Ore Genesis of the Jiawula Pb–Zn–Ag Deposit, Inner Mongolia: Constraints from C–H–O Isotopes, In Situ S Isotopes, Fluid Inclusions, and LA-ICP-MS Analysis of Chalcopyrite

The Jiawula large-scale Pb-Zn-Ag deposit occurs within Jurassic volcanic rocks, structurally controlled by NW-trending faults. This study integrates systematic analyses of chalcopyrite trace elements, fluid inclusions, and stable isotopes (C-H-O-S) to elucidate its ore-forming fluid evolution and mineralization processes. Fluid inclusion analyses reveal an evolutionary trajectory from an early H₂O-NaCl-CO₂ system to a late H₂O-NaCl-CH₄ system. Carbon isotopes indicate that magmatic degassing-derived CO₂ dominated the early stage (δ¹³C = -6.34‰), with subsequent methane input contributing to the late stage (δ¹³C = -16.73‰). Hydrogen-oxygen isotopes demonstrate that the ore-forming fluids represent mixtures of deep-sourced magmatic water and meteoric water. In situ sulfur isotopes (δ³⁴S = -0.1‰ to 5.2‰) suggest a predominantly magmatic sulfur source. Combined characteristicsincluding low-temperature (298.8-197.2 °C), low-salinity (<5 wt % NaCl eq) fluids, chalcopyrite trace-element signatures, mineral assemblages, and pore-filling texturesclassify the Jiawula deposit as an epithermal deposit. In contrast, adjacent porphyry-type Mo-Cu mineralization represents a distinct, subsequent overprinting event.