Sulphur in apatite: a potential monitor of the magmatic redox state in the world-class gold fields of the North China Craton

The redox condition, a key parameter of mineralization, is one of the most difficult parameters to constrain precisely. Here we employ electron probe and X-ray photoelectron spectroscopy (XPS) to analyse sulphur (S) in apatite grains from five granitoid plutons that are differentially related to gold mineralization in the world-class gold fields of Jiaodong, Xiaoqinling, and Wutai-Hengshan within the North China Craton (NCC) to constrain the redox condition of melt. The results show increasing order of the apatite S content and S6+/ΣS ratios in the Linglong (only spatially close the Jiaodong gold deposits), Sunzhuang (related with the Yixingzhai gold deposits), Huashan (weakly related with the Xiaoqinling gold deposits), Wenyu (closely related with the Xiaoqinling gold deposits) and Guojialing plutons (closely related with the world-class Jiaodong gold deposits), indicating that the oxidation state increased from the Linglong pluton to the Guojialing pluton. The S concentrations of Guojialing, Wenyu, Huashan and Sunzhuang plutons, are estimated using previous methods are, 120–208 ppm, 107–138 ppm, 72–77 ppm and 10–74 ppm, respectively. Combined with the regional differences in gold mineralization in the North China Craton, the gradual increase in mineralization scale is consistent with the trend of increasing oxidation state in the granitoid plutons from Wutai-Hengshan to Xiaoqinling to Jiaodong goldfields, thus also underpinning the contribution of Mesozoic granites to gold mineralization in the North China Craton through providing the thermal energy and medium for the activation and migration of ore-forming fluids.