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U-234/U-238 signatures associated with uranium ore bodies: part 3 Koongarra

Authors
  • Lowson, R T
Publication Date
Apr 01, 2013
Identifiers
DOI: 10.1016/j.jenvrad.2012.10.004
OAI: oai:apo-prod.ansto.gov.au:10238/5698
Source
ANSTO Publications Online
Keywords
Language
English
License
Unknown
External links

Abstract

The Koongarra ore body is an early Proterozoic U ore body in the Alligator Rivers U province, Northern Territory, Australia. It has surface expression with a redox front located similar to 30 m below the surface. The U-234/U-238 activity ratios (AR) for the ground water and the amorphous phase of the solid have been analysed for the ore zone and dispersion halo as a function of depth. The results display a U-234/U-238 AR signature with depth which may be common to all U ore bodies. The U-234/U-238 AR is depressed below secular equilibrium in the weathered material above the redox front; rises significantly above secular equilibrium in the vicinity of the redox front; and is followed by a gradual decrease with depth below the redox front. The amplitude of the profile is a function of local conditions. A model is proposed for the signature in which oxidising waters preferentially leach the U-234 sites at the redox front due to preconditioning of the U-234 sites by a recoil during the decay of U-238 to U-234. Mass balance requires the solid material left behind the redox front to have a U-234/U-238 AR reduced below I. Local second order effects may be superimposed on the signature. The signature may have application to calibrating scenarios for nuclear waste repositories, assisting in understanding historical climates, economic evaluation of U ore bodies and U exploration. © 2013, Elsevier Ltd.

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