Fig. 6

Schematic presentation of Pb–Pb isotopic data processed assuming low blank and high blank. Small ellipse corresponds to the blank assumed during data reduction: of 0.05 pg with 28% uncertainty, large ellipse—to the blank of 2 pg with the same relative uncertainty. Green arrow shows a mixing line between radiogenic Pb and the blank. Red arrow shows the direction toward primordial Pb, which is assumed to represent initial Pb in the sample. Semi-transparent red vertical bars on the y-axis represent projections of the ellipses from the point of primordial Pb, i.e., the ²⁰⁷Pb*/²⁰⁶Pb* dates and their uncertainties calculated assuming blanks of 0.05 pg and 2 pg, respectively