Genesis of the Bairendaba Ag-Zn-Pb Deposit, Southern Great Xing'an Range, NE China: A Fluid Inclusion and Stable Isotope Study

The Bairendaba deposit is the largest Ag-Zn-Pb deposit in Inner Mongolia. Vein and disseminated ores occur in biotiteplagioclase gneiss and quartz diorite along regional EW trending faults. Microthermometric data for H2O-NaCl +/- CH4 +/- CO2 fluid inclusions record a decrease in homogenization temperature and salinity of ore-forming fluids with time. Early and mainstage mineralization have homogenization temperatures of 242 degrees-395 degrees C and 173 degrees-334 degrees C, respectively, compared with 138 degrees-213 degrees C for late-stage mineralization. Fluid salinities for early mineralization have a bimodal distribution, dominantly 4.2-11.8 wt.% NaCl equivalent, with 35.2-37.8 wt.% NaCl equivalent for a small population of halite-bearing inclusions. Main-and late-stage fluids have salinities of 2.1-10.2 wt.% NaCl equivalent and 0.7-8.4 wt.% NaCl equivalent, respectively. Oxygen and hydrogen isotope data indicate the interaction of a magmatic fluid with wall rocks in early mineralization, followed by the introduction of meteoric water during late-stage mineralization. Values of -15.9% to -12% (delta C-13(PDB)) for hydrothermal quartz indicate that organic-rich strata were the source of carbon. Sulfur had a magmatic source, based on values of -0.1% to 1.5% (delta(34) SV-CDT) for sulfide minerals. The Bairendaba deposit is a typical mesothermal system with mineralization controlled by structure.