I n situ mica Rb‐Sr geochronology lacks a diverse range of widely utilised reference materials. Here, we characterize and evaluate six natural mica reference materials to test their suitability for in situ Rb‐Sr geochronology, including one phlogopite (Mica‐Mg‐NP phlogopite), three biotite (Mica‐Fe biotite, Mount Dromedary biotite and La Posta biotite) and two muscovite candidates (Högsbo muscovite, WA1ms muscovite). For each of these reference materials, we evaluate chemical and microstructural heterogeneity and assess age and/or Rb‐Sr isotopic homogeneity through 40 Ar/ 39 Ar, solution Rb‐Sr and long‐term in situ LA‐ICP‐MS/MS Rb‐Sr geochronology. Mount Dromedary biotite (99.37 ± 0.20 Ma; 2 s , including all sources of uncertainty) and Mica‐Fe biotite (307.75 ± 0.80 Ma) are effective low and high Rb reference materials for pulse and analogue collector modes on single‐collector systems, respectively, combining a wide spread of Rb/Sr ratios within and between grains, and producing accurate Rb‐Sr ages across multiple laser ablation sessions. La Posta biotite (91.30 ± 0.25 Ma) and Högsbo muscovite (1029.7 ± 2.0 Ma) are better suited as secondary low and high Rb reference materials due to minor chloritisation and alteration, respectively. Mica‐Mg‐NP phlogopite shows significant isotopic and age heterogeneity, outside of the precision of in situ Rb‐Sr geochronology, as well as showing different down‐hole fractionation compared with natural micas. WA1ms muscovite may prove a useful reference material, with a published 40 Ar/ 39 Ar age of 2613.3 ± 4.4 Ma, but further testing is required as its in situ Rb‐Sr age is significantly younger. All new reference materials investigated here are isochronous, rather than isotopically homogeneous, necessitating new data reduction schemes for processing isochronous data with accurate propagation of uncertainties and down‐hole fractionation corrections. The authors may be contacted to obtain vials of mica concentrates.
This chapter (Thermal Ionisation Mass Spectrometry) is a contribution to the Geostandards and Geoanalytical Research Handbook of Rock and Mineral Analysis – an online textbook that is a fully revised and updated edition of A Handbook of Silicate Rock Analysis (P. J. Potts, 1987, Blackie, Glasgow). Chapter 23 (from Section 4 of the handbook dealing with techniques for age determination and isotope ratio measurement) describes how ions are formed in the source of a TIMS instrument, how they are accelerated through the analyser and separated according to their mass/charge ratios, and how the resulting ion beams are measured in the collector. Throughout the chapter, the specificities of thermal ionisation mass spectrometry are emphasised. A particular emphasis is placed on understanding the thermal ionisation process for both positive and negative ions and how it is influenced by factors such as sample deposition. Recent advances in detection systems, such as the development of amplifiers with 10 13 ‐Ω resistors and capacitance‐type amplifiers, and in focusing systems (lenses, zoom optics, etc.) are reviewed. The chapter concludes with an overview of both established and more innovative TIMS applications.
A calcite reference material (CCMb) derived from Carrara marble was developed for calibrating in situ mass fraction measurements of selected minor and trace elements (Mg, Sr) and the isotope ratios of carbon (δ 13 C) and oxygen (δ 18 O). Chemical and isotopic properties were characterised by bulk solution and in situ techniques, with ten laboratories participating in an analytical round‐robin. Grains of CCMb were analysed by ion microprobe (SIMS) against a suite of calcite reference materials, including international reference material IAEA‐603, to evaluate the influence of minor amounts of Mg on the instrumental mass fractionation of δ 18 O values. CCMb consists of an assemblage of tightly interlocking calcite crystallites measuring 100–300 μm across. Fluid‐inclusion trails are abundant along crystallite grain boundaries. An offset was observed between δ 18 O values of CCMb determined by gas‐source isotope ratio mass spectrometry (GS‐IRMS) and SIMS measurement. The results of this study indicate the offset could be related to the presence of isotopically light calcite material in grain boundary regions and micro‐fissures, domains only several micrometres thick. When used for calibrating SIMS measurements, CCMb should be assigned a reference δ 18 O value of +28.81 ± 0.15‰ (VSMOW, 2 s, based on SIMS results), representative of the integrated crystallite volume less the contribution of the inferred low δ 18 O phase occupying intercrystalline space. Measurements of δ 13 C by ion microprobe reproduced the bulk‐grain, GS‐IRMS derived value of +1.95 ± 0.06‰ (VPDB, 2 s ). This study did not find evidence for matrix effects related to Mg‐substitution at mass fractions ≤ 3000 μg g ‐1 . The preferred reference values for the Mg and Sr mass fractions in CCMb are 0.36 ± 0.05% m/m (2 s ) and 156 ± 8 μg g ‐1 (2 s ), respectively.
