Greisenisation and Permeability Changes in Granitic Intrusions Related to Sn-W Deposits: Case of Panasqueira

Gaëtan Launay (1, 2) , Stanislas Sizaret (1) , Laurent Guillou-Frottier (2, 1) , Eric Gloaguen (2) , Jérémie Melleton (2, 1) , Michel Pichavant (1) , Rémi Champallier (1) , Filipe Pinto (3) , Paulo Ferraz (3)

1 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
2 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)
3 Beralt Tin & Wolfram, Geology Department

The W-Sn veins of Panasqueira are connected with a massive quartz-muscovite greisen cupola. This greisen results from interactions between granitic rock and acid Sn-W hydrothermal fluid, which causes the destruction of feldspars of the Panasqueira granite. Greisenisation can constitute an important factor of control on fluid flow, and its role on metal transport remains to be established. Mineral reactions of greisenisation involve a decrease of the rock volume and thus an increase porosity (~6%). Consequently permeability increases significantly (10-20 to 10-17 m²) enhancing fluid flow in the greisen cupola and promoting further hydrothermal alteration and transport of metals. Finally a part of the mineralization is trapped in this porosity, with precipitation of cassiterite and sulfides. Therefore, Sn-W fluids are able to generate their own pathways in initial impermeable granite via greisenisation reactions.

Domaines: Planète et Univers [physics]; Sciences de la Terre; Géologie appliquée; Planète et Univers [physics]; Sciences de la Terre; Minéralogie; Planète et Univers [physics]; Sciences de la Terre; Pétrographie

Gaëtan Launay, Stanislas Sizaret, Laurent Guillou-Frottier, Eric Gloaguen, Jérémie Melleton, et al.. Greisenisation and Permeability Changes in Granitic Intrusions Related to Sn-W Deposits: Case of Panasqueira. SGA 2017, Aug 2017, Quebec, Canada. ⟨hal-01520216⟩