Abandoned Mine Waste Research Articles

Unlocking the Secondary Critical Raw Material Potential of Historical Mine Sites, Lousal Mine, Southern Portugal

A steady supply of mineral raw materials is vital for the transition to a low-carbon, circular economy. The number of active mines in Europe has severely declined over the last century and half, giving rise to many abandoned mining waste sites and corresponding geological heritage. Also, the rise in minerals demand for large-scale deployment of renewable energy requires the continued and steady availability of key minerals. The supply risk associated with unpredicted geopolitical events needs to be eliminated/mitigated. Historical mine waste sites are the answer but evaluating mine waste is a lengthy and costly exercise. The study, undertaken in the Lousal Mine, used small unmanned aerial systems (sUASs) to model and determine mine waste volumes by generating orthomosaic maps with quick, inexpensive, and reliable results. Calculated mine waste volumes between 308,478 m3 and 322,455 m3 were obtained. XRD and p-XRF techniques determined the mineralogy and chemistry of waste, which varied from mineralization and host rocks with hydrothermal alteration and numerous neogenic sulphates (mostly gypsum, rhomboclase, ferricopiapite, coquimbite, and jarosite) related with supergene processes and weathering. The study shows the viability of using these sUASs to successfully model historical mine waste sites in an initial phase and for future monitoring programs.

The spatiotemporal variation in lead and zinc contents in the Moulouya River (northeastern Morocco)

In the context of the challenges imposed by climate change, which exerts constant pressure on water security in Morocco, the Moulouya River, one of the main sources of surface water, frequently undergoes spatiotemporal variations in its quality. This situation is particularly worrying in the upstream part of the river, where the old Zaida mine is located, which is now inactive and leaves significant residues in the form of slag heaps in direct contact with the waters of the Moulouya River. To assess the impact of this abandoned mining waste, eight (08) water sampling stations (S1 to S8) were chosen to analyse the concentrations of two (02) essential metals, namely, lead and zinc. The results revealed lead concentrations of approximately 0.13 mg/L on average during the dry period and 0.09 mg/L during the humid period. The average zinc concentration was 0.29 mg/L during the dry season and 0.32 mg/L during the humid season. The maximum concentrations were recorded at the stations closest to the aforementioned mine, in particular, S1, S2 and S3. Other maximum concentrations were observed at station S6. These results highlighted the significant impact of mining slag heaps exposed to the open sky on the physico-chemical and metallic quality of Moulouya waters. This finding highlights the urgency of continued monitoring of this vital water resource to protect it against potential risks of contamination.

Critical Raw Materials recovery potential from Spanish mine wastes: A national-scale preliminary assessment

In Spain, due to its important mining past, there are many abandoned mine waste facilities. This study evaluates the potential of Spanish mine wastes for the recovery of critical and strategic raw materials and other elements of economic relevance. For this purpose, 20 mine waste facilities have been selected in different parts of Spain based on criteria such as tonnage, element content or metal market price. Surface samples were taken at the facilities, considered representative of these, for subsequent granulometric, mineralogical and chemical analysis. The grain size data were obtained by standard sieving (ASTM 5000), while the mineralogy was obtained by X-ray Diffraction (XRD). For chemical characterization, Wavelength Dispersion X-ray Fluorescence Spectrometry (WDXRF) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) were used to analyze 38 chemical elements (Be, Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Ag, Cd, Sn, Sb, I, Cs, Ba, La, Ce, Nd, Sm, Hf, Ta, W, Tl, Pb, Bi, Th and U), many of them included in the European Union’s list of Critical Raw Materials (CRMs). In addition, leachate data from mine wastes in the Iberian Pyritic Belt were analyzed to assess their bioleaching potential. The calculated enrichment factors (EF) indicate that some critical elements, as well as others with strategic and economic interest, are highly enriched in the wastes, including Sb, Bi, As, Pb, Cu, Ag, Zn, Cd, Sn, Se and Th. The most promising facilities with the highest recovery potential are located in the historic Riotinto and Tharsis mines (both in Huelva, Iberian Pyrite Belt) and the Rubiais mine in Lugo, whose tailings could contribute up to 3.2 billion dollars gross, according to the current market metal prices. This paper aims to provide a first step to promote mine waste recycling and circular mining in Spain, an initiative that would also help to mitigate the environmental damage derived from abandoned mine wastes.

