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Fluid geochemistry and geothermometry in the unexploited geothermal field of the Vicano-Cimino Volcanic District (Central Italy)
... This region is characterized by (i) a Paleozoic-Triassic metamorphic basement, (ii) Mesozoic-Paleogene sedimentary rocks related to the Apennine orogenesis, and (iii) upper Mio-Pleistocene sedimentary basins related to a post-collisional extensional phase (Baiocchi et al., 2012;Piscopo et al., 2006) during which the Vicano-Cimino Volcanic District (VCVD) formed (Tassi et al., 2015, and references therein). Crustal thinning, igneous processes, and high heat flow in this area are responsible for the large number of CO 2 (H 2 S)-rich thermomineral springs and anomalously high CO 2 diffuse degassing sites (Cinti et al., 2014), whose location is strictly controlled by (i) hydrogeological settings and (ii) brittle structural elements (Minissale, 2004). ...
... The resulting complex geological setting has originated the occurrence of two main aquifers, as follows: (i) a shallower volcanic aquifer, characterized by cold and fresh waters with Ca-HCO 3 composition and low pCO 2 values, located within the Pleistocene volcanites, and (ii) a deeper aquifer, located in the deep Mesozoic-Cenozoic carbonate rocks, hosting thermal waters at 220°C with a Ca-SO 4 (HCO 3 ) composition and high pCO 2 values, mainly produced by thermometamorphic decarbonation processes and mantle degassing (Baiocchi et al., 2012;Cinti et al., 2014;Piscopo et al., 2006). The Viterbo geothermal system is located in coincidence with a structural high of the carbonate basement and a geothermal gradient greater than 100°C/km (Piscopo et al., 2006), resulting in CO 2 -and H 2 S-rich thermal waters, uprising through faults and fractures, with temperatures ranging around 50-60°C (Cinti et al., 2014;Duchi & Minissale, 1995;Minissale, 2004). ...
... The resulting complex geological setting has originated the occurrence of two main aquifers, as follows: (i) a shallower volcanic aquifer, characterized by cold and fresh waters with Ca-HCO 3 composition and low pCO 2 values, located within the Pleistocene volcanites, and (ii) a deeper aquifer, located in the deep Mesozoic-Cenozoic carbonate rocks, hosting thermal waters at 220°C with a Ca-SO 4 (HCO 3 ) composition and high pCO 2 values, mainly produced by thermometamorphic decarbonation processes and mantle degassing (Baiocchi et al., 2012;Cinti et al., 2014;Piscopo et al., 2006). The Viterbo geothermal system is located in coincidence with a structural high of the carbonate basement and a geothermal gradient greater than 100°C/km (Piscopo et al., 2006), resulting in CO 2 -and H 2 S-rich thermal waters, uprising through faults and fractures, with temperatures ranging around 50-60°C (Cinti et al., 2014;Duchi & Minissale, 1995;Minissale, 2004). ...
Active hydrothermal travertine systems are ideal environments to investigate how abiotic and biotic processes affect mineralization mechanisms and mineral fabric formation. In this study, a biogeochemical characterization of waters, dissolved gases, and microbial mats was performed together with a mineralogical investigation on travertine encrustations occurring at the outflow channel of a thermal spring. The comprehensive model, compiled by means of TOUGHREACT computational tool from measured parameters, revealed that mineral phases were differently influenced by either abiotic conditions or microbially driven processes. Microbial mats are shaped by light availability and temperature gradient of waters flowing along the channel. Mineralogical features were homogeneous throughout the system, with euhedral calcite crystals, related to inorganic precipitation induced by CO2 degassing, and calcite shrubs associated with organomineralization processes, thus indicating an indirect microbial participation to the mineral deposition (microbially influenced calcite). The microbial activity played a role in driving calcite redissolution processes, resulting in circular pits on calcite crystal surfaces possibly related to the metabolic activity of sulfur‐oxidizing bacteria found at a high relative abundance within the biofilm community. Sulfur oxidation might also explain the occurrence of gypsum crystals embedded in microbial mats, since gypsum precipitation could be induced by a local increase in sulfate concentration mediated by S‐oxidizing bacteria, regardless of the overall undersaturated environmental conditions. Moreover, the absence of gypsum dissolution suggested the capability of microbial biofilm in modulating the mobility of chemical species by providing a protective envelope on gypsum crystals.
... The intermediate position between the mantle region and the field of Lovozero samples is occupied by magmatic gases of the Zambales Ophiolite in the Philippines [78] and carbonatites from the Sallanlatwa and Sokli complexes of the Kola alkaline province (previously unpublished data collected by the author), abiogenic methane from the hot springs in China [37], as well as magmatic gases that partially enter the Lovozero field from the Xujiaweizi area of the Songliao Basin (China) [38] and abiogenic methane from the geothermal field of the Vicano-Cimino Volcanic District (Italy), which is formed due to the reduction of CO 2 [44]. In the latter cases, even if the samples included in the diagram fell into the mixing zone of the crust and mantle end members or, for example, in the Xujiaweizi area of the Songliao Basin, China, a strong correlation between CH 4 / 3 He and 3 He/ 4 He was found [38], in the aggregate of the different criteria the methane was not a mixture of thermogenic (or bacterial) and mantle. ...
... [78] and CHS-hot springs in China [37]. The dashed lines show the crust and mantle fields [31,33,34,37,45,46,77,79]; VCVD-the Vicano-Cimino Volcanic District, Italy [44], and XASB-the Xujiaweizi area of the Songliao Basin, China [38]. ...
... The intermediate position between the mantle region and the field of Lovozero samples is occupied by magmatic gases of the Zambales Ophiolite in the Philippines [78] and carbonatites from the Sallanlatwa and Sokli complexes of the Kola alkaline province (previously unpublished data collected by the author), abiogenic methane from the hot springs in China [37], as well as magmatic gases that partially enter the Lovozero field from the Xujiaweizi area of the Songliao Basin (China) [38] and abiogenic methane from the geothermal field of the Vicano-Cimino Volcanic District (Italy), which is formed due to the reduction of CO2 [44]. In the latter cases, even if the samples included in [78] and CHS-hot springs in China [37]. ...
The occurrence of hydrocarbon gases (HCG) in unusually high concentrations for magmatic complexes, in the Lovozero and some other alkaline massifs, is of both geochemical and practical interest. The nature of these gases, despite the long history of research, remains the subject of debate. As an approach to solving this problem, we studied the coupled distribution of occluded HCG and the recognized tracers of various geological processes, such as helium and argon isotopes. The extraction of the gas components trapped in fluid micro-inclusions was carried out by the mechanical crushing of rock and mineral samples. A positive correlation was found between the 3He/4He and CH4/C2H6 ratios, whereas a negative correlation of the latter was found with the 36Ar concentration, which in turn was directly related, in varying degrees, to the content of HCG and most strongly with pentanes. Conjugacy of the processes of the heavier gaseous hydrocarbons, a loss of the deep component of the fluid phase and dilution of it with the atmogenic component was established. In the absence of a correlation between CH4 and 3He, the value of the CH4/3He ratio in the Lovozero gas substantially exceeded the estimates of it in gases of a mantle origin, and mainly corresponded to the crustal values. However, in some samples, a small fraction of mantle methane was allowed. The peculiarities of the relationships between hydrocarbon gases and the isotopes of noble gases indicate a sequential process of abiogenic generation and transformation of HCG at the magmatic and post-magmatic stages during the formation of the Lovozero massif. The obtained results confirm the usefulness of this approach in solving the origin of reduced gases in alkaline igneous systems.
... These areas are characterized by the same geological and hydrogeological settings and by the exploitation of the geothermal resource for the production of electric power [8,15]. Thus, several conceptual hydrogeological models (CHMs) have been proposed [4,6,[16][17][18][19][20][21][22][23][24][25]. ...
... Cinti et al. [23,24] proposed a conceptual hydrogeological model almost identical to that of Baiocchi et al. [21,22]. ...
... The conceptual hydrogeological models described above are of two types: the first CHM is shown in Figure 3a [6,16,17,19,37,38] and in Figure 3c [20,25]; the second CHM is shown in Figure 3d [18,[21][22][23][24]. These types of models differ for three fundamental reasons: (1) the hydrogeological role of the flysch units (Tolfa Flysch) between the shallow volcanic aquifer and the deep carbonate aquifer that hosts the thermal fluids; (2) the non-existence of the thermal aquifer (TA); (3) the recharge area of the deep carbonate aquifer. ...
... ENI-AGIP and Enel Ltd.) for the assessment of geothermal resources (Cinti et al. 2014 and references therein). According to exploratory data, T to up to 218 °C were encountered during the drilling operations of the 2,153 m deep Cimino 1 well, which are in good agreement with the geo-thermometric results obtained by Cinti et al. (2014), showing evidence of deep equilibration for the reservoir fluids at temperatures slightly lower than 200 °C. ...
... A column showing the reference source of the data is also provided. Data are from Minissale et al. (1997), Pierotti et al. (2017), Tassi et al. (unpublished), Duchi and Minissale (1992), Cinti et al. (2014), Valentino and Stanzione (2004), Aiuppa et al. (2000), ), Servida et al. (2009, Dinelli et al. (2001). The analytical methods are those reported by , where the superscript numbers are corresponding to the water samples' IDs. ...
... A column showing the reference source of the data is also provided. Data are from Minissale et al. (1997), Pierotti et al. (2017), Tassi et al. (unpublished), Duchi and Minissale (1992), Cinti et al. (2014), Valentino and Stanzione (2004), Aiuppa et al. (2000), ), Servida et al. (2009, Raco et al. (2012), Dinelli et al. (2001). The analytical methods are those reported by , where the superscript numbers are corresponding to the water samples' IDs. ...
The present study is aimed at providing a brief overview of the Italian acidic waters based on literature and unpublished data. Acidic waters in Italy, as elsewhere, are relatively common and associated with extremely variable geological settings. Owing to their peculiar features, these waters may seriously affect the environment and the ecosystems. Along the Apennine belt, the western and inner sectors of the Italian peninsula record an anomalous geothermal gradient, mostly overlapping with the Neogene-to-present magmatism, that explains the presence of a huge amount of CO2(H2S)-rich gas and thermal water discharges, geothermal fields (e.g. Larderello and Mt. Amiata) and ore deposits (e.g. Fe- and polymetallic sulfides, e.g. Elba Island and Colline Metallifere). Acidic waters (pH ≤5) from volcanic and geothermal areas show outlet temperatures and Total Dissolved Solids (TDS) from 10 to 96°C and <1 to ≈30 g/L, respectively, with a chemical composition usually belonging to the Ca-SO4, NH4-SO4 or Na-Cl facies. Frequently, they are related to bubbling and boiling pools due to the interaction between deepsourced gases and shallow aquifers or meteoric waters. Concentrations of heavy metals and metalloids are in most cases high. Extremely high contents of metals are also recorded for those acidic waters that characterize the main Italian mining districts, mostly located in Sardinia (not included in the present study), Tuscany and NW Alps, where they are related to Acid Mine Drainage l.s. or Acid Rock Drainage. The pH values are as low as 2.08, with variable TDS concentrations. Compositionally, they are Na-SO4, Ca(Mg)-SO4, and/or Mg(Ca)-SO4 waters, prevalently due to oxidative processes affecting polymetallic sulfides.
... The average specific productivity of 40 t/h km 3 , calculated for the liquid-dominated geothermal systems of Latium by [14] has been used for calculations. Reservoir temperatures have been derived taking into account, hierarchically, data from: (1) deep drilling (i.e., bottom-hole temperatures); (2) geothermometric evaluations based on chemical equilibria of gas species [19,[39][40][41]; and (3) the map of temperature of the potential reservoir top [12]. Minimum and maximum temperatures ( Table 2) have been considered to obtain the minimum and the maximum theoretical thermal power, respectively. ...
... The shape of the frequency distribution of logpCO 2 (Figure 2) highlights the presence of two distinct populations of: (1) low pCO 2 values (≤0.045 bar), which can generally be interpreted as the normal enrichment in soil derived-CO 2 of infiltrating waters from zones of low CO 2 flux, and (2) medium-to-high pCO 2 values (>0.045 bar), reflecting the input of deeply derived CO 2 . This hypothesis is confirmed by the δ 13 C-CO 2 values of the sampled waters, ranging from −27.6 to +2.3‰ vs. VPDB [19,39,40], which suggest that CO 2 has a two-fold origin: relatively negative δ 13 C-CO 2 values of the low pCO 2 waters imply dominant CO 2 contribution from soil respiration and aerobic decay of organic matter [44]; conversely, less negative δ 13 C-CO 2 values of the medium-to-high pCO 2 waters point to CO 2 production from thermo-metamorphic reactions involving carbonate formations (δ 13 C-CO 2 values from −2.0 to +2.3‰ vs. VPDB [45]) and minor contribution from mantle degassing (δ 13 C-CO 2 values from −7.0 to −3.0‰ vs. VPDB [46]). Consistent with this hypothesis, the different populations highlighted in the QQ plot ( Figure 3) can be interpreted as representative of pCO 2 values fed by both biological and endogenous sources. ...
... The sampling sites have been homogeneously distributed all over the investigated area, and the sampling density is high (Figure 1). The pCO 2 of the sampled waters has been calculated with the PHREEQC code [47], operating with the Lawrence Livermore National Laboratory database and using as input data the groundwater physico-chemical parameters, whose full dataset is reported elsewhere [19,39,40]. ...
The evaluation of the theoretical geothermal potential of identified unexploited hydrothermal reservoirs within the Vicano-Cimino and Sabatini volcanic districts (Latium region, Italy) has been made on the basis of a revised version of the classical volume method. This method is based on the distribution of the partial pressure of CO2 (pCO2) in shallow and deep aquifers to delimit areas of geothermal interest, according to the hypothesis that zones of high CO2 flux, either from soil degassing and dissolved into aquifers, are spatially related to deep hydrothermal reservoirs. On the whole, 664 fluid discharges (cold waters, thermal waters, and bubbling pools) have been collected from shallow and deep aquifers in the Vicano-Cimino Volcanic District and the Sabatini Volcanic District for chemical and isotopic composition, in an area of approximately 2800 km 2. From this large hydro-geochemical dataset the pCO2 values have been computed and then processed to obtain a contour map of its spatial distribution by using geostatistical techniques (kriging). The map of pCO2 has been used to draw up the boundaries of potentially exploitable geothermal systems within the two volcanic districts, corresponding to the areas where endogenous CO2 raise up to the surface from the deep hydrothermal reservoirs. The overall estimated potential productivities and theoretical minimum and maximum thermal power of the two volcanic districts are of about 45 × 10 3 t/h and 3681-5594 MWt, respectively. This makes the Vicano-Cimino Volcanic District and the Sabatini Volcanic District very suitable for both direct and indirect exploitation of the geothermal resources, in view of the target to reduce electricity generation from conventional and poorly sustainable energy sources.
