Magnesium Isotope Compositions of Natural Reference Materials

This study presents a chemical protocol for the separation of Mg that is particularly adapted to alkali‐rich samples (granite, soil, plants). This protocol was based on a combination of two pre‐existing methods: transition metals were first removed from the sample using an AG‐MP1 anion‐exchange resin, followed by the separation of alkalis (Na, K) and bivalent cations (Ca²⁺, Mn²⁺ and Sr²⁺) using a AG50W‐X12 cation‐exchange resin. This procedure allowed Mg recovery of ～ 10 0 ± 8%. The [Σcations]/[Mg] molar ratios in all of the final Mg fractions were lower than 0.05. The Mg isotope ratios of eleven reference materials were analysed using two different MC‐ICP‐MS instruments (Isoprobe and Nu Plasma). The long‐term reproducibility, assessed by repeated measurements of Mg standard solutions and natural reference materials, was 0.14‰. The basalt (BE‐N), limestone (Cal‐S) and seawater (BCR‐403) reference materials analysed in this study yielded δ²⁶Mg mean values of ?0.28 ± 0.08‰, ?4.37 ± 0.11‰ and ?0.89 ± 0.10‰ respectively, in agreement with published data. The two continental rocks analysed, diorite (DR‐N) and granite (GA), yielded δ²⁶Mg mean values of ?0.50 ± 0.08‰ and ?0.75 ± 0.14‰, respectively. The weathering products, soil (TILL‐1) and river water (NIST SRM 1640), gave δ²⁶Mg values of ?0.40 ± 0.07‰ and ?1.27 ± 0.14‰, respectively. We also present, for the first time, the Mg isotope composition of bulk plant and organic matter. Rye flour (BCR‐381), sea lettuce (Ulva lactuva) (BCR‐279), natural hairgrass (Deschampsia flexuosa) and lichen (BCR‐482) reference materials gave δ²⁶Mg values of ?1.10 ± 0.14‰, ?0.90 ± 0.19‰, ?0.50 ± 0.22‰ and ?1.15 ± 0.27‰ respectively. Plant δ²⁶Mg values fell within the range defined by published data for chlorophylls.     

Basaltic and Solution Reference Materials for Iron,Copper and Zinc Isotope Measurements

Iron, Cu and Zn stable isotope systems are applied in constraining a variety of geochemical and environmental processes. Secondary reference materials have been developed by the Institute of Geology, Chinese Academy of Geological Sciences (CAGS), in collaboration with other participating laboratories, comprising three solutions (CAGS‐Fe, CAGS‐Cu and CAGS‐Zn) and one basalt (CAGS‐Basalt). These materials exhibit sufficient homogeneity and stability for application in Fe, Cu and Zn isotopic ratio determinations. Reference values were determined by inter‐laboratory analytical comparisons involving up to eight participating laboratories employing MC‐ICP‐MS techniques, based on the unweighted means of submitted results. Isotopic compositions are reported in per mil notation, based on reference materials IRMM‐014 for Fe, NIST SRM 976 for Cu and IRMM‐3702 for Zn. Respective reference values of CAGS‐Fe, CAGS‐Cu and CAGS‐Zn solutions are as follows: δ⁵⁶Fe = 0.83 ± 0.07 and δ⁵⁷Fe = 1.20 ± 0.13, δ⁶⁵Cu = 0.57 ± 0.06, and δ⁶⁶Zn = ?0.79 ± 0.12 and δ⁶⁸Zn = ?1.65 ± 0.24, respectively. Those of CAGS‐Basalt are δ⁵⁶Fe = 0.15 ± 0.07, δ⁵⁷Fe = 0.22 ± 0.10, δ⁶⁵Cu = 0.12 ± 0.08, δ⁶⁶Zn = 0.17 ± 0.13, and δ⁶⁸Zn = 0.34 ± 0.26 (2s).     

