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Geological, geochemical and mineralogical characteristics of the Asturias fluorspar district, northern Spain

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Abstract

The Asturian fluorspar district consists of vein and stratiform deposits where mineralization is controlled by a combination of lithological and tectonic factors. It is postulated that these fluorspar deposits have been formed under disequilibrium conditions created during circulation of ascending hydrothermal solutions along faults and other high permeability conduits. Mixing of solutions is inferred from fluid inclusion studies. Permian volcanic rocks in the area yield a regional positive geochemical anomaly in fluorine implying that Permian vulcanism may be a possible primary source of fluorine. On a regional scale a relationship can be established between some of the ore deposits and important tectonic lineaments. -from Authors
... The paragenesis of the mineralization in this area is composed by fluorite (CaF 2 ) and abundant barite (BaSO 4 ) (Tejerina and Zorrilla, 1980). Furthermore, cinnabar (HgS) is occasionally present in the form of fine inclusions in the fluorite and copper minerals (chalcopyrite, fahlore and Cu-carbonates are also abundant) (Iglesias and Loredo, 1994). Other potential contaminants are arsenic (As), related to the iron and copper sulfides in the area, and phosphorus (P), which is present as fine apatite crystals from pre-fluorite silicified rocks (Iglesias and Loredo, 1994). ...
... Furthermore, cinnabar (HgS) is occasionally present in the form of fine inclusions in the fluorite and copper minerals (chalcopyrite, fahlore and Cu-carbonates are also abundant) (Iglesias and Loredo, 1994). Other potential contaminants are arsenic (As), related to the iron and copper sulfides in the area, and phosphorus (P), which is present as fine apatite crystals from pre-fluorite silicified rocks (Iglesias and Loredo, 1994). ...
... The deposits are present either as vein or stratabound ores (Fig. 2). The former can be found in fractures or in faults, while stratabound beds occur between Carboniferous basements and Permo-Triassic cover rocks, or within the Permo-Triassic sedimentary rocks (Iglesias and Loredo, 1994). In the second half of the 20th century, fluorite mining made a significant visual impact on the whole area, whereas waste discharge from fluorite mineral processing in the zone reached the shoreline through rivers due to the absence of strict environmental controls (Gutiérrez Claverol, 2009). ...
Article
Samples from 13 beaches along the northern Spanish coast, a region with a history of heavy industries, were first screened to identify signs of pollution. High concentrations of Hg and Ba on Vega beach were found, both elements belong to the fluorite ore paragenesis, mined in the surroundings. Samples of beach and fluvial sediments, and nearby soils were collected in Vega beach area to address potential Hg pollution, fate and sources. Most samples showed a similar pollutants fingerprint to that of beach samples, especially those taken from white dunes, registering notable Hg concentrations. Hg was enriched in the finer fractions, and overall the main input was attributed to the mining waste discharged along the coast in the past. Although a specific risk assessment and study of the submerged sediments are advisable for this area, Hg bioavailability and methylation were low, thus indicating that this metal poses a reduced environmental risk.
... Other potential anthropogenic contamination sources are not known. Conversely, in nearby areas there are different outcrops of bituminous rocks and hydrothermal ores of fluorite that could potentially be the sources of As and Hg (Iglesias and Loredo, 1994;González-Fernández et al., 2018). Preliminary sediment analyses performed by the regional port authority have reported average concentrations of 11.3 μg g −1 for As and 0.18 μg g −1 for Hg (unpublished data). ...
... This suggests that the occurrence of Hg at site LL may be related to a different local source currently under investigation. Indeed, Forján et al. (2019) pointed out high concentrations of Hg at Vega beach (approximately 40 km west of site LL) due to the discharge of mine tailings from the district of Berbes which was one of the main fluorite mining areas in Europe where cinnabar was occasionally present (Iglesias and Loredo, 1994;Symons et al., 2017;Levresse et al., 2019). On account of the marine outfall, which has been built up for the discharge since 1990s (Forján et al., 2019), it is reasonable to expect that ocean and shoreline currents play a crucial role in transporting fine suspended particles enriched in Hg into the Llanes estuary (LL). ...
