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Le fantastique gisement de tungstène de Panasquera (Portugal), d’âge varisque, est depuis longtemps l’objet d’études géologiques. Les travaux récents qui lui ont été consacrés ont mis en jeu les techniques et les concepts les plus modernes. Marignac et Cathelineau, eux-mêmes acteurs de ces travaux, proposent une lecture critique, aiguisée, de cette minéralisation péri-granitique.

International audience; In the Neoproterozoic Arabo-Nubian Shield, the mined gold in the Ariab district (Red Sea Hills, Sudan) is in gossans reconcentrating primary gold overprinted over volcanogenic massive sulphide (VHMS) deposits, formed in the context of a Tonian ensimatic arc of the Haiya terrane. All the primary gold occurrences of the Ariab belt, whatever their style (VHMS-, quartz lode- or shear-zone-hosted), appear to have been syn-to late-kinematic, i.e., formed in the context of the final Pan-African collision leading to the Arabian-Nubian Shield (D3 event). Gold concentration occurs as native gold or electrum deposited in late (syn- to post-metamorphic) tectonic features, usually in sets of (micro)cracks, mostly within earlier pyrite or arsenopyrite. It is associated with either galena or bismuth tellurides. Gold deposition occurred in relation to an intense fluid circulation of metamorphic CO2-H2O rich fluids, which underwent significant strong decompression from lithostatic to hydrostatic pressures. Decompression and temperature decrease and dilution are probably at the origin of gold deposition, although no clear evidence of unmixing of the volatile was observed. The late-D3 gold event in the Ariab belt has all the makings of an orogenic gold system, notably similar to the Late Carboniferous gold event in the West European Variscan belt. Thus, it is possible to propose that, at the end of the collision events, fluids released from the newly formed terrane root were channelled towards the upper crust through the major D3 shear zones (the Oko shear zone for the Ariab belt). The fluids outpouring from these major drains were then conveyed through fault plays and damaged zones, up to specific chemical traps within massive sulphide ore bodies or quartz veins systems. Thus, the Ariab gold district could be classified as a representative of the class of orogenic gold deposits.

International audience; The Bou Jaber ore deposit is one of the numerous diapir-related Pb–Zn–F–Ba deposits of the Dome Zone in Northern Tunisia. Its location is controlled by the regional NE-SW Tajerouine Fault.Ore minerals are hosted in the Late Aptian limestones (Serdj Formation) as open space filling and stratabound replacement bodies. According to Bouhlel et al. (2016), the poly-phase mineralization resulted from the successive activity of three mineral systems, a Pb–Zn, then a barite, and eventually a fluorite deposition system. The latter, from the Late Miocene, is demonstrated in the present study.The fluorite system is characterized by the involvement of oil in the hydrothermal fluids. This oil was produced in the local environment of the deposit from the thermal maturation of the Albian Fahdene black shale source-rock at temperature range of~140 °C–~100 °C. Two brines were involved in the fluorite hydrothermal system. The first one (L1) is a Ca-rich brine (≥20 wt % bulk salinity), with Na/Ca ≤ 0.18, which is thought to have long resided in the basement, before its transfer into the Jurassic reservoir (Upper Nara Formation) and its eventual mobilization at the time of ore deposition. The second brine (L2), less saline (≤14 wt % bulk salinity) is more sodic, with Na/Ca up to 0.53, and represents unmodified brine originated from the nearby Triassic salt. The L1 brine was F-bearing, whereas the L2 brine was associated with oil. Fluorite deposition occurred at the estimated shallow depth of 1.7 km from cooling of the L1 brine due to the first isobaric cooling from ~160 °C to 135 °C under sub-lithostatic conditions (36 MPa). This stage is followed by mixing with the newly incoming L2 brines (transporting oil) along a sub-isochoric decompression path (down to the hydrostatic pressure at 17 MPa) and continuously cooling from 135 °C to 125 °C. The cooling and mixing caused fluorite deposition after which a transient heat advection episode (up to 145 °C) caused late calcite deposition prior to the end of hydrothermal circulation.

International audience; The Djebel El Hamra Pb-Zn-Ba-Sr (Hg) deposits in northern Tunisia are hosted in a post-nappe anticline with a core of a Triassicevaporite diapir affected by the NE–SW-trending Ghardimaou-Cap Serrat lineament. Three stages of mineralization occurred inthe Triassic dolostone: stages I and II caused alternating deposition of sulfate (Ba, Sr) and sulfide (sphalerite, galena) minerals;stage III formed late-stage calcite-marcasite-cinnabar. Zebra textures record the syntectonic transition from compression toextension in the Late Tortonian-Messinian interval. Two fluid end-members were involved in sulfate deposition: one lowsalinity(L1, ~3 wt% eq. NaCl) fluid, probably from a meteoric origin, and a Na-Ca-Cl brine (L2, ~22 wt% eq. NaCl) solutionwhich originated from the Triassic diapiric source. A third end-member fluid (L3) with long residence time in the basement wasalso involved in the Pb-Zn deposition. The δ34S values froma cluster of sulfates around +16‰, show a Triassic evaporate source.The sulfur in sphalerite resulted from bacterial sulfate reduction (BSR); however, crystallization in a closed system resulted in arange of δ34S between +1.6 and +26.5‰. The δ34S values in galena (−28.4 to +8.2‰) are consistent with a BSR and thermochemicalsulfate reduction (TSR) origin of the sulfur. Secondary ion mass spectrometry (SIMS) lead isotope data in galena(207Pb/204Pb: 15.595 to 16.193, 206Pb/204Pb: 18.673 to 18.939, 208Pb/204Pb: 38.330 to 40.572) point to local contributions(sedimentary and Cenozoic magmatic rocks) to the main source from the Precambrian basement. Ore deposition occurred at adepth of about 2 km at temperatures between 80 and 250 °C. A shallow magmatic heat source was the cause of these thermalfluctuations.

The Guerioune beryl is green or light green; the color is mainly due to the presence of Cr substituting Al in the beryl structure. The Cr2O3 and V2O3 contents in the Guerioune beryl are higher than in the other beryls of the Sahara region but lower than in the analyzed emeralds from Brazil (Capoierana, Nova Cruzeiro Ribeirao de Fogo). It remains unclear if the chromium in the beryl of Guerioune originated from the mafic rocks of the Laouni metamorphics or had a different origin. The Guerioune tardi-to post-cinematic massif intruded at shallow depth during the Pan-African orogeny (535–520 Ma) the Laouni terrane which is located 230km southwest of Tamanrasset, Algeria (Fig. 1). Guerioune granites are a peraluminous rare metal granites (RMG) poor in phosphorus but hosts beryl occurrences. The post-orogenic granites of Laouni Terrane form a set of small cupolas, aligned along with trending regional fault directed by NE-SW (Fig. 1b). The central part of the Guerioune massif is mainly composed of pink biotite granites that contains rounded enclaves of fine-grained granite. Stockscheider pegmatite type marks the contact to the albite–topaz granite. A muscovite granite and a porphyric biotite microgranite occurs as dike in the NE and NW of the massif. Beryl is found in three different associations: (i) pegmatites occur under quartz vein in muscovite granite (most of the beryl occurrences are associated with this type of pegmatite), (ii) in miarolitic cavities in the pink biotite–granite, and (iii) rarely in pegmatite veins. The micro-thermometric and Raman studies reveal a low salinity of the fluid inclusions ( 500° C. These results are in a total accordance with the hypothesis of magmatic or metamorphic fluids that are responsible of the crystallization of beryl.

The Puy-les-Vignes W deposit, located in the northwestern French Massif Central (FMC), is a rare occurrence of a wolframite-mineralized hydrothermal breccia pipe hosted in high-grade metamorphic gneisses. We present an integrated study of this deposit aiming to characterize the ore-forming hydrothermal system in link with the Variscan late-orogenic evolution of the FMC. Based on a set of representative samples from the host rocks and mineralization, we describe a detailed paragenetic sequence and we provide the major and trace element geochemistry of the granitic rocks and W–Nb–Ta–Sn–Ti oxide minerals, in situ U/Pb and 40Ar/39Ar geochronology, and a fluid inclusion study of quartz and wolframite. We demonstrate that the formation of this W-mineralized breccia pipe results from a multistage development related to four major episodes during the late Carboniferous. The first episode corresponds to the emplacement of an unexposed peraluminous granite at ca. 324 Ma, which generated microgranite dykes exposed at the present-day surface. The second episode is the formation of the quartz-supported breccia pipe and wolframite mineralization at ca. 318 Ma at a paleodepth of 7 km. The mineralizing fluids have a H2O–NaCl–CO2–CH4–N2 composition, a moderate-salinity ( 400 °C) during lithostatic to hydrostatic pressure variations caused by hydrofracturing of the host rocks. Wolframite deposition is interpreted to result from a W-rich intermediate-density magmatic fluid that exsolved from an evolved leucogranite and interacted with volatile-rich metasedimentary country rocks and/or possibly mixed with low-salinity metamorphic fluids of deep origin. The third episode corresponds to magmatic-hydrothermal Nb–Ta mineralization overprinting the W-mineralized system interpreted to be related to the intrusion at ca. 311 Ma of a rare-metal granite, which is part of a regional peraluminous rare-metal magmatism during the 315–310 Ma period. Finally, the last episode corresponds to disseminated Bi ± Au–Ag mineralization emplaced at ca. 300 Ma, which shares similar mineralogical features with late Carboniferous orogenic gold deposits in the FMC. The Puy-les-Vignes W deposit records, therefore, a multistage and long-lived development that extends over a timespan of 25 million years in a regional setting dominated by protracted peraluminous magmatism and high-temperature and low-pressure metamorphism. Although the local environment of ore deposition is atypical, our results show that the mineral assemblages, alteration styles, and fluid characteristics of the Puy-les-Vignes breccia pipe are similar to those of other peri-granitic W deposits in the FMC.

