1,720,996 research outputs found
Continuous-flow δ18O measurements: New approach to standardization, high-temperature thermodynamic and sulfate analysis
No full textThe continuous-flow method for the determination of the O-isotope composition of solid samples has significant advantages over off-line extraction methods, but the problem has arisen of the standardization of results that has only partially been resolved by the use of water standards. We propose a new approach to standardization that uses carbothermic reduction of calcium carbonate standards catalyzed by high-purity AgCl. Analytical accuracy, precision, variance homogeneity and long-term stability are proven. Preliminary data on the barium sulfate δ18O analyses are reported, with a closer look at the different results obtained by off-line and on-line methods on intercomparison standards NBS-127 and MSS3. Copyright © 2005 John Wiley & Sons, Ltd
Sulphide-bearing waters in Northern Apennines, Italy: General features and water-rock interaction
No full textStable isotopes (2H, 18O and 87Sr/86Sr) and hydrochemistry monitoring for groundwater hydrodinamics analysis in a karst aquifer (Gran Sasso, Central Italy)
No full textThe Salar de Atacama, northern Chile: chemical and isotopic compositions of lagunas and streams.
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The Serchio River catchment, Northern Tuscany: geochemistry of stream waters and sediments and isotopic composition of dissolved sulphate.
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Stable isotopes (2H, 18O and 87/86Sr) and hydrochemistry monitoring for groundwater hydrodynamics analysis in a karst aquifer (Gran Sasso, Central Italy).
No full textThis paper deals with chemical and isotope analyses of 21 springs, which were monitored 3 times in the course of 2001; the monitoring program was focused on the groundwater of the Gran Sasso carbonate karst aquifer (Central Italy), typical of the mountainous Mediterranean area. Based on the hydrogeological setting of the study area, 6 groups of springs with different groundwater circulation patterns were distinguished. The hydrogeochemistry of their main components provided additional information about groundwater flowpaths, confirming the proposed classification. The spatial distribution of their ion concentrations validated the assumptions underlying the hydrogeological conceptual model, showing diverging groundwater flowpaths from the core to the boundaries of the aquifer. Geochemical modelling and saturation index computation elucidated water-carbonate rock interaction, contribution by alluvial aquifers at the karst aquifer boundaries, as well as impacts of human activities. The analysis of 18O/ 16O and 2H/H values and their spatial distribution in the aquifer substantiated the hydrogeology-based classification of 6 groups of springs, making it possible to trace back groundwater recharge areas based on mean isotope elevations; the latter were calculated by using two rain monitoring stations. 87Sr/ 86Sr analyses showed seasonal changes in many springs: in winter-spring, the changes are due to inflow of new recharge water, infiltrating into younger rocks and thus increasing 87Sr/ 86Sr values; in summer-autumn, when there is no recharge and spring discharge declines, changes are due to base flow groundwater circulating in more ancient rocks, with a subsequent drop in 87Sr/ 86Sr values. The results of this study stress the contribution that spatio-temporal isotope monitoring can give to the definition of groundwater flowpaths and hydrodynamics in fissured and karst aquifers, taking into account their hydrogeological and hydrogeochemical setting
Sulphur Isotopes, Trace Elements and Mineral Stability Diagrams of Waters from the Abandoned Fe-Cu Mines of Libiola and Vigonzano (Northern Apennines, Italy).
No full textThe geochemical characteristics of rills draining pyrite-chalcopyrite tailings impoundments and of bordering streams were investigated at the ophiolite-hosted Libiola and Vigonzano abandoned massive sulphide mines, northern Apennines Italy. Water samples were analysed for major and
trace chemical composition, hydrogen and oxygen isotope composition, and sulphur isotope composition of aqueous sulphate. Sulphur isotope composition was determined also for some samples of ore sulphides. At Libiola, the newly acquired chemical results on waters corroborate
those from previous investigations, thus providing additional support to existing geochemical models in terms of metal distribution, solid phases precipitation, reaction path modelling and mixing reaction paths, and environmental problems. At Vigonzano, the chemical characteristics of
waters are similar to those at Libiola. In both localities, solution-secondary phase equilibria estimated using an updated thermodynamic dataset account for mineralogy in the field, including poorly crystalline phases like jurbanite and hydrowoodwardite. The hydrogen and oxygen isotope
composition of waters at Libiola and Vigonzano agrees with their meteoric origin. Acid to neutral mine waters do not show any significant isotope shift with respect to the initial water, in spite of the oxidation of even large amounts of pyrite/chalcopyrite ore. The sulphur isotope composition of
aqueous sulphate in mine rills at Libiola (δ 34S = 5.6 to 8.5‰; mean 6.5‰) matches that of massive sulphide ore (δ 34S = −0.5 to 6.7‰; mean 5.8‰), in keeping with the supergenic origin of the sulphate and related isotope effects in the sulphide oxidation process. Sulphate in mine waters at
Vigonzano displays lower δ 34S values in the range 0.6 to 1.5‰. The δ 34S signature of massive ore specimens is within the range reported for most volcanic-hosted massive sulphide deposits, including Cyprus-type deposits
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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