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In this paper a relatively inexpensive and efficient strategy for geothermal exploration by using geochemical prospecting tools to determine the placement of initial exploratory well(s) is proposed. The method involves categorizing the hierarchy of thermal manifestations from which the presence of a buried thermal anomaly can be identified in a given geothermal area, and then locating the centre of the thermal anomaly. This is done by using simple, easy to obtain data on the depth, temperature, and some common chemical parameters determined in wells of the shallow unconfined aquifer, from which thermal gradients can be calculated if the temperature of the local rainfall is known. The proposed strategy was applied by the author in Yemen; on a national scale in 2001–2006 ( Minissale et al., 2007 ), and a local scale in 2007–2010 in the Dhamar region ( Minissale et al., 2013 ). In the paper about the Dhamar area, briefly summarized here, how the placement of its first exploratory well was determined is described. The methodology proposed is particularly effective and convenient in developing countries, such as those located along the African Rift, e.g. Zambia and Malawi, where geothermal exploration is still in its infancy, and where waiting for expensive geophysical investigations might postpone the development of geothermal resources for decades.

By the year 2025 Yemen’s per capita water availability will be around 89 m3/year and the country will be highly water stressed. As a consequence, economic status of the farmers involved in qat (also referred as khat) cultivation, a product that supports 25% of the country’s GDP, will fall below the poverty line. With declining water table, the Mesozoic–Cenozoic aquifer of Yemen will be unable to support irrigation and the geothermal reservoir too will decline due to excessive withdrawal of water. A solution to this problem is to develop the geothermal resources around Damt and Dhamar to support desalination of the Red Sea and Gulf of Aden seawater to generate fresh water to contribute to the country’s food and energy security. Damt and Dhamar silicic volcanic sites have the potential to generate more than 134 × 106 kW of electricity. Fresh water generated through desalination using geothermal sources and wastewater treatment plants (WWTPs) will give the country food and energy security and reduce dependence on food imports.

This paper describes a data integration tool used to identify potentially undiscovered geothermal resources in the island of Sicily. The factors facilitating the recovery of exploitable geothermal energy were defined, and their spatial correlation established by Geographic Information System (GIS) models. By prioritizing favourable conditions using an Index Overly method, “favourability” maps of Sicily were obtained. The maps considered both geological and economic aspects, and energy recovery was considered for current technologies. Our approach and maps are useful for developing and planning local or national energy policies including geothermal energy.

Thermal springs lined up for about 350 km along the Western coast of Maharashtra, India, have been studied for major, minor, trace and rare earth elements, along with the boron isotope ratios for selected samples, to understand their evolution pattern. These alkaline springs have discharge temperatures varying from 40 to 72 degrees C. Based on the major ion composition, it is established that most of the thermal springs are of Na(Ca)-Cl or Ca(Na)Cl type, with a few of Na-Cl(SO4) type. Only one thermal spring at Rajapur is Na-HCO3 type behavior. Trace elements concentration vary significantly e.g., Li (19-386 ppb), B (104-1362 ppb), Sr (16-13560 ppb), Rb (13-220 ppb), Cs (0.75-44 ppb) and Ba (3-2077 ppb). Chondrite-normalized REE patterns indicate a pronounced 'Eu' anomaly probably due to the involvement of plagioclase, but the effect of temperature reaching more than 250 degrees C cannot be ruled out in case of some springs. First-time study of SHB isotope (range between 2.5 parts per thousand to 27.0 parts per thousand) of the West Coast thermal fluid suggests role of leaking marine sediments in their evolution. Water-rock interaction experiments with granite, basalt and diluted seawater at elevated temperatures and pressures have given an insight into the evolution of the thermal springs. Based on all the findings, a conceptual model has been prepared, which gives an overview of the evolution of the thermal springs.

In this study, the occurrence, chemical composition, origin and geothermal significance of thermal springs and fumaroles naturally discharging in the area located north of the Lake Abaya (western margin of the Main Ethiopian Rift, East Africa) are reviewed in relation with recent tectonics. All thermal springs showed a dominantly Na-HCO 3 composition, consistent with observations dating from at least 1972, and most of them displayed a narrow range of δD and δ 18 O isotopic compositions for water similar to regional meteoric origins. These observations suggest that water-rock interaction processes occur in all aquifers and dominate the contributions of water that actively circulate within thermal fluids, and also suggest a similar elevation of groundwater recharge throughout the study area. Most of the thermal springs are dominated by a CO 2 -rich gas phase and discharge along the active faults bordering the western edge of the Main Ethiopian Rift valley. The δ 13 C values of CO 2 and the 3 He/ 4 He isotopic ratios are consistent with the presence of mantle-derived fluids similar to what is observed in many other areas along the kinematically active African Rift, especially within Ethiopia. The application of geothermometric techniques in the liquid and the gas phases suggests the presence of a deep reservoir in which the fluids equilibrated at a maximum temperature of approximately 180 °C. Additionally, the presence of fumaroles at boiling temperatures and water/mud boiling pools in several places suggests that the geothermal reservoir is positioned at a relatively shallow depth and likely located in the western side of the study area. The analysis of data collected throughout time reveals that the waters of Lake Abaya have experienced an increase in salinity of 20% paralleled contemporaneously with a decrease in pH and δ 18 O and δD of water in the last 40 years; these changes do not appear to be related to climate change-induced increases in temperature or evaporation at the global scale.

The geochemistry of natural thermal fluids discharging in the Mondragone Plain has been investigated. Thermal spring emergences are located along the Tyrrhenian coast in two different areas: near Padule-S. Rocco (41 degrees 7.5'N 13 degrees 53.4'E) at the foot of Mt. Petrino, and near Levagnole (41 degrees 8.5'N 13 degrees 51.3'E) at the foot of Mt. Pizzuto. The water isotopic composition of both thermal discharges is lighter than the one of local shallow groundwater (delta O-18 congruent to -6.3 parts per thousand SMOW vs. congruent to -5.9 parts per thousand; delta D congruent to -40 parts per thousand SMOW vs. congruent to -36 parts per thousand, respectively) as a consequence of inland higher altitude of recharge by rainfall, suggesting that thermal water undergoes a deep and long flow-path before emerging along the coast. The chemical composition of the highest temperature samples of two areas points that fluids in the hydrothermal reservoir(s) interact with similar lithologies, since they are both hosted in the lower sedimentary carbonate formations of the Campanian-Latial Apennine succession. However, the two spring systems are different in terms of temperature and salinity (Levagnole: congruent to 50 degrees C and 8.9 g/L vs. Padule. congruent to 32 degrees C and 7.4 g/L, respectively). The higher salinity of Levagnole springs is due to a longer interaction with evaporite material embedded in Miocene sedimentary formations and to the eventual mixing, during rising, with fresh seawater close to the seashore. The chemical and isotopic composition of the free gases associated with the springs, again suggests a different source of the two hydrothermal systems. Comparing the He-3/He-4 measured ratios with other gas emissions located NE and SE of Mt. Massico-Roccamonfina alignment, it is evident that the Levagnole thermal springs are related to the northern Latial mantle wedge where the He-3/He-4 is about 0.5 R/Ra, whereas the Padule-S. Rocco springs, although being only 3.5 km south of Levagnole, are related to the Campanian mantle wedge where R/Ra is always >= 2.0. Such a difference in He-3/He-4 ratio in a very short distance, clearly, suggests a different source of the PaduleS. Rocco gas phase rising to the surface through the deep transpressive regional fault(s) system related to the NE-SW Ortona-Roccamonfina tectonic alignment.