Wolframite has been proposed as a U/Pb geochronometer for direct dating of W mineralisation events, but its isotopic analysis may be hampered by highly variable and low U contents (

The Djilouet complex forms a cupola made up of leucocratic granites associated with Sn-W mineralization. It could represent the Hoggar’s easternmost rare metal granite (RMG) comparatively to those of the Taourirt province in the central Hoggar. It is located in the Djanet terrane, 12 km NE of the town of the same name in the far east of the Tuareg shield in Algeria. The Djanet terrane is made of a thick low-grade (greenschist facies) sedimentary sequence which was intruded by several generations of granitic rocks. The subcircular Djilouet body is made of leucocratic granites with progressive mutual transitions. Most of the outcrop is occupied by a porphyritic coarse-grained biotite granite. A muscovite granite is found in the center of the cupola, whereas a garnet (almandine—spessartite) granite forms a discontinuous rim all around it. Black micas from the biotite granite are lithian annite (“protolithionite”). The white micas from the muscovite granite and the garnet granite are classified as Fe-Li muscovite. The muscovite granite and the garnet granite contain accessory minerals as rutile, xenotime, monazite, zircon, and minerals that may be members of the pyrochlore supergroup. All the facies are leucogranite with high SiO2 content and high K2O-Na2O ratio. They are poor in calcium and in mafic components and have very low phosphorus content (P2O5 ~ 0.1%). The peraluminous composition is low to mild (1.08 1.46). The evolved granites of the Djilouet suite are enriched in Th and U, but the tantalum and the niobium are not highly concentrated (Ta + Nb = 10.4–17.1). The total REE content is low (57–84 ppm), and the patterns are typically wing shaped with a strong negative Eu anomaly and a small tetrad effect. The Sn-W mineralization consists two systems of veins: large quartz veins with ferberite (H/F ~ 0.8) and quartz veinlets or stockworks with homogeneous cassiterite and minor wolframite (H/F ~ 48). The iso-content contours of tin and tungsten, as produced from a sampling covering the whole cupola, overlap very little. The differences which were noted throughout the study between the Taourirt granites and those of the Djilouet suite are to be related to the lithological nature of the crust rather than to a difference in the geodynamic environment.

The main event responsible for the deposition of tungsten at Panasqueira was closely associated with strong tourmalinization of the wall rocks. Tourmaline is coeval with a W-rich rutile (up to 8–10 wt % W), and both minerals record an early introduction of W in the system, just before the main W deposition. Uranium-Pb dating of the rutile by LA-ICP-MS yielded an age of 305.2 ± 5.7 Ma, which is 6 to 10 m.y. older than the K-Ar age of 296.3 ± 1.2 Ma obtained on muscovite, which was therefore not coeval with wolframite. Major and trace element concentration variations in tourmaline record fluid mixing between two end members, both considered to be of metamorphic derivation on the basis of rare earth element profiles. We report evidence for a fluid rich in Co, Cu, Pb, Sc, Sr, V, Cr, Nb, Ta, and Sn interpreted to be of local origin—e.g., well equilibrated with the host formations—and a fluid rich in Li, F, Fe, Mn, and W inferred to be of deep origin and related to biotite dehydration. The second fluid carried the metals (in particular Fe and Mn) that were necessary for wolframite deposition and that were not necessarily inherited from the wall rocks through fluid-rock interaction. Micrometer-scale variations in tourmaline and rutile crystal chemistry are indicative of pulsatory fluid input during tourmalinization.

International audience; The Variscan vein-type Panasqueira W-Sn(Cu) deposit, one of the main tungsten deposits in Western Europe, has a long and complicated geological history. The first vein infillings, which consist of the quartz-wolframite association as well as the first generation of topaz, underwent significant deformation. As a consequence, most fluid inclusions of the earliest hydrothermal event are deformed and destroyed. Two preserved fluid inclusion assemblages are, however, found in the topaz overgrowth band and are dense aqueous-carbonic inclusions as well as dense CO2 dominated fluid inclusions. The P-T conditions of fluid trapping are constrained by using the intersection between isochores, as well as graphite-water equilibrium data and yield the following trapping conditions: 500 ± 20°C and 250 ± 20 MPa. These P-T conditions are incompatible with fluid unmixing. Fluid chemistry results from water-graphite equilibrium, probably in metapelites, at two distinct temperatures: around 450-500°C for the predominant aqueous-carbonic fluid, and higher temperatures of maximal 550°C for the CO2-rich fluid enriched in N2. These P-T estimates are consistent with deep crustal levels around 8-10 km depth and a high geothermal gradient around c. 60°C/km-1. The ascending non-magmatic fluids, enriched in volatiles, are essential in the ore genesis. The high thermal gradients may be related either to new magma pulse after the formation of the Panasqueira granite intrusion or to anomalous heat flux produced by the hot fluids ascending from migmatitic levels present at greater depth. This hypothesis necessitates to consider the role of a crustal weakness, which is attested both by the successive intrusions of several granitic magmas at the same place, and the presence of inherited quartz filled structures so-called Seixo-Bravo found only in the Panasqueira area.

Elucidation of time-space relationships between a given wolframite deposit and the associated granites, the nature of the latter, and their alterations, is a prerequisite to establishing a genetic model. In the case of the world-class Panasqueira deposit, the problem is complicated because the associated granites are concealed and until now poorly known. The study of samples from a recent drill hole and a new gallery allowed a new approach of the Panasqueira granite system. Detailed petrographic, mineralogical, and geochemical studies were conducted, involving bulk major and trace analyses, BSE and CL imaging, EPMA, and SEM-EDS analyses of minerals. The apical part of the Pansqueira pluton consisted of a layered sequence of separate granite pulses, strongly affected by polyphase alteration. The use of pertinent geochemical diagrams (major and trace elements) facilitated the discrimination of magmatic and alteration trends. The studied samples were representative of a magmatic suite of the high-phosphorus peraluminous rare-metal granite type. The less fractionated members were porphyritic protolithionite granites (G1), the more evolved member was an albite-Li-muscovite rare metal granite (G4). Granites showed three types of alteration processes. Early muscovitisation (Ms0) affected the protolithionite in G1. Intense silicification affected the upper G4 cupola. Late muscovitisation (Fe&ndash, Li&ndash, Ms1) was pervasive in all facies, more intense in the G4 cupola, where quartz replacement yielded quartz-muscovite (pseudo-greisen) and muscovite only (episyenite) rocks. These alterations were prone to yield rare metals to the coeval quartz-wolframite veins.

International audience; The W-Sn Maoping deposit and related W-Sn deposits from the world-class Nanling Range in Southeast Chinaformed at ca. 160 Ma and experienced several phases of metal addition and metal redistribution between 160and 130 Ma. Isotopic dating of ore mineral (wolframite) of Maoping demonstrates that W was deposited first,during a hydrothermal event at ca. 160 Ma. Successive fluid episodes, at ca. 156 Ma (Mo and Sn-rich fluid) and152 Ma (REE-rich fluid), resulted in the formation of REE- and Fe-Cu-Zn-sulfide minerals. A last fluid eventoccurring at ca. 130 Ma was responsible for the deposition of Zr-REE-Nb-Ta minerals that are attributed tomagmatic fluids derived from unexposed magmatic bodies. The three episodes of fluid circulation post-dating Wdeposition resulted in partial to complete resetting of the isotopic systems (mica, wolframite, xenotime), whichare conventionally used for dating such deposits. We show that W and Sn mineralization in the Nanling Rangeformed during a unique fluid event at ca. 160 Ma. Later fluid episodes redistributed the previously depositedmetals and sequentially introduced additional metals, including Mo-Sn, Fe-Cu-Zn, and Zr-REE-Nb-Ta. Directdating of paragenetically well-constrained minerals is therefore critical for determining the age and the durationof mineralizing processes and for characterizing the fluid evolution of magmatic-hydrothermal systems, as exemplifiedin the Nanling Range.

The Hoggar shield belongs to the 3000 km-long Pan-African Trans-Saharan belt that was formed in the Neoproterozoic, between 750 and 500 Ma by continental collision between the converging West African craton, Congo craton and Saharan Metacraton. More than 600 gold occurrences have been identified by ORGM, which are confined along North-South Pan-African megashear zones stretching some hundreds of kilometres long. Until now, no global classification and mineral paragenesis characterisation have been proposed for the Hoggar's gold mineralization. In this paper, we briefly review the main gold mineralization, in order to classify them and to highlight their characteristics and controls. According to field work, spectral, microscopic and microthermometric studies, these mineralization can be globally classified asorogenic type shear zone, which can subdivided into three main sub-types according to the degree of their relationships with the major Pan-African shear zones: (i) Ultramylonite-mylonite hosted including Tirek and Amesmessa, world class deposits; (ii) Granite hosted, including Tekouyat occurrence (iii) Volcano-sediment hosted including Tiririne and In Abbegui deposits. All the deposits are coeval and were formed at the end of the post-collisional stage (530–520 Ma). InHoggar, gold mineralization depend on a double control, first order giant sub-meridian shear zone control and the gold districts disposed in N40°–50°E corridors that may be interpreted as extensional. Indeed, the Hoggar gold province appears to have been controlled at all scales by the late transtensive reactivation of the Pan-African mega-shear zones, and by the correlative heat flux associated with the linear lithospheric delamination processes accompanying this reactivation; which are also responsible for the very lateHoggar magmatic events. At Amesmessa, gold deposition was promoted by the mixing of metamorphic fluids issued from the In Ouzzal Archean-Proterozoic basement with magmatic, basinal and meteoric-derived water. These deposits and occurrences contains variable minerals and trace elements in order of decreasing importance: Pb, Zn, Cu, Ag, Bi, W, Te,Co, Cr, Mo, Ni, Nb, Ta, U, Hf, REE, PGE.

The Beauvoir granite (Massif Central, France) represents an exceptional case in the European Variscan belt of a peraluminous rare-metal granite crosscutting an early W stockwork. The latter was strongly overprinted by rare-metal magmatic-hydrothermal fluids derived from the Beauvoir granite, resulting in a massive topazification of the quartz-ferberite vein system. This work presents a complete study of primary fluid inclusions hosted in quartz and topaz from the Beauvoir granite and the metasomatized stockwork, in order to characterize the geochemical composition of the magmatic fluids exsolved during the crystallization of this evolved rare-metal peraluminous granite. Microthermometric and Raman spectrometry data show that the earliest fluid (L1) is of high temperature (500 to >600°C), high salinity (17–28 wt.% NaCl eq), and Li-rich (Te1–104 ppm) in rare-metals (W, Nb, Ta, Sn, and Li). This study demonstrates that primary fluid inclusions preserved the pristine signature of the magmatic-hydrothermal fluids in the Beauvoir granite but also in the metasomatized W stockwork, despite the distance from the granitic cupola (>100 m) and interaction with external fluids.

