Search

An in-situ microanalysis of Pb isotopic compositions in sulfide minerals is carried out by using femtosecond laser-ablation multi-collector inductively coupled plasma mass spectrometry (fsLA-MC-ICP-MS). High-temperature-activated carbon was used to filter Hg contained in the carrier gas, which reduced the Hg background signal by 48% and also lowered the detection limit of the analysis. Fractionation and mass discrimination effects existing in the ICP-MS analytical processes were corrected using an internal reference Tl in conjunction with an external reference NIST SRM 610. The proposed method was used to analyze the Pb isotopic compositions of chalcopyrite, pyrite, and sphalerite from the Dulong Sn-Zn-In polymetallic ore district. The results showed that in this ore district, the sulfide minerals and different grains of the same sulfide mineral show a large variation in Pb content up to 1000-fold. The studied pyrites show relatively higher Pb contents and homogeneous Pb isotopic compositions, whereas the sphalerites have low Pb contents but most variable Pb isotopic compositions. It is suggested that the large variation of Pb isotopic composition may reflect a late hydrothermal superimposition on the primary sulfide formation. In addition, radiogenic Pb accumulated by radioactive decay of trace amounts of U over time in the host minerals may also be one of the causes for the large variation range of Pb content and Pb isotopic composition of those low-Pb sphalerites. Chalcopyrite and sphalerite grains with Pb content greater than 10 ppm presented a consistent Pb isotopic distribution, whereas all the sulfide grains with Pb content greater than 100 ppm had consistent Pb isotopic composition within 2s measurement uncertainties. The in-situ analysis of Pb isotopic composition agreed well with the results obtained by conventional chemical methods within 2s measurement uncertainties, indicating that the data obtained by fsLA-MC-ICP-MS are reliable. Additionally, this study indicates that the Pb isotopic composition could truthfully record the source of ore-forming minerals only for sulfide minerals with high Pb content. On the contrary, the Pb isotopic composition of low-Pb sulfide minerals may be affected by trace amounts of U in the host minerals that may lead to a highly radiogenic Pb isotope ratio. Alternatively, it is also possible that late fluid metasomatic overprinting may alter the Pb isotopic compositions. [ABSTRACT FROM AUTHOR]

A new matrix‐matched reference material (NWU‐Brt) with sulfur isotope ratios resembling those of natural barites has been developed for in situ S isotope measurements by laser ablation multi‐collector inductively coupled plasma‐mass spectrometry (LA‐MC‐ICP‐MS). A 100 g quantity of natural barite crystal was milled to ultra‐fine particles and sintered to a solid block using a fast hot‐pressing sintering technique (FHPS). We report δ34S ratios determined by isotope ratio mass spectrometry (IRMS), solution nebuliser multi‐collector inductively coupled plasma‐mass spectrometry (SN‐MC‐ICP‐MS) and LA‐MC‐ICP‐MS, involving up to six participating laboratories. The homogeneity of δ34S ratios of the synthesised barite was tested by LA‐MC‐ICP‐MS with an analytical spot size of 53 μm. The LA‐MC‐ICP‐MS results show that NWU‐Brt demonstrates a satisfactory homogeneous composition and is an appropriate material for calibrating δ34S ratios in barite. IRMS and SN‐MC‐ICP‐MS produced mean δ34S values of +14.17 ± 0.42‰ (2s) and +14.27 ± 0.23‰ (2s), respectively. The results of LA‐MC‐ICP‐MS analyses are consistent with the IRMS and SN‐MC‐ICP‐MS ratios within uncertainty. Overall, our results confirm the suitability of NWU‐Brt for the calibration of δ34S ratios in barite using LA‐MC‐ICP‐MS. [ABSTRACT FROM AUTHOR]

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]

