Mineralizing fluids and genesis of the Heiniudong copper deposit in the Liwu copper orefield, Sichuan

The Heiniudong copper deposit has gone through the ductile deformation and metamorphism in the premetallogenic stages and ductile-brittle deformation in the metallogenic stages. In the pre-metallogenic stages, the CO₂-bearing fluids were differentiated from the host rocks due to the ductile deformation and metamorphism, which may facilitate the formation of elongated disseminated pyrrhotite and chalcopyrite mineralization. The ductile-brittle deformation in the metallogenic stages was accompanied by the uplifting of the Jianglang metamorphic core complexes. The fluid inclusions from the ore-bearing quartz veins are dominated by the aqueous fluid inclusions, and subordinately by gaseous fluid inclusions. The former consist of water, CO₂ and methane, whereas the latter mostly contain methane, implying that the ore-forming fluids are aqueous carbonaceous fluids. The water in the oreforming fluids mainly stemmed from the metamorphic water in the country rocks. The emplacement of the Yanshanian granites and the uplifting of the Jianglang metamorphic core complexes led to the formation of a series of detachment faults due to the ductile-brittle deformation. In the decompression and catathermal processes, the oreforming fluids were activiated, concentrated and filled into the detachment faults. The exsolution of CO₂ and CH₄ from the ore-forming fluids gave rising to the decrease of the dissolubility, precipitation and mineralization of the sulfides in the ore-bearing hydrothermal solutions, and finally to the formation of copper-rich ore bodies.