In the Besshi Mine, it was recognized that a drill hole tends to assume a direction at right angles to schistosity finally. For instance, a drill hole which was started horizontally at the collar has deviated upward by 25° degrees for a length of 200 meters. Another drill hole which was started vertically downward has changed by 60° degrees at a depth of 200 meters. Recently it has been recognized that a drill hole driven at a small angle to schistosity can advance straight for a length of more than 150 meters and that the deviation of the hole depends upon the angle between the hole and the schistosity. Using these facts in prospecting, we have been able to economize both time and cost 50 to 70% as long cross-cut tunnels became unnecessary.

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The Ariake Coal Mine is an inclosed undersea coal mine, located to the north of the Miike Coal Field of the Mitsui Mining Co. The district is shallow sea for the part, and is partly reclaimed land. The basement of this district consists of Palaeozoic, crystalline schists, covered by the Eocene formation-mainly coal measure-with a thickness of about 100-350 meters; the Quartanary system, about 100-200 200 meters in thickness, covers the whole district.
The prospecting of this district, mainly with seismic method and drilling, was started by the Nittetsu Mining Company in 1952. Main purpose of the prospecting is investigation of the geological structure, especially the distribution of faults, coal seams and underground water. In the seismic prospecting, the refraction method was used principally, supplemented with the reflection method. The refraction method was put into operation with a span of 500 meters. The total length of the line was about 411 kilo-meters. Five marine drilling towers of Pontoon type were constructed for drilling. The draft of these travelling towers is about 2.5 meters, with the capacity of accomodating 20 persons. About 140 holes were drilled, their total length ottaining to about 44, 000 meters. Using the drill holes, investigation of ground water was carried out by formation tester, electric logging and velocity logging.
The prospecting has confirmed nine coal seams, all being of coking bituminous coal. As. a result of the prospecting, this coal field has been developed since 1960; the man-made island with an area of 14 ha was constructed in the sea, and three shafts are now being sunk in this district. According to the development plan, the mine will produce 2 million tons of prepared coal annually, employing the horizontal mining method.

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The writer has studied about the geological structures in the Ashibetsu district, Sorachi Coalfield since 1941. Fault groups in the district are divided into the following five groups.
(i) The 1st fault group: Reverse fault group with a strike of NNW and an eastery dip. This fault group develops mainly in the central parts of Ashibetsu River district, between Cretaceous outcrops in the eastern side of the Sorachi Anticline and the Bibai-Ashibetsu Tectonic Line, and the Akabira, Tanzan and Raijyo Formations are repeated due to this fault group. This fault group is rare in the eastern and western sides of the Ashibetsu River district.
(ii) The 2nd fault group: Wrench fault group with a strike NW-NNW and an eastery dip. This fault group develops mainly in the western parts near the eastern side of the Sorachi Anticline and in the central parts of the reverse fault zone.
This fault group not only cuts and shifts the folding structures of which axis show NS-NNW, but also shifts northward the strata of the eastern side horizontally. Also, faults are often seen which cut and shift reverse faults.
Near the east side of the Sorachi Anticline, this fault group often changes the strike and decreases its throw towards the cretaceous outcrops. This fault group is not so conspicuous in the eastern side of the Ashibetsu River district.
(iii) The 3rd fault group : Wrench fault group with a NW strike and a west dip. This fault group develops mainly in the eastern parts of the Ashibetsu River district, especially in the Kogane district, and is not so conspicuous in the western side.
(iv) The 4th fault group : Normal fault group with the strike of EW and a dip to north or south. This fault group develops mainly in the Panke-Penkeporonai River district and two kinds of faults with the dip to north or south are seen as a pair. This fault group often cuts the axis of the folding. The strike of this fault group is parallel or oblique to the strike of the strata.
(v) The 5th fault group: Normal fault group with a strike of EW and a dip to south. This fault group develops mainly in the Ashibetsu River district, and its strike is often at a near right angle to the strike of the strata. It cuts often the 1st-3rd fault groups, and is characteristic of the low angle.

