Fluid Inclusions and C-H-O-S-Pb Isotopes: Implications for the Genesis of the Zhuanshanzi Gold Deposit on the Northern Margin of the North China Craton

摘要

The Zhuanshanzi gold deposit lies in the eastern section of the Xingmeng orogenic belt and the northern section of the Chifeng-Chaoyang gold belt. The gold veins are strictly controlled by a NW-oriented shear fault zone. Quartz veins and altered tectonic rock-type gold veins are the main vein types. The deposits can be divided into four mineralization stages, and the second and third metallogenic stages are the main metallogenic stages. In this paper, based on the detailed field geological surveys, an analysis of the orebody and ore characteristics, microtemperature measurement of fluid inclusions, the Laser Raman spectrum of the inclusions, determination of C-H-O-S-Pb isotopic geochemical characteristics, and so on were carried out to explore the origin of the ore-forming fluids, ore-forming materials, and the genesis of the deposits. The results show that the fluid inclusions can be divided into four types: type I - gas-liquid two-phase inclusions; type II - gas-rich inclusions; type III- liquid inclusions; and type IV - CO2-containing three-phase inclusions. However, they are dominated by type Ib - gas liquid inclusions and type IV - three-phase inclusions containing CO2. The gas compositions are mainly H2O and CO2, indicating that the metallogenic system is a CO2-H2O-NaCl system. The homogenization temperature of the ore-forming fluid evolved from a middle temperature to a low temperature, and the temperature of the fluid was further reduced due to meteoric water mixing during the late stage, as well as a lack of CO2 components, and eventually evolved into a simple NaCl-H2O hydrothermal system. C-H-O-S-Pb isotope research proved that the ore-forming fluids are mainly magmatic water during the early stage, with abundant meteoric water mixed in during the late stage. Ore-forming materials originated mostly from hypomagma and were possibly influenced by the surrounding rocks, suggesting that the ore-forming materials were mainly magmatic hydrothermal deposits, with a small amount of crustal component. The fluid immiscibility and the CO2 and CH4 gases in the fluids played an active and important role in the precipitation and enrichment of Au during different metallogenic stages. The deposit is considered a magmatic hydrothermal deposit of middle-low temperature.