Hydrogen and oxygen isotope ratios in the waters of the Ngawha hydrothermal area,North Auckland

The ratios of D/H and O¹⁸/O¹⁶ in natural waters from streams, boreholes, soda springs, hot pools, ponds and larger bodies of water in the Ngawha hydrothermal area were determined. The results are considered in relation to the isotopic changes known to occur in water subjected to evaporation. Where applicable chemical and other work was also considered. It is assumed that stream water isotope composition is the mean value for the isotopic composition of meteoric waters. Measurements on waters taken from boreholes drilled to 65 feet and 350 feet and from the other water sources mentioned, indicate that they were of meteoric origin as judged by stream isotope composition. The waters from the soda springs appeared to be isotopically the same as the stream water, a finding consistent with the absence of evaporative surface. These borehole waters were similar but slightly different in O¹⁸ due probably to exchange between rock and water. Heavy isotope enrichment of the ponds and larger bodies of water appeared to be due to non-equilibrium evaporation at ambient temperature. The hot pools in the Ngawha springs area proper were enriched in the heavier isotopes probably due to non-equilibrium evaporation at the usual hot pool temperature of about 40°C and also to exchange of O¹⁸ between water and rock. The water from a further borehole drilled to approximately 2,000 feet appeared also to be of meteoric origin but was changed in O¹⁸ content to an extent consistent with the assumption that oxygen isotope exchange with rock had taken place at approximately 230°C. The results are used to illustrate possibilities for the use of oxygen and hydrogen isotope measurements in hydrothermal investigations.     

Hydrogeochemistry of thermal and mineral water springs of the Azores archipelago (Portugal)

Mineral and thermal water chemistry from the Azores archipelago was investigated in order to discriminate among hydrochemical facies and isotopic groups and identify the major geochemical processes that affect water composition. A systematic geochemical survey of mineral and thermal water chemistry was carried out, incorporating new data as well as results from the literature. The Azores are a volcanic archipelago consisting of nine islands and samples were collected at São Miguel, Graciosa, Faial, São Jorge, Pico and Flores islands. Hydrothermal manifestations show the effects of active volcanism on several islands. Discharges are mainly related to active Quaternary central volcanoes, of basaltic to trachytic composition, but also some springs are related to older dormant or extinct volcanoes.Multivariate analysis – principal component and cluster analysis – enables classification of water compositions into 4 groups and interpretation of processes affecting water compositions. Groups 1 and 2 discharge from perched-water bodies, and mostly correspond to Na–HCO₃ and Na–HCO₃–Cl type waters. These groups comprise of cold, thermal (27 °C–75 °C) and boiling waters (92.2 °C–93.2 °C), with a wide TDS range (77.3–27, 145.7 mg/L). Group 3 is made of samples of dominated Na–SO₄ from very acid boiling pools (pH range of 2.02–2.27) which are fed by steam-heated perched-water bodies. Group 4 is representative of springs from the basal aquifer system and corresponds to Na–Cl type fluids, with compositions dominated by seawater.Results are used to further develop a conceptual model characterizing the geochemical evolution of the studied waters. Mineral and thermal waters discharging from perched-water bodies are of meteoric origin and chemically evolve by absorption of magmatic volatiles (CO₂) and by a limited degree of rock leaching. Existing data also suggest mixture between cold waters and thermal water. Water chemistry from springs that discharge from the basal aquifer system evolves by mixing with seawater; although, processes such as absorption of magmatic volatiles (CO₂), rock leaching and mixture with hydrothermal waters are not excluded by the data because the actual composition of these waters deviates from that expected considering only conservative mixing between fresh and seawater.     

