Magnetic Vector Inversion

A simple approach to the challenge of varying direction of rock magnetization

Modelling of local magnetic field anomalies, and in particular 3D voxel-based modelling, is now a primary tool in exploration targeting. The majority of current voxel-based magnetic inversions assume anomalous magnetization in the direction of the inducing earth's field as described by Li and Oldenberg (1993). However, as noted in numerous studies and the practical experience of many modellers, the direction of rock magnetization, particularly in strongly magnetized rocks, is often in a direction different from the primary geomagnetic field. This may be due to any combination of remanent magnetization, demagnetization, anisotropy of magnetic minerals or perhaps even other phenomena not yet understood.

Ellis et al (2012) developed the Magnetic Vector Inversion (MVI) method to directly model the vector of magnetization based only on anomalous TMI data. The method allows the modelling optimization process the freedom to orient the direction of magnetization to best fit the observed data. Notably, the MVI method does not concern itself with the reason for varying magnetization direction, which is left to the interpreter to ponder together with other information that may be at hand.

In this case-study work we demonstrate the application of MVI to particularly challenging and well known magnetic anomalies in both Brazil and Australia/

This seminar was presented and recorded at the Canadian Exploration Geophysical Society (KEGS) meeting on 2014-05-13.

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