Geological Characteristics And Genesis Of Gaoyan Manganese Deposit In Chengkou, Chongqing

Gaoyan manganese deposit has discovery more than 50 years,and many experts and scholars investigated the genesis of the deposit in-depth research from different angles.This article focus on geochemistry of gaoyan manganese deposit,through the characteristics of the main,trace and terrae rare elements,combine with the geological characteristics of the Gaoyan manganese deposit propose new understanding.Gaoyan manganese deposit are produced in black shale,occurs in upper section of the Doushantuo formation of Sinian?Z₁ds²?.The roof of the manganese mineralization is folium to middle-thick layer dolomitic limestone with grey-black and gray;the floor of the manganese mineralization is black carbonaceous shale.And the manganese mineralization strictly controlled by the horizons of Doushantuo formation?Z₁ds?and fold structures and secondary tectonic.Ore texture mainly is fine particle to coarse grain texture,spherulitic texture and radial morphology texture,microcrystalline texture and xenomorphic granular texture are followed.Ore structures mainly is massive structure,layered structure and banded structure,laminated structure,honeycombed structure and fringe structure are followed.The ore mineral include rhodochrosite and manganodolomite,the gangue minerals include calcites,dolomite,siliceous,hydromica,carbonaceous and pyrite.The major and trace elements analysis of the sample in Gaoyan manganese deposit show that,Ag,As,Ba,Bi,Cd,Co,Cr,Li,Mo,Ni,Pb,Rb,Sb,Se,Tl,V,W,Zn in the are sample is relatively highly enrichment,the ratio of MnO/TiO₂ is greater than 3.5,MnO and Al₂O₃ showed a significant negative correlation,the scheme of Si vs Al and Na₂O vs MgO respectively fall within the hydrothermal sedimentation and marine sediment area,the ratio of Fe/Ti is between 11.59 and 44.46,the ratio of?Fe+Mn?/Ti is between 189.75 and 1323.82,the ratio of Al/?Al+Fe+Mn?is less than 0.08,Co/Ni ratio is less than 0.55,V/?V+Ni?ratio is between 0.27 and 0.56,Ba/Sr ratio is between 1.65 and 28.8,Th/U ratio is less than 1.25,the logU-logTh diagram fall within the petrochemical hydrothermal ferromanganese sedimentation zone,All chert falls in the hydrothermal sediment areas in the Fe-Mn-?Ni+Co+Cu?triangle diagrams,reflecting the formation of Gaoyan manganese deposit is accompanied by a large number of seafloor hydrothermal activity,the manganese come from marine sediment,and enriched mineralization in the sedimentary environment from anoxic to oxidation.The ? REE of various types of rock samples and ore samples are large ranged in the study area?38.55ppm²24.88ppm?,and all the ratio of LREE/HREE were greater than1,the LREE is much enrichments compared with those of HREE.The obvious positive abnormal phenomena of Eu elements relate the seafloor hydrothermal activity,Ce element anomalies shows that the formation of Gaoyan manganese deposit is enriched mineralization in the sedimentary environment from anoxic to oxidation.Combined the regional tectonic evolution of Gaoyan manganese deposit with the structural distribution of Chengkou in the Doushantuo formation of Sinian period located in shallow-basin environment,performance of TST,The depth of water increases,contemporaneity the volcanic rock of the southeastern margin of Yangtze block is developing,the tuffaceous present in the manganese mineralization of Doushantuo formation of Sinian,described that the study area in the early Sinian is still volcanic activity.Volcanic activity provided ore-forming fluid with manganese-rich for the formation of Gaoyan manganese deposit.The ore-forming fluid with manganese-rich eject to the seafloor,under the reducing seabed bottom water conditions,Mn²⁺is difficult to precipitate,and gradually rises with oceanic circulation,When the Mn²⁺arrived to the highly productive water near the redox interface,due to the biological function,Fe³⁺and Mn²⁺formed rhodochrosite,and to compose the manganese mineralization.