Genesis of the gold deposits in the Kunlun River area, East Kunlun, Qinghai Province: Constraints from geology, fluid inclusions and isotopes

Abstract

The Kunlun River area, located in the central section of the East Kunlun orogenic belt and sandwiched between the Central and South Kunlun faults, includes a series of orogenic gold deposits (e.g., Heicigou, Dazaohuo, and Heihainan) that constitute a gold mineralization system closely related to the late Paleozoic to early Mesozoic collisional orogeny. These gold deposits are mainly hosted by the Ordovician and early-middle Triassic metamorphosed sedimentary rocks and controlled by NWW- to NW-trending secondary faults. The orebodies occur as auriferous quartz veins and surrounding altered rocks accompanied by silicification, sulfidation, carbonatization, sericitization and chloritization. Fluid inclusions, hydrogen and oxygen isotopes indicate that the ore-forming fluids are characterized by moderate temperature (mostly 200–250 ℃), low salinity (2.8–10.2% NaCleq), and CO2-bearing metamorphic water. Carbon, sulfur, and lead isotopes indicate that the ore-forming materials were derived from sedimentary rocks. Based on the ages of capture zircons in the auriferous quartz veins and the emplacement time of regional A-type granites, the gold mineralization time is confined between 239 and 200 Ma. Combined with regional tectonic evolution, these deposits were formed in the stage of tectonic system transformation from compression to extension in the middle-late Triassic. During this period, the release of tectonic stress resulted in the upward migration of ore-forming fluids along the regional faults and the gold precipitation in the secondary faults in the shallow crust by fluid immiscibility and fluid-rock interaction.