Chemical and isotopic characteristics and origin of spring waters in the Lanping–Simao Basin,Yunnan, Southwestern China

The chemical and isotopic characteristics (oxygen, hydrogen, and strontium) of spring waters and isotopic compositions of helium (He) and neon (Ne) in gases escaping from spring waters in the Lanping–Simao Basin are studied. A total of twenty-one spring water samples (twelve hot springs, four cold springs, and five saline springs) and eleven gas samples were collected from the study area, including one spring and one gas sample from northern Laos. It is found that saline spring waters in the study area are of chloride type, cold spring waters are of carbonate type or sulfate type, and hot spring waters are of various types. High total dissolved solids levels in saline springs are significantly related to Upper Cretaceous–Paleocene salt-bearing strata. On the basis of hydrochemical geothermometry, the reservoir temperatures (T_r) for hot springs, cold springs, and saline springs are 65.5–144.1, 37.8–64.4, and 65.1–109.0 °C, respectively, and the circulation depths of saline springs are much larger than those of hot and cold springs. The oxygen and hydrogen isotopic compositions of springs in the Lanping–Simao Basin and northern Laos are primarily controlled by meteoric waters with obvious latitude and altitude effects, and are also influenced by δ¹⁸O exchange to some extent. Most Sr²⁺ in spring waters of the study area is derived from varied sources (carbonate, evaporite, and silicate mineral dissolution), and the Sr isotopic compositions are greatly influenced by volcanic rocks. Wide distribution of crust-derived He in the Lanping–Simao Basin and northern Laos reveal that faults in these areas may not descend to the upper mantle. It is concluded that water circulation in the study area may be limited above the upper mantle, while saline springs may originate from the Upper Cretaceous–Paleocene evaporites. Hydrochemical characteristics demonstrate affinities among the Lanping–Simao Basin, northern Laos, and Yanjing, eastern Tibet, while disaffinities are observed between these areas and Tengchong on the basis of the hydrochemical characteristics and noble gas isotopic compositions.     

Hydrogeological characterization of carbonated Jurassic aquifers in the Gijón-Villaviciosa basin (Asturias,N Spain) by means of geochemical and isotopic techniques

Chemical and isotopic analyses of groundwater from the carbonated Jurassic aquifers in the Gijón-Villaviciosa basin (Asturias, northern Spain) were carried out. Nine springs were sampled to determine major cations and anions, as well as the stable isotopes of the water molecule (δ²H and δ¹⁸O) and sulphate (δ³⁴S) values. Also, δ³⁴S values from gypsum coming both from Triassic rocks and bottom of Jurassic sequence were also determined. The results obtained were used to classify the waters with a genetic criteria in three groups: (1) waters with a high gypsum influence, with sulphate coming from Jurassic gypsum, (2) waters without gypsum influence, where sulphate source could be atmospheric deposition from industrial processes and marine aerosol, and (3) waters with some gypsum influence, in which sulphate origin could be a combination of different sources. In relation to recharge, δ²H and δ¹⁸O values were close to those of Global Meteoric Water Line and fit a local line that suggests a meteoric origin. The estimated elevations for spring recharge are in agreement with those obtained from hydrogeological maps.     

Defining the dynamics of groundwater in Serra da Estrela Mountain area, central Portugal: an isotopic and hydrogeochemical approach

In a multidisciplinary approach, geological, geomorphologic, structural, hydrogeochemical and isotopic surveys were conducted on the Serra da Estrela groundwater system (central Portugal) in order to establish/develop a conceptual circulation model of the Caldas de Manteigas thermomineral system. A detailed study of the isotopic and geochemical composition of surface waters (e.g. Zêzere River), shallow groundwaters (cold dilute springs), and thermomineral waters was carried out to characterize the distribution of isotopes in waters of this mountainous region, and to determine the origin and possible recharge locations of the thermomineral system. Special attention was dedicated to isotopic tracers and their role in the definition of the thermomineral waters??conceptual model, considering: (1) the δ¹⁸O fractionation gradient; (2) the mean isotopic composition of the thermomineral waters in the region; and (3) the estimation of snowmelt contribution as a source of groundwater recharge at Serra da Estrela. The recharge of the thermomineral aquifer takes place on the more permeable zones of the granitic massif, associated with the main tectonic structures, whereas the recharge of the shallow aquifers seems to take place mostly in the plateaus, although another part of the recharge may occur in the slopes of the Zêzere River valley.     

