Genesis of alpinotype fissure minerals from Thasos Island, Northern Greece - Mineralogy, mineral chemistry and crystallizing environment.

Στην περιοχή της Θάσου, αλπινότυπα ορυκτά φιλοξενούνται εντός διακλάσεων γνευσίων, αμφιβολιτών, Mn-ούχων ασβεστοπυριτικών στρώσεων και σχιστολίθωνκαθώς και μάρμαρων της κατώτερης ενότητας του μεταμορφικού πυρήνα της Ροδόπης. Οι αλπινότυπες διακλάσεις τέμνουν τις μεταμορφικές δομές και συνδέονται στενά με τις διαδικασίες εκταφιασμού του Ροδοπικού συμπλέγματος κατά το Ολιγόκαινο-Μειόκαινο. Οι περισσότερες αλπινότυπες διακλάσεις αναπτύσσονται κατά μήκος μίας μεγάλης ζώνης αποκόλλησης, που διαχωρίζει τους ανώτερους στρωματογραφικά γνεύσιους από τους κατώτερους αμφιβολίτες και μάρμαρα. Το ορυκτολογικό περιεχόμενο των διακλάσεων είναι στενά συνδεδεμένο με την ορυκτολογία των περιβαλλόντων πετρωμάτων. Σε διακλάσεις εντός αμφιβολιτών εμφανίζεται αδουλάριος, αλβίτης, χαλαζίας, τιτανίτης, απατίτης, ακτινόλιθος, χλωρίτης, ασβεστίτης, αιματίτης και ρουτίλιο. Σε διακλάσεις παρα-, ορθογνευσίων και μεταπηγματιτών κρυσταλλώνονται χαλαζίας, αδουλάριος, μοσχοβίτης και αιματίτης, ενώ σε διακλάσεις που αναπτύσσονται εντός σπεσσαρτινικών-πιεμοντιτικών σχιστόλιθων κρυσταλλώνονται χαλαζίας, χλωρίτης, σπεσσαρτίνης, αιματίτης, ρουτήλιο, αλβίτης, επίδοτο και ζιρκόνιο. Τέλος διακλάσεις εντός ασβεστοπυριτικών στρώσεων περιέχουν Mn-ούχο γροσσουλάριο, χαλαζία και Mn-ούχο κλινοζωισίτη. Οι εξαλλοιώσεις που παρατηρούνται στα τοιχώματα των διακλάσεων υποδηλώνουν διαδικασίες u941 .κπλυσης των περιβαλλόντων πετρωμάτων από υδροθερμικά ρευστά. Οι κρύσταλλοι χαλαζία εμφανίζονται με μορφές σκήπτρου, σε πρισματικούς κρυστάλλους διάφορων γενεών να αναπτύσσονται πάνω σε χαλαζίες τύπου Τessin, υποδηλώνοντας πολλαπλά στάδια κρυστάλλωσης και αλλαγή των συνθηκών P-T-t. Η εφαρμογή γεωθερμόμετρου χλωρίτη υποδεικνύει αρχικές θερμοκρασίες σχηματισμού των παραγενέσεων τους 286 έως 366 °C. Οι χαλαζίες τύπου Τessin πιθανότατα δημιουργήθηκαν από ρευστά πλούσια σε CO2 και πιθανόν στη μετάβαση από ένα συμπιεστικό σε εφελκυστικό τεκτονικό καθεστώς. Αντίθετα οι μεταγενέστερες γενεές σκήπτρων υποδεικνύουν συμμετοχή κατερχόμενων μετεωρικών νερών. Η περιοχή μελέτης αντιπροσωπεύει μοναδικό ορυκτολογικό Γεώτοπο. Η γεωλογική-ορυκτολογική αυτή κληρονομιά μπορεί να προστατευθεί μέσω της ίδρυσης ενός Γεωπάρκου που θα συμβάλει επιπλέον και στην προώθηση φιλικής προς το περιβάλλον ανάπτυξης της Θάσου.Alpinotype fissure-minerals in Thasos Island are hosted in gneisses, amphibolites, Mn-rich schists and calc-silicate layers, and marbles of the Carboniferous-Permian Pangeon Unit, which represents the lower tectonostratigraphic unit of the southern Rhodope metamorphic core complex. Alpinotype fissures crosscut metamorphic fabrics and are closely related to the exhumation processes of the core complex during the Oligocene-Miocene. Most mineralized fissures occur close to a major detachment fault, which separates gneisses from marbles and amphibolites. The mineralogy of the alpinotype fissures is closely related to the host rocks: amphibolite-hosted fissures include adularia, albite, quartz, titanite, apatite, actinolite, chlorite, calcite, hematite and rutile. Fissures in para- and orthogneisses- and in metapegmatites are characterized by smoky and clear quartz, adularia, muscovite and hematite. Fissures within spessartite-piemontite schists contain quartz, chlorite, spessartite, hematite, rutile, albite, epidote and traces of zircon. Finally fissures in calc-silicate layers include Mn-grossular, quartz and Mn-clinozoisite. Hydrothermal alteration halos surrounding the fissures may suggest leaching of the wall rocks as a potential mechanism for mineral deposition. Scepter quartz crystals consist of a lower Tessinhabit crystal and several generations of upper prismatic quartz crystals, suggesting several stages of crystallization and changing P-T-x conditions with time. Chlorite geothermometry indicates temperatures of formation in the range between 286 and 366 °C. Tessin habit quartz was deposited from CO2-bearing fluids, probably at the transition from a compressional to an extensional tectonic regime and was later dissolved by meteoric water dominated fluids resulting in the formation of quartz scepters. Oxidizing conditions are indicated by the widespread occurrence of hematite in the mineralization. The studied area represents a unique mineralogical geotope. Its geological-mineralogical heritage should be protected through establishment of a mineralogical-petrological geopark that will also promote sustainable development of the area

