Impact de la recristallisation et du métamorphisme sur la mobilité du germanium et éléments associés dans les minéralisations Pb-Zn orogéniques : exemple des minéralisations de la Zone Axiale des Pyrénées (France-Espagne)

Rare metals are essential to the development of the green technologies that are at the core of emerging low-carbon societies. Germanium is a rare element considered critical by the European Union and the U.S. Geological Survey due to its several uses in optical and electronics devices. Non-deformed sphalerite crystals (ZnS) commonly contain Ge and other critical elements (In, Ga) which may grade up to a few thousands of ppm. Only few studies have described specific minerals with Ge contents above wt.%, because these are apparently rare in Pb-Zn(-Cu) deposits. These Ge-minerals appear to be more abundant in deformed and metamorphosed Pb-Zn(-Cu) deposits. This raises the question of the impact of deformation and metamorphism on Ge and other rare metals mobility. This type of orogenic deposits constitutes the largest known zinc concentrations on Earth and their potential for rare metal is yet to be assessed.The Pb-Zn deposits in the Pyrenean Axial Zone are an ideal target to study the impact of deformation and metamorphism on rare metals mobility as sphalerite is only locally recrystallized. A structural field study allows to discriminate four Pb-Zn mineralization types. Type 1 is a minor syngenetic and stratiform disseminated mineralization. Type 2a is an epigenetic stratabound mineralization, concordant to the S1 Variscan foliation. Type 2b ore are parallel to the S2 cleavage. Sphalerite ore is highly deformed by a late cleavage sub-parallel to S2 probably Pyrenean-Alpine in age. Fluid inclusions study shows the presence of two Type 2b fluids with a low salinity (<20 wt.% NaCl eq.) and high temperatures (200-350 °C) typical of Late-Variscan fluids whereas Mesozoic Type 2b ore exhibits high salinity (15-35 wt.% NaCl eq.) and low temperature (< 200 °C).Germanium and related elements such as Cu, In and Ga are present in the deformed Pyrenean vein mineralizations and are heterogeneously distributed. Electron Backscattered diffraction (EBSD) analyses and chemical investigations allow to define distinct sphalerite textures with specific chemical contents: i) Dark-brown patchy or stripped zonations in coarse parent grains exhibit high Ge-content (up to 600 ppm Ge) in the lattice. ii) Light-brown zonations in coarse parent grains contain low Ge-contents mostly below 100 ppm Ge. iii) Light-brown small recrystallized daughter grains (below ~ 100 µm) present systematically low to very low Ge-contents (~ 20 ppm Ge). Copper contents (up to 1265 ppm) are highly correlated to Ge in sphalerite and Ga only occur in coarse sphalerite crystals (below ~100 ppm). Ge-minerals, such as brunogeierite, carboirite, briartite and argutite (up to ~ 70 wt. % Ge) are mainly hosted in recrystallized sphalerite domains or close to twin boundaries in coarse grains. These observations demonstrate that recrystallization of sphalerite has led to the redistribution of Ge from the sphalerite lattice into Ge-minerals. We suggest that the interactions between intra-granular diffusion and fluid assisted processes are responsible for the formation of patchy-stripped zonations and the crystallization of Ge-oxides, sulfides or chloritoids. A large variability of sphalerite chemistry and texture is frequently reported from other orogenic world-class deposits: these may have been affected by similar recrystallization and redistribution processes. The redistribution of rare metals in sulfide environments must have induced the concentration of rare metal in accessory minerals. These tiny minerals may be missed by punctual chemical analyses without prior detailed textural investigation. Understanding how rare metals concentrate through metamorphism and syntectonic recrystallization at mineral scale is essential to emphasize their spatial redistribution and localization at deposit scale. This study highlights the importance of coupling in situ and