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The world-class San Rafael tin (-copper) deposit (central Andean tin belt, southeast Peru) is an exceptionally large and rich (>1 million metric tons Sn; grades typically >2% Sn) cassiterite-bearing hydrothermal vein system hosted by a late Oligocene (ca. 24 Ma) peraluminous K-feldspar-megacrystic granitic complex and surrounding Ordovician shales affected by deformation and low-grade metamorphism. The mineralization consists of NW-trending, quartz-cassiterite-sulfide veins and fault-controlled breccia bodies (>1.4 km in vertical and horizontal extension). They show volumetrically important tourmaline alteration that principally formed prior to the main ore stage, similar to other granite-related Sn deposits worldwide. We present here a detailed textural and geochemical study of tourmaline, aiming to trace fluid evolution of the San Rafael magmatic-hydrothermal system that led to the deposition of tin mineralization. Based on previous works and new petrographic observations, three main generations of tourmaline of both magmatic and hydrothermal origin were distinguished and were analyzed in situ for their major, minor, and trace element composition by electron microprobe analyzer and laser ablation-inductively coupled plasma-mass spectrometry, as well as for their bulk Sr, Nd, and Pb isotope compositions by multicollector-inductively coupled plasma-mass spectrometry. A first late-magmatic tourmaline generation (Tur 1) occurs in peraluminous granitic rocks as nodules and disseminations, which do not show evidence of alteration. This early Tur 1 is texturally and compositionally homogeneous; it has a dravitic composition, with Fe/(Fe + Mg) = 0.36 to 0.52, close to the schorl-dravite limit, and relatively high contents (10s to 100s ppm) of Li, K, Mn, light rare earth elements, and Zn. The second generation (Tur 2)—the most important volumetrically—is pre-ore, high-temperature (>500°C), hydrothermal tourmaline occurring as phenocryst replacement (Tur 2a) and open-space fillings in veins and breccias (Tur 2b) and microbreccias (Tur 2c) emplaced in the host granites and shales. Pre-ore Tur 2 typically shows oscillatory zoning, possibly reflecting rapid changes in the hydrothermal system, and has a large compositional range that spans the schorl to dravite fields, with Fe/(Fe + Mg) = 0.02 to 0.83. Trace element contents of Tur 2 are similar to those of Tur 1. Compositional variations within Tur 2 may be explained by the different degree of interaction of the magmatic-hydrothermal fluid with the host rocks (granites and shales), in part because of the effect of replacement versus open-space filling. The third generation is syn-ore hydrothermal tourmaline (Tur 3). It forms microscopic veinlets and overgrowths, partly cutting previous tourmaline generations, and is locally intergrown with cassiterite, chlorite, quartz, and minor pyrrhotite and arsenopyrite from the main ore assemblage. Syn-ore Tur 3 has schorl-foititic compositions, with Fe/(Fe + Mg) = 0.48 to 0.94, that partly differ from those of late-magmatic Tur 1 and pre-ore hydrothermal Tur 2. Relative to Tur 1 and Tur 2, syn-ore Tur 3 has higher contents of Sr and heavy rare earth elements (10s to 100s ppm) and unusually high contents of Sn (up to >1,000 ppm). Existence of these three main tourmaline generations, each having specific textural and compositional characteristics, reflects a boron-rich protracted magmatic-hydrothermal system with repeated episodes of hydrofracturing and fluid-assisted reopening, generating veins and breccias. Most trace elements in the San Rafael tourmaline do not correlate with Fe/(Fe + Mg) ratios, suggesting that their incorporation was likely controlled by the melt/fluid composition and local fluid-rock interactions. The initial radiogenic Sr and Nd isotope compositions of the three aforementioned tourmaline generations (0.7160–0.7276 for 87Sr/86Sr(i) and 0.5119–0.5124 for 143Nd/144Nd(i)) mostly overlap those of the San Rafael granites (87Sr/86Sr(i) = 0.7131–0.7202 and 143Nd/144Nd(i) = 0.5121–0.5122) and support a dominantly magmatic origin of the hydrothermal fluids. These compositions also overlap the initial Nd isotope values of Bolivian tin porphyries. The initial Pb isotope compositions of tourmaline show larger variations, with 206Pb/204Pb(i), 207Pb/204Pb(i), and 208Pb/204Pb(i) ratios mostly falling in the range of 18.6 to 19.3, 15.6 to 16.0, and 38.6 to 39.7, respectively. These compositions partly overlap the initial Pb isotope values of the San Rafael granites (206Pb/204Pb(i) = 18.6–18.8, 207Pb/204Pb(i) = 15.6–15.7, and 208Pb/204Pb(i) = 38.9–39.0) and are also similar to those of other Oligocene to Miocene Sn-W ± Cu-Zn-Pb-Ag deposits in southeast Peru. Rare earth element patterns of tourmaline are characterized, from Tur 1 to Tur 3, by decreasing (Eu/Eu*)N ratios (from 20 to 2) that correlate with increasing Sn contents (from 10s to >1,000 ppm). These variations are interpreted to reflect evolution of the hydrothermal system from reducing toward relatively more oxidizing conditions, still in a low-sulfidation environment, as indicated by the pyrrhotite-arsenopyrite assemblage. The changing textural and compositional features of Tur 1 to Tur 3 reflect the evolution of the San Rafael magmatic-hydrothermal system and support the model of fluid mixing between reduced, Sn-rich magmatic fluids and cooler, oxidizing meteoric waters as the main process that caused cassiterite precipitation.

International audience; The two main types of mineralisation in the Co-Ni-As Bou Azzer district, i.e., “contact” mineralisation” and “cross-cutting” structures have been re-defined based on new field, structural, textural and mineralogical observations. The main orebodies consists of elongated lenses of massive Ni-Co-Fe arsenide minerals. These lenses occur in a core of carbonate or siliceous gangue and are almost exclusively located along the contact between serpentinite and a quartz diorite intrusion. Vein systems, cross-cutting the different lithologies, are ore-bearing only along segments in contact with the serpentinite and/or the massive mineralisation. The two orebody types share a rather similar mineralisation history, starting with a Ni-rich arsenide stage (mainly expressed within the massive mineralisation), followed by a massive Co-arsenide stage recognised in both mineralisation styles, and ending with Fe-rich arsenide and base metal sulphide stage.Detailed field observations, microstructural, tectonic, textural and mineralogical analyses led us to propose a genetic model for the Bou Azzer ore district in which massive mineralisation was formed by alteration and transformation of previously formed breccia levels composed of serpentinite (transformed to gangue) and magnetite/spinel (transformed to Co-Ni arsenide minerals) fragments. Inversely, a tectono-hydrothermal event controlled by a NE oriented transtension generated the vein system, associated certainly with partial leaching and reconcentration of metals from the massive mineralisation because veins are principally mineralised when crossing massive orebodies. We discuss a possible temporal continuum between the two mineralisation styles: massive mineralisation, coeval with serpentinisation (serpentine neoformation), is related to the transformation of brecciated lenses and vein mineralisation is formed as an infill of large fractures during transtensive tectonics. This model has significant tectonic implications, because serpentinite breccia lenses, favourable high-permeability environment for the massive mineralisation formation, can be compared to ophicalcic rocks developed in a context of mantle exhumation by detachment. Two types of textures can be differentiated within the massive mineralisation: i) Brecciated Massive Mineralisation, developed in the core of ophicalcic levels, and ii) Laminated Massive Mineralisation, supposed to form within ancient mylonitic serpentinite levels corresponding to intensive deformation zones. Although the geodynamic significance will not be addressed in this article, we propose and discuss an alternative model in which the presence of exhumed mantle rocks allows the formation of specific massive arsenide deposits.

