Re–Os dating of molybdenite via improved alkaline fusion

Abstract

This study describes an improved alkaline fusion technique for the Re–Os dating of molybdenite. The molybdenite sample was digested in a zirconium crucible with NaOH and carbonized flour at 700 °C. The flour can reduce Os from a high oxidation state to a lower oxidation state during the high-temperature digestion so that isotope equilibration can be reached between the spike and the sample. Less amount of NaOH was used compared with the previously reported technique, lowering the procedure blank. Rhenium was separated by kinetic absorption with an anion exchange resin, and Os was purified by distillation with aqua regia and H₂O₂. Both Re and Os isotope compositions were measured via inductively coupled plasma mass spectrometry. The results obtained for the molybdenite reference material, JDC, were in good agreement with certified values, demonstrating that the proposed method is efficient for the Re–Os dating of molybdenite. Compared with Carius tube and high-pressure asher sealed acid digestion methods, the improved alkaline fusion method yields comparable Os blanks but has a more simple, quick, and secure procedure.