Full text loading...
-
Estimation of overburden thickness using airborne time-domain EM data and a few drill hole data
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 6th International AEM Conference & Exhibition, Oct 2013, cp-383-00031
Abstract
We present a technique for mapping the overburden thickness based on inversion of MEGATEM airborne electromagnetic data. These data are extensively available in many parts of Canada prospected for bedrock conductive targets in mineral exploration. The use of these data coupled with existing stratigraphic information at a few sites make possible the accurate estimation of the overburden thickness at very few expenses. Two sequential steps are used. The first step consists in inverting existing MEGATEM airborne electromagnetic data. The model to be inverted consists of two layers, a moderately conductive overburden lying over very resistive bedrock. Because the data are collected at long time gates with the MEGATEM system, the solution is non-unique, only the conductivity-thickness of the first layer can be well resolved but neither the conductivity nor the thickness. Actually the overburden can be generally modeled as a thin sheet. In the second step we use the expected correlation between depths known at a few drill holes and the estimated conductivity-thickness to estimate depths at sites where only conductivity-thickness data is available using the cokriging technique. In this study the overburden thickness known from drilling is the poorly sampled primary variable and the estimated conductivity-thickness from AEM inversion is the densely sampled secondary variable. The technique was tested on modeled data first, and then on existing survey data from the Octave river area, located in North-West Abitibi (Quebec, Canada), where overburden thickness data was available. The tests carried out in this project showed that the proposed technique allowed accurate thickness estimates even when very few drill hole data were available.