A Reflection on Mg, Cd, Ca, Li and Si Isotopic Measurements and Related Reference Materials

This contribution aims to report the reflections we had with the scientific community during two international workshops on reference materials for stable isotopes in Davos (2002) and Nice (2003). After evaluating the isotopic homogeneity of some existing reference materials, based on either certificates, literature data or specific inter-laboratory rounds, we confirm these as primary reference materials or propose new ones relative to which stable isotope compositions should be reported. We propose DSM-3 for Mg, NIST SRM 915a for Ca, L-SVEC for Li and NBS28 for Si. Cadmium does not yet have a well identified delta zero material, although three commercial mono-elemental Cd solutions have yielded the same isotopic composition relative to one another. In order to scale the linearity of any mass spectrometer, some secondary reference materials are also proposed: Cambridge-1 solution for Mg, the "Münster-Cd" and JEPPIM Cd solutions for Cd and the "Big Batch" silicate for Si. The team from Nancy propose to prepare a mixed spike solution for Li isotopes. Well-characterised natural samples such as ocean or continental waters, diatoms, sponges, rocks and minerals are needed to validate the entire analytical procedure, particularly to take into account the effect of sample mineralisation and of chemical manipulations for elemental separation prior to analysis.     

Characterisation of Three Sri Lankan Zircon Megacrysts as Potential Reference Materials for Microbeam U-Pb Geochronology and Hf-O-Zr Isotope Measurements

In situ U-Pb geochronology and hafnium, oxygen and zirconium isotope measurements in zircons using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and ion microprobe techniques can provide essential isotopic data to constrain geological evolutionary histories. Developing reliable zircon reference materials is the cornerstone for in situ zircon chronology and isotopic studies. In this study, the homogeneity of U-Pb ages and Hf-O-Zr isotope ratios in three Sri Lankan zircon megacrysts (SLZA, SLZB and SLZC) were investigated using multiple analytical methods. The obtained U, Th, Pb and Hf mass fractions of the SLZA zircon were 839 ± 56 μg g^-1 (1s), 151 ± 15 μg g^-1 (1s), 198 ± 28 μg g^-1 (1s) and 8635 ± 286 μg g^-1 (1s), respectively. The mass fractions of U, Th, Pb and Hf in the SLZB zircon were 1106 ± 106 μg g^-1 (1s), 331 ± 61 μg g^-1 (1s), 376 ± 57 μg g^-1 (1s) and 9673 ± 976 μg g^-1 (1s), respectively. The U, Th, Pb and Hf mass fractions determined in the SLZC zircon were 551 ± 35 μg g^-1 (1s), 111 ± 8 μg g^-1 (1s), 129 ± 18 μg g^-1 (1s) and 7881 ± 393 μg g^-1 (1s), respectively. The chemical abrasion isotope dilution thermal ionisation mass-spectrometry (CA-ID-TIMS) method yielded a Th-corrected weighted mean ²⁰⁶Pb/²³⁸U age of 556.94 ± 1.29 Ma (95% conf., n = 5) for the SLZA zircon, 552.90 ± 1.29 Ma (95% conf., n = 7) for the SLZB zircon and 560.83 ± 1.29 Ma (95% conf., n = 7) for the SLZC zircon. The obtained Hf isotopic compositions of the SLZA, SLZB and SLZC zircons determined with the solution MC-ICP-MS method were 0.281651 ± 0.000014 (2s, n = 10), 0.281704 ± 0.000008 (2s, n = 10) and 0.281676 ± 0.000006 (2s, n = 10), respectively. The obtained O isotopes of the SLZA and SLZB zircons measured with the laser fluorination method were 12.14 ± 0.56‰ (2s, n = 4) and 11.91 ± 0.30‰ (2s, n = 4), respectively. The Zr isotopes of the SLZA, SLZB and SLZC zircons determined with double spike TIMS analysis yielded mean δ⁹⁴/⁹⁰Zr_SRM3169 values of -0.03 ± 0.06‰ (2s, n = 10), -0.03 ± 0.04‰ (2s, n = 10) and 0.00 ± 0.07‰ (2s, n = 8), respectively. The SLZA zircon can be used as a primary reference or quality control material for microbeam U-Pb, Hf and Zr isotope measurements because of its slight heterogeneity. The U-Pb, Hf and Zr isotopic compositions of the SLZB and SLZC megacrysts were homogeneous. The O isotopic compositions in the SLZA and SLZB zircon were slightly dispersed, indicating that these two megacrysts can only serve as secondary reference materials for microbeam O isotope measurements.     

