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1.
The geochemical characteristics of hydrothermal waters from the Phlegraean Fields (P.F.) (Naples, Italy) were analysed for minor and trace elements, selectively mobilised in hydrothermal systems such as B, F, Hg, As, Pb and Tl.The water samples, collected from a shallow aquifer likely to be fed by deeper fluids, showed various geochemical features, resulting from the mixing of three components: (1) surface waters of meteoric origin; (2) hot deep waters deriving from water-rock interaction and including deep waters of marine origin; (3) magmatic fluids rising from the local magma chamber, lying a few kilometres below the town of Pozzuoli.This setting, although very complex, provides a reliable means of studying the distribution of the investigated trace elements. In particular, within the Phlegraean area, high contents of B (0.1-48 mg/l), F (0.5-8 mg/l), As (16-6050 μg/l) and Hg (0.7-232 μg/l) were observed. The levels of thallium in the springs close to Solfatara (about 7 μg/l) were in line with those normally recorded in hydrothermal areas, whereas high levels of this element (up to 23.3 μg/l) were identified in other wells of the study area. Lead (1.3 to 29.1 μg/l) appears to be anomalous with respect to its normal content in groundwater (about 1 μg/l), owing to the presence of high-density brines at depth, which enhance the solubility of Pb in volcanic rocks under hydrothermal conditions.The distribution of the investigated trace elements in the Phlegraean Fields thermal area is probably related to the different ascent pathways of the fluids. Clearly, apart from the influence exerted by anomalous thermal conditions, each element shows a different behaviour, depending on its geochemical affinity with mineral phases and as a consequence of the different enthalpy values, which determine ion partitioning in gaseous phases.Based on geochemical evidences and on the distribution of minor and trace elements, the source processes of the investigated hydrothermal waters were defined. Five main groups were identified: (1) acid sulphate waters, resulting from mixing of meteoric water with magmatic gases (mainly H2S); (2) high sulphate-chloride waters, from a deep reservoir located in the major upflow zone; (3) waters associated with significant degassing of magmatic CO2; (4) waters from a deep geothermal neutral chloride reservoir, resulting from heating of marine water modified by water-rock interaction processes; (5) cold waters from the inner area, influenced by low-temperature, water-rock interaction processes.  相似文献   

2.
The chemical composition and the isotopic characteristics of formation waters from the Siberian Platform are presented. The study involved samples of formation brines from depths ranging from 100 to ∼4000 m at five different sites covering a large area of the Siberian Platform. Four water types were identified. The two main water types that were found are: (1) Ca–Cl brines that are believed to be the residual of an evaporated paleoseawater; and (2) Na–Cl brines that are derived mainly from halite dissolution. The origin of a third group of highly saline samples was not determined. However, the chemical and isotopic characteristics of this group of samples suggest that they were produced by various complex scenarios such as metamorphism, water–rock interaction, permafrost freezing and mixing. The last group of samples represents fresh and brackish waters across the area.  相似文献   

3.
In the southern Upper Rhine Valley, groundwater has undergone intensive saline pollution caused by the infiltration of mining brines, a consequence of potash extraction carried out during the 20th century. Major and trace elements along with Sr and U isotopic ratios show that groundwater geochemical characteristics along the saline plumes cannot reflect conservative mixing between saline waters resulting from the dissolution of waste heaps and one or more unpolluted end-members. The results imply the occurrence of interactions between host rocks and polluted waters, and they suggest that cationic exchange mechanisms are the primary controlling process. A coupled hydrogeochemical model has been developed with the numerical code KIRMAT, which demonstrates that cationic exchange between alkalis from polluted waters and alkaline-earth elements from montmorillonite present in the host rock of the aquifer is the primary process controlling the geochemical evolution of the groundwater. The model requires only a small amount of montmorillonite (between 0.75% and 2.25%), which is in agreement with the observed mineralogical composition of the aquifer. The model also proves that a small contribution of calcite precipitation/dissolution takes places whereas other secondary mineral precipitation or host rock mineral dissolution do not play a significant role in the geochemical signature of the studied groundwater samples. Application of the model demonstrates that it is necessary to consider the pollution history to explain the important Cl, Na and Ca concentration modifications in groundwater samples taken over 2 km downstream of waste heaps. Additionally, the model shows that the rapidity of the cationic exchange reactions insures a reversibility of the cation fixation on clays in the aquifer.  相似文献   

