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491.
Late Permian foraminifers were found from six localities belonging to the Doi Chiang Dao Limestone, which is considered as having a Paleo-Tethyan seamount-capping carbonates origin, distributed in the Inthanon Zone of Northern Thailand. Among them, three age-diagnostic assemblages are recognized. They are represented by the occurrences of Codonofusiella kwangsiana, Palaeofusulina cf. minima, and P. prisca, and are referable to the Wuchiapingian, early Changhsingian, and late Changhsingian, respectively. In particular, the discovery of an assemblage characterized by advanced Palaeofusulina (P. prisca) is significant because it clearly indicates that the deposition of the Doi Chiang Dao Limestone had continued until the very end of the Permian. These three Late Permian assemblages can be compared with those recently reported from the Shifodong Formation of Pa-leo-Tethyan mid-oceanic carbonates in the Changning-Menglian Belt of West Yunnan, Southwest China. 相似文献
492.
493.
Takeshi Minami Akira Imai Michiaki Bunno Kunihiko Kawakami Setsuo Imazu 《Geoarchaeology》2005,20(1):79-84
This study represents an attempt to determine the sources of vermillion found in ancient Japanese burial mounds of the 1st–6th centuries A.D., by comparing their ratios of sulfur isotopes with those of cinnabar ore samples collected in Japan and China. Cinnabar ore samples were taken from three mines in central Japan (Niu in Mie, Yamato in Nara, and Sui in Tokushima prefectures), and from Wanshan in China, where mining activity has been recorded back to the 6th century A.D. and earlier. When the ratios of a 34S and 32S were compared with the Canyon Diablo meteorite standard, a high δ34S value of +22.6 ± 3.6‰ was found for the Wanshan mine, as opposed to low values ranging from −7.3 ± 1.9 to −2.1 ± 1.6‰ for the Japanese mines. The ratios of sulfur isotopes in vermillion collected from ancient Japanese burial mounds also divided into two groups. High ratios (+11.1 to +22.8‰) were found in 1st‐ and 2nd‐ century burials in the western regions of northern Kyushu and San'in, suggesting that local, powerful chiefs obtained vermillion through relations with China. Lower ratios (−8.4 to −2.0‰) were found in burials of the 2nd through 6th centuries in central Japan, where the ancient Yamato dynasty emerged as the first unified polity around the end of the 2nd century A.D. We, therefore, conclude that the Yamato dynasty exploited local sources of vermillion, rather than depending solely on China. The present study demonstrates the feasibility of determining sources of vermillion using sulfur isotope ratios, and the relevance of such findings for archaeological research. © 2005 Wiley Periodicals, Inc. 相似文献
494.
The Salu Bulo prospect is one of the gold prospects in the Awak Mas project in the central part of the western province, Sulawesi, Indonesia. The gold mineralization is hosted by the meta‐sedimentary rocks intercalated with the meta‐volcanic and volcaniclastic rocks of the Latimojong Metamorphic Complex. The ores are approximately three meters thick, consisting of veins, stockwork, and breccias. The veins can be classified into three stages, namely, early, main, and late stages, and gold mineralization is related to the main stage. The mineral assemblage of the matrix of breccia and the veins are both composed of quartz, carbonate (mainly ankerite), and albite. High‐grade gold ores in the Salu Bulo prospect are accompanied by intense alteration, such as carbonatization, albitization, silicification, and sulfidation along the main stage veins and breccia. Alteration mineral assemblage includes ankerite ± calcite, quartz, albite, and pyrite along with minor sericite. Pyrite is the most abundant sulfide mineral that is spatially related to native gold and electrum (<2–42 μm in size). It is more abundant as dissemination in the altered host rocks than those in veins. This suggests that water–rock interaction played a role to precipitate pyrite and Au in the Salu Bulo prospect. The Au contents of intensely altered host rocks and ores have positive correlations with Ag, Ni, Mo, and Na. Fluid inclusions in the veins of the main stage and the matrix of breccia are mainly two‐phase liquid‐rich inclusions with minor two‐phase, vapor‐rich, and single‐phase liquid or vapor inclusions. CO2 and N2 gases are detected in the fluid inclusions by Laser Raman microspectrometry. Fluid boiling probably occurred when the fluid was trapped at approximately 120–190 m below the paleo water table. δ18OSMOW values of fluid, +5.8 and +7.6‰, calculated from δ18OSMOW of quartz from the main stage vein indicate oxygen isotopic exchange with wall rocks during deep circulation. δ34SCDT of pyrite narrowly ranges from ?2.0 to +3.4‰, suggesting a single source of sulfur. Gold mineralization in the Salu Bulo prospect occurred in an epithermal condition, after the metamorphism of the host rocks. It formed at a relatively shallow depth from fluids with low to moderate salinity (3.0–8.5 wt% NaCl equiv.). The temperature and pressure of ore formation range from 190 to 210°C and 1.2 to 1.9 MPa, respectively. 相似文献
495.
