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The most commonly used paleoclimatic proxies in speleothem studies are the carbon and oxygen stable isotopes and the trace elements of calcite. However, assessing the incorporation of other components, such as organic matter, may also be of interest in interpreting and reconstructing the climate during speleothem growth. In this work, the incorporation of humic and fulvic acids derived from overlying soils is proposed as the cause of the red coloration of speleothems from the Goikoetxe Cave (Busturia, Bizkaia). Through the application of petrological studies combined with X-ray fluorescence, UV luminescence, Raman spectroscopy and Fourier-transform infrared spectroscopy (FTIR) analysis, it has been possible to correlate a variation of organic content in the overlying soils and the red coloration, being this stain a main proxy to study and reconstruct the seasonal paleoclimatic parameters during the speleothem formation.

We present the first study of a unique acidic lake formed in the Brunita open pit (La Union mines, Cartagena, SE Spain). This pit lake exhibits chemical characteristics typical of AMD, such as low pH (pH 2.2–5.0) and high iron content (500–6400 mg/L total Fe). It also has some of the highest sulfate concentrations reported to date in pit lakes (26,000–38,400 mg/L $${\text{SO}}_{ 4}^{ 2- }$$ ) and transition metals like Mn (up to 2000 mg/L), Zn (500 mg/L), or Cu (250 mg/L). In addition, we found abnormally high concentrations of salt-forming ions (e.g. 5500 mg/L Mg, 750–1300 mg/L Cl, and 300–630 mg/L Na). The resulting high salinity (58‰) at the bottom creates a meromictic lake despite the lake’s low relative depth (9%), with an anoxic, reducing monimolimnion isolated from the oxygenated mixolimnion. In the monimolimnion, we observed decreased metal concentrations (e.g. Cu, Zn, Cd, Cr, Pb, Th). We hypothesize that these metals are being removed by interaction with biogenic H2S and subsequent precipitation as metal sulfides. Scanning electron microscopy shows sub-micron, spherical particles of ZnS in close association with cocci and rod-like bacteria. Analysis of the microbial community composition through 16S rRNA gene amplicon sequencing revealed different genera of sulfate-reducing bacteria (SRB) in the monimolimnion, including Desulfobacca, Desulfomonile, Desulfurispora, and Desulfosporosinus. Their apparent ability to reduce sulfate and selectively precipitate potentially toxic metals, and their resistance to this lake’s extreme geochemical conditions, makes these bacteria of great interest for biotechnological applications (e.g. bioremediation and biomining).

The unique case of carbon dioxide accumulation in the bottom layer of the acidic lake formed in the Guadiana open pit (Herrerias mine, SW Spain) led to exceptionally high dissolved gas pressures (ca. 5.0 bar at depths of 50–70 m). This CO2 has formed by carbonate (calcite, dolomite) dissolution during decades of interaction of the acidic water with the rocks of the pit walls and associated mine tunnels. The elevated dissolved gas pressures were only comparable to those found in the volcanic crater lakes of Cameroon like Nyos and Monoun, which erupted in the 1980s and sadly triggered the loss of hundreds of human lives. This gas pressure was not far from the absolute (hydrostatic plus atmospheric) pressure limiting CO2 solubility at depth, thus making this pit lake potentially dangerous for the possibility of a hypothetical limnic eruption. Following detailed field and experimental studies aimed at deciphering the source and accumulation patterns of CO2 in the lake, a degassing project started in 2014, which followed an upscaling strategy with construction and installation of progressively bigger pipelines capable of extracting increasingly higher flow rates of CO2-charged water from the deep part of the lake. As of May 2019, the degassing systems have successfully extracted most of the CO2 originally present in the lake (i.e. ≈ 123,000 m3 CO2), which has been discharged to the atmosphere in a controlled and safe way. The fountains became progressively smaller and finally stopped, due to the decreased gas pressure at depth. The larger pipes will serve as a regulating system in the future. This paper describes the main findings encountered during the degassing project, some relevant technical issues observed during the last 5 years (2014–2019), and lessons learnt from the Guadiana pit lake experience.

The consideration of quartzite as a secondary raw material has relegated in-depth research of this raw material in favour of such other rocks as flint or obsidian. The latter two are the most researched raw materials because of the information derived from their study: long-distance transport of rocks and mobility of people. In contrast, information obtained from research into quartzite generally supported near-site procurement areas mainly related to secondary river deposits. Together with the wide range of rocks called quartzite by archaeologists, this has influenced the poverty of research on the second most-often used raw material during the Palaeolithic. To overcome this narrow perspective, it is necessary to put quartzite in the centre of the debate as a raw material, using an inductive proposal based on geoarchaeological methodologies. This issue is approached by the application of a geoarchaeological methodology that combines thin section analysis, stereomicroscope observation, and X-ray Fluorescence compositional analysis of the quartzite from Level-XXII-R at El Esquilleu. Potential areas where quartzite could be procured, especially river beaches, are also characterised here. The results show complex mechanisms of quartzite acquisition based on intensive and selective searching, not only in proximate river deposits, but also in more distant fluvial deposits and conglomerate formations. Finally, in combination with techno-typological criteria, complex mechanisms of exploitation are proposed. These depended on each quartzite type, which promoted not only lithological but also technological variability. All these data open new perspectives for the characterisation of the second best represented raw material in Europe, as well as for understanding acquisition mechanisms in fluvial deposits and conglomerate formations.

Raw material characterization in Paleolithic archaeology has widened our knowledge of Middle Paleolithic societies. Procurement of raw material, specifically flint, has allowed the tracing of the mobility of both stones and people, as well as selective processes to obtain specific types or even extraction activities. The analysis of quartzite has also developed in recent years, providing an opportunity to better understand prehistoric societies. This study characterizes the procurement strategies implemented by Middle Paleolithic people in the mountainous region of the Picos de Europa. To this end, we present a comprehensive characterization of potential catchment areas: massive outcrops, conglomerates, and river deposits. The exploitation of quartzite at the sites of El Habario and El Arteu allows us to understand the territorial management of this mountainous area through the combination of selective processes and mobility mechanisms in lower and middle altitudes. These perspectives enable us to view the mountainous region not as a barrier but as an environmental mosaic managed by Middle Paleolithic groups. This study shows strategies that bring together direct and embedded procurement based on both intensive and extensive searches. These discourses are more closely related to the daily life of people than those only considering the mobility of people and objects., A comprehensive geoarchaeological research project based on the integration of a geographic information system, field survey, stereomicroscopy, and thin‐section petrography, is presented to characterize potential procurement areas of quartzite. The application of this methodology in the Deva, Cares, and Güeña valleys and in three different geological contexts; massive outcrops, conglomerates, and secondary deposits, suggest potential acquisition processes of lithic resources. The analysis of the quartzite assemblages of El Habario and El Arteu unveils complex management of terrain based on a mobility mechanism that connects middle altitude plateaus with open and lower river valleys, as well as intensive and extensive procurement mechanisms of raw material., Education Department of the Government of the Basque Country, The Spanish Ministry of Science Project, The Consolidated Research Group in Prehistory of the Basque Country University