Tourmaline Reference Materials for the In Situ Analysis of Oxygen and Lithium Isotope Ratio Compositions

Three tourmaline reference materials sourced from the Harvard Mineralogical and Geological Museum (schorl 112566, dravite 108796 and elbaite 98144), which are already widely used for the calibration of in situ boron isotope measurements, are characterised here for their oxygen and lithium isotope compositions. Homogeneity tests by secondary ion mass spectrometry (SIMS) showed that at sub‐nanogram test portion masses, their ¹⁸O/¹⁶O and ⁷Li/⁶Li isotope ratios are constant within ± 0.27‰ and ± 2.2‰ (1s), respectively. The lithium mass fractions of the three materials vary over three orders of magnitude. SIMS homogeneity tests showed variations in ⁷Li/²⁸Si between 8% and 14% (1s), which provides a measure of the heterogeneity of the Li contents in these three materials. Here, we provide recommended values for δ¹⁸O, Δ’¹⁷O and δ⁷Li for the three Harvard tourmaline reference materials based on results from bulk mineral analyses from multiple, independent laboratories using laser‐ and stepwise fluorination gas mass spectrometry (for O), and solution multi‐collector inductively coupled plasma‐mass spectroscopy (for Li). These bulk data also allow us to assess the degree of inter‐laboratory bias that might be present in such data sets. This work also re‐evaluates the major element chemical composition of the materials by electron probe microanalysis and investigates these presence of a chemical matrix effect on SIMS instrumental mass fractionation with regard to δ¹⁸O determinations, which was found to be < 1.6‰ between these three materials. The final table presented here provides a summary of the isotope ratio values that we have determined for these three materials. Depending on their starting mass, either 128 or 512 splits have been produced of each material, assuring their availability for many years into the future.     

A Simplified, Accurate and Fast Method for Lithium Isotope Analysis of Rocks and Fluids, and δ7Li Values of Seawater and Rock Reference Materials

We report a new approach to conduct fast and accurate lithium isotope ratio measurements by MC-ICP mass spectrometry after wet chemical sample preparation. In contrast to most previously published methods our MC-ICP-MS set-up did not use a desolvating system to achieve appropriate ion beam intensities and, therefore, was less affected by matrix-induced shifts of the instrumental mass bias. As the total lithium background and build-up in the sample introduction system was low, previous sample residues could be washed out by an extended uptake of the new sample. Elimination of a nitric acid rinse step increased the sample throughput by a factor of two and allowed the instrumental mass bias drift to be tracked more precisely. δ⁷Li values of powdered silicate rock reference materials and seawater obtained in this study revealed good accuracy and an overall analytical uncertainty of typically 0.5‰ (2s). On the basis of a comparison between our lithium isotope data and compiled literature data, we recommend preliminary average δ⁷Li values for seawater (+30.8‰) and several silicate rock reference materials (BHVO-1: +5.0‰; JA-1: +5.6‰; JB-2: +4.8‰). The compilation of published δ⁷Li values for seawater suggests that the observed large lithium isotope differences are due to inter-method and/or interlaboratory bias. Most recently published δ⁷Li values for seawater show little variation and confirm a constant lithium isotope composition (at the sub ‰ level) of seawater in well mixed ocean basins.     