Asteroid return missions have brought back small amounts of pristine carbonaceous chondrite-like material to Earth to further our understanding of the origin and evolution of objects formed early in solar system history. To obtain the maximum amount of information from the smallest possible amounts of sample, optimisation of methods that allow determination of multiple chemical and physical parameters are required. Here we present a method that allows for sequential determination of primary mineralogy via micro computed X-ray tomography (micro-CT) and isotope ratios (delta-values) of seven different elements (Mg, Fe, V, Zn, Sr, Cd and Tl) on carbonaceous chondrite samples as small as 24.1 mg. These elements have the advantage that they cover a broad range in half-mass condensation temperatures, which allows simultaneous investigation of processes occurring throughout an asteroidal lifetime. We test our methodology via analyses of the USGS reference materials AGV-2 and BHVO-1 as well as three chips of CM carbonaceous chondrite ALH 83100 with masses of similar to 24-47 mg. We use sequential ion exchange chromatographic separation to produce pure mono-elemental solutions for each of the seven target elements. Subsequent isotope ratio measurements using a Neptune multi-collector inductively coupled plasma-mass spectrometer and a thermal ionisation mass spectrometer produced accurate data for AGV-2 and BHVO-1 with precisions comparable to those obtained in the recent literature. Isotope composition data obtained for the three ALH 83100 fragments are consistent with previous results reported for CM carbonaceous chondrites. We also combine our micro-CT data with the isotope data obtained for the three chips of ALH 83100. These comparisons suggest that different components of carbonaceous chondrites may preserve isotope variability in Fe, Sr, Zn, Cd and Tl isotopes as a function of their modal mineralogy.
This chapter (Analysis of Geological Materials – 3: Determination of Hydrogen, Carbon, Nitrogen, Sulfur, Ferrous Iron, Halogens, Gold and Platinum‐Group Elements) is a contribution to the Geostandards and Geoanalytical Research Handbook of Rock and Mineral Analysis – an online textbook that is a fully revised and updated edition of A Handbook of Silicate Rock Analysis (P. J. Potts, 1987, Blackie, Glasgow). In Chapter 2, Part 3 (from Section 1 of the handbook dealing with fundamentals of measurement and instrument design) six elements (H, C, N, S, Fe 2+ , Au) and two element groups (halogens, PGE) that require somewhat specialised pre‐concentration techniques prior to determination are examined and reviewed. In turn, these elements often require determination by measurement principles beyond the now well established (XRF spectrometry, ICP‐AES, ICP‐MS), such as element analysers , elemental analyser isotope ratio mass spectrometry , colorimetry , ion‐selective electrode and a suite of non‐destructive nuclear methods , amongst others. Part 3 also covers digestion (alkaline fusion, fire assay and acid digestion) of materials, chemical separation and extraction of element groups in some detail.