The potential of phosphorus in clinopyroxene as a geospeedometer: examples from mantle xenoliths

We investigate the potential to use concentrations and zoning patterns of phosphorus (P) in clinopyroxene as indicators of the rates of igneous and metasomatic processes, comparable to recent applications of P in olivine but applicable to more evolved rocks and lower temperatures of crystallization. Few high-P pyroxenes have been previously reported, and none have been analyzed in detail for the mechanism of P enrichment or the implications for mineral growth kinetics. Here, we report the discovery and characteristics of exotic phosphorus-rich secondary clinopyroxene in glassy pockets and veins in composite mantle xenoliths from the Cima Volcanic Field (California, USA) and the Middle Atlas Mountains (Morocco, West Africa). These glass-bearing xenoliths preserve evidence of melt infiltration events and the contrasting behavior of P in their pyroxene crystals constrains the different rates of reaction and extents of equilibration that characterized infiltration in each setting. We report optical petrography and chemical analysis of glasses and minerals for major elements by electron microprobe microanalyzer and trace elements by laser-ablation Inductively Coupled Plasma Mass Spectrometry. The Cima Volcanic Field specimen shows one end-member behavior, with unzoned P-rich clinopyroxene in a melt pocket. We attribute this occurrence to a slow crystallization process that occurred after the melt temperature reached near-equilibrium with the host rock and during which the P concentration in the melt was buffered by apatite saturation. In the Morocco xenolith, by contrast, clinopyroxene exhibits zonation with P increasing all the way to the rim, in contact with the glass. We ascribe this feature to a rapid growth process in which excess P was incorporated into the growing clinopyroxene from a diffusive boundary layer. We demonstrate quantitative agreement between the enrichment of P and other trace elements and their expected diffusion and partitioning behavior during rapid growth. We suggest that P has not been widely reported in clinopyroxene in large part because it has rarely been looked for and that its analysis offers considerable promise as a kinetic indicator both in xenoliths and volcanic rocks

The potential of phosphorus in clinopyroxene as a geospeedometer: examples from mantle xenoliths

