Geology, hydrothermal fluids, H-O-S-Pb isotopes, and Rb-Sr geochronology of the Daxintun orogenic gold deposit in Heilongjiang province, NE China

The newly discovered Daxintun Sb-Au deposit (Heilongjiang province, NE China) is located at the north-eastern margin of the Central Asian Orogenic Belt, and it is hosted by Neoproterozoic to Early-Cambrian two-mica schist and marble. The antimony-bearing minerals include stibnite, famatinite, tetrahedrite, boulangerite, freibergite, and minor andorite. Gold occurs largely as native gold microparticles (0.1-20 mu m) with high fineness (974-983) accompanied by quartz, stibnite, calcite and pyrite. Fluid inclusions in ore-bearing quartz and calcite phases mainly comprise liquid-vapor and minor CO2-bearing three-phase types, and the gas phases contain CO2, CH4 and H2S. The Daxintun fluid inclusions homogenize at 111.8-353.4 degrees C and are of low salinity (0.53-12.51 wt% NaCl equiv.). The delta O-18(SMOW) of the Daxintun quartz falls into a wide range (4.2 parts per thousand-16.9 parts per thousand), yet the delta D-SMOW falls into a narrow range (-108.0 parts per thousand to -87.3 parts per thousand), suggesting that the ore-forming fluids formed from metamorphic fluids that mixed with meteoric water. The stibnite delta S-34 ranges between -0.9 parts per thousand and 5.1 parts per thousand (mean = 2.8 parts per thousand). The stibnite has Pb-206/Pb-204 of 18.234-18.306, Pb-207/Pb-204 of 15.537-15.561 and Pb-208/Pb-204 of 38.103-38.227, implying a metamorphic fluid source. The conditions of gold and antimony precipitation are comprised of neutral pH and fluid mixing, with decreasing fS(2) and fO(2). Zircon U-Pb dating of the fine-grained Daxintun granite yields a Late-Jurassic age (154.0 +/- 2.0 Ma), and the Daxintun diorite dike yields a weighted mean age of 122.1 +/- 1.3 Ma. Stibnite Rb-Sr dating suggests that the SbAu mineralization has an age of approximately 152.8 +/- 2.4 Ma. The observed ore deposit geology, as well as new data on the ore-forming fluids, H-O-S-Pb isotopes, and Rb-Sr geochronology, suggest that the Daxintun SbAu deposit is best described as an orogenic type gold deposit that formed during subduction of the Palaeo-Pacific and the Mongolia-Okhotsk Oceans during the Late-Jurassic.