Three previously introduced titanites, Ontario, T3 and Pakistan, were evaluated as potential reference materials (RMs) for high spatial-resolution U-Pb microanalysis, offering valuable additions to the currently limited suite of titanite RMs. Comprehensive characterisation through microanalytical techniques, including scanning electron microscope, electron probe micro-analysis, secondary ion mass spectrometry (SIMS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), reveal that the Proterozoic-age Ontario titanite is inclusion-free and homogeneous within analytical uncertainty in terms of major and trace elements, U-Pb isotopes and U-Pb ages. The Miocene-age Pakistan titanite, though relatively low in U and Pb contents, also shows homogeneity in U-Pb isotopes and ages at the scale of analytical precision. Isotope dilution thermal ionisation mass spectrometry (ID-TIMS) results are reported for the first time for both Ontario and Pakistan titanites. Accordingly, analyses of the Ontario titanite fragments range from concordant to variably discordant but yield a robust weighted mean 207Pb/206Pb date of 1048.5 +/- 3.3 Ma (2s "internal" uncertainty, n = 9). Cross-calibration with other titanite RMs by LA-ICP-MS demonstrates that Ontario is suitable as a primary RM for determining U-Pb ages of titanite ranging in age from Precambrian to Neogene. ID-TIMS analyses of the Pakistan titanite yield overlapping data with a weighted mean 206Pb/238U date of 20.759 +/- 0.055 Ma (2s "internal" uncertainty, n = 10). Considering its relatively young age, Pakistan titanite is recommended as a secondary RM for quality control of young titanites dating by LA-ICP-MS and SIMS. In contrast, the T3 titanite exhibits significant intra- and inter-grain heterogeneity. The brighter zone in BSE images (T3-LG) has relatively high and homogeneous rare earth elements contents and yields a lower intercept age of 1099 +/- 3 Ma (2s, n = 78, MSWD = 1.3) by LA-ICP-MS. In contrast, darker domains display heterogeneous trace element and ages, rendering them unsuitable as RMs for microbeam U-Pb dating.
The rapidly growing number of studies investigating Mg isotopes in natural systems with ultra‐low Mg mass fractions (e.g., MgO < 0.05% m/m ) highlights the increasing need for precisely calibrated geological reference materials with similarly low Mg levels. However, accurate isotopic characterisation of such materials remains challenging due to limitations in traditional analytical procedures. To address this, we applied the critical mixture double spike (CMDS) technique to perform high‐intermediate precision Mg isotope measurements on nine geological reference materials with low‐Mg mass fractions from China and Japan. Results demonstrate that high‐silica granite JG‐2, alkali feldspar JF‐1, wollastonite GBW03123 and kaolinite GBW03121a exhibit excellent Mg isotopic homogeneity, making them promising candidates for Mg isotope reference materials. In contrast, alkali feldspar JF‐2, GBW03116 and GBW03134 display poorer internal consistency in Mg isotopic compositions among different digestions, likely attributable to a nugget effect arising from heterogeneous Mg distribution within sample powders. Additionally, alkali feldspars exhibit extremely low δ 26 Mg values relative to DSM‐3, ranging from ‐1.05‰ to ‐0.52‰, potentially linked to the high coordination number of Mg in their crystal structures.
This chapter (Analysis of Geological Materials – 2: Pre‐Concentration and Separation Procedures) is a contribution to the Geostandards and Geoanalytical Research Handbook of Rock and Mineral Analysis – an online textbook that is a fully revised and updated edition of A Handbook of Silicate Rock Analysis (P. J. Potts, 1987, Blackie, Glasgow). In Chapter 2, Part 2 (from Section 1 of the handbook dealing with fundamentals of measurement and instrument design) the principles and procedures of ion exchange chromatographic techniques and processes are first examined followed by a review of their application to isotope measurement by TIMS and MC‐ICP‐MS for radiogenic and stable isotope systems. Determination of platinum‐group and rare earth elements by ICP‐MS is also covered. Following this, liquid‐liquid (solvent) extraction and extraction chromatography are examined, including a review of EXC resins in the analysis of silicate materials. Part 2 Chapter 2 concludes with a treatment of coprecipitation and vapour generation (for hydrides, mercury and osmium).
