Search

This study compares three zircon synthesis techniques (synthesis, high-temperature and high-pressure sintering and fast hot-pressing sintering) for the preparation of reference materials for Hf isotope analysis of zircon by laser ablation multi-collector inductively-coupled plasma mass spectrometry (LA-MC-ICP-MS). Ultrafine milled zircon powder particles doped with Yb2O3 produced by wet milling were used to synthesize zircon samples by using high-temperature and high-pressure sintering and fast hot-pressing sintering techniques. Li–Mo flux was necessary to obtain synthetic zircon grains. Zr signals for synthetic zircon grains and high-temperature and high-pressure sintered zircon are consistent with those of natural zircons but higher than that of fast hot-pressing sintered zircon, indicating that high-temperature and high-pressure sintered zircon has approximated the theoretical maximum density due to high pressure. The Hf isotopic compositions of high-temperature and high-pressure sintered and fast hot-pressing sintered zircon are comparable to those of the initial starting materials, whereas the Hf isotopes in synthetic zircon grains deviate slightly from those of the initial Hf solution. Compared with Hf isotope ratios obtained by SN-MC-ICP-MS, all preparation techniques give reliable LA-MC-ICP-MS results, suggesting that all synthetic zircon samples have great potential as both tools for in situ method development and isotopic reference materials. [ABSTRACT FROM AUTHOR]

High-quality Sr isotope data are critically dependent on the quality of reference materials that are used for instrumental calibration and data monitoring during laser ablation (LA) multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) analysis. We have prepared a new natural calcite reference material MNP for in situ Sr isotope measurement by LA-MC-ICP-MS. Detailed textural examination and major element determination suggest that the MNP calcite reference material has no growth rim or zoning. Trace element analyses by LA-ICP-MS showed that the MNP calcite reference material has low Rb/Sr ratios, low amounts of heavy rare earth elements (HREEs) and high Sr contents. The MNP calcite reference material is homogeneous with respect to Sr isotopes based on a large number of measurements performed by single-grain solution nebulizer (SN)-MC-ICP-MS and LA-MC-ICP-MS. The traditional bulk isotope analyses by TIMS and SN-MC-ICP-MS yielded a mean 87Sr/86Sr ratio of 0.70617 ± 0.00005(2SD, n = 18). A total of 585 LA-MC-ICP-MS Sr isotope analyses on random calcite crystals show homogeneous Sr isotopic compositions with an average 87Sr/86Sr ratio of 0.70617 ± 0.00005 (2SD), identical with the solution-based data. These suggest that MNP calcite can be used as a potential reference material for microbeam Sr isotopic analysis. [ABSTRACT FROM AUTHOR]

The copper isotopic compositions of 12 copper-rich minerals (including native copper, sulfides, carbonates, oxides, and copper chloride) have been determined using a 206 nm ultraviolet femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry (UV-fs-LA-MC-ICP-MS). A pure copper wire NWU-Cu-B and a natural chalcopyrite TC1725 were used as bracketing standards for calibration. Reliable and precise (2SD<0.07‰) δ65Cu values can be obtained using matrix-matched standards under dry plasma condition and calibrated by the standard-sample bracketing method (SSB). However, the δ65Cu values calibrated by non-matrix-matched standards were seriously affected by matrix effect, with a deviation of up to 1.42‰. Therefore, matrix-matched standards are necessary for reliable in situ Cu isotope ratio measurement. Although the analytical precision (2SD) is slightly improved, the use of Ga as an internal standard combined with the SSB correction does not reduce the deviation caused by the matrix effect. However, the matrix effect can be significantly suppressed by adding 8.6 µL min−1 water into the carrier gas. The matrix-induced δ65Cu deviation of the TC1725 calibrated against the pure copper NWU-Cu-B was reduced from 0.99‰ in dry plasma mode to 0.03‰ in wet plasma mode and achieved a long-term reproducibility of 0.10‰ (2SD). For the Cu isotopic compositions of 12 natural copper-rich minerals determined under wet plasma mode, the deviation of δ65Cu was less than 0.13‰ if the mineral is homogeneous. These results indicate that the non-matrix-matched standardization can be achieved by fs-LA-MC-ICP-MS under wet plasma condition, whether using chalcopyrite or pure copper as the external bracketing standards. [ABSTRACT FROM AUTHOR]

