Granodiorite core recovered from Moomba 72 has enabled recent recognition of an altered zone at the top of pre-Permian 'basement'. This altered zone has been previously misinterpreted as Early Permian Tirrawarra Sandstone. Consequently, the depth equivalent of a third of a well for the Moomba Field has historically been needlessly drilled into 'basement'. In addition, 15 drill stem tests have effectively been wasted testing for hydrocarbon fluids in the pre-Permian. The long-held assumption that the Tirrawarra Sandstone (occasionally informally termed 'Tirrawarra conglomerate') occurs in the Moomba Field was inspired by the presence of a marked conglomeratic facies at the top of the Tirrawarra Sandstone in the neighbouring Big Lake Field. On well wireline logs commonly used for subsurface stratigraphic correlation in the two fields, both the altered Moomba granodiorite and the Big Lake 'Tirrawarra conglomerate' display elevated gamma-ray values which exceed 200 API. It would further appear that the alteration zone now recognised in granitoids of the Carboniferous Big Lake Suite can similarly be found in other Warburton Basin lithologies subcropping beneath the Cooper Basin. The significance and nature of this zone is currently unknown. However, in Lycosa 1 this zone appears to act as a seal for deeper Dullingari Group reservoirs.