The ore deposits of the Tomii Mine are localized under the control of a horst structure or some uplifts which were caused by the doming elongated north 20°east trend. Particularly, it is considered that the forming of fracture patterns of each vein group was based on local uplifts. And it determinedthe character of each ore body that fractures developed step by step, and the ore solution ascended asthe pulsatile action consisted with the doming.
There were some eruptions of liparitic complex as the last phase of intermittent igneous activities in the Tomii mining field. They were followed by mineralization at three different stages. It is inferredthat the ore solution was related originally to the source of activities of liparite eruptions, but theopening of fractures and the ascending of ore solutions were not caused by these igneous activities but by the doming.

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The Osarizawa Mine is known as one of the largest mines of vein type in Japan. A group of the Tanosawa veins, located in the southern part of the Osarizawa Mine area, has recently been developed. The stratigraphical succession of this area is as follaws:
Upper Miocene : Matsukozawa Formation
-unconformity-
Middle Miocene : Wakiagari Formation
Shishizawa Formation (Upper and Lower Members)
These formations consist of pyroclastic rocks and mudstone. The volcanic rocks as observed are; Akasawa Rhyolite, Shishizawa Propylite, Akasawa Dacite; and Tanosawa Basalt. Mineralzation of the Tanosawa area appears to have taken place some after the Akasawa Dacite intrustion (late Onnagawa stage-early Funagawa stage).
Two prominent veins, Tanosawa veins 3 and 5, are in the group of the Tanosawa veins. These two veins show a pattern of the shear fracture. In other veins, a pattern of the tension fracture is observed.
It is interesting to note that the position of their bonanza has been controled by sedimentary rocks and intrusives. In regard to the zonal arrangement of ore minerals, the veins appear to be a type identical with that of the eastern vein groups of the Osarizawa Mine.
This is noticeable from the top to the bottom, namely, galena-sphalerite zone, chalcopyrite-galena-sphalerite-pyrite-barite zone and chalcopyrite zone. It is extremely difficult to determine the temperature at which the ore deposits were formed, but it is estimated to be about 210°(C) from insufficient fluid inclusion data obtained by heating-stage method.

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The Ôe mine in the southwestern part of Hokkaido is producing monthly 8, 500 tons of crude ores from which Au, Ag, Cu, Pb, Zn, Fe-S and Mn are extracted. The ore deposits are of epithermal fissure-filling vein type. The ores are mainly composed of rhodochrosite, chalcopyrite, galena, sphalerite and pyrite with minor amounts of native gold, argentite, pyrargyrite, etc.
The Senzai vein, the largest one of this mine, is about 1, 500m long along the strike and extends to 500m along the dip with an average width of 5m. The gold contents are high at the upper and lower parts of the western ore shoot consisting of rhodochrosite and sulphide minerals. While at the upper parts of the vein, gold is associated with lead as shown by assays, at the lower parts and in the Manzai vein which runs parallel with the Senzai vein it is associated with copper. Originally, the native gold of this mine was discovered in lead concentrates about ten years ago.
At the lower part, the native gold-bearing ores occur as aggragates of fine sulphide minerals. On the other hand, they occur in the banded ores consisting of rhodochrosite, quartz and sulphide minerals at the lower part of the Senzai vein and in the Manzai vein. These minerals were crystallized at the late middle stage of mineralization.
Mineralogically, the native gold is closely associated with galena of 20μ average size at the upper part of the Senzai vein, while in the Manzai vein most native golds are associated with tetrahedrite of 15μ average size. By etching the polished surface of native gold with CrO₃+HCI, a concentric banded texture was developed. Hence, it is confirmed that the gold grains which show this texture are composed of alternating concentric bands which are relatively rich or poor in silver. The heterogeneity of the grains could be also detected by electron probe X-ray micro-analysis and reflectivity using a microphotometer.

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日本におけるじん肺対策のこれまでの歩みは、多くの書物によりまとめられているが、粉じんの計測に関しても、とりまとめておく必要性があると感じて、労働衛生工学の立場から、明治以降から現在までの粉じん濃度、粉じん計等粉じんに係る事項について、時系列的にまとめた。

