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Tennantite-(Cu), Cu12As4S13, was approved as a new mineral species from the Layo epithermal deposit, Castilla Province, Arequipa Department, Peru, where it occurs as black metallic anhedral grains, up to 0.1 mm across, replacing enargite and associated with chalcopyrite and vinciennite. In reflected light, tennantite-(Cu) is isotropic, grey with a bluish shade. Reflectance data for the four COM wavelengths in air are [λ (nm): R (%)]: 470: 29.1; 546: 28.4; 589: 27.4; and 650: 25.0. Electron microprobe analysis for holotype material gave (in wt.% – average of 10 spot analyses): Cu 49.32(27), Fe 2.20(12), Zn 0.09(2), Sn 0.03(5), As 19.45(43), Sb 1.94(10), Te 0.02(5), S 27.75(43), total 100.80(20). On the basis of (As + Sb + Te) = 4 atoms per formula unit (apfu), the empirical formula of tennantite-(Cu) is (Cu11.27Fe0.57Zn0.02)Σ11.86(As3.77Sb0.23)Σ4.00S12.57. Tennantite-(Cu) is cubic, I$\overline 4$3m, with unit-cell parameters a = 10.1710(10) Å, V = 1052.2(2) Å3 and Z = 2. Its crystal structure was refined by single-crystal X-ray diffraction data to a final R1 = 0.0178 on the basis of 263 unique reflections with Fo > 4σ(Fo) and 24 refined parameters. Tennantite-(Cu) is isotypic with other tetrahedrite-group minerals. Previous findings of tennantite-(Cu) are reported and some nomenclature issues, related to the Fe and Cu oxidation states, are discussed. At the Layo epithermal deposit, tennantite-(Cu) is the result of the replacement of enargite under decreasing $f_{{\rm S}_ 2}$ conditions.

International audience; The Salau deposit, located in the Axial Zone of the French Pyrenees, is the most important tungsten deposit ever mined in France.Two types of mineralization, both closely associated with a granodiorite intrusion, are distinguished. The first is a fine-grainedscheelite skarn related to contact metamorphic and metasomatism between the intrusion and the adjacent carbonate rocks. Thesecond type is represented by massive sulfides accompanied by coarse-grained scheelite, apatite, and electrum. This synkinematicmineralization is found enclosed within the skarn ore but occurs also within the granodiorite stock along majorductile–brittle shear zones. REE contents of scheelite and apatite from the two types of mineralization show differences suggestingthat the two types derived from two different fluids. U/Pb dating on zircon, apatite and scheelite illustrates that magmaticzircon and apatite formed at 295 ± 2 Ma during emplacement and cooling of the granodiorite intrusion. These are cogenetic to thefine-grained scheelite skarn. Hydrothermal apatite frommassive sulfide ores yields a younger age of 289 ± 2 Ma, whereas closelyassociated coarse-grained scheelite yields a consistent although less precise age of 284 ± 11 Ma. These results suggest that the latemassive sulfide ore with abundant coarse-grained scheelite and electrum is related to the emplacement of an underlying, moreevolved intrusion, accompanied during its ascent by the development of steeply dipping reverse-dextral shear zones

International audience; The Mo-Cu-W Azegour skarn, located in the High-Atlas in Morocco, is associated with a Late Hercynian alkaline granitic intrusion. Here the origin of the mineralisation via Re-Os geochronology and using Mo, S and Pb isotopes is discussed. The age of mineralisation defined by Re-Os molybdenite geochronology is 276 ± 1.2 Ma for the Azegour mine, and 267 ± 1.2 for the Tizgui deposit suggesting for multiple mineralisation events associated with the Hercynian alkaline granitic intrusion. The δ98MoNIST of molybdenite range from −0.60‰ to 0.42‰ (n = 26) for the Azegour mine and from 0.08‰ to 0.40‰ (n = 2) for the Tizgui mine. Variations of the δ98MoNIST occur either at the deposit scale with a difference of about 0.72‰, and at the sample scale (few cm), which exhibits a difference of up to 0.40‰. A multi-phased mineralisation is proposed as the main processes explaining the variation in the δ98MoNIST values although the influence of a Rayleigh fractionation process cannot be precluded. The high δ34S values determined from molybdenite, pyrrhotite, and chalcopyrite (8–14.7‰) suggest a sedimentary origin for sulphur from the Cambrian sedimentary country rocks. Whereas, the initial 206Pb/204Pb compositions of common lead (18.08–18.30) for chalcopyrite and pyrrhotite imply a strong contribution of lead from the host volcano-sedimentary units.

Shear zones hosted antimony (Sb) quartz vein-type deposits are the most important sources of Sb worldwide. They have been recognized and mined since the Antiquity in the European Variscan belt, and particularly in the French Variscan Massifs, as the Armorican Massif. Among this type of deposit two subtypes are identified, i) the Sb and gold (Au) quartz vein-type (Sb-Au) as the La Lucette deposit located in the North Armorican Domain, and ii) the Sb-As quartz vein-type as those from the la Bellière district in the Ligerian domain.The recent advances in the understanding of the Sb mineralizations in the European Variscan Belt are typically focused on the Sb ore-genesis and its regional implications, ignoring its potential valuable co-products as gold. In this study, detailed textural-mineralogical investigations coupled with geochemical analyses in rock-samples with in-situ EPMA and LA-ICPMS ore-minerals trace element analyses, were carried out for the first time in the Late-Variscan mineralizations from the La Bellière Sb-As occurrences, and the La Lucette Sb-Au deposit, to ascertain the distribution and amount of Au in the ore-minerals and provide new data on ore deposition conditions.In the La Bellière Sb-As occurrences, no visible gold has been observed, but low-grade gold, ranging between 0.2 to 1 g/t Au, are correlated with high-grade As in rock sample. In the La Lucette Sb-Au deposit, historical assays have shown high-grade gold with an average at 40 g/t Au. EPMA and LA-ICP-MS analyses have demonstrated that gold is already present during the early time of the mineralization as invisible gold, trapped in the lattice of the Sb-rich arsenopyrites, with an average grade of 70 ppm Au in La Bellière, and at higher average grade of 223 ppm Au for La Lucette. For both type of mineralization, the early invisible gold is concentrated preferentially in the borders of the arsenopyrite crystals, and is correlated with an increase of the As content, and a decrease of the Sb and Fe. We argue that gold could be added in the arsenopyrite by substitution with the Fe and Sb at high temperature > 300 °C.Visible gold corresponds to the economic gold ore of the Sb-Au mineralizations. In the La Lucette ore, it is emplaced in the late stages, as discrete electrum grains spatially associated with the arsenopyrites, as native gold inclusions within the stibnite, and associated with rare aurostibite. Remobilization processes of the gold-bearing arsenopyrite at lower temperature, coupled with a minor initial enrichment of the Sb-bearing ore-fluid might be responsible of the late high-grade gold ore, and the visible expression of this element. In the absence of such remobilization process with late ore-fluid-enrichment, only low-grade gold is present, under the form of invisible gold in auriferous-arsenopyrites.The presence of a valuable gold co-product, also present in the Sb-As mineralizations, unknown until now in the French Variscan Massifs, will improve its economic attractivity. Gold potential in the huge French Sb-districts as the Vendée or the Brioude-Massiac districts must be reassessed.

International audience; The Montebras cupola is a small massif of granite with rare metals (Sn,W, Li, Nb-Ta) located north of the French Massif Central which emplaced during the upper Carboniferous in an olderhost rock, the Chanon granite (357.2 ± 2.1 Ma). Two magmatic episodes, a microgranite (316.1 ± 4.3 Ma),and an albitic leucogranite (309.8 ± 3.9 Ma) are distinguished. The second develops contact formations at itsroof, in particular a thick stockscheider pegmatite (309.7 ± 4.5 Ma), passing east to lithium greisens and tinbearingflat quartz veins, previously exploited (303.8 ± 4.8 Ma). The cassiterite deposition (associated withmanganocolumbite) spreads from the magmatic phase with crystals disseminated in leucogranite, until theend of the pneumatolytic phase marked by cassiterite-bearing quartz veins. This spreading is marked by aprogressive drop in the concentrations of trace elements (Nb, Ta, Fe, Mn, Mg, Ti) in cassiterite but withoutreaching the domain of typically hydrothermal compositions. During the pneumatolytic phase, cassiterite isaccompanied by rare scheelite, the rare qitianlingite and a frequent wolframite, the composition of which(hubnerite) indicates a magmatic origin for the metal and the fluids involved during the deposition oftungsten. The deposition of sulfides rich in Cu, As and Sn (löllingite, chalcopyrite, tennantite, stannoidite,mawsonite...) marks the transition to the hydrothermal stage and suggests an origin in host rocks for copperand arsenic. The liasic fluorite-baryte event is manifested by the local appearance of veinlets with violetfluorite, baryte and manganapatite. The Montebras dome provides a representative example of the rare metalgranites of the Variscan orogen. It is contemporary with the other rare elements granitic magmas of thenorthern French Massif Central with which it presents similarities but also differences. Its emplacementcould result from a mechanism of the cauldron subsidence type.; -La coupole de Montebras est un petit massif de granite à métaux rares (Sn, W, Li, Nb-Ta) situé au nord du Massif Central Français qui se met en place au Carbonifère supérieur dans un encaissant plus ancien, le granite de Chanon (357,2 ± 2,1 Ma). Deux épisodes magmatiques, un microgranite (316,1 ± 4,3 Ma) et un leucogranite albitique (309,8 ± 3,9 Ma), sont distingués. Le second développe à son toit des formations de contact, notamment une puissante pegmatite stockscheider (309,7 ± 4,5 Ma), passant vers l'est à des greisens à lithium et des filons plats de quartz stannifères anciennement exploités (303,8 ± 4,8 Ma). Le dépôt de cassitérite (associée à la manganocolumbite) s'étale depuis la phase magmatique avec des cristaux disséminés dans le leucogranite, jusqu'à la fin de la phase pneumatolytique marquée par des filons de quartz stannifères. Cet étalement se traduit par une baisse progressive des concentrations en éléments-traces (Nb, Ta, Fe, Mn, Mg, Ti) dans la cassitérite mais sans que soit atteint le domaine des compositions typiquement hydrothermales. Lors de la phase pneumatolytique, la cassitérite est accompagnée de rare scheelite, de la rarissime qitianlingite et d'une wolframite fréquente dont la composition (hübnérite) indique une origine magmatique pour le métal et les fluides impliqués dans le dépôt du tungstène. La paragenèse à sulfures riches en Cu, As et Sn (löllingite, chalcopyrite, tennantite, stannoïdite, mawsonite...) marque le passage à la phase hydrothermale et suggère une origine dans les roches encaissantes pour le cuivre et l'arsenic. L'événement fluo-barytique liasique se manifeste par l'apparition locale de fissures à fluorine violette, barytine et manganapatite. La coupole de Montebras fournit un exemple représentatif des granites à métaux rares de la chaîne varisque. Elle est contemporaine des autres magmas granitiques à éléments rares du nord Massif central avec lesquels elle présente des points de similitude mais aussi des différences. Sa mise en place pourrait relever d'un mécanisme de type cauldron subsidence.

