Hydrogeologic characterization of the abandoned mining site of Castelejo, Portugal by VLF-EM & RMT-R geophysical surveying

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Yellow depict change areas. Boxes show three alteration zones (see <a class="elsevierStyleCrossRef" href="#tbl0030">table 6</a>)." ] ] ] "autores" => array:1 [ 0 => array:2 [ "autoresLista" => "Jorge Lira" "autores" => array:1 [ 0 => array:2 [ "nombre" => "Jorge" "apellidos" => "Lira" ] ] ] ] ] "idiomaDefecto" => "en" "EPUB" => "https://multimedia.elsevier.es/PublicationsMultimediaV1/item/epub/S0016716914714953?idApp=UINPBA00004N" "url" => "/00167169/0000005300000002/v2_201505081358/S0016716914714953/v2_201505081358/en/main.assets" ] "en" => array:18 [ "idiomaDefecto" => true "titulo" => "Hydrogeologic characterization of the abandoned mining site of Castelejo, Portugal by VLF-EM & RMT-R geophysical surveying" "tieneTextoCompleto" => true "paginas" => array:1 [ 0 => array:2 [ "paginaInicial" => "135" "paginaFinal" => "151" ] ] "autores" => array:2 [ 0 => array:4 [ "autoresLista" => "Vitor Manuel Gomes de Oliveira, Luís Filipe Tavares Ribeiro" "autores" => array:2 [ 0 => array:4 [ "nombre" => "Vitor Manuel Gomes" "apellidos" => "de Oliveira" "email" => array:1 [ 0 => "vgomesoliveira@ist.utl.pt" ] "referencia" => array:1 [ 0 => array:2 [ "etiqueta" => "*" "identificador" => "cor0005" ] ] ] 1 => array:2 [ "nombre" => "Luís Filipe Tavares" "apellidos" => "Ribeiro" ] ] "afiliaciones" => array:1 [ 0 => array:2 [ "entidad" => "CVRM, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, Lisboa Portugal" "identificador" => "aff0005" ] ] "correspondencia" => array:1 [ 0 => array:3 [ "identificador" => "cor0005" "etiqueta" => "*" "correspondencia" => "Corresponding author:" ] ] ] 1 => array:3 [ "autoresLista" => "María Catarina Rosalino da Silva" "autores" => array:1 [ 0 => array:2 [ "nombre" => "María Catarina Rosalino" "apellidos" => "da Silva" ] ] "afiliaciones" => array:1 [ 0 => array:2 [ "entidad" => "Centro de Geología, FCUL, Edifício C6, Campo Grande, Lisboa, Portugal" "identificador" => "aff0010" ] ] ] ] "resumenGrafico" => array:2 [ "original" => 0 "multimedia" => array:7 [ "identificador" => "f0010" "etiqueta" => "Figure 2" "tipo" => "MULTIMEDIAFIGURA" "mostrarFloat" => true "mostrarDisplay" => false "figura" => array:1 [ 0 => array:4 [ "imagen" => "gr2.jpeg" "Alto" => 1603 "Ancho" => 1739 "Tamanyo" => 482884 ] ] "descripcion" => array:1 [ "en" => "“Beiras Uraniferous Region”. On the map of Portugal (left), the Castelejo mine locates at the red rectangle (adapted from <a class="elsevierStyleCrossRef" href="#bib0045">Ferreira, 1971</a>)." ] ] ] "textoCompleto" => "<a name="p136"></a>IntroductionThe activities developed by mining are, from the very start of operations, capable of degrading the surrounding environment and causing major environmental modifications, unless they are properly monitored and then controlled in accordance with the data gathered from the monitoring.Main modifications to the environmental balance generally result from digging a part of the land surface, as well as from the production of deposits of varying kinds of waste and / or sterile minerals (tailings) and from the chemical products used in ore separation / purification (<a class="elsevierStyleCrossRef" href="#bib0135">Younger et al., eds, 2002</a>). All these modifications cause hydrological and hydrogeological impacts (on superficial and ground water), geochemical impacts (on sediment, ground and alluvium) and biochemical impacts (on living beings) (<a class="elsevierStyleCrossRef" href="#bib0065">Lottermoser, 2003</a>).The characteristics and consequences of these impacts diverge according to when they are produced, and they can cause sporadic and /or diffuse pollution.Sporadic pollution occurs when the mine is being worked; if there is a control system in operation (monitoring) the pollution can be prevented from spreading.Diffuse pollution tends to occur once a mine has been abandoned. As a rule (<a class="elsevierStyleCrossRef" href="#bib0095">Rapantova et al., eds, 2008</a>) when a reasonably long time is spent on closing down a mine there is no longer any concern with monitoring, which is only undertaken when it is active.This attitude disregards possible subsequent risks to the closed down mine without taking any type of prevention to forestall them, and therefore it contributes to the propagation of the contamination.The environmental liabilities of mining are expressed, as a rule, by the incidence of abnormal (very high) concentrations of heavy metals in the sediments, ground and alluvia, as well as in the water within the area of influence of this activity (<a class="elsevierStyleCrossRef" href="#bib0095">Rapantova et al., eds, 2008</a>). The presence of these elements is essentially due to the leaching of the materials inside the mine and to erosion and leaching processes acting on the tailing materials extracted from the mine (<a class="elsevierStyleCrossRef" href="#bib0135">Younger et al., eds, 2002</a>). In fact, in open cast mining these elements are vulnerable to the action of the wind and the rain, which are their main vehicles of dissemination.In many cases of mine exploration, the action of the water over the tailings and other mine wastes causes a phenomenon known as acid mine drainage (AMD). This phenomenon particularly occurs in metal ore workings in which sulphide is exposed to oxidating environments, or when acid leaching from poor ore with a view to its concentration and subsequent recuperation occurs (<a class="elsevierStyleCrossRef" href="#bib0065">Lottermoser, 2003</a>). When the mine is definitely abandoned and if the evolution of the characteristics and the processes of environmental alteration are not controlled the ominous consequences will get worse as years go by. One of the best-known is the contamination of the surface water and groundwater, which occurs both during the phase of functioning and after the mine’s closure.The hydrogeological impact is a serious problem in almost all underground mines and in open cast mines, too. A series of measures can help to avoid or reduce this contamination. Thus, when the mine is abandoned it is essential to have the most accurate knowledge possible of the hydrogeology, the geology, the mineralogical composition of the materials, and the method of extracting and processing the ore to enable the prevention, correction and mitigation of environmental degradation caused by the operation.The method used to decommission a mine directly influences the local hydrogeological conditions. In conjunction with the operation there are often problems of mining subsidence, which occurs because methods of dismantling are used that do not consider the full extent of the galleries.When in operation we can see, in brief, the following effects:<ul class="elsevierStyleList" id="lis0005"><li class="elsevierStyleListItem" id="lsti0005">-Differential settlements</li><li class="elsevierStyleListItem" id="lsti0010">-Fractures on the ground</li><li class="elsevierStyleListItem" id="lsti0015">-Lowering of groundwater levels</li><li class="elsevierStyleListItem" id="lsti0020">-Reduced flow of aquifers or even their exhaustion</li><li class="elsevierStyleListItem" id="lsti0025">-Contamination of water.</li></ul>It can be said that during the course of its history Portugal several times gained importance for major mining, and it is even one of those countries in which mining carried out by Romans is well documented (<a class="elsevierStyleCrossRef" href="#bib0045">Ferreira, 1971</a>; <a class="elsevierStyleCrossRef" href="#bib0020">Carvalho et al., 1971</a>).From north to south Portugal 55 Roman mining operations were recorded, and we think there were others that have not been <a name="p137"></a>surveyed. They were mostly for gold and several remained in operation until very recent times (<a class="elsevierStyleCrossRef" href="#bib0085">Nunes, 1983</a>).Identification of fracturingGeophysical surveying has long been used to characterize fracturing in various geological formations. Particularly in mining areas, where fractures are often related to mineralized veins, the joint use of geophysical and other methods enables one to characterize the ore potential of an area of interest (<a class="elsevierStyleCrossRef" href="#bib0060">Kearey et al., 2002</a>).Geophysical surveying today has a very broad range of applications: from mining to civil engineering, through archaeological, environmental, geological and hydrological investigations to aquifer characterization.In addition to obtaining different kinds of information of geological interest and detecting geological structures that may contain water (e.g. faults and fractures), geophysical surveying is also used to map and monitor the presence and behavior of contaminants in groundwater, ranging from saltwater intrusion in coastal aquifers to the presence of contaminants from mining, industrial or agricultural operations (<a class="elsevierStyleCrossRef" href="#bib0060">Kearey et al., 2002</a>; <a class="elsevierStyleCrossRef" href="#bib0090">Oliveira, V., 2010</a>).Several geophysical methods can be applied to characterize soil and groundwater contamination, particularly those using ground-penetrating radar (GPR) devices, magnetometers or conductivimeters (<a class="elsevierStyleCrossRef" href="#bib0035">Daniels et al., 1995</a>; <a class="elsevierStyleCrossRef" href="#bib0070">Milson, 2003</a>).Using more than one surveying method improves the accuracy of interpretations, so as in the work described here, it is possible to geologically characterize the suspected area of contamination using one method and to adopt another to detail its intensity and spread. In this study we use two electromagnetic methods, adapted and refined at the University of Neuchâtel, where they are starting to be used in the characterization of karst discontinuities (<a class="elsevierStyleCrossRef" href="#bib0115">Thierrin et al., 1988</a>; <a class="elsevierStyleCrossRef" href="#bib0125">Turberg et al., 1992</a>).Risks associated with abandoned U mining sitesSome of the risks associated with abandoned uranium mining sites are usually identified through an ecological and human risk-assessment process. In general terms, once the ore has been milled it becomes yellowcake, a U3O8 concentrate, through a series of processes that include crushing, leaching, drying and filtering the initial material.The composition of the tailings produced over all these processes is represented in <a class="elsevierStyleCrossRef" href="#tbl0005">Table 1</a>.<elsevierMultimedia ident="tbl0005"></elsevierMultimedia>Tailings pose several risks and threats, some of which are (see <a class="elsevierStyleCrossRef" href="#f0020">Figure 4</a>):<a name="p138"></a><elsevierMultimedia ident="f0020"></elsevierMultimedia>a)Radon exhalationRadon (222Rn) is a dangerous radioactive gas which migrates to the surface of a tailings pile through a process of diffusion and is then released into the atmosphere.One of the most feared characteristics of Rn is the danger that it poses to the lungs if inhaled. According to <a class="elsevierStyleCrossRef" href="#bib0130">USEPA (2007)</a>, Rn can affect the health of people living many kilometers from a tailings pile.b)Gamma radiationThe radioactivity present in the tailings, mainly due to the uranium decay products of radium (226Ra) and thorium (230Th) can be harmful to those directly exposed to the emitted radiation.c)Dust blowingThe action of the wind over the tailings causes dust blowing. Dust blowing can spread many kinds of contaminants in the air. This risk worsens after the closure of the mine, as the tailings materials dry out.d)Dam failureDam failure, although rare, might be caused by anthropogenic or natural factors. Among the former, bad conception or design of the dam can be blamed while natural disasters – earthquakes, rainfall, snowfall or flooding are examples of natural causes.e)SeepageGroundwater contamination may be a major problem when considering the risks associated with uranium mill tailings.In fact, there is a strong relationship between the geological environment of the mine and its surroundings and the migration of contaminants to the aquifer, as we can also see in this study.The hydrology of the site is also crucial, along with the chemistry and type of the tailings (sand, slime or liquid and their composition, see <a class="elsevierStyleCrossRef" href="#tbl0005">Table 1</a> for details). The soil composition and the characteristics of the mining processes (e.g. underground or surface mining, use of acid leaching) are likewise important. The acid leaching poses an additional problem related to the increased solubility caused in some products, thereby facilitating their migration to groundwater.f)Other risksAmong the risks not illustrated in <a class="elsevierStyleCrossRef" href="#f0020">Figure 4</a>, the improper use of tailings must be mentioned.Actually the use of sandy tailings as building materials raises the danger of radiation exposure for the inhabitants of such buildings.Study AreaCurrent situation in PortugalIn Portugal there are about 175 abandoned mine workings, dozens of which are currently undergoing environmental restoration. About 60 are former uranium mines, which are for the most part located in very intense fractured zones.1907 is the year of the discovery of the Urgeiriça uranium-radium deposit. Only radium was exploited until 1944, when the exploitation and production of uranium began, which had place in Urgeiriça until the operation was closed in 2001 with the ending of processing of ore.The uranium workings were abandoned with the decline of its economic and strategic interest, and the last mines of this radioactive metal were closed in the early 1990s.The present work concerns an old mine site at Castelejo, an ancient uranium exploitation, located about 2km W of Vila Cortês da Serra in Gouveia municipality, Guarda district, and connected to the Mondego River basin through the Paço Stream (<a class="elsevierStyleCrossRef" href="#f0035">Figure 8-B</a>).At present, the area is being environmentally rehabilitated by the Portuguese state-owned enterprise charged with the environmental rehabilitation of old abandoned mining areas. Exploitation started with two open cast pits (now both flooded) between 1979 and 1990 which produced about 132 tonnes of U3O8. From 1992 up to 1997 production started to be done through in situ H2SO4 leaching of the poor material taken from the mine itself, as well as that from other workings located nearby. This latter process was responsible for the production of (more or less) a further 22.5 tonnes U3O8.The coordinates of the central point of the mine, located between both open skies, referring to the Unified European Reference System (ED50) are: latitude 40° 33’ 20’’N and longitude 7° 33’ 5’’W (<a class="elsevierStyleCrossRef" href="#f0035">Figure 8-B</a>).GeologyMainland Portugal is formed by an ancient and hardened core, usually called the Hercynian Massif, part of the so-called Hesperian Massif, and by land coverage (<a class="elsevierStyleCrossRef" href="#f0005">Figure 1-A</a> and <a class="elsevierStyleCrossRef" href="#f0005">B</a>).