Field Trip #1 The Neves Corvo Mine and the Paleozoic Geology of Southwest Portugal

Abstract

Pre and Post Meeting trips (Figures 1.1 and 1.2) The aim of this visit is to observe and discuss stratigraphic, petrologic and structural features of selected outcrops of the Volcano Sedimentary Complex in the Neves Corvo mine vicinity. Emphasis is put on the felsic and mafic volcanic sequences exposed at the Neves Corvo-Rosario and Castro Verde Anticlines (Figure 1.3). The trip departs from the Neves Corvo mine. This stop is behind the main ventilation raise (CPV2) of the Neves Corvo mine. The exposed shales and thinly bedded siltstones belong to the Brancanes Formation, the uppermost unit of the allochthonous suite of the Volcano Sedimentary Complex. Although weathered to yellow or gray colors (the fresh rocks are dark) it is possible to observe the bedding planes and the shale/siltstone alternations. The siltstones display graded bedding, suggesting deposition by weak turbidity currents. The shales are rich in organic matter. Fossils of Posidonia becheri and goniatites are common, indicating a Late Visean age. The cleavage trends N135, 70 NE and its attitude relative to bedding shows that the outcrop is the normal limb of a large anticline. Intersection lineation L1 plunges 101 to SE. It is worth noting that the overlying Mértola Formation turbidites of the Baixo Alentejo Flysch Group provided the same faunal association and Late Visean spores. This suggests a gradual lithological transition between the Brancanes and the Mértola Formation. The cut to the north of the road between the mine main transformer station and the main entrance exhibits the siliceous

Physical property analysis and preserved relative amplitude processed seismic imaging of volcanogenic massive sulfides—a case study from Neves–Corvo, Portugal

“…Felsic volcanic rocks with rhyolites–rhyodacites and tuffs, as well as the Neves formation, with its dark and black pyritic shales and thin‐bedded siltstones, are found in between the massive sulfide and Phyllite–Quartzite formations (Oliveira et al . ; Oliveira et al . ).…”

Trace-Element Distribution in Cassiterite and Sulfides From Rubane and Massive Ores of the Corvo Deposit, Portugal

“…At Neves-Corvo, three main types of ore are recognized (Oliveira et al 1997): i) rubané ore, which occurs at the top of massive sulfides and is particularly well displayed in the Corvo orebody, ii) "massive sulfide", which is the most abundant type of ore, and iii) "fissural" ores, occurring in the footwall rocks. Each type of ore has been further subdivided by SOMINCOR (Sociedade Mineira de Neves-Corvo) on the basis of the dominant mineral (Table 1).…”

“…result of thrusting, presumably owing to Late Hercynian tectonics, over massive ore, of which the rubané would represent part of the feeder zone. There is geological evidence in favor of such a hypothesis: i) the footwall contact of the rubané ore is a clear structural unconformity, transecting the stratigraphy; ii) there are unequivocal, multi-scale kinematic criteria in the internal structures; iii) the rubané ore lies partially on hangingwall turbidites, which are about 20 Ma younger than the Corvo mineralization (Oliveira et al 1997); iv) there is a clear lateral equivalence between the rubané ore and the uppermost footwall sequence (stockwork). The massive ore is composed of fine-grained sulfides, mainly pyrite followed by chalcopyrite, sphalerite, tetrahedrite-tennantite, galena and other minerals.…”

The relationship between ore deposits and oblique tectonics: the SW Iberian Variscan Belt

“…at University of Iowa on July 13, 2015 http://sp.lyellcollection.org/ Downloaded from actually represent the key to understanding what in fact may have made this part of the world so favourable for hosting about 5 Ma of intensely productive hydrothermal activity around the end of Devonian times (Pereira et al 1996;Oliveira et al 1997;Nesbitt et al 1999;Mathur et al 1999;Nieto et al 2000;Relvas et al 2001).…”