Mapping Co–Cr–Cu and Fe Occurrence in a Legacy Mining Waste Using Geochemistry and Satellite Imagery Analyses

Abandoned mining wastes are both an environmental challenge and a possible secondary raw material source. The characterization and monitoring of these sites are often expensive and cumbersome because of the need of repeated field surveys. Remote sensing data are a cost-effective alternative that helps in producing multiscale maps of mining wastes. These maps can be used to investigate and monitor the spatial patterns of different elements within the mining wastes. In this work, Sentinel-2 images are combined with the geochemical samples in order to map the distribution of iron, copper, chromium, and cobalt. The target area was the Vigonzano mining wastes in Northern Apennines (Italy) where there are a small number of geochemical analyses but a large amount of satellite image data. We used the multivariate geostatistical estimation method (Co-Kriging) that exploit the meaningful spatial correlation between the elements of interest and band ratios (obtained from Sentinel-2 images). The concentration maps highlighted subareas for Cu and Cr with an estimated grade of about 0.3% and 0.2%, respectively. In addition, the critical element Co showed an enrichment in the south-east part of the mining wastes, in a similar pattern as Cr. Instead, the obtained maps show Ce, La, Rb, and Nb depletion compared to the surrounding agricultural areas. The concentration maps were intended as a prefeasibility study to determine enriched areas for further detailed investigation.

Natural radionuclides (NORM) in a Moroccan river affected by former conventional metal mining activities

The main aim of this work was to determine the levels of multiple natural radionuclides in an aquatic system (Moulouya river, Morocco) impacted by multiple abandoned Zinc and Lead mines. 238U, 234U, 232Th, 230Th and 210Po were determined by alpha-particle spectrometry in water and sediment samples collected along the river and in samples from three pit lakes of abandoned mines, located in the Upper Moulouya catchment area. The results enabled the analysis of the different levels of impact of former mining activities, depending on the natural radionuclides. While the activity concentration of U-isotopes in Moulouya river water was slightly elevated in the vicinity of abandoned mine wastes, other natural radionuclides (Th-isotopes and 210Po) levels were typical of a natural environment. This fact is clearly reflected in the magnitude and range observed in the distribution coefficients for the different radionuclides analyzed.

Comparative Assessment of Leaching Tests According to Lixiviation and Geochemical Behavior of Potentially Toxic Elements from Abandoned Mining Wastes

Comparative Assessment of Leaching Tests According to Lixiviation and Geochemical Behavior of Potentially Toxic Elements from Abandoned Mining Wastes

Socio-environmental conflict over abandoned mining waste in Copaquilla, Chile.

The material discarded by past mining extractive activities is exposed to the action of different environmental agents and constitutes the beginning of a problem that, inevitably, involves the population and the conditions of the environment where it is deposited. Bearing this in mind, a study of the Copaquilla-Chile valley was carried out with a focus on the socio-environmental conflict produced by the accumulation of abandoned mining waste in its vicinity. The objectives were to identify the role of the different actors and the main causes that originated the conflict and to characterize the physical-natural factors that conditioned the susceptibility and physical vulnerability of the studied environment. The methodological approach combined a set of qualitative and quantitative techniques, using participatory action research techniques (PAR) and multi-criteria evaluation models (MCE) through a geographic information system (GIS). The evaluation of the study area revealed quite severe levels in terms of the indices of susceptibility to processes of mass removal and vulnerability of the aquifer, which led us to infer that the morpho-climatic and hydrogeological characteristics of the sector generated the appropriate conditions to produce large damage to the complex socio-ecological system of the Copaquilla territory. This study generated participatory material, a chronology of the conflict, a database of the physical environment of the Copaquilla valley interpreted in thematic cartographies, and physicochemical soil and water samples to monitor contamination levels.

