Lead isotopic composition of the oxidized Cu ores, slags and soils from the Old Copper Basin, Poland and its implications for metal-provenance and environmental research

In this study, we report lead isotopic compositions from oxidized Cu ores, host rocks, metal smelting residues, and soils from the Zechstein Ca1 formation which is associated with the Kupferschiefer copper deposits. The lithology is dominated by marls and slates, where Cu mineralization appears in carbonates, mostly malachite. Historical smelting left numerous slag remnants around the site (Derkowska et al. 2023). The Pb isotope ratios in ores and slags are highly diverse in comparison to previous studies of Cu ores and smelting products in Poland (Tyszka et al. 2012), i.e. ²⁰⁶Pb/²⁰⁷Pb ratio ranges from 1.094 to 2.092 for ores and from 1.151 to 1.240 for slags. This diversity is likely related to the oxidized character of the ore, which contains less Pb compared to sulfide-dominated ores and, in consequence, its Pb isotopic composition is dominated by radiogenic Pb produced by U-rich host rocks. This translates to significant differences in Pb isotope records between oxidized and reduced (sulfide) deposits that can be utilized in environmental and provenance studies. Similar diversity in soil samples is consistent with contamination by such ores and/or slags. Analyzed soils show highly variable ²⁰⁶Pb/²⁰⁷Pb ratios in lower soil horizons, whereas Pb isotope ratios in topsoils are similar to those typical for a whole region of Lower Silesia in Poland (1.17-1.19). This suggests the dominance of modern atmospheric Pb in the surface environment which we link to Polish and Czech coal combustion and name as the Lower Silesian Contemporary Pollution Signal.

Our study shows that using oxidized Cu-ores may introduce high diversity in Pb isotopic composition to smelting products, wastes, and consequently the environment. This affects both environmental and provenance studies as only a restricted isotope ratio can be attributed to a single source. On the other hand, high diversity in ²⁰⁶Pb/²⁰⁷Pb ratios in slag samples may also indicate the addition of oxidized Cu ores during smelting thus may be also an asset to identify when oxidized ores were used or acted as a pollution source.

Acknowledgments: The study is funded by the National Science Centre grant to KD (2019/35/N/ST10/04524)

Derkowska K., Kierczak J., Potysz A., Pietranik A., Pędziwiatr A., Ettler V., Mihaljevič M., 2023, Combined approach for assessing metal(loid)s mobility and accumulation in a near-neutral (pH) environment of a former Cu-smelting area in the Old Copper Basin, Poland: when nature is the ‘bad guy’. Applied Geochemistry, 105670. https://doi.org/10.1016/j.apgeochem.2023.105670

Tyszka R., Pietranik A., Kierczak J., Ettler V., Mihaljevič M., Weber J., 2012, Anthropogenic and lithogenic sources of lead in Lower Silesia (Southwest Poland): an isotopic study of soils, basement rocks and anthropogenic materials. Applied Geochemistry, 27, 1089-1100, http://dx.doi.org/10.1016/j.apgeochem.2012.02.034