Trace Elements in Magnetite from the Pagoni Rachi Porphyry Prospect, NE Greece: Implications for Ore Genesis and Exploration

Magnetite is a common accessory phase in various types of ore deposits. Its trace element content has proven to have critical implications regarding petrogenesis and as guides in the exploration for ore deposits in general. In this study we use LA-ICP-MS (laser ablation-inductively coupled plasma-mass spectrometry) analyses of trace elements to chemically characterize magnetite from the Pagoni Rachi Cu–Mo–Re–Au porphyry-style prospect, Thrace, northern Greece. Igneous magnetite mostly occurs as euhedral grains, which are commonly replaced by hematite in fresh to propylitic-altered granodiorite porphyry, whereas, hydrothermal magnetite forms narrow veinlets or is disseminated in sodic/potassic-calcic altered (albite + K-feldspar + actinolite + biotite + chlorite) granodiorite porphyry. Magnetite is commonly associated with chalcopyrite and pyrite and locally exhibits martitization. Laser ablation ICP-MS analyses of hydrothermal magnetite yielded elevated concentrations in several trace elements (e.g., V, Pb, W, Mo, Ta, Zn, Cu, and Nb) whereas Ti, Cr, Ni, and Sn display higher concentration in its magmatic counterpart. A noteworthy enrichment in Mo, Pb, and Zn is an unusual feature of hydrothermal magnetite from Pagoni Rachi. High Si, Al, and Ca values in a few analyses of hydrothermal magnetite imply the presence of submicroscopic or nano-inclusions (e.g., chlorite, and titanite). The trace element patterns of the hydrothermal magnetite and especially the decrease in its Ti content reflect an evolution from the magmatic towards the hydrothermal conditions under decreasing temperatures, which is consistent with findings from analogous porphyry-style deposits elsewhere

First zunyite-bearing lithocap in Greece: The case of Konos Hill Mo-Re-Cu-Au porphyry system

The Konos Hill prospect, represents a telescoped Mo-Re-Cu-Au porphyry system overprinted by a high sulfidation event. Porphyry mineralization is exposed in the deeper parts of the study area and comprises quartz stockwork veins, hosted in subvolcanic bodies of granodioritic composition. In the upper topographic levels, a significant hydrothermal alteration overprint predominates, and consists of silicification and various advanced argillic alteration assemblages, related to N-S and E-W trending faults. Further outwards, advanced argillic alteration gradually evolves into phyllic assemblages dominated by sericite. Zunyite, described for the first time from a lithocap in Greece, along with various amounts of quartz, alunite, APS minerals, kaolinite, pyrophyllite and diaspore constitute the major advanced argillic alteration minerals in the area. Mineral-chemical analyses revealed significant variance in the SiO2, F and Cl content of zunyite. Alunite supergroup minerals display a wide compositional range corresponding to members of the alunite, beudantite and plumbogummite subgroups. Diaspore displays almost stoichiometric composition with traces of TiO2, BaO, Ce2O3 and Nd2O3. The presence of the above-mentioned minerals indicates that low pH hydrothermal fluids flowing through fault planes resulted in extensive advanced argillic alteration in the area. The discovery of zunyite points towards an enrichment of volatile elements like F and Cl in the hydrothermal fluid, and helps to set constrains on the physicochemical conditions and the evolution of the mineralization and associated alteration

Phosphate removal by Ca(OH)2-treated natural minerals : experimental and modeling studies

Adsorption of phosphate phosphorus (PO4-P) from wastewater onto eco-friendly geosorbents has gained great attention aiming at recovering an essential nutrient for crop production. Notably, the literature on PO4-P adsorption kinetics is limited to the application of either empirical reaction-based models lacking a physical significance or over-simplified diffusion-based models frequently used outside their applicability area. In this study, equilibrium and kinetic experiments are presented under a wide range of phosphate concentrations (50-500 mg P/L) using sustainable and low-cost modified adsorbents. The kinetics of PO4-P adsorption from aqueous solutions onto Ca(OH)2-treated zeolite (CaT-Z) and bentonite (CaT-B) was analyzed by a dimensionless two-phase homogeneous surface diffusion model (TP-HSDM) assuming constant diffusivity and coupled with the double selectivity isotherm model (DSM). The TP-HSDM fit to the data at four initial P concentrations (50, 100, 200 and 300 mg/L) resulted in an average relative error of 14.6% and 17.4% from the experimental data for CaT-Z and CaT-B, respectively. The average surface diffusion coefficient (Ds) ranged from 2.5 × 10-10 to 8.7 × 10-10 cm2/s for CaT-Z and from 1.6 × 10-10 to 4.78 × 10-9 cm2/s for CaT-B. The external mass transfer coefficient (kf) ranged from 2.72 × 10-4 to 8.38 × 10-4 cm/s for CaT-Z and from 5.63 × 10-4 to 2.24 × 10-3 cm/s for CaT-B. The dimensionless Biot (Bi) number exhibited values in the order of magnitude of 105 indicating that intraparticle diffusion is the controlling mass transfer mechanism for both materials

