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The world-class Sarbai, Kachar and Sokolovskoe ore deposits of the Turgai belt are part of the Carboniferous Valerianovka arc of northwest Kazakhstan. They contain an aggregate of more than 3 billion tonnes of mineable massive magnetite. The Valerianovka arc is part of the Transuralian zone that forms the eastern most boundary of the Uralide collisional zone. The Uralides, a 2500 km long, north-south trending mountain belt that extends northwards from the steppes of northern Kazakhstan to the Arctic Ocean were formed as a result of the collision of the Laurussia and Siberia-Kazakh plates during the Late Carboniferous to Early Permian period. Geochronological work completed during this study has shown that intrusive rocks within the Transuralian zone were formed along tow sub-parallel north-south trending volcanic arcs; the first with ages from 370 to 350 Ma near to the current surface expression of the Troitsk fault and the second approximately 100km East with ages from 340 to 310 Ma within the centre of the zone. Late sulphide mineralisation at the Sarbai deposit has a measured Re-Os age of 336.2 ± 1.3 Ma, within the estimatde range of intrusive age for the spatially associated Sarbai-Sokolov intrusive series. This age is also within error of the similar Magnitogorsk giant magnetite skarn deposit in the West of the Uralides, which was previously thought to be unrelated to the deposits in the Turgai belt. Younger granitic plutons of the Dzhabyk-Karagandski intrusive series and the Pridorogny granitic dykes that clearly cross cut mineralisation have measured U -Pb SHRIMP ages of between 300Ma and 280 Ma that correspond to an igneous event that affected all of the Southern Urals. The magnetite bodies of the iron skarn deposits replace limestone and tuffs, and are either distal or locally proximal to the contacts of gabbro-diorite-granodoirite intrusive complexes. Four main stages of alteration and mineralisation can be recognised at these deposits, namely: (l-)pre-ore; (2) the main magnetite forming; (3) late sulphide and (4) post- ore phases. The pre-ore stage is characterised by high temperature, metamorphic/metasomatic calc- and alurnino-silicates. The main magnetite ore phase formed when hot, sulphur poor, acidic-, iron and silica- and aluminium-rich fluids were structurally focused to dissolve and replace the dominantly limestone hosts. This was accompanied by a skarn assemblage gangue of epidote, calcic-pyroxenes, calcic-garnet and calcic-amphiboles, minor sulphide minerals and high field strength element (HFSE)-bearing accessory minerals such as titanite and apatite. The magnetite-skarn mineralisation was followed by a late sulphide phase, when comparatively cooler fluids, produced distinctive and extensive alteration assemblages of sod-rich scapolite, albite, chlorite and K-feldspar, accompanied by chalcopyrite, pyrite and minor sphalerite and galena. The post-ore phase, is characterised by cross-cutting barren veins composed of calcite, lesser albite, K feldspar, and minor quartz, and by widespread alteration comprising scapolite, albite and silica, which surrounds the deposit, and extends for several kilometers into the host rock. Many of the geological and mineralogical features of these deposits closely resemble those of the Iron Oxide-Copper-Gold (IOCG) deposits and provinces around the world though it is here proposed that these be classified as iron skarn deposits. Stable isotope (C, 0, S) studies carried out on a range of sulphides, carbonates and silicates, support an igneous, or igneous rock-equilibrated source for the mineralising fluids. Carbon and oxygen isotope data from gangue carbonates suggest that carbonate is derived from the interaction of igneous derived or igneous equilibrated fluids with host limestones. It is proposed that the source of the magmatic fluid is the diorites of the Sarbai-Sokolov intrusive series which underwent considerable fractionation and degassing after they were emplaced. This study aims to establish the link between the formation of the giant magnetite skarns and the tectonic history of the Uralides. Establishing a genetic model for these deposits to will lead to a better understanding of similar deposits worldwide.

