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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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No abstract available

[en] Structurally-controlled Fe-Ni sulphide ores at Windarra are associated with a metamorphosed, highly magnesian ultramafic unit overlying a thin metasedimentary unit within a metamorphosed ultramafic pile that includes ultramafic flows. A genetic model developed from ore distribution and geochemical data is proposed for the several ore types at Windarra. Disseminated ores originally were formed by gravity concentration of magmatic sulphide liquid droplets in an ultramafic flow or subvolcanic sill. During amphibolite facies metamorphism massive sulphides were generated from more disseminated ores by diffusion and/or segregation processes, and sulphide-rich ores apparently formed at the interface between the ultramafic unit and sulphide-bearing metasedimentary rocks by diffusion of ore components in metasomatic reaction zones. Breccia ore subsequently was formed by deformation of massive sulphides developed along this contact. Sulphur isotope ratios for the ore types show a tendency towards lighter means and a greater range corresponding to the following order: massive ore (mean delta³⁴S +0.4⁰/₀₀, range 0.8⁰/₀₀), disseminated ore (-0.5, 2.4), breccia ore (-1.3, 3.4), metasedimentary ore (-1.6, 4.7). Sulphides from the adjacent metasedimentary rocks, including the main unit underlying the ultramafic pile, show similar isotopic distributions to the metasedimentary ore. These data support a magmatic origin for the disseminated ore and indicate that massive sulphides did not develop from a sulphide pool beneath disseminated sulphides at the magmatic stage. The data are also consistent with derivation of sulphides in the metasedimentary rocks and metasedimentary ore by inorganic precipitation of volcanically derived sulphur. The origin of sulphur in the breccia ore cannot be defined unequivocally by the sulphur isotope data. (auth.)