Dissolved potassium in the shallow groundwaters circulating in the volcanic rocks of central-southern Italy

The water–rock interaction processes occurring in the low-temperature, shallow volcanic aquifers of central-southern Italy were simulated by means of the EQ3/6 Software Package in reaction progress mode. In the investigation both the Roman Magmatic Province and Monte Amiata, which belongs to the Tuscan Magmatic Province, were included. The average K2O content of the volcanic rocks from the two areas is similar but the main K-bearing phases are leucite, in the Roman Magmatic Province, and sanidine, at Monte Amiata. Computed concentrations of major dissolved components and SiO2 are consistent with analytical data, suggesting that the results of the EQ3/6 runs are reliable simulations of the natural water–rock interaction processes. Hence, EQ3/6 results can be used to investigate the transfer of K from rocks to water. It turns out that the attainment of saturation with sanidine, during early stages of rock dissolution, limits K concentration in the Monte Amiata groundwaters to around an average of 2.9 ± 1.3 mg L−1 (1SD). In the silica undersaturated Roman Magmatic Province, saturation with leucite is not attained during the evolution of groundwaters and, consequently, K concentration reaches comparatively high levels, with an average of 24.6 ± 27.1 mg L−1 (1SD). Most of these unusually high K concentrations are due to natural weathering of silicates without any anthropogenic influence.