Provenancing Central African copper croisettes: A first chemical and lead isotope characterisation of currencies in Central and Southern Africa

The Copperbelt is one of the richest copper deposits in the world and has been an important primary metal source for Central African cultures for over a millennium. The technology underlying this exploitation and the trade networks through which copper was exchanged, however, have not yet received much attention in archaeological research. This paper presents the first geochemical dataset for archaeological copper currencies in Central and Southern Africa: croisette ingots. Chemical and lead isotope analysis have been carried out for 45 precolonial copper artefacts with the aim of illuminating their provenance and production technology. The results show that highly pure copper with very low trace element content was produced, indicating the selection, beneficiation and smelting of specific Copperbelt ores. The variable croisette compositions and shapes reflected in burial assemblages support their suggested use as currencies over a large area. This study offers a highly novel contribution to provenance research in Central and Southern Africa, shedding new light on the broader trade networks associated with copper provisioning in these regions. The exploitation of a range of ore sources throughout the 2nd millennium CE has been identified, with a marked shift around the mid-15th century CE largely correlating to croisette typologies. Furthermore, these different geochemical copper signatures can be tentatively related to different Copperbelt zones. Combining these results with archaeological and historical evidence for regional copper production and consumption, this study provides a framework for the future study of copper production and exchange systems in the wider Central and Southern African region.