Interaction between sulfate-rich basin fluids and hydrocarbons triggers thermochemical sulfate reduction (TSR), a key process in ore formation. In the Lavrion Pb-Zn-Ag district (Attica, Greece), mineralization developed during post-subduction exhumation along the West Cycladic Detachment System (WCDS) and includes porphyry Mo-Cu, Fe-Cu skarn, carbonate-replacement Pb-Zn-Ag, and vein/breccia-type Pb-Zn-Ag deposits.Sector-zoned sphalerite and later brown sphalerite record the evolution of the hydrothermal system. Brown sphalerite is enriched in Fe, Mn, Cd, and Hg, whereas Ag, In, and Ga distributions are independent of color zoning. Fluid inclusions indicate H2O-CO2-NaCl-CaCl2 fluids with salinities of 10–20 wt% NaCl eq. and homogenization temperatures of 120–280 °C. They also contain hydrocarbons (n-alkanes (C1–C6), alkenes, benzene, toluene, styrene) and sulfur compounds. Calcite δ13C-δ18O values indicate infiltration of surface-derived fluids and an increase in fluid-to-rock ratio during the transition from ductile-brittle to brittle deformation, while sphalerite δ34S values are consistent with TSR in a non-equilibrated system.Two hydrothermal-metallogenic systems operated between 10 and 7 Ma: (1) a magmatic-related system responsible for porphyry and skarn, and (2) a 280–120 °C high-temperature TSR-driven system associated with carbonatization along the WCDS, forming carbonate-replacement, vein, and breccia ores. Outside magmatic centers, metals were likely derived from leaching of volcano-sedimentary schists, metagranitic and metabasic boudins, and earlier magmatic-related mineralization.

The Plaka porphyry Mo-Cu system occurs in the world-class Lavrion Ag-Pb-Zn district in Attica, southern Greece. It is spatially associated with a granodiorite porphyry that intruded the Attic-Cycladic Crystalline Complex in the late Miocene, along the footwall of the Western Cycladic detachment fault. A Re-Os age of 9.51 +/- 0.04 Ma indicates that molybdenite formed during the early stage of the granodiorite porphyry intrusion and that subsequent cooling was very rapid. Brittle deformation and hydrothermal fluid flow created a network of A-, B-, diopside-actinolite and D-veins, associated with potassic-, sodic-calcic and sericitic alterations. Potassic alteration is characterized by secondary biotite +K-feldspar + quartz + magnetite +/- apatite, contains disseminated molybdenite, pyrite, and chalcopyrite, and formed at 420-500 degrees C, at pressures up to 530 bars (< 5.3 km depth) from hydrothermal fluids that underwent phase separation. Sodic-calcic alteration is devoid of Cu-Mo mineralization and, consists of diopside + actinolite + oligoclase/andesine + titanite + magnetite +/- epidote-allanite +/- chlorite +/- quartz, which corresponded to a temperature range of between 350 and < 500 degrees C. Primary magnetite, titanite and biotite crystallized between the nickel-nickel oxide (NNO) and hematite-magnetite (HM) buffers, indicating fairly oxidizing conditions for the granodioritic magma. Hydrothermal biotite plots closer to the HM buffer suggesting increasing oxygen fugacity during exsolution of the hydrothermal fluids associated with potassic alteration. The system evolved toward more reducing conditions during sericitic alteration and associated pyrite-molybdenite mineralization. A combination of evaporated seawater and magmatic fluids likely caused formation of the sodic-calcic alteration through the decarbonation of the host marble.

