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Abstract:
The Iberian Pyrite Belt (IPB) is one of the outstanding metallogenic provinces worldwide, hosting great volumes of polymetallic massive sulphides. Felsic rocks account for up to 70% of the volcanic exposures in IPB and are the host of many sulphide orebodies. The Ervidel-Roxo (ER) and Figueirinha-Albernoa (FA) volcanic sequences (at the IPB northern sector, in Portugal) form two elongated and independent exposures roughly running WNW-ESE. The ER sequence is mainly composed of rhyolites with subordinated rhyodacites and rocks of intermediate composition, while the FA succession comprises mostly rhyodacitic to dacitic rocks. Rhyolitic and rhyodacitic magmas resulted from distinct degrees of melting of quartz-feldspar crustal rocks, while magmas of intermediate composition developed independently, representing outcomes of variably crustal contaminated basaltic magmas. The zircon saturation temperature (TSatZrn) and Ti-in-zircon thermometry were jointly used to assist the separation of volcanic series linked to high-temperature hydrothermal systems from those formed at lower temperature conditions, thus setting the ER and FA within an extensive regional database. The (TSatZrn was estimated according to the zircon solubility model reported in [1] and applying a regional database of whole- rock analyses with SiO2 > 60% and compositional factor M ranging from 1 to 1.9. The zircon crystallization temperatures (Ti-in-zircon) were estimated from measured Ti contents following the model proposed by Watson et al. [2] as modified by Clairborne et al. [3]. The combination of TSatZrn and Ti-in-zircon results suggest that the rhyolitic magmas feeding volcanic centers that host ore-forming systems mostly resulted from sources with minimal inherited zircon at high temperature (T > 800°C) In contrast, barren or weakly mineralized felsic volcanic sequences (rhyodacitic to dacitic) mainly preserve a large fraction of inherited zircon and formed under lower temperature conditions (< 800 °C, clustering at 700-750°C). The combination of both methods proved to be a useful exploration tool to assist in the discrimination of felsic volcanic series in terms of potential heat sources for initiating, driving and sustaining long-lived, high-temperature hydrothermal systems.