The Early Cretaceous (ca. 130 Ma) Nb-rich and Ta-poor Huangshan suite, South China, includes a series of medium-grained granites that contain Nb-rich mica and very low columbite contents, which are indicative of a potential Nb resource. In addition, the Huangshan suite contains fine-grained granites and aplo-pegmatites in which disseminated Nb–Ta columbite is an ore. Two types of fine-grained microcline-bearing and albite-rich leucogranite sills and dikes were identified. Sills and dikes of leucogranites and aplo-pegmatites intrude the medium-grained granites and surrounding hornfels. The aplo-pegmatites consist of large microcline and quartz crystals that are typically broken and embedded within a foliated albite-rich matrix. Niobium-rich and Mn-poor columbite with Ta# [Ta/(Ta + Nb)] ≤ 0.5 and Mn# [Mn/(Mn + Fe)]

International audience; This paper aims at providing new insights into W-Sn ore-forming processes within one of the largest granitic provinces in the world (Nanling Range, South China), which was emplaced during the Jurassic-Cretaceous period. The origin, composition and pressure-temperature conditions of fluids involved in the W-Sn ore-forming processes have been investigated by microthermometry, Raman spectroscopy, LA-ICPMS, hydrogen isotope analyses of fluid inclusions and oxygen isotope analyses of minerals from the Maoping and Piaotang W-Sn deposits. For each deposit, pre- (quartz), syn- (wolframite and cassiterite) and post-ore (quartz, topaz and fluorite) minerals were studied. In both deposits, the vast majority of fluid inclusions are aqueous with salinities between 0.0 and 12.6 wt. % equiv. NaCl and homogenization temperatures between 136 and 349 °C. A minor proportion (~5%) of inclusions observed in the ore-stage quartz from Maoping have aquo-carbonic compositions. For both deposits, four compositional groups are defined. Early quartz fluid inclusions are characterized by salinities between 0.4 and 9.0 wt. % equiv. NaCl, trapping temperatures between 150 and 350 °C, and pressures between 20 and 150 MPa. LA- ICPMS analyses of these fluid inclusions reveal a wide range of Na, K and Li concentrations, as well as relatively low metal contents (W < 40 ppm). Values of δ18O in quartz range from -3.6 to 5.3 ‰ VSMOW while δD values of the fluid inclusions range from -59 to -51 ‰ VSMOW. The salinity of fluid inclusions in wolframite, cassiterite, topaz and fluorite is between 2.4 and 11.2 wt. % equiv. NaCl, trapping temperatures are between 200 and 600 °C, and pressures range from 20 to 250 MPa. LA-ICPMS analyses of these fluid inclusions reveal higher concentrations of Na, K and Li as well as Cs and metals (e.g. between 10 and 220 ppm W). Values of δ18O in wolframite, cassiterite, topaz and fluorite crystals range from -3.0 to 3.3 3 ‰ VSMOW while δD values of fluid inclusions in these mineral phases range from -78 to -72 ‰ VSMOW. At Piaotang, fluid inclusions in wolframite as well as in post-ore quartz and fluorite have salinities of 5.6 to 12.6 wt.% eq. NaCl, trapping temperatures between 150 and 400 °C and pressures of 20 to 150 MPa. LA-ICPMS analyses of these fluid inclusions reveal similar compositions to early quartz fluid inclusions. Values of δ18O in wolframite and quartz crystals range from -0.8 to 5.2 ‰ VSMOW, while the δD values of fluid inclusions range from -66 to -62 ‰ VSMOW. Collectively, the data suggest the involvement of four aqueous fluid end-members, mixed episodically in the mineralization process: (A) a low-salinity, low-temperature, metal-poor, low-δ18O, low-δD fluid derived from meteoric water; (B) a high-salinity, high-temperature, metal-poor, high-δ18O, low-δD fluid derived from a differentiated peraluminous granitic magma; (C) a high-salinity, high-temperature, metal-rich, lower δD magmatic fluid derived from a more differentiated peraluminous granitic magma; and (D) a high-salinity, high-temperature, metal-rich, high-δ18O, low-δD magmatic fluid. This study shows that multiple fluids with distinct magmatic and meteoric origins were involved in the formation of these W-Sn deposits and that the dilution of metal-bearing magmatic fluids by meteoric fluids was probably the main driver for ore deposition. The common fluid history of the two deposits studied, as well as similarities with other deposits in the Jiangxi province, points towards common ore-forming processes at the regional scale.

International audience; L’ouvrage publié en 1994 dans la collection des DARA contenait l’essentiel des informations acquises sur les techniques d’abattage et de gestion du milieu souterrain (Bailly-Maître, Bruno Dupraz 1994 : 37-74). Depuis cette date, les connaissances ont peu évolué sur ces points précis, mais de nouvelles données sont venues enrichir la réflexion. De nouveaux sites extractifs ont été localisés, des datations ont été obtenues. Une collaboration a été engagée avec des géologues et des géochimistes afin de connaître la nature des minéralisations des sites inventoriés. Jean-Paul Deroin professeur à l’université de Reims, équipe de recherche GEGENAA – CREA (Groupe d’Étude sur les Géomatériaux et Environnements Naturels, Anthropiques et Archéologiques - EA 3795, pôle « AgroSciences, Sciences de l’Univers et Environnement » de l’Université de Reims Champagne-Ardenne - URCA) est venu à plusieurs reprises à Brandes et sur l’ensemble des sites du massif des Rousses. Les rares échantillons de mine...

Abundant W-rich rutile in the tourmalinized wall-rocks from the Panasqueira W-deposit appears to be a marker of the onset of the main wolframite depositing event. Rutile displays spectacular zoning, both sector (SZ) and oscillatory (OZ). An extensive set of compositional data obtained on crystals, beforehand studied using back-scattered electron images and X-ray maps, was used to address (i) the effects of SZ on differential trapping of minor elements, and (ii) the significance of the OZ in deciphering fluid sources and fluid circulation dynamics. Particular attention was paid to Sn, W (Nb, Ta) concentrations in rutile as pathfinders of the W deposition. Concerning the sector zoning, W is more incorporated than (Nb, Ta) onto more efficient faces, whereas Sn contents are nearly not impacted. The net effect of the sector zoning is thus a progressive increase of the relative weight of Sn from pyramid to prism faces, in combination with a less significant increase in the relative weight of Nb + Ta. The oscillatory zoning concerns most minor elements: W, Nb (Ta), Fe, V, Cr and Sn. In the frequent doublets, the clear bands are in general enriched in W relatively to the dark ones, whereas the inverse is true for Nb and Ta. The doublets may be viewed as the result of the successive influx of (i) a W-rich, Nb + Ta poor fluid, abruptly replaced by (or mixed to) (ii) a Nb + Ta-rich and W-poor fluid. The Nb + Ta-rich fluid could be in turn related to a rare-metal granite layer observed atop of the Panasqueira granite.

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International audience; The Koudia El Hamra silver - base metal (Pb-Zn) deposit is located in the Upper Visean - Namurian Sarhlef schist, Jebilet Hercynian Massif (Morocco). Ore bodies consist of N-S to NE-SW quartz-chlorite veins hosted by Hercynian black shale. Mineralogical and paleo-fluid investigations (microthermometry, Raman spectroscopy) and stable isotope data (O, C, S) have shown that high salinity brines (30 to 35 wt% NaCl+CaCl2 equiv.), likely from sedimentary origin deposited base metal (Zn) - carbonate assemblage at minimal temperature around 220°C. Then brines deposited silver ore - galena assemblage at lower salinity (9 to 15 wt% NaCl equiv.) and similar average minimal temperature (around 220°C). The main driving mechanism for silver ore deposition is the dilution of ore-bearing brines by low-salinity fluids probably combined with reduction of brines in the host black shale. Ore brines likely have come from the Permian-Triassic Atlasic basins related to the extension coeval with the Central Atlantic opening. Those brines probably have percolated into the basement through Hercynian faults (N-S to NE-SW) reworked during the Permian-Triassic to Lower Jurassic extensional events. The source of silver seems to be in black shale and/or in abundant mafic to intermediate magmatic rocks (i.e. microdiorite dykes) consistently observed close to the ore bodies. Silver ores are superimposed on the same lineament to preexisting Fe-As-(Sn) assemblages related to Hercynian events in the central Jebilet and mainly due to the circulation of magmatic and/or metamorphic fluids. However, silver ores have no genetic relationship with magmatic-metamorphic events as suggested by former models. The metallogenic model proposed for the Koudia El Hamra deposit is similar to those proposed for several other silver - base metal (Pb-Zn) deposits from Morocco like the Roc Blanc silver deposit (Jebilet massif) and major silver deposits from the Anti-Atlas belt (Imiter, Zgounder and Bou Azzer) and from Western Europe.

We present a complete dataset for major, minor and trace elements in wolframite ([Fe,Mn]WO4) based on the example of several peribatholitic hydrothermal W deposits located in the Variscan French Massif Central (FMC). The wolframite samples were characterized down to the micrometer scale by combining scanning electron microscopy observations and in situ chemical analysis by electron probe microanalyzer and laser ablation – inductively coupled plasma – mass spectrometry. Most samples are Fe-dominated wolframites and are characterized by variable Fe/(Fe + Mn) values for the studied deposits (from 0.36 to 0.86) without significant alteration features. Wolframites present intracrystalline variations for concentrations of several minor and trace elements, principally for Nb, Ta, and Sn, which reflect growth zoning. The minor and trace element compositions of the different wolframite samples show at first order similar enrichments in Ta, Nb, Sn, Zn, and In, as well as depletions in LREE, Li, Th, Ti, Zr, Hf, Pb, V, Co, and Mg, compared to the upper continental crust. Second order compositional variations are observed between the studied deposits, which can be separated in four main regional geochemical groups. This work highlights that the chemical composition of wolframite is controlled by both the crystallochemical parameters and the composition of the primary hydrothermal fluid. The regional variations observed in the geochemical signatures of wolframite reflect local variations in the composition of the hydrothermal fluid, i.e. variable metal sources. Therefore, this suggests that the minor and trace element contents in wolframite likely represent direct markers of the source of the hydrothermal fluid and ultimately of the metals. The comparison between the trace element compositions of wolframite with the compositions of regional granitic rocks and worldwide shales suggests that evolved peraluminous granites represent the main source of metals in peribatholitic hydrothermal W deposits from the FMC, whereas metasedimentary rocks have a limited to no influence on the metal budget.