4.
The complex geochemical interactions in the groundwater of the industrial area of Šalek Valley (Slovenia) between natural and anthropogenic fluids were studied by means of major (Ca, Mg, Na, K, HCO3 −, Cl− and SO4 2−) and trace elements’ (As , Cd, Cu, Pb, Zn, Hg, Se and V) abundances, geochemical classification and statistical analysis of data. Cation abundances indicate mixing between a dolomitic end-member and an evaporitic or geothermal end-member. Anion abundances indicate mixing between bicarbonate waters and either sulphate-enriched waters (suggesting hydrothermalism) or chlorine-rich waters. Principal component analysis (PCA) allowed the extraction of seven factors, which describe, respectively: water–rock interaction mainly on dolomitic rocks; redox conditions of water; Cd–Zn enrichment in chlorine-rich waters (probably from industrial wastes); hydrothermal conditions in waters close to major faults; Pb and Cu pollution; V and K enrichments, indicating their common organic source; the role of partial pressure of CO2 dissolved in water, which is highest in three wells with bubbling gases. Average underground discharge rates of solutes from the Valley range between 0.09 t/a (V) and 1.8 × 104 t/a (HCO3 −) and indicate how natural fluids can significantly contribute to the levels of elements in the environment, in addition to the amount of elements released by human activities.  相似文献   

5.
Geothermal resources are very rich in Yunnan, China. However, source of dissolved solutes in geothermal water and chemical evolution processes remain unclear. Geochemical and isotopic studies on geothermal springs and river waters were conducted in different petrological-tectonic units of western Yunnan, China. Geothermal waters contain Ca–HCO3, Na–HCO3, and Na (Ca)–SO4 type, and demonstrate strong rock-related trace elemental distributions. Enhanced water–rock interaction increases the concentration of major and trace elements of geothermal waters. The chemical compositions of geothermal waters in the Rehai geothermal field are very complicated and different because of the magma chamber developed at the shallow depth in this area. In this geothermal field, neutral-alkaline geothermal waters with high Cl, B, Li, Rb Cs, As, Sb, and Tl contents and acid–sulfate waters with high Al, Mn, Fe, and Pb contents are both controlled by magma degassing and water–rock interaction. Geothermal waters from metamorphic, granite, and sedimentary regions (except in the Rehai area) exhibit varying B contents ranging from 3.31 mg/L to 4.49 mg/L, 0.23 mg/L to 1.24 mg/L, and <0.07 mg/L, respectively, and their corresponding δ11B values range from −4.95‰ to −9.45‰, −2.57‰ to −8.85‰, and −4.02‰ to +0.06‰. The B contents of these geothermal waters are mainly controlled by leaching host rocks in the reservoir, and their δ11B values usually decrease and achieve further equilibrium with its surrounding rocks, which can also be proven by the positive δ18O-shift. In addition to fluid–rock reactions, the geothermal waters from Rehai hot springs exhibit higher δ11B values (−3.43‰ to +1.54‰) than those yielded from other areas because mixing with the magmatic fluids from the shallow magma. The highest δ11B of steam–heated waters (pH 3.25) from the Zhenzhu spring in Rehai is caused by the fractionation induced by pH and the phase separation of coexisting steam and fluids. Given the strong water–rock interaction, some geothermal springs in western Yunnan show reservoir temperatures higher than 180 °C, which demonstrate potential for electricity generation and direct-use applications. The most potential geothermal field in western Yunnan is located in the Rehai area because of the heat transfer from the shallow magma chamber.  相似文献   

