ABSTRACT
Epigenetic zinc-lead deposits in the Mesozoic basins of the Eastern Iberian Peninsula are mainly located in the Basque-Cantabrian and the Maestrat basins, and are hosted by dolomitised platform carbonates and talus facies of Aptian-Albian age. The Na-K-Cl-Br content of fluid inclusions has been determined in minerals using a crush-leach technique. Cl/Br and Na/Br ratios show that the origin of the ore-forming brines was sub-aerially evaporated seawater. Two fluids are recognized in the Basque-Cantabrian deposits, one with Cl/Br and Na/Br ratios indicating that the fluid did not attain halite saturation, the other has lower ratios which shows that it was a residual fluid remaining after halite precipitation. In the Maestrat deposits only the former fluid was present. In all carbonate-hosted deposits, the K/Na ratios denote very low fluid-rock interaction with K-rich units, which is consistent with fluid flow through largely carbonate units or into high permeability structures.
