Smelting of magnetite and magnetite-ilmenite iron ores in the northern Lowveld, South Africa, ca. 1000 CE to ca. 1880 CE

The Lowveld of north-eastern South Africa is poorly suited to agriculture or pastoralism but is rich in mineral resources. There is much evidence of exploitation of the copper, iron and salt resources of this region during the second millennium CE. The bloomery iron smelting technologies of this region show several unusual features: (1) all known smelting sites used almost pure oxide ores, requiring the addition of silicate flux to produce slag; (2) some used magnetite-ilmenite ores that produced slags containing up to 25 mass % TiO2; and (3) iron ore was carried substantial distances to smelting sites. Modern blast furnaces cannot use iron ores containing more than 2% TiO2, but in the bloomery process TiO2 combines with iron oxides and silica to produce highly fluid slags that separate cleanly from iron metal. This allowed ancient ironworkers to process a much wider range of iron ores than modern industry can use. The archaeological significance of this study is that we show that the geological source of ore used at any smelting site in the Lowveld can be determined by chemical analysis or thin-section microscopy of the slag. This will allow archaeologists to include iron production in future network analyses of past regional economic interaction in this region.