We present a high-resolution in situ study of oxygen and boron isotopes measured in tourmaline from the world-class San Rafael Sn (–Cu) deposit (Central Andean tin belt, Peru) aiming to trace major fluid processes at the magmatic-hydrothermal transition leading to the precipitation of cassiterite. Our results show that late-magmatic and pre-ore hydrothermal tourmaline has similar values of δ 18 O (from 10.6‰ to 14.1‰) and δ 11 B (from −11.5‰ to −6.9‰). The observed δ 18 O and δ 11 B variations are dominantly driven by Rayleigh fractionation, reflecting tourmaline crystallization in a continuously evolving magmatic-hydrothermal system. In contrast, syn-ore hydrothermal tourmaline intergrown with cassiterite has lower δ 18 O values (from 4.9‰ to 10.2‰) and in part higher δ 11 B values (from −9.9‰ to −5.4‰) than late-magmatic and pre-ore hydrothermal tourmaline, indicating important contribution of meteoric groundwater to the hydrothermal system during ore deposition. Quantitative geochemical modeling demonstrates that the δ 18 O- δ 11 B composition of syn-ore tourmaline records variable degrees of mixing of a hot Sn-rich magmatic brine with meteoric waters that partially exchanged with the host rocks. These results provide thus direct in situ isotopic evidence of fluid mixing as a major mechanism triggering cassiterite deposition. Further, this work shows that combined in situ δ 18 O and δ 11 B analyses of tourmaline is a powerful approach for understanding fluid processes in dynamic magmatic-hydrothermal environments.

The Passa Três granite is a 5 km2 intrusion in southern Brazil with an NNE–SSW-elongated shape, hosting gold-bearing quartz veins with fluorite, carbonates, sulphides (pyrite, chalcopyrite, aikinite, molybdenite) and native gold. Orebodies are hosted by the pluton roof zone, which is marked by various textures indicating magmatic–hydrothermal transition processes. Mineralisation formed between 613 and 608 Ma in extensional pull-apart structures controlled by two conjugated N–S and E–W fault systems. We report results from petrography, quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN), scanning electron microscopy (SEM), electron probe microanalyses (EPMA), X-ray fluorescence (XRF), trace element analyses of pyrite by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), sulphur isotope (δ34S) analyses, and fluid inclusion microthermometry. Hydrothermal alteration is dominantly developed as phengite–quartz–carbonate and sericite–carbonate–chlorite assemblages along mineralised structures. Fluid inclusion study indicates mineralising fluids with H2O-CO2-NaCl composition, low to moderate salinity (0.2–12.84 wt % NaCl eq.), and temperatures from 400 to 150 °C. The sulphur isotopic composition of pyrite (−0.1 to 1.1‰) suggests magmatic origin. These data, in conjunction with structurally controlled mineralisation enriched in Au-Bi minerals shortly post-dating the granite emplacement, appoint towards similarities between the Passa Três deposit and intrusion-related gold systems. The specific location of the mineralisation in the core (and in the roof zone, regarding its vertical position) of the Passa Três granitic intrusion defines it as “granite-hosted” thus, it is representative of a specific model that can be used for exploration of other intrusion-related/hosted gold deposits near the studied area or in other locations.

International audience; Germanium (Ge) is often found as trace element in undeformed sphalerite (ZnS). However, the presence of Ge-minerals (oxides, chloritoids and/or sulphides with up to 70 wt% Ge) is remarkable in Pb-Zn deposits from the Variscan Pyrenean Axial Zone. Their abundance is controlled by the chemical and/or the mechanical processes that affect rare element concentration from sulphides which have undergone deformation and metamorphism. In this study, we document the microstructures and chemical heterogeneities in sphalerite, based on EBSD (electron backscatter diffraction) coupled to LA-ICPMS in situ analyses. Deformation induces the dynamic recrystallization of sphalerite. Recrystallized domains have low Ge contents (1-50 ppm Ge) whereas porphyroclastic sphalerite grains commonly show higher Ge concentrations (up to 650 ppm Ge). Ge-minerals (up to 70 wt% Ge) are exclusively hosted by the Ge-poor recrystallized domains. We propose that Ge was removed from the sphalerite crystal lattice during sulphide recrystallization, and was subsequently concentrated in Ge-minerals, leaving behind a Ge-depleted fine-grained recrystallized sphalerite matrix. Numerous sulphide ore types enriched in rare elements like Pyrenean deposits may present recrystallization features and we suggest evaluating the potential of such deposits by integrating chemical and structural informations at the micrometer scale using state-of-the-art analytical techniques in exploration methods.

This compilation of publication results from more than 20 years of questioning and of applyingstructural geology in mining geology by the guest editor. If it is common to place the various depositsof the earth into large classes that allow recognizing and identifying some characters useful to detect,explore, and find other similar deposits, experience demonstrates that each deposit is unique andcannot answer perfectly to a generic model. This is why we suspect that there exists a gap betweentheory (i.e., the classical model) and reality that needs to be estimated and taken into account inany type expertise or study of an unknown mineral deposit. The following publications try to beconcerned by this way of working.My knowledge and interest in the structural control of mineral deposits benefited from severaldiscussions, suggestions, and field trip shared with a lot of persons that are greatly acknowledgedhere. An exhaustive list is impossible, but I want to particularly acknowledge the CVRD (Vale),Buenaventura, Cedimin, Managem, Kasbah Resource, CMS, SMI, and CTT mining companies andall geologists that took the time to discuss with me of structural problems in mining geology, witha special mention of A.S. Andr e, L. Badra, L. Bailly, L. Barbanson, Y. Branquet, X. Charonnat,A. Ennaciri, C. Ennaciri, M. Faure, L. Fontbot e,. A. Gaouzi, S. Gialli, E. Gloaguen, M. Iseppi;K. Kouzmanov, J. Onezime, P. Piantone, S. Sizaret, E. Tourneur, J. Tuduri, N. Volland. All the reviewersthat significantly improved the quality of this book are also warmly acknowledged

“Structural Control” remains a crucial point that is frequently absent in scientific and/or economic analyses of ore deposits, whatever their type and class, although a selection of references illustrates its importance [...]

International audience; Despite decades of petrological and geochemical studies, the nature and setting of obducted ophiolites remain controversial: the influence of supra-subduction zone environments on pre-existing oceanic lithosphere is yet to assess, and the processes leading to subduction/obduction initiation are still poorly constrained. Our study documents successive influx of slab-derived fluids and progressive strain localization within the upper mantle in a supra-subduction environment during the first few My of the subduction history. We focus on strongly sheared mafic amphibolites intruding peridotites near the mantle–crust transition of the New Caledonia obducted ophiolite and ~ 50 to 100 m above the basal thrust contact of the ophiolite. These m- to hm-long and several m-thick shear bands are interpreted as inherited small-scale intrusions of mafic melts, probably dikes or sills, which were derived from a moderately refractory mantle source refertilized by supra-subduction zone fluids. 40Ar/39Ar age constraints on pargasite at ca. 90 Ma suggest that they could be inherited from the former Pacific west-dipping subduction.Secondary deformation of these mafic intrusions is intimately associated to three major stages of fluid infiltration: (1) the first stage of deformation and metasomatism is marked by syn-kinematic growth of Ca-amphibole (at 700–800 °C and 3–5 kbar) with a distinctive supra-subduction zone signature, and controlled later channelization of aqueous fluids. 40Ar/39Ar dating on magnesio-hornblende indicates that this deformation episode occurred at ca. 55 Ma, coincident with east-dipping subduction initiation; (2) the main metasomatic stage, characterized by the development of a phlogopite-rich matrix wrapping peridotites and amphibolite boudins, points to the percolation of alkali-rich aqueous fluids at still high temperature (650–750 °C); (3) the last, low temperature (< 600 °C) metasomatic stage results in the formation of deformed veinlets containing talc, chlorite and serpentine.

