Compositions of Quaternary volcanic rocks from Oze area, central part of Honshu arc show trends inconsistent with the general trend of the arc. Analyzed volcanic samples include those from Pre-Nikura, Ooeyama, Chouzugatama volcanoes of shield volcano group, those from monogenetic volcano group, and those from Nikura volcano of stratovolcano group, younging in this order. They are mainly andesites but minor augite basalts are also found in Pre-Nikura volcano. Dacitic andesites of stages Nikurayama and Shiraoyama of Nikura volcano contain basic inclusions and show disequilibrium features such as quartz with pyroxene-jacket, plagioclase with dusty-zone and coexistence of magnesian olivine and quartz.
Most samples from Nikura volcano and monogenetic volcano group plot in the field of highalmina basalt series in the alkali vs. silica diagram. Whereas, samples of stage Nikurayama of Nikura volcano and shield volcano group plot in the field of tholeiite series. Samples of all the groups show higher K₂O/Na₂O ratios than those of Nasu volcanic zone to the north, reflecting a regional character. Interestingly they are richer in K₂O content than those from Niigata prefecture, to the side farther from the trench. When major element compositions of lavas are estimated at 60% silica for each volcano of central part of Honshu by linear regression, they show increase of K₂O content and K₂O/Na₂O ratio from Akagi volcano to Oze-Hiuchigatake volcano. In contrast, the Na₂O and CaO contents slightly decrease in the same direction.

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Sulfur isotopic compositions of pyrite, sphalerite, galena and barite, and also carbon and oxygen isotope ratios of rhodochrosite and calcite were measured so as to estimate the origin of ore-forming sulfur and carbon responsible for mineralizations found in the Oe deposit within the so-called “Green Tuff” Region, Japan. The δ³⁴S values of sulfides are in a comparatively narrow range of 5.0 to 10.0‰, which are similar to those of sulfide minerals from most Kuroko deposits in Japan. On the other hand, the δ¹³C and δ¹⁸O values of rhodochrosite measured are -6.4 to -9.4‰ and 2.9 to 9.9‰, respectively. Because formation temperature at the main stage is assumed to be near 240°C on the basis of sphalerite-galena and pyrite-sphalerite thermometers, the bulk isotope compositions of sulfur and carbon in the fluids can be considered on the log fO₂-pH diagram at 240°C. Consequently, it is proved that the isotope ratios of total sulfur and total carbon in the fluids can be regarded to be approximately 22‰ and -10‰, respectively. The former value corresponds to that for marine sulfate in the Neogene Tertiary age, so sea water sulfate is thought to have been related considerably to the sulfide mineralization. The latter value and oxygen isotope data, however, suggest a possibility that the ore-forming carbon responsible for the carbonate mineralization is meteoric in origin. Therefore, such a mechanism as leaching of “fossil” sea water sulfate by meteoric water should be taken into account for the Mn-Pb-Zn type mineralization observed in southwestern Hokkaido.

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Unusual monoclinic 11 Å tobermorite was found along with usual orthorhombic 11 Å tobermorite. Monoclinic tobermorite occurs in gehlenite-spurrite skarns at Fuka, Okayama Prefecture. It occurs as a vein-forming mineral in contaminated rock (hybrid) and in retrograde garnet. It is associated with orthorhombic 11 Å tobermorite, 14 Å tobermorite, calcite and appophyllite. It is found as colorless or white crystals up to 3mm.
The crystals are monoclinic, space group Cc or C2/c, with the unit cell dimensions: a 11.331, b 7.353, c 22.67 Å, β 96.59°. Microtwinning on (011) is always observed. The 002 spacing is reduced to 9.3 Å by dehydration at 300°C . Refractive indices are α 1.575, β 1.580, γ 1.585. Chemical analyses give a formula Ca_5.3Si₆(O, OH, F)₁₈•5.1H₂O. The chemical composition and the unit cell are closely related to those of orthorhombic tobermorite. Monoclinic tobermorite may be a low-temperature form of orthorhombic tobermorite.

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