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Structural map of the Agios Georgios area (box in the inset) showing the anticline which concentrated the mineralizing fluids. Schmidt nets of foliation and joints used by mineralizing fluids. A1 to A11 mark metalliferous veins.
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The Agios Georgios argentiferous galena deposit on Antiparos island lies ~12 km from the Miocene Paros pluton and is hosted by mineralized quartz veins in marbles of the Cycladic Blueschist Unit. Argentiferous galena and clear quartz were deposited in the epithermal stage in veins armoured by higher temperature milky quartz. The Paros pluton is a m...
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Context 1
... pegmatitic dykes intrude the entire sequence (Fig. 1, e.g., Thapsana site). Antiparos displays no exposed granitic intrusions with the exception of a few pegmatitic dykes, of similar mineral- ogy to those on Paros, encountered during fieldwork in this study. Early Pliocene rhyolites occupy the southern part of the island (innocenti et al. 1982) (Fig. ...
Context 2
... Agios Georgios vein system is hosted in biotite-mus- covite schists and marbles of the CBU , KevreKidiS 2013). The main tectonic element in the area of Agios Georgios is an open anticline (Fig. 2) whose axis plunges at shallow to moderate angles towards the SSE ( KevreKidiS 2013, evAnS & fiScher 2012. Foliation dips towards WSW to SSE at shallow to moderate angles and to ENE at moderate to steep angles. Formation of the anti- cline caused a decrease of lithostatic pressure in the axial hinge zone, which may have drawn ...
Context 3
... Agios Georgios vein system consists of eleven steeply dipping quartz veins (Fig. 2). Both marbles and schists are cut by two generations of syntaxial veins, an older NE-trending set filled with milky quartz and a younger set of clear quartz veins trending NW (Fig. 2). These veins developed parallel to the planes of folia- tion and joints, and also along the lithological contacts between marble and schist, forming ...
Context 4
... Agios Georgios vein system consists of eleven steeply dipping quartz veins (Fig. 2). Both marbles and schists are cut by two generations of syntaxial veins, an older NE-trending set filled with milky quartz and a younger set of clear quartz veins trending NW (Fig. 2). These veins developed parallel to the planes of folia- tion and joints, and also along the lithological contacts between marble and schist, forming extensive stock- works. Milky quartz veins range up to 80 cm in width, and contain sphalerite, pyrite and chalcopyrite (10 vol.%). The clear quartz veins form tension gashes up to 50 cm in ...
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Citations
... Rb-Sr isochron dating of the Panorama granite and mangan skarn yielded ages of 25.79 ± 0.24 Ma (MSWD = 0.93) and 24.92 ± 0.22 Ma (MSWD = 0.89), respectively ( . The geological exposure of the ore system in Paros and Antiparos Islands (simplified after Kevrekidis et al., 2015). and its host gneisses are relatively higher than those of the Panorama granite (respectively 0.7149 to 0.7156 and 0.7144 to 0.7152 for the leucogranite and 0.7149 to 0.7176 and 0.7144 to 0.7171 for the gneisses, Fig. 3f, Table 2). ...
... High endowment of manganese in late-stage peraluminous granitoid melts is demonstrated in principle through its partitioning in magmatic spessartine and cummingtonite and less so in tourmaline (Mn-schorl, ≤ 0.15 apfu), biotite (≤ 0.33 apfu), magnetite (≤ 0.10 apfu) and apatite (Mn ≤ 0.1 apfu), under reducing-to-mildly oxidizing conditions (McGrath, 1999;Kevrekidis et al., 2015). Such an assemblage attests to the primary capacity of the peraluminous granitoids to both store manganese in the solid phase, but also to have supplied much of it to exsolved fluids under the suitable physico-chemical conditions during cooling. ...
... Steeply dipping epithermal-style quartz veins containing galena with 800-2000 ppm Ag crosscut biotite-muscovite schists and marbles of the Cycladic Blueschist Unit at Agios Georgios of Antiparos Island (Kevrekidis et al., 2015). The mineralized veins were deposited from fluids in the epithermal stage with a significant magmatic contribution mixed with meteoric water. ...
