New constraints on the genesis and geodynamic setting of the Wulong gold deposit, Liaodong Peninsula, northeast China: evidence from geology, geochemistry, fluid inclusions, and C-H-O-S-Pb isotopes

摘要

The Wulong lode gold deposit is located in the Liaoning Province, northeast part of North China Craton. Gold ore bodies are mainly hosted in the Late Jurassic granite and structurally controlled by northeast-trending faults. Gold occurs in disseminated and auriferous quartz-sulfide veins and veinlets within hydrothermally altered rocks. Mineralization can be divided into three stages: (1) quartz-pyrite stage, (2) quartz-polymetallic sulfides stage, and (3) quartz-carbonate stage. Gold formed mainly in the middle stage. Quartz formed in the two earlier stages contains three compositional types of fluid inclusions, i.e., pure CO2, CO2-H2O and NaCl-H2O, but the late-stage minerals only contain NaCl-H2O inclusions. The inclusions in quartz formed in the early, main, and late stages yield total homogenization temperatures of 317-383 degrees C, 260-380 degrees C and 159-234 degrees C, respectively, with salinities of 5.14-9.44, 2.95-6.20, 1.23-4.34 wt% NaCl equivalent, respectively. Trapping pressures estimated from CO2-H2O inclusions are 200-390 MPa in the main stage. Fluid boiling and immiscibility caused rapid precipitation of sulfides and gold. Through immiscibility and inflow of meteoric water, the ore-forming fluid system evolved from CO2-rich to CO2-poor in composition, and from magmatic to meteoric, as indicated by delta O-18(water) values (4.5 parts per thousand-7.3 parts per thousand). The carbon (-12.2 parts per thousand to -11.5 parts per thousand), sulfur (0.9 parts per thousand-2.6 parts per thousand), and lead isotope (Pb-207/Pb-204 of 15.606-15.618) compositions suggest the host rocks to be a significant source of ore metals. Integrating the data obtained from the studies including regional geology, ore geology, fluid inclusion, and C-H-O-S-Pb isotope geochemistry, we conclude that the Wulong deposit is a decratonization gold deposit formed during lithospheric thinning associated with destruction of the North China Craton triggered by the subduction of the Paleo-Pacific Oceanic plate in the Early Cretaceous.