Effect of secondary minerals on electrokinetic phenomena during water‐rock interaction

The main geophysical application of spontaneous potentials (SP) anomalies, i.e., electrical signal generated by hydroelectric coupling, is the mapping of hydrothermal zones. Laboratory studies of hydroelectric coupling as a function of temperature are scarce, because of experimental difficulties. Up today experiments carried out by Ishido and Mizutani [1981] with quartz‐Al‐K‐NO 3 system for temperatures ranging from 20°C to 80°C are not well understood. In this work, we show that Ishido and Mizutani [1981]'s solutions are oversaturated with aluminium, and that the precipitation of Al(OH) 3s is expected. Triple Layer Model (TLM) calculations for a gibbsite‐KNO 3 system can account for Ishido and Mizutani [1981]'s measurements. These results highlight that (1) the precipitation of a secondary mineral can hide the electrical properties of the primary rock; (2) the geochemical fluid surveys should be taken into account to grasp the interfacial processes (precipitation/dissolution), and to interpret the SP measurements in the field.