6.
Geothermal fields distributed in the southern Tibet Plateau rifts such as Yangbajing - Dangxiong basin, and the Yaluzangbu suture are characterized by intensive hydrothermal activity and high enrichment of trace elements (e.g., Li, Rb, Cs, B and Br) in geothermal springs. However, the origin of these elements and their enrichment mechanisms in those geothermal waters remain unclear. This study presents data for the enriched elements, incompatible elements, and B and Sr isotopes, in the geothermal water in the Tibetan Plateau and compares them with some typical geothermal fields worldwide, in an attempt to provide new insights into the origin and mechanism of the enrichment of these trace elements. The results indicate that all geothermal water samples from the Tibetan Plateau show more negative δ11B values than those from local precipitation and rivers. Considering the wide existence of a high-conductivity zone in the middle or even upper-crust interpreted to correspond to re-melt magmatic fluids in the Tibet, the main sources of the typical chemical composition of geothermal waters in the Tibetan Plateau can be classified into two main types: residual magmatic fluids derived from crustal partial remelting and deep circulated groundwater modified by water–rock interactions. In particular, the possible source of magmatic fluids may play a more significant role for special geochemical compositions of geothermal water in the Tibet. Such resources are beneficial for the development and utilization of the geothermal water itself and also serve as a stable source for feeding the salt lake resources.  相似文献   

7.
《Applied Geochemistry》2005,20(10):1848-1856
Geochemical data on dissolved major, minor and trace constituents in groundwater samples from Xi-Sha coral islands (Paratas Islands) reveal the main processes responsible for their geochemical evolution. Multivariate statistical analysis indicates four sources of solutes: (1) seawater intrusion due to limited groundwater recharge; (2) leaching of heavy metals from imported granite soil; (3) leaching of toxic elements such as As due to guano-soil erosion and historical phosphatic guano mining; and (4) local and regional contamination characterized by high loadings of Cu, Ag and Hg. Although process 1 dominates the geochemical characteristics of the groundwater, process 4 indicates the significant role of anthropogenic impact by local (e.g., Cu) and regional (e.g., Hg) sources. Such contamination in groundwater will potentially impose adverse effects on the fragile ecosystem of the coral islands. It is necessary to monitor microorganisms associated with human feces in the nearshore water column as well as nutrient levels in coastal waters in order to further assess the impact of human activities on the ecosystem of these islands.  相似文献   

8.
The paper presents data on the specifics of the distributions of chemical elements in natural waters of the Kola North depending on the landscape–geochemical characteristics of the water catchment areas and aerotechnogenic pollution. The territory is subdivided into seven zones with different dominant rock types and typical landscapes. Lakes in the Kola region generally contain elevated concentrations of Cu, Ni, Co, Cr, V, Mo, U, Sb, Bi, Al, Fe, Mn, Sr, Li, Rb, Pb, Zn, Cd, La, and Ce. The waters of lakes in the influence zones of Cu–Ni mines are enriched in La, Ce, Sm, Gd, Pr, and Nd. In waterlogged landscapes, waters are enriched in certain trace elements because of their migration with humic acids. Technogenic acidic precipitation is proved to result in leaching of several elements, first of all Cd, Zn, and As (as well as other elements contained in rocks composing the water catchment areas) and their transfer into the waters.  相似文献   

9.
智利北部阿塔卡马富锂干盐湖地质   总被引：1，自引：0，他引：1  
智利北部阿塔卡马干盐湖位于一个内陆闭流构造盆地中，形成于晚第三纪。从中新世至今，全地内有强烈的火山作用。它是智利最大的干盐湖，也是世界上最大的富锂干盐湖之一。其盐矿物和卤水（包括锂）的物质来源如下；（１）火山活动形成的大量流纹岩质火山灰流凝灰岩，并伴随着大量地热水；（２）从火山岩中淋滤的可溶盐；（３）淋滤富锂粘土岩；（４）安第斯山东部湖和干盐湖的盐卤水沿着上新世（？）至第四纪形成的山前断裂流入阿塔卡马盆地，再通过沙漠环境的长期蒸发，因此盆地内积累了大量盐组分。  相似文献   

10.
 Sediment geochemistry of a shallow (6-m average) reservoir (Lake Waco) was evaluated for the spatial distribution of major and trace elements. Sixty bottom and core samples along a 21-km transect within the reservoir, 18 overbank sediment samples, and 8 rock types in the drainage area were collected and analyzed for major (Al, Ca, Fe) and trace elements (As, Ba, Cr, Cu, Hg, Mn, Ni, Pb, Sr, V, Zn). Elemental concentrations in the reservoir sediments closely correspond to concentrations in the regional rocks and represent a mixture of overbank sediment composition of the tributaries. Elemental concentrations were statistically regressed against Al concentrations in order to establish regional baseline levels and thereby distinguish natural from anthropogenic sources. Spatial geochemical trends, considered in terms of element-to-Al ratio versus V-to-Al ratio, relate to the natural and anthropogenic sources contributing to the elemental concentrations. The spatial elemental distribution in the reservoir, which receive sediments from two mineralogically contrasting basins, reflect textural and mineralogical transition within the reservoir and suggest a progressive mixing of sediment from the tributaries. The spatial elemental distribution and sediment texture suggest that the sediment-source, which determines the sediment-type, has a greater influence on the major- and trace-element distributions in shallow reservoir sediments than bathymetry. Received: 25 September 1997 · Accepted: 3 February 1998  相似文献   