mapping chemical analyzes with macro- and microtextural characterization when targeting rare metals in deformed ore.Les métaux rares sont essentiels au développement des technologies vertes qui sont maintenant au cœur de nos sociétés. Le germanium est un élément rare considéré critique par l’Union Européenne et l’US Geological Survey, du fait de ses nombreux usages dans l’industrie de l’optique et de l’électronique. Les cristaux non déformés de sphalérite (ZnS) sont souvent porteurs de Ge et d’autres métaux rares (In, Ga) avec des concentrations pouvant atteindre quelques milliers de ppm. Seulement peu d’études décrivent des minéraux avec des concentrations en Ge au-dessus du % poids, du fait de leur apparente rareté dans les gisements Pb-Zn(-Cu). En fait, ces minéraux à Ge semblent plus fréquents dans les gisements Pb-Zn(-Cu) déformés ou métamorphisés ce qui soulève la question de l’impact de la déformation et du métamorphisme sur la mobilité du Ge et d’autres métaux rares. Ce type de gites contiennent les plus grandes ressources de zinc sur Terre and actuellement leur potentiel en métaux rares reste à évaluer.Les gites Pb-Zn de la Zone Axiale des Pyrénées sont une cible idéale pour étudier l’impact de la déformation et du métamorphisme sur la mobilité des métaux rares car la sphalérite est seulement localement recristallisée. Une étude structurale de terrain a permis de discriminer quatre types de minéralisations Pb-Zn. La minéralisation Type 1 est disséminée, syngénétique et stratiforme. La minéralisation Type 2a est épigénétique et stratabound. Les minéralisations Type 2b tardi-Varisque et Mésozoïque sont parallèles à la schistosité S2. La sphalérite est largement déformée par une schistosité tardive, probablement Pyrénéenne (Sp). Le fluide tardi-Varisque présente de faible salinité (<20 %poids eq. NaCl) avec de relative haute temperature (200-350 °C) tandis que le fluide Mésozoïque contient de forte salinité (15-35 %poids eq. NaCl) et de faible température (< 200 °C). Le germanium est distribué de manière très hétérogène dans les minéralisations en veines. Des analyses texturales (EBSD) et chimiques (EPMA, LA-ICPMS, cartographie LIBS) permettent de définir différents domaines dans la sphalérite : i) des zonations marron sombres en patches ou rayées dans les gros grains parents présentent des concentrations en Ge élevées dans la maille cristallographique (jusqu’à 600 ppmGe). ii) des zonations marron claires dans les gros grains parents contiennent des concentrations en Ge faibles, le plus souvent en-dessous de 100 ppmGe. iii) des petits grains clairs recristallisés (en dessous de ~100 µm) presentent de très faibles concentrations en Ge (~20 ppm Ge). Les concentrations en Cu sont corrélées à celles du Ge tandis que le Ga est zoné que dans les gros grains. Les minéraux à Ge, comme la brunogéiérite, la carboirite, la briartite et l’argutite (jusqu’à ~70 %poids Ge) occurent dans les domaines de sphalérite recristallisée ou plus rarement proche des limites maclées dans les gros grains. Ces observations démontrent que la recristallisation de la sphalérite a permis la redistribution du Ge depuis la maille de la sphalérite jusqu’à la formation des minéraux à Ge. Nous suggérons que les intéractions entre des fluides et la diffusion intra-granulaire sont responsable de la redistribution du Ge. Des hétérogénéités chimiques et texturales sont fréquemment reportées dans d’autres gisements et ont pu être affectés par des processus similaires de redistributions dans des minéraux accessoires. Ces petits minéraux peuvents avoir été manqués par des analyses chimiques ponctuelles sans contrôle textural préalable. Comprendre comment les métaux rares se concentrent à travers la déformation et la recristallisation syn-tectonique à l’échelle du minéral est essentiel pour surligner leur localisation à l’échelle du gisement. Cette étude met en évidence l’importance de coupler les analyses chimiques in-situ et cartographiques avec la caractérisation macro- et micro texturale lors de l’exploration des métaux rares dans des minérais déformés

