Abstract
The lithostratigraphic sequence in the Rosário–Neves Corvo antiform comprises the Phyllite–Quartzite Group, whose top is of Famennian age, the Volcanic Sedimentary Complex, of Strunian to upper Visean age, and the Mértola Formation (the lower unit of the Baixo Alentejo Flysch Group) of upper Visean age. The volcanic sedimentary complex comprises a lower sequence of Strunian (Late Famennian) age and an upper sequence of lower to upper Visean age. Detailed mapping of the antiform towards NW of the Neves Corvo mine, supported by palynological dating, identified two new lithostratigraphic units: the Barrancão member (upper Famennian) ascribed to the Phyllite–Quartzite Group and made up of laminated dark shales with siliceous lenses and nodules, and the Ribeira de Cobres Formation of the Volcanic Sedimentary Complex, containing shales, siltstones and fine volcaniclastic rocks. Based on zircon U–Pb isotope dating, five discrete felsic magmatic events were identified at approximately 354, 359, 365, 373 and 384 Ma. This suggests that the volcanic activity in the area has extended for about 30 Ma, in a context of high regional heat flow as indicated by the geochemical signatures of the felsic volcanic rocks. The characteristics of magmatism and the depositional environment indicated by the sedimentary record should therefore have been highly favourable for massive sulphide formation. However, evidence of massive sulphide mineralization in the study area is still to be found. Moreover, reconstruction of the volcanic facies architecture demonstrated that the volcanic units in the Rosário area are strongly dominated by coherent facies typical of the inner part of thick lavas/domes. In fact, most of their external part, the more favourable location for possible massive sulphide mineralization, is missing. Palynological dating indicates a significant hiatus, recognised between the lower and upper sequences of the volcanic sedimentary complex, which implies erosion of the top of the volcanic centre, where VHMS deposits could possibly have formed. However, lateral areas of this volcanic centre, eventually preserved at depth, have good potential to host massive sulphide mineralization.
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Acknowledgments
This work was sponsored by Lundin Mining through project VOLCROSARIO—Physical Volcanology and Petrochemical Studies of Volcanic Rocks in the Neves Corvo Exploration Area, in the Pyrite Belt. We would also like to thank Paulo Fernandes and Bruno Rodrigues (University of Algarve) for their help with zircon separation, and acknowledge Berit Løken Berg and Siri Simonsen (University of Oslo) for their assistance with sample characterisation and assistance during LA-ICPMS work. The authors would also like to thank José Garras Leal (LNEG) for field work during geological mapping of the area. Jaime Máximo (LNEG) helped the team as for the GIS system associated with the Rosário mapping. This is contribution no. 33 from the Isotope Geology Laboratory of the Department of Geosciences, University of Oslo.
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ESM Table 1
Summary of U–Pb isotope geochronology results (PDF 74 kb)
ESM Table 2
Lithogeochemistry data (PDF 238 kb)
ESM Table 3
U–Pb zircon data (PDF 370 kb)
ESM Fig. 1
Volcanic rock classification according to the AFM ternary diagram of Irvine and Baragar (1971). Pale blue circles basalts, dark blue circles dacites, green crosses rhyodacites, and red squares rhyolites (JPEG 1,017 kb)
ESM Fig. 4
Selected miospores species (JPEG 3,456 kb)
Figure captions list the taxonomic name of the figured specimen, followed by the drill hole reference/outcrop location, sample reference, slide number and microscopic coordinates.
