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Input of 87Sr/86Sr ratios and Sr geochemical signatures to update knowledge on thermal and mineral waters flow paths in fractured rocks (N-Portugal)
Abstract
Strontium isotopes and other geochemical signatures are used to determine the relationships between CO2-rich thermal (Chaves: 76 °C) and mineral (Vilarelho da Raia, Vidago and Pedras Salgadas: 17 °C) waters discharging along one of the major NNE–SSW trending faults in the northern part of mainland Portugal. The regional geology consists of Hercynian granites (syn-tectonic-310 Ma and post-tectonic-290 Ma) intruding Silurian metasediments (quartzites, phyllites and carbonaceous slates). Thermal and mineral waters have 87Sr/86Sr isotopic ratios between 0.716713 and 0.728035. 87Sr/86Sr vs. 1/Sr define three end-members (Vilarelho da Raia/Chaves, Vidago and Pedras Salgadas thermal and mineral waters) trending from rainfall composition towards that of the CO2-rich thermal and mineral waters, indicating different underground flow paths. Local granitic rocks have 87Sr/86Sr ratios of 0.735697–0.789683. There is no indication that equilibrium was reached between the CO2-rich thermal and mineral waters and the granitic rocks. The mean 87Sr/86Sr ratio of the thermal and mineral waters (0.722419) is similar to the Sr isotopic ratios of the plagioclases of the granitic rocks (0.71261–0.72087). The spatial distribution of Sr isotope and geochemical signatures of waters and the host rocks suggests that the thermal and mineral waters circulate in similar but not the same hydrogeological system. Results from this study could be used to evaluate the applicability of this isotope approach in other hydrogeologic investigations.
... Strontium isotopes are also an important tool in hydrogeology since 87 Sr/ 86 Sr ratios are very good hydrogeochemical tracers, as the high atomic weight of Sr prevents fractionation during natural processes [5]. Thus, the transference from the bedrock to circulating waters, soils, biosphere, and food webs occurs without appreciable modification of the 87 Sr/ 86 Sr ratios [4,6,7]. ...
... The 87 Sr/ 86 Sr ratios in groundwater depend on the Rb/Sr ratios and the age of the rocks with which they interact along their path [1]. Therefore, variations in the 87 Sr/ 86 Sr ratios can be ascribed to the mixing of Sr derived from different rock sources with distinct isotopic compositions [5]. In addition, as the kinetics of mineral dissolution reactions range over orders of magnitude, the Sr isotope ratios of solutes will be dominated by the most easily weathered minerals. ...
... There are several case studies [4,5,[9][10][11] that highlight the use of 87 Sr/ 86 Sr as tracers of weathering processes and flow pathways in surface water and groundwater in different landscapes. Strontium isotopes have been used to assess the origin of salinity in highly saline waters as well as a tracer of the origin of the water [4]. ...
This study focused on 13 water samples collected from two of the main active volcanoes (Furnas and Fogo) at São Miguel, Azores. Based on the major element composition, the waters are classified into Na-HCO3 and Na-Cl types. While the concentrations of chloride seem to reflect the contribution of sea salt aerosols, the behavior of the main cationic species and Sr in the analyzed waters appear to have been largely controlled by the interaction between meteoric waters and the underlying bedrock. The temperature and input of CO2 from the secondary volcanic activity are enhancing the silicate leaching. The stable isotopic data show that these waters have a meteoric origin (δ 18 O = −2.03 to −4.29‰; δ 2 H = −7.6 to −17.4‰) and are influenced by a deep hydrothermal/vol-canic carbon source (δ 13 C = −4.36 to −7.04‰). The values of δ 34 S (0.13 to 12.76‰) reflects a juvenile sulfur source derived from the leaching of volcanic rocks. The Sr isotopic ratios show a slight difference between the values from Furnas (87 Sr/ 86 Sr = 0.705235-0.705432) and Fogo (87 Sr/ 86 Sr = 0.705509-0.707307) whereas the Furnas waters are less radiogenic. The Sr isotope also shows that the hydrochemical signatures of the groundwater was controlled by the rock leaching, and the samples Furnas reached water-rock isotopic equilibrium.
... Sendo a plagioclase sódica um dos constituintes minerais das rochas silicatadas encaixantes (granitos do Caramulo e metassedimentos do CXG) e uma fase facilmente hidrolisável (e.g. Marques et al., 2012), admite-se que a sua dissolução controlou, em grande medida, o comportamento do sódio nestas águas de escorrência. ...
... A dissolução preferencial de uma fase mineral com baixas razões Rb/Sr e 87 Sr/ 86 Sr, como é o caso da plagioclase, tem sido frequentemente invocada para explicar o desfasamento entre as assinaturas isotópicas das águas e as do substrato rochoso silicatado (e.g. Marques et al., 2012). No caso presente, o elevado grau de sobreposição entre as composições isotópicas de Sr nas águas estudadas e as reportadas na bibliografia para plagioclases de rochas graníticas ( 87 Sr/ 86 Sr = 0,716873-0,736393; Marques et al., 2012) vem apoiar a hipótese de os mecanismos de lixiviação desta fase mineral terem dominado os processos de interação água-rocha na região. ...
... Marques et al., 2012). No caso presente, o elevado grau de sobreposição entre as composições isotópicas de Sr nas águas estudadas e as reportadas na bibliografia para plagioclases de rochas graníticas ( 87 Sr/ 86 Sr = 0,716873-0,736393; Marques et al., 2012) vem apoiar a hipótese de os mecanismos de lixiviação desta fase mineral terem dominado os processos de interação água-rocha na região. ...
The chemical and isotopic data for riverine waters draining the Caramulo granite pluton (Águeda river and Teixo creek) show that these waters are sodium chloride waters (Cl = 4.1-18.8 mg L-1 ; Na = 3.52-7.96 mg L-1), with very low total dissolved solid contents (TDS = 9-151 mg L-1), pH values ranging from 5.61 and 7.25 and 87 Sr/ 86 Sr isotopic ratios varying between 0.71662 and 0.72147. While their sodium chloride typology reflects the contribution of sea salt aerosols from the Atlantic coast, the behaviour of the main cationic species in the analyzed waters and their Sr isotopic signatures appear to have been largely controlled by the interaction between meteoric waters and the underlying bedrock (granites and metasediments), with plagioclase hydrolysis playing a dominant role. On the other hand, the geochemical and isotopic compositions of the stream sediments related to these drainages is attributed to mixing between sediments derived from two source regions: the Caramulo granite and the Schist and Greywacke Complex.
... Several studies carried out on the northern part of the Portuguese mainland (e.g., [27][28][29][30][31][32][33][34][35][36][37][38]) have provided a comprehensive characterization of the Chaves low-temperature CO 2 -rich geothermal system. Several hypotheses have been formulated to assess the origin of the low-temperature geothermal waters and the mechanisms of their being upward from the reservoir towards the surface. ...
... In the Chaves region, the ascending low-temperature CO 2 -rich geothermal waters are structurally controlled by the so-called Verin-Régua-Penacova fault zone (VRPFZ - Figure 2) [40,41,46], related to Alpine Orogeny, which trends 70°-80°E and is hydrothermally active along a belt extending 150 km through mainland Portugal ( Figure 3). Along this tectonic megalineament lie not only the Chaves low-temperature CO 2 -rich geothermal waters (the only geothermal waters in the study region) but also numerous emanations of cold (17°C) CO 2 -rich mineral waters (e.g., Vilarelho da Raia, Vidago, and Pedras Salgadas), with no signs of a geothermal origin as discussed in detail by [27][28][29][30][31][32][33][34][35][36][37][38], which are used in local spas (see Figures 2 and 3). ...
... In fact, the model proposed by [43] for the Vidago and Pedras Salgadas regions, based on tectonic and geomorphological features, points out the existence of a narrow graben (1 to 2 km wide) related with an also shallow reservoir. Therefore, as stated by [43,44], deeper low-temperature geothermal water circulation occurs only in the Chaves area because of (i) high relief, (ii) deep fracturing, and (iii) thickness of graben-filling sediments (see [38]). ...
This paper reviews the results of a multi- and interdisciplinary approach, including geological, geomorphological, tectonic, geochemical, isotopic, and geophysical studies, on the assessment of a Chaves low-temperature (77°C) CO 2 -rich geothermal system, occurring in the northern part of the Portuguese mainland. This low-temperature geothermal system is ascribed to an important NNE-trending fault, and the geomorphology is dominated by the “Chaves Depression,” a graben whose axis is oriented NNE-SSW. The study region is situated in the tectonic unit of the Middle Galicia/Trás-os-Montes subzone of the Central Iberian Zone of the Hesperic Massif comprising mainly Variscan granites and Paleozoic metasediments. Chaves low-temperature CO 2 -rich geothermal waters belong to the Na-HCO 3 -CO 2 -rich-type waters, with pH≈7 . Total dissolved solids range between 1600 and 1850 mg/L. Free CO 2 is of about 500 mg/L. The results of SiO 2 and K ² /Mg geothermometers give estimations of reservoir temperature around 120°C. δ¹⁸ O and δ² H values of Chaves low-temperature CO 2 -rich geothermal waters indicate a meteoric origin for these waters. No significant ¹⁸ O-shift was observed, consistent with the results from the chemical geothermometry. δ¹³ C CO2 values vary between −7.2 and −5.1‰ vs. V-PDB, and CO 2 / ³ He ratios range from 1×10 ⁸ to 1×10 ⁹ , indicating a deep (upper mantle) source for the CO 2 . ³ He/ ⁴ He ratios are of about 0.9 (R/Ra). The Chaves low-temperature CO 2 -rich geothermal waters present similar ⁸⁷ Sr/ ⁸⁶ Sr ratios (between 0.728035 and 0.716713) to those of the plagioclases from granitic rocks (between 0.72087 and 0.71261) suggesting that water mineralization is strongly ascribed to Na-plagioclase hydrolysis. Geophysical methods (e.g., resistivity and AMT soundings) detected conductive zones concentrated in the central part of the Chaves graben as a result of temperature combined with the salinity of the Chaves low-temperature CO 2 -rich geothermal waters in fractured and permeable rock formations. This paper demonstrates the added value of an integrated and multi- and interdisciplinary approach for a given geothermal site characterization, which could be useful for other case studies linking the assessment of low-temperature CO 2 -rich geothermal waters and cold CO 2 -rich mineral waters emerging in a same region.
