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 degrees 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 degrees 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 degrees 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.
