Enhanced resolution of geological structures from magnetic data: an example from the Abitibi Greenstone Belt of Northern Ontario

Structural information about that portion of the economically important Des tor-Porcupine Deformation Zone and its associated faults, which lie buried under many metres of Clay Belt sediments in the region north of Matheson, O ntario, must rely principally on interpretation of geophysical data. In thi s area, the Archean greenstones of the Abitibi are crosscut by at least thr ee generations of strongly magnetic diabase dykes. The predominant dyke set , the Matachewan, trend north-south, orthogonal to structures in the greens tones. Directional horizontal derivative analysis of the total magnetic fie ld, which has a much sharper angular cutoff than that provided by standard Fourier-based filters, provides a method for separating the magnetic contri butions from these two sources. This analysis revealed the existence of a p reviously unidentified fault (the Winslow fault) located to the north of, a nd parallel to, the economically significant Pipestone Fault. We also defin e a second new fault, the Carr fault, that is intimately associated with th e existence of a buried felsic intrusive complex in Carr Township. Possible associations between these faults and previously known faults defined from surface mapping programs are explored.