Isotopic composition of waters from the Danakil depression (Ethiopia)

During two expeditions in the Danakil depression (Ethiopia), water samples were collected from: (a) hot springs in Dallol, Salt Plain, in the north of the depression; (b) cold and hot springs around Lake Giulietti; and c) Lake Giulietti.The isotopic results indicate: the water from Dallol hot springs is enriched in¹⁸O by isotopic exchange with the rocks as has been observed in many other geothermal areas of the world; b) the isotopic composition of the Lake Giulietti water changes with depth, probably as a consequence of a seasonal stratification; c) the springs in the Lake Giulietti region contain waters which result from the mixing of local meteoric water with a brine, or with lake waters.     

Sr isotope diversity of hot spring and volcanic lake waters from Zao volcano,Japan

The ratio of ⁸⁷Sr/⁸⁶Sr was measured from different water samples of thermal/mineral (hot spring as well as crater lake) and meteoric origins, in order to specify the location and to verify the detailed model of a volcano-hydrothermal system beneath Zao volcano. The ratio showed a trimodal distribution for the case of thermal/mineral water: 0.7052–0.7053 (Type A, Zao hot spring), 0.7039–0.7043 (Type B, Okama crater lake and Shin-funkiko hot spring), and 0.7070–0.7073 (Type C, Gaga, Aone, and Togatta hot springs), respectively. However, in comparison, the ratio was found to be higher for meteoric waters (0.7077–0.7079). The water from the central volcanic edifice (Type B) was found to be similar to that of nearby volcanic rocks in their Sr isotopic ratio. This indicates that the Sr in water was derived from shallow volcanic rocks. The ⁸⁷Sr/⁸⁶Sr ratio for water from the Zao hot spring (Type A) was intermediate between those of the pre-Tertiary granitic and the Quaternary volcanic rocks, thus suggesting that the water had reacted with both volcanic and granitic rocks. The location of the vapor–liquid separation was determined as the boundary of the pre-Tertiary granitic and the Quaternary volcanic rocks by comparing the results of this strontium isotopic study with those of Kiyosu and Kurahashi [Kiyosu, Y., Kurahashi, M., 1984. Isotopic geochemistry of acid thermal waters and volcanic gases from Zao volcano in Japan. J. Volcanol. Geotherm. Res. 21, 313–331.].     

Fluid geochemistry of natural manifestations from the Southern Poroto–Rungwe hydrothermal system (Tanzania): Preliminary conceptual model

The South Poroto–Rungwe geothermal field, in the northern part of the Malawi rift, Tanzania divides in two main areas. The relatively high altitude northern area around the main Ngozi, Rungwe, Tukuyu and Kyejo volcanoes, is characterised by cold and gas-rich springs. In contrast, hot springs occur in the southern and low-altitude area between the Kyela and Livingstone faults. The isotopic signature of the almost stagnant, cold springs of the Northern district is clearly influenced by H₂O–CO_2(g) exchange as evidenced from negative oxygen-shifts in the order of few deltas permil. In contrast, the isotopic signature of waters discharged from the hot springs of the Southern district is markedly less affected by the H₂O–CO_2(g) interaction. This evidence is interpreted as an effect of the large, permanent outflow of these springs, which supports the hypothesis of a regional-scale recharge of the major thermal springs. Measurements of carbon isotope variations of the dissolved inorganic carbon of waters and CO_2(g) from the Northern and Southern springs support a model of CO_2(g)-driven reactivity all over the investigated area. Our combined chemical and isotopic results show that the composition of hot springs is consistent with a mixing between (i) cold surface fresh (SFW) and (ii) Deep Hot Mineralised (DHMW) Water, indicating that the deep-originated fluids also supply most of the aqueous species dissolved in the surface waters used as local potable water. Based on geothermometric approaches, the temperature of the deep hydrothermal system has been estimated to be higher than 110 °C up to 185 °C, in agreement with the geological and thermal setting of the Malawi rift basin. Geochemical data point to (i) a major upflow zone of geothermal fluids mixed with shallow meteoric waters in the Southern part of the province, and (ii) gas absorption phenomena in the small, perched aquifers of the Northern volcanic highlands.     

