Geochronology, fluid inclusions, and isotopic characteristics of the Xiaoshan gold deposit, Henan Province, China

Abstract

The Xiaoshan gold deposit of western Henan Province is located in the southern margin of the North China craton (NCC). Ore bodies of the deposit occur as veins in the fault zones. The ore-forming process can be divided into three stages: an early quartz–pyrite stage, a middle quartz–polymetallic sulfide stage, and a late quartz–carbonate stage. The LA-ICP-MS zircon U–Pb age of the Houhe granite, which is related to Au mineralization of the Xiaoshan deposit, was 139–137 Ma. The initial 176Hf/177Hf values of the Houhe intrusion are 0.282126–0.282368, with the εHf(t), TDM1(Hf), and TDM2(Hf) values being −19.9 to −11.3, 1242–1583 Ma, and 1912–2454 Ma, respectively, indicating that the Houhe granite is formed by partial melting of the lower crust and that the source is mainly the Taihua Group. Two types of fluid inclusions (FIs) have been distinguished in various quartz veins including liquid-rich (WL-type) and H2O–CO2 (C-type) inclusions. The FIs in the quartz of the quartz–pyrite stage comprise WL- and C-type inclusions; their homogenization temperatures, salinities, and densities vary from 300 °C to 393 °C, 1.6 wt% to 11.0 wt% NaCl eqv., and 0.57 to 0.82 g/cm3, respectively. The FIs in the quartz of the quartz–polymetallic sulfide stage consist of WL- and C-type inclusions; their homogenization temperatures, salinities, and densities range from 261 °C to 298 °C, 1.1 wt% to 11.8 wt% NaCl eqv., and 0.74 to 0.89 g/cm3, respectively. Only WL-type inclusions are observed in the quartz of the quartz–carbonate stage; their homogenization temperatures, salinities, and densities vary from 193 °C to 258 °C, 2.2 wt% to 12.7 wt% NaCl eqv., and 0.87 to 0.97 g/cm3, respectively. The ore-forming fluids of the Xiaoshan gold deposit are generally characterized by medium temperature, moderate–low salinity, low density and belonging to an H2O–NaCl ± CO2 system. The δ18OH2O values calculated for ore-bearing quartz vary from 0.7‰ to 4.5‰, and the δDV-SMOW values from bulk extraction of fluid inclusion water vary from −69.5‰ to −47.8‰, suggesting that the ore-forming fluid consists dominantly of magmatic water. The δ34SV-CDT values range from 0.37‰ to 3.9‰. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of the ore minerals are in the ranges of 17.391–17.728, 15.420–15.577, and 37.420–37.923, respectively. The data from the S and Pb isotopic systems indicate that the ore-forming materials came from granitic magma. The Xiaoshan gold deposit is a mesothermal lode-gold deposit of magmatic-hydrothermal origin. Fluid phase separation and temperature decrease were the dominant mechanisms for the deposition of ore-forming materials.