Η νήσος της Τήνου (εικόνα 1), με εμβαδό περίπου 200 km2, βρίσκεται στη δυτική Ελλάδα και είναι τρίτη σε έκταση μεταξύ των νήσων που συγκροτούν το σύμπλεγμα των Κυκλάδων, στο Αιγαίο πέλαγος. Από γεωτεκτονικής απόψεως υπάγεται στην γεωτεκτονική ενότητα, γνωστή ως ‘Αττικοκυκλαδική Κρυσταλλοσχιστώδης Μάζα’. Από διάφορες γεωλογικές μελέτες που έχουν συνταχθεί κατά καιρούς, έχει προκύψει ότι στην γεωλογική της δομή μετέχουν μεταμορφίτες, μαγματίτες και τεταρτογενή ιζήματα. Από τα πετρώματα αυτά οι μεν μεταμορφίτες καλύπτουν το 79%, τα δε υπόλοιπα το 17% και 4%, αντίστοιχα, της επιφάνειας της νήσου.Με βάση μελέτες που πραγματοποιήθηκαν στις οφιολιθικές εμφανήσεις της Τήνου, προέκυψε πως η σύσταση του μανδυακού περιδοτίτη είναι χαρζβουργιτική, μέσα στον οποίο υπήρχαν αρκετές μικρές εμφανήσεις χρωμίτη. Οι χαρακτήρες που έχουν μελετηθεί γεωχημικά και ορυκτολογικά-πετρογραφικά, αφορούν κυρίως τον διάσπαρτο τύπο σπινελλίου και τον τεκτονίτη-περιδοτίτη που είναι ο δυνητικός ξενιστής κοιτασμάτων χρωμίτη.Το ενδιαφέρον της νήσου της Τήνου από απόψεως οικονομικής γεωλογίας περιορίζεται – σύμφωνα τουλάχιστον με τα δεδομένα που έχουν προκύψει από τις μέχρι τώρα έρευνες – αποκλειστικά και μόνο στα μάρμαρα και στα βιομηχανικά ορυκτά και πετρώματα (τάλκης). Μεταλλικά ορυκτά απατώνται μεν, σε φυσικές όμως συγκεντρώσεις τέτοιες, ώστε ούτε οι διαστάσεις τους ούτε και η περιεκτικότητά τους σε μέταλλο να αφήνουν περιθώρια για θετικές εκτιμήσεις. Παλαιότερα, έγινε προσπάθεια εκμεταλλεύσεως, σε διάφορες θέσεις, χωρίς θετικά αποτελέσματα όμως. Τα μεταλλευτικά έργα είναι μικρών διαστάσεων, συνήθως εκσκαφές, και σε λίγες περιπτώσεις στοές και κεκλιμένα. Σημειώνεται ότι σε πολλές από τις εκσκαφές δεν υπάρχουν σήμερα ίχνη μεταλλεύματος, ούτε στα τοιχώματά τους, ούτε στα μπάζα. Η συγκέντρωση της ομάδας του λευκόχρυσου (PGE) και του χρυσού στους χρωμιτίτες των οφιολίθων της Τήνου είναι της τάξεως των εκατοντάδων ppb. Αυτά τα στοιχεία συγκεντρώνονται κυρίως θειούχα μεταλλικά ορυκτά (σουλφίδια), όπως ο χαλκοπυρίτης, και σχηματίζονται στο ορθομαγματικό στάδιο, σχηματίζοντας ομάδες, μέσα στους κόκκους του χρωμίτη. / Tinos island (picture 1), with an area of about 200 km2, is located in weastern Greece and is the third largest island of the Cyclades group of islands, in the Aegean Sea. Geologically, is regarded, to belong to the geotectonic unit, known as the ‘Atticocycladic Crystalline Massif’. As a result of many geological studies, it was found that the geological structure of the island is made up from metamorphic and magmatic rocks, as well as Quaternary sediments. These rocks cover an area of about 79%, 17% and 4%respectively of the island’s surface area. Based on studies performed in the Tinos ophiolitic complex, showed that the composition of the mantle peridotites is harzburgitic, in which there were several small commulations of chromite. The characters studied geochemical and mineralogical-petrographical, mainly concern the disseminated spinel type and the peridotite which is a potential host rock for chromite deposits. The interest of Tinos island in terms of economic geology is limited - at least according to the data derived from the surveys so far - to marbles and industrial minerals and rocks (talc). Metallic minerals are occured, but in natural concentrations such that neither the dimensions nor the content of metal allow for positive evaluations. Previously, an exploitation attempt was made, in various positions, but without positive results. Mining projects are small, usually excavations, and in a few cases tunnels and ramps. Note that in many of the excavation does not exist today mines traces neither in their walls, nor in the rubble. The concentration of platinum group (PGE) and gold in chromitites of serpentines of Tinos are about of hundreds of ppb. These components are mainly concentrated sulphurous metallic minerals (sulfides) such as chalcopyrite, and formed in orthomagmatic stage, forming groups within the granules of the chromite.

