Geothermal potential of granitic rocks of the Mourne Mountains

The Palaeogene Mourne Mountains Complex in County Down is a potential geothermal energy resource due to the high levels of radioactivity in its granitic rocks. The regional Tellus geochemical and geophysical surveys mapped the radioelement distribution of the rocks at surface. Follow-up investigations confirmed the heat potential of these, some of the most radioactive rocks in the island of Ireland, and investigated their depth extent by electromagnetic (magnetotelluric, MT) depth sounding. The results suggest that resistive rocks, interpreted as the granitic intrusion, reach depths of 5 to 6 km in the Eastern Magmatic Centre and 4 to 5 km in the Western Magmatic Centre. The MT results are discussed in the context of the different models of granite emplacement proposed for the Mournes. Tellus aeromagnetic data and MT modelling suggest that the granite bodies extend at depth to the south of the outcrop, as predicted for the laccolith emplacement mechanism, although modelled granite thickness is greater than expected. The MT data indicate a high-conductivity zone of unknown origin beneath the granites, extending from depths of 8 to 20 km. The high radiogenic heat production and the modelled thicknesses of granites are favourable factors for the enhanced geothermal system (EGS) potential of the Mournes, although the measured geothermal gradients and calculated heat flows are lower than those in comparable EGS targets