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1.
The vertical distributions of dissolved Se species [Se(IV), Se(VI) and organic Se] and diagenetic constituents [Fe(II) and Mn(II)] were obtained in porewater samples of two Sudbury area lakes (Clearwater and McFarlane). The sedimentary concentration profiles of total Se, Se species bound to Fe–Mn oxyhydroxides and to organic matter, and of elemental Se were also determined along with the concentrations of Fe, Mn and S in different extractable fractions. Results indicated that the concentrations of total dissolved Se in porewater samples were very low, varying from around 2.0 nM to a maximum level of 6.5 nM, while the concentrations of total Se species in the solid phase varied between 2 and 150 nmol/g on a dry weight basis. The two lakes showed striking differences in the presence of Se(IV) and Se(VI) at the sediment–water interface (SWI). In Clearwater Lake, Se(VI) was present at this interface and Se(IV) was not detectable, whereas the opposite was found in McFarlane Lake. This suggests that reducing conditions might have existed near the SWI of McFarlane Lake at the sampling time; this hypothesis was confirmed by several other measured chemical parameters. The profiles of total dissolved Se of both lakes suggest upward and downward diffusion of dissolved Se species along the concentration gradients. Assuming that no precipitation occurred at the SWI, the fluxes of dissolved Se species across the SWI in Clearwater and McFarlane lakes were estimated to be 0.108 and 0.034 nmol cm−2 a−1, respectively. These values do not include the possible losses of volatile Se species due to microbial methylation. In the reducing sediments of both lakes, the formation of elemental Se and pyritic Se were found to be important mechanisms for controlling the solubility of Se in this environment. The main geochemical processes involving Se identified in this study are: the adsorption of Se onto Fe–Mn oxyhydroxides at or near the SWI, the release of adsorbed Se by the reduction of the same oxyhydroxides and the mineralization of organic matter, and the removal of Se from porewaters to form elemental Se and a S mineral phase such as Se–pyrite or pure ferroselite.  相似文献   

2.
The paper presents mineralogical, crystallochemical, and Rb–Sr age data on globular layer silicates of the glauconitic series from lower horizons of the Upper Riphean Kil'din Group, Srednii Peninsula. Chloritization significantly changed the globular Al-glauconite in sandstones of the Päräjarvinskaya Formation. However, it almost did not affect glauconite globules in sandstones of the Palvinskaya Formation and altered only clayey component of the rock. Mössbauer spectroscopy showed that Al-glauconite in the Palvinskaya Formation was affected by secondary transformations, which caused the Fe2+ oxidation in octahedral sheets and loss of radiogenic 87Sr. The transformations were presumably related to exhumation of rocks of the Päräjarvinskaya and Palvinskaya formations to the circulation level of the oxygen-rich meteoric waters. Thus, Rb–Sr datings obtained for Al-glauconites of the Palvinskaya (781–786 Ma) and Päräjarvinskaya(744–751 Ma) formations correspond to the tectonic uplift of Kil'din rocks and have no stratigraphic significance.  相似文献   

3.
Fractionation of silicon isotopes during biogenic silica dissolution   总被引：2，自引：0，他引：2  
Silicon isotopes have been investigated for their potential to reveal both past and present patterns of silicic acid utilization, primarily by diatoms, in surface waters of the ocean. Interpretation of this proxy has thus far relied on characteristic trends in the isotope composition of the dissolved and particulate silicon pools in the upper ocean, as driven by biological fractionation during the production of biogenic silica (bSiO2, or opal) by diatoms. However, other factors which may influence the silicon isotope composition of diatom opal, particularly post-formational aging and maturation processes, remain largely uninvestigated. Here, we report a consistent fractionation of silicon isotopes during the physicochemical dissolution of diatom bSiO2 suspended in seawater under closed conditions. This fractionation acts counter to that occurring during bSiO2 production and at about half its absolute magnitude, with dissolution discriminating against the release of the heavier isotopes of silicon at an enrichment factor εDSi–BSi of −0.55‰, corresponding to a fractionation factor α30/28 of 0.99945. The enrichment factor did not vary with source material, indicating the lack of a significant species effect, or with temperature from 3 to 20 °C. Thus, the dissolution of bSiO2 produces dissolved silicon with a δ30Si value that is 0.55‰ more negative than its parent bSiO2, an effect that must be accounted for when interpreting oceanic δ30Si distributions. The δ30Si values of both the dissolved and particulate silicon pools increased linearly as dissolution progressed, implying a measurable (±0.1‰) change in the relative δ30Si of opal samples whenever the difference in preservation efficiency between them is >20%. This effect could account for 10–30% of the difference in diatom δ30Si values observed between glacial and interglacial conditions. It is unlikely, however, that the inferred maximum possible change in δb30SiO2 of +0.55‰ would be manifested in situ, as a high mean percentage of dissolution would include complete loss of the more soluble members of the diatom assemblage.  相似文献   