Article
Estuarine sediments must be dredged to allow for navigation, and where these sediments are placed after dredging depends upon guidelines based only on the total concentration of contaminants. However, resuspension events could seriously affect the mobility and speciation of contaminants, including potentially toxic trace elements stored in sediments. The effects of resuspension on the cycling of mercury (Hg) and arsenic (As) between the sediment and water column was investigated in a mesocosm study. Four experiments were conducted in three estuaries in northern Spain based on samples collected from sites which have been impacted by decommissioned Hg and As mines and periodically subjected to dredging activities. Designed to mimic the resuspension of particles, each of the experiments revealed that the release of Hg and As species does not only depend on the total concentration in the sediments (16.3–50.9 mg kg⁻¹, for As and 0.52–5.01 mg kg⁻¹ for Hg). The contribution from porewaters and the subsequent reductive dissolution and/or desorption appears to be the main processes responsible for the abrupt increase in dissolved Hg and As species (maximum release of 427% and 125%, respectively). In some cases, As and Hg continued to remain at high concentrations in the water column even after the experiments were completed, thus testifying to their critical persistence in the dissolved form. Conversely, at the other sites, the restoration of pre-resuspension conditions was observed only a few hours after resuspension, mainly due to the role of Fe oxy-hydroxides which provides suitable surfaces for adsorption and/or co-precipitation involving dissolved Hg (maximum removal of −58%) and As (maximum removal of −25%) species. The results of this research could be helpful to take appropriate decisions regarding dredging especially at the Nalòn estuary, where the release of dissolved As(V) and MeHg appeared to be favoured by sediment resuspension.
... As mentioned in the Results section, X-ray diffraction data of both the soil and the sand samples indicate the abundant presence of fluorite (Table 1, Additional file 1: Figure S1). This is clearly related to the proximity of several fluorite mines in the vicinity of the studied area, i.e., the so-called Caravia-Berbes mining district (Fig. 1b) where the paragenesis of the mineralization involves fluorite (CaF 2 ) and abundant barite (BaSO 4 ) [22,44], in coincidence with the minerals found in this study (Table 1, Additional file 1: Figure S1). Furthermore, cinnabar (HgS) is present in the form of fine inclusions in the fluorite and copper minerals that are also plentiful in the area [22]. ...
... This is clearly related to the proximity of several fluorite mines in the vicinity of the studied area, i.e., the so-called Caravia-Berbes mining district (Fig. 1b) where the paragenesis of the mineralization involves fluorite (CaF 2 ) and abundant barite (BaSO 4 ) [22,44], in coincidence with the minerals found in this study (Table 1, Additional file 1: Figure S1). Furthermore, cinnabar (HgS) is present in the form of fine inclusions in the fluorite and copper minerals that are also plentiful in the area [22]. It is possible therefore that the extraction and treatment of fluorite in this zone could lead to contamination by mercury. ...
Article
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Background An essential requisite for controlling and monitoring mercury in the environment is to identify its species in different types of soils and sediments, as this will help not only to establish its mobility in the environment and ecosystem and the degree of its toxicity, but also to establish the source of contamination. The objective of this work was to identify the origin of mercury in beach sands and soil taken from a coastal region with previously high mining and industrial activity by characterizing the mercury species using the technique known as thermal desorption (HgTPD). Results Apart from quartz, the main mineral species identified in the raw sands and soil were calcite, fluorite and barite. The concentration of mercury ranges from 5 to 23 µg g⁻¹, and although it is distributed in different proportions in the function of the size, thermal desorption profiles demonstrated that the mercury species present in the samples do not vary with the mercury concentration and the particle size. By means of HgTPD, mercury oxide (HgO) was identified in the beach sands, whereas mercury sulfide (HgS) was found in the soil sample taken from the vicinity of the beach. Complementary methodologies foster the HgTPD conclusions and verify that mercury is present mostly in insoluble stable (HgS) or low-mobility (HgO) forms in the samples studied. Analyses by ICP-MS after sequential extraction and HPLC separation of mercury species show that inorganic mercury is the predominant form in the samples. Conclusions The technique HgTPD is a very useful tool to ascertain the origin of mercury in contaminated beach sands and shoreline soils. In the particular area studied in this work, the species identified indicate that previous mining activity was the source of the mercury and rule out the possibility that contamination is derived from coal combustion activities ongoing in the region.
... They mostly occur in passive margin carbonates and lack any spatial relationship with magmatic bodies. Therefore, the carbonate -hosted Akkaya, Yeşilyurt, and Tavşanlı fluorite veins can be compared with the MVT fluorite deposits of USA, Kentucky-Illinois region (Denny et al., 2008), England, Pennines region, (Bau et al., 2003), Mexico, La Encandata (Levresse et al., 2006) and Spain, Austrias (Iglesias and Loredo, 1994). The formation mechanism and source of fluorine for these deposits is still enigmatic and is not attributed to a magmatic activity. ...
