Fluoride incidence in groundwater in an area of Peninsular India

Groundwater samples were collected from Anantapur District, Andhra Pradesh, India. The district is mainly underlain by Peninsular Gneisses of Archaean age. The samples were analysed for fluoride (F^–) along with other chemical parameters. The results suggest that the main sources of F^– in groundwater in the district are the country rocks, in which fluorine is strongly absorbed in soils consisting of clay minerals. A strong positive correlation between F^– and lithogenic sodium reflects weathering activity. This is responsible for the leaching of F^–, which is also caused by the semi-arid climate and intensive irrigation in the area. An alkaline environment of circulating water in the investigated area mainly facilitates leaching of F^– from the soils, contributing to high F^–-containing groundwater. A longer residence time of water in the aquifer zone, caused by a high rate of evapotranspiration and a weathered zone of low hydraulic conductivity, which promotes the dissolution of fluorine-bearing minerals, is another factor that further increases the F^– content in groundwater. Suggestions are made to improve groundwater quality and, thus, the health status of the population.     

Statistical and geochemical assessment of groundwater quality in Teboursouk area (Northwestern Tunisian Atlas)

Teboursouk region, Northwestern Tunisia, is characterized by the diversity of its natural resources (petroleum, groundwater and minerals). It constitutes a particular site widely studied, especially from a tectonic stand point as it exhibits a complex architecture dominated by multi-scale synclinals and Triassic extrusions. It has typical karst landform that constitutes important water resources devoted for human consumption and agriculture activities, besides to the exploitation of the Mio-Plio-Quaternary aquifer (MPQ). Thus, hydrogeological investigations play a significant role in the assessment of groundwater mineralization and the evaluation of the used water quality for different purposes. Hence, the current study based on a combined geochemical–statistical investigation of 50 groundwater samples from the multilayered aquifer system in the study area give crucial information about the principal factors and processes influencing groundwater chemistry. The chemical analysis of the water samples showed that Teboursouk groundwater is dominantly of Ca–Mg–Cl–SO₄ water type with little contribution of Ca–Mg–HCO₃, Na–K–Cl–SO₄ and Na–K–HCO₃. The total dissolved solids (TDS) values range from 0.37 to 3.58 g/l. The highest values are located near the Triassic outcrops. Furthermore, the hydrogeochemistry of the studied system was linked with various processes such as carbonates weathering, evaporites dissolution of Triassic outcrops and anthropogenic activities (nitrate contamination). Additionally, the main processes controlling Teboursouk water system were examined by means of multivariate statistical analysis (PCA and HCA) applied in this study based on 10 physicochemical parameters (TDS, pH, SO₄, HCO₃, pCO₂, Ca, Mg, Na, K, Cl and NO₃). Two principal components were extracted from PCA accounting 61% of total variance and revealing that the chemical characteristics of groundwater in the region were acquired through carbonates and evaporite dissolution besides to nitrate contamination. Similarly, according to Cluster analysis using Ward’s method and squared Euclidean distance, groundwater from the studied basin belongs to five different groups suggesting that the geochemical evolution of Teboursouk groundwater is controlled by dissolution of carbonates minerals, chemical weathering of Triassic evaporite outcrops, cation exchange and anthropogenic activities (nitrate contamination).     

Hydrochemical status of groundwater in district Ajmer (NW India) with reference to fluoride distribution

