Marion Turuani

Flavien Choulet
email: flavien.choulet@univ-fcomte.fr

Aurélien Eglinger

Philippe Goncalves

Julie Machault

Julien Mercadier

Anne-Magali Seydoux-Guillaume

Stephanie Reynaud

Fabien Baron

Daniel Beaufort

Yann Batonneau

Sophie Gouy

Adel Mesbah

Stéphanie Szenknect

Nicolas Dacheux

Virginie Chapon

Maurice Pagel

Geochemical fingerprints of brannerite (UTi 2 O 6 ): an integrated study

Keywords: brannerite, fingerprints, hydrothermal, pegmatite, mineral chemistry

Introduction

Growing demand for energy requires a diversification of primary raw materials as well as a re-evaluation of low grade ores, which may occur in large tonnage deposits.

Current primary ores processed in the nuclear industry mostly include uraninite (UO2) and coffinite U(SiO4)1-x (OH)4x. Unconventional target ores include brannerite, a uranium titanate (UTi2O6), because of its high U content of up to 55 wt% U [START_REF] Patchett | Studies of radioactive compounds: X-The synthesis of crystallography of brannerite[END_REF]Skymanski and Scott, 1982). Worldwide, brannerite is reported in a variety of geological environments including sedimentary (e.g. Witwatersrand, South Africa;Smits, 1984), hydrothermal (e.g. Chateau-Lambert, France; [START_REF] Branche | Nouvelles espèces uranifères françaises[END_REF], magmatic (e.g. Crocker's Well, Australia; [START_REF] Ludwig | Geochronology of Precambrian granites and associated U-Ti-Th mineralization, northern Olary province, South Australia[END_REF] and metamorphic (e.g. San Bernardino county, USA; [START_REF] Hewett | Brannerite from San Bernardino County, California[END_REF] settings. In some deposits, brannerite is the main U-bearing mineral, like at Elliot Lake, Canada [START_REF] Szymanski | A crystal structure refinement of synthetic brannerite, UTi2O6, and its bearing on rate of alkaline-carbonate leaching of brannerite in ore[END_REF], Mount Isa, Australia [START_REF] Wilde | Geology and Mineralogy of Uranium Deposits from Mount Isa, Australia: Implications for Albitite Uranium Deposit Model[END_REF] and Olympic Dam, Australia [START_REF] Macmillan | Chemical and textural interpretation of late-stage coffinite and brannerite from the Olympic Dam IOCG-Ag-U deposit[END_REF]. In the Witswatersrand conglomerate, brannerite accounts for 8 to 19 wt% of the total uranium mineralization [START_REF] Lottering | Mineralogy and uranium leaching response of low grade South African ores[END_REF]. While U can be easily extracted from oxide minerals, brannerite has long been considered as refractory to direct leaching and for this reason it has not to date been extensively mined and/or processed (Vance et al., 2000, and references therein). Recent advances in hydrometallurgy have shown that U can be recovered from brannerite using acid solutions under physical-and chemicalcontrolled conditions [START_REF] Charalambous | Leaching behaviour of natural and heat treated brannerite-containing uranium ores in sulphate solutions with iron (III)[END_REF]. Uranium recovery from brannerite is not a straightforward process and the efficiency of recovery is strongly influenced by the ore paragenesis [START_REF] Lottering | Mineralogy and uranium leaching response of low grade South African ores[END_REF][START_REF] Sapsford | Factors influencing the release rate of uranium, thorium, yttrium and rare earth elements from a low grade ore[END_REF]. Although brannerite is formed in a large variety of geological environments, its crystal chemistry and petrogenesis remains under-investigated.

Brannerite crystallizes in the monoclinic system, with space group C2/m [START_REF] Szymanski | A crystal structure refinement of synthetic brannerite, UTi2O6, and its bearing on rate of alkaline-carbonate leaching of brannerite in ore[END_REF]. The general formula is best described to be AB2O6, where A is U and B is Ti. Both A and B sites are distorted octahedra (six-coordinated), which share corners and/or edges to form a structural framework [START_REF] Szymanski | A crystal structure refinement of synthetic brannerite, UTi2O6, and its bearing on rate of alkaline-carbonate leaching of brannerite in ore[END_REF], Fig. 1).

Natural brannerite is commonly non-stoichiometric, and exhibits variable compositions related to more or less complex substitution mechanisms [START_REF] Ditz | Th Thorium -Natural Occurrence. Minerals (Excluding Silicates)[END_REF][START_REF] Lumpkin | Chemistry, microstructure, and alpha decay damage of natural brannerite[END_REF][START_REF] Macmillan | Chemical and textural interpretation of late-stage coffinite and brannerite from the Olympic Dam IOCG-Ag-U deposit[END_REF]. The A site is mainly occupied by U, Ca, Th and rare earth elements (REE), whereas the B site includes Ti, Al and Fe. Due to the high content of radioactive elements (U, locally Th and their daughter elements), the self-irradiation of natural brannerite causes significant structural damage leading to the amorphization of the crystal lattice [START_REF] Smith | Uranium mineralogy[END_REF][START_REF] Lumpkin | Chemistry, microstructure, and alpha decay damage of natural brannerite[END_REF]. Such processes lead to favourable conditions for fluid circulation that contributes to the inception of alteration [START_REF] Seydoux-Guillaume | Nanoscale evidence for uranium mobility in zircon and the discordance of U-Pb chronometers[END_REF][START_REF] Duran | Fluid-mediated alteration of (Y,REE,U,Th)-(Nb,Ta,Ti) oxide minerals in granitic pegmatite from the Evje-Iveland district, southern Norway[END_REF] and further incorporation of impurities into the brannerite structure. Such variations in composition, together with the complex nature of brannerite ores have major effects on in dissolution rates of brannerite [START_REF] Goldney | Extraction Investigations with Some Australian Uranium Ores[END_REF][START_REF] Polito | The Proterozoic, albitite-hosted, Valhalla uranium deposit, Queensland, Australia: a description of the alteration assemblage associated with uranium mineralisation in diamond drill hole V39[END_REF][START_REF] Charalambous | Chemical and microstructural characterisation studies on natural and heat treated brannerite samples[END_REF].

The detailed chemical characterization of minerals, like colombite-tantalite [START_REF] Melcher | Fingerprinting of conflict minerals: columbite-tantalite ("coltan") ores[END_REF] and uraninite [START_REF] Mercadier | Origin of uranium deposits revealed by their rare earth element signature[END_REF][START_REF] Eglinger | Geochemical signatures of uranium oxides in the Lufilian belt: from unconformity-related to syn-metamorphic uranium deposits during the Pan-African orogenic cycle[END_REF][START_REF] Frimmel | Uraninite chemistry as forensic tool for provenance analysis[END_REF] had led to classifications of minerals based on their geological environment.

Such chemical fingerprints have also direct applications to the exploration industry and forensic science. Owing to the large variety of brannerite occurrences and its complex crystal chemistry, a similar chemical characterization approach is developed in this contribution. Based on both optical and electronic microscopy, major and trace element analyses of natural brannerite minerals collected from magmatic (pegmatitic) and hydrothermal occurrences, this study aims at identifying the chemical substitutions, leading to a large variety of compositions. This characterization leads to a classification of brannerite based on the genetic type of their occurrence. This enables us to discuss implications for: (1) ore deposits fingerprints; (2) using brannerite as a dating tool; (3) determining key parameters for optimized U recovery during leaching operations.

Material and methods

Brannerite ores

The studied samples include single crystals and ores collected from hydrothermal, and pegmatitic occurrences worldwide (Fig. 2). In this section, only a brief geological overview of the sampling localities is provided; more detailed information on ore deposits or occurrences can be found in the appendix and in the referred literature. Five samples from hydrothermal occurrences were studied: La Gardette (GD) from the French Western Alps, Bou Azzer (BA) from the Moroccan Anti Atlas Belt, Chhuling Khola Valley (HL) in the Nepalese Himalaya, Mont Chemin (MC) in the Western Swiss Alps, and Kratka Valley (KV) in the Bohemian Massif. These hydrothermal veins formed after local or regional events, without direct connection to a magmatic event, and they may record a complex evolution of the fluid composition. Within veins, brannerite is spatially associated with gangue minerals within a more or less polyphase paragenetic sequence.

Five samples from magmatic-pegmatitic occurrences were studied: Crocker's Well (CW) in Central Australia, Hidden Valley (HV) in the Finders Ridge, Australia, El Cabril (EC) in the Sierra Albararrana, Andalusia, Lodrino (BR1) in the South-Central Swiss Alps and Marienfluss Valley (NA12) in Northern Namibia. These occurrences are generally dykes spatially and/or temporally associated with magmatic and metamorphic complexes. Pegmatite, which often corresponds to the last stage of the magmatic evolution, is composed of K-feldspar, quartz, albite and, among accessory minerals (listed in the appendix and in the referred literature), brannerite. For simplification, brannerite formed in magmatic-pegmatitic environments will be named "pegmatitic brannerite", while those formed in non-magmatic hydrothermal settings will be named "hydrothermal brannerite".

