Mineralisation and fault zone architecture at Portheras Cove: Implications for deep geothermal exploration
Lead supervisor: Dr Billy Andrews
Location: School of Geography, Earth and Environmental Sciences, University of Plymouth
Duration: 8 weeks
Suitable undergraduate degrees: Earth Science, Geology, Physical Geography
Rational: The UK Government has committed to becoming carbon neutral by 2050, however, the decarbonisation of the heating and cooling sector remains a significant barrier to achieving this. Enhanced Geothermal Systems (EGS) extract heat by using fluid pathways between two deep (>500 m) boreholes, and have the potential to provide an economically viable heat resource in areas where bedrock favours high heat flows (e.g., granites) (Olasolo et al., 2016). Due to the low permeability of granites, fault and associated fracture damage zones are targeted, such as the United Downs Deep Geothermal Project and the Eden Deep Geothermal Plant in SW England. Additionally, waters from EGS schemes may contain key elements required for the green revolution (e.g., lithium) that can extracted following heat extraction. Whilst SW England has a large geothermal potential, the geological history of the region means fault and fractures display multiple stages of reactivation and mineralisation. Mineralisation may reduce the connectivity and permeability of the fracture system (e.g., Andrews et al., 2020). Surface exposure of faults/fractures in granite, such as the Portheras Cove Fault Zone (PCFZ) in Cornwall, can be investigated to understand the distribution and evolution of fluid pathways, which is essential information for planned EGS schemes that target similar structures.
Aims & Objectives: This 8-week project will study the structural and permeability evolution of the PCFZ and present the findings to industry partners Cornish Lithium. The objectives of the project are to:
1) Establish the temporal evolution of slip surfaces, fractures, and veins within the PCFZ through mapping drone imagery and geological fieldwork.
2) Deduce the spatial relationship between mineralisation/fracture infill and the principal slip surface of the PCFZ.
3) Discuss the implication for permeability close to fault zones in granite and the impact of this on EGS.
Workplan: The student will use a combination of computer-based data analysis and fieldwork to meet the aims and objectives of the project. High-resolution drone footage has previously been collected of Portheras Cove. The student will use QGIS to digitise the traces of faults, fractures and mineralised veins in the study area. These data will be ground-truthed during the fieldwork to ensure that the lineament mapping is an accurate representation. Fieldwork will also gather data that is not readily captured by drone imagery, such as fault kinematic indicators and identifying fracture infill/mineralisation. Finally, the fracture dataset will be analysed using NetworkGT (Nyberg et al., 2018) to investigate the connectivity of the fractures and speculate on applications to geothermal systems and extraction.
Skills development: The student will learn to use QGIS and NetworkGT to digitise fracture networks and analyse the networks to determine fluid flow pathways. During fieldwork the student will develop their geological field skills and how to ground truth remote data. Throughout the student will receive training in research methodologies, data presentation and communicating research to 3rd parties.
References: 1) Olasolo et al. (2016). Renew. Sustain. Energy Rev. 56 pp113-144; 2) Andrews et al., (2020). Solid Earth, 11, 2119-2140; 3) Nyberg et al., (2018). Geosphere, 14(4), 1618-1634.