Magnetotelluric (MT) methods are a passive geophysical method that infer the Earth’s subsurface resistivity though measuring naturally occurring geomagnetic and geoelectrical fields at the Earth’s surface. These naturally occurring fields occur over a wide band of frequencies. Low frequencies correspond to locations deep in the crust, while high frequencies correspond to shallow depths. MT surveys focus on depth ranges from 100-10,000m and therefore have a much greater depth of penetration than other electrical or electromagnetic methods. MT measurements allow geologists to determine resistivity as a function of depth. The electrical resistivity of rocks and soils is a function of mineralogy, porosity, permeability, temperature and fluid composition.
Fender Geophysics has been using an Advanced Geophysical Technologies (AGT) gDAS32 Distributed Array System for their MT data acquisition. The flexible configuration of the gDAS system allows for high quality Induced Polarisation data to be acquired during the day and MT data at night (when conditions are often better for MT data acquisition). This configuration allows for increases in survey efficiency and the acquisition of shallow and deep focused geophysical data.
Magnetotelluric methods are known to be effective for:
- Mineral exploration especially for porphyry style mineralisation
- Kimberlite mapping
- Exploring are in areas of conductive overburden
- Geothermal exploration
- Studies of the deep crust and mantle