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High precision analyses of all four sulfur isotopes in four pyrite and three sphalerite standards and in working reference samples were carried out using a CAMECA NanoSIMS 50L instrument. The measurements were made using three different settings of the Faraday cup (FC) and/or electron multiplier (EM) detectors, which meet different requirements for spatial resolution. The effects of EM aging and quasi-simultaneous arrival were corrected before the calibration of instrumental mass fractionation by a standard-sample-standard bracket method using the standards measured together with the samples. High analytical precision was achieved by counting 32S, 33S and 34S with the FCs and 36S with the EM (i.e. the FC-FC-FC-EM mode) using a 0.7 µm diameter ~350 pA Cs+ primary beam and scanning over areas of 5 x 5 µm². The standard deviations of spot-to-spot and grain-to-grain (external reproducibility 1 SD) measurements were less than 0.3, 0.3 and 0.7% for δ33 S, δ34 S and δ36S, respectively. To achieve a higher lateral resolution of ≤2 x 2 µm², the Cs+ beam was reduced to 7-10 pA with a diameter of 200 nm; S was measured with the FC and the other signals were measured with the EMs. The external reproducibility (1 SD) was better than 0.5& for both δ33S and δ34S and was 3% for δ36S. To achieve the highest lateral resolution for the analysis of submicron-sized sulfides, ~0.7 pA Cs+ beam of ~100 nm diameter was used, scanning over areas of 0.5 x 0.5 µm², and all 32S, 33S and 34S were counted with the EMs. The external reproducibility (1 SD) was better than 1.5& for both δ33S and δ34S. These three modes have important applications in the isotope analysis of micron-sized sulfur samples, such as pyrite framboids and areas of complex zoning in sul de minerals. [ABSTRACT FROM AUTHOR]

Reference materials play a crucial role in high accurate isotope and trace element analysis by secondary ion mass spectrometry, and they are used to calibrate instrumental fractionation of samples with various compositions. However, it is often a challenge to prepare natural or synthetic reference materials that are homogenous on a micron or even sub-micron scale. We report a novel method to synthesize homogeneous reference materials via sintering nano-crystals. Coarse-grained crystals (100-500 µm) of calcite have been grown from a starting material of 20-40 nm calcite powder at 1000 °C and 1 GPa for 24 h, which is ~400 °C below the liquidus line of calcite under the same pressure. The non-molten sintering process and high temperature of the experiments ensure a homogeneous composition of the synthesized calcite. In situ analysis of 18O/16O ratios of the synthetic calcite with a Cameca NanoSIMS 50L revealed no detectable variation within the analytical uncertainty (0.5‰, 1SD), which was further confirmed using a Cameca IMS 1280 with a higher precision (0.1‰, 1SD). In addition, trace elements, Sr and P, are also homogeneous in the synthetic calcite. Another important advantage of this method is that the compositions of synthetic reference materials can be accurately and conveniently determined from the bulk starting materials using independent analytical techniques. [ABSTRACT FROM AUTHOR]