Preliminary isotopic studies in the Bida basin,central Nigeria

The area of the Bida basin is lacking in essential data for effective groundwater management. Hydrological studies using environmental isotopes (²H,³H,¹³C,¹⁸O) were carried out in the basin during the 1987–1988 hydrological year on samples of rainfall, streams, springs, and groundwater. The results obtained results do not indicate the presence of paleowaters; rather all groundwaters in the basin are found to be of meteoric origin as bothD and ¹⁸O values of the samples, plotted in the conventional way, align with the meteoric water line (MWL). Moreover, these data show the deeper, and apparently older, groundwater to be more depleted in the heavy stable isotopes than the shallower, relatively younger groundwaters, indicating recharge under cooler climatic conditions for the former. Measured tritium values range from 0.7 to 23.8 TU and show a variation with both depth and lithology, while at the same time indicating that active recent recharge is taking place basin-wide. The few¹³C data available were used to illustrate the effect of pumping on the carbonate geochemistry of the groundwaters. Also, the stable isotope data from the basin were compared with similar data from other parts of the country to show the continental effect.     

Natural tracers in recent groundwaters from different Alpine aquifers

Groundwater with underground residence times between days and a few years have been investigated over more than 20 years from 487 remote sites located in different aquifer types in the Alpine belt. Analysis of the data reveals that groundwaters evolved in crystalline, evaporite, carbonate, molasse, and flysch aquifers can be clearly distinguished based on their major and trace element composition and degree of mineralisation. A further subdivision can be made even within one aquifer type based on the trace element compositions, which are characteristic for the lithologic environment. Major and trace element concentrations can be quantitatively described by interaction of the groundwater with the aquifer-specific mineralogy along the flow path. Because all investigated sites show minimal anthropogenic influences, the observed concentration ranges represent the natural background concentrations and can thus serve as a geo-reference for recent groundwaters from these five aquifer types. This geo-reference is particularly useful for the identification of groundwater contamination. It further shows that drinking water standards can be grossly exceeded for critical elements by purely natural processes.

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Resumen Durnate más de 20 años se ha investigado aguas subterráneas con una residencia subterránea con una duración de días a varios años en 487 puntos remotos localizados en diferentes tipos de acuíferos en la cadena alpina. El análisis de los datos revela que las aguas subterráneas que han evolucionado dentro de acuíferos cristalinos, evaporíticos, carbonatos, flysch, y molasse se pueden distignuir claramente en base a la composición de sus elementos mayores y marcadores y al grado de minerlización. Asimismo es posible hacer una subdivisión más específica incluso dentro de un tipo de acuífero en base a las composiciones de los elementos marcadores los cuales soncaracterísticos del ambiente litológico. Las concentraciones de los elementos marcadores se pueden describir cuantitativamente por la interacción de las aguas subterráneas con la mineralogía específica del acuífero a lo largo del trayecto del flujo. Puesto qze todos los puntos investigados muestran mínimas influencias antropogénicas, los rangos deconcentraciones observados representan las concentraciones delescenario natural y, por tanto, pueden servir como georeferencia para aguas subterráneas recientes que forman parte de estos cinco tipos de acuíferos. Esta georeferencia es particularmente útil para la identificcación de contaminación de aguas subterráneas. Asimismo muestra que los estándares de agua potable pueden mostrar excesos en elementos críticos por procesos puramente naturales.

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Résumé Leau souterraine ayant résidé sous la surface du sol entre quelques jours et quelques années a été étudiée sur une période de plus de 20 ans à partir de 487 sites éloignés situés dans différents types daquifères de la ceinture alpine. Lanalyse des données révèle que leau qui a évoluée dans des aquifères cristallins, évaporitiques, carbonatés, molassiques et composés de flysch, peut être facilement différenciée sur la base de sa composition en éléments majeurs et traces, ainsi que par son degré de minéralisation. Une subdivision supplémentaire peut être apportée à lintérieur même dun type daquifère en se basant sur la composition des éléments traces, lesquels sont caractéristiques de lenvironnement lithologique. La concentration en éléments majeurs et traces peut être expliquée quantitativement par linteraction de leau souterraine avec la composition minéralogique spécifique de laquifère le long des lignes découlement. Puisque la majorité des sites étudiés ne montrent que très peu dinfluences anthropogéniques, le registre de concentrations observées représente la concentration de fond naturelle et peut ainsi servir comme géo-référence pour les eaux souterraines récentes dans ces cinq types daquifères. Ces géo-références sont particulièrement utiles pour lidentification de la contamination des eaux souterraines. Par ailleurs, cela démontre que les standards deau potable peuvent être excédés pour certains éléments en raison de processus purement naturels.

