Inductive Source Resistivity: a tool for outlining silicification in gold exploration

Abstract

Galvanic resistivity mapping has been conventionally used to map zones of high resistivity produced by silicification or quartz veining, within which gold mineralisation often occurs. Induced polarization measurements may also be useful in locating sulphide mineralisation commonly associated with gold. An alternative method of resistivity mapping using UTEM instrumentation is presented, viz. an ungrounded inductive loop source combined with a grounded electric field receiver. Measurements obtained with the system are termed inductive source resistivity (ISR) and inductive source induced polarization (IIP). This system has an inherent advantage over galvanic resistivity methods in that the primary electric field induced in the ground is independent of the resistivity structure. In a field test at a gold prospect at Mt Aubrey, N.S.W., Australia, ISR surveying mapped in detail two zones of quartz veining, producing anomaly highs which in most cases correlated closely with the drilled locations of the veins. The ISR profiles were very similar to matching gradient array apparent resistivity profiles. In the one survey combined measurements of electric and magnetic field data from an inductive source can explore for both resistive and conductive features, map geological contacts and detect disseminated sulphides.