Mining Geology

The authors have been engaged in the exploration of black ore deposits (Kuroko) in the southern part of Shiretoko peninsula, Hokkaido, since May 1950.
In this paper, the ore deposits in this area are mainly reported. The general geology will be described in another paper in the near future.
The important ore deposits in this area are black ore and sulphur. This paper is concerned only with the black ore deposits.
The black ore deposits of the Nemuro, Rubeshu, Kunbetsu, Sakimui and Rikushibetsu mines have been explored. Those of the Shibetsu, Toa and Shinutoro mines are under exploration.
The southern part of Shiretoko peninsula consists of Neogene Tertiary and Quarternary rocks. The igneous rocks are generally divided by age into two groups, Neogene Tertiary and Quarternary. The Neogene Tertiary rocks are associated with the hinge zone of eastern Shiretoko, while the Quarternary rocks are associated with the Shiretoko central anticlinal structure.
The authors believe, the black ore deposits were formed as the post actions of the acidic igneous activities along the hinge zone.
The forms of each ore deposit in this area are characterized according to the types of associated igneous activities and geological structures. That is one of the key principles on which exploration of the ore deposits is based.

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The "Kajika", namely, bonanzas, of the Ashio Mine occur both in. Palaeozoic chert and in rhyolite. The Kajika in chert are localized in two groups, Arikoshi and Renkeiji.
The Arikoshi bonanza are formed almost perfect replacement of chert by mineralizing solutions, ascending along the Arikoshi synclinal axis, which plunges into the intersection line of two main tectonic planes. This intersection line is the most important channel for the mineralizing solutions that caused deposition of the bonanzas in chert.
The Renkeiji bonanzas are widely disseminated ore bodies in chert. The mineralizing solutions were of the same stage and source as the Arikoshi solutions, but differ only in that they caused mineralization along the anticlinal axial plane, branching numerous passages, shear veins, pebble and lamprophyric dikes, microfolding axes, and joints, etc. at upper levels.
Ore minerals are distributed zonally, the earlier stage is characterized by native bismuth, bis-muthinite, pyrrhotite and marmatite. Pyrrhotite is rich especially along and in the vicinity of passa-ges. At the later stage, chalcopyrite is predominant in distant and silicified chert.
It will be noted that the alterations of the wall rock, such as silicification, chloritization, sericitization and color change of grey chert to red, have been closely associated with the mineralization.

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Gogo-Myaku (No.5 Vein) is one of the representative veins in the Konomai Mine in the Kitami District, Hokkaido, the most famous gold-silver mine in Japan.
In this paper, the writer gives a preliminary account of the characteristic features and genesis of the vein. The vein is an epithermal gold-silver quartz vein type in which the mineralization may be divided into the following stages:
Facies 1 (F₁) Quartz-calcite-adularia, and pyrite facies. (early stage).
Facies 2 (F₂) Quartz-adularia, Au-Ag minerals, and pyrite facies. (middle stage).
Facies 3 (F₃) Quartz-clay, minerals, Au-Ag minerals, and pyrite-marcasite facies. (late stage).
Facies 4 (₄) Quartz-calcite, pyrite-marcasite facies. (last stage).
It is remarkable that marcasite is abundantly formed in F₃ facies. Pyrite and marcasite are not usually associated with Au and Ag minerals.

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