Sludge weathering and mobility of contaminants in soil affected by the Aznalcollar tailing dam spill (SW Spain)

As a result of the collapse of the Aznalcollar mine tailings dam, a large extension of the Guadiamar valley in SW Spain was covered with a layer of pyrite sludge. Although most of the sludge was removed, a small amount remains in the soil, constituting a potential source of water pollution. A column experiment was carried out in order to determine the rate of sludge oxidation in the soil, and the existence of metal retention processes. The column was filled with a mixture of sludge and a sandy soil common in the region. At different time intervals, the column was leached with water and the resulting solution analysed.

The pH of the water dropped to values around 2 after 260 days and then remained constant due to the buffering role of silicate dissolution. The concentration of Zn, Cd and Co in the leachates matched the expected values from flow-through experiments at atmospheric oxygen pressure. This indicates that oxygen diffusion in the pores was complete. Moreover, no efficient processes existed for retaining Zn, Cd and Co, which formed soluble salts and were entirely incorporated into the infiltrating water. During the first 2 months of the experiment, when pH was higher than 4.5, the concentrations of Fe and Al were very low. Saturation indices showed that the solution was in equilibrium with amorphous Fe(OH)₃ and Al(OH)₃. Subsequently, at lower pH values, jarosite [(Na,K)Fe₃(SO₄)₂(OH)₆] formed. This solid phase was identified by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Jarosite was also responsible for the depletion of As, Pb, Sb and probably Tl in the water resulting from infiltration.     

Iron isotopes in acid mine waters and iron-rich solids from the Tinto–Odiel Basin (Iberian Pyrite Belt, Southwest Spain)

The isotopic composition of Fe was determined in water, Fe-oxides and sulfides from the Tinto and Odiel Basins (South West Spain). As a consequence of sulfide oxidation in mine tailings both rivers are acidic (1.45 < pH < 3.85) and display high concentrations of dissolved Fe (up to 420 mmol l^− 1) and sulphates (up to 1190 mmol l^− 1).The δ⁵⁶Fe of pyrite-rich samples from the Rio Tinto and from the Tharsis mine ranged from − 0.56 ± 0.08‰ to + 0.25 ± 0.1‰. δ⁵⁶Fe values for Fe-oxides precipitates that currently form in the riverbed varied from − 1.98 ± 0.10‰ to 1.57 ± 0.08‰. Comparatively narrower ranges of values (− 0.18 ± 0.08‰ and + 0.21 ± 0.14‰) were observed in their fossil analogues from the Pliocene–Pleistocene and in samples from the Gossan (the oxidized layer that formed through exposure to oxygen of the massive sulfide deposits) (− 0.36 ± 0.12‰ to 0.82 ± 0.07‰). In water, δ⁵⁶Fe values ranged from − 1.76 ± 0.10‰ to + 0.43 ± 0.05‰.At the source of the Tinto River, fractionation between aqueous Fe(III) and pyrite from the tailings was less than would be expected from a simple pyrite oxidation process. Similarly, the isotopic composition of Gossan oxides and that of pyrite was different from what would be expected from pyrite oxidation. In rivers, the precipitation of Fe-oxides (mainly jarosite and schwertmannite and lesser amounts of goethite) from water containing mainly (more than 99%) Fe(III) with concentrations up to 372 mmol l^− 1 causes variable fractionation between the solid and the aqueous phase (− 0.98‰ < Δ⁵⁶Fe_{solid–water} < 2.25‰). The significant magnitude of the positive fractionation factor observed in several Fe(III) dominated water may be related to the precipitation of Fe(III) sulphates containing phases.     

The Salamón gold deposit (León, Spain)

Located 55 km NE of the provincial capital León, Salamón deposit, discovered in 1985, is located on the southern slope of the Cantabrian Mountains, in the north of the Iberian Peninsula. The deposit is located on the León fault, which is a late-Variscan, E–W trending, deep structure extending for more than 100 km. The León fault has a complex history, and many mines and occurrences are located near it. The deposit is also close to small stocks and dykes of igneous rocks with intermediate to basic composition to which the mineralisation is related. The mineralisation is hosted mainly by the limestones and bituminous shales of the Lena Group (Namurian–Westphalian). There is also some mineralisation in other stratigraphic units of the Upper Carboniferous, such as the Maraña Group or the Stephanian B sediments.Apart from local and regional exploration, a detailed mineralogical and metallogenic research has been carried out. The epithermal mineralisation of Salamón was developed in two phases: an early dominant and extensive stage, with very fine crystalline gold-bearing sulphides, mainly pyrite, arsenic-bearing pyrite and arsenopyrite, in a matrix of quartz–chalcedony (jasperoid) and dolomite, and a later stage, of a larger crystal size, which occurs replacing the early stage or in pockets and veins, with greater mineralogical variety. Last of all there is a stage of supergene mineralisation, a product of the oxidant action of meteoric waters over the previous minerals. The hydrothermal alterations of the host rocks related to the orebodies are fundamentally decarbonatisation–dolomitisation, silicification and argillitisation. The early stages of mineralisation were produced in a temperature of 148–241°C, while that in the later stages occurred at 86–123°C. The early stage has been dated as 269±5 Ma, and this agrees with the ages of the other deposits of the district, which lay between 292 and 263 Ma, and the igneous rocks of the Peña Prieta stock (277±1 Ma), all which are of Permian age.The results of the studies carried out until now lead to the conclusion that Salamón is a Carlin-type gold deposit.     