Gold deposits in Greece: Hypogene ore mineralogy as a guide for precious and critical metal exploration

Gold deposits in Greece are spatially associated with back-arc/arc related volcanic, subvolcanic and plutonic rocks, which were controlled by extensional kinematic conditions when metamorphic core complexes in the Rhodope-Serbomacedonian- and Attico-Cycladic Massifs were uplifted to near surface levels over the south-westward retreating Hellenic subduction zone. Porphyry Cu-Mo-Au, high-intermediate sulfidation epithermal Au-Ag deposits and other intrusion-related proximal to distal systems (skarn, carbonate replacement, metamorphic rock-hosted quartz veins) are characterized by enrichment of trace metallic minerals like bismuth sulfosalts and Bi-sulfotellurides, precious- and base metal tellurides and Se-bearing phases, which can be considered as pathfinder minerals for gold as they are intimately associated with gold-bearing ores. Mineralogical studies of various styles of gold deposits in Greece can be applied as an exploration tool and selected examples from well described mineralization/deposits are presented here

The Geology, Geochemistry, and Origin of the Porphyry Cu-Au-(Mo) System at Vathi, Serbo-Macedonian Massif, Greece

The Vathi porphyry Cu-Au ± Mo mineralization is located in the Serbo-Macedonian metallogenic province of the Western Tethyan Metallogenic Belt. It is mainly hosted by a latite and is genetically associated with a quartz monzonite intrusion, which intruded the basement rocks of the Vertiskos Unit and the latite, 18 to 17 Ma ago. A phreatic breccia crosscuts the latite. The quartz monzonite was affected by potassic alteration, whereas the latite was subjected to local propylitic alteration. Both styles of alteration were subsequently overprinted by intense sericitic alteration. M-type and A-type veins are spatially associated with potassic alteration, whereas D-type veins are related to the sericitic alteration. Three ore assemblages are associated with the porphyry stage: (1) pyrite + chalcopyrite + bornite + molybdenite + magnetite associated with potassic alteration; (2) pyrite + chalcopyrite related to propylitic alteration; and (3) pyrite + chalcopyrite + native gold ± tetradymite associated with sericitic alteration. A fourth assemblage consisting of sphalerite + galena + arsenopyrite + pyrrhotite + pyrite ± stibnite ± tennantite is related to an epithermal overprint. Fluid inclusion data indicate that the A-type veins and related porphyry-style mineralization formed at 390–540 °C and pressures of up to 646 bars

Ορυκτολογική, πετρογραφική και γεωχημική μελέτη ζωνών υδροθερμικών εξαλλοιώσεων και σχετιζόμενων μεταλλοφοριών πορφυρικού-επιθερμικού τύπου στην περιοχή Σαπών-Κίρκης, ΒΑ Ελλάδα

