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.     

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.     

Source and origin of active and fossil thermal spring systems,northern Upper Rhine Graben,Germany

Thermal water samples and related young and fossil mineralization from a geothermal system at the northern margin of the Upper Rhine Graben have been investigated by combining hydrochemistry with stable and Sr isotope geochemistry. Actively discharging thermal springs and mineralization are present in a structural zone that extends over at least 60 km along strike, with two of the main centers of hydrothermal activity being Wiesbaden and Bad Nauheim. This setting provides the rare opportunity to link the chemistry and isotopic signatures of modern thermal waters directly with fossil mineralization dating back to at least 500–800 ka. The fossil thermal spring mineralization can be classified into two major types: barite-(pyrite) fracture filling associated with laterally-extensive silicification; and barite, goethite and silica impregnation mineralization in Tertiary sediments. Additionally, carbonatic sinters occur around active springs. Strontium isotope and trace element data suggest that mixing of a hot (>100 °C), deep-sourced thermal water with cooler groundwater from shallow aquifers is responsible for present-day thermal spring discharge and fossil mineralization. The correlation between both Sr and S isotope ratios and the elevation of the barite mineralization relative to the present-day water table in Wiesbaden is explained by mixing of deep-sourced thermal water having high ⁸⁷Sr/⁸⁶Sr and low δ³⁴S with shallow groundwater of lower ⁸⁷Sr/⁸⁶Sr and higher δ³⁴S. The Sr isotope data demonstrate that the hot thermal waters originate from an aquifer in the Variscan crystalline basement at depths of 3–5 km. The S isotope data show that impregnation-type mineralization is strongly influenced by mixing with SO₄ that has high δ³⁴S values. The fracture style mineralization formed by cooling of the thermal waters, whereas impregnation-type mineralization precipitated by mixing with SO₄-rich groundwater percolating through the sediments.     

Using multiple chemical indicators to characterize and determine the age of groundwater from selected vents of the Silver Springs Group, central Florida, USA

The Silver Springs Group, Florida (USA), forms the headwaters of the Silver River and supports a diverse ecosystem. The 30 headwater springs divide into five subgroups based on chemistry. Five selected spring vents were sampled in 2007 to better understand the contaminant sources and groundwater flow system. Elevated nitrate-N concentrations (>0.8 mg/L) in the five spring vents likely originate from inorganic (fertilizers) and organic sources, based on nitrogen and oxygen isotope ratios of nitrate. Evidence for denitrification in the Lost River Boil spring includes enriched δ¹⁵N and δ¹⁸O, excess N₂ gas, and low dissolved O₂ concentrations (<0.5 mg/L). Multiple age-tracer data (SF₆, ³H, tritiogenic ³He) for the two uppermost springs (Mammoth East and Mammoth West) indicate a binary mixture dominated by recent recharge water (mean age 6–7 years, and 87–97% young water). Tracer data for the three downstream spring vents (Lost River Boil, Catfish Hotel-1, and Catfish Conventional Hall-1) indicate exponential mixtures with mean ages of 26–35 years. Contamination from non-atmospheric sources of CFCs and SF₅CF₃ precluded their use as age tracers here. Variations in chemistry were consistent with mean groundwater age, as nitrate-N and dissolved O₂ concentrations were higher in younger waters, and the Ca/Mg ratio decreased with increasing mean age.     

Mixing of hydrothermal water and groundwater near hot springs, Yellowstone National Park (USA): hydrology and geochemistry

Studies of hot springs have focused mainly on the properties of fluids and solids. Fewer studies focus on the relationship between the hot springs and groundwater/surface-water environments. The differences in temperature and dissolved solids between hot-spring water and typical surface water and groundwater allow interactions to be traced. Electromagnetic terrain (EMT) conductivity is a nonintrusive technique capable of mapping mixing zones between distinct subsurface waters. These interactions include zones of groundwater/surface-water exchange and groundwater mixing. Herein, hydrogeological techniques are compared with EMT conductivity to trace hot-spring discharge interactions with shallow groundwater and surface water. Potentiometric-surface and water-quality data determined the hydrogeochemistry of two thermally influenced areas in Yellowstone National Park, Wyoming (USA). Data from the sites revealed EMT conductivity contrasts that reflected the infiltration of conductive hot-spring discharge to local groundwater systems. The anomalies reflect higher temperatures and conductivity for Na⁺–Cl^?-rich hydrothermal fluids compared to the receiving groundwater. EMT conductivity results suggested hot springs are fed by conduits largely isolated from shallow groundwater; mixing of waters occurs after hot-spring discharge infiltrates groundwater from the surface and, generally, not by leakage in the subsurface. A model was proposed to explain the growth of sinter mounds.     

