Abstract
The Ningyo-Toge uranium deposit is one of the typical sedimentary uranium deposits in Japan. In general, during weathering, U is removed from the basal granite through underground water. The underground water in this area is rich in U, and has a comparatively high concentration of Fe and Mn. In this area, three types of Fe minerals can be recognized in different modes of occurrence: (1) in the oxide zone brownish Fe-hydroxide mineral with ferric ion, i.e. goethite (α-FeOOH); (2) in the reduced zone of the mine gallery pale-blue Fe-hydroxide mineral with some ferrous ion, i.e. lepidocrocite (γ-FeOOH); and (3) Fe-sulphate minerals such as melanterite (FeSO 4·7H 2O), etc. Some uranyl sulphate minerals, uranopilite and zippeite, are closely associated with these Fe-sulphate minerals. Under weakly alkaline conditions of the oxidizing environment, Mn-hydroxide (MnOOH) coexists with goethite as alternative thin laminae with shale, or coprecipitates resembling a marine Mn nodule, in the size of ∼0.5 cm in diameter. Radioactive anomalies have been recognized frequently for these Mn sediments due to absorption of Ra by the sediments.
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