Low-to-medium temperature fluid reservoirs hosted in carbonate rocks are some of the most promising and unknown geothermal systems. Western Sicily is considered a key exploration area. This paper illustrate a multidisciplinary and integrated review of the existing geological, geochemical and geophysical data, mainly acquired during oil and gas explorations since the 1950s, specifically re-analyzed for geothermal purposes, has led to understanding the western Sicily geothermal system as a whole, and to reconstructing the modalities and particular features of the deep fluid circulation within the regional reservoir. The data review suggests the presence of wide groundwater flow systems in the reservoir beneath impervious cap rocks. We identified the main recharge areas, reconstructed the temperature distribution at depth, recognized zones of convective geothermal flow, and depicted the main geothermal fluid flow paths within the reservoir. We believe that our reconstruction of geothermal fluid circulation is an example of the general behavior of low-to-medium enthalpy geothermal systems hosted in carbonate units on a regional scale. Due to the recent technological developments of binary plants, these systems have become more profitable, not only for geothermal direct uses but also for power production.

This paper deals with geothermal prospecting carried out in the Quaternary volcanic field of Dhamar, which is located almost in the centre of the main Oligo-Miocene basaltic trap plateau of Yemen. By applying geochemical and thermometric techniques in domestic wells producing water from the shallow unconfined aquifer in the area, which is prevalently hosted inside the Quaternary volcano-clastic material, a closed thermal anomaly associated with the Quaternary volcanic activity was well delineated. Although the aquifer(s) has a Ca–Na–HCO 3 composition, that is typical of shallow groundwater, there are several chemical anomalies in the hotter central area compared to typical aquifers: i) the p H is lower and, consequently, the calculated partial pressure of CO 2 in solution is higher, ii) the electrical conductivity is higher, iii) the total salinity is higher and iv) the fluoride ion concentration is higher. Such chemical anomalies in the hotter part of the aquifer do not seem to be generated by the rising and/or mixing of deep hydrothermal components rising into the shallow aquifer, but rather produced by enhanced water–rock interaction processes resulting from the higher temperature of the aquifer and its greater acidity. By applying some speculative calculations, based on the likely temperature of rainfall in the area and the depth and temperature of individual wells, the local thermal gradients in the area have been calculated. The thermal gradient varies from less than the average Earth gradient at the periphery of the delimitated thermal anomaly, to more than 250 °C/km, within an extensive area (exceeding 200 km 2 ) where the gradient is greater than 100/120 °C/km.

A multidisciplinary characterization of an active thermal spring in central Italy has been undertaken with the aim of (i) ascertaining whether microbiological activity plays a relevant role in hot-depositing travertines and (ii) establishing an experimental protocol able to identify similar effects in fossil travertines. Water, gas, and travertine samples were investigated by chemical (ICP/MS, SEM/EDS), physical (DTA–DTG), isotopic (δ18O, δD, and δ13C), mineralogical (XRPD), and spectroscopic (EPR) techniques. Twenty-four samples (three for each phase) were collected every 5 °C temperature drop, along a ∼100 m long artificial channel near Viterbo (Bullicame 3, Latium, central Italy). A microbiological characterization was carried out in parallel, sampling the channel every 10 °C temperature drop. The Bullicame 3 system is revealed to be composed of two markedly different subsystems: a water/gas interface, where a kinetically fast exchange allows equilibrium of components both in water and in gases; a solid/water interface, where travertine precipitation occurs, influenced by microbiological activity. A peculiar lattice shrinking of calcite was identified, as well as an anomalous value of the zero-field splitting parameter from the EPR measurements. The interpretation of these anomalies is confirmed by the identification of calcifying cyanobacteria throughout the channel path. Our results point out that microbiological activity can play a significant role in travertine deposition from hot springs. Furthermore, the proposed approach, representing a tool to identify crystal chemical remnants of past microbiological activity, could be applicable to fossil travertines.

This paper describes an indirect method to calculate the isotopic composition of rainfall by using the isotopic composition of karst springs fed by waters circulating in the most important regional aquifer of central Italy, i.e. the Mesozoic limestone sequence that forms the backbone of the Apennines. By using delta(18)O and delta D data and the delta(18)O (and/or delta D) average gradient for elevation, evaluated through the use of literature rainfall data and new measurements from a typical Alpine valley in northern Italy, the altitude of precipitation of their parent water has been re-calculated. Vertical descents of more than 2000 m, from recharge to discharge, have been assessed in some high flow-rate cold springs in the morphologically steep Adriatic sector of central Italy. A clear correlation between the vertical descents and more negative isotopic compositions at their relative emergence elevations is highlighted. In contrast, in the Tyrrhenian sector lower karstic drops (generally lower than 500 m) correlate with less negative isotopic composition of recharge areas. The delta(18)O iso-contour map of the "recalculated" parent rainfall in central Italy is more detailed than any possible isotopic map of rainfall made using pluviometers, unless large number of rainfall collectors were deployed on mountaintops. The data also show that the isotopic composition of rainfall depends on the source of the storm water. In particular, precipitation is isotopically heavier when originating in the Mediterranean Sea, and lighter when formed in the Atlantic Ocean. Consequently, the collision between air masses with such a different isotopic signature results in a relatively small latitudinal fractionation effect. The peninsular part of central Italy is very narrow, with several mountains and massifs more that 2000 m high, and any latitudinal variation in the isotopic composition between rainfall sourced in the Atlantic Ocean and in the Mediterranean Sea is much lower than that due to the isotopic fractionation due to elevation. (C) 2011 Elsevier Ltd. All rights reserved.

Summary In this paper the chemistry of major and trace elements and, for the first time, strontium isotopic ratios measured in running waters from the Arno River Basin (Tuscany, central-northern Italy) and thermal springs discharging in the same hydrographic system are presented and discussed. Classical graphical methods (e.g. mixing diagrams) have here been improved to identify, in a correct statistical sample space, extreme chemical compositions attributable to the action of geochemical processes and/or inherited from specific lithologies (namely contributions or components 1, 2 and 3) to be used in inverse modeling procedures, due to the absence of clear end-members. A linear least squares problem, with non-negativity constraints and distances, as required for compositional data (convex linear mixing) was solved by considering the contribution of the most discriminant variables given by the 87 Sr/ 86 Sr isotopic ratios and the concentration of Ca 2+ , Mg 2+ , Sr and Rb. Following such approach, it can be assumed ( p 2+ (Mg 2+ )– HCO 3 - radiogenic-rich ( 87 Sr/ 86 Sr = 0.71274; Rb/Sr = 0.039), represents a dominant feature at basin scale, with a weight ranging from 69% to 100%. Much lower percentages are related to component 2, represented by a Ca 2+ (Mg 2+ )– SO 4 2 - facies with intermediate 87 Sr/ 86 Sr (0.70874) and low Rb/Sr (2.8 × 10 −4 ) ratios and component 3, identified by Ca 2+ – HCO 3 - facies with less radiogenic 87 Sr/ 86 Sr (0.70827) and low Mg 2+ /Ca 2+ (0.011) ratios. These components are mainly dominated by the dissolution of evaporitic rocks and/or mixing with thermal waters in the southern part of the Arno River Basin and by dissolution of the carbonatic fraction, kinetically favored with respect to that of the silicatic minerals, in the upper reaches of the main course and its tributaries, respectively.

