The Tashiro Mine is situated in the so-called "Nishiaizu Kuroko Area", approximately 45km southwest of Aizu-wakamatsu city, Fukushima Prefecture. The ore deposits are divided into the Tashiro group and the Oshio group. The former consists of five orebodies, namely, Takamori No.1, No.2, Manakura North, Manakura and Shibozawa.
In gathering the previous geological data, the Oshio group were then chosen as the most promising exploration target and the following was established as the ore indicator;
the presence of
(1) Kuroko ore horizon,
(2) Structual weak zone with NW-SE trend,
(3) Ferruginous quartz zone, and
(4) Network and impregnated zone
Thus, the Oshio orebody (350m×150m×12m) and the Lower Oshio orebody (150m×100m×8m) have been discovered since 1960.
The ore deposits occur syngenetically in the pyroclastic rocks of the upper part of the Takizawa Formation. They underlie the alternation of perlitic tuff and mudstone of the Oshio Formation, which corresponds to the Nishikurosawa stage. Generally speaking, the ore deposit shows the zonal arrangement in the following order from the hangingwall toward the footwall; ferruginous quartz-, barite-, black ore-, pyrite-and network zone. However, it is characteristic that the gypsum occurs predominantly in the lower part of the Lower Oshio orebody.
With progress of the exploration, the following efforts have been made in addition to looking for the above ore indicators;
(1) To locate the altered zone (sericitisation-chloritisation zone)
(2) To clarify the sedimetation mechanism of the country rock.
(3) To study the distribution of the minor element.
(4) To explore the area of the mudstone hangingwall (Globorotalia-Hopkinsina zone).
It is expected that as the underground working is developed, the geological occurrence of the ore may be clarified and the more concrete indicators for the future exploration becomes available.

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Geologicic setting of the mining area is composed of the Miocene formations of thick volcanic rocksresting on the basement of the Mesozoic to Paleogene sedimentary formations. The Miocene formations are, in ascending order, two pyroxene andesite and its pyroclastics, hornblende-bearing two-pyroxene andesite and its pyroclastics, hornblende andesite, and biotite-bearing plagio-rhyolite. These formations are covered unconformably by two pyroxene andesite, the Quaternary welded tuffs and volcanic ash beds.
Epithermal gold-silver quartz veins the Honzan Group of simple mineral assemblages, occur in the andesite rocks just below the plagio-rhyolite formation. The vein pattern and the localization of ore shoots are well controlled by the regional structure and local geologic features. Total gold hitherto produced from twelve veins has amounted up to 1.3 million tons of 14.3 g/t Au in average.
Geological analyses, geothermal investigation, electrical prospectings using spontaneous polarization and resistivity methods, and drilling, which have been carried out on the puddy rice field about 2.5 km to the west of the Honzan Group, have been successful in discovery of the new Shimoushio vein group of the comparable scale. Intimate association of hot spring activities with veins experienced during mining of Honzan Group deposits were important hint for locating the new exploration area.