... The main geological formations are: (1) Hercynian granites (syntectonic: 310 Ma and post-tectonic: 290 Ma) and (2) Silurian metasediments which consist of a sequence of quartzites, phyllites and carbonaceous slates. As described in Marques et al. (2012), in the W block of the Chaves graben, the Vilarelho da Raia and Chaves syn-tectonic granites have a medium-to coarse-grained texture, with abundant biotite and muscovite (approximately 10-15% of the modal composition). In the E block of the Chaves graben, the post-tectonic granite has a coarse-grained to porphyritic texture, with biotite and muscovite (being biotite predominant). ...
... In the E block of the Chaves graben, the post-tectonic granite has a coarse-grained to porphyritic texture, with biotite and muscovite (being biotite predominant). To the S of the Chaves region, the post-tectonic granite of Vidago-Pedras Salgadas area has a medium-to fine-grained texture, sometimes porphyritic (see Marques et al. 2012). ...
... The minero-petrographic characterization presented by Marques et al. (2012) also indicates that quartzites are mainly composed of fine-grained quartz with interbedded coarser quartz grains with a strongly indented granoblastic texture. There are also visible thin discrete beds of white mica, spread in the quartz grains. ...
In the North of Portugal, thermal and mineral groundwater resources (e.g., Chaves CO2-rich thermal—76 °C—waters) are being used in the local Spas, and are considered one of the main sources of local/regional development/income. A multidisciplinary approach, including geological, tectonic, geochemical and isotopic (²H, ¹⁸O, ¹³C, ⁸⁷Sr, ³H, ¹⁴C and ³He/⁴He) methodologies, was used to assess local/regional conceptual circulation models. In the case of the Chaves CO2-rich thermal waters, this approach provided important data to answer the most commonly asked questions so as to enable the elaboration of a robust hydrogeological conceptual model, namely (1) Chaves thermal waters belong to the HCO3/Na/CO2-rich type (with pH ≈7), in that the result of meteoric waters–granitic rocks–gas (CO2) interaction; (2) Padrela Mountain (NE-Chaves), ascribed to high-fractured rocks, is the main recharge area; the stable isotopic composition of the groundwater samples indicate a mean recharge altitude higher than 1150 m a.s.l.; (3) the mean Sr isotopic ratio of the thermomineral waters (⁸⁷Sr/⁸⁶Srmean = 0.722419) is similar to that of the Sr isotopic ratios of the plagioclases of the granitic rocks (e.g. ⁸⁷Sr/⁸⁶Sr = 0.72087; ⁸⁷Sr/⁸⁶Sr = 0.71261), indicating that hydrolysis of plagioclase is the main water–rock interaction process, favoured by the presence of deep-seated (mantle-derived) CO2 (δ¹³C values in the range of −6 to −1‰ vs. PDB, and the CO2/³He values from 5.1 × 10⁸ to 7.5 × 10⁹, are typical of MORB fluids); (4) the income of carbon-14 free to Chaves CO2-rich thermal waters system does not permit reliable ¹⁴C groundwater dating; (5) the geothermometric results (e.g. K²/Mg and silica geothermometers) indicate equilibrium temperatures around 120 °C, and a maximum depth of about 3.5 km reached by the Chaves CO2-rich thermal waters system was estimated. The discharge zones are mainly related to the intersection of the main local/regional fault lineaments (and conjugate structures), responsible for promoting the mineral and thermal groundwater ascent.
... Recent studies have demonstrated that Sr isotopes provide a way of fingerprinting different mineral waters and may therefore be applied, in combination with other chemical and isotope data, for source authentication purposes (e.g. Négrel et al., 1997;Montgomery et al., 2006;Voerkelius et al., 2010;Marques et al., 2012). Since water is completely bio-available to plants and animals and can be transferred to any organic material without significant fractionation of Sr isotopes, the determination of 87 Sr/ 86 Sr isotope ratios has also been widely used to trace the geographic origin of a large variety of food products (e.g. ...
... A comparison of water and whole-rock isotope ratios is of little relevance, because full isotope equilibrium with the surrounding country rocks is rarely achieved (Négrel et al., 2001;Shand et al., 2009). Nevertheless, differences in the age and nature of granite reservoirs will have strong effects on the 87 Sr/ 86 Sr ratios of their silicate minerals, being therefore possible that the Sr isotopic variability recorded in the three types of granite waters analysed in this study reflects contrasts in the exchange rates and 87 Sr/ 86 Sr compositions of the plagioclase with which they have interacted, as also demonstrated by Marques et al. (2012). ...
This work presents the 87 Sr/ 86 Sr isotope compositions of nine samples of bottled waters from several regions of Portuguese mainland. The Sr isotopic variability displayed by the analysed waters is strongly correlated with the age and mineralogical composition of the aquifer source rocks, suggesting that the 87 Sr/ 86 Sr isotope signatures of these mineral waters are dominantly controlled by fluid-rock and/or fluid-mineral interaction processes. The lowest 87 Sr/ 86 Sr ratios are found in water samples from the Monchique aquifer (87 Sr/ 86 Sr = 0.70447), located in Late Cretaceous alkaline magmatic rocks of mantle origin. The Vimeiro waters hosted in carbonate and evaporite formations of Jurassic age have 87 Sr/ 86 Sr values of 0.70808 and appear to have reached bulk isotopic equilibrium with whole-rock, whereas the waters sourced in Cenozoic siliciclastic sediments tend to exhibit 87 Sr/ 86 Sr ratios close to the rainwater value (São Silvestre; 87 Sr/ 86 Sr = 0.71078). Finally, the waters coming from granitic and/or metamorphic terrains of the Iberian Variscan basement (Vitalis, Luso, Carvalhelhos, Fastio and Serra da Estrela) display the most radiogenic Sr isotopic signatures (87 Sr/ 86 Sr > 0.7136). In the modern commercial context, the differences encountered provide a powerful tool for fingerprinting the mineral water origin and may be used for purposes of mineral water authentication. The results obtained also show the relevance of Sr isotopes as geochemical tracers in hydrogeology. Resumo: Neste trabalho, apresentam-se e discutem-se as razões isotópicas 87 Sr/ 86 Sr obtidas em nove amostras de águas engarrafadas provenientes de vários pontos do território continental português. A variabilidade isotópica encontrada nas águas analisadas relaciona-se com a idade e com a composição mineralógica das rochas do aquífero de origem, o que sugere que as razões isotópicas de Sr são fortemente controladas por processos de interacção água-rocha e/ou a água-minerais. Os valores mais baixos de 87 Sr/ 86 Sr encontram-se nas águas do aquífero de Monchique (87 Sr/ 86 Sr = 0.70447), que estão associadas a ocorrências magmáticas alcalinas do Cretácico superior. As águas de Vimeiro, captadas em formações carbonatadas e evaporíticas do Mesozóico apresentam valores de 87 Sr/ 86 Sr de 0.70808, sugerindo que estas águas alcançaram o equilibrio isotópico com as rochas do aquífero, enquanto as águas associadas a rochas sedimentares siliciclásticas de idade cenozóica possuem razões isotópicas muito próximas dos valores que se encontram na água da chuva (São Silvestre; 87 Sr/ 86 Sr = 0.71078). Por último, as águas procedentes de rochas graníticas e/ou metamórficas do soco varisco (Vitalis, Luso, Carvalhelhos, Fastio e Serra da Estrela) apresentam composições isotópicas de Sr mais radiogénicas (87 Sr/ 86 Sr > 0.7136). Num contexto comercial as diferenças encontradas proporcionam uma ferramenta que poderá ser usada para fins de certificação da proveniência de águas minerais. Os resultados obtidos também mostram a importância dos isótopos de Sr como traçadores geoquímicos em hidrogeologia. Palavras-chave: Razões isotópicas 87 Sr/ 86 Sr, águas minerais engarrafadas, processos de interação água-rocha.
... Recent studies have demonstrated that Sr isotopes provide a way of fingerprinting different mineral waters and may therefore be applied, in combination with other chemical and isotope data, for source authentication purposes (e.g. Négrel et al., 1997;Montgomery et al., 2006;Voerkelius et al., 2010;Marques et al., 2012). Since water is completely bio-available to plants and animals and can be transferred to any organic material without significant fractionation of Sr isotopes, the determination of 87 Sr/ 86 Sr isotope ratios has also been widely used to trace the geographic origin of a large variety of food products (e.g. ...
