Interpretation of ground TEM data from conductive terranes

Abstract

Conductive regolith represents a geological-noise source which masks the transient EM response of conductive exploration targets in bedrock. Frequent effects are the loss of target response at early times, with a resultant loss of resolution in estimates of target size and depth, and presence of a subtle rather than distinct target response at late times. Overburden masking can be effectively reduced by computing and stripping the theoretical response of an equivalent layered conductive overburden model from field data. This process enhances subtle signatures attributable to bedrock conductors and improves target resolution by extracting useable TEM signatures at earlier times than is possible with raw data. Extraction of signatures attributable to deep bedrock targets requires temporal and spatial filtering of the data, followed by Hilbert transformation of vertical-component data to equivalent horizontal components. These processes facilitate identification of the subtle trends attributable to conductive targets below overburden when the processed data is presented either as stacked sections or in plan-view as images. These enhancement procedures are demonstrated on data from the Eloise copper?gold deposit, near Cloncurry, NW Queensland, which lies below 70 m of highly conductive Mesozoic shales.