Ore Genesis at the Jinchang Gold-Copper Deposit in Heilongjiang Province, Northeastern China: Evidence from Geology, Fluid Inclusions, and H-O-S Isotopes

The Jinchang gold-copper deposit is located in Eastern Heilongjiang Province, Northeastern China. The orebody comprises primarily hydrothermal breccias, quartz veins, and disseminated ores within granite, diorite, and granodiorite. Three paragenetic stages are identified: early quartz-pyrite-arsenopyrite (Stage 1), quartz-pyrite-chalcopyrite (Stage 2), and late quartz-pyrite-galena-sphalerite (Stage 3). Gold was deposited during all three stages and Stage 1 was the major gold-producing stage. Copper is associated with the mineralization but has low economic value. Fluid inclusions (FIs) within the deposit are liquid-rich aqueous, vapor-rich aqueous, and daughter-mineral-bearing types. Microthermometric data for the FIs reveal decreasing homogenization temperatures (T-h) and salinities of the ore-forming fluids over time. The T-h for Stages 1-3 of the mineralization are 421-479, 363-408, and 296-347 degrees C, respectively. Stage 1 fluids in vapor-rich and daughter-mineral-bearing inclusions have salinities of 5.7-8.7 and 49.8-54.4 wt% NaCl equivalent, respectively. Stage 2 fluids in vapor-rich, liquid-rich, and daughter-mineral-bearing inclusions have salinities of 1.2-5.4, 9.5-16.0, and 43.3-48.3 wt% NaCl, respectively. Stage 3 fluids in liquid-rich and daughter-mineral-bearing inclusions have salinities of 7.9-12.6 and 38.3-42.0 wt% NaCl equivalent, respectively. The estimated trapping pressures are 160-220 bar, corresponding to an entrapment depth of 1.6-1.2 km in the paleo-water table. Oxygen and hydrogen isotope data (O-18(V-SMOW) = 8.6 parts per thousand to 11.4 parts per thousand; DV-SMOW = -92.2 parts per thousand to -72.1 parts per thousand) suggest that the ore-forming fluids were derived from magmatic fluids during the early stages of mineralization and subsequently incorporated meteoric water during the late stages. The sulfide minerals have S-34(VCDT) values of 0.2 parts per thousand-3.5 parts per thousand, suggesting that the sulfur has a magmatic origin. The Jinchang deposit is a typical gold-rich gold-copper porphyry deposit.