Mineralogy and geochemistry of tin- and germanium-bearing copper ore, Barrigão re-mobilized vein deposit, Iberian Pyrite Belt, Portugal

Abstract

The Barrigão re-mobilized copper vein deposit, Iberian Pyrite Belt, southern Portugal, is located about 60 km south of Beja and 10 km southeast of the Neves Corvo ore deposit, in Alentejo Province. The deposit is structurally associated with a NE-SW striking fault zone inferred to have developed during late Variscan deformation. The copper ore itself is a breccia-type ore, characterized by up to four ore-forming stages, with the late stages showing evidence of fluid-driven element re-mobilization. The ore is dominated by chalcopyrite+tennantite-tetrahedrite, with minor arsenopyrite, pyrite, and löllingite. The supergene paragenesis is composed mainly of bornite, covellite, and digenite. Whole-rock analyses show anomalous tin and germanium contents, with averages of 320 and 61 ppm, respectively. Electron microprobe analysis of Barrigão ores revealed the germanium and tin to be restricted to chalcopyrite, which underwent late-stage hydrothermal fluid overprint along distinct vein-like zones. The measured zonal enrichment of tin and germanium is related to limited element re-mobilization associated with mineral replacement, which resulted in distinctive mineral disequilibrium. Fluid-driven element zoning affected chalcopyrite and tennantite coevally. The average contents of germanium and tin in chalcopyrite are of 0.19 and 0.55 wt.%, respectively, as confirmed through additional micro-proton-induced X-ray emission (micro-PIXE) analysis. The distribution of tin and germanium in chalcopyrite correlates strongly with iron. Tin and germanium covary. Minute sub-microscopic inclusions of an unknown Cu-Sn-Ge sulphide phase have been detected in chalcopyrite and in small vugs therein. These inclusions hint at a stanniferous sulphide as the most possible host for tin and germanium in chalcopyrite, although the idea of limited incorporation of these two elements through element substitution cannot be completely excluded.

Subsurface mapping in the Iberian Pyrite Belt using seismic reflection profiling and potential-field data

“…The upper, and in places, the lower VSC sequences are commonly stacked in tectonic sheets that were thrusted over the structurally lower Mér-tola Formation rocks. There are also Late Variscan nearvertical faults in two main families: NW-SE, dextral, and NE-SW, sinistral, both in places with small deposits and occurrences mostly of Cu, but also of Ba(Pb) and Sb(AU) (Matos et al 2003;Reiser et al 2011;Oliveira et al 2004Oliveira et al , 2013Inverno et al 2015b, see location in Matos and Filipe 2013). Mn-Fe small deposits related to VSC upper sequence lithologies are known at NW Neves-Corvo and Alcoutim (Leca 1976;Leca et al 1983;Matos and Filipe 2013).…”

“…Those strikeslip faults locally host small Late Variscan Cu (and other metals) vein deposits and occurrences (Carvalho 1991;Matos et al 2003;Reiser et al 2011;Matos and Filipe 2013), mostly forming a NW-SE Cu lineament anchored in Neves-Corvo mine and in close proximity to Neves-Corvo Fig. 9 Cotovio geological cross-section based on the logs of drill-holes CT01 (Somincor, 1992), CT08001 (AGC/Lundin Mining, 2008) and surface geological data.…”

“…The aim was to determine whether the structural framework associated with the Neves-Corvo mine, together with a lineament of Late Variscan vein-type Cu occurrences, extends SE to the Spanish border, south of Alcoutim (Carvalho 1991;Matos et al 2003;Reiser et al 2011), as suggested by several holes drilled in the flysch cover represented by the Mértola Formation shales and greywackes of Upper Visean age (Oliveira et al 2004). These data would also help to outline the upper and lower limits of the Volcanic-Sedimentary Complex (VSC) in the region.…”

Modelling of the Neves Corvo Area

“…It is also noteworthy that these faults host Cu (and Pb) sulphide veins with carbonates and barite mineralisations that were exploited in the 19th century (e.g. Barrigão, Ferrarias, Alcaria Queimada, Furnazinhas; Reiser et al 2011;Matos et al 2003) (see Fig. 11.24).…”

“…The regional trend of key tectonic structures such as the main Neves Corvo thrust (Leca et al 1983;Relvas et al 2006a;Oliveira et al 2006;Pereira et al 2008) was introduced in the predictive model, considering its exploration potential. The most important structural features are at least partially related with base metal mineralization, including volcanogenic massive sulphides such as Neves Corvo, Algaré and Montinho (Carvalho 1982;Barriga and Carvalho 1983;Oliveira et al 1984, 1992: Carvalho et al 1999) and Late Variscan vein-type deposits such as Ferrarias (Matos et al 2003), Cortes Pereiras (Mateus et al 2006) and Barrigão (Reiser et al 2011). Studies of fluid inclusions in quartz, stibnite, and barite as well as sulphur isotopic compositions from Late Variscan vein-type base metal deposits reveal different sources of sulphur and deposition conditions of the mineralizations (Germann et al 2003); different sources for the hydrothermal depositional fluids were also proposed by Relvas et al (2006b) for the Neves Corvo deposit based on O-, H-and C-isotope studies.…”