Pierre Martz

Julien Mercadier

Michel Cathelineau

Marie-Christine Boiron

David Quirt

Amber Doney

Olivier Gerbeaud

Etienne De Wally

Patrick Ledru

Formation of U-rich mineralizing fluids through basinal brine migration within basement-hosted shear zones: A large-scale study of the fluid chemistry around the unconformity-related Cigar Lake U deposit (Saskatchewan, Canada)

Keywords: basinal brines, unconformity-related uranium deposit, metals, microfracturing, uranium, Athabasca Basin. Highlights

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Introduction

Unconformity-related uranium deposits are the world largest high-grade U deposits with average grades reaching up to 20 wt.% U. They represent about 240,000 t of reasonablyassured recoverable U resources at a cost of < USD 80 / kg U. These resources correspond to around 20% of the world's U resources and the bulk of it occurs in the Athabasca Basin region of northern Saskatchewan, Canada (OECD/ NEA-IAEA, 2016). This study focuses on the Cigar Lake deposit which is the world's second-largest high-grade uranium deposit containing 613,400 t of mineral reserves at an average grade of 15.9% U3O8 (Cameco, 2016).

These deposits are called "unconformity-related" because of their spatial relationship to the unconformity between the Paleo-to Mesoproterozoic sedimentary cover and the underlying crystalline basement.

The formation of these deposits is thought to be related to a major ore-forming event dated between 1.6 and 1.3 Ga (Alexandre et al., 2007 and references therein). This event is linked to the circulation of two brines, one NaCl-rich and the other CaCl2-rich, that circulated before, during, and after UO2 deposition [START_REF] Chu | Thermal profiles inferred from fluid inclusion and illite geothermometry from sandstones of the Athabasca basin: Implications for fluid flow and unconformity-related uranium mineralization[END_REF][START_REF] Derome | Mixing of sodic and calcic brines and uranium deposition at McArthur River, Saskatchewan, Canada: a Raman and laser-induced breakdown spectroscopic study of fluid inclusions[END_REF][START_REF] Kotzer | Petrogenesis of the Proterozoic Athabasca Basin, northern Saskatchewan, Canada, and its relation to diagenesis, hydrothermal uranium mineralization and paleohydrogeology[END_REF]Pagel, 1975a;[START_REF] Pagel | Contribution to some Saskatchewan uranium deposits mainly from fluid inclusion and isotope data[END_REF][START_REF] Richard | Metal-rich fluid inclusions provide new insights into unconformity-related U deposits (Athabasca Basin and Basement, Canada)[END_REF][START_REF] Richard | Brine-rock interaction in the Athabasca basement (McArthur River U deposit, Canada): Consequences for fluid chemistry and uranium uptake[END_REF]. Both brines have been considered to have had a similar origin: sub-aerial evaporation of seawater, based on halogen (Cl-Br-I) and noble gas (Ar-Kr-Xe) systematics, high salinities, stable chlorine isotopic compositions, and also the B isotopic composition of tourmaline (sensu lato: "dravite"; [START_REF] Derome | Mixing of sodic and calcic brines and uranium deposition at McArthur River, Saskatchewan, Canada: a Raman and laser-induced breakdown spectroscopic study of fluid inclusions[END_REF][START_REF] Leisen | Determination of Cl and Br concentrations in individual fluid inclusions by combining microthermometry and LA-ICPMS analysis: Implications for the origin of salinity in crustal fluids[END_REF][START_REF] Mercadier | Boron-and magnesium-rich marine brines at the origin of giant unconformity-related uranium deposits:δ11B evidence from Mgtourmalines[END_REF][START_REF] Richard | Noble gases (Ar, Kr, Xe) and halogens (Cl, Br, I) in fluid inclusions from the Athabasca Basin (Canada): Implications for unconformity-related U deposits[END_REF][START_REF] Richard | An evaporated seawater origin for the ore-forming brines in unconformity-related uranium deposits (Athabasca Basin, Canada): Cl/Br and δ37Cl analysis of fluid inclusions[END_REF].

The CaCl2-rich brines contain up to one order of magnitude more uranium and associated metals (Cu, Pb, Zn, Mn) relative to the NaCl-rich brines [START_REF] Richard | Metal-rich fluid inclusions provide new insights into unconformity-related U deposits (Athabasca Basin and Basement, Canada)[END_REF][START_REF] Richard | Brine-rock interaction in the Athabasca basement (McArthur River U deposit, Canada): Consequences for fluid chemistry and uranium uptake[END_REF]. The compositional differences between the two brines are considered to be a result of different degrees of fluid-rock interaction, caused by variable availability of reactive rock along fluid migration pathways [START_REF] Richard | Metal-rich fluid inclusions provide new insights into unconformity-related U deposits (Athabasca Basin and Basement, Canada)[END_REF]. The greater Ca, Cl, and metal contents in the CaCl2-rich brine compared to the NaCl-rich brine are the result of processes that have been already described in other contexts, such as European Pb-Zn-F-Ba deposits [START_REF] Boiron | Fluid flows and metal deposition near basement /cover unconformity: lessons and analogies from Pb-Zn-F-Ba systems for the understanding of Proterozoic U deposits[END_REF][START_REF] Bons | Fluid mixing from below in unconformity-related hydrothermal ore deposits[END_REF]Burisch et al., 2017bBurisch et al., , 2016a;;[START_REF] Fusswinkel | Fluid mixing forms basement-hosted Pb-Zn deposits: Insight from metal and halogen geochemistry of individual fluid inclusions[END_REF][START_REF] Gleeson | Infiltration of basinal fluids into high-grade basement, South Norway: sources and behaviour of waters and brines[END_REF][START_REF] Gleeson | The origin and evolution of base metal mineralising brines and hydrothermal fluids, South Cornwall, UK[END_REF][START_REF] Heijlen | Carbonate-Hosted Zn-Pb Deposits in Upper Silesia, Poland: Origin and Evolution of Mineralizing Fluids and Constraints on Genetic Models[END_REF][START_REF] Kendrick | Noble gas and halogen evidence for the origin of Scandinavian sandstone-hosted Pb-Zn deposits[END_REF][START_REF] Markl | Natural fracking and the genesis of five-element veins[END_REF][START_REF] Walter | Major element compositions of fluid inclusions from hydrothermal vein-type deposits record eroded sedimentary units in the Schwarzwald district[END_REF][START_REF] Walter | Long-term chemical evolution and modification of continental basement brines -a field study from the Schwarzwald[END_REF][START_REF] Wilkinson | Ore-forming processes in Irish-type carbonatehosted Zn-Pb deposits: Evidence from mineralogy, chemistry, and isotopic composition of sulfides at the Lisheen mine[END_REF], Australian Pb-Zn deposits [START_REF] Feltrin | Basement metal scavenging during basin evolution: Cambrian and Proterozoic interaction at the Century ZnPbAg Deposit, Northern Australia[END_REF], North African Ag-Hg deposits [START_REF] Essarraj | Basinal Brines at the Origin of the Imiter Ag-Hg Deposit (Anti-Atlas, Morocco): Evidence from LA-ICP-MS Data on Fluid Inclusions, Halogen Signatures, and Stable Isotopes[END_REF][START_REF] Essarraj | Penetration of surface-evaporated brines into the Proterozoic basement and deposition of Co and Ag at Bou Azzer (Morocco): Evidence from fluid inclusions[END_REF], European and African Cu deposits [START_REF] Kotzer | Petrogenesis of the Proterozoic Athabasca Basin, northern Saskatchewan, Canada, and its relation to diagenesis, hydrothermal uranium mineralization and paleohydrogeology[END_REF][START_REF] Mcgowan | Origin of the Nchanga copper-cobalt deposits of the Zambian Copperbelt[END_REF][START_REF] Muchez | 7: Extensional tectonics and the timing and formation of basin-hosted deposits in Europe[END_REF] , as well as a few active hydrothermal systems such as the Rhine graben [START_REF] Cathelineau | Downward penetration and mixing of sedimentary brines and dilute hot waters at 5km depth in the granite basement at Soultz-sous-Forêts (Rhine graben, France)[END_REF] and the KTB drill hole fluids [START_REF] Lodemann | On the origin of saline fluids in the KTB (continental deep drilling project of Germany)[END_REF][START_REF] Möller | Main and trace elements in KTB-VB fluid: Composition and hints to its origin[END_REF]. All these examples share the following model: sedimentary brines of evaporitic origin (either primary or secondary) percolated within the basement and participated in specific water-rock interaction, resulting in cation exchange, salinity changes, and metal-leaching during fluid circulation. However, several uncertainties remain in this general model, especially for unconformity-related U deposits. Among these are: i) the mechanisms of conversion from NaCl-rich brine to CaCl2-metal-rich brine, ii) the vertical and horizontal extent of fluid flow within the basement, and iii) the fluid flow mechanisms. Such knowledge deficiencies are present because nearly all of the pertinent data have so far only been acquired from (1) the Athabasca Basin sedimentary rocks, and (2) the immediate surroundings of the deposits, not from the basement rocks or away from the mineralized areas.

For this purpose, this study examines at a multi-kilometer scale (1) the main fluid flow pathways, and (2) the spatial distribution of the P-T-X features of the brines, trapped in both the sedimentary rocks (quartz overgrowths around detrital quartz and hydrothermal quartz veins) and in the basement (fluid inclusion planes [FIPs] crosscutting magmatic and metamorphic quartz). Oriented samples have been selected within a 25 km² area surrounding the Cigar Lake deposit and specifically along perpendicular profiles that cross-cut several different basement-hosted fault zones. Semi-quantitative estimations of the microfracture paleoporosity within selected lithologies and the local stress regime at the time of brine circulation were obtained by measuring the relative abundance and orientations of the FIPs in the basement. These estimations were used to track the physico-chemical evolution of the basinal brines during fluid-rock interaction and to understand the main controls of the brine migration at scales previously not investigated: in and around the deposit.

Geological setting

Regional geology

The basement below the Athabasca Basin (Saskatchewan, Canada) can be subdivided into two lithostructural subprovinces of the Western Churchill structural province: the Rae Subprovince to the west and the Hearne Subprovince to the east, separated by the Snowbird Tectonic Zone (STZ; Lewry et al., 1985;Fig. 1). The Hearne Subprovince can be further divided into three sub-domains: the Virgin River, Mudjatik, and Wollaston Domains. Most of the known unconformity-related U deposits are located in the Hearne Subprovince and, there, they are spatially concentrated at the transition between the Mudjatik and Wollaston Domains (Wollaston-Mudjatik Transition Zone: WMTZ). The two latter domains formed during the ca.

1.8 Ga continent-continent collision of the Trans-Hudson Orogeny (THO; Lewry et al., 1985;Lewry and Sibbald, 1977). The rocks in the WMTZ mainly correspond to polydeformed and metamorphosed metasediments (up to granulite facies) of the Wollaston Group overlying elongated Archean granitoid and orthogneissic domes. Widespread quartzo-feldspathic anatectic sweats, leucogranites, and granitic pegmatites formed between ca. 1.86 and 1.80 Ga (Annesley et al., 2005 and references therein). Major graphitic shear zones formed in graphitic metasedimentary lithologies throughout the THO and contributed to the overall basement structural framework [START_REF] Annesley | Geology and thermotectonic evolution of the western margin of the Trans-Hudson Orogen: evidence from the eastern sub-Athabasca basement[END_REF][START_REF] Jeanneret | Tectono-metamorphic evolution of the pre-Athabasca basement within the Wollaston-Mudjatik Transition Zone[END_REF][START_REF] Martz | C-O-H-N fluids circulations and graphite precipitation in reactivated Hudsonian shear zones during basement uplift of the Wollaston-Mudjatik Transition Zone: Example of the Cigar Lake U deposit[END_REF]. Most of the unconformity-related uranium deposits discovered to date are located within or above graphitic shear zones.

Deposition within the Athabasca Basin occurred following the exhumation of the Trans-Hudson orogenic belt at ca. 1700 Ma [START_REF] Jeanneret | Tectono-metamorphic evolution of the pre-Athabasca basement within the Wollaston-Mudjatik Transition Zone[END_REF] and at least before ca. 1640 Ma, which is the age of the Wolverine Point Formation, present near the top of the currently preserved Athabasca stratigraphy [START_REF] Rainbird | Age, provenance, and regional correlation of the athabasca group, saskatchewan and alberta, constrained by igneous and detrital zircon geochronology[END_REF]. The sedimentary rocks within the Athabasca Basin belong to the undeformed Athabasca Group [START_REF] Ramaekers | Revised geological map and stratigraphy of the Athabasca group, Saskatchewan and Alberta[END_REF]. It consists mainly of thick sequences of Paleo-to Mesoproterozoic, polycyclic, fluvial to marine quartz sandstone deposited in a near-shore shelf environment [START_REF] Ramaekers | Revised geological map and stratigraphy of the Athabasca group, Saskatchewan and Alberta[END_REF]. The strata are divided into ten stratigraphic units: the earliest, quartz-rich conglomerate and sandstone with minor mudstone of the Fair Point Formation and subsequent Read, Smart, Manitou Falls, and Lazenby Lake Formations; sandstone and variably phosphatic siltstones/mudstones of the Wolverine Point Formations; sandstone and conglomeratic sandstones in the Locker Lake and Otherside Formations; mudstone, shale, and fine sandstone of the Douglas Formation, and finally stromatolitic carbonates with siliciclastic interbeds of the Carswell Formation [START_REF] Ramaekers | Revised geological map and stratigraphy of the Athabasca group, Saskatchewan and Alberta[END_REF]. The current maximum preserved thickness of the basin is about 1500 m but the maximum thickness has been interpreted to have reached a thickness of 3-5 km based on P-T estimations from fluid inclusions (Pagel, 1975a(Pagel, , 1975b)).

