Hi Ignasi
There is a book 'Conservation of Coinage: Monetary exploitation and its restraint in
France, Catalonia and Aragon c.1000-1225 AD' by
Thomas N. Bisson,
Oxford University Press 1979, which may answer some of
his questions.
It is mainly concerned with the extraction of profit from coinage by the various issuing authorities, and the way in which they began to charge for a charter guaranteeing to maintain the
standard of the coinage rather than going to the effort of actually manipulating the coins, but it does discuss the varying silver contents and equivalences.
27 representative issues are illustrated, incuding one gold and three silver from Barcelona.
Best wishes
Alan