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We present U-Pb thermal ionization mass spectrometer (TIMS) ages of wolframite from several granite-related hydrothermal W±Sn deposits in the French Massif Central (FMC) located in the internal zone of the Variscan belt. The studied wolframite samples are characterized by variable U and Pb contents (typically

We present U-Pb thermal ionization mass spectrometer (TIMS) ages of wolframite from several granite-related hydrothermal W±Sn deposits in the French Massif Central (FMC) located in the internal zone of the Variscan belt. The studied wolframite samples are characterized by variable U and Pb contents (typically

The Puy-les-Vignes deposit, located in the northwestern part of the French Massif Central, is a remarkable occurrence in the West European Variscan belt of hydrothermal tungsten mineralization associated with a breccia pipe structure. The late stage of the mineralization consists of a mineral paragenesis composed of zircon, xenotime, monazite, Nb-Fe-W rutile, and Nb-Ti-Y-HREE-W-U oxide minerals (hereafter referred to as NTox) within an adularia-tourmaline-chlorite matrix. This study is focused on these rare-metal oxides, which display complex internal textures and uncommon chemical compositions with variable concentrations of Nb, Ti, Y, HREE, and W, not described until now. They are characterized by low microprobe totals (76 to 95%), together with the presence of OH− groups within the crystallographic structure as detected by FTIR spectroscopy, which is interpreted as the result of alteration, such as hydration and/or metamictization. The crystallochemical study shows that these crystals appear as a complex multi-polar solid solution, involving chemical mixing between two groups of binary solid solutions: a first group of anatase-columbite solid solution and a second group of euxenite-(Y)-columbite solid solution. Interpretation of their internal texture and their chemistry suggest that the NTox were formed during multi-phase crystallization in an open system by the mixing of two different hydrothermal fluids: a first fluid (L1) enriched in Ti>Nb, Fe, and W, with the same geochemical signature as the main mineralization, and a second fluid (L2) enriched in Nb>Ti, Fe, Y, REE, and W, with a geochemical signature clearly contrasting with the former and coeval with the crystallization of adularia, xenotime, monazite, zircon, and rutile. This mineral paragenesis is characterized by a P, Y, HREE, Nb > Ta, Ti, Zr, and U geochemical signature, typical of rare-metal peralkaline magmatism, thus suggesting rare-metal mobilization by late hydrothermal fluids with a peralkaline signature, likely derived from an unknown source at depth ( e.g. , NYF pegmatites or related granite), during the late metallogenic stages at Puy-les-Vignes.

The West European Variscan chain is a remarkable illustration of how partial melting marks out the geodynamic evolution of mountain belt through time. Here, we focus on the Late Carboniferous melting events reported in the southeastern French Massif Central (Velay dome), with emphasis on the modes of partial melting, relationships between partial melting and magma emplacement, transition between the melting episodes and related P-T-t path. Following nappe stacking events under medium pressure/temperature conditions (M1 and M2 events), three melting events are identified in the southern envelope of the Velay dome. A first melting episode (M3 event) occurred within the biotite stability field at 325–315 Ma (T ≈ 720°C and P = 0.5–0.6 GPa). It led to the complete disappearance of muscovite and to the formation of migmatites consisting of biotite ± sillimanite melanosome and of granitic/tonalitic leucosomes depending on protolith composition. It is interpreted as the result of internal heating mainly linked to decay of heat producing elements accumulated in a thickened crust. It resulted in the formation of a partially molten middle crust with decoupling between the lower and upper crust, late-collisional extension and crustal thinning.The second episode of melting (M4 event) occurred at ca. 304 Ma (T 800°C and P 0.4 GPa), synchronously with emplacement of the Velay granites and growth of the dome. It led to the breakdown of biotite and growth of cordierite (locally garnet or tourmaline), with formation of diatexites and heterogeneous granites. This high-T event synchronous with crustal extension is considered to result from intrusion of hot mantle-derived and lower crustal magmas triggering catastrophic melting in the middle crust. This event ends with local retrograde hydrous melting within the stability field of biotite close to the solidus in response to local input of water during temperature drop in the late stage of emplacement of the Velay dome.The last evidence of melting in this area (M5 event) corresponds to emplacement of late granites generated under conditions estimated at ≈850°C and 0.4–0.6 GPa. They may have been generated from melting of specific lithologies triggered by injection of mafic magmas. These granites emplaced in a partly cooled crust (medium-grade conditions). The emplacement age of these granites is not well constrained (305–295 Ma) though they clearly post-date the Velay granites.The melting episodes in the Velay area and generation of granites appear to correspond to the conjunction between (i) the effects of collision-related crust thickening and (ii) those related to slab break off and asthenospheric mantle decompression melting. The driving process is mainly the internal radiogenic heat in a first stage, relayed by the propagation of a thermal anomaly initially located in the lower crust (M3 event), but which subsequently rose to the middle and upper crustal levels through magma transfer (M4 event). Overall, the Velay example is a remarkable illustration of the progressive dehydration and sterilisation of a thickened crustal segment. It documents how large amounts of granitic magmas can be produced at shallow crustal levels in relation to the injection of mantle-derived magmas.

International audience; The Nefza mining district in Northern Tunisia comprises late Miocene (Serravallian to Messinian) magmatic rocks belonging to the post-collisional magmatism of the Mediterranean Maghreb margin. They are mainly made up of Serravallian granodiorite (Oued Belif massif), Tortonian rhyodacites (Oued Belif and Haddada massifs) and cordierite-bearing rhyodacites (Ain Deflaia massif) in addition to rare Messinian basalts. They are all characterized by LILE and LREE enrichment and strong enrichment in Pb and W. The Messinian basalts, which are also enriched in LILE, exhibit transitional characteristics between calc-alkaline and alkaline basalts. Geochemical (major and trace elements) and Sr, Nd and Pb isotopic compositions indicate that: (1) granodiorite is linked to the differentiation of a metaluminous calc-alkaline magma derived from a lithospheric enriched mantle source and contaminated by old crustal materials; (2) rhyodacites result from the mixing of the same metaluminous calc-alkaline magma with variable proportions of melted continental crust. Cordierite-bearing rhyodacite, characterized by the highest Sr-87/Sr-86 isotopic ratios, is the magma comprising the highest crustal contribution in the metaluminous-peraluminous mixing and is close to the old crustal end-member; (3) late hasalts, transitional between the calc-alkaline and alkaline series, originated from an enriched mantle source at the lithosphere-asthenosphere boundary. In the Nefza mining district, magmatic rock emplacement has enhanced hydrothermal fluid circulation, leading to the deposition of polymetallic mineralizations (belonging to the Iron-Oxide-Copper-Gold and the sedimentary exhalative class of deposits, among others). Magmatic rocks are also a source for the formation of lead (and probably other metals) in these deposits, as suggested by their Pb isotopic compositions. Magmatic rock emplacement and connected mineralization events can be related to the Late Mio-Pliocene reactivation of shear zones and associated lineaments inherited from the Variscan orogeny.

International audience; The Katanga Copperbelt region of the Democratic Republic of Congo hosts world-class cobalt deposits accounting for similar to 50% of the world reserves. Heterogenite (CoOOH) is the most abundant Co-bearing secondary mineral in the region. Its occurrence is the result of oxidation of Cu-Co-sulfides and associated Co reprecipitation in the uppermost part of the deposits, during the Pliocene. In addition to sediment-hosted copper and cobalt ore deposits, the Katanga Copperbelt also hosts numerous uraniferous mineral occurrences and deposits, which can be associated with heterogenite. Within these deposits, heterogenite can have high concentrations of U (up to 3.5%) and Pb (up to similar to 4%). In situ SIMS U-Pb ages were obtained for heterogenite samples from the U deposits of Shinkolobwe, Kalongwe and Kambove. These analyses yield distinct Neoproterozoic ages, at similar to 876 Ma, similar to 823 Ma and in the similar to 720 to similar to 670 Ma age range. As the geological context prevailing at those times was not favorable for heterogenite formation, these ages most probably record geological events that are not the formation of the mineral itself. For instance, the heterogenites could have inherited the U-Pb signature of a U-rich mineral, most likely uraninite, formed and/or yet reworked at similar to 876 Ma, similar to 823 Ma and in the similar to 720 to similar to 670 Ma time interval and spatially associated with primary Co-sulfides. In this hypothesis, the ages obtained in this paper are significant for understanding the cycling and re-deposition of U at given moments in the regional geological history. In such context, the similar to 876 Ma and the similar to 823 Ma age are consistent with syn-early diagenetic concentration of uranium in sediments of the Katanga basin. The similar to 720 to similar to 670 Ma ages are interpreted as a phase of U remobilization related to hydrothermal fluid circulation induced by late Nguba proto-oceanic rifting or by early stages of Congo-Kalahari craton convergence, and associated hydrothermal circulation.

The Puy-les-Vignes W deposit is an atypical wolframite-bearing hydrothermal breccia pipe hosted in migmatitic biotite-sillimanite gneisses in the northwestern French Massif Central. The deposit is characterized by volumetrically important tourmaline alteration allowing to investigate the fluid evolution of the ore-forming hydrothermal system. Four generations of hydrothermal tourmaline (Tur 1–Tur 4) formed during pre-, syn-, and post-mineralization stages were identified based on detailed petrographic observations and were analyzed in situ for their chemical and boron isotopic compositions. At the grain scale, tourmaline commonly shows oscillatory zoning and dissolution textures resulting from a multi-stage crystallization in a fluid-dominated system. The different generations of hydrothermal tourmaline have dravite-schorl compositions and show similar major and trace element contents falling into the field of metamorphic rocks. High concentrations of V, Cr, Sr and low concentrations of Li, Sn in tourmaline suggest a metamorphic-dominated origin of these elements. The boron isotopic compositions of tourmaline range between −13.3‰ and −7.8‰ and cannot unambiguously distinguish between a magmatic and a metamorphic fluid origin. Our data indicate that the chemical and boron isotopic composition of tourmaline was dominantly controlled by high-temperature fluid-rock interactions between the metamorphic basement and boron-rich, reduced, and low-salinity hydrothermal fluids. Based on these results, we propose a fluid evolution scenario for the Puy-les-Vignes ore-forming hydrothermal system. Release of magmatic-hydrothermal fluids from an unexposed peraluminous leucogranite at ca. 324 Ma is proposed as the main mechanism responsible for early greisenization and formation of disseminated Tur 1. This episode was followed by massive tourmalinization and hydraulic brecciation of the overlying gneisses producing a tourmaline-rich (Tur 2) crackle breccia by interactions with boron-rich hydrothermal fluids. Fluid-assisted reopening and collapse of the former tourmalinite at ca. 318 Ma yielded a matrix-supported quartz-tourmaline breccia pipe and formation of wolframite-bearing quartz veins accompanied by deposition of Tur 3. Finally, post-ore hydraulic fracturing at ca. 300 Ma led to formation of tourmaline-rich microbreccias (Tur 4) possibly from metamorphic fluids.

