SPM Effect in Glacial Till

Abstract

The SPM effect is not traditionally associated with glacial tills. However, effects of viscous magnetization, i.e. superparamagnetism, are observed in many places in Northern Finland in high sensitivity and low frequency time domain ground EM surveys. These effects are typically observed on late time channels and they have a very good correspondence with magnetic anomalies. Usually there is also a clear reverse frequency domain RE component anomaly observed simultaneously with the SPM effect. In Ni ore prospecting it is essential to be able to recognize SPM effect because it has a response similar to a deep seated massive nickel ore body i.e. a deep seated very high conductivity conductor. Characteristic feature for SPM effect in time domain dB/dt data is its 1/t decay which can be used as a means to recognize this phenomenon. We also discuss alternative methods to recognize SPM effect.