Collapse dolines in miocene gypsum: an example from SW Sivas (Turkey)

 This study investigated the formation mechanism of dolines. Dolines are caused by dissolution of gypsum in the study area, 50–220 m in diameter. Two systems were applied to determine the support necessary for natural underground opening of given span in a given rock mass. From the characteristics of the rock mass, a 5 m-wide unsupported span in the gypsum can be expected to stand up for over 9 years. The designed span of an artificial opening would normally be considerably less than the span of a collapsed natural opening in the same rock. Dolines in the study area play an important role in the groundwater flow system. Received: 10 November 1995 · Accepted: 4 January 1996     

Use of mine spoils from Teruel coal mining district (NE,Spain)

Coal mine restoration projects increase public perception of mining companies. Spain has relatively few examples of completed opencast mine rehabilitation projects. This study seeks to obtain the use of mine spoils from coal mines in Teruel. The studied mine spoils may be used as raw material for the Spanish ceramic industry, located in the provinces of Castellon, Valencia and Teruel. This study specifically discusses the mineralogical and geochemical characteristics of the Lower Cretaceous materials from coal deposits in Estercuel basin, around Teruel and Castellon in Spain. These provinces have a large ceramic industry. A characterization of mine spoils from coal deposits has been carried out. This characterization is based on the data of both mineral and chemical analysis. The mineralogical characterization was complemented with SEM/EDAX. The study of the chemical composition allows the evaluation of the applicability of the studied mine spoils to the following industries: refractory, fine clay, red clay for pavement and coating, and heavy clay. The clay used for refractory industry has the highest compositional demand. The positive results obtained on this set of preliminary tests lead us to envisage new research programs, focusing on testing these mine spoils on a semi-industrial scale.     

Mercury mobility in mine waste from Hg-mining areas in Almería,Andalusia (Se Spain)

Mining wastes and calcines from two abandoned mining areas (Valle del Azogue and Bayarque in Almería) have been characterized. In the mining wastes, the dominant mercury phases are cinnabar and elemental mercury in the matrix. In the calcines, however, the dominant mercury phase is elemental mercury bounded to the matrix. Water-leaching experiments were conducted on low-grade stockpiles and calcines in order to simulate the mobilization of mercury by runoff under environmental conditions. The laboratory column-leaching experiments show a possible mobilization of mercury from Hg⁰ dissolution, colloid transport and a possible dissolution of calomel and other soluble phases in the mine wastes from the Valle del Azogue and Bayarque mines. Equilibrium speciation modeling of Hg, conducted using the numerical code MINTEQ, showed that the theoretical dominant mercury species in the calcine and mining wastes samples are Hg(OH)₂, HgCl₂, HgClOH and Hg⁰. In some leachates obtained from the Valle del Azogue mining wastes (sample A06), the high Hg concentrations may indicate the possible dissolution of mineral phases such as calomel and other soluble phases, which are subsaturated. The environmental results indicate a great environmental mobility of mercury, especially during wet episodes associated with intense precipitation events, when there are significative amounts of secondary soluble minerals.     