Sulfur isotopes are important tracers in various geochemical processes. A matrix-matched reference material is essential for in situ sulfur isotope ratio measurement in sphalerite (ZnS), an abundant zinc sulfide in base metal deposits. In this study, natural sphalerite powders (GBW07270) were ground into ultra-fine powders and then sintered by using a plasma-activated sintering (PAS) method at 1000 °C and 50 MPa for 10 minutes. The synthesized sphalerite has a smooth surface and dense structure, making it suitable for laser ablation analysis. To investigate whether the PAS-synthesized sphalerite is an appropriate matrix-matched reference material for in situ sulfur isotope determination, a large number of in situ S isotope measurements were performed on the PAS-synthesized sphalerite by laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). The LA-MC-ICP-MS results are highly consistent and yield a mean δ34SV-CDT value of −5.44 ± 0.20‰ (2SD, n = 1008), which agrees well with that measured by gas source isotope ratio mass spectrometry (GS-IRMS). Therefore, the PAS-synthesized sphalerite has a homogeneous sulfur isotopic composition and is a suitable matrix-matched reference material available for in situ S isotope measurements of sphalerite. [ABSTRACT FROM AUTHOR]

Microanalysis of tin isotopes in cassiterite by laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) has been an important tool to reconstruct the fluid evolution or discriminate petrological sources and processes. However, it is a major challenge to prepare the absolutely essential cassiterite reference material that has a homogeneous Sn isotope composition on a micron scale. In this study, we report a novel method to synthesize a homogeneous cassiterite reference material via sintering a micrometer powder. Under the optimized conditions (600 °C, 1 GPa), the synthesized cassiterite has a smooth surface and dense structure that is suitable for laser ablation analysis. The Sn signal for the synthesized cassiterite was consistent with that of natural cassiterite and lower than that of the pressed powder pellets by LA-ICP-MS, indicating that the sintered cassiterite approximated the theoretical maximal density. LA-MC-ICP-MS measurements suggest that the homogeneity (2SD) for δ124Sn/120Sn was improved from 0.64‰ (original cassiterite crystal) to 0.10‰ (synthesized cassiterite). The reproducibility of δ124Sn/120Sn was 0.07‰ (2SD) for the synthesized cassiterite. These data have demonstrated that the synthesized cassiterite has a homogeneous distribution of Sn isotopes. Therefore, we recommend combining ultra-fine powders with the high-temperature sintering technique to synthesize other minerals for microanalysis. [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 examined the micro‐homogeneity of zinc isotope composition of the NIST SRM 683 and NBS 123 reference materials using femtosecond laser ablation multi‐collector inductively coupled plasma‐mass spectrometry (fsLA‐MC‐ICP‐MS). NIST SRM 683 and NBS 123 are homogeneous in Zn isotope composition based on numerous measurements performed on twenty chips and four mounts of sphalerite using solution nebulisation (SN)‐MC‐ICP‐MS and fsLA‐MC‐ICP‐MS. The mean δ66ZnJMC‐Lyon values of NIST SRM 683 and NBS 123 determined by SN‐MC‐ICP‐MS were 0.11 ± 0.02‰ (2 standard deviation (2s), n = 100) and 0.16 ± 0.02‰ (2s, n = 62), respectively. The mean δ66ZnJMC‐Lyon values determined by fsLA‐MC‐ICP‐MS analyses for NIST SRM 683 and NBS 123 were 0.12 ± 0.05‰ (2s, n = 200) and 0.16 ± 0.05‰ (2s, n = 212), consistent with the bulk isotope compositions within uncertainty. The in situ measurement precision for NIST SRM 683 and NBS 123 was better than 0.06‰ (2s), suggesting NIST SRM 683 and NBS 123 are suitable to serve as microanalytical reference materials for Zn isotope measurement. Zinc isotopic compositions of Zn‐rich materials were also determined using fsLA‐MC‐ICP‐MS under wet/dry plasma conditions. Their δ66ZnJMC‐Lyon values were in agreement with those obtained by SN‐MC‐ICP‐MS analysis, suggesting that fsLA‐MC‐ICP‐MS is suitable to measure Zn isotopic ratios in Zn‐rich materials. Thus, this method could potentially analyse spatially resolved Zn isotope compositions at the mineral or even sub‐mineral scale, such as to address the process of ore formation or Zn redistribution in near‐surface environments. [ABSTRACT FROM AUTHOR]