常用锂同位素地质标准物质的多接收器电感耦合等离子体质谱分析研究

锂同位素研究是非传统稳定同位素地球化学研究的前沿,已广泛应用于从地表到地幔的岩石圈及流体等固体地球科学的研究领域。准确测定锂同位素比值是应用该同位素体系的前提。本文报道了国际上7种常用地质标准物质(BHVO-2、JB-2、BCR-2、AGV-2、NKT-1、L-SVEC、IRMM-016)的锂同位素组成数据。分析中采用硝酸-氢氟酸混合酸消解岩石标准样品,通过3根阳离子交换树脂(AG50W-X8,200~400目)填充的聚丙烯交换柱和石英交换柱对锂进行分离富集,利用Neptune型多接收器电感耦合等离子体质谱(MC-ICPMS)测定锂同位素比值,使用标准-样品交叉法(SSB)校正仪器的质量分馏。实验得到这7种常用地质标准物质的锂同位素组成与测试精度(2SD)分别为:δ7LiBHVO-2—L-SVEC=4.7‰±1.0‰(n=53),δ7LiJB-2—L-SVEC=4.9‰±1.0‰(n=20),δ7LiBCR-2—L-SVEC=4.4‰±0.8‰(n=8),δ7LiAGV-2—L-SVEC=6.1‰±0.4‰(n=14),δ7LiNKT-1—L-SVEC=9.8‰±0.2‰(n=3),δ7LiL-SVEC—L-SVEC=-0.3‰±0.3‰(n=10),δ7LiIRMM-016—L-SVEC=0.0‰±0.5‰(n=10),这些数据在误差范围内与国际上已发表的数据一致。Li同位素分析精度可以达到大约0.5‰,长期的分析精度即外部重现性≤±1.0‰,达到了国际同类实验室水平。7种常用地质标准物质的锂同位素组成数据的发表为锂同位素研究提供了统一的标准,使地质样品的锂同位素数据的质量监控成为可能。在基质效应的研究中,使用不同量的IRMM-016配制的标准溶液过柱,深入探讨了样品量对锂同位素测定值的影响,结果表明,在现有测试精度下,只要分析样品的锂含量达到100μg/L,且不超过树脂的承载量,样品的锂同位素组成在误差范围内与真值吻合,样品量的大小不影响锂同位素测定结果的准确性。     

Lithium Isotope Composition of Marine Biogenic Carbonates and Related Reference Materials

In this study, the accuracy and the precision corresponding to Li isotopic measurements of low level samples such as marine and coastal carbonates are estimated. To this end, a total of fifty‐four analyses of a Li‐pure reference material (Li7‐N) at concentrations ranging from 1 to 6 ng ml^?1 were first performed. The average δ⁷Li values obtained for solutions with and without chemical purification were 30.3 ± 0.4‰ (2s, n = 19) and 30.2 ± 0.4‰ (2s, n = 36), respectively. These results show that the chosen Li chemical extraction and purification procedure did not induce any significant isotope bias. Two available carbonate reference materials (JCt‐1 and JCp‐1) were analysed, yielding mean δ⁷Li values of 18.0 ± 0.27‰ (2s, n = 6) and 18.8 ± 1.8‰ (2s, n = 9), respectively. Small powder aliquots (< 15 mg) of JCp‐1 displayed significant isotope heterogeneity and we therefore advise favouring JCt‐1 for interlaboratory comparisons. The second part of this study concerns the determination of δ⁷Li value for biogenic carbonate samples. We performed a total of twenty‐nine analyses of seven different tropical coral species grown under controlled and similar conditions (24.0 ± 0.1 °C). Our sample treatment prior to Li extraction involved removal of organic matter before complete dissolution in diluted HCl. Our results show (a) a constant δ⁷Li within each skeleton and between the different species (δ⁷Li = 17.3 ± 0.7‰), and (b) a Li isotope fractionation of ?2‰ compared with inorganic aragonite grown under similar conditions. Comparison with literature data suggests a significant difference between samples living in aquaria and those grown in natural conditions. Finally, we investigate ancient (fossil) carbonate material and foraminifera extracted from marine sedimentary records. Different leaching procedures were tested using various HCl molarities. Results indicate that carbonate preferential dissolution must be carried out at an acid molarity < 0.18 mol l^?1. Possible contamination from silicate minerals can be verified using the Al/Ca ratio, but the threshold value strongly depends on the carbonate δ⁷Li value. When the silicate/carbonate ratio is high in the sediment sample (typically > 2), contamination from silicates cannot be avoided, even at low HCl molarity (? 0.1 mol l^?1). Finally, bulk carbonate and foraminifera extracted from the same core sample exhibited significant discrepancies: δ⁷Li values of foraminifera were more reproducible but were significantly lower. They were also associated with lower Sr/Ca and higher Mn/Ca ratios, suggesting a higher sensitivity to diagenesis, although specific vital effects cannot be fully ruled out.     

