LA-ICP-MS zircon U-Pb dating and genetic types of uranium-bearing granite porphyry in northern Xiangshan orefield, Jiangxi Province

The Xiangshan uranium orefield is the largest volcanic rock type uranium deposit so far found in China. The main uraniumore type in the north is the granite porphyry type uranium deposit.The uranium mineralization is related to the ultra-hallow intrusion-phase granite porphyry in time and space.Most of the previous work was aimed at the main rocks in a single deposit, and the age date of granite porphyry obtained were quite different, which has affected the in-depth study of Xiangshang granite porphyry uranium orefield. In this paper, the main mineral-granitic porphyry system of the uranium deposits in the northern part of Xiangshan, including Hengian, Youfang, Shazhou and Yunji, was selected to carry out field geological survey, geochemical characteristics study and LA-IXP-MS zircon U-Pb dating, with the purpose of determining the petrogenetic age and genesis type of one-bearing main rocks in Xiangshan granite porphyry uranium deposit.The weighted mean ²⁰⁶Pb/²³⁸U ages of granite of Hengjian, Youfang, Shazhou and Yunji are 135.6±1.3Ma (MSWD=0.45, n=26), 136.2±1.3Ma(MSWD=1.2, n=21Ma(MSWD=0.67, n=24) and 134.3±1.1Ma(MSWD=0.88, n=25) respectively, concentrated on the range of 132~137Ma, suggesting the Early Cretaceous period. It is concluded that the original type of granitic porphyry in the north of Xianghan is bounded by the transition type between A-type granite and S-type granite, named A-S granite. Granite porphyry magma originated from the Middle Proterozoic crust. Crustal material, as the main component, was involved in the formation of porphyry, with the addition of a small amount of mantle materal.The granite porphyry was formed by the stretching system under the intraplate tectonic environment.It might have been the effect of magmatic intrusion due to plate retreat after the Pacific plate subduction.