This study presents a practical method for high-precision Fe isotope determination without column chromatography purification for iron-dominated mineral samples using multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). A series of comparable experiments (with or without column chromatography) were performed to evaluate whether non-deviated Fe isotope ratios can be obtained directly by MC-ICP-MS using standard-sample bracketing (SSB) without column chromatography purification. Forty iron-dominated material/mineral samples (pure iron wire, pyrite, chalcopyrite, magnetite, hematite, siderite, goethite, pyrrhotite, arsenopyrite, specularite, ilmenite, limonite, lollingite, ilvaite, and Fe–Mn nodule) were investigated, and the results showed little bias in δ56Fe values compared with those of mineral materials via column chromatography purification, with Δδ56Fewithout–with ranging from −0.06‰ to +0.06‰. This means that Fe isotope ratios in Fe-dominated minerals can be achieved without column chromatography, due to the simple matrix and the stability of the machine by using the SSB method in high resolution wet plasma mode. The concentration effect and nitric acidity mismatch effects, as well as the matrix effect, were strictly assessed by MC-ICP-MS in high resolution wet plasma mode. Finally, a long-term reproducibility of better than ± 0.05‰ (n = 123, 2 sd) was achieved by repeatedly measuring pyrite without column chromatography over 6 months. Compared with the column chromatography purification method, the without column chromatography method significantly simplifies the chemical procedure and improves the efficiency of iron-dominated mineral Fe isotope analysis. [ABSTRACT FROM AUTHOR]

A new simple and rapid method was developed for the purification of Mg from carbonate samples, especially for calcite-rich carbonates. The proposed separation protocol consists of only two types of eluents (4 mol l−1 HNO3 and deionized water) based on 2 ml of DGA resin. 4 ml of HNO3 can effectively separate Mg from calcite-rich carbonates with a high yield within one hour. The Mg elution curve would not drift with different Mg and Ca loading onto the DGA resin. Ca/Mg ratios of the purified samples could be reduced by five orders of magnitude compared to the unpurified calcite-rich carbonate samples. The precision and accuracy of this new method have been evaluated by measurements of the synthetic solution, carbonate standard material, and ten readily available Chinese carbonate reference materials. All the Mg isotopic analytical results were, within analytical uncertainties, essentially identical with the data published previously. Therefore, the new method can be a great option for purifying Mg from carbonate samples for isotopic analysis. [ABSTRACT FROM AUTHOR]

We have prepared a large volume of pure, concentrated and homogeneous magnesium standard solution (GSB-Mg) to be used as a secondary reference standard by the magnesium isotope community. This new standard solution can also be used for quality assurance, including the development and validation of analytical procedures, preparation and test of analytical methods, quality control and training of analysts. The δ26Mg values relative to DSM3, measured by multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), are −2.038 ± 0.027‰ (n = 45, Lab 1), −2.024 ± 0.055‰ (n = 7, Lab 2), −2.078 ± 0.081‰ (n = 6, Lab 3), −2.037 ± 0.015‰ (n = 8, Lab 4), and −2.067 ± 0.039‰ (n = 12, Lab 5). The δ26Mg and δ25Mg values for the GSB-Mg standard solution are −2.049‰ and −1.056‰, with a combined expanded (k = 2) uncertainty of 0.049‰ and 0.028‰, respectively. These values show higher similarity to Mg isotopic compositions of carbonates and marine sediments compared to those of the mantle and crustal rocks, making the GSB-Mg solution a great reference material for Mg isotopic analysis of carbonates and marine sediments. [ABSTRACT FROM AUTHOR]

In sample preparation and mass spectrometry analysis, sample dissolution, column chemistry, concentration mismatches, and matrix effects have significant potential for introducing analytical artifacts during Mg isotope analysis. Based on the low MgO content and undesirable matrix elements in felsic rocks, the development of well-characterized felsic standards is essential to reduce inter-laboratory mass bias, enable the assessment of data accuracy, and facilitate the comparison of chemical separation procedures in different laboratories. In this work, the homogeneity and long-term stability of two felsic rock standards, GSR-1 and RGM-2, were evaluated due to their low MgO contents. Furthermore, synthetic solutions with doped matrix elements were used to evaluate potential Mg isotope analytical artifacts using multi-collector inductively coupled plasma mass spectrometry. The accuracy and precision of Mg isotopic compositions in GSR-1 and RGM-2 were assessed by repeated measurements over twelve months. The long-term tests show that the Mg isotopic compositions of the two low MgO felsic rocks (GSR-1 and RGM-2) are homogenous among batches and can be used as low MgO reference materials for accuracy assessments of Mg isotopic analyses. The Mg isotopic compositions (δ26Mg) of GSR-1 and RGM-2 were marked as -0.223‰±0.053‰ (2s, n=50) and -0.184‰±0.058‰ (2s, n=50) respectively. [ABSTRACT FROM AUTHOR]

