ABSTRACT

The U. S. Geological Survey has, for several years, been evaluating various logging techniques in mineral exploration drill holes. In addition to conventional electric logging, continuous measurements of magnetic susceptibility and induced polarization have been made. These various logging methods have proven useful in specific areas, as, for example:

  1. Electric resistivity logs can be used to distinguish enriched hematite ores from noncommercial carbonate iron-formations and other rocks, such as those in the iron ranges of the Lake Superior district.

  2. Magnetic susceptibility logs can be used to estimate the relative amounts of magnetite present in taconite ores (northern Wisconsin and central California).

  3. The combination of resistivity and magnetic susceptibility logs can be used to determine the amount of magnetite necessary for a rock to appear electrically continuous. These parameters vary for different types of magnetite deposits (northern Wisconsin versus central California).

  4. Induced polarization logs have been used to locate and determine the distribution of disseminated sulfides and native copper (northern Wisconsin and Michigan).

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