... Ra, upper mantle-derived helium has 3 He/ 4 He ratios of (8 ± 1Ra), and lower mantle-derived helium has 3 He/ 4 He ratios of > 30Ra (Poreda and Craig 1989;Hilton et al. 2002). A 3 He/ 4 He ratio > 0.1 Ra indicates that the source includes mantlederived components (Cinti et al. 2014). ...
... The main sources of CH 4 in the hydrothermal system are: (1) biogenetic CH 4 , mainly from bacterial reduction of organic matter, which is most common in shallow groundwater; (2) thermogenic CH 4 that decomposition of organic matter buried in sediments in generally at temperature > 150 °C; (3) abiogenic CH 4 , which is produced in a reducing environment with inorganic catalyst; and (4) degassing of juvenile carbon as CH 4 from the mantle, which is common in high-temperature hydrothermal systems (Clark and Fritz 1997). Among them, the biogenetic and thermogenic CH 4 are considered the main sources of genetic mechanisms in a sedimentary environment (Cinti et al. 2014). ...
... The δ 13 C-CH 4 values and CH 4 /(C 2 H 6 + C 3 H 8 ) (C 1 / (C 2 + C 3 )) ratios are effective tool to distinguish different biogenic and thermogenic CH 4 types. Thermogenic CH 4 is generally enriched in 13 C compared with biogenic CH 4 with a δ 13 C-CH 4 range from roughly − 50 to − 30‰, while the later has a wide range that from − 100‰ to − 50‰(Whiticar 1999; Kawagucci et al. 2013;Cinti et al. 2014). The proportion of CH 4 in a hydrocarbon gas mixture can be Fig. 9 Plot of the helium isotopic composition of gases in Niutuozhen geothermal system Fig. 10 Classification of CH 4 based on δ 13 C-CH 4 and δ 13 C-CO 2 values (a) and between the carbon isotope ratio of CH 4 and relative concentration of CH 4 and (C 2 + C 3 ) components (b) expressed on a volume percentage basis by the "Bernard parameter" C 1 /(C 2 + C 3 ) (Whiticar 1999). ...
Niutuozhen geothermal field is located in the Jizhong graben, belonging to the northern part of Bohai Bay Basin in North China. Chemical and isotopic analyses were carried out on 14 samples of the geothermal fluids discharged from Neogene Minghuazhen (Nm), Guantao (Ng), and Jixianian Wumishan (Jxw) formations. The δ2H and δ18O in water, δ13C in CH4, δ13C in CO2, and 3He/4He ratio in the gases were analyzed in combination with chemical analyses on the fluids in the Niutuozhen geothermal field. The chemical and isotopic compositions indicate a meteoric origin of the thermal waters. The reservoir temperatures estimated by chemical geothermometry are in the range between 60 and 108 °C. The results show that the gases are made up mainly by N2 (18.20–97.42 vol%), CH4 (0.02–60.95 vol%), and CO2 (0.17–25.14 vol%), with relatively high He composition (up to 0.52 vol%). The chemical and isotopic compositions of the gas samples suggest the meteoric origin of N2, predominant crustal origins of CH4, CO2, and He. The mantle-derived He contributions are calculated to be from 5 to 8% based on a crust–mantle binary mixing model. The deep temperatures in the Jxw reservoir were evaluated based on gas isotope geothermometry to be in the range from 141 to 165 °C. The mantle-derived heat fraction in the surface heat flow is estimated to be in the range of 48–51% based on 3He/4He ratios.
... Water samples were collected from cold and thermal springs, occasionally showing bubbling gases, as well as municipal and domestic wells. The chemical and isotopic dataset also includes published data (Cinti et al., 2014) of 34 waters and 4 bubbling gases (samples 190, 191, 201, 216) located at the border between the SVD and the Vicano-Cimino Volcanic District. The field and laboratory analytical results are listed in Table 1 and as supplementary material (Tables 1S and 2S). ...
... Gas contents are in mmol/mol except for Ne, C 2 H 6 and C 3 H 8 which are expressed in mmol/mol; d 13 C in CO 2 and CH 4 as ‰ V-PDB; dD in CH 4 as ‰ V-SMOW; d 15 N as ‰ NBS air; d 34 S as ‰ V-CDT. Data from samples 190e216 are taken from Cinti et al. (2014). were determined with an Agilent 6890N gas-chromatograph coupled to a Finnigan Delta plus XP mass spectrometer. ...
... The thermal water discharges are related to the well-recognized regional hydrothermal aquifer hosted in the Mesozoic carbonates at the top of the Triassic anhydrite layers and recharged by meteoric waters from the eastern Apennine range (Chiodini et al., 2000;Minissale, 2004;Minissale and Vaselli, 2011;Cinti et al., 2014 (Table 1S), possibly caused by mixing between the deep thermal fluids uprising from the carbonate-evaporitic aquifer and highly saline waters locally trapped in the Neogene marine sediments below the volcanic sequences (Calamai et al., 1976;Duchi et al., 1992;Dall'Aglio et al., 1994;Minissale et al., 1997b). The possible involvement of the deep and hot Na-Cl brine intercepted from the geothermal wells at Cesano (Calamai et al., 1976) in the chemical features of the Na-Cl-rich thermal waters cannot completely be discarded, since the Na þ /Cl À molar ratios of these waters are up to 2, i.e. higher than the stoichiometric ratio and approaching that shown by the geothermal fluid (Fig. 5b). ...
This study reports a complete geochemical dataset of 215 water and 9 gas samples collected in 2015 from thermal and cold discharges located in the eastern sector of the Sabatini Volcanic District (SVD), Italy. Based on these data, two main aquifers were recognized, as follows: 1) a cold Ca-HCO3 to Ca(Na)-HCO3 aquifer related to a shallow circuit within Pliocene-Pleistocene volcanic and sedimentary formations and 2) a deep CO2-pressurized aquifer hosted in Mesozoic carbonate-evaporitic rocks characterized by a Ca-HCO3(SO4) to Na(Ca)-HCO3(Cl) composition. A thick sequence of low-permeability formations represents a physical barrier between the two reservoirs. Interaction of the CO2-rich gas phase with the shallow aquifer, locally producing high-TDS and low-pH cold waters, is controlled by fractures and faults related to buried horst-graben structures. The δ18O-H2O and δD-H2O values indicate meteoric water as the main source for both the shallow and deep reservoirs. Carbon dioxide, which is characterized by δ13C-CO2 values ranging from −4.7 to +1.0‰ V-PDB, is mostly produced by thermo-metamorphic decarbonation involving Mesozoic rock formations, masking possible CO2 contribution from mantle degassing. The relatively low R/Ra values (0.07–1.04) indicate dominant crustal He, with a minor mantle He contribution. The CO2/3He ratios, up to 6 × 1012, support a dominant crustal source for these two gases. The δ34S-H2S values (from +9.3 to +11.3‰ V-CDT) suggests that H2S is mainly related to thermogenic reduction of Triassic anhydrites. The δ13C-CH4 and δD-CH4 values (from −33.4 to −24.9‰ V-PDB and from −168 to −140‰ V-SMOW, respectively) and the relatively low C1/C2+ ratios (<100) are indicative of a prevailing CH4 production through thermogenic degradation of organic matter. The low N2/Ar and high N2/He ratios, as well as the 40Ar/36Ar ratios (<305) close to atmospheric ratio, suggest that both N2 and Ar mostly derive from air. Notwithstanding, the positive δ15N-N2 values (from +0.91 to +3.7‰ NBS air) point to a significant extra-atmospheric N2 contribution. Gas geothermometry in the CH4-CO2-H2 and H2S-CO2-H2 systems indicate equilibrium temperatures <200 °C, i.e. lower than those measured in deep geothermal wells (∼300 °C), due to either an incomplete attainment of the chemical equilibria or secondary processes (dilution and/or scrubbing) affecting the chemistry of the uprising fluids. Although the highly saline Na-Cl fluids discharged from the explorative geothermal wells in the study area support the occurrence of a well-developed hydrothermal reservoir suitable for direct exploitation, the chemistry of the fluid discharges highlights that the uprising hydrothermal fluids are efficiently cooled and diluted by the meteoric water recharge from the nearby Apennine sedimentary belt. This explains the different chemical and isotopic features shown by the fluids from the eastern and western sectors of SVD, respectively, the latter being influenced by this process at a lesser extent. Direct uses may be considered a valid alternative for the exploitation of this resource.
... The volcanic products lie on a sed- In the study area, vigorous and structurally controlled CO 2 -rich gas bub-4. Study areas bling sites occur in the Vezza Creek, the stream being imposed along a NWstriking, SW-dipping high-angle normal fault (Cinti et al., 2014). Strong Chiodini et al., 1999). ...
... The CO 2 -dominated hydrothermal uids discharged from the VCVD are mainly produced by thermometamorphic reactions (e.g. decarbonation and sulfate reduction) occurring within the Mesozoic carbonates in the underlying Triassic anhydrites and/or in the metamorphic basement of the Tuscan series, with a minor contribution from a deeper seated source (mantle degassing) (Chiodini et al., 1995Minissale et al., 2000;Cinti et al., 2014 and references therein). Signicant concentrations of CH 4 , mainly produced by CO 2 reduction (Tassi et al., 2012d), and light hydrocarbons originating from thermogenic processes (Cinti et al., 2014) were also recognized. ...
... decarbonation and sulfate reduction) occurring within the Mesozoic carbonates in the underlying Triassic anhydrites and/or in the metamorphic basement of the Tuscan series, with a minor contribution from a deeper seated source (mantle degassing) (Chiodini et al., 1995Minissale et al., 2000;Cinti et al., 2014 and references therein). Signicant concentrations of CH 4 , mainly produced by CO 2 reduction (Tassi et al., 2012d), and light hydrocarbons originating from thermogenic processes (Cinti et al., 2014) were also recognized. ...
The PhD research project was aimed to improve the scientific knowledge about the composition and behaviour of volatile organic compounds (VOCs) in volcanic and hydrothermal systems, focusing on (i) primary processes occurring at high temperatures in deep fluid reservoirs and (ii) secondary processes occurring during the uprising of hydrothermal fluids toward the surface. The first goal was achieved following both experimental and empirical approaches. Laboratory experiments were performed in order to investigate the reaction pathways for benzene production under hydrothermal conditions, confirming that the aromatic compounds can be efficiently produced through dehydrocyclization and aromatization of normal-alkanes with cyclics as by-products. Moreover, the pivotal role of minerals in controlling organic reactivity and organic reaction pathways was demonstrated. The analysis of VOCs in fumarolic and venting gases from four volcanic-hydrothermal systems in the Mediterranean area characterized by different temperature and redox conditions at depth (Solfatara Crater, Nisyros Island, Poggio dell'Olivo and Cava dei Selci), supported by thermodynamic and experimental data, evidenced a strict control of physicochemical conditions of deep hydrothermal reservoirs on the composition of VOCs emitted at the surface. Alkanes were the most abundant VOCs, with decreasing abundances at increasing carbon chain length, in agreement with thermodynamic data. At relatively high temperatures, saturated hydrocarbons may undergo dehydrogenation to alkenes and/or dehydrocyclization and subsequent aromatization, as experimentally demonstrated. Accordingly, aromatics were enriched in fumarolic fluids from high temperature active volcanic systems, whilst cyclics were more abundant in hydrothermal systems characterized by lower temperatures, likely due to incomplete aromatization. The occurrence and abundances of S-bearing compounds were related to sulphur fugacity, whilst O-bearing compounds were mainly related to shallow processes. Interstitial soil gases were characterized by remarkably different compositions of VOCs when compared to those recorded in the fumarolic and venting gases, suggesting the relevant importance of secondary processes occurring at depth (dehydrocyclization of alkanes producing an enrichment in cyclics relative to fumarolic fluids) and at shallow depths (DMS oxidation, microbial production of O-bearing compounds). In particular, microbially-driven processes likely play a major role in modifying the composition of VOCs prior to their emission from soils in volcanic and hydrothermal systems.
... The region hosts many thermal springs and gas vents and is a part of a larger thermal anomaly that extends from southern Tuscany in the north to the active volcanic areas of Phlegrean Fields and Vesuvius in the south (Fig. 1a). The geothermal resource in the area is unexploited despite estimates that the extractable electrical power using binary cycle power plants in the Vico area can contribute to the energetic autonomy of the region (Cinti et al., 2014;Procesi et al., 2013). The specific goals of this study are to (1) characterize the processes controlling water chemistry in the Cimino-Vico area, (2) characterize the processes controlling the isotopic systematics of boron and strontium in low enthalpy hydrothermal systems, and (3) provide new insights on groundwater circulation in the area, which in turn, give information on the potential for geothermal energy production. ...
... The δ 18 O and δD show a progressive isotope lightening from the Tyrrhenian Sea to the Apennines Chain. The proposed vertical isotope gradient for Central Italy (− 0.3‰ per 100 m; Cinti et al., 2014;Longinelli and Selmo, 2003;Minissale and Vaselli, 2011;Zuppi et al., 1974,) suggests that recharge is at an elevation of 400 m to 700 m on the summit of Mount Cimino, consistent with previous studies (Baiocchi et al., 2006;Cinti et al., 2014;Piscopo et al., 2006). Thermal waters are slightly shifted in δ 18 O due to CO 2 -H 2 O exchange, with the CO 2 probably originating from carbonate dissolution and deep degassing. ...
... The δ 18 O and δD show a progressive isotope lightening from the Tyrrhenian Sea to the Apennines Chain. The proposed vertical isotope gradient for Central Italy (− 0.3‰ per 100 m; Cinti et al., 2014;Longinelli and Selmo, 2003;Minissale and Vaselli, 2011;Zuppi et al., 1974,) suggests that recharge is at an elevation of 400 m to 700 m on the summit of Mount Cimino, consistent with previous studies (Baiocchi et al., 2006;Cinti et al., 2014;Piscopo et al., 2006). Thermal waters are slightly shifted in δ 18 O due to CO 2 -H 2 O exchange, with the CO 2 probably originating from carbonate dissolution and deep degassing. ...
... It is possible that geothermal systems on Bali could be hosted by carbonate rocks, but CO 2 content alone is not sufficient to allow that conclusion. Carbonate rocks, such as limestone and dolomite, for example, were identified as the reservoir rock in some volcanic areas in Italy, e.g., Vicano-Cimino and Sabatini-Tolfa (Cinti et al., 2011;Cinti et al., 2014). There the thermal water is characterized by a (Ca 2+ + Mg 2+ )/ HCO 3 − molar ratio of~1 as a result of calcite and/or dolomite dissolution (Gemici and Filiz, 2001;Levet et al., 2002;Grassa et al., 2006;Capaccioni et al., 2011;Cinti et al., 2011;Cinti et al., 2014). ...
