A mise‐à‐la‐masse study of the Cavendish Geophysical Test Site

Abstract

The mise‐à‐la‐masse method of electrical prospecting is used when a conductive, mineralized zone has already been located. A current electrode is placed directly in the mineralized zone, and the resulting potential field is mapped on the surface or in the subsurface via drill holes or underground openings. The potential field reflects the shape, size, and orientation of the mineral deposit. A field study of this method was carried out at the Cavendish Geophysical Test Site in Ontario, Canada. Two vein‐type mineralized bodies, zone A and zone B, are known to exist at the site. Drill holes were used to implant a current electrode in each of the veins and surface potentials were measured. The extension of the two zones in the strike direction was established with the resulting mise‐à‐la‐masse potential profiles. However, no electrical continuity between zones A and B could be discerned, indicating that the veins are not connected at depth. The dip of zone A appears to be toward the west, contrary to that inferred from the drill hole logs. The measured potentials are influenced by the mutual proximity of the far current and potential electrodes as well as by the location of the electrodes with reference to the local geologic structure.