A combined geochemical and isotopic study of the fluids discharged from the Montecatini thermal system (NW Tuscany, Italy)

Abstract

a b s t r a c tThe thermo-mineral fluids discharges of Montecatini Terme (Northern Apennines, Tuscany, Italy) have been exploited since the Roman times and despite the fact that this thermal complex is one of the biggest in Europe, the most recent geochemical investigations were published almost 40 years ago. To fill this gap, in this paper a detailed geochemical and isotopic investigation on the main thermal springs and wells from the Montecatini thermal system (MTS) is presented.The chemical and isotopic features of the Montecatini waters suggested that they are mainly controlled by water-rock interaction processes between meteoric water, permeating at depth from the surrounding reliefs (up to 800 m a.s.l.), and the Triassic evaporites (Burano Formation) belonging to the Tuscan sedimentary series. The local stratigraphic and tectonic framework favors an efficient recharge of the hydrothermal reservoir by the meteoric precipitation from a large catchment area and this aspect plays a fundamental role for the longevity of the Montecatini thermal spas, notwithstanding the huge amount of thermal water exploited. The C-TDIC values were lower than those expected for a mantle/thermometamorphic CO 2 source. This can be explained by: (i) isotopic fractionation occurring during calcite precipitation and/or (ii) mixing with biogenically derived gases, occurring at relatively shallow depth.

Climate change and its effect on groundwater quality

“…Indeed, in Northern Apennines, cold to hot Na-Cl and Ca-SO4 waters interacting with evaporites of the Burano Formation (Late Triassic) showed a mean Sr/ Ba weight ratio of 336 ± 210 (N = 45; Boschetti et al, 2005;Boschetti et al, 2017;Capecchiacci et al, 2015;unpublished data). The lower value outliers (Sr/ Ba \ 100) are mainly related to waters mixed with Ca-HCO3 and freshwaters interacting with Mesozoic limestones (Sr/Ba \ 10).…”

Understanding the Origin and Mixing of Deep Fluids in Shallow Aquifers and Possible Implications for Crustal Deformation Studies: San Vittorino Plain, Central Apennines

“…Finally, the third group (G3) is characterized by groundwater with the highest concentrations of Li and Cs (S5, S11, S13, and S15) that suggests a different circulation model with respect to the other two groups. It is noteworthy that the samples of the second and third clusters are within or close to the ratios 1.2 < Rb/Cs < 3.0, typical of waters interacting with Upper Triassic Burano Formations [110][111][112], where the higher ratio is common of sulphate waters such as those from the Antrodoco area (S1, S2). In addition, the Li-Rb-Cs contents of the carbonatitic and silicate fractions of Cupaello rocks display red pentagons [41,42].…”

Analysis of the Recharge Area of the Perrot Spring (Aosta Valley) Using a Hydrochemical and Isotopic Approach

“…Some authors [25], using stable isotopes of water, showed, for example, a predominant influence of Mediterranean air masses on the karst aquifer near the Slovenian-Italian border. They also observed how some types of water are influenced by water-rock interaction processes and meteoric water infiltrating at depth from the Triassic evaporite belonging to the Tuscan sedimentary series forming the surrounding reliefs (central Italy) [26]. In addition, stable isotopes of water have been used as inert tracers to indicate the residence time of groundwater in aquifer systems and potential sources of recharge [27][28][29][30].…”