Aurélien Beaumais

Arnaud Mangeret

David Suhard

Pascale Blanchart

Mejdi Neji

Charlotte Cazala

Alkiviadis Gourgiotis
email: alkiviadis.gourgiotis@irsn.fr

Combined U-Pb isotopic signatures of U mill tailings from France and Gabon: A new potential tracer to assess their fingerprint on the environment

Keywords:

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

U mill tailings are the radioactive residual waste of the mining and milling of U-ores (crushed and leached ore residue), which is the first step of the nuclear fuel cycle [START_REF] Landa | Isolation of uranium mill tailings and their component radionuclides from the biosphere-some earth science perspectives[END_REF][START_REF] Landa | Geochemical and biogeochemical controls on element mobility in and around uranium mill tailings[END_REF], IAEA, 2004;[START_REF] Landa | Uranium mill tailings: nuclear waste and natural laboratory for geochemical and radioecological investigations[END_REF][START_REF] Abdelouas | Uranium mill tailings: Geochemistry, mineralogy, and environmental impact[END_REF][START_REF] Campbell | Biogeochemical aspects of uranium mineralization, mining, milling, and remediation[END_REF]. Uranium mining and milling activities involved around 250 sites in France from 1948 to 2001, and produced 50 Mt of tailings resulting from the chemical extraction of U from the U-ore, as well as 170 Mt of mine waste rock (database: Programme MIMAUSA, 2019). These tailings are now disposed into 17 Tailing Management Facilities (TMFs) spread over 16 sites in France (e.g. L'Ecarpière, Jouac, Bellezane, Le Bosc; Fig. 1). In Gabon, uranium mining and/or milling activities involved around 5 sites from 1961-1999 and produced 7.5 Mt of tailings from Mounana milling plants (Loueyit et al., 2000). The tailings were disposed into the Mounana Tailing Management Facility.

Milling consists of the mechanical and the chemical processes allowing the concentration of the uranium fraction from the ore [START_REF] Landa | Geochemical and biogeochemical controls on element mobility in and around uranium mill tailings[END_REF]. Ores that contain limestones contents greater than 15% are usually leached with alkaline solutions using sodium carbonatebicarbonate, while most other ores are leached using sulfuric acid. The uranium extracted by the leaching solution is concentrated by solvent extraction or solid-phase extraction using ion-exchange resins and subsequent precipitation (with ammonia, magnesium oxide, hydrogen peroxide) of a uranium ore concentrate (~85 wt. % of U). The leached ore residues (i.e. tailings) are transferred into a waste-retention pond, or in a mine-out undergroundworking. Sometimes, the mill waste solution is also added to the tailings in the disposal. The waste slurries (barren solid and liquid) at acid leach mills are sometimes neutralized (usually with lime or calcium carbonate) prior to discharge in order to precipitate contaminants (e.g. calcium sulfate, Fe-oxyhydroxide) [START_REF] Nirdosh | A review of recent developments in the removal of Ra-226 and Th-230 from uranium ores and mill tailings[END_REF][START_REF] Somot | Radium behaviour during the diagenesis of Jouac uranium mill tailings (Haute-Vienne, France)[END_REF][START_REF] Ballini | A multiscalar study of the long-term reactivity of uranium mill tailings from Bellezane site (France)[END_REF][START_REF] Chautard | Geochemical characterization of uranium mill tailings (Bois Noirs Limouzat, France) highlighting the U and Ra-226 retention[END_REF]. The water released from tailings impoundments is typically treated with Ba chloride to allow the precipitation of radiobarite (Ra-rich barite) [START_REF] Ring | Radionuclides in process and waste streams at an operational uranium mill[END_REF][START_REF] Snodgrass | The chemistry of 226Ra in the uranium milling process[END_REF]. U-ores are enriched in U decay products, mainly U-238 series that include 234 U (half-life: 0.246 Ma), 230 Th (half-life: 75.4 ka), 226 Ra (half-life: 1602 a), 210 Pb (half-life: 22.3 a). After the chemical extraction of U (~90%) from U-ores, 238 U decay products and one part of initial U remain in the U mill tailings. Therefore, U mill tailings hold ~ 85% of the radioactivity of the initial U-ore [START_REF] Landa | Uranium mill tailings: nuclear waste and natural laboratory for geochemical and radioecological investigations[END_REF], and thus provisions are taken with regard to their potential radiological impact. Uranium and its radioactive decay products can be transferred from Umine sites or TMFs in the environment via mine drainage, mine water runoff, or erosion even decades after cessation of the mining activities [START_REF] Abdelouas | Uranium mill tailings: Geochemistry, mineralogy, and environmental impact[END_REF]IAEA, 2004;[START_REF] Cuvier | Trace elements and Pb isotopes in soils and sediments impacted by uranium mining[END_REF]Stetten et al., 2018;[START_REF] Mangeret | Early diagenesis of radium 226 and radium 228 in lacustrine sediments influenced by former mining sites[END_REF][START_REF] Gourgiotis | New Insights into Pb Isotope Fingerprinting of U-Mine Material Dissemination in the Environment: Pb Isotopes as a Memory Dissemination Tracer[END_REF][START_REF] Martin | An integrated approach combining soil profile, records and tree ring analysis to identify the origin of environmental contamination in a former uranium mine (Rophin, France)[END_REF].

However, weathering and erosion of local bedrock, such as U-rich granite, could also allow the transfer of a significant amount of U and its radioactive products in the environment [START_REF] Bernhard | Speciation of uranium in environmental relevant compartments[END_REF][START_REF] Owen | Mountain wetlands -Efficient uranium filters -Potential impacts[END_REF][START_REF] Regenspurg | Speciation of naturally-accumulated uranium in an organic-rich soil of an alpine region (Switzerland)[END_REF]Lefebvre et al., 2021a, Lefebvre et al., 2021b). Fingerprinting the potential sources of radioactive elements in the vicinity of TMF would help for the management of U mine tailings as well as contaminated sediments or soils.

Various tracers, such as elemental content, rare earth elements, and also isotopes (e.g. U, Th, Pb) have been previously suggested in order to fingerprint the origin of U-rich material, such as U-ores and U ore concentrate [START_REF] Keegan | The provenance of Australian uranium ore concentrates by elemental and isotopic analysis[END_REF][START_REF] Varga | Application of Lead and Strontium Isotope Ratio Measurements for the Origin Assessment of Uranium Ore Concentrates[END_REF][START_REF] Svedkauskaite-Legore | Investigation of the isotopic composition of lead and of trace elements concentrations in natural uranium materials as a signature in nuclear forensics[END_REF][START_REF] Svedkauskaite-Legore | Investigation of the sample characteristics needed for the determination of the origin of uraniumbearing materials[END_REF][START_REF] Keegan | Attribution of uranium ore concentrates using elemental and anionic data[END_REF]Spano et al., 2017a, b;[START_REF] Corcoran | Multivariate Analysis Based on Geochemical, Isotopic, and Mineralogical Compositions of Uranium-Rich Samples[END_REF]. Geochemical studies of U mill tailings were mainly focused on their elemental content, U speciation and U-series disequilibrium [START_REF] Somot | Radium, uranium et métaux dans les résidus de traitement dynamique, acide et alcalin de minerai d'uranium[END_REF]Somot et al., 1997a;Somot et al., 1997b;[START_REF] Somot | Speciation of Ra-226, uranium and metals in uranium mill tailings[END_REF][START_REF] Somot | Radium behaviour during the diagenesis of Jouac uranium mill tailings (Haute-Vienne, France)[END_REF]Pagel and Somot 2002;Othmane et al., 2014;Déjeant et al., 2016;Liu et al., 2017;Robertson et al., 2019;[START_REF] Ballini | A multiscalar study of the long-term reactivity of uranium mill tailings from Bellezane site (France)[END_REF], Chautard et al., 2020) and only one study focused on stable Pb isotopic signatures of bulk U mill tailing samples [START_REF] Santos | Different lead sources in an abandoned uranium mine (Urgeirica -Central Portugal) and its environment impact -isotopic evidence[END_REF]. Two others studies provided Pb isotopic values for only one bulk U mill tailing that was used as an endmember in environmental studies [START_REF] Dang | Uranium dispersion from U tailings and mechanisms leading to U accumulation in sediments: Insights from biogeochemical and isotopic approaches[END_REF][START_REF] Liu | Provenance of uranium in a sediment core from a natural reservoir, South China: Application of Pb stable isotope analysis[END_REF], while Pb isotopic values from particles retained on filters related to the filtration process of waters collected in boreholes in U mill tailing dam were also reported [START_REF] Gulson | Lead isotopes as seepage indicators around a uranium tailings dam[END_REF].

