As a result of the systematic study on the basis of the stratigraphical consideration, the following features have been recognized in the ore of the Besshi type.
1. In the texture of ore, the ore-forming minerals show the gefuge corresponding to the linier structure of this area.
2. The grain size of pyrite in ore grows in proportion to the metamorphic grade, showing a zonal distribution in this area.
3. Pyrrhotite is found throughout the Kawaguchi formation, and in the lower Minawa formation zincblende is rich in contrast with the ore-deposits in the other formations.
4. Concerning minor elements in ore, the result of chemical quantitative analysis has revealed the following :
It is observed the distribution of minor elements in ore characterizes each formation.
Name of formation Minor element
Pb Zn Ti Ni Co Sb As Sn
Kawaguchi * * * * *
lower * * *
Minawa middle *
upper *
Thus, these bedded ore-deposits belonging to the same horizon have common characters. Therefore, the writer has come to support the syngenetic theory, i, e., these ore-deposits had been deposited with other sediments in the submarine geosyncline of Sanbagawa in the course of the post-volcanic activities, and afterward the ore-deposits had suffered remarkable metamorphism, having been derived from the orogenic movements in the pre-Cretaceous period ; consequently, the bedded ore-deposits had been deformed and recrystallized with their motherrocks.
Standing on the above points, the writer has attempted to trace the special horizon including excellent ore-deposits, and has effectively found new ore-bodies and ore-shoots which, are controlled by the folding structure.
At present, the continuity of ore-body or ore-shoot has been confirmed for a distance from 2, 000 meters up to about 4, 500 meters.

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The so-called "green tuff" formations derived from the submarine volcanism in the Miocene epoch are developed in the Kosaka mining district. They are characterized by the acidic effusive volcanics, and are divided into the Baramori volcanic rocks (lower part) and the Akamori volcanic rocks (upper part).
There are several ore deposits in the Kosaka mining district wihch belong to the "Kuroko" type. They are summarized into two types of occurrence : the network-disseminated ore type of pyrite-chal-copyrite (Keiko) in the Baramori volcanic rocks, and the bedded type (including breccia-block type) consisting of three kinds of ores, namely, pyrite-chalcopyrite (Oko), spharelite-galena-barite (Kuroko) and gypsum. They are restricted to the upper most horizon of the Baramori volcanic rocks.
Judging from the following geological facts-1. consistency of ore horizon, 2. absence of structural control of ore bodies by the Akamori volcanic rocks (absence of the cap rock), 3. occasional discordant relation of ore bodies with the Akamori volcanic rocks, 4. weak alteration of the Akamori volcanic rocks as compared with that of the Baramori volcanic rocks-the writer concludes that ore deposits of the Kosaka mine were formed in connection with the Baramori volcanic activities. The Baramori volcanic rocks consist of the lava flow of the Baramori rhyolite and the Motoyama breccia which is locally overlying the Baramori rhyolite. From field and underground observations, it is considered that the Motoyama breccia was derived from the Baramori rhyolite mass by the phreatic explosions.
It is noteworthy that all ore deposits of the Kosaka mine occur only where the Motoyama breccia are accumulated. This fact suggests strongly an intimate relation between the phreatic explosion and the ore deposition. In the previous paper on the Motoyama ore deposits, one of the ore deposits in the Kosaka mine, the writer reported that the condition of the deposition of Kuroko was substantially the same as that of the sedimentation of the Motoyama breccia.
From these facts, the writer considers that the bedded ores were formed syngenetically subsequent to phreatic explosions while network-disseminated ore were being formed in the Baramori volcanic rocks.

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The Yaso mine is a vein-type copper deposit in the Miocene tuffaceous and the Palaeozoic argillaceous rocks, belonging. to subvolcanic type. Monthly production of crude ore is about 15, 000 tons of 1.45% copper.
This region is geologically composed of Palaeozoic formation, granite, Miocene pyroclastic and sedimentary rocks, rhyolitic and andesitic dike rocks, and dacite lava flow. The Palaeozoic slate, sandstone and quartzite formation and the granite that belongs to the Mesozoic era form the basement of this region. The Miocene formation consisting of basal conglomerate, tuffaceous sandstone and rhyolitic tuff is widely developed. These rcoks are intruded by many dikes of lithoidite, rhyolite, and nevaditic plagioclase rhyolite and by a few smaller dikes of propylitized andesite. Though in the northeastern part of the area the above-stated rocks are covered by a later thick lava flow of dacite, the occurrence of the rhyolitic dikes shows a U-shape. As the inside blocks surrounded by the U shape dikes show a slight subsidence, it can be said that the occurrence of the dikes corresponds to the ring-dike in the sense interpreted by M.P. BILLINGS. The mineralization took place mainly along the western wing of the U-shaped ring-dike. Consequently, it is inferred that the ore solution originated from the underground acidic magma that made the rhyolitic ring-dike.
The deposits of the mine consist of four groups of typical chlorite-quartz-copper veins. They are Akakura, Kido, Maekura and Ooba deposits. The largest vein is the 905m-Vein in the Akakura area, and is developed as long as 1200m in strike side and as deep as 460m.
The ore minerals are chalcopyrite, pyrite, sphalerite, galena, bismuthinite, etc., and the gangue minerals are chlorite, quartz and calcite. Though the zonal distribution of minerals is not so conspicuous, the upper parts of the veins are rich in sphalerite and galena. Bismuthinite has an intimate relation with chalcopyrite and it is presumed that the mineral has been deposited mainly in the early stage of the. sulphide mineralization. The alteration of wall rocks comprises silicification and chloritization. The former is stronger in the upper parts of the deposits and the later is striking in the lower.

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