GEOCHEMICAL JOURNAL
Online ISSN : 1880-5973
Print ISSN : 0016-7002
ISSN-L : 0016-7002
Volume 50, Issue 5
Displaying 1-8 of 8 articles from this issue
  • Mizuho Koike, Yuji Sano, Naoto Takahata, Akizumi Ishida, Naoji Sugiura ...
    2016 Volume 50 Issue 5 Pages 363-377
    Published: September 30, 2016
    Released on J-STAGE: October 26, 2016
    JOURNAL OPEN ACCESS
    Supplementary material

    We measured the hydrogen isotopic composition (D/H ratios) and U-Pb chronology of phosphate minerals in a young Martian meteorite: LAR 06319. D/H ratios of melt-inclusions in the meteorite were also investigated to evaluate the presence of water reservoirs on Mars in recent times. The total Pb/U dating of multiple grains of apatite and merrillite yield a concordant date of 167 ± 57 Ma, interpreted as the crystallization age, suggesting that both apatite and merrillite in this meteorite have preserved their igneous histories. The D/H ratios of an apatite grain show good reproducibility yielding a δD value of 4250 ± 120‰, whereas those of merrillite show larger D/H variations with the maximum δD value of 5260 ± 790‰. However, mafic glass in melt-inclusions shows extremely large variation in δD, ranging from ca. 1070‰ to 6830 ± 460‰. The different D/H signatures recorded in these phases reflect the contributions of different hydrous components with distinct D/H ratios, possibly incorporated at different times. It is inferred that several isotopically distinct water reservoirs exist in the present Martian surface/sub-surface system.

    Download PDF (903K)
  • Sibele Ezaki, Raphael Hypolito, Annabel Pérez-Aguilar
    2016 Volume 50 Issue 5 Pages 379-392
    Published: September 30, 2016
    Released on J-STAGE: October 26, 2016
    JOURNAL OPEN ACCESS

    High natural fluoride (F) concentrations (up to 8.75 mg dm–3) were detected in the groundwater near Salto city (São Paulo State, Brazil), on the eastern border of the Paraná Sedimentary Basin, with an average of 1.19 mg dm–3 in a fissured aquifer and 2.01 mg dm–3 in the sedimentary aquifer systems. The aim of the study was to evaluate granitic and sedimentary rocks (using whole rock powders at <200 mesh size), as well as biotite crystals from granites (using grains in the 35–100 mesh size fraction), as possible F sources in the aquifer systems. Dissolution batch tests were performed in distilled water, simulating F liberation in deep (Experiment I) and shallow (Experiment II) portions of aquifers and from biotite grains under the influence of high temperature, alkalinity, and salinity (Experiments III, IV, and V). In Experiment I, the F levels in granite leaching were very high (6.53 to 10.30 mg dm–3) due to the small particle size fraction that increased the mineral contact area with water. The F concentrations (0.8 to 1.72 mg dm–3) in the sedimentary rock leachates were compatible with the average levels found in the wells of this aquifer. The alkaline pH (time = ∞), EC (time = ∞) values, and the chemical composition of the final solutions in contact with all sedimentary rocks reflected the conditions found in the deep wells (>150 m). In Experiment II, F was progressively released from all rocks. Granites released more F (up to 8.69 mg dm–3), which was controlled by the supersaturation of fluorite, due to Ca2+ from plagioclase dissolution, as well as biotite dissolution (2–5% by vol. of rocks). A good F/K value (r = 0.87) correlation implies that the F was released from biotite and K+ from biotite+K-feldspar. In sedimentary rocks, the F concentrations (0.12 to 0.91 mg dm–3) are related to the low fluorine rock concentrations, and Ca2+ removal was controlled by calcite precipitation and/or cationic exchange of Ca2+ for Na+ in the clay minerals. With regard to biotite alteration, the influence of higher temperatures proved to be noteworthy in the process of releasing F, which also was more efficient under high salinity conditions (800 μS cm–1, NaCl 0.1%) when compared with alkaline conditions (pH 8.0, NaOH 0.1%).

    Download PDF (1180K)
  • Sodov Ariunbileg, Olga Gaskova, Alexander Vladimirov, Altanbaatar Batt ...
    2016 Volume 50 Issue 5 Pages 393-401
    Published: September 30, 2016
    Released on J-STAGE: October 26, 2016
    JOURNAL OPEN ACCESS

    In the Dornogobi Aimag region of Southern Mongolia, the main source of groundwater contamination by U, As, and Se is hydrogenic- or sandstone-type uranium deposits. These environmentally hazardous deposits, located in close proximity to populated settlements, pose a serious threat to drinking water quality and human health. Fifty samples were analyzed and levels of uranium were found to be elevated in deep and shallow waters (200 and 34.7 μg/L, respectively), with nearly 25% exceeding the World Health Organization (WHO) guideline level for drinking water quality (30 μg/L). Local rocks and soils appear to be the natural source of uranium. In particular, water from deep hydrologic wells near the largest deposits (Dulaan Uul and Zoovch Ovoo) exceeds the WHO guideline levels for U, As, Se, Sb, Cd, and Fe. At the same time, shallow groundwater (Argalant area) contains 50.5 μg/L of As, 34.7 μg/L of U, and 35.9 μg/L of Cd. Although multiple metal and metalloid contamination of groundwater is an issue of global concern, our understanding of the physical-chemical conditions of its accumulation is limited. This study provides a plausible explanation of the geochemical situation at the uranium Dornogobi province based on thermodynamic calculations.

