Geochemical behaviour of mercury and other trace elements at the historical fahlore Cu-Sb(-Ag) Mt. Avanza mine (Carnic Alps, Italy)

Mining sites, characterised by different types of ore deposits, are affected by different environmental problems. In order to predict the effects on the environment, geochemical studies for different ore types must be performed. This multicompartmental geochemical characterisation approach provides one of the first case studies regarding the geochemical behaviour and fate of Hg, Sb, As, Cu and other elements in solid, water and gaseous matrices in an environment affected by the mining activity of a “fahlore-type” ore deposit: the ancient Cu-Sb-Ag Mt. Avanza mine (Carnic Alps, Italy), which is a rare example of a mostly monomineralic tetrahedrite exploited ore deposit. Elevated concentrations of the elements associated with the (Zn-Hg) tetrahedrite and to minor ore minerals (Cu, Sb, As, Pb, Zn, Hg) in mine wastes, soils and stream sediments were observed, although concentrations greatly decreased with increasing distance from the mining area. The fate of Hg at the investigated fahlore mining district appeared similar to cinnabar mining sites around the world. Weak solubility but the potential evasion of Gaseous Elemental Mercury (GEM) into the atmosphere also appears to be characteristics of Hg in non-cinnabar ores. Although GEM concentrations are such that they do not present a pressing concern, real-time field surveys allowed for the easy identification of Hg sources, proving to be an effective, suitable high-resolution indirect approach for optimising soil sampling surveys and detecting mine wastes and mine adits. Interestingly, Tl and Ge were associated with the “lithogenic component” and not to sulfosalt/sulfide minerals. Although mine drainage water often slightly exceeded the national regulatory limits for Sb and As, with Sb being more mobile than As, the relatively low dissolved concentrations indicate a moderate stability of the tetrahedrite.