Thomas T. Sorulen Ryohei Takahashi So Tanaka Kana Suzuki Akira Imai Yasushi Watanabe Shingo Kikuchi 《Resource Geology》2019,69(4):402-429
The Utanobori gold deposit is a low‐sulfidation, epithermal vein‐type deposit located in northern Hokkaido, Japan. The deposit is hosted by conglomerate, sandstone, and tuff of the Middle to Late Miocene Esashi Formation. These rocks were hydrothermally altered. Silica sinters and quartz‐adularia veins are common in the deposit. The quartz‐adularia veins either contain a ginguro band, which corresponds to the main gold‐bearing vein (Type 1 Veins), or do not contain a ginguro band but contain minor adularia (Type 2 Veins). Type 1 Veins are divided into three stages with 12–14 substages. Ore minerals identified include electrum, naumannite, chlorargyrite, bromargyrite, an unidentified Fe‐Sb mineral, and an Fe‐(Sb)‐As mineral. These ore minerals formed in the main mineralization stages I (bands I‐b and I‐d) and II (band II‐a). Scanning electron microscopy with cathodoluminescence images show that cathodoluminescence‐dark microcrystalline quartz exhibiting colloform (ghost‐sphere) texture is closely associated with ore minerals in the Type 1 Vein and Type 2 Vein, and the Al and K contents of such quartz are commonly >1000 ppm. This indicates that the ore minerals were crystallized from alkaline, silica‐saturated fluids at temperatures <200°C, which initially deposited amorphous silica that was recrystallized to microcrystalline quartz. The average Au content of electrum is 52.5 at% Au (n = 10), 65.7 at% Au (n = 20), and 55.5 at% Au (n = 5) in bands I‐b, I‐d, and II‐a, respectively, of Type 1 Veins. The δ34SCDT values of two fine‐grained disseminated pyrites in the altered conglomerate and bedded tuff in the argillic altered zone are ?4.3 and ?4.2‰. Ar‐Ar dating on adularia yielded 13.6 ± 0.06 Ma, 13.6 ± 0.07 Ma, and 13.6 ± 0.06 Ma for the stages I, II, and III of the Type 1 Vein, respectively. K‐Ar ages determined on adularia in the silica sinter and on whole‐rock of glassy rhyolite of the Esashi Formation are 15.0 ± 0.4 Ma and 14.6 ± 0.4 Ma, respectively. These radiometric ages indicate that silica sinter associated with the rhyolitic volcanic rocks formed prior to the main gold mineralization. 相似文献
496.
Mutsuo Ichinomiya Yasushi Gomi Miwa Nakamachi Masaki Honda Mitsuo Fukuchi Akira Taniguchi 《Polar Science》2008,2(1):33-40
To investigate the fate of ice algae released from sea ice, we investigated the abundance, species composition, and sinking flux of diatoms in the water column under fast ice near Syowa Station, Antarctica during the summer of 2005/2006. The diatom assemblage in the water column consisted of chain-forming planktonic species, in contrast to the under-ice assemblage dominated by pennate species reported from this site in the past; this dissimilarity suggests the presence of an unconsolidated platelet ice layer under the congelation ice, within which planktonic species can bloom. Among the dominant diatoms, Porosira pseudodenticulata and Pseudo-nitzschia cf. turgiduloides were dominant in the water column, and their water column stocks were higher than their mass sedimentation. These species apparently maintain their populations in the surface layer, as their production remains in the water column. In contrast, Fragilariopsis kerguelensis and Thalassiosira australis were scarce in the water column but rich in the flux, indicating active sinking and export of their production to the benthic ecosystem. This distinction in buoyancy control and sinking characteristics of the dominant diatoms on release from the fast ice influences the diatom species composition and carbon flow under the ice. 相似文献
497.
Nutrient concentrations (nitrate + nitrite, phosphate and silicate) in deep seawater (321 m depth) of Toyama Bay, Japan, were measured from August 1996 to July 1997 to determine the magnitude of daily variations. Significant daily variations were observed; concentrations ranged from 4.42 to 22.4 µM for nitrate + nitrite, from 0.86 to 1.98 µM for phosphate, and from 9.91 to 47.7 µM for silicate, respectively. However, there were not significant relationships between nutrient concentrations and water temperature, or between nutrients and salinity. Since temperature and salinity in the >300 m depth layer were constant through the year, the results suggest that there may be water masses with different nutrient concentrations in the deep layers (at about 320 m depth) of the bay, and a horizontal advection of these water masses may be responsible for the observed daily variations. 相似文献
498.