High fluoride in groundwater has been reported from many parts of India. However, a systematic study is required to understand the behaviour of fluoride in natural water in terms of local hydrogeological setting, climatic conditions and agricultural practices. Present study is an attempt to assess hydrogeochemistry of groundwater in Ajmer district in Rajasthan to understand the fluoride abundance in groundwater and to deduce the chemical parameters responsible for the dissolution activity of fluoride. Ajmer district falls in the semi-arid tract of central Rajasthan and is geologically occupied by Precambrian rocks (granites, pegmatites, gneisses, schists etc) where groundwater occurs under unconfined condition. A total of 153 well-water samples, representing an area of 8481 km² (further subdivided into eight blocks), were collected and chemically analyzed. The results of chemical analyses (pre-monsoon 2004) show fluoride abundance in the range of 0.12 to 16.9 mg/l with 66% of the samples in excess of permissible limit of 1.5 mg/l. Presence of fluoride bearing minerals in the host rock, the chemical properties like decomposition, dissociation and dissolution and their interaction with water is considered to be the main cause for fluoride in groundwater. Chemical weathering under arid to semi-arid conditions with relatively high alkalinity favours high concentration of fluoride in groundwater. Dental and skeletal fluorosis are prevalent in the study area which can be related to the usage of high fluoride groundwater for drinking. The suggested remedial measures to reduce fluoride pollution in groundwater include dilution by blending, artificial recharge, efficient irrigation practices and well construction.     

Groundwater solute chemistry,hydrogeochemical processes and fluoride contamination in phreatic aquifer of Odisha,India

The work investigates the major solute chemistry of groundwater and fluoride enrichment(F~-) in the shallow phreatic aquifer of Odisha.The study also interprets the hydrogeochemical processes of solute acquisition and the genetic behavior of groundwater F~-contamination.A total of 1105 groundwater samples collected from across the state from different hydro-geomorphic settings have been analyzed for the major solutes and F~-content.Groundwater is alkaline in nature(range of pH: 6.6–8.7; ave.: 7.9) predominated by moderately hard to very hard types.Average cation and anion chemistry stand in the orders of Ca~(2+) Na~+ Mg~(2+) K~+and HCO_3~- Cl~- SO_4~(2-) CO_3~(2-)respectively.The average mineralization is low(319 mg/L).The primary water types are Ca-Mg-HCO_3 and Ca-Mg-Cl~-HCO_3, followed by Na-Cl, Ca-Mg-Cl, and Na-Ca-Mg-HCO_3~-Cl.Silicate-halite dissolution and reverse ion exchange are the significant processes of solute acquisition.Both the geogenic as well as the anthropogenic sources contribute to the groundwater fluoride contamination,etc.The ratio of Na~+/Ca~(2+) 1.0 comprises Na-HCO_3(Cl) water types with F~- 1.0 mg/L(range 1.0–3.5 mg/L)where the F~-bears geogenic source.Positive relations exist between F~-and pH, Na~+, TDS, and HCO_3~-.It also reflects a perfect Na-TDS correlation(0.85).The ratio of Na~+/Ca~(2+) 1.0 segregates the sample population(F~- range: 1.0–4.0 mg/L) with the F derived from anthropogenic sources.Such water types include Ca-Mg-HCO_3(Cl) varieties which are recently recharged meteoritic water types.The F~-levels exhibit poor and negative correlations with the solutes in groundwater.The Na-TDS relation remains poor(0.12).In contrast, the TDS levels show strong correlations with Ca~(2+)(0.91), Mg~(2+)(0.80) and even Cl~-(0.91).The majority of the monitoring points with the anthropogenic sources of groundwater F~-are clustered in the Hirakud Canal Command area in the western parts of the state, indicating the role of irrigation return flow in the F~-contamination.     

Assessment of hot groundwater in an arid area in Tunisia using geochemical and fuzzy logic approaches

In this study, thermal groundwater from arid area in southeastern Tunisia was assessed for irrigation use. For this purpose, thirty-one water samples were collected and physiochemical parameters (EC, pH, TDS, major ions) were measured and analyzed. A fuzzy logic model was developed in which six parameters were integrated: electrical conductivity, sodium adsorption ratio, sodium percentage, Kelly ratio, permeability index and temperature. The membership functions for a fuzzy logic model were developed using linguistic terms and trapezoidal shapes. The fuzzy logic model developed was validated with a dataset of chemical analyses from groundwater sampled in the study area. The assessment indicated that 26% of the samples were in the “good” class, 10% in the “good to permissible” class, 55% are in the “permissible” class, 6% are in the “permissible to harmful” class and 3% were considered to be harmful and therefore unsuitable for use in irrigation. The effectiveness, simplicity and robustness of the fuzzy model assessment make this approach a more consistent and reliable way of assessing water quality than conventional methods of assessing water quality data.     