We describeand discuss the origin of short-term (hours) variations in the concentration of sulfur species (SO2 ,H 2S, and S8 0 ) of crater fumaroles discharging at different temperatures (up to 410 ◦ C) from five volcanic systems. Sulfur species can be investigated as an independent subsystem within the whole composition characterizing the fumarolic fluids, their chemical behavior being governed by similarlawsinvolcanic systems.The measureddataaretime dependentandshow regular oscillations whose amplitude is by far larger than the analytical error. The agreement between the theoretical and the measured concentrations of SO2, H2S, and S8 0 suggests that the formation of dissipative structures can explain the observed oscillations. Accordingly, the periodicity and the amplitude of the compositional oscillations werefoundtobe instrongrelationwiththeentropyexcess of the non-equilibrium systems under investigation. The results of our study suggest that the amplitude and magnitude of short-term natural (self-induced) fluctuations of the sulfur species caused by the presence of the dissipative structures,andtheircomparisonwiththecompositionalvariationsofothersubsystems, should be taken into serious account for geochemical monitoring purposes.

Carbonate aquifers in foreland tectonic settings can host important thermal springs although located in areas commonly not characterized by regional high heat flow values. In these cases, when thermal springs are located close or along the coastlines the subaerial and/or submarine thermal springs constitute the outflow of marine groundwater, flowing through localized fractures and karsitic rock-volumes. This is the case of springs occurring along the south-easternmost portion of the Apulia region (Southern Italy) where few sulphurous and warm waters (22–33 °C) outflow in partially submerged caves located along the shoreline, thus supplying the historical spas of Santa Cesarea Terme. Here, with the aim to define the origin of the thermal fluids and their deep path, we carried out the geo-structural survey of the area and detailed hydrogeological and geochemical analyses of the thermal spring fluids. In particular, the isotopes δ18O, δD, 13C in DIC, 34Ssulphate, 34Ssulphide, 3He/4He ratio and 13C in CO2 were used to define the origin of the thermal water and the recharge mechanism of the geothermal system while the isotopes 3H and 14C were determined for estimating the age of the thermal waters, resulting in older than roughly twenty thousands years BP. The results indicate that the thermal springs are fed by marine water, having reached Santa Cesarea Terme through a localized fracture network. This affects the evaporitic and carbonatic rocks that characterize the substratum of the Adriatic Sea in the offshore.

Most thermal springs of continental Yemen (about 65 emergences at 48 sampling sites) and a couple of fumaroles and boiling water pools have been sampled and analyzed for chemical and isotopic composition in the liquid phase and the associated free-gas phase. Whatever the emergence, all the water discharges have an isotopic signature of meteoric origin. Springs seeping out from high altitudes in the central volcanic plateau show a prevalent Na-HCO3-composition, clearly affected by an anomalous flux of deep CO2 deriving from active hydrothermal systems located in the Jurassic Amran Group limestone sequence and/or the Cretaceous Tawilah Group, likely underlying the 2000-3000 m thick volcanic suite. At lower elevations, CO2 also affects the composition of some springs emerging at the borders of the central volcanic plateau. Although mixing to a limited extent with organic CO2 infiltrating together with the meteoric recharge waters cannot be ruled out, all the CO2-rich gas samples have a δ13C-CO2 signature that falls in the range of mantle CO2 (-3 < δ13C < -7‰ V-PDB). The relatively high 3He/4He (1 < R/Ra < 3.2) ratios measured in all the CO2-rich springs and also some mixed N2-CO2 gas vents in the far east Hadramaut region support the presence of mantle magmas and related hydrothermal systems residing at the crust level in several areas of Yemen. This well agrees with the presence of Quaternary basaltic magmatic activity along the Gulf of Aden, as well as inside the central Yemen volcanic plateau. Presently, the thermal springs of Yemen are prevalently used for spas and/or bathing. Nevertheless, liquid- and gas-geothermometry and geological considerations suggest that there are at least three areas (Al Lisi, Al Makhaya and Damt) inside the Yemen volcanic plateau (around Dhamar) that may be promising prospects for the future development of geothermal energy in Yemen. Alternatively, they could be used as a source of energy for small-to-medium scale agriculture and/or industrial purposes. Moreover, most of the thermal water discharges have the chemical characteristics of potable waters and, in an arid country like Yemen, they have to be considered as long-term water supply resources if the country should face water shortages. © 2007 Elsevier Ltd. All rights reserved.

The determination of reduced S species in natural waters is particularly difficult due to their high instability and chemical and physical interferences in the current analytical methods. In this paper a new, rapid and reliable analytical procedure is presented, named the Cd–IC method, for their determination as ΣS2− via oxidation to SO 4 2 - after chemical trapping with an ammonia–cadmium solution that allows precipitation of all the reduced S species as CdS. The S2−–SO4 is analysed by ion-chromatography. The main advantages of this method are: low cost, high stability of CdS precipitate, absence of interferences, low detection limit (0.01 mg/L as SO4 for 10 mL of water) and low analytical error (about 5%). The proposed method has been applied to more than 100 water samples from different natural systems (water discharges and cold wells from volcanic and geothermal areas, crater lakes) in central-southern Italy.

An analytical approach, based on the electron paramagnetic resonance (EPR) spectroscopy of Mn(II) in travertines, has been developed in order to obtain relevant information about the local inhomogeneity of calcite and about the thermodynamic conditions which control the formation of travertine deposits. This information is crucial to constrain the precipitation of travertine under different geochemical contexts. An empirical correlation between the spectral features and the zero-field splitting (ZFS) interaction has been established through numerical simulations of EPR spectra. The variability of the investigated parameters and the applicability of the method have been tested on several travertines from Central Italy. (c) 2006 Elsevier Ltd. All rights reserved.

In the Buda Mts. (Hungary) several Pleistocene travertine outcrops are known. The subject of this paper is a stable isotope study on the Pleistocene travertine from Budakalasz that was deposited on the slope of Monalovac Hill of the Buda Mts. The principal goal of this work is to define the depositional environment and related implications by studying the petrographical and microfacies features and C and O stable isotope compositions. The Budakalasz travertine can be divided into two stratigraphic units. The lower part of the studied sections (approx. 15 m thick) consists of massive limestone, which represents a "smooth-slope" facies and has mean d13C and d18O values of 2.21‰ and -11.1‰ relative to V-PDB, respectively. Microbial shrub structures were also recognized in the lower part of the section, showing slightly higher d13C values (2.6-2.7‰) relative to the other samples. The upper unit of the sections is composed of what was originally calcareous mud. The studied samples have low d13C values (~1.8‰)...