Implications of ground water chemistry and flow patterns for earthquake studies

Ground water can facilitate earthquake development and respond physically and chemically to tectonism. Thus, an understanding of ground water circulation in seismically active regions is important for earthquake prediction. To investigate the roles of ground water in the development and prediction of earthquakes, geological and hydrogeological monitoring was conducted in a seismogenic area in the Yanhuai Basin, China. This study used isotopic and hydrogeochemical methods to characterize ground water samples from six hot springs and two cold springs. The hydrochemical data and associated geological and geophysical data were used to identify possible relations between ground water circulation and seismically active structural features. The data for delta18O, deltaD, tritium, and 14C indicate ground water from hot springs is of meteoric origin with subsurface residence times of 50 to 30,320 years. The reservoir temperature and circulation depths of the hot ground water are 57 degrees C to 160 degrees C and 1600 to 5000 m, respectively, as estimated by quartz and chalcedony geothermometers and the geothermal gradient. Various possible origins of noble gases dissolved in the ground water also were evaluated, indicating mantle and deep crust sources consistent with tectonically active segments. A hard intercalated stratum, where small to moderate earthquakes frequently originate, is present between a deep (10 to 20 km), high-electrical conductivity layer and the zone of active ground water circulation. The ground water anomalies are closely related to the structural peculiarity of each monitoring point. These results could have implications for ground water and seismic studies in other seismogenic areas.     

Chemical and isotopic compositions of thermal springs,fumaroles and bubbling gases at Tacaná Volcano (Mexico–Guatemala): implications for volcanic surveillance

This study presents baseline data for future geochemical monitoring of the active Tacaná volcano–hydrothermal system (Mexico–Guatemala). Seven groups of thermal springs, related to a NW/SE-oriented fault scarp cutting the summit area (4,100m a.s.l.), discharge at the northwest foot of the volcano (1,500–2,000m a.s.l.); another one on the southern ends of Tacaná (La Calera). The near-neutral (pH from 5.8 to 6.9) thermal (T from 25.7°C to 63.0°C) HCO₃–SO₄ waters are thought to have formed by the absorption of a H₂S/SO₂–CO₂-enriched steam into a Cl-rich geothermal aquifer, afterwards mixed by Na/HCO₃-enriched meteoric waters originating from the higher elevations of the volcano as stated by the isotopic composition (δD and δ¹⁸O) of meteoric and spring waters. Boiling temperature fumaroles (89°C at ~3,600m a.s.l. NW of the summit), formed after the May 1986 phreatic explosion, emit isotopically light vapour (δD and δ¹⁸O as low as −128 and −19.9‰, respectively) resulting from steam separation from the summit aquifer. Fumarolic as well as bubbling gases at five springs are CO₂-dominated. The δ¹³C_CO2 for all gases show typical magmatic values of −3.6 ± 1.3‰ vs V-PDB. The large range in ³He/⁴He ratios for bubbling, dissolved and fumarolic gases [from 1.3 to 6.9 atmospheric ³He/⁴He ratio (R _A)] is ascribed to a different degree of near-surface boiling processes inside a heterogeneous aquifer at the contact between the volcanic edifice and the crystalline basement (⁴He source). Tacaná volcano offers a unique opportunity to give insight into shallow hydrothermal and deep magmatic processes affecting the CO₂/³He ratio of gases: bubbling springs with lower gas/water ratios show higher ³He/⁴He ratios and consequently lower CO₂/³He ratios (e.g. Zarco spring). Typical Central American CO₂/³He and ³He/⁴He ratios are found for the fumarolic Agua Caliente and Zarco gases (3.1 ± 1.6 × 10¹⁰ and 6.0 ± 0.9 R _A, respectively). The L/S (5.9 ± 0.5) and (L + S)/M ratios (9.2 ± 0.7) for the same gases are almost identical to the ones calculated for gases in El Salvador, suggesting an enhanced slab contribution as far as the northern extreme of the Central American Volcanic Arc, Tacaná.     