    Download PDF (1060K)
  • Seiji Maruyama, Kentaro Hattori, Takafumi Hirata, Takehiko Suzuki, Toh ...
    2016 Volume 50 Issue 5 Pages 403-422
    Published: September 30, 2016
    Released on J-STAGE: October 26, 2016
    JOURNAL OPEN ACCESS

    Four volcanic glass samples on the INternational focus group on Tephrochronology And Volcanism (INTAV) sample mount described by Kuehn et al. (2011) were analyzed to establish a new methodology for measurement of major and trace elements in Quaternary tephras by femtosecond laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). NIST SRM 610 and 612 glasses were used for calibration of the measurement of 58 elements from Li to U in two rhyolitic glass samples (Lipari obsidian ID3506 and Old Crow tephra) and the phonolitic Sheep Track tephra. In addition to the NIST SRM glasses, USGS BCR-2G and BHVO-2G basaltic glasses were measured for calibration of the major elements (i.e., Na, Mg, Al, Si, K, Ca, Ti, Mn, and Fe) in the basaltic Laki tephra. Most major element data for the four volcanic glass samples, and those for ZrO2 in Lipari obsidian and Sheep Track tephra deviate <10% from the preferred values obtained by electron-beam analysis techniques complied in Kuehn et al. (2011). P2O5 values range from 74% to 110% of the preferred values in Kuehn et al. (2011), and are consistent within uncertainties. BaO values are 7–24% of the preferred values of Kuehn et al. (2011), but are similar to those obtained using other trace element analytical techniques, such as X-ray fluorescence and ICP atomic emission spectroscopy. Our trace element data are generally consistent with those obtained in previous studies. However, heterogeneously distributed microcrysts in the glass materials may affect some elements such as B, P, and Cr. The analytical data for the INTAV samples obtained using femtosecond LA-ICP-MS and the NIST SRM and USGS standard glasses demonstrate that this approach is a viable alternative to electron-beam microanalysis techniques for the determination of major elements in rhyolitic and basaltic glasses.

    Download PDF (1108K)
  • Bogdan Stefanov Vaglarov, Jun-ichi Kimura, Takashi Miyazaki, Qing Chan ...
    2016 Volume 50 Issue 5 Pages 423-429
    Published: September 30, 2016
    Released on J-STAGE: October 26, 2016
    JOURNAL OPEN ACCESS
    Supplementary material

    We report the origin of significant fractionation of Pb isotope ratios in Ca-doped 0.08 mol L–1 HNO3 solutions. We applied Tl-spiked standard bracketing mass fractionation correction using solution-based multiple collector-inductively coupled plasma mass spectrometry. The addition of matrix elements into the NIST SRM 981 Pb standard solution resulted in strong isotope fractionation of up to –150 ppm per AMU (atomic mass unit), when Ca was doped at 200 times the molar concentration of Pb. In contrast, only +20–60 ppm per AMU fractionation occurred upon addition of the same amounts of Mg, Al, or Fe. Strong fractionation by Ca only occurred when doping into a test tube containing Pb. In contrast, insignificant fractionation (+20–60 ppm) occurred when Ca was mixed immediately before sample nebulization. The results suggest that strong Pb isotope fractionation was probably due to precipitation of a Pb-Ca complex in the test tube, which is insoluble in the sparse 0.08 mol L–1 HNO3. Mixing of Ca immediately prior to sample nebulization prevented precipitation and caused a small (+22 ppm) positive fractionation, similar to that seen for other major elements. A small amount of fractionation was common in major-element-doped samples. This suggested different degrees of isotopic fractionation of Tl and Pb, perhaps by the space charge effect. In order to test the effect of Ca-Pb precipitation in practical sample analysis, a conventional anion exchange chromatographic separation of Pb after HF-HNO3 sample digestion was applied to 200–500 × Ca-doped SRM 981 and a large amount of Ca-doped basalt standard of JB-2 samples. No isotopic fractionation was observed, showing decomposition of the Ca-Pb precipitate by strong acid attack and during column chromatography. The results suggest the negligible effect of Pb isotope fractionation, even in Ca-rich samples after acid digestion.

    Download PDF (323K)
  • A. M. Agashev, Y. Orihashi, N. P. Pokhilenko, I. V. Serov, A. V. Tolst ...
    2016 Volume 50 Issue 5 Pages 431-438
    Published: September 30, 2016
    Released on J-STAGE: October 26, 2016
    JOURNAL OPEN ACCESS

    This paper presents new data related to the emplacement ages of the Amakinskaya and Taezhnaya kimberlites of the Mirny field, Siberia, located in the southern part of the Yakutian diamondiferous province. This study analyzed rutile and titanite grains along with zircons for U-Pb isotope composition by laser ablation (LA)-inductively coupled plasma-mass spectrometry (ICP-MS) and evaluated the applicability of rutile and titanite for the dating of kimberlite emplacements. Both minerals contain substantial admixtures of common Pb in their Pb isotope composition. Therefore, the 207Pb method was applied for common Pb correction during age calculation. The obtained U-Pb ages of the Taezhnaya pipe were 363 ± 12 and 359 ± 12 Ma, respectively, for zircon and titanite. Ages of 366 ± 10 and 361 ± 16 Ma was obtained from Amakinskaya pipe titanite and rutile, respectively. All age estimates correspond to the main epoch of diamondiferous kimberlite activity in the Siberian platform and suggest the formation of the Mirny kimberlite field within a single event or two separate events occurring close together in time. Results obtained from this study indicate that rutile and titanite can be useful for the dating of kimberlite emplacements.

    Download PDF (763K)
Notes
feedback
Top