In the Cigar Lake deposit area, the only preserved stratigraphic unit is the Manitou Falls Formation containing quartz-rich sandstones and microconglomerates. The thickness of the Athabasca strata in the study area ranges from about 260 to 470 meters [START_REF] Bruneton | Geological environment of the Cigar Lake uranium deposit[END_REF].

Local geology around the Cigar Lake deposit

The Cigar Lake deposit is a world-class unconformity-related uranium deposit located in the eastern part of the Athabasca Basin (Fig. 1). The deposit is in the form of an E-W elongated, ~1.9 km-long, 15-100 m-wide and ~10-20 m-high lens. Although the timing of U deposition remains open to debate, the main U stock, if not all of it, is believed to have precipitated between ca. 1.46 and 1.29 Ga [START_REF] Fayek | O and Pb isotopic analyses of uranium minerals by ion microprobe and U-Pb ages from the Cigar Lake deposit[END_REF][START_REF] Martz | Caractéristiques, chronologie et rôles des circulations fluides dans le bassin d'Athabasca et de son socle: implications dans la formation et l'évolution du gisement d'uranium de Cigar Lake. Characteristics, chronology and roles of fluid circulations in t[END_REF][START_REF] Philippe | Formation and evolution of the Cigar Lake uranium deposit based on. U-Pb and K-Ar isotope systematics[END_REF]. The deposit is almost entirely sandstone-hosted and occurs immediately above the unconformity between the Athabasca Group sedimentary cover and the underlying Paleoproterozoic metasediments of the Wollaston Group and Hudsonian plutonic rocks, and directly above a major E-W-oriented, S-dipping, graphitic-rich structure called the "Cigar Main conductor" [START_REF] Fouques | The Cigar Lake uranium deposit: Discovery and general characteristics[END_REF][START_REF] Bruneton | Geological environment of the Cigar Lake uranium deposit[END_REF]. This structure is characterized by several stacked graphite-bearing ductile-brittle shear zones developed within pelitic gneisses and lesser calcsilicate rocks. It forms a 10 km-long electromagnetic (EM) conductor that was the exploration target that resulted in the discovery of the deposit during the 1980-1981 winter field season.

There is a main regional ductile fabric (foliation) striking SW-NE, the formation of which has been attributed to the early THO deformation events (D1/D2, 1860 -1830 Ma; [START_REF] Annesley | Geology and thermotectonic evolution of the western margin of the Trans-Hudson Orogen: evidence from the eastern sub-Athabasca basement[END_REF]. Paleoproterozoic metasediments constitute the prominent basement lithology encountered in drill holes all over the Cigar Lake area and are thought to be bounded to the north by an Archean orthogneissic dome (Fig. 2). The contact between metasediments and orthogneisses, called the "Cigar North-East Trend", is characterized by a contrast of the magnetic properties (airborne data), and the occurrence of sheared rocks, mylonitized granite, and graphite-rich fault rocks.

Graphitic shear zones

Graphite-bearing basement shear zones constitute the geological source of the EM conductors identified in the Cigar lake area. Two main conductors have been identified, the Cigar Main (E-W oriented) and the Cigar North-East Trend, as well as a third subordinate conductor ("Power Line"), located 8 km to the south.

These shear zones contain a former ductile sheared fabric, characterized by the development of porphyroblastic textures (cordierite and feldspar porphyroblasts, typically wrapped by chlorite-graphite layers), locally showing S-C fabric, and the existence of dynamic quartz recrystallization textures (grain boundary migration). A gradual steepening of the metamorphic foliation is commonly observed, from 60 -70° to the south-south-west (regional trend) to 80° (locally subvertical) within the graphitic shear zones, in association with increase in the intensity of shearing and the graphite content (locally up to ~50%). The shear zones were initiated in C-rich Paleoproterozoic (meta)sedimentary layers at near-peak THO metamorphic conditions (6 -9 kbar and 750 -825 °C; [START_REF] Annesley | Geology and thermotectonic evolution of the western margin of the Trans-Hudson Orogen: evidence from the eastern sub-Athabasca basement[END_REF][START_REF] Martz | C-O-H-N fluids circulations and graphite precipitation in reactivated Hudsonian shear zones during basement uplift of the Wollaston-Mudjatik Transition Zone: Example of the Cigar Lake U deposit[END_REF][START_REF] Mckechnie | CANADA: MINERAL COMPOSITIONS, METAMORPHIC[END_REF]. They were reactivated under brittle conditions during the late stages of post-Hudsonian basement exhumation leading to focused C-O-N-H fluid circulation and subsequent formation of hydrothermal chlorite and graphite along brittle fault planes [START_REF] Martz | C-O-H-N fluids circulations and graphite precipitation in reactivated Hudsonian shear zones during basement uplift of the Wollaston-Mudjatik Transition Zone: Example of the Cigar Lake U deposit[END_REF]. An abundant vein network additionally developed within the shear zones, with formation of white dolomite and milky quartz veins (some also filled by later pyrite) either parallel to the foliation or sub-horizontal. These late structures are observed in both the E-W and NE-SW trends.

The overall fracture density increases toward the central part of the shear zones and progressively overprints the former ductile fabric. The central zones with the highest degree of brittle deformation are referred to as fault damage zones. The fault cores are characterized by intervals, several meters wide, of cohesive fault rocks (proto-to ultracataclasites; [START_REF] Sibson | Fault rocks and fault mechanisms[END_REF] that are bounded by non-cohesive fault gouges containing sooty graphite, chlorite, dolomite, and sometimes euhedral pyrite. Finally, later veinlets of clear quartz, pink dolomite, and chlorite are observed in and near the fault cores, crosscutting the earlier milky quartz veins. For the three studied distinct ductile-brittle shear zones, the relatively large spacing between the drill holes (typically 50m) does not allow to say with certainty if the fault continues into the basin strata or not. Particularly for the E-W trend, it is uncertain if there is a small offset at the unconformity or not.

The alteration halo

At Cigar Lake, a well-developed host-rock alteration halo in the sandstone extends more than 300 m above the main U mineralization. It also extends more than 50 m into the basement beneath the mineralization, however the extent of the alteration in the basement remains poorly constrained due to a lack of drill cores that reach these depths [START_REF] Pacquet | Pétrographie et minéralogie des halos d'altération autour du gisement de Cigar Lake et leurs relations avec les minéralisations[END_REF]. This alteration halo is composed of hydrothermal assemblages of illite and sudoite (Mg-chlorite). Unlike most other unconformity-related deposits in the Athabasca, occurrences of alkali-deficient dravitic tourmaline ("dravite") are rarely described. The illite-sudoite±dravite clay mineral assemblage is typical of the host-rock alteration around the unconformity-related deposits, both in the Athabasca region [START_REF] Hoeve | Mineralization and host rock alteration in relation to clay mineral diagenesis and evolution of the middle Proterozoic Athabasca basin[END_REF]Alexandre et al., 2005;[START_REF] Hoeve | On the genesis of Rabbit Lake and other unconformity-type uranium deposits in northern Saskatchewan, Canada[END_REF][START_REF] Kister | Thermodynamic constraints on the mineralogical and fluid composition evolution in a clastic sedimentary basin: the Athabasca Basin (Saskatchewan, Canada)[END_REF][START_REF] Laverret | Mineralogy and geochemistry of the host-rock alterations associated with the Shea Creek unconformity-type uranium deposits (Athabasca Basin, Saskatchewan, Canada). Part 1. Spatial variation of illite properties[END_REF][START_REF] Ng | Mineralogical and geochemical evolution of the unconformity-related McArthur river zone 4 orebody in the Athabasca Basin, Canada: Implications of a silicified zone[END_REF] and in the McArthur Basin in Australia [START_REF] Beaufort | Clay alteration associated with proterozoic unconformity-type uranium deposits in the East Alligator Rivers uranium field, Northern Territory[END_REF][START_REF] Fisher | 3D representation of geochemical data, the corresponding alteration and associated REE mobility at the Ranger uranium deposit[END_REF][START_REF] Nutt | Chloritization and associated alteration at the Jabiluka unconformity-type uranium deposit, Northern Territory, Australia[END_REF][START_REF] Polito | Significance of alteration assemblages for the origin and evolution of the Proterozoic Nabarlek unconformity-related uranium deposit, Northern Territory[END_REF][START_REF] Skirrow | The Ranger uranium deposit, northern Australia: Timing constraints, regional and ore-related alteration, and genetic implications for unconformity-related mineralisation[END_REF]. Within the halo, all the primary minerals of the basement rocks are replaced by the illite-sudoite(± dravite) assemblage while, in the Athabasca strata, illite replaces the early-and peak-diagenetic dickite (± earlier illite) clay mineral assemblage for over 400 m above the unconformity [START_REF] Hoeve | Mineralization and host rock alteration in relation to clay mineral diagenesis and evolution of the middle Proterozoic Athabasca basin[END_REF]Quirt, 2001;[START_REF] Pacquet | Pétrographie et minéralogie des halos d'altération autour du gisement de Cigar Lake et leurs relations avec les minéralisations[END_REF][START_REF] Percival | Clay mineralogy and isotope geochemistry of the alteration halo at the Cigar Lake uranium deposit[END_REF]. The alteration halo is also marked by intense quartz dissolution both in the sedimentary strata and the basement. Finally, a hematite-siderite cap can be observed just above the highly clay-altered material of the main mineralized zone (see also [START_REF] Hoeve | Mineralization and host rock alteration in relation to clay mineral diagenesis and evolution of the middle Proterozoic Athabasca basin[END_REF].

Sampling

The sample set includes specimens from the deposit, distal areas, the basement and the basin, which facilitates the reconstruction of physical-chemical conditions on a much larger scale (~25 km 2 ) than the spatial extent of the deposit. This greater spatial area of study both in the basin and the basement allows investigation of the overall conditions of basinal brine circulations and the physico-chemical changes in the brines that were induced by these migrations within the environments surrounding the deposit. The sampling was focused on the three main ductile-brittle shear zones in the area: Cigar Main, Cigar North-East Trend, and Power Line. 46 samples of basement rocks (42 of granitic pegmatite and 5 of pelitic gneiss) and 17 sandstone samples were taken from 26 drill cores. Drill hole locations are indicated in Fig. 2. Sample names include the name of the drill hole and the depth of the sample (in meters).

i)

In the deposit area, the sampling was from two horizontal geotechnical drill holes located in the basement below the deposit (U382 and U427) and from three vertical drill holes intersecting the deposit (SF-731-05 and SF-737-05 into its east part and WC372 into its west part).

ii)

Along the E-W Cigar Main structural corridor, the sampling covers 15 drill holes, located up to 7 km to the east of the deposit and mainly focused in two cross-sections through the shear zones (A-B and C-D on Fig. 2).

iii) Along the Cigar North-East Trend, the sampling covers three drill holes (WC473, WC448, and WC467). were specifically selected because these rocks contain large magmatic quartz crystals most suitable for FIP mapping and fluid inclusion analyses and they are a lithology representative of the host rocks. The pegmatites were formed during peak metamorphic conditions of the THO and are most suitable to record all different fluid events post-dating the peak metamorphism, both pre-and post-basin deposition (eg. Mercadier et al., 2010). Five representative samples of metapelitic gneiss were sampled to compare the geometry of the fracture network and the fracture paleoporosity at the time of brine migration with those in the pegmatites. The maximum investigated depth is about 200 m below the unconformity.

Collected sandstone samples represent variable intensities of hydrothermal alteration. Where available, druzy quartz, present in small fractures that crosscut the sandstone, was also studied.

Methods

Microthermometry

Microthermometry was carried out on fluid inclusions (FI) trapped in quartz overgrowths, quartz cement, and druzy quartz in sandstone samples, as well as on selected FIPs in magmatic quartz from basement samples. It was performed using a Linkam® MDS600 heating-cooling stage, adapted to an Olympus® microscope at the GeoRessources laboratory (Nancy, France). The stage was calibrated with in-house and certified standards by measuring the temperature of the final melting of pure water (0.0°C) in a silica glass capillary, the triple point of CO2 ± Ar in a synthetic FI (-56.9°C), and the homogenization temperature (L+V L) of a natural FI at 165 °C. The following microthermometric parameters were measured: eutectic temperature (Te), melting temperatures of ice and hydrohalite (Tmice and Tmhyd), halite dissolution (TsNaCl), and homogenization temperature (L+V→L or L+V+S→L+S; Th).

The temperatures of phase changes have a precision of about ± 5 °C for Te, ±0.1 °C for Tmice and Tmhyd, and ±1 °C for TsNaCl and Th. A significant number (about 30%) of the analyzed FI did not freeze, even at temperatures as low as -180 °C, as previously observed for similar inclusions in the Athabasca (eg. [START_REF] Chu | Thermal profiles inferred from fluid inclusion and illite geothermometry from sandstones of the Athabasca basin: Implications for fluid flow and unconformity-related uranium mineralization[END_REF][START_REF] Richard | Metal-rich fluid inclusions provide new insights into unconformity-related U deposits (Athabasca Basin and Basement, Canada)[END_REF]. Inclusions for which Tmice could not be unambiguously determined were excluded from the dataset.

Calculation of FI compositions

The actual methodologies used for calculation of FI bulk compositions depend on the considered system. The methodologies are presented with the FI nomenclature in Table 1.

