Geology and geochemical characteristics of the Xiajinbao gold deposit in the Hebei Province, China

摘要

The Xiajinbao gold deposit is located in the Yanshan District of the North China Craton. The geology of the Xiajinbao deposit consists of Archean gneiss, Proterozoic sedimentary rocks, granite porphyry, quartz porphyry dikes, and diorite dikes. The diorite contains a large quantity of magnetite. The granite porphyry and quartz porphyry dikes, which contain trace amounts of ilmenite without magnetite, have high aluminum saturation index values and a low magnetic susceptibility. These rocks are classified as ilmenite series granitic rocks. The pyrite quartz veins (Stage I), pyrite–chalcopyrite quartz veins (Stage II), and sphalerite–galena quartz veins (Stage III) of the Xiajinbao deposit were hosted in the granite porphyry. Major gold mineralization was associated with the sphalerite–galena quartz veins. The homogenization temperature and salinity of the sphalerite–galena quartz veins are 220 °C in a mode and 9.1–13.8 wt%, respectively. The sulfur fugacity of the Xiajinbao deposit ranged 10~(?7.8)–10~(?11) and 10~(?9.5)–10~(?14.3) atm for the pyrite–chalcopyrite quartz veins and sphalerite–galena quartz veins, respectively. The formation environment of the sphalerite–galena quartz veins of the Xiajinbao deposit is similar to that of zoned base metal veins associated with oxidized magma. The oxygen and hydrogen isotope ratios of the hydrothermal solution in equilibrium with quartz from the sphalerite–galena quartz veins range from +3.3 to +5.5 and ?38 to ?41‰, respectively, suggesting magmatic water. The range of sulfur isotope ratios of pyrite and galena from the sphalerite–galena quartz veins is from ?0.2 to +3.6‰. These sulfur isotope ratios are in the range of ratios for ores formed by igneous activity associated with oxidized magma. Therefore, the gold mineralization of the Xiajinbao deposit is inferred to be the result of igneous activities from oxidized magmas, such as the diorite dikes, with the granite porphyry forming the host rock of the sphalerite–galena quartz veins of the Xiajinbao deposit.