Publication date: November 2016Source:Journal of Archaeological Science, Volume 75
Author(s): David Killick, Duncan Miller, Thomas Panganayi Thondhlana, Marcos Martinón-Torres
We report chemical, petrographic and metallographic studies of copper ores and slags recovered during sporadic surface surveys and excavations over the past fifty years in the Phalaborwa and Murchison Range areas of the northern Lowveld of South Africa. The copper slags around Phalaborwa have unusual mineral assemblages, attributable to the unique geochemistry of the main ore body, the Phalaborwa Complex, where copper minerals were mined from a carbonatite composed of magnetite, calcite and apatite. Strongly reducing conditions had to be avoided to minimise contamination of the copper with iron and phosphorus. As the copper ores contain almost no silicates, silica/alumina flux was added to produce slag. The Precambrian zinc-copper ores of the Murchison Range were also smelted, but during smelting any zinc that was not volatilised was taken up by minerals in the slag, so brass was not produced.