In 1967, Nippon Mining Co. Ltd. commenced exploration in the west of the Lake Towada, and in 1968, a new Kuroko deposit was discovered. The deposit is located in the margin of the Namariyama basin, a small Miocene sedimentary basin between the Hokuroku and Hanawa major sedimentary basins where many Kuroko deposits occur.
The stratigraphical horizon of the Ginzan deposit, which is correlated with the upper part of the Nishikurosawa stage of Middle Miocene, is the same as the horizon of many Kuroko deposits in the Green Tuff region. Lithology of wall rocks, properties of ores, and nature of wall rock alteration are briefly described.

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Limestone bodies are weathered and eroded unevenly as exemplified by the presence of many doline sinkholes. Thus the shape of the bodies is quite irregular and the thickness of soft sediments covering the limestone varies markedly. This is one of the difficulties on mining of limestone. Moreover, the caves filled with mud water within the limestone bodies are often even dengerous for mining operation. Various methods of geophysical exploration were tried to make clear the modes of occurrence and structure of the limestone bodies.
By means of vertical electric sounding the distribution of soft sediments on the limestone bodies were disclosed more effeciently compared with the drilling and trenching methods. Electrodes were set on the earth's surface and limestone caves filled with mud, and electric potentials of pit walls were measured. This method was proved to be successful for finding limestone caves with mud. Various practical methods of geophysical exploration for limestone bodies are described and evaluated.

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The K-Ar ages of the minerals from several ore deposits in Japan were determined as follows :
Adularia from the Au-Ag-quartz vein of the Seikoshi mine,
Shizuoka Prefecture 3.7 m.y.
Adularia from the Au-Ag-quartz vein of the Takatama mine,
Fukushima Prefecture 8.4 m.y.
Adularia from the Cu-quartz vein of the Ani mine,
Akita Prefecture 11 m.y.
Orthoclase from the Ag-quartz vein of the Omidani mine,
Hyogo Prefecture 66-68 m.y.
Orthoclase and muscovite from the W-Sn-Cu-quartz vein of Kaneuchi mine,
Kyoto Prefecture 73 m.y. and 93 m.y., respectively
The ages of the mineralization of the Takatama and Seikoshi mines are considered to be the Pliocene and the late Miocene, respectively.
The K-Ar age of adularia from the Ani mine is similar to that of orthoclase and biotite of the Taishoko granitic rock where the major ore veins occur. The vein-type deposits of this mine are probably related to granitic intrusion of the middle Miocene.
The K-Ar age of the Omidani ore deposits is similar to that of the Ikuno and Akenobe xenothermal-type ore deposits. From the K-Ar dating as well as the zonal distribution of hypogene minerals, the Omidani silver deposits are thought to constitute an outer zone of the Ikuno-Akenobe metalliferous district. The mineralization seems to be a part of the late Cretaceous to Paleogene granitic activities.
The muscovite age of the tungsten deposits of the Kaneuchi mine belonging to the hypothermal or pegmatitic vein-type coincides with the isotopic ages of the granodiorite where the Otani tungsten deposits occur. It is inferred that the deposits of the Kaneuchi mine are genetically related to the late Cretaceous granitic activities.

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[in Japanese]

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[in Japanese]

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