The hydrothermal system of Mendeleev Volcano,Kunashir Island,Kuril Islands: The geochemistry and the transport of magmatic components

This paper reports a detailed geochemical study of thermal occurrences as observed in the edifice and on the flanks of Mendeleev Volcano, Kunashir Island in August and September 2015. We showed that three main types of thermal water are discharged there (neutral chloride sodium, acid chloride sulfate, and acid sulfate types); these waters exhibit a zonality that is typical of volcano-hydrothermal island arc systems. Spontaneous and solfataric gases have relatively low ³He/⁴He ratios, ranging between 5.4Ra and 5.6Ra, and δ¹³C-CO₂ between –4.8‰ and –3.1‰, and contain a light isotope of carbon in methane (δ¹³C ≈ –40‰). Gas and isotope geothermometers yield relatively low temperatures around 200°C. The isotope compositions in all types of water are similar to that of local meteoric water. The distribution of microcomponents varies among different types. The isotope composition of dissolved Sr varies considerably, from 0.7034 as observed in Kunashir rocks on an average to 0.7052 in coastal springs, which may have resulted from admixtures of seawater. The total hydrothermal transport rates of magmatic Cl and SO₄, as observed for Mendeleev Volcano, are 7.8 t/d and 11.6 t/d, respectively. The natural outward transport of heat by the volcano’s hydrothermal system is estimated as 21 MW.     

The silica supersaturated waters of northern Evia and eastern central Greece

The area of north Evia and eastern central Greece is characterized by strong geomorphological contrast and is built up mainly of consolidated rocks. Unconsolidated young sediments of Pleistocene to Holocene age cover the valley and basin flats, forming the most productive aquifers in this area. However, two more types of aquifers can be distinguished within the consolidated rock area. The first one is associated with karstified limestones and the second with strongly tectonized ultramafic rocks. The schist–chert formation, with intercalations of shales and cherts, seals the ultramafic masses underneath. Surface and spring waters associated with ultramafic rocks in north Evia and eastern central Greece were studied. Two types of water can be distinguished: (1) high Mg²⁺ and SiO₂ , bicarbonate as the dominant anion, pH 7·4–9·2, temperature 9·5–16·3 °C, low TDS (total dissolved solutes) (459–1037 mg/l), found both in peridotite and serpentinite areas, classified as Mg–HCO₃ type; (2) high Ca²⁺, low Mg²⁺ and SiO₂ , hydroxyl ion as the major anion, pH 11·2, temperature 28 °C, very low TDS (122 mg/l), found in peridotite areas, classified as Ca–OH type. The studied waters are highly supersaturated with respect to quartz, amorphous silica, brucite and most low temperature magnesium silicates (antigorite, sepiolite, talc, etc.). These waters show relatively narrow SiO₂ concentration ranges and a trend parallel to the amorphous silica saturation surface. The silica supersaturated waters have the potential to precipitate silica and consequently could affect the people of the local communities that use it as drinking water, causing health problems (kidney stones). Copyright © 1999 John Wiley & Sons, Ltd.     

Chemical and isotopic investigation of warm springs associated with normal faults in Utah

