Iron and manganese accumulations in Sardinia: the role of supergenic and hydrothermal processes

This paper examines the compositional features of some Fe and Mn accumulations of Sardinia in order to reconstruct the palaeoenvironmental conditions of ores formation, to better characterize the processes that lead to Fe and Mn minerals formation and to compare the Fe and Mn geochemical behavior within different depositional environments. The research focused on comparison between: 1) continental Fe oxyhydroxides concentrations, formed under oxic conditions on a palaeosurfaces of the Tacchi area, and the Uppermost Ordovician oolitic ironstones of shallow anoxic marine environment of the Nurra district; 2) marine supergene Mn ores of Logudoro Basin, hosted in a littoral conglomerate laying at the base of the Miocene transgressive calcareous sediments, and continental hydrothermal Mn mineralizations of San Pietro Island and Anglona district where they are the stockwork and veins filling within Miocene volcanic sequences. Chemical analyses (XRF, INAA and ICP-MS), XRD analysis, OM and SEM-EDS observations were performed on each samples. The analyses results suggest that although the Sardinian ores formed in different environments (marine vs continental) and under contrasting climatic (sub-glacial vs tropical) and environmental (supergene vs hydrothermal) conditions, they share similar mineralogical or geochemical features. Therefore, not necessarily dramatic palaeoenvironmental differences find a counterpart in geochemical features of the chemical sediments

REEs in the North Africa P‐Bearing Deposits, Paleoenvironments, and EconomicPerspectives: AReview

AreviewofthecompositionalfeaturesofTunisia,Algeria,andMoroccophosphoritesisproposedinordertoassessandcomparethepaleoenvironmentalconditionsthatpromotedthede‐positformationaswellasprovideinformationabouttheireconomicperspectiveinlightofgrowingworldwidedemand.Sincethesedepositsshareaverysimilarchemicalandmineralogicalcomposi‐tion,theattentionwasfocusedonthegeochemistryofrareearthelements(REEs)andmostlyonΣREEs,CeandEuanomalies,and(La/Yb)and(La/Gd)normalizedratios.TheREEsdistributionsrevealseveraldifferencesbetweendepositsfromdifferentlocations,suggestingmostlythattheTu‐nisianandAlgerianphosphoritesprobablywerepartofthesamedepositionalsystem.There,sub‐reducingtosub‐oxicconditionsandamajorREEsadsorptionbyearlydiagenesiswererecorded.Conversely,intheMoroccanbasins,sub‐oxictooxicenvironmentsandaminordiageneticalterationoccurred,whichwaslikelyduetoadifferentseawatersupply.Moreover,thedrasticenvironmentalchangesassociatedtothePaleocene–EoceneThermalMaximumeventprobablyinfluencedthecom‐positionofNorthernAfricanphosphoritesthataccumulatedthehighestREEsamountsduringthatspanoftime.BasedontheREEsconcentrations,andconsideringtheoutlookcoefficientofREEcomposition(Koutl)andthepercentageofcriticalelementsin ΣREEs(REEdef),thestudieddepositscanbeconsideredaspromisingtohighlypromisingREEoresandcouldrepresentaprofitableal‐ternativesourceforcriticalREEs

REEs and other critical raw materials in Cretaceous Mediterranean-type bauxite: the case of the Sardinian ore (Italy)

Mediterranean-type bauxite deposits in Sardinia formed during the Upper Cretaceous (Cenomanian–Turonian) due to the emergence of the south European margin of the Alpine Tethys in an area affected by monsoonal climate. The deposits were controlled by the structural frame formed in a transpressive tectonic regime and unconformably overlie carbonate rocks of different age and composition, which led to the formation of different bauxite types. In general, in the Sardinian bauxite deposits, boehmite is the main Al-phase, kaolinite is the main Si-rich mineral, and hematite as well as goethite are the Fe-rich phases. Secondary authigenic anatase and detrital rutile control the Ti contents. Eu/Eu* anomalies show that the bauxite types were derived from the Variscan basement. However, there are differences in Al2O3 and SiO2 contents, which suggest there was localised variability in the extent of epigenetic replacement of kaolinite by boehmite. R-mode factor analysis suggests that most critical raw materials (as defined by the devoted European Union working group), such as Sc, Ga, Nb, Hf, Ta, and W, covary with Al2O3 contents. In the Si-poor bauxite, these metals of economic interest are likely controlled by boehmite, whereas in the Si-rich bauxite they are mostly controlled by weathering-resistant minerals. Rare earth element (REE)-rich minerals, including fluorocarbonates and cerianite, are concentrated in the basal, illuvial horizon, especially in the silica-rich bauxite (ΣREE = 1006–2034 ppm). Cerianite formation required Ce oxidation, whereas fluorocarbonate formation involved mobilisation of trivalent REEs and further fluoride complexation. Both REE-rich mineral phases precipitated under alkaline pH conditions near to the carbonate bedrock. Our evaluation of the critical raw materials distribution in the Sardinian bauxite, coupled with the “economic importance” and “supply risk” parameters, indicate the ore contains large amounts of metals characterised by a “supply risk”, such as light and heavy REEs, and metals of “economic importance”, such as V and W. In this way, the Sardinian bauxite deposits could be reconsidered as a potential source of critical raw materials

Serpentinite Carbonation for CO2 Sequestration in the Southern Apennines: Preliminary Study

