A potential stibnite reference material for sulfur isotope determination by LA-MC-ICP-MS

Abstract

The identification of metal and sulfur sources in hydrothermal Sb ore deposits has long been recognized as a challenging task. Stibnite is commonly found as one of the primary ore minerals in most antimony deposits, and it can even occur as the sole ore mineral in some large antimony deposits; therefore, the sulfur isotope composition of stibnite often contains invaluable information for exploring the origin and ore-forming processes of Sb deposits. A well-characterized and matrix-matched material is imperative for conducting in situ S isotope microanalysis. However, the lack of standardized materials for stibnite hinders precise determination of sulfur isotope composition, thereby impeding the application of stibnite sulfur isotopes in deciphering the ore genesis of Sb deposits. The present study recommends the utilization of a natural stibnite (BJ-Snt) as a potential reference material for S isotope analysis employing laser ablation multicollector inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS). The sulfur isotope compositions, backscattered electron (BSE) maps, mineral phases, and elemental compositions were analyzed to evaluate the homogeneity of the stibnite BJ-Snt. The method validation was conducted through comparison of S isotope values obtained by LA-MC-ICP-MS and IRMS, as well as intercomparisons with two other laboratories. The consistent findings have established that BJ-Snt is a suitable standard for bracketing in situ S isotope measurement using LA-MC-ICP-MS, and the recommended δ³⁴S value determined by IRMS was −0.71 ± 0.32‰ (2 s, n = 15).