Silver isotopes: A tool to trace smelter-derived contamination

Abstract

Here, for the first time, we report the concentrations and isotopic data of Ag in a variety of ore and metallurgical samples and forest soils that have been polluted due to Ag-Pb smelter emissions. Similar to the Ag concentrations, we identified a large range of δ(109)Ag values (from -0.8 to +2.4%0), a ~3%o spread, within the primary and secondary materials (i.e., galena, fly ash, slag and matte). This phenomenon, however, is evidently unrelated to Ag isotopic fractionation during the smelting process, but it reflects the starting (109)Ag/(107)Ag signal in ore mineral and/or the specific type of ore genesis. The two studied soil profiles differed in Ag isotopic composition, but on the other hand, they consistently showed significantly lighter Ag (<+0.8%0) of metallurgical origin in the upper horizons compared to the bottom horizons and bedrocks, with low Ag amounts depleted of (107)Ag (<+2.9%0). This isotopic pattern can be attributed to a ternary mixing relationship involving two major anthropogenic Ag components and a minor contribution from geogenic Ag. Accordingly, we did not observe any post-depositional isotopic fractionation in our soils, since Ag was geochemically stable and it was not subjected to leaching. In summary, the Ag isotopes have a potential to trace variations in anthropogenic phases, to monitor specific geochemical processes, and are clearly applicable as anthropogenic Ag source and Ag load proxies.