Geothermal prospecting by geochemical methods in the Quaternary volcanic province of Dhamar (central Yemen)

By applying geochemical and thermometric techniques in domestic wells producing water from the shallow unconfined aquifer in the area, which is prevalently hosted inside the Quaternary volcano-clastic material, a closed thermal anomaly associated with the Quaternary volcanic activity was well delineated. Although the aquifer(s) has a Ca-Na-HCO3 composition, that is typical of shallow groundwater, there are several chemical anomalies in the hotter central area compared to typical aquifers: i) the pH is lower and, consequently, the calculated partial pressure of CO2 in solution is higher, ii) the electrical conductivity is higher, iii) the total salinity is higher and iv) the fluoride ion concentration is higher. Such chemical anomalies in the hotter part of the aquifer do not seem to be generated by the rising and/or mixing of deep hydrothermal components rising into the shallow aquifer, but rather produced by enhanced water-rock interaction processes resulting from the higher temperature of the aquifer and its greater acidity.