Rare earth elements, iron and manganese in ochre-precipitates and wetland soils of a passive treatment system for acid mine drainage

The rare earth elements (REE) along with iron and manganese distribution in ochre-precipitates and wetland soils in a passive system for acid mine drainage treatment (Jales, Portugal) was studied. The results obtained by instrumental neutron activation analysis showed a higher incorporation of the light REE (particularly La and Ce) by the ochre-precipitates resulting from the mine water-limestone interaction. These fluffy materials influence the entrance of the first wetland where a correlation between Fe and La and Ce was found. Then Mn phases appear to play a more important role controlling REE distribution in the remaining area of the wetland soils.Thanks to EDM (Empresa de Desenvolvimento Mineiro, S.A.) for providing access to the water treatment plant, and to the staff of the Portuguese Research Reactor (RPI) of CTN/IST. C2TN authors gratefully acknowledge the FCT (the Portuguese Science and Technology Foundation) support through the UID/Multi/04349/2013. This work is co-funded by European Union through the European Regional Development Fund, based on COMPETE 2020 (Programa Operacional da Competitividade e Internacionalização), project ICT (UID/GEO/04683/2013) with reference POCI-01-0145-FEDER-007690 and national funds provided by FCT.info:eu-repo/semantics/publishedVersio

Post-depositional processes of elemental enrichment inside dark nodular masses of an ancient aeolian dune from A Coruña, Northwest Spain

This paper focuses on a residual ancient aeolian climbing dune from Punta Penaboa (A Coruña, Northwest Spain) showing evidence of post-depositional weathering, particularly the presence of dark brown nodular masses. The partitioning of trace elements between nodular masses and host sand during post-depositional weathering of the dune is investigated in this work, with the main objective of studying the elemental enrichment patterns in the dark masses. Data of the concentrations of chemical elements were obtained by instrumental neutron activation analysis (INAA) and complemented by mineralogical and microchemical studies, using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) / energy dispersive X-ray spectrometry (EDS). The dune was dated by optically stimulated luminescence (OSL) , yielding an age of 300ka B.P.. The dark nodular masses preserved the dune sand structure, without defined concentric layers, suggesting an early stage of formation. They consist mainly of quartz grains cemented by clay materials enriched in the majority of the elements studied, especially in Mn, Co, Ba, Sb, Ce, Tb, Th, As, Zr and Hf. The post-depositional transformations of the dune were most likely influenced by migration of chemical compounds from the surrounding slope deposits and granitic rocks, as well as microbial activity that promoted metals concentration in the solutions percolating through the pore network of the dune. Seasonal changes in the redox potential were required to produce the accumulation of Mn and other trace elements in the dune pore network and to promote the fractionation between Ce4+ and trivalent rare earth elements that was observed in the geochemical patterns

Typology of the granitic stones of the cathedral of Evora (Portugal): A combined contribution of geochemistry and Fe-57 Mossbauer spectroscopy

International audienceA geochemical study, including a detailed investigation of Fe by Mössbauer spectroscopy, was undertaken to characterise the different varieties of the stones in the cathedral of Évora (Portugal). Ten representative stone samples were collected. Bulk analytical techniques, including ICPES, INAA and XRF, were performed, as well as Mössbauer spectroscopy. The stones have consistent linear geochemical variations, well constrained by a limited number of inter-element ratios involving Ti, Mg, Fe and Al. Taking into account the REE distribution, the Mg, Fe and Ti contents and the Fe3+/Fe2+ ratio, two types of stones were distinguished. The type-1 stones show REE normalised patterns with negative Eu anomaly, and are relatively Al rich. The type-2 stones without Eu anomaly, more REE fractionated, are relatively LREE, TiO2, MgO and Fe2O3 rich. In agreement with the geochemical results, the Mössbauer data have shown that the Fe3+/Fe2+ ratio was correlated with the magmatic differentiation and further suggested that the presence of Fe (Ti) oxides is related to a higher magmatic evolution. Both stone types have a MgO/TiO2 ratio close to 2, which is characteristic of calco-alcaline granite. The chemical inter-element variation along the same constant ratio, as well as the REE pattern and the Fe oxidation state, seems to indicate a magmatic filiation from type-2 to type-1 stones. The combination of REE patterns and Fe/Mg, Ti/Mg and Fe3+/Fe2+ geochemical indexes could be used as efficient discrimination tools for other stones of monuments built of granite

Heated flint TL-dating for Gruta da Oliveira (Portugal): dosimetric challenges and comparison of chronometric data

The Mousterian stratigraphy of Gruta da Oliveira (Torres Novas, Portugal) contains one of the latest occupations by Neanderthals on the Iberian Peninsula. Thermoluminescence (TL) dates on heated flints were obtained for layers 13 and 14, and compared with the radiocarbon (charcoal and burnt bone) and U/ Th (secondary carbonates) dating results available for those layers and the succession as a whole. As the internal dose rates are very low, the TL age estimates are very dependent on the external dose rates, which show significant variation, including indications of spatial patterning. Through close inspection of the radiation geometries of samples and dosemeters, the appropriate gamma dosimetry is identified and the weighted mean TL ages (1-s) calculated accordingly are 55 7 ka for layer 13 and 77 8 ka for layer 14. These ages are stratigraphically consistent with the radiocarbon chronology for layers 9e11 and with the termini ante and post quem provided by U-series dating for the beginning and end of the accumulation of the deposits. The TL results corroborate that all radiocarbon dates below layer 11 are minimum ages only and, given the constraints derived from the proxy data available, place layer 13 and 14 post MIS 5. Sample as well as dosemeter numbers are low at Gruta da Oliveira, which limits the precision of TLdating of a prehistoric human activity. Further refinement of the chronostratigraphy will be based on Useries dating of non-human-related, interstratified secondary carbonates.info:eu-repo/semantics/publishedVersio

