Electrical methods comprise a multiplicity of separate techniques that employ differing instruments and procedures, have variable exploration depth and lateral resolution, and are known by a large lexicon of names and acronyms describing techniques and their variants. Electrical methods can be described in five classes:
- direct current resistivity
- induced polarization, and
In spite of all the variants, measurements fundamentally are of the Earth's electrical impedance or relate to changes in impedance. Electrical methods have broad application to mineral and geo-environmental problems: they may be used to identify sulfide minerals, are directly applicable to hydrologic investigations, and can be used to identify structures and lithologies.
Remote Sensing Methods In Electrical methods
Thermal infrared observations, discussed previously under thermal methods, are also part of remote sensing. Remote sensing data are treated in image format, often in digital form, so that they can be processed conveniently. By comparison with known spectral responses of minerals or mineral groups, iron hydroxide minerals, silica, clay alteration, etc., can be defined over broad areas. Remote sensing can be used in geo-environmental studies to map surface alteration patterns and to identify anomalous vegetation patterns in areas related to abnormal metal content in soil.
A number of other geophysical or quasi-geophysical methods have been used, or have potential application, in mineral exploration. Application of these methods in geo-environmental investigations has been limited, but should not be dismissed. Some peripheral techniques that have special uses (as in archeology), whose utilization is not widely known in mineral exploration, that may directly apply to shallow geo-environmental investigations.
Examples of such techniques are ground-penetrating radar (used to image the shallow subsurface in electrically resistive rock; the piezoelectric method (used in studies of quartz veins; Volarovich and Sobolev, ultraviolet laser induced fluorescence (the Luminex method, used to identify scheelite, hydrozincite, and other fluorescent minerals; Seigel and Robbins, 1983), airborne gas sniffing (used in mercury exploration), the Russian CHIM (partial extraction of metals) electrogeochemical sampling technique, and radon sensing.