Intrusion-related orogenic gold deposit in the East Kunlun belt, NW China: A multiproxy investigation

Abstract

The Wulonggou gold district is one of the most important gold producers of the East Kunlun metallogenic belt in China. Due to its complex geological background and limited investigations, the age of mineralization and ore-forming process remain unclear. Here, we focus on the Yanjingou gold deposit which is the largest and most typical deposit in the Wulonggou gold district, with a view to investigate the metallogenic mechanism and timing of ore formation with a view to evaluate the ore-forming processes and sources through a comprehensive study of the ore mineralogy, monazite and zircon U-Pb dating, in situ trace element analysis and mapping, and in situ S isotopes. Our results show that the magmatism and mineralization were coeval, during 239 Ma and 244 Ma in the Middle Triassic. Four stages of mineralization are identified with distinct textures, mineral assemblages, trace element characteristics and S isotopes. Stage 1 is represented by euhedral pyrite bearing quartz veins, which originated from deep metamorphic fluid, and was rarely affected by magmatic hydrothermal fluids. Stage 2 is characterized by the occurrence of abundant oriented arsenopyrite, which originated from the mixture of deep metamorphic fluid and magmatic hydrothermal fluid. Stage 3 is characterized by the occurrence of polymetallic sulfide of copper, with two generation of pyrite (stage 3 Py1 and Py2). Stage 3 Py1 formed from magmatic hydrothermal fluids whereas Py2 originated from deep metamorphic fluid and was also slightly influenced by magmatic hydrothermal fluids. Stage 4 is represented by late calcite and pyrite combination, which originated from another stage of deep metamorphic fluid. Stage2 and 3 are the main gold mineralization stages, and Au has a close relationship with As, and an obvious inverse correlation with Co and Ni. Combined with the trace element characteristics, we infer that the denudation degree of the Yanjingou gold deposit is very shallow with good prospects for exploration. Through multi-proxy investigation of the different stages and types of pyrite, we postulate that the Yanjingou gold deposit is an orogenic gold deposit related to intrusive rocks formed during Middle Triassic compressional transformation.