AMT prospecting of kimberlites in the Arkhangelsk region

In 2005 NordWest Ltd accomplished the complex electromagnetic survey at the zones of magnetic field anomaliesВ  in Arkhangelsk region.

According to the drilling and aeromagnetic data interpretation, the kimberlite pipes are nearly vertical structures with their upper edges lying at 50-150 m depths from the surface. In plane the pipe shapes vary from isometric 100x100m to elliptic 300x700m.

The complex geophysical studies involved:

  1. TEM measurements using TEM-FAST measuring and processing system. Measurement grid cell 100x100m. Total volume of TEM measurements amounted to 634 stations.
  2. AMT electromagnetic prospecting with vertical magnetic field measurements (MTU-5A Phoenix instrumentation). Measurement grid cell 100x100m. Total volume of TEM measurements amounted to 737 stations.

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Standard AMT technique implies analyzing the impedance tensor determined by the ratio between horizontal components of the MT field. Additional measurements of the vertical magnetic field component allow determination of magnetovariational parameters (tipper) that are good indicators of resistivity inhomogeneities in the studied cross-section.

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Combined interpretation of TEM and AMT data revealed the regions within the studied area that are perspective for kimberlite structures. Of top interest are the zones of increased conductivity and their related regions of radial orientation of real tippers.

Thus, in section K-3A, according to the electromagnetic prospecting results, the verification well had been sunk (shown by a red circle in the figure on the left). Drilling resulted in the discovery of a new pipe.В 


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