International audience; The synthesis of 240 lead isotopes analyses, measured on Moroccan ore deposits of Ediacarian to Neogene ages located in all geotectonic domains of Morocco allows a global reflection on the metallogeny of Morocco. The isotopic compositions vary widely, from 17.738 (Bou Skour) to 18.905 (Draa Sfar) for the 206 Pb/ 204 Pb ratio, and from 15.521 to 15.706 for the 207 Pb/ 204 Pb ratio. The source of lead in the studied deposits is located in the upper continental crust, except for those in the Anti-Atlas (Bou Skour, Imiter, etc.) and some in the High Atlas (Azegour) with a clear mantellic contribution. Isotopic variations noted at the scale of a district result either from the presence of several superimposed hydrothermal events calling upon different local sources as at Tighza, or from a single event disturbed by the segmentation of a volcanosedimentary basin, as for the Jebilet and Guemassa ore deposits. At the scale of the deposit (Draa Sfar, Bou Skour), isotopic variations result from the superposition of several hydrothermal events each with their own lead and associated metals. Overall, we can distinguish three generations of lead incorporated successively into the Moroccan geological basement by magmatism and/or hydrothermalism, characterized by their 206 Pb/ 204 Pb ratios: 17.74–17.90 (Panafrican), 18.10–18.40 (Hercynian) and 18.75–18.90 (Alpine). Panafrican lead is present in the Anti-Atlas, and very locally in the Meseta (Bouznika), and feeds in part on the mafic magmatism of Gondwana. Hercynian lead is the most represented and displays a definitive rupture in the source of metals, which is now exclusively crustal. It invades all Moroccan areas, including the Anti-Atlas, where it re-mobilizes and mixes with the panafrican lead. Alpine lead, more discreet, marks out the large scarf going from Agadir to Nador which traces on the surface the mantle plume of the Canaries and accompanies a Neogene magmatism which may also have acted as a simple engine remobilizing Hercynian lead, in particular to form MVT deposits from Touissit. The Hercynian and Alpine lead influxes are partly responsible for resetting the Neoproterozoic mineralization, as at Bou Azzer or Imiter. In the Sawkins’s model, lead isotopic results support successive remobilisations of lead stored in primary and secondary tanks, as well as inheritance phenomena. Finally, the good transfer of the isotopic signature of lead from ore deposits to surface gossans shows that the isotopic geochemistry of lead is a useful tool for mineral exploration in Morocco, moreover for stratiform polymetallic sulphides ore deposits of Hajar type.; La synthèse de 240 analyses isotopiques du plomb, mesurées sur les gisements miniers marocains d’âges édiacarien à néogène appartenant à tous les domaines géotectoniques du Maroc autorise une réflexion globale sur la métallogénie du Maroc. Les compositions isotopiques varient grandement, de 17,738 (Bou Skour) à 18,905 (Draa Sfar) pour le rapport 206 Pb/ 204 Pb, et de 15,521 à 15,706 pour le rapport 207 Pb/ 204 Pb. La source du plomb des gisements étudiés se situe dans la croûte continentale supérieure, excepté pour ceux de l’Anti-Atlas (Bou Skour, Imiter…) et certains du Haut-Atlas (Azegour) à nette contribution du manteau. Les variations isotopiques relevées à l’échelle d’un district résultent soit de la présence de plusieurs événements hydrothermaux superposés sollicitant différentes sources locales comme à Tighza, soit d’un seul événement perturbé par la segmentation d’un bassin volcanosédimentaire, comme pour les amas sulfurés des Jebilet et Guemassa. À l’échelle du gisement (Draa Sfar, Bou Skour), les variations isotopiques résultent de la superposition de plusieurs événements hydrothermaux avec chacun leur propre plomb et métaux associés. Globalement, on peut distinguer trois générations de plomb incorporées successivement dans le socle géologique marocain par le magmatisme et/ou l’hydrothermalisme, caractérisées par leurs rapports 206 Pb/ 204 Pb : 17,74–17,90 (panafricain), 18,10–18,40 (hercynien) et 18,75–18,90 (alpin). Le plomb panafricain est présent dans l’Anti-Atlas, et très localement dans la Meseta (Bouznika), et se nourrit en partie du magmatisme mafique du Gondwana. Le plomb hercynien est le plus représenté et affiche une rupture définitive dans la source des métaux dès lors exclusivement crustale. Il envahit tous les domaines marocains, y compris l’Anti-Atlas, où il remobilise et se mélange avec le plomb panafricain. Le plomb alpin, plus discret, jalonne la large écharpe allant d’Agadir à Nador qui trace en surface le panache mantellique des Canaries et accompagne un magmatisme néogène qui peut aussi avoir agi comme simple moteur remobilisant le plomb hercynien, notamment pour former les gisements MVT de Touissit. Les plombs hercynien et alpin sont en partie responsables du rajeunissement des minéralisations néoprotérozoïques, comme à Bou Azzer ou Imiter. Le Maroc illustre le modèle de Sawkins avec un apport majeur du plomb lors du magmatisme fini-orogénique. Les résultats isotopiques plaident en faveur de remobilisations successives du plomb stocké dans des réservoirs primaires et secondaires avec des phénomènes d’héritage. Enfin le bon transfert de la signature isotopique du plomb des gisements aux gossans de surface, notamment pour les gisements stratiformes de sulfures polymétalliques de type Hajar, montre que la géochimie isotopique du plomb est un outil utilisable pour l’exploration minière au Maroc.

International audience; The La Bellière gold district, in the Ligerian domain of the Armorican Massif is the third one of France in term of production. It shows gold-bearing quartz veins neighboring with a complex network of Sb veins, hosted in the Neoproterozoic metasedimentary basement of the Mauges Nappe. New structural data, mineralogical, textural and geochemical assays have been carried out to clarify the gold and Sb veins relationships. Our results favor of two-step hydrothermal event with an early deep-seated gold event followed by a late shallower Sb event. The gold-bearing quartz veins are hosted by N60°E to N90°E sinistral strike-slip faults. These veins exhibit a four-stage paragenesis: 1) early barren quartz filling, 2) arsenopyrite-pyrite with minor scheelite assemblage, 3) gold and base metal sulfides crystallized after a ductile/brittle deformation stage, and 4) pyrite-carbonate coeval with a late brittle stage. These results support a continuous evolution model from a deep emplacement level (12 to 9 km) to a shallow one (7 to < 5 km) with a brutal change in the P/T conditions that triggered the deposition of gold (stage 2) controlled by a seismic-valve mechanism. On the contrary, Sb veins correspond to open space vein types, hosted in a N20°W to N20°E conjugated strike-slip fault network arranged in a Riedel shear model, controlled by N130-140°E regional dextral strike-slip shear zone associated to the South Armorican Shear Zone system. A two-stage evolution is recognized, the first one consists of early pyrite-arsenopyrite with microcrystalline quartz, followed by a late stibnite stage formed after geodic quartz deposition. Quartz texture argues for a shallow emplacement (< 5 km) of veins controlled by a suction-pump mechanism. Chronologically, the gold vein opening complies with a NE-SW maximum shortening direction different from the late-Variscan stress field responsible for the dextral Armorican shear zone during late Carboniferous, and constrains an indirect dating. Thus, a Visean age is proposed for the formation of gold veins. The overall features of gold deposits are close to those of mesozonal orogenic gold deposits in Europe. Conversely, Sb-bearing veins are generated by a N-S shortening during the late Carboniferous. The Sb event, distinct in time from the earlier gold one, might correspond to a different expression of the so-called “epizonal” type in the orogenic gold model. It is proposed that the Late Carboniferous “Or 300” event is not the unique metallogenic period for gold deposition in the French Variscan domain. Our study highlights the role of the sinistral strike-slip shearing of possible Visean age, in the gold metallogenesis of the Ligerian domain.

International audience; The Argemela mineralized area (AMA), central Portugal, exhibits a nearly continuous magmatic to hydrothermal ore-forming sequence typical of Variscan granite-related rare metal deposits. Disseminated and vein-type mineralization are distributed in two systems, the Argemela Mine (AM) and the Cabeço da Argemela (CA). Disseminated mineralization includes montebrasite, cassiterite and columbite-tantalite dispersed in rare metal granites. Vein-type mineralization occurs both in granites and country rocks. The CA system exposes three generations of intragranitic veins with montebrasite in the two earliest and montebrasite, wolframite, cassiterite and columbite-tantalite in the latest. Country rock veins include a swarm of cassiterite and montebrasite veins (AM) and rare isolated wolframite veins (CA). Disseminated cassiterites are enriched in Ta2O5 and Nb2O5 compared to vein cassiterites. Disseminated columbite-tantalites evolve toward Mn- and Ta-rich chemistries that contrast with the more Fe- and Nb-rich compositions in intragranitic veins. In the CA system, both intragranitic and country rock veins crystallize early Mn-rich wolframites followed by late more Fe-rich compositions associated with Nb-, Ta-poor cassiterite, the later replaced by stannite. Field relations, structural, mineralogical and geochemical data suggest that the disseminated and vein-type mineralization are expressions of a continuous metallogenic evolution initiated at the magmatic stage, pursued during the magmatic-hydrothermal transition and ended with hydrothermal circulations in country rock. The two mineralized systems share similarities, but they also show major differences. Structural analysis demonstrates that the intragranitic veins in the CA and the country rock veins in the AM were emplaced under the same tectonic regime. Therefore, the two systems are variants of the same local metallogenic evolution. Sn and W show markedly contrasted behaviors. Both have a magmatic source but only Sn reaches concentrations leading to saturation of the melt with cassiterite. W is deposited later and preferentially to Sn in intragranitic veins. At the hydrothermal stage, cassiterite and wolframite deposition are disconnected and, overall, wolframite occurs only in minor amounts. The metallogenic model proposed for the AMA emphasizes magmatic rare metal concentration processes, exsolution of magmatic fluids and selective deposition of metals during the magmatic-hydrothermal and later hydrothermal stages. The Sn-Li-(Nb-Ta)-dominated, and W-poor signature of the AMA makes it similar to LCT pegmatites of the Central Iberian Zone but is distinctive from the world class W-(Sn-Cu) Panasqueira deposit nearby.

