Tin and Bronze Production in the Iron Age of Southern Africa

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The Rooiberg valley in northwest South Africa, close to its border with Botswana, is notable for its abandoned prehistoric tin mines and associated furnaces for smelting tin, and for alloying tin with copper to make bronze. When tin mining was restarted here in the early 1900's, mining engineers estimated prehistoric production at about 2000 tons of tin metal. These are the only known instances of tin or bronze production in southern Africa, but after a century of unsystematic research at Rooiberg, basic questions remain unanswered. When did tin mining begin here, and why? When did it end, and why? And what happened to the large quantities of tin produced here? With National Science Foundation support, a team of American, British, South African and Zimbabwean researchers will begin to study these questions through one field season of excavations in 2006. This will be followed by a year of intensive scientific analysis of the excavated remains, and of related materials from prior excavations and museum collections in both South Africa and Zimbabwe. The fieldwork will concentrate upon locating and excavating smelting sites. We anticipate that the earliest evidence of tin production can be dated by radiocarbon. We do however expect that the peak of smelting activity was from the 17th through the early 19th centuries CE, a period in which radiocarbon dating is unusable. Sites in this period will be dated by optically-stimulated luminescence, backed up by the use of archaeomagnetism as a relative dating technique.The technology of tin and bronze production in the Rooiberg valley will be reconstructed by chemical analysis, metallography and thin-section petrography of the excavated remains. Since it is certain that the large quantity of tin mined here was not consumed in the Rooiberg area (which appears to have been lightly populated throughout the presumed time period of production) a major aim of this project is to develop trace element and isotopic fingerprints for tin and bronze produced from Rooiberg tin and copper ores. We will measure the concentrations of trace elements in excavated tin and bronze by plasma mass spectrometry, and the ratios of stable lead isotopes by high-precision multicollector plasma mass spectrometry. The final stage of the project will be to compare the trace element fingerprints for Rooiberg tin and bronze to those of tin and bronze objects from archaeological sites elsewhere in south Africa, Botswana and Zimbabwe, and to tin produced from other potential ores in southern Africa. The archaeological finds range in age from the 13th through the 19th centuries CE, while the find spots are up to 700 km distant from Rooiberg. Thus the main aim of the project is to document the emergence of an indigenous southern African industry and the extent of the trade network through which its products passed. The project will provide valuable postdoctoral training for a Zimbabwean archaeological scientists and predoctoral training for at least three graduate students from South Africa and one from America.