallogenic rules and material sources were less known.This paper makes a comprehensive study on the datangpo formation of Xiaochayuan manganese deposit based on the extend collection,and summarizes the geological characteristics of deposits,ore body and ores in the area,it provides some information for the sedimentary environment,tectonic environment,material source and genesis of ore deposits.Xiaochayuan manganese deposit is a typical"datangpo manganese deposit".The manganese-bearing rock series are mainly composed of black silty carbonaceous shale and sandy carbonaceous shale,and have the characteristics of gradually thinning from the center to the edge of the basin.Major elements show that Mn is positively correlated with Ca O and Mg O,Mn is negatively correlated with Si O₂,Ti O₂ and Al₂O₃,and Mn is not significantly correlated with P.Trace elements show that Ag,As,Bi,Pb,Sb,Ba and U are all higher than abundance of continental crust,while Co,V,Cu,Ni,Zn,Rb,Th,W and Zr are no significant difference from abundance of continental crust,while Cr,Nb and Sr are slightly lower than abundance of continental crust.Rare earth elements show that it is rich in light rare earth elements,loss of heavy rare earth elements,both has great differentiation.From rhododendrite to carbonaceous shale,Eu presents a weak negative anomaly,and Eu negative anomaly increases gradually,while Ce positive anomaly becomes smaller and negative.Combine with the ratios of relevant elements and the diagrams of Log U-log Th,Y-P₂O₅,Co/Zn-?Co+Ni+Cu?,Fe-Mn-?Ni+Cu+Co?×10,La-Ce,La/Yb-?REE,they show that the manganese deposit is related to hydrothermal sedimentary.C and O isotopes indicate that the Xiaochayuan manganese deposit is the origin of low temperature and hydrothermal sedimentary deposition.It is less different from magmatic source or deep mantle,the metallogenic material may comes from deep mantle.The Sr isotope test results show that the initial ratio of ⁸⁷Sr/⁸⁶Sr is between the continental crust and the mantle,the sources of metallogenic materials have dual characteristics,including both continental crust weathering materials and mantle materials.The S isotope test results show that the manganese-bearing rock series have higher?³⁴S,indicating that the manganese ore was in the hypoxia-reduction state when it was formed.In the manganese-bearing rock series,U,V and Mo are relatively enrich and locally obvious.The ratios of V/?V+Ni?,V/?V+Cr?,V/Cr,Ce/La reflect an oxygen-poor and anoxic environment.The anomalous high sulfur isotope values reflect that the sedimentary environment of manganese is a confined basin with relatively closed reductive conditions,which shows the characteristics of the restricted shallow sea environment of the continental margin.The ratios of Sr/Ba,Mg O/Ca O and Al₂O₃/Mg O show a warm and wet transition phase brackish water-mildly brackish water sedimentary environment.According to the ratios of Al₂O₃/?Al₂O₃+Fe₂O₃?,La/Ce-Al₂O₃/?Al₂O₃+Fe₂O₃?diagram,?K₂O+Na₂O?-Si O₂ diagram,and combine with the characteristics of rare earth elements,that Xiaochayuan manganese deposit are mainly passive continental margin tectonic background,at the same time with characteristics of continental island arc.The Si O₂/Al₂O₃ ratio,U-Th relationship,C and Sr isotopes show that the main metallogenic materials of the manganese deposit come from the deep mantle,and there are also weathered materials in the continental crust.