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The early Cambrian Takab iron ore deposit is situated in the northern part of the Sanandaj-Sirjan zone, western Iran. It consists of banded, nodular and disseminated magnetite hosted in folded micaschists. Trace element and Fe and O isotopic experiments reveal various hydrothermal precipitation environments under reduced to slightly oxidizing conditions. Disseminated magnetite has high Ti (945–1940 ppm) positively correlated with Mg + Al + Si, and heavy Fe (+0.76 to +1.86‰) and O (+1.0 to +4.07‰) isotopic compositions that support a magmatic/high-T hydrothermal origin. Banded magnetite has low Ti (15−200 ppm), V (≤100 ppm), Si and Mg (mostly ≤300 ppm) and variable Al. The ∂56Fe values vary from −0.2‰ to +1.12‰ but most values also support a magmatic/high-T hydrothermal origin. However, variable ∂18O (−2.52 to +1.22‰) values provide evidence of re-equilibration with lower-T fluid at ~200–300 °C. Nodular magnetite shows high Mn (≤1%), and mostly negative ∂56Fe values (average, −0.3‰) indicative of precipitation from an isotopically light hydrothermal fluid. Re-equilibration with carbonated rocks/fluids likely results in a negative Ce anomaly and higher ∂18O (average, +6.30‰). The Takab iron ore deposit has, thus, experienced a complex hydrothermal history.

Iron ore deposits from Iran are spatially related to the main suture zones of the Iranian continental fragmented block. In western Iran, the Sanandaj-Sirjan structural zone (SSZ) hosts several iron ore deposits interpreted being of volcano sedimentary, hydrothermal or mixed volcano sedimentary-skarn origin. In the northern part of the SSZ the early Cambrian (~530 Ma) Takab iron ore deposit consists of disseminated, layered and nodular magnetite mainly hosted in folded micaschists, and also in calcschists or metavolcanics. Quartz may show grain boundary migration and feldspar is partly altered. Accessory minerals are Mn-Ba-oxides, barite, monazite ± uraninite and Mn-carbonate (in calschists) in the matrix or in cross-cutting veins.The low concentrations of Cr (1in disseminated (1.2) and nodular magnetite (2.2), but

International audience; We investigate the mechanical characterisation of mortars incorporating ferronickel slags (FNS) as partial substitution for cement. The studied slags come from the ferronickel production in New Caledonia. The microstructural characterisation shows that these slags are polycrystalline heterogeneous material mainly composed of forsterite, quartz and enstatite in addition to silica glass. Cement is replaced by up to 20 wt.% of ferronickel slags in the mortars. This upper level of substitution is achieved without compromising mortar's strengths. For all mixes, the maximum compressive and flexural strengths at all curing ages is obtained with a 5 wt.% replacement of cement by ferronickel slags. The larger effectiveness of FNS is attributed to its larger silica content, which increases the polymerisation degree of the silica chains in the calcium silicate hydrate (C-S-H) structure. Slag recycling reduces the storage time, waste management and environmental impact. It significantly lowers costs related to metallurgical processing. Slag substitution for cement, also lowers the carbon footprint.

International audience; X-ray transmission (XRT) and computed tomography (CT) was used on five samples from the Niaz porphyry Cu–Mo deposit in Iran, representing different alteration zones. Analysis of three-dimensional CT data revealed structural information and groups of elements with low, medium and high attenuation, which were assigned to minerals previously determined by scanning electron microscopy. Thus, the mineralization can be located, and the metal/waste ratio can be estimated, leading to more precise ore body modelling and process parameter determination. CT is useful for selected samples as it is time consuming. XRT can be used as real-time process on conveyor belts.

International audience; Here, we report the first occurrence so far of cubic diamond and lonsdaleite in a siliceous breccia hosted in nickel laterite from the Tiébaghi mine, New Caledonia. Diamond and lonsdaleite polytype occurred as minerals in surficial formed siliceous rocks. The vibrational properties and the calculated elastic properties and electronic band structure of 3C-diamond and lonsdaleite were studied by micro-Raman spectroscopy and ab initio calculation. Our measured Raman spectra demonstrate the coexistence of cubic diamond and lonsdaleite based on the correlation between ab initio calculation and experimental results. We showed that the position of the single Raman vibration mode for cubic diamond corresponds to the first order scattering of F2g symmetry at 1332 cm−1. For lonsdaleite, the ab initio calculations predict three fundamental vibrational modes: 1207 cm−1 (E2g), 1307 cm−1 (A1g), and 1330 cm−1 (E1g). The calculated indirect bandgaps of 3C-diamond and lonsdaleite at room temperature are 5.7 eV and 5.2 eV, respectively. The elastic anisotropy calculations show that lonsdaleite has the greatest shear modulus, bulk modulus and young’s modulus compared to cubic diamond, which indicates a high degree of hardness of this hexagonal structure of diamond.

International audience; Cold, binder-free tableting experiments under controlled pressure (0-450 MPa), water addition (0-10 wt.%) and pH (4, 11) were performed on powder of pyrolusite ore concentrates, refined hausmannite, bentonite, kaolinite, as well as blends of those materials. It has been shown that increased pressure was beneficial for agglomeration of oxide materials, but pressure > 250 MPa triggered an elastic recovery in the clay minerals. Water addition up to 4 wt.% improved tabletability, increasing diametral resistance and reducing elastic recovery and fines generation. Amounts above 6 wt.% decreased diametral resistance. The presence of layered-structure minerals (such as montmorillonite, kaolinite, lithiophorite) appeared to be key to determine the agglomeration potential of a sample. This study also showed that tableting provides good performances for recycling industrial manganese oxide fines by obtaining industrial-grade resistance for tablets made with an 80/20 pyrolusite concentrate/hausmannite blends and 4 wt.% H2O.

