Abstract

Single filament whole rock lead isotope analyses were corrected for fractionation by using an internal standard (double spike). An estimated standard deviation of 0.15% was obtained for lead isotope ratios and 0.25% for lead and uranium concentrations. These are some of the first analyses of this accuracy for lead isotopes in whole rocks. Lead and uranium analyses from the Vogt–Hobbs area near Lake Timagami, Ontario and from the Rice Lake – Beresford Lake area, Manitoba gave ages with the pattern lead–lead age > uranium 235 – lead 207 age > uranium 238 – lead 206 age. This pattern was interpreted as arising from loss of lead from the systems studied. A similar three-stage history, marked by major events prior to 3000 m.y. ago and at approximately 2600 m.y. ago, fits both of these suites. This history is shown to be consistent with rubidium–strontium data, zircon uranium–lead ages, potassium–argon, and ore lead data.

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