The nomenclature is adapted from [START_REF] Derome | Mixing of sodic and calcic brines and uranium deposition at McArthur River, Saskatchewan, Canada: a Raman and laser-induced breakdown spectroscopic study of fluid inclusions[END_REF] and is based on both the Tmice ranges (Tmice < -30°C: Lw' and Lwh'; -30°C < Tmice < -15°C: Lw1, Lw2 and Lwh; -15°C < Tmice:

Lw") and the last observed phase to melt upon heating (ice: Lw1, Lw' and Lw"; hydrohalite:

Lw2 and Lw'; halite: Lwh and Lwh').

For Lw1 inclusions and Lw′ inclusions, within which the last phase to melt is ice, FI bulk compositions were calculated respectively in the H2O-NaCl and H2O-CaCl2 system using the AqSo2e program (Package FLUIDS 1, Bakker, 2003, and references therein). The composition of all the other inclusions were calculated in the H2O-NaCl-CaCl2 system according to [START_REF] Steele-Macinnis | Numerical model to determine the composition of H2O-NaCl-CaCl2 fluid inclusions based on microthermometric and microanalytical data[END_REF].

Raman spectrometry

The relative proportion of the gas species of the volatile phase of the fluid inclusions previously analysed by microthermometry was measured using a Horiba Jobin-Yvon LabRAM spectrometer equipped with a 1800 gr mm -1 grating and an Edge filter. Each analysis was repeated three times. The analytical uncertainty is below 5%. The confocal hole aperture is 500 µm and the slit aperture is 100µm. The excitation beam is provided by a Stabilite 2017 Ar + laser at 514.532 nm (Spectra Physics, Newport Corporation) and a power of 200 mW, focused on the fluid inclusions using x50 and x100 objectives on an Olympus BX40 microscope. The signal-to-noise ratio was optimized ideally to lower than 1% by adjusting the acquisition time and accumulation number. All Raman spectrometry analyses were performed at room temperature at the GeoRessources laboratory (Nancy, France).

LA-ICP-MS on fluid inclusions

Selected major, minor, and trace elements were analyzed in fluid inclusions using the LA-ICP-MS equipment at GeoRessources laboratory (Nancy, France) [START_REF] Lach | In Situ Quantitative Measurement of Rare Earth Elements in Uranium Oxides by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry[END_REF][START_REF] Leisen | Determination of Cl and Br concentrations in individual fluid inclusions by combining microthermometry and LA-ICPMS analysis: Implications for the origin of salinity in crustal fluids[END_REF]. It comprises a GeoLas excimer laser (ArF, 193 nm, Microlas, Göttingen, Germany;[START_REF] Günther | Capabilities of an Argon Fluoride 193 nm Excimer Laser for Laser Ablation Inductively Coupled Plasma Mass Spectometry Microanalysis of Geological Materials[END_REF] and an Agilent 7500c quadrupole ICP-MS. The laser beam is focused onto the sample, within a low-volume custom-made lozenge-shaped ablation cell designed for fluid inclusion analyses, using a Schwarzschild reflective objective (magnification × 25; numerical aperture 0.4) mounted onto an optical microscope (Olympus BX41) equipped with a X-Y motorized stage and CCD camera. The certified reference material NIST610 [START_REF] Jochum | Determination of Reference Values for NIST SRM 610-617 Glasses Following ISO Guidelines[END_REF] was used as the external standard. NIST612 was also used to monitor the analytical conditions (in particular, precision and accuracy). Analysis parameters include a fluence of 14 J/cm² and laser shot frequency of 5 Hz, He = 0.5 L.min -1 as a carrier gas mixed with Ar = 0.7 L.min -1 via a cyclone mixer prior to entering the ICP torch. Spot sizes varied from 24 µm up to 44 µm, depending on the inclusion size. The elemental isotopes analyzed were: 7 Li, 23 Na, 11 B, 24 Mg, 39 K, 44 Ca, 55 Mn, 57 Fe, 63 Cu, 66 Zn, 75 As, 88 Sr, 122 Sb, 137 Ba, 182 W, 208 Pb, and 238 U, using an integration time of 0.01 s per mass channel for a total cycle time of 0.22 s.

System calibration and signal integration were performed using the Matlab®-based SILLS program [START_REF] Guillong | SILLS: A MATLAB-based program for the reduction of laser ablation ICP-MS data of homogeneous materials and inclusions[END_REF]. Absolute element concentrations were calculated from the analyzed elemental ratios relative to the absolute concentration of Na [START_REF] Longerich | Inductively coupled plasmamass spectrometric analysis of geological samples: A critical evaluation based on case studies[END_REF].

This Na concentration was obtained from microthermometry using the charge-balance technique [START_REF] Allan | Validation of LA-ICP-MS fluid inclusion analysis with synthetic fluid inclusions[END_REF] that corrects the modelled amount of Na for contributions from other chloride salts using the analyzed elemental ratios to Na. No FIs interpreted through microthermometry as pure H2O-CaCl2 could be analyzed through La-ICP-MS. Limits of detection (LODs) were calculated using the 3σ criterion [START_REF] Longerich | Inter-laboratory note. Laser ablation inductively coupled plasma mass spectrometric transient signal data acquisition and analyte concentration calculation[END_REF]. The analytical precision of most elements is within 20-30% RSD [START_REF] Allan | Validation of LA-ICP-MS fluid inclusion analysis with synthetic fluid inclusions[END_REF].

FIP mapping and paleoporosity estimation

The intensity and geometry of fluid circulation in the basement were estimated through a statistical study of FIP densities and orientations along sampling profiles cross-cutting the graphitic shear zones. This work was carried out on polished wafers of oriented samples from different drill holes following a methodology similar to [START_REF] Martz | C-O-H-N fluids circulations and graphite precipitation in reactivated Hudsonian shear zones during basement uplift of the Wollaston-Mudjatik Transition Zone: Example of the Cigar Lake U deposit[END_REF], Mercadier et al. (2010) and [START_REF] Scheffer | CO2 flow during orogenic gravitational collapse: Syntectonic decarbonation and fluid mixing at the ductile-brittle transition (Lavrion, Greece)[END_REF]. For all oriented core samples, wafers were prepared in the horizontal plane from a selected region of the core. Mapping of FIPs was then carried out in each wafer using the AnIma software [START_REF] Lespinasse | Microfissural mapping of natural cracks in rocks: Implications for fluid transfers quantification in the crust[END_REF]. FIP orientations are presented in rose diagrams. An example of FIP mapping is given in Fig. 3, with pictures of the three mapped FIP types. The distinct types are based on the FIs that they contain; i) carbonic fluid inclusions, ii) aqueous fluid inclusions, and iii) a mixture of both aqueous and carbonic inclusions in the same FIP (mixed FIPs; see Section 5 for detailed description and explanation). Based on the mapping of the distinct FIP types crosscutting the primary quartz grains, the fracture paleoporosity of the quartz was semi-quantified from the reconstructed microfracture network for each sample following the methodology developed by [START_REF] Sausse | Evolution of crack permeability during fluid-rock interaction. Example of the Brézouard granite (Vosges, France)[END_REF] and [START_REF] Lespinasse | Microfissural mapping of natural cracks in rocks: Implications for fluid transfers quantification in the crust[END_REF]. Calculations are given in Appendix A. This method was first developed for total paleoporosity and paleopermeability calculations based on the total micro-fracture network. In this study, the method is applied only to FIPs in quartz and therefore it only allows calculation of the quartz fracture paleoporosity that is only a semiquantitative proxy for the fluid/rock ratio at the time of the distinct fluid migrations. Since this study is restricted to FIP microstructures in quartz, the estimated porosity will be overestimated as it does not take into account the size and irregular boundaries of the quartz grains. Moreover, the estimated connected porosity should also be considered as being a maximum instantaneous porosity, taking into account that microfracture sealing can be a rapid process [START_REF] Lander | Insights into rates of fracture growth and sealing from a model for quartz cementation in fractured sandstones[END_REF].

ShortWave InfraRed (SWIR) spectroscopy

Semi-quantitative determination of the relative proportions of a set of clay minerals has been carried out by AREVA Resources Canada (ARC) using the MINSPEC software developed by [START_REF] Earle | MINSPEC3 program for estimation of clay contents in Athabasca Group sandstones from reflectance spectral data[END_REF][START_REF] Earle | MINSPEC1 and CALSPEC1 interactive graphical programs for quantitative analysis of clay minerals from relectance data and for assessment of PIMA II calibration spectra[END_REF] on ShortWave InfraRed (SWIR) reflectance spectral data acquired using a field portable spectrometer (e.g. PIMA II, TerraSpec). The MINSPEC algorithm is based on the detection of characteristic absorption peaks (i.e. reflectance minima), as well as the shapes, shoulders, and slopes/inflections of the peaks and the intervening spectrum. The spectral measurements were performed on 10 to 20cm long drill core pieces every 3 m in all the selected drill holes, as well as on the individual samples from this study. Clay mineral types were confirmed through optical microscopy and SEM examinations at the GeoRessources laboratory (Nancy, France). The MINSPEC algorithm, designed specifically for Athabasca Group and Kombolgie Formation quartz-rich sandstones, semi-quantifies the relative proportions of six clay and clay-size minerals, including illite, three kaolin polymorphs (kaolinite, dickite, halloysite), sudoitic chlorite, and alkali-deficient dravite from each reflectance spectrum acquired. For this study, the three different kaolin polymorphs were not further distinguished -they all are simply given as kaolinite. In the same way, the proportion of illite may also include several illite polytypes, and may include muscovite in basement samples. The reported relative proportion of chlorite is based on sudoite (Al-Mg di,trioctahedral chlorite), however, it may also include clinochlore (trioctahedral Fe-Mg chlorite) in basement samples. Clinochlore does not occur in the Athabasca strata [START_REF] Hoeve | Mineralization and host rock alteration in relation to clay mineral diagenesis and evolution of the middle Proterozoic Athabasca basin[END_REF].

Results

Petrography

Fig. 4 summarizes the main petrographic features of the studied samples on a schematic cross-section through the deposit. The same hydrothermal alteration, occurring in and around the deposit, can be observed all along the Cigar Main Trend, but with significantly less intensity when moving out of the near-deposit area.

Basement rocks

The granitic pegmatites and anatectic rocks have an initial magmatic mineral assemblage of quartz, feldspar (K-feldspar ± plagioclase), biotite, muscovite, and accessory minerals such as sulfide, zircon, monazite, and apatite. The pelitic gneisses show a metamorphic mineralogy of quartz, feldspar (K-feldspar ± plagioclase), graphite, biotite, garnet, cordierite, sillimanite, tourmaline, ilmenite, pyrite and chalcopyrite plus accessory minerals including apatite, monazite, and zircon. In the basement rocks, three main types of superimposed alteration are observed: i) The retrograde alteration of late-Hudsonian age is present in all studied samples.

It is characterized by a partial or total chloritization (Fe-Mg-rich chlorite) of biotite with an associated crystallization of iron-titanium oxides and quartz, and formation of muscovites (star-like appearance; with possible phengitic substitution <10%). Additionally, late chlorite, graphite, pyrite, chalcopyrite, dolomite, and milky quartz are observed in fractures. ii) The regolithic alteration ("paleoweathering" ;[START_REF] Halter | Zonalite des alterations dans l'environnement des gisements d'uranium associes a la discordance du proterozoique moyen (Saskatchewan, Canada)[END_REF][START_REF] Macdonald | Mineralogy and geochemistry of a precambrian regolith in the Athabasca Basin[END_REF] occurs in the uppermost meters of the basement, immediately below the unconformity, and is related to the basement exhumation after the Trans-Hudson Orogeny. All the studied samples were taken from below the paleoregolith extent and therefore do not show features of this alteration. iii)

Finally, the post-Athabasca hydrothermal alteration stage occurs in variable degrees in almost all the studied samples, even in the deepest and most distal samples from the deposit. This alteration is mainly expressed by an illite-sudoite ± dravite assemblage occurring either as secondary minerals or alteration assemblages in fractures or replacing the primary minerals.

The relative proportion of sudoite to illite tends to be greater in the more altered samples, especially those located right under the deposit. Those samples usually show partial to total quartz dissolution features. Sudoite occurs as irregular flakes which are stacked in layers when present in high proportions [START_REF] Percival | SUDOITE FROM CIGAR LAKE, SASKATCHEWAN[END_REF].

Athabasca sandstones

The sandstone samples all contain more than 90% sub-rounded to rounded detrital quartz grains, with no evidence of detrital K-feldspar or plagioclase being observed. Accessory minerals include sparse tourmaline and zircon, with iron-titanium oxides occurring locally in the clay matrix. Most of the sandstones and conglomerates from Cigar North-East Trend drill hole WC473 and Power Line drill hole WC464 show features of unaltered regional samples with well compacted and quartz-cemented sandstones containing frequent iron oxides in a clay matrix, entirely consisting of pseudomorphic dickite after kaolinite, filling the interstitial space (Fig. 5A). The detrital quartz grains (Q0) show quartz overgrowths (Q1) clearly distinguished by a line of FIs and iron oxides (called dustline, Fig. 5B). In the regional samples, quartz dissolution features are minimal to absent. In contrast, samples occurring above the Cigar Main E-W shear zone typically have a low iron oxides content ("bleached" rock; c.f. [START_REF] Hoeve | Mineralization and host rock alteration in relation to clay mineral diagenesis and evolution of the middle Proterozoic Athabasca basin[END_REF] and display strong dissolution features affecting both the detrital grains (Q0) and quartz overgrowths (Q1; Fig. 5C andD). Diagenetic dickite (itself after earlier kaolinite) is replaced by illite, illite crystals being sometimes embedded in Q1 (Fig. 5E) and thus indicating that growth of Q1 may have continue during and after dickite replacement by illite. Small crystals of aluminum-phosphate-sulphate (APS) minerals are locally disseminated in the illitic clay mineral matrix. The presence of sudoite is typically restricted to the basal 5-20 meters of sandstone, above the basement graphitic structures, either intermixed with illite or mechanically interlayered at a micro/nanoscale. Here, quartz dissolution features are strongly developed (Fig. 5F). These features (sudoite occurrence plus strong quartz dissolution) occur in greater abundance directly in and below the deposit. The irregular presence of dustlines under Q1 indicates that at least one quartz dissolution event interrupted the diagenetic silicification pre-or syn-illite and sudoite crystallization.