     

应用大地热流和地下流体氦同位素组成资料计算中国大陆地壳生热元素丰度

根据能量守恒原理和中国大陆实测热流数据,给出中国大陆地壳生热率上限值为1.3μWm-3。根据热流值和地下流体氦同位素组成资料,估算出中国大陆地壳生热率为0.58～1.12μWm-3,中位数为0.85μWm-3,相应的铀、钍、钾丰度范围分别是0.83～1.76μg/g、3.16～6.69μg/g和1.0%～2.12%。中国陆壳铀、钍、钾元素整体丰度值明显高于太古宇地壳,反映中国陆壳成分演化程度较高。同时,中国大陆地壳成分具有明显的横向非均匀性特征:东部地壳相对西北部富集铀、钍、钾等强不相容元素,褶皱带相对克拉通地区富集铀、钍、钾元素。基于大陆地壳SiO2含量与地壳生热率之间的正相关关系推断,中国东部地壳较西部富长英质组分,褶皱带地壳成分较克拉通富长英质组分。此区域性变化特征与基于地震波速资料推断的结果相符。基于中国大陆地壳生热率变化范围以及地震波速低于全球平均值的特征,推断Rudnick和Fountain(1995)、Rudnick和Gao(2003)、Weaver和Tarney(1984)、Shaw等(1986)以及Wedepohl(1995)的全球陆壳成分模型均高估了铀、钍、钾等强不相容元素丰度。     

中国北方平原盆地地下水氢氧同位素组成特征

在系统收集整理中国北方河北平原、太原盆地、鄂尔多斯盆地以及银川平原的地下水氢氧同位素资料基础上,依据同位素形成演化相似性原理,对比分析同位素组成得出:深层地下水是在过去更寒冷的气候条件下形成;研究区的大气降水不但在现代气候条件下存在大陆效应和高程效应,而且在 25 kaB.P.以来的古气候条件下也存在大陆效应和高程效应;古气候条件下各盆地平原之间的蒸发强度的差异可能比现代气候条件下各盆地平原之间的蒸发强度的差异大.     

Oxygen isotopic ratios in fine quartz silt from sediments and soils of southern Africa

Fine quartz silt (1–10μm dia, important in aerosol dust) isolated from a large number of soils, as well as Phanerozoic shales, sandstones and recent sands of the southern African stratigraphie column (Carboniferous, Permian and Triassic) exhibits a mean δ¹⁸O of 12.2 ± 2.1%0. These values are similar to those reported for South Pacific pelagic sediments and adjacent land areas of similar latitude but are lower than those reported for this size fraction of 30 Mesozoic and Paleozoic shales (20.7 ± 1.8%.) and soils from mid-continental U.S.A., for aerosol quartz in the North Pacific pelagic sediments, and for eolian caps in high-elevation soils of Hawaii. The lower oxygen isotopic ratios in fine quartz silt of southern Africa reinforces the earlier indication that Southern Hemisphere detritai sedimentary reservoirs contain a higher proportion of igneous and metamorphic quartz (lower δ¹⁸O) and less lowtemperature authigenic quartz (higherδ¹⁸O) than Northern Hemisphere detritai sediments. The difference reflects climates, as continents drifted in latitude.     

Oxygen isotopic fractionation during inorganic calcite precipitation ― Effects of temperature, precipitation rate and pH

Stable oxygen isotopic fractionation during inorganic calcite precipitation was experimentally studied by spontaneous precipitation at various pH (8.3 < pH < 10.5), precipitation rates (1.8 < log R < 4.4 μmol m^− 2 h^− 1) and temperatures (5, 25, and 40 °C) using the CO₂ diffusion technique.The results show that the apparent stable oxygen isotopic fractionation factor between calcite and water (α_{calcite–water}) is affected by temperature, the pH of the solution, and the precipitation rate of calcite. Isotopic equilibrium is not maintained during spontaneous precipitation from the solution. Under isotopic non-equilibrium conditions, at a constant temperature and precipitation rate, apparent 1000lnα_{calcite–water} decreases with increasing pH of the solution. If the temperature and pH are held constant, apparent 1000lnα_{calcite–water} values decrease with elevated precipitation rates of calcite. At pH = 8.3, oxygen isotopic fractionation between inorganically precipitated calcite and water as a function of the precipitation rate (R) can be described by the expressions