The Jbel Saghro is interpreted as part of a long-lived silicic large igneous province. The area comprises two lithostructural complexes. The Lower Complex consists of folded metagreywackes and N070⁻090°E dextral shear zones, which roughly results from a NW⁻SE to NNW⁻SSE shortening direction related to a D1 transpressive tectonic stage. D1 is also combined with syntectonic plutons emplaced between ca. 615 and 575 Ma. The Upper Complex is defined by ash-flow caldera emplacements, thick and widespread ignimbrites, lavas and volcaniclastic sedimentary rocks with related intrusives that were emplaced in three main magmatic flare ups at ca. 575, 565 and 555 Ma. It lies unconformably on the Lower Complex units and was affected by a D2 trantensive tectonic stage. Between 550 and 540 Ma, the magmatic activity became slightly alkaline and of lower extent. Ore deposits show specific features, but remain controlled by the same structural setting: a NNW⁻SSE shortening direction related to both D1 and D2 stages. Porphyry Au(⁻Cu⁻Mo) and intrusion-related gold deposits were emplaced in an earlier stage between 580 and 565 Ma. Intermediate sulfidation epithermal deposits may have been emplaced during lull periods after the second and (or) the third flare-ups (560⁻550 Ma). Low sulfidation epithermal deposits were emplaced late during the felsic alkaline magmatic stage (550⁻520 Ma). The D2 stage, therefore, provided extensional structures that enabled fluid circulations and magmatic-hydrothermal ore forming processes.

International audience; The Tocantinzinho gold deposit is located in the north of Brazil, in the Tapajós Gold Province of the Amazon Craton. Current total measured and indicated resources are 70.2 Mt @ 1.06 g/t Au (2.4 Moz). The mineralized bodies are hosted in equigranular hornblende-biotite syeno and monzogranites plutons, with many aplite and pegmatite pockets. The magmas have I type signatures and were oxidized. The ages of the mineralized granites vary between 1996.1 ± 2.2 Ma and 1989.1 ± 1.1 Ma, and they are situated in the middle of a tectonic corridor formed by shear zones oriented parallel NW-SE that cut regional biotite-hornblende granodiorites with ages between 2007 ± 8 Ma and 1997 ± 10 Ma. Three hydrothermal phases, simultaneous to tectonic deformations, affected the Tocantinzinho Au deposit: the first, H1, occurred approximately at 1996.1 ± 2.2 Ma, during the magmatic-hydrothermal transition, which altered the igneous feldspars, biotite and hornblende. Then, the granites were brecciated in a transpressional, brittle and hydraulic fracturing regime, forming B1 breccias simultaneous to hydrothermal alteration H2, developed between 1996.1 ± 2.2 Ma and 1989.1 ± 1.1 Ma. The mineralization occurred during this phase, which simultaneously disseminated 1.0– 1.5 g/t of gold, together with pyrite and minor galena, and formed few quartz + pyrite veins with high gold contents, between 1.5 and 70.0 g/t. In an undated tectonic event occurred after and probably near 1989.1 ± 1.1 Ma, the entire mineralized region was cut by andesite dikes that reached the Proterozoic surface, and generated a new hydrothermal, degassing episode, H3. This last hydrothermal stage generated micro-fractures filled with B2 micro-breccia formed by high-pressure water-driven cataclasis, and probably remobilized previously precipitated gold but did not bring new gold to the deposit. Muscovite 40Ar/399Ar ages of the altered zone suggest that the isotopic system of this mineral was reseted at approximately 1860 Ma, about 130 Ma after the end of H3. The Tocantinzinho seems to be a single deposit, which combines characteristics of mesozonal, equigranular type, intrusion-related gold deposit, with those of porphyry-type gold deposits, although in both cases the differences are more frequent than the similarities. The available data does not allow discard that the Tocantinzinho is an orogenetic deposit.

International audience; The Passa Três granite is a NNE-SSW elongated shape intrusion located in the Paraná State (southern Brazil). This intrusion was emplaced within metapelites of the Mesoproterozoic Votuverava Group, which are part of the N040°E trending Lancinha Shear Zone. Gold mineralisation within the Passa Três granite is held by meter-scale quartz veins forming orebodies with variable massive, banded, sheared and/or brecciated internal textures. Structural data indicate the existence of two orthogonal directions of structures, N-S and E-W, dipping 60–75°W and 45–70°S respectively. Mineralised veins contain, in addition to the quartz of the gangue, and in chronological order: fluorite, pyrite, chalcopyrite, gold, aikinite, molybdenite, muscovite, carbonate and baryte. Gold occurs as native grains within fractures that affect pyrite, commonly associated with chalcopyrite and aikinite. Quartz veins are sometimes bordered by aplitic dykes. Additionally, some of the veins exhibit a thin margin of K-feldspar minerals that could represent the early stage of vein formation. These observations, the presence of Unidirectional Solidification Textures (UST), along with abundant expression of pegmatite-rich pockets within granite that crops out close to the surface allow the reconstruction of the granite architecture in terms of late magmatic evolution, magmatic-hydrothermal transition and position of the cupola. N-S and E-W systems are interpreted to be contemporaneous and conjugate. Normal displacements are predominant and main mineralised veins are essentially located within extensional pull-apart structures. The structural model suggests that the normal faults were initiated along former low-angle planes associated with aplite and/or early quartz veins that subsequently controlled the opening of the pull-apart structures that represent the economic orebodies. Zircon from the granite and muscovite grains from mineralised veins were dated by U-Pb and Ar-Ar methods, respectively. Zircons from the main facies (medium grained: GEM and microgranite: GEF) provided undistinguishable ages which were pooled to give an age of 611.9 ± 3.6 Ma. A less abundant, leucocratic facies (“white granite”: GEB) yielded a significantly younger age of 592.8 ± 7.1 Ma. Muscovites from quartz veins gave Ar-Ar ages of 612.9 ± 2 to 608.8 ± 2 Ma (transitional vein with a K-feldspar border), 611.7 ± 2 to 608.8 ± 2 Ma (mineralised veins) and 608.4 ± 2 Ma (barren quartz vein). Thus, the Passa Três granite and its gold mineralisation appear to represent a unique example of an intrusion-related gold system in which the mineralisation concentrates in the core of the magmatic intrusion in the form of meter-scale veins strongly controlled by tectonics.