... Carbonate rocks, such as limestone and dolomite, for example, were identified as the reservoir rock in some volcanic areas in Italy, e.g., Vicano-Cimino and Sabatini-Tolfa (Cinti et al., 2011;Cinti et al., 2014). There the thermal water is characterized by a (Ca 2+ + Mg 2+ )/ HCO 3 − molar ratio of~1 as a result of calcite and/or dolomite dissolution (Gemici and Filiz, 2001;Levet et al., 2002;Grassa et al., 2006;Capaccioni et al., 2011;Cinti et al., 2011;Cinti et al., 2014). Another characteristic of thermal waters hosted by carbonate rocks can be a pronounced positive 18 O-shift due to the heavier δ 18 O composition of carbonate rocks compared to magmatic rocks (Craig, 1966;Arana and Panichi, 1974;Gemici and Filiz, 2001). ...
... Another characteristic of thermal waters hosted by carbonate rocks can be a pronounced positive 18 O-shift due to the heavier δ 18 O composition of carbonate rocks compared to magmatic rocks (Craig, 1966;Arana and Panichi, 1974;Gemici and Filiz, 2001). Although a depletion of δ 18 O is also possible if there is isotope exchange between hydrothermal water and CO 2 , as demonstrated for some geothermal systems in Italy (Grassa et al., 2006;Cinti et al., 2011;Cinti et al., 2014). This paper presents new physicochemical and isotope ( 18 O, 2 H and 11 B) data for hot springs and shallow thermal wells on Bali with the objective to investigate the host rock of the geothermal systems and to determine the most applicable geothermometer for geothermal exploration. ...
This paper presents an overview of the geothermal systems on the island of Bali, Indonesia. Physicochemical data of hot springs and shallow geothermal wells were collected from four geothermal locations: Penebel, Batur, Banjar and Banyuwedang. The concentrations for the three main anions varied significantly indicating a different geothermal history. The values for Cl- ranged from 0.1 to 1000 mg/L, for HCO3- from 20 to 2200 mg/L and for SO42- from 0.1 to 500 mg/L Although the island of Bali is underlain by carbonate rocks, a carbonate host rock for the geothermal reservoirs could not be confirmed, because the (Ca2+ + Mg2+)/HCO3- molar ratios were approximately 0.4, well below 1.0 and the K/Mg ratios were approaching those of a calc-alkaline rock reservoir. The HCO3- of the thermal waters correlated with Ca2+, Mg2+, Se+ and K+ indicating water-rock interaction in the presence of carbonic acid. Phase separation was inferred for the Bedugul and Banjar geothermal systems, because of relatively high B/Cl ratios. Boron isotopes were determined for selected samples with values ranging from delta B-11 of 13 to 22.5%. (NBS 951). The heavy delta B-11 of +22.5% together with a low B/Cl ratio indicated seawater input in the Banyuwedang geothermal system. The hydrogen and oxygen isotopic composition of the thermal water plotted along the global meteoric water line (GMWL) and close to the mean annual value for precipitation in Jakarta indicating a meteoric origin of the geothermal water. Comparison of the Si, Na/K, Na/K/Ca and Na/Li geothermometers with actual reservoir temperature measurements and physicochemical considerations led to the conclusion that the Na/Li thermometer provided most reliable results for the determination of geothermal reservoir temperatures on Bali. Using this thermometer, the following reservoir temperatures were calculated: (1) Penebel (Bedugul) from 235 to 254 degrees C, (2) Batur 240 degrees C and (3) Banjar 255 degrees C. Due to seawater input this thermometer could not be applied to the Banyuwedang geothermal system. There application of a SiO2 thermometer indicated a reservoir temperature below 100 degrees C.
... Chemical characteristics of groundwater are coherent with this hydrogeological model. Thermal waters are of the sulfate alkaline earth type, have temperatures between 40 °C and 62 °C, electrical conductivity between 2700 μS/cm and 3400 μS/cm, tritium concentrations between 2 TU and 5 TU, and high gas content, e.g., CO2 and H2S up to 994 mmol/mol and 0.99 mmol/mol in dry gas, respectively [36][37][38][39]. In contrast, the waters of the perched and basal aquifers comprise fresh, cold waters of the bicarbonate alkaline earth type (electrical conductivity generally between 100 μS/cm and 1000 μS/cm, temperature generally between 13 °C and 20 °C, tritium concentrations between 8 TU and 11 TU). ...
... In contrast, the waters of the perched and basal aquifers comprise fresh, cold waters of the bicarbonate alkaline earth type (electrical conductivity generally between 100 μS/cm and 1000 μS/cm, temperature generally between 13 °C and 20 °C, tritium concentrations between 8 TU and 11 TU). In the hydrothermal area of Viterbo, the reduced thickness of the low-permeability layer that divides the basal aquifer from the deeper aquifer and its hydraulic heterogeneity give rise to a flow between the two overlapping aquifers and then to mixing between cold and thermal waters [17,[36][37][38][39]. All waters exhibit 18 O and 2 H values in a limited range (−5.6‰ to −7.2‰ and −34‰ to −44‰, respectively) and fall on the meteoric water lines, suggesting the presence of a common recharge area [36]. ...
... The presence of high concentrations of arsenic and other potentially toxic elements [54,60] in the volcanic rocks of the area, as well as in the whole Roman Comagmatic Province (RCP) is attributed to the enrichment of incompatible element during the final stages of rock formation and to a diffuse percolation of fluids through the crust. This occurrence is widespread over the RCP and, particularly, Vico area as several gas emissions and intense hydrothermal activity highlight [39,61]. ...
This study concerns the occurrence of arsenic in the groundwater system of the Cimino-Vico volcanic area (central Italy), different parts of which are currently widely used for local drinking water supply and for irrigation. The system shows a complex groundwater circulation, including a continuous basal aquifer, discontinuous perched aquifers, groundwater flows at high altitude, and local interactions with rising thermal fluids. Data on arsenic contents in 250 water samples from springs and wells and in 68 samples from rock outcrops were measured and combined with already existing information. Results highlight that arsenic concentrations of groundwater are influenced by type of aquifer, groundwater flow path, arsenic content of the aquifer rocks, and interaction with fluids rising from depth. Waters circulating in the Vico volcanics, one of the prominent rock units of the area, have high concentrations of arsenic, both for the basal OPEN ACCESS Water 2015, 7 5092 and the perched aquifers. A large fraction of the waters associated with this rock unit have arsenic contents higher than 10 μg/L (82 percent for basal, 40 percent for perched). In contrast, waters circulating in the Cimino volcanics have lower arsenic contents: 30 percent of the basal and 10 percent of the perched aquifers have arsenic concentrations greater than 10 μg/L. Through an integrated approach, including leaching tests to investigate the arsenic behavior concerning the water-rock interaction and a geostatistical modeling of data, it has been possible to identify and tentatively quantify suitable water resources that have arsenic content not exceeding the quality standards for human consumption.
... The second produced the Vicano complex (Laurenzi and Villa, 1987), a stratovolcano developed on a NW-SE elongated graben with a central depression caldera presently hosting Lake Vico, showing fall deposits, lava and pyroclastic flows having leucitites, phono-tephrites and leucite-phonolites (Perini et al., 2000). Volcanic products lie on a sedimentary series composed of (from top to bottom): (i) Plio-Pleistocene conglomerates, sandstones and mudstones, (ii) Cretaceous-Oligocene Ligurian and Sub-Ligurian units and (iii) Mesozoic carbonates overlying the Triassic evaporitic Burano Fm. (Cinti et al., 2014). ...
... The hydrogeological pattern is mainly related to (i) a hydrothermal reservoir hosted in the Mesozoic formations and (ii) relatively cold water system circulating within the volcanic units, the two aquifers being separated by the Ligurian units acting as aquiclude (Baiocchi et al., 2006). The water-dominated hydrothermal reservoir, having temperatures up to 220°C (Cinti et al., 2014), is the main source for thermal discharges that have been used for centuries as public pools and for health therapy (Chiocchini et al., 2001). Geophysical and geochemical prospection surveys aimed at evaluating the geothermal potential of this hydrothermal system were carried out in the last century (Cataldi et al., 1995 and references therein). ...
... In this area, the hydrothermal fluid emissions consist mainly of vigorous gas bubbling from several emission spots in the Vezza Creek, as well as strong CO 2 diffuse degassing that inhibits the growth of the vegetation cover in several zones (Fig. 2). The composition of hydrothermal fluids is dominated by CO 2 , produced mainly by thermometamorphic reactions (such as decarbonation) which occur within the Mesozoic carbonates and the Triassic anhydrites and/or in the metamorphic basement of the Tuscan series, with a minor contribution from a deeper seated (mantle degassing) source (Cinti et al., 2014). These gases also show a significant concentration of CH 4 , produced mainly by CO 2 reduction (Tassi et al., 2012a), and light hydrocarbons originating from thermogenic processes (Cinti et al., 2014). ...
This study investigated the effect of microbial activity on the chemistry of hydrothermal fluids related to the Vicano-Cimino system, central Italy. The database included the composition and δ13C CO2 and δ13C CH4 values of soil gas from an area characterized by intense degassing of fluids having a deep origin. The δ13C CH4 values along vertical profiles in the soil indicated that CH4 was controlled by microbial oxidation occurring at shallow (< 50 cm) depth, where free O2 was available. This was consistent with the vertical gradients of CH4, H2S and O2 concentrations. The δ13C CO2 values in soil gas, characterized by a composition similar to that of the hydrothermal fluids, were not significantly influenced by biodegradation. On the contrary, gas strongly affected by air contamination showed a significant δ13C CO2 fractionation. Microbial activity caused strong consumption of hydrothermal alkanes, alkenes, cyclics and hydrogenated halocarbons, whereas benzene was recalcitrant. Oxygenated compounds from hydrocarbon degradation consisted of alcohols, with minor aldehydes, ketones and carboxylic acids. A predominance of alcohols at a high rate of degassing flux, corresponding to a short residence time of hydrothermal gas within the soil, indicated incomplete oxidation. N-bearing compounds were likely produced by humic substances in the soil and/or related to contamination by pesticides, whereas α-pinene traced air entering the soil. The study demonstrates that microbial communities in the soil play an important role for mitigating the release to the atmosphere of C-bearing gases, especially CH4, through diffuse soil degassing, a mechanism that in central Italy significantly contributes to the discharge of CO2-rich gas from deep sources.
... The revised Volume Method (Doveri et al., 2010) was inspired by the good correspondence observed in geothermal areas between zones of high CO 2 fluxes of deep provenance and heat flux (Mahon et al., 1980;Marini and Chiodini, 1994). In particular, in the peri-Tyrrhenian sector of central Italy buried structural highs of the carbonate formations were considered as both geothermal reservoirs and traps for deep-originated CO 2 , from which fluids (thermal waters and gases) migrate towards the surface along preferential pathways such as faults (e.g., Chiodini et al., 1995Chiodini et al., , 1999Chiodini et al., , 2007Minissale, 2004;Frondini et al., 2009;Cinti et al., 2011Cinti et al., , 2014. Consequently, the extension of deep structures of potential geothermal interest can be evaluated at the surface based on the distribution of pCO 2 of emerging cold and thermal waters. ...
... A large geochemical dataset consisting of 333 water samples collected within the VCVD (Cinti et al., 2014), in an area of approximately 1,400 km 2 , was used to compute pCO 2 data by means of the Phreeqc code v. 2.12 (Parkhurst and Appelo, 1999). A statistical analysis was then carried out to describe the population of water samples with respect to pCO 2 . ...
... The second maximum characterize those waters with medium-to-high pCO 2 values (> 0.06 bar), reflecting the input of deeply derived CO 2 . Consistently, 13 C isotopic values of dissolved CO 2 have confirmed a twofold origin of carbon dioxide, from shallow organic processes and production at depth (through thermo-metamorphic reactions and mantle degassing), respectively (Cinti et al., 2014). After basic statistic analysis, data of pCO 2 were processed to obtain a map of its distribution. ...
The revised Volume Method is used here to evaluate the geothermal potential of the practically exploited Vicano-Cimino hydrothermal reservoir. This method is based on the distribution of pCO 2 (partial pressure of CO 2) in shallow and deep-originated waters to define areas of geothermal interest, according to the hypothesis that anomalous degassing zones of endogenous CO 2 , from either soil degassing and spring and well waters, are spatially related to deep fluids raising up from underlying hydrothermal reservoirs. On the whole, 333 fluid discharges (cold waters, thermal waters and bubbling pools) were collected within the Vicano-Cimino Volcanic District (VCVD) for chemical and isotopic compositions, in an area of approximately 1,400 km 2. From this large hydro-geochemical dataset the pCO 2 values were computed and then processed to obtain a map of its distribution by using geostatistical techniques (kriging). The resulting thematic map was then used to draw up the boundaries of high pCO 2 areas within the VCVD, potentially corresponding to the exploitable sectors of the deep hydrothermal reservoir. The estimated potential productivity and the total extractable thermal power of the VCVD are approximately of 10×10 3 t/h and 517-979 MW, respectively. This makes the VCVD suitable both for direct and indirect exploitation of the geothermal resources, in view of the target to reduce electricity generation from conventional and poorly sustainable energy sources.
... The perched aquifers both from volcanic and sedimentary deposits discharged from several springs, which are generally characterized by flow b0.005 m 3 /s (Baiocchi et al., 2006). A regional hydrothermal aquifer hosted in the Mesozoic units was recognized at depth (Cinti et al., 2014). It is separated from the shallow continuous volcanic aquifer by low-permeability Plio-Pleistocene sedimentary complex and the Ligurian s.l. ...
... Many springs and wells sampled from the shallow aquifers supply the local drinking water. The physical-chemical features of the studied waters and the composition of the main solutes were reported by Cinti et al. (2014). Samples for trace elements (As, U and V) analysis were collected in polyethylene bottles, which were pre-cleaned in the laboratory with diluted (1:3) Suprapur HNO 3 and then thoroughly rinsed with ultra-pure deionized water. ...
... Four subsets of the whole population were defined on the basis of the water type (Table 1), as previously proposed by Cinti et al. (2014): 1) cold waters from the aquifer hosted in the volcanic rocks, 2) cold waters from the aquifer in the sedimentary deposits, 3) thermal waters and 4) bubbling pools (i.e. cold waters associated with a CO 2 -rich bubbling gas phase). ...