International audience; Environmental impacts of building materials can be achieved by reducing the amount of cement in cementitious composites, specifically when incorporating wastes as partial replacement of Portland cement. In this work we substitute cement by shell by-products and Ferronickel Slags (FNS) while keeping interesting specific properties. FNS associated to Crepidula fornicata shells (CR) are good candidates to replace part of the Portland cement as they have appropriate physicochemical properties, and are available at high abundance.The effect of the association of FNS and CR on the mechanical properties of mortar is investigated. Microstructural characterization of these additives are carried out using Scanning Electron Microscopy, X-Ray diffraction and Raman spectroscopy. Formulated mortars contain different mixes of FNS-CR and Portland cement. Specific surface area, workability and setting times of fresh mortars are studied. The mechanical properties are investigated using 3-point bending and compressive tests for curing periods ranging from 2 to 28 days. In the fresh state, the replacement of cement by up to 20 wt.% of FNS-CR does not significantly affect mortar properties. However, at the hardened state, the setting time is increased using FNS-CR. With up to 20% wt.% of FNS-CR incorporation, the mechanical properties are similar or even slightly larger than that of the control mortar.

Different polytypes of SiC are described and predicted in literature. Here, we report the first occurrence of an orthorhombic 6O-SiC polytype as rock-forming mineral in the nickel laterite mine of Tiebaghi (New Caledonia). This new class of SiC crystallizes in the space group Cmc21 with 12 atoms per unit cell [a = 3.0778(6) Å, b = 5.335(2) Å, c = 15.1219(6) Å, α = 90°, β = 90°, γ = 120°]. The density of 6O-SiC is about 3.22 g/cm3 and the calculated indirect bandgap at room temperature of 3.56 eV is identical to 6H-SiC. Our results suggest that 6O-SiC is the intermediate state in the wurtzite to rocksalt transformation of 6H-SiC.

Natural and synthetic iron oxides and iron hydroxides are important minerals for many industrial sectors (e.g. steel making, colors, pigment for coating, electronics, catalysis, soil, waste water and gas treatments, and medicine). In natural environments, such as iron ore mines or iron rich soils (laterites or bauxites), iron oxy-hydroxide associations are complex and evolve related to varying physico-chemical conditions, including. biological interactions. For efficient resource use, unambiguous multiscale characterization is indispensable. Synthetic iron oxides, produced for medical and electronic sector, needs to be failure-free pure phases, thus a continuous quality control is required. Complex iron oxy-hydroxide association can be related to various processes, topotactic transition, pseudomorphosis by substitution and alteration paramorphosis, and corrosions, leading to massive, porous, fibrous and acicular textures or poorly crystalline crusts.We present examples from iron ore deposits, where coupling of X-Ray diffraction (XRD) with scanning electron microscopy (SEM) and micro-Raman spectroscopy is a powerful tool to distinguish hematite, maghemite and magnetite at grain scale. Oxygen analyses by electron microprobe at (EMPA) fixed carbon coating thickness help to distinguish magnetite and hematite, and contribute with quantitative trace element analyses to chemically differentiate both oxides. At micro- and nano-scale, Transmission Electron Microprobe analyses coupled to X-Ray Diffraction (XRD) and Electron Energy Loss Spectroscopy (EELS) on nanometric inclusions can unambiguously identify various iron oxy-hydroxide phases. In Nickel-laterite and bauxite profiles, iron oxy-hydroxides (e.g. lepidocrocite, ferrihydrite, goethite…) are abundant and may form complex intergrowth with various types of phyllosilicates. Part of it host valuable metals such as Nickel. Combined XRF-XRD and Raman spectroscopy allow phase mapping and differentiation at micron scale of these phases, and even detect solid solutions (e.g. Ni-rich and Ni-poor goethite; El Mendili et al., 2019). Results from coupled laboratory analyses are necessary for building up data bases. They allow calibrating recently developed combined XRF-XRD-Raman benchtop systems. For industrial applications coupled and combined analyses will increase resource efficiency, and ensure a quality control for natural and synthetic iron oxide products. Such systems are recently developed by EU projects, such as SOLSA (www.solsa-mining.com).El Mendili, Y., Chateigner, D., Orberger, B., Gascoin, S, Bardeau, JF., Petit, S., Le Guen, M., Pillière, H. (2019). Combined XRF, XRD, SEM-EDS, and Raman analyses on serpentinized harzburgite (Nickel Laterite Mine, New Caledonia): Implications for Exploration and Geometallurgy. ACS Earth and Space Chemistry. 3, 10, 2237-2249; DOI: 10.1021/acsearthspacechem.9b00014