Structurally-controlled pervasive silicification (Q2) consists of quartz cement entirely filling interstitial pores between the quartz overgrowths (Q1). Q2 is however very rarely observed at Cigar Lake (in only one sample WC311-342.6; Fig. 5G), although it is common in the McArthur River area [START_REF] Derome | Mixing of sodic and calcic brines and uranium deposition at McArthur River, Saskatchewan, Canada: a Raman and laser-induced breakdown spectroscopic study of fluid inclusions[END_REF]. Euhedral quartz crystals (Q3; <150 µm in size)

that crystallized in small open fractures cutting the sandstone, detrital grains, and quartz overgrowths, were observed in nine samples out of the nineteen selected. Thick illite ± sudoite rich dustlines are sometimes observed at the base of Q3 indicating crystallization of Q3 was post-illite+sudoite alteration (Fig. 5H).

Fluid Inclusion petrography

FIs in the basement rocks

In magmatic and metamorphic quartz in basement rocks, FIs occur as secondary fluid inclusion planes (FIPs) cross-cutting the quartz. They have been grouped into six major types: i) dark, negative crystal-shaped, two-or three-phase carbonic (CO2-CH4-N2±H2O) fluid inclusions (Fig. 3B), ii) two-phase aqueous-carbonic (H2O-CO2-CH4-N2) fluid inclusions, iii) dark vapor monophase CH4-N2-rich fluid inclusions, iv) solid-bearing aqueous fluid inclusions, v) low-salinity, two-phase, liquid-dominated, aqueous fluid inclusions, and finally vi) high-salinity aqueous fluid inclusions. Types i) to iv) are only observed in the basement rocks and discussed in [START_REF] Martz | C-O-H-N fluids circulations and graphite precipitation in reactivated Hudsonian shear zones during basement uplift of the Wollaston-Mudjatik Transition Zone: Example of the Cigar Lake U deposit[END_REF], and are interpreted to have formed during pre-Athabasca retrograde metamorphic events. This study focuses only on the P-T-X properties of the basinal brines (Type vi) in the Paleoproterozoic Athabasca Basin, therefore the other types will not be discussed in this paper.

The brine fluid inclusions are aqueous liquid inclusions with a vapor phase of about 5-10 vol.

% and can be either two-phase (liquid and vapor H2O) (Fig. 6E), three-phase (with a halite cube) (Fig. 6F), or multi-phase (with halite and clay minerals). Carbonic fluid inclusions and high-salinity aqueous fluid inclusions are by far the most dominant types and can be easily distinguished from each other, as they present very distinct optical features.

FIs in the Athabasca sandstones

Fluid inclusions in quartz overgrowths (Q1), cements (Q2), and euhedral quartz (Q3) from sandstones are small (<15 µm; often 3-10 µm in size) and fairly rare. They are aqueous liquid inclusions with a vapor phase of about 5-10 vol. % and sometimes contain a halite cube and/or a clay mineral (either dickite, illite, or sudoite) and iron oxides (Fig. 6A). FIs in Q1

occur either along the dustlines, as pseudosecondary planes, isolated, or in small clusters (Fig. 6B). FIs in Q2 and Q3 occur isolated or in clusters (Fig. 5H and 6B and C). In dickite-rich samples, FIs are dominated by two-phase inclusions Lw1 and Lw2. In illite and/or sudoiterich samples, FIs can be two-phase (liquid and vapor H2O: Lw1, Lw2, Lw'), three-phase (with a halite cube, Lwh, Lwh'), or multi-phase (with halite and clay mineral) inclusions.

Halite and/or clay minerals can occur either as heterogeneously-trapped minerals or as daughter minerals (same solid-vapor-fluid relative proportion in the whole FIA).

Fluid microthermometry

Microthermometric data for the post-Athabasca FIs are provided as supplementary data in ESM-1.

Inclusions with highly saline Na-Ca brines

In higher minimal pressure trapping conditions compared to the Lwh inclusions (Fig. 7B).

Low salinity inclusions

Lw" inclusions in FIPs from the basement rocks show Tmice ranging from -4.2 to -1.2 °C and Th ranging from 93 to 196 °C. Lw" inclusions in the sandstone samples occur in Q1 and Q3.

They are rare and were mainly observed in the same location (drill holes WC426 and WC441). They never occur in the same FIA with the brines (Lw1, Lw2, Lw', Lwh, or Lwh' inclusions), indicating the presence of local conditions disconnected from the main basinal brine circulation events. Their Tmice range from -10.2 to -0.1 °C and their Th from 84 to 132 °C.

Spatial distribution of microthermometric data and gas contents of

FIs

There is a spatial distribution of FI types around and at distance from the deposit as follows:

FIs in the basement rocks

Away from the Cigar Main shear zone, i.e. in the Power Line (South conductor) and Cigar

North-East Trend shear zones, and outside the shear zones, only Lw1, Lw2, and Lwh FIs with Tmice > -26.3°C and Na/(Na+Ca) > 0.7 can been observed (Fig. 8). For nearly all of the samples from these areas, the mean and median salinity for the FIs are about 25 wt.% eq.

NaCl + CaCl2. The exception is sample WC254-460.5. In this sample 5 analyzed Lwh inclusions occur with Lw1 inclusions in the same FIP. The FIs for these samples present the lowest Th values, with a mean of 98 °C for the Cigar North-East Trend, 100 °C for Power Line, and 122.5 °C away from conductors (Fig. 8).

Along the Cigar Main shear zone, both NaCl-and CaCl2-rich inclusions have been observed.

Here, samples show overall a greater proportion of Lwh and Lwh' inclusions (up to 100%) and therefore FIs with higher salinities (up to ca. 40 wt.% eq. NaCl + CaCl2). Mean and median Tmice values for FIs of samples occurring in this zone are usually below -26°C and Na/(Na+Ca) ratio are variable, but overall low, with mean values ranging from 0.57 to 0.82 indicating significant calcium content in the trapped FIs. These FIs show an overall higher range of Th values (80 to 200 °C) compared to the other structures.

Below the deposit, NaCl-rich Lwh and CaCl2-rich Lwh' and Lw' FIs predominate, and they

show high salinities (up to ca. 40 wt.% eq. NaCl + CaCl2), the lowest Tmice (down to -50.8 °C), and a significant proportion of FIs with very low Na/(Na+Ca) ratio (<0.65 and down to 0) . There is no clear difference in the Th values compared to the barren portions of Cigar Main.

FIs in the sandstone

The composition of the FIs trapped in the quartz overgrowths and in druzy quartz in the sandstone varies according to the clay assemblage, which is directly dependent on the location of the samples relative to the Cigar Main shear zone and to the Cigar Lake deposit (Fig. 9).

Above the barren NE-SW trending shear zones (i.e. Cigar North-East Trend and Power Line), the sandstones are dominated by dickite. In these rocks, the FIs are Lw1, Lw2, and Lwh inclusions. They display overall high Tmice (mean at -22.5 °C), almost pure NaCl compositions with Na/(Na+Ca) = 1, high salinities (around 25 wt.% eq. NaCl + CaCl2), and low Th (around 90-100 °C, Fig. 9). However, in the basal 15 m above the unconformity both above the Cigar North-East Trend and Power Line, illite and sudoite occur nonetheless, replacing dickite (cf. sample WC473-385.4). In these areas, the FIs show lower Tmice and Na/(Na+Ca) ratio (mean at 0.73), higher Th and higher salinities (Fig. 9).

Above the Cigar Main shear zone, the illite alteration extends up to the current surface, whereas sudoite is present only in the basal 20 m above the basement shear zone. In contrast to the FIs described above, here, the FIs trapped in Q1, Q2,, and Q3 show a significant content of CaCl2 as expressed through overall low Tmice and Na/(Na+Ca) ratio, and significantly higher Th (around 100-150 °C).

Toward the deposit, the proportion of CaCl2-rich FIs per sample increases and those same CaCl2-rich inclusions show overall lower Tmice and Na/(Na+Ca) ratio, so higher CaCl2 contents, toward the deposit, without visible Th gradient as a function of the distance to the deposit.

Low-salinity fluid inclusions Lw" are locally present to the east of the studied zone in both Q1 and Q2, above both the Cigar Main and Cigar North-East Trend, and occur in higher proportions compared to the basement samples. They display high Tmice (up to 0 °C) and slightly higher Th (up to 180 °C) compared to other FIs.

Gas contents in FIs and spatial distribution

Due to the limited size of the vapor phases, the vapor bubbles often show Brownian motion.

Therefore, the gas contents of only a few FIs could be successfully analyzed by Raman spectroscopy. Furthermore, the uncertainty is high due to the small size of the inclusions and the overall low gas content. No volatile components have been detected in the liquid phase.

The presence of trace amounts of CH4, CO2, N2, H2, and O2 have occasionally been detected in the vapor phase, but only in high salinity FIs trapped in basement rocks. None of these constituents have been detected in the vapor phase of the sandstone hosted FIs (ESM-1). The relative proportions of these gases are highly variable (Fig. 10). FIs in shear zone-hosted samples (Cigar Main and Cigar North-East Trend) are usually dominated by traces of CO2, CH4, and N2; CH4 being the dominant gas. H2 and O2 have only been detected within the deposit (U427-200, SF-731-05-445.9, WC372-457.9), in association with CO2, CH4, and/or N2. The samples occurring outside of the structures contain only traces of CO2 (WC254-460.5; Fig. 10).

Chemical composition of the basinal fluids and spatial distribution

Overall, fluid inclusion compositions in the vicinity of the Cigar Lake deposit demonstrate a continuum between a Cl>Na>Ca>Mg>K end-member and a Cl>Ca≈Mg>Na>K end-member.

The proportion of analysed FIs with element concentrations above the LOD is indicated in Table 2. A significant evolution in fluid composition is observed from barren areas away from Cigar Lake to the Cigar Main shear zone and the deposit area, confirming the trend deduced from microthermometry (Fig. 11).

In In contrast, the compositions of the FIs trapped both in and above the E-W shear zone, outside the deposit area, emphasize an additional process in addition to the Na ↔ (Ca ± Mg) cationic exchange: an increase in the content of divalent cations. Such increase occurs with a relative constant content of monovalent cation (mainly Na) and expresses a compositional evolution toward higher chlorinities (from 4.5 to 6.1 mol/kg). This evolution occurs along with an enrichment in Mg, K, Mn, Ba, Sr, B, U and a depletion of Li (ESM-1, Fig. 12).

Directly below the deposit, the trapped FIs are CaCl2-rich. They show the same general features as the FIs trapped along the E-W shear zone, but with even more evolved compositions. Compared to the NaCl-rich fluid trapped in the barren Cigar North-East Trend, here, the FIs show a very high chlorinity (around 6.5 mol/kg), a strong depletion of Na (from about 2 to almost 0 mol/kg) and Li (from about 36 to 8.4 mmol/kg), and a strong enrichment in Ca (from about 1 to 2.5 mol/kg), Mg (from about 150 to 490 mmol/kg), K (from about 110 to 280 mmol/kg), Mn (from about 7.5 to 10 mmol/kg), Ba (from 2.7 about to 24 mmol/kg),

Sr (from about 11 to 23 mmol/kg), B (from about 2 to 5 mmol/kg), Zn (from about 2 to 6 mmol/kg), Pb (from about 0.8 to 2.5 mmol/kg), U (from about 0.03 to 0.3 mmol/kg), Sb (from about 0.12 to 0.6 mmol/kg) (ESM-1, Fig. 11 and12). This compositional evolution translates into an enrichment in the Mg content of about × 1.4 to × 5.9, in K of about × 1.8 to × 5.8, in Mn of 0 up to × 3.6, in Ba of about × 1.3 to × 32.2, in Sr of about × 1.4 to × 3.4, in B of about 1.2 to × 4.9 and finally in U of about × 2.5 to × 388, and a depletion of Li of about 60 to 100% (ESM-1, Fig. 13). The Cu, Fe, Zn and Pb contents show an erratic behavior during this evolution, with highly variable contents in both brines, making evaluation of their concentrations difficult (ESM-1 and Fig. 13).