Analytical methods and data processing

Polished thin-sections and plugs were prepared from rock samples and mineral chips at GeoRessources, Nancy (France). Identification of the paragenesis and textures was carried out using optical microscopy and scanning electron microscopy (SEM). SEM instrumentation consists of FEI Quanta 450, equipped with an EDS spectrometer and a backscatter electron detector (BSE), hosted by the MIMENTO platform (RENATECH Network) at the Femto-ST lab, Besançon (France). We operated at acceleration voltages between 10 and 15 kV.

As representative of pegmatite and hydrothermal settings, respectively, two thin lamellae from Lodrino and Bou Azzer samples were prepared using a FEI Helios 600i FIB/SEM instrument (MANUTECH USD, Saint-Etienne, France). After localization of the area of interest by backscattered electron imaging, a first 300 nm-thick protective coating of platinum was deposited. A thick amorphous carbon coating was then deposited using a gallium ion beam. The TEM lamellae were firstly pre-thinned at 30 kV, transferred on a Cu semi grid and thinned down to be sufficiently transparent to the electron beam (i.e. less than 100 nm). The lamellae were finally cleaned at low voltage (down to 1 kV) in order to remove defects created by the FIB process and to optimize its thickness.

Foils were cut within the apparently unaltered (homogenous domains with limited grey-scale variations under the SEM in BSE mode) domains of brannerite grains from Bou Azzer and Lodrino, considered as representative of hydrothermal and pegmatitic settings. Raman microspectroscopy was performed at ambient temperature on polished thin-sections and plugs at IC2MP, Poitiers (France). Raman spectra were acquired using a LabRAM HR800UV confocal microspectrometer (Horiba Jobin Yvon, Villeneuve d'Ascq, France) equipped with a Peltier effect-cooled CCD (Charged Coupled Device) detector.

The excitation wavelength was set at 632.8 nm (He-Ne laser), or at 514.5 nm (Ar + laser), or at 532.4 nm (diode solid laser). Laser power delivered at the sample was ca 19 mW (without filtering) and filters of optical densities of either 1 or 2 were used for all spectra.

Samples were analysed using a confocal high-stability BXFM Olympus microscope equipped with either a 50 ⨯ LMPlan (numerical aperture: 0.55), or a 100× MPlan (numerical aperture: 0.9) Olympus objective. The spatial resolution was ca 1⨯1 µm 2 . The spectrometer was calibrated with a pure silicon wafer using the Raman scattering line centred on 520.7 cm -1 , which resulted in an accuracy of no less than 0.5 cm -1 . It consisted in an 1800 grooves mm -1 holographic grating. Spectra were recorded in the 50-1000 cm - 1 Raman shift range with a spectral bandwidth of either 3.2 cm -1 (with a confocal hole aperture of 200 µm at 532.4 nm), or of 8.4 cm -1 (with a confocal hole aperture of 400 µm at 514.5 nm). Data acquisition and processing were carried out using the LabSpec version 5 software (Horiba Jobin Yvon).

Major element composition of brannerite was obtained by electron probe microanalyzer (EPMA), at GeoRessources, Nancy (France), using a Cameca SX100 equipped with five wavelength dispersion spectrometers (WDS). Carbon-coated polished thin sections were analysed with an acceleration voltage of 20 kV, and a current of 100 nA. The spatial resolution is ca. 1 μm, with an average acquisition time of 5 minutes. Oxides, silicates, and pure metals were used as standards (Table A1). In addition, quantitative and qualitative elemental composition maps were obtained using (1) a Field-Emission Gun (FEG) Cameca SXFive FE, equipped with five WDS at Centre de MicroCaractérisation Raimond Castaing at Toulouse (France) (for samples from Himalaya and El Cabril) and

(2) a JEOL 8200 Superprobe equipped with five WDS, hosted at University of Geneva (for sample from Bou Azzer), respectively. In theses cases, acceleration voltage was of 10 kV and a current of 100 nA. Elemental composition maps were produced with a resolution of 1 μm and an acquisition time of 600 ms per pixel. Following Collela et al. (2005), U 4+ , U 5+ or U 6+ relative content was estimated on a basis of 6 oxygen atoms and 3 cations. There is no unique solution to balance charges, therefore the average valence state has been chosen as the most reliable parameter.

The minor and trace element contents were quantified using a laser ablation (193nm excimer Geolas Q Plus System) coupled to an inductively-coupled plasma mass Spectrometer (Agilent 7500c Quadrupole) at Georessources, Nancy (France). The fluence was 5 J cm -2 , using a repetition rate of 5 Hz. The laser spot sizes were 24 or 32 µm in diameter, depending on the size of brannerite crystals. The total acquisition time, including background and signal was limited to 200 s per analysis, with a background acquisition of 30 s before ablating the material for 40 s. The following elements were measured: B, Mb, Al, Si, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Nb, Mo, the REEs, Pb, Th, U with a dwell time of 10 ms (except 5 ms for U and Pb). The cycle time was 394 ms. The He flux was fixed at 0.5 l.min -1 and 0.9 l.min -1 of Ar was added before entering the plasma. The reference material was a SRM NIST 610 glass standard [START_REF] Pearce | A compilation of new and published major and trace element data for NIST SRM 610 and NIST SRM 612 glass reference materials[END_REF] and Ti and/or U contents measured by EPMA on the same area were used as an internal standard. Data reduction was carried out with IOLITE software [START_REF] Paton | Iolite: Freeware for the visualisation and processing of mass spectrometric data[END_REF]. Analytical precision is calculated for all elements analyzed using standard deviation of recorded intensity and is better than ±15% for concentrations higher than 10 ppm and becomes greater (±50% to ±70%) for concentration lower than 10 ppm. Limit of detection varies for each element as a function of signal intensity and was calculated for each ablation from signal intensities using the 3σ criterion [START_REF] Longerich | Laser ablation inductively coupled plasma mass spectrometric transient signal data acquisition and analyte concentration calculation[END_REF]. The most commonly achieved LODs are below 2 ppm for the measured trace elements.

The comparison between chemical compositions of brannerite from different deposits was achieved by estimating the difference in content of a given element (see detailed procedure in [START_REF] Machault | Mineralogical and microtextural parameters in metals ores traceability studies[END_REF]. For this, we first calculated the coefficient of variation defined by Cv (%) = σ/μ (where σ is the standard deviation and μ is the average) to describe the degree of homogeneity for the distribution of the analysed elements. The non-parametric Kolmogorov-Smirnov test (e.g. [START_REF] Press | Numerical Recipes, The Art of Scientific Computing[END_REF] was then used to compare two populations and therefore evaluate the homogeneity between two samples.

We also applied multivariate statistical processing, to highlight the substitution trends within brannerite. The principal component analysis (PCA) is a powerful variablereduction technique, which is more and more applied to geochemical data (e.g. [START_REF] Belissont | LA-ICP-MS analyses of minor and trace elements and bulk Ge isotopes in zoned Ge-rich sphalerites from the Noailhac-Saint-Salvy deposit (France): Insights into incorporation mechanisms and ore deposition processes[END_REF]. By recalculating principal components, which are defined as orthogonal linear combinations of the initial variables, it is possible to project multivariate data in two-dimensions with minimal data loss. The two first principal components, which are used in this study, carry the highest explained variance, corresponding to the most significant relationships between the variables. More detailed about PCA method can be found in [START_REF] Koch | Analysis of multivariate and high-dimensional data theory and practice[END_REF]. For all calculations, we used R software and FactorMin R package for PCA [START_REF] Lê | FactoMineR: An R Package for Multivariate Analysis[END_REF].

Results

Petrography of brannerite ores

Hydrothermal brannerite

Brannerite crystals from La Gardette occur as laths, associated with Bi-Cu minerals (emplectite and wittichenite), native gold and quartz (Fig. 3a). A corroded boundary is always observed and composed of newly formed and chemically different brannerite, cerussite, REE phosphates, and iron oxides. Brannerite include minute inclusions of Urich minerals (not determined), while inclusion-free brannerite veins are also very common in the studied crystals.

Samples from Bou Azzer exhibit elongated laths of brannerite associated with quartz, barite and minor galena (Fig. 3b). Except for the presence of galena inclusions, BSE images of brannerite crystals show a rather homogeneous internal structure suggesting that brannerite crystals may be chemically homogeneous. However, element distribution mapping reveals a complex inner structure within crystals (Fig. 4a-d), marked by the presence of sub-rounded domains with varying Fe contents (Fig. 4d) Alteration also occurs as partial to full replacement (Fig. 3b), marked by an intricate association of U-rich and U-poor Ti oxides that coexist with coffinite and sulphate minerals (barite, anglesite) (Fig. 3c).