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The mode of occurrence of silver or silver minerals in the Toyoha lead, zinc and iorn sulphides mine is classified into several types. The chracteristics of each type are described in detail. Mode of occurrence of silver and silver minerals in lead, zinc and iron sulphides concentrates is also discussed. Finally the ratio of the amount contained in each type of occurrence in the ore is calculated quariti-tatively.

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The Kushikino mine is an epithermal vein-type gold-silver deposit related to the Neogene volcanism, and is one of the largest gold mines in Japan. The microscopical and mineralogical studies of the gold-silver ores in the eastern part of the mine revealed the presence of electrum, naumannite and a mineral of polybasite group as main Au and Ag minerals, and pyrite, chalcopyrite, tetrahedrite, pyrargyrite, sphalerite, galena and three undetermined minerals as minor ore minerals, accompanied by quartz and a small amount of calcite as gangue minerals. The sequence of ore formation is reconstructed from the textures of veins as follows : 1. formation of siliceous altered rocks, 2. deposition of quartz and ore minerals, 3. deposition of calcite. The optical properties of the naumannite are discussed, with the results of etch reactions and X-ray powder data.

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The mercury deposits in Mexico may be divided into two major groups of distribution, one in the Sierra Madre Occidental district, and the other in the Mesa del Norte. Most of the ore deposits are found in the opening of pre-existing fault fractures and fractured zone, sometimes with many bonanzas in the flatter portion of reversed faults or thrust faults. This indicates that the formation of the ore deposits is largely controlled by the geological structure. The scale of the ore deposits is usually large when its host rock consists of Cretaceous sedimentary rocks, and generally small when of Tertiary igneous rocks.
Most of the sedimentary rocks are weakly-silicified, or argilitized, except some limestones which are dolomitized. The igneous rocks are silicified, kaolinized, and sometimes altered to clay. In most cases alteration in the deposits is not so remarkable, generally accompanied by mineralization. This also leads to a conclusion that localization of the deposits is much more closely related with the geological structure.
The principal ore mineral is cinnabar with an eminent exception of livingstonite in Huitzuco. Native mercury and metacinnabar are also produced in small amounts, followed by mercury minerals such as guadalcazarite, montroydite, tiemannite, onofrite, terlinguaite, barcenite, egalestonite and calomel.
In the process of formation of the mercury deposits, at first, the earliest geologic activity which affected the scale and localization of the ore took place, forming the many sheared and fractured zones to be mineralized. The mineralization was performed in three different stages, namely, 1. silicate stage (opal, chalcedony), 2. sulphide stage (pyrite, marcasite, cinnabar and livingstonite), and 3. carbonate stage (calcite). In one place, another source brought about acidic hydrothermal action in the last stage of mineralization.

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The Uchinotai ore-deposits of the Kosaka mine belong to "Kuroko (black ore)" type deposits, which are bedded sulfide and sulfate ore-deposits in the volcanic rocks and pyroclastic. strata of Miocene. The ore-deposits consist of siliceous ore, gypsum ore, cupriferous pyrite ore (yellow ore), cupriferous galena and sphalerite ore (black ore) in ascending order. These deposits are overlain by the sericitized. tuff with subordinated bedded red rook.
The red rocks in the sericitized tuff is observed as a thick stratified bed in one place and an aggregate of lenticular rocks in the other. The rock is generally called "ferruginous quartz". It is divided into. the following three groups by the appearance, in ascending order ; compact ferruginous quartz, shagreen ferruginous quartz and ferruginous clay. The red rock is often laminated and contain some Foraminifera, a mixed fauna of arenaceous species and calcareous ones. Some geologists believe that the bedded red rock is a replacement material accompanied by the formation of the Kuroko ore deposits. However, judging from the lamination and fossils tound init, t seems to be a marine sediment of the Miocene Nishikurosawa stage. This conclusion suggests that the "Kuroko" ore deposits of the Uchinotai mine were syngenetically formed by the material derived from submarine volcanism.

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