This study introduces WJS810, a new natural zircon reference material designed for microbeam-based U-Pb geochronology and Hf-O isotope geochemistry. Extensive analyses using secondary ion mass spectrometry (SIMS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) have confirmed that WJS810 exhibits uniform U-Pb, Hf and O isotopic ratios. Six chemical abrasion isotope dilution thermal ionisation mass spectrometry (CA-ID-TIMS) U-Pb isotopic measurements yielded weighted mean Pb-206/U-238, Pb-207/U-235 and Pb-207/Pb-206 ages of 816.88 +/- 0.61 Ma (2s, n = 6), 816.90 +/- 0.59 Ma (2s, n = 6) and 816.79 +/- 0.93 Ma (2s, n = 6), respectively. Results from SIMS and LA-ICP-MS yielded concordant ages are in agreement with the TIMS age within analytical uncertainty. The mean Hf-176/Hf-177 ratio determined by LA-MC-ICP-MS is 0.282548 +/- 0.000043 (2s, n = 121), which is in good consistency with the mean of 0.282548 +/- 0.000005 (2s, n = 6) determined by solution-MC-ICP-MS. The delta O-18 value determined by SIMS is 6.65 +/- 0.36 parts per thousand (2s, n = 117), which is consistent with the mean of 6.46 +/- 0.21 parts per thousand (2s, n = 8) determined by laser fluorination. Raman microspectroscopy demonstrates that WJS810 exhibits exceptionally low (minimal) radiation damage, with a mean full width at half maximum (FWHM) of 4.06 cm(-1), comparable to the widely used 91500 reference material (mean FWHM = 4.47 cm(-1)). WJS810 represents a valuable addition to the existing suite of Neoproterozoic zircon reference materials for microbeam-based U-Pb geochronology and Hf-O isotope measurement.
The large range of Rb and Sr mass fractions in natural micas presents a challenge for LA-ICP-MS/MS Rb-Sr geochronology. Mica with disparately high Rb and low common Sr mass fractions are particularly problematic given the limited linear dynamic range (1-2 & times; 10(6) cps) of ICP-MS/MS systems. Here we quantify sources of uncertainty and inaccuracy associated with the in situ Rb-Sr method, including assessing laser-ICP-MS/MS timing issues, evaluating statistical bias at low count rates and quantifying non-linearity of the electron multiplier between pulse and analogue detection. These considerations are tested on natural mica with high Rb-87/Sr-86 ratios (> 1000), including ca. 92 Ma biotite (Tombstone pluton, Yukon) and ca. 2620 Ma muscovite (Tanco pegmatite, Manitoba), with Rb mass fractions of ca. 2300 and 30000 mu g g(-1), respectively. Our results highlight the importance of: (1) optimising analytical parameters (e.g., laser energy, spot size), (2) potential application of non-linearity corrections for high Rb signals and (3) judicious selection of data reduction methods (e.g., signal integration methods, incorporating all sources of uncertainty, error correlation) for the determination of precise and accurate Rb-Sr ages. With these considerations in mind, in situ Rb-Sr measurements of Tombstone and Tanco mica yielded isochron ages within similar to 1% of their accepted Rb-Sr TIMS ages.
We present a systematic evaluation of high spatial-resolution zircon U-Pb dating using a Thermo Scientific Neoma multi-collector ICP-MS coupled to a Resolution 193 nm excimer laser, operated at 7-15 mu m spot diameters under routine high-throughput production conditions. Performance was assessed during extended measurement sessions comprising 300-400 analyses per run, with reference materials interspersed among unknowns. Three configurations were tested: 15 mu m (8 Hz, 15 s), 7 mu m (8 Hz, 12 s) and 7 mu m (6 Hz, 9 s). Zircon reference materials (Ple & scaron;ovice, 91500, BB) were used to evaluate precision, accuracy, repeatability and down-hole fractionation (DHF). At 15 mu m, individual Pb-206/U-238 uncertainties were typically 0.5-1% (2s), with intermediate measurement precision better than 0.5% (2s). DHF was smooth and repeatable, adequately modelled by linear or polynomial corrections. At 7 mu m (8 Hz, 12 s), Pb-206/U-238 measurement repeatability precision for single spots of 0.5-1% was routinely achieved, overlapping with the best reported <= 10 mu m LA-(MC)-ICP-MS performance. Reduced ablated mass (<= 1 ng zircon), however, increased counting-statistical noise and DHF sensitivity. This primarily affects Pb-207/Pb-206 precision in Phanerozoic zircons, where low radiogenic Pb-207 yielded single-spot uncertainties > 5% and intermediate measurement precision of 8-10% RSD. Lower repetition rates further reduced ion yield, increasing Pb-206/U-238 uncertainties to 1.5-3% while improving depth control for ultra-thin domains. Application to Devonian silicic rocks from western Victoria demonstrates the geological value of 7-15 mu m analyses. Small-spot data resolve Late Silurian-Early Devonian inherited cores (438-398 Ma) within younger Middle Devonian overgrowths, revealing widespread crustal inheritance not detectable with conventional 25-35 mu m spots. These results indicate repeated entrainment of zircon derived from deep-crustal magmatism associated with the Benambran and Bindian orogenies, supporting a model of prolonged Devonian crustal reworking and magma recycling in the Lachlan Orogen.