Natural radionuclides (NORM) in a Moroccan river affected by former conventional metal mining activities

The main aim of this work was to determine the levels of multiple natural radionuclides in an aquatic system (Moulouya river, Morocco) impacted by multiple abandoned Zinc and Lead mines. 238U, 234U, 232Th, 230Th and 210Po were determined by alpha-particle spectrometry in water and sediment samples collected along the river and in samples from three pit lakes of abandoned mines, located in the Upper Moulouya catchment area. The results enabled the analysis of the different levels of impact of former mining activities, depending on the natural radionuclides. While the activity concentration of U-isotopes in Moulouya river water was slightly elevated in the vicinity of abandoned mine wastes, other natural radionuclides (Th-isotopes and 210Po) levels were typical of a natural environment. This fact is clearly reflected in the magnitude and range observed in the distribution coefficients for the different radionuclides analyzed.

Effect of bioavailable arsenic fractions on the collembolan community in an old abandoned mine waste.

Mine waste from abandoned mines poses a risk to soil ecosystems due to the dispersion of arsenic (As) in the mine waste to the nearby soil environment. Because the bioavailability of As varies depending on the As chemical fraction and exposure conditions, chemical assessment of As fractions in soil around mine waste is essential to understand their impact on soil ecosystem. Here, six sites around the mine waste were selected for investigating toxic effects of As-contaminant soil on Collembola community. To measure the As chemical fraction in soil and bioavailability, Wenzel sequential extraction employed. Meanwhile, the collembolans that live in each sampling site were identified at the species level, and the characteristics and composition of the collembola community were investigated. The mobility fraction (F1 + F2 + F3; MF) was related to the risk to the collembolan community, and the adverse impact of high MF appeared to lead to a decrease in abundance, richness, and Shannon index. According to non-metric multidimensional scaling analysis, F1, F2, F3, and pH were shown as the significant factor explaining the NMDS space. Especially, the sampling site with the highest concentration of F3 showed statistically different species composition from the other sites. In the case of As-contaminated soil around the old mine waste, the toxic effects of the remaining F3 in soil, as well as that of F1 and F2, should be fully considered. This study suggested that collembolan community could be used for understanding the impact of bioavailable As fraction in the old abandoned mine area.

3D Spatial Distribution of Arsenic in an Abandoned Mining Area: A Combined Geophysical and Geochemical Approach

Abandoned mine wastes, containing high sulfide contents, are of particular concern because of the formation of acid mine drainage (AMD), becoming an active and harmful point source of potentially toxic elements (PTEs) to the environment. A detailed evaluation of the chemical and mineralogical composition of mining wastes is necessary to determine effective remediation actions. Due to the high amount of generated wastes as a result of mining and processing activities, the cost and time consumed for this characterization are limiting. Hence, efficient tools could be applied to predict the composition of these wastes and their spatial distribution. This study aims to determine the physico-chemical characterization of wastes from mining activities using geochemical and geophysical techniques. The obtained results, both geochemical and geophysical, allow us to locate areas with a high potential risk of contamination by As in an economic and simple way, and enable us to design detailed geochemical sampling campaigns. In addition, the fact that there are conductive fractures in depth suggests the possible circulation of contaminants through them as well as the preferential lines of circulation.

