Electrical prospecting techniques, that use natural and artificial electromagnetic fields, are widely applied in geophysical studies
They include a group of geophysical methods are based on measurements of rocks electric properties such as: electric resistivity (ρ) or conductivity (ρ=1/σ), electrochemical activity (α), electric chargeability (η), dielectric permittivity (ε).
Measurements of electric resistivity (ρ) and conductivity (σ) are the most common.. Resistivity values of different rocks can vary more than 100 000 times depending on their interstitial water mineralization, porosity & fissuring, water and clay content, temperature etc.
The resistivity values are also depend on the content of minerals with electronic type of conductivity, they are sulfides, graphite, oxides etc. For example, massive sulfide bodies of pyrite and nickel-copper (polymetallic) deposits are very conductive in comparison to host rocks. Such rocks as black shales, which are often considered as an attribute of large-scale gold deposits, also have very low resistivity values.
The majority of electro-prospecting methods deal with the resistivity of rocks. Its measurements allow one to divide efficiently the soils with different conductivity values. There are exist a plenty of rock resistivity determination approaches. DC methods deal with electric current flows through the rocks, whereas electromagnetic methods use response functions of geologic media has been excited by EM waves.
The IP method lays apart from the classic resistivity methods since it deals with both ρ and η. The SP method is a unique tool to study the electrochemical activity (α) of rocks.
Any electro-prospecting method has its own area of application and it is necessary to select the measurement technique depending on the desirable resistivity and spatial resolution, depth of investigation etc.
Different techniques and equipment of electro-prospecting can be applied depending on tasks to be solved. The complex of geo-electric methods is also determined by geographic and financial conditions etc. The technique of measurements may be realized either in profiling mode, which is a geophysical analog of geological mapping along several profiles, or in sounding mode – a counterpart of well-drilling.