<a name="p139"></a><elsevierMultimedia ident="f0005"></elsevierMultimedia>The Hercynian Massif comprises ante-Mesozoic lands, and consists of sedimentary, eruptive and metamorphic rocks (<a class="elsevierStyleCrossRef" href="#bib0100">Ribeiro et al., 1979</a>).The land coverage includes sedimentary and some Meso-Cenozoic eruptive rocks which form the western and southern edges of the country, as well as modern deposits, consisting of alluvial flood plains and different beach levels, which result from various basins of sedimentary filling (<a class="elsevierStyleCrossRef" href="#bib0105">Teixeira, 1966</a>; <a class="elsevierStyleCrossRef" href="#bib0100">Ribeiro et al., 1979</a>; <a class="elsevierStyleCrossRef" href="#f0005">Figures 1-A</a> and <a class="elsevierStyleCrossRef" href="#f0005">B</a>).The Hesperian Massif is crossed by the Central Cordillera, a ENE-WSW lying mountain range, which divides it into two: the north Meseta (Meseta signifies Little Table, so the expression has an essential geomorphological meaning) with an average altitude of 800meters, and the south Meseta, with an average altitude of about 400m.The formations that form the Hesperian Massif, mainly schists, granites and graywackes, suffered the action of Caledonian, Hercynian and Alpine orogenies, although the Hercynian orogeny is the one whose effects are better documented here.In the Iberian Peninsula, the Hercynian orogeny began in the Middle Devonian and continued until the Late Carboniferous period (<a class="elsevierStyleCrossRef" href="#bib0100">Ribeiro et al., 1979</a>).Although it has developed over several stages, two main phases can be distinguished (dated by the presence of unconformities in the outer zones or by radiometric dating of certain granites (<a class="elsevierStyleCrossRef" href="#bib0015">Araújo, M.A. (2002)</a>; <a class="elsevierStyleCrossRef" href="#bib0005">Abranches, M.C.B. et al. (1982)</a>):<ul class="elsevierStyleList" id="lis0010"><li class="elsevierStyleListItem" id="lsti0030">-First one, which ran from Middle Devonian to Visean</li><li class="elsevierStyleListItem" id="lsti0035">-Second, a phase dating from Westphalian. The orogenic actions caused folding in a general NW-SE orientation, as well as synorogenic magmatism and regional metamorphism.</li></ul>Between the Late Westphalian and Late Permian periods the Hercynian chain suffered uplifts, the results of erosion and post-tectonics intrusive actions, mainly consisting of alkaline and calc-alkaline granitoid rocks, which gave rise to considerable filonian mineralization.The last stages of Hercynian orogeny induced intense fracturation in the Massif, causing various movements of uplifting and sinking.During the Cenozoic era the Hesperian Massif suffered fracturation again, now predominantly in the NE-SW direction, as a result of the Alpine orogeny actions that occurred (<a class="elsevierStyleCrossRef" href="#bib0100">Ribeiro et al., 1979</a>).<a name="p140"></a>In geological terms (see <a class="elsevierStyleCrossRef" href="#f0010">Figures 2</a> and <a class="elsevierStyleCrossRef" href="#f0015">3</a>) the Castelejo mine is located in medium-grained two-mica monzonitic granite, with porphyritic tendency.<elsevierMultimedia ident="f0010"></elsevierMultimedia><elsevierMultimedia ident="f0015"></elsevierMultimedia>Various granitic intrusions occurred in the late Hercynian age (the mineralizations that occurred are related to quartz veins and usually consist of uranium phosphates - torbernite, autunite and sabugalite - secondary minerals derived from uraninite and other uranium weathering product compounds).The distribution of U in PortugalMost known uraniferous deposits lie in central Portugal, in the region covered by the four districts (a district corresponds to an administrative territorial division) of Viseu, Guarda, Coimbra and Porto, although the largest number of mining operations are concentrated in the first two districts (which are, in general terms, presented in <a class="elsevierStyleCrossRef" href="#f0010">Figure 2</a>).The uranium deposits are related to post-tectonic Hercynian magmatism, usually in the form of monzonitic granite intrusions, medium to coarse-grained, two-mica and having a porphyritic tendency.They usually lie in a NE-SW direction. Most deposits are related to quartz veins installed in fractures in granites.There are various opinions about the genesis of uranium deposits. In brief, most <a name="p141"></a>authors (<a class="elsevierStyleCrossRef" href="#bib0030">Cerveira, A., 1951</a>; <a class="elsevierStyleCrossRef" href="#bib0080">Neiva, J.M.C., 1995</a>) albeit with slight variations, considered primary deposits as coming from hydrothermal deposits, while the secondary deposits -impregnation deposits - are considered as coming from the leaching of the first and subsequent precipitation in favourable structures.Scope of the studyThe superficial and groundwater circulation is structurally conditioned by the intense fracturing in the area (<a class="elsevierStyleCrossRef" href="#bib0110">Teixeira, C. et al., 1967</a>). To characterize the fracturing, two superficial geophysical exploration field campaigns were conducted. The first consisted of a very low frequency (VLF) survey that enabled the identification of major fault systems that may constitute prime pathways for groundwater flow. The second campaign was a radio magnetotelluric (RMT) survey conducted at a fault gauge fulfilled with weathered granite material. This fault gauge collects the mine’s natural gradient flow, and from the survey we have obtained the resistivities and thicknesses of the weathered material.EDM, the Portuguese state-owned enterprise, in charge of the environmental rehabilitation of the old abandoned mining areas, has been monitoring several water points (wells and piezometers) located in the vicinity of the old Castelejo mine on a more or less regular basis since 1991. However, the collected data are difficult to process since neither the piezometer geometrical characteristics nor its depths of abstraction are known. Besides, data collected over time vary both quantitatively as qualitatively, which makes data analysis difficult.<a name="p142"></a>Furthermore, the collected data relate to two different realities – dug wells and drilled wells - and it is reasonable to apply them a conceptual model based on the supposition that they concern two equally different aquifers: a porous aquifer located near the surface, in the superficial zone of granite weathering, taken as an unconfined aquifer and shown up by countless flooded zones and superficial abstractions detected in the field, and a fissured aquifer, located under the first one in a deeper fractured rock zone, taken as a confined aquifer (<a class="elsevierStyleCrossRef" href="#bib0010">Afonso, M.J.C. 2003</a>; <a class="elsevierStyleCrossRef" href="#bib0025">Carvalho, J.M., 2006</a>).Therefore, in view of the hydrogeological characterization of the former mining area and the identification of main drainage pathways, supplementary data was needed to enable us to confirm (or not) the layout of the several unpublished reports. For this, two geophysical surveys were undertaken, using two different geophysical methods. This was intended to supplement the information obtained in each campaign.main fractures identified in the initial study performed, which was based on photogeological analysis of the studied area.Materials and MethodsBases and methodsIt is common to be faced with problems of several orders when approaching the hydrogeological study of fractured rocks with a view to their hydraulic characterization.In the case of granitic rocks, in particular, which, when fresh, are practically impermeable to water, it is well known that its secondary porosity, namely due to several physical processes, can very often play a determinant role in water circulation.The circulation of the water in this type of rock prompts a fundamental question, which is linked to the identification of the fractures from where the drainage can proceed: these fractures are not always easy to identify, bearing in mind the thickness of the covering layer that sometimes overlies the rock (<a class="elsevierStyleCrossRef" href="#bib0010">Afonso, M.J.C. 2003</a>).So, we need to resort to indirect survey methods that enable us to identify any abnormalities of hydrogeological interest.The methods used in the current work are very low frequency – electromagnetics (VLFEM) and radio magnetotelluric – resistivity (RMT-R). Both methods are based on radio waves from low frequency to very low frequency – from 12 kHz to 300 kHz in both methods – which are emitted by antennas located all over the world (<a class="elsevierStyleCrossRef" href="#bib0115">Thierrin, J. et al., 1988</a>; <a class="elsevierStyleCrossRef" href="#bib0125">Turberg, P. et al., 1992</a>; <a class="elsevierStyleCrossRef" href="#bib0120">Turberg, P., 1993</a>).These waves also propagate in the basement, with the depth of penetration of their generated primary field being given by :<elsevierMultimedia ident="eq0005"></elsevierMultimedia><a name="p143"></a>where :P - depth of penetration of the primary field generated by the radio waves (m)ρa - apparent resistivity (ohm.m)F - wave frequency (Hz).But these waves also give rise to a secondary electromagnetic field, which depends on the nature of the material crossed and can be detected at the surface (<a class="elsevierStyleCrossRef" href="#bib0115">Thierrin, J. et al., 1988</a>; <a class="elsevierStyleCrossRef" href="#bib0125">Turberg, P. et al., 1992</a>). Consequently the resultant electromagnetic field consists of the sum of the primary and secondary fields, which are distinguished by intensity, phase and direction.VLF-EM MethodWith the VLF-EM method, special, well-adjusted devices make use of one horizontal axis coil to measure the intensity of the primary electromagnetic field (Hp), while the intensity of the secondary field (Hs) is measured through one vertical axis coil.The equipment used was specifically developed for hydrogeological purposes by Prof. Imre Müller, of the Centre of Hydrogeology of the University of Neuchâtel (<a class="elsevierStyleCrossRef" href="#bib0075">Müller, I., 1983</a>).It differs from commercial appliances since it continuously registers the variation of the signal. The joint use of a data logger and a GPS secures the right location of registered anomalies (<a class="elsevierStyleCrossRef" href="#bib0075">Müller, I., 1983</a>; <a class="elsevierStyleCrossRef" href="#bib0115">Thierrin, J. et al., 1988</a>; <a class="elsevierStyleCrossRef" href="#bib0125">Turberg, P. et al., 1992</a>).The vertical components are either in phase or out of phase relative to the primary field.The expression of the results is given by the relation Hs/Hp %, as illustrated in <a class="elsevierStyleCrossRef" href="#f0025">Figure 5</a>.<elsevierMultimedia ident="f0025"></elsevierMultimedia>The method permits detection of the presence of electricity-conducting bodies such as faults filled with clay materials exhibiting equally great sensitivity to other important hydrogeologic characteristics, such as lateral facies variations (<a class="elsevierStyleCrossRef" href="#bib0040">Dill, A. et al., 1998</a>).The method has the additional advantage of not requiring contact with the ground –once the antenna is automatically oriented, it can be used manually or installed in vehicles.RMT-R MethodThe RMT-R method measures the electric field, Ex, in the direction of propagating radio waves (e.g. in the emitter antenna direction). The electric field is measured between two electrodes inserted in the ground at a certain distance from each other (in our work this distance is 5meters).<a name="p144"></a>The RMT-R method also measures the magnetic field, Hy, which is measured through a coil whose horizontal axis is normal to the emitter antenna direction.The apparent resistivity, ρa, results from the application of <a class="elsevierStyleCrossRef" href="#eq0010">equation (2)</a>:<elsevierMultimedia ident="eq0010"></elsevierMultimedia>where:Ex - electric component of the resultant field (Volt/m)Hy - magnetic component of the resultant field (Ampere/m)μ0 - permeability of free space (Henry/m).F - wave frequency (Hz).This method also measures the phase-shift, ϕ, between the electric and magnetic components. The phase-shift enables inference of the stratigraphic characteristics of the place under study: there will be a conductive layer over a resistive one if ϕ<45°, there will be a resistive layer over a conductive one if ϕ>45º, and the medium is considered homogeneous if ϕ=45°.Given the fact that emitter antennas being located far apart from the receiver device, we could consider all directions of propagation as essentially parallel, which in practice reduces to only one direction. Once the device allows the simultaneous measurement of 4 frequencies, we can interpret it as supplying information from 4 depths (see <a class="elsevierStyleCrossRef" href="#f0030">Figure 6</a>). An inversion program (FITVLF2) for the personal computer was used to obtain the real resistivities and the thicknesses of the layers traversed. Although its description is beyond the scope of this article, detailed information about the method of inversion and its implementation can be found at <a class="elsevierStyleCrossRef" href="#bib0050">Fischer, G. et al. (1981)</a>, <a class="elsevierStyleCrossRef" href="#bib0055">Fischer, G. (1985)</a> and <a class="elsevierStyleCrossRef" href="#bib0125">Thierrin, J. (1992)</a>.<elsevierMultimedia ident="f0030"></elsevierMultimedia>Since it is a quick method that enables measurements (soundings) to be taken at 5m intervals it allows the detection of heterogeneities, and it is possible to infer the permeability of the formations from their resistivity values, although this has not been done in the present study.Multidirectional soundings can also be carried out to get information about the anisotropy of the studied medium.Results and DiscussionVLF-EMIn <a class="elsevierStyleCrossRef" href="#f0035">Figure 8</a> we present a photographic map of the places surveyed by VLF-EM method.