Genesis of the Xinfang gold deposit, Liaodong Peninsula: Constraints from fluid inclusions, H-O-S-Pb isotopes, pyrite trace element concentrations, and chronology

Abstract

The Xinfang gold deposit is situated in the southwest of the Liaodong Peninsula, and represents the first large-scale gold deposit hosted by the Xinfang Metamorphic Core Complex. We conduct pyrite and galena Rb-Sr isotope dating, multiple isotope compositions (H-O-S-Pb-Sr), fluid inclusions (FIs), and pyrite laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) trace element analysis to constrain the genesis of the deposit. Our fluid inclusion analyses show that the ore-forming fluids belong to a medium–low-temperature and moderate-low salinity NaCl-H2O-CO2 fluid system. Fluid boiling is the key factor for Au precipitation in the Xinfang gold deposit. In-situ sulfide S-isotope data (δ34S = −1.64 ‰ to 6.07 ‰) favor a magmatic source. The initial 87Sr/86Sr ratios of the sulfide samples range from 0.709556 to 0.710731, indicating that the ore-forming materials came from a mixture of the crust and mantle. The in-situ lead compositions of sulfides (206Pb/204Pb = 16.562–18.367, 207Pb/204Pb = 15.257–17.071, 208Pb/204Pb = 37.005–38.750) reveal that the ore-forming materials originated from the crustal source with a small amount from the mantle source. The δ18OH2O (−3.28 ‰ to 3.64 ‰) and δDH2O (−89.6 ‰ to − 81.3 ‰) values suggest that the ore-forming fluids came from magmatic water with a contribution of meteoric water. LA-ICP-MS trace element analyses reveal that stage II was the main gold mineralization stage, and Archean gneiss may have contributed ore-forming materials. The Co/Ni ratios suggest that the pyrite may have formed from hydrothermal fluids. Pyrite and galena samples from the quartz-polymetallic sulfide-gold vein yielded a Rb-Sr isochron age of 122.6 ± 2.1 Ma (Initial 87Sr/86Sr = 0.710255 ± 0.000059, MSWD = 1.2), which is interpreted to be the ore-formation age. In combining all available data results, we propose a magmatic-hydrothermal source for the Xinfang gold deposit and that the ore formation is related to the subduction of the Paleo-Pacific Plate beneath Eurasia.