No abstract available

No abstract available

[en] An experimental study of sulfur isotope separation by infrared photolysis of SF₆, shows evidence of some reaction products. The enrichment coefficient β was measured in pure SF₆ and in mixtures SF₆+H₂ and SF₆+O₂

[en] Sulfur and selenium isotopes are used for labeled compounds and as precursors for radioisotope production; however, both limited availability and high costs are problems. A new method is needed for large-scale separation of theses isotopes. Experimental distillation columns were used to measure isotopic separations for sulfur and selenium compounds. The maximum total isotope separations of ³²S vs. ³⁴S were 1.127 for H₂S, 1.048 for COS, 0.838 for SF₄, and 1.058 for CH₃SH. Relative volatilities of ³²S and ³⁴S are 1.0006 for COS and 0.9976 for SF₄. There is a reverse isotope effect for carbon in COS. No isotopic separation was observed for dimethyl selenide. The lower mass selenium isotopes in H₂Se are more volatile. Distillation is a promising method for separating sulfur isotopes on a production scale. Existing distillation technology produces separated isotopes with an effect similar to that found for sulfur in SF₄. (author). 8 refs.; 2 tabs

[en] On the west side of Lee Bay on the northeast coast of Stewart Island, ventifact cobbles of pyrite-coated granite occur on the beach near the high tide mark and appear to be derived from a sand-cemented gravel deposit that forms a low bank at the back of the beach. The pyrite coat (up to 1 mm thick) completely covers the granitic cobbles and is zoned, with an inner zone of fine-grained colloform pyrite and an outer framboidal zone. Framboidal pyrite is typically formed in anoxic sedimentary environments. Subrounded grains of hematite, ilmenite with hematite blebs, magnetite, feldspar, biotite, quartz and zircon are present in the outer framboidal zone, with some ilmenite and hematite grains being partially replaced by pyrite. The assemblage of ilmenite-hematite-magnetite-biotite-zircon is similar both in mineralogy and size range to that found in heavy mineral beach sands. Sulphur isotope values of the pyrite coat are consistent with formation of the pyrite by microbial sulphate reduction of seawater sulphate. The framboidal texture together with the presence of grains of beach sand in the pyrite coating indicate that it was deposited in a low-temperature sedimentary environment. (author)

[en] Short communication

[en] ALH84001 is a coarse-grained, clastic orthopyroxenite meteorite related to the SNC meteorite group (shergottites, nakhlites, Chassigny). Superimposed upon the orthopyroxene-dominant igneous mineral assemblage is a hydrothermal signature. This hydrothermal overprint consists of carbonate assemblages occurring in spheroidal aggregates and fine-grained carbonate-sulfide vug-filling. The sulfide in this assemblage has been identified as pyrite, an unusual sulfide in meteorites. Previously, Burgess et al. (1989) reported a bulk δ ³⁴S for a SNC group meteorite (Shergotty) of -0.5 ± 1.5%. Here, we report the first martian δ ³⁴S values from individual sulfide grains. Using newly developed ion microprobe techniques, we were able to determine δ ³⁴S of the pyrite in ALH84001 with a 1 α precision of better than ±0.5%. The δ ³⁴S values for the pyrite range from +4.8 to +7.8%. Within the stated uncertainties, the pyrite from ALH84001 exhibits a real variability in δ ³⁴S in this alteration assemblage. In addition, these sulfides are demonstrably enriched in ³⁴S relative to Canon Diablo troilite and sulfides from most other meteorites. This signature implies that the planetary body represented by ALH 84001 experienced processes capable of fractionating sulphur isotopes and that hydrothermal conditions changed during pyrite precipitation (T, pH, fluid composition, etc.). These new data are not consistent with the pyrite recording either biogenic activity or atmospheric fractionation of sulphur through nonthermal escape mechanisms or oxidation processes. This study also demonstrates the usefulness of ion microprobe measurements of sulphur isotopes in constraining conditions on other planetary bodies

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[en] Proteus vulgris metabolized thiosulfate to H₂S. The amount evolved and its sulfur isotope composition identifed it solely with sulfane sulfur. In contrast, Salmonella heidelberg sequentially reduced the sulfane sulfur of S₂O₃^2- with slight enrichment of the evolved sulfide in ³²S and then reduced the sulfonate sulfur of S₂O₃^2- with large isotopic selectivities and an inverse isotopic fractional pattern. The inverse isotope fractionation then reduced the sulfonate sulfur of S₂O₃^2- with large isotopic selectivities and an inverse isotopic pattern for the H₂S derived from the sulfonate sulfur was almost identical to that observed during the reduction of high concentrations of sulfite by S. heidelberg. (auth)

No abstract available