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The Obanazawa mine is situated about 9.5km north-east of Obanazawa City, Yamagata Prefecture, northeastern Japan. The ore deposit is made up of copper-zinc quartz veins developed in dacite and dacitictuff of Miocene age. Ore minerals are chalcopyrite, sphalerite, pyrite, tetrahedrite and ferberite. The pyrite has either pentagonal dodecahedral form or colloform textures. This is the first occurrence of ferberite in the green tuff region of the inner zone of northeastern Japan. Hexagonal; platy crystals of pyrite are observed in the vein found in the Komatazawa valley. It seems that they were crystallized as pyrrhotite single crystals and altered to pyrite aggregates after the formation of the vein. Gangue mineral is quartz accompanied by a small amount of barite. Argillization (mainly sericitization) and silicification are distinguished.
Ferberite was identified by means of X-ray and chemical analysis; the composition is (Fe_0.90 Mn_0.10)WO₄. Occurrence of ferberite and pyrite after pyrrhotite means that the veins may have formed at high temperature but the properties of other vein minerals suggest that they crystallized at low temperature. They have been explained as a telescoping phenomena of xenothermal type deposits in the greentuff region.
The Obanazawa mine is situated at the intersection of N-S and NWSE main structural lines of northeastern Japan ; the basement of this area seems to be uplifted. The mineral assemblages of this ore deposit may be explained by assuming that a subvolcanic magma chamber exists in this area.

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As I was one of the founders of this Nippon Institute of Mining and Metallurgical Engineers (Nippon Kogyo Kai), Dr. Hirota, President of the Institute, asked me to write a short sketch relating to the procedure and progress of the Institute during the past 50 years (1885-1935); that is, from its very begining up to this day. In January 18, 1885, our friends consisting mining engineers, metallurgists and geologists assembled together in a room of Geological Society, Nishi-Konyacho in Ginza, Tokyo.
These engineers and geologists discussed earnestly how to carry out to organize an Institute to promote the mining and metallurgical engineerings, and geological investigations in Nippon. We came to the conclusion to establish a very complete institution under the name of Nippon Kogyo Kai (Nippon Institute of Mining and Metallurgical Engineers). The final meeting we held was on the day of January 28th, 1885. That day has been considered as The Day of the Establishment of our Institute. And those who gathered on that day were 20 in number, but sorry to say that 18 men among them had already gone, remaining only two of them. These two survivors are Mr. Shigeru Sugata and myself, who are still quite healthy and vigorous as ever.
In this sketch, some outlines of important events happened in the 50 years, was described and brief notes on the personality of late Takato Oshima and Wataru. Watanabe, with whom I worked in Sado Mines, myself as chief mining engineer under them, or some time under one of them, for 11 years from 1884 to 1895. Both of these enlightened great men did splendid achievements in modernizing our mining and metallurgical engineerings of Nippon, in the Great Meiji Era. They and their deeds are all imperishable forever in our mining history.
Short descriptions of our distinguished honorary members, Yajiro Ito, Tsunashiro Wada and Marquis Kaworu Inouye, were somewhat precisely described. Yajiro Ito was one who sdid much for our Institute in promoting it to its perfect condition from very beginning soon after its organisation.
I have written somewhat in detail what we have done in welcoming the party of the members of the American Institute of Mining and Metallurgical Engineers who came to Nippon in the year of 1911. The party consisted of 82 ladies and gentlemen, among whom there were many prominent and distinguished mining authorities, including most honorable and esteemed authority in the mining circle, Dr. R. W. Raymond, who was so well known not only in America but all over the world. We paid a special attention to Mrs. Raymond and Dr. Raymond while they were in Nippon.
In the last part of this sketch, some future view of the Institute has been mentioned as my expectation for the prosperity of the Institute in the day coming as next 50 years.

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The Okuzo prospect is located 20 km southeast of Odate city, Akita prefecture. The Metal Mining Agency of Japan (MMAJ) discovered Kuroko-style mineralisation accompanying lead, zinc, gold and silver during a regional geological survey of the area.
The Okuzo prospect is located on the southeastern rim of the Hokuroku Kuroko Basin, which is closed along a line extending from the Gacchimaeda fault to the boundary of the southern rim of the Gattsu basin based on geological and gravity data. As a result of the geological survey by the MMAJ, a fragment of Kuroko ore with a diameter of 15cm was discovered in an outcrop of volcaniclastic rock; analysis returned 0.75g/t Au, 160g/t Ag, 0.2% Cu, 5.2% Pb, 23.0% Zn and 39.5% BaSO4.
Based on induction polarization and drilling surveys, the characteristics or hanging-wall and foot-wall alteration associated with Kuroko mineralisation were identified as the presence plagioclase and chlorite-sericite, respectively. It is proposed that volcanic activity had been continuous at the middle Miocene after the Kuroko mineralisation and resulted in the formation of vent breccia.

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Ore finding by geologic features has been highly developed in recent years. Yet it may be said that such a method still leaves something to be desired in the way of locating the exact position of new ore body of vein-type, especially, compared with those of massive- or bedded-type. In order to locate new veins effectively, the writer presents helpful suggestions on the prospecting by geologic features, as well as on the exploration by drifting.

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