We investigate the potential to use concentrations and zoning patterns of phosphorus (P) in clinopyroxene as indicators of the rates of igneous and metasomatic processes, comparable to recent applications of P in olivine but applicable to more evolved rocks and lower temperatures of crystallization. Few high-P pyroxenes have been previously reported, and none have been analyzed in detail for the mechanism of P enrichment or the implications for mineral growth kinetics. Here, we report the discovery and characteristics of exotic phosphorus-rich secondary clinopyroxene in glassy pockets and veins in composite mantle xenoliths from the Cima Volcanic Field (California, USA) and the Middle Atlas Mountains (Morocco, West Africa). These glass-bearing xenoliths preserve evidence of melt infiltration events and the contrasting behavior of P in their pyroxene crystals constrains the different rates of reaction and extents of equilibration that characterized infiltration in each setting. We report optical petrography and chemical analysis of glasses and minerals for major elements by electron microprobe microanalyzer and trace elements by laser-ablation Inductively Coupled Plasma Mass Spectrometry. The Cima Volcanic Field specimen shows one end-member behavior, with unzoned P-rich clinopyroxene in a melt pocket. We attribute this occurrence to a slow crystallization process that occurred after the melt temperature reached near-equilibrium with the host rock and during which the P concentration in the melt was buffered by apatite saturation. In the Morocco xenolith, by contrast, clinopyroxene exhibits zonation with P increasing all the way to the rim, in contact with the glass. We ascribe this feature to a rapid growth process in which excess P was incorporated into the growing clinopyroxene from a diffusive boundary layer. We demonstrate quantitative agreement between the enrichment of P and other trace elements and their expected diffusion and partitioning behavior during rapid growth. We suggest that P has not been widely reported in clinopyroxene in large part because it has rarely been looked for and that its analysis offers considerable promise as a kinetic indicator both in xenoliths and volcanic rocks

Beneficiation Process of Kyanite-Rich Mineral Assemblages from Thassos Island Aegean Sea, Greece

Kyanite-rich rock samples from Thassos Island, Greece, underwent beneficiation tests aiming to examine their potential as commercial refractory materials. The extracted material was compared to commercial samples of kyanite, andalusite and sillimanite. The experimental procedure combined mineral processing and material characterization. The mineral processing included grinding of the Thassos samples and grain size distribution, then gravity separation, using heavy liquid media (sodium polytungstate), and magnetic separation. Material characterization included XRF analysis on the bulk samples, XRD analysis on both the bulk and the commercial samples, and combined reflected light microscopy, SEM, XRF and XRD analysis on the final product. Gravity separation tests showed that the optimum liberation size of kyanite is any grain size finer than 500 μm, since coarser grain size fractions are characterized by elevated content of accessory minerals in the concentrates. Magnetic separation followed, removing the magnetic minerals from the concentrates, with ilmenite being a possible Ti-rich by-product to be recovered. The results indicate that the obtained percentage of kyanite reaches up to 95%. Furthermore, chemical analysis reveals that the composition of the processed material, in terms of concentration of alumina (and other major oxides), meets the standards of the Chinese and the American industry. It is therefore suggested that the Thassos kyanite-bearing assemblages constitute a promising resource that should be further tested in a semi-industrial scale, to fully establish their industrial potential. © 2021 Taylor & Francis Group, LLC

Ophicalcites from the Upper Tectonic Unit on Tinos, Cyclades, Greece: mineralogical, geochemical and isotope evidence for their origin and evolution

