Exploring through cover ? the integrated interpretation of high resolution aeromagnetic, airborne electromagnetic and ground gravity data from the Grant's Patch area, Eastern Goldfields Province, Archaean Yilgarn Craton Part C: Combining geophysical metho

Abstract

Grant's Patch is a semi-mature lode gold corridor located 45 km NW of Kalgoorlie in Western Australia. Gold mineralisation at Grant's Patch sits within geological structures less than 20 m wide (lithological contacts, ductile shears and brittle cross-faults). These structures are masked by 10 to 100 m of regolith cover and are often impossible to correlate between exploration drillholes. The southern part of this corridor is covered by high-resolution aeromagnetic, airborne electromagnetic and ground gravity data. This provides dense, regularly spaced data coverage to image patterns reflecting the sub-surface geometry of the regolith and bedrock geology. There is also uniform exploration drillhole coverage to non-weathered bedrock and very little surface disturbance from mining infrastructure. Aeromagnetics identifies magnetic greenstone units, such as mafic to ultramafic sills and dolerite horizons, faults as disruptions crossing proterozoic dykes, and paleochannels containing ferruginous gravel. Patterns in the filtered gravity data reflect subtle density differences between rock units, regolith features, and weathered fault zones that cannot be detected in the aeromagnetic data. The airborne electromagnetic (AEM) response is dominated by conductive clays, predominately in situ as saprolite, and saline groundwaters in the regolith that follow litho-dependant weathering of bedrock units. Cross-faults are mapped as disruptions of the conductive units and may be either conductive or resistive. Geophysical 'pattern mapping' from such surveying is relatively inexpensive when compared to drilling. It increases success rates by identifying mineralised structures and fluid pathways at the early stages of an exploration program and should also be routinely applied in 'brownfields' project areas.