Orientations and surface density of fluid inclusions planes

The fluid inclusions planes (FIPs) from basement rocks were divided into two distinguishable groups, as previously proposed by Mercadier et al. (2010) and [START_REF] Martz | C-O-H-N fluids circulations and graphite precipitation in reactivated Hudsonian shear zones during basement uplift of the Wollaston-Mudjatik Transition Zone: Example of the Cigar Lake U deposit[END_REF]: i) Cdominated (carbonic) FIPs formed during basement uplift and before the deposition of the Athabasca Basin, and ii) basinal brine (aqueous) FIPs, linked to the major stages of U body formation at ca. 1.46 -1.29 Ga [START_REF] Fayek | O and Pb isotopic analyses of uranium minerals by ion microprobe and U-Pb ages from the Cigar Lake deposit[END_REF][START_REF] Martz | Caractéristiques, chronologie et rôles des circulations fluides dans le bassin d'Athabasca et de son socle: implications dans la formation et l'évolution du gisement d'uranium de Cigar Lake. Characteristics, chronology and roles of fluid circulations in t[END_REF][START_REF] Philippe | Formation and evolution of the Cigar Lake uranium deposit based on. U-Pb and K-Ar isotope systematics[END_REF]. Some mixed FIPs, with both types of fluids, correspond to metamorphic FIPs reopened and cemented by brines (Fig. 3D). Most FIPs, whatever their nature, occur in orientations both perpendicular and parallel to the foliation (Fig. 14). In addition, some local orientations (Fig. 14) are observed: N0°, observable in samples from the drill hole WC-448, corresponds to a structurally more complex area, and N140-N170° plus N50°-N70° FIPs, found in some samples located along the E-W conductor (WC372, WC335, and WC313, for example). At the sample scale, aqueous brine FIPs show the same main orientations as the carbonic and mixed FIPs.

The FIP density( ) and quartz fracture paleoporosity( ) of the quartz microfracture network at the time of both carbonic fluid migration and brine migration has been estimated for each sample by FIP mapping (Fig. 15). The density and associated quartz fracture paleoporosity based on mixed FIPs have been added to those measured and calculated for both carbonic and brine FIPs, as the mixed FIPs record both types of fluid migration. Table 3 summarizes the geometrical parameters used for quartz paleoporosity reconstruction. There is a significant difference in the density of the microfracture network around the Cigar Main shear zone (cross-section C-D, Fig. 2) compared to the other structures, such as the Cigar North-East

Trend (cross-section E-F, Fig. 2). For example, in the 20 m surrounding each structure, the reconstructed quartz fracture paleoporosity during basement uplift (i.e. during carbonic fluid migration) are higher in Cigar Main (from 2.5 to 15.8 %, Fig. 15) compared to Cigar North-East Trend (from 4.6 to 7.6%, Fig. 15). In the same way, the overall quartz fracture paleoporosity at the time of brine migration is higher in the rocks from Cigar Main (from 0.3% up to 7.8 % toward the fault core) compared to the samples from the Cigar North-East

Trend (below 2%). Similarly, samples from the Power Line structure (drill hole WC466A, Fig. 2) and structures away from the shear zones (drill hole WC254, Fig. 2) also show a very low quartz fracture porosity at the time of brine migration (Table 3).

FIP mapping of pelitic gneiss samples occurring in the Cigar Main structure show somewhat different features. They have very low quartz fracture paleoporosity based on brine FIPs (< 1%) relative to both the paleoporosity determined for pegmatites in this area and the high paleoporosity based on carbonic FIPs (3.8 to 7.7 %) (Table 3).

Discussion

Conversion of NaCl-rich brine into CaCl2-rich brine during fluid migration through the basement

The earliest brine end-member is represented by the NaCl-rich fluid found in quartz overgrowths from barren ("regional") sandstones where dickite preservation attests to the lack of subsequent fluid circulations, particularly in areas away from reactivated basement structures (Fig. 8 and9). This NaCl-rich fluid presents restricted ranges for Th and salinity, with values between 84 and 121°C and 15.7 to 25.6 wt. % eq. NaCl + CaCl2. This brine is similar to that described elsewhere in Athabasca ore deposits and considered as a primary evaporitic brine [START_REF] Derome | Mixing of sodic and calcic brines and uranium deposition at McArthur River, Saskatchewan, Canada: a Raman and laser-induced breakdown spectroscopic study of fluid inclusions[END_REF][START_REF] Richard | From evaporated seawater to uranium-mineralizing brines: Isotopic and trace element study of quartz-dolomite veins in the athabasca system[END_REF][START_REF] Richard | An evaporated seawater origin for the ore-forming brines in unconformity-related uranium deposits (Athabasca Basin, Canada): Cl/Br and δ37Cl analysis of fluid inclusions[END_REF]. Depending on the considered pressure regime, the pressure correction for this diagenetic fluid results in trapping temperatures of i) around 90-150°C, assuming a typical 30-40 °C/km hydrostatic gradient under a 2.5-5 km thick sedimentary cover (case A in Fig. 16.) or ii) around 120-220°C, if lithostatic conditions are assumed (case B in Fig. 16.). A hydrostatic pressure regime is, however, preferred because of the porous sandstone-dominated nature of the Athabasca strata [START_REF] Hoeve | Mineralization and host rock alteration in relation to clay mineral diagenesis and evolution of the middle Proterozoic Athabasca basin[END_REF] forming a relatively permeable environment [START_REF] Chi | Numerical modeling of fluid pressure regime in the Athabasca basin and implications for fluid flow models related to the unconformity-type uranium mineralization[END_REF].

CaCl2-rich FIs, containing brines with variable low (Na/Na+Ca) ratios in between 0 and 0.65, were almost exclusively trapped in sandstones and basement rocks along, above and all along the reactivated E-W shear zone hosting the deposit, unlike the regionally-trapped NaCl-rich fluid (Figs. 7,8,9,12). Despite their own distinct spatial distributions, halogen and noble gas systematics of both CaCl2-rich and NaCl-rich FIs demonstrate that they share a common origin; that being seawater that underwent evaporation up to epsomite saturation (Leisen et al. 2012a, Richard et al., 2011a, 2014). It is thus apparent that the CaCl2-rich brine was derived from the initial NaCl-rich brine through fluid-rock interactions in this particular area (as proposed by [START_REF] Derome | Mixing of sodic and calcic brines and uranium deposition at McArthur River, Saskatchewan, Canada: a Raman and laser-induced breakdown spectroscopic study of fluid inclusions[END_REF]andRichard et al., 2010, 2016).

All the basement rocks sampled along the E-W shear zone, even several km to the East of the deposit, are marked by the same hydrothermal alteration associated with U deposition in the Athabasca Basin (Alexandre et al., 2005;[START_REF] Halter | Zonalite des alterations dans l'environnement des gisements d'uranium associes a la discordance du proterozoique moyen (Saskatchewan, Canada)[END_REF][START_REF] Hoeve | Mineralization and host rock alteration in relation to clay mineral diagenesis and evolution of the middle Proterozoic Athabasca basin[END_REF][START_REF] Kister | Mineralogy and geochemistry of the host-rock alterations associated with the Shea Creek unconformity-type uranium deposits (Athabasca Basin, Saskatchewan, Canada). Part 2. Regional-scale spatial distribution of the Athabasca Group sandstone matrix mineral[END_REF][START_REF] Kister | Thermodynamic constraints on the mineralogical and fluid composition evolution in a clastic sedimentary basin: the Athabasca Basin (Saskatchewan, Canada)[END_REF][START_REF] Ng | Mineralogical and geochemical evolution of the unconformity-related McArthur river zone 4 orebody in the Athabasca Basin, Canada: Implications of a silicified zone[END_REF]Pacquet and Weber, 1993, among others). However, the deposit area is characterized by a much higher intensity of hydrothermal alteration, both in the sandstone and the basement, indicating that the deposit formed where the brine-rock interactions were the most developed [START_REF] Hoeve | Mineralization and host rock alteration in relation to clay mineral diagenesis and evolution of the middle Proterozoic Athabasca basin[END_REF]. Here, not only do the CaCl2rich FIs occur in higher proportions (up to 100% of the total analyzed FIs per sample), but they also show the highest Ca content (>1.5 mol/kg, Fig. 12), corresponding to the lowest Tmice (Fig. 8,9), and the highest chlorinity (about 6.5 mol/kg, Fig. 11). These points indicate that the CaCl2-rich brine is a direct product of the fluid-rock interactions between the initial NaCl-rich brine and the basement lithologies within the reactivated shear zones. Additionally, it also indicates that there is a chemical gradient in brine compositions along the main EW corridor from the barren zones to the Cigar Lake deposit (Fig. 17).

The Chlorine increase in the CaCl2-rich brine

The noteworthy chlorinity increase of the CaCl2 brine from that of the NaCl brine can be explained from earlier experimental works. Burisch et al. (2016) investigated, through leaching experiments, the chemical evolution of both pure water and NaCl-brine (25%wt.

NaCl) through cataclastic deformation (increases the fluid/rock ratio) in granite and gneisses of compositions similar to those of the sub-Athabasca basement lithologies. They demonstrated that grain size reduction through cataclasis strongly increased the chlorinity of the percolating fluid via i) leaching of Cl-bearing minerals (micas, apatites), and iii) removal of H2O from the fluid by replacement of anhydrous minerals (feldspars and plagioclases) by hydrated ones (clay minerals) [START_REF] Bons | Fluid mixing from below in unconformity-related hydrothermal ore deposits[END_REF][START_REF] Gleeson | Infiltration of basinal fluids into high-grade basement, South Norway: sources and behaviour of waters and brines[END_REF][START_REF] Stober | Fluid sinks within the earth's crust[END_REF][START_REF] Walter | Long-term chemical evolution and modification of continental basement brines -a field study from the Schwarzwald[END_REF]. Similarly, in the altered basement rocks of the Athabasca region, the replacement of anhydrous minerals, such as feldspars, can explain the chlorinity increase.

The Uranium uptake

Tectonically-controlled brine percolations have affected larger volumes than only clay-rich halo surrounding the U ores. Consequently the volume of rock from which U was leached is significantly larger than previously thought. Among the basement lithologies, pegmatites and metapelitic gneisses are dominant. In those rocks, the hydrothermal alteration is expressed by the progressive replacement of the primary mineralogy, (i.e. K-feldspars, plagioclases, muscovites, biotites, retrograde Fe-rich chlorites, and some accessory minerals such as monazites) by a clay mineral assemblage of illite and sudoite with accessory alkali-deficient dravite and APS minerals replacing monazite. Basement alteration like this present at Cigar Lake is similar to that described elsewhere in Athabasca (Alexandre et al., 2005;[START_REF] Gaboreau | Significance of aluminum phosphate-sulfate minerals associated with U unconformity-type deposits: The Athabasca basin, Canada[END_REF]Mercadier et al., 2010;Ng et al., 2013, among others). This rock alteration is characterized by a gain of Mg, Li, B, and H2O, and a loss of Ca, Na, K, Fe, Mn, Ba, Sr, Pb, and U during alteration (Alexandre et al., 2005[START_REF] Mercadier | Conditions de genèse des gisements d'uranium associés aux discordances protérozoïques et localisés dans les socles. exemple du socle du bassin d'Athabasca[END_REF].

The microthermometric and LA-ICP-MS analyses of brine inclusions show that the CaCl2rich end-member is characterized, relative to the NaCl-rich one, by a higher chlorinity, higher contents of Ca, K, Mg, B, Mn, Ba, Sr, and U, and lower contents of Na and Li (Fig. 13).

However, except for the conceptual model of variations of volume and major element contents in the basement rocks provided in Alexandre et al. (2005), no clear geochemical budget associated with the hydrothermal alteration of those rocks has been presented yet.

Nonetheless, the chemistry of the brine resulting from the brine-rock interactions in general confirms the gains and losses shown by the whole rock lithogeochemistry. In particular, the gain in U for the CaCl2 brine reaches up to 400%, suggesting that uranium is extracted from the basement rocks though the alteration of the main U-bearing accessory minerals, such as through monazite to APS conversion [START_REF] Gaboreau | Significance of aluminum phosphate-sulfate minerals associated with U unconformity-type deposits: The Athabasca basin, Canada[END_REF][START_REF] Hecht | Hydrothermal alteration of monazite in the Precambrian crystalline basement of the Athabasca Basin (Saskatchewan, Canada): implications for the formation of unconformity-related uranium deposits[END_REF]. This study provides strong evidence for a basement-derived U source in the long-lasting debate about the uranium source for unconformity-related deposits in the Athabasca Basin [START_REF] Jefferson | Unconformity-associated uranium deposits of the Athabasca basin, Saskatchewan and Alberta[END_REF][START_REF] Kyser | Basins and uranium deposits, In: Geology and Geochemistry of Uranium and Thorium Deposits[END_REF] and references therein) and tackles previous arguments stating that no large-volume high permeability altered basement rocks have been detected

beneath the Athabasca Basin [START_REF] Hoeve | Mineralization and host rock alteration in relation to clay mineral diagenesis and evolution of the middle Proterozoic Athabasca basin[END_REF][START_REF] Thomas | Athabasca Basin unconformity-type uranium deposits: a synopsis of the empirical model and review of exploration and production trends[END_REF].

Structurally controlled fluid flow in the basement.

