Geochronology and compositions of ore-forming fluids of the Qinglonggou gold deposit in the northern margin of Qaidam Basin, NW China

• Qinglonggou gold mineralization age of 452 ± 4.6 Ma. • Fluid-rock interaction controls pyrite texture and geochemistry. • Proto-Tethys-related gold mineralization events. The northern margin of the Qaidam Basin is an orogenic gold metallogenic belt associated with the Tethyan orogenesis. However, the precise timing of gold mineralization and the compositions of the ore-forming fluids in this region remain enigmatic. Geological observations, mineral assemblages, texture, trace elements, and in situ S isotope analyses of pyrite, and in situ U-Pb dating of rutile in the Qinglonggou gold deposit were carried out to solve the puzzles. The orebodies of the Qinglonggou gold deposit controlled by NW (NNW)-trending faults are dominantly distributed along the contact zone between the Mesoproterozoic Wandonggou Group dolomitic marble and quartz diorite porphyrite. Hydrothermal alteration types include quartz, sericite, chlorite, epidote, and carbonate. Gold mineralization can be classified into three stages: (I) quartz-pyrite (Py1), (II) quartz-pyrite (Py2)-polymetallic sulfides, and (III) quartz-carbonate stages. The Py1 comprises a porous core with galena inclusions and a smooth, regular rim. The rim of Py1 is enriched in Au, As, Cu, Pb, Zn, and Sb, whereas the core is enriched in Au and As. The Py2 is characterized by a microporous core with elevated Au, As, Cu, Pb, Zn, and Sb, in contrast to a smooth, irregular rim with depleted concentrations of these elements. The δ 34 S values of Py2 are 4.2 ∼ 5.5 ‰, lower than those of Py1 with values of 5.2 ∼ 9.6 ‰. The pyrite from gold orebodies has δ 34 S values of 4.2 ∼ 9.6 ‰, which are significantly lower than those from the host rocks (10.0 ∼ 14.3 ‰). These variations in pyrite texture and geochemistry can be attributed to the interactions of ore fluids with various lithologies. In situ U-Pb dating of rutile coexisting with Py1 constrains mineralization at 452.0 ± 4.6 Ma. This study highlights that the Qinglonggou gold deposit belongs to orogenic gold deposits associated with the Proto-Tethyan orogenesis. These findings have practical significance for guiding gold exploration in the northern margin of the Qaidam Basin.