Concentrations and isotopic variability of mercury in sulfide minerals from the Jinding Zn-Pb deposit, Southwest China

Abstract

Mercury (Hg) isotopes have been proven as a useful tracer in understanding sources and biogeochemical processes of Hg in the environment. However, the use of this tracer has not yet been explored in economic geology. This paper investigates the concentrations and isotopic compositions of Hg in sulfide minerals from the Jinding deposit, the largest Zn-Pb deposit in China. Total mercury concentration (HgT) is highly variable: with the highest in sphalerite (472–1010ng·g−1), intermediate concentrations in pyrite (195–342ng·g−1) and the lowest in galena (65–310ng·g−1). The variation was likely due to the fact that Hg2+ can more readily substitute for Zn2+ than for Fe2+ and Pb2+, but an influence of different parental fluids on the isotopic composition of the sulfide minerals cannot be excluded. An overall range of δ202Hg from −3.17 to −0.57‰ is observed in the sulfides. Samples from the early stage feature the enrichments of light Hg isotopes, with δ202Hg ranging from −3.17 to –1.59‰, suggesting significant mass-dependent fractionation during the transport and/or deposition of Hg. However, the volatilization of aqueous Hg(0) during boiling of hydrothermal fluids was likely the most important process causing the observed fractionation. Relatively higher δ202Hg values (−1.84 to −0.57‰) of the late stage samples indicate that the Hg was rarely fractionated from its sources. Additionally, small but significant mass-independent fractionations are measured for the deposit with Δ199Hg ranging from −0.06 to 0.10‰, indicating that the Hg may have been derived from the sedimentary rocks of the Lanping Basin. Finally, we conclude that Hg isotopes have the potential to be a new tracer of sources of ore-forming materials, as well as pathways of fluid evolution in hydrothermal deposits.