H₂S is carried upward by the superheated vapour, probably generated by the contamination of acidic plutonic rocks. Variable types of sulphur deposits have been formed by the difference in the location of the deposits. According to the alteration and mineralization, the physical and chemical features of the environments during the formation of sulphur and pyrite are summarized as follows: sulphur mineralization is caused by strongly acidic gases at temperatures between 130-100°C, which is transported by saturated vapour in ore bodies. The pyrite ore bodies are formed in acidic hydrothermal solutions ranging from pH 1.O to 5.O at temperatures between 120-100°C. Most of the iron in pyrite has teen derived from the country rocks.

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Takahara volcano, 1795m above the sea level, about 150km north of Tokyo, occupies a significant position, by which the Nasu Volcanic Zone is divided into the southern subzone and northern subzone. This volcano forms the northern end of the southern subzone, lying on the basement composed of sediments of Paleozoic, Cretaceous granitic rocks and Neogene sediments and volcanics. The main part of the volcano is made of the basalts and pyroxene andesites of tholeiite series and the pyroxene andesites of calc-alkali rock series in the early and middle stages (middle to late Pleistocene). This activity was followed by the eruption of dacitic pumice flow southeastward, about 1.2km³ in volume, covering an area of about 60km². The last stage is represented by the eruption of the pyroxene andesite and hornblende dacite of calc-alkali rock series, resulting in the small two domes.
Sixteen representative rocks are chemically analysed. They are characterized by high lime and low alkalies contents (alkali-lime index=65.6 in calc-alkali rock series). The MgO-FeO+Fe₂O₃-Na₂O+K₂O diagram shows clearly the difference between tholeiite series and calc-alkali rock series. The tholeiite series is slightly enriched in iron in the middle stage of differentiation, whereas the calc-alkali rock series does not show such tendency. The boundary curve between tholeiite series and calc-alkali rock series is slightly lower than that of Nasu northern subzone, but is slightly higher than that of Nyoho-Akanagi and Nanati volcanoes which belong to Nasu southern subzone.

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[in Japanese]

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