Geostandards and Geoanalytical Research最新文献

Uranium (U) associated with coal can be an important source of U and result in environmental pollution during coal combustion. In this study, we developed a method for measurement of U isotope ratios in coals using multiple-collector inductively coupled plasma-mass spectrometry. The ²³³U-²³⁶U double-spike was utilised to calibrate the instrumental isotopic fractionation. High-pressure bomb and dry ashing were adopted to digest the coal samples. The δ²³⁸U_CRM-145 values obtained from the two different digestion procedures were in good agreement. The δ²³⁸U_CRM-145 of seven coal and one fly ash reference materials are reported. Furthermore, the results of fly ash, bottom ash and feed coal samples reveal that the combustion processes lead to relatively small U isotopic fractionation between the samples within the same coal-fired power plant, indicating that U isotope data can be used as a tracer for heavy metal pollution resulting from coal combustion. The U isotope measurement method of coal established in this study provides technical support to understand the behaviour of U during coal formation and combustion.

Iron-titanium oxides such as ilmenite (FeTiO₃), titanite (CaTiSiO₅) and perovskite (CaTiO₃) are the common Ti-rich mineral phases crystallised during magmatic and metamorphic processes on Earth. Depending on magma types or conditions of phase equilibria, formation of these Ti-rich minerals can result in Ti isotopic fractionation in the range of -1.52‰ to +2.90‰ on δ⁴⁹Ti_OL-Ti (i.e., the per mil difference of ⁴⁹Ti/⁴⁷Ti ratio relative to the OL-Ti reference material), making the Ti isotope ratios of these minerals potential tracers for conditions of magmatism and metamorphism. Due to their resistance to aqueous alteration, these Ti-rich accessory minerals are also commonly present as pristine, detrital phases in sedimentary rocks, which offer an opportunity to study the evolution of magmatism and metamorphism throughout the Earth's geological history. Here we have developed a novel technique for in situ Ti isotopic measurement in ilmenite, titanite and perovskite using femtosecond laser ablation multi-collector inductively coupled plasma-mass spectrometry (fs-LA-MC-ICP-MS) under wet plasma conditions. Samples were ablated with different laser spot sizes (15–50 μm) and different laser energy densities (0.6–4.2 J cm^-2) to obtain adequate Ti signal intensity at a fixed laser repetition rate of 2 Hz. When ⁴⁹Ti signal intensity of samples ranged from 0.3 to 3.7 V, no significant signal-dependent Ti isotopic fractionation was observed under wet plasma conditions. Repeated measurements on twelve Ti-rich minerals using different analytical protocols provided comparable δ⁴⁹Ti_OL-Ti values within uncertainties, confirming the accuracy of the proposed fs-LA-MC-ICP-MS method. With one exception (i.e., RUS1), all analysed minerals are homogeneous in their Ti isotopic compositions between individual chips with an intermediate precision of ±0.13‰ to ±0.17‰ (2s) on δ⁴⁹Ti_OL-Ti. Collectively, these minerals record a significant δ⁴⁹Ti_OL-Ti variation ranging from -0.46‰ to +2.12‰. These warrant the suitability of these materials as Ti isotopic reference materials for in situ Ti isotopic measurement.

The recent development of LA-ICP-MS/MS techniques enables in situ Rb-Sr dating of micas, but there is not yet a matrix-matched reference material (RM). In this contribution we optimised laser conditions and developed a new data reduction approach for Rb-Sr dating of micas with non-matrix-matched RMs Mica-Mg-NP and NIST SRM 612. This was achieved by systematically investigating the effects of laser ablation settings, data reduction methods and the selection of the RMs on the Rb-Sr dating quality of a 306 ± 1 Ma hydrothermal muscovite. We then tested this approach using twelve mica samples with known ages from 306 to 1.4 Ma. The results show that this technique can achieve accuracy of 2.5% or better, and precision of ~1–3% for micas > 15 Ma. The dating accuracy (> 9%) and precision (> 21%) decrease for micas younger than 5 Ma due to the short radiogenic accumulation time. This technique provides a way to date many types of mineral deposits and rocks, with a relatively high spatial resolution (down to 38 μm), a fast turnaround time and a higher closure temperature for muscovite than the Ar-Ar system, which makes it a powerful tool in geochronological studies.

