Κατά τη διάρκεια της δεύτερης συνάντησης του A.U.Th. S.E.G. Student Chapter, στις 22 Φεβρουαρίου 2019, είχαμε την ευκαιρία να φιλοξενήσουμε τη Μαργαρίτα Μέλφου, απόφοιτο του Τμήματος Γεωλογίας του Αριστοτελείου Πανεπιστημίου Θεσσαλονίκης και πλέον Μεταπτυχιακή φοιτήτρια στο Πανεπιστήμιο της Λωρραίνηςστο Νανσύ της Γαλλίας. Η Μαργαρίτα μαζί με άλλους 15 φοιτητές και φοιτήτριες συμμετείχαν στην άσκηση υπαίθρου της S.E.G. στη Χιλή από 11 έως 19 Ιανουαρίου 2019, και είχαν την ευκαιρία να μελετήσουν την ορυκτολογία, τη γεωχημεία και την τεκτονική των υδροθερμικών συστημάτων στη Βόρεια Χιλή, τα οποία εκτείνονται από την έρημο Ατακάμα, έως και τις περιοχές Κοπιαπιό και Ανφοφαγκάστα. Η άσκηση υπαίθρου περιλάμβανε επισκέψεις σε μεταλλεία και μελέτη πυρήνων γεωτρήσεων των πορφυριτικών συστημάτων Cu- Mo, υψηλής θείωσης Au- Ag- (Cu) επιθερμικών, τα τύπου Cu- Au skarn- φλεβικά και τα Χιλιανά “manto- type” Cu-Ag. Επίσης, κατά την παρουσίασή της η Μαργαρίτα αναφέρθηκε στη γεωλογία των περιοχών που επισκέφθηκαν και μοιράστηκε μαζί μας τις εμπειρίες της με τους υπόλοιπους συμμετέχοντες φοιτητές και τους συνοδούς. Η παρουσίαση καθώς και η ακόλουθη συζήτηση αποτέλεσε σημαντικό κίνητρο για όλους μας να συμμετάσχουμε μελλοντικά σε παρόμοιες δραστηριότητες της SEG.
Η συνάντηση έκλεισε με την κοπή της βασιλόπιτας, αναδεικνύοντας τυχερό νικητή τον προπτυχιακό φοιτητή Σωτήρη Κεχαγιά.
Τέλος, θα θέλαμε να ευχαριστήσουμε την Μαργαρίτα για την προθυμία της να μοιραστεί μαζί μας τις εμπειρίες της και τις γνώσεις που απέκτησε.
Εικόνα 1. Η Μαργαρίτα κατά την παρουσίασή της για την άσκηση υπαίθρου της SEG στη Β. Χιλή.
Αντιπρόεδρος του A.U.Th. S.E.G. Student Chapter
AUTh SEG Student Chapter
Field trip at the Lavrion ore district, Attica, Greece
10th-11th February 2018
Members of the chapter that participated at the fieldtrip visiting the ancient theater of Thorikos (5th cent. BC), Lavrion
Submitted by: Sofia Christoforidou, Secretary
A total of nine postgraduate and undergraduate students, members of the AUTH SEG student chapter, participated at the field trip to the world-class Pb-Zn carbonate replacement ore deposit of Lavrion, in Attica, Southern Greece. They were accompanied by the Academic Advisor, Associate Professor Vasilios Melfos, who has published several papers about the Lavrion mineralization and is familiar with this deposit. This field trip was financially supported by the Municipality of Lavreotiki which covered our accommodation costs and the meals for two days.
Greece is located in southeastern Europe and the geological evolution is strongly related with the Alpine orogenesis. The collision between African and Eurasia plates and the subduction of the remnants of the Tethys oceanic plate in south Aegean, resulted in the famous Southern Aegean Active Volcanic Arc. The Miocene magmatism had an effective role at the formation of many ore mineralizations in the Attico-Cycladic massif. Lavrion has a very interesting geological history, which is related with the exhumation of the Attico-Cycladic massif. This exhumation is documented by the extensive Western Cyclades detachment fault system observed in many locations on the surface. The subsequent Miocene magmatism resulted in the deposition of several multi-elemental ore mineralization types.
Lavrion deposit covers an area of ~150 km2 and is famous for the exploitation of Pb-Ag-rich ore during the antiquity, mainly during the Classical period, from 6th to 4th cent BC (Conophagos 1980). However mining in the region has started already in the early 3rd millennium, and lasted until the 6th cent AD. It provided with silver the Athenians and as a result it had a direct and major effect on their power and on the “Golden Age” of the Athenian Democracy that followed. After the decline of Athens, the mines were closed and then operated again in the 19th century. The exploitation of the sulfide ores continued until the 1970s.
There are four mineralization types in Lavrion: porphyry type, skarn type, vein type and carbonate replacements (Voudouris et al. 2008a,b; Bonsall et al. 2011; Melfos and Voudouris 2017). The porphyry Mo-W mineralization occurs as sheeted quartz veins and stockworks cutting the late Miocene granodiorite stock in the Plaka area. The mineralization consists of pyrite, molybdenite, chalcopyrite, pyrrhotite and minor scheelite. Quartz, hydrothermal biotite, K-feldspar, amphibole and sericite are gangue minerals. The granodiorite was intensely altered to potassic, sodic, propylitic, and sericitic assemblages, locally with silicification.