International audience; Li-micas have been used as indicators of the evolution of granites. However, hydrothermal Li-micas are less documented. World-class W-Sn deposits associated with Early Yanshanian granites (South Jiangxi, China) show magmatic and hydrothermal Li-micas which could help unravelling the magmatic-hydrothermal evolution of rare metal deposits. Six types of Li-micas have been identified in the vein system of the Maoping W-Sn deposit through detailed petrography and EPMA and LA-ICP-MS analyses, by chronological order: (i) late-magmatic Li-micas in feldspar veins, associated with late crystallization of a peraluminous melt; (ii) hydrothermal Fe-Li micas (Fe-Li mica veins and selvages); (iii) hydrothermal Fe-Li micas in W-Sn veins; (iv) Fe-Li micas in later banded quartz veins; (v) Li-muscovite in the final stages; and finally (vi) micas associated with alteration at each stage. Based on oscillatory variations and trends in major elements composition, the chemical variations in Li-micas from the successive stages and in hydrothermal micas that crystallized in the veins are interpreted to reflect mixing between at least three fluids of possible magmatic, meteoric and metamorphic origins. The crystallization of zircons and REE minerals, combined with variations of major and trace element concentrations in the Li-micas, notably an enrichment of rare metals (W-Sn-Ta-Nb) in the Li-micas, implies emplacement of a hidden peralkaline REE-rich magma during the crystallization of the banded quartz veins, a source which was different to the pre-existing peraluminous granites. The possible involvement of both peraluminous and peralkaline intrusives suggests the existence of polyphase magmatic-hydrothermal systems in the Maoping deposit, during the Yanshanian event (190–80 Ma)

The Nefza region (Nappe Zone, northern Tunisia) is known both as a Late Miocene magmatic province and a base-metal district. In this region, small, post-nappe, continental extensional basins (Sidi Driss and Douahria) host syndiagenetic Pb–Zn ore deposits that have been classified as Sediment-Hosted Massive Sulphide (SHMS)–Sedimentary-exhalative (Sedex). In addition to this mineralization, the Nappe zone contains other Pb–Zn and polymetallic deposits that show similarities both to the SHMS-Sedex and MVT deposits of the Dome and Graben zones, namely the “peri-diapiric” deposits of Jebel (Jb) el Hamra, Jalta, and Jebel Ghozlane. All of the Nappe Zone deposits share common characteristics, including: (1) age—the deposits formed between late collisional events (Late Tortonian) and inception of the Early Messinian extensional regime, in the context of the Alpine Maghrebide belt formation; (2) presence of pre-existing sulphates—these were likely the main source of sulphur for the sulphides; and (3) hydrothermal systems leading to their genesis—these testify to alternating influx of cold and warm fluids. The involvement of high temperature fluids are deduced from fluid inclusion studies (Th values of 140–240 °C), whereas the presence of distinctive sphalerite textures (microspherules and colloform textures) and sulphur isotopic compositions demonstrate in situ bacterial sulphate reduction, and consequently deposition at temperatures below 80 °C. These data constitute unifying characteristics for these mineralizations that are in contrast to the features of Pb–Zn(–fluorite) MVT deposits occurring in the Dome and Graben zones of Tunisia. The geodynamic context prevailing during the Late Miocene in the Nappe Zone is the underlying common factor that explains the diversity of ore deposits formed at that time in this region. Most deposits are located in the vicinity of shear zones and associated lineaments inherited from the Variscan orogeny. These deep structures were reactivated by transtensional processes during the Alpine orogeny and controlled post-collisional magmatism, circulation of hydrothermal fluids, and locations of related ore deposits and showings in the Nappe Zone.

In northeast Algeria, the internal Edough massif of the Alpine Maghrebide belt, is an inlier of basement rocks under a cover of Cretaceous (Kabylian) and Cenozoic (Numidian) flysch nappes. During the late Oligocene-early Miocene, the Edough massif was an Oligo-Miocene metamorphic core complex involving the basement rocks (Pan-African gneiss, marble, amphibolite) and its Paleozoic cover. In a short time interval from latest Burdigalian to early Langhian (ca. 17–15 Ma), felsic intrusive rocks were emplaced in the basement and its tectonic cover under progressively shallower conditions (granite to rhyolite) that define the Edough-Cap de Fer magmatic district. At Ain Barbar, during intrusion of microgranites at ca. 16 Ma, a high-enthalpy, liquid-dominated geothermal system was active in the Cretaceous flysch reservoir, with Oligo-Miocene Numidian flysch serving as an impermeable cap. Temperatures as high as ca. 350–375 °C were attained in the deep parts of the Ain Barbar paleogeothermal field, at a depth of ca. 1.3–1.5 km. Input of massive amounts of sodium resulted in the formation of metasomatic plagioclase-rich hornfels (Chaiba domain), whereas higher in the Cretaceous flysch aquifer, invasion of hot fluids (300–270 °C) was associated with hydrothermal metamorphism (quartz-chlorite, calcite-chlorite, wairakite-chlorite, and epidote domains). The source of these hot fluids was a basement of the Edough type, in which advection of heat was likely related to emplacement of a granite batholith at depth. Concomitant with the paleogeothermal circulations, fault activity created N170° E fracture zones that progressively channelled fluid flow, with related development of linear propylitically altered zones and precipitation of Zn–Pb–Cu sulphides at temperatures between 330 and 285 °C. At ca. 15 Ma, renewed magmatic activity (subvolcanic rhyolite dikes) was associated with a new and shallower (ca. 800 m depth) geothermal system, involving the convective circulation of surficial fluids (meteoric and possibly seawater) at temperatures between 300 and 250 °C. Epithermal quartz and sulphides were deposited in the same vein systems as in the previous mineralization stage, but remained uneconomic. However, concomitant formation of massive adularia during alteration of the Chaiba rhyolite produced an economic K-feldspar body mined for ceramics.

Esta es una versión PREPRINT. El artículo final está publicado por GEOFLUIDS y se encuentra disponible en: http://onlinelibrary.wiley.com/doi/10.1111/gfl.12139/abstract, This is a PREPRINT version (pre-refereeing) of the paper: Dyja, V., Hibsch, C., Tarantola, A., Cathelineau M., Boiron M.C., Marignac C, Bartier, D., Carrillo-Rosúa, J., Morales-Ruano, S., Boulvais, P. (2015). From deep to shallow fluid reservoirs: evolution of fluid sources during exhumation of the Sierra Almagrera, Betics, Spain. Geofluids, doi: 10.1111/gfl.12139., Palaeo-fluids trapped in quartz and siderite-barite veins hosted by graphitic schists recorded the fluid and metal transfers during the Neogene exhumation of the Sierra Almagrera Metamorphic Core Complex. First quartz veins registered the ductile then brittle-ductile extensional shearing. The reservoir at that time was wetted by high-salinity fluids with a low density volatile phase resulting from the dissolved Triassic evaporites. Low salinity fluids occurred during the exhumation within the brittle domain as revealed by transgranular fluid inclusion planes affecting previous veins. This suggests an opening of the system and the penetration of surficial fluids from uplifted ranges during Serravalian to early Tortonian times. Transcurrent tectonics generated marine basins since late Tortonian. At depth quartz veins discordant to the foliation were associated to hematite indicating oxydizing conditions. A stop of the low-saline record is revealed by high-salinity Fe-rich fluids issued from the underlying metamorphic reservoir. The Messinian ongoing activity of the sinistral Trans-Alboran tectono-volcanic trend led to the formation of ore deposits. Reducing conditions and Fe-rich fluid led to the formation of siderite and pyrite. The subsequent formation of galena and barite under oxydizing conditions has been related to a probable increase of temperature. A higher salinity and the Cl/Br ratio indicate another source of secondary brine issued from dissolved Messinian evaporites as confirmed by δ34S signature of barite. Transcurrent tectonics clearly modified the hydrogeology of the upper reservoir. The faulting connected the deeper and upper reservoir generally separated by the brittle/ductile transition rheological and hydrogeological barrier under extensional tectonic regimes as confirmed by the stage of low-saline fluids., Université de Lorraine, GeoRessources, CNRS, CREGU, Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Universidad de Granada. Departamento de Didáctica de las Ciencias Experimentales, Universidad de Granada. Departamento de Mineralogía y Petrología, Université de Rennes 1, Géosciences Rennes - UMR CNRS, This work was supported by the Ministry of Higher Education and Research (MESR, France) and the CNRS ST-INSU-CT5 programme.

During the late Oligocene-early Miocene, three main hydrothermal events formed polymetallic deposits of the Edoug-Cap de Fer in the Edough massif of the Alpine Maghrebide belt. At ca. 17 Ma, the Karezas As (lollingite)-F (fluorite)-W (scheelite) deposit formed at a depth of ca. 2 km and temperatures of ca. 450–500 °C, from mixing between magmatic-hydrothermal hypersaline fluids issued from a concealed rare-metal granite and several metamorphic fluids derived from the metamorphic core complex. Slightly later, at ca. 16 Ma, the intrusion of microgranites produced high-enthalpy, liquid-dominated geothermal fields at the basement-Kabylian flysch boundary, with Numidian flysch acting as an impermeable lid and host for “mesothermal” polymetallic vein fields (Ain Barbar, Mellaha, Saf-Saf). Temperatures as high as ca. 350–375 °C were attained in the deep parts of the Ain Barbar field, at depths of ca. 1.3–1.5 km, accompanied by massive input of sodium that formed metasomatic plagioclase-rich hornfels (Chaiba domain); higher in the Cretaceous flysch aquifer, influx of hydrothermal fluids (300–270 °C) produced hydrothermal metamorphic assemblages of quartz-chlorite, calcite-chlorite, wairakite-chlorite, and epidote. The source of these hot fluids was a basement of the Edough type, in which heat advection was likely related to emplacement of a granite batholith at depth. Concomitant with the paleogeothermal circulations, fault activity created N170° E-trending fracture zones that progressively channeled fluid flow, with the development of propylitically altered linear zones and ore precipitation (Zn–Pb–Cu) at temperatures between 330 and 285 °C. At ca. 15 Ma, renewed magmatic activity (subvolcanic rhyolite dikes) was associated with the generation of new and shallow (ca. 800 m depth) geothermal fields, wherein convected surficial fluids (meteoric and possibly seawater) formed “epithermal” deposits including polymetallic quartz veins, quartz-stibnite metasomatic deposits in marble, and quartz-arsenopyrite-gold showings, at mostly lower temperatures of 300–250 °C. Excepting the Karezas skarn, for which a magmatic origin of the tungsten is likely, the metals deposited by the different hydrothermal systems were mainly sourced in rocks of the metamorphic core complex and its tectonically emplaced cover of Cretaceous flysch. Only a minor contribution of metals came from the magmatic rocks, as shown by lead isotope data for the Ain Barbar area. In particular, amphibolite of the Marble Complex in the Edough sequence may have been a major source of copper and the epithermal antimony (and gold?). The Edough-Cap de Fer district is directly linked to the evolution of the Edough metamorphic core complex. Although metallogenic activity began after the end of ductile deformation, metamorphic fluids derived from the core complex seem to have played a key role in the first stages of the hydrothermal circulation and related mineralization (Karezas W skarn, mesothermal polymetallic veins). However, the role of the late Miocene magmatism, induced by collisional processes through slab break-off and/or lithospheric delamination, was of equal importance in the genesis of the Edough-Cap de Fer metallic deposits, being the source of the heat advection responsible for hydrothermal convection during the meso- and epithermal mineralization. Finally, it appears that the transition from extension (related to opening of the Algerian-Provencal oceanic basin) to transpression (when the collision resumed), at the end of the Miocene, was the ultimate control on the mineralizing events in the Edough metamorphic core complex.

