Characterising thermal water circulation in fractured bedrock using a multidisciplinary approach: a case study of St. Gorman’s Well, Ireland

Blake, Sarah; Henry, Tiernan; Moore, John Paul; Murray, John; Campanyà, Joan; Muller, Mark R.; Jones, Alan G.; Rath, Volker; Walsh, John

Characterising thermal water circulation in fractured bedrock using a multidisciplinary approach: a case study of St. Gorman’s Well, Ireland | Caractérisation de la circulation d’eau thermale dans le substratum rocheux fracturé à l’aide d’une approche multidisciplinaire: une étude de cas à St. Gorman’s Well, Irlande Caracterización de la circulación de aguas termales en rocas fracturadas mediante un enfoque multidisciplinar: un estudio de caso de St. Gorman’s Well, Irlanda 使用多学科方法表征裂隙基岩中的热水循环:以爱尔兰圣戈尔曼井为例 Caracterizando a circulação de água termal em rocha fraturada usando uma abordagem multidisciplinar: um estudo de caso do poço de St. Gorman, Irlanda

2021

A hydrogeological conceptual model of the source, circulation pathways and temporal variation of a low-enthalpy thermal spring in a fractured limestone setting is derived from a multidisciplinary approach. St. Gorman’s Well is a thermal spring in east-central Ireland with a complex and variable temperature profile (maximum of 21.8 °C). Geophysical data from a three-dimensional(3D)audio-magnetotelluric(AMT) survey are combined with time-lapse hydrogeological data and information from a previously published hydrochemical analysis to investigate the operation of this intriguing hydrothermal system. Hydrochemical analysis and time-lapse measurements suggest that the thermal waters flow within the fractured limestones of the Carboniferous Dublin Basin at all times but display variability in discharge and temperature. The 3D electrical resistivity model of the subsurface revealed two prominent structures: (1) a NW-aligned faulted contact between two limestone lithologies; and (2) a dissolutionally enhanced, N-aligned, fault of probable Cenozoic age. The intersection of these two structures, which has allowed for karstification of the limestone bedrock, has created conduits facilitating the operation of relatively deep hydrothermal circulation (likely estimated depths between 240 and 1,000 m) within the limestone succession of the Dublin Basin. The results of this study support a hypothesis that the maximum temperature and simultaneous increased discharge observed at St. Gorman’s Well each winter is the result of rapid infiltration, heating and recirculation of meteoric waters within a structurally controlled hydrothermal circulation system.

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