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ALUNITE OCCURRENCES IN GREECE: GEOLOGICAL MINERALOGICAL CONSTRAINTS AND EXPLOITATION
No full textIn this article, occurrences of alunite in northern Greece (Thrace) and the Aegean Islands (Lesvos, Limnos and Milos) are presented and their geological, mineralogical and depositional characteristics are discussed. All alunite-bearing rocks are part of advanced argillic alteration zones in porphyry-epithermal systems hosted in Neogene magmatic rocks. Evidence for early exploitation of alunite in Sapes, Lesvos and Milos, suggest various uses, especially in medicine, in fabric dying, purification of water, or as pigment from classical until recent times
MINERALOGY AND PETROGRAPHY OF THE NW TINOS ISLAND OPHICALCITES, CYCLADES, GREECE.
No full textOphicalcites from Tinos Island, Cyclades, Greece,
better known as ‘green marble of Tinos’, comprise
polygenetic serpentinitic breccias with calcitic
matrix and numerous carbonate veins crosscutting
the formation. They have undergone intense
exploitation for building and decorative purposes
since ancient times. Serpentinitic clasts of the
ophicalcites are composed mainly of antigorite
and they show characteristic mesh textures, while
locally pseudomorphic and non-pseudomorphic
textures are developed. The carbonate phase
consists mostly of calcite, whereas dolomite
replaces calcite locally, especially along zones of
intense tectonic activity. Calcite, mostly as cement
material, presents a strong granoblastic texture
that bonds tightly the serpentinitic clasts. Chlorite
is present in many samples and seems to be a
quite common accessory mineral of the formation
whereas talc, spinel, hematite and magnetite can
also be found. Meter-sized bodies of chromitites
with irregular shapes were also observed in the
studied ophicalcites. They consist of aluminian
chromite, partially replaced by magnetite, Crchlorite,
calcite and base metal sulphides.
Mineralogical, textural and field relationships
data support the idea of a combined tectonichydrothermal
origin of these ophicalcites, while
sedimentary mechanisms have played a minor role
to their formation
A new occurrence of pyrophanite from the amphibolite-hosted skarn in Western Kimmeria, Xanthi, Northern Greece
No full textA new occurrence of pyrophanite (MnTiO3) in Greece is described from the garnetclinopyroxene-
wollastonite exoskarn of western Kimmeria. Hostrock of the pyrophanite-
bearing skarn is amphibolite (retrogressed eclogites) of the Nestos suture
zone in the Rhodope massif. In addition endo- and exo-skarns occur both in the Xanthi
granodiorite and the surrouding marbles and consinst of diopside-vesuvianitequartz
and wollastonite-garnet-calcite-quartz respectively. Pyrophanite formed in
the prograde stage, together with garnet, pyroxene, wollastonite, titanite, zircon,
rutile, thorite and ouranothorianite. Retrograde minerals are quartz, epidote, calcite,
hematite, and sulfides. Chlorite-geothermometry revealed temperatures in the
range from 300 to 350 oC for the retrograde event. Calcic garnets (andraditegrossular
solid solutions) from the prograde amphibolite-hosted skarn are chemically
zoned with either isotropic or anisotropic cores surrounded by non-cubic anisotropic
rims, thus suggesting chemical disequilibrium or disordering phenomena
during crystal growth. The pyrophanite crystals are included in titanite and are accompanied
by U-rich thorium minerals (uranothorianite, thorite) and by rutile. Electron
microprobe analyses indicate that the studied pyrophanites are solid solutions
between end-member pyrophanite and ilmenite, with isomorphous substitution of
Mn2+ by Fe2+. No Mg has been detected (geikielite end-member). The alteration of
pyrophanite and rutile to titanite suggests an increase of fO2 values of the fluids,
probably due to increased incursion of meteoric waters to the system. The assemblage
thorite, uranothorianite, pyrophanite and zircon indicates a magmatic contribution
from the Xanthi granodiorite
GENESIS OF ALPINOTYPE FISSURE MINERALS FROM THASOS ISLAND, NORTHERN GREECE - MINERALOGY, MINERAL CHEMISTRY AND CRYSTALLIZING ENVIRONMENT
No full textAlpinotype 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
MN-ANDALUSITE, SPESSARTINE, MN-GROSSULAR, PIEMONTITE AND MNZOISITE/ CLINOZOISITE FROM TRIKORFO, THASSOS ISLAND, GREECE
No full textMylonitized manganiferous schists and calc-silicate layers intercalated within
amphibolite- to greenschist facies mica schists from the Trikorfo area (Thassos
Island, Greece), host an unusual Mn-rich paragenesis of metamorphic silicate
minerals, most of them in large, gemmy crystals. The silicates occur both in layers