International audience; In the Moroccan Eastern Anti-Atlas, the Thaghassa intrusion-related gold deposit is hosted in hornfelsed metasedimentary rocks that lie adjacent to the Ikniwn granodiorite. Fields studies reveal three tectono-magmatic stages controlling the formation of the deposit. i) The first stage refers to the top-to-the-south asymmetry and the syn-kinematic Ikniwn pluton emplacement controlled by a compressional or transpressional strain regime. ii) The second stage is characterized, from older to younger and further away from the intrusion, by: metatexite with leucocratic stromatic bands, aplo-pegmatite sills, intermediate veinlets composed of quartz, K-feldspar and muscovite, and then gold-bearing striped foliation-veins. All these features are assumed to have been emplaced during a large-scale ENE-WSW dextral shearing process that results from an ESE-WNW shortening direction during transtensive tectonics. We suggest that the progressive and continuous shearing was initiated since the aplo-pegmatite stage and achieved during the hydrothermal phase. The existence of intermediate veins characterized by quartz-rich core and apatite-muscovite-feldspar-rich rims demonstrates the progressive evolution from the magmatic to the hydrothermal stage and evidence for the persistence of the magmatic character, at least until the onset of the hydrothermal process. iii) The late stage developed large volcanic dyke swarm and brittle faulting.Zircon U-Pb LA-ICP-MS dating yields a Concordia age of 563.5 ± 6.3 Ma for the Ikniwn granodiorite intrusion. The fluid inclusions data besides the mineral thermometry indicate that two main types of fluids can been highlighted: i) a hot aquo-carbonic (H2O-NaCl-CO2) fluid with N2 and CH4, evolving from vapour-rich N2 and CH4 inclusions for the magmatic stage (∼550°C) to CH4-CO2 biphased inclusions for the ongoing hydrothermal stage (∼450-300°C) and ii) an always secondary low T (∼200°C) saline aqueous type (probably NaCl) free from volatiles, with very variable salinity. Eventually, we highlight that in the hornfels-hosted IRG deposits, fluid sources may originate from both magmatic processes and devolatization of the metamorphic host rocks.

The presence of unique accessory Ge-minerals (containing up to 70 wt% Ge) is a widespread phenomenon in Pb-Zn deposits of the Variscan Pyrenean Axial Zone (PAZ). Such a mode of occurrence is, however, rare worldwide with germanium more typically occurring as a trace component of sulfides, notably sphalerite (

During basin burial, interstitial fluids initially trapped within the sedimentary pile easily move under thermal and pressure gradients. As the main mechanism is linked to fluid overpressure, such fluids play a significant role on frictional mechanics for fault reactivation and sediment deformation. The Lodeve Permian Basin (Herault, France) is an exhumed half-graben with exceptional outcrop conditions providing access to barite-sulfide mineralized systems and hydrocarbon trapped into syn-rift roll-over faults. Architectural studies show a cyclic infilling of fault zone and associated bedding-parallel veins according to three main fluid events during dextral/normal faulting. Contrasting fluid entrapment conditions are deduced from textural analysis, fluid inclusion microthermometry and sulfur isotope geothermometer. We conclude that a polyphase history of trapping occurred during Permian syn-rift formation of the basin. The first stage is characterized by an implosion breccia cemented by silicifications and barite during an abrupt pressure drop within fault zone. This mechanism is linked to the dextral strike-slip motion on faults and leads to a first sealing of the fault zone by basinal fluid mineralization. The second stage consists of a succession of barite ribbons precipitated under overpressure fluctuations, derived from fault-valve action. This corresponds to periodic reactivations of fault planes and bedding-controlled opening localized at sulphide-rich micro-shearing structures showing a normal movement. This process formed the main mineralized ore bodies by the single action of fluid overpressure fluctuations undergoing changes in local stress distribution. The last stage is associated with the formation of dextral strike-slip pull-apart infilled by large barite and contemporaneous hydrocarbons under suprahydrostatic pressure values. This final tectonic activation of fault is linked to late basinal fluids and hydrocarbon migration during which shear stress restoration on the fault plane is faster than fluid pressure build-up. This integrated study shows the interplay action between tectonic stress and fluid overpressure in fault reactivation during basin burial that clearly impact potential economic reservoirs.

International audience; The Tapajós Domain in the Amazonian Craton comprises hundreds of gold occurrences mainly hosted by Paleoproterozoic granitic rocks, whose geotectonic evolution and deformation style are poorly understood. The Tocantinzinho granite hosts a large amount of gold, forming the largest gold deposit known in the Tapajós Domain. The Tocantinzinho area is formed by plutonic rocks cut by subvolcanic rocks shallowly emplaced and constrained by NW-SE strike-slip faults, probably in a transtensive site. The magmatism started with the emplacement of huge granodiorite that presently formed the basement country rocks (2007–1997Ma), it was followed by the Tocantinzinho granite magmatism (1989–1979 Ma), and the coeval to late andesite emplacement. Petrological and textural evidence suggest the complex and synchronous occurrence of tectonics and few magmatic events expressed by the emplacement of successive granite, aplite, pegmatite, andesite, and dacite. The magmatic event finished with the cooling of this set of rocks below c. 320 °C, at c. 1950 Ma. The cooling rates vary from c. 3.6–14.7°C/Ma, with an average of 7.5°C/Ma, indicating no important vertical exhumations. The elongated geometry of the Tocantinzinho granite and related rocks, features of solid-state deformation within granites and syntectonic deformation of some andesite dikes imply the existence of wrench type tectonic control. The I-type signature of these rocks, their high-K calc-alkaline and metaluminous to peraluminous affinities combined with the tectonic style indicate a post-collisional tectonic setting. Based on geochemical and structural constrains, the rocks from the Tocantinzinho area are interpreted as a part of the Creporizão Suite and probably represent the first expressions of this syn-to late-tectonic magmatism in the region. A continuous and progressive process of magmatic emplacement controlled by tectonics will be proposed and discussed in conclusion.

International audience; Structural controls are critical during magmatic-to-hydrothermal transition in the formation of intrusion-related gold deposits. They may explain why only some parts of intrusions are mineralized and why only very few intrusions host large deposits. Moreover, most of these gold deposits postdate peak regional metamorphism and were formed in zones of relatively low strain. Indeed, the efficiency of structural gold traps is highest along favourably oriented intrusion/host-rock contacts where mechanical instability maintains high permeability in the cracked thermal aureole. This may be reinforced by melt injections from an underlying root zone. We present a structural analysis of the deformation features of a granite-pluton roof; large-scale dykes and a network of gold veins are intensively developed in this roof, recording a succession of mechanical instabilities. Our gravity survey underlines the presence of a pluton feeder zone located just beneath the mineralized network. It is argued that interferences between regional stress and melt injection in the feeder zone favoured the development of the network by strain located close to the granite roof. This stresses the role of mechanical instabilities triggered by the combined effects of regional stress and melt dynamics in determining the location and size of this type of gold deposit.

International audience; The major role played by pre-existing structures in the formation of vein-style mineral deposits is demonstrated with several examples. The control of a pre-existing decollement level on the formation of a crustal extension-related (collapse) gold deposit is first illustrated in the Quadrilátero Ferrífero from Brazil. Shear zone and decollement structures were also examined and shown to control veins formation by three distinct processes: (i) re-aperture and re-using of wrench shear zones in the case of Shila gold mines (south Peru); (ii) remobilisation of metal in volcanic-hosted massive sulphide (VHMS) deposit by subsequent tectonic events and formation of a secondary stockwork controlled by structures created during this event (Iberian Pyrite Belt, Spain); (iii) formation of economic stockwork by contrasting deformation behaviours between ductile black schist versus brittle more competent dolomite (Cu-Ifri deposit, Morocco). Two examples involve changing of rheological competence within zones affected by deformation and/or alteration in order to receive the mineralisation (case studies of Achmmach, Morocco, and Mina Soriana, Spain). The last case underscores the significance of the magmatic-hydrothermal transition in the formation of mesothermal gold deposits (Bruès mine, Spain). All these examples clearly demonstrate the crucial role played by previously formed structures and/or texture in the development and formation of ore deposits.

