Geostandards and Geoanalytical Research最新文献

In this study, we present a high precision and high spatial resolution in situ Fe isotope protocol using femtosecond (fs) laser ablation multi-collector inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS). The intermediate measurement precision obtained over a period of ca. 3 years for the USGS glass BIR-1G against the Puratronic reference material is 0.17‰ (2s) for δ⁵⁶Fe. Uncertainties achieved on individual analyses of glass and olivines were < 0.15‰ for δ⁵⁶Fe. This high precision is associated with high spatial resolution of about 170 × 25 μm. Our results display good consistency between LA-MC-ICP-MS and solution nebulisation MC-ICP-MS data from the literature. Obtained δ⁵⁶Fe values on different USGS glasses (BIR-1G, BHVO-2G and BCR-2G) show that these reference materials have homogenous Fe isotope ratio and therefore can be used as bracketing calibrators during laser ablation measurement sessions. On the other hand, the San Carlos Olivine displays high Fe isotope heterogeneity, and therefore cannot be considered as a good bracketing standard (calibrator). We also applied our fs-LA-MC-ICP-MS protocol to olivines and pyroxene from the Kerguelen Archipelago. This technique appears to be a relevant tool to resolve isotopic zoning in chemically zoned silicate phenocrysts, even of small size (< 1 mm). We demonstrate that within single lavas, olivine crystals display various zoning depending on their size, related to their residence time in the magma. Both equilibrium and diffusive processes were observed in olivine crystals from Kerguelen, uncovering complex histories. Hence, iron isotope ratio measurements by fs-LA-MC-ICP-MS open new possibilities for studying highly zoned silicate minerals in magmatic rocks to better understand their formation.

Isotope geochemistry requires isotope ratios measured using secondary ion mass spectrometry (SIMS) to be made with optimal precision and accuracy. Under some analytical conditions when using electron multiplier detectors, secondary ions may be under-counted because of quasi-simultaneous arrival (QSA) at the first dynode. The relative magnitude of the associated QSA correction to raw measured isotopic ratios can be up to seventy permil or more. Therefore, not applying the correction, or misapplication of it could lead to significant inaccuracies in published isotope ratio data. Examples and ramifications of the latter are described in addition to a straightforward procedure for QSA under-counting correction.

A simple method was developed for the determination of REEs, Zr, Hf, Th and U in ultramafic rocks by inductively coupled plasma-mass spectrometry with a combination of RE and UTEVA extraction resins for their separation and pre-concentration. Ultramafic rocks were digested with HNO₃-HF-HClO₄ and finally turned into 11 mol l⁻¹ HCl solutions together with H₃BO₃ to remove insoluble fluorides. The removal of matrix elements was achieved during the loading procedure. Following this, REEs on RE resin, and Zr, Hf, Th and U on UTEVA resin were eluted with 10 ml of 0.24 mol l⁻¹ HCl, with recoveries better than 94.4%. This method was validated using reference materials JP-1, DTS-2B, OKUM, UB-N, MUH-1 and DZΣ-2, and the measurement results for target analytes were comparable to literature values, indicating its applicability to the determination of REEs, Zr, Hf, Th and U at ultra-trace level in ultramafic rocks.

A series of three CGSP-P phosphate matrix reference materials, with variable element mass fractions, were synthesised by co-precipitation with CaCl₂ and (NH₄)₃PO₄ to form a hydroxylapatite matrix. Each powder sample was packaged into multiple bottles and pressed into tablets as replicates. The within-bottle homogeneity was evaluated by the repeatability of element mass fractions of six spots in per tablet of CGSP-Ps by LA-ICP-MS. For the between-bottle homogeneity evaluation, one approach adopted the % RSD of element mass fractions in twelve different tablets from twelve bottles in the same reference material in comparison with the repeatability field of LA-ICP-MS analyses obtained from homogeneous glasses, and the other used a one-way analysis of variance (ANOVA) approach. Most of the elements (e.g., Mg, Ca, P, Mn and REE) were homogenous within 10% RSD, and other elements (e.g., Si, Al, K, Rb, Cs and Ni) were considered heterogeneous (with > 20% RSD). All of the elements passed the t-test except Ni in CGSP-P3, and V, Cr, Ni, Zr, Gd, Dy and Th in CGSP-P4 after a 29-month period stability examination by LA-ICP-MS. The preliminary reference values and standard uncertainties for CGSP-Ps are given with a network of methods and eight laboratories by bulk analysis according to ISO Guide 35:2006 and JJF 1343-2012.