Thermal springs associated with normal faults in Utah have been analyzed for major cations and anions, and oxygen and hydrogen isotopes. Springs with measured temperatures averaging greater than 40°C are characterized by Na + K- and SO₄ + Cl-rich waters containing 10³ to 10⁴ mg/l of dissolved solids. Lower temperature springs, averaging less than 40°C, are more enriched in Ca + Mg relative to Na + K. Chemical variations monitored through time in selected thermal springs are probably produced by mixing with non-thermal waters. During the summer months at times of maximum flow, selected hot springs exhibit their highest temperatures and maximum enrichments in most chemical constituents.Cation ratios and silica concentrations remain relatively constant through time for selected Utah thermal springs assuring the applicability of the geothermometer calculations regardless of the time of year. Geothermometer calculations utilizing either the quartz (no steam loss), chalcedony or Mg-corrected Na/K/Ca methods indicate that most thermal springs in Utah associated with normal faults have subsurface temperatures in the range of 25 to less than 120°C. This temperature range suggests fluid circulation is restricted to depths less than about three kilometers assuming an average thermal gradient of about 40°C/km.Thermodynamic calculations suggest that most thermal springs are oversaturated with respect to calcite, quartz, pyrophyllite, (Fe, Mg)-montmorillonite, microcline and hematite, and undersaturated with respect to anhydrite, gypsum, fluorite and anorthite. Chalcedony and cristobalite appear to be the only phases consistently at or near saturation in most waters. Theoretical evaluation of mixing on mineral saturation trends indicates that anhydrite and calcite become increasingly more undersaturated as cold, dilute groundwater mixes with a hot (150°C), NaCl-rich fluid. The evolution of these thermal waters issuing from faults appears to be one involving the dissolution of silicates such as feldspars and micas by CO₂-enriched groundwaters that become more reactive with increasing temperature and/or time. Solution compositions plotted on mineral equilibrium diagrams trend from product phases such as kaolinite or montmorillonite toward reactant phases dominated by alkali feldspars.Isotopic compositions indicate that these springs are of local surface origin, either meteoric (low TDS, < 5000 mg/l) or connate ground water (high TDS, > 5000 mg/l). Deviations from the meteoric water line are the result of rock-water isotopic exchange, mixing or evaporation. Fluid source regions and residence times of selected thermal spring systems (Red Hill, Thermo) have been evaluated through the use of a σ D-contour map of central and western Utah. Ages for waters in these areas range from about 13 years to over 500 years. These estimates are comparable to those made for low-temperature hydrothermal systems in Iceland.     

The stable isotope geochemistry of volcanic lakes, with examples from Indonesia

Stable isotope compositions (δD, δ¹⁸O and δ³⁴S) of volcanic lake waters, gas condensates and spring waters from Indonesia, Italy, Japan, and Russia were measured. The spring fluids and gas samples plot in a broad array between meteoric waters and local high-temperature volcanic gas compositions. The δD and δ¹⁸O data from volcanic lakes in East Indonesia plot in a concave band ranging from local meteoric waters to evaporated fluids to waters heavier than local high-temperature volcanic gases. We investigated isotopic fractionation processes in volcanic lakes at elevated temperatures with simultaneous mixing of meteoric waters and volcanic gases. An elevated lake water temperature gives enhanced kinetic isotope fractionation and changes in equilibrium fractionation factors, providing relatively flat isotope evolution curves in δ¹⁸O–δD diagrams. A numerical simulation model is used to derive the timescales of isotopic evolution of crater lakes as a function of atmospheric parameters, lake water temperature and fluxes of meteoric water, volcanic gas input, evaporation, and seepage losses. The same model is used to derive the flux magnitude of the Keli Mutu lakes in Indonesia. The calculated volcanic gas fluxes are of the same order as those derived from energy budget models or direct gas flux measurements in open craters (several 100 m³ volcanic water/day) and indicate a water residence time of 1–2 decades. The δ³⁴S data from the Keli Mutu lakes show a much wider range than those from gases and springs, which is probably related to the precipitation of sulfur in these acid brine lakes. The isotopic mass balance and S/Cl values suggest that about half of the sulfur input in the hottest Keli Mutu lake is converted into native sulfur.     