Phyllosilicate content and related permeability of fault zones form primary controls on hydraulic and mechanical behavior of the brittle crust. Hence, understanding and predicting the localization of these ubiquitous minerals is a major issue for fundamental and applied geosciences. We describe normal fault zones cutting a foreland arkosic turbiditic formation suffering high-T diagenesis and formed under conditions (~200°C) typical of deeply buried reservoirs and common within the seismogenic interval. Microstructural analyses show a large proportion of phyllosilicates (up to 34%) in the fault rock, derived from near-complete feldspar alteration and disaggregation during deformation. This study shows that even faults with offsets (~20 cm) much lower than bed thickness can have such large feldspar-to-phyllosilicate transformation ratios, implying that the origin of the phyllosilicates is purely transformation related. These results imply that the potential sealing capacity and strength of faults could be predicted from the host rock feldspar content. Where sealing capacity and fault strength can be related to phyllosilicate content, these properties can then also be inferred from the predicted phyllosilicate content: this opens up new horizons concerning the hydraulic and the mechanical behavior of the upper crust.

The history of the peneplain in East Sayan was studied using apatite fission-track analysis (AFTA). This method is suitable for determining the formation time of the erosional surface and estimating its denudation rate. The largest known relic of the peneplanation surface in this area is the Oka Plateau, separated from the Kropotkin Ridge by the Oka–Zhombolok fault. The AFTA shows that the peneplain on the Oka Plateau formed in the Late Jurassic–Early Cretaceous. This peneplain is much younger than the erosional surfaces that persist today in the Tien Shan, Gobi Altai, and Mongolian Altai (Early Jurassic). However, it is older than the peneplain on the Chulyshman Plateau, Altai (Late Cretaceous), suggesting asynchronous formation of the ancient peneplain in Central Asia. The similar exhumation histories of samples from the Oka Plateau and Kropotkin Ridge indicate that these morphotectonic structures developed from Jurassic to late Miocene as a single block, which underwent continuous slow denudation at an average rate of 0.0175 mm/yr. Active tectonic processes in the Late Miocene caused the destruction of the peneplanation surface and its partial uplifting to different altitudes. The rate of Pliocene–Quaternary vertical movements along the Oka–Zhombolok fault is roughly estimated at 0.046–0.080 mm/yr, which is several times higher than the denudation rate in this area. During the Pliocene–Quaternary, the Oka Plateau has not undergone any significant morphologic changes owing to its intermediate position between the summit plain and datum surface of East Sayan and to its partial shielding by basaltic lavas.

[1] The Pyrenees, north of the North Pyrenean fault, display a complex structure involving a succession of peridotite massifs, basement massifs, and mid-Cretaceous to Late Cretaceous basins located in a narrow domain, which was affected by a mid-Cretaceous, preorogenic, high-temperature, low-pressure metamorphism. The Late Cretaceous basins were interpreted either as pull-apart basins formed during transcurrent motion of Iberia relative to Eurasia or as remnants of a larger extensional basin. Recent models support that peridotite massifs result from the exhumation of the mantle during this preorogenic event. The northern boundary of the Agly basement massif shows evidence of ductile deformation of the basal formations of the Agly sedimentary cover. Macroscopic and microscopic kinematics indicators consistent with asymmetry of crystallographic fabrics suggest normal sense of shear and thus suggest detachment, at least partial, of the Mesozoic cover from its basement. Triassic to Early Cretaceous limestones are mylonitic and consistently shows a foliation, a NS- to NE-trending lineation, shear criteria suggesting top-to-the-north shearing and locally boudinage. At the microscopic scale, mylonites are characterized by a very fine grain size, frequently

The Achmmach tin mineralization (NE of the Moroccan Central Massif) is associated with tourmaline-rich alteration halos, veins, and faults hosted in sandstones and metapelites of the Upper Visean-Namurian. These deposits are reported to be late Hercynian in age and related to the emplacement of late-orogenic granite not outcropping in the studied area. Structural and paragenetic studies of the Achmmach tin deposit were conducted in order to establish a general model of the mineralization. From field constraints, the late Hercynian phase is marked by a transition from transpression to extension with deformation conditions evolving from ductile to brittle environments. The transpression (horizontal shortening direction roughly trending E-W) is coeval with the emplacement of the first tourmaline halos along several conjugated trends (N070, N020, and N120). Thereafter, a tourmaline-rich breccia formed in response to the fracturing of early tourmaline-altered rocks. Subsequently, during the extensional phase, these structures were reactivated as normal faults and breccias, allowing the formation of the main tin mineralization (cassiterite) associated with a wide variety of sulfides (arsenopyrite, chalcopyrite, sphalerite, galena, pyrrhotite, bismuthinite, pyrite, and stannite). This evolution ends with fluorite and carbonate deposition. The hydrothermal fluid flow velocity, calculated by applying statistical measures on the tourmaline growth bands, varies with the lithology. Values are lower in metapelites and higher in breccia. In the general evolution model proposed here, tourmaline alteration makes the rock more competent, allowing for brittle fracturing and generation of open space where the main Sn mineralization was precipitated.

International audience; Subduction infancy corresponds to the first few million years following subduction initiation, when slabs start their descent into the mantle. It coincides with the transient (yet systematic) transfer of material from the top of the slab to the upper plate, as witnessed by metamorphic soles welded beneath obducted ophiolites. Combining structure–lithology–pressure–temperature–time data from metamorphic soles with flow laws derived from experimental rock mechanics, this study highlights two main successive rheological switches across the subduction interface (mantle wedge vs. basalts, then mantle wedge vs. sediments; at ∼800 °C and ∼600 °C, respectively), during which interplate mechanical coupling is maximized by the existence of transiently similar rheologies across the plate contact. We propose that these rheological switches hinder slab penetration and are responsible for slicing the top of the slab and welding crustal pieces (high- then low-temperature metamorphic soles) to the base of the mantle wedge during subduction infancy. This mechanism has implications for the rheological properties of the crust and mantle (and for transient episodes of accretion/exhumation of HP-LT rocks in mature subduction systems) and highlights the role of fluids in enabling subduction to overcome the early resistance to slab penetration.

We carried out morphotectonic studies along the left-lateral strike-slip Bogd Fault, the principal structure involved in the Gobi-Altay earthquake of 1957 December 4 (published magnitudes range from 7.8 to 8.3). The Bogd Fault is 260 km long and can be subdivided into five main geometric segments, based on variation in strike direction. West to East these segments are, respectively: the West Ih Bogd (WIB), The North Ih Bogd (NIB), the West Ih Bogd (WIB), the West Baga Bogd (WBB) and the East Baga Bogd (EBB) segments. Morphological analysis of offset streams, ridges and alluvial fans-particularly well preserved in the arid environment of the Gobi region-allows evaluation of late Quaternary slip rates along the different faults segments. In this paper, we measure slip rates over the past 200 ka at four sites distributed across the three western segments of the Bogd Fault. Our results show that the left-lateral slip rate is similar to 1 mm yr(-1) along the WIB and EIB segments and similar to 0.5 mm yr(-1) along the NIB segment. These variations are consistent with the restraining bend geometry of the Bogd Fault.;Our study also provides additional estimates of the horizontal offset associated with the 1957 earthquake along the western part of the Bogd rupture, complementing previously published studies. We show that the mean horizontal offset associated with the 1957 earthquake decreases progressively from 5.2 m in the west to 2.0 m in the east, reflecting the progressive change of kinematic style from pure left-lateral strike-slip faulting to left-lateral-reverse faulting. Along the three western segments, we measure cumulative displacements that are multiples of the 1957 coseismic offset, which may be consistent with a characteristic slip. Moreover, using these data, we re-estimate the moment magnitude of the Gobi-Altay earthquake at M-w 7.78-7.95.;Combining our slip rate estimates and the slip distribution per event we also determined a mean recurrence interval of similar to 2500-5200 yr for past earthquakes along the different segments of the western Bogd Fault. This suggests that the three western segments of the Bogd Fault and the Gurvan Bulag thrust fault (a reverse fault bounding the southern side of the Ih Bogd range that ruptured during the 1957 earthquake) have similar average recurrence times, and therefore may have ruptured together in previous earthquakes as they did in 1957. These results suggest that the western part of the Bogd Fault system, including the Gurvan Bulag thrust fault, usually behaves in a 'characteristic earthquake' mode.

