Fluid evolution in Tertiary magmatic-hydrothermal ore systems at the Rhodope metallogenic province, NE Greece. A review

Characterization of various fluid parameters in magmatic-hydrothermal ore mineralizationsis potentially essential for interpretation of the conditions of formation and therefore formineral exploration. Fluid inclusions can provide a useful and promising tool in the researchof the ore forming processes in these systems. This review focuses on the nature,composition and origin of magmatic-hydrothermal ore forming fluids involved in the formationof representative Tertiary ore deposits at the Rhodope metallogenic province in NEGreece. These deposits are spatially related to Tertiary magmatism in NE Greece. Casestudies are presented here and include an intrusion-hosted sheeted vein system (Kavala), aAu-rich carbonate replacement and quartz-vein mineralization (Asimotrypes), mineralizedveins in Eptadendro-Rachi and Thasos island (Kapsalina and Panagia), porphyry Cu-Mo-Re-Au deposits in Pagoni Rachi and Maronia and epithermal Au-Ag mineralizations inPerama and Loutros. Hydrothermal fluids rich in CO2 together with elevated Au and Tecontent are common and occur at the Kavala intrusion hosted sheeted vein system, at theAsimotrypes Au-rich carbonate replacement mineralization and at the Panagia (Thasos)vein system. We classify all these ore mineralizations as intrusion-related gold systems(IRGS)v. Transport and precipitation of metals including Au and Te is favoured when CO2is present. Precipitation of the ore mineralization takes place due to the immiscibility of thecarbonic and the aqueous fluids which have a magmatic origin with the contribution ofmeteoric water. Cooling of magmatic hydrothermal fluids and dilution with meteoric wateris a common cause for ore mineral formation in the vein mineralizations of Eptadendro/Rachi and Kapsalina Thasos. At the Pagoni Rachi and Maronia porphyry deposits, boilingand the high proportion of the vapour phase are the most essential fluid processes whichaffected ore formation. The epithermal veins overprinting the Pagoni Rachi and the Maroniaporphyry systems and the HS-IS epithermal system in Perama Hill and the IS epithermalmineralization in Loutros are characterized by low to moderate temperatures and lowto moderate salinities. Cooling and dilution of the ore fluids are the main process for goldprecipitation. We conclude that the different fluid parameters and microthermometric dataindicate a variety of fluid origin conditions and sources which can affect the strategy forexploration and prospecting for gold, rare and critical metals

Morfološke značilnosti in pogoji nastanka jam v speleoparku Almopia (Loutra Almopias, severna Grčija)

The Almopia Speleopark caves are located at the Almopia basin in northern Greece, at the foothill of Voras Mountain, and are formed in the Maestrichtian limestones of the Pelagonian zone. They are studied on the basis of their meso- and micro-scale morphology as well as their horizontal pattern, in order to investigate the character of the forming aquifer. Emphasis is given on the morphological description of the Loutra Almopias Cave. Cave morphology is dominated by the presence of cupolas, rock bridges, ridges and “windows”, abrupt terminations of fracture guided passages, pendants, rising channels, pseudonotches, false-floors and spongework. Speleogens indicate a speleogenesis due to slowly natural convecting hot water bodies. Phreatic calcite from the Varathron Cave is analyzed on the basis of the fluid inclusions in order to investigate the physicochemical conditions of the convecting water bodies. This has shown that the calcite was formed at temperatures ranging between 120 and 189 ºC, with a peak around 150 ºC. The fluids were dominated by NaCl of very low salinities (0.2-1.0 wt% NaCl equiv.), showing probably the incorporation of meteoric waters.Speleopark Almopia je ob vznožju gore Voras v porečju Almopije v Severni Grčiji. Jame so nastale v maastrichtskih apnencih Pelagonske cone. Z analizo jamskih skalnih oblik in tlorisov jam smo raziskovali pogoje njihovega nastanka. Največ raziskav smo naredili v jami Loutra Almopias. Med oblikami so značilne kupole, skalni mostovi, skalni grebeni, okna, nezvezni zaključki rovov nastalih ob razpokah, dvigajoči se kanali, lažne korozijske zajede in tla ter prepleti drobnih kanalov. Iz skalnih oblik sklepamo, da so jame nastale s korozijo počasnih konvekcijskih tokov termalne vode. Fizikalno-kemične pogoje speleogene­ze smo določali z analizo tekočinskih vključkov v freatičnem kalcitu iz jame Varathron. Temperatura izločanja kalcita je bila med 120°C in 180°C, z vrhom temperaturne porazdelitve pri 150°C. Nizka slanost tekočinskih vključkov, masni delež soli je med 0,1% in 1%, kaže da tekočinske vključke sestavlja pretežno meteorna voda

