Geostandards and Geoanalytical Research最新文献

The sulfur (S) mass fraction of carbonate minerals can be used to reconstruct the environmental conditions and S sources at the time of precipitation. As S is present in a wide range of host materials, there is an urgent need to develop a method to extract S from a single mineral phase. We have developed a method to extract structurally substituted sulfate, termed carbonate-associated sulfate (CAS), from geological and biogenic carbonate minerals using weakly acidic cation exchange resins. Two types of weakly acidic cation exchange resin (methacrylic acid and acrylic acid types) were tested to minimise the blank S contents and decompose carbonate. After repeated cleaning of the resins with high-purity water or HCl, the blank S contents were reduced to < 0.1 μg, which is < 0.1% of the CAS in the samples. The cleaned resin was used to dissolve 10 and 25 mg of the JCp-1 carbonate certified reference material (CRM; Japanese National Institute of Advanced Industrial Science and Technology, AIST). Samples and resin were added to 8 ml of high-purity water at resin/sample ratios of 2, 5, 10 and 20, set on a shaking table, and reacted. The supernatant solutions were sampled sequentially from 0.5 h to 87 h after the start of experiments. The results show that the optimal conditions for decomposing 10 mg of carbonate is a resin/sample ratio of ≥ 10 with a reaction time of ≥ 40 h. Carbonate-associated S mass fractions were measured for six geological and biogenic carbonate CRMs. The coefficient of variation in carbonate-associated S mass fractions was ≤ 7%, regardless of the type of resins used. The mass fractions determined with this method recover 74–94% of the total S mass fractions reported in previous studies, suggesting that this method dissolved carbonate, and did not leach other S-bearing fractions that are not resistant to weak acids. Another benefit of this method is that the decomposed solution can be introduced directly into the ion chromatograph, allowing for more sensitive analyses. We emphasise that this method can also be used for S isotopic measurements, as S contamination from other S-bearing mineral phases is low.

The multi-collector inductively coupled plasma-mass spectrometer is an instrument suited to measuring sulfur isotopes in all types of samples, from ice cores and river waters to carbonates and Archaean rocks. Its main advantage is the more convenient method of sample preparation, as sulfate does not need to be reduced but purified from the sample through ion exchange. This method allows the measurement of unbiased and precise δ³⁴S values from samples as small as 10-nmol with a typical intermediate precision of 0.15‰ (2s) at 95% confidence. So far, no attempt has been made to understand at which levels of analytical precision and bias MC-ICP-MS could provide ∆³³S values. Here, the first standard addition experiment undertaken for ∆³³S evaluation shows that measurement results on a Neptune Plus MC-ICP-MS allows us to calculate ∆³³S values identical to those established by other measurement principles, for samples down to 30 nmol S, with an intermediate precision as good as 0.05‰ (2s). Though this precision is not as good as the analytical precision of data acquired by the SF₆ method, the advantages of small sample size and straightforward sample handling make it a very useful tool for investigating past and modern aspects of the sulfur cycle.

This Geostandards and Geoanalytical Research Bibliographic Review 2022 presents an overview of a wide range of publications in 2022 focusing on the characterisation of new geoanalytical reference materials (RMs) as well as studies which published measurement results for established RMs. The development of highly accurate new methods and techniques leads to large new analytical data sets for RMs with improved accuracy and precision, which we present in this review.

Secondary ion mass spectrometry was used to test the δ¹⁸O and δ³⁴S nanogram-scale homogeneity of a suite of candidate sulfate minerals, ultimately selecting three barite, two anhydrite, and two gypsum samples from the Royal Ontario Museum that have repeatabilities for their SIMS measurements of better than ±0.39‰ and ±0.37‰ (1s) for oxygen and sulfur isotope ratios, respectively. Metrological splits of each of the seven materials were sent to multiple gas source isotope ratio mass spectrometry laboratories in order to establish their absolute ¹⁸O/¹⁶O and ³⁴S/³²S ratios. The inter-laboratory results of GS-IRMS analyses yielded reasonably narrow ranges in δ¹⁸O_VSMOW, whereas larger variations in δ³⁴S_VCDT values were found between the results from the gas source laboratories. All samples have good reproducibility within laboratories of GS-IRMS 10³δ¹⁸O values of between ±0.24‰ and ±0.44‰ (1s). The reproducibility within laboratories of GS-IRMS 10³δ³⁴S values range from ±0.07‰ to ±0.99‰ (1s). Here we also discuss some of the current analytical limitations affecting these isotope-mineral systems. A total of 256 metrological splits have been prepared from each of these seven materials; these aliquots will be made available to the global geochemical community.

