Cretaceous–Neogene basin control on the formation of uranium deposits in South China: evidence from geology, mineralization ages, and H–O isotopes

The South China Uranium Province (SCUP) contains the largest number of discovered uranium deposits in China. This province includes seven uranium mineralization belts, at Wuyishan, Taoshan–Zhuguang, Chenzhou–Qinzhou, Gan–Hang, Xixia–Luzong, Mufushan–Hengshan, and Xuefengshan–Jiuwandashan. The uranium deposits can be classified according to their ore-hosting rocks into four general types: granite-, volcanic-, black-shale-, and sandstone-related. These uranium deposits crop out at the peripheries of Cretaceous–Neogene (K–N) redbed basins or are connected to the basins by NE–SW- to NNE–SSW-trending regional faults. Most of the volcanic-related uranium deposits were formed during the mid-Cretaceous (118 to 88 Ma); granite-related deposits have a wider range of ages from 124 to 11 Ma; the black-shale-related deposits have ages of 120 to 7 Ma; sandstone-related deposits yield ages of 111 to 22.5 Ma. As such, these four types of uranium deposits in South China have similar ages, irrespective of location, and are similar in age to K–N redbed basins in this region. δDVSMOW(fluid) and δ18OVSMOW(fluid) values of the volcanic-related uranium deposits generally range from – 105.9‰ to – 38.0‰ and – 11.1‰ to +5.3‰, respectively. The black-shale-related uranium deposits yield δDVSMOW(fluid) and δ18OVSMOW(fluid) values of – 74.5‰ to – 33.0‰ and – 4.4‰ to 9.3‰, respectively. However, the granite-related uranium deposits have a much wider range of δDVSMOW(fluid) and δ18OVSMOW(fluid) values from – 104.4‰ to – 23.1‰ and – 9.4‰ to +7.3‰, respectively. H–O isotopic compositions of the SCUP ore-forming fluids are similar to those of basinal fluids, again demonstrating the link between the uranium deposits and the basins. The spatial–temporal relationships and fluid isotopic similarities between the K–N basins and uranium mineralization indicate that the uranium deposits of the SCUP are genetically related to the K–N redbed basins, and are unconformity-related uranium deposits.