Natural uranium is a mixture of three radioactive isotopes: 238 U (99.274%; half-life: 4.468 Ga), 235 U (0.720%; half-life: 0.704 Ga) and 234 U (0.005% half-life: 0.246 Ma). ( 234 U/ 238 U) activity ratios are widely used in geosciences and environmental sciences as a powerful process tracers, as this ratio can show a disequilibrium during fluid-rock interaction due to the so-called alpha recoil effect: (1) direct ejection of the α-recoiled 234 Th (which decay into 234 U) from the solid phase into the solution [START_REF] Kigoshi | Alpha-recoil thorium-234 -Dissolution into water and uranium-234/uranium-238 disequilibrium in nature[END_REF] and (2) damages to the crystal lattice and/or (3) the oxidation of 234 U(IV) into 234 U(VI) during the alpha decay results in the preferential release of the 234 U into solution (e.g. [START_REF] Chabaux | U-Th-Ra fractionation during weathering and river transport[END_REF]. Thus, it comes that the waters are generally characterized with ( 234 U/ 238 U) > 1, while the recently weathered product usually show ( 234 U/ 238 U) < 1 (e.g. [START_REF] Osmond | Theory and uses of natural uranium isotopic variations in hydrology[END_REF][START_REF] Dequincey | Chemical mobilizations in laterites: Evidence from trace elements and U-238-U-234-Th-230 disequilibria[END_REF][START_REF] Chabaux | U-Th-Ra fractionation during weathering and river transport[END_REF][START_REF] Dosseto | The evolution of weathering profiles through time: New insights from uranium-series isotopes[END_REF]. The ( 234 U/ 238 U) ratios measured in worldwide waters (e.g. river, seawater, groundwater) range from 0.5 to 40 [START_REF] Osmond | Theory and uses of natural uranium isotopic variations in hydrology[END_REF]Gilkeson and Cowart, 1987;Osmond and Ivanovitch, 1992), and ( 234 U/ 238 U) ratios measured in altered product (e.g. soil, laterite) range from 0.5-1.8 (Suhr et al., 2018 and references therein). Waters that interacted with U mill tailings could exhibit high U content, and ( 234 U/ 238 U) close to unity, as shown by studies of groundwater samples in the vicinity of U mill tailing disposals (Zielinsky et al., 1997;Kamp and Morrison, 2014), while weathered profiles developed on U mineralized area show ( 234 U/ 238 U) that range from 0.89 to 1.20 [START_REF] Shirvington | Fixation of radionuclides in the U-238 decay series in the vicinity of mineralized zones .1. the austatom uranium prospect, Northern-Territory, Australia[END_REF]Lowson et al., 1986;[START_REF] Ahamdach | U-series disequilibrium in lateritic profiles on a U-mineralized area (Lagoa Real, Brazil): a preliminary study[END_REF]. The average ( 234 U/ 238 U) activity ratio value recorded in worldwide U-ores of various deposit types is 1. 00±0.10 (2σ, n=181;Richter et al., 1999;[START_REF] Uvarova | Variations in the uranium isotopic compositions of uranium ores from different types of uranium deposits[END_REF][START_REF] Keatley | Uranium isotope variation within vein-type uranium ore deposits[END_REF].

( 230 Th/ 238 U) and ( 226 Ra/ 230 Th) activity ratio are widely used in geosciences and environmental sciences as powerful process tracers, as U-Th-Ra fractionate during fluid-rock interaction, U and Ra being preferentially mobilized into the fluid phase compared to Th [START_REF] Chabaux | U-Th-Ra fractionation during weathering and river transport[END_REF]. For instance, the ( 230 Th/ 238 U) tracer allow to fingerprint the addition (low 230 Th/ 238 U) or loss (high 230 Th/ 238 U) of U in a weathering profile. The ( 230 Th/ 238 U) activity ratio was used to highlight the U mobility [START_REF] Mangeret | An evidence of chemically and physically mediated migration of U-238 and its daughter isotopes in the vicinity of a former uranium mine[END_REF][START_REF] Gourgiotis | New Insights into Pb Isotope Fingerprinting of U-Mine Material Dissemination in the Environment: Pb Isotopes as a Memory Dissemination Tracer[END_REF] in wetlands mainly impacted by particle transport from U mining activities. For U mill tailings, the ( 230 Th/ 238 U) activity ratio was also used to quantify the extraction yield of uranium [START_REF] Somot | Radium, uranium et métaux dans les résidus de traitement dynamique, acide et alcalin de minerai d'uranium[END_REF], while the ( 226 Ra/ 230 Th) was used to fingerprint the mobility either of 226 Ra or of 230 Th in the disposals [START_REF] Somot | Radium behaviour during the diagenesis of Jouac uranium mill tailings (Haute-Vienne, France)[END_REF]Pagel and Somot, 2002).

( 210 Pb/ 226 Ra) activity ratio is also used in geosciences as a geochronometer for processes occurring within the time scale of a century, as the selective high mobility of gaseous 222 Rn radionuclide (which is the decay product of 226 Ra) can create a disequilibrium between 226 Ra and 210 Pb [START_REF] Reagan | Pb-210-Ra-226 disequilibria in young gas-laden magmas[END_REF][START_REF] Li | A review of current and emerging approaches for Quaternary marine sediment dating[END_REF]. 226 Ra and 210 Pb activities were also used in environmental sciences as tracer of the impact of U milling activities on the environment (Strok and Smodis, 2013a;Strok and Smodis, 2013b;[START_REF] Sauvé | Quantifying historical releases and preoperation levels of metals and radionuclides[END_REF].

Radiogenic lead isotopes 206 Pb, 207 Pb, 208 Pb are respectively the stable end-products of the decay chains of 238 U (99.27%; half-life: 4.47 Ga), 235 U (0.72%; half-life: 0.70 Ga) and 232 Th (99.98%, half-life: 14.1 Ga) radionuclides, while the stable 204 Pb isotope is only primordial.

These isotopes are widely used in geosciences and environmental sciences as a powerful source tracers, as they do not fractionate significantly during geological processes or chemical processes occurring in industrial plants. Moreover, radiogenic lead isotopes have commonly been used for U-ore exploration purposes [START_REF] Dickson | Evaluation of lead isotopic methods for uranium exploration, Koongarra area, Northern-Territory, Australia[END_REF][START_REF] Dickson | Further assessment of stable lead isotope measurements for uranium exploration, Pine Creek geosyncline, Northern-Territory, Australia[END_REF][START_REF] Quirt | Lead Isotopes in Exploration for Basement-Hosted Structurally Controlled Unconformity-Related Uranium Deposits: Kiggavik Project (Nunavut, Canada)[END_REF] and also in a few studies related to isotope fingerprinting of the dissemination U mine material in the environment (France: [START_REF] Cuvier | Trace elements and Pb isotopes in soils and sediments impacted by uranium mining[END_REF][START_REF] Gourgiotis | New Insights into Pb Isotope Fingerprinting of U-Mine Material Dissemination in the Environment: Pb Isotopes as a Memory Dissemination Tracer[END_REF][START_REF] Martin | An integrated approach combining soil profile, records and tree ring analysis to identify the origin of environmental contamination in a former uranium mine (Rophin, France)[END_REF]Worldwide: Bollhöfer et al., 1989;Coetzee et al., 2006;[START_REF] Santos | Different lead sources in an abandoned uranium mine (Urgeirica -Central Portugal) and its environment impact -isotopic evidence[END_REF][START_REF] Dang | Uranium dispersion from U tailings and mechanisms leading to U accumulation in sediments: Insights from biogeochemical and isotopic approaches[END_REF][START_REF] Liu | Provenance of uranium in a sediment core from a natural reservoir, South China: Application of Pb stable isotope analysis[END_REF], as U-rich minerals (e.g. ~88 wt. % of U in uraninite) are highly enriched in both uranogenic 206 Pb (the most abundant) and 207 Pb (the second most abundant) compared to 208 Pb and 204 Pb isotopes. Therefore, U-ore have a specific Pb isotopic signature compared to Pb-bearing rocks (e.g. peridotite, basalt, granite, Pb-ore; Stacey and Krammers, 1976) and Wieser, 2011). This specific isotope signature depends on the U-ore content in U and Th, the age of mineralization and the rate of mixture between the radiogenic (Pb from the U-ore) and common Pb.

The main objective of this study was to explore if 238 U-series disequilibrium and stable lead isotopes can be used as potential relevant tracers to highlight the uranium mine and mill tailings impact on the environment. Actually, there is no or little information in the literature on this topic. In order to answer this question, we analyzed in this study the elemental content, 238 U-chain disequilibrium (bulk sample analysis) and Pb isotopes composition (bulk sample and in situ micro-analysis) of different types of U mill tailings collected in five Tailings Management Facilities: alkaline mill tailings (Le Bosc, France), neutralized acid mill tailings (L'Ecarpière, Le Bernardan, Bellezane, France), and acid mill tailings (Mounana, Gabon). The 238 U-chain disequilibrium was studied first in order to determine if there is a specific signature associated to the U mill tailings. Secondly, particular attention was paid to stable Pb isotopes to figure out if the specific Pb isotope signature of the U-ores (hereafter radiogenic Pb) is preserved in the U mill tailings. Moreover, a first insight into Pb-bearing phases in U mill tailings was carried out using SEM and SIMS in-situ techniques in order to determine whether the Pb from the U-ore is still associated with the remaining primary Ubearing phases or with post-treatment neo-formed mineral phases. This work bring new insights into the fingerprinting of the impact of U milling activities in the environment.

Materials and Methods

Site description and sampling

The U mill tailings of this study were collected between 1985 and 2011 by the IRSN (French Institut of Protection and Nuclear Safety (IPSN) before 2002) and are now stored at IRSN-Fontenay-aux-Roses (Table 1). This set of samples cover various types of U mill tailings treatments from different types of U-ores of various ages: four neutralized acid U mill tailings derived from Paleo-Mesozoic granite-related ores from France (ECA-85, JOU-97, JOU-DT, BZN samples), two alkaline U mill tailings derived from Mesozoic sandstone-related ores from France (LOD-FS, LOD-MA samples) and one acid U mill tailing derived from Proterozoic sandstone-related ores from Gabon. The samples have been stored in special ventilated cabinets at room temperature (20 °C) and have not been conserved under anoxic conditions nor under specific sealing conditions preventing 222 Rn emanation. The precise sampling area and method in the respective TMFs is not known.

The alkaline U mill tailing samples are from Le Bosc (France). U-mineralization are tectoniclithologic sandstone-related deposits and are located in the Lodève basin. U-ores (0.28 wt. % on average) were mainly mined in two deposits (Mas Lavayre and Mas d'Alary). U mineralization formed during two events 183-172 Ma and 103-113 Ma ago and consist mainly of pitchblende and U associated with organic matter. The extraction of U from U-ore, using an alkaline chemical treatment with sodium carbonate and bicarbonate solution due to their high carbonate content, generated 4.1 Mt of dynamic mill tailings at the SIMO (Société Industrielle des Minerais de l'Ouest) Le Bosc mill between 1950 and 1997.

