Cu isotope fractionation during prehistoric smelting - A contribution of modern pyrometallurgy

Today the advanced development of tools and methods in archaeometallurgy enables a more accurate reconstruction and understanding of ancient smelting techniques. Especially pyrometallurgical experiments allow the establishment of secure links between ores and their respective smelting products. As copper was the first metal to be smelted from ore, interest in copper metallurgy has dominated the field of archaeometallurgy from its beginning. The aim of this contribution is to fuel the research on copper isotope fractionation during the smelting process. To analyse the fractionation behaviour seven smelting experiments with malachite were carried out in a small induction furnace and different portions of the melt were extracted from the crucible during the process. Our results show a significant fractionation of copper isotopes during the smelting process. As predicted by the stable isotope fractionation theory, the lighter isotope is enriched in the metallic melt. Although no significant differences between ore and metal were measured, the sole appearance of fractionation questions the direct link between both. Therefore existing applications of copper isotopes in archaeometallurgy must be re-evaluated for their suitability.