The Niaz porphyry Cu-Mo deposit in the Arasbaran metallogenic belt of NW Iran exhibits extensive hydrothermal alteration developed in three temporally and spatially overlapping zones: early potassic, transitional phyllic and intermediate argillic, and late advanced argillic. The early and transitional zones contain biotite, either of magmatic (re-equilibrated) or hydrothermal (replacement and/or neoformed) origin. This study aims to understand the petrography and chemistry of the hydrothermal biotite for evaluating the fluid compositional changes during alteration processes. Selected samples from the different alteration zones were studied for petrography crossing from inner to outer parts of the Niaz deposit. Electron microprobe analyses (Cameca SX100) including halogens (F and Cl) were performed on the hydrothermal micas at the Centre CAMPARIS, Institut des Sciences de la Terre de Paris (ISTeP), Sorbonne University, France. The biotite composition displays an increase in Al2O3, FeO and Cl, but a decrease in TiO2, MgO and F, from the potassic to the transitional phyllic and intermediate argillic alteration zones. The hydrothermal biotite with high Mg (XMg = 0.61-0.72) inside potassic zone tends to incorporate more F and less Cl compared to the biotite with lower Mg; a crystal-chemical effect referred to as “Fe-F and Mg-Cl avoidance rules”. The biotite from the potassic zone possesses a moderate range of F content (0.24 to 0.91wt. %) that is significantly higher than in the phyllic (0.45 to 0.62 wt. %) and argillic (0.19 to 0.37 wt. %) zones, exhibiting a positive correlation with XMg and a negative correlation with Cl. However, the biotite from transitional phyllic as well as intermediate argillic alteration zones shows a scattered relationship.The biotite from the central potassic to transitional phyllic and intermediate argillic alteration zones have average log (XF/XOH) values of ‑1.16, ‑1.19, and ‑1.44, respectively. The log (XCl/XOH) values are ‑2.10, ‑1.97, and ‑1.98, whereas log (XCl/XF) val­ues vary from 0.95, 0.78 to 0.54. The systematic variation of the logarithmic ratios reflects a sys­tematic variation of the F content in biotite associated with these alteration zones.Microthermometric data of fluid inclusions show a decrease in temperature from potassic through phyllic to intermediate argillic zones (420, 360 and 280 °C, respectively). The log (fH2O/fHF) and log (fH2O/fHCl) values calculated for fluids equilibrated with biotite increase progressively outward in these alteration zones (6.04, 6.42 and 7.39, respectively). The decrease in halogen content of hydrothermal fluids toward outer parts of the deposits reflects an increase in the degree of mixing between magmatic fluid and meteoric water.The F content of biotite decreases systematically toward the outer part of the deposit, while the Cl content shows unsystematic variations crossing the alteration zones. This finding suggests that the Cl content cannot be used as exploration tool for vectoring the mineralization. However, the positive correlation between the F content in biotite and bulk concentration of Cu in the different alteration zones may provide a possible geochemical tool to vectoring the Cu mineralization in porphyry deposits.

International audience; Different techniques have been combined to identify the structure and the chemical composition of siliceous breccia from a drill core of nickel laterites in New Caledonia (Tiebaghi mine). XRD analyses show quartz as a major phase. Micro-Raman spectroscopy confirmed the presence of reddish microcrystalline quartz as a major phase with inclusion of microparticles of iron oxides and oxyhydroxide. Lithoclasts present in breccia are composed of lizardite, chrysotile, forsterite, hedenbergite and saponite. The veins cutting through the breccia are filled with Ni-bearing talc. Furthermore, for the first time, we discovered the presence of diamond microcrystals accompanied by moissanite polytypes (SiC), chromite (FeCr2O4) and uranophane crystals (Ca(UO2)2(SiO3OH)2.5(H2O)) and lonsdaleite (2H-[C-C]) in the porosities of the breccia. The origin of SiC and diamond polytypes are attributed to ultrahigh-pressure crystallization in the lower mantle. The SiC and diamond polytypes are inherited from serpentinized peridotites having experienced interaction with a boninitic melt. Serpentinization, then weathering of the peridotites into saprolite, did not affect the resistant SiC polytypes, diamond and lonsdaleite. During karstification and brecciation, silica rich aqueous solutions partly digested the saprolite. Again, the SiC polymorph represent stable relicts from this dissolution process being deposited in breccia pores. Uranophane is a neoformed phase having crystallized from the silica rich aqueous solutions. Our study highlights the need of combining chemical and mineralogical analytical technologies to acquire the most comprehensive information on samples, as well as the value of Raman spectroscopy in characterizing structural properties of porous materials.

Detailed sedimentological investigations on numerous outcrops and drill-core sections in the 2.1-Ga-old Franceville basin, Gabon, provide evidence for a large-scale injectite network. The injectites were formed by the injection of sands through a thickness of about 150 m of the FB1 Member, and now cover a minimum area of 70 km 2 corresponding to the Bangombe plateau, but are also recognized close to Franceville 35 km farther south-east. The injectite lithology corresponds to a mud- or carbonate-supported sandstone characterized by a loose and uncompacted fabric contrasting with the host-rock. Because the injectites are often parallel to subparallel to the stratification, they were misinterpreted as depositional beds by previous authors. At outcrop, the injectite bodies exhibit sill, dyke, wing and protrusive geometries emplaced during early burial within poorly compacted material, with partial wall erosion and dissociation. The source of the sand material is attributed to a channel-levee turbidite depositional system located in the lower part of the FB1 Member. These deposits were buried by a thick biochemical muddy cap deposited during a starvation phase, which increased the seal capacity of the system. This type of architecture has a high potential to develop compaction disequilibrium during burial. Moreover, in the case of the Francevillian injectites, the abundance of microbial organic matter favoured early methane degassing and lateral charging of the sand reservoir. The overpressure in the channels was periodically released during early burial, through the effect of rapid sedimentary and tectonic loading, and possible seismic activity. The fluidized sand was injected according to a symmetrical wing pattern. Thus, the injected masses caused a local decrease in the grade of the lateritic manganese ore deposit of the Bangombe plateau.

