TARGET: Possible buried stratiform or Mississippi Valley type base metal deposits, that may have formed within the eastern Officer Basin where the Middle Cambrian Observatory Hill Beds formation onlaps an east-northeast trending basement ridge. The latter feature had previously been inferred by SADME to exist on the basis of their interpretation of regional aeromagnetic survey data. EXPLORATION: Ground gravity and magnetic survey traverses were run over the most likely areas of shallow basement, followed by the drilling of 10 diamond cored stratigraphic holes totalling 2549.5 m. These holes were put down to reach the ?Archaean basement at selected ground geophysical anomalies newly disclosed along 9 traverses, where 12 rotary/percussion precollared drilling sites had been prepared. RESULTS: Gneissic granite basement was penetrated by all of the currently completed drillholes at depths of between 132 and 463 m, thus proving the structural interpretation of an elongate shallowly buried ridge (later designated the Nawa Ridge) which separates the Tallaringa Trough from the Officer Basin proper. Probable Permian sediments of the Arckaringa Basin were encountered in all holes. However, the target Observatory Hill Beds unit was only intersected in 5 of the WMC drillholes, and therefore may largely flank but clearly does not drape over the Precambrian basement ridge. The Cambrian sediments encountered in holes ODB6, ODB7 and ODB9 are sandy and lack carbonate horizons. Information from adjacent holes ODB10 and ODB12 located on the south-eastern side of the ridge shows that the carbonate facies rocks become shallower heading towards the ridge. No anomalous base metal values were found in assays of drill core from hole ODB9.