• We report in situ S isotope analysis for multiple types of sulfides by LA-MC-ICPMS. • In situ S isotope analysis is applied to the study of the Erlihe Zn-Pb ore deposit. • Sulfur of the massive ores is likely sourced from the TSR process for the deposit. Sulfur isotopic composition is useful for tracing sources of ore-forming materials. In situ sulfur isotope analysis by laser ablation coupled with multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) has an advantage over traditional bulk analysis in tracing sources of sulfur in an ore deposit that has complex mineral types and multiple ore-forming processes. However, in using this method, matrix effects exist widely for sulfides from ore deposits. In this work, matrix effects of different sulfides were examined by matrix-unmatched tests, in which the δ34S values of different types of sulfides were calibrated against a laboratory pyrite standard. The results show that the δ34S values of pyrrhotite, chalcopyrite, molybdenite, sphalerite, and arsenopyrite are in agreement with the reference values, suggesting that the matrix effect was negligible. However, a significant matrix effect occurred in the analyses of Ag 2 S and galena, leading to significant deviations in δ34S values of up to 1.2‰ and 3.2‰, respectively. The matrix effect occurred not only during the laser ablation stage but also during the transition of ions into the mass spectrometer, resulting in significant space charge effects caused by heavy-mass elements. Thus, pyrite can be used as an external bracketing standard for sulfides that do not have a heavy-mass matrix. Based on our matrix-effect study, the following available external standards were selected for the in situ sulfur isotope analysis of complex-type minerals from the Erlihe Zn-Pb deposit. The coarse-grained sphalerite grains (Sph1) and euhedral to subhedral pyrite grains (Py1) from massive ores have δ34S values ranging from 9.2‰ to 18.1‰. Such heavy sulfur isotopic compositions indicate the derivation of sulfur from the deposits of seawater sulfate, related to a thermochemical reducing process. Fine-grained sphalerite (Sph2) and pyrite (Py2) from vein and disseminated ores coexist with pyrrhotite and chalcopyrite, and have relatively light sulfur isotopic compositions, with δ34S values of about 7‰. The slightly positive δ34S values are similar to those of sulfides from sulfide-rich quartz veins, which contain δ34S values of about 4‰, and granodiorite rocks, with δ34S values of about 6‰. Based on previous studies, the light sulfur of the late-stage sulfides may have resulted from a metamorphic or magmatic hydrothermal event during the Indosinian orogeny. In situ sulfur analysis by LA-MC-ICPMS provides new evidence for sources of sulfur from each stage of mineralization in the Erlihe deposit, suggesting that this is a promising method for studying complex ore deposits. [ABSTRACT FROM AUTHOR]

Silicon isotope analysis traditionally uses a standard-sample bracketing (SSB) method that relies upon greater instrument stability than can be consistently expected. The following proposed method reduces the level of instrumental stability required for the analysis process and provides a valid solution for high-precision and accurate studies of Si isotopic compositions. Rock samples were dissolved by using alkali fusion and acidification. Silicon isotopes were purified with an ion exchange resin. Interfering peaks for isotopes were separated by using a Nu Plasma 1700 multi-collector inductively coupled plasma mass spectrometry (MS) system in high-resolution mode ( M/Δ M > 8000 RP). Two magnesium isotopes (Mg and Mg) and three silicon isotopes (Si, Si, and Si) were analyzed in the same data collection cycle. Mg isotopes were used as an internal standard to calibrate the mass discrimination effects in MS analysis of Si isotopes in combination with the SSB method in order to reduce the effects of MS interference and instrumental mass discrimination on the accuracy of measurements. The conventional SSB method without the Mg internal standard and the proposed SSB method with Mg calibration delivered consistent results within two standard deviations. When Mg was used as an internal standard for calibration, the analysis precision was better than 0.05 ‰ amu. [ABSTRACT FROM AUTHOR]