Brine penetration into the basement

The occurrence of brine FIPs cross-cutting magmatic quartz in almost all the studied basement rocks, within and outside the Hudsonian structures, indicates that brine percolation was ubiquitous in the studied area. Therefore, the basin/basement interface was not a watertight interface and basinal brines percolated into the basement rocks at a larger scale than previously estimated [START_REF] Kotzer | Petrogenesis of the Proterozoic Athabasca Basin, northern Saskatchewan, Canada, and its relation to diagenesis, hydrothermal uranium mineralization and paleohydrogeology[END_REF]Mercadier et al., 2010a;[START_REF] Pascal | Fluids preserved in variably altered graphitic pelitic schists in the Dufferin Lake Zone, south-central Athabasca Basin, Canada: implications for graphite loss and uranium deposition[END_REF]. In the Athabasca region, the maximum depth of brine inclusion occurrence so far observed in the basement rocks is 400 m below the unconformity [START_REF] Richard | Metal-rich fluid inclusions provide new insights into unconformity-related U deposits (Athabasca Basin and Basement, Canada)[END_REF]. It may however be inferred that the brines could have percolated to even greater depths since basinal brines with a chlorinity similar to the Athabasca brines have been observed elsewhere down to several kilometers below the unconformity in crystalline basement rocks (Boiron et al., 2010;[START_REF] Bons | Fluid mixing from below in unconformity-related hydrothermal ore deposits[END_REF]Burisch et al., 2017a;[START_REF] Cathelineau | Downward penetration and mixing of sedimentary brines and dilute hot waters at 5km depth in the granite basement at Soultz-sous-Forêts (Rhine graben, France)[END_REF][START_REF] Munz | Deep penetration of sedimentary fluids in basement rocks from southern Norway: Evidence from hydrocarbon and brine inclusions in quartz veins[END_REF]. In addition, fluid flow simulations focussed on the case of the Athabasca Basin proposed km-scale percolations of brines in the basement through reactivated structures [START_REF] Chi | Numerical modeling of hydrocarbon generation in the Douglas Formation of the Athabasca basin (Canada) and implications for unconformityrelated uranium mineralization[END_REF][START_REF] Cui | Tectonic Deformation and Fluid Flow: Implications for the Formation of Unconformity-Related Uranium Deposits[END_REF][START_REF] Li | The effects of basement faults on thermal convection and implications for the formation of unconformity-related uranium deposits in the Athabasca Basin[END_REF].

The similar distributions of micro-fracture surface densities obtained for metamorphic Cdominated fluid FIPs and brine FIPs along cross-sections perpendicular to shear zones (Fig. 15) indicate that the brine circulation was greatly influenced by the microfracture network inherited from pre-Athabasca Hudsonian exhumation events. In addition, the same dominant strike directions of the FIP networks of both the retrometamorphic and the brine events (Fig. 14) may also indicate that the stress directions were similar during those two events. In comparison to the pegmatites, only a few brine FIPs were observed in the pelite gneisses, regardless of proximity to the fault cores. Yet, the intense hydrothermal alteration (illitesudoite) displayed by these gneisses suggests that brines nonetheless percolated through these rocks, probably along the foliation planes.

Brine fluid flow

Fluid flow is demonstrated by the increased number of brine FIPs, and therefore an enhanced microfracture paleoporosity, toward the damage zones of the main shear zones (Fig. 15). The shear zones themselves are frequently occupied by glide planes full of graphite and pyrite that decrease their permeability. This is a typical feature of the distribution of permeability around faults, as shown for present day fluid flows in basement reservoirs (eg. the Soultz hot dry rock project; [START_REF] Géraud | Physical properties of fault zones within a granite body: example of the Soultz-sous-Forêts geothermal site[END_REF] and rift faults [START_REF] Dimmen | Quantifying structural controls on fluid flow: Insights from carbonate-hosted fault damage zones on the Maltese Islands[END_REF][START_REF] Kristensen | Structure and flow properties of syn-rift border faults: The interplay between fault damage and fault-related chemical alteration (Dombjerg Fault, Wollaston Forland, NE Greenland)[END_REF]. The overall global structure of a shear zone includes a fault core surrounded by damage zone domains that are characterized by minor faults and an overall enhanced fracture density compared to the protolith [START_REF] Bense | Fault zone hydrogeology[END_REF][START_REF] Caine | Fault zone architecture and permeability structure[END_REF]. The damage zones within the Athabasca basement faults, in particular within the complex association of graphite-rich gneisses and lenses of pegmatite, show an increase in number, length, aperture, and connectivity of microfractures, healed in the case of quartz, and sometimes filled by pyrite, graphite, and chlorite. These features result in an increased permeability towards the fault plane over around 20 to 40 meters (Fig. 15), whereas the fault core itself is characterized by a lower permeability graphitic and clay-rich breccia with microfissures being clogged by clay minerals, graphite-rich shear planes, and shear-related grain size reduction.

Lateral evolution from barren zones towards the ore deposit.

There is an increased degree of host-rock alteration around the ore deposit that is expressed by the enhanced development of clay minerals at the expense of feldspars, the total bleaching of the rock due to the total disappearance of mafic minerals (Fe-Mg phyllosilicates [biotite, chlorite], amphiboles), and in the most intense alteration facies, total dissolution of quartz [START_REF] Pacquet | Pétrographie et minéralogie des halos d'altération autour du gisement de Cigar Lake et leurs relations avec les minéralisations[END_REF]. This enhanced alteration was favored by: i) increased focused brine flow resulting from increased deformation rate, and ii) maintenance of favorable mineral reaction conditions for a period of sufficient length. As the main E-W Cigar Main fault corridor extends for more than 10 kilometers, the local increases in permeability and fluid flow around the deposit needs to be explained by an additional local factor. The largest zones of fluid percolation correspond to volumes at the intersection of faults where the damage zones are larger [START_REF] Dimmen | Quantifying structural controls on fluid flow: Insights from carbonate-hosted fault damage zones on the Maltese Islands[END_REF]. Therefore, the higher fluid flows and efficient fluid conduits occur where the structural complexity is highest, such as in the Cigar Lake area. This structural complexity is caused by: i) a series of N-S to NNE-SSW faults that intersect the main E-W graphite-bearing fault corridor, and ii) potential stress perturbation causing wider fracture apertures and further increase permeability in areas of fault interactions. A precise lithological and structural map of the basement at around the 500 m depth level is unfortunately not available, thus making difficult identification of the main causes for the enhanced permeability.

P-T conditions of fluid mixing and fluid flow mechanisms in and above reactivated basement-hosted shear zones

FIs show varying Tmice and varying (Na/Na+Ca) ratios in individual FIAs both in the euhedral quartz (Q3) in the sandstones above the E-W structure and in the basement rocks in the structure. This indicates that NaCl-and CaCl2-rich brines specifically mixed within and above this structure. Knowing that the CaCl2-rich brine results from the interactions between the initial NaCl-rich basinal brine and the basement rocks, it implies that the initial brine first percolated downward into the basement-hosted shear zone during reactivation. Then, this brine chemically reacted with the basement lithologies to form the CaCl2-rich brine. This evolved brine was finally expulsed upward from the basement back into the sandstones where it mixed with the ubiquitous formation waters (i.e. the initial NaCl-rich brine). Fluid movement in the context of basin-basement interface is generally attributed either to temperature, pressure, deformation (Burisch et al., 2016b;[START_REF] Garven | Continental-Scale Groundwater Flow and Geologic Processes[END_REF] or density gradients [START_REF] Kotzer | Petrogenesis of the Proterozoic Athabasca Basin, northern Saskatchewan, Canada, and its relation to diagenesis, hydrothermal uranium mineralization and paleohydrogeology[END_REF]. In the Athabasca case, fluid density gradients are unlikely as both fluids are brines with similar densities. Thermally-driven or pressure-driven fluid migration is thus envisaged. Around the reactivated shear zone, the FIs show a wide range of Th values (mainly between 80 and 170 °C) which is overall higher compared to the initial diagenetic fluid (80-120°C) (Figs 7,8,and 9). At this time, no unequivocally independent temperature or pressure constraints exist and thus only assumptions on the geothermal gradients can be used to constrain the temperature and pressure trapping conditions of the CaCl2 brines and the subsequent mixing. Therefore, the overall higher Th range of the FIs in this area can be interpreted through two scenarios that vary depending on the assumed pressure regime:

Thermally-driven convection under a hydrostatic pressure regime Assumption of a typical 30-40 °C/km hydrostatic gradient [START_REF] Peters | An overview of basin and petroleum system modeling: Definitions and concepts[END_REF] in the Athabasca Basin during the trapping of the NaCl-rich brine implies initial P-T diagenetic conditions of around 90-150°C under a 2.5-5 km thick sedimentary cover (Fig. 16).

Considering this thickness of sedimentary cover, the higher Th of the FIAs with mixed NaClrich brines and CaCl2-brines (up to 200°C) are best explained by a localized thermal disturbance in the shear zone related to a high geothermal gradient (path A in Fig. 16). P-T conditions occurring in the E-W shear zone at this time would thus be mainly 110-200 °C and hydrostatic pressure would be around 250-500 bars with a geothermal gradient of 60°C/km.

Those conditions imply that the E-W shear zone was an area of thermal convection with hotter fluids assending from deeper parts of the shear zone. Heat input can be attributed to two main causes : i) heat derived from intrusives or mantle anomalies: there is no evidence of intrusions at the time of formation of the deposit, and no clear geodynamic cause explaining abnormal heat flows. ii) heat brought by the ascending fluids: this is the likely hypothesis for explaining lateral thermal gradients. Thermal disturbance and convection in this area is furthermore supported by the abundance of illite above the structure (Fig. 17) and especially in the illite clay mineral halo above the deposit in which both 2M and 3T (now considered to be 1Mc and 1Mt, respectively) illite polytypes have been described and whose crystallinity indicates temperature of formation approximating 200 °C or more [START_REF] Kister | Thermodynamic constraints on the mineralogical and fluid composition evolution in a clastic sedimentary basin: the Athabasca Basin (Saskatchewan, Canada)[END_REF]. [START_REF] Chu | Thermal profiles inferred from fluid inclusion and illite geothermometry from sandstones of the Athabasca basin: Implications for fluid flow and unconformity-related uranium mineralization[END_REF] considered also that some localities in the basin underwent upwelling fluid convection. The shear zone hosting the deposit could have acted as an upwelling flow zone from deeper zones in the basement to basin between two thermal convection cells perpendicular to the structure as predicted earlier [START_REF] Hoeve | Mineralization and host rock alteration in relation to clay mineral diagenesis and evolution of the middle Proterozoic Athabasca basin[END_REF] and through 2D numerical modeling [START_REF] Li | The effects of basement faults on thermal convection and implications for the formation of unconformity-related uranium deposits in the Athabasca Basin[END_REF]. Another possibility would be convection inside and parallel to the fault plane itself with possible upwelling sites corresponding to the areas showing abundant CaCl2-FIPs and strong alteration features, such as those found below the deposit area (Fig. 17).

Deformation-driven convection under a hydrostatic pressure regime

In this scenario, the same initial typical gradient of 30-40 °C/km [START_REF] Peters | An overview of basin and petroleum system modeling: Definitions and concepts[END_REF]) is assumed, but this time under a lithostatic pressure regime. This implies initial P-T diagenetic conditions of around 120-220°C under a 2.5-7 km thick sedimentary cover (Fig. 16). In this scenario the higher Th recorded in the E-W shear zone could as well be explained by a pressure drop (path B in Fig. 16) due to change of pressure regime from lithostatic to hydrostatic during tectonic reactivation of the basement fault and propagation into the sandstone. Pressure changes during seismic pumping along the faults following the model of [START_REF] Sibson | Seismic pumping -a hydrothermal fluid transport mechanism[END_REF] and Behr et al. (1987) are in this way envisaged. The recent study of twodimensional fluid flow modeling applied on the shear zones hosting the Gryphon and Phoenix U-deposits [START_REF] Li | Synchronous egress and ingress fluid flow related to compressional reactivation of basement faults: the Phoenix and Gryphon uranium deposits, southeastern Athabasca Basin, Saskatchewan, Canada[END_REF] 2014), [START_REF] Stober | Fluid sinks within the earth's crust[END_REF][START_REF] Stober | Fluid sinks within the earth's crust[END_REF][START_REF] Walter | Long-term chemical evolution and modification of continental basement brines -a field study from the Schwarzwald[END_REF].

In any case, the estimated P-T pairs are much above those proposed by [START_REF] Rabiei | Hydrothermal Rare Earth Element (Xenotime) Mineralization at Maw Zone, Athabasca Basin, Canada, and Its Relationship to Unconformity-Related Uranium Deposits[END_REF] for a low burial (<2.5 km) scenario and a P-T pair close to the L/V curve, yielding to subsequent boiling of the fluids. As no reliable aqueous vapor inclusions have been found in this study, the latter hypothesis can be ruled out. The very high thermal gradients linked to hydrothermal-epithermal systems are thus rather unprobable. However, hypotheses involving localized thermal anomalies are easier to understand, as fluids can convect deep into the basement and bring heat upwards from below.

Significance of the trace amounts of volatile in the brines

The studied FIs contain gases, with a specific spatial distribution between sandstone and basement, and between the deposit area, the E-W shear zone, and the other sampled zones.

CH4, N2 and CO2 are the dominant gases and are only observed in basement FIPs (Fig. 10).

