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.     

Coral-stromatolite reef framework, Upper Miocene, Almería, Spain

Stromatolitic crusts on stick-like and platy Porites corals forming Messinian reefs in Almería played an important role in supporting and binding the brittle corals. The crusts were previously regarded as probable marine cements. However, their clotted, peloidal, and micritic fabrics are directly comparable with those of stromatolites. They accreted allochthonous grains even on vertical faces, and include bushy fabrics closely comparable with those produced by cyanobacterial calcification. They contain numerous fenestrae, exhibit rapid fabric variation, and locally form micro-columns and laminated domes. Their similarities to peloid micrite crusts in Recent reefs suggest that at least some of these Recent crusts are microbial in origin, even though they have widely been interpreted as marine cements. The sedimentary effects of crust development substantially affected both the morphology and relief of the reefs and the generation of reefal clasts. Binding of the reef-frame in the Pinnacle and Thicket zones in the lower and middle parts of the reef created a rigid margin which shed large (commonly up to 5 m) cuboidal blocks of coral-stromatolite frame. The blocks broke along planes of weakness provided by the vertical Porites sticks and were deposited on the Fore-Reef Slope. In the uppermost parts of the reefs crusts dominate the structure, constituting 80% or more of the rock. Veneers up to 15 cm thick encrust thin irregular Porites plates to create a solid Reef Crest Zone which has not been recognized before. The coral-stromatolite framework is associated with echinoids, crustose corallines and halimedacean algae which, together with the scleractinians, indicate normal marine salinity throughout reef growth.     

Palaeoceanographic controls on reef deposition: the Messinian Cariatiz reef (Sorbas Basin, Almería, SE Spain)

The Cariatiz section lies at the toe of the palaeoslope of the Messinian Cariatiz fringing reef, at the northern margin of the Neogene Sorbas Basin in SE Spain. Distal-slope reef deposits in the upper part of the section can be traced laterally to the reef core of the last episodes of reef progradation. The underlying deposits are alternating diatomitic marl, marl and silty marl that intercalate with sandstone beds. Combined lithological changes, variations in proportions of warm-water planktic foraminifera and δ 18O values suggest that at least seven, probably precessional, cycles are recorded throughout the Cariatiz section. The correlation of seven cycles in the pelagic deposits to seven reef progradation cycles, and associated vertical shifts in reef facies, indicates relative sea-level oscillations of several tens of metres. Biostratigraphic and palaeomagnetic data suggest that both the Cariatiz section and the fringing reef formed during the reverse polarity Chron C3r. Surface-water temperatures seem to be the major factor controlling carbonate production in the reef system. Deposition of bioclastic calcirudite and calcarenite, with no active coral growth, took place at the lowest sea-level within each reef cycle during temperature minima within each precessional cycle. Porites framework and reef-slope deposits with Halimeda gravel, in contrast, formed during temperature rises and thermal maxima within precessional cycles.     

Submarine lobes and feeder channels of redeposited, temperate carbonate and mixed siliciclastic-carbonate platform deposits (Vera Basin, Almería, southern Spain)

Temperate carbonates and mixed siliciclastics-carbonates of Upper Tortonian age were deposited on a narrow platform along the southeastern margin of the Sierra de los Filabres on the western side of the Vera Basin. The temperate carbonates were unlithified or were only weakly lithified on the seafloor and so were easily prone to synsedimentary removal. Part of the shelf sediments were eroded, reworked and redeposited in submarine lobes, up to 40 m thick and 1 km wide. The lobes consist of turbiditic carbonates (calcarenites and calcirudites) and mixed siliciclastics-carbonates, which contain up to 30% siliciclasts, derived from the Sierra de los Filabres to the northwest, and abundant bioclasts of coralline algae, bivalves and bryozoans. In the inner platform, the feeder channels of the lobes cross-cut beach and shoal deposits, and are filled by strings of debris flow conglomerates (up to 3 m thick and a few metres wide). These channels presumably developed as the continuation of river courses entering the sea. Further towards the outer platform, they pass into large channels (up to several hundred metres wide and 20 m deep) steeply cutting into the horizontally bedded strata of the platform. Significant quantities of platform sediment were removed by erosion during their excavation. Once abandoned, they were filled by new platform sediments. Further towards the basin, the channels associated with the lobes exhibit lateral accretion and internal cut-and-fill structures, and are intercalated between hemipelagic deposits. The channel-filling sediments are in this latter case coarse-grained carbonates and mixed siliciclastics-carbonates. Lobe development concentrated first at Cortijo Grande on the western side of the study area, and then to the east at Mojácar. This migration may relate to the uplift of the Sierra Cabrera, a major high occurring immediately to the south of the channel and lobe outcrops.     