Terra Nova, 23, 162–170, 2011 Abstract Most fault-related pseudotachylytes in the Val Sesia area, Ivrea zone, NW Italian Alps, occur in two areas: near the Canavese Line in the Kinzigite Formation paragneisses and in an elongate belt in the Mafic Complex gabbros away from the Canavese Line. 40Ar/39Ar dating indicates that pseudotachylytes from the Kinzigite Formation were formed in the late Eocene, likely during the early stages of the collision between the NW corner of the Adriatic indenter and the European margin. Pseudotachylytes from the Mafic Complex were formed under a transpressive strain regime, as suggested by kinematic indicators, and yield Early Cretaceous (Albian) 40Ar/39Ar ages. Their formation is possibly related to shortening during the inception of the tectonic inversion of the Adriatic passive margin.

International audience; Crystal growth driven by a flowing solution is modeled for a flow with low Reynolds number using a computational dynamic software. Considering equivalent crystallographic faces, the chemical flux is calculated along upstream and downstream faces. Upstream flux is higher compared to downstream and leads to a symmetry breakdown of the crystal shape and develops mirror symmetry parallel to the flow velocity. Moreover the ratio of these two fluxes (upstream / downstream) gives a quantitative relation between the relative crystal growth rate and the flow velocity. Thus, using an inverse method, the flow direction and velocity can be deduced by the study of the variation of the growth band thicknesses of equivalent crystallographic faces. This new method was applied to the formation of metasomatic tourmalinite associated with a leucogranite sill. The approach is complemented by a study of the chemistry of the tourmaline. In the studied case, the application of the new method gives the high fluid velocities in pores (10-3 - 10-4 m/s) during metasomatism. Equivalent Darcy velocities are estimated and discussed accounting for the major role played by the regional deformation. Finally, a two-stage tectono-hydrodynamic model is proposed for the metsomatism. The first stage is genetically linked to the sill injection, and the second is characterized by a wider event with hydrothermal flow passing along the leucogranite sills.

IntroductionPropagation of mountain belt thrustfront can submit foreland basin sedi-ments to tectonic deformation andburial below thrust units soon aftertheir deposition, thus playing a majorrole in their compaction, temperatureand fluid–rock interaction history. Inthis paper, we describe the case historyof the Gre`sdAnnot Formation, aPalaeogene turbidite succession of theAlpine foreland basin of SE France.The Gre`sdAnnot have been thesource of influential models of turbi-ditic system development (Joseph andLomas, 2004), but although severalstudies dealt with the sandstonepetrography (Jean et al., 1985; Garciaet al., 2004) there is no publishedwork on their diagenetic evolution.Combining a petrographic study withapatite fission track analysis (apatiteFTA), we show the strong correlationbetween the gradient of diagenesisacross the basin and the westwardwedging of the nappes that over-thrust the basin soon after turbiditedeposition.Geological settingThe Gre`sdAnnot Formation caps theMesozoic–Palaeogene succession ofthe inner part of the external Alpineunits (the Digne, Castellane and NiceArcs), the Palaeozoic substratum ofwhich outcrops in two antiformalstructures, the Argentera and Barrotmassifs (Fig. 1). In the NE, the Gre`sdAnnot are thrust by the Penninicfront. Ahead of this front, the north-ern part of the formation is covered bythe Embrunais–Ubaye nappes, issuedfrom the internal Alpine domain andmainly composed of Late CretaceousHelminthoid Flysch. Equivalent nap-pes also occur SE of the Argenteramassif.The Gre`sd relatively, sedimentation migratedAnnot Formation cor-responds to a sand-rich turbidite sys-tem fed from the south by fan deltasand featuring a down-current transi-tion from channel-fill deposits in theSE to tabular sand bodies in the NW(Du Fornel et al., 2004; Joseph andLomas, 2004). The sandstone has anarkosic composition mainly sourcedin the Variscan crystalline basement ofthe Corsica–Sardinia massif (Jeanet al., 1985; Garcia et al., 2004).Foreland subsidence in the externalAlps began during the Middle–LateEocene and resulted in the successivedeposition of transgressive platformlimestones, slope hemipelagic marl-stones and the Gre`sdAnnot turbi-dites (Ravenne et al., 1987). The onsetof turbidite deposition registered thewestward shift of depocentres, fromBartonian in the east to Early Rup-elian in the west (Ford et al., 1999; DuFornel et al., 2004). The turbiditesfilled distinct SE–NW-trending depo-centres formed by early folding of thesub-stratum (Apps et al., 2004), withlocal thicknesses of up to 1200 m.Their deposition ceased during theRupelian with the emplacement of anolistostrome derived from the front ofthe Embrunais–Ubaye nappes, fol-lowed by thrusting of the lower nap-pes (the Autapie and Subbrianc¸onnaisnappes) above the NE part ofthe basin (Kerckhove, 1969). Cor-south-westward in shallow-marine⁄continental depocentres (Ford et al.,1999). Further thrusting above theGre`sdAnnot occurred during theLate Oligocene–earliest Miocene withthe emplacement of the Penninic frontand upper Embrunais–Ubaye nappe(the Parpaillon nappe) (Kerckhove,1969; Fry, 1989; Corsini et al., 2004).During the Miocene, basement thrust-ing uplifted the Argentera and Barrotmassifs (Bigot-Cormier et al., 2006),and gravitational equilibration of thethickened crust resulted in the forma-tion of normal faults that cut thenappes and their substratum down toABSTRACT

International audience; Fault pseudotachylytes form by frictional melting during seismic slip and therefore are widely interpreted as “earthquake fossils.” Rapid movement along a rupture surface typically forms a pseudotachylyte generation vein, the thickness of which increases with earthquake magnitude. The direction and sense of seismic slip cannot always be determined due to the generally complex geometry of pseudotachylyte veins. Here we show, for the first time, that the orientation of the magnetic fabric of fault pseudotachylytes indicates both direction and sense of seismic slip. The magnetic fabric, acquired in a manner similar to that of other magmas, arises in this case from the asymmetric preferred orientation of paramagnetic grains during viscous shear of the friction melt. This kinematic information, coupled with fault plane orientation and generation vein thickness, provides new and critical insight for the earthquake focal mechanism. The magnetic fabric of pseudotachylytes therefore not only constitutes a valuable kinematic criterion for these fault rocks, but also could expand our knowledge of prehistoric seismic events.

