Published in: CEN Technical Journal, volume 9, number 1, pp. 71–92, 1995.

© 1995 Answers in Genesis A. C. N. 010 120 304. All Rights Reserved.

Abstract

As with other radiometric “dating” methods, the U-Pb and Pb-Pb isochron methods have been questioned in the open literature, because often an excellent line of best fit between ratios obtained from a set of good cogenetic samples gives a resultant “isochron” and yields a derived “age” that has no geological meaning. At the Koongarra uranium deposit, Australia, there is ample evidence of open system behavior, or repeated migration, of U and Pb—ore textures, mineral chemistry, supergene alteration, uranium/daughter disequilibrium, and groundwater and soil geochemistry. Yet U-Th-Pb isotopic studies of the uranium ore, host rocks, and soils have produced an array of false “isochrons” that yield “ages” which are geologically meaningless. Even a claimed near-concordant U-Pb “age” of 862 Ma (million years) on one uraninite grain is identical to a false Pb-Pb isochron “age,” but neither can be connected to any geological event. The open system behavior of the U-Th-Pb system is clearly the norm, as is the resultant mixing of radiogenic Pb with “common” or background Pb, even in soils in the surrounding region, apparently even up to 17 km away! Because no geologically meaningful results can be interpreted from the U-Th-Pb data at Koongarra (three uraninite grains even yield a ²³²Th/²⁰⁸Pb “age” of 0 Ma), serious questions must be asked about the validity of the fundamental/foundational basis of the U-Th-Pb “dating” method. This makes the task of creationists building their model for the geological record much easier, since claims of U-Th-Pb radiometric “dating” having “proven” the claimed great antiquity of the earth, its strata and fossils can be justifiably ignored.

Keywords

Radiometric Dating, U-Pb and Pb-Pb Isochron Methods, Koongarra, Uranium Deposit, Open-System Behavior, Ore Textures, Mineral Chemistry, Supergene Alteration, Uranium-Daughter Disequilibrium, Groundwater and Soil Geochemistry, Uraninites, Galenas, False Isochrons, Mixing, Zero “Ages”

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