at 5, 25, and 40 °C, respectively.The impact of precipitation rate on 1000lnα_{calcite–water} value in our experiments clearly indicates a kinetic effect on oxygen isotopic fractionation during calcite precipitation from aqueous solution, even if calcite precipitated slowly from aqueous solution at the given temperature range. Our results support Coplen's work [Coplen T. B. (2007) Calibration of the calcite–water oxygen isotope geothermometer at Devils Hole, Nevada, a natural laboratory. Geochim. Cosmochim. Acta 71, 3948–3957], which indicates that the equilibrium oxygen isotopic fractionation factor might be greater than the commonly accepted value.     

东天山东段同造山到后造山花岗岩幔源组分的递增及陆壳垂向生长意义——Sr、Nd同位素证据

显生宙陆壳垂向生长是一个新的值得进一步深入探索的课题.在已有的地质、地球化学研究基础上,本文报导了东天山东段矿物组成、成因类型相似的早古生代同造山花岗岩体和晚古生代-早中生代后造山花岗岩体新的Sr、Nd同位素测试结果,并进一步对比研究了它们的Sr、Nd同位素差异.前者ⅠSr值较高(0.7087～0.7288),εNd(t)值较低(-5.8～-15.8),模式年龄TDM大(1.29～2.37Ga),显示以古老陆壳物质为主的物源特征;后者ISr低(0.7069～0.708),εNd(t)值高(-3.8～ 0.3),TDM较年轻(0.80～1.28Ga为主),显示混有较多的年轻幔源组分;同期的煌斑岩脉ISr为0.7080,εNd(t)值为 4.3,TDM为0.8 Ga.这些特征为探讨显生宙地壳垂向生长提供了良好实例.一般而言,显生宙高εNd(t)值后造山花岗岩中的年轻幔源组分至少有3个可能的来源:(1)前造山(前寒武纪)底侵形成的年轻基性下地壳;(2)同造山水平增生的年轻地壳再循环;(3)后造山底侵的幔源岩浆.这3种来源分别揭示了3种陆壳生长方式和时限:前造山垂向生长;同造山水平生长;后造山垂向生长.通常,这3种情况仅仅依据地球化学特征不易鉴别;而通过花岗岩物源演变的对比研究有可能提供鉴别的线索.该区早古生代花岗岩以古老壳源为特点;而地点相同、矿物组成和地球化学相似、侵位深度相近的晚古生代-早中生代花岗岩幔源组分增多,并伴随有辉绿岩、煌斑岩侵入.这种新的年轻组分最可能与新底侵的幔源岩浆有关,它们随后造山花岗岩加入地壳,导致地壳垂向生长,这是造山后垂向生长的一种特征.该研究为中亚造山带后碰撞或后造山陆壳垂向生长的存在提供了一个证据.     

Study of exchangeable metal on colloidal humic acids and particulate matter by coupling ultrafiltration and isotopic tracers: Application to natural waters

A new method is proposed to characterize the complexation properties of colloids and metal–colloid interactions in natural waters. Based on the association of ultrafiltration with isotopic tracing, this method could quantify the pool of elements in an exchangeable position and also address the kinetic aspects of these exchanges. Basically, it consists of the comparison of isotopic compositions between the bulk sample and a succession of filtrates through time. Exchanges between colloidal humic acids (HA) and metals were first characterized, before applying such manipulations on natural waters. A few elements, representative of a wide range of complexation properties, were chosen: Cu, Zn, Cd, Pb, Sr, Nd, Ni, Th and U. In the case of humic acids, very small (less than 10% of isotopes), but significant isotopic shifts were observed compared to the isotopic equilibrium. It means that more than 90% of the isotopes were exchanged just after addition of isotopic tracers. Experiments on natural organic-rich waters (Mengong and Nyong streams) indicate isotopic composition variations close to those of humic acids. On the contrary, ultrafiltration performed on the total Sanaga River water (including suspended matter “SM”) shows an important isotopic shift between the filtered and unfiltered solutions. It means that in the case of the Sanaga River, a significant part of the chemical elements did not exchange.     

