Lead isotope data on three North Australian galena localities

Gas-source intercomparison data from three Precambrian locations, reproducing to within 0.1 to 0.2 percent in each ratio at the 95 percent level, have been normalized through the Broken Hill standard to the NBS lead, SRM 981. The bedded Pb-Zn deposits at Mount Isa and McArthur River show the marked isotopic uniformity long associated with major stratiform deposits. At Mount Isa this uniformity extends meridionally for at least 35 km, and over the full depth of the host formation. It encompasses samples of fault-fill sulphides within the mine area, thus emphasizing the dominance of the ore lead during subsequent remobilization. At McArthur River there is strong evidence that veins cutting the adjacent formations comprise a mixture of ore Pb with material of different provenance; the evidence for comparable mixtures at Mount Isa is not strong. At the intervening Law Hill field, the Pb in vein deposits is similar to the more extreme of the McArthur River vein leads. This could possibly indicate a geochemical and age similarity between the source rocks in these two widely-separated areas.