Laser ablation with quadrupole ICP-MS has become a crucial tool that is widely used in geochronology and geochemistry. The growing demand for a large number of ablation spots, e.g., large-n detrital zircon U-Pb geochronology, raises experimental costs and requires substantial time. To address this, a rapid aerosol transport system, ARIS (Teledyne Technologies Inc.) is being utilised. Although developed to enhance 2D mapping via faster repetition rates, the system has also demonstrated suitability for large-n ablation. However, insufficient sampling of the periodic signal (especially with low repetition rate) can lead to signal aliasing, resulting in high uncertainty. In our study, a 3D-printed Tesla valve was designed and integrated into the ARIS to smooth the signal fluctuations during the rapid U-Pb analysis. When operated at a 10 Hz repetition rate and 2 J cm(-2) laser fluence, with a duty cycle of 40 ms on each mass, the Tesla valve can reduce signal oscillations by more than tenfold, achieve a signal wash-in time of similar to 0.7 s, and completes 98% signal decay within 0.8 s during the wash-out. Spot analyses of zircon reference materials (GJ-1, Plesovice, Qinghu and Mud Tank) with 15 s ablation durations yielded Pb-206/U-238 ages consistent with their recommended values (< 1.5% deviation). Furthermore, a re-analysed detrital zircon sample demonstrated that the short ablation durations (15 s per spot) could produce large-n age spectra statistically indistinguishable from those obtained with conventional long ablation durations (> 30 s per spot). Therefore, the Tesla valve-based smoothing device offers a cost-effective and easily implementable solution that is particularly well suited for fast aerosol transport systems (e.g., ARIS) and low-repetition-rate laser ablation applications.
The rapidly growing number of studies investigating Mg isotopes in natural systems with ultra-low Mg mass fractions (e.g., MgO < 0.05% m/m) highlights the increasing need for precisely calibrated geological reference materials with similarly low Mg levels. However, accurate isotopic characterisation of such materials remains challenging due to limitations in traditional analytical procedures. To address this, we applied the critical mixture double spike (CMDS) technique to perform high-intermediate precision Mg isotope measurements on nine geological reference materials with low-Mg mass fractions from China and Japan. Results demonstrate that high-silica granite JG-2, alkali feldspar JF-1, wollastonite GBW03123 and kaolinite GBW03121a exhibit excellent Mg isotopic homogeneity, making them promising candidates for Mg isotope reference materials. In contrast, alkali feldspar JF-2, GBW03116 and GBW03134 display poorer internal consistency in Mg isotopic compositions among different digestions, likely attributable to a nugget effect arising from heterogeneous Mg distribution within sample powders. Additionally, alkali feldspars exhibit extremely low delta Mg-26 values relative to DSM-3, ranging from -1.05 parts per thousand to -0.52 parts per thousand, potentially linked to the high coordination number of Mg in their crystal structures.
