Genesis of the South Zhuguang Uranium Ore Field, South China: Pb Isotopic Compositions and Mineralization Ages

U–Pb isotopic analyses indicate that ores from the South Zhuguang uranium ore field, south China, have high common (non‐radiogenic) Pb contents, with variable and relatively radiogenic initial Pb contents. The U–Pb isochron method was used to date these ores, with plots of 208Pb/204Pb and 207Pb/204Pb versus 206Pb/204Pb being used to identify sample suites with similar initial Pb isotopic ratios and to normalize variable initial Pb isotopic ratios. The resulting U–Pb isochrons indicate two substages of uranium mineralization at ~57 and 52 Ma, with a later hydrothermal reformation at ~49 Ma, which homogenized Pb isotopic compositions. Initial Pb isotopic systematics indicate that the ore‐forming fluid was characterized by high 206Pb/204Pb and 207Pb/204Pb ratios and low 208Pb/204Pb ratios, suggesting that the ore‐forming fluid was sourced from Cretaceous–Paleogene red‐bed basins, rather than from magma or the mantle, with consideration of mineralization ages.

U - Pb同位素分析表明，中国南方诸广山南部铀矿田的矿石具有较高的普通（非放射性成因）铅含量，以及变化的且相对具有放射性成因的初始铅含量。采用U - Pb等时线法对这些矿石进行测年，通过绘制²⁰⁸Pb/²⁰⁴Pb和²⁰⁷Pb/²⁰⁴Pb相对于²⁰⁶Pb/²⁰⁴Pb的图表，来识别具有相似初始铅同位素比值的样品组，并对变化的初始铅同位素比值进行归一化。所得的U - Pb等时线表明在约57 Ma和52 Ma存在两个铀矿化亚阶段，在约49 Ma发生了后期热液改造，使铅同位素组成均一化。初始铅同位素体系特征表明，成矿流体具有高²⁰⁶Pb/²⁰⁴Pb和²⁰⁷Pb/²⁰⁴Pb比值以及低²⁰⁸Pb/²⁰⁴Pb比值的特征，考虑到成矿年龄，这表明成矿流体来源于白垩纪 - 古近纪红层盆地，而非岩浆或地幔。