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Title

Late-orogenic Au-bearing magmatic-hydrothermal systems of the Cévennes area (South French Massif Central)

Dates

June 5-9th 2017

Organizer(s)
Speakers

Dr. Alain Chauvet, Directeur de recherche CNRS, UMR 5243 – Géosciences Montpellier, Université de Montpellier 2

Description

The late-hercynian evolution of the French Massif Central is synchronous with the emplacement of numerous calc-alkaline granites around 300 Ma. This magmatism has been intensively studied and most models argue for a magmatic activity related to the late-orogenic extension, postdating the main compressional event at 340 Ma. During this event, large-scale magmatic hydrothermal fluid circulation occurred in the crust, generating various hydrothermal ore manifestations, the latest event being associated with the formation of gold-bearing quartz veins. The main objective of the field trip is to characterize and understand field relations between tectonic, magmatic, and hydrothermal features in order to construct a geological model of the mineralized system. The three days of intensive field work will include: First day: Characterization of the deformation in the Cévennes micashists (host for magma emplacement and mineralization) and distinction between hydrothermal features related to compression and those related to the late magmato-tectonic extensional events and relationship between fluid circulations, fluid trapping and shearing structures. Second day: Characterisation of the magmatic system - observations on several outcrops of the Mont-Lozère porphyritic granite and distinction between sub-solidus and magmatic foliation; defining the tectonic context that prevailed during magma emplacement and characterization of syn-tectonic late-magmatic features (aplite and pegmatite veins) along the borders of the granitic intrusion. Third day: Work on the link between magmatic and hydrothermal events using structural analysis on magmatic bodies and hydrothermal veins at the "Le Travers" outcrop; detailed geological mapping in an old gallery, with arsenopyrite mineralization containing invisible gold (the Le Gal lode). General discussion about the global tectono-magmatic and metallogenic model, including the available geochronological and geochemical data and potential consequences for exploration programs in similar terrains.

Location

Massif des Cévennes, France

Information
Places

11

Deadline for registration 28.05.2017
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