The Archean Val-d’Or orogenic gold vein field (Abitibi, Canada) is characterized by quartz-carbonate-tourmaline veins in which at least two temporally distinct Au deposition events are commonly recognized, including Au-Ag-Te-Bi inclusions in pyrite formed during the main quartz mineralizing event, and Au-Te-Bi-Cu-Pb minerals in late quartz ± carbonate brittle veinlets. SEM-CL imaging combined with in situ SIMS oxygen isotope of quartz in four orogenic Au deposits (Beaufor, Lac Herbin, Sigma-2, Triangle) of the Val-d’Or vein field reveal similar quartz vein generations and relative timing. In SEM-CL images, early idiomorphic oscillatory-zoned Qz1 is light grey and formed in vein open space. Qz2, dominant in volume, forms light to medium grey sub-equant grains overprinting Qz1. Later Qz3 forms irregular medium grey bands with sharp or gradual contacts with Qz1 and Qz2, indicating a second recrystallization event. Qz4, minor in volume, forms brittle thin veinlets (< 400 μm in width) and stockworks characterized by dark grey luminescence, cutting Qz1, 2 and 3. Qz4 veinlets host Au- Ag-Te-Bi-Cu-Pb minerals. In situ SIMS oxygen isotope analyses of the successive quartz types show a similar, small progressive increase of 𝛅18Oquartz values, typically by 1‰ between Qz1 and Qz2, and by up to 3.3‰, from Qz1 to the later quartz generations. The 𝛅18Oquartz values at each deposit follow the 𝛅18Oquartz regional variation recorded in previous studies, suggesting that later Qz2 and Qz3 are a product of local dissolution and reprecipitation of Qz1. The higher 𝛅18Oquartz values in Qz2 and Qz3 are interpreted to result from pressure solution/dissolution of Qz1 and reprecipitation either in equilibrium with a fluid with a higher proportion of high 𝛅18O metamorphic fluids, or from a small amount of cooling. The Qz4 veinlets with Au-Ag-Te-Bi-Cu-Pb minerals result from vein-scale quartz and metal (including gold) dissolution and precipitation into brittle fractures during cooling triggered by a regional thermal event.

The Augmitto-Bouzan deposit is a 12 km long segment of the Larder Lake-Cadillac Deformation Zone (LLCDz) south of Rouyn-Noranda (Québec, Canada) that is characterized by an uneven gold distribution hosted in quartz-carbonate ± tourmaline veins within Piché Group ultramafic rocks. This study compares the fluid flow conditions between the variable gold-endowed sectors to identify deposit-scale processes responsible for gold endowment. Stable isotopes indicate that quartz and tourmaline have equilibrium temperatures (228–⁠420 °C) that likely define a high vertical thermal gradient ( 30 °C/100 m) along the LLCDz. Covariation between temperature and computed δ18OH2O and δDH2O is interpreted to result from mixing between a high temperature (> 420 °C), high δ18O (> 10.8‰), and low δD (< –29‰) deep-seated metamorphic fluid, and a low temperature (< 230 °C), low δ18O (< 4‰) and high δD ( 0‰) upper crustal pore fluid. Local upwelling of auriferous deep-seated fluid, shown by interpolation of δ18OH2O in the gold-endowed Augmitto-Cinderella and Astoria segments, was likely focused along higher permeability deformation-related pathways. Sectors of low gold endowment have lower δ18OH2O and fluid/rock ratios, likely reflecting a larger proportion of upper crustal fluid and differences in fluid-flow behavior. Modeling of fluid flow shows that this is due to 1) weaker metamorphic fluid flux in the thinner band of Piché Group rocks and 2) more porous volcanic rocks north of the LLCDz, drawing more pore fluid into the fault. We suggest that most of the variation of gold endowment is related to variations in advection of auriferous metamorphic fluid along the segment, whereby a weaker metamorphic fluid flux or increased admixture of upper crustal fluids decrease the gold potential along the LLCDz.

The Rouyn-Noranda mining district of Quebec contains 20 Cu-Zn (+/- Au +/- Ag) volcanogenic massive sulfide (VMS) deposits, including the giant and gold-rich Quemont and Horne deposits. Mineralized epigenetic veins are also present, but their origin and relative timing remain enigmatic. The nature and extent of their alteration signatures and the effect of their superposition on district-scale alteration patterns is unknown. The VMSrelated quartz-sulfide Cu-Zn-Ag veins have delta O-18(quartz) values of 8.5 +/- 0.8 parts per thousand, reflecting delta O-18(fluid) compositions of -0.4 to 3.1 parts per thousand (250 degrees-350 degrees C) that are typical of Archean seawater. They are associated with a proximal Fe-rich chlorite alteration and marginal spotted sericite-chlorite alteration with whole-rock delta O-18 values of 2.9 to 5.9 parts per thousand and are interpreted to have formed within the structurally controlled discordant upflow zones of a VMS hydrothermal system. Younger gold-bearing quartz-carbonate veins were emplaced along mechanical anisotropies created by mafic dikes during north-south compression and the formation of regional E-trending faults, folds, and cleavage. They are characterized by delta O-18(quartz) values of 11.3 +/- 0.8 parts per thousand, reflecting delta O-18(fluid) compositions of 2.4 to 5.9 parts per thousand (250 degrees-350 degrees C), typical of a metamorphic fluid, possibly mixed with a lower delta O-18 upper crustal fluid. They are associated with ankerite, calcite, muscovite, chlorite, albite, and quartz +/- hematite alteration with whole-rock delta O-18 values of 5.8 to 10.3 parts per thousand. Chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb zircon ages for two tonalite intrusions constrain the maximum age of the Cu-Zn-Ag veins to 2697.6 +/- 0.7 Ma and the minimum age to 2695.3 +/- 1.0 Ma, which is also the maximum age of the gold quartz-carbonate veins. Superposition of alteration related to the gold quartz-carbonate veins on previously chlorite- and sericite-altered rocks has resulted in mixed alteration signals with whole-rock delta O-18 values of similar to 6 to 8 parts per thousand that have perturbed and masked regional alteration patterns related to older VMS mineralization, such as those found in the Quemont and Horne deposits. These results indicate that defining alteration vectors in camps that have superimposed hydrothermal systems requires full consideration of the hydrothermal history of the camp, and if such constraints are lacking, whole-rock delta O-18 values should not be used as a stand-alone exploration method.