The increase, in quantitative and qualitative terms, of research attending to the geological nature of rocks found in archaeological contexts is changing our perspectives about social and economic territories articulated by Palaeolithic societies in the Cantabrian Region. Practically the only raw material researched in a solid geoarchaeological approach in this area is flint. This paper addresses how the near absence of in-depth geoarchaeological research into raw materials other than flint is modifying our perception of the procurement and management mechanism of raw material in the Cantabrian Region during the Palaeolithic. To consider this matter in depth, we present the bibliographic and quantitative analysis of 30 representative archaeological sites from the Cantabrian Region whose assemblages were described lithologically using basic and primary categories. The state of play depicts a geographic distribution of raw material in the Cantabrian Region where quartzite is associated with the western sector and flint with the east. Interconnected with this axis, there is a chronological tendency that promotes standardisation in the use of flint by Palaeolithic societies following a chronological order, from the older to the more recent periods. This information, and its contextualisation with the new perspectives resulting from the application of the geoarchaeological proposal used to understand flint procurement, allows us to understand the general tendencies of raw material distribution of the region. Especially, we can detect how the absence of geoarchaeological methodologies of other raw materials than flint has modified the perception of the economic and social dynamics articulated around raw material by Palaeolithic people. This bias does not only affect the geographical and chronological axes, emphasising information from the regions and periods where flint is represented, but also promotes the over-interpretation of long-distance procurement, therefore, building up narratives exclusively based on human mobility. This situation has generated an incomplete and unbalanced picture of the procurement and management strategies followed by Palaeolithic societies because quartzite, the second most-often used lithic raw material, and other raw materials have only been studied using geoarchaeological methods within the last few years. This research finally points to the continuation of in-depth research of quartzite and other raw materials as the next steps to re-interpret the current paradigms about procurement and management of raw material by Palaeolithic societies, and, therefore, modify our perspectives of social and economic territories.

Acidic pit lakes are abandoned open pit mines filled with acid mine drainage (AMD)highly acidic, metalliferous waters that pose a severe threat to the environment and are rarely properly remediated. Here, we investigated two meromictic, oligotrophic acidic mine pit lakes in the Iberian Pyrite Belt (IPB), Filón Centro (Tharsis) (FC) and La Zarza (LZ). We observed a natural attenuation of acidity and toxic metal concentrations towards the lake bottom, which was more pronounced in FC. The detection of Cu and Zn sulfides in the monimolimnion of FC suggests precipitation of dissolved metals as metal sulfides, pointing to biogenic sulfide formation. This was supported by microbial diversity analysis via 16S rRNA gene amplicon sequencing of samples from the water column, which showed the presence of sulfidogenic microbial taxa in FC and LZ. In the monimolimnion of FC, sequences affiliated with the putative sulfate-reducing genus Desulfomonile were dominant (58%), whereas in the more acidic and metal-enriched LZ, elemental sulfur-reducing Acidianus and Thermoplasma spp., and disproportionating Desulfocapsa spp. were more abundant. Furthermore, the detection of reads classified as methanogens and Desulfosporosinus spp., although at low relative abundance, represents one of the lowest pH values (2.9 in LZ) at which these taxa have been reported, to our knowledge. Analysis of potential biomarker lipids provided evidence that high levels of phosphocholine lipids with mixed acyl/ether glycerol core structures were associated with Desulfomonile, while ceramide lipids were characteristic of Microbacter in these environments. We propose that FC and LZ function as natural bioremediation reactors where metal sulfide precipitation is mediated by biosulfidogenesis starting from elemental sulfur reduction and disproportionation at an early stage (LZ), followed by sulfate reduction at a later stage (FC)., This work is part of the research program STW under project number 14797, which is financed by the Dutch Research Council (NWO). I.S.-A. was funded by the Netherlands Ministry of Education, Culture and Science through a SIAM Gravitation grant 024.002.002. Field work and sampling was partly funded by the Spanish Ministry of Science through grant number CGL2016-74984-R. N.J.B. is funded by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement number 694569). S.A.S. was supported by the UNLOCK grant (NRGWI.obrug.2018.00)., info:eu-repo/semantics/publishedVersion

Several isolated studies have tried to understand quartzite from an archaeological perspective by applying two different methodological approaches. The first one is based on non-destructive characterisation, aiming to understand human procurement and management of quartzite, without solid geoarchaeological criteria. The second characterised the material from archaeological sites using only petrographic or geochemical perspectives of a limited sample. Currently, both perspectives are unconnected, creating a methodological gap that needs to be solved to study the procurement and management of quartzite in greater depth. The present study, mainly methodological, will explore the gap between petrographic analysis and non-destructive characterisation. Doing so, we could fill this vacuum of information and generate a solid geoarchaeological basis to characterise not only a sample but complete assemblages. To this end, we analyse the lithic assemblages at El Arteu and El Habario, two Middle-Palaeolithic sites in the Cantabrian Region, northern Spain. We summarise the main results derived from petrographic analysis, but especially we will focus on non-destructive criteria to characterise the lithic surfaces of archaeological quartzite using stereoscope microscopy. This process allows us to understand the complete assemblage but also, through technological characterisation, understand the management of different quartzite petrogenetic types in both sites.

Biogeochemical processes occurring in lake sediments are crucial for element cycling. In acidic pit lakes, they play a major role in acidity neutralization and toxic metal immobilization. However, the relationship between bacterial activity (e.g., iron and sulfate reduction), mineral neoformation, and metal mobility is often difficult to establish and has been rarely reported. The aim of this study was to identify mineral products formed by bacterial activity and their influence on trace metal dynamics during early diagenesis. The study focuses on several acidic pit lakes in SW Spain. We combined chemical analyses of intact sediment cores taken from shallow and deep zones with experimental sediment core incubations aimed at visualizing geochemical and mineralogical transformations occurring in the sediments during early diagenesis. The sediment incubations commenced with a total resuspension and homogenization and lasted for periods of several months. During this time, pore water and overlying water was extracted and analyzed to record geochemical changes. The sediments were also sectioned and chemically analyzed after the experiments to investigate carbon, nutrient, sulfur, iron, and trace metal mobility. Intact sediment cores were analyzed by sequential extraction and differential X-ray diffraction to examine metal speciation and the presence of secondary minerals not detectable by conventional techniques. Shallow sediments are more biogeochemically reactive due to their higher organic carbon content. In columns prepared with these littoral sediments, a sharp pH gradient appeared in the upper 4 cm soon after the beginning of the incubations, suggesting alkalinity generation and concentration of microbial metabolisms (iron and sulfate reduction). This pH gradient provokes the precipitation of Al and leads to the formation of a milky, gelatinous layer in the water/sediment interface. This layer quickly dehydrates and recrystallizes to more stable phases. At the same time, bacterially produced H2S reacts with different metals (Cu, Zn) which are thus immobilized in the sediments as secondary sulfides. However, these two metals are also removed from solution by purely abiotic mechanisms like sorption or coprecipitation. Carbon seems to be the major factor limiting bacterially mediated metal and acidity attenuation in sediments of these acidic pit lakes. Metal immobilization is not a simple process and takes place through a combination of direct precipitation (Al oxyhydroxysulfates, Cu and Zn sulfides) and indirect mechanisms (sorption, coprecipitation, cation exchange). The precipitation of Al is of prime importance for pH buffering and immobilization of other metals (Cu, Zn). This process is not evident in routine chemical analyses of sediment cores, but it can be inferred by a combination of experimental and laboratory techniques such as the ones used here. P and N fertilization of these pit lakes would greatly increase the natural rates of acidity neutralization.

