DOUBLE-SPIKE CALIBRATION OF BROKEN HILL STANDARD LEAD

The absolute lead isotope composition of the UBC No. 1 Standard has been estimated with the double-spike measurement technique. Values have been obtained relative to two markedly different spike mixtures, each of which was repeatedly calibrated against the SRM 981 Standard. The two very similar results average at 206Pb/204Pb = 16.003, 206Pb/207Pb = 1.0398, 206Pb/208Pb = 0.4488. These results, which have been thus normalized to the Catanzaro values for SRM 981, must therefore be close to absolutely correct. They are similar in 206Pb/208Pb and 206Pb/ 207Pb to those produced by several other analysts, whose 204Pb measurements appear however to have been in error. An absolute ore-lead growth curve has been calculated using appropriate corrections to ore-lead values which had been intercompared with UBC No. 1, along with Oversby's primeval meteoritic lead values, by employing the curve-fitting procedure of Russell and Reynolds (1965). The new parameters are a = 18.322, b = 15.622, μ = 8.79, to = 4.58 × 109y. The adjusted curve allows some re-interpretation of other data. © 1969.