Petrophysical signature of gold mineralization and alteration assemblages at the Canadian Malartic deposit, Quebec

Abstract

The rock physical properties of samples from the Canadian Malartic gold deposit in the Abitibi greenstone belt of Quebec have been measured to relate lithology and alteration assemblages to physical properties contrasts, and to provide geological interpretation of geophysical survey analyses for this type of ore deposit. Disseminated gold deposits are seldom directly characterized by a clear geophysical signature. However, we propose that a geophysical characterization of such ore deposits can be achieved by combining cost-effective geophysical surveys to identify zones of interest for gold exploration. This study has shown that the metasedimentary rocks and porphyritic intrusions that host the gold mineralization show similar variations in rock physical properties, probably because both rock types have similar geochemical and mineralogical compositions. However, the intrusive rocks show both magnetic and non-magnetic phases, and have a slightly lower density than metasedimentary rocks. Hydrothermal alteration produced continuous trends for magnetic susceptibility, density, and electric chargeability, but with no apparent variation in magnetic remanence and resistivity. These trends of decreasing density and magnetic susceptibility and increasing chargeability are correlated with alteration facies (carbonate saturation index), gold concentration, and proximity to ore. Based on this correlation, a principal component analysis petrophysical proxy has been established to represent this gradual hydrothermal mineralization process. This petrophysical proxy is a valid estimation of the variability of the rock physical properties inside the actual pit area of the Canadian Malartic deposit. Based on composite geophysical surveys (gravity, magnetic, and induced polarization) and inversion of the surface data for rock physical properties at depth, a petrophysical proxy, such as presented here, could help target zones of interest for orebodies similar to that at Canadian Malartic.