Description: The Pagoni Rachi/Kirki Cu-Mo ± Re ± Au deposit is a telescoped porphyry-epithermal system that contains molybdenite with up to 4.7 wt.% Re and the rare mineral rheniite (ReS 2 ). The deposit is spatially related to an Oligocene, calc-alkaline hornblende-biotite- bearing granodiorite-tonalite porphyry stock; however, a genetic link to a buried stock of quartz-feldspar porphyry magma beneath Pagoni Rachi cannot be excluded. Alteration types and vein relationships suggest that mineralization can be divided into four paragenetic stages, which are, from early to late: (1) sodic/potassic-calcic alteration with quartz- and magnetite-bearing veins (A- and M-type) and distal propylitic alteration, (2) sodic/potassic alteration with quartz-pyrite-chalcopyrite-molybdenite veins (B-type), (3) sericitic alteration with "transitional" porphyry to epithermal pyrite-chalcopyrite-molybdenite veins (D-type), and (4) argillic alteration with quartz-calcite base metal and precious metal rich veins (E-type) with epithermal affinity. Bulk ore analyses and mineralogical data are consistent with deposition of precious metals in all mineralization stages: electrum in A- and M-type veins is spatially associated with bornite and chalcopyrite, whereas tellurides (cuprian hessite, stützite, petzite) and Ag-Au alloy occur in the epithermal veins. The D-type veins contain the highest gold grades (up to 5 g/t) and include Ag-, Bi-, Te-, and Se-bearing minerals indicating a possible genetic relationship with E-type epithermal veins. Fluid inclusion data indicate that A- and B-type veins (porphyry style mineralization) were deposited at 360–510 °C and at pressures up to 690 bars (〈2 km depth) in A-veins and up to 360 bars (〈1.5km depth) in B-veins, from boiling hydrothermal fluids. This process produced coexisting low to moderately saline (1.7–10.7 wt.% NaCl equiv.) and highly saline (36–〉74 wt.% NaCl equiv.) fluids. Subsequent dilution of the moderately saline fluid formed a lower temperature (210–340 °C), less saline (1.4–2.9 wt.% NaCl equiv.) fluid in late epithermal E-veins. Based on the Au and Re grades, Cu/Mo ratios, presence of rheniite and the extremely high Re content of molybdenite, Pagoni Rachi may be considered as a distinct class of porphyry deposits, a Cu-Mo±Re±Au system that is derived from rocks transitional between calc-alkalic and alkalic porphyries. Its similarity with other Re-Au enriched porphyry-style deposits in northeastern Greece indicates that this area may represent a new Au-Re-Te metallogenetic province.

Description: Arsenic-copper-gold-bismuth mineralization in the Stanos area is hosted by a km-long, NW-SE trending ductile to brittle shear zone within Silurian orthogneisses of the Vertiskos terrane of the Servomacedonian Massif, Chalkidiki Peninsula, northern Greece. Shearing was accompanied by iron-potassic alteration of the gneisses including biotite, muscovite, chlorite, apatite, zircon, quartz, and minor rare-earth element phosphates. Metallic minerals form disseminated to massive aggregates along foliation planes, asymmetric crenulation cleavages, and S-C' fabrics. Detailed textural investigation of the ore assemblages revealed two stages of hydrothermal mineralization during shearing. An initial introduction of iron sulfdes (pyrite, arsenopyrite, and pyrrhotite) was followed by a copper-bearing stage that is associated with the formation of chalcopyrite, minor sulfdes (galena, sphalerite, and molybdenite), and Bi-Cu-Pb-Au-Ag-Te minerals. The stage II metallic mineral association consists mainly of Bi sulfosalts (bismuthinite derivatives, lillianite homologues, matildite), native elements (bismuth, electrum), and bismuth chalcogenides (joséite-A, joséite-B, ikunolite, and unnamed Bi-Pb-bearing sulfotellurides). The bismuthinite derivatives are mainly bismuthinite (including cuprian varieties), gladite-krupkaite, paarite, salzburgite, and an unnamed CuPbBi 7 S 12 phase. The ikunolite is Se-free, corresponding to the formula Bi 4 S 3 , and is the first known occurrence in Greece. Most stage II minerals exist in two-, three-, and, more rarely, four-component blebs or patches generally with curvilinear boundaries, suggesting the possibility that they were precipitated in a molten form. Phase relationships among minerals in the system Au-Bi-Te-Pb-Ag-Cu indicate that they formed by successive hydrothermal pulses from fluids that penetrated the shear zone at different times contemporaneous with ductile deformation. These pulses deposited the following assemblages in paragenetic order: molybdenite + cosalite + native bismuth + galenobismutite -〉 gustavite/lillianite + native gold + native bismuth + bismuth sulfotellurides -〉 bismuthinite-aikinite solid solution series-〉 matildite + native bismuth + galena -〉 chalcopyrite + bornite. The observed association suggests that the system evolved under fluctuating f (S 2 ) and f (O 2 ) conditions and precious metals may have been scavenged by composite Bi-Te-Pb-S melts at temperatures well above 350 ºC. The enrichment of Bi, Mo, Pb likely indicates a magmatic contribution to the ore-forming fluid.