Detailed field work (mapping and sampling) at the broader Sapes-Kirki area took place focusing on the porphyry/epithermal mineralization centers of Konos and Pagoni Rachi. Beyond these already known occurrences, new mineralized centers were also discovered (e.g., Papadokoryphi). The study area is occupied by volcanosedimetary rocks, set in E-trending tectonic basins, that were created by extensional tectonism due to a slab roll-back since Eocene times. Further to the North of the study area, metamorphic rocks of the Rhodope Massif predominate, while to the South, metamorphic rocks of the Circum-Rhodope belt occur (e.g., Makri Unit etc.). The studied mineralization is hosted in sub-volcanic to intrusive bodies of Oligocene age, which are characterized by intermediate to acidic composition and high-K calc-alkaline geochemical affinities. Three distinctive intrusive phases were identified in the study area. The granodiorite porphyry consists of biotite-hornblende-augite phenocrysts along with a few resorbed quartz phenocrysts, set in a matrix of fine-grained feldspar and quartz. It hosts most of the mineralized zones and usually suffers from severe hydrothermal alteration. The next intrusive phase, which mostly crops out in the northern part of the study area, is a monzodiorite with a characteristic equigranular texture composed by varying amounts of amphibole, pyroxene, biotite, and feldspar. Finally, the latest intrusive phase in the area comprises small bodies of microgranite porphyry, set along a N0-20°W-trending direction. These bodies commonly exhibit a severe phyllic alteration overprint. Geochemical analyses (of fresh or least-altered) granodiorite porphyry and monzodiorite show a pronounced calc-alkaline signature with post collisional affinities. The porphyry-style mineralization at Konos area is located along a tectonic line NΒ10°W and occurs as a very dense stockwork of quartz veins. At the deeper parts of the system, relict sodic (albite- and chlorite-dominated) alteration zones occur, mostly overprinted by sericite. Quartz veins (mostly A-, and B-type veins) appear banded at places, comprising fine alternations of black and milky quartz. They host pyrite, chalcopyrite, Re-rich molybdenite and rheniite, along with minor quantities of magnetite, enargite, colusite, sphalerite, galena, and tetrahedrite/tennantite. Many quartz veins have been re-opened at a later stage (D-event), and pyrite was deposited forming a center line, in association with pervasive sericitic alteration. At places, gypsum veins are also associated with sericitic alteration and host Se-bearing galena, pyrite, sphalerite, and tetrahedrite/tennantite. Porphyry-style mineralization at Konos is characterized by anomalies in Mo and Re. It is severely overprinted by a high-sulfidation epithermal system (lithocap), which comprises silicification zones and widespread alunite-rich alteration assemblages, also containing kaolinite, dickite, diaspore, pyrophyllite and zunyite. The porphyry-style mineralization at Papadokoryphi area was discovered during the present study. It occurs in the form of quartz veins (stockwork) and disseminations set in potassic-altered (secondary biotite) granodiorite porphyry, and to a lesser extent in monzodiorite. The veins carry magnetite, pyrite, chalcopyrite and minor molybdenite, while bulk ore geochemical analyses revealed high concentrations of Mo (e.g., 150 ppm). The Pagoni Rachi porphyry-style mineralization develops in the form of an impressive stockwork, composed of various generations of veins. Potassic, sodic and calcic alteration assemblages predominate in the lower topographic levels of the system, while a phyllic overprint is widespread in the higher parts. The main ore minerals of the Pagoni Rachi system are pyrite, chalcopyrite, bornite, Re-rich molybdenite, rheniite, native gold. Four major porphyry vein types were identified: early magnetite veinlets (M-type) and banded A-type quartz veins are associated with sodic/calcic-potassic alteration of the granodiorite porphyry; linear, B-type quartz veins with sharp walls, associated with sodic/potassic alteration; and finally D-type, massive pyrite (+ chalcopyrite + molybdenite) veins, accompanied by intense sericitic alteration. The porphyry system is locally overprinted by epithermal-style, quartz-calcite veins and faults (E-type veins), associated with lateral argillic alteration of the host rocks. Main ore minerals of this stage are galena, sphalerite, pyrite Ag-Au alloy and tennantite/tetrahedrite (Cu-excess and Zn-rich varieties). Peripheral to the porphyry centers, propylitic alteration assemblages occur, composed by varying amounts of albite, epidote, amphibole, chlorite, and calcite. Mineral-chemical analyses of magmatic and hydrothermal biotite (form the Pagoni Rachi prospect, as well as from Papadokoryphi and the nearby Koryphes prospect, for comparison) revealed significant differences: Hydrothermal (secondary) biotite is Mg-rich (phlogopite), it displays varying amounts of Ti and high concentrations of halogens (up to 5.21 wt% F and up to 0.36 wt% Cl). In contrast, magmatic (primary) biotite is typically iron-rich) and commonly carries a high-Ti contnet. LA-ICP-MS analyses, conducted for the first time in hydrothermal biotite from porphyry systems in Greece revealed a relative enrichment in elements like Cs, La, Th etc. Especially the Pagoni Rachi hydrothermal biotite, appears to be