Hydrogeology and hydrogeochemistry of Günyüzü semi-arid basin (Eski?ehir, Central Anatolia)

Groundwater is often the only water source in semi-arid regions of Turkey. Günyüzü Basin, located in the Sakarya River basin, SW of Eskişehir, exhibits semi-arid conditions. The study area is composed of Paleozoic metamorphic rocks, Eocene granitic rocks, Neogene sedimentary rocks, and Quaternary alluvium. In the basin, Paleozoic Marbles are the main reservoir rocks for hot and cold water, bordered by impermeable diabases dykes at the sides and by impermeable granites and schists. Neogene-aged limestones, conglomerates and alluvium represent the other significant aquifers. Water samples chosen to exemplify the aquifer characteristics, were collected from springs and wells in both the dry and the wet seasons. The cation and anion permutation of the samples show that carbonates are the dominant lithology in the formation of chemical composition. δ¹⁸O (−11.2 to −8.9‰) and δ²H (−79 to −60‰) isotopic values show that all waters (thermal and cold) are meteoric in origin. The hydrological, hydrochemical, and isotopic properties of the waters reveal that there exist two main groups of groundwater systems; one of these is deep circulating, while the other one is shallow. Tritium values, 0–4 TU (Tritium Unit) indicate the presence of old, static water in these aquifer systems.     

Hydrogeochemical and isotopic characteristics of the Ilica geothermal system (Erzurum,Turkey)

In this paper, the hydrochemical isotopic characteristics of samples collected from geothermal springs in the Ilica geothermal field, Eastern Anatolia of Turkey, are examined and described. Low-temperature geothermal system of Ilica (Erzurum, Turkey) located along the Eastern Anatolian fault zone was investigated for hydrogeochemical and isotopic characteristics. The study of ionic and isotopic contents shows that the thermal water of Ilica is mainly, locally fed by groundwater, which changes chemically and isotopically during its circulation within the major fault zone reaching depths. The thermal spring has a temperature of 29–39 °C, with electrical conductivity ranging from 4,000 to 7,510 µS/cm and the thermal water is of Na–HCO₃–Cl water type. The chemical geothermometers applied in the Ilica geothermal waters yielded a maximum reservoir temperature of 142 °C according to the silica geothermometers. The thermal waters are undersaturated with respect to gypsum, anhydrite and halite, and oversaturated with respect to dolomite. The dolomite mineral possibly caused scaling when obtaining the thermal waters in the study area. According to the enthalpy chloride-mixing model, cold water to the thermal water-mixing ratio is changing between 69.8 and 75 %. The δ¹⁸O–δ²H compositions obviously indicate meteoric origin of the waters. Thermal water springs derived from continental precipitation falling on to higher elevations in the study area. The δ¹³C ratio for dissolved inorganic carbonate in the waters lies between 4.63 and 6.48 ‰. In low-temperature waters carbon is considered as originating from volcanic (mantle) CO₂.     

Hydrochemistry of a complex volcano-sedimentary aquifer using major ions and environmental isotopes data: Dalha basalts aquifer, southwest of Republic of Djibouti

In the Republic of Djibouti (Horn of Africa), fractured volcanic aquifers are the main water resources. The country undergoes an arid climate. Alluvial aquifers exist in the wadis (intermittent streams) valleys and, in relation with volcanic aquifers, form complex volcano-sedimentary systems. Due to increasing water demands, groundwater resources are overexploited and require a rigorous management. This paper is focused on the Dalha basalts aquifer, located in the Dikhil area (Southwest of Djibouti). This aquifer is of vital importance for this area. Hydrochemical data and isotopic tracers (¹⁸O and ²H) were used to identify factors and phenomena governing the groundwater’s mineralization. The Piper diagram shows complex water types. Results from multivariate statistical analyses highlight three water families according to their locations: (1) groundwater characterized by low ionic concentrations located at the wadis zones; (2) groundwater characterized by moderate salinity and (3) highly mineralized waters mainly flowing in the eastern and central part of the study area, in volcanic aquifers. Results from scatter plots, especially Na versus Cl and Br versus Cl, suggest that the origin of more saline waters is not from dissolution of halite. The δ¹⁸O and δ²H data indicate that the groundwater flowing in the alluvial aquifer is of meteoric origin and fast percolation of rainwater occurs in the volcanic aquifers. These findings provide a preliminary understanding of the overall functioning of this complex volcano-sedimentary system. Additional investigations (pumping tests, numerical modeling) are in progress to achieve a more comprehensive understanding of this system.     