The O-H isotope composition of orogenic gold-bearing veins along the Cadillac Larder Lake Fault Zone (CLLFZ) between Val-d'Or and Kirkland Lake is documented in detail to unravel the fluid sources of orogenic gold deposits. Coexisting vein minerals show common oxygen isotope equilibrium, which yields temperatures between similar to 250 and similar to 550 degrees C. Temperature covariation with fluid O and H isotope compositions demonstrates mixing between a higher temperature (> 500 degrees C), deep-seated metamorphic fluids with high delta(OH2O)-O-18 (>9 parts per thousand), low delta D-H2O (<-40%), with lower temperature (<250 degrees C) upper crustal fluids with lower delta O-18(H2O) (<4 parts per thousand), and higher delta D-H2O that ranges from 0 to 30%. Along the Augmitto-Bouzan segment (Rouyn-Noranda), decreasing temperatures from 420 degrees C at 700 m depth, to 230 degrees C at 100 m depth, show the vertical ascent of the deep-seated metamorphic fluids along the CLLFZ. In the eastern part of the CLLFZ (Val-d'Or to Malartic) the metamorphic fluid has an end-member O isotope composition of 9-10%, whereas to the west from Malartic to Kirkland Lake, it has a delta O-18(H2O) between 11-13%. The switch in metamorphic fluid reservoirs occurs where the CLLFZ has an inflection in strike. The upper crustal fluids, that cannot be distinguished despite differences in the composition of the country rocks hosting the orogenic gold deposits.

The Lavrion mining district (SE Attica, Greece) comprises ore deposits of (1) low-grade Mo-Cu porphyry style, (2) Cu-Fe skarn, (3) high-temperature carbonate replacement Pb-Zn-Ag-(Au), and (4) vein and breccia Pb-Zn-Ag mineralizations. These are the result of the transport and deposition of economic elements from fluids that circulated from the construction to the gravitational collapse of the Hellenides-Aegean Domain along the Africa-Eurasia convergent plate boundary active for the last 80 Ma. Oceanic and continental rocks of the African plate were buried to high pressure conditions in the subduction zone. Progressive southward slab retreat was accompanied by magmatism and exhumation of metamorphic rocks along high- and low-angle detachment systems, with associated mineralized systems. The porphyry and skarn deposits are spatially and genetically related to the Plaka magmatic in tru sion dated 12 – 8 Ma. Carbonate replacement is associated with decarbonation and the liberation of CO2 during exhumation at the ductile to brittle transition. Fluorite and calcite gangue minerals enclosing the vein and breccia Pb-Zn-Ag mineralization were precipitated during brittle deformation from a fluid resulting from mixing of meteoric water with evaporated seawater closer to the surface. Base and precious metals were exploited since the Bronze Age to the late 20th century. As such, the Lavrion area represents an exceptional site to study the evolution of mining technologies through history.