... A comparison of water and whole-rock isotope ratios is of little relevance, because full isotope equilibrium with the surrounding country rocks is rarely achieved (Négrel et al., 2001;Shand et al., 2009). Nevertheless, differences in the age and nature of granite reservoirs will have strong effects on the 87 Sr/ 86 Sr ratios of their silicate minerals, being therefore possible that the Sr isotopic variability recorded in the three types of granite waters analysed in this study reflects contrasts in the exchange rates and 87 Sr/ 86 Sr compositions of the plagioclase with which they have interacted, as also demonstrated by Marques et al. (2012). ...
This work presents the 87Sr/86Sr isotope compositions of nine samples of bottled waters from several regions of Portuguese mainland. The Sr isotopic variability displayed by the analysed waters is strongly correlated with the age and mineralogical composition of the aquifer source rocks, suggesting that the 87Sr/86Sr isotope signatures of these mineral waters are dominantly controlled by fluid-rock and/or fluid-mineral interaction processes. The lowest 87Sr/86Sr ratios are found in water samples from the Monchique aquifer (87Sr/86Sr = 0.70447), located in Late Cretaceous alkaline magmatic rocks of mantle origin. The Vimeiro waters hosted in carbonate and evaporite formations of Jurassic age have 87Sr/86Sr values of 0.70808 and appear to have reached bulk isotopic equilibrium with whole-rock, whereas the waters sourced in Cenozoic siliciclastic sediments tend to exhibit 87Sr/86Sr ratios close to the rainwater value (São Silvestre; 87Sr/86Sr = 0.71078). Finally, the waters coming from granitic and/or metamorphic terrains of the Iberian Variscan basement (Vitalis, Luso, Carvalhelhos, Fastio and Serra da Estrela) display the most radiogenic Sr isotopic signatures (87Sr/86Sr > 0.7136). In the modern commercial context, the differences encountered provide a powerful tool for fingerprinting the mineral water origin and may be used for purposes of mineral water authentication. The results obtained also show the relevance of Sr isotopes as geochemical tracers in hydrogeology.
... This sample is exposed to the fumarolic fluids, which are mainly composed of steam water (e.g., Caliro et al., 2015). The boiling pools that produce the steam have strontium isotopic values ranging from 0.705408 (Caldeira Asmodeu) to 0.705432 (Caldeira Grande; Ferreira et al., 2023) and, based on the fact that the high atomic weight of strontium prevents its isotopes from fractionating during natural processes (Shand et al., 2009;Marques et al., 2012;Xie et al., 2013), it is probable that the water vapor have the same ratio as the water from the boiling pools. The sample from Furnas Village Fumarolic Field (CC) is projected within the 87 Sr/ 86 Sr ratios of the seawater and the boiling pools (Fig. 8), indicating that this sample receives contributions by both endmembers, as it was demonstrated by the hydrogeochemical data. ...
... Based on this approach, several studies have been carried out by the team, for example in aquifers located in coastal regions, presenting issues related to the increase of salinization (due to anthropogenic activities), as well as other pollution issues which were characterized using similar approaches, namely at Sines coastal aquifer, Portugal , Lower Sado basin, Portugal (Carreira et al. 2014b), Essaouira basin, Morocco (Ouhamdouch et al. 2019;Bahir et al. 2021), or even at Santiago Island, Republic of Cape Verde . Not forgetting other case studies ascribed to different geological environments like the Serra da Estrela Mountain region, Portugal (Carreira et al. 2011) or the CO 2 -rich thermal and mineral waters issuing in the north of Portugal (Marques et al. 2012;Carreira et al. 2021). ...
Groundwater management and protection must be confronted under ethical and moral concerns, with regulations and water policies for proper and sustainable civilization development. Approximately half of the world population relies on groundwater as the main source of supply, representing a vital requirement for human life and progress. Often in many regions of the world, water authorities are facing scarcity and over-exploitation of the available fresh water reserves. In these circumstances, geoethical aims to represent a way to reach the entire community (water authorities, stakeholders, scientists, and the population in general), focusing on the importance and awareness of water sustainability. In this paper, two case studies from Portugal will be reviewed and discussed aiming to highlight the importance of isotope hydrology as a way to obtain a unique characterization of groundwater resources foreseeing a proper management and sustainability of the groundwater systems. The first case study, Melgaço-Messegães CO2-rich mineral waters, is located in a granitic environment (NW Portugal). The study allowed to establish the preferential recharge altitude (delimitation of protection limits) based on the δ²H and δ¹⁸O content; the ³H data indicates a mean residence time of 40 years; the carbon isotopes (δ¹³C and ¹⁴C values) highlight methanogenesis and/or mantle-derived carbon as the main carbon source. In the second case study, Moura−Ficalho aquifer (carbonate formations, SE of Portugal), the combined use of geochemical and isotopic (stable and radioactive) data allowed the identification of different (much smaller) flow velocities in the deepest layers of the Moura−Ficalho aquifer and the δ¹⁸O data indicates recharge under different climate conditions.
... [51] conducted oxygen and hydrogen isotope analyses of groundwater used in open-loop systems for one year, and provided LSI and RSI values. Strontium isotope analysis of bedrock minerals and surface waters provides information on the history of groundwater movement related to hydrological processes [52][53][54][55]. ...
The use of shallow geothermal energy systems utilizing groundwater temperature for the air-conditioning of buildings is increasing worldwide. The impact of these systems on groundwater quality has become crucial for environmental regulations and system design. For the long-term operation of geothermal systems, it is important to evaluate their influence on the geochemical properties of groundwater, including precipitation and dissolution of secondary minerals. This research was conducted in a real-scale geothermal system, consisting of a groundwater heat pump (GWHP). Hydrochemical data were obtained from samples collected from an aquifer before heating, during heating, and before cooling operations of the GWHP. The Langelier Saturation Index and Ryznar Stability Index were calculated, and the saturation index was simulated with the PHREEQC program. Evidence from water table variation, temperature change, and 87 Sr/ 86 Sr isotope distribution showed that groundwater flows from a well located on the northwest side of the geothermal well. The saturation index values showed that the pristine groundwater favors carbonate dissolution, however, manganese oxides are more sensitive to temperature than carbonate minerals. In addition, mineral precipitation and dissolution were found to vary with depth and temperature.
... The carbonate levels reflect the equilibrium between carbonate rock dissolution and carbonate coprecipitation into secondary carbonate minerals. The only exception is the geothermal water from the granitic area of Oulmes (#9), where the bicarbonate content was very high (1000 mg/L), reflecting intensive-water-rock interactions with silicate minerals, which is common for geothermal waters from silicate rocks systems (Nicholson, 1993;Favara et al., 2001;Vengosh et al., 2002;Carreira et al., 2008;Marques et al., 2006Marques et al., , 2012Dupalova et al., 2012;Loges et al., 2012). ...
The geochemical and isotopic (strontium, boron, radium, oxygen, hydrogen) variations of geothermal waters from five different regions in Morocco were investigated in order to evaluate the sources of solutes and the mechanisms of water-rock interaction. During 2008 to 2010, twenty-two geothermal water samples were collected from the southern, central, and northern parts of Morocco. The water samples were analyzed for major and trace elements, stable isotopes (δ¹⁸O, δ²H) naturally occurring radionuclides (²²⁶Ra, ²²⁸Ra, ²²⁴Ra), and isotopes of dissolved strontium (⁸⁷Sr/⁸⁶Sr) and boron (δ¹¹B). The Moroccan geothermal waters exhibited a wide range of salinity, ranging from 590 to 25,000 mg/L with predominance of chloride, sodium, sulfate, calcium, and bicarbonate ions. Integration of the geochemical and isotope data suggests that the geothermal waters in Morocco originate from recharge of meteoric water and water-rock interactions. The predominance of chloride and sodium and the relatively low Br/Cl ratios (<1.5 × 10⁻³), combined with Ca/SO4 ratios ∼1 suggest that halite and sulfate (gypsum/anhydrite) minerals are the major rock sources for mineralization of the geothermal waters. The variations of ⁸⁷Sr/⁸⁶Sr ratios (0.7076–0.7122) and δ¹¹B (5.3‰–29.3‰) were used to distinguish two rock sources (1) dissolution of marine sulfate/carbonate rocks with Sr isotope composition that correspond to the expected ratios in seawater during time of deposition; and (2) non-marine sources with higher ⁸⁷Sr/⁸⁶Sr and δ¹¹B, presumably from interactions with clay minerals and shale rocks. The variations of radium isotopes indicate that the alpha-recoil of the parent nuclides on the host rocks caused mobilization of the short-lived ²²⁴Ra and ²²⁸Ra to the geochemical waters. The low ²²⁸Ra/²²⁶Ra ratios (activity ratios of 0.04–0.14) measured in the geothermal waters mimic the Th/U ratios in the source rocks, which indicate predominance of uranium over thorium. Our data show that some of the geothermal waters in Morocco are characterized by high salinity, and in some systems also by elevated radioactivity above international drinking water standards, which limits their utilization for agricultural and domestic applications. Adequate treatment is therefore required to use geothermal waters in Morocco as an alternative or additional water source. Other geothermal waters with low mineralization can be utilized as alternative resource for the agricultural and domestic sectors without any restrictions.
... Regional and local studies of certain characteristics have been conducted (Juncosa et al. , 2015Delgado et al. 2007Delgado et al. , 2011Delgado et al. , 2013, including hydrogeochemical studies developed in specific basins. There are similar studies in NW Portugal (Carvalho 1996;Marques et al. 2012). Hernández et al. (2012), Corral et al. (2012), and Martínez-Pledel et al. (2012) can be cited, among others, as hydrogeological studies. ...