The acid U mill tailing sample is from Mounana Tailing Management Facility (Gabon sample). U mineralizations are tectonic-lithologic sandstone-related deposits and are located in the Franceville Basin. U-ores (0.37 wt. % on average) were mainly mined in five deposits (Mounana, Oklo, Okelobondo, Boyindzi, Mikouloungou). U-mineralizations formed 2.05 Ga ago [START_REF] Gancarz | U-Pb age (2.05 Ga) of the Oklo uranium deposit[END_REF] and consist mainly of pitchblende-uraninite associated with organic matter (Pagel and Somot, 2002;Lecomte et al., 2020). The extraction of U from U-ore using a chemical treatment with sulfuric acid generated 7.5 Mt of mill tailings between 1961 and 1999 by the COMUF (Compagnie des Mines d'Uranium de Franceville).

The neutralized acid mill tailing samples (chemical treatment with sulfuric acid at 65°C and neutralization of barren residues and solutions with CaCO 3 and/or lime) are from l'Ecarpière, Le Bernardan and Bellezane Tailings Management Facilities. The related U-mineralizations are granite-related deposits.

U-ores (0.10 wt. % on average) milled at the SIMO Ecarpière plant were mainly mined in three deposits (Ecarpière, Commanderie, Chardon) located in the Mortagne granitic massif and its surrounding metamorphic series. U mineralization formed 322-308 and 286-264 Ma ago and consists mainly of pithchblende-uraninite [START_REF] Cathelineau | Metallogenesis of the french part of the variscan orogen. Part II: Time-space relationships between U, Au and Sn-W ore deposition and geodynamic events -mineralogical and U-Pb data[END_REF]Horie and Hidaka, 2019). The extraction of U-ore generated 11.4 Mt of tailings (7.6 from dynamic leaching and 3.8 from heap leaching) from 1952-1990. Mill tailings disposed at the Bernardan open pit were generated at the SMJ mill (Société des Mines de Jouac, ex-Dong Trieu ; Jouac, France) from 1978 to 2002 from U-ores (0.57 wt. % on average) that were mined in the Mailhac sur Benaize mining division (mainly Bernardan and Les Loges deposits). The U-ores came mainly from Western Marche granitic Massif (e.g. Bernardan episyenitic deposit) and from surrounding gneisses (Piégut deposit). The U deposits at Piégut formed 280 Ma ago [START_REF] Turpin | Isotopic investigation of the Piegut uranium deposit (Marche, northwest Massif-Central, France) -U-series disequilibrium and geochronology[END_REF], while those at Bernardan formed 170-140 Ma ago (Patrier et al., 1997) and consists mainly of pitchblende and coffinite.

1.57 Mt of mill tailings (1.51 Mt from dynamic leaching and 0.06 from heap leaching) disposed in the two open pits at Bellezane Tailing Management Facility (from 1989-1993) were generated at the SIMO mill located at Bessines sur Gartempe [START_REF] Ballini | A multiscalar study of the long-term reactivity of uranium mill tailings from Bellezane site (France)[END_REF]. The U-ores (0.143 wt. % on average) were mined in the La Crouzille mining division and came from the Saint Sylvestre granitic Massif. The U deposits formed 276-270 Ma ago and 183-170 Ma ago (e.g. Margnac Fanay deposits: [START_REF] Leroy | Mineralogical, chemical and isotopic (U-Pb method) studies of hercynian uraniferous mineralizations (Margnac and Fanay mines, Limousin, France)[END_REF][START_REF] Cathelineau | Metallogenesis of the french part of the variscan orogen. Part II: Time-space relationships between U, Au and Sn-W ore deposition and geodynamic events -mineralogical and U-Pb data[END_REF] and consists mainly of pitchblende and coffinite, as well as surficial minerals, such as autunite and gummite.

Sample information is summarized in Table 1 and supplementary information about the milling processes can be found in the supplementary materials section.

Elemental and isotopic analyses

Around 50 mg of sample were fully digested using a mixture of concentrated HF-HNO 3 -HClO 4 (1:1:0.3) ultrapur® acids in Savillex® PFA vials at 90°C on a hotplate during 48h, then dried down at 160°C overnight until full dryness. Then, the residues were taken up two times in 10 drops of concentrated HNO 3 and dried down. Finally, the residues were dissolved in 40 ml of 3M HNO 3 . Aliquots of these stock solutions were used for elemental analysis (ICP-AES and QQQ-ICP-MS), as well as U, Th and Pb isotopic analysis performed by QQQ-ICP-MS and HR-ICP-MS.

Elemental analyses

All samples were analysed for major and trace elements. Major element analyses (Al 2 O 3 , Fe 2 O 3 , MgO, CaO, Na 2 O, K 2 O, P 2 O 5 , MnO, TiO 2 ) of whole rock samples were performed in solution by ICP-OES Thermo Scientific ICAP-7000®. S content of the samples was analysed using an elemental analyser FlashSmart (ThermoScientific) in CHNS mode, after calcination of the sample under oxygen steam at 1400°C and further oxidation of the produced gas by contact with Cu oxides. Trace element concentrations (Pb and Ba) of wholerock samples were determined in solution by QQQ-ICP-MS Agilent Technologies 8800® (PATERSON analytical platform, IRSN Fontenay-aux-Roses, France) using a standard calibration regression based on the analysis of standards having various elemental content that encompass the range of variation of elemental content of the analysed samples. A machine drift correction based on a Bi spike was also applied. Thus, a Bi solution was mixed with the sample before the introduction into the nebuliser using a 3 port T-junction. The Pb content was calculated by taking into account the concentrations of each Pb isotope ( 204 Pb, 206 Pb, 207 Pb, 208 Pb) due to the important contrast of the Pb isotope composition between the U mill tailing samples and the Pb calibration standards (natural Pb abundances). Uncertainties for all analyses are lower than 10 % (Supplementary Table 1).

Stable Pb isotopes analyses

Aliquot of the solutions (3M HNO 3 ) containing more than 200 ng of Pb were taken up and dried down on a hot plate at 90°C. Then, the residues were evaporated and dissolved two times in 10 drops of concentrated ultrapur® HBr. Then, the residues were dissolved in 1 mL of ultrapur® 0.2M HBr.

Chemical separation of lead from others elements was carried out in a class 10000 laminarflow hood using only reagent produced from ultrapure® acid (Merck) and 18.2 MΩ.cm -1 ultrapure water (Milli-Q ultrapure water system, Merck Millipore). Pb was separated from the matrix and interfering element by ion-exchange gravity chromatography, using 100 µl of anionic resin BioRAD AG1-X8 100-200 mesh loaded into a 1 mL pipet tips, based on a protocol adapted from Manhès et al. (1984). After 4 cleaning steps of the resin (1 mL of 0.25M HNO 3 , water, 0.2M HCl, water) and a conditioning step of the resin with 1 mL of 0.5M HBr, the dissolved sample was introduced into the column. Then, the matrix elements were eluted with 5 mL of 0.5M HBr, and finally the Pb was eluted with 5 mL of 0.2M HCl.

The overall Pb yields after the purification were higher than 90%, while the total procedural chemistry blanks during the course of this study were less than 150 pg. These values are totally negligible in comparison to the amount of Pb present in the samples (higher than 1µg).

Lead isotopes analyses were performed using an HR-SF-ICPMS Thermo Scientific Element XR (PATERSON analytical platform) using the standard-sample bracketing technique. The certified reference material NIST981 was run before and after each sample in order to correct all the Pb isotopic ratios for the mass bias using an exponential law with the values recommend by Doucelance and Manhes, 2001. Each run consists of 15 runs of 100 passes, of 10 ms per canal (i.e. 2 canals). The average 204 Pb/ 207 Pb, 206 Pb/ 207 Pb, 208 Pb/ 207 Pb ratios measured for certified reference materials were 0.065±0.002, 1.09±0.01, 2.35±0.05, (2SD, n=4) for NIST981 (common lead), and 0.00503±0.00001, 14. 0±0.1,0.197±0.002,(2SD,n=3) for NIST983 (radiogenic lead) and for international rock standards were 0.064±0.002, 1.21±0.01, 2.46±0.03, (2SD, n=3) for AGV2 and 0.064±0.001, 1.20±0.01, 2.48±0.01, (2SD, n=3) for BCR-2.

U-Th isotopes analyses by ICP-MS

The 234 U/ 238 U isotopes ratios as well as the 238 U and 230 Th content used for the calculation of the 238 U/ 230 Th were determined by isotope dilution mass spectrometry ( 238 U/ 236 U, 230 Th/ 229 Th).

Aliquots of the stock solutions (3M HNO 3 ) were taken up and mixed with a 233 U-236 U-229 Th triple spike (mixture of certified reference materials 233 U-236 U enriched solution IRMM3636

with 229 Th-enriched solution described in [START_REF] Essex | A new thorium-229 reference material[END_REF]).

Chemical separation of U and Th from the other elements was carried out following the protocol described in [START_REF] Douville | Rapid and accurate U-Th dating of ancient carbonates using inductively coupled plasmaquadrupole mass spectrometry[END_REF] in a fume-hood using UTEVA resin and high purity reagent made from distilled acids (evapoclean system for HCl, Savillex DST1000 system for HNO 3 ) and ultrapure water. Column were cleaned and conditioned using 3M HNO 3 . Samples were introduced into the column. Matrix elements were discarded using 4 mL 3M HNO 3 . Th was then eluted using 4 mL 3M HCl, and finally U was eluted using 5 mL 1M HCl. After separation, Th fractions were spiked with IRMM3636 solution.

