Mercury Isotopes as Proxies to Identify Sources and Environmental Impacts of Mercury in Sphalerites

During the past few years, evidence of mass independent fractionation (MIF) for mercury (Hg) isotopes have been reported in the Earth's surface reservoirs, mainly assumed to be formed during photochemical processes. However, the magnitude of Hg-MIF in interior pools of the crust is largely unknown. Here, we reported significant variation in Hg-MIF signature (Delta Hg-199: -0.24 similar to + 0.18 parts per thousand) in sphalerites collected from 102 zinc (Zn) deposits in China, indicating that Hg-MIF can be recorded into the Earth's crust during geological recycling of crustal material. Changing magnitudes of Hg-MIF signals were observed in Zn deposits with different formations, evidence that Hg isotopes (especially Hg-MIF) can be a useful tracer to identify sources (syngenetic and epigenetic) of Hg in mineral deposits. The average isotopic composition in studied sphalerites (delta Hg-202(average): -0.58 parts per thousand;Delta Hg-199(average): +0.03 parts per thousand) may be used to fingerprint Zn smelting activities, one of the largest global Hg emission sources.