Rare Earth Elements Geochemical Characteristics and Geological Significance of Black Rock Series
There is uranium-rich phosphorite with industrial value in the black rock series at the bottom of Niutitang For-mation in Bahuang area of Tongren,Guizhou province.In order to explore the nature of source areas of ore-host rock series and the redox environment of ancient oceans,rare earth geochemistry of rocks was studied in this paper.The results showed that the geochemical data of rare earth element(REE)were not obviously affected by diagenesis and analytical methods,which could be used to explore the geological significance of diagenesis and mineralization.Ceanom value revealed that the redox environment changed from reducing environment to fluctuating secondary oxidation environment during the transition from Doushantuo Formation to Niutitang Formation,and the environment gradually changed to weak reduction until Niutitang Forma-tion was rich in polymetallic shale deposits.Abnormal Ce value indicated that the depth of the water body was in a dynamic change from the late Neoproterozoic to the early Cambrian and experienced an obvious transgression-regression process.LREE/HREE ratio,REE partitioning model,Y/Ho and Y diagrams,Er/Nd ratio,(La/Sm)N value,and others indicated that(bearing)siliceous dolomite,(calcareous)dolomite,black shale,polymetallic-rich shale,iron-bearing argillaceous sili-ceous rock,and clayey phosphorite were all polluted by terrigenous clastic materials to different degrees except for the obvious seawater chemical sedimentation characteristics of phosphorites in the study area.In addition,the"cap type"distribution curve,Ce/La ratio,highly abnormal Eu value,and La/Yb-REE diagram indicated that there were hydrothermal inputs in polymetallic shale and(clayey)phosphorite,which indicates that hydrothermal exhalation is strong and active when phosphor-us and polymetallic elements are enriched in the early Cambrian study area.
rare earth elementsuranium-rich phosphoriteblack rock series