U and Th analyses were performed using a QQQ-ICPMS Agilent Technologies 8800® (PATERSON analytical platform). The instrumental mass bias correction was performed using the certified 233 U/ 236 U ratio of the IRMM3636 solution. In order to assess the precision and the accuracy of our measurement (Supplementary Table 1), we prepared solutions from Harwell Uraninite (HU-1) which is known to be close to secular equilibrium with respect to 234 U/ 238 U = (54.903±0.011) × 10 -6 ) and to 230 Th/ 238 U = (1.6953±0.0003) × 10 -5 [START_REF] Cheng | Improvements in Th-230 dating, Th-230 and U-234 half-life values, and U-Th isotopic measurements by multi-collector inductively coupled plasma mass spectrometry[END_REF].

Th-230, Ra-226 and Pb-210 analyses by gamma spectrometry

The activities of 238 U-series nuclides were determined in the U mill tailing samples at the IRSN/LUTECE laboratory using either (i) a High Purity coaxial Germanium detector (EGPC 20, Intertech) or (ii) a well-type HP Ge detector (GWL-220-15, ORTEC®). The first detector displays a better resolution (0.75 and 1.75 keV at the photopeaks 122 keV of 57 Co and 1332 keV for 60 Co), two times lower than the well-type detector, while for the latter a significant higher efficiency was obtained for low energy rays (i.e. the peak of 210 Pb at 46.5 keV) which was therefore appropriate for the analysis of low-weight solid samples. These two detectors were calibrated according to the international IAEA standards RGU-1 and RGTh-1, two silica-diluted ores of U and Th respectively, as it was performed previously [START_REF] Mangeret | An evidence of chemically and physically mediated migration of U-238 and its daughter isotopes in the vicinity of a former uranium mine[END_REF], Mangeret et al., 2020, Supplementary Table 1). The 230 Th activities were measured at 67.7 KeV, 226 Ra activities were measured from the 214 Pb rays at 295.2 and 351.9 keV and the 214 Bi ray at 609.3 keV. 210 Pb activities were determined from the ray at 46.5 keV. The samples have been sealed (to prevent any loss of gaseous 222 Rn) 3 weeks before the analysis in order to reach the complete regrowth of both 214 Bi and 214 Pb. From 39 to 94 g of sample were used for analysis performed by the coaxial detector, while lower amounts (from 1.4 to 2.6 g) of sample were used for analysis with the well-type detector.

In situ analysis

In order to identify radiogenic Pb-bearing phases, two U mill tailings (Gabon and JOU-97) containing the highest level of radiogenic Pb were selected for further in-situ analysis using secondary electron microscopy (SEM) and secondary ion mass spectrometry (SIMS) techniques. For this study, around a hundred milligrams of U mill tailing samples were embedded in an Epoxy resin (modified recipe of EMbed-812 kit, EMS, Hatfield; with BDMA replacing the DMP-30 in order to reduce the resin viscosity) and degassed under vacuum before being transfered into a 10 mm diameter stainless steel ring holder. The resin polymerization was reached after 48h at 60°C in an oven. The samples sustained several polishing steps (1) using a 5 µm Si-C disk, followed by (2) a 3 µm and then a 1 µm diamond powder onto soft-disks. The samples were finally coated with a thin layer of C.

SEM analyses

In order to identify the Pb-rich phases, the secondary electron microscope (SEM) Hitachi S3500N (LUTECE platform, IRSN, Fontenay-aux-Roses) was used to localize the phases that host heavy elements using the SEM-Back Scattered Electron (BSE) detector under a voltage of 25 kV accelerating voltage. Then, the SEM-Energy Dispersive X-ray Spectroscopy (EDS) analysis was performed with two EDS Brücker 5030 XFlash SDD detectors working under a voltage of 25 keV at a working distance of 16.8 mm in order to characterize the elemental composition of the phases, especially with respect to Pb and U. The SEM-EDS data were acquired at 8 µs/pixels at 100 kcps/s using the Esprit software 1.9 for a pixel size of 0.3 µm.

SIMS analyses

The SIMS analyses of Pb-rich phases were performed using a CAMECA IMS 4F-E7 instrument (PATERSON Platform, IRSN, Fontenay-aux-Roses) in order to localise the radiogenic (uranogenic) Pb-bearing phases (i.e. 206 Pb-rich, 208 Pb-poor) at the grain scale. For this preliminary study, only images were acquired, not isotope ratios, as the isotopic difference between the common Pb and the radiogenic Pb is very high. A homemade three holes sample holder were especially designed in order to introduce 3 samples (hosted in 1 mm diameter rings) at the same time in the analysis chamber (pressure of 5 × 10 -9 mbar) of the instrument. Analysis were performed with a 1 nA, 12 kV O 2 -primary beam projected on a ~ 1 µm area which scan the area of interest (raster of 250 µm x 250 µm for JOU-97 and 500 x 500 µm for Gabon). The positively charged secondary ions or molecules were accelerated at 10 kV into the mass spectrometer, measured with a mass resolution of 400 by ion counting in monocollection mode and sequentially converted into an image with a lateral resolution of around 1 µm. Each analysis was preceded by a 5-min pre-sputtering performed with a ~ 100 nA primary beam. The analysis of JOU-97 sample consisted in 65 integration cycles of 1 s for 23 Na, 24 Mg, 27 Al, 28 Si, 39 K 40 Ca, 56 Fe (major elements) and 300 integration cycles of 5 s for 204 Pb, 206 Pb, 207 Pb, 208 Pb, and of 2 s for 238 U 16 O. The analysis of Gabon sample consisted in 80 integration cycles of 1 s for major elements and 700 integration cycles of 10 s for Pb isotopes and 238 U 16 O. The mass calibration of the instrument was performed using enriched material, such as for instance a Si-rich plate, a Pb-rich metal plate having a common Pb isotopic composition, or a U-doped resin.

Results and discussion

Elemental content of U mill tailings

The major elements contents (Al, Mg, Fe, Ca, Na, K, Ti, Mn, P) of U mill tailings from

France are close to the average value reported for the upper continental crust (UCC) [START_REF] Rudnick | Composition of the Continental Crust[END_REF]; Fig. 2). However, the major elements contents of the U mill tailings from Gabon show a strong depletion of Mg, Ca, Na, and Mn (in a lesser extent for Al, K, Fe, Ti, P) compared to UCC, which is probably due to the low content of these elements in the mineralized quartzite sediment (Gauthier-Lafaye et al., 1986;Bankole et al., 2020).

The Ba content of U mill tailings is similar to UCC. This suggests either that the potential addition of radiobarite (precipitated during the treatment of the liquid effluent with BaCl 2 ) into the U mill tailings had only a minor impact on the bulk Ba content of U mill tailings or that the Ba content of U-ores was lower compared to the UCC.

The neutralized acid mill tailings show a high enrichment in S with values that range from 20 to 60 times higher than the one for the UCC, while the alkaline U mill tailings do not display a S enrichment or depletion. This demonstrates the impact of the addition of S during the milling via sulphuric acid leaching and the precipitation of secondary sulphate on the U mill tailings composition. The lack of S enrichment in U mill tailings from Mounana, Gabon could be related to the lack of neutralization process (the addition of Ca-carbonate or lime allows the precipitation secondary CaSO 4 into the U mill tailing). The low S content of Le Bosc (LOD-FS, LOD-MA) alkaline mill tailing samples could be explained by the lack of sulfuric acid involved in the treatment of the U-ores.

All U-mill tailings of this study exhibit a strong U enrichment with values that range from 10 to 200 times higher than the UCC's one. This U enrichment is consistent with the uncomplete U extraction (i.e. extraction yields < 100%) from the U-ore (Fig. 2). U mill tailings display also a high enrichment in Pb with values that range from 6 to 80 times higher than the UCC's one. Except some particular U mineralization (e.g. parsonsite which is a hydrated phosphate of U and Pb related to weathering processes) that contains high common Pb concentrations, the Pb enrichment is generally related to the accumulation of stable radiogenic Pb produced by the U-ore. In addition, the U mill tailings show no Th ( 232 Th) enrichment, which suggests that the U-ores were not enriched in Th ( 232 Th).

Detailed information about element concentrations can be found in table 2.

U-238 decay chain disequilibrium in U mill tailings

In a closed system the secular equilibrium (activity ratios equal to one) of the U-238 decay chain is reached in about 2 million years (i.e. ~ 8 times of the longer half-life decay product:

234 U). Any deviation from the secular equilibrium can be used to highlight physicochemical processes that led to the gain or loss of the chain radionuclides.

( 234 U/ 238 U) activity ratio

The ( 234 U/ 238 U) activity ratios of the studied U mill tailings of this study range from 1.27 (LOD-FS and BZN samples) to 1.87 (Gabon sample) (Fig. 3a; Table 3). The U mill tailings samples from Lodève and from Mounana have higher ( 234 U/ 238 U) ratios compared to the values from the corresponding U-ores reported by Richter et al. (1999) (respectively 0.94 and 0.99). Overall, the U mill tailings of this study have significantly higher ( 234 U/ 238 U) activity ratios compared to the average value (( 234 U/ 238 U) = 1.00±0.10, 2σ, n=181) recorded in worldwide U-ores of various deposit types (Richter et al., 1999;[START_REF] Uvarova | Variations in the uranium isotopic compositions of uranium ores from different types of uranium deposits[END_REF][START_REF] Keatley | Uranium isotope variation within vein-type uranium ore deposits[END_REF] and to typical values (0.99±0.19, 2σ, n=335) of natural weathered materials (Suhr et al., 2018 and references therein) or weathered profiles developed on U mineralized area that show ( 234 U/ 238 U) ranging from 0.89 to 1.20 [START_REF] Shirvington | Fixation of radionuclides in the U-238 decay series in the vicinity of mineralized zones .1. the austatom uranium prospect, Northern-Territory, Australia[END_REF]Lowson et al., 1986;[START_REF] Ahamdach | U-series disequilibrium in lateritic profiles on a U-mineralized area (Lagoa Real, Brazil): a preliminary study[END_REF]. In addition, U mill tailings have also higher ( 234 U/ 238 U) activity ratios compared to the average value for U-ore concentrate (0.97±0.09, 2σ, n=56;

Kayzar-Boggs et al., 2021) that derived from the U-rich leachate during the milling process.

