Lead isotopic signatures at the Klein Aub Mine,Namibia — Implications for mineralisation models

Pb and U isotopic data have been obtained for stratabound, sediment-hosted Cu-mineralisation and igneous, volcanic and sedimentary rocks from other stratigraphic levels in the vicinity of the Klein Aub Mine, Namibia, with the aim of investigating possible sources and metal emplacement mechanisms. The results indicate the existence of a pervasive Cu-sulphide mineralisation event, and support metal introduction during a syn-metamorphic (epigenetic) phase. Some indications are also found of another, earlier and possibly syn- or diagenetic, mineralisation event but this aspect requires confirmation by further study. Differences in the degree of radiogenicity of the Pb characterize the various mineralisation styles, the epigenetically mineralised laminite containing Pb of a more radiogenic nature than the other laminites, but also having lower absolute concentrations of Pb and U. A mineralisation age of ca. 600 Ma is indicated but the Pb data can neither confirm nor disprove the conclusions of Borg (1988) and Borg and Maiden (1987) that the basalt of the Doornpoort Formation is a source of the Cu in the Klein Aub deposits.