Assessment of interconnection between surface water and groundwater in Sawa Lake area,southern Iraq,using stable isotope technique

Interaction between surface water represented by the Euphrates River, natural springs, and Sawa Lake with groundwater (11 wells) in southern Iraq was investigated in this study. Water samples were collected for hydrochemistry and stable isotope (²H and ¹⁸O) analysis. Sampling of water from determined stations (10 stations along the Euphrates, 3 springs, and Sawa Lake) were carried out during two stages; the first was in October 2013(dry season) and the second one was in March 2014 (wet season). The aim of the research is to assess the interaction of groundwater–surface water, which includes Al-Atshan River (branch of the Euphrates River), Sawa Lake, and the groundwater in the study area by using hydrochemistry and stable isotope techniques. The results indicate that surface waters have a different type of water from that of groundwater. In δ ²H and δ ¹⁸O diagrams, all groundwater, springs, and Sawa Lake waters are plotted below the Global Meteoric Water Line (GMWL) and the local meteoric water line (LMWL) indicating the influence of evaporation processes and seasonal variation. The LMWL deviates by a d-excess about +13.71 toward the East Mediterranean meteoric water line (EMWL) indicating that the origin of the vapor source is the Mediterranean Sea. The river water has different isotopic compositions from that of groundwater, springs, and Sawa Lake. The final conclusion is that there is no clear influence of the groundwater on the river water while there is an intermixing between the groundwater in the different locations in the study area.     

A multi-isotope approach (O,H, C,S, B and Sr) to understand the source of water and solutes in some the thermal springs from West Coast geothermal area,India

The West Coast belt, consisting of nearly 60 thermal springs, is one of the most diversified geothermal fields in India. The present work describes the multi-isotopic (O, H, C, S, B and Sr) characterization of thermal waters carried out in the Tural-Rajwadi geothermal field, situated in southern sector of the west coast geothermal area. The aim of this study is to delineate the origin of thermal water as well as to ascertain the sources of carbon, sulphur, boron and strontium dissolved in those thermal springs. The stable isotopes (δ²H and δ¹⁸O) and tritium data indicate that these thermal springs are not recently recharged rain water rather, it contains very old component of water. Oxygen-18 shift is observed due to rock-water interaction over a long period of time. Carbon isotopic composition of DIC points out to the silicate weathering with soil CO₂ coming from C₃ type of plants whereas δ³⁴S of dissolved sulphate confirms the marine origin of sulphate. This marine signature is basically derived from paleo-seawater possibly entrapped within the flows. Boron isotopic data reveals that both the seawater and rock dissolution are the sources of boron in the thermal waters whereas high ⁸⁷Sr/⁸⁶Sr ratios (0.7220–0.7512) of the thermal waters conclusively establishes that archean granitic basement is the predominant rock source of strontium, not the Deccan flood basalts. In addition, like strontium, concentrations of lithium, rubidium and caesium are also governed by the rock-water interaction. Thus, the combined use of this multi-isotope technique coupled with trace element concentrations proves to be an effective tool to establish the sources of solutes in the thermal water.     

Chemical and physical characteristics of springs discharging from regional flow systems of the carbonate-rock province of the Great Basin, western United States

The regional carbonate aquifer in the carbonate-rock province of the Great Basin, USA, covers thousands of square kilometers. It is a significant potential source of water for growth in this arid area. Few wells penetrate the carbonate aquifer, so information on water quantity and quality is derived in large part from ‘regional springs’ that discharge from regional interbasin flow systems. For this study, springs in the carbonate-rock province were sampled; their physical, chemical, and isotopic characteristics were compared to those of known regional springs to identify previously unrecognized regional waters using both examination of the data and multivariate statistical analysis. Criteria for comparison included temperature, discharge, ³H activity, carbon isotope values, and ratios of major and trace ions. Of the 18 springs selected for detailed chemical and isotopic sampling, five springs—Hot, Littlefield, Petrified, Saratoga, and Warm (a)—were identified as regional, and one (Monte Neva Hot) was identified as a possible regional spring. Regional springs provide an easy, low-cost means of investigating aquifer properties; identification of regional springs thus increases the ability to understand the regional carbonate aquifer. The techniques applied in this study can also be used in other regional aquifer systems with diverse and complex geology.     

