Isotopic geochemistry of the Jinwozi gold deposit in the eastern Tianshan orogen, NW China: implications for the ore genesis

Abstract

The Jinwozi gold deposit in the eastern Tianshan orogenic belt in northwest China has been mined for more than 100 years and previous studies have mostly classified it as an intrusion‐related gold deposit. In this paper, the age of the Jinwozi intrusion and the isotopic geochemistry characteristics of the deposit were studied to investigate the ore genesis and ore genetic type. Results showed that: (1) The Jinwozi pluton, which is the host rock of the orebodies, was emplaced during 395–390 Ma, thus substantially predating gold mineralization (243–228 Ma); (2) δ18O values of fluid in the main mineralized stage (stage II) vary from −0.9 to 5.0‰, with an average of 2.0‰. Those of late quartz–calcite stage (stage III) fluids are between −13.3 and 0.4‰, with an average of −7.6‰. δD values of fluids in stage II vary from −97 to −84‰, with an average of −89‰, slightly higher than those of stage III fluids (−85 to −120‰, average −108‰). δ13C values of the ore‐forming fluid in stage II vary from −0.3 to 3.2‰, with an average of 1.3‰. δ34S values of pyrite from both stage II and III are generally high, ranging from 3.9 to 7.7‰, with an average of 6.0‰. Lead isotopic compositions of sulphides from stage II and III are similar, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios have ranges from 17.7780 to 18.4750, 15.4881 to 15.6965, 38.1560 to 38.7370, respectively. Two Pb isotope model ages of 450 and 268 Ma were yielded from these data. The oxygen, hydrogen, carbon, sulphur and lead isotope compositions all indicate that the ore‐forming fluids at Jinwozi may dominantly derive from a mixture of metamorphic and meteoric water, but is unlikely from a magmatic–hydrothermal source. Based on the geological and geochemical evidence, we infer that the Jinwozi gold mineralization may have occurred during the collision between the Kazakhstan–Junggar Plate and the Tarim Plate, accompanied by metamorphism which generated the ore‐forming fluids through the dehydration and decarbonation of country rocks. Such processes, combining with other geological and geochemical characteristics, indicate that the Jinwozi gold deposit can be classified as orogenic type. Copyright © 2014 John Wiley & Sons, Ltd.