In this work, we prepared three CaWO₄ single crystals (CaW-0, CaW-1 and CaW-3) doped with rare earth elements (REEs) at nominal mass fractions of 50, 250 and 5000 μg g^-1 using the Czochralski method. Electron probe microanalysis (EPMA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) were employed to evaluate the within- and between-unit homogeneity of major elements and REEs, respectively. The within-unit variation (s_r) of 0.40–0.84% and between-unit s_r of 0.14–1.48% for major elements were obtained. Within- and between-unit s_r of 0.53–5.56% were also found for REEs by LA-ICP-MS spot analyses. A comparison of the s_r of repeat analyses was compared with the analytical uncertainty (u), i.e., the mean square weighted deviation (MSWD), which is close to or slightly higher than 1, indicating that no obvious chemical heterogeneity was found in these crystals. Reference values for these elements were obtained through various analytical methods across four different laboratories and applications of the reference materials to calibrating REE mass fractions in a natural scheelite were performed. No significant difference of the results was found as t values are less than 2.75 at the 99% confidence interval. The excellent linearity (R² > 0.98) between the REE mass fractions and both LA-ICP-MS signal intensity and wafer absorbance was found, but the crater height and the absolute mass transported into ICP-MS decreased when REE mass fractions as well as the colour of crystals increased. These results suggest that the reference materials have the potential to calibrate REE mass fractions in natural scheelite.

We characterise zircon megacrysts from the Kawisigamuwa carbonatite as a new potential reference material for laser ablation-inductively coupled plasma-mass spectrometry U-Pb and Hf isotope measurement. We studied ten 0.5–4 cm long, brown megacrysts that consist of oscillatory zoned (OZ) and nearly featureless cathodoluminescence-bright recrystallised (RX) zircon domains. The zircons have low to moderate radiation damage (total α-dose < 0.5 x 10¹⁸ events g^-1), tested by the measured FWHM of the ν₃ (SiO₄) Raman band < 5 cm^-1. An ID-TIMS weighted mean ²⁰⁶Pb/²³⁸U age of 532.39 ± 0.66 Ma (2s uncertainty) was determined for OZ zircon domains of three grains. While hafnium content varies within and between crystals (6630–9960 μg g^-1) the in situ mean ¹⁷⁶Hf/¹⁷⁷Hf ratios of ten crystals overlap within uncertainty. We recommend a mean ¹⁷⁶Hf/¹⁷⁷Hf ratio of 0.282003 ± 0.000020 (2s) as preliminary working value for OZ domains. Two OZ megacrysts yield indistinguishable δ¹⁸O_VSMOW of 12.1 ± 0.4‰ and 12.2 ± 0.4‰ (2s). Elevated Th/U (> 1.5), Zr/Hf (59–75) and low hafnium contents in OZ domains are similar to those of zircons from carbonatites of mantle origin, while high δ¹⁸O and low εHf_i (-15.8 to -17.1) indicate a crustal contribution. The zircons probably grew from crustal-derived carbonate melts under high grade metamorphic conditions.

Tungsten (W) isotopes are useful tools in geological and cosmochemical research, but the chemical separation of W is cumbersome for high-precision measurement. Here, a novel alkali (sodium hydroxide, NaOH) precipitation method for separation and purification of W in geological samples is described, which simplifies the chemical procedure. The amphoteric character of W is exploited to separate it from most matrix elements in alkaline conditions. Subsequently, TEVA resin was applied to further purify W for measurements using a multi-collector inductively coupled plasma-mass spectrometer. Importantly, the introduction of a certain amount of Na in the W analyte can increase the signal intensity by approximately 1.6 times, which may be caused by Coulomb fission. Such Na-triggered signal enhancement reduces the test portion mass required for analysis. Our results show that the Alfa Aesar W standard solution and geological reference materials JB-3, BCR-2 and BHVO-2 yield ¹⁸²W/¹⁸⁴W ratios consistent with previously reported values within uncertainty. Repeated measurement of the Alfa Aesar W standard solution shows that the intermediate precision of ¹⁸²W/¹⁸⁴W was better than 5 ppm (2s), which is sufficient to identify subtle ¹⁸²W isotope variations in terrestrial and extra-terrestrial samples. Above all, the alkali precipitation method in this study optimises the experimental process and mass spectrometric analysis.