Development of Synthetic Clinopyroxene Reference Materials for In Situ Lithium Isotope Measurement by LA-MC-ICP-MS

The isotopic composition of lithium (Li) in clinopyroxene (Cpx), determined via in situ micro-analysis, has been employed as a potential geochemical tool for studying various geological processes such as crust-mantle recycling, silicate weathering and fluid-rock interaction. To obtain precise and accurate Li isotopic compositions in Cpx by LA-MC-ICP-MS, synthetic Cpx matrix-matched reference materials (RMs) were prepared in this study. Six Cpx-matrix RMs were prepared by mixing metallic oxides with GSP-2 (granodiorite) or pure L-SVEC solution and melting them into glasses (GSP-2 + oxide; L-SVEC + oxide). Two representative synthetic glasses, CPXA01 and CPXB01, were subjected to a series of analyses to investigate the possible qualification of the RMs for in situ Li isotope measurement by LA-MC-ICP-MS, including elemental homogeneity analysis (elemental mapping analysis and spot analysis), Li isotopic homogeneity analysis and accurate Li isotopic determination. The applicability of the synthetic Cpx-matrix RMs was highlighted by comparing the δ⁷Li values of three natural Cpx calibrated against the synthetic Cpx-matrix RMs and other commonly used RMs with different matrices (NIST SRM 612, BCR-2G, GOR128-G, StHs6/80-G, KL2-G and T1-G), respectively. Additionally, CPXB01-05 RMs with the same matrix but different Li contents were prepared to explore the Li content mismatch effect, which is significant for accurate determination of in situ Li isotopic composition by LA-MC-ICP-MS. The results of the cross-calibration of Li isotopes in CPXA01 and CPXB01 suggested no obvious Li isotopic fractionation between the two types of glasses (GSP-2 + oxide; L-SVEC + oxide). Thus, the two methods of producing Cpx-matrix RMs are suitable for preparing the matrix-matched RMs for in situ microanalysis for Li isotopes.     

Precise/ Small Sample Size Determinations of Lithium Isotopic Compositions of Geological Reference Materials and Modern Seawater by MC-ICP-MS

The Li isotope ratios of four international rock reference materials, USGS BHVO-2, GSJ JB-2, JG-2, JA-1 and modern seawater (Mediterranean, Pacific and North Atlantic) were determined using multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). These reference materials of natural samples were chosen to span a considerable range in Li isotope ratios and cover several different matrices in order to provide a useful benchmark for future studies. Our new analytical technique achieves significantly higher precision and reproducibility (< ± O.3%o 2s) than previous methods, with the additional advantage of requiring very low sample masses of ca . 2 ng of Li.     

Rubidium Isotope Ratios of International Geological Reference Materials

In this study we determined rubidium isotope ratios in twenty-one commonly used international geological reference materials, including igneous, sedimentary and metamorphic rocks, as well as an IAPSO seawater reference material. All δ⁸⁷Rb results were obtained relative to the NIST SRM 984 reference material. For most reference materials, Rb was purified using a single column loaded with Sr-spec resin. For reference materials containing low Rb but high mass fractions of matrix elements (such as basic rock and seawater), Rb was purified using two-column chromatography, with the first column packed with AGMP-50 resin and the second column packed with Sr-spec resin. Two methods for instrumental mass bias correction, sample-standard bracketing (SSB) mode, and the combined sample-standard bracketing and Zr internal normalisation (C-SSBIN) method, were compared for Rb isotopic measurements by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). The long-term reproducibility of Rb isotopic measurements using both methods was similar, better than 0.06‰ (2s, standard deviation) for NIST SRM 984. Significant Rb isotopic fractionation was observed among the reference materials, with an overall variation in δ⁸⁷Rb values of approximately 0.5‰. The δ⁸⁷Rb values of igneous rocks ranged from -0.28‰ to +0.06‰, showing a trend from heavier isotopic compositions in mafic rocks to lighter δ⁸⁷Rb values in the more evolved felsic rocks. The sedimentary and metamorphic rocks had Rb isotope ratios similar to those of igneous rocks. The δ⁸⁷Rb values of the reference materials related to low-temperature geological processes showed a wider range than those of high-temperature processes. Notably, the IAPSO seawater reference material had a δ⁸⁷Rb value of +0.14‰, which deviated from that of igneous rocks, and represents the heaviest reservoir of Rb isotopes found thus far on Earth. The comprehensive dataset presented here has the potential to serve for quality assurance purposes, and provide a framework for interlaboratory comparisons of Rb isotope ratios.     

