A hydrogeochemical approach to the characterization of low-enthalpy geothermal systems: the Scordia – Lentini graben (Sicily, Italy)

Gloria Maria Ristuccia Gloria Maria Ristuccia,Pietro Bonfanti Pietro Bonfanti,Salvatore Giammanco Salvatore Giammanco

doi:10.4401/ag-8536

Gloria Maria Ristuccia Gloria Maria Ristuccia, Pietro Bonfanti Pietro Bonfanti + Show 1 more

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https://doi.org/10.4401/ag-8536

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Abstract

We describe the geochemical characteristics of groundwater samples collected in 23 water wells located on the northern margin of the Hyblean plateau (East Sicily). This area, mostly made of highly permeable carbonate rocks, is rich in low temperature (T < 50° C) hydrothermal groundwaters, distributed in an active sismogenetic zone, with several ENE-WSW-directed tectonic structures that drove magma to the surface during Upper Pliocene and Pleistocene. The chemical features suggest complex mixing between rainwater, CO2-rich groundwater, steam-heated groundwater and geothermal brines, as highlighted by Principal Component Analysis (PCA). Some parameters, however, indicate widespread pollution of the aquifers from human activities. Stable isotopes analysis confirms the meteoric origin of groundwater and supports the origin of dissolved CO2 mostly from mantle degassing through deep tectonic faults. Geothermometric estimates, mostly based on quartz and Saturation Indexes geothermometers, suggest minimum reservoir temperature between 100 and 120° C.

Highlights

In Italy, most of the energy used for industrial and domestic purposes is produced through the use of fossil fuels, which are mostly imported
We describe the geochemical characteristics of groundwater samples collected in 23 water wells located on the northern margin of the Hyblean plateau (East Sicily)
In this paper we report geochemical data from 23 hypo-thermal waters (T « 85° C) collected from wells mainly drilled for irrigation purposes

Summary

Introduction

In Italy, most of the energy used for industrial and domestic purposes is produced through the use of fossil fuels, which are mostly imported. Etna, are not the best sites for the exploitation of geothermal resources, due to the presence of a large aquifer with cold groundwater that hampers the development of an efficient geothermal reservoir inside of the volcano [Giammanco et al, 1998a, 2018; Aiuppa et al, 2000a] For this reason, our attention focused on other areas of Sicily, where volcanism was active in recent geological times and marked by deep regional faults where mantle gases are diffusely emitted in large amounts [Bonfanti et al, 1993; Dall’Aglio et al, 1995; De Gregorio et al, 2002; Grassa et al, 2002, 2006; Giammanco et al, 2007]. East Sicily represents the most interesting area for carrying out this type of research, due to both its peculiar volcanological and geological features [Lentini et al, 1996; Behncke, 2004; Bonforte et al, 2012] and the preliminary geochemical studies carried out in the past [Chiodini et al, 1996; Grassa, 2002; Minissale et al, 2019; Ristuccia et al, 2019]

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