A Simplified Method for the Determination of Re and PGE Mass Fractions, and Os Isotope Ratios in Ultramafic Rocks Combined with Se-SnCl2 Co-Precipitation

A new measurement procedure was developed for determining Re, PGE mass fractions and Os isotope ratios in geological samples using ICP-MS and N-TIMS. Two sample decomposition techniques, including Carius tube digestion and NaOH-Na₂O₂ fusion, were used to compare digestion efficiency. Osmium was separated from the sample matrix by distillation, while Re and other PGE were separated by Se-SnCl₂ co-precipitation and further purified using chelating resin. Rhenium and PGE mass fractions in WPR-1, WMG-1 and GPt-6 demonstrate good precision (RSD), with values under 5% for acid digestion and 10% for alkaline fusion. Relatively poor precision was obtained for the results of TDB-1, WGB-1, GPt-3, GPt-4 and CHR-Bkg, due to sample heterogeneity at a test portion size of 1 g. Furthermore, a more significant variance of PGE data was observed in DZ∑-1, DZ∑-2, GPt-5, GAN Pt-1 and HHH. From the point of view of sample digestion, refractory minerals (e.g., laurite, PGE alloys) can be completely decomposed by the NaOH-Na₂O₂ fusion process, resulting in much higher PGE mass fraction yields and thereby making the heterogeneity of mantle rocks and chromitites visible. Consequently, the proposed method could significantly simplify the chemical procedure and yield more accurate data when measuring ¹⁸⁷Re-¹⁸⁷Os-PGE in samples with very refractory minerals.