Timing of rare-elements (Li-Be-Ta-Sn-Nb) magmatism in the European Variscan belt

International audienceHigh-phosphorus peraluminous rare-elements granites and rare-elements LCT (Lithium, Caesium, Tantalum) pegmatites are the most important sources of raw materials for some critical metals like tantalum (1,2)represent important economic storehouses for industrial minerals like feldspar, quartz, mica or kaolin. They principally emplace in orogenic settings (3). Afast overview of three mainEuropean Variscan districts, i.e. the Moldanubian domain of the Bohemian massif, the French Massif Central (FMC) and the NW Iberia provides a basis for questioning the origin of rare-elements magmatism and the actual classification of rare-elements pegmatites, in particular the LCT pegmatites. Granitic pegmatites are widespread in most of the Bohemian Massifbut LCT pegmatites are most common in the Moldanubian domain. In this area, their emplacements seem mainly controlled by migmatitic domes and shear zones and correspond to two events(4). The older at ~ 333 ± 3 Ma just follow HT-MP event of the end of the Moravo-Moldanubian phase and the younger at ~ 325 ± 4 Ma is contemporaneous with beginning of the Bavarian phase (U-Pb ages on colombite and tantalite). In the FMC, most of the actually known rare-elements magmatic bodies form a province in the North Limousin area, which represents the northwestern part of the FMC.U-Pb dating of columbite-group minerals from Beauvoir, Montebras and Chèdeville rare-elements magmatic bodies leads to emplacement ages at 317 ± 6 Ma, 314 ± 4 Ma and 309 ± 5 Ma respectively. The contemporaneous Marche fault system (5), which crosscuts in a general E-W trend all the northern part of the Limousin, seems to be a key-structure for the rare-elements magmatism of the area

Typology of hard-rock Li-hosted deposits in Europe

International audienceLithium became a strategic metal in the last decade due to its widespread use in electromobility and green technologies. Consequently, demand has increased significantly reviving European interest in lithium mining and leading many countries to assess their own mineral resources/reserves to secure their own supplies. A compilation of European lithium hard-rock occurrences and a systematic assessment of metallogenic processes related to Li-mineralization have been produced. Accordingly, it appears that lithium is well represented through various deposit types related to several orogenies from Precambrian to Miocene ages. Thus, these deposits have been identified as mostly resulting from endogenous processes such as lithium-cesium-tantalum (LCT) pegmatites (e.g. Sepeda in Portugal; Aclare in Ireland; Läntta in Finland), rare-metal granites (RMG; Beauvoir in France; Argemela in Portugal) and greisens (e.g. Tregonning-Godolphin, Meldon in UK; Cinovec in Czech). Local exogenous processes may be related to significant Li-endowments such as jadarite precipitation in the Jadar Basin (Serbia) but are rarely related to economic grade and tonnage of lithium. Moreover, common parameters are identified in the Li endowment processes including: 1) a pre-existing Li-rich source; 2) a lithospheric thickening; and 3) an extensional regime

Mapping the Follicle-Stimulating Hormone-Induced Signaling Networks

Follicle-stimulating hormone (FSH) is a central regulator of male and female reproductive function. Over the last decade, there has been a growing perception of the complexity associated with FSH-induced cellular signaling. It is now clear that the canonical Gs/cAMP/PKA pathway is not the sole mechanism that must be considered in FSH biological actions. In parallel, consistent with the emerging concept of biased agonism, several examples of ligand-mediated selective signaling pathway activation by gonadotropin receptors have been reported. In this context, it is important to gain an integrative view of the signaling pathways induced by FSH and how they interconnect to form a network. In this review, we propose a first attempt at building topological maps of various pathways known to be involved in the FSH-induced signaling network. We discuss the multiple facets of FSH-induced signaling and how they converge to the hormone integrated biological response. Despite of their incompleteness, these maps of the FSH-induced signaling network represent a first step toward gaining a system-level comprehension of this hormone’s actions, which may ultimately facilitate the discovery of novel regulatory processes and therapeutic strategies for infertility and non-steroidal contraception

Palaeozoic oolitic ironstone of the French Armorican Massif: a chemical and structural trap for orogenic base metal-As-Sb-Au mineralization during Hercynian strike-slip deformation.

