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.

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The Tomii Mine lies at about 16 kilometers north-northwest of Utsunomiya City, Tochigi prefecture. The ore veins occur in lower Tertiary quartz-porphyry stock, Miocene tuffaceous beds and liparitic complex.
Almost all veins of the mine show symmetrical or asymmetrical banding structures, and often have complex vein structures. They are recognized by detailed observation of mutual relations of ten ore facies having characteristic mineral assemblage. The aforesaid structures were explained by J. Kutina's classification for the boundaries of ore facies, and relationship between the ore deposition and the tectonic movement was inferred by the observations.
It was concluded that the ore bodies of the mine were deposited from a solution of a consecutively different composition, and characters of each vein were controled under the condition of opening for orefilling fractures and the discrepancy of opening stages of ascending channels for ore sloution.

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The author's discussion on the genesis of zonal distribution in ore veins of the Tomii Mine is mainly based on the observation of the Honpi Vein.
The vein was divided into four zones, namely, (1) uppermost zone consisting of gold-bearing quartz vein, (2) upper zone consisting of gold-and bismuthinite-bearing ore, (3) middle zone consisting of ore of relatively concentrated bismuth and copper, and (4) lower zone consisting of pyrite ore. This zoning was formed by the mineralization of early stage. The zone of barite molded quartz which formed by the mineralization of middle stage overlapped the lower zone, and the zone of zincblende formed by the mineralization of late stage overlapped the middle zone.
Some factors of this zonal distribution in veins of the mine are summarized as follows ; (1) zonality due to the overlap of different ores by the mineralizations of time-separated stages, (2) zonality due to the overlap of different ore deposition phases in a mineralization, (3) zonality due to physico-chemical. conditions of the mineral deposition, and (4) zonality due to inter-ore metasomatic conditions.
It is inferred that the zonal distribution in ore veins of the mine resulted from the aforesaid factors combined together, and was mainly composed of different ore deposition phases. Therefore, it falls under the "poly-ascendent zoning" by J. Kutina.

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The ore deposits of the Tomii Mine are localized under the control of a horst structure or some uplifts which were caused by the doming elongated north 20°east trend. Particularly, it is considered that the forming of fracture patterns of each vein group was based on local uplifts. And it determinedthe character of each ore body that fractures developed step by step, and the ore solution ascended asthe pulsatile action consisted with the doming.
There were some eruptions of liparitic complex as the last phase of intermittent igneous activities in the Tomii mining field. They were followed by mineralization at three different stages. It is inferredthat the ore solution was related originally to the source of activities of liparite eruptions, but theopening of fractures and the ascending of ore solutions were not caused by these igneous activities but by the doming.

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The Kômori mine is located in Koyto prefecture, south-western Japan.
The Kômori mine is composed of pyrrhotite-copper deposits occurring in ultrabasic rocks, monthly producing about 8, 000 tons of crude ore containing 1.85% copper.
This region is geologically composed of Paleozoic formation, ultrabasic (including basic) rocks of Jurassic period and granite of Cretaceous period. The ultrabasic rocks consist of serpentinized peridotite. serpentine, pyroxenite and gabbro.
The ore deposits are classified into two types, i.e., the vein type and the impregnated type. The former occurs along the sheared zones in the serpentine near the contact with the gabbro or dioritic stocks, which intruded the serpentine. The impregnated type deposits exist in the above-mentioned gabbroic or dioritic stocks, especially in the marginal parts. It is noticeable that the impregnated deposits always occur close to the vein type deposits.
The granite is widely developed in the nothern part of this region, but it is inferred from the geologic. reconnaissance that the cupola of a cryptobatholithic granite exists underneath the deposits of the Kômori mine.
Ore minerals in the vein type deposit are pyrrhotite, chalcopyrite, sphalerite, cubanite, nickel-bearing mackinawite, cobalt-bearing pentlandite, molybdenite, star-shaped sphalerite, galena, native bismuth, bismuthinite, polybasite(?), arsenopyrite, magnetite, pyrite, etc., and gangue minerals are chlorite, talc, quartz and carbonate minerals; whereas ore minerals in the impregnated ores consist of pyrrhotite, chalcopyrite, sphalerite, ilmenite, etc., and gangue minerals are chlorite, quartz, sphene, talc, amphiboles, apatite, plagioclase and carbonate minerals.
The, pyrrhotites in the vein type deposit have usually strong magnetism, but the pyrrhotites in the impregnated type show two different degrees of magnetism, strong and weak.
The decrepitation method revealed that pyrrhotites in the vein ores contain only primary fluid inclusions which have decrepitation temperatures of over 350°C, whereas pyrrhotites in the impregnated ores. contain not only primary fluid inclusions with decrepitation temperatures of 300°-350°C but also secondary fluid inclusions which have decrepitation temperatures of 170°-200°C.
No difference in magnetic properties is recognized between the pyrrhotites with secondary inclusionss and those without.
With regard to the genesis of ore deposits of the Kômori mine, the writer believes that they were formed probably by the activities of granitic magma.

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The minor elements in sulphide ores composed of pyrrhotite, chalcopyrite, cubanite and sphalerite from the Komori mine and those in igneous rocks from the Komori mining district were analyzed by spectrographic method.
The minor elements of Mn, In, So, Bi, Ag and Ni are detected generally in each sulphide mineral, and among these Mn, In, Sn, and Bi are charactrized by high contents, Ni and Co in pyrrhotite and Cd in sphalerite are recognized in high contents, but Ag shows no variation of content with the kindd of sulphide minerals.
The distribution of these elements shows the similar tendency in sulphide minerals from the high temperature type deposits related to acidic magma rather than to basic magma.
This will suggest that the ore deposit in the ultrabasic rocks of the Komori mine is genetically related to from acidic magma.
In the igneous rocks, Ba and Sr increase and Ni, Cr and Co decrease in contents from basic to acidic rocks.

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