4.
Plants and soils from central Euboea, were analyzed for Cr(totai), Cr(VI), Ni, Mn, Fe and Zn. The range of metal concentrations in soils is typical to those developed on Fe-Ni laterites and ultramafic rocks. Their bioavailability was expressed in terms of concentrations extractable with EDTA and 1 M HNO3, with EDTA having a limited effect on metal recovery. Cr(VI) concentrations in soils evaluated by alkaline digestion solution were lower than phytotoxic levels. Chromium and Ni — and occasionally Zn — in the majority of plants were near or above toxicity levels. Cr(VI) concentrations in plants were extremely low compared to total chromium concentrations. Cr(total) in ground waters ranged from <1 μg.L?1 to 130 μg.L?1, with almost all chromium present as Cr(VI). With the exception of Cr(total) and in some cases Zn, all elements were below regulatory limits for drinking water. On the basis of Ca, Mg, Cr(total) and Si ground waters were classified into three groups: Group(I) with Cr concentrations less than 1 μg.L?1 from a karstic aquifer; Group(II) with average concentrations of 24 μg.L?1 of Cr and relatively high Si associated with ophiolites; and Group(III) with Cr concentrations of up to 130 μg.L?1, likely due to anthropogenic activity. Group(III) is comparable to ground waters from Assopos basin, characterized by high Cr(VI) concentrations, probably due to industrial actrivities.  相似文献   

5.
Adsorption of U(VI) on 6 samples of natural Fe-rich sands from Oyster, VA was studied over a range of U(VI) concentrations (0.1–100 μM), pH values (3–7.6), and dithionite–citrate–bicarbonate (DCB) extractable amounts of Fe (3.1–12.3 μmol/g). Four modeling approaches were applied to represent the U(VI) adsorption data. Model I was a two-site, diffuse double layer, surface complexation model based on data for synthetic ferrihydrite [Geochim. Cosmochim. Acta 58 (1994) 5465–5478]. Considering the magnitude of approximations necessary for application of the laboratory-based model to natural sands, Model I was surprisingly accurate, as determined by the goodness of fit parameter, χ2/N of 53.1–22.2. Model II was based on the reactions and diffuse double layer treatment of Model I, but was calibrated to a portion of U(VI) adsorption data for each sand, and then used to predict adsorption data for the same sand under different experimental conditions. Model II did not increase the accuracy of the predictions made with Model I, χ2/N of 42.4–27.6. Models III and IV were four-site affinity spectrum models, without an explicit electric double layer model or explicit surface hydrolysis reactions. Model III was based on a discrete log K spectrum approach, and Model IV was obtained from adjusting all surface stability constants and site concentrations for all surface sites. Models III and IV represented the U(VI) adsorption data with the greatest accuracy, χ2/N ranged from 13.8 to 4.4. Model I provides evidence supporting the practice of using pure phase thermodynamic reaction constants for describing the adsorption characteristics of environmentally important sorbents in certain simple cases. Yet, affinity spectrum approaches (Models III and IV) become increasingly important as more accurate interpolation of adsorption data is necessary, the sorbent becomes increasingly complex, or the range of experimental conditions expands.  相似文献   