Microstructure and fabric transitions in calcite tectonites from the Sierra Alhamilla (Spain)

A suite of marble specimens from the Sierra Alhamilla (Spain), deformed to large strains under natural conditions at about 300° C shows distinct variations in microstructure and fabrics. It can be demonstrated that the development of crystallographic preferred orientations and grain shape fabrics are strongly dependent on recrystallized grain size. This is interpreted to reflect the relative importance of various deformational mechanisms. Superplasticity seems to have a sharp upper grain size limit at 10–15 /smm. Within the power law creep regime, deformation in fine grained aggregates is probably dominated by diffusional, in coarser ones by dislocation mechanisms. The transition is a gradual one, and may span a grain size range of 30 /sm.     

Evaluation of heavy metal bio-availability from Almagrera pyrite-rich tailings dam (Iberian Pyrite Belt,SW Spain) based on a sequential extraction procedure

The beginning of polymetallic sulphide ore exploitation at Almagrera, Iberian Pyrite Belt, SW Spain, has been dated back to pre-Roman times; mining activity lasted until 2001 when it was definitely halted. The Almagrera sulphide tailings dam was built at the Sotiel–Coronada mine, where Cu, Zn and Pb concentrates were obtained by flotation processes, and sulphide (mainly pyrite) wastes formed. The dam was built as a water-reservoir, on a tectonic fault; its hazard is currently documented by the released wastes after a strong storm in the region, then, its stability is not monitored by the owner.     

Geochemistry and petrogenesis of two-Pyroxene andesites from Sierra de Gata (SE Spain)

Summary The Miocene volcanic suite of Sierra de Gata (Betic Cordillera) is composed of dacites, rhyodacites and rhyolites, besides basaltic andesites and andesites. The latter are very fresh and are the least fractionated rock types; thus they have been investigated in order to put some constraints on the genetic interpretation of the volcanic sequence. These rocks are composed of plagioclase, orthopyroxene, clinopyroxene and magnetite both as phenocrysts and in the groundmass. Olivine and ilmenite occur occasionally. The andesites exhibit orogenic chemical features. They are characterized by very low Ni, Co and Cr contents and show negative Eu anomalies, which support fractionation of mafic phases and plagioclase at depth. The petrogenesis of the andesites, however, cannot be related simply to fractionation processes of a single mafic magma since the lack of good interelemental correlations, the scattering of Sr-isotope ratios and the isotope disequilibrium between the phases conflict with such a simple mechanism. A model which can better explain the petrogenesis of the analyzed andesites considers the intervention of different mafic melts, generated in a heterogeneous mantle and characterized by different chemical and isotopic compositions, which fractionated at depth and concomitantly interacted significantly with the continental crust.

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Geochemie und Petrogenese von Pyroxen-Andesiten der Sierra de Gata (SE Spanien)

Zusammenfassung Die miozäne Vulkanitabfolge der Sierra de Gata (Betische Kordillere) wird von Daciten, Rhyodaciten, Rhyoliten sowie basaltischen Andesiten and Andesiten aufgebaut, letztere sind in einem guten Erhaltungszustand and zeigen die geringste Fraktionierung. Sie wurden daher genauer untersucht, um Aussagen über die Genese dieser Vulkanite machen zu können.Phenokrysten und Grundmasse bestehen aus Plagioklas, Orthopyroxen, Klinopyroxen und Magnetit. Manchmal kommen Olivin und Ilmenit hinzu. Die Geochemie der Andesite folgt typisch orogenen Trends. Sie sind durch sehr niedrige Ni-, Co- und Cr-Gehalte und negative Eu-Anomalien charakterisiert; dies belegt eine Fraktionierung der mafischen Gemengteile und des Plagioklases in der Tiefe. Die petrogenetische Entwicklung der Andesite kann allerdings nicht einfach mit Fraktionierungsprozessen eines einzigen mafischen Magmas erklärt werden. Das Fehlen von Element-Korrelationen, das starke Streuen der Sr-Isotopenverhältnisse und das Isotopenungleichgewicht zwischen den einzelnen Mineralphasen stehen in Widerspruch zu einem derartigen einfachen Modell. Ein Modell, das die Petrogenese der untersuchten Andesite besser erklärt, zieht die Beteiligung verschiedener mafischen Schmelzen-sie bildeten sich in einem heterogenen Mantel und sind durch Unterschiede im Chemismus und ihrer Isotopenzusammensetzung charakterisiert—in Betracht. Dabei kam es zu Fraktionierung dieser Magmen in der Tiefe und zu beträchtlichen Reaktionen mit kontinentalem Krustenmaterial.