Groundwater–Stream Connectivity Mediates Metal(loid) Geochemistry in the Hyporheic Zone of Streams Impacted by Historic Mining and Acid Rock Drainage

High concentrations of trace metal(loid)s exported from abandoned mine wastes and acid rock drainage pose a risk to the health of aquatic ecosystems. To determine if and when the hyporheic zone mediates metal(loid) export, we investigated the relationship between streamflow, groundwater–stream connectivity, and subsurface metal(loid) concentrations in two ~1-km stream reaches within the Bonita Peak Mining District, a US Environmental Protection Agency Superfund site located near Silverton, Colorado, USA. The hyporheic zones of reaches in two streams—Mineral Creek and Cement Creek—were characterized using a combination of salt-tracer injection tests, transient-storage modeling, and geochemical sampling of the shallow streambed (<0.7 m). Based on these data, we present two conceptual models for subsurface metal(loid) behavior in the hyporheic zones, including (1) well-connected systems characterized by strong hyporheic mixing of infiltrating stream water and upwelling groundwater and (2) poorly connected systems delineated by physical barriers that limit hyporheic mixing. The comparatively large hyporheic zone and high hydraulic conductivities of Mineral Creek created a connected stream–groundwater system, where mixing of oxygen-rich stream water and metal-rich groundwater facilitated the precipitation of metal colloids in the shallow subsurface. In Cement Creek, the precipitation of iron oxides at depth (~0.4 m) created a low-hydraulic-conductivity barrier between surface water and groundwater. Cemented iron oxides were an important regulator of metal(loid) concentrations in this poorly connected stream–groundwater system due to the formation of strong redox gradients induced by a relatively small hyporheic zone and high fluid residence times. A comparison of conceptual models to stream concentration–discharge relationships exhibited a clear link between geochemical processes occurring within the hyporheic zone of the well-connected system and export of particulate Al, Cu, Fe, and Mn, while the poorly connected system did not have a notable influence on metal concentration–discharge trends. Mineral Creek is an example of a hyporheic system that serves as a natural dissolved metal(loid) sink, whereas poorly connected systems such as Cement Creek may require a combination of subsurface remediation of sediments and mitigation of upstream, iron-rich mine drainages to reduce metal export.

Overview of existing information on important closed (or in closing phase) and abandoned mining waste sites and related mines in Slovenia

The presented work provides a comprehensive inventory of data on closed (or in closing phase) and abandoned underground and surface mines and mining waste sites in Slovenia, collected within the framework of the Geological Survey of Slovenia (GeoZS) over the last two decades. Furthermore, a detailed overview of information on closed and abandoned mining waste sites in Slovenia is given. In order to establish the inventory, a definition of the work methodology, a comprehensive research of the archived and published literature, and the harmonisation and management of the collected data was carried out. Based on a selected methodology, the inventory contains information on 33 metal mines, 43 coal mines, 51 non-metallic mineral resource mines, 156 waste sites from metal mines and 18 waste sites from coal mines. The inventory is in the open access Google Earth file. It provides a basis for further research into the environmental impact of mining waste, which has been carried out since the EU Directive on the management of waste from extractive industries (Directive 2006/21/EC hereafter) was adopted into national law. In general, about 11,621,333 m3 of waste sites from metal mines and 76,188,000 m3 of waste sites from coal mines are covering about 678 hectares of Slovenian territory. More than half (64 %) of the waste from metal mines was produced in the Mežica lead and zinc mine, while the other two mines with a still significant share of produced waste were the Idrija mercury mine (18 %) and the Žirovski vrh uranium mine (15 %). Among the closed coal mines, the largest amount (46 %) of waste was generated by the coal mine Trbovlje-Hrastnik, while the other two coal mines with still significant share of waste produced were Kočevje (28 %) and Kanižarica (17 %).