1. G. echinata Hacquebard, 1957; Ribeira Porteiros outcrop, sample X3, slide 1, 1225–105
2. R. flexuosa (Juschko) Byvscheva, 1985; borehole CP2, sample 17, 359.0 m, slide 1, 1435–56
3. V. verrucosus Hacquebard, 1957; borehole CP2, sample 17, 359.0 m, slide 2, 1125–150.
4. R. lepidophyta (Kedo) Playford, 1976; borehole CP2, sample 17, 359.0 m, slide 1, 1037–75.
5. Diducites sp.; borehole CP2, sample 18, 363.20 m, slide 1, 1392–210.
6. Rugospora explicata Gonzalez et al., 2005; borehole NC 16, sample 6, 90.90 m, slide 1, 1375–40.
7. Indotriradites sp.; borehole CP2, sample 17, 359.0 m, slide 2, 1125–180.
8. Indotriradites explanatus (Luber) Kedo, 1963; borehole CP2, sample 18, 363.20 m, slide 1, 1455–115.
9. Pustulatisporites dolbii Higgs, Clayton, Keegan, 1988; borehole CP2, sample 11, 254.70 m, slide 1, 1235–210.
10. G. lemurata Balme emend. Playford, 1983; borehole CP2, sample 17, 359.0 m, slide 1, 1135–175.
11. Retusostriletes planus Dolby, Neves, 1970; Borehole CP2, sample 17, 359.0 m, slide 1, 1015–75.
12. Retusotriletes sp.; borehole CP2, sample 18, 363.20 m, slide 1, 1510–65.
13. Verruciretusispora loboziakii Higgs, Finucane, Tunbridge, 2002; borehole CP2, sample 8, 220.0 m, slide 1, 1400–35.
14. V. premnus Richardson, 1965; borehole CP2, sample 11, 254.70 m, slide 1, 1385–212.
15. V. premnus Richardson, 1965; Borehole CP2, sample 4, 169,50 m, slide 1, 1390–50.
16. V. premnus Richardson, 1965; borehole CP2, sample 4, 169.50 m, slide 1, 1256–132.
17. V. bulliferus Richarson, 1965; borehole NC16, sample 6, 90.90 m, slide 2, 1020–110.
18. V. scurrus (Naumova) McGregor, Camfield, 1982; borehole CP2, sample 8, 220.0 m, slide 1, 1425–133.
19. V. scurrus (Naumova) McGregor, Camfield, 1982; borehole CP2, sample 8, 220.0 m, slide 1, 1075–128.
20. R. incohatus Sullivan, 1964; Borehole CP2, sample 18, 363.20 m, slide 2, 1165–125.
ESM Fig. 5
Selected acritarchs and prasinophytes species (JPEG 2,708 kb)
Figure captions list the taxonomic name of the figured specimen, followed by the drill hole reference/outcrop location, sample reference, slide number and microscopic coordinates.
1. Gorgonisphaeridium elongatum; borehole CP2, sample 18, 363.20 m, slide 2, 1322–105.
2. Gorgonisphaeridium sp.; borehole CP2, sample 18, 363.20 m, slide 2, 1345–89.
3. G. plerispinosum Wicander, 1974; Borehole CP2, sample 17, 359.0 m, slide 1, 1520–150.
4. G. plerispinosum Wicander, 1974; borehole NC16, sample 9, 173.40 m, slide 1, 1358–140.
5. G. plerispinosum Wicander, 1974; borehole CP2, sample 17, 359.0 m, slide 1, 1098–125.
6. U. saharicum Jardiné, Combaz, Magloire, Peninguel, Vachey, 1972; borehole A6-1, sample 26.25 m, slide 2, 1165–205.
7. Crassiangulina sp.; borehole CP2, sample 17, 359.0 m, slide 1, 1126–138.
8. Cymatiosphaera sp.; borehole CP2, sample 18, 363.20 m, slide 1, 1075–55.
9. N. bacilla (Deunff) Playford, 1977; Borehole CP2, sample 18, 363,20 m, slide 1, 1035–200.
10. Baltisphaeridium sp., Borehole CP2, sample 18, 363.20 m, slide 1, 1045–107.
11. Cymatiosphaera perimembrana Staplin, 1961; Borehole CP2, sample 18, 363.20 m, slide 1, 1160–142.
12. Cymatiosphaera sp.; Borehole CP2, sample 18, 363.20 m, slide 2, 1270–130.
13. Maranhites perplexus Wicander, Playford, 1985; borehole NC16, sample 2, 81.05 m, slide 1, 1240–163.
14. Chitinozoans; borehole CP2, sample 17, 359.0 m, slide 1, 1200–55.
15. Maranhites mosesii (Sommer) Brito, 1967; borehole CP2, sample 6, 193.40 m, slide 1, 1390–230.
16. M. mosesii (Sommer) Brito, 1967; Ribeira Porteiros outcrop, sample X3, 1, 1345–15.
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Oliveira, J.T., Rosa, C.J.P., Pereira, Z. et al. Geology of the Rosário–Neves Corvo antiform, Iberian Pyrite Belt, Portugal: new insights from physical volcanology, palynostratigraphy and isotope geochronology studies. Miner Deposita 48, 749–766 (2013). https://doi.org/10.1007/s00126-012-0453-0
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DOI: https://doi.org/10.1007/s00126-012-0453-0