The 187Re-187Os and 190Pt-186Os Radiogenic Isotope Systems: Techniques and Applications to Metallogenic Systems

Abstract Rhenium, Os, and Pt are redox sensitive elements that concentrated in highly reducing environments such as those associated with black shales but mobile under more oxidizing conditions arc volcanism. They chalcophile many terrestrial ore-forming environments, their isotopic systematics provide unique opportunities to date the formation of sulfide ore deposits understand petrogenesis. Fractional crystallization magmatic ores generates primary variations Re/Os Pt/Os allow mineral whole rock isochron ages be determined discrimination crustal mantle sources based on initial Os compositions. Molybdenite is especially well suited for geochronology due its high resistance resetting. Rhenium concentrations molybdenite tend reflect composition or provenance fluids, higher primitive oxidized fluids lower evolved and/or reduced conditions, although local regional factors also have a significant influence. Many studies used pyrite dating typically low Re concentration, variable (reflecting fluid mxing), susceptibility re-equilibration makes use geochronometer problematic cases. Other minerals bornite arsenopyrite shown promise Re–Os isotope additional needed evaluate broader applicability deposits. The isobaric beta decay parent 187 has restricted investigation this system by microbeam techniques ion microprobe laser ablation mass spectrometry, geochronology. This requires either chemically processing sample separate novel collision-cells preferentially ionize during analysis. Thermal ionization spectrometry (TIMS) inductively-coupled plasma (ICPMS) most widely applied Re-Pt-Os analyses. Specialized digestion ensure equilibrium between isotopically enriched spikes dilution measurements required. chapter briefly reviews development Re- 190 Pt- 186 systems earth science, physico-chemical controls behavior applications metallogenic systems.