CRAE's approach to downhole TEM at Broken Hill

Abstract

Downhole TEM is being used extensively by CRA Exploration Pty Ltd (CRAE) in the Broken Hill district as a means of detecting massive base metal sulphides which may be close to but not intersected by drillholes. Coupling diagrams used in conjunction with drill sections help to plan loop layout and to develop starting models for quantitative forward modelling schemes. Nomograms for estimating time constants and for relating these to target sizes and tonnages assist interpretation, and help maintain an economic perspective. A field example from the NBHC mine at Broken Hill illustrates the significance of drillhole depth and the importance of establishing the relative polarities of transmitter and receiver in the field.