The Hoggar massif, a part of the Tuareg shield in the Trans-Saharan Pan-African orogen, is endowed in gold and rare metals (Sn, W, Ta, Be). Most of these metals are present at low levels compared to other Precambrian or collisional belts worldwide, but tantalum is concentrated in a series of evolved granitic cupolas, making the Hoggar a promising tantalum province. The Tuareg shield was built in three stages during the convergence of two cratonic masses, the West African Craton (WAC) to the west and the East Saharan craton to the east. The first stage (730–630 Ma; Cryogenian) involved the accretion of island and continental arcs to several cratons. The second stage (630–580 Ma, Ediacaran) was a collisional event, involving (1) northward escape of the Tuareg terranes between the two main cratons, along N-S mega-shear zones with up to 1000 km of lateral displacement; (2) emplacement of large high-K calc-alkaline (HKCA) linear batholiths resulting from mantle-crust interaction through linear lithospheric delamination along the mega-shear zones; and (3) concomitant high temperature-low pressure metamorphism. As a result, the small Eburnean cratons included in the Tuareg shield (In Ouzzal; Laouini-Azrou-n-Fad-Tefedest-Egere-Aleksod, or LATEA) were more or less reworked (metacratonization). The third stage (575–540 Ma, late Ediacaran) was limited to the eastern Hoggar province, and involved the intracratonic collision of terranes within the margin of the East Saharan metacraton (Murzukian event, Fezaa et al. 2010). Immediately following the Murzukian event (540–520 Ma, terminal Ediacaran-early Cambrian) was simultaneous reactivation of late (transtensional) mega-shear zones, intrusion of high-level granite plutons related to rare-metal mineralization, and inception of crustal-scale hydrothermal systems and gold mineralization. The granite plutons comprise a series of A-type granites that evolved towards F-rich (topaz-bearing) alaskites, and true peraluminous, F–Na–Li-rich rare-metal granites (RMGs), with evidence of mixing between the two lineages. However, only the RMG suites are associated with Sn–W quartz veins, whereas Ta-rich cupolas may be found either in the Taourirt lineage (Tim Mersoi and highly fractionated Rechla cupolas) or in the RMG suites (Ebelekan)—the rare-metal enrichment being, in any case, of magmatic origin. Emplacement of these late granites was controlled either by the mega-shear zones, as in the Iskel island arc terrane, or by secondary shears of various orientation (N10° E, N50° E, N140° E) that dissect the terranes, as in the LATEA metacraton. The quartz-gold deposits are of the “orogenic gold” class and display contrasting relationships with the shear-zone systems, from close spatial associations with mega-shear zones as in the shear-zone-hosted In Ouzzal deposits (Tirek-Amesmessa) and the Iskel showings, to the very distal association with the Raghane shear zone as in the Tiririne deposits, through the connexion with secondary N10° E shear zones of the In Abeggui deposits in the LATEA. In all of the deposits, the hosting quartz veins were plastically deformed prior to gold deposition, which was uniformly a very late event occurring under brittle conditions, typically during extension. Both gold lodes and RMGs were emplaced into evolving stress-strain fields, involving a rotation of the shortening direction (σ1) from ca. N100° E to N30–40° E and finally close to N-S. In addition to rare-metal and gold mineralization, minor fracturing, magma emplacement, and hydrothermal activity are associated with these orientations in the entire Tuareg shield, far to the west of the locus of the Murzukian collision. We therefore conclude that the terminal Ediacaran-early Cambrian Hoggar gold and rare-metal province was controlled, at all scales, by the latest transtensional reactivation of Pan-African mega- and second-order shear zones, following and prolonging the late Ediacaran Murzukian event. Both magmatism and hydrothermal circulation were triggered by the heat flux associated with a renewal of linear lithospheric delamination processes that accompanied this reactivation. All of the known gold and rare metal deposits are hosted by metacratonic terranes with an indisputable Eburnean basement, whereas the juvenile terranes are either very poorly endowed (Iskel) or apparently barren. Although the connection with the gold mineralization seems likely, the reasons remain obscure. It may, however, be suggested that gold endowment is ultimately linked to an influx of mantle-derived CO2 and the formation of ultra-high temperature granulites in the Eburnean lower crust.

International audience; Ain Allega and El Aguiba are among the largest barite-celestite deposits attributed to the Triassic period in Tunisia. They are located in the flysch zone on the eastern edge of the Triassic diapir of Jebel Hamra. The ore body consists of dolomite intensely brecciated and surrounded by marls, clay, gypsum and dolomite which forms the hanging wall of the deposit, and rimmed by Paleocene marls. The ore the surface structure, which in turn controls the mechanism of adsorption and incorporation of minor and trace elements into the growing crystal. For a solid solution, the transitional supersaturation for different growth mechanisms can be significantly different for the two end members. One of the most interesting and intriguing phenomena observed in natural crystals of the (Ba, Sr) SO4 solid solution from this study area is the development of compositional oscillatory zoning, consisting of alternating Ba-rich and Sr-rich layers. The sulfur isotope analyses show significant variability for barite and celestite (from 16.2 to 23 ‰). These values are interpreted as the result of the mixing of two sulfur end-members in the mineralizing fluids, corresponding to thermochemical sulfate reduction of Messinian seawater, together with Triassic sulfate, as sulfur sources. Fluid inclusion studies of celestite show that the BaSO4-SrSO4 solid-solution in both deposits was precipitated from hot saline solution (Th=190±20°C; 16.37 wt. % NaCl equivalent in Ain Allega and 8.2 wt. % NaCl equivalent in El Aguiba). Consequently, the precipitation could be from mixing of basinal brines with magmatic-meteoric fluid. minerals show a cap-rock type mineralization with various forms and types, in particular impregnation in dolomite, breccia cement, replacement of carbonate caprock and open space-filling in the dissolution cavities and fractures. Ore minerals include sphalerite, galena, marcasite and pyrite. Principal gangue minerals are barite, celestite, calcite, dolomite and quartz .The ore minerals are hosted by the Triassic carbonate rocks, which show hydrothermal alteration, dissolution and brecciation. The study of barite-celestite solid-solution shows a bimodal distribution in which the composition is not continuous. Some intermediate compositions are missing; 20-80% SrSO4 for El Aguiba ore deposit and 50-70% SrSO4 for the Ain Allega ore deposit. X-ray diffraction peaks in the BaSO4-SrSO4 series display considerable broadening at intermediate compositions. The unit cell volume varies from 346.97 Å3 in barite (100% BaSO4) to 308.29 Å3 in celestite (100% SrSO4). This variation in cell parameters is attributed to the degree of substitution of barium by strontium since there is less variation between ionic radii of these elements. Consequently, these substitutions caused variation in morphologies, position and d-spacing of peaks (200, 011, 113, 312,122, 112, and 111). Some barite crystals have small-scale, strontium compositional banding which suggests that the crystals responded to regular fluctuations in physiochemical conditions during deposition. The degree of supersaturation in Ba2+ and Sr2+ controls the growth mechanism and consequently