Acceptable soil baseline levels in Taltal, Chile, and in Tampere, Finland

Soil geochemical baselines of potentially toxic elements were studied in two cities: Tampere in Finland and Taltal in Chile. Soil samples were sieved to the <2 mm grain-size fraction and the concentrations of As, Cd, Co, Cr, Cu, Hg, Ni, Pb, Sb, V and Zn were measured after aqua regia extraction. The upper limit of baseline variation was defined for the topsoils of Tampere and for soil samples from various lithological units in Taltal. Arsenic was the potentially toxic element of most concern in both towns. In both cases, arsenic concentrations were mostly geogenic. Anthropogenic activities related to the long mining history had caused elevated As concentrations in the topsoil samples in parts of Taltal city and soils surrounding abandoned mining wastes. In the case of this study, the geochemical baseline was useful to show the pollution level of As. Vanadium concentrations were also higher than the global average values in soils of Taltal commune. Heatmap plots based on compositional data analysis revealed that the abundance of mica minerals and soil organic matter controlled the distribution of most of the studied elements in Tampere, while the clustering of metals in Taltal was probably related to either abandoned mining sites or active mining operations. Regional baseline values should be used for the assessment of soil contamination with these elements in both cities.

Distribution of potentially toxic elements in soils surrounding abandoned mining waste located in Taltal, Northern Chile

Taltal is a commune located in Northern Chile, where former activities in copper ores processing left large amounts of mining waste enriched with potentially toxic elements, PTE. A soil pollution assessment using geochemistry and spatial distribution maps was conducted. A total of 101 surrounding soil samples from 3 abandoned mining waste sites (S1, S2, and S3) were taken to determine their content of PTE (Cu, Mo, Sb, Hg, Pb, Ni, Co, As, Mn, Cr, Cd, and Zn) and major elements. As guideline values of PTE in soils have not been established, the soil pollution index (PI) was assessed by comparing the soil PTE concentrations with the regional geochemical baseline (GBL) values and, for the first time, health risk for residents near Taltal city was evaluated.The measured PTE concentrations (mgkg−1) were Cu 18–6740, Mo 0.2–44, Sb 0.2–90, Hg 0.005–47, Pb 2.8–1510, Ni 7.0–138, Co 1.1–77.1, As 4.2–2691, Mn 83.4–11,400, Cr 7.7–46.1, Cd 0.05–23, and Zn 14.1–1394. Spatial distributions maps showed greatly polluted zones and under special concern are the concentrations of As, Co, Cu, Mo, Ni, Pb, Sb, Hg, Cd and Zn, which exceeded the GBL, the world-soil average and the USEPA and Finnish soil guidelines. Arsenic in site S2 and Cu and Pb in site S3 are the key factor that influences the potential ecological risk. Moreover, As in sites S1 and S2, and As, Pb and Cu in site S3 may pose non-carcinogenic effects for adults and children. Total cancer risk values were above the acceptable risk limit due to As, Cr, and Cd in sites S1 and S2, and due to As, Cr, Cd and Pb in site S3. Site S3, the largest abandoned site, represents the main environmental concern because of its high volume of waste and content of PTE. Based on the results, it can be suggested that the abandoned mining waste were dispersed and are the source of soil pollution in Taltal city. It is concluded that the abandoned mining waste sites have led to substantial contamination of the surrounding soils with As, Cu, Pb, Cr and Cd, which exceed ecological and/or human health risk guideline concentrations.

Airborne Lead (Pb) From Abandoned Mine Waste in Northeastern Oklahoma, USA.

Active and abandoned mines pose serious health threats to humans, aquatic, and terrestrial biota. Northeastern Oklahoma, home to a number of Native American Tribes, is part of the well‐known Tri‐State Mining District. More than 100 years of mining production in this area has left numerous, large chat piles in the surrounding environment. Despite numerous studies and efforts on the restoration of metal contamination in this area, no studies have attempted to distinguish the contributions of different sources, particularly from the atmospheric deposition, of metals to the aquatic environment. Here, we analyzed the atmospheric deposition of Pb from Picher, a town surrounded by chat piles, and Tulsa, a primary metropolitan area in northeastern Oklahoma, from 2010 to 2016. We found that chat piles in Picher contain ~20% and 6% of fine particles that are subjective to windborne transport and human inhalation, respectively, and these fine particles contain disproportionally high concentrations of Pb. Despite the absence of industrial and human activities, airborne Pb in Picher is 2–5 times higher than that of Tulsa. A conservative estimate showed that airborne Pb may contribute up to 10% of annual Pb mass flux to a lake 18 km away from the chat piles in Picher and probably a much higher contribution for soil and water located adjacent to Picher. Despite known limitations, our study represents the first attempt to evaluate the significance of Pb‐laden airborne particulate matter from a large‐scale abandoned mining area where the humans are particularly vulnerable to metal exposure.