Origin and metamorphic evolution of rocks with braunite and pyrophanite from the Iberian Massif (SW Spain)

Summary ?Rocks containing braunite from the Ossa-Morena central belt (Iberian Massif, SW Spain) have been studied; these include nodules and layers of braunite (association I), Mn-slates (association II) and Mn-metatuffs (associations III and IV). Geochemical features of braunite nodules such as Mn/Fe ratios around 2, positive Ce-anomalies and good correlations among Mn, Fe, Co, Cu and REE contents indicate that the protolith of the braunite-nodules was precipitated from oxidising sea water. Greenschist facies Hercynian metamorphism reduced initial Mn⁴⁺ to Mn³⁺ and Mn²⁺. High initial fO₂ of oxide beds (association I) limited reduction to the formation of braunite. Reduction continued until the formation of garnet + piemontite (associations II and III), and pyroxmangite + pyrophanite (association IV). Ti-rich braunites (up to 6.8% of TiO₂) occur in slates and metatuffs in which the (Mn + Fe)/Ti ratio of the whole rock is lower than 30, while braunites have lower Ti contents in slates and metatuffs with (Mn + Fe)/Ti ratios around 90. Fe-rich braunite crystallized in rocks with Mn²⁺ oxide and silicate where low Mn³⁺/Mn²⁺ in the whole rock facilitated substitution of Fe³⁺ for Mn³⁺. Received January 30, 2002; revised version accepted May 7, 2002 Published online November 22, 2002     

Metal extractability in acidic and neutral mine tailings from the Cartagena-La Unión Mining District (SE Spain)

Mine tailings are ubiquitous in the landscapes of mined areas. Metal solubilities were compared in two chemically distinct mine tailings from the old Mining District of Cartagena-La Unión (SE Spain). One of the tailings was acidic (pH 3.0) with 5400 mg/kg Zn, 1900 mg/kg As and 7000 mg/kg Pb. The other was neutral (pH 7.4) with 9100 mg/kg Zn, 5200 mg/kg Pb and 350 mg/kg As. In samples from the acidic tailings, more than 15% of the Zn and 55% of the Cd were extractable with 0.1 M NaNO₃, and distilled water. In the neutral tailings, using the same reagents, less than 1% of the metals were extractable. A sequential extraction procedure revealed that the sum of the residual and the Fe oxide fractions of Cu, Zn and Pb comprised 80–95% in the acidic tailings and 70–90% in the neutral tailings. The acidic mine tailings had a higher metal solubility, resulting in more metal leaching in the short-term, but also a higher fraction of inert metal. In contrast, in the neutral tailings, the metals were evenly distributed between, oxides and the residual fraction. This implies lower metal mobility in the short-term, but that metal mobility may increase in the long-term. When applied to mine tailings, sequential extractions may provide misleading results because the strong cation exchange capacity of some extractants may induce pH changes and thereby significantly change metal solubility.     

Pollution characteristics of polycyclic aromatic hydrocarbons （PAHs） in oily sludge from the Zhongyuan Oilfield and its peripheral soils

The purpose of this study is to determine the degree of contamination caused by polycyclic aromatic hydrocarbons (PAHs) in oily sludge and soils around it in the Zhongyuan Oilfield. The contents of polycyclic aromatic hydrocarbons in oily sludge samples were determined with HPLC. The contents of PAHs of oily sludge from three different oil production plants vary from high to low in the order of the Wenming oily sludge dumping site of No. 3 Oil Production Plant (3W)>the Mazhai oily sludge dumping site of No. 3 Oil Production Plant (3M)>the Wen’er oily sludge dumping site of No. 4 Oil Production Plant (4W). Naphthalene, acenaphthylene, acenaphthene, fluorine and phenanthrene are the major pollutants of PAHs in oily sludge. The contents of PAHs in soil samples around the oily sludge dumping sites vary widely from 434.49 to 2408.8 ng/g. Naphthalene, acenaphthene, fluorine, phenanthrene and pyrene are the characteristic factors of PAHs in soil samples of 3M and 3W, and naphthalene, acenaphthene, fluorine and phenanthrene are the characteristic factors of PAHs in soil samples of 4W. According to these data and the ratios of Fl/Py, PAHs in oily sludge samples come mainly from petrogenic sources, and soil samples are divided into petrogenic soil samples and mixed-source soil samples, and both petrogenic and pyrogenic soil samples in terms of the sources of PAHs. The classification by Nemero index P indicates that soils around the oily sludge dumping sites have been seriously polluted.     

Interaction of acid mine drainage with waters and sediments at the Corona stream, Lousal mine (Iberian Pyrite Belt, Southern Portugal)

This study investigates the geochemical characteristics of the acid mine drainage discharged from the abandoned mine adits and tailing piles in the vicinity of the Lousal mine and evaluates the extent of pollution on water and on the stream sediments of the Corona stream. Atmospheric precipitation interacting with sulphide minerals in exposed tailings produces runoff water with pH values as low as 1.9–2.9 and high concentrations of (9,249–20,700 mg l⁻¹), Fe (959–4,830 mg l⁻¹) and Al (136–624 mg l⁻¹). The acidic effluents and mixed stream water carry elevated Cu, Pb, Zn, Cd and As concentrations that exceed the water quality standards. However, the severity of contamination generally decreases 4 km downstream of the source due to mixing with fresh waters, which causes the dilution of dissolved toxic metals and neutralization of acidity. Some natural attenuation of the contaminants also occurs due to the general reduced solubility of most trace metals, which may be removed from solution, by either co-precipitation or adsorption to the iron and aluminium precipitates.     

