Constraints on the metallogenesis of the Liba gold deposit, West Qinling Orogen, China: Evidence from rutile U-Pb dating, pyrite geochemistry and sulfides in-situ S-Pb isotopes

The Liba gold deposit, located in the northeastern Zhongchuan granite pluton of the West Qinling Orogen, contains the largest known gold reserve (115.8 t Au) in the region. Despite extensive research, the precise age and origin of mineralization remain debated. Laser Raman spectroscopy, trace element analysis and U-Pb dating of rutile, combined with pyrite geochemistry and isotope analyses, provide new perspectives on the mineralization age and material sources of the Liba deposit. Three types of pyrite are identified, which signify multistage hydrothermal evolution. Py1 is moderately enriched in Au (avg. 1.37 ppm) and As (avg. 5795 ppm), with minor chalcophile elements such as Pb, Sb, and Bi. Py2 exhibits similar geochemical behavior to Py1 but shows higher trace element enrichment, with elevated Au (avg. 16.1 ppm) and As (avg. 38,168 ppm), and contains sulfide inclusions (e.g., galena, chalcopyrite, electrum), interpreted as a result of fluid immiscibility. Py3 is depleted in Au and As, but relatively enriched in Co and Ni, reflecting late-stage hydrothermal evolution. LA-ICP-MS analyses reveal a positive correlation between As and Au, with low Au/As ratios below the solubility limit of gold in pyrite, suggesting that invisible gold is mainly hosted as structurally bound Au1+. In-situ delta 34S values of sulfides at Liba range from 5.97 %o to 14.55 %o, and Pb isotopic compositions suggest that the ore-forming materials originated from Devonian strata of the West Qinling Orogen influenced by Triassic metamorphism. Hydrothermal rutile, associated with gold-bearing sulfides, exhibits elevated concentrations of W, V, and Sb, with U-Pb dating yielding consistent ages of 222.8 +/- 6.8 Ma and 223.5 +/- 5.4 Ma. The Indosinian gold mineralization events in the Zhongchuan region, as recorded in the Liba gold deposit, reflect a tectonic shift from a compressional to an extensional regime in the West Qinling Orogen. This study further highlights that hydrothermal rutile associated with gold mineralization can serve as a reliable geochronometer and tracer of ore genesis, offering a valuable tool for future exploration and research on orogenic gold deposits.