Ore-forming fluids in the Dongping gold deposit, northwestern Hebei Province

The Dongping gold deposit is contained within an inner contacting zone of t he Hercynian Shuiquangou alkali syenite. The ores occur as veins or as repl acement bodies. Fluid inclusion observation shows that in early and main mi neralizing stages inclusion types are gas and gas-liquid inclusions, respec tively. Gas inclusions occur in isolation in vein quartz, their homogenizat ion temperature is 372-306 degreesC, and salinity 3.7-1.0 wt% NaCl. Gas-liq uid inclusions occur in clusters or healed fractures but do not cut quartz boundary with homogenization temperature 342-267 degreesC and salinity 1.9- 0.8 wt% NaCl. Stable isotope measurements show that at main gold mineraliza tion, hydrogen and oxygen isotopic ratios of the mineralizing fluids are -7 0.8 parts per thousand -108.4 parts per thousand and 2.44 parts per thousan d -4.05 parts per thousand, respectively. Primary ore fluids in Dongping ar e higher temperature and lower salinity NaCl-CO2-H2O fluids, and come from Yanshanian granitic magmatism. Fluid immiscibility, fluid-rock interactions and meteoric water adding were main reasons for gold deposition.