HoistEM data processing for discovery of high-grade manganese ore under regolith cover

Abstract

A time-domain airborne electromagnetic (AEM) survey was flown with the HoistEM system over the Woodie Woodie manganese mine corridor in the east Pilbara of Western Australia. Conductivity Depth Image (CDI) processing helped to discriminate shallow, regolith-related responses from conductive ore. About half of the known manganese ore zones correlate with elevated conductivities on the CDIs, and recent drilling of several new EM targets in areas of regolith and bedrock cover has discovered over six large-tonnage manganese ore bodies to date. EMFlow software has made it practical to process data gathered by HoistEM to separate the ore body response from the responses of conductive palaeochannels and other conductive features related to bedrock geology or the regolith. Experimentation with EMFlow input parameters helped to produce CDI results that were more reliable. The CDI results were further refined by calibrating conductivity values from CDI processing to correlate with borehole conductivity results. Borehole-calibrated CDI results have lower noise, line levelling problems are suppressed, and depths of conductive horizons are more accurate. The HoistEM survey-design tests and processing results demonstrate that HoistEM is a cost-effective method for exploration of podiform, high-grade manganese ore bodies, as long as the host rocks are comparatively resistive, and a flight line spacing of 80 m or less is used.