Chemical (major and trace elements) and isotopic compositions (dD and d 18 O in waters and d 13 Ci n CO 2 and 3 He/ 4 He in gases) of natural thermal (11) and cold (39) fluids (spring waters and gases) discharging from a tectonic window of Mesozoic limestones in central Italy, have proved to be the result of mixing processes inside the limestone formations. The limestones provide a preferential route for subsurface fluid migration and they gather both descending cold, Ca-HCO3, B-depleted groundwaters and rising convective Ca-SO4(HCO3), CO2-saturated, B-rich thermal waters. Atmospherically-derived descending gas components (N2, Ne, He), dissolved in rainfall that infiltrates the limestone system mix with N2, Ne, He-depleted hot rising waters. Boron in the liquid phase and N2 and Ne in the gas phase are the most useful elements to trace the mixing process. The deeper gas samples recognised in the area are associated with the hotter waters emerging in the area. In spite of being depleted in Ne and He and light hydrocarbons they have the higher measured 3 He/ 4 He ratios, suggesting a contribution of mantle 3 He to the gas phase. This contrasts with deep circulation in the crust which would lead to increased concentration of 4 He in the deeper gases. Paradoxically, there is more relative concentration of 4 He in the more air-contaminated gas samples than in the deeper gas samples. A similar paradox exists when the d 13 Co f CO 2 in the deeper gas samples is considered. The shallower air-contaminated gas samples, although they should be affected by the addition of soil- 13 C depleted organic C, have d 13 Ci n CO 2 more positive than the deeper gas samples recognized. Since any deep hydrothermal source of CO2 should generate CO2 with more positive values of d 13 C than those measured at surface, a multiple (single) calcite precipitation process from hydrothermal solutions, with C isotopic fractionation along the rising path inside the Mesozoic limestone formations, is proposed. # 2002 Elsevier Science Ltd. All rights reserved.

Chemical and isotopic characteristics of natural gas and thermal water discharges from the western back-arc Tyrrhenian Sea across the Apennine thrust-belt to the Po Valley and Adriatic coast foredeep basins in the Northern Apennines (central-northern Italy) reveal a large-scale fluid motion in the upper crust, both vertically and horizontally. On the basis of gas compositions, two different domains of rising fluids have been distinguished: (1) CO2-rich, He-poor, 3He/4He-high domain in the western peri-Tyrrhenian extensional sector; (2) CH4-rich, He-rich, 3He/4He-low domain in the eastern Adriatic compressional sector. Such gases, rising from various depths, are crossed by a huge lateral N2-rich water flow, in the peri-Tyrrhenian sector, of Ca–SO4(HCO3) meteoric-derived waters that move in a regional wide aquifer hosted in a quite thick Mesozoic carbonate series. Morphologically, the CO2 vents consist of mud basins with high gas-rate emission, where the rising fluids move upwards through diatremes. On the other hand, CH4 emissions seep out from typical mud volcanoes with a reduced gas flow-rate, where the fluid motion is likely related to saline diapir extrusions, and the methane is mostly carried to the surface by the associated mud. The two rising mechanisms described locate southwest and northeast of the Apennine watershed respectively. From a seismic point of view the CH4 domain in the thrust-belt and foredeep areas is characterized by a large number of earthquakes, indirectly pointing to a different rheological behavior of the terrains with respect to the more internal peri-Tyrrhenian area. Owing to the quite high thermal gradient of the latter, the boundary of the brittle–ductile crust in the peri-Tyrrhenian sector can be located at a

The Damt thermal springs (40-45 degrees C), flowing through travertine deposits, belong to the Na-HCO3 type of water, and have higher pCO(2) (from -1.18 to -0.58 = PCO2 from 0.07 to 0.26 atm) relative to cold Ca-SO4-(Cl) groundwaters. The cold waters have pCO(2) ranging from -1.86 to -2.50 (=PCO2 from 0.014 to 0.0035 atm). The chemical composition of the cold springs is controlled by evaporite deposits present in the Tawilah sandstone and Amran limestone formations, while simple crustal dissolution, coupled with CO2-rich fluid-rock interaction control the chemical signature of the hot spring waters. The temperature of the feeding system, based on the K-2/Mg geothermometer, varies between 80 and 120 degrees C. Damt thermal springs appear to be related to a 10,000 year-old volcanic activity that led to the appearance of several craters in the area. (C) 1999 CNR. . .

More than 5 800 chemical analyses on water samples collected during 1987–1995 from 528 monitoring wells located in the southernmost part of the Po Valley (Emilia-Romagna region, northern Italy), one of the most urbanized, industrialized and agriculturally developed areas of Italy, have been processed. The analysis of data showed that: (1) waters are discharging from both confined and unconfined aquifers; (2) the water in the unconfined aquifer(s) is Ca(Mg)-HCO3 in composition while confined ones are Na-Cl and/or Na-(HCO3); (3) both confined and unconfined aquifer samples have δ18O and δD isotopic values of meteoric signature; (4) waters from both the aquifers are at least 40 years old; (5) the pumping rate has caused subsidence, particularly where the aquifer(s) is (are) unconfined; (6) the unconfined aquifer(s) is exposed to the risk of NO3 pollution; (7) considering the present "pressure" (i.e. pumping rate) on this natural environment by human activity, care must be taken in the future to preserve this "strategic" resource.

In this paper a strategy is presented for geothermal prospecting in developing countries that brings to locate the first exploratory geothermal well by using only geochemical parameters in fluid phase in natural thermal emergences. The paper suggests a hierarchy of natural thermal manifestations, briefly describing how to interpret the most relevant chemical parameters. Once the selection of the most promising area on a country, or a regional scale has been done, local investigation of the aquifer(s), especially in flat areas, in terms of: temperature and pH, and eventual tele-thermal parameters that can be analyzed in the field (e.g. NH4, SiO2, Hg) should bring to the delimitations of closed anomalies. If more parameters will converge to the same area(s), it is very likely that that place is the top of a buried thermal fluid convective high and likely the best place to drill the first exploratory well.

Thermal spring waters and associated gases discharging on several volcanic islands and on mainland Greece along the Hellenic Volcanic Arc (HVA) in the south Aegean sea have been investigated. The chemical characteristics of most of the spring waters suggest that the water in their feeding aquifers is largely derived from seawater that enters the hydrological circuits and mixes with local neutral low-salinity bicarbonate waters. There are however discrepancies between the simple theoretical mixing line between local meteoric waters and seawater, and the actual mixing line. This mixing is accompanied by partial Mg and SO4 precipitation to secondary minerals and by the addition of K, Ca, HCO3, B, NH4, and SiO2 to the solutions as a result of water-rock interaction processes. At Milos and Nisyros, where active hydrothermal systems are present at shallow depth, the silica content of the thermal springs is much higher than that of springs on the other islands and mainland Greece. This suggests higher thermal gradients at depth there, and the ascent of geothermal fluids to the surface along fractures prevalently located in the fumarolic fields within the latest eruptive centers and calderas. The fact that the springs are anomalously enriched in silica only at Milos and Nisyros suggests indirectly that, apart from Santorini island, where steam vents are present at the surface, the fluids from the active high-enthalpy geothermal systems do not rise to the surface anywhere else along the HVA. If present, they are well confined under thick and impermeable covers.