Geochemical and boron,oxygen and hydrogen isotopic constraints on the origin of salinity in groundwaters from the crystalline basement of the Alpine Foreland

The B isotopic composition, in combination with O and H isotopes and hydrochemical tracers, is utilized to constrain the evolution of basement-hosted groundwaters via water–rock interactions and fluid infiltration from external (sedimentary) reservoirs. Two distinct groundwater types have been identified in the Central European crystalline basement (N Switzerland–SW Germany): (1) fresh groundwaters characterized by low values of δ¹¹B (−3.5 to −0.6‰), δ¹⁸O (−12.0 to −10.0‰), and δD (−86.8 to −71.9‰), and (2) brackish groundwaters with distinctly heavier B, O, and H isotopic compositions (δ¹¹B=+6.4 to +17.6‰, δ¹⁸O=−9.4 to −5.6‰, δD=−67.6 to −60.8‰). Fresh groundwaters show a systematic decrease in δ¹¹B, related to an increase in B concentrations (and degree of total mineralization), along the pathway of groundwater migration which can only be interpreted in terms of leaching of crystalline host rocks. A δ¹¹B value of −3.3‰ is inferred for the crustal B source (mainly Hercynian granites) involved in the leaching process, in agreement with the known δ¹¹B range of granitic rocks. The evolution of brackish groundwaters, derived from crystalline basement reservoirs with little water circulation, is more complex. As indicated by B–O–H stable isotope and hydrochemical (e.g. B/Cl, Na/Cl, and Br/Cl) constraints, brackish groundwaters from the study area are influenced by admixture of sediment-derived fluids which infiltrated from Late Paleozoic (Permo-Carboniferous) and Early Mesozoic (Lower Triassic) sedimentary strata. The data presented show that B isotopes are sensitive to mixing processes of fluids derived from different crustal reservoirs and, hence, may be utilized as a tracer for constraining the internal (autochthonous) vs external (allochthonous) origin of salinity in basement-hosted groundwaters.     

Geochemical and Nd–Pb isotopic characteristics of the Tethyan asthenosphere: implications for the origin of the Indian Ocean mantle domain

It is unclear why the Pb, Nd, and Sr isotopic composition of the modern mid-ocean ridge basalts (MORB) from the Indian Ocean is different from that of the North Atlantic and Pacific Oceans. A possible explanation for this is that the Indian MORB-type isotopic signature is a long-lived regional feature of the mantle, as evidently shown by the isotopic composition of the 350 Ma MORB-like Mian-Lue northern ophiolite, which was formed in the same region presently occupied by the Indian Ocean. However, this hypothesis is in conflict with the lack of Indian MORB-type isotopic signature in a number of 150 Ma Tethyan and Indian Ocean crusts. To further constrain the origin of the Indian MORB-type isotopic signature, we analyze the geochemical and Pb, Nd, and Sr isotopic composition of representative mafic rocks from four Tethyan ophiolites ranging in age from 90 to 360 Ma. The Sr isotopic composition of the samples is unreliable due to alteration, but the age-corrected Nd and Pb isotopic ratios and geochemical data indicate that these Tethyan rocks were derived from a geochemically depleted asthenospheric source that had a clear Indian MORB-type isotopic signature. We therefore conclude that the bulk of the Indian suboceanic mantle was most probably inherited from the Tethyan asthenosphere. A few regions in both the Tethyan and Indian Oceans, however, are most probably underlain by Pacific and North Atlantic MORB-type mantle (and vice-versa) because of the flow of the asthenosphere in response to tectonic plate reorganizations that lead to openings and closures of ocean basins. The Indian MORB-type isotopic signature of the western Pacific marginal basin crusts could be due to either flow of the Indian Ocean mantle into the western Pacific or to endogenous production of such an isotopic signature from delaminated East-Asian sublithospheric materials during closure of the Tethys Ocean.     

西宁黄土白云石和碳同位素记录的轨道尺度季风气候变化

第四纪轨道尺度东亚季风变化的主控周期及其驱动机制还没有一致的认识,高纬地区冰量和低纬岁差变化如何驱动季风气候变化没有定论。沉积过程连续、堆积速率快的黄土-古土壤序列是揭示轨道时间尺度季风气候变化的良好材料。我们选择青藏高原东北部西宁泮子山黄土堆积上部的60 m作为研究对象,通过钻探取样和分析最近280 ka以来黄土-古土壤序列的磁化率、碳酸盐含量、白云石含量、碳酸盐碳同位素等古气候代用指标,探讨青藏高原东北部东亚夏季风气候的变化规律和控制因素。利用频谱和小波分析方法对季风气候变化的时间序列进行分析。结果显示,最近280 ka以来东亚夏季风变化具有轨道尺度的变化周期,并与高纬冰量和北半球温度变化有一定的联系;同时,西宁黄土古气候时间序列具有显著23 ka的岁差周期,表明低纬过程对东亚季风的重要作用。岁差调制的低纬太阳辐射变化可能是驱动青藏高原东北部轨道尺度季风降水变化的主导因素,高纬冰量和温度变化对轨道尺度的季风变化也有一定的影响。