Hydrogeochemical evaluation of Umut geothermal field (SW Turkey)

Tekkehamam geothermal field is located in the South of Menderes Graben (Aegean region) and is one of the most important geothermal sites of Western Anatolia. Umut geothermal field is a part of the Tekkehamam field. This study was conducted in order to determine the origin and hydrogeochemical properties of the geothermal waters. For this purpose, sampling was done in order to check the chemistry of the water, and ¹⁸O, ²H isotope analyses done at four wells, nine natural springs and three cold water sources. According to the results of the chemical analysis, the geothermal waters were determined to be of Na + K-SO₄ type. Additionally, ¹⁴C and ³H analyses were done in selected well and spring waters for the purpose of age determination of groundwater; most of the waters were determined to be submodern. Geothermometer calculations show that the reservoir temperature for the Umut geothermal field ranges between 148 and 180 °C. Stable isotope results indicate that Umut geothermal waters are meteoric in origin. Mixing between shallow and deep waters is the dominant subsurface process that determines the physical and chemical character of the waters.     

The thermal springs of Jordan

The thermal springs alongside Wadi Araba, Dead Sea and Jordan valley, Jordan, were investigated and sampled in a comprehensive field study of 2 weeks. Conventional physicochemical properties were measured in situ; dissolved solids and isotopic composition were analyzed. Two main spring locations on the east side of the Dead Sea were mapped. It became evident, that the hottest springs are among the closest to prominent faults; some springs are controlled by gas lift. Jordan’s hot springs are described by means of a broad hydrochemical and physicochemical data set and several figures are presented. Based on their hydrochemistry, the thermal springs are classified into four thermal provinces. Water genesis is discussed. Several geothermometers are applied to estimate reservoir temperatures. Observed discharge rate, water temperature and isotopic composition are compared with data from the literature. Although discharge and water temperature are reported to be constant over the last decades, groundwater overexploitation led to a shift of the isotopic composition, what is documented for the first time in Jordan. Thus, the effect of groundwater mining on Jordan’s hot springs can be stated as a fact.     

Mixing of shallow and deep groundwater as indicated by the chemistry and age of karstic springs

Large karstic springs in east-central Florida, USA were studied using multi-tracer and geochemical modeling techniques to better understand groundwater flow paths and mixing of shallow and deep groundwater. Spring water types included Ca–HCO₃ (six), Na–Cl (four), and mixed (one). The evolution of water chemistry for Ca–HCO₃ spring waters was modeled by reactions of rainwater with soil organic matter, calcite, and dolomite under oxic conditions. The Na–Cl and mixed-type springs were modeled by reactions of either rainwater or Upper Floridan aquifer water with soil organic matter, calcite, and dolomite under oxic conditions and mixed with varying proportions of saline Lower Floridan aquifer water, which represented 4–53% of the total spring discharge. Multiple-tracer data—chlorofluorocarbon CFC-113, tritium (³H), helium-3 (³He_trit), sulfur hexafluoride (SF₆)—for four Ca–HCO₃ spring waters were consistent with binary mixing curves representing water recharged during 1980 or 1990 mixing with an older (recharged before 1940) tracer-free component. Young-water mixing fractions ranged from 0.3 to 0.7. Tracer concentration data for two Na–Cl spring waters appear to be consistent with binary mixtures of 1990 water with older water recharged in 1965 or 1975. Nitrate-N concentrations are inversely related to apparent ages of spring waters, which indicated that elevated nitrate-N concentrations were likely contributed from recent recharge.The online version of the original article can be found at     

Stable sulfur and oxygen isotope ratios of the Świętokrzyski National Park spring waters generated by natural and anthropogenic factors (south-central Poland)

