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Uranium-Lead Radiometric Age Determinations of Naturally Occurring U(VI) Minerals: Application to Radwaste Storage

Published online by Cambridge University Press:  15 February 2011

Douglas G. Brookins
Douglas G. Brookins*
Affiliation:
Department of Geology, University of New Mexico, Albuquerque, NM 87131
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Abstract

U(VI) bearing species are commonly formed under oxidizing laboratory rock-water-HLW experimental conditions. The experimental stability of artificially produced Na-Cs-Rb weeksite (alkali uranyl hydrosilicate), and other U(VI) species, is uncertain. Naturally occurring U(VI) bearing minerals (uranophane and tyuyamutrite) from the Grants mineral belt, New Mexico, have been studied for their U-Pb systematics as natural analogs to these experimentally produced phases. Samples from highly oxidized rocks and from chemically reducing environments have been studied. The samples from oxidized rocks are mixed with hematite-barite-gypsum-calcite gangue and are close to, but not in contact with, pyritiferous-organic carbon-uraniferous (U(NIV))-chloritic are. The reduced rock uranophane yields nearly concordant238U - 206Pb and 235U - 207Pb ages of 8.32 and 8.33 MYBP (millions of years before the present); the oxidized rock uranophane and tyuyam .nite yield more discordant ages (n=8) between 7.4 and 2.7 MYBP. These data argue for long range stability of U(VI)-rich phases in the geologic environment.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 6: Symposium D – Scientific Basis for Nuclear Waste Management IV , 1981 , 265
Copyright
Copyright © Materials Research Society 1982

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References

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