Evaluating copper isotope fractionation in the metallurgical operational chain: an experimental approach

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Until today information about archaeological copper objects and linkage to their ores is mainly gained from impurities in the metal (e. g. lead). Only rarely the copper itself was characterised geochemically by using both stable copper isotopes 63Cu and 65Cu. This is routed in the lack of systematic studies analysing their isotopic fractionation during the smelting of copper ores. Without this knowledge, a reliable link between ore and metal cannot be established. In contrast to lead isotopes a considerable fractionation can be expected. This is particularly true for the roasting of sulphidic copper ores and the subsequent separation of the copper sulphides and oxides during smelting. However, past studies were limited to the smelting of pure malachite and do not represent the full spectrum. The submitted project aims to establish the first systematic approach to Cu isotope fractionation during the smelting process. To reach this goal, smelting experiments with copper sulphides will be conducted in accordance with archaeological evidence from the Mitterberg region. Additionally based on early metallurgical findings from the Ancient Near East oxide copper ore will be smelted in crucibles. The materials obtained from the experiments will be analysed for their copper isotopes. Based on the combination of analytical results and the data obtained during the experiments (e. g. temperatures) a mass balance model will be established. This model will allow calculation of the copper isotope fractionation during the smelting process, to establish a profound scientific base for the existing archaeometallurgical application of copper isotopes and perhaps to identify new applications.