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

• Published in: Canadian mineralogist Vol. 41; no. 2; pp. 307 - 320
• Main Authors: Kosler, J, Simonetti, A, Sylvester, Paul J, Cox, R. A, Tubrett, M. N, Wilton, D. H. C
• Format: Journal Article
• Language: English
• Published: Mineralogical Association of Canada 01-04-2003
• Subjects: Abitibi Belt; absolute age; accuracy; Belcice Mountains; Bohemian Massif; Canada; Canadian Shield; Central Europe; chemical composition; concentration; detection limit; Eastern Canada; Europe; geochemistry; Geochronology; grains; ICP mass spectra; instruments; isotope fractionation; Kasperske Mountains; laser ablation; laser methods; mass spectra; metal ores; metals; methods; mineralization; Mokrsko Mountains; molybdenite; North America; osmium; platinum group; Precambrian; precision; Quebec; Re-187/Os-187; Re/Os; rhenium; samples; spectra; sulfides; Superior Province; techniques; X-ray diffraction data
• ISSN: 0008-4476; 1499-1276; 1499-1261
• DOI: 10.2113/gscanmin.41.2.307

Results for molybdenite samples from Preissac, Quebec, and Mokrsko, Belcice and Kassperske Hory Au 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. Such decoupling could affect the accuracy of Re-Os ages if disturbed patterns of molybdenite are sampled for dating by conventional isotope-dilution N-TIMS or ICP-MS techniques. There is a critical need for homogenization of quantities of molybdenite sufficiently large to capture the bulk Os/Re of the sample. LA-sampling, when used with a multicollector magnetic-sector ICP-MS instrument, is able to produce Re-Os ages with a precision better than 2% 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.