Language：English  

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Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1111/rge.12266

Repository Public URL： https://hdl.handle.net/2324/7177960

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.scitotenv.2021.145183

Repository Public URL： https://hdl.handle.net/2324/7173533

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.gca.2020.12.009

Repository Public URL： https://hdl.handle.net/2324/7177959

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.chemgeo.2020.119863

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.chemgeo.2020.119863

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/min9070442

Repository Public URL： https://hdl.handle.net/2324/7177958

Language：English   Publishing type：Research paper (scientific journal)  

Carbonatites undergo various magmatic-hydrothermal processes during their evolution that are important for the enrichment of rare earth elements (REE). This geochemical, petrographic, and multi-isotope study on the Kangankunde carbonatite, the largest light REE resource in the Chilwa Alkaline Province in Malawi, clarifies the critical stages of REE mineralization in this deposit. The δ56Fe values of most of the carbonatite lies within the magmatic field despite variations in the proportions of monazite, ankerite, and ferroan dolomite. Exsolution of a hydrothermal fluid from the carbonatite melts is evident based on the higher δ56Fe of the fenites, as well as the textural and compositional zoning in monazite. Field and petrographic observations, combined with geochemical data (REE patterns, and Fe, C, and O isotopes), suggest that the key stage of REE mineralization in the Kangankunde carbonatite was the late magmatic stage with an influence of carbothermal fluids i.e. magmatic–hydrothermal stage, when large (~200 µm), well-developed monazite crystals grew. The C and O isotope compositions of the carbonatite suggest a post-magmatic alteration by hydrothermal fluids, probably after the main REE mineralization stage, as the alteration occurs throughout the carbonatite but particularly in the dark carbonatites.

DOI： 10.3390/min9070442

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.15243/jdmlm.2018.054.1403

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.apgeochem.2017.05.007

Repository Public URL： https://hdl.handle.net/2324/7177957

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.5185/amlett.2017.7061

Language：English   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

<p>²³⁴U and ²³⁸U are naturally occurring radioisotopes, and the ratio of their decay rates is expressed as activity ratio (<i>AR</i>). <i>AR</i> is an index of the degree of deviation from the secular equilibrium and has been used as a tracer in shallow groundwater systems. This study examined the distribution of ²³⁸U and ²³⁴U in deep groundwater in the northern Hokkaido, Japan, to assess the usefulness of <i>AR</i> as a geochemical indicator in the reducing groundwater. Samples consist of saline groundwater derived from seawater at the time of deposition of the strata, and meteoric water infiltrated during the glacial period before about 12,000 years ago. The results showed that <i>AR</i> increased in the sampling depths of 350 < 160 < 250 meters up to ~11 depending on the percentage of meteoric water infiltration, and positively correlated with inverses of uranium concentrations. In addition, uranium concentration in groundwater showed negative and positive correlations with meteoric water infiltration percentages and chloride ion concentrations, respectively. These results indicate that the uranium concentration in the fossil seawater was diluted by the infiltration of the meteoric water, resulting in a decrease in ionic strength. As the consequence, the desorption of sorbed ions and dissolution of precipitates in groundwater may have progressed at higher proportions of meteoric water, leading to increases in <i>AR</i>. Furthermore, the timing of the infiltration was estimated from initial <i>AR</i> values of carbonate precipitation observed in the formation. ²³⁴U/²³⁸U isotope ratio will be a useful indicator to understand the changes in water flow environment for low-flow reducing groundwater.</p>

DOI： 10.2343/geochemj.gj24028

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CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2343/geochemj.GJ24028

Language：English   Publisher：The Mass Spectrometry Society of Japan  

<p>A simple and rapid analytical method was developed for the simultaneous determination of two chromium species, Cr(III) and Cr(VI), in the environmental waters by high-performance liquid chromatography–inductively coupled plasma-mass spectrometry (HPLC-ICP-MS). This study incorporated a chelating pretreatment with 2,6-pyridinedicarboxylic acid (PDCA) to convert Cr(III) species into a stable Cr(III)-PDCA anion complex, which was then separated from Cr(VI) oxyanion using an anion exchange column. Building on the fundamental analytical approach proposed by Shigeta <i>et al</i>. (doi: 10.2116/analsci.18P012), the mobile phase was optimized to ensure stability for ICP-MS detection, avoiding nonvolatile salts. Chromium species and chloride ions were effectively separated within 6 minutes at a flow rate of 0.6 mL min⁻¹ with the optimized mobile phase, which consisted of 50 mmol L⁻¹ ammonium acetate (pH 6.80) and 2 mmol L⁻¹ PDCA. The detection limits were 0.18 μg L⁻¹ and 0.09 μg L⁻¹ for Cr(III) and Cr(VI), respectively, at <i>m/z</i> 52 under He collision mode.</p>

