Case Studies - Mineral Exploration

GEOTEM^® in Ireland: Lisheen Mine

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During the period 1995 to 1999, extensive GEOTEM airborne electromagnetic (EM) surveying was carried out in Ireland by Fugro Airborne Surveys for several clients. Many of these are available as Open File Reports from the Exploration and Mining Division of the Department of the Marine and Natural Resources, Republic of Ireland (www.emd.ie). The illustrated results (Figure 1) over the Lisheen mine demonstrate the application of GEOTEM in this geological environment.

GEOTEM airborne EM data collected along a north to south line flown over the Lisheen mine in Ireland. The ore body is a massive sulphide comprising sphalerite, galena, marcasite and pyrite. The airborne EM data was collected with a base frequency of 75 Hz. The z- and x-component profiles are on the top two panels. The amplitudes along the whole profile are generally large, but show a slower decay (enhanced late time response) between 167000 and 166000. The conductivity depth images provided by Jim Macnae (middle panels) show the ore body more clearly. The downward dipping tail at the right side is an artifact of the imaging procedure which assumes that the conductive layers are flat lying and extend to infinity in the horizontal directions. The conductor is imaged at about 200 m depth and interpreted to be flat lying. This agrees very well with the geological control from the drilling (bottom panel).

Acknowledgement
This image was taken from Nabighian M.N. and Asten M.A. (2002) "Metalliferous mining geophysics - State of the art in the last decade of the 20th century and the beginning of the new millennium". Published in Geophysics, Vol. 67, pp 964-978.