Millimetre-sized anhedral crystals of brannerite from Himalaya are enclosed in albite. BSE images and X-ray mapping reveal at least three distinct stages of brannerite crystallization (Figs. 3d, 4e-h). The first stage (Br I) is characterized by oscillatory-zoning and U, Th and Y chemical variation (Fig. 4f-h). This primary brannerite is cross-cut by two successive generations of veins (Br II and Br III) that may ressemble stockwerk. These veins are rich in U and poor in Y and Th. Alteration rims are very limited, but a Cu-U-bearing arsenate, possibly (meta-) zeunerite, and unidentified phosphate minerals are commonly found around these crystals.

Brannerite from Mont Chemin occurs as small crystals (less than 150 μm), associated with anatase, biotite, K-feldspar, REE carbonates and minor uraninite inclusions. Crystals are usually prismatic and display a large rim of altered brannerite (Fig. 3e). At Kratka Valley, brannerite occurs as sub-rounded crystals within a quartz matrix. Fractures are frequent and numerous inclusions of Ti oxides and uraninite are observed (Fig. 3f). Alteration is pervasive.

In the sample from Bou Azzer, TEM-Bright Field (BF, Fig. 5a) and STEM-HAADF (High Angle Annular Dark Field) (STEM-DF, Fig. 5b) images reveal the presence of a dense network of inclusions, either enriched in U (Fig. 5c) or in Pb (Fig. 5e). Selected Area Electron Diffraction (SAED) patterns identified within brannerite and dark U-rich inclusions result in broad diffuse rings equivalent to amorphous material (inset in Fig. 5a). The only trace of nano-crystalline material within the Bou Azzer sample corresponds to the cubic-like Pb-rich inclusion, certainly galena. The amorphous state of natural hydrothermal brannerites is also evidenced by Raman microspectroscopy (Fig. A1). The Raman spectra of hydrothermal brannerite samples, acquired in unaltered domains (Fig. 3), do not exhibit the characteristic features of pure synthetic brannerite [START_REF] Mesbah | Direct synthesis of pure brannerite UTi2O6[END_REF]. The Raman spectra of brannerite samples exhibit a small but significant feature at 151 cm -1 (only for La Gardette sample) and broad and poorly resolved features around 600, 750, and 820 cm -1 (Fig. A1).

Pegmatitic brannerite

Samples from Crocker's Well display sub-rounded elongated crystals of brannerite that displays intensive microfracturation (Fig. 6a). Brannerite is associated with Ti oxides, which are also present as micrometre-sized euhedral inclusions within brannerite. Along fractures and in the rim, U-Th rich silicates (possibly uranothorite) coexist with brannerite, although no genetic relationships can be demonstrated. This association is characteristic of an altered zone, which may also display U-depleted zones (Fig. 6a) and apatite. Microfractures are filled with U-Th secondary products, which are too small to be identified with the techniques employed here.

Brannerite from Hidden Valley is a single elongated millimetre-sized crystal, which displays well-developed corroded boundaries and transversal fracturing with alteration (Fig. 6b). Preserved brannerite exhibits tiny uraninite inclusions. The rim is zoned, showing differences in U depletion; it also contains secondary U-Th minerals, which belong to the thorite-coffinite series, according to Raman spectroscopic analyses.

The studied single crystal of brannerite from El Cabril is also characterized by a pervasive corroded boundary (Fig. 6c), but we also observed the presence of parallel fractures filled with a symplectite-like association of uraninite, Ti-oxides and an unknown yttrium-rich phase (Figs. 6d,. At sites of dilational jogs, uraninite crystals are bigger in size, but still anhedral. This fracturation/filling stage predates alteration, which occurs as a large and complex rim, surrounding the single crystal. This rim presents a succession of U-depleted domains with locally botryoidal aggregates and thin lamina of U-Ti oxides.

Euhedral prismatic brannerite crystals from Lodrino are associated with Kfeldspar. They do not display any evidence of internal texture, but, locally, a complex zoned rim of altered brannerite has been observed (Fig. 6e). Brannerite from Namibia is also a single crystal, which presents a sub-rounded irregular shape. Inclusions are rare within brannerite, but fractures are locally filled with uraninite partially replaced by coffinite (Fig. 6f). Interestingly, brannerite can also occurs with a collomorph texture, very similar to frequently observed pitchblende (Fig. 6f).

In the Lodrino sample, BF-TEM and DF-STEM images show the presence of altered domains within brannerite (Fig 8a-b), with a variation in composition for U, Ti, and Si (Fig. 8c-e). The brightest parts within this area (Fig. 8b) seem to be enriched in Si sometimes correlated with U enrichment. In contrast, darker areas are depleted in U and Ti. Pristine brannerite areas only reveal U and Ti. The diffraction pattern within the unaltered brannerite domain indicated it is completely amorphous (inset in Fig. 8a above); in contrast the diffraction pattern from the altered domain shows evidence of nanocrystalline material, with two intense rings with d-spacings of 3.45 Å and 1.87 Å (inset at the bottom in Fig. 8a). The amorphous state of natural pegmatite brannerites is confirmed by Raman microspectroscopy (Fig. A1), since like for hydrothermal brannerite, the Raman spectra acquired in unaltered domains (Fig. 6), do not exhibit the characteristic features of pure synthetic brannerite [START_REF] Mesbah | Direct synthesis of pure brannerite UTi2O6[END_REF]. Again, with the exception of the welldefined feature at 151 cm-1 for the sample from Namibia, only broad and poorly resolved features around 600, 750, and 820 cm -1 (Fig. A1).

Major and minor element content

The composition of brannerite was obtained from domains that appear homogenous and middle grey under the SEM (Figs 3,6), away from corroded grain boundaries (e.g. Figs. 3a,6c) and altered domains e.g. along fractures (e.g. Figs. 6b,6f).

Table 1 and boxplots of Fig. 9 summarize the distribution of major and minor element contents, expressed in atom per formula unit (apfu), following Collela et al. (2005; see section "Materials and Methods"). The measured U content is always less than 1 atom per formula unit. While Ti content of hydrothermal brannerite ranges from 1.9 to 2.1 apfu, this value is always less than 2 apfu for pegmatitic brannerite, except for BR1.

For major and minor elements, we observe variations in chemical composition between geological settings. For instance, aluminium in hydrothermal brannerite is always lower than 0.01 apfu, while brannerite from pegmatites have wider range in Al contents. Chemical variations are also observed within a single geological environment.

Ti, Fe and Y for hydrothermal brannerite show significant variations, while U, Ca and Th are the most variable components in pegmatitic brannerite. Finally, significant chemical variations are also observed for a given occurrence: e.g. U, Y, and Th for Himalaya and Ti, Fe and Si for Bou Azzer. Such variability of element content within a single sample is also revealed by element chemical maps, which display chemical zoning within crystals (e.g.

U, Th and Y in brannerite from Himalaya, Fig 4e-h).

Trace element content

The trace element content may vary by several orders of magnitude depending on samples, sample locality and sample type (Table 2, Fig. 10). Trace element concentration may reflect the local geological environment, like the high chromium content in Bou Azzer that is related to the occurrence of metasomatized ophiolites hosting the deposit (Fig. 10a). In the case of Mn and Nb, no clear signature can be pointed out at the scale of deposit type (Fig. 10b-c), although the Mont Chemin sample shows high concentrations in these two elements. For metals like Cu and Zn (Fig. 10d-e), no clear trend can be observed, except local enrichment in Cu and Zn for brannerite from Mont Chemin. The Pb content distribution between samples is very heterogeneous (Fig. 10f): this may either reflect local Pb enrichment as it correlates with high Zn and Cu contents (e.g. Mont Chemin), and/or enrichment due to production of radiogenic lead (as a result of elapsed time since crystallization). In this latter case, old and high U+Th brannerite like Crocker's Well and Hidden Valley have a Pb content that displays orders of magnitude higher than the youngest brannerite from Lodrino.

Principal component analysis major and minor elements

The results of the PCA applied to the EPMA dataset are displayed in Figure 8, where spot analyses (individuals, to the left) and elements (variables, to the right) are projected on the PC1 vs. PC2 plane. For the hydrothermal brannerite dataset, loadings of PC1 and PC2 represent 49.85% of the element content variability (Fig. 11a-b). The PCA plot underlines two main opposed pairs of element clusters. For the first pair mostly loaded by PC1, one group is composed of Ce, P, Y, and Nd, while the other group includes U and Th. For the second pair mostly loaded by PC2, a cluster composed of Fe, Mg, Ca and Si is opposed to Ti. Spot representation in the PC1 vs. PC2 plane refers to the sample location. PC1 (mostly loaded by U, Th, and REE) is correlated with samples from Mont Chemin and Himalaya, whereas PC2 (loaded by Ti, Ca, Fe) is correlated with samples from Bou Azzer, Kratka Valley and La Gardette.