Article
Rare Earth Element (REE)-bearing fluorite deposits in Turkey occur in association with Cenozoic post-collisional alkaline-carbonatite systems and can be divided into three groups: (1) carbonatite-associated; (2) those associated with subalkaline to alkaline magmatic rocks of Cretaceous to Cenozoic age; and (3) those in sedimentary successions, typically in areas dominated by limestone. Some of these deposits show significant enrichment in the REE, especially the Kızılcaören deposit which has average REE grades of almost 30,000 ppm; others have very low REE contents but have potential fluorite resources. The homogenization temperature and salinity values of fluid inclusions in these deposits vary between 600 °C and 150 °C, and 10–65 wt% NaCl eq., respectively. The carbonatite-associated deposits have the highest bulk REE contents and are LREE-enriched. As a general feature, the REE contents of the fluorite deposits decrease with decreasing homogenization temperatures and salinity of the fluorite fluid inclusions. Fluorite ore chemistry indicates that a plot of Nb + Ta versus total REE differentiates the carbonatite- hosted from the alkali intrusive- hosted and carbonate- hosted deposits. Beyond the cooling and/or dilution of the fluids, REE and fluorite deposition was driven by changes in pH, instead of change in Eh, according to our geostatistical treatment. The chondrite-normalized rare earth element patterns of each group of deposits show some similar features, indicating that the REE in the fluorite are independent of their host lithology, but reflect the magmatic systems from which they were derived. Overall, the F-REE deposits of the Anatolides-Taurides in Turkey are considered to be largely related to the post-collisional magmatic systems, but with variable contributions of fluids from other sources.
... This scenario provides access for hot low-salinity fluorine-rich hydrothermal brines to ascend to surface through geothermal systems driven by gravity flow from adjacent Variscan highlands. At the seafloor the ascending brine mixed with descending oxygenated saline seawater to precipitate fluorite as mantos and veins at~140-150°C in the presence of calcareous rocks by open-space filling and/or replacement (Garcia-Iglesias and Touray, 1977;Tornos et al., 1991;Galindo et al., 1994;García Iglesias and Loredo, 1994;Johnson et al., 1996;Fanlo et al., 1998;Sánchez et al., 2010). At Caravia-Berbes the 206 ± 8 Ma age indicates that the Emilio manto was formed at the end of a Late Triassic period of uplift and erosion from~260 to~206 Ma. ...
Article
The Caravia-Berbes district is a major fluorite producing area in Europe. The fluorite occurs as mantos replacing breccio-conglomerates of the Middle Permian Caravia Formation and as veins and irregular replacive bodies in the unconformably underlying limestone of the Late Carboniferous Caliza de Montaña Formation. Paleomagnetic analyses were done using alternating field and thermal step demagnetization and saturation remanence methods. Ten sites (82 specimens) in massive and disseminated fluorite ore from the Emilio manto yielded a stable chemical remanent magnetization (CRM) in hematite inclusions with a direction of Decl. 20.1°, Incl. 67.3° (α95 = 6.1°). After correction for Neogene Pyrenean tilt, the manto's paleoinclination gives a CRM acquisition age of 206 ± 8 Ma that dates a major hydrothermal and ore emplacement event. The age is coeval with the onset of Pangea's break up as the Iberian microplate began to split from the Armorican terrane of Eurasia as part of the ocean-forming CAMP (Central Atlantic Magmatic Province) event. Another 11 sites (109 specimens) of silicified dolostone of the Caliza de Montaña Formation just below the Cueto L'Aspa manto yielded a stable CRM that resides in single and pseudosingle domain magnetite inclusions that has a direction of Decl. 328.7°, Incl. 76.6° (α95 = 4.9°). After Neogene tilt correction, the altered zone's paleopole gives a CRM acquisition age of 115 ± 3 Ma. This age shows that the western Cantabrian basin also underwent a major hydrothermal alteration and remagnetization event by fluid flow through steep re-activated faults when Iberia rotated 35 ± 2° away from Eurasia during Aptian-Albian time.