Greece hosts a variety of magmatic-hydrothermal ore deposits/prospects with porphyry- and epithermal styles playing a major role in its total gold endowment. These deposit types are mainly clustered in two areas, the Rhodope- and Attico-Cycladic massifs, and formed from about 33 Ma to the Pleistocene, as a result of back-arc extension in the Aegean Sea, metamorphic core complex formation, and contemporaneous post-subduction and arc magmatism. In the Serbo-Macedonian massif, porphyry Cu-Au deposits include Skouries, Fisoka, Tsikara, Vathi and Gerakario. Causative intrusives are Oligocene to Miocene granodiorites to monzonites. Gold and PGE mineralization is associated with potassic alteration of the intrusives. In the eastern Rhodope massif and the NE Aegean islands, porphyry prospects occur at Pagoni Rachi, Konos Hill, Myli, Melitena (west Thrace), Fakos, Sardes, and Kaspakas (Limnos island) and Stypsi (Lesvos island). Mineralization is associated with Oligocene to Miocene subvolcanics of calc-alkaline to shoshonitic affinity. Feature of these prospects, which they share in common with several porphyry Au-only systems, is their shallow depth of emplacement, the presence of potassic/sodic-calcic and/or phyllic alteration, a strong epithermal overprint, their low Cu content, an extreme Re-enrichment, the multistage introduction of Au, the presence of banded quartz veinlets, and the local presence of tourmaline. New discoveries of porphyry-style mineralization at King Arthur, St. Philippos and Aisymi, increases the gold potential in west Thrace. High-intermediate sulfidation epithermal Au-Ag polymetallic deposits/prospects overprint and/or occur laterally from porphyry-style mineralization, where they are spatially associated with lithocaps of advanced argillic alteration. High-intermediate sulfidation Au-Ag epithermal mineralization at Perama Hill, Mavrokoryfi and Pefka in west Thrace, and at Pterounda, Mesotopos and Megala Therma on Lesvos island is controlled by steeply-dipping extensional faults within volcanic rocks, without any obvious genetic relationship to spatially-related porphyry-style mineralization. Polymetallic epithermal deposits and prospects contain critical and energy critical metals (e.g., Te, Se, Bi, Sb, In, Ge and Ga), which may be considered as by-products.
In the Attico-Cycladic area, porphyry Mo-W mineralization occurs as sheeted quartz veins and stockworks cutting a potassic- to sericitic-altered Miocene granodiorite stock in the Lavrion district. Bonanza grade Au- and/or Ag-rich veins with epithermal affinities crosscut metamorphic rocks at Lavrion, and on Syros, Tinos, Antiparos and Anafi islands. Milos island is characterized by shallow submarine volcanic-hosted IS-HS epithermal Au-Ag-Te and base metal deposits. Antimony-As-Ag-Au deposits/prospects on Chios, Samos and Kos islands in the eastern Aegean Sea, indicate the potential for Carlin-style mineralization in Greece. Several factors played a role to the metal endowment of the Aegean porphyry-epithermal systems: magma fertility in the source regions, depth of emplacement of causative intrusives, relative contribution of mantle versus crustal material, redox state of subduction-related magmas, and physico-chemical fluid conditions at the site of ore deposition.
... The Miocene granitic intrusions of Paros occur as small ellipsoid laccoliths, pipes and apophyses in the areas of Kolymbithres, Kamares, Paroikia, Taxiarxes, Logovathra (at the northern part of Paros), Thapsana and Trypiti (at the central and southern parts of Paros) (Figure 1). These intrusive bodies are classified as monzogranites-to-granites and leucogranites, appear highly porphyritic and intense sericitized and propylitized and contain dioritic enclaves [22,23]. They have been dated at 11.5-12.4 ...
... The Paros leucogranites compose of quartz, orthoclase and microcline, oligoclase to andesine, allanite, zircon, Mg-hornblende, biotite and magnetite [23]. The peraluminous character of the Paros leucogranite is also reflected in its accessory mineralogy containing sillimanite, tourmaline, Li-rich muscovite and lepidolite, apatite and garnet [23]. ...
... The Paros leucogranites compose of quartz, orthoclase and microcline, oligoclase to andesine, allanite, zircon, Mg-hornblende, biotite and magnetite [23]. The peraluminous character of the Paros leucogranite is also reflected in its accessory mineralogy containing sillimanite, tourmaline, Li-rich muscovite and lepidolite, apatite and garnet [23]. The Paros leucogranite is enriched in volatiles (e.g., B, F), contains ~ 7 wt. ...
