Confronted with this precariously balanced rock formation on the northeast side of Kyushu Island, Japan, our survey crew was grateful there were no earth-quake in the area Many mining companies are enthusiastically embracing MT (Magnetotellurics) and AMT (Audio Frequency MT) for exploration; the techniques are experiencing rapid growth.
The present wave of interest started quietly in 1992 when two MT soundings were made on either side of INCO's 1750-meter deep Trillabelle nickel deposit in the famous Sudbury nickel mining area, 400 km north of Toronto.
(Although earlier work by the University of Toronto during the 1970's aroused interest with surveys over a number of shallow ore bodies, it didn't lead to routine application of the technique.)
First 3-D MT/AMT surveys in 1997 !
But the 1992 soundings at Trillabelle showed unmistakable evidence of deep conductive mineralization. That positive evidence, combined with the great depth of investigation (three times deeper than previous surface-based Electromagnetic surveys) stimulated more surveys every year since. With each survey came more knowledge, improved field procedures, increased efficiency and lower costs.
The initial surveys in the Sudbury area soon led to more work in Canada and other countries , including USA, Chile, Bolivia, Peru, Argentina, Australia, Papua New Guinea, China and Japan. AMT I 1 Hz to 10,000 Hz) and MT 1100 Hz to 0.0005 Hz) are becoming recognized as fast, efficient, deep-looking techniques. They can detect conductive ore bodies as deep as 2000m, perform general subsurface geological mapping, Jarify fault geometry, correlate faults with geology and help focus can zones and structures favourable for mineralization.
Today many major mining companies (including INCO, Falconbridge, CODELCO, and Placer Dome) utilize MT and AMT.
So far the surveys have been 2-D (the soundings are made along a number of profiles). In 1997, the first 3-D AMT/MT surveys will be done, providing the ultimate in achievable spatial resolution. Surveys in 3-D are feasible even where access difficulties rule out continuous profiling.
ADVANTAGES OF AMT / MT
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