Interpretation of magnetic susceptibility: a new approach to geophysical evaluation of the degree of rock alteration

Magnetic susceptibility measurements on cores from boreholes in the Eye–Dashwa lakes pluton, an Archean granitic pluton near Atikokan, Ontario, give a quantitative evaluation of the alteration level of these rocks. The histogram of the 5406 magnetic susceptibility measurements taken from 3.3 km of cores shows a multimodal distribution. In order to differentiate these subpopulations and to recognize their geological significance a numerical …