The Taisyu Mine, famous in Japan for the excellent high grade Pb-Zn ore it produces, is in the western part of Tsusima island.
The sedimentary rocks of Tsusima are said to belong to the Taisyu formation of Palaeogene age and consist of sandstone, shale, and an alternation of the two.
The Utiyama granite batholith, with its long axis trending N30°-40°E, intruded the sedimentary rocks and converted them to hornfels.
There is a synclinal axis in the southeastern part of the mine, and the Komoda fault group is in the northwestern part. Both parallel the long axis of the granite. The principal ore deposit of the mine is a mesothermal fissure-filling galena-zincblende-pyrrhotite vein, found in the N-S fault, which is developed in the zone between the synclinal axis and the Komoda fault group.
The more than thirteen known veins form three main vein groups-east, central, and west-that are arranged en echelon with a 700 to 800m interval.
Vein inclination of this mine has been recognized as being related to the granite. The prominent geologic features that dominantly controlled placement of the ore deposits are the synclinal axis, hornfels, quartzporphyry, the N-S fault, and the reverse fault in sandstone.
The mode of occurrence of the ore-body has the following characteristics:
(1) The zonal arrangement of minerals is remarkable in each vein.
(2) In the N-S fault, the main path of ore-solutions has followed the axes of bends in the strike of the fault plane, and ore bodies have formed in favorable places near these axes.
(3) Likely places for the formation of ore bodies are the intersecting lines between the N-S fault and a N 40°-50°W fault, the sandstone, the quartz-porphyry dikes, and bedding faults, and also the junctions between small faults.
A "standard program of prospecting" was made in this mine from the recognized relations of geologic structure and ore deposition mentioned above. The prospecting practices following this program have been effective and, as a result, many new ore bodies have been discovered.

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The Yoshiwara Mine is located in the well known copper zone of the Hiraodai-Sannotake District belonging to the late Mesozoic, metallogenetic province of West Chugoku ane North Kyushu. The prevailing rocks in the environs of the mine are Paleozoic sediments, such as clayslate, sandstone and limestone, and basic lava and tuff. These strata are intruded by discordant granodiorite batholiths and porphyrite dikes of Cretaceous age. The pyrometasomatic deposit of the mine is genetically related to the grano diorite.
The recognized sequence of igneous activity and mineralization is as follows : (1) intrusion of porphyrite, (2) intrusion of granodiorite, (3) formation of garnet-pyroxene skarn with deposition of copper-gold minerals, (4) deposition of iron minerals such as pyrite, hematite and magnetite, and (5) deposition of lead-antimony minerals. After the mineralization, the deposits were cut by some high-angle strike-slip faults trending N10°-40°E.
The most important factor in the localization of the main ore bodies is the fold structure of the limestone bed, and also, porphyrite dikes are a contributing factor in some pyrite ore bodies.
(1) Copper Ore Deposit No. 1 consists of some skarn ore bodies in a saddle-reef form. They lie along the crest of an east-plunging anticlinorium between clayslate (hanging wall) and limestone (foot wall). From this the writers consider that replacement has taken place along the anticlinorium apex of the folded limestone bed and that the clayslate of the hanging wall forms a cap rock for ascending mineralizing solutions.
(2) The upper part of the Copper Ore Deposit No. 2 shows a lenticular form in cross-section along the strike. It lies in the north limb of the anticline, where the limestone bed is irregularly intercalated with other sedimentaries.
(3) The lower part of the Ore Deposit No. 2 occurs as a pipe-like mass. It is enclosed within the folded thick limestone bed, and further, is associated with porphyrite dikes. The boundary between the ore body and the surrounding limestone is not sharp.
(4) Iron-sulphide deposits, such as the Sugitani, the Koguchi, the East, and the West Ore Bodies are lenticular or pipe-like bodies of massive pyrite which replace skarn-copper ore, porphyrite, limestone, etc. Some of them are controlled by the pre-existing porphyrite dikes.
The granite contact is not observed in the mining area. Ore may have come from hidden intrusives of granodiorite.

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1. Als zweite Arbeit über die Beziehung zwischen der geologischen Struktur and der Inkohlung hat der Verfasser das Kohlenflöz Kishima-Goshaku des Karatsu Kohlenbeckens gewählt, und dasselbe mikroskopisch und chemisch untersucht.
Nach den Ergebnissen seiner Untersuchungen hat die Kohle in den Lage, wo sich das Kohlenfloz gut entwickelte, ein höheres atomares Verhältnis H/C; dagegen hat die Kohle in anderen Lage, wo sich das Kohlenflöz mager entwickelte, verhältnismässig niedrige Werte.
Diese chemischen Eigenschaften der Kohlen stimmen gut mit den mikroskopischen Beobachtungen überein. Diese Verschiedenheiten wurden durch die lokalen Senkungsunterschiede des Bodens hervor-gerufen und haben sich in der zweiten Inkohlungsstufe weiter gut erhalten.
2. Die Hauptinkohlung des Kishima-Goshaku Kohlenlagers erfolgte vor der Faltung, and ist eigen-tlich prätektonisch. Durch die Einwirkung der Vulkanismen aber wird these seine Metamorphose etwas beschleunigt und im "Kohlenband" von VAN KREVELEN wurde das Kishima-Goshaku von einer höheren (hoch H/C and O/C) zu der jetztigen niederen Stelle geschoben. Dieser Inkohlungsverlauf erscheint etwa Verkohlung ähnlich zu sein.
3. Die geologische Struktur "Amakusa-Typ" dieses Beckens ist wesentlich anders als die in Amakusa; die Faltungsstruktur des Beckens erscheint erat nach der vulkanischen Aktivität, die als ein Haupt inkohlungsfaktor betrachtet werden muss, dagegen erfolgte die Faltungsstruktur des Amakusa Bekens schon vor der Vulkanismus. Infolgedessen muss man die Faltungsstruktur des ersten Beckens als "augenscheinliche Amakusa-Typ" Struktur bezeichnen und sie von der eigentlichen Struktur in Amakusa unterscheiden.

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In the Mobara natural gas field the gas-water ratio rises greatly as the gas is removed from the well. This probably results from the fact that the free gas which is contained in the underlying Otadai formation and in the thick mudstone of the Kiwada formation rises through a zone fractured by. faults. It is necessary, of course, that there be good sand reservoirs for the gas, but the thick mudstone under the gas reservoir is thought to be the main source of the natural gas in the field.

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