11.
Molybdenum concentrations in Icelandic geothermal waters lie in the range 1–70 ppb. Warm waters and dilute high-temperature waters which contain high concentrations of sulphide are lowest in molybdenum. No correlation is otherwise observed between molybdenum concentrations and temperature. Surface waters and cold ground waters do not contain detectable molybdenum (<1 ppb). It seems likely that leaching rate is the prime factor in limiting molybdenum levels in these waters. Within individual geothermal fields molybdenum concentrations are either approximately constant or they vary regularly across the field. This regular variation may often be correlated with variations in other solute concentrations and subsurface temperatures and is taken to indicate a control of molybdenum mobility by a temperature dependent equilibrium. The evidence suggests that the solubility of molybdenite is responsible. Molybdenite has not been found in active geothermal systems in Iceland but is known to occur in some New Zealand geothermal systems and it has been identified in hydrothermally altered Tertiary basalt formations at Reydarártindur in southeast Iceland. Boiling and mixing with cold water leads to molybdenite undersaturation and thus these processes favour leaching of molybdenum from the rock. On the other hand, conductive cooling leads to supersaturation which favours removal of molybdenum from solution.  相似文献   

12.
This study presents data on the geochemical composition of boiling mud pools at the Mutnovsky volcano. The physicochemical characteristics of the pools and the concentrations of major, minor and trace elements in pool solutions vary widely. A comparison of the geochemical compositions of host rocks and solutions indicates that leaching from rocks is not the only source of chemicals in thermal solutions. Geophysical studies reveal the inner structure of thermal fields, which reflect the shapes of the underground reservoirs and feed channels. Using geophysical methods (electrical resistivity tomography and frequency domain investigations), it was shown that the vertical structure and complex geochemical zonation of the feed channels leads to a high contrast in the compositions of the mud solutions. These findings answer questions about the origin and composition of surface manifestations. To elucidate the mechanisms of solution formation, an attempt was made to describe the magmatic fluid evolution and the resulting mixing of waters by physical and mathematical models. The model illustrates fluid migration from a magma chamber to the surface. It is shown that the formation of brines corresponding to the mud pool composition is possible during secondary boiling.  相似文献   

13.
福州盆地地热水微量元素特征   总被引：2，自引：0，他引：2  
福州地热田是以燕山晚期侵入岩为主要热储层的中低温对流型地热系统.通过对福州盆地不同类型地下水的取样分析发现,福州盆地不同类型地下水中微量元素质量浓度变化关系较复杂.研究表明,地热水微量元素质量浓度主要受含水介质的岩性控制,也与地下水温度有关.对所检测的19个微量元素,除个别元素外,第四系孔隙水微量元素质量浓度均大于基岩裂隙水;Ga、Rb、Sb、Se、Sr、Tl元素质量浓度随水温的升高而增高.基岩裂隙热水与第四系孔隙水混合形成的第四系热水中,As、Cd、Cu、Mo、Pb、Sb、Se、Sr等元素质量浓度明显增高,说明在混合过程中这些元素又发生了溶解作用.根据地热水微量元素与盆地周围不同期次侵入岩体微量元素质量浓度的聚类分析,得出福州地热水形成的地球化学环境主要与福州岩体、魁岐岩体和文笔山岩体的岩性有关.地热水微量元素是地热水在形成过程中与这些岩体的岩石接触发生水-岩相互作用形成的.  相似文献   