Stable W Isotope Measurements of Geological Reference Materials and Tungsten Ore Minerals by Double Spike MC-ICP-MS

This study presents high-precision W isotopic measurement results using the ¹⁸⁰W-¹⁸³W double spike technique with MC-ICP-MS. The effects of isobaric and polyatomic interferences on W isotopic measurements were evaluated. The δ^186/184W values were not significantly affected when the solution had Hf/W ≤ 3 × 10^-4, Ta/W ≤ 1, Os/W ≤ 0.06, Ce/W ≤ 0.0075, Nd/W ≤ 3.5 and Sm/W ≤ 5. The intermediate measurement precisions of both standard solutions (NIST SRM 3163 and Alfa Aesar W) and geological reference materials (NOD-A-1) were better than ±0.024‰ (2s). We also obtained a precision of 0.026‰ for a minimum sample loading mass of 5 ng, allowing the analysis of samples with low W contents. Replicated measurements of geological reference materials (AGV-2, BCR-2, BHVO-2, GSP-2, RGM-1, SDC-1, NOD-A-1 and NOD-P-1) yielded δ^186/184W values ranging from 0.017‰ to 0.144‰. The δ^186/184W values of two major tungsten ore minerals (scheelite and wolframite) were reported and compared herein. Scheelites had systematically slightly heavier W isotopic compositions than wolframites, which may reflect differences in the crystal structure. The resolvable variations of stable/mass-dependent W isotopic compositions in rocks and ore minerals make W isotopes a novel tool for studying hydrothermal mineralisation processes and the W cycle of geological reservoirs.     

Potential Orthopyroxene,Clinopyroxene and Olivine Reference Materials for In Situ Lithium Isotope Determination

Over 1400 electron probe and 700 ion probe microanalyses were performed on eleven mineral separates to evaluate their potential as reference materials for in situ Li isotopic determination. Our results suggest the homogenous distributions of major elements, Li and its isotopes for each sample. Hence, these samples are suitable to be used as reference materials for in situ measurements of Li abundance and Li isotopes by secondary ion mass spectrometry (SIMS) or laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS). These samples have the advantage of mitigating probable matrix effects during calibration owing to the wide range of compositions. The effect of composition on the δ⁷Li of olivine measured by SIMS is a linear function of composition, with δ⁷Li increasing by 1.0‰ for each mole per cent decrease in forsterite component.     

Sodic Pyroxene and Sodic Amphibole as Potential Reference Materials for In Situ Lithium Isotope Determinations by SIMS

Two large pegmatitic crystals of sodic pyroxene (aegirine) and sodic amphibole (arfvedsonite) from the agpaitic igneous Ilímaussaq Complex, south Greenland were found to be suitable as reference materials for in situ Li isotope determinations. Lithium concentrations determined by SIMS and micro‐drilled material analysed by MC‐ICP‐MS generally agreed within analytical uncertainty. The arfvedsonite crystal was homogeneous with [Li] = 639 ± 51 μg g^?1 (2s, n = 69, MC‐ICP‐MS and SIMS results). The aegirine crystal shows strongly developed sector zoning, which is a common feature of aegirines. Using qualitative element mapping techniques (EPMA), the homogeneous core of the crystal was easily distinguished from the outermost sectors of the crystals. The core had a mean [Li] of 47.6 ± 3.6 μg g^?1 (2s, n = 33) as determined by SIMS. The seven micro‐drilled regions measured by solution MC‐ICP‐MS returned slightly lower concentrations (41–46 μg g^?1), but still overlap with the SIMS data within uncertainty. Based on MC‐ICP‐MS and SIMS analyses, the variation in δ⁷Li was about 1‰ in each of the two crystals, which is smaller than that in widely used glass reference materials, making these two samples suitable to serve as reference materials. There was, however, a significant offset between the results of MC‐ICP‐MS and SIMS. The latter deviated from the MC‐ICP‐MS results by ?6.0 ± 1.9‰ (2s) for the amphibole and by ?3.9 ± 1.9‰ (2s) for the aegirine. This indicates the presence of a significant matrix effect in SIMS determinations of Li isotopes for amphibole and pyroxene relative to the basalt glasses used for calibration. Based on the MC‐ICP‐MS results, mean δ⁷Li values of +0.7 ± 1.2‰ (2s, n = 10) for the arfvedsonite crystal and of ?3.7 ± 1.2‰ (2s, n = 7) for the core of the aegirine crystal were calculated. Adopting these values, SIMS users can correct for the specific IMF (instrumental mass fractionation) of the ion probe used. We propose that these two crystals serve as reference materials for in situ Li isotope determinations by SIMS and pieces of these two crystals are available from the first author upon request.     

