ABSTRACT

Uranium deposit samples were radiochemically separated for thorium, protactinium and uranium and each fraction was submitted to alpha ray spectrometry for the determination of ²³⁸U, ²³⁴U, ²³²Pa, ²³²Th and ²³⁰Th. In an ore body of Ningyo-Toge Mine, Okayama, Japan, the relationship between the uranium isotopes and their daughter nuclides indicates an extensive migration of uranium. The migration was also verified by the high radium and protactinium contents of a manganese nodule sample. The thorium-bearing samples in a neighboring district were also analyzed to elucidate the origin of these uranium deposits. The ages of two secondary uranium minerals in Tono district, Gifu, were estimated to be 5×10³ y and 34×10³ y. on the basis of their isotopic compositions. For the radioactive phosphate samples in Noto district, Ishikawa, secondary enrichment of uranium by phosphate was confirmed with their isotopic compositions and their phosphate contents.