Sulfur isotopes are important geochemical tracers in the diverse fields of geosciences. Controlling the accuracy and precision of the microanalysis of sulfur isotopes requires well-characterized reference materials with matrices similar to those of unknown samples. This study introduces a new natural chalcopyrite reference material, TC1725, for S isotope analysis by laser ablation multiple-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). The chalcopyrite grain is homogeneous with respect to S isotopes based on a large number of measurements by LA-MC-ICP-MS and solution nebulizer (SN)-MC-ICP-MS. Isotope ratio mass spectrometry (IRMS) for S isotopic analysis produced a mean δ34SVCDT value of +12.78 ± 0.16‰ (2 s, n = 11). Results of SN-MC-ICP-MS and LA-ICP-MS analyses are consistent with the IRMS ratios within the uncertainty. A total of 981 sulfur isotope ratio spot measurements conducted on the cruciform sections and randomly selected chalcopyrite grains of TC1725 by LA-MC-ICP-MS yielded highly consistent sulfur isotope ratios. [ABSTRACT FROM AUTHOR]

A new natural chalcopyrite reference material TC1725 is prepared for in situ Cu isotope measurement by femtosecond laser ablation multi‐collector inductively coupled plasma‐mass spectrometry (fsLA‐MC‐ICP‐MS). Detailed textural examination and major element determination suggest the TC1725 chalcopyrite grains have no growth rim or zoning. The chalcopyrite grain is homogeneous with respect to Cu isotopes based on a large number of measurements performed by bulk solution nebuliser (SN)‐MC‐ICP‐MS, single‐grain SN‐MC‐ICP‐MS and fsLA‐MC‐ICP‐MS. The traditional bulk isotope analyses by SN‐MC‐ICP‐MS yielded a mean δ65Cu value of −0.06 ± 0.03‰ (2s, n = 132). Randomly selected single chalcopyrite grain of TC1725 determined by SN‐MC‐ICP‐MS without column chromatography gave a mean δ65Cu value of −0.06 ± 0.04‰ (2s, n = 188). The intermediate measurement precision for four measurement sessions was better than 0.04‰ (2s), suggesting TC1725 chalcopyrite is suitable as a microanalysis reference material for Cu isotope measurement. The mean δ65Cu value determined by fsLA‐MC‐ICP‐MS analyses on different individual chalcopyrite mounts and strips was −0.06 ± 0.03‰ (2s, n = 393), consistent with the bulk isotope composition within uncertainty. The recommended mean δ65Cu value for this chalcopyrite reference material is −0.06 ± 0.03‰ (2s, n = 132) as determined by bulk SN‐MC‐ICP‐MS. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydrothermal titanite yields a weighted mean 206Pb/238U age of 160.1 ± 4.4 Ma. • Sulfur isotope compositions of ore sulfides indicate minor contributions from the host rocks via fluid-rock interaction. • The variations of in-situ Cu isotope compositions (δ65Cu: −1.13 to +0.12 ‰) are inconsistent with the ancient VMS deposits. • Our results suggest that the Tieshajie deposit has a Late Jurassic magmatic-hydrothermal origin instead of a Meso-Neoproterozoic VMS origin. The Tieshajie Cu deposit, located in the northeastern part of the Qin-Hang Metallogenic Belt (QHMB), South China, has long been regarded as a representative Meso-Neoproterozoic volcanogenic massive sulfide (VMS) deposit. Here we present a hydrothermal titanite U-Pb age, Re-Os and in-situ S-Cu isotope data for chalcopyrite to constrain the timing and ore genesis of the Tieshajie deposit. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb dating of titanite from the disseminated Cu ore yielded a weighted mean 206Pb/238U age of 160.1 ± 4.4 Ma. Chalcopyrite from different ore types has low 187Os/188Os (0.85–3.60) and 187Re/188Os (46.1–614.0) ratios, combined with initial 187Os/188Os (0.74–2.00), excluding a mantle source. A Re-Os isochron age (188 ± 30 Ma) for five chalcopyrite samples is consistent with the titanite U-Pb age within errors. Moreover, the variations in Cu isotope compositions (δ65Cu: −1.13 to +0.12 ‰) and δ34S values (+3.8 to +7.7 ‰) of chalcopyrite are inconsistent with those reported from the ancient VMS deposits in previous studies. Therefore, our results are indicative of a Late Jurassic magmatic-hydrothermal origin instead of a VMS origin for the Tieshajie deposit. In combination with previous studies, we propose that the Tieshajie Cu deposit belongs to the distal part of the Mid-Late Jurassic (170–150 Ma) porphyry-skarn Cu mineralization event in the QHMB, likely triggered by the subduction of the Paleo-Pacific plate during the Late Mesozoic. This study also has new insights into the genesis of Cu mineralization in the QHMB and further provides implications for future exploration. [ABSTRACT FROM AUTHOR]