Thallium Mass Fraction and Stable Isotope Ratios of Sixteen Geological Reference Materials

Thallium stable isotope ratio and mass fraction measurements were performed on sixteen geological reference materials spanning three orders of magnitude in thallium mass fraction, including both whole rock and partially separated mineral powders. For stable isotope ratio measurements, a minimum of three independent digestions of each reference material was obtained. High‐precision trace element measurements (including Tl) were also performed for the majority of these RMs. The range of Tl mass fractions represented is 10 ng g^?1 to 16 μg g^?1, and Tl stable isotope ratios (reported for historical reasons as ε²⁰⁵Tl relative to NIST SRM 997) span the range ?4 to +2. With the exception – attributed to between‐bottle heterogeneity – of G‐2, the majority of data are in good agreement with published or certified values, where available. The precision of mean of independent measurement results between independent dissolutions suggests that, for the majority of materials analysed, a minimum digested mass of 100 mg is recommended to mitigate the impact of small‐scale powder heterogeneity. Of the sixteen materials analysed, we therefore recommend for use as Tl reference materials the USGS materials BCR‐2, COQ‐1, GSP‐2 and STM‐1; CRPG materials AL‐I, AN‐G, FK‐N, ISH‐G, MDO‐G, Mica‐Fe, Mica‐Mg and UB‐N; NIST SRM 607 and OREAS14P.     

铝土矿中锂同位素分离提纯方法的建立

铝土矿是极端风化作用的产物,也是锂的重要载体,由于其资源量巨大,对铝土矿中锂的富集机制和分布规律的研究将有利于找矿预测。锂同位素的高效准确分析是深入认识矿物中锂的富集机制和分布规律的基础。铝土矿样品由于化学稳定性较强,溶样过程较为复杂,且Al、Na、Ca、K等基体元素含量远高于锂,给锂的纯化增加不少难度。本文采用内径5mm、柱长190mm的聚四氟乙烯离子交换柱和AG50W-X12阳离子交换树脂,以0.5mol/L硝酸为淋洗液淋洗34mL,收集最后的12mL,即可完成对铝土矿中锂的完全纯化回收。该纯化方法减少了淋洗液的使用量,提高了实验效率。采用该方法对国际标样L-SVEC、RGM-2、GSP-2进行锂的纯化,通过多接收电感耦合等离子体质谱仪(MC-ICP-MS)测试锂同位素组成,得到的δ~7Li测试值分别为-0.26‰±0.09‰(2SD,n=3)、3.19‰±0.37‰(2SD,n=3)、-0.78‰±0.22‰(2SD,n=3),与前人报道一致,验证了该方法的可靠性。此外,采用本方案对铝土矿国家标样(GBW07182)进行锂的纯化,δ~7Li测定值为10.16‰±0.21‰(2SD,n=3)。     

New Reference Materials and Assessment of Matrix Effects for SIMS Measurements of Oxygen Isotopes in Garnet

Accurate ion microprobe analysis of oxygen isotope ratios in garnet requires appropriate reference materials to correct for instrumental mass fractionation that partly depends on the garnet chemistry (matrix effect). The matrix effect correlated with grossular, spessartine and andradite components was characterised for the Cameca IMS 1280HR at the SwissSIMS laboratory based on sixteen reference garnet samples. The correlations fit a second‐degree polynomial with maximum bias of ca. 4‰, 2‰ and 8‰, respectively. While the grossular composition range 0–25% is adequately covered by available reference materials, there is a paucity of them for intermediate compositions. We characterise three new garnet reference materials GRS2, GRS‐JH2 and CAP02 with a grossular content of 88.3 ± 1.2% (2s), 83.3 ± 0.8% and 32.5 ± 3.0%, respectively. Their micro scale homogeneity in oxygen isotope composition was evaluated by multiple SIMS sessions. The reference δ¹⁸O value was determined by CO₂ laser fluorination (δ¹⁸O_LF). GRS2 has δ¹⁸O_LF = 8.01 ± 0.10‰ (2s) and repeatability within each SIMS session of 0.30–0.60‰ (2s), GRS‐JH2 has δ¹⁸O_LF = 18.70 ± 0.08‰ and repeatability of 0.24–0.42‰ and CAP02 has δ¹⁸O_LF = 4.64 ± 0.16‰ and repeatability of 0.40–0.46‰.     

