The ore deposits of Taio mine are typical epithermal gold-silver veins in Tertiary apo-andesite. In rich ores of the No.3 and No.4 Veins, the most productive lodes of this mine, the black crustified bands or patches called "Ginguro" (silver black) are commonly found. From microscopic observations, it is known that the textural and mineralogical characters, and the mode of occurrence of gold in the ore differ remarkably in these two veins.
The ore consists essentially of common ore minerals, such as pyrite, chalcopyrite, galena and sphalerite, with quartz, chalcedony and calcite. Sphalerite, a principal constituent, amounts to about 70 percent of all ore minerals. Polybasite occurs as the only sulphosalt mineral in the No.4 Vein, but is present in a very small amount. Argentite is commonly found in the No.4 Vein, but is relatively rare in the No.3 Vein.
Gold, as electrum, is concentrated in the Ginguro. From observation on 2000 gold particles under the microscope, the mode of occurrence of gold was revealed as follows:
I. No.3 Vein.
1) Gold particles are generally granular and about 90 percent of the particles are intimately associated with sulphide minerals such as galena and chalcopyrite, and especially with sphalerite. But some particles are associated with argentite and pyrite. Gold which is not enclosed in sulphide minerals is about 3 percent.
2) The grain size of the gold particles ranges from 0.5 to 85 microns, and grains from 3 to 10 microns in size are most predominant.
II. No.4 Vein.
1) Most of the gold particles are not enclosed by the sulphide minerals but filling the interstices of quartz crystals. These free particles amount to 44 percent of all. Grains which are associated with galena, chalcopyrite and sphalerite are about 30 percent. Grains associated with pyrite and argentite are notably greater in number than in the No.3 Vein.
2) It is revealed that the size of the gold particles of this vein is finer than that of No.3 Vein and the peak of the size frequency curve is between 3 to 7 microns. The size are widely distributed ranging from 0.3 to 400 micrns.

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The general features of lateral changes of propylitized andesite caused by a vein-forming agency was studied by recording the properties of several rock specimens collected at intervals of 5-10m. along a cross-cut tunnel, from the vein toward its outlet. The wall rock at more than 60m. distance from the vein has been unaffected by the vein-forming agency and is characterized by the development of chlorite and albite or by the lack of pyrite. The rock at less than 60m. distance from the vein has been affected by hydrothermal vein-forming solution. Chloritization and sericitization are particularly intense near the vein; this fact is revealed on the D.T.A. curves of the rock specimens collected at less than 20m. from the vein. Away from the vein, silicification is remarkably intense in place. Pyritization appears to be uniform all over the region and small amounts of adularia and carbonates are often found. The degree of staining by "Safranine Y" seen on the thin slices is proportional to the quantities of chlorite and sericite. The abrasion pH of the rock specimens in water is estimated sensitively by the intensity of fluorescence seen by adding "Fluorescein" to the water suspension. The intensity is strong near the vein and weak in the silicified part.

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1. One of conspicuous features of coal industry in Japan, is the development of submarine mining. The output from submarine fields amounted to about 13% (6.1 millions metric tons) of the total coal production of Japan in fiscal year 1951. On the other hand, the reserves of the submarine fields are assumed to exceed 24% of overall Japanese coal reserves. It is very obvious from these figures that the coal industry will require much more effort of geologists to discover new prospecting methods in order to explore submarine fields.
2. The Takasima coal field, situated in western Kyûsyû, off Nagasaki harbour, consists of a few small islands and occupies an area, measuring about 15km north-south by 10 km east-west. The coal is of prime quality for the manufacture of gas with a heating value of 7800 calories and containing 8% ash. The Mitsubishi Mining Co. is operating two pits in this coal field (Hutago and Hasima) under the name of Takasima Colliery.
3. Since 1949, electrical prospecting of sea floor has been carried out with the cooperation of Dr. J. Iwatu of Osaka Municipal University. The basic feature of the method used is the continuous measurement recorded on oscillograph film of spontaneous polarization and apparent resistivity as electrodes are towed along by steam boat. The circuit usually adopted, is the configuration by Dr. Iwatu which can express on one curve both SP and ρ, by the distance from neutral line to the curve and by the amplitude of oscillation, respectively. ρ is usually not effective for detection of geological features, due to the low resistivity of sea water except where coal seams and coal bearing formations are present. The recording of SP and ρ on separate curves, using a specified commutator and the adoption of slow period vibrator, however, makes it possible to detect ρ effectively. To locate the position and course of boat, two sextants are used. The current of 30-70 mA is supplied from dry cells (45 volt) and passed through a commutator to the electrodes. Echo sounding records are made for each traverse in order to avoid misunderstanding anomalies on curves, caused by the boundary between rocky shoals and flat bottom covered by recent deposits.

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