Article
Several international organisations have recommended the use of bioindicators to improve the evaluation of ecological risk in marine ecosystems. In this context, wild mussels, a recognised bioindicator, were collected from thirty sampling points along the Asturias coastline and studied in order to identify any relationship between metal(oid) concentrations in wild mussel tissues and the geological and environmental conditions of the coastal area via biochemical analyses. Two main concentration trends were observed: Concentrations of As, Cd, Cr, Ni, Pb and Zn slightly decrease from the western to the eastern areas of the region, while the opposite occurred for Fe, Hg and Se whose concentrations increased from the westernmost part of Asturias to the east. Correlations between the elements showed how essential metals for organisms such as Fe, Ni and Cr have good correspondences among them but not with other metal(oid)s. On the other hand, Cd, Hg, Se and Zn were found to be correlated with each other, suggesting the presence of the mussels’ natural bio-defence against Cd and Hg. In addition, samples were also grouped by a cluster analysis based on their element concentrations, showing two independent groups. Group 1 was associated with the sampling sites whose concentrations were related to anthropic sources, while mussel concentrations in Group 2 were attributed to natural sources. This last group was divided into two subgroups based on the lithology of the dominant geological materials of each area. Both geological and anthropic sources have caused an increase in the metal loads of mussels which at times surpassed international environmental criteria.
Article
Sediments from 35 beaches along the Asturian coastline in the north of Spain were studied. Geochemical analyses were conducted to assess the distribution of metal(oid) concentrations on the coast. Samples were correlated by a cluster analysis based on their geochemical concentrations, showing three different groups. Group 1 and Group 2 were composed of the samples of the occidental and oriental beaches, respectively, while Group 3 was formed by the beaches that are in the area of influence of one of the main harbours in the north of Spain where there is an established metal and chemical industry. These associations may explain the origin of the metal concentrations in the coastline. Both geological and anthropic sources generated geochemical anomalies in the sediment concentrations that sometimes surpassed quality OSPAR criterion.
Article
The fluid history of “diamond” quartz crystals from Caravia-Berbes Fluorite district is intimately related with episodes of maturation and migration of hydrocarbons within the Asturian basin, probably linked to the structural activation of a Mesozoic rift system. These “diamond” quartz record the migration of hydrothermal silica-rich brines and associated hydrocarbons that recorded a temperature increase (outlined by fluid inclusion studies) from ∼90 to ∼140 °C. This gradient is also recorded by a change in the organic matter species trapped in quartz, from bitumen located in the inner quartz growth zones to liquid hydrocarbons trapped within the outer quartz overgrowths. Secondary ion mass spectrometer (SIMS) oxygen isotope microanalyses allowed to differentiate two δ¹⁸OH2O values corresponding to the oil-dominated zone (core) and the water-dominated zone (outer growth zone). The heavier δ¹⁸OH2O values in the water-dominated zone do not only record a higher temperature of formation, but also an increase in the δ¹⁸OH2O of the parental fluid. Isotopic compositions of diamond quartz suggest a heterogeneous source of surficial fluids and formation-waters expelled from claystones. Within the basin history, the diamond quartz precipitation took place during early Jurassic to Eocene subsidence periods. Pressure Temperature and composition (PTX) and δ¹⁸OH2O characteristics point out a probable relationship with Albian diagenetic events reported in Cantabrian and north Pyrenean basins.
Article
With the aim of acquiring a better knowledge of the potential for unconventional gas resources in Spain, 134 rock samples were taken from 12 lithostratigraphic units in the Cantabrian Zone (north‐west Spain) and studied for a 3‐year period. The selected units gather, a priori, the basic conditions to constitute potential source rocks for unconventional hydrocarbons. Petrographic studies and total organic carbon analyses were carried out for all samples, whereas Rock‐Eval pyrolysis and vitrinite reflectance measurements with kerogen visual analysis were performed on selected samples. Lutites, litharenites, limestones, and slates are the predominant petrographic types. In most cases, the mean total organic carbon content is below the 2% limit for good quality potential source rocks. Only the Jurassic Rodiles and Tereñes limestones show total organic carbon values above this threshold. Rock‐Eval data reveal very low potential for hydrocarbon generation in almost all cases, with the exception of the dark mudstones of the Carboniferous Barcaliente Formation and the Rodiles Formation (fair and good potential for hydrocarbon generation, respectively). As regards thermal maturation, only the Ordovician formations are located in the peak of the gas generation interval. The Barcaliente and Rodiles formations are near the frontier oil/wet gas maturation areas, and the rest of the units are immature for gas generation.
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