The Pb-As-Sb-Cu-Ag rich banded Filoni 80 vein with epithermal affinities trending ESE-WNW, is up to 2 m thick and up to 1 km long (Voudouris et al. 2008a). This vein includes early deposition of pyrrhotite followed by arsenopyrite, löllingite, pyrite, marcasite, a Cu-Bi bearing assemblage including lillianite homologues, pyrargyrite, chalcopyrite, Bi-bearing tetrahedrite/tennantite, bournonite, lead sulfantimonides and finally by galena and native arsenic. Quartz, siderite, fluorite and calcite are the main gangue minerals.
The carbonate-replacement Pb-Zn-Ag mineralization is the most economically important in the Lavrion district and occurs in the form of stratabound lenses, bedded replacements (mantos), and chimneys up to tens of meters in length, in the Kamariza and Sounion areas (Voudouris et al. 2008a,b; Bonsall et al. 2011). According to Voudouris et al. (2008a,b), Bonsall et al. (2011), and Berger et al. (2013) the ore deposits in Lavrion are genetically related to the Miocene Lavrion granitoids, and ore formation occurred under extensional kinematic conditions. The carbonate-replacement and vein mineralogy is dominated by pyrite, arsenopyrite, sphalerite, chalcopyrite and galena, with various silver sulfosalts and native gold and quartz, fluorite, calcite and sericite gangue. Skarn deposits also occur around the Lavrion granodioritic body, and consist of early magnetite followed by pyrrhotite, pyrite, arsenopyrite, sphalerite, chalcopyrite, galena, bismuthinite, tetradymite, and native bismuth. Extensive zones of supergene mineralization occur above the primary mineralization zones.
The field trip
On Saturday 10th February 2018, the first day of the field trip, the members of the AUTH SEG student chapter met Hercules Katsaros, Vasilios Stergiou and Konstantinos Voukelatos, all inhabitants of the Lavrion city. Mr. Voukelatos had been working for over 20 years in this gallery as a miner. Our guests are very experienced in entering the abandoned underground mines of Lavrion, which form a very complicated underground system with modern galleries cutting the ancient narrow galleries and shafts. We were informed by Nikos Leloudas, one of the best skilled cave specialists in Greece, about the safety instructions and we all entered the Plaka underground mine (Fig. 1). The entrance in this mine is permitted by the authorities. Plaka mine is also known as ‘‘Vein 80’’ or ‘‘Filoni 80’’, and was opened in mid-1950’s along the major Pb-As-Sb-Cu-Ag rich banded vein. This vein is up to 2 m thick and 1 km long.
Figure 1. The members of the AUTH SEG student chapter in front of the Plaka underground mine, together with the academic advisor, V. Melfos, H. Katsaros, N. Leloudas and K. Voukelatos.
The students had an experience with the ore minerals including galena, tennantite, arsenopyrite, pyrite, bournonite and many lead sulfo-antimonides. We examined the textures and the relation of the vein with the host metamorphic rocks, e.g. marble and schist. At the deepest parts of the gallery we had the opportunity to observe the detachment fault. The galena-rich ore was concentrated underneath the fault, at the footwall, forming a breccia with a thickness up to 3 m (Fig. 2). This was the ore which was mined in this part of the Plaka mine. It was an amazing experience entering this gallery and we realized many geological events which are not visible at the surface.
Although the weather was rainy, after exiting the underground mine, we continued and visited the Plaka porphyry system where we observed the granodiorite intruding the metamorphic rocks along the detachment fault. The alteration zones and the characteristic minerals for each zone were examined carefully.
Figure 2. The group, including the members of the AUTH SEG student chapter, in the Plaka underground mine where the brecciated galena-rich ore was extracted at the foot wall of the detachment fault.
In the second day of our fieldtrip, on Sunday 11th Febrauary 2018, the members of the AUTH SEG student chapter visited several sites of ancient mining, ore processing and metallurgy, around Thorikos. Thorikos was an ancient Greek city in southern Attica, close the mines of Lavrion, where lead and silver have been mined since the prehistoric times. Mycenaean tholos tombs (15th century BC) and a Late Mycenaean installation (12th century BC) were probably connected with the mines in this area. There is also a theatre, dated in 525–480 BC, which is one of the first theaters in ancient world. This shows the wealth of the Thorikos citizens, which is attributed to the rich mines of Lavrion.
It is remarkable that the ancient Athenians had realized in Thorikos the occurrence of exploitable ore exactly below the detachment fault and they developed the proper techniques to open large underground mines. We therefore recognized the high geological knowledge of ancient Greeks, who focused on the ore occurrences along or below the Western Cyclades detachment fault or between the Lower Marble and the schist of the Kamariza unit.
We also visited the carbonate-replacement Pb-Zn-Ag mineralization at the “3rd kilometer” mine, which has been the most economically important in Lavrion district since the classical period. It occurs in the form of stratabound lenses to bedded replacement (mantos) and chimneys, up to tens of meters in length.
The members of the AUTH SEG student chapter in front of an ancient ore washing table at Thorikos of Lavrion.
We would like to thank the Municipality of Lavreotiki which covered our accommodation costs and the meals for two days and especially the Mayor Mr. D. Loukas. Special thanks are also due to H. Katsaros, V. Stergiou, K. Voukelatos and N. Leloudas who joined our student chapter and took care about our safety in the underground mine of Plaka. They also showed us several significant parts of the mine with geological importance.
The students who participated: Eftychia Petika, Sofia Christoforidou, Fivos Kiniklis, Eftychia Peristeridou, Sofia Ketikidou, Vaggelis Tataris, Vaggelis Skoupras, Margarita Melfou, Vaggelis Katsis.