International audience

SOLSA is the first automated expert system for on-site cores analysis. The scope is to provide a prototype to be an innovative and necessary tool for geo-metallurgy, in order to optimize the valorization of the ore. The Expert System consists in the combination of an integrated drilling rig providing cores of high quality, an automated scanner and phase identification software, developed for nickel laterites and bauxites but usable as well in other sectors. SOLSA combines non-destructive sensors and the whole system is driven by an innovative, user-friendly and intelligent software. SOLSA provides more complete information while optimizing the exploration stage, with a significant reduction of costs and return time. Such objective involves, in the first place, to fast, cheaper and systematic acquisition of the data needed for optimizing the process. The adding value takes place first at the exploration or grade control stage, furnishing systematic characterization and regionalization of the different types of ore. Then such information can be used for improving the ore scheduling at the mining and processing stages, toward improving the recovery and efficiency of the processing

International audience; Fine particles (

International audience; On-line, real-time chemical and mineralogical analyses on drill cores are highly demanded by mining companies. However, they are a challenge because of drill core surface state and sample heterogeneities. We selected four rock samples: highly porous, siliceous breccia and serpentinized harzburgite coming from the base of a nickel laterite profile in New Caledonia which were sonic drilled, and fine grained, homogeneous sandstone and coarse grained granite which were diamond drilled and provided by Eijkelkamp Sonic Drill with unknown origin. The samples were analysed at five surface states (diamond or sonic drilled, cut as squares, polished at 6 and 0.25 μm, powdered

International audience; Banded iron formations (BIFs) exhibit alternating silica- and iron-rich laminae, potentially reflecting the dynamics of the paleo-environments in which they were formed, although the exact mechanism remains unclear. Here the formation of a 2.7–2.9 Ga BIF from Dharwar Craton, India, is deciphered by analyzing the inter-band variations of the redox-sensitive isotope biomarkers, 15N/14N and 56Fe/54Fe. Organic matter with δ15N values as high as +12.0±0.8‰+12.0±0.8‰ appears to be trapped in silica. Iron oxides exhibit systematically positive δ56Fe values, ranging between +0.80±0.05‰+0.80±0.05‰ and +1.67±0.02‰+1.67±0.02‰. Compared to the iron-rich bands, silica-rich bands, which show higher δ56Fe values, exhibit an order of magnitude higher concentrations of 15N-rich organic nitrogen, normalized by the abundances of its host silica. The presence of 15N-rich organic matter may imply the emergence of a modern-like biological nitrogen cycle that requires the formation of oxidized nitrogen compounds. The higher concentration of 15N-rich organic nitrogen for the silica-rich bands possibly suggests that the photosynthetic activity was higher during the formation periods of these bands. The heavier iron isotope compositions of the silica-rich bands cannot be explained alone by iron oxidation through probable pathways. The relative 56Fe-enrichment in silica-rich bands is explained here by the progressive dissolution of iron oxides to the ocean, through iron reduction by 15N-rich organic matter actively produced at the ocean surface. The formation of iron-rich bands possibly corresponds to periods of reduced biological productivity, when precipitated iron was not effectively dissolved to the ocean. The observed shift in the organic concentration between Fe- and Si-rich bands could be the switch that triggered the BIF laminations. This shift could conceivably represent periodic fluctuations in the oxygen generation, which possibly occurred over periods of millennia, at the dawn of the Great Oxidation Event.

The fully open character of the Raman Open Database makes this novel database freely and completely usable by anybody worldwide: academics, those working in industry and the general public., Detailed crystallographic information provided by X-ray diffraction (XRD) is complementary to molecular information provided by Raman spectroscopy. Accordingly, the combined use of these techniques allows the identification of an unknown compound without ambiguity. However, a full combination of Raman and XRD results requires an appropriate and reliable reference database with complete information. This is already available for XRD. The main objective of this paper is to introduce and describe the recently developed Raman Open Database (ROD, http://solsa.crystallography.net/rod). It comprises a collection of high-quality uncorrected Raman spectra. The novelty of this database is its interconnectedness with other open databases like the Crystallography Open Database (http://www.crystallography.net/cod and Theoretical Crystallography Open Database (http://www.crystallography.net/tcod/). The syntax adopted to format entries in the ROD is based on the worldwide recognized and used CIF format, which offers a simple way for data exchange, writing and description. ROD also uses JCAMP-DX files as an alternative format for submitted spectra. JCAMP-DX files are compatible to varying degrees with most commercial Raman software and can be read and edited using standard text editors.

International audience; The objective of the SOLSA project (EU-H2020) is to develop an analytical expert system for on-line-on-mine-real-time mineralogical and geochemical analyses on sonic drill cores. As one aspect of the system, this paper presents the building of the hyperspectral library and its incorporation into sparse unmixing techniques for mineral identification. Twenty seven spectra representing 14 minerals have been collected for the library. Three sparse unmixing techniques have been investigated and evaluated using simulated data generated from our hyperspectral library, and real hyperspectral data acquired from a serpentinized harzburgite sample. Among the three techniques, the collaborative sparse unmixing by variable splitting and augmented Lagrangian (CLSUnSAL) method provided the best accurate results on the simulated data. In addition, the results of the CLSUnSAL method show high correlation with that of the QEMSCAN® analysis on the harzburgite hyperspectral data.