Identifying sources of salinization using hydrochemical and isotopic techniques, Konarsiah, Iran

Konarsiah salt diapir is situated in the Simply Folded Zone of the Zagros Mountain, south Iran. Eight small permanent brine springs emerge from the Konarsiah salt body, with average total dissolved solids of 326.7 g/L. There are numerous brackish to saline springs emerging from the alluvial and karst aquifers adjacent to the diapir. Concerning emergence of Konarsiah diapir in the study area, halite dissolution is the most probable source of salinity in the adjacent aquifers. However, other sources including evaporation and deep brines through deep Mangerak Fault are possible. The water samples of the study area were classified based on their water-type, salinity, and the trend of the ions concentration curves. The result of this classification is in agreement with the hydrogeological setting of the study area. The hydrochemical and isotopic evaluations show that the groundwater samples are the result of mixing of four end members; Gachsaran sulfate water, Sarvak and Asmari carbonate fresh waters, and diapir brine. The molar ratios of Na/Cl, Li/Cl, Br/Cl, and SO₄/Cl; and isotopic signature of the mixed samples justify a groundwater mixing model for the aquifers adjacent to the salt diapir. The share of brine in each adjacent aquifer was calculated using Cl mass balance. In addition, concentrations of 34 trace elements were determined to characterize the diapir brine and to identify the possible tracers of salinity sources in the mixed water samples. B, Mn, Rb, Sr, Cs, Tl, and Te were identified as trace elements evidencing contact of groundwater with the salt diapir.     

Composition and origin of thermal waters in the Gulf of Suez area,Egypt

Thermal waters with discharge temperatures ranging from 32 to 70°C are being discharged along the Gulf of Suez (Egypt) from springs and shallow artesian wells. A comprehensive chemical and isotopic study of these waters supports previous suggestions that the waters are paleometeoric waters from the Nubian sandstone aquifer. The chemical and isotopic compositions of solutes indicate possible contributions from Tertiary sedimentary aquifer rocks and windblown deposits (marine aerosols and/or evaporite dust) in the recharge area. There is no chemical or isotopic evidence for mixing with Red Sea water. Gas effervescence from the Hammam Faraoun thermal water contains about 4% CH₄ (δ¹³C = −32.6‰) and 0.03% He having an isotopic ratio consistent with a mixture of crustal and magmatic He (³He/⁴He = 0.26 Re). Geothermometers for the thermal waters indicate maximum equilibration temperatures near 100°C. The waters could have been heated by percolation to a depth of several km along the regional geothermal gradient.     

Roles of hydrogeochemical evaluations in estimating protection zones of Koçpınar springs in Aksaray, central Anatolia, Turkey

The present study indicates estimation of protection zones of KoçpLnar springs in Aksaray area by means of hydrogeochemical methods. Relevant hydrogeochemical studies were carried out to achieve this objective. KoçpLnar springs emerge on strike-slip Hasanda<L fault set (HFS) along the Tuzgölü (Salt Lake) fault zone (TFZ) in central Anatolia. The outcrops of volcanic origin exhibit different hydrogeological properties in the study area. The hydrogeochemical evaluations of KoçpLnar springs represent good results about the available main groundwater flow systems that exist in this area. Marbles of Palaeozoic age form the main aquifer that recharges KoçpLnar springs. The CO₂ gas content of the spring waters is significantly high. Based on the ion concentrations, the water of this spring has mainly two hydrochemical facies: Ca-Mg-HCO₃ and Na-HCO₃. Although, the hydrochemical analyses showed that waters of these springs meet the drinking and irrigation water standards, the area around the springs is continuously being contaminated by both domestic and agricultural wastes. Therefore, detailed hydrogeological, hydrochemical and isotopic investigations were carried out to accurately estimate the protection zones of KoçpLnar springs. These studies showed that three main protection zones could be proposed against external pollution effects around the spring's area.     

