Geological Mapping Capabilities of the QUESTEM Airborne Electromagnetic System for Mineral Exploration — Mt. Isa Inlier, Queensland

Airborne electromagnetic (AEM) surveys are now being flown to assist in geological mapping programs. In areas of varying electrical conductivity AEM data provide significant information that can be used in conjunction with aeromagnetic and ground geological data to build up a three-dimensional interpretation of the geology. Image presentations enable interpretation and mapping of the geology.

A QUESTEM airborne geophysical survey was flown over the Lady Loretta deposit in the Lawn Hill Platform, north-west Queensland, with the aim of mapping the geology, using both AEM and airborne magnetics. The survey area comprises folded and faulted Middle Proterozoic sediments unconformably overlain by Cambrian sediments in the east of the area.

High electrical conductivity contrasts between the different stratigraphic units has enabled a detailed geological interpretation to be made from the AEM data. For example, the Esperanza and Gunpowder Creek Formations are strongly conductive relative to overlying and underlying formations allowing fold structures and faults to be mapped. The Upper Lady Loretta Formation includes strongly conductive pyritic shale that hosts the lead-zinc mineralisation. In addition broad subtle changes in conductivity enable different lithologies to be distinguished. The aeromagnetic data does not provide the detail seen in the AEM data due to the lack of magnetic susceptibility contrast within the Proterozoic sediments. Faults interpreted from the aeromagnetic data generally correlate with those evident in the AEM.

In the eastern part of the survey area conductive units can be traced below the Cambrian sandstone. These may represent areas of further exploration interest.