High Plains groundwater isotopic composition in northeastern New Mexico (USA): relationship to recharge and hydrogeologic setting

Hydrogeology Journal - In the High Plains (HP) region of northeastern New Mexico (NE NM), USA, underlying bedrock aquifers are utilized where the High Plains Aquifer is thin, absent, or...     

Geochemical characterization of groundwater from an arid region in India

A study on the geochemical processes in arid region of western India (Kachchh district) was carried out using major, minor, trace metal data and isotopic composition (δ²H, δ¹⁸O) of groundwaters. Results indicate that the distribution of chemical species in groundwater of this district is controlled by leaching of marine sediments, dissolution of salts in root zone and incongruent dissolution of carbonate minerals. Common inorganic contaminants such as fluoride, nitrate and phosphate are within drinking water permissible limits. However, most of the samples analyzed contain total dissolved salts more than desirable limits and fall in doubtful to unsuitable category with regard to irrigational purpose. Trace metal data indicates no contamination from toxic elements such as arsenic and lead. An increased salt content is observed in groundwater at shallower depths indicating mixing with surface water sources. The chemical characteristics of the groundwater have found to be strongly dependent on the local lithological composition. Environmental isotopic data indicates that the groundwater is of meteoric origin and has undergone limited modification before its recharge. The processes responsible for observed brackishness are identified using chemical and isotope indicators, which are in agreement with subsurface lithology and hydrochemistry. These data though represent hydrochemical scenario of 2001 can still be used for understanding the long-term fluctuations in water chemistry and would be quite useful for the planners in validating groundwater quality models.     

Appraisal of highly fluoride zones in groundwater of Kurmapalli watershed,Nalgonda district,Andhra Pradesh (India)

Fluoride (F) contamination study had been carried out to see its allocation in Kurmapalli watershed, Nalgonda district, Andhra Pradesh, India. The study area is located about 60 km SE of Hyderabad city. The groundwater is the main source of water for their living. The groundwater in villages and its surrounding are affected by fluoride contamination and consequently the majority of the people living in these villages has health hazards and is facing fluorosis. The purpose of this study is to identify the wells with high F, raise awareness in people, study the water chemistry, and also find out the source of F in groundwater. A total of 32 groundwater samples were collected from different wells in both shallow aquifers and deeper fractures zones during October 2004. The chemical analysis of groundwater has been done. Fluoride values vary from 0.7 to 19.0 mg/l. It is noted that the maximum value (19.0 mg/l) is one of the highest values found in groundwater in India and 78% of the total samples show F concentrations that exceeds the permissible limit value (1.5 mg/l). The highest value of F is found at Madanapur bore well which is located at central part of the watershed. The F value of this bore well was monitored from October 2004 to October 2006. During this period the F concentration varies from 17.8 to 21.0 mg/l with mean 19.3 mg/l. There is no correlation of F with chemical parameters except calcium. The Ca has shown inverse proportional with F. Water–rock interaction studies were also carried out to understand the behavior of F in groundwater at prominent F affected areas. Rock samples were collected and analyzed, and found their enrichment of F. The anthropogenic possibility of F is almost negligible. The rocks of this area are enriched in F from 460 to 1,706 mg/kg. It is indicated that the rock–water interaction is the main source of F in groundwater. The highest values of F are found in middle part of the region and are related to the occurrence of fluoride rich rocks and their chemical kinetic behavior with groundwater.     