For pegmatite samples, PC1 and PC2 represent 56% of chemical composition variations (Fig. 11c-d). The PCA also reveals some differences like Si and Th that are now observed as clusters in association with REE and P. The group of elements opposed to Ti includes Al, but not Ca, which occupies an intermediate position. All individuals are grouped, without any overlap of sample localities (Fig. 11c). As a result, two subgroups can be distinguished. While a first one (PC1 loading) including the Crocker's Well, Hidden Valley, and El Cabril samples correlates with U, Th and REE, a second one (PC2 loading) composed of Namibia and Lodrino samples, correlates with Ti, Al and Fe.

Inferred chemical substitutions in brannerite

The EPMA analytical totals, expressed as weighted per cent of oxides (wt%) for each analysis range between 95% and 100%, except for samples from Bou Azzer (mean 92.11 wt%) and Crocker's Well (mean 92.61 wt%) samples (Table 1). This range is consistent with values provided by [START_REF] Charalambous | Synthesis, characterisation and dissolution of brannerite[END_REF] and [START_REF] Macmillan | Chemical and textural interpretation of late-stage coffinite and brannerite from the Olympic Dam IOCG-Ag-U deposit[END_REF].

Totals lower than 100% can be related to several factors:

(1) Among REEs, only Ce and Nd were measured by EPMA, and both elements account for only 15 to 50% of the total REE of the sample, depending on the LREE anomaly (see section Trace elements variation);

(2) We assumed that EPMA-measured oxygen only occurs as O 2-anions within the brannerite structure. However, U (and Th) -decays induce radiation damage leading to amorphization of the brannerite crystals as confirmed by TEM imaging (Figs. 5,8) and the complete loss of the Raman vibrational mode (Fig. A1). The self-radiation damages (metamictization), which affect the crystal structure of brannerite can contribute to incorporation of either H2O or OH - [START_REF] Lumpkin | Chemistry, microstructure, and alpha decay damage of natural brannerite[END_REF]. These authors reported H2O contents between 0 and 3.7 wt%, and up to 7.4 wt% in highly damaged crystals from Crocker's Well. Other deviations from ideal stoichiometry (AB2O6) can be achieved through vacancies or excess oxygen [START_REF] Colella | Determination of the uranium valence state in the brannerite structure using EELS, XPS, and EDX[END_REF];

(3) Calculations of weighted oxide content assumed a unique valence for U (U 4+ ), Fe (Fe 3+ ), Ce (Ce 3+ ) and Pb (Pb 2+ ). While this is probably correct for the three latter ones, direct measurements of uranium chemical states on brannerite samples have demonstrated that higher valence states (5+ and 6+) should be considered [START_REF] Vance | Crystal chemistry, radiation effects and aqueous leaching of brannerite, UTi2O6[END_REF][START_REF] Vance | Crystal chemistry and stabilization in air of brannerite, UTi2O6[END_REF][START_REF] Finnie | Examination of U valence states in the brannerite structure by near-infrared diffuse reflectance and X-ray photoelectron spectroscopies[END_REF].

Our dataset confirms the variability of brannerite compositions reported in the literature [START_REF] Lumpkin | Chemistry, microstructure, and alpha decay damage of natural brannerite[END_REF][START_REF] Macmillan | Chemical and textural interpretation of late-stage coffinite and brannerite from the Olympic Dam IOCG-Ag-U deposit[END_REF], but in these studies, no distinctions were made based on the geological environment where brannerite crystallized. As shown by the respective locations of variable (elements) and individuals (samples) clusters in the PCA plots (Fig. 11), chemical heterogeneity is mostly due to replacement of Ti by Fe, Al and U by other cations, like Th, Ca, REE and Y with similar ionic radius in 6-fold coordination sites [START_REF] Shannon | Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides[END_REF].

Uranium substitutions in the A site by Th, Ca, REE and Y account for up to 50% of A site occupancy (Table 1). Substitution between U and Th is straightforward:

U 4+ = Th 4+ (1)
But this substitution is important only in brannerites from Mont Chemin, Hidden Valley and Crocker's Well (Fig. 12a-b). For other cations (Ca, REE, Y), coupled substitutions must be considered to account for their incorporation [START_REF] Lumpkin | Chemistry, microstructure, and alpha decay damage of natural brannerite[END_REF]. The Ca content in the A site is always associated with higher calculated average U valences (Fig. 12c), which may reflect the following substitutions.

2U 4+ = Ca 2+ + U 6+ (2) 3U 4+ = Ca 2+ + 2U 5+ (3)
While the presence of U 6+ is commonly observed in U minerals formed under oxidizing conditions, the presence of U 5+ was presumed in the Ca-rich brannerite from El Cabril [START_REF] Vance | Crystal chemistry and stabilization in air of brannerite, UTi2O6[END_REF]. [START_REF] René | Uraninite, Coffinite and Brannerite from Shear-Zone Hosted Uranium Deposits of the Bohemian Massif (Central European Variscan Belt)[END_REF] also proposed these substitutions to explain the high Ca content of brannerite from the Bohemian Massif.

PCA analysis shows an excellent correlation between P and Y + REE (Fig. 11) suggesting that phosphorus could also be involved in the substitution of U 4+ in the A site via the substitution:

2U 4+ = (Y, REE) 3+ + P 5+ (4)
Although the ionic radius of P 5+ (0.38 Å) is very different from that of U 4+ (0.89 Å), the partial destruction of the crystal structure of brannerite through metamictization may have favoured the incorporation of P into the octahedral coordination A site [START_REF] Shannon | Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides[END_REF]. In our case, the REE + Y contents (up to 5 x 10 4 ppm) cannot be counterbalanced via substitution (4), because of low average P contents (10 2 ppm). The incorporation of REE and Y in the A site is also made possible by substituting and oxidizing U 4+ into U 5+ through substitution 2U 4+ = (Y, REE) 3+ + U 5+ (5) Fig. 12c-f shows that hydrothermal brannerite from La Gardette and Himalaya are characterized by a clear relationship between Y + Ce and U 4+ or average U valence consistent with the substitution vector of equation ( 5). Brannerites from pegmatites also show a correlation between U 4+ and Y + Ce apfu, but with a different slope. This difference can be due to either unanalysed REE (and fractionation between the REE) or a different substitution mechanism. This relationship between Y + REE substitution in the A site and the genetic type has also been reported in Olympic Dam brannerite, which belongs to different generations [START_REF] Macmillan | Chemical and textural interpretation of late-stage coffinite and brannerite from the Olympic Dam IOCG-Ag-U deposit[END_REF].

Composition variability of brannerite is also due to replacement of Ti by different cations up to a maximum of 25% of the B site occupancy. PCA analysis of Fig. 11 shows that Ti and Fe 3+ +/-Al 3+ are correlated in both hydrothermal and pegmatitic brannerite.

In the pegmatitic brannerite, substitution of Ti by these tetravalent cations induces a charge deficit on the B site that could be compensated by higher valences of U on the A site, through coupled substitutions like (Fe, Al) 3+ + U 5+ = Ti 4+ + U 4+ (6) 2(Fe, Al) 3+ + U 6+ = Ti 4+ + 2U 4+ (7) Fig. 10 shows a correlation between Ti or U average valence with Fe 3+ + Al 3+ , which is consistent with substitutions ( 6) and ( 7). The respective contribution of substitutions (2),

(3), ( 5), ( 6) and ( 7) in the A and B sites to the average valence is difficult to ascertain, except for pegmatitic brannerite from Namibia (Fig. 13). In this case, the limited amount of Ca, REE and Y (<0.1 apfu) (Fig. 12) cannot account for the high average valence (4.63) of U that is better explained by high Fe and Al content (0.25 to 0.4 apfu; Fig. 13). Coupled substitutions involving Ti or other cations of the B site, as proposed in [START_REF] Lumpkin | Chemistry, microstructure, and alpha decay damage of natural brannerite[END_REF] and [START_REF] Macmillan | Chemical and textural interpretation of late-stage coffinite and brannerite from the Olympic Dam IOCG-Ag-U deposit[END_REF] could also explain the absence of direct correlation between U and Ca in the PCA plots for hydrothermal and pegmatitic brannerite (Fig. 11). [START_REF] Lumpkin | Chemistry, microstructure, and alpha decay damage of natural brannerite[END_REF] proposed an alternative substitution to compensate the charge deficit induced by the replacement of Ti by Fe and Al:

(Fe, Al) 3+ + Nb 5+ -> 2Ti 4+ (8)

In our case, there is no positive correlation between Fe, Al, and Nb. Fe-Al-poor hydrothermal brannerite is rich in Nb, whereas pegmatitic brannerite generally presents higher Al and Fe contents and is depleted in Nb ( Figs 9c-d, 10c). [START_REF] Macmillan | Chemical and textural interpretation of late-stage coffinite and brannerite from the Olympic Dam IOCG-Ag-U deposit[END_REF] also suggests that missing charges could be due to the removal of OH -anions through the substitution Ti 4+ + OH -= (Fe 3+ , Al 3+ ) (9), since appreciable water contents up to 7.4 wt% have been measured in natural brannerite [START_REF] Lumpkin | Chemistry, microstructure, and alpha decay damage of natural brannerite[END_REF].