Description: A bstract Molybdenite from the Voznesensk porphyry Cu ± (Mo,Au) deposit, southern Urals, Russia, displays high Re content and a well-documented oscillatory zoning for this mineral. The molybdenite forms part of a quartz-molybdenite-pyrite-chalcopyrite assemblage cemented at low-temperatures by pumpellyite and tobermorite. Oscillatory zoning occurs as micro-bands up to 200 μm wide and 200–600 μm long oriented parallel to the basal cleavage, as well as within basal planes of molybdenite sheets. The micro-bands are Re-enriched to different degrees (0.3–1.0 wt.%, typically they contain 0.6–0.8 wt.% Re). Outside these structures the Re content in molybdenite is up to 0.25 wt.%, usually 〈0.10–0.15 wt.%. It is suggested that the Re in the Voznesensk molybdenite retains its original growth pattern, marked by sharp concentration variations, and is not the result of leaching through post-crystallization diffusion. Variations in the number, width, and Re-content in individual micro-zones observed within the oscillatory zones may suggest involvement of extrinsic mechanisms of micro-zone formation. However, the Re content of the Voznesensk molybdenite (ICP-MS and EPMA data) is almost uniform along the studied vertical and lateral interval of the mineralization, suggesting no major variation in Re concentration in the fluid and favoring uniform, self-organization processes causing Re enrichment and oscillatory zoning in molybdenite. Despite the strong degree of epigenetic post-crystallization deformation of the molybdenite flakes and their cementation by low-temperature tobermorite, there is no essential change of the primary micro-zoning in the distribution of Re and any evidence of its epigenetic migration.

Description: Gem-quality (cabochon) ruby-bearing occurrences (here termed PAR-1 and PAR-5) located near Paranesti, north eastern Greece have been systematically studied for the first time in this paper. Tectonically, the occurrences are located within the Nestos Shear Zone (NSZ). The NSZ separates two distinct geological units. The Rhodope Terrane is a heterogeneous unit of gneisses, mafic, ultramafic, and meta-sedimentary rocks in the hanging wall. The footwall Pangaion-Pirin Complex consists of marbles and acid gneisses of a Mesozoic carbonate platform on pre-Mesozoic continental basement. In this paper, a range of petrographic and geochemical techniques were used to determine (1) any similarities and differences to other mafic-ultramafic hosted ruby deposits worldwide; (2) distinctive geochemical fingerprints for Paranesti; and (3) the likely P - T conditions of formation. Detailed petrographic and whole-rock analyses utilizing ICP-MS, XRF, and XRD have found the Paranesti corundum to be of a mafic/ultramafic protolith with approximately 40 wt.% SiO 2 , 16 wt.% Mg, 11000 ppm Cr, and 440 ppm Ni. EMPA major element analysis determined the mineral inclusions within the corundum grains to be picotite and hercynite spinels. Pargasite is the dominant amphibole within the corundum-bearing amphibole schist host. The surrounding non-corundum bearing chlorite schist mainly comprises clinochlore. Petrographic examination of the mineral assemblages within the corundum-bearing schists revealed strong fracturing and alignment (parallel to the main regional foliation) of the corundum grains and margarite reaction rims around the corundum. The surrounding non-corundum amphibolites also contain anorthite, along with relict sillimanite, kyanite, and chlorite/muscovite/epidote overprinting. Detailed LA-ICP-MS trace element analysis of the color range of corundum from the two occurrences showed the corundum to be mainly of metamorphic origin, though pale rubies from PAR-5 suggest some metasomatic influence. The corundum displays distinctive geochemical locality signatures, with a combination of high Cr (average 2300 ppm with 15% sample points on core positions 〉5000 ppm and maximum 8600 ppm); high Si (average 1400 ppm with 40% over 1500 ppm and maximum 2500 ppm), low Mg (average 30 ppm), and very low V, Ti, and Ga. Based on the literature for similar occurrences, and the mineral assemblages observed at Paranesti, the estimated P - T conditions of corundum formation are 〈7 kbar and 〈750 °C, similar to the mafic African amphibolite-hosted rubies. This study has found the Paranesti occurrences to be most similar to the Winza, Tanzania ruby deposit, whilst there are some similarities to other high-Cr ruby deposits, primarily the Fiskenæsset, Greenland and metamorphic amphibolitic schist hosted African deposits. The Paranesti corundum most likely formed during regional amphibolite facies metamorphism which created the Nestos Shear Zone, along with a lesser influence (primarily observed in the PAR-5 occurrence) of more localized metasomatism. Subsequent multiple greenschist facies retrogression of the occurrences resulted in the current-day host amphibole-chlorite schist assemblages.

