A possible genetic relationship between orogenic gold mineralization and post-collisional magmatism in the eastern Kunlun Orogen, western China

Abstract

Controversies in orogenic gold deposits remain, especially regarding the relative contribution of magmatic fluids to the mineralization. The Shuizhadonggou-Huanglonggou gold deposit in the Wulonggou gold field of the eastern Kunlun Orogen, western China consists mainly of sulfide disseminations in hydrothermally altered rocks with minor amounts of quartz-sulfide veins coeval to or overprinting the disseminated ores. Gold mineralization is hosted in diverse lithologies (i.e., Early Palaeozoic metamorphic rocks, Late Silurian syenogranite and Late Triassic porphyritic granodiorite and quartz diorite) and is structurally controlled by a second-order NW-trending sinistral-normal ductile shear zone and its subsidiary structures along the first-order Central Kunlun Fault. Gold-related hydrothermal alteration formed chlorite, sericite, quartz and calcite, with associated sulfide minerals dominated by pyrite, arsenopyrite, löllingite and pyrrhotite. Two types of hydrothermal sericite separates from a gold mineralized syenogranite yielded two 40Ar/39Ar ages of 237.0±2.0Ma and 230.8±1.7Ma, respectively, which postdated the Early Triassic regional metamorphism and ductile deformation by ~13m.y. Field relationships suggest that gold mineralization also overprinted ~220Ma porphyritic granodiorites and quartz diorites. These data indicate three gold mineralization events in the Late Triassic overlapped with post-collisional magmatism in the orogen. Gold-bearing sulfides have δ34S values mostly in the range of 2.0–5.5‰, consistent with a magmatic source of sulfur. Quartz from quartz-pyrite-sericite veins has calculated δ18OH2O values of 1.8–6.1‰ and δDH2O of −63 to −107‰. The stable isotopic and geochronological data suggest a magmatic origin for the ore-forming fluids. Therefore, the Shuizhadonggou-Huanglonggou and other gold deposits in the eastern Kunlun Orogen share many features of orogenic gold deposits (e.g., multiple-order ore-controlling structures, hydrothermal alteration, mineralization styles, close association between mineralization and magmatism, and H-O-S stable isotope compositions) and are genetically related to Late Triassic post-collisional magmatism.