AbstractOrogenic gold deposits formed in various terranes of most ages since the Paleoarchean and generally consist of quartz veins hosted in shear zones formed at the ductile brittle transition under greenschist to lower amphibolite metamorphic conditions. Vein mineralogy is dominated by quartz with various amounts of silicates, carbonates, phyllosilicates, borates, tungstates, sulfides, and oxides. The isotopic composition of these minerals and fluid inclusions has been investigated since the 1960s to constrain the characteristics of orogenic fluid systems involved in the formation of gold deposits worldwide. This review is based on 8580 stable isotope analyses, including δ18O, δD, δ13C, δ34S δ15N, δ11B, and δ30Si values, from 5478 samples from 558 orogenic gold deposits reported in the literature from 1960 to 2010. This contribution describes the variability of the light stable isotopic systems as function of the minerals, the age of the deposits, their regional setting, and their country rocks. The temperature of isotopic equilibrium of orogenic gold veins is estimated from mineral pairs for oxygen and sulfur isotopes. Based on these temperatures, and on fractionation between mineral and fluid components (H2O, CO2 and H2S), the isotopic composition of fluids is estimated to better constrain the main parameters shared by most of auriferous orogenic fluid systems. Orogenic gold deposits display similar isotopic features through time, suggesting that fluid conditions and sources leading to the formation of orogenic gold deposits did not change significantly from the Archean to the Cenozoic. No consistent secular variations of mineral isotope composition for oxygen (−8.1‰ ≤ δ18O ≤ 33‰, n = 4011), hydrogen (−187‰ ≤ δD ≤ −4‰, n = 246), carbon (−26.7‰ ≤ δ13C ≤ 12.3‰, n = 1179), boron (−21.6‰ ≤ δ11B ≤ 9‰, n = 119), and silicon (−0.5‰ ≤ δ30Si ≤ 0.8‰, n = 33) are documented. Only nitrogen (1.6‰ ≤ δ15N ≤ 23.7‰, n = 258) and sulfide sulfur from deposits hosted in sedimentary rocks (−27.2‰ ≤ δ34S ≤ 25‰, n = 717) display secular variations. For nitrogen, the change in composition is interpreted to record the variation of δ15N values of sediments devolatilized during metamorphism. For sulfur, secular variations reflect incorporation of local sedimentary sulfur of ultimate seawater origin. No significant variation of temperature of vein formation is documented for orogenic gold deposits of different ages. Quartz-silicate, quartz-carbonate and sulfide-sulfide mineral pairs display consistent temperatures of 360 ± 76 °C (1σ; n = 332), in agreement with the more common greenschist facies hostrocks and fluid inclusion microthermometry. Fluid sources for orogenic gold deposits are complex but the isotopic systems (hydrogen, boron, carbon, nitrogen, oxygen, sulfur) are most consistent with contributions from metamorphic fluids released by devolatilization of igneous, volcano-sedimentary and/or sedimentary rocks. The contribution of magmatic water exsolved from magma during crystallization is not a necessary component, even if permissible in specific cases. Isotopic data arrays can be interpreted as the result of fluid mixing between a high T (~550 °C)—high δ18O (~10‰)—low δD (~−60‰) deep-seated (metamorphic) fluid reservoir and a low T (~200 °C)—low δ18O (~2‰)—high δD (~0‰) upper crustal fluid reservoir in a number of orogenic gold deposits. The origin of the upper crustal fluid is most likely sea- or meteoric water filling the host rock porosity, with a long history of water–rock isotope exchange. Mixing of deep-seated and upper crustal fluids also explains the large variation of tourmaline δ11B values from orogenic gold veins. Regional spatial variations of oxygen and hydrogen isotope compositions of deep-seated fluid reservoirs are documented between orogenic gold districts. This is the case for the Val-d’Or (Abitibi), Coolgardie and Kalgoorlie (Yilgarn) where the oxygen isotope composition of the deep-seated fluid end-member is 4‰ lower compared to that from the Timmins, Larder Lake, and Kirkland Lake districts (Abitibi). However, both mixing trends converge towards a common, low δ18O upper crustal fluid end-member. Such variations cannot be related to fluid buffering at the site of deposition and suggest provinciality of the fluid source. The contribution of meteoric water is mainly recorded by fluid inclusions from Mesozoic and Cenozoic age deposits, but micas are not systematically in isotopic equilibrium with fluid inclusions trapped in quartz from the same vein. This suggests late involvement of meteoric water unrelated to deposit formation. Yet, a number of deposits with low δD mica may record infiltration of meteoric water in orogenic gold deposits. Isotope exchange between mineralizing fluid and country rocks is documented for oxygen, carbon, sulfur and silicon isotopes. Large variations (> 10‰) of sulfide δ34S values at the deposit scale are likely related to evolving redox conditions of the mineralizing fluid during reaction with country rocks. Deposits hosted in sedimentary rocks show a shift to higher δ18O values as a result of fluid/rock oxygen exchange with the regional sedimentary country rocks.

