Background
The provenance of ancient raw materials for the production of metal artifacts are commonly investigated with isotope geochemistry, i. e. the chemical behaviour of atoms of the same element with different masses. The underlying assumtion of this approach is the identical behaviour of all isotopes of the same element during the metallurgical processes, especially during smelting. For stable copper isotopes, previous laboratory scale experiments and data from the literature indicate that this might not be the case and fractionation of the copper isotopes occurs. Verification is still pending for prehistoric smelting processes, although this would have strong implications for the applicability of stable copper isotopes in archaeometallurgical research.
Aim and structure
The DFG-funded project of Prof. Dr. Sabine Klein and me from the Deutsches Bergbau-Museum Bochum aims to establish the first systematical approach to copper isotope fractionation during smelting. In order to reach this goal, the project is split in three parts.
During the first part, smelting experiments with malachite and sulfidic ores will be conducted together with Dr. Michael Herdick and Erica Hanning from the RGZM and an international group of volunteers. The Experiments will take place at the Laboratory for Experimental Archaeology in Mayen, which is part of the RGZM’s competence field “Experimental Archaeology”. Sulfide ores will be smelted in furnaces according to the reconstructed Bronze Age smelting technologies of the Mitterberg area (Eastern Alps, Austria). Additionally malachite will be reduced to copper in crucibles placed in fire pits.
In the second part, all raw materials and the materials obtained in the experiments will be analysed for their copper isotope composition, their chemical composition, and the mineralogical phases in order to quantify the partitioning of copper and changes in the copper isotope composition.
In the final part of the project, the observations made during the experiments and the analytical data will be combined in a mass balance model. This model does not only allow to quantify the flux of copper and the copper isotope fractionation but will also allow to identify which processes are particularly prone for copper isotope fractionation. Based on these results, the potential of copper isotopes for archaeometallurgical research can be estimated.
Results
The smelting experiments (see our blog) were successful in creating a series of materials with detailed information about the conditions under which they were created. They can serve as reference series for future research.
Out of four smelting experiments, two were sampled, resulting in about 100 copper isotope data and a large amount of data from other analytical techniques. We were able to show that copper isotopes do not fractionationate significantly between ore and metal. However, the copper isotope composition of the ore might be altered during smelting by the impact of external materials (fuel, flux) and if a high concentration of copper remained in the slag, including the mechanical extraction of copper prills from the slag. The copper isotope composition of the metal might also be decoupled from the ore’s signature of such slag is reworked in later times.
Involved institutions
Funded by
Publications
- Rose T, Hanning EK, Klein S (2019) DBM @ RGZM: Experimente zur prähistorischen Kupferverhüttung im Labor für Experimentelle Archäologie. Archäologie Schweiz 42:44–45.
- Rose T, Hanning EK, Klein S (2019) Verhüttungsexperimente mit Chalkopyrit-Erz nach Vorbildern aus dem bronzezeitlichen Ostalpenraum und Nepal. Experimentelle Archäologie in Europa 18:47–60. https://doi.org/10.23689/fidgeo-3706
- Klein S, Rose T (2020) Evaluating copper isotope fractionation in the metallurgical operational chain: An experimental approach. Archaeometry 62:134–155. https://doi.org/10.1111/arcm.12564
- Rose T, Klein S, Hanning EK (2020) Copper isotope fractionation during prehistoric smelting of copper sulfides: experimental and analytical data. GFZ Data Services. https://doi.org/10.5880/fidgeo.2020.013
- Rose T, Hanning EK, Klein S (2020) Smelting Experiments with Chalcopyrite Ore based on Evidence from the Eastern Alps. Metalla 25:77–100.
Presentations
- Rose T, Hanning EK, Herdick M, Klein S (2018) Archaeological Smelting Experiments for Evaluating Copper Isotope Fractionation During Smelting. Young Researchers in Archaeometry 2, Berlin.
- Rose T, Hanning EK, Herdick M, Klein S (2018) Archaeological smelting experiments as a foundation for the development of stable metal isotope applications in archaeology. EXAR-Tagung 2018, Unteruhldingen.
- Hanning EK, Rose T, Klein S (2019) Reconstruction and Innovation: Experimental Archaeology in Interpreting Copper Smelting Processes. Experimental Archaeology Conference 11, Trento.
- Rose T, Klein S, Hanning EK (2019) Evaluation of copper isotope fractionation during chalcopyrite smelting. Archaeometallurgy in Europe, Miskolc.
- Rose T, Klein S, Hanning EK (2019) Copper isotopes in prehistoric copper smelting: Linking experimental and analytical approaches. Young Researchers in Archaeometry 3, Nanterre.
- Rose T, Klein S (2020) Copper isotope fractionation during prehistoric copper smelting: Evidence from archaeological smelting experiments. 26th Annual Meeting of the European Association of the Archaeologists (EAA), online.
- Hanning EK, Rose T, Klein S (2021) Reconstruction of Copper Smelting Processes: Possibilities and Limitations: (Abstract published in Geo.Alp 17, 2020, 41-42). International Workshop Alpenkupfer im Vinschgau / Alpine Copper in the Vinschgau, online.