Bulletin of the Geological Survey of Japan Top Page

Bulletin of the Geological Survey of Japan Vol.53 No.9/10 (2002)

Cover photograph | Table of Contents | Abstract

Cover photograph

   Xenothermal-type ore veins of the Chiemon 15th vein at 13mL, Akenobe mine, Hyogo Prefecture. The Akenobe mine was opened in 807 and mined systematically since 1599. The veins scatter in an area of E-W 4.6 km, N-S 3.9 km in the central Hyogo Prefecture, and provided composite ores containing Sn, W, Cu, Zn, Pb, and Ag. The mine was closed in March 1987 by lowering domestic prices of the recovered metals.

(Shunso Ishihara)

Table of Contents

Title	Author	PDF
Article
Diatom biostratigraphy and molluscan fossils of the Miocene formations in the southern part of Miyagi Prefecture and the northern part of Fukushima Prefecture, Japan.	Yukio Yanagisawa snd Yukito Kurihara (635-643)	53_09_01.pdf [3,573 KB]
Revised diatom biostratigraphy of the Miocene Sugata Formation in the Nadaura area, Toyama Prefecture, central Japan	Mahito Watanabe (645-655)	53_09_02.pdf [803 KB]
Chemical characteristics of the mineralized granitoids (I): Mo and W provinces of the Inner Zone of Southwest Japan.	Shunso Ishihara (657-672)	53_09_03.pdf [1,060 KB]
Chemical characteristics of the mineralized granitoids (II): Polymetallic province of the west-central Hyogo Prefecture, Japan.	Shunso Ishihara (673-688)	53_09_04.pdf [1,117 KB]
Late Jurassic radiolarian fauna from the Ikenohara Formation of the Kurosegawa Belt in the Toyo-Izumi area, Kumamoto Prefecture, Kyushu, Japan.	Nobuharu Hori, Makoto Saito and Seiichi Toshimitsu (689-724)	53_09_05.pdf [7,645 KB]

Abstract

Diatom biostratigraphy and molluscan fossils of the Miocene formations in the southern part of Miyagi Prefecture and the northern part of Fukushima Prefecture, Japan.

Yukio Yanagisawa snd Yukito Kurihara

   Diatom and molluscan fossils are reported from the Miocene Yamairi Formation in the southern part of Miyagi Prefecture, and the Akashiba Formation in the northern part of Fukushima Prefecture, Japan. The marine diatom assemblages from the two formations are correlative with the lowest part of the upper Middle Miocene Thalassiosira yabei Zone (NPD 5C) of the Neogene North Pacific diatom zonation. The molluscan assemblage from the middle part of the Akashiba Formation includes elements of the Shiobara-type molluscan fauna. The age of the Shiobara-type molluscan fauna is consistent with the diatom age. The diatom biostratigraphy of this study provides a precise chronology for the Miocene sequence in this area.

Revised diatom biostratigraphy of the Miocene Sugata Formation in the Nadaura area, Toyama Prefecture, central Japan.

Mahito Watanabe

   Diatom biostratigraphy is revised for the Sugata Formation (Miocene) in the Nadaura area, Toyama Prefecture, central Japan. The Sugata Formation is mainly composed of diatomaceous mudstone, containing diatom fossils throughout the formation. Crucidenticula nicobarica Zone (NPD 5A), Denticulopsis praedimorpha Zone (NPD 5B) and Thalassiosira yabei Zone (NPD 5C) are identified with diatom biohorizons of Yanagisawa and Akiba (1998) including D 51, D 52, D 53 and D 55 in the Sugata Formation. C. nicobarica occurs 10 to 20 percent of total assemblage in most of the samples from the upper part of NPD 5A to the lower part of NPD 5B, and decreases rapidly to less than 1 percent between the biohorizon D51 (first occurrence of Denticulopsis praedimorpha var. minor; 12.9 Ma) and D 52 (last occurrence of C. nicobarica ; 12.7-12.8 Ma). The sediment accumulation rate curve of the Sugata Formation suggests that a hiatus exists between the diatomaceous mudstone and the glauconite Sandstone in the uppermost part of the Sugata Formation.

