Chemistry of Fe-Ti oxide minerals in the Hobenzan granitic complex,SW Japan: Subsolidus reduction in relation to base metal mineralization     

K. Nakashima 《Mineralogy and Petrology》1996,58(1-2):51-69

Summary The mineralized stock of the Hobenzan granitic complex is composed of tonalite and a continuous differentiation series of biotite-hornblende granodiorite, hornblende biotite granite and biotite granite. Texture and mineral chemistry of the Fe-Ti oxide minerals in the Hobenzan granitic complex exhibit two different processes of magma evolution: one is an oxyexsolution process related to the magmatic and high temperature subsolidus stage, and the other is a reduction process of consecutive subsolidus stage. Rocks distributed in the northern part of the granitic complex preserve well the oxyexsolution process and show higher magnetic susceptibility, whereas those in the southern part of the complex, record the reduction process and show lower magnetic susceptibility.The magnetite-ilmenite geothermometer indicates temperatures of ca. 730°C for the oxide pairs of the early stage. Oxygen fugacity of one to three orders of magnitude higher than the annite-sanidine-magnetite (ASM) univariant curve, and an aqueous sulfur composition,fSO₂/fH₂S, of around 1.0 is indicated. This first stage corresponds to the crystallization of phenocrystic hornblende and plagioclase at depth. At about 700°C crystallization changed to biotite, K-feldspar and quartz, and continued to about 600°C. ThefO₂ during this second stage is buffered by the ASM assemblage. This second stage defines the oxyexsolution process. Below about 600°C, a reduction process, caused by assimilation of carbonaceous matter of country rocks, overprinted the southern part of the complex. Oxide pairs show that thefO₂ is about four orders of magnitude lower than the ASM univariant curve, andfSO₂/fH₂S is 10^–8.0 or less at 550°C for this reduced assemblage. The drastic change in composition of sulfur-bearing aqueous species may be one of the principal factors allowing base metal mineralization.

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Chemismus von Fe-Ti Oxiden des Hobenzan Granitkomplexes, SW Japan: Subsolidus Reduktion und ihre Beziehung zu metallischen Vererzungen

Zusammenfassung Der mineralisierte Hobenzan Granitkomplex setzt sich aus Tonaliten und einer kontinuierlichen Differentiationsserie, bestehend aus Biotit-Hornblende-Granodioriten, Hornblende-Biotit-Graniten und Biotit-Graniten, zusammen. Die Texturen und die Mineralchemie der Fe-Ti Oxide belegen zwei unterschiedliche Prozesse bei der Entwicklung des Hobenzan Granitkomplexes: einerseits einen Oxyexsolution-Prozeß, während des magmatischen und hochtemperierten Subsolidus-Stadiums, andererseits einen Reduktionsprozeß während des tiefertemperierten Subsolidus-Stadiums. Gesteine im nördlichen Hobenzan Komplex belegen vor allem den Oxyexsolution Prozeß und zeigen höhere magnetische Suszeptibilität, während jene im südlichen Teil den Reduktionsprozeß widerspiegeln und niedrigere magnetische Suszeptibilität zeigen.Das Magnetit-Ilmenit Geothermometer ergab Temperaturen von ca. 730°C für Oxidpaare des Frühstadiums. Die Sauerstoff Fugazität liegt um eine bis drei Größenordnungen über der univarianten Reaktionskurve Annit-Sanidin-Magnetit (ASM), und dasfSO₂/fH₂S Verhältnis der wässrigen Schwefelkomplexe bei ca. 1.0. Dieses Frühstadium korrespondiert mit der Kristallisation von Horblende und Plagioklas im Magma in größerer Tiefe. Ab ca. 700°C erfolgt die Kristallisation von Biotit, Alkalifeldspat und Quarz bis etwa 600°C, wobeifO₂ durch die ASM Mineralassoziation gepuffert wird. Dieses zweite Stadium wird als Oxyexsolution Prozeß beschrieben. Unter 600°C erfolgte eine Reduktion durch Assimilation von kohlenstoffreichem Material vor allem im südlichen Teil des Komplexes. Oxidpaare dieses Stadiums belegen, daßfO₂ um etwa vier Größenordnungen unterhalb des ASM Puffers liegt, undfSO₂/fH₂S ist 10^–8 bei 550°C. Die dramatische Änderung in der Zusammensetzung der Schwefelkomplexe in den Lösungen wird als der Hauptfaktor für die Bildung der Erzmineralisationen angesehen.