Through the use of scanning transmission electron microscopy (STEM) combined with other complementary techniques (SEM, cryo-TEM, HRTEM, and EELS), we have studied the interaction of microorganisms inhabiting deep anoxic waters of acidic pit lakes with dissolved aluminum, silica, sulfate, and ferrous iron. These elements were close to saturation (Al, SiO2 ) or present at very high concentrations (0.12 m Fe(II), 0.12-0.22 m SO42- ) in the studied systems. The anaerobic conditions of these environments allowed investigation of geomicrobial interactions that are difficult to see in oxidized, Fe(III)-rich environments. Detailed chemical maps and through-cell line scans suggest both extra- and intracellular accumulation of Al, Si, S, and Fe(II) in rod-like cells and other structures (e.g., spherical particles and bacteriomorphs) of probable microbial origin. The bacterial rods showed external nanometric coatings of adsorbed Fe(II) and Al on the cell surface and cell interiors with significant presence of Al, Si, and S. These microbial cells coexist with spherical particles showing similar configuration (Fe(II) external coatings and [Al, Si, S]-rich cores). The Al:Si and Al:S ratios and the good Al-Si correlation in the cell interiors suggest the concurrent formation of two amorphous phases, namely a proto-aluminosilicate with imogolite-like composition and proto-hydrobasaluminite. In both cases, the mineralization appears to comprise two stages: a first stage of aluminosilicate and Al-hydroxysulfate precipitation within the cell or around cellular exudates, and a second stage of SO42- and Fe(II) adsorption on surface sites existing on the mineral phases in the case of (SO42- ) or on presumed organic molecules [in the case of Fe(II)]. These microbially related solids could have been formed by permineralization and mineral replacement of senescent microbial cells. However, these features could also denote biomineralization by active bacterial cells as a detoxification mechanism, a possibility which should be further explored. We discuss the significance of the observed Al/microbe and Si/microbe interactions and the implications for clay mineral formation at low pH.

Se presenta el estudio metalográfico de un vástago metálico recuperado en el abrigo de Peña Parda (Laguardia, Álava), para determinar su composición química, que resulta mayoritariamente cobre.

The precipitation of dissolved aluminum is among the most important geochemical processes affecting the water chemistry and trace metal dynamics of acid mine drainage (AMD). In this study, we focus on the in situ formation of Al precipitates and their subsequent interaction with trace metals, dissolved silica and microbial cells under anoxic conditions (e.g., deep strata of pit lakes, flooded underground mines). In the presence of sulfate (0.1–0.2 M), dissolved aluminum precipitates at pH ~ 4.0 and forms an amorphous, globular hydroxysulfate precipitate with composition corresponding to hydrobasaluminite. This proto-hydrobasaluminite shows an important capacity to incorporate SiO 2 (aq), divalent metal cations (Fe II , Pb II , Be II ), and many anion-forming trace elements (As, Cr, Sb, V, Se, U) by coprecipitation. Removal efficiencies obtained experimentally with freshly formed hydrobasaluminite under anoxic and oxic conditions were consistent with metal profiles obtained in the pit lakes and suggest that the behaviour of many toxic metals is closely linked to the Al particles. Detailed transmission electron microscopy (TEM) shows that hydrobasaluminite may coexist with more crystalline minerals like gibbsite, bayerite and/or allophane, which are present as nanocrystals embedded in the amorphous matrix and appear to form by transformation of the former. Hydrobasaluminite precipitation is favoured by the activity of iron- and sulfate-reducing microbes in the water column and at the sediment/water interface. Our study shows that, at solubility equilibrium, microbial cells often serve as nuclei for Al precipitation. Further, chemical mapping of Al-coated cells by scanning/TEM shows an important incorporation of SiO 2 , Fe 2 + (valence confirmed by electron energy loss spectroscopy) and other metal cations (e.g., Mg 2 + ) in the Al cell coatings as compared to Al particles presumed to form via abiotic precipitation. These Al cell coatings are amorphous to X-rays and their compositions likely result from coprecipitation of SiO 2 and Fe 2 + resulting in Si-rich and Fe(II)-rich hydrobasaluminite. The disparity between field and laboratory data, the serendipitous detection of nontronite-like smectite in precipitates formed in the acidic waters under laboratory conditions, and the apparent saturation with respect to different clay minerals (e.g., kaolinite, halloysite) are all evidences suggesting thermodynamic feasibility of aluminosilicate precursor formation in these systems.

Micromorphological analysis is an invaluable research tool for reconstructing detailed depositional and post-depositional processes of cave infill sequences and for providing paleoenvironmental insight. In this work, we present the results of a micromorphological and mineralogical study of the sedimentary sequence at the Lezetxiki II cave (northern Iberian Peninsula). The cave forms part of the Lezetxiki archaeological complex which has yielded early Middle Palaeolithic tools and archaic human remains. We have identified three main clastic sedimentary processes as being significant at Lezetxiki II: 1) fluviokarst or runoff processes, which are characterised by yellow sandy illite-rich microfacies; 2) infiltration processes, which produce a massive red silty-clay vermiculite-rich microfacies; and 3) inwash processes, which generate a reworked illite and vermiculite rich silty sand microfacies. The most common post-depositional processes observed are calcite precipitation infilling pore spaces, and compression structures derived from specific vertical loading events. In order to improve the chronological framework of the sedimentary sequence at Lezetxiki II, we have revised previous radiometric and relative dating results from faunal and archaeological remains and have dated the lowermost stratigraphic level using single-grain thermally-transferred optically-stimulated luminescence dating. Sedimentation at the Lezetxiki II cave started during Marine Isotope Stage (MIS) 7 through fluviokarst processes. We interpreted that runoff prevailed during MIS 6, while soil infiltration processes became more significant towards the MIS 5 optimum. Gradually, inwash processes prevailed over infiltration until the end of the interglacial phase. During the following glacial phases, runoff and erosion dominated but were subsequently replaced by inwash processes during MIS 1., PALEOGATE project, funded by the Spanish Ministry of Economy and Competitiveness (HAR2014-53536-P) as well as the US14/16 project funded by the University of the Basque Country and Basque Coast Geopark, and Basque Government (IT1029-16-GBV6). We would also like to thank Tim Nicholson for his work in translating and editing different versions of the English text. Additional financial support for this research was provided by Australian Research Council (ARC) Future Fellowship project FT130100195, ARC Discovery Early Career Researcher Award DE160100743

Cueva de la Mora and Guadiana are two acidic mine pit lake in the Iberian Pyrite Belt (south-west Spain) that exhibit depth-related stratification, which is in turn reflected in the bacterial community population the different layers. Here we describe the microbial communities present in samples of sediments located close to the surface and deep within the lakes, which show interesting contrasts to planktonic communities.

