Brownfields copper exploration undertaken by WMC in the Phillips Ridge area, located about 24 km east-southeast of the Olympic Dam discovery, initially consisted of the acquisition of gravity and ground magnetic traverses across a regional gravity anomaly which it was hoped might be a continuation of the Olympic Dam coincident magnetic and gravity geophysical feature. However, the newly detailed gravity anomaly at Phillips Ridge showed less symmetry, and appeared to be a more complicated feature. Three possible drilling sites were chosen nevertheless, and in May 1977 a single vertical diamond drillhole, PD1a, was completed to a total depth of 414 m at one of them, bottoming beneath a fault zone in a leucocratic, banded biotite-rich gneiss. This drillhole encountered a green, chloritic quartz-veined basaltic rock at 336 m depth, which contained minor pyrite and chalcopyrite (best drill core assay result 7.5 m @ 0.25% Cu from 340 m depth). The metavolcanic unit, which is 18 m thick, overlies chlorite, haematite and sericite - altered granitic basement. While the results of this drilling were being evaluated, attention was shifted to another regional gravity anomaly present in the vicinity of Bills Lookout, immediately east of the Andamooka Opalfield. After some delays experienced in gaining on-ground access, further gravity (1624 stations read) and ground magnetic surveying was performed in this location. A strong positive gravity anomaly was detected that coincides with a strong negative magnetic anomaly, approximately 2 km north-east of Teatree Dam. WMC thought that the negative magnetic anomaly could be caused by a remanently magnetised body lying at an estimated 800 m below the surface, and made plans to drill a deep stratigraphic test hole into this target.