GNGTS 2013 - Atti del 32° Convegno Nazionale

of the potential recharge area of the site, it has been calculated a regression line, based on the isotopic composition of cold waters. Isotopic analysis of total carbon suggests a mixing between a biogenic source of CO 2 and carbonates in most cold waters; while, the measured values for the thermal waters suggest the tendency of these waters to isotopic equilibrium with the Mesozoic marine carbonates, favored by prolonged water-rock interaction and high temperatures. A first geothermometric evaluation on the waters sampled can be introduced by analyz- ing the Mg-Na-K geothermometer (Gibbenbach, 1988). This geothermometer evidenced the immaturity of waters sampled, emphasizing their unsuitability for any estimate of deep tem- peratures. However, the evaluation of deep temperatures was carried out by applying selected geothermometer equation. We selected and applied the SO 4 /F 2 geothermometer (Marini et al. , 1986), that indicated a realistic deep temperature estimate of about 50-60°C. This results is in accord with the normal geothermal gradient (30°C/km) estimated for Contursi Terme area (Cataldi et al. , 1995), leaving assume that the thermal waters reach depths of 2-3 km. Conclusions. Lamezia Terme. Considering all collected data three hydrological circulations were recognized in the area, each one is characterized by different WRI: • A fast interaction of cold waters with Palaeozoic metamorphic units (cropping out in the Sila Massif and in the Serre mountains) and hypothermal waters with Plio-Quaternary shallow sediments (filling the plain). These waters have a limited WRI (i.e. low salinity, < 600 μS/cm) and a chemistry from Ca-HCO 3 to Na-Cl; • A relatively deep circulation of the hypothermal waters in the Miocene-aged terrigenous sedimentary succession (conglomerates, sands, calcarenites and clays) of the Catanzaro Trough. Waters have low to medium salinity, that locally become high due to evaporite (mainly halite and gypsum) dissolution. As a result, chemistry varies from Ca-HCO 3 to Ca (Na)-SO 4 ; • A deep and slow circulation of thermal waters belonging to the Caronte system in the fractured Mesozoic carbonate complex. Waters have relatively high salinity (up to 2500 μS/cm) and a Ca-SO 4 chemistry. Waters infiltrate in the southern edge of the Sila Massif, go through the fractured Palaeozoic units and circulate at depth in the Mesozoic carbonate complex. The regional LCF plays a key role in permitting the existence of a dense fracture network and the maintenance of the geothermal system, throughout a continuous slip, as recognized in other sectors of Calabria (e.g. Gioia Tauro Fault: Pizzino et al. , 2004). Finally, waters ascent toward surface, discharging as thermal springs. Considering the mineral assemblage of the carbonate complex, we selected and tentatively applied the SO 4 /F 2 geothermometer, mostly used in other similar geological environments in Italy (Marini et al. , 1986), that indicated a realistic deep temperature estimate of about 50- 60°C, confirming the low enthalpy of the Caronte hydrologic system, as emphasized by the use of environmental isotopes. Contursi Terme. Considering all collected data, two main hydrological circuits have been recognized in the study area, each one is characterized by different water-rock interaction processes, depth circuits, residence time in the aquifer, temperature deep, composition of dissolved gases: • A shallow and fast circulation of cold water (T ≤ 20°C) that originate from rainwater infiltrating in the main massive area (Mt. Polveracchio, Mt. Marzano) and interact with limestone formations and/or with the clay-sandy conglomeratic of continental origin and Plio-Quaternary marine deposits. These waters have modest CO 2 , alkaline pH, limited interaction with rocks and sediments and Ca-HCO 3 chemistry. Locally, the cold waters have a considerable gaseous contribution (CO 2 , up to 400 cc/l as dissolved phase) with a consequent decrease in the pH value and a considerable increase of their salinity. These 261 GNGTS 2013 S essione 1.3