The epithermal Shila-Paula Au–Ag district is characterized by numerous veins hosted in Tertiary volcanic rocks of the Western Cordillera (southern Peru). Field studies of the ore bodies reveal a systematic association of a main E–W vein with secondary N55–60°W veins—two directions that are also reflected by the orientation of fluid-inclusion planes in quartz crystals of the host rock. In areas where this pattern is not recognized, such as the Apacheta sector, vein emplacement seems to have been guided by regional N40°E and N40°W fractures. Two main vein-filling stages are identified. stage 1 is a quartz–adularia–pyrite–galena–sphalerite–chalcopyrite–electrum–Mn silicate–carbonate assemblage that fills the main E–W veins. stage 2, which contains most of the precious-metal mineralization, is divided into pre-bonanza and bonanza substages. The pre-bonanza substage consists of a quartz–adularia–carbonate assemblage that is observed within the secondary N45–60°W veins, in veinlets that cut the stage 1 assemblage, and in final open-space fillings. The two latter structures are finally filled by the bonanza substage characterized by a Fe-poor sphalerite–chalcopyrite–pyrite–galena–tennantite–tetrahedrite–polybasite–pearceite–electrum assemblage. The ore in the main veins is systematically brecciated, whereas the ore in the secondary veins and geodes is characteristic of open-space crystallization. Microthermometric measurements on sphalerite from both stages and on quartz and calcite from stage 2 indicate a salinity range of 0 to 15.5 wt% NaCl equivalent and homogenization temperatures bracketed between 200 and 330°C. Secondary CO2-, N2- and H2S-bearing fluid inclusions are also identified. The age of vein emplacement, based on 40Ar/39Ar ages obtained on adularia of different veins, is estimated at around 11 Ma, with some overlap between adularia of stage 1 (11.4±0.4 Ma) and of stage 2 (10.8±0.3 Ma). A three-phase tectonic model has been constructed to explain the vein formation. Phase 1 corresponds to the assumed development of E–W sinistral shear zones and associated N60°W cleavages under the effects of a NE–SW shortening direction that is recognized at Andean scale. These structures contain the stage 1 ore assemblage that was brecciated during ongoing deformation. Phase 2 is a reactivation of earlier structures under a NW–SE shortening direction that allowed the reopening of the preexisting schistosity and the formation of scarce N50°E-striking S2-cleavage planes filled by the stage 2 pre-bonanza minerals. Phase 3 coincides with the bonanza ore emplacement in the secondary N45–60°W veins and also in open-space in the core of the main E–W veins. Our combined tectonic, textural, mineralogical, fluid-inclusion, and geochronological study presents a complete model of vein formation in which the reactivation of previously formed tectonic structures plays a significant role in ore formation.

Resume Base sur l'etude de nouvelles donnees geometriques et mineralogiques, un modele de formation en trois stades des veines du gisement d'argent d'Imiter (Anti-Atlas oriental, Maroc) est propose. Le premier stade est caracterise par le developpement des veines les plus riches, a remplissage de quartz puis dolomite rose, dans un contexte transpressif dextre associe a une direction de raccourcissement NW–SE a WNW–ESE. Le second stade, a remplissage de dolomite rose, est associe a un cisaillement senestre normal, controle par une direction de raccourcissement nord–sud, reutilisant certaines des structures du stade 1. Des phenomenes d'alteration contribuent a un enrichissement local en Ag. Pour citer cet article : J. Tuduri et al., C. R. Geoscience 338 (2005).

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

Thermogravimetric analysis was used to study the sublimation and vaporisation processes of S(−) efaroxan hydrochloride, a potent and highly selective α-2-adrenoreceptor antagonist. The kinetic parameters of the sublimation were investigated by conventional, isothermal thermogravimetric analysis (TGA) and modulated TGA (MTGA). The physico-chemical characterisation of the sublimate was determined by HPLC, elemental analysis, and DSC FTIR spectroscopy. Sublimation followed a zero-order mechanism and the activation energy and pre-exponential factor were calculated. The sublimation and vaporisation enthalpies were evaluated and used to determine the melting enthalpy, which was seen to be consistent with DSC data. The solubility parameter, which can be used to predict the miscibility of a drug in a polymer, was calculated from vaporisation enthalpy and crystallographic data. Finally, the Langmuir equation was used to construct the diagram of the sublimation process, p=f(T). The data were fitted using the Antoine equation by a least squares method.

The Cu ore of Ifri is a chalcopyrite stockwork hosted by Cambrian formations and was until now interpreted as a syngenetic massive sulphide deposit. Textural studies highlight two generations of pyrite early (Py I) and late (Py II) with respect to the regional deformation. The chalcopyrite stockwork overprinted Py II, outlining the epigenetic nature of the Cu mineralization. Regarding the origin of Cu-depositing fluids, the presence in the stockwork paragenesis of an U, W, Sn association and preliminary Pb/Pb dating of a brannerite belonging to this association suggest a contribution of the Tichka granite.

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

The South Portuguese Zone (SPZ) represents the southernmost unit of the Iberian Massif. It is mainly composed of three structural domains, from north to south, the Beja–Acebuches Ophiolitic Complex (BAOC), The Pulo do Lobo Antiform (PLA) and the Iberian Pyrite Belt (IPB). This study proposes a structural analysis of the Spanish part of the SPZ that allows us to point out two main kinds of deformation; one accommodated by early top-to-the-south and following sinistral strike-slip tectonics in the northern part of the SPZ and the other by top-to-the-south thrusting in a wide southern branch. This transition, underlining the strain partitioning, is analysed by lattice preferred orientation of quartz using the texture goniometry method. It shows that the deformation is accommodated in the PLA at low to middle temperature by basal and prismatic left angle bracketaright-pointing angle bracket slip. Quartz textures suggest increasing thermal conditions of deformation from thrust to strike-slip tectonics. Our work within the IPB allows us to present a sequence of deformation showing a primary south-verging ductile thrusting and coeval crustal thickening in response to the thin-skinned tectonics. The progressive deformation generated backthrusts while it turns shallower southward. These features are summarised in an interpretative cross-section of the SPZ that underlines the main structural style of deformation, the fore-mentioned southward propagating thin-skinned thrusts.

International audience; The Madeira Sn-Nb-Ta deposit corresponds to the albite-enriched facies of Madeira granite (Madeira Suite) that is part of a NE-SW alignment of three granitic bodies. Structural analyses suggest that the albite-enriched granite emplacement and development of related structures occurred in a different tectonic setting than earlier facies of the granitic bodies in the NE-SW alignment and that the structure was dominated by a N-NE-trending shortening related to a left-lateral motion along a NE-SW corridor within a Riedel shear. Three types of structures (flat-lying, near vertical fractures, and geodes/miaroles) concentrated the last magmatic-related fluid in the albite-enriched granite. U-Pb in situ zircon dating of the albite-enriched granite yielded an age of 1,822 ± 22 Ma. The other granitic plutons of the Madeira Suite, Água Boa granite (topaz-granite facies), and Europa per-alkaline granite formed at 1,825 ± 14 Ma, 1,831± 11 Ma, and 1,839 ± 10 Ma, respectively. The granite bodies of the Madeira Suite occur in an area occupied by a cauldron complex composed of volcanic sequences (Iricoumé Group) and associated A-type granites (Mapuera Suite), and their formation was controlled by the reactivation of the cauldron structures and the pre-existing structures. The gap between the cauldron complex and the Madeira Suite is no greater than 35 Ma. The geological evolution was reanalyzed from the perspective of an entire extensional environment where three successive episodes of A-type magmatism and basin formation (Urupi Formation) occurred. The data and interpretations of this work imply crucial constraints on the petrologic models proposed for the albite-enriched granite and, consequently, on the genesis of the Madeira deposit

Structural and metallogenic studies of the Ifri copper deposit (western High Atlas, Morocco) demonstrate that a great part of the mineralization was linked to a stockwork developed during a Late-Variscan NNW-verging shearing event. With this significant result, the until now accepted syngenetic character for this mineralization has to be reconsidered and allows to suggest a new guide of prospection for this kind of deposit.

