A recent study by Dr. Ignacio Montero-Ruiz and his colleagues examined the provenance of ancient copper artifacts discovered on the Island of Ibo off Mozambique's coast. The study, published in Azania: Archaeological Research in Africa, provides new insights into the role small coastal villages played in the early development of the Indian Ocean trade.

For much of the Swahili trade history, the role of northern Mozambique has been considered marginal.

However, in 2016, a test pit dug on the island of Ibo revealed various artifacts linking the area to the wider Swahili trade, including Persian Gulf or Iranian glazed ceramics, a fragment of a soft-stone ware possibly from Iran or Oman, and glass beads traded from India and Central Asia.

Among the finds were also three bronze coins, a chain, and metal fragments. The metal objects were subject to elemental analysis by X-ray fluorescence (XRF) and lead isotope analysis.

The elemental analysis revealed that the coins had a unique elemental composition unlike any other known Swahili coins.

The Ibo coins were made up of an unusually high tin-lead ratio and, unlike Swahili coins, contained no arsenic. The researchers proposed that this may indicate a shift in the source of copper (needed to make bronze) for Swahili coins during the 11th and 12th centuries.

Lead isotope analysis was conducted on two of the coins and a fragment of the coin to determine the geological origin of the copper.

Using a specialized mass spectrometer, the researchers compared the isotope signatures with sources across Africa and Eurasia.

The results showed that none of the metals had originated in the Islamic world, as their alloy composition did not match. Neither were they recycled metal.

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12th-century bronze coins reveal role of Northern Mozambique in Swahili trade history(https://phys.org/news/2025-04-12th-century-bronze-coins-reveal.html#google_vignette)