Harunobu Masuko Kohei Arai Naoto Ebuchi Masanori Konda Masahisa Kubota Kunio Kutsuwada Teruko Manabe Akira Mukaida Tetsuo Nakazawa Atsushi Nomura Akira Shibata Yoshihiko Tahara 《Journal of Oceanography》2000,56(5):495-505
In order to validate wind vectors derived from the NASA Scatterometer (NSCAT), two NSCAT wind products of different spatial resolutions are compared with observations by buoys and research vessels in the seas around Japan. In general, the NSCAT winds agree well with the wind data from the buoys and vessels. It is shown that the root-mean-square (rms) difference between NSCAT-derived wind speeds and the buoy observations is 1.7 ms–1, which satisfies the mission requirement of accuracy, 2 ms–1. However, the rms difference of wind directions is slightly larger than the mission requirement, 20°. This result does not agree with those of previous studies on validation of the NSCAT-derived wind vectors using buoy observations, and is considered to be due to differences in the buoy observation systems. It is also shown that there are no significant systematic trends of the NSCAT wind speed and direction depending on the wind speed and incidence angle. Comparison with ship winds shows that the NSCAT wind speeds are lower than those observed by the research vessels by about 0.7 ms–1 and this bias is twice as large for data observed by moving ships than by stationary ships. This result suggests that the ship winds may be influenced by errors caused by ship's motion, such as pitching and rolling. 相似文献
499.
Mineral Paragenesis, Fluid Inclusions and Sulfur Isotope Systematics of the Lepanto Far Southeast Porphyry Cu-Au Deposit, Mankayan, Philippines 总被引:1,自引:0,他引:1
Akira IMAI 《Resource Geology》2000,50(3):151-168
Abstract: The Lepanto Far Southeast porphyry Cu‐Au deposit is located beneath and to the southeast of the Lepanto enargite‐luzonite Cu–Au deposit in Mankayan, Benguet Province, Philippines. The principal orebody consists of potassic alteration subjected to partial retrograde chlorite alteration that rims stock‐work of quartz‐anhydrite veinlets. Fluid inclusions found in stockwork quartz and anhydrite in the biotitized orebody center are dominated by polyphase inclusions that homogenize at temperatures of >500C. Sulfur isotopic thermometry applied to the sulfides‐anhydrite pairs suggests around 500C. The principal ore minerals associated with quartz‐anhydrite stockworks are chalcopyrite and pyrite with minor bornite and Bi–Te–bearing tennantite, with trace of native gold. Rounded pyrite grains appear fractured and corroded and are interpreted as remnants of primary intermediate solid solution + pyrite assemblage. A breccia pipe truncates the deposit. Mineralization in the breccia pipe is brought by quartz‐anhydrite veinlets and infilling in the interstices between clasts. Chalcopyrite‐Au mineralization associated with molybdenite is recognized in the deeper zone in the breccia pipe. Fluid inclusion microthermometry on polyphase inclusions in veinlet quartz as well as sulfur isotope thermometry applied for the pair of anhydrite and sulfides suggests >450C. Fluid inclusions in veinlet quartz and anhydrite in the fringe advanced argillic alteration are chiefly composed of coexisting liquid‐rich inclusions and gas‐rich inclusions, in addition to coexisting polyphase inclusions and gas‐rich inclusions. These inclusions exhibit a wide range of homogenization temperatures, suggesting heterogeneous entrapping in the two‐fluid unmixing region. Sulfur isotopes of aqueous sulfide and sulfate exhibit a general trend from the smallest fractionation pairs (about 11%) in the biotitized orebody center to the largest fractionation (about 25%) pairs in the fringe advanced argillic alteration, suggesting a simple evolution of hydrothermal system. The slopes of arbitrary regression lines in δ34S versus 34S[SO4 = –H2S] diagram suggest that the abundance ratio of aqueous sulfate to sulfide in the hydrothermal fluid has been broadly constant at about 1:3 through temperature decrease. The intersection of these two regression lines at the δ34S axis indicates that the bulk δ34S is about +6%. Thus, the Lepanto FSE deposit is a further example which confirms enrichment in 34S in the hydrous intermediate to silicic magmas and associated magmatic hydrothermal deposits in the western Luzon arc. 相似文献
500.
Variation of the southward interior flow of the North Pacific subtropical gyre,as revealed by a repeat hydrographic survey 总被引:2,自引:1,他引:1
Akira Nagano Hiroshi Ichikawa Yasushi Yoshikawa Shoichi Kizu Kimio Hanawa 《Journal of Oceanography》2012,68(2):361-368
Baroclinic variations of the southward flow in the interior region of the North Pacific subtropical gyre are presented with
five hydrographic sections from San Francisco to near Japan during 2004–2006. The volume transport averaged temperature of
the interior flow, which varies vigorously by a maximum of 0.8°C, is negatively correlated with the transport in the layer
of density 24.5–26.5σ
θ, associated with changes in the vertical current structure. Transport variation in this density layer is thus mainly responsible
for the thermal impact of the interior flow on the heat transport of the subtropical gyre. 相似文献