Evidence for a hypogene paleohydrogeological event at the prospective nuclear waste disposal site Yucca Mountain,Nevada, USA,revealed by the isotope composition of fluid-inclusion water

Secondary calcite residing in open cavities in the unsaturated zone of Yucca Mountain has long been interpreted as the result of downward infiltration of meteoric water through open fractures. In order to obtain information on the isotopic composition (δD and δ¹⁸O) of the mineral-forming water we studied fluid inclusions from this calcite. Water was extracted from inclusions by heated crushing and the δD values were measured using a continuous-flow isotope-ratio mass spectrometry method. The δ¹⁸O values were calculated from the δ¹⁸O values of the host calcite assuming isotopic equilibrium at the temperature of formation determined by fluid-inclusion microthermometry.The δD values measured in all samples range between ? 110 and ? 90‰, similar to Holocene meteoric water. Coupled δ¹⁸O–δD values plot significantly, 2 to 8‰, to the right of the meteoric water line. Among the various processes operating at the topographic surface and/or in the unsaturated zone only two processes, evaporation and water–rock exchange, could alter the isotope composition of percolating water. Our analysis indicates, however, that none of these processes could produce the observed large positive δ¹⁸O-shifts. The latter require isotopic interaction between mineral-forming fluid and host rock at elevated temperature (>100 °C), which is only possible in the deep-seated hydrothermal environment. The stable isotope data are difficult to reconcile with a meteoric origin of the water from which the secondary minerals at Yucca Mountain precipitated; instead they point to the deep-seated provenance of the mineral-forming waters and their introduction into the unsaturated zone from below, i.e. a hypogene origin.     

Geochemistry of waters in the Valley of Ten Thousand Smokes region, Alaska

Meteoric waters from cold springs and streams outside of the 1912 eruptive deposits filling the Valley of Ten Thousand Smokes (VTTS) and in the upper parts of the two major rivers draining the 1912 deposits have similar chemical trends. Thermal springs issue in the mid-valley area along a 300-m lateral section of ash-flow tuff, and range in temperature from 21 to 29.8°C in early summer and from 15 to 17°C in mid-summer. Concentrations of major and minor chemical constituents in the thermal waters are nearly identical regardless of temperature. Waters in the downvalley parts of the rivers draining the 1912 deposits are mainly mixtures of cold meteoric waters and thermal waters of which the mid-valley thermal spring waters are representative. The weathering reactions of cold waters with the 1912 deposits appear to have stabilized and add only subordinate amounts of chemical constituents to the rivers relative to those contributed by the thermal waters. Isotopic data indicate that the mid-valley thermal spring waters are meteoric, but data is inconclusive regarding the heat source. The thermal waters could be either from a shallow part of a hydrothermal system beneath the 1912 vent region or from an incompletely cooled, welded tuff lens deep in the 1912 ash-flow sheet of the upper River Lethe area.Bicarbonate-sulfate waters resulting from interaction of near-surface waters and the cooling 1953–1968 southwest Trident plug issue from thermal springs south of Katmai Pass and near Mageik Creek, although the Mageik Creek spring waters are from a well-established, more deeply circulating hydrothermal system. Katmai caldera lake waters are a result of acid gases from vigorous drowned fumaroles dissolving in lake waters composed of snowmelt and precipitation.     

Detecting Small Groundwater Discharge Springs Using Handheld Thermal Infrared Imagery

Ground‐based handheld thermal infrared imagery was used for the detection of small‐scale groundwater springs at the northwestern beach of Spiekeroog Island (northwest Germany). The surveys and in situ measurements of electric conductivity were carried out from shortly before to shortly after low tide along the low water line. Several brackish groundwater discharge springs with a diameter of 1–2 cm were observed along the beach at a distance of 2–3 m above the low water line. The high fresh water portion in the discharging water derives from the fresh water lens in the center of the island. During cold weather, the springs were identified by a significantly increased temperature (3–5 °C higher) and a lower electric conductivity (<10 mS/cm) in contrast to the surrounding sea water (1–2 °C, >30 mS/cm). During warmer weather conditions, an inverse temperature contrast was observed. The measurements confirm the applicability of thermal imagery for the detection of small‐scale groundwater discharge locations as an extension to the established method of aerial thermal scans and prove the existence of submarine groundwater seeps in porous systems. A ground‐based handheld thermal infrared imagery survey enables a precise installation of sampling devices as, for example, seepage meters.     

