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Paper 1981 T :: Add Item

ABSTRACT The complex geologic history of Precambrian metamorphic rocks creates a formidable interpretation problem for the log analyst. The metamorphic rocks logged in this study contain components that represent the following geologic conditions: (1) metavolcanics and metasediments, with little secondary alteration, (2) silicification, (3) chloritization, (4) iron and copper mineralization, and (5) ground water alteration. These varied geologic regimes can be defined by using a wide variety of borehole geophysical tools. Depth intervals with iron mineralization can usually be determined with standard induced polarization (IP) measurements. However, non-linear complex resistivity (NLCR) can separate the IP response of sulfides from that of high cation exchange capacity alteration products. Silicified zones are characterized by high resistivities, low densities, and low gamma radiation. Subtle geologic features (such as the state of alteration product fractures which transmit ground waters) can be determined by simultaneously interpreting the responses from several different types of geophysical well logs.