Identification of massive sulphide targets using the Galvanic Source EM (GSEM) signal from a Sub-Audio Magnetic (SAM) survey at the Far South Project, Western Australia

Abstract

The Far South project is located five kilometres along strike from the Deep South mine, where gold mineralisation is commonly associated with semimassive pyrrhotite and pyrite. Data from a Sub-Audio Magnetic (SAM) survey set up in galvanic configuration were acquired over the project principally to map stratigraphy and structure using the on-time Magnetometric Conductivity (MMC) and Total Magnetic Intensity (TMI) responses. The off-time Galvanic Source EM (GSEM) data were subsequently extracted from the raw data and examined. Four late time anomalous responses were identified. Two of these responses are strong late-time (>45ms) anomalies up to 350m in strike length, and the remaining two are weaker mid-time, more subtle and less diagnostic responses. Follow-up Moving Loop Transient Electromagnetics (MLEM) and Fixed Loop Transient Electromagnetics (FLEM) surveys confirmed well defined conductive responses over all four follow-up areas. Modelling of the GSEM data over the two strongest anomalies is in good agreement with modelling of the MLEM/ FLEM data, confirming the ability to identify and model conductive targets from SAM GSEM data. The two weaker GSEM responses could not be reliably modelled and use of the MLEM/ FLEM data was necessary to produce robust models. The identified conductors were all interpreted as having good exploration potential, and a subsequent drill program intersected the source of all four as sulphide zones of varying widths and types.