slightly enriched in REE’s, compared to secondary biotite form the Papadokoryphi and Koryphes porphyry-style prospects. Significant F values (up to 0.8 apfu) were measured in secondary calcic amphiboles while mineral-chemical analyses of epidote from various alteration zones (e.g., calcic/potassic, propylitic) yielded typical clinozoisite compositions, with no systematic differences. This fact was also remarked for chlorites from different alteration zones, except for some variation of the Fe content in chlorites from the calcic/potassic assemblages. Native gold was not remarked in the Konos Hill porphyry system, however, at the Pagoni Rachi prospect, it is present in various forms and mineralization stages: Early M-type and A-type veins carry electrum (aver. 78% at. Αu), D-type veins host native gold (aver 89% at. Au), and finally epithermal-style veins carry Ag-Au alloy (aver. 30% at. Au). The rare sulfide rheniite was identified in both porphyry prospects (Konos Hill and Pagoni Rachi), along with Re-rich molybdenite. (up to 2.20 and 3.15 wt% Re, at Konos Hill and Pagoni Rachi, respectively). At Pagoni Rachi, the Re content correlates with gold, and displays an important enrichment in the D-type veins, compared to the other vein types. Chalcopyrite is always present with stoichiometric compositions. Enargite, sphalerite, galena, bismuthinite, colusite and tetrahedrite/tennantite, occur mostly in the epithermal-style veins as well as disseminations, overprinting/postdating the porphyry-style minerals. Bulk ore geochemical analyses showed an enrichment of the porphyry-style ores in a series of precious and critical metals like Au, Ag, Bi, Te, Se, Mo, Re, In, Sn and V, with prominent correlations between Mo-Re and Au-Se.The Konos Hill porphyry system is characterized by very low gold grades (up to 0.12 g/t), however, the gold grade of the Pagoni Rachi prospect is very high (0.36 g/t), partly due to the very high gold content of its D-type veins (up to 6.3 g/t Au). In contrast to the porphyry-style ores, the epithermal-style mineralization at the study area is characterized by enrichment in elements like Ag, Ga, In, Sn, Te, Bi, Se και V. In an attempt to identify any spatial/genetic correlations between the various ore stages and alteration assemblages, that could be used as exploration tools, part of this dissertation focused on the advanced argillic alteration zone that crops out at the western part of the study area. The Konos Hill porphyry system is telescoped by an advanced argillic lithocap that is located at the higher topographic levels of the area and hosts high sulfidation epithermal mineralization. Vuggy and massive silica zones at the central part of the lithocap trend N-S, NNW-SSE and E-W and grade outwards in assemblages rich in advanced argillic alteration minerals. Towards the lower topographic levels, the alteration is dominated by sericite. Detailed mineralogical and petrographic investigation, revealed the presence of the rare mineral zunyite (described here for the first time in a porphyry-related lithocap in Greece), along with alunite supergroup minerals (from which florencite-Ce is described for the first time in Greece), kaolinite, dickite, diaspore and pyrophyllite. Mineral chemical analyses of zunyite revealed varying F and Cl contents while the members of the alunite supergroup (also including APS minerals) are characterized by a great chemical variation, covering the range of all three subgroups (i.e. alunite, beudantite and plumbogummite). Bulk ore geochemical analyses from the HS-style mineralization at Konos Hill revealed a relative enrichment in Se, Mo, and Bi, elements that are known to reflect a magmatic contribution to the system, thus suggesting a genetic link between the epithermal-style event and the porphyry-style mineralization. Trace element geochemistry of magnetite was tested as a potential exploration tool at the Pagoni Rachi porphyry prospect. Magnetite is a common mineralogical constituent at Pagoni Rachi and occurs in two distinct modes: (i) as accessory magmatic/primary mineral in fresh to slightly propylitised granodiorite porphyry, and, (ii) as an important alteration mineral formed during the early stages of porphyry-style mineralization (such type of magnetite was not remarked at the Konos Hill porphyry prospect). Counting on the ability of magnetite to incorporate a plethora of trace elements, LA-ICP-MS analyses were used to identify any geochemical differences in magmatic and hydrothermal magnetite for the first time from a porphyry system in Greece. Detailed textural and geochemical investigation revealed that the two types of magnetite display significant differences. Primary (magmatic) magnetite usually occurs as disseminated euhedral grains in the matrix of fresh granodiorite porphyry. In contrast, the secondary (hydrothermal) magnetite forms fine-grained anhedral crystals that occur either as disseminations or, most commonly, as tiny veinlets crosscutting sodic/calcic-potassic altered granodiorite porphyry, and is associated with ore minerals like pyrite, chalcopyrite, molybdenite and electrum. Trace element analyses showed that hydrothermal magnetite is enriched in elements like V, Pb, W, Mo, Ta, Zn, Cu, Nb, in contrast to its magmatic counterpart, which carries mostly Ti, and minor Cr, Ni, and Sn. Especially the decrease of the Ti content in the hydrothermal magnetite is a common feature in many porphyry