Comparison Between Time- and Frequency-Domain Induced Polarisation Parameters

Physical properties of rock samples from exploration or mining sites are often needed to assist in the planning of geophysical surveys or in the interpretation of geophysical results. For example, the output from a physical property study may be used in numerical model studies aimed at assessing the applicability or performance of a geophysical technique. Physical properties are also useful for constraining model parameters during processing and in the interpretation of field data. Electrical property data are often recorded in the time-domain, yielding resistivity and chargeability values; however, a frequency-domain, or even complex resistivity approach, may also be followed. The latter approach, for example, would produce resistivity magnitude and phase angle outputs. It is shown that both the commonly used standard time-domain chargeability parameters and the (single-frequency) complex resistivity phase angle parameter could produce misleading estimates of the polarisable nature of mineralised rocks and of the contrast between different rock types. It is further shown that a multi-frequency (spectral) approach can be used to avoid this pitfall; similarly, the calculation of different time-domain induced polarisation (IP) parameters, (using different definitions) may provide better insight into the polarisable nature of rock samples than a single, arbitrary chargeability value.