Lead smelting slags near Nal,Balochistan Province,Pakistan

Samples of slag from three sites of a traditional lead industry located between Khuzdar and Nal were studied to determine their petrology, chemical composition, smelting conditions, source material, and age. Polished thin sections viewed in reflected light revealed a white glassy matrix with occasional rare mineral grains. Using an automated microprobe, typical glass composition was found to be 40% SiO₂, 17% FeO, 11% CaO, 12% PbO, and 10% BaO. Repeated applications of Principal Component Analysis to the data revealed that the compositions of our slags fell within a tetrahedron. The ratios of most components to other components were found to be nearly constant, suggesting that the same indigenous source materials were mixed in almost the same proportion at all the sites. A comparative study of the composition of our slag in relation with various binary and ternary phase diagrams after necessary normalization of the data showed that addition of CaO and BaO by the traditional smelters and the formation of PbO during the process of smelting helped to lower the temperature required for smelting below 1200°C. Lead isotopic compositions suggested that our lead is isotopically distinct from sites in Greece. © 1993 John Wiley & Sons, Inc.