Fluid inclusion and S, Pb isotope study of the Shizhaigou gold deposit in Henan Province

Abstract：The Shizhaigou gold deposit, located in Xiaoshan terrain of Huashan-Xiong’ershan massif on the southern margin of the North China Craton, is a small gold deposit discovered in recent years. The strata in the Shizhaigou gold orefield are composed of intermediate-basic and intermediate-acid volcanic rocks of the Majiahe and Xushan Formations of the Mesoproterozoic Xiong’er Group. The intrusions only include minor intermediate-acid intrusive rocks. The fracture zone controls the distribution of the ore bodies. The ores are mainly of massive, disseminated and breccia structures, and classified as altered rock type. The wall rock alterations in the deposit include silicification, pyritization, sericitization, carbonatization and chloritization. The evolution of the hydrothermal mineralization system comprised the quartz-pyrite stage, quartz-polymetallic sulfides stage and quartz-carbonate stage, and gold was manly deposited in the quartz-polymetallic sulfides stage. Fluid inclusions of the quartz-polymetallic sulfides stage are mainly liquid-rich aqueous two-phase, vapor-rich aqueous two-phase and CO2-bearing three-phase inclusions, and their homogenization temperatures and salinities vary from 260°C to 320°C and from 2.0 wt% to 9.0 wt% NaCl equivalent, respectively. The fluid inclusions of the quartz-carbonate stage are mainly composed of liquid-rich aqueous two-phase inclusions, with homogenization temperatures being 140 ~ 200°C and salinities 5.6 wt% ~ 8.1 wt% NaCl equivalent, respectively. The immiscible action of ore-forming fluid was the dominant factor for metallic sulfide deposition. The δ34S values of sulfides within the ores vary from +3.7‰ to +7.7‰, with an average of +5.6‰. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of sulfide are in the range of 16.951 ~ 17.035, 15.370 ~ 15.466 and 37.188 ~ 37.512, respectively. The composition of lead isotope in the ores are similar to that of the Taihua Group, and higher than that of the Xiong’er Group but lower than that of the Huashan intrusive rock, indicating that the ore-forming material of the Shizhaigou gold deposit originated from the Taihua Group.