Post-depositional processes of elemental enrichment inside dark nodular masses of an ancient aeolian dune from A Coruña, Northwest Spain

This paper focuses on a residual ancient aeolian climbing dune from Punta Penaboa (A Coruña, Northwest Spain) showing evidence of post-depositional weathering, particularly the presence of dark brown nodular masses. The partitioning of trace elements between nodular masses and host sand during post-depositional weathering of the dune is investigated in this work, with the main objective of studying the elemental enrichment patterns in the dark masses. Data of the concentrations of chemical elements were obtained by instrumental neutron activation analysis (INAA) and complemented by mineralogical and microchemical studies, using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) / energy dispersive X-ray spectrometry (EDS). The dune was dated by optically stimulated luminescence (OSL) , yielding an age of 300ka B.P.. The dark nodular masses preserved the dune sand structure, without defined concentric layers, suggesting an early stage of formation. They consist mainly of quartz grains cemented by clay materials enriched in the majority of the elements studied, especially in Mn, Co, Ba, Sb, Ce, Tb, Th, As, Zr and Hf. The post-depositional transformations of the dune were most likely influenced by migration of chemical compounds from the surrounding slope deposits and granitic rocks, as well as microbial activity that promoted metals concentration in the solutions percolating through the pore network of the dune. Seasonal changes in the redox potential were required to produce the accumulation of Mn and other trace elements in the dune pore network and to promote the fractionation between Ce4+ and trivalent rare earth elements that was observed in the geochemical patterns

Post-depositional processes of elemental enrichment inside dark nodular masses of an ancient aeolian dune from A Coruña, Northwest Spain

This paper focuses on a residual ancient aeolian climbing dune from Punta Penaboa (A Coruña, Northwest Spain) showing evidence of post-depositional weathering, particularly the presence of dark brown nodular masses. The partitioning of trace elements between nodular masses and host sand during post-depositional weathering of the dune is investigated in this work, with the main objective of studying the elemental enrichment patterns in the dark masses. Data of the concentrations of chemical elements were obtained by instrumental neutron activation analysis (INAA) and complemented by mineralogical and microchemical studies, using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) / energy dispersive X-ray spectrometry (EDS). The dune was dated by optically stimulated luminescence (OSL) , yielding an age of 300ka B.P.. The dark nodular masses preserved the dune sand structure, without defined concentric layers, suggesting an early stage of formation. They consist mainly of quartz grains cemented by clay materials enriched in the majority of the elements studied, especially in Mn, Co, Ba, Sb, Ce, Tb, Th, As, Zr and Hf. The post-depositional transformations of the dune were most likely influenced by migration of chemical compounds from the surrounding slope deposits and granitic rocks, as well as microbial activity that promoted metals concentration in the solutions percolating through the pore network of the dune. Seasonal changes in the redox potential were required to produce the accumulation of Mn and other trace elements in the dune pore network and to promote the fractionation between Ce4+ and trivalent rare earth elements that was observed in the geochemical patterns

Soils in the semi-arid area of the El Melah Lagoon (NE Tunisia) -- Variability associated with a closing evolution

International audienceSoils of the semi-arid area of the El Melah coastal lagoon (NE Tunisia), with a closing evolution dynamic, were studied aiming: (1) the chemical and mineralogical characterization of surface and subsurface layers of soil profiles from locations previously submerged and of soils developed on dunes; (2) to evaluate the dependence on the environment conditions of the geochemical patterns of the soils; and (3) to determine chemical and mineralogical variations with the emersion of the sediments resulting from the decrease in the extent of the area permanently covered by water in the lagoon. The compositional results obtained showed significant differences depending on the environment (littoral plain, old dunes and sandy spit), but soils of the different environmental zones studied do not appear to be significantly polluted as far as trace elements are concerned. Among the elements studied, high element/Sc ratios and variations were found for As, Sb and Zn. Antimony is more concentrated in coarser samples suggesting its adsorption in Fe or Mn oxides coating quartz grain surfaces. Arsenic and zinc may be incorporated into the carbonates structure, as well as adsorbed on, or coprecipitated with, iron oxides. Zinc may also be significantly incorporated in clay minerals. Iron was found to be more oxidized in the cultivated soil from the old dune strand; and more reduced in the sandy spit where ankerite occurs suggesting the reduction of Fe3+ in oxide/hydroxides by microorganisms and incorporation of Fe2+ in carbonates. REE patterns, particularly the HREE/LREE are correlated with carbonates, indicating preferential incorporation of the HREE in carbonates, and of the LREE in clay minerals/ iron oxides. High Ga contents were found in soils and sediments rich in clay minerals/Al, suggesting its incorporation in clay minerals structure. Therefore, Ga may be used as an indicator of the clay minerals proportion in sediments and soils. Carbonates, sulphates, besides Fe and/or Mn oxides and clay minerals, appear to play an important role on the trace elements distribution