Geochronology of the Shazijiang Uranium Ore Deposit,Northern Guangxi,China:U-Pb Ages of Pitchblende and Their Geological Significance

Miaoershan uranium ore field, one of the five large-scale uranium ore fields in central South China, hosts the largest carbonaceous-siliceous-pelitic rock type uranium ore deposit in China-the Chanziping uranium ore deposit, along with many other granite-type uranium deposits. The Shazijiang deposit is one of important granite-type uranium deposits in the ore field. Pitchblende is not only ideal sample to date uranium mineralization directly but good mineral for measurement of U-Pb isotope testing as well. U-Pb isotope measurements of pitchblende samples from the Shazijiang uranium ore deposit in northern Guangxi of China indicate that there existed two mineralization stages, 104.4 Ma and 53.0±6.4 Ma. Combined with the major mineralization age of 74.1±9.9 Ma for the Chanziping uranium ore deposit, three major mineralization stages can be defined for the Miaoershan uranium ore field (104.4 Ma, 74.1±9.9 Ma and 53.0±6.4 Ma). High initial Pb isotope ratio obtained by pitchblende U-Pb isochron method for the Shazijiang uranium ore deposit suggests that pre-mineralization had already occurred before this major mineralization stage. Three major mineralization stages are consistent with epochs of lithospheric extension in South China as indicated by mafic dikes geochronology, implying that uranium mineralization was constrained by the geodynamic setting of lithospheric extension.