Ore geology, fluid inclusion geochemistry and 40Ar/39Ar geochronology of the Wulasigou Cu deposit, Altay, Xinjiang, China: a case study of orogenic-type Cu deposit

The Wulasigou Cu deposit is hosted as veins controlled by NW-directions structure in the Devonian volcanic-sedimentary basin of the Altay orogenic belt. The hydrothermal ore-forming process can be divided into the early, middle and late stage, represented by pyrite-quartz, polymetallic sulfide-quartz and carbonate-quartz veinlets, respectively. The fluid inclusion geochemistry indicates that the metallogenic fluid system evolved from CO2-rich, metamorphic to CO2-poor, meteoric fluids and that a significant CO2-escape must occur during the evolution. The metal precipitation was resulted from fluid boiling, CO2-escape and transient oversaturation. The estimated trapping pressures of boiling FIs assemblage range from 60 to 220 MPa at the depth of 6-8 km. Mica 40Ar/39Ar geochronology indicates he orogenic mineralization occurred in Triassic epoch ranging of about 220 Ma. Based on the above, we conclude the Wulasigou Cu deposit is likely an example of orogenic Cu systems formed in collision orogeny; and a new metallogenic model is proposed to interpret the formation of the Wulasigou Cu deposit.