Source of ore-forming fluids and metallogenic mechanism of the Shengligou gold deposit in the northern margin of Qaidam Basin, Qinghai Province, China

The northern margin of the Qaidam Basin is a key Proto-Tethyan collision zone and a prospective orogenic gold metallogenic belt, however, the evolution and source of its ore-forming fluids has long been controversial. The Shengligou gold deposit, a representative deposit in the western segment of the northern margin of the Qaidam Basin, was investigated in this paper through large-scale mapping, petrographic observations, and in situ trace element and sulfur isotope analyses of multi-generation pyrite to constrain this controversy. Three pyrite generations (Py1, Py2, Py3) are identified, including gold-bearing Py2 (quartz-polymetallic sulfide stage) and Py3 (quartz-carbonate stage). While Py1, aligned with ductile shear foliation and displaying cataclastic texture, is enriched in Co-Ni (averaging 201.9×10-6 Co, 174.3×10-6 Ni). Furthermore, the Py2 exhibits oscillatory zoning, with Au-As-Pb rich cores and Cu-Zn-Sb rich rims, recording dynamic fluid influx that triggered episodic gold deposition; the Py3 forms fine-grained disseminations with high Ag (mean 251.5×10-6). The δ34S values of pyrite at Shengligou range from -1.8‰ to +3.7‰ (averaging at 0.29‰), suggesting a derivation of ore-forming materials from an enriched mantle source. Systematic Co/Ni decreases (Py1→Py3: 1.25→1.14) and low S/Fe ratios (< 1.2) confirm a hydrothermal origin. Se/Te fluctuations track a "low-high-low" fO2 path. Gold, transported as Au(HS)2- at ~172℃ and incorporated as Au+ into pyrite, precipitated during multi-fluid events, dominated by mantle-derived fluids in the main stage (Py2). This study proposes a new exploration model based on the triad of an enriched mantle source, NW-trending ductile-brittle shear zones, and a metamorphosed volcanic sequence, offering a novel framework for gold exploration in the North Qaidam Tethyan orogen.