The gold deposits of the Ouro Preto area (Minas Gerais, Brazil) occur along the main tectonic contact responsible for the thrusting of the Paleoproterozoic units (Minas Supergroup) onto the gneissic and metasedimentary Archean units (Rio das Velhas Supergroup) during the Brasiliano (ca. 600 Ma) tectonic event. These deposits are claimed to be the most complex of the Quadrilatero Ferrifero, with orebodies lying parallel to the thrust-related stretching lineation. Based on structural, mineralogical, geochronological, and fluid inclusion constraints, our study demonstrates that the gold-bearing quartz veins were formed in response to late orogenic collapse tectonics that led, in this area, to gravity backsliding of the nappes. During these movements, sigmoidal voids were created and filled by elongate quartz grains associated with sulfides, tourmaline, and carbonates. Inferred hydrothermal effects were responsible for the formation of illite, sulfides, carbonate, garnet, and green biotite within the matrix. Large arsenopyrites within the veins were affected by three stages of fracturing during which the metallic phases and associated gold were deposited. Gold, wherever it is in contact with Bi-related minerals, occurs in the form of electrum, maldonite, or aurostibite. Fluid inclusion studies show that this event was associated with the entrapment of both CO2-rich and H2O salt-rich fluids. The process was initiated after the Brasiliano thrusting event (ca. 500°C, 8 kbars) and in P-T conditions close to 300° to 400°C and 2 kbars. An age of ca. 485 to 490 Ma has been obtained by 40Ar/39Ar dating of hydrothermal biotite and muscovite. This study demonstrates that the Ouro Preto gold deposits were formed in a context of late orogenic collapse tectonics, drastically different from the conventional auriferous shear zone model. This could account for their relative paucity compared to other mesothermal gold deposits.

Gold-bearing quartz veins from the El Callao district (Guyana Shield, Venezuela) are filled with several comb quartz generations. Their formation results from successive opening and filling stages during which low salinity mineralized fluids composed by CO2–H2O–salt–(±CH4) were trapped.

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

The comparative analysis of gold mineralization of the Cevennes area (Bulidou boulder and Alteyrac/Pont-de-Rastel veins) shows that these deposits resulted from the same polyphase process characterized by successive opening, crystallization and brecciation. The mineralized pebbles exhibit opening facies (geodic structures) with specific aquocarbonic three-phase fluid inclusions that do not occur within the veins. It is thus proposed that the original site for mineralized pebbles is not directly the Alteyrac/Pont-de-Rastel quartz veins.

The auriferous mineralizations of the Cevennes area (French Massif Central) are space- and time-related to the granite emplacement during the Late-Hercynian extension (Mont-Lozere-Borne Massifs). At first, barren siliceous fluids percolate through the metamorphic basement using Hercynian thrust planes reworked as normal faults. Some of these NE-SW faults, changed into strike-slip faults by the rotation of regional stresses, are used as drains by the Au-As-Sb-rich fluids. During the Stephanian, erosion partly destroyed the lodes and created paleoplacers in the Ales coal basin.

This new structural map of the Cevennes area shows below the stack of micaschist nappes the presence of a gneiss window which cannot be correlated to the lower gneiss nappe of the Massif Central. In the northern part, the S-SW verging deformations are reworked by an anatexis which is older than the Cevennes plutonism and the Velay migmatites. The granodiorites emplaced around 315 Ma during the postcollision thinning are the driving power of hydrothermal convective flows responsible for the formation of gold bearing quartz veins.

Petrological and mineralogical analysis of gold-bearing quartz veins of the Ouro Preto area (Minas Gerais, Brazil) demonstrates: i) that gold, always associated with bismuth, is located within open fractures of quartz vein arsenopyrite; ii) that mineral association related to the mineralizing event developed later with respect to the regional metamorphism. These results are consistent with the structural studies that suggest a gold-bearing veins emplacement posterior to the regional metamorphism.

The thermodynamics and kinetics of the solidification process of several mixtures of SR 33557 and PEG 6000 have been analyzed by differential scanning calorimetry. The calculated phase diagram showed a negative interaction energy between the constituents in the liquid phase. A unified description for solidification accounting for isothermal and continuous cooling is presented. The onset of solidification shifts to higher temperatures on decreasing the cooling rate and to longer times on decreasing the annealing temperature under continuous cooling and isothermal holding, respectively. The analysis is based on the fact that nuclei have to be created prior to any crystal growth. The driving force for nucleation is considered proportional to the undercooling, ΔT (= TL − T). By coupling the isothermal and continuous cooling experiments, the high temperature part of the time-temperature transformation and temperature-cooling rate transformation diagrams are constructed under a wide range of conditions.

International audience; The Baikal Rift System in southern Siberia is one of the main intracontinental extensional features on Earth. The rift system represents the northwestern boundary of the Amuria plate and in that respect can be considered as an evolving plate boundary. The Baikal Rift System has been widely studied both in terms of geology and geophysics and many models have been proposed for its formation and evolution. However, the age of the initiation of deformation and the mechanism driving this deformation are still largely debated. While major extension has occurred since the Late Miocene-Pliocene, the onset of extension seems older than the India-Asia collision, implying that several driving mechanisms may have acted together or in relay through time. In this work, we review the available data and models for deformation in an area encompassing the Baikal Rift System, the Sayan ranges to the west and the Transbaikal to the east. Using a synthesis of this data and our own field and mapping observations, we show that the Baikal Rift System, along with transpressional deformation in the Sayan ranges and transtension in the Transbaikal area, can be explained through major left-lateral strike-slip systems. The deformation is strongly controlled by inherited crustal and lithospheric structures, and is distributed over a wide area within the western Amuria plate that consequently cannot be considered as a rigid block. Such distributed deformation is likely to have a strong effect on the structure of the future continental margin if extension evolves towards the formation of oceanic crust.

International audience; We describe the structure, microstructure, and petrophysical properties of fault rocks from two normal fault zones formed in low-porosity turbiditic arkosic sandstones, in deep diagenesis conditions similar to those of deeply buried reservoirs. These fault rocks are characterized by a foliated fabric and quartz-calcite sealed veins, which formation resulted from the combination of the (1) pressure solution of quartz, (2) intense fracturing sealed by quartz and calcite cements, and (3) neoformation of synkinematic white micas derived from the alteration of feldspars and chlorite. Fluid inclusion microthermometry in quartz and calcite cements demonstrates fault activity at temperatures of 195degC to 268degC. Permeability measurements on plugs oriented parallel with the principal axes of the finite strain ellipsoid show that the Y axis (parallel with the foliation and veins) is the direction of highest permeability in the foliated sandstone (10-2 md for Y against 10-3 md for X, Z, and the protolith, measured at a confining pressure of 20 bars). Microstructural observations document the localization of the preferential fluid path between the phyllosilicate particles forming the foliation. Hence, the direction of highest permeability in these fault rocks would be parallel with the fault and subhorizontal, that is, perpendicular to the slickenlines representing the local slip direction on the fault surface. We suggest that a similar relationship between kinematic markers and fault rock permeability anisotropy may be found in other fault zone types (reverse or strike-slip) affecting feldspar-rich lithologies in deep diagenesis conditions.