International audience; Carbonaceous matter is generally known to be problematic for metal recovery during metallurgical processing of black shales. In particularly, metal upgrading during beneficiation prior to (bio-) hydrometallurgical and/or pyrometallurgical processing is hindered by the presence of abundant carbonaceous matter (CM). This study presents the characterization of CM and mineral bound carbonaceous matter (CMP) in three manganese carbonate-rich shales hosting 6–8 wt% total organic carbon. Non-destructive methods, such as incident light microscopy, scanning electron (SEM) and focused-ion-beam-transmission electron microscopy (FIB-TEM), QEMSCAN and electron microprobe, were used to show that free CM is adsorbed onto illite-smectite surfaces. This form of CM ranges in grain size from sub-micrometer up to ≈100 μm. The most efficient method to show the illite-smectite association is SEM and for quantification of this association, QEMSCAN should be used. Mineral-bound carbonaceous matter may be relicts of extrapolymers (pyrite and/or carbonate) and needs characterization using FIB-TEM. The quantity of CM can then be estimated by a rough calculation as the difference between the total organic carbon (Rock Eval) and the free carbon calculated from normative mineral compositions based on X-ray Fluorescence (XRF) and X-ray-Diffraction (XRD) analyses. The mineral bound CM could not be detected by QEMSCAN under conventional analytical conditions. We estimated that about 85% of the CM in the test samples was adsorbed on mineral surfaces and about 15% was bound to minerals. The physical protection of the CM by clays, and the morphological and density differences between pyrite, carbonates and biochemically-bound CM in pyrite/carbonates needs to be taken into consideration in the process design.

International audience

Future improving of the innovative technology of Lithium air batteries correlates with an increased demand for Li-resources. We analyzed and compared stable isotopic compositions from 4 Argentinean Li rich salars. The Pozuelos (PS), Centenario (CN), Ratones (RT) and Hombre Muerte (HM) belong to the world class brine resources of the Atacama triangle. CN has a halite core surrounded by fine grained clastic sediments, while RT comprises lesser evaporates, but coarser grained volcanoclastics. Two Cl-Na SO4 brine aquifers (down to 250 m depth) host several hundreds of mg/l of Li. The surface waters are characterized by Li < 7mg/l, δ7Li of ≈ 9.5, δD: -66 ‰ and δ18OSMOW: -7.8 ‰. The stable isotopic composition differs slightly from the upper aquifer (δ7Li ≈9.2 ‰, δD -47.2 ‰ and δ18OSMOW -0.8 ‰) to the lower aquifer (δ7Li: 9.7 ‰, δD: -51.6 ‰ and δ18OSMOW: -1.7 ‰). The dominant source of Li is related to water–rock interactions (surface, saline waters with andesites, pegmatites, pyroclastics). The comparison of our RT and CN data to those of the close-by PS and HM, shows that each salars has its own geological, hydrological and climate history which can be defined by crossing isotope tracers. However, the development of pertinent isotopic regional and local exploration proxies, needs identical data sets on systematically defined samples of the same aquifer type, on country rocks and minerals.

International audience; The SOLSA project aims to develop an innovative on-line-on-mine-real-time expert system, combining sonic drilling, mineralogical and chemical characterization and data treatment. Ideally, this combination, highly demanded by mining and metallurgical companies, will speed up exploration, mining and processing. In order to evaluate the instrumental parameters for the SOLSA expert system, portable and laboratory analyses have been performed on four samples with contrasting lithologies: siliceous breccia, serpentinized harzburgite, sandstone and granite. More precisely, we evaluated the influence of the surface state of the sample on the signals obtained by portable X-Ray Fluorescence (pXRF) for chemistry and portable Infra-Red spectroscopy (pIR) for mineralogy. In addition, laboratory Raman spectroscopy, X-Ray Diffraction (XRD), XRF and ICP-OES laboratory analyses were performed to compare surface bulk mineralogical and chemical analyses. This presentation highlights (1) the importance of coupling chemical and mineralogical analytical technologies to obtain most complete information on samples, (2) the effect of the sample surface state on the XRF and IR signals from portable instruments. The last point is crucial for combined instrumental on-line sensor design and the calibration of the different instruments, especially in the case of pXRF.

The pseudomorphic transformation of magnetite into hematite (martitization) is widespread in geological environments, but the process and mechanism of this transformation is still not fully understood. Micro- and nano-scale techniques—scanning electron microscopy, focused ion bean transmission electron microscopy, and Raman spectroscopy—were used in combination with X-ray diffraction, Curie balance and magnetic hysteresis analyses, as well as Mossbauer spectroscopy on martite samples from a banded iron formation (2.9 Ga, Dharwar Craton, India), and from lateritic soils, which have developed on siliciclastic and volcanic rocks previously affected by metamorphic fluids (Minas Gerais, Brazil). Octahedral crystals from both samples are composed of hematite with minor patches of magnetite, but show different structures. The Indian crystals show trellis of subhedral magnetite hosting maghemite in sharp contact with interstitial hematite crystals, which suggests exsolution along parting planes. Grain boundary migrations within the hematite point to dynamic crystallization during deformation. Dislocations and fluid inclusions in hematite reflect its precipitation related to a hydrothermal event. In the Brazilian martite, dislocations are observed and maghemite occurs as Insel structures and nano-twin sets. The latter, typical for the hematite, are a transformation product from maghemite into hematite. For both samples, a deformation-induced hydrothermally driven transformation from magnetite via maghemite to hematite is proposed. The transformation from magnetite into maghemite comprises intermediate non-stoichiometric magnetite steps related to a redox process. This study shows that martite found in supergene environment may result from earlier hypogene processes.

