The remarkable Re-Os chronometer in molybdenite: how and why it works (with a comparative look at the Lobash Mo Deposit, Russia)

The Re-Os (rhenium-osmium) chronometer applied to molybdenite (MoS₂) is now demonstrated to be remarkably robust, surviving intense deformation and high-grade thermal metamorphism. Successful dating of molybdenite is dependent on proper preparation of the mineral separate and analysis of a critical quantity of molybdenite such that recognized decoupling of ¹⁸⁷Re parent and ¹⁸⁷Os daughter within molybdenite is overcome. The use of a reference or control sample is necessary to establish laboratory credibility and for inter-laboratory comparisons. High precision, accurate, and reproducible age results are derived through isotope dilution and negative thermal ion mass spectrometry (ID-NTIMS). The laser ICP-MS technique should not be used for Re-Os dating of molybdenite. Successful dating of molybdenite by Re-Os is recognized when Re-Os age results are in agreement with the generally robust U-Pb dating method and with observed geologic relationships. The Rb-Sr, K-Ar, and ⁴⁰Ar/³⁹Ar chronometers are susceptible to chemical and thermal disturbance, particularly in terranes that have experienced subsequent episodes of hydrothermal/magmatic activity, and therefore should not be used as a basis for establishing accuracy of the Re-Os dating, as has been done in the past.