Due to the high atomic mass, the high ( 234 U/ 238 U) activity ratios of U mill tailings cannot be explained by U isotope fractionation (kinetic or at equilibrium) during mining and milling processes or mill tailing disposal.

During the milling process, U-ore are crushed and leached using alkaline or acid solution in order to dissolve the U-rich phases, leaving a leached ore residue corresponding to the U mill tailings. Acid-leaching experimental studies performed on U-bearing minerals (carnotite, uraninite, euxenite), using different acids (HCl, HNO 3 , HF, HClO 4 ) have shown that the resulting leachates (liquid phase) have ( 234 U/ 238 U) < 1 [START_REF] Kobashi | Radioactive disequilibrium with uranium, thorium and radium isotopes leached from euxenite[END_REF], while the acid-leaching residue (solid phase) have ( 234 U/ 238 U) activity ratio up to 400 in the smallest grain fraction (Sheng and[START_REF] Sheng | The alpha-recoil effects of uranium in the oklo reactor[END_REF]Kuroda, 1986a;Sheng and Kuroda, 1986b;[START_REF] Essien | Uranium isotope anomaly in minerals[END_REF]. However, another study performed on U-bearing minerals (uraninite, samarskite) with dilute HCl reported that the leachates from uraninite samples have ( 234 U/ 238 U) > 1 while the leachates from the samarskite sample has ( 234 U/ 238 U) = 1 [START_REF] Kobashi | Study on physicochemical states of uranium, thorium, and radium isotopes in some radioactive minerals by the leaching method[END_REF]. More recently, acid-leaching experimental studies have been performed on U-ores using sulphuric acid in order to reproduce an industrial U-ore leaching processing [START_REF] Satybaldiyev | Understanding sulphuric acid leaching of uranium from ore by means of U-234/U-238 activity ratio as an indicator[END_REF][START_REF] Keatley | Uranium isotope variation within vein-type uranium ore deposits[END_REF]. In the flow-through experimental study performed by [START_REF] Satybaldiyev | Understanding sulphuric acid leaching of uranium from ore by means of U-234/U-238 activity ratio as an indicator[END_REF] on uraninite with dilute sulphuric acid, the leachates collected containing most of the U were characterized by a ( 234 U/ 238 U) < 1 (0.92-1.00), which is related to the oxidation and the dissolution of uraninite. In the batch experimental study performed by [START_REF] Keatley | Uranium isotope variation within vein-type uranium ore deposits[END_REF] with diluted sulfuric acid of various vein-type U-ores including oxidized (e.g. autunite, torbernite) and reduced (e.g. uraninite, pitchblende, coffinite) U-bearing minerals, some of the leachates and residues have different ( 234 U/ 238 U) values (ranging from 0.83 to 1.12) compared to the bulk starting U-bearing phase, with both higher and/or lower values. In general, but not exclusively, the leachates from oxidised U-ores tend to exhibit lower ( 234 U/ 238 U) values, while leachates from the reduced Uores tend to show higher ( 234 U/ 238 U) compared to their respective U-ores. Overall, all these experiments of U-ore leaching suggest that a 234 U-238 U radioactive disequilibria can be produced between the leachate and the ore residue. The various type of experimentally observed 234 U-238 U disequilibria have been interpreted in terms of difference in oxidation states between 238 U and 234 U, preferential leaching of 234 U from damaged crystal lattice due to alpha-recoil displacement, 234 U implantation into a U-poor acid-resistant phase from the adjacent U-rich acid soluble phase, incongruent dissolution area depleted in 234 U (near grain boundary between U-rich phase and U poor phase).

Decays of 238 U yield alpha recoil of 234 Th which decay via beta decays to 234 Pa giving 234 U.

Emission of alpha recoiled nuclide forms ~20-30 nm-long damages in the crystalline lattice [START_REF] Fleischer | Isotopic disequilibrium of uranium -alpha-recoil damage and preferential solution effects[END_REF]Ordonez-Regil et al., 1989) and part of the alpha recoiled nuclides can be implanted into the outermost part of the adjacent crystal. Several authors reported that the residue of acid-leaching experiments of U-ores could have ( 234 U/ 238 U) > 1 suggesting that 234 U is recoiled from an acid-soluble U-rich phase to a neighbouring acid-resistant U-poor phase in the U-ore [START_REF] Sheng | The alpha-recoil effects of uranium in the oklo reactor[END_REF]Sheng and Kuroda 1986a,b;[START_REF] Essien | Uranium isotope anomaly in minerals[END_REF]. As a result, U-poor phase become enriched in 234 U through time with respect to 238 U, while the Urich phase becomes depleted (Fig. 4.1). During dissolution via leaching, U-rich phases are preferentially removed, and thus the residue become enriched in 234 U (Fig. 4.2). Nuclides located into the alpha recoil tracks may have higher reactivity with fluid, leading to their preferential removal during acid leaching if the track has not been sufficiently annealed.

However, the U mill tailings of this study exhibit ( 234 U/ 238 U) greater than one, which suggest that at least a fraction of the the recoil nuclides became trapped into the crystal lattice of the U-poor phase via track annealing process [START_REF] Eyal | Timescale of natural annealing in radioactive minerals affects retardation of radiation-damage-induced leaching[END_REF]Lumpkin et al., 1989), thus preventing their mobility during acid-leaching.

In order to explain the range of ( 234 U/ 238 U) values in the mill tailings a mixing model was used [START_REF] Langmuir | General mixing equation with applications to icelandic basalts[END_REF] between a U-rich and U-poor phases in a ( 234 U/ 238 U) vs. 238 U diagram (Fig. 5). For the U-rich phase end-member (U-rich phases with their boundaries that are depleted in 234 U by α-recoil effect), the U content was set to 700 mg.g -1 , which is a typical average value for uraninite (Ecarpière, France: Horie and Hidaka, 2019; Worldwide: [START_REF] Alexandre | Chemical composition of uraninite[END_REF], whereas the ( 234 U/ 238 U) ratio was set to 1, which is close to the average value for the U-ores (Richter et al, 1999 ;[START_REF] Uvarova | Variations in the uranium isotopic compositions of uranium ores from different types of uranium deposits[END_REF]Keatley et al., 2001) and U-ore concentrates (Kayzar-Boggs et al., 2021) that derived from the U-rich leachate during the milling process. For the U-poor phase end-member, the ( 234 U/ 238 U) ratio was set to 400, which is the highest value reported for the acid-leach U ore residue (mixture of U-poor phases implanted with 234 U and phases non-implanted with 234 U, Sheng and Kuroda, 1986), while two different low level of U contents were used in order to encompass all the U mill tailing data with the mixing curves. The first one was set to 0.05 ppm of U which is an intermediate value between quartz (0.01 µg.g -1 ; [START_REF] Gotze | Trace element incorporation into quartz: A combined study by ICP-MS, electron spin resonance, cathodoluminescence, capillary ion analysis, and gas chromatography[END_REF]) and K-feldspar (0.09-0.26 µg.g -1 of U; [START_REF] Arzamastsev | Trace elements in minerals of the Khibiny massif as indicators of mineral formation evolution: Results of LA-ICP-MS study[END_REF], which are the two dominant phases in the U mill tailings [START_REF] Somot | Radium, uranium et métaux dans les résidus de traitement dynamique, acide et alcalin de minerai d'uranium[END_REF][START_REF] Ballini | A multiscalar study of the long-term reactivity of uranium mill tailings from Bellezane site (France)[END_REF]. The second was set to 0.6 ppm of U which is intermediate between the value used for quartz and K-feldspar and the value for the upper continental crust (3 µg.g -1 of U; [START_REF] Rudnick | Composition of the Continental Crust[END_REF]. Mixing curves are drown in Figure 5 and validate the process that could explain the high ( 234 U/ 238 U) activity ratio described above. According to the mixing model, the variation of ( 234 U/ 238 U) activity ratios is dependent to U concentration in the U mill tailing. This concentration is related to the initial U content of the processed U-ore and to the U extraction yield reached during the milling process.

( 230 Th/ 238 U) activity ratio and U extraction yield

The ( 230 Th/ 238 U) activity ratios of U mill tailings range from 6.6 (Gabon sample) to 65 (ECA-85 sample) (Table 3; Fig. 3a). For comparison, the U mill tailings from Australia display also ( 230 Th/ 238 U) values higher than 1, that range from 2.5 to 10 ( Lowson and Short, 1986). In addition, the worldwide U-ore concentrates, resulting from selective U extraction from the Uore exhibit ( 230 Th/ 238 U) activity ratio values much lower than 1 [START_REF] Keatley | Uranium isotope variation within vein-type uranium ore deposits[END_REF]. The high ( 230 Th/ 238 U) activity ratio values in the U mill tailings reflect the preferential U extraction from the ore while the others 238 U-decay products mainly remain in the U mill tailing [START_REF] Landa | Geochemical and biogeochemical controls on element mobility in and around uranium mill tailings[END_REF].

210 Pb, 226 Ra and 230 Th disequilibrium

The ( 226 Ra/ 230 Th) and ( 210 Pb/ 226 Ra) were also investigated by gamma spectrometry.