deposits and marks the transition from the magmatic to the hydrothermal environment. An uncommon feature for porphyry-related magnetite is its relatively high Mo, Pb and Zn content. This fact emerges as a unique feature of hydrothermal magnetite from the Pagoni Rachi prospect and can be further evaluated as a potential exploration tool, since magnetite-rich zones spatially coincide with that the high-Au part of the system. An analogous trace element geochemical study focused on another very common mineral at both Pagoni Rachi and Konos Hill systems. Pyrite, which is present throughout the depositional history of the systems, displays significant textural and geochemical differences. From a morphological standpoint, in the porphyry-style stages, pyrite forms fine, anhedral grains, occasionally with a spongy texture or rich in small inclusions of pyrrhotite and chalcopyrite. In contrast, epithermal-style pyrite forms coarse-grained, euhedral crystals. Geochemical analyses of different pyrite generations through LA-ICP-MS, revealed different enrichment patterns between the porphyry and the epithermal pyrite. Porphyry-style pyrite is generally depleted in trace elements, except for Co, Se, Cu, and minor Zn. In contrast, epithermal-style pyrite is enriched in As, Bi, Pb, Ni και Se. Gold is present in the form of non-stoichiometric substituting element and not as submicroscopic inclusions. Its values reach up to 4ppm in pyrite from D-type veins at Pagoni Rachi. The increase of As content in pyrite from the D event towards the E event comes in agreement with remarks form other porphyry mineralization elsewhere, however at Pagoni Rachi, a distinctive feature is that the As content increases from the early M towards the D event as well, in accordance with the gold content of pyrite Overall, the identified chemical differentiations come in agreement with analogous remarks from porphyry/epithermal deposits elsewhere, fact the highlights the significance of pyrite chemistry as an exploration tool in the ore systems of Thrace. In addition, the enrichment of pyrite in Se seems to be higher than in any other porphyry deposit elsewhere, thus emerging as a unique geochemical feature that points towards high-Au zones at the studied systems (especially since geochemical analyses have already shown a close correlation between the two elements). Moreover, pyrite chemistry stands for (an at least partial) contribution of the acidic (microgranite porphyry bodies) magmatism to the mineralization, through the addition of elements like Sn, Ta, etc., thus recording a multi-stage evolution of the ore-forming systems. To summarize, the detailed geochemical and mineralogical research on porphyry and epithermal style mineralization in the study area highlights its promising precious and critical metal potential. The studied porphyry mineralization is characterized by an extreme enrichment in Re, which along with an enrichment in Mo and Au, seem to be their most important commodities. In contrast to other porphyry-style ore systems in Greece (e.g., Skouries, Chalkidiki peninsula), the studied systems are relatively Cu-poor (Cu sulfides are not the most common metallic minerals) and the dominance of pyrite is their most important characteristic. The abundance of pyrite and the presence of banded quartz veins have been recently described as important features of Au-only porphyry systems (e.g., Kişladağ, Turkey, Biely Vrch, Slovakia). Given the fact that (especially) the Pagoni Rachi prospect shares these similarities with other porphyry-Au systems elsewhere, as well as its relatively high gold grade (0,36 g/t based solely on surface data), it becomes obvious that the studied systems should become targets for drilling projects, as they may significantly increase the precious metal endowment of N. Greece.Στην περιοχή μεταξύ Σαπών και Κίρκης (Θράκη), έγινε λεπτομερής εργασία υπαίθρου και χαρτογράφηση, γύρω από τα πορφυρικά/επιθερμικά μεταλλοφόρα κέντρα των Σαπών (Κώνος) και της Κίρκης (Παγώνη Ράχη). Πέραν των ήδη γνωστών αυτών ζωνών μεταλλοφορίας, ανακαλύφθηκαν νέες θέσεις με αντίστοιχου τύπου μεταλλοφορίες (π.χ. Παπαδοκορυφή). Η περιοχή μελέτης καλύπεται από ηφαιστειοκλαστικούς σχηματισμούς, που έχουν αποτεθεί σε τεκτονικές λεκάνες διεύθυνσης Α-Δ, οι οποίες οφείλουν την δημιουργία τους σε εφελκυστκή τεκτονική, και πιο συγκεκριμένα σε έκταση λόγω οπισθοχώρησης (slab roll-back) της υποβυθιζόμενης λιθόσφαιρας του ωεκανού της Ανατολικής Μεσογείου κάτω από το Ευρασιατικό περιθώριο, ήδη από το Hώκαινο. Βορειότερα της περιοχής μελέτης, εμφανίζονται τα μεταμορφωμένα πετρώματα της Ροδοπικής μάζας, ενώ προς Νότο, υπάρχουν εμφανίσεις πετρωμάτων που ανήκουν στην Περιροδοπική ζώνη (π.