Galicia is located in the NW corner of the Iberian Peninsula (Spain). From a geological point of view, the territory belongs to the Hercynian chain and, more specifically, to a large outcrop dominated by igneous and metamorphic rocks called the Hesperian Massif or Iberian Massif. In some sectors the Hesperian Massif is partially covered by more recent sedimentary deposits. The geology of Galicia is very complex due to the age of the rocks that make up its substrate and their diversity. Thus, the hydrogeological behaviour of the underground medium (hydrodynamic and hydrogeochemical characteristics) will determine the therapeutic properties of the water emanating from the surface. In Galicia, aquifers are generally shallow with low mineralization, except for those whose waters come from deep fractured mediums. The chemical characteristics of the water are directly related to the geological matrix. The groundwater flows through the geological medium and is mineralogically enriched by heterogeneous chemical reactions. Galicia turns out to be an area rich in the potential exploitation, applications and use of different water resources. These resources are thermal, mineral-natural and mineral-medicinal waters. In this work, we have developed a study that relates the geology, hydrogeological and hydrogeochemical characteristics of the Galician substrate and their potential therapeutic indications. To achieve that, we have chosen to study the exploited waters with higher flow rates, including the natural mineral waters for human use.
... Strontium isotopes are also widely used in hydrogeology to characterize mineralization processes conditioned by water-rock interactions with magmatic rocks Negrel, 1999;Negrel, 2006;Negrel et al., 2010) or with carbonates (Armstrong et al., 1998;Barbieri et al., 2005;Bishop et al., 1994;Dogramaci and Herczeg, 2002;Ettayfi et al., 2012;Frost and Toner, 2004;Vinson et al., 2012). It has also been successfully employed to describe mixing processes between different groundwater flow lines availing the distinctive strontium signatures of the minerals in the host rocks (Bishop et al., 1994;Bullen et al., 1996;Cartwright et al., 2007;Casanova et al., 2001;Franklyn et al., 1991;Marques et al., 2012;Negrel et al., 2002;Petelet-Giraud et al., 2003;Petelet-Giraud et al., 2006;Xie et al., 2013). Strontium isotope ratios in rocks vary principally according to the Rb/Sr ratio and the age of parent material because 87 Sr is released by beta-decay of 87 Rb (Kendall and McDonnell, 1998). ...
This study aims at identifying the water-rock interactions and mixing rates within a complex granite-carbonate coastal aquifer under high touristic pressure. Investigations have been carried out within the coastal aquifer of Bonifacio (southern Corsica, France) mainly composed of continental granitic weathering products and marine calcarenite sediments filling a granitic depression. A multi-tracer approach combining physico-chemical parameters, major ions, selected trace elements, stable isotopes of the water molecule and ⁸⁷Sr/⁸⁶Sr ratios measurements is undertaken for 20 groundwater samples during the low water period in November 2014. 5 rock samples of the sedimentary deposits and surrounding granites are also analysed. First, the water-rock interactions processes governing the groundwater mineralization are described in order to fix the hydrogeochemical background. Secondly, the flow conditions are refined through the quantification of inter aquifer levels mixing, and thirdly, the kinetics of water-rock interaction based on groundwater residence time from a previous study using CFCs and SF6 are quantified for the two main flow lines. A regional contrast in the groundwater recharge altitude allowed the oxygene-18 to be useful combined with the ⁸⁷Sr/⁸⁶Sr ratios to differentiate the groundwater origins and to compute the mixing rates, revealing the real extension of the watershed and the availability of the resource. The results also highlight a very good correlation between the groundwater residence time and the spatial evolution of ⁸⁷Sr/⁸⁶Sr ratios, allowing water-rock interaction kinetics to be defined empirically for the two main flow lines through the calcarenites. These results demonstrate the efficiency of strontium isotopes as tracers of water-rock interaction kinetics and by extension their relevance as a proxy of groundwater residence time, fundamental parameter documenting the long term sustainability of the hydrosystem.
This investigation analyses the erosion degree in the coastal edge sector of Punta Couso, a granitic area in the Galician coast (NW Iberian Peninsula). For this purpose, high-resolution images were used; geomorphological parameters, such as joint density or terrain ruggedness (calculated from LiDAR data) and fieldwork information obtained with Proceq's Equotip 3 portable hardness tester. Based on this information, this research could verify that the mean joint direction is oriented to the main wave component (Western). Also, there is a negative correlation between rock hardness values and the joint density (−0.43). This correlation increases significantly when the measurements are grouped in 10 m areas since the low tidal water edge (an estimated shoreline) reaches −0.87. With this aggrupation method, the relation between rock resistance and joint density is clear. On the other hand, it is necessary to do a more detailed analysis of the rock composition, especially in granitic sectors, to improve these relationships’ understanding.KeywordsGranitic rocksCoastal geomorphologyHardness testerEquotipGalicia
The main goal of this essay is to outline a prospective approach related to the hydromineral and geothermal field of Chaves (NE Portugal). The Verin–Régua–Penacova megastructure, trending NNE-SSW, controls the Chaves basin. The thermal water springs in the Chaves urban area have been well known since Roman times with magnificent Roman Bath buildings. Since 1983, the geothermal power available in Caldas de Chaves in three production wells supports a small heat network. Currently, with a long delay of over 35 years, Chaves will enter the roadmap of European cities benefiting from a geothermal district-heating network. The Roman Baths legacy suggests the design and development in Chaves of a geothermal project for direct, continuous, and sustainable use. This project must be adjusted to the resource and demand to promote the region, Chaves city, and the Thermal Bath and comfort its inhabitants and visitors.KeywordsGeothermicsHydromineral resourcesConceptual modelsSustainabilityChaves basinN Portugal
B-Sr isotopes and selected trace elements were used to assess the multiphase fluid flow path in the Changbaishan volcanic two-phase geothermal system (Jilin, Northeast China). The Ca/Sr ratio can distinguish volcanic and sedimentary rock reservoirs, while clastic and carbonate rocks need to be combined with the Sr/Na ratio. The lithology of the reservoir can be further ensured through contrastive water and rock 87Sr/86Sr ratios. Additionally, with caution in determining chemical composition of different endmembers, the B-Sr isotope model is useful in tracing the steam-heated/condensate water (group 1, which can be further divided into Group 1–1 and Group 1–2, according to the reservoir lithology), karst water (group 2) and residual water (group 3) flow paths. From the geochemistry and isotopes in the Changbaishan geothermal system, we infer that (1) basalt, clastic and carbonate rocks are the three main reservoirs and (2) the geochemical character of thermal waters is the result of four fluid-participating endmembers: surface water (TC), near-surface water (EM-2), residual sea water (EM-4) and vapor separated from deep sea water (EM-5). In addition, based on the B-Sr isotope model, we also established a simple conceptual model: group 1–1 represents mixing between EM-5 and TC after fluid-basalt interaction; group 1–2 indicates mixing EM-2 with EM-5 and experienced a Mesozoic granite leaching process; and group 3 is the result of EM-2 mixing with EM-4 after interaction with carbonates. The formation of Group 2 is mainly related to karst water, which is directly affected by hot magmatic volatile inputs.
We demonstrate a strategy of investigating recharge potential of a shallow aquifer in a hard rock terrain through flow in a fractured zone using self-potential (SP) anomaly and other ancillary (published) data related to the area of investigation. Our study area is Vilarelho da Raia, northern Portugal which possesses a shallow aquifer within a granitic terrain. We explain the phenomenon responsible for generating SP anomaly due to groundwater flow through a fractured conduit associating a fault. We propose delineating parameters associated with such structure from SP profile across it using a thin 2D conducting sheet model buried below subsurface. We propose a data based robust interpretation using derivative analysis of SP anomaly. We demonstrate that for sufficiently smooth SP anomaly across a 2D buried sheet model the first and the second order vertical derivatives of SP anomaly are the only necessary tools in delineating model parameters using characteristic features of derivatives curves and a set of closed form formulas. We propose using Savitzky–Golay derivative filter to get robust estimate of the first and second order horizontal derivatives. The first and second order vertical derivatives are obtained using Hilbert transform and Laplaces harmonic equation respectively. We applied the proposed technique on SP anomaly profile across a fault at Vilarelho da Raia in estimating parameters of a sheet model which represents the fault plane. We used the estimated parameters and the ancillary data taken from published literature to delineate hydrogeological parameters related to recharging of an aquifer within a granitic terrain.
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The spring waters of the Sierra Nevada result from the attack of high CO2 soil waters on typical igneous rocks and hence can be regarded as nearly ideal samples of a major water type. Their compositions are consistent with a model in which the primary rock-forming silicates are altered in a closed system to soil minerals plus a solution in steady-state equilibrium with these minerals. Isolation of Sierra waters from the solid alteration products followed by isothermal evaporation in equilibrium with the earth's atmosphere should produce a highly alkaline Na-HCO3-CO3 water; a soda lake with calcium carbonate, magnesium hydroxysilicate, and amorphous silica as precipitates.
