Molybdenum isotopic compositions in iron meteorites and molybdenites determined by thermal ionization and multiple collector inductively coupled plasma mass spectrometry

Large mass-independent molybdenum isotope abundance anomalies in iron meteorites were determined with Thermal Ionization Mass Spectrometry (TIMS). The molybdenum isotope abundance anomalies vary from -0.6% to 0.8% measured relative to a 99.993% pure molybdenum standard from Johnson Matthey Chemicals Limited (JMC 726 Laboratory No. S-8555). The large enrichments and depletions of the molybdenum isotopes in the iron meteorites likely reflect large scale isotopic heterogeneity in the early solar system.; Ore genesis processes are thought to cause small mass-dependent variations of terrestrial molybdenite ores and very high precision measurements of isotope abundances are needed to resolve these deviations. Multiple Collector Inductively Coupled Mass Spectrometry (MC-ICP-MS) combined with a rigorous double spike correction was used to determine the molybdenum isotope abundance variations of selected molybdenite samples. The molybdenites are mass fractionated by ∼0.02% per atomic mass unit relative to the laboratory standard.