The uranium deposit at Nakamaruke, Sekigawa-mura, Iwafune-gun, Niigata Prefecture, was discovered in 1960 and surveyed by the authors from 1960 to 1964, as a part of regional prospecting for uranium in Neogene Tertiary sediments accompanied with the so-called "Green Tuff", with is widely distributed in the border district between Niigata and Yamagata Prefectures.
The tabular-form uranium deposits of Japan in Neogene Tertiary sediments, the so-called "Ningyotoge type" deposits, are in general considered to have been controlled by the basement structures and are epigenetic deposits related to such an environment where groundwater circulates or stagnates.
The Nakamaruke deposit, one of these tabular-form deposits in Neogene Tertiary sediments, differs to a considerable extent from the "Ningyo-toge type" deposits in mode of occurrence, paragenesis of minerals, and other features, and can be said to be a peculiar type deposit newly found in Japan.
(1) In the Nakamaruke area, the Kitaoguni formation (lower Miocene), the Tsugawa formation (middle Miocene), and the Nanatani formation (upper Miocene) rest in ascending order unconformably upon the basement composed mainly of granite, and these Neogene Tertiary sediments show a monoclinic structure with a relatively gentle dip.
(2) Uranium is concentrated in arkose just below the bentonite bed in the upper part of the marine Tsugawa formation directly overlying the basement granite. This uranium deposit might have a close genefical relation to apatite contained in the arkose.
(3) Such occurrences of uranium associated with apatite in Neogene Tertiary sediments are found in some places within 40 km from north to south around Nakamaruke, and deposits of this type may be expected to exist widely throughout this district, as well as the possibility of existence of the "Ningyo-toge type" deposits.

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Pressure effects on the solvi of some sulphide binary systems, NiS₂-FeS₂, Cu₅FeS₄-Cu₉S₅, Cu₅FeS₄-CuFeS₂, and ZnS-FeS, were investigated on the basis of thermodynamical considerations. It is assumed that activity coefficients and ΔV in phases are independent of pressure.
The result of the investigation has revealed that as confining pressure increases, the two phase region of the NiS₂-FeS₂ system is narrowed, while those of other systems are broadened. By finding equicomposition curves on the pressure-temperature coordinates, it is suggested that there is a possibility of determining the pressure-temperature condition under which these mineral assemblages were formed. This method requires, however, at least two suitable pairs of mineral aggregates which belong to mutually independent systems.

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The stratigraphical position, structure and mineral composition of ores of the Iimori, Ozu, and Amana ore deposits are described. Folds of the schists in the region can be divided into two types. One has an axial plane parallel to the schistosity plane, and the other across the plane at high angles, accompanied by axial plane cleavage. Ore deposits are folded, in gereral, harmonious with the country rocks after both types of fold. The eastern part of the Iimori ore body, which is rather tabular in shape is located in "the Northern flexure zone" of "the Iimori syncline", while the western part in "the Ozu folded zone", where it is intensely affected by the two types of fold. Most of the field evidences suggest a syngenetic origin of the ore deposits in the area, presumably metamorphosed from exhalation deposits generically related to the submarine volcanism during the geosynclinal sedimentation.

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The Seikyu mine, in eastern Shimane Prefecture is one of the most productive Japanese molybdenum mines, It is located in a part of the late Creataceous Chugoku batholith in the Inner zone of the Southwestern Japan. The area is a zone of various granitic rocks such as schistose hornfels (Hfs), schistose biotite hybrid (Hgs), biotite adamellite (Gad), granitic complex (Gc) consisting largely of leucocratic rocks, hornblende-biotite hybrid (Ghb), two-mica granite (Gm), aplite (Ga), and adamellite porphyry-porphyritic granite (Gp), Many molybdenum deposits are found between two large batholiths, of hornblende-biotite granodiorite (Gd) and biotite granite (Gb).
The main deposits called Seikyu-Honzan are distributed at the southeastern margin of the biotite adamellite, and embedded in the lower adamellite, in the granitic complex, and in the upper hornblende-biotite hybrid in descending order. The vertical ore zone is about 300 meters thick.
The deposits are composed of fourteen gently dipping mdybdenite-quartz veins, which can be grouped into the fallowing three systems : 1) N50-80°E, 10-20°SE; 2) N 50-80°W, 10-20°SW; and 3) N-S- N20°E, 10-20°E. There are no steeply dipping veins. The thickness of veins is wostly 5 to 20 cm. No distinct structural control is observed throughout the deposits.
Major constituents of the veins are quartz and molybdenite. The veins consist of small amounts of pyrite occurring all over the veins, in parts magnetite (hematite), sphalerite, galena, chalcopyrite, and secondary molybdenum minerals. In general the veins are surrounded by 30 cm wide zone of alteration such as silicification, sericitization, weak carbonatization. There are small amounts of potash feldspars, pale brown biotite, garnet, epidote, zeolites, clay minerals other than quartz, sericite, chlorite, calcite, dolomite, and siderite. This mineral assemblage puts the main molybdenum mineralization in a mesothermal stage.
Fault pattern of the Seikyu-Honzan deposits is of grid, indicated by WNW and NNE of steeply dipping faults and gently dipping ore veins. Movement along these fractures after the formation of the veins is rather small, less than a few meters, except two normal faults of WNW series-"Giant Fault" (drops 150 m) and "Sheared Zone" (drops 30 m). Sheets and dikes of andesite intrude along the ore veins and NNE faults.

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