We present high precision negative ion thermal ionisation mass spectrometry (N-TIMS) Os isotope measurement results for the DROsS isotope reference material (iCRM), to investigate the limits on the precision of TIMS-based ¹⁸⁶Os/¹⁸⁸Os results. We used analytical conditions previously highlighted to optimise precision, present a new flexible data processing protocol, and measured ¹⁸⁴Os intensities on a Faraday Cup equipped with an amplifier using a 10¹² Ω resistor. Despite a measurement procedure that minimised uncertainty contributions from counting statistics and Johnson-Nyquist noise, the intermediate measurement precision of our approach does not significantly improve on previous high precision Os isotope measurements, with the exception of ¹⁸⁴Os/¹⁸⁸Os. This is probably due to uncertainties in measured amplifier gain factors, which are greater when using mixed arrays of 10¹¹ and 10¹² Ω resistors than when using 10¹¹ Ω resistors alone, though Faraday Cup deterioration could also contribute. We propose that multi-dynamic Os isotope measurements could largely eliminate both of these uncertainties. Our ¹⁸⁴Os/¹⁸⁸Os measurement results are the most precise yet, yielding ¹⁸⁴Os/¹⁸⁸Os = 0.0013036 ± 0.0000007 (2s, n = 38). Additionally, we average our data with published data to recommend the following isotope ratios for DROsS: ¹⁸⁶Os/¹⁸⁸Os = 0.1199319 ± 0.0000024, ¹⁸⁷Os/¹⁸⁸Os = 0.1609227 ± 0.0000022, ¹⁸⁹Os/¹⁸⁸Os = 1.219709 ± 0.000010, ¹⁹⁰Os/¹⁸⁸Os = 1.983793 ± 0.000011.

Various methods have been developed to extract a primary seawater Sr isotope signal from carbonate rocks for strontium isotope stratigraphy. However, there is little consensus around the best method due to variable sample purity and mineralogy. For this study, we applied sequential leaching to a range of rock samples in order to explore strontium isotope leaching systematics of less favoured argillaceous and dolomitic limestone samples. Following an ammonium acetate (NH₄Ac) prewash that removed ~ 10% of the carbonate fraction, a subsequent dilute acetic acid leach (10–30% aliquot) was shown to extract the lowest, demonstrably least altered seawater ⁸⁷Sr/⁸⁶Sr isotope ratios, along with in most cases seawater-like rare earth element (REE) plus yttrium (Y) patterns with the highest Y/Ho ratios (mostly > 36). Subsequent dissolution steps exhibited significantly elevated ⁸⁷Sr/⁸⁶Sr isotope ratios, Rb/Sr, Al/Ca and Mg/Ca ratios, indicating greater contributions from aluminosilicates and dolomite in the leachates. The new dissolution method by comparison significantly increases the likelihood of obtaining primary seawater ⁸⁷Sr/⁸⁶Sr isotope ratios from argillaceous and dolomitic limestones where the other established procedures failed. Broad application of this approach could improve the temporal resolution of the seawater Sr isotope curve, especially where high purity limestone samples are scarce.

S-Fe-Cu isotope systems are powerful tracers for revealing geochemical processes. However, the microanalysis of S-Fe-Cu isotopes is critically limited by the lack of suitable reference materials. Herein, we present three potential reference materials Ll-Cpy (chalcopyrite), Ll-Po (pyrrhotite) and Ll-Sp (sphalerite) for in situ S-Fe-Cu isotope measurements. Numerous in situ S-Fe-Cu isotope measurements were performed over two years to assess isotopic homogeneity. The bulk S isotopic compositions were determined independently in seven laboratories by isotope ratio mass spectrometry (IRMS); the preferred δ³⁴S_V-CDT for Ll-Cpy, Ll-Po, Ll-Sp are 6.13 ± 0.37‰ (2s), 6.42 ± 0.37‰ (2s) and 6.28 ± 0.38‰ (2s), respectively. The bulk Fe isotope ratios in Fe-bearing Ll-Cpy and Ll-Po were determined using solution nebulisation multi-collector inductively coupled plasma-mass spectrometry, and the obtained δ⁵⁶Fe_IRMM-014 values are 0.57 ± 0.07‰ (2s) and -0.62 ± 0.07‰ (2s), respectively. The mean bulk δ⁶⁵Cu_{NIST SRM 976} value of Ll-Cpy is 0.57 ± 0.06‰ (2s). All the bulk values are in good agreement with the long-term statistical results of laser ablation-MC-ICP-MS and proposed as the recommended values. These sulfides are well characterised and isotopically homogeneous (at 30–40 μm spatial resolution), and can be used as potential calibration materials for in situ S-Fe-Cu isotope measurements.

