Uranium Deposits in the Oguni-Kanamaru District on the Border of Niigata and Yamagata Prefectures

Abstract

In recent years, some uranium deposits of sedimentary type have been found in the Neogene Tertiary sediments of the Uetsu massif region, Northeast Japan. Most of them occur in the basal part of the Tsugawa formation of middle Miocene age.
The Tsugawa formation is rich in muddy facies in the eastern part of the distribution area, whereas it is so in sandy and/or conglomeratic facies in the western part along the coast of the Japan Sea. In the Oguni-Kanamaru district, this formation involves conglomeratic or sandy facies in the lower and middle parts, and muddy facies in the upper.
A tabular uranium deposit is found in arkose of the Tsugawa formation of the Oguni-Kanamaru district. Genetically this may belong to the "water table type", judging from the modes of occurrence, the texture of ores, and other geologic features.