<elsevierMultimedia ident="f0035"></elsevierMultimedia>The marked points show the paths walked along and color gradation indicates that the relation Hs/Hp % is (the deeper the color, the stronger the relationship Hs/Hp %):<ul class="elsevierStyleList" id="lis0015"><li class="elsevierStyleListItem" id="lsti0040">-red color – positive Hs/Hp % relationship;</li><li class="elsevierStyleListItem" id="lsti0045">-blue color – negative Hs/Hp % relationship;</li><li class="elsevierStyleListItem" id="lsti0050">-white color - near zero Hs/Hp % relationship.</li></ul>All profiles were carried out at 16 kHz frequency and some important conclusions can be drawn from their interpretation (see <a class="elsevierStyleCrossRef" href="#f0035">Figure 8</a>).Very negative or very positive values (Hs/Hp<-40 % or Hs/Hp>40 %) correspond to measurements taken under the influence of high tension power lines and so they must not be considered. Negative Hs/Hp % values are usually related to major resistivity layers, whereas positive Hs/Hp % values indicate major electricity conductivity layers (for instance, the presence of clay materials).Successive inflections of Hs/Hp % indicate fracture zones, the more important the greater the registered amplitude.In <a class="elsevierStyleCrossRef" href="#f0040">Figure 9</a> we present a summarized interpretation of the obtained results, in order to illustrate the stated above. The joint interpretation of the VLF-EM results with information gathered on EDM internal reports and field reconnaissance data made it possible to draw a map summarizing the fractures in the studied area, from which main drainage trends can be established (see <a class="elsevierStyleCrossRef" href="#f0045">Figure 10</a>, wherein places where the presence of water was noted are marked in blue).<elsevierMultimedia ident="f0040"></elsevierMultimedia><elsevierMultimedia ident="f0045"></elsevierMultimedia>RMT-RApparent resistivity and phase difference between the electric and magnetic fields were measured in RMT-R survey profiles. These profiles were defined in the sectors marked with circles, and they were quite enlightening (see <a class="elsevierStyleCrossRef" href="#f0045">Figures 10</a> and <a class="elsevierStyleCrossRef" href="#f0050">11</a>).<a name="p145"></a><elsevierMultimedia ident="f0050"></elsevierMultimedia><elsevierMultimedia ident="f0065"></elsevierMultimedia><a name="p146"></a><a name="p147"></a>In particular, the profiles located NW of the mining site, in the Castelejo Valley (see <a class="elsevierStyleCrossRef" href="#f0055">Figure 12</a>), have revealed very interesting features.<elsevierMultimedia ident="f0055"></elsevierMultimedia>After processing the obtained results using an inversion program (<a class="elsevierStyleCrossRef" href="#bib0055">Fischer, G., 1985</a>), the real resistivities and thicknesses of the different layers were computed (<a class="elsevierStyleCrossRef" href="#f0060">Figure 13</a>). Mid sector values were calculated next.<elsevierMultimedia ident="f0060"></elsevierMultimedia>We noted that all the profiles defined along the Castelejo Valley exhibit a decrease in resistivity with depth. Once we are away from the mineralized vein, this may suggest either more alteration of granites with depth, or a situation of deep-contamination.The profile P1 reproduced in <a class="elsevierStyleCrossRef" href="#f0060">Figure 13</a> (referring to deep pink points in <a class="elsevierStyleCrossRef" href="#f0045">Figures 10</a> and <a class="elsevierStyleCrossRef" href="#f0050">11</a>) is located near the old mining site: resistivity values correspond to those obtained for almost unweathered granite blocks (with resistivity values>1000 Ω.m) immersed in a weathered matrix (with resistivity values≈700 Ω.m).On the other side, the profile P6, also reproduced separately in <a class="elsevierStyleCrossRef" href="#f0060">Figure 13</a> (here referring to light green points in <a class="elsevierStyleCrossRef" href="#f0045">Figures 10</a> and <a class="elsevierStyleCrossRef" href="#f0050">11</a>) is located along the main fault valley near the confluence with the mine stream: resistivity values corresponding to a situation of very weathered rock material, decreasing with depth.The profiles carried out along the valley that spreads out WNW from washing pools, indicate that this is a fault valley, filled in with erosion material. As before mentioned, all profiles show a decrease of resistivity not only with depth but also as we go away from the mine towards the main fault valley (e.g. from P1 to P6, see <a class="elsevierStyleCrossRef" href="#f0055">figure 12</a>).<a name="p148"></a><a name="p149"></a><a name="p150"></a>ConclusionsAt the beginning of the study it was known the situation in terms of regional tectonics, which was known complex for being associated with a number of episodes of tardi-Hercynian fracturing, as well with the Alpine tectonics.In order to better characterize the underlying geology of the old Castelejo mine, two geophysical surveying campaigns were conducted at the site. Both the results of the first campaign (VLF-EM results) and the references consulted, particularly in EDM internal reports, pointed to the presence of faults and fractures which might constitute the main pathways of superficial and underground drainage.In the second campaign, measurements of RMT-R were performed to the WNW and ESE of the centre of exploration. Apparent resistivity and phase difference between the electric and magnetic fields were the measured values. The obtained values were projected graphically and processed, after which real resistivities and thicknesses were determined through the use of an inversion program.After matching the literature data with the data obtained during field work, it was concluded that the direction of maximum compressive stress, s1, located NNW-SSE to NW-SE, where extension fractures are developed, should be the one wherein groundwater flows more easily, since the larger openings of the fractures provide a better flow.However, it was not possible to establish a direct correspondence between real resistivity values and permeability values, which, although outside the scope of this article, may be relevant for v.g. hydrogeological purposes.All profiles also reveal a singular situation – their resistivity values decrease with depth.This can be due to natural causes (more weathered layers) or it can indicate a situation of deep contamination with acid drainage (increased mineralization).In fact, we are in the presence of a former uranium exploration, in which ore acid leaching took place in a flooded open sky, with a number of negative implications in the surroundings, particularly over groundwater. Treatment operations of the mine water still occur. However, any risks to populations seem weak, given the isolation of the area in terms of population.Also the use of water seems to be aimed to agricultural purposes rather than for human consumption.This point will be addressed in the future through the implementation of a hydrochemical monitoring plan." "textoCompletoSecciones" => array:1 [ "secciones" => array:11 [ 0 => array:3 [ "identificador" => "xres498008" "titulo" => "Resumen" "secciones" => array:1 [ 0 => array:1 [ "identificador" => "abst0005" ] ] ] 1 => array:2 [ "identificador" => "xpalclavsec519555" "titulo" => "Palabras clave" ] 2 => array:3 [ "identificador" => "xres498007" "titulo" => "Abstract" "secciones" => array:1 [ 0 => array:1 [ "identificador" => "abst0010" ] ] ] 3 => array:2 [ "identificador" => "xpalclavsec519554" "titulo" => "Key words" ] 4 => array:3 [ "identificador" => "sec0005" "titulo" => "Introduction" "secciones" => array:2 [ 0 => array:2 [ "identificador" => "sec0010" "titulo" => "Identification of fracturing" ] 1 => array:3 [ "identificador" => "sec0015" "titulo" => "Risks associated with abandoned U mining sites" "secciones" => array:6 [ 0 => array:2 [ "identificador" => "sec0020" "titulo" => "Radon exhalation" ] 1 => array:2 [ "identificador" => "sec0025" "titulo" => "Gamma radiation" ] 2 => array:2 [ "identificador" => "sec0030" "titulo" => "Dust blowing" ] 3 => array:2 [ "identificador" => "sec0035" "titulo" => "Dam failure" ] 4 => array:2 [ "identificador" => "sec0040" "titulo" => "Seepage" ] 5 => array:2 [ "identificador" => "sec0045" "titulo" => "Other risks" ] ] ] ] ] 5 => array:3 [ "identificador" => "sec0050" "titulo" => "Study Area" "secciones" => array:4 [ 0 => array:2 [ "identificador" => "sec0055" "titulo" => "Current situation in Portugal" ] 1 => array:2 [ "identificador" => "sec0060" "titulo" => "Geology" ] 2 => array:2 [ "identificador" => "sec0065" "titulo" => "The distribution of U in Portugal" ] 3 => array:2 [ "identificador" => "sec0070" "titulo" => "Scope of the study" ] ] ] 6 => array:3 [ "identificador" => "sec0075" "titulo" => "Materials and Methods" "secciones" => array:3 [ 0 => array:2 [ "identificador" => "sec0080" "titulo" => "Bases and methods" ] 1 => array:2 [ "identificador" => "sec0085" "titulo" => "VLF-EM Method" ] 2 => array:2 [ "identificador" => "sec0090" "titulo" => "RMT-R Method" ] ] ] 7 => array:3 [ "identificador" => "sec0095" "titulo" => "Results and Discussion" "secciones" => array:2 [ 0 => array:2 [ "identificador" => "sec0100" "titulo" => "VLF-EM" ] 1 => array:2 [ "identificador" => "sec0105" "titulo" => "RMT-R" ] ] ] 8 => array:2 [ "identificador" => "sec0110" "titulo" => "Conclusions" ] 9 => array:2 [ "identificador" => "xack161017" "titulo" => "Acknowledgments" ] 10 => array:1 [ "titulo" => "References" ] ] ] "pdfFichero" => "main.pdf" "tienePdf" => true "fechaRecibido" => "2012-11-27" "fechaAceptado" => "2013-08-28" "PalabrasClave" => array:2 [ "es" => array:1 [ 0 => array:4 [ "clase" => "keyword" "titulo" => "Palabras clave" "identificador" => "xpalclavsec519555" "palabras" => array:5 [ 0 => "prospección geofísica" 1 => "acuífero fisurado" 2 => "agua de mina" 3 => "VLF" 4 => "RMT-R" ] ] ] "en" => array:1 [ 0 => array:4 [ "clase" => "keyword" "titulo" => "Key words" "identificador" => "xpalclavsec519554" "palabras" => array:5 [ 0 => "geophysical surveying" 1 => "fissured aquifer" 2 => "mine water" 3 => "VLF" 4 => "RMT-R" ] ] ] ] "tieneResumen" => true "resumen" => array:2 [ "es" => array:2 [ "titulo" => "Resumen" "resumen" => "Hay alrededor de 175 minas abandonadas en Portugal, de las cuales unos 60 son antiguas explotaciones de uranio. La mina de uranio Castelejo está ubicada a unos 2km al W de Vila Cortês da Serra, en el distrito de Guarda, en la cuenca del río Mondego. En términos geológicos, la mina se localiza en un granito de grano medio e dos micas con tendencia porfiroidal. La explotación comenzó con dos minas a cielo abierto entre 1979 y 1990, que produjeron alrededor de 132 toneladas de U3O8. Desde 1992, la producción comenzó a llevarse a cabo a través de la lixiviación in situ con H2SO4 de materiales de bajo contenido en uranio. La circulación de las aguas superficial y subterránea está estructuralmente condicionada por la fracturacion intensa en la zona. Dos campañas geofísicas de exploración se llevaron a cabo a fin de caracterizar el sistema de fracturas. La primera fue una investigación con el método VLF que nos permitió identificar los principales sistemas de fallas que pueden proporcionar rutas para el flujo de las aguas subterráneas. A partir de la segunda campaña, que fue un estudo llevado a cabo con el método RMT en una caja de falla que reproduz o gradiente natural de la mina, se obtuvieron las resistividades y espesores del material de granito intemperizado. Los perfiles obtenidos muestran que la resistividad disminuye con el aumento de profundidad.Este aspecto puede deberse a causas naturales - el material que llena la caja de falla es más intemperizado en profundidad que en la superficie - o puede indicar contaminación en profundidad, debido al drenaje ácido de las minas." ] "en" => array:2 [ "titulo" => "Abstract" "resumen" => "There are about 175 abandoned mining sites in Portugal, of which about 60 are old uranium workings. The Castelejo mine is an old uranium located about 2km W of Vila Cortês da Serra, in Guarda district, on the River Mondego basin. In geologic terms, the mine is located in medium-grained two-mica monzonitic granite, with porphyroidal tendency. Exploitation started with two open cast mines between 1979 and 1990 which produced about 132 tonnes U3O8. From 1992, production started to be carried out through the in situ H2SO4 leaching of the mine’s low-grade materials. The superficial and groundwater circulation are structurally conditioned by the intense fracturing in the area. Two exploratory geophysical field campaigns were conducted in order to characterize the fracturing. The first was a VLF survey that allowed us to identify major fault systems that may provide paths for groundwater flow. From the second campaign, which was an RMT survey conducted at a fault gauge which records the mine natural gradient flow, we obtained the resistivities and thicknesses of the weathered granite material. The profiles obtained show that resistivity declines with increasing depth. This fact may arise from natural causes – the material which fills the fault gauge is more weathered at depth than on the surface – or it may indicate contamination at depth, due to acid mine drainage." ] ] "multimedia" => array:16 [ 0 => array:7 [ "identificador" => "f0005" "etiqueta" => "Figure 1" "tipo" => "MULTIMEDIAFIGURA" "mostrarFloat" => true "mostrarDisplay" => false "figura" => array:1 [ 0 => array:4 [ "imagen" => "gr1.jpeg" "Alto" => 906 "Ancho" => 1772 "Tamanyo" => 191390 ] ] "descripcion" => array:1 [ "en" => "a) Paleogeographic and tectonic zones of the Hesperian Massif. Adapted from <a class="elsevierStyleCrossRef" href="#bib0100">Ribeiro et al. 1979</a>. b) Major hydrogeological units of portuguese metropolitan territory. Adapted from SNIRH, Instituto da Água, 2009" ] ] 1 => array:7 [ "identificador" => "f0010" "etiqueta" => "Figure 2" "tipo" => "MULTIMEDIAFIGURA" "mostrarFloat" => true "mostrarDisplay" => false "figura" => array:1 [ 0 => array:4 [ "imagen" => "gr2.jpeg" "Alto" => 1603 "Ancho" => 1739 "Tamanyo" => 482884 ] ] "descripcion" => array:1 [ "en" => "“Beiras Uraniferous Region”. On the map of Portugal (left), the Castelejo mine locates at the red rectangle (adapted from <a class="elsevierStyleCrossRef" href="#bib0045">Ferreira, 1971</a>)." ] ] 2 => array:7 [ "identificador" => "f0015" "etiqueta" => "Figure 3" "tipo" => "MULTIMEDIAFIGURA" "mostrarFloat" => true "mostrarDisplay" => false "figura" => array:1 [ 0 => array:4 [ "imagen" => "gr3.jpeg" "Alto" => 1472 "Ancho" => 1842 "Tamanyo" => 433643 ] ] "descripcion" => array:1 [ "en" => "Castelejo mine geological setting" ] ] 3 => array:7 [ "identificador" => "f0020" "etiqueta" => "Figure 4" "tipo" => "MULTIMEDIAFIGURA" "mostrarFloat" => true "mostrarDisplay" => false "figura" => array:1 [ 0 => array:4 [ "imagen" => "gr4.jpeg" "Alto" => 780 "Ancho" => 1205 "Tamanyo" => 121286 ] ] "descripcion" => array:1 [ "en" => "Some ecological and human risks associated with uranium mill tailings (adapted from http://www.wise-uranium.org/uwai.html)." ] ] 4 => array:7 [ "identificador" => "f0025" "etiqueta" => "Figure 5" "tipo" => "MULTIMEDIAFIGURA" "mostrarFloat" => true "mostrarDisplay" => false "figura" => array:1 [ 0 => array:4 [ "imagen" => "gr5.jpeg" "Alto" => 970 "Ancho" => 1599 "Tamanyo" => 148308 ] ] "descripcion" => array:1 [ "en" => "Basis of VLF-EM method, adapted from <a class="elsevierStyleCrossRef" href="#bib0125">Turberg and Müller (1992)</a> Reproduced from <a class="elsevierStyleCrossRef" href="#bib0040">Dill et al. (1998)</a>." ] ] 5 => array:7 [ "identificador" => "f0030" "etiqueta" => "Figure 6" "tipo" => "MULTIMEDIAFIGURA" "mostrarFloat" => true "mostrarDisplay" => false "figura" => array:1 [ 0 => array:4 [ "imagen" => "gr6.jpeg" "Alto" => 1909 "Ancho" => 1352 "Tamanyo" => 355533 ] ] "descripcion" => array:1 [ "en" => "Basis of RMT-R method, adapted from <a class="elsevierStyleCrossRef" href="#bib0115">Thierrin and Müller (1988)</a>. Reproduced from <a class="elsevierStyleCrossRef" href="#bib0040">Dill et al. (1998)</a>." ] ] 6 => array:7 [ "identificador" => "f0035" "etiqueta" => "Figure 8" "tipo" => "MULTIMEDIAFIGURA" "mostrarFloat" => true "mostrarDisplay" => false "figura" => array:1 [ 0 => array:4 [ "imagen" => "gr7.jpeg" "Alto" => 601 "Ancho" => 1881 "Tamanyo" => 232348 ] ] "descripcion" => array:1 [ "en" => "a) Start point and end point of the seven profiles carried out in the VLF-EM survey b) Photographic map of Castelejo former mine site surroundings, with profile location where VLF-EM survey was conducted (color variation explained in the text; P – Profiles)." ] ] 7 => array:7 [ "identificador" => "f0040" "etiqueta" => "Figure 9" "tipo" => "MULTIMEDIAFIGURA" "mostrarFloat" => true "mostrarDisplay" => false "figura" => array:1 [ 0 => array:4 [ "imagen" => "gr8.jpeg" "Alto" => 2692 "Ancho" => 1467 "Tamanyo" => 513272 ] ] "descripcion" => array:1 [ "en" => "Interpretation of the results of the VLF-EM survey profiles." ] ] 8 => array:7 [ "identificador" => "f0045" "etiqueta" => "Figure 10" "tipo" => "MULTIMEDIAFIGURA" "mostrarFloat" => true "mostrarDisplay" => false "figura" => array:1 [ 0 => array:4 [ "imagen" => "gr9.jpeg" "Alto" => 1470 "Ancho" => 1881 "Tamanyo" => 241125 ] ] "descripcion" => array:1 [ "en" => "Fracture map of the studied area." ] ] 9 => array:7 [ "identificador" => "f0050" "etiqueta" => "Figure 11" "tipo" => "MULTIMEDIAFIGURA" "mostrarFloat" => true "mostrarDisplay" => false "figura" => array:1 [ 0 => array:4 [ "imagen" => "gr10.jpeg" "Alto" => 1414 "Ancho" => 1258 "Tamanyo" => 492532 ] ] "descripcion" => array:1 [ "en" => "– Location of all RMT-R profiles performed in the surroundings of Castelejo mining site (P – Profiles)." ] ] 10 => array:7 [ "identificador" => "f0055" "etiqueta" => "Figure 12" "tipo" => "MULTIMEDIAFIGURA" "mostrarFloat" => true "mostrarDisplay" => false "figura" => array:1 [ 0 => array:4 [ "imagen" => "gr11.jpeg" "Alto" => 1274 "Ancho" => 1461 "Tamanyo" => 484373 ] ] "descripcion" => array:1 [ "en" => "– Location of RMT-R profiles performed in the Castelejo Valley." ] ] 11 => array:7 [ "identificador" => "f0060" "etiqueta" => "Figure 13" "tipo" => "MULTIMEDIAFIGURA" "mostrarFloat" => true "mostrarDisplay" => false "figura" => array:1 [ 0 => array:4 [ "imagen" => "gr12.jpeg" "Alto" => 1210 "Ancho" => 1460 "Tamanyo" => 487527 ] ] "descripcion" => array:1 [ "en" => "The profile P1 is located near the old mining site, with resistivity values." ] ] 12 => array:7 [ "identificador" => "tbl0005" "etiqueta" => "Table 1" "tipo" => "MULTIMEDIATABLA" "mostrarFloat" => true "mostrarDisplay" => false "tabla" => array:1 [ "tablatextoimagen" => array:1 [ 0 => array:2 [ "tabla" => array:1 [ 0 => """ <table border="0" frame="\n \t\t\t\t\tvoid\n \t\t\t\t" class=""><thead title="thead"><tr title="table-row"><th class="td" title="table-head " align="center" valign="top" scope="col" style="border-bottom: 2px solid black">Type of tailing \t\t\t\t\t\t\n \t\t\t\t</th><th class="td" title="table-head " align="center" valign="top" scope="col" style="border-bottom: 2px solid black">Size (μm) \t\t\t\t\t\t\n \t\t\t\t</th><th class="td" title="table-head " align="center" valign="top" scope="col" style="border-bottom: 2px solid black">Composition \t\t\t\t\t\t\n \t\t\t\t</th></tr></thead><tbody title="tbody"><tr title="table-row"><td class="td" title="table-entry " align="center" valign="top">Sand \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="top">75 - 500 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="top">SiO2 plus≈1 weight % Al, Fe, Mg, Ca, Na, K, Se, Mn, Ni, Mo, V silicates and metal oxides; approximately 0.004-0.01 weight % U3O8; with H2SO4leaching process: 26-100 pCi 226Ra/g and 70-600 pCi 230Th/g; \t\t\t\t\t\t\n \t\t\t\t</td></tr><tr title="table-row"><td class="td" title="table-entry " align="center" valign="top">Slime \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="top">45 - 75 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="top">SiO2 and Na, Ca, Mn, Mg, Al, Fe silicates and metal oxides; Concentration of U3O8 and 226Ra≈2 x concentration in sands; with H2SO4 leaching process: 150-400 pCi 226Ra/g and 70-600 pCi 230Th/g; \t\t\t\t\t\t\n \t\t\t\t</td></tr><tr title="table-row"><td class="td" title="table-entry " align="center" valign="top">Liquid \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="top">- \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="top">with H2SO4leaching process: pH 1.2-2.0; Na+, NH4+, SO42-, Cl-, PO43-; dissolved solids≈1 weight %; approximately 0.001-0.01 weight % U3O8; 20-7500 pCi 226Ra/l and 2000-22000 pCi 230Th/l; \t\t\t\t\t\t\n \t\t\t\t</td></tr></tbody></table> """ ] "imagenFichero" => array:1 [ 0 => "xTab795079.png" ] ] ] ] "descripcion" => array:1 [ "en" => "Properties of uranium mill tailings (adapted from USEPA 2007)." ] ] 13 => array:7 [ "identificador" => "f0065" "etiqueta" => "Figure 7" "tipo" => "MULTIMEDIAFIGURA" "mostrarFloat" => false "mostrarDisplay" => true "figura" => array:1 [ 0 => array:4 [ "imagen" => "gr13.jpeg" "Alto" => 1425 "Ancho" => 1100 "Tamanyo" => 190289 ] ] "descripcion" => array:1 [ "en" => "VLF-EM method: equipment adapted to a vehicle (Castelejo mining site)." ] ] 14 => array:6 [ "identificador" => "eq0005" "etiqueta" => "(1)" "tipo" => "MULTIMEDIAFORMULA" "mostrarFloat" => false "mostrarDisplay" => true "Formula" => array:5 [ "Matematica" => "P=503ρaF" "Fichero" => "si1.jpeg" "Tamanyo" => 1044 "Alto" => 29 "Ancho" => 88 ] ] 15 => array:6 [ "identificador" => "eq0010" "etiqueta" => "(2)" "tipo" => "MULTIMEDIAFORMULA" "mostrarFloat" => false "mostrarDisplay" => true "Formula" => array:5 [ "Matematica" => "ρa=ExHy212π0F" "Fichero" => "si2.jpeg" "Tamanyo" => 1206 "Alto" => 28 "Ancho" => 107 ] ] ] "bibliografia" => array:2 [ "titulo" => "References" "seccion" => array:1 [ 0 => array:2 [ "identificador" => "bibs0005" "bibliografiaReferencia" => array:27 [ 0 => array:3 [ "identificador" => "bib0005" "etiqueta" => "Abranches and Canilho, 1982" "referencia" => array:1 [ 0 => array:2 [ "contribucion" => array:1 [ 0 => array:2 [ "titulo" => "Determinação de idade pelo método do Rb-Sr de granitos antigos portugueses" "autores" => array:1 [ 0 => array:2 [ "etal" => false "autores" => array:2 [ 0 => "M.C.B. 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Vitor Manuel Gomes de Oliveira

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vgomesoliveira@ist.utl.pt

Corresponding author:

, Luís Filipe Tavares Ribeiro

CVRM, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, Lisboa Portugal

María Catarina Rosalino da Silva

Centro de Geología, FCUL, Edifício C6, Campo Grande, Lisboa, Portugal

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    "textoCompleto" => "<span class="elsevierStyleSections"><span id="sec0005" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0025"><a name="p136"></a>Introduction</span><p id="par0005" class="elsevierStylePara elsevierViewall">The activities developed by mining are&#44; from the very start of operations&#44; capable of degrading the surrounding environment and causing major environmental modifications&#44; unless they are properly monitored and then controlled in accordance with the data gathered from the monitoring&#46;</p><p id="par0010" class="elsevierStylePara elsevierViewall">Main modifications to the environmental balance generally result from digging a part of the land surface&#44; as well as from the production of deposits of varying kinds of waste and &#47; or sterile minerals &#40;tailings&#41; and from the chemical products used in ore separation &#47; purification &#40;<a class="elsevierStyleCrossRef" href="#bib0135">Younger <span class="elsevierStyleItalic">et al</span>&#46;&#44; eds&#44; 2002</a>&#41;&#46; All these modifications cause hydrological and hydrogeological impacts &#40;on superficial and ground water&#41;&#44; geochemical impacts &#40;on sediment&#44; ground and alluvium&#41; and biochemical impacts &#40;on living beings&#41; &#40;<a class="elsevierStyleCrossRef" href="#bib0065">Lottermoser&#44; 2003</a>&#41;&#46;</p><p id="par0015" class="elsevierStylePara elsevierViewall">The characteristics and consequences of these impacts diverge according to when they are produced&#44; and they can cause sporadic and &#47;or diffuse pollution&#46;</p><p id="par0020" class="elsevierStylePara elsevierViewall">Sporadic pollution occurs when the mine is being worked&#59; if there is a control system in operation &#40;monitoring&#41; the pollution can be prevented from spreading&#46;</p><p id="par0025" class="elsevierStylePara elsevierViewall">Diffuse pollution tends to occur once a mine has been abandoned&#46; As a rule &#40;<a class="elsevierStyleCrossRef" href="#bib0095">Rapantova <span class="elsevierStyleItalic">et al</span>&#46;&#44; eds&#44; 2008</a>&#41; when a reasonably long time is spent on closing down a mine there is no longer any concern with monitoring&#44; which is only undertaken when it is active&#46;</p><p id="par0030" class="elsevierStylePara elsevierViewall">This attitude disregards possible subsequent risks to the closed down mine without taking any type of prevention to forestall them&#44; and therefore it contributes to the propagation of the contamination&#46;</p><p id="par0035" class="elsevierStylePara elsevierViewall">The environmental liabilities of mining are expressed&#44; as a rule&#44; by the incidence of abnormal &#40;very high&#41; concentrations of heavy metals in the sediments&#44; ground and alluvia&#44; as well as in the water within the area of influence of this activity &#40;<a class="elsevierStyleCrossRef" href="#bib0095">Rapantova <span class="elsevierStyleItalic">et al</span>&#46;&#44; eds&#44; 2008</a>&#41;&#46; The presence of these elements is essentially due to the leaching of the materials inside the mine and to erosion and leaching processes acting on the tailing materials extracted from the mine &#40;<a class="elsevierStyleCrossRef" href="#bib0135">Younger <span class="elsevierStyleItalic">et al</span>&#46;&#44; eds&#44; 2002</a>&#41;&#46; In fact&#44; in open cast mining these elements are vulnerable to the action of the wind and the rain&#44; which are their main vehicles of dissemination&#46;</p><p id="par0040" class="elsevierStylePara elsevierViewall">In many cases of mine exploration&#44; the action of the water over the tailings and other mine wastes causes a phenomenon known as acid mine drainage &#40;AMD&#41;&#46; This phenomenon particularly occurs in metal ore workings in which sulphide is exposed to oxidating environments&#44; or when acid leaching from poor ore with a view to its concentration and subsequent recuperation occurs &#40;<a class="elsevierStyleCrossRef" href="#bib0065">Lottermoser&#44; 2003</a>&#41;&#46; When the mine is definitely abandoned and if the evolution of the characteristics and the processes of environmental alteration are not controlled the ominous consequences will get worse as years go by&#46; One of the best-known is the contamination of the surface water and groundwater&#44; which occurs both during the phase of functioning and after the mine&#8217;s closure&#46;</p><p id="par0045" class="elsevierStylePara elsevierViewall">The hydrogeological impact is a serious problem in almost all underground mines and in open cast mines&#44; too&#46; A series of measures can help to avoid or reduce this contamination&#46; Thus&#44; when the mine is abandoned it is essential to have the most accurate knowledge possible of the hydrogeology&#44; the geology&#44; the mineralogical composition of the materials&#44; and the method of extracting and processing the ore to enable the prevention&#44; correction and mitigation of environmental degradation caused by the operation&#46;</p><p id="par0050" class="elsevierStylePara elsevierViewall">The method used to decommission a mine directly influences the local hydrogeological conditions&#46; In conjunction with the operation there are often problems of mining subsidence&#44; which occurs because methods of dismantling are used that do not consider the full extent of the galleries&#46;</p><p id="par0055" class="elsevierStylePara elsevierViewall">When in operation we can see&#44; in brief&#44; the following effects&#58;<ul class="elsevierStyleList" id="lis0005"><li class="elsevierStyleListItem" id="lsti0005"><span class="elsevierStyleLabel">-</span><p id="par0060" class="elsevierStylePara elsevierViewall">Differential settlements</p></li><li class="elsevierStyleListItem" id="lsti0010"><span class="elsevierStyleLabel">-</span><p id="par0065" class="elsevierStylePara elsevierViewall">Fractures on the ground</p></li><li class="elsevierStyleListItem" id="lsti0015"><span class="elsevierStyleLabel">-</span><p id="par0070" class="elsevierStylePara elsevierViewall">Lowering of groundwater levels</p></li><li class="elsevierStyleListItem" id="lsti0020"><span class="elsevierStyleLabel">-</span><p id="par0075" class="elsevierStylePara elsevierViewall">Reduced flow of aquifers or even their exhaustion</p></li><li class="elsevierStyleListItem" id="lsti0025"><span class="elsevierStyleLabel">-</span><p id="par0080" class="elsevierStylePara elsevierViewall">Contamination of water&#46;</p></li></ul></p><p id="par0085" class="elsevierStylePara elsevierViewall">It can be said that during the course of its history Portugal several times gained importance for major mining&#44; and it is even one of those countries in which mining carried out by Romans is well documented &#40;<a class="elsevierStyleCrossRef" href="#bib0045">Ferreira&#44; 1971</a>&#59; <a class="elsevierStyleCrossRef" href="#bib0020">Carvalho <span class="elsevierStyleItalic">et al</span>&#46;&#44; 1971</a>&#41;&#46;</p><p id="par0090" class="elsevierStylePara elsevierViewall">From north to south Portugal 55 Roman mining operations were recorded&#44; and we think there were others that have not been <a name="p137"></a>surveyed&#46; They were mostly for gold and several remained in operation until very recent times &#40;<a class="elsevierStyleCrossRef" href="#bib0085">Nunes&#44; 1983</a>&#41;&#46;</p><span id="sec0010" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0030">Identification of fracturing</span><p id="par0095" class="elsevierStylePara elsevierViewall">Geophysical surveying has long been used to characterize fracturing in various geological formations&#46; Particularly in mining areas&#44; where fractures are often related to mineralized veins&#44; the joint use of geophysical and other methods enables one to characterize the ore potential of an area of interest &#40;<a class="elsevierStyleCrossRef" href="#bib0060">Kearey <span class="elsevierStyleItalic">et al</span>&#46;&#44; 2002</a>&#41;&#46;</p><p id="par0100" class="elsevierStylePara elsevierViewall">Geophysical surveying today has a very broad range of applications&#58; from mining to civil engineering&#44; through archaeological&#44; environmental&#44; geological and hydrological investigations to aquifer characterization&#46;</p><p id="par0105" class="elsevierStylePara elsevierViewall">In addition to obtaining different kinds of information of geological interest and detecting geological structures that may contain water &#40;e&#46;g&#46; faults and fractures&#41;&#44; geophysical surveying is also used to map and monitor the presence and behavior of contaminants in groundwater&#44; ranging from saltwater intrusion in coastal aquifers to the presence of contaminants from mining&#44; industrial or agricultural operations &#40;<a class="elsevierStyleCrossRef" href="#bib0060">Kearey <span class="elsevierStyleItalic">et al</span>&#46;&#44; 2002</a>&#59; <a class="elsevierStyleCrossRef" href="#bib0090">Oliveira&#44; V&#46;&#44; 2010</a>&#41;&#46;</p><p id="par0110" class="elsevierStylePara elsevierViewall">Several geophysical methods can be applied to characterize soil and groundwater contamination&#44; particularly those using ground-penetrating radar &#40;GPR&#41; devices&#44; magnetometers or conductivimeters &#40;<a class="elsevierStyleCrossRef" href="#bib0035">Daniels <span class="elsevierStyleItalic">et al</span>&#46;&#44; 1995</a>&#59; <a class="elsevierStyleCrossRef" href="#bib0070">Milson&#44; 2003</a>&#41;&#46;</p><p id="par0115" class="elsevierStylePara elsevierViewall">Using more than one surveying method improves the accuracy of interpretations&#44; so as in the work described here&#44; it is possible to geologically characterize the suspected area of contamination using one method and to adopt another to detail its intensity and spread&#46; In this study we use two electromagnetic methods&#44; adapted and refined at the University of Neuch&#226;tel&#44; where they are starting to be used in the characterization of karst discontinuities &#40;<a class="elsevierStyleCrossRef" href="#bib0115">Thierrin <span class="elsevierStyleItalic">et al</span>&#46;&#44; 1988</a>&#59; <a class="elsevierStyleCrossRef" href="#bib0125">Turberg <span class="elsevierStyleItalic">et al</span>&#46;&#44; 1992</a>&#41;&#46;</p></span><span id="sec0015" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0035">Risks associated with abandoned U mining sites</span><p id="par0120" class="elsevierStylePara elsevierViewall">Some of the risks associated with abandoned uranium mining sites are usually identified through an ecological and human risk-assessment process&#46; In general terms&#44; once the ore has been milled it becomes yellowcake&#44; a U<span class="elsevierStyleInf">3</span>O<span class="elsevierStyleInf">8</span> concentrate&#44; through a series of processes that include crushing&#44; leaching&#44; drying and filtering the initial material&#46;</p><p id="par0125" class="elsevierStylePara elsevierViewall">The composition of the tailings produced over all these processes is represented in <a class="elsevierStyleCrossRef" href="#tbl0005">Table 1</a>&#46;</p><elsevierMultimedia ident="tbl0005"></elsevierMultimedia><p id="par0130" class="elsevierStylePara elsevierViewall">Tailings pose several risks and threats&#44; some of which are &#40;see <a class="elsevierStyleCrossRef" href="#f0020">Figure 4</a>&#41;&#58;<a name="p138"></a></p><elsevierMultimedia ident="f0020"></elsevierMultimedia><span id="sec0020" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleLabel">a&#41;</span><span class="elsevierStyleSectionTitle" id="sect0040">Radon exhalation</span><p id="par0135" class="elsevierStylePara elsevierViewall">Radon &#40;<span class="elsevierStyleSup">222</span>Rn&#41; is a dangerous radioactive gas which migrates to the surface of a tailings pile through a process of diffusion and is then released into the atmosphere&#46;</p><p id="par0140" class="elsevierStylePara elsevierViewall">One of the most feared characteristics of Rn is the danger that it poses to the lungs if inhaled&#46; According to <a class="elsevierStyleCrossRef" href="#bib0130">USEPA &#40;2007&#41;</a>&#44; Rn can affect the health of people living many kilometers from a tailings pile&#46;</p></span><span id="sec0025" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleLabel">b&#41;</span><span class="elsevierStyleSectionTitle" id="sect0045">Gamma radiation</span><p id="par0145" class="elsevierStylePara elsevierViewall">The radioactivity present in the tailings&#44; mainly due to the uranium decay products of radium &#40;<span class="elsevierStyleSup">226</span>Ra&#41; and thorium &#40;<span class="elsevierStyleSup">230</span>Th&#41; can be harmful to those directly exposed to the emitted radiation&#46;</p></span><span id="sec0030" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleLabel">c&#41;</span><span class="elsevierStyleSectionTitle" id="sect0050">Dust blowing</span><p id="par0150" class="elsevierStylePara elsevierViewall">The action of the wind over the tailings causes dust blowing&#46; Dust blowing can spread many kinds of contaminants in the air&#46; This risk worsens after the closure of the mine&#44; as the tailings materials dry out&#46;</p></span><span id="sec0035" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleLabel">d&#41;</span><span class="elsevierStyleSectionTitle" id="sect0055">Dam failure</span><p id="par0155" class="elsevierStylePara elsevierViewall">Dam failure&#44; although rare&#44; might be caused by anthropogenic or natural factors&#46; Among the former&#44; bad conception or design of the dam can be blamed while natural disasters &#8211; earthquakes&#44; rainfall&#44; snowfall or flooding are examples of natural causes&#46;</p></span><span id="sec0040" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleLabel">e&#41;</span><span class="elsevierStyleSectionTitle" id="sect0060">Seepage</span><p id="par0160" class="elsevierStylePara elsevierViewall">Groundwater contamination may be a major problem when considering the risks associated with uranium mill tailings&#46;</p><p id="par0165" class="elsevierStylePara elsevierViewall">In fact&#44; there is a strong relationship between the geological environment of the mine and its surroundings and the migration of contaminants to the aquifer&#44; as we can also see in this study&#46;</p><p id="par0170" class="elsevierStylePara elsevierViewall">The hydrology of the site is also crucial&#44; along with the chemistry and type of the tailings &#40;sand&#44; slime or liquid and their composition&#44; see <a class="elsevierStyleCrossRef" href="#tbl0005">Table 1</a> for details&#41;&#46; The soil composition and the characteristics of the mining processes &#40;e&#46;g&#46; underground or surface mining&#44; use of acid leaching&#41; are likewise important&#46; The acid leaching poses an additional problem related to the increased solubility caused in some products&#44; thereby facilitating their migration to groundwater&#46;</p></span><span id="sec0045" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleLabel">f&#41;</span><span class="elsevierStyleSectionTitle" id="sect0065">Other risks</span><p id="par0175" class="elsevierStylePara elsevierViewall">Among the risks not illustrated in <a class="elsevierStyleCrossRef" href="#f0020">Figure 4</a>&#44; the improper use of tailings must be mentioned&#46;</p><p id="par0180" class="elsevierStylePara elsevierViewall">Actually the use of sandy tailings as building materials raises the danger of radiation exposure for the inhabitants of such buildings&#46;</p></span></span></span><span id="sec0050" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0070">Study Area</span><span id="sec0055" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0075">Current situation in Portugal</span><p id="par0185" class="elsevierStylePara elsevierViewall">In Portugal there are about 175 abandoned mine workings&#44; dozens of which are currently undergoing environmental restoration&#46; About 60 are former uranium mines&#44; which are for the most part located in very intense fractured zones&#46;</p><p id="par0190" class="elsevierStylePara elsevierViewall">1907 is the year of the discovery of the Urgeiri&#231;a uranium-radium deposit&#46; Only radium was exploited until 1944&#44; when the exploitation and production of uranium began&#44; which had place in Urgeiri&#231;a until the operation was closed in 2001 with the ending of processing of ore&#46;</p><p id="par0195" class="elsevierStylePara elsevierViewall">The uranium workings were abandoned with the decline of its economic and strategic interest&#44; and the last mines of this radioactive metal were closed in the early 1990s&#46;</p><p id="par0200" class="elsevierStylePara elsevierViewall">The present work concerns an old mine site at Castelejo&#44; an ancient uranium exploitation&#44; located about 2<span class="elsevierStyleHsp" style=""></span>km W of Vila Cort&#234;s da Serra in Gouveia municipality&#44; Guarda district&#44; and connected to the Mondego River basin through the Pa&#231;o Stream &#40;<a class="elsevierStyleCrossRef" href="#f0035">Figure 8-B</a>&#41;&#46;</p><p id="par0205" class="elsevierStylePara elsevierViewall">At present&#44; the area is being environmentally rehabilitated by the Portuguese state-owned enterprise charged with the environmental rehabilitation of old abandoned mining areas&#46; Exploitation started with two open cast pits &#40;now both flooded&#41; between 1979 and 1990 which produced about 132 tonnes of U<span class="elsevierStyleInf">3</span>O<span class="elsevierStyleInf">8</span>&#46; From 1992 up to 1997 production started to be done through in situ H<span class="elsevierStyleInf">2</span>SO<span class="elsevierStyleInf">4</span> leaching of the poor material taken from the mine itself&#44; as well as that from other workings located nearby&#46; This latter process was responsible for the production of &#40;more or less&#41; a further 22&#46;5 tonnes U<span class="elsevierStyleInf">3</span>O<span class="elsevierStyleInf">8</span>&#46;</p><p id="par0210" class="elsevierStylePara elsevierViewall">The coordinates of the central point of the mine&#44; located between both open skies&#44; referring to the Unified European Reference System &#40;ED50&#41; are&#58; latitude 40&#176; 33&#8217; 20&#8217;&#8217;N and longitude 7&#176; 33&#8217; 5&#8217;&#8217;W &#40;<a class="elsevierStyleCrossRef" href="#f0035">Figure 8-B</a>&#41;&#46;</p></span><span id="sec0060" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0080">Geology</span><p id="par0215" class="elsevierStylePara elsevierViewall">Mainland Portugal is formed by an ancient and hardened core&#44; usually called the <span class="elsevierStyleItalic">Hercynian Massif</span>&#44; part of the so-called Hesperian Massif&#44; and by land coverage &#40;<a class="elsevierStyleCrossRef" href="#f0005">Figure 1-A</a> and <a class="elsevierStyleCrossRef" href="#f0005">B</a>&#41;&#46;<a name="p139"></a></p><elsevierMultimedia ident="f0005"></elsevierMultimedia><p id="par0220" class="elsevierStylePara elsevierViewall">The <span class="elsevierStyleItalic">Hercynian Massif</span> comprises ante-Mesozoic lands&#44; and consists of sedimentary&#44; eruptive and metamorphic rocks &#40;<a class="elsevierStyleCrossRef" href="#bib0100">Ribeiro <span class="elsevierStyleItalic">et al</span>&#46;&#44; 1979</a>&#41;&#46;</p><p id="par0225" class="elsevierStylePara elsevierViewall">The land coverage includes sedimentary and some Meso-Cenozoic eruptive rocks which form the western and southern edges of the country&#44; as well as modern deposits&#44; consisting of alluvial flood plains and different beach levels&#44; which result from various basins of sedimentary filling &#40;<a class="elsevierStyleCrossRef" href="#bib0105">Teixeira&#44; 1966</a>&#59; <a class="elsevierStyleCrossRef" href="#bib0100">Ribeiro <span class="elsevierStyleItalic">et al</span>&#46;&#44; 1979</a>&#59; <a class="elsevierStyleCrossRef" href="#f0005">Figures 1-A</a> and <a class="elsevierStyleCrossRef" href="#f0005">B</a>&#41;&#46;</p><p id="par0230" class="elsevierStylePara elsevierViewall">The Hesperian Massif is crossed by the Central Cordillera&#44; a ENE-WSW lying mountain range&#44; which divides it into two&#58; the north Meseta &#40;Meseta signifies Little Table&#44; so the expression has an essential geomorphological meaning&#41; with an average altitude of 800<span class="elsevierStyleHsp" style=""></span>meters&#44; and the south Meseta&#44; with an average altitude of about 400<span class="elsevierStyleHsp" style=""></span>m&#46;</p><p id="par1230" class="elsevierStylePara elsevierViewall">The formations that form the Hesperian Massif&#44; mainly schists&#44; granites and graywackes&#44; suffered the action of Caledonian&#44; Hercynian and Alpine orogenies&#44; although the Hercynian orogeny is the one whose effects are better documented here&#46;</p><p id="par0240" class="elsevierStylePara elsevierViewall">In the Iberian Peninsula&#44; the Hercynian orogeny began in the Middle Devonian and continued until the Late Carboniferous period &#40;<a class="elsevierStyleCrossRef" href="#bib0100">Ribeiro <span class="elsevierStyleItalic">et al</span>&#46;&#44; 1979</a>&#41;&#46;</p><p id="par0245" class="elsevierStylePara elsevierViewall">Although it has developed over several stages&#44; two main phases can be distinguished &#40;dated by the presence of unconformities in the outer zones or by radiometric dating of certain granites &#40;<a class="elsevierStyleCrossRef" href="#bib0015">Ara&#250;jo&#44; M&#46;A&#46; &#40;2002&#41;</a>&#59; <a class="elsevierStyleCrossRef" href="#bib0005">Abranches&#44; M&#46;C&#46;B&#46; <span class="elsevierStyleItalic">et al</span>&#46; &#40;1982&#41;</a>&#41;&#58;<ul class="elsevierStyleList" id="lis0010"><li class="elsevierStyleListItem" id="lsti0030"><span class="elsevierStyleLabel">-</span><p id="par0250" class="elsevierStylePara elsevierViewall">First one&#44; which ran from Middle Devonian to Visean</p></li><li class="elsevierStyleListItem" id="lsti0035"><span class="elsevierStyleLabel">-</span><p id="par0255" class="elsevierStylePara elsevierViewall">Second&#44; a phase dating from Westphalian&#46; The orogenic actions caused folding in a general NW-SE orientation&#44; as well as synorogenic magmatism and regional metamorphism&#46;</p></li></ul></p><p id="par0260" class="elsevierStylePara elsevierViewall">Between the Late Westphalian and Late Permian periods the Hercynian chain suffered uplifts&#44; the results of erosion and post-tectonics intrusive actions&#44; mainly consisting of alkaline and calc-alkaline granitoid rocks&#44; which gave rise to considerable filonian mineralization&#46;</p><p id="par0265" class="elsevierStylePara elsevierViewall">The last stages of Hercynian orogeny induced intense fracturation in the Massif&#44; causing various movements of uplifting and sinking&#46;</p><p id="par0270" class="elsevierStylePara elsevierViewall">During the Cenozoic era the Hesperian Massif suffered fracturation again&#44; now predominantly in the NE-SW direction&#44; as a result of the Alpine orogeny actions that occurred &#40;<a class="elsevierStyleCrossRef" href="#bib0100">Ribeiro <span class="elsevierStyleItalic">et al</span>&#46;&#44; 1979</a>&#41;&#46;<a name="p140"></a></p><p id="par0275" class="elsevierStylePara elsevierViewall">In geological terms &#40;see <a class="elsevierStyleCrossRef" href="#f0010">Figures 2</a> and <a class="elsevierStyleCrossRef" href="#f0015">3</a>&#41; the Castelejo mine is located in medium-grained two-mica monzonitic granite&#44; with porphyritic tendency&#46;</p><elsevierMultimedia ident="f0010"></elsevierMultimedia><elsevierMultimedia ident="f0015"></elsevierMultimedia><p id="par0280" class="elsevierStylePara elsevierViewall">Various granitic intrusions occurred in the late Hercynian age &#40;the mineralizations that occurred are related to quartz veins and usually consist of uranium phosphates - torbernite&#44; autunite and sabugalite - secondary minerals derived from uraninite and other uranium weathering product compounds&#41;&#46;</p></span><span id="sec0065" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0085">The distribution of U in Portugal</span><p id="par0285" class="elsevierStylePara elsevierViewall">Most known uraniferous deposits lie in central Portugal&#44; in the region covered by the four districts &#40;a district corresponds to an administrative territorial division&#41; of Viseu&#44; Guarda&#44; Coimbra and Porto&#44; although the largest number of mining operations are concentrated in the first two districts &#40;which are&#44; in general terms&#44; presented in <a class="elsevierStyleCrossRef" href="#f0010">Figure 2</a>&#41;&#46;</p><p id="par0290" class="elsevierStylePara elsevierViewall">The uranium deposits are related to post-tectonic Hercynian magmatism&#44; usually in the form of monzonitic granite intrusions&#44; medium to coarse-grained&#44; two-mica and having a porphyritic tendency&#46;</p><p id="par0295" class="elsevierStylePara elsevierViewall">They usually lie in a NE-SW direction&#46; Most deposits are related to quartz veins installed in fractures in granites&#46;</p><p id="par0300" class="elsevierStylePara elsevierViewall">There are various opinions about the genesis of uranium deposits&#46; In brief&#44; most <a name="p141"></a>authors &#40;<a class="elsevierStyleCrossRef" href="#bib0030">Cerveira&#44; A&#46;&#44; 1951</a>&#59; <a class="elsevierStyleCrossRef" href="#bib0080">Neiva&#44; J&#46;M&#46;C&#46;&#44; 1995</a>&#41; albeit with slight variations&#44; considered primary deposits as coming from hydrothermal deposits&#44; while the secondary deposits -impregnation deposits - are considered as coming from the leaching of the first and subsequent precipitation in favourable structures&#46;</p></span><span id="sec0070" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0090">Scope of the study</span><p id="par0305" class="elsevierStylePara elsevierViewall">The superficial and groundwater circulation is structurally conditioned by the intense fracturing in the area &#40;<a class="elsevierStyleCrossRef" href="#bib0110">Teixeira&#44; C&#46; <span class="elsevierStyleItalic">et al</span>&#46;&#44; 1967</a>&#41;&#46; To characterize the fracturing&#44; two superficial geophysical exploration field campaigns were conducted&#46; The first consisted of a very low frequency &#40;VLF&#41; survey that enabled the identification of major fault systems that may constitute prime pathways for groundwater flow&#46; The second campaign was a radio magnetotelluric &#40;RMT&#41; survey conducted at a fault gauge fulfilled with weathered granite material&#46; This fault gauge collects the mine&#8217;s natural gradient flow&#44; and from the survey we have obtained the resistivities and thicknesses of the weathered material&#46;</p><p id="par0310" class="elsevierStylePara elsevierViewall">EDM&#44; the Portuguese state-owned enterprise&#44; in charge of the environmental rehabilitation of the old abandoned mining areas&#44; has been monitoring several water points &#40;wells and piezometers&#41; located in the vicinity of the old Castelejo mine on a more or less regular basis since 1991&#46; However&#44; the collected data are difficult to process since neither the piezometer geometrical characteristics nor its depths of abstraction are known&#46; Besides&#44; data collected over time vary both quantitatively as qualitatively&#44; which makes data analysis difficult&#46;<a name="p142"></a></p><p id="par0315" class="elsevierStylePara elsevierViewall">Furthermore&#44; the collected data relate to two different realities &#8211; dug wells and drilled wells - and it is reasonable to apply them a conceptual model based on the supposition that they concern two equally different aquifers&#58; a porous aquifer located near the surface&#44; in the superficial zone of granite weathering&#44; taken as an unconfined aquifer and shown up by countless flooded zones and superficial abstractions detected in the field&#44; and a fissured aquifer&#44; located under the first one in a deeper fractured rock zone&#44; taken as a confined aquifer &#40;<a class="elsevierStyleCrossRef" href="#bib0010">Afonso&#44; M&#46;J&#46;C&#46; 2003</a>&#59; <a class="elsevierStyleCrossRef" href="#bib0025">Carvalho&#44; J&#46;M&#46;&#44; 2006</a>&#41;&#46;</p><p id="par0320" class="elsevierStylePara elsevierViewall">Therefore&#44; in view of the hydrogeological characterization of the former mining area and the identification of main drainage pathways&#44; supplementary data was needed to enable us to confirm &#40;or not&#41; the layout of the several unpublished reports&#46; For this&#44; two geophysical surveys were undertaken&#44; using two different geophysical methods&#46; This was intended to supplement the information obtained in each campaign&#46;</p><p id="par0325" class="elsevierStylePara elsevierViewall">main fractures identified in the initial study performed&#44; which was based on photogeological analysis of the studied area&#46;</p></span></span><span id="sec0075" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0095">Materials and Methods</span><span id="sec0080" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0100">Bases and methods</span><p id="par0330" class="elsevierStylePara elsevierViewall">It is common to be faced with problems of several orders when approaching the hydrogeological study of fractured rocks with a view to their hydraulic characterization&#46;</p><p id="par0335" class="elsevierStylePara elsevierViewall">In the case of granitic rocks&#44; in particular&#44; which&#44; when fresh&#44; are practically impermeable to water&#44; it is well known that its secondary porosity&#44; namely due to several physical processes&#44; can very often play a determinant role in water circulation&#46;</p><p id="par0340" class="elsevierStylePara elsevierViewall">The circulation of the water in this type of rock prompts a fundamental question&#44; which is linked to the identification of the fractures from where the drainage can proceed&#58; these fractures are not always easy to identify&#44; bearing in mind the thickness of the covering layer that sometimes overlies the rock &#40;<a class="elsevierStyleCrossRef" href="#bib0010">Afonso&#44; M&#46;J&#46;C&#46; 2003</a>&#41;&#46;</p><p id="par0345" class="elsevierStylePara elsevierViewall">So&#44; we need to resort to indirect survey methods that enable us to identify any abnormalities of hydrogeological interest&#46;</p><p id="par0350" class="elsevierStylePara elsevierViewall">The methods used in the current work are very low frequency &#8211; electromagnetics &#40;VLFEM&#41; and radio magnetotelluric &#8211; resistivity &#40;RMT-R&#41;&#46; Both methods are based on radio waves from low frequency to very low frequency &#8211; from 12 kHz to 300 kHz in both methods &#8211; which are emitted by antennas located all over the world &#40;<a class="elsevierStyleCrossRef" href="#bib0115">Thierrin&#44; J&#46; <span class="elsevierStyleItalic">et al</span>&#46;&#44; 1988</a>&#59; <a class="elsevierStyleCrossRef" href="#bib0125">Turberg&#44; P&#46; <span class="elsevierStyleItalic">et al</span>&#46;&#44; 1992</a>&#59; <a class="elsevierStyleCrossRef" href="#bib0120">Turberg&#44; P&#46;&#44; 1993</a>&#41;&#46;</p><p id="par0355" class="elsevierStylePara elsevierViewall">These waves also propagate in the basement&#44; with the depth of penetration of their generated primary field being given by &#58;</p><p id="par0360" class="elsevierStylePara elsevierViewall"><elsevierMultimedia ident="eq0005"></elsevierMultimedia></p><p id="par0365" class="elsevierStylePara elsevierViewall"><a name="p143"></a>where &#58;</p><p id="par0370" class="elsevierStylePara elsevierViewall"><span class="elsevierStyleItalic">P</span> - depth of penetration of the primary field generated by the radio waves &#40;m&#41;</p><p id="par0375" class="elsevierStylePara elsevierViewall"><span class="elsevierStyleItalic">&#961;</span><span class="elsevierStyleInf"><span class="elsevierStyleItalic">a</span></span> - apparent resistivity &#40;ohm&#46;m&#41;</p><p id="par0380" class="elsevierStylePara elsevierViewall"><span class="elsevierStyleItalic">F</span> - wave frequency &#40;Hz&#41;&#46;</p><p id="par0385" class="elsevierStylePara elsevierViewall">But these waves also give rise to a secondary electromagnetic field&#44; which depends on the nature of the material crossed and can be detected at the surface &#40;<a class="elsevierStyleCrossRef" href="#bib0115">Thierrin&#44; J&#46; <span class="elsevierStyleItalic">et al</span>&#46;&#44; 1988</a>&#59; <a class="elsevierStyleCrossRef" href="#bib0125">Turberg&#44; P&#46; <span class="elsevierStyleItalic">et al</span>&#46;&#44; 1992</a>&#41;&#46; Consequently the resultant electromagnetic field consists of the sum of the primary and secondary fields&#44; which are distinguished by intensity&#44; phase and direction&#46;</p></span><span id="sec0085" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0105">VLF-EM Method</span><p id="par0390" class="elsevierStylePara elsevierViewall">With the VLF-EM method&#44; special&#44; well-adjusted devices make use of one horizontal axis coil to measure the intensity of the primary electromagnetic field &#40;Hp&#41;&#44; while the intensity of the secondary field &#40;Hs&#41; is measured through one vertical axis coil&#46;</p><p id="par0395" class="elsevierStylePara elsevierViewall">The equipment used was specifically developed for hydrogeological purposes by Prof&#46; Imre M&#252;ller&#44; of the Centre of Hydrogeology of the University of Neuch&#226;tel &#40;<a class="elsevierStyleCrossRef" href="#bib0075">M&#252;ller&#44; I&#46;&#44; 1983</a>&#41;&#46;</p><p id="par0400" class="elsevierStylePara elsevierViewall">It differs from commercial appliances since it continuously registers the variation of the signal&#46; The joint use of a data logger and a GPS secures the right location of registered anomalies &#40;<a class="elsevierStyleCrossRef" href="#bib0075">M&#252;ller&#44; I&#46;&#44; 1983</a>&#59; <a class="elsevierStyleCrossRef" href="#bib0115">Thierrin&#44; J&#46; <span class="elsevierStyleItalic">et al</span>&#46;&#44; 1988</a>&#59; <a class="elsevierStyleCrossRef" href="#bib0125">Turberg&#44; P&#46; <span class="elsevierStyleItalic">et al</span>&#46;&#44; 1992</a>&#41;&#46;</p><p id="par0405" class="elsevierStylePara elsevierViewall">The vertical components are either in phase or out of phase relative to the primary field&#46;</p><p id="par0410" class="elsevierStylePara elsevierViewall">The expression of the results is given by the relation Hs&#47;Hp &#37;&#44; as illustrated in <a class="elsevierStyleCrossRef" href="#f0025">Figure 5</a>&#46;</p><elsevierMultimedia ident="f0025"></elsevierMultimedia><p id="par0415" class="elsevierStylePara elsevierViewall">The method permits detection of the presence of electricity-conducting bodies such as faults filled with clay materials exhibiting equally great sensitivity to other important hydrogeologic characteristics&#44; such as lateral facies variations &#40;<a class="elsevierStyleCrossRef" href="#bib0040">Dill&#44; A&#46; <span class="elsevierStyleItalic">et al</span>&#46;&#44; 1998</a>&#41;&#46;</p><p id="par0420" class="elsevierStylePara elsevierViewall">The method has the additional advantage of not requiring contact with the ground &#8211;once the antenna is automatically oriented&#44; it can be used manually or installed in vehicles&#46;</p></span><span id="sec0090" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0110">RMT-R Method</span><p id="par0425" class="elsevierStylePara elsevierViewall">The RMT-R method measures the electric field&#44; <span class="elsevierStyleItalic">E</span><span class="elsevierStyleInf"><span class="elsevierStyleItalic">x</span></span>&#44; in the direction of propagating radio waves &#40;e&#46;g&#46; in the emitter antenna direction&#41;&#46; The electric field is measured between two electrodes inserted in the ground at a certain distance from each other &#40;in our work this distance is 5<span class="elsevierStyleHsp" style=""></span>meters&#41;&#46;<a name="p144"></a></p><p id="par0430" class="elsevierStylePara elsevierViewall">The RMT-R method also measures the magnetic field&#44; <span class="elsevierStyleItalic">H</span><span class="elsevierStyleInf"><span class="elsevierStyleItalic">y</span></span>&#44; which is measured through a coil whose horizontal axis is normal to the emitter antenna direction&#46;</p><p id="par0435" class="elsevierStylePara elsevierViewall">The apparent resistivity&#44; <span class="elsevierStyleItalic">&#961;</span><span class="elsevierStyleInf">a</span>&#44; results from the application of <a class="elsevierStyleCrossRef" href="#eq0010">equation &#40;2&#41;</a>&#58;</p><p id="par0440" class="elsevierStylePara elsevierViewall"><elsevierMultimedia ident="eq0010"></elsevierMultimedia></p><p id="par0445" class="elsevierStylePara elsevierViewall">where&#58;</p><p id="par0450" class="elsevierStylePara elsevierViewall"><span class="elsevierStyleItalic">E</span><span class="elsevierStyleInf"><span class="elsevierStyleItalic">x</span></span> - electric component of the resultant field &#40;Volt&#47;m&#41;</p><p id="par0455" class="elsevierStylePara elsevierViewall"><span class="elsevierStyleItalic">H</span><span class="elsevierStyleInf"><span class="elsevierStyleItalic">y</span></span> - magnetic component of the resultant field &#40;Ampere&#47;m&#41;</p><p id="par0460" class="elsevierStylePara elsevierViewall">&#956;<span class="elsevierStyleInf">0</span> - permeability of free space &#40;Henry&#47;m&#41;&#46;</p><p id="par0465" class="elsevierStylePara elsevierViewall"><span class="elsevierStyleItalic">F</span> - wave frequency &#40;Hz&#41;&#46;</p><p id="par0470" class="elsevierStylePara elsevierViewall">This method also measures the phase-shift&#44; <span class="elsevierStyleItalic">&#981;</span>&#44; between the electric and magnetic components&#46; The phase-shift enables inference of the stratigraphic characteristics of the place under study&#58; there will be a conductive layer over a resistive one if <span class="elsevierStyleItalic">&#981;</span><span class="elsevierStyleHsp" style=""></span>&#60;<span class="elsevierStyleHsp" style=""></span>45&#176;&#44; there will be a resistive layer over a conductive one if <span class="elsevierStyleItalic">&#981;</span><span class="elsevierStyleHsp" style=""></span>&#62;<span class="elsevierStyleHsp" style=""></span>45&#186;&#44; and the medium is considered homogeneous if <span class="elsevierStyleItalic">&#981;</span><span class="elsevierStyleHsp" style=""></span>&#61;<span class="elsevierStyleHsp" style=""></span>45&#176;&#46;</p><p id="par0475" class="elsevierStylePara elsevierViewall">Given the fact that emitter antennas being located far apart from the receiver device&#44; we could consider all directions of propagation as essentially parallel&#44; which in practice reduces to only one direction&#46; Once the device allows the simultaneous measurement of 4 frequencies&#44; we can interpret it as supplying information from 4 depths &#40;see <a class="elsevierStyleCrossRef" href="#f0030">Figure 6</a>&#41;&#46; An inversion program &#40;FITVLF2&#41; for the personal computer was used to obtain the real resistivities and the thicknesses of the layers traversed&#46; Although its description is beyond the scope of this article&#44; detailed information about the method of inversion and its implementation can be found at <a class="elsevierStyleCrossRef" href="#bib0050">Fischer&#44; G&#46; <span class="elsevierStyleItalic">et al</span>&#46; &#40;1981&#41;</a>&#44; <a class="elsevierStyleCrossRef" href="#bib0055">Fischer&#44; G&#46; &#40;1985&#41;</a> and <a class="elsevierStyleCrossRef" href="#bib0125">Thierrin&#44; J&#46; &#40;1992&#41;</a>&#46;</p><elsevierMultimedia ident="f0030"></elsevierMultimedia><p id="par0480" class="elsevierStylePara elsevierViewall">Since it is a quick method that enables measurements &#40;soundings&#41; to be taken at 5<span class="elsevierStyleHsp" style=""></span>m intervals it allows the detection of heterogeneities&#44; and it is possible to infer the permeability of the formations from their resistivity values&#44; although this has not been done in the present study&#46;</p><p id="par0485" class="elsevierStylePara elsevierViewall">Multidirectional soundings can also be carried out to get information about the anisotropy of the studied medium&#46;</p></span></span><span id="sec0095" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0115">Results and Discussion</span><span id="sec0100" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0120">VLF-EM</span><p id="par0490" class="elsevierStylePara elsevierViewall">In <a class="elsevierStyleCrossRef" href="#f0035">Figure 8</a> we present a photographic map of the places surveyed by VLF-EM method&#46;</p><elsevierMultimedia ident="f0035"></elsevierMultimedia><p id="par0495" class="elsevierStylePara elsevierViewall">The marked points show the paths walked along and color gradation indicates that the relation Hs&#47;Hp &#37; is &#40;the deeper the color&#44; the stronger the relationship Hs&#47;Hp &#37;&#41;&#58;<ul class="elsevierStyleList" id="lis0015"><li class="elsevierStyleListItem" id="lsti0040"><span class="elsevierStyleLabel">-</span><p id="par0500" class="elsevierStylePara elsevierViewall">red color &#8211; positive Hs&#47;Hp &#37; relationship&#59;</p></li><li class="elsevierStyleListItem" id="lsti0045"><span class="elsevierStyleLabel">-</span><p id="par0505" class="elsevierStylePara elsevierViewall">blue color &#8211; negative Hs&#47;Hp &#37; relationship&#59;</p></li><li class="elsevierStyleListItem" id="lsti0050"><span class="elsevierStyleLabel">-</span><p id="par0510" class="elsevierStylePara elsevierViewall">white color - near zero Hs&#47;Hp &#37; relationship&#46;</p></li></ul></p><p id="par0515" class="elsevierStylePara elsevierViewall">All profiles were carried out at 16 kHz frequency and some important conclusions can be drawn from their interpretation &#40;see <a class="elsevierStyleCrossRef" href="#f0035">Figure 8</a>&#41;&#46;</p><p id="par0520" class="elsevierStylePara elsevierViewall">Very negative or very positive values &#40;Hs&#47;Hp<span class="elsevierStyleHsp" style=""></span>&#60;-40 &#37; or Hs&#47;Hp&#62;<span class="elsevierStyleHsp" style=""></span>40 &#37;&#41; correspond to measurements taken under the influence of high tension power lines and so they must not be considered&#46; Negative Hs&#47;Hp &#37; values are usually related to major resistivity layers&#44; whereas positive Hs&#47;Hp &#37; values indicate major electricity conductivity layers &#40;for instance&#44; the presence of clay materials&#41;&#46;</p><p id="par0525" class="elsevierStylePara elsevierViewall">Successive inflections of Hs&#47;Hp &#37; indicate fracture zones&#44; the more important the greater the registered amplitude&#46;</p><p id="par0530" class="elsevierStylePara elsevierViewall">In <a class="elsevierStyleCrossRef" href="#f0040">Figure 9</a> we present a summarized interpretation of the obtained results&#44; in order to illustrate the stated above&#46; The joint interpretation of the VLF-EM results with information gathered on EDM internal reports and field reconnaissance data made it possible to draw a map summarizing the fractures in the studied area&#44; from which main drainage trends can be established &#40;see <a class="elsevierStyleCrossRef" href="#f0045">Figure 10</a>&#44; wherein places where the presence of water was noted are marked in blue&#41;&#46;</p><elsevierMultimedia ident="f0040"></elsevierMultimedia><elsevierMultimedia ident="f0045"></elsevierMultimedia></span><span id="sec0105" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0125">RMT-R</span><p id="par0535" class="elsevierStylePara elsevierViewall">Apparent resistivity and phase difference between the electric and magnetic fields were measured in RMT-R survey profiles&#46; These profiles were defined in the sectors marked with circles&#44; and they were quite enlightening &#40;see <a class="elsevierStyleCrossRef" href="#f0045">Figures 10</a> and <a class="elsevierStyleCrossRef" href="#f0050">11</a>&#41;&#46;<a name="p145"></a></p><elsevierMultimedia ident="f0050"></elsevierMultimedia><p id="par0540" class="elsevierStylePara elsevierViewall"><elsevierMultimedia ident="f0065"></elsevierMultimedia></p><p id="par0545" class="elsevierStylePara elsevierViewall"><a name="p146"></a><a name="p147"></a>In particular&#44; the profiles located NW of the mining site&#44; in the Castelejo Valley &#40;see <a class="elsevierStyleCrossRef" href="#f0055">Figure 12</a>&#41;&#44; have revealed very interesting features&#46;</p><elsevierMultimedia ident="f0055"></elsevierMultimedia><p id="par0550" class="elsevierStylePara elsevierViewall">After processing the obtained results using an inversion program &#40;<a class="elsevierStyleCrossRef" href="#bib0055">Fischer&#44; G&#46;&#44; 1985</a>&#41;&#44; the real resistivities and thicknesses of the different layers were computed &#40;<a class="elsevierStyleCrossRef" href="#f0060">Figure 13</a>&#41;&#46; Mid sector values were calculated next&#46;</p><elsevierMultimedia ident="f0060"></elsevierMultimedia><p id="par0555" class="elsevierStylePara elsevierViewall">We noted that all the profiles defined along the Castelejo Valley exhibit a decrease in resistivity with depth&#46; Once we are away from the mineralized vein&#44; this may suggest either more alteration of granites with depth&#44; or a situation of deep-contamination&#46;</p><p id="par0560" class="elsevierStylePara elsevierViewall">The profile P1 reproduced in <a class="elsevierStyleCrossRef" href="#f0060">Figure 13</a> &#40;referring to deep pink points in <a class="elsevierStyleCrossRef" href="#f0045">Figures 10</a> and <a class="elsevierStyleCrossRef" href="#f0050">11</a>&#41; is located near the old mining site&#58; resistivity values correspond to those obtained for almost unweathered granite blocks &#40;with resistivity values<span class="elsevierStyleHsp" style=""></span>&#62;<span class="elsevierStyleHsp" style=""></span>1000 <span class="elsevierStyleItalic">&#937;</span>&#46;m&#41; immersed in a weathered matrix &#40;with resistivity values<span class="elsevierStyleHsp" style=""></span>&#8776;<span class="elsevierStyleHsp" style=""></span>700 <span class="elsevierStyleHsp" style=""></span><span class="elsevierStyleItalic">&#937;</span>&#46;m&#41;&#46;</p><p id="par0565" class="elsevierStylePara elsevierViewall">On the other side&#44; the profile P6&#44; also reproduced separately in <a class="elsevierStyleCrossRef" href="#f0060">Figure 13</a> &#40;here referring to light green points in <a class="elsevierStyleCrossRef" href="#f0045">Figures 10</a> and <a class="elsevierStyleCrossRef" href="#f0050">11</a>&#41; is located along the main fault valley near the confluence with the mine stream&#58; resistivity values corresponding to a situation of very weathered rock material&#44; decreasing with depth&#46;</p><p id="par0570" class="elsevierStylePara elsevierViewall">The profiles carried out along the valley that spreads out WNW from washing pools&#44; indicate that this is a fault valley&#44; filled in with erosion material&#46; As before mentioned&#44; all profiles show a decrease of resistivity not only with depth but also as we go away from the mine towards the main fault valley &#40;e&#46;g&#46; from P1 to P6&#44; see <a class="elsevierStyleCrossRef" href="#f0055">figure 12</a>&#41;&#46;<a name="p148"></a><a name="p149"></a><a name="p150"></a></p></span></span><span id="sec0110" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0135">Conclusions</span><p id="par0575" class="elsevierStylePara elsevierViewall">At the beginning of the study it was known the situation in terms of regional tectonics&#44; which was known complex for being associated with a number of episodes of tardi-Hercynian fracturing&#44; as well with the Alpine tectonics&#46;</p><p id="par0580" class="elsevierStylePara elsevierViewall">In order to better characterize the underlying geology of the old Castelejo mine&#44; two geophysical surveying campaigns were conducted at the site&#46; Both the results of the first campaign &#40;VLF-EM results&#41; and the references consulted&#44; particularly in EDM internal reports&#44; pointed to the presence of faults and fractures which might constitute the main pathways of superficial and underground drainage&#46;</p><p id="par0585" class="elsevierStylePara elsevierViewall">In the second campaign&#44; measurements of RMT-R were performed to the WNW and ESE of the centre of exploration&#46; Apparent resistivity and phase difference between the electric and magnetic fields were the measured values&#46; The obtained values were projected graphically and processed&#44; after which real resistivities and thicknesses were determined through the use of an inversion program&#46;</p><p id="par0590" class="elsevierStylePara elsevierViewall">After matching the literature data with the data obtained during field work&#44; it was concluded that the direction of maximum compressive stress&#44; s<span class="elsevierStyleInf">1</span>&#44; located NNW-SSE to NW-SE&#44; where extension fractures are developed&#44; should be the one wherein groundwater flows more easily&#44; since the larger openings of the fractures provide a better flow&#46;</p><p id="par0595" class="elsevierStylePara elsevierViewall">However&#44; it was not possible to establish a direct correspondence between real resistivity values and permeability values&#44; which&#44; although outside the scope of this article&#44; may be relevant for v&#46;g&#46; hydrogeological purposes&#46;</p><p id="par0600" class="elsevierStylePara elsevierViewall">All profiles also reveal a singular situation &#8211; their resistivity values decrease with depth&#46;</p><p id="par0605" class="elsevierStylePara elsevierViewall">This can be due to natural causes &#40;more weathered layers&#41; or it can indicate a situation of deep contamination with acid drainage &#40;increased mineralization&#41;&#46;</p><p id="par0610" class="elsevierStylePara elsevierViewall">In fact&#44; we are in the presence of a former uranium exploration&#44; in which ore acid leaching took place in a flooded open sky&#44; with a number of negative implications in the surroundings&#44; particularly over groundwater&#46; Treatment operations of the mine water still occur&#46; However&#44; any risks to populations seem weak&#44; given the isolation of the area in terms of population&#46;</p><p id="par0615" class="elsevierStylePara elsevierViewall">Also the use of water seems to be aimed to agricultural purposes rather than for human consumption&#46;</p><p id="par0620" class="elsevierStylePara elsevierViewall">This point will be addressed in the future through the implementation of a hydrochemical monitoring plan&#46;</p></span></span>"
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          "titulo" => "Introduction"
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              "titulo" => "Identification of fracturing"
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              "titulo" => "Risks associated with abandoned U mining sites"
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                  "titulo" => "Radon exhalation"
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                  "titulo" => "Gamma radiation"
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                  "titulo" => "Dust blowing"
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          "titulo" => "Study Area"
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              "titulo" => "The distribution of U in Portugal"
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        "resumen" => "<span id="abst0005" class="elsevierStyleSection elsevierViewall"><p id="spar0010" class="elsevierStyleSimplePara elsevierViewall">Hay alrededor de 175 minas abandonadas en Portugal&#44; de las cuales unos 60 son antiguas explotaciones de uranio&#46; La mina de uranio Castelejo est&#225; ubicada a unos 2<span class="elsevierStyleHsp" style=""></span>km al W de Vila Cort&#234;s da Serra&#44; en el distrito de Guarda&#44; en la cuenca del r&#237;o Mondego&#46; En t&#233;rminos geol&#243;gicos&#44; la mina se localiza en un granito de grano medio e dos micas con tendencia porfiroidal&#46; La explotaci&#243;n comenz&#243; con dos minas a cielo abierto entre 1979 y 1990&#44; que produjeron alrededor de 132 toneladas de U<span class="elsevierStyleInf">3</span>O<span class="elsevierStyleInf">8</span>&#46; Desde 1992&#44; la producci&#243;n comenz&#243; a llevarse a cabo a trav&#233;s de la lixiviaci&#243;n <span class="elsevierStyleItalic">in situ</span> con H<span class="elsevierStyleInf">2</span>SO<span class="elsevierStyleInf">4</span> de materiales de bajo contenido en uranio&#46; La circulaci&#243;n de las aguas superficial y subterr&#225;nea est&#225; estructuralmente condicionada por la fracturacion intensa en la zona&#46; Dos campa&#241;as geof&#237;sicas de exploraci&#243;n se llevaron a cabo a fin de caracterizar el sistema de fracturas&#46; La primera fue una investigaci&#243;n con el m&#233;todo VLF que nos permiti&#243; identificar los principales sistemas de fallas que pueden proporcionar rutas para el flujo de las aguas subterr&#225;neas&#46; A partir de la segunda campa&#241;a&#44; que fue un estudo llevado a cabo con el m&#233;todo RMT en una caja de falla que reproduz o gradiente natural de la mina&#44; se obtuvieron las resistividades y espesores del material de granito intemperizado&#46; Los perfiles obtenidos muestran que la resistividad disminuye con el aumento de profundidad&#46;</p><p id="spar0015" class="elsevierStyleSimplePara elsevierViewall">Este aspecto puede deberse a causas naturales - el material que llena la caja de falla es m&#225;s intemperizado en profundidad que en la superficie - o puede indicar contaminaci&#243;n en profundidad&#44; debido al drenaje &#225;cido de las minas&#46;</p></span>"
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        "resumen" => "<span id="abst0010" class="elsevierStyleSection elsevierViewall"><p id="spar0020" class="elsevierStyleSimplePara elsevierViewall">There are about 175 abandoned mining sites in Portugal&#44; of which about 60 are old uranium workings&#46; The Castelejo mine is an old uranium located about 2<span class="elsevierStyleHsp" style=""></span>km W of Vila Cort&#234;s da Serra&#44; in Guarda district&#44; on the River Mondego basin&#46; In geologic terms&#44; the mine is located in medium-grained two-mica monzonitic granite&#44; with porphyroidal tendency&#46; Exploitation started with two open cast mines between 1979 and 1990 which produced about 132 tonnes U<span class="elsevierStyleInf">3</span>O<span class="elsevierStyleInf">8</span>&#46; From 1992&#44; production started to be carried out through the <span class="elsevierStyleItalic">in situ</span> H<span class="elsevierStyleInf">2</span>SO<span class="elsevierStyleInf">4</span> leaching of the mine&#8217;s low-grade materials&#46; The superficial and groundwater circulation are structurally conditioned by the intense fracturing in the area&#46; Two exploratory geophysical field campaigns were conducted in order to characterize the fracturing&#46; The first was a VLF survey that allowed us to identify major fault systems that may provide paths for groundwater flow&#46; From the second campaign&#44; which was an RMT survey conducted at a fault gauge which records the mine natural gradient flow&#44; we obtained the resistivities and thicknesses of the weathered granite material&#46; The profiles obtained show that resistivity declines with increasing depth&#46; This fact may arise from natural causes &#8211; the material which fills the fault gauge is more weathered at depth than on the surface &#8211; or it may indicate contamination at depth&#44; due to acid mine drainage&#46;</p></span>"
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          "en" => "<p id="sp0005" class="elsevierStyleSimplePara elsevierViewall">a&#41; Paleogeographic and tectonic zones of the Hesperian Massif&#46; Adapted from <a class="elsevierStyleCrossRef" href="#bib0100">Ribeiro <span class="elsevierStyleItalic">et al</span>&#46; 1979</a>&#46; b&#41; Major hydrogeological units of portuguese metropolitan territory&#46; Adapted from SNIRH&#44; Instituto da &#193;gua&#44; 2009</p>"
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          "en" => "<p id="sp0010" class="elsevierStyleSimplePara elsevierViewall">&#8220;Beiras Uraniferous Region&#8221;&#46; On the map of Portugal &#40;left&#41;&#44; the Castelejo mine locates at the red rectangle &#40;adapted from <a class="elsevierStyleCrossRef" href="#bib0045"><span class="elsevierStyleItalic">Ferreira&#44; 1971</span></a>&#41;&#46;</p>"
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          "en" => "<p id="sp0020" class="elsevierStyleSimplePara elsevierViewall">Some ecological and human risks associated with uranium mill tailings &#40;adapted from <span class="elsevierStyleInterRef" id="intr0005" href="http://www.wise-uranium.org/uwai.html">http&#58;&#47;&#47;www&#46;wise-uranium&#46;org&#47;uwai&#46;html</span>&#41;&#46;</p>"
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          "en" => "<p id="sp0025" class="elsevierStyleSimplePara elsevierViewall">Basis of VLF-EM method&#44; adapted from <a class="elsevierStyleCrossRef" href="#bib0125">Turberg and M&#252;ller &#40;1992&#41;</a> Reproduced from <a class="elsevierStyleCrossRef" href="#bib0040"><span class="elsevierStyleItalic">Dill et al</span>&#46; &#40;1998&#41;</a>&#46;</p>"
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          "en" => "<p id="sp0030" class="elsevierStyleSimplePara elsevierViewall">Basis of RMT-R method&#44; adapted from <a class="elsevierStyleCrossRef" href="#bib0115">Thierrin and M&#252;ller &#40;1988&#41;</a>&#46; Reproduced from <a class="elsevierStyleCrossRef" href="#bib0040"><span class="elsevierStyleItalic">Dill et al&#46; &#40;1998&#41;</span></a>&#46;</p>"
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          "en" => "<p id="sp0035" class="elsevierStyleSimplePara elsevierViewall">a&#41; Start point and end point of the seven profiles carried out in the VLF-EM survey b&#41; Photographic map of Castelejo former mine site surroundings&#44; with profile location where VLF-EM survey was conducted &#40;color variation explained in the text&#59; P &#8211; Profiles&#41;&#46;</p>"
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                  <table border="0" frame="\n
                  \t\t\t\t\tvoid\n
                  \t\t\t\t" class=""><thead title="thead"><tr title="table-row"><th class="td" title="table-head  " align="center" valign="top" scope="col" style="border-bottom: 2px solid black">Type of tailing&nbsp;\t\t\t\t\t\t\n
                  \t\t\t\t</th><th class="td" title="table-head  " align="center" valign="top" scope="col" style="border-bottom: 2px solid black">Size &#40;&#956;m&#41;&nbsp;\t\t\t\t\t\t\n
                  \t\t\t\t</th><th class="td" title="table-head  " align="center" valign="top" scope="col" style="border-bottom: 2px solid black">Composition&nbsp;\t\t\t\t\t\t\n
                  \t\t\t\t</th></tr></thead><tbody title="tbody"><tr title="table-row"><td class="td" title="table-entry  " align="center" valign="top">Sand&nbsp;\t\t\t\t\t\t\n
                  \t\t\t\t</td><td class="td" title="table-entry  " align="center" valign="top">75 - 500&nbsp;\t\t\t\t\t\t\n
                  \t\t\t\t</td><td class="td" title="table-entry  " align="center" valign="top">SiO<span class="elsevierStyleInf">2</span> plus<span class="elsevierStyleHsp" style=""></span>&#8776;<span class="elsevierStyleHsp" style=""></span>1 weight &#37; Al&#44; Fe&#44; Mg&#44; Ca&#44; Na&#44; K&#44; Se&#44; Mn&#44; Ni&#44; Mo&#44; V silicates and metal oxides&#59; approximately 0&#46;004-0&#46;01 weight &#37; U<span class="elsevierStyleInf">3</span>O<span class="elsevierStyleInf">8</span>&#59; with H<span class="elsevierStyleInf">2</span>SO<span class="elsevierStyleInf">4</span>leaching process&#58; 26-100 pCi <span class="elsevierStyleSup">226</span>Ra&#47;g and 70-600 pCi <span class="elsevierStyleSup">230</span>Th&#47;g&#59;&nbsp;\t\t\t\t\t\t\n
                  \t\t\t\t</td></tr><tr title="table-row"><td class="td" title="table-entry  " align="center" valign="top">Slime&nbsp;\t\t\t\t\t\t\n
                  \t\t\t\t</td><td class="td" title="table-entry  " align="center" valign="top">45 - 75&nbsp;\t\t\t\t\t\t\n
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                  \t\t\t\t</td></tr><tr title="table-row"><td class="td" title="table-entry  " align="center" valign="top">Liquid&nbsp;\t\t\t\t\t\t\n
                  \t\t\t\t</td><td class="td" title="table-entry  " align="center" valign="top">-&nbsp;\t\t\t\t\t\t\n
                  \t\t\t\t</td><td class="td" title="table-entry  " align="center" valign="top">with H<span class="elsevierStyleInf">2</span>SO<span class="elsevierStyleInf">4</span>leaching process&#58; pH 1&#46;2-2&#46;0&#59; Na&#43;&#44; NH<span class="elsevierStyleInf">4</span>&#43;&#44; SO<span class="elsevierStyleInf">4</span><span class="elsevierStyleSup">2-</span>&#44; Cl-&#44; PO<span class="elsevierStyleInf">4</span><span class="elsevierStyleSup">3-</span>&#59; dissolved solids<span class="elsevierStyleHsp" style=""></span>&#8776;<span class="elsevierStyleHsp" style=""></span>1 weight &#37;&#59; approximately 0&#46;001-0&#46;01 weight &#37; U<span class="elsevierStyleInf">3</span>O<span class="elsevierStyleInf">8</span>&#59; 20-7500 pCi <span class="elsevierStyleSup">226</span>Ra&#47;l and 2000-22000 pCi <span class="elsevierStyleSup">230</span>Th&#47;l&#59;&nbsp;\t\t\t\t\t\t\n
                  \t\t\t\t</td></tr></tbody></table>
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          "en" => "<p id="spar0005" class="elsevierStyleSimplePara elsevierViewall">Properties of uranium mill tailings &#40;adapted from USEPA 2007&#41;&#46;</p>"
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                      "titulo" => "Determina&#231;&#227;o de idade pelo m&#233;todo do Rb-Sr de granitos antigos portugueses"
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                        "tituloSerie" => "Mem&#243;rias da Academia das Ci&#234;ncias de Lisboa"
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                        "volumen" => "XXIV"
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                      "titulo" => "Hidrogeologia de rochas gran&#237;ticas da regi&#227;o do Porto &#40;NW de Portugal&#41;"
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                          "etal" => false
                          "autores" => array:1 [
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              ]
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                      "titulo" => "Principais jazigos minerais do Sul de Portugal&#46; I Congresso Hispano-LusoAmericano de Geologia Econ&#243;mica&#44; LivroGuia da Excurs&#227;o n&#186; 4"
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                          "autores" => array:3 [
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                      "titulo" => "Import&#226;ncia do uso de m&#233;todos geof&#237;sicos electromagn&#233;ticos Very Low Frequency Electromagnetics &#40;VLF-EM&#41; e Radio Magnetotelluric-Resistivity &#40;RMT-R&#41; no estudo de aqu&#237;feros c&#225;rsicos do Alentejo e do Algarve&#46; 4&#186; Congresso da &#193;gua"
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                            3 => "J&#46;P&#46; Monteiro"
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Article information

ISSN: 00167169
Original language: English

DOI:10.1016/S0016-7169(14)71496-5

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2015 October	18	7	25
2015 September	19	6	25
2015 August	33	5	38
2015 July	32	4	36
2015 June	12	6	18
2015 May	3	2	5
2015 April	3	6	9
2015 March	4	1	5

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