14.
《Applied Geochemistry》2003,18(6):863-882
New geochemical data on dissolved major and minor constituents in 276 groundwater samples from Etna aquifers reveal the main processes responsible for their geochemical evolution and mineralisation. This topic is of particular interest in the light of the progressive depletion of water resources and groundwater quality in the area. Multivariate statistical analysis reveal 3 sources of solutes: (a) the leaching of the host basalt, driven by the dissolution of magma-derived CO2; (b) mixing processes with saline brines rising from the sedimentary basement below Etna; (c) contamination from agricultural and urban wastewaters. The last process, highlighted by increased concentrations of SO4, NO3, Ca, F and PO4, is more pronounced on the lower slopes of the volcanic edifice, associated with areas of high population and intensive agriculture. However, this study demonstrates that natural processes (a) and (b) are also very effective in producing highly mineralised waters, which in turn results in many constituents (B, V, Mg) exceeding maximum admissible concentrations for drinking water.  相似文献   

15.
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16.
In order to better understand the relative importance of hydrologic variation and anthropogenic disturbance and their complex interactions within the trace elemental geochemical cycle, water samples were collected monthly over 1 year in the Min River, eastern Tibetan Plateau, and analyzed for trace element composition. The dissolved trace elements exhibited different relationships with increasing discharge compared with major elements. The elements analyzed can be divided into three groups according to their behavior in response to changing discharge: (1) elements that showed weak positive correlation with discharge, e.g. Cu, V, and Ba; (2) elements that exhibited weak negative correlation with discharge, including Rb, Sr, Pb, Sb, Zn, Cr, Cd, and U; and (3) elements that displayed no significant correlation with variation in discharge, e.g. Ti, Fe, Co, Ni, and As. Cu was strongly affected by anthropogenic activities and flushed into the river with increasing discharge. Ba has a strong solubility in the terrestrial environment, dissolved quickly, and was released into the river. The positive relationship between V concentration and discharge may be attributed to secondary reactions, such as precipitation and adsorption on oxides and aluminosilicate clays. Conservative behavior had an impact on the geochemical behavior of Sr and Rb across hydrologic variation. Pb, Zn, Sb, Cd, and Cr underwent a mild dilution effect connected with anthropogenic activities. The chemostatic behavior of U was regulated by carbonate dissolution and biological uptake. In addition, higher temperatures enhanced biotic activities, affecting the concentrations of Fe and Ni. The relationship between power law slopes and coefficient of variation for discharge and solute concentration suggests that concentrations of trace elements vary significantly with increasing discharge compared with major elements. Silicate mineral weathering had less effect on the fluvial solutes with increasing discharge. Mining activity may exert an additional control on concentration–discharge dynamics of anthropogenic trace elements.  相似文献   

17.
The formation of natural cryogenic brines   总被引：1，自引：0，他引：1  
The source of salts in the Ca-chloridic, hypersaline brines (up to 190 g Cl L−1) occurring in crystalline basement rocks in the Canadian, Fennoscandian and Bohemian Shields and their evolution have been investigated and reported. The Cl-Br-Na relationship indicates that these waters have been concentrated from seawater, by freezing during glacial times. The Na/Cl ratio (0.25 to 0.35) in the more saline fluids is compatible with cooling down to −30°C, where the most saline waters have been concentrated by a factor of 25 to 30 relative to the parent seawater.The brines formed from seawater within cryogenic troughs, along the subarctic continental margins, around ice sheets. The depressions within which the brines formed are the cryogenic analogues of the classic, evaporitic lagoon. One million years suffice to saturate with brine a 2000km-radius by 1km-depth rock volume at an H2O removal rate of only 2.8 mm/yr. Density-induced brine migration on a continental scale takes place via fissures below the ice.Our calculations, that were performed on a hypothetical ice sheet with dimensions compatible with the Laurentide ice sheet, demonstrate that during 1m.y., a 60m thick cryogenic sediment section could have formed. However, the precipitated minerals (mirabilite and hydrohalite) are repeatedly dispersed by the advance and retreat of the ice sheet, dissolved by melt water-seawater mixtures, and eroded during postglacial uplift, leaving almost no trace in the geological record.The cryogenic brines formed intermittently during and between glacial periods. The repeating advance and retreat of the ice sheets exerted a major control on the direction and intensity of brine flow. The cryogenic concentration of seawater and the migration of brine towards the center of the glaciostatic depression occurred mainly during the build up of the ice sheet, while reversal of the water flow from the center of the cryogenic basin outwards happened upon deglaciation. The flow of the waters in the subsurface was, inevitably, accompanied by significant dilution with melt water from the ice sheets.Using a “granitic” U concentration of 4 ppm and a (Ca-Mg mass balance based) rock/water ratio anywhere between 3.4 and 6.8 kg L−1, a few hundred thousand years of brine-rock interaction are sufficient for the growth of 129I in the most saline Canadian Shield brine to its present concentration (3.4×108 atoms 129I L−1). Hence, both the formation of the saline fluids and their emplacement in their present sites occurred most likely within the Pleistocene.The young age calculated for cryogenic brines in crystalline shields and the dynamic water flow therein should raise concern about the planning and construction of high-grade nuclear waste repositories in such rocks, which are already under way.  相似文献   

