Geological and geochemical constraints on the genesis of the Huachanggou gold deposit, western Qinling region, Central China

• The Huachanggou gold deposit is an orogenic deposit controlled by ductile shear zone.
• Ore fluids were derived from metamorphic water, extracting materials from wall rocks.
• Massive sulfidation of dissolved Fe triggered Au deposition.

The Huachanggou gold deposit is located in Lueyang County, Shaanxi Province, central China; it is situated in the Mian–Lue sutural zone in the western Qinling Orogen and controlled by a WNW-striking ductile shear zone. The ore deposit is developed in spilite, limestone and phyllite in the Middle–Lower Devonian Sanhekou Group, and the wall rocks show evidence of deformation. Pyrite is the main gold-bearing mineral, and the native gold is either visible or microscopic.The Huachanggou gold deposit is considered to be an orogenic gold deposit controlled by a ductile shear zone related to the Indosinian Qinling orogenic event. The ores show a strong enrichment in Au, Ag and As but exhibit a simple assemblage of Au and Ag that are strongly correlated together. Gold was deposited from a moderate to low salinity, salt solution–CO2 hydrothermal fluid at medium temperature. Variations in S, Pb, C, and O isotopic composition indicate that the sulfur was derived from the reduction of seawater sulfate in the wall rocks; the lead was derived mainly from the wall rocks; the carbon was derived from the dissolution of marine carbonate. The variations in H and O isotopic composition indicate that the ore-forming fluids were derived originally from metamorphic fluid with meteoric water mixing in later stages. Au migrated mainly in the form of Au(HS)2− to form the deposit. Boiling of the fluid triggered the precipitation of the metal sulfides that contain the gold.