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To solve the mechanism of uranium concentration in stratabound uranium deposits occurring in the basal part of Neogene sediments overlying granite basement, attention has been paid to uranium leaching from weathered granite by circulating carbonated fissure waters, to effective adsorbents for fixing uranium from uraniferous ground waters, to structural features controlling the ground-water circulation, and other relevant factors. The evidence for uranium transportation by hydothermal solutions, including hot spring waters, is hard to observe. Conclusions are summarized as follows:(1) Uranium in the deposits is supplied from surrounding source rocks, mostly from granite.(2) Uranium is transported by circulating ground-water solutions.(3) The uranium dissolved in ground water is fixed in minerals in various ways, the most important being adsorption by carbonaceous matter.(4) Ore-grade uranium concentrated from very dilute solutions occurs by multiple repetition of a leaching-and-fixation cycle between minerals or adsorbents and circulating uraniferous ground water.(5) Important factors for uranium mineralization are sufficient uranium, supplied mostly from granite, the existence of effective adsorbents such as carbonaceous matter in the host rocks, and favorable geological, geochemical, and geophysical environments.The last seem to require not only physical and chemical conditions but also correct flow and volume of ground water. Geological settingDistribution of important uranium deposits in Neogene sediments in Japan is shown in Figure 1 and their general features are summarized in Table 1.The deposits occur exclusively in basal coarsegrained sediments of Neogene age unconformably overlying granites which are mainly of pre-Tertiary age. The deposits are generally flat, lenticular in shape, and concordant. Most important deposits are located in sediments rich in carbonaceous matter and cover depressions or troughs in basement rocks. In some deposits, such as Tono, Ningyotoge, and others, ore shoots occur along shear zones, faults, or dikes cutting the host sediments. Generally speaking, however, the uranium mineralization occurs in a definite horizon in each district.Uranium content and thickness of the orebodies vary considerably.Effects on the uranium mineralization due to volcanism or hydrothermal activity are hard to observe. MineralogyCoffinite and uraninite are the most common primary ore minerals of the deposits, but ningyoite (Muto, 1962(Muto, , 1965 is found as a primary constituent in the Ningyotoge and Okushiri deposits. In many cases, the uranium present is adsorbed on carbonaceous matter and zeolites, and in some deposits uranian apatite occurs as the major uraniumbearing mineral. The most common ore mineral in the oxidized zone is autunite. Other secondary uranium-bearing minerals occur in accordance with the geochemical environments of the deposits. Pyrite 628 URANIUM IN SEDIMENTARY ROCKS 629 is the most common accompanying mineral and is widely distributed in ore-bearing horizons associated with ca...

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Investigations concerning the concentration of minor ele ments (Co, Ni, Mn, As) in pyrites and cube-edge measurements were carried out on thirty-nine specimens taken from the Chichibu mine (26 samples), the Taishu mine (7 samples), and the Ashio mine (6 samples), by using X-ray fluorescent method as well as X-ray diffraction method. The results obtained are as follows;

In sulphide deposits, generally, various sulphide minerals occur in massive or crystalline aggregates showing the relations of int imate paragenesis, and these minerals usually contain small amounts of selenium as their minor constituents. It is a significant subject from a view point of economic geology to clarify the relations between the selenium content in various sulphide minerals which exist in the sulphide deposits and their mode of occurrence. In present work, as a portion of these problems, the manner of dist ribution of selenium in several sulphide minerals which co-exist in one hand specimen and show the relations of intimate paragenesis was mainly studied. And furthermore, it was examined whether selenium distribution in given minerals can or cannot be utilized as a geological thermometer when the formation-temperatures of minerals should be discussed.