Genesis of the Xinfang magmatic-hydrothermal gold deposit, Liaodong Peninsula, China: Constraints from pyrite Re-Os isotopes, C, O, S, Pb, Si, He and Ar isotopes

Abstract

The Xinfang gold deposit (>20 t@ 2.85 g/t) is situated in the southwest of the Liaodong Peninsula. Ore bodies are hosted by the Archean gneiss in the footwall and Neoproterozoic metasandstone in the hangingwall of the Xinfang Metamorphic Core Complex. Here, we conduct pyrite Re-Os dating, C, O, Si, He-Ar, S, and Pb isotopes in order to constrain the ore-forming age and genesis of the deposit. Field observations show that three ore-forming processes are recognized: (1) quartz- coarse-grained pyrite stage (stage Ⅰ), (2) quartz-polymetallic sulfide-gold stage (stage Ⅱ), and (3) quartz – calcite ± pyrite stage (stage III). Pyrite from the quartz-polymetallic sulfide-gold vein yielded Re-Os isochron age of 121.1 ± 1.2 Ma (Initial 187Os/188Os = 1.49 ± 0.01, MSWD = 1.2), which is interpreted to be the ore-formation age.Theδ13CV-PDB and 18Ov-SMO W values of calcite from stage III range from −5.1‰ to −4.9‰ and from 9.7‰ to 10.1‰, and the δ30Si values of quartz from stage Ⅰto stage III range from −0.5‰ to −0.4‰, −0.1‰ to −0.3‰, and −0.2‰ to −0.1‰, respectively, indicating that ore-forming fluids were derived from a magmatic-hydrothermal source. Sulfur isotopic compositions of sulfides between −1.9 ‰ and 4.4 ‰ (mean = 2.4 ‰), are consistent with that of magmatic sulfur. The galena yielded a wide range of lead isotopic composition (206Pb/204Pb = 16.995–17.252, 207Pb/204Pb = 15.335–16.343, 208Pb/204Pb = 37.461–37.580) suggesting an external lead source. The He and Ar isotope compositions of pyrite and galena (3He/4He = 0.14Ra-0.62Ra), indicate a crustal source with minor mantle contributions. Combining all available data results, we propose that a magmatic -hydrothermal source for the Xinfang gold deposit and the ore formation was related to the subduction of the Paleo-Pacific Plate beneath Eurasia.