Source and pathway determination of mine seepages using sulfate and Pb isotopes at the Daema and Okdong mines, South Korea

• Published in: Applied geochemistry 2020-07, Vol.118, p.104642, Article 104642
• Main Authors: Kim, Duk-Min, Lim, Woong-Lim, Im, Dae-Gyu, Seo, Eui-Young
• Format: Article
• Language: English
• Subjects: Dissolved Pb isotope; Environmental forensics; Groundwater; Tailings dump
• ISSN: 0883-2927; 1872-9134
• DOI: 10.1016/j.apgeochem.2020.104642

Utilization of multiple stable isotopes including metal isotopes have been useful to trace sources and pathways of contamination. Contaminated seepages flow out from tailings dumps at the Daema gold-silver mine and the Okdong copper mine in South Korea. Ion concentrations, δ34SSO4, δ18OSO4, and Pb isotopes, as well as leaching tests were used to evaluate the sources and pathways of seepages from tailings dumps at the Daema and Okdong mines. The δ34SSO4 and δ18OSO4 values of the seepage were similar to that of the groundwater at the tailings layer and differed from that of the groundwater at the coal shale layer of the tailings dump at the Daema mine. The Pb isotopic ratios of groundwater at the tailings layer also approached those of the tailings, although the Pb concentration in the seepage that was too low (0.559 μg L−1) did not indicate isotopic signatures of tailings. This suggests that the source of contaminants in the seepage is the tailings of the Daema mine rather than waste rocks (coal shale) of an adjacent mine in the tailings dump. In the Okdong mine, the contamination of seepage may be a result of a 67–71% contribution of groundwater from the northern side of the dump through buried waste rock (OD-T2) and a 19–23% contribution of groundwater from the eastern valley (OD-T3), as calculated by the isotopic mixing of δ34SSO4 and δ18OSO4. Adit water is not considered to be the major source of the seepage because of the large difference in Mn concentrations (22.0 mg L−1 and 0.10 mg L−1 in adit water and seepage, respectively) and the undersaturation with respect to Mn phases before and after mixing with tailings water. To reduce the contamination load of seepage in a tailings dump, we should prevent water inflow not only from the surface but also from the side of the tailings dump. Both studied areas suggest that a dual isotopic approach using δ34SSO4 and δ18OSO4 is especially useful in identifying the contamination sources and pathways. Additionally, a leaching test for waste evaluation proved helpful in qualitatively simulating the composition of leachate from the tailings at the Daema mine and adit water from ore rocks at the Okdong mine. Dissolved Pb isotopic ratios were effective in determining the solid sources of dissolved Pb, if the Pb concentration is greater than 0.6–1.8 μg L−1 in the cases of the studied mines. Pb isotopic ratios at five sites including Nakdong mine and two other sites suggest that dissolved Pb with too low concentration m