Browsing by Author "Dias, Pedro"
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- 3D Constrained Gravity Inversion and TEM, Seismic Reflection and Drill-Hole Analysis for New Target Generation in the Neves-Corvo VMS Mine Region, Iberian Pyrite BeltPublication . Marques, Fábio; Dias, Pedro; Carvalho, João; Represas, Patricia; Spicer, Bill; Araújo, Vítor; Matos, João Xavier; Morais, Igor; Albardeiro, Luís; Sousa, Pedro; Pacheco, Nelson; Gonçalves, Pedro; Barbosa, DiegoABSTRACT: Located in the Iberian pyrite belt, the Neves-Corvo mine is a world-class massive sulfide deposit and the largest operating mine in Portugal with underground mining down to 1000 m depth focused on massive and stockwork Cu, Zn, Pb rich ores. Gravimetric data have had a leading role in the discovery of the seven known deposits, together with time-domain electromagnetic (TEM) ground data. In this work, we present the results of a 3D constrained gravity inversion carried out with legacy ground gravity data. The 3D gravity inversions were carried out using an updated density database containing approximately 142,000 measurements. A recently constructed 3D geological model based on reprocessed 2D seismic reflection, 3D seismic, TEM and updated geology from detailed surface mapping and drill-hole data, was used to constrain the inversions. The results show multiple high-density anomalies that may indicate the presence of mineralization at depth. These anomalies were therefore cross-checked with holes previously drilled. Approximately 97% of more than 1000 available surface drill-holes located on or at a distance of less than 200 m from the high-density anomalies intersected mineralization. However, gravity anomalies have been drilled in the past and particularly dense black shales or rhyolitic/gabbroic rocks have been intersected. To increase the success of future drilling, gravimetric anomalies have been correlated spatially with high-conductivity TEM zones and strong-amplitude seismic reflections, because igneous rocks usually present weak-to-moderate conductivity and a massive column of black shales presents a seismic signature quite different from that of mineralization. We concluded that some of these locations represent high-quality targets to consider following up with drilling and further exploration.
- A drill‑hole, geological and geophysical data‑based 3D model for target generation in Neves‑Corvo mine region, PortugalPublication . Carvalho, João; Dias, Pedro; Revaux, Charles; Matos, João Xavier; Araújo, Vítor; Inverno, Carlos; Marques, Fábio; Donoso, George; Pacheco, Nelson; Morais, Igor; Albardeiro, Luis; Batista, Maria Joao; MALEHMIR, Alireza; Spicer, Bill; de Oliveira, Daniel Pipa SoaresABSTRACT: 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, confdential models in 2007 and 2017. The latest Lundin model incorporates the same geophysical data used in this work (2D and 3D seismic refection 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 diferent 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.
- Geophysical investigation of the down-dip extension of the Lombador massive sulphide deposit, Neves-Corvo, PortugalPublication . Dias, Pedro; Thunehed, Hans; Represas, Patricia; Carvalho, João; Inverno, Carlos; Spicer, Bill; Ramalho, Elsa; Donoso, George; Araújo, Vítor; Marques, Fábio; Morais, Igor; MALEHMIR, Alireza; Pacheco, NelsonABSTRACT: 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 Forma tion 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 confrm the presence and amount of stockwork mineraliza tion down-dip the Lombador deposit inside the Neves-Formation or the Phyllite-Quartzite basement.
- Modelação estrutural e gravimétrica da estrutura salífera de Monte Real, Leiria, PortugalPublication . Dias, Pedro; Figueiredo, Fernando; Lopes, Fernando CarlosRESUMO: A estrutura salífera de Monte Real (ESMR) situa-se na Bacia Lusitânica. A sua evolução está associada às principais fases tectónicas desta bacia. Na distensão mesozoica desenvolve-se uma dinâmica salt withdrawal, individualizando-se a estrutura diapírica e as respetivas bacias de afundimento. Na fase de compressão cenozoica ocorreram migrações da massa evaporítica controlada por estruturas de direção NW-SE a WNW-ESE. Foram construídos mapas gravimétricos para reformular os mapas existen tes e posteriormente proceder à modelação direta 2D de perfis selecionados. Os modelos gravimétricos, com base em perfis de reflexão sísmica, demonstram relativamente à ESMR: i) assemelha-se a um salt overhang ligado à mother salt layer, através de um “pescoço de sal”; ii) unidades Meso-Cenozoicas têm uma geometria assimétrica nos seus dois flancos; iii) Formações mesozoicas mostram-se bastante arqueadas; iv) formações jurássicas estão, provavelmente ausentes no flanco W e no topo da estrutura; v) o topo possui uma língua de sal projetada para ESE.