A calcite reference material (CCMb) derived from Carrara marble was developed for calibrating in situ mass fraction measurements of selected minor and trace elements (Mg, Sr) and the isotope ratios of carbon (delta 13C) and oxygen (delta 18O). Chemical and isotopic properties were characterised by bulk solution and in situ techniques, with ten laboratories participating in an analytical round-robin. Grains of CCMb were analysed by ion microprobe (SIMS) against a suite of calcite reference materials, including international reference material IAEA-603, to evaluate the influence of minor amounts of Mg on the instrumental mass fractionation of delta 18O values. CCMb consists of an assemblage of tightly interlocking calcite crystallites measuring 100-300 mu m across. Fluid-inclusion trails are abundant along crystallite grain boundaries. An offset was observed between delta 18O values of CCMb determined by gas-source isotope ratio mass spectrometry (GS-IRMS) and SIMS measurement. The results of this study indicate the offset could be related to the presence of isotopically light calcite material in grain boundary regions and micro-fissures, domains only several micrometres thick. When used for calibrating SIMS measurements, CCMb should be assigned a reference delta 18O value of +28.81 +/- 0.15 parts per thousand (VSMOW, 2s, based on SIMS results), representative of the integrated crystallite volume less the contribution of the inferred low delta 18O phase occupying intercrystalline space. Measurements of delta 13C by ion microprobe reproduced the bulk-grain, GS-IRMS derived value of +1.95 +/- 0.06 parts per thousand (VPDB, 2s). This study did not find evidence for matrix effects related to Mg-substitution at mass fractions <= 3000 mu g g-1. The preferred reference values for the Mg and Sr mass fractions in CCMb are 0.36 +/- 0.05% m/m (2s) and 156 +/- 8 mu g g-1 (2s), respectively.
Calcic garnet is a common component of skarns, alkaline igneous rocks and carbonatites. Recent studies report garnet laser ablation-ICP-MS U-Pb ages ranging from ca. 20 to 3100 Ma demonstrating the advantages of garnet for U-Pb geochronological studies. However, calibration using well-characterised matrix-matched reference materials is a critical issue for accurate age determinations. In this study we present the major and trace element compositions, and U-Pb systematics obtained from isotope dilution-TIMS and LA-ICP-MS measurements for Kovdor (Kovdor-GRT) andradite-shorlomite-morimotite garnet (Kola Alkaline Province, Kola Peninsula) as a potential reference material for LA-ICP-MS U-Pb dating. ID-TIMS gave 206Pb/238U, 207Pb/235U and 207Pb/206Pb Pbc-corrected weighted mean ratios of 0.06008 +/- 0.00018 (2s, MSWD = 4.5), 0.4495 +/- 0.0013 (2s, MSWD = 1.6) and 0.0542 +/- 0.0006 (2s, MSWD = 0.001), respectively. The weighted mean 206Pb/238U age is 376.50 +/- 0.9 Ma (MSWD = 1.3), the 207Pb/235U age is 376.5 +/- 0.62 Ma (MSWD = 0.83) and the 207Pb/206Pb age is 380.6 +/- 1.7 (MSWD = 0.27). The Concordia age of 376.6 +/- 0.86 Ma (MSWD = 0.79) for Kovdor-GRT, determined by ID-TIMS, is interpreted as the best estimate for its crystallisation age. The low common Pb (Pbc) content (Pbc/Pbt varies from 0.05 to 0.08), moderate U mass fraction (12.4-33.0 mu g g-1) and isotopically homogeneous composition allowed meaningful 206Pb/238U age determinations using various LA-ICP-MS systems. LA-ICP-MS measurement results are characterised by precisions fit for purpose and yield consistent 206Pb/238U ages indistinguishable from those obtained by ID-TIMS. The results highlight the potential of Kovdor garnet as a reference material for in situ U-Pb dating.
Iron isotope ratios of Fe(-Ti) oxide minerals have been widely used in constraining different geological processes. Laser ablation-MC-ICP-MS has been commonly used to identify subtle Fe isotopic variations of these iron oxides, but matrix-matched reference materials for calibration are still lacking. Here, five mineral pellets were prepared using a high-temperature and high-pressure sintering method. These pellets are proved to be homogenous in Fe isotope ratio by femtosecond LA-MC-ICP-MS. The reference values (delta 56FeIRMM-014) determined by solution nebulisation MC-ICP-MS are 0.08 +/- 0.03 parts per thousand, 0.29 +/- 0.02 parts per thousand, 0.20 +/- 0.06 parts per thousand, 0.23 +/- 0.03 parts per thousand and 0.32 +/- 0.01 parts per thousand for MtFe-2 (magnetite), HemFe-1 (haematite), IlmFe-1 (ilmenite), VTiMtFe-1 (V-Ti magnetite) and VTiMtFe-2 (V-Ti magnetite), respectively. Previous magnetite reference material MtFe-1 can be used as the bracketing calibrator for MtFe-2 and HemFe-1. Similarly, there is no matrix effect between MtFe-2 and HemFe-1. IlmFe-1 can be used as the bracketing calibrator for VTiMtFe-1 and VTiMtFe-2. VTiMtFe-1 and VTiMtFe-2 can be used as the bracketing calibrator for each other. The effects of blank on the determination of Fe isotopes are negligible. The analysis of natural magnetite and ilmenite validates their practical use in geological studies. The prepared reference materials are in sufficient quantities to be shared with other laboratories.