6.
Thermal mineral waters and extractable geothermal energy are an important and still underestimated natural wealth of Bulgaria. Their diversity is due to the complex geological structure, intense neotectonic activity, and the resulting complex character of meteoric water circulation. Reproductive hydrogeothermal systems with low-mineralized thermal waters of meteoric origin and resrvoir temperatures ranging between 30 and 100 (maximum 120) °C occur in the southern and north-eastern part of the country. Their total reproductive potential is estimated at 14–15 m3s–1. In the northern part (Moesian platform), regional hydrogeothermal reservoir with connate (marine) and mixed (marine and meteoric) mineral waters and brines are identified, the temperatures varying from 40 to 140 (maximum 150) °C. Huge resources of geothermal energy with commercial importance are accumulated in them. The hydrogeothermal wealth of Bulgaria provides as important basis for the development of balneological and multi-seasonal tourism, bottling industries, geothermal heating of buildings and greenhouses, aquaculture and other related activities.  相似文献   

7.
A series of monazite dissolution experiments was conducted in a hydrous (1–6 wt.%) granitic melt at 8 kbar over the temperature range 1,000–1,400° C. A polished cube of monazite was immersed in a natural obsidian melt and allowed to partially dissolve. Electron microprobe traverses perpendicular to the crystal-melt interface revealed concentration gradients in the LREEs and P. Diffusivities of the LREEs and P were calculated from these profiles, yielding the following Arrhenius relations for the LREEs: D=0.23 exp(–60.1 kcal mol–1/RT) at 6% water D=2.30×107 exp(–122.1 kcal mol–1/RT) at 1% water These results demonstrate the importance of dissolved water on REE diffusion. Phosphorus diffusivities are nearly identical to those of the rare-earths, suggesting that P diffusion charge-compensates REE diffusion. The concentration of LREEs required for monazite saturation in these melts is given by the level of dissolved LREEs at the crystal-melt interface. These values also show a dependence on dissolved water, with LREEsat=60 ppm at 6% H2O when extrapolated down to 700° C, and LREEsat=30 ppm at 1% H2O. Calculated dissolution rates based on the above parameters indicate that minute (<30 m diameter) monazite crystals will be readily digested by an enclosing anatectic magma under reasonable geologic conditions (i.e., T=700–800° C and >2% H2O), whereas larger (> 50 m) crystals will likely be residual over the duration of an anatectic event. The low solubility of monazite in this melt suggests that the LREE depletion observed in some felsic differentiation suites may be the result of monazite crystallization. Limited experimental and geochemical/petrologic evidence indicates that compositional changes in the melt accompanying differentiation decrease the solubility of monazite drastically. Kinetic and chemical constraints may also lead to localized monazite saturation and inclusion in major phases or even other accessories. Variations in the REE composition of monazite from different parageneses probably reflects the REE pattern of the parent melt, and may be due to gradational differences in the stability of individual or subgroup REE-complexes as a function of melt composition. Particularly important in this regard seems to be the lime+alkali/alumina balance of the melt and its volatile content.  相似文献   

8.
Natural zeolitic rocks consisting mainly of chabazite-phillipsite, clinoptilolite, and volcanic glass have been evaluated by means of batch methods to remove arsenic from waters with different mineralization degree (from deionized water to natural water with a specific conductivity of 1,600 μS cm− 1). Arsenic was previously spiked in the studied waters at concentrations of about 100 µg l− 1 to simulate actual cases. The compositional range of natural waters is representative of large hydrogeochemical regions around the world. The experiments were focussed on the application of natural common zeolitic rocks to water treatment for human consumption. The removal efficiency observed rises, in the better cases, 60–80% for chabazite-phillipsite raw materials whereas is 40–60% for clinoptilolite-bearing ones. The arsenic removal tends to increase with water mineralization degree, independently of the zeolitic rock type. A large zeolitic content in the chabazite-phillipsite raw materials increase the removal. Instead, the inverse situation is observed in the clinoptilolite-bearing rocks. The relevance of the quantitative mineralogical analysis, determining also the content of volcanic glass, as well as the use of natural waters in the removal tests has been demonstrated.  相似文献   

