Preparation of SF 6 for sulfur isotope analysis by laser heating sulfide minerals in the presence of F 2 gas

Abstract

The feasibility of in-situ fluorination of sulfide minerals for sulfur isotope analyses has been demonstrated. Laser fluorination of powdered samples, previously analyzed by conventional bulk SO 2 or BrF 5 methods, verifies that comparable precision and accuracy can be achieved with the new method. The δ 34 S CDT and δ 33 S CDT values of powdered samples are independent of F 2 gas pressure over a range of from 15 to 120 torr. Furthermore, δ 34 S CDT values are independent of SF 6 yields from 40 to 100% for powders that do not fluorinate spontaneously at room temperature. The precision of replicate analyses of powdered pyrite, troilite, chalcopyrite, sphalerite, galena, acanthite, and greenockite is typically 0.1–0.2‰. Interlaboratory comparisons of previously analyzed powders agree as closely as 0.1‰ and disagree by as much as 0.8‰ over a range of δ 34 S CDT from −30 to +34‰. The technique of in-situ laser fluorination was validated by comparison of analyses of side-by-side laser craters and powders from drill holes in polished sulfide mineral surfaces. For isotopically homogeneous samples, laser craters and drill hole powders agree within 0.1–0.3‰ for both δ 34 S Cdt and δ 33 S CDT , depending on the mineral analyzed.