Mineralogical Constraints on the Formation of the Perama Hill High-Sulfidation Epithermal Au-Ag-Te Deposit, Northeastern Greece

The Perama Hill deposit is a high- to intermediate-sulfidation Au-Ag-Te epithermal system hosted within silicic and argillic altered andesitic hyaloclastic rocks and overlying sandstones. New combined EPMA and fluid inclusion data from the deeper parts of the deposit suggest early deposition of native gold, Bi-chalcogenides (kawazulite/tetradymite solid solutions) and thiostannates (probably at 291-349°C), followed by precious metal tellurides and electrum between 193 and 269°C. There is a trend from high- to intermediate-sulfidation state fluid conditions with time. The coexistence of both liquid- and vapor-rich inclusions homogenizing within the same temperature range demonstrates that boiling occurred during formation of the ore minerals. The kawazulite/tetradymitess-gold association at Perama Hill suggests that it could have formed from a sulfide melt in the system Bi-Au-Se-Te system as gold was scavenged from the hydrothermal ore-forming fluid at elevated temperatures

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

A New Occurrence of Rheniite (ReS2) and Telluride Enrichment in the Pagoni Rachi-Kirki Porphyry-style Mo-Cu-Ag-Au Prospect, Northern Greece

The rare mineral rheniite (ReS2) has been found along with Re-rich molybdenite, Fe-Cu sulfides and oxides, in quartz veins crosscutting sericitic- and transitional sericitic-sodic/potassic altered granodioritetonalite porphyry of the Pagoni Rachi-Kirki prospect. The quartz-molybdenite-rheniite veins postdate an earlier mineralizing event, which introduced gold-chalcopyrite ±molybdenite in quartz- and magnetite veins associated with sodic/potassic-calcic alteration. A late, epithermalstyle, telluride-bearing stage, spatially related to carbonate-quartz veins with argillic alteration that contains minor amounts of Re-free molybdenite, overprints earlier mineralization and redistributes precious and base metals in the ore system. The structural analysis of Re-rich molybdenite crystals demonstrates that they crystallize in the 2H polytype and not in the 3R polytype as previously hypothesized. EMPA data indicate that rheniite is almost stoichiometric and that tellurides and electrum are the major carriers of Au and Ag in the deposit. Preliminary fluid inclusion studies of quartz in the rheniite-bearing veins indicate that rheniite (and molybdenite) likely precipitated at 350° to 400oC during phase separation. Alternatively, rheniite (and tellurides) may have formed directly from the vapor as sublimates

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

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

Mineralogical Constraints on the Potassic and Sodic-Calcic Hydrothermal Alteration and Vein-Type Mineralization of the Maronia Porphyry Cu-Mo ± Re ± Au Deposit in NE Greece

The Maronia Cu-Mo ± Re ± Au deposit is spatially related to a microgranite porphyry that intruded an Oligocene monzonite along the Mesozoic Circum-Rhodope belt in Thrace, NE Greece. The magmatic rocks and associated metallic mineralization show plastic and cataclastic features at the south-eastern margin of the deposit that implies emplacement at the ductile-brittle transition, adjacent to a shear zone at the footwall of the Maronia detachment fault. The conversion from ductile to brittle deformation caused a rapid upward magmatic fluid flow and increased the volume of water that interacted with the host rocks through high permeable zones, which produced extensive zones of potassic and sodic-calcic alteration. Potassic alteration is characterized by secondary biotite + K-feldspar (orthoclase) + magnetite + rutile + quartz ± apatite and commonly contains sulfides (pyrite, chalcopyrite, pyrrhotite). Sodic-calcic alteration consists of actinolite + sodic-calcic plagioclase (albite/oligoclase/andesine) + titanite + magnetite + chlorite + quartz ± calcite ± epidote-allanite. The high-oxidation state of the magmas and the hydrothermal fluid circulation were responsible for the metal and sulfur enrichments of the aqueous fluid phase, an increase in O2 gas content, the breakdown of the magmatic silicates and the production of the extensive potassic and sodic-calcic alterations. Brittle deformation also promoted the rapid upward fluid flow and caused interactions with the surrounding host rocks along the high temperature M-, EB-, A- and B-type veins