9.
Uranium in Phosphorites   总被引：1，自引：0，他引：1  
The uranium concentration in phosphorites on continents and modern seafloor varies from 0.nto n· 102ppm (average 75 ppm). The average uranium concentration is 4–48 ppm in Precambrian and Cambrian deposits, 20–90 ppm in Paleozoic and Jurassic deposits, 40–130 ppm in Late Cretaceous–Paleogene deposits, 30–130 ppm in Neogene deposits, and 30–110 ppm in Quaternary (including Holocene) deposits. On the whole, the variation range is almost similar for phosphorites of different ages. The U/P2O5ratio in phosphorites ranges from less than unity to 24 · 10–4(average 3.2 · 10–4). Major phosphorite deposits of the world with ore reserves of approximately 250 Gt (or 58 Gt P2O5) contain up to 19 Mt of uranium. Uranium is present in phosphorites in the tetra- and hexavalent, i.e., U(IV) and U(VI) forms, and their ratio is highly variable. At the early diagenetic stage of the formation of marine phosphorites in a reductive environment, U(VI) diffuses from the near-bottom water into sediments. It is consequently reduced and precipitated as submicroscopic segregations of uranium minerals (mainly uraninite) that are probably absorbed by phosphatic material. During the subsequent reaction between phosphorites and aerated water and the weathering in a subaerial environment, uranium is partly oxidized and lost. The uranium depletion also occurs during catagenesis owing to a more complete crystallization of calcium phosphate and replacement of nonphosphatic components.  相似文献   

10.
This paper reviews the geochemical, isotopic (2H, 18O, 13C, 3H and 14C) and numerical modelling approaches to evaluate possible geological sources of the high pH (11.5)/Na–Cl/Ca–OH mineral waters from the Cabeço de Vide region (Central-Portugal). Water–rock interaction studies have greatly contributed to a conceptual hydrogeological circulation model of the Cabeço de Vide mineral waters, which was corroborated by numerical modelling approaches. The local shallow groundwaters belong to the Mg–HCO3 type, and are derived by interaction with the local serpentinized rocks. At depth, these type waters evolve into the high pH/Na–Cl/Ca–OH mineral waters of Cabeço de Vide spas, issuing from the intrusive contact between mafic/ultramafic rocks and an older carbonate sequence. The Cabeço de Vide mineral waters are supersaturated with respect to serpentine indicating that they may cause serpentinization. Magnesium silicate phases (brucite and serpentine) seem to control Mg concentrations in Cabeço de Vide mineral waters. Similar δ2H and δ18O suggest a common meteoric origin and that the Mg–HCO3 type waters have evolved towards Cabeço de Vide mineral waters. The reaction path simulations show that the progressive evolution of the Ca–HCO3 to Mg–HCO3 waters can be attributed to the interaction of meteoric waters with serpentinites. The sequential dissolution at CO2 (g) closed system conditions leads to the precipitation of calcite, magnesite, amorphous silica, chrysotile and brucite, indicating that the waters would be responsible for the serpentinization of fresh ultramafic rocks (dunites) present at depth. The apparent age of Cabeço de Vide mineral waters was determined as 2790 ± 40 a BP, on the basis of 14C and 13C values, which is in agreement with the 3H concentrations being below the detection limit.  相似文献   

11.
During a semi-lunar tidal cycle from full moon till new moon, tide is characterized by the periodic change in spring and neap tide. Under the in situ conditions of light and temperature, the influence of a semi-lunar spring and neap tidal cycle on nutrient cycling in intertidal flat of the Yangtze estuary was simulated in the laboratory in July 2002. Lab experiments showed that NH4+ and PO43– were always released into overlying waters, while NO3– was directed into sediments in the permanently waterlogged systems, suggesting that the long-term waterlogged sediment acts as a significant source for NH4+ and PO43–, and a sink for NO3– in water columns. In contrast, reflooding of intertidal sediments after long-term desiccation promoted the considerable effluxes of NH4+, NO3– and PO43– into overlying waters, reflecting that the long-term exposed sediment is an important source for nutrients in overlying waters. In addition, the semi-lunar tidal cycle led to the intricate depth distribution patterns of nutrients in intertidal sediments. During long-term exposure, NH4+ in sediments was quickly transformed into NO2– and NO3–, while organic P pool might be converted to slightly adsorbed and iron-bound P. Therefore, it is considered that the semi-lunar tidal circulation has the significant influence on the biogeochemical cycle of nutrients in intertidal systems.  相似文献   

