Abstract
The 150 Mt Lombador massive sulphide deposit is one of the seven known deposits of the Neves-Corvo mine. The deposit dips approximately 30º–35º to the NE and is open down dip, with current exploitation reaching down at 1 km depth. To investigate the possible downwards continuation of the deposit, a 1D constrained inversion of time-domain electromagnetic (TEM) ground loop data was conducted, followed by 3D electromagnetic (EM) forward modeling and a constrained 3D gravimetric inversion over the same area. To perform the EM and gravity modeling/inversion, a 3D geologic model was built using a density database comprising of approximately 300 drill-holes, and an electrical conductivity database with measurements from resistivity surveys and 1D inversion of the TEM data. The EM modeling shows that the Neves Formation shales are a regional conductive layer extending down to approximately 1.6 km depth in the Lombador area. This layer, often topped by massive sulphides, has an average density of 2.83 g/cm3, whereas stockwork and massive sulphide reach on average 3.1 g/cm3 and 4.5 g/cm3, respectively. The 3D constrained gravity inversion results do not support the hypothesis of the presence of massive sulphides located in the down-dip direction of the Lombador deposit in the immediate vicinity of the known deposit. The lack of spatial resolution of the gravity grid, the study area limited size and the lack of information from within the basement suggest further studies are required to confirm the presence and amount of stockwork mineralization down-dip the Lombador deposit inside the Neves-Formation or the Phyllite-Quartzite basement.
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Beowulf (Amira codes); Maxwell (EMIT); VOXI/Oasis Montaj (Geosoft).
References
Al-Chalabi M (1974) An analysis of stacking, RMS, average, and interval velocities over a horizontally layered ground. Geophys Prospect 22:458–475. https://doi.org/10.1111/j.1365-2478.1974.tb00099.x
Carvalho J, Inverno C, Matos J, Rosa C, Granado I, Branch T, Represas P, Carabaneanu L, Matias L, Sousa P (2017) Subsurface mapping in the Iberian pyrite belt using seismic reflection profiling and potential field data. Int J Earth Sci 106:899–915. https://doi.org/10.1007/s00531-016-1340-1
Carvalho J, Dias P, Revaux C, Inverno C, Pacheco N, Matos J, Malehmir A, Marques F, Araujo V, Batista MJ, Spicer B, Donoso GA, Albardeiro L, Morais I, Ramalho E, Filipe A, Oliveira D (2020) A new 3D geological model for the Neves-Corvo Mine Region, Iberian Pyrite Belt, Portugal. In: Extended abstracts of the near surface geoscience conference & exhibition 2020, Amsterdam, 7–10 December
Dias P, Represas P, Pacheco N, Thunehed H, Carvalho J, Ramalho E, Donoso G, Inverno C, Marques F, Araújo V (2020) 3D TEM and gravity modeling over the lombador deposit, Neves-Corvo, Portugal. In: Extended abstracts of the 82nd EAGE conference & exhibition 2020, Amsterdam, 6–9 December, We_E106_19
Donoso G, Malehmir A, Pacheco N, Araujo V, Penney M, Carvalho J, Spicer B, Beach S (2019) Potential of legacy 2D seismic data for deep-targeting and structural imaging at the Neves-Corvo massive sulphide-bearing site, Portugal. Geophys Prospect 68:44–61
Donoso GA, Malehmir A, Brodic B, Pacheco N, Carvalho J, Araujo V (2021) Innovative seismic imaging of VMS deposits, Neves-Corvo, Portugal: Part II - Surface Array, GEO-2020-0336.R2. https://doi.org/10.1190/geo2020-0336.1
Inverno C, Rosa C, Matos J, Carvalho J, Castello-Branco JM, Batista MJ, Granado I, Oliveira JT, Araújo V, Pereira Z, Represas P, Solá AR, Sousa P (2015) Chap. 11—modelling of the Neves Corvo Area. In: Weihed P (ed) 3D, 4D and predictive modelling of major mineral belts in Europe, Springler Verlag, Mineral Resource Reviews, pp 231–261. https://doi.org/10.1007/978-3-319-17428-0_9