Abridged English version. – The Variscan Pyrenean belt (fig. 1) has been for long famous for its Late Carboniferous LP-HT metamorphism, characterised by the prograde succession, in medium grade metapelites, of biotite, cordierite, andalusite and sillimanite, together with staurolite and garnet [Guitard et al., 1996]. However, the discovery of two kyanite generations lead Azambre and Guitard [2001] to propose a polymetamorphic evolution, with an early (MI) and a late (MIII) kyanite-bearing Barrovian stage, preceding and following the main LP-HT stage (MII).Geological settingThe Variscan orogeny in the Pyrenees occurred from Namurian to Early Stephanian (c. 325-300 Ma), following the deposition of thick Ediacarian-Ordovician silico-clastites, Silurian to Early Caboniferous carbonates, and pre-orogenic Mid-Carboniferous flyschs.Two main tectonic events are recorded, each one subdivided into regionally correlated sub-events (phases) (table I), allowing a detailed correlation between tectonics, metamorphism and plutonism. The Namurian to Westphalian D1 event (c. 325-310 Ma) resulted in a S-vergent fold and thrust belt (with 100–150 km of N-S shortening) and the development of the main, sub-horizontal, Sr schistosity (D1c phase), coeval with MI. The Westphalian-Early Stephanian D2 event (310-300 Ma) was more complex. First, a syn-convergence extensional phase (N-vergent backfolds and E-W extension) resulted in the E-directed escape of the upper crust (D2a phase). Then, a renewal of the N-S shortening was marked by large upright anticlines (domes) and narrower synclines, with up to 10 km amplitudes (e.g., the Canigou anticline-Villefranche syncline pair) (D2b phase). Both D2a and D2b were coeval with MII and the emplacement of early granitoid sills and laccoliths (e.g., the Ansignan hypersthene-granite in the Agly Massif). Later on, D2 evolved into a transcurrent regime, with belt-parallel dextral transpression (D2c and D2c phases). D2c was coeval with the main stage of granite emplacement under low-grade conditions, allowing the expression of a conspicuous Mγ contact metamorphism (e.g., Mont-Louis pluton). D2d ended the D2 event, with the development of retrograde dextral-reverse mylonites. The late MIII metamorphic event encompassed D2c and D2d (and possibly D2b).The early MI Barrovian metamorphic eventThe MI Barrovian metamorphic event resulted from the crustal thickening associated with the development of the D1 intra-cratonic wedge. It was of low-grade, with a chlorite-muscovite Sr schistosity, in the part of the belt that was subsequently overprinted by the syn-MII transformation of chlorite into biotite. The only remnants of MI medium-grade conditions are found as early kyanite in the deepest domains of the Castillon, St-Barthélémy, Agly and Aston massifs, being there obliterated under high-grade MII conditions, and in the core of the Canigou anticline (Velmanya, point v in fig. 2), where a relict kyanite-staurolite-anorthite paragenesis is known, shielded by MII cordierite. The reconstructed P-T conditions at the thermal peak of MI are 5 kbar (19 km) and 575oC (fig. 2), implying the existence of a (now eroded) major D1 nappe (≥ 7 km thick).The main MII LP-HT metamorphic eventStructural domes and medium– or high-grade MII zones are broadly coincident, high-grade conditions being only encountered in the core of the Albères massif, the southern Aston Dome and the North-Pyrenean massifs (grading there up to the LP granulite facies) (fig. 1).Subdivisions of the MII eventThe prograde MII metamorphism is essentially syn-D2a, with clear syn-kinematic growth of the medium-grade minerals, and the main regional tectono-metamorphic D2a/MII structure is evidently deformed and strongly folded by the D2b phase: the D2b domes are basically post-metamorphic. However, a detailed examination of the blastesis-deformation relationships shows that staurolite is pre- to-synkinematic for D2a, whereas andalusite is strictly synkinematic (and consequently is often observed shielding the staurolite), cordierite being syn-to post-kinematic and syn-D2b in some instances. This allows a subdivision of the MII event into three stages:– MIIs, pre-to-syn-D2a, characterised by the staurolite-andalusite (And1 without cordierite) association, with development of a staurolite zone grading downwards into an andalusite (St → And1) zone. – MIIa, syn-to post-D2a (but always developed prior to D2b), characterised by the cordierite (Cord1)-andalusite (And2) association (without staurolite), with development of a thin cordierite zone grading downwards into an andalusite (Cord1 → And2) zone. – MIIb, post-D2a and syn-D2b, characterised by a large cordierite (Cord2) zone developed at the expense of an-dalusite (And → Cord2), only found in the core of the D2b anticlines (e.g., the Garonne dome).Thus, although MII is basically pre-D2b, and the MIIs and MIIa medium-grade isogrades are folded, it appears that metamorphism was still active in the cores of the ascending D2b domes (MIIb). Moreover, in the core of some domes, prograde sillimanite is also syn-kinematic of the D2b phase, and the sillimanite-muscovite isograde may obliquely overprint the MIIa isogrades, as in the Canigou dome. This is related to the syn-D2b emplacement of granite sheets (e.g., the Canigou granite) and may be interpreted as an aureola of “regional-contact” metamorphism, noted MIIγ, that was evidently coeval with MIIb, and enhanced its effects.P-T-t path of the MII eventThe P-T-t path of the MII event may be described using the petrogenetic grids of Pattison et al. [2002] and Pattison and Vogl [2005] (fig. 3). From MIIs to MIIb, it records a prograde anti-clockwise path, following a post-MI clockwise exhumation path, with ≥ 7 km eroded (fig. 2B). The MIIs pressure was close to 3 kbar (10–11 km) in the St zone and decreased to 2.5 kbar (9 km) at the MIIa stage (And2 isograde), for an estimated temperature of 540oC (based on the triple point of Holdaway [1971], the thermobarometer of Pattison et al. [2002] and independent fluid inclusion data by Kister et al. [2003]). A further pressure decrease, down to 2 kbar (7 km), and a temperature increase (up to 600oC) is registered in the MIIb cordierite zone in the core of active D2b domes. Except for the cores of the domes, MIIa remained the peak temperature event, and during MIIb pressure remained constant (or was re-increasing in the syncline cores) and temperature was constant or decreasing. At the end of the MII event (MIIb-MIIγ), extreme conditions of c. 4 kbar and 700–730oC are recorded in the deepest parts of the belt, where anatexis, succeeding to a sillimanite-K-feldspar zone, is observed, as in the Albères Massif and some North-Pyrenean Massifs.The MII metamorphism as a syn-tectonic plutono-metamorphic eventBased on the observation of the deep crust outcropping in the North Pyrenean massifs, Vielzeuf [in Guitard et al., 1996] concluded that emplacement of mafic melts in the Carboniferous lower crust was responsible for the MII metamorphism. At the beginning of the process, a regional thermal anomaly is superimposed to the middle crust (MIIs-MIIa), directly reflecting the emplacement of mafic sills in the underlying lower crust (fig. 4A). Heat is transferred conductively and, most likely, advected by the aqueous-carbonic fluids issued from the devolatilising lower crust (fluid inclusion data). Heat advection by melts characterised the end of the MII event, with development of more or less local thermal anomalies: still “regional” (MIIbγ) as in the Garonne dome, or directly liked to sheet-like granite intrusions (MIIγ) as at the bottom of the Mont-Louis pluton (fig. 4B) or at the contact of the Canigou granite (fig. 4C).The late MIII Barrovian metamorphic eventThe MIII event is mainly characterised in the eastern massifs (Albères, Cap de Creus), where a retrogressive kyanite (so-called “hysterogenic” kyanite) is overprinting high-grade assemblages. Although poorly expressed, MIII minerals in these massifs define two zones, with an external chloritoid zone and an internal kyanite-staurolite zone. A MIII chloritoid zone (sillimanite → chloritoid) is also observed in the core of the Canigou dome. Under the kyanite-staurolite equilibrium hypothesis, the peak MIII P-T conditions in the eastern massifs are estimated at 5 kbar and 575oC, that would imply a pressure increase of 1 to 1.5 kbar (4–6 km deepening) starting from the end of MII, associated with a severe temperature decrease of 150oC. Such an overpressure cannot be due to the D2d dextral-inverse mylonites. However, a fluid inclusion study [Kister et al., 2003] demonstrated that the rocks of the Villefranche syncline did register a pressure increase at the D2b stage, i.e., experienced effective downwards displacement during the syncline formation, and it may be estimated that, in the core of the syncline, a depth increase of 7–8 km could have been attained. Now, in the Cap de Creus massif, the highest MIII grade is observed in the core of the D2b Birba syncline, analogous to the Villefranche syncline. Thus, D2b deepening in the syncline cores may have contributed to the pressure increase. An additional increase may have been provided by sedimentary accumulation in an overlying (and now eroded) syn-orogenic basin (fig. 5). While such a process may explain the development of MIII associations in the D2b synclines, it remains to explain its appearance in the anticlines (Albères, Canigou). However, in the same fluid inclusion study referred to just above [Kister et al., 2003], it is demonstrated that, post-dating D2c and the late pluton emplacement, the studied area suffered a severe isobaric temperature drop, allowing the appearance of chloritoid in the Canigou core (fig. 5). A similar explanation may hold for the Albères massif, if it is accepted there that late kyanite and staurolite were not in equilibrium: starting from the peak MII conditions (c. 4 kbar and 650o–700oC), a strong isobaric cooling would have allowed the successive appearance of staurolite and kyanite.Discussion and conclusionTimingThe youngest pre-orogenic flyschs are dated (in the Axial Zone) from the Namurian-Westphalian boundary (315±5 Ma), thus setting a minimal age for D1-MI. On the other hand, in the northern Pyrenean Agly massif, the Ansignan hypersthene-granite, which is coeval with MII, is dated at around 315-305 Ma, and the associated norites, likely testifying for the mafic magmatism at the origin of the heat flux responsible for MII, are themselves dated at c. 315 Ma. Finally, the large syn-D2c (post-MII) granite plutons are all dated at 307±3 Ma (i.e., close to the Westphalian-Stephanian boundary). Taken together (with the possibility of a slight diachronism between the North Pyrenean massifs and the Axial Zone, and, within the Axial Zone, between east and west), these data indicate that the MI-MII transition and the whole D2a–c/MII development took place in a very restricted time interval (c. 10 Ma), in Westphalian to Stephanian times.Crustal rheology and orogenic developmentAt the end of the Namurian crustal subduction (D1-MI), the Pyrenean crust, that had been thickened with at least a doubling of the upper crust thickness, had begun to experience uplift and erosion. This exhumation process rapidly changed from retrograde to prograde (MIIs-MIIa) during the D2a (MII) syn-convergence extensional phase.The D2a sub-event was marked by the development of three interrelated processes: (i) isotherm upwelling, regional stratiform MII metamorphism and partial melting in the middle crust, as a result from the intrusion, in the lower crust, of mafic magmas of mantellic derivation; (ii) thinning of the thickened crust; (iii) first arrival of granite plutons in the middle crust. It is thought, according to Vielzeuf [inGuitard et al., 1996], that these processes were initiated by a lithospheric delamination process.At the end of D2a, the crustal rheology had been modified, with a partially melted middle crust that received granitic melts issued from the melting of the lower crust. This highly ductile middle crust was sandwiched between a thick (≥ 10 km) rigid upper crust and a less ductile granulitised hot lower crust (800o–900oC), thus allowing the progressive decoupling of the upper and lower crust from D2a to D2c. The buckling of the upper crust, with formation of the large upright D2b folds, became therefore possible, forcing the injection of deep anatectic melts in the anticline cores (a probable explanation of the MIIbγ thermal culmination), and creating, in the deepened syncline cores, the strong pressure increase that favoured MIII inception.However, the MII isogrades are frozen in their folded position, indicating that cooling of the belt had indeed begun since at least the end of the D2b phase. The cooling was sufficiently rapid to be expressed in the Axial Zone by a sub-isobaric temperature decrease, at the origin of the MIII Barrovian and retrograde event, coeval with the late D2c and D2d phases. In the North Pyrenean Massifs, where the D2d phase was extensive, the retrograde MIII event could not be expressed, due to both decompression and thermal effects of the extension.A summary of this complex evolution is given in figure 6. Finally, the interrelated D2 and MII events appear as the record, in the middle-upper crust, of a very short, but very intense heating event that strongly modified the rheologic behaviour of the crust inherited from the D1 crustal subduction and allowed a transitory decoupling of the upper and lower crust. The isobaric MIII event records an exceptionally rapid return to the “normal” thermal and rheologic structures of the crust.The rapidly changing tectonic and thermal conditions that characterise the Variscan Pyrenees during the D2 event may be understood if the position of the Pyrenees within the southern branch of the West European Variscan belt is considered (fig. 7).

The Sidi Driss and Douahria sulfide ore deposits and showings are located in the Nefza mining district, northern Tunisia. The ores are hosted within Upper Miocene (Messinian) basins, within carbonate lenses composed of Fe–Mn-enriched dedolomite partially or totally replaced by early barite and celestite. The ore mainly consists of galena and spherulitic/colloform sphalerite (partially replaced by later Fesulfides). It is present as disseminated or banded ores and has been deposited within the host-rock through dissolution/replacement process or through void infilling. The remaining voids are filled by late calcite/barite locally associated with a late oxidation event. In situ ion microprobe sulfur isotope analyses show significant variability for sphalerite (from −43.9 to 1.2‰), galena (from −30.3 to −2‰) and marcasite δ 34 S( from −35.9 to 25.8‰). These values are interpreted as the result of (i) the mixing of two sulfur end-members in the mineralizing fluids, corresponding to different reduction processes (bacterially-mediated sulfate reduction and thermochemical sulfate reduction, with early celestite and barite and/or contemporaneous Messinian seawater, together with Triassic sulfate, as sulfur sources, and (ii) Rayleigh fractionation process in a closed system. Several arguments (Fe–Mn enrichment in early diagenetic carbonates, involvement of Messinian seawater as a sulfur source, low temperature of deposition and soft-style sedimentary figures within sulfides) suggest that the Sidi Driss and Douahria Pb–Zn ore deposits are syn-diagenetic. Moreover, the properties of the ore deposits, with Fe–Mn carbonates having a wider distribution than that of the base metal sulfides, and the characteristics of the mineralization, in which diagenetic sulfates are a sulfur source and Cd enrichment in sphalerite, support the classificatio no f the Sidi Driss and Douahria Pb–Zn deposits as SHMS-Sedex type. Late Miocene extension, comprising rifting dynamics and basalt emplacement, favored a thermally-driven fluid circulation origin for the Sidi Driss and Douahria deposits, enhancing inception of small-scale shallow convection cells. Such sulfide emplacement is significantly different from that of southernmost MVT ore deposits of Tunisia, which are associated with diapirs and are interpreted as the result of a Serravalian– Tortonian gravity-driven fluid circulation event related to late Alpine convergence. © 2008 Elsevier B.V. All rights reserved.