For hydrothermal brannerite, substitutions on the B site are limited and in many cases the calculated Ti amount exceeds 2 apfu (Fig. 13a). Such deviation was also reported in magmato-hydrothermal brannerites from Olympic Dam [START_REF] Macmillan | Chemical and textural interpretation of late-stage coffinite and brannerite from the Olympic Dam IOCG-Ag-U deposit[END_REF] and different hypotheses can be advanced: (1) coupled substitutions across the two sites; (2) nanometric inclusions of Ti oxides intergrown with brannerite, similar to macroscopic structures in magmatic and metamorphic brannerite (Figs 2, 4); (3) vacancies or other substituents at the anion sites, causing overestimation of the cation content in the structural formula calculation; (4) alteration processes leading to a partial removal of U, without changing the crystal texture at the microscale. The Raman spectra obtained from La Gardette and Namibia brannerites show a very small and broad band at around 640 cm -1 and the characteristic Eg mode at 151 cm -1 (Fig. A1). Such features are interpreted as a spectroscopic signature of nanocrystalline anatase, probably blue-shifted with regard to the corresponding mode of its core crystalline counterpart, displaying a significant broadening of its profile [START_REF] Bonne | Surface properties and thermal stability of SiO2-crystalline TiO2 nanocomposites[END_REF]. This is the result of the metamictization of brannerite crystals, even in the unaltered domains.

As noted by [START_REF] Lumpkin | Chemistry, microstructure, and alpha decay damage of natural brannerite[END_REF] and [START_REF] Macmillan | Chemical and textural interpretation of late-stage coffinite and brannerite from the Olympic Dam IOCG-Ag-U deposit[END_REF], there is almost no correlation between Ti and Si abundances, as occupancy of octahedral sites by Si is impossible in low-pressure oxide compounds [START_REF] Mysen | Silicate Glasses and Melts: Properties and Structure[END_REF]. PCA plots display very heterogeneous trends for Si relative to other elements (Fig. 11). While, for hydrothermal brannerite, we may note a correlation between Si and Ti, for pegmatitic samples we rather observe Si opposed to U along the PC1 (Fig. 11). This suggests either an addition of Si within A sites, or the presence of nanoscale U-bearing silicates such as coffinite. TEM-EDS chemical mapping revealed that parts of brannerite altered domains are enriched in Si and depleted in U (Fig. 8a-e). ). From the SAED patterns taken in this altered domain (Fig. 8a), apart from diffuse rings corresponding to amorphous material, additional diffraction spots with equivalent d-spacings of 3.45 Å and 1.87 Å could correspond to the ( 200) and (321) planes of coffinite (3.41 Å and 1.88 Å, respectively from [START_REF] Pointeau | Synthesis and characterization of coffinite[END_REF], although those of brannerite (3.50 Å and 1.85 Å) are very close. For comparison, in (Y, REE, U, Th)-(Nb-Ta-Ti) oxide minerals, altered domains were also characterized by Si gain and U loss. This alteration results from fluid-mineral interaction, favoured by fracturing due to radiation damage accumulated in U and Th-rich oxide minerals [START_REF] Duran | Fluid-mediated alteration of (Y,REE,U,Th)-(Nb,Ta,Ti) oxide minerals in granitic pegmatite from the Evje-Iveland district, southern Norway[END_REF]. A very similar process probably occurs for brannerite as (1) all crystals of natural brannerite are metamict (Figs. 5, 8, A1) and (2) Si-rich brannerite (e.g. Crocker's Well and Hidden Valley) are characterized by radial fracturing and welldeveloped altered domains (Fig. 6a-b). Further careful nanometric observations and additional brannerite synthesis in Si-rich environments are necessary to better understand the mechanisms for Si incorporation within brannerite.

Brannerite fingerprints

Major element and substitution

These new results show that each locality and each genetic type are characterized by various types and degrees of substitution, either on the A or on the B sites (Fig. 14). Fig. 14a shows that hydrothermal brannerite is mostly characterized by a predominance of A site substitution (90%), while pegmatitic brannerite generally presents a higher proportion (20%) of B site substitution. Pegmatitic brannerite from Namibia represents an extreme case, with a predominance of B site substitution (70 to 90%). The incorporation of Si, whose mechanism is not well understood, seems to increase when both A and B site substitutions are present (Fig. 14a). However, this could also reflect the degree of alteration and mirrors the possible modification of the initial chemical composition of brannerite.

Brannerite populations can also be distinguished based on the cations incorporated in sites A and B via the substitutions described previously. In hydrothermal brannerite, except for Th-rich brannerite from Mont Chemin, A site substitution is mostly characterized by high REE + Y contents, with local enrichment in Ca such as in Bou Azzer (Fig. 14b). For pegmatitic brannerite, A site is characterized by (1) an equal distribution of Th and Y + Ce and (2) various degree of Ca substitution (Fig. 14b). In uraninite formed under hydrothermal conditions, the Th content is usually negligible as Th is less mobile and Th 4+ displays very low solubility [START_REF] Cuney | Physicochemical and crystal-chemical controls on accessory mineral paragenesis in granitoids: implications for uranium metallogenesis[END_REF]. In magmatic environments, the Th content generally increases (e.g. [START_REF] Förster | The chemical composition of uraninite in Varsican granites of the Erzgebirge, Germany[END_REF][START_REF] Frimmel | Uraninite chemistry as forensic tool for provenance analysis[END_REF], except if the source of radiogenic elements (magma or protolith) is initially poor in Th. In the B site, while only Fe 3+ replaces Ti in hydrothermal brannerite, pegmatite brannerite are characterized by the incorporation of both Fe 3+ and Al, with an Al/Fe 3+ ratio around 1:6 (Fig. 14c).

Strong variations in chemical composition are also observed at the scale of a given sample or locality, as exemplified by the case of Himalaya. Although morphological differences support the presence of three brannerite generations (Fig. 4e-h), their composition follows the same substitution trends (1) and ( 5). This suggests dissolutionreprecipitation process of brannerite without an external chemical contribution. This observation differs from the results reported at Olympic Dam, in which four generations of brannerite are related to distinct substitutaion mechanisms [START_REF] Macmillan | Chemical and textural interpretation of late-stage coffinite and brannerite from the Olympic Dam IOCG-Ag-U deposit[END_REF].

In addition to substitution-related fingerprints (Fig. 14), it is possible to obtain individual signatures for either the brannerite genetic type or the brannerite locality using statistical methods. The non-parametric Kolmogorov-Smirnov test was used to compare the distribution of two populations and therefore evaluate the homogeneity between two samples for a given element. The statistical analysis shows that element content distributions significantly differ (at 95%) between samples, suggesting that each locality has its own mineral chemistry (Fig. 15). However several samples show a weaker range of differing elements, supporting that these localities are close in terms of mineral chemistry (e.g. BA and KV or CW and HV). This is an agreement with the distribution observed in PCA (Fig. 11) and classification plots (Fig. 14).

Trace elements variation

Fingerprints can also be deduced from trace elements measured in brannerite. As mentioned in section 3.3, interpreting the trace element content (Fig. 10) is difficult as some elements may either (1) be or not be associated with coupled substitution (e.g. Nb);

(2) reflect the local geological environment (Cr at Bou Azzer); (3) derive from different sources (e.g. common versus radiogenic Pb). In the case of REE, their incorporation is associated with stoichiometric rules, as ionic radii of REE are close to U, despite a relative lack of knowledge of charge balance mechanisms. The shapes of REE patterns differ between the two genetic types:

(1) Hydrothermal brannerites are marked by a bell-shape (Fig. 16a). MREE such as Tb (0.92 Å), Dy (0.91 Å), Ho (0.90 Å) and Er (0.89 Å) have ionic radii very close to that of U 4+ (0.89 Å) in 6-fold coordination [START_REF] Shannon | Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides[END_REF] and, therefore, are most easily incorporated in the brannerite structure. Similar patterns were observed for uraninites formed in unconformity deposits [START_REF] Pagel | The rare earth elements in natural uranium oxides[END_REF][START_REF] Mercadier | Origin of uranium deposits revealed by their rare earth element signature[END_REF][START_REF] Frimmel | Uraninite chemistry as forensic tool for provenance analysis[END_REF]. The total amount of REE is usually high (more than 10000 ppm) and the LREE/HREE ratio oscillates between 0.3 and 3.8 (Fig. 17).

