The Mesoproterozoic Gawler Range Volcanics - Hiltaba Granite Suite - related Olympic Dam style Cu-U-Au mineralisation, and Menninnie Dam replacement style Pb-Zn-Ag mineralisation, have served to raise the prospectivity of rocks in and underlying the Gawler Ranges. The release by CRA of detailed aeromagnetic data in 1993 prompted renewed industry interest in the YARDEA 1:250 000 map area. Geological investigations and drilling were undertaken by MESA in 1994, centred on the search for possible vents and intrusions with associated late stage fluid conduits and alteration haloes. 63 reverse circulation and 5 deeper air-hammer drilled holes (total 2558 m) were drilled to investigate basement geology and structure in areas selected on the basis of interpreted regional aeromagnetic anomalies. The holes were sited along 18 confirmatory ground magnetic and gravity traverses laid out across these anomalies. This work uncovered: - a possible vent structure with exotic matrix supported blocks in the Yardea Homestead area; - a possible concealed vent with associated alteration and silicification, WNW of Kolendo; - a haematite breccia - epithermal quartz stockwork above a possible granite intrusion located near Sherry Dam and Tanner Dam; - evidence of fluid flow in open fractures, with associated terminated quartz crystals and minor fluorite, in outcrop and in drill cuttings. During drilling, additional notice was taken of the nature and depositional history of the sedimentary cover, if present, besides testing of the salinity and potential flow of any groundwater encountered, particularly when holes were sunk in the vicinity of inferred Tertiary palaeochannels. No aquifers containing potable water were found.