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.

氧化还原条件是成矿作用的关键参数之一，也是最难精准限定的参数之一。本文采用电子探针与X射线光电子能谱（XPS），对华北克拉通（NCC）内世界级金矿区——胶东、小秦岭及五台-恒山——中与金矿化存在不同关联程度的5个花岗岩类岩体的磷灰石颗粒中的硫（S）进行分析，以限定熔体的氧化还原条件。结果显示，玲珑岩体（仅空间上紧邻胶东金矿床）、孙庄岩体（与义兴寨金矿床相关）、华山岩体（与小秦岭金矿床关联较弱）、文峪岩体（与小秦岭金矿床密切相关）及郭家岭岩体（与世界级胶东金矿床密切相关）的磷灰石硫含量及S⁶⁺/ΣS比值依次升高，表明从玲珑岩体到郭家岭岩体，熔体氧化状态逐渐升高。郭家岭、文峪、华山及孙庄岩体的硫浓度经前人方法估算，分别为120~208 ppm、107~138 ppm、72~77 ppm及10~74 ppm。结合华北克拉通金矿化的区域差异，成矿规模的逐渐增大与五台-恒山→小秦岭→胶东金矿区花岗岩类岩体氧化状态逐渐升高的趋势相一致，从而进一步佐证了中生代花岗岩通过为成矿流体的活化与迁移提供热能及介质，对华北克拉通金矿化的贡献。