Geologic history of the area, especially on the development of geologic structure, volcanic activity, sedimentary environment and metallic mineralization, is summarized here mainly based on drilling data with some geophysical measurements.
Geology of the Kunitomi mine area consists of acid volcanic rocks of Miocene in age which are represented by tuff breccias, tuffs, lava domes, lava flows and dykes of dacitic in composition. The volcanic pile is covered by normal sediments of tuffaceous mudstone, sandstone and tuff with some dolerite lava flows.
Geologic structure in this area is characterized by complicated pattern of sheared zones represented by two main systems of E-W and N-S directions. The pattern is thought to control the location of dacitic volcanic activities.
Ore deposits of the mine are of so-called Kuroko type. The mineralization is classified into the following two types. The first shows very close genetical relation with eruption of dacite-A and is characterized by the development of bedded ore body with massive Kuroko ore on the top of dacitic lava dome, as No. 3, 4, 6 or 7 Ore Body. The other is dissiminated or stock-worked deposit mainly in the brecciated part of lava dome of dacite-B as No. 5 or Fuden Ore Body.

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The relationship between geological properties and geophysical properties of the underground structure is very complicated. For example, carbonaceous slates commonly show a low resistivity, whereas limestones usually show a high resistivity but it is noticed that the use of geophysical explorations for geological surveys is not so much adopted.
In this paper, the authors intend to explain a trial study for the relationship between geological surveys and geophysical explorations, mainly electrical explorations, in the case of the Kunitomi Mine, Sumitomo Metal Mining Co., Ltd.
The geological survey map is shown in Fig. 2 and the resistivity exploration map is shown in Fig. 15. In these maps, the weakly altered zone correlates with the low resistivity zone and the dolerite zone correlates with the high resistivity zone.

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The lead-zinc deposit of the Toyoha Mine consists of two different groups of epithermal veins, e.g., one is the earlier vein which is controlled by E-W fracture system (Tajima, Harima, Bizen etc.) and the other, the later one running to NW-SE trend (Soya, Hiyama etc.). The former is mainly composed of sphalerite, galena and a lot of quartz, and the latter is characterized by the presence of rhodochrosite and poverty of quartz.
The iron-rich banded ore occurs in Bizen-vein, especially in a limited area adjacent to the intersecting point with Hiyama-vein. The pretty stripe of the banded ore has the paragenesis of earthy hematite-wedge shaped hematite-magnetite-pyrite-quartz. There exists, however, nearby the banded ore, the semi-banded one with the paragenesis of earthy hematite-goethite. This one occurs in siderite-chlorite rock and we take it to be an embryo of the normal banded ore.
The formation temperature of these ores was determined by the homogenization temperature of liquid inclusions in quartz associated with the ore minerals.
Judging from the mode of occurrence and the nature of the ore it is considered that the banded ore might have been formed as the result of the diffusion metasomatism caused by the later mineralization. The metasomatism should be characterized by the movement of mobile components such as CO₂, O and S relating to the oxidation-reduction process of the hydrothermal solution.

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