18.
Attention is drawn to the fact that the warm geothermal brines of Matupi Harbour (New Britain) are of sea water origin, contain amounts of total dissolved solids comparable to those in sea water, but are remarkably enriched in heavy metals (Ferguson and Lambert, 1972). This evidence supports the proposal that metal enriched brines, of sea water origin, may be generated in sub-sea-floor geothermal systems by a high temperature leaching process, and may form a metal enriched sedimentary component on discharge back into sea water (Spooner and Fyfe, 1973).The chloride contents of the Matupi Harbour brines are low, relative to other known hydrothermal solutions which carry comparable amounts of heavy metals in solution. This evidence indicates that high dissolved chloride contents of the order of 160000 ppm, compared with sea water which contains 19800 ppm, are not a prerequisite for a high metal carrying capacity in natural brines.  相似文献   

19.
Saline groundwaters were recovered from undisturbed (Restigouche deposit) and active (Brunswick #12 mine) Zn-Pb volcanogenic massive sulfide deposits in the Bathurst Mining Camp (BMC), northern New Brunswick, Canada. These groundwaters, along with fresh to brackish meteoric ground and surface waters from the BMC, have been analyzed to determine their major, trace element and stable isotopic (O, H, C, and B) compositions. Saline groundwaters (total dissolved solids = 22-45 g/L) are characterized by relatively high Na/Ca ratios compared to brines from the Canadian Shield and low Na/Clmolar and δ11B isotopic compositions (−2.5‰ to 11.1‰) compared to seawater. Although saline waters from the Canadian Shield commonly have oxygen and hydrogen isotopic compositions that plot to the left of the global meteoric water line, those from the BMC fall close to the water line. Fracture and vein carbonate minerals at the Restigouche deposit have restricted carbon isotopic compositions of around −5‰ to −6‰. The carbon isotopic compositions of the saline waters at the Restigouche deposit (+12‰ δ13CDIC) are the result of fractionation of dissolved inorganic carbon by methanogenesis. We suggest that, unlike previous models for shield brines, the composition of saline waters in the BMC is best explained by prolonged water-rock reaction, with no requirement of precursor seawater. We suggest that elevated Br/Cl ratios of saline waters compared to seawater may be explained by differential uptake of Br and Cl during groundwater evolution through water-rock reaction.  相似文献   

20.
The Trifilia karst aquifer presents a complex hydrochemical character due to the intricate geochemical processes that take place in the area. Their discernment was achieved by using the chemical analyses of major, trace elements and boron isotopes. Major ion composition indicates mixing between seawater and freshwater is occurring. Five hydrochemical zones corresponding to five respective groundwater types were distinguished, in which the chemical composition of groundwater is influenced mainly due to the different salinization grade of the aquifer. The relatively increased temperature of the aquifer indicates the presence of hydrothermal waters. Boron isotopes and trace elements indicate that the intruding seawater has been hydrothermally altered, as it is shown by the δ11B depleted signature and the increased concentrations of Li and Sr. Trace elements analyses showed that the groundwater is enriched in various metallic elements, which derive from the solid hydrocarbons (bitumens), contained in the carbonate sediments of the Tripolis zone. The concentration of these trace elements depends on the redox environment. Thus, in reductive conditions As, Mn, Co and NH4 concentrations are high, in oxidized conditions the V, Se, Mo, Tl and U concentration increases while Ni is not redox sensitive and present high concentration in both environments.  相似文献   

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