A computerized compilation of geochemical data, named DATA BASEment, has been created under MS-Windows and Macintosh platforms, within a research program of stratigraphic recontruction and correlation of the Paleozoic successions of the Northern Apennines. The database now contains about 600 geochemical analyses of rock samples, mainly obtained by the authors, and partly taken from the literature. Descriptions of formations and lithologies, major and trace element data, as well as other information (that is the availability of thin sections, mineralogical analyses, photos, etc.) are also included. The software package used (MS-FoxPro 2.5) allows for simple and powerful data management; the data files can be easily imported into mainframe systems for a multiuser access to the data, or integrated in geographical information systems. Studies in progress using DATA BASEment include: 1) the geochemical characterization of every Paleozoic formation of the Northern Apennines; 2) the application of multivariate statistical techniques (discriminant functions) to large sets of geochemical data, in order to compare units of uncertain stratigraphic position with others whose places are well known; 3) the study of distribution patterns of immobile trace elements, such as Sc, Y, Zr, and REE, from which the geodynamic environment of emplacement both for magmatic and for sedimentary protoliths can be inferred; 4) the study of trace element mobility and partition in magmatic and sedimentary rocks affected by low-to-medium grade metamorphism.

This paper presents new geochemical data of hydrocarbon-rich gases released from some mud volcanoes of Azerbaijan. Methane is considerably the most abundant component of all the sampled gases, which show δD-CH 4 and δ 13 C-CH 4 values likely related to a dominant thermogenic source. These gases are characterized by the presence of more than 20 different cyclic compounds with concentrations up to several μmol/mol. A similar gas composition has recently been found to characterize many mud volcanoes of the Northern Apennines and Sicily (Italy). The data of the Azerbaijan mud volcanoes corroborate the notion that cyclic compounds can be considered reliable tracers for hydrocarbon gas production at considerable depths and temperatures up to 120–150 °C, which correspond to a 6.5–8.3 km depth range assuming an average geothermal gradient of 18 °C/km. This depth interval is consistent with both the depth of potential source rocks imaged seismically beneath some mud volcanoes, and the results of previous estimates that used the 13 C/ 12 C values of methane and ethane. Such deep-sourced gases and material (fluidized clayey mass and rock fragments) ascend into the core of anticlines and accumulate at shallower reservoirs, where fold-parallel outer-arc faults or fold-orthogonal fractures may penetrate and transfer the fluids to the surface. Finally, the basically equivalent composition of the different hydrocarbon groups (C 2 –C 10 alkanes, aromatics and cyclic) determined in the gases sampled in both Azerbaijan and Italy manifests the lack of evident relationships between the chemistry of light hydrocarbons and the type of source rock.

A geochemical study of thermal springs, cold springs, stream waters and natural gas emissions has been carried out in the Campania region of southern Italy. This region hosts four Quaternary volcanic areas, and thermal springs and gas emissions occur in three of them. Most thermal springs discharge Na-Cl composition waters of connate origin derived from post-orogenic volcanic and sedimentary formations. Although high-enthalpy systems are present in two of the four volcanic areas, there appear to be no magmatic contributions to the thermal springs. Solute geothermometers are unreliable as spring waters are strongly affected by mixing with “shallow” brines before discharging. Thermal springs and gas emissions also occur in non-volcanic areas, where an extensive carbonate unit acts as a regional aquifer for cold, low-salinity, bicarbonate waters. Thermal features in these areas occur in fractured zones associated with active faults. Their compositions are determined only by the type of rock encountered by solutions before surface discharge. As in other areas of north-central Italy, the widespread occurrence of hot and cold CO2-rich springs, and gas emissions in both volcanic and non-volcanic zones, suggests a deep origin for the CO2.

Radon concentrations in soil gas were measured by the track-etch method in 60 shallow holes, each 70 cm deep and supported by a capped plastic tube, along several major faults in central California during 1975–1985. This set of data was analyzed to investigate the seasonal variability of soil-gas radon concentration in an area which has various geological conditions but similar climate. The results show several different patterns of seasonal variations, but all of which can be largely attributed to the water-saturation and moisture-retention characteristics of the shallow part of the soil. During the rainy winter and spring seasons, radon tended to be confined underground by the water-saturated surface soil which had much reduced gas permeability, while during the sunny summer and autumn seasons, it exhaled more readily as the soil became drier and more permeable. At several sites located on creeping faults, the radon-variation patterns changed with time, possibly because of disturbance of site condition by fault movement.

Chemical analyses of thermal springs and gas emissions on the volcanic island of Pantelleria, southern Italy, suggest the presence, at depth, of a Na Cl thermal aquifer near 100°C; 80–90% of the water in this aquifer is fed by rainfall and the remainder of the mixture is seawater. Chemical analyses of the gas emissions reveal that below this shallow aquifer, a deeper hydrothermal degassing system (150°C) may exist. Rising CO 2 causes alterations of the upper aquifer host rocks (mostly pantellerites), favors formation of Na HCO 3 type waters, and causes eventual rpecipitation of CaCO 3 and coprecipitation of MgCO 3 and silica. Comparison of the present chemical data with older data from the literature suggests that the shallow Pantelleria thermal aquifer has increased in salinity and decreased in temperature during the last 25 a. Both effects were apparently caused by increased flow of recent seawater into the system because of increased ground water abstraction in the northern part of the island.

A geochemical study on 26 thermal springs and 5 samples from thermal wells (t > 20°C), 19 cold springs, 11 cold gas pools, and 14 stream samples from the Tolfa and Sabatini Mountains volcanic district (about 1300 km2) has clarified their genesis and evolution. Meteoric waters infiltrate the more permeable exposed rocks (carbonates and/or volcanites) and percolate down into two main aquifers. One is deep and located in Mesozoic anhydritic-carbonate formations, and is the regional geothermal reservoir that feeds springs that emerge at the margins of the carbonate series (either exposed or barely covered); its waters display typical bicarbonate-sulfate alkaline earth composition. The other aquifer(s) is shallower, consisting of waters that circulate primarily in volcanic deposits. The chemical characteristics of these shallow waters are heavily influenced by lithology and by a gas phase, mainly CO2, originating at depth. Temperature estimates obtained with SiO2 and gas geothermometers, which seem to be the most reliable under these conditions, indicate the widespread occurrence of deep fluids at temperatures higher than 110°C under the area covered by the Sabatini volcanites. In some areas (Manziana, Trevignano, Nepi, and Cesano) the subsurface waters reach temperatures within the range characteristic of medium to high enthalpy systems (120–160°C).

Flow and chemical measurements have been made about once a month, and more frequently when required, since 1976 at two springs in Alum Rock Park in eastern San Jose, California, and since 1980 at two shallow wells in eastern Oakland in search of earthquake-related changes. All sites are on or near the Hayward Fault and are about 55 km apart. Temperature, electric conductivity, and water level or flow rate were measured in situ with portable instruments. Water samples were collected for later chemical and isotopic analyses in the laboratory. The measured flow rate at one of the springs showed a long-term decrease of about 40% since 1987, when a multi-year drought began in California. It also showed several increases that lasted a few days to a few months with amplitudes of 2.4 to 8.6 times the standard deviations above the background rate. Five of these increases were recorded shortly after nearby earthquakes of magnitude 5.0 or larger, and may have resulted from unclogging of the flow path and increase of permeability caused by strong seismic shaking. Two other flow increases were possibly induced by exceptionally heavy rainfalls. The water in both wells showed seasonal temperature and chemical variations, largely in response to rainfall. In 1980 the water also showed some clear chemical changes unrelated to rainfall that lasted a few months; these changes were followed by a magnitude 4 earthquake 37 km away. The chemical composition at one of the wells and at the springs also showed some longer-term variations that were not correlated with rainfall but possibly correlated with the five earthquakes mentioned above. These correlations suggest a common tectonic origin for the earthquakes and the anomalies. The last variation at the affected well occurred abruptly in 1989, shortly before a magnitude 5.0 earthquake 54 km away.