O2 and H2 are only detected in FIs located in the deposit area, in both sandstones and basement rocks. This latter restricted distribution is in agreement with a radiolytic origin [START_REF] Derome | Fluid inclusion evidence of the differential migration of H2 and O2in the McArthur River unconformity-type uranium deposit (Saskatchewan, Canada). Possible role on post-ore modifications of the host rocks[END_REF][START_REF] Richard | Radiolytic (H2, O2) and other Trace Gases (CO2, CH4, C2H6, N2) in Fluid Inclusions from Unconformity-related U Deposits[END_REF]. The occurrence of CH4, N2, and CO2 in the brine FIs has been also recorded in other studies [START_REF] Derome | Mixing of sodic and calcic brines and uranium deposition at McArthur River, Saskatchewan, Canada: a Raman and laser-induced breakdown spectroscopic study of fluid inclusions[END_REF][START_REF] Derome | Fluid inclusion evidence of the differential migration of H2 and O2in the McArthur River unconformity-type uranium deposit (Saskatchewan, Canada). Possible role on post-ore modifications of the host rocks[END_REF]Mercadier et al., 2010;Richard, 2017, among others). Increasing interest in those gases has developed in recent years since it has been shown that focused flow of such reduced gases along brittle faults could provide the needed reducing agents for the precipitation of uraninite from U VI transported in oxidized brines (Burisch et al., 2017a;[START_REF] Dargent | Reduction kinetics of aqueous U(VI) in acidic chloride brines to uraninite by methane, hydrogen or C-graphite under hydrothermal conditions: Implications for the genesis of unconformity-related uranium ore deposits[END_REF]. The occurrence of trace amounts of CO2, CH4, and N2 gases involves the interaction of the oxidizing basinal brines with the graphite-bearing metapelitic gneisses, with alteration by the brines of NH4-bearing feldspars and biotite and graphite destabilization [START_REF] Richard | Radiolytic (H2, O2) and other Trace Gases (CO2, CH4, C2H6, N2) in Fluid Inclusions from Unconformity-related U Deposits[END_REF]. Such an explanation remains plausible and valid but it faces the difficulty that no clear evidence of graphite destabilization has been provided at this time.

The scale of the present study allows an alternative hypothesis to be expressed. The spatial distribution of the dominant gases appears to show a spatial distribution similar to that of the retrograde metamorphism-related C-O-H-N dominated FIs trapped in graphite-bearing shear zones (i.e. an evolution from pure CO2 toward CO2-CH4-N2-H2O compositions with proximity to the graphite-rich fault cores, [START_REF] Martz | C-O-H-N fluids circulations and graphite precipitation in reactivated Hudsonian shear zones during basement uplift of the Wollaston-Mudjatik Transition Zone: Example of the Cigar Lake U deposit[END_REF]. This observation, together with evidence of reopening of retrometamorphic carbonic FIPs (forming mixed FIPs), suggests instead that the trace amounts of gases detected in the brine FIs may result from the release of earlier C-O-H-N dominated fluids either trapped as FIPs in magmatic and metamorphic quartz or adsorbed on chlorite layers in the gneisses. If such a hypothesis is correct, it would mean that those trace amounts of gases cannot be used as proxies for focused flow of reducing agents and subsequently U deposition.

Conclusion

The systematic and multi-method analysis of brines trapped as fluid inclusions in both Athabasca Group sandstones and their basement rocks within a 25 km² area surrounding the Cigar Lake U deposit (Saskatchewan, Canada) has allowed the full description of the physicochemical features of these fluids and their changes through time and space related to the genesis of this exceptional U deposit:

-The seawater-derived initial diagenetic NaCl-rich and Ca-poor brine of the Athabasca Basin percolated into most basement lithologies at temperatures ranging from 90 to 150 °C under a 2.5-5 km thick sedimentary cover. Thus the basin/basement interface is not a watertight interface and basinal brines percolated into the basement rocks at a larger scale than previously estimated.

-In quartz-rich basement rocks such as pegmatites, the similar abundance of microfractures containing i) C-dominated fluid inclusions issued from fluid stages related to the basement uplift (ca. 1.80 -1.72 Ga) and ii) brine inclusions trapped at ca. 1.46-1.29 Ga, indicate that the brine circulation was greatly influenced by the pre-existing microfracture networks inherited from Hudsonian exhumation events. The increase in the density of FIP surfaces along profiles perpendicular to shear zones reflect the fault damage zones that affect the rocks over 20 to 40 m on both sides of the shear zones. These zones are where the basinal fluid flows focused in the basement.

-In the damage zone of the reactivated E-W structure hosting the deposit, the enhanced circulation of the NaCl-rich brine induced: i) the formation of the illite-sudoitedominated alteration that characterizes the unconformity-related U deposits, ii) the subsequent chemical evolution of the NaCl-rich brine towards CaCl2-rich and Mg, B, K, Mn, Ba, Sr, and U-rich compositions, and iii) the chlorinity increase of the brines through desiccation by clay precipitation during alteration. These processes were active all along the E-W shear zone, i.e.

on a scale of several kilometers, but their intensity increase significantly towards the deposit.

-There is a spatial correlation between the samples showing i) the highest intensity of hydrothermal alteration, ii) the highest proportion of CaCl2-rich brines, and iii) the FIs with the highest Ca contents and salinities. This suggests that the CaCl2-rich brine was a direct product of the fluid-rock interactions between the initial NaCl-rich brine and the basement lithologies. The fluids related to the U mineralization are thus the most evolved brines.

-The two brines mixed in and above the reactivated E-W shear zone. Based on the assumed pressure regime, two scenarios can be proposed. i) The first one, which is also the preferred one, involves thermally-driven convection occurring under hydrostatic pressure regime with isobaric mixing at higher temperature (110-200 °C) in upwelling limbs of convection cells. ii) The second is defined by deformation-driven circulations occurring through seismic pumping and isothermal episodic pressure fluctuations from lithostatic to hydrostatic.

These conclusions provide new perspectives to the processes related to the genesis of unconformity-related U deposits and, at a broader scale, to the processes leading to the generation of Ca-dominated brines in basement rocks. This work strongly demonstrates that brine migration and/or convection into basement reactivated shear zones is a key and indispensable process for the development of the ore-forming fluid and thus for U-deposit formation.

(2017). It should be mentioned that this method was developed for paleoporosity and paleopermeability calculations based on the total microfracture networks, however, in this study the method is applied only to FIPs in quartz and therefore only allows the calculation of the maximum quartz paleoporosity. The quartz paleoporosity is only a semi-quantitative assessment of the fluid/rock ratio at the time of the distinct fluid migrations. The method is based on the characterization of the geometry of the microfracture network, with the assumption that each microfracture can be considered as a "penny-shaped cylinder". The quartz fracture porosity ( ) at a given time ( ) of fluid ( ) migration is assumed to be entirely represented by the connected quartz fracture network [START_REF] Cox | Coupling between deformation, fluid pressures, and fluid flow in ore-producing hydrothermal systems at depth in the crust[END_REF] and is defined as :

= (1)
Where ( ) is the cylinder height corresponding to the aperture of the microfracture and, here, approximated to 10 µm (mean size of the inclusions). However some statistical procedures are required to evaluate the fracture volumetric density ( ) and the mean radius ( ), as the observed length ( ) of each FIP in the polished wafer does not correspond to the real and maximum length value of the microfractures (i.e. the diameter of the disc) [START_REF] Dehoff | Microscopie Quantitative[END_REF].

Based on the assumption that a penny-shaped FIP population is randomly cut by the plane of observation and that the mean observed length will be less than their true length, the radius ( ) is defined as:

= (2)
Where is the mean value of the inverse (1/ ) of the measured FIP lengths of the fluid ( ) in the section plane:

= ∑ ! (3)
The volumetric density ( ) at the time is hence defined as:

= " # $%& ' (4)
Where the surface density ( ) is the cumulated measured lengths of all the FIPs ( ) per unit surface and (() is the dip of the microfractures.

Knowing the thickness of the oriented polished wafers, dip measurements of FIPs have been calculated for a few samples based on the perpendicular distance between the trace of a selected FIP on the lower surface of the polished wafer and the trace on the upper surface. Dip measurements range from 20 to 60° and a mean value of ( = 45° has been used. Figure 4: Schematic cross-section through the main deposit. The U deposit is mainly associated with illite and sudoite alteration and is located at the unconformity immediately above a ductile-brittle graphitic shear zone referred as the Cigar Main E-W shear zone.

Figure captions:

Regional Athabasca sandstone is well-cemented and contains dickite as the main clay mineral infilling interstitial pore space. Two-phase aqueous inclusions are present at dustlines and in quartz overgrowths (Q1). Above the deposit, an illite halo extends upwards 400 m. Within this halo, the sandstone shows evidence of quartz dissolution and sometimes local recrystallization (Q2, not represented here as it is rare in this deposit), partial to total replacement of dickite by illite, and some euhedral quartz (Q3) crystallizing in fractures. The later quartz generations show aqueous two and/or three-phase (with halite cube) inclusions.

Below the deposit, an alteration halo, the depth extent of which is currently unknown, is characterized by partial quartz dissolution and replacement of plagioclas, K-feldspar, and retrograde (chloritic) biotite into an illite + sudoite assemblage. Both carbonic and two and/or three-phase aqueous inclusions are trapped as FIPs cross-cutting magmatic and metamorphic quartz. Abbreviations: Dick -dickite, ill -illite, Fld-K -K-feldspar, Bt -biotite, Qtz -quartz. FIPs density and calculated quartz paleoporosity based on mixed FIPs have been added to both carbonic and brine FIPs as they contributed to the overall paleoporosity network, both at the times of carbonic and brine migrations. Pegmatite samples are labelled from 01 to 21, correspondences are given in Table 1.

Q 0 Q 0 Q 0 Q 1 Q 1 Q 1 Q 3 Q 3 Q 3 Q 3 Q 2 Q 0 Q 0 Q 0 Q 0 Q 1 Q 1 Q 1 dickM Fld3KMQ illMQMsud Fld3KMQ illMQMsud illM illM dickM Qtz Qtz Bt BasinalMbrineM Fluid inclusions CarbonicMfluidM dustline B A Q 0 Q 0 Q 0 Q 0 Q 1 Q 1 Dick Q 1 Q 1 ill E ill Q 1 5µm WC455-456 C 100 µm Q 1 Q 0 Hem. d u s t l i n e ill Qtz dissolution Q 1 Q 0 Q 0 Q 0 Q 1 Qtz dissolution WC473-205 WC464-165 WC372-431 F sud + ill Q 1 Qtz dissolution Q 1 WC449-358.4 50.0um D dissolution pits Q 1 ill ill WC372-431 Q 0 Q 3 100 µm ill Q 0 2cm 2 cm WC311-342.6 WC467-325.9 G H ill ill Silicification (Q 1 +Q 2 ) Q 0 Q 0 Q 1 Dick H 2 O V H 2 O L 50Pµm 5µm 5µm Dick Dick H 2 O V H 2 O L 20Pµm Qtz m NaCl H 2 O V P+ єPCH 4 P-PH 2 H 2 O L b r i n e P F I P B Q 1 H 2 O V H 2 O L NaCl Chlorite Q 0 5Pµm WC372-431 C E F A B D Q 0 Q 0 Q 0 Q 1 Q 1 Q 2 10µm NaCl H 2 O V H 2 O L 100Pµm WC311

  iv)Along the NE-SW Power Line structure, two drill holes (WC464 and 466A) were sampled. v) One additional barren drill hole (WC254), located about 500 m south of the deposit and outside of the Cigar Main shear zone, was sampled. Sampling of the basement lithologies included a selection of representative oriented-core samples of Hudsonian pegmatites and metapelitic gneisses showing various and distinct alteration intensities. Pegmatites (anatectic sweats, leucogranites, and granitic pegmatites)

  the basement, microthermometric parameter ranges are: Te ranging from -75 to -54 °C, Tmice from -50.8 °C to -16.8 °C, Tmhyd from -25.3 to -0.5 °C, Th from 78 to 204 °C, TsNaCl from 89 to 305 °C. In the sandstones: Te ranges from -74 to -57 °C, Tmice from -42.5 to -15.2 °C, Tmhyd from -15.2 to -0.2 °C, Th from 84 to 226 °C, and finally TsNaCl from 112 to 305 °C (ESM-1, Fig.7A and B).In the sandstones, there are significant variations in the temperature of phase transitions in the FIs which correlate with the relative proportions of the clay mineral phases filling the interstitial pore spaces. FIs in Q1 for samples dominated by diagenetic dickite are mainly Lw1 inclusions. They show relatively high Tmice ranging from -25.1 to -20.5 °C (Fig. 7A and B), specific to the NaCl-rich end-member, and low Th ranging from 84 to 121°C. The Th-Tmice pairs for these FIs display a narrow range compared to the other studied FIs. Samples showing partial to total dickite to illite replacement have FIs in Q1, Q2, and Q3 displaying Tmice ranging from -40.3 to -24.3 °C, Th ranging from 88 to 182 °C, and TsNaCl from 148 to 305 °C with no clear differences between the distinct quartz types. Finally, samples containing sudoite have FIs in Q1 and Q3 with Tmice ranging from -42.5 to -23.2 °C, Th ranging from 85 to 226 °C, and TsNaCl from 112 to 246°C (Fig. 7A and B). A large Tmice variability can be observed in a single FIA, either in a single Q3 crystal (Fig. 6C) or in FIPs from the basement. In these FIA, the Th remains constant. Th(L+V→L) -TsNaCl pairs of Lwh and Lwh' inclusions from both sandstone and basement samples are presented in Fig 7B. Most of the Lwh FIs plot near the 1:1 slope in the Th(L+V→L) -TsNaCl diagram (Fig 7B) indicating similar pressure trapping conditions with a fluid density close to the isochoric path intersecting in a P-T diagram the point at which the halite liquidus for its composition intersects the three-phase (liquid + vapor + halite) curve (Type B homogenization in Becker et al., 2008). In contrast, most of the Lwh' inclusions show halite dissolution after vapor disappearance upon heating (Type C homogenization in Becker et al., 2008) and a wide range of TsNaCl values, from about 130 up to 300 °C, together with a limited Th(L+V→L) range mostly between 100 and 150 °C (Fig 7B). The observed scattering of the TsNaCl values expresses mainly heterogeneous trapping of halite (varying TsNaCl and constant Th in a single FIA, Fig 7B), indicating that the fluid trapped in Lw' and Lwh' became saturated with respect to halite. Nonetheless, some FIAs show Lwh' inclusions with similar TsNaCl -Th(L+V→L) pairs and TsNaCl > Th(L+V→L) (Fig 7B) indicating slightly

  the barren Cigar North-East Trend (sample WC473-440.8), the FIs located in the basement are dominated by NaCl-rich brines. They plot along the 1:1 slope in the [Na + K] vs. 2 [Ca + Mg] binary diagram (main monovalent cations vs. main divalent cations). This slope indicates cationic exchange at constant charge, i.e. at constant chlorinity (4.5 mol/kg).

