人形峠地域ウラン鉱床の発見および探査・開発の成果
1964 年 14 巻 63 号 p. 1-10
詳細
1964 年 14 巻 63 号 p. 1-10
The prospecting for nuclear raw material resources in our country was undertaken in 1954 by the Geological Survey of Japan. Based upon the geological consideration, the prospecting operations were carried out in the so-called "massif" region consisting mainly of granites. The first discovery of uranium mineralization in sedimentary rocks was made by a car-borne team towards the end of the year at Ningyô-tôgé in the Chugoku massif, Southwest Japan. It was confirmed by the geological research that the uranium minerals occur in conglomerates and sandstones of the Neogene Tertiary unconformably overlying the granites.
The task of detailed survey for economic development was handed over to the Atomic Fuel Corporation which was established in 1956. The Corporation proceeded to trenching, geophysical and geochemical prospecting, drilling and tunnelling. As the result of these operations, three million tons of the ore reserves containing two thousands tons of uranium metal have been recognized.
The uranium ores of Ningyô-tôgé are soft and porous, and the uranium minerals occurring as finegrained crystals in the matrix are easily soluble in acid. Such characteristice of the ore enable 1) to raise their grade several times as high by washing and screening, 2) to exploit by the hydraulic method and 3) to extract the uranium under the mild condition. Furthermore, it must be noted that there are almost no minerals containing elements which interfere with the refining process or possess high cross-section for neutron absorption.
