Mineralogical Study Of Uraninite From The Shijiaowei Uranium Deposit,Northern Guangdong Province,China

Uraninite,the main ore mineral of all kinds of uranium deposits,is widely distributed in medium-low temperature hydrothermal uranium deposit and epigenic uranium deposits.Xiazhuang is one of the typical granite type ore field of China.The Shijiaowei uranium deposit,is the highest uranium content deposit in Xiazhuang uranium ore field,which is located in eastern Guidong granite complex of Nanling region.The uranium deposit is controlled by intersecting positions between silicated fault system and diabase dyke swarm.Mineralization has been paid much attention by scholars,however,there are still some problems in ore-forming fluid,uranium ore-forming chronology,ore-forming geodynamics background,etc.The research in mechanism of mineralization lags behind relatively.Uraninite is the main ore mineral of the Shijiaowei granite-type uranium.On the basis of detailed field geological survey,the lithography,isotope chronology,geochemistry of uraninite by SEM,EPMA and LA-ICP-MS,provide new insight for uranium metallogenic mechanism and background of this deposit.The uranium deposit develops siliceous vein type uranium mineralization,the grain size of the uranium ore is about 30?60?m.Under the microscope,there are stellate pyrite and the veinlike and grape-like structures of uranium to be observed.And the hydrothermal alteration such as greenslitization,sericitization,silicification and hematitization are develop.The main components of uraninite in the samples have tiny difference and higher content of Ca O.There was no significant alteration of uraninite in the test area.The uraninite with low?REE,Th,Co and Ni,and the content of LREE is much high than HREE,indicating that the uraninite in Shijiaowei uranium deposit should be formed in the medium and low temperature hydrothermal environment.The content of Th,Co and Ni is lower than the detection limit of EPMA.It shows that the metallogenic elements are derived from the granitic magmatic hydrothermal solution,and mantle-derived materials are added scarcely in the mineralization process.Uraninite is the the best mineral for geochronology in uranium deposit.In-situ LA-ICP-MS U-Pb dating seems to accurate and suitable for chronological study of granite-type uranium mineralization.The new ²⁰⁶Pb/²³⁸U age for the uraninite of Shijiaowei deposit of 54.7±0.5Ma is consistent with that of the regional NE fault structure(65.5?55.0Ma),smaller than the host granite and diabase,indicating that Shijiaowei deposit developed at the Paleogene lithospheric extension of South China.