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Of all of the metals, only lead, displays natural variations among mining districts in the relative abundances of its stable (non-radioactive) isotopes. The abundances of the four stable isotopes are commonly expressed as 206/204, 206/207, and 206/208 atomic ratios, is usually determined by mass spectrometry. Precisions of 0.5% for 206/204 and even better for the other pairs are obtainable.
The three ratios covary strongly and depend on when the ore was formed. Older, Precambrian ores such as from Coer d'Alene, Idaho have 206/204 near 16. More recent ores, such as in Missouri, have ratios above 20. These variations provide a tracer for following a particular batch of lead.
A major limitations to this method is that it is useful to only those problems where the potential sources are few in number and isotopically distinct. Several examples are offered where this method has been successfully employed in the fields of archeology, environmental pollution, childhood lead poisoning, and biokinetic modeling of bone lead.
Lead, stable isotopes, mass spectrometry, isotope tracer, isotopic composition, ore, paint, mass fractionation
Associate Scientist, Marine Biological Laboratory, Woods Hole, MA