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This review summarizes the existing data about the geological sources of As in Greece; their variety and the relevant concentrations make Greece a peculiar territory to generalize and better understand the methodology for their assessment. These sources concern As-containing ores in active and abandoned mining areas, geothermal/hydrothermal waters, lignites in exploited and unexploited deposits, As-minerals in various rock types such as metamorphic rocks, and mineral dust originating in Sahara desert. It is considered that As release from the above sources, in conjunction with various anthropogenic As fluxes, occasionally creates distinct areas with contaminated groundwater, soils, marine and atmospheric environment. In general, Greece has been reported as a global As "hot spot" and it is argued that a significant amount of the Hellenic population might be affected by As pollution. The most important and permanent As source seems to be geothermal/hydrothermal fluids, due to faults and volcanic activity, affecting the underground, surface, and marine aquatic environment. © 2016 Springer-Verlag Berlin Heidelberg.

Amorphous orpiment-like As-sulfides (As2S3) are the most common As phases precipitating in hydrothermal systems, yet there is a lack of information regarding their solid-state characterization. Using a combination of optical, SEM-EDS, micro-Raman and XANES/EXAFS applications, we investigated yellow-orange As- and S-rich sediments occurring in the shallow-water hydrothermal system off the coast of Milos Island, Greece. The precipitates have several morphologies, but are dominantly colloidal. Intriguing "biological" morphologies also exist (e.g., cell-like (~10μm), spirals (~20μm), and rounded "cinnamon bun" shapes (~20μm)). SEM-EDS data indicated that the precipitates have an As:S ratio similar to orpiment (average=0.58, range 0.51-0.63; n=8). Micro-Raman spectra indicated that orange colored precipitates appear to be dominated by poorly crystalline and/or amorphous arsenic sulfides with micro-amounts of more crystalline orpiment and impure sulfur. The yellow sediments also contained crystalline elemental sulfur in the form S8. Bulk As K-edge XANES spectra of the As-sulfide precipitates proved a valence of As corresponding to orpiment-type (As2S3) compounds (-1 to +3). EXAFS fitting results indicated that the studied material exhibits an amorphous orpiment-like structure with As ions coordinated by 3 sulfur atoms (CN=3.0). The As-S interatomic distance of the first shell is calculated at 2.279Å and the Debye-Waller factor (σ2) is 0.00427. These data suggest that the modeled structure of the studied precipitates is slightly S-deficient and ordered only in the first shell around As, resembling an orpiment-type structure, whereas higher shells are not present and must be disordered. The disorder phenomenon may be strictly produced either by the existence of occasional As-S-As bridges with As-As bonds or by the occurrence of As-O-As bridges, causing twisting of the AsS3 pyramids in the initial orpiment structure. This distortion in the higher coordination shells of the structural sheets creates the amorphous orpiment. © 2015 Elsevier B.V..

We report on integrated geomorphological, mineralogical, geochemical and biological investigations of the hydrothermal vent field located on the floor of the density-stratified acidic (pH ∼ 5) crater of the Kolumbo shallow-submarine arc-volcano, near Santorini. Kolumbo features rare geodynamic setting at convergent boundaries, where arc-volcanism and seafloor hydrothermal activity are occurring in thinned continental crust. Special focus is given to unique enrichments of polymetallic spires in Sb and Tl (±Hg, As, Au, Ag, Zn) indicating a new hybrid seafloor analogue of epithermal-to-volcanic-hosted- massive-sulphide deposits. Iron microbial-mat analyses reveal dominating ferrihydrite-type phases, and high-proportion of microbial sequences akin to Nitrosopumilus maritimus, a mesophilic Thaumarchaeota strain capable of chemoautotrophic growth on hydrothermal ammonia and CO 2. Our findings highlight that acidic shallow-submarine hydrothermal vents nourish marine ecosystems in which nitrifying Archaea are important and suggest ferrihydrite-type Fe 3+ -(hydrated)-oxyhydroxides in associated low-temperature iron mats are formed by anaerobic Fe 2+ -oxidation, dependent on microbially produced nitrate.

