Comparing induced polarization responses from airborne inductive and galvanic ground systems: Tasmania

Abstract

We have first analyzed the ability of polarizable and superparamagnetic thin sheets in the near surface to fit airborne electromagnetic (AEM) data using data from western Tasmania. Then we analyzed the results of such fitting in the context of geologic mapping and available ground induced polarization (IP) data. Small to large IP effects were found to considerably improve the fit to the observed AEM data, and the overall fitted IP parameters were spatially consistent. However, the locations of anomalous IP parameters were quite distinct from anomalies in other geophysical data. The airborne chargeability highs were adjacent to or surrounded the ground chargeability highs in the five cases analyzed from Tasmanian data. Modeling using the established Cole-Cole physical property values for sulfides predicts that an inductive airborne system is insensitive to many conventional IP targets, unless the mineral grain size is substantially less than 1 mm. In the cases in which airborne IP responses were adjacent to ground IP targets, we hypothesized that the airborne IP may be finer grained minerals in an alteration halo surrounding the sulfide sources of the large ground IP anomalies. Surficial clays encountered in drillholes did not have significant ground or airborne IP responses. A companion paper comes to a similar conclusion using ground and airborne data from a copper deposit in New South Wales.