Antimony isotope fractionation trace drainage waters of an abandoned Zn-Fe-Pb mine deposit in the Harz Mountains, Germany

Heavy metal contamination of abandoned mines affects natural ecosystems long after mining has ceased. Recent analytical developments have shown that Sb isotopes can be used as a powerful geochemical tool to trace sources and processes of contamination in regions affected by Sb mining [1]. However, despite its toxicity, the Sb cycle in aqueous systems apart from Sb-mine contaminated waters remains poorly understood.

To address this issue and better understand Sb isotope behavior in abandoned mines without a (known) occurrence of Sb mineralization, we investigated Sb isotopes in drainage waters of the Ernst-August Stollen in Bad Grund, Harz Mountains (Germany), which was famous for its Zn-Fe-Pb mineralization. The water samples distributed throughout the mine and (anthropogenic) floating iron at the separator basin were collected during winter and summer seasons in 2024. The variable Sb concentrations (0.1 to 0.9 μg/L) and Sb isotope compositions of 0.2 μm filtered water (0.13 ≤ δ¹²³Sb ≤ 0.50 ‰) are most likely related to natural Sb weathering and adsorption processes at variable conductivity (635 to 5300 μS/cm). In contrast, the floating iron has high Sb concentrations (~30 μg/g) and a heavier Sb isotope composition (~1.3 ‰). This Sb isotope fractionation between floating iron and circumneutral drainage water may reflect a combination of adsorption, weathering and subsequent leaching processes.

[1] Wen et al. 2023 J. Hazard Mater. 446, 130622.