Geophysical characteristics of shear zone-hosted Proterozoic gold, Nuckulla Hill, South Australia

Abstract

Gold mineralisation was discovered at the Sheoak and Myall prospects in the Nuckulla Hill region of the central Gawler Craton in December 1995 and at the Bimba Prospect in early 1997, following regional calcrete sampling and subsequent RAB/aircore drilling. The region was selected by Equinox Resources NL for copper-gold exploration in 1993 based on structural interpretation of South Australian Exploration Initiative aeromagnetic data. That interpretation identified the Yarlbrinda shear zone as a major craton-scale shear zone active at the time of emplacement of Hiltaba Suite granites ca. 1595-1585 Ma and hence potentially mineralised. Subsequent detailed aeromagnetic and ground magnetic surveys have accurately defined the nature and location of the Yarlbrinda shear zone. Calcrete gold anomalism in the Sheoak-Myall area is coincident with an intense demagnetised zone and there is a subtle ground magnetic anomaly associated with bedrock gold mineralisation at the Sheoak prospect. Gradient-array IP data reflect the depth of weathering and nature of the ~40 m thick regolith developed over the shear zone.