ABSTRACT

Concentrations of uranium and other elements in bauxite deposit from Yangwa mine at Jiaozuo area in Henan Province, China, were determined, and geochemical behavior of ²³⁴U and sedimentation process were studied by leaching experiments. An inverse correlation between two major components, Al₂O₃ and Fe₂O₃, was observed. Al₂O₃ has a distinct correlation with Ti, Cr, U and V, while Fe₂O₃ correlated with Mn, Ca and Cu. Cr, V and U were enriched in the deposit compared with crustal abundance, while SiO₂, MnO, MgO, CaO, Na₂O, Cu, Sr and Ba were depleted. In phase extraction experiments, the Fe, Mn, Mg, Ca, and Sr were predominantly in the “HCl soluble fraction”. With one exception, most of the U in the bauxite was in the “HF soluble fraction” (∼60%), and ∼30% of the U was in the “resistate fraction”. The ²³⁴U/²³⁸U activity ratios in these fractions were less than unity, and have a good correlation with the fractional U content. This relation suggests that ²³⁴U was leached out from the surface of the U-containing mineral grains. In comparison, the activity ratios of HCl soluble U were more than unity, and are inversely correlated with the fractional U contents. This suggests that an almost constant amount of mobile ²³⁴U was present in the deposits. The principal bauxite ore body could be thought to be sedimentary in origin: A terra rossa was formed on the karstic Ordovician limestone. It was rich in Fe₂O₃, which suggests relatively oxidative sedimentary condition. The clay minerals, fine-grained materials originated from Pre-Cambrian basement were then transported and deposited repeatedly on the terra rossa. The deposition of the clay minerals changed the sink from oxidative to reducing condition, favoring for the deposition of U. The original clay minerals in the bauxite deposit were kaolinite and gibbsite. As the reversible change from kaolinite to gibbsite depends on the H₄SiO₄ concentration, the alteration degree of gibbsite might have been controlled by the movement of H₄SiO₄. ²³⁴U was estimated to have been ejected from the surface of U-containing minerals and migrated through the ore deposits, then adsorbed by iron hydroxides at the bottom of the ore body.