Biotite Reference Materials for Secondary Ion Mass Spectrometry 18O/16O Measurements

Five new biotite reference materials were calibrated at the SwissSIMS laboratory (University of Lausanne) for oxygen isotope determination by secondary ion mass spectrometry (SIMS) and are available to the scientific community. The oxygen isotope composition of the biotites, UNIL_B1 to B5, was determined by laser‐heating fluorination to be 11.4 ± 0.11‰, 8.6 ± 0.15‰, 6.1 ± 0.04‰, 7.1 ± 0.05‰ and 7.6 ± 0.04‰, respectively. SIMS analyses on spots smaller than 20 μm gave a measurement repeatability of 0.3‰ (2 standard deviation, 2s). The matrix effect due to solid solution in natural biotite could be expressed as a linear function of X_Mg and X_F for biotite. No effect was found for different crystallographic orientations. SIMS analysis allows the oxygen isotope composition of biotite to be measured with a measurement uncertainty of 0.3–0.4‰ (2s) for biotites with similar major element compositions. A measurement uncertainty of 0.5‰ (2s) is realistic when F poor biotites (lower than 0.2% m/m oxides) within the compositional range of X_Mg of 0.3–0.9 were compared from different sessions. The linear correlation with F content offers a reasonable working curve for F‐rich biotites, but additional reference materials are needed to confirm the model.     

Multi-collector ICP-MS Analysis of Pb Isotope Ratios in Rocks: Data, Procedure and Caution

The authors measured Pb isotope compositions of seven USGS rock reference standards, i.e. AGV-1, AGV-2, BHVO-1, BHVO-2, BCR-2, BER-1/1 and W-2, together with NBS 981 using a micromass isoprobe multi-collector inductively-coupled plasma mass spectrometer (MC-ICP-MS) at the University of Queensland. 203Tl-205Tl isotopes were used as an internal standard to correct for mass-dependant isotopic fractionation. The results for both NBS 981 and USGS rock standards AGV-1 and BHVO-1 are comparable to or better than double- and triple-spike TIMS (thermal ionization mass spectrometry) data in precision. The data for BHVO-2 and, to a lesser extent, AGV-2 and BCR-2 are reproducibly higher for 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb than double-spike TIMS data in the literature. The authors also obtained the Pb isotope data for BIR-1/1 and W-2, which may be used as reference values in future studies. It is found that linear correction for Pb isotopic fractionation is adequate with the results identical to those corre     

New Reference Materials,Analytical Procedures and Data Reduction Strategies for Sr Isotope Measurements in Geological Materials by LA-MC-ICP-MS

Laser ablation multi-collector mass spectrometry (LA-MC-ICP-MS) has emerged as the technique of choice for in situ measurements of Sr isotopes in geological minerals. However, the method poses analytical challenges and there is no widely adopted standardised approach to collecting these data or correcting the numerous potential isobaric inferences. Here, we outline practical analytical procedures and data reduction strategies to help establish a consistent framework for collecting and correcting Sr isotope measurements in geological materials by LA-MC-ICP-MS. We characterise a new set of plagioclase reference materials, which are available for distribution to the community, and present a new data reduction scheme for the Iolite software package to correct isobaric interferences for different materials and analytical conditions. Our tests show that a combination of Kr-baseline subtraction, Rb-peak-stripping using βRb derived from a bracketing glass reference material, and a CaCa or CaAr correction for plagioclase and CaCa or CaAr + REE²⁺ correction for rock glasses, yields the most accurate and precise ⁸⁷Sr/⁸⁶Sr measurements for these materials. Using the analytical and correction procedures outlined herein, spot analyses using a beam diameter of 100 μm or rastering with a 50–65 μm diameter beam can readily achieve < 100 ppm 2SE repeatability ("internal") precision for ⁸⁷Sr/⁸⁶Sr measurements for materials with < 1000 μg g^-1 Sr.