GNGTS 2013 - Atti del 32° Convegno Nazionale

Results and discussion. Lamezia Terme area. The chemical composition of the samples is described in terms of major ion contents, in the Langelier-Ludwig diagram. Four geochemical families have been recognized, each one is characteristic of a different water-rock interaction processes: i) Ca-HCO 3 , characterized by low salinity (EC < 600 µS/ cm), temperature between 10 and 18°C and oxidizing condition. Both chemical and physical characteristics are typical of a fast interaction in circulating waters with both Plio-Quaternary sediments (filling the plain) and Paleozoic igneous rocks (cropping out in the main mountains of the area); ii) Ca-SO 4 , characterizing the thermal water of Caronte and some hypothermal water of the plain. They have strong reducing conditions and high salinity (up to 2500 µS/ cm). Sulphate concentrations derive from the gypsum contained in the Triassic carbonates in thermal waters and from gypsum lenses contained in sandy clays in hypothermal waters; iii) Na-Cl typical of marine sediments leaching; iv) Na-SO 4 , represented by a salty artesian aquifer sampled in the plain, characterized by a slow hydraulic circuit interacting with evaporates in a clayey environment. Dissolved gases in the sampled waters show an average value of N 2 , O 2 and CO 2 equal to 20.25, 5.04 and 16.42 cc/l, respectively. As in other areas of Calabria (Italiano et al. , 2010), the investigated area is characterized by the absence of a common degassing of CO 2 in groundwater. This feature is well highlighted by the absence of a clear positive correlation between the CO 2 and electrical conductivity. Moreover, the lack of a high flux of CO 2 in the water sampled is also pointed out by non-correlation between the concentration of CO 2 and radon content. Dissolved radon shows an average concentration of 8 Bq/l, with noticeable values found in thermal springs (100-130 Bq/l) and in one cold water discharging in the Serre mountains, with more than 1000 Bq/l. These values can be explained with the presence of a deep circulation into fractured carbonates driven by the LCF and the presence of uranium-bearing mineralization (already found in similar geological settings in Calabria: Calcara et al. , 1996). Environmental isotopes minimizing the existence of high temperature (> 150°C) at depth due to the lack of any oxygen-shift, even in the thermal area of Caronte. O and H isotopes point out a common meteoric origin of the sampled waters. In fact, in the graph (Fig. 2) all waters sample are positioned between the Global Me- teoric Water Line (that represent the isotopic compositions of the glob- al rainfalls: Craig, 1961) and the Regional Meteor- ic Water Line (RMWL, that represent the isotopic composition of the me- teoric precipitations in southern Italy, defined by Longinelli and Selmo, 2003). In order to individ- uate the elevation of the potential recharge area of the thermal waters, it has been calculated a regres- sion line, based on the isotopic composition of cold waters discharging in the Caronte area. Fig. 2 – Environmental isotopes diagram of the water collected in the Lamezia Terme area. 259 GNGTS 2013 S essione 1.3