Impact of recrystallization and metamorphism on the mobility of germanium and related elements in orogenic Pb-Zn deposits : example of the Pyrenean Axial Zone mineralizations (France-Spain)

Les métaux rares sont essentiels au développement des technologies vertes qui sont maintenant au cœur de nos sociétés. Le germanium est un élément rare considéré critique par l’Union Européenne et l’US Geological Survey, du fait de ses nombreux usages dans l’industrie de l’optique et de l’électronique. Les cristaux non déformés de sphalérite (ZnS) sont souvent porteurs de Ge et d’autres métaux rares (In, Ga) avec des concentrations pouvant atteindre quelques milliers de ppm. Seulement peu d’études décrivent des minéraux avec des concentrations en Ge au-dessus du % poids, du fait de leur apparente rareté dans les gisements Pb-Zn(-Cu). En fait, ces minéraux à Ge semblent plus fréquents dans les gisements Pb-Zn(-Cu) déformés ou métamorphisés ce qui soulève la question de l’impact de la déformation et du métamorphisme sur la mobilité du Ge et d’autres métaux rares. Ce type de gites contiennent les plus grandes ressources de zinc sur Terre and actuellement leur potentiel en métaux rares reste à évaluer.Les gites Pb-Zn de la Zone Axiale des Pyrénées sont une cible idéale pour étudier l’impact de la déformation et du métamorphisme sur la mobilité des métaux rares car la sphalérite est seulement localement recristallisée. Une étude structurale de terrain a permis de discriminer quatre types de minéralisations Pb-Zn. La minéralisation Type 1 est disséminée, syngénétique et stratiforme. La minéralisation Type 2a est épigénétique et stratabound. Les minéralisations Type 2b tardi-Varisque et Mésozoïque sont parallèles à la schistosité S2. La sphalérite est largement déformée par une schistosité tardive, probablement Pyrénéenne (Sp). Le fluide tardi-Varisque présente de faible salinité (<20 %poids eq. NaCl) avec de relative haute temperature (200-350 °C) tandis que le fluide Mésozoïque contient de forte salinité (15-35 %poids eq. NaCl) et de faible température (< 200 °C). Le germanium est distribué de manière très hétérogène dans les minéralisations en veines. Des analyses texturales (EBSD) et chimiques (EPMA, LA-ICPMS, cartographie LIBS) permettent de définir différents domaines dans la sphalérite : i) des zonations marron sombres en patches ou rayées dans les gros grains parents présentent des concentrations en Ge élevées dans la maille cristallographique (jusqu’à 600 ppmGe). ii) des zonations marron claires dans les gros grains parents contiennent des concentrations en Ge faibles, le plus souvent en-dessous de 100 ppmGe. iii) des petits grains clairs recristallisés (en dessous de ~100 µm) presentent de très faibles concentrations en Ge (~20 ppm Ge). Les concentrations en Cu sont corrélées à celles du Ge tandis que le Ga est zoné que dans les gros grains. Les minéraux à Ge, comme la brunogéiérite, la carboirite, la briartite et l’argutite (jusqu’à ~70 %poids Ge) occurent dans les domaines de sphalérite recristallisée ou plus rarement proche des limites maclées dans les gros grains. Ces observations démontrent que la recristallisation de la sphalérite a permis la redistribution du Ge depuis la maille de la sphalérite jusqu’à la formation des minéraux à Ge. Nous suggérons que les intéractions entre des fluides et la diffusion intra-granulaire sont responsable de la redistribution du Ge. Des hétérogénéités chimiques et texturales sont fréquemment reportées dans d’autres gisements et ont pu être affectés par des processus similaires de redistributions dans des minéraux accessoires. Ces petits minéraux peuvents avoir été manqués par des analyses chimiques ponctuelles sans contrôle textural préalable. Comprendre comment les métaux rares se concentrent à travers la déformation et la recristallisation syn-tectonique à l’échelle du minéral est essentiel pour surligner leur localisation à l’échelle du gisement. Cette étude met en évidence l’importance de coupler les analyses chimiques in-situ et cartographiques avec la caractérisation macro- et micro texturale lors de l’exploration des métaux rares dans des minérais déformés.Rare metals are essential to the development of the green technologies that are at the core of emerging low-carbon societies. Germanium is a rare element considered critical by the European Union and the U.S. Geological Survey due to its several uses in optical and electronics devices. Non-deformed sphalerite crystals (ZnS) commonly contain Ge and other critical elements (In, Ga) which may grade up to a few thousands of ppm. Only few studies have described specific minerals with Ge contents above wt.