Geophysical vectors to IOCG mineralisation in the Gawler Craton

Abstract

IOCG deposits within the Gawler Craton are an attractive exploration target that has been the focus of considerable exploration. Due to the extensive Neoproterozoic and Phanerozoic cover over prospective geology, geophysics is the predominant and most cost effective exploration tool. The eastern Gawler Craton contains multiple deposits and prospects in areas defined by high amplitude gravity and magnetic anomalies. Seismic surveys define the craton boundary and large scale structures. Gravity, magnetics and structural breaks are terrane scale vectors. Within tenements geological interpretation from geophysical data is critical due the many 'false alarm' anomalies. Vectors to targets from gravity highs, associated offset magnetic responses, chargeability highs and resistivity lows are important. Ambiguity in interpretation due to palaeotopography is a significant issue that seismic surveying is beginning to resolve. Within an IOCG deposit the geophysical response of iron oxides dominates the sulphide response. Neither direct-detection of, or vectors to mineralisation within a deposit are provided from gravity, magnetics, chargeability, resistivity or acoustic properties. Geophysics provides excellent vectors to IOCG deposits at the terrane and tenement scale but do not provide vectors within the iron oxide alteration envelope.