URANIUM DISTRIBUTION IN MINERAL PHASES OF ROCK BY SEQUENTIAL EXTRACTION PROCEDURE

A sequntial extraction procedure was used to study the distribution of uranium in mineral phases of rock at the Koongarra uranium deposit (Northern Territory of Australia). This work forms a part of the natural analogue study carried out in the International Alligator Rivers Analogue Project, which is being sponsored by the OECD/NEA. The following mineral phases: adsorbed trace material and carbonate minerals, amorphous iron minerals and secondary uranium minerals, crystalline iron minerals, clay minerals, and remaining resistant mineral phases, were extracted successively by treatment with: 1 M sodium acetate (pH = 5) (Morgan's solution), Tamm's acid oxalate (TAO) (pH = 3), citrate-dithionitebicarbonate (CDB), 6 M hydrochloric acid, and fusion respectively. The majority of uranium in samples from the secondary ore body at Koongarra was contained in crystalline iron minerals (42-60%). In the primary ore body, the uranium distribution between mineral phases varies with depth. About 70% of the total uranium was incorporated with the Tamm's extractable mineral phases, in the weathered region of the drill hole DDH1 (19.4-20.5 m). In the deeper region of the drill hole DDH2 (33.0-34.3 m), most of the uranium was extractable with 6 M HCl. The U-234/U-238 activity ratios in each extraction are discussed on the basis of the alpha recoil effect, which occurs with the decay of U-238 through Th-234 to U-234.