Chemical characterization of a chromitite reference sample GPt-5 using INAA and ICP-MS

New major, minor, and trace element (Mg, Al, Ca, Sc, V, Cr, Mn, Fe, Co, Ni, Zn, and Ir) abundances for a chromitite reference sample, GPt-5, were obtained using instrumental neutron activation analysis (INAA), and are presented in this report. Replicate analyses of GPt-5 with sample masses ranging from 22 to 64 mg showed a precision of less than 8% (1 s) for most elements, except for Ca and Ir, implying that a small amount of the GPt-5 sample (22 to 64 mg) is enough to obtain representative elemental abundances with the exception of these two elements. The large variation (44.5% for 1 s) observed in the abundance of Ir was attributed to sample heterogeneity. By using isotope dilution inductively-coupled plasma mass spectrometry (ICP-MS) coupled with NiS fire-assay pre-concentration, the concentrations of the platinum group elements (PGE; Ru, Rh, Pd, Os, Ir, and Pt) were determined for the sample powders previously used for the INAA to avoid the sampling bias in assessing the effectiveness of the NiS fire-assay digestion. It was possible to determine the abundance of Ir using both the INAA and ICP-MS, and the values obtained were consistent with each other within the measurement precision. This approach confirmed that the NiS fire-assay procedure applied in this study can digest chromite and that the accurate determination of PGE for chromite-containing rocks can be performed by using our analytical method. Based on the Ru/Rh ratio, the GPt-5 chromitite reference sample was classified as a podiform chromitite.