The Pilanesberg Complex and related igneous rocks

Abstract The Mesoproterozoic Pilanesberg Complex (PC) is one of the world’s biggest and best-preserved complexes of intrusive and extrusive felsic alkaline and peralkaline igneous rocks and belongs, together with smaller centres of alkaline silicate and carbonatitic rocks that are mainly concentrated to its east, to the Pilanesberg Alkaline Province (PAP). Recent work on this province has varied from age dating to mineralogy and geochemistry to paleomagnetism. New U-Pb dating on the silicate rocks converges on intrusive ages of ca. 1.4 Ga, but the carbonatite complexes need revisiting in view of their more scattered and up to 150 Myr younger ages. The new ages present a problem for paleomagnetic results, with different apparent palaeopoles for rocks of broadly the same age. The PC has been found to contain a highly peralkaline agpaitic ignimbrite unit, the Beacon Heights Phonolite, previously classified as a tinguaite sheet. Mineralogical investigations on the peralkaline units have led to the discovery of the mineral pilanesbergite, and have shown the importance of varying levels of water activity on the mineral assemblages. Enrichments of rare elements (“critical minerals”) are modest in the PC, and the carbonatites within the province may prove to be more prospective.