χ. ενότητα Μάκρης κλπ.). Οι μεταλοφορίες που ερευνήθηκαν, φιλοξενούνται σε διεισδύσεις Ολιγοκαινικής ηλικίας, ενδιάμεσης έως όξινης σύστασης και υψηλού Καλίου ασβεσταλκαλικό γεωχημικό τύπο. Τρία διαφορετικά μαγματικά σώματα αναπτύσσονται στην περιοχή μελέτης. Ο γρανοδιοριτικός πορφύρης αποτελείται από φαινοκρυστάλλους βιοτίτη, αμφιβόλων/κεροστίλβης, πυροξένου/αυγίτη, τιτανίτη και σπανιότερα χαλαζία με την μορφή αποστρογγυλωμένων κόκκων (resorbed quartz/quartz eyes), που φιλοξενούνται σε μία λεπτόκοκκη κύρια μάζα αστρίων και χαλαζία. Το σώμα αυτό είναι η παλαιότερη διείσδυση στην περιοχή, ενώ σχεδόν πάντα συναντάται έχοντας υποστεί ισχυρή υδροθερμική εξαλλοίωση και φιλοξενεί τις μελετηθείσες μεταλλοφορίες. Ακολουθεί ο χαλαζιακός μονζοδιορίτης, ο οποίος έχει μεγάλη ανάπτυξη στο βόρειο τμήμα της περιοχής μελέτης, χωρίς όμως να φιλοξενεί κάποια μεταλλοφορία. Πρόκειται για ένα λεπτόκοκκο πέτρωμα, κατά βάση ισοκοκκώδες, αποτελούμενο από διάφορες αναλογίες αμφιβόλων, πυροξένων, βιοτίτη και αστρίων. Στην περιοχή μελέτης ανευρίσκεται είτε χωρίς να έχει υποστεί εξαλλοίωση, είτε με προπυλιτικού τύπου εξαλλοίωση, ή ακόμα και σερικιτίωση, ειδικά κατά μήκος ζωνών ρηγμάτων. Τέλος, στην περιοχή συναντώνται διάσπαρτα σώματα μικρογρανιτικού πορφύρη, κατά κανόνα μικρών διαστάσεων (μερικές δεκάδες τετραγωνικά μέτρα). Τα σώματα αυτά δείχνουν έναν προτιμητέο προσανατολισμό Β0-20°Δ, ενώ όπως στην περιοχή Παγώνης Ράχης, αναπτύσσονται και σε διεύθυνση Α-Δ. Συνήθως έχουν υποστεί ισχυρή σερικιτική εξαλλοίωση. Γεωχημικές αναλύσεις των πιο πάνω μαγματιτών (αφορά κυρίως στα δύο πρώτα σώματα και στις λιγότερο εξαλλοιωμένες εμφανίσεις τους), έδειξαν ότι πρόκειται για πετρώματα της ασβεσταλκαλικής σειράς, με ένα χαρακτηριστικό μετα-συγκρουσιακό (post-collisional) χαρακτήρα. Η πορφυρικού τύπου μεταλλοφορία της περιοχής Κώνου, εμφανίζεται σε τεκτονικά ελεγχόμενη ζώνη διεύθυνσης Β10°Δ και αναπτύσσεται με την μορφή πλέγματος χαλαζιακών φλεβιδίων (stockwork), αλλά και διασπορών. Στα βαθύτερα τμήματα του συστήματος, εντοπίστηκαν υπολείμματα ζώνης νατριούχου μετασωμάτωσης, με την κυρίαρχη παρουσία αλβίτη και λιγότερο χλωρίτη, με σημαντική όμως επικάλυψη από σερικιτίωση, η οποία είναι και η πιο διαδεδομένη ζώνη εξαλλοίωσης στην περιοχή. Κατά θέσεις, οι χαλαζιακές φλέβες (που είναι κυρίως Α-, και Β-τύπου) εμφανίζουν ζωνώδη δομή (banded veins), με χαρακτηριστικές επάλληλες αναπτύξεις λευκού και σκουρόχρωμου χαλαζία. Φιλοξενούν σιδηροπυρίτη, χαλκοπυρίτη, πλούσιο σε ρήνιο μολυβδαινίτη, ρηνιίτη, καθώς και μικρές ποσότητες εναργίτη, μαγνητίτη, κολουζίτη, σφαλερίτη, γαληνίτη και τετραεδρίτη/τενναντίτη. Πολλές από τις φλέβες αυτές, φέρουν μία κεντρική ζώνη σιδηροπυρίτη, ο οποίος αποτέθηκε σε μεταγενέστερο επεισόδιο (D-event), με το οποίο σχετίζεται και η ζώνη σερικιτίωσης στην περιοχή. Σπάνια, φλεβίδια γύψου με μεταλλοφορία γαληνίτη, σφαλερίτη, σιδηροπυρίτη και τετραεδρίτη/τενναντίτη εντοπίζονται στην περιοχή. Η πορφυρικού τύπου μεταλλοφορία χαρακτηρίζεται από ανωμαλίες σε μολυβδαίνιο και ρήνιο, και επικαλύπτεται από σύστημα επιθερμικού τύπου υψηλής θείωσης (lithocap) με κύριο χαρακτηριστκό τις ζώνες πυριτίωσης και την διαδεδομένη παρουσία ορυκτών της υπερ-ομάδας του αλουνίτη, καολινίτη, δικίτη, διάσπορου, πυροφυλλίτη, καθώς και του σπάνιου ορυκτού ζουνιίτη. Η περιοχή της Παπαδοκορυφής έδωσε ενθαρρυντικά αποτελέσματα για την πιθανή ύπαρξη νέου πορφυρικού κέντρου. Εκεί αναπτύσσεται ζώνη καλιούχου μετασωμάτωσης (με κύριο ορυκτό τον δευτερογενή βιοτίτη), που συνοδεύει πλέγμα φλεβιδίων χαλαζία και μαγνητίτη. Τα φλεβίδια, αν και εμφανίζουν περιορισμένη επιφανειακή ανάπτυξη, φιλοξενούν μεταλλοφορία χαλκοπυρίτη, σιδηροπυρίτη και μολυβδαινίτη, ενώ γεωχημικές αναλύσεις έδωσαν σημαντικές ανωμαλίες μολυβδαίνιου. Η μεταλλοφορία πορφυρικού τύπου της Παγώνης Ράχης, αναπτύσσεται με εντυπωσική μορφή πυκνού πλέγματος χαλαζιακών φλεβιδίων. Συνοδεύεται από νατριούχο και/ή καλιούχο (και λιγότερο ασβεστούχο) μετασωμάτωση, με χαρακτηριστικά δευτερογενή ορυκτά τον Κ-άστριο, αλβίτη, βιοτίτη, αμφίβολο, επίδοτο, χλωρίτη, τιτανίτη και ασβεστίτη. Στα υψηλότερα τοπογραφικά σημεία, επικρατεί έντονη σερικιτίωση. Τα κύρια μεταλλικά ορυκτά είναι σιδηροπυρίτης, χαλκοπυρίτης, βορνίτης, μολυβδαινίτης (πλούσιος σε ρήνιο), ρηνιίτης, χρυσός, κλπ. Τουλάχιστον 4 τύποι πορφυρικών φλεβών/φλεβιδίων διακρίθηκαν: πρώιμα φλεβίδια μαγνητίτη (Μ-τύπου) αλλά και ζωνώδεις (banded), κυματοειδείς χαλαζιακές φλέβες (Α-τύπου), σχετιζόμενες με νατριούχο/καλιούχο εξαλλοίωση, ευθύγραμμες, Β-τύπου χαλαζιακές φλέβες, συνοδευόμενες από νατριούχο/καλιούχο εξαλλοίωση, D-τύπου φλέβες σιδηροπυρίτη (+χαλκοπυρίτη+μολυβδαινίτη), που επικαλύπτουν προηγούμενους τύπους φλεβιδίων και σχετίζονται με ισχυρή σερικιτική εξαλλοίωση (σερικίτης, ασβεστίτης). Το πορφυρικό σύστημα επικαλύπτεται κατά θέσεις από επιθερμικού τύπου μεταλλοφόρες φλέβες και ρήγματα, που αποτελούνται από χαλαζία και ασβεστίτη, και σχετίζονται με αργιλική εξαλλοίωση (σερικίτης, χαλαζίας, ασβεστίτης). Οι επιθερμικές αυτές φλέβες (Ε-τύπου) φιλοξενούν γαληνίτη, σφαλερίτη, σιδηροπυρίτη, κράμα αργύρου-χρυσού (Αg-Au alloy), τετραεδρίτη/τενναντίτη (πλούσιες σε Zn ποικιλίες). Περιφερειακά των πορφυρικών συστημάτων, αναπτύσσονται ζώνες προπυλιτικής εξαλλοίωσης, με κυμαινόμενα ποσοστά πλαγιοκλάστου, επιδότου, αμφιβόλων, χλωρίτη και ασβεστίτη, που αναπτύσσονται κατά κύριο λόγο εις βάρος πρωτογενών μαφικών ορυκτών και αστρίων. Ορυκτοχημικές αναλύσεις πρωτογενούς και υδροθερμικού βιοτίτη (τόσο από την Παγώνη Ράχη, όσο και από την περιοχή Παπαδοκορυφής αλλά και Κορυφών-Σαπών, για λόγους σύγκρισης χημισμού) έδειξαν σημαντικές διαφορές στην ορυκτοχημεία. Οι υδροθερμικοί βιοτίτες είναι πλούσιοι σε μαγνήσιο (φλογοπίτες), εμφανίζουν κυμαινόμενη συμμετοχή τιτανίου, υψηλές περιεκτικότητες σε αλογόνα (έως 5.21% φθόριο και 0.36% χλώριο), σε αντίθεση με τους μαγματικούς, οι οποίοι είναι τυπικοί (σιδηροπλούσιοι) βιοτίτες. Αναλύσεις LA-ICP-MS που γίνονται για πρώτη φορά σε δείγματα υδροθερμικών βιοτιτών από πορφυρικό σύστημα του Ελλαδικού χώρου, έδειξαν ότι αυτοί εμφανίζονται εμπλουτισμένοι σε συγκεκριμένα ιχνοστοιχεία (π.χ. Cs, La, Th κλπ.). Χαρακτηρίζονται από σχετικά ομοιογενή κατανομή σπανίων γαιών, αν και τα δείγματα δευτερογενούς βιοτίτη της Παγώνης