Vulnerability of groundwater in an industrial (Bauxite) valley of Lanjigarh (Orissa), India

Groundwater, particularly in the shallow zone aquifer is an easily available source of freshwater that serves various needs of people around it. Due to rapid growth in the industrial sector, the shallow groundwater regime becomes vulnerable to industrial toxicity and human activity. In the case of bauxite ore processing industry it is not only the groundwater potential that gets affected, but often the quality of groundwater is at risk from the ore processing activity. Bauxite processing plant has been setup in the Lanjigarh (Orissa State), India during 2007. An attempt has been made to evaluate the groundwater regime in the watershed that comprises the plant and its various disposal sites. Although the groundwater has not been found affected due to waste disposals, however, areas vulnerable to pollution have been demarcated.     

Spinel-peridotite xenoliths from Kapfenstein (Graz Basin,Eastern Austria): A geochemical and petrological study

Summary Ultramafic xenoliths from the basaltic tuff of Kapfenstein (Graz Basin) are mainly protogranular and protogranular- to- porphyroclastic spinel lherzolites. In addition to these common rocks, a coarse-grained spinel harzburgite and a heterogeneous spinel peridotite consisting of a clinopyroxene-poor harzburgite and a clinopyroxene-rich lherzolite have been found. Interstitial amphiboles (pargasite and kaersutite) are present in most xenoliths. The magmatic activity which brought these xenoliths to the surface is part of the Plio-Pleistocene extension-related alkali basalt volcanism which took place in the Carpatho-Pannonian Region, post-dating the subduction-related calc-alkaline volcanism which formed the Inner Carpathian arc.Mineralogical and bulk geochemical data for Kapfenstein xenoliths are similar to those for other sub-continental shallow mantle xenolith suites. Correlation diagrams for major and trace elements indicate that their chemical variations are related to different degrees of partial melting due to the extraction of mafic melts. Rare earth element (REE) patterns of separated clinopyroxenes from the xenoliths are generally light rare earth element (LREE)-depleted, although LREE-enriched and more complex patterns have also been found.⁸⁷Sr/⁸⁶Sr and¹⁴³Nd/.¹⁴⁴Nd isotopic ratios of separated clinopyroxenes vary between 0.70193 and 0.70330 (^Sr, = – 36.4 to –17.0) and 0.512824 and 0.513589 (_NdNd = 4.2 to 18.l), respectively. The highest⁸⁷Sr/⁸⁶Sr and lowest¹⁴⁴³Nd/¹⁴⁴Nd.Nd ratios occur in those samples which have the most refractory character and also have the most unusual REE patterns. REE determined by ion microprobe on separated interstitial amphibole grains indicate equilibrium with the host peridotite in most of the xenoliths but disequilibirum conditions have been observed, including some extreme LREE enrichments.Striking textural and some geochemical and isotope geochemical similarities have been recognised between Kapfenstein xenoliths and those from the Eastern Transylvanian Basin, both of which are situated on the edges of the diapiric upwelling located in the central part of the Pannonian Basin. The deformation, depletion and enrichment processes which occurred in these two areas are thought to be similar. The LREE-enriched interstitial amphiboles and the presence of cross-cutting amphibole veins suggest that the shallow depleted lithospheric mantle beneath the Graz Basin has been affected by metasomatising events related to the mafic alkaline host magmas rather than by subduction-related fluids or melts.

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Spinel-peridotit Xenolithe von Kapfenstein (Grazer Becken, Ostösterreich): Eine geochemische und petrologische Studie

