Copper ore analyses reveal deep connections between ancient African civilizations

Jay Stephens (right) collects samples of copper ore. (Image by Jay Stephens, courtesy of the University of Missouri).

An international team of researchers ran chemical and isotopic analyses of copper artifacts from southern Africa and discovered new cultural connections among people living in the region between the 5th and 20th centuries.

In a paper published in the journal Plos One, the researchers explain that people in the area between northern South Africa and the Copperbelt region in central Africa were more connected to one another than scholars previously thought.

“Over the past 20 to 30 years, most archaeologists have framed the archaeological record of southern Africa in a global way with a major focus on its connection to imports coming from the Indian Ocean,” said Jay Stephens, lead author of the study and a post-doctoral fellow at the University of Missouri.

“But it’s also important to recognize the interconnected relationships that existed among the many groups of people living in southern Africa. The data show the interaction between these groups not only involved the movement of goods but also flows of information and the sharing of technological practices that come with that exchange.”

Mining copper ore

For years, scholars debated whether the artifacts analyzed, called rectangular, fishtail and Croisette copper ingots, were made exclusively from copper ore mined in the Copperbelt region or from Zimbabwe’s Magondi Belt. As it turns out, both theories are correct.

“We now have tangible linkages to reconstruct connectivity at various points in time in the archeological record,” Stephens said. “There is a massive history of interconnectivity found throughout the region in areas now known as the countries of Zambia, Zimbabwe and the Democratic Republic of the Congo. This also includes people from the contemporary Ingombe Ilede, Harare, and Musengezi traditions of northern Zimbabwe between at least the 14th and 18th centuries A.D.”

To arrive at these conclusions, Stephens and his colleagues took small samples from 33 copper ingots and analyzed them at the University of Arizona. All samples were carefully selected from archeological samples found in the collections of the Museum of Human Sciences in Harare, Zimbabwe, and the Livingstone Museum in Livingstone, Zambia.

“We didn’t want to impact the display of an object, so we tried to be aware of how museums and institutions would want to interact with the data we collected and share it with the general public,” Stephens said. “We also want our knowledge to be accessible for the individuals in these communities who continue to interact with these objects. Hopefully, some of the skills linked with these analyses can be used by whoever wants to ask similar questions in the future.”

One of the croisette copper ingots analyzed in the study
One of the croisette copper ingots analyzed in the study. (Image by Jay Stephens).

In the researcher’s view, copper ingots are excellent objects for these types of analyses because they often have emblematic shapes that allow archaeologists to identify specific markings and follow changes over different time periods.

“By looking at their changes in shape and morphology over time, we can pair those changes with how technology changed over time,” he said. “This often comes from observing the decorative features produced from the cast object or mould, or other surface attributes found on these objects.”

No previous data

Once the pieces arrived at the University of Arizona lab, the researchers took a small amount of each sample—less than one gram—and dissolved it with specific acids to leave behind a liquid mixture of chemical ions. Then the samples were analyzed for lead isotopes and other chemical elements. One challenge the team encountered was a lack of existing data to match their samples with.

“One part of the project included analyzing hundreds of ore samples from different geological deposits in southern Africa—especially ones mined before the arrival of European colonial forces—to create a robust data set,” Stephens said. “The data can provide a scientific foundation to help back up the inferences and conclusions we make in the study.”

Stephens noted that the data he and his team collected are one of the only remaining tangible links that exist today to those precolonial mines in Africa.

“Unfortunately, large open-pit mines have destroyed a lot of the archaeological sites and broader cultural landscapes around these geological deposits,” he said. “This makes it a challenge to reconstruct the history related to these mines. It’s a concerning development, especially with the global push toward more electric vehicles which use minerals like copper and cobalt found in the Copperbelt.”