Tin isotopes have become a valuable tracer for geological, archaeological and cosmochemical investigations because of their distinctive multi-isotopic system of ten stable isotopes and their affinity for both sulfide and chalcophile phases. However, the refractory nature of cassiterite (SnO2) presents a major challenge for Sn isotope measurement, as its resistance to conventional acid digestion leads to prolonged, incomplete dissolution and problematic isotopic fractionation. Thus, this study presents a novel method for cassiterite dissolution employing the sealed Carius tube technique, with an evaluation of three acid systems: 11.6 mol l(-1) concentrated HCl, 7.6 mol l(-1) HBr, and 9.1 mol l(-1) HBr. A key finding is that complete removal of residual HBr via pre-treatment is critical to avoid analytical interference. Applying this approach, the mean delta Sn-122/118(3161A) for sample DL 16 was -0.04 +/- 0.02 parts per thousand (2s, n = 16). A 9.1 mol l(-1) HBr solution demonstrated the highest dissolution efficiency, achieving complete cassiterite breakdown about 700% faster than previous methods. delta Sn-122/118(3161A) was consistent across the different acid systems and varying recovery rates, confirming minimal isotopic fractionation. Method validation using the cassiterite reference material #CAS 2 yielded delta Sn-122/118(3161A) = 0.29 +/- 0.06 parts per thousand (2s, n = 4), in agreement with the certified reference value. The proposed method offers several advantages: (1) high recovery rates within short processing times; (2) complete dissolution of cassiterite; (3) negligible Sn isotopic fractionation. This protocol effectively overcomes key limitations of conventional approaches, such as incomplete dissolution, use of hazardous reagents, and potential isotopic bias, thereby establishing a reliable procedure for precise Sn isotope measurement in geochemical and planetary research.
Iron isotope ratios of haematite (Fe2O3) and magnetite (Fe3O4) provide insights into geochemical, environmental and planetary processes. In most studies, Fe isotope measurements are commonly performed using solution nebulisation multi-collector inductively coupled plasma-mass spectrometry (SN-MC-ICP-MS). Nanosecond laser ablation multi-collector inductively coupled plasma-mass spectrometry (ns-LA-MC-ICP-MS) requires minimal sample preparation, and provides spatially resolved variation of iron isotopes at micro-scale. However, homogeneous and matrix-matched haematite/magnetite reference materials are lacking for precise in situ isotopic measurement. The iron isotope ratios of two potential reference materials resembling natural haematite (HMIE-NP-B01) and natural magnetite (MAKP-NP-B01) were characterised. Size fractions between 5-63 mu m of the powdered Fe oxides were milled to nanoparticles, freeze-dried, homogenised, and pressed into pellets. The materials were then evaluated using SN-MC-ICP-MS and LA-MC-ICP-MS. Sample powders of the two materials were measured by SN-MC-ICPMS after sample digestion and column separation and pressed pellets were analysed directly via ns-LA-MC-ICP-MS. In both cases iron isotope delta values are reported relative to the certified reference material IRMM-014, used as the bracketing standard (calibrator). The solution measurements yielded delta 56Fe values of -0.25 +/- 0.08 parts per thousand (N = 13, 2s) for HMIE-NP-B01, and -0.05 +/- 0.09 parts per thousand (N = 12, 2s) for MAKP-NP-B01, considered as the preferred Fe isotope delta values. In situ isotopic analysis via ns-LA-MC-ICP-MS yielded delta 56Fe values of -0.28 +/- 0.28 parts per thousand (N = 19, 2s) for HMIE-NP-B01 and -0.12 +/- 0.24 parts per thousand (N = 22, 2s) for MAKP-NP-B01, consistent with the solution Fe isotope data. The homogeneity of Fe isotopes of the pellets was evaluated by ns-LA-MC-ICP-MS analyses of three different positions to further confirm that both materials are isotopically homogeneous. Both materials can be considered as potential quality control and bracketing reference materials for Fe isotopic measurements by in situ ns-LA-MC-ICP-MS analysis.
