Geochemical and Nd isotopic signature of felsic volcanic rocks as a proxy of volcanic-hosted massive sulphide deposits in the Iberian Pyrite Belt (SW, Spain): The Paymogo Volcano-Sedimentary Alignment

Abstract

The Iberian Pyrite Belt (IPB), located in the South Portuguese Zone of the Iberian Massif (Spain), is a world-class VHMS province containing numerous, huge mineral deposits hosted by bimodal volcanic sequences. The province can be subdivided in several domains, which differ from each other both in the nature and relative abundance of their volcanic sequences, and in the distribution of associated VHMS deposits. In spite of its geological and economic interest, information available for the northern part of the province is still relatively scarce. We present a new dataset of geochemical and Nd isotopic analyses on the Paymogo Volcano-Sedimentary Alignment (PVSA), an area that is considered to be representative of this northern segment of the IPB.Volcanic sequences in the PVSA contain very scarce mafic rocks. In contrast, felsic rocks are abundant and have been classified in two groups: (i) the Paymogo rhyolitic sequence, hosting most of the VHMS deposits and (ii) a dacitic sequence. Although approximately coeval, these groups of felsic rocks clearly differ in geochemical features and ƐNd signature. In view of these differences, it is suggested that felsic rocks were produced from different mid-crustal domains during a major event of partial melting related to a regional, late Devonian/Early Carboniferous transtensional event. It is further suggested that some volcanic rocks previously described as andesites, are better interpreted as dacites.The age (347.3 ± 0.8 Ma), geochemical features, (Zr < 200 ppm) and ƐNd signature (−3.2 to −2.9) of the Paymogo rhyolites are very similar to those in other parts of the IPB including those hosting the deposits in the Riotinto Mining District, where petrographic, geochemical features and ƐNd signature had already been proposed as a proxy of VHMS mineralization. These similarities between the Riotinto and Paymogo areas suggest that their geochemical features and Nd isotope signature could provide useful exploration criteria throughout the IPB, in order to distinguish potential VHMS-bearing units from barren volcanic successions.