DETERMINATION OF OSMIUM ABUNDANCE IN MOLYBDENITE MINERAL BY ISOTOPE-DILUTION MASS-SPECTROMETRY WITH MICROWAVE DIGESTION USING POTASSIUM DICHROMATE AS OXIDIZING-AGENT

An efficient and reliable method was developed for the accurate determination of osmium abundance in molybdenite (MoS2) by isotope dilution mass spectrometry. The sample solution of molybdenite was prepared by acid decomposition using the microwave digestion technique with addition of potassium dichromate (K2Cr2O7) as oxidizing agent and osmium in the sample solution was purified by distillation.There was no change in the ratios of Os-187 derived from molybdenite relative to Os-192 of an osmium standard with progress of distillation, indicating that isotopes of osmium derived from the two sources were completely homogenized. The precision of the osmium abundance obtained in the developed method was 1 % (1-sigma). The technique was applied to a natural molybdenite sample for Re-Os age determination and the result was in good agreement with that obtained by the U-Pb method for zircon.