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Sulphur isotope exchange between sulphides and fluid sulphur; consequences for geothermometric application

U. D. Hoeppener, U. E. Kramar and H. Puchelt
Sulphur isotope exchange between sulphides and fluid sulphur; consequences for geothermometric application
European Journal of Mineralogy (October 1990) 2 (5): 655-665

Abstract

The kinetics of sulphur isotope exchange between fine-grained solid sulphides (ZnS, PbS, HgS, sphalerite and galena) and a fluid sulphur phase has been experimentally investigated. The reactions were performed at 250 and 500 degrees C for durations of 0.3 to 5000 h. The experimentally determined time dependence of the isotope distribution in the sulphide phase can be simulated by a combination of three functions. After a rapid change in isotope distribution at the very beginning of the experimental runs, the early stage of exchange can be expressed by the relation: -In (1-F) approximately r . t, where F = fractional isotope exchange in the sulphide, r = reaction rate constant, t = time of exchange. This stage of the process is interpreted as a surface reaction. The subsequent slow equilibration of the bulk of the sulphide can be described by a solid state diffusion model. The reaction rate constants and diffusion coefficients obtained for the synthetic systems all follow the Arrhenius relation. Exchange reactions with natural sulphides give lower exchange rates, different equilibrium values, and more scattered plots. These deviations can be explained by lattice distortions caused by impurities in the natural sulphides. The experimentally derived activation energies for the sulphur isotope exchange in sulphides are within the range 48.2-289.2 kJ/mol, which makes a redistribution of sulphur isotopes probable on geological timescale, even at low temperatures. Natural sulphides show sulphur isotope equilibrium values which differ from those obtained in laboratory experiments with pure sulphides. Inconsistencies in temperature estimates obtained by sulphur isotope geothermometry and fluid inclusion thermometry, for example, can be explained either by the reequilibration of sulphur isotopes in the sulphide or by a shift in the sulphur isotope equilibrium distribution as compared to the standard based on pure sulphides.


ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 2
Serial Issue: 5
Title: Sulphur isotope exchange between sulphides and fluid sulphur; consequences for geothermometric application
Affiliation: Kernforsch. Zentr. Karlsruhe, Inst. Radiochem., D-7500 Karlsruhe, Federal Republic of Germany
Pages: 655-665
Published: 199010
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 35
Accession Number: 1995-050513
Categories: Isotope geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: 5 tables
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Geoline, Bundesanstalt fur Geowissenschaften und Rohstoffe, Hanover, Germany
Update Code: 199518
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