Le thème principal de cette recherche est la remédiation des sols contaminés par des hydrocarbures en utilisant des traitements d'oxydation chimique à pH neutre. Les minéraux à base de fer sont susceptibles de catalyser cette réaction d'oxydation. L'étude concerne donc dans un premier temps la synthèse des minéraux réactifs contenant des espèces FeII et FeIII (la magnétite et la rouille verte) et, dans un second temps, leur utilisation pour catalyser l'oxydation chimique. Les procédés d'oxydation testés incluent l'oxydation de type « Fenton-like (FL) » et de type persulfate activé (AP). La formation de la magnétite et de la rouille verte a été étudiée par des transformations abiotiques de différents oxydes ferriques (ferrihydrite, goethite, hématite et lépidocrocite) mis en présence de cations FeII. La magnétite a été utilisée pour catalyser les oxydations (FL et AP) dans la dégradation des hydrocarbures aliphatiques et aromatiques polycycliques (HAP) à pH neutre. Une dégradation importante des hydrocarbures aliphatiques a été obtenue par ces deux oxydants, aussi bien pour des pétroles dégradés naturellement que pour un pétrole brut. L'oxydation catalysée par la magnétite a également été efficace pour la remédiation de deux sols contaminés par HAP provenant d'anciens sites de cokerie. Aucun sous-produit n'a été observé dans nos expériences d'oxydation. En revanche, une très faible dégradation des hydrocarbures a été observée lorsque les espèces FeII solubles ont été utilisées comme catalyseur. Des expériences d'oxydation ont également été réalisées en colonne. Ces études d'oxydation ont révélé l'importance du type de catalyseur utilisé pour l'oxydation, la disponibilité des HAP dans les sols et l'effet de la matrice du sol. Les résultats suggèrent que la magnétite peut être utilisée comme source de fer pour activer les deux oxydations par Fenton-like et persulfate à pH neutre. Ce travail a de fortes implications sur la remédiation par oxydation chimique in situ des sols pollués par des hydrocarbures / The main theme of this research is the use of reactive iron minerals in the remediation of hydrocarbon contaminated soils via chemical oxidation treatments at circumneutral pH. The contribution of this thesis is two-fold including the abiotic synthesis of mixed FeII-FeIII oxides considered as reactive iron minerals (magnetite and green rust) and their use to catalyze chemical oxidation. Oxidation methods tested in this study include Fenton-like (FL) and activated persulfate oxidation (AP). The formation of magnetite and green rust was studied by abiotic FeII-induced transformations of various ferric oxides like ferrihydrite, goethite, hematite and lepidocrocite. Then, the ability of magnetite was tested to catalyze chemical oxidation (FL and AP) for the degradation of aliphatic and polycyclic aromatic hydrocarbons (PAHs) at circumneutral pH. Significant degradation of oil hydrocarbons occurring in weathered as well as in crude oil was obtained by both oxidants. Magnetite catalyzed oxidation was also effective for remediation of two PAHs contaminated soils from ancient coking plant sites. No by-products were observed in all batch slurry oxidation systems. Very low hydrocarbon degradation was observed when soluble FeII was used as catalyst under the same experimental conditions. Magnetite also exhibited high reactivity to catalyze chemical oxidation in column experiments under flow through conditions. Oxidation studies revealed the importance of catalyst type for oxidation, PAHs availability in soils and the soil matrix effect. Results of this study suggest that magnetite can be used as iron source to activate both Fenton-like and persulfate oxidation at circumneutral pH. This study has important implications in the remediation of hydrocarbon polluted soils through in-situ chemical oxidation