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Oxygen isotope evolution of the Lake Owyhee volcanic field,Oregon, and implications for the low-δ18O magmatism of the Snake River Plain–Yellowstone hotspot and other low-δ18O large igneous provinces     

Tyler B. Blum  Kouki Kitajima  Daisuke Nakashima  Ariel Strickland  Michael J. Spicuzza  John W. Valley 《Contributions to Mineralogy and Petrology》2016,171(11):92

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Effect of oxidation state on Bi mineral speciation in oxidized and reduced granitoids from the Uetsu region,NE Japan     

Yuya Izumino  Teruyuki Maruoka  Kazuo Nakashima 《Mineralium Deposita》2016,51(5):603-618

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The Cretaceous Ofuku Pluton and Its Relation to Mineralization in the Western Akiyoshi Plateau,Yamaguchi Prefecture,Japan          下载免费PDF全文

Yuka Sasaki  Teruyoshi Imaoka  Mariko Nagashima  Kazuo Nakashima  Takafumi Sonehara  Koshi Yagi  Tetsumaru Itaya 《Resource Geology》2016,66(2):85-113

The relationship between the magmatism of the Cretaceous Ofuku pluton and mineralization in and around the Akiyoshi Plateau, Yamaguchi Prefecture, Japan was investigated using a combination of field observation, petrographic and geochemical analyses, K–Ar geochronology, and fluid inclusion data. The Ofuku pluton has a surface area of 1.5 × 1.0 km, and was intruded into the Paleozoic accretionary complexes of the Akiyoshi Limestone, Ota Group and Tsunemori Formation in the western part of the Akiyoshi Plateau. The pluton belongs to the ilmenite‐series and is zoned, consisting mainly of early tonalite and granodiorite that share a gradational contact, and later granite and aplite that intruded the tonalite and granodiorite. Harker diagrams show that the Ofuku pluton has intermediate to silicic compositions ranging from 60.4 to 77.9 wt.% SiO₂, but a compositional gap exists between 70.5 to 73.4 wt.% SiO₂ (anhydrous basis). Modal and chemical variations indicate that the assumed parental magma is tonalitic. Quantitative models of fractional crystallization based on mass balance calculations and the Rayleigh fractionation model using major and trace element data for all crystalline phases indicate that magmatic fractionation was controlled mainly by crystal fractionation of plagioclase, hornblende, clinopyroxene and orthopyroxene at the early stage, and quartz, plagioclase, biotite, hornblende, apatite, ilmenite and zircon at the later stage. The residual melt extracted from the granodiorite mush was subsequently intruded into the northern and western parts of the Ofuku pluton as melt lens to form the granite and aplite. The age of the pluton was estimated at 99–97 Ma and 101–98 Ma based on K–Ar dating of hornblende and biotite, respectively. Both ages are consistent within analytical error, indicating that the Ofuku pluton and the associated Yamato mine belong to the Tungsten Province of the San‐yo Belt, which is genetically related to the ilmenite‐series granitoids of the Kanmon to Shunan stages. The aplite contains Cl‐rich apatite and REE‐rich monazite‐(Ce), allanite‐(Ce), xenotime and bastnäsite‐(Ce), indicating that the residual melt was rich in halogens and REEs. The tonalite–granodiorite of the Ofuku pluton contains many three‐phase fluid inclusions, along with daughter minerals such as NaCl and KCl, and vapor/liquid (V/L) volume ratios range from 0.2 to 0.9, suggesting that the fluid was boiling. In contrast, the granite and aplite contain low salinity two‐phase inclusions with low V/L ratios. The granodiorite occupies a large part of the pluton, and the inclusions with various V/L ratios with chloride daughter minerals suggest the boiling fluids might be related to the mineralization. This fluid could have carried base metals such as Cu and Zn, forming Cu ore deposits in and around the Ofuku pluton. The occurrence and composition of fluid inclusions in the igneous rocks from the Akiyoshi Plateau are directly linked to Cu mineralization in the area, demonstrating that fluid inclusions are useful indicators of mineralization.  相似文献   

Testing of a towed CTD     

Yukio Fujinawa  Yoshinobu Tsuji  Isao Watabe  Ken Sasaki  Masao Nomoto  Toshiaki Hara  Yoshito Tsuji 《Journal of Oceanography》1980,36(5):253-258

The results of laboratory and field experiments on a CTD measuring unit attached to a controllable towed body is described. It was verified that the three-dimensional distribution of salinity and temperature could be observed with sufficient accuracy (to 0.03 in salinity and to 0.01°C in temperature if proper correction is adopted) while cruising at up to 4 knots. A double integrated A/D converter is used to compensate for effects of extraneous environmental changes.  相似文献   

Is beach-spawning success for capelin, Mallotus villosus (Muller), a function of the beach?     

Nakashima  Brian S.; Taggart  Christopher T. 《ICES Journal of Marine Science》2002,59(5):897-908

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Ag-Cu-Pb-Bi-S Minerals Newly Discovered from the Ohori Base Metal Deposit, Yamagata Prefecture, NE Japan: Implications for Bi-metallogenesis in the Green-Tuff Region     