This paper reviews the isotopic 18O16O and D/H ratios reported in the literature for phreatic waters in the plain of Vulcano island off Sicily and condensates from high-temperature fumaroles at the top of the summit crater. The Vulcano phreatic waters have a rather high average annual temperature (greater than 30|dgC), but do not seem to be heated directly by mixture with condensates of fumarolic steam. They seem to originate from rainwater and to undergo high evaporation, particularly in summer, owing to high conductive heat flow in the island. By comparing the 18O16O and D/H ratios with Cl− (as HCl) content, it is estimated that 75% of the steam from the high-temperature fumaroles comes from seawater and 25% from low-salinity waters. The latter, however, do not seem to come directly from the shallow aquifer of Vulcano because the steam from the fumaroles does not contain radiogenic tritium. This mixing model and the lack of steam condensation in the Vulcano aquifer implies, indirectly, that there are no steam losses during the rise of deep fluids, and that some observed variations in the outlet temperatures without accompanying variations in the composition of the associated gas phase may be due to increased (or decreased) extent of fracturation in the volcanic edifice (as a result, for instance, of tectonic movements), which cause more (or less) vaporization of low-salinity fresh water into the volcanic ducts as well as faster (or slower) outflow of deep gases.

The thermal springs discharging in the Siena-Radicofani basin and the deep fluids within the geothermal systems of Piancastagnaio (Mt Amiata), Torre Alfina and Latera (Vulsini Mts) have a common origin. The chemical composition and evolution towards the low enthalpy of the springs as compared to the high enthalpy of the geothermal fluids are affected by both the structural setting of the region and the deep hydraulic conditions. Recharge of both the shallow thermal aquifer and the deep geothermal systems takes place in the outcrop areas of Mesozoic carbonate rocks, which constitute the main potential geothermal reservoir in central Italy. The waters of meteoric origin are heated at depth, as a consequence of anomalous heat flow in the region; these waters acquire a CO 2 -rich rising gas phase, equilibrate equilibrate with the reservoir rocks and, finally, assume their CaHCO 3 SO 4 composition. If these waters discharge rapidly from the border fault systems of the Siena-Radicofani basin they maintain their original composition. If, instead, they emerge from the inner faults of the graben, their temperature and dissolved solids increase so that they become NaCl with a high content of NH 4 , H 3 BO 3 and Li + . The chemical evolve towards high enthalpy. In this case the deep fluids again acquire an NaCl composition similar to carbonate reservoir is at a structural high, buried by both allochthonous flyschoid series (“Ligurids”) and by Neogenic pelitic formations, a slower recharge occurs in the reservoir, and consequently the fluids evolve towards high enthalpy. In this case the deep fluids again acquire an NaCl composition similar to that of the springs emerging inside the graben, since part of the reservoir recharge also occurs through the leakage of saline fossil waters stored within the Neogenic sedimentary formations at the border of the geothermal systems.

The chemical composition of the shallow and deep natural hydrothermal fluids discharged from the Larderello geothermal field (central Italy) is related to the main hydrological and lithological characteristics of the rock formations present in the reservoir as well as to the chemico-physical changes that have occurred in the geothermal field since exploitation for the production of electric energy started. The chemico-physical modifications caused by exploitation reveal that the fluids feeding the field may be partly derived from meteoric waters directly infiltrating through formations once considered cap rocks. Finally, the persistence of some of the field production parameters and the permanence of some natural manifestations seems to suggest that the reservoir is still at a stage where its resources are not yet fully assessed.

This paper reviews published geological, geophysical, petrological and geochemical data, together with reservoir engineering parameters, of the Larderello geothermal reservoir of southern Tuscany, Italy. Some theories are proposed on the deep origin, evolution in time, and natural state of this geothermal field prior to its exploitation. The interaction between the vapor-dominated reservoir and surrounding aquifers is discussed. Analysis of hydrogeochemical data suggests that meteoric waters from shallow external aquifers contribute little to the production of steam. The vapor-dominated system and the cold external aquifers are separated by areas of very low permeability where physical conditions change greatly over short distances. The presence and significance of liquid phases in the peripheral areas of the vapor-dominated reservoir are interpreted as being due to steam condensation. The latter is a consequence of: (a) low permeability conditions in the deep buried parts of the carbonate reservoir formations in the north-northwestern sector of the field, and (b) by the mixing of ascending superheated steam from depth with cold CaSO4 meteoric waters circulating in unconfined shallow aquifers within the outcrops of the carbonate reservoir formations in the south-southeastern parts of the field. The presence of steam below these liquid-dominated sectors of the reservoir seems possible. The limited natural recharge of the system, the constant steam production rate for geothermal power generation (3000 t h−1, since 1951), the persistence of natural thermal features, and the fact that reinjection has had little effect on the characteristics of the fluid discharged, seem to indicate a steady state for the Larderello field. The main contribution to production seems to be from superheated steam ascending from depth and the in situ evaporation of water stored in the small pores of the rocks present in Larderello, in a system that is much larger than the one known at present.

The large scale circulation of thermal waters in Italy is reviewed from both a chemical and an isotopic point of view. Two main areas are recognized: one in the Alpine region and the other in the central-southern Apennine region. The Alps are an area of very high hydraulic heads and low thermal gradients, where hot, deep-seated waters of meteoric origin rapidly reach the surface along active boundary fault systems. The Apennines, in contrast, are characterized by lower hydraulic heads and higher thermal gradients. All thermal springs in Italy (including those in active volcanic areas) originate essentially from meteoric waters, and most follow long pathways in Mesozoic carbonate-anhydritic aquifers before emerging, as indicated by relations among present hydrothermal activity in central-southern Italy, deep crustal structures and PCO2 content in thermal waters.

Injection of spent (cooled) thermal fluids began in the Tianjin geothermal district, north-eastern China, at the end of the 1990s. Well injectivities declined after 3-4 years because of self-sealing processes that reduced reservoir permeability. The study focuses on the factors that may have caused the observed decrease in permeability, using chemical and isotopic data on fluids (water and gas) and mineral phases collected from production and injection wells. The results of data processing and interpretation indicate that (1) it is very unlikely that calcite and silica precipitation is taking place in the reservoir; (2) the Fe- and Zn-rich mineral phases (e.g. sulfides, hydroxides and silicates) show positive saturation indexes; (3) SEM and XRD analyses of filtered material reveal that the latter mineral phases are common; (4) visual observation of casings and surface installations, and of corrosion products, suggests that a poor quality steel was used in their manufacture; (5) significant quantities of solids (e.g. quartz and feldspar crystals) are carried by the geothermal fluid; (6) seasonal changes in fluid composition lead to a reduction in casing corrosion during the summer. It was concluded that the decrease in injectivity in the Tianjin wells is caused only in part by the oxidation of casings, downhole pumps, and surface installations, triggered by free oxygen in the injected fluids; the utilization of better quality steels should drastically reduce this type of corrosion. Self-sealing of pores and fractures by reservoir formation solids and by the Fe-corrosion products suspended in the injected fluids seems to be a more important phenomenon, whose effect could be greatly reduced by installing filtering devices at all sites. © 2008 Elsevier Ltd. All rights reserved.