( 226 Ra/ 230 Th) activity ratios range from 0.60 to 3.13 (Fig. 3b, (Pagel and Somot, 2002). For JOU-DT sample, as suggested by [START_REF] Somot | Radium behaviour during the diagenesis of Jouac uranium mill tailings (Haute-Vienne, France)[END_REF], the 226 Ra and 230 Th disequilibria suggests the selective migration of 226 Ra via slightlyacidic rain water. The slight disequilibrium of 226 Ra and 230 Th for ECA-85 samples implies either an addition of 230 Th or a loss of 226 Ra probably during the milling process or subsequent management steps. However, the lack of detailed information concerning the milling process and the geochemical composition of liquid effluent or underground mine waters that were occasionally added to the mine tailings in the pond/pile [START_REF] Somot | Radium, uranium et métaux dans les résidus de traitement dynamique, acide et alcalin de minerai d'uranium[END_REF], as well as the sampling area and method, prevent us to decipher precisely the origin of this disequilibrium.

The ( 210 Pb/ 226 Ra) activity ratios of the studied U mill tailings are all lower than 1 (Fig. 3, Table 3). This low activity ratio could be explained by the loss of 222 Rn leading thus to a lower production of 210 Pb compared to the activity of 226 Ra. A large quantity of 222 Rn nuclides is produced in the U mill tailings disposal and migrate into the cover materials, designed to prevent significant radon fluxes to reach the atmosphere (Ferri et al., 2002, Saâdi et Guillevic, 2016). The ( 210 Pb/ 226 Ra) < 1 recorded in the U mill tailing of this study are therefore likely due to continuous 222 Rn loss in these porous and permeable types of materials either in the disposal or during the samples storage in the laboratory.

Pb isotope signature of U mill tailings

Bulk samples

The Pb isotope signature of Th-poor U-ores (France: [START_REF] Cathelineau | Metallogenesis of the french part of the variscan orogen. Part II: Time-space relationships between U, Au and Sn-W ore deposition and geodynamic events -mineralogical and U-Pb data[END_REF]; Gabon: 4; Fig. 6).

Similarly to U-ores, the U mill tailing samples show a wider Pb isotopic range compared to the whole range reported for common Pb in chemical or natural materials in the environment, excluding U-ores (IUPAC, Berglund and Wieser, 2011), with higher ( 206 Pb/ 207 Pb) and lower ( 208 Pb/ 207 Pb) ratios compared to the values reported for the PDAC. This suggests that the radiogenic signature of the U-ores is preserved in the U mill tailings.

All the U mill tailings from France display a negative linear correlation and plot along a line that link the PDAC to the range of highly radiogenic Pb composition of the U-ores from France (Fig. 6). Moreover, the U mill tailings from Gabon do not plot on this trend and exhibit a Pb isotopic composition intermediate between the PDAC and the U-ores from Gabon.

The various proportion of mixing between two components are represented by a line in a Pb-Pb isotopic diagram, suggesting that the U mill tailings are mixture between (1) phases that have common Pb composition coming from either the U-ore host rock or from the reagent used for the U extraction and (2) phases that have a radiogenic Pb isotope composition of the U-ore (Gabon or France).

The proportion of radiogenic Pb from the U-ore hosted in each U mill tailing was estimated using the approach (i.e. k factor) described in [START_REF] Gourgiotis | New Insights into Pb Isotope Fingerprinting of U-Mine Material Dissemination in the Environment: Pb Isotopes as a Memory Dissemination Tracer[END_REF]. The Pb isotopes composition of the PDAC has been used for the geochemical background end-member. The 6b). Similarly, the 208 Pb/ 207 Pb ratio of the radiogenic end-member has been calculated by the intercept in a 208 Pb/ 207 Pb vs. 204 Pb/ 207 Pb diagram and was found to be 0.10. For U mill tailing from Gabon, the Pb isotopes composition of the radiogenic end-member was calculated for a Th-free U phase that crystallized 2.05 Ga ago (Gancarz, 1978; 206 Pb/ 207 Pb = 7.9 and 208 Pb/ 207 Pb = 0). The estimated proportion of radiogenic Pb range from 14% to 66% for U mill tailings from France and is 95% for U mill tailing from Gabon.

Radiogenic-Pb bearing phases in the U mill tailings

The samples having the highest ( 206 Pb/ 207 Pb) and lowest ( 208 Pb/ 207 Pb) ratios (GABON and JOU-97) were selected in order to determine the radiogenic Pb bearing phases. The aim of this preliminary study is to determine if the radiogenic Pb is associated to the remaining U bearing phases (probably partially altered) in the U mill tailings or if the "radiogenic Pb" is associated to neo-formed phases. Thanks to isotope imaging by SIMS, the radiogenic Pb was identified when 206 Pb isotope signal was higher than the 208 Pb signal (Figs. 7 and8).

Some preliminary results show that in JOU-97 sample, the radiogenic Pb was mainly identified in U-rich phases and in a lesser extent in micrometric-sized U-poor phases that potentially host Si, Al, Mg, Fe, K, Ca and Pb or S (interference of S on Pb for their respective Kα rays) based on SEM-EDX spectrum of 18 to 27 μm 2 areas (Supplemental figure A1).

However, the precise identification of the mineralogy of theses phases is difficult to assess due to the small size of the particles, as the area taken into account for SEM-EDX spectrum could potentially involve neighbouring phases that do not host radiogenic Pb. In Gabon sample, the radiogenic Pb was encountered in U-rich and in U-free S-rich phases that could be either Pb-sulphide or Pb-sulphate. The radiogenic Pb is therefore hosted for both samples in primary U-rich phases that remain after the milling process. For GABON sample the radiogenic Pb is also encountered in U-free S-rich phases that could be either (i) remaining

Pb-sulphide (galena) related to natural hydrothermal alteration of U-rich phases (Gauthier-Lafaye et al., 1996) or (ii) neo-formed Pb-Ba-Ra sulphate related to the milling process involving sulphuric acid (Pagel and Somot, 2002;[START_REF] Schmandt | Uptake of trace elements by baryte during copper ore processing: A case study from Olympic Dam, South Australia[END_REF][START_REF] Rollog | Rapid, competitive radium uptake in strontium, barium, and lead sulfates during sulfuric acid leaching[END_REF].

For JOU-97 sample the radiogenic Pb is also encountered in association with micrometricsized U-poor phases that could potentially be either clay minerals or oxyhydroxides related to (i) the weathering of minerals from the mineralized granites or (ii) the rapid diagenesis of neutralized U mill tailing after deposition in the disposal [START_REF] Somot | Speciation of Ra-226, uranium and metals in uranium mill tailings[END_REF][START_REF] Somot | Radium behaviour during the diagenesis of Jouac uranium mill tailings (Haute-Vienne, France)[END_REF][START_REF] Cook | Pb-210 and Po-210 in Geological and Related Anthropogenic Materials: Implications for Their Mineralogical Distribution in Base Metal Ores[END_REF][START_REF] Ballini | A multiscalar study of the long-term reactivity of uranium mill tailings from Bellezane site (France)[END_REF][START_REF] Chautard | Geochemical characterization of uranium mill tailings (Bois Noirs Limouzat, France) highlighting the U and Ra-226 retention[END_REF]Ram et al., 2021b).

Moreover, U-rich phases without or with minor radiogenic Pb content were also identified (Fig. 7), suggesting U or Pb mobility [START_REF] Syverson | Oxidation state and coordination environment of Pb in U-bearing minerals[END_REF]Ram et al., 2021a;Ram et al., 2021c;Ram et al., 2021d).

Tracking the presence of U mill tailing in the environment

In the context of U mines environmental impact assessment, U mill tailings are one of the source to be considered for the release of radionuclides into the environment. Transfer of radionuclides related to U mining or milling activities into the environment, where they can accumulate (e.g. wetlands, lake sediments, soils), could occur via particulate or dissolved species transport (Bollhoefer et al., 2006;Sinclair et al., 2006;[START_REF] Strok | Fractionation of natural radionuclides in soils from the vicinity of a former uranium mine Zirovski vrh, Slovenia[END_REF][START_REF] Smodis | Radioecology around a closed uranium mine[END_REF][START_REF] Morin | Mononuclear U(IV) complexes and ningyoite as major uranium species in lake sediments[END_REF]Liu et al., 2017;Stetten et al., 2018;[START_REF] Dang | Uranium dispersion from U tailings and mechanisms leading to U accumulation in sediments: Insights from biogeochemical and isotopic approaches[END_REF][START_REF] Liu | Provenance of uranium in a sediment core from a natural reservoir, South China: Application of Pb stable isotope analysis[END_REF][START_REF] Yin | Mechanism of uranium release from uranium mill tailings under long-term exposure to simulated acid rain: Geochemical evidence and environmental implication[END_REF][START_REF] Yin | Critical insight and indication on particle size effects towards uranium release from uranium mill tailings: Geochemical and mineralogical aspects[END_REF][START_REF] Yin | Mechanism of uranium release from uranium mill tailings under long-term exposure to simulated acid rain: Geochemical evidence and environmental implication[END_REF][START_REF] Mangeret | Early diagenesis of radium 226 and radium 228 in lacustrine sediments influenced by former mining sites[END_REF][START_REF] Paradis | Field experiments of surface water to groundwater recharge to characterize the mobility of uranium and vanadium at a former mill tailing site[END_REF][START_REF] Gourgiotis | New Insights into Pb Isotope Fingerprinting of U-Mine Material Dissemination in the Environment: Pb Isotopes as a Memory Dissemination Tracer[END_REF][START_REF] Wang | Geochemical and U-Th isotopic insights on uranium enrichment in reservoir sediments[END_REF][START_REF] Yin | Uranium re-adsorption on uranium mill tailings and environmental implications[END_REF].