Ophicalcites exposed on the island of Tinos, Greece, occur as ellipsoidal bodies within greenschist-facies phyllites of the Upper Cycladic Unit. Close to their outcrops, blocks of serpentinites, metabasic rocks and metasediments were identified, implying a tectonically dismembered ophiolitic sequence in the study area. The ophicalcites comprise brecciated serpentinites cemented by calcite. Based on textural, mineralogical and deformation features, five ophicalcite varieties were discriminated, reflecting calcite precipitation, sedimentary features and increasing brecciation. Serpentinitic fragments comprise antigorite, while Cr-spinel, magnetite, talc and chlorite are accessory minerals. Carbonate veins consist of calcite and minor dolomite, talc, chlorite, and rarely epidote. Bulk rock chemical compositions and Cr-spinel mineral composition point towards a supra-subduction environment. Carbon and oxygen isotope ratios of calcite imply precipitation from mixed marine and hydrothermal fluids, followed by isotope exchange due to late, greenschist-facies overprint. The Tinos ophicalcites record intraoceanic exhumation of the ultramafics at the seafloor, where faulting and serpentinization caused an extensive network of fractures, healed by carbonates. Such intraoceanic deformation can be attributed either to obduction tectonics expressed by thrusting of oceanic piles, or to transpressional(?) transform faults, or more probably to slip along detachment fault of an oceanic core complex. © 2021, Geologische Vereinigung e.V. (GV)

On the color and genesis of prase (Green quartz) and amethyst from the island of serifos, cyclades, Greece

The color of quartz and other minerals can be either caused by defects in the crystal structure or by finely dispersed inclusions of other minerals within the crystals. In order to investigate the mineral chemistry and genesis of the famous prase (green quartz) and amethyst association from Serifos Island, Greece, we used electron microprobe analyses and oxygen isotope measurements of quartz. We show that the color of these green quartz crystals is caused by small and acicular amphibole inclusions. Our data also shows that there are two generations of amphibole inclusions within the green quartz crystals, which indicate that the fluid, from which both amphiboles and quartz have crystallized, must have had a change in its chemical composition during the crystallization process. The electron microprobe data also suggests that traces of iron may be responsible for the amethyst coloration. Both quartz varieties are characterized by isotopic compositions that suggest mixing of magmatic and meteoric/marine fluids. The contribution of meteoric fluid is more significant in the final stages and reflects amethyst precipitation under more oxidizing conditions. © 2018 by the authors. Licensee MDPI, Basel, Switzerland

The potential of phosphorus in clinopyroxene as a geospeedometer: Examples from mantle xenoliths

We investigate the potential to use concentrations and zoning patterns of phosphorus (P) in clinopyroxene as indicators of the rates of igneous and metasomatic processes, comparable to recent applications of P in olivine but applicable to more evolved rocks and lower temperatures of crystallization. Few high-P pyroxenes have been previously reported, and none have been analyzed in detail for the mechanism of P enrichment or the implications for mineral growth kinetics. Here, we report the discovery and characteristics of exotic phosphorus-rich secondary clinopyroxene in glassy pockets and veins in composite mantle xenoliths from the Cima Volcanic Field (California, USA) and the Middle Atlas Mountains (Morocco, West Africa). These glass-bearing xenoliths preserve evidence of melt infiltration events and the contrasting behavior of P in their pyroxene crystals constrains the different rates of reaction and extents of equilibration that characterized infiltration in each setting. We report optical petrography and chemical analysis of glasses and minerals for major elements by electron microprobe microanalyzer and trace elements by laser-ablation Inductively Coupled Plasma Mass Spectrometry. The Cima Volcanic Field specimen shows one end-member behavior, with unzoned P-rich clinopyroxene in a melt pocket. We attribute this occurrence to a slow crystallization process that occurred after the melt temperature reached near-equilibrium with the host rock and during which the P concentration in the melt was buffered by apatite saturation. In the Morocco xenolith, by contrast, clinopyroxene exhibits zonation with P increasing all the way to the rim, in contact with the glass. We ascribe this feature to a rapid growth process in which excess P was incorporated into the growing clinopyroxene from a diffusive boundary layer. We demonstrate quantitative agreement between the enrichment of P and other trace elements and their expected diffusion and partitioning behavior during rapid growth. We suggest that P has not been widely reported in clinopyroxene in large part because it has rarely been looked for and that its analysis offers considerable promise as a kinetic indicator both in xenoliths and volcanic rocks. © 2019 Elsevier Lt