This paper presents the results of an extensive chemical and isotopic investigation on natural thermal and cold fluids (spring waters and associated gases) discharging throughout the main geological domains of Morocco. The chemical features of the thermal springs are mainly dependent on rock dissolution involving Triassic evaporite formations, producing either Na–Cl or Ca–SO4 composition, although mixing with shallower connate high-saline waters in Neogene post-orogenic sedimentary layers cannot be ruled out. Only in the Moroccan Meseta and Anti-Atlas domains have spring discharges probably undergone equilibration as a result of water–rock interaction in granites. Of the chemical and isotopic features of the gas seeps, He/He ratios and dC–CO2 values indicate the occurrence of a significant contribution of mantle-derived gas, especially at Oulmes (Moroccan Meseta) and Tinejdad-Erfoud (AntiAtlas), where associated waters are found to equilibrate at relatively high temperatures (c. 130 8C). These areas are also characterized by the presence of Pliocene to Quaternary basaltic volcanic rocks. Thermal discharges located along the Rif front and related to the NE–SW-oriented main strike-slip faults are associated with a CH4and/or N2-rich gas phase, derived respectively from a crustal or an atmospheric source. Some of them have significant contents of He that could indicate the rising of mantle fluids. Such a striking isotopic signature, which is not related to any recent volcanism visible at surface, is likely to be associated with cooling magma at depth related to transpressive fault systems. Similarly, in the northeastern area, the small, although significant, enrichment of He in the gas discharges seeping out along the Nekor seismic active fault and related to Pliocene–Quaternary basalts also suggests a deep-seated (magmatic) contribution. The distribution of thermal discharges is strongly related to the main active tectonic structures of Morocco. Moreover, this study indicates the presence of deep active tectonic structures in areas until now considered as stable. In particular, the NE–SW-trending Nekor fault may be part of a major system that extends to the Moroccan Meseta and into the Smaala–Oulmes fault system, thus emerging as a deep structure with crustal significance. The geochemical features of natural fluid discharges, such as cold and thermal springs and associated gas phases, have an important role in comprehending physico-chemical processes acting at depth (i.e. water–rock interaction, mixing) and in retrieving clues of deep-seated inputs (hydrothermal, metamorphic and magmatic). Fluid circulation in the shallow crust is particularly active at plate boundaries as a result of: (1) rugged morphology; (2) perturbations of the thermal vertical profiles induced by subduction slabs and the rise of mantle material, which favour convection of fluids (e.g. Oliver 1986, 1992; Sverjensky & Garven 1992); (3) active tectonics. Active faults provide open pathways for the circulation of such fluids (Barnes et al. 1978). When deep-sourced fluids pass through the shallow From: MORATTI, G. & CHALOUAN, A. (eds) 2006. Tectonics of the Western Mediterranean and North Africa. Geological Society, London, Special Publications, 262, 131–145. 0305-8719/06/$15.00 # The Geological Society of London 2006. crust, they may undergo, while rising to the surface, phase separation, mixing with meteoric-dominated aquifers and chemical re-equilibration. As a consequence, on a regional scale, their resulting chemical and isotopic composition at the surface is highly variable (e.g. Vaselli et al. 2002; Minissale 2004). A detailed study of the chemical characteristics of fluid discharges is worth while in Morocco, whose tectonic setting reflects a long-lived and complex evolution. Three Alpine chains (the Rif, the NE–SW-trending Middle Atlas and the east–west-oriented High Atlas) develop north of the Anti-Atlas Domain, which represents the northern limit of the African Shield, and are superimposed on the Hercynian belt, which largely crops out in the Moroccan Meseta (Fig. 1). The entire orogenic system is strongly affected by inherited structures, some of which are still active. In particular, field evidence supports the fact that the Middle Atlas Shear Zone is a complex active boundary (Bernini et al. 2000), as is also suggested by the many Pliocene– Quaternary basaltic outcrops, scattered from the Anti-Atlas to the Mediterranean coast (e.g. Maury et al. 2000). Fig. 1. Schematic geological map of Morocco (data from Carte Geologique du Maroc 1975, 1985, 1988, 1991; Suter 1980a,b; Baudin et al. 2001b; Bendkik 2004; Chenakeb 2004) and location of the water and gas sampling sites. In the inset, dotted isolines suggest the rough trend of heat flow density (Rimi & Lucazeau 1987). F. TASSI ET AL. 132

In the period 1998–2002 thermal spring discharges of Rincon de la Vieja volcano (NW Costa Rica) have been sampled and analyzed for major, trace and isotopic ( 18 O/ 16 O and D/H in waters and 3 He/ 4 He and 13 C/ 12 C in CO 2 in gases) composition. The boiling pools hosted inside the summit crater (Active Crater) are characterized by high contents of magmatic-related compounds (SO 2 , HCl and HF) that strongly affect the chemistry of the crater lake. These chemical features are not shown by the thermal discharges seeping out in the surrounding area of the volcano. Here, the shallow aquifer apparently masks any possible clues related to the magmatic system. This suggests that the fluid vents located inside the Active Crater are likely to represent the most appropriate sampling sites for geochemical surveillance purposes, although the high gas discharge rate from the lake may occasionally prevent any fluid sampling. Alternatively, as already suggested by recent studies on the behavior of light hydrocarbons in different volcanic environments, the compositional features of the organic gas fraction in the more accessible outer flank thermal discharges could usefully be utilized, at least, to assess the thermodynamic conditions of the volcanic-hydrothermal system, since these compounds are affected by secondary processes only at limited extent.

The understanding of processes that give rise to travertine deposits is important. This is so because of its widespread use as decorative material, but more so in environmental studies due to the significance, by proxy, of travertine in climatology. In this paper, a multifrequency EPR spectroscopy study of the behaviour of an ubiquitary vicariant of Ca in calcite, Mn(II), is presented. EPR spectra were obtained from a natural sample at 9.5 (X-band), 95, 190, and 285 GHz, and interpreted through numerical simulation. An analysis of the distribution of the zero-field splitting interaction revealed the source of some unexpected spectral features in the width of the lines in the X-band. By contrast, the homogeneous broadening plays only a minor role. Moreover, field-dependent anisotropies of the Zeeman and hyperfine tensors were observed at higher frequency. On the basis of results garnered in this study, the ZFS interaction of Mn(II) has been ascribed to the microstructural anomalies of the Mn(II) distribution in calcite. This may be considered as the fingerprint of the physical–chemical conditions at the time of travertine deposition. As a consequence, X-band EPR spectroscopy represents a specific tool to investigate the genesis, and to check the homogeneity of Mn(II) distribution in travertines as well as in other calcite-based materials.