(2) At high temperature (>500°C), the brannerite structure dilates [START_REF] Zhang | Recrystallization of amorphous natural brannerite through annealing: the effect of radiation damage on the chemical durability of brannerite[END_REF] allowing the incorporation of REE, without any fractionation due to differences in ionic radii. Pegmatitic brannerites are marked by LREE depletion, or a regular decrease from HREE towards LREE (Fig. 16b). The total amount of REE shows strong variations (Fig. 17), probably due to competitive substitutions at site A (Fig. 14c). In addition to a general fractionation between LREE and HREE, it is worth noting that the fractionation rate (LREE/HREE) increases with the total amount of REE (Fig. 17).

For the same sample type or locality, the REE patterns are very consistent (Fig. 16).

Minor differences may be mostly due to variations of total REE and/or a change in the europium anomaly. In most cases, the Eu anomaly is absent or slightly negative attesting for an early fractionation of Eu by feldspars, which are described in almost all mineral associations. Eu positive anomalies are reported in La Gardette and El Cabril and could be associated to a local change of redox conditions. It is noteworthy that positive anomalies in El Cabril samples tend to be associated with the high total REE analysis (Fig. 16b).

Cerium also shows a frequent positive anomaly, which is also related to redox conditions (e.g. Mont Chemin). Under oxidizing conditions, Ce 3+ changes to Ce 4+ , which is preferentially incorporated in site A of brannerite, since its ionic radius (0.87 Å for Ce 4+ in 6-fold coordination; [START_REF] Shannon | Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides[END_REF] is close to that of U 4+ (0.89 Å) and its addition does not require charge balance.

These results suggest, that beyond crystal-scale controls, addition of REE also depends on external parameters such as temperature, but also of the presence of other mineral phases that may trigger REE fractionation (Fig. 16c). Among them, monazite, which was reported in several brannerite-bearing samples, preferentially partition LREE and could be at the origin of the LREE-depleted patterns of most of brannerite.

Implication of brannerite systematics

Fingerprints for tracking origin of ore

Defining brannerite fingerprints offers a potential useful application in tracking down the source of possibly illegally mined uranium ores. Such an approach was applied to a variety of conflict or strategic minerals, like colombo-tantalite [START_REF] Melcher | Fingerprinting of conflict minerals: columbite-tantalite ("coltan") ores[END_REF][START_REF] Melcher | Tantalum-(niobium-tin) mineralisation in African pegmatites and rare metal granites: constraints from Ta-Nb oxide mineralogy, geochemistry and U-Pb geochronology[END_REF], gems [START_REF] Giuliani | Oxygen isotope systematic of emerald: relevance for its origin and geological significance[END_REF][START_REF] Giuliani | Oxygen isotope composition as a tracer for the origins of rubies and sapphires[END_REF] and uraninite [START_REF] Mercadier | Origin of uranium deposits revealed by their rare earth element signature[END_REF][START_REF] Frimmel | Uraninite chemistry as forensic tool for provenance analysis[END_REF][START_REF] Spano | Trace element and U isotope analysis of uraninite and ore concentrate: applications for nuclear forensic investigations[END_REF]. Chemical fingerprints of brannerite consists of a combined characterization of the major substitution trends (A and B sites), the nature of elements incorporated, and the shape of REE patterns. Other trace elements can be used as they may represent a locality-specific feature, which may be useful in forensic studies.

However, as shown by this study and reported in previous literature (e.g. [START_REF] Charalambous | Chemical and microstructural characterisation studies on natural and heat treated brannerite samples[END_REF][START_REF] Lumpkin | Chemistry, microstructure, and alpha decay damage of natural brannerite[END_REF][START_REF] Macmillan | Chemical and textural interpretation of late-stage coffinite and brannerite from the Olympic Dam IOCG-Ag-U deposit[END_REF], brannerite ores are generally complex and include other uranium minerals (e.g. uraninite, coffinite) and/or successive generations of brannerite with variable mineral chemistry (Fig. 4e-h). Hence, traceability studies cannot be done at ore scale, but require careful consideration of U-bearing mineral phases. A complementary signature using isotope systematics (O, U, Th, Pb) as proposed for uraninite (e.g. [START_REF] Pajo | Investigation of the oxygen isotopic composition in oxidic uranium compounds as a new property in nuclear forensic science[END_REF] could also be a useful tool to provide unequivocal source for brannerite.

Using brannerite as a tool for dating mineralizing events

The high U (and Th) abundance makes brannerite a good candidate tool for dating mineralizing events. Previous geochronology was carried out using a variety of techniques including the ID-TIMS [START_REF] Ludwig | Geochronology of Precambrian granites and associated U-Ti-Th mineralization, northern Olary province, South Australia[END_REF][START_REF] Copeland | An early pliocène thermal disturbance of the main central thrust, central Nepal: Implications for Himalayan tectonics[END_REF] and the LA-ICPMS (Oberthür et al., 2009) over a large range of ages (4.8 Ma to 670 Ma). These published geochronological data lack in most cases detailed petrography to support unequivocal evidence for (1) unique brannerite chemistry close to ideal composition to limit matrix effects and (2) single crystallization stage to avoid mixing between different age populations. The nature of Pb is another crucial issue that needs to be considered for dating application. In 6-fold coordination, the respective ionic radii of Pb 4+ and Pb 2+ are 0.77 Å and 1.19 Å, respectively [START_REF] Shannon | Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides[END_REF], suggesting that Pb poorly substitutes for U at the A site. The dilatation of the crystal structure at high temperature probably enables a larger addition of Pb 2+ in brannerite, but this cannot explain the local Pb enrichment (e.g. more than 10000 ppm at Montchemin; Fig. 10f). Radiogenic Pb produced by decay of U and Th, can be present in significant concentration in old brannerite, like Hidden Valley and Crocker's Well (Fig. 10f). Significant lead loss has also been reported, which makes geochronological data interpretation even more challenging [START_REF] Lumpkin | Chemistry, microstructure, and alpha decay damage of natural brannerite[END_REF].

Furthermore, the common association of brannerite with galena at various scales (Figs. 3,5,6) also questions the origin of the measured Pb. Lead is a network modifier and thus, as brannerite becomes metamict with time, lead is often trapped in nanometric galena (Fig. 5; [START_REF] Lumpkin | Chemistry, microstructure, and alpha decay damage of natural brannerite[END_REF]. Furthermore, [START_REF] Macmillan | Chemical and textural interpretation of late-stage coffinite and brannerite from the Olympic Dam IOCG-Ag-U deposit[END_REF] suggest that galena can also be (1) cogenetic with brannerite; (2) a product of the recrystallization of early Pb-rich brannerite; (3) a product of uraninite dissolution. The issue of U loss in altered domain (Fig. 8) and the presence of exsolution of U-rich nanodomains (Fig. 5a-c) in brannerite, are also of primary importance for geochronological purposes. Accurate interpretation of ages, obtained either by bulk (ID-TIMS) or high resolution in-situ techniques (SIMS, LA-ICPMS) requires the petrogenesis and chemistry of both brannerite and associated phases, from the microscale down to the nanoscale to be determined.

Recovery of U and other elements from natural brannerite

While brannerite has been explored as a matrix storage for nuclear wastes (e.g. [START_REF] Lumpkin | Alpha-decay damage and aqueous durability of actinide host phases in natural systems[END_REF], its refractory nature to leaching has been recently challenged in order to evaluate potential uranium recovery (e.g. [START_REF] Lottering | Mineralogy and uranium leaching response of low grade South African ores[END_REF][START_REF] Charalambous | Leaching behaviour of natural and heat treated brannerite-containing uranium ores in sulphate solutions with iron (III)[END_REF]Gilligan and Nikoloski, 2015a,b). Based on tests made on natural and synthetic crystals, these authors have shown that several parameters can influence the recovery rates such as temperature, pH, and Fe 3+ concentrations in the solvents. This last parameter is very important, as the amount of extracted U from brannerite is proportional to the Fe 3+ concentration [START_REF] Gogoleva | The leaching kinetics of brannerite ore in sulfate solutions with iron(III)[END_REF][START_REF] Charalambous | An investigation on the dissolution of synthetic brannerite (UTi2O6)[END_REF][START_REF] Charalambous | Leaching behaviour of natural and heat treated brannerite-containing uranium ores in sulphate solutions with iron (III)[END_REF]. Iron substitutes for titanium in the B site and its abundance, which varies between samples, depends on the genetic types of brannerite (Figs. 11b,12c). The high Fe content of some pegmatitic occurrences (Namibia) makes them good candidates for naturally magnifying U recovery.