Automated mineralogy is a software addition usually seen on scanning electron microscopes designed to provide rapid insight into sample chemistry and texture in routine petrology workflows. The specific purpose of automated mineralogy is to provide mineral classifications to uniquely identified phases typically using energy dispersive spectroscopy, thus removing laborious and time-consuming human input for routine tasks. These mineral classifications can then be applied to image data to quantify which mineral is associated with any particular texture. Automated mineralogy systems were primarily designed to generate quantitative textural analysis of particle samples to the mining industry and have remained a critical technique in this setting for the last several decades. Automated mineralogy has become more widely used in academia, and this has changed the focus of the technique, applying it to a broader range of workflows and applications. Here we show petrology examples focussing where combined geochemical and textural analysis are widely used. Critically, the use of quantitative geochemical data means that mineral classifications are based on their quantitatively measured chemistry. By making both the chemical and textural analysis quantitative, automated mineralogy can become highly flexible and provide a unique system for petrologists in both industry and academia.

Following a full assessment of the GeoPT proficiency testing scheme against the recommendations in ISO Guide 35:2017 for the use of proficiency testing in the certification of reference materials, this paper presents the first application of the GeoPT certification protocol in the characterisation of a new geochemical CRM, IAG GMN-1, Meissen Granite. This protocol is applied to the measurement results reported in Round 51 of the GeoPT programme in which the candidate CRM was used as the test material, together with an established CRM (CGL 008 MGT-1 Granite) to provide validation of the results. Following the presentation of mineralogy, grain-size analysis and homogeneity testing data for IAG GMN-1, certified values for nine major elements and thirty-nine trace elements are reported.

Due to the incorrect speciation of iron during thermometry modelling, Coulthard et al. (2024) produced an incorrect olivine-liquid equilibrium diagram, which failed to identify multiple potential equilibrium olivine-melt pairs. With the new pairs identified here, the temperatures inferred from olivine-groundmass pairs move closer in temperature space to those inferred from olivine-glass pairs. Additionally, it is recognised that the most significant difference between these thermometry data is due to differences in inferred melt water mass fraction. If a mean value of water is used for all thermometry, the mean temperatures calculated for olivine-glass and olivine-groundmass pairs converge to within 10 °C of one another. This indicates that groundmass compositions inferred via the defocused beam analysis of a polyphase groundmass may reproduce enough information to confidently perform olivine-melt thermometry despite the glass and groundmass data representing significantly different compositions in multivariate space.

Re-Os isotope-dilution geochronology has been widely used to date the timing of molybdenite, pyrite and chalcopyrite formation across a variety of geological settings. However, in situ methods have been impeded by the isobaric interference of ¹⁸⁷Re on ¹⁸⁷Os. In situ Re-Os geochronology using LA-ICP-MS/MS has been shown to be a useful technique to chemically separate Os from Re, as Os reacts with CH₄ to create higher-mass reaction products, which can then be measured with minimised interference of ¹⁸⁷Re. However, application of the method requires matrix-matched primary reference materials, e.g., age-homogenous molybdenite amenable to laser ablation. Here, we characterise and present two new molybdenite mineral reference materials for in situ Re-Os geochronology by LA-ICP-MS/MS, verified by ID-TIMS Re-Os measurements. We also present case studies from molybdenite samples with varying Re mass fractions and Re-Os age mapping. The method provides accurate and precise age data, with excellent precision for high Re samples. The benefits of the LA-ICP-MS/MS approach include: (1) simple sample preparation, (2) rapid data acquisition, (3) targeting of specific textural domains including growth zones and (4) the ability to simultaneously collect trace elements used to link the timing and conditions of ore-formation.

The two most common oxidation states of iron can be determined by wavelength-dispersive X-ray fluorescence spectrometry relatively fast with an accuracy comparable to that of alternative methods. Main advantages for the analysis of sediments and soils are that organic matter does not interfere and solid samples can be analysed directly with minimal preparation effort. The limited availability of appropriate reference materials with certified data on their ferrous iron content turned out to be the major obstacle to implementing the method. For this reason and because no influence of the analysed geological materials on the intensity ratios of the closely adjacent Fe Kβ₅ / Fe Kβ_1,3 lines became evident, several rock types were selected in addition to sediments and soils to broaden and improve the calibration. Nevertheless, most reference data for calibration had to be determined by ⁵⁷Fe Mössbauer spectroscopy. Plotting Fe Kβ₅/Fe Kβ_1,3 intensity ratios versus w FeO/w Fe₂O₃^total ratios resulted in a correlation with R² = 0.962 for the linear regression of all calibration data.