International audience; Afield study combined with a laboratory study and 3D modeling have been performed in orderto decipher the genesis of the Salau deposit W-Au mineralization (Pyrenees, France), one of the mostimportant for tungsten in Europe. Results show the existence of two superimposed ore types, emplaced ca.10 km depth and within decreasing temperature conditions: a calcic silicates skarn with rare scheelite anddisseminated sulphides followed by a mineralized breccia with massive sulphides (pyrrhotite andchalcopyrite dominant), coarse-grained scheelite and gold, representing the main part of the ore mined in thepast. This breccia is localized in ductile-brittle shear-zones which crosscut the granodiorite. U/Pb dating onzircon, apatite and scheelite, previously realized, confirmed this polyphase evolution. These two types ofmineralization, linked to the emplacement of two successive intrusions as confirmed by sulphur isotopicanalysis, granodioritic then leucogranitic, can be classified as belonging to the Intrusion-Related GoldDeposit type (IRGD). The emplacement of the high-grade gold and scheelite breccia was initiated by theprogressive localization of the regional deformation in the Axial Zone of the Pyrenees during the Permianwithin E-W dextral-reverse faults.; Une étude de terrain combinée à une étude de laboratoire et demodélisation 3D a été réalisée afin de décrypter la genèse de la minéralisation à W-Au du gisement de Salau(Pyrénées, France), une des plus importantes d’Europe pour le tungstène. Les résultats montrent qu’il existedeux types de minéralisations superposées, mises en place vers 10 km de profondeur et dans des conditionsdécroissantes de température : un skarn à silicates calciques, rare scheelite et sulfures disséminés, suivid’une brèchefilonienne à sulfures massifs (pyrrhotite et chalcopyrite dominante), scheelite grossière et orqui a constitué l’essentiel du minerai lors de la phase d’exploitation. Cette brèche se localise dans une sériede zones de cisaillement ductile-fragile recoupant l’intrusion granodioritique. Les datations U/Pb sur zircon,apatite et scheelite réalisées antérieurement, confirment ce polyphasage. Ces deux minéralisations, associéesà deux intrusions successives comme le confirment les analyses isotopiques du soufre, granodioritique puisleucogranitique, s’inscrivent dans l’évolution d’un modèle Intrusion Related Gold Deposit. La mise en placede la brèchefilonienne à forte teneur en or et scheelite est initiée par la localisation progressive de ladéformation régionale dans la Zone axiale des Pyrénées durant le Permien au sein de failles E-W dextresinverses.

International audience; In the Brioude-Massiac district (French Massif Central: FMC), a network of WAs -Bi-Au quartz veins constitutes the Bonnac deposit, where tungsten is the major economic element, together with high-grade gold (up to 15 g/t Au). The evolution of this mineralization has been divided into 3 stages: (i) an early deep-seated wolframite-löllingite stage formed between 12 to 9 km, at up to 400°C; (ii) a ductile/brittle deformation stage associated with scheelite and arsenopyrite deposition, with an estimated temperature of 480-300°C; (iii) a late stage controlled by fluid-overpressure potentially triggered by fault-valve mechanism, at a depth of 7 to 5 km, and a temperature estimated between 266 to 240°C, is marked by microfracturing infilled by native bismuth, bismuthinite, hedleyite, electrum, pyrite and base-metals. Structural analysis and apatite LA-ICP-MS U/Pb dating demonstrate a spatial and temporal link between the emplacement of the peraluminous leucogranitic dykes and the Bonnac mineralization. In more details, the mineralization was deposited between 321-316 Ma, during, or just after, the emplacement of the peraluminous dykes estimated around 329-315 Ma, suggesting a magmatic-hydrothermal transition for the ore-forming process. In the proposed model, the cooling of a hidden two-mica granitic pluton could have generated a magmatic fluid, and acted as the heat source responsible for fluid flow towards inherited permeability zones. The magmatic fluid could have then re-equilibrated at high temperature by fluid-rocks interaction. The sharp changes in pressure, associated with the decrease of the temperature, and sulfidefugacity generated by a late input of meteoric fluid were responsible for the deposition of the late gold-stage. At the regional scale, the tungsten-gold event is ascribed to an early hydrothermal stage, dissociated from the formation of the antimony event in the district. The leucogranitic dykes and Bonnac quartz veins are controlled by a NW-SE stretching direction, interpreted as an expression of the Serpukhovian-Bashkirian syn-orogenic extension (D4 event of the FMC). These new data provide evidence for an early tungsten and gold metallogenic event in the FMC, prior the "Or300" event. The genetic classification of the Bonnac mineralization is equivocal. The WAs -Bi-Au-quartz veins exhibit the features of both an "orogenic gold" deposit at a relatively deep emplacement level (mesozonal), and an Intrusion-Related-Gold-Deposit (IRGD) type with a spatial-temporal link with the peraluminous intrusion emplacement. We propose that the Bonnac deposits represent an intermediate type between a typical orogenic-gold deposit and an IRGD. We argue that the presence of economic high-grade gold content in tungsten vein-type, and more generally the IRGD deposits, have been underestimated in the Variscan French Massif Central.

Isotopic compositions of Mo in molybdenites were used for deciphering a possible genetic link between isotopic variations and mineralizing processes, based on a worldwide molybdenite databank. We compared the δ98/95Mo (hereafter referred as δ98MoNIST) of 391 molybdenite samples (193 from the literature, 198 for this study) from different localities, different types of occurrences and different ages. The 198 molybdenite samples we analysed represent various types of mineralization in 6 granites, 11 pegmatites, 6 perigranitic veins, 2 greisen, 28 porphyry deposits, 5 skarns, 1 IOCG, and 9 Alpine-type fissure veins, with ages varying from 5 Ma to 2.7 Ga. The Mo isotopic composition was determined with an MC-ICP-MS Neptune after aqua regia dissolution and adjustment to [Mo] = 1 μg·ml− 1. Mass bias was corrected by using Zr as dopant and standard-sample-standard bracketing. The δ98MoNIST ratios were normalized to NIST3134. External reproducibility is 0.07‰ (2σ). The overall range of the δ98MoNIST ratio in the 391 molybdenite samples varied from − 1.62 to 2.27‰, being higher for molybdenite formed in Alpine-type veins, greisen, perigranitic veins and IOCG, than for that in granite, pegmatite, porphyry deposits and skarns. The crystallization temperature can explain some of these differences, as polymetallic Alpine-type fissure veins broadly crystallize at lower temperatures than granite, pegmatite and porphyry deposits. For some occurrences the δ98MoNIST was determined on several molybdenite samples, showing variability at occurrence scale. For example, in the Azegour skarn (Morocco) the δ98MoNIST varies from − 0.60 to 0.42‰ (n = 29), and in “Ravin de la Ruine” Alpine-type fissure veins (France) the variation is from − 0.08 to 0.77‰ (n = 3). No correlation is seen between δ98MoNIST and the age of the deposits.

Le skarn minéralisé en Mo, W et Cu d’Azegour se forme aux dépens d’une série cambrienne essentiellement sédimentaire carbonatée dans l’auréole de métamorphisme d’un granite permien. Les bancs métasomatisés plurimétriques du skarn sont pour l’essentiel des grenatites et wollastonitites massives, plus rarement des pyroxénites. L’étude minéralogique montre que les grenatites sont composées pour l’essentiel d’andradite (grenat vert-noir et grenat brun-noir zoné) plus rarement de grossulaire (grenat orangé). Le pourcentage de spessartite est toujours faible (maximum 4 %). La wollastonite est légèrement manganésifère, la vésuvianite fluorée (jusqu’à 3,3 %) et chlorée (1,2 %). Les paragenèses permettent d’établir les conditions de formation du skarn aux alentours de 620–650 °C pour une pression de 1,7 à 2 kbar, avec une fCO2 de 31 mole %, en contexte réducteur (fO2 de 10−18 et 10−17 atm.). Le skarn d’Azegour est un marqueur de la fin de l’orogenèse hercynienne, et dénote la persistance de conditions réductrices, un environnement très favorable à la cristallisation de sulfures. Le skarn d’Azegour semble ainsi se former à des températures plus élevées que d’autres skarns à tungstène hercyniens comme Salau (Ariège, France).

International audience; The Lalla Zahra W-(Cu) prospect of northeastern Morocco is hosted in a Devonian volcaniclastic and metasedimentary sequence composed of graywacke, siltstone, pelite, and shale interlayered with minor tuff and mudstone. Intrusion of the 284 ± 7 Ma Alouana concentrically zoned, two micas, calc-alkaline, and post-collisional Alouana granitoid pluton has contact metamorphosed the host rocks, giving rise to a metamorphic assemblage of quartz, plagioclase, biotite, muscovite, chlorite, and alusite, and cordierite. The mineralization occurs in and along subvertical, 20 to 40 cm thick, and structurally controlled tensional veins composed of quartz accompanied by molybdenite, wolframite, scheelite, base metal sulphides, carbonates, barite, and fluorite. Three main stages of mineralization (I, II, and III), each characterized by a specific mineral assemblage and/or texture, are recognized. Quartz dominates in all the veins and commonly displays multiple stages of vein filling and brecciation, and a variety of textures. The early tungsten-bearing stage consists of quartz-1, tourmaline, muscovite, wolframite, scheelite, and molybdenite. With advancing paragenetic sequence, the mineralogy of the veins shifted from stage I tungsten-bearing mineralization through stage II, dominated by base metal sulphides, to stage III with late barren carbonates and barite ± fluorite mineral assemblages. Pervasive hydrothermal alteration affected, to varying degrees, the Alouana intrusion, resulting in microclinization, albitization, episyenitization, and greisenization of all the granitic units. Fluid inclusion data yield homogenization temperatures ranging from 124°C to 447°C for calculated salinity estimates in the range of 0.4 to ~60 wt% NaCl equiv. Similarly, the δ18O values for the three generations of quartz range from 11.7‰ to 13.9‰ V-SMOW. Calculated δ18O values of the parent fluid in the range between −3‰ and +9‰ V-SMOW are consistent either with a mixture of water of different origins, including magmatic water, or an origin from seawater or meteoric water that probably exchanged oxygen with rocks at elevated temperatures. The coexistence of CO2-rich and H2O-rich fluid inclusions reflect the presence of a boiling fluid associated with the deposition of the early tungsten-bearing stage mineralization at relatively high temperature. The general temperature and salinity decrease with advancing paragenetic sequence suggest that the early high temperature, magmatic, highly saline, and boiling fluid mixed with meteoric non-boiling fluid results in the precipitation of base metal sulphide and carbonate-barite stage mineral assemblages, respectively.

International audience; Koudiat Aïcha is a Visean stratiform, volcanogenic massive sulphide (VMS) zinc-copper-lead deposit, situated northwest of Marrakech, within the Central Domain of the Jebilet massif of the Western Moroccan Meseta. The Central Domain is formed mainly of sedimentary (argillite, siltstone, sandstone, carbonate) and magmatic (gabbro and rhyodacite) rocks that host numerous massive sulphide deposits (e.g., Koudiat Aïcha, Kettara and Draa Sfar) in a thick grayish argillite sequence (rhythmic metapelite). The deposit is stratabound and consists of highly deformed, sheet-like lenses of massive sulphide located structurally on the eastern flank of a large anticline. Prior to metamorphism, the country rocks were subjected to hydrothermal alteration which is particularly pronounced in the immediate vicinity of the sulphide deposits where chloritization and sericitization are prevalent. Hydrothermal alteration extends into both the stratigraphic footwall and the stratigraphic hanging wall. The footwall lacks an obvious pipe zone (sulphide stringers or vent complex) beneath the sulphide mineralization, but is characterized by an increase in the modal proportion of Mg-chlorite and by the breakdown of feldspar and sericite. Chloritization, the most extensive and readily recognizable alteration useful in mineral exploration, is evident for more than 60 m above the subcropping sulphide deposits. The hanging wall rocks show a pervasive sericitization (over 30 m wide) and a weak chlorite alteration accompanied by disseminated nodules of pyrrhotite stretched parallel to the S1 foliation. Because chlorite and sericite are metamorphic minerals that also occur in unaltered rocks surrounding the sulphide deposits, abundant Mg-rich chlorite and the absence of feldspar in the footwall are used to distinguish hydrothermal alteration facies from metamorphic facies. The chlorite geothermometer reveals temperatures between 250 and 330 °C. Higher temperatures (up to 300 °C) are associated with chlorite located in and adjacent to sulphide mineralization, whereas lower temperatures correlate with distal chlorite in both the footwall and hanging wall rocks. Chemical trends in altered footwall rocks are shown by absolute mass gains for Fe2O3total, MnO and MgO, by absolute mass losses for CaO, K2O and Na2O, and by a moderate loss in SiO2. Oxygen and hydrogen isotope compositions of Koudiat Aïcha lithofacies (6.2-12.4‰ for oxygen and −51‰ to −36‰ for hydrogen) have also been used to determine the temperature and origin of metalliferous fluids. The couple plagioclase-amphibole of gabbros provides equilibrium temperatures between 310 and 380 °C and suggests that the heat source for the ore-forming fluid system may have been igneous. On the other hand, oxygen and hydrogen isotope ratios cluster between normal values for sedimentary and magmatic rocks, suggesting a magmatic-metamorphic origin for the ore fluid.

