The Geochemical Characteristics And Mineralization Of Uranium Polymetallic In The Black Rock Series In Northwestern Hunan

In Early Cambrian period,because of extension between Yangtze plate and Cathaysian plate,formed the original oceanic crust,a suite of black-rock series deposited on carbonate platform,this suite of black-rock series is significant source bed of vanadium,nickel,molybdenum,uranium,barite and so on.Black-rock series in northwestern Hunan be selected as research object for this paper,based on field geological survey and lab sample analysis,the geochemical characteristics,mineral occurrence and mineralization of this suite of uranium polymetallic-bearing black-rock series is discussed,several opinions have been gained:?1?Based on element association uranium polymetallic-bearing black-rock series in northwestern Hunan be divided into 3 types:?1?U-V-Ni-Mo type,?2?U-V-Cu type,?3?U-V type.?2?The major elements characteristic parameters of n?Al₂O₃?/n?Al₂O₃+Fe₂O₃?,TFe₂O₃/TiO₂-Al₂O₃/?Al₂O₃+Fe₂O₃?,Mn O/TiO₂ show that the ancient sedimentary environment of uranium polymetallic-bearing black-rock series in northwestern Hunan was continental margin and marginal sea.The characteristic parameters of n?SiO₂?/n?Al₂O₃?,n?Si?/n?Si+Al+Fe?show that biohydrothermal take part in the process of sedimentation.?3?The trace elements characteristic parameters of V/?V+Ni?,Cu/Zn,V/Cr,Ni/Co,?U,?Ce show that the uranium polymetallic-bearing black-rock series was deposited in oxygen-deficient environment,the characteristic parameters of Sr/Ba,Co/Zn,?Eu and Zn-Ni-Co,Lg U-Lg Th,Cr-Zr diagrams show that the uranium polymetallic-bearing black-rock series have the characteristic of hot water sedimentation.?4?The result of carbon and oxygen isotope study show that,a large amount of deep materials which from submarine spout hydrothermal take part in the process of sedimentation.The values of ?Nd show that the sedimentary of black-rock series have the ancient upper crust materials sources future.Based on U-Pb isotopic dating get the rock-and ore-forming age was 503±29Ma,based on Sm-Nd isotopic dating get the rock-and ore-forming age were 586±113Ma,584±82Ma,454±44Ma.?5?This is the first time to discover uraninite,pitchblende,brannerite,coffinite in the uranium polymetallic-bearing black-rock series northwestern Hunan,and found uranium-polymetallic mineral occurrence location were sediment fissure,intergranular pore space,dissolved pores,bubble holes,this is significance for separate valuable minerals and element extraction from uranium polymetallic-bearing black-rock series.?6?This is the first time to discover tiemannite in company with clausthalite,most of selenium is enrich in the mantle and core,in most cases selenide minerals indicate the tectonic rift environment,this time tiemannite and clausthalite discovered provide evidence of submarine spout hydrothermal take part in the process of sedimentation.?7?The high temperature mineral association: cleveite + molybdenite + gersdorffite+blende,and the middle-low temperature mineral association: pitchblende+ coffinite + galena + tiemannite+clausthalite be discovered in U-V-Ni-Mo mineralization type;The high-temperature mineral association: brannerite + cleveite + rutile + cube-like galena+ blende,and the middle-low temperature mineral association: pitchblende+tennatite+clausthalite+ nowackiite be discovered in U-V-Cu mineralization type;The middle-high temperature mineral association: brannerite +pitchblende+ coffinite+galena+ blende be discovered in U-V mineralization type.Based on the above research,the mineralization and mineralizing process can be come down to: when the Niutitang formation sedimentary period,the Yangtze platform is in the geological background of global sea level rise,deep ocean currents bring phosphorus,vanadium,copper,nickel,molybdenum,barium,uranium etc.which from submarine spout hydrothermal to preliminary enrichment in surface layer by biogeochemistry,when these biology death to sink,a lot of oxygen be used up,the ocean became to oxygen-deficient environment,in the meantime H2 S which release from biology death to make ocean became to reducing environment,so more organic material be conserved.The mineralization elements which from submarine spout hydrothermal enrichmen in the sediment fissure and dissolved pores,the cause of reducing action not only because biology death to release H2 S,but also because organic material thermal decomposition to release H2S?H2?CH4?CO,by these gas reduction mechanism,the uranium polymetallic minerals were sedimented and formed uraninite,coffinite,brannerite,tennatite,blende,barite,etc.