The removal of dissolved trace metals during neutralization of acid mine drainage has usually been described and modelled as a progressive, pH-dependent sorption onto standard ferric or aluminous adsorbent. In the absence of adsorbent mineral surfaces, trace metals tend to form amorphous to low-crystallinity compounds which are often difficult to characterize. Here, we study the behaviour of the more soluble metals (Cu2+, Zn2+, Mn2+, Co2+, Ni2+, Cd2+) in the absence of ferric and aluminous adsorbent by neutralization experiments with waters from two acidic pit lakes. The objectives of our study were to identify the mineral products formed by trace-metal precipitation and the pH ranges at which these metals are removed from the solutions. Both geochemical modelling and detailed mineralogical and chemical analyses (XRD, SEM, TEM, XRF, ICP-AES) were undertaken to characterize the products. The schwertmannite and hydrobasaluminite colloids formed in the initial neutralization stages were removed from the waters at pH 3.5 and 5.1, respectively. These two minerals had previously adsorbed the Cr3+ and Pb2+ initially present in the solutions. The Cu precipitates were amorphous to X-rays, though chemical and modelling data suggest that Cu probably precipitated as a precursor of brochantite (Cu4(SO4)(OH)6·2H2O) at pH >6.0, together with minor quantities of other Cu hydroxysulfates (langite, antlerite) and Cu(OH)2. At higher pH, other divalent metals (Zn2+, Mn2+) precipitated as silicates, carbonates and/or (possibly) minor oxides and (oxy)hydroxides. The high concentration of aqueous SiO2 in the solutions allowed Zn to precipitate as willemite (Zn2SiO4) at pH >7.0. Similarly, the presence of inorganic carbon (originally as CO2 (aq.)) greatly influenced the nature of the corresponding precipitate of Mn. This metal was initially present as Mn2+ and experienced a partly oxidative precipitation forming, in combination with Mg2+, the hydroxyl carbonate desautelsite (Mg6Mn2(CO3)(OH)16·4H2O) at pH 9.0–10.0. The formation of Mn3+/Mn4+ oxides and hydroxides (hausmannite, manganite, birnessite) could not be demonstrated, although geochemical calculations support their subordinate formation. Other metallic cations such as Co2+, Ni2+ and Cd2+ did not form discrete mineral phases but were totally removed by sorption onto and/or incorporation into the cited Zn and Mn compounds. The discrepancies between theoretical and demonstrated mineralogy and the significance of these minerals for future pit-lake remediation initiatives are discussed.

© 2014 Elsevier Ltd and INQUA. The western Pyrenean area contains extensive karst areas, however, their genesis and development are still mostly unknown. In this work, we make a general description of the karst landscape in different karst areas: 1) Rasa type; 2) Cone-type karst; and 3) Alpine-type karst. The first two types are present in the littoral area, where geomorphological evolution mostly depends on sea level and climatic changes. We focused our study in two karst areas of the littoral cone-type karst. We correlate different caves created from different stable water table levels. Three representative caves are studied in detail, studying their stratigraphic record based on allostratigraphy. Finally we dated the different phases of speleothem formation in the three caves. Using all this information, we defined four stable paleowater table levels, at 50, 150, 220 and 350masl, controlled by sea level changes and isostatic uplift events. The lowest level is the youngest, with an age of c. 1Ma. We discovered that the interior of the three caves display very similar endokarst allostratigraphic sequences, characterized firstly by an erosion phase, a fluvio-karst input, flowstone speleothem formation and finally dripping speleothem formation. The chronological data shows a correlation between these phases and Pleistocene climatic phases; the erosion phase is related to the falling sea level, fluviokarst detrital input is related to cold (glacial) stages and the formation of speleothems is related to the warmest (interglacial) moments and high sea level periods., This research was funded by the University of the Basque Country's projects (UPV/EHU11/21 and UFI11/09). M. Arriolabengoa and M. del Val are funded by predoctoral grants (BFI-2012-289 and BFI-2010-379) from the Basque Government.

The characteristics and provenance of the fine sediment forming the matrix of detrital endokarst fill can vary greatly, and their study provides valuable information about the paleoenvironment and the different sedimentary and diagenetic processes in which it was formed and deposited. This paper applies this study to the case of Lezetxiki II cave (Arrasate, Gipuzkoa). Using X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM–EDS) analysis with samples of endokarst sediment, rocks and soils in the surroundings of the cave, the following source areas and sedimentary processes have been identified: 1) allochthonous sedimentation through the fluviokarst processes which eroded soils formed on siliciclastic formations. It is characterised by a high percentage of illite in the sediment and predominated in relatively cold periods in MIS 6 and MIS 2–4; 2) sedimentation through infiltration from karst fissures of the autochthonous soils formed on the limestone substrate (terra rossa). It is characterised by a higher vermiculite content, and prevailed in the warm MIS 5 period and the Holocene; 3) chemical sedimentation, where calcite precipitated in the form of speleothems in warmer and more humid periods; and 4) deposition of microfauna bones in owl pellets.

Parte del número especial "Biohydrometallurgy", Concentrations of aluminium in acidic waste waters are frequently much higher than in circum-neutral pH water bodies, and can represent a significant environmental hazard. In very low pH (, College of Natural Sciences, Bangor University, Reino Unido, Departamento de Mineralogía y Petrología, Universidad del País Vasco, España, Instituto Geológico y Minero de España, España

19 Pags.- 7 Tabls.- 11 Figs., Oxygen depletion (temporal or permanent) in freshwater ecosystems is a widespread and globally important environmental problem. However, the factors behind increased hypolimnetic anoxia in lakes and reservoirs are often diverse and may involve processes at different spatial and temporal scales. Here, we evaluate the combined effects of different anthropogenic pressures on the oxygen dynamics and water chemistry of Lake Enol, an emblematic mountain lake in Picos de Europa National Park (NW Spain). A multidisciplinary study conducted over a period of four years (2013–2016) indicates that the extent and duration of hypolimnetic anoxia has increased dramatically in recent years. The extent and duration of hypolimnetic anoxia is typical of meso-eutrophic systems, in contrast with the internal productivity of the lake, which remains oligo-mesotrophic and phosphorus-limited. This apparent contradiction is ascribed to the combination of different external pressures in the catchment, which have increased the input of allochthonous organic matter in recent times through enhanced erosion and sediment transport. The most important among these pressures appears to be cattle grazing, which affects not only the import of carbon and nutrients, but also the lake microbiology. The contribution of clear-cutting, runoff channelling, and tourism is comparatively less significant. The cumulative effects of these local human impacts are not only affecting the lake metabolism, but also the import of sulfate, nitrate- and ammonium-nitrogen, and metals (Zn). However, these local factors alone cannot explain entirely the observed oxygen deficit. Climatic factors (e.g., warmer and drier spring and autumn seasons) are also reducing oxygen levels in deep waters through a longer and increasingly steep thermal stratification. Global warming may indirectly increase anoxia in many other mountain lakes in the near future., This Project was funded by Organismo Autónomo de Parques Nacionales (OAPN) through CLAM-1 Project (Ref. 533S/2012).