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With 5 Figures     

Progressive extensional shear structures in a detachment contact in the Western Sierra Nevada (Betic Cordilleras,Spain)

Abstract

The present contact caused by the superposition of the Alpujarride complex over that of the Nevado-Filabride in the western area of Sierra Nevada and Sierra de Filábres corresponds to a detachment. The deformation in the footwall associated with this contact, produced mylonitic fabrics with a significant stretching-lineation, over which brittle structures are superimposed. The deformation in the hanging wall associated with this contact is, on the other hand, essentially brittle. These deformations are subsequent to a series of syn-to post-metamorphic structures related to thrust phases.

The micro- and meso-structures indicate that the hanging wall has moved towards the west-south-west.

Other brittle structures, which began during the same extensional regime, are superimposed on the detachment and have continued to develop up to the present time. These structures were produced in an extensional regime with a non-coaxial deformation component and suggest the possibility of a tectonic evolution similar to that described for core complexes in the USA.     

Glaucony from the Cretaceous of the Sierra de Guadarrama (Central Spain) and its application in a sequence-stratigraphic context

Detailed sedimentological and geochemical analyses of Upper Cretaceous glaucony-bearing deposits from the middle portion of the Castro de Fuentidueña Formation, in Central Spain, enable identification of a multiphase history of glaucony accumulation. Despite its relatively high maturity (K₂O > 7%), glaucony from the transgressive subtidal sandstones has anomalously low concentration in the host rock (generally <10%), suggesting remobilization from a different source. The remarkable thickness of the glaucony-bearing horizons, concurrently with concentration of glaucony in laminae, small size, and high degree of roundness and sorting provide further evidence for an allochthonous origin of the green grains. In contrast, authigenic glaucony from the overlying offshore clays exhibits higher abundance (up to 45%) and lower maturity (K₂O < 7%) and is interpreted to have formed in situ. Allochthonous glaucony originally developed in more distal areas during a prolonged period of sediment starvation. The green grains were then swept away from their place of origin and concentrated into tidal bars and channels within the upper transgressive systems tract of the third-order depositional sequence. Maximum concentration of autochthonous glaucony is recorded at the transition from tidal-influenced to offshore deposits: this glaucony, which is relatively less evolved due to lower time available for maturation, is interpreted to reflect the turnaround from transgressive to highstand conditions, marking the condensed section of the depositional sequence. As postulated by previous sequence-stratigraphic models, this study documents that allochthonous glaucony can be widespread throughout the transgressive systems tract (TST), while the condensed section (CS) typically hosts autochthonous glaucony. Contrary to the existing literature, however, this study shows that glaucony from the TST may be even more mature than glaucony from the CS, if enough time for maturation during transgression is allowed before the ultimate concentration of the green grains. Identification of spatial and temporal characteristics of glaucony, thus, is critical to a reliable sequence-stratigraphic interpretation of the glaucony-bearing deposits.     