In this study, Pb isotope ratios in ferromanganese nodules were determined with good repeatability and minimum laboratory bias using laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). One certified ferromanganese nodule reference material, NOD-A-1, in the form of pressed powder pellets (PPPs) produced upon ultrafine processing, was homogeneous enough to be used as an in-house matrix-matched standard or quality control sample for Pb isotopic microanalysis. The Tl normalization exponential law correction method with CTl-NIST SRM 997/CTl-sample≥ 15 (method 1) and the standard-sample-bracketing (SSB) method (method 2) were utilized to determine Pb isotope ratios with good repeatability and laboratory bias. In situ measurements of the Pb isotopes yielded a good relative standard deviation (2RSD) of ＜0.036% for 207,208Pb/206Pb and ＜0.066% for 206,207,208Pb/204Pb. In addition, the matrix effect was insignificant when the silicate glass reference material was employed as the external standard in the ferromanganese nodules using these two methods, resulting in relative errors (RE) of ＜0.064% for 206,207,208Pb/204Pb, and ＜0.046% for 207,208Pb/206Pb. The in situ Pb isotopic compositions of three Chinese ferromanganese nodules, GBW07249, GBW07295, and GBW07296, were in good agreement with those obtained by solution nebulization MC-ICP-MS (SN-MC-ICP-MS) within 2s (standard deviation) measurement uncertainties, demonstrating the reliability and robustness of our proposed analytical protocol. [ABSTRACT FROM AUTHOR]

Controlling the accuracy and precision of sulfur and lead isotopic compositions in natural sulfide minerals requires the use of well-characterized reference materials with matrices similar to those of the unknown samples being analyzed. However, it is often a challenge to prepare natural or synthetic reference materials with homogeneous isotope compositions on a micro-scale. Herein, we report a novel method to synthesize homogeneous sulfide reference materials in the form of nano-particulate pressed sulfide powder tablets (PSPTs). Non-matrix-matched external calibration was used to obtain accurate and precise lead isotopic ratios, while mass bias was corrected using a standard-sample bracketing method and a thallium standard solution doping process. In situ analysis of lead isotopic ratios of PSPTs using laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) yielded good external precisions of <0.026% for 207,208 Pb/ 206 Pb and <0.057% for 206,207,208 Pb/ 204 Pb (2RSD). Meanwhile, the standard deviations of results afforded by LA-MC-ICP-MS were better than 0.41‰ for 34 S/ 32 S (2SD). The in situ analytical results of PSPTs were consistent with the values obtained using solution nebulizer MC-ICP-MS, thus demonstrating the reliability and robustness of our analytical protocol. This method can also be used to synthesize different material matrices with homogeneous sulfur and lead isotopes to correct mass bias when using standard-sample bracketing for in situ analysis. [ABSTRACT FROM AUTHOR]

