Sub-project leader:
Jim Craven, Geological Survey of Canada

An experimental magnetotelluric survey was proposed for 2001-02 in case additional funds became available for the EXTECH IV project, subject to consultation on previous MT surveys with Industry, the potential success of a modified approach, and consensus approval by Steering Committee. The primary target would be graphite at a depth of 500-1000 m and therefore conductive material beneath or related to the deep McArthur R. ore zone. Model studies incorporating the known resistivity distribution and that inferred from borehole measurements could be used to plan a tight MT survey to detect a conductor near the McArthur R. ore zone. The experiment may be conducted using a contract survey or GSC staff. This survey can be done in the winter at the same time and along the same line as the high resolution seismic survey. The Steering Committee supports this survey as a valuable improvement on earlier technology.

Lightning used in EM surveys as a natural transmitter

Unlike most electrical and electromagnetic (EM) geophysical techniques that deploy a man-made transmitter to probe the Earth's resistivity structure, audio-magnetotellurics (AMT) uses distant electrical activity (i.e. lightning) and resultant resonances in the ionosphere as a natural transmitter of EM waves. Natural EM sources in the audio band have the distinct advantage of sufficient power to reveal the conductivity structure to depths of a few kilometres or more in the Athabasca Basin.

portable sensors used to determine the resonance in the earth's magnetic field

The resonances in the Earth's natural electric and magnetic fields induced by distant electrical storms are measured using portable sensors easily deployed by a small field crew. Perturbations in the resonances caused by the spatial variation of the conductivity of the Earth are used to locate deep conductive material, such as graphite, commonly associated with uranium ore in the Basin.

2002-2003 Activities and Results

EXTECH IV Sub-project 9T: A 3D Audio-Magnetotelluric Survey at the McArthur River Mining Camp (PDF)