Mapping laterally varying conductance using EM gradients over dry tailings ponds

Abstract

Mine waste or the saprolite associated with nickel latentes have a conductivity thickness (conductance) that varies laterally. In order for EM methods to be used to easily map lateral changes in conductance, a simple inversion needs to be developed. Through forward modeling we show that, assuming a uniform conductance and inverting for an apparent conductance is sensitive enough to identify lateral conductance changes. However, one of the required terms in the inversion is the vertical derivative of the secondary vertical magnetic field (dHz/dz). The accurate measurement of spatial electromagnetic derivatives requires a good signal‐to‐noise ratio. Field studies performed over a relatively resistive dry tailings pond showed that the gradient noise is sufficiently lower than the expected signal, suggesting that dHz/dz should be measurable.