%, because these are apparently rare in Pb-Zn(-Cu) deposits. These Ge-minerals appear to be more abundant in deformed and metamorphosed Pb-Zn(-Cu) deposits. This raises the question of the impact of deformation and metamorphism on Ge and other rare metals mobility. This type of orogenic deposits constitutes the largest known zinc concentrations on Earth and their potential for rare metal is yet to be assessed.The Pb-Zn deposits in the Pyrenean Axial Zone are an ideal target to study the impact of deformation and metamorphism on rare metals mobility as sphalerite is only locally recrystallized. A structural field study allows to discriminate four Pb-Zn mineralization types. Type 1 is a minor syngenetic and stratiform disseminated mineralization. Type 2a is an epigenetic stratabound mineralization, concordant to the S1 Variscan foliation. Type 2b ore are parallel to the S2 cleavage. Sphalerite ore is highly deformed by a late cleavage sub-parallel to S2 probably Pyrenean-Alpine in age. Fluid inclusions study shows the presence of two Type 2b fluids with a low salinity (<20 wt.% NaCl eq.) and high temperatures (200-350 °C) typical of Late-Variscan fluids whereas Mesozoic Type 2b ore exhibits high salinity (15-35 wt.% NaCl eq.) and low temperature (< 200 °C).Germanium and related elements such as Cu, In and Ga are present in the deformed Pyrenean vein mineralizations and are heterogeneously distributed. Electron Backscattered diffraction (EBSD) analyses and chemical investigations allow to define distinct sphalerite textures with specific chemical contents: i) Dark-brown patchy or stripped zonations in coarse parent grains exhibit high Ge-content (up to 600 ppm Ge) in the lattice. ii) Light-brown zonations in coarse parent grains contain low Ge-contents mostly below 100 ppm Ge. iii) Light-brown small recrystallized daughter grains (below ~ 100 µm) present systematically low to very low Ge-contents (~ 20 ppm Ge). Copper contents (up to 1265 ppm) are highly correlated to Ge in sphalerite and Ga only occur in coarse sphalerite crystals (below ~100 ppm). Ge-minerals, such as brunogeierite, carboirite, briartite and argutite (up to ~ 70 wt. % Ge) are mainly hosted in recrystallized sphalerite domains or close to twin boundaries in coarse grains. These observations demonstrate that recrystallization of sphalerite has led to the redistribution of Ge from the sphalerite lattice into Ge-minerals. We suggest that the interactions between intra-granular diffusion and fluid assisted processes are responsible for the formation of patchy-stripped zonations and the crystallization of Ge-oxides, sulfides or chloritoids. A large variability of sphalerite chemistry and texture is frequently reported from other orogenic world-class deposits: these may have been affected by similar recrystallization and redistribution processes. The redistribution of rare metals in sulfide environments must have induced the concentration of rare metal in accessory minerals. These tiny minerals may be missed by punctual chemical analyses without prior detailed textural investigation. Understanding how rare metals concentrate through metamorphism and syntectonic recrystallization at mineral scale is essential to emphasize their spatial redistribution and localization at deposit scale. This study highlights the importance of coupling in situ and mapping chemical analyzes with macro- and microtextural characterization when targeting rare metals in deformed ore