In this study, lead isotopic ratios in bronze artifacts were non-matrix-matched determined directly by femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry (fsLA-MC-ICP-MS). We evaluated the necessity of matrix matching for lead isotope ratio analyses of bronzes by adopting thallium solution to correct mass discrimination during mass spectrometer measurements. Lead isotope ratios of four bronze reference materials were measured by fsLA-MC-ICP-MS to determine the quality of data when calibrating samples with standards having different physical characteristics and chemical compositions. The average 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, 208 Pb/ 204 Pb, 207 Pb/ 206 Pb and 208 Pb/ 206 Pb ratios determined by fsLA-MC-ICP-MS were within 0.06% of that by solution nebulizer MC-ICP-MS (SN-MC-ICP-MS). The results indicate that accurate lead isotopic compositions could be obtained by fsLA-MC-ICP-MS technique after non-matrix-matched standards calibration. Additionally, the lead isotopic compositions are presented for five Chinese bronze reference materials using fsLA-MC-ICP-MS. Homogeneity of lead isotope distribution was expressed as the RSD range from 0.010% to 0.017% for 208 Pb/ 204 Pb, 207 Pb/ 204 Pb, 206 Pb/ 204 Pb ratios. Therefore, the five bronze materials could potentially serve as external calibration standards and quality control samples for in situ lead isotope measurements of ancient bronze artifacts. The fsLA-MC-ICP-MS technique could be applied to differentiate the high radiogenic lead in bronze artifacts from common lead. [ABSTRACT FROM AUTHOR]

[Display omitted] • In situ Cu isotope data show large fractionation between Sn-rich and Cu-rich ores. • Cu isotopes and modeling show water–rock interaction crucial in Sn-Cu mineralization. • Cu source of the Sn-Cu coexisting deposit may be the Cu-rich country rocks. This study presents high-resolution in situ Cu isotope data for chalcopyrite from the Jinkeng Sn-Cu deposit, Guangdong Province, China, with the aim of understanding how the Sn-Cu mineralization was formed. Results show that early chalcopyrite (quartz-cassiterite stage) has the lowest δ65Cu values (–0.01 to +0.02 ‰), similar to δ65Cu values (∼0‰) in most granites. In contrast, chalcopyrite from the subsequent cassiterite-sulfide stage exhibits the highest δ65Cu values (+0.90 to +0.97 ‰), comparable to those of the volcanic country rocks (+0.87 to +1.00 ‰). δ65Cu values in late chalcopyrite gradually decrease (from +0.79 to +0.45 ‰) across the latest ore-forming stages, from quartz-sulfide to quartz-calcite-sulfide mineral assemblages. Observed variation in δ65Cu is explained by water–rock interaction. Quantitative geochemical modeling also demonstrates that the Cu isotopic compositions of chalcopyrite record variable degrees of water/rock ratios during water–rock interactions. Therefore, our results suggest that water–rock interaction plays a critical role in providing Cu for Sn-Cu ore systems. The study further indicates that in situ Cu isotope analysis provides an accurate and efficient tool for diagnosis of magmatic-hydrothermal processes. [ABSTRACT FROM AUTHOR]

This study presented a chemical protocol for purification of calcium and magnesium from a single aliquot of biological and geological samples. The separation protocol was based on a two-step cation exchange chromatography using DGA resin and AG50W-X12 (200–400 mesh) resin. Calcium fraction was first collected using 0.25 mL of DGA resin, and Mg fraction was then collected using 0.5 mL of AG50W-X12 cation exchange resin. For Ca isotope analysis, the effect of acidity and concentration mismatch as well as the matrix effect were rigorously evaluated using the Neptune Plus MC-ICP-MS with a wet-plasma mode. Based on repeated measurements on BHVO-2 and NIST SRM 1400, the long-term reproducibility was evaluated at 0.08‰ (2SD) for δ44/42Ca 915a. The δ26Mg ratios of the analyzed reference materials varied from −1.22‰ to 0.03‰ with the external precision better than 0.11‰ (2SD). The robustness of the protocol has been validated by replicated analyses of biological and geological standards. Calcium and magnesium isotopic ratios of all reference materials measured in this study agreed well with previous data within uncertainties. Therefore, the proposed method can be used for simultaneous determination of Ca and Mg isotopic ratios from a single aliquot of biological and geological samples. Image 1 • Purification of calcium and magnesium from a single aliquot of biological and geological samples. • Mg isotopic ratios of GSH-1, GSV-3, NIST SRM 1400, and NISR SRM 1486 were reported for the first time. • The method reduces the amount of acid used, saves time and is more efficient. [ABSTRACT FROM AUTHOR]