The aim of this paper is to review the results of the assessment of low-temperature geothermal resources (issue temperatures
between 41 and 77 °C) that occur in the Portuguese mainland. For this purpose, a multidisciplinary approach, including geologic,
tectonic, geochemical, geophysical and isotopic (δ2H, δ18O, δ13C, 3H and 14C) techniques, was applied in order to update local and/or regional conceptual circulation models. Three case studies of N-Portugal
are presented and discussed. This paper describes different low-temperature geothermal waters presenting similar hydrogeological
conceptual models but rather different geochemical signatures (e.g., HCO3-Na with pH ≈ 8, HCO3/Na/CO2-rich with pH ≈ 7 and HCO3-Na with pH ≈ 9, type waters). In fact, in the studied low-temperature geothermal systems, local/regional high altitude sites
associated with highly fractured rocks play an important role in conducting the infiltrated meteoric waters towards the discharge
zones near the Spas. The discharge zones are mainly related to the intersection of major regional fault lineaments (and conjugate
structures), responsible for creating the mineral waters ascent. In some cases, geochemical and isotopic data point out to
the existence of anthropogenic contamination of some geothermal spring waters related to the intense use of fertilizers in
areas of widespread agricultural practices.
Chemical and strontium isotopic analyses have been performed on 10 geothermal waters from the Valles caldera/Jemez Mountain region, as well as 10 rock samples collected in the VC-1 scientific core hole. The 87Sr/86Sr values of other rocks sampled in the Jemez Mountains have also been used in this study to understand relations between the fluids and rocks of the volcanically driven geothermal system and the lateral outflow plume, discharging down the Jemez fault zone. The strontium content of ground-water is linked to the host rock composition, the aquifer temperature, and therefore the solubility of Sr-containing minerals. Low Sr concentrations in the fluid are found with a high temperature and/or volcanic host rocks, whereas high Sr concentrations are characteristic of a low temperature and/or a Paloezoic sedimentary aquifer. Important variations of the 87Sr/86Sr value in hydrothermal waters (0.70842-0.72193) are related to chemical composition, Sr content, and host rocks. For VC-1 core samples, the Sr isotopic ratios are also markedly variable (0.70459-0.75686), low for the Quaternary volcanics and high for the Paleozoic sedimentary rocks. The same observation is made for other Jemez Mountains rocks (0.70465-0.8163) with, in addition, high 87Sr/86Sr values for Precambrian crystalline rocks. A good correspondence is generally found between the waters and the reservoir rocks studied here, which indicates that isotopic equilibrium is rapidly attained. The following suite of hydraulically related fluids displays a progressive enrichment in radiogenic strontium: Baca wells (87Sr-86Sr=0.7084-0.7094), VC-1 core hole at 483 m (0.7152-0.7154), Main Jemez Spring (0.7217), and Soda Dam (0.7219). This trend is associated with flow through Paleozoic rocks and with the length of the flow path from the center of Valles caldera (primary geothermal fluids) toward San Deigo Canyon, along the Jemez fault zone (derivative waters).
Multidisciplinary studies integrating, U–Pb geochronology, whole-rock geochemical data, isotope geochemistry, anisotropy of magnetic susceptibility (AMS) studies and gravimetry were carried out on the Vila Pouca de Aguiar and the Águas Frias-Chaves porphyritic biotite granite plutons. Both plutons occur independently in a distance of about 20 km. The Vila Pouca de Aguiar and Águas Frias-Chaves plutons are examples of late to post-orogenic felsic Variscan granites in northern Portugal (NW Iberian Peninsula). The U–Pb zircon analyses yield a consistent age of 299 ± 3 Ma which is considered to be the emplacement age of the two plutons. These granites are weakly peraluminous, show high HREE and Y (and low P) contents which are consistent with them being I-type. This is also supported by their weakly evolved isotopic compositions, 87Sr/86Sri = 0.7044–0.7077 and εNd = − 2.0 to − 2.6, as well as by the whole rock oxygen isotope (δ18O VSMOW) ranging from + 9.7‰ to + 11.0‰. The emplacement of granite magma took place after the third Variscan deformation phase (D3) in an extensional tectonic regime, large scale uplift and crustal thinning. The integration of different data suggests that both plutons have the same feeding zone aligned within the Penacova-Régua-Verin fault (PRVF) and that both have the same structure which is related to late Variscan phases. The thicker shape for the Águas Frias-Chaves pluton comparing to that of the Vila Pouca de Aguiar pluton is compatible with different depths of PRVF sectors. The available data led us to propose a model of partial melting of a meta-igneous lower crustal source rather than an open-system of mantle–crust interaction. The interaction between the continental crust and invading mafic magmas could have been limited to mere heat transfer and, perhaps, local intermingling.
Groundwaters collected at deep levels in the granitic body of Stripa in central Sweden, are of a saline type. Our results clearly discard a marine origin for the primary waters, but they do not definitely address the alternative possibility which is a leaching of fluid inclusions.-from Authors
Based upon dissolution of feldspars under controlled laboratory conditions, we conclude that Sr release, at pH 3, is neither consistently stoichiometric nor constant for the feldspars measured. Bytownite, microcline, and albite all initially release Sr at rates which are 5 (bytownite) to 160 (microcline) times faster than steady-state release rates. The Sr/Si ratios in the early effluents are significantly elevated compared to the bulk mineral values. The 87Sr/86Sr measured in effluent early in dissolution is higher than the bulk mineral 87Sr/86Sr for bytownite, but lower than bulk mineral ratios for microcline and albite. 87Sr/86Sr ratios for the feldspar powders also changed markedly during dissolution of the three phases. In part, nonstoichiometric release of Sr can be explained by the presence of secondary phases (exsolution lamellae or minute quantities of accessory phases) or by surface leaching. Although we infer that these feldspars eventually release Sr with isotopic composition roughly equal to that of the bulk mineral at steady-state, the feldspars dissolve at extremely different rates (bytownite releases Sr at a steady-state rate ∼102 to 103 times faster than albite and microcline, at pH 3). Therefore, a mixture of these feldspars, or of other minerals exhibiting vast differences in dissolution rate, will release 87Sr/86Sr ratios distinctly different from the bulk whole rock. In addition, initial Sr release rates of the minerals (bytownite > microcline > albite) differ from steady-state release rates (bytownite > albite > microcline), complicating analysis of weathering solutions. Log (rate constants) for bytownite, albite, and microcline decrease from −13.5 to −16.4 to −17.2 (mol Sr cm−2 s−1). Interpretation of catchment scale riverine 87Sr/86Sr ratios on the basis of whole-rock Sr isotopes is, therefore, problematic at best, and would require normalization of bulk isotopic ratios by relative rates of dissolution of Sr-contributing phases.
New determinations of the isotopic composition of strontium and of the concentration of K, Rb, Cs, Sr, and Ba rocks and meteorites are given. The isotopic abundance of Sr87 in the upper mantle and the crust appears to be lower than that found for chondrites. Furthermore, for a chondritic earth model, the concentrations of potassium, rubidium, and cesium in the earth's crust are anomalous when compared with those of uranium, barium, and strontium. These two concurring arguments indicate that the upper mantle and crust of the earth do not contain K, Rb, Cs, U, Ba, and Sr, in the proportions found in chondrites, and that the alkali metals are depleted relative to U, Sr, and Ba. This depletion may be an indication of a nonchondritic earth composition; it may also result from an earth differentiation in which K, Rb, and Cs were concentrated or retained in the lower mantle.
The East Bull Lake pluton is a 2.48 Ga-old, layered mafic intrusion located on the southern margin of the Superior Province, Precambrian Shield in Ontario, Canada. The groundwaters have been studied as part of a detailed geological mapping and geochemical study of the pluton for the Canadian Nuclear Fuel Waste Management Program.All groundwater samples are dilute—the most concentrated NaCl type water contains 3.1 g/l total dissolved solids. Present day87Sr/86Sr values of the rock samples varies from 0.705 to 0.714 and the groundwaters from 0.711 to 0.720. The CaHCO3 recharge waters show the greatest range in values, in contrast to the deeper NaHCO3 and deep NaCl waters where a narrow range of 0.712–0.713 is found. Fracture-filling laumontite, calcite and gypsum have the same isotopic signature as the deep water.The CaHCO3 water is the youngest component of the groundwater system and its spread in isotopic values reflects local conditions at the surface. The NaCl water is considered to be the oldest component and its Sr isotopic ratio value indicates equilibration with silicate fracture mineral phases. The isotopic data suggest that laumontite, calcite, and gypsum fracture phases have either crystallized from this water or are currently controlling its isotopic composition by dissolution. No age can be assigned to the deep waters, except that the NaCl component may date from the Early Paleozoic, based on geological arguments or, more likely, be 104–106 years old based on kinetic studies of rock-water interaction and other isotopic data.If seawater was one component of the NaCl water history, there is no record of this in the87Sr/86Sr ratios.
The upflow zone of more than 40 cold and hot mineral springs of [und Na]-(Ca)-(Mg)-[und HCO[sub 3]]-Cl type is restricted to an extensional structure within the seismically active. North Anatolian Fault Zone. The chemistry of the waters, which are probably more than 10,000 years old, is influenced effectively in a low-temperature environment by the CO[sub 2] originating from the decomposition of marine carbonates and outgassing of the earth mantle. This gas is thus attributed to the interaction of the minor plates of Turkey and the Black Sea in this area. A strong positive [sup 18]O-shifts is due to water-rock interaction with very long contact times, rather than to isotopic influence of the CO[sub 2]-on the [delta][sup 18]O-value of the waters.
The recent literature on the kinetics of water-rock interactions is reviewed. The data are then extended to provide a quantitative framework for the description of weathering and alteration. The available experimental data on dissolution of silicates verifies quantitatively the usual mineral stability series in sedimentary petrology. The rate of hydration of carbonic acid is shown to be a possible limiting factor in water-rock interactions. The framework is developed to enable use of laboratory dissolution experimental results and thermodynamics to arrive at a rate law applicable up to equilibrium and therefore applicable to natural systems. The kinetic justification for the significance of a water-rock ratio is discussed. With a proper treatment of fluid flow, the equations are applied to the weathering profile leading to the development of bauxites from nepheline syenites.
