Uranium distribution and 234U/238U activity ratios in a sedimentary bauxite deposit, from Yangwa mine, China, and its implication for sedimentation process.

Abstract

Concentrationsof 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, A1203 and Fe203, was observed. A1203 has a distinct correlation with Ti, Cr, U and V, while Fe203 correlated with Mn, Ca and Cu. Cr, V and U were enriched in the deposit compared with crustal abundance, while Si02, MnO, MgO, CaO, Na20, Cu, Sr and Ba were depleted. In phase extraction experiments, the Fe, Mn, Mg, Ca, and Sr were predominantly in the "HC1 soluble fraction".With one exception, most of the U in the bauxite was in the "HF soluble fraction" ( 60%), and -r 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 Fe203, which suggests relatively oxidative sedimentary condition. The clay minerals, fine-grained materials originated from Pre-Cambrian base ment 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 H4Si04. 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.

Geochemical micro-behavior of natural U-series nuclides in granitic conglomerate from the Tono mine, central Japan.

“…It is applied to the study of soils, clay minerals, sediments, etc., and con tains various methodologies depending on the subjects and objectives. We have applied this technique to the sediments and elucidated the sedimentary environments by using some trace elements (for example, Kanai, 1986aKanai, , 1992Kanai, , 1994Kanai et al, 1990a). Although this technique provides important information about the phase and existing elements, only a few studies con cerning uranium ore deposit are reported, for ex ample, by Lowson et al (1986) and Yanase et al (1991).…”