Geochronological constraints and fluid source tracing for the Dixu pyroclastic-hosted gold deposit: An implication for Carlin-type gold metallogeny in the Youjiang Basin, SW China

• Late Triassic (∼220 Ma) Au mineralization in the Dixu deposit linked to Indosinian post-collisional extension. • Magmatic-metamorphic-meteoric fluid mixing defines the ore-forming processes. • Sulfidation of mafic minerals drives Au precipitation, distinct from sedimentary-hosted systems. • The Late Triassic mineralization was not an isolated local phenomenon, but rather a regional-scale event. The Youjiang Basin in southwestern China constitutes a world-class gold province, predominantly characterized by Carlin-type gold deposits hosted in both sedimentary and intrusive rocks. The Dixu gold deposit represents a key example of Carlin-type mineralization occurring within Permian pyroclastic rocks, offering significant insights into the metallogenic processes of the basin. This study integrates U-Pb geochronology and oxygen isotope analysis of hydrothermal zircons to constrain the timing and source of ore-forming fluids at the Dixu deposit. The results indicate that the main gold mineralization event occurred at ca. 220 Ma. Hydrothermal zircons from mineralized samples yield δ 18 O values between +5.2 ‰ and +8.8 ‰, exhibiting a moderately wide range of calculated δ 18 O H2O values from +5.6 ‰ to +9.1 ‰, which suggests that the ore-forming fluids were derived from deep-circulating crustal waters with magmatic contributions. Based on diagnostic mineral assemblages and cross-cutting relationships of vein systems, the mineralization process can be divided into three stages: early-, main-, and late-ore stages. The main-stage mineralization occurred via sulfidation reactions between hydrothermal fluids and iron released through alteration of mafic minerals, leading to the formation of arsenian pyrite and arsenopyrite. This stage is characterized by a diagnostic alteration assemblage (silicification-chloritization-hydrothermal rutile), with a notable absence of decarbonation. These distinctive mineralogical signatures differ from those of carbonate- and siliciclastic-hosted deposits and bears similarities to basalt- and dolerite-hosted counterparts. Our findings demonstrate that the Late Triassic mineralization event in the Youjiang Basin was not an isolated local phenomenon, but rather a regional-scale event associated with post-collisional magmatic activity during the Indosinian orogeny. Moreover, this study reveals the critical role of multi-sourced fluids and lithology-controlled alteration processes in the formation of pyroclastic-hosted Carlin-type gold deposits.