Tufa and travertines of southern Italy: deep‐seated,fault‐related CO2 as the key control in precipitation

Continental carbonates of Quaternary age in southern Italy commonly exhibit the facies of calcareous tufa, often reported as related to shallow aquifers fed by meteoric waters and to organic processes. A close spatial relationship exists between the mappable tufa deposits and major Quaternary extensional faults. With respect to the Ca‐Mg‐HCO₃ composition of limestone aquifers’ springs, tufa‐depositing springs exhibit higher salinity and alkalinity, are slightly warmer, have lower pH and are enriched in SO₄ and CO₂. Their δ¹³C values are systematically positive and compatible with a deep‐seated carbon source. A clear input of soil‐derived organic carbon is indicated only for small, non‐mappable tufas deposited by perched springs. The dataset indicates that the large tufa deposits owe their origin to a supplementary source of CO₂ advected by degassing through active faults, as a necessary prerequisite for inducing a rise of total dissolved salts and alkalinity. Meteoric waters that have come from a shallow aquifer are able to precipitate only limited amount of carbonates.     

Isotopic composition of thermal waters in Chukotka

Twenty three groups of thermomineral springs in eastern Chukotka with the discharge temperature of 2 to 97°C and mineralization of 1.47 to 37.14 g/l are studied and compared with surface freshwater from their localities. The δD and δ¹⁸O values in surface waters vary from ?121.4 to ?89.5‰ and from ?16.4 to ?11.1‰, respectively, while respective values in thermomineral waters range from ?134.2 to ?92.5‰ and from ?17.6 to ?10.5‰. The δD value in surface waters decreases from the east to west, i.e., toward interior areas of the peninsula. Hydrothermal springs most depleted in deuterium (δD < ?120‰) are localized in the geodynamically active Kolyuchinskaya-Mechigmen Depression. According to the proposed formation model of Chukotka thermomineral waters, their observed chemical and isotopic characteristics could result from the mixing (in different proportions) of surface waters with the deep-sourced isotopically light mineralized component (δD ≈ ?138‰, δ¹⁸O ≈ ?19‰, M = 9.5?14.7 g/l). The latter originates most likely from subpermafrost waters subjected to slight cryogenic metamorphism.     

Mixing processes in hydrothermal spring systems and implications for interpreting geochemical data: a case study in the Cappadocia region of Turkey

Mixing is a dominant hydrogeological process in the hydrothermal spring system in the Cappadocia region of Turkey. All springs emerge along faults, which have the potential to transmit waters rapidly from great depths. However, mixing with shallow meteoric waters within the flow system results in uncertainty in the interpretation of geochemical results. The chemical compositions of cold and warm springs and geothermal waters are varied, but overall there is a trend from Ca–HCO₃ dominated to Na–Cl dominated. There is little difference in the seasonal ionic compositions of the hot springs, suggesting the waters are sourced from a well-mixed reservoir. Based on δ¹⁸O and δ²H concentrations, all waters are of meteoric origin with evidence of temperature equilibration with carbonate rocks and evaporation. Seasonal isotopic variability indicates that only a small proportion of late spring and summer precipitation forms recharge and that fresh meteoric waters move rapidly into the flow system and mix with thermal waters at depth. ³H and percent modern carbon (pmC) values reflect progressively longer groundwater pathways from cold to geothermal waters; however, mixing processes and the very high dissolved inorganic carbon (DIC) of the water samples preclude the use of either isotope to gain any insight on actual groundwater ages.     

