Abstract

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Title:: Forming Mechanism of the Reducing Gas from Mineralization Fluid in West Junggar of Xinjiang, China

Author(s):: LI Chang-hao; SHEN Ping; PAN Hong-di; CAO Chong; 1. Division of Solid Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China; 2. University of Chinese Academy of Sciences, Beijing 100049, China; 3. School of Earth Science and Resources, Chang’an University, Xi’an 710054, Shaanxi, China

Keywords:: porphyry deposit; orogenic gold deposit; reducing gas; thermal decomposition of organic mater; Fischer-Tropsch reaction; carbonaceous stratum; Xinjiang

Abstract:: West Junggar is an important mineral exploitation region in Xinjiang. There are many types of deposits, including porphyry Cu deposit, porphyry Mo deposit and orogenic Au deposit. However, the mineralization fluid in these deposits always contain the reducing gas (such as CH₄and C₂H₆), which conflict with the characteristics of the typical porphyry deposit and orogenic Au deposit around the world. According to the comprehensive analysis of gas composition, C isotope and source of the reducing gas in geological process, the reducing gas in the mineralization fluid associates with the wall rock containing carbonaceous material, and the reducing gas is produced by thermal decomposition of organic matter. However, a little reducing gas may come from hypomagma or abiogenic process. The reducing gas mainly forms at late magmatism or hydrothermal stage; meanwhile, the metallogenic magma has high oxygen fugacity (more than Ni-NiO(NNO)). Therefore, West Junggar has great potential to explore huge porphyry Cu deposits.