Application of Electron Microprobe Chemical Dating to Datian Uraninite in Panzhihua and Its Significance

As the main industrial uranium minerals in hydrothermal uranium deposits, uraninite and pitchblende are of great significance in the study of ore genesis and metallogenic regularity of hydrothermal uranium deposits. The Datian area in Panzhihua is one of the important areas of migmatite type hydrothermal uranium deposit in China. There is ultra-rich-uranium ore (U>10%) in rolling stone and the richer uranium-rich bedrock ore (U=0.1%-2%) where uraninite is the main uranium mineral. The study of the composition and forming age of two types of uraninite has important significance for metallogenic regularity of mixed rock type hydrothermal uranium deposits in the Datian area. In this study, mineralogical and Electron Microprobe analyses of uraninite in rolling stone and bedrock from the Datian area were carried out to determine the composition and age. Results show that the chemical compositions of uraninite in rolling stone and bedrock are similar except Pb contents with UO₂ contents of 77.36%-84.04%, ThO₂ contents of 0.98%-5.59%, and PbO contents of 1.79%-8.8%. Lead contents of uraninite in rolling stone are lower than those of uraninite in the bedrock, but thorium contents are contrary. Electron Microprobe chemical dating indicates that the uraninite in bedrock ore has ages of 774.9-785.5 Ma, whereas the uraninite in rolling stones has an age of 783.7 Ma. The dating results are consistent with traditional isotopic dating (775-777.6 Ma). The indicates that the uraninite in rolling stones and bedrock formed at the same time and the electronic probe in situ dating method is credible. In the late hydrothermal alteration, the uraninite experienced silicification, carbonization, and hematitization at 730.6 Ma, 699.8 Ma, and 664.0 Ma, respectively. This study provides evidences for the metallogenic epoch and mineralization process of the hydrothermal uranium deposits.