The largest black ore deposit in Japan was discovered in the Hanaoka mine, Akita Pref., during June 1963 to May 1966. The ore confirmed by drilling amounts to about 30 million tons, and it was named the Matsumine Ore Deposit. The authors describe history of discovery, exploration and development for this deposit. The ore deposit was syngenetically emplaced within the intermediate to acidic volcanic rocks, especially in these pyroclastic rocks of the Miocene age. It consists successively of gypsum body, pyrite ore, copper-pyrite ore (yellow ore), and zinc-lead-copper-pyrite ore (black ore) from the lower to the upper. The deposit extends horizontally up to 500m from east to west and 800m from north to south. The depth is about 200m to 300m below the surface. It shows generally a shape of blanket.
Underneath the blanket ore body occurs siliceous ore, or white altered rhyolite and its breccia-tuff. Above the black ore lies a clay bed or ferruginous, quartz-clay bed which is in turn. overlaid by the mudstone layer (M2). These geological successions are closely similar to those of the main deposits of the Hanaoka and Kosaka mines.
Until 1955 the prospecting in these mines was done with the conception that black ore deposits were formed epigenetically hydrothermal replacement. The detailed geological investigations, however, brought about such a working hypothesis that the deposit might be formed by syngenetic and hydrothermal sedimentary processes. Thus, extensive drillings on the basis of this hypothesis has led to discovery of the "Matsumine Ore Deposit".
It is now expected that more ore bodies may be discovered similarly in this district by refinement of the working hypothesis and exploration technique.

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The Joyama ore deposit is a covered sulphur deposit which was found in 1964 by means of drilling, and it is now on its way of development.
The present paper gives an outline of the Joyama ore deposit and some discussions on the geologic features compared with those of the already well-known Komenashi ore deposit, about 900m to the sowthwest.
1) The ore bodies of the Komenashi deposit have a distinct cap rock which is called "Nakaban Lava" in the mine. On the other hand, at the Joyama deposit, the Nakaban Lava might not exist originally or might be eroded away before the mineralization.
2) The Komenashi deposit are composed of several small ore bodies, while the Joyama deposit shows a roughly bedded and gently sloped form of a large scale. Although the shape of the Joyama deposit suggests that the deposit might be developed in a open sulphur pond at the ground surface, it seems possible that the deposit is of dissemination-replacement type, according to present geologic data.
3) The Komanashi deposit is located at about 1, 600m above the sea level and the Joyama deposit at about 1, 400m to 1, 500m. These altitudes correspond to a general tendency of the locations of numerous sulphur deposits on the shape of a volcano of this region.
4) The Joyama ore deposit is associated with a considerable iron sulphide ore zone at the hangingwall, while the Komenashi deposit is not.
5) The volume of underground water. flow containing H2S gas, is larger in the Joyama ore deposit than in the Komenashi at present. Around the former ore deposit there exist many hot springs.
It appears that the above characteristics of these deposits were due mainly to the following factors, i.e. the topography of the konide-type volcano, the flow and level of the underground water.
The geologic features of the basement rocks apparently controlled the emplacement of the sulphur deposit. These features are not only characteristics of the ore deposits of the Ishizu mine but also of those in the Kusatsu-Shirane region.

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The Hashima coal mine of the Mitsubishi Mining Co. is located at the semi-artificial tiny Hashima Island, well known as "Warship Island", about 20 km to the south-west of the Nagasaki Harbour.
The mine was put into operation in 1887 and has yielded highest class coking coal ever since. Nevertheless, the mining condition was becoming unfavorable in recent years and new coal fields have been actively searched in this area.
Since 1953, many geologists and their assistants collected large number of rock samples from the sea-bottom by means of the specially designed dredger backet. They dived with aqualung to observe directly the outcrops at the sea bottom, and examined heavy mineral frequencies of the rock samples collected. Intensive geophysical prospecting, such as marine seismic prospecting by reflection method with floating cables and pressure sensitive geophones, and sonic prospecting was also introduced, in 1957.
Thus, the detailed geological maps could be constructed, and the underground geological structure in this off-shore area was revealed. Several coal seams in the Mitsuse area could be traced at the sea bottom exactly, and the coal reserves were clarified.
The Mitsuse area has been mined, since Oct. 1965, 14 months after the previous working area was closed owing to a mining accident. The Mitsuse area produces monthly more than 30, 000 tons of high class coking coal at present.
In the Hashima area, there is a large reverse fault, named the Hashima-oki fault. Since the depth of the coal seams beyond this fault is rather shallow and there is a large quantity of coal reserves, this huge area is much promising as the next working area.

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Dolomite deposits of western Shikoku are distributed in some definite stratigraphic and geotectonic zone. They are classified into the following group.
1) Siliceous dolomite deposits of the northern zone of upper Carboniferous in age. These deposits are associated with red tuff, red chert, and other clastic sediments of volcanic materials.
2) Some workable dolomite deposits of the southern zone of lower Triassic Uonashi formation, independent of volcanic activities.
Chief factors of the formation of dolomite are temperature, pH, Eh and concentration of Mg-ion in the sea-water of geosynclinal basin. These factors are related to some paleogeographical environments, such as submarine volcanism (Northern zone) and development of shallow sedimentary basin of nearshore line (Southern zone).
Chemical compositions of mineral dolomites, mechanism of dolomitization, deformation and recrystallization of ores, and relation of dolomite bed to other submarine sedimentary ore deposits are also discussed in this paper.

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The Oe mine mostly produces manganese ore, and small amounts of copper, lead, zinc and iron sulphides.
The Senzai vein of the mine is one of the representative ore deposits of the manganese carbonate ore. The country rocks consist of the Miocene quartz-diorite, green tuff and basalt.
Manganese silicate minerals, which are mixtures of pyroxmangite and rhodonite, are locally found in the rhodochrosite-quartz ores. Some sulphides-quartz ores contain magnetite and hematite microcrystals. The magnetite is pseudomorph after hematite. The pyrrhotite is rarely found in pyrite and marcasite bands crustifying or cutting the banded rhodochrosite ores. It belongs to monoclinic system and Weiss type, and its chemical formula is estimated to be FeS_1.14.
These minerals may be crystallized in the intermediate stage of the mineralization at which the ore shoots were formed. It is considered that the occurrences and properties of the pyroxmangite-, magnetite-, and pyrrhotite-bearing ores did not show the existence of the xenothermal condition during the mineralization forming the Senzai vein.

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