Abstract: The Fanjiashan copper and gold mine of the metallogenic subzone is located in the north of West Qinling Mountains, at the core of the Wenquan composite granite-Tianshui porphyry-skarn molybdenum copper and gold zone. The geological characteristics of the deposit show that the Fanjiashan copper and gold mine is dominated by gold and copper mineralization and mainly controlled by the rock-wall rock contact belt and fracture zone surrounding the nearby rocks. The wall rocks feature alterations by skarnization, amphibolitization, silicification and sericitization. We studied the temperature, salinity and H-O isotope of mother lode inclusions in the Fanjiashan copper and gold deposit. The results show that the main metallogenic fluid has a salinity (S) of 2.0%11.0%(w(NaCl)eq) and a homogeneous temperature of 120 – 345 ℃(mostly in 150 – 280 ℃). This medium temperature and medium to low salinity fluid can be characterized as a mixture of magmatic water and atmospheric precipitation. The zircon U-Pb age of metallogenic granite porphyry is 248.3±1.9 Ma (MSWD=0.67, N=9), indicating mineralization in early Indosinian. Based on the regional tectonic setting, the Fanjiashan copper and gold mine is a skarn deposit, arising from the crust thickening during the early-stage of Indosinian collision, and has deep ground porphyry mineralization potential.

Key words: copper and gold mine, skarn type, Fanjiashan, West Qinling Mountains