A Strontium isotope study of a high-K diorite complex at Yeoval, N.S.W. (Australia) points to clear time differences (40 m.y.) between the diorite suite (gabbro-diorite-grano-diorite) and surrounding granites. Such a time interval, in association with other data, precludes a genetic relationship between these rock groups whereas the data support a common origin for the diorite suite and associated andesitic volcanics. The low (0.705) initial Sr ratios for the diorite suite and volcanics are similar to those of other diorite and andesite occurrences.