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The chemical interaction of groundwater with granitic rock under hydrothermal conditions is relevant to understanding the origin of pore fluid chemistry in granite plutons and cratonic shield areas, late-stage hydrothermal mineralisation associated with granite emplacement and the assessment of Hot Dry Rock geothermal energy systems in crystalline rocks. In order to interpret fossil hydrothermal systems, or predict reactions in a geothermal reservoir, models have been developed which incorporate kinetic and equilibrium features of these reactions. This report describes the application of EQ3NR/EQ6 to the problem of understanding experimental water-rock reactions carried out in relation to the development of a HDR geothermal system in granite at Rosemanowes, Cornwall. The model was used to evaluate the results of a batch autoclave experiment, reacting Carnmenellis Granite with a fluid similar to the composition of circulation fluids currently being used at the test site at a 10:1 fluid /solid ratio. Kinetic data for the dissolution of the minerals from the granite for input to EQ6 were obtained in separate flow-through autoclave experiments at 80 C and subsequently fine-tuned with an iterative procedure. Evidence of the natural historic reaction of the granite with groundwater in the temperature regime 25 -200 C was provided by the composition of deep groundwater and vein infillings within the granite.

Additional information

Authors: FALCK W E, British Geological Survey, Nottingham (GB);SAVAGE D, British Geological Survey, Nottingham (GB)
Bibliographic Reference: EUR 12364 EN (1988) 40 pp.
Availability: British Geological Survey, Keyworth, Nottingham NG12 5GG (UK) as Technical Report WE/88/44, 1988
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