The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists
Online ISSN : 1883-0765
Print ISSN : 0021-4825
ISSN-L : 0021-4825
Volume 82, Issue 10
Displaying 1-4 of 4 articles from this issue
  • YASUHIRO SHIBUE
    1987 Volume 82 Issue 10 Pages 353-361
    Published: October 05, 1987
    Released on J-STAGE: August 07, 2008
    JOURNAL FREE ACCESS
    Fluid inclusion study on the Itaga tungsten deposit is carried out in order to characterize the hydrothermal solution responsible for this deposit. Polyphase fluid inclusions and vapor-rich ones as well as liquid-rich inclusions are found in quartz of the disseminated ore in the Itaga granite. Vapor-rich and liquid-rich inclusions are found in vein quartz, scheelite, and topaz from this deposit, but polyphase inclusions are not found in these minerals.
    Homogenization temperatures of primary fluid inclusions in quartz of the disseminated ore, vein quartz, scheelite, and topaz range from 518° to 261°C, from 388° to 265°C, from 336° to 301°C, and from 420° to 370°C, respectively. Salinities of primary fluid inclusions in quartz of the disseminated ore, vein quartz, scheelite, and topaz range from 45.1 to 0.9, from 21.0 to 8.3, from 7.9 to 5.3, and from 14.3 to 3.1 NaCl eq. wt%, respectively. The highest temperature and salinity reported in the present study are higher than any other data previously obtained for the Japanese tungsten deposits.
    Based on the plots of homogenization temperature against salinity, it is suggested that there were at least two hydrothermal solutions, i.e., very saline and dilute ones, responsible for the mineralization of the Itaea deoosit.
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  • Noriyoshi Tsuchiya, Shunichi Suzuki, Yukito Oda
    1987 Volume 82 Issue 10 Pages 362-369
    Published: October 05, 1987
    Released on J-STAGE: August 07, 2008
    JOURNAL FREE ACCESS
    The Kuga Group of Triassic-Jurassic age is mainly composed of black pelitic rocks and chert which were thermally metamorphosed by intrusion of Cretaceous granite. Graphitization of carbonaceous material in pelitic rocks of the Kuga Group was investigated using X-ray diffraction method. Samples were collected from six boreholes, of which three boreholes reached to the granite.
    Crystallite thickness Lc(002) value increases toward the granite pluton and is 300Å at a vertical distance of 200-300m from the contact. Near the contact Lc(002) is 400Å or more. Lattice strain εc decreases with increasing Lc(002).
    Vertical and lateral changes in Lc(002) of carbonaceous material in the Kuga Group are illustrated in the geological section showing the isopleth of Lc(002). The isopleth of Lc(002) is generally parallel to the contact. These features suggest that heat transfer through the Kuga Group depends chiefly on thermal conduction. Graphitization of carbonaceous material in sedimentary rocks is applicable to the prediction of the subterranean pluton.
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  • Masahiro Daishi, Masao Hayashi, Yuzo Kato
    1987 Volume 82 Issue 10 Pages 370-381
    Published: October 05, 1987
    Released on J-STAGE: August 07, 2008
    JOURNAL FREE ACCESS
    The radio-metric ages on 13 volcanic rocks from the Ryukyu Islands have been measured by one of fission track methods (viz. arranged fixed area population method, external-surface external-detecter method and external-surface internal-detecter method) or K-Ar method. The ages obtained are as follows: Takarajima propylite/1.4±0.4Ma (KAG-001), 5.05±0.38Ma (KAG-002), and 1.1±0.3Ma (KAG-003); Tairajima andesite/4.79±0.96Ma (KAG-004); Suwanosejima andesite/0.64±0.16Ma (KAG-006); Nakanoshima andesite/1.75±0.22Ma (KAG-008), and 0.14±0.06Ma (KAG-009); Okinawajima andesite/16.6±1.4Ma (OKA-011); Agunijimadacite/6.24±0.46 (OKA-021); Kumejima andesite/12.8±2.1Ma (OKA-023), and 15.1±2.6Ma (OKA-024); Ishigakijima rhyolite/44.1±1.8Ma (OKA-033), and 43.5±1.8Ma (OKA-035). Of these, two samples of KAG-001 and KAG-003 were measured by the whole-rock K-Ar method. The age determination has resulted in the recognition of four stages of volcanism in the Ryukyu Islands: middle Eocene Green-Tuff, middle to late Miocene Green-Tuff, late Miocene to early Pleistocene Older-Volcanic Islands, and early Pleistocene to Recent Younger-Volcanic Islands.
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  • Mitsuo Shimazu, Itsuo Ishimaru
    1987 Volume 82 Issue 10 Pages 382-394
    Published: October 05, 1987
    Released on J-STAGE: August 07, 2008
    JOURNAL FREE ACCESS
    The Kushigatayama Subgroup, Kurosawa basalt-mudstone and Tsukimibashi andesite of the Nishiyatsushiro Group of middle Miocene are distributed in the eastern part of the Koma mountain and are composed of basaltic and andesitic lavas and pyroclastic rocks and small amounts of mudstones and acid tuffs. Most of the volcanic rocks were altered to low-grademetamorphic rocks ranging from laumontite to prehnite-pumpellyite facies.
    Volcanic rocks of the Kushigatayama Subgroup are composed of olivine basalt, diopsideolivine basalt, diopside-augite basalt, augite andesite, hypersthene-augite andesite and augitehornblende andesite. Almost of olivine phenocrysts are altered to saponite or chlorite/saponite mixed layered mineral. Phenocryst clinopyroxenes are diopside, endiopside, salite and augite and groundmass clinopyroxenes range augite through subcalcic augite to pigeonite. Mafic phenocryst content is 38.8 percent in maximum. Abnormal phenocryst content results from the presence ofmegacryst or cumulate.
    Most of volcanic rocks may belong to tholeiite series. Basalts having FeO*/MgO ratios(0.91-1.00) are very close to the primitive basalt in composition, although some basalts include cumulates. Differentiation from olivine basalt to andesite is mainly interpreted by fractionation of olivine, clinopyroxene and plagioclase.
    From whole rock chemical compositions, P2O5/MnO/TiO2 ratios in Mullen's diagram and chondrite-normalized REE concentration, basalts of this area as well as those of the Misaka and Tanzawa areas are obvious to be island arc tholeiite.
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