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Volume 70, Issue 7
Displaying 1-4 of 4 articles from this issue
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KENZO YAGI, HIDEO ISHIKAWA, MASANORI KOJIMA1975 Volume 70 Issue 7 Pages 213-224
Published: July 05, 1975
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSA large lamprophyre sheet, about 10-20m thick and almost 20km long is exposed within the Tertiary formations of Tanegashima Island, Kagoshima Prefecture, Kyushu. Although the sheet is fairly homogeneous throughout the outcrop, minor-scale crystallization differentiation in situ is observed, forming chilled contacts and coarse-grained inner parts, associated with transitional parts. The constituent minerals include plagioclase, anorthoclase, kaersutite, titan-biotite, augite, magnetite, apatite and secondary minerals, such as chlorite, epidote, zoisite, calcite, etc. Quartz and olivine are entirely absent.
Chemical composition of various parts of the sheet shows rather wide variation, ranging from 49.7 to 56.8% SiO2. With decreasing soldification index, SiO2, Al2O3 and K2O increase, FeO, MgO, Fe2O3 and TiO2 decrease, while Na2O and CaO remain more or less constant. Although K2O is always less than Na2O, a rather high K2O/Na2O+K2O ratio is noticed. Petrochemical features are discussed compared with alkalic rocks in Japan and the surrounding areas. From the mineralogical composition it is estimated that the rock was formed under moderate water pressure from alkali basaltic magma, resulting in the formation of kaersutite and biotite, in place of olivine and titan-augite.View full abstractDownload PDF (1724K) -
Hirosato Yamamoto, Masanori Teshima1975 Volume 70 Issue 7 Pages 225-235
Published: July 05, 1975
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSAmphibolite in the Sangun metamorphic rocks of Sasaguri district was studied from petrological and petrochemical point of view. The Sasaguri metamorphic rocks, which are mainly composed of greenschist and blackschist, were found to be the products of the glaucopbanitic metamorphism. Closely accompanied with these rocks, serpentinite and amphibolite occur in the southeastern part of this district.
In the northeastern part of the area the Sangun metamorphic rocks suffered contact metamorphism by the later intrusion of the Hagio granodiorite. The contact aureole around it can be divided into two zones, of which zone I belongs to the albite epidote hornfels facies, and zone II to the hornblende hornfels facies. However, among the Sangun metamorphic terrane, high grade metamorphic rocks corresponding to the amphibolite facies have never been found. So far amphibolite of this district has ever been considered to be the product of contact metamorphism of the Sangun metamorphic rocks by the Hagio granodiorite.
But the present study clarified that amphibolite occurs beyond the contact aureole of granodiorite mass. This fact indicates the possibility that amphibolite may be formed by the pre-Sangun metamorphism. The recent finding that K-Ar ages of hornblende from this amphibolite are 295±20 and 383±14 m. y. may support this aspect.View full abstractDownload PDF (3201K) -
Yôichi Muramatsu, Matsuo Nambu, Tsunehiko Takeuchi1975 Volume 70 Issue 7 Pages 236-244
Published: July 05, 1975
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSValleriite occurs as thin tabular or lenticular aggregates of small prismatic crystals up to 0.02×0.3 mm in size in so called “high temperature skarn” consisting mainly of vesuvianite, grossular, wollastonite and calcite near the no. 4 ore body of Sakae contact metasomatic copper-iron ore deposit at no. 8 level of Akagane mine located at the western extremity of central Kitakami mountainland. The associated ore mineral is just cobalt-bearing pentlandite. X-ray powder diffraction data for the present material was found to conform very closely to the data on valleriite from Loolekop, S. Africa given by Evans et al. (1964). Quantitative electron probe microanalysis yields the formula [Cu1.13Fe0.83S2]• 1.77[Mg0.82Al0.18(OH)2]. This true valleriite is the first occurrence in Japan.
Mackinawite occurs as emulsions, bleds, dots, needles and irregular veinlets in a microscopic size as exsolution products in chalcopyrite of pyrrhotite-chalcopyrite massive ore at the 7 level of Hozumi deposit. The mineral is accompanied by cubanite, magnetite, sphalerite and quartz. EPMA gives the formula of (Fe0.83Co0.12Cu0.01Ni0.01)0.97S. Textural evidence and the results of the studies for the breakdown temperature of mackinawite suggest that the exsolution of the mineral from the chalcopyrite solid solution occurs at lower temperatures than about 130_??_230°C shown in the preceding literature.View full abstractDownload PDF (1279K) -
Masashi Yoshida, Ryuichi Yashima1975 Volume 70 Issue 7 Pages 245-248
Published: July 05, 1975
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSAragonite crystals grown in the geodes of Ryozen basalts, Fukushima Prefecture, Japan, were described by means of optical microscope, chemical analysis and X-ray diffraction. The specimen consists of aggregate crystals and each crystal is prismatic, acicular and platy as shown in Fig. 2 and 3. The color of lower part of the crystal is white, the middle part is brownish or amber-like and the top transparent.View full abstractDownload PDF (1381K)
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