MT methods jointly measure electric and magnetic field variations. This enables calculation of the resistivity structure of underlying rocks, the depth being related to the period of the signal. Shallow exploration requires short period (high frequency), while deeper exploration needs low frequency. Bartington’s fluxgate sensors have the advantage over other sensors in low frequency, offering higher sensitivity and lower noise. This method can be used for a range of mineral and oil exploration studies to determine either the location of ore bodies or the shape of potential oil traps, using the Mag-03MSL or MSESL sensor.
Time Domain Electromagnetics
In the TDEM method, an AC magnetic field is created by injecting an AC current in loop. The response of underlying rocks to this AC field is then examined. If conductive material is present, the AC magnetic field will generate eddy currents which will in turn generate a secondary field that varies in intensity with the conductivity of rocks. Fluxgate sensors detect this secondary field. A fluxgate sensor is superior to coils for highly conductive targets because induction coils work on decay of the magnetic field rather than intensity: the higher the conductivity, the slower this decay. Bartington Mag-03 low noise sensors can be used – the Mag-03MC or MS for ground work, or unpackaged or in two-parts for borehole work.
Controlled Source Electromagnetics
The CSEM method – similar to TDEM but applied at sea – requires very low noise because the strength of the variations is very small. An array of Bartington Mag-03MSSL sensors is ideal for this application.
Borehole Magnetic susceptibility
The Bartington Instruments BSS-02B Sonde can be used to measure the variation in magnetic susceptibility in a borehole with very high spatial resolution. As an example, diamonds are found in volcanic formations known as kimberlites, which have very high susceptibility, and so are readily detectable with the BSS-02B Sonde. Iron ore bodies also have an relatively high susceptibility, the intensity of the susceptibility being related to the percentage of iron in the rocks.
Core logging Correlation
Magnetic susceptibility measurement provides additional information in petrophysical studies. For both mineral and oil exploration, the Bartington MS2/MS3 meter combined with the MS2C probe allows for high resolution stratigraphic analysis of well cores. Combining the results from a number of cores enables the user to determine the geometry of a structure, for instance an ore body or oil trap.