This paper presents the results of an isotopic study of spring waters in ?wi?tokrzyski (Holy Cross Mountain) National Park (?NP), south-central Poland. The δ³⁴S_V-CDT and δ¹⁸O_V-SMOW of soluble sulfates (n = 40) varied from 0.5‰ to 18.1‰ and from 3.5‰ to 12.2‰, respectively. The average δ³⁴S values are closely similar to those of rainwater, soils and rocks (comprising scattered pyrite). This suggests that soluble sulfates in the springs originated from mixing of recent and historic deposition, sulfates derived from pyrite oxidation, and CS-mineralization in soils and debris. An additional anthropogenic sulfur input (inorganic fertilizer) occurs in the water of spring S-61 located in the ?wi?tokrzyski National Park buffer zone. The δ¹⁸O_V-SMOW of spring waters (n = 4) were in the range of −10.6‰ to −10.2‰ indicating that they are derived from vadose groundwater in ?NP. This was the first isotope study of spring waters in the national parks of Poland. It enabled the determination of sulfur pathways and discrimination between natural and anthropogenic sources of this element in a relatively pristine area.     

Mixing of shallow and deep groundwater as indicated by the chemistry and age of karstic springs

Large karstic springs in east-central Florida, USA were studied using multi-tracer and geochemical modeling techniques to better understand groundwater flow paths and mixing of shallow and deep groundwater. Spring water types included Ca–HCO₃ (six), Na–Cl (four), and mixed (one). The evolution of water chemistry for Ca–HCO₃ spring waters was modeled by reactions of rainwater with soil organic matter, calcite, and dolomite under oxic conditions. The Na–Cl and mixed-type springs were modeled by reactions of either rainwater or Upper Floridan aquifer water with soil organic matter, calcite, and dolomite under oxic conditions and mixed with varying proportions of saline Lower Floridan aquifer water, which represented 4–53% of the total spring discharge. Multiple-tracer data—chlorofluorocarbon CFC-113, tritium (³H), helium-3 (³He_trit), sulfur hexafluoride (SF₆)—for four Ca–HCO₃ spring waters were consistent with binary mixing curves representing water recharged during 1980 or 1990 mixing with an older (recharged before 1940) tracer-free component. Young-water mixing fractions ranged from 0.3 to 0.7. Tracer concentration data for two Na–Cl spring waters appear to be consistent with binary mixtures of 1990 water with older water recharged in 1965 or 1975. Nitrate-N concentrations are inversely related to apparent ages of spring waters, which indicated that elevated nitrate-N concentrations were likely contributed from recent recharge.An erratum to this article can be found at     

浅循环泉简析

泉按照出露原因通常可以分为侵蚀泉、接触泉、溢流泉（溢出泉）和断层泉等。根据泉眼和地下水循环深度（或径流位置）的相对关系,泉可以分为表层泉、浅循环泉和深循环泉。地下水在地下流动(循环)的最深处仍然高于泉口,这类泉称为浅循环泉。浅循环泉出露的位置并不在地形最低处,其补给来源主要是大气降水入渗,地下水受到重力作用自高处往低处流动,在地下径流的途径短、时间短,流量一般不大。浅循环泉通常是常温泉、淡水泉（也有咸泉和盐泉）,多是常年性泉,也有部分是季节性泉或暂时性泉。广西北竂岭北坡泉和云南顺荡井盐泉是典型的浅循环泉。     

Integration of geochemical and isotopic tracers for elucidating water sources and salinization of shallow aquifers in the sub-Saharan Drâa Basin,Morocco

