PREPARATION OF SF6 FOR SULFUR ISOTOPE ANALYSIS BY LASER HEATING SULFIDE MINERALS IN THE PRESENCE OF F2 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[sub 2] or BrF[sub 5] methods, verifies that comparable precision and accuracy can be achieved with the new method. The [delta][sup 34]S[sub CDT] and [delta][sup 33]S[sub CDT] values of powdered samples are independent of F[sub 2] gas pressure over a range of from 15 to 120 torr. Furthermore, [delta][sup 34]S[sub CDT] values are independent of SF[sub 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[per thousand]. Interlaboratory comparisons of previously analyzed powders agree as closely as 0.1[per thousand] and disagree by as much as 0.8[per thousand] over a range of [delta][sup 34]S[sub CDT] from [minus]30 to +34[per thousand]. 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[per thousand] for both [delta][sup 34]S[sub CDT] and [delta][sup 33]S[sub CDT], depending on the mineral analyzed.