A new ranking scale for assessing leaching potential pollution from abandoned mining wastes based on the Mexican official leaching test

Potentially toxic elements (PTEs) present in abandoned mining wastes (AMW) are of great concern because of potential risks to human health and ecosystems. Indices of contamination (IC) applied to mining wastes are calculated using the total concentration of PTEs and comparing them with regional geochemical backgrounds. However, determining the total content of heavy metals is insufficient to assess the hazard of mining wastes. Therefore, in addition to total concentration, the potential risk is also evaluated through water mobility of elements. Accordingly, leaching procedures are useful tools for the geochemical characterization of soluble constituents that are mobilized. In this study, the solubility of PTEs from different types of mining wastes is comparatively assessed using three standard leaching methods (European; U.S. Geological Survey and; Mexican). The Hazard Average Quotient (HAQ) was calculated to assess the potential Toxicity Factor (TF). TF is an indicator of the relative potential toxicity of wastes and is the basis for the classification of AMW. A comparative assessment provides evidence that there are no statistically significant differences in PTEs solubility by the three leaching methods and it was also found that the pH of the eluates was dictated by the type of waste. Results suggest that the IC gives an indicator of the potential contamination of soils and sediments by erosive processes, or a long-term measure, whereas TF assesses the possibility of contaminating water in the short term. The most significant finding is the new ranking scale of TF, as a function of HAQ, applied to the Mexican standard leaching test. This factor, together with other considerations relating to risk-generating processes, might then be applied in places having large amounts of recorded AMW, such as the Iberian Peninsula and Latin America, where effective management is required to rank sites, based on preliminary environmental and human risk assessment.

Exposure to uranium and co-occurring metals among pregnant Navajo women

Navajo Nation residents are at risk for exposure to uranium and other co-occurring metals found in abandoned mine waste. The Navajo Birth Cohort Study (NBCS) was initiated in 2010 to address community concerns regarding the impact of chronic environmental exposure to metals on pregnancy and birth outcomes. The objectives of this paper were to 1) evaluate maternal urine concentrations of key metals at enrollment and delivery from a pregnancy cohort; and 2) compare the NBCS to the US general population by comparing representative summary statistical values. Pregnant Navajo women (N = 783, age range 14–45 years) were recruited from hospital facilities on the Navajo Nation during prenatal visits and urine samples were collected by trained staff in pre-screened containers. The U.S. Centers for Disease Control and Prevention (CDC), National Center for Environmental Health's (NCEH) Division of Laboratory Sciences (DLS) analyzed urine samples for metals. Creatinine-corrected urine concentrations of cadmium decreased between enrollment (1st or 2nd trimester) and delivery (3rd trimester) while urine uranium concentrations were not observed to change. Median and 95th percentile values of maternal NBCS urine concentrations of uranium, manganese, cadmium, and lead exceeded respective percentiles for National Health and Nutrition Evaluation Survey (NHANES) percentiles for women (ages 14–45 either pregnant or not pregnant.) Median NBCS maternal urine uranium concentrations were 2.67 (enrollment) and 2.8 (delivery) times greater than the NHANES median concentration, indicating that pregnant Navajo women are exposed to metal mixtures and have higher uranium exposure compared to NHANES data for women. This demonstrates support for community concerns about uranium exposure and suggests a need for additional analyses to evaluate the impact of maternal metal mixtures exposure on birth outcomes.