The White Marbles of the Tomb of Christ in Jerusalem: Characterization and Provenance

In this work, samples of the white marbles enclosing the Tomb of Christ, as well as samples from the interior marble facades of the Holy Aedicule structure surrounding the Tomb of Christ in the Church of Resurrection in Jerusalem, are investigated using petrographic and isotopic analysis. The aim is to characterize the marble samples and investigate their provenance. The results demonstrate that all examined marble samples originate from Proconnesos (Marmara island), and can be attributed to the so-called Proconnesos-1 variety. Published maximum grain size (MGS) and isotopic (δ18O and δ13C) values of Proconessos quarries are compared with the respective values displayed by the marble samples of the Holy Aedicule, aiming to achieve—to a certain degree—intra-site discriminations. A number of ancient quarries are excluded through this double parameter criterion as sources for the examined Holy Aedicule marbles. The discussion of petrographic and isotopic results in relation to historical testimonies and previously published archaeometry results, regarding the mortars of the Holy Aedicule, reveal that Proconnesos marble was the material of choice used at different construction phases of the Holy Aedicule, from the time of Constantine the Great and throughout the centuries, both for the cladding of the Holy Tomb and the interior facings of the Tomb Chamber and the Chapel of the Angel

Mineral Chemistry of Olivine, Oxy-Spinel, and Clinopyroxene in Lavas and Xenoliths from the Canary, Azores, and Cape Verde Islands (Macaronesia, North Atlantic Ocean): New Data and Comparisons with the Literature

