In-mine (tunnel-to-tunnel) electrical resistance tomography in South African platinum mines

Abstract

The applicability of tunnel-to-tunnel electrical resistance tomography (ERT) for imaging disruptive geological structures ahead of mining, in an igneous platinum mining environment is assessed. The geophysical targets of interest are slump structures or ‘potholes’ that disrupt the lateral continuity of the thin, tabular platinum orebodies of the Bushveld Complex, South Africa. The study involves a combination of model studies, laboratory property measurements and trial surveys. The property studies indicate that the problem reduces to the challenging scenario of a high-resistivity background (orebody horizon) in which an even more resistive target (pothole) is embedded. The model studies show that ERT can potentially image disruptive potholes ahead of mining. It is further demonstrated that the 2D approach can generally be used as a reconnaissance tool, but that a variety of three-dimensional (3D) effects need to be considered, and, in some instances, appropriate corrections should be applied. 3D scenarios that are considered include targets with limited extent perpendicular to the image plane, targets with a relatively small volume and targets that are asymmetrical about the image plane. Other 2D model assumption violations considered include the effect of tunnels and multi-layered backgrounds. Finally, results from an experimental in-mine survey are included to illustrate that ERT can be used to detect and delineate potholes ahead of mining