International audience; New insights on the circulation of fluids around magmatic intrusions have been obtained through coupled hydrothermal numerical modelling that takes into account i) a continuous variation of permeability with depth, ii) the period of intrusion emplacement, iii) the physical likelihood of ore deposition using a restricted rock alteration index, and iv) the so-far unexplored pluton floor, and then comparing the results against well-constrained natural cases showing different emplacement depths, high permeability zones (cracked thermal aureoles), faults and plutonic apexes. We show that emplacement depth is a key physical parameter controlling the extent and geometries of advective heat dissipation zones, and that shallow apexes strongly modify the fluid-flow pattern by acting as a focus for convective fluids and mineralization zones. We also show that the cooling phase is not the main convective phase for large plutons commonly associated with long-lived magma emplacement; major advective heat dissipation and mineral deposition zones may also develop before and during the hottest phase of the emplacement, i.e. before magma crystallization. The comparison with natural cases shows that we successfully reproduce, in space and time, the physical conditions required for mineral deposition. In particular, extensional detachment is able to restrain and modify classical fluid-flow patterns induced by coeval intrusion. Finally, even though lacking chemical arguments, we conclude that convection induced by granite emplacement plays a major role in the genesis of granite-related Au deposits. Moreover, the formation of this type of deposit is favoured and controlled by the presence of a fractured thermal aureole around the intrusion.

International audience; In order to better define the dependence of the mineral texture on flow, Anisotropy of Magnetic Susceptibility (AMS) and microscopic observations have been performed on calcite rich precipitations occurring in a horizontal pipe where the flow direction is clearly defined. Sixty-five cubes were cut from 5 slices, magnetic studies identified-pseudo-single domain magnetite as the major AMS carrier. Horizontal foliation characterizes the magnetic fabrics and the lineation is parallel to the pipe axis, i.e. the flow direction. The origin of this lineation is discussed and is interpreted to be mainly the consequence of elongated pseudo single domain magnetite. To complete the magnetic fabric studies, shape preferred orientation statistics were performed on 563 calcite sections in the (0001) calcite plane. It shows elongated shapes with a general orientation parallel to the pipe axis. The mean shape orientation is the average of two distinct sub-populations that deviated slightly from the pipe axis. Observation on calcite shapes and the direction of the magnetic lineation are coherent, suggesting that it is possible to track hydrothermal paleo-circulation using magnetic lineation and petrographic fabrics.

Resume Le gisement argentifere de Zgounder (Anti-Atlas, Maroc) est encaisse dans une serie volcano-sedimentaire proterozoique, rapportee aux PII et PIII. La mineralisation disseminee est a argent natif mercurifere (2 a 30 % Hg) dominant, sulfosels d'argent (acanthite, pearceite), arsenopyrite et sulfures de metaux de base. La teneur en arsenic de l'arsenopyrite, ainsi que les temperatures d'homogeneisation des fluides precoces temoignent de conditions initiales de haute temperature (plus de 400 °C). Les compositions isotopiques du plomb confirment un âge fini-Proterozoique et tracent une origine crustale des metaux. Les similitudes avec le gisement argentifere proche d'Imiter sont fortes et amenent a considerer Zgounder comme un autre exemple d'epithermal neoproterozoique dans l'Anti-Atlas marocain, qui apparait ainsi de plus en plus comme une province metallogenique argentifere. Pour citer cet article : E. Marcoux, A. Wadjinny, C. R. Geoscience 337 (2005).

The Sando Alcalde ore deposit (southwestern Peru) has been studied in order to characterize the physicochemical parameters of the ore fluids and to determine the fluid process (mixing or boiling) which involves the precious metal mineralization. Mineralogy, δ18Oquartz isotopic values and fluid inclusion data give arguments in favour of a boiling phenomenon. This conclusion corroborates fluid inclusion studies previously performed in this area on the low-sulphidation epithermal deposits of Arcata, Orcopampa and Apacheta, where boiling has been described as the main factor for ore deposition. To cite this article: A.-S. Andre-Mayer et al., C. R. Geoscience 337 (2005).

This study presents a possible use of anisotropy of magnetic susceptibility (AMS) to describe the mineralizing process in hydrothermal systems. Ba–F–Fe-rich deposits within the Chaillac Basin are on the southern border of the Paris Basin. In these deposits hydrothermal textures and tectonic structures have been described in veins, sinters, and sandstone cemented by hydrothermal goethite. 278 oriented cores from 24 sites have been collected in these formations. In addition, a lateritic duricrust superimposed on the hydrothermal formation has been sampled. Rock magnetic investigations show that the principal magnetic carrier is goethite for the hydrothermal mineralization and for the laterite level. The AMS measurements show distinguishable behaviors in the different mineralogical and geological contexts. The K1 magnetic lineation (maximum axis) is strongly inclined for the vertical veins. For the horizontally mineralized sinters, the magnetic lineation is almost horizontal with an azimuth similar to the sedimentary flow direction. The AMS of goethite-rich sandstone close to the veins shows strongly inclined K1 as they are probably influenced by the vertical veins; however, when the distance from the vein is larger than 1 m, the AMS presents rather horizontal K1 directions, parallel to the sedimentary flow. The laterite has a foliation dominance of AMS with vertically well-grouped K3 axes and scattered K1 and K2 axes. Field structural observations suggest that the ore deposit is mainly controlled by EW extension tectonics associated with NS trending normal faults. Combining the AMS results on the deposit with vein textures and field data a model is proposed in which AMS results are interpreted in terms of hydrothermal fluid flow. This work opens a new investigation field to constrain hydrodynamic models using the AMS method. Textural study combined with efficient AMS fabric measurements should be used for systematic investigation to trace flow direction in fissures and in sand porosity.

The Nuevo Entredicho deposit contains the richest concentration of mercury in the Almadén district, locally grading as much as 45% Hg. This ore deposit is hosted within an alkaline, conically shaped diatreme, about 150 m in diameter, which was subsequently filled with phreatomagmatic breccias. The diatreme cuts an Ordovician to Silurian clastic sedimentary rock sequence that is intercalated with basaltic sills. Structural analysis reveals a complex tectonic history with three main phases of Hercynian deformation. Mineralisation occurs as cinnabar replacements in volcanic tuffs and breccias and as recrystallised veins in tensions cracks associated with pyrophyllite and hydrothermal pyrite, which is strongly enriched in Cu, Pb and Hg. Lead isotopes in pyrite are characterised by high 207Pb/204Pb ratios (15.70-15.75), suggesting a contribution of ancient upper continental crust remobilised by Silurian-Devonian volcanism, with no mantle involvement. Sulphur isotopes of epigenetic cinnabar and pyrite range from +10.3 to +10.8‰ and from +10.6 to +11.9‰ respectively, suggesting a uniform sulphur source or a constant mixing ratio in the ore fluids. These isotopic compositions differ from those measured in the syngenetic deposits of the Almadén district; they suggest a higher temperature of ore formation of about 300 °C, and a genesis related to a distinct hydrothermal flow path at the Nuevo Entredicho deposit. Deposition of anomalously high-grade mercury ore at Nuevo Entredicho is related to a combination of (1) an abundance of black shale that provided sulphur and increasingly reducing conditions with high sulphide/sulphate ratios, (2) explosive Silurian-Devonian mafic magmatism that provided an initial source of mercury, (3) tectonic activity that lead to structurally favourable sites for ore deposition, and (4) replacement of secondary, carbonate-rich volcanic rocks.

The Baia Mare district (Romania) represents a complex segment of the Neogene/Quaternary, subduction-related, volcanic chain of the Carpathians. In this province, the calc-alkaline volcanism and associated mineralization are closely related to a major strike-slip fault and an underlying pluton. The ore deposits of the district have many features typical of low-sulfidation (or adularia-sericite) epithermal deposits. The combination of fluid-inclusion microthermometry, Raman spectroscopy, bulk crush-leach analysis, laser ablation-optical emission spectrometry (LA-OES) of individual fluid inclusions and stable isotope data has been used to characterize the ore-forming solutions involved with gold/polymetallic mineralization in three of the largest deposits. Ore fluids at Baia Sprie, Cavnic and Sasar deposits had temperatures of 320 to 150 °C and salinities in the range 0–21 wt% NaCl equiv. During phreatomagmatic activity, fracturing and periods of vein dilation, the pressure fluctuations may have caused boiling. The hydrothermal fluids were Na–K–Li–Ca chloride solutions with lesser amounts of SO4 and F. The Na/K ratios and the stable isotope compositions are consistent with equilibration of the fluids with country rocks at progressively lower temperatures. The halogen ratios (Br/Cl×103 in the range 0.13–1.21), together with sulfur isotopic systematics (δ34S=0.3–5.2 per mil), are consistent with a dominantly magmatic origin of the solutes, and probably of the ore fluids themselves.

The Valea Morii Cu–Au ore deposit (Apuseni mountains, Romania) is characterised by a spatial association of a porphyry copper (Cu±Au) with a low-sulfidation epithermal deposit (Au). Microthermometric and sulphur isotopic data, obtained on both porphyry and epithermal veins, express a telescoping between these two types of mineralization, which can be explained either by an erosion phenomenon during the hydrothermal activity or by a collapse of the upper part of the hydrothermal system.

International audience; The Au-Ag epithermal mineralization of the Shila Cordillera is dated at about 10.7 Ma (K/Ar on adularia). The vein system is characterized by the association of a major east-west vein and N120-135°E secondary fractures. The strike-slip faults controlling the veins indicate an initial NE-SW to ENE-WSW shortening direction, which is compatible with that generally accepted for this period. These structures were reopened during a second phase and channelized mineralizing fluids, the circulation of which may have began at the end of stage 1.; Les minéralisations épithermales à Au-Ag de la Cordillera Shila sont datées à environ 10,7 Ma (K/Ar sur adulaire). Le système de veines est caractérisé par l'association entre une veine principale sensiblement est-ouest et des fractures satellites N120 à N135°E. Les décrochements contrôlant les veines indiquent une direction de raccourcissement initiale NE-SW à ENE-WSW, compatible avec celle généralement admise pour cette période. Dans un deuxième stade, ces structures sont ré-ouvertes pour servir de réceptacle aux fluides minéralisateurs, dont la circulation débute probablement dès la fin du stade 1.

