Fluid Inclusion, H-O, S, Pb and noble gas isotope studies of the Aerhada Pb-Zn-Ag deposit, Inner Mongolia, NE China

The Aerhada Pb-Zn-Ag deposit is located in the western segment of the Great Hinggan Range Ag-Pb-ZnCu-Mo-Au-Fe metallogenic belt in NE China. Orebodies occur mainly as vein type and are hosted by sandstone and siliceous slate. Three stages of primary mineralization, including an early arsenopyrite-pyritequartz, a middle polymetallic and silver sulfides-quartz and a late sphalerite-pyrite-calcite-fluorite are recognized. Four types of fluid inclusions have been identified in the ore-bearing quartz and fluorite veins, i.e.,liquid-rich, gas-rich, three-phase CO2 aqueous inclusions, and pure gas or liquid aqueous inclusions. Microthermometric studies on fluid inclusions reveal that homogenization temperatures from early to late stages range from 253 degrees to 430 degrees C, 195 degrees to 394 degrees C and 133 degrees to 207 degrees C, respectively. Fluid salinities range from 2.9 to 14.0 wt.% NaCl equiv. The vapor composition of the ore fluid is dominated by H2O, CO2 and CH4, with minor proportions of N-2. The fluid delta O-18(H2O) and delta D-H2O values vary from +1.6 to+9.3 parts per thousand and -122 to -56 parts per thousand, respectively, and reflect a magmatic fluid and a meteoric fluid dominant hydrothermal system for the early and late stages of mineralization, respectively. The calculated (delta S-34(H2S) values of hydrothermal fluids in equilibrium with sulfides range from +5.2 to +7.1 parts per thousand, suggesting a mixed source for sulfur, i.e.,the local magmatic and sedimentary rocks. The Pb isotope compositions of sulfides are similar to those of the local magmatic and sedimentary rocks, implying that lead and possibly silver relate to these sources. The noble gas isotope compositions of fluid inclusions hosted in ore minerals suggest that the ore-forming fluids were dominantly derived from a deep mantle source. Fluid mixing and dilution are inferred as the dominant mechanisms for ore deposition. The Aerhada Pb-Zn-Ag deposit can be classified as a medium to low temperature hydrothermal vein type deposit. (C) 2017 Elsevier B.V. All rights reserved.