A newly synthesized reference material for in situ sulfur isotope measurement of sphalerite using laser ablation MC-ICP-MS

Abstract

Sulfur isotopes are important tracers in various geochemical processes. A matrix-matched reference material is essential for in situ sulfur isotope ratio measurement in sphalerite (ZnS), an abundant zinc sulfide in base metal deposits. In this study, natural sphalerite powders (GBW07270) were ground into ultra-fine powders and then sintered by using a plasma-activated sintering (PAS) method at 1000 °C and 50 MPa for 10 minutes. The synthesized sphalerite has a smooth surface and dense structure, making it suitable for laser ablation analysis. To investigate whether the PAS-synthesized sphalerite is an appropriate matrix-matched reference material for in situ sulfur isotope determination, a large number of in situ S isotope measurements were performed on the PAS-synthesized sphalerite by laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). The LA-MC-ICP-MS results are highly consistent and yield a mean δ³⁴S_V-CDT value of −5.44 ± 0.20‰ (2SD, n = 1008), which agrees well with that measured by gas source isotope ratio mass spectrometry (GS-IRMS). Therefore, the PAS-synthesized sphalerite has a homogeneous sulfur isotopic composition and is a suitable matrix-matched reference material available for in situ S isotope measurements of sphalerite.