U AND Pb ISOTOPE ANALYSIS OF URANIUM MINERALS BY ION MICROPROBE AND THE GEOCHRONOLOGY OF THE McARTHUR RIVER AND SUE ZONE URANIUM DEPOSITS, SASKATCHEWAN, CANADA

A method for in situ U–Pb isotopic analyses by secondary ion mass spectrometry (SIMS) has been developed for uranium minerals with a range of chemical compositions. This method combines the advantages of conventional U–Pb dating (i.e., use of concordia) and in situ analysis, and therefore is ideally suited for the study of chemically complex and fine-grained uranium oxides associated with uranium deposits. An ion-yield normalizing coefficient (� SIMS) that accounts for variation in relative ion-yields with chemical composition of the mineral of interest was calculated using uraninite standards that cover a range of U