Hydrogeochemical effects of groundwater mining of the Sierra de Crevillente Aquifer (Alicante,Spain)

The groundwater mining of the Crevillente aquifer (southeastern Spain) has resulted in the progressive deterioration of water quality, with particularly significant increases in chloride, sulfate, and sodium. The possibility of a vertical hydrochemical zoning is deduced that would require examining the importance of the geometry and lithology (evaporitic materials) in the salinization process. The time of water-rock contact (residence time) and dilution by infiltration of rainwater also influences the hydrogeochemistry of the aquifer. The hydrochemical data are useful in defining the conceptual model of the aquifer, completely karstified with relative homogeneity.Project AMB92-0211 (CICYT)     

Shallow landslides in deeply weathered slates of the Sierra de Collcerola (Catalonian Coastal Range, Spain)

Stability conditions in an area located NW of Barcelona (Spain) are discussed. Here, several mass movements were observed, mainly affecting weathered Paleozoic slates. Many of these failures involved slopes cut along recent infrastructures: debris flows, wedge and plane failures, generally surficial, occurred more frequently. After a detailed geological and geomorphologic survey, geomechanic characterization was carried out, according to RMR and SMR classifications. This rating gave a prediction of slope behaviour, in fairly good agreement with the real observed one.

Stability numerical analysis was carried out for the main cut slopes, based upon the Limit Equilibrium Method. First of all, the deterministic factor of safety was computed using the mean values of parameters. After that, a simulation technique based upon the Monte Carlo Method was applied in order to obtain factor of safety distributions. The probability of failure was estimated as P(F<1).

Finally, results from deterministic and probabilistic approaches were compared. The effectiveness of different possible remedial measures was highlighted by means of a sensitivity analysis, which showed that the more important parameters in the study area are the geometrical ones (height, slope and failure plane angles). The final technical solutions adopted are briefly outlined.     

Geological and environmental implications in the reclamation of limestone quarries in Sierra de Callosa (Alicante,Spain)

Sierra de Callosa have an area of 8 km² and a maximum altitude of 566 masl. Geologically, it is found to be primarily comprised of carbonated rocks. Mine spoils coming from limestone quarries extraction are often used in the working reclamation process. These materials could be actually employed profitably once conveniently amended with organic matter. A study on the temporary evolution of nutrients and several physical–chemical parameters in a mineral waste amended with municipal solid waste (MSW) compost has been carried out. The effect of incorporating such waste to mine spoils in an arid gravel quarry has been studied, quantifying the temporal evolution of nutrients and several physical–chemical parameters in the mixture. Three plots have been prepared with mine spoils proceeding from a limestone quarry located in the south of the province of Alicante (municipality of Redován). These plots have been amended with 3 kg/m² of MSW compost. Texture, pH, electrical conductivity, oxidizable organic matter, N-Kjeldahl, available P, Na, K, Ca, Mg, Fe, Mn, Cu and Zn were analysed. The results reflected the contribution of nutrients to the substrate after the MSW addition. The variability of the information indicated the heterogeneity of the MSW composition, as well as the difficulty of obtaining a homogeneous MSW mixture–mineral waste.     

Centuries of artificial recharge on the southern edge of the Sierra Nevada (Granada,Spain)

In the Alpujarra (southern Spain), every year between the March and June, an ancestral practice continues in the form of diverting water from the rivers by way of an extensive network of irrigation channels (acequias) to well-defined, highly permeable areas. This practice, known ascareos, constitutes an ancient example of artificial recharge. The objective is to guarantee a supply of drinking water during the dry months, as well as improve the physicochemical characteristics of the water. In addition, this system helps maintain moisture in the immediate environment, and thus has a positive effect on local vegetation.     

Isotope geochemistry of waters affected by mining activities in Sierra Minera and Portman Bay (SE,Spain)

The objective of this work was to evaluate processes affecting waters from Portman Bay by way of stable isotopic analysis, particularly H and O stable isotopes from water and S and O from dissolved sulfates. In addition, surface waters from Sierra Minera were examined for the purpose of determining if these waters are affected by similar processes. The results obtained indicate that Portman Bay waters are meteoric, and marine infiltration only takes place in the deepest layers near the shore or if water remains stagnated in sediments with low permeability. The main source of sulfate was the oxidation of sulfides, resulting in the liberation of acid, sulfate and metals. In order to assess the mechanism responsible for sulfide oxidation, the stoichiometric isotope balance model and the general isotope balance model were tested, suggesting that the oxidation via Fe³⁺ was predominant in the surface, and controlled by Acidithiobacillus ferrooxidans, while at depth, sulfate reduction occurred.     

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.     

