Geostandards and Geoanalytical Research最新文献

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.

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.