A large paleo-river of Miocene age traversing Libya from south to north has been previously demonstrated by seismic, stratigraphic, paleontological, and remote sensing data. The depositional environment of As Sahabi Formation in north central Libya is this large and now extinct Eosahabi River. However, the source of this major African river has remained controversial. Dark-colored sedimentary material with magnetic properties suggested a source from the basaltic Haruj as Aswad massif in south central Libya. To test this hypothesis, mineralogical and geochemical study of clayey sediments from three localities, P25, P28 and P96c, from fossiliferous Member U1 of the As Sahabi Formation, were carried out. Results strongly indicate very mature and re-processed sediments of continental origin, and felsic sources with no basaltic contribution. Thus the origin can be traced to an upland area of outcrop of rocks of Precambrian continental origin in northeastern Chad. An alternative scenario is that the Sahabi sediments originated from Precambrian outcrops in Ethiopia through an east-west river connection with the Nile. We consider this hypothesis unlikely, since it is based only on remote sensing data, and lacks any time control or geological supporting evidence. The abundant vertebrate fauna from the Sahabi Formation shows strong similarities with penecontemporaneous fossil faunas in Chad and is supportive of an origin of the Eosahabi River in Neogene mega-Lake Chad. © 2012 Elsevier Ltd.

Bottom and fly ash samples (BASH and FASH) from the APOTEFROTIRAS S.A. medical waste incinerator (Athens, Greece) were investigated. Powder-XRD data and geochemical diagrams showed BASH to be an amorphous material, analogous to basaltic glass, and FASH consisting of crystalline compounds (mainly CaClOH). Bulk analyses by ICP-MS and point analyses by SEM-EDS indicated a high content of heavy metals, such as Fe, Cu and Cr, in both samples. However, BASH was highly enriched in Ni while FASH was additionally enriched in Zn and Pb. Gamma-ray measurements showed that the radioactivity of both ash samples, due to natural and artificial radionuclides (137Cs, 57Co), was within the permissible levels recommended by IAEA. According to EN-type leaching tests, BASH was practically inert with regard to the mobility of the hazardous elements in aqueous media. FASH, however, showed a relatively high EN (and TCLP) leachability with regard to Pb and Zn. Finally, the stabilisation method, suggested for the treatment of FASH, included compression of the powder into briquettes using an appropriate machine and embedding the briquettes into pozzolanic cement blocks. After this treatment, TCLP and EN-type tests showed minimal release of Pb and Zn, thereby demonstrating a reliable management of ash waste. © 2011 Elsevier B.V.

Typical red-brown (Fe-rich) and high-quality white-grey (Fe-depleted) bauxite samples from active mines of the Parnassos-Ghiona area, central Greece, were investigated. According to XRF and ICP-MS analyses their actinide content, and particularly of Th, is relatively increased. Fe-depleted samples contain up to 62.75 ppm Th corresponding to 220 Bq/kg due to 228Ac ( 232Th-series), whereas Fe-rich samples are less Th-radioactive (up to 58.25 ppm Th, 180 Bq/kg due to 228Ac). Powder-XRD patterns showed that Th-enriched (Fe-depleted) bauxite consists mostly of diaspore (AlOOH polymorph), anatase and rutile (TiO2 polymorphs). SEM-EDS indicated the presence of Ti-Fe-containing phases (e.g. ilmenite, FeTiO3), chromite (Cr-spinel) and besides LREE-minerals (mostly bastnäsite/parisite- group) and zircon (ZrSiO4) hosting a part of the bulk Th. The presence of Th in diaspore and in Ti-containing phases (not detected by SEM-EDS as in the case of REE-minerals and zircon) was investigated, into distinct pisoliths of Fe-depleted bauxite, using μ-XRF and μ-XAFS in the SUL-X beamline of the ANKA Synchrotron facility (KIT, Germany). XAFS spectra of Th salts and Th-containing reference materials were obtained as well. Accordingly it was revealed, for the first time in the literature, that Ti-phases, and particularly anatase, host significant amounts of Th. This novel conclusion was complementary supported by LA-ICP-MS analyses indicated an average of 73 ppm Th in anatase grains together with abundant Nb (3356 ppm), Ta (247 ppm) and U (33 ppm). The Th LIII-edge XAFS spectra as compared to reference materials, give also evidence that Th4+ may not replace Ti 4+ in distorted [TiO6] fundamental octahedral units of anatase and ilmenite lattice (CN = 6). The occupation of either extraframework sites of higher coordination (CN = 6.9 or even CN = 7.4), according to EXAFS signals evaluation, or of defected/vacant () sites is more probable. This is likely explained by the difficulty of Th4+ to replace directly Ti4+ in [6]-coordinated (octahedral) sites due to the large difference in the relevant ionic radii (0.940 and 0.605 respectively). © 2011 Elsevier B.V. All rights reserved.