Yu Yokoro    Kazuo Nakashima 《Resource Geology》2010,60(1):1-17

The Ohori deposit, one of the base metal deposits in the Green-Tuff region, NE Japan, is composed of two types of mineralization; a skarn-type (Kaninomata orebody) made by the replacement of the Miocene calcareous layer, and a vein-type (Nakanomata orebody). While the ore mineral assemblage of the deposit (chalcopyrite, pyrite, sphalerite and galena) has been known for being rather simple, some Pb-Bi-S minerals have been discovered for the first time in the present study. The minerals mainly occur in the chalcopyrite-rich ores of both orebodies. They essentially belong to the Pb-Bi-S system and contain Cu and Ag in minor amounts, which correspond to the lillianite–gustavite solid solution series (phases Z and X), cosalite, neyite, felbertalite, krupkaite and Bi-bearing galena. The chalcopyrite-rich (Bi-bearing) ores from both orebodies are richer in chalcopyrite, pyrite and chlorite, and have higher homogenization temperatures (>300°C) of fluid inclusions, and higher FeS contents in sphalerite compared to the Bi-free ores. In the Green-Tuff region, Bi-minerals have been reported from many base metal deposits. Most of these Bi-bearing ore deposits are referred to as xenothermal-type deposits, and are characterized by the following common features; composite mineralization of high- and low-temperatures in the shallower environments, and close relationships with the Tertiary granitic rocks. The whole mineralization at the Ohori deposit also has a similar xenothermal character because of the coexistence of high-temperature chalcopyrite-rich ores with Pb-Bi-S minerals, which were formed by the influence of the Tertiary granitic rocks at a shallow depth.  相似文献   

High-pressure transformations in silicates,germanates, and titanates with ABO3 stoichiometry     

Eiji Ito  Yoshito Matsui 《Physics and Chemistry of Minerals》1979,4(3):265-273

High-pressure phase transformations were investigated for two silicates, MgSiO₃ and ZnSiO₃; six germanates, MGeO₃ and six titanates, MTiO₃ (M=Ni, Mg, Co, Zn, Fe, and Mn) at about 1,000°C and pressures up to ca. 30 GPa. CoGeO₃ was found to assume the ilmenite form. The ilmenite phases were confirmed to transform in the following schemes: to perovskite in MgSiO₃ and MnGeO₃, to corundum in MgGeO₃ and ZnGeO₃, to rocksalt plus rutile in ZnSiO₃ and CoGeO₃ and to rocksalt plus TiO₂ (possibly of some denser structure) in NiTiO₃, MgTiO₃, CoTiO₃, ZnTiO₃ and FeTiO₃. In the case of FeTiO₃, the corundum form appeared as an intermediate phase. The possibility that the corundum type MnTiO₃ might transform to some denser modification could not be excluded. The compound NiGeO₃ was nonexistent throughout the pressure range studied. High-pressure phases of ABO₃ (A=Ni, Mg, Co, Zn, Fe, and Mn; B=Si, Ge and Ti) are summarized, and those stabilized at pressures higher than 20 GPa are discussed.  相似文献   

Synthesis of γ-Mg₂SiO₄     

Eiji Ito  Yoshito Matsui  Kaichi Suito  Naoto Kawai 《Physics of the Earth and Planetary Interiors》1974,8(4):342-344

Magnesium orthosilicate with spinel structure (γ-Mg₂SiO₄) was synthesized at about 250 kbar and 1000°C. Unit cell dimension was established to be 8.076 ± 0.001Å. X-ray powder diffraction pattern revealed a significant difference between γ-Mg₂SiO₄ and other γ-M₂SiO₄ spinels (M = Fe, Co, and Ni) in the intensities of (111) and (331) reflections, both of which are virtually absent in the Mg₂SiO₄ spinel. This feature could be thoroughly understood by the calculation of the intensities for several silicate spinels.  相似文献   

δC and δD identification of sources of lipid biomarkers in sediments of Lake Haruna (Japan)     

Yoshito Chikaraishi  Hiroshi Naraoka 《Geochimica et cosmochimica acta》2005,69(13):3285-3297

Organic materials in lacustrine sediments are from multiple terrestrial and aquatic sources. In this study, carbon (δ¹³C) and hydrogen isotopic compositions (δD) of phytol, various sterols, and major n-fatty acids in sediments at Lake Haruna, Japan, were determined in their solvent-extractable (free) and saponification-released forms (bound). The δ¹³C-δD distributions of these lipid molecules in sediments are compared with those of terrestrial C3 and C4 plants, aquatic C3 plants, and plankton to evaluate their relative contributions. δ¹³C-δD of free phytol in sediments is very close to that of phytol in plankton samples, whereas δ¹³C-δD of bound phytol in sediments is on a mixing line between terrestrial C3 plant and plankton material. Unlike phytol, no significant δ¹³C-δD difference between free and bound forms was found in sterols and n-fatty acids. δ¹³C-δD values of algal sterols such as 24-methylcholesta-5,22-dien-3β-ol in sediments are close to those of plankton, whereas δ¹³C-δD of multiple-source sterols such as 24-ethylcholest-5-en-3β-ol and of major n-fatty acids such as n-hexadecanoic acid in sediments are between those of terrestrial C3 plants and plankton samples. Thus, δ¹³C-δD distributions clearly indicate the specific source contributions of biomarkers preserved in a lacustrine environment. Free phytol and algal sterols can be attributed to phytoplankton, and bound phytol, multiple source sterols, and major n-fatty acids are contributed by both terrestrial C3 plants and phytoplankton.  相似文献