12.
The evolution of the organic geochemistry and carbonate alkalinity of oilfield waters is apparently regular and predictable; this evolution can be typified by five generalizations (1) at or near 80°C there appears to be an exponential rise in the concentration of organic acid anions; (2) the maximum concentration of organic acid anions occurs over approximately the 80–100°C temperature interval; (3) the highest concentrations of difunctional acid anions are associated with the other organic species maxima; (4) difunctional acid anions are the first to be decarboxylated, typically at temperatures of 100–110°C; (5) with increasing temperature (110–130°C) monofunctional acid anions begin to become decarboxylated, resulting in a fluid alkalinity dominated by bicarbonate. Dissolution experiments using artificial and natural oilfield waters demonstrate that mono- and difunctional carboxylic acid anions and hydroxybenzoic acid anions (present in both oilfield waters and the aqueous phase of hydrous pyrolysates) are capable of greatly enhancing Al, Si, Fe and Ca concentrations in solutions from dissolution of minerals by organometallic complexation. This enhancement of mineral solubility has been called upon to explain aluminosilicate dissolution porosity which is quantitatively important in many subsurface reservoirs; certainly, no other viable mechanism has been proposed to explain aluminum transport in the subsurface. When integrated into basin models, the regular evolution of organic and carbonate alkalinity in oilfield waters and the changing mineral stabilities that accompany that evolution help explain commonly observed diagenetic sequences in clastic systems.  相似文献   

13.
Abstract In the Mesozoic basement and Neogene filling of Sofia tectonic graben a non-homogenous system of thermal water reservoirs connected to a united hydrogeothermal basin occurred. The basin contains and reproduces five types of low mineralized thermal waters and four types of mineralized thermal waters with exotic composition. The water temperatures are 30–80(90) °C. The total potential of the basin is assessed at 500 l/s thermal waters and 48 MWt thermal power. The utilization of thermal waters in the area of the Bulgarian capital has its roots and traditions in antiquity, and a promising future. The new town plan of Sofia provides construction of 35 centers for developing a versatile and prosperous hydrothermal business.  相似文献   

14.
Groundwaters and surface water in the Shihongtan sandstone-hosted U ore district, Xinjiang, NW China, were sampled and analyzed for their major-, and trace element concentrations and oxygen, hydrogen, boron and strontium isotope compositions in order to assess the possible origins of the waters and water–rock interactions that occurred in the deep aquifer system. The waters in the study district have been grouped into three hydrochemical facies: Facies 1, potable spring-water, is a pH neutral (7.0), Na–Ca–HCO3 type water with low total dissolved solids (TDS; 0.2 g/l, fresh) and has δ18O of − 8.3‰, δD of − 48.2‰,δ11B of 1.5‰, and 87Sr/86Sr of 0.70627. Facies 2 groundwaters are mildly acidic to mildly alkaline (pH of 6.5–8.0, mean 7.3), Na–Ca–Mg–Cl–SO4 type waters with moderate TDS (8.2 g/l–17.2 g/l, mean 9.3 g/l, brackish) and haveδ18O values in the − 5.8‰ to − 9.3‰ range (mean − 8.1‰), δD values in the − 20.8‰ to − 85.5‰ range (mean − 47.0‰),δ11B values in the + 9.5‰ to + 39.1‰ range (mean + 17.1‰), and 87Sr/86Sr values in the 0.70595 to 0.70975 range (mean 0.70826). Facies 3, Aiting Lake water, is a mildly alkaline (pH = 7.4), Na–Ca–Mg–Cl–SO4 type water with the highest TDS (249.1 g/l, brine) and has δ18O of − 2.8‰, δD of − 45.8‰,δ11B of 21.2‰, and 87Sr/86Sr of 0.70840. The waters from the study district show a systematic increase in major, trace element and TDS concentrations and δ11B values along the pathway of groundwater migration which can only be interpreted in terms of water–rock interaction at depth and strong surface evaporation. The hydrochemical and isotopic data presented here confirm that the groundwaters in the Shihongtan ore district are the combined result of migration, water–rock interaction and mixing of meteoric water with connate waters contained in sediments.  相似文献   