... This lake has formed as sinkhole atop a layer of travertine deposits exceeding 20 m in thickness (Sabatini, 1907;Pirro et al., 2013). The lake is currently characterized by springs emitting CO 2 -and SO 4 -rich cold waters (Cinti et al., 2014), but in the past it has experienced several paroxysmal events that have been even mentioned by Pliny the Elder (e.g., Sabatini, 1907;Pirro et al., 2013). In particular, such events were characterized by the violent ejection of mud and waters that often formed small ephemeral extrusive mud cones raising from the centre of the lake. ...
... Vertical PGV produced by this earthquake at the Lake Vadimone is estimated at 0.75 cm s −1 , which in turn yields a peak dynamic stress in the range 13-32 kPa (Table 2). Normal stress changes have been calculated using a NE-dipping normal fault as source fault (strike = 315°, dip = 50°, rake = −85°, depth = 7.5 km; Bonini et al., 2016b), and sampled on a N140° trending feeder dike representative of the region (e.g., Cinti et al., 2014). The magnitude of static stress is obviously negligible at such a far-field distance (Table 2), and therefore the postseismic Lake Vadimone eruption of April 28, 1917 was triggered entirely by dynamic stress changes. ...
Earthquakes can occasionally trigger the eruption or increase the activity of mud volcanoes and other fluid seepage systems. One long pending question is how static and dynamic stress changes can trigger eruptions of fluid expulsion features and modulate their activity. This study addresses the potential role of static and dynamic stress changes by investigating some well documented examples of triggered historical and recent eruptions in the Northern Apennines (Italy) and partly Azerbaijan. Peak dynamic stress at triggered fluid expulsion features has been estimated using measured PGV, or PGV estimated from attenuation relationships. The results suggest that seepage features are often triggered by dynamic stress changes created by earthquake faults located in the intermediate- to far-field. Paroxysmal activity of the considered fluid expulsion systems was influenced by minimum dynamic stress thresholds ranging from approximately 30–50 kPa to 15 kPa. Regarding co-seismic static stress changes, their magnitude can be large enough to dilate fault-controlled fluid pathways located in the near-field of a ruptured fault. This may be the case of the Pede-Apennine thrust (in northern Italy), which ruptured in 1501 (Mw ~6) beneath many mud volcanoes. Apart from this case, the considered fluid expulsion systems that responded to the earthquakes were stressed by negligible or subordinate changes in static stress, with few exceptions. Earthquake-related stresses have the ability to influence the eruptive activity of fluid seepage systems, but the recovery time between two consecutive eruptions is usually irregular. This variability in the repose time suggests that the achievement of a critical or trigger-able state is governed by a complex interplay among independent factors (e.g., production rate of driving gases, plumbing system characteristics, frequency of triggering earthquakes).
... LG91 has the highest CO 2 concentration (91%) and ␦ 13 C CO2 value of −7.3‰ falling in the range of mantle. Potential sources of CH 4 in a hydrothermal system are: 1) biotic, produced by thermogenic degradation of organic matter in rocks or by microbial processes 2) abiotic, originated by reaction that does not involve organic matter (Clark and Fritz, 1997;Cinti et al., 2014). Although carbon isotope exchange may exist between coexisting CH 4 and CO 2 (Horita, 2001), it is important to note that the carbon isotope compositions remain roughly constant for each specific source (Whiticar, 1999). ...
... 10f). All analyzed gas samples plot within the thermocatalytic field, allowing to propose that CH 4 formation is mainly due to the decomposition of organic matter buried in sediments at temperatures >150 • C ( Fig. 10f; Cinti et al., 2014;Pang et al., 2018). The ␦D CH4 value of sample LG56 (−167‰ VSMOW, Table 4) together with quite constant ␦ 13 C CH4 values (−37.8 to −40.1‰) further confirms the thermogenic origin of CH 4 . ...
This study focuses on the geochemical and isotopic composition of natural spring waters and gases discharging at Los Geysers thermal area (northern Trans-Mexican Volcanic Belt, TMVB) and its relations to the regional tectonic framework. Water is of Na-HCO3 type and samples were collected at temperatures ranging from 48 °C to 98 °C and pH from 6.8 to 9.3. Stable isotope compositions (−10.0 to −8.0‰ for δ¹⁸O and −75.6 to −69.7‰ for δD) deviate from the global and local meteoric lines suggesting fractionation by steam loss The ⁸⁷Sr/⁸⁶Sr values of the thermal waters range from 0.70664 to 0.70698 indicating that most of the strontium comes from the dissolution of carbonate belonging to the late Berriasian to early Valanginian in the Guanajuato conglomerate group and a minor component of less radiogenic Sr from Paleogene–Neogene volcano-sedimentary and volcanic rocks. Solute geothermometers reveal a reservoir temperature around 164 °C. A mixture between air and hydrothermal CO2 composes the bubbling gases. Helium isotopes data (R/Ra = 0.96–1.71) and ⁴He/²⁰Ne ratios (0.53–9.41) reveal that helium is dominated by a radiogenic component with a considerable mantle-He contribution (up to 20.8%). Since there is no active volcanism at the northern TMVB, mantle-He is best explained by transport of volatiles along active faults reaching the crust-mantle boundary. The conceptual hydrogeochemical model involves a thermal aquifer at ∼1000 m depth which is recharged by regional meteoric water flow, a high thermal gradient (∼153 °C/km) and fast fluid upflow to the surface along discontinuities related to regional horst and graben tectonics.
... Water samples (N ¼ 659) collected from springs, domestic and municipal wells and homogeneously distributed over an area of about 2800 km 2 ( Fig. 1) were analyzed for As, F À and 222 Rn concentrations. Other physical, chemical and isotopic data were analyzed and discussed elsewhere (Cinti et al., 2011(Cinti et al., , 2014(Cinti et al., , 2017. Waters were sampled from i) the cold and shallow volcanic aquifer, which is the main local source of drinking water supplies, ii) the cold and shallow perched aquifers hosted in permeable layers of the sedimentary deposits and iii) the deep hydrothermal reservoir hosted in the carbonate formations. ...
... On the other hand, the significantly lower 222 Rn concentrations recorded in the thermal waters relative to coldvolcanic waters (Fig. 2d) are likely due to the fast decrease of 222 Rn solubility as water temperature increases. However, as thermal waters are commonly associated with a vigorous CO 2 -dominated gas phase uprising through fractures and faults (Cinti et al., 2011(Cinti et al., , 2014(Cinti et al., , 2017, the gas flux may exert a control on the transport of dissolved minor and trace gases, locally producing elevated 222 Rn concentrations (up to 698 Bq/L; SM 1, 2). ...
659 water samples from springs and wells in the Sabatini and Vicano-Cimino Volcanic Districts (central Italy) were analyzed for arsenic (As), fluoride (F-) and radon (222Rn) concentrations. Waters mostly sourced from a shallow and cold aquifer hosted within volcanic rocks, which represents the main public drinking water supply. Cold waters from perched aquifers within sedimentary formations and thermal waters related to a deep hydrothermal reservoir were also analyzed. The highest concentrations of As and F- were measured in the thermal waters and attributed to their enhanced mobility during water-rock interaction processes at hydrothermal temperatures. Relatively high concentrations of As and F- were also recorded in those springs and wells discharging from the volcanic aquifer, whereas waters hosted in the sedimentary units showed significantly lower contents. About 60% (As) and 25% (F-) of cold waters from the volcanic aquifer exceeded the maximum allowable concentrations for human consumption. Such anomalously high levels of geogenic pollutants were caused by mixing with fluids upwelling through faulted zones from the hydrothermal reservoir. Chemical weathering of volcanic rocks and groundwater flow path were also considered to contribute to the observed concentrations. Cold waters from the volcanic aquifer showed the highest 222Rn concentrations, resulting from the high contents of Rn-generating radionuclides in the volcanic units. Approximately 22% of these waters exceeded the recommended value for human consumption. A specific Quality Index (QI), comprised between 1 (very low) and 4 (very high), was computed for each water on the basis of As, F- and 222Rn concentrations and visualized through a spatial distribution map processed by means of geostatistical techniques. This map and the specific As, F- and 222Rn maps can be regarded as useful tools for water management by local authorities to both improve intervention plans in contaminated sectors and identify new water resources suitable for human consumption.
... Many studies in the last few years have focused on creating 3D models aimed at encouraging the geothermal exploration in central Italy, with particular attention on the Lazio Region (Cinti et al., 2011(Cinti et al., , 2014Procesi and Poncia, 2013;Giordano et al., 2014;Petracchini et al., 2015). ...
... = below detection limit. Data source: a) this work; b)Minissale et al. (1997a); c)Carapezza et al. (2012); d)Carapezza et al. (2005); e)Giggenbach et al. (1988); f)Cinti et al. (2011); g)Chiodini and Cioni (1989); h)Chiodini (1994); i)Chiodini et al. (2007); j)Bertrami et al. (1985); l)Chiodini and Frondini (2001); m)Chiodini et al. (2011); n)Cinti et al., (2014). ...
Estimation of the geothermal potential of the Caldara di Manziana site in the Sabatini Volcanic District (central Italy) by integrating geochemical data and 3D-GIS modelling
... Many studies in the last few years have focused on creating 3D models aimed at encouraging the geothermal exploration in central Italy, with particular attention on the Lazio Region (Cinti et al., 2011(Cinti et al., , 2014Procesi and Poncia, 2013;Giordano et al., 2014;Petracchini et al., 2015). ...
... = below detection limit. Data source: a) this work; b)Minissale et al. (1997a); c)Carapezza et al. (2012); d)Carapezza et al. (2005); e)Giggenbach et al. (1988); f)Cinti et al. (2011); g)Chiodini and Cioni (1989); h)Chiodini (1994); i)Chiodini et al. (2007); j)Bertrami et al. (1985); l)Chiodini and Frondini (2001); m)Chiodini et al. (2011); n)Cinti et al., (2014). ...
... Gas geothermometry has been widely applied in geothermal exploration (e.g., D'Amore and Panichi, 1980;Arnòrsson and Gunnlaugsson, 1985;Giggenbach, 1991;Fischer et al., 1997;Marini, 1998, Powell, 2000;Aguilera et al., 2005;Cinti et al., 2014;Minissale et al., 2017;Dobson et al., 2018;Pereira et al., 2022), providing an estimate of geothermal reservoir temperature based on the thermodynamic equilibrium between gas species (H 2 O, H 2 , CO 2 , CO, CH 4 ). The thermodynamic evaluation of gas equilibria in the CO 2-H 2 system has widely demonstrated its effectiveness in providing information on the dominant thermodynamic conditions at depth (e.g., Giggenbach, 1991;Powell, 2000;Sepúlveda et al., 2007;Taussi et al., 2023a). ...
The Alpehue Hydrothermal Field (AHF) near the Sollipulli Volcano in the Southern Volcanic Zone of Chile shows promise as a significant geothermal resource. A comprehensive geothermal exploration survey was conducted, including the evaluation of hydrothermal gases, geothermometer calculations, and CO2 flux measurements, to assess the AHF's geothermal potential. Our results indicate that the hydrothermal gasses at the AHF primarily originate from primitive, mantle-derived sources, with some contribution from crustal sediments. Two different CO2 populations of fluxes were identified. One corresponds to the background emission related to the soil biological activity (mean ∼7.7 g·m−2·d−1), and the other, much more significant, emanates from an endogenous source related to the Alpehue hydrothermal reservoir (mean ∼461 g·m−2·d−1). Reservoir temperatures were calculated using gas geothermometry yielding average temperatures of 249 °C. The calculated heat flow rate of the AHF is approximately 3.3 MW and the heat flux corresponds to 156 thermal MW⋅km−2, which could be considered a medium geothermal potential comparable to other systems worldwide. Although further studies are needed to fully address its exploitability, this study presents favorable characteristics of the AHF that make it a promising avenue for further exploration.
... Some examples are the Vicano-Cimino Volcanic District and Sabatini Volcanic District (Central Italy), where brines originated from the mixing of two different type of water. (Cinti et al., 2014;. Oil field brines often contain significant concentrations (up to 20 mg/l) of Li, as in the case of the Eastern oil and gas region, Ukraine (Reva et al., 2021), as well as in the Paris basin, France (up to 3 mg/l) (Fontes and Matray, 1993) and the North German Basin (Lüders et al., 2006). ...
The aim of the BrineRIS project is to explore brines in RIS countries potential for critical metal extraction. In the frame of this project, the concentration of mineral brines in three geothermal wells located in the Beiuș Basin (northwestern Romania) was determined by analyzing the water from the wells. Until recently, no reliable trace element data were available from Beiuș Basin. Following the new analyses, the geothermal water extracted by TRANSGEX SA company from wells F-3001H, F-3003H, and F-3005H revealed exceptionally low concentrations of associated chemical compounds. The Li-concentration is only ~ 22-32 µg/l. Zn, I, Rb and As present in similar concentrations, while other trace elements (e.g. Co, V, Ti) are below detection limit. The Sr (~ 540-680 µg/l), Ba (~ 170-200 µg/l) and B (~ 70-100 µg/l) concentrations are slightly elevated, but still low. Therefore, the water in this "geothermal reservoir" can be classified as relatively potable, but it is not appropriate for critical metal extraction. In this paper, some documented concentrations from previous years have been compared to recent concentrations. In addition, the relationship between geology and water chemistry is emphasized in order to determine the reason for the absence of solutes that were expected to be found in this water.
... The aquifer lies on a low-permeability cover of Flysch units (Upper Cretaceous-Oligocene) and Plio-Pleistocene sediments, under which a geothermal reservoir is hosted in a Mesozoic carbonatic sequence. This setting gives rise to numerous thermal springs in the region (Cinti et al 2014). The water table aquifer is overlain by a permeable unsaturated zone that makes it relatively vulnerable to both diffuse and point source pollution. ...
Groundwater is an important freshwater resource and hosts specialized microbial assemblages providing fundamental ecosystem services. The current knowledge on the role of aquatic microorganisms in subsurface ecosystems is still limited. This work aimed to explore the links between groundwater hydrogeochemical properties and microbial community traits in a volcanic unconfined aquifer, moderately impacted by anthropic activities. The main physical and chemical parameters of groundwater samples were analyzed, along with microbial biomass (total cell counts, ATP-active biomass concentration), potential metabolic activity, and physiological profiles at the microbial community level (Biolog ™ EcoPlates). The results showed the coexistence of oxidizing and reducing groundwater conditions across the study area. We discriminated two groups of oxidizing/reducing groundwater samples (Ox and Red), each including two subgroups with different chemical conditions attributed to contrasting levels of anthropogenic impact for non-intensive agricultural practices and waste disposal activities (Ox − and Ox + ; Red − and Red +). Although the microbial biomass was likely not affected by changing redox, the microbial metabolic potential and functional diversity changed significantly. In the Ox samples, the community-level physiological profiles were different, mainly owing to the utilization of carboxylic acids (Ox − > Ox +) and carbohydrates (Ox + > Ox −). In the Red samples, a wider set of organic substrates were consumed by the microbial communities, including those less bioavailable (e.g., phenols). Significant differences were also found between Red − and Red + , mainly owing to the relative increase in the utilization of amino acids in Red − , polymers and amines in Red + , along with the active biomass. By reflecting the local redox conditions and moderate levels of anthropogenic impact, the applied approach highlighted changes of microbial metabolic potential and physiological profiles that imply direct repercussions on biogeochemical cycling and the ecosystem services provided by groundwater microorganisms.