3D gravity modeling of the Triassic salt diapirs of the Cubeta Alavesa (northern Spain)

Up to now subsurface information permitted the delineation of the top of the Triassic salt, all throughout the Cantabro–Navarro domain, although little was known on the location and geometry of its base and thus on the estimation of the total salt thickness. A 3D-gravity inversion scheme combined with a 3D analytic method has been conducted to map out the geometry of the main salt structures of the basin. The gravity modeling results have been constrained by well log information and available geological and reflection seismic data. The combined 3D scheme integrated with available geological and geophysical data has allowed us to obtain the geometry of the main diapirs that characterize the central and marginal regions of the basin.From our interpretation, the Salinas de Añana diapir has almost vertical flanks and can be divided into two different parts, one of them forming a lateral overhang of the main body.The Salinas de Oro diapir has near vertical flanks and a main axis in the N–S direction. Also, the anomaly is rather more extensive than the outcrop of the diapir, which implies an important expansion of non-outcropping salt in this area. Like the Hoz-Sobrón diapir, the Salinas de Ollo diapir is long and narrow. stretching in the NW–SE direction, which includes three important highs, plus an intense zone of salt migration.The Estella and Alloz diapirs crop out individually in spite of being connected at depth. Also two non-outcropping salt domes have been detected to the south of Atauri that, like the Estella diapir, are related to the thrust front. We point out the gravity signature of the Murguia diapir, which shows an intense gravity high probably due to the presence of high-density rocks in the cap rock or more probably due to the existence of Triassic volcanites of ophitic texture pinched-off into the diapir.     

Structural and physiographic control on the Holocene marine sedimentation in the bay of Cadiz (SW Spain)

The Quaternary tectonic activity in the Gulf of Cadiz has considerably influenced the depositional regime and distribution of Holocene marine deposits. The aim of this work is to determine the nature of the recent sedimentary filling in the Bay of Cadiz sea bottom and adjacent continental shelf and to establish the main controlling factors on the Holocene marine sedimentation.

The sedimentary record indicates siliciclastic sedimentation supplied from the continent, with alternating episodes of high and low sedimentation rates. The recent sedimentary evolution of this marine area was controlled by the Late Quaternary eustatic fluctuations. Bathymetric, geophysical and drilling data have been employed to prepare a detailed isopach map of the non-consolidated recent sedimentary cover. Thickness distribution shows significant variations related to the infilling of former fluvial palaeochannels incised during the Late Pleistocene lowstand, and highly controlled by the structural neotectonic trends of faults and joints: NNW-SSE, NNE-SSW and ENE-WSW. The general distribution of isopachs in this area is clearly influenced by these morphostructural lines, which controlled the sedimentary processes during the Holocene. These results are coherent with the main regional neotectonic structures previously described in the nearby continental area, and confirm their prolongation towards the marine domain.     

Interaction between sedimentary processes,historical pollution and microfauna in the Tinto Estuary (SW Spain)

The analysis of a short core collected in the Tinto Estuary (SW Spain) permits to delimitate the influence of historical mining activities on sediments and microfauna (Foraminifera and Ostracoda). In very shallow palaeochannels of the middle estuary, a first mining period (~3,600 cal years BP) caused high sediment pollution by Cu, with a significant diminution of the palaeontological record due to continuous acid mining drainage processes. In this core, the polluted levels derived from both Roman extractions (2,000–1,900 years BP) and the extensive mining activities between 1870 and 1935 have been eroded. The 1,800–200 years BP period is characterized by a limited mining activity and an important improvement of this ecosystem. In addition, the effects of recent industrial wastes have been limited in this area.     