The stable Zr isotope ratios in zircon yield a novel geochemical tracer that, together with the Lu-Hf and U-Pb radiogenic isotope systems, allows for a better understanding of the magmatic evolution of silicate melts. We present a solution-based procedure for coupled stable Zr, Lu-Hf and U-Pb isotope ratio determinations for individual zircons using a ⁹¹Zr-⁹⁶Zr tracer purified from Hf and a late-spiking protocol for Zr. This method yields high-precision Zr and Hf isotope results while maintaining low blank levels for U-Pb isotope and Lu/Hf ratio determinations. With a two-fold improvement on the precision relative to previous solution-based work, we report δ⁹⁴Zr_IPGP-Zr values (deviation of the ⁹⁴Zr/⁹⁰Zr ratio in the sample relative to the IPGP-Zr reference material) and associated intermediate precisions (2s) for the zircon reference materials 91500, Mud Tank, Plešovice and Penglai of -0.041 ± 0.015‰, 0.018 ± 0.013‰, 0.089 ± 0.020‰ and -0.117 ± 0.021‰, respectively. Furthermore, this method yields un-biased δ⁹⁴Zr_IPGP-Zr and ¹⁷⁶Hf/¹⁷⁷Hf results for 25-ng Zr and 0.56-ng Hf aliquots of the Mud Tank zircon with intermediate precisions (2s) of 0.027‰ and 1.7 ε (parts per ten thousand), respectively. Thus, the presented method is applicable for the analysis of extremely small and rare zircon grains.

Rutile stands as a classical mineral within U-Pb geochronology, offering insights into both magmatic and metamorphic events, and contributing to the understanding of provenance of detrital sedimentary rocks. Addressing the paucity of high-quality Archaean rutile reference materials suitable for microbeam U-Pb dating, we present a natural rutile (RKV01) sourced from the Kaap Valley pluton, South Africa, positing it as a potential Archaean reference material. Major element determination was executed via electron probe microanalysis, while trace element determination was conducted using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The determination of U-Pb ages involved the application of isotope dilution-thermal ionisation mass spectrometry (ID-TIMS), secondary ion mass spectrometry (SIMS) and LA-ICP-MS. The ID-TIMS mean ²⁰⁷Pb/²⁰⁶Pb age is 3225.61 ± 0.64 Ma (2s, MSWD = 0.83), interpreted as the best estimate for the crystallisation age. The relatively high U mass fraction (~ 83 μg g^-1), extremely low Th mass fraction (~ 0.003 μg g^-1), negligible common Pb and isotopically homogeneous compositions collectively facilitated precise ²⁰⁷Pb/²⁰⁶Pb age determination via microbeam methods. Both LA-ICP-MS and SIMS ²⁰⁷Pb/²⁰⁶Pb ages are characterised by reproducibility and were consistent with the ID-TIMS age within 2s analytical uncertainty. The results underscore the potential of RKV01 rutile as an Archaean reference material for microbeam U-Pb dating.

Solution MC-ICP-MS is an established technique for high precision boron isotope measurement results (δ¹¹B_{SRM 951}) in carbonates, yet its application to silicate rocks has been limited. Impediments include volatilisation during silicate dissolution and contamination during chemical purification. To address this, we present a low-blank sample preparation procedure that couples hydrofluoric acid-digestion and low-temperature evaporation (mannitol-free), to an established MC-ICP-MS measurement procedure following chemical purification using B-specific Amberlite IRA 743 resin. We obtain accurate δ¹¹B_{SRM 951} values (intermediate precision ±0.2‰) for boric acid (BAM ERM-AE121 19.65 ± 0.14‰) and carbonate (NIST RM 8301 (Coral) 24.24 ± 0.11‰) reference materials. For silicate reference materials covering mafic to felsic compositions we obtain δ¹¹B_{SRM 951} with intermediate precision < ±0.6‰ (2s), namely JB-2 6.9 ± 0.4‰; IAEA-B-5 -6.0 ± 0.6‰; IAEA-B-6 -3.9 ± 0.5‰ (2s). Furthermore, splits of these same reference materials were processed by an alternative fusion and purification procedure. We find excellent agreement between δ¹¹B_{SRM 951} measurement results by MC-ICP-MS of the reference materials using both sample processing techniques. These measurement results show that our sample processing and MC-ICP-MS methods provide consistent δ¹¹B_{SRM 951} values for low B-mass fraction samples. We present new data from Mid Ocean Ridge Basalt (MORB) glass, documenting a range in δ¹¹B_{SRM 951} from -5.6 ± 0.3‰ to -8.8 ± 0.5‰ (2s), implying some upper mantle δ¹¹B_{SRM 951} heterogeneity.