An emplacement age of 1497 ± 38 Ma for the felsic Spilsby Suite exposed on islands in southern Spencer Gulf is anomalously young with respect to magmatism elsewhere within the Gawler Craton, and is approximately 75 to 90 million years younger than the voluminous anorogenic Gawler Range Volcanics and comagmatic Hiltaba Suite. Comparable U-Pb zircon ages have not yet been recorded anywhere else within South Australia, and the nearest known equivalent may be the Mundi Mundi Granite of western New South Wales. The Spilsby Suite is highly fractionated, is enriched in high-field strength elements, particularly Rb, Th and Ce, and contains anomalous W and Mo mineralisation as has been mapped by the SADM on Spilsby and Langton islands.