Abstract
IF the isotopic ratios [206Pb/204Pb]0, [207Pb/204Pb]0, and [208Pb/204Pb]0 of primeval lead are known, the time t of formation of ore of lead (the present time = 0) and the present-day atomic ratios [238U/204Pb] and [232Th/204Pb] which would be observed in the original source of lead in ores can be estimated1,2 from the measured isotopic ratios [206Pb/204Pb], [207Pb/204Pb] and [208Pb/204Pb] by: where λ232, λ238 and λ235 are the decay constants of thorium-232 (0.499 × 10−10/yr.), uranium-238 (1.54 × 10−10/yr.) and uranium-235 (9.78 × 10−10/yr.), 138 the isotopic ratio of uranium-238 to uranium-235 at present, and T0 the age of the Earth (4.55 × 109 yr.). However, no attempt has been made to use these equations in order to determine the relationship, so far as distribution is concerned, of thorium, uranium and lead.
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MASUDA, A. Relative Distribution of Thorium, Uranium and Lead estimated from the Isotopic Composition of Lead in Ores. Nature 203, 1062 (1964). https://doi.org/10.1038/2031062a0
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DOI: https://doi.org/10.1038/2031062a0
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