Study of fluid inclusions and ore genesis of the Duanhe gold deposit in Luoning County, Henan Province

Abstract：The Duanhe gold deposit is a quartz-vein type gold deposit, located in Luoning County, Henan Province. The gold deposit mainly includes Shizhaigou and Lingdong mining areas that comprise of three to four gold-bearing quartz veins, respectively. The ore-forming process includes three stages, i.e. the early, middle and late stages, characterized by mineral assemblages of quartz-pyrite, quartz-polymetallic sulfides and quartz-carbonate, respectively. The most intensive gold mineralization is developed in the middle stage, secondarily in the early stage. Fluid inclusions in quartz of three stages are mainly H2O-rich. Some inclusions contain a little of CO2 in gas and liquid phases. Pure H2O inclusions can be also observed. Homogeneous temperatures of the early-, middle- and late-stage fluid inclusions are 240.9~315.9 °C, 188.7~304.5 °C, and 137.3~259.3°C respectively in the Shizhaigou; while in the Lingdong mining area are 303.7~343.1°C, 251.8~325.4°C, and 305.7~355.0℃, respectively. In the Shizhaigou the salinities are (6.74~12.85)wt% NaCl.eq, (2.41~8.68) wt% NaCl.eq and (2.24~7.86) wt% NaCl.eq, respectively; and in the Lingdong mining area are (5.11~11.70) wt% NaCl.eq, (2.74~10.11) wt% NaCl.eq and (0.53~6.74) wt% NaCl.eq, respectively. The ore-fluids of these two mining areas were characterized by moderate-temperature and low-salinity at the main metallogenic stage. The early-stage ore-fluids were mixed hydrothermal solutions of reworking and metamorphic fluids, containing a small amount of CO2. From early to late stage, the CO2 content and salinities of fluids gradually decreased. From early to late, homogeneous temperatures of fluid inclusions in Shizhaigou mining area decrease gradually, whereas increase after a firstly decrease in Lingdong mining area. This, together with that the temperatures of each stage of the Lingdong area are generally higher those of the Shizhaigou area, suggests that the ore-forming fluid-system were driven by magmatic heat, and that the Lingdong area is more close to and was reheated by the blinded pulsing magmatic intrusion which was possibly seated beneath the south of the Duanhe deposit.