Neogene exhumation and relief evolution in the eastern Betics (SE Spain): Insights from the Sierra de Gador

The Betics are a key area to study an orogenic landscape disrupted by late‐orogenic extension. New low‐temperature thermochronology (LTT) data (AHe and AFT) coupled with geomorphic constraints in the Sierra de Gador (Alpujarride complex) are used to reconstruct the cooling history and evolution of relief during the Neogene. We document three stages: (1) a fast cooling event between 23 and 16 Ma associated with the well‐known extensive tectonic exhumation of the Alpujarride unit, (2) a period of slow cooling between 16 and 7.2 Ma related to a planation event and (3) a post‐7.2 Ma surface uplift associated with the inversion of the Alboran domain undetected by LTT. The planation event followed by this late uplift can explain the occurrence of inherited low‐relief surfaces overlain by Tortonian–Messinian platform deposits at the top of the range. Finally, we propose that the Sierra de Gador is a more transient landscape than the nearby Sierra Nevada.     

Weathering profiles in granites, Sierra Norte (Córdoba, Argentina)

Two weathering profiles evolved on peneplain-related granites in Sierra Norte, Córdoba province, were examined. Several weathering levels, of no more than 2 m thickness, were studied in these profiles. They had developed from similar parent rock, which had been exposed to hydrothermal processes of varying intensity. Fracturing is the most notable feature produced by weathering; iron oxides and silica subsequently filled these fractures, conferring a breccia-like character to the rock. The clay minerals are predominantly illitic, reflecting the mineral composition of the protolith. Smaller amounts of interstratified I/S RO type are also present, as well as scarce caolinite+chlorite that originated from the weathering of feldspar and biotite, respectively. The geochemical parameters define the weathering as incipient, in contrast to the geomorphological characteristics of Sierra Norte, which point to a long weathering history. This apparent incompatibility could be due to the probable erosion of the more weathered levels of the ancient peneplains, of which only a few relicts remain. Similar processes have been described at different sites in the Sierras Pampeanas. Reconstruction and dating of the paleosurfaces will make it possible to set time boundaries on the weathering processes studied and adjust the paleographic and paleoclimatic interpretations of this great South American region.     

Plagioclase porphyroblast growth and its relation to deformation in the Alhamilla unit (Sierra Alhamilla, Betic Cordilleras, SE Spain)

Abstract. Plagioclase porphyroblasts from silvergrey schists belonging to the Nevado Filabride Complex in the Sierra Alhamilla (Betic Zone, SE Spain) are interpreted as having been formed preand synkinematically with respect to the second phase of deformation. Different types of inclusion patterns represent 'snap-shots'(high growth-rate/strain-rate ratio features) of the formation of a diffentiated crenulation cleavage during this second phase of deformation, by the processes of kinking, crenulation and associated differentiation.
Regional considerations indicate an Alpine age for this tectono-metamorphic event, which can be explained by the'hot emplacement'of the higher Nevado Filabride units. The observed structural evolution is not consistent with a pre-Alpine polyphase deformation history.     

Strain patterns of pluton emplacement in a crust undergoing non-coaxial deformation,Sierra Morena,Southern Spain

This paper investigates the problem of interference between regional and local strain fields, the latter corresponding to a pluton ballooning. Natural examples from the Sierra Morena (Southern Spain) are described. Two distinct patterns have been recognised, according to whether transcurrent motions or thrusting motions predominate in the regional deformation. The map of foliation trajectories shows typical features such as triple points and geometric continuity between pluton internal fabric and country rock cleavage even when these are oblique to the contact.A simple mathematical model of interference between ballooning and simple shear is presented. In this model, the ballooning may be circular or elliptical. The model is used to predict the position of triple points, patterns of principal trajectories and variations of finite strain. A comparison is made with plutons from the Sierra Morena.     

Local people unprotected by protected (depopulated) natural areas: the case of Sierra Norte Guadalajara,Spain

The aim of this study is to place the current geographical debate on nature in the context of protected natural areas severely affected by depopulation processes, in which the daily lives of the inhabitants have been altered by changes in the traditional balance between human and non-human populations. A significantly humanized area within the Sierra Norte de Guadalajara National Park in central Spain is considered as an example. The qualitative methodology followed is based on documentary analysis and interviews with key inhabitants in the area, revealing narratives with a productive or consumer view of the nature. The national park appears as a container of a cultural nature, initially created by the traditional inhabitants, which generates an artificial, excessive nature and accelerates regressive sociodemographic dynamics.