Chemical characteristics of the mineralized granitoids (I): Mo and W provinces of the Inner Zone of Southwest Japan.

Shunso Ishihara

   In order to know chemical parameters useful for mineral exploration including Mo, W and Sn, selected granitoids of 47 samples from the Mo province, W province and barren province were analyzed by polarized XRF spectrometer, XLAB 2000. The granitoids of the Mo province are least in Al₂O₃ and ASI, Ga, K₂O and Rb, compared with those of the W and barren provinces. Mafic trace elements such as V, Cr, Zn and Co are controlled by ferric/ferrous state of the granitoids.Trace amounts of Mo is high in the granitoids of the Mo province and least in the barren province. It is rather strange that W is high in both W and Mo provinces. Mo appears to be a useful indicator for molybdenum deposits, and both W and Sn could be useful parameter for mineral exploration of Sn-bearing tungsten deposits in rock geochemical exploration. Compared with conventional wet-chemical analyses of the 1960s, low correlation coefficients (r) are obtained from MnO (0.83), P₂O₅ (0.85), Al₂O₃ (0.87) and Na₂O (0.88). Diversity from unity (m) is low on P₂O₅ (0.79) and MnO (0.83), but high on K₂O (1.15), implying that the Lawrence Smith's method gives onsistently low values on K₂O contents relative to the XRF. Good correlations between the two methods are seen on CaO and SiO₂ , and also on trace amount of Sn with AA method.

Chemical characteristics of the mineralized granitoids (II): Polymetallic province of the west-central Hyogo Prefecture, Japan.

Shunso Ishihara

   In the west-central Hyogo Prefecture, there occur the late Cretaceous volcanic and plutonic rocks of intermediate to felsic compositions. Small vein, replacement and disseminated-type deposits with copper, arsenic and iron are associated with the granitoids. The granitoids are found to be composed of magnetite-series including the Yazu-Kanzaki plutonic complex and the Hikihara Granite, and ilmenite-series consisting of the Mochigase Granite and Wadayama Granite. Fourteen major components and 31 minor components were analyzed by polarized XRF. The ore deposits are associated with the magnetite-series granitoids having particularly high magnetite contents. Petrochemical contrasts are seen between the magnetite-series and ilmenite-series granitoids. Within the magnetite series, the mineralized ganitoids may be higher in bulk Cu contents than the barren granitoids. Copper contents of granitoids could be an indicator to copper mineralization, because CuS phase (intermediate solid solution, iss) is stable in a magmatic temperature. An average Cu content of the Yazu-Kanzaki granitoids is 4 ppm, while main copper producing area with similar volcano-plutonic history such as North Chile is averaged as 62 ppm (Ishihara et al., 1984), indicating a poor potentiality of copper in the west-central Hyogo Prefecture. The magnetite-series granitoids are too low in SiO₂ and Al₂O₃ contents to be qualified as Pb-Zn mineralized granitoids.

Late Jurassic radiolarian fauna from the Ikenohara Formation of the Kurosegawa Belt in the Toyo-Izumi area, Kumamoto Prefecture, Kyushu, Japan.

Nobuharu Hori, Makoto Saito and Seiichi Toshimitsu

   Abundant well-preserved radiolarians were obtained from the Kurosegawa Belt in the Toyo - Izumi Area, Kumamoto Prefecture, Kyushu. Radiolarian-bearing rocks were collected from the Upper Jurassic Ikenohara Formation, which is composed mainly of mudstone. The samples GSJ R76489 and GSJ R76490 include 330 and 329 radiolarian species, respectively. The radiolarian faunas of both samples are very similar in composition. Based on the radiolarian zonation of Matsuoka (1995a), the radiolarian fauna represents the Kilinora spiralis Zone and is assigned to Oxfordian in age. This radiolarian fauna includes greater numbers of spumellarians and quite differs from radiolarian faunas reported from the Jurassic accretionary complex of Japan. This evidence may imply that the depositional environment of the Ikenohara Formation is different from that of the Jurassic accretionary complex, and the Ikenohara Formation possibly deposited in a trench slope environment.