Rubidium and strontium are used as tracers in the history of ; differentiation of the continental sial, and for this purpose it is assumed that ; the Rb/Sr ratio follows the aggregate enrichment of sialic components ; sufficiently well to represent an approximately linear measure of the entire ; process. Measurements of the Srâ¸â·/Srâ¸â¶ ratios in basalts and other ; igneous rocks of subsialic origin suggest that the source regions of sial have ; had a Srâ¸â·/Srâ¸â¶ ratio in the range 0.705 to 0.710 in different areas ; and at different times in the span of geologic history. Measurements of the Rb/; Sr ratio in sialic rocks of the continental crystalline basement have indicited ; that the weighted average value for this ratio is in the vicinity of 0.25. This ; means that the Srâ¸â·/Srâ¸â¶ ratio in average sialic rocks of the ; continental basement would increase at a faster rate than that in the subsialic ; source regions, by an amount equal to approximately 0.010 per billion years. ; This is more than five times the standard deviation precision error in ; measurement. A comparison of the ratio Srâ¸â·/Srâ¸â¶ with the geologic ; age of the rock, in samples of typical sialic basement rocks leads to the ; conclusion that there has been a continuous generation of primary sial from ; subsialic source regions that has caused the continental areas to grow roughly in ; proportion to the extent of the geological age provinces. In North America this ; areal growth is estimated to be at the average rate of about 7000 km²/m.y., ; and it seems to have been operative over most of geologic time. A model is ; formulated in which the proportion and age of reworked material that is ; incorporated into new sialic basement are related to the Srâ¸â·/Srâ¸â¶ ; development in the various materials involved. The model is generalized with all ; the parameters left open. An example set of values for the various parameters is ; tested on the model to indicate where there is need for more definitive data. ; This example set is derived from data available at present which, although very ; limited, indicate clearly that if the reworked material is young enough it can ; constitute a major proportion of a new sialic basement area, but if it is ancient ; (1 to 2 b.y. in primary age prior to incorporation) it could not be present in ; more than a minor proportion of the typical new basement. (auth);
We discuss geochemical and isotopic (18O/16O, 2H/1H and 87Sr/86Sr) data recording the hydrothermal alteration of northern Portuguese Hercynian granites by Na–HCO3–CO2-rich mineral waters. Whole-rock samples from drill cores of Vilarelho da Raia granite have δ18O values in the +11.47 to +10.10‰ range. The lower values correspond to highly fractured granite samples displaying vein and pervasive alteration. In the pervasive alteration stage, which probably results from a convective hydrothermal system set up by the intrusion of the granites, the metamorphic waters are in equilibrium with hydrous minerals. In contrast, the vein alteration of these granitic rocks was caused by water of meteoric origin. The oxygen ratios between water (W) and rock (R), the so-called W/R ratios, obtained for the open system (where the heated water is lost from the system by escape to the surface) range between 0.05 and 0.11, suggesting that the recrystallization of the veins was influenced by a small flux of meteoric water. Stable isotope analyses performed on the cores show that the vein alteration stage relates to post-emplacement tectonic stresses acting on the granite, probably of late Hercynian age. Our results are consistent with the existence of two separate alteration events (pervasive and vein) caused by hydrothermal waters of different isotopic characteristics. The studies presented in this paper should be viewed as a natural analogue that uses the alteration features observed in a “fossil” geothermal system at Vilarelho da Raia to assess possible water–rock reactions presently occurring at depth in granitic rocks of the nearby Chaves area.
The upflow zone of more than 40 cold and hot mineral springs of —(Ca)—(Mg)——Cl type is restricted to an extensional structure within the seismically active North Anatolian Fault Zone. The chemistry of the waters, which are probably more than 10,000 years old, is influenced effectively in a low-temperature environment by the CO2 originating from the decomposition of marine carbonates and outgassing of the earth mantle. This gas is thus attributed to the interaction of the minor plates of Turkey and the Black Sea in this area. A strong positive 18O-shift is due to water-rock interaction with very long contact times, rather than to isotopic influence of the CO2 on the δ 18O-value of the waters.
Surface and mineral waters from a geothermal area (Cézallier) in the centre of the Massif Central, France, were analysed for Sr isotopes, Sr and major elements in order to use Sr isotopes to investigate the discharge of a mineralised water area, especially in the case of disseminate mineralised water emergences.The 87Sr86Sr ratios of mineralised waters ranged from 0.715541 to 0.716773. The variation in 87Sr86Sr values was small for the 5 mineral springs sampled over two periods (5 × 10−6–14 × 10−6). Regarding the reproductivity of the 87Sr86Sr ratio measurements, no differences can be seen and the 87Sr86Sr ratio of mineral waters can be considered to be constant with time. The 87Sr86Sr ratios of surface waters collected along the Zagat River ranged from 0.705303 to 0.715091. The lowest values were always observed in the headwaters. The difference in the 87Sr86Sr ratios between the two sampling periods was ∼ 22 × 10−4 and can be related to the hydrological situation (low or high flow). The 87Sr86Sr ratios of surface waters collected in the drain ranged from 0.715072 to 0.716585. The difference in the 87Sr86Sr ratios between the two sampling periods is ∼ 11 × 10−4 for the drain headwaters and ∼ 13 × 10−5 at the outlet of this area. Likewise, these variations can also be related to the hydrological situation.Plots of 87Sr86Sr vs. 1Sr ratios show two distinct binary mixing trends and the existence of at least four end-members. A mixing parameter f giving the proportions of the two components can be estimated for assumed 87Sr86Sr ratio and Sr content values of the pure end-members.An estimate of the mineral water discharge can be calculated using the results of the mixing model and the measured flow. In the drain area, the mixing model gives an estimate ∼ 0.5–1 l s−1, or 10–13% of mineral water in the total flow. A similar calculation was done for the river where the mineral water flow was ∼ 0.96 l s−1 (3.5 m3 h−1 100 m downstream from the bridge in April 1994, and 6 m3 h−1 20 m downstream from the bridge in September 1994.
The major element and Sr isotope geochemistry of surface waters, bedrock, and river sands was investigated in the Raikhot watershed within the High Himalayan Crystalline Series (HHCS) in northern Pakistan. Mass-balance calculations of mineral-weathering contributions to the dissolved flux of ions from the watershed indicate that 82% of the HCO3- flux is derived from the weathering of carbonate minerals and only 18% is derived from silicate weathering, even though the bedrock is predominantly quartzofeldspathic gneiss and granite with only ˜1% carbonate in the watershed. This study demonstrates the importance of trace amounts of bedrock carbonate in controlling the water chemistry of glacial watersheds. We suggest that the flux of Sr with a high 87Sr/86Sr ratio in the major Himalayan rivers may be derived in large part from weathering of trace amounts of calcite within the largely silicate HHCS. Models that use the flux of radiogenic Sr from the Himalayas as a proxy for silicate weathering rates may, therefore, overestimate the amount of CO2 consumption due to silicate weathering in the Himalaya.
In order to update the geohydrologic characterisation of Chaves geothermal area, coupled isotopic and chemical studies have been carried out on hot and cold CO2-rich mineral waters discharging, in northern Portugal, along one of the major regional NNE-trending faults (the so-called “Verin-ChavesPenacova Depression”). Based upon their location, and chemical and isotopic composition, the analysed waters can be divided into two groups. The northern group belongs to the HCO3/Na/CO2-rich type, and consists of the hot spring waters of Chaves and the cold spring waters of Vilarelho da Raia. The δD and δ18O values show that these waters are of meteoric origin. The lack of an 18O shift indicates that there is no evidence of water/rock interaction at high temperatures. The southern group includes the cold spring waters of Campilho/ Vidago and Sabroso/Pedras Salgadas. Their chemistry is similar to that of the northern group but their heavier δD and δ18O values could be attributed to different recharge altitudes. Mixing between deep mineralised waters and dilute superficial waters of meteoric origin might explain the higher 3H activity found in the Vidago and Pedras Salgadas mineral waters. Alternatively, they could be mainly related to shallow underground flowpaths. The δ13C values support a deep-seated origin for the CO2. The δ37Cl is comparable in all the mineral waters of the study area, indicating a common origin of Cl. The 87Sr/86Sr ratios in waters seem to be dominated by the dissolution of plagioclases of granitic rocks.
We have determined K, Rb and Sr concentrations and 87Sr/86Sr ratios in fresh surface waters, a rain water sample and five geothermal waters from the Cantal volcanic area in the Massif Central, France. A comparison with appropriate rock types of the region showed no apparent chemical and isotopic fractionation occurring in the fresh water-surface rock system. The thermo-mineral water results suggest that all springs discharge dissolved Sr from the following contributors: Hercynian granito-metamorphic basement, lacustrian sediments underlying the volcano, Miocene-Pliocene volcanic rocks of basaltic to rhyolitic composition.
This is a text in isotope geology/geoscience that integrates material taught in various courses into a unified picture of the earth sciences. It presents an exposition of the principles used in the interpretation of isotopic data and shows how such interpretations apply to the solution of geological problems. References up to 1985 are included with chapters in this edition. New chapters on Sm-Nd, Lu-Hf Re-Os, and K-Ca decay schemes and cosmogenic radionuclides have been added. Data summaries and references have been expanded.