Description: Boiling is a crucial process triggering ore formation in magmatic-hydrothermal systems and controlling the enrichment of precious and rare metal(loid)s in epithermal-porphyry mineralizations. Steep physicochemical gradients during boiling of hydrothermal fluids at shallow water depths caused metal(loid) precipitation along a 3 km long Pb-Zn-Ag vein system on Milos Island in the South Aegean Volcanic Arc. We present new trace element and Pb, Sr, and S isotope data from sulfides providing insights into the diversity of mineralization processes in shallow-marine hydrothermal systems. Lead and Sr isotope compositions of sulfides and sulfates reflect the mixing of fluids that reacted with metamorphic basement and the volcanic host rocks, whereas some of the S were derived from seawater. Investigation of mineralized samples along the Kondaros-Vani fault zone revealed distinct chemical variations that represent a vertical profile through the boiling zone of a hydrothermal system. Boiling during fluid ascent at decreasing temperatures (230–150 ◦C) and sulfur fugacities triggered the precipitation of sulfides rich in Zn, Pb, Fe, Cu, Ag, Sb, and As, resulting in increasing Pb, Ag, and Sb contents with decreasing depth. A pyrite group with high Tl/Cu and low As/Sb ratios, as well as δ34SVCDT values reaching as low as -6‰, is interpreted as precipitating from high-Cl liquids that underwent vigorous boiling at deeper crustal levels subsequent to tectonic faulting. Condensation of vapor (high Hg, Bi, and As contents) and mixing with seawater (high Mo contents) in the shallow-marine subseafloor sequences at Vani caused Hg-Bi-Mo-As-rich mineralization similar to the active hydrothermal system at Milos.

Description: Drill core samples from the Profitis Ilias Pb-Zn-Cu-Ag-Au vein mineralization on Milos Island, Greece provide new insights into (i) the metal sources, (ii) the primary vertical metal(loid) distribution, and (iii) the supergene enrichment processes in a transitional shallow-marine to subaerial hydrothermal environment. Metal contents of unaltered and altered host rocks combined with Pb isotope analyses of hydrothermal sulfides suggest that most metal(loid)s were derived by leaching of basement rocks, whereas the distinct enrichment of Te is related to the addition of Te by a magmatic fluid. The trace element contents of base metal sulfides record decreasing Au, Te, Se, and Co, but increasing Ag, Sb, and Tl concentrations with increasing elevation that can be related to progressive cooling and fluid boiling during the hypogene stage. The formation of base metal veins with porous pyrite hosting hessite inclusions at ~ 400 m below the surface was triggered by vigorous fluid boiling. By contrast, the enrichment of native Au associated with oxidized Fe and Cu phases in the shallower part of the hydrothermal system resulted from supergene remobilization of trace Au by oxidizing meteoric water after tectonic exhumation to subaerial levels. Disseminated pyrite with higher Tl/Pb ratios and locally elevated Hg concentrations relative to vein pyrite reflects infiltration of the host rocks by boiled liquids and condensed vapor fluids. The vertical and temporal evolution of the Profitis Ilias mineralization, therefore, provides unique insights into the transport and precipitation of Au, Ag, Te, and related metal(loid)s by multiple fluid processes.