Exploration of the recently defined Tertiary Cummins-Wanilla Basin on central southern Eyre Peninsula is targeting possible economic buried sedimentary uranium deposits which may have formed in proximity to known uraniferous Precambrian basement rocks. Initial work comprised geochemical sampling of groundwater from local water wells (70 samples), and borehole radiometric logging carried out in 45 of these wells which remained accessible at depth to a wireline gamma ray probe. A geophysical consultant was hired to interpret available aeromagnetic survey data, in order to elucidate the basin structure by interpreting depths to basement. The majority of groundwater samples analysed returned less than 10 ppm U, and subsurface gamma log radiation peak values were between 2 and 4 times background. John Webb reported to Endeavour that the BMR/SADM 1953 aeromagnetic survey data was of too low a sensitivity to be used to reliably contour the basin's outline and subsurface extent. During April 1971 the licensee conducted a programme of scout vertical open hole rotary drilling (14 holes for a total penetration of 2316 feet) to directly test the basin fill, with holes sited along two drill traverses crossing the centre and southern, inferred outflow end of the basin respectively. All of the drillholes were wireline geophysically logged and their cuttings sampled for detecting uranium mineralisation. 13 of the drillholes reached the basement, but one hole, RC2, did not, thereby showing that a previously unknown major palaeochannel sedimentary section >440 feet thick exists in the south near Wanilla. The drilling was successful in locating buried palaeochannel sand, clay and peat strata in various holes, which yielded gamma log radiometric anomalies of up to 1000 counts per second. It was decided to conduct follow-up core drilling to sample the >10x background radiometrically anomalous zones, and this work commenced in June 1971. Full-hole coring attempts made in four holes with conventional rotary core equipment, after a total of 647 feet of hole re-drilling, did not succeed in recovering intact core of the mineralised sediments, and so a side-wall core barrel was instead utilised during July to recover acceptable percentages of core from eight of the original holes, to submit for laboratory testing. The highest uranium content obtained was from hole RC8, which returned 110 ppm U3O8 from the depth interval 112.5-115 feet. Geological logging of the drillholes revealed that the Precambrian basement metamorphic and acid igneous rocks, which form north-south trending ridges and valleys beneath the basin, are overlain by up to 50 feet of saprolitic kaolinite and quartzose material. The weathered layer is succeeded by a thick section of medium to coarse-grained sand which can be up to 100 feet thick. In most of Endeavour's drillholes this sand is succeeded by an Eocene peat-bearing unit up to 60 feet thick, although it reaches 120 feet in hole RC12. This unit is generally overlain by 30 to 50 feet of clay, ferruginous laterite and siliceous duricrust, with a thin layer of kunkar at the surface in the central part of the basin. The main sources of downhole radiation lie in sediments or weathered material in contact with fresh basement rocks, in the peat-bearing sediments, and to a smaller extent in the sand section below the peat.