Time-domain electromagnetic data interpretation using moving-loop configurations for sheet-like base metal ore deposits in resistive hosts

Abstract

A simple, useful, and practical tool is proposed for the interpretation of moving-loop time-domain electromagnetic (TEM) surveys over two-dimensional (2D) sheet-like conductors embedded in a resistive host. It is based on the relationship observed between attributes of the displayed responses and the geometrical and electrical parameters of the conductive ore body. The ore body is modelled as a plate conductor for which the depth, dip, and conductance parameters are estimated. Numerical and scale modelling are used to establish the interpretative expressions. Responses computed for the various plate parameters are classed according to the following response attributes: time constant, asymmetry, and peak-to-peak distance. Three expressions relating depth, dip, and conductance to the response attributes are determined using multiple linear regression. The relationships are validated using scale-modelling data. The method allows the determination of the plate depth, conductance, and dip with an accuracy of ±10%, ±10% and ±5° respectively. The method is tested on SIROTEM survey data from Chutes-des-Passes in Quebec (Canada), where drill hole information is available. The results show that the regression relationships provide accurate estimates of the basic characteristics of the deposits.