Mn-skarn ore deposits are relatively infrequent worldwide. A typical example of a Mn-skarn in the Attico-Cycladic Metallogenetic Massif is located at the mining area of Thapsana, Paros Island. The skarn occurs adjacent to the Thapsana, highly sericitized, biotite-garnet-tourmaline-lepidolite leucogranite apophyses of the Paros granitoid and related pegmatites and aplites dated 11,5-12,4±0,2 Ma (K-Ar biotite and muscovite, Durr et al., 1978; Altherr et al., 1982) and 17,1 Ma (K-Ar and Rb-Sr, Durr et al., 1978; Altherr et al., 1982), respectively. According to Baltatzis (1996), the other granitoids body of Paros (Naousa, Kamares, Leykes, Paroikia, Taxiarches, Logovathra and Tripiti) dated 7-15Ma. The Mn-skarns orebodies occur as lenses and NE-trending veins hosted in the Cyclades Blueschist Unit (CBU) marbles and intercalated calcic schists. They comprise two discontinuous paragenetic zones (with widths of ≤ 10 m): A zone that contains rhodonite, vesuvianite, Mn-enriched salite to johannsenite-diopside and spessartine with cores enriched in grossular component (Sps~75Grs~15), placed close to the Thapsana leucogranite, and the second zone of grossular (Sps~85Grs~5), actinolite to Mn-cummingtonite (with Mn ~ 0.8 apfu) and phlogopite (with Mn ~ 0.6 apfu) more distal from the leucogranite and replaced the minerals of the first skarn zone. The Mn-skarns are crosscut by later WNW- to W-trending veins filled with Ca-K-Mg-bearing hollandite, pyrolusite, manganite, rhodonite and rhodochrosite, carbonates, hydroxylapatite and johnbaumite.
The Mn-ores occur as massive aggregates or disseminated comprising jacobsite, hausmannite, Mn- enriched magnetite, braunite and hollandite (with crystals of ≤ 2cm). Occasionally jacobsite and hausmanite display oriented intergrowths. The ore paragenesis also includes secondary pyrolusite, manganite, rhodonite, rhodochrosite, cryptomelane, manjiroite, vernadite and supergene Fe-oxides. Geothermo-oxygen-barometry suggests that the main zones of the Mn-skarns at Thapsana have been formed at temperatures ranging from ~ 440º to ~ 510ºC, pressures of 0.11 to 0.12 GPa. Almost constant average isotopic compositions obtained from the Mn-ores (n = 10) of δ44CaBSE and δ26MgDSM-3 of 0.5 ± 0.05 and -0.6 ± 0.1 and δ18O and δD of 7.2 ± 0.5 and -92 ± 2 per mil, suggest a magmatic source for the metasomatic ore fluids related to the Thapsana leucogranite which have also interacted and isotopically equilibrated with the host CBU marbles.
... In the area of Agios Georgios, veins of quartz are observed, which are hosted in biotite-muscovite schists and marbles. There are two types of quartz veins, the NE-trending milky quartz and the NWtrending clear quartz veins [35]. ...
This study presents the combined use of field mapping, remote sensing data analysis, mineralogy, spectroscopy and GIS techniques for the geological mapping of Antiparos Island. Antiparos is part of the Cyclades Blueschist Belt located in central Aegean, where gneisses, schists and Pliocene volcanic rocks occurred. During the extended field work, a number of volcanic rock samples were collected from the southern part of Antiparos. The sampling strategy was to collect samples from the primary as well as the altered rocks in specific areas in which they were previously located from the remote sensing data processing. In this study, high resolution satellite images have been carried out in order to detect, allocate and separate the different geological formations. Furthermore, the existing geological map was georeferenced and all the tectonic lines and boundaries were digitized. All these features were implemented in a Mobile Mapper CE GPS using Arcpad GIS and checked in situ. The collected samples were analyzed in the laboratory using various techniques including XRD, Petrographic Microscopy and SEM. The qualitative mineralogical analyses were conducted by using XRD. The study was supplemented by the petrographic observations providing a detailed characterization of rock textures. In addition, SEM study and SEM-EDS analyses of the samples were emphasized on the genetic relations of the minerals. The laboratory results revealed that specific corrections should be made in the previous geological map of Antiparos concerning the volcanic rocks, especially at the southern part of the island. A significant conclusion is that the rock described as volcanic in the previous map proved to be a fossiliferous limestone which includes micritic matrix of calcite with an insignificant amount of fossils. All the analogical and digital data and the results of the petrographic analysis were imported in a geodatabase specially designed for geological data. After the necessary topological control and corrections, the data were unified and processed in order to create the final layout at 1/25.000 scale.
