New Potential Sulfide Reference Materials for Microbeam S-Fe-Cu Isotope Measurements

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 delta S-34(V-CDT) for Ll-Cpy, Ll-Po, Ll-Sp are 6.13 +/- 0.37 parts per thousand (2s), 6.42 +/- 0.37 parts per thousand (2s) and 6.28 +/- 0.38 parts per thousand (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 delta Fe-56(IRMM-014) values are 0.57 +/- 0.07 parts per thousand (2s) and -0.62 +/- 0.07 parts per thousand (2s), respectively. The mean bulk delta Cu-65(NIST SRM 976) value of Ll-Cpy is 0.57 +/- 0.06 parts per thousand (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 mu m spatial resolution), and can be used as potential calibration materials for in situ S-Fe-Cu isotope measurements.