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Studi geochimica sulla mobilizzazione di metalli tossici in acque naturali e in suoli di aree a rischio di contaminazione.
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Impatto ambientale dell’attività mineraria nel giacimento epitermale a oro di Furtei, Sardegna: dati mineralogici
No full textTamarugite from the gold mine of Furtei, Sardinia, Italy
No full textTamarugite forms inside a grotto excavated in hydrothermally altered andesitic rocks at the gold mine of Furtei, Sardinia, Italy. The mineral mainly occurs as single phase in globular aggregates, with only small amounts of gypsum, halite and halotrichite-pickeringite. Tamarugite also occurs intimately mixed with alunogen and pickeringite-halotrichite, or associated with alunogen and magnesian aubertite. The formation of tamarugite is the result of the interaction between acidic sulfate waters, deriving from oxidation of disseminated sulfides (mainly pyrite), and the hydrothermally altered country rocks. The arid conditions of the Furtei area favour the formation of tamarugite and other water-soluble secondary minerals of evaporation of the scanty, saline waters percolating through the walls of the grotto. Unlike other world tamarugite occurrences, the main source of sodium is not sea spray, but can be referred to the sodium content of the volcanic rocks which were affected by hydrothermal circulation. A least-squares unit-cell refinement of 47 reflections from X-ray powder diffraction analysis of the Furtei tamarugite gave the following results for a monoclinic cell: a = 7.358(2), Å, b = 25.244(9) Å, c = 6.095(2) Å, β = 95.16(4)°, V = 1127.4(5) Å3
Bulachite, a rare aluminium arsenate from Sardinia, Italy: the second world occurrence
No full textA second world occurrence for bulachite, Al2(AsO4)(OH)3 · 3H2O, has been found in a few specimens collected on a mine dump from old workings in an arsenopyrite lens in south Sardinia (Italy). The mineral occurs as sparse, whitish, satiny, crumbly polycrystalline aggregates on mansfieldite and goethite encrusting quartzite clasts. Bulachite is intimately mixed with kaolinite, illite and an amorphous allophane-like phase, and with minor amounts of quartz and Fe3+ oxyhydroxides. Bulachite crystals occur as very slender, curved fibres (about 250 nm in diameter and up to 150 μm long) aggregated into radial or sub-parallel groups. A least-squares unit-cell refinement of 34 reflections from X-ray powder diffraction analysis gave the following results for an orthorhombic cell: a = 15.53(3) Å, b = 17.79(3) Å, c = 7.01(1) Å, V=1936(4) Å3
Magnesian aubertite, (Cu,Mg)Al(SO4)2Cl . 14H2O, from the gold mine of Furtei in Sardinia, Italy
No full textMagnesian aubertite, an intermediate term between aubertite and magnesioaubertite with theoretical formula (Cu,Mg)Al(SO4)2Cl · 14H2O, occurs inside a grotto excavated in hydrothermally altered andesitic rocks at the gold mine of Furtei (Sardinia, Italy). The mineral is strictly associated with tamarugite and alunogen; the complete assemblage also includes natrojarosite, halotrichite-pickeringite, gypsum, halite, paratacamite-atacamite, growing on kaolinite-dickite, montmorillonite and quartz. A least-squares unit-cell refinement of 52 reflections from X-ray powder diffraction analysis gave the following results for a triclinic cell: a = 6.302(4) Å, b = 13.195(9) Å, c = 6.288(5) Å, α = 91.77(6)°, β = 94.53(5)°, γ = 82.63(6)°, V = 516.8(4) Å3. Quantitative wet-chemical analysis gave the following composition on the basis of Cu + Mg= 1: (Cu0.56 Mg0.44)Al1.12 (SO4)2.34Cl1.09 · 14H2O, with an atomic Cu/Mg ratio of 1.28. The formation of magnesian aubertite is linked to the generation of acidic sulfate waters following oxidation of pyrite disseminated in the country rocks. Interaction of these waters with the hydrothermal alteration minerals releases Mg and Al into solution, while Cu derives from oxidation of Cu-bearing sulfides (mainly enargite)
Microbioerosion on the shells of recent foraminifers in polluted shallow water environment
No full textInvestigation on recent benthic foraminifers used as bioindicators for monitoring coastal pollution revealed that phototrophic bacterial colonies infest the surfaces of the calcareous benthic foraminifers. Many traces of microborers have been observed in foraminiferal shells coming from shallow waters in an industriai polluted coast. Samples were collected in the end of July 2006. Sampling depths ranged from the intertidal to two meters; water temperature were about 27°C to 31°C and salinity values of about 37 g/I. Preliminary results from SEM pictures have allowed to recognize the following ichnotaxa: Fasciculus acinosus Glaub related to the modern cyanobacterial species Hyella balani Lehmann, Orthogonun sp., which biological identity of its producers is unknown, and Scolecia filosa Radtke related to modern cyanobacterium Plectonema terebrans Bornet & Flahanet. Geochemical analysis performed on sediments show that the investigated industriai area is contaminated mainly by heavy metals (Fe, Mn, Pb, Zn, Cd). Increasing pollution results in low species diversity and population density, associated with an increase in tolerant or opportunistic species. In this contaminated environment aberrant foraminiferal tests were frequently found. Microanalysis reveals that deformed specimens locally contain high level of heavy metals. This suggests that heavy metals pollution may represent a particular microenvironment able for developing microbial communities. In fact the unpolluted coastal areas near the studied sites at the same batimetry don't show bioerosion traces; higher species diversity and population density than polluted areas and very scarce deformed forms were found
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