JOURNAL OF MINERALOGY, PETROLOGY AND ECONOMIC GEOLOGY
Online ISSN : 1881-3275
Print ISSN : 0914-9783
ISSN-L : 0914-9783
Volume 91, Issue 10
October
Displaying 1-2 of 2 articles from this issue
ORIGINAL ARTICLES
  • El Sayed A.A. YOUSSEF
    1996 Volume 91 Issue 10 Pages 353-363
    Published: 1996
    Released on J-STAGE: October 28, 2006
    JOURNAL FREE ACCESS
    Kaolin deposits initially formed as a lateritic crust on a nearby basement complex, then were transported to the central Wadi Kalabsha and deposited as flood plain and river bar deposits. Repeated fluvial influx and drying out of the kaolin resulted in the following facies: a) Intraformational disorganized conglomerate over the flood plain and/or on the flat bar-tops; b) Intraformational partially organized and organized conglomerates on the slip faces of bars and river banks, and/or as lateral point bars in sinuous streams; and c) Pisolites of kaolinite, kaolinite-hematite, hematite-kaolinite and hematite composition, either in erosion hollows and/or on the slip faces at the downstream end of lognitudinal and diagonal bars in braided rivers.
         The surface of the fluvial kaolin deposits was subjected to a second phase of in situ lateritization which resulted in a partial or complete dissolution of quartz and the formation of pisolitic laterites containing traces of gibbsite, geothite, hematite and anatase. Isotopic analyses of δ18O and δD of separated kaolinites showed that the pisolitic kaolin deposits are sedimentary and weathering in origin. The original reworked sedimentary-lateritic pisolites may be deposited during the late Mesozoic while the pisolitic laterites may be formed later as a crust in the Tertiary.
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SHORT NOTE
  • —— Granitic rocks of Matsukawa-ura drillhole ——
    Hiroshi KANAYA
    1996 Volume 91 Issue 10 Pages 364-372
    Published: 1996
    Released on J-STAGE: October 28, 2006
    JOURNAL FREE ACCESS
    Granitic rocks, collected 327-850 meters below the surface near Matsukawa-ura, were chemically and magnetically investigated. The main phase is medium-grained tonalite, but one interval (565-675 meters) contains fine-grained tonalite and weakly shistose medium-grained tonalite.
          Microscopic observations show that many samples are affected by weathering and alteration.
         Twelve major elements of 26 samples were analyzed, as were trace elements Rb, Sr, Y, Zr, Ba, Th and U. Magnetic susceptibility, saturation magnetization, and Curie temperature of the same samples were also measured.
         The results of the chemical analysis demonstrate the homogenity of medium-grained tonalite but magnetic properties varies widely in each sample.
         In comparing the abundance of chemical elements with the Miyako and Senmaya granitic bodies, in Kitakami Mountains and the granitic rocks in the Onikobe area (eastern area), western area of Kitakami Mountains, the medium-grained tonalite samples from the Matsukawa-ura drillhole are characterized by low K2O, Rb, Zr, Th and U content and high MgO, Na2O and Sr content relative to the averages of other granites with similar silica content.
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