The use of O,H, B,Sr and S isotopes for tracing the origin of dissolved boron in groundwater in Central Macedonia,Greece

The groundwater B concentration in Mesozoic karst, Neogene and alluvial aquifers in the West part of Chalkidiki province in Central Macedonia, Greece reaches 6.45 mg L⁻¹, which exceeds the limit of 1 mg L⁻¹, set by the European Union for drinking water. The high B contents have been detected in this area, not only near the shoreline, where seawater intrusion occurs, but also in the inland part of the basin. Multi isotope (²H, ¹⁸O, ³⁴S, ¹⁸O_(SO4), ¹¹B, ⁸⁷Sr/⁸⁶Sr) data from borehole and thermal water springs allow identification of the possible B sources. The B dissolved in groundwater in the Chalkidiki area is mainly geogenic. The low δ¹¹B values, 0–1‰, similar to those of thermal fluids from continental geothermal fields, and the low Cl/B ratio compared to seawater both indicate a geothermal origin for B and reflect deep circulation and interaction with igneous rocks. The ⁸⁷Sr/⁸⁶Sr ratio also indicates that the deep-aquifer granodiorite is the predominant rock source of Sr, while the shallow limestone unit has negligible effects on the dissolved Sr budget in these thermal karst waters which O and H isotopes show to be of meteoric origin. The main source of high B in borehole water is mainly mixing with B-rich geothermal water. The mixing between geothermal water and water from the Neogene aquifer is also reflected by isotopic contents of SO₄.     

Environmental isotopic study on the recharge and residence time of groundwater in the Heihe River Basin, northwestern China

The recharge and origin of groundwater and its residence time were studied using environmental isotopic measurements in samples from the Heihe River Basin, China. δ¹⁸O and δD values of both river water and groundwater were within the same ranges as those found in the alluvial fan zone, and lay slightly above the local meteoric water line (δD=6.87δ¹⁸O+3.54). This finding indicated that mountain rivers substantially and rapidly contribute to the water resources in the southern and northern sub-basins. δ¹⁸O and δD values of groundwater in the unconfined aquifers of these sub-basins were close to each other. There was evidence of enrichment of heavy isotopes in groundwater due to evaporation. The most pronounced increase in the δ¹⁸O value occurred in agricultural areas, reflecting the admixture of irrigation return flow. Tritium results in groundwater samples from the unconfined aquifers gave evidence for ongoing recharge, with mean residence times of: less than 36 years in the alluvial fan zone; about 12–16 years in agricultural areas; and about 26 years in the Ejina oasis. In contrast, groundwater in the confined aquifers had ¹⁴C ages between 0 and 10 ka BP.     

Hydrological characteristics of karstic groundwater in the northeast Viet Nam as studied by isotopic techniques

The stable water isotopic composition (δ²H and δ¹⁸Ο), tritium (³H) activity, dissolved organic carbon, alkalinity, as well as the composition of carbon 13 (δ¹³C) in dissolved inorganic carbon (DIC) of 36 water samples taken from 16 resurgences in the northeast provinces of Viet Nam in the dry (Mar 2008) and rainy (June 2008) seasons were analyzed to elucidate hydrological characteristics of the karstic aquifers in the area. The stable water isotopic composition of the water samples collected clearly demonstrated that the karstic groundwater in the region was recharged from the local meteorological water. The tritium activity in the samples was found to be in between 3 and 4 TU, falling in the range of the ³H activity in the local precipitation and thus meaning that the traveling of recharge water to the resurgences was very short. Concentrated and diffuse allogenic recharges seem to be important sources of karstic groundwater in the study region. Water in the karstic aquifers could be classified into three types as: (a) water from karstic areas with dense vegetation cover that causes DIC be depleted in carbon 13 (¹³δ<?12‰ vs. Pee Dee Belemnite standard of Vienna, VPDB); (b) water from karstic areas with poor vegetation cover that originates DIC with carbon 13 composition ranging from ?11 to ?12‰; and (c) surface water from lakes, springs and rivers that has DIC with enriched carbon 13 (δ¹³C >?10‰). This implies that there are several sources of carbon dioxide contributing to the DIC in water of the karstic aquifers in the study region. Among other potential sources, the atmospheric CO₂, CO₂ from carbonate rock dissolution, biomineralization of soil organic matters and plant roots respiration seem to be important sources of the DIC in the waters of this region. The results show high vulnerability towards anthropogenic contaminants of karstic groundwater in the study region.     