  has shown that deformation-driven fluid flow in this context can result in both downward and upward flow at the same time depending on local heterogeneities in the basement geology under a common compressional stress field. In the case of the Cigar Lake deposit, such heterogeneities may have controlled the areas of upwelling or downwelling migrations in the same fault plane.Finally, one additional fluid flow mechanism may have participated in either case especially for focusing the mineralizing brine in the ca. 2 km-long portion of the shear zone hosting the deposit. The dessication process (loss of water from the fluid) during the hydrolytic clay mineral formation would have been more intense in the alteration halo surrounding the deposit and may have created a hydraulic gradient around the areas of higher fluid-rock interactions. This mechanism follows the "dessication suck" model proposed in the Variscan Schwarzwald (Germany) byBons et al. (

Figure 1 :

 1 Figure 1: Simplified geological map of the Athabasca Basin and underlying basement rocks, Canada, modified from Jefferson et al. (2007). The location of the Cigar Lake deposit is indicated by the red square. Basement domains are identified by distinct colors. TD -Talston Domain, WMTZ -Wollaston-Mudjatik Transition Zone, WWD -Western Wollaston Domain, EWD -Eastern Wollaston Domain, VRSZ -Virgin River shear zone, BLSZ -Black Lake Shear Zone. The Snowbird Tectonic Zone (STZ) separates the Rae Subprovince in the west from the Hearne Subprovince in the east.

Figure 2 :

 2 Figure 2: Simplified geological map of the basement at the unconformity around the Cigar Lake uranium deposit, coupled with the aeromagnetic map. Magnetic data have been acquired by AREVA Resources Canada. The Cigar Lake deposit is an elongated lens occurring immediately above a major EW graphite-rich shear zone forming a major electromagnetic (EM) conductor. Archean domes correspond to magnetic high values whereas the mainly Paleoproterozoic metapelitic gneiss environment correspond to magnetic low values.

Figure 3 :

 3 Figure 3: A) Example of a FIP map of quartz from pegmatite sample WC450-429.7. FIPs are grouped into three types on the basis of the hosted fluid inclusions type (aqueous, carbonic, or mixed FIP). Orientations of FIPs are presented in rose diagrams with the orientation of the surrounding gneissic fabric together with the percentage number indicating the percentage value of the outer circle of the rose diagram. B) Example of a carbonic FIP. C) Example of a aqueous (brine) FIP. D) Mixed FIP showing both carbonic and brine inclusions interpreted as a reopening of carbonic FIP during later brine circulation. Abbreviations: Bt -biotite, Qtzquartz.

Figure 5 :

 5 Figure 5: A) SEM image of a quartz-cemented sandstone showing aggregates of pseudomorphic dickite platelets, after vermicular kaolinite. Detrital quartz grains (Q0) have quartz overgrowths (Q1), both showing slight dissolution features. B) Image of early diagenetic authigenic quartz overgrowth separated from the detrital grain by a dustline of iron oxides. C) Image of a thick section of sandstone showing quartz dissolution affecting both detrital quartz and quartz overgrowth with a clay matrix of illite. D) SEM image of platy and hairy illite grains filling interstitial space; with corrosion pits on quartz overgrowth. E) SEM image of fine grains of hairy illite on the quartz overgrowth surface. F) SEM image of a partially dissolved quartz overgrowth with infilling assemblage of sudoite and illite. G) Photomicrograph of rare structurally-controlled pervasive silicification (Q2) in an illitedominated faulted sandstone. H) Image of small euhedral quartz grains (Q3) separated from detrital quartz by a thin illite layer. The red rectangle corresponds to Fig. 6C.

Figure 6 :

 6 Figure 6: A) Three-phase aqueous fluid inclusion (FI) in quartz overgrowth from sandstone (Q1) with heterogeneously trapped dickite. B) Isolated three-phase aqueous FI with a halite cube in quartz cement from structurally-controlled pervasive silicification in sandstone (Q2). C) Two-phase fluid inclusions trapped in euhedral quartz from a fracture in sandstone (see location in Fig. 5H.) with distinct Tmice indicating fluid mixing at the time of trapping. D)

Figure 7 :

 7 Figure 7: A) Th -Tmice pairs of analyzed FIs. Note that both FIs trapped in quartz overgrowth in dickite-dominated sandstones and FIs trapped as FIPs in barren structures and outside structures are restricted to a narrow area. In contrast, the other FIs (except Lw"), both in sandstone and basement, show a wide range of Tmice (equal to lower) and Th (equal to higher). B) Th(L+V→L) -TsNaCl pairs of Lwh and Lwh' FI. Lwh inclusions are tight to the 1:1 slope, whereas Lwh' inclusions mainly showed vapor disappearance before halite melting. Pressure correspondences at halite dissolution (so minimal pressure of trapping) are indicated and based on numerical modeling from Lecumberri-Sanchez et al. (2012). Two Th(L+V→L) -TsNaCl pairs from two FIPs with either heterogeneous or homogeneous trapping of halite mineral are shown and pictures of the fluid inclusion assemblage (FIA) are presented at the bottom of the Figure. FIs with heterogeneously-trapped halite show varying TsNaCl and constant Th(L+V→L), whereas homogeneously trapped FIs show constant Th(L+V→L) -TsNaCl pairs in the FIA.

Figure 8 :

 8 Figure 8: Spatial distribution of FI types and microthermometric parameter ranges for analyzed FIs in FIPs in the basement. Relative proportion of FI types per drill hole are given in pie chart above the simplified geological map. Tmice, salinity, and Th ranges, mean, and median values per sample are given in box plot. FIs from the South conductor (Power Line), NE-SW conductor (Cigar North-East Trend), and off-conductor are Na-dominated with

Figure 9 :

 9 Figure 9: Spatial distribution of FI types and microthermometric parameter ranges for analyzed FIs in quartz overgrowths, cement, and euhedral quartz in the Athabasca Group. Relative proportion of FI types per drill hole are given in the pie chart above the simplified geological map. Tmice, salinity, and Th ranges, mean, and median values per sample are given in a box plot. Percentages of relative clay proportion per sample obtained from SWIR field spectrometry are provided and are indicated by the colored bar chart. Samples located above the Power Line and the NE-SW conductor (Cigar North-East Trend) are dominated by dickite, contain Na-dominated FIs with relatively slightly lower Th, and define the regional diagenetic fluid (except for sample WC473-385.4 located right at the unconformity and containing illite+ sudoite with Ca-dominated inclusions). In contrast, FIs located on the Cigar Main E-W structure contain significant proportions of illite and sudoite with high proportions of Cadominated FIs with lower Tmice, higher salinity, and higher Th.

Figure 10 :Figure 11 :

 1011 Figure 10: Spatial distribution of maximum amounts of detected gases in brine FIs per basement sample. H2 and O2 occurrence is restricted to the mineralized area. When gases were detected, the FIs are dominated by CO2-CH4-N2

Figure 12 :

 12 Figure 12: La-ICP-MS geochemical data of fluids from individual brine FIs from both sandstone and basement samples. Selected element concentrations are plotted against the calcium content. The FIs occurring in the NE-SW barren conductor (Cigar North-East Trend) are dominated by the NaCl-rich end-member, whereas the FIs occurring below and above the deposit are dominated by the CaCl2-rich end-member

Figure 14 :

 14 Figure 14: Geological map of the basement at the unconformity near the Cigar Lake deposit with rose diagrams showing the preferred orientation of both carbonic and brine fluid inclusion planes (FIP) per drill holes. Main orientations of the two FIP types are indicated in rose diagrams with the foliation of the gneissic surrounding rocks. The percentage number indicates the value of the outer circle. Both carbonic and brine FIPs show similar orientations at the scale of drilling.

Figure 15 :

 15 Figure 15: Evolution of FIP density and calculated quartz fracture paleoporosity based on both carbonic and brine FIP networks from cross-sections C -D and E -F (Fig. 2.). Mixed

Figure 16 :

 16 Figure16: Estimated P-T evolution of basinal brine in and above the E-W structure controlling the Cigar Lake deposit. Two scenarios are proposed. A) Brine evolution and mixing under hydrostatic regime from regional Na-dominated brine toward evolved Cadominated brines during isobaric heating induced by thermal convection. B) Episodic brine evolution and mixing between Na-and Ca-dominated brines during isothermal pressure drop by pressure regime change from lithostatic to hydrostatic, induced by seismic pumping.

Figure 17 :

 17 Figure17: Schematic 3D block diagram of the brine circulations and physicochemical changes induced by brine-basement rock interactions in the 10 km² area surrounding the Cigar Lake deposit; at the time of deposit formation. Two interpretative cross-sections have been added: i) the first (on the right) is in a priori barren basement graphitic structure and show features of regional background: diagenetic dickite-dominant clay matrix in the sandstone and ubiquitous presence of Na-dominated brine that slightly and pervasively percolate a in a low permeability basement. ii) The second (on the left) is located through the Cigar Main E-W ductile brittle structure. This structure was reactivated at the time of U deposition due to weakening during earlier Hudsonian basement uplift. The regional Na-dominated brines evolved into a Cl, Mg, K, Mn, Ba, Sr, Pb, U-enriched and Li depleted Ca-dominated brine through brine-basement interactions resulting from a higher fluid-rock ratio in the damage zone of this structure. The Ca-dominated basinal brines mixed with regional Na-dominated brines in and above the structure due to thermo-and/or deformation-driven convection either in the fault plane or perpendicular to it. Brine convection induced intense hydrothermal illite

  σS -FIP density, Zf -mean value of the inverse of the measured FIP lengths, Cf -mean radius. Calculated maximum paleoporosity of quartz at the time of carbonic or brine fluid migration is indicated in %. As Quartz paleoporosity calculated from mixed FIPs is effective both during carbonic fluid and brine circulation, it is added to quartz paleoporosity based only on carbonic or brine FIPs. Correspondences between the samples names (I.D.) and the labels used in Fig.14are also given here.Appendix A: Methodology for the reconstruction of the microfracture network and calculation of the quartz fracture paleoporosity.ESM-1: SWIR spectroscopy and microthermometry parameters of analyzed fluid inclusions.Calculated bulk salinity from microthermometric data is given in Cl (mol/kg). Abbreviations: Fe-chl -ferromagnesian retrograde chlorite; I -illite; Sud -Sudoite; K -kaolin minerals; Ps.p.-pseudosecondary plane. La-ICP-MS data are given after.

  + NaCl(S) → H2O(L) + Ice + HH + NaCl(S) → H2O(L) + HH + NaCl(S) → H2O(L) + NaCl(+ NaCl(S) → H2O(L) + Ice + HH + NaCl(S) → H2O(L) + HH + NaCl(S) → H2O(L) + NaCl(

  h e a n U t o U P a l e o p r o t e r o z o i c U b a s e m e n

Table 1 :

 1 Fluid inclusion nomenclature. The nomenclature is based on microthermometric observations and Tmice ranges. The considered system and the methodology used for the calculations of bulk compositions per inclusion types are indicated. HH -hydrohalite.

Table 2 :

 2 Proportion of analyzed FIs with element concentrations above the L.O.D.

Table 3 :

 3 Geometrical parameters of the FIP networks for the carbonic, brine, and mixed FIPs.

Acknowledgments

This work was carried out as part of a PhD thesis done in the CREGU, GeoRessources, Université de Lorraine (Nancy, France), and entirely supported by AREVA Resources CANADA (ARC). We thank AREVA for the permission to publish these results. We also thank Cameco Corporation for logistical assistance during the sampling. We are grateful to Antonin Richard for fruitful discussions and help with the LA-ICP-MS data treatment. Marie-Camille Caumon is thanked for Raman data acquisition and treatment, and Lise Salsi from the SCMEM for the SEM pictures. This work has been carried out thanks to the access to the analytical capabilities of the GeoRessources laboratory (Université de Lorraine, CNRS, CREGU), with equipment financed by the CPER program (national funds-Lorraine Region-FEDER) and Labex Ressources 21 (supported by the French National Research Agency through the national program 'Investissements d'avenir' with reference ANR-10-LABX-21-LABEX RESSOURCES 21). The authors also thank Dr. Mathias Burisch and Dr. Gregor Markl for their detailed reviews that helped to improve a former version of this manuscript, and both Dr. Klaus Mezger and Dr. Alexandre Tarantola for editorial handling.

Archean7dome WC372x457v9 U427x2OO U382x77v6 SFx73=xO5x45O SFx73=xO5x445v9 WC449x4O2v8 WC449x562v= WC449x537v7 WC449x565v2 WC254x46Ov5 WC426x338 WC473x452v6 2O7molek 4O7molek 6O7molek 8O7molek =OO7molek