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Geophysical investigation of the down-dip extension of the Lombador massive sulphide deposit, Neves-Corvo, Portugal
International Journal of Earth Sciences ( IF 1.8 ) Pub Date : 2021-03-02 , DOI: 10.1007/s00531-021-01998-x
Pedro Dias , Hans Thunehed , Patrícia Represas , João Carvalho , Carlos Inverno , Bill Spicer , Elsa Ramalho , George A. Donoso , Vitor Araújo , Fábio Marques , Igor Morais , Alireza Malehmir , Nelson Pacheco

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.



中文翻译:

葡萄牙内维斯-科尔沃Lombador块状硫化物矿床下倾扩展的地球物理研究

150吨Lombador块状硫化物矿床是Neves-Corvo矿的七个已知矿床之一。矿床向东北倾斜约30º–35º,且为露天倾角,目前开采深度达1 km。为了研究沉积物可能的向下连续性,​​进行了时域电磁(TEM)接地回路数据的一维约束反演,然后进行了同一区域内的3D电磁(EM)正演模拟和约束3D重力反演。为了进行EM和重力建模/反演,使用密度数据库(包括大约300个钻孔)和电导率数据库(通过电阻率测量和TEM数据的一维反演)构建了3D地质模型。电磁建模表明,涅夫斯组页岩是区域性的导电层,在Lombador地区向下延伸至大约1.6 km的深度。该层通常顶有大量硫化物,平均密度为2.83 g / cm3,而原料和块状硫化物分别平均达到3.1 g / cm 3和4.5 g / cm 3。3D约束重力反演结果不支持以下假设:在已知矿床的紧邻区域内,存在大量的硫化物,其位于Lombador矿的下倾方向。重力网格缺乏空间分辨率,研究区域有限,地下室内部也缺乏信息,这表明需要进一步的研究,以确认在Neves-Forms内Lombador矿床或下沉Lombador矿床的存量矿化的存在和数量。 Phyllite-石英岩地下室。

更新日期:2021-03-03
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