... Crustrelated 4 He is produced by the radioactive α -decay of uranium ( 235 U, 238 U), thorium ( 232 Th), and samarium ( 147 Sm), with R/Ra ratio of the end-member of 0.01 (R = 3 He/ 4 He (sample) ; Ra = 3 He/ 4 He (atm) = 1.39 × 10 −6 ), while 3 He is degassed from the upper mantle with R/Ra end-member ratio of 8 ± 1 (Hilton et al., 2002;Poreda and Craig, 1989). A slight increase above the 3 He/ 4 He (atm) ratio, (>1.0 R/Ra) suggests that the source includes mantle-derived components (Cinti et al., 2014). We have plotted the δ 13 C TDIC values in relation to the He isotope ratios reported in González-Guzmán (2019) for the same spring discharges. ...
This study examines the water-rock-gas interaction of the Los Geysers geothermal system in the northern Trans-Mexican Volcanic Belt (TMVB). Physico-chemical parameters, δ¹³C of total dissolved inorganic carbon (TDIC), and Rare Earth Elements (REE) composition on 14 thermal water discharges are reported and discussed. Waters had temperatures ranging from 40 °C to 98 °C, pH from 7.4 to 9.2, and total dissolved solids from 598 mg L⁻¹ to 992 mg L⁻¹. Signals of thermophilic biota, mainly diatom frustules, were found in the suspended particulate matter of spring waters. The range of δ¹³CTDIC was between −7.55‰ and −4.13‰ (avg. −7.10‰). Although potentially affected by secondary processes, the dissolved C species of the studied waters likely have a predominant deep, mantle-related origin. The lanthanoids concentrations (∑REE) were variable over practically one order of magnitude, with average values between 1463 pmol L⁻¹ for Ce and 9.0 pmol L⁻¹ for Lu. Post-Archean Australian Shale (PAAS)-normalized patterns showed a slight enrichment in middle lanthanides, numerically expressed as [Sm/La]N and [Sm/Yb]N, ranging from 1.43 to 2.06 and 0.84 to 2.03, respectively. We propose that the overall signature of the REE is inherited during the regional migration of the liquid and from the primary aquifer. Moreover, PHREEQC computer code was run to calculate the dominant REE complexing ligands in the geothermal system at different temperatures. Our calculations indicate that F⁻ complexes dominate over CO3 species at outlet temperatures, but oxyhydroxide complexes (REE-O2H, REE-O2–, and REE-O⁺) act as sinks after leaching from the source rock. The ¹⁴³Nd/¹⁴⁴Nd ratio of one of the studied samples was measured (0.512320 ± 0.19; εNd = −6.20 ± 0.37, 2s.e.). The conceptual model in this paper highlights a mixing waters process between geothermal waters and cold shallow waters in the Queretaro Graben.
... This may be because the CO 2 -CH 4 system had obvious H 2 rebalancing when the geothermal fluid rose to the surface. In addition, the oxidation state of the CO 2 -CH 4 -H 2 equilibrium system was stronger than that of the original hydrothermal system (R H = − 2.8) (Giggenbach, 1987;Sepúlveda et al., 2007;Cinti et al., 2014). This low R H value generally considers the gas-liquid interactions that occur at ~140-160 • C. Therefore, it can be inferred that the CO 2 -CH 4 -H 2 equilibrium system is very sensitive to the rebalancing of H 2 due to the decreased temperature. ...
Exploring and exploiting high-temperature (even supercritical) geothermal resources are significant to meet energy demands and reduce carbon emissions. The Yangbajing geothermal field is the most exploited in China, with the currently highest temperature (329.8°C) measured in a geothermal well. However, whether there are supercritical geothermal fluids beneath the deep parts of this geothermal field is under controversy. In this paper, the water isotope, chemical compositions, and C–He isotopes of gas samples were collected and analyzed. The geothermal water originated from the mixing of meteoric water and magmatic water (25%). The sources of CO2 in the geothermal field were dominated by the thermogenic degassing of carbonates and metasediments in the crust while the radioactive decay of U and Th in granite is the dominated source of He. The temperatures of three different reservoirs were 150 ± 15°C, 250 ± 10°C, and ∼320°C (with a depth of ∼8 km), respectively. These were obtained using dissolved gas, soil CO2 flux, and noble gas geothermometers. Unlike other supercritical geothermal fields worldwide with larger, shallower, basaltic magma chambers, the Yangbajing geothermal field has a deep-seated, small-scale, granitic magma chamber. Thus, its geological conditions are not conducive for gestating supercritical fluids. These results are of great significance for exploring and developing high-temperature (even ultra-high-temperature) geothermal resources in China.
... Although considered as the main source of carbonate ions in groundwater, the carbonate minerals dissolution is not their only one source everywhere. In volcanic regions, the dissolution of can be an important source of bicarbonate (Cinti et al., 2014). In relatively deep oxygen-poor ground waters, bicarbonate rich waters originate from either dissolution of or condensation of geothermal steam (Harsh & Sukanta, 2007). ...
Une étude géochimique a été effectuée sur l'eau d'une source géothermale appelé Lilida, située dans la province de l'Ituri, dans la partie nord-est de de la République Démocratique du Congo. Ses objectifs étaient de définir le faciès chimique de ladite eau, de déterminer la nature lithologique de son réservoir et d'estimer la température qu'elle possède dans son réservoir. Les échantillons d'eau ont été prélevés au mois de février de l'année 2017 et soumis à des analyses chimiques et physiques. En plus, les diagrammes de D'Amore et al. (1983), de Giggenbach (1991) et de Piper (1944) ont été élaborés pour obtenir la classification de cette eau thermale. Au terme de cette étude, l'eau de la source Lilida s'est révélée du type bicarbonaté calcosodique. Son facies géochimique étant pour les cations > > et pour les anions > >. Il s'est avéré que son réservoir était une formation argileuse peu profonde contenant certainement des calcaires dolomitiques et des dérivées des flyschs ou « volcanites ». L'application de la géothermométrie a révélé que l'eau étudiée aurait, dans son réservoir, une température de 45,7 °C. En tant que telle, elle ne peut faire objet que d'une exploitation géothermique basse énergie. Abstract A geochemical survey on the thermal water released by the Lilida Spring, located in the Congolese Northeastern Province of Ituri was undertaken. The aims of this study were to determine the chemical facies of this water; to determine the lithological nature of its reservoir and to predict its subsurface temperature. The water samples were collected in February 2017. Then physical and chemical analyzes were done. The graphics of D'Amore, Giggenbach and Piper were applied on the water analyzes to obtain its classification. The studied water was characterized as a bicarbonated calcosodic shallow fresh groundwater, with this following geochemical facies for the cations > > and this one for the anions > >. Its reservoir was characterized as an argillaceous formation containing certainly dolomitic limestone and flysch derivate or «volcanites». Assessments from chemical geothermometer 1 Adresse pour le courrier électronique : 45 suggest the existence of a peripheral geothermal reservoir of low enthalpy (45.7 °C). Thus, in that state, this thermal water can only be used for geothermal low energy exploitation.
... Although considered as the main source of carbonate ions in groundwater, the carbonate minerals dissolution is not their only one source everywhere. In volcanic regions, the dissolution of can be an important source of bicarbonate (Cinti et al., 2014). In relatively deep oxygen-poor ground waters, bicarbonate rich waters originate from either dissolution of or condensation of geothermal steam (Harsh & Sukanta, 2007). ...
A geochemical survey on the thermal water released by the Lilida Spring, located in the Congolese Northeastern Province of Ituri was undertaken. The aims of this study were to determine the chemical facies of this water; to determine the lithological nature of its reservoir and to predict its subsurface temperature. The water samples were collected in February 2017. Then physical and chemical analyzes were done. The graphics of D’Amore, Giggenbach and Piper were applied on the water analyzes to obtain its classification. The studied water was characterized as a bicarbonated calcosodic shallow fresh groundwater, with this following geochemical facies for the cations Na+ > Ca2+ > Mg2+ and this one for the anions HCO3->SO4=>Cl-. Its reservoir was characterized as an argillaceous formation containing certainly dolomitic limestone and flysch derivate or «volcanites». Assessments from chemical geothermometer suggest the existence of a peripheral geothermal reservoir of low enthalpy (45.7 °C). Thus, in that state, this thermal water can only be used for geothermal low energy exploitation.
... Numerous thermal and mineralized springs, as well as strong free-and diffuse-dry gas emissions and travertine deposits, are widespread along the western margin of central Italy (Dall'Aglio et al., 1994;Cinti et al., 2011;Giustini et al., 2018). These manifestations appear to be controlled by the tectonic structures that provide permeable pathways for the deep-sourced ascending fluids; the largest manifestation of the study area is located east of the Bolsena lake,~5 km south to Celleno, where a diffuse degassing area, controlled by a NW striking, SW-dipping high-angle normal fault, discharges a CO 2 flux estimated to be 230 * 10 3 kg/d (Chiodini et al., 1999;Cinti et al., 2014). ...
A detailed geochemical study on radon related to local geology was carried out in the municipality of Celleno, a little settlement located in the eastern border of the Quaternary Vulsini volcanic district (central Italy). This study included soil-gas and terrestrial gamma dose rate survey, laboratory analyses of natural radionuclides (²³⁸U, ²²⁶Ra, ²³²Th, ⁴⁰K) activity in rocks and soil samples, and indoor radon measurements carried out in selected private and public dwellings. Soil-gas radon and carbon dioxide concentrations range from 6 to 253 kBq/m³ and from 0.3 to11% v/v, respectively. Samples collected from outcropping volcanic and sedimentary rocks highlight: significant concentrations of ²³⁸U, ²²⁶Ra and ⁴⁰K for lavas (151, 150 and 1587 Bq/kg, respectively), low concentrations for tuffs (126, 123 and 987 Bq/kg, respectively), and relatively low for sedimentary rocks (108, 109 and 662 Bq/kg, respectively). Terrestrial gamma dose rate values range between 0.130 and 0.417 μSv/h, being in good accordance with the different bedrock types. Indoor radon activity ranges from 162 to 1044 Bq/m³; the calculated values of the annual effective dose varied from 4.08 and 26.31 mSv/y.
Empirical Bayesian Kriging Regression (EBKR) was used to develop the Geogenic Radon Potential (GRP) map. EBKR provided accurate predictions of data on a local scale developing a spatial regression model in which soil-gas radon concentrations were considered as the response variable; several proxy variables, derived from geological, topographic and geochemical data, were used as predictors. Risk prediction map for indoor radon was tentatively produced using the Gaussian Geostatistical Simulation and a soil-indoor transfer factor was defined for a ‘standard’ dwelling (i.e., a dwelling with well-defined construction properties). This approach could be successfully used in the case of homogeneous building characteristics and territory with uniform geological characteristics.
... In particular, the origin of H 2 S can be ascribed to thermogenic reduction of Triassic anhydrites, which are present at the base of the Mesozoic carbonate sequence (Giordano et al., 2014), as also observed in H 2 S-bearing gases discharging from the northern part of the Roman Magmatic Province (e.g. Sabatini and Vicano-Cimino volcanic districts; Cinti et al., 2011Cinti et al., , 2014Cinti et al., , 2017. In particular, the H 2 S production from the evaporitic formations may proceed through thermochemical sulfate reduction (TSR), a process involving hydrocarbons, according to the following reaction (Worden and Smalley, 1996): ...
The Colli Albani volcanic complex (Lazio, Italy) hosts areas characterized by anomalously high emissions of CO2-rich gases (e.g. Tivoli, Cava dei Selci, Tor Caldara, Solforata). The source of these gases is a regional aquifer within the Mesozoic carbonate rock sequences. These degassing zones release significant concentrations of H2S and other toxic gases (e.g. GEM: Gaseous Elemental Mercury, and Rn) and represent a serious hazard for local inhabitants, especially for those living at Cava dei Selci (near Rome, Italy), where the emitting areas are nested inside residential neighborhoods. In April 2016, a comprehensive geochemical survey was carried out in an abandoned stone quarry nearby the urban settlement aimed to: (i) investigate the gas composition from both punctual discharges and anomalously high diffuse soil degassing sites, and (ii) evaluate their environmental impact on the local air quality. The spatial distribution of the soil CO2 fluxes was mainly dependent on the local geostructural setting, whereas shallow secondary processes (e.g. oxidation and gas-water interaction) likely represent the main controlling factor on reactive and/or water-soluble gas species, such as CH4 and H2S. The total output of CO2 from the abandoned stone quarry accounted for 0.53% of total CO2 discharged from the whole Colli Albani volcanic district. The naturally emitted toxic gases (e.g. CO2, H2S, CH4, GEM) largely affect the air quality and pose a serious threat for the health of the local residents. A mobile multi-instrumental station able to continuously and simultaneously acquire CO2, H2S, SO2, CH4, GEM and CO was deployed to verify the concentrations of both the main deep-originated gas compounds and potential secondary gaseous contaminants (i.e. SO2) around and inside the urban settlement most exposed to the lethal gases. Hydrogen sulfide was found to be the most impacting gas, occasionally exceeding the 24-h air quality guideline for ambient air and causing odor annoyance at a distance up to more than 250 m downwind from the emitting area. In poorly ventilated basements, toxic gas accumulations up to hazardous levels were measured, producing anomalous outdoor air concentrations at the street level in front of the descending vehicular access to private garages and relatively far from the main emitting area. The geochemical survey, carried out via mobile station and soil gas measurements, resulted to be particularly efficient for evaluating the potential effects caused by gas emissions in inhabited areas. The multi-measurement approach adopted in the present study is of paramount importance for managing future urban development plans.
