Isotopic analyses of leads from Broken Hill, Australia with spectrographic analyses

This paper presents the results of isotopic analyses of 25 leads extracted from galenas from Broken Hill, New South Wales, Australia, and analysed at the University of Toronto. Some of the galenas occurred in conformable ore deposits of the Broken Hill type and some occurred in weak, gently dipping fractures and are of the Thackaringa type. We interpret the isotopic analyses as indicating that the conformable ores are ordinary leads and the Thackaringa ores are anomalous leads, that the probable age of the ordinary leads is about 1500 ± 150 m y, that the Thackaringa leads were derived from the conformable ores in a process that involved the addition of anomalous proportions of radiogenic lead from the country rocks, and that the addition of the anomalous radiogenic component occurred a few hundred million years after the time of formation of the conformable ores. Qualitative spectographic analyses of some of the ores were carried out at Queen's University, Ontario, and are included in the paper. Most significant is the fact that the anomalous leads are distinguishable from the ordinary leads on the basis of trace element content. The significance of the spectrochemical analyses is discussed.