Investigating raindrop size distributions in the (L-)skewness–(L-)kurtosis plane

Skewness–kurtosis (β3−β4) and L-skewness–L-kurtosis (τ3−τ4) planes are proposed here as diagnostic tools to guide the identification of drop size distributions (DSDs) of rainfall at the ground. Firstly, we have determined β3−β4 and τ3−τ4 domains of 13 distribution families, namely normal, exponential, gamma, truncated gamma, log-normal, truncated log-normal, Weibull, hyperbolic, generalized hyperbolic, log-logistic, skewed Laplace, Johnson SB and Johnson SU. These include those most used to represent DSDs and, in general, particle size distributions (PSDs). Secondly, we have considered 1 min and 2 min disdrometric data, collected at six sites in the United States, and reported the empirical couples (β3,β4) and (τ3,τ4) in the moment diagrams. The location uncertainty of the empirical couples in the diagrams, mostly due to the occurrence of sampling errors, has been thoroughly investigated. The variability of the empirical DSD couples (β3,β4) and (τ3,τ4) is well described by truncated gamma, truncated log-normal and Johnson SB over the other considered distributions. However, a Monte Carlo analysis has shown that the Johnson SB is the most adequate distribution in describing the drop size variability, being characterized by the lowest level of uncertainty

Structure et texture des minéralisations Pb-Zn dans la zone axiale des Pyrénées

International audienceCette étude donne un nouvel aperçu des minéralisations à métaux de base pouvant contenir des concentrations en métaux critiques comme le germanium associé à la sphalérite, dans la Zone Axiale des Pyrénées. La caractérisation de ces minéralisations se compose d’une analyse de données de terrains ainsi que d’une comparaison texturale et chimique des deux types majeurs de sphalérite

Aerosol removal due to precipitation and wind forcings in Milan urban area

Air pollution represents a critical issue in Milan urban area (Northern Italy). Here, the levels of fine particles increase, overcoming the legal limits, mostly in wintertime, due to favourable calm weather conditions and large heating and vehicular traffic emissions. The main goal of this work is to quantify the aerosol removal effect due to precipitation at the ground. At first, the scavenging coefficients have been calculated for aerosol particles with diameter between 0.25 and 3 μm. The average values of this coefficient vary between 2×10-5 and 5×10-5 s−1. Then, the aerosol removal induced separately by precipitation and wind have been compared through the introduction of a removal index. As a matter of fact, while precipitation leads to a proper wet scavenging of the particles from the atmosphere, high wind speeds cause enhanced particle dispersion and dilution, that locally bring to a tangible decrease of aerosol particles’ number. The removal triggered by these two forcings showed comparable average values, but different trends. The removal efficiency of precipitation lightly increases with the increase of particle diameters and vice versa happens with strong winds

Diagnosis and correction methods for spectral interference in the framework of LIBS imaging

International audienceLaser-Induced Breakdown Spectroscopy (LIBS) has become a powerful imaging technique for elemental characterization in analytical chemistry due to its advantages over other techniques. Major, minor, and trace elements are detected with high measurement dynamic, a low limit of detection and a high acquisition rate, allowing for the quick analysis of large sample surfaces. Today, chemometric tools are commonly used to ensure the most comprehensive and unbiased exploration of such spectroscopic data. However, the integration of the signal from a wavelength assumed to be specific to the element of interest remains the basic tool for generating a chemical distribution map from a hyperspectral dataset. This classical approach is based on a strong assumption, the specificity of the chemical information on the spectral domain being considered. Any spectral interference inevitably result in the generation of a biased distribution image. In this publication, we demonstrate how Principal Component Analysis (PCA) can diagnose the potential presence of a spectral interference and how Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) can ultimately correct it if necessary using a LIBS imaging dataset obtained from the analysis of a complex rock sample. The proposed approach combines the simplicity and effectiveness of the integration method with the diagnostic and correction capabilities of chemometric tools, providing a comprehensive solution for spectral interference in LIBS imaging

On the functional form of particle number size distributions: Influence of particle source and meteorological variables

