Interpretation of the magnetic gradient tensor and normalized source strength applied to the Tallawang magnetite skarn deposit, New South Wales, Australia

Abstract

Summary Acquisition of magnetic gradient tensor data is likely to become routine in the near future. In the meantime, significant value can be added to conventional TMI surveys of sufficiently high quality by calculating vector and tensor components and applying newly developed methods to interpretation of these more complex data forms. New methods for inverting gradient tensor surveys to obtain source parameters have been developed for a number of elementary, but useful, models. These include point dipole (sphere), vertical line of dipoles (narrow vertical pipe), line of dipoles (horizontal cylinder), thin dipping sheet, and contact models. A key simplification is the use of eigenvalues and associated eigenvectors of the tensor. The normalized source strength (NNS), calculated from the eigenvalues, is a particularly useful rotational invariant that peaks directly over 3D compact sources, 2D compact sources, thin sheets and contacts, independent of magnetization direction. In combination the NSS and its vector gradient determine source locations uniquely.