The Pongkor gold-silver epithermal deposit with reserves of at least 98 tonnes of gold and 1026 tonnes of silver, average grades 16.4 g/t Au and 171.2 g/t Ag is one of the most recent and largest gold and silver discoveries in Indonesia, proven within a short period (1988–1991). 40Ar/39Ar dating on adularia samples give an age of 2.05 ± 0.05 Ma. The deposit is of the low-sulfidation epithermal type and consists of four main mineralized quartz veins located close to the internal rim of a volcano-tectonic depression (caldera). This resulted from an explosive ignimbritic eruption that produced pyroclastic flows and accretionary lapilli with rare intercalations of epiclastic rocks. This volcanic unit unconformably overlies Miocene subaqueous volcanic andesitic rocks with interbedded epiclastic rocks. The mineralized bodies are thick (average 4.2 m), steeply dipping, quartz-carbonate-adularia veins with a very low sulfide content (

Dans l’introduction de leur comment nos commentateurs (Touil A. et Hibti M.) estiment que « Les relations chronologiques et reactionnelles entre les differents stades hydrothermaux ainsi que leurs relations avec les mineralisations ne sont pas bien illustrees » dans notre article et ils proposent ce qu’ils appellent « des elements de reponse et eventuellement de nouvelles donnees permettant une meilleure comprehension des alterations hydrothermales et leurs roles dans la mise en place et la formation des mineralisations liees aux skarns d’Azegour ». Le probleme de fond de ce comment est que dans notre article nous n’avons pas aborde l’etude des mineralisations, ni du point de vue descriptif ni du point de vue genetique. Ce n’etait pas l’objectif de notre article, la mine etant aujourd’hui inaccessible, ce qui est clairement ecrit dans les premieres lignes de notre article. D’apres les commentateurs « Berrada et al. [2015] considerent que les bancs a wollastonite alternent avec les grenatites. En effet, l’allure sur le terrain laisse penser a des recurrences a wollastonite-grenatite. En revanche, l’observation detaillee sur cassure fraiche et au microscope montrent que le contact entre les grenatites du stade III et les wollastonitites du stade II est diffus et progressif » . Dans notre article nous avons effectivement utilise le terme alternance « Les wollastonitites se presentent en bancs et en lentilles sub-monominerales d’extension decametrique et de puissance variable (de 10 cm jusqu’a 2 m) alternant avec des bancs de grenatites » , mais …

The Au-Cu-Zn-Sb epithermal mineralisations of the Baia Mare district (north Romania) and their Mio-Pliocene calc-alkaline volcanic host rocks are linked to the presence, at depth, of the Baia Mare batholith, recognised by geophysical and field studies. The salinity and temperature evolution of fluid inclusions from Baia Sprie and Sasar deposits are interpreted as being linked to the thermal evolution of the underlying laccolith. The global evolution, however, shows many irregularities related to brittle tectonic activity and phreatomagmatism during mineral deposition.

The true reproducibility of lead-isotope measurements by thermal-ionization mass-spectrometer (TIMS) was assessed on both the international standard (NBS 982) and sulphide samples from the South Iberian Pyrite Belt (SIPB). Lead-isotope analyses were made on 21 pyrite and galena samples from Rio Tinto sulphide orebodies in the Spanish part of the SIPB. Independent lead-isotope analyses were made in the UM2 laboratory (Montpellier), using a VG Sector 54 mass spectrometer, and at BRGM (Orleans) using a Finnigan Mat 262 mass spectrometer. Internal precision and reproducibility of the isotope measurements were calculated for lead-isotope standards (NBS 982), and for pyrite and galena samples. The reproducibility (2σ) is 0.12% for 206Pb/204Pb, 0.16% for 207Pb/204Pb and 0.22% for 208Pb/204Pb while the internal precision is on average 0.01% for each isotope ratio (2σm). This indicates that the usually adopted errors of between 0.10% and 0.25% are appropriate for geological samples. TIMS has been the most common method for measuring U/Pb ratios by isotopic dilution, but since a few years ICP–MS has also been used for such determinations. We thus checked the reproducibility of U/Pb-ratio measurements by ICP–MS, in order to apply this method to sulphide samples. Independent measurements (2 to 7) for each of 20 analysed samples showed that the measured average reproducibility for U/Pb ratios is better than 5%. This method is thus suitable for determination of U/Pb ratios in sulphide samples and most other geological materials. Lead analyses for the Rio Tinto deposit were made of the pyritic and orebodies, and the stringers. This deposit, one of the biggest massive sulphides in the world, is remarkably homogeneous from a lead-isotope viewpoint, and no difference can be seen between pyritic and polymetallic orebodies. The isotope composition of the deposit can be considered as the average composition of the South Iberian crust during the Devonian–Early Carboniferous period of crustal fusion.

The Late Devonian-Early Carboniferous (Dinantian) within the Western Hercynides is marked by the formation of volcanic-hosted massive sulphide deposits: Chessy and Chizeuil in the Brevenne and Somme successions of the French Massif Central; Bodennec and La Porte-aux-Moines in the Châteaulin Basin of the French Armorican Massif; Rio Tinto, Neves-Corvo, Tharsis, etc., in the Volcano-Sedimentary formation of the Iberian Pyrite Belt; and Ketara, Draa Sfar and Hajar in the Jebilet-Guemassa district of the Moroccan Southern Meseta. Although these deposits show a slightly diachronous emplacement in response to a progressive migration of the metalliferous event from Late Devonian in France to Dinantian in Morocco, it is nevertheless possible to define an overall metalliferous ‘‘peak” around 350 Ma. The mineralization of the Armorican, Iberian and Moroccan sectors took place in epicontinental domains of the outer zone of the Hercynian belt, whereas that of the northeastern Massif Central occurred within the inner zone of the belt. This difference is registered by variations both in the geochemical characteristics of the ores (Sn in the outer zone and Mo-Ni in the inner zone) and in their lead isotopic signatures (clear mantle participation exclusively in the inner zone). In many cases the ores appear to be closely related to the felsic member of a bimodal magmatic association, although the massive sulphide deposits in the outer zone are more commonly associated with sedimentary rocks whereas those in the inner zone are hosted by felsic volcanic rocks. Another feature that should be noted is that the host sequences of the massive sulphide deposits commonly seem to be underlain by chaotic formations (notably with olistoliths) reflecting the beginning of Hercynian orogenic activity in the outer zone. It can be concluded that the peak mineralization took place within tensional domains developed during a period of plate convergence, and that it occurred around 350 Ma after a major period of Devonian compression but before the Carboniferous continental closure.

The Iberian Pyrite Belt (IPB) has, over the past decade, been an area of renewed mining activity and scientific research that has resulted in a wealth of new data and new geological and metallogenic concepts that are succinctly presented in this Thematic Issue. The reason for this interest in the IPB, which forms part of the Hercynian orogenic belt, is that its Late Devonian to Middle Carboniferous rocks host a huge quantity of volcanic-hosted massive sulphide (VMS) mineralization (1700 Mt of sulphides, totalling 14.6 Mt Cu, 13.0 Mt Pb, 34.9 Mt Zn, 46100 t Ag and 880 t Au). The mineralization and its environment display a number of typical signatures that can be related to the mineralogy and zoning of the sulphide orebodies, to the lead isotopes of the mineralization, to the geochemical and mineralogical variations in the hydrothermal alteration halos surrounding the orebodies, to the geochemical characteristics of the bimodal volcanics hosting the VMS, to the complex structural evolution during the Hercynian orogeny, to the presence of palaeofaults and synsedimentary structures that acted as channels and discharge traps for the metalliferous fluids, and to the gossans developed over VMS. Discriminant geological criteria have been deduced for each domain which can be helpful in mineral exploration, complementing the more traditional prospecting techniques. Although the question of the IPB's geodynamic setting is still under debate, any interpretation must now take into account some incontrovertible constraints: for example, the geochemical characteristics of a large part of the basic lavas are comparable to those of mantle-derived basalts emplaced in extensional tectonic settings, and the associated acidic rocks were produced by melting of a basic crustal protolith at low- to medium-pressures and a steep geothermal gradient, thus, the sulphide-bearing volcano-sedimentary sequence differs strongly from recent arc-related series. It is considered here that the tectonic setting was extensional and epicontinental and that it developed during the Hercynian plate convergence, that culminated in thin-skinned deformation and accretion of the South Portuguese terrane to the Iberian Paleozoic continental block.

International audience; In Neogene times, the whole Mediterranean Sea was the center of an intense magmatic activity. This post-collisional magmatism produced a large amount of volcanic edifices through the Alpine belts, together with some intrusives. These plutonic bodies can be associated with skarn-type mineralization, well-known in Elba Island or Serifos Island (Cyclades), where they are generally exhumed by detachment faults. In Morocco, the plutons hosted by the Beni Bou Ifrour massif are connected to the biggest skarn-type iron concentrations of the country (production > 60 Mt, reserves ≈ 25 Mt). The purpose of this work is to explain the late uplift of this massif and subsequent exhumation of the intrusives. As a final product of the Africa-Eurasia plate convergence since ca. 70 Ma, the Rif Mountains constitute the westernmost segment of the Mediterranean Alpine belts. In the oriental part of this range, volcanic summits and Paleozoic to Mesozoic massifs outcrop in the surrounding Mio-Pliocene plains. The Beni Bou Ifrour massif, in the Nador province, consists in a dome-shaped folded Mesozoic series (Domerian to Barremian) affected by a slight epizonal regional metamorphism (ca. 14-12 Ma), dislocated by Neogene NE-SW faults and eventually sealed by upper Miocene transgressive sediments. The hosted intrusives (7.58 ± 0.03 Ma; Duggen et al., 2005) are the plutonic equivalents to the potassic calc-alkaline lavas (andesites mainly) from the surrounding "satellite" volcanic massifs. They turn out to stand in higher topographic position than the younger shoshonitic lavas of the neighboring Gourougou stratovolcano (6.12 ± 0.01 Ma; Duggen et al., 2005). Previous studies have attributed this uplift to the action of normal faults (pull-apart basins; Guillemin & Houzay, 1982), thrusting (Kerchaoui, 1985; 1995) or even of a caldeira resurgence (El Bakkali, 1995). To discriminate against those exhumation mechanisms, field work has been performed, coming along with new cross-sections to illustrate the geometry of the Beni Bou Ifrour massif. A paleomagnetism campaign was conducted, to determine if the plutonic intrusions have been tilted since their emplacement. Apatite fission tracks and 40Ar-39Ar dating allow us to estimate the exhumation age of the igneous bodies, and therefore add chronological constraints to the tectonic model. Geochemical study has also been performed on the magmatic rocks, and added to an extensive dataset (El Bakkali, 1995; Kerchaoui, 1995; Duggen et al., 2005). The existence of a magmatic chamber below the Beni Bou Ifrour dome will thus be discussed. Once established, the tectonic model of the Beni Bou Ifrour massif will help to precise the emplacement of the mineralized bodies and to integrate the iron-skarn metallogenesis within the structural evolution of the Rif orogenic segment.