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The ore deposits of the Yubaridake manganese mine were discovered in a blank part of the distribution area of this kind of ore deposits. Later, it was found that ore deposits of this kind are distributed sporadically along the median zone of Hokkaido.
The ore deposits of the Yubaridake mine are irregular flat masses or cylindrical in shape, occurring in diabase, schalstein (diabasic clastic rock) and chert of the Sorachi group which. is correlated with the Jurassic to the early Cretaceous. They consist of four ore bodies, two of which have been already mined.
The manganese minerals of the ore are braunite, rhodochrosite, alabandite, penwithite, rhodonite and manganese dioxide. A mineral closely resembling manganosite in external appearance was identified as alabandite as a result of various studies. This mineral was hitherto thought to be rare in the low temperature hydrothermal metasomatic ore deposits.
Both the country rock and the ore contain such microfossils as radiolaria belonging to Superfamily LIOSPHAERICAE, Superfamily ARCHIPILIICAE and Family STYLOSPHAERIDAE. The ore also shows the colloform texture, which seems to have been replaced by braunite and rhodochrosite, and the fossil-replacing texture in which the metasomatism might have advanced successively with the order of quartz, rhodochrosite and braunite. In some cases the fossil-replacing texture is weakly altered, so that the internal structure of fossil is distinct, and only quartz is the replacing mineral. In other cases the alteration is much more advanced so that the internal structure is indistinct, and the replacing minerals are rhodochrosite and braunite, with scarce quartz. In such cases, rhodochrosite remains in microfossils of a relatively large size, but in small fossils rhodochrosite is replaced by braunite. In fossils of an intermediate size, rhodochrosite is partly replaced by braunite. Thus, different degrees of metasomatic alteration are recognized.
Since the manganese ore deposits, inclusive of those of the Yubaridake mine, having the above characteristics, are distributed along the median zone of Hokkaido and they are similar in the mode of occurrence, these ore deposits may be sedimentary ore beds or they were formed under low temperature conditions in a shallow depth.
In the past it was considered that all of the ore deposits of this kind in Hokkaido were formed by metasomatism along the shear zones. However, the origin of some of the ore deposits should be reexamined from the syngenetic viewpoint.

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The occurrence of malayaite (CaSnO⋅SiO₄) has been studied at several mines such as the Mitate mine, Miyazaki Prefecture, the Hoei mine, Oita Prefecture and the Kuga mine, Yamaguchi Prefecture. In each ore deposit, this mineral has been found from the periphery of pyrometasomatic deposists, or from the silicified zones of the country rocks near skarn bodies. From the results of the macroscopic and microscopic studies of the occurrence of malayaite, it is inferred that this mineral would have been formed by the following three processes.
1) Sn has been concentrated at the front of skarnization or at the silicified zone, and it has reacted with Ca and Si to form malayaite.
2) Ca- and Si-rich hydrothermal solutions have reacted with tin-bearing minerals such as cassiterite and tin-bearing andradite in the skarn, and malayaite has been formed using Sn supplied from these tin-bearing minerals.
3) Sn, Ca and Si have been transported into veinlets by the hydrothermal solutions and malayaite has been formed there with quartz and calcite.
Under the Fe-rich condition such as the skarnization, Ca and Si would have reacted with Fe, forming garnet or clinopyroxene, and Sn would have crystallized as cassiterite without forming malayaite. According to the electron probe microanalysis, malayaite from the Mitate mine contains 2.0%-4.6% Ti, while the one from the Kuga mine contains 0.3% Ti. The contents of Sn and Ti within a single crystal grain of malayaite vary distinctively and the negative correlation between the two elements is conspicuous.

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The Itaya mine, the largest domestic kaolin mine for paper clay, is located on the eastern slope of the Quaternary Azuma volcano where formations of lavas, pyroclastic rocks and mud flows are extensively distributed. The underlying Tertiary formations are exposed at several places as windows.
Two kaolin bodies are under operation at present. Kaolinite is a common mineral of both bodies, while sericite is found only in the layer deposit No.1, and dickite is locally found at the center of the deposit No.2. It has been made clear that they were both formed by hydrothermal alteration. Nevertheless, the controversy about the age of original rocks and alteration has not been settled.
In 1968, the writer found a piece of coalified wood in a kaolinized andesite lava of the deposit No.2. The absolute age of the coalified wood was determined by ¹⁴C method in the laboratory of Prof. Kigoshi, Gakushuin University, to be
30, 600±2, 200 yrs. B.P.
This result reveals the highest possibility of the Upper Pleistocene age of original rocks of the deposit No. 2, and denies the Tertiary mineralization. The actual age of the hydrothermal alteration that formed the kaolin deposit must be some time between the age determined and the present. Geologic evidences and the dating result indicate that the deposit No.2 was formed by volcanic activities of the Azuma volcano.

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