Chemical and stable isotopic models for boundary creek warm springs, southwestern Yellowstone National Park, Wyoming

Thermal springs of the Boundary Creek hydrothermal system in the southwestern part of Yellowstone Park outside the caldera boundary vary in chemical and isotopic composition, and temperature. The diversity may be accounted for by a combination of processes including boiling of a deep thermal water, mixing of the deep thermal water with cool meteoric water and/or with condensed steam or steam-heated meteoric water, and chemical reactions with surrounding rocks. Dissolved-silica, Na⁺, K⁺ and Ca²⁺ contents of the thermal springs could result from a thermal fluid with a temperature of 200 ± 20°C. Chloride-enthalpy and silica-enthalpy mixing models suggest mixing of 230°C, 220 mg/l Cl⁻ thermal water with cool, low-Cl⁻ components. A 350 to 390°C component with Cl⁻ ≥ 300 mg/l is possibly present in thermal springs inside the caldera but is not required to fit observed spring chemical and isotopic compositions. Irreversible mass transfer models in which a low-temperature water reacts with volcanic glass as it percolates downward and warms, can account for observed pH and dissolved-silica, K⁺, Na⁺, Ca²⁺ and Mg²⁺ concentrations, but produces insufficient Cl⁻ or F⁻ for measured concentrations in the warm springs. The ratio of a_Na/a_H, and Cl⁻ are best accounted for in mixing models. The water-rock interaction model fits compositions of acid-sulfate waters observed at Summit Lake and of low-Cl⁻ waters involved in mixing.The cold waters collected from southwestern Yellowstone Park have δD values ranging from −118 to −145 per mil and δ¹⁸O values of −15.9 to −19.4 per mil. Two samples from nearby Island Park have δD values of −112 and −114 per mil and δ¹⁸O values of −15.1 and −15.3 per mil. All samples of thermal water plot significantly to the right of the meteoric water line. The low Cl⁻ and variable δD values of the thermal waters indicate isotopic compositions are derived by extensive dilution with cold meteoric water and by steam separation on ascent to the surface. Many of the hot springs with higher δD values may contain in addition a significant amount of high-D, low-Cl⁻, acid-sulfate or steam-heated meteoric water. Mixing models, Cl⁻ content and isotopic compositions of thermal springs suggest that 30% or less of a deep thermal component is present. For example, the highest-temperature springs from Three Rivers, Silver Scarf and Upper Boundary Creek thermal areas contain up to 70% cool meteoric water and 30% hot water components, springs at Summit Lake and Middle Boundary Creek spring 57 are acid-sulfate or steam-heated meteoric water; springs 27 and 48 from Middle Boundary Creek and 49 from Mountain Ash contain in excess of 50% acid-sulfate water; and Three Rivers spring 46 and Phillips could result from mixing hot water with 55% cool meteoric water followed by mixing of acid-sulfate water. Extensive dilution by cool meteoric water increases the uncertainties in quantity and nature of the deep meteoric, thermal component.     

Time scale of hydrothermal water-rock reactions in Yellowstone National Park based on radium isotopes and radon

We have measured ²²⁴Ra (3.4 d), ²²⁸Ra (5.7 yr), and ²²⁶Ra (1620 yr) and chloride in hot spring waters from the Norris-Mammoth Corridor, Yellowstone National Park. Two characteristic cold-water components mix with the primary hydrothermal water: one for the travertine-depositing waters related to the Mammoth Hot Springs and the other for the sinter-depositing Norris Geyser Basin springs. The Mammoth Hot Springs water is a mixture of the primary hydrothermal fluid with meteoric waters flowing through the Madison Limestone, as shown by the systematic decrease of the (²²⁸Ra/²²⁶Ra) activity ratio proceeding northward. The Norris Geyser Basin springs are mixtures of primary hydrothermal water with different amounts of cold meteoric water with no modification of the primary hydrothermal (²²⁸Ra/²²⁶Ra) activity ratio. Using a solution and recoil model for radium isotope supply to the primary hydrothermal water, a mean water-rock reaction time prior to expansion at 350°C and supply to the surface is 540 years assuming that 250 g of water are involved in the release of the radium from one gram of rock. The maximum reaction time allowed by our model is 1150 years.     

