The Mount Woods South Joint Venture (Adelaide Resources Ltd and Perilya Ltd) successfully made application for a share of the SA Government's PACE Initiative funding in 2004 to test geophysical anomalies located on EL 2901 which were defined by airborne magnetic and ground-based gravity surveys carried out in 2002. That geophysical surveying had defined in detail a 3 km x 2 km oval cluster of three discrete magnetic basement features, termed Gemini A, B and C, aligned with a semi-coincident weak gravity anomaly. The prospect area is located 7 km south-west of the Prominent Hill Cu-Au-Ag-U deposit discovery, and is interpreted from the magnetics to occupy the same geological domain. Geophysical modelling of the magnetic data over Gemini prospect led to interpretations of the Gemini A and Gemini B anomalies being sourced by magnetic material with a maximum depth to top of 250 m, while the Gemini C target was modelled as having a maximum depth to top of 380 m. Based upon these depth estimates, Gemini A and Gemini B were selected for drill testing in the PACE project. Three vertical RC drillholes totalling 910 m were completed in October and November 2004, with the two latter holes successfully penetrating into basement rocks consisting of weathered but recognisable Gawler Range volcanic lithotypes (vesicular basalt, rhyolite and dacite). Accessory titanomagnetite in basaltic rocks in the basement is thought to account for the magnetic anomalies at Gemini, and the presence of mafic volcanics may explain the subtle semi-coincident gravity feature. No economic mineralisation was encountered, however, weak hydrothermal alteration of probable IOCG association was noted. Drillhole sample assay results are not considered to be anomalous, with the possible exception of weakly elevated U over a narrow interval in GEMRC2, and possibly elevated Ce and La in the same hole. Hydrothermal alteration and weak veining are present, and are probably of iron-oxide copper-gold system style. Whether weak alteration of similar style is widespread and of limited significance in the Mount Woods area, or represents possible distal alteration to a significant local hydrothermal system, remains unresolved. The petrological observation that the hydrothermal system once active at Gemini has destroyed primary accessory magnetite is potentially of exploration significance. The Gemini magnetic highs targeted in this drilling project form a cluster that clearly appears to be dissected by two faults or fractures, which are evident as demagnetised linears where magnetite may have been destroyed by hydrothermal alteration. These fractures strike SW and NW, two orientations considered to be of possible genetic significance at the Prominent Hill deposit. Therefore these structures may represent areas of more intense, and possibly more prospective, hydrothermally altered basement at Gemini. Significant volumes of brackish (21,000 ppm NaCl equivalent) ground water were intersected near the basal Permian unconformity in abandoned drillhole GEMRC1, and the contents of such permeable aquifers may form a valuable future water resource for the planned Prominent Hill development.