Technical Papers - Airborne Electromagnetics

How to Find Localised Conductors in GEOTEM Data

Peter Wolfgram and Stephen Thomson, Fugro Airborne Surveys, Australia
Marina Hyde, Encom Technologies Pty Ltd, Level 2, 118 Alfred Street, Milsons Point, NSW 2061, Australia

Abstract

Orebodies, mineralised zones, faults, folds, contacts, etc. may represent localised electrical conductors that create airborne electromagnetic (AEM) responses of interest to explorationists. However, typical AEM datasets in conductive regimes exhibit numerous features besides those of interest and it is left to the interpreter to identify the ones that are of significance to the interpretation task at hand. 

Synthetic data can be used to illustrate typical effects of host medium and conductive overburden on target responses, and how these might be identified in the presence of noise such as variations in aircraft ground clearance. Although an understanding of the complex anomaly features is possible, analysing large data sets will require rapid methods of pinpointing anomalous areas and allowing the user to employ visual correlation over a map to aid in the interpretation.

Different transformations of the data can enhance different features of interest to the explorationist. The conductivity depth transform (CDT) maps broad conductive zones and their depths - it is less suitable for detecting localised conductors. The stationary current image (SCIT) on the other hand indicates areas where electric currents become trapped in localised conductive features such as isolated bodies, faults, folds, etc. The SCI emphasises structural features because it is optimised for lateral contrasts in electrical conductivity. 

Published in Exploration Geophysics, 1998, volume 29, pages 665-670. 

No pdf file for this paper is available for download. Requests for a paper copy can be made to  pwolfgram@fugroairborne.com.au or  s.thomson@fugroairborne.com.au.