1,720,966 research outputs found
Weathering of Pb-Zn mine tailings in PH buffered environment
No full textThe Ingurtosu Pb-Zn mine in south-western Sardinia, exhibits three main weathering processes: 1) oxidation without acidification derived from Pb and Zn sulphides; 2) oxidation with acidification derived from Fe sulphides; 3) pH buffering due to Ca and Mg carbonate dissolution. These weathering processes are followed by adsorption of metals on iron oxyhydroxides and precipitation of hydrated sulphates (sometimes carbonates). Nearly all iron sulphides and carbonate (siderite, ankerite) grains, have alteration rims made up of iron oxyhydroxides (goethite), where Zn, Cu and Pb are adsorbed after sulphide oxidation. Moreover, the occurrence of slightly weathered clay minerals confirms the low pH values are never reached. -from Author
Geochimica delle acque nelle grotte di miniera del Monte San Giovanni, Iglesias
No full textIn the framework of a National Project PRIN 2001-2003 “Morphological and Genetic study of
Speleothems of particular karst environments of Italy and of Central-South America” some water
samples have been taken in Mount San Giovanni (Iglesias-Gonnesa) in the homonymous lead-zinc
mine, presently abandoned, that contains one of the most interesting and beautiful mine caves
known in the world, Santa Barbara cave, open to public thanks to the work and the dedication
of IGEA S.p.A. of Iglesias.
The main objective of this research was to supply some preliminary data on the chemical composition
of the drip waters, and put these in relation with the chemical deposits actually forming
and the ones formed in the past. Aside the basic chemistry and the main chemical-physical
parameters also the content in many minor and trace elements has been analysed, with special
interest for base metals (e.g. Pb, Zn) contained in the mineralization and those elements (e.g. Mg,
Sr, Ba) that can influence the type of chemical deposit in formation. The determination of the
thermodynamic state of the waters, by means of speciation and saturation calculations performed
using the software PHREEQC, has allowed to model the processes of present water-rock
interaction, and to simulate the geochemical conditions of the past that have brought to the formation
of peculiar cave minerals such as Hydrozincite
Architettura deposizionale degli accumuli a minerali pesanti (placers): esempio nell’Ordoviciano della Sardegna e della Bretagna
No full text
Transformation of cumulate mafic rocks to granulite and re-equilibration in amphibolite and greenschist facies in NE Sardinia, Italy
No full textThe ultramatic amphibolites hosted in the Hercynian migmatite of NE Sardinia consist of three main compositional layers (A, B, C) from a few metres to a few decametres thick. Layer A is made up of coarse-grained olivine, chlorite, amphibole, spinel, minor pyroxene, garnet and, rarely, plagioclase. Layer B is made up of coarse-grained plagioclase, olivine, pyroxene, spinel, garnet and amphibole. Layer C consists mainly of porphyroblastic garnet, pyroxene, large amphibole grains (up to 5 cm) and minor plagioclase. On the basis of mineral assemblages and microstructures, three stages of mineralogical re-equilibration can be recognised: granulite, amphibolite and greenschist. Primary igneous olivine and anorthite reacted under granulite conditions to produce coronas consisting of orthopyroxene, clinopyroxene, green spinel and garnet. The amphibolite stage is characterised by the formation of brown and green clinoamphiboles (between pyroxene and corona garnet), anthophyllite, tale, Mg-rich chlorite, plagioclase and Cr-bearing spinel. Greenschist stage minerals, mostly replacing the mafic minerals, consist of tremolite, fayalite, epidote, albite, calcite, dolomite and serpentine. The history of the ultramatic amphibolites started with igneous crystallisation and continued through granulite (T=700-740 degreesC, P= similar to 8-10 kbar), amphibolite (T=580-640 degreesC, P=4-6 kbar) and greenschist facies (T= similar to 330-400 degreesC, P<2-3 kbar). Evaluation of P-T conditions indicated a P-T path from the protolith to granulite stage, characterised by an increase in pressure and temperature, and then from the granulite facies through amphibolite to the greenschist stage, characterised by a decrease in pressure and temperature. The petrological evolution of the ultramafic amphibolites and the P-T time path is discussed in the context of the Hercynian orogeny in Sardinia. (C) 2002 Published by Elsevier Science B.V
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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