The Danba–Dadu River gold belt on the western Yangtze Craton margin is a major gold province in China. The Dulanggou gold deposit is a large quartz-vein-type deposit recently discovered in this belt. Ore bodies are fault-controlled veins hosted in high-grade metamorphic rocks of the Devonian Weiguan Formation. Mineralization includes three stages: early (quartz–minor sulfide), main (quartz–abundant sulfide–native gold–Te–Bi minerals), and late (quartz–minor sulfide–calcite). Fluid inclusion studies show the following. Early-stage inclusions are mainly CO2–H2O-type (homogenization temperature 307–388 °C, salinity 0.4–7.1 wt.% NaCl eqv) with minor NaCl–H2O-type. Main-stage inclusions are dominated by CO2–H2O and NaCl–H2O types, with minor pure CO2 inclusions (homogenization temperature 207–307 °C, salinity 0.2–11.2 wt.% NaCl eqv). Late-stage inclusions are mainly NaCl–H2O-type (168–223 °C, 4.6–10.1 wt.% NaCl eqv). Laser Raman analysis detects CH4 in the fluid. The ore-forming fluid is a reducing, medium–low temperature, low-salinity H2O–CO2–NaCl–CH4 system. Thermodynamic calculations of CO2–H2O inclusions yield total densities of 0.94–1.03 g/cm3 and total homogenization pressures of 170–276 MPa for the early stage, and slightly lower densities (0.94–1.01 g/cm3) with pressures of 170–246 MPa for the main stage, indicating a progressive pressure decrease during fluid evolution. Hydrogen and oxygen isotopes (early stage: δD –96.4‰ to –78.9‰, δ18OH2O 6.1‰ to 6.5‰; main stage: δD –104.3‰ to –75.1‰, δ18OH2O 5.3‰ to 7.1‰) indicate that the ore-forming fluid was mainly derived from primary magmatic water. Immiscible CO2–H2O and NaCl–H2O inclusion assemblages in the main stage suggest that fluid immiscibility was the key mechanism for gold precipitation. The Dulanggou deposit resembles classic orogenic gold deposits in host rocks, ore-controlling structures, mineral assemblages, and low-salinity CO2-rich fluids. However, its H–O isotopes and thermodynamic data point to a magmatic water source, distinct from the metamorphic water source of typical orogenic gold deposits. This highlights the diversity of fluid sources in orogenic gold systems along the western Yangtze Craton margin.
Zhang et al. (Thu,) studied this question.