A dc resistivity and IP borehole survey at the Casa Berardi gold mine in northwestern Quebec

Abstract

In the spring of 1996, a direct current (dc) resistivity and induced polarization (IP) borehole survey was carried out at the Casa Berardi gold mine in northwestern Quebec to study the spatial extent of the economic disseminated zone of an auriferous quartz vein type orebody. Crosshole pole‐pole and single‐hole pole‐dipole configurations were used to delineate the geometry of the body associated with the Casa Berardi fault system. Since the spatial data sampling was insufficient for 3D inversion, the interpretation has been done using 3D dc and IP forward modeling. Model changes were applied iteratively to match synthetic with field data. Sensitivities provide information on how to alter the models efficiently. Furthermore, they indicate the significant regions of the model, giving evidence on where the model is meaningful. A model study using a simple prismatic block structure is shown to enhance understanding of the physical response associated with the two types of borehole survey. The algorithms used for the interpretation offer a so‐called grid‐independent electrode positioning technique, which is a helpful modus operandi to significantly facilitate the simulation process. The result is a resistivity and chargeability model that produces the observed physical response and incorporates all known geological a priori information. Particularly, the IP response carries detailed information on the appearance of the orebody, whereas the potential response reflects the resistivity contrast between metavolcanic and metasedimentary rocks at the Casa Berardi fault.