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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]

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]

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]