Geophysical characteristics of the Eloise Cu?Au deposit north-west Queensland

Abstract

The Eloise Cu?Au deposit is located approximately 60 km south-east of Cloncurry in northwest Queensland. It is hosted within interpreted Early to Middle Proterozoic metasediments of the Soldiers Cap Group, and comprises a number of steeply plunging, structurally complex mineralised zones. The deposit is overlain by between 50 and 70 m of highly conductive, flat-lying Mesozoic age sediments. Geophysical methods assumed leading roles in the discovery of the Eloise deposit. The systematic evaluation of linear aeromagnetic trends using moving-loop transient EM (TEM) profiling led to the initial recognition of the Eloise anomaly. Fixed-loop TEM surveying detailed a strong bedrock conductor broadly coincident with a moderately intense magnetic ridge. Drillhole END17, sited to test the conductive source, intersected 20 m of chalcopyrite?pyrrhotite mineralisation. The geometry of the deposit limited the extent to which surface TEM methods could confidently define targets for subsequent drilling. As a consequence, downhole TEM was identified as an effective tool to guide exploration drilling. This technique proved extremely useful, both in detecting additional mineralised bodies and in helping to define the dip extent of the deposit. Lines of gravity and dipole?dipole IP have also been completed over the deposit to further characterise its response. In both instances sizeable anomalies were recorded, attributable in part to a significant mafic alteration system associated with the mineralisation.