The lack of a common reference material and notation for Sn isotope measurement has hindered inter-laboratory data comparison. Six laboratories using various methodologies participated in this inter-calibration study to identify a suitable reference material and notation for Sn isotope data, enabling reliable cross-laboratory comparison. We report Sn isotope data for nine USGS geological reference materials (AGV-1, AGV-2, BCR-2, BHVO-1, BHVO-2, GSP-2, SCo-2, SRG-1 and W-2a, with SCo-2 data reported for the first time), and for single-element reference solutions (NIST SRM 3161a, SPEX CertiPrep Sn of type CLSN2 and PLSN5, Puri Sn CEZA, Sn Lyon, Sn IPGP). The SPEX CertiPrep Sn types differ in their Sn isotope composition: CLSN2 reference solutions (ICP-MS standards) are identical to each other, unlike PLSN5 reference solutions (AA and ICP standards). Our Sn isotope data demonstrate that NIST SRM 3161a (lots 070330 and 140917) is isotopically identical across lots and remains stable over time. To facilitate comparison across laboratories using other in-house reference solutions, we derived conversion factors to NIST SRM 3161a for Puri Sn CEZA (Delta 122/118SnPuri Sn CEZA-NIST SRM 3161a = 0.132 +/- 0.011 parts per thousand), Sn Lyon (Delta 122/118SnSn Lyon-NIST SRM 3161a = 0.229 +/- 0.016 parts per thousand) and Sn IPGP (Delta 122/118SnSn IPGP-NIST SRM 3161a = 0.162 +/- 0.018 parts per thousand), demonstrating that the ENS "Sn Lyon" reference solution is not a NIST SRM 3161a reference solution, unlike stated in earlier publications. IPGP data published after 2020 can be converted with our Sn IPGP conversion factor, while earlier IPGP data are more accurate through normalisation to BHVO-2. For future studies, we recommend using the stable, available and widely used NIST SRM 3161a as the primary Sn isotope reference material and reporting Sn isotope compositions as delta 122/118SnNIST SRM 3161a.
A megacryst zircon from Brazil, referred to here as Peixe#0, was evaluated as a potential reference material for LA-ICP-MS U-Pb dating. Results from multi-method characterisation - including CA-ID-TIMS, SIMS and a long-term LA-ICP-MS data set - enabled us to assess this crystal's suitability as a reference material for routine quality control in age determinations by LA-ICP-MS. Using CA-ID-TIMS, Peixe#0 yielded mean 206Pb/238U and 207Pb/235U ratios of 0.09257 +/- 0.1% and 0.7561 +/- 0.1%, respectively (precisions expressed as 2RSD), and weighted mean 206Pb/238U age of 570.85 +/- 0.30 Ma (2s, MSWD = 0.40, n = 4). With the LA-ICP-MS compiled database (2063 individual age determinations distributed over 167 sessions spanning eight years) acquired during routine analysis at the Isotope Geology Laboratory (LAGIS) at Unicamp, Brazil, we propose a 206Pb/238U weighted mean age of 569 +/- 13 Ma (2s), which includes the long-term excess variance in the total uncertainty. Oxygen isotopes presented a homogeneous distribution (delta 18OSMOW = +5.13 +/- 0.15 parts per thousand (1s)). The trace element chemical compositions varied substantially depending on the chosen cathodoluminescence zone containing distinct features. Approximately 4 g of Peixe#0 zircon are available for distribution upon request.