The Pliocene Cirotan gold deposit provides an exceptional example of mineralized breccias, and in particular cockade breccias. Analysis of these breccias, approached through both field observation and image analysis on photographs, made it possible to determine their method of graded formation. The mineralized structure, as much a 25 m thick in places, is a right-lateral strike-slip fault that evolved to a normal fault at the end of the system's development. It consists of juxtaposed breccia bodies separated by major slip, or "septa," which formed at a major inflection of the host fault. The breccia bodies all show a similar internal organization. From footwall to hanging wall, one passes from a siliceous breccia with angular clasts to a thick infill of cockade breccia showing a reverse grading with small centimetre-size cockades (aspect ratios of 1:10) passing to larger (up to 1 m) more equant cockades (aspect ratios 1:3) in contact with the hanging wall. The different stages of cockade formation demonstrate genesis in an open milieu through rolling-accretion and collapse of the clasts, which show signs of mechanical attrition. The large cockades are formed of an agglomeration of several small cockades. Ore deposition occurred during a pulsating process that was active throughout the complex evolution of the structure. The final ore stage, filling the intercockade spaces, marked the end of the structure's evolution. High fluid pressures and the local structural context combined to maintain open the hydrothermal channelways, enabling cockade growth and collapse. The process of breccia formation at Cirotan was therefore exclusively of hydrothermal origin in an active tectonic context. It represents a self-organizing system within a fault zone.

Epithermal gold mineralization of the adularia-sericite type in West Java is hosted by strike-slip faults cutting Miocene to Pliocene volcanic and plutonic formations. Mineralization consists of two styles of discordant gold-bearing quartz veins: crustiform banding veins of the “Pongkor” type, with electrum, some minor sulphides and manganese oxides, and breccia veins of the “Cirotan” type with rhodochrosite, rhodonite, electrum, abundant polymetallic sulphides and some cassiterite and wolframite. Except for the Pongkor ore deposit, whose age is Miocene (8.5 Ma), K/Ar dating of adularia gave a Pliocene-Pleistocene (2.1-1.5 Ma) age for both styles of epithermal gold deposits. Most are hosted by volcanic and intrusive rocks related to extensive Pliocene magmatism that we dated in the centre of the Bayah Dome as forming between 5.7 and 2.0 Ma. Lead-isotopic compositions of Miocene volcanic rocks show mantle affinities, whereas the lead of Pliocene volcanic rocks and Miocene-Pliocene gold deposits is highly radiogenic and clearly crustal ( 207 Pb/ 204 Pb = 15.66 to 15.72). This indicates that this lead and possibly associated metals have their source in an underlying Precambian crust, which must extend at depth from West Java to the Tin Islands. Mineralogical data, especially the presence of magmatic-related minerals, sulphur isotopes with δ34S clustered around 0‰, and lead isotopic results, all suggest that the metal content and probably most of these ore-forming fluids of epithermal gold deposits originated from a crustal magmatism through a reworking of the underlying Precambrian crust.

International audience; Most of Morocco's barite production comes from deposits of epigenetic origin emplaced during Mesozoic time and hosted by Cambrian formations. Located in the Hercynian Meseta, the Bouznika deposit is associated with the Cambrian Oued Rhebar bimodal volcanic complex. Barite occurs as both stockworks and stratiform lenses within felsic tuffs and epiclastites, and is associated with a potassic alteration characterized by the presence of sericite. Lead and sulphur isotope analyses demonstrate that emplacement occurred during Cambrian time when barite-enriched hydrothermal fluids, likely of volcanic origin, mixed with sulphur from seawater. The Cambrian formations hosting the Bouznika, Jbel Irhoud and Seksaoua barite deposits are located near the faulted limit of the Meseta's lower Palaeozoic Iapetus rift on the northwestern edge of the Gondwana continent, suggesting that they formed during the Mesozoic reworking of early Cambrian concentrations.

The Early Proterozoic of the West African craton comprises a series of volcanic troughs and sedimentary basins (the Birimian) with granitic terranes accreted on Archean nuclei in the Man and Reguibat shields. Studies of the Birimian of the Man Shield indicate a model of polycyclic evolution, with a major collision event (D 1 ; 2.1 Ga) thrusting part of the Proterozoic terrane over the Archean before individualization of numerous volcanic troughs and clastic-infill basins. The proposed evolution for the Birimian orogenic belt comprises: (1) deposition of the sedimentary Lower Birimian (B1) with minor tholeiitic volcano-sedimentary intercalations (containing chert and/or Mn-formations), and with most of the detritus being derived from Early Proterozoic sources, apart from contamination near the Proterozoic/Archean contact; (2) pre-B2 crustal thickening related to D 1 thrusting; (3) formation, over about 40 Ma, of the Upper Birimian (B2) with numerous volcanic troughs of different composition (tholeiitic and rare komatiitic, bimodal tholeiitic to calc-alkaline, volcano-plutonic) and Tarkwaian clastic-infill basins; and (4) major transcurrent tectonics with sinistral (D 2 ) and dextral (D 3 ) strike-slip faults. Such a tectonic evolution from a collision (D 1 ) phase to a transcurrent (D 2 , D 3 ) phase is typical of collision belts, and in the present case the evolution of the Birimian orogenic belt can be extended into Guyana. The metallogenic history of the Birimian shows a three-phase evolution coinciding with the orogenic evolution, and extends over almost 150 Ma from the Perkoa massive (ZnAg) sulfides (2.12 Ga) with a clear mantle affinity to the latemesothermal Au quartz veins (∼2 Ga) with (according to lead isotopes) a high crustal participation. The economic mineralization of belt thus consists of: 1. (1) “Pre-orogenic” (pre-D 1 ) deposits related to early extension zones. This was diverse with stratiform Au tourmalinite (type 1 Au: Loulo in Mali; Dorlin in Guyana), stratiform Fe (Cu) (Faleme in Senegal) and Mn (Nsuta in Ghana; Tambao in Burkina Faso), and a single massive ZnAg sulfide deposit (Perkoa in Burkina Faso) associated with regional volcanosedimentary (variably tholeiitic) stratigraphic marker beds; 2. (2) “Syn-orogenic” (post-D 1 to syn-D 2 /D 3 ) deposits with disseminated Au-sulfides (type 2 Au: Yaoure in the Ivory Coast) in extensional zones of the B2 followed by auriferous paleoplacers (type 3 Au) in B2 extensional zones (Tarkwaian Banket conglomerate) or syn-D 2 transtensional zones (debris flow of Orapu in Guyana). 3. (3) “Late-orogenic” (post-peak D 2 /D 3 ) deposits with mesothermal Au mineralization evolving from a “disseminated gold-bearing arsenopyrite and Au-quartz lode” type (type 4 Au: Ashanti in Ghana) to a “quartz-vein” type with free gold and CuPbZnAgBi paragenesis. Most of the gold in West Africa comes from this phase. Finally, the metallogeny of the Birimian appears as rich in Au- and Mn-formations and poor in volcanogenic mineralization and BIF. It differs from the Archean metallogeny of West Africa and other regions, through the presence of certain deposit types (such as Au-stratiform tourmalinite, gold-bearing conglomerate with Au and FeTioxides but no uranium or sulfides, and Au-arsenopyrite-rich shear-zone deposits) that are very common in, but not exclusive to, the Proterozoic and Paleozoic.

This paper presents a ground investigation into the properties of a tape-spring hinge mechanism, for use in deploying a multi-layer membrane structure for space antenna applications. The repeatability results of deploying those membrane layers using this mechanism are explored, as well as the flatness expected of the surfaces deployed for signal transmission and reception. This membrane is a prototype for the development of an on-orbit flight experiment in thin structure deployment, where such an experiment addresses necessary questions related to the use of this technology for membrane synthetic aperture radar. The prototype includes multiple layers

Key-words. - Fluorite, Barite, Hydrothermal processes, Early Jurassic, Isotopes, Chaillac Abstract. - During the earliest Jurassic, a widespread hydrothermal event occurred in western Europe producing large veins and stratiform F-Ba-Pb-Zn ore deposits. Previous work argued about genetic processes involving circulation of mineralising brines. Two main alternative genetic models are proposed. The first one proposes a convection of brines through the crust to produce ore deposits, the second an early infiltration of brine in the basement followed by expulsion during Mesozoic extension. In the northern French Massif Central, new data on the F-Ba Chaillac deposit suggest that the genesis of these mineralising brines requires a new discussion. Located in the northern French Massif Central, the Chaillac barite and fluorite ore deposit is an exceptional site where a stratiform deposit is rooted onto a vein. The ore deposition is split in two stages: 1) precipitation of green and purple fluorite within the vein (Fg-p stage), with associated fluid inclusions indicating 135 o C for deposition from a low salinity fluid, and 2) yellow fluorite and barite stage (Fy-Ba) filling the vein and forming the stratiform deposit. Fluid inclusions depict a mineralising brine at 110 o C. The 87 Sr/ 86 Sr and 143 Nd/ 144 Nd isotopic ratios measured in the fluorite are compared to those of French Massif Central rocks. The ratios in green and purple fluorite are similar to those of monzogranite and granodiorite of the basement; those measured in yellow fluorite involve the granulites and other meta- morphic rocks of the basement. Measurements of the Sr isotopic ratio and 34 SCDT in barite and D in fluorite fluid in- clusions suggest a deposition process by the mixing of a hydrothermal fluid with meteoric water. At the scale of the northern Massif Central district, the successive hydrothermal fluid salinities are highly con- trasted as in Chaillac deposit. We propose that the two types of hydrothermal fluids have been produced by the boiling of a single fluid at depth.

International audience; The Chouichiat peraluminous structure, located in the northern domain of the Bou Azzer – El Graara (Central Anti-Atlas, Morocco), outcrops as a discontinuous whitish ridge 10 to 60 m wide extending E–W for more than 2 km. This structure coincides with a large reverse-sense steeply dipping shear corridor, marked by penetrative schistosities and folds. The Chouichiat structure displays a strong zoning due to the combined effects of metamorphism, hydrothermal alteration, and deformation of a rhyodacite protolith. It has 1) a central quartz–pyrophyllite zone, surrounded on both sides by 2) a pyrophyllite–quartz -rich proximal zone with small amounts of diaspore, kaolinite and zunyite, and spots of hematite, and 3) a distal pyrophyllite zone with quartz–pyrophyllite in smaller amounts, common hematite and diaspore. The zoning expresses the gradual transformation of rhyodacite to pyrophyllitic rocks, enhanced by the development of the shear zone, which has strongly increased the permeability owing to fluid–rock reaction. Such an interaction is represented by a set of reactions, the most important of which is the hydrolysis of white mica in the rhyodacite to produce pyrophyllite: 2KAl2AlSi3O10(OH)2 + 6 SiO2 + 2H+ ! 3Al2Si4O10 (OH)2 + 2K+. A decrease in temperature and an increase in silica activity led to replacement of early diaspore by pyrophyllite. Zunyite crystallized later, mostly at the interface between proximal and distal zones, together with spectacular rosettes of fibroradial hematite. The main kaolinite – pyrophyllite – quartz assemblage likely was generated around 273° ± 10°C and 1 kbar. Mass-balance calculations indicate a significant leaching of mobile elements, promoting the residual concentration of Al, and a substantial addition of silica, both due to hydrolysis of aluminum silicates. The pyrophyllite – diaspore – zunyite assemblage is characteristic of hydrothermally altered aluminous felsic volcanic rocks and very similar to rocks altered by acidic fluid associated with gold-bearing epithermal ore deposits.

