The Taishu mine, well known as one of the high-grade lead-zinc deposits in Japan, is located in Tsushima islands, Nagasaki Prefecture, Japan. The ore deposits are of mesothermal or xenothermal vein types of the late Miocene age, consisting predominantly of galena, sphalerite (marmatite) and pyrrhotite with minor amounts of chalcopyrite, arsenopyrite and pyrite. There are two kinds of veins. The one is the veins which occur along the N-S fault, and the N-S strike slip faults dipping about 60° to the east. The other is the veins formed along the bedding-plane faults which trend. N 35°E and dip about 35° to the southeast in sandstones and alternations of sandstone and shale.
Since 1952, structural analyses of the bedding-plane veins have been made. The results are as follows.
(1) The reverse faults along the bedding plane were formed during folding of the Taishu formations of the Tertiary age, prior to N-S faulting.
(2) Ore shoots of a large scale are found in places where many structural features of faults and sandstone are favorable to the ore deposition.
(3) It seems that the mineralizing solution ascended earlier along the bedding plane faults, and then later penetrated into the N-S faults.
Since 1962, prospecting for a great number of new bedding-plane veins, based on the analyses of the structural control, has been successfully carried out. The minable ore reserves discovered since spring 1962 up to December 1967, have amounted to about 2, 369, 400 tons.

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An undersea exploration has been carried out at the Taiheiyo Coal Mine since 1939, adopting the dredging, aqualung or sparker methods. From 1964 to 1967, seven offshore drillings were operated applying the single column or floating barge methods. The results of the explorations were as follows:
(1) By dredging, aqualung or sparker methods, the geologic structure of this undersea district was made clear.
(2) As a result of the explorations a new district called Minami-masuura was discovered to the cast of the present mining district where four offshore drillings had been worked. Thus, the presence of some favorable coal seams have been confirmed.
(3) By operating three more drillings some distance offshore from the present mining district, the uncertain geologic structure of the Higashi-masuura deep has been made clear as well as the presence of a fault, of which vertical throw is more than 200 meters. It was also confirmed that there are at least some favorable coal seams in each of the seven drillings.

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On the basis of geological data obtained from diamond drilling, surface and underground survey, the Miocene acidic volcanism of the Kamikita mine district can be summarized as follows :
1) The acidic volcanic activity was predominant in the Okunosawa Formation and the overlying formation.
2) The Okunosawa Formation is composed of acidic lava flow (so-called lava dome), pyroclastic rocks accompanied by the acidic volcanic activity and sedimentary tuff.
3) The pyroclastic volcanic activity in the Okunosawa Formation is divided into two stages, OB₁ and OB₂, respectively. The OB₁ stage was the initial volcanism which formed pyroclastic rocks and several lava domes. The OB₂ stage is the final of which activity was violent and widespread.
4) An explosive eruption took place at the beginning of OB₂, during which the black ore deposits of the Kamikita Mine was formed. The other explosion took place during the OB₂ volcanism. Thus, the primary ore deposits had been destroyed and the beded deposits were formed.

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The Iwami kuroko mine, located at 5 kilometers west of Iwami-Ohta City is producing copper, lead and zinc concentrates.
The geology of this area is mainly composed of the Miocene pyroclastics and sediments. The kuroko deposits occur between black shale and conformably underlying rhyolitic tuff. The environments in which kuroko deposits were formed, appear to be those of a shallow sea near the land, considering from the existence of pisolites in the rhyolitic tuff.
A cave-in had occured in the vicinity of kuroko deposits right after ore deposition. Thus, the deposits avalanched into the basin and formed talus piles.
At he upper part of the Kuroko deposits, some sedimentary structures, such as flow casts, load casts, cross bedding, wash-out, etc. were observed. These structures indicate that the kuroko deposits were formed syngenetically at the depth of not more than 20 meters where the long shore current could be influential.

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Lithologic characters and stratigraphic succession of the Miocene formations in this area can be summarized, from oldest to youngest, as follows: Formation III; rhyolite and basalt in the Early-Middle Miocene (Nishikurosawa stage): Formation IV; alternations of mudstone and tuff in the Middle Miocene (Nishikurosawa-Onnagawa stage): Formation V; alternations of mudstone and tuff breccia in the Middle-Upper Miocene (Onnagawa stage).
The tectonic elements are three uplift belts and two basins. They are separated by NNE-trending faults. Analyses of isopach and lithologic mud-tuff ratios of the formations support the conclusion that the pyroclastic sedimentations were controlled by differential movements of the elements, and submarine volcanisms took place along the boundaries between the uplift and basin blocks. The base metal mineralizations of veins and some black ore deposits are associated with the volcanisms and confined in the Formations III and IV.

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