BULLETIN OF THE GEOLOGICAL SURVEY OF JAPAN
Online ISSN : 2186-490X
Print ISSN : 1346-4272
ISSN-L : 1346-4272
Volume 62 , Issue 5-6
Showing 1-4 articles out of 4 articles from the selected issue
Article
  • Shunso Ishihara, Hideo Hirano, Mihoko Hoshino, Pham Ngoc Can, Pham Thi ...
    2011 Volume 62 Issue 5-6 Pages 197-209
    Published: October 31, 2011
    Released: July 02, 2013
    JOURNALS FREE ACCESS
        Selected ores from the Sin Quyen allanite-rich Au-bearing chalcopyrite-magnetite deposits were studied microscopically and chemically. The ore minerals tend to occur along the NW-SE-trending sheared zone of altered host rocks; yet the ore minerals show no stress effect, implying the mineralization later than the regional shearing. The ore minerals occur associated with the metasomatic minerals consisting mainly of clinopyroxene, hastingsite, allanite, epidote, biotite, titanite, carbonate minerals and rarely quartz. Allanites containing almost all of the rare earth element (REE) components of the ores occur in disseminated manner and are euhedral to subhedral. The mineral is an early crystallized mineral replaced by magnetite and chalcopyrite. The allanite contains around 16 wt.% REE and is low in mafic components having chemical composition of Mn-poor type, which tends to occur in the magnetite-series granitic rocks in Japan. The REE components could have been derived from an oxidized alkaline granitic activity of mid-Tertiary. Both chalcopyrite and magnetite are well separated by the mineral dressing, and all the allanites moved to the tailings. Therefore, the tailing pond turns out to be an excellent LREE reservoir in future.
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  • Hiroshi Kanaya, Shigeo Okuma
    2011 Volume 62 Issue 5-6 Pages 211-233
    Published: October 31, 2011
    Released: July 02, 2013
    JOURNALS FREE ACCESS
        About 1500 granitic rocks exposed in the inner zone of Southwest Japan were collected and measured on their physical properties such as density, porosity, magnetic susceptibility and Natural Remanent Magnetization (NRM). The results were classified in seven areas (Hokuriku, Chubu, east Kinki, west Kinki, east Chugoku, central Chugoku and north Kyushu) and their geologic time (late Cretaceous: K1-2 , K2 , Paleogene: PG1 , PG2 , Neogene: N1 , N3) and compared with the same geologic time between each area.
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  • Toru Shimizu
    2011 Volume 62 Issue 5-6 Pages 235-241
    Published: October 31, 2011
    Released: July 02, 2013
    JOURNALS FREE ACCESS
        Four new K-Ar ages of adularia at the Koryu Au-Ag epithermal vein deposit along with the mineralization stages were determined. One age is 1.4 Ma for the first mineralization stage and the other three ages are 1.19-1.10 Ma for the most economically important Au-Ag mineralization stage. Combined with published data of K-Ar ages, mineral description, and fluid inclusion study, the results suggest that the hydrothermal activities waxed and waned, forming ore veins with ten mineralization stages for 0.55 million years in the Koryu deposit.
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  • Yasuhiro Umeda, Satoshi Itaba
    2011 Volume 62 Issue 5-6 Pages 243-257
    Published: October 31, 2011
    Released: July 02, 2013
    JOURNALS FREE ACCESS
        The vertical crustal movement before the 1946 Nankai earthquake was obtained by the leveling of the Geographical Survey Institute(GSI). In Shikoku district, however, the leveling was carried out 7 years before the earthquake. The Hydrographic Bureau(HB) surveyed the co-seismic vertical changes and measured the difference between the measurement of last and just after the earthquake, on the bench mark of GSI or HB. The leveling data of GSI were obtained the Japanese vertical datum origin as a standard, on the contrary, the measurements of HB were obtained based on the mean sea level at each point. The error of latter values has +/-0.10m against that of GSI. The data of co-seismic vertical change have an error of +/-0.15m, because the vales were obtained by viewing of the HB staffs. In the case that the measurement value and co-seismic change are greater than above errors, it is effective to use them with the leveling data. We combined the data of GSI and HB, and obtained the vertical variation curves at 13 points in Shikoku, between 1898 and 1969. The co-seismic upheaval region has subsided in a long term before the earthquake. The co-seismic subsidence region has up heaved gradually about 15 years before the earthquake. It seems that the upheaval speed was accelerated just before the earthquake. The variation curves of vertical crustal movement in a long term will become a base when we assume a prediction curve for the next Nankai earthquake.
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