... Steeply dipping quartz veins containing galena with 800-2000 ppm Ag crosscut biotite-muscovite schists and marbles of the Cycladic Blueschist Unit at Agios Georgios of Antiparos Island (Kevrekidis et al., 2015). The mineralized veins were deposited from fluids in the epithermal stage with a significant magmatic contribution mixed with meteoric water. ...
... The mineralized veins were deposited from fluids in the epithermal stage with a significant magmatic contribution mixed with meteoric water. Kevrekidis et al. (2015) suggested that the mineralization is genetically related to the neighboring Miocene Paros leucogranite. ...
... At Lavrion, the West Cycladic Detachment Fault operated under ductile-tobrittle conditions (Grasemann et al., 2012;Scheffer et al., 2016) and, based on U-Th/He dating of titanite, zircon and apatite (Seman et al., 2013a,b), accommodated exhumation of the metamorphic rocks in at least two major periods: Middle Miocene (16-12 Ma) and Late Miocene (6-9 Ma), the latter also coinciding with mineralization. Similarly to Lavrion, other mineral occurrences in the Cyclades are in part spatially associated with Miocene plutonic rocks, which intrudes the footwall units along detachment faults under ductile to brittle extensional kinematic conditions (e.g., Mykonos, Menant et al., 2013), in part by extensional structures in the footwall of detachment faults without any adjacent granitoids (e.g., Tinos, Sifnos, Syros, Kallianou) (Neubauer, 2005;Tombros et al., 2007;Voudouris et al., 2014;Kevrekidis et al., 2015). On Mykonos Island (Cyclades), epithermal style baritebase metal mineralization occurred when the pluton crossed the ductile-to-brittle transition during its exhumation below the North Cycladic Detachment System at $11-10 Ma (Menant et al., 2013;Tombros et al., 2015). ...
The Cenozoic metallogeny in Greece includes numerous major and minor hydrothermal mineral deposits, associated with the closure of the Western Tethyan Ocean and the collision with the Eurasian continental plate in the Aegean Sea, which started in the Cretaceous and is still ongoing. Mineral deposits formed in four main periods: Oligocene (33-25 Ma), early Miocene (22-19 Ma), middle to late Miocene (14-7 Ma), and Pliocene-Pleistocene (3 to 1.5 Ma). These metallogenic periods occurred in response to slab-rollback and migration of post-collisional calc-alkaline to shoshonitic magmatism in a back-arc extensional regime from the Rhodopes through the Cyclades, and to arc-related magmatism along the active south Aegean volcanic arc. Invasion of asthenospheric melts into the lower crust occurred due to slab retreat, and were responsible for partial melting of metasomatized lithosphere and lower crustal cumulates. These geodynamic events took place during the collapse of the Hellenic orogen along large detachment faults, which exhumed extensive metamorphic core complexes in mainly two regions, the Rhodopes and the Cyclades. The detachment faults and supra-detachment basins controlled magma emplacement, fluid circulation, and mineralization.