This study evaluates the applicability of the clumped isotope thermometry to mesothermal hydrothermal systems (5-10 km depth; 250-450 degrees C). We measured Delta(47), delta O-18 and delta C-13 of calcite as well as delta O-18 of cogenetic minerals from typical quartz-calcite +/- tourmaline +/- chlorite orogenic veins from the Neoarchean Augmitto-Bouzan orogenic gold deposits (Abitibi, Canada). Our findings show that caution is required when utilizing the clumped isotope thermometry in the study of old mesothermal deposits. Temperatures calculated from Delta(47) values are systematically and significantly shifted to low temperature, i.e., similar to 150 degrees C rather than the similar to 350 +/- 50 degrees C expected for orogenic gold deposit formation and documented using oxygen isotope equilibrium between mineral pairs. We show that the low temperatures estimates resulted from solid-state reordering that occurred in calcite grains during the cooling history of the vein-hosting rocks. Because systems are geologically unrealistic, we suggest that refractory minerals (i.e., minerals with higher blocking temperature such as magnesite, dolomite, ankerite) should be investigated to apply clumped isotope thermometry in such context.

In orogenic gold systems, the source of the fluids and the processes leading to mobilization, transport, and deposition of gold remain debated. Most studies focus on endowed rather than on gold-poor orogenic systems to unravel the “key” parameters of gold mineralizing processes. Here, we present stable isotope (O, H) data from the Moly-Desgagné–Guercheville fault system (gold-free to low gold endowment) in the Chibougamau area, Abitibi greenstone belt, Canada. The gold-free Moly-Desgagné showing and nearby poorly endowed Hazeur showing and Monster Lake deposit share similar features typical of orogenic systems. The stable isotope compositions of tourmaline and quartz from the Moly-Desgagné–Guercheville fault system also display similar characteristics, such as (1) temperature of vein formation of 345 ± 86 °C (1σ); (2) fluid mixing between an upper crustal reservoir (low T – high δD – low δ18O) and a metamorphic water reservoir (high T – low δD – high δ18O); and (3) positive δDfluid values consistent with multiple boiling-condensation cycles related to fault-valve processes. These characteristics are similar to those from the gold-endowed Val-d’Or vein field. The difference in gold endowment between the Moly-Desgagné–Guercheville and Val-d’Or vein fields may be related to the nature of the fault system (i.e., terrane-bounding or “intragreenstone belt”) and the volume and (or) composition (i.e., gold, its ligands, CO2) of the fluid source rocks.

The gold-endowed Larder Lake Cadillac deformation zone (LLCDZ) in the Abitibi greenstone belt of the Archean Superior Province generally trends east but swings to the southeast along the Malartic segment in Quebec. Immediately north of the LLCDZ along this segment, deformation of the less than ca. 2687 Ma metasedimentary Cadillac Group began with the formation of isoclinal F1 folds, which are overprinted by post-2676 ± 2.0 Ma regional F2 folds with an axial planar S2 cleavage oriented parallel to the trend of the Malartic segment. Auriferous quartz veins strike east–west (085°) anticlockwise to bedding and S2. They are folded into sigmoidal S-shaped folds due to sinistral shear parallel to bedding. Later dextral shearing segmented the veins and folded the F2 folds into Z-shaped F3 folds. The veins are similar in structural chronology, fluid isotopic composition (calculated [Formula: see text] value between –9.5‰ and –3.4‰ and [Formula: see text] values of 12‰), and isotopic re-equilibration temperatures (469 and 498 °C, quartz–biotite oxygen thermometer) to the veins at the nearby Canadian Malartic deposit to the east. They possess comparable Au–As–Sb association and sericite-arsenopyrite alteration halo, as other Cadillac-Group-hosted veins at the Lapa mine to the west. Collectively, they constitute a vein field that extends across the entire length of the Malartic segment. Contrary to recent interpretations of the Malartic segment as an early accretionary structure that controlled the emplacement of gold deposits, its southeast trend is interpreted as the short limb of a broad Z-shaped flexure that formed during later F3 folding of the LLCDZ.

