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Sun J.,Laboratory of Isotope Geology | Zhu X.,China University of Geosciences | Tang S.,China University of Geosciences | Chen Y.,Laboratory of Isotope Geology
Chinese Journal of Geochemistry | Year: 2013

Some elements normally occur at trace levels while the majority of natural geological materials may be exceedingly enriched in some special cases, such as the Bayan Obo ore deposit where REE and Nb are extremely enriched. These elements may not be removed completely during purification. Therefore, matrix effects will be caused during stable isotope ratio measurement in the MC-ICP-MS. Experiments have shown that the established methods of chromatographic separation of Cu, Fe, and Zn using AG MP-1 Anion Exchange Resin cannot make effective separation of Nb, W, and Cu from Fe using 20 mL 6 M HCl. It is also observed that the elution curves of W and Cu overlap at working conditions and thus W is present in measurable amounts in some sample solutions. Matrix effects in the MC-ICP-MS induced by Nb, W, and Cu during Fe isotope ratio measurements and by W during Cu isotope ratio measurements were thus investigated by examining their changes in delta values between doped and undoped standards. The results show that the effects of the matrix elements Nb, W, or Cu on Fe isotope ratio measurements are minimal in the case of m(Nb)/m(Fe)<0. 005, m(W)/m(Fe)<0. 01, or m(Cu)/m(Fe)<0. 6. This finding, combined with the extremely low levels of W and Cu, and the fact that nearly 90% of Nb can be removed during purification, demonstrates that the methods of chromatographic separation of Fe established before are suitable for Bayan Obo ore samples and that the methods can be simplified when Cu elution is unnecessary. The effects of the matrix element W on Cu isotope determinations are minimal in the case of m(W)/m(Cu)<0. 7. Therefore, W exerts no significant effect on the measurements of Cu isotopes for the majority of natural geological materials. © 2013 Science Press, Institute of Geochemistry, CAS and Springer-Verlag Berlin Heidelberg.

Wen H.,Chinese Academy of science | Wen H.,University of Lorraine | Carignan J.,University of Lorraine | Cloquet C.,University of Lorraine | And 2 more authors.
Journal of Analytical Atomic Spectrometry | Year: 2010

We report the isotopic composition of five molybdenum (Mo) standard reference solutions and four fractions from one of these solutions eluted through anion resin column relative to a sixth reference solution. The reference solutions were National Institute of Standards and Technology (NIST) SRM 3134 (lot#891307), Johnson Matthey Specpure (JMC)-Mo Sie (lot #602332B), JMC-Mo Wen (lot#13989C), Merck (lot#170334), Sigma-Aldrich (lot#207306) and Prolabo. Measurements were conducted using Isoprobe multi collector inductively coupled plasma mass spectrometer (MC-ICP-MS) at the Centre de Recherches Pétrographiques et Géochimiques (France) and Nu Plasma MC-ICP-MS at either the Ecole Normale Supérieure de Lyon (France) or the Laboratory of Isotope Geology in the Ministry of Land and Resources (China). The sample-standard bracketing method was employed to correct the mass bias for Mo isotopes during instrumental measurement. Except for the Merck Mo solution, all the Mo solutions were identical in isotopic composition within error. Although the JMC Mo solution has been used as the internal reference material by various groups, uncertainty may still occur with different lot numbers and availability might be limited. Here, we propose the NIST 3134 Mo solution as a new candidate for delta zero reference material, used for reporting Mo isotopic composition of natural samples. Isotopic compositions for four eluted fractions of the Sigma-Aldrich Mo solution were 2.18‰, 0.98‰, -1.10‰ and -1.95‰ for δ97/95Mo relative to the NIST Mo standard. These values span the range of reported isotopic compositions for natural terrestrial and experimental samples (approximately -0.5‰ to 1.6‰ for δ97/95Mo). We propose these eluted fractions to be used as a secondary reference for Mo isotope measurements. Mo solutions are available at CRPG upon request. © The Royal Society of Chemistry 2010.

Li Z.,Laboratory of Isotope Geology | Li Z.,Chinese Academy of Geological Sciences | Zhu X.,Laboratory of Isotope Geology | Zhu X.,Chinese Academy of Geological Sciences
Acta Petrologica Sinica | Year: 2012

The results of major, trace, rare earth elements, Fe and Nd isotopic compositions of Xuanlong type iron ore deposit are reported. The average bulk compositions of iron ore are characterized by highest total Fe2O 3, and relative enrichment in Al2O3, TiO 2 and P2O5. The overall contents of trace elements are similar to those of the average crust, but with distinct enrichments of redox - sensitive trace elements (V, U, Mo). The total rare earth element contents are high, and the Shale-normalized REE patterns display depletion of light REE relative to heavy REE, non-significant positive anomalies of Eu and low Y/Ho values. Isotopically the iron ore samples have negative value of εNd. These characteristics demonstrate that the iron source of Xuanlong type iron ore deosit are from detrital input. Hematites show heavy Fe isotope enrichment relative to IRMM-014, which is different from the negative or zero iron isotopic composition of modern analogues formed by cyanobacteria. Therefore, the iron isotope data of hematite provide evidence for the presence of Fe-oxidizing bacteria. Geochemical features including the lack of Ce negative anomalies, enrichments of V, U, Mo, and the heavy Fe isotope enrichment of hematite samples implies the oxygen fugacity in the depositional environment was relatively low.

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