Rui Moura

Abstract
Associated with the exploitation of metallic minerals in Europe during the 20th century, several mining areas were abandoned without adequate environmental intervention. Furthermore, these areas lack studies to characterize the impact of pollution on the hydrogeological system. The area surrounding the tungsten mine of Regoufe, in northern Portugal, is one such area exploited during the Second World War. The accumulation of sulfide-rich tailings may have caused an acid mine drainage (AMD), where the leaching processes caused by seepage water led to soil contamination, evidenced by its acid character and anomalous concentrations of some Potentially Toxic Elements (PTE) reported in previous studies. The present research proposes an innovative approach that seeks the integration of different geophysical techniques to characterize the impact of mining activity on the subsurface. Electrical resistivity (ER) and electromagnetic (EM) were used to measure subsurface electrical properties. In addition, seismic refraction and Multichannel Analysis of Surface Waves (MASW) were performed to characterize the geometry, depth, and geomechanical behavior of the soil and rock bodies. The integration of these techniques allowed the interpretation of hydrogeological sections and a 3D resistivity volume to gain insight into the distribution of potentially contaminating fluids and tailings material present in the mining valley.

Abstract

Abstract
In recent years, with the rise of a growing economic and technological interest in lithium mineral resources, there has been a parallel concern, on the part of some local populations and even national environmental groups, for a hypothetical contamination problem that this type of exploitations may cause on the quality of groundwater. Thus, the present study was based on an evaluation of an open-pit quarry, in the socalled Alijo quarry, located in the North of Portugal, in the parish of Canedo, Ribeira de Pena municipality and Vila Real district. This exploitation, under concession by the company Jose Aldeia Lagoa & Filhos, SA, has been going on for at least 11 years and mainly supplies the ceramic and glass industry. It is in this context that this work is carried out. The general objectives are to assess signs of impacts that extractive activities, carried out in the open-pit exploitation area of Alijo, may have caused on the surrounding subsoil. In this sense, it was necessary to consider the aforementioned hypothesis of the existence of possible sources of water drainage with ionic anomalies for the surrounding environment. If this hypothesis were confirmed, then the level of underground conductivity would have to be proportionally high and obtainable through equivalent low values of electrical resistivity (high electrical conductivity). The current study was limited to geophysical tools along with a few chemical analysis of water samples collected in the open-pit exploration for control purposes. The signs we sought for could possibly be manifested in the form of anomalous concentrations of some of the elements of the mineralization of this lithiniferous pegmatite and whose effects could, hypothetically, be measured in the form of anomalous low values of underground electrical resistivity, as well as anomalous pH valuespresent in the drainage water. To this end, a study mainly supported by the electrical resistivity method was carried out. This method is based on the measurement of electrical resistivity variations of different subsoil geological materials, since rocks and soils, depending on their mineralogical composition, texture, porosity, fracturing and the content/chemical composition of the water contained in them, could exhibit anomalous, low electrical resistivity. The results revealed that no low resistivity values were found, typical of areas that normally exhibit natural or anthropogenic geochemical anomalies, or even, in more extreme cases, contaminations with acid drainages whose acidity and resistivity would be even lower and more anomalous.

Abstract
The Alto do Sobrido and Ribeiro da Serra Mines, are two antimony-gold mines located in Gondomar, Portugal, and are part of the Durico-Beirao Mining District (DBMD). In this work, we use four geophysical methods, such as gravity, radiometry, magnetic and electromagnetic, to improve the knowledge about these mineralizations and the lithologies and structures associated with them. These four methods allowed us to study these mineralizations through different physical properties. The gravimetric method allowed us to add more data to the hypothesis that the goldantimony mineralizations of the DBMD could be genetically associated with a nonoutcropping granite intrusion, which functioned either as a heat engine that promoted the circulation of fluids and/or as a source of fluids and metals itself. A 2D model was proposed, created with both modelling and inversion, to show that the presence of this granite could indeed fit the response of the negative anomalies found in the residual anomaly. The radiometric method was used mainly as a mapping tool, where we were able to distinguish between some of the lithologies of the area, like the Lower Ordovician quartzites and the metasediments of the Middle Ordovician to the Carboniferous, but also to observe different element concentrations within the Pre-Ordovician SchistGreywacke Complex (SGC). These variations within the SGC lithology don?t have a clear explanation as to why they occur. Still, we believe that they could occur due to the influence of the abovementioned non-outcropping granite. With the very low frequency (VLF) electromagnetic method, it was possible to locate areas of lower resistivities that correspond to the location of several known mineralized veins, as well as the probable location for a new vein. It was also possible to observe some weathered rocks near faults and fractures associated with the Durico-Beirao Shear Zone (DBSZ). With the magnetic method, it is possible to contribute to areas with the prevalence of lithologies and minerals with higher magnetic susceptibilities. Several magnetic anomalies found near the Alto do Sobrido mining works correspond to the mineralized veins paragenesis. Other anomalies appear to be related to the location of faults and fractures associated with the DBSZ. The use of all these methods allowed us to observe the mineralization responses and its associated lithologies and structures through the different geophysical properties while adding knowledge about the genesis of these mineralizations and possibly the location of new mineralized veins.

Abstract