... Other studies at hydrothermal sites have described wider ranges of carbon isotope composition of CO 2 (e.g., from −2.4 to −7.8‰ in submarine hydrothermal vents [29] and from −1.0 to −9.1‰ in hot springs [30]). Taking these δ 13 C CO2 values as references, a higher δ 13 CO 2 may indicate the addition of CO 2 directly from volcanic sources [31] or from underlying sedimentary rocks containing more marine carbonate minerals (i.e., CO 2 produced mainly by thermal decarbonation [32]). On the contrary, lighter δ 13 CO 2 values suggest a likely contamination by crustal organic sediments [33]. ...
The hydrothermal caves linked to active faulting can potentially harbour subterranean atmospheres with a distinctive gaseous composition with deep endogenous gases, such as carbon dioxide (CO 2 ) and methane (CH 4 ). In this study, we provide insight into the sourcing, mixing, and biogeochemical processes involved in the dynamic of deep endogenous gas formation in an exceptionally dynamic hypogenic karst system (Vapour Cave, southern Spain) associated with active faulting. The cave environment is characterized by a prevailing combination of rising warm air with large CO 2 outgassing (>1%) and highly diluted CH 4 with an endogenous origin. The δ¹³ C CO2 data, which ranges from −4.5 to −7.5‰, point to a mantle-rooted CO 2 that is likely generated by the thermal decarbonation of underlying marine carbonates, combined with degassing from CO 2 -rich groundwater. A pooled analysis of δ¹³ C CO2 data from exterior, cave, and soil indicates that the upwelling of geogenic CO 2 has a clear influence on soil air, which further suggests a potential for the release of CO 2 along fractured carbonates. CH 4 molar fractions and their δ D and δ¹³ C values (ranging from −77 to −48‰ and from −52 to −30‰, respectively) suggest that the methane reaching Vapour Cave is the remnant of a larger source of CH 4 , which was likely generated by microbial reduction of carbonates. This CH 4 has been affected by a postgenetic microbial oxidation, such that the gas samples have changed in both molecular and isotopic composition after formation and during migration through the cave environment. Yet, in the deepest cave locations (i.e., 30 m below the surface), measured concentration values of deep endogenous CH 4 are higher than in atmospheric with lighter δ¹³ C values with respect to those found in the local atmosphere, which indicates that Vapour Cave may occasionally act as a net source of CH 4 to the open atmosphere.
... Water isotope datas reveal that shows almost all of the samples are plotted along the meteoric water line (Figure 8), which indicates that meteoric water is a source for thermal fluids. Some data show the negative shifting of O-18, effected by seasonal water cycle (Belgaman et al., 2017;Suwarman et al., 2013) or likely produced by isotope exchange between water and CO2 (Cartwright et al., 2002;Cinti et al., 2014). Positive shifting of the CHY data can be affected by other reasons, such as evaporation, magmatic input or sedimentary fluids. ...
Geochemistry is one of the most effective methods used in the geothermal exploration process, especially related to subsurface temperature, interaction process, and geothermal fluid source. This preliminary research is aimed to clarify the origin of geothermal fluid and process of rock and fluid interaction that occurred in the Tampomas geothermal field in the northern Bandung Basin, one of the geothermal potential fields in this basin. The potential in the northern Bandung basin is estimated to be lower than the southern basin in which several fields such as Kamojang, Darajat, and Wayang Windu produce considerable geothermal energy, ranging from 200 to 300 MWe. To reveal this potential difference is an important issue for the geothermal system in the plate subduction zone. The geochemical analysis was applied to it. Generally, water type of hot spring in the Tampomas area is dominated by chloride-bicarbonate water, where water is formed in the marginal area near the surface. CO2 gas and water vapor are condensed into cold groundwater as well as steam heated processes. The low B / Cl ratio in the hot springs indicates a close relationship with the magmatic geothermal system. The Ciuyah hot spring has the highest concentrations of chloride, calcium, and lithium among the other manifestations, which is probably due to fluid interaction with the Tertiary marine sedimentary rocks in this area, in particular the Tertiary claystone of the Subang Formation. The maximum subsurface temperature in the Tampomas area is 168˚C168˚C based on a silica geothermometer. Study on stable isotopes of oxygen and hydrogen suggest that the recharge area in the Tampomas geothermal manifestation is located in the elevation range from 425 to 900 m.a.s.l. Consequently, through our geochemical data, the geothermal fluids originating from meteoric water have been influenced by the volcanic process of Mt.Tampomas and interacting with the sedimentary rocks around it.
... In peri-Tyrrhenian area of Tuscany and Latium gases have lower R/ Ra values from 0.4 to 0.8 (Hooker et al., 1985;Minissale et al., 1997a;Cinti et al., 2011Cinti et al., , 2014, although a significant 3 He enrichment was measured in geothermal fluids from Larderello (up to 3.2; Minissale et al., 1997a), Cesano (1.2-2.0; Minissale et al., 1997a;Cinti et al., 2017) and in the gas discharges from the Alban Hills (0.9-1.9; Barberi et al., 2007) and Riardo area, at SE of Roccamonfina volcanic edifice (1.89; Cuoco et al., 2017). ...
In recent years, two research projects specifically conceived by Italian Institutions of Research to promote the implementation of the use of geothermal energy in Southern Italy has allowed the review of most data on chemical and isotopic compositions of natural thermal manifestations in the territory of Italy. Two large databases, one for thermal springs and CO2-rich springs, and a second one for fumarolic condensates and associated gas phase have been produced and are available on line, with data spanning in time from the early 70's to the present. We have used those data, after careful evaluation of the quality and reliability of them, to produce correlation diagrams and isodistribution maps of some relevant geochemical/geothermal parameters, such as: pCO2 in thermal springs, %CO2 and δ¹³C in CO2 of gas phases, ³He/⁴He ratio and %He. In this way, we have been able to delimit the areal patterns of thermal anomalies potentially related with geothermal reservoirs. The cross correlation among the many parameters (>40) selected has allowed the overview on the circulation of fluids at shallow crust, in one of the most active tectonic boundary of the Earth between the African and the Eurasian continents. Shallow circulation of hot fluids is particularly active in the Roman Comagmatic Province, the Neapolitan area and Sicily (both at Etna, Aeolian Archipelago and Pantelleria island in the Sicily Channel) where active geothermal systems are already known, whose areal extension is probably much larger than what envisaged at present. The geothermometric evaluation of data has not allowed to clearly identity new areas apart from those already known but, nevertheless, some areas in the inner Apennines, as well as Sicily and Sardinia have shown anomalous ³He/⁴He values that point to the presence of mantle fluids located inside the crust. Being most of active volcanic islands likely much smaller than the thermal anomaly they are associated with, a futuristic perspective of utilizing geothermal fluids off shore is suggested. Moreover, the database and the proposed maps can be a useful tool both scientific community and stakeholders to perform geothermal favourability maps and to identify potential new areas interesting from a geothermal perspective.
... Thermo-mineral and carbo-gaseous hydrosystems, well known for their economic importance, have been exploited for centuries for thermal and spa activities. Sparkling natural mineral waters, bottled in Europe since the early 17th century (Lopoukhine, 1998), still constitute a dynamic industry (Renac et al., 2009;Cinti et al., 2014). These hydro-systems are associated with specific geological struc Lachassagne et al., 2011;Petrella et al., 2015;Tokan-Lawal et al., 2015). ...
Crystalline thermo-mineral and carbo-gaseous (CTMCG) hydrosystems are well known for their economic importance in fields such as thermal, spa activities and natural mineral water (NMW) bottling. Such systems are usually associated with strong structural complexity, which is rarely characterised in detail or robustly. This research focuses on a CTMCG hydrosystem associated with a peri-alpine graben. A multidisciplinary approach with a very large set of data and methods - geological modelling with geophysics and geological data from outcrops and several boreholes, hydrodynamic data, hydrochemistry, hydrogeological and geochemical modelling - reveals very novel results and allows a robust conceptual model to be constructed. The aquifer at the origin of the carbogaseous natural mineral water is the 100-125 m-thick fractured stratiform layer of the weathering profile of the crystalline rock (granite). It forms a rather large and thick inertial aquifer that can be numerically modelled, in a similar fashion to a porous medium. The majority of tectonic faults length act as impervious boundaries that divide this aquifer into around ten elongated compartments that were precisely delineated. These tectonic faults are permeable only along two small areas that were also precisely located. These permeable zones feed some aquifer compartments with deep, highly mineralised carbo-gaseous water, which mixes with “fresher” water and forms the exploited NMW. These results can be generalised and in particular show a strong opposition between low-inertia CTMCG hydrosystems without a subsurface reservoir, as the weathering profile was eroded, and high-inertia hydrosystems such as the one studied.
... The probable presence of secondary dissolution, such as Triassic anhydrite, produced by fluid-rock redox causes the consummation of H 2 , which can affect the calculated equilibrium temperature (Joseph et al. 2011;Magro et al. 2013). The resultant H 2 S of the rising gas could be promptly oxidized in the interaction with cold ground water and could lead to sulfate waters with higher SO 4 content (Cinti et al. 2014). ...
This study focuses on the water and gas chemistry of the northeastern Algerian thermal waters. The helium gas was used to detect the origin of the geothermal fluid. In the Guelma Basin, the heat flow map shows an anomaly of 120 ± 20 mW/m² linked to the highly conductive Triassic extrusion. The chemical database reveals the existence of three water types, Ca-SO4/Na-Cl, which are related to evaporites and rich in halite and gypsum minerals. The third type is Ca (Na)-HCO3, which mostly characterizes the carbonated Tellian sector. The origin of thermal waters using a gas-mixing model indicates a meteoric origin, except for the El Biban hot spring (W10), which shows a He/Ar ratio of 0.213, thus suggesting the presence of batholith. The helium distribution map indicates a lower ³He/⁴He ratio between 0 Ra and 0.04 Ra in the W10 and W15 samples, which is compatible with the crustal ratio. Reservoir temperatures estimated by silica geothermometers give temperatures less than 133 °C. The geothermal conceptual model suggests that a geothermal system was developed by the deep penetration of infiltrated cold waters to a depth of 2.5 km and then heated by a conductive heat source (batholith for El Biban case). The thermal waters rise up to the surface through the deep-seated fractures. During their ascension, they are mixed with shallow cold groundwater, which increase the Mg content and cause the immature classification of the water samples.
... In questo gruppo ricadono le acque più ricche in CO 2 della zona di Roma (campioni 6,11,21,22,[32][33][34][35][36][37] che circolano principalmente nel settore meridionale e in quello sud-orientale; alcuni campioni sono ubicati anche nel settore nord della capitale (zona Salaria-Tor di Quinto, figura 1). I valori della pCO 2 di queste acque (> 0.20 bar) sono molto simili a quelli calcolati nelle aree a più intenso degassamento dell'Italia centrale (per un quadro generale si veda Minissale 2004), come Monte Amiata (Gambardella et al. 2005), Vicano-Cimini (Cinti et al. 2014), Sabbatini (Cinti et al. 2011), Colli Albani (Chiodini e Frondini 2001;Pizzino et al. 2002) e Roccamonfina (Cuoco et al. 2010). La CO 2 disciolta in questi acquiferi è di origine endogena, legata a processi ad alta temperatura che avvengono nel basamento calcareo profondo e/o al degassamento del mantello (Minissale, 2004;Chiodini e Frondini 2001;Pizzino et al. 2015). ...
In summer 2015 a geochemical survey on groundwater was carried out at 31 sampling points (wells and piezometers) belonging to the new “Official monitoring groundwater network of Rome Municipality” (GMNR). The following parameters were measured: temperature, pH, electrical conductivity (i.e. salinity) and alkalinity; these data were used to compute partial pressure of CO2 (pCO2). Furthermore, samples were collected to characterise waters from a chemical point of view (major elements). To implement our data - base, chemical analyses of 6 CO2 - rich mineral waters of Rome were considered. Hydrochemical survey was mainly devoted to: i) classify waters in chemical facies; ii) investigate the main water-rock interaction processes governing the water’s chemical evolution, also affected by variable amounts of dissolved CO2 and iii) define the pCO2 level in groundwater in the frame of the knowledge so far acquired in the Tyrrhenian sector of central Italy.. Groundwater shows a dominant Ca-HCO3 chemistry; some samples belong to Na-HCO3, Na-Cl and CaCl2 hydrochemical facies. In the dominant facies waters show a large variability in the abundance of chemical elements, in their salinity (ranging between 0.46 e 3.83 g/l) and pH (in the interval 5.87-7.22); these features are mainly due to different water-rock interaction processes together with the presence of variable CO2 contents. Na-HCO3 waters show the lowest salinity values (TDS up to 0.32 g/l) and strongly alkaline pH; cation exchange processes with clays, causing Na enrichment and Ca and Mg removal from solution, can be invoked to justify the observed chemistry. Waters of the Castel Fusano Natural Reserve (CFNR) belong to the Na-Cl and Ca-Cl2 facies; the different chemistry reflects the geochemical processes going on in the considered coastal aquifers such as: i) mixing between freshwater and saline waters of marine origin (fossil waters, seawater intrusion) and ii) cationic exchanges with clays that make up the less permeable sediments of the area. Two samples of the CFNR group have Ca-HCO3 chemistry and represent aquifers not affected by salinization processes. Calculated pCO2 distribution is highly variable, from low (0.03 bar) to high values (0.72 bar), implying different CO2 input (and origin) in the studied aquifers. Highest levels of carbon dioxide are linked to the degassing processes going on in the Tyrrhenian sector of Central Italy.
... In the last decade, in Italy and specifically in the Lazio Region, the CNR Water Research Institute (Vivona et al. 2007), the National Institute of Geophisics and Volcanology (Cinti et al. 2014) and the Institute of Health (Achene et al. 2010) deeply studied the problem publishing several scientific papers. ...
A brief review on the occurrence of high natural concentrations of potentially toxic elements (PHEs) in soils and water is presented, analysing also various approaches and strategies applied in different Countries to address the problem of “natural” contamination. Starting from the well known case of arsenic, the situation for other elements such as beryllium, uranium and nickel, among the most interesting, is analysed. The analysis is based on already evidenced geochemical anomalies and on the possible evolution both in the estimate of their toxicological effects and the redefinition (lowering) of the limits at the moment imposed by legislation or suggested by guidelines. New data obtained in the ENEA laboratory in the last years on arsenic and beryllium are presented. The growing need of “geochemical maps” at regional, national and European level and of a continuous monitoring activity is highlighted. At the same time the importance of considering concentration and speciation of elements and how an element is bound and under what circumstances it may be bioavailable and able to damage the ecosystem, is recalled. Finally it is suggested to concentrate efforts on the development of screening methodologies that could play a key role in the characterisation of contamination and on standardising fast procedures that enable a guided real-time survey. The clear definition of a “geochemical risk” requires a complex and multidisciplinary approach, so the emerging role of Medical Geology is underlined.
