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Iron isotope ratios in magnetite have been widely used to reveal critical geological and biological processes. Laser ablation multi‐collector inductively coupled plasma‐mass spectrometry (LA‐MC‐ICP‐MS) is ideally suited for measurement of Fe isotope ratios, however the lack of suitable reference materials poses a significant challenge for in situ Fe isotopic measurements in magnetites. In this study, five high‐quality natural magnetite crystals were characterised for Fe isotope ratios using solution nebulisation (SN)‐MC‐ICP‐MS and LA‐MC‐ICP‐MS. The effects of LA‐MC‐ICP‐MS analytical conditions were investigated to obtain precise and accurate Fe isotope ratios. The yielded intermediate measurement precisions for the δ56Fe values in the five investigated magnetites were ± 0.05–0.06‰ (2s) using SN‐MC‐ICP‐MS and ± 0.08–0.14‰ (2s) using LA‐MC‐ICP‐MS. Magnetites with homogeneous Fe isotopic compositions in hand‐specimen measurements and microanalysis can serve as potential reference materials for in situ Fe isotopic measurement. Furthermore, the Fe isotope ratios in the magnetites from the Jinchuan Ni‐Cu‐PGE sulfide deposit were measured using LA‐MC‐ICP‐MS with natural magnetite as the bracketing calibrator. The increase in the Fe isotopic composition with magmatic sulfide evolution was primarily dominated by oxygen fugacity (fO2) and hydrothermal fluids. This finding implies that the Fe isotopic composition of magnetite can serve as a potential geochemical indicator of magmatic Ni‐Cu sulfide mineralisation. [ABSTRACT FROM AUTHOR]

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 δ34SV‐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 δ56FeIRMM‐014 values are 0.57 ± 0.07‰ (2s) and ‐0.62 ± 0.07‰ (2s), respectively. The mean bulk δ65CuNIST 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. [ABSTRACT FROM AUTHOR]

Using boron as a test analyte, laser ablation (LA) solution sampling multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) is proposed and validated as a fast method for isotopic analysis in natural liquids and digested samples without any prior purification process. We demonstrated that the solution reference standard can be used as a bracketing standard for in situ δ 11 B analysis in solids. Based on a sensitivity enhancement of 8- to 9-fold, all testing solutions were diluted in a 5% (v/v) NH 3 ·H 2 O instead of classical 2% (v/v) HNO 3 . With a discrete and minimal sample solvent loading by the LA sampling strategy, it produces nearly "dry" plasma conditions that tolerate the sample matrix remarkably. The memory effect, one of the most difficult challenges in boron analysis, was dramatically eliminated with only 15 s wash time; thus, each analysis took less than 100 s. No significant matrix effects were observed for varying 50-100% boron concentrations in the samples and varying 20-60% NH 3 ·H 2 O matrix used for the dilution, as well as for samples doped with a 1/100 synthetic seawater matrix. The external precision of δ 11 B measurements in NIST 951a was ± 0.30‰ (2SD). Good agreement with the values described in literature studies was achieved for δ 11 B measurements in eight geological reference materials, with precisions between 0.4 and 0.7‰ (2SD), confirming the accuracy of the proposed method. The proposed method offers advantages of simple sample preparation, fast analysis, and little use of chemical reagents.