Zusammenfassung Die ultramafischen Xenolithe aus dem Basaltuff von Kapfenstein (Grazer Becken) bestehen großteils aus protogranularem und porphyroklastischem Spinell-Lherzolith. Abgesehen von diesen weitverbreiteten Gesteinen wurden auch ein grobköringer Spinell-Harzburgit und ein heterogener Spinell-Peridotit, der aus einem Klinopyroxen-armen Harzburgit und einem Klinopyroxen-reichen Lherzolith besteht, gefunden. Interstitielle Amphibole (Pargasit und Kaersutit) sind in den meisten Xenolithen vorhanden. Die magmatischen Prozesse, die diese Xenolithe an die Erdoberfläche befördeten, stehen mit dem mit Extension assoziierten Alkali-Basalt-Vulkanismus, der während des Pliozän/ Pleistozäns dem durch Subduktion ausgelösten Kalk-alkalischen Vulkanismus des inneren Karpathenbogens folgte, in Zusammenhang.Die mineralogischen und geochemischen Vollanalysen der Kapfensteiner Xenolithe sind mit den Daten von anderen Gruppen von subkontinentalen Xenolithen des oberen Mantels vergleichbar. Korrelationsdiagramme für Haupt- und Spurenelemente zeigen, daß die chemische Variation auf verschiedene Grade von Teilschmelzbildung zurück-zuführen ist. Die Verteilungsmuster der Seltenen Erden in Klinopyroxenen der Xenolithe sind generall LREE-verarmt, aber LREE angereichte und kompliziertere Verteilungsmuster kommen vor. Die⁸⁷Sr/⁸⁶Sr und¹⁴³Nd/1⁴⁴Nd Isotopenverhältnisse der Klinopyroxene schwanken zwischen 0.70193 und 0.70330 (_Sr = von – 36.4 bis –17.0), beziechungsweise zwischen 0.512854 und 0.513589 (_Nd=von –4.2 bis 18.l). Die höchsten⁸⁷Sr/⁸⁶Sr und niedrigsten¹⁴³Nd/¹⁴⁴Nd Isotopenverhältnisse treten in den Proben mit dem stärksten refraktären Charakter und den ungewöhnlichsten REE-Verteilungsmustern auf. Die mittels Zonensonde ermittelten Gehalte an REE der interstitiellen Amphibole deuten ein Gleichgewicht mit dem Wirt-Peridotit an, obwohl auch Anzeichen von gestörtem Gleichgewicht, unter anderem extreme Anreicherungen an LREE, beobachtet wurden.Ein Vergleich der Kapfenstein-Xenolithe mit denen aus dem östlichen Transsylvanischen Becken zeigt bemerkenswerte strukturelle und einige geochemische und isotopengeochemische Ähnlichkeiten. Beide Gegenden befinden sich am Rande des Erdmantel diapirs, im Zentrum des Pannonischen Beckens. Die Deformationen und Verarmungsund Anreicherungsprozesse, die in beiden Gebieten stattfanden, sind vergleichbar. Die an LREE angereicherten interstitiellen Amphibole und das Auftreten von diskordanten Amphibolgängen legen nahe, daß der obere verarmte lithosphärische Mantel unter dem Grazer Becken von, mit den mafischen alkalischen Grund-Magmen verwandten, metasomatischen Prozessen erfaßt worden ist, und nicht von mit Subduktion assoziierten Flüssigkeiten oder Schmelzen.

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

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

Hydrochemistry of groundwater (GW) and surface water (SW) for assessment of fluoride in Chinnaeru river basin,Nalgonda district, (AP) India

Hydrochemical studies were conducted in Chinnaeru river basin of Nalgonda district, Andhra Pradesh, India, to explore the causes of high fluorides in groundwater and surface water causing a widespread incidence of fluorosis in local population. The concentration of fluoride in groundwater ranges from 0.4 to 2.9 and 0.6 to 3.6 mg/l, stream water ranges from 0.9 to 3.5 and 1.4 to 3.2 mg/l, tank water ranges from 0.4 to 2.8 and 0.9 to 2.3 mg/l, for pre- and post-monsoon periods, respectively. The modified Piper diagram reflects that the water belongs to Ca²⁺–Mg²⁺–HCO₃ ^? to Na⁺–HCO₃ ^? facies. Negative chloroalkali indices in both the seasons prove that ion exchange between Na⁺ and K⁺ in aquatic solution took place with Ca²⁺ and Mg²⁺ of host rock. The interpretation of plots for different major ions and molar ratios suggest that weathering of silicate rocks and water–rock interaction is responsible for major ion chemistry of groundwater/surface water. High fluoride content in groundwater was attributed to continuous water–rock interaction during the process of percolation with fluorite bearing country rocks under arid, low precipitation, and high evaporation conditions. The low calcium content in rocks and soils, and the presence of high levels of sodium bicarbonate are important factors favouring high levels of fluoride in waters. The basement rocks provide abundant mineral sources of fluoride in the form of amphibole, biotite, fluorite, mica and apatite.     

