Sr isotope ratios indicate that the Herbert River and Elizabeth Creek Granites at the northeastern margin of the Georgetown Inlier of northeast Queensland are closely related to each other and to the spatially-associated Featherbed Volcanics. Although there is field evidence for a range of granite ages, the isotopic evidence is that a large proportion of the granite was formed within the Late Carboniferous (328 ± 5 m.y.). The Featherbed Volcanics are about 30 m.y. younger, at 299 ± 13 m.y. These are post-dated by other granites of the region.