234U238U and 230Th234U activity ratios in mineral phases of a lateritic weathered zone

A selective phase extraction procedure was developed for the identification of the significant phases of a typical deep soil profile sampled in the vicinity of the Ranger No. 1 uranium ore body, Alligator Rivers region, N.T., Australia. The significant phases were identified as amorphous iron oxide, crystalline iron oxide and a clay/quartz resistate. The distribution of ²³⁸U, ²³⁴U, ²³⁰Th and ²²⁶Ra between the phases was measured. The results indicated that the amorphous iron oxide phase is in adsorption/desorption equilibrium with the ground water. The crystalline iron oxide phase contains a chemical control, the kinetics of which are commensurate with or less than the half-life of ²³⁰Th (7.52 × 10⁴ y). The clay/quartz resistate is enriched in ²³⁸U descendants in such a way that they are not readily accessible to the ground water.