Lead isotopic provenance of some coins and other bronze items from an early Swahili site in Ibo Island (northern Mozambique)

Northern Mozambique has traditionally been considered marginal within the Swahili trade of the western Indian Ocean due to the absence of outstanding harbour stone-built towns. However, our research on Ibo island (Quirimbas Archipelago) proves the role played by small coastal villages in the early development of the Indian Ocean trade route. In this paper, we discuss the result of a lead isotope analysis performed on samples of two coins and some fragments of a wire and chain recovered on a Swahili dwelling floor dated to the eleventh/twelfth centuries AD. They were probably cast with copper from mines in present-day Congo-Kinshasa. If so, then they are the most distant findings of copper from these ores to date. Along with other exotica, they point to the Middle Limpopo Valley as their most probable route of arrival in the Quirimbas and insert small local villages such as that on Ibo island within the wider Indian Ocean trade route system