DOI： 10.5702/massspectrometry.a0161

Scopus

PubMed

CiNii Research

Language：English   Publisher：(公社)日本分析化学会  

水の多い条件下で親水性相互作用クロマトグラフィー(HILIC)と誘導結合プラズマ質量分析法(ICPMS)を組み合わせ、環境水中のCr(VI)とCr(III)を同時測定する迅速分析法を開発した。種々の化学形態のCr(III)種を2,6-ピリジンジカルボン酸(PDCA)により安定したCr(III)-PDCAアニオン錯体に誘導し、次にジオール結合ポリマーのHILICカラムでCr(VI)オキシアニオンから分離した。水性移動相(50mmol/L酢酸アンモニウム(pH7.0)、2mmol/L PDCA、4%アセトニトリル)でCr種とClイオンを分離できた。この手法にて、Cr(III)-PDCAよりCr(VI)が優先的に溶出するため、Cr(VI)を迅速に測定でき両Cr種を6.2分以内に分析しえた。He衝突モード下のCr(VI)m/z52の検出限界は0.19μg/L、Cr(III)の検出限界は0.35μg/Lで、従来のイオン交換クロマトグラフィー/ICPMS法と同等以上であり、種々のレベルのCr種を含む河川水試料のスパイク回収試験で定量的な回収を得た。

Language：Japanese   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

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DOI： 10.14862/geochemproc.71.0_35

CiNii Research

Language：Japanese   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

<p></p>

DOI： 10.14862/geochemproc.71.0_30

CiNii Research

Language：Japanese   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

<p></p>

DOI： 10.14862/geochemproc.71.0_42

CiNii Research

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Myanmar has a drier sub-tropical climate than countries that typically contain Ni laterite deposits, but hosts a Ni laterite deposit at Tagaung Taung. Given that Ni enrichment processes in the Tagaung Taung deposit are poorly understood, we investigated the geochemical and mineralogical evolution of two weathering profiles developed on different bedrocks in the central part of Myanmar: a partly serpentinized harzburgite at Tagaung and an almost completely serpentinized peridotite at Budaung. The whole-rock geochemical data indicate that Si was retained relative to Fe and Al in the weathering profiles. Nickel has been enriched to contents as high as 4.89 wt.% NiO in the saprolite layers at Tagaung, whereas the saprolite layers at Budaung contain ≤ 1.55 wt.% NiO. Smectite is the main mineral that formed in the saprolite layers at Tagaung, whereas secondary serpentine dominates the saprolite layers at Budaung. Microscopic observations indicate that Ni-smectite (> 10 wt.% NiO), which is only observed at Tagaung, formed as a replacement product of orthopyroxene. In addition to the high Ni fixation capacity of smectite relative to secondary serpentine, Ni-rich pore water derived from the dissolution of olivine likely contributed to the high Ni contents of smectite. Our results imply that high-grade Ni laterite deposits may develop on unaltered or partly serpentinized harzburgite under the climatic conditions typical of Myanmar.

DOI： 10.1007/s00126-021-01089-6

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Other Link： https://link.springer.com/article/10.1007/s00126-021-01089-6/fulltext.html

Publisher：Geochemical Journal  

Slab-dehydrated fluid is considered to be involved in island arc magmatism. In this study, Li isotope ratios were determined for deep groundwater samples from the non-volcanic forearc region of SW Japan. The contribution of the slab-dehydrated fluid from the Philippine Sea Plate (PHS) was investigated in the Arima area and the eastern Kii Peninsula area, corresponding to the slab depths of ~60 km and 20-30 km, respectively. In the Arima area, the high-temperature thermal waters with high salinity called the Arima-type fluid were clarified to have low δ⁷Li values of +1-+3‰. The low δ⁷Li values with high Li concentrations are thought to be the result of fluid-rock interactions at high temperatures, which is consistent with the characteristics of the slab-dehydrated fluid. On the other hand, the δ⁷Li values of deep groundwaters in the eastern Kii Peninsula showed a wide range of +2 to +29‰. Several groundwater samples had a similar chemical property to the Arima-type fluid: low δ⁷Li values, low Cl/Li ratios, and ⁸⁷Sr/⁸⁶Sr ratios around 0.708-0.710. They are distributed along the Median Tectonic Line (MTL) and within about 20 km south of the MTL. These results indicate a common supply of slab-dehydrated fluids to the non-volcanic forearc region in SW Japan from PHS along the large faults, and Li isotope ratios will be a useful indicator to detect their contribution.

DOI： 10.2343/geochemj.GJ22015

Scopus

Event date： 2023.6

Language：Japanese  

Country：Japan  

Event date： 2023.6

Language：Japanese  

Country：Japan  

Event date： 2023.6

Language：Japanese  

Country：Japan  

Distribution of hydrothermal alteration zones in the southwestern part of the Shin-Iriki mine, northern Kagoshima, Japan

Event date： 2023.6

Language：English  

Country：Japan  

Event date： 2023.6

Language：Japanese  

Country：Japan  

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Event date： 2023.6

Language：Japanese  

Country：Japan  

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Event date： 2023.6

Language：Japanese  

Country：Japan  

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Event date： 2023.6

Language：English  

Country：Japan  

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Event date： 2023.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

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Event date： 2023.6

Language：Japanese  

Country：Japan  

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Event date： 2023.5 - 2024.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：幕張メッセ   Country：Japan  

Presentation type：Oral presentation (general)  

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Presentation type：Oral presentation (general)  

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Presentation type：Oral presentation (general)  

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Event date： 2024.8

Language：English   Presentation type：Poster presentation  

Event date： 2024.8

Language：English   Presentation type：Poster presentation  

Event date： 2024.8

Language：English   Presentation type：Poster presentation  

Venue：Melbourne  

Event date： 2024.8

Language：English   Presentation type：Poster presentation  

Event date： 2023.8 - 2024.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Language：Japanese  

Presentation type：Oral presentation (invited, special)  

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Type：Other

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