Its Induced Role 1n Polarization and Mineral Exploration
H. 0. SEIGEL
Induced Polarization includes many types of dipolar charge distributions set up by the passage of current through consolidated or unconsolidated rocks. Among its causes are concentration polarization and electrokinetic effects in all rocks and the phenomenon of Overvoltage in rocks containing electronic conductors such as metallic sulphides and graphite. In normal rocks the polarization effects may be usually confined within relatively narrow limits and any large departures may be attributable to the presence of electronic conductors. In practice, Induced Polarization is measured in one of two ways. In the first a steady current of some seconds duration is passed and abruptly interrupted and the slowly decaying transient voltages existing in the ~round are measured after interruption. This is known as the "pulse", "transient", or Direct Current Induced Polarization (D.C.I.P.). The second method entails a comparison of apparent resistivities using sinusoidal alternating current of two or more frequencies, generally within the range of 1/ 10 to 10 c.p.s. Induced Polarization extends the range of detectible sulphide occurrences to concentrations far below those detectible by electromagnetic means. It is of value in 'Canada primarily in base metal occurrences such as in the Highland Valley, Gaspe and Pine Point Areas, and in gold camps such as Malartic and Red Lake where there is an association with disseminated sulphides. Although considerable study has taken place, the method has not yet been made to differentiate between sulphide and graphite polarization. Whereas it can detect concentrated sulphide bodies it is inferior fundamentally and economically to the standard electrical methods for such occurrences. To complicate the use of the method there are occasionally found materials of abnormally high but non-metallic polarization for which no adequate explanation is available at present. Despite these limitations the Induced Polarization method has broadened the scope of geologic problems amenable to a geophysical approach.
Electrodes, Frequency, Induced polarization, magnetite, polarization, porphyry copper, pyrite, sinusoidal, Overvoltage, Polarization, Rock, Rocks, sulphide, Sulphides