Genesis of the Shangxu Orogenic Gold Deposit in Northern Tibet: Constraints from Fluid Inclusions and Isotopic Compositions
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    Abstract:

    The Shangxu gold deposit locates to the south of the middle part of the Bangong-Nujiang suture zone in northern Tibet. The gold ore bodies, hosted in the Middle-Lower Jurassic metamorphic flysh Mugagangri Group, are controlled by NWW-trending faults. The mineralization of gold is closely related to quartz veins. Auriferous quartz veins contain lots of sulfides, such as pyrite, chalcopyrite, galena and sphalerite. Natural gold is mostly distributed in cracks of quartz, with minor in cracks of pyrite. Laser Raman analysis shows that the Shangxu gold deposit contains two types of fluid inclusions: (1) NaCl-H2O inclusions (type L); (2) CO2 inclusions (type C), which can be subdivided into two-phase and three-phase inclusions. Microthermometric measurements indicate that: (1) NaCl-H2O inclusions are characterized by homogenization temperature of 89.6 to 409.8 ℃, salinity of 0.35 % to 9.34 %, and density of 0.55 to 0.98 g/cm3; (2) CO2 inclusions are characterized by homogenization temperature of 264.3 to 395.2 ℃, salinity of 4.62 % to 9.74 %, and density of 0.66 to 0.81 g/cm3. The ore-forming fluid of the Shangxu gold deposit is characteristic of CO2-rich, low to moderate homogenization temperature, low salinity and low density, which are similar to those of typical orogenic gold deposits. Measured δD values for the gold-bearing quartz range between -108 and -89 per mil, the estimated δ18O fluid values range from -0.8 to 5.8 per mil. The result of hydrogen and oxygen isotopes suggests that the ore-forming fluid is mainly derived from the mix of metamorphic fluid and formation water. Fluid inclusions and isotopic composition features imply that the Shangxu gold deposit may be an orogenic gold deposit formed under collisional orogenic belt.

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PEI Yingru, YANG Zhusen, ZHAO Xiaoyan, ZHANG Xiong, XU Yutao, MA Wang, MAO Jingtao, ZHUANG Liangliang.2015. Genesis of the Shangxu Orogenic Gold Deposit in Northern Tibet: Constraints from Fluid Inclusions and Isotopic Compositions[J]. Acta Geologica Sinica,89(10):1814-1825

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History
  • Received:July 04,2015
  • Revised:September 15,2015
  • Adopted:September 16,2015
  • Online: October 26,2015
  • Published: