PREPARATION OF SF6 FOR SULFUR ISOTOPE ANALYSIS BY LASER-HEATING SULFIDE MINERALS IN THE PRESENCE OF F2 GAS

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 SO2 or BrF5 methods, verifies that comparable precision and accuracy can be achieved with the new method. The deltaS-34(CDT) and deltaS-33(CDT) values of powdered samples are independent of F2 gas pressure over a range of from 15 to 120 torr. Furthermore, deltaS-34(CDT) values are independent of SF6 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 parts per thousand. Interlaboratory comparisons of previously analyzed powders agree as closely as 0.1 parts per thousand and disagree by as much as 0.8 parts per thousand over a range of deltaS-34(CDT) from -30 to +34 parts 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 parts per thousand for both deltaS-34(CDT), and deltaS-33(CDT), depending on the mineral analyzed.