Abstract
Uranium (U) concentration and the activities of 238U, 234U, and 230Th were determined for groundwaters, spring waters, and lake water collected from the Shihongtan sandstone-hosted U ore district and in the surrounding area, NW China. The results show that the groundwaters from the oxidizing aquifer with high dissolved oxygen concentration (O2) and oxidation-reduction potential (Eh) are enriched in U. The high U concentration of groundwaters may be due to the interaction between these oxidizing groundwaters and U ore bodies, which would result in U that is not in secular equilibrium. Uranium is re-precipitated as uraninite on weathered surfaces and organic material, forming localized ore bodies in the sandstone-hosted aquifer. The 234U/238U, 230Th/234U, and 230Th/238U activity ratios (ARs) for most water samples show obvious deviations from secular equilibrium (0.27–2.86), indicating the presence of water-rock/ore interactions during the last 1.7 Ma and probably longer. The 234U/238U AR generally increases with decreasing U concentrations in the groundwaters, suggesting that mixing of two water sources may occur in the aquifer. This is consistent with the fact that most of the U ore bodies in the deposit have a tabular shape originati from mixing between a relatively saline fluid and a more rapidly flowing U-bearing meteoric water.
Highlights
Bulk dissolution of most rocks >1 Ma that have not experienced recent water-rock interactions yield dissolved uranium (U) with a 234 U/238 U activity ratio (AR) near 1 [1,2,3,4,5,6,7]
The U concentrations are obviously higher than in unmineralized where Uin concentrations the groundwaters typically less than and300 m is Allthat analytical data areareas presented
The solubility of U in the groundwaters is very sensitive to changes in redox conditions
Summary
Bulk dissolution of most rocks >1 Ma that have not experienced recent water-rock interactions yield dissolved uranium (U) with a 234 U/238 U activity ratio (AR) near 1 [1,2,3,4,5,6,7]. 234 U, radiation-induced oxidation of 234 U, and preferential leaching of 234 U from the α-recoil tracks [8]. The. U concentration and 234 U/238 U AR along a groundwater flow path depends on the balance between factors such as pH, oxidation potential, partial pressure of CO2 , mineral dissolution, aquifer rock composition, flow-path length, and ground-water flux [3]. Uranium-series disequilibrium data from groundwater can give information concerning recent migration history of radionuclide and geochemical conditions associated with water-rock interaction [11,12]. From a dating point of view, the method covers the time period extending back over the last 1.7 million years, which is interesting for paleohydrogeological research [13,14]
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