However, these ores are generally complex and brannerite also contains other elements such as Ca, REE and Si (Fig. 12a). While leaching mechanisms remain unknown, it appears that when uranium is partially replaced in the brannerite structure by other elements (Ce, Ca…), the extraction of uranium is reduced [START_REF] Charalambous | Characterisation and dissolution studies on various forms of brannerite[END_REF]. Hence, several elements that could represent economically interesting co-products (e.g. REE) may also represent a limit for acceptable recovery rates of uranium from brannerite

Conclusion

Based on original analytical data from a variety of brannerite occurrences, this study demonstrates that chemical contents and REE abundances of brannerite reflect the geological conditions of their formation. Combining both results, it is possible to obtain a reliable geochemical classification at the scale of ore locality and genetic types. Such fingerprints are useful for forensic science, the exploration industry, understanding metallogenic process and optimizing extraction of uranium. Our dataset is not exhaustive though, and it is necessary to complement it with other occurrences from other genetic environments, such as uraniferous conglomerates (e.g. Elliot lake, Witwatersrand) or metamorphic domains (Domes Region in Zambia). Applying our approach also requires not only blind spot analyses, but a careful preliminary study or ore petrography, as brannerite ores can be polyphase and chemically complex.

This study also points out the partial misunderstanding of various geochemical processes at the atomic scale. One of the major points is the valence state of U, its origin (e.g. the role of redox conditions for brannerite formation) and the major consequences for the present complex mineral chemistry of brannerite. Itself, the presence of uranium has severe effects on brannerite crystal structure and the metamict aspect of variously aged natural brannerite was demonstrated (e.g. [START_REF] Lumpkin | Chemistry, microstructure, and alpha decay damage of natural brannerite[END_REF]. This may be responsible for the origin of various crystal defects, which may represent possible nonstoichiometric traps for a variety of elements (e.g. Si). How to reconcile such crystallographic self-alteration with the apparent pristine mineral geochemistry is not therefore straightforward. Further study on natural brannerite is required to follow this holistic approach and to combine various scale observation and techniques, in order to meet such a challenge. FIG. 9. Boxplots of major and minor element contents for each studied brannerite sample, considering its genetic type. Contents are given in apfu calculated on a basis of 6 oxygen atoms from EPMA results (Table 1). For Y, abundances obtained by LA-ICPMS measurement and available in Table 2 are For each element, its distribution was compared between two samples (locality or genetic type). The more red coloured cases there are, the more significant differences in mineral chemistry between samples there are.

Appendix -Geological setting of studied brannerite samples

Geological setting of hydrothermal brannerite

La Gardette Mine (GD) is located in Western French Alps close to Bourg-d'Oisans city. Alpine-type quartz veins crosscut the amphibolite of the Variscan basement and its Triassic carbonate cover [START_REF] Barféty | Carte géologique détaillée de la France à 1/50.000°[END_REF]. Ore minerals include native gold, galena, pyrite, chalcopyrite, tennantite and brannerite [START_REF] Geffroy | La brannerite du filon aurifere de la Gardette (Isere) et sa signification metallogenique[END_REF]. Age of mineralization is currently unknown but it could be related to Upper Miocene (ca. 5-11 Ma) episodes of hydrothermal fluid circulation recorded in the Belledonne Massif to the Northwest [START_REF] Gasquet | Miocene to Messinian deformation and hydrothermal activity in a pre-Alpine basement massif of the French western Alps: new U-Th-Pb and argon ages from the Lauzière massif[END_REF].

The Bou Azzer (BA) deposit is located in the Moroccan Anti Atlas Belt. It occurs within a Proterozoic ophiolitic unit covered by unconformable Palaeozoic sedimentary rocks [START_REF] Leblanc | Cobalt arsenide ore bodies related to an upper Proterozoic ophiolite; Bou Azzer (Morocco)[END_REF]. Bou Azzer is classified as a particular case of Five-Element Vein-Type deposits [START_REF] Leblanc | Co-Ni arsenide deposist with accessory gold, in ultramafic rocks from Morocco[END_REF][START_REF] Kissin | Five-element (Ni-Co-As-Ag-Bi) veins[END_REF]; it is currently mined for Co Ni, Ag and Au. The polyphase mineralization includes an early Ni-Co-Fe arsenide stage followed by a late Cu-Zn-Fe sulfide stage [START_REF] Ennaciri | Brine inclusions from the Co-As(Au) Bou Azzer district, Anti-Atlas Mountains, Morocco[END_REF] related to high salinity brines [START_REF] Leblanc | Native silver mineralization along a rodingite tectonic contact between serpentinite and quartz diorite (Bou Azzer, Morocco)[END_REF]. While uraninite is present throughout the whole mineralization evolution, brannerite only occurs during the latest stage in association with molybdenite, chlorite, and quartz [START_REF] Ennaciri | Contribution a l'étude du district a Co, As[END_REF]. Brannerite stage has been dated by U-Pb LA-ICPMS method at 310 ± 5 Ma (Oberthür et al., 2009). Brannerite (HL) was collected in the Chhuling Khola Valley in Nepal. This area consists of a series of schists, gneisses, and migmatites that belong to the Greater Himalayan Sequence, which is thrusted over the low-grade metamorphic rocks of the Lesser Himalayan Sequence, along the Main Central Thrust [START_REF] Pêcher | The metamorphism in the Central Himalaya[END_REF]. Among these high-grade gneisses, an albitized and U-mineralized zone is exposed (Maruejol, 1988).

While biotite gneisses have recorded an early sodic metasomatic stage coeval with ductile deformation along the MCT, brannerite co-precipitated with secondary albite in brittle veins forming a stockwork zone. Formation of brannerite is considered as the result of alteration of Ti oxides of the biotite gneisses by Na-U alkaline and oxidizing fluids (Maruejol, 1988) under low-grade metamorphic conditions. Isotope Dilution termal ionization mass spectrometry (ID-TIMS) U-Pb dating on brannerite has given a crystallization 206 Pb/ 238 U age at 4.8 Ma [START_REF] Copeland | An early pliocène thermal disturbance of the main central thrust, central Nepal: Implications for Himalayan tectonics[END_REF].

The Mont Chemin (MC) mines are located in the eponymous mountain in Western Valais, Switzerland. The mines have been exploited from Middle Age until to the 20 th century for Au, Ag, Pb, Fe, and fluorite [START_REF] Ansermet | Le Mont Chemin. Nouvelles Imprimeries Pillet[END_REF]. The veins crosscut the metamorphic Variscan basement (external crystalline massif) and particularly small late Palaeozoic granite intrusions within gneisses. At the Tête des Econduits, quartz veins include scheelite, anatase, fluorite, native Au, and brannerite [START_REF] Meisser | La géologie et les concentrations minérales du Mont Chemin[END_REF]. These Alpine-type veins are probably related to a regional Miocene episode of hydrothermal fluid circulation at ca 10 Ma [START_REF] Marshall | Fluid inclusion, stable isotope and Ar-Ar evidence for the age and origin of gold-bearing quartz veins at Mont Chemin, Switzerland[END_REF].

The Kratka Valley (KV) occurrences are located to the north of Gemerska Poloma between Dobsina and Kosice in Eastern Slovakia. U-bearing quartz veins occur within the Ordovician Vlachovo Formation of the Southern Gemericum Unit (Vozarova et al., 2010). This volcano-sedimentary sequence was further intruded by Permian granites, covered by Mesozoic sediments and affected by Cretaceous regional metamorphism (Vozarova et al., 2014). A wide range of U mineralization is found within the Gemericum Unit, including U-Mo mineralized horizons, stratiform Cu-U redbeds and U-Mo stockworks [START_REF] Rojkovic | Stratiform and vein U, Mo and Cu mineralization in the Novoveskfi Huta area[END_REF]. U-Ti oxides, including brannerite, were reported from several localities [START_REF] Rojkovic | U-Ti minerals at the deposit Novoveska Huta (Slovenske Rudohorie Mts.)[END_REF]. At Kratka Valley, brannerite-bearing quartz veins also contain gold, arsenopyrite, chalcopyrite, molybdenite, pyrite, rutile, uraninite as well as many secondary U minerals. Timing of brannerite formation is currently unknown, but Lower Jurassic (Stevko et al., 2014) and Lower Cretaceous [START_REF] Rojkovic | Stratiform and vein U, Mo and Cu mineralization in the Novoveskfi Huta area[END_REF] mineralizing events have been reported in the area.