Geochemical study on natural gas and water discharges in the Southern Latium (Italy): circulation, evolution of fluids and geothermal potential in the region

The waters discharged in Southern Latium (south of Rome) are mainly meteoric in origin. Two types of circulation occur in the region: one infiltrates the carbonate sediments outcropping in the area and emerges from fractures along their borders, the other consists of waters that infiltrate and circulate essentially within the Albani volcanic rocks.The first type produces either alkaline earth bicarbonate-sulfate waters or, if they mix with fossil marine waters or interact with recent marine sediments, alkaline-chloride waters (on the Pontina Plain). The chemistry of the waters produced by the second type of circulation (alkaline earth-bicarbonate or alkaline-bicarbonate) is strictly related to their gaseous phases, which consist for the most part of the CO₂ produced at depth.Silica and gas geothermometers, whose results correlate well, indicate that low enthalpy fluids (≤ 80°C) are present throughout the study area, with the exception of the northwestern part where medium enthalpy fluids (150°C) also appear.     

Geochemical and hydrogeological characterization of thermal springs in Western Sicily, Italy

Thermal and cold waters from Castellammare–Alcamo (Western Sicily-Italy) were collected between May 1994 and May 1995 and studied for their chemical and isotopic composition. During the same period, mean monthly samples of meteoric water were also collected and measured for their isotopic composition. The main purpose of this study was the characterization of the acquifers and, if possible, of their recharge areas. According to the results obtained, the acquifers were divided into three main groups: (a) selenitic waters, (b) cold carbonatic waters, and (c) deep thermal waters resulting from the mixing of the other two types. Besides a mixing process between carbonatic and selenitic waters, contamination processes of thermal waters by seawater take place during their ascent. The water temperature of the acquifer feeding the thermal springs was estimated by means of various geothermometers to range between 60°C and 97°C. Isotope data on rainwater samples show a wide seasonal variation of both δ and δD values. The fairly constant values of thermal waters through time and the lack of an apparent correlation with the isotopic values of rainwater suggest the existence of a deep circuit determining an almost complete homogenisation of the seasonal variations of the isotopic values.     

Noble gas anomalies related to high-intensity methane gas seeps in the Black Sea

Dissolved noble gases and tritium were analyzed at a series of high-intensity methane gas seeps in the Black Sea to study the transport and gas exchange induced by bubble-streams in the water column. These processes affect marine methane emissions to the atmosphere and are therefore relevant to climate warming. The seep areas investigated are located in the Dnepr paleo-delta, west of Crimea, and in the Sorokin Trough mud volcano area, south-east of Crimea. Noble gas concentration profiles at active seep sites revealed prominent anomalies compared to reference profiles that are unaffected by outgassing. Supersaturations of the light noble gases helium and neon observed relatively close to the sea floor are interpreted as effects of gas exchange between the water and the rising bubbles. Depletions of the heavy noble gases argon, krypton and xenon that were detected above an active, bubble-releasing mud volcano appear to be related to the injection of fluids depleted in noble gases that undergo vertical transport in the water column due to small density differences. In both cases, the noble gas anomalies clearly document seep-specific processes which are difficult to detect by other methods. Helium is generally enriched in the deep water of the Black Sea due to terrigenic input. Although exceptionally high helium concentrations observed in one seep area indicate a locally elevated helium flux, most of the seeps studied seem to be negligible sources of terrigenic helium. Noble gas analyses of sediment pore waters from the vicinity of a mud volcano showed large vertical gradients in helium concentrations. The helium isotope signature of the pore waters points to a crustal origin for helium, whereas the deep water of the Black Sea also contains a small mantle-type component.