The Cornubian geothermal province: heat production and flow in SW England: estimates from boreholes and airborne gamma-ray measurements

Abstract

The Cornubian granite batholith provides one of the main high heat production and flow provinces within the UK. An extensive programme of borehole measurements was undertaken in the 1980s to characterise the geothermal resource. Here we revisit the published data on heat flow and heat production from 34 boreholes and revise the published heat flow values in accord with modern palaeoclimate knowledge. This leads to a more rigorous (and increased) set of estimated temperatures at depth across the granite outcrops. Predicted temperatures at a depth of 5 km largely exceed 200 °C and are 6-11 % higher than previously estimated values. We also reconsider the borehole heat production values in conjunction with new heat generation information from a recent regional-scale airborne geophysical survey. The radiometric (gammaray) data provide detailed (~70 m along-line) ground concentration estimates of the heat-producing radioelements. These are then combined to estimate heat production in the near surface. The airborne estimates are subject to attenuation by the soil profile. Here we demonstrate and then adopt an assumption that the observations of the soilbedrock medium undergo a flux attenuation by a factor of about two compared to the response of the underlying material. The revised estimates are then correlated with their equivalent deeper borehole estimates. Linear regression is then used to correct the shallow airborne estimates to values that are consistent with the deeper borehole determinations. The procedure provides a detailed and extensive mapping of heat production at both on-and off-granite locations across SW England. The Dartmoor and Land's End granite offer the greatest spatial geothermal potential in terms of their intrinsic radionuclide concentrations and associated heat production. District-scale heat production is studied using the airborne data acquired uniformly across conurbations. The analysis identifies the towns of Camborne, Penzance, St. Austell, Redruth and St Ives as having relatively high values (>4 μW m −3 ) within their urban perimeters.

Geothermal heat flow in Antarctica: current and future directions

“…Gamma ray spectrometry can be surveyed in the field, on samples, or from the air. Airborne surveys can cover large areas, and have been used to survey Western Australia, SW England, and all of Finland (Beamish and Busby, 2016;Bodorkos et al, 2004;Hyvönen et al, 1972). However, the data requires multiple corrections, and the recorded data integrates the radiation from the bedrock, surface cover (including soil and vegetation), the atmosphere, cosmic radiation, and the aircraft, making the data less accurate than ground measurements or sample analysis (Veikkolainen and Kukkonen, 2019).…”

Differences in natural gamma radiation characteristics of Erinpura and Malani granites in NW India

“…Several methods are used for the survey and mapping of U and Th concentrations in natural rock exposures. For larger-scale surveys, airborne gamma ray spectrometer measurements are useful, e.g., for geological mapping (Patra et al 2016), for radon hazard forecast in Norway (Smethurst et al 2008) or for establishing heat production maps for granitic terrains (Beamish and Busby 2016). The disadvantages of this method are difficulties in correlation with in-situ data (Beamish and Busby 2016;.…”

“…For larger-scale surveys, airborne gamma ray spectrometer measurements are useful, e.g., for geological mapping (Patra et al 2016), for radon hazard forecast in Norway (Smethurst et al 2008) or for establishing heat production maps for granitic terrains (Beamish and Busby 2016). The disadvantages of this method are difficulties in correlation with in-situ data (Beamish and Busby 2016;. In addition, various factors can lead to the inaccuracy of the in-situ data such as topography or weathering (for review, see McCay et al 2014, and references therein).…”

U–Pb Geochronology of Hydrothermal Monazite from Uraniferous Greisen Veins Associated with the High Heat Production Mount Douglas Granite, New Brunswick, Canada

“…Gravity modeling in the eastern part of the Saint George Batholith, near the Welsford heat-flow site (northeastern part of the Mount Douglas Granite, Figure 2) indicates a thickness of about 6.5 km for the granite, considerably thicker than the thickness estimated by Drury et al [76] who used a heatflow-heat-generation relationship (1.4-3.3 km radiogenic thickness). The difference between estimated geothermal and gravity depth may be attributed to the enrichment of the intrusion with HHP granites are evolved granites with anomalously high Th, U, K, and total REE [37,54,[57][58][59] and are responsible for parts of the crustal heat flow due to radiogenic decay of Th, U, and K [60,61] and have been reported from different places (e.g., [45,[62][63][64][65][66][67][68][69][70][71]). Granites with approximately four times or more uranium than the average crustal abundance (3.5 ppm U [72]; 4 ppm U [73]) are considered to be HHP granites.…”