Mercury mobilization by oxidative dissolution of cinnabar (α-HgS) and metacinnabar (β-HgS)

Cinnabar (α-HgS) and metacinnabar (β-HgS) dissolved at environmentally significant rates in oxygenated slurry experiments simulating a low-flow fluvial system. Based on SO₄²⁻ production, cinnabar dissolution rates were 2.64 to 6.16 μmol (SO₄²⁻) m^− 2 day^− 1, and metacinnabar dissolution rates were 1.20 to 1.90 μmol (SO₄²⁻) m^− 2 day^− 1. Monodentate-bound thiosulfate (S₂O₃²⁻) was identified as an oxidation product on the HgS surface by ATR-IR spectroscopy based on strong infrared absorption bands in the 1140–1145 cm^− 1 and 1006–1014 cm^− 1 regions. The presence of sulfide oxidation intermediates on the HgS surface indicates that SO₄²⁻ concentration underestimates α-HgS and β-HgS dissolution in this setting. Mercury release rates during dissolution were more than two orders of magnitude less than SO₄²⁻ production, but were significant: 0.47 mg (Hg) m^− 2 y^− 1 from cinnabar [6.45 nmol (Hg) m^− 2 day^− 1], and 0.17 mg (Hg) m^− 2 y^− 1 from metacinnabar [2.29 nmol (Hg) m^− 2 day^− 1]. The Hg mobilized during α-HgS and β-HgS dissolution is sufficient to form natural Au–Hg amalgam in downstream placer settings. The proportion of mercury that is not remobilized during α-HgS and β-HgS dissolution likely adsorbs to the dissolving mercuric sulfide. Adsorption of Hg²⁺ to cinnabar was detected in situ by anodic stripping voltammetry using a cinnabar-modified carbon paste electrode following accumulation of Hg²⁺ on the electrode at open circuit potential.     

Mitigation of adverse effects at the Lezama-Leguizamon abandoned open-pit mine (Bilbao, northern Spain)

Solid fills arranged in 1-m-thick layers were prepared with stone blocks and pebbles of a drainage bed every 8 m. Runoff gathering in a well and the use of silts and mud lands for bordering and sealing the limestones are the main techniques employed for minimizing unfavorable effects at the Lezama-Leguizamon abandoned open-pit mine. Since there were waste disposal problems in the area, the rate of disposal has made the activity profitable. No significant faults have been detected by control studies, and the objectives are being achieved without problems.     

Paleomagnetism of Carboniferous sediments from the West Sudetes (SW Poland)

The studied Carboniferous flysch and molasse sediments from the Intra-Sudetic Basin correspond to the period from Middle Visean to Early Autunian. Main magnetic minerals carrying the natural remanent magnetization (NRM) are goethite, magnetite, maghemite and hematite, all usually secondarily formed and/or remagnetized due to several tectonometamorphic events. In most samples several NRM components were isolated. One of them is usually a Jurassic-Triassic overprint. Some others define the Westphalian-Early Permian segment of the declination and inclination trajectory for the Sudetes calculated according to the reference apparent polar wander path for the Baltica plate. The Sudetic path is slightly shifted to the east compared to the reference path, suggesting the possibility of independent movements of the Sudetes during this time. The majority of isolated NRM components are secondary and related to the Sudetic orogenic phase and later tectonometamorphic activity.     

An approximation to short-term evolution and sediment transport pathways along the littoral of Cadiz Bay (SW Spain)

This work presents the results of a beach-monitoring program carried out in the Bay of Cadiz (SW Spain), which consists of urban, natural and nourished beaches. In the present study, 24 topographic profiles have been monthly monitored during the 1996–1998 period, in order to draw the morphodynamic behavior of this coast and the general characterization of short-term coastal trends. This way, total volumetric budgets have been calculated for each beach profile in order to group beaches in different erosive/accreting sectors. Studied beaches recorded both erosion and accretion: the greatest accretionary trends have been observed at Aguadulce, La Costilla and Rota beaches, with values ranging from 30 to 70 m³/m. The largest erosion episodes have been recorded in the southernmost end of Valdelagrana spit, with values over 50 m³/m, and in Rota and Vistahermosa, after nourishment works. Main erosion and accretion pathways have been related to the existence of natural and human structures, which blocked the longshore drift suggesting the existence of littoral cells.     

Acid mine drainage and acid rock drainage processes in the environment of Herrerías Mine (Iberian Pyrite Belt, Huelva-Spain) and impact on the Andevalo Dam

The present work describes the process of acid water discharge into the Andévalo Dam (Iberian Pyrite Belt, Huelva-Spain) starting from the interpretation of rainfall data and chemical analyses regarding pH, conductivity, metal and sulphate content in water, from a time series corresponding to the sampling of two confluent channels that discharge water into the referred dam. Statistical data treatment allows us to conclude the existence of acid mine drainage processes in the Chorrito Stream, which are translated into very low pH values and high sulphate and metal concentrations in the water coming from Herrerías Mine. On the other hand, the Higuereta Stream shows, for the same parameters, much lower values that can be interpreted as the channel response to acid rock drainage processes in its drainage basin induced by the rocky outcrops of the Iberian Pyrite Belt.