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

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

Isotope chemistry is commonly used in archaeometry to provenance the ancient raw material used for the production of metal objects. The fundamental assumption for this approach is the absence of isotope reactions during the smelting process to produce metal from ores. The project aims to understand smelting processes and their influence on the isotope chemistry of archaeological copper objects. In a former project, this question was investigated by small-scale crucible smelting. The current project continues this work with outdoor experiments including the construction of a roasting bed and a furnace. Clean room laboratory work will evaluate isotope changes and a mass balance model will allow more general conclusions about the behaviour of copper isotopes during smelting.

The DFG-funded project aims to establish the first systematic approach to Cu isotope fractionation during the smelting and refining process. Based on previously obtained data from laboratory scale experimentswith malachite, the potential of Cu isotopes as a tool in archaeometallurgical research will be systematically evaluated and potential areas of application of the method will be identified. To reach this goal, the project will be split in three parts. The first part consists of smelting experiments at the Laboratory for Experimental Archaeology (LEA) in Mayen, part of the competence field “Experimental Archaeology” at the Römisch-Germanisches Zentralmuseum, Archaeological Research Institute (RGZM), Mainz. Because all sources and sinks of Cu shall be recorded quantitatively, material from published smelting experiments cannot be used due to the lack of documentation and/or material. In the second part, the obtained material will be analysed by ICP-MS, MC-ICP-MS, and XRD, in order to identify the chemical composition, the copper isotope composition, and mineralogical phases to quantify the partition of Cu and changes in Cu isotope composition. In the final step, the observations made during the experiments and the analyses are combined to establish a mass balance model. This model will not only describe the flux of Cu and the fractionation of copper isotopes during the experiments but for the first time will allow the deduction of fractionation factors for Cu isotopes throughout the whole operational chain and the establishment of fractionation factors between silicates (slag), Cu metal, and Cu ores.


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