Geoenvironmental appraisal of groundwater quality in Bengal alluvial tract,India: a geochemical and statistical approach

Groundwater is an essential natural resource which has enormous use throughout the world, but with the enhanced population pressure, its quality and quantity gets affected. Consequently, assessment and categorization of groundwater quality is necessary and the availability of safe water for utilization is to be ensured. The present study was based on groundwater samples, collected over 5,324 km² from the alluvial tract of Bengal plain, India. Ten geochemical parameters viz. arsenic, pH, total dissolved solids, electrical conductivity, iron, total hardness as calcium carbonate, sulphate, nitrite and depth were analysed, and multivariate statistical analyses were performed on the data set. Factor analysis depicted four factors, which explained 66.57 % of total variability of data. Factor 1 represented high positive loadings on total dissolved solids and electrical conductivity. Factor 2 was associated with depth, arsenic and iron and indicated process of reduction in groundwater. Over extraction of groundwater showed probable relationship with arsenic concentration in groundwater. Parameters of Factor 3 and 4 had been related with agricultural activities and local geological conditions. Further, four clusters observed from hierarchical cluster analysis, assisted in grouping groundwater geochemistry of the region. The results coupled with GIS facilitated in categorizing and mapping the groundwater quality.     

宿南矿区地下水同位素地球化学特征及地质意义

煤矿区地下水既是重要的地下水资源,又影响煤矿安全生产。为了解宿南矿区地下水同位素化学特征,采集了宿南矿区松散层水、砂岩水和灰岩水样品进行T、D、18O、87Sr/86Sr和溶解碳酸盐岩中13C、18O等同位素测试分析,并利用传统图示等方法探讨了地下水演化年龄、同位素特征及影响因素。结果表明：矿区3个含水层地下水中T含量较低,整体反映了矿区地下水多位时间久远的亚现代水补给;地下水中D、18O受到明显围岩的影响,其组成为-68.5‰~-44.3‰和-8.78‰~-6.29‰,平均值分别为-61.15‰和-8.16‰;围岩中碳酸盐岩含量决定了13CDIC与 18ODIC的变化关系;87Sr/86Sr值为0.710 6～0.712 3,平均为0.711 2,87Sr/86Sr比值主要受到了水岩作用的影响,可以有效地识别3个不同含水层水源。     

Mineralogical and geochemical investigation of some pegmatites from the Mashad area,northeastern Iran

Summary Pegmatitic dikes and masses of various sizes occur in a granite intrusion in the Mashad area, northeastern Iran. Their geochemistry, as well as that of the parent granite was investigated using some 40 specimens. Major constituents and trace elements were determined by means of X-ray fluorescence and spectrographic methods. Anomalously high concentrations of Be and Nb and indications of their minerals beryl and columbite were observed. Therefore, the pegmatites of this area may prove to be a potential source for Be, Nb, Ta and possibly Li.

