Metallogeny and environmental impact of Hg in Zn deposits in China

Zinc smelting is currently regarded as one of the most important atmospheric Hg emission sources in the world. In order to assess the potential environmental impacts of Hg from Zn smelting in China, the distribution of total Hg concentration (HgT) in Zn concentrates (ZCs) from 100 Zn deposits in China was investigated. It was found that HgT varies depending on the ore types and their geneses. Zinc concentrates from sedimentary-exhalative deposits (SEDEX, geometric mean = 48.2 μg/g) have the highest HgT. The possible explanation is that the sources of mineralizing solutions for SEDEX deposits are deep formational brines in contact with sedimentary rocks, and there are much higher background Hg contents in sedimentary rocks. Zinc concentrates from volcanic hosted massive sulfide deposits (VMS, geometric mean = 11.5 μg/g) and Mississippi Valley-Type (MVT, geometric mean = 10.1 μg/g) deposits have intermediate HgT. VMS may receive most of their Hg from fluid–rock interaction and/or by direct input of gaseous Hg from a mantle source. However, the source of metals within MVTs may be the low-temperature hydrothermal solution formed by diagenetic recrystallization of the carbonates. Intrusion related deposits (IRs) have the lowest HgT (Geomean = 2.4 μg/g), and the dispersion of Hg in the IRs seems to be influenced by the temperature of ore formation and/or the nature of wall–rock alteration. Finally, it was estimated that the annual Hg emission to the atmosphere from Zn smelting in China was about 107.7 tons in 2006.