The Ag/Au ratio of native gold and electrum and the geochemical environment of gold vein deposits in Japan     

N. Shikazono  M. Shimizu 《Mineralium Deposita》1987,22(4):309-314

The chemical composition of native gold and electrum from auriferous vein and gold-silver vein deposits in Japan has been analyzed and summarized. The Ag/Au ratios of native gold and electrum from these two types of deposits are distinct, i.e., 10–20 Ag at % (auriferous vein) and 30–70 Ag at % (gold-silver vein). Thermochemical calculations suggest that the Ag/Au ratio of native gold and electrum should decrease with increasing chloride concentration and temperature. This is consistent with analytical results of native gold and electrum and fluid inclusion studies. Based on the Ag content of native gold and electrum, the Fe content of sphalerite, and the estimated temperatures, it is deduced that the sulfur activity for auriferous vein-type systems was lower than that of gold-silver vein-type systems.  相似文献   

Sea navigation, challenges and potentials in South East Asia: an assessment of suitable sites for a shipping canal in the South Thai Isthmus     

Rajesh B. Thapa  Michiro Kusanagi  Akira Kitazumi  Yuji Murayama 《GeoJournal》2007,70(2-3):161-172

This paper discusses the situation of sea navigation in south East Asia focusing on the Strait of Malacca. The strait links the Indian and Pacific oceans, which is considered one of the busiest in several narrow channels around the world. The paper highlights the significance of the strait to global maritime trade, volume of traffic, and rising environmental and social consequences in the strait. A feasibility study of constructing a new shipping canal in the South Thai Kra Isthmus as an alternative option of Malacca route had been studied since 19th century. The paper explores suitable sites for a potential shipping canal in the Kra Isthmus using physiographic spatial data i.e., elevation, sea charts, geology, soils and river systems. Each spatial data was considered as a separate decision variable for site evaluation. Separate evaluation criterions were prepared for each variable based on shipping canal requirements. Overlaying the maps in GIS environment, the variables were carefully evaluated, and five geographic sites for the canal were derived. The length of the shipping canal over sea and land was computed for each site. Site B located in south of Ranong and Chumphon provinces, was the shortest one, whereas site C in Surat Thani, Pangnna and Krabi provinces was the longest. However, each site consisted of benefits and constraints.  相似文献   

Garnet metagabbro-ultramafic complexes in the Pekulney Range, northeast Russia     

Akira  Ishiwatari  Galina V.  Ledneva  Boris A.  Bazylev  Yasutaka  Hayasaka  Suren A.  Palandzhyan  Odin L.  Morozov  Kazuto  Koizumi  Vasily D.  Stcherbakov  Sergey D.  Sokolov 《Island Arc》2007,16(1):1-3

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Dual publication     

Simon Wallis  Akira IshiwatariEditors-in-Chief  Keiji Takeuchi  Toshiaki TsunogaeExecutive Editors 《Island Arc》2007,16(2):211-211

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Carbonate deposits on submerged seamounts in the northwestern Pacific Ocean     

Hideko  Takayanagi  Yasufumi  Iryu  Tsutomu  Yamada  Motoyoshi  Oda  Kazuyuki  Yamamoto  Tokiyuki  Sato  Shun  Chiyonobu  Akira  Nishimura  Tsutomu  Nakazawa  Satoshi  Shiokawa 《Island Arc》2007,16(3):394-419

Abstract   The lithology of shallow-water carbonates collected from 19 sites on 16 seamounts in six areas of the northwestern Pacific Ocean using the Deep-sea Boring Machine System are described. The areas include the Amami Plateau, Daito Ridge, Oki-Daito Ridge, Urdaneta Plateau, Kyushu-Palau Ridge and Ogasawara Plateau. Chronological constraint is provided by calcareous nannofossil biostratigraphy, planktonic foraminiferal biostratigraphy, larger foraminiferal biostratigraphy and strontium (Sr) isotope stratigraphy. Large amounts of shallow-water carbonates accumulated on the seamounts during the Oligocene, a relatively cool period, whereas limited carbonate deposits formed during the Early Miocene, a relatively warm period. This might indicate that deposition of shallow-water carbonates on seamounts in the northwestern Pacific Ocean was not necessarily controlled by climatic conditions, but was related to volcanism and tectonics that served as foundations for reef/carbonate-platform formation. Remarkable differences in biotic composition exist between Cretaceous and Cenozoic shallow-water carbonates. Late Cretaceous shallow-water carbonates are distinguished by the occurrence of rudists, solenoporacean algae and microencrusters. Middle Eocene to Early Oligocene shallow-water carbonates are dominated by Halimeda or nummulitid and discocyclinid larger foraminifers. Scleractinian corals became common from the Oligocene onward. Nongeniculate coralline algae and larger foraminifers were common to abundant throughout the Eocene to the Pleistocene. The replacement of major carbonate producers in the shallow-water carbonate factory during post-Cretaceous time is in accordance with previous studies and is considered to reflect a shift in seawater chemistry.  相似文献   