The Yaou deposit, located in French Guiana within the Guiana Shield, is one of the most promising gold deposits of the regional Paleoproterozoic greenstone belt. It displays numerous quartz monzodiorite bodies aligned along a sinistral shear zone where a five-deformation phases model is established at the camp scale. The ductile D1/2YA phase is responsible for the main penetrative foliation while the D3YA phase is related to shearing. An intrusive event is identified as being pre to syn-D3YA. The following phase D4YA represents a brittle quartz-carbonate veining set hosted preferentially within intrusive bodies and along the shear zone. A local D5YA brecciation event crosscuts the D4YA veins. Among this deformation history, two auriferous events (D3YA and D4YA) control the overall grade of the Yaou gold deposit. More specifically, most of the Au grade is associated with the main economic D4YA veining event, where the gold is visible and linked to Py4 within an ankerite/hematite rich alteration halo. At the microscopic scale, results of in situ analyses using LA-ICP-MS on pyrite show that metasediment-hosted Py0 is a primary source of submicroscopic gold having a low contribution to the total endowment. Py3 shows some gold content due to possible remobilization of AuD0YA. Gold in Py4 is found as submicroscopic gold, as micro-inclusions and as infilling fractures in association with elements such as Te, Ag and Bi. Most contribution to the Au grade is from micro-inclusions and, to a lesser extent, from free and submicroscopic gold. The ore shoot locations are lithologically controlled for AuD0YA (metasedimentary unit-hosted), structurally controlled (shear zone-hosted) for AuD3YA and rheologically controlled for the AuD4YA (intrusion-hosted). The deposit is clearly polyphase both at the macroscopic and the microscopic scales, invisible gold is associated with As whereas visible gold is observed as inclusions in pyrite with high contents of Ag, Te and Bi. We define an early low-grade enrichment of AuD0YA to AuD3YA followed by a later high-grade event, AuD4YA supporting polyphase mineralization processes. This study confirms that orogenic gold deposits can be formed by remobilization and/or new gold inputs during multiple deformation, veining and hydrothermal events.

The Lavrion area corresponds to the western part of the Attic-Cycladic metamorphic belt, in the back-arc region of the active Hellenic subduction zone. Between the Eocene and the Miocene, metamorphic rocks (mainly marbles and schists) underwent several stages of metamorphism and deformation due to collision and collapse of the Cycladic belt. Exhumation during the Miocene was accommodated by the movement of a large-scale detachment fault system, which also enhanced emplacement of magmatic rocks, leading to the formation of the famous Lavrion silver deposits. The area around the mines shows the stacking of nappes, with ore deposition mainly localized within the marbles, at marble-schist contacts, below, within, or above the detachment. The Lavrion deposit comprises five genetically-related but different styles of mineralization, a feature never observed in another ore deposit elsewhere, containing the highest number of different elements of any known mining district. The local geology, tectonic, and magmatic activity were fundamental factors in determining how and when the mineralization formed. Other key factors, such as the rise and the fall of sea level, which resulted from climate change over the last million years, were also of major importance for the subsequent surface oxidation at Lavrion that created an unmatched diversity of secondary minerals. As a result, the Lavrion deposit contains 638 minerals of which Lavrion is type-locality for 23 of them, which is nearly 12% of all known species. Apart from being famous for its silver exploitation, this mining district contains more minerals than any other district on Earth. The unique geological, mineralogical, and educational (mining, archaeological, and environmental) features suggest that it is highly suitable to be developed as a future UNESCO Global Geopark.

The Regional Isotopic Survey Systematics (RISS) is part of a Metal Earth thematic project, which focuses on the characterization through time and space of the auriferous fluid-flow system(s) as ‘sourceto-sink’ systems. The objective of the RISS is to characterize the spatial variation of auriferous fluid flows and their isotopic composition (O, C, H, S) along the main deformation zones where the orogenic gold deposits are localized. Indeed, the general orogenic gold model of fluid circulation consists in the circulation of auriferous fluid along a major lithospheric-scale shear zone and in the connected anastomosed network of lower-order shear zones, in which orogenic gold deposits occur (Robert et al., 1995, 2005). This spatial distribution of gold deposits could suggest that spatial variation of fluid-flow and related variation of fluid–rock interaction are important parameters in their formation.

The Trikorfo area (Thassos Island, Rhodope massif, Northern Greece) represents a unique mineralogical locality with Mn-rich minerals including kyanite, andalusite, garnet and epidote. Their vivid colors and large crystal size make them good indicators of gem-quality materials, although crystals found up to now are too fractured to be considered as marketable gems. The dominant lithology is represented by a garnet–kyanite–biotite–hematite–plagioclase ± staurolite ± sillimanite paragneiss. Thermodynamic Perple_X modeling indicates conditions of ca. 630–710 °C and 7.8–10.4 kbars. Post-metamorphic metasomatic silicate and calc-silicate (Mn-rich)-minerals are found within (i) green-red horizons with a mineralogical zonation from diopside, hornblende, epidote and grossular, (ii) mica schists containing spessartine, kyanite, andalusite and piemontite, and (iii) weakly deformed quartz-feldspar coarse-grained veins with kyanite at the interface with the metamorphic gneiss. The transition towards brittle conditions is shown by Alpine-type tension gashes, including spessartine–epidote–clinochlore–hornblende-quartz veins, cross-cutting the metamorphic foliation. Kyanite is of particular interest because it is present in the metamorphic paragenesis and locally in metasomatic assemblages with a large variety of colors (zoned blue to green/yellow-transparent and orange). Element analyses and UV-near infrared spectroscopy analyses indicate that the variation in color is due to a combination of Ti4+–Fe2+, Fe3+ and Mn3+ substitutions with Al3+. Structural and mineralogical observations point to a two-stage evolution of the Trikorfo area, where post-metamorphic hydrothermal fluid circulation lead locally to metasomatic reactions from ductile to brittle conditions during Miocene exhumation of the high-grade host-rocks. The large variety of mineral compositions and assemblages points to a local control of the mineralogy and fO2 conditions during metasomatic reactions and interactions between hydrothermal active fluids and surrounding rocks.