This work reports chemical and isotope data and temperature estimates for seven water samples collected
from Triassic formations in the Paris Basin in France. Four samples were collected in the central part of the
Basin (saline waters) and three were collected at the edge of the Basin near the recharge zone (dilute waters).
The saline waters collected from the Chaunoy and Champotran boreholes have high salinities (around
120 g/L) and very similar chemical and isotopic compositions. The saline water sample from the La Torche
borehole has much higher salinity (168 g/L) and significantly different isotope characteristics. The chemical
geothermometers applied to these fluids from the centre of the Basin give temperature values ranging
between 80 and 100 °C. The fresh water samples collected at the edge of the Basin have very different
chemical and isotopic compositions. These dilute water samples (Santenay and Châteauroux) are shallow,
with colder temperatures of around 45 to 50 °C. The study of uranium activity ratios for these Triassic
formation waters allows us, as a first approximation, to estimate a mean apparent fluid circulation velocity of
around 0.2 m/yr, which corresponds to a “mean age” slightly higher than 1 My for waters sampled in the
Chaunoy, Champotran and La Torche fields in the centre of the Basin. The multi-isotope characterization of
Triassic formation waters shows that our data are in agreement with literature values as concerns
“traditional” isotope systematics (δ18O, δD, 87Sr/86Sr). Li and B isotope signatures in the centre of the Paris
Basin are in a good agreement with a fluid signature derived mainly from water/rock interactions involving
clastic rocks with water essentially resulting from a seawater-derived brine endmember diluted by meteoric
waters. The data reported in the present work for Li and B isotopes could be used as a reference for future
studies to characterize sandstone formation waters.
Analyses of saline waters, fracture minerals, and host rocks from seven localities on the Canadian Shield demonstrate the utility of the ratio in the study of groundwater systems in crystalline rocks. The ratios range from 0.704 to 0.753 and have obtained their signatures by mineral/rock interactions, primarily involving the feldspars. We have identified brines from isolated pockets in the same mines where extensive flow regimes exist. There is mixing of different brines as well as mixing with meteoric waters.The isotopic results on calcites from fractures and shear zones show more than one generation of mineral growth in a given fracture. The ratios of the calcites vary from values identical to the present-day brine in the fracture zone to ratios with Archean signatures. This implies that activity may occur in fault zones over a very long time.The brines are very rich in Sr (up to 2400 mg/1), very low in Rb, and have relatively radiogenic ratios. They are ubiquitous in Shield rocks and, if they were present throughout geological time, they may be one reason why ages of felsic plutons are commonly younger than associated ages.
Fluid-granite interaction at near-equilibrium conditions was investigated by doping an experimental system with 84Sr. Reactions were performed at 453 K, saturated vapour pressure, and fluid/rock ratio of 20. The initial composition of the experimental fluid corresponded to the theoretical saturation with respect to kaolinite, quartz, laumontite, low-temperature albite, calcite and adularia. Sr was used to trace parent-mineral dissolution, neogenic phase precipitation, and to identify the reactions at Sr2+ steady state.The interaction is described, initially, by the isotopic mixing of the solution ratio and the granite ratio. However, in the rock end-member every main mineral has a different ratio. The evolution of ratio in solution as a function of showed that in the early stage of the interaction (where the dissolution of the rock is the dominant reaction) 87Sr-enriched phases, such as biotite, strongly influence the isotopic budget. After some time, the ratio of the fluid approaches the Sr isotopic ratio of the bulk rock, suggesting that fluid-granite isotopic equilibration is attained. When the dissolution of the granite is stopped and once the Sr2+ concentration reached steady state, variations of the ratio with time can be interpreted by an isochemical dissolution-precipitation of neogenic phases.
The 87Sr/86Sr values of thermal waters and hydrothermal calcites of the Long Valley caldera geothermal system are more radiogenic than those of young intracaldera volcanic rocks. Five thermal waters display 87Sr/86Sr of 0.7081-0.7078 but show systematically lighter values from west to east in the direction of lateral flow. We believe the decrease in ratio from west to east signifies increased interaction of deeply circulating thermal water with relatively fresh volcanic rocks filling the caldera depression. All types of pre-, syn-, and post-caldera volcanic rocks in the west and central caldera have (87Sr/86Sr)m between about 0.7060 and 0.7072 and values for Sierra Nevada granodiorites adjacent to the caldera are similar. Sierran pre-intrusive metavolcanic and metasedimentary rocks can have considerably higher Sr-isotope ratios (0.7061-0.7246 and 0.7090-0.7250, respectively). Hydrothermally altered volcanic rocks inside the caldera have (87Sr/86Sr)m slightly heavier than their fresh volcanic equivalents and hydrothermal calcites (0.7068–0.7105) occupy a midrange of values between the volcanic/plutonic rocks and the Sierran metamorphic rocks. These data indicate that the Long Valley geothermal reservoir is first equilibrated in a basement complex that contains at least some metasedimentary rocks. Reequilibration of Sr-isotope ratios to lower values occurs in thermal waters as convecting geothermal fluids flow through the isotopically lighter volcanic rocks of the caldera fill.
The geological, geoelectrical, geochemical and temperature data related to the Chaves geothermal system have been integrated to obtain a better understanding of the Chaves basin. Geoelectrical surveys carried out in the basin reveal a low-resistivity zone (10 ohm m), associated with a shallow geothermal reservoir, in the central part of the graben, bounded by higher-resistivity rocks. The top of this zone varies between 400 and 200 m and its maximum thickness (1600 m) is located at the centre of the basin. Thermal models for the Chaves basin and for the region are presented using the structure obtained by geoelectrical methods and a mean heat flow value of 95 mW m-2 derived from borehole measurements. The heat transfer takes place mainly by conduction, except near the faults, where convective flow is important. The medium is considered dishomogeneous and there is a great thermal conductivity contrast between the sediments in the basin and the surrounding rocks. The results obtained for the Chaves basin show that the mean temperature value in the shallow geothermal reservoir is 62°C. The maximum temperature value predicted to the bottom of this reservoir is 95°C. A regional forced convective-circulation model is suggested based on geomorphological, geochemical, isotopic data and to rmal models.
The Eye-Dashwa Lakes pluton is a Sr-rich felsic intrusive of the sanukitoid suite located in NW Ontario in the Superior Province of the Canadian Shield. The 87Sr/86Sr values of the CaNaCl-type saline, deeper groundwaters fall in the narrow range of 0.7057–0.7070, similar to the 87Sr/86Sr value in plagioclase but not to that in K-feldspar, biotite, or the whole rock. This suggests that the water isotopic composition is the result of plagioclase-water interaction. The fracture minerals gypsum and calcite have similar 87Sr/86Sr ratios, indicating that they have crystallized from waters similar to the present deep groundwaters. The shallow, CaHCO3-type, dilute groundwaters show a wider spread in the Sr ratio of 0.7065–0.7278, reflecting their derivation from minerals in the overlying soil.The results for the saline groundwaters are consistent with thermodynamic and kinetic models that demonstrate the relatively rapid dissolution of plagioclase with respect to other rock-forming silicates, and should have application to most brines located in silicate host rocks.
Sr isotope data from surface, shallow and deep groundwaters from the granitoids of the Vienne District (France) are presented in this paper. In surface waters, the Sr contents in the rocks and groundwaters agree with previous data for groundwaters sampled from granitic and sedimentary rocks in France where a large range in 87Sr/86Sr ratios is observed. After correction for the Sr input from rain, the surface water samples plot within a mixing field that can be explained by three end-members, one anthropogenic (low 87Sr/86Sr and high Cl/Sr ratio) and two end-members characterised by low Cl/Sr ratios and a large range in 87Sr/86Sr ratios (from around 0.707–0.720).For deep groundwaters, the 87Sr/86Sr ratios and Sr contents are also determined by applying a correction to account for the influence of cleaning waters during drilling operations. The results are scattered amongst five different groups and the lack of a direct linear relationship between any of the samples implies that, as found for the shallow groundwaters, the results are due to mixing between more than two end-members.A model to determine the 87Sr/86Sr ratio (Irf) of groundwater after interaction with an actively weathering granite is developed. The results yield a low Irf value for waters associated with weathering of the tonalite (0.70463) and a higher one for waters associated with weathering of the monzogranite (0.70704). Given the much higher Irf values derived from the deep groundwater samples, these results indicate that the deep groundwaters analysed within the Vienne hydrosystem cannot be directly related to weathering of either tonalite or monzogranite. It is speculated that this high 87Sr/86Sr source originated from marine incursions during the Jurassic and have been diluted by mixing with former groundwaters produced by water–rock interaction (WRI) with the granites.
Geochemical and isotopic studies have been undertaken to assess the origin of CO2-rich waters issuing in the northern part of Portugal. These solutions are hot (76°C) to cold (17°C) Na–HCO3 mineral waters. The δ2H and δ18O signatures of the mineral waters reflect the influence of altitude on meteoric recharge. The lack of an 18O-shift indicates there has been no high temperature water–rock interaction at depth, corroborating the results of several chemical geothermometers (reservoir temperature of about 120°C). The low 14C activity (up to 9.9 pmC) measured in some of the cold CO2-rich mineral waters (total dissolved inorganic carbon) is incompatible with the presence of 3H (from 1.7 to 4.1 TU) in those waters, which indicates relatively short subsurface circulation times. The δ13C values of CO2 gas and dissolved inorganic carbon range between −6‰ and −1‰ versus Vienna-Peedee Belemnite, indicating that the total carbon in the recharge waters is being diluted by larger quantities of CO2 (14C-free) introduced from deep-seated (upper mantle) sources, masking the 14C-dating values. The differences in the 87Sr/86Sr ratios of the studied thermal and mineral waters seem to be caused by water–rock interaction with different granitic rocks. Chlorine isotope signatures (−0.4‰ < δ37Cl < +0.4‰ versus standard mean ocean chloride) indicate that Cl in these waters could be derived from mixing of a small amount of igneous Cl from leaching of granitic rocks.
