Fixation of radionuclides in the 238U decay series in the vicinity of mineralized zones: 1. The Austatom Uranium Prospect,Northern Territory,Australia |
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| Authors: | PJ Shirvington |
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| Institution: | AAEC Research Establishment, Lucas Heights, NSW, Australia |
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| Abstract: | The minimum age of a zone of secondary uranium mineralization, located at the Austatom Prospect in the Alligator Rivers region of Australia, is estimated to be 3.6 × 105y. This is derived from a geochronological model based on retarded leaching of 234U with respect to 238U and on ratios within the ore of these members of the 238U decay series. Although kaolinite is a dominant mineral in the weathered schist-host-rocks, retarded dissolution of 234U occurs only in the presence of the clay minerals illite and montmorillonite. In their absence the reverse occurs. A model is proposed to explain the results. Ratios of 230Th to 238U indicate that the mineralization has probably remained stationary within the weathered schist for at least 1 to 2 × 105y. Future use of clay minerals as buffers in radioactive waste repositories is supported by the excellent long-term retention obtained for oxidized uranium, probably due in part to isomorphic substitution into the clay crystal lattice. |
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