Geochemical anomalies for the determination of surface stream sediments pollution: case of Sierra de Cartagena-La Unión mining district, Spain.

This work explores the ability of the Spanish Geochemical Database to identify the existence of polluted stream sediments due to the presence of abandoned mine wastes. The mining district of Sierra de Cartagena-La Unión has been used as test area. A total of 18 abandoned tailings facilities were selected and samples were taken for analysis of the content in potential toxic elements. The results were contrasted with geochemical background values in order to identify which geochemical elements could entail anomalies potentially reflected in the Spanish Geochemical Database. For the study area, As, Cd, Pb, and Zn have been identified as potential toxic elements which can be used as geochemical indicators of sediment pollution processes originated in abandoned mine wastes. Furthermore, the correlation between Cd and Zn allows them to be considered as the best indicators of potential sediment contamination. The study of anomaly thresholds, through the analysis of accumulated frequencies of the contents of these elements in the sediments of the Spanish Geochemical Database, allows identifying sediments that may have been contaminated. A Mann-Whitney test contrasting the data of tailings, polluted sediments, and non-polluted sediments has been performed in order to verify differences among these types of samples. In addition, a geospatial analysis has demonstrated a very close relationship between contaminated sediments and the presence of mining wastes upstream. This methodology can be applied to any other mining region, to recognize the possible influence of pollution processes derived from the presence of abandoned mine wastes taking advantage of existing geochemical databases.

Environmental isotopes as tracers of mining activities and natural processes: A case study of San Antonio de los Cobres River Basin, Puna Argentina

High concentrations of arsenic (As) in water have been detected in the San Antonio de los Cobres (SAC) River. Historically, the upper basin has been exposed to mining districts spread in the high altitudes of the Puna Argentina, intense evaporation and discharge of hot springs from a near geothermal area (Tuzgle-Tocomar Complex). This work evaluate possible sources of As in surface waters, applying major and minor ions and trace elements, as well as multi-isotope analysis (3H, 2H/H, 13C/12C,18O/16O and 34S/32S). Four main water types were defined: waters with no signs of contribution from mineralized areas or hot springs (P); waters with thermal origin (T); waters with natural sulphide oxidation (M); and acid mine drainage waters (AMD) waters from abandoned mine wastes. δ34S-SO42− used in combination with sulphate concentration, discriminate sulphate derived from sulphides oxidation and those from thermal waters inputs. All sampled surface water result from mixing between two or three end-members (P-M; P-AMD; P-M-T). The proposed mixing models estimate their relative contribution. δ18O-SO42− and δ18O-H2O corroborate the influence on the SAC River of water coming from AMD rather than from natural sulphides oxidation. δ13C-DIC identifies samples with thermal influence. δ18O-H2O and δ2H-H2O deviate from meteoric water, indicating evaporation of 7% to 17%. The distribution of arsenic along the San Antonio River together with the δ18O-SO42− values show that both, natural sulphides oxidation and thermal springs contribute to highly rise concentrations. The current drinking water for the town of SAC is not being affected by the AMD.

Potential mobility assessment of metals in salt marsh sediments from San Antonio Bay

The BCR method was applied on sediments from the salt marsh of San Antonio Bay (SAB). It presents several channels among which the Encerrado is the most important and is impacted by abandoned mining wastes. The pseudototal concentrations of metals measured within this channel were relatively higher than in outer sites, and according to the Igeo index, its contamination level was low. The metal distribution in the different phases of sediment particles showed that the residual component, considered the safest from the environmental point of view, accounted for most of the Fe, Cd, Cu, and Zn contents. Conversely, Pb was mainly in the non-residual component as part of the reducible fraction, thus constituting the main environmental hazard among the studied elements. The predominance of residual and reducible fractions indicated a historic contamination of metal such as Pb, Cu, and Zn from the mining wastes. The low exchangeable and oxidizable fractions would indicate no actual input of metals.