Mantle volatiles and heat contributions in high sulfidation epithermal deposit from the Zijinshan Cu-Au-Mo-Ag orefield, Fujian Province, China: Evidence from He and Ar isotopes |
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The source of metal and sulphur in porphyry and related epithermal deposits is a long debated issue. The role of mantle-derived magmas in providing the metals has proved particularly problematic. Here we report new He and Ar isotope determinations from ore fluids from the Zijinshan high sulfidation-epithermal Cu-Au deposit and Wuziqilong transitional Cu deposit from the giant Zijinshan porphyry-epithermal Cu-Au-Mo-Ag ore system (from 105 to 91 Ma), to decipher the contribution of mantle-derived volatiles and heat. Hydrothermal fluids in pyrite and digenite have He-3/He-4 up to 5.7 R-a, among the highest measured in ancient ore-forming fluids. A linear correlation between He and Ar isotopes indicate that the ore fluids were, to a first order, a mixture between a shallow crustal fluid, with low He-3/He-4, and a dominantly mantle-derived fluid with high He-3/He-4. The mantle He-3/He-4 is close to values typical of the upper mantle indicating the initial magmas that provided the heat for hydrothermal systems did not assimilate large volumes of continental crust. The ore-forming fluids have He-3/heat ratios that are 10 to 80 times higher than that of mid-oceanic ridge hydrothermal fluids, indicating that the metal-bearing fluids acquired heat and volatiles in a convective, rather than conducive, hydrothermal regime. It appears that mantle-derived volatiles, heat and probably metals have made a major contribution to the Cu-AuMo-Ag mineralization in the Zijinshan orefield. Publication name | CHEMICAL GEOLOGY, 480 58-65; SI 10.1016/j.chemgeo.2017.08.005 MAR 5 2018 | Author(s) | Wu, Li-Yan; Hu, Rui-Zhong; Li, Xiao-Feng; Stuart, Finlay M.; Jiang, Guo-Hao; Qi, You-Qiang; Zhu, Jing-Jing | Corresponding author(s) | HU Ruizhong huruizhong@vip.gyig.ac.cn Chinese Acad Sci, Inst Geochem, State Key Lab Ore Deposit Geochem, Guiyang 550002, Guizhou, Peoples R China. | View here for the details
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