International audience; The low-grade carbonate banded iron formation of the Aguas Claras mine, from the transition of the Caûe to the Gandarela Formation (2.4 Ga, Itabira Group, Brazil), is composed of porous and microsparitic dolomite, quartz, iron oxides and (oxy)hydroxides. Iron oxides occur as bands, veins and as inclusions in the dolomite crystals, whereas iron (oxy)hydroxides only occur as inclusions. Combined mineralogical analyses (X-ray diffraction, Raman spectroscopy, focused-ion-beam thinning and transmission electron microscopy) identified the inclusions in porous dolomite as hematite and minor goethite and/or ferrihydrite, whereas microsparitic dolomite only hosts hematite. Curie balance analysis on whole rock reveals that, at temperatures between ∼680 °C and ∼900 °C, hematite and iron (oxy)hydroxide inclusions react with the surrounding dolomite resulting in the assemblage: magnesioferrite (MgFe 2 O 4), srebrodolskite (Ca 2 Fe 2 O 5), lime (CaO), portlandite (Ca(OH) 2) and periclase (MgO), whereas hematite and pure dolomite do so only at ∼900 °C. This difference is an indirect argument for the presence of iron hydroxide inclusions within the dolomite. The inclusions are either single crystals or form clusters in pores. The fast-Fourier-transform diffraction pattern of one single crystal can be indexed as goethite and ferrihydrite. This finding suggests an incipient solid-state transformation of ferrihydrite to goethite rather than a dissolution-precipitation process. It is suggested that the clustered hematite and the goethite/ferrihydrite precipitated from Fe-and Si-bearing fluid inclusions, which were trapped during early diagenesis at about 2.4 Ga under oxygenated conditions. Microstructural evidence (e.g. dislocations in dolomite from hematite inclusions) point to maximum T < 420 °C. The preservation of goethite/ ferrihydrite clustered inclusions during this low-temperature event may be due to their silica contents increasing their stability.

International audience; Within the framework of responsible mining, a SOLSA project (www.solsa-mining.eu) to develop an in-situ tool allowing a quick mineralogical identification of site drill cores has been recently launched. Its objective is to develop new or improved highly-efficient and cost-effective, sustainable exploration technologies. It combines and integrates non-destructive sensors: X-ray fluorescence, X-ray diffraction, infra-red and Raman spectroscopy and 3D imaging. The challenge is to address mixtures of hard and soft rocks, as encountered in a lateritic environment. This paper focuses on the determination of spectral characteristics of laterite drill-cores in the visible to short wave infrared spectral range. One of the most important prerequisites is to study the influence of the surface roughness effect on infra-red spectroscopy analyses. For this purpose, four different rock samples: breccia, sandstones, granite and peridotite, each at five surface states have been considered: as-drilled, as-sawn, polished at 6 µm, polished at 0.25 µm and crushed to powder. The reflectance spectra have been acquired with an ASD Fieldspec 3® spectroradiometer with a contact probe at a sampling surface of 1.76 cm 2 , allowing a spectral analysis at wavelengths from 350 up to 2500 nm. The powder spectrum of breccia presents a higher reflectance than the four other spectra from the same material but weak absorption features. The as-sawn sample presents the higher absorption depth, followed by as-drilled sample and the two polished samples (figure 1). At wavelength 2219 nanometers, a peak of absorption is present. The presence of clay minerals is assumed like illite/sericite with more or less smectite, due to the relatively deep water absorption around wavelength 1900 nanometers. Figure 1: Spectra of Breccia Breccia as-drilled Breccia as-sawn Breccia polished 6 µm Breccia polished 0.25 µm Breccia powder

In order to evaluate the potential of felsic sediments as a CO2-sink in the Archean, we studied felsic volcaniclastic/epiclastic sedimentary rocks of the 3.45 Ga Hooggenoeg Formation, Barberton greenstone belt, which were affected by metasomatic processes during seafloor alteration and diagenesis. Water–rock interactions leading to K-, Si- and CO2-metasomatism were quantified. The precursor rock, a K-metasomatized dacite, was leached of Ca, Mg, Fe, Na, Sr, and Ba and enriched in K, Rb and Si prior to erosion and deposition. The formation of K-mica and quartz (and minor K-feldspar) in the dacites suggests low pH metasomatic conditions, likely produced by hydrothermally induced circulation of hot, acidic and reduced Archean seawater in equilibrium with a high P C O 2 atmosphere. Erosion and transport of K-metasomatized dacitic detritus away from the felsic volcanic centers resulted in the deposition of conglomerate, sandstone and shale by mass flow processes. Early diagenetic silicification affected mainly the fine-grained sediments with higher silica sorption capacity, forming impermeable layers, while sand-rich sediments were partly silicified and remained permeable. Trapped fluids precipitated two generations of Fe-rich dolomites and finally calcite. Up to 30 vol.% of siliciclastic coarse-grained sediment was replaced by carbonates in a shallow-burial, high heat-flow diagenetic regime (depth: ∼750 m, temperature: 80–160 °C), and likely throughout deposition of overlying volcano–sedimentary units. The carbon isotopic composition of Fe-rich dolomites (δ13CPDB = +1.9 to +2.4‰) and the strong Fe–Ca–Mg leaching of the Paleoarchean volcanic formations support the influence of seawater-derived fluids throughout CO2-metasomatism. For each gram of eroded dacite, the overall chemical exchange involved by K–Si–CO2-metasomatism was characterized by a mass transfer of Fe (1.2 mmol/g), Na (2.1 mmol/g) and O2− (2.0 mmol/g) to seawater. In contrast, seawater was depleted in Si (10 mmol/g), Ca (0.51 mmol/g), Mg (0.43 mmol/g), K (1.5 mmol/g) and H (0.93 mmol/g) during incorporation of these elements in the volcanic and sedimentary rocks. The average CO2 uptake by the sedimentary rocks studied here is estimated to be 1.8 mmol/g, in the same order of magnitude as previous estimates for the Paleoarchean basaltic crust. Although mafic-ultramafic rocks are the most abundant rocks in Paleoarchean greenstones belts, and represent the most important atmospheric CO2-sink upon seafloor alteration in the Paleoarchean, coarse felsic sedimentary rocks provide a non-negligible contribution to the build-up of the continental CO2 reservoir.

