Fitting SPM and distributed Cole-Cole parameters to AEM data

Abstract

Polarizable and superparamagnetic thin sheets in the near surface improve the model fit of airborne electromagnetic data. Surficial conductors are asserted to be the source of IP effects. In this case history from Lac Brule, Quebec over an anorthosite intrusion, small to large induced polarization effects were found to be essential to fit most of the observed data. It was also possible in some areas to separate SPM effects from IP effects in the data. Most induced polarization effects in this unusually polarizable area were fit a Cole-Cole decay characterized with a frequency dependence of c = 0.3, but some required a sharper response characterized by c = 0.8. Generally, fitted IP time constants were anti-correlated with fitted frequency dependence, with short time constants fitted to the larger c values and vice versa. SPM effects were detected in a small but significant fraction of the data, and appear to be spatially related to static magnetic anomalies. The SPM in this case is presumably related to fine grained rock magnetism, rather than the more common case of weathering products.