Water quality indices (WQIs) are numeric parameters that summarize the overall quality status of freshwaters compared to quality standards by aggregating multiple physicochemical data into a single value. Among the available WQIs in the literature, several criticalities were recognized including: (a) mathematical complexity of the computation, (b) lack of inclusivity, (c) arbitrary weight assignment method, and (d) site-specificity of most of the indexes. The proposed index, the Chemical Water Quality Index (CWQI), aims to overcome these flaws and provides a computation based on simple mathematic equations that are easily manageable on spreadsheet software. The computation is divided into two steps: (i) parametrization of the variables and (ii) index determination. The parametrization consists of assigning a score (s) from ~1 to 10 to each chemical variable based on (i) measured concentrations and (ii) quality targets (e.g., the limits provided by the European legislation for drinking waters). In the second step, a weight (w), directly proportional to the score (s), is assigned to each parameter, allowing to overcome any bias related to subjective assignments from the user. The resulting CWQI ranges from ~1 (very good quality) to 10 (extremely poor quality). The reliability and accuracy of the CWQI were assessed by (i) applying the computation to 1,810 waters and (ii) comparing our results with another available WQI. The CWQI outputs showed an optimal response with the number of variables exceeding the quality target with high correlation coefficients (r = 0.94; R 2 = 0.89). Due to the simplicity of its computation, the absence of arbitrariness in the weightage of selected variables, and the independence of the proposed approach regarding the choice of the chemical parameters, CWQI can be easily and universally applied.
This study provides a review of the issues of occurrence, management and protection of mineral and thermal waters in volcanic areas of central and southern Italy. These waters have a great economic importance being widely used for therapeutic and water bottling purposes, although they have a limited influence on the total yield of hydrogeological systems (generally below 17%). The present study examines the hydrogeological environment where mineral and thermal waters originate, focusing on the hydrostratigraphic and structural conditions generating different hydrochemical facies. The complexity of the examined volcanic systems makes the interpretation of the hydrochemical facies and the building of reliable hydrogeological models often difficult. Mineral and thermal waters (up to 100 °C) originate from different flow paths and interactions among waters with different qualities. In this framework, current European, national and regional regulations do not specify the criteria of abstraction and management. The examined cases show how the management and protection of mineral and thermal waters are inseparable from the management of the other groundwater resources used for drinking, irrigation and industrial purposes, being the various hydrochemical facies related to different circuits within the same system. To maintain different water qualities and permit a sustainable multipurpose use of groundwater resources, a participatory and unitary management of the aquifer system seems to be the most appropriate approach.
The conceptual hydrogeological model of the Viterbo thermal area in central Italy and the yield of the groundwater system have been examined. This area is of great geothermal interest. Through new investigations, three overlapping aquifers have been found. This study examines in detail the two shallower aquifers, characterized by different hydraulic and chemical characteristics. The first aquifer is related to the regional groundwater flow of the Cimino-Vico volcanic system and is generally characterized by cold, fresh waters used for irrigation and drinking water supply. The second aquifer, i.e. the thermal aquifer, supply thermal spas and public pools; it is present where the local hydrostratigraphic, structural and geothermal conditions permit a relatively active flow of higher salinity thermal waters (40˚C - 62˚C). These two aquifers interact vertically and laterally, giving rise to mixed waters circulating in the first aquifer. The first aquifer is recharged by direct infiltration and inflow from regional groundwater, as well as inflow from the second aquifer. The yield of the thermal aquifer is at least 170 L/s, discharging into thermal springs and wells, besides feeding the shallow aquifer vertically and laterally. Even if a future development of the second aquifer is potentially achievable on a global scale, the exploitation of the thermal waters is strictly dependent on the specific local hydrogeological equilibrium between the overlapping aquifers, different from place to place. The case study highlights that, in the volcanic hydrogeological environment, one of the most stringent constraints in determining the correct usage of a resource is the variable level of interaction of groundwater with different qualities.
The conceptual hydrogeological model of the Viterbo thermal area in central Italy and the yield of the groundwater sys-tem have been examined. This area is of great geothermal interest. Through new investigations, three overlapping aqui-fers have been found. This study examines in detail the two shallower aquifers, characterized by different hydraulic and chemical characteristics. The first aquifer is related to the regional groundwater flow of the Cimino-Vico volcanic sys-tem and is generally characterized by cold, fresh waters used for irrigation and drinking water supply. The second aqui-fer, i.e. the thermal aquifer, supply thermal spas and public pools; it is present where the local hydrostratigraphic, struc-tural and geothermal conditions permit a relatively active flow of higher salinity thermal waters (40˚C -62˚C). These two aquifers interact vertically and laterally, giving rise to mixed waters circulating in the first aquifer. The first aquifer is recharged by direct infiltration and inflow from regional groundwater, as well as inflow from the second aquifer. The yield of the thermal aquifer is at least 170 L/s, discharging into thermal springs and wells, besides feeding the shallow aquifer vertically and laterally. Even if a future development of the second aquifer is potentially achievable on a global scale, the exploitation of the thermal waters is strictly dependent on the specific local hydrogeological equilibrium be-tween the overlapping aquifers, different from place to place. The case study highlights that, in the volcanic hydro-geological environment, one of the most stringent constraints in determining the correct usage of a resource is the vari-able level of interaction of groundwater with different qualities.
We investigate the relationship between sulfur and oxygen fugacity at
Erta Ale and Masaya volcanoes. Oxygen fugacity was assessed utilizing
Fe3+/∑Fe and major element compositions measured in
olivine-hosted melt inclusions and matrix glasses. Erta Ale melts have
Fe3+/∑Fe of 0.15-0.16, reflecting fO2 of
ΔQFM 0.0 ± 0.3, which is indistinguishable from
fO2 calculated from CO2/CO ratios in
high-temperature gases. Masaya is more oxidized at ΔQFM +1.7
± 0.4, typical of arc settings. Sulfur isotope compositions of
gases and scoria at Erta Ale (δ34Sgas -
0.5‰; δ34Sscoria + 0.9‰) and
Masaya (δ34Sgas + 4.8‰;
δ34Sscoria + 7.4‰) reflect distinct
sulfur sources, as well as isotopic fractionation during degassing
(equilibrium and kinetic fractionation effects). Sulfur speciation in
melts plays an important role in isotope fractionation during degassing
and S6+/∑S is <0.07 in Erta Ale melt inclusions
compared to >0.67 in Masaya melt inclusions. No change is observed in
Fe3+/∑Fe or S6+/∑S with extent of S
degassing at Erta Ale, indicating negligible effect on fO2,
and further suggesting that H2S is the dominant gas species
exsolved from the S2--rich melt (i.e., no redistribution of
electrons). High SO2/H2S observed in Erta Ale gas
emissions is due to gas re-equilibration at low pressure and fixed
fO2. Sulfur budget considerations indicate that the majority
of S injected into the systems is emitted as gas, which is therefore
representative of the magmatic S isotope composition. The composition of
the Masaya gas plume (+4.8‰) cannot be explained by fractionation
effects but rather reflects recycling of high δ34S
oxidized sulfur through the subduction zone.
The compositional features of fluids from both fumarolic discharges and
productive geothermal wells of Ahuachapan-Chipilapa, Berlin-Chinameca,
and San Vicente geothermal systems (El Salvador) are described and
discussed in order to investigate the complex geochemical interactions
involving geothermal fluids within the shallowest part of the
hydrothermal circulation pathways. Our results highlight that secondary
processes are able to strongly affect and modify the chemical
characteristics of geothermal gases once they discharge to the surface
as natural manifestations, mainly in relation to the chemical-physical
properties of each gas species. The effects of both gas dissolution in
shallow aquifers and gas-water-rock chemical interactions on gas
discharge composition make it difficult to get a correct evaluation of
the thermodynamic conditions that characterize the geothermal reservoirs
by applying the common geoindicators based on the chemical equilibria of
the H2O-CO2-H2-CH4-CO
system. Differently, the composition of the
C1-C2-C3 alkanes and the C3
and C4 alkane-alkene pair, established within the geothermal
reservoirs under the control of chemical reactions, remains stable in
samples collected from discharging gas vents. These results suggest that
the relative abundances of hydrocarbons characterized by similar
structure and molecular size seem to be mainly regulated by the
diffusion velocity of gases through the liquid-dominated system.
Therefore the chemical features of the light organic gas fraction of
naturally discharging fluids can be successfully utilized for the
evaluation of geothermal reservoir temperatures and redox conditions,
providing useful indications in terms of geothermal exploration and
exploitation. On this basis, the distribution, speciation, and relative
abundances of light hydrocarbons can also be considered highly promising
in geochemical monitoring of active volcanic systems.
The volcanic complex of Mts. Cimini (~0.90-1.30Ma) represents the geographical and chronological transition between the Tuscan Magmatic Province (TMP) and the Roman Magmatic Province (RMP), in central Italy. Major and trace elements, and Sr, Nd and Pb isotopes of whole-rock, as well as mineral chemistry analyses, were carried out on samples representative of the different petrographic and chronological units of Mts. Cimini. In particular, we focused on the olivine-bearing latites of Mts. Cimini that are the most mafic magmas, belong to the last phase of this volcanic activity, and are heterogeneous in highly incompatible element ratios and Sr-isotope compositions. We suggest that such heterogeneity reflects the occurrence of a heterogeneous upper mantle beneath central Italy, in which different portions, e.g., the sources of both the TMP and RMP, are characterized by distinct geochemical and petrographic features. In this scenario, about 900ka ago, the olivine-bearing latites mark the progressive decline of the TMP magma production in favour of partial melting of the RMP mantle region, thus recording the coexistence of both ultrapotassic alkaline and calc-alkaline magmas in the same volcanic region.
Carbon isotopic composition was measured in products of the
Fischer-Tropsch synthesis in flow reactor on the modified by clays
Fe-catalyst at 280-300C and 30 atm. The initial gas mixture
(synthesis-gas, SG) consisted of 50 vol% of N2, 20% of CO and 30% of H2.
Using the GS-MS technique we analyzed 13C/12C in CO, CO2, CH4, higher
hydrocarbons until C4 and the oil fraction in the reaction products. Two
catalysts with different modification were used: with high and low yield
of olefins. Three of 70-hours runs for each catalyst were realized. Five
gas samples were taken during each run: 10, 20, 30, 50 and 70 hours and
one cumulative oil sample after each run. The 13C/12C distribution vs
carbon number is time-dependent for the olefin-rich products. For the
olefin-poor runs the stationary state is characterized by depletion in
13C of heavier than CH4 hydrocarbons, thus, showing the "synthetic"
pattern, like in DesMarais et al. (1982) experiments or in Murchison
meteorite. However, the olefin-rich runs demonstrate these patterns only
in the non-stationary, initial (10 h, 20 h) time range. The steady-state
(50-70h) distribution (high and stable conversion of CO) for olefin-rich
runs shows almost no fractionation between CH4 and higher hydrocarbons.
The concentration distribution of light hydrocarbons in our experiments
was similar to that obtained by Hu et al. (1998), but with much higher
conversion of CO (>95%).
PHREEQC version 2 is a computer program written in the C programming language that is designed to perform a wide variety of low-temperature aqueous geochemical calculations.
Thermogenic hydrocarbons entirely deriving from the thermal degradation of organic matter usually exhibit methane to ethane plus propane ratios smaller than 100. We present hydrocarbon distribution data of continental hydrothermal gases, whose methane has been inde-pendently identifi ed to derive from the abiogenic reduction of CO 2 . We fi nd that excess amounts of methane with respect to thermogenic hydrocarbon distributions are characteristic for the investigated gases. A similar pattern is observed for well discharges whose temperatures are too high to support any microbially mediated methanogenesis. These fi ndings strongly suggest that abiogenic methane production in continental-hydrothermal systems is a more widespread process than previously assumed. The maximum contribution of such emissions to the modern atmospheric CH 4 budget is estimated at ~1%. INTRODUCTION The identifi cation of natural pathways leading to the formation of methane (CH 4) and higher hydrocarbons is of ultimate importance for reasons of energy exploitation, understanding the origin of life on Earth, modeling global atmospheric levels of CH 4 through time, and looking for indicators of extraterrestrial life (e.g., Zahnle, 1986; Catling et al., 2001; Etiope and Klusman, 2002; Formisano et al., 2004). The natural occurrence of biogenic (microbial and thermogenic) hydrocarbon production is well documented (e.g., Whiticar, 1999). Abiogenic formation of hydrocarbons from gaseous or dissolved CO 2 and CO is known to proceed under labora-tory conditions according to the Fischer-Tropsch-type (FTT) Reactions 1 and 2 (e.g., Foustoukos and Seyfried, 2004; McCollom and Seewald, 2007): CO + [2 + (m/2n)] H = (1/n) C H + 2H O
We have addressed the origins of methane in fumarolic, thermal and cold emissions discharging from a diversity of geological settings spread all over the Italian Peninsula and at Panarea and Pantelleria islands. Fluid discharges from the main geothermal systems of the peri-Tyrrhenian area (including Mt. Amiata, Larderello, Latera and Manziana) show δ13C-CH4 and δD-CH4 values >−28‰ V-PDB and >−160‰ V-SMOW, respectively, and C1/C2 + concentration ratios > 1000. These patterns suggest that CH4 discharged from these systems is primarily generated by abiogenic reduction of CO2 and/or CO. Methane seems to have, at least partially, a different origin than the higher hydrocarbons that might be entirely related to the thermal decomposition of organic matter or, alternatively, to methane polymerization. Fumaroles from the volcanic systems of Solfatara, Vesuvio, Panarea and Pantelleria have C1/C2 + concentration ratios in a wide range (from 17 to 4300), but δ13C-CH4 and δD-CH4 values >−21‰ V-PDB and >−120‰ V-SMOW, respectively. Such isotopic values are very similar to those reported for CH4 discharging from ultramafic hydrothermal systems. In agreement with recent evidence provided for Solfatara and Pantelleria we, therefore, infer that the CH4 in the volcanic fumaroles is mainly abiogenic, too. The δ13C-CH4 (from − 21.6 to − 36.9‰ V-PDB) and δD-CH4 (from − 113 to − 164‰ V-SMOW) values, as well as the C1/C2 + concentration ratios (from 19 to 2240), in the CO2-rich fluid discharges located between the geothermal-volcanic systems and the Apennine sedimentary chain tend to decrease eastwards as the temperatures of the fluid reservoirs progressively diminish, suggesting that the CH4 production is mainly related to thermogenic processes. According to this general trend, the CH4-dominated fluids from mud volcanoes located eastwards of the CO2-rich emissions are fed by an almost pure thermogenic source. The easternmost fluid discharges from the Po valley and the Adriatic coast, where organic matter evolves at relatively shallow depths in the presence of a low geothermal gradient, record the lowest δ13C-CH4 and δD-CH4 values, i.e. as low as − 69‰ V-PDB and <−190‰ V-SMOW, respectively, and C1/C2 + concentration ratios up to 5500, suggesting that the CH4 production is mainly from microbially driven processes.
