Characteristics of ore-forming fluids of the Zhongshangou gold deposit, Zhangjiakou-Xuanhua area, Hebei Province: Limitation on the intrusive rock related telluride-gold deposits

This paper is the result of mineral exploration engineering.

Objective The Zhongshangou gold deposit is located in the north margin of North China Craton and the south side of Shangyi-Chongli-Chicheng deep fault. It is one of the typical gold deposits in Zhangjiakou-Xuanhua gold concentration area, Hebei Province. This paper discusses the characteristics and evolution of ore-forming fluids, in order to provide a theoretical basis for the exploration of the deposit.

Methods This paper summarizes the regional mineralizing setting, geological characteristics of the mining area, ore body and ore characteristics. Representative samples from four metallogenic stages were selected to conduct research on fluid inclusion petrography and micro thermometry, hydrogen and oxygen isotopes, and helium and argon isotopes.

Results The results indicate that it can be divided into four metallogenic stages: K-feldspar-pyrite-quartz stage (Ⅰ), milky white quartz-pyrite stage (Ⅱ), smoky gray quartz-sulfide stage (Ⅲ) and sulfide-poor-carbonate stage (Ⅳ). Gas-liquid two-phase primary fluid inclusions are mainly developed in each mineralization stage. The temperature measurement data of fluid inclusions show that the homogenization temperature and salinity of main ore-forming stage are respectively 210-250℃ and 6.01%-13.62%NaCleqv. Hydrogen and oxygen isotope show that δ¹⁸O_H2O and δD_V-SMOW values are respectively -2.97‰-6.96‰ and -94.6‰--80.2‰, which show that the δ¹⁸O_H2O values drift to the atmospheric water line and show a linear change. Helium and argon isotope of the pyrite show that ³He/⁴He values are 1.82×10^-7-9.24×10^-7, ⁴⁰Ar/³⁶Ar values are 699.9-2200.4, R/Ra values are 0.13-0.66, radiogenic ⁴⁰Ar^* values are 55.89%-86.57%, and mantle derived helium values are 2.00%-10.86%.

Conclusions The ore-forming fluid has experienced a continuous evolution process from medium-high temperature and medium-low salinity to low temperature and medium-low salinity. The main ore-forming stage experienced strong boiling. In the late stage of mineralization, there mixed in a large amount of meteoric water. With the development of mineralization, the proportion of mantle derived materials in mineralization increased gradually. The ore-forming fluid has the characteristics of magma fluid mixed with the crust and mantle. To sum up, the ore-forming fluid of Zhongshangou gold deposit is characterized by the intrusive rock related telluride-gold deposit.