Helium, radon, and hydrothermal circulation associated with the Carnmenellis radiothermal granite of southwest England

Abstract

The Carnmenellis granite of southwest England has higher than average radioelement concentrations and a heat flow greater than 100 mW m−2, more than twice the United Kingdom average. Measurements were made of 4He concentrations and 222Rn activities in surface waters over the granite and its immediate host rocks. High values (greater than 48 ppb 4He, 160 c/min 222Rn) for either or both gases are interpreted as indicating discharge of groundwater from the upwelling limbs of hydrothermal convection cells. 4He has a spatial distribution which agrees well with the observed variations of heat flow within the pluton, but 222Rn is also influenced by lithology and depth of groundwater flow. Although the distribution of convection cells is partly determined by the presence of NW‐SE faults, there is close similarity with theoretical models of groundwater circulation. It is concluded that 4He and 222Rn surveys provide a simple but effective method for mapping areas of modern hydrothermal activity.

Geological and geochemical factors affecting the radon concentration in homes in Cornwall and Devon, UK

“…An alternative model to explain radon and helium distributions in waters on the Dartmoor and Carnmenellis Granites was suggested by Heath (1982), Durrance and Heath (1985) and Gregory and Durrance (1987). They coneluded that broad zones of ground-water movement could be recognised by the radon activity in stream waters, high activities showing areas of ascent on rising limbs of convection ceils, whereas descending zones gave low values.…”

Characterization and disequilibrium cases of radioelements in some Syrian hot waters

“…where T is the half-life of the alpha emitter, K is the kinetic energy of the alpha particle, and A and B are constants (Gregory and Durrance 1986). The 234 U/ 238 U-activity ratios of all hot water samples were found to be nearest to unity.…”

Applicability of radon emanometry in lithologically discontinuous sites contaminated by organic chemicals

“…These areas were flanked by measurements clearly above the local background, and even exceeding 50,000 Bq m-3 . The occurrence ofthese maxima can be exp lained if they are associated with the presence o fa fracture system in the subsoil and ifthese fractures constitute a preferential pathway for gas migration, enhancing the coadvective transport processes with the flow of C0 2 and Cli¡ (Durrance and Gregory 1990;Toutain and Baubron 1999;Etiope and Martinelli 2002;Yang et al 2003;Etiope et al 2005;Voltattorni et al 2009). Another possible interpretation for those high values may be the formation of a radon emanation halo around a hydrocarbon pool.…”

“…Due to its relatively low half-life (3.8 days), 222 Rn is expected to have a low mobility in the vadose zone through diffusion processes (Cothem and Smith 1987;Martinelli 1998). However, co-advective transport processes with carrier gases (mainly C0 2 ) (Durrance and Gregory 1990;Toutain and Baubron 1999;Etiope and Martinelli 2002;Yang et al 2003;Etiope et al 2005;Voltattomi et al 2009) may be responsible of the ascent of 222 Rn from deeper formations (Kristiansson and Malmqvist 1987;Etiope and Lombardi 1996;Etiope and Martinelli 2002) making the "radon-deficit technique" suitable for the detection of NAPL in the vadose and saturated zones (Semprini et al 2000;De Simone et al 2017). In fractured zones, there is an intensification of the Rn signal dueto the increase in soil permeability.…”