53 research outputs found
Fossichnus solus and Oichnus simplex, two peculiar ichnospecies in modern benthic foraminifera from a polluted area in SW coast of Sardinia, Italy
The modern benthic foraminiferal tests collected from a coastal area of south-western Sardinia (Portoscuso-Portovesme) that is heavily polluted by industrial activity reveal intense and widespread bioerosional structures induced by diversifi ed microborers. A large number of the foraminifera reveals microscopic round holes (1-60 μm in diameter) and roundish concavities (25x40 μm in external diameter) on their surface that belong, respectively, to the ichnospecies Oichnus simplex Bromley, 1981, and Fossichnus solus Nielsen et al., 2003. These traces just occur in the tests of the foraminifera which are heavily infested by microendolithic cyanobacteria, algae and fungi suggests comparable ethological behaviour between the ichnospecies Fossichnus and Oichnus and the microbial euendoliths that are ascribed to individual biological taxa. The greater occurrence of F. solus and O. simplex in the high-Mg foraminiferal porcelanaceous tests than in the low-Mg foraminiferal hyaline tests reveals that the bioerosional processes seem to be related to the Mg/Ca ratio, as well as to morphological structures of the taxa
MINERALOGICAL STUDIES OF THE W-Sn VEIN SKARNS OF MONTE TAMARA (NUXIS, SULCIS DISTRICT): INSIGHTS FOR STRATEGIC MINERALS EXPLORATION IN SW SARDINIA (ITALY).
Skarn deposits are a relevant source of critical raw materials such as W, Sn, and In. Recent studies conducted in
South Sardinia pointed out the relationships between various Sn-W-Mo deposits and the early Permian (289-286 Ma)
F-bearing, ilmenite-series ferroan granites (e.g., Sulcis pluton). This new evidence triggered a broad re-examination
of granite-related deposits including skarn deposits hosted by Cambrian limestones of the low-grade Variscan
basement of the Sulcis district (SW Sardinia). With this purpose, field investigations and OM, SEM-EDS, EMPA,
and LA-ICP-MS observations, and analyses have been conducted on the skarn ores of Monte Tamara (Nuxis, northern
Sulcis) where scheelite has been reported in the old San Pietro and Sinibidraxiu mines. The San Pietro mine exploited
a 1-5 m thick and 70 m deep, steeply dipping skarn orebody located at the tectonized contact between early Cambrian
sandstones and limestones. The orebody includes layers of Grt-Cpx-Wo, magnetite, and Zn-Pb-Cu-Fe sulfide bands.
Prograde and retrograde stages with oxides and sulfides can be recognized. Clinopyroxene is the foremost mineral
of the prograde stage; garnets (andradite-grossular) are usually dark green with typical anomalous birefringence and
distinctly zoned (Fe-rich cores and Al-rich rims). Hematite turned to mushketovite, and Mo-rich scheelite, followed
by In-bearing cassiterite, occasionally occur in the prograde assemblages. Amphiboles and epidotes mark the
retrograde stage, together with abundant Zn-Cu-Fe-Pb sulfides and accessory molybdenite, stannite, bismuthinite,
and Bi-Ag-Pb sulfosalts. At San Pietro, dominant sphalerite displays highly variable Fe, Mn, and Cd contents. Relictlooking
blebs of Fe-Mn-poor Sp are scattered in high-Fe-Mn Sp where Sn EMPA peaks may correlate with
cassiterite-stannite micro-inclusions. Galena composition suggests localized intergrowths with micro-inclusions of
bismuthinite, Bi-Se, and Bi-Te sulfosalts. The stannite-sphalerite geothermometer provided a temperature range of
325-200°C for the sulfide stage. The Sinibidraxiu old mine exploited a 1,5 m thick and 60 m deep columnar body,
hosted in early Cambrian marbles. It consists of a sphalerite-wollastonite assemblage with late sulfides, quartz, and
calcite, hosting cm-sized arsenopyrite and scheelite. Scheelite is Mo-poor; Sn-, other Mo-phases and Bi-phases are
absent. High-Fe Sp, rimmed by low-Fe Sp and blebby galena, is finely intergrown with wollastonite cockades. The
results from this study suggest that a wide range of skarn-related mineralizing phenomena occurred in the Monte
Tamara area. Both orebodies resulted from a structurally controlled migration of metasomatic fluids inside the hosting
carbonate formation. Mineral zonation and composition of the San Pietro skarn point towards skarn development
under varying fO2 conditions, oxidizing then rapidly turning to moderately reducing within the prograde W-Sn skarn
stage and into the sulfide stage. The features of the Sinibidraxiu orebody (e.g., Mo-poor, As-devoid scheelite) suggest
a formation from reducing metasomatic fluids but S-poor compared to San Pietro, probably at more distal
environments (e.g. low Sn-Bi contents). From this point of view, the Monte Tamara area still maintains an economic
potential, linked to the possible presence of proximal skarn ores at depth; thereby representing a key area for further
exploration for granite-related strategic and critical metals in SW Sardinia
PRELIMINARY STUDIES ON BIOPRECIPITATION PROCESSES MEDIATED BY SULFATE REDUCING BACTERIA (SRB) AND METAL IMMOBILIZATION IN MINE IMPACTED ENVIRONMENTS.
