Abstract
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 (Th) and salinities of the ore-forming fluids over time. The Th for Stages 1–3 of the mineralization are 421–479, 363–408, and 296–347 °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 (δ18OV-SMOW = 8.6‰ to 11.4‰; δDV-SMOW = −92.2‰ to −72.1‰) 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 δ34SVCDT values of 0.2‰–3.5‰, suggesting that the sulfur has a magmatic origin. The Jinchang deposit is a typical gold-rich gold–copper porphyry deposit.
Highlights
Most metallic ore deposits are associated with hydrothermal fluids
Ongoing exploration has provided 96,725 m of drill core from >200 holes and led to the development of 6339 m of underground tunnels. The results of this exploration indicate that the deposit represents an 80.4 t gold resource with a grade of 8 g/t Au, and a 4683 t copper resource with a grade of 1.44% Cu. Previous studies of this deposit have focused on its geological features, alteration, geochemistry, Fluid inclusions (FIs) systematics, and geochronology [9,10,11,12]
For vein-type orebodies, with increasing distance from the orebody the wall-rock has been affected by potassic, phyllic, and subsequently argillic alteration, the boundaries between these domains are gradational [19,20] (Figure 3D)
Summary
Most metallic ore deposits are associated with hydrothermal fluids. The genesis of the deposits is closely related to the temperature, pressure, and composition of the hydrothermal fluid. FI analysis is one of the main approaches used to identify the geochemical properties of ore-forming fluids and determine the physical and chemical conditions of hydrothermal deposit formation. Ongoing exploration has provided 96,725 m of drill core from >200 holes and led to the development of 6339 m of underground tunnels The results of this exploration indicate that the deposit represents an 80.4 t gold resource with a grade of 8 g/t Au, and a 4683 t copper resource with a grade of 1.44% Cu. The results of this exploration indicate that the deposit represents an 80.4 t gold resource with a grade of 8 g/t Au, and a 4683 t copper resource with a grade of 1.44% Cu Previous studies of this deposit have focused on its geological features, alteration, geochemistry, FI systematics, and geochronology [9,10,11,12]. New H–O–S isotope data enable the investigation of the source of the mineralizing fluids and ore materials, which allows us to propose a model for the formation of the Jinchang deposit
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