Mapping depth to basalt using magnetic spectra

Summary

Between 30 and 40% of the Northern Territory is underlain by basalts, mainly the late early Cambrian Kalkarindji Large Igneous Province. These basalts provide a solid floor to mining activities in the overlying strata. They might also provide a buffer of alkalinity and reduction during ore genesis, and should therefore be included in modelling by mineral explorers. A key parameter in the modelling of prospective mineralised zones is the depth to the basalts.

Using the power spectra of open file airborne magnetic data, depths to subsurface basalts can be mapped. A point-and-click package was developed for this purpose, is currently being used to map the depths to the basalts of the Kalkarindji LIP in the Northern Territory.

Open file surveys of magnetic data have varying quality, affecting the ease of extraction of magnetic depths. Although successful depth results can be expected from modern 10 Hz aeromagnetic surveys, the older, 1 Hz proton procession magnetometer data, is more problematic. However some good depth results have been obtained.

Key words::

• magnetic depths
• flood basalts
• power spectra