We present the results of a study to generate reference glasses that reflect an environment analogous to historic nuclear fallout samples of interest for post-detonation nuclear forensics. The glasses were generated by melting and then quenching SiO₂, Al₂O₃ and CaCO₃ powders. Two suites of glasses with three distinct U isotopic ratios were successfully made with enrichments in the ²³⁵U isotope (~ natural [0.72%], ~ 53% and 94%), but the bulk elemental data showed heterogeneity (~ 10% RSD) with U mass fractions ranging from 331.47 to 373.63 μg g^-1. Spatially resolved U isotopic measurements were performed using three mass spectrometry techniques (secondary ion mass spectrometry-single stage accelerator mass spectrometry [SIMS-SSAMS], large geometry [LG] - SIMS, and laser ablation-inductively coupled plasma-mass spectrometry [LA-ICP-MS]) across five National Laboratories. The results showed good agreement with the bulk U isotopic data for the low, medium, and high U mass fractions. We conclude that despite elemental heterogeneity, these samples can serve as useful working reference materials for spatially resolved nuclear fallout analyses, as well as for other related spatially resolved analyses.

Carbonate clumped isotope, quantified by Δ₄₇ value, has wide application potential in Earth science. A recently proposed carbonate standardisation scheme based on community-available reference materials (i.e., ETH-1–4) has proven to improve interlaboratory comparability in Δ₄₇ measurement. However, the shortage of these reference materials may be problematic in future; therefore, developing traceable and supplementary in-house reference materials may become necessary, especially when supplies run out. Here, we describe a method of producing synthetic witherite carbonates with variable bulk isotopic compositions and clumped isotope ordering states, for which Δ₄₇ values were determined together with ETH carbonate reference materials. Results indicate that the witherite carbonates allow effective corrections for instrumental linearity and scale variations, improving long-term reproducibility. Additionally, by normalising witherite Δ₄₇ values to agreed ETH carbonate values on the Intercarb-Carbon Dioxide Equilibrium Scale, the witherite reference materials can be used to determine Δ₄₇ values without using equilibrated gases and reduce the consumption of ETH carbonates.

An interlaboratory comparison (ILC) was organised to characterise ⁸⁷Sr/⁸⁶Sr isotope ratios in geological and industrial reference materials by applying the so-called conventional method for determining ⁸⁷Sr/⁸⁶Sr isotope ratios. Four cements (VDZ 100a, VDZ 200a, VDZ 300a, IAG OPC-1), one limestone (IAG CGL ML-3) and one slate (IAG OU-6) reference materials were selected, covering a wide range of naturally occurring Sr isotopic signatures. Thirteen laboratories received aliquots of these six reference materials together with a detailed technical protocol. The consensus values for the six reference materials and their associated measurement uncertainties were obtained by applying a Gaussian, linear mixed effects model fitted to all the measurement results. By combining the consensus values and their uncertainties with an uncertainty contribution for potential heterogeneity, reference values ranging from 0.708134 mol mol^-1 to 0.729778 mol mol^-1 were obtained with relative expanded uncertainties of ≤ 0.007 %. This study represents an ILC on conventional ⁸⁷Sr/⁸⁶Sr isotope ratios, within which metrological principles were considered and the compatibility of measurement results obtained by MC-ICP-MS and by MC-TIMS is demonstrated. The materials characterised in this study can be used as reference materials for validation and quality control purposes and to estimate measurement uncertainties in conventional ⁸⁷Sr/⁸⁶Sr isotope ratio measurement.