Geophysical Characteristics of the Carrapateena Iron-Oxide Copper-Gold Deposit

Abstract

The Carrapateena iron-oxide copper-gold deposit is located 160km north of Port Augusta, within the eastern margin of the Gawler Craton, South Australia. The deposit was discovered, in 2005, by RMG Services Pty. Ltd. Subsequent exploration by joint venture partner, Teck Australia Pty. Ltd., demonstrated strong similarities with Olympic Dam, albeit at a much smaller scale. In April 2011, Oz Minerals purchased Carrapateena and soon afterwards released an inferred resource for the southern portion of the deposit of 203Mt @ 1.31% Cu, 0.56g/t Au, 270ppm U3O8 and 6g/t Ag. Carrapateena lies beneath approximately 470m of moderately conductive Stuart Shelf sediments, presenting significant technical challenges to exploration. Therefore, geophysical surveys played an important role in both discovery of the deposit and subsequent delineation. Work undertaken by Teck comprised laboratory petrophysical measurements and gravity, aeromagnetic, IP/resistivity/MT, EM and down hole surveys. Results show that Carrapateena lies on the south-western margin of a broad magnetic anomaly of moderate amplitude, being associated with a weak, discrete, ellipsoidal magnetic response, and near-coincident, weak, bullseye gravity high. The mineralised system is also associated with a distinct conductivity anomaly. However, chargeability data are less convincing, being strongly impacted by the thick and conductive nature of the cover sequences. EM surveys did not provide any responses attributable to bedrock conductors and are not recommended for this style of deposit. The observed geophysical responses at Carrapateena are dominated by the presence of Fe-oxides, particularly hematite, with sulphide mineralisation playing a lesser role.