We prepared a series of pressed powder tablets and chalcopyrite glass standards to correct mass bias when using standard–sample bracketing for in situ sulfur isotope measurements. A femtosecond laser ablation coupled multi-collector inductively coupled plasma mass spectrometry (fsLA-MC-ICP-MS) method was used to determine the sulfur isotope composition of these standards. Chalcopyrite glass (YN411-m) was prepared by quickly quenching the fused chalcopyrite, which was melted at 1000 °C under a protective N2 atmosphere. Multiple experiments were conducted for homogeneity testing of YN411-m by fsLA-MC-ICP-MS and the external precision was 0.28‰ (n = 35). Mineral particles, pressed powder tablets, and chalcopyrite glass were used as bracketing standards when determining the δ34S of a natural chalcopyrite (GC). The results showed that the concentration, elemental composition, and crystal structure caused the matrix effect. Considering practicability, the melted glass was a more appropriate standard than the pressed powder tablet. We also found that the carrier gas flow rate, laser fluence, and spot size impacted the regularity of results. Therefore, we can obtain accurate δ34S by adjusting the laser and MC-ICP-MS parameters when using non-matrix matching standards. Furthermore, fsLA-MC-ICP-MS is advantageous for in situ sulfur isotope measurement because the sensitivity can be improved and it dramatically improves the spatial resolution (10–20 μm), which can be used to explain the origin of multi-genesis deposits by analyzing smaller mineral micro-areas, especially mineral fracture-filling sulfides later in mineralization. [ABSTRACT FROM AUTHOR]

In this study, a method for solidifying sulfide and sulfate nanoparticulate powder to prepare bracketing standards and samples for in situ S isotopic analysis using laser ablation multicollector inductively coupled plasma–mass spectrometry (LA-MC-ICP–MS) was developed. Sulfide or sulfate powder was transformed into a stable and mechanically resistant target by mixing it with epoxy resin. Using this method, seven bracketing standards with diverse matrix minerals (pyrite, chalcopyrite, sphalerite, galena, arsenopyrite, barite, and gypsum) were synthesized in the form of resin-preserved powders (RPPs). The effects of ablation behavior, powder particle size, and homogeneity on the S isotopic ratios in these RPPs were rigorously evaluated. The precision of the δ34S VCDT sulfur isotopic results obtained by LA-MC-ICP–MS was better than 0.47‰ (2SD uncertainty, n ≥ 20 over 4 months) for the S-bearing mineral RPPs. Finally, the in situ S isotope results of the seven RPPs measured by LA-MC-ICP–MS were consistent with the values obtained using solution nebulizer (SN)-MC-ICP–MS. The isotopic composition and homogeneity of a range of sulfide mineral RPPs (seven minerals referred to above) were characterized for use as potential reference materials. Our method provides the opportunity to prepare bracketing standards and samples for in situ S isotope analysis for a wide range of sulfur-bearing materials and is particularly appropriate for geologic samples with complex matrices and for which high spatial resolution in situ microbeam analysis is critical. More importantly, this method provides new prospects for the preparation of homogenized reference materials from natural minerals that are urgently needed for matrix-matched calibration and quality control of LA-ICP–MS geochemical and isotope data. [Display omitted] • A method for preparing bracketing S isotope standard has been developed. • Seven bracketing standards with diverse S matrices were synthesized in RPPs. • The precision of δ34S VCDT obtained were better than 0.47‰ for the S-bearing RPPs. • The S-bearing mineral RPPs solidifying method is reliability and robustness. • Isotopic composition and homogeneity of 7 RPPs were characterized for use as RMs. [ABSTRACT FROM AUTHOR]