Late Triassic epithermal Au-Te overprinting on a Silurian volcanogenic massive sulfide system: Geochronology and fluorine-mediated metal remobilization in the Yinzishan deposit, Southwest China

The genetic relationship between Cu and Au in auriferous volcanogenic massive sulfide (VMS) systems remains ambiguous due to the imprecise timing of Au mineralization. We conducted a study in Southwest China on the Yinzishan Au-Te and Dapingzhang VMS Cu-Pb-Zn (429 Ma) deposits in the Sanjiang Tethyan belt, which potentially formed a superimposed VMS−epithermal system. By integrating in situ U-Pb dating of rutile and hydrothermal zircon, K-Ar illite geochronology, trace-element geochemistry, and sulfur isotopic analysis of pyrite, our findings reveal two distinct mineralization episodes. The Late Silurian magmatic rutile (Rt-1), with an age of 421.2 ± 4.8 Ma, provides evidence of magmatic activities during this period. The Late Triassic (220−208 Ma) was marked by epithermal overprinting, as indicated by the presence of Au-Te−rich Rt-3 clusters (219.7 ± 5.3 Ma), hydrothermal zircon (208.8 ± 6.3 Ma), and illite associated with mineral-controlling faults (218.0 ± 20 Ma). Trace-element analysis indicates that Rt-1 and Rt-2 have higher average Zr concentrations (2135 ppm and 1940 ppm, respectively) than Rt-3 (232 ppm). This suggests a hydrothermal origin for Rt-3, which is closely associated with calaverite and F-rich topaz. The F-rich magmatic fluid dissolved Rt-1, forming porous Rt-2 through a coupled dissolution-reprecipitation (CDR) mechanism and leaching elements such as Ti, Zr, Nb, and Te. After the precipitation of topaz, the fluid became depleted in F, reducing the solubility of Ti, Zr, and other high field strength elements (HFSEs). This led to Ti saturation and the precipitation of Rt-3, accompanied by the deposition of Au and Te nanoparticles at the boundaries between Rt-2 and Rt-3. Regarding pyrite, Py-1 mainly occurs as euhedral crystals and contains low average concentrations of Au (470 ppm) and Te (203 ppm), with a wide δ34S range (+0.64‰ to +4.47‰), similar to the pyrite formed during the Dapingzhang VMS Cu mineralization stage (δ34S = −1.24‰ to +4.32‰). In contrast, Py-2, which is closely associated with tellurides, has significantly higher average concentrations of Au (2268 ppm) and Te (13,532 ppm) and a narrow δ34S range (+1.81‰ to +2.26‰), suggesting an independent magmatic-hydrothermal fluid source. The results show that Late Triassic F-rich fluids remobilized pre-enriched Au-Te from the Silurian VMS precursors, resulting in high-grade mineralization. This study demonstrates that the auriferous overprinting fluids did not originate from coeval submarine epithermal processes of the VMS system but from discrete, subaerial, high-sulfidation epithermal activity, and redefines multistage enrichment in ancient hydrothermal systems in collisional orogens.