50 years State of the Art in IP and Complex Resistivity

The use of resistivity and spontaneous potential by the Schlumberger brothers is documented at least as early as 1900 - over 100 years ago! Conrad Schlumberger received a patent on the IP technique in 1912. However, it was almost forty years before Newmont renewed interest in its use and application. From that time (the late 1940's) activity flourished for roughly forty years in both theory and practice, mainly in the search for disseminated sulfides; more specifically porphyries. However, with the crash of copper prices in 1983, interest in disseminated sulfide (porphyry copper) deposits declined dramatically with a concurrent drop in research concerning the source and nature of the induced polarization (IP) response. The precipitous decline in oil prices in 1985 further reduced interest in IP, which was being used as one of the non-seismic alternatives in hydrocarbon exploration. Only in the last few years has interest been renewed.

Despite this general lack of interest in the use of IP and IP research during the past 15 years, the development of instrumentation applicable to resistivity and IP surveys has continued at a fast pace, capitalizing on the development of powerful, high speed, low cost microprocessors. These new microprocessors also fueled the development of robust data processing routines and 2- and 3-D modeling and inversion programs.

Today research continues on the effects of hydrocarbons and other groundwater contaminants on the IP response. IP is used extensively in the search for precious metals by mapping areas hosting disseminated sulfides that may occur in conjunction with precious metals. Interest has been renewed in porphyry deposits in third-world countries, and complex resistivity (CR) or spectral IP is being used in attempts to discern the source of IP responses and to discriminate between valid metallic IP responses and electromagnetic (EM) coupling effects. Most recently IP has been found to be a cost-effective method in environmental surveys.