Genesis and metallogenic geodynamic background of the Banmiaozi gold deposit in the Jiapigou mining district, Jilin Province: Evidence from geology, ore-fluid, isotope geochemistry and metallogenic chronology

• The Banmiaozi deposit is a mesothermal lode gold deposit. • Fluid boiling, mixing and cooling jointly led to the precipitation of gold. • Ore-forming fluids mainly came from magmatic water. • Temperature and fluid‒rock interactions may cause δ 34 S difference in JMD. • Banmiaozi deposit formed at the shallow level of gold metallogenetic system. The Jiapigou mining district (JMD) in Jilin Province, renowned for its mesothermal lode gold deposits, hosts the representative Banmiaozi gold deposit in its northwestern sector. Through integrated analysis of regional geology, fluid inclusions (FIs), H-O isotopes, in situ S-Pb isotopes, and Rb-Sr isotope chronology, this study elucidates the origin and metallogenic mechanisms of the Banmiaozi deposit. Key findings include: (1) Ore bodies occur as quartz veins within Neoarchean–Paleoproterozoic supracrustal rocks and granitic gneiss, structurally controlled by WNW- and EW-trending brittle faults. Three distinct metallogenic stages are identified: early (quartz–pyrite), main (quartz–pyrite–chalcopyrite), and late (quartz–calcite). (2) Fluid inclusion data reveal decreasing homogenization temperatures (280–320 °C, 180–302 °C and 134–204 °C) and salinities (10.5–16.1 wt%, 4.0–13.7 wt%, and 0.4–5.3 wt% NaCl equiv.) across successive stages, characteristic of a CO 2 –H 2 O–NaCl system. (3) Stable isotope analyses (δ 18 O H2O = –4.3 to 5 %; δD H2O = –114.8 to –91.9 %) indicate magmatic water dominance in the ore-forming fluids. (4) Sulfur isotopes (δ 34 S = 9.4–11.6 %) suggest magmatic sulfur with fluid-rock reaction, while Pb isotopes ( 206 Pb/ 204 Pb = 16.441–16.634; 207 Pb/ 204 Pb = 15.504–15.606; 208 Pb/ 204 Pb = 36.807–37.191) reflect mixed lower crustal and minor mantle sources. (5) Rb-Sr isotopes yield an isochron age of 174.1 ± 2.6 Ma, constraining mineralization to the Middle Jurassic. Regional synthesis demonstrates that vein-type deposits (e.g., Banmiaozi) formed at shallow levels of the metallogenic system, whereas breccia-type deposits developed at deeper structural levels under an extensional tectonic regime