     

Abundances and isotopic compositions of rhenium and osmium in pyrite samples from the Huaibei coalfield,Anhui, China

Two pyrite samples from the Shihezi Formation (Lower Permian), Huaibei coalfield, Anhui, China, have been analyzed for abundances and isotopic compositions of rhenium and osmium using negative thermal ion mass spectrometry. The Re–Os ages of the pyrites are 64.4 and 226 Ma, which are younger than the formation age of the coal seam. The pyrite samples may consist of pyrite formed at various stages during the history of coal formation. The γ_Os values of the two pyrite samples are + 17 and + 18, respectively. Such high γ_Os values are reported for the first time for recycles crustal materials from a sedimentary basin.     

Oxygen and hydrogen isotope ratios in freshwater chert as indicators of ancient climate and hydrologic regime

The oxygen and hydrogen isotopic composition of Eocene and Miocene freshwater cherts in the western United States records regional climatic variation in the Cenozoic. Here, we present isotopic measurements of 47 freshwater cherts of Eocene and Miocene age from the Great Basin of the western United States at two different sites and interpret them in light of regional climatic and tectonic history. The large range of δ¹⁸O of terrestrial cherts measured in this study, from 11.2‰ to 31.2‰ (SMOW: Standard Mean Ocean), is shown to be primarily the result of variations in δ¹⁸O of surface water. The following trends and patterns are recognized within this range of δ¹⁸O values. First, in Cenozoic rocks of northern Nevada, chert δ¹⁸O records the same shift observed in authigenic calcite between the Eocene and Miocene that has been attributed to regional surface uplift. The consistent covariation of proxies suggests that chert reliably records and retains a signal of ancient meteoric water isotopic composition, even though our analyses show that chert formed from warmer waters (40°C) than coexisting calcite (20°C). Second, there is a strong positive correlation between δ¹⁸O and δD in Eocene age chert from Elko, Nevada and Salina, Utah that suggests large changes in lake water isotopic composition due to evaporation. Evaporative effects on lake water isotopic composition, rather than surface temperature, exert the primary control on the isotopic composition of chert, accounting for 10‰ of the 16‰ range in δ¹⁸O measured in Eocene cherts. From authigenic mineral data, we calculate a range in isotopic composition of Eocene precipitation in the north-central Great Basin of −10 to −14‰ for δ¹⁸O and −70 to −100‰ for δD, which is in agreement with previous estimates for Eocene basins of the western United States. Due to its resistance to alteration and record of variations in both δ¹⁸O and δD of water, chert has the potential to corroborate and constrain the cause of variations in isotope stratigraphies.     

Boron geochemistry from some typical Tibetan hydrothermal systems: Origin and isotopic fractionation

The Tibetan plateau is characterized by intense hydrothermal activity and abnormal enrichment of trace elements in geothermal waters. Hydrochemistry and B isotope samples from geothermal waters in Tibet were systematically measured to describe the fractionation mechanisms and provide constraints on potential B reservoirs. B concentrations range from 0.35 to 171.90 mg/L, and isotopic values vary between −16.57 ‰ and +0.52 ‰. Geothermal fields along the Indus-Yarlung Zangbo suture zone and N–S rifts are observed with high B concentrations and temperatures. The similar hydrochemical compositions of high-B geothermal waters with magmatic fluid and consistent modeling of B isotopic compositions with present δ¹¹B values imply that the B in high-B geothermal waters is mainly contributed by magmatic sources, probably through magma degassing. In contrast, geothermal fields in other regions of the Lhasa block have relatively low B concentrations and temperatures. After considering the small fractionation factor and representative indicators of Na/Ca, Cl/HCO₃, Na + K and Si, the conformity between modeling results and the isotopic compositions of host rocks suggests that the B in low-temperature geothermal fields is mainly sourced from host rocks. According to simulated results, the B in some shallow geothermal waters not only originated from mixing of cold groundwater with deep thermal waters, but it was also contributed by equilibration with marine sedimentary rocks with an estimated proportion of 10%. It was anticipated that this study would provide useful insight into the sources and fractionation of B as well as further understanding of the relationships between B-rich salt lakes and geothermal activities in the Tibetan plateau.     