A comparative study of French hydrothermal sulfide deposits shows how paragenetic studies and Pb isotope geochemistry are complementary tools in the understanding of inheritance and recycling phenomena in metallogenesis. The sulfide deposits are a major result of interaction between earlier ore deposits and later remobilizing hydrothermal fluids. These interactions have a different expression depending on whether the earlier ore deposits or the remobilizing fluids, or both, were Pb bearing or not. The type of the ore minerals and the shape of the Pb isotope pattern of a mineral deposit, which is based on the distinct isotopic signatures of the various Pb-bearing events, are governed by these different interactions.On the scale of an ore deposit consisting of several successive parageneses, detailed paragenetic studies serve to distinguish the various parageneses, each of which is usually the result of a specific metallogenic process with its own Pb isotope composition. Pb isotope analyses then establish any relationships between these successive parageneses. When all parageneses have Pb-bearing minerals, one can estimate the degree of contamination of a later stage paragenesis (newly introduced Pb) by lead that was remobilized or recycled from earlier parageneses. Thus, the Pb isotope heterogeneity of an ore deposit generally results from a polyphase history with associated inheritance phenomena that calls on several sources. When lead is present throughout a complex mineral deposit but its isotopic-lead composition is homogeneous, then the later parageneses have simply recycled the earlier Pb. In some cases of layered epithermal barite-galena veins, such homogeneity means that the successive parageneses belonged to a single metallogenic event, usually without any tectonic break between the various parageneses.When considering metallogeny on a regional scale, this complementary approach of comparing Pb isotope geochemistry and parageneses can reveal regeneration phenomena, as is well represented by the hybrid Pb-Sb veins of the French Massif Central, where Pb, Sb, and S were inherited from older deposits.Pb isotope analyses on the scale of individual mineral grains, carried out on galena as well as on other Pb-bearing minerals and on berthierite, all of which have well-defined places in the paragenetic sequence, not only can quantify remobilization phenomena but also can demonstrate genetic relationships between deposits of different age in the same district.This, in turn, leads to an estimate of the weight of the recycled metals of a mineral deposit (the "ore source"), relative to that of metals newly extracted from rocks by hydrothermal fluids (the "lithologic source"). This method, which has proven to be valid for most of the sulfide deposits in France, can be applied to any other mineral deposit or mineral district with a complex metallogenic history.

International audience; Draa Sfar is a Visean, stratabound, volcanogenic massive sulphide ore deposit hosted by a Hercynian carbonaceous, black shale-rich succession of the Jebilet terrane, Morocco. The ore deposit contains 10 Mt grading 5.3 wt.% Zn, 2 wt.% Pb, and 0.3 wt.% Cu within two main massive sulphides orebodies, Tazakourt (Zn-rich) and Sidi M'Barek (Zn–Cu rich). Pyrrhotite is by far the dominant sulphide (70 to 95% of total sulphides), sphalerite is fairly abundant, chalcopyrite and galena are accessory, pyrite, arsenopyrite and bismuth minerals are rare. Pyrrhotite is monoclinic and mineralogical criteria indicate that it is of primary origin and not formed during metamorphism. Its composition is very homogeneous, close to Fe7S8, and its absolute magnetic susceptibility is 2.10− 3 SI/g. Ar–Ar dating of hydrothermal sericites from a coherent rhyolite flow or dome within the immediate deposit footwall indicates an age of 331.7 ± 7.9 Ma for the Draa Sfar deposit and rhyolite volcanism. The Draa Sfar deposit has undergone a low-grade regional metamorphic event that caused pervasive recrystallization, followed by a ductile–brittle deformation event that has locally imparted a mylonitic texture to the sulphides and, in part, is responsible for the elongated and sheet-like morphology of the sulphide orebodies. Lead isotope data fall into two compositional end-members. The least radiogenic end-member, (206Pb/204Pb = 18.28), is characteristic of the Tazakourt orebody, whereas the more radiogenic end-member (206Pb/204Pb not, vert, similar 18.80) is associated with the Sidi M'Barek orebody, giving a mixing trend between the two end-members. Lead isotope compositions at Draa Sfar testify to a significant continental crust source for the base metals, but are different than those of the Hajar and South Iberian Pyrite Belt VMS deposits. The abundance of pyrrhotite versus pyrite in the orebodies is attributed to low fO2 conditions and neither a high temperature nor a low aH2S (below 10− 3) is required. The highly anoxic conditions required to stabilize pyrrhotite over pyrite are consistent with formation of the deposit within a restricted, sediment-starved, anoxic basin characterized by the deposition of carbonaceous, pelagic sediments along the flank of a rhyolitic flow-dome complex that was buried by pelitic sediments. Deposition of sulphides likely occurred at and below the seafloor within anoxic and carbonaceous muds. Draa Sfar and other Moroccan volcanogenic massive sulphide deposits occur in an epicontinental volcanic domain within the outer zone of the Hercynian belt and formed within a sedimentary environment that has a high pelagic component. In spite of the diachronous emplacement between the IPB deposits (late Devonian to Visean) and Moroccan deposits (Dinantian), all were formed around 340 ± 10 Ma following a major phase of the Devonian compression.

International audience; Draa Sfar is a siliciclastic–felsic, volcanogenic massive sulphide (VMS) Zn–Pb–Cu deposit located 15 km north of Marrakesh within the Jebilet massif of the western Moroccan Meseta. The Draa Sfar deposit occurs within the Sarhlef series, a volcano-sedimentary succession that hosts other massive sulphide deposits (e.g., Hajar, Kettara) within the dominantly siliciclastic sedimentary succession of the lower Central Jebilet. At Draa Sfar, the footwall lithofacies are dominated by grey to black argillite, carbonaceous argillite and intercalated siltstone with localized rhyodacitic flows and domes, associated in situ and transported autoclastic deposits, and lesser dykes of aphanitic basalt and gabbro. Thin- to thick-bedded, black carbonaceous argillite, minor intercalated siltstone, and a large gabbro sill dominate the hanging wall lithofacies. The main lithologies strike NNE–SSW, parallel to a pronounced S1 foliation, and have a low-grade, chlorite–muscovite–quartz–albite–oligoclase metamorphic assemblage. The Draa Sfar deposit consists of two stratabound sulphide orebodies, Tazakourt to the south and Sidi M'Barek to the north. Both orebodies are hosted by argillite in the upper part of the lower volcano-sedimentary unit. The Tazakourt and Sidi M'Barek orebodies are highly deformed, sheet-like bodies of massive pyrrhotite (up to 95% pyrrhotite) with lesser sphalerite, galena, chalcopyrite, and pyrite. The Draa Sfar deposit formed within a restricted, sediment-starved, fault-controlled, anoxic, volcano-sedimentary rift basin. The deposit formed at and below the seafloor within anoxic, pelagic muds. The argillaceous sedimentary rocks that surround the Draa Sfar orebodies are characterized by a pronounced zonation of alteration assemblages and geochemical patterns. In the more proximal volcanic area to the south, the abundance of medium to dark green chlorite progressively increases within the argillite toward the base of the Tazakourt orebody. Chlorite alteration is manifested by the replacement of feldspar and a decrease in muscovite abundance related to a net addition of Fe and Mg and a loss of K and Na. In the volcanically distal and northern Sidi M'Barek orebody alteration within the footwall argillite is characterized by a modal increase of sericite relative to chlorite. A calcite–quartz–muscovite assemblage and a pronounced decrease in chlorite characterize argillite within the immediate hanging wall to the entire Draa Sfar deposit. The sympathetic lateral change from predominantly sericite to chlorite alteration within the footwall argillite with increasing volcanic proximity suggests that the higher temperature part of the hydrothermal system is coincident with a volcanic vent defined by localized rhyodacitic flow/domes within the footwall succession.

In the Saint-Aubin-des-Châteaux quarry (Armorican Hercynian belt, western France), an epigenetic hydrothermal alteration affects an oolitic ironstone layer intercalated within the Lower Ordovician Gres armoricain Formation. The hydrothermal overprint produced pervasive and massive sulphidation with stratoid pyritised lenticular bodies within the oolitic ironstone layer. These sulphide lenses are spatially associated with strike-slip faults and extend laterally from them. After the massive sulphidation stage (Fe–As, stage 1), subsequent fracturing allowed the deposition of base metals (stage 2) and Pb–Sb–Au (stage 3) parageneses in veins. The dominant brittle structures are vertical extension veins, conjugate shear veins and strike-slip faults of various orders. All these structures are filled with the same paragenetic sequence. Deformation analysis allows the identification of structures that developed incrementally via right-lateral simple shear compatible with bulk strain affecting the Central Armorican Domain. Each increment corresponds to a fracture set filled with specific parageneses. Successive hydrothermal pulses reflect clockwise rotation of the horizontal shortening direction. Geothermometry on chlorite and arsenopyrite shows an input of hot hydrothermal fluids (maximum of 390–350°C) during the main sulphide stage 1. The subsequent stages present a marked temperature drop (300–275°C). Lead isotopes suggest that the lead source is similar for all hydrothermal stages and corresponds to the underlying Neo-Proterozoic basement. Lead isotope data, relative ages of deformation and comparison with neighbouring deposits suggest that large-scale fluid pulses occurred during the whole Hercynian orogeny rather than pulses restricted to the late Hercynian period. The vicinity of the Hercynian internal domain appears as a key control for deformation and fluid flow in the oolitic ironstones, which acted as a chemical and structural trap for the hydrothermal fluids. The epigenetic mineralisation of Saint-Aubin-des-Châteaux appears to be very similar to epigenetic sulphidation described in banded iron formation-hosted gold deposits.

The Meillers “quartzite” deposit represents a major hydrothermal siliceous sinter, some 50 m thick and covering an area of some 30 ha within Autunian sandstone of the northern Massif Central. This siliceous sinter comprises three facies of microcrystalline quartz: (i) a dark-colored facies (black chalcedony), locally rich in pyrite, at the base, (ii) a gray-brown fairly massive facies (gray-brown chalcedony) in the middle; and (iii) a white, finely banded, facies (white chalcedony) at the top. Orientation measurements of the banding have revealed the paleo-flow channels of the silica-saturated fluids. The geochemistry of the deposits shows modest metal values, in particular for gold (average of 0.58 g/t Au, giving a gold metal content of some 20 t). The hydrothermal event is stratigraphically well correlated with the basal Autunian (around 295 Ma); an age that has been confirmed through radiochronological determination (300±21 Ma; SHRIMP on hydrothermal zircon). The lead isotopic composition is not very radiogenic (206Pb/204Pb=18.20) and is similar to that of the Late Hercynian gold lodes in the Massif Central. The mineralized sinter appears to have derived from a geyser-type hot springs. This hydrothermal activity coincides with the auriferous metallogenic peak that occurred in the Hercynides around 300 Ma. This is the first known epithermal-type surface manifestation described for the Hercynian gold event.

