Unique mercury isotopic signature of mercury-bearing hydrothermal systems in South China and its geological and environmental implications
Bizheng Yang, Chenchen Yang, Zhendong Tian, Changzhou Deng, Bernd Lehmann, Runsheng Yin
Abstract
Abstract The giant South China low-temperature metallogenic domain (LTMD) hosts many low-temperature hydrothermal systems (e.g., the Youjiang Au-As-Sb-Hg ore deposits, Xiangzhong Sb-Au ore deposits, and Xiangqian Hg ore deposits), which provide ~80% of the global Hg metal production. Here, we study the Hg isotopic composition of the Xiangqian Hg deposits and re-evaluate available data on the Youjiang Au-As-Sb-Hg deposits and Xiangzhong Sb-Au deposits. Cinnabar samples from eight Xiangqian Hg deposits display negative to near-zero Δ199Hg values, suggesting that their Hg is from two sources: (1) the asthenospheric mantle with near-zero Δ199Hg values, and (2) the Precambrian basement with negative Δ199Hg values. Such mixing is also observed in the Youjiang Au-As-Sb-Hg deposits and Xiangzhong Sb-Au deposits. Combining the ages of these deposits, we infer that plate subduction and collision during Caledonian, Indosinian, and Yanshanian tectonic-thermal events triggered lithospheric extension, asthenospheric upwelling, and basement remobilization within the South China craton, leading to the generation of magmatic-hydrothermal fluids and metal-rich crustal fluids to form low-temperature hydrothermal systems in the LTMD. This work demonstrates that Hg-bearing low-temperature hydrothermal deposits in China have distinct δ202Hg-Δ199Hg patterns from those in Europe and North and South America, implying that Hg isotopes can be used for tracing the sources of Hg in the global market.