Genesis of the Xiaotongjiapuzi gold deposit of the Liaodong gold province, Northeast China: Fluid inclusion thermometry and S–Pb–H–O–He isotope constraints

Abstract

The Xiaotongjiapuzi gold deposit is located in the Liaodong gold province, NE China. The deposit is hosted in the metamorphic rocks of the Proterozoic Liaohe Group, consisting of marble, schist, and granulite. Three alteration/mineralisation stages were identified, namely (a) quartz–pyrite, (b) quartz–polymetallic sulfides, and (c) quartz–carbonate. Four fluid inclusion types were distinguished: liquid‐rich two‐phase, gas‐rich two‐phase, CO2‐bearing, and pure CO2. Stage 1 quartz contains liquid‐rich two‐phase inclusions with salinity of 5.9–14.3 wt.% NaCl equiv. and homogenisation temperatures of 311°C–408°C. Stage 2 quartz contains all four inclusion types, of which the liquid‐rich two‐phase, gas‐rich two‐phase, and CO2‐bearing inclusions yielded homogenisation temperatures of 268°C–376°C and salinity of 4.1–13 wt.% NaCl equiv. In stage 3 quartz, only liquid‐rich two‐phase inclusions were found, which contain relatively low salinity (1.6–7.6 wt.% NaCl equiv.) and homogenisation temperatures (201°C–254°C), indicating an H2O–NaCl–CO2 system for ore precipitation. Stage 2 δ18Ow and δD values of quartz minerals are of 0.3‰ to 2.3‰ and −100‰ to −96‰, respectively. Hydrogen and oxygen isotopic compositions indicate that the ore fluids were a mix of magmatic fluid and meteoric water. δ34S values of the metallic sulfides from the Xiaotongjiapuzi deposit range from +4.6‰ to +12.9‰, whilst Pb isotopes show small variations: 206Pb/204Pb = 17.671 to 18.361, 207Pb/204Pb = 15.569 to 15.659, and 208Pb/204Pb = 37.695 to 37.937. Sulfur and lead isotopes suggest that the ore‐forming materials were derived from the Liaohe Group metamorphic rocks and the Triassic granitoids. 3He/4He and 40Ar/36Ar ratios of the fluid inclusions derived of ore‐bearing pyrite ranges from 0.27 to 0.53 Ra and 362.2 to 1113.1, respectively, implying that both mantle‐ and crust‐derived fluids were involved in the gold mineralisation. The Xiaotongjiapuzi deposit could be a mesothermal gold deposit, and the fluid phase separation or immiscibility is the dominant mechanism for the deposition of ore‐forming materials.