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

Tectonic and climatic forcing on the Panj river system during the Quaternary

Abstract HKT-ISTP 2013 B

Mode of formation of gold-bearing mineralization on top of the boboras (Galicia, Spain) - The combined role of mechanical instabilities, strain localization and vein formation.

International audienceThe Galician Hercynian segment constitutes the core of the Ibero-Armorican orogenic arc, characterized by few tectonic units that record three main phases of deformation (D1 to D3). Four generations of granite, syn- to post-D3 intruded the major tectonic units. From older to younger, we find: i) syn-kinematic biotite-rich granodiorite (G1); ii) syn-kinematic two micas granites (G2) ; iii) biotite-dominant granites (G3) and iii) late-kinematic biotite-rich granodiorite (G4). Numerous sills, dykes and vein systems are widespread within the metasediments of the para-autochton unit. Gold-bearing quartz veins were spatially associated with G3 granites likely the Boborás intrusion, concerned by this work. The Boborás granite (G3) outcrops as a small NS-elongated elliptical intrusion. Granite is homogeneous and exhibits an equigranular texture composed of quartz, oligoclase, microcline, biotite dominant and muscovite

Geochronological constraints on the magmatic and hydrothermal evolution of the tras-os-montes hercynian domain (Galica, Spain) : position of the AU, SN-W mineralizing events.

International audienceThe study area is located in the Galicia-Trás-os-Montes Zone (GTMZ zone, Arenas et al. 1986, Fig. 1), that belongs to the internal zone of the Hercynian belt and is composed of a relative autochthonous and parautochthonous units overthrusted by allochthonous complexes (Ribeiro et al. 1990). This domain of Palaeozoic schists is affected by a low to high temperature – medium pressure metamorphism. These rocks exhibit a well-developed regional schistosity related to nappes emplacement (D1 and D2 events) and are affected by NS-trending crenulation lineation and folds (D3 event) The late D3 event is characterized by a high-temperature metamorphism leading to development of local migmatite. Both parautochthonous and allochthonous units are intruded by syn- and post-kinematic plutons. Four generations of granites (G1 to G4) are identified by their textural and geochemical characteristics and by crosscutting relationships. Gold deposits are spatially associated with the G3 granites whereas Sn-W deposits are represented, in the study area, by disseminated and vein-type mineralization spatially close to the G2 granites (fig. 1)

Transition State Spectroscopy of the Photoinduced Ca + CH3F Reaction. 2. Experimental and Ab Initio Studies of the Free Ca***FCH3 Complex

International audienceThe Ca* + CH3F CaF* + CH3 reaction was photoinduced in 1:1 Ca***CH3F complexes formed in a supersonic expansion. The transition state of the reaction was explored by monitoring the electronically excited product, CaF, while scanning the laser that turns on the reaction. Moreover, the electronic structure of the Ca***FCH3 system was studied using ab initio methods by associating a pseudopotential description of the [Ca2+] and [F7+] cores, a core polarization operator on calcium, an extensive Gaussian basis and a treatment of the electronic problem at the CCSD(T) (ground state) and RSPT2 (excited states) level. In this contribution we present experimental results for the free complex and a comparison with the results of a previous experiment where the Ca***CH3F complexes are deposited at the surface of large argon clusters. The ab initio calculations allowed an interpretation of the experimental data in terms of two reaction mechanisms, one involving a partial charge transfer state, the other involving the excitation of the C-F stretch in the CH3F moiety prior to charge transfer

Seixoso-Vieiros Rare Element Pegmatite Field: Dating the Mineralizing Events.

