Some case histories of source discrimination using time‐domain spectral IP

Abstract

It has long been known that induced polarization (IP) transient voltages decay with time at a rate that is dependent strongly on the mean grain size of the metallic conducting particles in the IP source. The Cole‐Cole model provides a three‐parameter representation (M, τ and C) for IP responses. The time‐constant (τ), in particular, has been found to be very useful in resolving IP sources with differing mean particle size. The characterization of IP responses in terms of these parameters has been termed “spectral IP.” These parameters may be determined either through the analysis of the response of the earth to sequential transmission of ac currents of different frequencies (i.e., frequency‐domain IP), or through the analysis of the transient decays resulting from the transmission of interrupted square‐wave currents (i.e., time‐domain IP). The latter approach offers the major convenience of being applicable to data obtained in the course of routine production surveys, with no increase in survey time. In practice, spectral IP parameters are determined most readily from time‐domain transients through the computer matching of the observed data to the best fit in a family of precalculated Cole‐Cole curves. This may be done, off‐line, using a PC, or, in a recent receiver, essentially on‐line, using software imbedded in the receiver. Field case histories from Canada, Finland, and Australia are given to illustrate the application of spectral IP to the resolution of IP sources in the time domain. It is recommended that this approach to the processing and presentation of time‐domain IP data should be applied routinely, as a very cost‐effective enhancement to the exploration value of such data. An additional benefit from this presentation is that it will facilitate a sharing of experimental results with workers in the frequency domain who may also use the spectral IP approach.

Efficient spectral IP-modelling in the time domain

“…In particular, this applies to apparent resistivity pseudosections of Cole-Cole parameters (e.g. Johnson, 1984;Vanhala and Peltoniemi, 1992;Seigel et al, 1997). The relationship between intrinsic and apparent time-dependent resistivities in the intermediate time range was not resolved until now, and the meaning of apparent Cole-Cole parameters calculated from transient decay curves was not clear.…”

“…Cole-Cole parameters from the decay curves (Tombs, 1981;Johnson, 1984), and the interpretation of timedomain SIP profiles was frequently based on pseudosections of apparent Cole-Cole parameters (Johnson, 1984;Vanhala and Peltoniemi, 1992;Seigel et al, 1997). More recently, a concept for a 2-D inversion of time-domain SIP data was presented by Yuval and Oldenburg (1997).…”

“…Wait, 1959;Vanhala and Peltoniemi, 1992;Seigel et al, 1997). More recently, the method has been applied to engineering and environmental problems, such as the detection of contaminants and the derivation of grain size distribution parameters in unconsolidated sediments (e.g.…”

Induced polarization with in-loop transient electromagnetic soundings: A case study of mineral discrimination at El Arco porphyry copper, Mexico

“…14a). From studies in the galvanic IP frequency band, Seigel et al (1997) and Luo and Zhang (1998) suggested that values of about 0.1 of this Cole-Cole parameter are associated with a wide distribution of the size of the mineral particles, while high values (about 0.6) indicate a sharply peaked distribution. Our estimated frequency exponents are generally high (average 0.66 +/− 0.16).…”

Application of concentration-volume fractal method in induced polarization and resistivity data interpretation for Cu-Mo porphyry deposits exploration, case study: Nowchun Cu-Mo deposit, SE Iran

“…The IP phenomena are of electrochemical origin and caused either by metallic mineral particles in a rather poorly conducting rock matrix or by differences in the ion concentrations in the pore space or at the interface between matrix and pore space (Sumner, 1976;Weller et al, 2000). Disseminated sulfide minerals produce high values of polarization effects and IP anomalies are evidence of sulfide mineralization zones existence in different depths of the deposits (Seigel et al, 1997). The spectral induced polarization (SIP) method has been used so far for exploration of disseminated ores and mineral discrimination (Hördt et al, 2006).…”