Resume L'evolution fini-hercynienne du Massif central francais correspond au passage entre un metamorphisme BP–HT (phase M3 a 314 ± 5 Ma) et un metamorphisme de plus haute temperature accompagne de la mise en place du dome granitique du Velay (phase M4 a 301 ± 5 Ma). Nous montrons que cette transition est marquee par le developpement de feuillets a sillimanite, qui representent des plans preferentiels de dissolution acide accompagnant une deformation ductile. Cela implique un chemin P – T – t retrograde antihoraire, en conditions subsolidus entre M3 et M4. Pour citer cet article : P. Barbey et al., C. R. Geoscience 337 (2005).

The recent paper by Sanchez-Espana et al. (2003) presents new fluid inclusion (FI) and stable isotope data on several massive sulphide deposits of the northern Iberian Pyrite Belt (IPB). Using these results together with previously published data on some large deposits of the southern IPB, they concluded that the ore-forming fluids in the IPB were a mixture of highly evolved seawater, exchanged with the underlying sedimentary and magmatic rocks, and a significant deep fluid component, either of metamorphic or magmatic origin (the latter is the favoured conclusion). However, this conclusion essentially depends on the fundamental assumption that neither FIs nor stable isotope records were disturbed during the late Variscantectono-thermal event(s). Yet, according to the current knowledge on metamorphosed deposits (e.g., Marshall and Spry 2000; Marshall et al. 2000), FIs in such deposits generally do not preserve data pertinent to the pre-metamorphic ore stage, and the stable isotope data are usually difficult to interpret. Here, we would like (1) to discuss the possibility of finding pristine FIs in the IPB massive sulphide deposits that would have survived the late Variscan low-grade tectono-thermal event, (2) to present evidence for a significant, gold-depositing, post-kinematic hydrothermal stage in the IPB deposits, with the concomitant development of pervasive lateto post-kinematic fluid percolation through the ore bodies, and (3) to discuss the real significance of the (O, H) stable isotope data. Our discussion is mainly based on our study of the Tharsisstockwork (Marignac et al. 2003), with additional information from the La Zarza and Rio Tintostockworks (Diagana2001) and from the NevesCorvo deposit (Moura et al. 1997a, b). We conclude that all FI data and many stable isotope data are in fact a record of the late Variscan post-kinematic hydrothermal overprint and that only few data may be of significance for the early syn-sedimentary ore-forming event in the IPB massive sulphide deposits.

The Bou Madine ore deposit is located SW of Jbel Ougnat, the easternmost inlier of the Anti-Atlas Pan-African belt in Morocco. The host rocks are high-K calc-alkaline volcanic rocks, that are part of the Neoproterozoic Tamerzaga-Timrachine Formation (TTF, lower PIII). The TTF consists of ignimbrites of rhyolitic to dacitic compositions, andesite flows and hypovolcanic bodies (andesite dykes and rhyolite chonoliths) emplaced along N160°E tension gashes associated with a regional N30°E sinistral fault system. The mineralization is related to a high enthalpy geothermal system, eventually evolving into a low temperature epithermal system. A regional propylitisation (T around 260 °C) overprinted the TTF rocks prior to the emplacement of the mineralization. There were two main hydrothermal stages. During the first stage, massive veins with pyrite, arsenopyrite and minor pyrrhotite and cassiterite were formed. The veins were emplaced along N160°E-trending en echelon joints related to N120°E dextral arrays. A quartz-sericite-pyrite alteration overprinted the propylites around the veins (“bleached haloes”), at temperatures up to 300–310 °C. The second stage of mineralization was coeval with dextral re-activation of the N160°E veins, in relation with a NE-ward shift of the shortening direction. First, polymetallic sulphides (sphalerite, chalcopyrite, stannite, galena) were deposited at temperatures ⩾260 °C. Younger quartz veinlets contain arsenopyrite and minor micrometre-size sulphides and sulpho-salts, hosting the precious metals. This was the low temperature epithermal stage (≈150 °C), in relation with invading meteoric water.

The Tharsis massive sulphide deposit, one of the major VMS-type deposits in the Iberian pyrite belt (IPB) was severely deformed by the Variscan tectono-thermal events. The question of whether or not these events affected the metal distribution in the deposit has been addressed by simultaneously studying the mineral parageneses (Tharsis stockwork) and the fluid circulation (at local and regional scales). The results are: (1) The early paragenesis in the stockwork (Q1 quartz–pyrite–chlorite–phengiteFcobaltiteFankerite) was strongly overprinted by a late post-kinematic mineral deposition, including new quartz veins (Q3 quartz) and base metal sulphides (chalcopyrite, sphalerite, Bi and Te minerals, pyrite and galena) and gold. (2) At a regional scale, fluids accompanying the peak metamorphism conditions (ca. 300 MPa, ca. 300 jC) were of C–O–H– N–NaCl type, CO2-dominated with CH4 and N2, and are considered to be ‘‘metamorphic’’ on the basis of microthermometry and geochemistry. The late- to post-kinematic evolution (‘‘retrograde’’ stage) was characterised by a pressure drop, down to 40 MPa (lithostatic to hydrostatic transition), and a heat input leading to temperatures z430 jC, then decreasing to temperature around 170 jC. Fluids of the ‘‘retrograde’’ type exhibit both dilution of the C–O–H–N–NaCl fluid by a low salinity ‘‘meteoric’’ water and progressive loss of volatile components. (3) Fluids of the retrograde type pervasively percolated through the Tharsis stockwork and were responsible for the strong mineral overprint on the early (deformed) paragenesis. All the measurable fluid inclusions (f.i.) record these late fluids. There are primary fluid inclusions in Q1, but they are systematically imploded due to the external overpressure generated by the Variscan tectonic events. Although base metal distribution in the stockwork is basically the result of the

The gold showings at Bleida are hosted in Late Pan-African N50–80 °E quartz–hematite–chlorite 1 tension lenses that are related to the activity of major sinistral sub-east–west thrusts. Ores result from three superimposed stages of fluid migration. Gold occurs in microcracks offsetting the earlier minerals. Fluids evolved from COHN compositions with a saline component to boiling aqueous fluids. Pressure and temperature decreased from 50 MPa and 300 °C to less than 4 MPa and 150 °C. Thus, the gold showings at Bleida were formed in a typical geothermal (epithermal) setting, likely controlled by the Late Pan-African magmatism. To cite this article: A. Barakat et al., C. R. Geoscience 334 (2002) 35–41

Mg-K mafic intrusive rocks are commonly observed during the late stages of the evolution of orogenic belts. The Variscan French Massif Central has many outcrops of these rocks, locally called vaugnerites. Such magmas have a mantle-derived origin and therefore allow discussion of the role of mantle melting and crust-mantle interactions during late-orogenic processes. In the Southern Velay area of the French Massif Central, LA-ICPMS U-Pb dating on zircons and monazites from three vaugnerites and four coeval granites reveals that the two igneous suites formed simultaneously, at c. 305 Ma. This major igneous event followed after an early, protracted melting stage that lasted for 20-30 My and generated migmatites, but the melt was not extracted efficiently and therefore no granite plutons were formed. This demonstrates that widespread crustal anatexis, melt extraction and granite production were synchronous with the intrusion of vaugneritic mantle-derived melts in the crust. The rapid heating and subsequent melting of the crust led to upward flow of partially molten rocks, doming and collapse of the belt., JHS was financially supported by the Spanish grant CGL2008–02864 and the Andalusian grant RNM1595.

A zincian ilmenite paragenesis is found in metapelites from a contact metamorphic zone (central Jebilet, Morocco) induced by the emplacement of microgranitic intrusions. The zincian ilmenite is mainly preserved in syntectonic andalusite porphyroblasts. The growth of zincian ilmenite is related either to sphalerite breakdown during prograde metamorphism, or to the pervasive flow of a mineralizing fluid within the metapelites. The chlorine-rich fluid carried zinc and other metals leached in the microgranites, during its flow to discharge zones which were probably the Jebilet sulfide deposits.

The Vaulry W–(Sn) mineralisation, located at the eastern boundary of the Blond rare metal leucogranite, is contained in a set of subvertical quartz veins, locally with muscovite and minor quartz selvages. The sequence of deposition was: (1) milky quartz, predominantly as fracture filling, generally affected by subsequent ductile deformation; (2) hyaline quartz–wolframite–cassiterite; (3) minor sulphides. Other sets of quartz veinlets, although generally barren are observed in the Blond massif. Fluid migration at the microscopic scale within the granite and in the vicinity of quartz fractures was constrained by studying the geometry of fluid-inclusion planes and fluid-inclusion chemistry in and outside the mineralised area. Three major sets of subvertical fluid-inclusion planes are recognised: a N050°–060°E set, mostly developed in the veins and in the immediate vicinity, a N110°–130°E set, regionally developed in the granite and a N140–160°E set of local extent. As a whole, the density of FIP decreases from the mineralised zones toward the barren part of the pluton, except for the N140°–160°E set. These are locally abundant around quartz veinlets with similar orientations that form a broad “N–S” band near the Blond locality. Mineralising fluids observed as primary inclusions in cassiterite and in undeformed hyaline quartz are mostly aqueous, with moderate salinity and a minor volatile component, at variance with many other W–(Sn) deposits in the Variscan belt. Ore deposition occurred around 315°C, at an estimated depth of 5.5 km, under hydrostatic to slightly suprahydrostatic pressures. It resulted from fluid mixing, in the central part of a large hydrothermal system, between two end-members: (i) a hot (425–430°C) moderately saline fluid, that contained a diluted volatile component and, although Na-dominated, minor amounts of Li and Ca. The estimated δ18O indicates that this fluid was completely equilibrated with the tectono-magmatic pile (pseudo-metamorphic fluid). (ii) a “cold” (230°C) low-salinity fluid (evolved meteoric water), that mixed with, and eventually overprinted, the early moderately saline fluid responsible for granite muscovitization at 425–430°C. Later, a second hydrothermal system was initiated by the percolation of heated meteoric water, with very low salinity. The system was by then at least 3.5 km deep and the fluid was heated to 300°C. These characteristics are reminiscent of the ca. 305 Ma episyenitic hydrothermal system known elsewhere in the N Limousin.