The Triassic volcaniclastic sequence in the Cycladic Blueschist Unit (CBU) of Greece is known to contain several occurrences of metamorphosed Mn mineralization. Despite previous literature reports, a comprehensive and holistic review of the origin of these occurrences is hitherto lacking. Here we revisit the Mn metallogenic system of the CBU through a comprehensive study of Mn mineralisation at Varnavas area, Northern Attica, and its correlation with a similar occurrence at Mparades Hill, Andros island. Manganese mineralogy at both localities is manifested in a typical high-P metamorphic silicate assemblage dominated by piemontite, spessartine garnet, and minor pyroxmangite (rhodonite). Whereas at Andros Mn-rich subdomains contain brecciated braunite micronodules, preservation of tetravalent Mn oxides in a similar nodular form is documented from Varnavas, comprising dominant todorokite along with lesser hollandite, pyrolusite, and minor Mn-bearing hematite. The contrasting Mn oxide mineralogy and comparable textural characteristics at the two sites are tentatively interpreted as the result of locally incomplete reduction of precursor Mn(IV) phases during metamorphism. Bulk Mn concentrations of the studied materials generally do not exceed the value of 10wt% Mn, unless small-scale subsampling of Mn-rich domains is undertaken. Key geochemical characteristics of the Mn-rich rocks include low transition metal concentrations (sum of Co+Ni+Cu+Zn between 0.02 and 0.06 wt%); positive-sloping, PAAS-normalised REE spidergrams at a maximum Nd sn /Yb sn ratio of 0.3; positive Ce anomalies, albeit of variable magnitude across individual samples; and high As (up to 1930 ppm) and Ba (up to 2767ppm) contents. A combination of structural, geochemical and mineralogical evidence from the two localities along with published results from similar occurrences elsewhere (e.g., Kythnos) suggest that Mn-oxide accumulation in the CBU is genetically linked to hydrothermal venting in a back-arc rift setting during the Triassic. The geochemical variability recorded is attributed primarily to the variable mixing of a hydrothermal-sourced, hydrogenous metalliferous component that precipitated broadly contemporaneously with the deposition of the host tuffs. Low transition metal contents coupled with substantial enrichments in elements such as Ba, As, Pb and REY, attest to the felsic/intermediate character of back-arc magmatism/volcanism and associated hydrothermal activity. Primary Mn precipitates are thought to have been in the form of tetravalent Mn assemblages, which may locally be partially preserved through metamorphism, as appears to be the case in the Varnavas occurrence. The fully oxic and hydrogenous character of the precursor Mn(IV) oxy-hydroxides is supported by the consistently positive Ce anomalies observed in practically all samples from both sites. Although the Mn concentrations and distribution of the studied assemblages are sub-economic at best, we consider possible that their geographically widespread occurrence may still hold untapped potential for future discovery of commercially viable Mn ores sensu stricto, both in the Hellenic arc and in other regions of similar geotectonic and metallogenic activity.
Polymetallic ore deposits of the Aegean Sea, Greece, are temporally and spatially associated with the emplacement of Miocene granitoids and Pliocene to Quaternary volcanic units along the active volcanic arc and occur adjacent to the crustal-scale detachment systems. A variety of mineral deposits (e.g., carbonate-replacement, skarn, porphyry, vein-type, and low- to high-sulfidation epithermal deposits) formed during different stages of back-arc evolution and can be found in the footwall and hanging wall of the major detachment systems and all tectono-stratigraphic units. New galena Pb-isotope data collected by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis exhibit a range of isotopic ratios: ²⁰⁶Pb/²⁰⁴Pb: 18.68–18.91, ²⁰⁷Pb/²⁰⁴Pb: 15.67–15.75 and ²⁰⁸Pb/²⁰⁴Pb: 38.83–39.18, with a resolvable geographic pattern. Together with compiled Pb-isotope data of Cycladic galena, large-scale regional similarities in the Pb-isotope signatures are recognized, suggesting distinct sources of lead in the underlying basement. Base metal-rich deposits in the west Cyclades have a common lead source with a more radiogenic signature, whereas lead in the deposits in the north-central Cyclades was derived from a less radiogenic source. Similarities between the Pb-isotopic signature of galena and regional host rocks suggest, that the pre-Alpine Cycladic Basement was the main source of lead for the deposits in the north and central, and the metamorphosed volcano-sedimentary Lower Cycladic Blueschist Nappe was the source of lead for the deposits in the west. Moreover, there is a close spatial relationship of the ²⁰⁶Pb/²⁰⁴Pb 18.84 line and trace of the proposed Trans-Cycladic Thrust. Regional trends were also observed in the new LA-ICP-MS trace element analysis in galena. Galena in carbonate-replacement and skarn deposits in the west is enriched in base metals and silver, whereas galena in vein-type deposits in the north and low- to high-sulfidation epithermal deposits along the active volcanic arc is enriched in gold, tellurides and selenium. Combined trace element and isotopic data of galena indicate distinct metal sources in the Cyclades. Heterogenous rock assemblages of mixed provenance and age account for the differences in lead isotopes. Whereas the base metals and silver are ultimately sourced from the basement, the precious metals might be derived from the metasomatized lithospheric mantle.