Particle number size distributions (PNSDs) have been collected periodically in the urban area of Milan, Italy, during 2011 and 2012 in winter and summer months. Moreover, comparable PNSD measurements were carried out in the rural mountain site of Oga-San Colombano (2250ma.s.l.), Italy, during February 2005 and August 2011. The aerosol data have been measured through the use of optical particle counters in the size range 0.3-25 μm, with a time resolution of 1 min. The comparison of the PNSDs collected in the two sites has been done in terms of total number concentration, showing higher numbers in Milan (often exceeding 103 cm-3 in winter season) compared to Oga-San Colombano (not greater than 2×102 cm-3), as expected. The skewness-kurtosis plane has been used in order to provide a synoptic view, and select the best distribution family describing the empirical PNSD pattern. The four-parameter Johnson system-bounded distribution (called Johnson SB or JSB) has been tested for this aim, due to its great flexibility and ability to assume different shapes. The PNSD pattern has been found to be generally invariant under site and season changes. Nevertheless, several PNSDs belonging to the Milan winter season (generally more than 30 %) clearly deviate from the standard empirical pattern. The seasonal increase in the concentration of primary aerosols due to combustion processes in winter and the influence of weather variables throughout the year, such as precipitation and wind speed, could be considered plausible explanations of PNSD dynamics

Germanium-rich nanoparticles in Cu-poor sphalerite: A new mechanism for Ge enrichment

Germanium (Ge) is a critical raw material used in high-technology industry (i.e., optical industry) applications, and it is predominantly concentrated in coals and Zn-rich deposits. Previous studies on Zn-rich deposits have documented a correlation between Ge enrichment and the Cu, Ag, and/or Pb-Mn contents in the sphalerite crystal lattice. In this study, we observed Ge-rich nanoparticles hosted in Cu-poor sphalerite from the Banbianjie Zn-Ge deposit (&amp;gt;800 t graded at ∼100 ppm Ge), located in southwest China. Laser-ablation−inductively coupled plasma−mass spectroscopy (LA-ICP-MS) analyses revealed that sphalerite contains very heterogeneous Ge contents (172−1553 ppm). Germanium contents showed positive correlations with Fe, Mn, and Pb contents and negative correlations with Cd contents. Higher Ge contents were detected in the darker zones, whereas the lighter zones showed systematically low Ge contents and were enriched in Cd. Using transmission electron microscopy (TEM), Zn-Ge-Pb-S nanoparticles were identified in the darker zones of sphalerite. These nanoparticles exhibited Ge/Pb ratios (0.48−1.96) very similar to those measured in sphalerite (0.36−2.04), suggesting that Ge could be essentially hosted within the nanoparticles. We propose that the amounts of Zn-Ge-Pb-S nanoparticles are related to a self-organization model induced by rapid crystal growth. This self-organization processes may control the fluctuations of element concentrations in the boundary layer. This study highlights the importance of studying the nanoscale expression of critical elements to understand their incorporation mechanisms into natural materials.</p

Nanoscale distribution of Ge in Cu-rich sphalerite

A large proportion of the critical elements resources Ge, Ga, and In are associated with sphalerite in Pb-Zn ore deposits. Germanium in sphalerite has been proposed to be structurally bound in the crystal lattice. Using a combination of microstructural, geochemical and nanoscale observations, we show that Ge can be hosted in sphalerite crystal structure as well as nanoparticles of briartite (Cu2(Zn,Fe)GeS4). The structurally-bound Ge was preserved in undeformed sphalerite grains from the Saint-Salvy Pb-Zn vein deposit (France), whereas the briartite nanoparticles were observed in metamorphosed sphalerite from Arre. The briartite nanoparticles likely exsolved from sphalerite during the Pyrenean-Alpine metamorphism and deformation. The presence of nanoparticles may harden the sphalerite during crystalplastic deformation and help to preserve the critical elements resources of Pb-Zn deposits during metamorphism.</p