Genesis and age of the Toudaoliuhe breccia-type gold deposit in the Jiapigou mining district of Jilin Province, China: Constraints from fluid inclusions, H–O–S–Pb isotopes, and sulfide Rb–Sr dating

Abstract

The Jiapigou mining district (JMD) in the northeastern part of the North China Block mainly contains quartz vein- and altered rock-type gold deposits that have been prospected and mined for over 200 years. Recently, a breccia-type gold deposit, known as Toudaoliuhe, was discovered in the JMD, that has attracted attention for prospecting and exploration. In this paper, we report the ore geology, gold-bearing sulfide (i.e., pyrite, galena, and sphalerite) Rb–Sr age, fluid inclusions (FIs), and H–O–S–Pb–Sr isotope data of the Toudaoliuhe gold deposit to determine its genesis and ore-forming mechanisms. Gold orebodies mainly occur in the breccia cements, as well as in several quartz veins controlled by NW-trending brittle faults. There were three hydrothermal stages: the early (quartz–pyrite), main (quartz–polymetallic sulfide), and late (quartz–carbonate) stages. Gold mineralization occurred in the main hydrothermal stage. Three types of FIs were identified: CO2–H2O–NaCl (C-type), H2O–NaCl (W-type), and pure CO2 (PC-type). The FIs in quartz from the early hydrothermal stage are predominantly of the C- and W-types (with traces of PC-type), and have homogenization temperatures of 299.8–340.0 °C and salinities of 6.5–14.8 wt% NaCl equivalent (E). The FIs in the quartz and sphalerite forming the main hydrothermal stage are also predominantly of the C- and W-types (with trace PC type), and have homogenization temperatures of 169.1–298.7 °C and salinities of 5.7–16.5 wt% E. The FIs in the quartz and calcite from the late hydrothermal stage were solely of the W-type, and have homogenization temperatures of 126.0–210.2 °C and salinities of 2.1–11.4 wt% E. The ore-forming fluids are characterized by moderate temperature and low salinity, suggesting a CO2–H2O–NaCl system. The H–O–S–Pb–Sr isotopic results suggest that the ore-forming fluids were dominated by magmatic water, and that the ore-forming materials were mainly extracted from the Middle Jurassic magmatic reservoir (177–163 Ma), sourced mainly from the lower crust with trace mantle components. Fluid boiling was the dominant mechanism for gold and associated sulfide precipitation. The Rb–Sr isochron age of the gold-bearing sulfides at 177.7 ± 1.7 Ma indicates that gold mineralization occurred in the early Middle Jurassic. We therefore proposed that the Toudaoliuhe is a mesothermal gold deposit that formed in an extensional setting related to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent.