The Hiendelaencina district in Spain was the most important silver producer in Europe during 1844–1925. At the end of the 20th century, with mines having closed, some waste rock dumps were ...reprocessed, and the sludge from the flotation process was stored in two tailings ponds. When this activity ceased, the residues began to be eroded and disperse. In this study, the state of degradation of both deposits was evaluated using historical mapping and light detection and ranging (LiDAR) data, incorporated into a Geographic Information System. In the aerial images (1946–2018), mine tailings and their main erosive and sedimentary forms were mapped. Geoforms linked to hydrological (channels, gullies, alluvial cones), wind (eolian mantles), hydric–gravitational (colluvium) and anthropic (motorbike tracks) processes which move sludge into the surrounding areas were identified. A net loss of 8849 m3 of sludge, a release of 10.3 t of potentially polluting substances and a high erosion rate of 346 t/ha*year were calculated based on LiDAR data from 2009 and 2014. The ponds show a current high degree of erosion that could increase due to both human activity and the growing frequency of drought and torrential rain periods if stabilization measures are not undertaken.
This study presents the results of the geoenvironmental characterization of La Matildes riverbed, affected by mine tailings in the Cartagena–La Unión district, Murcia (southeast Spain). Soils and ...riverbeds in this area are highly polluted. Two Electrical Resistivity Imaging (ERI) profiles were carried out to obtain information about the thickness of the deposits and their internal structure. For the mine tailings deposits of La Murla, a tributary of the El Miedo riverbed, the geophysical method imaged two different units: the upper one characterized by low resistivity values and 5–8 m thickness, correlated with the mine tailings deposits; and the lower more resistive unit corresponding to the Paleozoic metasediments bedrock. The ERI profile transverse to the Las Matildes dry riverbed revealed the existence of three different units. The uppermost one has the lowest resistivity values and corresponds to the tailings deposits discharged to the riverbeds. An intermediate unit, with intermediate resistivity values, corresponds to the riverbed sediments before the mining operations. The lower unit is more resistive and corresponds to the bedrock. Significant amounts of pyrite, sphalerite, and galena were found both in tailings and riverbed sediments. The geochemical composition of borehole samples from the riverbed materials shows significantly high contents of As, Cd, Cu, Fe, Pb, and Zn being released to the environment. Mining works have modified the natural landscape near La Unión town. Surface extraction in three open-pit mines have changed the summits of Sierra de Cartagena–La Unión. Rock and metallurgical wastes have altered the drainage pattern and buried the headwaters of ephemeral channels. The environmental hazards require remediation to minimize the environmental impact on the Mar Menor coastal lagoon, one of the most touristic areas in SE Spain.
This study presents the results of the geoenvironmental characterization of the Brunita mine pond in the Cartagena-La Unión mining district, Murcia (SE Spain). The main objective was to evaluate the ...present conditions of the mine tailings in order to identify related environmental hazards. Since 1956, the Brunita mine tailings were being stored in four stepped ponds at the watercourse of a NNO-SSE trending ravine. Subsequently, they were stored in a single, large pond. After the closure of the pond operations, certain work on dike stabilization was performed and debris from the Brunita mine started to accumulate. The mining works for >50years have led to the complete burial of the surrounding valleys and hills by mine waste material. Electrical resistivity tomography (ERT) has allowed the determining of both the general geometry of the pond base and the thickness of the mine tailings. Surveys along a total of 6 ERT profiles, 3 longitudinal and 3 transverse profiles to the largest dimension of the pond were carried out. The strong resistivity contrast between the infilling and the bedrock is high enough to clearly define the bottom pond boundary. Low resistivity values (<10Ω·m) characterize the infilling of the pond, whereas resistivity values>200Ω·m correspond to the Paleozoic rocks that constitute the base of the deposit. Vertical steps have been recognized defining strong variations in the thickness of the deposit. This geometry results from the interaction between the paleotopography of the previous valley and the different growth stages of the deposit. The depth of the pond's base obtained from two boreholes has confirmed the results obtained from ERT profiles. Significant amounts of pyrite and siderite and an appreciable presence of sphalerite and galena were determined by XRD of representative samples. Accordingly, high contents of toxic metals (Cd, Cu, Pb, Sn and Zn) and As were detected in chemical analyses, which show the potential of the tailings to release substantial amounts of these pollutants into the surrounding soils and watercourses. AMD has been identified and percolation through the base of the pond could occur at its northeast sector, where a low resistivity area is recognized. The manifest instability of the tailings pond makes it necessary to include physical stabilization in remediation and monitoring in order to minimize the environmental impact of the tailings on the areas affected, which is located in one of the most popular tourist areas in SE Spain.
•Joint use of geophysical and geochemical methods for environmental characterization•Resistivity data reveals ~8m thick mine deposits with significant acid water leakage.•Significant toxic metal and metalloid content have been measured.•The pond instability makes it necessary to work on remediation and monitoring.•One of the most touristic areas of SE Spain
More than twenty years after the last mining operations were completed in the Hiendelaencina Mining District, it is necessary to carry out a geochemical characterisation of the tailings stored in two ...contiguous mine ponds. Both have significant amounts of quartz, siderite, barite and muscovite and show significant contents of As, Ba, Pb, Sb and Zn. The tailings show alkaline pH and low electrical conductivity values, which support the visual observation that rules out acid drainage into the environment. The comparison of the National Topographic Map of 1954 with LiDAR data from 2014 has allowed estimating the volume of abandoned waste. Based on the volume of slurry and its average density, the total tonnage of pollutants has been estimated at 279 ± 9 t stored in Pond North and 466 ± 11 t stored in Pond South. Although these are significant quantities that pose a risk to the environment and nearby populations, they are lower than those present in other Spanish districts, such as the Iberian Pyrite Belt or Cartagena-La Unión. The combined use of LiDAR data, aerial imagery and geochemical methods has proven to be very useful for the estimation of the volume of pollutants stored in mine ponds.
La Banya spit, located at the south of the River Ebro Delta, is a sandy formation, developed by annexation of bars forming successive beach ridges, which are oriented and modeled by the eastern and ...southern waves. The initial ridges run parallel to the coastline, and above them small dunes developed, the crests of which are oriented by dominant winds, forming foredune ridges and barchans. This study attempted to test a number of techniques in order to understand the dune dynamic on this coastal spit between 2004 and 2012: LiDAR data were used to reconstruct changes to the surface and volume of the barchan dunes and foredunes; ground-penetrating radar was applied to obtain an image of their internal structure, which would help to understand their recent evolution. GPS data taken on the field, together with application of GIS techniques, made possible the combination of results and their comparison. The results showed a different trend between the barchan dunes and the foredunes. While the barchan dunes increased in area and volume between 2004 and 2012, the foredunes lost thickness. This was also reflected in the radargrams: the barchan dunes showed reflectors related to the growth of the foresets while those associated with foredunes presented truncations associated with storm events. However, the global balance of dune occupation for the period 2004–2012 was positive.
Rift zones are fundamental features in oceanic island volcanoes, although their origin is still controversial, especially at the Canary Islands where the role of volcanic spreading is under debate. ...For this reason, we have performed a field study of >400 dykes at 20 outcrops in the Lower Old Edifice and 2 outcrops of the Upper Old edifice of La Gomera Island, identifying different dyke swarms. We propose the development of an unnoticed E-W volcanic rift (Hermigua Rift) restricted to the Lower Old Edifice East flank, with up to 25% of extension and structural characteristics compatible with the spreading of the edifice over a basal weak decollement. Contemporaneously a dyke swarm of outward-dipping dykes intruded at the W-SW zones, indicating a progressive radial sliding of the edifice. This asymmetric volcano structural pattern suggests that volcano stresses were predominately local in origin, probably related to the buttressing effect of the neighbor contemporaneous Roque del Conde edifice (Tenerife Island). Additionally, we have deduced two different rift zones (NW-SE Enchereda and N-S Erque rifts) during the growth of the Upper Old Edifice, evidencing that La Gomera rifts were dynamic evolving structures. The structure and regional setting of the Upper Old Edifice rifts suggest a change to a predominance of regional stresses. Our results have implications for the understanding of the origin and evolution of rifts at oceanic island volcanoes, since: 1) confirm a principal role for volcanic spreading processes; 2) support that the location of neighbor volcanic loads strongly influences rifts development; and 3) suggests, in some situations, a possible main role for the regional stress field.
•We identify several unnoticed rift zones at Old Volcanic Edifice of La Gomera by their underlying coherent dike complexes.•An unnoticed E-W structure (Hermigua Rift) developed at the east flank of the Lower Old Edifice with up to 25% of extension.•Contemporaneously a singular swarm of outward dipping dikes developed at the volcano west flank.•Asymmetric volcano structural pattern suggests that volcano stresses were local in origin related to the volcano spreading.•The neighbour contemporaneous Roque del Conde edifice (Tenerife Island) produced a buttressing effect.•Two new rift zones (NW-SE Enchereda and N-S Erque rifts) developed during the growth of the Upper Old Edifice.•Rifts of the Old Volcanic Edifice of La Gomera were dynamic evolving structures.•The character of the Upper Old Edifice rifts suggest a change to a predominance of regional stresses during its growth.
Geophysical methods based on electrical properties can be used to study tailings ponds studies because a site’s spatial and temporal subsurface electrical resistivity values vary depending on its ...physical and chemical properties (texture, salinity, metals, water content, temperature, pH, etc.). This paper reviews published case studies in which electrical resistivity tomography (ERT) was successfully used to characterize and monitor tailings ponds.
Metallic mining wastes are a crucial environmental concern because of the accumulation and emission of toxic elements. The abandoned San Quintín mine tailings, from the exploitation of galena and ...sphalerite (Puertollano mining district, Spain), are surrounded by farmland and are crossed by the European Cultural Itinerary known as the “Don Quixote Route”. Geophysical, mineralogical and geochemical techniques have been applied to determine the geometry and composition of mine ponds and the possible occurrence of AMD that could entail ecosystem and human risks. Seven electrical resistivity tomography profiles were surveyed, and re-worked tailing samples of two ponds, five soil samples, nine water samples and gaseous mercury emissions were analyzed. Both mine ponds are ~8m deep and overlie Quaternary colluvial sediments deposited over Precambrian metasediments. The pond infilling is mainly composed of quartz and clay minerals, and minor amounts of gypsum and sulfides, with significant As, Cd, Hg, Pb, Sb and Zn contents. This metal emission source affects the underlying colluvial sediments and high Hg and Pb contents have also been found in nearby agricultural soils. AMD has been identified, but metal contamination in the stream that borders the tailings is below the USEPA's recommended limits. Although gaseous mercury emissions from a cinnabar stockpile increase in summer, the measured levels do not reach the WHO's recommended limit. The Enrichment Factor and Igeo indexes for As, Cd, Hg, Pb, Sb and Zn indicate strong to extreme contamination in the mine ponds and moderate contamination in the colluvial sediments/metasediments. Aeolian dispersion is the most important contaminant agent. The surrounding soils show strong to extreme levels of Hg and moderate to extreme levels of As, Cd, Pb and Sb. Restoration of these abandoned wastes is recommended to reduce the health risks for residents and tourists due to this aeolian contaminant dispersion.
•Joint use of geophysical, mineralogical, and geochemical techniques•A significant contamination from the mine tailings was revealed.•Human health risks associated with the aeolian dispersion of contaminants•The San Quintín mine, crossed by the longest Eco-tourist Itinerary in Europe.•It represents an environmental hazards that need to be characterized and restored.
One of the concerns of underground CO2 onshore storage is the triggering of induced seismicity and fault reactivation by the pore pressure increasing. Hence, a comprehensive analysis of the tectonic ...parameters involved in the storage rock formation is mandatory for safety management operations. Unquestionably, active faults and seal faults depicting the storage bulk are relevant parameters to be considered. However, there is a lack of analysis of the active tectonic strain field affecting these faults during the CO2 storage monitoring. The advantage of reconstructing the tectonic field is the possibility to determine the strain trajectories and describing the fault patterns affecting the reservoir rock. In this work, we adapt a methodology of systematic geostructural analysis to underground CO2 storage, based on the calculation of the strain field from kinematics indicators on the fault planes (ey and ex for the maximum and minimum horizontal shortening, respectively). This methodology is based on a statistical analysis of individual strain tensor solutions obtained from fresh outcrops from the Triassic to the Miocene. Consequently, we have collected 447 fault data in 32 field stations located within a 20 km radius. The understanding of the fault sets' role for underground fluid circulation can also be established, helping further analysis of CO2 leakage and seepage. We have applied this methodology to Hontomín onshore CO2 storage facilities (central Spain). The geology of the area and the number of high-quality outcrops made this site a good candidate for studying the strain field from kinematics fault analysis. The results indicate a strike-slip tectonic regime with maximum horizontal shortening with a 160 and 50∘ E trend for the local regime, which activates NE–SW strike-slip faults. A regional extensional tectonic field was also recognized with a N–S trend, which activates N–S extensional faults, and NNE–SSW and NNW–SSE strike-slip faults, measured in the Cretaceous limestone on top of the Hontomín facilities. Monitoring these faults within the reservoir is suggested in addition to the possibility of obtaining a focal mechanism solutions for micro-earthquakes (M<3).
This study presents the results of the geoenvironmental characterization of San Cristóbal and Las Moreras riverbeds, both affected by mine tailings in the Mazarrón district, Murcia (SE Spain). The ...main objective of the study was to characterize the present conditions of the riverbeds in order to identify related environmental problems. The goal is particularly relevant, because the abandoned mine wastes remain a continual source of acid mine drainage (AMD) and metal contamination, and soils and watercourses in this zone are still highly polluted. For the San Cristóbal site, the electrical resistivity tomography survey indicated a two-unit sequence, in good agreement with borehole data: an upper unit extends down to a 1.5m depth that corresponds to the upper part of sandy tailings, and a lower unit of lower resistivity values extends down to 6m depth corresponding with clayed tailings and riverbed deposits. At the Las Moreras site, a 2m thick upper unit of low resistivity values and a 4m thick lower unit of higher resistivity values were distinguished, also in good agreement with borehole data. Significant amounts of pyrite, sphalerite, and galena were determined in tailings from both sites. The alluvial materials from both riverbeds showed significant toxic metal and metalloid contents (Ag, As, Cu, Sb, Pb, and Zn). An important level of contamination by AMD from the surficial tailings to the watercourse sediments and waters also occurs. Mineral wastes, intensive agricultural activities, and the population of the town of Mazarrón overlap in the district, so both remediation and monitoring are necessary to minimize environmental impact on the areas affected, in one of the most touristic areas in SE Spain.
► We studied two dry watercourses affected by mine tailings in Mazarrón district. ► ERT has provided the stratigraphy of the alluvial deposits confirmed by two boreholes. ► Geochemical analyses have revealed significant toxic metal and metalloid contents. ► AMD from tailings to the sediments and waters of the watercourses has been detected. ► Combining geophysical and geochemical methods a complete characterization can be done.
PDF
