Relaxation time distribution approach of mineral discrimination from time domain-induced polarisation data

Abstract

ABSTRACTSource characterisation in time-domain induced polarisation (IP) data is more cumbersome than in frequency-domain IP data. The time-domain IP phenomenon is a linear superposition of individual relaxations caused by various polarisable sources. We have adopted the relaxation time distribution (RTD) method, a technique used in dielectric and chemical physics for analysing the relaxation phenomenon to characterise these sources. In this paper, the RTD method is first tested on synthetic data to evaluate its ability to estimate Cole–Cole spectral parameters, and then the effect of using a number of repetition rates is tested. Results indicate that chargeability and relaxation time are underestimated if the measurement duration is less than or equal to the relaxation time. Spectral parameters estimated using the RTD method on the published time-domain IP data are in good agreement with those estimated from empirical methods. The RTD method has also been tested on time-domain IP data measured on borehole core samples in the laboratory. These results inferred the possible polarisable sources and agree with petrological microscope observations. The RTD method was employed successfully to characterise the IP sources from ground time-domain IP data over four known mineralised bodies.