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 talc-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 Stypsi Cu-Mo-Au-Re prospect, Lesvos island, a shallow porphyry-epithermal system hosted within a middle Miocene microgranite porphyry, was emplaced along NNE-, NWand NE-trending structures, within trachyandesites to trachydacites and felsic pyroclastics of the Stypsi caldera. The mineralization comprises three stages: Stage I is characterized by magnetite-actinolite±quartz in transitional and banded quartz veins mostly developed within the microgranite and the surrounding lavas related to calcic-potassic and propylitic alteration of the host rocks. In the banded veins, quartz is botryoidal, suggesting crystallization from a gel. Abundant vapor-rich inclusions in the bands produce a dark grey to black color. Within the veins, magnetite, chalcopyrite, bornite and native gold were followed in time by pyrite, hematite, sphalerite and galena. Stage I mineralization was synchronous and also postdates quartz formation in the veins, since it crosscuts and/or fills vugs in the center of the veins. Sulfides are associated with various combinations of K-feldspar, actinolite, epidote, chlorite, and calcite gangue minerals. Pyrite-molybdenite-chalcopyrite (Stage II) and late intermediate sulfidation epithermal veins (Stage III) overprint earlier mineralization and alteration, and are associated with sericite-calcite and sericite-kaolinite alteration of the porphyry system and

The Stypsi Cu-Mo-Au-Re prospect, Lesvos island, is a shallow porphyry-epithermal system hosted within a middle Miocene microgranite porphyry, which was emplaced along NNE-, NW- and NE-trending structures, within trachyandesites to trachydacites and felsic pyroclastics of the Stypsi caldera. The mineralization comprises three stages: Stage I is characterized by magnetite-actinolite +/- quartz in transitional and banded quartz veins mostly developed within the microgranite and the surrounding lavas related to calcic-potassic and propylitic alteration of the host rocks. In the banded veins, quartz is botryoidal, suggesting crystallization from a gel. Abundant vapor-rich inclusions in the bands produce a dark grey to black color. Within the veins, magnetite, chalcopyrite, bornite and native gold were followed in time by pyrite, hematite, sphalerite and galena. Stage I mineralization was synchronous and also postdates quartz formation in the veins, since it crosscuts and/or fills vugs in the center of the veins. Sulfides are associated with various combinations of K-feldspar, actinolite, epidote, chlorite, and calcite gangue minerals. Pyrite-molybdenite-chalcopyrite (Stage II) and late intermediate sulfidation epithermal veins (Stage III) overprint earlier mineralization and alteration, and are associated with sericite-calcite and sericite-kaolinite alteration of the porphyry system and spatially associated lavas, respectively. Molybdenite is widespread in the first two mineralization stages, with Re content ranging from about 0.3 wt% in Stage I to 1.96 wt% in Stage H. A barren silicic and advanced argillic (alunite-kaolinite) lithocap, is exposed on top of the porphyry-style mineralization and is crosscut by non-mineralized high-sulfidation epithermal chalcedony-barite veins. Bulk ore analyses of surface samples from the Stypsi prospect yielded values of up to 276 ppm Mo, 978 ppm Cu, up to 0.5 g/t Au, up to 3 g/t Ag, and up to 70 ppb Pd and Re. Fluid inclusion data indicate that the Stage I transitional and banded quartz veins were deposited at 420 degrees C-530 degrees C and at pressures up to 450 bars, from boiling hydrothermal fluids. The fluid in the veins consists of a brine (40-61 wt% NaCl equiv) that coexists with a lower salinity (6-14 wt% NaCl equiv) liquid phase and a low-density vapor-rich fluid. Fluid inclusions in quartz of the Stage III intermediate-sulfidation epithermal veins are characterized by relatively low homogenization temperatures (231 degrees C-288 degrees C) and salinities (up to 1.9 wt% NaCI equiv), which was the result of subsequent dilution of the moderately saline fluids by circulating meteoric water. This study verifies earlier works suggesting that Au-enriched felsic magmas are able to crystallize Re-rich molybdenite, and that Re may also be redistributed and enriched in later stages during the deposition of porphyry-style mineralization. The Stypsi prospect ressembles in many respects (e.g., Au grades, Cu/Mo ratios, the Re content of molybdenite and the presence of ore-grade calcic-potassic alteration), other porphyry Cu-MoRe-Au systems hosted in calc-alkaline rocks in northeastern Aegean, Greece.

