Tailings dust characterization and impacts on surface water chemistry at an abandoned Zn-Pb-Cu-Au-Ag deposit

Abstract

The increased potential for dust mobilization as a result of climate change indicates a need to better understand interactions between dust and water. This research investigates the geochemical effects of tailings dust on surface waters near Stirling mine, Nova Scotia. Tailings were sieved to <63 μm as a proxy for dust and analyzed geochemically and mineralogically for the identification of primary and secondary metal-bearing phases using a scanning electron microscope with automated mineralogy, electron microprobe analysis and synchrotron-based microanalysis. Metal-hosting phases identified include in order of abundance; sphalerite (ZnS), cerussite (PbCO3), chalcopyrite (CuFeS2), Pb–Mn phases (possibly cesàrolite (PbMn3O6(OH)2)), smithsonite (ZnCO3), goethite (FeO(OH), aurichalcite ((Zn,Cu)5(CO3)2(OH)6), hydrohetaerolite (ZnMn2O4·H2O), tennantite (Cu6(Cu4Zn2)As4S12S), and galena (PbS). Shake flask tests were conducted in simulated stream waters (pH = 7) using sieved tailings and passive dry deposition collector filters to investigate the solubility of metal-hosting mineral phases within dust. Results indicate metal leaching at near neutral pH conditions. Sphalerite, cerussite and chalcopyrite are likely the main sources of Zn, Pb, and Cu in the shake flask leachate, based on calculated saturated indices and mass balance. Analyses of stream waters indicate similar conditions (pH, ORP, saturation indices, etc.) compared to the results of the shake flask tests, suggesting they provide reasonable insight about processes occurring in the field. Tailings dust generated at the site is therefore a potential source of metals to surface waters.