Rpm – Residual Potential Mapping; A New Approach To Mise-A-Lamasse

Better methods are needed for the detection and mapping of low-contrast hydrogeophysical<br>targets. Several publications within the last two decades show merit in the application of the mise-a-lamasse<br>method to hydrologic problems such as fracture flow, plume detection, and plume migration.<br>This presentation suggests a modification to the conventional approach that will enhance low contrast<br>targets.<br>The mise-a-la-masse method is a simple application of electrical methods where a buried<br>conductive feature is electrically energized and the resulting distorted electric field on the ground<br>surface is mapped. Mise-a-la-masse has been in use for decades in the mining industry on massive<br>sulfide orebodies, but, the requirement that the orebody be both massive and electrically contiguous has<br>limited the method’s application.<br>The normal interpretation of mise-a-la-masse data depend on the ability to observe the desired Efield<br>distortions caused by the energized target. In the case of low physical property contrasts,<br>distortions can be very difficult to see, if at all. The primary field observed in the proximity of the<br>energizing electrode dominates the response. Unless the target is particularly conductive and-or rather<br>shallow, it will not produce an E-field distortion distinct from the primary field. The observed E-field<br>consists of the superposition of several electrical responses.<br>The observed E-field at the ground surface is a combination of all of the effects created by the<br>energized target and various heterogeneities, conductive or resistive, that influence the distribution of<br>the current flux. These various effects may be due to geometry, such as layering; lateral paths, such as<br>fractures; and localized high-contrast features, such as culture.