Soil gas physico-chemical survey for geothermal exploration at Madre del Agua mining grid in the Tenerife SRZ volcano, Canary Islands

Abstract

The Canarian archipelago comprises seven major oceanic volcanic islands located off the northwest coast of Africa. Due to recent volcanic activity, the Canary Islands boast significant high enthalpy geothermal potential. Extensive soil gas surveys, combined with magnetotelluric and ambient noise tomography studies for geothermal exploration, have been conducted on the island of Tenerife (Canary Islands). The findings from these studies have highlighted the necessity of undertaking detailed surface exploration work in areas with the greatest geothermal potential.

Here we present the findings from a comprehensive soil gas survey (∼500 sampling sites/km²) conducted in a 0.7 km² area known as Madre del Agua on the Tenerife north-south rift zone (SRZ) volcano, where surface geothermal features are not readily apparent. The selection of the study area followed a preliminary low-density soil gas survey (5 sampling sites/km²) and a magnetotelluric survey, which indicated a thinning of a broad-scale clay alteration cap. At each of the 362 sampling sites, measurements of soil CO₂ efflux and ²²²Rn activity were conducted in situ. Additionally, soil gas samples were collected at a depth of 40 cm for further chemical and isotopic analysis (δ¹³C-CO₂). Statistical-graphical analysis and the assessment of spatial distribution of the soil physico-chemical data confirms the presence of a relative enrichment of deep-seated gases in the soil gas atmosphere. The detection of these soil gas anomalies holds potential for identifying permeable areas and possible upwelling or boiling zones.