Laser-ablation ICP-MS measurements of Re/Os in molybdenite and implications for Re-Os geochronology

Jan Košler, Antonio Simonetti, Paul J. Sylvester, Richard A. Cox, Michael N. Tubrett, Derek H.C. Wilton

Research output: Contribution to journalArticlepeer-review

53 Scopus citations

Abstract

Laser-ablation quadrupole ICP-MS analyses of molybdenite samples from Preissac, Quebec, and Mokrsko, Bělčice and Kašperské Hory gold deposits in the Bohemian Massif, Czech Republic, for Re and radiogenic 187Os suggest the presence of strong zoning in Re and in 187Os/187Re values within grains. The zoning patterns indicate decoupling of daughter 187Os from parent 187Re after molybdenite crystallization. Whereas Re is not homogeneously distributed in the molybdenite grains studied, the lack of correlation between the calculated 187Os/187Re value and the Re content also reflects the mobility of 187Os within individual grains of molybdenite. Such decoupling of Re and Os could affect the accuracy of Re-Os ages if disturbed portions of molybdenite are sampled for dating by conventional isotope-dilution N-TIMS or ICP-MS techniques. The results re-emphasize the critical need for homogenization of quantities of molybdenite sufficiently large to capture the bulk Os/Re of the sample to be dated by these methods. Laser-ablation sampling, when used with a multicollector magnetic-sector ICP-MS instrument, is able to produce Re-Os ages with a precision better than 2% (1σm from single spots in certain old and Re-rich molybdenite grains, but would be difficult to use as a dating tool given the extreme 187Os/187Re heterogeneity seen in individual grains.

Original languageEnglish
Pages (from-to)307-320
Number of pages14
JournalCanadian Mineralogist
Volume41
Issue number2
DOIs
StatePublished - Apr 2003

Keywords

  • Age dating
  • Element decoupling
  • Laser-ablation ICP-MS
  • Molybdenite
  • Re-Os

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