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A preliminary interpretation of Tellus airborne magnetic and electromagnetic data for Northern Ireland

By B.C. Chacksfield


An airborne geophysical survey of the whole of Northern Ireland was flown in 2005 and 2006 as\ud part of the Tellus project. This project was funded by the Northern Ireland Department of\ud Enterprise Trade and Investment and by the Rural Development Programme through the\ud Northern Ireland Programme for Building Sustainable Prosperity (\ud The aircraft used was a De Havilland Twin Otter which carried magnetic, electromagnetic and\ud radiometric sensors. It was operated as a joint venture between the British Geological Survey\ud (BGS) and the Geological Survey of Finland (GTK). Survey lines were spaced 200 m apart and\ud orientated NNW or ESE (165 and 345º). The flying height was 56 m above ground (185') in rural\ud areas rising to 240 m over urban areas. This report presents a preliminary interpretation of the\ud airborne magnetic and electromagnetic data and shows examples of the types of geological\ud feature that can be identified from the data on a regional scale. A few comments on the\ud radiometric results are also included together with a brief evaluation of the mineral potential of\ud Northern Ireland based on the airborne geophysical data. For the preliminary interpretation many\ud high resolution images of the magnetic, electromagnetic and radiometric data were generated and\ud analysed in a GIS system along with existing regional gravity, digital geological mapping and\ud mineral occurrences data. The main structural elements were identified and digitised and a\ud structure map produced.\ud The Tellus data have provided a wealth of new information about the geology, regional structure\ud and mineral potential of Northern Ireland and the GIS has proven a powerful tool for analysing\ud these data at both regional and local scales. The strong magnetic signature of the Antrim basalts\ud allows their surface extent to be mapped accurately in areas of poor exposure, and within the\ud basalt outcrop lineaments associated with bounding faults of sedimentary basins have been\ud identified. The margins of the Tyrone Igneous Complex and the internal structure of the complex\ud itself are revealed in stunning detail and many new faults and sheared rocks identified. Within\ud the adjacent Dalradian rocks arcuate linear magnetic anomalies related to fold structures and\ud several important magnetic marker horizons have been revealed. The full extent of the dyke\ud swarms that cross Northern Ireland has only now come to light with the new Tellus magnetic\ud data. Dykes reveal regional stress fields, and those that are offset can be used to measure post\ud Palaeogene fault displacements. The margins of the major intrusive centres of the Newry\ud Igneous Complex, Mourne Mountains, Slieve Gullion and Carlingford and their internal\ud structure have also been delineated by the magnetic and gravity data.\ud The rocks that make up Northern Ireland show a considerable variation in their electrical\ud properties and where contrasts between geological formations are sufficiently large their\ud geological distribution can be mapped.\ud The main mineral prospectivity target in Northern Ireland lies within the area covering the Upper\ud Dalradian rocks of the Sperrins area, the Omagh Thrust Fault and the sheared rocks of the\ud Tyrone Igneous Complex where this area shows the greatest degree of shearing and faulting.\ud Magnetic anomalies depict a series of arcuate structures within which mineralisaton is located in\ud a series of distinct belts and appears to be spatially related to shearing and faulting. A\ud prospectivity study of this area is highly recommended

Publisher: British Geological Survey
Year: 2010
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