Visible near infrared and shortwave infrared (VNIR-SWIR, 350 to 2500 nm) reflectance spectra obtained from an analytical spectral device (ASD) have been used to define alteration zones adjacent to porphyry copper deposits (PCDs), in the central part of Kerman magmatic arc, SE Iran. The spectral analysis identified sericite, illite, halloysite, montmorillonite, dickite, kaolinite, pyrophyllite, biotite, chlorite, epidote, calcite, jarosite, and iron oxyhydroxides (e.g. hematite, goethite) of hydrothermal and supergene origin. Identified alteration zones are classified into six principal types namely phyllic, phyllic/propylitic, propylitic, potassic, argillic and advanced argillic. The iron oxide minerals in the oxidized zone were also identified using spectral analysis. Results of spectral analyses of samples are consistent with mineralogical data obtained from X-ray diffraction (XRD) and petrographic studies. Spectroscopic studies by ASD demonstrate that this tool is very useful for semi-quantitative and cost effective identification of different types of alteration mineral assemblages. Furthermore, it can provide a valuable tool for evaluating aerial distribution of alteration minerals while coupled with remote sensing data analysis.

Production of H2S by bacterial sulphate reduction in the water column of Cueva de la Mora pit lake (SW Spain) may favour an important self-mitigating capacity with respect to metal pollution. The interaction of bacterially produced H2S with dissolved metal(loid)s provokes the precipitation of various sulphides, which in turn form a 10 m-thick turbidity layer below the redoxcline. The main goal of this study was to identify the main factors driving the formation of these sulphide precipitates and their impact on the pit lake water quality. Given the severe geochemical conditions found in this lake (low pH, high metal concentrations), our findings may be relevant for a wide spectrum of environmental systems where BSR-based biotechnologies are applied. The water column has been studied by spatially resolved samplings and detailed chemical analyses, physico-chemical profiling and geochemical modelling. The suspended particulate matter forming the turbidity has been chemically and mineralogically characterized. Our results suggest that the low pH (3.0–4.0) and the high metal concentrations are not inhibitory for the sulphate-reducing bacteria (SRB). The intensity of sulphide precipitation seems to be closely related with the activity of SRB, which in turn appear to depend on the availability of organic carbon produced in the photic zone. The relative location of oxygen and iron gradients and the redoxcline thickness are influencing the development of the sulphate reducing zone. The most common sulphides are CuS, As2S3 and ZnS, though formation of some other minor phases (PbS, CdS, NiS) has been also detected and/or deduced by geochemical calculations. Metal sulphide precipitation has provoked a complete removal of Cu from the monimolimnion (though it is still present at concentrations of 5.5 mg/L in the mixolimnion) and a net decrease in highly toxic trace metals (Cd, Pb, U, Th) and metalloids (As, Sb).

The main aim of the present study was to examine the feasibility of the EO-1 Hyperion data in discriminating and mapping diagnostic alteration minerals around porphyry copper deposits (PCDs), verified by field surveys and laboratory analyses. A partial sub-pixel method, mixture tuned matched filtering (MTMF), was implemented on a pre-processed and calibrated Hyperion dataset. The tested area is situated at the Central Iranian Volcano-Sedimentary Complex, where abundant porphyry copper deposits like Sarcheshmeh, Darrehzar, and Sereidun are located. The characteristic alteration minerals identified by Hyperion data included biotite, muscovite, illite, kaolinite, goethite, hematite, jarosite, pyrophyllite, and chlorite. Discrimination of these minerals especially biotite and iron oxide (hematite and goethite) can provide valuable evidences for PCD exploration projects. Results revealed that Hyperion data prove to be powerful in discriminating and mapping various types of alteration zones while the data were subjected to adequate pre-processing.

This paper focuses on mapping jarosite and different types of alteration minerals for mineral exploration, particularly porphyry copper deposits and discriminating alteration zones with high-potential mineralization from those showing low potentials. The study area is situated at the Central Iranian Volcano-Sedimentary Complex, where the large copper deposits like Sarcheshmeh as well as numerous occurrences of copper exist. The visible near infrared and shortwave infrared (VNIR-SWIR) bands of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data were used for mineral mapping. The spectra of diagnostic alteration mineral groups, including sericite-illite, pyrophyllite-alunite, kaolinite-dickite, chlorite-calcite-epidote, and jarosite were extracted from VNIR-SWIR bands of the ASTER imagery. These spectra were used for mineral identification through mixture tuned matched filtering (MTMF) algorithm. Results showed that alteration minerals, and the areas containing jarosite were discriminated from the surrounding districts, which illustrate the ASTER ability to provide information on the occurrence of these minerals. Identification of these areas is valuable for mineral exploration, discrimination of strong pyritization, gossans, and the mine tailings. Results also support the role of MTMF as an effective image processing technique for mineral mapping and exploration.

Twelve massive sulphide deposits from the Iberian Pyrite Belt (IPB) show well-preserved iron caps, some of which were mined during the last century to recover precious metals (e.g., Tharsis, Rio Tinto, San Miguel). Field observations and correlation assays between the distinct mineral sequences at different deposits suggest that all the gossans were developed under similar conditions and have undergone the same geological events. All the gossans have a mushroom-like morphology in sharp contact with the underlying massive sulphide orebodies. In most cases these are located over an apparent supergene enrichment zone rich in secondary sulphides. Some gossans extend into tongues of alluvial heterolithic breccias consisting of eroded transported gossans displaced as far as several hundred meters away from their sources. The distribution of major minerals throughout the gossan profiles (goethite, hematite, quartz and jarosite) and the statistical analysis of the geochemical data distinguish three separate zones, with gradual contacts roughly parallel to the current topography: (1) the lower zone dominated by goethite and subordinate jarosite, with significant enrichment in S, As, P, Pb, Sn, Sb, Ag and Au; (2) the middle or principal zone dominated by goethite and lacking jarosite, which is depleted in S, and As, as well as heavy and precious metals; and (3) the upper zone near the surface, mainly composed of hematite and quartz with only weak anomalies in P, Pb and Sn. The origin and variations occurred in the profiles are explained by a three-stage process. This involves an initial acidic stage of gossan development centred on the oxidation of sulphides that lead to the formation of the first Fe-rich oxyhydroxides and sulphates (mainly goethite and jarosite, respectively). Over time, a progressive stage of maturity is reached progressively downwards through the gossan profile due to the intensification of the oxidation and leaching processes. The ongoing gossan formation produced alteration and reprecipitation of pre-existing oxyhydroxides, the loss of the majority of the previously sorbed heavy metals, and a major dilution of trace elements especially in the zones near the surface. The main results of this stage of formation are the production of heavy metal-depleted oxyhydroxides, most commonly goethite and hematite, and the disappearance of jarosite. Subsequently, local uplift of the gossanous rocks by neotectonic movements facilitated the rejuvenation of the oxidation of the ores. This final stage complicated the previously developed zonation with the formation of jarosite in mature areas. Possible major breaks in this gossan development ocurred in Messinian times (7–8 Ma) and at the beginning of the Early Quaternary (1–2 Ma?).