Marques F, Matos JX, Sousa P, Spicer B, Penney M, Represas P, Araújo V, Carvalho J, Morais I, Pacheco N, Albardeiro L, Gonçalves P (2019) The role of legacy land gravity data in the Neves-Corvo mine discovery and its use in present-day exploration and new target generation. First Break 37:97–102
Oliveira JT, Pereira Z, Carvalho P, Pacheco N, Korn D (2004) Stratigraphy of the tectonically imbricated lithological succession of the Neves Corvo mine area, Iberian Pyrite Belt, Portugal. Miner Deposita 39:422–436
Oliveira JT, Romão J, Matos JX, Leal J, Rosa C (2016) Sheet 46-C (Almodôvar) from Geological Map of Portugal, scale 1:50 000, Un. Geologia, Hidrogeologia e Geologia Costeira, Laboratório Nacional de Energia e Geologia, Lisbon
Raiche A, Wilson G, Sugeng F (2007) Practical 3D inversion—the P223F Software Suite. In: 19th geophysical conference and exhibition abstracts, ASEG, pp 68–69
Ramalho EC, Gonçalves P, Trindade L, Monteiro Santos F, Matos JX (accepted) Reinterpretation of Electrical Resistivity from the Mértola–Serra Branca Sector (Northern Region of the Iberian Pyrite Belt and Southern Area of Polo do Lobo Domain). Comunicações Geológicas
Represas P, Sousa P, Torres L, Bengala M, Matos JX (2016) Gravimetric Map (Bouguer anomaly, density 2.6) of the South Portuguese Zone, Iberian Pyrite Belt, scale 1/400 000. LNEG/URMG, Lisboa (ISBN: 978-989-675-046-6)
Wilson G, Raiche A, Sugeng F (2006) 2.5D inversion of airborne electromagnetic data. Explor Geophys 37:363–371
Yavuz S, Kinkela J, Dzunic A, Penney M, Neto R, Araujo V, Ziramov S, Pevzner R, Urosevic M (2015) Physical property analysis and preserved relative amplitude processed seismic imaging of volcanogenic massive sulfides—a case study from Neves-Corvo, Portugal. Geophys Prospect 63:798–812
Acknowledgements
The authors thank Somincor/Lundin Mining for providing drill-hole, geological and TEM data used in this work, and LNEG for the land gravity data. This work was conducted through Smart Exploration and Explora projects. Smart Exploration has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 775971 and Explora under regional H2020 (ALT20-03-0145-FEDER-000025). We are also grateful to EMIT and Emerson for providing academic licenses of Maxwell and GoCad software, respectively, and Naphtali and Geosoft for the facilities related with Oasis and VOXI licences. We also acknowledge Matt Penney for providing useful comments that led to this work, and reviewer Taha Rabeh and Editor Wolf-Christian Dullo for their time improving this manuscript.
Funding
H2020 project Smart Exploration, Grant No. 775971 and project Explora ALT20-03-0145-FEDER-000025.
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PD, HT, BS and ER worked on the 1D inversion and 3D forward modeling of TEM data; NP, VA and CI participated on the drill-holes geological logs and geological interpretation; GD and AM reprocessed the seismic reflection data; IM and FM compiled the density database and the latter the gravimetric Bouguer anomaly grid; PR performed the 3D gravity inversion; JC coordinated and collaborated in all tasks.
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Gravity data are the property of LNEG and is commercially available upon request; electromagnetic data are the property of Somincor/Lundin and is not available.
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Dias, P., Thunehed, H., Represas, P. et al. Geophysical investigation of the down-dip extension of the Lombador massive sulphide deposit, Neves-Corvo, Portugal. Int J Earth Sci (Geol Rundsch) 110, 911–922 (2021). https://doi.org/10.1007/s00531-021-01998-x
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DOI: https://doi.org/10.1007/s00531-021-01998-x