Mining activity often leaves a critical legacy represented by huge volumes of mine wastes and residues, usually made
up of highly reactive materials, which lead to the mobilization and dispersion of harmful elements in soils and waters.
Although these extreme environments are adverse to the development of living organisms, it has been observed that
some microorganisms are able to adapt, playing a role in metal mobility, and becoming part of the resilience of the
system itself.
The Iglesiente and Arburese (SW Sardinia, Italy) mine districts, now abandoned, have been exploited for centuries
by mining activities aimed at Pb-Zn extraction from sulfides and non-sulfides (calamine) deposits. Here,
biogeochemical barriers naturally occur as an adaptation of the ecosystem to environmental stresses. Studies, from
macroscale to microscale, showed that sulfate-reducing bacteria (SRB) may influence metal mobility by mediating
the precipitation of secondary authigenic metal sulfides under reducing conditions. Specifically, framboids of Zn
sulfides and Fe sulfides have been observed in the sections of stream sediments core characterized by the presence
of abundant organic matter, especially residues of vegetal tissues (e.g. roots and stems of Juncus acutus and
Phragmites australis).
Laboratory-scale experiments were performed to better understand the bioprecipitation processes. For this purpose,
anaerobic batch tests were carried out using high polluted mining waters (Zn and sulfate concentrations up to 102
and 103 mg/l, respectively) inoculated with native selected sulfate-reducing bacteria from stream sediments collected
in the investigated areas. Dramatic decrease (up to 100%) in Zn and sulfate was observed in solutions. Moreover,
scanning electron microscopy - energy dispersive spectroscopy (SEM-EDS) analysis, performed on solids recovered
at the end of the experiments, showed the presence of precipitates characterized by a tubular morphology and made
up by S and Zn. SRB inocula were studied by next-generation sequencing (NGS) approach, with the aim to compare
the microbial diversity of the different SRB communities and to search for indigenous novel metal-tolerant
sulfidogenic microorganisms.
These findings represent a valuable step forward to plan effective bioremediation strategies for reducing metal
mobility and dispersion. Also, bioprecipitation mediated by SRB can have great potentialities for metal recovery and
our results can help to develop biomining techniques.
The authors acknowledge CESA (E58C16000080003) from RAS and RAS/FBS (F72F16003080002) grants, and the
CeSAR (Centro Servizi d'Ateneo per la Ricerca) of the University of Cagliari, Italy, for SEM analysis
In situ investigation of galena dissolution in oxygen saturated solution: Evolution of surface features and kinetic rate
A Modeling Infrastructure Based on SWAT for the Assessment of Water and Soil Resources
Many regions around the world, and the Mediterranean basin is just one example, are characterized by scarcity of water and limited productive soils. Agricultural practices in such areas are being based on the intensive use of fertilizers and on the use of limited water resources. Contamination levels in water bodies, both ground and surface waters in Mediterranean countries, are found to be increasing and local and regional authorities are now facing this awkward environmental problem.
In the frame of the regional TESTARE and of the EU SUPREME funded projects, we aim at supporting the set up of a sustainable agricultural production frame, addressing vulnerable communities living in semi-arid and arid areas within the Mediterranean. The scope is to progress web-based observation systems through the integration of state-of-the-art leading edge characterization, monitoring and modeling tools. The modeling infrastructure is being build and here presented to analyze the water, sediment and nutrient cycle at the catchment’s scale, and crop growth. In this work, we particularly address the problem of agricultural drought and the impact of agriculture on water quality in Sardinia (Italy, Europe). Local communities have been increasingly challenged by water scarcity that is lowering agricultural productivity. Different soils and crops are considered in the test site
Geochemical behaviour of rare earth elements in mining environments under non-acidic conditions
The rare earth elements (REE) were determined in water and solid samples at the abandoned mine of Ingurtosu
(Sardinia, Italy). Research was performed to evaluate the main factors that control the geochemical behaviour of REE
in near-neutral pH mining environments. REE show the highest concentrations (13-100 μg/l) in drainages from mine
tailings, especially when water sampling was carried out under high flow conditions. Positive correlations between
ΣREE and Zn and Pb were observed, possibly indicating REE sorption on Zn- and Pb-rich fine particles (<0.4 μm).
Fractionation processes were observed normalizing REE in waters with respect to REE in mining-related residues.
The Naracauli waters show an enrichment in HREE, probably due to the high stability of dissolved HREE(CO3)2-
complexes in the studied waters. REE fractionation was not observed during hydrozincite bioprecipitation
Galena Surface Dissolution : an evaluation of pH effect on the apparent activation energy
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