Simultaneous measurement of Re–Os and S isotopic compositions of sulfur-bearing minerals using a Carius tube digestion-based N-TIMS and MC-ICP-MS approach

Abstract

This study reports an improved procedure for the simultaneous determination of Re–Os and S isotopic compositions of sulfur-bearing minerals using negative thermal ionization mass spectrometry (N-TIMS) and multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS), respectively. This approach uses a Carius tube digestion technique during inverse aqua regia digestion to avoid the incomplete decomposition of sulfide minerals and the partial loss of S and Os during acid digestion. The sequential separation and purification of S and Re from sample matrix elements is undertaken after Os separation by CCl₄ solvent extraction and utilizes a two-stage tandem column setup using cation and anion exchange resins. Sulfur is not adsorbed onto either of the cation or anion exchange resin columns and can be directly eluted using 0.1 mol L⁻¹ HNO₃, whereas Re is adsorbed onto the anion exchange resin column. This approach allowed the quantitative recovery of S (99.8%) and Re (99.7%), and the efficient removal of matrix elements from the final purified sample. The δ³⁴S values of IAEA S-2, S-3, and IAPSO seawater standards determined during this study (calibrated using the IAEA S-1 standard) are consistent with the certified values and are of higher precision than the values obtained using conventional analytical techniques. Our approach can also be used with different kinds of sulfide minerals. This combined Re–Os–S isotopic analysis provides useful information on the timing of ore deposit formation and constrains the source of the ore-forming fluid material. This approach also allows the determination of Re–Os and S isotopic compositions of single sample digestion, thereby avoiding problems with sample heterogeneity that can arise when comparing S and Re–Os isotopic data generated by conventional approaches.