International audienceThe Seixoso-Vieiros Rare Element Pegmatite fined by Farias et al (1987). The Seixoso-Vieiros pegmatite field is known for containing numerous granitic pegmatite-aplite veins (Seixoso and Vieiros pegmatites). The area is bounded at the north by the Variscan Celorico de Basto granite massif. On the SE it is bounded by the syn-tectonic Felgueiras granodiorite. Several pegmatites outcrop within cordierite-andalusite isograde Silurian schists. The field is also known for mining of cassiterite and columbite-tantalite in the last century (Maijer, 1965). In the Seixoso area, an unusual heterogeneous granitic intrusion outcrops as two main apices in Seixoso and Outeiro as granites cupolas (Lima et al., 2009). These rocks show a typical granitic mineral assemblage and exhibit a textural variation from biotite-bearing, at depth, to two mica, or muscovite tourmaline, near the apex roof (Helal et al., 1993). The Seixoso granite is described as a fine to medium-grain leucogranite, with biotite and muscovite, strongly altered with albitization and greisenization close to the contact zones. The Outeiro granite is layered and shows pegmatitic segregations. In the latter, Li-bearing minerals, such as petalite and spodumene, have been observed. In addition, minerals from the amblygonite-montebrasite series have also been noted within the granitic mineral assemblage (Lima et al., 2009). Other notable accessory minerals include: beryl, chrysoberyl, tourmaline and sekaninaite, and others. In the Vieiros area, the granitic aplite-pegmatite veins mainly cross-cut schists of Silurian age within the andalusite isograde. A dozen N-S to NE-SW-trending Sn-bearing granitic aplite-pegmatite veins outcrop in the area. They present a rich mineralogy: quartz, K-feldspar, albite, muscovite, petalite, spodumene, amblygonite-montebrasite, cassiterite, columbite-tantalite, tourmaline, and many different sulfides. An albite type pegmatite is exposed in the Vieiros mine and measures 300 meters in length, an average 5 meters in width, and is subvertical, striking E-W, and dips N25°. During this study (Melleton et al., submitted), columbite and tantalite grains were dated by the U-Pb method, using the LA-SF-ICP-MS technique, from the Outeiro mine granite and the Vieiros mine albite type pegmatite. Results of dating (figure 1) from the Vieiros pegmatite yield an age of emplacement of 301 ± 4 Ma (12 analyses). Ages obtained from the Outeiro granite yield 301 ± 5 Ma (9 analyses) and 316 ± 9 Ma (from two analyses located in cores of two different single grains, and with significantly low concentrations of U). This latter age is interpreted as age of crystallization of the Outeiro granite, and the younger age corresponds to post-emplacement disturbance related to the Vieiros-Seixoso pegmatite emplacement, located in the surrounding area. Located hundred meters from the Outeiro mine granite, the Seixoso pegmatite shows similar structural and mineralogical features as the Vieiros pegmatite. Therefore, emplacement of these pegmatites and associated fluids could have been the cause of the Outeiro Mine columbite-tantalite rim age. The Celorico de Basto late-D3 granite in the north and the Felgueiras syn-D3 granodiorite in the south had not been directly dated. However, Dias et al. (1998) dated equivalent granitoids and obtained ages around 305-308 Ma for the late D3 granite and early ages ranging between 310 and 320 Ma for the syn-D3 granites. Thus, there is not a temporal link between the Vieiros pegmatite emplacement and the surrounding granites of this field. New samples are being collected in order to understand the different mineralizing events and relationships between other pegmatites and surrounding granitic cupolas of the studied area

Laser Spectroscopic Studies of the E 1£+ State of the MgO Molecule

The E1Σ+ ‘Rydberg' state of 24Mg16O has been characterized by two-color resonance-enhanced two-photon ionization (R2PI) spectroscopy in the 36 000–40 000 cm−1 region. Several rotationally resolved bands, assigned consistently to 24Mg16O(E1Σ+←X1Σ+) vibronic transitions, have been analyzed. The effective Bv′(v′=0−8) constants determined exhibit an unusual variation with v′. Possible causes of this variation are discussed. Estimated spectroscopic constants for the E1Σ+ state are reported