The effects of K–Si-metasomatism during the formation of Early Archean replacement cherts have been quantified in this study by the investigation of two well-known stratigraphic sections: the Msauli chert (MC, Barberton greenstone belt, South Africa) and the Kittys Gap chert (KGC, Pilbara craton, Western Australia). The KGCs have a dacitic precursor similar to Duffer Formation dacites (Pilbara craton), while the MCs are derived from Al-depleted komatiites similar to those from the Weltevreden Formation (Barberton greenstone belt). Mass balance calculations reveal that the volcaniclastic deposits had initial porosities of up to 85 vol.% for the KGC and of 65 vol.% for the MC. Secondary porosities (27 vol.%: MC, 8 vol.%: KGC) produced during K-metasomatism are proportional to the dissolution of Fe, Ca, Mg-rich glass and precursor minerals. Komatiites have a higher chemical exchange potential than dacites, each gram releasing 1.2 mmol Fe2+, 2.8 mmol Mg2+, 1.4 mmol Ca2+ and 1.1 mmol Na+ to seawater, together with 4.4 mmol O2−. K-metasomatism of 1 g of komatiite further implies an uptake of 0.67 mmol of K+ and 2.7 mmol of H+. The highest silica uptake is achieved for the KGC (82 mmol/g of precursor). This silica enrichment most likely operated in the water column and at the sediment–water interface by sorption mechanisms on the surface of detrital particles and particulate organic matter, as a result of seawater silica-saturation. Acidic conditions (pH 5.5–6.5) and hot temperatures (>70 °C) favored the formation of K-rich phyllosilicates by interaction with seawater during the early diagenetic alteration of the volcaniclastic particles. The widespread occurrence of K–Si-metasomatism in volcanic and sedimentary rocks can be regarded as a general alteration process of the Early Archean seafloor, with a major influence on seawater composition. The highly K-selective metasomatism confirms previous studies suggesting that the Archean ocean was acidic and probably in equilibrium with a CO2-rich atmosphere.

Black shales of the Lower Cambrian Niutitang Formation in southern China (Huangjiawan mine, Zunyi region, northern part of the Guizhou Province) host regionally distributed stratiform polymetallic Ni-Mo-platinum group elements (PGE)-Au phosphate- and sulfide-rich ores. These are confined to a ≥0.2-m thick ore horizon composed of mineralized bodies of algal onkolites, phosphate nodules, and sulfide and shale clasts in a mineralized phosphate- and organic matter-rich matrix. Compared to footwall and hanging wall shales, the ore bed is strongly enriched in Ni (up to 100-fold), As (up to 97-fold), Mo (up to 95-fold), Sb (up to 67-fold), Rh (up to 49-fold), Cu (up to 37-fold), Pd (up to 33-fold), Ru (up to 24-fold), Zn (up to 23-fold), Pt (up to 21-fold), Ir (up to 15-fold), Co (up to 14-fold), and Pb (up to 13-fold). Even footwall and hanging wall black shales are significantly enriched by Mo (21-fold) and Ni (12-fold) but depleted in Cr in comparison to average Cambrian black shale. Organic matter is represented by separate accumulations dispersed in the rock matrix or as biotic bitumen droplets and veinlets in ore clasts. Similar organic carbon (Corg) values in an ore bed and enclosing footwall and hanging wall shales of little mineralization indicate that metal accumulation was not controlled only by biogenic productivity and organic matter accumulation rate. Evaporitic conditions during sedimentation of the basal part of the Niutitang Formation were documented by an occurrence of preserved Ni-, V-, Cr-, and Cu-enriched phosphate-rich hardground with halite and anhydrite pseudomorphs on the paleosurface of the underlying Neoproterozoic carbonates. Neoproterozoic black shales of the Doushantuo Formation are characterized by increased metal concentrations. Comparison of metal abundances in both hardground and Doushantuo black shales indicate that black shales could have become a source of metal-rich hardground during weathering. The polymetallic Ni-Mo-PGE sulfide-rich ore bed is interpreted to represent a remnant of shallow-water hardground horizon rich in metals, which originated in a sediment-starved, semi-restricted, seawater environment. During the Early Cambrian transgression an influx of fresh seawater and intensive evaporation, together with the hydrothermal enrichment of seawater in a semi-restricted basin, resulted in the formation of dense metalliferous brines; co-precipitation of metals together with phosphates and sulfides occurred at or above the oxic–anoxic sediment interface. Metal-enriched hardground was disintegrated by the action of waves or bottom currents and deposited in a deeper part of the anoxic basin. Contemporaneously with the formation of a polymetallic Ni-Mo-PGE-Au sulfide ore bed, economic sedimentary exhalative (SEDEX)-type barite deposits were forming in a stratigraphically and geotectonically similar setting. The results of geochemical study at the Shang Gongtang SEDEX-type Ba deposit indicate that concentrations of Ag, As, Cr, Cu, Fe, Mn, Ni, Pb, Sb, V, Zn and other metals decrease from top of the barite body toward the hanging wall black shale. Lower Cambrian black shales of the Niutitang Formation above the barite body also display similar element abundances as Neoproterozoic black shales of the Doushantuo Formation, developed in the footwall of the barite body. But the geochemical composition of the sulfide layer is different from the Ni-Mo ore bed, showing only elevated Pb, Cu, Ni and Mo values. It is suggested that hydrothermal brines at Shang Gongtang might have leached metals from footwall Neoproterozoic sequences and became, after mixing with normal seawater, an additional source of Ag, Cr, Cu, Pb, Sb, Zn, Ni, PGE, V and other metals.

