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Volume 75, Issue 11
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Yasuhiro Kiyosu1980 Volume 75 Issue 11 Pages 353-358
Published: November 05, 1980
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe abundance and sulfur isotope composition were investigated for sulfur compounds in the Matsukawa geothermal well 8.
Pyrite is present in concentrations ranging from 1.14 to 12.9% by weight, and is abundant at depths of 300-600m. Anhydrite occurs mainly below 600 m zone and its content is mostly below 1%.
The hydrothermal pyrite sulfur has δ34S values ranging from -6.8 to -2.1 permil. Pyrite is slightly enriched in the heavy isotope with depths between 500 and 600m. The sulfur isotopic composition of anhydrite ranges from +14.9 to 21.2 permil except two samples. Deep anhydrite have heavier isotope compositions.
At temperatures between 250 and 350°C, the observed isotopic fractionation among pyrite, hydrogen sulfide and anhydrite agrees with equilibrium fractionation factors, suggesting that there was establishment of isotopic equilibrium between sulfates and sulfides. Hydrogen sulfide-anhydrite pairs from deep zone show both isotopic and chemical equilibrium giving isotope temperatures in good agreement with measured well temperatures (260°C).View full abstractDownload PDF (269K) -
Yasuko Okuyama1980 Volume 75 Issue 11 Pages 359-371
Published: November 05, 1980
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe Miyamori-Ohazama district, central Kitakami Mountains, is occupied by the late Paleozoic formations composed chiefly of black shales and fossiliferous limestones. These Paleozoic rocks have been intruded by the Cretaceous Tono granodiorite pluton and undergone contact metamorphism.
Three progressive metamorphic zones are recognized on the basis of mineral parageneses in metapelites. Zone I, most of which have been regarded as unmetamorphosed, is characterized by the assemblages of various phyllosilicates alined parallel to slaty cleavages. Zone II is characterized by the appearance of andalusite accompanied by muscovite, biotite, cordierite, garnet and occasionally gedrite. In zone III, sillimanite appears together with K-feldspar, biotite and cordierite.
Microscopic observation and X-ray powder diffraction study revealed that metapelites in low-temperature part of zone I consist of the assemblage of paragonite, pyrophyllite, albite and calcite with invariable association of chlorite, muscovite, quartz and carbonaceous matter, suggesting metamorphic grade lower than the greenschist facies. In high-temperature part of zone I, however, porphyroblastic chloritoid, formed by the reaction with pyrophyllite and Fe-rich chlorite, appears in metapelites of lateritic chemical composition (Al2O3 23wt%, FeO/(FeO+MgO)>0.79).
The degree of graphitization of carbonaceous matter in the metapelites progressively increases from zone I to zone III, showing a continuous thermal structure around the Tono granodiorite pluton. Judging from the graphitization-profile, all the assemblages mentioned above are considered to have been equilibrated under the thermal structure controlled by the Tono granodioritic intrusion.View full abstractDownload PDF (699K) -
HIDEO ISHIZUKA1980 Volume 75 Issue 11 Pages 372-376
Published: November 05, 1980
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESS“Soda-tremolite” having an intermediate composition between tremolite and richterite has been newly found in dunites from the Horokanai ophiolite in the Kamuikotan tectonic belt, Hokkaido, and its occurrence is the first report in alpine-type ultramafic rocks. The optical properties and crystal chemical formula of soda-tremolite are as follows; colorless in thin section, 2Vx(mean)=80°, r<v weak, c∧Z=15°, b=Y, and (Na0.6) (Ca1.4Na0.6) (Mg4.6Fe2+0.2Cr0.1Al0.1)(Al0.2Si7.8)O22(OH)2, respectively. The formation of the Horokanai soda-tremolite is probably explained by a local metasomatic process which increased the Na/Al ratio in the host dunite.View full abstractDownload PDF (1035K) -
YOICHI MURAMATSU, MATSUO NAMBU1980 Volume 75 Issue 11 Pages 377-384
Published: November 05, 1980
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe first occurrence of tochilinite and its variety, cuprian tochilinite in Japan were found in the so called “high temperature skarn” consisting mainly of vesuvianite, tilleyite, titaniferous andradite and calcite in the Shinyama pyrometasomatic copper-iron ore deposit of the Kamaishi mine, Iwate Prefecture. Two minerals occur as microscopic irregular aggregates ranging from about 100 to 500 microns in size composed of fibrous fine crystals along cracks and grain boundaries of vesuvianite in intimate association with calcite, hexagonal pyrrhotite and sphalerite.
Under the ore microscope, the reflection colour is yellowish brown. Reflection pleochroism is strong with colours changing from yellowish brown to yellowish grey, and also it is strongly anisotropic, with interference colours from pale yellowish brown to greyish white with yellowish tint. Reflectivities measured in air are: 486 nm 10.0-13.3%, 546 nm 10.2-14.9%, 589 nm 10.6-15.8%, 644 nm 10.8-17.6%. The polishing hardness is considerably lower than that of coexisting pyrrhotite, chalcopyrite and sphalerite. Optical properties of cuprian tochilinite resemble closely those of tochilinite above mentioned, actually indistinguishable from it.
Electron microprobe analyses of two tochilinite grains and three cuprian tochilinite grains yield to the empirical formulae 2[Fe0.78-0.77S]⋅1.85-1.81[Mg0.79Al0.20Ca0.01(OH)2] and 2[Fe0.68-0.63Cu0.15-0.24S]⋅1.71-1.65[Mg0.78Al0.21-0.20Ca0.01-0.02(OH)2], respectively.
The ore containing two minerals may be crystallized under the same condition as that of main copper ores at the Shinyama deposit.
X-ray study could not be made due to its extremely small amounts of these minerals.View full abstractDownload PDF (1742K)
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