Geophysical exploration for gold

The world-wide interest in gold that has characterized mineral exploration in the 1980s has had a profound effect on the focus and style of geophysical prospecting. In the 1950s and 1960s, direct detection methods (chiefly airborne and ground electromagnetics (EM)) were applied widely in the search for massive sulphide-hosted base-metal deposits (Paterson, 1967). At the same time, induced-polarization (IP) methods were developed for the direct detection of porphyry coppers and other disseminated sulphide ores (Hallof, 1967). In the 1970s, refinements were made to extend the search by electrical methods under deeply weathered rocks (Sumner, 1977; Ward 1977; Hallof, 1980). In all of this direct search for sulphides, there also lay the possibility of finding gold. Hannington et al. (this volume) estimate that about 5% of massive sulphide deposits world wide contain mineable gold, and some of the richest gold deposits have been found while exploring for base metals (e.g. Crone, 1984; Dowsett and Krause, 1984)