15.
Based on the compilation of numerous data obtained with various methods, the paper discusses primary productivity (PP) in the Atlantic Sector of the Southern Ocean. The distribution of PP values follows the law of zonality: PP values increase southward from 0.25--0.50 gC m–2 day–1, in the waters of the Subtropical frontal zone, to > 1.00 gC m–2 day–1 at the Antarctic coast. Deviations from zonality law were observed in the waters of frontal zones, on the Patagonia Shelf, and in neritic areas. The spatial heterogenities in PP distribution is determined by structural particularities of the horizontal circulation of waters and the respective distribution of different water masses and their modifications. Factors determining PP in the region, as well as correlation of PP and productivity on higher trophic levels, are discussed.  相似文献   

16.
A detailed model is presented of methane photochemistry in the primitive terrestrial atmosphere along with speculation about its interpretation. Steady-state CH4 mixing ratios of 10−6–10−4 could have been maintained by a methane source of about 1011 cm−2 s−1, which is comparable to the modern biogenic methane production rate. In the absence of a source, methane would have disappeared in <104 years, being either oxidized, or polymerized into more complex hydrocarbons. The source strength needed to maintain a steady CH4 mixing ratio and the degree to which methane could have polymerized to form higher hydrocarbons depend upon the amount of CO2 present in the early atmosphere. The dependence on H2 is much weaker. Infrared absorption by methane, and especially by other hydrocarbon species, may have supplemented the greenhouse warming due to carbon dioxide. A radiative model is needed to establish this effect quantitatively. The destruction of the methane greenhouse early in the Proterozoic may have triggered the Huronian glaciation.These calculations also suggest that atmospheres rich in both CO2 and CH4 may be photochemically unstable with respect to conversion to CO.  相似文献   

17.
The Langmuir and Freundlich adsorption isotherm equations were used to model Cs sorption in 6 Welsh soils. The pH (in water), of the soils ranged from 3.5 to 6.5, and the estimated organic matter (determined by loss-on-ignition) ranged from 4.8% to 46%. According to the Langmuir adsorption isotherm, highest sorption maxima,b, were displayed by the loams at 102–204 mg kg−1, compared with organic soils at 37–86 mg kg−1. Subsoil horizons (15–30 cm depth) did not always display higher sorption maxima than their topsoil (0–15 cm depth) counterparts. Where an improved fit to the Freundlich model was found over the Langmuir model, it was assumed that either concurrent desorption of other species, or bond-energy heterogeneity in the substrate, were significant for these soils.  相似文献   

18.
A reconnaissance exploration survey over 14 000 km2 of Precambrian terrain in South Greenland using stream-sediment and stream-water samples delineated a central uranium district of 2000 km2 with enhanced uranium levels and smaller anomalous zones in the south of the field area.The area is underlain by Archean and Proterozoic gneisses, granites and metasediments all of which have been intruded by late Proterozoic alkaline intrusions (Gardar Province). The terrain is mountainous and the streams are either steep torrents or impeded drainages typical of glaciated terrains with boggy organic rich sediments.The central uranium district was defined by a high uranium background in both stream sediments (5–20 ppm) and stream waters (0.5–1.0 ppb) and a markedly higher frequency of very anomalous values in the order of 50–100's ppm in the stream sediments and 1–10 ppb in the stream waters. An areal correlation of uranium, in this district, with high pH and conductivity in the stream water in addition to a higher organic content noted in the stream sediment raised the question of a possible enhancement of uranium values due to secondary environmental effects. On the other hand, an areal correlation of uranium with niobium and other trace elements characteristically associated with alkaline rocks, and the geographic proximity of this uraniferous district to the alkaline intrusions suggested a genetic relationship between uranium mineralization and the alkaline igneous activity.Limited follow-up work located 8 pitchblende occurrences in this extensive district. The pitchblende is in veins which contain quartz, calcite, iron oxide, fluorite and minor sulphides. The isotopic (U-Pb) age of the pitchblende, which ranges from 1180-1090 Ma, corresponds to the late stages of Gardar alkaline igneous activity. It is concluded, therefore, that the reconnaissance geochemistry reflects a district-wide hydrothermal event related to the late volatile differentiates derived from the highly fractionated alkaline magma. A combination of primary and secondary features have complemented each other in enhancing the geochemical reconnaissance data and emphasized its importance but has not materially altered the interpretation.The south of the field area also has a relatively high uranium background in both the sample media with some discrete anomalous zones, usually with a slightly lower order of magnitude than the central area, but still with a distinct contrast of 5–10 times. Fine-grained uraninite has been found in the area occurring as disseminated grains in pegmatitic elements as in the central district. Isotopic ratios (U-Pb) suggest an age of 1728 ± 30 Ma which probably reflects the long cooling of the granite.It is concluded that the geochemical reconnaissance data delineated two uranium metallogenic districts characterized by distinctly different types of uranium mineralization. It is suggested that South Greenland may be part of a much wider uranium geochemical province which includes parts of Labrador. To the present plate-tectonic models, which suggest such a connection (Le Pichon et al., 1977), must be added the comparable reconnaissance geochemical results (G.S.C. Open Files nos. 748 and 749), and the similar 1730 Ma age of the Kitts uranium mineral occurrence in Labrador (Gandhi, S.S , 1978) to that of the uraninite found in the south of the field area in Greenland.  相似文献   