Most thermal spring discharges of Rajasthan and Gujarat in northwestern India have been sampled and analysed for major and trace elements in both the liquid and associated gas phase, and for O-18/O-16, D/H (in water), He-3/He-4 and C-13/C-12 in CO2 (in gas) isotopic ratios. Most thermal springs in Rajasthan are tightly associated to the several regional NE-SW strike-slip faults bordering NE-SW ridges formed by Archaean rocks at the contact with Quaternary alluvial and aeolian sedimentary deposits of the Rajasthan desert. Their Ca-HCO3 immature character and isotopic composition reveals: (1) meteoric origin, (2) relatively shallow circulation inside the crystalline Archaean formations, (3) very fast rise along faults, and (4) deep storage temperatures of the same order of magnitude as discharging temperatures (50-90degreesC). Thermal spring discharges in Gujarat are spread over a larger area than in Rajasthan and are associated both with the NNW-SSE fault systems bordering the Cambay basin and the ENE-WSW strike-slip fault systems in the Saurashtra province, west of the Cambay basin. Chemical and isotopic compositions of springs in both areas suggest a meteoric origin of deep thermal waters. They mix with fresh or fossil seawater entering the thermal paths of the spring systems through both the fault systems bordering the Cambay basin, as well as faults and fractures occurring inside the permeable Deccan Basalt Trap in the Saurashtra province. The associated gas phase, at all sampled sites, shows similar features: (1) it is dominated by the presence of atmospheric components (N-2 and Ar), (2) it has high crustal He-4 enrichment, (3) it shows crustal He-3/He-4 signature, (4) it has low CO2 concentration, and (5) the only analysed sample for C-13/C-12 isotopic ratio in CO2 suggests that CO2 has a strong, isotopically light organic imprint. All these features and chemical geothermometer estimates of spring waters suggest that any active deep hydrothermal system at the base of the Cambay basin (about 2000-3000 m) has low-to-medium enthalpy characteristics, with maximum deep temperature in the storage zone of about 150degreesC. In a regional overview, both thermal emergences of Rajasthan and Gujarat could be controlled by the counter-clockwise rotation of India. (C) 2003 Elsevier B.V. All rights reserved.

In the Tyrrhenian region of central Italy, late Quaternary fossil travertines are widespread along two major regional structures: the Tiber Valley and the Ancona–Anzio line. The origin and transport of spring waters from which travertines precipitate are elucidated by chemical and isotopic studies of the travertines and associated thermal springs and gas vents. There are consistent differences in the geochemical and isotopic signatures of thermal spring waters, gas vents and present and fossil travertines between east and west of the Tiber Valley. West of the Tiber Valley, δ13C of CO2 discharged from gas vents and δ13C of fossil travertines are higher than those to the east. To the west the travertines have higher strontium contents, and gases emitted from vents have higher 3He/4He ratios and lower N2 contents, than to the east. Fossil travertines to the west have characteristics typical of thermogene (thermal spring) origin, whereas those to the east have meteogene (low-temperature) characteristics (including abundant plant casts and organic impurities). The regional geochemical differences in travertines and fluid compositions across the Tiber Valley are interpreted with a model of regional fluid flow. The regional Mesozoic limestone aquifer is recharged in the main axis of the Apennine chain, and the groundwater flows westward and is discharged at springs. The travertine-precipitating waters east of the Tiber Valley have shallower flow paths than those to the west. Because of the comparatively short fluid flow paths and low (normal) heat flow, the groundwaters to the east of the Tiber Valley are cold and have CO2 isotopic signatures, indicating a significant biogenic contribution acquired from soils in the recharge area and limited deeply derived CO2. In contrast, spring waters west of the Tiber Valley have been conductively heated during transit in these high heat-flow areas and have incorporated a comparatively large quantity of CO2 derived from decarbonation of limestone. The elevated strontium content of the thermal spring water west of the Tiber Valley is attributed to deep circulation and dissolution of a Triassic evaporite unit that is stratigraphically beneath the Mesozoic limestone. U-series age dates of fossil travertines indicate three main periods of travertine formation (ka): 220–240, 120–140 and 60–70. Based on the regional flow model correlating travertine deposition at thermal springs and precipitation in the recharge area, we suggest that pluvial activity was enhanced during these periods. Our study suggests that travertines preserve a valuable record of paleofluid composition and paleoprecipitation and are thus useful for reconstructing paleohydrology and paleoclimate.

The chemical and isotopic composition of several thermal springs and associated gas phases in a large sector of central-western peninsular India has been investigated. Such springs have meteoric isotopic signature and emerge, after very well developed convective circulation at depth, along important tectonic structures such as the Son–Narmada–Tapti rift zone and the West Coast Fault. Chemical components in both gas and liquid phases and geothermometric estimations suggest that such springs are not related to the presence of any active hydrothermal systems at shallow depth in any of the studied areas. The hottest convective water emerges at Tattapani at near boiling point for water at atmospheric pressure (>90°C) in association with an N2-rich gas phase of clear meteoric signature. Since such fluids do not carry any corrosive components, they could be conveniently exploited for industrial purposes, such as drying processes. From a tectonic point of view, the presence of thermal emergences scattered in a wide area along geologically well defined structures, which also generate frequent moderate earthquakes, suggests that such structures are active. Although the isotopic composition of thermal springs points to a meteoric origin, their feeding aquifers are not topographically driven as in most active Alpine orogenic belts. The relative high quantity of total helium in the associated gas phase suggests also that they are really deep, old, long circulating waters. We propose for such waters the term ‘intracratonic thermal waters’ since the isotopic signature of He in the gas phase does not show any release of primordial 3He in any of the areas of spring emergence. Based on the quite low 3He/4He ratio in the gas phase we suggest also that, in spite of its morphological shape, the Narmada–Son–Tapti rift zone cutting the Indian subcontinent in two is more related to paleo-suture rather than to a mid-continental rift system, © Elsevier

In this context, it is worth studying their behaviors and isotopic compositions in the largely anthropized Seine River Basin. Elemental analysis indicated obvious Zn and Cu concentration increases in dissolved phase ( 200 mL). The protocol was proven to be reproducible, with no isotopic fractionation and an output ratio of about 100% (mean 866Zn for ten purification tests on standard solution is 0.005%o). No remaining interferences were observed for Zn and Cu after matrix separation. MC-ICP-MS measurements were carried out on 0.05N nitric acid solutions with Zn and Cu concentrations around 100xl0 "9. Instrumental mass discriminations were corrected statistically for each measurement session, using a method of internal reference element doped sample (addition of Zn standard for Cu measurements, and of Cu standard for Zn measurements) and standard bracketing. Repeated measurements of Zn and Cu AAS standards (Alfa Aesar, Johnson Matthey Company) during six months led to precisions of 0.06 and 0.02 (Is) for Zn and Cu, respectively. Preliminary results on the Seine samples showed light isotope enrichment in Paris (~66Zn= -4.89%o) compared to rain waters (~66Zn=-0.29%o) and basin headwaters (~66Zn=-0.8%o). Isotopic characterization of Zn and Cu in the various phases (dissolved, suspended, colloidal) provides us clues about both the sources of these metals and the geochemical and biochemical processes in the river water system.

The chemical and isotopic compositions of low-temperature mineral waters discharged over the Colli Albani region (south of Rome, Italy) are those of highly immature waters of essentially meteoric origin formed through absorption of gases emanating from greater depth, followed by cation leaching of country rock at shallow levels. The composition of the gases discharged points to the presence, at depth, of a CO2-producing high temperature system in its waning stage. Low H2 and unsaturated hydrocarbon contents, as well as relative He, Ar and N2 contents indicate long residence time for the rising gas phase of the order of 1 Ma. On the basis of these findings, temperatures higher than 120°C appear unlikely to exist at shallow depth.