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Volume 78, Issue 9
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Yoshiki Yamamoto1983 Volume 78 Issue 9 Pages 313-323
Published: September 05, 1983
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe Wada-gawa area, central part of the Hida metamorphic belt, consists of diverse gneisses of the upper amphibolite facies, which were later intruded by several small granitic bodies.
Garnet porphyroblasts in pelitic gneisses are replaced by biotite along their rims and cracks, and are separated into smaller parts by biotites films. The replacement proceeds more remarkably in the neighbourhood of the small granitic bodies, suggesting that the replacement is closely related to the granitic intrusion. Each of the separated parts of the garnet shows a reverse zoning in which Fe and Mn contents increase and Mg content decreases from the core to the rim, although the core of some larger garnet is homogeneous. The compositional contour of the reverse zoning is concordant with irregular outline of the resorbed garnet.
The mode of occurrence and the zoning pattern of garnet suggest that the reverse zoning of garnet was formed by volume diffusion in garnet crystal during the retrogression of garnet which was closely associated with the intrusion of small granitic bodies.View full abstractDownload PDF (1533K) -
Taisei Sato, Shunso Ishihara1983 Volume 78 Issue 9 Pages 324-336
Published: September 05, 1983
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSAbout 320 Tertiary granitoids from the Outer Zone of southwest Japan and the Hidaka Belt of central Hokkaido are statistically compared on major element chemistry. These granitoids occur along the tectonic zones facing fore-arc basin, and have similarities in geological age and opaque mineralogy (il-series). The main conclusions are as follows:
(1) The granitoids from the Hidaka Belt are similar to those from the Outer Zone of southwest Japan, being rich in K2O and FeO but poor in CaO and Fe2O3 compared with the average of Japanese granitoids (Aramaki et al., 1972).
(2) A considerable difference, however, is noted in Na2O content between granitoids of both regions. The granitoids of the Hidaka Belt have higher Na20 content than those of the Outer Zone of southwest Japan. The sodic character of granitoids in the Hidaka Belt may be ascribed to the sodic nature of the source material which is the sedimentary and metamorphic rocks of the Hidaka supergroup that contained originally abundant volcanic materials. The granitoids of the Outer Zone of southwest Japan may have interacted with both the gneissic basement and the Shimanto supergroup having low Na2O and high K2O contents.
(3) TiO2 content of granitoids from both zones are higher than the average of Japanese granitoids.
(4) Al2O3 content of the granitoids of the two zones is similar to that of the Japanese average, but their excess Al2O3 calculated as normative corundum (corundum index) is higher than the average.
(5) In the Hidaka Belt, occurrence of S-type granitoid besides I-type one is suggested from the major element chemistry, which is consistent with recent finding of cordieritebearing granitic rocks from this belt.View full abstractDownload PDF (944K) -
Shunichi Suzuki, Yukito Oda, Yoshihiko Oyama, Matsuo Nambu1983 Volume 78 Issue 9 Pages 337-349
Published: September 05, 1983
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe area southeast of the Lake Towada lies in the eastern border of the Green Tuff region, which are characterized by submarine volcanic activities in the Miocene. Recently a number of boreholes were drilled through the Miocene sediments for the exploration of ore deposits. Core samples from these boreholes were used for vitrinite reflectivity study. Lateral and vertical changes in vitrinite reflectivity of the Miocene sediments are illustrated in the sections and plan showing isoreflectivity lines. Vitrinite reflectivity of the Miocene sediments increases rapidly from the east to the west. The isoreflectivity map at the top of the Yotsuzawa Formation shows changes in rank from subbituminous to anthracite at a short distance. Reflectivity gradient of the boreholes in the west of the area is steeper than in the east. Stratiform ore bodies of Kuroko and copper-lead-zinc veins occur in the west of the area. The mineralization were restricted to zones above 2% Rmax at the top of the Yotsuzawa Formation. Isoreflectivity pattern indicates the development of hydrothermal activities associated with the volcanism in the Miocene age.View full abstractDownload PDF (851K) -
SEON GYU CHOI, NAOYA IMAI1983 Volume 78 Issue 9 Pages 350-360
Published: September 05, 1983
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSMiharaite has been found from sulphide-sulphosalt ore rich in bornite occurring as a stringer vein, which cuts calcite-marble in diamond drill cores at the Ulsan mine, Republic of Korea by the present authors.
The Ulsan miharaite occurs as microscopic grains, up to 500 μm long and 150 μm wide, but grains as large as 100 μm in maximum dimension are rather common. It occurs in bornite closely associated with wittichenite. In reflected light, it shows very weak bireflectance with reflection colour from pale-grey to white with greyish tinges. Between crossed polars, it shows moderate anisotropism, giving colour effects from greyish blue to yellowish brown. The optical properties of miharaite are quite similar to those of the associated wittichenite, however, the discrimination of these two minerals may readily be made by means of etch test; i.e., HNO3 (1:1) etches wittichenite slowly, gradually staining to brown colour, but does not miharaite at all. The reflectance, Rmax and Rmin (percent) in air are; λo=480 nm:32.0 and 31.3, 540 nm:33.0 and 32.2, 580 nm:33.5 and 32.2 and 660 nm: 35.1 and 32.4, respectively. Vickers hardness number (VHN): 195-230 kg/mm2 at a 25-g load.
The average chemical composition of thirteen spot analyses by electron microprobe gives: Cu 27.62, Fe 6.05, Pb 23.10, Bi 23.54, S 20.66, Total 100.97 (all in weight percent), corresponding to the formular Cu4.00 Fe1.00Pb1.03Bi1.04S5.94 on the basis of total atoms =13, being very close to the ideal formula, Cu4FePbBiS6. The strongest reflections in X-ray diffraction patterns are 3.03 Å (vs) (211), 3.00 Å (s) (040), 2.19 Å (w) (250, 411, 241) and 1.934 Å (m) (431, 002).
The Ulsan miharaite is considered to have been formed during the later stage of skarn formation by copper-rich polymetallic mineralization under relatively lower temperature, which has followed the main iron-tungsten mineralization.View full abstractDownload PDF (2370K)
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