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Les minéralisations à Sb et Au tardi-varisques : vers un modèle génétique unifié ? : Exemples du Massif armoricain et du Massif central

Abstract : The French Variscan domains, particularly the Armorican Massif and the Central Massif, contain most of the antimony vein ore deposits. Despite their intense exploitation, there is no consensus on their general metallogenic model and on the relationships between antimony and gold remains unclear. This studyfocuses on 4 districts: i) la Bellière, ii) Vendée, iii) la Lucette, in the Armorican Massif, and, iv) Brioude-Massiac district in the Central Massif to compare with the Armorican Massif. Our results show that antimony ore deposits studied are very similar to each other with a shallow depth formation (<5 km), and an evolutionin 2 stages: i) an early one with arsenopyrite formed between 350-280°C, formed by metamorphic aquocarbonic fluids, ii) a late one with stibnite-gold between 120-200°C formed in response to a temperature drop due to arrival in the system of low-salinity meteoric water. All antimony and antimony-gold ore deposits have"invisible" gold trapped in arsenopyrites (and berthierite?), and/or native gold with stibnite. This native gold is responsible for high grade ore, and is largely due to reconcentration processes (la Lucette). At the scale of the Armorican Massif, the Sb ore is structurally controlled by large crustal-scale dextral strike-slip faults thatdrain fluids during the late-Variscan period, around 310-300 Ma. This chronological setting is confirmed by U-Pb dating by LA-ICP-MS on the apatites of la Lucette deposit. They are younger than the "orogenic gold" mineralization formation in the Armorican Massif (le Bellière) set-up between 340-325 Ma, but coeval withthe "or 300" event in the Central Massif. We propose that all antimony ore deposits can be grouped in the "epizonal" subtype of the "orogenic gold" model.
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Florent Cheval-Garabedian. Les minéralisations à Sb et Au tardi-varisques : vers un modèle génétique unifié ? : Exemples du Massif armoricain et du Massif central. Sciences de la Terre. Université d'Orléans, 2019. Français. ⟨NNT : 2019ORLE3097⟩. ⟨tel-03211983⟩

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