Ferric precipitates in the water column at the San Telmo acidic mine pit lake in the Iberian Pyrite Belt, southwest Spain, have been studied by scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction, X-ray fluorescence, inductively coupled plasma mass spectrometry and other complementary techniques. These Fe(III) precipitates were recovered from sediment traps which were left at different depths (25, 35, 40 and 100 m) in the lake for several months. Seasonal variations in the water chemistry were recorded to link the mineralogical findings to vertical and temporal changes in aqueous composition. The results indicate that schwertmannite is the first Fe(III) mineral to crystallize after the oxidation of Fe(II), in agreement with previous studies. Schwertmannite is kinetically favoured in comparison to other Fe(III) minerals, and it buffers the pH at 2.6–3.0. It is metastable, and alters to a (H3O+)- and (K+)-bearing jarosite (containing 58 mol.% H3O+ and 42 mol.% K+ on average) at lower pH (e.g. at pH 2.2–2.5 in the summer season), either in the water column (during settling) and/or in the benthic sediments, in a time period of weeks to months. The extent of hydronium substitution at the alkali site in the jarosite reflects the higher activity of free aqueous protons in solution (10–2.2 to 10–3.0) in comparison to the activities of K+ (10–4.5) and Na+ (10–3.2). Microscopic examination of mixed schwertmannite–jarosite precipitates found in the water column suggest that some textural and compositional features of metastable schwertmannite (e.g. the internal 'pincushion' arrangement and incorporation of trace amounts of Mg, Al, As and Pb) are conserved in the jarosite during the early stages of the mineralogical transformation, but many of these relics are lost in the later stages of crystal growth. Despite the hydronium-rich nature of the jarosite solid solution, this material is also an important sink for K+, which decreases in concentration with decreasing pH unlike most of the other major cations in the water column (notably Na+, Mg2+, Ca2+, Al3+, Fe3+, Cu2+, Zn2+). In addition to the release of Fe3+ to the aqueous solution, the conversion of schwertmannite to (H3O+, K+)-bearing jarosite consumes protons and thus may represent an additional pH control at San Telmo and other acidic mine pit lakes of the area, Unidad de Mineralogía e Hidrogeoquímica Ambiental, Departamento de Investigación en Recursos Geológicos, Instituto Geológico y Minero de España, España, Unidad de Mineralogía e Hidrogeoquímica Ambiental, Departamento de Mineralogía y Petrología, Universidad del País Vasco, España, Departamento de Física Aplicada II, Universidad del País Vasco, España

This work examines the geochemical behavior of dissolved aluminum in sulfate-rich acidic waters. Our observations were obtained during several years of geochemical and mineralogical research in the San Telmo acidic pit lake and other pit lakes of SW Spain. The work includes scanning and transmission electron microscopy (SEM, TEM) of suspended mineral colloids found in deep lake waters. Energy dispersive spectroscopy (EDS) coupled to scanning and high resolution transmission electron microscopy (STEM, HRTEM) revealed not only the presence and formation of discrete, sub-micron Al solids like alunite, but also the abundance and distribution of Al into Fe(III) phases typical of acid mine drainage, such as schwertmannite and jarosite, at a nanometric resolution. The main conclusion emerging from our work is that the fate and transport of Al at low pH ( 3.3, as suggested by mineralogical observations and geochemical modelling. Below this pH, and contrary to the extended assumption, Al is not truly conservative, and in the presence of ferric iron, both metals may co-precipitate at a substantial extent to form either particles of Al-rich schwertmannite (containing up to ca. 8 at.% Al with [Fe/(Fe + Al)] = 0.77) and/or crystals of H3O+- to K+-jarosite (containing up to ca. 10 at.% Al with [Fe/(Fe + Al)] = 0.54). This Al incorporation seems to take place by adsorption on particle surfaces in schwertmannite and by atomic substitution for Fe3+ in jarosite. Alunite is also unstable at this low pH range with respect to jarosite, which may lead either to isomorphic transformation and/or to chemically zoned crystals with jarositic rims around previously formed alunite cores. As a whole, the compositional spectrum of the analyzed jarosites and alunites describes a discontinuous, coupled (Al3+–Fe3+, H3O+–K+) solid solution series with an apparent gap at intermediate compositions. However, this gap seems to follow geochemical aspects more than crystallographic factors (i.e., immiscibility). The combination of this macroscopically invisible Al incorporated into Fe(III) solids along with subordinate alunite formation may cause significant Al removal even at very low pH (e.g., 20% decrease in Al concentration in San Telmo at pH < 3.1). Furthermore, this Fe(III)–Al co-precipitation may also affect the fate of toxic trace elements like As and Pb., Unidad de Mineralogía e Hidrogeoquímica Ambiental, Instituto Geológico y Minero de España, España, Unidad de Mineralogía e Hidrogeoquímica Ambiental, Departamento de Mineralogía y Petrología, Universidad del País Vasco, España, Materials Research Institute, The Pennsylvania State University, Estados Unidos, Department of Civil and Environmental Engineering, The Pennsylvania State University, Estados Unidos

High gas charges in deep waters of lakes can represent a hazard to the lives of human beings and animals in the surrounding. As this danger was feared, we quantified the amount of dissolved gas in Guadiana pit lake (Las Herrerias, Huelva; southwest Spain) and documented the temporal evolution over a period of two years. Gas pressure due to dissolved gases, such as carbon dioxide, methane and nitrogen was measured. Based on these data, we assessed the risk and the associated danger of limnic eruptions from the lake and concluded that the present situation cannot be considered safe. By deploying a vertical pipe, the updraft of degassing water was tested and demonstrated: the pilot plant provided enough energy to drive a self-sustained flow. Such a system could be implemented to remove the extreme gas pressure from the deep water. Measurements of discharges could be extrapolated to indicate the size for an efficient plant for the gas removal. The construction of such a system would be technically and economically viable. A reintroduction of degassed water into the monimolimnion would be advisable.

