Abstract
The Neves-Corvo world class Iberian Pyrite Belt volcanogenic massive sulphide (VMS) deposit located in southern Portugal, constitutes an important Cu–Zn–Pb active mine. Seven deposits are currently known, among which the Lombador deposit alone has estimated 150 Mt of massive sulphides. The life-time of the mine is dependent on the discovery of new exploration targets and it is vital to have accurate 3D geological models, not only to guide drilling campaigns but also to drive a winning/new strategy, which in the past has led to Semblana and Monte Branco discoveries: geophysical inversion and modelling. Furthermore, 3D geological models can contribute to the understanding of the tectonic and stratigraphic evolution of the region. Therefore, the goal of this study is to produce a realistic 3D geological model of the Neves-Corvo region, as only one model is presently publicly available: the PROMINE model, which includes the study area of this work and extends from Aljustrel to the border with Spain. Lundin Mining has also produced two unpublished, confidential models in 2007 and 2017. The latest Lundin model incorporates the same geophysical data used in this work (2D and 3D seismic reflection and time-domain electromagnetic (TEM) ground loop data) and approximately 7500 surface and underground drill-holes. The model presented in this research has much more detail than the 2012 PROMINE model in the Neves-Corvo region and uses an updated and revised drill-hole database with approximately 8000 drill-holes, revised geological cross-sections built from surface geology and drill-hole logs, new geological outcrop data, petrophysical and reprocessed geophysical data, and is therefore more detailed and accurate than any of the previous models, in particular the 2007 and PROMINE models. Land gravimetric and aeromagnetic data are also available in the study area but were not directly used to build the geological model but rather to investigate and check the model produced. Modelling was performed with industry standard software and the 3D curves resulting from the geological/geophysical interpretation were interpolated using different approaches to respect the hard data (interpretation lines and drill-holes). The resulting 3D stratigraphic surfaces required strong manual editing to respect the interpretation, due to the presence of folds, thrusts and tectonic nappes in the study area. The surfaces were afterwards tied to the drill-holes, resulting in a 3D model with great accuracy and detail in the near mining area and covering a larger area than previously available 3D geological models. The model has three major stratigraphic layers: the Mértola Flysch Formation and the Volcano-Sedimentary Complex (VSC), overlying the Phyllite-Quartzite Formation basement, and also the known VMS deposits (underlying the top of the Lower VSC) geometries according to drill-hole data. In the central part of the study area, where more drill-holes are available, the top of the Lower VSC sequence surface was also built. This approach will contribute to a better exploration drill-hole planning and the generation of new targets for exploration.
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adapted from Matos et al., 2020b) and the approximate locations of the previously available 3D geological modelling areas from the PROMINE project (red line), other unpublished, confidential studies (green), and the area with a more detailed model constructed in this work (cyan). Black rectangle shows approximate area displayed in b. b Geology of the central study area and the surface projections of the seven known deposits of Neves-Corvo after Matos et al., 2020b, based on the work of Oliveira et al. (1988)
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Acknowledgements
The authors thank Somincor/Lundin Mining for providing drill-hole, geological and EM data used in this study, and LNEG for the geological, land gravity and drill-hole data. This work was conducted through Smart Exploration (European Union’s Horizon 2020 programme grant agreement No. 775971) and EXPLORA (ALT20-03-0145-FEDER-000025) projects. Tomás Oliveira is acknowledged for several discussions on the 3D geological model. We are grateful to EMIT and Emerson for providing academic licenses of Maxwell and SKUA-GoCad software, respectively, and to Naphtali and Geosoft/Seequent for support along this project. Our thanks also to reviewer Luís Matias, the topic editor David McNamara and an anonymous reviewer for their contributions that significantly improved this work.
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Appendix
Appendix
Residual of the Bouguer anomaly map of the study area. A second degree polynomial was used to extract the regional and a reference density of 2.76 g/cm3 to produce the Bouguer anomaly. The geological limits shown in Fig. 1 are overlaid for location purposes
Total-field magnetic intensity, IGRF reduced and reduced-to-pole map of the study area. The reduction-to-pole was carried out using the central point of the map. The geological limits shown in Fig. 1 are overlaid for location purposes
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Carvalho, J., Dias, P., Revaux, C. et al. A drill-hole, geological and geophysical data-based 3D model for target generation in Neves-Corvo mine region, Portugal. Int J Earth Sci (Geol Rundsch) 111, 403–424 (2022). https://doi.org/10.1007/s00531-021-02120-x
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DOI: https://doi.org/10.1007/s00531-021-02120-x