The U mill tailings are radioactive materials that have higher content of U (30-600 ppm) and Pb (60-800 ppm) compared to the average value encountered in the environment (3 and 10 ppm, respectively). Therefore, the transfer of U and Pb from U mill tailing into the environment, via solid particles or dissolved species, would contribute to the U and Pb content in the local geochemical background. However, U-ores outcrops potentially occurring outside of the U mine sites present also similar geochemical signature with even higher content of U and Pb. Moreover, weathering and erosion of the local bedrock that is often granitic in the case of the French U-mines areas can also play an important role in increasing these concentration levels. Indeed, high U contents have already been documented in sites non-impacted by mining activities, such as Alpine soils (up to 4000 ppm) and lacustrine sediments (up to 400 ppm) [START_REF] Regenspurg | Speciation of naturally-accumulated uranium in an organic-rich soil of an alpine region (Switzerland)[END_REF]Lefebvre et al., 2021a, b) as well as ground and surface waters [START_REF] Owen | Mountain wetlands -Efficient uranium filters -Potential impacts[END_REF] where the surrounding bedrock consists mainly of crystalline rocks that commonly contain trace amounts of U [START_REF] Bernhard | Speciation of uranium in environmental relevant compartments[END_REF].

The U mill tailings of this study have a Pb isotope signature with high 206 Pb/ 207 Pb and low 208 Pb/ 207 Pb ratios, similar to their related U-ores (Fig. 6). Therefore, for an environmental sample displaying a radiogenic isotope signature, it is not possible to decipher the origin of this signature between (1) the natural weathering of U-ore, (2) the U-ore mining activities and

(3) the U milling activities, by using only stable Pb isotopes.

Previous studies have shown that ( 234 U/ 238 U) ratio could be used to track the impact of U mill tailings in the environment, as the water that interacted with U mill tailings (Zielinsky et al., 1997;[START_REF] Ketterer | Envirogeochemical exploration for "NORM" wastes: quadrupole inductively coupled plasma mass spectrometric measurements of thorium and uranium isotopes[END_REF]Bush and Morrisson, 2012;Kamp and Morrison, 2014;Wang et al., 2021) could have high U content associated to a ( 234 U/ 238 U) near to unity, which contrast with the groundwater (0.5<( 234 U/ 238 U)<30; Osmond and Cowart, 1992) and the dissolved load of major rivers (1.3±0.5, 2σ; [START_REF] Suhr | Th/U and U series systematics of saprolite: importance for the oceanic U-234 excess[END_REF] that have a lower U content associated usually with a ( 234 U/ 238 U)>1. The U mill tailings of this study show a disequilibrium with higher ( 234 U/ 238 U) activity ratios compared to (1) U-ores, (2) the average weathered solid products, excluding U-ores ( 234 U/ 238 U) = 0.99±0.19 [START_REF] Suhr | Th/U and U series systematics of saprolite: importance for the oceanic U-234 excess[END_REF] or to the range covered by weathered U-mineralizations (0.89-1.20; Lowson et al., 1986).

In this study we propose to use the U-Pb isotopic composition of U mill tailings which is unique as it combines both (1) the highly radiogenic Pb signature related to U-ores and (2) the high disequilibrium with ( 234 U/ 238 U), related to the milling process of U-ores. Thus, this signature is distinct compared to (1) U-ores, which exhibit radiogenic Pb isotopes signature, but are on average at secular equilibrium with respect to 234 U-238 U, and (2) weathered solid products which exhibit mostly small or moderate disequilibrium associated to a common (weathered crust, excluding U-ores) or radiogenic (weathered U mineralizations) Pb isotopes signature.

The impact of a contamination from U mill tailings in the environment on the U-Pb signature of a contaminated sample was investigated with a mixing model [START_REF] Langmuir | General mixing equation with applications to icelandic basalts[END_REF] between the U mill tailings from this study and the PDAC (Stacey and Krammers, 1976;[START_REF] Rudnick | Composition of the Continental Crust[END_REF]) at secular equilibrium. The mixing curves are plotted in the figure 9.

The results of this model show that only a fraction of 5 wt. % of U mill tailings added to a sediment is sufficient in most cases to get a material with a distinct U-Pb isotopic signature ( 226 Ra/ 230 Th) activity ratios altering the initial U mill tailing signature limiting thus their use as a relevant tracer of U mill tailings. Finally, regarding elemental composition, we believe that S concentration seems to be a promising tracer to highlight the impact of acid U mill tailings or tailing activities on the environment.

Conclusions

The goal of this study was to identify relevant tracers that can be used for environmental impact assessment studies involving U mill tailings. The results put in light the U series disequilibrium in the U mill tailings, especially with higher ( 234 U/ 238 U) compared to most of the solid weathered products and high ( 230 Th/ 238 U) activity ratios related to the selective U extraction during the milling process. This high ( 234 U/ 238 U) activity ratios were likely acquired by the removal of labile U-rich phases by dissolution, while the neighbouring milling-resistant U-poor phases that are enriched in recoiled 234 U remain in the U mill tailings. This study also suggest the conservation of the specific Pb isotopic signature of Uores into the U mill tailings with higher 206 Pb/ 207 Pb and lower 208 Pb/ 207 Pb compared to common lead. This specific Pb signature have been encountered in the U mill tailing into the remaining U-rich phases, (remaining or secondary) S-rich phases and potentially in association with clay minerals or oxyhydroxides. As a consequence, we recommend to use stable Pb isotopes combined with ( 234 U/ 238 U) activity ratios as multi-tracking tool providing a relevant fingerprinting for the impact of U milling activities on the environment.

Acknowledgements

29

We would like to warmly thank Gilles Alcade, Olivier Diez and Cyrielle Jardin for their helpful contributions on elemental analysis. This is PATERSON, the IRSN mass spectrometry platform, contribution n°12.

Figures

Figure 1: [START_REF] Kigoshi | Alpha-recoil thorium-234 -Dissolution into water and uranium-234/uranium-238 disequilibrium in nature[END_REF]) associated to the annealing of the alpha-recoil damage (Eyal and Fleisher, 1985;[START_REF] Lumpkin | Alpha-recoil damage in titanite (CaTiSiO5): Direct observation and annealing study using high resolution trans;ission electron microscopy[END_REF].

32

The size of alpha recoil damages (20-30 nm) is coming from [START_REF] Fleischer | Isotopic disequilibrium of uranium -alpha-recoil damage and preferential solution effects[END_REF]Ordonez-Regil et al., 1989). The ( 234 U/ 238 U)≈1 is derived from the average value (0.97±0.09, 2σ, n=56) of Uore concentrates (Kayzar-Boggs et al., 2021) that derived from the U-rich leachate during the milling process. 1956). Small orange circles represent the Pb isotope ratios for U oxides from Gabon [START_REF] Gancarz | U-Pb age (2.05 Ga) of the Oklo uranium deposit[END_REF]. Large orange circles represent the theoritical 206 Pb/ 207 Pb ratios calculated for the U deposit in the Francevillian basin (Gabon) at 2050±30 Ma [START_REF] Gancarz | U-Pb age (2.05 Ga) of the Oklo uranium deposit[END_REF]. The blue activity ratio of the weathered crust and dissolved load of major rivers comes from [START_REF] Suhr | Th/U and U series systematics of saprolite: importance for the oceanic U-234 excess[END_REF]. ( 234 U/ 238 U) of the seawater [START_REF] Osmond | Theory and uses of natural uranium isotopic variations in hydrology[END_REF]. Field of weathered Uores was drawn using the range of ( 234 U/ 238 U) reported in Lowson et al., (1986) Somot et al., (1997), Pagel and Somot (2002), [START_REF] Ballini | A multiscalar study of the long-term reactivity of uranium mill tailings from Bellezane site (France)[END_REF]. The type of U deposit comes from the classification suggested by IAEA (2018). (I) and (II) correspond to the age of the main stage of U deposition from [START_REF] Cathelineau | Metallogenesis of the french part of the variscan orogen. Part II: Time-space relationships between U, Au and Sn-W ore deposition and geodynamic events -mineralogical and U-Pb data[END_REF] and references therein, Horie and Hidaka (2019) and Gancartz, (1978) ), the Pb from the U-ore, was calculating using the method described in [START_REF] Gourgiotis | New Insights into Pb Isotope Fingerprinting of U-Mine Material Dissemination in the Environment: Pb Isotopes as a Memory Dissemination Tracer[END_REF].

  Figure 1: a) Geological map of France (1/1000000 series, © BRGM) and b) modified

Figure 2 :

 2 Figure 2: Major and trace elements patterns of U mill tailings from France and Gabon

Figure 3 :

 3 Figure 3: (a) ( 230 Th/ 238 U) vs. ( 234 U/ 238 U) and (b) ( 210 Pb/ 226 Ra) vs. ( 226 Ra/ 230 Th) activity ratio

Figure 4 :

 4 Figure 4: Sketch showing the process suggested bySheng and Kuroda (1986) that would produce the ( 234 U/ 238 U)>1 in the U mill tailings. The implantation of 234 Th (which decay into 234 U) from a U-rich phase into U-poor phase by alpha-recoil effect(Kigoshi, 1971) associated

Figure 5 :

 5 Figure 5: ( 234 U/ 238 U) vs. U diagram. Solid gray lines represent the mixing curves between a

Figure 6 :

 6 Figure 6: (a) 206 Pb/ 207 Pb vs. 208 Pb/ 207 Pb and (b) 207 Pb/ 206 Pb vs. 204 Pb/ 206 Pb diagrams for U

(

  France) and the orange (Gabon) areas represent the possible range of composition resulting from the mixing between a material having the composition of the PDAC and the respective U ores. The fraction of radiogenic Pb coming from the U ores in the U mill tailing (k factor, in grey) have been determined from the equation proposed by[START_REF] Gourgiotis | New Insights into Pb Isotope Fingerprinting of U-Mine Material Dissemination in the Environment: Pb Isotopes as a Memory Dissemination Tracer[END_REF]. The Pb isotopic compositions used for the end-members are described in the text. (b) The dashed lines represent the linear regression of the six U mill tailings from France (orange) and from U mill tailings from Gabon and PDAC (blue). The apparent age of formation of U deposits was calculated using the respective intercept values.

