Rhenium-osmium geochronology of oxide minerals

187Re-187Os analysis of magnetite and other oxide minerals from various well dated geological settings (kimberlites, lamprophyres, Manicouagan impact melt rock, Great Bear magmatic zone iron ore deposits and Laramie Anorthosite complex) worldwide have been used to investigate the potential for precise geochronology. 187Re-187Os isotopes in groundmass oxide minerals from kimberlites and lamprophyres are not suitable for emplacement geochronology due to low Re contents and large quantities of un-radiogenic Os. TRD and TMA ages can be calculated however, and correlate well with previously published depletion ages and large magmatic events in the overlying crust, indicating the effectiveness of this technique. Geochronology using magnetite from the remaining settings is im-precise due to very low Re and Os contents but the ages produced are in the correct area. Young ages produced from the Laramie anorthosite complex indicate that magnetite may have a low closure temperature to Os diffusion (∼200-300°C).