Discoveries through innovation in applications of airborne and ground TDEM in very conductive environment

Abstract

In the Buffalo Head Hills diamond province of Alberta, Canada, kimberlites have intruded a thick sequence of sedimentary rock units with thickness in excess of 300-500 m and resistivities of 5?10 ohm-m. In contrast to the conductive sedimentary rock the kimberlite intrusion is invariably characterised by a much higher electrical resistivities. These ``resistive' kimberlites can be detected by both airborne and ground time domain EM methods. Because of the host sedimentary rock?s very low resistivity, the resistive kimberlite response in many cases appears counterintuitive to the expectations based on the simpler analysis of the problem which ignores the EM interactions between a 3D body and a conductive host. For similar reasons, successful detection of kimberlites in the Buffalo Head Hills province also required developments of algorithms which facilitate correction of airborne TDEM data for variations in aircraft altitude and pitch. ``Anomaly hunting' analysis which decompose the spatial and temporal characteristics of the EM response into a number of components and innovations in the inversion and transformations of ground TDEM data sets was also required. Application of standard Conductivity-Depth-Image (CDI) techniques was not appropriate to the solution to the problem. A new pseudo 1D-inversion algorithm was developed to partially assist in the assessment of the data. A number of areas previously covered by detailed airborne magnetic surveys were re-surveyed with the Geotem airborne TDEM system. Use of the developed concepts and insights has resulted in a number of new diamonds-bearing non-magnetic kimberlite discoveries. New discoveries, for example, include kimberlites K296 (with a surface area of some 500 by 500 m), and K252 (with an estimated minibulk sample diamond content of 55.0 cpht), the highest estimated diamond content of all Alberta kimberlites to date.