We studied the geological and technological features of altered pyroclastic rocks from the main Bentomine Kimolian Enterprises S.A. quarry, in the Prassa region on the northeastern part of the Kimolos island, Greece. Particular emphasis was given to a MOR-type (mordenite) zeolite-rich material, tuff, which also contains K-feldspars, opal-CT and clays (mainly smectite) according to X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy-dispersive spectrometry (EDS). Additionally, it was characterised by a relatively low SiO2 component (av. 70 wt%) compared to surrounding volcanic rocks. Mordenite crystals are alkali- (Na- and moreover K-) rich. According to trace-element discrimination diagrams (Zr/TiO2-b/Y), the protoliths of the mordenite-bearing tuffs could be trachyandesites, whereas Ti/Al-Eu/Eu* diagrams indicated a clear felsic affinity. Normalised REE patterns confirmed an expected negative Eu anomaly and a relative HREE depletion, whereas relevant multi-element diagrams indicated positive Cs, Rb, Th, Pb, U and Ta, negative Ba, P and Ti and compatible elements anomalies. The SSABET of the rocks reached a value of 63 m2/g. In that case, the CEC was measured to be 98 meq/100 g. The above data suggest that the industrial minerals exploited in the Prassa quarry show good capabilities for the development of new products for innovative industrial and daily uses. © 2010 E. Schweizerbart'sche Verlagsbuchhandlung, D-70176 Stuttgart.

Mortar that was used in building as well as in conservation and restoration works of wall paintings have been analysed isotopically (δ13C and δ18O) in order to evaluate the setting environments and secondary processes, to distinguish the structural components used and to determine the exact causes that incurred the degradation phenomena. The material undergoes weathering and decay on a large proportion of its surface and in depth, due to the infiltration of water through the structural blocks. Mineralogical analysis indicated signs of sulphation and dissolution/ recrystallisation processes taking place on the material, whereas stable isotopes provided information relative to the origin of the CO2 and water during calcite formation and degradation processes. Isotopic change of the initial δ13C and δ18O in carbonate matrix was caused by alteration of the primary source of CO2 and H2O in mortar over time, particularly by recrystallisation of calcite with porewater, evaporated or re-condensed water, and CO2 from various sources of atmospheric and biogenic origin. Human influence (surface treatment) and biological growth (e.g. fungus) are major exogenic processes which may alter δ18O and δ13C in lime mortar. © 2009 Springer-Verlag.

Geochimica Et Cosmochimica Acta

The understanding of ophiolites as hosts to economic–scale chromitite ore deposits requires the integration of research relating their geochemical metallogenesis with studies of the mode and nature of their lithospheric-scale deformation. The Neotethyan Vourinos ophiolite in Northern Greece represents a well-preserved ophiolite complete with sheeted dikes, an in-situ Moho transition zone, and a nearly 8-km-thick upper mantle sequence. Chromitite bodies and sub-economic chrome ores occur throughout its ultramafic section, and above and below the petrological Moho; but, economic concentrations of chromitite are restricted to a region referred to as the “metalliferous zone” within the upper mantle domain. Ductile deformation, which developed synchronously with mineral re-equilibration and late magmatic activity, re-concentrated chromite grains in mesoscopic fold noses and created massive-textured ore bodies. Re-equilibration of chromite and chromite–olivine grains on microscopic–scale during this ductile deformation produced geochemical patterns that are compatible with strain distribution. Whether re-equilibration varied with strain rate in the mantle lithosphere due to regional heterogeneous conditions, or whether the change in deformation–induced modal distribution of the mineral aggregate more strongly affected the process of re-equilibration is yet to be determined. The richest ore bodies in Vourinos are represented by the schlieren ores of the Xerolivado Mine, and occur as extensive lenses of mylonitic chromitite, marking the highest degree of deformation within the complex. These textures display patterns of re-equilibration geochemical halos and transition from ductile into brittle deformation conditions.

Antimony is a common metalloid occurring in the form of Sb-sulfides and sulfosalts, in various base and noble metal deposits. It is also present in corresponding metallurgical products (concentrates) and, although antimony has been considered a penalty element in the past, recently it has gained interest due to its classification as a critical raw material (CRM) by the European Union (EU). In the frame of the present paper, representative ore samples from the main Sb-bearing deposits of Greece (Kilkis prefecture, Chalkidiki prefecture (Kassandra Mines), and Chios Isl.) have been investigated. According to optical microscopy and electron probe microanalysis (EPMA) data, the Greek ores contain stibnite (Sb2S3), boulangerite (Pb5Sb4S11), bournonite (PbCuSbS3), bertherite (FeSbS4), and valentinite (Sb2O3). Bulk analyses by inductively coupled plasma mass spectrometry (ICP-MS) confirmed, for the first time published, the presence of a significant Hg content in the Kilkis Sb-ore. Furthermore, Kassandra Mines ores are found to contain remarkable amounts of Bi, As, Sn, Tl, and Se (excluding Ag, which is a bonus element). The above findings could contribute to potential future exploration and exploitation of Sb ores in Greece.