A mathematical basis for the application of power spectrum analysis to aeromagnetic map interpretation is developed. An ensemble of blocks of varying depth, width, thickness, and magnetization is considered as a statistical model. With the use of the fundamental postulate of statistical mechanics, a formula which can be used to analyze the power spectrum of an aeromagnetic map is developed. The influences of horizontal size, depth, thickness, and depth extent of the blocks on the shape of the power spectrum are assessed. Examples which include power spectra of maps from Canada and Central America demonstrate the application of the approach. In the cases studied a double ensemble of blocks appears to best explain the observed power spectrum characteristics.

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A new method for calculating anomaly patterns and type curves of apparent resistivity and apparent chargeability over three‐dimensional bodies imbedded in a half‐space is practicable. The solution of the boundary‐value problem for a point source of current near a body of arbitrary shape in the form of an inhomogeneous integral equation is solved numerically by the method of least squares. The solution is then used to construct the apparent resistivity and apparent chargeability functions for three and four‐electrode arrays in the vicinity of the body in a straightforward manner. Type curves show the application to an actual field example. Finally, some simple, direct aids for interpreting anomalies over mineralized zones of compact (i.e. roughly spherical) shape result. This study represents the results of the first phase of a continuing program of research into resistivity and IP interpretation theory.

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