Geophysical Response of the Atlántida Cu-Au Porphyry Deposit, Chile ? An Undercover Discovery in an Old District

Abstract

The discovery of the Atlántida Cu-Au-Mo porphyry deposit is a recent example of exploration success under cover in a traditional mining jurisdiction. Early and appropriate acquisition of geophysics was a key tool in the discovery and in guiding resource definition drilling through the lifecycle of the project. Close review of the geophysical response of the deposit with respect to its lithological distribution and petrophysical properties has allowed it to be fully characterised despite no mineralisation being exposed at surface. Data acquired over the project includes induced polarisation, ground and airborne magnetics, gravimetry and petrophysics. The distribution of the key lithologies is demonstrated to be readily defined via a combined application of susceptibility and density properties, which agree well with geophysical data acquired at surface. This is in contrast to the electrical properties which instead map the extent of mineralisation associated with the hydrothermal system via chargeability, and the location of copper bearing sulphides via resistivity In combination these characteristics can be used to infer depth to exploration targets and potential for high grade mineralisation in a geological context. Future exploration will be increasingly reliant on the understanding of the surface manifestations of buried deposits in remotely acquired data. This review summarises the application and results of these principles at the Atlántida project.