Uranium isotope disequilibria as a function of mineral phase in the vicinity of a uranium body

A method has been developed for the chemical separation of the principal phases in soil sampled from the vicinity of the Ranger No. 1 uranium orebody, in the Alligator Rivers region of the Northern Territory of Australia. The principal phases are identified as amorphous iron oxide, crystalline iron oxide and resistate. The distribution of 238U and its decay products among the phases is determined. The isotopic distribution indicates that the phases are, to a certain extent, acting independently. The amorphous iron phase is considered to be a record of local and temporal abnormalities in the total ground water/soil system. The crystalline iron oxide phase involves a chemical control process, the kinetics of which are commensurate with or less than the half-life of 230Th (7.52 x 104 y). The changes in isotope concentrations with radioactive decay in the resistate phase are interpreted in terms of a net flux of material entering or leaving the phase over the period of the decay process. In one of the models, the flux can be interpreted as a direct measure of the transport of uranium through a 'quartz-clay' crystal grain. (author)