Pb isotopic ratios are present-day values, corrected for fractionation using the NBS 981 standard values of Todt et al. (1984); the total ranges measured for NBS 981 are +0.008 for 206Pb/2O4Pb, ±0.008 for 207Pb/204Pb, and ±0.030 for 208Pb/2O4Pb. Within-run uncertainties (2 sigma m) on the isotopic data above are generally less than these values, and in all cases less than ±0.012, ±0.012, and ±0.038. Estimated uncertainty on Pb abundances is <l %. Total procedural blanks are negligible at 5-30 picograms.