The N–S Jacobina foreland basin is a Paleoproterozoic basin (2080 to 1900 Ma) of stacked detrital and schist formations developed along a sinistral wrench–overthrust fault of the Transamazonian orogeny. At least five successive stages are identified in the westward progradation of the basin, wherein bedding-parallel strike–slip thrusts and prograde metamorphism indicate progressive involvement in the Transamazonian collision. Shearing and associated metamorphic recrystallization indicate a high geothermal gradient and a gradual loading of the underthrust units, with those to the east being deeper seated than those to the west. Basic–ultrabasic dykes and granite stocks cross-cut the lithologies and contributed to the thermal evolution. Conglomerates and chaotic breccia layers found in several formations mark periods of tectonic instability accompanied by erosion of the earlier stages of basin development. Multistage hydrothermal activity is indicated by a widespread alteration with gold-bearing quartz lodes, conglomerates showing a sulphide–gold–Cr–mineral association, leaching of ultrabasic rocks, and emerald mineralization related to late-tectonic granite emplacement. The economic gold-bearing clastic sediments (conglomerates and minor quartzites deposited during the fourth unit/stage of basin development) have generally been interpreted according to the "modified paleoplacer" model. Such a model, which implies the existence of a gold preconcentration within the quartz–pebble conglomerates, is supported by the lithological controls, reworked pebbles (e.g. cataclastic quartz, quartz–pyrite mylonite and rare fuchsite-bearing rocks) that had been hydrothermally altered during an earlier hydrothermal stage, and lead isotopic compositions revealing an Archean inheritance that is partly preserved in galena inclusions. New basin-scale structural and metallogenic data obtained by the authors, suggest a basin model characterized by successive cycles of sedimentation–faulting/thrusting–erosion ("cannibalism" model) that favours both a "paleoplacer" model and a "mesothermal shear-zone-related epigenetic" model. Heterochronous shear zones, formed between 1988 and 1912 Ma during the development of the basin, acted as feeder zones for postsedimentary mesothermal quartz–tourmaline–muscovite/fuchsite lodes, which constitute a possible source of the reworked hydrothermally altered pebbles. These shear zones controlled (a) an acid leaching of the sediments and the subsequent development of Al-rich assemblages interpreted as advanced argillic alteration zones, and (b) a sulphidation process affecting detrital ilmenite and magnetite and responsible for the high concentration of gold within shear veins containing assemblages of Cr–Ni-bearing minerals (euhedral chromite, Cr–rutile, linnaeite, Cr–tourmaline and fuchsite) and euhedral pyrite that crystallized over andalusite. The conglomerates, with their pore and fissure permeability, acted as a "reservoir and trap" for the mineralizing fluids to give a "hydrothermal shear-reservoir" model.

Lead isotope analyses have been performed on the two major Miocene mining districts of Romania, Baia Mare and Apuseni Mountains. These two districts have different non-overlapping 206Pb/204Pb isotopic signatures ranging from 18.752 to 18.876 and 18.497 to 18.740. In the Baia Mare district, epithermal deposits are overall homogeneous in their lead isotopic compositions and have values similar to the average of the calc-alkaline volcanic rocks. These results suggest a magmatic signature for the Pb (and possibly other metals) in the hydrothermal fluids. However, magmas in this district show isotopic evidence of crustal assimilation. In the southern Apuseni Mountains, the lead isotope compositions of sulfide minerals in porphyry copper deposits are clustered, confirming that Pb, and probably other metals, were derived principally from associated porphyry stocks. On the other hand, lead isotope data on sulfides in epithermal ore deposits are much more scattered, indicating a notable contribution of Pb from local country rocks. In the Apuseni Mountains, 'fertile' volcanics are few and appear to come from a more primitive mantle-derived source. Most of the analysed volcanic rocks seem 'barren'. Differences in lead isotopic compositions between the Baia Mare district and the Apuseni Mountains are due to a different basement, and probably to variations in crustal assimilation superimposed on variations in the mantle source composition. In the Apuseni Mountains, Pb may be partly inherited from the previous Mesozoic magmatic–hydrothermal stage. From a geodynamic point of view, it seems that the nature and the source of volcanic rocks and their position related to the collision area of the Carpathian arc are not the only factors controlling the 'fertility' of a volcanic district.

Lead isotope study has been performed on massive sulphide deposits of Ossa-Morena and Aracena Belt (South Iberia). Results suggest the existence of at least two ancient hydrothermal events. The first one, Upper Brioverian in age (∼600–570 Ma), gave birth to Maria-Luisa and Puebla de la Reina massive sulphide deposits; it thus confirms the existence of a Cadomian orogen in South Iberia. Isotopic compositions indicate a local contribution of mantle-derived material (Maria Luisa mine), confirming the presence of ancient oceanic crust in Aracena Belt. This mineralising event seems to extend till the Armorican Massif. The second episode, Eo-Hercynian in age (∼400–350 Ma) has allowed genesis of massive sulphide deposits of la Nava Paredon and Aguas Blancas, and could be coeval with the emplacement of South-Iberian massive sulphide ore deposits in the neighbouring South-Portuguese Zone. A more continental crustal source for later ore deposits could explain the much more important metal accumulation in this zone. To cite this article: E. Marcoux et al., C. R. Geoscience 334 (2002) 259–265.

The Au-Ag (-Pb-Zn) Apacheta deposit is located in the Shila district, 600 km southeast of Lima in the Cordillera Occidental of Arequipa Province, southern Peru. The vein mineralization is found in Early to Middle Miocene calc-alkaline lava flows and volcanic breccias. Both gangue and sulfide mineralization express a typical low-sulfidation system; assay data show element zoning with base metals enriched at depth and higher concentrations of precious metals in the upper part of the veins. Three main deposition stages are observed: (1) early pyrite and base-metal sulfides with minor electrum 1 and acanthite; (2) brecciation of this mineral assemblage and cross-cutting veinlets with subhedral quartz crystals, Mn-bearing calcite and rhombic adularia crystals; and finally (3) veinlets and geodal filling of an assemblage of tennantite/tetrahedrite + colorless sphalerite 2 + galena + chalcopyrite + electrum 2. Fluid inclusions in the mineralized veins display two distinct types: aqueous-carbonic liquid-rich Lw-c inclusions, and aqueous-carbonic vapor-rich Vw-c inclusions. Microthermometric data indicate that the ore minerals were deposited between 300 and 225 °C from relatively dilute hydrothermal fluids (0.6-3.4 wt% NaCl). The physical and chemical characteristics of the hydrothermal fluids show a vertical evolution, with in particular a drop in temperature and a loss of H2S. The presence of adularia and platy calcite and of co-existing liquid-rich and vapor-rich inclusions in the ore-stage indicates a boiling event. Strong H2S enrichment in the Vw-c inclusions observed at -200 m, the abundance of platy calcite, and the occurrence of hydrothermal breccia at this level may indicate a zone of intense boiling. The vertical element zoning observed in the Apacheta deposit thus seems to be directly related to the vertical evolution of hydrothermal-fluid characteristics. Precious-metal deposition mainly occurred above the 200-m level below the present-day surface, in response to a liquid/vapor phase separation due to an upward boiling front.

International audience; Anisotropy of magnetic susceptibility (AMS) determinations and trace-element analyses have been firstly carried out, at Chaillac, on two ferruginous sandstone sections of hydrothermal and lateritic origins, respectively. The goethite has been identified as the main AMS carrier. Distinct AMS patterns and characteristic Ti-As anomalies have been observed, which allows to quantify the importance of hydrothermal and lateritic processes when both are superimposed. These preliminary results show that the 'Fe-Ba complex' of hydrothermal origin at Chaillac has been lateritized for a few meters from the present erosion surface.

Mineralogical and fluid-inclusion studies have been conducted on Mn-rich breccias from three low-sulfidation epithermal gold deposits, Cirotan (Indonesia), Orcopampa (Peru) and Cavnic (Romania). In these deposits, the manganiferous minerals occur within cockade breccias that precede most of the deposition of sulfide. Cockade breccias consist of a lithic or sulfide nucleus, a few centimeters across, encrusted by several concentric envelopes that can be subdivided into three successive zones. Each zone may be composed of several stacked sequences of deposition. The Mn minerals are mainly clustered within the internal pinkish zone close to the nucleus, that also comprises quartz, “adularia” and sparse sulfides. Within this Mn mineral zone, each sequence begins with the deposition of Mn silicate, close to the rhodonite end-member (MnSiO 3 ), that fully or partially grades into Mn carbonate, close to the rhodochrosite (MnCO 3 ) end-member, before the deposition of the next sequence. The intermediate zone (the quartz–sulfide zone) consists of quartz–sulfide sequences, with minor Mn silicates. Each sequence begins with fine-grained quartz, indicating a high rate of nucleation, which becomes coarser grained and irregular at the end of the sequence. Chlorite and sulfides are associated with quartz at the end of this zone. The external zone of the cockades is characterized by comb quartz, associated with illite, calcite and, sparingly, manganoan dolomite. The mineralogical zonation illustrated by the cockades expresses a general evolution of the depositional process with time, with a progressive Mn-depletion and Ca-enrichment. No kutnohorite has been observed. Fluid inclusions from the three zones are all two-phase aqueous inclusions (L + V). The fluid salinities are similar in all the deposits and do not exceed 2.6 wt% NaCl eq., the final comb quartz from Orcopampa excepted. Two isenthalpic boiling events are recorded in relation with brittle deformation. The replacement of rhodonite by rhodochrosite revealed in each sequence of the Mn mineral zone could result in a temperature drop in relation to these boiling events, which release CO 2 and increase pH.

The stringer zones and commonly the interaction zone at the base of the massive sulphide mounds in the Iberian Pyrite Belt contain bismuth and cobalt minerals that are not found in the overlying massive sulphides. These are fairly rare cobalt sulphoarsenides (cobaltite, alloclasite, galucodot) that were formed at the beginning of the massive sulphide genesis, and fairly common bismuth sulphides (bismuthinite, hammarite, wittichenite, cosalite, kobellite, joseite, etc.), including species rare at world scale (nuffieldite, giessenite, jaskolskiite) that were deposited from last stage high-temperature (> 300 °C) copper-bearing fluids containing Bi (Te, Se). The last stage fluids precipitated chalcopyrite containing Cu, Bi, Te, (Se) sulphosalts at the base of the sulphide mound to form a high cupriferous zone. Their interaction with the massive sulphides is reflected by the formation of an exchange zone, a few metres thick, showing chalcopyrite disease textures, at the base of the mound; this zone forms the upper limit of potentially economic copper enrichment and of bismuth minerals. Gold is undoubtedly in part, if not totally, related to this last phase. The bismuth concentrations being equivalent in the massive sulphides and the stringers, the presence of bismuth minerals in the stringer zones results from high-temperature conditions combined with a rarity of galena, which impedes absorption of available Bi. The distribution of these bismuth minerals provides a basic mineralogical zoning in the stringer zone, with a deep, low-aS2 zone containing native bismuth and tellurides and a shallow, higher-aS2 zone in contact with the massive ore sensu stricto and containing complex bismuth sulphides. These results make it possible to distinguish between sulphide veinlets belonging to stockwork zones of massive orebodies and veinlets of an ambiguous nature, and provide mineralogical criteria for the proximity of copper-rich zones. They enrich the very complex mineralogy of the Iberian Pyrite Belt.