The formation of ore deposits in the Lavrion Pb-Zn-Ag district was associated with Miocene detachment that accommodated orogenic collapse and exhumation of high-grade nappes across the ductile-brittle transition. This district consists of (1) low-grade porphyry Mo style, (2) Cu-Fe skarn, (3) high-temperature carbonate replacement Pb-Zn-Ag, and (4) vein and breccia Pb-Zn-Ag mineralization. The vein and breccia mineralization locally contains high-grade silver in base metal sulfides that are cemented by fluorite and carbonate gangue. The rare earth element contents of these gangue minerals, chondrite-normalized patterns, and fluid inclusion studies suggest that they precipitated from a low-temperature hydrothermal fluid. Primary and pseudosecondary fluid inclusions in fluorite and calcite are characterized by a wide range of homogenization temperatures (92°–207°C) and salinities of up to 17.1 wt % NaCl equiv. Secondary fluid inclusions only represent <5 vol % of the total fluid trapped. Fluids extracted from inclusions in fluorite have values of δD = –82.1 to –47.7‰ (Vienna-standard mean ocean water [V-SMOW]) and δ18O = –10.4 to –5.1‰ (V-SMOW). These data and low ratios of Cl/Br measured by crush-leach analyses for fluids in fluorite (102–315) and calcite (162–188) are compatible with the ore fluid being the result of mixing of meteoric water with evaporated seawater. These data suggest that fluids leading to the deposition of late Pb-Zn-Ag–rich vein- and breccia-style mineralization in Lavrion were related to circulation of mixed evaporated seawater and meteoric fluids that was enhanced by brittle deformation. This contrasts with the fluids of magmatic origin related to the formation of low-grade porphyry Mo, Cu-Fe skarn, and high-temperature carbonate replacement deposits spatially related to the Plaka granodiorite.

Vein-type Pb-Ni-Bi-Au-Ag mineralization at the Clemence deposit in the Kamariza and “km3” in the Lavrion area, was synchronous with the intrusion of a Miocene granodiorite body and related felsic and mafic dikes and sills within marbles and schists in the footwall of (and within) the Western Cycladic detachment system. In the Serpieri deposit (Kamariza area), a porphyry-style pyrrhotite-arsenopyrite mineralized microgranitic dike is genetically related to a garnet-wollastonite bearing skarn characterized by a similar base metal and Ni (up to 219 ppm) enrichment. The Ni–Bi–Au association in the Clemence deposit consists of initial deposition of pyrite and arsenopyrite followed by an intergrowth of native gold-bismuthinite and oscillatory zoned gersdorffite. The zoning is related to variable As, Ni, and Fe contents, indicating fluctuations of arsenic and sulfur fugacity in the hydrothermal fluid. A late evolution towards higher sulfur fugacity in the mineralization is evident by the deposition of chalcopyrite, tennantite, enargite, and galena rimming gersdorffite. At the “km3” locality, Ni sulfides and sulfarsenides, vaesite, millerite, ullmannite, and polydymite, are enclosed in gersdorffite and/or galena. The gersdorffite is homogenous and contains less Fe (up to 2 wt.%) than that from the Clemence deposit (up to 9 wt.%). Bulk ore analyses of the Clemence ore reveal Au and Ag grades both exceeding 100 g/t, Pb and Zn > 1 wt.%, Ni up to 9700 ppm, Co up to 118 ppm, Sn > 100 ppm, and Bi > 2000 ppm. The “km3” mineralization is enriched in Mo (up to 36 ppm), Ni (>1 wt.%), and Co (up to 1290 ppm). Our data further support a magmatic contribution to the ore-forming fluids, although remobilization and leaching of metals from previous mineralization and/or host rocks, through the late involvement of non-magmatic fluid in the ore system, cannot be excluded.