Chaves thermal waters (76C) are the most important external manifestations of low-temperature geothermal systems occurring in Portuguese mainland. They are related to crystalline granitic rocks. This paper describes the use of the environmental isotopic composition (oxygen-18, deuterium, and tritium) of hot and cold waters of the Chaves area as an important hydrogeological tool to solve specific problems arising in the appraisal of the geothermal resources of the area (e.g., origin and age of waters, recharge area, and underground flow paths).18O and D analyses seem to confirm the meteoric origin of Chaves thermal waters. The local altitude dependence of meteoric waters was determined by18O and D analyses of superficial and shallow groundwaters of the Chaves plain and its bordering mountains. Chaves thermal waters seem to be related to meteoric waters, infiltrated on the highest topography areas (Bolideira granitic outcrop NE Chaves), that percolate at great depth and emerge in a discharge area at lower altitude (Chaves plain). Chaves thermal waters showing little oxygen-18 shift and low tritium concentrations could be considered external manifestations of an old geothermal system in which the isotopic water-rock interaction is adjusted to equilibrium.
A small watershed (89 km2) underlain by granite or granite-gneiss in the Margeride mountains, southern Massif Central (France), has been studied using the chemical and isotopic composition of its dissolved load, bed sediments and soils. Dissolved concentrations of major ions (Cl, SO4, NO3, HCO3, Ca, Na, Mg, K, Al and Si), trace elements (Rb and Sr) and strontium isotopes have been determined for three different hydrologic periods in the main stream of the Desges river and its tributaries.
The aim was to characterize the chemical and isotopic signatures of each reservoir in the watershed; signature changes are interpreted as fluctuations in the different influencing components: rainwater, weathering products and anthropogenic addition. In the study area, as in other watersheds in granite environments, the only source for input of chemical species into the dissolved load at high altitude is chemical weathering and atmospheric deposition, whereas at lower altitude, human influence plays a non-negligible role.
As precipitation is a major vehicle for the addition of dissolved chemical species into the hydrosystem, a systematic rainwater study using an automatic collector was carried out over one year in order to better constrain rain elemental input. Corrections for rainwater addition, using chloride as an atmospheric-input reference, were computed for selected elements and for 87Sr/86Sr ratios. After these correction, the geochemical budget of the watershed was determined and the role of anthropogenic addition was evaluated based on strontium isotope relationships.
For particulate matter, we used the normalization of chemical species relative to parent rocks and the element ratios which reflect the depletion or enrichment in soils and sediments. Both the immobile- and mobile-element approaches have been tested, using Ti/Zr and La/Ce ratios for the former and Ca/Sr, K/Rb, and K/Fe ratios for the latter.
At the northern part of the Portuguese mainland, the upflow zone of several hot and cold HCO3/Na/CO2-rich mineral waters is mainly associated with important NNE–SSW faults. Several geochemical studies have been carried out
on thermal and non-thermal hydromineral manifestations that occur along or near these long tectonic alignments. The slight
chemical differences that exist between these meteoric hot and cold HCO3/Na/CO2-rich mineral waters seem to be mainly caused by CO2. δ13C(TIDC) values observed in these groundwaters range between –6.00 and –1.00‰ versus V-PDB (V denotes Vienna, the site of the International
Atomic Energy Agency; PDB originates from the CaCO3 of the rostrum of a Cretaceous belemnite, Belemnitella americana, collected in the Peedee formation of South Carolina, USA) indicating a deep-seated (mantle) origin for most of the CO2. Nevertheless, in the case of the heavier δ13C(TIDC) values, the contribution of metamorphic CO2 or the dissolution of carbonate rock levels at depth cannot be excluded. Concerning the hot waters, the lack of a positive
18O-shift should be attributed to water-rock interaction in a low temperature environment, rather than to the isotopic influence
of CO2 on the δ18O-value of the waters.
A multi-isotopic study of thermo-mineral waters from the Limagne Basin (French Massif Central) is reported. Lithium, B, Sr and Nd isotopic signatures in thermo-mineral waters and bedrocks were combined in order to determine the origin of these fluids from a reservoir point of view. Strontium and Nd isotopic systems showed that the thermo-mineral waters are mostly derived from a granitic reservoir type, with the exception of a few water samples having Sr and Nd isotopic signatures also reflecting a volcanic contribution (basalts). In a second step, Li and B isotopes were investigated, given that Li and B isotopic systematics are potentially affected by mass dependent fractionation during water/rock interaction and could provide some information on what takes place during this process. A great diversity of thermo-mineral waters within the Aigueperse area was clearly observed, which is directly related to the origin of these thermal waters in terms of reservoirs. These different geothermal reservoirs are characterized by different geological settings and intensity of water/rock interaction (i.e. depth and temperature).The combination of Li, B, Sr and Nd isotopic systems highlight the complexity of the study of these geothermal reservoirs and that the use of only one isotopic tool could lead to an incomplete interpretation of the origin of water. The new approach using Li isotopes shows a very interesting potential with additional information on the intensity of water/rock interaction.
The 87Sr/86Sr ratios of dissolved strontium in six Sierra Nevada streams at base flow are 0.00070 to 0.00175 higher than the average whole-rock value for the granodiorite bedrock underlaying the drainage basins. We suggest that the strontium isotope ratios and major cation compositions of the stream waters are controlled predominantly by the weathering reactions: plagioclase ⇒ kaolinite and biotite ⇒ vermiculite. Stream drainages that were glaciated ∼10 kyr ago (exposing fresh bedrock surfaces) have 87Sr/86Sr ratios 0.00036 to 0.00105 higher than drainages that were not glaciated in the past ∼100 kyr. We interpret the 87Sr/86Sr ratios of the stream water to indicate that biotite is weathering ∼6 times and ∼4 times more rapidly than plagioclase in the recently glaciated and nonglaciated drainages, respectively. Our results suggest that continental glaciation may have the effect of accelerating biotite weathering, significantly elevating riverine 87Sr/86Sr ratios in regions draining silicate bedrock for periods of ∼100 kyr.
Rb and Sr concentrations and Sr isotopic composition have been measured in thermo-mineral waters from the Massif Central in France. Rocks and mineral fractions which are thought to be important Sr contributors were also analyzed. The results suggest the waters to be mixtures of two or three components from different reservoirs, which can be associated with possible source rock types like granite and syenodiorite occurring in the region. The strontium isotopic ratios found in the separated minerals of the syenodiorite stratum indicate no chemical fractionation during the water-rock interaction. A RbSr internal isochron age of(265 ± 10) × 106yr is inferred for the Roche d'Enval syenodiorite.
Accessory calcite, present at concentrations between 300 and 3000 mg kg⁻¹, occurs in fresh granitoid rocks sampled from the Merced watershed in Yosemite National Park, CA, USA; Loch Vale in Rocky Mountain National Park CO USA; the Panola watershed, GA USA; and the Rio Icacos, Puerto Rico. Calcite occurs as fillings in microfractures, as disseminated grains within the silicate matrix, and as replacement of calcic cores in plagioclase. Flow-through column experiments, using de-ionized water saturated with 0.05 atm. CO2, produced effluents from the fresh granitoid rocks that were dominated by Ca and bicarbonate and thermodynamically saturated with calcite. During reactions up to 1.7 yr, calcite dissolution progressively decreased and was superceded by steady state dissolution of silicates, principally biotite. Mass balance calculations indicate that most calcite had been removed during this time and accounted for 57–98% of the total Ca released from these rocks. Experimental effluents from surfically weathered granitoids from the same watersheds were consistently dominated by silicate dissolution. The lack of excess Ca and alkalinity indicated that calcite had been previously removed by natural weathering.
A standard, based on the set of ocean water samples used by Epstein and Mayeda to obtain a reference standard for oxygen-18 data, but defined relative to the National Bureau of Standards isotopic reference water sample, is proposed for reporting both deuterium and oxygen-18 variations in natural waters relative to the same water. The range of absolute concentrations of both isotopes in meteoric-waters is discussed.
The abundance of radiogenic Sr(87) relative to Sr(86) at the time of crystallization has been determined for 45 rocks. The total range in the ratio Sr(87)/Sr(86) is less than 2 percent. Ratios for recent lavas range from 0.702 to 0.711. Oceanic basalts are closely grouped at 0.703, whereas ratios for continental volcanic rocks spread from 0.702 to 0.711. Among the volcanic rocks, ranging from basalt to rhyolite, no correlation was found between original ratio and rock type. Older mafic and felsic rocks that include both plutonic and extrusive types also cover this same range in original Sr(87)/Sr(86) ratios; however, there is a definite trend with geologic time. Precambrian rocks give values as low as 0.700. The data indicate that Sr(87)/Sr(86) of the weathering crust has changed 1.1 percent in 3000 million years, while the ratio in the mantle has changed no more than 0.5 percent.
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Tectonics and geomorphology of Pedras Salgadas region and associated mineral springs
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Genesis of some groundwaters from igneous rocks
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