Examination of the gravity & electromagnetic survey methods applied to coal exploration in the area of the Southern Gunnedah Basin

Abstract

The New South Wales Department of Mineral Resources (DMR) and the Japanese New Energy and Industrial Technology Development Organisation (NEDO), have entered into a Joint Coal Exploration Research Agreement aimed at developing advanced coal exploration technologies with particular emphasis on geophysical technologies. As part of the first year’s project an investigation into the applicability of gravity and transient electromagnetic geophysical methods for coal exploration was undertaken.The Caroona coal prospect has a resource of high quality multi-seam coal lying within relatively complex geology. While significant drilling has been undertaken in the area, a number of aspects of the geology cannot be adequately identified by drilling. The area is known to contain thrust faulting and igneous intrusions. The coal seams are covered by 40-80 m of alluvial materials, which can reduce the seismic energy transmission for conventional seismic surveys.Trial gravity and electromagnetic surveys were undertaken to test the potential of these geophysical methods and to supplement the seismic data. The aim was to provide a much better estimate of the bedrock-alluvium interface and to define the distribution of intrusions and faulting.The field work involved undertaking a gravity and electromagnetic survey along a 3.5 kilometre traverse which coincides with a seismic survey line (L972) in the Caroona area. It is believed that the integration of these geophysical methods has facilitated the extrapolation of geological models derived from the seismic interpretations. The regional geophysical coverage that can be provided by these techniques is extremely cost effective and will assist the evaluation and modeling of areas involving complex geology.In the Caroona area the preliminary results have shown that the gravity and electromagnetic data has defined the alluvium thickness and structural zones.