Eight drill cores cutting through the Mn-carbonate bearing black shales from the Bangombé Plateau were studied. Mn-carbonates (up to 80 m thick) are underlain by laminated pyrite rich shales with organic carbon contents of about 4 wt. % and MnO contents of about 6 wt. %. Mn and Fe, S poor shales are intercalated. Mn-carbonate rich shales (20-29 wt. % MnO) have low contents of phyllosilicates, but are rich in organic carbon (about 7 wt. %) with moderate S contents (about 2 wt. %). All shale facies were deposited in a closed basin through suspension settling and precipitations under anoxic conditions. The Mn-carbonates, towards the top, were formed most likely under suboxic conditions. Pyrite and Mn-carbonates are characterized by bacteriomorphous structures. The latter are composed of micrometric carbonates finely intergrown with clays, quartz and organic matter. They formed around and corroded the dolomite and/or organic matter. Mn-carbonates and pyrite both form also several tenths of micrometer large agglomerates and sub-automorphous grains. The agglomerates can be attributed to evolving diagenesis. Carbonate chemistry varies mainly from rhodochrosite to dolomite. The present results point to primary microbial Mn-carbonate formation. No signs for a Mn-oxide precursor were detected. Slumping and shearing structures, distortion and disruption of thin pyrite beds indicate synsedimentary deformations.

New datings of calcareous sandstone lenses and olistolites exposed in the middle part of the siliciclastic Mouchenkour Formation indicate a Late Asbien/Early Brigantian age (Cfm7/Cfm8 Moroccan biozone). The calcareous microfossil assemblages are characterized by the problematic algae Ungdarella, Fasciella and Koninckopora and foraminifers Archaediscus (concavus stage), Pseudoendothyra and Eostafella. An Asbien/Brigantian palaeogeography based on the depositional environments is reconstructed from northwest to southeast, from the Tizra to the Mouchenkour areas. The units, although in tectonic contacts, nearly preserve their initial location and relations.

Selected mineralized black shales of Devonian age from the Selwyn Basin, Northwest Territories (Canada) were analyzed by Nuclear Reaction Analyses (NRA) and electron microprobe for nitrogen and carbon in silicates, sulfides, phosphates and organic matter in order to give new insights on nitrogen and carbon fractionation processes during diagenesis and hydrothermal infiltration. Hydrothermal feldspars show tri-modal composition: albite, high nitrogen-bearing K-feldspar (∼56 mol% buddingtonite (NH4AlSi3O8·1/2H2O, hydrous ammonium-feldspar, ∼51 mol% orthoclase) and hyalophane (∼32 mol% celsian). Barium-rich feldspars (hyalophane) contain lowest nitrogen contents. Potassium and nitrogen are positively correlated, while nitrogen and barium are negatively correlated due to the replacement of monovalent NH4+ by divalent Ba2+. The Ba-rich K-feldspar rim shows penetrative textures towards an internal K–N-rich core that is interpreted as diffusive overgrowth. These feldspars are interpreted to be deposited from hot hydrothermal Ba-bearing fluids. The second important nitrogen carrier is organic matter (from 0.6 to 0.66 wt.%). Hydrothermal quartz (N=527 ppm), diagenetic biogenic F-rich apatite (conodonts: N=468 ppm,), biogenic Fe–Ni sulfides (N=380–620 ppm) and abiogenic Ni–Fe sulfides (N>440 ppm) contain homogeneously distributed nitrogen with amounts 10-fold lower than those measured in organic matter. A two-step nitrogen-release model is suggested to explain the nitrogen-partitioning in these minerals. Primary organic matter breakdown is considered to liberate nitrogen, phosphate and sulfur to pore fluids and the water column, providing nutrients for vent fauna growth. Sulfurization, due to microbial sulfate reduction, and silicification of the vent fauna releases nitrogen in a second step. Minor nitrogen was trapped as organic molecules in conodonts, while the majority was transported by hydrothermal fluids and was incorporated as ammonium in feldspars substituting for potassium.

Biophile elements nitrogen and carbon were found in hydromuscovite aggregates of an Archean chert from Kittys Gap, W. Australia, hosting probable evidence of life. Their concentrations do not show a linear relationship, as expected if they where produced by a common organic source. The lack of a linear relationship is related to N and C fractionation at the mineral scale. N occurs in the form of NH 4 + , tightly retained at the K+ lattice sites, while C could occurs as a dispersed organic phase in hydromuscovite aggregates or in a weakly bounded form, possibly HCO 3 - .