19.
About 500 well and spring waters were collected on an approximately 1-km spacing in an area centered on six small U and Cu-U occurrences near Monticello, N.Y., as an orientation survey in the NURE program. Rocks of the area belong to the Devonian Catskill Group and are predominantly red sandstones and shales of fluvial origin. The sediments dip 0–5° in the main part of the area, but steepen to 45° in the east. The ground waters were analyzed for 46 elements plus several other water properties.An R-mode factor analysis extracted 10 factors. The strongest factor, termed “Dissolved solids”, has heavy loadings on most major elements, plus U, B, Li, Sr, and Zn. This factor is attributed to varying degrees of interaction between original rainwater and rocks. Recognition of anomalies for elements loaded on this factor is aided by evaluation of ratios or plots against total dissolved solids or conductivity. Three weaker factors apparently represent admixtures with two types of deep brine and with waters of enhanced Fe-Mn resulting from reducing conditions. Other factors include an assemblage of insoluble trace metals and a Zn-Cu-P factor, both possibly related to contamination and/or analytical problems, a rare earth group, and an Se-As-Ag factor. The waters are clearly complex mixtures of effects.The geographic distribution of high U values shows some correlation with the distribution of U occurrences, but many equally high values occur outside the known mineralized area. When the data are projected to a vertical section normal to the strike, high U values define two gently dipping aquifers. The upper anomalous aquifer contains the known occurrences but extends downdip. Samples within this aquifer show patterns in U, dissolved O2, and conductivity, apparently related to influx of fresh water from updip, along major rivers, and along possible fractured zones. High He values are also most numerous near the occurrences and define the deeper U-rich aquifer. The interpretation of the data is greatly clarified by separation of individual aquifers.Saturation indices are generally −3.4 to −5 and show patterns similar to dissolved U, except for values of −6 to −9 in a few samples with high phosphate. Predominant U species are usually UO2(CO3)22−, or less commonly UO2CO30 or UO2(HPO4)22−.  相似文献   

20.
Profound biotic changes accompanied the late Cenomanian δ13C excursion and OAE2 in planktic foraminifera in the Tarfaya Basin of Morocco. Planktic foraminifera experienced a severe turnover, though no mass extinction, beginning with the rapid δ13C excursion and accelerating with the influx of oxic bottom waters during the first peak and trough of the excursion. Species extinctions equaled the number of evolving species, though only the disaster opportunists Guembelitria and Hedbergella thrived along with a low oxygen tolerant benthic assemblage. The succeeding δ13C plateau and organic-rich black shale deposition marks the anoxic event and maximum biotic stress accompanied by a prolonged drop in diversity to just two species, the dominant (80–90%) low oxygen tolerant Heterohelix moremani and surface dweller Hedbergella planispira. After the anoxic event other species returned, but remained rare and sporadically present well into the lower Turonian, whereas Heterohelix moremani remained the single dominant species. The OAE2 biotic turnover suggests that the stress to calcareous plankton was related to changes in the watermass stratification, intensity of upwelling, nutrient flux and oxic levels in the water column driven by changes in climate and oceanic circulation. Results presented here demonstrate a 4-stage pattern of biotic response to the onset, duration, and recovery of OAE2 that is observed widely across the Tethys and its bordering epicontinental seas.  相似文献   

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