subparallel to the foliation and within discordant veins cross-cutting the metamorphic
fabric. Piemontite (up to 12.7 wt. % Mn2O3), Mn-rich epidote (up to 7.8 wt. % Mn2O3),
Mn-rich andalusite (up to 15.6 wt. % Mn2O3), Mn-poor pink clinozoisite-epidote (up
to 0.87 wt. % Mn2O3), Mn-poor pink zoisite (up to 0.21 wt. % Mn2O3), spessartine (up
to 47.7 wt. % MnO) and Mn-rich grossular (up to 3.6 wt. % MnO) are associated with
diopside, hornblende, phlogopite, muscovite, tourmaline, hematite and iron-bearing
kyanite. The studied assemblages are indicative of high fO2 conditions due to the
presence of highly-oxidized pre-metamorphic Mn-rich mineral associations. They
developed during prograde metamorphism of a Mn-rich sedimentary protolith(s),
followed by re-equilibration to post-peak metamorphic conditions, vein formation and
metasomatism during retrograde metamorphism accompanying the exhumation of the
Thassos Island during the Oligocene-Miocene. Alternatively, the skarn-similar
mineralogy of the calc-silicate layers could have been formed by fluids released by
granitoids during contact metamorphism. 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
Viridine, Piemontite and Epidote Group Minerals from Thassos Island, Northern Greece
No full textViridine (Mn-andalusite) is a rare variety of andalusite whose deep emerald-green colour is attributed to the Jahn-Teller distortion caused by the presence of Mn3+ in its structure [1]. Viridine from Thassos Island, northern Greece (Fig. 1), is of particularly high gem-quality and is associated with piemontite and other Mn-bearing silicates of the epidote group. Their conditions of formation and the source of Mn is the primary focus of this study. The main viridine occurrence is in the Trikorfo area, ~3.2 km E of the nearest township, Theologos. Viridine occurs as large subhedral-euhedral crystals to crystallised masses. Initial studies [3] of the epidote minerals identified dark brick-red piemontite (usually associated with the viridine, Fig. 2) and rose-pink Mn-rich epidote and Mn-bearing zoisite (commonly known as ‘thulite’). Kyanite in a range of colours occurs within the actinolite schists [3]. It is also found inter-overgrown with viridine at the main locality, indicating that during formation, an inversion of pressure and temperature conditions may have occurred [4], resulting in metastable coexistence of the two phases [1]. Recently developed pXRD [5] and pXRF techniques will be used to identify mineral assemblages, phase relations and geochemistry, in order to trace the source of Mn during metamorphism
Amethyst occurrences in Tertiary volcanic rocks of Greece: mineralogical and genetic implications
No full textEpithermal-altered volcanic rocks in Greece host gem-quality amethyst veins in
association with various silicates, carbonates, oxides, sulfides and halides. Host
rocks are Oligocene to recent calc-alkaline to shoshonitic lavas and pyroclastics of
intermediate- to acid composition. The amethyst-bearing veins occur in the
periphery of porphyry-type and/or high-sulfidation epithermal mineralized centers
in northern Greece (e.g. Sapes, Kirki, Kornofolia/Soufli, Lesvos island) and on
Milos island in the active Aegean Volcanic Arc. Hydrothermal alteration around the
quartz veins includes sericitic, K-feldspar (adularia), argillic, propylitic and zeolitic
types. Precipitation of amethyst in the northern Greece occurrences, took place
during the final stages of the magmatic-hydrothermal activity from near-neutral to
alkaline fluids, as indicated by the presence of gangue adularia, calcite, smectite,
chlorite, sericite, pyrite, zeolites (laumontite, heulandite, clinoptilolite), analcime
and minor amounts of barite, halite, epidote and fluorite in the quartz veins.
Amethyst at Milos Island (Chondro Vouno and Kalogries-Vani areas), is
accompanied by barite, smectite and lepidocrocite. Colloform-crustiform banding
with alternations of amethyst, chalcedony and/or carbonates is a common
characteristic of the studied amethyst-bearing veins. Fluid inclusion- and
mineralogical data suggest that the studied amethyst were formed at: 174-246 °C
(Sapes area), 100-175 °C (Kirki and Kornofolia areas) and 223-234°C (Lesvos
island). The amethyst formation requires oxidizing conditions and is probably the
result of mixing between meteoric or seawater with upwelling hydrothermal fluids.
The involvement of seawater in the studied mineralization is supported by the
presence of halite and abundant barite in the veins. Finally, the studied amethyst
deposits should be evaluated as potential gemstone sources in Greece
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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