I propose to develop a geochronometer of platinum-rick minerals based on the decay of 190Pt to 186Os. Despite the long half-life (600 b.y.) and low parent isotope abundance (0.013%), I have established in preliminary work that sperrylite (PtAs2) has very large Pt/ZOs ratios, and should generate easily measurable quantities of radiogenic 186Os. I will develop a suitable chemistry for Os separation, and determine parent/daughter isotope ratios using isotope dilution/ion microprobe analysis. The half-life of 190Pt will be precisely determined using natural sperrylites of well documented age. Other Pt-rich minerals will be surveyed for possible use with this decay scheme, and a variety of Pt ore deposits will be dated to test the applicability of the Pt-Os geochronometer.