The solubility of schwertmannite and hydrobasaluminite and their control on the concentration of Fe(III) and Al in acid-sulfate aqueous systems has been re-examined through a series of titration experiments with waters from two acidic pit lakes (Cueva de la Mora and San Telmo) from the Iberian Pyrite Belt in SW Spain. The work also includes a microscopic study (SEM–EDS) of natural Fe(III) precipitates found in the water column of both lakes. The microscopic study of natural precipitates confirms that schwertmannite constitutes a major control of Fe3+ concentration in the lakes at pH ∼ 3.0, whereas jarosite may also be abundant at near-surface conditions and is typical of low pH ( SO 4 2 - and H+ in solution, allowed the calculation of ionic activity products (log IAP) and solubility product constants (log Ksp) for the precipitating phases. The solubility product constants have been deduced by two independent approaches. The first one averages ionic activity products obtained for a given pH range, whereas the second one deduces log Ksp values from linear regression lines in ion activity-pH plots. Both methods tend to converge and give log Ksp = 18.8 ± 1.7 for schwertmannite, and log Ksp = 23.9 ± 0.7 for hydrobasaluminite. In the pH range 5–9, the results are compatible with additional solubility controls from ferrihydrite and an amorphous to nano-crystalline Al(OH)3 phase on the aqueous concentrations of Fe and Al, respectively, although formation of these latter compounds could not be demonstrated. The present work confirms the results originally obtained for schwertmannite solubility and reports a reliable solubility product constant for freshly precipitated hydrobasaluminite. Integration of the resulting log Ksp values in the MINTEQ.V4 database and the PHREEQCI geochemical modeling program provides a precise description of the geochemical behaviour of Fe and Al in these acidic pit lakes.

Este documento corresponde a una versión PREPINT (versión enviada originalmente a la revista, previa a las modificaciones sugeridas por los revisores). El artículo final ha sido publicado originalmente por la revista Ore Geology Review de la Editorial Elsevier. La URL del mismo es: http://dx.doi.org/10.1016/j.oregeorev.2015.10.005, This is a PREPRINT version (pre-refereeing process version). The final article has been published in Ore Geology Review by Elsevier. The URL is: http://dx.doi.org/10.1016/j.oregeorev.2015.10.005, Geological evidence and mineralogical, fluid inclusion temperature and geochemistry data suggest that the Mazarrón Zn-Pb-Cu-Ag-Fe deposit is a volcanic-hosted epithermal deposit. It is hosted by dacites with advanced argillic alteration, argillic alteration, propylitic alteration and silicification halos. K-Ar dating of illite from the argillic alteration gives an age of 9.7 ± 1.2 Ma, which suggests that mineralization took place very close to the volcanism. The fluid inclusion study in the ore veins shows epithermal temperatures (between 190 and 260ºC), but moderate salinities, between 12 and 18 wt. % NaCl eq), compatible with mixing between surface waters and polygenic deep hydrothermal fluids. Two mineralization types are identified: iron sulfide mineral association and polymetallic mineral association (sphalerite-galena-chalcopyrite-fahlore bearing). According to isotopic data, the first mineralization was mainly formed by interaction between basinal fluids that leached Triassic sulfates (+ surface waters), and C-bearing reduced deep waters. This interaction developed a Thermochemical Sulfate Reduction (TSR) supporting extreme and geologically unusual fractionation, with a range up to +30‰ δ34S, and reaching +53‰ δ34S. The second mineralization event is compatible with the irruption of a magmatic fluid discharge. Although this study suggests that Mazarron could be classified as an intermediate sulfidation deposit, the genetic model includes processes such as TSR that are not typical features of volcanic-hosted epithermal deposits., Universidad de Granada. Departamento de Mineralogía y Petrología, Instituto Andaluz de Ciencias de la Tierra (UGR-CSIC), Universidad del País Vasco. Departamento de Mineralogía y Petrología, Scottish Universities Environmental Research Centre (SUERC), Universidad de Granada. Departamento de Didáctica de las Ciencias Experimentales, Grupo de Investigación Mineralogía, Petrología y Yacimientos Minerales (GIMPY) (RNM131) de la Junta de Andalucía., Grupo de Investigación Didáctica de las Ciencias Experimentales y de la Sostenibilidad (HUM613)de la Junta de Andalucía, This research has been supported by the Project of ExcellenceP05-RNM-0736 (founded by Consejería de Innovación, Ciencia y Empresa, Junta de Andalucia, Spain) and the Spanish projectCGL-2006-02594-BTE (founded by Ministry of Science and Innovation/Ministry of Education and Science and Fondo Europeo de Desarrollo Regional, FEDER).

Short-wave infrared reflectance (SWIR) spectra obtained from a Portable Infrared Mineral Analyser (PIMA) were applied to map acidic mine soils at San Miguel massive sulphide deposit, Iberian Pyrite Belt, Spain. Field spectral measurements and laboratory analysis were performed on samples from 58 stations from two very polluted grounds. These analyses identified secondary and tertiary Fe-rich sulphate–hydrate minerals associated with the alteration of sulphide-bearing mine wastes and other associated infrared active minerals. The spectral absorption features for the pure salt types found in these areas allowed the preparation of a specific reference library for automatic mineral identification. Using this approach three separate zones around the sources of contamination have been discriminated: a “proximal” zone dominated by rozenite + hexahydrite, a “transitional” zone dominated by copiapite + coquimbite and a “distal” zone of hydronium–jarosite. An additional zone of “gypsum” was also recognized locally at the areas, where, last decade the neutralization of the acid soils with limestones was attempted. In addition to discriminating distinct mineralogical zones quantitative spectral data allowed contoured mineral maps to be produced that are comparable with the estimated mineralogical data obtained from conventional methods, such as XRD and field observations. These maps demonstrate that sulphate minerals were firstly formed by oxidation of the pyrite-rich ores followed by dissolution and precipitation involving a combination of oxidation, dehydration, and neutralization reactions. The study shows the potential of SWIR spectral analysis to identify and understand the distribution of efflorescent salts and other products of pyrite decomposition and provides a methodology to assist the research and monitoring of sources of environmental contamination.

