A preliminary interpretation of Tellus airborne radiometric data

An airborne geophysical survey of the whole of Northern Ireland was flown by the Geological Survey of Northern Ireland in 2005 and 2006 as part of the Tellus project funded by the Department of Enterprise, Trade and Investment of Northern Ireland and by the Rural Development Programme through the Northern Ireland Programme for Building Sustainable Prosperity. Magnetic, electromagnetic and radiometric data were acquired at 200 m line spacing and a flying height of 56 m (240 m over built-up areas) using the Joint Airborne Capability of the British Geological Survey and the Geological Survey of Finland. In total, 82,000 line-km of data were acquired. The radiometric data were collected as full 256 channel gamma-ray spectra every 1 s or approximately 70 m of ground coverage. The Tellus project also included a baseline geochemical survey of Northern Ireland for which 22,000 samples, of soils, stream sediments and stream waters, were collected. A preliminary assessment of the radiometric data has been carried out to illustrate the type of features present in the dataset, at both regional and local scales, and provide pointers to possible areas of future research. At the scale of the whole of Northern Ireland the data reflect the major solid geological subdivisions; the Lower Palaeozoic greywackes and Palaeogene intrusives of the SE have relatively high K, U and Th contents. In contrast the Palaeogene basalts in the NE have much lower radioelement concentrations, although Palaeogene rhyolites, and inliers of Palaeozoic and Precambrian rocks in this area, have higher values. Surrounding the basalts to the south and west, the Triassic sedimentary rocks have moderate K, eU and eTh levels. The more heterogeneous geology of the western part of Northern Ireland is reflected in the radiometric data with juxtaposed areas of relatively high and low radioelement content. Formation boundaries within the basement and Upper Palaeozoic rocks, sometimes faulted, are clear in places as ENEWSW and NE-SE-trending features.