Incipient wolframite deposition at Panasqueira (Portugal): W-rutile and tourmaline compositions as proxies for early fluid composition

Eleonora Carocci (1) , Christian Marignac (1) , Michel Cathelineau (1) , Laurent Truche (2) , Marc Poujol (3) , Marie-Christine Boiron (1) , Filipe Pinto (4)

1 GeoRessources
2 ISTerre - Institut des Sciences de la Terre
3 GR - Géosciences Rennes
4 Instituto de Ciências da Terra

The main event responsible for the deposition of tungsten at Panasqueira was closely associated with strong tourmalinization of the wall rocks. Tourmaline is coeval with a W-rich rutile (up to 8-10 18 wt% W) and both minerals record an early introduction of W in the system, just before the main W deposition. Uranium-Pb dating of the rutile by LA-ICP-MS yielded an age of 305.2±5.7 Ma, which is 6-10 Ma older than the K-Ar age of 296.3±1.2 Ma obtained on muscovite, which was therefore not coeval of wolframite. Major and trace element concentration variations in tourmaline record fluid mixing between two end-members, both considered to be of metamorphic derivation on the basis of REE profiles. We report evidence for a fluid enriched in Co, Cu, Pb, Sc, Sr, V, Cr, Nb, Ta, Sn, interpreted to be of "local" origin, e.g., well-equilibrated with the host formations, and a fluid rich in Li, F, Fe, Mn, W inferred to be of deep origin and related to biotite dehydration. The second fluid carried the metals (in particular Fe and Mn) necessary for wolframite deposition, which were not necessarily inherited from the wall rocks through fluid-rock interaction. Micrometer scale variations in tourmaline and rutile crystal-chemistry are indicative of pulsatory fluid input during tourmalinization.

Domains: Geochemistry

Eleonora Carocci, Christian Marignac, Michel Cathelineau, Laurent Truche, Marc Poujol, et al.. Incipient wolframite deposition at Panasqueira (Portugal): W-rutile and tourmaline compositions as proxies for early fluid composition. Economic Geology, 2021, 16 (1), pp.123-146. ⟨10.5382/econgeo.4783⟩. ⟨insu-02965235⟩