方解石矿物包裹体中水的氢同位素组成在线测试方法

水是矿物流体包裹体的重要组成,承载着流体性质和演化信息。提取矿物包裹体中水的方法主要有真空破碎法及爆裂法。为了减少真空破碎法表面积增大引起水的吸附以及爆裂法在高温下发生同位素交换反应,本文自制了一个在线提取装置,以高纯He作为载气,与高温裂解装置—稳定同位素质谱仪(EA/HT-IRMS)相连,进行一系列的条件实验,确认了方解石矿物包裹体中水的氢同位素组成在线测试的关键技术参数。实验证实,当爆裂温度为420℃、爆裂时间为5 min、含水量为0.1～0.3μL时,利用在线提取装置—EA/HT-IRMS对方解石矿物包裹体中水的δD进行测试的精密度优于±1.5‰(1σ)。相对于传统离线分析方法,本方法实现方解石矿物包裹体中水的在线提取及氢同位素组成的在线测试,简化了操作流程,并提高实验测试效率。     

同步变化的东亚季风和印度季风:来自年层石笋氧同位素的证据

印度季风和东亚季风是亚洲季风的两个子系统.现代器测数据和地质历史重建记录均证明两个季风在季节和轨道尺度上具有相同的特征.然而,在年一年代际尺度上,两者的相互关系尚不清楚.笔者通过比较两个分别来自印度季风区(阿曼Defore洞)和东亚季风区(中国和尚洞)的超高分辨石笋氧同位素序列,研究780 a以来印度和东亚季风变化及其相互作用.阿曼石笋氧同位素记录印度季风的变化,而和尚洞石笋δ18 O则是东亚季风变化的指示器.笔者发现,在年代际尺度上阿曼石笋和中国石笋具有相同的氧同位素组成变化特征,同时反映了亚洲季风的强弱变化,表明了印度季风和东亚季风变化是同步的.     

Br/Cl ratios and O, H, C, and B isotopic constraints on the origin of saline waters from eastern Canada

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/Cl_molar 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‰ δ¹³C_DIC) 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.     

Distribution and genesis of high-fluoride groundwaters in Ninh Hoa district, Vietnam

In 2003, we initiated the first systematic investigation of the occurrence of high-fluoride groundwaters in the Ninh Hoa district, China. The study involved the measurement of F- and other ionic species （by FISE and HPIC techniques） in well and bore samples throughout the district. The results helped ascertain the precise extent of fluorosis risk within the local population. Treatment of the data within a GIS enables recognition of particular hot-spots of fluoride concentration, and provides a valuable tool for the minimizing of local health risks and identification of possible source, or sources, of fluoride.     

西太平洋海底海山富钴结壳惰性气体同位素组成及其来源

采用高真空气体质谱系统测定了西太平洋麦哲伦海山富钴结壳不同层圈及其基岩的惰性气体丰度和同位素组成,结果显示:(1)西太平洋富钴结壳主要是水成成因,其中惰性气体来源不同,He 绝大多数来自宇宙尘(IDPs),少量来自陆源风成微粒;Ar 主要来自海水溶解的大气,少量来自陆源风成微粒或沉积岩建造水;Ne 和 Xe 主要来自海水中溶解大气, 少量来自宇宙尘;(2)在具三层结构的结壳中,亮煤层(致密层)的惰性气体同位素相对外层和疏松层有较大的不同,显示大洋磷酸岩化对早期沉积的结壳惰性气体组成有较大的影响,如导致~4He 的升高和~3He/~4He 的显著降低;(3)太平洋富钴结壳玄武岩基岩的~3He/~4He 非常低,为0.0095～0.074Ra,与本区磷块岩基岩(0.087Ra)相似,而远低于正常海底玄武岩的~3He/~4He 比值,显示这些基岩曾与富含放射性成因~4He 和 P 的上升洋流或沉积物中建造水发生过水/岩反应,这个过程将释放出较多的成矿元素,有利于富钴结壳的形成,海底海山玄武岩中较低的 He 同位素组成可作为富钴结壳的找矿标志之一。