Abstract During "Mineral CO2 sequestration" the CO2 is chemically stored in solid carbonates by the carbonations of minerals. The sequestration of CO2 is permanent and safe. Mineral carbonation is an exothermic reaction and occurs naturally in the subsurface as a result of fluid–rock interactions within serpentinite. In situ carbonation aims to promote these reactions by injecting CO2 into porous, subsurface geological formations. In the northern sector of the Pollino Massif (southern Italy) extensively occur serpentinites; they are the subject of a project devoted to their possible use for in situ geological sequestration of CO2

Mineralogy and heavy metal assessment of the Pietra del Pertusillo reservoir sediments (Southern Italy)

The Pietra del Pertusillo freshwater reservoir is a major artificial lake of environmental, biological, and ecological importance located in the Basilicata region, southern Italy. The reservoir arch-gravity dam was completed in 1963 for producing hydroelectric energy and providing water for human use, and nearby there are potential sources of anthropogenic pollution such as urban and industrial activities. For the first time, the minero-chemistry of the lake and fluvio-lacustrine sediments of the reservoir have been evaluated to assess the environmental quality. Moreover, the composition of fluvial sediments derived from the peri-lacual zone of the reservoir and of local outcropping bedrock were also studied to understand the factors affecting the behavior of elements in the freshwater reservoir, with particular attention paid to heavy metals. In Italy, specific regulatory values concerning the element threshold concentration for lake and river sediments do not exist, and for this reason, soil threshold values are considered the standard for sediments of internal waters. The evaluation of the environmental quality of reservoir sediments has been performed using enrichment factors obtained with respect to the average composition of a reconstructed local upper continental crust. We suggest this method as an innovative standard in similar conditions worldwide. In the studied reservoir sediments, the trace elements that may be of some environmental concern are Cr, Cu, Zn, As, and Pb although, at this stage, the distribution of these elements appears to be mostly driven by geogenic processes. However, within the frame of the assessment and the preservation of the quality of aquatic environments, particular attention has to be paid to As (which shows median value of 10 ppm, reaching a maximum value of 26 ppm in Quaternary sediments), constantly enriched in the lacustrine samples and especially in the fine-grained fraction (median = 8.5 ppm)

Petrography and Geochemistry of the Leucocratic Rocks in the Ophiolites from the Pollino Massif (Southern Italy)

In the Tethyan realm, leucocratic rocks were recognized as dikes and layers outcropping in the ophiolitic rocks of the Western Alps, in Corsica, and in the Northern Apennines. Several authors have suggested that the origin of leucocratic rocks is associated with partial melting of cumulate gabbro. Major and trace elements composition and paragenesis provided information about the leucocratic rocks genetic processes. This research aims at disclosing, for the first time, the petrographical and geochemical features of Timpa delle Murge leucocratic rocks, Pollino Massif (southern Italy), in order to discuss their origin and geodynamic significance through a comparison with other Tethyan leucocratic rocks. These rocks are characterized by high amounts of silica with moderate alumina and iron-magnesium contents showing higher potassium contents than plagiogranites, due to plagioclase alteration to sericite. Plagioclase fractionation reflects negative Eu anomalies indicating its derivation from gabbroic crystal mushes. The chondrite normalized REEs patterns suggest the participation of partial melts derived from a metasomatized mantle in a subduction environment. The results reveal some similarities in composition with other Tethyan leucocratic rocks, especially those concerning Corsica and the Northern Alps. These new data provide further clues on the origin of these leucocratic rocks and the Tethyan area geodynamic evolutio

Twenty-Year Follow-Up of Excimer Laser Photorefractive Keratectomy: A Retrospective Observational Study

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Hydrogeochemistry and Groundwater Quality Assessment in the High Agri Valley (Southern Italy)

The High Agri Valley (southern Italy) is one of the largest intermontane basin of the southern Apennines affected by intensive agricultural and industrial activities. The study of groundwater chemical features provides much important information useful in water resource management. In this study, hydrogeochemical investigations coupled with multivariate statistics, saturation indices, and stable isotope composition (δD and δ18O) were conducted in the High Agri Valley to determine the chemical composition of groundwater and to define the geogenic and anthropogenic influences on groundwater quality. Twenty-four sampling point ( including well and spring waters) have been examined. The isotopic data revealed that groundwater has a meteoric origin. Well waters, located on recent alluvial-lacustrine deposits in shallow porous aquifers at the valley floor, are influenced by seasonal rainfall events and show shallow circuits; conversely, spring waters from fissured and/or karstified aquifers are probably associated to deeper and longer hydrogeological circuits. The R -mode factor analysis shows that three factors explain 94% of the total variance, and F1 represents the combined effect of dolomite and silicate dissolution to explain most water chemistry. In addition, very low contents of trace elements were detected, and their distribution was principally related to natural input. Only two well waters, used for irrigation use, show critical issue for NO3- concentrations, whose values are linked to agricultural activities. Groundwater quality strongly affects the management of water resources, as well as their suitability for domestic, agricultural, and industrial uses. Overall, our results were considered fulfilling the requirements for the inorganic component of the Water Framework Directive and Italian legislation for drinking purposes. The water quality for irrigation is from "good to permissible" to "excellent to good" although salinity and relatively high content of Mg2+ can occasionally be critical