In the arid sub-Saharan of southern Morocco, groundwater salinization poses a direct threat for agricultural production in six oases’ basins that are irrigated by water imported from the High Atlas Mountains. Here the geospatial distribution of salinity is evaluated in shallow groundwater, springs and surface waters in the Drâa Basin, integrating major and trace element geochemistry and isotopic tracers (O, H, Sr and B). The data show that water discharge from the High Atlas Mountains to the Upper section of the Drâa Basin is characterized by both low and high salinity, a distinctive low δ¹⁸O and δ²H composition (as low as −9‰ and −66‰, respectively), typical for meteoric water from high elevation, a ⁸⁷Sr/⁸⁶Sr range of 0.7078–0.7094, and δ¹¹B of 12–17‰. The Ca–Mg–HCO₃, Na–Cl–SO₄, and Ca–SO₄ compositions as well as the Br/Cl, ⁸⁷Sr/⁸⁶Sr, and δ¹¹B values of the saline water suggest dissolution of Lower Jurassic carbonates and evaporite rocks in the High Atlas Mountain catchment. Storage and evaporation of the imported water in a man-made open reservoir causes an enrichment of the stable isotope ratios with a δ¹⁸O/δ²H slope of <8 but no change in the Sr and B isotope fingerprints. Downstream from the reservoir, large salinity variations were documented in the shallow groundwater from the six Drâa oases, with systematically higher salinity in the three southern oases, up to 12,000 mg/L. The increase of the salinity is systematically associated with a decrease of the Br/Cl ratio, indicating that the main mechanism of groundwater salinization in the shallow aquifers in the Drâa oases is via salt dissolution (gypsum, halite) in the unsaturated zone. Investigation of shallow groundwater that flows to the northern Drâa oases revealed lower salinity (TDS of 500–4225) water that is characterized by depleted ¹⁸O and ²H (as low as −9‰ and −66‰, respectively) and higher ⁸⁷Sr/⁸⁶Sr ratios (∼0.7107–0.7115) relative to irrigation water and groundwater flow from the Upper Drâa Basin. This newly-discovered low-saline groundwater with a different isotopic imprint flows from the northeastern Anti-Atlas Jabel Saghro Mountains to the northern oases of the Lower Drâa Basin. This adjacent subsurface flow results in a wide range of Sr isotope ratios in the shallow oases groundwater (0.7084–0.7131) and appears to mitigate salinization in the three northern Drâa oases. In contrast, in the southern oases, the higher salinity suggests that this mitigation is not as affective and increasing salinization through cycles of water irrigation and salt dissolution appears inevitable.     

Investigating the hydrogeological properties of springs in a karstic aquifer in Dorfak region (Guilan Province,Iran)

Karstic aquifers are considered as the main sources of groundwater in the northeast of Rudbar, Iran. The present study was conducted to evaluate the hydrogeological properties of karstic springs in this region. For this purpose, saturation indices (SI values) were calculated using the geochemical PHREEQC model for a number of minerals in the groundwater in the karstic aquifer. Moreover, AqQA-RockWare software packages were used to prepare hydrogeochemical plots for the aquifer, using which the sources of the ions in the water were identified. The origin of bicarbonate, calcium, and magnesium ions in water was determined using chloro-alkaline indices. Moreover, through plotting a Piper diagram for spring water samples, it was discovered that water type of all springs is the Ca-HCO₃ type, confirming the karstic characteristic of springs in the area. A Durov diagram also suggests that the water composition of the springs is of the bicarbonate type with the dominant Ca cation, suggesting the calcareous effects of the region on the quality of groundwater and exhibiting a single source for the springs. The calculated saturation indices show that most of the water samples are undersaturated with respect to calcite, dolomite, and CO₂. The stable isotopes (δ¹⁸O and δ²H) and deuterium excess values were used to get information about transport pathways in groundwater, atmospheric moisture, and the degree of interaction between these reservoirs. The degree of karstification of the recharge area of the karst aquifer was determined to be 5.5 from an analysis of the hydrograph Sefidab Spring.     

Hydrogeological and hydrochemical investigation of groundwater using environmental isotopes (18O, 2H, 3H, 14C) and chemical tracers: a case study of the intermediate aquifer,Sfax, southeastern Tunisia

Major element concentrations and stable (δ¹⁸O and δ²H) and radiogenic (³H and ¹⁴C) isotopes in groundwater have proved useful tracers for understanding the geochemical processes that control groundwater mineralization and for identifying recharge sources in the semi-arid region of Sfax (southeastern Tunisia). Major-ion chemical data indicate that the origins of the salinity in the groundwater are the water–rock interactions, mainly the dissolution of evaporitic minerals, as well as the cation exchange with clay minerals. The δ¹⁸O and δ²H relationships suggest variations in groundwater recharge mechanisms. Strong evaporation during recharge with limited rapid water infiltration is evident in the groundwater of the intermediate aquifer. The mixing with old groundwater in some areas explains the low stable isotope values of some groundwater samples. Groundwaters from the intermediate aquifer are classified into two main water types: Ca-Na-SO₄ and Ca-Na-Cl-SO₄. The high nitrate concentrations suggest an anthropogenic source of nitrogen contamination caused by intensive agricultural activities in the area. The stable isotopic signatures reveal three water groups: non-evaporated waters that indicate recharge by recent infiltrated water; evaporated waters that are characterized by relatively enriched δ¹⁸O and δ²H contents; and mixed groundwater (old/recent) or ancient groundwater, characterized by their depleted isotopic composition. Tritium data support the existence of recent limited recharge; however, other low tritium values are indicative of pre-nuclear recharge and/or mixing between pre-nuclear and contemporaneous recharge. The carbon-14 activities indicate that the groundwaters were mostly recharged under different climatic conditions during the cooler periods of the late Pleistocene and Holocene.