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Mineralogische und geochemische Untersuchung einiger Pegmatite aus der Gegend von Mashad, Nordost-Iran

Zusammenfassung In einer Granitintrusion in der Gegend von Mashad, Nordost-Iran, kommen pegmatitische Gänge und Massen verschiedener Größe vor. Unter Verwendung von etwa 40 Proben wurde ihre Geochemie und die ihres Muttergranites untersucht. Die Hauptbestandteile und Spurenelemente wurden mit Röntgenfluoreszenz und spektrographischen Methoden bestimmt. Außergewöhnlich hohe Konzentrationen an Be und Nb und Hinweise auf ihre Minerale Beryll und Columbit wurden beobachtet. Die Pegmatite dieser Gegend könnten sich folglich als potentielle Lieferanten für Be, Nb, Ta und möglicherweise Li herausstellen.

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东昆仑拉陵高里河沟脑地区晚三叠世花岗闪长斑岩年代学、岩石地球化学及Hf同位素特征

笔者等对东昆仑拉陵高里河沟脑花岗闪长斑岩开展详细的全岩地球化学、LA-ICP-MS锆石U-Pb年代学、锆石Hf同位素研究,确定其形成时代,并探讨其岩石成因及成岩构造背景。结果显示,花岗闪长斑岩LA-ICP-MS锆石U-Pb年龄为231.1±1.2 Ma,指示其侵位于晚三叠世早期。全岩K₂O/Na₂O值为0.69～0.71,Mg^#值为40.5～41.6,里特曼指数σ为1.90～2.09,A/CNK=1.01～1.03,属弱过铝质中—高钾钙碱性岩石系列。岩石的轻重稀土元素分异明显,(La/Yb)_N值为19.54～25.52,具弱负Eu异常(δEu为0.96～0.97),富集大离子亲石元素K、Rb、Ba、Th,亏损高场强元素Nb、Ta、Ti等,具有高的Sr含量(606.0×10^-6～647.9×10^-6)和Sr/Y值(60.38～62.99),较低的Y(9.62×10^-6～10.66×10^-6)和Yb(0.86     

Geochemical processes regulating groundwater chemistry with special reference to nitrate and fluoride enrichment in Chhatarpur area, Madhya Pradesh, India

The present study focuses on the hydrogeochemical composition of groundwater in Chhatarpur area with special focus on nitrate and fluoride contamination, considering the fact that groundwater is the only major source of drinking water here. Carbonate and silicate mineral weathering followed by ground water–surface water interactions, ion exchange and anthropogenic activities are mainly responsible for high concentrations of cations and anions in the groundwater in the region. The average concentration of nitrate and fluoride found in 27 samples is 1.08 and 61.4 mg/L, respectively. Nitrate enrichment mainly occurs in areas occupied with intense fertilizer practice in agricultural fields. Since the area is not dominated by industrialization, the possibility of anthropogenic input of fluoride is almost negligible, thus the enrichment of fluoride in groundwater is only possible due to rock–water interaction. The highly alkaline conditions, which favor the fluorite dissolution, are the main process responsible for high concentration of fluoride.     

Origin of carbonatites of eastern taimyr deduced from an isotopic and geochemical study of zircons

Injection carbonatites of volcanic-plutonic origin with Au-bearing base-metal sulfide mineralization were established in 2006–2007 along the southern slope of the Byrranga Range in the Russian continental sector of the Arctic. According to thermobarogeochemical data, carbonatites were formed at a temperature not lower than 380–410°C from boiling gas-liquid H₂O-CO₂-salt fluids under decompression. The REE concentrations and patterns of sedimentary and magmatic carbonates are sharply distinct. Carbonatites are enriched in REE as compared to carbonates from limestone and are characterized by an REE distribution close to MORB. The geochronological and isotopic geochemical study of zircons has shown that carbonatite bodies (lavas?) were formed 238–219 Ma ago (Middle-Late Triassic); zircon crystallized at a high temperature. Detrital zircons from the Lower Carboniferous crinoid limestone are not younger than 594 Ma. The absolute predominance of Precambrian zircons, which are variable in age, indicates that they were captured from the crust, when carbonatitic magma ascended from subcrustal depths.