Crustal structure in and around the region of the 1995 Kobe Earthquake deduced from a wide-angle and refraction seismic exploration     

Takeshi Ohmura  Takeo Moriya  Chengshi Piao  Takaya Iwasaki  Toshikastu Yoshi  Shin'ichi Sakai  Tetsuya Takeda  Kaoru Miyashita  Humihito Yamazaki  Kiyoshi Ito  Akira Yamazaki  Yoji Shimada  Katsuya Tashiro  Hiroki Miyamachi 《Island Arc》2001,10(3-4):215-227

Abstract The 1995 Kobe (Hyogo-ken Nanbu) earthquake (M_JMA 7.2, M_w 6.9) occurred on Jan. 17, 1995, at a depth of 17 km, beneath the areas of southern part of Hyogo prefecture and Awaji Island. To investigate P-wave velocity distribution and seismological characteristics in the aftershock area of this great earthquake, a wide-angle and refraction seismic exploration was carried out by the Research Group for Explosion Seismology (RGES) . The profile including 6 shot points and 205 observations was 135 km in length, extending from Keihoku, Northern Kyoto prefecture, through Kobe, to Seidan on Awaji Island. The charge of each shot was 350–700 kg. The P-wave velocity structure model showed a complicated sedimentary layer which is shallower than 2.5 km, a 2.5 km-thick basement layer whose velocity is 5.5 km/s, overlying the crystalline upper crust, and the boundary between the upper and lower crust.
Almost all aftershock hypocenters were located in the upper crust. However, the structure model suggests that the hypocenters of the main shock and some aftershock clusters were situated deeper than the boundary between the upper and lower crust. We found that the P-velocity in the upper crust beneath the northern part of Awaji Island is 5.64 km/s which is 3% lower than that of the surrounding area. The low-velocity zone coincides with the region where the high stress moment release was observed.  相似文献   

The use of sintered diamond anvils in the MA8 type high-pressure apparatus     

Tadashi Kondo  Hiroshi Sawamoto  Akira Yoneda  Manabu Kato  Akihito Matsumuro  Takehiko Yagi  Takumi Kikegawa 《Pure and Applied Geophysics》1993,141(2-4):601-611

A new multi-anvil type high-presure apparatus has been developed using sintered diamond anvils to generate pressures over 30 GPa and temperatures up to about 2000°C. A maximum sample volume of about 1 mm³ is available in this system. The pressure was confirmed by dissociation of forsterite into Mg-perovskite and periclase. The basic techniques and problems in utilizing sintered diamond in the MA8 type high-pressure apparatus are discussed with an emphasis on the future prospect of incorporating simultancous X-ray diffraction observation.  相似文献   

Strong interaction between the ring system and the ionosphere of saturn     

Mikio Shimizu 《Earth, Moon, and Planets》1980,22(4):521-522

An abnormally low electron density in the Saturnian ionosphere observed by the radio occultation experiment of the Pioneer 11 may be explained in terms of the contamination of water in the Saturnian upper atmosphere from its ring system.  相似文献   

The structure of cometary atmospheres     

Mikio Shimizu 《Astrophysics and Space Science》1976,40(1):149-155

The temperature distributions in cometary atmospheres at various heliocentric distances for comets of Bennett and Encke types have been calculated by taking into account heating due to the absorption of solar ultraviolet radiation, cooling by H₂O far infrared emission, and various dynamical processes (expansion, advection, and thermal conduction). The agreement of the results with the observations is in general satisfactory. The conversion of CH₄ and NH₃ to CO and N₂ through thermochemical reaction with H₂O is concluded to be impossible, since the temperature is too low at a heliocentric distance 1.5 AU where CO⁺ ions begin to be observable.  相似文献   

Spatial distribution of deuterium in atmospheric water vapor: Diagnosing sources and the mixing of atmospheric moisture   总被引：1，自引：0，他引：1  

Tsutomu Yamanaka  Ryosuke Shimizu 《Geochimica et cosmochimica acta》2007,71(13):3162-3169

We measured the stable isotopic composition of hydrogen (δD) within atmospheric water vapor collected simultaneously at six sites in the vicinity of a lake (Lake Kasumigaura, Eastern Japan) to determine its spatial distribution characteristics and thereby diagnose sources and mixing of atmospheric moisture. The measured spatial distribution of δD showed no relation to distance from the lake, although it showed a correlation with the distribution of the water-vapor mixing ratio Q. For two of the three sampling days, we found a simple two-component (i.e., water vapor transpiring from local land surfaces and pre-existing vapor in the background atmosphere) mixing line in a Keeling plot (i.e., δ − 1/Q diagram). On a third day, however, contributions from lake evaporation were detected in addition to the above components. On this day, lake-derived vapor accounted for approximately 10-20% of atmospheric water vapor at the sites located leeward of the lake. The observed differences in mixing patterns among sampling days can be explained by a simple atmospheric moisture budget. Thus, it is likely that simultaneous isotopic measurements of atmospheric water vapor at multiple locations with aid of Keeling plot are capable of giving us useful information in diagnosing the sources and mixing pattern of the vapor.  相似文献