Figure 7 :

 7 Figure 7: (a) SEM-BSE imaging (U,Pb)-rich phases of JOU-97 sample. (b), (c), (d) SIMS mapping of 206 Pb, 208 Pb, 238 U 16 O.

Figure 8 :

 8 Figure 8: (a) SEM-BSE imaging of (U,Pb)-rich phases of GABON sample. (b) and (c) SEM-EDS mapping of Pb and S. (d), (e), (f) and (g) SIMS mapping of 28 Si, 206 Pb, 208 Pb, 238 U 16 O.

Figure 9 :

 9 Figure 9: ( 234 U/ 238 U) vs 206 Pb/ 207 Pb diagram showing the specific signature of U mill tailings

  or leaded materials coming from anthropogenic activities (e.g. gasoline or industrial emissions; Monna et al., 1997) on Earth's ( 204 Pb: 1.0-1.7%; 206 Pb: 20.8-27.5%; 207 Pb: 17.6-23.7%; 208 Pb: 51.3-56.2%; Berglund

  Table3). Four U mill tailings samples (LOD-FS, LOD-MA, JOU-97 and BZN) have ( 226 Ra/ 230 Th) activity ratios close to secular equilibrium (i.e. 0.95-1.05), which suggest that 226 Ra and 230 Th were not significantly fractionated during the U-ore treatment and/or subsequent U mill tailing management.However, two others U mill tailings samples (Jouac-DT, Gabon) have ( 226 Ra/ 230 Th) > 1, while ECA-85 sample has ( 226 Ra/ 230 Th) < 1. For Gabon sample, the 226 Ra and 230 Th disequilibrium points out the selective migration of Th due to the acidity of non-neutralized barren solutions and accumulation of 226 Ra in the samples thanks to the precipitation of Ba-

	Pb-Ra sulfates

  [START_REF] Gancarz | U-Pb age (2.05 Ga) of the Oklo uranium deposit[END_REF];Gauthier-Lafaye et al., (1996)) is characterized by higher ( 206 Pb/ 207 Pb) and lower ( 208 Pb/ 207 Pb) ratios compared to the common Pb isotope signature of the Present Day Average Crust (PDAC; 206 Pb/ 207 Pb = 1.20; 208 Pb/ 207 Pb = 2.47;Stacey and Krammers, 1975; Fig.6). The U mill tailings have 204 Pb/ 207 Pb, 206 Pb/ 207 Pb, 208 Pb/ 207 Pb ratios that range from 0.00396 to 0.06111, from 1.86 to 7.15 and from 0.22 to 2.39, respectively (Table

  206 Pb/ 207 Pb ratio of the radiogenic end-member used for U mill tailings from France (19.55) has been determined by the intercept (1/intercept) in a 207 Pb/ 206 Pb vs.204 Pb/ 206 Pb diagram (Fig

  compared to the natural range, with both 206 Pb/ 207 Pb > 1.6 and ( 234 U/ 238 U) > 1.2.It is worth mentioning that combining Pb isotopes to U isotopes is more relevant than to ( 230 Th/ 238 U) activity ratio which can exhibit important variations due to chemical fractionation. Higher 238 U mobility compared to that of 230 Th can lead to ( 230 Th/ 238 U) values similar to that observed in uranium mill tailings. Chemical fractionation can also influence ( 210 Pb/ 226 Ra) and

Table 1 :

 1 and the range of 206 Pb/ 207 Pb for U-ores. The natural Pb isotopic variation (excluding U-ores) comes from Berglund and Wieser (2011). U mill tailings description. Information about the U mill tailings are coming from

	7 Tables
	U mill	TMF		U mineralization		U-ore milling process
	tailings						and effluent treatment
			Mining	Deposit	Geological	Age	Mill	Milling	Effluent
			division	type	unit		factory	type	treatment
	LOD-FS LOD-MA	Le Bosc (Lodève)	Lodèvois	Tectonic-lithologic sandstone	Lodève basin	(I) 183-172Ma (II) 103-113Ma	SIMO Le Bosc	Alkaline	Not neutralized
	ECA-85	L'Ecarpière	Bretagne-Vendée	Granite related	Mortagne massif	(I) 322-308Ma (II) 286-264Ma	SIMO Ecarpière	Acid	CaCO3, Lime
	BZN	Bellezane	La Crouzille	Granite related	Saint Sylvestre massif	(I) 276-270Ma (II) 183-170 Ma	SIMO Bessines	Acid	Lime
	JOU-97 JOU-DT	Le Bernardan (Jouac)	Mailhac-sur-Benaize	Granite related	Western Marche massif	(I) 280Ma (II) 170-140Ma	SMJ Jouac	Acid	Lime, BaCl2
	Gabon	Mounana	Mounana	Tectonic-lithologic sandstone	Francevillian basin	(I) 2050Ma	COMUF Mounana	Acid	Not neutralized

  . Abbreviations: TMF, for Tailing Management Facilities ; FS, for faille sud; MA, for Mas d'Alary; DT, for Dong Trieu; SIMO, for Société Industrielle des Minerais de l'Ouest; SMJ, for Société des Mines de Jouac; COMUF, for Compagnie des Mines d'Uranium de Franceville.

	Sample	LOD-FS LOD-MA	ECA-85	BZN	JOU-97	JOU-DT	GABON
	TMF	Le Bosc	Le Bosc	L'Ecarpièr	Bellezan	Le	Le	Mounan
		(Lodève)	(Lodève)	e	e	Bernarda	Bernarda	a
							n (Jouac)	n (Jouac)
	Major elements (wt. %)
	Al 2 O 3	16.57	15.43	12.98	14.34	10.85	15.25	6.14
	Fe 2 O 3 (T)	6.18	6.72	3.69	2.53	2.68	3.86	1.00
	MgO	3.81	3.72	0.86	0.52	1.41	1.51	0.20
	CaO	6.45	7.21	6.71	2.36	4.05	4.60	0.10
	Na 2 O	2.72	2.90	1.48	1.89	1.28	1.62	0.11
	K 2 O	5.65	4.82	3.64	5.34	4.07	5.78	1.39
	TiO 2	0.65	0.62	0.35	0.25	0.16	0.26	0.16
	MnO	0.13	0.17	0.03	0.06	0.08	0.17	0.01
	P 2 O 5	0.15	0.13	0.34	0.26	0.14	0.17	0.02
	S (T)	0.12	0.09	3.04	2.77	1.87	3.07	0.05
	Trace elements (µg/g	-1 )
	Ba	688	652	320	480	1193	532	592
	Pb	542	443	66	418	76	201	805
	Th (ID)	11.2	10.8	17.6	15.3	8.8	10.5	21.0
	U (ID)	594	321	30	169	101	131	71

Table 2 :

 2 Major and trace element contents of U mill tailings from France and Gabon. Major elements were measured using ICP-OES technique, while S (T) content was measured using a CHNS elemental analyser. Trace elements were measured using an ICPMS/MS with a standard calibration technique (Ba and Pb) or by isotope dilution (ID for U and Th).

	Sample	238 U	2σ	( 238 U)	2σ	( 234 U/ 238	2σ	( 230 Th/ 238	2σ	( 226 Ra/ 230 T	2σ	( 210 Pb/ 226 R	2σ
						U)		U)		h)		a)
		µg/g		Bq/kg		AR		AR		AR		AR
	LOD-FS	590	±1. 5	7342	±1 9	1.29	±0.0 3	7.1	±0. 3	0.91	±0.0 5	0.69	±0.02
	LOD-MA	319	±1. 1	3966	±1 3	1.64	±0.0 4	7.9	±0. 2	0.95	±0.0 4	0.71	±0.01
	ECA-85	29.6	±0. 1	369	±1	1.78	±0.0 2	65.0	±0. 3	0.63	±0.0 4	0.92	±0.04
	BZN	168	±0. 5	2086	±7	1.29	±0.0 1	15.4	±0. 2	1.00	±0.0 0	0.83	±0.01
	JOU-97	100	±0. 7	1243	±9	1.27	±0.0 2	23.1	±0. 3	0.60	±0.0 3	0.68	±0.02
	JOU-DT	129. 7	±0. 5	1615	±6	1.51	±0.0 1	19.1	±0. 3	2.55	±0.1 2	0.828	±0.00 4
	GABON	70.4	±0. 4	877	±5	1.87	±0.0 5	6.6	±0. 2	3.13	±0.4 0	0.89	±0.01

Table 3 :

 3 Activities of 238 U and activity ratios (AR) of long-live radionuclides of U mill tailings from France and Gabon. U and Th isotopes were measured by ICP-MS. ( 230 Th/ 226 Ra) and ( 210 Pb/ 226 Ra) were measured by gamma spectrometry.

	Sample	204 Pb/	207 Pb	2σ	206 Pb/	207 Pb	2σ	208 Pb/	207 Pb	2σ	%Pb rad
											k
	LOD-FS	0.0592	±0.0008	2.455	±0.019	2.304	±0.016	24%
	LOD-MA	0.0606	±0.0005	2.053	±0.015	2.353	±0.012	18%
	ECA-85	0.0475	±0.0004	5.812	±0.049	1.871	±0.009	60%
	BZN	0.0611	±0.0003	1.862	±0.007	2.388	±0.005	14%
	JOU-97	0.0437	±0.0005	6.900	±0.126	1.731	±0.004	66%
	JOU-DT	0.0505	±0.0004	4.948	±0.041	1.981	±0.014	53%
	GABON	0.0040	±0.0001	7.157	±0.082	0.222	±0.001	95%

Table 4 :

 4 Pb isotopes of U mill tailings from France and Gabon measured by HR-ICPMS. The fraction of radiogenic Pb (%Pb rad