     

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 stable isotope study of cave seepage waters

An isotope study (δ¹⁸O, δ²-H) of 62 samples of waters from both the interior of the Nerja cave (Málaga, Southern Spain) and the exterior sinkholes and springs at the site was carried out. Rainfall water in the study area was also studied. The mean value of seepage waters can be considered as the mean isotopic value of the precipitation waters of the area. The origin and aquifers of these different types of waters has also been studied, obtaining a clear meteoric origin both for the seepage waters and the waters from the wells and springs, but the aquifer of the latter is different, showing more negative isotopic values. This suggests that they could have mixed with waters from other aquifers which are either deeper or originate at other altitudes.     

A geochemical and stable isotope investigation of groundwater/surface-water interactions in the Velenje Basin,Slovenia

The geochemical and isotopic composition of surface waters and groundwater in the Velenje Basin, Slovenia, was investigated seasonally to determine the relationship between major aquifers and surface waters, water–rock reactions, relative ages of groundwater, and biogeochemical processes. Groundwater in the Triassic aquifer is dominated by HCO₃ ^–, Ca²⁺, Mg²⁺ and δ¹³C_DIC indicating degradation of soil organic matter and dissolution of carbonate minerals, similar to surface waters. In addition, groundwater in the Triassic aquifer has δ¹⁸O and δD values that plot near surface waters on the local and global meteoric water lines, and detectable tritium, likely reflecting recent (<50 years) recharge. In contrast, groundwater in the Pliocene aquifers is enriched in Mg²⁺, Na⁺, Ca²⁺, K⁺, and Si, and has high alkalinity and δ¹³C_DIC values, with low SO₄ ^2– and NO₃ ^– concentrations. These waters have likely been influenced by sulfate reduction and microbial methanogenesis associated with coal seams and dissolution of feldspars and Mg-rich clay minerals. Pliocene aquifer waters are also depleted in ¹⁸O and ²H, and have ³H concentrations near the detection limit, suggesting these waters are older, had a different recharge source, and have not mixed extensively with groundwater in the Triassic aquifer.     

Comparison of age distributions estimated from environmental tracers by using binary-dilution and numerical models of fractured and folded karst: Shenandoah Valley of Virginia and West Virginia, USA

Measured concentrations of environmental tracers in spring discharge from a karst aquifer in the Shenandoah Valley, USA, were used to refine a numerical groundwater flow model. The karst aquifer is folded and faulted carbonate bedrock dominated by diffuse flow along fractures. The numerical model represented bedrock structure and discrete features (fault zones and springs). Concentrations of ³H, ³He, ⁴He, and CFC-113 in spring discharge were interpreted as binary dilutions of young (0–8  years) water and old (tracer-free) water. Simulated mixtures of groundwater are derived from young water flowing along shallow paths, with the addition of old water flowing along deeper paths through the model domain that discharge to springs along fault zones. The simulated median age of young water discharged from springs (5.7  years) is slightly older than the median age estimated from ³H/³He data (4.4  years). The numerical model predicted a fraction of old water in spring discharge (0.07) that was half that determined by the binary-dilution model using the ³H/³He apparent age and ³H and CFC-113 data (0.14). This difference suggests that faults and lineaments are more numerous or extensive than those mapped and included in the numerical model.     

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.     

Determination of the origin of the Helvadere drinking springs by means of hydrochemical and isotopic techniques, Aksaray, Central Anatolia, Turkey

The main aquifer of the Helvadere springs that emerges on the strike-slip of the Hasanda?? fault set alongside the Tuzgölü (salt lake) fault zone, and trends in a NW–SE direction of Aksaray city, in the western part of Central Anatolia, is the exposed rocks of Hasanda?? which are volcanics that have distinct hydrogeological properties. The meteoric origin of the spring waters is deduced from hydrochemical and environmental isotope (¹⁸O, ²H, ³H) studies. The springs have high discharge (Q>100?l/s) and low ion concentrations because of fast circulation along the groundwater flow path in the aquifer. Furthermore, because it has Ca-Na-Mg-HCO₃ hydrochemical facies, it conforms to high standards of drinking and irrigation water.