Complex resistivity of mineral rocks in the context of the generalized effective-medium theory of the IP effect Vladimir Burtman*, University of Utah and TechnoImaging , Masashi Endo, TechnoImaging, Wei Lin, University of Utah, and Michael S. Zhdanov, University of Utah and TechnoImaging Summary One of the major problems in mineral exploration is the inability to reliably distinguish between economic mineral deposits and uneconomic mineralization. While the mining industry uses many geophysical methods to locate mineral deposits, until recently, there was no reliable technology for identification and characterization of mineral resources. The main goal of this paper is an application of the generalized effective-medium theory of induced polarization (GEMTIP) to studying the complex resistivity of typical mineral rocks. We collected representative rock samples from the Cu-Au deposit in Mongolia, and subjected them to the mineralogical analysis using Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCan) technology. We also conducted an analysis of the electrical properties of the same samples using the laboratory complex resistivity (CR) measurement system. As a result, we have established relationships between the mineral composition of the rocks, determined using QEMSCan analysis, and the parameters of the GEMTIP model defined from the lab measurements of the electrical properties of the rocks. These relationships open the possibility for remote estimation of types of mineralization using spectral IP data. Introduction The physical-mathematical principles of the IP effect were originally formulated in the pioneering works of Wait (1959, 1982) and Sheinman (1969). However, the IP method did not find wide application in mineral exploration until the 1970's with the work of Zonge (e.g., Zonge, 1974; Zonge and Wynn, 1975) and Pelton (Pelton et al., 1977, Pelton, 1978). Significant contributions were also made by Kennecott research team between 1965 and 1977 (e.g., Nelson, 1997). Over the last 40 years several conductivity relaxation models have been developed, which provided quantitative characterization of the electric charging phenomena, including the empirical Cole-Cole model (Cole & Cole, 1941; Pelton et al., 1978), electrochemical model of Ostrander & Zonge (1978), the GEMTIP model of Zhdanov (2008), based on generalized effective-medium theory of induced polarization, and electrochemical model of Revil et al. (2013). The GEMTIP resistivity model uses the effective- medium theory to describe the complex resistivity of heterogeneous rocks and incorporates the physical and electrical characteristics of rocks at the porous/grain scale and translates them into an analytic expression for the effective complex resistivity. It was shown in the paper by Zhdanov (2008) that the widely accepted Cole-Cole model is a special case of the GEMTIP model, where all the grains have a spherical shape. In the present paper, we investigate a more general case with the grains having elliptical shape. By choosing different values of the ellipticity coefficient, one can consider the oblate or prolate ellipsoidal inclusions, which provides a wide class of models to be used in the analysis of the complex conductivity of the mineral rocks. An important goal of this paper is an application of the developed GEMTIP models to studying the complex resistivity of the typical mineral rocks. We have collected several dozens of representative rock samples from the Cu- Au deposit in Mongolia. These rock samples were subjected to the mineralogical analysis using Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCan) technology. We also conducted an analysis of the electrical properties of the same samples using laboratory complex resistivity (CR) measurement system. As the result of this study, we have established the relationships between the mineral composition of the rocks, determined using QEMScan analysis, and the parameters of the GEMTIP model defined from the lab measurements of the electrical properties of the rocks. These relationships open a possibility for remote estimation of the type of mineralization using the spectral IP data. Multiphase heterogeneous medium filled with ellipsoidal inclusions The GEMTIP model provides a general solution of the effective conductivity problem for an arbitrary multiphase composite polarized medium (Zhdanov, 2008, 2009, 2010). The GEMTIP theory opens a possibility of determining the effective conductivity for grains with arbitrary shape; however, the calculation of the parameters of the GEMTIP model may become very complicated. In a special case of inclusions with spherical shape, the GEMTIP model can be reduced to the classical Cole-Cole model of complex resistivity. There exists another special case of inclusions with ellipsoidal shape, where the solution of the GEMTIP formulas can be obtained in close form, similar to a model with spherical inclusions. The advantage of the model with ellipsoidal inclusions is that in this case one can use different shapes of ellipsoids, from oblate to prolate, to model different types of heterogeneous rock formations and different types of inclusions (see Figure 1). The three- phased GEMTIP model, developed by Zhdanov (2008), in a Page 2238 © 2016 SEG SEG International Exposition and 86th Annual Meeting Downloaded 09/28/16 to 155.101.18.153. Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/