The Reocin Zn-Pb deposit, 30 km southwest of Santander, Spain, occurs within Lower Cretaceous dolomitized Urgonian limestones on the southern flank of the Santillana syncline. The Reocin deposit is one of the largest known strata-bound, carbonate-hosted, zinc-lead deposits in Europe. The total metal endowment of the deposit, including past production and remaining reserves, is 62 Mt of ore grading 8.7 percent Zn and 1.0 percent Pb. The epigenetic mineralization consists of sphalerite and galena, with lesser marcasite and trace pyrite with dolomite as gangue. Microprobe analyses of different generations of dolomite revealed nonstoichiometric compositions with various amounts of iron (up to 14 mol % of FeCO3). Replacement of host dolomite, open-space filling of fractures, and cementation of breccias derived from dissolution collapse are the principal types of ore occurrence. Detailed cross-section mapping indicates a stratigraphic and structural control on the deposit. A stratiform morphology is present in the western part of the orebody (Capa Sur), whereas mineralization in the eastern part is highly discordant but strata bound (Barrendera). Stratigraphic studies demonstrate that synsedimentary tectonic activity, related to the rifting of the North Atlantic (Bay of Biscay), was responsible for variation in sedimentation, presence of unconformities (including paleokarsts), local platform emergence and dolomitization along the N60 fault trend. In the Reocin area, two stages of dolomitization are recognized. The first stage is a pervasive dolomitization of the limestone country rocks that was controlled by faulting and locally affected the upper part of the Aptian and the complete Albian sequence. The second dolomitization event occurred after erosion and was controlled by karstic cavities. This later dolomitization was accompanied by ore deposition and, locally, filling of dolomite sands and clastic sediments in karstic cavities. The circulation of hydrothermal fluids responsible for sulfide deposition and the infilling of karst cavities were broadly contemporaneous, indicating a post-Albian age. Vitrinite reflectance data are consistent with previously measured fluid inclusion temperatures and indicate temperatures of ore deposition that were less than 100°C. Carbon and oxygen isotopic data from samples of regional limestone, host-rock dolostone and ore-stage dolomite suggest an early hydrothermal alteration of limestone to dolostone. This initial dolomitization was followed by a second period of dolomite formation produced by the mixing of basinal metal-rich fluids with local modified seawater. Both dolomitization events occurred under similar conditions from fluids exhibiting characteristics of basinal brines. The δ 34S values of sulfides are between –1.8 and +8.5 per mil, which is consistent with thermochemical sulfate reduction involving organic matter as the main source of reduced sulfur. Galena lead isotope compositions are among the most radiogenic values reported for Zn-Pb occurrences in Europe, and they are distinct from values reported for galena from other Basque-Cantabrian deposits. This suggests that a significant part of the lead was scavenged from the local underlying Asturian sediments. The stratigraphic and structural setting, timing of epigenetic mineralization, mineralogy, and isotopic geochemistry of sulfide and gangue minerals of the Reocin deposit are consistent with the features of most of Mississippi Valley-type ore deposits.

Xonotlite, ideally Ca6Si6O17(OH)2, occurs as a major phase in the leucocratic dyke complex that intruded the Ronda peridotites, near the village of Carratraca, Malaga, Spain. Xonotlite occurs as acicular grains in veins parallel to the dykes, as tabular grains along the reaction zone between the serpentinite host-rock and the leucocratic dykes, and as acicular grains replacing hydrogrossular in the matrix of the dykes. It is associated with albite, pectolite and hydrogrossular. Electron-microprobe analyses give a formula (Ca6.05)(Si5.96Al0.01)O17(OH)2 for the acicular and tabular xonotlite, and (Ca6.11)(Si5.92Al0.03)O17(OH)2 for xonotlite replacing hydrogrossular. X-ray powder-diffraction patterns of xonotlite show the presence of two polytypes: M2a2b2c and Ma2b2c. This unusual association (xonotlite, hydrogrossular, pectolite) was produced by the rodingitization of the leucocratic dykes during the serpentinization of the ultramafic massif at low-temperature conditions, 300° to 350°C; it was associated with the production of lizardite in the surrounding serpentinites.

We quantify the gas pressure and concentration of a gas-charged acidic pit lake investigated in SW Spain. We measured total dissolved gas pressure, CO2 concentration, major ion concentration, isotopic composition of dissolved inorganic carbon (13CDIC) and other physico-chemical parameters. Carbon dioxide (CO2) is the dominant dissolved gas in this lake and mainly results from carbonate dissolution during the interaction of acidic water with wall rocks, followed by diffusive and advective transport through the water column. The 13CDIC values suggest that the biological contribution is comparatively small. Maximum CO2 concentrations higher than 0.1 molar (~5,000 mg/L) have been measured, which are only comparable to those found in volcanic crater lakes. The corresponding gas pressures of CO2 alone (pCO2~3.6 bar) imply 60% saturation relative to local pressure at 50m depth. High CO2 concentrations have been observed in other pit lakes of the region. We recommend gas-specific monitoring in acidic pit lakes and, if necessary, the design of feasible degassing strategies. Language: en

The Cueva Mayor karst system of Atapuerca, in Northern Spain, hosts a highly significant record of human occupation from the Pleistocene. The climatic context of the human activities during the Pleistocene-Holocene for this inland site has not been well constrained, since existing records of the palaeoclimatic evolution of the Northern Iberian Peninsula are from more distal coastal and high-elevation sites. In this study, we interpret the palaeoenvironmental information recorded on the petrography of a stalagmite and the pollen spectra of the Sierra de Atapuerca karst system during the last 20 kyr. The integration of both types of records has allowed us to define four palaeoenvironmental stages. During the Upper Pleistocene and until 12.8 kyr BP, the climate was cold and dry, toward the end of the interval evolving to wetter and warmer conditions. From 12.8 to 7.7 kyr BP, during the Mesolithic-Neolithic, a major erosion event in both records marks the Pleistocene-Holocene transition. Around 5.9 kyr BP, the Late Neolithic, environmental conditions indicate a climatic optimum with a marked seasonality. The environmental conditions became drier from 4.2 kyr BP until the present, with a decrease in the woodlands. This aridity signal might be amplified by the impact of a more intense human agricultural activity after 3.1 kyr BP, during the Bronze Age.

Massive sulphide deposits of the northern Iberian Pyrite Belt (IPB) are mainly hosted by felsic volcanic rocks of rhyolitic to dacitic composition. Beneath most of the massive ores of this area (e.g., Concepcion, San Miguel, Aguas Tenidas Este or San Telmo deposits) there is usually a wide hydrothermal alteration halo associated with stockwork-type mineralization. Within these alteration envelopes there are two principal rock types: (1) chlorite-rich rocks, linked to the inner and more intensely altered zones and dominantly comprising chlorite+pyrite+quartz+sericite (+carbonate+rutile+zircon+chalcopyrite), and (2) sericite-rich rocks, more common in the peripheral zones and showing a dominant paragenesis of sericite+quartz+pyrite+chlorite (+carbonate+rutile+zircon+sphalerite). Mass-balance calculations comparing altered and least-altered felsic volcanic rocks suggest that sericitization was accompanied by moderate enrichment in Mg, Fe and H2O, with depletion in Si, Na and K, and a slight net mass loss of about 3%. Chloritization shows an overall pattern which is similar to that of the sericitic alteration, but with large gains in Fe, Mg and H2O (and minor enrichment in Si, S and Mn), and a significant loss of Na and K and a minor loss of Ca and Rb. However, chloritization has involved a much larger net mass change (mass gain of about 28%). Only a few elements such as Nb, Y, Zr, Ti, P and LREE appear to have remained inert during hydrothermal alteration, whilst Ti and Al have undergone very minor mobilization. The results point to the severity of the physico-chemical conditions that prevailed during the waxing stage of the ore-forming hydrothermal systems. Further, mineralogical and geochemical studies of the altered footwall rocks in the studied deposits indicate that hydrothermal ore-bearing fluids reacted with host rocks in a multi-stage process which produced a succession of mineralogical and chemical changes as the temperature increased.