Lookup NU author(s): Professor David Manning,
Professor Paul Younger
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The first deep geothermal exploration borehole (995 m) to be drilled in the UK for over 20 years was completed at Eastgate (Weardale, Co. Durham) in December 2004. It penetrated 4 m of sandy till (Quaternary), 267.5 m of Lower Carboniferous strata (including the Whin Sill), and 723.5 m of the Weardale Granite (Devonian), with vein mineralization occurring to 913 m. Unlike previous geothermal investigations of UK radiothermal granites that focused on the hot dry rock concept, the Eastgate Borehole was designed to intercept deep fracture-hosted brines associated with the major, geologically ancient, hydrothermal. vein systems. Abundant brine (≤46 °C was encountered within natural fracture networks of very high permeability (transmissivity c. 2000 darcy m) within granite. Evidence for the thermal history of the Carboniferous rocks from phytoclast reflectance measurements shows very high values (≥3.3%) indicating maximum temperatures of 130 °C prior to intrusion of the Whin Sill. Geochemical analysis of cuttings samples from the Eastgate Borehole suggests radiothermal heat production rates for unaltered Weardale Granite averaging 4.1 μW m-3, with a mean geothermal gradient of 38 °C km-1. The Eastgate Borehole has significant exploitation potential for direct heat uses; it demonstrates the potential for seeking hydrothermal vein systems within radiothermal granites as targets for geothermal resources.
Author(s): Manning DAC, Younger PL, Smith F, Jones J, Dufton D, Diskin S
Publication type: Article
Publication status: Published
Journal: Journal of the Geological Society
Print publication date: 01/03/2007
ISSN (print): 0016-7649
Publisher: Geological Society Publishing House
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