An electron microprobe study was carried out on olivine, clinopyroxene, and oxy-spinel occurring in basalts and dunite xenoliths from the archipelagos of the Azores, the Canary Islands, and Cape Verde. By comparing our results with previously published data from the volcanic islands of Macaronesia, we confirmed the validity of the compositions of olivine, clinopyroxene, and oxy-spinel as geochemical tracers. The origin of olivine, i.e., crystallized in the lithospheric mantle or in volcanic rocks, was successfully discriminated. Olivine from Lanzarote dunite xenoliths, which represent fragments of the mantle transported to the surface by host magmas, exhibited higher Fo% values (Fo91.02 to Fo91.94) and a different distribution of minor elements Ca, Ni, and Mn (CaO up to 0.42 wt%, NiO 0.07–0.41 wt%, MnO 0.06–0.3 wt%) when compared with olivine occurring as phenocrysts in basaltic lavas from the Macaronesian islands. The highly variable forsterite contents (Fo75.1 to Fo94.4) in olivine from gabbro and peridotite xenoliths found across the islands of Macaronesia were attributed to fractional crystallization that started in a deep magma reservoir, suggesting that these xenoliths represent cumulate rocks and not mantle fragments. Alternatively, these xenoliths may have been affected by the interaction with metasomatic fluids. The composition of clinopyroxene phenocrysts was used to decipher formation conditions under extensional tectonics. Their composition suggests that the host lavas have an alkaline to calc-alkaline signature. Furthermore, clinopyroxene euhedral shapes and compositions suggest an origin by fractional crystallization in a closed magmatic system. The composition alone of oxy-spinel from Macaronesian basalts and xenoliths was not sufficient to draw conclusions about the geodynamic environment where they were formed. Nevertheless, the relationship between oxy-spinel and olivine crystallized in equilibrium was successfully used as oxybarometers and geothermometers. The oxy-spinel–olivine pairs show evidence that the basaltic lavas were crystallized from melts with higher oxygen fugacity and different cooling histories than those of the mantle xenoliths, as the latter crystallized and re-equilibrated much slower than the basalts