Metallogenic age and fluid evolution of the Kangshan Au-polymetallic deposit in the southern margin of the North China Craton: Constraints from monazite U-Pb age, and in-situ trace elements and S isotopes of pyrite

The Xiaoqinling-Xiong'ershan Au concentration area, located in the southern margin of the North China Craton, has many gold deposits accompanied with lead, zinc and silver metals, which has become a natural laboratory to reveal the origin of craton destructive gold deposits. The Kangshan gold polymetallic deposit, located in the Xiaoqinling-Xiong'ershan gold metallogenic area, is controlled by NE trending Mesozoic brittle faults and occurs in Neoarchean metamorphic rocks and Mesoproterozoic volcanic rocks. Ore-forming process can be divided into four hydrothermal ore-forming stages: quartz +/- pyrite stage, quartz-pyrite-chalcopyrite-native gold stage, polymetallic sulfide-native gold-quartz-ankerite stage, and quartz-calcite +/- fluorite stage. The U-Pb age of hydrothermal monazite from the Kangshan gold-polymetallic deposit is 131.7 +/- 4.6Ma, which is consistent with the age of magmatic mineralization related to the destruction of the North China Craton in the Late Mesozoic. In-situ trace element analysis and mapping of pyrite at various stages, we found that Au was positively correlated with Co, Ni and As in Stage 2, and the oscillating zones in pyrite is obvious. The contents of Cu, Ag, Sb, Pb and Bi gradually decreased from the core to the edge of pyrite grains, and there are mineral inclusions rich in these elements in pyrite grains. It shows that fluid boiling happened in this stage. The content of trace elements in pyrite of Stage 3 is the lowest among all stages. There is no oscillating zone in pyrite grains and the fissure is filled with sulfides rich in these trace elements, indicating that all the elements are well unloaded in this stage, and the chemical properties of ore-forming fluid are stable. Together with previous fluid inclusion analysis, show that fluid boiling is the main precipitation mechanism of Au, while fluid mixing is the main precipitation mechanism of Pb, Zn and Ag. The content of the trace elements in pyrite indicates that the fluid temperature decreases from Stage 1 to Stage 3; the fluid fO(2) in the stages 2 and 3 is higher than that in Stage 1, and the latter two are similar. According to the contents and ratios of Co and Ni contents in pyrite, the pyrite in the stages 1 and 2 is considered to be magmatic hydrothermal origin, and the pyrite in the third stage is affected by surrounding rock material. The delta S-34 values of pyrite from Stage 1 to Stage 3 are + 6.6 parts per thousand similar to + 8.9 parts per thousand, + 5.0 parts per thousand similar to + 7.2 parts per thousand and + 6.0 parts per thousand similar to + 8.7 parts per thousand, respectively, which are similar to those of granitoids. We infer that the Kangshan Au-polymetallic deposit was formed in magmatic mineralization related to the China Craton destruction in the Early Cretaceous.