The thermal springs discharging in the Siena-Radicofani basin and the deep fluids within the geothermal systems of Piancastagnaio (Mt Amiata), Torre Alfina and Latera (Vulsini Mts) have a common origin. The chemical composition and evolution towards the low enthalpy of the springs as compared to the high enthalpy of the geothermal fluids are affected by both the structural setting of the region and the deep hydraulic conditions. Recharge of both the shallow thermal aquifer and the deep geothermal systems takes place in the outcrop areas of Mesozoic carbonate rocks, which constitute the main potential geothermal reservoir in central Italy. The waters of meteoric origin are heated at depth, as a consequence of anomalous heat flow in the region; these waters acquire a CO2-rich rising gas phase, equilibrate equilibrate with the reservoir rocks and, finally, assume their CaHCO3SO4 composition. If these waters discharge rapidly from the border fault systems of the Siena-Radicofani basin they maintain their original composition. If, instead, they emerge from the inner faults of the graben, their temperature and dissolved solids increase so that they become NaCl with a high content of NH4, H3BO3 and Li+. The chemical evolve towards high enthalpy. In this case the deep fluids again acquire an NaCl composition similar to carbonate reservoir is at a structural high, buried by both allochthonous flyschoid series (“Ligurids”) and by Neogenic pelitic formations, a slower recharge occurs in the reservoir, and consequently the fluids evolve towards high enthalpy. In this case the deep fluids again acquire an NaCl composition similar to that of the springs emerging inside the graben, since part of the reservoir recharge also occurs through the leakage of saline fossil waters stored within the Neogenic sedimentary formations at the border of the geothermal systems.
A simple method based on the phase equilibrium between gas bubbles and water is developed for the determination of the relative gas content in bubbling springs. For the calculation of the gas-water ratio it is necessary to know only the concentration of one of the ``atmogenic'' components (N2, Ar, or Ne) in a gas sample from the gas analysis. The total gas content calculated by this method can be used for the gas geothermometry and for the estimations of the gas fluxes and water flow rates from mineral and thermal springs.
Fischer–Tropsch synthesis (FTS) is the core technology for the sustainable transformation of nonpetroleum carbon resources into liquid fuels and valuable chemicals. FTS has received intensive interest and achieved great advances in recent years. Herein, we concisely describe the reaction mechanism, reactor, and catalyst relating to FTS, with special emphasis on the catalyst because of its critical role in FTS. This outline presents the basic feature of FTS and affords the basis for the rational design and development of new FTS technology.
Results obtained using both the SiO2 and Na-K-Ca geothermometers for the study of the temperatures of hot waters in depth, are convergent in the two methods and show very little differences in the dermined temperatures. -from English summary
The durability and selectivity of catalysts are urgent problems. Of immediate concern are Fe catalysts for the Fischer-Tropsch synthesis that will withstand disintegration by elemental C deposition and oxidation, and for Ni methanation catalysts that are resistant to disintegration by elemental C deposition and deactivation by carbide formation. Further studies are being conducted.
The study area covers the Cimini and Vico volcanic complexes in the province of Viterbo (Northern Lazio Region, Italy), where a large-scale exploitation of the water resources co-exists with fragile environmental conditions. The Vico caldera and the lake of the same name form the central nucleus of a Nature Reserve and are an important source of drinkable water for a number of municipalities. The main aim of the study was to improve our knowledge of the hydrogeological setting of the system in order to quantify the groundwater resource and to examine the interaction between the groundwater and Lake Vico in their specific geological framework. The hydrogeological investigations included: i) reconstruction of local hydrostratigraphy; ii) collection of data from wells and springs; iii) flow measurement of streams; iv) development of some pumping tests; v) analysis of climatic data. The volcanic aquifer consists primarily of Pleistocene pyroclastic deposits (tuffs, ignimbrites, ashes, pumice and scoriae) and various lava flows and domes. Its base and part of its SW and NE boundaries are well defined by low-permeability rocks, including sandy-clayey deposits (Pliocene-Pleistocene) and marly-calcareous flysch (Upper Cretaceous-Oligocene). The remaining boundaries are formed by highly permeable Quaternary alluvial and sandy-conglomeratic deposits. The groundwater flow occurs mainly through the unconfined basal volcanic aquifer and to a lesser extent through various perched aquifers. The basal volcanic aquifer has a centrifugal radial flow network; the groundwater discharges primarily into streams (not less than 1.4 m 3/s) and in part into small springs (less than 0.5 m 3/s). The volcanic aquifer also feeds the aquifer of the surrounding plain, especially where the Quaternary sandy-conglomeratic deposits flank the volcanic hills (about 2 m 3/s). The pumping test data were correlated with the equipotential surface of the unconfined basal aquifer to define diverse transmissivity zones. The resulting wide range of transmissivity values obtained (between 10 -6 and 10 -2 m 2/s) are in agreement with the heterogeneity of the volcanic products and with the variability of the saturated thickness. An average annual evaluation of groundwater resources points to a volume between 162 and 227 × 10 6 m 3/year. Taking the area of the volcanic system into account, the mean yield of the aquifer amounts to between 5.7 and 8.0 l/s per km 2, consistent with other Tyrrhenian volcanic areas. The analysis of the historical hydro-meteorological data set indicates that precipitation follows a negative trend, i.e. there is a progressive decline of groundwater resources. In this hydrogeological environment, Lake Vico is closely conditioned by the groundwater, being fed by the basal aquifer on its northern side (about 6% of the total inflow) and drained from the other sides (between 26 and 37% of the total outflow). According to the mean water budget of the lake, in addition to the amounts of water taken from the lake, the surface-groundwater exchange has a considerable effect on the reservoir resources. These factors can influence heavily the level of the lake, artificially regulated by a gated outlet which is not always managed according to a rational strategy of conjunctive use of water resources.
Over 200 S isotope data (δ34S) are presented on a variety of mineral occurrences and aqueous species. Results provide evidence of many successive phases of mineralization which occurred from depths of a few km to the surface. On the basis of their isotopic characteristics and petrogenetic environment, four types of sulphide and five types of sulphates can be distinguished. Conditions are discussed under which equilibrium or disequilibrium reactions, chemical isotope fractionation and biological activity may have influenced the S isotope composition. -from Authors
40Ar/39Ar dating experiments on 5 sanidines and 2 leucites from the Vico Volcanic Complex (Northern Latium) allow us to put timemarks on the volcanological evolution. The ages obtained for three successive explosive events (Ignimbrite B, C, D) are 157 ± 3 ka, 151 ± 3 ka and 138 ± 2 ka, respectively. The paleosoil between ignimbrites B and C thus formed at a rate of about 0.1 m/ka. The lava immediately underlying the ignimbrites yields a plateau age of 258 ± 2 ka for the sanidine and a perturbed spectrum with excess 40Ar for the coexisting leucite; the latter does not, however, contain any of the peculiar "high temperature excess Ar' observed in the southern Roman Volcanic Province. The best age estimate for the basal event (Tufi Stratificati Varicolori) is 419 ± 6 ka. -from Authors
Oxygen, hydrogen, and sulfur isotope data for fluids and minerals associated with the crater lake of Poas Volcano, Costa Rica, are interpreted in the context of the chemical and hydrologic structure of the volcano. Oxygen and hydrogen isotope data were obtained for rain, spring, and river water, low-temperature fumarole condensates, and acid brines collected from the hot crater lake before its disappearance in April 1989. Sulfur isotope data are presented for H2S and SO2 gas collected from low temperature fumaroles; dissolved sulfate in spring, river, and crater lake waters; and native sulfur and gypsum found in the acid lake and active crater area. -from Author
The kinetic and equilibrium fractionation effects for 13C during CO2 gas transfer (εk and εag−g) have been measured in acidified distilled water. The equilibrium fractionation effects between bicarbonate and carbonate and gaseous C02 (εHCO3−g and εCO3−g) have been measured in NaHC03 and NaHC03 + Na2C03 solutions, respectively, from 5° to 25°C. The measured fractionations, except εCO3−g, agreed with earlier work to within 0.2‰. εCO3−g was about 2‰ smaller than most values previously reported. The temperature dependence of the fractionation for 13C between bicarbonate and carbonate and gaseous CO2 was found to be εHCO3−g = −(0.141 ± 0.003)T(°C) + 0.05)‰ and εCO3−g = −(0.052 ± 0.03) T(°C)E+ (7.22 ± 0.46)‰ respectively. The fractionation during gas dissolution was εCO3−g = −0.03)T(°C) + (1.31 ± 0.06%. and the kinetic effect during gas transfer, εk, was −0.81 ± 0.16‰ at 21°C and −0.95 ± 0.20‰ at 5°C.
Within the framework of research in the marginal areas of the Larderello–Travale geothermal system, several exploration wells have disclosed an extension of the deep reservoir even below zones of medium or low superficial thermal anomaly. NE of the Larderello field, Sesta_6bis well crossed a known low temperature (100°C) CO 2 saturated carbonate aquifer, but, at greater depth, in the phyllitic metamorphic basement, a steam reservoir has been discovered at 2400–2800 m. The temperature and pressure are similar to those recorded at the Travale field (300°C and 70 bar). Two other wells have been drilled in the area south of Travale characterized by large outcrops of permeable carbonate rocks. These constitute the shallow reservoir, bearing fresh meteoric waters, which mask any deeper thermal information. The well Travale Sud_1 crossed several steam productive layers between 2280 and 2890 m in thermometamorphic and granitic rocks. The reservoir temperature and pressure are 300°C and 70 bar. The well Montieri_4 crossed a thick carbonate sequence and then a granitic body from 2000 m to the bottom hole (3700 m), with rather low permeability but with the same temperature and pressure as the deep Travale reservoir. Surprisingly, injection and acidification tests have improved the hydraulic connection with the reservoir. All the above-mentioned exploration wells have proved to be productive and confirmed the extension of the deep steam-dominated reservoir in marginal areas where the superficial thermal gradient is low. The deep reservoir is located at a depth of about 3 km inside the metamorphic basement and the granitic body. On the basis of these results, the exploration has been extended and specific development projects have been planned.
During the period from January 1991 to January 1994, the 10-yr geochemical monitoring in the Campi Flegrei (Southern Italy), usually performed using the inorganic gas fraction, was implemented by discontinuous monitoring of the hydrocarbon gas fraction. The measured compositions have revealed the presence of significant amounts of at least 11 hydrocarbon species, related to alkane, alkene, and aromatic classes. Thermodynamic calculations showed the possible existence of partially independent equilibria within the C 1/C 2/C 3 and C 1/C 2/C 3/C 4 alkane systems, as well as among alkene/alkane pairs at redox conditions controlled by the geothermal (FeO/Fe 1.5O) redox buffer system, at temperatures between 200 and 400°C and P H20 controlled by the presence of a saline brine. Unlike the constancy of the measured and calculated 'inorganic' temperature, equilibrium temperature based on organic species has displayed fluctuations and a significant increase starting from the second half of 1993. According to their apparent correlation with other independent observations, such as the measured increases of vapor fraction, H 2S/CO 2 and H 2/N 2 ratios on the monitored fumarole in addition to a general increase of dissolved CO 2 in the Campi Flegrei groundwaters, the observed variations of the organic parameters were interpreted as the result of a general increase in acid-bearing gas flux throughout the re-equilibration zone.
Volcanic degassing represents an essential component of the global geochemical cycles that determine the state of the atmosphere and climate. It also exerts a first-order influence on the ways in which volcanoes erupt and is thus vital to understanding how volcanoes work and assessing their hazards. This article reviews the sources of volcanic volatiles, their behavior in ascending magmas and surficial reservoirs (including isotopic fractionation), and the processes by which gases separate from melt and reach the atmosphere. A range of field, laboratory, and remote sensing techniques can be applied to measurements and monitoring of volcanic gas and aerosol compositions (elemental, molecular, and isotopic) and flux. It summarizes their application and the general characteristics of volatile emissions associated with different geodynamic settings and volcanic manifestations. Some methods, including those based on petrological and ice core analysis, can even provide estimates of volatile budgets of eruptions that occurred in the distant past. Having considered the source-to-surface processes related to volcanic degassing, it reviews the impacts of emissions on the atmosphere, climate, and environment, from local to global scales, and the associated human and animal health hazards of volcanogenic pollution.
Accepted concepts of principal stages of hydrocarbon formation fail to satisfactorily explain the accumulation of supergiant gasfields in West Siberia, U.S.S.R., such as for example Urengoy, which comprise 30% of the proven gas reserves of the world. A new mathematical model has been developed which applies the concept of activation energy distribution to the formation of gases. Characteristic differences in the molecular structure of humic and sapropelic source organic matter are expressed in different activation energy distributions. The model allows the calculation of isotope values for different types of organic matter and their dependence on maturity. Application of the model to West Siberia suggests that the supergiant gas accumulations in Urengoy are more likely formed from terrestrial organic matter through thermochemical reactions at moderate depths and are not the result of either deep, overmature, or bacteriogenic processes. The new mathematical model suggests that humic organic matter, in general, has a high methane-generating capacity at comparably low maturities of organic matter equivalent to 0.5–0.7% on the vitrinite reflectance scale.
Noble Gas Geochemistry gives a comprehensive description of the physical chemistry and cosmochemistry of noble gases, before leading on to applications for problem-solving in the earth and planetary sciences. There have been many developments in the use of the noble gases since publication of the first edition of this book in 1983. This second edition has been fully revised and updated. The book will be invaluable to graduate students and researchers in the earth and planetary sciences who use noble gas geochemistry techniques.
This paper describes an indirect method to calculate the isotopic composition of rainfall by using the isotopic composition of karst springs fed by waters circulating in the most important regional aquifer of central Italy, i.e. the Mesozoic limestone sequence that forms the backbone of the Apennines. By using δ18O and δD data and the δ18O (and/or δD) average gradient for elevation, evaluated through the use of literature rainfall data and new measurements from a typical Alpine valley in northern Italy, the altitude of precipitation of their parent water has been re-calculated. Vertical descents of more than 2000 m, from recharge to discharge, have been assessed in some high flow-rate cold springs in the morphologically steep Adriatic sector of central Italy. A clear correlation between the vertical descents and more negative isotopic compositions at their relative emergence elevations is highlighted. In contrast, in the Tyrrhenian sector lower karstic drops (generally lower than 500 m) correlate with less negative isotopic composition of recharge areas.