The variation of sulfur isotopic composition (δ34S) in sulfide ores is important to understand ore forming processes. In nature, the δ34S isotope ratio varies between -30‰ and +30‰ or even greater; this large variation implies that a precision of about 1‰ is sufficient for many geological investigations, especially for low-temperature processes. Only a limited number of sulfur isotope standard reference materials are commercially available from IAEA (S1, S2, S3, S5, SO5 and SO6) and NIST (RM 8556 and 8557), as fine grain powders (0.5 g) originally prepared for gas sourced mass spectrometry. The IAEA sulfur isotope reference materials must be pressed into pellets for laser ablation analysis, which is difficult as the mass is only 0.5g. In addition, it ablates as a pressed powder which is different than crystallized minerals such as sphalerite, pyrite and other natural samples, possibly resulting in fractionation. The precision and accuracy for δ34S and δ33S analysis by in-situ laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) is hampered by the lack of matrix matched reference materials. Using the MUL-ZnS-SI, this problem can be overcome for sphalerite (ZnS), an important carrier of critical metals like Ge, Ga and In. The material was produced by pressing commercially available ZnS nano-powder to pellets and subsequent sintering using Ar as inert gas. The ZnS shows a homogeneous distribution of the δ34S and δ33S isotopes as demonstrated by LA-MC-ICP-MS. LA-MC-ICP-MS analysis gives a variation of δ34S between 20.30 ‰ and 20.85 ‰, and of δ33S between 10.18 and 10.87 ‰. This variation is suitable for the sulfur isotope system in natural sulfides, especially in sphalerite that may show a strong variation within single grains (Cerny 1989). The benefit of MUL-ZnS-SI-1 is that this material can be refurbished by repolishing and has similar ablation properties than natural minerals.



References:
ROBINSON, B.W., "Sulphur isotope standards", Reference and intercomparison materials for stable isotopes of light elements, Proceedings of a consultants' meeting held in Vienna, 1-3. Dec. 1993, IAEA-TECDOC-825, IAEA, Vienna, Austria (1995) 39-45.

Cerny I. (1989) Die karbonatgebundenen Blei-Zink-Lagerstätten des alpinen und außeralpinen Mesozoikums. Die Bedeutung ihrer Geologie, Stratigraphie und Faziesgebundenheit für Prospektion und Bewertung. Archiv für Lagerstättenforschung Geologische Bundesanstalt, 11, 5-125