Abstract

The potential of scalar audiomagnetotellurics (AMT) for base-metal exploration in Finland has been used on a trial basis since 1976. The behavior of the source fields changes depending upon the season and the weather. Techniques similar to reference stations have been applied. In the search for elongated conductors, an azimuth of the minimum apparent resistivity is taken at every station to utilize the E-polarized field. Nevertheless, there are severe restrictions as to where AMT can be applied reliably. The target should be highly conductive; it should be large or elongated; and there should be no other good conductors at shallow depth or manmade sources nearby. A practical depth limit seems to be 2 000 m when frequencies between 8 and 3 700 Hz are used.

A one-dimensional model is convenient for modeling sounding data, and the model can be theoretically extended to more complex structures. It is important to have a dense array of stations. Two reconnaissance surveys and three detailed cases demonstrate the unique character of the AMT method. Difficult though it has been to squeeze reliable facts out of the data, at times they have provided fascinating new information. The next step is to improve observation techniques with a more sophisticated measuring device.

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