Rare earth elements,neodymium and strontium isotopic systematics in mineral waters: evidence from the Massif Central,France

Rare Earth Elements (REEs), and Sr and Nd isotope distributions, have been studied in mineralized waters from the Massif Central (France). The CO₂-rich springs are characterized by a neutral pH (6–7) associated with total dissolved solids (TDS) from 1 to 7 g l⁻¹. The waters result from the mixing of very mineralized water pools, thought to have equilibrated at a temperature of around 200°C with superficial waters. These two mineral water pools evidenced by Sr isotopes and dissolved REEs could reflect 2 different stages of water–rock interaction and an equilibrium with different mineral assemblages.The concentrations of individual dissolved REEs and total dissolved REEs (ΣREE), in the mineral waters examined, vary over several orders of magnitude but are not dependent on the main parameters of the waters (TDS, T°C, pH, Total Organic C). The dissolved REE concentrations presented as upper continental crust normalized patterns show HREE enrichment in most of the samples. The time evolution of REE patterns does not show significant fluctuations except in 1 borehole, located in the Limagne d’Allier area, which was sampled on 16 occasions over an 18 month period. Ten samples are HREE-enriched, whereas 6 samples show flat patterns.The aqueous speciation of REEs shows that CO²⁻₃ complexes dominate (>80%) over the free metal, F⁻, SO²⁻₄ and HCO⁻₃ complexes. The detailed speciation demonstrates that the fractionation of REEs (i.e. the HREE enrichment) in CO₂-rich and pH neutral fluids is due essentially to the predominance of the CO²⁻₃ complexes.The Sr isotopic composition of the mineral waters in the Massif Central shows different mixing processes; in the Cézallier area at least 3 end-member water types exist. The most dilute end-member is likely to originate as poorly mineralized waters with minimal groundwater circulation. Two other mineralized end-members are identified, although the link between the geographical location of spring outflow and the mixing proportion between the 2 end-members is not systematic. The range in ϵ_Nd(0) for mineralized waters in the Massif Central correlates well with that of the known parent rocks except for 4 springs. One way to explain the ϵ_Nd(0) in these instances is a contribution from drainage of volcanic rocks. The isotopic systematics help to constrain the hydrogeological models for this area.     

Geochemical constraint on origin and evolution of solutes in geothermal springs in western Yunnan,China

Geothermal resources are very rich in Yunnan, China. However, source of dissolved solutes in geothermal water and chemical evolution processes remain unclear. Geochemical and isotopic studies on geothermal springs and river waters were conducted in different petrological-tectonic units of western Yunnan, China. Geothermal waters contain Ca–HCO₃, Na–HCO₃, and Na (Ca)–SO₄ type, and demonstrate strong rock-related trace elemental distributions. Enhanced water–rock interaction increases the concentration of major and trace elements of geothermal waters. The chemical compositions of geothermal waters in the Rehai geothermal field are very complicated and different because of the magma chamber developed at the shallow depth in this area. In this geothermal field, neutral-alkaline geothermal waters with high Cl, B, Li, Rb Cs, As, Sb, and Tl contents and acid–sulfate waters with high Al, Mn, Fe, and Pb contents are both controlled by magma degassing and water–rock interaction. Geothermal waters from metamorphic, granite, and sedimentary regions (except in the Rehai area) exhibit varying B contents ranging from 3.31 mg/L to 4.49 mg/L, 0.23 mg/L to 1.24 mg/L, and <0.07 mg/L, respectively, and their corresponding δ¹¹B values range from −4.95‰ to −9.45‰, −2.57‰ to −8.85‰, and −4.02‰ to +0.06‰. The B contents of these geothermal waters are mainly controlled by leaching host rocks in the reservoir, and their δ¹¹B values usually decrease and achieve further equilibrium with its surrounding rocks, which can also be proven by the positive δ¹⁸O-shift. In addition to fluid–rock reactions, the geothermal waters from Rehai hot springs exhibit higher δ¹¹B values (−3.43‰ to +1.54‰) than those yielded from other areas because mixing with the magmatic fluids from the shallow magma. The highest δ¹¹B of steam–heated waters (pH 3.25) from the Zhenzhu spring in Rehai is caused by the fractionation induced by pH and the phase separation of coexisting steam and fluids. Given the strong water–rock interaction, some geothermal springs in western Yunnan show reservoir temperatures higher than 180 °C, which demonstrate potential for electricity generation and direct-use applications. The most potential geothermal field in western Yunnan is located in the Rehai area because of the heat transfer from the shallow magma chamber.