Geological setting of pegmatitic brannerite

The Crocker's Well (CW) prospect, located in the southern part of Central Australia is a uranium occurrence discovered in 1951. Ore is hosted by peraluminous sodic granitoids, mainly adamellite and trondhjemite, and minor sodic gneisses (Ashley, 1984, and reference therein). Emplacement of this suite has been dated by zircon ID-TIMS (isotopic Dilution Thermal ionization Mass spectrometry) U-Pb at 1579.2 ± 1.5 Ma [START_REF] Ludwig | Geochronology of Precambrian granites and associated U-Ti-Th mineralization, northern Olary province, South Australia[END_REF]. Although the distribution of brannerite is controlled by fractures [START_REF] Campana | Regional geology and mineral resources of the Olary province[END_REF], the vein systems and the mineralized breccia are restricted to the host granite, which did not experience hydrothermal alteration.

Brannerite is associated with quartz, F-bearing phlogopite, sodic plagioclase, fluorapatite, niobian rutile, monazite, muscovite, chlorite, tourmaline, and fluorite [START_REF] Ashley | Sodic granitoids and felsic gneisses associated with uranium-thorium mineralisation, Crockers Well, South Australia[END_REF].

Brannerite formation probably results from the evolution of a late peraluminous magmatic system, as indicated by the younger 206 Pb/ 238 U ages obtained directly on brannerite (550-572 Ma, [START_REF] Ludwig | Geochronology of Precambrian granites and associated U-Ti-Th mineralization, northern Olary province, South Australia[END_REF]. In this sense, Crocker's Well uranium occurrence shares many analogies with Rössing and Limousin types (e.g. [START_REF] Cuney | Evolution of uranium fractionation processes through time: driving the secular variation of uranium deposit types[END_REF], with the exception of the sodic enrichment.

The Hidden Valley (HV) area is located at Brannerite Hill in the North Finders Ridge in south Central Australia. This area is characterized by Mesoproterozoic migmatitic gneisses associated with Neoproterozoic metasediments and volcanics [START_REF] Coats | Regional and Economic Geology of the Mount Painter Province[END_REF], which recorded metamorphism related to the Delamerian orogeny [START_REF] Foden | The timing and duration of the Delamerian Orogeny: correlation with the Ross Orogen and implications for Gondwana Assembly[END_REF]. Palaeozoic leucogranites and pegmatites dated around 450 Ma are intrusive within this metamorphic sequence [START_REF] Wülser | Uranium metallogeny in the North Flinders Ranges region of South Australia[END_REF]. Among the pegmatite intrusions, one displays an alkaline syenite composition and includes albite, K-feldspar, quartz, biotite, alkaline amphibole and brannerite [START_REF] Wülser | Uranium metallogeny in the North Flinders Ranges region of South Australia[END_REF]. Other brannerite occurrences (not studied) are within quartz-ilmenite veins such as Charlotte and Jacob mineralizations characterized by large euhedral brannerite crystals [START_REF] Wülser | Uranium metallogeny in the North Flinders Ranges region of South Australia[END_REF].

The El Cabril (EC) occurrence is located in the Sierra Albarrana, Andalusia (Spain).

This massif belongs to the late Proterozoic to Lower Cambrian Ossa Morena zone and is mainly composed of paragneisses, micaschists and garnet-bearing amphibolites [START_REF] Del Tánago | Amfibolitas graatiferas de Sierra Albarrana (Cordoba). Termobarometria e implicaciones para el desarrollo del metamorfismo regional[END_REF]Azor and Balle vre, 1997). Metamorphic rocks are cross cut by pegmatite intrusions, which are composed of quartz, K-feldspar, albite, muscovite, tourmaline, garnet, biotite, monazite, ilmenite, rutile and primary uranium minerals, such as brannerite and uraninite [START_REF] Garotte | Los yacimentos de pegmatitas de Sierra Albarrana[END_REF][START_REF] Contreras | Pegmatitas en materiales metamórficos del norte de la provincia de Córdoba: mineralogía y posibilidades económicas[END_REF].

Age of brannerite crystallization is unknown but is not older than the Devonian thermal event (351Ma -391Ma) recorded by amphibolite and metapelite in the Sierra Albarrana [START_REF] Dallmeyer | Cadomian vs. variscan evolution of the Ossa Morena Zone (SW Iberia): field and 40Ar/30Ar mineral age constraints[END_REF].

The Lodrino (BR1) pegmatite in Ticino, Switzerland crosscuts the Variscan orthogneisses of the Leventina Nappe (Rütti et al., 2008) and is mainly composed of quartz and orthoclase, with minor albite, muscovite, brannerite, molybdenite, scheelite, apatite, titanite, powellite and rutile [START_REF] Bianconi | La brannerite e la sua paragenesis nelle pegmatite di Lodrino (Ct. Ticino)[END_REF]. Age of pegmatite emplacement is unknown, but it is probably related to the well-known Tertiary pegmatite field that extends over Southwestern Switzerland [START_REF] Wenk | Zur Regionalmetamorphose und Ultrametamorphose im Lepontin[END_REF][START_REF] Burri | Tertiary migmatites in the Central Alps: Regional distribution, field relations, conditions of formation, and tectonic implications[END_REF]. This area overlaps the zone of alpine migmatization and available U-Pb geochronological constrains span between 29 and 20 Ma [START_REF] Guastoni | Tertiary pegmatite dikes of the Central Alps[END_REF]. This age is significantly older than the K-Ar age at ca. 11.4 Ma reported for the Lengenbach brannerite mineralization in Eastern Valais [START_REF] Purdy | K-Ar Ages of Fissure Minerals from the Swiss Alps[END_REF][START_REF] Graeser | Brannerite from Lengenbach, Binntal (Switzerland)[END_REF]. Sample NA12 is a single crystal from a pegmatite collected along the Marienfluss Valley, to the West of Hartmann Mountains, Northern Namibia. This pegmatite is intrusive within the Paleoproterozoic Epupa Metamorphic Complex, made of migmatized granitoid gneisses with rare intercalations of metasediments [START_REF] Kröner | SHRIMP zircon dating and Nd isotope systematics of Palaeoproterozoic migmatitic orthogneisses in the Epupa Metamorphic Complex of NW Namibia[END_REF]. This unit was intruded by Mesoproterozoic granitoids related to extension in the Southern Congo craton [START_REF] Kröner | Mesoproterozoic (Grenville-age) granitoids and supracrustal rocks in Kaokoland, northwestern Namibia[END_REF] and further experienced further overprinting due to the late Neoproterozoic to early Palaeozoic Pan-African event related to the Kaoko orogeny [START_REF] Goscombe | The metamorphic architecture of a transpressional orogen: the Kaoko Belt, Namibia[END_REF]. This later event, characterized by polyphase deformation and magmatism has produced biotite-muscovite pegmatite dykes, especially in the Hartmann Mountains [START_REF] Goscombe | Event geochronology of the Pan-African Kaoko Belt, Namibia[END_REF]; sample (NA12) is spatially related to this ca. 500 Ma episode [START_REF] Goscombe | Event geochronology of the Pan-African Kaoko Belt, Namibia[END_REF], but further studies are required to confirm this hypothesis.

Foils

  observations were carried out at Centre Technologique des Microstructures (CTµ) in Lyon 1 University (France), with a JEOL2100F transmission electron microscope (TEM) operated at 200 KeV, equipped with an energy dispersive spectrometer (SDD Oxford) and a High Angle Annular Dark Field (HAADF) detector used in Scanning Transmission Electron Microscopy (STEM) mode.

Figure captions FIG. 1 .

 captions1 Figure captions

  FIG. 10. Boxplots of trace element abundance measured by LA-ICPMS for each studied

  FIG. 16. Chondrite-normalized REE patterns from brannerite (a) to (b) and associated

  FIG. A1Raman spectra of a synthetic brannerite and studied natural brannerite samples.

  Figure 1 1222

  Figure 11 1252

TABLE A1

 A1 Standard used for calibration of EPMA analyses.

Acknowledgements

This article was part of the UTILE multi-disciplinary project and was sponsored by the NEEDS (CNRS-AREVA-CEA) program. We greatly thank Olivier Rouer (GeoRessources, Nancy), Martin Robyr (Univ Lausanne), Philippe de Parseval (centre de microcaratérisation Raimond Castaing, Toulouse) for EPMA analyses and mapping and Nadia Guignard (IC2MP, Poitiers) for Raman spectrometry. We express our gratitude to Lubos Vrtiska (Narodni Museum, Prag), Michel Cuney (GeoRessources), Jean-Claude Leydet and Marc Brouand (Orano) for providing a part of the samples. We thank Roger Mitchell and Jason Harvey for handling the manuscript and three anonymous rewievers for their constructive comments, which helped to significantly improve the manuscript.